MC 2023 Abstracts

Content Abstracts of plenary- and invited talks are shown in the proceedings, given they were submitted. Plenary Lectures (PL) ......................................................................................................................................................... 3 Material Science (MS) ....................................................................................................................................................... 14 MS1: Energy-related materials and catalysts ..................................................................................................................... 14 MS2: Metals and alloys ....................................................................................................................................................... 99 MS3: Low-dimensional and quantum materials ................................................................................................................ 150 MS4: Functional thin films ................................................................................................................................................. 200 MS5: Functional organic materials .................................................................................................................................... 241 MS6: Geoscience and construction materials, cultural heritage ....................................................................................... 266 MS7: Ceramics and composites ....................................................................................................................................... 283 Life Sciences (LS) ........................................................................................................................................................... 302 LS1: High-resolution cryo-EM ........................................................................................................................................... 302 LS2: Cryo-electron microscopy and cryo-electron tomography ........................................................................................ 318 LS3: Imaging of large volumes and plastic section tomography ....................................................................................... 325 LS4: Image analysis of large data sets ............................................................................................................................. 344 LS5: Correlative and multimodal microscopy .................................................................................................................... 350 LS6: Pathology, pathogens and diagnostics ..................................................................................................................... 370 LS7: Advances in sample preparation .............................................................................................................................. 387 Instrumentation and Methods (IM) ................................................................................................................................ 399 IM1: Progress in instrumentation and ultrafast EM ........................................................................................................... 399 IM2: Spectroscopy ............................................................................................................................................................ 426 IM3: SEM and FIB developments ..................................................................................................................................... 474 IM4: Development of cryo-EM instrumentation and techniques ....................................................................................... 498 IM5: Quantitative image and diffraction data analysis ...................................................................................................... 509 IM6: Phase related techniques & 4D STEM ..................................................................................................................... 561 IM7: In situ/operando electron microscopy ....................................................................................................................... 627 Late Breaking Abstracts ................................................................................................................................................. 681 Workshops (WS) ............................................................................................................................................................. 742 WS1: Data management ................................................................................................................................................... 742 WS2: Tricks and pitfalls for FIB sample preparation in materials and life sciences ......................................................... 750 ISBN 978-3-948023-29-4 2

PL.001 Integrative imaging analysis of the replication cycle of plus-strand RNA viruses R. Bartenschlager1 1Heidelberg University, Department of Infectious Diseases, Molecular Virology, Heidelberg, Germany Plus-strand RNA viruses such as SARS-CoV-2, hepatitis C virus (HCV), dengue virus (DENV) and Zika virus (ZIKV) comprise a large group of pathogens of high medical relevance. In spite of their divergent biological properties, they have in common the remodeling of intracellular membranes that serve as scaffold for the formation of a cytoplasmic replication organelle. To study the 3D architecture of these factories we employ an integrative imaging approach in which we combine various light and electron microscopy techniques. In this way, we found that plus-strand RNA viruses create two morphotypes of replication organelles: double-membrane vesicles (exemplified by SARS-CoV-2 and HCV) and spherules (e.g. DENV and ZIKV). By combining genetic and biochemical approaches, we study the mechanisms underlying the formation of the replication organelles while their dynamics is analyzed by means of live cell imaging. In my presentation, I will provide selected examples of plus-strand RNA viruses, focusing on the 3D structure and biogenesis of their replication organelle and the cell biology driving organelle formation. These examples shall illustrate that evolutionarily distant viruses share striking similarities in the common use of host cell factors and mechanisms with gained knowledge providing new approaches for antiviral therapy. 3

PL.002 From cryoEM, cryoET to ptychography – an overview P. Zhang1 1University of Oxford, Nuffield Department of Medicine, Oxford, United Kingdom Cryo-electron microscopy (cryoEM) is a powerful method for the high-resolution three-dimensional structural characterization of a wide range of biological samples in a close-to-native, frozen-hydrated state [1]. Such biological samples, preserved in vitrified ice, are extremely radiation sensitive, therefore images of these have low signal-to- noise ratios [2] and low contrast [3,4]. Recent development in microscope instrumentation, direct electron detector, microscope automation and high throughput imaging, and advanced software for data processing and image reconstruction, has revolutionized the field of structural biology, allowing protein structures to be determined at the atomic resolution, especially using cryoEM SPA method (Fig. 1). For studying macromolecular complexes that are intrinsically flexible and dynamic, and often function in higher-order assemblies that are difficult to purify, cryoET and subtomogram averaging (cryoET STA) has emerged as a potent tool to obtain structures of these at near-atomic resolution (Fig. 1). The study of such complexes and assemblies in situ using cryoET STA, coupled with cryoFIB and correlative and integrative imaging, opens a new frontier in structural cell biology [5]. While cryoEM SPA and cryoET STA rely on the use of conventional phase-contrast images that require the correction for the contrast transfer function, cryo-electron ptychography (cryoEPt) [6] (Fig. 2) is a new alternative technique that is based on dose-efficient diffractive imaging [7]. Ptychography uses a defocused probe to scan over a specimen with highly overlapping probe positions and computationally reconstructs the wavefunction of the sample. Such an approach has been widely employed in physical and material sciences, and now shows great promise for radiation- sensitive biological samples. I will present an overview of these cryo-electron microscopy modalities, using examples of our recent studies on human viruses, including HIV-1, SARS-CoV-2, and Rotavirus [8-10], to demonstrate the power of each method to image vitrified native biological samples. Figure legends: Figure 1. Schematic workflow of cryoEM using three imaging modalities, cryoEM single particle analysis (cryoEM SPA), cryo-electron tomography and subtomogram averaging (cryoET STA) and cryo-electron diffraction (cryoED). The workflow involves 1) sample preparation, 2) sample vitrification, 3) data acquisition, and 4) 3D reconstruction. A representative structure from each modality is shown. Figure 2. Schematic optical configuration diagram for cryo-ptychography (a), array of diffraction patterns as a function of probe positions (b), and reconstructed phase of rotavirus double-layered particles (c). Scale bars: 100 nm References: [1] R. Henderson et al., Journal of Molecular Biology 213, 899 (1990). [2] R. Henderson, Quarterly Reviews of Biophysics 28, 171 (2009). [3] R. Danev et al., Ultramicroscopy 88, 243 (2001). [4] R. Danev et al., Proceedings of the National Academy of Sciences 111, 15635 (2014). [5] P. Zhang, Curr Opin Struct Biol. doi: 10.1016/j.sbi.2019.05.021. (2019) [6] L. Zhou, et al., Nature Communications 11, 2773 (2020). [7] J.M. Rodenburg, Advances in Imaging and Electron Physics 150, 87-184 (2008). [8] T. Ni et al., Sci Adv 7(47):eabj5715 (2022) [9] L. Mendonça et al., Nat Commun. 12(1):4629 (2021) 4

PL.003 Enhancing electron spectroscopies using light M. Kociak1 1CNRS-CEMHTI, LPS, Orsay, France Introduction The wealth of information collected by electron spectroscopies, such as EELS, CL, PINEM, or EEGS, on the physical or material properties of nanobjects is now beyond dispute1. It is pretty amazing to see how A. Howie's once-promised ability to research nanooptics with free electrons has developed into a reality that surpasses even his exhilarating predictions from almost 25 years ago. Objectives I wish to address two crucial questions among the new possibilities provided by cutting edge electron monochromators, light injection and detection tools, electron detectors, and lasers. The first is technical: how can we maintain the famed spatial resolution of the electron microscope while achieving the sub-meV spectral resolution required to study excitations like excitons or photonic modes? The second question is more conceptual: how can we comprehend an optical excitation's life cycle, from its creation as a result of interacting with a free electron to its light emission? Materials and Methods I'll discuss CL, EELS, and EEGS experiments that try to provide answers to these questions. A high-precision, high-efficiency light injection and detection technology is the common factor among them all. Although it has been utilized here in conjunction with a time-resolved EELS direct detector or a highly monochromated STEM, its design has also found utility in other techniques, such as scanning tunneling microscopes. Results I shall therefore demonstrate that EEGS can be several orders of magnitude better resolved than EELS, much in the vein of the work of Henke et al., but here proven on arbitrary photonic samples, despite the very high monochromaticity of modern electron microscopes beams (30 meV at 200 keV). We will see how the combination of sub-10 meV EELS and high efficiency CL in the context of 2D semiconducting structures enables us to illustrate a direct analogy between macroscopic optical absorption and luminescence on the one hand, and EELS and CL on 2D semiconducting materials on the other. We'll focus on remarkable differences like the direct observation of trions in CL but not in EELS. However, at this point, it is still unclear what causes these physical distinctions. Therefore, beyond correlation, we will demonstrate that the coincidence between an absorption event at a certain energy (as revealed by EELS) and a potential emission event at a different energy (as revealed by CL) can shed light on the various routes from absorption to emission, ultimately revealing the fate of an optical excitation. Conclusions It is now possible to open numerous locks in nanooptics by combining high spectral resolution EELS, CL, and EEGS. Having the appropriate light injection and detection equipment definitely helps. Although the use of electron 6

PL.004 Atomic resolution dynamics imaged using 2D heterostructure liquid cells S. Haigh1, N. Clark1, D. Kelly1, Y. Zou1, A. Weston1, R. Gorbachev1 1University of Manchester, Materials, Manchester, United Kingdom Stacking 2D materials to build van der Waals (vdW) heterostructures can result in artificial crystals with perfect interfaces, enabling investigation and exploitation the unique electronic and optical properties of 2D crystals [1]. Transmission electron microscope (TEM) imaging has provided essential input on the nature of local defects and interface structure during the development of such vdW heterostructures [2]. For example, we have used scanning TEM (STEM) imaging to observe the atomic reconstruction that occurs when two transition metal dichalcogenide crystals are stacked with a small twist angle (Fig 1a) [3,4]. We have also used vdW heterostructures to study chemical degradation for air sensitive 2D materials such as CrBr3 TaS2 and GaSe, where mechanical exfoliation in an argon glove box and graphene encapsulation is used to protect the 2D material before TEM imaging [5-7]. VdW heterostructures also enable pioneering study of confined gases and liquids. Nanochannels with precisely controlled dimensions can be integrated in to the heterostructure by lithographic etching of specific layers but our TEM imaging is needed to ensure reliable, contamination free fabrication (Fig. 1b) [8,9]. Nanosized pockets of fluid are also highly desirable for TEM studies of atomic behavior in liquids. Commercial in-situ liquid cells enable TEM of liquid samples but the thick silicon nitride windows often prevent atomic resolution imaging and can also limit the sensitivity of spectroscopic analysis. Graphene liquid cells overcome these restrictions but the original fabrication method, suffers from poor control of the liquid dimensions and results in cells with limited stability. We have pioneered a new approach to fabrication of liquid cells based on 2D heterostructure stacking technology [10]. Our 2D heterostructure liquid cell approach also enables liquid mixing, triggered by the electron beam (Fig. 1c), allowing studies of the earliest stage of chemical synthesis at the atomic scale; something that was not previously possible by any technique [11]. Our experimental set-up contains two pockets of liquid separated by an atomically thin membrane, where mixing is induced by nanofracture of the separation membrane with the electron beam [11]. Furthermore, our platform enables the first studies of adatom dynamics at solid liquid interfaces (Fig. 1d)[12] and provides a route to understanding the enormous differences in ionic diffusion behavior for interplanar spaces as a result of changes to local crystal structure.[13] References: [1] Frisenda et al. Chem. Soc. Rev., (2018), 47, 53 [2] Haigh et al. Nature Mat. (2012) 11, 764 [3] Weston et al, Nature Nano. (2020), 15, 592 [4] Weston et al Nature Nano. (2022), 17, 390 [5] Hamer et al Nano Lett. (2020), 20, 6582 [6] Bekaert, et al, Nano Lett., (2020), 20, 3808 [7] Hopkinson, et al. ACS Nano, (2019), 13, 5112 [8] Q Yang et al, Nature, (2020) 588, 250 [9] A Keerthi et al, Nature (2018) 558, 420 [10] Kelly et al Nano Letters (2018) 18, 1168 [11] Kelly et al, Advanced Materials (2021) 33, 2100668 [12] Clark et al. Nature (2022) 609, 942 [13] Zou et al. Nature Mat. (2021), 20, 1677 8

PL.005 New microscopy possibilities with electron beam shaping V. Grillo1 1CNR, Istituto di Nanoscienze, Gattatico, Italy While electron microscopy has reached incredible spatial and energy resolution thanks to sophisticated and bulky electron-optics, a new, somehow orthogonal, research field has emerged based on the idea of giving near-arbitrary transformation to the electron beam before or after its interaction with the sample. By controlling the electron wavefunction we can improve the measurement sensibility, the spatial resolution, measure new quantities in microscopy, reduce the required dose in experiments, optimise the amount of information that can be extracted by a single electron. The mathematical instruments supporting this research are the concepts like unitary wave transformation, single pixel imaging, and conformal mapping. The experimental keys are new hardware like electron holograms, miniaturised electrostatic optical elements, electron light interaction and new automatization of hardware control by the innovative use of neural networks. I will dedicate part of the talk to describe these technical progresses: even not reaching the complexity of the largest innovation in electron optics like spherical aberration correction, they are introducing a little revolution in the way we conceive measurements. I will conclude summarising the results on the OAM-sorter and the prospective of computational and real ghost imaging, but also a few further ideas for the future. I acknowledge here the help of all my colleagues and co-workers in my group of CNR Istituto Nanoscienze Modena and in Università di Modena e Reggio Emilia, and all co-workers in QSORT, MINEON and SMART –ELECTRON project. A special thank is due to Prof. Rafal E.Dunin-Borkowski. This work has received funding from the European Union"s Horizon 2020 Research and Innovation Programme under grant agreements 766970 (QSORT), 964591 (SMART-electron) and 101035013 (MINEON). 10

PL.006 Geometric constraints on quantum behavior revealed by spatially resolved EELS P. E. Batson1 1Rutgers University, Physics and Astronomy, Piscataway, New Jersey, United States For most of the 20th century, the large size of electron probes restricted our view of physical science to measurements of energy and momentum, leading to many misconceptions about the electronic behavior of nanoscale structures. Thus, measurements of Al nanoparticles using angle resolved EELS showed strong surface plasmons, but very little bulk plasmons, suggesting that small structures are dominated by a surface/bulk ratio considerations.[1] When nm probes became available, experiments showed that EELS scattering depended more on the local probe/specimen geometry, than the particle size.[2] This realization contributed to an exciting period of EELS equipment development aimed at high spatial and energy resolution that continues today.[3] At first, simple boundary value calculations, using plane waves, were used to predict energy loss spectra as a function of transferred momentum. The energy transfer was assumed to be stochastic, carrying no phase information about the specimen excited state. In 1976, Rose proposed a Mixed Dynamical Form Factor for EELS to allow imaging of the phase of a surface plasmon.[4] His convincing argument led me to a channeling experiment in 1993 that cleanly separated the bulk plasmon from inter-band scattering in diamond, based on the transverse spatial parity of the scattered electron wavefunction.[5] After the success of sub-Ångstrom imaging using aberration correction, observation of atomic motion became ubiquitous, and yet difficult to understand.[6] It was generally thought that an attractive, dielectric response would dominate the forces between a passing keV electron and a polarizable object. Yet for very close approaches, nanoparticles were observed to move away from the passing electron beam. Using time-dependent force calculations based on experimental dielectric data, we found that the magnetic field carried by the relativistic electron appeared to mediate the repulsive behavior.[7] This conclusion is tantalizing but has not yet been confirmed by other workers. These findings of significant dependence on space and time suggest that spatially resolved EELS might soon enter the arena of relativistic space-time physics, using the geometric space-time algebra of Hestenes.[8] In addition, this kind of treatment might synergistically couple with ongoing work in quantum gravity, through the AdS-CFT correspondence that relates electromagnetism to quantum gravity.[9] In the spirit of this reasoning, I will show an EELS experiment from Vincent and Silcox, in 1973, [10] that appears to match the topology of a Penrose Diagram for entropy information exchange through an event horizon of a black hole. References [1] H. Petersen, Solid State Communications 23 931-934, (1977). [2] P.E. Batson, Solid State Communications 34 477 - 480, (1980). [3] M.J. Lagos, I. Bicket, S. Mousavi and G. Botton, Microscopy, 71S i174-i199 (2022). [4] H. Rose, Optik 45 139 (1976), Ultramicroscopy 15 173-192 (1984). [5] P.E. Batson, Phys. Rev. Lett., 70 1822-1825 (1993). [6] P.E. Batson, N. Dellby and O.L. Krivanek, Nature, 418 617 - 620 (2002). [7] M.J. Lagos, A. Reyes-Coronado, A. Konečná, P.M. Echenique, J. Aizpurua and P.E. Batson, Phys. Rev. B, 93 205440 (2016). [8] D. Hestenes, Oersted Medal Lecture, American Journal of Physics 71, 104 (2003). [9] A.V. Ramallo, https://doi.org/10.48550/arXiv.1310.4319 12

MS1.001-invited Probing local electrochemical and electrocatalytic processes in oxygen- evolving oxides in real-time V. Tileli1, T. H. Shen1 1EPFL, Materials, Lausanne, Switzerland Surface and interface sensitive operando characterization methodologies are required to unlock electrochemical and electrocatalytic processes. Liquid phase electrochemical transmission electron microscopy (TEM) can provide the sensitivity and selectivity at single particle level. Herein, we investigate oxygen-evolving cobalt-based oxides in alkaline solution and we retrieve morphological, structural, chemical information during cyclic voltammetry measurements. We compare the highly active Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) to the spinel Co3O4 and rocksalt CoO. The potential-dependent variation of the local contrast is associated to the modification of the wettability from hydrophobic to hydrophilic character at the oxide surfaces through interfacial capacitance phenomena. Molecular oxygen is probed in real-time during its evolution which results to further dewetting of the surfaces. Our work on catalysts exemplifies the crucial role that surface sensitive and electrochemical microcell TEM techniques can play in detailing the mechanism of electrocatalytic processes and can provide a new characterization framework aiding development of novel design routes for targeted catalyst preparation. 14

MS1.002-invited A new relativistic ultrafast electron diffraction and imaging (RUEDI) national facility for microscopic dynamics in the UK Y. Murooka1, W. Bryan2, J. Clarke3,4, M. Ellis3,4, A. I. Kirkland5, S. Maskell1, J. McKenzie3,4, B. L. Mehdi1, R. J. D. Miller6, T. C. Q. Noakes3,4, I. Robinson7, S. L. M. Schroeder8,9,10, J. van Thor11, C. Welsch4,1, N. D. Browning1 1University of Liverpool, Physical Sciences & Engineering, Liverpool, United Kingdom 2University of Swansea, Physics, Swansea, United Kingdom 3STFC Daresbury Laboratory, ASTeC, Warrington, United Kingdom 4Sci-Tech Daresbury, Cockcroft Institute, Warrington, United Kingdom 5Rosalind Franklin Institute, Didcot, United Kingdom 6University of Toronto, Departments of Chemistry & Physics, Toronto, Canada 7University College, London Centre for Nanotechnology, London, United Kingdom 8University of Leeds, School of Chemical and Process Engineering, Leeds, United Kingdom 9Diamond Light Source Ltd., Didcot, United Kingdom 10Research Complex at Harwell (RCaH), Rutherford Appleton Laboratory, EPSRC Future Continuous Manufacturing and Advanced Crystallisation Hub, Didcot, United Kingdom 11Imperial College London, Department of Life Sciences, London, United Kingdom 1. Introduction In the last two decades, there has been rapid progress in time-resolved electron diffraction and imaging using femtosecond pulsed electron beams. While light and X-ray probes are also common, electrons can probe all of lattice, charge, spin, and electromagnetic waves with high spatial resolution. Using femtosecond laser, for example, induced dynamics of lattice, charge transfer, magnetization, polaritons, have been clarified in both reciprocal space and real space. When the acceleration voltage is about 10- a few 100 kV, dynamics is often needed to be a reversible process with a short relaxation time in a sub 0.1 um thin specimen. The number of electrons per pulse is in the single electron regime due to the space charge effect. A long experimental time and high stability are often necessary. When it is at MeV, the number can be increased by more than one million, making it possible to observe a um thick specimen in the single shot regime. The MeV approach, on the other hand, has been realized only in diffraction but not in microscopical imaging. 2. Objectives At present, the requirements to observe dynamics have become so advanced that the conventional method often do not work. They are, for example, specimens in liquid/gas phases, complex systems as battery electrode surfaces, excitations under intense laser irradiation, and sub-100 femtosecond lattice dynamics. While attosecond phenomena have been explored in electron dynamics, it has also become important to clarify the correlation between electrons, lattices and spins. In addition, it is also urgent to improve the efficiency of experimental methods and to link them with other ultrafast techniques. RUEDI [1] has been designed and developed to enable these. 3. Materials & Methods RUEDI utilizes accelerator technology to generate a beam at MeV with 10 fs pulse duration and high brightness, integrates electron diffraction and electron microscope imaging, and achieve high efficiency using AI technology. For the sample environment, RUEDI has not only laser and high frequency field irradiations but also liquid/gas sample holders and in-situ, operando capabilities. Under well-controlled environments, electron diffraction plays a key role to test hypothesis and consistency as an analytical science method. Microscopic imaging becomes important in order to do observations at nm spatial resolution and, as a field science method, to obtain an overall information from a complex system where it is difficult to discover a hypothesis. RUEDI project focuses on five research themes. They are energy materials, materials in extreme conditions, chemical dynamics, quantum materials and in vivo life science. Some examples are, interfacial dynamics in liquid phase, photocatalytic dynamics, high-pressure and temperature materials, ultrafast chemical/molecular dynamics, and observation of biological specimens under hydration. 4. Results & Conclusion: 15

MS1.003 Unraveling (de)lithiation dynamics inside graphene sheets at atomic scale Y. Li1, F. Börrnert1, S. Fecher2, M. Ghorbani-Asl3, Z. Li1, J. Biskupek1, S. Yang2, M. Kühne2, D. Bresser4, A. Krasheninnikov3, J. Smet2, U. Kaiser1 1Ulm University, Ulm, Germany 2Max Planck Institute for Solid State Research, Stuttgart, Germany 3Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Dresden, Germany 4Helmholtz Institute Ulm, Ulm, Germany Graphite has succeeded as a lithium-ion anode material in the last 30 years, since it enhances energy densities due to its low (de)lithiation potential and high capacity. LiC6 had been known as the densest intercalation compound for the graphite anode. However, we observed a denser lithium phase inside graphene sheets in-situ during (de)lithiation by using spherical and chromatic aberration-corrected low-voltage high-resolution transmission electron microscopy. To meet the challenge of observing the (de)lithiation processes in-situ inside TEM, an electrochemical cell architecture including graphene sheets and polymer electrolyte was designed and placed on the Si3N4 membrane of a custom- made TEM sample carrier chip, as shown in Figure 1a. The lithium ions were inserted into the graphene sheets when applying a constant voltage during lithiation, while transferred back into the polymer electrolyte when the voltage was removed during delithiation (Figure 1b). Our HRTEM investigation confirms that the crystal structure of the lithium inside graphene sheets is fcc, which is denser than the LiC6 intercalation compound. In addition, we observed that the shape of the lithium crystals is dramatically different during the (de)lithiation processes, as shown in Figure 2. During lithiation, lithium crystals nucleate at the positions of graphene defects, and grow with triangular shape further. During delithiation, the lithium crystals shrink with irregular shape. The reason for that is the introduction of oxygen atoms at different positions inside the lithium crystals. Some oxygen atoms are introduced during lithiation, and bond with lithium atoms at the octahedral interstitial positions. The distribution of the oxygen atoms is uniform. However, during delithiation, the oxygen atoms gather at the edge of the lithium crystals, and keep at the edge position while the lithium crystals are shrinking. The oxygen atoms lock part of lithium atoms, resulting in the formation of amorphous lithium oxide finally. Our work gives a detailed insight of the existence and diffusion of lithium inside graphene sheets, which may have relevance also in anode materials. This work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm- Karlsruhe) and was funded by the German Research Foundation (DFG) under Project ID 390874152 (POLiS Cluster of Excellence). We acknowledge financial support from the Baden-Württemberg Stiftung gGmbH (project CT 5) and from the Ministry of Science, Research and the Arts (MWK) of the federal state of Baden-Württemberg in the frame of the SALVE project. Reference: [1] Nature 564, 234-239 (2018) [2] Nat. Nanotechnol. 12, 895–900 (2017) Figure 1: Device layout and working principle. (a) Self-designed electrochemical cell architecture including graphene sheets and polymer electrolyte placed on the Si3N4 membrane of a custom-made TEM sample carrier chip. Electron beam is illustrated in blue. (b) Schematic side view of the device during the in-situ TEM investigation. Figure 2: Overview of (de)lithiation inside graphene sheets. (a) The lithiation process. Lithium crystals nucleate and grow with triangular shape. (b) The delithiation process. The lithium crystals shrink with irregular shape. 17

MS1.004 Imaging structural defects and associated oxygen positions in Li-rich Li1.2Ni0.13Mn0.54Co0.13O2 W. Song1, P. Nellist1 1University of Oxford, Materials, Oxford, United Kingdom Li-rich Li1.2Ni0.13Mn0.54Co0.13O2 (Li-rich NMC) can deliver a high capacity over 250 mAh g-1 as a Li-ion battery cathode material compared with conventional layered metal oxides (<200 mAh g-1). Such high capacity results from the redox reaction of the lattice O2- ions and transition metals (TMs). Despite the boost in the capacities, Li-rich NMC suffers from voltage hysteresis and degradation in the voltage and capacity over cycling [1]. Synthesis efforts aim to overcome the issues but its structure is rather inhomogeneous and the role in affecting the materials performance is unclear [2]. The as-prepared material contains a number of defects, such as stacking faults, and has raised debates on whether the material is a coherent mixture of C2/m Li2MnO3 and R-3m LiTMO2 phase or a solid solution with the monoclinic phase [2]. In this work, we performed simultaneous annular dark field (ADF) imaging and electron ptychography on Li-rich NMC. Figure 1a shows the ADF image containing three types of monoclinic domains projected along [100], [110] and [1-10] zone axis, respectively. The domain variants are due to the faulted stacking of the TM layers in c direction. The TM layers composing the three types of domains have an in-plane rotation angle of 120 degree with respect to each other and the resulting stacking faults are referred to as rotation type. In the TM layers, Li+/Ni2+ and Co3+/Mn4+ cation ordering in a honeycomb pattern leads to the dumbbell contrast in ADF that arising from the Co/Mn atom columns. The dumbbell contrast is not uniformly seen as shown in Figure 1b, where cation disordering contrast is seen in the transition regions between the [110] and [1-10] domains. Such transition regions possibly result from the boundaries of the two types of domains or the in-plane cation disordering. Figure 1c displays several types of TM layers with cation ordering (O), mixing ordering/disordering (O/D) and disordering (D) contrast in ADF imaging. In addition to the rotation-type stacking faults, Figure 1d shows another type resulting from out-of-plane TMs layer shift in c direction, namely shift type. Both types of stacking faults rely on the imaging of TMs whilst lack the understanding of oxygen stacking. To probe the oxygen lattice, we carried out focused-probe electron ptychography to reconstruct the phase image and use the ADF image to point out TMs. Figures 2 show the ADF and ptychographic image and their composite image, respectively. Although TM layers possess a number of stacking faults, the oxygen layers are seen in an O3-type stacking. The imaging on the TMs and O layer stacking shows different structure defects in Li-rich NMC that can affect the electrochemical performance [3]. Figure 1 Stacking faults of Li-rich NMC. (a) ADF image of rotation-type stacking fault. White region is magnified in (b). The red, green and orange tetragons indicate monoclinic domains projected along [100], [110] and [1-10] zone axis, respectively. (c) ADF image of various types of TMs layers. (d) ADF image of shift-type stacking fault. Scale bar is 1 nm. Figure 2 Imaging of faulted stacking. (a-c) Rotation type. (d-f) Shift type. (a, d) ADF image. (b, e) Ptychographic image. (c, f) Composite image. Superposed is the crystal model. Purple sphere is TM, green is Li and red is O. Scale bar is 0.5 nm. Reference [1] House, R.A., et. al., (2020) Nat. Energy 5, 777-785. [2] Shukla, A.K., et. Al., (2018) Energ. Environ. Sci. 11, 830-840. 19

MS1.005 Establishing in-situ heating experiments of monolithic LiNiO2 particles in O2 atmosphere T. Demuth1, M. Malaki1, S. Ahmed1, P. Kurzhals2, A. Beyer1, J. Janek2, K. Volz1 1Philipps-University Marburg, Materials Science Center (WZMW) and Department of Physics, Marburg, Germany 2Justus-Liebig-Universität, Institute of Physical Chemistry & Center for Materials Research, Giessen, Germany The state-of-the-art cathode materials for lithium-ion batteries are the layered transition metal oxides Li(Ni1-x- yCoxMny)O2 (NCM) and Li(Ni1-x-yCoxAly)O2 (NCA). They deliver specific capacities of more than 170 mAh g-1 [1]. Manufacturers and researchers constantly try to reduce the cost as well as increase the capacity of batteries. Increasing the Ni content to 80% or higher fulfills on the one hand these goals but leads on the other hand to a reduced cycling stability of the battery, as the polycrystalline particles undergo an anisotropic volume change during (de-)lithiation [2]. By using monolithic crystals instead of polycrystalline materials, these drawbacks may be mitigated [3]. Furthermore, an annealing step at elevated temperatures can optimize the surface morphology and structure of the particles leading to an improved electrochemical performance [4]. The annealing process is executed in an oxygen atmosphere to prevent oxygen loss from the grains [5]. This study aims at gaining a thorough understanding of the influence of the annealing process on the structure of Ni- rich layered transition metal oxides. For this purpose, the model system LiNiO2 (LNO) is investigated during annealing in an oxygen atmosphere in in-situ high angle annular darkfield (HAADF) scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) experiments. The monolithic LNO particles agglomerate to secondary particles with a diameter of approximately 4 μm. To prepare an electron transparent sample, the focused ion beam (FIB) cutting method is employed. For apposite placement of the particle on the SiN window of the heating chip, a Si lamella with a cut-out hole, in which the particle is placed before thinning, is used as support. The chip with the particle is then mounted in the enclosed gas cell TEM holder, which is connected to an oxygen bottle. Between the bottle and the holder, a flow valve controls the flow of oxygen, whereas a pressure valve downstream of the holder regulates the pressure to 1 bar in the holder tip. We report on our experiments to heat a secondary LNO particle in an oxygen atmosphere. A heating ramp of 1 °C / s was employed up to a temperature of 700 °C. Starting at around 450 °C, structural changes of the particle begin to arise. These changes firstly appear at the grain boundaries of the monolithic crystals and later proceed to the bulk of the grains. Eventually, the whole secondary particle is severely disintegrated, as the HAADF STEM image in figure 1 shows. We propose that this disintegration occurs due to oxygen loss from the particles as EELS data in figure 2 obtained from the same region before and after heating implies. The first experimental data has shown that our work-flow from the elaborate sample preparation to in-situ heating and the particles" investigation works fundamentally. In future experiments we will refine our set-up and parameters to try to suppress oxygen loss and disintegration of the LNO particles during heating. Figure 1: HAADF STEM images of LNO secondary particle a) before and b) after in-situ heating to 700 °C. Figure 2: STEM EELS signal of oxygen before (blue) and after (red) in-situ heating to 700 °C. [1] de Biasi, L. et al. Adv. Mater. 31 (2019) [2] Kurzhals, P. et al. J. Electrochem. Soc. 168 (2021) [3] Langdon, J. et al. Energy Stor. Mater. 37 (2021) [4] Huang, B. et al. Solid State Ion. 345 (2020) [5] Karki, K. et al. ACS Appl. Mater. Interfaces 8 (2016) 21

MS1.006 Low dose STEM imaging and in situ TEM of metal halide perovskites N. Schrenker1, S. Toso2, C. P. Yu1, B. Pradhan3, E. Debroye3, M. Roeffaers3, J. Hofkens3, L. Manna2, J. Verbeeck1, S. van Aert1, S. Bals1 1University of Antwerp, EMAT, Department of Physics, Antwerp, Belgium 2IIT, Department of Nanochemistry, Genova, Italy 3KU Leuven, Leuven, Belgium Metal halide perovskites (MHP) are promising semiconductors for the next generation of optoelectronic devices. Due to their tunable bandgap, they fulfil the requirement for various applications, including solar cells, light-emitting diodes, lasers and photodetectors. Unfortunately, MHPs still lack of long-term stability. Degradation occurs due to their phase instability and under environmental triggers, such as moisture and oxygen. In order to be able to extend the life time of MHPs a fundamental understanding of degradation mechanisms is required. To investigate these mechanisms we apply in situ HRSTEM under oxygen and moisture. Another challenge for TEM investigations of MHPs is their high electron beam sensitivity. Therefore, we developed low-dose protocols using integrated differential phase contrast (iDPC)1, see Fig.1b. Hence, we are able to investigate the MHP without degradation due to Pb-cluster formation or amorphization and quantitatively interpret the STEM images using statistical parameter estimation theory. For heterostructures, consisting of perovskite nano cubes and a chalcohalide, we applied the described STEM techniques to study the interface nature (Fig. 1c,d)2. Interestingly, the cationic subnetwork of Pb and Cs is maintained through the interface, which results in an epitaxial relationship. We also found that the perovskite can be used as disposable epitaxial template for the phase-selective synthesis of lead sulfochloride nanocrystals. Furthermore, in order to study perovskites with organic cations as well as the exchange of cations or halides, we utilize 4D STEM data sets to retrieve the phase information via integration center of mass (iCOM) reconstructions. This enables us to study the organic cations, which would not be possible using HAADF imaging. The developed methods provide important insights into the structure of the perovskites and enable in situ TEM investigations, which are essential to improve the properties and increase their chemical stability. Figure 1. High resolution STEM imaging of metal halide perovskites. (a) HAADF image of a CsPbCl3 nanocrystal (NC). (b) Corresponding iDPC image of the NC in panel (a) revealing the Cl atomic columns. (c) High-resolution HAADF STEM image of a single Pb4S3Cl2/CsPbCl3 heterostructure. At the top is a model of the Pb4S3Cl2/CsPbCl3 epitaxial interface superimposed on a close-up view of panel (c), highlighting the continuity of the Pb2+/Cs+ cationic subnetwork. Atom color code: Cs = cyan; Pb = orange/white; S = yellow; Cl = green. (d) Column intensity map of the Pb-containing columns in the perovskite phase and of the Pb columns in the Cs2PbX4-like subnetwork of the Pb4S3Cl2 domain. The color in the intensity map correlates with the total intensity scattered from the corresponding atomic column (red = higher intensity; blue = lower intensity). (c,d) Reprinted from Ref. [2]. References • • Fig. 1 [1] Otero-Martinez, C., Imran, M., Schrenker, N. et al. Fast A-site cation cross-exchange at room temperature: Single-to double- and triple cation halide -perovskite nanocrystals. Angew. Chem. Int. Ed., e202205617 (2022) [2] Toso, S., Imran, M., Mugnaioli, E. et al. Halide perovskites as disposable epitaxial templates for the phase- selective synthesis of lead sulfochloride nanocrystals. Nat Commun 13, 3976 (2022) 23

MS1.007 Operando SEM and XPS insights of self-sustained oscillatory dynamics of ethylene to syngas over nickel catalysts C. Claudiu1, M. G. Willinger2, J. A. van Bokhoven3, M. Plodinec1, L. Artiglia4 1ScopeM, Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093, Zürich, Switzerland, Zurich, Switzerland 2TU Munich, Electron Microscopy with research focus on energy materials, Munich, Germany 3ETH Zurich, Department of Chemistry and Applied Biosciences, Zurich, Switzerland 4Paul Scherrer Institute, Laboratory for Catalysis and Sustainable Chemistry, Villigen, Switzerland As scientists, it is our duty to pave the way for the development of a sustainable economy based on renewable energy resources and to reduce greenhouse gas emissions with an expected market value of 48Bn $ by 2027 [1], the catalyst—whether heterogeneous, homogeneous, or enzymatic—represents one of the pillars on which modern society is built. However, apart from the simplest model reactions, the scientific community is still unable to fully comprehend the underlying mechanism of catalysis and the atomistic details of the active state. The objective is to obtain mechanistic insights into the role of surface species present in the catalytic process of partial oxidation of ethylene to syngas on a model polycrystalline nickel foil. Using a combination of operando scanning electron microscopy (OSEM) for real-time observation of structural dynamics and ambient pressure x-ray photoelectron spectroscopy (APXPS) we correlate the state of the catalyst with its activity. Although challenging to study, the self-sustained oscillating reaction mode enables detailed analysis of the successive elementary steps of the catalytic act (Figure S1). The obtained insights are envisioned to expand the research on the self-regenerating operation of real-world catalysts. We were able to extend the functionality of a TFS Quattro S ESEM by developing a mobile in-situ that enabled the ambient pressure x-ray photoemission spectroscopy and operando scanning electron microscopy studies to be performed under identical conditions. This unit is composed of a modified sample holder that can achieve working temperatures of up to 1250C in reactive gas atmospheres, an automated heating unit and an automated gas feeding system. By maintaining a constant gas composition in isothermal conditions, a synchronized self-sustained oscillation mode was identified, in which the reaction`s product distribution reflects the catalyst morphology and chemical state. We were able to pinpoint the catalytic behavior down to competing species that influence catalyst deactivation with excellent spatial resolution and to discriminate between local and non-local mechanisms that impact the collective dynamics usually reported using traditional approaches. The combination of spatially resolved real-time imaging [2], [3] with integral surface-sensitive spectroscopy enables the chemical identification of surface species and simultaneous visualization of their evolution as a function of reaction conditions. We were able to provide insight into structure sensitivity and coupling phenomena between reactive gas- phase and catalyst states that are related to the emergence of catalytic activity in a synchronized self-sustained oscillatory mode. The here described structure-activity correlations are not accessible through integral characterization techniques or by studying steady-states alone, highlighting the importance of real-time, laterally resolved direct observation of active catalysts. Figure S1: Time series of a Ni surface during ethylene to syngas conversion. HFOV is 33.5µm. [1] Catalyst Market Size, Share & Trends Analysis Report By Raw Material 2020 – 2027 [2] Danilatos,Gerasimos D. "Environmental scanning electron microscopy and microanalysis." Microchimica Acta 114.1 (1994): 143-155 [3] Sandoval-Diaz, Luis, et al. "Visualizing the importance of oxide-metal phase transitions in the production of synthesis gas over Ni catalysts." Journal of Energy Chemistry (2020). 24

MS1.008 Evaluating charge carrier mobility of organic semiconductor using ultra-low voltage spectral SEM W. S. Zhang1, R. R. Schröder1 1Ruprecht-Karls University Heidelberg, Bioquant, Heidelberg, Germany Introduction The pivotal property of organic semiconductors (OSCs) to achieve high performance devices is a high charge carrier mobility. However, the mobility is commonly measured from a model device, most often a field-effect transistor, making the mobility value material- and device-dependent. Both, the intrinsic factors - such as energy levels of all materials involved, molecular packing of the OSC, its crystalline domain size and orientation - and the extrinsic factors - likewise device structure, morphological defect, contact defect - will influence the final result. On the other hand, computational methods can provide intrinsic mobilities, which deviate frequently over several orders of magnitudes from the experimental data. Thus, material scientists need a reliable method to (re-)evaluate the existing and newly developed materials in order to gain a rational structure-function-relationship. Objectives Herein, we present an electron-spectroscopic method to evaluate the charge carrier mobility directly from thin-films or microcrystals. Such samples can easily be obtained for most materials. With the proposed method the effects of the extrinsic impact factors are reduced to only one - the contact resistance. This factor remains, as it is necessary to ground the sample for electron spectroscopic data collection. We show that the relative lateral mobilities between different OCSs can thus be directly determined. Materials & methods Polycrystalline thin-films of small molecules were prepared via thermal evaporation under vacuum. Microcrystals of small molecules and polymers were obtained by wet techniques. We use a demonstrator of an electron-spectroscopic SEM, i.e. Zeiss Delta-SEM, for recording the secondary electron (SE) emission spectrum. The dynamic charging map, generated from the SE spectra on each pixel, is used for the mobility evaluation (see Figure 1). Results First, the beam-material interaction was investigated and the electrically neutral energy points were determined under various charging conditions. Depending on n-type or p-type OSCs, suitable charging conditions that results in negative or positive charging was selected.1 With step-wise increase of charging intensity, the OSCs turned from electrically neutral to severely charged. By comparing the stage currents among different OSCs, which exhibit the same/similar charging maps, one can evaluate OSCs in terms of lateral charge carrier mobility (example see Figure 2). The horizontal mobility is also accessible by analyzing the charging maps near and on the metal contacts. In addition, space charge, impacts from crystal orientation and molecular packing on mobility can be observed. Conclusion The lateral mobilities estimated with the presented method agree very well with the theoretical calculation (eg. transfer integral)2. Contact between OSC and electrode can be individually tested and thus a suitable device structure can be proposed according to the intrinsic lateral mobility. Ref. [1] Adv. Electron. Mater. 2021, 2100400. [2] Chem. Eur. J. 2015, 21, 17691-17700. 26

MS1.009 Hydrogen uptake and phase change in Pd nanoparticles at nanometer scale with in-situ TEM S. Korneychuk1, S. Wagner1, G. Melinte2, R. Darius3, P. Vana3, A. Pundt1 1Karlsruher Institut of Technologie (KIT), IAM-WK, Karlsruhe, Germany 2Karlsruher Institut of Technologie (KIT), INT, Karlsruhe, Germany 3Georg-August-University Göttingen, Institute of Physical Chemistry, Göttingen, Germany Introduction Palladium-based nanomaterials play an important role in hydrogen technology. Unique properties of Pd, such as high affinity to hydrogen, good solubility of up to H/Pd = 1 atomic ratio and fast hydrogen absorption and desorption at room temperature are very attractive for various applications. Besides catalysis, Pd nanoparticles can assist in hydrogen delivery into other materials for hydrogen storage. Pd-based materials are also used as hydrogen purification membranes and hydrogen detectors. Objectives The hydrogenation and dehydrogenation process of Pd nanoparticles is hence of high interest in the applications mentioned above. Nanoscale systems reveal significant thermodynamic deviations from the bulk due to higher surface to volume ratio, the absence of grain boundaries, and different behavior of defects. In this work we investigate the behavior of Pd nanoparticles and the formation of PdHx in real time with in-situ gas TEM at room temperatures and elevated temperatures which are required by many applications. Materials & methods The experiment was carried out at 80 kV on the ThermoFisher Scientific Themis Z equipped with Gatan GIF Continuum. In-situ hydrogen loading and unloading of Pd nanoparticles was accomplished with the gas system from Protochips. The sample was tightly sealed between two chips which both have electron transparent SiN windows, and analyzed at pressures of up to half atmosphere and temperatures of up to 200°C. Results and Conclusions We can observe the local phase change at different temperatures and pressures by measuring the position of the Pd bulk plasmon shift in low loss EELS [1]. With this technique we can study the direction of hydrogenation and dehydrogenation, hysteresis, size and shape related effects of the nanoparticles at various temperatures and pressures. In this work we also discuss the distinction of the quasi-planar surface plasmon modes in Pd nanoparticles from the PdHx signal. Fig.1. EELS mapping of the Pd NPs at 140 °C and 13 kPa H2 showing the separation of Pd-H phases: solid solution (blue) and palladium hydride (orange). [1] A. Baldi, et al, Nature Materials, 2014, DOI: 10.1038/NMAT4086 28

MS1.010 Structural evolution of a Cu/ZnO/Al2O3 catalysts revealed by operando TEM M. Boniface1, R. Schlögl1,2, T. Lunkenbein1 1Fritz-Haber Institut, AC, Berlin, Germany 2Max-Planck-Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, Mülheim an der Ruhr, Germany Introduction: Cu–ZnO/Al2O3 catalysts have been used industrially since the mid-1960s for both the water-gas shift (WGS) reaction and methanol synthesis. Methanol produced from CO2 and H2 is believed to play a key role as an energy storage molecule [1]. The catalyst is activated by reduction in situ, which promotes the formation of a partially reduced ZnOx overlayer over Cu NPs through the strong metal-support interaction (SMSI). The SMSI has been observed in the spent catalyst after reaction [2], but has so far scarcely been investigated operando. Materials and Methods: The catalyst (Cu–ZnO/Al2O3) was synthesized by calcination of a zincian malachite precursor with a Cu:Zn ratio of 70:30 and 3 mol % Al, following a protocol published previously [3]. A sample was mounted in a DENS Climate environmental TEM holder, which was connected to our homebuilt gas feed setup. Selected area electron diffraction (SAED) temperature series were corrected for astigmatism and centered with sub- pixel accuracy[4], enabling us to track small lattice parameter changes and phase fractions from Rietveld refinement with the fast time resolution of SAED. Results: The calcined sample is first activated (pH2 = 79 mbar, 10% H2, 4K.min-1) during a 2-step process involving the segregation of CuO NPs from a (Cu,Zn) carbonate phase from 110C to 200C, then reduction and sintering of these NPs from CuII to Cu0. A CuI intermediate is detected as well between 200C and 250C, with all 3 oxidation states co- existing at these temperatures until only Cu0 remains after 2h at 250C. The SMSI ZnOx overlayer only partially covers few particles after the reduction is complete after 2h at 250C. Cooling the sample to 50C leads to a much fuller overlayer on a much larger NPs population, indicating that the SMSI overlayer is not stable at high temperatures and forms reversibly. This is compounded by results in MeOH synthesis conditions (H2:CO2:He = 3:1:0.5) and reverse water gas shift conditions (H2:CO2:He = 1:1:0.5), shedding tremendous insight into how Cu wetting by ZnOx is mediated by temperature as well as H2 and CO2 partial pressures (Figure 1.a) through a delicate balance of Cu-Zn alloy formation and reoxidation on Cu NPs surfaces [5]. Increasing the temperature to 400C showed a sudden increase of the Cu lattice parameter, which then leveled off to the expected Cu lattice parameter over 30 minutes, demonstrating the potential of operando SAED to track alloying and reoxidation in real time and revealing the time constant of these phenomena (Figure 1.b). Figure 1. a) Evolution of the catalyst throughout activation and operating conditions. Cooling after reduction leads to a full ZnOx coverage on the Cu NP. This overlayer is thicker and more stable as the CO2 fraction increases disappears reversibly as the temperature increases. b) Evolution of the Cu lattice parameter in RWGS conditions. The increase and decrease corresponds to Cu-Zn and re-oxidation. References 1. A. Olah, A. Goeppert, G. K. Surya Prakash, in "Beyond Oil and Gas: The Methanol Economy", Wiley- VCH, Weinheim, 2006. 2. Lunkenbein, T., Schumann, J. et al., Angewandte Chemie54, 15 (2015). 3. Schumann, J., Lunkenbein, T. et al. ChemCatChem6, 10 (2014). 4. Frisch, B., Wu, M., Ultramicroscopy 235 (2022) 5. Amann, P., Klötzer, B. et al., Science 376, 6593 (2022). 30

MS1.P001 On the structure of small oxide-supported metal particles H. Eliasson1, R. Erni1, W. Dachraoui1 1Empa, 299, Dübendorf, Switzerland To design stable, active and selective catalyst materials, an understanding of a system's active sites is necessary. Today, many catalysts are based on materials decorated with either single metal atoms, clusters or nanoparticles, where the metal species act as reaction hubs in the catalytic process. It is known that the catalytic activity of particle based catalysts often correlates with the particle size, structure and morphology [1]. Despite this, there are not many experimental studies showing atomically resolved structural information about supported nanoparticles, and those that do are usually focused on larger particles [2, 3]. This study aims at revealing differences in the particle-support interface and particle structure of small oxide supported metal particles with diameters in the range of 1-3 nm. Samples were prepared by dropping a dispersion of methanol with grinded catalyst powder onto regular TEM grids. Metal species were then deposited directly onto the grid by sputtering giving rise to a natural particle growth process by diffusion on the support surface. The samples are imaged with sub-Ångström spatial resolution in a probe- corrected FEI Titan Themis S/TEM microscope operated at 300 kV. High-angle annular dark-field (HAADF) STEM was chosen as imaging mode because of the incoherent nature of the signal. The inherent Z-contrast of HAADF- STEM along with the lack of Bragg diffraction contrast makes for easy image interpretation, especially useful for smaller particles with larger atomic number (Z) than the supporting material. Images were formed by aligning and summing a series of fast scans to limit the electron dose and the influence of sample drift. We observe changes in particle shape from hemispherical to more facetted truncated octahedral-like shapes with increasing particle size, and also report the preferential orientation relations between particle and support. For particles with a favorable orientation in regards to visibility of atomic columns, the analysis was taken further and displacement and strain maps were calculated. These results lay a foundation for further studies both in situ and ex situ. For example, to investigate electronic states in particles and interfaces by electron energy loss spectroscopy (EELS), but also to study particle behavior in situ in different gas environments and at different temperatures. 32

MS1.P002 Molecular mechanism of copper-based catalytic reaction of water oxidation: in-situ electrochemical liquid phase transmission electron microscopy study A. Sologubenko1, E. Balaghi2, G. Patzke3, M. Najafpour4 1ScopeM ETH Zurich, Zurich, Switzerland 2University of Freiburg, Freiburg Center for Interactive Materials and Bioinspired Technologies, Freiburg, Germany 3University of Zurich, Chemistry, Zurich, Switzerland 4Institute for Advanced Studies in Basic Sciences, Zanjan, Iran The understanding of molecular mechanisms of water oxidation reactions is very important for development of renewable energy storage solutions. Inspired by a naturally occuring water splitting catalyst, the Mn4CaO5 particles [1], many first-row transition metal compounds are being synthesized and studied as catalysts in oxygen-evolution reactions (OER) at various conditions [2]. Copper(II) complexes are considered to be very promising, with the [Cu(TMC) (H2O)](NO3)2 (TMC = 1,4,8,11‐ tetramethyl‐1,4,8,11‐tetraazacyclotetradecane) compound (further, the Cu(II)-complex) reported among the most efficient copper-based catalyst for electrocatalytic OER in neutral aqueous solutions [3, 4, 5]. However, the control over the stability and catalytic activity of the compound is handicapped by a complicated reaction path, and general lack of understanding of its molecular mechanism [5]. In our study, we followed the OER in the presence of the Cu(II)-complex by employing the most advanced analytical and computational techniques, including in-situ vis-spectroelectrochemistry, in-situ electrochemical liquid-phase transmission electron microscopy (EC-LPTEM) and extended X-ray absorption fine structure (EXAFS) studies. Our in-situ EC-LPTEM and post-reaction analytical and electron diffraction studies revealed that already in the first anodic scan, small CuO nanoparticles formed at the surface of working electrode at a significantly lower potential than required for OER (Figure). This indicates that these can be the true catalysts rather than the Cu(II)-complex. Further, during the OER, the small CuO particles dissolved to form larger ones. Moreover, during cyclic voltammetry (CV) runs, we observed the formation of a very thin, nearly continuous Cu-oxide film at the working electrode of the reactor cell of the TEM holder. These data accord very well with the electrochemical impedance spectroscopy (EIS) curves acquired in a separate experiment. We show that even at the very beginning of the OER, the compound can undergo transformation. We also show that the actual OER mechanism in the presence of the Cu(II)-complex is more complicated than a mere molecular mechanism. All these evidences that the metal catalyst cannot be presumed to stay intact during the OER, unless the reaction path is known and fully controlled. In-depth studies of the particular reaction path using the advanced morphological and analytical methods are therefore crucially important for the catalyst design. Figure. (a) Degradation of Cu-complexes during anodic scan of cyclic voltammetry (Ag/AgCl reference electrode). TEM micrographs presents the snap-shots of the early stages of the nucleation of the copper oxide particles (bright yellow) at the surface of the working electrode (blue). The phase state change of the material at the electrolyte is verified by electron diffraction pattern (eDP) analyses: (b) the eDP of the Pt-working electrode. (c) Pt-electrode & CuO-phase particles. (d, e) The EDS SI elemental content analyses by of the electrode adjacent region (frame in d). The EDS SI confirms the formation of CuO phase in the electrolyte. (f) Schematic of the CuO unit cell. [1] Y. Umena, K. Kawakami, J. R. Shen, N.Kamiya, Nature, 473 (2011). [2] M. M. Najafpour et al., Chem. Rev. 116 (2016). [3] X. Liu et al., Electrochem. Commun. 46 (2014). [4] M. M. Najafpour, S. Mehrabani, Y. Mousazade, M. Holynska, Dalton Trans. 47 (2018). [5] F. Yu et al., Chem. Commun. 52 (2016). 35

MS1.P003 3D-microstructure of spindle-like Li1Ti2(PO4)3 particles revealed by electron microscopy R. Schierholz1, K. Dzieciol1, S. Yu1, Q. Zhang1, H. Tempel1, H. Kungl1, R. Eichel1 1Forschungszentrum Jülich GmbH, Institut für Energie ud Klimaforschung Grundlagen der Elektriochemie (IEK-9), Jülich, Germany 1. Introduction Pure Li1Ti2(PO4)3 (LTP) is an anode material with NASICON structure and a lithiation potential of 2.31 V.[1] This potential fits the electrochemical stability window of the promising isostructural solid state electrolyte Li1+xAlxTi2-x(PO4)3 (LATP), which is obtained by trivalent substitution and application in an all-phosphate solid state battery has been demonstrated.[2] Comparison of different synthesis methods revealed an enhanced cycling performance of solvothermally prepared LTP with spindle-like particles of 2 – 5 µm size compared to the same material prepared by sol-gel based Pecchini method.[3] 2. Objectives Scanning electron microscopy (SEM) suggests that spindle-like particles are formed by sub particles of about 300 nm size, but as only the surface is accessible by SEM the origin of the enhanced performance remains unclear. With focused ion beam (FIB) and (Scanning) Transmission Electron Microscopy the inner volume can be characterized to give a complete picture of the particles crystal- and micro-structure as well as its local chemical composition. 3. Materials and methods The particles were synthesized by solvothermal reaction, consecutively vacuum dried and annealed at 800 °C.[3] These particles were then dispersed in ethanol and a droplet was put on a silicon wafer for FIB-SEM experiments. FIB tomography and TEM-lamella preparation were conducted with a Helios Nanolab 460F1, FEI, Netherlands.[4] TEM and STEM analysis was conducted in a Tecnai F20 and a Titan G2 Crewley.[5] 4. Results SEM imaging shows the morphology, with sub particles forming a dumbbell like particle, and already provides hints for the presence of two secondary phases, on nanoparticles, the other a bulky phase with different surface morphology. The presence oof different phases is approved by chemical contrast in BSE-images of cross sections and STEM HAADF imaging. STEM-EDS gives an estimate of the chemical compositions which is completed by STEM-EELS for the detection of Lithium. HRTEM and HRSTEM could then identify the crystallographic structures of these secondary phases to be TiO2 anatase for the nanoparticles and LiTiPO5 (Pnma ICSD #153522) for the bulky secondary phase. FIB-tomography revealed that the majority of the TiO2 nanoparticles are interconnected. 5. Conclusions The complex microstructure of the spindle-like LTP particles can only be solved by a combination of FIB-tomography and STEM-analysis. The three-dimensional network of TiO2-nanoparticles seem to improve the cycling behavior, as it may enhance the diffusion and can also contribute to capacity and is no dead material.[6] [1] S. Yu et al., ACS Appl. Mater. Interfaces (2018) Vol. 10, No. 26 p. 22264-22277, https://doi.org/10.1021/acsami.8b05902 [2] H. Aono et al., Journal of The Electrochemical Society , (1990) 137, 4, p. 1023-1027 https://doi.org/10.1149/1.2086597 [3] S. Yu et al., ChemElectroChem (2016) Vol. 3, No. 7, p. 1157-1169 https://doi.org/10.1002/celc.201600125 [4] M. Kruth et al., Journal of large-scale research facilities JLSRF (2016) 2, A59 https://doi.org/10.17815/jlsrf-2-105 [5] A. Kovács et al., Journal of large-scale research facilities JLSRF (2016) 2, A43 https://doi.org/10.17815/jlsrf-2-68 37

MS1.P004 Probing the microscopic properties of Cu(In,Ga)Se2 absorbers in thin film solar cells via correlative scanning electron microscopy techniques S. Thomas1, W. Witte2, D. Hariskos2, S. Paetel2, C. Y. Song3, H. Kempa3, N. El-Ganainy4, D. Abou-Ras5 1Helmholtz Zentrum Berlin, Berlin, Germany 2Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Stuttgart, Germany 3Martin-Luther-Universität Halle-Wittenberg, Institut für Physik, Fachgruppe Photovoltaik, Halle (Saale), Germany 4Competence Centre Photovoltaics Berlin (PVcomB) / Helmholtz Zentrum Berlin für Materialien und Energie (HZB), Berlin, Germany 5Helmholtz-Zentrum Berlin, Abteilung Struktur und Dynamik von Energiematerialien, Berlin, Germany There are several challenges in the field of solar-cell research which cannot be solved without an in-depth investigation of the materials and devices. In the case of Cu(In,Ga)Se2 (CIGSe) thin-film solar cells, the band-gap energy of the polycrystalline photoabsorber can be tuned by varying the [Ga]/([Ga]+[In]) (GGI) ratio. However, there are several obstacles that prevent from achieving the desired device efficiency[1]. We aim to assess the issues that deteriorate the device performance on the sub-micrometer scale. In the present work, we employ several scanning electron microscopy (SEM) techniques to examine the microscopic properties of the CIGSe photoabsorber layer of the solar cell [2]. Electron backscatter diffraction (EBSD) is used for the crystallographic characterization to determine the average grain size (dgrain) and identify features such as twin grain boundaries (GBs), surface texture and preferred crystallographic orientation of the grains [3]. The local radiative recombination activities are characterized via cathodoluminescence (CL) spectroscopy. We extract information of the charge carrier recombination velocity (SGB) at the grain boundaries from hyperspectral CL images in combination with time-resolved photoluminescence spectroscopy. Energy-dispersive X-ray spectroscopy (EDS) is applied to determine the distribution pattern of the elements within the absorber depth. The presence of secondary phases can also be detected via EDS mapping. As shown in the Figure below, we apply these scanning electron microscopy techniques in a correlative manner on identical sample positions. Thus, we are able to detect changes in the microscopic properties when varying the GGI ratio in the CIGSe absorber layer and to investigate the microstructure-property relationships in several CIGSe thin- film solar cells. Indeed, it is found that the changes in the microscopic properties of the CIGSe photoabsorber have a substantial effect on the macroscopic device performance. References [1] Stanbery BJ, Abou-ras D, Yamada A, Mansfield L. CIGS Photovoltaics : Reviewing a New Paradigm, Phys. D: Appl. Phys. 55 (2022) 173001. [2] Abou-Ras D, Kirchartz T, Rau U. Advanced Characterization Techniques for Thin Film Solar Cells. Weinheim, Germany: Wiley; 2016. [3] Abou-Ras D, Kavalakkatt J, Nichterwitz M, Schäfer N, Harndt S, Wilkinson AJ, et al. Electron backscatter diffraction: An important tool for analyses of structure-property relationships in thin-film solar cells. Jom. 2013;65(9):1222–8. Figure 1 : A) SEM cross section of the CIGSe absorber layer. B) EBSD image showing the local grain orientation and grain sizes. C) EDS map of the Ga-L series D) CL emission energy distribution, σlat.CL and σver.CL are the fluctuations in the CL emission energy in the lateral and vertical directions. 39

MS1.P005 Probing sodium storage mechanism in hollow carbon nanospheres anode using liquid phase transmission electron microscopy J. Hou1, N. V. Tarakina1, M. Antonietti1 1Max Planck Institute of Colloids and Interfaces, Colloid Chemistry Department, Potsdam, Germany Carbon-based electrode materials are considered promising anode materials for sodium-ion batteries. Understanding the Na transport and storage mechanism is crucial for developing more reliable anode materials. However, it has remained elusive. [1] The combination of an enclosed chamber with other stimuli in TEM brings advances in in- situ/operando detecting of dynamic phenomena in the liquid phase with high temporal and spatial resolution without risking sample modification in vacuum. Here, we synthesized hollow carbon spheres (HCSs) with tailored composition and desirable morphology for probing the Na-storage behavior in carbon-based electrode materials by means of in- situ TEM. [2] We tracked the absorption of Na ions at the slope region of discharging nitrogen-doped porous HCSs (NPHCSs), which is followed by Na deposition at the potential plateau under the overpotential condition, by step-wise SEM-EDX experiments. NPHCSs surface remains partially covered after Na stripping (Fig. 1). We monitored the dynamic procedure of SEI formation and Na deposition within and around the NPHCSs by running micro batteries liquid phase TEM experiments (Fig. 2a-c). We observed the carbon shell expansion as a result of Na filling, SEI layer assisted NPHCSs binding, and partially reversible Na deposition (Fig. 2d-f). Na filling into carbon shells was further confirmed by energy-filtered TEM. Moreover, the electronic and ionic distribution after sodiation suggests the existence of Na0 and Na+1 within NPHCSs (Fig. 2g-h). At the beginning of sodiation, Na absorbs on the surface of the nanospheres, accompanied by SEI formation essentially filling gaps between nanospheres within the NPHCS-based electrode. Consequently, this facilitates the Na ions' transport into the hollow spheres or through the tunnels between them until the current collector is reached. Although the curvature-induced electron density gradient in the hollow spheres can partially drive Na deposition inside the spheres at a low cycling rate, most Na deposition takes place underneath the electrode layer. Both Na storage paths contribute to improving the safety of sodium-ion batteries by preventing dendrite growth on the anode. We gratefully acknowledge ﬁnancial support of the Max Planck Society and European Research Council (ERC). Reference: [1] C. Vaalma, et al. Nat. Rev. Mater. 2018 34 2018, 3, 1. [2] Z. L. Wang, et al. J. Phys. Chem. Solids 2000, 61, 1025. Fig. 1: SEM images of NHPCSs at different stages of sodiation/disodiation and the schematic illustration of sodiation procedure with Na content detected by EDX. Fig. 2: (a-c) In-situ STEM image of partially sodiated NPHCSs during cycling. Na is highlighted in yellow. Hollow arrows in (a) indicate the empty spheres while solid arrows in (b) indicate the Na-filled spheres. (d) STEM-HAADF image of pristine NPHCSs. STEM-BF(e) and HAADF(f) image of cycled NPHCSs. (g) Low-loss EELS comparison of pristine and cycled particles. (h) EFTEM comparison of pristine (black) and cycled particles (red). Electron density and sodium mapping are corresponding to the selected energy range between 4-7eV and 30-33 eV respectively, as highlighted in yellow in (g). 41

MS1.P006 In-situ TEM studies of phase change thermoelectric MgAgPtSb M. O. Cichocka1, R. He1, D. Pohl2, B. Rellinghaus2, K. Nielsch1,3, N. Perez Rodriguez1 1Leibniz IFW Dresden, Dresden, Germany 2Dresden Center for Nanoanalysis (DCN), Technische Universität Dresden, Dresden, Germany 3Institute of Material Science, Technische Universität Dresden, Dresden, Germany The structure of thermoelectric materials largely determines their characteristics. Hence, a better understanding of the details of the structural transformation conditions can open doors for new applications. Therefore, a microscopic comprehension of the impact on the nanoscale structure dynamics is crucial, especially with the progress of intensified miniaturization. In this study, the effect of heat treatment on the structure of phase change MgAgPtSb is investigated [1,2]. The material was heated in-situ in the transmission electron microscope (TEM). Using a combination of scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) we unveil the structural and chemical state of the thermoelectric. Thus, we can correlate real-time changes during the heating process with the presence of structural distortions, impurities and compositional transformations. Additionally, the crystal structure of MgAgPtSb thermoelectric material undergoes a phase transformation when the temperature changes. The tetragonal I-centered phase transforms to the P-centered tetragonal crystal system and at approximately 400°C to a cubic Heussler structure [3]. In this work, we study the changes taking place during the phase transitions as it usually leads to increased defects and second phase precipitation [4]. Keywords: thermoelectrics, in-situ transmission electron microscopy, phase transformation References [1] Chem. Mater. 2015, 27, 909-913. [2] Adv. Funct. Mater. 2017, 27, 1604145. [3] Phys. Rev. B 2012, 85, 144120. [4] Chem. Mater. 2017, 29, 6378-6388. 43

MS1.P007 Correlative microscopic analyses of PbI2 precipitates on the surface of triple- halide perovskite films D. R. Wargulski1, K. Xu1, S. Albrecht1, H. Hempel1, D. Abou-Ras2 1Helmholtz-Zentrum Berlin, Berlin, Germany 2Helmholtz-Zentrum Berlin, Abteilung Struktur und Dynamik von Energiematerialien, Berlin, Germany Introduction Triple-halide perovskites1 form a promising but complex material system that offers the possibility to vary band-gap energies via compositional changes for tandem solar cell applications. Perovskite-silicon tandem solar cells already exceeded the 31% of efficiency2 and represent today's most promising tandem solar cell technology. Main obstacles to bring this technology to the market are the upscaling to industrial cell sizes and through-puts. Objectives The aim of the present study is to investigate triple-halide perovskite absorber layers for solar cells by correlative electron microscopy. These layers were deposited by slot-die coating plus N2 gas quenching, a deposition technique suitable for large-area and high-throughput production. Optimal process parameters for this technique, such as substrate temperatures, have not yet been well investigated. Therefore, we analyzed absorber layers produced at various substrate temperatures by several electron microscopy methods and correlated these results with photovoltaic parameters of cells made of absorbers with identical composition. Materials & Methods the films with the study, present triple-halide In composition (Cs0.22FA0.78)Pb(I0.85Br0.15)3 + 5 mol% MAPbCl3 were analyzed. These thin films were prepared by means of slot-die coating and subsequently annealed at temperatures of 125 °C, 150 °C, 160 °C and 170 °C. We conducted secondary electron (SE) imaging, electron backscatter diffractometry (EBSD), energy-dispersive X-ray spectroscopy (EDX), and cathodoluminescence (CL) in scanning electron microscopy on these thin films and determined solar cell parameters (short-circuit current JSC, open-circuit voltage VOC, fill factor FF and photo-conversion efficiency PCE) under one sun illumination in a solar simulator. perovskite thin Results The SE imaging indicated and EBSD measurements confirmed an increased average grain size with increasing annealing temperature, as it had been expected. By means of EBSD, EDX and CL, PbI2 precipitates were detected and their area fraction on the perovskite-type thin films were quantified (Fig. 1). When varying the annealing temperature from 125 to 170 °C the efficiency maximum of almost 20% was found at 125 °C, and the efficiency decreases with increasing temperature (mainly owing to decreasing Voc and FF values). The area fraction of PbI2 increases from 5% to more than 20% within the studied temperature range, which enhances nonradiative recombination (thus, decreasing the Voc) and increases significantly the series resistance of the solar cells (thus, decreasing the FF). Figure 1: Triple-halide perovskite films analyzed by SE imaging, EBSD, CL and EDX. Green colors correspond to the triple-halide perovskite phase, and blue to PbI2. Conclusion We found an increasing amount of PbI2 precipitates with increasing annealing temperatures on the surface of triple- halide perovskite films by means of various electron microscopy techniques. It was possible to correlate the presence of the PbI2 phase on the triple-halide perovskite thin-film surface to deteriorated solar cell performances. For the further improvement of these solar cells, it is mandatory to reduce the area fraction of the PbI2 precipitates to a minimum. 44

MS1.P008 Microscopic insight into the stability and activity of Pt single atom photocatalysts on TiO2 J. Will1, N. Denisov2, S. Qin2, T. Yokosawa1, J. Wirth1, P. Schmuki2, E. Spiecker1 1Institute of Micro- and Nanostructure Research (IMN) & Center for Nanoanalysis and Electron Microscopy (CENEM), Materials Science, Erlangen, Germany 2Chair for Surface Science and Corrosion, Materials Science, Erlangen, Germany In this study, we investigate the stability and activity of Pt single atoms (SAs) deposited on TiO2 via a facile dark- deposition approach [1]. We aim to identify stable and active Pt SAs on both anatase nanosheets and ~7 nm thick polycrystalline anatase films sputtered on electron transparent SiO2 TEM grids to get an atomistic understanding on the SA anchoring as well as their stability upon photocatalytic water splitting. To identify stable species, anatase nanosheets where loaded with Pt SAs and further step-by-step leached by cyanide to reduce the SA loading while monitoring the photocatalytic activity as well as the atomistic configuration by aberration corrected high-angle annular dark field scanning transmission microscopy (STEM) [2]. In addition, we exploit the TiO2 model thin films in combination with identical location STEM investigations to visually follow the photoinduced destabilization over 24 h of operation time. Here, a machine learning-based algorithm is used to segment SAs as well as their agglomerates at various regions of interest. Within this approach we get quantitative information about the abundance and arrangement of the SAs as function of photocatalytic operation time. We show that neither the majority of anchored Pt SAs nor metallic Pt0 species are responsible for the overall observed high photocatalytic activity. In fact, >90% of the deposited Pt can be removed by cyanide leaching without significant loss in photocatalytic activity (Fig. 1). In this way, we could identify an optimized SA loading quantity for anatase nanosheets, which is accompanied by a remarkable turnover frequency of ~4.87 x 105 h-1 for H2 evolution. Identical location microscopy (see Fig. 2) after five different photocatalytic operation times reveals that the majority of initial deposited Pt is in a SA or multimere state. Within 1 min, ~90% of the SAs and multimeres agglomerate rapidly to 2D rafts. This agglomeration process continues, however, at a much slower speed within the next 24 h. Here, mainly the 2D rafts coarsen to nanoparticles with an average size of ~4 nm, whereas the photocatalytic activity stays unchanged and still 7% of the Pt loading maintains its SA state. In addition, the observed SA agglomeration is heavily influenced by the presence of methanol as a hole scavenger, elucidating the role of charge carriers on the stability of Pt SAs on TiO2. Moreover, identical location microscopy allows to follow various additional phenomena, like dissolution of 2D rafts, as well as morphological changes and ripening of agglomerated Pt species revealing the high dynamics in the system under photocatalytic conditions. In conclusion, high resolution STEM on nanostructures and thin model systems is an ideal tool for studying Pt SA photocatalysts, their local arrangement as well as stability after different operation times. The correlation with photocatalytic data as well as spectroscopy (e.g. XPS, XAAS) allows to establish structure property relationships further improving the material efficient SA approach for photocatalytic applications. [1] Cha, G., Mazare, A., Hwang, I., Denisov, N., Will, J., Yokosawa, T., ... & Schmuki, P. (2022). Electrochimica Acta, 412, 140129. [2] Qin, S., Denisov, N., Will, J., Kolařík, J., Spiecker, E., & Schmuki, P. (2022). Solar RRL, 2101026. 46

MS1.P009 Surface reduction studied by in situ STEM on Pt-Ceria catalysts used for CO oxidation C. B. Maliakkal1, P. Dolcet2, L. Braun2, A. R. Lakshmi Nilayam1, A. De Giacinto3, M. Casapu2, J. D. Grunwaldt2, S. Gross3, D. Wang1, C. Kübel1 1Karlsruher Institut of Technologie (KIT), Eggenstein-Leopoldshafen, Germany 2Institute of Technical and Polymer Chemistry, Karlsruhe, Germany 3Department of Chemical Sciences, Padua, Italy Heterogeneous catalyst systems used in exhaust gas treatment typically consist of precious metal nanoparticles (often Pt, Pd, Rh) supported on a metal oxide supports (often ceria, i.e. cerium IV oxide). The scarcity and cost of such catalysts demands careful design of more active and cost-efficient systems. Such theoretical predictions can happen only if there is a detailed understanding of the substrate-catalyst-gas interactions, the dynamic behavior of the catalyst system during catalysis and relevant gas atmospheres, and ultimately the reaction mechanism. One important parameter that should be ideally incorporated into such theoretical modelling, especially in systems such as CeO2 where the surfaces are known to have oxygen vacancies[1], is the spatially resolved quantitative information about the oxygen vacancies on ceria and at Pt-ceria interface. However, this information at CO oxidation conditions is missing. We measure electron energy loss spectroscopy (EELS) maps to find spatially resolved information of Ce oxidation state experimentally under vacuum, CO oxidation conditions and at other relevant gas conditions. Since the study aims at distinguishing the reduced surface layer (i.e. region containing Ce3+) to that of the bulk (Ce4+) it is important to study CeO2 crystals with well-defined facets. Hence in this study we use CeO2 cubes (with {100} crystal planes forming the surface facets). CeO2 cubes were prepared by Ce(NO3)3.6H2O using an acetate-acetic acid buffer- mediated hydrothermal synthesis (similar to that of reference [2]) (Fig.1 a,b). Pt nanoparticles were prepared by microfluidic synthesis (similar to [3]) (Fig. 1 c). EELS is done in a Themis Z; while the gas experiments are conducted with Atmosphere holder from Protochips. The EELS mapping of ceria cubes in vacuum shows that there is a surface layer containing Ce3+ atoms (Fig.2). When oxygen is introduced into the system we observe that this surface layer with Ce3+ atoms becomes narrower than in vacuum at the same temperature (Fig.3). The effect on this surface layer in N2, H2, CO and CO+O2 mixture at different temperatures, pressures, and waiting duration after the introduction of gas, are underway. The effect of the multiple catalytic cycles on the surface layer will also be investigated. The effect of electron beam on the EELS spectrum maps is studied to find that it causes additional surface reduction, while in the bulk region no significant changes are noticed in the spectral features within the range of electron doses we studied yet. We will attempt to study the Ce and Pt oxidation state on the samples with Pt nanoparticle loaded on CeO2 cubes. We also intend to study the structural/morphological dynamics of the Pt-CeO2 catalyst using in situ STEM. Since the catalyst system is extremely dynamic during catalytic activity, in situ (s)TEM can provide valuable information on the active structure and its evolution in different relevant gas environments and reaction conditions. Results about Ce oxidation state mapping and catalyst dynamics will be presented. References [1] Goris et al. ACS Nano 2014 (8) 10878 [2] Lyu et al. Nanoscale 2016 (8) 7923 [3] Tofighi et al. Reaction Chemistry & Engineering 2017 (2) 876 Fig. captions: (a, b) Ceria cubes; (c) Pt nanoparticles on ceria cubes 1. 2. Oxidation state maps corresponding to Ce4+ and Ce3+ of a ceria cube in vacuum. 3. Normalised average EELS spectra showing the Ce core loss edge in vacuum and O2 at both surface and interior. 48

MS1.P010 Energy dispersive X-ray spectroscopy (EDS) applied on energy related materials and Li quantification as fraction of not identified element U. Golla-Schindler1, J. Niedermeyer1, E. Barbosa Sa1, C. Weisenberger1, T. Bernthaler1, V. Knoblauch1, G. Schneider1 1University Aalen, Materials Research Institute, Aalen, Germany Energy storage and conversion technologies are key technologies for the future on the way of "going green". The quantification of Li and limited spatial resolution of EDS analysis are bottlenecks to overcome. There the spectroscopy of low energy x-rays with the windowless Oxford extreme EDS detector open new prospects. This enables to reduce the accelerating voltages and/or beam currents and therefore additionally radiation damage. Fig 1a) show spectra of Li metal, where the grey spectrum is recorded directly after the transfer from the glove box to the SEM and the red spectrum after 9 days storage at air. The significant changes of the Li peak content, shape and peak position document the sensitivity and reactivity of Li, exemplary to air exposure. One sensitive part in Li-Ion batteries is the interface between the anode and the separator with the solid electrolyte interface covering the anode surface and eventually with reaction products on top. Fig. 1 b), c) show such reaction products of a Li-Ion battery with a LiFePO4 cathode and a carbon anode. The EDS spectra show significant enrichment for the dark surface coated areas on top of the massive anode encrustation spectrum16 and the round shaped particle spectrum 17. This enables to determine precipitations, which reduce the amount of Li inventory and on this way the battery performance. Starting quantification consistently upcoming questions are: How reliable are EDS studies for real life application and what are the influences of etc. sample preparation. Therefore a systematic study was performed on Li(NixMnyCoz)O2 cathode material and the first topic was the determination of the stoichiometric composition of Ni, Mn and Co, where Ni, Mn and Co share one position, therefore x+y+z=1. Fig, 2 a) shows the results for studies obtained with different sample treatment like: 1. shuttle => argon atmosphere and SEM vacuum, top view 2. air => in air, top view 3. gold => in air and coated with gold ( 4 nm), top view 4. carbon => in air and coated with carbon (10 nm), top view 5. cross section => in air cross section obtained with an argon ion mill All performed studies (Fig. 2) deliver a stoichiometric relationship close to NMC (811). This shows the robustness of the performed studies. One limitation for the chemical quantification of Li-Ion battery materials is, that bonded Li cannot directly detected by EDS. We determine the Li amount as the missing element fraction of not normalized quantitative EDS analysis. Precondition is that during the measurement no dynamic processes like contamination, radiation damage, charging etc. are taking place. Additionally we solely take those spectra for the quantification into account, where the oxygen weight percent of the EDS spectra is ±3% of the expected weight percent for oxygen in Li(Ni8Mn1Co1)O2 . We obtained mean values of the Li weight percent for the analytic conditions: 1. shuttle: 6,0±0,5% ; 2. air: 6,1±0,8% ; 3. gold: 10,6±0,8% ; 4. carbon: 10,4±0,7% and 5. cross section: 6,4±0,6%. The expected value for a 100% lithiated cathode material is 7,1%, where this value overestimate the real content and will be reduced by approx. 10% formation loss after the first battery cycle. The results of the studies performed with the conditions 1, 2, 5 agree nicely with the expectation, where the gold and carbon coating lead to a significantly overestimation of the Li content. [1] [1] The authors gratefully acknowledge the German BMBF for financial support. 50

MS1.P011 Improvement of SEM-SXES analysis for beam sensitive materials by using cooling stage Y. Yamamoto1, T. Murano1, S. Koshiya1, K. Yamashita1 1JEOL Ltd., Akishima, Japan Soft X-Ray Emission Spectrometer (SXES), which can be installed on SEM and EPMA (Electron probe microanalyzer), is a useful method for chemical state analysis by detecting the energy state of valence electrons. In particular, since it is possible to detect low-energy characteristic X-rays such as lithium (Li) K-line and analyze the chemical state, it is expected as a method for chemical state analysis of Lithium Ion secondary Battery (LIB) materials in a charged state. Field Emission-SEM equipped with SXES enables us to obtain chemical state information in the vicinity of the bulk top surface by using low-kV analysis. (1) However, it is known that the irradiation of an electron beam causes a change in the chemical state of the beam-sensitive materials such as lithium compounds during the observation. (2) This study shows the improvement of chemical state analysis for beam-sensitive materials using the SEM-SXES system with a cooling stage. The Schottky FE-SEM, JSM-IT800(JEOL), combined with the SXES, SS-94000SXES (JEOL), and cooling stage C1003 (Gatan, Inc.), was used to examine Lithium Sulfide (Li2S) reagent for the solid electrolyte of LIB. To prevent deterioration of the samples due to atmospheric exposure, these samples were transferred to the SEM-SXES system using a transfer vessel for air isolation. The changes in the chemical state of Li2S were confirmed by time-resolved SXES analysis. (2) SXES point analysis for Li2S at room temperature (RT), was performed at an accelerating voltage of 3 kV and a probe current of 20 nA (Fig. 1 and Fig. 2). When Li2S is continuously irradiated with an electron beam for 450 seconds, formation of deposition on the sample surface can be confirmed in the backscattered electron (BSE) image (Fig.1). And the spectrum of the precipitated Li and S are detected in the SXES analysis result at an acquisition time of 450 seconds (Fig.2 left). By contrast, in the time-resolved SXES analysis performed every 15 seconds from 0 to 450 seconds, the Li spectrum shape changes in response to the irradiation time (Fig.2 right). This demonstrates that Li is metallized as the dose of the electron beam increases. Figure 3 shows the result of SXES point analysis with -100℃ cooling at 3kV and 20 nA prove current. In the BSE image (Fig.3 left), there are no change in contrast. It can be seen that no precipitation has occurred on the surface of Li2S after performing SXES analysis with an acquisition time of 450 seconds. Even in the SXES spectrum (Fig. 3 right), which was time-resolved every 15 seconds from 0 to 450 seconds, no spectral change with the passage of time was confirmed. Comparing the SXES results obtained at room temperature and at -100 ° C, it can be seen that the Li K spectrum derived from metallic lithium was not detected and the Li K spectrum derived from Li2S was obtained by cooling at -100 ° C (Fig. 4). This result lead to the possibility of a new technique for SEM-SXES analysis using specimen cooling system for materials whose chemical state changes due to electron beam irradiation.In this presentation, more examples of specimen cooling application for SEM-SXES analysis of materials whose chemical state changes due to electron beam irradiation, such as polymers and negative electrodes of solid-state batteries, will also be introduced. References: (1) Yamamoto. Y et al, Microscopy and Microanalysis 24(S1):1062-1063(2018) (2) Yamamoto. Y et al, Microscopy and Microanalysis 26(S2):68-70(2020) 53

MS1.P012 TEM analysis of the water and acid treated LNMO faceted particles D. Geiger1, J. Biskupek1, T. Böhler2,3, M. Künzel2,3, D. Bresser2,3, U. Kaiser1 1Universität Ulm, Ulm, Germany 2Helmholtz Institute Ulm (HIU), Ulm, Germany 3Karlsruher Institut of Technologie (KIT), Karlsruhe, Germany Steady progress of battery performances attests the necessity of intense battery research. As promising high-voltage and high-capacity cathode material LiNi0.5Mn1.5O4 (LNMO) was investigated for Co-free next-generation Li-ion batteries. Our investigation focused on determining the structure property relationship of these materials at the microscopic and preferrably atomic level via different TEM methods to unravel the morphologic, crystallographic and chemical structure of carefully designed LNMO. The main objectives of our research-project "H2O-LIMO" are related to the overcoming of the water sensitivity of Li transition metal oxides, especially LNMO, as Co-free cathode, which is possible only if a fundamental understanding of occurring processes is established: -general effect of water exposure and the impact of tailored surface facets of LNMO; -effect of adding inorganic acids (e.g., H3PO4), which have been proven [1] to stabilize the LNMO surface by forming a thin metal phosphate surface layer; -understanding processes occurring at the LNMO/water interface. First, the synthesis of single-crystalline LNMO particles with tailored surface facets has been carried out according to a combined precipitation/evaporation method [2]. Perfectly octahedral LNMO particles with solely {111} surface facets as well as truncated LNMO particles with a combination of {100} and {111} surface facets were obtained. Depending on the temperature and duration of the annealing, the preparation of either ordered (space group (sp): P4332) or disordered (sp: Fd-3m) LNMO is achieved. The mentioned cation ordering, the presence of Mn3+ in disordered LNMO as a result of oxygen vacancies, and that of solely Mn4+ in the ordered phase is expected. The Mn:Ni ratio, the vacancies as well as the initial oxidation state of the Mn cations is expected to play an essential role for the interaction with water. Similarly, the varying acidity of the different surface facets is expected to play a key role for the reaction with the aqueous environment. The size morphology and crystallographic orientations were investigated by TEM bright- (fig.1a,c,d) and dark-field (fig. 1b) imaging, diffraction (fig.1e) and HRTEM (fig.1f) showing the expected octahedron faceted primary particles. Since the powder particles are disordered agglomerations of overlapping primary particles, it is difficult to find an isolated octahedron particle for the foreseen TEM analysis.Further, the effect of the (acidic) aqueous treatment on the electrochemistry of the new faceted synthesized particles has been studied by STEM-EDX. The atom concentration distributions especially at and around the particle surface (fig.2a,b) shows a change of the ratio Mn:Ni at the surface and an increased P concentration in this region. HRTEM and STEM-EDX were performed with a Thermofisher Talos 200X TEM at 200 kV and with an image Cs-corrected TEM FEI Titan 80-300 at 300kV. The first results are promising a better understanding of the influence of the (acidic) aqueous treatment on the faceted synthesized LNMO particles and their electrochemical behaviour. The investigation will be extended to other material treatments (e.g. other acids). [1] M. Künzel et al., ChemSusChem 11 (2018) 562 [2] M. Kuenzel et al., Materials Today 2020 (39) 127 Acknowledgement: This work was supported by DFG in the frame of the research project "H2O-LIMO" (Wechselwirkung von Wasser und wässrigen Säuren mit Lithiumübergangsmetalloxiden). 56

MS1.P013 Novel enhanced particle size analysis algorithm using enhanced circular Hough transformation J. Guckel1,2, M. Görke3, G. Garnweitner2,3, H. Bosse1,2, D. Park1,2 1Physikalische-Technische Bundesanstalt, 5, Braunschweig, Germany 2Laboratory of Emerging Nanometrology (LENA), Braunschweig, Germany 3Technische Universität Braunschweig, Institute for Particle Technology (iPAT), Braunschweig, Germany Nanoparticles (NP) have a wide range of applications in diverse research fields, such as lithium ion batteries, catalysis, medical engineering, etc., due to their specific characteristics [1]. The surface effects become predominant as the dimension of the particles is reduced. Therefore, physical and chemical properties of NPs are closely intertwined with their particle size [2]. Due to this critical parameter of particle size, only a slight deviation from the target size is usually intended to achieve uniform characteristics for a specific application. Hence, the reliable analysis of the particle size distribution is an important task for successful implementation of advanced nanotechnological applications. NPs size distribution can be analyzed by measuring individual particle size from a large number of images of NPs obtained by electron microscopy. The automatic analysis tools are essential, as a large number of images are required for obtaining reliable statistics for the size distribution [3]. However, currently available automatic procedures are limited to provide accurate results if the NPs are severely overlapping. In order to overcome these limitations, we developed a novel approach for the detection of spherical NPs based on the iterative particle analysis using the enhanced circular Hough transformation (CHT) algorithm. This approach solves the issue of overlapping particle clusters by iteratively detecting large particles first, removing them from the image and then find the smaller particles from the remainder of the cluster. The main loop of our iterative routine splits a singular particle size interval into multiple smaller ones and passes through them one by one. This approach keeps consistent detection quality over very large intervals. The CHT algorithm involves finding the best fit based on only contour detection of particles. However, utilizing this approach leads to critical problems, such as the halo error, void error and particle group error, as the CHT algorithm includes no local intensity analysis as explained in detail in Figure 1. In order to avoid the aforementioned problems, additional local intensity criteria are included. We investigated synthesized FePt NPs using high angle annular dark field contrast (HAADF) imaging via a double- abberation corrected JEOL NeoARM 200F. From the single HAADF image of the FePt NPs at the magnification of roughly 2 million, 630 particles were automatically detected after manual removal of badly detected 19 particles using our algorithm (Figure 2). The measured mean particle size was 2.563 nm with a standard deviation of 0.485 nm. Although the size of NPs varies significantly with severely overlapping particles forming complex clusters in the selected system, overall our novel iterative particle analysis algorithm provided promising results in particle size distribution, showing very minor problems which can be corrected with available manual correction. References: [1] Görke, M. and Garnweitner, G., Crystal engineering of nanomaterials: current insights and prospects , CrystEngComm, 2021 [2] Issa, B. et al., Magnetic Nanoparticles: Surface Effects and Properties Related to Biomedicine Applications, International Journal of Molecular Science, 2009 [3] Meng, Y. et al., Automatic detection of particle size distribution by image analysis based on local adaptive canny edge detection and modified circular Hough transform, Micron, 2018 58

MS1.P014 Unraveling the structural properties of Bi(Fe1-xCrx)O3 thin films O. Wenzel1, S. Petrick1, A. Zintler1, H. Störmer1, M. Hoffmann1, D. Gerthsen1 1Karlsruher Institut of Technologie (KIT), Laboratorium für Elektronenmikroskopie (LEM), Karlsruhe, Germany This work focuses on the structural, chemical, and optoelectronic properties of Bi(Fe1-xCrx)O3 thin films synthesized by spin-coating for future ferroelectric solar-cell absorber layers. We want to use laterally polarized ferroelectric domains and their electric fields to drive the photogenerated charge carrier towards the domain walls, along which they can be extracted into the electrodes. Early results on the efficacy of this idea were achieved with methylammonium lead halide (MAPH) perovskites [1]. However, we strive for a non-toxic ceramic-based material with similar properties. A possible material system with desirable properties and suitable bandgap energy is Bi(Fe1-xCrx)O3 (BFCO), where Bi2+ occupies the A site with alternating Fe2+ and Cr2+ on the B site in the ABO3 perovskite structure. In this contribution, the material properties are investigated in detail by different electron microscopic techniques on the nanoscale to understand the bulk material's optoelectronic properties and to improve material synthesis. BFCO films with different Fe/Cr concentrations were deposited by spin coating an Fe-, Cr- and Bi- containing sol onto fluorine-doped tin oxide (FTO) substrates followed by a calcination step at 350 °C in air. We used several analytical scanning/transmission electron microscopy (S/TEM) techniques for comprehensive characterization, such as quantitative energy-dispersive X-ray spectroscopy (STEM-EDXS), electron energy loss spectroscopy (STEM-EELS), selected area electron diffraction (SAED), and other imaging modes. Nanoscale investigations were accompanied by X-ray diffractometry (XRD) and UV-Vis spectroscopy to analyze the films. The BFCO thin films are polycrystalline with a thickness of about 400 nm. Bright-field S/TEM images reveal a homogeneous microstructure with 30-50 nm grain sizes. The crystal structure is predominantly tetragonal BiFeO3, however, we do note that occasional metal Bi nanoparticles and amorphous Cr-Fe oxide can be seen in some synthesis batches. Quantitative analysis of STEM-EDXS maps shows that the average composition of the thin film follows the expected stoichiometry Bi(Fe1-xCrx)O3 . Furthermore, core loss STEM-EELS accompanied by an analysis of the fine structure of Fe and Cr confirms the 2+ oxidation state and shows that both Fe and Cr are located at the B- site in the perovskite. Analyses of the crystal structure with SAED, HRTEM and the coordination environment revealed with STEM-EELS fits with the bulk crystal structure determined by XRD. Further, the nanoscale secondary phases which occur in individual synthesis batches help explain additional contributions to the bulk the UV-Vis signal. Based on comprehensive electron microscopic analyses, this study demonstrates that BFCO thin films can be successfully synthesized by tuning the sol-gel synthesis conditions. Looking ahead, we are aiming to fine-tune the ferroelectric domain structure. [1] H. Röhm et al., Adv. Mater., 2019, 26, 1806661] [2] Mustonen, O. et al Chem. Commun., 2019, 55, 1132-1135 [3] Herber, R-P and Schneider, G.A., J. Mater. Res., 2007, 22 60

MS1.P015 TEM investigation of (Ag,Cu)(In,Ga)Se2 solar cells X. Jin1, R. Schneider1, D. Hariskos2, S. Paetel2, W. Witte2, D. Wang3,4, C. Kübel3,4, M. Powalla2, D. Gerthsen1 1Karlsruher Institut of Technologie (KIT), Laboratorium für Elektronenmikroskopie (LEM), Karlsruhe, Germany 2Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Stuttgart, Germany 3Karlsruher Institut of Technologie (KIT), Institut für Nanotechnologie (INT), Karlsruhe, Germany 4Karlsruher Institut of Technologie (KIT), Karlsruhe Nano Micro Facility (KNMF), Karlsruhe, Germany The performance of Cu(In,Ga)Se2 (CIGS) thin-film solar cells can be improved by partial substitution of Cu with Ag, forming (Ag,Cu)(In,Ga)Se2 (ACIGS) [1]. However, the photovoltaic properties of ACIGS solar cells are significantly influenced by the Ag concentration and its spatial distribution. In order to determine an optimum Ag content and to identify experimental conditions for the fabrication of high-efficient ACIGS devices, ACIGS thin films in this work were prepared by supplying the Ag by two different methods. Providing Ag in both experimental campaigns, the power conversion efficiency (PCE) of the cells decreased around 2% absolute. The chemical and structural properties of the ACIGS layers were studied by (scanning) transmission electron microscopy ((S)TEM) combined with energy- dispersive X-ray spectroscopy (EDXS). In the first experimental campaign two ACIGS layers were fabricated by in-line co-evaporation of CIGS on Mo coated glass substrates, which were pre-plated with a 40 and 80 nm Ag layer, respectively, acting as precursor. In the second experimental campaign four ACIGS films with integral Ag/(Ag+Cu) ratios (AAC) of 0, 0.05, 0.11, and 0.20, as determined by X-ray fluorescence, were fabricated by co-evaporation of all matrix elements (including Ag) on Mo substrates without a Ag precursor. Cross-sectional TEM lamellae were prepared from these samples by focused-ion- beam milling using an FEI dual beam Helios G4 FX microscope. For TEM and STEM/EDXS investigations, a 200 kV FEI Tecnai Osiris and a 300 kV Thermo Fisher Themis 300 transmission electron microscope was used, where the latter has a Cs-probe corrector. Fig. 1 shows the depth-dependent line profiles of the Ag concentrations (Figs. 1a,c) together with the resulting Ga/(Ga+In) ratios (GGI) (Figs. 1b,d) of the ACIGS layers deposited with the Ag precursors or by Ag co-evaporation. The average Ag contents are also given in Figs. 1a,c. In general, the GGI profiles determined by STEM/EDXS are in good agreement with corresponding measurements by glow discharge optical emission spectroscopy (not shown here). Evidently, the GGI gradients are flattening with increasing Ag content (Figs. 1b,d). It is noted that the GGI gradient of the Ag-free CIGS with AAC = 0 (red line in Fig. 1d) resembles that of ACIGS with AAC = 0.05 (green line), which is likely due to the small difference in Ag content. For the precursor-deposited ACIGS films, Ag segregation was observed in some grain-boundary regions, which is more pronounced in the sample with the higher Ag content. Fig. 2 shows elemental maps for a representative Ag- enriched grain boundary in the ACIGS sample with 80 nm Ag precursor. An In and Ag enrichment combined with Se deficiency was detected at the grain boundary with a length of several hundred nanometers. In comparison, Ag segregation was not detected at grain boundaries of the co-evaporated ACIGS films, even for the high AAC ratios. Since the PCEs of all ACIGS devices in this work decrease with increasing Ag contents, the Ag enrichment at grain boundaries and/or the flattening of the GGI gradients are likely to contribute to the deterioration of the device performance. [1] M. Edoff et al., IEEE J. Photovolt. 7 (2017) 1789. [2] The support of the German Federal Ministry for Economic Affairs and Climate Action (BMWK) within the EFFCIS-II project under contract No. 03EE1059A (ZSW) and contract No. 03EE1059E (KIT) is acknowledged. 61

MS1.P016 OsO4 staining as a tracer for the visualization of degradation of porphyrin- based battery electrode material G. Neusser1, T. Philipp1, E. Abouzari-Loft2,3, S. Shakouri3, F. D. H. Wilke4, M. Fichtner2,3, M. Ruben3,5,6, C. Kranz1 1Institute of Analytical and Bioanalytical Chemistry, Ulm University, Ulm, Germany 2Helmholtz Institute Ulm (HIU), Ulm, Germany 3Karlsruher Institut of Technologie (KIT), Institute of Nanotechnology, Karlsruhe, Germany 4GFZ German Research Centre for Geosciences, Potsdam, Germany 5Karlsruher Institut of Technologie (KIT), Institute of Quantum Materials and Technology, Karlsruhe, Germany 6Centre Européen de Science Quantique (CESQ), Université de Strasbourg, Institute de Science et d’Ingénierie Supramoléculaires (ISIS), Strasbourg, Germany Due to the growing need for sustainable, rechargeable energy storage systems, efforts are made towards the development and improvement of battery electrode components based on organic compounds. Electron donor- acceptor metalloporphyrin complexes like [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) are promising materials for rechargeable lithium[1], sodium[2] and magnesium batteries[3]. In this study we demonstrate that structural changes of composite CuDEPP electrode material (50 wt.% CuDEPP active material, 40 wt.% carbon black and 10 wt.% poly(vinylidene difluoride)) for Li/ LiPF6/CuDEPP batteries can be visualized including the initial self-conditioning step during the first charge-discharge cycle and changes of the active material after longer charge-discharge cycles via focused ion beam/scanning electron microscopy (FIB/SEM) and energy dispersive/wavelength dispersive X-ray spectroscopy (EDX/WDX) measurements. Pristine CuDEPP electrode and electrodes cycled for 1, 200 and 2000 times in Li half-cell with LiPF6 electrolyte were treated with OsO4 vapor and embedded in silicone resin. After staining and embedding, the samples were investigated using FIB/SEM cross-sectioning and tomography (Helios Nanolab600), EDX measurements using a Quanta 3D FEG (both Thermo Fisher) equipped with a SDD Apollo XV (EDAX) and WDX measurements obtained with a JXA- 8530FPlus (JEOL). For the pristine sample, EDX and WDX measurements show no uptake of Os, as the aromatic conjugated double and triple bonds that occur in pristine CuDEPP are not affected by OsO4 staining. However, all cycled samples show a gradient in grey values in BSE images with highest values at the edges of each grain due to the incorporation of Os. The occurrence of Os coincides with increased P content (Fig.1) and therefore with the penetration of electrolyte (LiPF6) into the CuDEPP particles during cycling. As OsO4 does not react with the pristine material, a measurable Os content within the cycled CuDEPP directly indicates structural changes of CuDEPP (degradation) given the fact that Os enrichment is related to the formation of non-aromatic double bonds [4]. Fig.1: BSE image (a) and WDX map of P (c) and Os (d) of CuDEPP particles after 200 cycles. (b) show intensity profiles of BSE, P and Os signal along the yellow line. Two CuDEPP particle marked by red line in (a). [1] P. Gao et al. Angew. Chemie Int. Ed. 56 (2017) 10341–10346. [2] X. Chen et al. Nano-Micro Lett. 13 (2021) 71. [3] E. Abouzari-Lotf et al. ChemSusChem. 14 (2021) 1840–1846. [4] T. Philipp et al. J. Power Sources. 522 (2022) 231002. 63

MS1.P017 Cryo-SEM/FIB material and water contents analysis of fuel cell proton exchange membranes J. Wissler1, I. Lüdeking2, F. Regnet2, H. Baechler2, F. Wilhelm2, L. Joerissen2 1TESCAN, Dortmund, Germany 2Zentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW), Ulm, Germany Proton exchange membranes (PEM) are crucial to the functionality of fuel cells (FC). In those cells H2 and O2 is reacting to H2O, generating electric energy and heat. Material types, composition and particle distribution within the catalyst coated membrane determine the efficiency of the hydrogen/oxygen to water chemical conversion process. The generated microscopic water distribution cannot be determined with sufficient resolution during the cell operation. Furthermore, ex-situ determination of the product water distribution within the meso-porous cell components and the membrane is neither easy nor unambiguous. The establishment of a reliable workflow for the microscopic determination of the material distribution, including water, would be very beneficial. Therefore, we elaborated a correlative workflow, using TESCANs cryo-SEM/FIB approach, for the determination of water and material distributions in PEMs. The correlative cryo-EDS approach enables the determination of the PEM layer- and material- compositions in different membrane types, whether fresh or used after operation in a FC stack. Fig.1 shows i.e., the uneven water distribution of a PEM FIB cross-section by cryo-EDS imaging. PEM-materials of different ageing states can thus reliably be tested. Generated water agglomerations can be located and imaged down to the nano-meter scale within the PEM. The relative amount can be correlated to the microporous structure. This enables to test different PEM materials which contributes to the understanding of the FC stack efficiency. (Authors 1-4 contributed equally) (Fig.1: Water distribution (blue) of a fresh cryo-FIB cross-sectioned PEM) Fig. 1 65

MS1.P018 Atomic scale electron microscopy characterisation of the aging processes in solid oxide cells Q. Tran1, H. Türk1, F. P. Schmidt1, T. Götsch1, A. Hammud1, D. Abou-Ras2, D. Ivanov1, E. Stotz1, L. G. J. de Haart3, I. C. Vinke3, R. Eichel3, K. Reuter1, R. Schlögl1, A. Knop-Gericke1, C. Scheurer1, T. Lunkenbein1 1Fritz Haber Institute of the Max Planck Society, Berlin, Germany 2Dep. Structure and Dynamics of Energy Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, Berlin, 14109 Germany 3Fundamental Electrochemistry (IEK-9), Institute of Energy and Climate Research, Forschungszentrum Jülich GmbH, Jülich, Germany High temperature solid oxide electrolysis cells (SOECs) are a promising technology for intermittent energy conversion and storage. However, their wider adoption for commercial applications is still limited by the rapid degradation of the cells even under steady state conditions. This calls for an in-depth understanding of their structure-performance relationship during operation, especially at the chemically and kinetically active regions between the electrolyte, electrode, and gas phase. A recent study has also confirmed the existence of a so-called complexion region at such an interface (1, 2). In this study, we aim to elucidate the atomic scale structure and chemistry at the boundaries between the electrolyte and electrode using Cs-corrected scanning transmission electron microscopy (STEM). For this purpose, we investigated a half cell consisting of LSM (La0.8Sr0.2)0.95MnO3-δ) || LSM YSZ composite, which represents the air electrode of the electrolysers, screen printed on top of a dense 8YSZ electrolyte (ZrO2 with 8 mol% Y2O3) after thermal treatment in air at 1173 K for 150 h without any biasing operations. Our Electron Energy Loss Spectroscopy (EELS) analysis reveals the enrichment of divalent Mn2 not only at the LSM/YSZ interface, but also at the nearby YSZ grain boundaries, which is in contrast to the dominant Mn3 /Mn(2 ,3 ) within the bulk LSM (Fig. 1). Such a high level of Mn2 reflects an increased concentration of oxygen vacancies and may promote electron transfer for oxygen gas evolution and transport at these interfaces. With this result, we show that thermal annealing independently plays an important role for such an elemental segregation, in contrast to another report of cathodic polarisation being the main driving factor (3). Moreover, with atomic-resolution imaging, numerous nano-scale domains with a characteristic two-fold ordered structure can be found within the YSZ grains in contact with the LSM (Fig. 2). Their origin is likely related to the formation of a solid solution of La3 and Mn2 within the YSZ structure, assisted by the long-range diffusion of these ions along the grain boundaries. This requires further insights. In conclusion, our study offers atomic insights into the local structures at the electrolyte/electrode interface boundaries. The result is of scientific and technological importance toward the design of more efficient and durable cells. References (1) Türk, H. et al., Adv. Mater. Interfaces 2021, 8, 2100967. (2) Türk, H. et al., ChemCatChem, https://doi.org/10.1002/cctc.202200300. (3) Backhaus-Ricoult, M., Solid State Ion. 2006, 177, 2195-2200. Fig. 1: a) HAADF images at the YSZ/LSM interface, b), c) Sequential spectra along the line scan indicated in (a) using energy dispersive spectroscopy EDS and EELS, respectively. Fig. 2: Colour-enhanced high angle annular dark field (HAADF) image at the YSZ grain boundaries which shows the presence of nano-scale ordered structure domains. 66

MS1.P019 Advancing battery development with raman-SEM imaging U. Schmidt1, T. Meyer1, D. Zimmer2, T. Dieing1 1WITec GmbH, Applications, Ulm, Germany 2Oxford Instruments GmbH NanoAnalysis, Wiesbaden, Germany Understanding structure-composition-property-performance relationships is essential for the development of more powerful, long-lived and affordable lithium ion batteries. Raman imaging microscopy can visualize structural and chemical information acquired from the battery"s internal components, such as details of their molecular composition, grain fractures, and electrode degradation. A confocal Raman system integrated with an SEM (RISE microscope) provides sufficient resolution to evaluate variations within single particles that can be correlated with structure. The atomic composition of a Li-ion cathode can be determined using EDS, leading to a comprehensive understanding of the cathode material. Fig. 1 shows correlative SEM, EDS and RISE images acquired from the same sample area of a Li-ion battery cathode composed of various grains. Although the particles appear as uniform in the SEM image (Fig. 1a), the EDS image shows that the particles contain a high amount of oxygen, shown in green (Fig. 1b). Red in the EDS image corresponds to the carbon matrix in which fluoride atoms could be detected. The Raman image (Fig. 1c) visualizes grains that consist of LiCoO2 in blue and LiNixCoyMnzO2 grains in green. During electrochemical cycling of Li-ion batteries, microstructural changes can lead to a loss of energy, especially under rapid charging. Changes in performance are often nonuniform as a result of inhomogeneous degradation in which some regions in battery electrodes may experience more significant degradation than others. Such inhomogeneous deterioration can be studied using RISE microscopy. SEM images show deterioration of the large uniform lithium metal oxide-containing grains of pristine cathodes into sub-grains after rapid charging-discharging cycles. Raman images, on the other hand, reveal that not all Li-Metal-Oxide grains are affected in the same way by such rapid charging cycles and changes in the concentration of Li-Metal-Oxide composition is observed [1]. The integration of SEM with Raman imaging and EDS provides the opportunity to explore electrode inhomogeneity in a unique way. These results reveal heterogeneous deterioration of structure in Li-ion oxide cathode particles that can contribute to reduced performance and longevity in lithium-ion cells. [1] K. Hollricher, D. Strom, and U. Schmidt, G.I.T. Imaging & Microscopy 2 (2021), 14 Wiley-VCH GmbH, Weinheim, Germany Fig. 1: Correlative SEM (left) – EDS (middle) – RISE (right) images of a Li-ion cathode. Fig. 1 68

MS1.P020 Al current collector corrosion studies using liquid cell electron microscopy M. Binggeli1, V. Tileli1 1École Polytechnique Fédérale de Lausanne (EPFL), Institute of Materials, Lausanne, Switzerland Lithium-ion batteries (LIBs) are the state-of-art rechargeable batteries. With the ongoing growth of the electric vehicles market, driven by the global tendency aiming toward the decrease of fossil fuel consumption [1, 2], the improvement of the current LIBs technology is required and more particularly their performance, their safety and their lifetime[1, 2]. The research in this domain has mainly been focused on electrodes and electrolyte optimization. However, the role of the current collectors (CCs) on the LIBs performance remains poorly understood [3]. The intrinsic complex and interlinked chemistry of LIBs requires a deconvolution of all effects to gain insights on the mechanisms of their degradation. In bulk devices, the cathode side CC is aluminum, which overall presents good corrosion resistance [1]. However, its corrosion is still occurring and the exact mechanism and its implication on the whole LIB cell are yet not fully understood [2, 3]. To understand the impact of the degradation of the Al CC on the performance of LIB, we use liquid cell electron microscopy (LCEM) [4]. This technique is enabled by using specific transmission or scanning EM holders that are enclosing liquid solution between two micro-electromechanical systems (MEMS) chips. On one of these chips, electrodes can be patterned and electrically biased for performing in situ or operando electrochemical experiments. First, we developed in-house microfabricated MEMS chips that include a Al electrode and two Pt electrodes, all having a thickness of 50 nm. To determine appropriate electrochemical conditions for Al corrosion in LCEM, we performed linear sweep voltammetry (LSV) and chronopotentiometry (CP) measurement on the bench in a simplified chloride- based aqueous environment. Al corrosion was thus performed ex situ in 0.1 M NaCl solution (>99.5%, Carl Roth) using the Al electrode of produced chip as working electrode (WE), a Pt wire as counter electrode (CE) and a Ag/AgCl reference electrode (RE). CP was also performed in situ in a SEM, using on chip Al WE and Pt CE, and a bulk Ag/AgCl RE. LSV results showed that the current increases at the pitting potential, resulting in a large part of the Al electrode being corroded within less than 10 s. This timescale is very short for properly imaging Al corrosion using LCEM. In contrast, during CP measurements, pit formation occurred between tenths of seconds and several minutes, indicated by the potential increase as a function of time. The constant potential that follows is indicative of active corrosion of the aluminum electrode. The large pits density suggests that CP measurements can be used to study the corrosion using LCEM. It is noted that gas bubble formation on the corroded region was also observed and its role on the corrosion is being investigated. In conclusion, we report the development of a MEMS chip containing an Al electrode for use as CC on the positive electrode of the lithium-ion microbatteries. We also report that galvanostatic experiments are more appropriate than potentiodynamic for imaging Al corrosion using LCEM. References: [1] V. Etacheri et al., Energy Environ. Sci. vol. 4 (2011), pp. 3243–3262, doi: 10.1039/c1ee01598b. [2] L. Guo et al., J. Phys. Energy vol. 3 (Jul. 2021), p. 032015, doi: 10.1088/2515-7655/ac0c04. [3] T. Ma et al., J. Phys. Chem. Lett. vol. 8 (2017), pp. 1072–1077, doi: 10.1021/acs.jpclett.6b02933. [4] F. M. Ross, Science (80-. ). vol. 350 (2015), doi: 10.1126/science.aaa9886. 69

MS1.P021 Liquid-phase electron microscopy studies of Cu/Cu2O nanocatalyst evolution during CO2 electroreduction S. Toleukhanova1, P. Albertini2, R. Buonsanti2, V. Tileli1 1École Polytechnique Fédérale de Lausanne (EPFL), Institute of Materials, IMX, Lausanne, Switzerland 2École Polytechnique Fédérale de Lausanne (EPFL), Institute of Chemical Sciences and Engineering, Sion, Switzerland Recent advancement in the design of novel catalysts for CO2 reduction reaction (CO2RR) increases demand for standardized methods for assessment of the catalyst's efficiency in CO2 conversion to valuable hydrocarbons. Among the catalysts for CO2RR, Cu nanocatalysts (Cu NCs) have attracted considerable attention due to copper's ability to produce a wide range of C2+ products and facet-dependent selectivity of Cu nanocrystals towards certain hydrocarbons1. However, Cu NCs undergo rapid restructuring upon CO2RR which results in their deactivation. Therefore, a considerable amount of research is dedicated to discerning the degradation mechanisms of Cu NCs2. In this regard, in situ electron microscopy (in situ EM) has great potential as it allows the imaging of samples in a liquid medium under applied bias. Nevertheless, commercially available electrochemical chips with CO2RR compatible glassy carbon (GC) working electrodes demonstrate a relatively narrow inert potential range in the cathodic region3. As a result, the competing hydrogen evolution reaction (HER) takes lead causing gas bubble formation, delamination, and electrical disconnection of GC electrodes within the short time of the reaction. In this work, we present correlative in situ transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM) extended time studies of 40 nm Cu/Cu2O NCs under CO2RR conditions. Samples for in situ EM experiments were prepared by drop-casting Cu/Cu2O NCs on the membrane region of plasma- treated electrochemical chips. Thereafter, assembled in a holder the cell was filled with CO2 saturated 0.1 M KHCO3 electrolyte. Linear sweep voltammetry and chronoamperometry were utilized to drive CO2 electroreduction. TEM images were acquired at an electron dose rate of 42 e-nm-2s-1, and in ESEM experiments, a beam current was 36 pA. Energy-filtered TEM was used to enhance the contrast of catalyst particles in the liquid electrolyte. In situ EM results indicate that in-house fabricated GC electrodes have a longer stability time as compared to values from the previous studies4: up to 4 min in TEM and 10 min in ESEM at a cathodic potential of -0.8 VRHE. The shorter time in TEM is hypothesized to stem from an order of magnitude higher beam energy used in TEM. Nonetheless, utilizing TEM we were able to monitor the unique restructuring pathway of core-shell Cu/Cu2O NCs inclusive of the facet selective core etching while the shell remained intact. The results were reproduced in ESEM, showing similar hollow cube particles after 10 min of CO2RR. However, these observations diverge from bulk cell results, which points towards further studies needed to elucidate this different behavior. In conclusion, in situ TEM and ESEM experiments are complementary for providing structural and morphological information on Cu NCs dissolution driven by CO2RR at the nano- and meso-scale. 1. G. De Gregorio et al. ACS catalysis 10, 4854-4862 (2020) 2. S. Popović et al. Angew. Chem.. 59, 14844-14854 (2020) 3. R. Girod et al. Microscopy and Microanalysis 25, 1304-1310 (2019) 4. J. Vavra et al. Angew. Chem. 60, 1347-1354 (2021) 70

MS1.P022 Nanoparticle transformations retrieved by a combination of electron tomography and atomistic simulations E. Arslan Irmak1, W. Albrecht2,1, A. Pedrazo-Tardajos1, S. van Aert1, S. Bals1 1EMAT and NANOlab Center of Excellence, University of Antwerp, Antwerp, Belgium 2Center for Nanophotonics, AMOLF, Amsterdam, Netherlands The properties of metallic nanoparticles (NPs) are linked to their three-dimensional (3D) structure. However, these particles exhibit structural and morphological transformations under the conditions relevant to their applications, and subtle changes in the structure may significantly modify their performance. Hence, an atomic-scale understanding of the transformations under realistic conditions has a vital importance in preserving the functionalities of metal NPs. In situ transmission electron microscopy is a valuable technique to observe the dynamics of NPs. Combining the in situ experiments with fast electron tomography even enables 3D in situ measurements. [1] Despite the progress in this field, atomic-scale transformations cannot always be understood by experimental techniques alone as these measurements do not provide the necessary time or spatial resolution. In this study, we have demonstrated that such limitations can be overcome by linking 3D characterization techniques with atomistic simulations. A first example is the in situ 3D investigation of the thermal stability of Au@Pt NPs, which is important to understand their behavior during catalytic reactions. However, since the heating cycles were interrupted during the experiments to acquire tomography tilt series, the ongoing transformations could not be fully monitored by experimental observations. We therefore used experimentally determined 3D reconstructions of Au@Pt NPs as realistic input models (Fig 1) for molecular dynamics (MD) simulations. In this manner, it has been possible to unravel atomic-scale dynamics at elevated temperatures, and to systematically investigate the parameters that influence the thermal stability of these NPs. [2] This approach becomes even more important when the environmental triggers cannot be applied in situ. For example, in many optical and photothermal applications, Au NPs are excited by laser irradiation. However, due to the ultrafast time scales, laser-induced restructuring of NPs cannot be monitored by experiments. To do so, tomography tilt series of the same NP was acquired before and after laser excitation (ex situ) and the laser heating regime was modelled to mimic the experiments. By performing MD simulations based on the 3D reconstructions and the heating regime, laser- induced complex atomistic rearrangements causing shape and structural deformations have been unraveled (Fig 2). [3] The approach presented in this study is of great potential as it enables performing simulations based on the experimentally measured surface structure. Moreover, it enables us to capture the ongoing processes at the atomic scale, as well as to understand the driving mechanisms behind the complex transformations that possibly occur during applications. References [1] W. Albrecht, S. Bals, J. Phys. Chem. C 124 (2020), 50, 27276–27286. [2] A. Pedrazo-Tardajos, E. Arslan Irmak et al., ACS Nano 16 (2022), 6, 9608–9619. [3] W. Albrecht, E. Arslan Irmak et al., Adv. Mater. 33 (2021), 2100972. [4] This work was supported by the European Research Council (770887 PICOMETRICS to SVA and 815128 REALNANO to SB, 823717 ESTEEM3), Marie Sklodowska-Curie Actions (797153 SOPMEN to WA), and Research Foundation Flanders (G.0267.18N, G.0502.18N, G.0346.21N). Fig 1. 3D reconstructions and corresponding 3D models of a Au (a,b) and Au@Pt (c,d) NP. [2] Fig 2. 3D reconstructions of a Au NP before (a) and after (b) laser excitation. c) The results of MD simulations. [3] 71

MS1.P023 Cryo-electron microscopy for the study of sensitive energy materials Z. Kochovski1, Y. Xu1, 2, Y. Lu1, 3 1Department of Electrochemical Energy Storage (CE-AEES), Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, 14109 Berlin, Germany 2Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA, 02139 USA 3Institute of Chemistry, Potsdam University, Karl-Liebknecht-Str. 24–25, 14476 Potsdam, Germany INTRODUCTION As current batteries are nearing their theoretical limits, future generation high-energy-density battery chemistries demand a fundamental understanding of their operation and failure pathways at the atomic level. However, most energy materials and most notably lithium (Li) are sensitive and unstable under the electron beam in conventional TEM. This problem has been addressed in recent years by the application of Cryo-EM methods, borrowed from structural biology [1]. OBJECTIVES A major obstacle hindering the implementation of Li-metal batteries is the limited understanding of the Li nucleation and growth mechanisms. Furthermore, the solid-electrolyte interphase (SEI) is essential for the reversibility of the lithium Li-metal electrode, but the lack of in-depth understanding of its structure and unclear formation/evolution mechanisms have significantly hampered its rational design. We applied Cryo-EM and Cryo-ET to unravel the morphology and inner structure of Li deposits and to investigate the morphological evolution of Li deposition and the interface confined SEI. MATERIALS & METHODS We have used a JEM2100 Cryo-TEM equipped with a bottom mounted 4k TVIPS F416 camera and a Gatan 914 cryo- transfer holder. We have used a cryo-transfer procedure where the TEM grids containing the Li deposits are transferred to the TEM column without exposure to the ambient environment. Cryo-EM micrographs and tilt series have been acquired using SerialEM. Tilt series have been processed with IMOD and segmentation has been done in Amira. RESULTS In one work, Cryo-EM revealed two distinct types of Li deposits, depending on the current density: Li-balls, which were found to be primarily amorphous and Li-whiskers, which were found to be highly crystalline [2]. Additionally, their solid electrolyte interface (SEI) layers showed a difference in structure and composition, correlated to the underlying deposition mechanism (Fig. 1). In another work (accepted manuscript), we used Cryo-EM to reveal the morphological evolution of the SEI layer during Li plating, showing a thick (~100 nm) and wrinkled SEI layers forming in the initial stage, which progressively stretched and thinned to up to 7nm after 24 min of Li deposition (Fig 2a-c). Cryo-EM and Cryo-ET also revealed in detail the morphologies of the Li deposits (Fig2d-i). CONCLUSION Cryo-EM and Cryo-ET, which are methods well established in the field of structural biology, could be well adapted to the study of sensitive energy materials. REFERENCES [1] Y. Li et al., Chem, 4 (2018), pp. 2250-2252 [2] K. Dong et al., ACS Energy Lett. 6 (2021), pp. 1719-1728 FIGURE LEGENDS 73

MS1.P024 Unravelling the selective oxidation of 2-propanol on Co3O4: operando TEM as a central part in a multi-modal operando toolset for understanding catalytic reactions T. Götsch1, D. Cruz1, A. Rabe2,3, M. Dreyer2, M. Behrens2,3, R. Schlögl1,4, A. Knop-Gericke1,4, T. Lunkenbein1 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Berlin, Germany 2Universität Duisburg-Essen, Faculty of Chemistry and Center for Nanointregration Duisburg-Essen (CENIDE), Essen, Germany 3Christian-Albrechts-University Kiel, Institute of Inorganic Chemistry, Kiel, Germany 4Max Planck Institute for Chemical Energy Conversion, Department of Heterogeneous Reactions, Mülheim an der Ruhr, Germany Selective oxidation reactions, in many cases catalyzed by noble metals, are some of the most important industrial processes, used to synthesize base chemicals such as acetone from 2-propanol. Consequently, finding more efficient catalysts that are based on cheaper and more abundant materials is desirable. One example is Co3O4, which is highly active in the oxidation of 2-propanol to acetone. On this catalyst, the reaction is split into two distinctive activity regimes: one centered around 150 °C ("low- temperature") and one up to 300 °C ("high-temperature"). While the catalyst is very selective at low temperature, it deactivates rapidly. At higher temperature, there is no deactivation, although total oxidation to CO2 and H2O becomes a prominent side reaction. The mechanism behind the low temperature deactivation is still unclear, with different reasons being postulated such as changes in oxidation state or simple carbon deposition.[1] Here, we present a combined operando investigation of the selective 2-propanol oxidation using operando TEM (OTEM) together with synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) under near-identical conditions in order to unravel the origins behind the low-temperature activity region and its deactivation. OTEM was conducted using a DENSsolutions Climate holder and a self-built gas feeding and analysis setup[2] at an image-corrected ThermoFisher Scientific Titan 80–300. After pre-sintering (600 °C, 20% O2/He) of the nanocrystalline catalyst, hexagonal Co3O4 platelets derived from thermal decomposition of Co(OH)2 precursors, the introduction of the reaction feed (4.5% 1:1 O2/2-propanol in He, total pressure of 500 mbar) leads to the formation of nanoparticles beneath the {111} facets already at room temperature (see Fig. 1), which coincides with a slight reduction of the cobalt species as evidenced by NAP-XPS. Subsequent increases in temperature elicit an exsolution of these particles before they coalesce again to an overlayer at around 200 °C, coinciding with the transition to the high-temperature regime. At 300 °C, they roughen up significantly, accompanied by a continuous increase of Co(II) in the XPS spectra and increased conversion. According to HRTEM recorded under reaction conditions, these exsolved particles are CoO, although there is no bulk phase transition occurring. Cooling down from 300 °C back to room temperature reveals a lattice expansion, most likely due to the formation of O vacancies. When re-oxidizing in O2/He at 600 °C, the nanoparticles are dissolved, and the CoO signals in the SAED patterns disappear. Additionally, the original lattice parameter is recovered too. As no carbon deposition is observed in OTEM and NAP-XPS reveals no significant build-up during the reaction either, this investigation indicates that the rapidly deactivating nature of the low-temperature regime is not simply due to carbon accumulation. Instead, because the partial reduction of Co(III) to Co(II) already occurs at room temperature, there possibly is a more complex reason for the deactivation. More experiments are currently being conducted to probe the chemical nature of the catalyst surface. (1) Anke et al. ACS Catal. 2019, 9, 5974–5985 (2) Plodinec et al. Microsc. Microanal. 2020, 26, 220–228 Fig. 1: Operando bright field images during the oxidation of 2-propanol on Co3O4 show the restructuring of the {111} facets. 75

MS1.P025 Bridging scales: imaging at intermediate length scales reveals the long-range effect of hydrogen spill-over H. Frey1, A. Beck2,3, A. Kleibert4, J. A. van Bokhoven2,3, M. G. Willinger1,5 1ETH Zurich, ScopeM, Zurich, Switzerland 2ETH Zurich, D-CHAB, Zurich, Switzerland 3PSI, LSK, Villigen, Switzerland 4PSI, LSC, Villigen, Switzerland 5TU Munich, Fakultät für Chemie, Garching, Germany In catalysis, electron microscopy is often employed to reveal atomistic information regarding the structure and composition of the fresh catalyst or to study, post-mortem or in-situ, reaction induced changes. Information is then oftentimes linked to data acquired with integral methods such as mass spectrometry or X-ray based spectroscopy methods. However, both methods fail to resolve processes that are dominant at intermediate length scales. They involve the collective transport of heat or mass and play a role in the formation and propagation of reaction fronts [1], for example. X-ray Photoelectron emission microscopy (XPEEM) enables wild field spectral imaging of planar surfaces in the micrometer range and is therefore suited to fill the information gap between local, atomic-level observation and averaging integral methods. Hydrogen spillover concerns the surface migration of activated hydrogen atoms from a metal catalyst particle, on which molecular hydrogen dissociates, onto the catalyst support. It is of high importance for heterogeneous catalysis, hydrogen storage materials, and fuel cell technology. Its occurrence on metal oxide surfaces is established [2], yet questions remain about how far from the metal center spillover is reaching. By employing in-situ XPEEM on a planar model catalyst [3], we were able to gather direct evidence that spillover is occurring over several microns across the oxide surface [4]. The wide filed nature of XPEEM and the tunability of the incoming X-ray beam allows for quantification of the chemical states of the oxide surface in a time resolved manner with spatial resolution. These findings and the derived understanding at which temperatures hydrogen spillover in affecting the surface will help to improve and exploit the process of hydrogen spillover for application. Figure 1. Time and spatial resolved oxidation state of oxide film during exposure to hydrogen. Color resembles oxidation state: Red = fully oxidized, blue = reduced. Reduction is initiated at metal (indicated by lines) and propagates over the oxide support. 1] C. Barroo, Z.-J. Wang, R. Schlögl, M.-G. Willinger, R. Schlögl. Nat. Catal., 2019, 3, 30–39. [2] Prins R. Chem. Rev., 2012, 112(5), 2714-2738 [3] Karim W., Spreafico C., Kleibert A., Gobrecht J., Vandevondele J, Ekinci Y., van Bokhoven J. A. Nature, 2017, 541(7635), 68-71. [4] Beck A., Frey H., Willinger M-G., Kleibert A., van Bokhoven J. A. in preparation Fig. 1 77

MS1.P026 Biphasic layered material strengthened by tenon-and-mortise structure for robust sodium ion batteries cathode T. Yang1, M. Yang2, L. Jin1, Y. Xiao2, R. E. Dunin-Borkowski1 1Forchungszentrum Juelich, ER-C-1, Jülich, Germany 2Peking University Shenzhen Graduate School, School of Advanced Material, Shenzhen, China Layered cathode materials are commonly used in lithium and sodium ion batteries, but their structures prone to degradation during battery operation. The rigid fracture is the one of the key factors for degradation of functional materials, in particular the layered materials. Recently, the microstructure and defect engineering have broken a new ground in decreasing the rigid fracture and facilitating electrochemical performance of cathode materials. Herein, we design a buffer structure (tenon-and-mortise structure) at the biphasic boundary of Na0.67Fe0.1Cu0.1Mn0.8O2 layered oxide with a P'2/P2 biphasic structure (denoted as BP), which can inhibit the destructive evolution of layered oxides. We observe that the biphasic boundaries overlap by atomic-resolution scanning transmission electron microscopy (STEM) with spherical aberration correction. As shown in Figure 1, this phases overlap is deemed to a tenon-and-mortise structure that has been widely served as the buffer structure in traditional Chinese wooden architecture [1]. The structure Rietveld refinement combined with neutron powder diffraction (NPD) and X-ray diffraction (XRD) determine that the ration of P'2/P2 phase in BP is about 70%:30%. In addition, equipped with X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and electrochemical tests, we find that BP with low vacancy concentration is able to experience reversibly deeper desodiation/sodiation benefitted from the enhanced biphasic structure. Consequently, BP provides a competitive specific capacity of 200 mAh g-1 at 0.05C (1C = 150 mA g-1) and a superior cycling life for the retention of 84.2% after 1000 cycles at 8C. Ex-situ HAADF-STEM characterizations of cathode materials after different cycles illustrate that the dense tenon-and-mortise structures are stable under the operating condition. Furthermore, in-situ XRD demonstrates that the competition between the oxidation/reduction of transition metals and desodiation/sodiation in dense tenon-and-mortise structures buffers the interlayer spacing variation of BP, resulting in a mild snake-shaped evolution. This work provides an artful phase engineering to strengthen the original layered structure of SIBs cathodes without sacrificing the intrinsic properties. Figure 1. (a,b) HAADF and ABF-STEM images of biphasic boundary for BP along [010] zone axis. The line scan profiles along the corresponding rectangles are shown on the right of (a). (c, d) HAADF and ABF-STEM images of biphasic boundary with clear tenon-and-mortise structure. (e) Schematic diagram of the biphasic boundary reinforced by tenon-and-mortise structure. [1] Q. N. Liu, Z. Hu, W. J. Li, C. Zou, H. L. Jin, S. Wang, S. L. Chou, S. -X. Dou, Sodium transition metal oxides: the preferred cathode choice for future sodium-ion batteries? Energy Environ. Sci. 14, 158-179 (2021). Fig. 1 78

MS1.P027 Correlating electrocatalyst re-structuring with its impact on catalytic properties S. W. Chee1, A. Yoon1, F. Yang1, B. Roldan Cuenya1 1Fritz Haber Institute of the Max Planck Society, Interface Science, Berlin, Germany 1. Introduction Establishing a direct link between the morphology of a catalyst and its associated properties is a non-trivial challenge. It is especially complicated in electrocatalytic reactions where the catalysts can re-structure and further adopt thermodynamically unfavorable motifs due to kinetic limitations. In addition, since most property measurement techniques (such as voltammetry and gas chromatography) average over the entire catalyst ensemble, a detailed accounting of the catalyst morphologies and their relative distributions at different points of the reaction is needed to establish such correlation. Electrochemical cell transmission electron microscopy (EC-TEM) is one method that can provide us with such detailed information. 2. Objectives The aim of our research is to reveal the restructuring dynamics of catalysts during reaction and to correlate these dynamics to their impact on the catalytic properties. In particular, I will focus on my group's EC-TEM studies of Cu- based catalysts for the electrochemical reduction of carbon dioxide (CO2RR). 3. Materials & Methods We adopted catalyst synthesis strategies that allow us to tune the catalyst morphology, size, and loading in a controlled manner while also being applicable to different support geometries such that we have near identical electrocatalysts in different setups. The in situ experiments are conducted inside a 300 kV Titan TEM from Thermo Fisher in STEM mode using a Hummingbird Scientific Bulk Liquid Electrochemistry holder and with an electrolyte of CO2-saturated 0.1 KHCO3. The samples were also characterized ex situ after reaction. The activity and selectivity of the catalysts were measured on the benchtop using standard techniques, such as gas chromatography. 4. Results I will discuss two examples of our work, one using electro-deposited Cu2O cubes and the other using lithographically patterned Cu-island arrays. Our studies using Cu2O cubes with controlled size and loading showed that drastic reconstructions occurred in the first few minutes of potential application [1]. More importantly, the catalyst ensemble is made up of two motifs, fragmented cubes, and re-deposited nanoparticles. Then, we established the impact of the observed dynamics on catalytic performance by comparing the behavior of differently sized cubes with their time- resolved changes in product selectivity. Next, Cu-islands were used to follow how iodide species in the electrolyte cause the formation of CuI pyramids and how these pyramids restructure under reaction conditions [2]. While the CuI pyramids also restructure drastically like the Cu2O cubes, the catalyst morphology is different, taking the form of long fragmented filaments. Furthermore, our EC-TEM observations suggest that the presence of residual iodide stabilizes Cu+ species that have a known beneficial effect on hydrocarbon selectivity in CO2RR. 5. Conclusions Our results show how the re-structuring of Cu-based catalysts during CO2RR can be very complex and how EC-TEM can provide valuable insight into the morphologies present during reaction. References: 1. Grosse, P. et al. Dynamic Transformation of Cubic Copper Catalysts during CO2 Electroreduction and its Impact on Catalytic Selectivity. Nat. Commun. 12, 6736 (2021). 2. Yoon, A., Poon, J., Grosse, P., Chee, S. W. & Roldan Cuenya, B. Iodide-mediated Cu catalyst restructuring during CO2 electroreduction. J. Mater. Chem. A 10, 14041–14050 (2022). 79

MS1.P028 Investigation of complex nanostructured particles made of Cu and Cu-oxide for catalytic applications J. Müller1, J. Frohne1, C. Wiktor1, B. Butz1 1University of Siegen, Micro- and Nanoanalytics Group, Siegen, Germany Nanoparticles are widely used for catalytic applications. Their catalytic properties are largely defined by their size, shape, and surface chemistry. In general research is focused on small particles or, in recent years, even on single atoms. However, their synthesis is often complicated, involves toxic and expensive chemicals and the amount that can be produced is limited. Moreover, the particles themselves may pose a threat to the environment when they leak into fresh water as their size makes them difficult to filter. Instead of using single nanoparticles, an alternative way is to employ highly porous materials for catalysis. Like nanoparticles, they exhibit enormous surfaces which provide active sites for catalytic reactions. Moreover, they are bulky and are therefore much easier to handle than nanoparticles. In many cases, however, only the first few surface-near pores are available for the catalytic reaction. Deeper pores are hardly accessible to educts and products due to kinetic transport limitations. The aim of this work is to produce larger (up to 2 µm) nanostructured metallic and metal-oxide particles that contain pores in the range of a few tens of nanometers. This way, the advantages of using particles and porous systems are combined as they are on the one hand small enough to be accessible from all sides while on the other hand are large enough to be handled easily. The pores in the materials used for this work are first produced by using a well-known controlled oxidation process called dealloying where a less noble component of a metallic solid solution is leached out in an acid bath. At the same time, the more noble component forms a bi-continuous open pore network. This process is well-established for noble elements like Au and Pt. Recently, transition metals (Cu, Ni, etc.) have come into research focus as cheaper alternatives. The Cu particles used in this work are produced by first dealloying a bulk Cu0.3Mn0.7 alloy in HCl or H2SO4 to form the porous network with pore sizes between 10-100 nm followed by sonication to break down the porous structure into smaller fragments. The resulting particles are complex in shape and highly porous (fig. 1, TEM bright field image). The size of the porous particles ranges between 200 nm and 2 µm. After fabrication, the reactive Cu particles can further be modified or functionalized. By a simple and controlled oxidation process in air, core-shell particles with a defined oxide layer can be produced, whereas fully oxidized particles form a hollow-core structure (fig. 2, HAADF-STEM image). In order to employ such particles for catalytic applications, it is necessary to reveal the complex structure along the formation process of the Cu particles as well as their respective oxides in a three-dimensional manner. Therefore, tomography in scanning transmission electron microscopy mode has been performed at different stages of the preparation route. To prove the nature of the oxidation state of the Cu, electron energy loss spectroscopy was performed. Moreover, small amounts of Mn below 1 at% can still be found in the fully processed particles by energy dispersive X- ray spectroscopy. It is envisioned that the remaining Mn(-oxide) can act as a dopant in the particle boosting its catalytic performance. Therefore, first tests are planned to evaluate the catalytic behavior of those particles at different oxidation conditions. Fig. 1 Fig. 2 80

MS1.P029 STEM-EELS investigation of Cu/CeO2-TiO2 used in CO oxidation N. Rockstroh1, C. R. Kreyenschulte1, J. Mosrati1, T. H. Vuong1, J. Rabeah1, A. Brückner1 1Leibniz-Intitut für Katalyse e.V. (LIKAT Rostock), Rostock, Germany The heterogeneous catalytic oxidation of CO is an important reaction which impacts many technical applications such as fuel cells (preferential oxidation of CO instead of H2), air purification, exhaust-gas emission treatment, CO sensors and CO2 lasers.[1] Therefore, research focuses on the development and investigation of active and selective catalysts, preferentially containing abundant metals. Copper is a promising and well-investigated candidate, which, upon immobilization on CeO2, forms redox-active Cu2+/Cu+ couples. CeO2 itself has a high oxygen mobility and the ability to form Ce4+/Ce3+ couples, two properties which can be even improved by incorporation of titanium. Three Cu doped CeO2-TiO2 catalysts and the pure support were prepared by a sol-gel method adding 0 (support), 0.06 (Cat1), 0.26 (Cat2), or 0.66 wt% Cu (Cat3) with Cat2 showing the best catalytic performance. To elucidate structure-activity relationships, the materials have been characterized by XRD, Raman and IR spectroscopy, STEM- EELS, NAP-XPS, and operando EPR. STEM-EELS was thereby applied to spatially resolve potential differences in the oxidation state of the containing elements. A probe corrected JEOL JEM-ARM200F (Schottky emitter) with a Gatan Enfinium ER EELS were used for electron microscopic investigation of the catalysts. A rather high beam current was applied to keep the acquisition time low. The FWHM of the zero-loss peak (ZLP) was about 1.2 eV and the lack of de-scan was compensated by the DualEELS mode. The spectra were recalibrated at each pixel by the position of ZLP. Cat2 (0.26 wt% Cu) shows the best catalytic performance. The relative intensity of the Raman band at 463 cm-1 and the appearance of separate CeO2 entities observed by STEM increase with the Cu content. However, Cu is not visible in the STEM HAADF and BF images due to its small Z contrast and high dispersion. This high dispersion could be proven by EPR and DRIFTS. STEM-EELS enabled the determination of the oxidation state of Ce and its distribution with respect to TiO2 (Fig. 1 and 2). It revealed that Ce is present either as Ce3+ in well-dispersed form or as Ce4+ in separate CeO2 crystallites. It could be shown that Ce3+ and Ti4+ form a Ce-Ti oxide solid solution. Figure 1. STEM ADF image of Cat2 (left) with the corresponding Ce M edge electron energy loss (EEL) spectra of the highlighted areas (right). The shape and intensity of the edge signal points to Ce3+ in Area 1 and Ce4+ in Area 2.[2] Reprinted with permission from ref [1]. Copyright © 2021, American Chemical Society. Figure 2. STEM ADF image of Cat2 (left) with an overlaid false color elemental map. On the right, the distribution of two different cerium species (Ce-M (a) and Ce-M (b)) and titanium is shown independently as well as in a single-color elemental map. Reprinted with permission from ref [1]. Copyright © 2021, American Chemical Society. Using STEM-EELS with this catalyst system, it was possible to benefit from this additional spectroscopic method by providing information on the Ce oxidation state distribution which is not possible with EDXS. Although EPR and XPS provide already evidence for Ce3+, its exact localization is only possible with STEM-EELS. [1] J. Mosrati, A.M. Abdel-Mageed, T.H. Vuong, R. Grauke, S. Bartling, N. Rockstroh, H. Atia, U. Armbruster, S. Wohlrab, J. Rabeah, A. Brückner, ACS Catal. 2021, 11, 10933-10949. [2] Y. Zhang, S. Bals, G. Van Tendeloo, Part. Part. Syst. Charact. 2019, 36, 1800287. 81

MS1.P030 Cross-sectional preparation of complex energy devices and their characterization by advanced microscopic methods M. Hepp1, V. Muhl1, T. Dursun1, B. Butz1 1University of Siegen, Micro- and Nanoanalytics Group, Siegen, Germany Energy devices like batteries, fuel cells and solar cells are assembled from multiple functional components with different material properties. To gain a fundamental understanding of structure-property relations, to systematically contribute to performance enhancement and to unravel device degradation and failure mechanisms, high quality cross-sections of entire devices or of as large regions as possible are required. Since many devices not only consist of different classes of materials but also of liquid and/or air sensitive components, working under cryogenic and/or inert conditions is essential to conserve their pristine state. To enable scale-bridging cross-sectional characterization of those devices all the way down to the atomic level, we utilize different preparation tools. A novel self-built cryo-cutter allows us to produce cross-sections of entire devices, e.g., pouch-cells, in a quick one-step process and to observe them in their pristine state by OM even on the centimeter scale. For smaller scales (cryo-)ultramicrotomy as well as FIB are routinely applied and capable to prepare cross- sections not only for investigations by OM and SEM but also for (atomic resolution) TEM, as high-quality thin samples below 50 nm are provided. In this contribution we demonstrate the scale-bridging capabilities of those preparation techniques applied on various devices and their components in conjunction with advanced (electron) microscopic and spectroscopic methods. Examples include devices like batteries (Fig. 1) and complex PEM fuel cells (Fig. 2) as well as battery components (Fig. 3). The applied techniques are ideally suited to investigate the integrity of complete devices as well as the interfaces of individual layers and components in terms of their morphology and contact as well as the systematic identification of their composition and chemical bonding states. Part of this work was performed at the Micro-and Nanoanalytics Facility (MNaF) of the University of Siegen. Fig. 1 83

MS1.P031 Wetting properties of water in gas diffusion electrodes investigated with environmental scanning electron microscopy M. Bozzetti1, A. Berger2, M. Fikry3, T. J. Schmidt3, H. A. Gasteiger2, V. Tileli1 1École Polytechnique Fédérale de Lausanne (EPFL), Materials Science, Lausanne, Switzerland 2Technical University of Munich, Chemistry and Catalysis Research, Munich, Germany 3Paul Scherrer Institute, Villigen, Switzerland Proton exchange membrane fuel cells (PEMFC) are promising energetic devices for automotive applications that have been widely investigated in the last decades 1. In order to achieve their full theoretical potential, water management at the cathode side needs to be improved to avoid mass transport losses. Although water formation in the catalyst layer comes mostly from the cathodic reaction, condensation still plays an important role, as it was proven by the effect of humidifying reactants 2. Pore size of diffusion media ranges from tenths of nanometres to few microns, and pore constrictions hindering water percolation are in the range of hundreds of nanometres 3. Environmental scanning electron microscopy (ESEM) is therefore a suitable technique to investigate the condensation mechanism at the relevant scale for water saturation 4,5. Previous studies have correlated the wetting behaviour of microporous layers (MPL) in the ESEM with water breakthrough from diffusion media in flooding conditions 6, while more recent studies took advantage of water condensation to compare the wettability of nanoporous carbon scaffolds to the conventional MPL 7. However, many parameters related to the condensation mechanism are still poorly investigated experimentally, and the benefits of environmental electron microscopy have not been fully exploited yet. Microporous layers and catalyst layers with different hydrophobicity have been observed in the ESEM at a pressure of 900 Pa varying the relative humidity. Temperature below 5°C were controlled by a cooling stage with a ramp of 0.1°C/min. Recordings of water breakthrough and droplet growth were acquired and methods to segment and analyse droplets were developed. Preliminary results suggest that larger pore size MPLs have slower droplet growth, which may be explained by the larger coalescence contribution in narrower pore size MPLs. In this work, we report on the effects of the condensation mechanism parameters, such as droplet nucleation rate, spatial density of nucleation sites, droplet growth and coalescence rate of dissimilar gas diffusion layers. Further insights into water nucleation and growth could aid towards the optimization of the transport of reactants to the electrodes. References 1. Majlan, E. H., Rohendi, D., Daud, W. R. W., Husaini, T. & Haque, M. A. Electrode for proton exchange membrane fuel cells: A review. Renewable and Sustainable Energy Reviews 89, 117–134 (2018). 2. Sanchez, D. G. et al. Effect of the Inlet Gas Humidification on PEMFC Behavior and Current Density Distribution. ECS Trans. 64, 603–617 (2014). 3. Bozzetti, M. et al. On the role of pore constrictions in gas diffusion electrodes. Chem. Commun. 58, 8854– 8857 (2022). 4. Lv, L., Zhang, J., Xu, J. & Yin, J. Heterogeneous condensation process observed by environmental scanning electron microscopy (ESEM): On smooth single aerosol particle. Aerosol Science and Technology 54, 1515– 1526 (2020). 5. Rykaczewski, K. Microdroplet Growth Mechanism during Water Condensation on Superhydrophobic Surfaces. Langmuir 28, 7720–7729 (2012). 6. Nam, J. H., Lee, K.-J., Hwang, G.-S., Kim, C.-J. & Kaviany, M. Microporous layer for water morphology control in PEMFC. International Journal of Heat and Mass Transfer 52, 2779–2791 (2009). Islam, M. N. et al. Highly Ordered Nanoporous Carbon Scaffold with Controllable Wettability as the Microporous Layer for Fuel Cells. ACS Appl. Mater. Interfaces 12, 39215–39226 (2020). 7. 84

MS1.P032 FIB ToF-SIMS and EDS analysis of LLZO garnet electrolyte for solid-state batteries L. Berner1, B. Schröppel2, R. R. Schröder1, I. Wacker1, Y. Sun3, M. Nojabaee3, A. Friedrich3, C. Burkhardt2 1University Heidelberg, Cryo Electron Microscopy, BioQuant, Im Neuenheimer Feld 267, Heidelberg, Germany 2NMI Natural and Medical Sciences Institute at the University of Tübingen, Nanoanalytic, Reutlingen, Germany 3Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38-40, Stuttgart, Germany Introduction Secondary ion mass spectroscopy (SIMS) in combination with scanning electron microscopy (SEM), focused ion beam (FIB) and energy-dispersive X-ray spectroscopy (EDS) is a powerful tool for chemical imaging of various technical devices. For the development and optimization of new Lithium batteries FIB-ToF (time of flight)-SIMS is essential as Lithium is not detectable with conventional EDS detectors and only hardly detectable with windowless EDS detectors. The solid-state electrolyte [1] family based on Lithium-Lanthanum-Zirconium-Oxide (LLZO) garnet is a promising material for next generation solid-state batteries. This electrolyte offers higher energy density and safer operation compared to standard Lithium ion batteries. To understand the internal composition and the interface of the Lithium cathode we analyzed the lateral and depth distribution of Lithium inside a LLZO pellet after processing and cycling with different parameters. Materials & methods LLZO pellets with a diameter of 12mm and thickness of 1mm are in development at DLR institute for technical thermodynamics. For FIB-SEM and ToF-SIMS investigation we used a ZEISS Crossbeam 540 FIB-SEM microscope equipped with a Tofwerk SIMS detector. The SIMS detector uses an orthogonal ToF system therefore no complex trigger timing for the primary gallium ion beam is necessary. A transfer optics collects the secondary ions from the sample surface and transfers the ions to the ToF detector for mass discrimination. A mass range from 1 to 500 is measured. SIMS is an optimal addition to EDS because it offers high surface sensitivity, detection of Lithium, and detection of isotopes. A lateral resolution of better than 100nm is possible. LLZO pellets were mounted on SEM sample holders. SEM, EDS and FIB- SIMS analysis was performed on the surface and on cross section of the LLZO pellets. Results The combination of SEM imaging with EDS and FIB-SIMS imaging gives important analytical data regarding the distribution of the elements and impurities inside the LLZO ceramic. With SIMS we could clearly resolve the distribution of Lithium inside the solid state electrolyte with high depth resolution and high lateral resolution. In the case of aluminium doped LLZO we find inhomogeneous distribution of aluminium oxide in the volume of the pellet. Conclusion ToF-SIMS in combination with FIB/SEM and EDS is a powerful tool in the field of Lithium ion battery research as Lithium is detectable with very high sensitivity with SIMS. It is also possible to detect the oxidation of Lithium with high depth and lateral resolution. In this way it is possible to optimize the production of LIBs and Lithium metal batteries as well as understanding degradation processes while operating the battery. References [1] Lei Cheng et al., J. Mater. Chem. A, 2014, 2, 172-181 [2] https://www.tofwerk.com/products/fibtof. 85

MS1.P033 Insights into the degradation of metallic core-shell nanoparticles under fuel cell conditions by 3D identical location STEM M. Vega Paredes1, R. Aymerich Armengol1, N. Rivas Rivas1, A. Garzón Manjón1, C. Scheu1 1Max Planck Institute für Eisenforschung, Nanoanalytics and interfaces, Düsseldorf, Germany Proton exchange membrane fuel cells (PEMFCs) are electrochemical devices capable of generating electricity by oxidizing H2, reformate (H2 rich gas with carbon monoxide (CO) impurities) or other fuels. In recent times, metallic core-shell nanoparticles (NPs) (M@Pt, M=Ru, Rh…) have attracted a big interest as anode catalysts of reformate fed PEMFCs [1]. The high catalytic activity of Pt towards the hydrogen oxidation reaction, together with the CO poisoning tolerance introduced by the accompanying metal make them ideal for heavy-duty applications. Furthermore, since in M@Pt NPs the less stable metal (Rh or Ru) is not directly exposed to the electrolyte, their stability is expected to be higher than in the corresponding alloyed NPs, which commonly suffer from dissolution and dealloying [2]. However, M@Pt can still suffer from degradation under fuel cell conditions by processes that are yet not fully understood, which hinders the design of more stable and durable catalysts. We investigated the degradation behavior of Rh@Pt NPs by means of identical location-scanning transmission electron microscopy (IL-STEM). This quasi in-situ technique allows to overcome the limitations of the ex-situ techniques, in which only statistical general insights are possible, since in IL-STEM the changes of individual particles are tracked between potential cycles. In particular, we characterized the Rh@Pt NPs after 0, 1000, 4000 and 10000 potential cycles (0.06-0.8V, 0.1V/s). Furthermore, since many of the degradation phenomena take place in 3D (e.g., particle migration and corresponding aggregation), selected regions were reconstructed in 3D by means of electron tomography (Figure 1). Figure 1. STEM and 3D reconstruction of Rh@Pt at 0 and 10000 cycles We observed particle migration on the carbon support in all the stages of the potential cycling. However, no widespread particle aggregation was observed, even after 10000 potential cycles. A slight Rh dissolution (up to 5 at.%) during the cycles was detected, which decreased as the number of cycles increased. Even though some small particles dissolved during the first 1000 cycles, the main degradation mechanism responsible for the loss of electrochemically active surface area was found to be particle detachment. Our results indicate that the investigated Rh@Pt NPs present a remarkable stability, and show how IL-STEM can be used for studying the degradation of catalyst NPs. [1] A. Garzón Manjón, M. Vega Paredes, V. Berova, T. Gänsler, T. Schwarz, N. Rivas, K. Hengge, T. Jurzinsky, C. Scheu, Insights into the performance and degradation of Ru@Pt core-shell catalysts for fuel cells by advanced (scanning) transmission electron microscopy, [Submitted]. [2] M. Vega Paredes, A. Garzón Manjón, B. Hill, T. Schwarz, N. Rivas, T. Jurzinsky, K. Hengge, F. Mack, C. Scheu, Evaluation of functional layers thinning of high temperature polymer electrolyte membrane fuel cells after long term operation, Nanoscale. (2022). https://doi.org/10.1039/D2NR02892A. 87

MS1.P034 Understanding of the degradation and aging mechanisms in Ni-rich NMC cathode material at the nanoscale L. Ahrens1,2, M. Meledina2, S. Basak1,3, R. Eichel3, J. Mayer1,2 1Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons (ER-C), Jülich, Germany 2Central Facility for Electron Microscopy, Aachen, Germany 3Institute of Energy and Climate Research (IEK-9), Jülich, Germany Ni-rich NMC (NixMnyCo1-x-yO2 with x > 0.8) has been a promising candidate for cathode active materials (CAMs) in Li- ion batteries (LIBs) [1,2]. Reducing the Cobalt content in NMC cathodes leads to a more environment-friendly and affordable material. Also, the specific capacity of Ni-rich NMC is significantly increased compared to conventional NMC material. However, the cycle stability is reduced. To improve the lifetime of Ni-rich NMCs, it is important to gain a deeper understanding of the degradation and aging mechanisms appearing during material synthesis and cycling. Therefore, studies of the micro- and nanostructure are key for tailoring material properties specifically, for instance through doping or coating. Modern focused-ion-beam (FIB) preparation allows cutting of extremely thin samples, enabling high-resolution imaging. Figure 1 shows a lamella of a polycrystalline Ni-rich NMC particle, which was prepared by FIB and a corresponding HRSTEM image of a layered structure. In addition to ex-situ experiments at the atomic scale, in-situ experiments play a key role in understanding degradation and aging mechanisms in LIBs [3,4]. By applying voltage or temperature more realistic scenarios can be represented. Therefore, we focus both on ex-situ and on in-situ setups (Figure 2). Figure 1: Polycrystalline NMC particle prepared by FIB (a) and ex-situ study of the layered structure at the atomic scale (b). Figure 2: Setup of a biasing in-situ experiment using NMC prepared using FIB. [1] Chao Xu et al., Adv. Energy Mater. 2021, 11, 2003404. [2] Yu Xia et al., Nano Energy, Volume 49, 2018, 434-452. [3] Shibabrata Basak et al., ACS Appl. Energy Mater. 2020, 3, 6, 5101-5106. [4] Shibabrata Basak et al., Chem. Commun., 2022, 58, 3130-3133. Fig. 1 89

MS1.P035 A real space understanding of the short range order in disordered rocksalt cathode materials E. Hedley1, L. Pi1, N. Roth2, M. Danie3, W. Song1,4, P. Bruce1,2,4,5, P. Nellist1 1University of Oxford, Materials, Oxford, United Kingdom 2University of Oxford, Inorganic Chemistry, Oxford, United Kingdom 3electron Physical Sciences Imaging Centre (ePSIC, Diamond Light Source, Didcot, United Kingdom 4The Faraday Institute, Didcot, United Kingdom 5The Henry Royce Institute, Oxford, United Kingdom Layered cathode materials such as Li-rich NMCs (containing nickel, manganese and cobalt) show promise as new high capacity materials, as the layered structure allows the intercalation and deintercalation of lithium ions during the cycling of the battery. Many of the elements currently used in the cathode are expensive and have low natural abundance, the scope for introducing new more abundant materials is limited. Disordered rocksalt materials overcome with a much larger scope for different elements to be combined, with many examples have shown good performance using only more abundant transition metals such as manganese and titanium (1)(2). The diffraction patterns of these materials contain clear diffuse scattering which takes many different forms depending on the composition, synthesis method and often exhibit changes on cycling of the material. This diffuse scattering is typical of materials with short range order, this type of diffuse scattering has previously been reported for many disordered rocksalt materials but to the best of our knowledge no precise understanding of the nature of this ordering has been achieved. The disordered rocksalt Li1.2Mn0.4Ti0.4O2 (LMTO) has been studied because it is potentially commercially important material due its composition only containing relatively cheap and earth abundant elements. However, it shows poor capacity retention on cycling and poor ionic conductivity which leads to poor performance at room temperature and slow rate capability for cycling (3). Electron diffraction has been used to study the nature of the short-range order in reciprocal space but does not give precise local information about the distribution of the ordering within a particle. In addition to TEM diffraction nanobeam electron diffraction has been used to gain real space information about the origin of the diffuse scattering. The intensity of atomic columns scales with the atomic number in for ADF images, meaning that the Li and the transition metal in the real space images have very different intensities. While the disordered nature of these materials means that the atomic columns contain a mixture of the cations. However atomic columns with a higher number of transition metals will appear brighter than those with more lithium. The ADF images of the particles show fluctuations in the intensity of the atomic columns, in what appears to be a random distribution. However, a Fourier transform of the ADF image reveals diffuse shapes which are like the diffuse scattering observed in the electron diffraction. This link between the diffraction in the traditional sense and the spatial information which comes from the nanobeam diffraction with real space ADF images allows us to examine the precise nature of the local ordering in these materials and its spatial distribution. 1. Ji, H. et al. Nat. Commun. 10, (2019). 2. Sato, T., Sato, K., Zhao, W., Kajiya, Y. & Yabuuchi, N, J. Mater. Chem. A 6, 13943–13951 (2018) 3. Clement, R. J., Lun Z., Ceder, G., Energy and Enviro. Sci, 13, 345 (2020) Figure 1: a) ADF image of LMTO b) Fourier transform of image a. c) Electron diffraction pattern of LMTO Figure 2: (a-c) Radial integration profiles of the a) pristine LiMnO2, b )after 1 cycle and c)8 cycles. Insets show the area where the azimuthal integration profiles are generated from. (f-g) Show virtual dark-field images which show the small crystallites 91

MS1.P036 Phase analysis of (Li)FePO4 by selected area electron diffraction and integrated differential phase contrast imaging N. Šimić1, D. Knez2, I. Hanzu3, W. Grogger2 1Graz Centre for Electron Microscopy (ZFE), Graz, Austria 2Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Graz, Austria 3Institute for Chemistry and Technology of Materials, Graz University of Technology, Graz, Austria Lithium iron phosphate (LiFePO4) is a well-studied compound with a lot of promise as cathode material in rechargeable batteries. Due to its low cost, low toxicity, safety and the abundance of iron LFP is considered a very attractive energy storage option for the automotive industry. LiFePO4 has an orthorhombic crystal structure with Pnma space group [1]. During the discharge process lithium intercalates from a graphite anode into the FePO4 cathode, where it is stored in between FeO6 octahedra and PO4 tetrahedra, thus slightly changing the lattice vector length of the unit cell while maintaining the same crystal structure. Our aim is to better understand the lithium deintercalation process in (Li)FePO4 battery cells on atomic and macroscopic scale. Fully delithiated, fully lithiated and partially lithiated cells are prepared using chemical- and electrochemical delithiation as well as bio templating. We use Selected Area Electron Diffraction (SAED) and integrated Differential Phase Contrast imaging (iDPC) in the TEM in order to differentiate between lithiated and (partially) delithiated particles. FIB lamellas are prepared from electrochemically delithiated cells for this purpose. We also aim to compare the results from our findings in the TEM with Raman microscopy measurements. Preliminary Raman experiments on bio-templated (Li)FePO4 already showed that LiFePO4 and FePO4 phases are differentiable with their respective Raman-shift. With SAED measurements we successfully managed to differentiate between LiFePO4 and FePO4 phases as well as partially delithiated phases for single particles as seen in figure 1. High-Resolution STEM as well as iDPC imaging have confirmed the feasibility of SAED for detection of lithium content. The lattice spacings obtained by HR-STEM FFT analysis were similar to the lattice spacings obtained by SAED. Using iDPC imaging we were able to directly show the presence of lithium in a partially delithiated particle as seen in figure 3. We conclude that SAED analysis is feasible for differentiation between lithiated and (partially) delithiated states in LixFePO4 as confirmed by HR-STEM FFT analysis and iDPC imaging. Raman microscopy may provide further insight on the delithiation process on a macroscopic scale in future work. Figure 1: Diffraction pattern of a LiFePO4 particle in 011 direction. The lattice spacing of the 001 plane indicates partial delithiation after comparison with simulated powder diffraction data from LiFePO4 and Li0.6FePO4. Figure 2: Theoretical model of LiFePO4 in 011 direction. The model shows Li atoms in green, Fe in orange, O in red and P in grey. Figure 3: Integrated Differential Phase Contrast image of the same particle seen in figure 1. All corresponding columns in the image show clear contrast at the theoretical Li positions which implies Li presence, thus confirming the diffraction results. See figure 2 for better reference with the theoretical model. [1] V.S.L. Satyavani, A. Srinivas Kumar, P.S.V. Subba Rao, et. al., Engineering Science and Technology, an International Journal, 19 (1), 178-188 (2016) 93

MS1.P037 Silicon microparticles for Li-ion batteries: tracking crystalline-amorphous transition H. Valencia Naranjo1,2, P. Rapp3, M. Graf3, H. A. Gasteiger3, S. Basak4,1, R. Eichel4, J. Mayer1,2 1Forschungszentrum Jülich GmbH, Ernst Ruska-Centre (ER-C 2), Jülich, Germany 2RWTH Aachen University, Central Facility for Electron Microscopy (GFE), Aachen, Germany 3Technical University of Munich, Department of Chemistry, Garching, Germany 4Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Grundlagen der Elektrochemie (IEK-9), Jülich, Germany The improvement of modern Li-ion batteries (LIBs) is an important step in the development of energy storage systems with regard to the growing market of electric vehicles and the realization of the European goal for climate neutrality by 2050 [1]. Silicon (Si) is one of the most promising anodes for next-generation LIBs, with its bestselling point being the theoretical capacity of 3579 mAh/g which is approximately ten-fold than that of the commonly used graphite-based materials used nowadays [2-4]. However, the ~300% volume change during (de)lithiation, which also results in crystalline-amorphous transition, limits the commercialization of Si-based anodes, particularly the Si microparticles. This transition takes place during the first lithiation cycle of the crystalline Si, which is amorphized and stays amorphous after delithiation, causing degradation. One approach to reducing the degradation is to operate the Si anode under its capacity limit, e.g., by using only ~30 % of the capacity the volume expansion is reduced to only one- third of the maximal expansion and leaving part of the crystalline Si phase unchanged during lithiation. This allows the Si anode to cycle over 200 times [5]. in-depth insight into to have an In order to further understand the lithiation process and the resulting capacity fading due to degradation within the Si microparticles, one needs the Si microparticles. Transmission electron microscopy (TEM) is the method of choice to study morphology and chemical composition of the crystalline and amorphous phases within partially lithiated polycrystalline Si microparticles. For the TEM investigation, FIB lamellas are prepared from the 5-10 µm pristine and cycled (lithiated/delithiated) particles. Bright-field (BF) imaging, selected area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDX) revealed the presence of the crystalline phase and the complex vein-like amorphous Si phase within the cycled microparticles, the latter not being present in the pristine Si microparticles (Figure 1). This shows the complex expansion of the amorphous phase not only present at the Si microparticle shell but also along stacking faults and grain boundaries. the structural arrangements within Figure 1: Bright field (BF) TEM image and corresponding diffraction images of Si particles. The images in the upper row a) correspond to the pristine Si anode and in the lower row b) the cycled Si anode is visible. [1] European Commission Communication (COM(2019) 640) "The European Green Deal". [2] U. Kasavajjula, C. Wang, and A. J. Appleby, J. Power Sources, 163, 1003 (2007). [3]. M. N. Obrovac and V. L. Chevrier, Chem. Rev., 114, 11444 (2014). [4] J.R. Dahn, T. Zheng, Y. Liu, J.S. Xue, Science 270 (1995) 590e593. [5] Maximilian Graf et al 2022 J. Electrochem. Soc. 169 020536. 95

MS1.P038 ADF/EDS/EELS characterization of spontaneous cathode/electrolyte reaction in air- and beam-sensitive solid-state Li-ion batteries R. Zhang1, A. Sheader1, W. Song1,2, E. Liberti1,3, P. Bruce4,1,2,5, P. Nellist1 1University of Oxford, Department of Materials, Oxford, United Kingdom 2The Faraday Institute, Didcot, United Kingdom 3Rosalind Franklin Institute, Didcot, United Kingdom 4University of Oxford, Department of Chemistry, Oxford, United Kingdom 5The Henry Royce Institute, Oxford, United Kingdom Solid-state Li-ion batteries (SSLIBs) have potential to revolutionise the electric-vehicle industry due to their superior capacity and improved safety relative to conventional liquid cells. However, commercialisation of SSLIBs is at present hindered by the electrode-electrolyte interface side reaction which leads to voltage hysteresis and capacity fading[1]. High-resolution characterisation techniques such as STEM provides comprehensive analysis of the microstructure and chemistry of SSE/cathode interphase. However, STEM studies of SSLIBs are complicated due to the extreme air- and electron-beam sensitivity of battery materials. It is therefore important to understand the effects of such damage to the native interface structure, and operate below these thresholds during imaging and spectroscopy experiments. In this work, we applied ADF/EDS/EELS to study the spontaneously formed interface between cathode material LiNi0.6Mn0.2Co0.2O (NMC622) and SSE Argyrodite Li6PS5Cl. We developed an anaerobic sample transfer protocol to prevent oxygen-related sample degradation. Beam damage on argyrodite was studied from the diffraction pattern revolution. Initial observations showed that air exposure of the solid-state electrolyte argyrodite (Li6PS5Cl) is characterised by Cl inhomogeneity and O contamination, significant morphology change and also sulphur deficiency (Fig.1). Particle tilting can be observed as a result of beam damage from the Laue Zone shift in Fig.2(a)-(e). Critical dose thresholds were calculated to be 500 e Å-2 by monitoring the diffraction spots intensity decay with time (Fig.2(f)). EELS mapping was used to reveal the extent of side reaction by tracking the Ni L2,3 white line ratio on the NMC622/argyrodite interface. We quantified Ni L2,3 white line ratio by performing model fitting (Fig.3(c)) in Hyperspy on raw data from single pixel.[3] A trend of Ni reduction in NMC622 towards the interface with argyrodite due to the spontaneous redox reaction was observed. The ability to characterise air- and electron beam-damage is key to managing the particular experimental challenges relating to (S)TEM studies of solid-state battery materials. Such challenges are of particular importance for high- resolution characterisation, as needed to further our understanding of, for example, the argyrodite-NMC622 interface.[3] References: [1] J -M T., and M A., Materials for sustainable energy: a collection of peer-reviewed research and review articles from Nature Publishing Group (2011) p. 171-179. [2] FDL P., et al, Microscopy and Microanalysis, 23(S1) (2017) p.214-215. [3] The authors acknowledge use of characterization facilities within the David Cockayne Centre for Electron Microscopy, Department of Materials, University of Oxford and in particular the Faraday Institution (FIRG007, FIRG008), the EPSRC (EP/K040375/1 "South of England Analytical Electron Microscope") and additional instrument provision from the Henry Royce Institute (Grant reference EP/R010145/1). Figure 1 (a) EDS elemental maps on argyrodite at oxygen content of 5 at% and 65 at% (b) S: P element ratio against oxygen content Figure 2 Diffraction pattern of argyrodite at 300kV at (a) t=0min (b) t=0.5min (c) t=1min, (d) t=2min (e) t=3min (f) integrated diffraction spots intensity over radius 97

MS2.001-invited Small scale model systems for in situ TEM studies: multilayered and alloyed nanowires L. Vogl1, P. Schweizer1, L. Pethö1, I. Utke1, J. Michler1 1Laboratory of Mechanics for Materials and Nanostructures, Swiss Federal Laboratories for Materials Science and Technology (Empa), Thun, Switzerland To understand the behavior of complex alloys and composites under mechanical and thermal loading small scale model systems are needed. Only such model systems provide the opportunity to analyze mechanisms of plastic deformation, interdiffusion and phase transformation down to the atomic scale. Tailored nanowires are ideal in this role as they can be directly studied with in situ TEM to elucidate the effect of compositional complexity, multilayered coatings and local ordering. Multilayered coatings prevent the underlying core material from degradation and enhance the mechanical and wear- resistant behavior. Such a coating consists for example of alternating nm-sized layers of metals and metal-oxides. The coating life-time crucially depends on crack initialization and propagation at the interfaces. To further optimize the performance and to prevent early failure like layer delamination, the underlying failure mechanisms on the atomic scale have to be studied. Small scale model systems of such coatings allows characterizing application-limiting factors inside the Transmission Electron Microscope (TEM) with a view to optimize the mechanical stability of the bulk counterpart. In this work, we use a combinatorial process based on advanced Physical Vapor Deposition (PVD) and Atomic Layer Deposition (ALD) to create complex one-dimensional nanowires (NW). These wires are ideal model-systems that enable studying the performance of different coatings. In order to analyze the effect of multilayers on the mechanical behaviour, we compare conventional coatings on metals (Al2O3-Cu) (Figure 1a) with nanolaminates consisting of alternating layers of Al2O3-ZnO (Figure 1b). Defect nucleation at the metal-metal oxide interface as well as crack propagation are studied via in situ mechanical testing inside the TEM. Figure 1c shows a cracked multi-shell NW after mechanical loading. Figure 1: Core-shell NWs as small scale model system for bulk-coatings. Exemplary STEM images. a) Al2O3-Cu core-shell NW. The Cu NW has been subsequently coated with a conformal ALD layer. b) Nanolaminate on Cu NW. The Energy-dispersive X-ray spectroscopy (EDX) map shows the layered Al2O3-ZnO structure. c) Nanolaminate after mechanical loading. Next to metal-metal oxide structures, intermetallic (Cu-Au) nanostructures are used to study the effect of compositional complexity on the material properties as well as diffusion processes at interfaces. By using co- sputtering at elevated temperatures alloyed NWs (Cu3Au/Au3Cu) are directly achieved. Figure 2 a shows an exemplary intermetallic Cu3Au NW with corresponding EDX mapping. The line scan across the NW is shown in figure 2c. The High-Resolution Scanning Transmission Electron Microscopy (HR-STEM) image in figure 2c emphasizes the ordering and figure 2d shows the corresponding diffraction pattern of the NW. In comparison with solid-solutions (of the same composition), such intermetallic model systems are used to characterize the effect of atomic ordering on the mechanical behavior, which is of great interest for the development of complex alloys. Beside the direct creation of the ordered phase via co-sputtering, intermetallic NWs can also be produced by heating core-shell NWs which consist of a copper core covered by a gold layer. These bimetallic nanostructures are ideal systems to study diffusion phenomena and ordering in situ in TEM. Figure 2e shows an EDX mapping of an initial Cu-Au NW before and after heating and figure 2f the corresponding line scans for different time intervals (initial, 50s to 2327s). Based on the Wagner equation, we calculated the interdiffusion coefficients of Cu (8.75· 10-18 m2/s) and Au (3.27·10-18 m2/s). To achieve the intermetallic phase and to observe the ordering, the NWs are annealed at 300°C (see diffraction pattern in figure 2g). Figure 2: Intermetallic NWs as small scale model system for complex alloys. a) Exemplary Cu3Au NW directly obtained via co-sputtering. STEM image with EDX mapping. The corresponding line profile is shown in figure 2b. c) HR-STEM image with Fast Fourier Transform (FFT) and d) diffraction pattern of the NW. Cu-Au core-shell NWs as small scale model system to analyze diffusion processes. e) EDX mapping of Cu-Au NW before and after heating at 400°C. g) Diffraction pattern before and after annealing at 300°C. Reversible formation of an ordered intermetallic phase. 99

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MS2.002 Heat-induced alloying in individual Au@Ag core-shell nanoparticles as a function of size, shape, and presence of defects M. Mychinko1, A. Skorikov1, W. Albrecht1, X. Zhuo2, A. Sànchez-Iglesias2, L. M. Liz-Marzán2, S. Bals1 1Universiteit Antwerpen, EMAT, Antwerp, Belgium 2Basque Research and Technology Alliance, CIC BiomaGUNE, San Sebastian, Spain The recent and ongoing development of advanced colloidal synthetic techniques has allowed scientists to routinely produce bimetallic nanoparticles of various shapes, sizes, composition, and elemental distribution. Novel synthetic routes enable precise control of specific optical properties based on surface plasmon resonance. Thus, nanoplasmonic-based materials are of great interest for the utilization in biosensing, photocatalysts, medicine, data storage, etc. However, operation in real conditions (e.g. at elevated temperatures) may cause particle reshaping and redistribution of metals between the core and shell of the particle, which in turn gradually alter the properties of nanoplasmonics. Hence, a deeper understanding of the influence of the size, shape, and presence of defects on the nature of such processes is essential for the further development of nanoplasmonic-based technologies. The recently developed combination of fast tomography based on High Angle Annular Dark Field Scanning Transmission Electron Microscopy with in situ heating holders has enabled the investigation of heat-induced processes at the single nanoparticle level with high spatial resolution in 3 dimensions (3D). Using this approach, we evaluated the influence of various parameters (size, shape, defect structure) on heat-induced elemental redistribution in Au@Ag core-shell nanoparticles qualitatively and quantitatively. In more detail, the elemental redistribution at high temperature in single-crystalline Au@Ag nanocubes with similar size and composition, but with different shapes of the core (truncated octahedra and sphere), was shown to be uniform along all directions (Figure 1c-d, upper rows). By performing 3D simulations of diffusion based on Fick"s law, similar diffusion constants were found (Figure 1a-b and Figure 1c-d, lower rows). Additionally, our investigation indicated faster alloying kinetics for pentatwinned Au@Ag nanorods in comparison to single-crystalline nanorods of comparable sizes and composition. This may be related to the presence of twinning planes, which cause the formation of distortions and vacant sites in the crystal lattice, facilitating diffusion of atoms. Finally, the influence of the core shape was demonstrated to be negligible in the case of two pentatwinned nanorods with different Au cores (rod and bipyramid). In conclusion, using our fast tomography approach we gained a fundamental insight into the nature of elemental diffusion at high temperature and its dependence on various factors, e.g. size, shape, and presence of twinning defects. We believe, that detailed knowledge of thermal stability and/or thermal degradation of bimetallic nanoplasmonic materials will drastically improve the application of these materials in the future. The project has received funding from European Research Council (ERC Consolidator Grant 815128, REALNANO) and European Commission (grant 731019, EUSMI). Figure 1. (a) – (b) Comparison of the alloying progress of single-crystalline nanocubes (with octahedral and spherical core, respectively) to diffusion simulations performed for different diffusion coefficients. (c) – (d) The upper rows show slices through the experimentally determined 3D elemental distribution at different stages of alloying of single- crystalline nanocubes (with octahedral and spherical core, respectively). The lower rows display slices through the simulated 3D elemental distribution using the optimal diffusion coefficient. 101

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MS2.003 Utilizing gradient samples to investigate solid state dewetting of bimetallic alloys C. Volland1, M. Dierner1, R. Branscheidt1, M. Landes1, J. Will1, E. Spiecker1 1Friedrich-Alexander-Universität Erlangen-Nürnberg, Institute of Micro- and Nanostructure Research & Center for Nanoanalysis and Electron Microscopy (CENEM), Erlangen, Germany Solid-state-Dewetting (SSD) is a typical degradation process of thin metallic films deposited on a substrate when annealed below the melting point. The process is driven by the minimization of total energy through surface- and interfacial energy reduction. While it used to be an undesirable effect, nowadays it is utilized as a powerful tool to fabricate bimetallic alloyed nanostructures for e.g. catalysis [1]. Here, switching from a single component film to binary systems makes the whole process more complex. A detailed understanding of this process is, however, unavoidable in order to fabricate nanostructures with targeted composition, shape and size. In the present study, we present an elegant route for the fabrication of single-gradient (Fig.1 A) and triple gradient (Fig.1 B) samples via e-beam evaporation of Au and Ni on (0001) oriented α-Al2O3. Subsequently, rapid thermal annealing is utilized at 890°C for 120s in reducing atmosphere (Ar/5% H2). The temperature is chosen in order to anneal the samples above the miscibility gap of the Au-Ni system for the production of AuxNi1-x alloys. This type of sample preparation allows i) the preparation of AuNi alloys with fine concentration differences to study the effect of alloying on SSD and ii) to study alloying effects and film thickness effects using a single sample. Ex-situ scanning electron microscopy (SEM) studies of the thermal annealed single-gradient sample are displayed in Fig. 2A. The homogeneous back-scatter contrast in the particles confirm a successful formation of an AuNi solid solution for all compositions ranging from 1 at% Au up to 99 at% Au. Via segmentation of the SEM images, the ratio between the exposed and unexposed are extracted to visualize the Au concentration dependent dewetting kinetics (Fig. 2B). An increased dewetting kinetic can be found in the range of 50 at% to 70 at% which is in good agreement with our recent studies [2]. Using EBSD measurement the texture of the formed particles is investigated (Fig. 2 C). The pole figures show a strong 111 out-of-plane texturing for a wide concentration range. Furthermore, the microstructure is fibre-like with tendencies towards epitaxial orientation relationships of AuNi (111)[1-10] || α-Al2O3 (0001)[10-10]. Interestingly this texture is substanial lost for the sample with 60at% Au leading to a texture free microstructure of the particles. With the presented approach, the influence of a multitude of different factors like atomic size mismatch during alloying onto the SSD of bimetallic alloys can be investigated in just one single sample. Furthermore, we demonstrate, that the concentration can be tuned continuously over a concentration range from 1 at% to 99 at% Au, which allows a systematic investigation of the influence of the misfit between metal particles and ceramic substrate, which is currently part of further investigations. [1] Shahvaranfard et al., CS Appl. Mater. Interfaces 2020, 12, 34, 38211–38221 [2] Dierner et al., unpublished work 103

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MS2.004-invited Unravelling shear band formation and propagation in metallic glasses through 4D-STEM C. Gammer1, H. Sheng1, S. Fellner1, D. Sopu1, J. Eckert1 1Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria Metallic glasses (MGs) are an exciting new class of materials due to their unique mechanical and functional properties. Still, potential applications are hindered by their limited ductility caused by the formation of shear bands leading to catastrophic failure. A fundmental understanding of the shear banding process is key for improving the mechanical properties of MGs. While progress in the understanding of deformation localization was made using colloidal solids or atomistic simulations, highlighting the importance of nanoscale structural variations and local strains for shear banding, direct experimental studies are scarce due to limited characterization techniques. In the current work we study the deformation of metallic glasses at the nanoscale by scanning transmission electron microscopy (STEM) imaging using a JEOL 2200FS equipped with an in-column energy filter. To quantify local density and strain, a map of precession nanodiffraction patterns is recorded using 4D-STEM. Scanning and precession of the electron beam is controlled by a TVIPS universal scanning generator and the nanodiffraction patterns are recorded using a fast CMOS camera (TVIPS XF416) and a direct electron detector (Quantumdetectors MerlinEM 4R). A Cu46Zr46Al8 bulk MG plate is made by suction casting and shear bands (SB) are introduced by uniaxial compression. Cross section specimens are extracted on major SBs using a focused ion beam dual-beam workstation. Precession nanodiffraction enables to map the strain at at sufficient spatial resolution (<2 nm) to quantify atomic density and strain distribution within an individual SB. Figure 1 shows a HAADF image and a local density map, revealing a decrease in atomic density within the SB [1]. In addition, the SB shows density alternations from the atomic scale to the submicron scale. The nanoscale density alternations show good agreement with molecular dynamic simulations indicating that they are linked to the autocatalytic generation of shear transformation zones, while the density alternation at submicron scale results from the progressive propagation of the SB front. The current results demonstrate that a direct quantitative measurement of strain in amorphous nano-volumes is important for revealing fundamental deformation processes in MGs, eventually allowing to tune their mechanical properties in a more controlled fashion. This work was supported by the Austrian Science Fund (FWF): Y1236-N37. [1] H. Sheng, D. Şopu, S. Fellner, J. Eckert, C. Gammer PHYSICAL REVIEW LETTERS 128, 245501 (2022) Fig. 1 105

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MS2.005 Electron time correlation microscopy and the stability of the numerical evaluation M. Peterlechner1, D. Radić1, K. Spangenberg1, O. Vaerst1, M. Demming1, G. Wilde1 1University of Münster, Institute of Materials Physics, Münster, Germany The high spatial and temporal resolution of electron microscopy opens new ways of characterizing matter. Electron Correlation Microscopy (ECM) is a comparably new method analyzing time-intensity correlations in thermodynamic equilibrium [1,2]. For amorphous materials, transmission electron microscopy (TEM) dark-field (DF) images show speckle contrast arising by local structural arrangements. ECM measures basically a speckle lifetime. In the present work, the ECM data evaluation and the resulting accuracy are discussed. Measuring ECM out of thermodynamic equilibrium at room temperature (RT) was shown recently for a metallic glass [3,4]. ECM measurements out of thermodynamic equilibrium are here denoted Electron time Correlation Microscopy (EtCM). This brings additional evaluation criteria, visualized by calculating two-time correlation functions. A schematic of EtCM is shown in Figure 1. An amorphous sample is imaged in TEM-DF mode to detect structural arrangements fulfilling the chosen DF condition leading to speckle contrast. Typically about 50 nm in thickness samples and a beam current density of about 105 e-/nm²s at exposure times of seconds are applied. From the image time series, a correlation function (g2(t)) is calculated, which is fitted to a stretched exponential function ( A*[1-exp(- t/τ)β], see Figure 1 top-right). A β=1 leads overall to a single exponential function, β<1 to a stretched, and β>1 to a compressed exponential function. The β therefore reflects the energy landscape of the underlying processes. Depending on the material, the correlation time at RT can be extremely large (> 10 k seconds). Consequently, the corresponding data quality is limited due to the limited experimental accessible time. One approach is to extrapolate τ and β to infinitely long measurement times [3] by using e.g. a*[1-exp(-x/b)], where a is the value of τ or β for time to infinity, b is a parameter reflecting how fast the data analysis comes to a numerical steady state and x denotes the experimentally determined τ or β for different, finite times. It should be noted, that τ and β also depend on the DF condition as the beam tilt selects the scattering vector magnitude. In Figure 2, an example of β and τ as a function of the evaluated stack length is shown. Evaluating short measurement time leads to numerically unstable values. Evaluating longer times leads to more stable values, underestimating the real values. The dependence of β and τ on the evaluated time are different. However, the data analysis using different fractions of a DF-time series is a robust way to gain insights into the stability of the fitting parameters β and τ. Moreover, by extrapolating β and τ to timeàinfinity allows to estimate the real values (at a given beam current), or at least to estimate a proper measurement time for an EtCM experiment. Based on literature and numerical tests, the τ and β values are reviewed and discussed. [1] L. He at al., Microsc. and Microanal. 21 (2015) 1026-1033. [2] P. Zhang et al., Nature Communications (2018) 9:1129. [3] K. Spangenberg et al., Adv. Funct. Mater. 31 (2021) 2103742. [4] M. Stringe et at., J. Alloys Compd. 915 (2022) 165386. Fig. 1: Schematic EtCM measurement: (left) data acquisition and (right) data analysis including a two-time correlation plot to confirm a quasi-equilibrium condition. Fig. 2: Streching exponent β and correlation time τ obtained by fitting a (fraction of a) dataset. 106

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MS2.006 Segregation to creep-induced planar faults in Ni-base SX superalloys Z. Long1, C. Dolle1, D. Bürger2, Y. M. Eggeler1 1Karlsruher Institut of Technologie (KIT), Laboratory for Electron Microscopy, Karlsruhe, Germany 2Ruhr University Bochum, Institute for Materials, Bochum, Germany Ni-base single-crystal (SX) superalloys find application in turbine blades for gas engines due to the high-temperature and high-stress strength originating from the coherent γ/γ" microstructure. It is well-known at sufficiently high stresses, two 1/2 dislocation families with different Burgers vector can react and dissociate into two partial dislocations in γ channels. This allows the leading 1/3[-1-12] Shockley partial dislocation continuously gliding on {111} planes to cut into γ" precipitates where they create planar faults [1]. We study the segregation behaviours of alloying elements across the planar faults by performing the [11-2] (111) creep shear experiments, to intentionally activate the slip system [11-2] (111) with the highest Schmid factor of 1 where the resolved shear stress is exactly equal to loading stress. The creep-deformed specimens are interrupted after 1% and 2% shear strain under 250 MPa at 750°C. The resulting microstructure is investigated using conventional transmission electron microscopy (TEM), analytical scanning TEM (STEM) with energy-dispersive X-ray spectroscopy (EDXS) focussing on structural, physical, and chemical details of the local deformation. Fig. 1 presents the specimen perpendicular to the (111) plane with the [1-10] direction parallel to the electron beam. Numerous stacking faults (SF) are observed after 1% and 2% creep strains. Fringe contrasts under two-beam conditions indicate inclined stacking faults, shown in Fig 1a and 1d, where the 2% strain sample has more planar faults within one γ" precipitate indicating a higher density of planar faults in the 2% sample. High-resolution STEM micrographs illustrate the superlattice extrinsic nature of stacking faults (SESF) in the 1% and 2% strained samples, see Fig1b and 1e. The chemical distributions across SESF are measured by EDXS and the corresponding concentration profile of 1% and 2% samples are shown in Fig. 1c and 1f respectively. Both samples show almost similar segregation tendency, which is that γ forming elements Cr, Co and Re are enriched across the SESF while γ" alloying elements Ni and Al are depleted, which is partly in agreement with theoretical predictions [2]. For these measurements all microscope parameters and sample thickness for EDXS analysis are kept the same to quantitatively find out how creep strain and time affect the evolution of segregation. Figure 1. (S)TEM micrographs of the [1-10] foil normal sample show typical planar faults in Ni-base SX superalloys crept at 750 °C/250 MPa to creep strains of 1% (upper row) and 2% (lower row). TEM bright filed images present fringe contrast of inclined stacking faults under two-beam conditions in (a) g = (00-2) and (d) g = (002) excitation condition. High resolution STEM micrographs indicate the superlattice extrinsic nature of edge-on stacking faults of (b) 1% and (e) 2% strain specimens. Alloying concentration profiles across SESF of (c) 1% and (f) 2% from corresponding EDXS mappings. References [1] Eggeler, Y. M. et al. Annu. Rev. Mater. Res., 2021, 51, 209–240. [2] Zhao, X. et al. Comput. Mater. Sci, 2022, 202, 1–8. [3] Authors gratefully thank Christian Kübel, Di Wang and Yuting Dai (Electron Microscopy and Spectroscopy Laboratory, KIT) for HRSTEM micrographs and EDXS results, and acknowledge the DFG priority program SFB‐TR 103. 108

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MS2.P002 In-situ observation of structural and optical properties changes in Ag-Cu plasmonic nanoparticles by using specimen heating holder A. Yasuhara1,2, M. Homma2, T. Sannomiya2 1JEOL Ltd., EM Application department, Tokyo, Japan 2Tokyo Institute of Technology, Yokohama, Japan [Introduction] Plasmonic nanoparticles are widely studied and used in various fields because they show unique optical properties. The optical properties, due to the surface plasmon resonances around the nanoparticles, are known to be dependent on their sizes, shapes, and dielectric functions of materials. Previously we fabricated several kinds of nanoparticles with different elemental compositions using the dewetting method[1, 2], and studied their optical properties and nanostructures by Transmission Electron Microscope (TEM). However, there are still unclear parts in the formation process of the nanoparticles during the heating procedure. In order to control and optimize the optical properties properly, the knowledge of the fabrication process of the nanoparticles becomes to be essential and important information. [Objectives] We aim to clarify the process of nanoparticle formations and their structural changes during the dewetting procedure using a TEM and a dedicated specimen heating holder. [Materials and Methods] The initial state of the sample was prepared by co-evaporating pure Ag and pure Cu on a thin SiO2 film for TEM observation. In order to characterize the structural changes of nanoparticles, we performed in- situ TEM observation by elevating the temperature from room temperature (RT) to 400 °C by a specimen heating holder. Besides, we measured the bulk optical properties of the nanoparticles during the heating process, comparing to their structural changes. [Result] Figure 1 shows the in-situ measurement results of the optical properties of Ag-Cu nanoparticles. The peaks of the extinction spectrum were shifted to the shorter wavelength during the heating process and the double peaks were observed at higher temperatures. Figure 2 shows the elemental distributions of Ag-Cu nanoparticles by EELS at RT and 400 °C. The core-shell type nanoparticles were formed at RT. After the heating process, we found the nanoparticles changed to the Janus-type phase-separated nanoparticles. [Conclusion] We investigated the structural changes of Ag-Cu nanoparticles by in-situ TEM observation. From the in- situ TEM results, we found that the size of the nanoparticles increased notably and in addition the Ag and Cu phases are more clearly separated at 400 °C. The red-shift of extinction spectrum is thought to be caused by the changes in the sizes and shapes of nanoparticles. The double peaks of the extinction spectrum are concluded to be related to the phase separation of the nanoparticles. Figure 1. Extinction spectrum of Ag-Cu binary nanoparticles during the heating process Figure 2. Elemental maps of Ag-Cu binary metal nanoparticles at room temp (a) and 400 °C (b) measured by Electron Energy Loss Spectroscopy (EELS). Green and red colors in elemental maps indicate Cu and Ag elemental distribution, respectively. [References] [1] C. Wadell et al., J. Phys. Chem. C. 121 (48), 27029-27035, 2017, [2] A. Yasuhara et al., J. Phys. Chem. C. 124 (28), 15481–15488, 2020 110

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MS2.P003 Electron correlation microscopy study of thermally pre-treated PdNiP bulk metallic glass O. Vaerst1, G. Wilde1, M. Peterlechner1 1Westfälische Wilhelms-Universität Münster - Institute of Material Physics, Münster, Germany Achieving both temporal and spatial resolution in an analysis opens new ways of investigating materials. Electron Correlation Microscopy (ECM) is a rather new method proposed by He et al. [1] yielding temporally resolved data on structural rearrangements in spatially well-resolved transmission electron microscopy (TEM). This opens up the possibility of observing atomic processes that govern basic mechanisms and the unique properties of amorphous metals. In the present study, the focus lies on amorphous PdNiP. Pre-treatments, such as annealing and treatments of thermo-mechanical kind, significantly influence the local structure, kinetic stability, and mechanical properties of this bulk metallic glass. Thus, it is of great interest to study the dynamics in the material on the atomic scale after treatment to shed light on the origin of the property changes. For these investigations, Pd40Ni40P20 samples are produced via copper-mould casting. Basic characterizations of the material are performed, including verifying the amorphous state and the composition. Subsequently, samples are pre- treated thermally in a differential scanning calorimeter (DSC) by implementing an annealing routine below the glass transition temperature. The atomic dynamics of different thermally treated sample states are investigated at room temperature using ECM. This technique is based on investigating the speckle contrasts in dark-field images over time. By that, atomic rearrangements and local dynamics can be studied with nanometer spatial resolution [1,2]. The schematic of an ECM measurement and the corresponding analysis are shown in Fig. 1. The obtained time series of dark-field images from ECM measurements need to be corrected for drift before speckle contrasts can be analysed. The drift-correction method that we found to work for all our data sets consists of three steps including a contrast enhancement step for more precise drift measurements. From changing speckle contrasts over time an autocorrelation function g2(t) can be calculated. By fitting a Kohlrausch-Williams-Watts function (KWW) to g2(t) the characteristic relaxation times τ are found. We analysed partial data stacks to evaluate the resilience of the obtained relaxation times and compared calculated autocorrelation functions of different sample states. The obtained relaxation times for a PdNiP as-cast state depicted in Fig. 2 are a measure of the local dynamics within the time spectrum accessible by the method. To conclude, the effect of thermal pre-treatments on ECM evaluation parameters of amorphous PdNiP is discussed. Such investigations of atomic mobilities give further insight into the amorphous phase as well as into the local relaxation dynamics of a bulk metallic glass. [1] L. He at al., Microsc. and Microanal. 21 (2015) 1026-1033. [2] K. Spangenberg et al., Adv. Funct. Mater. 31 (2021) 2103742. [3] P. Zhang et al., Nat. Commun. (2018) 9:1129. Funding by DFG is acknowledged. Fig. 1: Schematic setup for ECM measurement (left) and data analysis (right), adapted from [3]. Speckle contrast changes in dark-field images over time are correlated and fitted by a stretched exponential function (KWW). Fig. 2: Relaxation times τ for as-cast PdNiP as obtained after fitting a KWW function to the correlated speckle contrast changes over a measurement time of 20000s. 112

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MS2.P004 Epitaxy and solid-state-dewetting of Au on polar surfaces of ZnO M. Landes1, M. Dierner1, J. Will1, E. Spiecker1 1Institue of Micro- and Nanostucture Reserach, Materials Science and Engineering, Erlangen, Germany Metal/oxide heterointerfaces are omnipresent in functional materials and their microstructure often determines macroscopic properties. For ceramics with a wurtzit lattice like zinc oxide the surface polarity plays a major role, because it can change electronic properties [1] and influence the properties of deposited metal films [2]. In this study, the epitaxial and microstructural evolution of thin gold films on (0001)/(000-1) oriented ZnO substrates is investigated. For this, Au thin films with a thickness of 40 nm are deposited directly onto the (0001) Zn-ZnO and (000- 1) O-ZnO surfaces by electron beam evaporation. Annealing of the samples at elevated temperatures was carried out with an rapid thermal annealing (RTA) furnace. During heating a constant nitrogen flow is introduced, whereas a fast cooling rate of ~200 °C/s is achieved by dropping the sample on a water-cooled steel plate. SEM imaging and EBSD measurements reveal that both epitaxial grain growth (Figure 1) and solid-state-dewetting of the film highly depend on the polarity of the ZnO surface. to temperatures 600°C the as-deposited state up From fine grains with a predominant orientation of Au(111)[110]||ZnO(0001)[11-20] (OR2) are present on both ZnO terminations. EBSD imaging shows, that during heating at 800 °C and above large grains form in the Au film on the Zn terminated substrate. These grains have an Au(111)[110]||ZnO(0001)[10-10] orientation (OR1) and exhibit a higher thermal stability. In contrast, grain growth and solid-state dewetting of the Au film are retarded and accelerated on the oxygen terminated surface, respectively. As a result, a fiber texture with both OR1 and OR2 evolves. The different dewetting rates can be explained by a larger binding energy of Au to the zinc terminated surface [3], which lowers the Au/Zn-ZnO interface energy and makes it more resistant to dewetting than the weakly bound oxygen side. High-resolution STEM imaging was carried out to investigate the Au ZnO interface. For Au on O-ZnO a semi-coherent interface with misfit dislocations is present (Figure 2a). For the epitaxial Au/Zn-ZnO, interface reconstruction (Figure 2c) with a regular spacing is observed. This reconstruction of the Zn and Au atoms close to the interface likely reduces the interface energy of OR1, thus facilitating the transformation from OR2 to OR1. [1] Rahman, Faiz. "Zinc oxide light-emitting diodes: a review." Optical Engineering 58.1 (2019) [2] Dulub, Olga, Matthias Batzill, and Ulrike Diebold. "Growth of copper on single crystalline ZnO: surface study of a model catalyst." Topics in Catalysis 36.1 (2005): 65-76. [3] Shuyi Wei, Zhiguo Wang, Zongxian Yang, "First-principles studies on the Au surfactant on polar ZnO surfaces", Physics Letters A, Volume 363, Issue 4, (2007) Fig. 1 114

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MS2.P005 Effects of damage dose and temperature on the radiation induced formation of rhenium clusters in tungsten M. Klimenkov1, U. Jäntsch1, M. Rieth1 1Karlsruher Institut of Technologie (KIT), Institute for Applied Materials - Applied Materials Physics, Eggenstein-Leopoldshafen, Germany The development of appropriate materials for fusion reactors that can sustain high neutron fluence at elevated temperatures remains a great challenge. Tungsten is one of the promising candidate materials for plasma-facing components of future fusion reactors, due to several favorable properties as for example a high melting point, a high sputtering resistivity, and a low coefficient of thermal expansion. Pure W was neutron irradiated at 600 °C, 900 °C, 1000 °C, 1100 °C, and 1200 °C with a dose of ~1 dpa, and its microstructure was subsequently analyzed using transmission electron microscopy (TEM). The study provides the basis for a deeper understanding of the microstructural evolution of W under neutron irradiation. Three types of defects forms in W as result of neutron irradiation: (i) voids, (ii) dislocation loops and (iii) W-Re-Os containing precipitates. The TEM study includes a detailed examination of the defect structure and, in particular, the distribution of transmutation-induced Re and Os, whose content is expected to be in the range of ~2% for Re and 0.2% for Os under the applied irradiation conditions. Analytical investigations show that the voids, precipitates and loops are surrounded by 8-15 nm Re- and Os-rich "clouds" (Fig. 01). The "clouds" do not produce any diffraction contrast in TEM images and can only be visualized by analytical methods. Grain boundaries act as sinks for all types of point defects, i.e., vacancies and interstitials, as well as Re and Os atoms, leading to the formation of a 10-20 nm wide zone adjacent to the grain boundaries that is free of voids and precipitates (the so-called depleted zone). In addition, we found that Re and Os are often inhomogeneously distributed along grain boundaries, which is due to segregation at boundary dislocations (Fig. 1). The elemental maps in Fig.1, show the general distribution of transmutation elements on the large scale and are less useful for identifying concentration differences within individual clouds. The minor intensity variations are not well reproducible and identifiable in the color map. For this reason was used the intensity profile analysis across defects to show differences in Re and Os distribution in W irradiated at 600 °C (Fig.2). The elemental profiles in Fig. 2e shows that the Re intensity decreases slightly in the center, reflecting the position of the void. Precipitates, on the contrary, show a higher local Re and Os concentration in the center (Fig. 2e`). The intensity profiles across the marked loop are plotted in Fig. 2e``. It is notable that Re exhibits a uniform distribution in the area inside the loop, while Os tends to segregate at the dislocation line (Fig. 2e,e``). This study presents the results of extensive microstructural analyses of W samples, which were neutron irradiated at temperatures between 600 °C and 1200 °C, up to a damage dose of ~1.0 dpa. The formation of dislocation loops, voids, and precipitates consisting of Re-Os- χ-phases was observed and characterized in detail. Fig. 01. STEM-EDX spectrum images show the distribution of transmutation-induced Re (green) and Os (blue) inside W irradiated at 600 °C (a,a`), 900 °C (b, b`) and 1100 °C (e, e`). Fig.02. Re, Os and combined Re/Os elemental maps obtained in W irradiated at 600 °C (a-d). The Re and Os intensity profiles of void (magenta arrow), a precipitate (yellow arrow) and a dislocation loop (white arrow) shown in parts (e-e``). 116

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MS2.P006 The peculiarity of FeRh alloys: a thorough TEM investigation E. Adabifiroozjaei1, N. Kani1, R. Winkler1, T. Jiang1, O. Recalde-Benitez1, A. Zintler2, A. Chirkova3, K. Skokov3, O. Gutfleich3, L. Molina-Luna1 1TU Darmstadt, Advanced Electron Microscopy, Darmstadt, Germany 2Karlsruher Institut für Technologie (KIT), Laboratorium für Elektronenmikroskopie, Karlsruhe, Germany 3TU Darmstadt, Functional Materials, Darmstadt, Germany Introduction: Fe50Rh50 alloys are known to have a B2 BCC structure with an antiferromagnetic (AFM) to ferromagnetic (FM) transition at near room temperature. The transition is isostructural with about 1% change in volume and is accompanied by giant magnetoresistive and magnetocaloric effects. Therefore, there has been a lot of interest on the Fe50Rh50 alloy as a model system [1]. Interestingly, the majority of the previously reported work do not provide extensive local atomic structure investigations (mostly thin films). Thus, the structural characteristics of the alloy at the AFM or FM states remains controversial [2]. Since this alloy is among the betta alloy series (CdAu, TiNi, Fe-C, etc…), it is expected to present a pre-martensite structure followed by a martensite structure upon cooling at cryogenic temperature[3]. The martensite was also predicted by extensive first principal calculations[2,4]. However, so far, no evidence has been given regarding the formation of either pre-martensite or martensite structures in the Fe50Rh50 alloy. Objective: To use various TEM techniques to investigate the FeRh 50/50 alloy and demonstrate that at the AFM state, the alloy is in the pre-martensite state. Materials and methods: Fe50Rh50 alloys were prepared at the German Electron Synchrotron (DESY) using an electromagnetic levitation facility developed and constructed at the IFW Dresden. The Fe50Rh50 material was alloyed by arc-melting of the appropriate amounts of the pure Fe (99.995%, Alfa Aesar) and Rh (99.9%, Alfa Aesar). After casting, the alloys were heat-treated at 1150°C for 9 days and quenched in water. During the heat-treatment the alloys were sealed in quartz tube with Ar atmosphere. Afterwards, the bulk alloys were cut by wire cutter and thin slices were polished to thickness of ~50 µm. Then, the slices were milled using precision ion polishing system (PIPS) with energy of 3 KeV and angles of 4 degrees. The prepared thin sections were investigated using a variety of TEM techniques including CTEM, HRTEM, STEM (HAADF), and EDS. Results: Fig. 1 shows the HRTEM and corresponding Fast Fourier Transformed (FFT) images of the FeRh 50/50 alloy in three principal directions ([001], [-110], and [111]). As seen, although the structure of the alloy match perfectly with the B2 BCC structure, there is systematic modulation along certain reflexes (100 and 110). This was also confirmed by HAADF-STEM imaging, the results of which are given as Fig. 2. In the corresponding Z-contrast images, the modulation can only be easily seen in the [111] zone axis. Conclusions: Our results show that the B2 BCC alloy of FeRh 50/50 at the AFM state possess a pre-martensite structure. We acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG) within the CRC/TRR 270 (Project-ID 405553726). Figure 1. Representative nanostructure of FeRh alloys in three principal directions: a, b and c are HRTEM images in [001], [-110], and [111] zone axes, while d, e, and f are FFT images of a, b, and c. Modulation in HRTEM images are shown as parallel pale green lines, while in FFT images related superlattice reflexes are distinguished by red circles. Figure 2. Representation of arrangement of Fe (small) and Rh (large) atoms in three principal zone axes of alloy. Modulated structure (dashed parallelograms) is visible in [111] zone axis. For comparison, ideal arrangement of atoms exported from B2-BCC structure are imposed on nanostructures. In imposed images, green and yellow atoms stand for Fe and Rh, respectively. 118

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MS2.P007 TEM studies of the long-term high-temperature stability of TiAl electrodes for high-temperature surface acoustic wave devices M. Seifert1, B. Leszczynska1, S. Menzel1, T. Gemming1 1IFW Dresden, Dresden, Germany There is a great need in industry for wireless sensors working at high temperatures (above 300 °C) to monitor and control high-temperature processes. Surface acoustic wave (SAW) sensors are promising candidates to realize such devices. A SAW sensor consists basically of a piezoelectric substrate on which metallic electrodes with a defined geometry are prepared. Both materials, the substrate as well as the metallic electrodes, have to be high-temperature stable to enable the application at the aimed high temperatures. Up to now, mainly noble metals, such as Pt-based materials, were reported as a high-temperature stable metallization. However, the strong tendency to agglomeration and the high costs are drawbacks. In former work, we studied the Al-based alloy TiAl as a cost-efficient alternative metallization with promising high-temperature stability up to 600 °C for 10 h by analyzing extended films [1,2]. To study the long term high-temperature stability of TiAl electrodes, TiAl-based SAW sensors were annealed at temperatures up to 600 °C for up to 192 h in air. STEM investigations in combination with EDX and EELS measurements of the electrodes were performed to study their morphology and degradation behavior. To evaluate the influence of the limited dimension of the structured electrodes, the much larger contact pads were analyzed as well. The samples were realized by e-beam evaporation of alternating thin layers of pure Ti and Al with an individual thickness of 10 nm and a total film thickness of 200 nm on piezoelectric Ca3TaGa3Si2O14 (CTGS) substrates. To prevent a chemical reaction between the metallization and the substrate, a 20 nm thick AlNO barrier layer was deposited on top of the substrate prior to the deposition of the metallization. The structured electrodes were obtained using the lift-off technique. Finally, the whole SAW structure was covered with a 40 nm thick AlNO protection layer. Figure 1 shows STEM images of the electrodes after the annealing in air at 400 and 500 °C for 192 h and at 600 °C for 24 and 192 h. After annealing at 400 °C, an incomplete interdiffusion of the individual metallic layers was observed. EDX analysis revealed a composition of the layers corresponding to the Ti3Al and TiAl2 phase. After annealing at 500 °C, a layered structure was still visible, corresponding to the TiAl and TiAl2 phase. The annealing at 600 °C for 24 h led to a complete interdiffusion and only minor degradation was observed at the edges of the finger. In contrast to this, annealing at 600 °C for 192 h led to a strong oxidation [3]. The results demonstrated that the TiAl-based SAW sensors are promising devices for a long-term application up to at least 500 °C and allow short- and medium-term application at 600 °C in air. [1] Seifert M, Lattner E, Menzel SB, Oswald S, Gemming T. Materials. 2020;13(9):2039. [2] Seifert M, Lattner E, Menzel SB, Oswald S, Gemming T. JMRT 2021;12:2383-95. [3] Seifert M, Leszczynska B, Menzel S, Gemming T. JMRT 2022;19:989-1002. The authors gratefully acknowledge funding from German BMWI (grant number 03ET1589 A) and DFG (470028346). Figure 1: STEM images (predominant element contrast) of the electrodes annealed in air at (a) 400 °C for 192 h, (b) 500 °C for 192 h, (c) 600 °C for 24 h, and (d) 600 °C for 192 h 120

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MS2.P008 Helical dislocations in ion-irradiated Fe-9Cr studied by scanning transmission electron microscopy K. Vogel1, H. J. Engelmann2, P. Chekhonin1, F. Bergner1, C. Kaden1 1Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Dresden, Germany 2Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Dresden, Germany Fe-9Cr is a model alloy for studying irradiation effects relevant for potential applications of high-chromium ferritic/martensitic steels in nuclear energy devices. Ion irradiation is a tool extensively employed with the aim to emulate the neutron damage characteristic for irradiation environments in fission or fusion reactors. Here we report on STEM studies of the microstructure of ion-irradiated Fe-9Cr with special emphasis on the effects of pre-existing dislocations. Irradiations with 8 MeV Fe3+ ions were carried out at the 3 MV tandetron accelerator at the Ion Beam Center at HZDR. Profiles of displacement damage and implanted ions were calculated using the binary collision code SRIM. Cross-sectional TEM specimens were prepared by focused ion beam lift-out technique using a Thermo Fisher Helios 5CX. The microstructure was studied in a Talos F200X. Figs. 1a and b display STEM images of a large ferrite grain, which were acquired along the [001] zone axis, Fig. 1c contains the damage profiles calculated by SRIM. In the depth range of the highest concentration of implanted ions, a dark band is visible similar to the defect-rich bands observed in previous studies [1]. The most striking feature of the irradiated microstructure in the range of high displacement damage, but low concentration of implanted ions, is the presence of helical dislocations (examples are labelled H1 and H2). These helices are aligned at an angle of about 45° or -45° with respect to the [100] direction. No helices are present in the non-irradiated substrate. Here we observe a network of curved dislocation segments as well as nearly straight dislocation lines (S1 and S2), the latter showing the same alignment as the helices. The higher magnified image in Fig. 1b reveals a large number of small dislocation loops appearing as black dots, most of them located close to the helices. For Burgers vector analysis, STEM images were acquired under two-beam conditions with different diffraction vectors g as displayed in Fig. 2. The helix H1 and the straight dislocation S1, both aligned at 45°, are visible with g = -110 but invisible with g = 110. To fulfill the g · b = 0 invisibility criterion, the Burgers vector b must be ±½[-111] or ±½[1-11]. In contrast, H2 and S2, aligned at -45°, must have a Burgers vector of ±½[11-1] or ±½[111]. The straight dislocations as well as the helices are aligned nearly parallel to the projection of their Burgers vectors (indicated by the blue and red arrows), which means that the straight dislocations have a dominating screw component and that the helices are formed from this type of pre-existing dislocations. The presence of helical dislocations and the accumulation of loops close to them resembles observations reported for neutron-irradiated Fe-9Cr [2]. Hence we conclude that - in the depth range of low implanted ion concentration - ion irradiation can produce similar defect configurations like neutron irradiation if the arrangement of pre-existing dislocations is comparable. [1] K. Vogel et al., NME 27 (2021) 101007 [2] J.C. Haley et al., Acta Mater. 181 (2019) 173 [3] This work has received funding from the Euratom research and training programme 2014-2018 under grant agreement No. 755039 (M4F project). Fig. 1: (a), (b) STEM images acquired along the [001] zone axis, (c) damage profiles calculated by SRIM. Fig. 2: STEM images acquired with different diffraction vectors g as indicated by the white arrows. 122

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MS2.P009 Confined chemical intermixing in Ni/Fe multilayers by He+-ion irradiation N. Wolff1, G. Masciocchi2,3, A. Lotnyk4, J. W. van der Jagt5,6, M. A. Syskaki2,7, A. Lamberti8, J. Langer7, G. Jakob2, B. Borie5, A. Kehlberger3, D. Ravelosona5,9, M. Kläui2, L. Kienle1 1Kiel University, Department of Material Science, Kiel, Germany 2Johannes Gutenberg University Mainz, Institute of Physics, Mainz, Germany 3Sensitec GmbH, Mainz, Germany 4Leibniz Institute of Surface Engineering e.V. (IOM), Leipzig, Germany 5Spin-Ion Technologies, Palaiseau, France 6Université Paris-Saclay, Gif-sur-Yvette, France 7Singulus Technologies AG, Kahl am Main, Germany 8university, CNR-IMM, Agrate Brianza, Italy 9Université Paris-Saclay, C2N, CNRS, Palaiseau, France The control of the magnetoelastic properties of thin films is existentially relevant for the technological development of new devices which are based on the strong interaction of the material with the surrounding magnetic field. Dependent on the application, i.e. for magnetic field sensors or magnetic actuators, the magnetoelastic coefficient λs of the thin film requires dedicated tuning. One facile approach for this optimization of magnetostriction is the material combination achieved in multilayers systems [1] and to engineer the coupling properties via modification of interfaces, e.g. controlling atomic intermixing across the interfaces [2,3]. In this contribution, the progressive intermixing at the interfaces of a (2 nm 2 nm)4 Ni/Fe multilayer caused by light-ion irradiation is characterized by spectroscopic methods of probe aberration-corrected STEM, such as energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy to identify induced changes to the film"s chemical and atomic structure. Elemental mapping revealed the introduced chemical intermixing at the Ni/Fe interfaces, suggesting the formation of NixFe1-x alloys for the ion-irradiated multilayers without introducing discernible modifications to the initial crystalline structure of the stack [3]. The local chemical analyses are congruent to averaging ToF-SIMS measurements. In conclusion, the comparison of untreated and He+-ion irradiated Ni/Fe multilayers using dedicated chemical analysis by STEM-EDX and EELS suggest that the post-growth ion-irradiation method is able of locally modifying the degree of interfacial intermixing. Thereby the saturation magnetostriction of the magnetic stack is changed and can be tuned towards the specific needs of application. [1] Y. Nagai, M. Senda, and T. Toshima, "Properties of ion-beam-sputtered Ni/Fe artificial lattice film," Journal of Applied Physics 63, 1136–1140 (1988). [2] J. Fassbender, D. Ravelosona, and Y. Samson, "Tailoring magnetism by light-ion irradiation," Journal of Physics D: Applied Physics 37, R179 (2004). [3] G. Masciocchi et al. (2022), "Control of magnetoelastic coupling in Ni/Fe multilayers using He+ irradiation," ArXiV:2207.02493 124

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MS2.P010 Influence of repeated heat treatments on microstructure and properties of EUROFER97 (EF97)-type steels M. Dürrschnabel1, T. Lenoir1, R. Gaisin1, U. Jäntsch1, D. Bolich1, M. Rieth1 1Karlsruher Institut of Technologie (KIT), Institute for Applied Materials - Applied Materials Physics (IAM-AWP), Eggenstein-Leopoldshafen, Germany 1. Introduction Current geopolitical events as well as the racing climate change demand for sustainable structural materials for CO2- neutral energy. Future fusion reactors require large quantities (1000-ton range) of high-performance structural materials such as EF97 that can withstand elevated temperatures up to 550°C as well as a high neutron damage larger than 20 dpa. 2. Objectives Joints of martensitic steels, specifically after liquid phase welding processes like W inert gas or laser beam welds, typically require post-welding heat treatments. The fabrication of breeding blankets for fusion reactors may involve several production steps with consecutive welding. Therefore, the structural material EF97 would be exposed to a series of heat treatments. The objective of this analysis is to study the effect of repeated heat treatments on the microstructure and mechanical properties of EF97-type steel, in the context of materials technology for nuclear fusion reactor applications. 3. Materials & methods The samples have been heat treated (details see below) and analyzed regarding Vickers hardness. Subsequently, scanning electron microscopy with electron backscatter diffraction (SEM-EBSD in a Zeiss Merlin) scanning and transmission electron microscopy in combination with energy-dispersive X-ray analysis (STEM-EDX in a Thermofisher Talos F200X) has been performed on selected samples to determine grain sizes as well as size and composition of precipitates. • HT1, as received: 980°C/0.45h+air quenching (AQ)+760°C 2.5h • HT1: 980°C/0.5h+AQ • HT2: 980°C/0.5h+AQ+750°C/2h 4. Results Figure 1: Development of Vickers hardness with the number of heat treatments. Figure 1 shows the development of the Vickers hardness for the different applied heat treatments compared to the as received state of the material. For HT1 a slight decrease of the Vickers hardness is observed whereas for HT2 it is quite constant compared to the as received state. The SEM-EBSD data was evaluated regarding the martensitic lath size a well as for the prior austenitic grain (PAG) size in dependence on the applied number of heat treatments. Both quantities were found to remain constant up to 20 heat treatment repetitions, only small variations were observed in Table 1. Table 1: Martensitic lath sizes and PAG sizes summarized for selected heat treatments. Figure 2: STEM-EDX elemental maps after applying 20x HT1 and HT2. Figure 2 shows two STEM-EDX elemental mappings after 20 repetitions of each heat treatment. In case of HT1 there are no M23C6-type precipitates observed because without tempering, C remains mainly dissolved in the Fe-Cr matrix, whereas the MX-type precipitates (TaC & VN) form. The microstructure after 20x HT2 is comparable to other EUROFER-type steels. From these elemental maps, precipitate grain sizes, number densities and compositions were extracted and compared to thermodynamic calculations. 125

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MS2.P011 Microstructural evolution and thermal stability of AlCrFeNiCu quinary alloy W. Piyawit1, K. Antanam1, N. Chomsaeng2, S. Kuimalee3, P. Buahombura1 1Suranaree University of Technology, School of Metallurgical Engineering, Nakhon Ratchasima, Thailand 2Burapha University, Faculty of Engineering, Chonburi, Thailand 3Maejo University, Faculty of Science, Chiang Mai, Thailand High temperature alloys have been remarkably known for their good mechanical behaviors at elevated temperature. Nickel-based and cobalt-based superalloys alongside with their minor alterations by adding small amount of transition elements are commercially known for their exceptional high-temperature strength, outstanding resistance to oxidizing environments up to 1150°C, premier resistance to nitriding environments, and excellent long-term thermal stability. However, the production cost effectiveness, specific strength, and high alloy homogeneity have been the major drawbacks of these superalloys. Quinary alloys with five equiatomic elemental composition have been emerged with promising properties. They can be prepared through different routes. The different processing schemes create distinct microstructures and most likely suitable for different applications. In this study, the equiatomic AlCrFeNiCu alloy was prepared by arc melting method with the expensed graphite electrodes. The fifty-gram as cast ingots were homogenized at 1,200°C with various times. To verify the stability at elevated temperature, tempering at 700°C for 2 hours was subsequently performed. Microstructures were investigated under scanning electron microscope (Zeiss, Auriga) equipped with energy dispersive spectroscopy. Phase identification was performed using X-ray diffraction (Bruker, D8). The local geometric of Fe and Ni were studied using X-ray absorption spectroscopy at SUT-NANOTEC- SLRI XAS beamline (BL5.2) facilitated by Synchrotron Light Research Institute (Nakhon Ratchasima, Thailand). The alloys were dendritically solidified. Microstructural observation suggested that the dendritic region composed of Fe-Cr and Ni-rich lamellar structures. The interdendritic regions consisted of Cu-rich phase containing nanosized precipitates alongside intermetallic compound. The modulated microstructure in dendritic regions enhanced mechanical properties. Even at high temperature tempering, the microhardness had not been sacrificed. Moreover, the phase transformation detected by X-ray diffraction measurements showed that nanoprecipitates and morphological changes occurred during heat treatments. X-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy were used to determine the local structures of Fe and Ni atoms in the alloy lattice. The spectra confirmed the formation of disordered BCC structure. 128

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MS2.P012 Microstructure of EUROFER97 coated with an Al2O3 layer U. Jäntsch1, M. Dürrschnabel1, M. Klimenkov1, M. Rieth1, M. E. Angiolini2 1Karlsruher Institut of Technologie (KIT), Institute for Applied Materials - Applied Materials Physics (IAM-AWP), Eggenstein-Leopoldshafen, Germany 2ENEA-Brasimone Research Centre, Camugnano, Italy 1. Introduction Reduced-activation materials that exhibit high radiation resistance are required for the design, construction, and reliable operation of environmentally friendly fusion power plants. One of the promising candidates for such an application, the reduced activation ferritic-martensitic steel (RAFM) EUROFER97 (EF97), has been systematically developed and extensively characterized in Europe for this purpose. Liquid metal corrosion is a significant problem for structural materials that needs to be avoided using a corrosion protection layer. In this case Al2O3 is used to separate the Pb-Li liquid metal from the EUROFER. 2. Objectives A 5 µm thick Al2O3 layer was deposited by chemical vapor deposition on EF97 to evaluate the corrosion resistance of this composite in a Pb-Li liquid metal. The aim of this study is the comprehensive characterization of the oxide layer as well as the EF97/Al2O3 interface. The particular focus is on the analysis of the microstructural changes in both the Al2O3 layer and the EF97 substrate after liquid metal corrosion. 3. Materials & methods The Al2O3 layer and its interface to the EF97 substrate have been analyzed in cross section by scanning electron microscopy (Crossbeam Auriga, ZEISS) and transmission electron microscopy (TEM) in combination with energy- dispersive X-ray analysis (STEM-EDX in a Thermo Fisher Scientific - Talos F200X). For TEM experiments a lamella was prepared using the Crossbeam FIB/SEM Auriga, ZEISS. 4. Results Figure 1 shows a SEM cross-section of the sample structure with the 5 µm Al2O3 layer on EF97 substrate. The EF97/Al2O3 interface appears to be smooth and free of visible structural defects. Channeling contrast using a FIB scan reveals that the EF97 grain size is reduced in a 1-2 µm wide region close to interface. Furthermore, the figure shows that M23C6 and MX precipitates are located along grain or package boundaries. Figure 1: SEM Cross-Section showing the Al2O3 layer on EF97. TEM analysis shows that the Al2O3 layer consists of 50-300 nm grains, which are randomly oriented. The crystalline structure of the layer corresponds to the Al2O3 modification. Figure 2 shows a STEM-EDX elemental mapping of the EF97/Al2O3 interface. In the EF97 several M23C6 and MX- type precipitates (TaC and VN) can be identified, which are comparable to bulk EF97 measurements indicating that the EF97 structure is still intact. At the EF97/Al2O3 interface a 10-15 nm thick V enrichment exists with localized Al and N rich particles having a size up to 200 nm. The presumable case of the V enrichment at the interface is related to the manufacturing of the layer or the treatment process. Close to the interface, diffusion of W, Cr and C along EF97 grain or lath boundaries was detected. This behavior is also observed in bulk EF97. The STEM bright- and dark-field images show that Al2O3 layer is not grown homogeneously, i.e., voids and Al platelets are observed. Figure 2: STEM-EDX elemental maps after applying corrosion tests. 5. Conclusions The microstructure of EF97 protected by a 5 µm Al2O3 layer has been examined in detail. As a result, significant changes in the EF97 substrate could not been observed. In addition, there is no evidence of oxidation in the EF97 matrix. 131

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MS2.P013 TEM investigation of planar faults in Ni-base superalloy ERBO1 B. Holtermann1, D. Bürger2, Y. M. Eggeler1 1KIT, Laboratory for Electron Microscopy, Karlsruhe, Germany 2Ruhr-Universität Bochum, Institut for Materials, Bochum, Germany Single crystal nickel-base superalloys are an important class of high-temperature materials used as blade substrate material in industrial gas turbines and jet engines. Their excellent creep properties are due to a high volume fraction of L1_2 y'-precipitates embedded in a FCC y-matrix forming a coherent y/y'-microstructure [1]. With increasing creep strain dislocations from the y-channels cut into the y'-precipitates forming complex planar faults, which show a different chemical composition than its hosting y'-phase [2]. An in-depth understanding of these diffusion-assisted microstructural deformation mechanisms is needed for further practical improvement of the next generation of nickel base superalloys [3]. In the present study TEM/STEM-methods are used to investigate the evolution of creep-induced solute segregation to planar faults and their formation in y'-precipitates in single crystal ERBO1 nickel base superalloy double shear creep specimens [4]. The specimens were creep deformed at 750°C and 250 MPa and interrupted upon 1% plastic deformation. For a detailed characterization of the planar faults, TEM thin foils were prepared with a foil normal that allows to analyze the planar faults in edge-on [1-10] and in-plane [111] configurations. First preliminary results of planar faults in edge-on configuration show planar fault traces in single or multiple y'-precipitates for 1% strain states, see Fig. 1. The planar faults are formed by partial dislocations which can be found attached to the faults within the precipitates (see arrow 1) and at the y/y'-interface (see arrow 2). Applying the g.b/R effective invisibility criterion (Fig. 1c) shows that with an excitation condition using the reciprocal space vector g(-1-1-1) the planar faults are out of contrast indicating a displacement in the [11-2] direction. With respect to the crystallographic orientations of the single crystal double shear creep specimen and the derived highest resolved shear stress and Schmid factor for the shear system [11-2](111) this displacement vector is expected. For the in-plane configuration partial dislocations that form planar faults while cutting through the y'-precipitate can be observed, see Fig. 2. Arrow 1 marks one cutting event where dislocations have cut into a y'-precipitate leaving a planar fault in their wake, indicated by a visible change in contrast. At the same time these dislocations extend into the y-channel and seem to split up, marked by arrow 2 in the WBDF image (Fig. 2b), additional LACBED and HR-STEM analysis is needed to prove this. To assess the evolution of solute segregation to the planar faults and gain a better understanding of the y'-precipitate cutting processes the specimens will be further evaluated. Future investigations will include a characterization of the intrinsic and extrinsic nature of planar faults and their atomic stacking sequence with HR-STEM. Furthermore, a detailed burgers vector analysis of the dislocations interacting at the y/y'-interface is planned. The authors acknowledge the DFG priority program SFB‐TR 103. [1] R.C. Reed - Superalloys, Cambridge University Press 2006 [2] Y.M. Eggeler et al. - Acta Materialia 113. 2016. 335-349 [3] Y.M. Eggeler et al. - Annu. Rev. Mater. Res. 2021. 51:209–40 [4] D. Bürger et al. - Crystals 2020. 10. 134 133

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MS2.P014 Design of lattice-matched AuxNi1-x(111)/α-Al2O3(0001) interfaces and their investigation by X-ray diffraction and electron microscopy M. Dierner1, J. Will1, M. Landes1, T. Yokosawa1, T. Przybilla1, T. Zech2, P. Herre3, T. Unruh2, E. Spiecker1 1Friedrich-Alexander Universität, Lehrstuhl für Mikro- und Nanostrukturforschung (IMN) & Center for Nanoanalysis and Electron Microscopy (CENEM), Erlangen, Germany 2Friedrich-Alexander-Universität, Institute for Crystallography and Structural Physics (ICSP), Erlangen, Germany 3Institut für Nanotechnologie und korrelative Mikroskopie (INAM), Forchheim, Germany Metal/ceramic interfaces are of great scientific and technological importance, with applications in electroceramic devices, structural composites and catalysis [1]. Due to different thermal expansion coefficients of metals and ceramics and, in many cases, a high lattice mismatch applications suffer from mechanical stresses making the metal- ceramic interfaces the weak point in the device. The usage of a binary alloy system on the metal side offers the possibility to tailor the mismatch , leading to a less strained interface with improved mechanical stability. In the present study, this concept is elaborated for the epitaxial interface between AuxNi1-x and α-Al2O3. For this Au/Ni bilayers are e-beam evaporated on (0001) oriented α-Al2O3. Rapid thermal annealing of the bilayers above the miscibility gap at 890°C for 120s in reducing atmosphere is used to fabricate AuxNi1-x alloy nanoparticles (NPs), which are subsequently quenched into a metastable supersaturated solid solution. Here, the Au concentration (c Au) is utilized to tune the {220} d-spacing of the alloyed NPs towards lattice matching with the {30-30} d-spacing of α-Al2O3. The influence of cAu on the structure of the NP and the interface as well as the interplay of solute atoms and the substrate is monitored by complementary X-ray and electron techniques. XRD out-of-plane scans (Fig.1A) confirmed the formation of AuNi alloy NPs. Furthermore, an influence of the lattice mismatch (e.g. at%Au) on the texturing of the NP can be seen. While all NPs show the typical <111>-OOP texture, interestingly this texture is partially lost for samples close to lattice matching (0.3%≥ δ≤ -1%). In XRD in-plane measurements (Fig. 1B), the convergence of the NP lattice parameter towards lattice matching as well as the evolution of the diffuse background can be traced. For 59at% Au the in-plane NP and substrate peak match and the diffuse background, which stems from disorder at the interface, vanishes, both revealing the (semi-)coherent nature of the interface in contrast to an incoherent or delocalized coherent [2] interface for larger lattice mismatch. Furthermore, EBSD ODFs revealed i) a pronounced AuNi (111)[1-10] || α-Al2O3 (0001)[10-10] orientation relationship (OR1) for NP with δ>0.3% and ii) a change in OR to AuNi (111)[1-10] || α-Al2O3 (0001)[11-20] (OR2) with δ<-1%. To get a deeper understanding of the interface and the interplay of solute atoms and the substrate, cross-sectional EM-investigations on a <110> oriented lamella were carried out on a Ni-rich particle (Fig.2). The ADF image reveals a modulated contrast in the range of two interfacial layers, correlating perfectly with the disordered interface seen in IP XRD. Additionally HR HAADF imaging confirmed the semi-coherent nature of the interface with the appearance of stand-off misfit dislocations (DL). Via EDX we revealed the segregation of Au on the interface, which is driven by the minimization of strain energy by i) reducing the misfit and ii) shifting the DL to higher stand-off positions [2]. Overall, we demonstrate an elegant route to produce lattice matched alloy NPs on a ceramic substrate and provide insight into the structure and chemistry of the system by complementary scattering probes. In our contribution, the origin of the findings reported above will be discussed in light of existing literature and basic physical principles. [1] Sinnott et al., 10.1016/j.mser.2003.09.001 [2] Herre et al., 10.1016/j.actamat.2021.117318 135

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MS2.P015 Complementary microscopy and scattering experiments on the magnetic textures in the antiskyrmion compound Mn1.4PtSn using LTEM and REXS M. Winter1,2,3,4, M. Rahn4, D. Wolf3, S. Schneider2, M. Valvidares5, C. Shekar1, P. Vir1, H. Popescu6, N. Jaouen6, G. van der Laan7, T. Hesjedal8, B. Rellinghaus2, C. Felser1 1Max Planck Institute for Chemical Physics of Solids, Dresden, Germany 2Dresden Center for Nanoanalysis (DCN), Dresden, Germany 3IFW Dresden, Dresden, Germany 4TU Dresden, IFMP, Dresden, Germany 5ALBA Synchrotron, Barcelona, Spain 6Synchrotron SOLEIL, Saint-Aubin, France 7Diamond Light Source Ltd., Didcot, United Kingdom 8University of Oxford, Clarendon Laboratory, Oxford, United Kingdom 1. Introduction More than a decade has passed since the first experimental evidence of magnetic Bloch-type skyrmions in MnSi [1]. Since then, driven by their high potential for applications in future magnetic memory devices, skyrmions and related magnetic nano-objects of non-trivial topology have been in the focus of intensive research in the scientific community, and many novel spin textures have been discovered. In the course of these efforts, antiskyrmions (aSks) were recently observed in the tetragonal Heusler material Mn1.4PtSn by Lorentz Transmission Electron Microscopy (LTEM). Beyond that, the material is known to host a wide range of other magnetic structures such as non-topological (NT) bubbles, elliptical skyrmions and spin helices [3]. 2. Objectives In order to better understand the formation of aSks we have conducted complementary experiments of resonant elastic x-ray scattering (REXS) and LTEM on an identical lamella of Mn1.4PtSn. REXS enables us to directly measure the orientation and magnitude of the spin propagation vectors of the various magnetic phases occurring in Mn1.4PtSn. While REXS provides for diffraction patterns, LTEM allows to directly image and identify the underlying magnetric structures and to navigate the material"s complex phase diagram, which depends not only on temperature and sample shape, but also on strength and orientation of an external magnetic field as well as on the history of its application. 3. Materials & methods We use high quality single crystals of Mn1.4PtSn grown by self-flux method for our experiments. In order to realize complementary measurements on identical samples, thin lamellas were cut by FIB-Milling and placed on specifically designed molybdenum-discs (d=3 mm) fitting to commercially available TEM holders. Custom-designed sample hoilders haver been developed to ensure compatibility with the REXS setup. The REXS experiments were carried out at the I10 end station at the Diamond Lightsource (UK). The experimental setup was equipped with an octupole vector magnet, which allowed to explore the highly complex magnetic phase diagram of Mn1.4PtSn by offering 360° of freedom in magnetic field direction and fields of up to 600 mT. 4. Results Our complementary approach allows us to unambiguously link the helical phase, NT bubble and aSks phase in Mn1.4PtSn as identified from LTEM measurements to the REXS scattering patterns we measured on the identical sample (Fig 1). In combination with the quantitative analysis of the REXS pattern the study provides new insights into the various (field-induced) magnetic phase transitions in the materials. 5. Conclusion Along this approach, the intimate correlation of LTEM and REXS experiments conducted on identical samples has proven an ideal tool to not only doubtlessly identify individual phases but also to navigate the high-dimensional parameter space and characterize the nature of the occurring phase transition in great detail. Acknowledgement(s): 137

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MS2.P016 Structure of the high entropy alloy CoCrFeMnNi after low cycle fatigue D. Litvinov1, K. Lu1, J. Aktaa1 1Karlsruher Institut of Technologie (KIT), Eggenstein-Leopoldshafen, Germany Microstructural characterization of the high entropy alloy CoCrFeMnNi (HEA) after low cycle fatigue (LCF) at a temperature of 550°C was carried out by transmission electron microscopy (TEM). For the determination of the actual composition, high angle annular dark field (HAADF) scanning TEM (STEM) with an energy-dispersive X-ray (EDX) spectroscopy was used. For the crystallographic investigations, conventional TEM with selected area diffraction (SAD) was applied. The TEM samples after LCF test were prepared by electrochemical or mechanical thinning parallel to the stain direction. We observe in the samples after LCF many additional defects in comparison to the as received sample. Fig. 1 shows inverted HAADF STEM images in large scale of the samples after LCF deformation under lowest and highest strain amplitudes of ± 0.2% (Fig. 1a) and ± 0.75% (Fig. 1b), where we can see a lot of defects. First of all, in both deformed samples, we observe thin twins (TW) and slip bands (SB). Similar twins were detected in the unreformed sample. Therefore, the kind of the twins, annealing or deforming, is not clear from these images. The broad of slip bands increases with strain amplitude. Moreover, in both samples there are two kinds of dislocations inside the grains: discrete dislocations (D1) and pileup dislocations along lines (D2). The density of dislocations D1 and D2 increases also with strain amplitude. In the sample deformed under strain amplitude ± 0.75 % (Fig. 2b), pileup of dislocations forms cells which were detected only in the sample deformed under high strain amplitudes from ± 0.5% to ± 0.75%. The density of such cells increases remarkably with strain amplitude. These cell substructures are formed because of dislocations cross slip and contribute to the near-steady state of the cyclic stress response. The quantitative TEM EDX analysis of many grains shows an almost homogeneous distribution of alloying elements in the deformed sample with a concentration of (20 ± 3) at % for each element. However, additional secondary phases with an irregular morphology are observed close to grain boundaries with their sizes varying up to a few mm. One such case is presented in Fig. 2, where a HAADF STEM micrograph with EDX line scan (a) combined with a bright- field TEM image with SAD (b) of the same area are shown. Variation in the contrast along the inclusion in both, the STEM (Fig. 2a) and the TEM (Fig. 2b) images clearly indicate changes in chemical composition. The EDX line scan along the dashed line as well as area analysis in Fig. 2a shows that lower part of the inclusion is Mn- and Ni-rich (area 1, both elements having an atomic concentration of ca. 50 %) and the long upper part is Cr-rich (area 2). SAD from the latter part of the inclusion in Fig. 2b, which correspond to area 2, indicates a intermetalic σ phase. This phase consists of significantly more Cr and also some Mn, Fe and Co, but very little Ni. Fig. 1. Inverted HAAD STEM images of the samples after deformation under strain amplitudes of ± 0.2% (a) and ± 0.75% (b). D1, D2 and cells indicate two kinds of dislocations. TW denotes twins, SB - slip bands. The scale bar in (b) is valid for (a). Fig. 2. (a) HAADF STEM image with EDX line scan along the dashed arrow and elemental compositional measurements and (b) bright-field TEM image with SAD of circled areas of the same region of the sample tested under strain amplitude of ±0.3%. 139

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MS2.P017 Transmission electron microscopy of secondary carbides formed by annealing in high chromium cast iron A. Wiengmoon1, K. Ruangchai1, H. Kurata2, M. Haruta2, R. Tongsri3, S. Nusen4, J. T. H. Pearce4, T. Chairuangsri4 1Naresuan University, Department of Physics, Phitsanulok, Thailand 2Kyoto University, Division of Electron Microscopy and Crystal Chemistry, Kyoto, Japan 3National Science and Technology Development Agency, National Metal and Materials Technology Center, Pathum Thani, Thailand 4Chiang Mai University, Department of Industrial Chemistry, Chiang Mai, Thailand Introduction The as-cast microstructures of the 22-30wt.%Cr and 2.0-2.7wt.%C high chromium cast irons (HCCIs) consist of primary austenite dendrites and eutectic M7C3 carbide. The wear resistance of these irons can be improved by alloying and heat treatments. In some applications, annealing treatment is necessary for machining operations [1- 2]. There are few reports on the morphology of coarse and fine secondary carbides forming during annealing. Objectives The purpose of this research is to use TEM for studying the secondary carbide in the annealed structure. A preliminary EELS examination of the carbides will also be presented. Materials and methods As-cast specimens of the 28wt.%Cr (R) and the 28wt.%Cr-1wt.%Mo (Mo1) irons were annealed at 800oC for 4 h, followed by slow cooling to 500oC and then furnace cooling. A JEOL JEM-2010 TEM equipped with an Oxford® Inca detector was used for conventional TEM and EDS microanalysis. A JEOL, ARM200F TEM equipped with a Gatan Quantum ERS electron energy loss spectrometer was used for EELS. Both microscopes were operated at an accelerating voltage of 200 kV. Results BF-TEM images in Figs. 1 (a & b) show that the microstructures after annealing of the reference (R) and the Mo1 irons, consisted of eutectic carbide with faulting contrast and precipitated coarse secondary carbides in areas close to eutectic carbides and fine secondary carbides in the centres of the dendritic matrix. The Mo1 iron contains finer and denser secondary carbides. The selected area diffraction patterns (SADPs) confirmed that the eutectic carbides are M7C3, the secondary carbides are M23C6, and the matrix is ferrite (α). The coarse secondary carbides may be nucleated along preferred directions during the early stages of annealing. The finer secondary carbide precipitation may have occurred later during longer holding time or during slow cooling. TEM-EDS in Fig. 2(a) revealed that the Fe/Cr wt.% ratio of eutectic M7C3 carbides was 0.4, while that of coarse and fine secondary M23C6 carbides were in range of 0.52-0.69. Preliminary EELS results are given in Fig. 2(b). The differences in the spectra of ELNES of the C K-edge of M7C3 and M23C6 were (i) the peak at 289 eV (marked by arrows) has been observed only in the case of M7C3, and (ii) the relative heights of peaks 1 and 2 were higher in M7C3. Conclusion TEM revealed that coarse and fine secondary carbides formed by annealing of the 28wt.%Cr without and with 1wt.%Mo addition are M23C6 carbides. The finger print of the C K-edge, including the Fe/Cr wt.% ratio can be used to distinguish M7C3 from M23C6 carbides. References 1. K.A. Kibble and J.T.H. Pearce, Cast Metal, 1995, 8, 123-127. 2. Y.G. Song et. al., Metals 2021, 11, 1690. 141

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MS2.P018 Growth and magnetic structure of a skyrmion-hosting Co-Zn-Mn alloy A. Kovács1, L. Yang1, M. Feuerbacher1, C. Thomas1, D. Kong1, T. Denneulin1, F. Zheng1, R. E. Dunin-Borkowski1 1Forschungszentrum Jülich, Ernst Ruska Centre, Jülich, Germany Magnetic skyrmions have attracted considerable interest over the last decade, in particular for novel information storage applications. The swirling vortex-shaped magnetic field texture of a skyrmion has topological particle-like properties and is stabilized by the Dzyaloshinskii-Moriya interaction in bulk systems and multilayers of ferromagnets and heavy metals. Co-Zn-Mn with a β-Mn-type structure is a skyrmion-hosting bulk system that has the cubic chiral space group P4132 (or P4332) and allows continuous tuning of magnetic interactions and hence control of the ferromagnetic transition temperature (Tc). However, only Co10-x/2Zn10-x/2Mnx alloys (x = 2-4) exhibit skyrmion lattice formation above room temperature [1]. Here, we present a reproducible growth route for Co-Zn-Mn alloys with Tc close to 100 ºC and microstructural, compositional and magnetic imaging studies performed using various transmission electron microscopy (TEM) methods. A Co-Zn-Mn alloy was grown using a self-flux method in a closed, tapered quartz crucible placed on a cold finger in a buffered box furnace starting from a melt of composition Co3Zn6Mn1. Following a dedicated temperature transient with final water quenching, a conical ingot was produced, with the tip corresponding to the primarily solidified material (Fig. 1a). TEM specimens were prepared by using focused Ga ion-beam sputtering in a dual-beam scanning electron microscope (FEI Helios). Conventional TEM and electron probe aberration corrected scanning TEM (STEM) were used to study the microstructure of the alloy. Fresnel defocus imaging and off-axis electron holography [2] were carried out in magnetic field-free conditions (Lorentz mode) using aberration-corrected (FEI Titan) TEMs operated at 300 kV. High-resolution STEM imaging along [100] is consistent with a chiral β-Mn-type structure (Fig. 1b). The chemical composition was measured to be Co8Zn10Mn2 using inductively-coupled optical emission spectroscopy. The magnetic transition temperature was determined by observing magnetic contrast elimination during in situ heating of a TEM specimen in magnetic field-free conditions. The helical spin texture and skyrmions disappeared in Fresnel defocus images at 98 ºC, which was assumed to correspond to Tc. Figure 1c shows a Fresnel defocus image illustrating skyrmion lattice formation in the Co8Zn10Mn2 specimen. Quantitative magnetic characterization of the skyrmion spin structure was carried out by combining phase shift measurements obtained using off-axis electron holography with model-based iterative reconstruction of the projected in-plane magnetization, as well as through comparisons of the recorded contrast with micromagnetic simulations. This work was supported by the European Union"s Horizon 2020 Research and Innovation Programme (Grant No. 856538, project ""3D MAGiC"") and the Deutsche Forschungsgemeinschaft through CRC/TRR 270 (Project ID 405553726). Figure 1. (a) Flux-grown Co8Zn10Mn2 ingot. (b) High-resolution HAADF STEM image along [100] with overlaid structure model. (c) Fresnel defocus image of a skyrmion lattice recorded at 86 ºC in the presence of an 89 mT field applied perpendicular to the surface plane. References [1] Y. Tokunaga, et al., Nat. Comm. 6 (2015) 7638. [2] A. Kovács, R.E. Dunin-Borkowski, In Handbook of Magnetic Materials; Brück, E., Ed.; Elsevier: 2018; Vol. 27, pp 59-153. Fig. 1 143

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MS2.P019 Correlative imaging of the biodegradation of Mg-based alloys using in situ synchrotron radiation-based nano CT and (S)TEM J. Reimers1, M. Lipiska-Chwalek2, L. Kibkalo2, J. Mayer1, R. Willumeit-Römer3, B. Zeller-Plumhoff4 1Ernst Ruska-Centre for Microscopy and Spectroscopy/ Jülich Research Centre, ER-C-2, Jülich, Germany 2Ernst Ruska-Centre for Microscopy and Spectroscopy/ Jülich Research Centre, ER-C-1, Jülich, Germany 3Institute of Materials Research/ Helmholtz-Zentrum Hereon, Metallic Biomaterials, Geesthacht, Germany 4Institute of Materials Research/ Helmholtz-Zentrum, Imaging and Data Science, Hamburg, Germany INTRODUCTION: Multi scale analysis of functional materials combining different imaging techniques for the same region of interest (ROI) is key for the development of digital twins[1]. These numerical models of the material and its behaviour accelerate the development of functional materials like biodegradable implants. Magnesium based alloys are gaining high interest for implant applications due to their biocompatibility and biodegradability.[2] Understanding the underlying degradation processes and their interdependencies during the biodegradation is necessary to control and tailor them and thus for the development of digital twins. In situ synchrotron radiation nano computed tomography (SRnanoCT) can be used as a non-destructive 3D imaging method to investigate dynamic degradation processes with nominal resolutions below 100nm. The investigation of the chemical compositions and morphology down to atomic- scale is possible with (scanning) transmission electron microscopy ((S)TEM). The correlation of the two techniques enable to achieve a complementary picture of the degradation process, but, at the same time, it brings a number of challenges, such as sample transfer, identification of ROI (e.g. precipitates) and image registration. OBJECTIVES: The goal of this study is to develop a correlative workflow enabling to understand the biodegradation of Mg-based alloys at different length scales. For this purpose, a three-step workflow was developed (see Fig.1). Firstly, in situ SRnanoCT providing information on degradation rates, homogeneity, degradation layer (DL) formation and presence of larger precipitates within the alloy, and therewith enabling identification of degradation-relevant ROIs for further in-depth characterisation. Secondly, the transfer into a focused ion beam (FIB) and identical-location lamella preparation for the third step, i.e. correlated, in-depth (S)TEM investigation of structural defects and degradation layer. MATERIALS & METHODS: A flow-cell setup is used for in situ SRnanoCT. Mg-x-wt.%Ag and Mg-y-wt.%Gd wires (80μm diameter) have been degraded in simulated body fluid (SBF) under physiological conditions (37 °C, pH 7.4, flow rate 1 ml/min) resulting in tomographic scans every 13-30 minutes. FIB lamellas for identical-location TEM characterization were prepared by a lift-out method in a dual-beam FIB FEI Helios NanoLab 400S. STEM imaging and EDX analyses were conducted with the aid of probe-corrected FEI Titan G2 80-200 at 200kV [3]. RESULTS: Figure 1 shows the correlative workflow. First results from SR tomograms (A) of Mg-4wt.%Ag yield a degradation rate of 9.4 mm/year after approx. 5 hours. A FIB lamella (B) depicts the preparation and the EDX analysis (C) shows Mg-rich bulk material , an inner and outer degradation layer, Ag-rich precipitates and FIB protection layers as well as a voids. Figure 1: Mg-based alloy degraded in SBF: (A) SR nano tomogram (B) lamella preparation in FIB and (C) elemental map with EDX. CONCLUSION: Preliminary results from tomograms show inhomogeneous degradation behaviours. Further studies are necessary to understand the influences on biodegradation processes, as the precipitates do not seem to act as micro galvanic elements, as no enhanced degradation can be observed in their vicinity. REFERENCES: 1M. Abdalla, et al., Corrs. Mater. Degrad. (2020), 219-248. 2M. P. Staiger, et al., Biomaterials (2006), 1728–1734. 3FEI Titan G2 80-200 CREWLEY (2016) A43. 144

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MS2.P020 Rafting in single crystal superalloys: on the influence of stress state and the transition towards topological inversion A. Parsa1, D. Bürger1, L. Cao1, G. Eggeler1 1Ruhr University Bochum, Bochum, Germany Rafting is the directional coarsening of small cuboidal γ'-phase particles in Ni base superalloys during high temperature creep deformation. During a [001] tensile creep testing rafting occurs perpendicular to the direction of the applied stress in Ni-base superalloy single crystals with a negative misfit between the two coherent phases γ and γ' [1,2]. In the present work we take a new look at the phenomenon of rafting. Some recent results on the influence of different stress states, comparing crept microstructures after uniaxial creep, shear creep and after creep of circular notched specimens are presented. We also consider the effect of internal stresses of microstructural origin on rafting. We further look at the topological inversion within the microstructure where the initial microstructure in which small γ'- cubes are separated by thin interconnected γ-channels evolves towards a material state where the γ-phase forms isolated islands and the γ'-phase percolates through the system [3]. The changes are obvious when comparing Figure 1a (initial state after processing), 1b (material state after creep: 1223 K/200 MPa/1%) and 1c (material state after creep: 1223 K/300 MPa/26%) where after prolonged periods of creep exposure, the microstructural evolution results in the formation of isolated γ-phase regions. Our findings are interpreted on the basis of the underlying elementary deformation and coarsening mechanisms, which govern the evolution of γ/γ' microstructures. Creep testing in the high temperature low stress creep regime is combined with analytical scanning and transmission electron microscopy. Special emphasis will be placed on the microstructural transition from a rafted to a topologically inverted microstructure. Figure 1: SEM images of ERBO1 singly crystal superalloy, (a) Initial state microstructure; (b) Rafted microstructure after uniaxial creep exposure at 1223 K, 200 MPa and 1% accumulated strain; (c) Topologically inverted microstructure after uniaxial creep exposure at 1223 K, 200 MPa and 26% accumulated strain. γ and γ′ phases shown in bright and dark contrast, respectively. Keywords: Single crystal Ni-base superalloys, high temperature uni- and multiaxial low stress creep, scanning electron microscopy, transmission electron microscopy, rafting, topological inversion References: [1] R.C. Reed, The Superalloys: Fundamentals and Applications, Cambridge University Press, Cambridge, 2006. [2] L. Agudo Jácome et al., High-temperature and low-stress creep anisotropy of single-crystal superalloys, Acta Mater., 61, 2013, 2926-2943. [3] A. Epishin et al., Kinetics of the topological inversion of the γ/γ′-microstructure during creep of a nickel-based superalloy, Acta Mater., 49, 2001, 4017-4023. Fig. 1 146

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MS2.P021 Microstructural investigations of the crept eutectic MoSiTi alloy using the conventional transmission electron microscopy (CTEM) H. Thota1, H. Wu1, D. Schliephake2, C. Dolle1, A. Kauffmann2, M. Heilmaier2, A. Pundt2, Y. M. Eggeler1 1Karlsruher Institut of Technologie (KIT), Laboratory for Electron Microscopy, Karlsruhe, Germany 2Karlsruher Institut of Technologie (KIT), Institute for Applied Materials (IAM-WK), Karlsruhe, Germany The current state-of-the-art, single-crystal nickel-based superalloys operate close to 80 to 90% of their melting temperatures. There is a continuous need to design newer materials that can withstand higher operating temperatures above 1100 °C, as the operation of turbine engines at higher operating temperatures leads to improved energy efficiency in the power generation and aerospace sectors [1]. On the other hand, during operation at higher temperatures, the materials undergo higher creep deformation. The recently developed eutectic MoSiTi alloy (Mo-20Si-52.8Ti in at.%) exhibits a good combination of pesting oxidation and creep properties [2]. It consists of two phases: body centred cubic (bcc) solid solution and hexagonal Ti- rich silicide, M5Si3 (where M-Ti, Mo). The accumulation of creep strain in the two phases, particularly the deformation behavior of the two phases and lattice defects generated in response to the applied stress has to be thoroughly understood. Compressive creep tests were performed under vacuum at 1200 °C and 100 MPa stress to assess the creep behavior. The samples are tested at various true strains of 1.3, 10, 20, and 40% to understand the deformation mechanism of the alloy. The crept samples were characterized using scanning electron microscopy (SEM)- backscattered electron (BSE) imaging to analyse the microstructure of phases, their arrangement and detect precipitation. Conventional transmission electron microscopy (CTEM) techniques such as bright field (BF), dark field (DF) and weak beam dark field (WBDF) are employed to image dislocations and analyse dislocation substructure in all crept conditions [3]. Deformation mechanisms can be drawn from the type of dislocation (edge, screw, or mixed) and the dominant slip plane in the bcc phase. In addition, dislocations in the silicide phase are imaged and the operative slip system (basal, prismatic or pyramidal) is identified. Scanning transmission electron microscopy (STEM)-energy dispersive spectroscopy (EDS) is used to determine the composition of the precipitates and analyse any segregation of the alloying elements to the dislocations in the crept samples. The high angle annular dark field (HAADF) STEM image in Fig. 1a shows the precipitation of Ti-rich silicides in the bcc matrix, that are semi-coherently embedded in the matrix. Based on diffraction analysis (Fig. 1b), the precipitates are hexagonal and dislocations are observed in the silicide phase of 10% crept samples (Fig. 1c). Fig.1: Transmission electron microscopy (TEM) investigations of the crept eutectic MoSiTi alloy a) Scanning transmission electron microscopy (STEM)-high angle annular dark field (HAADF) image of Ti-rich silicide precipitates in body centered cubic (bcc) solid solution b) Diffraction pattern of precipitates in the bcc phase aligned to [001] zone axis in 1.3% true strain and c) Weak beam dark field (WBDF) image of dislocations in hexagonal silicide phase of 10% crept sample. The dislocations are marked with alphabets: A represents long dislocation line and B denotes dislocations inclined to the TEM foil. [1] J.H. Perepezko, The hotter the engine, the better, Science 326 (2009) 1068–1069. [2] Schliephake et al., Constitution, oxidation and creep of eutectic and eutectoid Mo-Si-Ti alloys, Intermetallics. 104 (2019) 133–142. [3] D.B. Williams, C.B. Carter, Transmission Electron Microscopy, Springer US, Boston, MA, 2009. Fig. 1 147

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MS2.P022 An investigation of thermal stability and mechanical properties of Cu alloys by high-pressure torsion Y. Dai1 1Karlsruher Institut of Technologie (KIT), Karlsruhe, Germany The grain refinement can be described as a process of counterbalanced generation and annihilation (recovery, dynamic recrystallization) of dislocations during deformation. The stacking fault energy (SFE) or the solid solution hardening (SSH) contribution plays a decisive role and affects the grain refinement including the saturation grain size. [1, 2] The goal of this study is to investigate the solute effects on mechanical behavior, microstructure changes, and thermal stability in the Cu alloys after HPT processing at room temperature. Cu and Cu alloys (CuSn5, CuZn5, CuZn30) were processed by severe plastic deformation (SPD) using a semi- constrained high-pressure torsion press under 4.5GPa. The isochronal heat treatment at different temperatures was applied to study the thermal stability of this alloy. Transmission electron microscopy (TEM) investigations indicated that dislocation wall structures are the main feature of Cu and Cu alloys after annealing treatment at different temperatures. Automated crystal orientation mapping (ACOM), which can provide full orientation maps with nanometer resolution, was used to test grain orientation, a fraction of high-angle grain boundaries, and mean grain size. The grain growth kinetics in alloys are typically governed by the local elemental distribution e.g. the presence or absence of segregations (solute drag) or secondary phases (Zener drag). The Cu-X series remains single-phase upon annealing, indicating that the enhanced thermal stability of the alloys compared to pure Cu is related to the solute content, which provides dragging forces for grain boundary migration. A comparison of CuZn5 and CuZn30 indicates higher microstructural stability for CuZn5, as CuZn5 shows a constant hardness up to 250°C where CuZn30 has already started to soften significantly. [1] Mohamed, F.A. and Dheda, S.S., On the minimum grain size obtainable by high-pressure torsion. Materials Science and Engineering: A, 2012. 558: p. 59-63 DOI: 10.1016/j.msea.2012.07.066. [2] Bruder, E., Braun, P., Rehman, H.u., Marceau, R.K.W., Taylor, A.S., Pippan, R., and Durst, K., Influence of solute effects on the saturation grain size and rate sensitivity in Cu-X alloys. Scripta Materialia, 2018. 144: p. 5-8 DOI: 10.1016/j.scriptamat.2017.09.031. Fig. 1 148

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MS3.001-invited Analyzing and assembling layered materials, atom by atom and layer by layer, in 2D and 3D J. C. Meyer1,2,3, C. Hofer1,2,3, J. Haas1,2, J. Kotakoski3, T. Susi3, C. Mangler3, V. Skakalova3, A. Mittelberger3, G. Argentero3, M. R. A. Monazam3, C. Kramberger-Kaplan3, R. S. Pennington1,2, X. Wang4, K. Braun5 1University of Tübingen, Institute of Applied Physics, Tübingen, Germany 2NMI Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany 3University of Vienna, Faculty of Physics, Vienna, Austria 4Hunan University, School of Physics and Electronics, Hunan, China 5University of Tübingen, Institute of Physical and Theoretical Chemistry, Tübingen, Germany Aberration-corrected electron microscopy is emerging as a versatile tool not only for analyzing, but also for manipulating materials down to the level of single atoms. I will discuss both of these aspects and present some of our recent developments in the context of layered, two-dimensional materials: On the analysis side, we developed means to identify the 3D atomic configuration of defects, grain boundaries or impurities, from only two exposures of the same structures [1,2]. The same approach, combined with the simple dependence of the intensity in annular dark field scanning transmission electron microscopy images on the atomic number provides (to some extent) chemical information about the sample, and hence allows an elemental identification in the case of light-element single-layer samples [3]. However, the intensity of individual atoms and atomic columns is affected by residual aberrations and the confidence of an identification is limited by the available signal to noise. As shown in Fig. 1, already in presence of small non-round aberrations, the histogram of intensities is significantly broadened if these aberrations are not taken into account. Here, we show that matching a simulation to an experimental image by iterative optimization provides a reliable analysis of atomic intensities even in presence of residual non-round aberrations [4]. We compare this method with other approaches demonstrating its high reliability at limited dose and with different aberrations. This is of particular relevance for analyzing moderately beam-sensitive materials, such as most 2D materials, where the limited sample stability makes it difficult to obtain spectroscopic information at atomic resolution. Towards an atomic-level manipulation, I will present a recent development where we combine spatially controlled modifications of 2D materials, using focused electron irradiation or electron beam induced etching, with the layer-by- layer assembly of van der Waals heterostructures [5] (Fig. 2). A new transfer and assembly process makes it possible to stack the layers under observation in an electron microscope, such that pre-patterned features can be aligned to each other. The aligned stacking of individually patterned 2D materials layers can be considered as a form of 3D printing, where each layer is only one or a few atoms thick, and features within each layer can be defined with a nm- scale resolution. Moreover, as each layer can be chosen from the large zoo of 2D materials, it should be possible to directly generate a wide variety of functional devices. Fig. 1. Intensity histograms from a simulated image in presence of small non-round aberrations (C1,0 = 2 nm, C1,2 = 1 nm, C2,1=50 nm, C2,3=50 nm). (a) Part of the simulated image, and (b) the simulated probe. (c) Intensity histogram using the optimization method, Gaussian fits, local maxima and the Voronoi cell integration (from left to right) [4]. Fig. 2. (a-c) Schematic of cutting a pattern into individual graphene layers (a,b) followed by aligned stacking (c). (d-f) Experimental realization, (d,e) SEM images of crosshair structures cut into graphene, (f) Dark-field TEM image showing the assembled structure, set for highlighting one of the two layers. Scale bars are (d,e) 500 nm and (f) 200 nm [5]. References [1] 2D Materials 5, 045029 (2018) [2] Appl. Phys. Lett. 114, 053102 (2019) [3] Nature Commun. 10, 4570, (2019) [4] Ultramicroscopy 227, 113292 (2021) [5] ACS Nano 16, 1836-46 (2022) 150

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MS3.002-invited Seeing into organic 2D materials: defects, dynamics, and resolution H. Qi1,2, B. Liang1, D. Mücke1, C. Leist1, H. Wilson3, C. J. Russo3, U. Kaiser1 1Ulm University, Central Facility for Electron Microscopy, Electron Microscopy Group of Materials Science, Ulm, Germany 2Technische Universität Dresden, Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Dresden, Germany 3MRC Laboratory of Molecular Biology, Cambridge, United Kingdom Probing the structure of organic 2D materials (O2DMs), ultimately down to the atomic scale, has been a long-sought goal of materials science. AC-HRTEM is capable of direct imaging atomic structures with sub-Ångström resolution 1. However, electron irradiation damage leads to rapid disintegration of the molecular network during the imaging process, severely limiting achievable resolution regardless of TEMs' optical performance. Here we present various experimental efforts to extract high-resolution information from O2DMs in particular imine- based 2D polymer thin films 2,3. Two samples were synthesized using the surfactant-monolayer-assisted interfacial synthesis (SMAIS) 4 (Fig. 1). Using low-dose methods at room temperature, we examined 2D-PI-DhTPA 2, and directly observed the grain boundaries with a resolution of 2.3 Å at 300 kV, giving insight into the formation mechanism of the 2D crystals. Although HRTEM imaging of inorganic 2D materials can benefit substantially by restricting the electron energy below 80 keV 1, the rare TEM studies on organic 2D crystals are still usually carried out at 300 keV. We systematically evaluated the electron accelerating voltages for AC-HRTEM imaging of O2DMs 3. We reached an image resolution of 1.9 Å at 120 kV (Fig. 2a-b). The improvement in resolution has been achieved by maximizing the efficiency of electron usage, among the acceleration voltages of 300 kV, 200 kV, 120 kV, and 80 kV. Not only could the porphyrin pores be clearly resolved, but linkers with and without hydroxyl groups could also be distinguished. We occasionally observed abnormal contrast in the vicinity of the porphyrin cores (Fig. 2c-d), conflicting with their previously reported structures. DFT calculations revealed that the additional contrast could be attributed to molecular interstitial defects (Fig. 2e) – a defect type that had not been discovered in 2D polymers before. Recently, drawing from electron cryomicroscopy (cryoEM) in biology 5, we explored the potential of imaging our radiation-sensitive O2DMs at low temperature with direct electron detectors. This combination improved the information in a single micrograph such that reflections beyond a resolution of 1.3 Å are clearly resolved. We envisage that our results will bring new insights into the defect types and pore interfaces in O2DMS and promote a deeper understanding of structure-function correlations in this rising class of materials. Fig. 1. Reaction scheme and atomic models of 2D-PI-BPDA and 2D-PI-DhTPA. Fig. 2. a-d AC-HRTEM imaging of 2D-PI-BPDA at 120 kV, showing regions without and with TAPP interstitials. e, Plausible stacking modes of TAPP interstitials derived by DFTB calculations and corresponding simulated images. References 1. Linck, M. et al. Phys. Rev. Lett. 117, 76101 (2016). 2. Qi, H. et al. Sci. Adv. 6, eabb5976 (2020). 3. Liang, B. et al. Nat. Commun. 13, 3948 (2022). 4. Liu, K. et al. Nat. Chem. 11, 994–1000 (2019). 5. Russo, C. J., & Egerton, R. MRS Bulletin 44, 935–941 (2019). Acknowledgment We gratefully acknowledge the funding from DFG – 492191310; 426572620; 417590517 (SFB-1415), as well as the financial support from the European Union's Horizon2020 research and innovation program under Grant Agreement No. 881603 (GrapheneCore3). This work was also supported by an Astex SIPD Fellowship (HW) and Medical Research Council grant MC_UP_120117. 152

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MS3.003 Tunable eccentricity of Bloch skyrmions in Fe1.9Ni0.9Rh0.2P S. Schneider1,2, J. Masell2,3, F. S. Yasin2, L. Peng2, K. Karube2, Y. Taguchi2, D. Pohl1, B. Rellinghaus1, Y. Tokura2,4,5, X. Yu2 1TU Dresden, Dresden Center for Nanoanalysis (DCN), Dresden, Germany 2RIKEN, Center for Emergent Matter Science (CEMS), Wako, Japan 3Karlsruher Institut of Technologie (KIT), Institute of Theoretical Solid State Physics, Karlsruhe, Germany 4University of Tokyo, Department of Applied Physics, Tokyo, Japan 5University of Tokyo, Tokyo College, Tokyo, Japan 1. Introduction The experimental discovery of antiskyrmions in Mn1.4PtSn [1] has opened new pathways towards using microscopically small magnetic whirls as information carriers [2]. For this purpose, a thorough understanding of the detailed three-dimensional spin texture of these magnetic solitons, including their stabilization mechanisms is essential. Quite recently, the compound Fe1.9Ni0.9Pd0.2P was found to host antiskyrmions at room temperature, which can be transformed into skyrmions, e.g., by tuning the external magnetic field [3]. 2. Objectives In this study we investigate this elliptical skyrmion phase as a function of the external magnetic field and temperature in a similar material, Fe1.9Ni0.9Rh0.2P, where Pd was substituted by Rh, to gain further insight into the formation mechanisms of topological spin solitons. 3. Materials & methods The occurrence and nature of skyrmions in a Fe1.9Ni0.9Rh0.2P lamella fabricated using a focused ion beam (FIB) were studied in a JEOL Jem F-200C by means of off-axis electron holography that allows for the quantitative determination of the projected in-plane magnetic induction Bip. The sample temperature was controlled with a Mel-Build LN2 Atmos Defend - In-situ double-tilt LN2 cooling holder. 4. Results In Fig. 1 the magnitudes of Bip in the lamella upon exposure to magnetic fields of 170 mT and 330 mT applied along [001] at room temperature are displayed. In zero field, the skyrmions initially possess an elliptical shape with the semi- major axes parallel to the ⟨110⟩ directions due to dipole–dipole interactions [5, 6]. Increasing the external out-of-plane magnetic field leads to (i) a reduction of the skyrmion size, (ii) an enhancement of Bip and (iii) a deformation of the skyrmions. The initially elliptical skyrmions are transformed into skyrmions with circular shapes until a critical field is reached, where the system undergoes a transition into the field-polarized phase. 5. Conclusion The current investigations provide a first insight how the balance between the symmetric and antisymmetric exchange and dipole-dipole interaction can tune the skyrmion structure in Fe1.9Ni0.9Rh0.2P. By combining our experimental results with magnetostatic simulations, we can shed light on the complex interplay of these interactions in the stabilization of topological spin textures in three dimensions. [1] A. K. Nayak et al., Nature 548 (2017), 561 – 566. [2] B. Göbel et al., Physics Reports 895 (2021), 1 – 28. [3] K. Karube et al., Nature Materials 20 (2021), 335 – 340. [4] K. Karube et al., Adv. Mater. 34 (2022), 2108770. [5] L. Peng et al., Nat. Nanotechnol. 15 (2020), 181 – 186. 154

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MS3.004 Synthesis and characterization of metal sulfide nanoribbons on graphene by self-assembly of inorganic ions X. Zhang1, K. Anggara1, V. Srot1, X. Wu1, P. A. van Aken1, K. Kern1 1Max Planck Institute for Solid State Research, Stuttgart, Germany Bottom-up synthesis of nanostructures on surfaces depends on the self-assembly of nanoscale building blocks. The diversity of accessible nanostructures, however, have been constrained by the limited choice of atomic and molecular building blocks that can be evaporated on a surface. Here, we bypass this limitation by using complex inorganic ions generated from electrospray ionization as building blocks to synthesize nanostructures on surfaces. We deposited HMonS3n+1– (n = 4-8) ions onto a freestanding single-layer graphene by electrospray ion-beam deposition (ESIBD), and imaged the resulting nanostructures by aberration-corrected scanning transmission electron microscopy (STEM). The molecules form anisotropic, single-layered, crystalline MoS2 nanoflakes (< 20 nm2), which in turn self-assemble into MoS2 nanoribbons extending as far as 1 μm (Fig. 1). The widths of the nanoribbons were tuned by the precursors, as the HMonS3n+1– (n = 4-8) ions formed 4 ± 1 nm wide nanoribbons, the HMonS3n+1– (n = 5-8) ions 5 ± 2 nm wide nanoribbons, and the HMonS3n+1– (n = 6-8) ions formed 8 ± 3 nm wide ones. This first observation of such nanostructures evidences the potential of this approach to prepare previously inaccessible nanomaterials on surfaces. Figure 1 HMonS3n+1– ions were deposited onto single layer graphene by ESIBD, and self-assembled into 1 μm long monolayer MoS2 nanoribbons as observed by STEM. Fig. 1 156

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MS3.005 Hexagonal hybrid bismuthene by molecular interface engineering C. Dolle1,2, V. Oestreicher2, A. M. Ruiz2, M. Kohring3, M. Wu4, G. Sánchez-Santolino5, Y. M. Eggeler1, E. Spiecker4, J. Canet-Ferrer2, H. B. Weber3, M. Varela5, J. J. Baldoví2, G. Abellán2 1Karlsruher Institut of Technologie (KIT), Karlsruhe, Germany 2Instituto de Ciencia Molecular, Valencia, Spain 3Lehrstuhl für Angewandte Physik, Erlangen, Germany 4Institute of Micro- and Nanostructure Research, Erlangen, Germany 5Instituto Pluridisciplinar de Física de Materiales, Madrid, Spain Since the rise of graphene as playground for scientists in different fields, the fascination for two-dimensional materials did not cool down but rather remains at a peak interest due to the exceptional properties those ultrathin, layered structures show. While physicists are intrigued by transport properties for TMD's and material scientists praise the mechanical stabilities of even single layer thick atomic layers, chemists mainly use 2D materials as perfectly defined substrate for functionalization approaches. In contrast to widely studied materials, we will present a chemical approach towards two-dimensional bismuth with unprecedented material quality and a surprisingly unexpected structure. In an one-pot colloidal reductive reaction, we synthesized single crystalline hexagonal platelets with diameters up to 2 µm and a thickness around 5 nm. Due to the chemical approach for the generation of these ultrathin bismuth material, we were able to introduce structurally modified bismuthene on the basal planes of the crystallites that are stabilized by a covalent functionalization. To reveal the nature and resulting properties of this sandwiched hybrid structure we made use of a battery of characterization techniques ranging from microscopy (HRTEM, HRSTEM, EELS, EDS, SAED, AFM) to spectroscopy (XPS, Raman) and finally simulations (DFT) and single-particle transport measurements. The combination of all these techniques allowed us to describe the stabilized bismuthene capping layers as fundamentally different from pristine rhombohedral bismuth. Firstly, while bismuth shows the typical zig-zag arrangement with a lattice constant of 4.5 Å, the bismuthene layers are flat with a lattice parameter of 7.5 Å. Monochromated STEM-EELS reveals LSPR modes that are highly unexpected for a semimetal like bismuth and the calculated band structure, based on the simulated structure, shows metallic behaviour. The metallic nature of individual crystals was measured by transport experiments at room temperature. In this contribution we show the wholistic process of an exceptional new material with a strong spin orbit coupling and postulated spin torque effects from the bottom-up synthesis to the characterization and conceivable future applications in devices. Fig. 1 A Colloidal synthesis of the sandwich material with equivalents for the reaction. B PXRD pattern of synthesized material with expected diffraction peaks indicated. C Typical unprocessed Raman spectrum. No indication of surface oxidation. Inset optical micrograph of crystallite. D BF-TEM data and E typical indexed diffraction pattern of hybrid material with superstructural reflections indicated. F Colorized large area HRSTEM data with FFT as inset. Superstructure indicated in FFT. G AFM with height profile. H Experimental series of integrated EELS intensity, showing localized surface plasmon modes and I simulation of plasmonic modes based on model hexagon. Fig. 2 A Integrated STEM-EDX intensity for individual crystallite with artistic representation of functionalized material. B Spatially integrated mean EDX spectrum with signals related to Bi. C Overview XPS before (red) and after (black) surface etching with Ar ions and D high resolution XPS of S/ Bi binding energies. A clear indication of S 2p before the surface etching can be noticed between 165–170 eV. E Structurally optimized bismuth/ bismuthene hybrid with simulated ED. Bottom right cross sectional HRTEM and respective image simulation. 157

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MS3.006 Ordered electronic states in 2D quantum materials: imaging effects of hydrostatic pressure at the atomic scale M. K. Kinyanjui1, J. Ebad-Allah2, M. Krottenmüller2, C. A. Kuntscher2 1Ulm University, Electron Group of Materials Sciences, Ulm, Germany 2University of Augsburg, Experimental Physics II, Institute of Physics, Augsburg, Germany Introduction Charge density waves (CDW) are an ordered electronic state with periodic modulation of electron density and periodic lattice distortion (PLD) modulation of the atomic positions.1 CDW is represented by an order parameter Ψ =Δeiφ characterized by a phase φ, giving position of the CDW with relation to the lattice, and amplitude,Δ, giving the value of the energy gap.1 In some quantum materials, CDW are in competition / coexistence with the superconducting phase.2- 3 The nature of this relationship is still not well understood. Application of pressure is one experimental approach used to probe the nature of this relationship. 3 However, this also leads to the necessity to understand effects of pressure on the nature and the structure of the CDW at the atomic scale. Objectives Here, we have used atomic-scale transmission electron microscopy imaging to determine the influence of applied pressure on the structural properties of 1T-TaS2 and the CDW at the atomic-scale.4 Materials & Methods 1T-TaS2 samples were exposed to hydrostatic pressures of up to 2.5 GPa in a diamond anvil cell (DAC) (Fig.1 (a)). Pressurized samples were then prepared for TEM investigations through mechanical exfoliation. In high-resolution TEM (HRTEM) imaging CDW wave vectors and their respective phases are accessible and their evolution as a function of applied pressure can be mapped at the atomic scale.4 Results A HRTEM image from a pressurized sample characterized by a deformation defect is shown in Fig. 1(b). Strong coupling of lattice and electronic degrees of freedom means that changes in lattice structure and ensuing deformation defects due to the applied pressure have an effect on the structure of the CDW electronic state. The modulation of CDW around the structural defect is shown in Figs 1(d)-(e). The magnitude of the CDW wave-length |λ1| and the respective phase φ1 are shown as intensity maps in Figs. 1(d) and (e) respectively. The high and low intensity in the magnitude images respectively show the elongated or shortened CDW wavelength. The magnitude of the CDW wavelength and its phase are strongly modulated in the vicinity of the deformation defects. This strong modulation is characterized by (1) CDW strain which leads to local changes in the modulation wavelenght (2) Topological phase defects in the CDW order parameter in form of CDW dislocations (marked by dotted circles in Figs. 1(c)-(d)). Conclusion In conclusion we have mapped the atomic-scale response of the CDW order parameter in 1T-TaS2 exposed to 2.5 GPa hydrostatic pressure. The CDW order parameter responds to the lattice defects arising from the applied pressure by showing an elastic-like strain response and topological phase defects in the electronic order. References [1].J. Wilson, F. D. Salvo, and S. Mahajan, Adv. Phys. 24, 117 (1975). [2] E. Fradkin et al., Rev. Mod. Phys. 87, 457 (2015) [3] A. F. Kusmartseva et al., Phys. Rev. Lett. 103, 236401(2009) [4] M. K. Kinyanjui et al.Phys. Rev. B 104, 125106(2021) 159

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MS3.P001 Composition and strain of pseudomorphic α-(AlGa)2O3 on sapphire (0001) substrates M. Schowalter1, P. Vogt1, J. A. Bich1, A. Karg1, C. Mahr1, T. Grieb1, T. Mehrtens1, F. F. Krause1, M. Eickhoff1, A. Rosenauer1 1University Bremen, Institut für Festkörperphysik, Bremen, Germany Recently, it was reported that in initial stages of Ga2O3 growth on (0001) sapphire substrates a thin (~3 ML) layer of α- Ga2O3 is forming before the formation of β-Ga2O3 for three growth techniques [1]. A surprising result, since the most stable polymorph of Ga2O3 is the beta phase, whereas the alpha phase is only the third [2]. The authors explain the stabilization of the alpha phase as being a strain effect due to the pseudomorphic character of the layer within an isotropic strain model. In this contribution a similar α-Ga2O3 layer was grown on a (0001) sapphire without overgrowth with β-Ga2O3 using molecular beam epitaxy (MBE) and investigated using TEM. Fig. 1 shows HAADF STEM image of the layer in a) together with a simulated image of an α-Ga2O3 layer on α-Al2O3 in b) for the [11-20] zone axis. The respective images for the [11-00] zone axis are depicted in c) and d). The observed contrast pattern qualitatively agrees between experiment and simulation. A close inspection of the contrast pattern for the [1-100] zone axis shows that it does not agree between substrate and layer, which can be explained by the different contributions of Ga and O to the image intensity in the layer compared to Al and O in the substrate. This was already reported in reference [1]. Fig.1: a) and c) HAADF STEM images of the layer in [11-20] and [1-100] zone axis. b) and d) Respective simulated images of Al2O3 with a Ga2O3 layer, for respective zone axes. EDX mappings showed a concentration of 26% Ga. To confirm this concentration composition maps were derived from the HAADF STEM images by a quantitative comparison with simulations according to the method suggested by Rosenauer et al. [3]. A Ga concentration map and a linescan along growth direction are shown in Fig. 2 a) and b). Indeed, the EDX result of 26 % is in good agreement with the HAADF STEM measurement of about 25%. Fig. 2: Ga composition map (a)) and linescan along growth direction (b)). In fact, the presence of the α-Ga2O3 in ref. [1] was explained by stabilization of the phase due to strain within an isotropic model. Fig. 3 shows the biaxial stress as a function of the assumed bulk modulus for a Poisson ratio of 0.3 for different compositions (25%, 50%, 75% and 100% Ga). Additionally, single points are added, which correspond to critical stresses, for which the alpha phase is starting to become energetically more favourable than the beta phase. For 100%, 75% and 50 % the stress is still significantly high to be the reason for the stabilization of the alpha phase, which is not given for the measured concentration of 25 %. Nevertheless, the assumption of an isotropic strain model is certainly not correct, especially since the layer seems to be pseudomorphically grown on the substrate and therefore a tetragonal distortion of the material in the layer will take place. We will measure this tetragonal distortion and compare it with density functional theory computations in order to determine, whether α-(AlGa)2O3 can be stabilized by a distortion corresponding to a Ga concentration as low as 25 %. Fig. 3: Biaxial stress as function of bulk modulus in isotropic approximation for different Ga concentrations. [1] R. Schewski et al., J. Phys: Cond. Mat. 19 (2007), 346211 [3] A. Rosenauer et al., Ultramicroscopy 109 (2009), 1171 [4] H. He et al., Phys. Rev. B 74 (2006), 195123 [5] K.E. Lipinska-Kalita et al., Phys. Rev. B 77 (2008), 094123 [6] H. Wang et al., J. Appl.Phys. 107 (2010), 033520 161

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MS3.P002 In situ reflection electron microscopy for investigation of sublimation and van- der-Waals epitaxy on Bi2Se3(0001) D. Rogilo1, S. Ponomarev1, K. Zakhozhev1,2, N. Kurus1, L. Basalaeva1, K. Kokh1, A. Milekhin1, D. Sheglov1, A. Latyshev1 1Rzhanov Institute of Semiconductor Physics SB RAS, Novosibirsk, Russian Federation 2Novosibirsk State University, Novosibirsk, Russian Federation 1. Introduction Since the beginning of the XXI century layered two-dimensional (2D) materials have been promising candidates for use in microelectronics, photonics, and photovoltaics. To grow high-quality heterostructures and superlattices, molecular beam epitaxy is used, but various defects are generated during the growth. Therefore, the growth of wafer- scale high-quality films is a fundamental issue of van der Waals (vdW) epitaxy that requires profound investigation of growth mechanism using in situ experimental techniques. 2. Objectives In this work, we aim to visualize and study surface transformations during sublimation and van-der-Waals epitaxy of 2D metal chalcogenides by in situ reflection electron microscopy. 3. Materials & methods We used an in situ reflection electron microscope (REM, 100 kV accelerating voltage) equipped with three separate evaporators for Se and metal (Bi, In, or Sn). Samples were prepared from a Bi2Se3 single crystal by cleavage along (0001) plane and were heated during experiment resistively by passing direct electric current. Above 100°C, the samples were exposed to a Se molecular beam (up to ~0.1 nm/s) to avoid noncongruent Bi2Se3 sublimation. Ex situ analysis of surface morphology was carried out by atomic force microscopy (AFM, Multimode 8, Bruker). The same equipment was used for creation of 15–30-nm-deep grooves by probe lithography. The crystal phase of obtained films was analyzed by ex situ Raman scattering measurements (XploRa Plus, Horiba, 532 nm laser). 4. Results When Bi2Se3(0001) surface is heated above 400°C, in situ REM images show that atomic steps move in ascending direction (towards higher terraces), which corresponds to congruent crystal sublimation. During sublimation, many 2D vacancy islands nucleate, grow, and coalesce on wide (~1–100 μm) terraces between the steps. The grooves preformed by probe lithography widen and deepen, and the center of each groove acts as a source of atomic steps that generates new steps moving in the ascending direction away from the source. We used this phenomenon to create self-organized regularly-spaced 1-nm-high atomic steps on the Bi2Se3(0001) surface. The onset of Bi deposition reverses the step motion direction (towards lower terraces), which corresponds to the onset of epitaxial layer-by-layer Bi2Se3 growth. These processes were first observed on the Bi2Se3 surface by in situ REM [J. Phys. Conf. Ser. 1984 (2021) 012016]. When In (or Sn) is deposited onto the Se-exposed sublimating Bi2Se3(0001) surface, In2Se3 (or SnSe2) heteroepitaxy begins with periodic 2D island nucleation and growth. After 3–5 nm growth, this mode switches to 3D growth (mounding). Ex situ Raman spectra of the grown films display a set of vibrational modes typical for the β-In2Se3 (or 1T- SnSe2) crystal phase. 5. Conclusions Our results show that in situ REM technique can be applied to study real-time surface dynamics of layered 2D materials during sublimation and van-der-Waals epitaxy. Using in situ REM, we have first visualized motion of atomic steps, evolution of lithographically patterned grooves, and 2D island nucleation on the Bi2Se3(0001) surface. Acknowledgments 163

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MS3.P003 4D-STEM on epitaxially grown vertical heterostructures of WS2 on Graphene O. Maßmeyer1, J. Belz1, S. Patil1, R. Günkel1, J. Glowatzki1, S. Krotkus2, M. Heuken2, A. Beyer1, K. Volz1 1Philipps-University Marburg, Physics, Marburg, Germany 2Aixtron SE, Herzogenrath, Germany Introduction: Two-dimensional (2D) materials received a lot of interest over the past decade. Especially van der Waals (vdW) 2D materials, such as transition metal dichalcogenides (TMDCs), and their heterostructures, exhibit semiconducting properties. Mixing and matching these materials with different properties and stacking them under an arbitrary in-plane angle causes structural changes as well as charge redistribution in the heterostructure, highly interesting for novel device applications.1 For these device structures, precise control of the composition and high uniformity of the layers is desired. Therefore, bottom-up synthesis methods, like metal-organic chemical vapor deposition (MOCVD) are currently being explored.2 Objectives: In this study, we aim to investigate charge redistributions occurring in 2D vertical heterostructures grown by MOCVD and to identify the epitaxial relationship of the layers within the heterostructure utilizing 4D-STEM. Materials and Methods: Vertical heterostructures of mono- to few-layer WS2 on few-layer graphene were deposited by MOCVD in a 19x2 inch Close Coupled Showerhead (CCS) Aixtron reactor on c-plane sapphire substrates. These structures are then transferred onto a 3 nm carbon film TEM-Grid by the PMMA transfer method.3 The samples are then characterized in a JEOL 3010 TEM and in an aberration-corrected JEOL 2200 FS STEM in conjunction with a fast pixelated pn-CCD detector, opening the possibility to analyze the samples by 4D-STEM.4 Results: The heterostructures of WS2 on graphene were successfully transferred by PMMA onto the TEM-Grids. The sample exhibits regions of monolayer WS2 and multiple stacking rotations between the vertically stacked WS2 and graphene layers. An annular bright field (ADF) image, exhibiting one of the resulting Moiré patterns is shown in fig. 1. The observed pattern aligns very well, to a rotation of about 11° between the lower and upper WS2 layer. In the FFT additional spots originating from the different lattice plane spacing of WS2 can be observed, which to the {100} lattice spacing of the underlying graphene layers. For the graphene layers in-plane rotations of about 34° and 10° are identified. In addition to the in-plane orientation of the layers, hopping of W and S atoms induced by the electron beam was seen for imaging at 200 keV as well as 80 keV. Studying this process should allow further insights into the crystal formation process. Furthermore, the heterostructures are investigated by 4D-STEM to reveal potential charge redistributions in these structures. Conclusion: Our results show a successful growth of high-quality vertical heterostructures of WS2 on graphene on sapphire and subsequent transfer to TEM-Grids. The first results are very promising to give insights into the nucleation process, the orientation relation of WS2 on graphene and into the charge redistributions in vertical vdW heterostructures. Figure 1. a) ABF-STEM image of 2 layers of WS2 on top of 2-3 layers of graphene recorded at 80 keV. b) Reduced FFT calculated from the STEM image in a). c) Lattice spacings determined from the FFT spots. d) Monolayer of WS2 on WS2 rotated by 10.7°.5 References: [1] K. S. Novoselov et al. Science 353, (2016). [2] S. M. Eichfeld, et al. 2D Materials 3, (2016). 165

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MS3.P005 Multi-core iron oxide nanoparticles: on their hierarchical architecture and coherence of their cores S. Neumann1, L. Kuger2, C. R. Arlt2, M. Franzreb2, D. Rafaja1 1TU Bergakademie Freiberg, Institute of Materials Science, Freiberg, Germany 2Karlsruher Institut of Technologie (KIT), Institute of Functional Interfaces, Eggenstein-Leopoldshafen, Germany Multi-core iron oxide nanoparticles (IONPs), usually consisting of the spinel compounds magnetite (Fe3O4) and maghemite (γ-Fe2O3), possess superparamagnetic behavior, high saturation magnetization, good biocompatibility, and interactive surface characteristics. These properties predestine IONPs for biomedical applications, for example as carrier for drug delivery in the human body, as heat mediator for hyperthermia cancer treatment, or as contrast agent for magnetic resonance imaging. However, a profound description of the hierarchical structure of multi-core IONPs, in particular the crystallographic interconnection and coherence of the individual cores which strongly influence their magnetic properties, has not been provided so far. The aim of this study was to describe the correlations between the internal structure of the IONPs and their magnetic properties. The IONPs investigated here were commercially available, dextran-coated multi-core IONPs (synomag-D, micromod Partikeltechnologie GmbH, Rostock, Germany), which were synthesized using a polyol method [1]. Their structural characteristics and magnetic properties were investigated using transmission electron microscopy (TEM), X- ray diffraction (XRD) and alternating gradient magnetometry (AGM). High-resolution TEM (HRTEM) showed that the IONPs consist of several cores with specific orientation relationships. HRTEM in combination with geometric phase analysis [2] disclosed that larger cores are further fragmented into small domains that have a mutual misorientation of less than 1°. The fragmentation of the cores was confirmed by XRD that revealed a dependence of the line broadening on the magnitude of the diffraction vector, which is typically observed for slightly misoriented, partially coherent nanocrystallites [3]. The particle size and the core size distributions of the IONPs were determined in a statistical manner by applying a multi-stage semi-automatic segmentation routine to several low-magnification high-angle annular dark-field scanning TEM images [4] and correlated with the microstructure characteristics. The structural properties determined in a correlative manner are related to the magnetic properties of the multi-core IONPs that were obtained from the AGM measurements. References [1] H. Gavilán et al., Part. Part. Syst. Charact. 34 (2017) 1700094. [2] M. Hytch et al., Ultramicroscopy 74 (1998) 131-146. [3] D. Rafaja et al., J. Appl. Crystallogr. 37 (2004) 612-620. [4] S. Neumann et al., CrytEngComm 22 (2020) 3644-3655. 168

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MS3.P006 Novel synthesis routes for nitrogen doped graphene and atomic level characterization I. Musil1, L. Rieger1, J. Haas1, K. Strobel1, J. C. Meyer1 1Institute for Applied Physics, University of Tübingen, AG Meyer: Advanced Materials, Tübingen, Germany Graphene has been subject of intense research and holds promising perspectives for future applications due to its unique properties. However, controlled structural modifications are desirable in order to fine-tune its properties, e.g. via the introduction of dopant atoms. In this work, we analyzed and compared nitrogen doping via ion implantation (as in [1]) with newly developed and experimentally very simple techniques of gas arc discharges in a nitrogen environment and plasma treatment with nitrogen plasma. For this purpose, several experimental setups were built, utilising (a) pure, energy-constrolled ion beams (b) gas discharge between the sample and a counter-electrode at pressures between 0.1 and 10 mbar (example in Figure 1), or (c) treatment inside a commercial plasma cleaner for TEM-holders. HRTEM is used to examine the doped graphene, allowing to evaluate and compare different doping methods. HRTEM, combined with image simulations, allow identifying nitrogen impurities inside the treated graphene samples [2], as exemplified in Figure 2, and provides insight into the implantation processes. Several synthesis routes were established, giving the opportunity to either study the underlying processes of ion implantation or allowing straightforward production of nitrogen doped graphene that can be implemented quite easily. [1] U. Bangert et al., Nano lett. 13:4902, 2013 [2] J. C. Meyer et al., Nat. Mat. 10:209, 2011 Fig. 1 169

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MS3.P007 A TEM preparation technique to relate the electronic signature of defects with their atomic structure M. Quincke1, T. Lehnert2, I. Keren3, N. M. Badlyan4, F. Port1, M. Goncalves1, J. Mohn1, J. Maultzsch4, H. Steinberg3, U. Kaiser1 1Ulm University, Physics, Ulm, Germany 2Karlsruher Institut of Technologie (KIT), Laboratory for Electron Microscopy, Karlsruhe, Germany 3Hebrew University, Recah Institute for Physics, Jerusalem, Israel 4Friedrich-Alexander-Universität, Department of Physics, Erlangen, Germany Atomic-resolution transmission electron microscopy (TEM) is the technique of choice for the structural characterization of two-dimensional (2D) materials on the atomic scale. With spherical and chromatic aberration correction (CC/CS- correction), low acceleration voltages of 20-80 kV still offer atomic resolution while allowing for good control over electron-beam-induced modifications in the sample [1]. In contrast to TEM experiments which are usually performed with the 2D materials being freely suspended on TEM-grids, many other measurement techniques such as electrical transport measurements require the 2D materials to be placed on other substrates [2]. This makes linking electron microscopy with complementary characterization techniques very challenging, as the samples may need to be transferred from a TEM grid to another substrate after TEM investigation. In our work, we aim for a controlled defect production in TEM experiments to engineer quantum dots (QDs) for subsequent electrical transport measurements. These QDs are considered as promising platforms for quantum information storage [3]. We exfoliate transition metal dichalcogenides (TMDs) on polyvinyl-alcohol coated SiO2 and transfer them to TEM grids. Following this, we use the TEM for engineering and simultaneous imaging of defects. When transferring the TMD flakes back to an arbitrary substrate, we observe that the exposure to the electron beam makes the flakes adhere more strongly to the TEM grid. This challenge is solved by the here presented "reverse transfer" preparation technique. We show proof-of-principle experiments in which we transfer electron exposed TMD flakes from a TEM grid to arbitrary substrates and measure the produced defects in photoluminescence and transport measurements. [1] M. Linck et al., Phys. Rev. Lett. (2016) [2] T. Dvir et al., Phys. Rev. Lett. (2019) [3] J. M. Elzerman et al, Nature 430, 431-435 (2004) Fig. 1 171

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MS3.P008 In-situ formation of Mo6Te6 nanowire in single-layer 2H-MoTe2 by annealing and electron irradiation J. Köster1, M. K. Kinyanjui1, U. Kaiser1 1Ulm University, Electron Microscopy Group of Materials Science, Ulm, Germany HRTEM, enables the investigation of electron beam-induced structural transformations, properties and single atom dynamics in two-dimensional (2D) materials. Furthermore, electron irradiation has been shown to lead to local transformations in single-layer MoTe2; from the semiconducting 2H to the metallic 1T" phase [1]. Here, we report about the in-situ formation of Mo6Te6 nanowires by heating and under electron irradiation in freestanding 2H-MoTe2 in TEM, as well as graphene-encapsulated samples. The transformation is specifically analysed in freestanding single- and few-layer samples. HRTEM images were acquired at the Cc/Cs-corrected Sub-Ångström Low-Voltage Electron microscope (SALVE) at an electron accelerating voltage of 80kV [2]. 2H-MoTe2 single-layers were prepared by mechanical exfoliation [3] onto Quantifoil grids and by stamping flakes with the help of a PMMA layer [4] onto a ThermoFisher MEMS-chip (see Fig. 1 (a-c)). Graphene-encapsulated MoTe2 was prepared by transferring three separate flakes to a TEM grid by iterative mechanical exfoliation. By increasing the annealing temperature under constant electron irradiation (Figs. 1 (d-f)), the structural evolution from layered 2H-MoTe2 to one-dimensional (1D) Mo6Te6 chains [5] can be observed and analysed. An experimentally acquired freestanding nanowire formed within a single-layer region at a temperature of about 600°C is shown in (f). Pure electron irradiation showed in contrast to heating, nanowires are formed more slowly and at the edges of holes within the single-layer, thus the electron beam enables the precise formation of Mo6Te6. Figs. 2 (a-c) shows experimental images of a single-layer MoTe2 bombarded by electrons forming holes and nanowires. The supreme electric and thermal conduction [6], as well as the strong intralayer covalent bonding (mechanical strength) [7] makes graphene an excellent candidate for protecting 2D materials in TEM. Fig. 2 (d) shows a schematic depiction of the solid-to-solid transformation in planar 1H-MoTe2 (encapsulated between Graphene) which transforms to 1D Mo6Te6 nanowires under electron irradiation. A hole in one of the graphene layers, driven by the interaction with the electron beam, enables Te atoms to escape the graphene-encapsulation and form nanowires. Our results demonstrate the controlled step by step transformation of freestanding single- and few-layers 2H-MoTe2 to 1D Mo6Te6 nanowires and thus provide a comprehensive picture of the response of MoTe2 crystals to heat and to electron irradiation. Furthermore, we compare the effect of electron irradiation and annealing on the formation of nanowires. Fig. 1. (a-c) llustrates the sample preparation of 2H-MoTe2 onto a MEMS-chip. (d-f) show the formation of freestanding Mo6Te6 at high temperatures. Fig. 2. (a-c) Single-layer MoTe2 under constant electron irradiation at 80kV. (d) Illustrates the formation of one- dimensional Mo6Te6 nanowires encapsulated between graphene under electron bombardment. [1] J. Köster, et al., The Journal of Physical Chemistry C, 125(24), 13601-13609, 2021. [2] M. Linck, et al., Phys. Rev. Lett., 117, 076101, 2016. [3] P. Blake, et al., Applied physics letters 91.6: 063124, 2007. [4] M. Ibrahim, et al., Sensors 20.6: 1572, 2020. [5] H. Kim, et al., Small 16.47: 2002849, 2020 [6] A. A. Balandin, Nature materials, 10(8), 569-581, 2011. [7] C. Lee, et al., science, 321(5887), 385-388, 2008. 172

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MS3.P009 Characterisation of doped graphene with focal-series reconstruction G. Algara-Siller1, J. Köster2, G. Kornilov1, M. Kühbach1, U. Kaiser2, C. T. Koch1 1Humboldt Universität zu Berlin, Institut für Physik, AG Strukturforschung/Elektronenmikroskopie, Berlin, Germany 2Ulm University, Materialwissenschaftliche Elektronenmikroskopie, Ulm, Germany Introduction Phase recovery techniques such as focal series reconstruction have been shown to allow characterization of materials in terms of electrostatic potential, electric and magnetic field, as well as charge density down to the atomic level. It has the advantage that, without additional physical modification to a standard microscope the exit wave"s amplitude and phase can be recovered with high spatial resolution and with relatively low noise [1,2,3]. Being very flexible regarding beam setting protocols, this technique is therefore well suited for the characterization of complex systems or materials where, for example, the contrast of different atoms in the structure is indiscernible and as such a HRTEM image is not directly interpretable or when radiation damage of a material is a limitation [4]. Objectives The main goal of this experiment is to characterize N, O and Si doped graphene using focal series reconstruction. It is known that each of these dopant atoms occupies specific positions in the graphene structure, e. g. substitutional nitrogen, or oxygen forming an epoxy group bridging between two carbon atoms [5]. Accordingly, each dopant atom in each configuration will affect the structure and the properties of graphene differently and in a specific manner. Materials & Methods The fabrication of the graphene samples for TEM follows the general CVD graphene transferring method to grids [6]. The doping of graphene with nitrogen and oxygen was made by plasma generation. While silicon doping was just made with the intrinsic Si contamination on the sample, which in this case was exacerbated by removing hydrocarbon contamination on graphene [6] and the subsequently plasma generation or the electron beam irradiation. The samples were characterised in the SALVE TEM microscope [7] operated at 60 kV. The series of defocused images were taken with linear focus increments and the reconstruction was performed using the full-resolution wave-reconstruction algorithm [1]. Structure calculations and image simulations were carried out using the abTEM package [8]. Results & Conclusions With the phase-reconstructed images it is possible to resolve the atomic position, distinguish if the doping atoms are substitutional or superficial, and ascertain the chemical composition of the dopants by phase analysis with complementary theoretical calculations and image simulations. In our experiments all three types of dopants in their most common configurations [5, 9, 10] could be characterised within the same field of view (e. g. approx. 40 nm x 40 nm). This was only possible by sequentially treating and doping the graphene. The latter experiment also highlights the robustness of graphene to external manipulation and the possible extent of graphene functionalization. [1] C. T. Koch. Micron 63 (2014) 69 [2] S.J. Haigh, et al. Ultramicroscopy 133 (2013) 26 [3] M. Huang et al., Ultramicroscopy 231 (2021) 113264 [4] I. Biran et al. Adv. Mat. 34 (2022) 2202088 [5] X. Qi, et al. Appl. Surf. Sci. 259 (2012) 195 [6] G. Algara-Siller et al. Appl. Phys. Lett. 104 (2014) 153115 [7] https://www.salve-project.de/tools/salve3/ [8] J. Madsen et al. Open Res. Europe 1:24 (2021) 174

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MS3.P010 Dynamics of single atoms and molecules encapsulated in carbon nanotubes J. Biskupek1, I. Cardillo-Zallo2, S. T. Skowron2, C. T. Stopiello2, G. A. Rance2, Q. Ramasse3,4, E. Besley2, A. N. Khlobystov2, U. Kaiser1 1University of Ulm, Central Facility of Electron Microscopy, Ulm, Germany 2University of Nottingham, School of Chemistry, Nottingham, United Kingdom 3SuperSTEM Laboratory, Daresbury, United Kingdom 4University of Leeds, School of Chemical and Process Engineering and School of Physics, Leeds, United Kingdom Introduction and Objectives Molecular motion and bond dissociation are two of the most fundamental phenomena underpinning properties of molecular materials. We have entrapped single atoms such as atoms (Kr) or basic molecules (HF and H2) within the fullerene C60 cage, encapsulated within a single-walled carbon nanotube. The use of the electron beam simultaneously as a stimulus of chemical reactions in molecules and as a sub-Å resolution imaging probe allows investigations of the molecular dynamics and reactivity in real time and at the atomic scale, which are probed directly by chromatic and spherical aberration-corrected high-resolution transmission electron microscopy (CC/CS-corrected HRTEM) imaging. Methods Working at reduced voltages, however, decreases the obtainable resolution to about 0.2 nm at 80 kV when using standard 3rd order aberration correctors such as the hexapole-type correctors [1]. The correction of 5th order geometric aberration correction together with chromatic aberration correction is necessary to archive atomic resolution at voltages at voltages even at 20 kV. The dedicated CS/CC SALVE (sub-Ångström low voltage electron microscopy) TEM [2] operates between 20 to 80 kV and still delivers sub-Å resolution at 40 kV. EDX and monochromated EELS spectroscopy used to verify elemental composition of the tube fillings and to determine bonding information. Molecular dynamic (MD) and density functional theory (DFT) calculations are used to describe and understand the reaction processes. Results We present the study of single atoms and simple molecules HF and H2O embedded into C60 clusters using atomic resolved HRTEM and STEM accompanied by local electron energy loss spectroscopy (EELS) and X-Ray spectroscopy (EDX). In contrary to plain C60 clusters the embedded atoms and molecules change the behavior of dimerization and general damage behavior of the clusters. The neutral Kr atoms are trying to keep a van-der-Waals distance of 0.4 nm and this effects the dimerization behavior. For the case of H2O and HF we demonstrate the rotation of the HF@C60 resp. H2O@C60 clusters under the influence of the electron beam (Fig.1) [3]. Depending on the electron voltage and the atom species the H2O and HF molecules dissociates at different rates. Figure captions Figure 1. (a) Experimental time series (2 s time interval) of 30 keV Cc/Cs-corrected HRTEM images of (HF@C60)@SWNT, showing blinking of the F-atoms. The green arrows indicate examples when the F-atoms are clearly visible, these appear to be visible and invisible in the same molecules over time (see Supporting Video 1). (b) Line profile across the centre of a fullerene molecule (as shown in green and white boxes indicated in micrographs (a)) showing variation of image contrast when F-atom is visible (green plot) or invisible (black plot) within the same molecule. (c) Model and corresponding HRTEM image simulations for four different orientations of HF@C60 in SWNT (four principal projections along elements of symmetry of the C60 cage C2, S6, C1 and C5). Only some orientations are able to produce a "dot" contrast at the centre of the fullerene cage due to an overlap of F-atom with two C-atoms of C60, indicated with green arrows. References [1] M. Haider et al. Ultramicroscopy, 75 (1998) 53 [2] M. Linck et al. Phys. Rev. Let. 117 (2016) 076101 176

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MS3.P011 Novel nanostructures and materials enabled by graphene embedding and sandwiching K. Mustonen1, M. Längle1, A. Trentino1, G. Zagler1, C. Hofer1,2, A. Markevich1, H. Inani1, C. Mangler1, T. J. Pennycook1,2, V. Skakalova1,3, T. Susi1, J. C. Meyer1,4, J. Kotakoski1 1University of Vienna, Vienna, Austria 2University of Antwerp, EMAT, Antwerp, Belgium 3Danubia Nanotech s.r.o., Bratislava, Slovakia 4Eberhard Karls University of Tübingen, Tübingen, Germany Graphene--the one-atom-thick sheet of carbon--is the most famous of 2D materials due to its unique electronic properties and mechanical strength. However, its chemical inertness makes graphene also an excellent nearly electron-transparent support for other materials and nanostructures. In this presentation, I will give an overview of our recent work, partially enabled by a unique interconnected vacuum system containing an aberration-corrected scanning transmission electron microscope (Nion UltraSTEM 100) with a unique objective area that allows sample cleaning via laser, in situ chemical experiments, and direct vacuum transfer to an atomic force microscope (AFSEM by GeTEC Microscopy), an argon glove box, a chamber for alteration and growth of materials equipped with a plasma ion source and evaporators, and long-term vacuum sample storage. Specifically, I will show that otherwise unstable structures such as a monolayer of fullerenes [1], 2D CuI [2] and small noble gas clusters [3] can be stabilized in the van der Waals gap between two graphene sheets allowing also their atomic-resolution imaging. If time allows, I will further demonstrate that defect-engineering of graphene [4] enables its substitutional heteroatom doping [5] and growth of nanoclusters with a well-defined concentration and a narrow size distribution, as well as its atomic structure and mechanical properties. the direct correlation of References [1] Mirzayev et al., Sci. Adv. 3, e1700176 (2017) [2] Mustonen et al., Adv. Mater., 202106922 (2022) [3] Längle et al., Microsc. Microanal. 26 S2, 1086-1089 (2020) [4] Trentino et al., Nano Lett. 21, 5179-5185 (2021) [5] Inani et al., J. Phys. Chem. C 123, 13136-13140 (2019); Zagler et al., 2D Mater. 9, 035009 (2022); Trentino et al., 2D Mater. 9, 025011 (2022) 178

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MS3.P012 Thickness dependent critical dose of an extremely beam-sensitive two- dimensional polymer D. Mücke1, U. Kaiser1, H. Qi1,2 1Ulm University, Central Facility for electron microscopy, electron microscopy group of material science, Ulm, Germany 2TU Dresden, Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Dresden, Germany AC-HRTEM imaging is capable of atomically precise observation of two-dimensional materials. It has also proven itself to be a very powerful tool for probing the structures of 2D polymers, covalent and metal organic frameworks1. However, for these organic materials the achievable resolution is often limited by the low number of electrons the material under study can accept before it is destroyed. In extreme cases the total dose for amorphization can be as low as a single electron per square Ångström. Thus, increasing this critical dose of these sensitive materials is of highest importance. This can be achieved by various techniques developed in the past. For layer-stacked materials especially, the thickness dependency of the critical dose is a key feature, due to the easily controllable thickness. However, the effects an increase of the thickness has on the electron resilience is not completely understood2,3. The current assumption is, that additional layers build a cage around the inner parts, holding in produced radicals2. Through this recombination is made possible and the material can self-heal. Aimed at gathering a better understanding of this effect, in our study the thickness dependency of the critical dose was examined in more detail. To achieve this, the critical dose of a triazine-based 2D polymer4 was measured for a wide thickness range. The polymer samples, obtained by mechanical exfoliation, ranged from 15 nm to 85 nm thickness. The thickness of the polymer was obtained by combining light microscopy and atomic force microscopy. In order to find the critical dose for the polymer, sequences of electron diffraction patterns with a dose of only 0.5 electrons per Å2 were obtained and the fading of diffraction spots was monitored (Fig 1). The measurements revealed that the critical dose for amorphization of this polymer is only 1-2 e-/Å2 (Fig. 2), surprisingly independent of sample thickness and HRTEM imaging is made extremely challenging if not impossible. The lack of increase in critical dose with growing thickness is attributed to the porous structure of the polymer, leading to escape paths for the produced radicals. With that the caging effect is circumvented. This assumption is further strengthened by the application of graphene layers on top and bottom, preventing the escape of atoms from the polymer layers. Through that the critical dose is increased, independent of specimen thickness. References 1. Haoyuan, Q. et al. Sci. Adv. 6, eabb5976 (2020). 2. Egerton, R. F. Ultramicroscopy 127, 100–108 (2013). 3. Fryer, J. R. Ultramicroscopy 14, 227–236 (1984). 4. Hu, F. et al. J. Am. Chem. Soc. 143, 5636–5642 (2021). Acknowledgement We acknowledge the funding from Deutsche Forschungsgemeinschaft (DFG) – 492191310; 426572620; 417590517 (SFB-1415), and European Union GrapheneCore3 (881603). We thank Yingjie Zhao from Qingdao University for providing the polymer. Fig 1. a) Model of the trianzine-based polymer. b) Selected area electron diffraction pattern of the polymer. c) Series of diffraction patterns. e) With the measured intensity in every image d), the relation between intensity and accumulated dose can be obtained. The critical dose is reached, if the intensity falls below 1/e of its starting value. Fig. 2. Diffraction patterns obtained on a) a (15.8 ± 0.9) and b) a (85 ± 4) nm thick area. c) Thickness dependent first order peak intensity of the first image of the dose series. d) Thickness dependent critical dose of the 2DP. 179

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MS3.P013 Design-optimized conductive 2D conjugated metal-organic frameworks allowing sub-Ångstrom resolution HRTEM imaging B. Liang1, D. Mücke1, C. Leist1, I. Cooley2, E. Besley2, U. Kaiser1, H. Qi3,1 1Universität Ulm, Central Facility for Electron Microscopy, Electron Microscopy Group of Materials Science, Ulm, Germany 2University of Nottingham, School of Chemistry, Nottingham, United Kingdom 3Technische Universität Dresden, Faculty of Chemistry and Food Chemistry & Center for Advancing Electronics Dresden (cfaed), Dresden, Germany Recent years have witnessed the rise of two-dimensional conjugated metal-organic frameworks (2D c-MOFs). 2D c- MOFs with strong in-plane π-d conjugation are particularly interesting because of their intrinsic conductivity, anisotropic charge transport, and potential (opto-) electronic applications1. Recently, interfacial synthesis has emerged as a new production method for highly crystalline 2D c-MOFs1–3. However, the AC-HRTEM structural determination of 2D c-MOFs, particularly down to the atomic scale, remains a formidable task. The electron radiation damage severely limits the achievable resolution 4,5. Enhancing the intrinsic electron resilience of MOFs is vital to circumventing this physical limitation and improving achievable resolution. Previous researches provide insights into the empirical rules for electron radiation resilience of organic materials. For example, aromatic compounds are more electron resilient than aliphatic due to π electron delocalization and conjugation6,7, suggesting higher stability of conductive 2D c-MOFs than conventional insulating ones. In addition, exchanging protium for chlorine on coronene molecules has increased the crosslinking dose by two orders of magnitude due to the reduced displacement cross-section of chlorine 8,9, indicating a potential negative correlation between hydrogen content and electron resilience in MOFs. Nevertheless, the effects of organometallic bonds on MOF stability remain unexplored. In this work, we investigate the electron resilience of 2D c-MOFs with systematically altered structural attributes, including hydrogen content, framework density, and organometallic bonding, the atomic structures see Fig. 1. The critical fluence, which represents the electron resilience, is quantitatively determined at 300 kV condition for each material. The experimental results are explicated by ab initio quantum calculation. The highly conductive Cu3(BHT) demonstrates exceptional stability, allowing information transfer to the sub-Ångstrom regime in the characterization by Cs/Cc-corrected HRTEM at 80 kV (Fig. 2), the carbon atoms in the benzene ring structure can be unambiguously distinguished. Fig. 1. (A) Atomic models of 2D c-MOFs. (B) Intensity profile of the first-order reflections in 2D c-MOFs as a function of accumulated electron dose. The critical dose is reached when the reflection intensity drops to e-1 of the original value. Fig. 2. CS+ CC-corrected atomic-resolved imaging of Cu3(BHT) at 80 kV. (A) Experimental and simulated AC-HRTEM images of Cu3(BHT). Acquisition dose: 3.2 × 103 e- Å-2. (B) Enlarged image of A. (C) Intensity profile from the line- scan region in (B), the peak represents the center of the carbon atom, and the distance between the two peaks is 1.4 Å. Acknowledgment 2D c-MOF samples were synthesized by the group of Prof. Xinliang Feng and Dr. Renhao Dong. Reference 1. Wang, M., Dong, R. & Feng, X. Chem. Soc. Rev. 50, 2764–2793 (2021). 2. Yu, M., Dong, R. & Feng, X. J. Am. Chem. Soc. 142, 12903–12915 (2020). 3. Liu, J., Chen, Y., Feng, X. & Dong, R. Small Struct. 2100210 (2022). 4. Skowron, S. T. et al. Acc. Chem. Res. 50, 1797−1807 (2017). 5. Russo, C. J. & Egerton, R. F. MRS Bull. 44, 935–941 (2019). 6. Alexander, P. & Charlesby, A. Nature 173, 578–579 (1954). 7. Fryer, J. R.Ultramicroscopy 23, 321–327 (1987). 8. Stenn, K. & Bahr, G. F. J. Ultrastructure Res. 31, 526–550 (1970). 9. Chamberlain, T. W. et al. Small 11, 622–629 (2015). 182

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MS3.P014 Aligned stacking of nanopatterned 2D materials for high-resolution 3D device fabrication J. Haas1,2, F. Ulrich1,2, C. Hofer1,2, X. Wang3, K. Braun4, J. C. Meyer1,2 1University of Tübingen, Institute for Applied Physics, Tübingen, Germany 2NMI Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany 3Hunan University, School of Physics and Electronics, Hunan, Germany 4University of Tübingen, Institute of Physical and Theoretical Chemistry, Tübingen, Germany Additive manufacturing, often referred to as 3D printing, creates structures typially by depositing material layer-by- layer. However, feature sizes in 3D printing are still not sufficient for the creation of devices on the nanometer-scale. A promising method for building smaller structures is the layer-by-layer assembly of 2D materials. The creation of these so-called van-der-Waals heterostructures can also be regarded as a type of additive manufacturing. While the feature size of each layer in the out-of plane direction is by nature in the order of a few atoms, the common techniques for building van-der-Waals heterostructures can not manipulate and control the in-plane direction on a similar scale. In this work, we developed a method for the assembly of van-der-Waals heterostructures to overcome these limitations. Free-standing 2D materials are patterned on the nanometer-scale prior to the assembly. This is done by resist-free methods such as water-assisted electron beam etching and by sputtering with high-energy electrons in a scanning transmission electron microscope. Stacking is performed under observation in a scanning electron microscope and with the help of nanomanipulators, allowing a precise in-plane alignment (Fig. 1). The assembled structures are analyzed by means of scanning electron microscopy and transmission electron microscopy. Several samples are fabricated to verify the method and investigate the accuracy of the in-plane alignment. Currently, layers can be aligned with an accuracy of about 10 nm. As an example, a ten-layer stack with a parabolic thickness profile is built that serves as phase plate for electrons, with the effect of focussing a plane electron wave (Fig. 2). In principle, phase plates with arbitrary shapes could be made by this approach. The presented method surpass the limits of previous techniques for the assembly of van-der-Waals heterostructures. Having the individual layers as free-standing membranes, the 2D materials can be patterned with highest resolution prior to the stacking. Accurate alignment during the assembly is ensured by observation in an electron microscope. Together, the method enables the fabrication of 3D structures with highest spatial resolution. [1] Haas, Jonas, et al. "Aligned Stacking of Nanopatterned 2D Materials for High-Resolution 3D Device Fabrication." ACS Nano 16.2 (2022): 1836-1846. Fig. 1: (a) Schematic of the stacking process. (1) The free-standing 2D material is patterned, (2-3) brought into contact with a target support, and (4-5) detached from the initial support grid. The process is repeated for subsequent layers (6-10) under SEM observation, thereby enabling a precise lateral alignment. (b) Illustration of the setup used for the process. (c-h) SEM image sequence of placing a single layer. Scale bars are (c) 500 µm, (d,e) 10 µm and (f-h) 5 µm. Adapted from [1]. Fig. 2: (a) Ten-layer stack of 2D materials with increasing hole diameter that can be tailored to form a parabolic electron lens as shown in (b). (c-d) Intensity profile of a plane electron wave focused by a structure as shown in (a). Adapted from [1]. 184

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MS3.P015 Correlative raman imaging characterizes crystal properties of 2D materials U. Schmidt1, J. Englert1, T. Dieing1, O. Hollricher1 1WITec GmbH, Applications, Ulm, Germany Due to their unique optical and electronic properties, two-dimensional (2D) materials have great potential for application in optoelectronic devices. Diverse crystal properties such as the number of layers and growth defects influence the optical and electronic properties of the 2D materials. Research, development and quality control thus require powerful and non-destructive imaging techniques for monitoring these crystal properties and to evaluate synthesis processes. To comprehensively characterize the 2D material, it is advantageous to combine several imaging techniques. Here, we present correlative Raman imaging as a versatile tool for investigating prominent examples of 2D materials, namely graphene and the transition metal dichalcogenides (TMDs) molybdenum disulfide (MoS2) and tungsten disulfide (WS2). In combination with imaging techniques such as second harmonic generation (SHG), photoluminescence (PL), atomic force microscopy (AFM) or scanning electron microscopy (SEM), Raman imaging is able to provide a thorough characterization of the 2D materials. Crystal properties and features such as grain boundaries, surface structure, layer number, defect density, doping and strain fields can thus be identified and visualized. Fig. 1: Correlative imaging of a MoS2 crystal using white light imaging (A), SHG intensity revealing grain boundaries (B), polarization dependent SHG characteristic for crystal orientation and strain (C), Raman spectrum of a monolayer of MoS2 (D) intensity of the E2g (E) and PL image revealing strain fields. Fig. 1 186

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MS3.P016 Control and characterization of a piezo TEM stage for automated atomic- resolution and atomic-precision image mapping K. Strobel1,2, J. C. Meyer1,2 1University of Tübingen, Institute of Applied Physics, Tübingen, Germany 2NMI Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany The information gained from a native specimen is limited by the introduced dosage. One way to reduce dose, is to distribute it across an area, which is typically larger than the field of view of the detector, when acquiring atomically resolved TEM images. Therefore, in low dose experiments, a region of interest in the specimen can be mapped, by iterative displacements of the specimen, thus always exposing a fresh region of the sample. The stability and resolution of the TEM stage limits the quality of the final image map. This motivated the use of a piezo TEM stage for image mapping. The characterization of the lateral stepsize, the stage and imaging system control, as well as the automated low dose image acquisition was the objective of this work. The mapping system was implemented on an image corrected JEOL JEM-ARM200F microscope, equipped with a Gatan OneView. These systems were controlled via the backend of the Gatan and JEOL user interfaces (DigitalMicrograph, Temcenter), using custom python servers on each control computer. These servers were controlled simultaneously on a third computer, serving as a host. The stage was characterized by using a freestanding 2D material, and visible features served as a reference in the observed area, as illustrated in Figure 1. The reference was periodically displaced for 10,5 nm within the image and the stage start and end positions were recorded from the temcenter UI. The standard deviation from the start and end positions were smaller than 0,5 Å as well as the calculated step size at the lowest speed setting in the temcenter UI. The standard deviation of the start and end positions indicate that the stage is atomically precise, when conducting a unidirectional displacement. The step size was used in the mapping, to displace the specimen to a set of coordinates and to acquire a stack of images at each position, as illustrated in Figure 2. The electron beam was blanked during each displacement, reducing the dosage during mapping. In conclusion, the accuracy and precision of the piezo stage allows a mapping with non overlapping (or minimally overlapping) field of view in each exposure, which are closer packed together than for standard non piezo driven TEM stages. This enables the collection of low dose images from a smaller sample area, which might be especially helpful for 2D specimen with smaller patches of non-contaminated area or specimen with small regions of interest. Also, it enables the acquisition of an atomic resolution image from a large area (up to 380x380 nm) by stitching together a large number of exposures with a smaller field of view. Figure 1: Characterization for the X direction of a piezo super fine stage of an JEOL ARM200F. The intended periodic forth and back displacement is indicated with arrows and the step size is illustrated as dimensioning arrows. The Precision is indicated along the edge of the reference structure (highlighted in red) with two barred lines. Figure 2: Illustration of an atlas acquisition using the piezo stage of a JEOL JEM-ARM200F TEM. The field of view was 21,5x21,5 nm and the spacing along the stage x and y-axis were 18 nm. Videos for each spot were acquired with a Gatan OneView with 14fps. Fig. 1 187

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MS3.P017 Revealing the stacking configuration of ideal Moiré structures in CVD grown MoSe2-WSe2 heterobilayers B. März1, I. Bilgin2, L. Richter1, B. Diederichs3, A. Högele2, K. Müller-Caspary1 1Ludwig-Maximilians-University Munich, Department of Chemistry, Munich, Germany 2Ludwig-Maximilians-University Munich, Department of Physik, Munich, Germany 3Helmholtz Zentrum München, Munich, Germany A MoSe2-WSe2 heterobilayer (HBL) consists of stacked monolayers (MLs) of each respective material. Because of slightly different lattice parameters a Moiré superstructure is formed by periodic self-reconstruction, with regions showing ideal Moiré patterns and according transitional regions in between [1]. When using chemical vapour deposition (CVD) to fabricate a HBL the actual stacking is hardly under control. In theory several R- and H-type ideal stacking configurations are possible. Depending on the Moiré interference pattern varying electrical and optical properties arise, as has been indicated by spectroscopic analysis [2]. In order to reliably link these properties to the respective stacking, knowledge is required about which Moiré structures are present. Due to the periodicity of the Moiré superstructure with small Moiré cells, and the limited spatial resolution of the applied spectroscopic methods, it could not yet be fully determined how the different properties relate to each stacking. A probe-corrected STEM operated at 120kV was used for high-angle annular dark field (HAADF) imaging and recording of four-dimensional (4D) scanning transmission electron microscopy (STEM) data with a Merlin Medipix3 camera. The MoSe2-WSe2 HBL was prepared by CVD and transferred on a Cu Quantifoil TEM grid. Multislice simulations of 4D-STEM data of ideal Moiré patterns were conducted. In this study the local Moiré stacking in MoSe2-WSe2 HBLs was identified using HAADF and 4D-STEM, supported by multislice simulations. We use both signals to determine the stacking order, vacancies and additional atoms. By evaluating the gradients of the pixel wise 4D-STEM and HAADF signals with respect to stacking, atom positions and vacancies we evaluate the validity of the results from the respective signals. The atom structure in the experimental HAADF-STEM image shown in Fig.1(a) represent three groups of differently stacked atom columns because of their different Z-contrast. Simulated ADF-STEM signals of ideal Moiré patterns are shown in Fig.1(b-e). Ideal Moirés that, in contrast to the experiment, do not show an additional centred atom in the hexagonal ring were excluded. By comparing the relative intensities in the experimental HAADF image with the relative intensities expected from the respective atom columns and which constituting atom species are known, a RXM stacking depicted in Fig.1(e) was in best agreement with the experiment. The bright columns represent 1Mo+2Se, the darker ones W or 2Se atoms. The line profiles in Fig.1(f) highlight the differences in the ADF signal of each ideal Moiré. The according atomic structures are shown in Fig.2. (2022) [1] S. Zhao et al. Excitons [2] M. Förg et al. Moiré excitons in MoSe2-WSe2 heterobilayers and heterotrilayers. Nat Commun 12, 1656 (2021) [3] We acknowledge financial support from the DFG under grant number EXC 2089/1-390776260 (e-conversion) and the EQAP project Munich. reconstructed Moiré heterostructures, pre-print, in mesoscopically Fig.1 Comparison of (a) an experimental HAADF-STEM image (noise filtered) with (b,c,d,e) simulated images of the ideal Moiré structures HMM, HXX, RMX and RXM of a MoSe2-WSe2 HBL. Profiles along red arrows are shown in (f); field of view in b,c,d,e is 1.5nm Fig.2 Atomic structures of ideal Moiré configurations of the HBL; super- and subscript indices in the notation represent the top and bottom layer atoms stacked on top of another; R and H indicate the stacking type 189

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MS3.P019 Structural transformations in transition metal phosphorus trichalcogenides studied by analytical transmission electron microscopy A. Storm1, J. Köster1, M. Asl-Gohrbani2, S. Kretschmer2, T. Gorelik1, A. Krasheninnikov2,3, U. Kaiser1 1Ulm University, Ulm, Germany 2Helmholt-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Dresden, Germany 3Aalto University, Department of Applied Physics, Aalto, Finland Few-layer transition metal phosphorous trichalcogenides (TMPTs) is a promising class of materials due to their inherent interesting properties [1], making these materials ideal candidates to study 2D magnetism [2], as well as promising candidates for future energy storage related applications [3]. In this work, we study structural modifications of few-layer TMPTs caused by electron-irradiation, as well as thermal annealing in transmission electron microscopy (TEM), and experiments are rationalized using ab-initio calculations. Thin TMPT flakes were prepared with the help of a newly developed polymer-based preparation method [4], which significantly enhances the sample quality. The Cc/Cs-corrected Sub-Ångström Low Voltage Electron Microscope (SALVE) at 80kV was used to study structural modifications caused by the probing electrons. Furthermore, in-situ annealing experiments were conducted with a dedicated FEI NanoEx-i/v TEM specimen heating holder. Electronic, and magnetic properties of newly emerging phases were predicted using spin-polarized density functional theory (DFT) as implemented in VASP [5]. Continuous irradiation of 4-layer NiPS3 showed a degradation of individual layers, thus single- and double-layer regions within the layer system emerge. Fig. 1 (a) presents a sulphur vacancy in double-layer NiPS3. By using the McKinley-Feshbach formalism [6] estimated atom displacement cross-sections were calculated predicting the preferential removal of sulphur (see Fig. 1 (b)). Further, the emergence of different MnS phases (e.g. Fig. 2 (a)) in MnPS3, and MnSe phases in MnPSe3 were observed due to structural modifications caused by the impinging electrons, and the growth of these ultrathin phases could be controlled by the illuminated area, and applied total electron dose. In-situ thermal annealing induced structural modifications showed the possibility of engineering various phases depending on the observed TMPT (e.g. MnPSe3, and NiPS3, transforms to MnSe (see Fig. 2 (b)), and NiP, respectively). Further, the phase transition temperatures of freestanding TMPTs in vacuum were determined. Eventually, ab-initio calculations predict distinct properties of the new phases, which strongly depend on the orientation and the thickness of the transformed facets. In conclusion, displacement cross-sections predict that more S should be removed than P due to elastic interaction in the acceleration voltage range of 50-300kV. Further, our experiments show that structural modififations can attributed to the growth of specific phases in MnPS3 and MnPSe3, caused by electron-irradiation or thermal annealing. Fig. 1. (a) 80kV Cc/Cs-corrected HRTEM image of a double-layer NiPS3. A line-scan shows the position of a missing S atom. (b) Displacement cross-sections of sulphur and phosphorous in XPS3 (X=Fe, Mn, Ni). Fig. 2. (a) 80kV Cc/Cs-corrected HRTEM image of a -MnS crystal. A magnified area of the patch with overlaid structure model is shown beside. The structure emerged after irradiation of a MnPS3 flake in TEM. (b) HRTEM image of an -MnSe crystal, which formed after annealing a MnPSe3 in-situ to 600°C. [1] Xu et al., Microstructures, 2, 2022011, (2022). [2] Long et al., ACS Nano, 11, 11330-11336, (2017). [3] Glass et al., J. Electrochem. Soc., 167, 110512, (2020). [4] Köster et al., Nanotechnology, 32, 075704, (2021). [5] Kresse et al., Phys. Rev. B, 54, 11169-11186, (1996). [6] Meyer, et al., Phys. Rev. Lett., 108 (19), 196102, (2012). 191

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MS3.P020 Characterization of two-dimensional WSe2 using differential phase contrast STEM M. Groll1, J. Bürger1, I. Caltzidis1, M. Sartison1, K. D. Jöns1, J. K. Lindner1 1University of Paderborn, Physics, Paderborn, Germany Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2 and WSe2, exhibit exciting electrical and optical properties due to their low dimensionality and are therefore promising candidates for next generation optoelectronic devices [1]. Comparable to graphene, TMDs consist of molecular layers which are bound to each other only by weak van der Waals interlayer interactions and are covalently bound within each layer. TMDs show varying physical properties depending on the number of stacked layers, such as a direct band gap for a monolayer of WSe2 compared to an indirect band gap of its bulk form [2,3]. Many of these layer thickness-dependent properties are determined by the electric field and charge density distributions around individual atoms and defects within the crystal structure. However, only a few measurement methods allow characterization of electric fields with such a high spatial resolution. One of these is differential phase contrast (DPC) imaging in STEM, which, in combination with state-of-the-art Cs correction, allows the investigation of electric fields with subatomic resolution even at the sufficiently low acceleration voltage of 80 kV. It is, thus, the objective of this study to image and quantify atomic electric fields and the field distribution of defects in mono- and multilayer WSe2 using STEM-DPC imaging. In order to investigate 2D WSe2 by STEM-DPC, mechanically exfoliated WSe2 flakes with different thicknesses are transferred to TEM grids. STEM-DPC imaging is performed using an eight-fold segmented STEM detector at an acceleration voltage of 80 kV. The measurement of electric fields by DPC in general relies on the measurement of the center of mass (CoM) of the bright-field intensity distribution. Due to Coulomb interaction of the incident electron beam with the electrostatic potential inside the specimen, a shift of the CoM in the detection plane can be measured in presence of electric fields. These electric fields can be quantified by the difference of intensity on opposing detector segments and an adequate calibration. Measurements are compared with corresponding multislice image simulations. We show the atomic structure as well as the corresponding electric field and charge density distribution of 2D WSe2, which are in good qualitative agreement with multislice image simulations. As 2D materials are prone to various defects which can influence physical properties, we also show the electric field distribution of defects and disclose characteristic changes in the electric field distribution in the vicinity of defects. In conclusion, DPC measurements on atomically thin WSe2 offer a great possibility to reveal the electronic structure achieve a deeper understanding of the optoelectronic properties of this material system. [1] J. An, et al., Perspectives of 2D Materials for Optoelectronic Integration, Adv. Funct. Mater. 32 (2022) 2110119. https://doi.org/10.1002/adfm.202110119 [2] J. Gusakova, et al., Electronic Properties of Bulk and Monolayer TMDs: Theoretical Study Within DFT 1700218. https://doi.org/10.1002/pssa.201700218. Framework Method), Phys. Status 214 (2017) (GVJ-2e Solidi A. [3] T. Yan, et al., Photoluminescence properties and exciton dynamics Appl. Phys. Lett. 105 (2014) 101901. https://doi.org/10.1063/1.4895471. in monolayer WSe2, 193

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MS3.P021 Characterization of two-dimensional transition metal dichalcogenides and their heterostructures by (S)TEM techniques M. Mohn1, A. Storm1, J. Köster1, T. Gorelik1,2,3, J. Schulz1, U. Kaiser1 1Ulm University, Central Facility Materials Science Electron Microscopy, Ulm, Germany 2Helmholtz Centre for Infection Research, Braunschweig, Germany 3Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Saarbrücken, Germany In recent years, two-dimensional transition metal dichalcogenides (2D TMDs) have been intensively studied to explore their electronic and optical properties. While basic research on these materials can be conducted with exfoliated monolayers and manually assembled heterostructures, the focus is more and more placed on the application of materials prepared with scalable bottom-up techniques such as chemical vapor deposition (CVD). However, CVD- grown materials can have very different quality in terms of defect densities, grain sizes, and the number of layers. In this study, we discuss how transmission electron microscopy techniques help to elucidate the relation between the growth parameters, atomic structure, number of layers, and electronic and optical properties of TMDs and their heterostructures. We investigate mono- and few-layer MoS2 and MoTe2, as well as lateral MoSe2-WSe2 heterostructures. The TEM techniques we apply include high-resolution TEM and STEM imaging at low voltages (20– 80 kV), electron diffraction, energy-dispersive X-ray spectroscopy (EDX), and electron energy-loss spectroscopy (EELS). The results from all techniques are compared with simulations. We first address the question of the exact number of layers in few-layer TMDs. We demonstrate that 3D electron diffraction and momentum-resolved EELS allow for unambiguous identification of 1–4 layers of MoS2 or MoTe2 [1]. Secondly, we show that the density of intrinsic defects in TMD monolayers can be obtained from atomically resolved Cc/Cs-corrected TEM images. The evaluation of the defect density can be performed very efficiently using convolutional neural networks, which can be trained using simulated TEM images and are able to identify atomic positions and chalcogen vacancies [2]. Thirdly and lastly, we evaluate that lateral heterostructures of monolayer TMDs can be best investigated with STEM, using the high-angle annular dark-field signal as well as EDX elemental mapping. These signals can be used to analyse the widths of interfaces between TMDs with different transition metals like Mo and W. In summary, a variety of TEM techniques have been used to study 2D TMDs and their heterostructures. Specific applications have been found for each technique, be it the determination of the number of layers, the analysis of intrinsic defects, or the width of interfaces in lateral heterostructures. We acknowledge funding from the European Union's Horizon 2020 research and innovation programme under Grant Agreement No. 881603 (GrapheneCore3). [1] J. Köster, A. Storm, et al., Micron 160, 103303 (2022). [2] J. Schulz, M.Sc. thesis, Ulm University (2022). 194

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MS3.P022 Locally excited plasmon resonances of size-selected silver nanoparticles K. Oldenburg1,2, I. Barke2,3, K. H. Meiwes-Broer1,2,3 1University of Rostock, ELMI-MV, Rostock, Germany 2University of Rostock, Department "Life, Light and Matter", Rostock, Germany 3University of Rostock, Institute of Physics, Rostock, Germany Based on their plasmonic properties, noble metal nanoparticles find many technical applications including solar cells, catalysis, cancer treatment, sensors amongst others. Since the characterization of small individual free clusters remains extremely challenging due to the low interaction cross-section with light, most analysis is done by averaging over many clusters. Alternatively, plasmon resonances have been studied for deposited nanoparticles where the dielectric environment influences the plasmon resonance leading to diverse observations in literature [1,2]. In this contribution, we want to reassess the intrinsic plasmonic properties of size selected gas-phase deposited silver nanoparticles in the size range of 10 nm and well below. By means of STEM-EELS we investigate the locally excited plasmonic response of individual nanoparticles. Figure 1 exemplarily shows a HAADF STEM image of a 4 nm silver nanoparticle at the edge of a carbon substrate. Clearly visible is its plasmon resonance in the electron energy loss spectrum. The results are discussed with respect to the inhomogeneous dielectric surrounding, i.e. the substrate and possible surface adsorbates. [1] A. Campos et al., Nature Physics 15 (2019), 275 [2] J. A. Scholl et al., Nature 483 (2012), 421 Figure 1: HAADF STEM image of a 4 nm silver nanoparticle at the edge of a carbon substrate together with the unprocessed electron energy loss spectrum taken at the marked position. Fig. 1 195

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MS3.P023 Solving complex nanostructures with ptychographic atomic electron tomography P. Pelz1,2,3, S. Griffin3, S. Stonemeyer4,5, D. Popple4,5,6,7, A. Zettl4,5,6,7, P. Ercius3, H. Devyldere2, M. Scott2,3, C. Ophus3 1Friedrich-Alexander-Universität Erlangen-Nürnberg, Materials Science, Nuremberg, Germany 2University of California, Berkeley, Materials Science & Engineering, Berkeley, CA, United States 3The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA, United States 4University of California, Berkeley, Physics, Berkeley, CA, United States 5University of California, Berkeley, Chemistry, Berkeley, CA, United States 6Kavli Energy NanoSciences Institute at the University of California at Berkeley, Physics, Berkeley, CA, United States 7Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States Knowledge of the three-dimensional atomic structure of natural and manufactured materials allows us to calculate their physical properties and deduce their function from first principles. Phase-contrast electron microscopy methods like ptychography are ideally suited to solve the 3D atomic structure of nanomaterials containing light and heavy elements. We perform mixed-state electron ptychography from 34.5 million diffraction patterns to reconstruct a high- resolution tilt series of a double wall-carbon nanotube (DW-CNT), encapsulating a complex ZrTe sandwich structure. Class averaging of the resulting reconstructions and subpixel localization of the atomic peaks in the reconstructed volume reveals the complex three-dimensional atomic structure of the core-shell heterostructure with 17 picometer precision. 196

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MS3.P024 Atomic-scale study of the number of graphene layer-dependent growth of cesium iodide cluster deposited by electrospray ion-beam deposition N. Vats1, U. Kaiser1 1University of Ulm, Electron Microscopy Group of Materials Science, Ulm, Germany The structure and morphology of an adsorbed atomic or molecular species depend critically on the interaction with the substrate that provides the energy landscape that governs the reaction dynamics and, in turn, influences the final product.1-4 Surprisingly we found in an earlier scanning transmission electron microscopy study that the morphology and size of the forming cesium iodide (CsI) clusters drastically changes when adsorbed on single layer graphene (SLG) or bi-layer graphene (BLG) surfaces.4 The formation of 2D-CsI crystals is observed explicitly on BLG and 3D- molecular clusters consisting of 4, 6, 7, and 8 atoms are only formed on SLG. As a possible hypothesis, the observed discrepancy in the adsorption behavior of the CsI clusters on SLG and BLG was discussed in the light of the presence of additional conjugated pi-electrons in the BLG, stimulating the growth of 2D crystals.4 However a thorough experimental study comparing the adsorption characteristic of CsI clusters in dependence on the numbers of graphene layers as well as on the TEM imaging parameters has not been performed so far. Here, we investigate the structure, chemistry, and stability of 2D-CsI crystals for varying number of graphene layers (1-5) using the sub-angstrom low-voltage electron microscope (SALVE) operated at electron accelerating voltages from 40 to 80 kV. We used commercially available CVD-grown single and bi-layer graphene on a copper foil (Graphenea S.A.). In the first step, copper foil is etched in an 8% ammonium persulfate solution. Then the SLG and BLG are transferred to the platinum coated (thickness ~ 10 nm) perforated silicon nitride TEM grid. Subsequently, by directly stacking another SLG or BLG onto the already transferred SLG/BLG onto a TEM grid, a combination of two, three, four, and five stacked layers of graphene sheets are prepared. In order to minimize the hydrocarbon contamination, the TEM grid was annealed at 300o C in the air for 30 minutes, where the platinum layer, deposited on the TEM grid, catalyzes the oxidation of the hydrocarbon contaminations. Finally, CsI cluster ions (MX)nM+ (where M and X represent the cation and anion, respectively) are deposited using the electrospray ion-beam deposition (ES- IBD) technique5 on free-standing graphene TEM grids under high vacuum conditions. In addition, we employ ab- initio calculations to gain comprehensive insight regarding the stability of 2D-CsI crystals to the underlying graphene sheets. In this work, we combine two unique techniques: low-voltage spherical and chromatic aberration-corrected transmission electron microscopy and highly pure, chemically selective deposition of mass-filtered molecular ion beams to further unravel the mystery of number of layer-dependent growth of 2D-CsI crystals. Furthermore, we anticipate that our atomically resolved number of graphene-layer-dependent and electron accelerating voltage- dependent analysis not only sheds light into the adsorption and growth behavior of CsI clusters but also helps to understand crystal growth of other alkali-iodide species on graphene. References: 1. Hardcastle, T. P., et al. Physical Review B 87.19 (2013): 195430. 2. Al Balushi, Z. Y., et al. Nature materials 15.11 (2016): 1166-1171. 3. Shi, G., et al. Nature Chemistry 10.7 (2018): 776-779. 4. Vats, N., et al. ACS nano 14.4 (2020): 4626-4635. 5. Rauschenbach, S., et al. small 2.4 (2006): 540-547. 197

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MS3.P025 Spatially-resolved properties of twisted 2D TMDs R. Leiter1, A. Storm1, B. Haas2, A. Eljarrat2, C. T. Koch2, U. Kaiser1 1Ulm University, Ulm, Germany 2Humboldt-Universität zu Berlin, Institut für Physik & IRIS Adlershof, Berlin, Germany Since the discovery of superconductivity in twisted bilayer graphene at a so-called magic angle [1], there has been an increasing interest in twisted bilayers of two-dimensional materials. Various interesting electronic and optical phenomena have been shown or predicted for these materials [2], and the pronounced moiré patterns occurring at certain twist angles [3,4] have led to the materials also being referred to as "moiré materials". Furthermore, it has been shown that for low twist angles (typically <2°), the moiré structure may deviate from the static lattice by forming large domains of differently stacked layers [5]. Here, we elucidate the difference in the low-loss EELS data between single-, bilayer, and twisted bilayer tungsten diselenide at both high and low twist angles. For the latter, we analyze the local variations in the low-loss EELS data in conjunction with high-resolution (S)TEM imaging in order to correlate effects of local strains originating from domain formation. We use mechanically exfoliated WSe2 samples deposited on SiO2 wafers, with a second layer stacked on top using a PMMA film. These are subsequently transferred to TEM grids using the KOH assisted method. For high-resolution TEM imaging, we use the Cc/Cs-corrected SALVE TEM operated at 80 kV in order to minimize beam damage. For high-resolution STEM-EELS spectral the aberration-corrected and monochromated NION HERMES STEM instrument operated at an acceleration voltage of 60 kV. imaging, we use Exciton peaks are fitted with Lorentzian functions on a linear background, which was adapted from the paradigm presented in [6]. We have developed a framework for analyzing exciton peak shifts of twisted bilayer TMD samples in low -loss EELS with high lateral resolution in order to match these shifts to features observed in the high-resolution TEM and STEM images. Care needs to be taken to avoid strong contamination, as we found that the exciton peaks vanish in the center of a trapped contamination bubble. In the case of a boundary between a single layer and a twisted bilayer of WSe2 at a twist angle of 8.7° (figure 1), investigation in high-resolution (S)TEM shows an atomically sharp, but jagged interface. When analyzing the scanning EELS data, we observe a reduction in the energy of the exciton peaks when crossing the boundary between the single layer and the bilayer region. Furthermore, comparing the maps of peak positions of the A and D excitons, respectively, we observe a broader transition area between the single- and bilayer for the former. We attribute this behavior to stronger delocalization at lower energies. In the next step, we correlate high-resolution (S)TEM images with mapped peak shifts originating from strain due to lattice reconstruction at low twist angles. Figure 1: 60 kV HAADF STEM image (a) and map of peak positions of A and D excitons (b and c, respectively), showing a broader transition area in the case of the A exciton. [1] Cao et al. Nature 556 (2018), 43–50 [2] Tran et al. Nature 567 (2019), 71–75 [3] Shallcross et al. Phys. Rev. B 81 (2010), 165105 [4] Campos-Delgado et al. Small 9 (2013), 3247-3251 [5] Weston et al. Nat. Nanotechnol. 15 (2020), 592–597 [6] Hong et al. Phys. Rev. Lett. 124 (2020), 087401 198

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MS4.001-invited Planar defects in non-stoichiometric SrFeO3-δ perovskite type thin films studied by analytical scanning transmission electron microscopy R. Erni1, M. D. Rossell1 1Empa, Swiss Federal Laboratories for Materials Science and Technology, Electron Microscopy Center, Dübendorf, Switzerland Strontium-ferrite (SFO), SrnFenO3n-1, provides a fascinating system in which stoichiometric changes can be explored in order to study their impact on the material's crystallographic structure, its properties, and, in particular, on defect formation. For n = 2, SFO adopts a brownmillerite-type structure of alternating layers of FeO6 octahedra and FeO4 tetrahedra with iron exclusively in +3 oxidation state. Increasing the oxygen content, with n = 4 and n = 8, SFO reveals tetragonal and orthorhombic structures with iron in +3 and +4 oxidation states (see, e.g., [2]). For the limiting case that n → ∞, SFO is found in the stoichiometric, cubic perovskite structure as SrFeO3, where Fe is uniquely in +4 oxidation state, forming the well-known FeO6 octahedra as building blocks of the perovskite structure. From a properties point- of-view, SFO is known to be a mixed ionic-electronic conductor and consequently, tuning the structure and defects provides a mean to control its conductivity. We present an experimental study of non-stoichiometric SrFeO3-δ, where the loss of oxygen (δ > 0) must lead to oxygen vacancies, possibly structural defects, and thus resulting in changes in the oxidation state of Fe as well. We used HAADF- and ABF-STEM to develop a structural model of planar defects, which run "packman"-style along {001} planes in the SFO film grown on SrTiO3, and which are formed due to the oxygen deficiency [2] (see Fig. 1). Atomic- resolution EDX spectroscopy reveals that the defective bands are formed by Fe2O2 double layers. The defects strongly resemble the Sr4Fe6O12+δ structure viewed along the pseudocubic [107] direction, which consists of bands of corner-sharing FeO6 octahedra separated by bands formed of periodically arranged FeO5 polyhedra identified as trigonal bipyramids and tetragonal pyramids, respectively. To assess the impact of these chemistry-driven structural defects on the physical properties, EELS was used to measure the Fe L3,2 and the O K excitation edges. Subtle but significant differences in the fine structure of the O K edge at the defect planes compared to bulk spectra were identified and interpreted by complementing the experimental data with simulations using FEFF9. This analysis suggests an increased electron doping of the Fe 3d e g bands in the Fe2O2 defect layers compared to the bulk SrFeO3, which as a consequence must affect SFO's electron- hole conductivity. Moreover, analysis of the Fe L3,2 excitation edge uncovers the expected change of the Fe oxidation state in the defective planes from +4 towards +3. In summary, STEM imaging combined with EDX and EELS measurements revealed the nature of planar defects present in SrFeO3-δ thin films grown on SrTiO3 and their effect on the electron-hole conductivity. Controlling the amount of oxygen vacancies in these perovskite-based SFO thin films thus allows the electronic conductivity of these films to be adjusted. Figure 1 HAADF STEM: overview (a) and detail (b) of the atomic structure of the planar defects formed in oxygen deficient, perovskite-type SrFeO3. References [1] M. D. Rossell, A. M. Abakumov, Q. M. Ramasse, R. Erni, ACS Nano 7 (2013) 3078-3085. [2] M. D. Rossell, P. Agrawal, M. Campanini, D. Passerone, R. Erni, Phys. Rev. Mater. 4 (2020) 075001. [3] P. Agrawal and D. Passerone are kindly acknowledged for providing support for interpretation of the FEFF9 data, and we would like to thank M. Campanini providing the script for peak-pair analysis. 200

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MS4.002 Tuning interface sharpness and interface superconductivity at La2CuO4 heterostructures Y. E. Suyolcu1, Y. M. Wu1, G. Kim1, G. Christiani1, B. Keimer1, G. Logvenov1, P. A. van Aken1 1Max Planck Institute for Solid State Research, Stuttgart, Germany Heterostructures of transition-metal oxides enable emerging unique physical properties at their interfaces [1]. The structural adaptability of La2CuO4 allows for designing different heterostructures, and superconductivity takes place at the interface between overdoped (metallic) and undoped (insulating) La2CuO4 layers grown by oxide molecular beam epitaxy (MBE)[2]. In addition to homo-epitaxial systems[3], heterogeneous multilayers of La2CuO4 with, for example, perovskite 113-type and 214-type lanthanum nickelate layers revealed the impact of the interface sharpness on thermoelectric and superconducting properties, respectively [4,5]. In this work, we fabricate (La,Sr)2CuO4–SrMnO3–LaMnO3–La2CuO4 superlattices [6] using oxide MBE and focus on the interface sharpness and the related superconducting mechanism compared to cuprate–cuprate interfaces. We use scanning transmission electron microscopy (STEM) techniques, including high-angle annular dark-field (HAADF) and annular bright-field (ABF) imaging, electron energy-loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDXS) to examine the interfaces. A JEOL JEM-ARM200F STEM equipped with a cold field-emission electron source, a probe Cs-corrector (DCOR, CEOS GmbH), a Gatan GIF Quantum ERS spectrometer and a large solid-angle JEOL Centurio SDD-type EDXS detector was used for atomic-resolution analyses. Our findings demonstrate that hetero-epitaxial cuprate–manganite layers can achieve sharper Sr-doped La2CuO4 interfaces. The dopant distribution in La2CuO4 is affected by the elemental intermixing in the first atomic LaMnO3 monolayer. We further underline that structurally sharp interfaces can be chemically rough (Fig. 1), and the chemical intermixing dominates the physical properties. Importantly, different superconducting behaviour (e.g., interface vs filamentary) can be customized with interfacial design [7]. References [1] Y. E. Suyolcu, G. Christiani, P. A. van Aken, G. Logvenov, J. Supercond. Nov. Magn. 2020, 33, 107. [2] A. Gozar, G. Logvenov, L. F. Kourkoutis, A. T. Bollinger, L. A. Giannuzzi, D. A. Muller, I. Bozovic, Nature 2008, 455, 782. [3] Y. E. Suyolcu, Y. Wang, F. Baiutti, A. Al-Temimy, G. Gregori, G. Cristiani, W. Sigle, J. Maier, P. A. van Aken, G. Logvenov, Sci. Rep. 2017, 7, 453. [4] F. Baiutti, G. Gregori, Y. E. Suyolcu, Y. Wang, G. Cristiani, W. Sigle, P. A. van Aken, G. Logvenov, J. Maier, Nanoscale 2018, 10, 8712. [5] P. Kaya, G. Gregori, F. Baiutti, P. Yordanov, Y. E. Suyolcu, G. Cristiani, F. Wrobel, E. Benckiser, B. Keimer, P. A. van Aken, H.-U. Habermeier, G. Logvenov, J. Maier, ACS Appl. Mater. Interfaces 2018. [6] G. Kim, Y. Khaydukov, M. Bluschke, Y. E. Suyolcu, G. Christiani, K. Son, C. Dietl, T. Keller, E. Weschke, P. A. van Aken, G. Logvenov, B. Keimer, Phys. Rev. Mater. 2019, 3, 084420. [7] This work has received funding the European Union's Horizon 2020 research and innovation programme under grant agreement No. 823717 – ESTEEM3. Figure 1. (a) STEM-HAADF image of a La2CuO4–SrMnO3–LaMnO3–La2CuO4 superlattice demonstrating coherent "A" and "B" interfaces. (b) EDX line-scan profiles reveal Cu (red) and Mn (green) intermixing at the interfaces. Sr (orange) and La (blue) profiles are given as guides indicating the individual layers. The blue arrow depicts the region of the acquired EDX line scan profiles. 202

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MS4.003 Spatially localized electronic states at the LaAlO3/TiO2 interface: mapping of a 2D electron gas M. Ederer1, M. Oberaigner2, G. Kothleitner2,3, S. Löffler1 1TU Wien, USTEM, Vienna, Austria 2Graz University of Technology, Institute of Electron Microscopy and Nanoanalysis, Graz, Austria 3Graz Centre for Electron Microscopy, Graz, Austria Perovskite heterostructures play an increasingly important role in optoelectronics applications, such as solar cells, LEDs and photo detectors [1]. The combination of two different semiconducting materials often leads to drastic changes of the electrical, magnetic or optical properties in the vicinity of the interface. Thus, full characterization of the localized electronic states is of utmost importance. We approach this goal with a combined ab-initio and experimental study of the electronic states localized at the LaAlO3/TiO2 interface. The material of interest is a heterostructure consisting of the cubic perovskite LaAlO3 and TiO2 in anatase phase. Bulk anatase is typically a semiconductor with a few eV wide direct band gap. In combination with LaAlO3, however, unoccupied states appear directly above the Fermi energy for 2-3 TiO2 layers closest to the interface. When a small energy window is chosen for imaging, similar to elemental mapping albeit with a window of 0.5 eV or even smaller, the localized electronic states can be mapped in real space [2]. We compare the experimental results to inelastic channeling simulations of a Ti-La terminated interface based on [3]. The simulated spectrum image for an energy loss of 456.4 eV can be seen in Figure 1(c). Ti atoms at least 1 unit cell from the interface show negligible intensity or no intensity at all and can therefore be considered "bulk-like" in this context. Ti atoms close to the Ti-La terminated interface, however, show significant intensity at this energy loss, which is especially apparent in the second atomic column from the interface. The orbital there resembles the shape of a dxy- orbital with x the horizontal axis and y the vertical axis in the figure. The experimental map of the Ti L3-edge onset pre- peaks lies in close agreement with the simulations (see Figure 1(b)). Due to the difficult mapping conditions presented by the low signal-to-noise ratio and due to elastic channeling, the original shape of the orbitals is not exactly reproduced. More importantly, however, the spatial confinement of the relevant electronic orbitals and the resulting local increase in intensity is clearly visible. Electrons occupying these states can, thus, be identified as a two-dimensional electron gas. The direct mapping of such an electron gas opens up new ways of investigating heterostructures in electronics with future application of understanding and designing new and improved optoelectronic materials. [4] Figure 1. (a) HAADF image of a 12 nm thick heterostructure oriented in the [100] crystallographic directions of both anatase TiO2 and LaTiO3 recorded at a high tension of 300 kV. (b) STEM-EELS spectrum image for a collection semi- angle of 24 mrad and an energy window at the Ti L3-edge onset. (c) Simulated spectrum image for an energy loss of 456.4 eV and a 1 unit cell thick sample with the same parameters as in (a) and (b). [1] Cheng et al., Adv. Optical Mater. 10, 2102224 (2022) [2] Löffler et al., Ultramicroscopy 177, 26 (2017) [3] Wang et al., Journal of Applied Physics 108, 113701 (2010) [4] The authors gratefully acknowledge funding from FWF under grant nr. I4309-N36. 204

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MS4.004-invited Probing the interplay of atomic structure and properties in perovskite oxide thin films D. T. L. Alexander1, C. Domínguez2, H. Meley2, L. Varbaro2, S. Gariglio2, J. M. Triscone2, B. Mundet1,2 1École Polytechnique Fédérale de Lausanne (EPFL), Electron Spectrometry and Microscopy Laboratory (LSME), Institute of Physics (IPHYS), Lausanne, Switzerland 2University of Geneva (UNIGE), Department of Quantum Matter Physics (DQMP), Geneva, Switzerland Perovskite-structured oxide thin films provide a fascinating playground for the study of condensed matter physics, owing to the strong coupling of lattice composition and structural distortions to functional properties. Here, we illustrate how recent developments in electron microscopy are vital for study of their structure–property relationships. Measurements are made in scanning transmission electron microscopy (STEM) mode using a double aberration- corrected FEI Titan Themis 60-300 at 200/300 kV. For measuring atomic structure, high angle annular dark field (HAADF) and annular dark field (ABF) 90° rotation image series are recorded, and then corrected for linear and non- linear scan distortions. Electron energy-loss spectroscopy (EELS) is carried out using a Gatan GIF Quantum ERS. Samples are prepared via mechanical polishing and broad ion beam milling, or by focused ion beam and lift out, and cleaned with an IBSS MCA. First, we look at NdNiO3/SmNiO3 superlattices, where macroscopic measurements of a metal-to-insulator transition (MIT) show an unexpected transition from two electronic phases to a single one as layer thickness decreases below a critical value. Using monochromated EELS to measure subtle changes in the Ni L3 and O K ionization edges, we not only confirm this behavior, but also map the electronic phases with a sub-nm spatial resolution [1]. STEM structure measurements show, however, that each layer retains the composition and lattice distortions of its parent lattice; a result that helps motivate a new Landau theory of electronic phase boundary energy [2]. To further study this behavior, we test decoupling the layers by incorporating LaAlO3 interlayers into the superlattices. Here, atomic resolution STEM is essential for diagnosing deposition problems and for measuring the coupling of structural distortions across interfaces; see Fig. 1. Lattice distortion connections next come to the fore in the study of LaVO3 films. STEM helps show how epitaxial strain plays a key role in determining the film's orientation, giving an out-of-plane orthorhombic long axis under the tensile strain set by a (110) DyScO3 substrate [3]. Since the DyScO3 instead has an orthorhombic long axis that is in-plane, such a film inherently forces an interface that couples the incommensurate oxygen octahedra rotations of the two orthorhombic orientations. Remarkably, STEM reveals this rotation-coupled interface forms within film, rather than at the substrate/film interface, creating a sharp 90° domain boundary within a single compound. Justified by second principles energetic simulations, this finding promises new avenues for creating novel functional properties [4]. In summary, we illustrate myriad ways that aberration-corrected STEM is critical for uncovering the interplay between atomic structure and physical properties in functional thin films. Looking towards the future, in order to achieve further insights, our aim is to couple these precision measurements with variable sample conditions. [1] B. Mundet et al., Nano Lett. 21, 2437 (2021). [2] C. Domínguez et al., Nat. Mater. 19, 1182 (2020). [3] H. Meley et al., APL Mater. 6, 046102 (2018). [4] D.T.L. Alexander et al., under review. Fig. 1. (a) HAADF STEM image of a NdNiO3/SmNiO3 superlattice with LaAlO3 interlayers. (b) depth profile of average Δy displacements of A-site cations from their "ideal" cubic positions (right) shows how each layer recovers the distortions of its parent compound. 206

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MS4.005 Microstructure-functionality relationships of pulsed laser deposited CuI thin films S. Selle1, P. Storm2,3, R. Busch1, M. Lorenz2, M. Grundmann2 1Fraunhofer IMWS, Microstructure of Optical Materials, Halle (Saale), Germany 2Felix Bloch Institute for Solid State Physics, Universität Leipzig, Leipzig, Germany 3Robert Bosch Semiconductor Manufacturing Dresden GmbH, Dresden, Germany In the field of transparent p-type semiconductors, copper iodide (CuI) holds an outstanding position. It combines high transparency in the visible spectral range with excellent hole transport properties [1]. To make CuI thin films suitable for complementary electronics, i. e. to develop CuI into an equivalent partner for well investigated transparent n-type semiconductors, control of electrical and morphological properties is required. Pulsed laser deposition (PLD) showed recently successful outcomes regarding film quality and systematic functionality tuning [2]. The use of powder-based targets allows a high flexibility regarding composition and can provide lateral and vertical composition gradients as well as controlled doping. With the possibility to change source targets in-situ, template layers can be grown to improve lattice match and surface smoothness due to the decrease of grain boundaries. This works focuses on the microstructural investigation of (doped) CuI films employing EBSD, SEM, FIB, TEM and STEM-EDX. The obtained results are used to explore microstructure-functionality relationships by linking XRD findings and electrical properties with the results gained by the aforementioned electron microscopy techniques. The first part of this work examines the impact of intentional p-doping with selenium (Se) on the film morphology. CuI with a lateral Se gradient was PLD grown on a two-inch diameter sapphire wafer. Site-specific TEM samples were prepared by focused ion beam (FIB) machining corresponding to a certain Se content. Whereas for each Se value, growth starts with the ´default´ zinc-blende γ-phase, high resolution TEM showed that a relatively high Se content seems to favor the CuI beta phase (trigonal crystal system) within the ongoing growth process. For a lower Se content, a new CuI phase, presumably with an up to now unpublished wurtzite 4H structure, was discovered with high- resolution TEM and related diffraction analysis (Fig. 1). This crystalline phase change also matches with results regarding XRD and electrical properties, where considerable changes occur for a selenium content above x(Se) = 1 at% [3]. The second part investigates the possibility to suppress rotational domains by employing PLD grown template layers such as sodium bromide (NaBr). By growing NaBr on cubic SrF2 (111) substrates before depositing the CuI thin film, a heterostructure was constructed where the moisture sensitivity of NaBr could be employed to obtain free standing CuI thin films. XRD phi-scans showed single-crystallinity and no occurrence of rotational domains up to 1-2 µm film thickness. Nevertheless, films need to be sufficiently thicker to be utilized as, for example, front-back device processing. Samples out of reasonable thick films could be prepared for EBSD to visualize domain orientation, SEM to depict surface roughness and TEM to analyze grain boundaries to examine the cross-section as well as the front- and backside of the CuI film. It was shown that for thicknesses above 1-2 µm, the single crystallinity gets lost, probably due to accumulation of defects during the PLD growth [4]. [1] M. Grundmann et al., phys. stat. sol. (a) 210, 1671-1703 (2013). [2] P. Storm et al., APL Mater. 8, 091115 (2020). [3] P. Storm et al., Phys. Status Solidi RRL 15(8), 202100214:1-6 (2021). [4] P. Storm et al., J. Mater. Chem. C 10, 4124-4127 (2022). Fig. 1: CuI:Se film with lateral Se composition gradient on 2-inch diameter c-sapphire wafer with marked position for FIB sample extraction (left). High-resolution TEM images 1,2, and 3 close to the interface substrate-film (right). 208

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MS4.006 Seeing structural evolution of organic molecular nano-crystallites using 4D- scanning confocal electron diffraction (4D-SCED) M. Wu1, C. Harreiß1, C. Ophus2, M. Johnson3, R. Fink3, E. Spiecker1 1Friedrich-Alexander-Universität Erlagnen-Nürnberg, Materials Science, Erlangen, Germany 2Lawrence Berkeley National Laboratory, National Center for Electron Microscopy, Berkeley, CA, United States 3Friedrich-Alexander-Universität Erlagnen-Nürnber, Department of Chemistry und Pharmacy, Erlangen, Germany Direct observation of organic molecular nanocrystals using electron microscopy is highly challenging, due to their radiation sensitivity and complex structure. 4D-STEM nano-beam diffraction (NBD) using small convergence α has been demonstrated to reveal the rich structural information in soft materials [1]. In this context, homogeneous beam- specimen interaction is desired to maximize dose/information efficiency before total structural damage, and spot diffraction signals are preferred for sensitivity and accuracy of Bragg peaks detection in dense reciprocal lattices typical in organic crystals. In NBD, the beam illuminates the sample with an Airy disk profile, and diffraction disks size is coupled to α, not optimized for dose efficiency and Bragg peaks detection due to spread signals and possible disks overlapping. Here, we introduce 4D-scanning confocal electron diffraction (4D-SCED) which combines high dose efficiency and high angular resolution. 4D-SCED applies defocused pencil beam illumination (Fig. 1b) on the sample and combines a confocal electron optic setup with a camera to record spot diffraction patterns (Fig. 1c). The defocused illumination reduces the dose with a homogenous beam sample interaction, and the confocal optics transfer spot-like diffraction signals, optimized for Bragg peaks detection. The spatial and angular resolution can be estimated using geometric considerations (Fig. 1d), which is largely decoupled from α. We first compare SCED and NBD with a single crystal thin film of 2D molecular α,ω-DH6T bilayer (fig. 1e-h). An order- of-magnitude higher diffraction signal is seen in SCED compared to NBD, enabling accurate Bragg peak detection for structural studies, e.g. layer rotation relation. We apply 4D-SCED to study an active layer in organic solar cells, DRCN5T:PC71BM BHJ thin films after solvent vapor annealing (Fig. 2a-c). With careful balancing spatial and angular resolution for the given dose budget, structural details of DRCN5T nano-crystallites oriented both in- and out-of-plane are imaged at ~5 nm resolution and dose budget of ~5 e-/Å2. Finally, we use 4D-SCED to study the structural evolution during thermal annealing by in situ heating the thin film in the TEM (Fig. 2d). The evolution of crystallite size (coarsening) and texture, as well as the progressive enrichment of PC71BM at interfaces are directly revealed [2]. The unique combination of high dose efficiency and high angular resolution makes 4D-SCED an ideal technique for studying beam-sensitive soft materials. The new possibilities of the technique are currently employed to explore further soft materials. Refs: [1] Bustillo, K., et. al., Acc. Chem. Res. 11 (2021) 2543 [2] Wu, M., et. al. Nat. Commun. 13 (2022) 2911 The authors acknowledge financial support from DFG via projects GRK1896 and SFB953. Work at the Molecular Foundry has been supported by U.S. DoE under contract No. DE-AC02-05CH11231. Fig 1. (a) STEM setup. (b) Defocusing the probe mitigates dose for beam-sensitive samples. (c) Scheme of SCED. (d) A geometric scheme for considering spatial and angular resolution. (e-h) Comparison of NBD and SCED applied to an α,ω-DH6T bilayer. Fig 2. Visualizing (a) edge-on (with color wheel) domain orientation and (b) face-on (grayscale) domain location of the donor crystals in DRCN5T:PCBM blends. (c) Mapping the whole area with 4D-SCED dataset. (d) The structural evolution of donor nano-crystallites during an in situ annealing experiment in the TEM. 210

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MS4.P001 The impact of rapid thermal annealing on ferroelectric HfO2 analyzed by conventional TEM in plan-view and in cross-section O. Gronenberg1, R. Marquardt2, U. Schürmann1, H. Kohlstedt2, L. Kienle1 1CAU, Institute for Material Science, Kiel, Germany 2CAU, Institute for Electrical Engineering and Information Engineering, Kiel, Germany Introduction HfO2 and related compounds attracted considerable interest for different non-volatile storage elements. The functionality and device performance of memory related applications is strongly affected by oxygen vacancies, which can stabilize the metastable ferroelectric phase of HfO21. The wake-up effect of ferroelectric HfO2 was attributed to defect related changes2, phase transitions3 and structural transformations4. Objectives Ferroelectric capacitors consisting of TiN electrodes and sputtered HfO2 on an 1 cm2 Si substrate showed different ferroelectric properties due to a temperature gradient during rapid thermal annealing (RTA). Devices from the hot corner had low remnant polarization of 10 µC/cm2 without changing during field cycling, while devices from the cold corner showed a strong wake-up effect with 0 µC/cm2 in pristine devices and up to 26 µC/cm2 after 106 cycles. TEM analysis of devices from both positions was applied to correlate the electrical characteristics with microstructural differences. Materials & methods These devices were prepared by reactive sputtered TiN electrodes and RF sputtered HfO2. TiN top electrodes were deposited after RTA and patterned with UV lithography. In the RTA set-up, approximately 600 °C were applied for 10 s in N2 atmosphere. IR thermal imaging after RTA revealed a thermal gradient due to a disaligned filament inside the projector lamp used for heating. Plan-view TEM samples from the hot and the cold corner were prepared by PIPS after the devices in the center were trained for 105 cycles with +/- 3 V (see Fig. 1). Additionally, cross-sectional TEM samples were prepared by FIB. TEM analysis in plan-view and in cross-section via electron diffraction (ED), HRTEM and EELS was correlated with the electrical characteristics. Fig. 1: The Si substrate with TiN/HfO2/TiN capacitors is shown on the left with trained devices marked with blue circles. On the right the PIPS sample is shown with two trained devices close to the hole. Results The combination of ED in plan-view and cross-sectional TEM analysis, revealed different microstructures and interfaces to the TiN top electrodes. At the interface to the TiN top electrode a TiOxNy interlayer was confirmed with EELS, which was thicker in the cold corner. Regarding the microstructure, the cold corner shows a stronger [110] texture while in the hot corner the <111> oriented grains became dominating due to Ostwald ripening. The in-plane polarization of the [110] textured HfO2 and the observed structural transformation of the ex situ trained devices hints towards a ferroelastic switching during wake-up. Conclusion In-depth structural characterization in close correlation with the electrical response of ferroelectric TiN/HfO2/TiN capacitors revealed a strong structural influence on the wake-up effect induced by a temperature gradient during RTA. The hot corner showed wake-up free remnent polarization due to increased <111> texture, while the cold corner has a strong wake-up effect due to [110] oriented grains with a pristine in-plane polarization. Gradual ferroelastic switching to [011] and [101] orientations increases the remnent polarization with field cycling. References 212

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MS4.P002 Epitaxial growth mechanism of magnetic Fe4N thin films - Intrinsic formation of metastable interface layers M. Kamp1, D. Seidler1, J. McCord1, L. Kienle1, R. M. Islam1 1Materials Science, Kiel, Germany Introduction Due to its ferromagnetic properties, γ´´-Fe4N can be applied in spintronic applications, while the microstructure and crystal orientation influence the switching behavior 1. The focus of this contribution is set on the deposition of epitaxial thin films on single-crystal substrates like MgO by reactive magnetron sputtering. In contrast to other physical or chemical vapor deposition methods (molecular beam epitaxy, electron beam physical vapor deposition, atomic layer deposition) 2, phase-pure epitaxial vapor deposition by magnetron sputtering is more challenging, however, this method is much more widely used and allows easier scaling of the production process. Objectives The analysis of the γ´´-Fe4N thin films allows to elucidate the growth conditions of epitaxial thin films. In particular, conclusions may be drawn about the nucleation phase of thin film growth by reactive DC magnetron sputter deposition. An interface layer, between the substrate and the film, might originate from a tetragonal distortion of the cubic γ´´-Fe4N crystal structure or a phase transformation with local variations in chemical composition. Materials & methods The microstructure, chemical composition, and the magnetic properties of γ´´-Fe4N thin films are investigated by XRD, vibrating sample magnetometry, magneto-optical microscopy, and spectrum imaging including high resolution scanning transmission electron microscopy, energy dispersive X-ray, and electron energy-loss spectroscopy. To verify the chemical composition of the thin (5 nm) interface layer, EDX and EELS spectroscopy has to be to be applied. Results The epitaxially grown γ´´-Fe4N thin films indicate the formation of an interface layer between the substrate and the thin film with a tetragonal distortion of the cubic crystal structure and a lower nitrogen concentration. This observation indicates the formation of a metastable tetragonal phase such as α´´-Fe8N 3. Next to the inhomogeneous interface layer, the epitaxial γ´´-Fe4N thin film is rotated against the substrate by 2.4° along the growth direction, which agrees with the observed tilting of cubic magnetocrystalline anisotropy. Conclusion The analysis of the chemical composition of the interfacial layer of γ´´-Fe4N thin films provide insight into the growth conditions of epitaxial thin films. In particular, the nucleation phase of thin film growth by reactive DC magnetron sputter deposition is investigated. The intrinsic interface layer shows a tetragonal distortion of the cubic γ´´-Fe4N crystal structure and a phase transformation with local variations in chemical composition. 1 Seema, P. Gupta, D. Kumar, V. R. Reddy and M. Gupta, Applied Surface Science Advances, 2021, 5, 100088. 2 N. I. M. Nadzri, D. M. S. Ibrahim and S. Sompon, IOP Conf. Ser.: Mater. Sci. Eng., 2019, 701, 012047. 3 I. Dirba, P. Komissinskiy, O. Gutfleisch and L. Alff, Journal of Applied Physics, 2015, 117, 173911. 214

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MS4.P003 Extended grain boundary structures in quasi-epitaxial TiN1-x electrode thin films grown on c-Al2O3 A. Zintler1, R. Winkler2, S. Petzold2, S. U. Sharath2, E. Bruder2, N. Kaiser2, L. Alff2, L. Molina-Luna2 1Karlsruher Institut für Technologie (KIT), Laboratorium für Elektronenmikroskopie, Karlsruhe, Germany 2Technische Universität Darmstadt, Materialwissenschaften, Darmstadt, Germany Titanium nitride (TiN) thin films are intensively studied in their application at room temperature (RT) as electrode materials in oxide electronics[1] and at low temperatures (LT) for microwave resonators and superconducting (SC) Josephson junctions.[2, 3] In these applications, low surface roughness, high electrical conductivity and high critical temperatures (TC) for SC applications are essential.[4] Here, TiN1-x films of 25 nm thickness have been deposited by reactive molecular beam epitaxy (RMBE) on c-cut sapphire substrates. For the sample series, increasing nitrogen deficiency was introduced by lowering the substrate temperature and increasing the Ti deposition rate. In their application as bottom electrodes in oxide electronic valence change memories (VCM) the nitrogen deficiency is discussed to enable electrical device performance.[5] Besides characterization of the RT and LT electrical conductivity, a scale bridging set of characterization methods has been employed to create a global (mm scale) down to atomistic (Å scale) understanding of the microstructure and resulting grain boundaries. Starting from X-ray diffraction (XRD) over backscatter electron (BSE) imaging and ion channeling contrast imaging (iCCI) and atomic resolution high-angle annular dark-field (HAADF) STEM imaging, a comprehensive analysis has been carried out. All samples showed highly textured out-of-plane growth (TiN (111)||Al2O3(001)) and two options for in-plane orientations, separated by 60°, for the TiN grains. iCC imaging revealed near identical grain sizes for all samples. For the low film thickness of 25 nm, the lateral grain size of over 100 nm indicated quasi-epitaxial growth introduced by domain matching epitaxy. The grain boundaries present are mainly twin boundaries of the <112> type. For the most deficient TiN0.7 sample, these twin boundaries emit <112> {111} stacking faults, resulting in a low transparency for electrical transport of the extended grain boundary. Critical temperatures of up to 4.9 K are reported for the first time for TiN films of low thickness on c-cut sapphire. Figure 1: (a,b) BSE images of the surfaces of the TiN (A) and TiN0.7 (B) thin film showing GBs in BSE contrast only for TiN0.7. (c,d) iCC images for the same samples, indication the two in-plane oriented grain types (60° in-plane rotation) and near identical grain sizes for both samples. (e,f) HAADF-STEM images of twin boundaries of the same samples, the TiN0.7 GB shows an extended GB structure resulting from the emission of stacking faults into the neighboring grain. (g) Temperature dependent resistivity measurements showing the anomalous increase in resistivity for the TiN0.7 sample and SC transition temperatures of the 25 nm TiN1-x films. [1] Sharath SU, Vogel S, et al., Adv. Funct. Mater. 31 (2017) 10.1002/adfm.201700432 [2] Gao R, Yu W, et al., Phys. Rev. Materials 3 (2022) 10.1103/PhysRevMaterials.6.036202 [3] Krockenberger Y, Karimoto S, et al., Journal of Applied Physics 8 (2012) 10.1063/1.4759019 [4] Zintler A, Eilhardt R, et al.,(2022) 10.1021/acsomega.1c05505 [5] Niu G, Calka P, et al., 3 (2019) 10.1080/21663831.2018.1561535 Fig. 1 215

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MS4.P004 Microstructure of GeTe-Sb2Te3 heterostructures grown by pulsed laser deposition S. Cremer1, L. Voss2, N. Braun1, L. Kienle2, A. Lotnyk1,3 1Leibniz Institute of Surface Engineering e.V. (IOM), Leipzig, Germany 2University of Kiel, Faculty of Engineering, Kiel, Germany 3Ningbo University, Laboratory of Infrared Materials and Devices, Ningbo, China Introduction: Ge-Sb-Te based phase change memory (PCM) is a highly promising technology for e.g., in memory or neuromorphic computing application. Relying on reversible amorphous-crystalline phase change, PCM is non-volatile, scalable, and fast. Heterostructured PCM show optimized performance, especially regarding power consumption and multi-level operation [1,2]. However, further investigations are necessary to understand in-detail the relationship of structure and properties. Objectives: The influence of systematically varying deposition parameters on the microstructure of GeTe-Sb2Te3 heterostructured thin films was investigated to comprehend their outstanding properties. Materials & methods: Non-periodic (npHS) and periodic (pHS) GeTe-Sb2Te3 heterostructures were deposited at room temperature by pulsed laser deposition (PLD). Detailed microstructure analysis was performed by combination of advanced transmission electron microscopy and X-Ray measurement techniques. Results: For the npHS a decreased laser fluence and number of pulses resulted in a decreased layer thickness which goes along with an increased intermixing and a composition approaching GeSb2Te4 (Fig. 1a-d). Unlike amorphous GeTe layers, the Sb2Te3 layers are nanocrystalline after PLD growth. Similar to fully crystalline Sb2Te3 [3], the nanocrystals consist of different defects like grain boundaries and bi-layer defects (Fig. 2a, b). Moreover, the grain size and crystalline phases vary (Fig. 2a, c). Apart from the known t- and c-phases, a vacancy-ordered (vo) phase was observed [4]. Similar to vo-Ge2Sb2Te5 [5], this structure transforms into the c-phase by electron beam exposure (Fig. 2d). Confirmed by XRD, overall, the Sb2Te3 layer mainly consists of {00l}-textured t-Sb2Te3 phase. Despite the small layer thickness, the layers of the pHS are still separated with alternating Sb- and Ge-rich layers, respectively (Fig. 1e- h). Conclusion: Whereas the layers intermixing depends on the deposition parameters and despite the room temperature deposition as well as the use of an amorphous substrate, as-grown Sb2Te3 layers are nanocrystalline while GeTe layers are amorphous in the HS. Since for Sb2Te3-GeSb2Te4-HS already an enhanced operation energy efficiency was reported [6], the results of the present work provide a starting point to establish structure-property relationships for PLD grown GeTe-Sb2Te3-HS in addition. References [1] T. C. Chong et al., Appl. Phys. Lett. 88, 122114 (2006). [2] L. Zhou et al., Adv. Electron. Mater. 6, 1900781 (2020). [3] J.-J. Wang et al., Phys. Status Solidi RRL 13, 1900320 (2019). [4] Y. Zheng et al., Nano Res. 9, 3453 (2016). [5] A. Lotnyk et al., Acta Mater. 105, 1 (2016). [6] J. Feng et al., ACS Appl. Mater. Interfaces 12, 33397 (2020). Acknowledgements We thank Mrs. A. Mill for assistance in the FIB preparation. This work was supported by the German Research Foundation (DFG 445693080). 216

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MS4.P005 Phase transitions in Cu-Sb2Te3 thin film systems induced by focused ion beam milling N. Braun1, V. Roddatis2, A. Mill1, S. Cremer1, H. Bryja1, L. Voss3, S. Sun4, L. Kienle3, W. Zhang4, A. Lotnyk1,5,6 1Leibniz Institute of Surface Engineering e.V. (IOM), Material Characterization and Analytical Service, Leipzig, Germany 2GFZ German Research Centre for Geosciences, Potsdam, Germany 3University of Kiel, Institute for Materials Science, Faculty of Engineering, Kiel, Germany 4Xi’an Jiaotong University, Center for Advancing Materials Performance from the Nanoscale, State Key Laboratory for Mechanical Behavior of Materials, Xi’an, China 5Ningbo University, Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies, Ningbo, China 6Harbin Engineering University, College of Physics and Optoelectronic Engineering, Harbin, China Specimen preparation for transmission electron microscopy (TEM) using focused ion beam (FIB) is a commonly used method [1]. While it offers many advantages over other methods, like site specific specimen preparation, it also suffers from many disadvantages. Artifacts induced by FIB range from ion implantation to thermal effects [2,3]. In this work, we study the impact of FIB milling on the microstructure of Cu (electrode)-Sb2Te3 (thin films) systems used for memory applications [4]. The influence of different factors such as ion beam current, layer stacking sequence, Sb2Te3 structure and layer thickness are evaluated. Sb2Te3 thin layers are epitaxially grown on p-type Si (111) substrates, while polycrystalline Sb2Te3 thin films are grown on SiO2 using pulsed laser deposition (PLD) [4]. Cu, Pt/Cu and Cr layers are deposited by magnetron sputtering on top of the Sb2Te3 layers. TEM specimens are prepared at varied beam currents using a standard cross-section FIB preparation method [1]. FIB specimens are investigated using advanced methods of aberration-corrected scanning TEM such as atomic-scale HAADF imaging and atomic-scale chemical analysis (EDX and EELS). In situ x-ray diffraction heating of the Cu-Sb2Te3 thin film is performed to confirm structural changes. Dependent on beam current used during FIB lamella preparation and Sb2Te3 layer thickness, hole formation in the Cu layer, thickness change and chemical changes of the Sb2Te3 layers are observed (Fig. 1). Samples with a 17 nm Sb2Te3 layer show uniform intercalation of Cu while a sample with 100 nm thick Sb2Te3 layer exhibits differential intercalation behavior. In specimen prepared from the in situ heated samples Sb2Te3 and Cu-Te grains are observed. The introduction of a Pt layer between the Cu electrode and Sb2Te3 layers hinders structural changes caused by FIB (Fig. 2). Moreover, Cr-Sb2Te3 and a Cu-GeTe layer systems show no modifications of Sb2Te3 and GeTe thin films during FIB preparation. In polycrystalline Sb2Te3 specimen the intercalation of Cu and formation of new phases is also observed. This work demonstrates that structural changes in Sb2Te3 thin film systems can be induced during FIB specimen preparation of Cu (electrode)-Sb2Te3 (thin films) systems. The changes are thermally induced transitions caused by FIB process due to local heating, while redeposition of Cu plays a minor role. The authors thank P. Hertel for magnetron sputtering. We acknowledge the financial support by the German Research Foundation (DFG 448667535). [1] T. Ishitani, et al., Microscopy 43.5 (1994): 322-326. [2] J. Mayer, et al., MRS bulletin 32.5 (2007): 400-407. [3] R. Schmied, et al., Physical Chemistry Chemical Physics (2014), 6153. [4] H. Bryja, et al., 2D Materials (2021), 045027. Fig. 1: (a) EDX Map of a lamella prepared with FIB, (b-c) Overview HAADF-STEM images of specimen prepared with normal and reduced FIB beam currents. (d) Atomic-resolution HAADF-STEM image showing new Cu-Te phases. Fig. 2: Cu/Pt/Sb2Te3 layer stack. (a) Overview HAADF-STEM image. (b) Overview EDX elemental map. (c) Atomic- resolution HAADF-STEM image, showing initial Sb2Te3 structure. 218

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MS4.P006 Diffusion processes in HfO2-based memristors investigated by in situ STEM and atom probe tomography R. Winkler1, T. Luo2, A. Zintler3, E. Matheret1, T. Jiang1, O. Recalde-Benitez1, D. Nasiou1, S. Petzold4, N. Kaiser4, E. Piros4, T. Vogel4, K. McKenna5, L. Alff4, B. Gault2,6, L. Molina-Luna1 1TU Darmstadt, Advanced Electron Microscopy, Institute of Materials Science, Department of Materials and Earth Sciences, Darmstadt, Germany 2Max-Planck-Institut für Eisenforschung, Atom Probe Tomography, Department Microstructure Physics and Alloy Design, Düsseldorf, Germany 3Karlsruher Institut für Technologie (KIT), Laboratorium für Elektronenmikroskopie, Karlsruhe, Germany 4TU Darmstadt, Advanced Thin Film Technology, Institute of Materials Science, Department of Materials and Earth Sciences, Darmstadt, Germany 5University of York, Department of Physics, York, United Kingdom 6Imperial College, Department of Materials, Royal School of Mines, London, United Kingdom Ionic movement is an essential part of Resistive Random Access Memory[1]. During resistive switching (RS) operations, the memory type determines the diffusing species: in the case of electrochemical metallization memory (ECM), the electrode material migrates and for the valence change memory (VCM) type, the oxygen anions and vacancies[2]. Moreover, the interfacial interactions in the metal-insulator-metal (MIM) RRAM cell can further impact RS[3]. To give insight into the diffusion processes for both ECM and VCM type HfO2-based memristors we have employed in situ scanning transmission electron microscopy (STEM) in combination with atom probe tomography (APT). The goal is to reveal the role of the microstructure of the insulator and the impact of the metal electrode on the ionic migration process. The investigated memristive devices consist of highly textured TiN (M) and HfO2 (I) thin films subsequently grown on c-cut sapphire by using reactive molecular beam epitaxy (RMBE), complemented by sputter deposition of Cu and Pt (M). These result in an ECM and VCM devices, respectively. From the VCM device, focused ion beam (FIB) lamellae for STEM and APT tips were prepared for a pristine device and a device that has been operated for 100 bipolar resistive switching (BRS) cycles. From the ECM device, FIB lamellae were transferred onto Micro Electrical Mechanical System (MEMS) based heating chips (DENSsolutions) for in situ STEM. For the BRS cycled VCM device, Figure 1 shows the Hf+O density variation retrieved from one APT data set overlaid on a medium-angle annular dark-field (MAADF) STEM plan view image of TiN. The highest variation occurs along a distinct line which, based on the feature size, is related to a TiN grain boundary (GBs). This indicates that the RS operation could be confined to the TiN GBs. For the ECM device, a low-loss electron energy loss spectroscopy (EELS) spectrum image (SI) map is overlaid on a cross-sectional high-angle annular dark field (HAADF) STEM image after in situ heating, shown in Figure 2. Cu diffusion started at ~350°C and the Cu feature in the EELS map at ~19.6 eV becomes present at a HfO2 GB. This demonstrates that Cu diffusion could primarily occur along GBs. We have shown that GBs influence and locally confine diffusion processes. For filament-type RS like in metal-oxide based memristor, this could lead to an improvement in variability and reliability by providing pre-defined diffusion pathways and thus, avoiding random diffusion. References: [1] R. Waser et al., Advanced Materials 21, 2632 (2009). [2] I. Valov, Semicond. Sci. Technol. 32, 093006 (2017). [3] S. R. Bradley et al., Microelectronic Engineering 109, 346 (2013). Figure 1: The Hf+O2 density variation retrieved from one APT data set for a VCM HfO2-based memristor cycled for 100 BRS operations shows the highest variation along a distinct line. As overlaid here with a plan-view MAADF STEM image from TiN it becomes clear, that the feature shown in the Hf+O density variation must be related to a TiN grain boundary based on the feature size. Figure 2: The EELS SI map overlaid on the cross-sectional AADFSTEM image of an ECM type HfO2-based memristor after in situ heating reveals, that the Cu feature located at ~19.6 eV becomes present at the grain boundary (GB). This showcases, that Cu should primarily diffuse along GBs. 220

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MS4.P007 Depicting atomic-resolution orbital occupation in hole doped high-tc superconducting superlattices N. Bonmassar1, G. Christiani1, G. Logvenov1, Y. E. Suyolcu1, P. A. van Aken1 1Max Planck Institute for Solid State Research, Stuttgart Center for Electron Microscopy, Stuttgart, Germany La2CuO4 changes from an antiferromagnetic Mott-insulator into a superconductor upon hole doping. This phase transition can be observed via spectral features in the pre-edge region of the O-K edge by means of electron energy- loss spectroscopy (EELS). The O-K energy-loss near-edge structures (ELNES) allow the direct probing of this hole doping with atomic resolution. We designed superlattices for the observation of evolving mobile carrier peaks (MCPs), the presence of the upper Hubbard band (UHB), and different Sr and Oxygen concentrations in direct proximity to each other. We link such electronic configurations and chemical distributions to the subsequent physical properties. Direct probing at the atomic-scale in order to differentiate between superconducting, metallic, and insulating parts in one single sample is unique, which to the best of our knowledge has not been shown before. This prospect, however, is of paramount interest for exploring future oxide-based quantum technologies, such as Josephson junctions. The two heterostructures presented here consist of five repetitions of a bilayer with four and three unit cells La2CuO4 (LCO) and one unit cell Sr2CuO3 (SCO) with an additional capping layer of three and four unit cells La2CuO4, respectively. All superlattices have been grown via molecular-beam epitaxy (MBE) monitored by in-situ reflection high- energy electron diffraction (RHEED) under an ozone atmosphere on a LaSrAlO4 (LSAO) (001)-oriented substrate. The samples have been characterized by resistance (R) versus temperature measurements, and scanning transmission electron microscopy (STEM); including EELS and high-angle annular dark-field (HAADF) imaging. Transport properties of both heterostructures (Fig. 1) yield critical temperatures (Tc) of 32K for the 5x[4LCO + SCO] and 40K for the 5x[3LCO + SCO] superlattices, respectively. Due to the chemical potential between LCO and SCO, different amounts of intermixing between La and Sr can be observed at the top and bottom interfaces. This leads to a partial formation of insulating areas without charge carriers, superconducting areas with mobile carriers, and metallic areas with mobile carriers and oxygen vacancies. These phase-separated sample regions are further discussed with respect to their orbital occupation via a combination of atomically resolved EELS mappings and O-K ELNES analyses (Fig. 2). Further investigations of the blue-shaded area in Figure 2 highlight differences in the out-of-plane and in- plane orbital occupation by the introduced electron holes. Here, we show for the first time that one can distinguish insulating, superconducting, and metallic areas within one single sample via O-K ELNES analyses and atomically resolved EELS. We want to highlight, that EELS experiments gave direct insights into the differences in orbital occupation of out-of-plane and in-plane orbitals, which open new possibilities for analyses of high-Tc superconductors answering open questions with respect to superconductivity. Figure1: Resistance vs temperature of the two superlattices 5x[3LCO + SCO] (blue), and 5x[4LCO + SCO] (red). Figure2: (a) 2D elemental EELS mapping (Sr: blue, Cu: green, La: red) of three different regions highlighting areas without Sr intermixing (red) and heavy Sr intermixing (blue). (b), (c) and (d) Gaussian fits with energy constraints for the MCP (blue) at 528 eV, the UHB (red) at 530.5 eV, and for the leading O-K edge-onset, a peak at 534 eV (turquoise). 222

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MS4.P008 Revealing the nanostructure of filamentary HfO2-based memristors by scanning precession electron diffraction (SPED) D. Nasiou1, A. Zintler2, R. Winkler1, T. Vogel3, T. Kim3, O. Recalde-Benitez1, T. Jiang1, L. Alff3, L. Molina-Luna1 1Technische Universität Darmstadt, Advanced Electron Microscopy, Darmstadt, Germany 2Karlsruher Institut für Technologie (KIT), Laboratorium für Elektronenmikroskopie, Karlsruhe, Germany 3Technische Universität Darmstadt, Advanced Thin Film Technology, Darmstadt, Germany Introduction: Resistive random-access memory (RRAM) devices are under intense research as they have low-power consumption, excellent scalability, enhanced storage density and, high speed operation [1]. The resistive switching phenomenon is thought to be governed by the formation and dissolution of a conductive nanofilament when a voltage is applied [2,3]. As previously investigated, the electrical behaviour of hafnia-based RRAM devices is correlated to the local crystallographic texture and microstructure [4]. Objectives: SPED was used to investigate two different Cu/HfO2/Pt RRAM devices. The layer structure is shown in fig1(a). The goal was to map the microstructure and establish a structure-property correlation. Materials & methods: By using reactive molecular beam epitaxy (RMBE) 20 nm thick HfO2 thin films were grown on top of sputtered Pt bottom electrodes. The top Cu electrode was deposited with different ways by an (i) ion beam etching (IBE) procedure and by (ii) simple lift out (SLO). Electron transparent cross sectional TEM lamellas were fabricated using a JEOL JIB 4600F Focused Ion Beam. For SPED acquisition, a scanning nanoprobe (in 2D real space) was controlled with a NanoMEGAS P1000 scanning unit integrated into a JEOL-ARM200F and a dynamic Medipix3 detector was used for synchronized electron diffraction patterns (EDP) acquisition (in 2D reciprocal space). Results: Experimental EDP was cross correlated and statistically matched with suitable simulated EDP with the software ASTAR to generate the orientation fig2(a,c) and phase fig2(b,d) maps. For both devices the orientation and grain size (5 -20 nm) of the dielectric is similar as they were grown under the same conditions. From the phase maps, the monoclinic phase of the HfO2 is revealed and matches to the XRD data. The results show that the Cu is homogeneously grown on the SLO devices and that it is not well distributed in the IBE devices. In the last ones, unexpected Pt traces were found which might have an influence on the electrical performance of the device. In fig1(b) the leakage currents of both devices are shown, in SLO the magnitude is lower than in IBE which could be due to the inhomogeneous Cu and the Pt traces on top of HfO2. Conclusion: The generated maps confirm the monoclinic phase of the HfO2 dielectric layer and reveal a similar grain distribution in both SLO and IBE devices. Also, from the phase maps, the SLO devices show well distributed layers which might explain their electrical performance. [1] Zahoor et al. Nanoscale Res Lett 15 (90) (2020) [2] R Waser et al., Adv. Mater. 21 (25–26) (2009) 2632-2663 [3] M. Lanza et al., Appl. Phys. Lett. 100 (12) (2012) 123508. [4] S. Petzold, A. Zintler et al., Adv. Electron. Mater. 5 (10) (2019) 1900484 The authors acknowledge funding from the ERC "Horizon 2020" Program under Grant No. 805359-FOXON and Grant No. 957521-STARE, from the DFG grant No. 384682067, from the BMBF under contract 16ESE0298 and 16MEE0154, from the DAAD, from the EPSCR and support by the framework of the the WAKeMeUP and StorAIge projects. Fig1: (a) The thin film stacks of the two different studied devices: IBE and SLO. (b) Their corresponding leakage current measurements. Fig2: SLO devices: (a) orientation map of Cu/HfO2/Pt device. Each colour reveals an orientation and (b) phase map of the three layers: Cu in red, m-HfO2 in blue and Pt in green. IBE devices: (c) orientation map and (d) phase map. Scale bar: 50 nm. 224

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MS4.P009 Study of local indium concentration in Ga(1-x)InxN quantum wells using quantitative scanning transmission electron microscopy D. Park1,2, J. Guckel1,2, P. Horenburg3, H. Bremers3,2, U. Rossow3, A. Hangleiter3,2, H. Bosse1,2 1Physikalische Technische Bundesanstalt, Braunschweig, Germany 2Laboratory of Emerging Nanometrology (LENA), Braunschweig, Germany 3Technische Universität Braunschweig, Institute of Applied Physics, Braunschweig, Germany Multiple quantum wells (MQW) and single quantum wells (SQW) of Ga(1-x)InxN on GaN are promising candidates for nanooptical light emitters due to high quantum efficiency. The band gap of Ga(1-x)InxN can be controlled over a wide wavelength range by tailoring the variation of the indium concentration [1]. In addition, the epitaxially grown quantum well structures can be easily modified using chemical etching for the formation of a pyramid containing quasi quantum dot structure. As the dimension of the quantum structure shrinks, the variation of the local indium concentration becomes detrimental to the optical properties. Therefore, a robust characterization technique is required to understand and optimize such complex structures on the atomic scale. In this study, a single quantum well of Ga(1-x)InxN between GaN layers on an Al2O3 substrate was grown using metal organic vapor phase epitaxy. The cross-sectional specimen was prepared using focused ion beam (FIB), including the final low kV milling step. The prepared specimen was characterized using a double-aberration corrected JEOL NeoARM 200F equipped with a cold field emission gun. We directly measured local lattice parameters based on the analysis of individual atomic column positions obtained from the high-angle annular dark-field (HAADF) image in real space. For a precise local lattice parameter analysis, drift-corrected HAADF imaging was utilized based on a sequential imaging technique with reasonably short acquisition time (1 sec/frame) accompanied by post rigid registration technique for drift correction between acquired images (Fig. 1). Then, the local indium concentration was derived using a modified Vegard's law including biaxial elastic strain effects. Fig. 2(a) shows the HAADF image of the epitaxially grown GaN/Ga(1-x)InxN/GaN structure and the individual indium contents derived using the modified Vegard's law is shown at the unit cell level in Fig. 2(b). The mean indium concentration inside the single quantum well from this analysis was 15.7 at. %, showing a very good agreement with the X-ray diffraction (XRD) analysis result. This result was compared with the local composition information obtained from a quantitative intensity analysis of the HAADF image. Absolute quantification of scanning transmission electron microscopy (STEM) - HAADF intensity (normalized intensity by the incident electron beam) was applied based on frozen phonon multislice calculation results [2]. The local thickness information obtained using position averaged convergent beam electron diffraction (PACBED) supported the quantitative intensity analysis [3]. In addition, the local composition information obtained from the intensity analysis was compared with the results from the quantitative STEM – electron energy-loss (EEL) spectroscopy analysis on the unit cell level. The combination of STEM imaging, PACBED and spatially resolved EEL spectroscopy techniques shows the validation of Vegard"s law for the Ga(1-x)InxN quantum well, providing more detailed information at the interfaces. The relationship between atomic structure and composition could be thoroughly studied. This robust combined STEM techniques will be ultimately applied to understand the effect of the changes in indium concentration on complex quantum dot structures. [1] U. Rossow et. al., Phys. Status Solidi B, 258, (2021) [2] J. LeBeau et. al., Physical review Letters, 100, (2008) [3] J. LeBeau et. al., Ultramicroscopy, 110(2), (2010) 226

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MS4.P010 Identification of a new structural polymorph of quenched high-pressure CrTe3 (P2/m) L. Voss1, M. Etter2, N. Gaida3, A. L. Hansen4, N. Wolff1, V. Duppel5, A. Lotnyk6,7, W. Bensch8, L. Kienle1 1Christian-Albrechts-University Kiel, Technical Faculty, Kiel, Germany 2Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany 3Nagoya University, Department of Materials Physics, Nagoya, Japan 4Karlsruher Institut of Technologie (KIT), Karlsruhe, Germany 5Max Planck Institute for Solid State Research, Stuttgart, Germany 6Leibniz Institute of Surface Engineering e.V. (IOM), Leipzig, Germany 7Laboratory of Infrared Materials and Devices, The Research Institute of Advanced Technologies, Zhejiang, China 8Christian-Albrechts-University Kiel, Inorganic Chemistry, Kiel, Germany CrTe (P21/c) is of potential interest for spintronic devices because of its layered structural motif and antiferromagnetic and semiconducting properties (Eg = 0.3 eV)[1]. Modifying these properties towards a ferromagnetic state and metallic-like conduction upon structure deformation is suggested by theoretical studies which describe a high strain sensitivity of the material when the dimensions are reduced to a monolayer of CrTe3 [2]. Such studies are motivation to investigate the CrTe3 system further. In the past, structural polymorphs of binary TE have been identified and described using high-p and high-T experiments as a vital approach to explore structural modifications with unprecedented properties [3,4]. In this work, the layered phase of CrTe3 was used as a starting material and subjected to pressures as high as 6GPa at an applied temperature of 250°C to investigate new structural polymorphs of CrTe3 and their magnetic properties. The structural polymorph of the quenched CrTe3 high-p phase was investigated by the combined methods of synchrotron radiation scattering experiments (PDF and XRD) and PED as well as atomic resolution STEM. Model- based simulations of STEM and ED data were conducted and compared with structural refinements by Rietveld analysis for structure determination. With our experiments, we were able to identify a phase transition from the monoclinic CrTe3 phase (P21/c) into a structural polymorph with space group P2/m. At first, the superposition of two potential structure candidates of CrTe2 (Pnn2) and CrTe4 (P21/m) were refined. These initial models were tested to PED data which excluded the CrTe2 model and suggested the introduction of a 1/3 occupied Cr position at the corners of the unit cell into the supposed CrTe4 structure to explain the kinematic intensity patterns. Further, large area EDX analysis confirmed the chemical homogeneity within large grains of the CrTe3 polymorph with stoichiometry of Cr:Te 1:3. The here proposed structure of the new polymorph after refinement to the synchrotron diffraction data is depicted in Figure 1. Atomic scale imaging by aberration corrected STEM supported the proposed model by imaging the Te sub-structure. In conclusion, a new structural polymorph of the CrTe3 system was identified after high-pressure synthesis and subsequent quenching by the combined approach of TEM and synchrotron diffraction. In ongoing research, first SQUID measurements indicate interesting changes of the magnetic properties which could provide similarities to the theoretical calculations made by Z.-W. Lu et al[2]. [1] M. A. McGuire et al., Phys. Rev. B, vol. 95, no. 14, p. 144421, Apr. 2017, doi: 10.1103/PhysRevB.95.144421. [2] Z.-W. Lu, S.-B. Qiu, W.-Q. Xie, X.-B. Yang, and Y.-J. Zhao, J. Appl. Phys., vol. 127, no. 3, p. 033903, Jan. 2020, doi: 10.1063/1.5126246. [3] A. Pawbake et al., Phys. Rev. Lett., vol. 122, no. 14, p. 145701, Apr. 2019, doi: 10.1103/PhysRevLett.122.145701. [4] W. C. Yu and P. J. Gielisse, Mater. Res. Bull., vol. 6, no. 7, pp. 621–638, Jul. 1971, doi: 10.1016/0025- 5408(71)90011-0. Figure 1: Crystal structure of the quenched high-pressure phase of CrTe3 with space group P2/m shown for a unit cell of 2x2x2 size. The corner-sharing motif can be best seen by a view along the crystallographic b-axis(a). Golden atoms are Te, blue are Cr. The edge-sharing motif and columnar ordering of the CrTe6 octahedra can be best seen by a view along the crystallographic c-axis (b). 228

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MS4.P011 Insight into the atomic structure and misfit relaxation mechanisms in micrometer-thick SrMoO3 oxide electrodes grown on scandate substrates T. Jiang1, O. Recalde-Benitez1, Y. Ruan1, T. Zhang1, F. Liang1, L. Alff1, P. Komissinsky1, L. Molina-Luna1 1TU Darmstadt, Darmstadt, Germany Introduction: Understanding the microstructure and related defect structures and their relationship with the physical properties is fundamental for the realization and optimization of oxide electronics-based devices. For instance, in the case of varactors or so-called metal-insulator-metal (MIM) tunable ferroelectric microwave capacitors, the tunable permittivity of the insulator layer and/or the thickness of the bottom oxide electrode exceeding the skin depth is crucial for its performance. To investigate the relationship between the thickness and other structural properties of these oxide thin films, i.e., alteration of stoichiometry and lattice constants, we performed Scanning Transmission Electron Microscopy along with X-ray diffraction (XRD) and Photoemission spectroscopy (PES). Objectives: We characterized a set of heterostructure multilayer devices (scandates/SrTiO3/SrMoO3) by STEM. For the analysis of the HAADF-STEM images we implemented an automated-quantitative STEM method that allows to analyze a set of real-space images to (i) extract atomic position information and (ii) to identify local structural defects. The goal was to provide insight into the underlying strain accommodation mechanism in micrometer-thick SrMoO3 (SMO) oxide electrodes grown on various scandate substrates. Materials and methods: The preparation procedure of the oxide-based multilayer devices can be found in P. Salg et al. [1]. The TEM lamellae were obtained using a JEOL JIB 4600F. For STEM, images with 5x5 frames along [001] and [100] directions of the epitaxial SMO layer were obtained using a JEOL ARM200F. Local in-plane/out-of-plane lattice constants were extracted along [001] growth direction by implementing customized codes, based on the python packages Atomap and Hyperspy. Picometer level precision was achieved. First principal calculations for SMO using density function theory (DFT) with the CASTEP package. Results: Both, XRD and STEM imaging (Fig.1a) confirmed the epitaxial growth (in-plane locked) of the SMO layer on top of all scandate substrates used. By performing automated-quantitative STEM analysis, atomic position information was obtained, as well as statistical out-of-plane/in-plane lattice constants (Fig.1b). The variation of this statistical lattice constants implies another strain accommodation mechanism, i.e., off stoichiometry, in heterostructure material in addition to interfacial defects. The DFT calculations for SMO layer confirmed the relationship between the variation of lattice constants and the off stoichiometry. Conclusions: A set of heterostructure multilayer devices were characterized by the combination of PES, XRD and STEM. The use of the automated-quantitative image analysis showed a reliable way to measure the local lattice constants with picometer-scale accuracy. Together with the help of DFT calculations, the relationship between the interfacial defects, the lattice constant, the off stoichiometry, and the accumulative strain was studied. References: [1] P. Salg, D. Walk and L. Zeinar et al., APL Mater., vol. 7 (2019), p. 051107. doi: 10.1063/1.5094855. The authors acknowledge funding from the ERC "Horizon 2020" Program under Grant No. 805359-FOXON and Grant No. 957521-STARE. Fig 1(a). HAADF-STEM image of heterostructure interface scandate/SrTiO3/SrMoO3. (b) Atom position information were extracted using customized codes based on the Atomap python package. 230

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MS4.P012 Ordering of scandium into monolayers of aluminium nitride and its implication for AlScN based nitride semiconductor devices U. Bläß1, M. Wu2, B. Epelbaum1, E. Meißner1,3 1Fraunhofer Institute for Integrated Systems and Device Technology (IISB), Erlangen, Germany 2Institute of Micro- and Nanostructure Research (IMN) & Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander- Universität Erlangen-Nürnberg, Erlangen, Germany 3Department of Electrical-Electronic-Communication Engineering, Chair of Electron Devices, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany Recently the incorporation of scandium (Sc) into aluminium nitride (AlN) attracted severe attention for III-V nitride semiconductors. The sufficiently larger ionic size of Sc increases significantly the spontaneous polarisation of AlN (1), which is e.g. responsible for the formation of a two dimensional electron gas at the heterojunction to another, compositional slightly different nitride compound (2). This allows to fabricate high-electron mobility transistors (HEMT) with very high switching frequencies and high efficiencies. However, the growths of well-crystalline AlScN material is impeded by a huge immiscibility gap between AlN and ScN. The material films deposited by magnetron sputtering or recently epitaxy are considered to exist only metastable (3). Intense annealing at temperatures beyond 1400°C for three hours, lead in this study to the formation of a layered structure of the compound, observed for the first time. The structural properties were intensely studies by atomic resolution STEM-HAADF images, EDS and EELS spectroscopy and will be reported in this contribution. The results from STEM-HAADF images show clearly that bright atomic monolayers are developed every 5-8 layers, after annealing at 1700°C. They run straight through the whole crystal and extend several µm (Fig. 1a) along the basal plane. Following EDS data, the bright appearance is due to an ordering of Sc into these layers (Fig. 1 b,c) coupled to a strong increase in oxygen content. The Sc coordination changes from four-fold in the wurtzite structure to six-fold as preferred by Sc. Whereas the sequence of cation positions in atomic STEM-HAADF images is strongly determined, the sequence of bright layers varies randomly between 5 and 8, leading to a partial disorder along c-direction. Further structural observations after annealing of samples at 1400°C allow some insight into their formation. Rarely platy seed of two octahedral Sc-bearing layers with only one intermittent AlN layers were observed. They are assumed to be thermodynamically favourable, similar to GdN platelets formed in Gd-doped GaN (4), but in contrast, significantly lower strain allows their two dimensional growths in the Sc-bearing system. Hence, this model of metastable formation resembles thermodynamical exsolution lamellae of mono-atomic widths. The presented observations are not only intriguing from a structural point of view, the obtained insight into the material behaviour has also implications on the growths of future ScAlN material for semiconductor devices as well as their long-time stability during device operation. References: • • • • (1) Akiyama et al., Adv. Mater. 21, 593–596 (2009). (2) Leone et al., Phys. Status Solidi RRL. 14, 1900535 (2020). (3) A. Moram and S. Zhang, J. Mater. Chem. A. 2, 6042–6050 (2014). (4) Wu et al., Acta Materialia. 76, 87–93 (2014). Fig. 1: Left: atomic resolution STEM-HAADF image showing bright Sc-bearing layers at variable distance. Right: EDS elemental distribution maps and integrated counts perpendicular the layers. 232

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MS4.P013 The effect of metal concentration and annealing temperature on the growth of ultrasmall metallic nanoparticles inside a silica matrix H. Jatav1, D. Kabiraj1, A. Mishra1 1Inter University Accelerator Centre, Materials science department, New Delhi, India The nanocomposites (NCs) comprising ultra-small metallic Nanoparticles (NPs) embedded in silica matrix are more stable over time than chemically grown NPs and have shown improved practical efficiency, leading to a wide range of applications in plasmonics, nano-photonics, bio-medical and catalysis due to Localized Surface Plasmon Resonance (LSPR) [1-2]. The stability of these ultra-small NPs (diameter < 10 nm) is essential for high-temperature applications [3].The LSPR frequencies associated with NPs are strongly dependent on particle morphology and metal concentration, thus knowledge about the effect of metal concentration and the growth mechanisms of NPs at different annealing temperatures (ATs) are crucial to controlling the morphology of NPs for application purposes. We have prepared Ag-SiO2 NC thin films using the atom beam co-sputtering technique at two different metal concentrations [4]. The evolution of silver NPs inside the silica matrix was discussed in Ref [4] utilising UV-Visible spectroscopy and High-Resolution Transmission Electron Microscopy (HRTEM) up to the annealing temperature of 400 °C. This work is now extended to the high annealing temperature of 900 °C. At each AT, HRTEM pictures, diffraction patterns, and STEM images are acquired to closely monitor the growth process of Ag NPs. A similar temperature-dependent growth investigation is also performed on Au and Au-Ag alloy NPs embedded in silica surrounds. For Ag-SiO2 NC, UV-Visible absorption spectra show a red shifting in the LSPR peak position, indicating the increase in the size of NPs with ATs. A quantum model simulation is combined with absorption results to estimate the size of the NPs at different ATs, suggesting the size of NPs is increasing. The morphological changes in NPs with ATs are monitored by HRTEM. We observed that the majority of the NPs are spherical in shape and remain in quantum size or ultra-small size regime (diameter < 10 nm). The diameter of the NPs varies from ~5 nm to 6.5 nm when the temperature rises from RT to 800 °C. However, exponential growth is observed at 900 °C. We observed that these ultra-small NPs have shown excellent stability up to the temperature of 800 °C, hence suitable for high-temperature applications. Similar primary results are observed for Au and Au-Ag alloy NCs, however, their detailed analysis is still ongoing. Based on the results, a three-stage mechanism is proposed to understand the process of nucleation and growth of the silica-embedded Ag NPs. References: [1] Campos, A., Troc, N., Cottancin, E., Pellarin, M., Weissker, H. C., Lermé, J.,& Hillenkamp, M. Nature Physics 2019, 15, 275-280. [2] Amendola, V., Pilot, R., Frasconi, M., Marago, OM. Iati, MA. Jour. of Phy.: Cond. Mat. 2017, 29, 203002. [3] Goodman, E.D., Carlson, E.Z., Dietze, E.M., Tahsini, N., Johnson, A., Aitbekova, A., Taylor, T.N., Plessow, P.N. and Cargnello, M., Nanoscale 13(2), 930-938 (2021) [4] Jatav, Hemant, Ambuj Mishra, and D. Kabiraj. Materials Today: Proceedings 57 (2022): 234-238. 234

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MS4.P014 Dimensionality-controlled interface properties in infinite-layer nickelate superlattices C. Yang1, Y. Wang1,2, W. Sigle1, R. A. Ortiz1, H. Wang1, E. Benckiser1, B. Keimer1, P. A. van Aken1 1Max Planck Institute for solid state research, Stuttgart, Germany 2Nanjing University of Aeronautics and Astronautics, Center for Microscopy and Analysis, Nanjing, China The interface polarity plays a vital role in physical properties of oxide heterointerfaces since it can enforce the reconstruction of the electronic and atomic structure. A strong polar interface possibly exists in recently discovered nickelate superconductors and the superconductivity is absent in its bulk material, attracting increasing attentions on interface effects [1-4]. This motivated our investigation of the electronic and atomic structure at atomic scale at the interfaces of infinite-layer nickelates. Recently, we reported that advancedfour-dimensional scanning transmission electron microscopy (4D-STEM) technique can provide clear phase-contrast imaging of the oxygen sublattice [5]. Here, by employing 4D-STEM and atomic-resolution electron energy-loss spectroscopy (EELS), we systematically studied the oxygen distribution and atomic structure at the interface of infinite-layer NdNiO2 (NNO) and SrTiO3 (STO). Figure 1a shows an HAADF image of a 4NNO/2STO superlattice, where the STO and NNO layers can be easily identified due to their distinctly different mean inner potentials. It has been well accepted that the infinite layer of NNO can be synthesized by the topotactic reduction method. In order to understand the deintercalation process of oxygen ions and the variation of oxygen concentration in NNO layers, we acquired all oxygen positions by Gaussian fitting and then extracted the oxygen intensity map as displayed in Figure 1d. The corresponding intensity line profile of apical oxygen is presented in Figure 1e, identifying the reduction procedure about the local symmetry variations from octahedral to square planar. By calculating the white-line ratio, we obtained the valence variations of Ni and Ti ions across the interfaces as shown in Figure 2. The valence of Ti intermixed on Ni sites for the 4NNO/2STO superlattice tends to be 3+ while it almost maintains 4+ for the 8NNO/4STO superlattice (Figure 2c and 2f). The Ni valence varies between 1+ and 2+ since it depends on the extent of deintercalation of the apical oxygen in the NNO inner layer. An apparent gradient variation of Ni valence is visible in the NNO layer for the 8NNO/4STO superlattice. Furthermore, we will discuss the effects of elemental intermixing, cation distortion, and oxygen distribution as well as occupancy on the observed valence variations near the interfaces. References [1] D. F. Li, et al. Nature 2019, 572 (7771), 624-627. [2] B. H. Goodge, et al. arXiv:2201.03613, 2022. [3] B. Geisler et al. Phys. Rev. B 2020, 102 (2), 020502. [4] R. He et al. arXiv:2006.00656, 2020. [5] C. Yang et al. Nano Lett. 2021, 21 (21), 9138-9145. [6] This project has received funding from the European Union"s Horizon 2020 research and innovation programme under Grant Agreement 823717 – ESTEEM3. Figure 1 Atomic structure of a 4NNO/2STO superlattice. (a) An overview HAADF image of a 4NNO/2STO superlattice. (b) An enlarged HAADF image and (c) the iCoM image obtained in the region marked by a yellow dashed box in (a). (d) The oxygen intensity map calculated from the oxygen columns in (c). (e) The extracted intensity line profile of apical oxygen columns from the white dashed line marked in (d). Figure 2 Valence variations of Ni and Ti ions in 4NNO/2STO and 8NNO/4STO superlattices. HAADF images of (a) the 4NNO/2STO superlattice and (d) the 8NNO/4STO superlattice. (b) Ni L3/L2 intensity ratio and (c) Ti L3/L2 intensity ratio of the 4NNO/2STO superlattice. (e) Ni L3/L2 intensity ratio and (f) Ti L3/L2 intensity ratio of the 8NNO/4STO superlattice. The references of Ni3+ and Ni1+ valences are from our NdNiO3 and NdNiO2 samples, respectively. The Ni2+ reference is from a NiO film in the Gatan EELS database. The Ti4+ reference is from our SrTiO3 sample. 235

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MS4.P015 Atomic-scale investigation of nickelate-based perovskite superlattices F. Misják1, R. A. Ortiz2, D. Geiger1, M. K. Kinyanjui1, E. Benckiser2, U. Kaiser1 1Ulm University, Central Facility of Electron Microscopy, Ulm, Germany 2Max Plank Institute for Solid State Research, Stuttgart, Germany Nickelate-perovskite heterostructures offer outstanding oppportunities to design technologically relevant structures with functionalities such as unconventional magnetic, electric, catalytic features and even the possibility of superconductivity [1]. The wide variety of fuctional properties stems from the strong hybridisation between the Ni d and oxygen p orbitals. Targetted manipulation of the oxygen environment of the Ni can be realised by structural distortions, which are associated with the deformation or rotations of oxygen octahedra of the perovkites [2]. Superlattices consisting of dissimilar perovskite-oxides offer several tuning parameters for direct control over the octahedral network. Besides the epitaxial strain, spatial confinement, octahedral connectivity and symmetry mismatch at the heterointerfaces can alter the crystal structure and induce sizable changes in the electronic properties. However, targetted design of properties through the orbital-lattice interaction is impeded by poor understanding of the heterostructuring parameters on the structure and their resultant effect on the orbital response. In order to disentagle the effects of heterostructuring parameters and understand the underlaying mechanisms, atomic scale investigation of the oxygen octahedral network is necessary. In this work, we investigated structural and transport properties of LaNiO3/LaGaO3 (LNO/LGO) superlattices (SLs). SLs with stacking sequences of LNO/LGO: 8/4, 4/4, and 4/8 pseudocubic unit cell were grown on (001) SrTiO3 substrate by pulsed-laser deposition. Cross-sectional HRTEM specimens were prepared by focused ion beam. Negative-spherical-aberration imaging was used to resolve the oxygen atomic columns using Cs-corrected HRTEM (FEI TITAN) operated at an electron accelerating voltage of 300 kV. Electrical transport measurements were performed in van-der-Pauw geometry. The results revealed, that the three stacking sequences of LNO/LGO stabilised different non-equilibrium states of the LNO. Within the LNO layers, we found significant variation in octahedral rotations and distortions in the vicinity of the LGO-LNO interface and away from the interface. We explained these results based on the varying contribution degree of epitaxial strain and spatial confinement by LGO on the structure evolution. The relative thickness ratio of the components also has an influence on the "strength" of the interfacial octahedral connectivity determining different structural distortions under the same epitaxial-strain condition. Thus the contribution of octahedral connectivity to epitaxial strain became tunable. Associated tunability of the electronic properties was comfirmed by transport measurements. The results show, that superlattices are effective platforms to optimize perovskite nickelate functionalities and manipulate the material properties in a controllable way. Acknowledgements We are grateful for financial support from DFG 323667265. We gratefully acknowledge Manuel Mundszinger for TEM sample preparation. [1] S. Catalano, M. Gibert, J. Fowlie, J. Íñiguez, J.-M. Tricone, and J. Kreisel, Rep. Prog. Phys., 2018 [2] J.M. Rondinelli, S.J. May, and J.W. Freeland, MRS Bulletin, 2012 237