Microscopy Conference 2023

Prof. Dr.

Session chairs

The session is focused on generating insights into the function of materials for energy storage, energy conversion and catalysis. Topics can be – but are not restricted to - charge transport, dynamics at interfaces (electrolyte/electrode or gas-phase/catalyst surface), cycling behavior and aging/deactivation. We are very interested in contributions that attempt to capture the relevant functional state of energy materials and catalysts, i.e., studies that reach beyond imaging of isolated systems in vacuum or investigations that employ an embedded multi-scale (in space and time) approach that allows to link between atomistic and collective dynamics. We also call for contributions regarding efficient detection of various generated signals, correlative application of analytical methods, as well as utilizing and developing quantitative data-analysis and machine learning. Studies on the impact of the electron beam for (in-situ) investigation of materials for energy-related or catalysis applications are also highly welcome.

Prof.

Probing local electrochemical and electrocatalytic processes in oxygen-evolving oxides in real-time

MS 1: Energy-related materials and catalysts

IM 7: In situ/operando electron microscopy

Abstract text (incl. figure legends and references) 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.

Invited talk

A new relativistic ultrafast electron diffraction and imaging (RUEDI) national facility for microscopic dynamics in the UK

IM 1: Progress in instrumentation and ultrafast EM

Abstract text (incl. figure legends and references) 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. 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. Materials &amp; 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. Results &amp; Conclusion: We are developing RUEDI facility to elucidate static and dynamic structures in systems those are difficult be studied with current techniques. RUEDI will be applied to systems such as thick specimens, complex sample environments, and sub-100 femtosecond dynamics. References: [1] RUEDI is supported by EPSRC / UK Infrastructure Fund under grant number EP/W033852/1.

Unraveling (de)lithiation dynamics inside graphene sheets at atomic scale

Abstract text (incl. figure legends and references) 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.

Abstract talk

Imaging structural defects and associated oxygen positions in Li-rich Li1.2Ni0.13Mn0.54Co0.13O2

IM 6: Phase-related techniques & 4D STEM

Abstract text (incl. figure legends and references) 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 (&lt;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.

Establishing in-situ heating experiments of monolithic LiNiO2 particles in O2 atmosphere

Abstract text (incl. figure legends and references) 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&quot; 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)

Low dose STEM imaging and in situ TEM of metal halide perovskites

Abstract text (incl. figure legends and references) 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 [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)

MS 1a
Energy-related materials and catalysts I

Appointment

Session chairs

Description

Programme

MS 1aEnergy-related materials and catalysts I

Appointment

Session chairs

Description

Programme

MS 1a
Energy-related materials and catalysts I