Friday Lectures

Misha Mychinko

Advanced Electron Tomography to Investigate the Growth and Stability of Complex Metal Nanoparticles

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

During the past decades, metallic nanoparticles (NPs) have attracted great attention in materials science due to their specific optical properties based on surface plasmon resonances. Because of these phenomena, plasmonic NPs (or nanoplasmonics) are very promising for application in biosensing, photocatalysis, medicine, data storage, solar energy conversion, etc. Currently, colloidal synthesis techniques enable scientists to routinely produce mono and bimetallic NPs of various shapes, sizes, composition, and elemental distribution, with superior properties for plasmonic applications. Two primary directions for further advancing nanoplasmonic-based technologies include synthesizing novel morphologies, such as highly asymmetric chiral NPs, and gaining deeper insights into the factors affecting the stability of produced nanoplasmonics.

With the increasing complexity of nanoplasmonics morphologies and higher stability requirements, there is a pressing need for thorough investigations into their 3D structures and their evolution under different conditions, with high spatial resolution. Electron tomography (ET) emerges as an ideal tool to retrieve shape and element-sensitive information about individual nanoparticles in 3D, achieving spatial resolution down to the atomic level. Moreover, ET techniques can be combined with in situ holders, enabling detailed studies of processes mimicking real applications of nanoplasmonic-based devices.

The first part of my presentation will focus on detailed studies of chiral Au NPs, promising for spectroscopy techniques based on the differential absorption of left- and right-handed circularly polarized light. Specifically, I will discuss the primary strategies for wet-colloidal growth of the various types of intrinsically chiral Au NPs. Advanced ET methods, such as high-resolution ET or HAADF-STEM ET combined with electron diffraction tomography (3D-ED), will be demonstrated as powerful tools for characterizing the final helical morphologies of the produced Au NPs and for studying the chiral growth mechanism by examining intermediate structures obtained during chiral growth.

The second part will focus on the heat-induced stability of various Au@Ag core-shell NPs. Operating in real conditions, such as elevated temperatures, may cause particle reshaping and redistribution of metals between the core and shell, gradually altering nanoplasmonics properties. Hence, a thorough understanding of the influence of size, shape, and defects on these processes is crucial for further developments. Recently developed techniques, combining fast HAADF-STEM ET with in-situ heating holders, have allowed me to evaluate the influence of various parameters (size, shape, defect structure) on heat-induced elemental redistribution in Au@Ag core-shell nanoparticles qualitatively and quantitatively. Additionally, I will discuss the prospects of high-resolution ET for visualizing the diffusion of individual atoms within complex nanostructures.

Christoph Hofer

Can we measure the redistribution of electrons between atoms due to bonding?  

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

Chemical bonding between atoms in a material involves the redistribution of electrons. Detecting this effect is far more challenging than imaging the atomic structure because bonding only involves a small perturbation of the total charge density dominated by the atomic nuclei. This requires an atomic-resolution imaging method which is highly sensitive to the electron charge. In this talk, we show how electron ptychography is capable of detecting small changes of the phase as a result of electron redistribution at the atomic scale. Compared to other methods, ptychography has the possibility of correcting residual aberrations which can alter the atomic phase and might lead to wrong interpretation of the images. Equally crucial, we developed a new method to quantify phases in atomic resolution phase images which is robust to unwanted experimental disturbances. Experimentally, we quantify the atomic phases of monolayer WS2 and show a significant bonding effect in both, pristine an defective configurations.

Yi-Chieh Yang

Introducing Thermal Gradients during In Situ TEM Heating Experiments  

National Center for Nano Fabrication and Characterization (DTU Nanolab), Technical University of Denmark (DTU), Kgs. Lyngby, Denmark 

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

Nowadays, microelectromechanical system (MEMS)-type microheaters enable very accurate control of local temperature during in situ TEM experiments. So far, these heating experiments can only be carried out with a homogeneous temperature distribution over the area of interest. However, in certain engineering and manufacturing applications such as additive manufacturing (AM) and semiconductor device operations, materials experience non steady state conditions far from thermal equilibrium, such as fast cooling/heating rates and exposure to high thermal gradients. To study these specific thermally activated processes in a TEM, here, we report a method to introduce thermal gradients across a specimen during in situ TEM heating experiments, relevant, e.g. to study microstructural evolution in metal materials under far-from-equilibrium AM process conditions. This was achieved by using a commercially available MEMS-based microheater but placing the TEM sample over a special, by focused ion beam (FIB) milling, cut window adjacent to the actual heater. By the technique, we aim at obtaining a depth understanding of non-equilibrium process conditions and their effect on the resulting microstructure in the material. Additionally, we predict the temperature distribution by the finite element analysis and are inclined to utilize ex situ Raman spectroscopy and in situ plasmon energy expansion thermometry (PEET) to measure the actual temperature (thermal gradient) of the lamella itself to confirm our findings.

By Robin Girod

Multidimensional Electron Imaging of Fuel Cell Catalyst Layer Materials 

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

Proton exchange membrane fuel cells (PEMFCs) are envisioned as an alternative to engines in heavy-duty vehicles. However, for cost and performance competitiveness, improvements

are still required in efficiency and durability. Optimisation of the complex structure of the multicomponent cathode catalyst layers (CL), where electrochemical reactions take place, is a promising strategy to conciliate these needs. Yet, much of the morphology of these layers remains poorly known, calling for advances in characterisation at the nanoscale.

CLs are typically made of Pt nanocatalysts (NCs) supported on porous carbon black supports (Pt/C) and include an ion-conductive binder. To understand the interactions of these components, three-dimensional imaging is required, individual NCs must be resolved and careful consideration to the electron dose must be given. In addition, the operative conditions of CLs are far from equilibrium and in situ experiments are therefore of high value.

In light of these challenges, I will present in this talk our investigations of CL materials with electron tomography (ET) and in situ electrochemical liquid phase (ec-LP)TEM. I will first show how the combination of ET at cryogenic temperature, low-dose imaging and deep-learning tools for image restoration and segmentation enabled the quantitative analysis of all three CL’s components simultaneously. Then, a method for high resolution ET of Pt/C particles using full range tilting enabled by a novel sample preparation will be demonstrated. The results provided insights into the diffusion of reactants into porous carbons and open the way for fundamental studies of carbon nanopores. Finally, I will present our recent progress towards electrochemical cycling of Pt catalysts inside the TEM to study their degradation mechanisms in real time. Taken together, these results will demonstrate how multidimensional TEM can aid the development of improved PEMFC.

By Qiang Lu

Synergy of multiple precipitate/matrix interface structures for a heat resistant high-strength Al alloy 

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

High strength aluminum alloys are widely used but their strength is reduced as nano-precipitates coarsen rapidly in medium and high temperatures, which greatly limits their application. Single solute segregation layers at precipitate/matrix interfaces are not satisfactory in stabilizing precipitates. Here we obtain multiple interface structures in an Al-Cu-Mg-Ag-Si-Sc alloy including Sc segregation layers, C and L phases as well as a newly discovered χ-AgMg phase, which partially cover the θ′ precipitates. By atomic resolution characterizations and ab initio calculations, such interface structures have been confirmed to synergistically retard coarsening of precipitates. Therefore, the designed alloy shows the best combination of heat resistance and strength among all series of Al alloys, with 97% yield strength retained after thermal exposure, which is as high as 400 MPa. In addition, combined with ex-situ TEM characterization results performed at EMAT, it is further verified that the thermal stability of the C interface phase is better than that of the χ-AgMg interface phase and can more effectively hinder the coarsening of θ′ precipitates. In this Friday lecture, I will discuss what I have found so far and research plan I will do at EMAT. 

By Francisco Vega

Exploring Adaptive Optics in the Transmission Electron Microscope

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

In light optics, many different applications have seen a revolution with the introduction of the spatial light modulator. These tools allow the user to arbitrarily shape light waves to maximize the efficiency of the measurement or, in other words, the information transferred onto the detecting device.

We explore the possibility of using a tool similar to spatial light modulators in the electron microscope, taking inspiration from their success in light microscopy. To achieve this, we designed an electrostatic phase plate consisting of 48 individual phase pixels capable of shaping coherent electron waves. We provide a detailed analysis of the device's response and then discuss some theoretical and experimental results showing the potential applications of the phase plate for electron microscopy, including aberration correction, self-tuning, novel imaging routines, and phase-programmed ptychography.

References

1. Bliokh, K. Y., et. al. (2023). Roadmap on structured waves. ArXiv. /abs/2301.05349
2. Verbeeck, J., Béché, A., Guzzinati, G., Luong, M. A., & Hertog, M. D. (2017). Demonstration of a 2x2 programmable phase plate for electrons. ArXiv. /abs/1711.11373.
3. Ibáñez, F. V., Béché, A., & Verbeeck, J. (2022). Can a Programmable Phase Plate Serve as an Aberration Corrector in the Transmission Electron Microscope (TEM)? ArXiv. https://doi.org/10.1017/S1431927622012260
4. Yu, C., Ibañez, F. V., Béché, A., & Verbeeck, J. (2023). Quantum Wavefront Shaping with a 48-element Programmable Phase Plate for Electrons. ArXiv. /abs/2308.16304.

By Romy Poppe

Quantitative comparison between the diffuse scattering from single-crystal X-ray and single-crystal electron diffraction

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

 In contrast to perfectly periodic crystals, materials with short-range order produce diffraction patterns that contain both Bragg reflections and diffuse scattering. As short-range order lies at the origin of the physical properties of a compound, many open questions in materials science are related to it. Our study shows, for the first time, a quantitative comparison between single-crystal electron and single-crystal X-ray diffraction, both for the Bragg reflections ánd the diffuse scattering. The single-crystal electron diffraction data were acquired using threedimensional electron diffraction (3D ED), for which the amount of multiple scattering is drastically reduced compared to in-zone electron diffraction patterns. Single-crystal electron diffraction allows the study of nanometre-sized crystals, which are too small to be studied with single-crystal X-ray diffraction. Both electron and X-ray diffraction data were acquired on single crystals of the thermoelectric Nb0.83CoSb. The average structure (occupancies and relaxations) was refined from the Bragg reflections, whereas the local structure (the vacancy distribution) was refined from the diffuse scattering. A model of the short-range order in Nb0.83CoSb was created by assuming that nearest and next-nearest neighbour vacancies avoid each other. Relaxations of the Co and Sb atoms around the vacancies were also included in the model. An evolutionary refinement algorithm in DISCUS was used to refine the correlations between the first and next-nearest neighbour vacancies. A good agreement was achieved between the simulated and the experimental intensity distribution of the diffuse scattering (Fig. 1). The 3D-∆PDF of the simulated 3D diffuse scattering also agrees well with the 3D-∆PDF of the experimental 3D diffuse scattering. We can thus conclude that short-range order parameters can successfully be refined from the diffuse scattering in both single-crystal X-ray and single-crystal electron diffraction data. We will also show that the model of the short-range order in Nb0.83CoSb can easily be applied to determine the short-range order parameters in other materials with similar diffuse scattering, such as the lithium-ion battery cathode material LiNi0.5Sn0.3Co0.2O2

By Matthias Quintelier

In situ TEM studies of potential catalysts and catalyst holder materials for CO2 Reduction Reactions

Practical

• location (online link) by invitation only
• Time: 11:30

Abstract

Carbon dioxide (CO­2) is a prominent greenhouse gas driving climate change and global warming. As a society, we should not only try to reduce our output of this gas, but also to convert and reduce this gas into less harmful products to increase sustainability. The 4AirCRAFT initiative, a Horizon 2020 project, endeavours to advance sustainability by developing novel chemical and electrocatalysts, catalyst carriers, and advanced reactors.

Layered Double Hydroxides (LDHs) and Metal Organic Frameworks (MOFs) are promising candidates for these catalysts and carriers. However, their properties strongly depend on their atomic structure. Despite existing studies describing these structures, limited in situ direct observations hinder our understanding and potential applications of these materials. This knowledge gap underlines the significance of our TEM experiments.

In this EMAT lecture, I will delve into the challenges, breakthroughs, and insights learned from my in situ High Resolution TEM (HRTEM) and 3D Electron Diffraction (3DED) TEM research. Firstly, I will make a comparison between different detectors for 3DED on beam sensitive materials like MOFs, after which I will talk about challenges and the structural evolution during an in situ TEM activation experiment of Zn-MOF-74. Lastly, I will talk about challenges and strategies for the in situ heating and CO2 absorption studies with LDHs. Furthermore, I will outline future experiments using the in situ gas holder for CO2, offering a perspective on the possibilities of in situ studies with the TEM on these materials.

This project has received funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No 101022633. This project is supported by Japan Science and Technology Agency (JST) (Grant Agreement No JPMJSC2102) and São Paulo Research Foundation (FAPESP) (Grant number 2022/04751-0).