Friday Lectures

by Nadine Schrenker

Correlation of doping, microstructure, and morphology in perovskite systems

Practical

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

Abstract

Metal halide perovskites (MHPs) are highly promising semiconductors for novel optoelectronic devices. Doping has been explored as a promising approach to control the electronic, magnetic, and optical performances of NCs. Lanthanide (e.g., Yb3+) doped MHP NCs show exceptionally high near-infrared photoluminescence quantum yields (PLQYs), and the lanthanide dopants promote phenomena of photomultiplication. Therefore, the objectives of my research stay at Monash University (Melbourne, Australia) were to understand the role of lanthanide doping in CsPbCl3 NCs and correlate the local microstructural insights with the optical properties. Via quantitative low-dose TEM experiments, it was observed that the CsPbCl3 NCs contain Ruddlesden-Popper (RP) phases, i.e., the structure is composed of n layers of CsPbCl3 unit cells that are separated by an additional CsCl layer. Moreover, the density of the RP defects decreases significantly for small NCs, which indicates that the RP defects compensate for strain in larger NCs.  The occurring RP defect configurations were also studied as a function of the added dopant (Mn2+ and Yb3+) and as a function of the initial synthesis conditions. The correlation of TEM investigations and optical measurements revealed that a slight Cs-excess in the precursor solution results in optimized optical properties despite a high density of RP defects.

In addition, prospectively combining perovskites and chirality will enable circularized polarized light emission or detection in novel optoelectronic devices. Two promising approaches to achieve chiral perovskites are through chiral cations or a chiral morphology of assembled nanocrystals. However, detailed mechanisms behind the chirality transfer, when chiral cations are used, are not yet fully understood and require more research at atomic scale. Therefore, the goal of this current project is to investigate the local structure of chiral perovskites via advanced 4D-STEM and tomography methods.

by Francisco Vega

Exploring Adaptive Optics in the Transmission Electron Microscope

Practical

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

Abstract

Over the years, electron microscopes (EM) have evolved from basic imaging and magnification tools into versatile characterization instruments. They are now capable of reaching atomic resolution, reconstructing nanoparticles down to the atomic-position level, capturing dynamic processes in real time, resolving internal strains in crystal structures, and obtaining chemical compositions of various materials and alloys, among others.

All the applications mentioned above are largely enabled by the multidimensionality that can be achieved with the active elements within the EM column, i.e., the ability to control the electron wavefront as it propagates before and after its interaction with the sample. 

However, this multidimensionality is relatively limited compared to what can be achieved in other fields, such as light optics. There, the spatial light modulator (SLM) has revolutionized the field by introducing a position-dependent phase shift in the wavefront. In contrast, wavefront shaping in electron microscopy is significantly constrained by the spatial and physical limitations imposed on its active elements. 

Building on the capabilities provided by the multidimensional nature of the EM and motivated by the advancements in optics introduced by SLMs, the primary goal of this work is to develop a tool that enhances the multi-dimensional manipulation of wavefronts in electron optics. 

After designing and characterizing a spatial electron modulator (electrostatic phase plate), we will discuss the potential applications of this advanced wavefront shaping technology. Integrating this technology into the EM could enhance its capabilities and address current challenges in phase retrieval and the characterization of soft matter.

by Min Tang

Using in situ TEM to investigate the dynamic evolutions of Ni-TiO2 catalyst under oxidating and reducing conditions

Practical

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

Abstract

Oxide-supported Ni catalysts are critical for a wide range of industrial manufacturing processes of fuels, chemicals and materials. It is now generally accepted that support materials are not inert and typically interact with Ni nanoparticles (NPs) through various routes, which significantly affects the properties of the solid catalysts. In particular, strong metal-support interaction (SMSI) refers to Ni NPs covered by overlayers from reducible oxide supports, such as TiO2, under high-temperature reduction. SMSI has been widely used to tune catalytic performances, including activity, selectivity, and stability for various chemical reactions. So far, most studies have investigated SMSI after pretreatment and linked the pre-formed SMSI states with catalytic performance. However, it is unclear how the SMSI formed after pretreatment will affect the structural evolutions of Ni-TiO2 with temperature or gas changes. By using in situ TEM, the dynamic changes of Ni-TiO2 were directly visualized at the atomic scale.”

by Matthias Quintelier

Practical

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

Abstract

LDHs are layered materials with a wide range of applications, including electrocatalysis, fire retardants, chemical and electromagnetic absorption, ion exchange, biomedical uses, and environmental remediation. Their performance and properties are heavily influenced by their behavior at elevated temperatures, making in situ TEM heating experiments crucial for understanding these materials. By using HRTEM, HAADF-STEM, and µProbe 4DSTEM, I investigated the phase transformations of ZnAl LDH in both vacuum and air. While a porous structure formed in both conditions, the phase evolution was significantly affected by the environment. In vacuum, the material transitioned from LDH to spinel ZnAl2O4, then to ZnAl2O4 with Al2O3, and finally to a combination of Al2O3 and ZnO. In air, the transitions were from LDH to a mixture of LDH and ZnO, then to ZnO and ZnAl2O4, and finally to pure ZnAl2O4.

The second study focuses on PLE-4, a novel MOF synthesized using a cost-effective method to extend linkers. Despite its innovative synthesis, the resulting crystals exhibited poor crystallinity and low-resolution diffraction patterns, making it impossible to fully solve the structure using synchrotron XRD. However, 3DED experiments successfully resolved the structure despite similar resolution limitations. Standard structure solution methods like charge flipping and direct methods were unsuccessful, so we employed simulated annealing. In the second part of this talk, I will explain this technique, discuss the challenges encountered, and present the final structural solution. This study highlights the importance of looking beyond simple numerical indicators like R-factors to ensure accurate and meaningful structural interpretations.

by Nathalie Claes

Direct visualisation of ligands on gold nanoparticles in a liquid environment

Practical

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

Abstract

The interaction between Au nanoparticles, their surface ligands and the solvent critically influences the properties of nanoparticles. Despite employing spectroscopic and scattering techniques to investigate their ensemble structure, a comprehensive understanding at the nanoscale remains elusive. Electron microscopy enables characterization of the local structure and composition but is limited by insufficient contrast, electron beam sensitivity and ultra-high vacuum, which prevent the investigation of dynamic aspects. In this talk it will be demonstrated that high-quality graphene liquid cells can overcome these existing limitations. This approach enables the investigation of the structure of the ligand shell around Au nanoparticles, as well as the ligand-Au interface in a liquid environment. Using this graphene liquid cell, the anisotropy, composition and dynamics of ligand distribution at the Au nanorod surface are visualized. Our results indicate a micellar model for the surfactant organisation. This work opens up a reliable and direct visualization of ligand distribution around colloidal nanoparticles.

by Héléna Verbeeck - Department of Materials Engineering, Faculty of Engineering KULeuven

Pyrometallurgical Recovery of Platinum Group Metals from Spent Automotive Catalysts: a Computational Approach

Practical

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

Abstract

Recycling of Spent Automotive Catalysts (SACs) is crucial from both environmental and economic standpoints, as they are the primary source of valuable Platinum Group Metals (PGMs). PGMs, found in SACs as nanoparticles within a γ-Al2O3 layer on a cordierite substrate, are typically recycled through pyrometallurgical smelting. This process involves melting ground SACs with a flux, collector metal (CM), and reducing agent, forming a slag where CM droplets collect PGMs from the Al2O3 carrier. Encapsulation of PGMs by Al2O3 can impede their recovery, necessitating understanding Al2O3 dissolution in the slag and PGM collection in the CM during smelting. The phase-field method is the preferred numerical method for investigating diffusion and material interactions in this system. However, conventional phase-field models face limitations in simulating stoichiometric compounds, scaling to experimentally relevant length scales, and capturing interactions driven by large driving forces. We recently overcame challenges [1] by rederiving the phase-field equations to include composition independent Gibbs energy expressions for stoichiometric compounds in a multi-phase phase-field framework. Moreover, challenges related to spatial resolution and large driving-force interactions have been successfully overcome for diffusioncontrolled phase-field simulations. By integrating these advancements, we have developed a large-scale multi-phase multi-component phase-field model capable of simulating diffusion-controlled dissolution in systems with solution phases and stoichiometric compounds. This model facilitates the understanding dissolution of Al2O3 in CaO-Al2O3-SiO2 slags and PGMs partially encapsulated by Al2O3 in Cu CM droplets, crucial for pyrometallurgical recovery of PGMs from SACs, advancing computational methods in metallurgical engineering.  

References [1] Verbeeck, H., Feyen, V., Bellemans, I., & Moelans, N. (2024). Multi-phase-field modeling of the dissolution behavior of stoichiometric particles on experimentally relevant length scales. In Computational Materials Science (Vol. 245, p. 113288). Elsevier BV. https://doi.org/10.1016/j.commatsci.2024.113288.

by Valentina Girelli

Insight into the microstructure and porous network of zeolites

Practical

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

Abstract

Porous materials represent an attractive class of materials due to their high specific surface and mass transport. Zeolites, a category of microporous crystalline aluminosilicates, combine these properties with an intrinsic acidic character, making them ‘first choice’ catalysts. However, hydrothermal instability and deactivation of catalytic sites can drastically reduce the efficiency of zeolites. Therefore, new strategies have been adopted in terms of material design, with the purpose of enhancing both the longevity and the activity in zeolites. The one presented in this study involves the extraction of Al from the lattice of zeolites Y of the Faujasite topology through thermochemical treatments, also termed dealumination. This process not only leads to a gain in thermal stability and acidity by tuning the Si/Al ratio, but it is responsible for the introduction of an auxiliary network of mesopores within the zeolite lattice, too. In such a context, this research aims to understand the role of each dealuminating treatment considering the morphological, structural and chemical modification in zeolites Y at the nanometric scale. These questions were tackled by using a series of stepwise treated samples, and by employing complementary (S)TEM-based techniques. DF-STEM tomography has allowed the quantification of the morphological descriptors of the mesoporous network at the different stages of the dealumination. In situ gas microscopy has tried to simulate the hydrothermal treatment inside the TEM environmental cell (Protochips systems), in the presence of water vapor, in order to reveal the structural rearrangement in the zeolite. EDX-STEM and EELS-STEM have led to a semi-quantitative mapping of the Si and Al indicating the heterogeneity of the treated samples. Finally, STXM-XAS characterization based on synchrotron light aimed to investigate the spectral signature of the Al on the K-edge during the dealumination and compare with reference aluminum oxide materials to understand which Al environments are dominant.​

by Saleh Gholam

4D-STEM Tomography as a Tool for Solving the Structure of Nanoparticles

Practical

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

Abstract

Over the past decade, 3D Electron Diffraction (3D ED) has firmly established its position next to single-crystal X-ray diffraction (SC-XRD) and powder X-ray or neutron diffraction as a structure solution technique. Owing to the strong interaction of the accelerated electron beam with matter, there are no particle size limitations, in contrast to SC-XRD. Also, thanks to the high spatial resolution of transmission electron microscopes, impurities are not a serious problem, like in powder diffraction. However, in practice, an electron crystallographer can still face a lot of challenges.

“Conventional” 3D ED is still fundamentally a technique for single crystals and relies on parallel TEM illumination. Therefore, multi-phase or multi-grained particles, as well as any form of agglomeration, can complicate data collection and data processing. Furthermore, due to imperfections in the TEM stage, collecting tomography data becomes increasingly difficult as particle size decreases. In the case of tiny particles, assuming they have any contrast to be observed in TEM mode, maintaining illumination during tomography experiments as well as achieving a high signal-to-noise ratio are considerable challenges. These issues are further aggravated while dealing with beam-sensitive samples.

In this talk, I aim to demonstrate how 4D-STEM tomography, using fast pixelated detectors, can address these challenges by providing spatial resolution to the tomography experiments. To this end, we have automated data acquisition on our TEMs, as well as on a dedicated SEM for diffraction studies. We have analyzed multiple challenging samples, and propose several data analysis approaches. In the end, a graphical user interface is provided to facilitate the analysis of these heavy datasets for the users.

by Andrey Orkhov

Advantages and disadvantages of automation in electron microscopy: do we need an operator?

Practical

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

Abstract

In the current era of artificial intelligence and automation, it is crucial to understand how these algorithms function and how we can apply them in our work. In my talk, I will try to critically examine the methods employed in electron microscopy and explore the potential benefits of automation. As examples, I will discuss several projects I have worked on where microscope automation facilitated the analysis of large fields of view, automated electron diffraction acquisition, stage manipulation, minimized beam damage, and ultimately saved time for other projects.

In the AutomatED project, we developed an automated electron diffractometer for high-throughput analysis of nanocrystalline powder samples. I will present recent advancements in technique development for obtaining electron diffraction data from non-electron transparent samples. The efficiency of the automated electron diffractometer was validated using relevant samples provided by the industry partners of the project. The results of this project demonstrate that the automated electron diffractometer can be a viable alternative to expensive transmission electron microscopes or X-ray diffractometers

by Songge Li

Direct visualization of electromagnetic fields via electron ptychography

Practical

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

Abstract

Electric and magnetic fields are present inside and outside (nano)materials. Revealing these microscopic fields provides insight into their behaviors and properties. In this presentation, we propose electron ptychography as a phase retrieval method based on 4D scanning transmission electron microscope (STEM) to visualize the electromagnetic fields within and around a nanomaterial.

The presentation consists of two parts. In the first part, I will provide an overview of electron ptychography, explaining its working mechanism and highlighting its advantages. I will also discuss my previous work on an aberration correction technique in single side-band (SSB) ptychography, which significantly improves dose tolerance during the aberration correction process.

In the second part, I will demonstrate how the electrostatic and magnetic Aharanov Bohm effect can be used to reveal these fields from the phase shift the electrons experience when traversing this field. By employing electron ptychography as the phase retrieval method, we can reconstruct these fields with the potential to reconstruct them in 3D. I will discuss the challenges in doing this and showcase some examples where it already provides a rich insight into the electromagnetic state of nanoscale samples. 

by Deema Balalta

Enabling in situ electron microscopy  investigations of thermo and electro catalysis by optimization of loading stage for MEMS chips

Practical

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

Abstract

In situ transmission electron microscopy (TEM) has emerged as a powerful technique for studying dynamic processes at the nanoscale, enabling real-time observation of reactions and behaviors in realistic environments. Within the scope of the Catchy-ITN project, which focuses on the design and fabrication of cluster-based catalysts for the CO2 reduction reactions (CO2RR), in situ TEM plays a crucial role in characterizing both thermocatalytic and electrocatalytic processes. However, selective deposition of catalyst samples on liquid biasing and gas heating MEMS chips presents significant challenges. The small area and fragility of the electron-transparent window, combined with the compact design of the electrodes, complicates the precise control of material deposition, especially for samples produced by physical vapor deposition or dispersed in solvents.

To overcome these challenges, we propose a simple, low-cost 3D-printed loading stage for accurate and controlled sample deposition. Our system enables targeted material placement onto MEMS chips, as demonstrated by the successful deposition of laser-ablated Cu clusters on gas heating chips for thermocatalytic reaction characterization. For liquid-based processes, the system is equipped with a mask to ensure precise depositeion, as verified by successful placement of sputtered Au clusters and AuPdPt nanoparticles from liquid suspension on the working electrode of liquid biasing chips. Our innovative design is versatile, compatible with various sample types, and can be easily fabricated in any electron microscopy lab, significantly lowering the barrier for researchers to access this targeted deposition technique. Furthermore, it is adaptable to various MEMS in situ chips, offering wide potential applications for researchers working in diverse fields.

by Yansong Hao

Towards atom counting from first moment STEM images: methodology and possibilities

Practical

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

Abstract

Through a simulation-based study we develop a statistical model-based quantification method for atomic resolution first moment scanning transmission electron microscopy (STEM) images. This method uses the uniformly weighted least squares estimator to determine the unknown structure parameters of the images and to isolate contributions from individual atomic columns. In this way, a quantification of the projected potential per atomic column is achieved. Since the integrated projected potential of an atomic column scales linearly with the number of atoms it contains, it can serve as a basis for atom counting. The performance of atom counting from first moment STEM imaging is compared to that from traditional HAADF STEM in the presence of noise. Through this comparison, we demonstrate the advantage of first moment STEM images to attain more precise atom counts. Finally, we compare the integrated potential extracted from first-moment images of a wedge-shaped sample to those values from the bulk crystal. The excellent agreement found between these values proves the robustness of using bulk crystal simulations as a reference library. This enables atom counting for samples with different shapes by comparison with these library values. 

by Jenthe Verstraelen

High quality graphene supports for high resolution TEM

Practical

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

Abstract

The transmission electron microscopy (TEM)  field has significantly evolved during the last decade through the implementation of improved aberration correctors, novel detectors, more stable stages/holders and the implementation of many new low dose techniques. However, further progress in spatial resolution, contrast an potentially beam damage can still be achieved from improvements in sample preparation, particularly from the optimization of the TEM sample support.

Graphene based TEM grids have recently appeared as a promising alternative to the regular carbon coated TEM grids [1]. Graphene, a monolayer of tightly bound carbon atoms, possesses exceptional properties. The monoatomic thickness of graphene minimizes the background signal [2], significantly improving signal to noise ratio which is crucial for high resolution imaging. Additionally, graphene’s excellent electrical and thermal conductivity makes it an ideal candidate for dissipating excess heat and charge from the sample, mitigating electron beam induced damage [3].

However, commercially available graphene grids are often plagued by cracks, folds, metal nanoparticles and polymer residues. Such impurities add background noise, introduce undesired obstructions in TEM images and degrade the conductive properties of the graphene. Therefore, a novel method for manufacturing graphene TEM grids was developed at EMAT that yields much cleaner graphene.

In this presentation I will show how I made this novel process reproducible, thereby creating a more reliable substrate for the microscopist and increasing the value of the process for valorization. Also, I will demonstrate some applications for In-situ TEM where graphene can alleviate some of the drawbacks in the current systems.

[1] Gao, X. et al. (2022) advanced functional materials

[2] Aleman et al. (2010) ACS Nano

[3] Algara-Siller et al. (2013) Applied Physics Letters