Friday Lectures

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