Friday Lectures

by Chuang Gao

Exploring electron ptychography for low dose imaging

Practical

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

Abstract

Ptychography is an imaging method which can retrieve the phase information of a specimen from the diffraction patterns acquired with a probe scanning across the sample. With recent advances in pixelated detector technology, electron ptychography is increasingly popular in the electron microscopy community due to its many advantages such as super resolution [1] and dose efficiency[2]. In recent years, researchers have successfully applied electron ptychography to image light elements and beam sensitive materials such as 2 dimensional materials and biological samples.

From a hardware perspective, the relatively slow speed of most frame based direct detection 4D STEM cameras is still a bottleneck for practical application. The susceptibility to instabilities such as drift and jitter resulting from their relatively low speeds remains a major problem for precision measurements. In my presentation, I will demonstrate how the event driven Timepix3 detector[3] can reach the equivalent of millions frames per second with experimental results and the advantages of ptychographic methods with the Timepix3 camera.

However, ptychographic algorithms are often based on either the phase approximation or weak phase approximation. When the sample gets thicker, contrast reversals can occur which can hinder our interpretation of the phase images. We find that with a phase offset method[4] which is quite similar with Zernike phase contrast imaging method[5] in principle, contrast reversals can be overcome for thick samples. I will give an explanation on the reason and demonstrate some simulation and experimental results.

[1]Y, Jiang. et al Nature 559, 343–349 (2018)

[2]C, Gao. et al Appl. Phys. Lett. 121, 081906 (2022)

[3]D. Jannis. et al Ultramicroscopy 194,193-198 (2021)

[4]C. Hofer et al Ultramicroscopy 258, 113922 (2024)

[5]F. Zernike. Science. 121, 3141 (1955)

by Arno Annys​​

Bridging the gaps between advanced STEM techniques and the (S)TEM community

Practical

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

Abstract

Over the last decades, STEM has seen a number of advances strengthening its position as a powerful technique for low-dose electron microscopy. Many of these advances are related to the development of novel hardware and software technologies. On the hardware-level, direct electron detectors (DED), with their single electron counting capabilities, have perhaps made the most profound impact on low-dose capabilities. For STEM, the improved readout speed of DED has enabled experiments where the diffraction pattern at each probe-position can be recorded within a reasonable acquisition time. Additionally, an event-based readout mechanism for these DED enables momentum resolved STEM experiments at the speeds of common single pixel STEM experiments like HAADF-STEM [1]. Another significant hardware development is the programmable scan engine, which is not only essential in the synchronization of these fast 4D-STEM experiments, but also allows to improve the scan strategy beyond the conventional raster-scan [2].

Each of these developments bring significant advantages to  low-dose STEM experiments investigating beam-sensitive materials. However, the impact of these techniques also depends on their integration into routine electron microscopy workflows. In this talk, I will discuss recent efforts in developing hardware-software interfaces that increase the ease of use of these advanced techniques and enable their combination. Use cases are discussed where the developed interfaces enable new advances like automated 4D-STEM tomography and inline processing of DED data streams [3], with first results towards live ptychography.

[1] D. Jannis, C. Hofer, C. Gao, X. Xie, A. Béché, T.J. Pennycook, J. Verbeeck. Event driven 4D STEM acquisition with a Timepix3 detector: Microsecond dwell time and faster scans for high precision and low dose applications. Ultramicroscopy 233 (2022)

[2] A. Velazco, A. Béché, D. Jannis, J. Verbeeck. Reducing electron beam damage through alternative STEM scanning strategies, Part I: Experimental findings. Ultramicroscopy 232 (2022)

[3] CP. Yu, T. Friedrich, D. Jannis, S. Van Aert, J. Verbeeck. Real-Time Integration Center of Mass (riCOM) Reconstruction for 4D STEM. Microscopy and microanalysis 28 (2022)

by Nicolas Gauquelin​​

Biasing experiments in the TEM: The strength of combining electric field with analytical techniques at the local scale.

Practical

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

Abstract

Over the last years, I have been working on a lot of subjects, but the most challenging were without any doubt the biasing experiments. In this lecture I will recapitulate some of the attempts (with mitigated success) in understanding different materials’ response to an electric field, current, voltage applied in-situ through the holder (PZT fatigue, Ca2RuO4 MIT phase transition, CGO field induced vacancy migration and electrostriction,…). I will finish by discussing the perspectives offered by the newest equipments recently purchased (soon to come) at EMAT

by Rajeshreddy Ninakanti​

Self-assembled Au-TiO2 supraparticles and Au-Ag hollow nanoparticles for plasmon enhanced photocatalysis

Practical

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

Abstract

Plasmonic nanoparticles deposited on semiconductors have shown great promise in photocatalysis. However, plasmonic enhancement for photo upconversion photocatalysis is still limited, as most of metal-semiconductor building blocks depend on LSPR contribution of isolated metal nanoparticles. To enhance the interaction of plasmonic nanoparticles for photocatalysis, in the present talk, I will discuss synthesis of self-assembled Au-TiO2 supraparticles leading to collective plasmonic excitation as an effective strategy to enhance the utilization of plasmon energy transfer to TiO2. Au-TiO2 supraparticles are synthesized via electrostatic interaction between poly(allylamine hydrochloride)-coated Au nanoparticles and titanium bis(ammonium lactate) dihydroxide (TALH). The suprastructure size could be controlled by varying the volume of TALH in the Au@polymer matrix. The use of large supraparticles enabled to double the hydrogen peroxide yield compared to small supraparticles. Our mechanistic investigation points at a pivotal role of a stongly increased near-electric field enhancement and associated hot electrons that partake in the reaction. Radical quenching experiments further confirm the importance of a two electron or four electron O2 reduction pathway as the reason for enhanced photocatalytic H2O2 production. In the concluding segment of the talk, I will share insights and preliminary results on the utilization of hollow Au-Ag nanoparticles as a strategy for plasmon-enhanced photocatalytic hydrogen evolution. Conducted during the final stages of my PhD, this research offers promising leads in advancing plasmon-enhanced photocatalysis.

by Daniel Arenas Esteban

Unraveling the True 3D Structure of Colloidal Assemblies by Liquid Cell Electron Tomography

Practical

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

Abstract

The colloidal bottom-up approach of nanoparticles self-assembling into ordered structures with tailored properties has recently attracted significant interest in various scientific fields. Therefore, their comprehensive structural and morphological characterization is essential, as the properties of these nanostructures are strongly correlated with their three-dimensional (3D) arrangement. Electron tomography is a common technique used for such nanoparticle characterization. However, external forces that can affect the structure, such as the capillary forces caused by the common vacuum environment inside the microscope, are often neglected, resulting in misconnections between the obtained structure and the properties of the assemblies. As these materials are intended to be used in dispersion, the goal is to analyze the 3D arrangement of the assemblies in their native liquid environment. A comparison between similar 3D investigations performed in the native liquid environment and in dry state revealed a general decrease in interparticle distances in the latter. This effect can be assigned to the compression effect of the capillary forces generated by the vacuum environment of the electron microscope during dry characterization. These observations emphasize the importance of conducting measurements under liquid-state conditions to accurately characterize NP self-assemblies and provide essential insights into the underlying physical and chemical mechanisms that govern these structures.

by Mohammed Noorul Hussein

Atomic Resolution Imaging of chiral materials

Practical

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

​Abstract​

Chirality is the phenomena where the mirror image of an object is not superimposable on the original form. Chirality can occur at different scales, from subatomic particles to crystals and beyond [1]. Enantiomers of a chiral material can display different thermal, physical and chemical properties which can either be beneficial or detrimental in their intended application. Due to this effect, it is important to have effective and reliable methods for studying the chirality of materials. Transmission Electron Microscopy (TEM) is a powerful tool which gives the ability to image materials at atomic scales. TEM can be used effectively to unravel chirality at atomic and molecular scales, which is either difficult or impossible with other methods [2].

The aim of this work is to use TEM to study the chirality of different materials such as Tellurium and metal phthalocyanines. While beam resistant materials like Tellurium can be investigated with basic methods like HAADF-STEM, beam sensitive materials like Lead Phthalocyanine require low dose techniques. Techniques like riCOM – Real Time Integration Center of Mass [3], AIRPI – Neural Network based reconstruction [4] and ptychography are explored for imaging phthalocyanine samples.

In this lecture an overview of the experiments conducted with Tellurium and Lead Phthalocyanine will be presented. Results obtained and challenges faced in imaging materials with basic and low dose techniques will be discussed. In addition, an outlook of further work in imaging chiral materials will also be shared.

[1] Atkins, P. W., Ratcliffe, R. G., de Paula, J., & Wormald, M. (2023). Physical chemistry for the life sciences. Oxford University Press.

[2] Dong, Z., & Ma, Y. (2020). Atomic-level handedness determination of chiral crystals using aberration-corrected scanning transmission electron microscopy. Nature Communications, 11(1), 1588.

[3] Yu, C. P., Friedrich, T., Jannis, D., Van Aert, S., & Verbeeck, J. (2022). Real-time integration center of mass (riCOM) reconstruction for 4D STEM. Microscopy and Microanalysis, 28(5), 1526-1537.

[4] Friedrich, T., Yu, C. P., Verbeeck, J., & Van Aert, S. (2023). Phase object reconstruction for 4D-STEM using deep learning. Microscopy and Microanalysis, 29(1), 395-407.

by Robin De Meyer

In-situ Plasma Studies using a Direct Current Microplasma in a Scanning Electron Microscope

Practical

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

​Abstract​

R. De Meyer1,2,3,*, L. Grünewald1, D. Chezganov1,2, A. Orekhov1, S. Van Aert1,2, A. Bogaerts3, S. Bals1,2, and J. Verbeeck1

1 EMAT, University of Antwerp, Groenenborgerlaan 171, Antwerp B-2020, Belgium

2 NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, Antwerp B-2020, Belgium

3 PLASMANT, University of Antwerp, Universiteitsplein 1, Antwerpen-Wilrijk B-2610, Belgium

*Corresponding Author: robin.demeyer@uantwerpen.be

A scanning electron microscope (SEM) enables structural and chemical investigations of materials from the mm- down to the nm-scale. In this work, we incorporated a DC microplasma inside an SEM [1]. We were able to perform microscopic electron-based imaging while treating the sample with a plasma at the same time. In our setup, a metal tube with a small orifice at the end is introduced in the vacuum chamber of the SEM. This tube is connected to the outside of the microscope where it is connected to a gas cylinder. At the same time, the metal tube is powered by a DC power supply and placed close (ca. 100 µm) to the grounded sample. By applying a sufficiently high voltage, a stable DC glow plasma was formed. Furthermore, we were able to acquire true in-situ SEM images of the sample being treated by the plasma, where we could obtain a real-time view of the sputtering characteristics of the plasma [2]. Moreover, energy dispersive X-ray (EDX) spectroscopy enabled the visualisation of the elemental composition of the sample, which was acquired quasi in-situ, between plasma treatments. These analyses illustrated the oxidative properties of a CO2 plasma affecting a Cu surface. Finally, the polarity of the powered electrode was reversed. Hereby, the positive ions accelerated toward the nozzle, sputtering the steel orifice and depositing some of that material on the sample. At the same time, the sputtering of the sample was eliminated and the oxidation by CO2 plasma was observed for a broad area.

This work reports the technical details and requirements for achieving true in-situ SEM analyses. The characteristics of the plasma are studied, and the properties of the setup are analysed. This work serves as a stepping stone toward more advanced plasma diagnostic techniques, as well as potential novel applications. A number of paths forward are envisioned, for example the addition of an optical fibre for spectroscopic analyses, EDX analyses of the plasma discharge, analysis of the downstream gas composition, incorporating different types of plasma (e.g., dielectric barrier discharge), and more.

References

[1] K. Matra, Y. Mizobuchi, H. Furuta, A. Hatta, Local sputter etching by micro plasma jet in SEM,

Vacuum, 2013, 87, 132.

[2] L. Grünewald, D. Chezganov, R. De Meyer, A. Orekhov, S. Van Aert, A. Bogaerts, S. Bals, J. Verbeeck, In Situ Plasma Studies Using a Direct Current Microplasma in a Scanning Electron Microscope. Advanced Materials Technologies, 2024, 2301632.

by Ihtasham Ul Haq

Investigation of the nanoscale plasticity/damage mechanisms in Earth mantle silicates by transmission electron microscopy

Practical

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

​Abstract​

Ihtasham Ul Haq1, Patrick Cordier2,3, Dominique Schryvers1, Hosni Idrissi1,4
1EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium
2Univ. Lille, CNRS, INRAE, Centrale Lille, UMR 8207 - UMET - Unité Matériaux et Transformations, F-59000 Lille, France
3Institut Universitaire de France, F-75005 Paris, France
4Institute of Mechanics, Materials and Civil Engineering (IMMC), UCLouvain, B-1348, Louvain‐la‐Neuve, Belgium

Abstract

Olivine is the most abundant (> 60 % in volume) and weakest phase in the Earth’s upper mantle of which it controls the rheology. The lack of slip systems in this crystal leads to the activation of other intergranular deformation mechanisms to accommodate a general strain. Our study focuses on the grain boundary sliding mechanism, based on grain boundary amorphization which was reported recently (1). For this elementary deformation mechanism, quantitative investigations are carried out on a bi-crystal forsterite tensile specimen by in-situ TEM test with a Push-to-Pull device. This work uses synthetic forsterite (the magnesium-rich end member of the olivine solid solution) samples.  We show that specimens deform exclusively by grain boundary sliding. Detailed microstructural investigation shows direct evidence of stress-induced amorphization in the sliding grain boundaries. In addition, the localization of the small strain onset of the grain boundary sliding mechanism was probed with the help of the in-situ TEM digital image correlation technique. Moreover, the effect of the iron addition (Fayalite; iron-rich end member of olivine solid solution) has been investigated. It is observed that the iron makes the sliding of the grain boundary more difficult.

After successfully adopting the nanomechanical technique on the olivine, it is extended to study the mechanical properties of phyllosilicates. Talc mineral (phyllosilicate) is the alteration product of stress-induced dolomite and silica-rich fluids in fault zones, where it can escalate into a long network that influences crustal mechanics. The formation of the interconnected network in the host rock contributes to the weakening of the fault through the frictional slip mechanism (2). One of the most intriguing aspects of talc is its mechanical anisotropy, which refers to the variation of mechanical properties in different crystal orientations (3). Taking advantage of the in-situ nanomechanical testing, the response of the talc has been determined between different crystallographic directions. This will bridge the gap between materials science and geoscience, contributing to a deep understanding of rock mechanisms, and frictional behavior in geological settings.

1.        Samae V, Cordier P, Demouchy S, Bollinger C, Gasc J, Koizumi S, Mussi, A., Schryvers, D., & Idrissi, H. (2021). Stress-induced amorphization triggers deformation in the lithospheric mantle. Nature. 2021 Mar 4;591(7848):82–6.

2.        Viti C, Collettini C. Growth and deformation mechanisms of talc along a natural fault: A micro/ nanostructural investigation. Contributions to Mineralogy and Petrology. 2009;158(4):529–42.

3.        Gatta GD, Merlini M, Valdrè G, Liermann HP, Nénert G, Rothkirch A, et al. On the crystal structure and compressional behavior of talc: A mineral of interest in petrology and material science. Phys Chem Miner. 2013 Feb 1;40(2):145–56. 

by Saffiyye Kavak

Exploring Metal-Organic Frameworks (MOFs) Through High-Resolution TEM Imaging with Low-Dose Techniques

Practical

• location (online link) by invitation only
• Time: 10:30

Abstract

Metal-organic frameworks (MOFs) possess remarkable features, including high porosity, crystallinity, and customizable chemistry. This flexibility enables precise control over their morphologies, the incorporation of additional elements, and the introduction of defects. Their unlimited combinations of metal ions and organic linkers render them versatile materials applicable in diverse fields, such as catalysis,1 controlled drug delivery,2,3 energy storage,4 gas storage, and separation5,6. Gaining insights into local features of MOFs, including defects and incorporated elements, is very important to fundamentally understand these materials.

Transmission electron microscopy (TEM) is an excellent technique to achieve local characterization. However, the extreme sensitivity of MOFs to the electron beam represents a significant challenge. Radiolysis emerges as the main mechanism behind beam-induced damage in MOFs,7,8 leading to structural alterations and loss of crystallinity.

In this lecture, I will first delve into the beam stability of MOFs, quantifying their critical dose (Dc) and half-life time dose (D1/2) to understand their structural changes over accumulated electron dose. Furthermore, the impact of working conditions, such as gaseous mixtures, on MOF stability will be also presented.

High-resolution investigation of various MOFs performed by respecting their D1/2 will be presented. To achieve this, we employ low-dose imaging techniques. These include integrated differential phase contrast (iDPC) by using segmented DF4 detector, and 4D-STEM datasets acquired using pixelated Timepix39 detector, from which the signal is reconstructed by using real-time integrated center of mass (riCOM)10 algorithm. These methods enable us to study pristine and pure-phase MOFs, as well as MOF-MOF interfaces, where two similarly structured MOFs are intergrown. Additionally, recent electron tomography results from MOFs will be discussed, on the way to achieve high-resolution 3D imaging while minimizing damage. 

1.         Yang, D.; Gates, B. C. Catalysis by Metal Organic Frameworks: Perspective and Suggestions for Future Research. ACS Catal 2019, 9, 1779–1798.

2.        Zheng, H.; Zhang, Y.; Liu, L.; Wan, W.; Guo, P.; Nyström, A. M.; Zou, X. One-Pot Synthesis of Metal–Organic Frameworks with Encapsulated Target Molecules and Their Applications for Controlled Drug Delivery. J Am Chem Soc 2016, 138, 962–968.

3.        Picchi, D. F.; Biglione, C.; Horcajada, P. Nanocomposites Based on Magnetic Nanoparticles and Metal–Organic Frameworks for Therapy, Diagnosis, and Theragnostics. ACS Nanoscience Au 2023.

4.        Baumann, A. E.; Burns, D. A.; Liu, B.; Thoi, V. S. Metal-Organic Framework Functionalization and Design Strategies for Advanced Electrochemical Energy Storage Devices. Commun Chem 2019, 2, 86.

5.        Li, B.; Wen, H.-M.; Zhou, W.; Chen, B. Porous Metal–Organic Frameworks for Gas Storage and Separation: What, How, and Why? J Phys Chem Lett 2014, 5, 3468–3479.

6.        Li, H.; Wang, K.; Sun, Y.; Lollar, C. T.; Li, J.; Zhou, H.-C. Recent Advances in Gas Storage and Separation Using Metal–Organic Frameworks. Materials Today2018, 21, 108–121.

7.        Liu, L.; Zhang, D.; Zhu, Y.; Han, Y. Bulk and Local Structures of Metal–Organic Frameworks Unravelled by High-Resolution Electron Microscopy. Commun Chem2020, 3, 99.

8.        Ghosh, S.; Kumar, P.; Conrad, S.; Tsapatsis, M.; Mkhoyan, K. A. Electron-Beam-Damage in Metal Organic Frameworks in the TEM. Microscopy and Microanalysis 2019, 25, 1704–1705.

9.        Poikela, T.; Plosila, J.; Westerlund, T.; Campbell, M.; Gaspari, M. De; Llopart, X.; Gromov, V.; Kluit, R.; van Beuzekom, M.; Zappon, F.; Zivkovic, V.; Brezina, C.; Desch, K.; Fu, Y.; Kruth, A. Timepix3: A 65K Channel Hybrid Pixel Readout Chip with Simultaneous ToA/ToT and Sparse Readout. Journal of Instrumentation 2014, 9, C05013.

10.       Yu, C.-P.; Friedrich, T.; Jannis, D.; Van Aert, S.; Verbeeck, J. Real-Time Integration Center of Mass (RiCOM) Reconstruction for 4D STEM. Microscopy and Microanalysis 2022, 28, 1526–1537.