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“Novel class of nanostructured metallic glass films with superior and tunable mechanical properties”. Ghidelli M, Orekhov A, Bassi AL, Terraneo G, Djemia P, Abadias G, Nord M, Béché, A, Gauquelin N, Verbeeck J, Raskin J-p, Schryvers D, Pardoen T, Idrissi H, Acta Materialia , 116955 (2021). http://doi.org/10.1016/j.actamat.2021.116955
Abstract: A novel class of nanostructured Zr50Cu50 (%at.) metallic glass films with superior and tunable mechanical
properties is produced by pulsed laser deposition. The process can be controlled to synthetize a wide
range of film microstructures including dense fully amorphous, amorphous embedded with nanocrystals
and amorphous nano-granular. A unique dense self-assembled nano-laminated atomic arrangement
characterized by alternating Cu-rich and Zr/O-rich nanolayers with different local chemical enrichment
and amorphous or amorphous-crystalline composite nanostructure has been discovered, while
significant in-plane clustering is reported for films synthetized at high deposition pressures. This unique
nanoarchitecture is at the basis of superior mechanical properties including large hardness and elastic
modulus up to 10 and 140 GPa, respectively and outstanding total elongation to failure (>9%), leading to
excellent strength/ductility balance, which can be tuned by playing with the film architecture. These
results pave the way to the synthesis of novel class of engineered nanostructured metallic glass films
with high structural performances attractive for a number of applications in microelectronics and
coating industry.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 27
DOI: 10.1016/j.actamat.2021.116955
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“Atom column detection”. Fatermans J, de Backer A, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 177 (2021).
Abstract: By combining statistical parameter estimation and model-order selection using a Bayesian framework, the maximum a posteriori (MAP) probability rule is proposed in this chapter as an objective and quantitative method to detect atom columns from high-resolution scanning transmission electron microscopy (HRSTEM) images. The validity and usefulness of this approach is demonstrated to both simulated and experimental annular dark-field (ADF) STEM images, but also to simultaneously acquired annular bright-field (ABF) and ADF STEM image data.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT); Vision lab
DOI: 10.1016/BS.AIEP.2021.01.006
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“Atom counting”. de Backer A, Fatermans J, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 91 (2021).
Abstract: In this chapter, a statistical model-based method to count the number of atoms of monotype crystalline nanostructures from high-resolution annular dark-field (ADF) scanning transmission electron microscopy (STEM) images is discussed in detail together with a thorough study on the possibilities and inherent limitations. We show that this method can be applied to nanocrystals of arbitrary shape, size, and atom type. The validity of the atom-counting results is confirmed by means of detailed image simulations and it is shown that the high sensitivity of our method enables us to count atoms with single atom sensitivity.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT); Vision lab
DOI: 10.1016/BS.AIEP.2021.01.004
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“Efficient fitting algorithm”. de Backer A, Fatermans J, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 73 (2021).
Abstract: An efficient model-based estimation algorithm is introduced to quantify the atomic column positions and intensities from atomic-resolution (scanning) transmission electron microscopy ((S)TEM) images. This algorithm uses the least squares estimator on image segments containing individual columns fully accounting for overlap between neighboring columns, enabling the analysis of a large field of view. To provide end-users with this well-established quantification method, a user friendly program, StatSTEM, is developed which is freely available under a GNU public license. In this chapter, this efficient algorithm is applied to three different nanostructures for which the analysis of a large field of view is required.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT)
DOI: 10.1016/BS.AIEP.2021.01.003
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“Enhancing the hydrogen evolution properties of kesterite absorber by Si-doping in the surface of CZTS thin film”. Vishwakarma M, Kumar M, Hendrickx M, Hadermann J, Singh AP, Batra Y, Mehta BR, Advanced Materials Interfaces , 2002124 (2021). http://doi.org/10.1002/ADMI.202002124
Abstract: In this work, the effects of Si-doping in Cu2ZnSnS4 are examined computationally and experimentally. The density functional theory calculations show that an increasing concentration of Si (from x = 0 to x = 1) yields a band gap rise due to shifting of the conduction band minimum towards higher energy states in the Cu2Zn(Sn1-xSix)S-4. CZTSiS thin film prepared by co-sputtering process shows Cu2Zn(Sn1-xSix)S-4 (Si-rich) and Cu2ZnSnS4 (S-rich) kesterite phases on the surface and in the bulk of the sample, respectively. A significant change in surface electronic properties is observed in CZTSiS thin film. Si-doping in CZTS inverts the band bending at grain-boundaries from downward to upward and the Fermi level of CZTSiS shifts upward. Further, the coating of the CdS and ZnO layer improves the photocurrent to approximate to 5.57 mA cm(-2) at -0.41 V-RHE in the CZTSiS/CdS/ZnO sample, which is 2.39 times higher than that of pure CZTS. The flat band potential increases from CZTS approximate to 0.43 V-RHE to CZTSiS/CdS/ZnO approximate to 1.31 V-RHE indicating the faster carrier separation process at the electrode-electrolyte interface in the latter sample. CdS/ZnO layers over CZTSiS significantly reduce the charge transfer resistance at the semiconductor-electrolyte interface.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.279
DOI: 10.1002/ADMI.202002124
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“General conclusions and future perspectives”. de Backer A, Fatermans J, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 243 (2021).
Abstract: This chapter provides an overview of statistical and quantitative methodologies that have pushed (scanning) transmission electron microscopy ((S)TEM) toward accurate and precise measurements of unknown structure parameters for understanding the relation between the structure of a material and its properties. Hereby, statistical parameter estimation theory has extensively been used which enabled not only measuring atomic column positions, but also quantifying the number of atoms, and detecting atomic columns as accurately and precisely as possible from experimental images. As a general conclusion, it can be stated that advanced statistical techniques are ideal tools to perform quantitative electron microscopy at the atomic scale. In the future, statistical methods will continue to be developed and novel quantification procedures will open up new possibilities for studying material structures at the atomic scale.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT); Vision lab
DOI: 10.1016/BS.AIEP.2021.01.008
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“Image-quality evaluation and model selection with maximum a posteriori probability”. Fatermans J, de Backer A, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 215 (2021).
Abstract: The maximum a posteriori (MAP) probability rule for atom column detection can also be used as a tool to evaluate the relation between scanning transmission electron microscopy (STEM) image quality and atom detectability. In this chapter, a new image-quality measure is proposed that correlates well with atom detectability, namely the integrated contrast-to-noise ratio (ICNR). Furthermore, the working principle of the MAP probability rule is described in detail showing a close relation to the principles of model-selection methods.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT); Vision lab
DOI: 10.1016/BS.AIEP.2021.01.007
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“Introduction”. de Backer A, Fatermans J, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 1 (2021).
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT)
DOI: 10.1016/BS.AIEP.2021.01.001
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“Optimal experiment design for nanoparticle atom counting from ADF STEM images”. de Backer A, Fatermans J, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 145 (2021).
Abstract: In this chapter, the principles of detection theory are used to quantify the probability of error for atom counting from high-resolution scanning transmission electron microscopy (HRSTEM) images. Binary and multiple hypothesis testing have been investigated in order to determine the limits to the precision with which the number of atoms in a projected atomic column can be estimated. The probability of error has been calculated when using STEM images, scattering cross-sections or peak intensities as a criterion to count atoms. Based on this analysis, we conclude that scattering cross-sections perform almost equally well as images and perform better than peak intensities. Furthermore, the optimal STEM detector design can be derived for atom counting using the expression of the probability of error. We show that for very thin objects the low-angle annular dark-field (LAADF) regime is optimal and that for thicker objects the optimal inner detector angle increases.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT); Vision lab
DOI: 10.1016/BS.AIEP.2021.01.005
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“Selectivity in ligand functionalization of photocatalytic metal oxide nanoparticles for phase transfer and self‐assembly applications”. Borah R, Ninakanti R, Nuyts G, Peeters H, Pedrazo-Tardajos A, Nuti S, Vande Velde C, De Wael K, Lenaerts S, Bals S, Verbruggen S, Chemistry-A European Journal , chem.202100029 (2021). http://doi.org/10.1002/CHEM.202100029
Abstract: Functionalization of photocatalytic metal oxide nanoparticles of TiO 2 , ZnO, WO 3 and CuO with amine‐terminated (oleylamine) and thiol‐terminated (1‐dodecanethiol) alkyl chained ligands was studied under ambient conditions. A high selectivity was observed in the binding specificity of a ligand towards nanoparticles of these different oxides. It was observed that oleylamine binds stably to only TiO 2 and WO 3 , while 1‐dodecanethiol binds stably only to ZnO and CuO. Similarly, polar to non‐polar solvent phase transfer of TiO 2 and WO 3 nanoparticles could be achieved by using oleylamine, but not by 1‐dodecanethiol, while the contrary holds for ZnO and CuO. The surface chemistry of ligand functionalized nanoparticles was probed by ATR‐FTIR spectroscopy, that enabled to elucidate the occupation of the ligands at the active sites. The photo‐stability of the ligands on the nanoparticle surface was determined by the photocatalytic self‐cleaning properties of the material. While TiO 2 and WO 3 degrade the ligands within 24 hours under both UV and visible light, ligands on ZnO and CuO remain unaffected. The gathered insights are also highly relevant from an application point of view. As an example, since the ligand functionalized nanoparticles are hydrophobic in nature, they can thus be self‐assembled at the air‐water interface, for obtaining nanoparticle films with demonstrated photocatalytic as well as anti‐fogging properties.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Sustainable Energy, Air and Water Technology (DuEL); Intelligence in PRocesses, Advanced Catalysts and Solvents (iPRACS)
Impact Factor: 5.317
Times cited: 15
DOI: 10.1002/CHEM.202100029
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“Statistical parameter estimation theory : principles and simulation studies”. de Backer A, Fatermans J, den Dekker AJ, Van Aert S Advances in imaging and electron physics
T2 – Advances in imaging and electron physics. page 29 (2021).
Abstract: In this chapter, the principles of statistical parameter estimation theory for a quantitative analysis of atomic-resolution electron microscopy images are introduced. Within this framework, electron microscopy images are described by a parametric statistical model. Here, parametric models are introduced for different types of electron microscopy images: reconstructed exit waves, annular dark-field (ADF) scanning transmission electron microscopy (STEM) images, and simultaneously acquired ADF and annular bright-field (ABF) STEM images. Furthermore, the Cramér-Rao lower bound (CRLB) is introduced, i.e. a theoretical lower bound on the variance of any unbiased estimator. This CRLB is used to quantify the precision of the structure parameters of interest, such as the atomic column positions and the integrated atomic column intensities.
Keywords: H2 Book chapter; Electron microscopy for materials research (EMAT); Vision lab
DOI: 10.1016/BS.AIEP.2021.01.002
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Skorikov A (2021) Fast approaches for investigating 3D elemental distribution in nanomaterials. 143 p
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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“The Influence of Size, Shape, and Twin Boundaries on Heat‐Induced Alloying in Individual Au@Ag Core–Shell Nanoparticles”. Mychinko M, Skorikov A, Albrecht W, Sánchez‐Iglesias A, Zhuo X, Kumar V, Liz‐Marzán LM, Bals S, Small , 2102348 (2021). http://doi.org/10.1002/smll.202102348
Abstract: Environmental conditions during real-world application of bimetallic core–shell nanoparticles (NPs) often include the use of elevated temperatures, which are known to cause elemental redistribution, in turn significantly altering the properties of these nanomaterials. Therefore, a thorough understanding of such processes is of great importance. The recently developed combination of fast electron tomography with in situ heating holders is a powerful approach to investigate heat-induced processes at the single NP level, with high spatial resolution in 3D. In combination with 3D finite-difference diffusion simulations, this method can be used to disclose the influence of various NP parameters on the diffusion dynamics in Au@Ag core–shell systems. A detailed study of the influence of heating on atomic diffusion and alloying for Au@Ag NPs with varying core morphology and crystallographic details is carried out. Whereas the core shape and aspect ratio of the NPs play a minor role, twin boundaries are found to have a strong influence on the elemental diffusion.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.643
Times cited: 8
DOI: 10.1002/smll.202102348
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“3D Atomic‐Scale Dynamics of Laser‐Light‐Induced Restructuring of Nanoparticles Unraveled by Electron Tomography”. Albrecht W, Arslan Irmak E, Altantzis T, Pedrazo‐Tardajos A, Skorikov A, Deng T‐S, van der Hoeven JES, van Blaaderen A, Van Aert S, Bals S, Advanced Materials , 2100972 (2021). http://doi.org/10.1002/adma.202100972
Abstract: Understanding light–matter interactions in nanomaterials is crucial for
optoelectronic, photonic, and plasmonic applications. Specifically, metal
nanoparticles (NPs) strongly interact with light and can undergo shape
transformations, fragmentation and ablation upon (pulsed) laser excitation.
Despite being vital for technological applications, experimental insight into
the underlying atomistic processes is still lacking due to the complexity of
such measurements. Herein, atomic resolution electron tomography is performed
on the same mesoporous-silica-coated gold nanorod, before and after
femtosecond laser irradiation, to assess the missing information. Combined
with molecular dynamics (MD) simulations based on the experimentally
determined 3D atomic-scale morphology, the complex atomistic rearrangements,
causing shape deformations and defect generation, are unraveled.
These rearrangements are simultaneously driven by surface diffusion, facet
restructuring, and strain formation, and are influenced by subtleties in the
atomic distribution at the surface.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 19.791
Times cited: 8
DOI: 10.1002/adma.202100972
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“Modelling ADF STEM images using elliptical Gaussian peaks and its effects on the quantification of structure parameters in the presence of sample tilt”. De wael A, De Backer A, Lobato I, Van Aert S, Ultramicroscopy , 113391 (2021). http://doi.org/10.1016/j.ultramic.2021.113391
Abstract: A small sample tilt away from a main zone axis orientation results in an elongation of the atomic columns in ADF STEM images. An often posed research question is therefore whether the ADF STEM image intensities of tilted nanomaterials should be quantified using a parametric imaging model consisting of elliptical rather than the currently used symmetrical peaks. To this purpose, simulated ADF STEM images corresponding to different amounts of sample tilt are studied using a parametric imaging model that consists of superimposed 2D elliptical Gaussian peaks on the one hand and symmetrical Gaussian peaks on the other hand. We investigate the quantification of structural parameters such as atomic column positions and scattering cross sections using both parametric imaging models. In this manner, we quantitatively study what can be gained from this elliptical model for quantitative ADF STEM, despite the increased parameter space and computational effort. Although a qualitative improvement can be achieved, no significant quantitative improvement in the estimated structure parameters is achieved by the elliptical model as compared to the symmetrical model. The decrease in scattering cross sections with increasing sample tilt is even identical for both types of parametric imaging models. This impedes direct comparison with zone axis image simulations. Nonetheless, we demonstrate how reliable atom-counting can still be achieved in the presence of small sample tilt.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
DOI: 10.1016/j.ultramic.2021.113391
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“Interface Pattern Engineering in Core‐Shell Upconverting Nanocrystals: Shedding Light on Critical Parameters and Consequences for the Photoluminescence Properties”. Hudry D, De Backer A, Popescu R, Busko D, Howard IA, Bals S, Zhang Y, Pedrazo‐Tardajos A, Van Aert S, Gerthsen D, Altantzis T, Richards BS, Small , 2104441 (2021). http://doi.org/10.1002/smll.202104441
Abstract: Advances in controlling energy migration pathways in core-shell lanthanide (Ln)-based hetero-nanocrystals (HNCs) have relied heavily on assumptions about how optically active centers are distributed within individual HNCs. In this article, it is demonstrated that different types of interface patterns can be formed depending on shell growth conditions. Such interface patterns are not only identified but also characterized with spatial resolution ranging from the nanometer- to the atomic-scale. In the most favorable cases, atomic-scale resolved maps of individual particles are obtained. It is also demonstrated that, for the same type of core-shell architecture, the interface pattern can be engineered with thicknesses of just 1 nm up to several tens of nanometers. Total alloying between the core and shell domains is also possible when using ultra-small particles as seeds. Finally, with different types of interface patterns (same architecture and chemical composition of the core and shell domains) it is possible to modify the output color (yellow, red, and green-yellow) or change (improvement or degradation) the absolute upconversion quantum yield. The results presented in this article introduce an important paradigm shift and pave the way toward the emergence of a new generation of core-shell Ln-based HNCs with better control over their atomic-scale organization.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 8.643
Times cited: 17
DOI: 10.1002/smll.202104441
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“3D Atomic Structure of Supported Metallic Nanoparticles Estimated from 2D ADF STEM Images: A Combination of Atom –, Counting and a Local Minima Search Algorithm”. Arslan Irmak E, Liu P, Bals S, Van Aert S, Small methods , 2101150 (2021). http://doi.org/10.1002/smtd.202101150
Abstract: Determining the three-dimensional (3D) atomic structure of nanoparticles (NPs) is critical to understand their structure-dependent properties. It is hereby important to perform such analyses under conditions relevant for the envisioned application. Here, we investigate the 3D structure of supported Au NPs at high temperature, which is of importance to understand their behavior during catalytic reactions. To overcome limitations related to conventional high-resolution electron tomography at high temperature, 3D characterization of NPs with atomic resolution has been performed by applying atom-counting using atomic resolution annular darkfield scanning transmission electron microscopy (ADF STEM) images followed by structural relaxation. However, at high temperatures, thermal displacements, which affect the ADF STEM intensities, should be taken into account. Moreover, it is very likely that the structure of a NP investigated at elevated temperature deviates from a ground state configuration, which is difficult to determine using purely computational energy minimization approaches. In this paper, we therefore propose an optimized approach using an iterative local minima search algorithm followed by molecular dynamics (MD) structural relaxation of candidate structures associated with each local minimum. In this manner, it becomes possible to investigate the 3D atomic structure of supported NPs, which may deviate from their ground state configuration.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Times cited: 12
DOI: 10.1002/smtd.202101150
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“Creation of Exclusive Artificial Cluster Defects by Selective Metal Removal in the (Zn, Zr) Mixed-Metal UiO-66”. Feng X, Jena HS, Krishnaraj C, Arenas-Esteban D, Leus K, Wang G, Sun J, Rüscher M, Timoshenko J, Roldan Cuenya B, Bals S, Voort PVD, Journal Of The American Chemical Society , jacs.1c05357 (2021). http://doi.org/10.1021/jacs.1c05357
Abstract: The differentiation between missing linker defects
and missing cluster defects in MOFs is difficult, thereby limiting the
ability to correlate materials properties to a specific type of defects.
Herein, we present a novel and easy synthesis strategy for the
creation of solely “missing cluster defects” by preparing mixed-metal
(Zn, Zr)-UiO-66 followed by a gentle acid wash to remove the Zn
nodes. The resulting material has the reo UiO-66 structure, typical
for well-defined missing cluster defects. The missing clusters are
thoroughly characterized, including low-pressure Ar-sorption, iDPCSTEM
at a low dose (1.5 pA), and XANES/EXAFS analysis. We
show that the missing cluster UiO-66 has a negligible number of missing linkers. We show the performance of the missing cluster
UiO-66 in CO2 sorption and heterogeneous catalysis.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 29
DOI: 10.1021/jacs.1c05357
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“Towards Exotic Layered Materials: 2D Cuprous Iodide”. Mustonen K, Hofer C, Kotrusz P, Markevich A, Hulman M, Mangler C, Susi T, Pennycook TJ, Hricovini K, Richter CM, Meyer JC, Kotakoski J, Skákalová, V, Advanced materials , 2106922 (2021). http://doi.org/10.1002/adma.202106922
Abstract: Heterostructures composed of two-dimensional (2D) materials are already opening many new possibilities in such fields of technology as electronics and magnonics, but far more could be achieved if the number and diversity of 2D materials is increased. So far, only a few dozen 2D crystals have been extracted from materials that exhibit a layered phase in ambient conditions, omitting entirely the large number of layered materials that may exist in other temperatures and pressures. Here, we demonstrate how these structures can be stabilized in 2D van der Waals stacks under room temperature via growing them directly in graphene encapsulation by using graphene oxide as the template material. Specifically, we produce an ambient stable 2D structure of copper and iodine, a material that normally only occurs in layered form at elevated temperatures between 645 and 675 K. Our results establish a simple route to the production of more exotic phases of materials that would otherwise be difficult or impossible to stabilize for experiments in ambient.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
DOI: 10.1002/adma.202106922
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Pedrazo Tardajos A (2021) Advanced graphene supports for 3D in situ transmission electron microscopy. 247 p
Abstract: Transmission electron microscopy (TEM) is an ideal tool to investigate nanomaterials. The information from TEM experiments allows us to link the structure and composition of nanomaterials to their intrinsic physical properties. However, despite the significant evolution of the TEM field during the last two decades, major progress is still possible through the development of optimal TEM techniques and supports. The results presented in this thesis focus on the optimization of sample supports and their application. Among the different options, graphene has previously been reported as useful sample support for electron microscopy due to its unparalleled properties, for example, it is the thinnest known support and provides a protective effect to the sample under investigation. Unfortunately, commercial graphene grids show poor quality, in terms of intactness and cleanness, inhibiting their wide application within the field. Therefore, this thesis focuses on the application of optimized graphene TEM grids, obtained by transferring high quality graphene using an advanced procedure. This improvement on the transfer has enabled the visualization of materials with low contrast and high sensitivity towards the electron beam, such as surface ligands capping gold nanoparticles or metal halide perovskites. Furthermore, the implemented protocol is not only of interest for conventional TEM grids but also a major benefit for in situ TEM studies, where the sample is investigated in real time under certain stimuli. Hence, the same graphene transfer technology can be also applied to advanced in situ MEMS holders dedicated for both heating and gas experiments, where the thickness and insulating nature of the silicon nitride (Si3N4) support may hamper some applications. By engineering periodic arrays of holes in their Si3N4 membrane by focused ion beam, onto which the graphene is transferred, it has been possible to get proof-of-concept 3D in situ investigations of heat-induced morphological and compositional transformations of complex nanosystems. As an example, it has enabled the investigation of the possible phase-transition of metal halide perovskites upon heating using 2D and 3D structural characterization. Moreover, it has allowed the study of in situ three-dimensional nanoparticle dynamics during gas phase catalysis as well as the first steps that would lead towards the design and creation of the first Graphene Gas Cell. Consequently, implementation of the advanced graphene transfer technology described in this thesis is envisaged to impact a broad range of future experiments.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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Skorikov A, Heyvaert W, Albrecht W, Pelt DM, Bals S (2021) EMAT Simulated 3D Nanoparticle Structures Dataset
Abstract: This dataset contains 1000 simulated nanoparticle-like 3D structures and noisy EDX-like elemental maps based on them. These data are intended to be used for quantitative analysis of data processing methods in (EDX) tomography of nanoparticles and training the data-driven approaches for these tasks. The dataset is structured as follows: voxel_data/clean 3D voxel grid representation of the simulated nanoparticles. Voxel intensities are adjusted so that the total intensity equals 103. All 3D structures have unique identifiers in 0..999 range. The data derived from a 3D structure preserves this unique identifier. sinograms/clean Tilt series of projection images obtained from the corresponding 3D structures over an angular range of -75..75 degrees with a tilt step of 10 degrees to simulate a typical tilt series used in EDX tomography. Total intensity in each projection image equals 103. sinograms/noisy Tilt series of projection images corrupted with Poisson noise and an additional spatially uniform background noise. projections/clean Projection images extracted from the clean tilt series at 0 degrees tilt angle. projections/noisy Projection images extracted from the noisy tilt series at 0 degrees tilt angle. images/clean Visualizations of the clean projections as PNG images with the intensity range adjusted to 0..255 images/noisy Visualizations of the noisy projections as PNG images with the intensity range adjusted to 0..255
Keywords: Dataset; Electron microscopy for materials research (EMAT)
DOI: 10.5281/zenodo.4580545
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Du K (2021) In situ TEM study on the manipulation of ferroelectrics. 91 p
Abstract: The strong correlated oxide systems attract a lot of attentions of scientists recently, the coexistence and interplay between various degrees of freedom, such as charge, spin and orbital, has been demonstrated to induce some fancy physical properties and phenomenon, including metal-insulator transition, high temperature superconductivity, colossal magnetoresistance. As a part of the strong correlated oxide systems, the ferroelectrics is abundant in both physical properties and application. First, if the electric dipole continuously rotating around a stable core then a topological structure is produced. If people could manipulate the topological structure and simultaneously observe the structure evolution, with external field applied on the topological structure, then it is very likely for such kind of ferroelectrics to be the next generation of storage, for it is reported to need low power input and produce high density of storage. In the other hand, in solids, charge polarity can one-to-one correspond to spin polarity phenomenologically, such as ferroelectricity and ferromagnetism, antiferroelectricity and antiferromagnetism, but ferrielectricity and ferrimagnetism kept telling a disparate story in microscopic level. The claimed “ferrielectrics” in existing research is equivalent to ferroelectric ones, thus the findings of such a real irreducible solids would complete the last piece of the ferroelectrics family. While solving the above two questions remain challengeable: the size of topological structure is small (typically below 10 nm), general characterization methods are insufficient for such high demand on space resolution, not to mention manipulating and observing its dynamic behavior at an atomic level. Here, employing the spherical aberration corrected electron microscope, we applied external field (heating and bias) on ferroelectrics. Combined with high-end characterization methods including the high-angle annular dark field (HAADF-STEM) image, Electron Energy Loss Spectroscopy (EELS) and integrated differential phase contrast (iDPC), the dynamic evolution of ferroelectrics are observed and analyzed. The main findings of this paper could be concluded as listed here: (1) PbTiO3(001)// SrTiO3(001) is grown on DyScO3 and SrRuO3 by pusled laser deposition, the atomical EDS mapping results reveal that the interface between PTO and STO is atomically sharp. Increasing the thickness of PTO from 1 uc to 21 uc, the topological structure wihtin PTO layer would transform from a/c domain to wave, vortex and finally flux closure domain. The geometric phase analysis results (GPA) reveal that above topological structures are corresponding to various strain. (2) Combined with in-situ biasing holder, the electric bias was applied on polar vortex, and it evolved from vortex (0 V) to polar wave (2 V) and finally polar down (5 V). EELS analysis was performed and we find that negative charge is gathered at vortex core, which turns the Ti4+ to Ti3+ there. The oxygen vacancy at negative polarization surface and the negative charge at the positive polarization surface realized the polarization screening of polar down domain. (3) Through the atomic inspection and analysis on lattice structure of BaFe2Se3, the near ladders within single unit are found to be different in degree of tetramerization, thus leading to a residual polarization along the a-axis. The further in-situ heating and biasing experiment was conducted on BaFe2Se3, and the strong and weak ladders are proved to be independent for their behavior under external field. This findings distinguishes ferrielectrics from ferroelectrics in solids.
Keywords: Doctoral thesis; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
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Prabhakara V (2021) Strain measurement for semiconductor applications with Raman spectroscopy and Transmission electron microscopy. 149 p
Abstract: Scaling down the size of transistors has been a trend for several decades which has led to improved transistor performance, increased transistor density and hence the overall computation power of IC chips. The trend slowed in recent years due to reliability and power consumption issues at the nanoscale. Hence strain is introduced into transistor channels that has beneficial effects on improving the mobility of charge carriers, providing an alternative pathway for enhancing transistor performance. Therefore, monitoring strain is vital for the semiconductor industry. With the recent trend of decreasing device dimensions (FinFETS ~ 10-20nm) and strain modulation being used throughout, industry needs a reliable and fast method as quality control or defect characterisation. Such a universal strain measurement method does not exist, and one relies on a combination of quantitative in-line methods and complex off-line approaches. In this thesis, I investigated TEM and Raman spectroscopy-based methodologies for strain measurement. In terms of TEM methodologies, advancements are made for the STEM moiré imaging, targeting strain spatial resolution enhancement. I introduce advanced quadrature demodulation and phase stepping interferometry applied to STEM moiré that greatly enhances the spatial resolution while providing enhanced field of view and sensitivity for strain measurement. We introduce ways to reduce scan distortions in strain maps using an alternative scan strategy called “Block scanning” and the non-linear regression applied for strain extraction. Prospects for 3D strain analysis using high-resolution tomography is also investigated which gives direct access for the full second order strain tensors calculation. Finally, we compare strain measurements from TEM techniques with inline techniques like Raman spectroscopy. Raman stress measurement involves sensitive identification of the TO and LO phonon peaks. Raman spectrum of strained Ge transistor channel consists of strongly overlapping peaks within the spectral resolution of the spectrometer. Hence, the process of deconvolution of the two peaks is rather challenging. Hence, we explore new polarisation geometries like radially polarised incoming light which was shown to ease the deconvolution problem resulting in improved precision for Raman stress–strain measurements.
Keywords: Doctoral thesis; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
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“&alpha, phase growth and branching in titanium alloys”. Shi R, Choudhuri D, Kashiwar A, Dasari S, Wang Y, Banerjee R, Banerjee D, Philosophical magazine (2021). http://doi.org/10.1080/14786435.2021.1998693
Abstract: The morphology and spatial distribution of alpha (α) precipitates have been mapped as a function of Mo content in Ti-Mo binary alloys employing a combinatorial approach. Heat-treatments were carried out on compositionally graded Ti-xMo samples processed using a rapid throughput laser engineered net shape (LENS) process. The composition space spans 1.5 at% to 6 at% Mo with ageing at 750°C, 650°C and 600°C following a β solution treatment. Three distinct regimes of α morphology and distribution were observed. These are colony-dominated microstructures originating from grain boundary α allotriomorphs, bundles of intragranular α laths, and homogeneously distributed individual fine-scale α laths. Branching of the α precipitates was observed in all these domains in a manner reminiscent of solid-state dendritic growth. The phenomenon is particularly apparent at low volume fractions of α. Similar features are present in a wide variety of alloy compositions. 3-dimensional features of such branched structures have been analysed. Simulation of the branching process by phase field methods incorporating anisotropy in the α/β interface energy and elasticity suggests that it can be initiated at growth ledges present at broad faces of the α laths, driven by the enhancement of the diffusion flux at these steps. The dependence of branching on various parameters such as supersaturation and diffusivity, and microstructural features like ledge height and distribution and the presence of adjacent α variants has been evaluated.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 1.505
DOI: 10.1080/14786435.2021.1998693
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Velazco Torrejó,n A (2021) Alternative scan strategies for high resolution STEM imaging. 131 p
Abstract: Currently, a large variety of materials are studied by transmission electron microscopy (TEM) as it offers the possibility to perform structural and elemental analysis at a local scale. Relatively recent advances in aberration correctors and electron sources allow the instrument to achieve atomic resolution. Along with these advances, a state-of-the-art technology has been reached in TEM. However, the instrument is far from being perfect and imperfections or external sources can make the interpretation of information troublesome. Environmental factors such as acoustic and mechanical vibrations, temperature fluctuations, etc., can induce sample drift and create image distortions. These distortions are enhanced in scanning operation because of the serial acquisition of the information, which are more apparent at atomic resolution as small field of views are imaged. In addition, scanning distortions are induced due to the finite time response of the scan coils. These types of distortions would reduce precision in atomic-scale strain analysis, for instance, in semiconductors. Most of the efforts to correct these distortions are focused on data processing techniques post-acquisition. Another limitation in TEM is beam damage effects. Beam damage arises because of the energy transferred to the sample in electron-sample interactions. In scanning TEM, at atomic resolution, the increased electron charge density (electron dose) carried on a sub-Å size electron probe may aggravate beam damage effects. Soft materials such as zeolites, organic, biological materials, etc., can be destroyed under irradiation limiting the amount of information that can be acquired. Current efforts to circumvent beam damage are mostly based on low electron dose acquisitions and data processing methods to maximize the signal at low dose conditions. In this thesis, a different approach is given to address drift and scanning distortions, as well as beam damage effects. Novel scan strategies are proposed for that purpose, which are shown to substantially overcome these issues compared to the standard scan method in TEM.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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Roegiers J (2021) Development of combined photocatalytic and active carbon fiber technology for indoor air purification based on Multiphysics models. XXX, 197 p
Abstract: Exposure to volatile organic compounds (VOCs) remains a major public health concern. Indoor VOC concentrations typically far exceed outdoor levels due to a variety of emission sources and the stringent insulation measures that are imposed today. Many attempts have been made to use photocatalysis for indoor air purification. In an ideal situation, photocatalysis is capable of complete mineralization of VOCs to H2O and CO2, without any byproduct formation. Moreover, the process can take place at standard atmospheric conditions, i.e. ambient temperature and atmospheric pressure. However, successful exploitation is still impeded due to low conversion efficiency, significant pressure loss (and hence a high energy consumption) and byproduct formation. In the first part of this thesis an attempt was made to tackles these problems by designing a novel type of photocatalytic (PCO) reactor. The PCO device consists of a cylindrical vessel filled with TiO2-coated glass tubes and equipped with UV fluorescence lamps. It was investigated in terms of fluid dynamics, coating properties, UV-light distribution and photocatalytic activity. Experimental data was later used to develop and calibrate a Multiphysics model. The model proved to be a useful tool for designing and upscaling the PCO reactor. Consequently, an optimized prototype reactor was constructed and tested according the CEN-EN-16846-1 standard for VOC removal. Although the prototype showed promising results for lab-scale conditions, it struggled with byproduct formation when purifying ppb-level VOCs. In the second part of this thesis, activated carbon adsorption was investigated in order to combine it with photocatalysis. Activated carbon fiber was opted for its fast kinetics, high adsorption capacity and thermo-electrical regeneration. The filter was studied in detail regarding the adsorption of polar and apolar VOCs at indoor air concentration levels and regeneration capabilities. Experimental data was used to develop a Multiphysics model for activated carbon adsorption as well. Consequently, a novel type of ACF filter was developed using the Multiphysics model, which was equipped with electrodes in the tips of the pleats for effective thermal regeneration. In the last part, the combination of both ACF and PCO was studied using a realistic case study. Based on the Multiphysics model, the feasibility of a so-called hybrid air purification device could be investigated. The Multiphysics model shows promising results for this hybrid PCO-ACF system and hence, a demo setup was constructed for future research.
Keywords: Doctoral thesis; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Sustainable Energy, Air and Water Technology (DuEL)
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De wael A (2021) Model-based quantitative scanning transmission electron microscopy for measuring dynamic structural changes at the atomic scale. xiv, 146 p
Abstract: Nanomaterialen kunnen uiterst interessante eigenschappen vertonen voor een verscheidenheid aan veelbelovende toepassingen, gaande van zonnecrème tot batterijen voor elektrische auto’s. Een nanometer is een miljard keer kleiner dan een meter. Op deze schaal kunnen de materiaaleigenschappen volledig verschillen van bulkmaterialen op grotere schaal. Bovendien hangen de eigenschappen van nanomaterialen sterk af van hun exacte grootte en vorm. Kleine verschillen in de posities van de atomen, in de grootte-orde van een picometer (nog eens duizend maal kleiner dan een nanometer), kunnen de fysische eigenschappen al drastisch beïnvloeden. Daarom is een betrouwbare kwantificering van de atomaire structuur van kritisch belang om de evolutie naar materiaalontwerp mogelijk te maken en inzicht te verwerven in de relatie tussen de fysische eigenschappen en de structuur van nanomaterialen. Daarnaast kan de atomaire structuur van nanomaterialen ook veranderen in de loop van de tijd ten gevolge van verschillende fysische processen. Het onderzoek dat in deze thesis gepresenteerd wordt, maakt het mogelijk om de dynamische structuurveranderingen van nanomaterialen betrouwbaar te kwantificeren op atomaire schaal door gebruik te maken van raster transmissie elektronenmicroscopie (STEM). Ik heb dit gerealiseerd door methodes te ontwikkelen waarmee ik het aantal atomen “achter elkaar” kan tellen in elke atoomkolom van een nanomateriaal, en dit op basis van beelden opgenomen met een elektronenmicroscoop. Een belangrijk verschil met telmethodes voor de analyse van een enkel beeld is het schatten van de kans dat een atoomkolom atomen zal verliezen of bijkrijgen van het ene naar het andere beeld in de tijdreeks. Deze kwantitatieve methode kan het ontrafelen van de tijdsafhankelijke structuur-eigenschappen relatie van een nanomateriaal mogelijk maken, wat uiteindelijk kan leiden tot efficiënter design en productie van nanomaterialen voor innovatieve toepassingen.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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Jannis D (2021) Novel detection schemes for transmission electron microscopy. iv, 208 p
Abstract: Electron microscopy is an excellent tool which provides resolution down to the atomic scale with up to pm precision in locating atoms. The characterization of materials in these length scales is of utmost importance to answer questions in biology, chemistry and material science. The successful implementation of aberration-corrected microscopes made atomic resolution imaging relatively easy, this could give the impression that the development of novel electron microscopy techniques would stagnate and only the application of these instruments as giant magnifying tools would continue. This is of course not true and a multitude of problems still exist in electron microscopy. Two of such issues are discussed below. One of the biggest problems in electron microscopy is the presence of beam damage which occurs due the fact that the highly energetic incoming electrons have sufficient kinetic energy to change the structure of the material. The amount of damage induced depends on the dose, hence minimizing this dose during an experiment is beneficial. This minimizing of the total dose comes at the expense of more noise due to the counting nature of the electrons. For this reason, the implementation of four dimensional scanning transmission electron microscopy (4D STEM) experiments has reduced the total dose needed per acquisition. However, the current cameras used to measure the diffraction patterns are still two orders of magnitude slower than to the conventional STEM methods. Improving the acquisition speed would make the 4D STEM technique more feasible and is of utmost importance for the beam sensitive materials since less dose is used during the acquisition. In TEM there is not only the possibility to perform imaging experiments but also spectroscopic measurements. There are two frequently used methods: electron energy-loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDX). EELS measures the energy-loss spectrum of the incoming electron which gives information on the available excitations in the material providing elemental sensitivity. In EDX, the characteristic x-rays, arising from the decay of an atom which is initially excited due to the incoming electrons, are detected providing similar elemental analysis. Both methods are able to provide comparable elemental information where in certain circumstances one outperforms the other. However, both methods have a detection limit of approximately 100-1000 ppm which is not sufficient for some materials. In this thesis, two novel techniques which can make significant progress for the two problems discussed above.
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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“Phase-transformation-induced giant deformation in thermoelectric Ag₂Se semiconductor”. Liang Q, Yang D, Xia F, Bai H, Peng H, Yu R, Yan Y, He D, Cao S, Van Tendeloo G, Li G, Zhang Q, Tang X, Wu J, Advanced Functional Materials , 2106938 (2021). http://doi.org/10.1002/ADFM.202106938
Abstract: In most semiconducting metal chalcogenides, a large deformation is usually accompanied by a phase transformation, while the deformation mechanism remains largely unexplored. Herein, a phase-transformation-induced deformation in Ag2Se is investigated by in situ transmission electron microscopy, and a new ordered high-temperature phase (named as alpha '-Ag2Se) is identified. The Se-Se bonds are folded when the Ag+-ion vacancies are ordered and become stretched when these vacancies are disordered. Such a stretch/fold of the Se-Se bonds enables a fast and large deformation occurring during the phase transition. Meanwhile, the different Se-Se bonding states in alpha-, alpha '-, beta-Ag2Se phases lead to the formation of a large number of nanoslabs and the high concentration of dislocations at the interface, which flexibly accommodate the strain caused by the phase transformation. This study reveals the atomic mechanism of the deformation in Ag2Se inorganic semiconductors during the phase transition, which also provides inspiration for understanding the phase transition process in other functional materials.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
DOI: 10.1002/ADFM.202106938
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“TEM investigation of SCC crack tips in high Si stainless steel tapered specimens”. Penders A, Konstantinovic MJ, Van Renterghem W, Bosch RW, Schryvers D, Corrosion Engineering Science And Technology (2021). http://doi.org/10.1080/1478422X.2021.1961665
Abstract: The stress corrosion cracking (SCC) mechanism is investigated in high Si duplex stainless steel in a simulated PWR environment based on TEM analysis of FIB-extracted SCC crack tips. The microstructural investigation in the near vicinity of SCC crack tips illustrates a strain-rate dependence in SCC mechanisms. Detailed analysis of the crack tip morphology, that includes crack tip oxidation and surrounding deformation field, indicates the existence of an interplay between corrosion- and deformation-driven failure as a function of the strain rate. Slow strain-rate crack tips exhibit a narrow cleavage failure which can be linked to the film-induced failure mechanism, while rounded shaped crack tips for faster strain rates could be related to the strain-induced failure. As a result, two nominal strain-rate-dependent failure regimes dominated either by corrosion or deformation-driven cracking mechanisms can be distinguished.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 0.879
DOI: 10.1080/1478422X.2021.1961665
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