| Records |
Author  |
Wang, A.; Chen, F.R.; Van Aert, S.; van Dyck, D. |
| Title |
Direct structure inversion from exit waves : part 2 : a practical example |
Type |
A1 Journal article |
| Year |
2012 |
Publication |
Ultramicroscopy |
Abbreviated Journal |
Ultramicroscopy |
| Volume |
116 |
Issue |
|
Pages |
77-85 |
| Keywords |
A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab |
| Abstract |
This paper is the second part of a two-part paper on direct structure inversion from exit waves. In the first part, a method has been proposed to quantitatively determine structure parameters with atomic resolution such as atom column positions, surface profile and the number of atoms in the atom columns. In this part, the theory will be demonstrated by means of a Au[110] exit wave reconstructed from a set of focal-series images. The procedures to analyze the experimentally reconstructed exit wave in terms of quantitative structure information are described in detail. |
| Address |
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| Corporate Author |
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Thesis |
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| Publisher |
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Place of Publication |
Amsterdam |
Editor |
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| Language |
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Wos |
000304473700011 |
Publication Date |
2012-03-28 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
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Series Issue |
|
Edition |
|
| ISSN |
0304-3991; |
ISBN |
|
Additional Links |
UA library record; WoS full record; WoS citing articles |
| Impact Factor |
2.843 |
Times cited |
8 |
Open Access |
|
| Notes |
Fwo |
Approved |
Most recent IF: 2.843; 2012 IF: 2.470 |
| Call Number |
UA @ lucian @ c:irua:96660 |
Serial |
724 |
| Permanent link to this record |
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| Author |
Wang, A.; Chen, F.R.; Van Aert, S.; van Dyck, D. |
| Title |
A method to determine the local surface profile from reconstructed exit waves |
Type |
A1 Journal article |
| Year |
2011 |
Publication |
Ultramicroscopy |
Abbreviated Journal |
Ultramicroscopy |
| Volume |
111 |
Issue |
8 |
Pages |
1352-1359 |
| Keywords |
A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab |
| Abstract |
Reconstructed exit waves are useful to quantify unknown structure parameters such as the position and composition of the atom columns at atomic scale. Existing techniques provide a complex wave in a flat plane which is close to the plane where the electrons leave the atom columns. However, due to local deviation in the flatness of the exit surface, there will be an offset between the plane of reconstruction and the actual exit of a specific atom column. Using the channelling theory, it has been shown that this defocus offset can in principle be determined atom column-by-atom column. As such, the surface roughness could be quantified at atomic scale. However, the outcome strongly depends on the initial plane of reconstruction especially in a crystalline structure. If this plane is further away from the true exit, the waves of the atom columns become delocalized and interfere mutually which strongly complicates the interpretation of the exit wave in terms of the local structure. In this paper, we will study the delocalization with defocus using the channelling theory in a more systematic way. |
| Address |
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| Corporate Author |
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Thesis |
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| Publisher |
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Place of Publication |
Amsterdam |
Editor |
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| Language |
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Wos |
000300461100049 |
Publication Date |
2011-05-03 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
|
Series Issue |
|
Edition |
|
| ISSN |
0304-3991; |
ISBN |
|
Additional Links |
UA library record; WoS full record; WoS citing articles |
| Impact Factor |
2.843 |
Times cited |
3 |
Open Access |
|
| Notes |
Fwo |
Approved |
Most recent IF: 2.843; 2011 IF: 2.471 |
| Call Number |
UA @ lucian @ c:irua:88941 |
Serial |
2017 |
| Permanent link to this record |
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| Author |
Wang, A.; Turner, S.; Van Aert, S.; van Dyck, D. |
| Title |
An alternative approach to determine attainable resolution directly from HREM images |
Type |
A1 Journal article |
| Year |
2013 |
Publication |
Ultramicroscopy |
Abbreviated Journal |
Ultramicroscopy |
| Volume |
133 |
Issue |
|
Pages |
50-61 |
| Keywords |
A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab |
| Abstract |
The concept of resolution in high-resolution electron microscopy (HREM) is the power to resolve neighboring atoms. Since the resolution is related to the width of the point spread function of the microscope, it could in principle be determined from the image of a point object. However, in electron microscopy there are no ideal point objects. The smallest object is an individual atom. If the width of an atom is much smaller than the resolution of the microscope, this atom can still be considered as a point object. As the resolution of the microscope enters the sub-Å regime, information about the microscope is strongly entangled with the information about the atoms in HREM images. Therefore, we need to find an alternative method to determine the resolution in an object-independent way. In this work we propose to use the image wave of a crystalline object in zone axis orientation. Under this condition, the atoms of a column act as small lenses so that the electron beam channels through the atom column periodically. Because of this focusing, the image wave of the column can be much more peaked than the constituting atoms and can thus be a much more sensitive probe to measure the resolution. Our approach is to use the peakiness of the image wave of the atom column to determine the resolution. We will show that the resolution can be directly linked to the total curvature of the atom column wave. Moreover, we can then directly obtain the resolution of the microscope given that the contribution from the object is known, which is related to the bounding energy of the atom. The method is applied on an experimental CaTiO3 image wave. |
| Address |
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| Corporate Author |
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Thesis |
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| Publisher |
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Place of Publication |
Amsterdam |
Editor |
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| Language |
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Wos |
000324471800007 |
Publication Date |
2013-05-23 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
|
Series Issue |
|
Edition |
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| ISSN |
0304-3991; |
ISBN |
|
Additional Links |
UA library record; WoS full record |
| Impact Factor |
2.843 |
Times cited |
|
Open Access |
|
| Notes |
FWO; Hercules; Esteem2; esteem2_jra2 |
Approved |
Most recent IF: 2.843; 2013 IF: 2.745 |
| Call Number |
UA @ lucian @ c:irua:109919 |
Serial |
90 |
| Permanent link to this record |
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| Author |
Wang, A.; Van Aert, S.; Goos, P.; van Dyck, D. |
| Title |
Precision of three-dimensional atomic scale measurements from HRTEM images : what are the limits? |
Type |
A1 Journal article |
| Year |
2012 |
Publication |
Ultramicroscopy |
Abbreviated Journal |
Ultramicroscopy |
| Volume |
114 |
Issue |
|
Pages |
20-30 |
| Keywords |
A1 Journal article; Engineering Management (ENM); Electron microscopy for materials research (EMAT); Vision lab |
| Abstract |
In this paper, we investigate to what extent high resolution transmission electron microscopy images can be used to measure the mass, in terms of thickness, and surface profile, corresponding to the defocus offset, of an object at the atomic scale. Therefore, we derive an expression for the statistical precision with which these object parameters can be estimated in a quantitative analysis. Evaluating this expression as a function of the microscope settings allows us to derive the optimal microscope design. Acquiring three-dimensional structure information in terms of thickness turns out to be much more difficult than obtaining two-dimensional information on the projected atom column positions. The attainable precision is found to be more strongly affected by processes influencing the image contrast, such as phonon scattering, than by the specific choice of microscope settings. For a realistic incident electron dose, it is expected that atom columns can be distinguished with single atom sensitivity up to a thickness of the order of the extinction distance. A comparable thickness limit is determined to measure surface steps of one atom. An increase of the electron dose shifts the limiting thickness upward due to an increase in the signal-to-noise ratio. |
| Address |
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| Corporate Author |
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Thesis |
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| Publisher |
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Place of Publication |
Amsterdam |
Editor |
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| Language |
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Wos |
000301954300003 |
Publication Date |
2012-01-06 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
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Series Issue |
|
Edition |
|
| ISSN |
0304-3991; |
ISBN |
|
Additional Links |
UA library record; WoS full record; WoS citing articles |
| Impact Factor |
2.843 |
Times cited |
5 |
Open Access |
|
| Notes |
Fwo |
Approved |
Most recent IF: 2.843; 2012 IF: 2.470 |
| Call Number |
UA @ lucian @ c:irua:94116 |
Serial |
2692 |
| Permanent link to this record |
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| Author |
Yu, C.-P.; Friedrich, T.; Jannis, D.; Van Aert, S.; Verbeeck, J. |
| Title |
Real-Time Integration Center of Mass (riCOM) Reconstruction for 4D STEM |
Type |
A1 Journal article |
| Year |
2022 |
Publication |
Microscopy and microanalysis |
Abbreviated Journal |
Microsc Microanal |
| Volume |
|
Issue |
|
Pages |
1-12 |
| Keywords |
A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT) |
| Abstract |
A real-time image reconstruction method for scanning transmission electron microscopy (STEM) is proposed. With an algorithm requiring only the center of mass of the diffraction pattern at one probe position at a time, it is able to update the resulting image each time a new probe position is visited without storing any intermediate diffraction patterns. The results show clear features at high spatial frequency, such as atomic column positions. It is also demonstrated that some common post-processing methods, such as band-pass filtering, can be directly integrated in the real-time processing flow. Compared with other reconstruction methods, the proposed method produces high-quality reconstructions with good noise robustness at extremely low memory and computational requirements. An efficient, interactive open source implementation of the concept is further presented, which is compatible with frame-based, as well as event-based camera/file types. This method provides the attractive feature of immediate feedback that microscope operators have become used to, for example, conventional high-angle annular dark field STEM imaging, allowing for rapid decision-making and fine-tuning to obtain the best possible images for beam-sensitive samples at the lowest possible dose. |
| Address |
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| Corporate Author |
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Thesis |
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| Publisher |
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Place of Publication |
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Editor |
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| Language |
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Wos |
000792176100001 |
Publication Date |
2022-04-25 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
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Series Issue |
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Edition |
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| ISSN |
1431-9276 |
ISBN |
|
Additional Links |
UA library record; WoS full record; WoS citing articles |
| Impact Factor |
2.8 |
Times cited |
7 |
Open Access |
OpenAccess |
| Notes |
Bijzonder Onderzoeksfonds UGent; H2020 European Research Council, 770887 ; H2020 European Research Council, 823717 ; H2020 European Research Council, ESTEEM3 / 823717 ; H2020 European Research Council, PICOMETRICS / 770887 ; Fonds Wetenschappelijk Onderzoek, 30489208 ; Herculesstichting; esteem3reported; esteem3jra |
Approved |
Most recent IF: 2.8 |
| Call Number |
EMAT @ emat @c:irua:188538 |
Serial |
7068 |
| Permanent link to this record |
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| Author |
Zhang, Z.; Lobato, I.; Brown, H.; Jannis, D.; Verbeeck, J.; Van Aert, S.; Nellist, P. |
| Title |
Generalised oscillator strength for core-shell electron excitation by fast electrons based on Dirac solutions |
Type |
Dataset |
| Year |
2023 |
Publication |
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Abbreviated Journal |
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| Volume |
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Issue |
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Pages |
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| Keywords |
Dataset; Electron microscopy for materials research (EMAT) |
| Abstract |
Inelastic excitation as exploited in Electron Energy Loss Spectroscopy (EELS) contains a rich source of information that is revealed in the scattering process. To accurately quantify core-loss EELS, it is common practice to fit the observed spectrum with scattering cross-sections calculated using experimental parameters and a Generalized Oscillator Strength (GOS) database [1]. The GOS is computed using Fermi’s Golden Rule and orbitals of bound and excited states. Previously, the GOS was based on Hartree-Fock solutions [2], but more recently Density Functional Theory (DFT) has been used [3]. In this work, we have chosen to use the Dirac equation to incorporate relativistic effects and have performed calculations using Flexible Atomic Code (FAC) [4]. This repository contains a tabulated GOS database based on Dirac solutions for computing double differential cross-sections under experimental conditions. We hope the Dirac-based GOS database can benefit the EELS community for both academic use and industry integration. Database Details: – Covers all elements (Z: 1-108) and all edges – Large energy range: 0.01 – 4000 eV – Large momentum range: 0.05 -50 Å-1 – Fine log sampling: 128 points for energy and 256 points for momentum – Data format: GOSH [3] Calculation Details: – Single atoms only; solid-state effects are not considered – Unoccupied states before continuum states of ionization are not considered; no fine structure – Plane Wave Born Approximation – Frozen Core Approximation is employed; electrostatic potential remains unchanged for orthogonal states when – core-shell electron is excited – Self-consistent Dirac–Fock–Slater iteration is used for Dirac calculations; Local Density Approximation is assumed for electron exchange interactions; continuum states are normalized against asymptotic form at large distances – Both large and small component contributions of Dirac solutions are included in GOS – Final state contributions are included until the contribution of the previous three states falls below 0.1%. A convergence log is provided for reference. Version 1.1 release note: – Update to be consistent with GOSH data format [3], all the edges are now within a single hdf5 file. A notable change in particular, the sampling in momentum is in 1/m, instead of previously in 1/Å. Great thanks to Gulio Guzzinati for his suggestions and sending conversion script. Version 1.2 release note: – Add “File Type / File version” information [1] Verbeeck, J., and S. Van Aert. Ultramicroscopy 101.2-4 (2004): 207-224. [2] Leapman, R. D., P. Rez, and D. F. Mayers. The Journal of Chemical Physics 72.2 (1980): 1232-1243. [3] Segger, L, Guzzinati, G, & Kohl, H. Zenodo (2023). doi:10.5281/zenodo.7645765 [4] Gu, M. F. Canadian Journal of Physics 86(5) (2008): 675-689. |
| Address |
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Thesis |
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Place of Publication |
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Editor |
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| Language |
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Wos |
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Publication Date |
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| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
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Series Issue |
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Edition |
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| ISSN |
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ISBN |
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Additional Links |
UA library record |
| Impact Factor |
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Times cited |
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Open Access |
Not_Open_Access |
| Notes |
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Approved |
Most recent IF: NA |
| Call Number |
UA @ admin @ c:irua:203392 |
Serial |
9042 |
| Permanent link to this record |
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| Author |
Zhang, Z.; Lobato, I.; De Backer, A.; Van Aert, S.; Nellist, P. |
| Title |
Fast generation of calculated ADF-EDX scattering cross-sections under channelling conditions |
Type |
A1 Journal article |
| Year |
2023 |
Publication |
Ultramicroscopy |
Abbreviated Journal |
|
| Volume |
246 |
Issue |
|
Pages |
113671 |
| Keywords |
A1 Journal article; Electron microscopy for materials research (EMAT) |
| Abstract |
Advanced materials often consist of multiple elements which are arranged in a complicated structure. Quantitative scanning transmission electron microscopy is useful to determine the composition and thickness of nanostructures at the atomic scale. However, significant difficulties remain to quantify mixed columns by comparing the resulting atomic resolution images and spectroscopy data with multislice simulations where dynamic scattering needs to be taken into account. The combination of the computationally intensive nature of these simulations and the enormous amount of possible mixed column configurations for a given composition indeed severely hamper the quantification process. To overcome these challenges, we here report the development of an incoherent non-linear method for the fast prediction of ADF-EDX scattering cross-sections of mixed columns under channelling conditions. We first explain the origin of the ADF and EDX incoherence from scattering physics suggesting a linear dependence between those two signals in the case of a high-angle ADF detector. Taking EDX as a perfect incoherent reference mode, we quantitatively examine the ADF longitudinal incoherence under different microscope conditions using multislice simulations. Based on incoherent imaging, the atomic lensing model previously developed for ADF is now expanded to EDX, which yields ADF-EDX scattering cross-section predictions in good agreement with multislice simulations for mixed columns in a core–shell nanoparticle and a high entropy alloy. The fast and accurate prediction of ADF-EDX scattering cross-sections opens up new opportunities to explore the wide range of ordering possibilities of heterogeneous materials with multiple elements. |
| Address |
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| Corporate Author |
Zezhong Zhang |
Thesis |
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| Publisher |
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Place of Publication |
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Editor |
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| Language |
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Wos |
000995063900001 |
Publication Date |
2022-12-28 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
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Series Issue |
|
Edition |
|
| ISSN |
0304-3991 |
ISBN |
|
Additional Links |
UA library record; WoS full record; WoS citing articles |
| Impact Factor |
2.2 |
Times cited |
|
Open Access |
OpenAccess |
| Notes |
European Research Council 770887 PICOMETRICS; Fonds Wetenschappelijk Onderzoek No.G.0502.18N; Horizon 2020, 770887 ; Horizon 2020 Framework Programme; European Research Council, 823717 ESTEEM3 ; esteem3reported; esteem3JRa |
Approved |
Most recent IF: 2.2; 2023 IF: 2.843 |
| Call Number |
EMAT @ emat @c:irua:195890 |
Serial |
7251 |
| Permanent link to this record |
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| Author |
Zheng, Y.-R.; Vernieres, J.; Wang, Z.; Zhang, K.; Hochfilzer, D.; Krempl, K.; Liao, T.-W.; Presel, F.; Altantzis, T.; Fatermans, J.; Scott, S.B.; Secher, N.M.; Moon, C.; Liu, P.; Bals, S.; Van Aert, S.; Cao, A.; Anand, M.; Nørskov, J.K.; Kibsgaard, J.; Chorkendorff, I. |
| Title |
Monitoring oxygen production on mass-selected iridium–tantalum oxide electrocatalysts |
Type |
A1 Journal article |
| Year |
2021 |
Publication |
Nature Energy |
Abbreviated Journal |
Nat Energy |
| Volume |
|
Issue |
|
Pages |
|
| Keywords |
A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT) |
| Abstract |
Development of low-cost and high-performance oxygen evolution reaction catalysts is key to implementing polymer electrolyte membrane water electrolyzers for hydrogen production. Iridium-based oxides are the state-of-the-art acidic oxygen evolution reactio catalysts but still suffer from inadequate activity and stability, and iridium's scarcity motivates the discovery of catalysts with lower iridium loadings. Here we report a mass-selected iridium-tantalum oxide catalyst prepared by a magnetron-based cluster source with considerably reduced noble-metal loadings beyond a commercial IrO2 catalyst. A sensitive electrochemistry/mass-spectrometry instrument coupled with isotope labelling was employed to investigate the oxygen production rate under dynamic operating conditions to account for the occurrence of side reactions and quantify the number of surface active sites. Iridium-tantalum oxide nanoparticles smaller than 2 nm exhibit a mass activity of 1.2 ± 0.5 kA “g” _“Ir” ^“-1” and a turnover frequency of 2.3 ± 0.9 s-1 at 320 mV overpotential, which are two and four times higher than those of mass-selected IrO2, respectively. Density functional theory calculations reveal that special iridium coordinations and the lowered aqueous decomposition free energy might be responsible for the enhanced performance. |
| Address |
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| Corporate Author |
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Thesis |
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| Publisher |
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Place of Publication |
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Editor |
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| Language |
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Wos |
000728458000001 |
Publication Date |
2021-12-09 |
| Series Editor |
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Series Title |
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Abbreviated Series Title |
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| Series Volume |
|
Series Issue |
|
Edition |
|
| ISSN |
2058-7546 |
ISBN |
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Additional Links |
UA library record; WoS full record; WoS citing articles |
| Impact Factor |
|
Times cited |
95 |
Open Access |
OpenAccess |
| Notes |
Y.-R.Z. and Z.W acknowledge funding from the Toyota Research Institute. This project has received funding from VILLUM FONDEN (grant no. 9455) and the European Research Council under the European Union’s Horizon 2020 research and innovation programme (grants no. 741860-CLUNATRA, no. 815128−REALNANO and no. 770887−PICOMETRICS). S.B. and S.V.A. acknowledge funding from the Research Foundation Flanders (FWO, G026718N and G050218N). T.A. acknowledges the University of Antwerp Research Fund (BOF). STEM measurements were supported by the European Union's Horizon 2020 Research Infrastructure-Integrating Activities for Advanced Communities under grant agreement No 823717 – ESTEEM3.; sygmaSB |
Approved |
Most recent IF: NA |
| Call Number |
EMAT @ emat @c:irua:184794 |
Serial |
6903 |
| Permanent link to this record |
