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“Description of the thermalization process of the sputtered atoms in a glow discharge using a 3-dimensional Monte Carlo method”. Bogaerts A, van Straaten M, Gijbels R, Journal of applied physics 77, 1868 (1995). http://doi.org/10.1063/1.358887
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.183
Times cited: 87
DOI: 10.1063/1.358887
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“Hybrid Monte Carlo-fluid model of a direct current glow discharge”. Bogaerts A, Gijbels R, Goedheer W, Journal of applied physics 78, 2233 (1995). http://doi.org/10.1063/1.360139
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.183
Times cited: 117
DOI: 10.1063/1.360139
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“Intersubband-coupling and screening effects on the electron transport in a quasi-two-dimensional δ-doped semiconductor system”. Hai G-Q, Studart N, Peeters FM, Koenraad PM, Wolter JH, Journal of applied physics 80, 5809 (1996). http://doi.org/10.1063/1.363573
Abstract: The effects due to intersubband coupling and screening on the ionized impurity scattering are studied for a quasi-two-dimensional electron system in delta-doped semiconductors. We found that intersubband coupling plays an essential role in describing the screening properties and the effect of ionized impurity scattering on the mobility in a multisubband system. At the onset of the occupation of a higher subband, the screening due to the intersubband coupling leads to a reduction of the small angle scattering rate in the lower subband. We showed that such an effect is significant in a delta-doped quantum well and results in a pronounced increase of the quantum mobility at the onset of the occupation of a higher subband. (C) 1996 American Institute of Physics.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.183
Times cited: 40
DOI: 10.1063/1.363573
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“Microstructural and physical properties of layered manganite oxides related to the magnetoresistive perovskites”. Laffez P, Van Tendeloo G, Seshadri R, Hervieu M, Martin C, Maignan A, Raveau B, Journal of applied physics 80, 5850 (1996). http://doi.org/10.1063/1.363578
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.183
Times cited: 36
DOI: 10.1063/1.363578
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“The role of fast argon ions and atoms in the ionization of argon in a direct current glow discharge: a mathematical simulation”. Bogaerts A, Gijbels R, Journal of applied physics 78, 6427 (1995). http://doi.org/10.1063/1.360526
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.183
Times cited: 60
DOI: 10.1063/1.360526
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“Role of sputtered Cu atoms and ions in a direct current glow discharge: combined fluid and Monte Carlo model”. Bogaerts A, Gijbels R, Journal of applied physics 79, 1279 (1996). http://doi.org/10.1063/1.361023
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.183
Times cited: 81
DOI: 10.1063/1.361023
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“Structural defects and epitaxial rotation of C60 and C70 (111) films on GeS(001)”. Bernaerts D, Van Tendeloo G, Amelinckx S, Hevesi K, Gensterblum G, Yu LM, Pireaux JJ, Grey F, Bohr J, Journal of applied physics 80, 3310 (1996). http://doi.org/10.1063/1.363241
Abstract: A transmission electron microscopy study of epitaxial C-60 and C-70 films grown on a GeS (001) surface is presented. The relationship between the orientation of the substrate and the films and structural defects in the films, such as grain boundaries, unknown in bulk C-60 and C-70 crystals, are studied. Small misalignments of the overlayers with respect to the orientation of the substrate, so-called epitaxial rotations, exist mainly in C-70 films, but also sporadically in the C-60 overlayers. A simple symmetry model, previously used to predict the rotation of hexagonal overlayers on hexagonal substrates, is numerically tested and applied to the present situation. Some qualitative conclusions concerning the substrate-film interaction are deduced. (C) 1996 American Institute of Physics.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.183
Times cited: 6
DOI: 10.1063/1.363241
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“Theoretical investigation of CoSi2/Si1-xGex detectors: influence of a Si tunneling barrier on the electro-optical characteristics”. Chu DP, Peeters FM, Kolodinski S, Roca E, Journal of applied physics 79, 1151 (1996)
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.183
Times cited: 3
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“Bloch and localized electrons in semiconductor superlattices”. Helm M, Hilber W, Fromherz T, Peeters FM, Alavi K, Pathak RN, Semiconductor science and technology 9, 1989 (1994). http://doi.org/10.1088/0268-1242/9/11S/022
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.19
Times cited: 1
DOI: 10.1088/0268-1242/9/11S/022
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“Hot magneto-phonon and electro-phonon resonances in heterostructures”. Peeters FM, Devreese JT, Semiconductor science and technology: B 7, 15 (1992). http://doi.org/10.1088/0268-1242/7/3B/004
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Theory of quantum systems and complex systems
Impact Factor: 2.19
Times cited: 12
DOI: 10.1088/0268-1242/7/3B/004
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“Novel nonlinear transport phenomena in a triangular quantum well”. Kastalsky A, Peeters FM, Chan WK, Florez LT, Harbison JP, Semiconductor science and technology: B 7, 530 (1992). http://doi.org/10.1088/0268-1242/7/3B/138
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.19
Times cited: 4
DOI: 10.1088/0268-1242/7/3B/138
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“Warm-electron transport in a two-dimensional semiconductor”. Xu W, Peeters FM, Devreese JT, Semiconductor science and technology 7, 1251 (1992)
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Theory of quantum systems and complex systems
Impact Factor: 2.19
Times cited: 3
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“Conserving African biosphere reserves : a workshop on the valuation of ecosystem services in Man and the Biosphere Reserves”. Janssens de Bisthoven L, Rochette A-J, Verheyen E, Akpona TJ-D, Verbist B, Vanderhaegen K, Naturinda Z, Van Passel S, Berihun D, Munishi L, Hugé, J, Oryx 53, 609 (2019). http://doi.org/10.1017/S003060531900070X
Keywords: A1 Journal article; Engineering Management (ENM); Evolutionary ecology group (EVECO)
Impact Factor: 2.191
DOI: 10.1017/S003060531900070X
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“Conversion of platelets into dislocation loops and voidite formation in type IaB diamonds”. Evans T, Kiflawi I, Luyten W, Van Tendeloo G, Woods GS, Proceedings of the Royal Society of London: series A: mathematical and physical sciences 449, 295 (1995). http://doi.org/10.1098/rspa.1995.0045
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.192
Times cited: 32
DOI: 10.1098/rspa.1995.0045
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“Evaluation of different rectangular scan strategies for STEM imaging”. Velazco A, Nord M, Béché, A, Verbeeck J, Ultramicroscopy , 113021 (2020). http://doi.org/10.1016/j.ultramic.2020.113021
Abstract: STEM imaging is typically performed by raster scanning a focused electron probe over a sample. Here we investigate and compare three different scan patterns, making use of a programmable scan engine that allows to arbitrarily set the sequence of probe positions that are consecutively visited on the sample. We compare the typical raster scan with a so-called ‘snake’ pattern where the scan direction is reversed after each row and a novel Hilbert scan pattern that changes scan direction rapidly and provides an homogeneous treatment of both scan directions. We experimentally evaluate the imaging performance on a single crystal test sample by varying dwell time and evaluating behaviour with respect to sample drift. We demonstrate the ability of the Hilbert scan pattern to more faithfully represent the high frequency content of the image in the presence of sample drift. It is also shown that Hilbert scanning provides reduced bias when measuring lattice parameters from the obtained scanned images while maintaining similar precision in both scan directions which is especially important when e.g. performing strain analysis. Compared to raster scanning with flyback correction, both snake and Hilbert scanning benefit from dose reduction as only small probe movement steps occur.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 13
DOI: 10.1016/j.ultramic.2020.113021
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“Atom column detection from simultaneously acquired ABF and ADF STEM images”. Fatermans J, den Dekker Aj, Müller-Caspary K, Gauquelin N, Verbeeck J, Van Aert S, Ultramicroscopy 219, 113046 (2020). http://doi.org/10.1016/j.ultramic.2020.113046
Abstract: In electron microscopy, the maximum a posteriori (MAP) probability rule has been introduced as a tool to determine the most probable atomic structure from high-resolution annular dark-field (ADF) scanning transmission electron microscopy (STEM) images exhibiting low contrast-to-noise ratio (CNR). Besides ADF imaging, STEM can also be applied in the annular bright-field (ABF) regime. The ABF STEM mode allows to directly visualize light-element atomic columns in the presence of heavy columns. Typically, light-element nanomaterials are sensitive to the electron beam, limiting the incoming electron dose in order to avoid beam damage and leading to images exhibiting low CNR. Therefore, it is of interest to apply the MAP probability rule not only to ADF STEM images, but to ABF STEM images as well. In this work, the methodology of the MAP rule, which combines statistical parameter estimation theory and model-order selection, is extended to be applied to simultaneously acquired ABF and ADF STEM images. For this, an extension of the commonly used parametric models in STEM is proposed. Hereby, the effect of specimen tilt has been taken into account, since small tilts from the crystal zone axis affect, especially, ABF STEM intensities. Using simulations as well as experimental data, it is shown that the proposed methodology can be successfully used to detect light elements in the presence of heavy elements.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.2
Times cited: 9
DOI: 10.1016/j.ultramic.2020.113046
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“HAADF-STEM block-scanning strategy for local measurement of strain at the nanoscale”. Prabhakara V, Jannis D, Guzzinati G, Béché, A, Bender H, Verbeeck J, Ultramicroscopy 219, 113099 (2020). http://doi.org/10.1016/j.ultramic.2020.113099
Abstract: Lattice strain measurement of nanoscale semiconductor devices is crucial for the semiconductor industry as strain substantially improves the electrical performance of transistors. High resolution scanning transmission electron microscopy (HR-STEM) imaging is an excellent tool that provides spatial resolution at the atomic scale and strain information by applying Geometric Phase Analysis or image fitting procedures. However, HR-STEM images regularly suffer from scanning distortions and sample drift during image acquisition. In this paper, we propose a new scanning strategy that drastically reduces artefacts due to drift and scanning distortion, along with extending the field of view. It consists of the acquisition of a series of independent small subimages containing an atomic resolution image of the local lattice. All subimages are then analysed individually for strain by fitting a nonlinear model to the lattice images. The method allows flexible tuning of spatial resolution and the field of view within the limits of the dynamic range of the scan engine while maintaining atomic resolution sampling within the subimages. The obtained experimental strain maps are quantitatively benchmarked against the Bessel diffraction technique. We demonstrate that the proposed scanning strategy approaches the performance of the diffraction technique while having the advantage that it does not require specialized diffraction cameras.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 4
DOI: 10.1016/j.ultramic.2020.113099
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“Hidden Markov model for atom-counting from sequential ADF STEM images: Methodology, possibilities and limitations”. De wael A, De Backer A, Van Aert S, Ultramicroscopy 219, 113131 (2020). http://doi.org/10.1016/j.ultramic.2020.113131
Abstract: We present a quantitative method which allows us to reliably measure dynamic changes in the atomic structure of monatomic crystalline nanomaterials from a time series of atomic resolution annular dark field scanning transmission electron microscopy images. The approach is based on the so-called hidden Markov model and estimates the number of atoms in each atomic column of the nanomaterial in each frame of the time series. We discuss the origin of the improved performance for time series atom-counting as compared to the current state-of-the-art atom-counting procedures, and show that the so-called transition probabilities that describe the probability for an atomic column to lose or gain one or more atoms from frame to frame are particularly important. Using these transition probabilities, we show that the method can also be used to estimate the probability and cross section related to structural changes. Furthermore, we explore the possibilities for applying the method to time series recorded under variable environmental conditions. The method is shown to be promising for a reliable quantitative analysis of dynamic processes such as surface diffusion, adatom dynamics, beam effects, or in situ experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2020.113131
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“Source/drain materials for Ge nMOS devices: phosphorus activation in epitaxial Si, Ge, Ge1-xSnx and SiyGe1-x-ySnx”. Vohra A, Makkonen I, Pourtois G, Slotte J, Porret C, Rosseel E, Khanam A, Tirrito M, Douhard B, Loo R, Vandervorst W, Ecs Journal Of Solid State Science And Technology 9, 044010 (2020). http://doi.org/10.1149/2162-8777/AB8D91
Abstract: This paper benchmarks various epitaxial growth schemes based on n-type group-IV materials as viable source/drain candidates for Ge nMOS devices. Si:P grown at low temperature on Ge, gives an active carrier concentration as high as 3.5 x 10(20) cm(-3) and a contact resistivity down to 7.5 x 10(-9) Omega.cm(2). However, Si:P growth is highly defective due to large lattice mismatch between Si and Ge. Within the material stacks assessed, one option for Ge nMOS source/drain stressors would be to stack Si:P, deposited at contact level, on top of a selectively grown n-SiyGe1-x-ySnx at source/drain level, in line with the concept of Si passivation of n-Ge surfaces to achieve low contact resistivities as reported in literature (Martens et al. 2011 Appl. Phys. Lett., 98, 013 504). The saturation in active carrier concentration with increasing P (or As)-doping is the major bottleneck in achieving low contact resistivities for as-grown Ge or SiyGe1-x-ySnx. We focus on understanding various dopant deactivation mechanisms in P-doped Ge and Ge1-xSnx alloys. First principles simulation results suggest that P deactivation in Ge and Ge1-xSnx can be explained both by P-clustering and donor-vacancy complexes. Positron annihilation spectroscopy analysis, suggests that dopant deactivation in P-doped Ge and Ge1-xSnx is primarily due to the formation of P-n-V and SnmPn-V clusters. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.2
DOI: 10.1149/2162-8777/AB8D91
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“Reducing electron beam damage through alternative STEM scanning strategies, Part I: Experimental findings”. Velazco A, Béché, A, Jannis D, Verbeeck J, Ultramicroscopy 232, 113398 (2022). http://doi.org/10.1016/j.ultramic.2021.113398
Abstract: The highly energetic electrons in a transmission electron microscope (TEM) can alter or even completely destroy the structure of samples before sufficient information can be obtained. This is especially problematic in the case of zeolites, organic and biological materials. As this effect depends on both the electron beam and the sample and can involve multiple damage pathways, its study remained difficult and is plagued with irreproducibility issues, circumstantial evidence, rumors, and a general lack of solid data. Here we take on the experimental challenge to investigate the role of the STEM scan pattern on the damage behavior of a commercially available zeolite sample with the clear aim to make our observations as reproducible as possible. We make use of a freely programmable scan engine that gives full control over the tempospatial distribution of the electron probe on the sample and we use its flexibility to obtain multiple repeated experiments under identical conditions comparing the difference in beam damage between a conventional raster scan pattern and a newly proposed interleaved scan pattern that provides exactly the same dose and dose rate and visits exactly the same scan points. We observe a significant difference in beam damage for both patterns with up to 11 % reduction in damage (measured from mass loss). These observations demonstrate without doubt that electron dose, dose rate and acceleration voltage are not the only parameters affecting beam damage in (S)TEM experiments and invite the community to rethink beam damage as an unavoidable consequence of applied electron dose.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 18
DOI: 10.1016/j.ultramic.2021.113398
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“Event driven 4D STEM acquisition with a Timepix3 detector: Microsecond dwell time and faster scans for high precision and low dose applications”. Jannis D, Hofer C, Gao C, Xie X, Béché, A, Pennycook Tj, Verbeeck J, Ultramicroscopy 233, 113423 (2022). http://doi.org/10.1016/j.ultramic.2021.113423
Abstract: Four dimensional scanning transmission electron microscopy (4D STEM) records the scattering of electrons in a material in great detail. The benefits offered by 4D STEM are substantial, with the wealth of data it provides facilitating for instance high precision, high electron dose efficiency phase imaging via centre of mass or ptychography based analysis. However the requirement for a 2D image of the scattering to be recorded at each probe position has long placed a severe bottleneck on the speed at which 4D STEM can be performed. Recent advances in camera technology have greatly reduced this bottleneck, with the detection efficiency of direct electron detectors being especially well suited to the technique. However even the fastest frame driven pixelated detectors still significantly limit the scan speed which can be used in 4D STEM, making the resulting data susceptible to drift and hampering its use for low dose beam sensitive applications. Here we report the development of the use of an event driven Timepix3 direct electron camera that allows us to overcome this bottleneck and achieve 4D STEM dwell times down to 100 ns; orders of magnitude faster than what has been possible with frame based readout. We characterize the detector for different acceleration voltages and show that the method is especially well suited for low dose imaging and promises rich datasets without compromising dwell time when compared to conventional STEM imaging.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 31
DOI: 10.1016/j.ultramic.2021.113423
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“Reliable phase quantification in focused probe electron ptychography of thin materials”. Hofer C, Pennycook TJ, Ultramicroscopy 254, 113829 (2023). http://doi.org/10.1016/j.ultramic.2023.113829
Abstract: Electron ptychography provides highly sensitive, dose efficient phase images which can be corrected for aberrations after the data has been acquired. This is crucial when very precise quantification is required, such as with sensitivity to charge transfer due to bonding. Drift can now be essentially eliminated as a major impediment to focused probe ptychography, which benefits from the availability of easily interpretable simultaneous Z-contrast imaging. However challenges have remained when quantifying the ptychographic phases of atomic sites. The phase response of a single atom has a negative halo which can cause atoms to reduce in phase when brought closer together. When unaccounted for, as in integrating methods of quantification, this effect can completely obscure the effects of charge transfer. Here we provide a new method of quantification that overcomes this challenge, at least for 2D materials, and is robust to experimental parameters such as noise, sample tilt.
Keywords: A1 Journal Article; Electron Microscopy for Materials Science (EMAT) ;
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2023.113829
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“Nanowire facilitated transfer of sensitive TEM samples in a FIB”. Gorji S, Kashiwar A, Mantha LS, Kruk R, Witte R, Marek P, Hahn H, Kübel C, Scherer T, Ultramicroscopy 219, 113075 (2020). http://doi.org/10.1016/J.ULTRAMIC.2020.113075
Abstract: We introduce a facile approach to transfer thin films and other mechanically sensitive TEM samples inside a FIB with minimal introduction of stress and bending. The method is making use of a pre-synthetized flexible freestanding Ag nanowire attached to the tip of a typical tungsten micromanipulator inside the FIB. The main advantages of this approach are the significantly reduced stress-induced bending during transfer and attachment of the TEM sample, the very short time required to attach and cut the nanowire, the operation at very low dose and ion current, and only using the e-beam for Pt deposition during the transfer of sensitive TEM samples. This results in a reduced sample preparation time and reduced exposure to the ion beam or e-beam for Pt deposition during the sample preparation and thus also reduced contamination and beam damage. The method was applied to a number of thin films and different TEM samples in order to illustrate the advantageous benefits of the concept. In particular, the technique has been successfully tested for the transfer of a thin film onto a MEMS heating chip for in situ TEM experiments.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
DOI: 10.1016/J.ULTRAMIC.2020.113075
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“Dynamical diffraction of high-energy electrons investigated by focal series momentum-resolved scanning transmission electron microscopy at atomic resolution”. Robert Hl, Lobato I, Lyu Fj, Chen Q, Van Aert S, Van Dyck D, Müller-Caspary K, Ultramicroscopy 233, 113425 (2022). http://doi.org/10.1016/j.ultramic.2021.113425
Abstract: We report a study of scattering dynamics in crystals employing momentum-resolved scanning transmission
electron microscopy under varying illumination conditions. As we perform successive changes of the probe
focus, multiple real-space signals are obtained in dependence of the shape of the incident electron wave.
With support from extensive simulations, each signal is shown to be characterised by an optimum focus for
which the contrast is maximum and which differs among different signals. For instance, a systematic focus
mismatch is found between images formed by high-angle scattering, being sensitive to thickness and chemical
composition, and the first moment in diffraction space, being sensitive to electric fields. It follows that a single
recording at one specific probe focus is usually insufficient to characterise materials comprehensively. Most
importantly, we demonstrate in experiment and simulation that the second moment (
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2021.113425
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“Farmers' preferences towards water hyacinth control : a contingent valuation study”. Van Oijstaeijen W, Van Passel S, Cools J, Janssens de Bisthoven L, Huge J, Berihun D, Ejigu N, Nyssen J, Journal Of Great Lakes Research 46, 1459 (2020). http://doi.org/10.1016/J.JGLR.2020.06.009
Abstract: Lake Tana is the most important freshwater lake in Ethiopia. Besides pressures on water quality resulting from urbanization and deforestation, the invasion of the exotic water hyacinth (Eichhornia crassipes) poses new threats to the ecosystem. Water hyacinth, endemic to South America, is widely considered as the world's worst aquatic invasive weed. In 2011, the weed appeared on the northern shores of Lake Tana, expanding in south-eastern direction. The lake area affected by water hyacinth was last estimated in 2015 at 34,500 ha, which equals 16% of the total lake surface. In this research, the benefits of water hyacinth control and eradication for the rural population inhabiting the northern and northeastern villages bordering Lake Tana, are investigated. In the area, the population largely depends on farming and fishing. An assessment of the total economic benefit of eradication was conducted. The stakeholder-centered approach led to measuring the willingness to contribute in labor and cash terms. Results showed smallholders in the study are willing to contribute over half-a-million euros annually. Costs of management actions can be weighed to the benefits, where further research is needed on the impact on other stakeholder groups. Moreover, wetland management should advance to explore multiple pathways in an integrated approach: water hyacinth control, water hyacinth utilization and sustainable waste water management. (C) 2020 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Engineering Management (ENM)
Impact Factor: 2.2
DOI: 10.1016/J.JGLR.2020.06.009
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“Reducing electron beam damage through alternative STEM scanning strategies, Part II: Attempt towards an empirical model describing the damage process”. Jannis D, Velazco A, Béché, A, Verbeeck J, Ultramicroscopy , 113568 (2022). http://doi.org/10.1016/j.ultramic.2022.113568
Abstract: In this second part of a series we attempt to construct an empirical model that can mimick all experimental observations made regarding the role of an alternative interleaved scan pattern in STEM imaging on the beam damage in a specific zeolite sample. We make use of a 2D diffusion model that describes the dissipation of the deposited beam energy in the sequence of probe positions that are visited during the scan pattern. The diffusion process allows for the concept of trying to ‘outrun’ the beam damage by carefully tuning the dwell time and distance between consecutively visited probe positions. We add a non linear function to include a threshold effect and evaluate the accumulated damage in each part of the image as a function of scan pattern details. Together, these ingredients are able to describe qualitatively all aspects of the experimental data and provide us with a model that could guide a further optimisation towards even lower beam damage without lowering the applied electron dose. We deliberately remain vague on what is diffusing here which avoids introducing too many sample specific details. This provides hope that the model can be applied also in sample classes that were not yet studied in such great detail by adjusting higher level parameters: a sample dependent diffusion constant and damage threshold.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 4
DOI: 10.1016/j.ultramic.2022.113568
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“Phase offset method of ptychographic contrast reversal correction”. Hofer C, Gao C, Chennit T, Yuan B, Pennycook TJ, Ultramicroscopy , 113922 (2024). http://doi.org/10.1016/j.ultramic.2024.113922
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2024.113922
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“Optimal experiment design for element specific atom counting using multiple annular dark field scanning transmission electron microscopy detectors”. Sentürk DG, De Backer A, Friedrich T, Van Aert S, Ultramicroscopy 242, 113626 (2022). http://doi.org/10.1016/j.ultramic.2022.113626
Abstract: This paper investigates the possible benefits for counting atoms of different chemical nature when analysing multiple 2D scanning transmission electron microscopy (STEM) images resulting from independent annular dark field (ADF) detector regimes. To reach this goal, the principles of statistical detection theory are used to quantify the probability of error when determining the number of atoms in atomic columns consisting of multiple types of elements. In order to apply this theory, atom-counting is formulated as a statistical hypothesis test, where each hypothesis corresponds to a specific number of atoms of each atom type in an atomic column. The probability of error, which is limited by the unavoidable presence of electron counting noise, can then be computed from scattering-cross sections extracted from multiple ADF STEM images. Minimisation of the probability of error as a function of the inner and outer angles of a specified number of independent ADF collection regimes results in optimal experimental designs. Based on simulations of spherical Au@Ag and Au@Pt core–shell nanoparticles, we investigate how the combination of two non-overlapping detector regimes helps to improve the probability of error when unscrambling two types of atoms. In particular, the combination of a narrow low angle ADF detector with a detector formed by the remaining annular collection regime is found to be optimal. The benefit is more significant if the atomic number Z difference becomes larger. In
addition, we show the benefit of subdividing the detector regime into three collection areas for heterogeneous nanostructures based on a structure consisting of three types of elements, e.g., a mixture of Au, Ag and Al atoms. Finally, these results are compared with the probability of error resulting when one would ultimately use a pixelated 4D STEM detector and how this could help to further reduce the incident electron dose.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2022.113626
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“A decade of atom-counting in STEM: From the first results toward reliable 3D atomic models from a single projection”. De Backer A, Bals S, Van Aert S, Ultramicroscopy , 113702 (2023). http://doi.org/10.1016/j.ultramic.2023.113702
Abstract: Quantitative structure determination is needed in order to study and understand nanomaterials at the atomic scale. Materials characterisation resulting in precise structural information is a crucial point to understand the structure–property relation of materials. Counting the number of atoms and retrieving the 3D atomic structure of nanoparticles plays an important role here. In this paper, an overview will be given of the atom-counting methodology and its applications over the past decade. The procedure to count the number of atoms will be discussed in detail and it will be shown how the performance of the method can be further improved. Furthermore, advances toward mixed element nanostructures, 3D atomic modelling based on the atom-counting results, and quantifying the nanoparticle dynamics will be highlighted.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
Times cited: 3
DOI: 10.1016/j.ultramic.2023.113702
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“Fast generation of calculated ADF-EDX scattering cross-sections under channelling conditions”. Zhang Z, Lobato I, De Backer A, Van Aert S, Nellist P, Ultramicroscopy 246, 113671 (2023). http://doi.org/10.1016/j.ultramic.2022.113671
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.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.2
DOI: 10.1016/j.ultramic.2022.113671
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