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“Selective imaging of sublattices in complex structures”. Amelinckx S, Milat O, Van Tendeloo G, Ultramicroscopy 51, 90 (1993). http://doi.org/10.1016/0304-3991(93)90138-N
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.436
Times cited: 8
DOI: 10.1016/0304-3991(93)90138-N
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“Locating light and heavy atomic column positions with picometer precision using ISTEM”. van den Bos KHW, Krause FF, Béché, A, Verbeeck J, Rosenauer A, Van Aert S, Ultramicroscopy 172, 75 (2016). http://doi.org/10.1016/j.ultramic.2016.10.003
Abstract: Recently, imaging scanning transmission electron microscopy (ISTEM) has been proposed as a promising new technique combining the advantages of conventional TEM (CTEM) and STEM [1]. The ability to visualize light and heavy elements together makes it a particularly interesting new, spatially incoherent imaging mode. Here, we evaluate this technique in term of precision with which atomic column locations can be measured. By using statistical parameter estimation theory, we will show that these locations can be accurately measured with a precision in the picometer range. Furthermore, a quantitative comparison is made with HAADF STEM imaging to investigate the advantages of ISTEM.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 8
DOI: 10.1016/j.ultramic.2016.10.003
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“Hybrid statistics-simulations based method for atom-counting from ADF STEM images”. De wael A, De Backer A, Jones L, Nellist PD, Van Aert S, Ultramicroscopy 177, 69 (2017). http://doi.org/10.1016/j.ultramic.2017.01.010
Abstract: A hybrid statistics-simulations based method for atom-counting from annular dark field scanning transmission electron microscopy (ADF STEM) images of monotype crystalline nanostructures is presented. Different atom-counting methods already exist for model-like systems. However, the increasing relevance of radiation damage in the study of nanostructures demands a method that allows atom-counting from low dose images with a low signal-to-noise ratio. Therefore, the hybrid method directly includes prior knowledge from image simulations into the existing statistics-based method for atom-counting, and accounts in this manner for possible discrepancies between actual and simulated experimental conditions. It is shown by means of simulations and experiments that this hybrid method outperforms the statistics-based method, especially for low electron doses and small nanoparticles. The analysis of a simulated low dose image of a small nanoparticle suggests that this method allows for far more reliable quantitative analysis of beam-sensitive materials.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 8
DOI: 10.1016/j.ultramic.2017.01.010
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“Automatic correction of nonlinear damping effects in HAADF-STEM tomography for nanomaterials of discrete compositions”. Zhong Z, Aveyard R, Rieger B, Bals S, Palenstijn WJ, Batenburg KJ, Ultramicroscopy 184, 57 (2018). http://doi.org/10.1016/J.ULTRAMIC.2017.10.013
Abstract: <script type='text/javascript'>document.write(unpmarked('HAADF-STEM tomography is a common technique for characterizing the three-dimensional morphology of nanomaterials. In conventional tomographic reconstruction algorithms, the image intensity is assumed to be a linear projection of a physical property of the specimen. However, this assumption of linearity is not completely valid due to the nonlinear damping of signal intensities. The nonlinear damping effects increase w.r.t the specimen thickness and lead to so-called \u0022cupping artifacts\u0022, due to a mismatch with the linear model used in the reconstruction algorithm. Moreover, nonlinear damping effects can strongly limit the applicability of advanced reconstruction approaches such as Total Variation Minimization and discrete tomography. In this paper, we propose an algorithm for automatically correcting the nonlinear effects and the subsequent cupping artifacts. It is applicable to samples in which chemical compositions can be segmented based on image gray levels. The correction is realized by iteratively estimating the nonlinear relationship between projection intensity and sample thickness, based on which the projections are linearized. The correction and reconstruction algorithms are tested on simulated and experimental data. (C) 2017 Elsevier B.V. All rights reserved.'));
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 8
DOI: 10.1016/J.ULTRAMIC.2017.10.013
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“Creating arrays of electron vortices”. Niermann T, Verbeeck J, Lehmann M, Ultramicroscopy 136, 165 (2014). http://doi.org/10.1016/j.ultramic.2013.10.002
Abstract: We demonstrate the production of an ordered array of electron vortices making use of an electron optical setup consisting of two electrostatic biprisms. The biprism filaments are oriented nearly orthogonal with respect to each other in a transmission electron microscope. Matching the position of the filaments, we can choose to form different topological features in the electron wave. We outline the working principle of the setup and demonstrate fist experimental results. This setup partially bridges the gap between angular momentum carried by electron spin, which is intrinsic and therefore present in any position of the wave, and angular momentum carried by the vortex character of the wave, which can be extrinsic depending on the axis around which it is measured. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 9
DOI: 10.1016/j.ultramic.2013.10.002
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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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“Dynamical effects in strain measurements by dark-field electron holography”. Javon E, Lubk, Cours R, Reboh S, Cherkashin N, Houdellier F, Gatel C, Hytch MJ, Ultramicroscopy 147, 70 (2014). http://doi.org/10.1016/j.ultramic.2014.06.005
Abstract: Here, we study the effect of dynamic scattering on the projected geometric phase and strain maps reconstructed using dark-field electron holography (DFEH) for non-uniformly strained crystals. The investigated structure consists of a {SiGe/Si} superlattice grown on a (001)-Si substrate. The three dimensional strain held within the thin TEM lamella is modelled by the finite element method. The observed projected strain is simulated in two ways by multiplying the strain at each depth in the crystal by a weighting function determined from a recently developed analytical two-beam dynamical theory, and by simply taking the average value. We demonstrate that the experimental results need to be understood in terms of the dynamical theory and good agreement is found between the experimental and simulated results. Discrepancies do remain for certain cases and are likely to be from an imprecision in the actual two-beam diffraction conditions, notably the deviation parameter, and points to limitations in the 2-beam approximation. Finally, a route towards a 3D reconstruction of strain fields is proposed. (C) 2014 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 10
DOI: 10.1016/j.ultramic.2014.06.005
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“Effect of amorphous layers on the interpretation of restored exit waves”. Van Aert S, Chang LY, Bals S, Kirkland AI, Van Tendeloo G, Ultramicroscopy 109, 237 (2009). http://doi.org/10.1016/j.ultramic.2008.10.024
Abstract: The effects of amorphous layers on the quality of exit wave restorations have been investigated. Two independently developed software implementations for exit wave restoration have been used to simulated focal series of images of SrTiO3 with amorphous carbon layers incorporated. The restored exit waves have been compared both qualitatively and quantitatively. We have shown that amorphous layers have a strong impact on the quantitative measurements of atomic column positions, however, the error in the position measurements is still in the picometer range.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 10
DOI: 10.1016/j.ultramic.2008.10.024
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“In situ HREM study of electron irradiation effects in AgCl microcrystals”. Goessens C, Schryvers D, van Landuyt J, de Keyzer R, Ultramicroscopy 40, 151 (1992). http://doi.org/10.1016/0304-3991(92)90056-P
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.436
Times cited: 10
DOI: 10.1016/0304-3991(92)90056-P
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“Real space maps of atomic transitions”. Schattschneider P, Verbeeck J, Hamon AL, Ultramicroscopy 109, 781 (2009). http://doi.org/10.1016/j.ultramic.2009.01.016
Abstract: Considering the rapid technical development of transmission electron microscopes, we investigate the possibility to map electronic transitions in real space on the atomic scale. To this purpose, we analyse the information carried by the scatterer's initial and final state wave functions and the role of the different atomic transition channels for the inelastic scattering cross section. It is shown that the change in the magnetic quantum number in the transition can be mapped. Two experimental set-ups are proposed, one blocking half the diffraction plane, the other one using a cylinder lens for imaging. Both methods break the conventional circular symmetry in the electron microscope making it possible to detect the handedness of electronic transitions as an asymmetry in the image intensity. This finding is of important for atomic resolution energy-loss magnetic chiral dichroism (EMCD), allowing to obtain the magnetic moments of single atoms.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 10
DOI: 10.1016/j.ultramic.2009.01.016
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“Real space maps of magnetic moments on the atomic scale: theory and feasibility”. Schattschneider P, Ennen I, Stoger-Pollach M, Verbeeck J, Mauchamp V, Jaouen M, Ultramicroscopy 110, 1038 (2010). http://doi.org/10.1016/j.ultramic.2009.11.020
Abstract: The recently discovered EMCD technique (energy loss magnetic chiral dichroism) can detect atom specific magnetic moments with nanometer resolution, exploiting the spin selectivity of electronic transitions in energy loss spectroscopy. Yet, direct imaging of magnetic moments on the atomic scale is not possible. In this paper we present an extension of EMCD that can overcome this limit. As a model system we chose bcc Fe. We present image simulations of the L3 white line signal, based on the kinetic equation for the density matrix of the 200 kV probe electron. With actual progress in instrumentation (high brightness sources, aberration corrected lenses) this technique should allow direct imaging of spin moments on the atomic scale.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 10
DOI: 10.1016/j.ultramic.2009.11.020
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“A simple method to clean ligand contamination on TEM grids”. Li C, Tardajos AP, Wang D, Choukroun D, Van Daele K, Breugelmans T, Bals S, Ultramicroscopy 221, 113195 (2021). http://doi.org/10.1016/j.ultramic.2020.113195
Abstract: Colloidal nanoparticles (NPs) including nanowires and nanosheets made by chemical methods involve many organic ligands. When the structure of NPs is investigated via transmission electron microscopy (TEM), the organic ligands act as a source for e-beam induced deposition and this causes substantial build-up of carbon layers in the investigated areas, which is typically referred to as “contamination” in the eld of electron mi- croscopy. This contamination is often more severe for scanning TEM, a technique that is based on a focused electron beam and hence higher electron dose rate. In this paper, we report a simple and effective method to clean drop-cast TEM grids that contain NPs with ligands. Using a combination of activated carbon and ethanol, this method effectively reduces the amount of ligands on TEM grids, and therefore greatly improves the quality of electron microscopy images and subsequent analytical measurements. This ef cient and facile method can be helpful during electron microscopy investigation of different kinds of nanomaterials that suffer from ligand- induced contamination.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Applied Electrochemistry & Catalysis (ELCAT)
Impact Factor: 2.843
Times cited: 10
DOI: 10.1016/j.ultramic.2020.113195
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“Computational comparisons between the conventional multislice method and the third-order multislice method for calculating high-energy electron diffraction and imaging”. Chen JH, van Dyck D, op de Beeck M, van Landuyt J, Ultramicroscopy 69, 219 (1997)
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 11
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“Homogeneity and composition of AlInGaN : a multiprobe nanostructure study”. Krause FF, Ahl JP, Tytko D, Choi PP, Egoavil R, Schowalter M, Mehrtens T, Müller-Caspary K, Verbeeck J, Raabe D, Hertkorn J, Engl K, Rosenauer A, Ultramicroscopy 156, 29 (2015). http://doi.org/10.1016/j.ultramic.2015.04.012
Abstract: The electronic properties of quaternary AlInGaN devices significantly depend on the homogeneity of the alloy. The identification of compositional fluctuations or verification of random-alloy distribution is hence of grave importance. Here, a comprehensive multiprobe study of composition and compositional homogeneity is presented, investigating AlInGaN layers with indium concentrations ranging from 0 to 17 at% and aluminium concentrations between 0 and 39 at% employing high-angle annular dark field scanning electron microscopy (HAADF STEM), energy dispersive X-ray spectroscopy (EDX) and atom probe tomography (APT). EDX mappings reveal distributions of local concentrations which are in good agreement with random alloy atomic distributions. This was hence investigated with HAADF STEM by comparison with theoretical random alloy expectations using statistical tests. To validate the performance of these tests, HAADF STEM image simulations were carried out for the case of a random-alloy distribution of atoms and for the case of In-rich clusters with nanometer dimensions. The investigated samples, which were grown by metal-organic vapor phase epitaxy (MOVPE), were thereby found to be homogeneous on this nanometer scale. Analysis of reconstructions obtained from APT measurements yielded matching results. Though HAADF STEM only allows for the reduction of possible combinations of indium and aluminium concentrations to the proximity of isolines in the two-dimensional composition space. The observed ranges of composition are in good agreement with the EDX and APT results within the respective precisions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 11
DOI: 10.1016/j.ultramic.2015.04.012
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“Deconvolution of core electron energy loss spectra”. Verbeeck J, Bertoni G, Ultramicroscopy 109, 1343 (2009). http://doi.org/10.1016/j.ultramic.2009.06.010
Abstract: Different deconvolution methods for removing multiple scattering and instrumental broadening from core loss electron energy loss spectra are compared with special attention to the artefacts they introduce. The Gaussian modifier method, Wiener filter, maximum entropy, and model based methods are described. Their performance is compared on virtual spectra where the true single scattering distribution is known. A test on experimental spectra confirms the good performance of model based deconvolution in comparison to maximum entropy methods and shows the advantage of knowing the estimated error bars from a single spectrum acquisition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 13
DOI: 10.1016/j.ultramic.2009.06.010
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“A holographic biprism as a perfect energy filter?”.Verbeeck J, Bertoni G, Lichte H, Ultramicroscopy 111, 887 (2011). http://doi.org/10.1016/j.ultramic.2011.01.042
Abstract: It has often been stated that a holographic biprism represents a near perfect energy filter and only elastically scattered electrons can participate in the interference fringes. This is based on the assumption that the reference wave does not contain inelastically scattered electrons. In this letter we show that this is not exactly true because of the delocalised inelastic interaction of the reference wave with the sample. We experimentally and theoretically show that inelastic scattering plays a role in the fringe formation, but it is shown that this contribution is small and can usually be neglected in practice. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 13
DOI: 10.1016/j.ultramic.2011.01.042
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“Inelastic electron holography as a variant of the Feynman thought experiment”. Potapov PL, Verbeeck J, Schattschneider P, Lichte H, van Dyck D, Ultramicroscopy 107, 559 (2007). http://doi.org/10.1016/j.ultramic.2006.11.003
Abstract: Using a combination of electron holography and energy filtering, interference fringes produced after inelastic interaction of electrons with hydrogen molecules are examined. Surprisingly, the coherence of inelastic scattering increases when moving from the surface of a hydrogen-containing bubble to the vacuum. This phenomenon can be understood in terms of the Feynman two-slit thought experiment with a variable ambiguity of the which-way registration. (C) 2006 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 13
DOI: 10.1016/j.ultramic.2006.11.003
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“Three dimensional mapping of Fe dopants in ceria nanocrystals using direct spectroscopic electron tomography”. Goris B, Meledina M, Turner S, Zhong Z, Batenburg KJ, Bals S, Ultramicroscopy 171, 55 (2016). http://doi.org/10.1016/j.ultramic.2016.08.017
Abstract: Electron tomography is a powerful technique for the 3D characterization of the morphology of nanostructures. Nevertheless, resolving the chemical composition of complex nanostructures in 3D remains challenging and the number of studies in which electron energy loss spectroscopy (EELS) is combined with tomography is limited. During the last decade, dedicated reconstruction algorithms have been developed for HAADF-STEM tomography using prior knowledge about the investigated sample. Here, we will use the prior knowledge that the experimental spectrum of each reconstructed voxel is a linear combination of a well-known set of references spectra in a so-called direct spectroscopic tomography technique. Based on a simulation experiment, it is shown that this technique provides superior results in comparison to conventional reconstruction methods for spectroscopic data, especially for spectrum images containing a relatively low signal to noise ratio. Next, this technique is used to investigate the spatial distribution of Fe dopants in Fe:Ceria nanoparticles in 3D. It is shown that the presence of the Fe2+ dopants is correlated with a reduction of the Ce atoms from Ce4+ towards Ce3+. In addition, it is demonstrated that most of the Fe dopants are located near the voids inside the nanoparticle.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 13
DOI: 10.1016/j.ultramic.2016.08.017
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“Depth sectioning combined with atom-counting in HAADF STEM to retrieve the 3D atomic structure”. Alania M, Altantzis T, De Backer A, Lobato I, Bals S, Van Aert S, Ultramicroscopy 177, 36 (2016). http://doi.org/10.1016/j.ultramic.2016.11.002
Abstract: Aberration correction in scanning transmission electron microscopy (STEM) has greatly improved the lateral and depth resolution. When using depth sectioning, a technique during which a series of images is recorded at different defocus values, single impurity atoms can be visualised in three dimensions. In this paper, we investigate new possibilities emerging when combining depth sectioning and precise atom-counting in order to reconstruct nanosized particles in three dimensions. Although the depth resolution does not allow one to precisely locate each atom within an atomic column, it will be shown that the depth location of an atomic column as a whole can be measured precisely. In this manner, the morphology of a nanoparticle can be reconstructed in three dimensions. This will be demonstrated using simulations and experimental data of a gold nanorod.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 13
DOI: 10.1016/j.ultramic.2016.11.002
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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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“Dynamical electron diffraction in substitutionally disordered column structures”. De Meulenaere P, van Dyck D, Van Tendeloo G, van Landuyt J, Ultramicroscopy 60, 171 (1995). http://doi.org/10.1016/0304-3991(95)00040-8
Abstract: For column structures, such as fee-based alloys viewed along the cube direction, the concept of electron channelling through the atom columns is more and more used to interpret the corresponding HREM images. In the case of(partially) disordered columns, the projected potential approach which is used in the channelling description must be questioned since the arrangement of the atoms along the beam direction might affect the exit wave of the electrons. In this paper, we critically inspect this top-bottom effect using multi-slice calculations. A modified channelling theory is introduced which turns out to be very appropriate for the interpretation of these results. For substitutionally disordered column structures, it is also discussed how to link the chemical composition of the material to statistical data of the HREM image. This results in a convenient tool to discern images taken at different thicknesses and focus values.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.436
Times cited: 14
DOI: 10.1016/0304-3991(95)00040-8
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“Electron diffraction effects of conical, helically wound, graphite whiskers”. Luyten W, Krekels T, Amelinckx S, Van Tendeloo G, van Dyck D, van Landuyt J, Ultramicroscopy 49, 123 (1993). http://doi.org/10.1016/0304-3991(93)90219-N
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.436
Times cited: 14
DOI: 10.1016/0304-3991(93)90219-N
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“Nonlinear imaging using annular dark field TEM”. Bals S, Kilaas R, Kisielowski C, Ultramicroscopy 104, 281 (2005). http://doi.org/10.1016/j.ultramic.2005.05.004
Abstract: Annular dark field TEM images exhibit a dominant mass-thickness contrast that can be quantified to extract single atom scattering cross sections. On top of this incoherent background, additional lattice fringes appear with a nonlinear information limit of 1.2 angstrom at 150 kV. The formation of these fringes is described by coherent nonlinear imaging theory and good agreement is found between experimental and simulated images. Calculations furthermore predict that the use of aberration corrected microscopes will improve the image quality dramatically. (c) 2005 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 15
DOI: 10.1016/j.ultramic.2005.05.004
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“The Fresnel effect of a defocused biprism on the fringes in inelastic holography”. Verbeeck J, Bertoni G, Schattschneider P, Ultramicroscopy
T2 –, 16th International Microscopy Congress, SEP 03-08, 2006, Sapporo, JAPAN 108, 263 (2008). http://doi.org/10.1016/j.ultramic.2007.06.007
Abstract: We present energy filtered holography experiments on a thin foil of Al. By propagating the reduced density matrix of the probe electron through the microscope, we quantitatively predict the fringe contrast as a function of energy loss. Fringe contrast simulations include the effect of Fresnel fringes created at the edges of the defocused biprism, the effect of partial coherence in combination with inelastic scattering, and the effect of a finite energy distribution of the incoming beam. (c) 2007 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 15
DOI: 10.1016/j.ultramic.2007.06.007
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“Fast versus conventional HAADF-STEM tomography of nanoparticles: advantages and challenges”. Vanrompay H, Skorikov A, Bladt E, Béché, A, Freitag B, Verbeeck J, Bals S, Ultramicroscopy 221, 113191 (2021). http://doi.org/10.1016/j.ultramic.2020.113191
Abstract: HAADF-STEM tomography is a widely used experimental technique for analyzing nanometer-scale crystalline structures of a large variety of materials in three dimensions. Unfortunately, the acquisition of conventional HAADF-STEM tilt series can easily take up one hour or more, depending on the complexity of the experiment. It is therefore far from straightforward to investigate samples that do not withstand long acquisition or to acquire large amounts of tilt series during a single TEM experiment. The latter would lead to the ability to obtain statistically meaningful 3D data, or to perform in situ 3D characterizations with a much shorter time resolution. Various HAADF-STEM acquisition strategies have been proposed to accelerate the tomographic acquisition and reduce the required electron dose. These methods include tilting the holder continuously while acquiring a projection “movie” and a hybrid, incremental, methodology which combines the benefits of the conventional and continuous technique. However, until now an experimental evaluation has been lacking. In this paper, the different acquisition strategies will be experimentally compared in terms of speed, resolution and electron dose. This evaluation will be performed based on experimental tilt series acquired for various metallic nanoparticles with different shapes and sizes. We discuss the data processing involved with the fast HAADF-STEM tilt series and provide a general guideline when which acquisition strategy should be preferentially used.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 15
DOI: 10.1016/j.ultramic.2020.113191
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“Model-based quantification of EELS spectra: treating the effect of correlated noise”. Verbeeck J, Bertoni G, Ultramicroscopy 108, 74 (2008). http://doi.org/10.1016/j.ultramic.2007.03.004
Abstract: Correlated noise is generally present in experimentally recorded electron energy loss spectra due to a non-ideal electron detector. In this contribution we describe a method to experimentally measure the noise properties of the detector as well as the consequences it has for model-based quantification using maximum likelihood. The effect of the correlated noise on the maximum likelihood fitting results can be shown to be negligible for the estimated (co)variance of the parameters while an experimentally obtained scaling factor is required to correct the likelihood ratio test for the reduction of noise power with frequency. Both effects are derived theoretically under a set of approximations and tested for a range of signal-to-noise values using numerical experiments. Finally, an experimental example shows that the correction for correlated noise is essential and should always be included in the fitting procedure. (c) 2007 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 16
DOI: 10.1016/j.ultramic.2007.03.004
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“A model based reconstruction technique for depth sectioning with scanning transmission electron microscopy”. van den Broek W, Van Aert S, van Dyck D, Ultramicroscopy 110, 548 (2010). http://doi.org/10.1016/j.ultramic.2009.09.008
Abstract: Depth sectioning in high angular annular dark field scanning transmission electron microscopy is considered a candidate for three-dimensional characterization on the atomic scale. However at present the depth resolution is still far from the atomic level, due to strong limitations in the opening angle of the beam. In this paper we introduce a new, parameter based tomographic reconstruction algorithm that allows to make maximal use of the prior knowledge about the constituent atom types and the microscope settings, so as to retrieve the atomic positions and push the resolution to the atomic level in all three dimensions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 16
DOI: 10.1016/j.ultramic.2009.09.008
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“Inelastic scattering of high-energy electrons in a crystal in thermal equilibrium with the environment: 1: theoretical framework”. Fanidis C, van Dyck D, van Landuyt J, Ultramicroscopy 41, 55 (1992). http://doi.org/10.1016/0304-3991(92)90094-Z
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.436
Times cited: 17
DOI: 10.1016/0304-3991(92)90094-Z
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“A model based atomic resolution tomographic algorithm”. van den Broek W, Van Aert S, van Dyck D, Ultramicroscopy 109, 1485 (2009). http://doi.org/10.1016/j.ultramic.2009.08.003
Abstract: Tomography with high angular annular dark field scanning transmission electron microscopy at atomic resolution can be greatly improved if one is able to take advantage of prior knowledge. In this paper we present a reconstruction technique that explicitly takes into account the microscope parameters and the atomic nature of the projected object. This results in a more accurate estimate of the atomic positions and in a good resistance to noise. The reconstruction is a maximum likelihood estimator of the object. Moreover, the limits to the precision have been explored, allowing for a prediction of the amount of expected noise in the reconstruction for a certain experimental setup. We believe that the proposed reconstruction technique can be generalized to other tomographic experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 17
DOI: 10.1016/j.ultramic.2009.08.003
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“Structures and phase transitions in C60 and C70 fullerites”. Van Tendeloo G, Amelinckx S, Muto S, Verheijen MA, van Loosdrecht PHM, Meijer G, Ultramicroscopy 51, 168 (1993). http://doi.org/10.1016/0304-3991(93)90145-N
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.436
Times cited: 17
DOI: 10.1016/0304-3991(93)90145-N
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