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Zhang Z, Lobato I, De Backer A, Van Aert S, Nellist P. Fast generation of calculated ADF-EDX scattering cross-sections under channelling conditions. Ultramicroscopy 2023; 246:113671. [PMID: 36621195 DOI: 10.1016/j.ultramic.2022.113671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2022] [Revised: 12/21/2022] [Accepted: 12/26/2022] [Indexed: 12/29/2022]
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.
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Affiliation(s)
- Zezhong Zhang
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom.
| | - Ivan Lobato
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Annick De Backer
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Sandra Van Aert
- Electron Microscopy for Materials Research (EMAT), University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium; NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
| | - Peter Nellist
- Department of Materials, University of Oxford, 16 Parks Road, Oxford OX1 3PH, United Kingdom.
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Naresh-Kumar G, Alasmari A, Kusch G, Edwards PR, Martin RW, Mingard KP, Trager-Cowan C. Metrology of crystal defects through intensity variations in secondary electrons from the diffraction of primary electrons in a scanning electron microscope. Ultramicroscopy 2020; 213:112977. [PMID: 32361281 DOI: 10.1016/j.ultramic.2020.112977] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 03/15/2020] [Indexed: 11/28/2022]
Abstract
Understanding defects and their roles in plastic deformation and device reliability is important for the development of a wide range of novel materials for the next generation of electronic and optoelectronic devices. We introduce the use of gaseous secondary electron detectors in a variable pressure scanning electron microscope for non-destructive imaging of extended defects using electron channelling contrast imaging. We demonstrate that all scattered electrons, including the secondary electrons, can provide diffraction contrast as long as the sample is positioned appropriately with respect to the incident electron beam. Extracting diffraction information through monitoring the modulation of the intensity of secondary electrons as a result of diffraction of the incident electron beam, opens up the possibility of performing low energy electron channelling contrast imaging to characterise low atomic weight and ultra-thin film materials. Our methodology can be adopted for large area, nanoscale structural characterisation of a wide range of crystalline materials including metals and semiconductors, and we illustrate this using the examples of aluminium nitride and gallium nitride. The capability of performing electron channelling contrast imaging, using the variable pressure mode, extends the application of this technique to insulators, which usually require conducting coatings on the sample surface for traditional scanning electron microscope based microstructural characterisation.
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Affiliation(s)
- G Naresh-Kumar
- Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom.
| | - A Alasmari
- Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
| | - G Kusch
- Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
| | - P R Edwards
- Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
| | - R W Martin
- Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
| | - K P Mingard
- National Physical Laboratory, Middlesex TW11 0LW, United Kingdom
| | - C Trager-Cowan
- Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG, United Kingdom
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Oveisi E, Spadaro MC, Rotunno E, Grillo V, Hébert C. Insights into image contrast from dislocations in ADF-STEM. Ultramicroscopy 2019; 200:139-148. [PMID: 30925259 DOI: 10.1016/j.ultramic.2019.02.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 01/02/2019] [Accepted: 02/06/2019] [Indexed: 10/27/2022]
Abstract
Competitive mechanisms contribute to image contrast from dislocations in annular dark-field scanning transmission electron microscopy (ADF-STEM). A clear theoretical understanding of the mechanisms underlying the ADF-STEM contrast is therefore essential for correct interpretation of dislocation images. This paper reports on a systematic study of the ADF-STEM contrast from dislocations in a GaN specimen, both experimentally and computationally. Systematic experimental ADF-STEM images of the edge-character dislocations reveal a number of characteristic contrast features that are shown to depend on both the angular detection range and specific position of the dislocation in the sample. A theoretical model based on electron channelling and Bloch-wave scattering theories, supported by numerical simulations based on Grillo's strain-channelling equation, is proposed to elucidate the physical origin of such complex contrast phenomena.
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Affiliation(s)
- E Oveisi
- Interdisciplinary Centre for Electron Microscopy, École Polytechnique Fédérale de Lausanne (CIME-EPFL), Lausanne, Switzerland; Electron Spectrometry and Microscopy Laboratory, École Polytechnique Fédérale de Lausanne (LSME-EPFL), Lausanne, Switzerland.
| | - M C Spadaro
- Interdisciplinary Centre for Electron Microscopy, École Polytechnique Fédérale de Lausanne (CIME-EPFL), Lausanne, Switzerland
| | - E Rotunno
- Institute of Nanoscience, National Research Council (NANO-CNR), Modena, Italy
| | - V Grillo
- Institute of Nanoscience, National Research Council (NANO-CNR), Modena, Italy; Institute of Materials for Electronics and Magnetism, National Research Council (IMEM-CNR), Parma, Italy
| | - C Hébert
- Interdisciplinary Centre for Electron Microscopy, École Polytechnique Fédérale de Lausanne (CIME-EPFL), Lausanne, Switzerland; Electron Spectrometry and Microscopy Laboratory, École Polytechnique Fédérale de Lausanne (LSME-EPFL), Lausanne, Switzerland.
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