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Title: Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions

Abstract

Annular dark field scanning transmission electron microscopy (ADF-STEM) image simulations were performed for zone-axis-oriented light-element single crystals, using a multislice method adapted to include charge redistribution due to chemical bonding. Examination of these image simulations alongside calculations of the propagation of the focused electron probe reveal that the evolution of the probe intensity with thickness exhibits significant sensitivity to interatomic charge transfer, accounting for observed thickness-dependent bonding sensitivity of contrast in all ADF-STEM imaging conditions. Because changes in image contrast relative to conventional neutral atom simulations scale directly with the net interatomic charge transfer, the strongest effects are seen in crystals with highly polar bonding, while no effects are seen for nonpolar bonding. Although the bonding dependence of ADF-STEM image contrast varies with detector geometry, imaging parameters, and material temperature, these simulations predict the bonding effects to be experimentally measureable.

Authors:
;  [1];  [2];  [3]
  1. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States)
  2. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 and Materials Department, University of California, Santa Barbara, California 93106 (United States)
  3. Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 and Theory and Simulations of Materials, National Centre for Computational Design and Discovery of Novel Materials, École polytechnique fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland)
Publication Date:
OSTI Identifier:
22592862
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films; Journal Volume: 34; Journal Issue: 4; Other Information: (c) 2016 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; BONDING; CHEMICAL BONDS; COMPUTERIZED SIMULATION; ELECTRON PROBES; ELECTRONS; FORECASTING; GEOMETRY; IMAGES; MONOCRYSTALS; SENSITIVITY; THICKNESS; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Odlyzko, Michael L., Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu, Himmetoglu, Burak, and Cococcioni, Matteo. Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions. United States: N. p., 2016. Web. doi:10.1116/1.4954871.
Odlyzko, Michael L., Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu, Himmetoglu, Burak, & Cococcioni, Matteo. Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions. United States. doi:10.1116/1.4954871.
Odlyzko, Michael L., Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu, Himmetoglu, Burak, and Cococcioni, Matteo. Fri . "Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions". United States. doi:10.1116/1.4954871.
@article{osti_22592862,
title = {Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions},
author = {Odlyzko, Michael L. and Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu and Himmetoglu, Burak and Cococcioni, Matteo},
abstractNote = {Annular dark field scanning transmission electron microscopy (ADF-STEM) image simulations were performed for zone-axis-oriented light-element single crystals, using a multislice method adapted to include charge redistribution due to chemical bonding. Examination of these image simulations alongside calculations of the propagation of the focused electron probe reveal that the evolution of the probe intensity with thickness exhibits significant sensitivity to interatomic charge transfer, accounting for observed thickness-dependent bonding sensitivity of contrast in all ADF-STEM imaging conditions. Because changes in image contrast relative to conventional neutral atom simulations scale directly with the net interatomic charge transfer, the strongest effects are seen in crystals with highly polar bonding, while no effects are seen for nonpolar bonding. Although the bonding dependence of ADF-STEM image contrast varies with detector geometry, imaging parameters, and material temperature, these simulations predict the bonding effects to be experimentally measureable.},
doi = {10.1116/1.4954871},
journal = {Journal of Vacuum Science and Technology. A, Vacuum, Surfaces and Films},
number = 4,
volume = 34,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2016},
month = {Fri Jul 15 00:00:00 EDT 2016}
}
  • Quantitatively calibrated annular dark field scanning transmission electron microscopy (ADF-STEM) imaging experiments were compared to frozen phonon multislice simulations adapted to include chemical bonding effects. Having carefully matched simulation parameters to experimental conditions, a depth-dependent bonding effect was observed for high-angle ADF-STEM imaging of aluminum nitride. This result is explained by computational predictions, systematically examined in the preceding portion of this study, showing the propagation of the converged STEM beam to be highly sensitive to net interatomic charge transfer. Thus, although uncertainties in experimental conditions and simulation accuracy remain, the computationally predicted experimental bonding effect withstands the experimental testing reportedmore » here.« less
  • The interfacial misfit (IMF) dislocation array of an epitaxial GaSb film on a Si substrate has been imaged with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The mismatch strain accommodation through dislocation formation has been investigated using geometric phase analysis (GPA) on HAADF-STEM images with atomic resolution to probe the defects' local strain distribution. These measurements indicate that the lattice parameter of the epitaxial film recovers its bulk value within three unit cells from the interface due to the relaxation through IMF dislocations. The atomic number contrast of the HAADF-STEM images and energy dispersive x-ray spectrometry illustrate the formationmore » of islands of AlSb buffer layer along the interface. The role of the AlSb buffer layer in facilitating the GaSb film growth on Si is further elucidated by investigating the strain field of the islands with the GPA.« less
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  • In this report, we show that an annular dark-field detector in an aberration-corrected scanning transmission electron microscope allows the direct observation of light element columns in crystalline lattices. At specific imaging conditions, an enhancement of the intensities of light element columns in the presence of heavy element columns is observed. Experimental results are presented for imaging the nitrogen and carbon atomic columns at the GaN-SiC interface and within the GaN and SiC compounds. The crystal polarity of GaN at the interface is identified. The obtained findings are discussed and are well supported by image simulations.