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Title: Sub Angstrom imaging of dislocation core structures: How well areexperiments comparable with theory?

Abstract

During the past 50 years Transmission Electron Microscopy (TEM) has evolved from an imaging tool to a quantitative method that approaches the ultimate goal of understanding the atomic structure of materials atom by atom in three dimensions both experimentally and theoretically. Today's TEM abilities are tested in the special case of a Ga terminated 30 degree partial dislocation in GaAs:Be where it is shown that a combination of high-resolution phase contrast imaging, Scanning TEM, and local Electron Energy Loss Spectroscopy allows for a complete analysis of dislocation cores and associated stacking faults. We find that it is already possible to locate atom column positions with picometer precision in directly interpretable images of the projected crystal structure and that chemically different elements can already be identified together with their local electronic structure. In terms of theory, the experimental results can be quantitatively compared with ab initio electronic structure total energy calculations. By combining elasticity theory methods with atomic theory an equivalent crystal volume can be addressed. Therefore, it is already feasible to merge experiments and theory on a picometer length scale. While current experiments require the utilization of different, specialized instruments it is foreseeable that the rapid improvement of electron opticalmore » elements will soon generate a next generation of microscopes with the ability to image and analyze single atoms in one instrument with deep sub Angstrom spatial resolution and an energy resolution better than 100 meV.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE Director. Office of Science. Office of AdvancedScientific Computing Research. Office of Basic EnergySciences
OSTI Identifier:
903040
Report Number(s):
LBNL-59237
R&D Project: 503601; BnR: KC0201010; TRN: US200718%%364
DOE Contract Number:
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Philosophical Magazine; Journal Volume: 86; Journal Issue: 19-31; Related Information: Journal Publication Date: Oct-Nov 2006
Country of Publication:
United States
Language:
English
Subject:
75; ACCURACY; ATOMS; CRYSTAL STRUCTURE; DIMENSIONS; DISLOCATIONS; ELASTICITY; ELECTRONIC STRUCTURE; ELECTRONS; ENERGY RESOLUTION; ENERGY-LOSS SPECTROSCOPY; MICROSCOPES; SPATIAL RESOLUTION; STACKING FAULTS; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Kisielowski, C., Freitag, B., Xu, X., Beckman, S.P., and Chrzan, D.C.. Sub Angstrom imaging of dislocation core structures: How well areexperiments comparable with theory?. United States: N. p., 2005. Web.
Kisielowski, C., Freitag, B., Xu, X., Beckman, S.P., & Chrzan, D.C.. Sub Angstrom imaging of dislocation core structures: How well areexperiments comparable with theory?. United States.
Kisielowski, C., Freitag, B., Xu, X., Beckman, S.P., and Chrzan, D.C.. Fri . "Sub Angstrom imaging of dislocation core structures: How well areexperiments comparable with theory?". United States. doi:. https://www.osti.gov/servlets/purl/903040.
@article{osti_903040,
title = {Sub Angstrom imaging of dislocation core structures: How well areexperiments comparable with theory?},
author = {Kisielowski, C. and Freitag, B. and Xu, X. and Beckman, S.P. and Chrzan, D.C.},
abstractNote = {During the past 50 years Transmission Electron Microscopy (TEM) has evolved from an imaging tool to a quantitative method that approaches the ultimate goal of understanding the atomic structure of materials atom by atom in three dimensions both experimentally and theoretically. Today's TEM abilities are tested in the special case of a Ga terminated 30 degree partial dislocation in GaAs:Be where it is shown that a combination of high-resolution phase contrast imaging, Scanning TEM, and local Electron Energy Loss Spectroscopy allows for a complete analysis of dislocation cores and associated stacking faults. We find that it is already possible to locate atom column positions with picometer precision in directly interpretable images of the projected crystal structure and that chemically different elements can already be identified together with their local electronic structure. In terms of theory, the experimental results can be quantitatively compared with ab initio electronic structure total energy calculations. By combining elasticity theory methods with atomic theory an equivalent crystal volume can be addressed. Therefore, it is already feasible to merge experiments and theory on a picometer length scale. While current experiments require the utilization of different, specialized instruments it is foreseeable that the rapid improvement of electron optical elements will soon generate a next generation of microscopes with the ability to image and analyze single atoms in one instrument with deep sub Angstrom spatial resolution and an energy resolution better than 100 meV.},
doi = {},
journal = {Philosophical Magazine},
number = 19-31,
volume = 86,
place = {United States},
year = {Fri Dec 16 00:00:00 EST 2005},
month = {Fri Dec 16 00:00:00 EST 2005}
}
  • The development of Z-contrast imaging in the scanning transmission electron microscope has enabled dislocation core structures to be visualized with increasing detail. In single-component systems, core structures have been generally found to be as expected from simple considerations or theoretical predictions. In more complex structures, however, cores are generally seen to take on configurations that were not previously anticipated, utilizing reconstructions or non-stoichiometry to lower the elastic strain field. We present an overview of these developments in a variety of materials. In suitable circumstances, impurity segregation sites have been directly imaged at dislocation cores. More generally, electron energy loss spectroscopymore » gives detailed, atomicresolution information on stoichiometry and impurity concentrations. These additional variables introduce additional degrees of freedom into the whole issue of structure/property relationships. We show examples of an impurity-induced core structure transformation and a cooperative doping effect. First-principles density functional calculations are used to link observed core structures to macroscopic properties. We also show that planar dislocation arrays are accurate descriptions of tilt grain boundaries, with the structural units geometrically equivalent to individual dislocation cores.« less
  • The development of Z-contrast imaging in the scanning transmission electron microscope has enabled dislocation core structures to be visualized with increasing detail. In single-component systems, core structures have been generally found to be as expected from simple considerations or theoretical predictions. In more complex structures, however, cores are generally seen to take on configurations that were not previously anticipated, utilizing reconstructions or non-stoichiometry to lower the elastic strain field. We present an overview of these developments in a variety of materials. In suitable circumstances, impurity segregation sites have been directly imaged at dislocation cores. More generally, electron energy loss spectroscopymore » gives detailed, atomicresolution information on stoichiometry and impurity concentrations. These additional variables introduce additional degrees of freedom into the whole issue of structure/property relationships. We show examples of an impurity-induced core structure transformation and a cooperative doping effect. First-principles density functional calculations are used to link observed core structures to macroscopic properties. We also show that planar dislocation arrays are accurate descriptions of tilt grain boundaries, with the structural units geometrically equivalent to individual dislocation cores.« less
  • By improving temporal coherence (chromatic aberration) and compensating spatial incoherence, we have achieved the goal of the one-Angstrom microscope (O Angstrom M) project at the LBNL National Center for Electron Microscopy by extending the limits of high-resolution transmission electron microscopy to sub-Angstrom levels. The O Angstrom M combines focal-series image-processing software with a modified 300 keV electron microscope equipped with a highly-coherent field-emission electron gun. By operating at an 'alpha-null' focus in order to minimize the effects of spatial incoherence, and by reducing the O Angstrom M's electron-gun extraction voltage to improve temporal coherence, we are able to transfer informationmore » below 0.8 Angstrom. In a test specimen of silicon viewed in [112] orientation in the O Angstrom M, we are able to 'see' atoms separated by only 0.78 Angstrom. Sub-Angstrom resolution at this level offers the materials researcher an effective tool for the characterization of defects with unprecedented precision.« less
  • The reaction of Re{sub 2}O{sub 7} with XeF{sub 6} in anhydrous HF provides a convenient route to high-purity ReO{sub 2}F{sub 3}. The fluoride acceptor and Lewis base properties of ReO{sub 2}F{sub 3} have been investigated leading to the formation of [M][ReO{sub 2}F{sub 4}] [M = Li, Na, Cs, N(CH{sub 3}){sub 4}], [K][Re{sub 2}O{sub 4}F{sub 7}], [K][Re{sub 2}O{sub 4}F{sub 7}]{center_dot}2ReO{sub 2}F{sub 3}, [Cs][Re{sub 3}O{sub 6}F{sub 10}], and ReO{sub 2}F{sub 3}(CH{sub 3}CN). The ReO{sub 2}F{sub 4}{sup {minus}}, Re{sub 2}O{sub 4}F{sub 7}{sup {minus}}, and Re{sub 3}O{sub 6}F{sub 10{sup {minus}} anions and the ReO{sub 2}F{sub 3}(CH{sub 3}CN) adduct have been characterized in the solidmore » state by Raman spectroscopy, and the structures [Li][ReO{sub 2}F{sub 4}], [K][Re{sub 2}O{sub 4}F{sub 7}], [K][Re{sub 2}O{sub 4}F{sub 7}]{center_dot}2ReO{sub 2}F{approximately}3}, [Cs][Re{sub 3}O{sub 6}F{sub 10}], and ReO{sub 3}F(CH{sub 3}CN){sub 2}{center_dot}CH{sub 3}CN have been determined by X-ray crystallography. The structure of ReO{sub 2}F{sub 4}{sup {minus}} consists of a cis-dioxo arrangement of Re-O double bonds in which the Re-F bonds trans to the oxygen atoms are significantly lengthened as a result of the trans influence of the oxygens. The Re{sub 2}O{sub 4}F{sub 7}{sup {minus}} and Re{sub 3}O{sub 6}F{sub 10}{sup {minus}} anions and polymeric ReO{sub 2}F{sub 3} are open chains containing fluorine-bridged ReO{sub 2}F{sub 4} units in which each pair of Re-O bonds are cis to each other and the fluorine bridges are trans to oxygens. The trans influence of the oxygens is manifested by elongated terminal Re-F bonds trans to Re-O bonds as in ReO{sub 2}F{sub 4}{sup {minus}} and by the occurrence of both fluorine bridges trans to Re-O bonds. Fluorine-19 NMR spectra show that ReO{sub 2}F{sub 4}{sup {minus}}, Re{sub 2}O{sub 4}F{sub 7}{sup {minus}}, and ReO{sub 2}F{sub 3}(CH{sub 3}CN) have cis-dioxo arrangements in CH{sub 3}CN solution. Density functional theory calculations at the local and nonlocal levels confirm that the cis-dioxo isomers of ReO{sub 2}F{sub 4}{sup {minus}} and ReO{sub 2}F{sub 3}(CH{sub 3}CN), where CH{sub 3}CN is bonded trans to an oxygen, are the energy-minimized structures. The adduct ReO{sub 3}F(CH{sub 3}CN){sub 2}{center_dot}CH{sub 3}CN was obtained by hydrolysis of ReO{sub 2}F{sub 3}(CH{sub 3}CN), and was shown by X-ray crystallography to have a facial arrangement of oxygen atoms on rhenium.« less
  • It is reported that lattice imaging with a 300 kV field emission microscope in combination with numerical reconstruction procedures can be used to reach an interpretable resolution of about 80 pm for the first time. A retrieval of the electron exit wave from focal series allows for the resolution of single atomic columns of the light elements carbon, nitrogen, and oxygen at a projected nearest neighbor spacing down to 85 pm. Lens aberrations are corrected on-line during the experiment and by hardware such that resulting image distortions are below 80 pm. Consequently, the imaging can be aberration-free to this extent.more » The resolution enhancement results from increased electrical and mechanical stability's of the instrument coupled with a low spherical aberration coefficient of 0.595 + 0.005 mm.« less