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Title: Interpreting atomic resolution spectroscopic images

Abstract

Core-loss electron energy loss spectroscopy is a powerful experimental tool providing information about electronic structure essential for understanding the properties of new and emerging materials. Here we show that the shape and width of spectroscopic images do not show a simple variation with binding energy, as commonly assumed. Rather they exhibit a complex dependence on the effective nonlocal scattering potential, and also on the dynamical channeling and absorption of the incident probe through the specimen. Consequently, in LaMnO$$_3$$, the low lying La N$$_{4,5}$$ edge at 99 eV can produce images of similar width to higher lying edges such as the O $K$ edge at 532 eV.

Authors:
 [1];  [1];  [1];  [1];  [2];  [2];  [1]
  1. ORNL
  2. University of Melbourne, Australia
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931652
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review B; Journal Volume: 76
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; BINDING ENERGY; ELECTRONIC STRUCTURE; ENERGY-LOSS SPECTROSCOPY; RESOLUTION; SCATTERING; SPECTRA; DATA ANALYSIS

Citation Formats

Oxley, Mark P, Varela del Arco, Maria, Pennycook, Timothy J, van Benthem, Klaus, Findlay, Scott D., Allen, L. J., and Pennycook, Stephen J. Interpreting atomic resolution spectroscopic images. United States: N. p., 2007. Web. doi:10.1103/PhysRevB.76.064303.
Oxley, Mark P, Varela del Arco, Maria, Pennycook, Timothy J, van Benthem, Klaus, Findlay, Scott D., Allen, L. J., & Pennycook, Stephen J. Interpreting atomic resolution spectroscopic images. United States. doi:10.1103/PhysRevB.76.064303.
Oxley, Mark P, Varela del Arco, Maria, Pennycook, Timothy J, van Benthem, Klaus, Findlay, Scott D., Allen, L. J., and Pennycook, Stephen J. Mon . "Interpreting atomic resolution spectroscopic images". United States. doi:10.1103/PhysRevB.76.064303.
@article{osti_931652,
title = {Interpreting atomic resolution spectroscopic images},
author = {Oxley, Mark P and Varela del Arco, Maria and Pennycook, Timothy J and van Benthem, Klaus and Findlay, Scott D. and Allen, L. J. and Pennycook, Stephen J},
abstractNote = {Core-loss electron energy loss spectroscopy is a powerful experimental tool providing information about electronic structure essential for understanding the properties of new and emerging materials. Here we show that the shape and width of spectroscopic images do not show a simple variation with binding energy, as commonly assumed. Rather they exhibit a complex dependence on the effective nonlocal scattering potential, and also on the dynamical channeling and absorption of the incident probe through the specimen. Consequently, in LaMnO$_3$, the low lying La N$_{4,5}$ edge at 99 eV can produce images of similar width to higher lying edges such as the O $K$ edge at 532 eV.},
doi = {10.1103/PhysRevB.76.064303},
journal = {Physical Review B},
number = ,
volume = 76,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Core-loss electron energy loss spectroscopy is a powerful experimental tool with the potential to provide atomic-resolution information about electronic structure at defects and interfaces in materials and nanostructures. Interpretation, however, is nonintuitive. Comparison of experimental and simulated compositional maps in LaMnO{sub 3} shows good agreement, apart from an overall scaling of image contrast, and shows that the shape and width of spectroscopic images do not show a simple variation with binding energy, as commonly assumed, or with the size of the orbital excited. For the low lying La N{sub 4,5} edge with threshold at around 99 eV, delocalization does notmore » preclude atomic resolution, but reduces the image contrast. The image width remains comparable to that of the much higher lying O K edge with threshold at around 532 eV. Both edges show a volcanolike feature, a dip at the column position not previously seen experimentally. In the case of the O K edge, this represents an experimental verification of nonlocal inelastic scattering effects in electron energy loss spectroscopy imaging. In the case of the N{sub 4,5} edge, the volcanolike feature is due to dynamical channeling and absorption of the probe through the specimen thickness. Simulation is therefore critical to the interpretation of atomic-resolution elemental maps.« less
  • We report the first atomic resolution scanning tunneling microscopy (STM) images of S overlayers on the Fe(111) surface. S overlayers were obtained by annealing the Fe(111) crystal to elevated temperatures to induce the segregation of S from the bulk. STM images of the (1{times}1)-S structure are consistent with the proposed model of one {open_quotes}geometric{close_quotes} monolayer of S atoms occupying {ital on-top} three-fold hollow sites of the Fe(111) surface. The STM data also revealed the presence of nanoscopic triangular pits on the (1{times}1)-S surface. These pits are only one atom deep. Increased segregation of S results in the formation of amore » (2{radical}3 {times}1){ital R}30{degree} structure and an increase in the size and depth of the triangular pits. This new structure corresponds to S coverage corresponding to more than one {open_quotes}geometric{close_quotes} monolayer of S based on one geometric monolayer coverage for the (1{times}1)-S structure. STM images obtained within large pits reveal a periodic {open_quotes}staircase{close_quotes} topography consisting of terraces with (111) orientation. These terraces are made up of five atomic rows (14 {Angstrom}) separated by monatomic steps. Images obtained on flat areas in between large pits reveal surface buckling. Two different packing arrangements of surface buckling were observed both consisting of vertically displaced atomic rows with a 14 {Angstrom} periodicity, identical to the terrace widths of the staircase surface found inside large triangular pits. We propose that additional segregation of S to the (1{times}1)-S phase to form the (2{radical}3 {times}1){ital R}30{degree} structure involves the segregation of S to the {ital subsurface} three-fold hollow sites on the Fe(111) surface. The close proximity of S atoms located at {ital on-top} and {ital subsurface} three-fold hollow sites can result in strong S{endash}S repulsive interactions which consequently drives the surface to undergo structural changes, similar to other reported adsorbate-induced faceting of bcc(111) surfaces. {copyright} {ital 1998 American Vacuum Society.}« less
  • A real-space description of inelastic scattering in scanning transmission electron microscopy is derived with particular attention given to the implementation of the projected potential approximation. A hierarchy of approximations to expressions for inelastic images is presented. Emphasis is placed on the conditions that must hold in each case. The expressions that justify the most direct, visual interpretation of experimental data are also the most approximate. Therefore, caution must be exercised in selecting experimental parameters that validate the approximations needed for the analysis technique used. To make the most direct, visual interpretation of electron-energy-loss spectroscopic images from core-shell excitations requires detectormore » improvements commensurate with those that aberration correction provides for the probe-forming lens. Such conditions can be relaxed when detailed simulations are performed as part of the analysis of experimental data.« less
  • This letter describes an image analysis technique capable of enhancing atomic ordering in high-resolution electron micrographs of quasiamorphous materials. The technique cross correlates the full micrograph with a template selected from the micrograph image field and examines the cross-correlation function (CCF) as a function of template dimension. A critical dimension is found for which the CCF yields evidence of local atomic ordering.