Nanoscale Structure/Property Correlation Through Aberration-Corrected Stem and Theory
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NANOSCALE STRUCTURE/PROPERTY CORRELATION THROUGH ABERRATION-CORRECTED STEM AND THEORY S. J. PENNYCOOK 1,2, A. R. LUPINI1, M. VARELA 1, A. BORISEVICH1, M. F. CHISHOLM1, E. ABE1,3, N. DELLBY4, O. L. KRIVANEK4, P. D. NELLIST4, L. G. WANG 1#, R. BUCZKO1,2,5, X. FAN1*, and S. T. PANTELIDES1,2, 1 Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 2 Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 3 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Japan 4 Nion Co., 1102 8th Street, Kirkland, WA 5 Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland # Now at National Renewable Energy Laboratory, Golden, CO * Now at Center for Advanced Microscopy, Michigan State University, East Lansing, MI INTRODUCTION The combination of atomic-resolution Z-contrast microscopy, electron energy loss spectroscopy and first-principles theory has proved to be a powerful means for structure property correlations at interfaces and nanostructures1,2,3,4. The scanning transmission electron microscope (STEM) now routinely provides atomic-sized electron beams5, allowing simultaneous Z-contrast imaging and EELS as shown in Fig. 1. The feasiblity of correcting the inherently large spherical aberration of microscope objective lenses promises to at least double the achievable resolution6,7. The potential benefits for the STEM, however, may turn out to be much greater than those for the conventional TEM because it is very much less sensitive to chromatic instabilities8. The 100 kV VG Microscopes HB501UX at Oak Ridge National Laboratory (ORNL) is now fitted with an aberration corrector constructed by Nion Co., which improved its resolution from 2.2 Å (full-width-half-maximum probe intensity) to around 1.3 Å. It is now very comparable in performance to the uncorrected 300 kV HB603U STEM at ORNL which, before correction, also had a directly interpretable resolution of 1.3 Å, although information transfer had been demonstrated down to 0.78 Å8. Initial results after installing an aberration corrector on the 300 kV STEM indicate a resolution of 0.84 Å. The theoretically achievable probe size in the absence of instabilities is predicted to be 0.5 Å. The Z-contrast image9,10,11 is a very convenient and intuitive method for revealing atomic arrangements, even if those configurations are unexpected. Examples include isolated dislocation cores12 and also dislocation arrays that comprise grain boundaries.13, 14 The STEM appears to be the only viable means for obtaining spectroscopic analysis at atomic resolution. Locating the probe on an individual atomic column selected from the image allows EELS measurements of local elemental concentrations and electronic structure.15,16 These techniques are ideally complementary to first-principles total-energy calculations. The structures suggested from experiment avoid the need to search the large number of possible defect configurations. Theory can efficiently perform structural relaxations of configurations suggested from experim
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