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Determination of Atomic Structure at Surfaces and Interfaces by High-Resolution Stem

Published online by Cambridge University Press:  10 February 2011

S. J. Pennycook,
P. D. Nellist,
M. F. Chisholm,
N. D. Browning,
D. J. Wallis and
E. C. Dickey
S. J. Pennycook
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831–6030
P. D. Nellist
Affiliation:
now at Cavendish Laboratory Madingley Road, Cambridge CB3OHE, UK
M. F. Chisholm
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831–6030
N. D. Browning
Affiliation:
Department of Physics, University of Illinois at Chicago, Chicago, IL 60607–7059
D. J. Wallis
Affiliation:
now at Defence Research Agency, Malvern, UK
E. C. Dickey
Affiliation:
Dept. of Materials Science & Engineering, Northwestern University, Evanston, IL 60208
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Extract

It is just over one hundred years since Lord Rayleigh first showed the differences between coherent and incoherent imaging in the light microscope, pointing out the advantages of the latter for resolution and image interpretation. The annular detector in the high-resolution STEM provides the same advantages for electrons, allowing incoherent imaging at atomic resolution, with image contrast strongly dependent on atomic number (Z). Since incoherent imaging has no phase problem, these Z-contrast images may be directly inverted to give the (projected) atomic positions. A maximum entropy method avoids false detail associated with direct deconvolution, and gives atomic coordinates to an accuracy of ± 0.1 Å. Electron energy loss spectroscopy can provide valuable complementary information on light element bonding and the presence of impurities in specific atomic planes selected from the image. Together, these techniques have revealed some surprisingly complex interfacial structures. For surface studies, the 1.3 A probe of the VG Microscopes HB603U STEM provides sufficient penetration and contrast to image single Pt and Rh atoms on γ-alumina supports. Such images reveal preferred atomic configurations, and allow possible surface adsorption sites to be deduced.

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References

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