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The XPS Searchlight Effect: A New Analytical Tool for Layered Structures, Epitaxy, and Interfaces

Published online by Cambridge University Press:  26 February 2011

W. F. Egelhoff Jr
W. F. Egelhoff Jr*
Affiliation:
Surface Science Division, National Bureau of Standards, Gaithersburg, MD 20899
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Abstract

Enhanced core-level peak intensities at angles corresponding to the internuclear axes among the near surface atoms is a characteristic feature of angle resolved XPS. This phenomenon, which is due to constructive interference in forward scattering of photoelectrons, acts, in effect, as a search-light allowing relatively easy mapping out of the structural arrangement atoms in the near-surface region. Examples which illustrate the usefulness of the XPS searchlight effect are presented.

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Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 37: Symposium D – Layered Structures, Epitaxy, and Interfaces , 1984 , 443
Copyright
Copyright © Materials Research Society 1985

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References

1) For a good overview, see: Tong, S. Y., Physics Today, Aug. 1984, p. 50.Google Scholar
2) Egelhoff., W. F. Jr., J. Vac. Sci. Tech. A 2, 350 (1984).CrossRefGoogle Scholar
3) Egelhoff, W. F. Jr., Phys. Rev. B30, 1052(1984).CrossRefGoogle Scholar
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7) The principles of photoelectron forward scattering have been recognized in previous studies of the carbon ls polar intensity distribution in adsorbed molecular CO, [8] and in studies of the oxygen ls azimuthal intensity distribution for oxygen adatoms. [9J However, only very recently has it been found to apply to angle resolved XPS of bulk single crystals and its great potential as a structural tool for epitaxy and interfaces been recognized. [3,4]Google Scholar
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11) See for example, Practical Surface Analysis, Briggs, D. and Seah, M. P., Eds., John Wiley & Sons, New York, 1983, p. 136; or Electron Spectroscopy, Vol.2, C. R. Brundle and A. D. Baker, Eds., Academic Press, London, 1977, p. 132.Google Scholar
12) Note here that the core-levels, being filled shells, are sperically synmetric, and the angle between the incident photon beam and the collected photoelectrons is a constant 90° (the sample is rotated).Google Scholar
13) Egelhoff, W. F. Jr., J. Vac. Sci. Tech., submitted.Google Scholar
14) To be more precise, unless the XPS system is automated it will take two angular sweeps, one with the spectrometer set on the peak and one with it set for a few eV larger kinetic energy to record the background which should subtracted off. See Ref. 3.Google Scholar
15) It should be stated that this particular advantage, elemental specificity, is shared by SEXAFS and NEXAFS. 1 However, they do not provide the same kind of information as the XPS searchlight effect.Google Scholar
16) Information on the third layer in an epitaxial structure is not manifest in data on deep core levels (low photoelectron kinetic energy). Higher kintic energy peaks do, however, provide such information. See Refs. 3 and 4 for further details.Google Scholar