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       Session AS-MoA

Paper AS-MoA6
Comparisons of Practical Effective Attenuation Lengths and Inelastic Mean Free Paths for Applications in AES and XPS

Monday, October 29, 2001, 3:40 pm, Room 134

Session: Quantitative Analysis and Data Interpretation II: Electron Spectroscopies
Presenter: C.J. Powell, National Institute of Standards and Technology
Authors: C.J. Powell, National Institute of Standards and Technology
A. Jablonski, Polish Academy of Sciences
Correspondent: Click to Email
The practical effective attenuation length (EAL), defined in terms of changes in signal-electron intensities, is needed (as the "lambda parameter") for measurements of overlayer thicknesses by AES and XPS.@footnote 1@ We have calculated practical EALs for principal photoelectron and Auger-electron lines in Si, Cu, Ag, and W using an algorithm based on solution of the kinetic Boltzmann equation within the transport approximation.@footnote 2@ These calculations were made for values of the angle of emission @alpha@ between 0 and 80° and, for XPS, a configuration in which the angle between the x-ray source and the analyzer axis was 55°. For @alpha@ < 60°, the ratio of the practical EAL to the corresponding inelastic mean free path (IMFP) is nearly constant with emission angle, and varies in magnitude between 0.68 and 0.91. The deviation of this ratio from unity is due to the effects of elastic-electron scattering. We find that the ratio varies approximately linearly as a function of the single-scattering albedo that is defined in terms of the IMFP and the transport mean free path (TMFP). While the albedo varies in a complicated manner with atomic number and electron energy, it provides a convenient measure of the effects of elastic-electron scattering. For @alpha@ > 60°, the ratio of the practical EAL to the IMFP increases rapidly with emission angle. At these more grazing emission angles, practical EALs should be determined for the specific film thicknesses and emission angles of interest in order to obtain reliable measurements of film thicknesses. @FootnoteText@ @footnote 1@A. Jablonski and C. J. Powell (to be published). @footnote 2@I. S. Tilinin, J. Zemek, and S. Hucek, Surf. Interface Anal. 25, 683 (1997).