AVS 46th International Symposium
    Applied Surface Science Division Wednesday Sessions
       Session AS-WeM

Paper AS-WeM6
Relationships between Parameters Describing Inelastic Electron Scattering in Solids

Wednesday, October 27, 1999, 10:00 am, Room 6A

Session: Gaede-Langmuir Award Address and Quantitative Surface Analysis
Presenter: C.J. Powell, National Institute of Standards and Technology
Authors: A. Jablonski, Polish Academy of Sciences
C.J. Powell, National Institute of Standards and Technology
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The terms inelastic mean free path (IMFP), effective attenuation length (EAL), and mean escape depth (MED) are frequently used to specify the surface sensitivity of AES and XPS and also for quantitative applications. These terms are different conceptually because of the effects of elastic-electron scattering, and generally have different numerical values. In addition, EAL and MED values depend on the instrumental configuration. We apply an analytical formalism developed from a solution of the kinetic Boltzmann equation within the transport approximation@footnote 1@ to demonstrate the relationships between the IMFP, EAL, and MED for selected elemental solids and for common measurement conditions. It is shown that EAL and MED values can be derived from an analytical representation of the emission depth distribution function and values of the IMFP and the transport mean free path.@footnote 2@ Examples are given to show the magnitude of elastic-scattering effects on MED values for angle-resolved XPS and AES. If XPS or AES data are acquired for emission angles between zero and 60°, the ratio of the MED to that found with elastic scattering neglected is approximately constant (to within 10 %), and this ratio can be used to determine an average value for the EAL. This EAL value can then be used to establish the depth scale in the data analysis. For emission angles greater than 60°, conventional data analysis (in which elastic-scattering effects are neglected) becomes unreliable. Finally, we show ratios of the EAL to the IMFP for XPS from the Au 4s subshell with Mg K@alpha@ x rays as a function of emission angle and depth; this ratio has a weak dependence on emission angle from zero to 40° but a more pronounced dependence for larger emission angles. @FootnoteText@ @footnote 1@I. S. Tilinin, A. Jablonski, J. Zemek and S. Hucek, J. Electron Spectrosc. 87, 127 (1997). @footnote 2@A. Jablonski and C. J. Powell, J. Electron Spectrosc. (in press).