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    Applied Surface Analysis Monday Sessions
       Session AS-MoA

Paper AS-MoA5
The Attenuation Length Revisited

Monday, October 29, 2001, 3:20 pm, Room 134

Session: Quantitative Analysis and Data Interpretation II: Electron Spectroscopies
Presenter: A. Jablonski, Polish Academy of Sciences
Authors: A. Jablonski, Polish Academy of Sciences
C.J. Powell, National Institute of Standards and Technology
Correspondent: Click to Email
The attenuation length, and the preferred replacement term effective attenuation length (EAL), have been a source of confusion in surface analysis by Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The EAL is formally defined in terms of the local slope of the emission depth distribution function (EDDF). This definition is relevant to the determination of the depth of a thin marker layer. The EAL is also frequently used as a term to determine the thicknesses of thin overlayer films from measurements of AES or XPS signal intensities. We show that while the formal EAL definition does not correspond conceptually to this important application, numerical EAL values calculated from changes of signal intensities are similar to values obtained from the formal EAL definition for some experimental configurations. The EALs for the marker-layer and overlayer-film applications are what we term "local" EALs since they were derived from the reasonable assumption that the EDDF could be regarded as an exponential function of marker depth or overlayer-film thickness for small ranges of depths or thicknesses. We point out that it is also useful to define "practical" EALs for a wider range of depths or thicknesses. We have made calculations of local and practical EALs for XPS with Mg K@alpha@ X-rays in a range of measurement configurations for Si 2s photoelectrons in Si (for which elastic-electron scattering effects are relatively weak) and for Au 4s photoelectrons in Au (for which the elastic-scattering effects are relatively strong). In general, the local and practical EALs for each solid vary with the measurement conditions. Nevertheless, the practical EALs for overlayer- film thickness measurements in conventional XPS experiments do not vary appreciably with emission angle for emission angles between 0 deg and about 65 deg with respect to the surface normal. A similar result was found for three Auger transitions in Au.