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Publication Citation: Surface Sensitivity of Auger-Electron Spectroscopy and X-Ray Photoelectron Spectroscopy

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Author(s): Cedric J. Powell; E Jablonski; I Tilinin; David R. Penn;
Title: Surface Sensitivity of Auger-Electron Spectroscopy and X-Ray Photoelectron Spectroscopy
Published: August 09, 1999
Abstract: A convenient measure of surface sensitivity in Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) is the mean escape depth (MED). If the effects of elastic-electron scattering are neglected, the MED is equal to the electron inelastic mean free path (IMFP) multiplied by the cosine of the emmision angle with respect to the surface normal, and depends on the material and electron energy of interest. An overview is given here of recent calculations of IMFPs for 50-2000 eV electrons in a range of materials. This work has led to the development of a predictive formula based on the Bethe equation for inelastic electron scattering in matter from which IMFPs can be determined. Estimates show, however, that elastic-electron scattering can significantly modify the MED. Thus, for AES, the MED will be reduced by up to about 35%. For XPS, however, the MED can be changed by up to {plus or minus}30% for common measurement conditions although it can be much larger (by up to a factor of 2) for near-grazing emission angles. Ratios of MED values, calculated with elastic scattering considered and neglected for XPS from the 3s, 3p, 3d subshells of silver with Mg Kα X-rays are approximately constant (to about 10%) over a range of emission angles that varies from 40° to 60° depending on the subshell and the angle of the X-ray incidence. Recommendations are given on how to determine the optimum range of emission angles for satisfactory analysis of angle-resolved XPS (ARXPS) data. Definitions are included of three terms often used for describing surface sensitivity (IMFP, MRD, and effective attenuation length (EAL)), and examples are given of the varying magnitudes of these quantities for different analytical conditions.
Citation: Journal of Electron Spectroscopy and Related Phenomena
Volume: 98-99
Pages: pp. 1 - 15
Keywords: auger-electron spectroscopy;elastic-electron scattering;inelastic mean free path;mean escape depth;surface sensitivity;x-ray photoelectron spectroscopy
Research Areas: Surface Physics