Inelastic mean free pathlengths of electrons for quantitative investigations of ultrathin technological surface layers by angle-resolved x-ray photoelectron spectrometry

Abstract

Angle-resolved self-ratio x-ray photoelectron spectrometry is shown to yield quantitative information on the depth composition of technological surfaces. The inelastic mean free pathlengths (IMFP) of x-ray photoelectrons required for quantification of the experimental data are obtained from a new universal formula (documented here for the first time). For the energy range 200–2000 eV, the two fitting parameters of the formula were deduced from the optical-data-derived IMFP of Tanuma, Powell, and Penn. These ‘‘optical’’ IMFP are presently being checked against IMFP derived from stopping data of high-energy protons and from mean-energy-loss-per-collision data (obtained from electron energy loss spectra). These latter IMFP are found to be significantly shorter than the optical IMFP. Equations are presented for conversion of proton-stopping powers to electron-stopping powers, and thence to IMFP.