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The idea of extracting in-depth composition information through an analysis of the x-ray photoelectron spectroscopy (XPS) peak shape was investigated. The peak shape is described by a single parameter D which is the ratio of the peak area to the increase in background signal 30 eV below the peak energy. Based on a first-order calculation, analytic expressions for D were found for homogeneous solids as well as for the situation where impurities are located at a certain depth underneath the solid surface. An evaluation which includes all inelastic scattering events showed that for an exact treatment, higher-order terms are important. Therefore an empirical formula based on a calculation to infinite order gives a more general description. In experimental XPS one has to deal with the problem of background subtraction. This problem was discussed and an approximate description was suggested.
S. Tougaard (Wed,) studied this question.