Effects of elastic photoelectron collisions in quantitative XPS

Abstract

AbstractA fast Monte Carlo algorithm calculating the effects of elastic photoelectron collisions is presented. The algorithm is applicable to analyzer geometries with axial symmetry and with axis perpendicular to the surface (e.g. the CMA). The calculations were performed for four photoelectron lines: carbon 1s, aluminium 2s, cobalt 3p, and palladium 3d5/2. The following photoelectron characteristics were considered. (i) The angular distribution of photoelectrons leaving the surface. The distribution was found to follow the cosine distribution in practically all considered cases. Taking into account the elastic collisions did not change the shape of the distribution but decreased the photoelectron current leaving the surface, the difference increasing with atomic number of element. (ii) The distribution of emission depths of photoelectrons entering the analyzer. As a result of elastic collisions, more photoelectrons originate from the layer at the surface and less from the deeper layers. Thus, the actual depth of analysis is decreased. (iii) The total photoelectron current entering the analyzer. This current was also decreased by the elastic collisions. The difference reaches 1.6% for carbon 1s line, but increases to 16–19% for palladium 3d5/2 line. An elastic scattering correction in formalism of quantitative XPS is suggested. (iv) The average depth of analysis. This parameter was found to be most significantly affected by elastic scattering of photoelectrons. The depth of analysis was decreased by elastic collisions from 3–5% for carbon 1s line to 60–80% for palladium 3d5/2 line.