Surface roughness effects in quantitative XPS: magic angle for determining overlayer thickness

The use of X-ray photoelectron spectroscopy (XPS) as a technique for non-destructive depth profiling of technical samples is often hindered by their roughness. In this paper, we elaborate on earlier work where we reported on the apparent existence of a ‘magic’ angle for the determination of the thickness of uniform overlayers on rough substrates. Simple calculations for fully three-dimensional model rough surfaces strongly suggest that the thickness of an overlayer on a rough substrate can be determined accurately without taking the roughness into account in the analysis of the XPS intensities, the neglect of roughness effects leading to an average error less than 10% in the determined thickness.