Surface analysis, peak intensities and angular distributions in XPS

Abstract

Purely instrumental contributions to the angular dependence of XPS peak intensities are considered theoretically and experimentally, and it is found that peak-ratio angular distributions should be free of all instrumental effects, and thus amenable to more direct analysis in terms of specimen-related properties. This is demonstrated experimentally for gold specimens with thin carbon-containing surface layers. The effects of surface roughness on XPS angular distributions are also investigated. For the triangular-periodic surfaces of aluminium diffraction gratings, pronounced surface profile effects on oxide/metal ratio angular distributions are observed; these effects are in good agreement with model theoretical calculations. For unidirectionally-polished aluminum specimens of more random surface profile, oxide/metal ratio angular distributions are distinctly different for angle variation parallel to and perpendicular to the polishing grooves, with much more surface enhancement being possible at low electron emission angles for parallel variation. This difference is qualitatively consistent with theoretical expectations. For the highly random surface contours of Al₂O₃ powder specimens subjected to solution adsorption of Si and Ca, it is also possible to do qualitative depth profiling of the various atoms present according to their relative enhancements at low angles of electron emission.