A self-modeling approach to the resolution of XPS spectra into surface and bulk components

A method of resolving XPS spectra into surface and bulk component spectra for cases of moderate energy resolution is designed based on an analysis of a family of spectra acquired at different polar angles from flat specimens. Assumptions about line shapes are not required, but an analytical model of the angular dependence of the bulk and surface XPS signals is needed when the component spectra overlap in the range of binding energies of interest. Recommendations are made of the error limits of experimental variables for the successful application of the self-modeling method. The method was used successfully in the separation and quantitative analysis of the O(1s) XPS spectra of surface silanols from bulk silicon dioxide of a fully hydrated silicon dioxide surface. The surface (silanol) and bulk (oxide) components were found to be separated by 0.30 eV, and the surface component was found to be broader (1.58 eV) than the bulk component (1.15 eV).