The Use of Energy Loss Structures in XPS Characterisation of Surfaces

Abstract

ABSTRACTThis paper describes advances in the use of the energy loss background associated with individual photoelectron peaks. The subtraction of a Shirley-type background is now normal practice in quantitative XPS analysis. However, in the case of a composite peak containing features from differing depths the subtraction of a common background has a clear disadvantage: i.e. the proportion of background rise associated with each component should be different but is, in fact, fixed. A peak-fitting procedure is described which enables individual backgrounds to be used for each component. The method has been tested using evaporated overlayers and this enables a mean free path for electrons undergoing small energy losses (less than 10 eV) to be determined. The findings are in accord with those of Tougaard and Sigmund and suggest that the use of background intensities in conjunction with the peaks themselves enables the information depth of XPS to be extended by about 10%. A few observations on the behaviour and use in analysis of the large energy loss structure are made.The use of the findings to aid in characterisation of the near surface distribution of elements and ions is described for the following systems: the distribution within oxide films on alloys; the locus of disbondment of organic films on metals; and the surface contamination of surfaces removed from aqueous media.