Determination of photoelectron attenuation lengths in calcium phosphate ceramic films using XPS and RBS

Abstract

Calcium phosphate (CaP) coatings are used to improve the biological performance of an implant. A technique that is often used to measure the composition of this material is XPS. When extremely thin coatings are measured, for example to study the interface between CaP and a substrate, the quantification of the XPS results is complicated by the varying attenuation lengths (ALs) of the photoelectrons at different energies. To correct for this, AL data are needed. In this work we measured these ALs by comparing XPS yields with the coating coverage (as measured by Rutherford backscattering spectrometry). We were able to determine the AL for several calcium and phosphorus peaks. Determination of the oxygen ALs was not possible owing to diffusion of oxygen into the polymeric substrates. For the peaks that are most often used for quantification of XPS yields (the Ca 2p and the P 2p peak), we found ALs of 21.8 × 10