Quantitative analysis of overlapping XPS peaks by spectrum reconstruction: determination of the thickness and composition of thin iron oxide films

The composition and thickness of thin iron oxide films on polycrystalline pure iron were evaluated from Fe 2p spectra as measured by x-ray photoelectron spectroscopy. To this end the experimental spectra were reconstructed from reference spectra of the constituents Fe0, Fe2+ and Fe3+. The background contributions in the spectra owing to inelastic scattering of signal electrons were calculated from the depth distributions of these constituents and their reference spectra. In the reconstruction procedure the film thickness and the concentrations of Fe2+ and Fe3+ in the oxide film were used as fit parameters. The values obtained for the oxide film thickness were compared with thickness values determined from the intensity of the corresponding O 1s spectra and with thickness values resulting from ellipsometric analysis. The sensitivity of the reconstruction procedure with regard to film thickness and film composition was tested.