A consistent method for quantitative XPS peak analysis of thin oxide films on clean polycrystalline iron surfaces

We report a method for the quantitative analysis of the Fe(2p) and O(1s) core level XPS spectra which allows the determination of the Fe2+/Fe3+ ratio within a thin oxide film. The method involves the determination of the intensity of specific shake-up features within the Fe(2p) spectrum. This analytical method is demonstrated by comparing the Fe(2p) spectra of electrochemically modified Fe2+-rich and Fe3+-rich electrodes in a combined UHV-XPS-electrochemical system. Exposure of clean polycrystalline Fe surfaces to low pressures of O-2 gas for different time intervals has also been carried out. Quantitative XPS analyses of the oxide films produced by O-2 exposures reveal that the oxide films are predominantly trilayers of FeO, Fe3O4 and FeOOH phases, the latter due to ambient background contamination. The analyses demonstrate that a multiplicity of Fe2+ and/or Fe3+ chemical environments and binding energies is present in such films, and this must be explicitly accounted for during quantitative analyses. (C) 1997 Elsevier Science B.V.