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The electronic interactions at SiO2/TiO2and SiO2/Al2O3interfaces have been studied by X-ray photoemission spectroscopy. Both interfaces were formed by deposition of SiO2(evaporation of silicon monoxide followed of oxygen plasma treatment) on the surface of TiO2and Al2O3substrates. The variation of the binding energy (BE) of the Si 2p peaks and Auger parameter of silicon from the SiO2deposits is followed as a function of coverage. The BE of Si 2p peaks of the Si atoms at the SiO2/TiO2(SiO2/Al2O3) interface decreases 1.3 eV (1.0 eV) from submonolayer coverages up to the bulk SiO2material. Simultaneously, the Auger parameter of Si varies +0.9 eV (−0.3eV). These changes are discussed in terms of initial and final state effects of the photoemission process. Quantum mechanical calculations with cluster models confirm the origin of the observed shifts in these parameters. These findings preclude the systematic use of BE as an absolute parameter to determine the chemical state of elements at oxide interfaces.

The validity of the software packet QUASESTM, developed by Tougaard et al., for quantitative analysis by XPS of nano-scale surface structures is considered. We study the ability of the software to consistently determine the same amount of Au atoms within the surface region of a series of solids where the depth distribution of a fixed number of Au atoms is varied. The sets of samples were produced by first evaporating a few monolayers of gold onto the surface of a polycrystalline copper sample and then evaporating varying amounts of copper on top. A synchrotron radiation source is used to produce the photons. For two series of samples where the measured Au 4d peak intensities vary by a factor of 10, the quantitative amount of gold determined by this formalism is found to be constant to within an RMS deviation of 7% and 15%. When the spectra from the same set of samples using photons of 950 and 750 eV energy are analyzed, the RMS deviation in the total number of gold atoms is ∼ 20%.