X-ray photoemission study of the calcium/titanium dioxide interface

X-ray photoelectron spectroscopy (XPS) has been used in order to study the CaTiO2 (rutile) interface. It has been observed that the growth of calcium on TiO2 is accompanied by the oxidation of the calcium film. The consequence of this reaction is the reduction of TiO2 into TiO, Ti2O3 and other non-stoichiometric oxides. When the thickness of the deposit increases up to about 10 nm, the Ca 2p peak revealed that the film consists essentially of metallic calcium. When annealing under UHV up to 900 K, the Ca 2p line exhibits an oxide structure and titanium is not detected on the surface. Rutherford backscattering spectrometry (RBS) experiments performed on thick coatings (10 to 1000 nm) prepared and annealed in poor vacuum conditions revealed that the diffusion coefficients were in the range of 10−14 cm2/s. As result of annealing the formation of CaCO3 is suggested. On the RBS spectra, no plateau indicating the formation of a titanium compound has been observed at different temperatures.