Determination of nanoscale titanium oxide thin film phase composition using X-ray photoelectron spectroscopy valence band analysis

The phase compositions of nanoscale thick titania films on the titanium were determined using X-ray photoelectron spectroscopy valence band analysis for the first time, by deconvoluting the two-peak structure of valence band into five peaks and analyzing the relative peak area. The titania films of thickness varying from about 2 nm to 8 mu m were obtained by the air oxidation of commercially pure titanium at different temperatures. The titania films formed on titanium for oxidizing temperatures up to 200 degrees C were amorphous, with thickness < 10 nm. The sub-stoichiometric oxides present at the TiO2-Ti interface were composed of Ti3+, Ti2+ and Ti1+ states when the film of thickness was < 10 nm. At 300 degrees C, when the titania film thickness was < 20 nm, it was fully converted to ruffle phase and remained stable up to 1000 degrees C. A broadening of full-width half-maxima of the core level peaks for the titania layers was attributed to the presence of surface hydroxyl group and stress gradient within the oxide layer. The absence of metastable anatase phase in the titania layers at lower temperatures was attributed to the presence of high stresses within the oxide layers owing to their nanoscale thickness.