Ultra-thin TiO2 films were grown on a Mo(112) substrate by stepwise vapor depositing of Ti onto the sample surface followed by oxidation at 850 K. X-ray photoelectron spectroscopy showed that the Ti 2p peak position shifts from lower to higher binding energy with an increase in the Ti coverage from sub- to multilayer. The Ti 2p peak of a TiO2 film with more than a monolayer coverage can be resolved into two peaks, one at 458.1 eV corresponding to the first layer, where Ti atoms bind to the substrate Mo atoms through Ti-O-Mo linkages, and a second feature at 458.8 eV corresponding to multilayer TiO2 where the Ti atoms are connected via Ti-O-Ti linkages. Based on these assignments, the single Ti 2p(3/2) peak at 455.75 eV observed for the Mo(112)-(8 x 2)-TiOx monolayer film can be assigned to Ti3+, consistent with our previous results obtained with high-resolution electron energy loss spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.