Sputter deposited Mo thin films on soda-lime glass are studied by x-ray photoelectron spectroscopy. It is found that the proportion of metallic Mo at the surface decreases and the number of Mo6+ species increases as the Ar gas pressure used for sputtering is increased. Sodium, diffusing during deposition from the substrate, is also detected on the surface of the Mo thin films. The implications for optimizing Mo thin films for Cu(InGa)Se-2 applications are discussed. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3425634]