The low-temperature oxidation during deposition by evaporation of molybdenum thin films has been investigated. Analysis by x-ray photoelectron spectroscopy and x-ray diffraction reveals that small differences in the substrate temperature during deposition may give rise to important changes in the final composition and structure of the molybdenum oxide. Changes in binding energy and line shape of the Mo 3d5/2-Mo 3d3/2 doublet attributed to oxygen incorporation have been studied. Two principal steps can be distinguished, with a transition temperature of ∼310°C. Up to substrate temperatures of ∼310°C, the superficial Mo remains almost unaffected, with some oxygen dissolved. At ∼310°C, mixing of Mo0 metal and molybdenum oxide (Moδ+0<δ<4) clusters or islands is observed. Finally, above this temperature a surface layer of molybdenum oxide, Mo6+, is formed. In addition, an abrupt change in d100 interplanar parameter of Mo is observed. © 1999 American Institute of Physics.