Molybdenum oxide (MoO3) thin films were deposited by electron beam evaporation. The chemical composition, microstructure, optical and electrical properties of MoO3 thin films depend on the annealing temperature and ambient atmosphere. X-ray diffraction (XRD) shows that crystalline MoO3 films can be obtained at various post-annealing temperatures from 200 to 500 degrees C in N-2 and O-2. X-ray photoelectron spectroscopy (XPS) results reveal that the O-1s emission peak was shifted slightly toward lower binding energies as the annealing temperature in N-2 was increased. The oxygen vacancies and conductivity of MoO3 film increased with the annealing temperature. However, when the MoO3 films were annealed in an atmosphere of O-2, the optical transmission, the O/Mo ratio and the photon energy increased with the annealing temperature. The results differ from those for films annealed in a N-2 atmosphere. (c) 2008 Elsevier B.V. All rights reserved.