Nanostructured vanadium oxide (nano-VOx) thin films were prepared by direct current magnetron reactive sputtering in mixed O-2/Ar discharges and subsequent annealing in oxygen atmosphere. X-ray diffraction and field emission scanning electron microscope were employed to characterize the crystal structures and morphologies, respectively. Fourier transform infrared spectroscopy was applied to analyze the vanadium-oxygen bonds of films. X-ray photoelectron spectroscopy revealed the compositions of the surface and inner portion of nano-VOx thin films. It was shown that the as-deposited films were amorphous, and in-situ annealing of these films in ambient oxygen for 10 min can lead to the growth of nano-VOx thin films. Results of electrical studies indicated that the absolute values of temperature coefficient of resistance and activation energy of films increased significantly after oxygen annealing. Optical investigations carried out in the UV-visible range showed that the absorption edges of nano-VOx films exhibited large red shifts compared with as-deposited film, and that dual optical absorptions were observed in nano-VOx films. (C) 2011 Elsevier B.V. All rights reserved.