Study of nanocrystalline VO 2 thin films prepared by magnetron sputtering and post-oxidation

Nanocrystalline VO 2 thin films were deposited onto glass slides by direct current magnetron sputtering and post-oxidation. These films undergo semiconductor-metal transition at 70 °C, accompanied by a resistance drop of two magnitude orders. The crystal structures and surface morphologies of the VO 2 films were characterized by x-ray diffraction (XRD) and atomic force microscope (AFM), respectively. Results reveal that the average grain size of VO 2 nanograins measured by XRD is smaller than those measured by AFM. In addition, Raman characterization indicates that stoichiometric VO 2 and oxygen-rich VO 2 phases coexist in the films, which is supported by x-ray photoelectron spectroscopy (XPS) results. Finally, the optical properties of the VO 2 films in UV-visible range were also evaluated. The optical band gap corresponding to 2p—3d inter-band transition was deduced according to the transmission and reflection spectra. And the deduced value, E op t 2p —3d = 1.81 eV, is in good agreement with that previously obtained by theoretical calculation.