Phase composition and valence of pulsed laser deposited vanadium oxide thin films at different oxygen pressures

In this paper, mixed valence VOx thin films have been achieved by pulsed laser deposition on silicon substrates using a pure vanadium target. During the focused laser irradiates the vanadium target, oxygen gas is supplied into the irradiation chamber. The oxygen pressure is varied in a range of 0.008 to 10 Pa. It is observed that the phase composition of VOx thin films is changed and the VOx thin films are gradually oxidized by increasing oxygen pressure during pulsed laser deposition, which is demonstrated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The XRD results show that the higher the oxygen pressure is, the more complex phase composition is. With increasing the oxygen pressure, the phases of vanadium oxide thin films undergo the following transformation: amorphous, VO2, VO2 + V3O7, VO2 + V3O7 + V6O13 and VO2 + V3O7 + V6O13 + V2O5. The XPS results confirm that the pulsed laser deposited VOx thin films include mixed valence (V5+, V4+ and V3+). The oxygen pressure about 0.08 Pa is found to be an optimum pressure to fabricate perfect stochiometric VO2 thin film.