Composition evolution and electrical properties of VO thin films induced by annealing temperature

In this study, vanadium dioxide thin films were fabricated on AlO (0001) substrates by sol-gel method and subsequent annealing process. The effects of annealing temperature on the structure, chemical state, surface morphology and electrical properties of the films were systematically studied. The results displayed that with the annealing temperature increasing up to 520 °C, the composition evolution experienced four processes: the reduction of V to V (or V), the comproportionation of V/V to V, the oxidation of V to V, and the secondary reduction of V to V. Accompanied with the secondary reduction at 520 °C, the disappearance of grain boundaries was observed on the film surface. Furthermore, as the annealing temperature increased from 420 °C to 470 °C and then 520 °C, the prepared films showed good phase transition property with the resistance change up to nearly four orders of magnitude, and the phase transition temperatures were 62.8 °C, 61.8 °C and 61.1 °C respectively, showing a slow downward trend. The results not only revealed the mutual transformation of various vanadium oxides during the annealing treatment, but also supplied some clues for optimizing the parameters for VO film preparation with high quality. [Figure not available: see fulltext.]