Vanadium oxide (VO2) thin films have been studied extensively because of their thermochromic properties, i.e. reversible optical change as a function of temperature. These reversible optical changes, also accompanied by electrical changes make these films interesting from application point of view. Many applications such as smart windows, sensing devices, variable reflectance mirrors and many others can be envisiioned. VO2 undergoes a reversible insulator-to-metallic (MIT) phase transition at a temperature of ~ 68° C. This phase change is accompanied by a change of the optical and electrical properties. The electric resistance decreases to a few ohms and the film changes from transparent to opaque in the IR region after a phase transition occurs.
Sputtering technique was used to deposit pure vanadium thin films on glass and quartz substrates. Subsequently, the films were annealed at 500°C in a vacuum chamber in the presence of oxygen gas for 1 hour to oxidize the films to obtain stoichiometric VO2. Both electrical and optical changes during the transition insulator to metal (MIT) were studied. All the fabricated films exhibit efficient thermochromic changes. The films deposited on quartz substrates were found to show an unusual hysteresis in their resistivity in the first few cycles. XRD and XPS studies were done to understand this unusual behaviour of VO2 films on quartz substrates.