Annealing effect on phase transition and thermochromic properties of VO2 thin films

Vanadium dioxide (VO2) is one kind of desired thermochromic material for many smart devices because of its notable temperature-responsive infrared modulation and metal insulator transition with underlying structural phase transition (SPT). Understanding on the tuning of these properties in an anticipated manner is essential to accomplish device realization. Here, we report the annealing time induced modifications in SPT and the thermochromic properties of VO2 thin films. Using RF sputtering deposition, VO2 thin films were grown at room temperature and their ex-situ annealing was carried out at 600 degrees C for different time from 2 min to 60 min. Structural, electronic and thermochromic properties of these films were investigated. VO2 thin films samples annealed for longer time exhibit larger crystallite size, higher surface roughness and SPT temperature, and the reduced hysteresis width of SPT during heating and cooling cycle. X-ray absorption spectroscopy results indicate that the variation in the annealing time do not alter the electronic structure significantly. Nevertheless, VO2 thin film samples with prolonged annealing display higher IR transmittance modulation across the SPT.