Maximizing Infrared Transmission Contrast upon Phase Transition of Thermally Grown Vanadium Dioxide Thin Films by Rapid Thermal Processing

Pristine vanadium dioxide (VO2), an insulator-to-metal transition (IMT) material, is grown via furnace oxidation followed by rapid thermal annealing with forming gas (5% H2/95% N2) which reduces surface over-oxides such as V2O5 formed during the oxidation. The evolutional IMT behaviors of the thermochromic film and vanadium oxide states over different reduction times are systematically studied with temperature-dependent infrared spectrometry, electrical resistivity, and X-ray diffraction measurements. After optimally reducing surface over-oxides to VO2, infrared transmission contrast upon phase transition is enhanced to 46% (at 9 μm wavelength) compared to 23% from full oxidation without any reduction. Moreover, the pristine VO2 thin film obtained from thermal oxidation and optimal reduction processes exhibits sharp phase transition and narrow thermal hysteresis within 2–4 °C in both infrared transmission and electrical resistivity, which are comparable to the best quality VO2 prepared by other sophisticated fabrication techniques. The thermally grown method presented here would facilitate the scalable fabrication of high-quality VO2 thin films and tunable radiative coatings for high-performance thermal control applications.