Recent advance in phase transition of vanadium oxide based solar reflectors and the fabrication progress
Vanadium dioxide (VO2) as a phase-change material controls the transferred heat during phase transition process between metal and insulator states. At temperature above 68°C, the rutile structure VO2 keeps the heat out and increases the IR radiation reflectivity, while at the lower temperature the monoclinic structure VO2 acts as the transparent material and increase the transmission radiation. In this paper, we first present the metal-insulator phase transition (MIT) of the VO2 in high and low temperatures. Then we simulate the meta-surface VO2 of metamaterial reflector by Ansys HFSS to show the emittance tunability (Δɛ) of the rutile and monoclinic phase of the VO2. In next section, we will review the recent progress in the deposition of thermochromic VO2 on glass and silicon substrate with modifying the pressure of sputtering gases and temperature of the substrate. Finally, we present the results of the in-situ sputtered VOx thin film on thick SiO2 substrate in different combination of oxygen and argon environment by V2O5 target at temperature higher than 300°C and then, analyze it with x-ray diffraction (XRD) method. The thermochromic VO2 based metamaterial structures open a new route to the passive energy-efficient optical solar reflector in the past few years.