Abstract
High quality of thermochromic VO2 coatings were grown onto ITO-coated quartz by thermal oxidation of ac magnetron sputtered vanadium oxide films. The thermochromic properties of VO2 coatings were investigated by means of IR transmittance and Raman scattering measurements as a function of temperature (up to 100 degrees C). It is observed that the IR transmittance of VO2 decreased by increasing temperature, that is the signature of the semiconductor-to-metallic transition (SMT). The associated transition temperature was found to be around 56 degrees C. At room temperature, the Raman analysis showed only the presence of vibrational modes of the pure VO2 phase. However, the temperature dependent Raman measurements showed that the scattered signals decreased by increasing the temperature and they disappeared completely when the VO2 switched to its metallic state. The structural phase transition from a monoclinic crystalline structure (at room temperature) to a tetragonal rutile type structure (at high temperature) appeared at relatively high temperature (similar to 75 degrees C) compared to the SMT transition temperature (similar to 56 degrees C). The evolution of vibrational Raman modes in the heating and cooling cycles showed relatively large hysteresis (similar to 10 degrees C).