PREPARATION AND OPTICAL-PROPERTIES OF PHASE-CHANGE VO2 THIN-FILMS

In this work, VO2 thin films were prepared on three kinds of substrate s by the sol-gel dip-coating method followed by heat treatment under v acuum. These thin films were analysed by x-ray diffraction (XRD) and X -ray photoelectron spectroscopy (XPS) techniques. The infrared and ult raviolet-visible spectra of the VO2 thin films were also recorded duri ng heating and cooling between room temperature and 100-degrees-C. The experimental results show that VO2 thin films thus prepared exhibit t hermally induced reversible phase transition, and the largest changes in transmittance and reflectivity are approximately 58 and 25%, respec tively, in the case of vacuum heat treatment at 400-degrees-C and sili ca glass substrates. The refractive index (n) decreases and the absorp tion coefficient (k) increases when heating these thin films from room temperature to 100-degrees-C, and vice versa for cooling. The reasons why the optical constants and infrared absorption spectra change so r emarkably are discussed.