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

In this work, VO2 thin films were prepared on three kinds of substrates by the sol-gel dip-coating method followed by heat treatment under vacuum. These thin films were analysed by x-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The infrared and ultraviolet-visible spectra of the VO2 thin films were also recorded during heating and cooling between room temperature and 100-degrees-C. The experimental results show that VO2 thin films thus prepared exhibit thermally induced reversible phase transition, and the largest changes in transmittance and reflectivity are approximately 58 and 25%, respectively, in the case of vacuum heat treatment at 400-degrees-C and silica glass substrates. The refractive index (n) decreases and the absorption 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 remarkably are discussed.