Optical properties of VO2 thin films deposited on different glass substrates

Abstract

This work investigated the effect of sodium (Na) and potassium (K) ions permeation on optical properties of vanadium dioxide (VO2) deposited on three different glass substrates: silica-soda-lime (SL), silica-potash-soda (PS) and fused quartz (FQ), respectively. The VO2 thin films were prepared by reactive magnetron sputtering. Microstructure and compositions were determined by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Morphology of the films was characterized by atomic force microscopy (AFM), and the optical properties of the films, including refractive index and extinction coefficient, were characterized by spectroscopic ellipsometry (SE). Results show that the optical properties of the VO2 films grown on different substrates exhibited different dispersion trends at room temperature, which could be attributed to the penetration of Na and K ions. In addition, the influence of temperature on the optical properties of VO2 thin films was also studied by varying temperature ellipsometry. Below the phase transition temperature, the peak of the refractive index showed a clear blue shift with increasing temperature; above the phase transition temperature, the peak of refractive index also showed a blue shift, which was different from the trend below the phase transition temperature. This phenomenon indicates that the VO2 film has undergone a phase change.