A highly-efficient approach for reducing phase transition temperature of VO2 polycrystalline thin films through Ru4+-doping

Abstract

A low semiconductor-metal transition (SMT) temperature (TSMT) is highly desirable for advancing practical applications of VO2. The doping with tetravalent metal elements attracts little attention as an effective approach for reducing the TSMT of VO2. Here we investigate the effect of Ru-doping on the microstructure and SMT characteristics of VO2 polycrystalline thin films. X-ray photoelectron spectroscopy reveals that Ru ions exist in the tetravalent oxidation state in Ru-doped VO2 thin films. X-ray diffraction patterns and Raman spectra indicate that substitutional Ru4+ ions decrease the crystallite size of films and induce the local tetragonal symmetry in the framework of monoclinic VO2 lattice. As a result, Ru4+-doping reduces the TSMT of VO2 polycrystalline thin films at the rate of 10.5 °C/at%. Moreover, the room temperature resistivity of thin films decreases from 9.98 Ω·cm for undoped VO2 to 0.63 Ω·cm for Ru-doped one with Ru atomic concentration of 2.32 at%, which is ascribed to the narrowed band gap and enhanced density of states of the V 3d band.