Sol-gel synthesis of VO2 thin films and the effects of W and Re doping


  • Moffatt Claire
  • Wigstein Anders

Publish date: 2005-01-01

Report number: FOI-R--1684--SE

Pages: 41

Written in: English


Vanadium dioxide (VO2) is a thermochromic material that undergoes a semiconductor-to- metal phase transition around 68 C. This transition is accompanied by changes in the electrical, optical and magnetic properties of VO2. At room temperature the material is transparent and non-conductive but above the transition temperature the material becomes metallic and IR reflecting. Potential practical applications for VO2 thin films are, for example, optical (IR) or electrical switching devices and energy-efficient windows. VO2 has also become interesting in defence applications due to its property to reflect IR radiation. However, for these purposes the transition temperature needs to be lowered which can be achieved by doping of the VO2 film with other metal cations. In this project the first step was to develop a process for the production of VO2 films from a vanadium alkoxide precursor by the sol-gel technique. When this was accomplished, doping of the VO2 films with tungsten and rhenium was performed with doping levels of 1 to 12 at-%. The crystal structure and the optical switching characteristics were investigated with X-ray powder diffraction (XRPD) and Fourier transform infrared spectroscopy (FTIR), respectively. The surface morphology and chemical compositions of the films were analysed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). A maximum lowering of the transition temperature was obtained for VO2 films doped with 4-at% W, resulting in a transition temperature of 22 C. The Re doping did not succed, no Re could be detected in the films.