Oxidizing annealing effects on VO2 films with different microstructures

Abstract Vanadium dioxide (VO 2 ) films have been prepared by direct-current magnetron sputter deposition on m -, a -, and r -plane sapphire substrates. The obtained VO 2 films display different microstructures depending on the orientation of sapphire substrates, i.e. mixed microstructure of striped grains and equiaxed grains on m -sapphire, big equiaxed grains on a -sapphire and fine-grained microstructure on r -sapphire. The VO 2 films were treated by the processes of oxidation in air. The electric resistance and infrared transmittance of the oxidized films were characterized to examine performance characteristics of VO 2 films with different microstructures in oxidation environment. The oxidized VO 2 films on m -sapphire exhibit better electrical performance than the other two films. After air oxidization for 600 s at 450 °C, the VO 2 films on m -sapphire show a resistance change of 4 orders of magnitude over the semiconductor-to-metal transition. The oxidized VO 2 films on a -sapphire have the highest optical modulation efficiency in infrared region compared to other samples. The different performance characteristics of VO 2 films are understood in terms of microstructures, i.e. grain size, grain shape, and oxygen vacancies. The findings reveal the correlation of microstructures and performances of VO 2 films, and provide useful knowledge for the design of VO 2 materials to different applications.