Continuous Tuning of Phase Transition Temperature in VO Thin Films on c-Cut Sapphire Substrates via Strain Variation.

Vanadium dioxide (VO) thin films with controlled thicknesses are deposited on c-cut sapphire substrates with Al-doped ZnO (AZO) buffer layers by pulsed laser deposition. The surface roughness of AZO buffer layers is varied by controlling oxygen pressure during growth. The strain in the VO lattice is found to be dependent on the VO thickness and the VO/AZO interface roughness. The semiconductor-to-metal transition (SMT) properties of VO thin films are characterized and the transition temperature (T) is successfully tuned by the VO thickness as well as the VO/AZO interface roughness. It shows that the T of VO decreases with the decrease of film thickness or VO/AZO interface roughness. Other SMT properties of the VO films are maintained during the T tuning. The results suggest that the strain tuning induced by AZO buffer provides an effective approach for tuning T of VO continuously.