Continuous Tuning of Phase Transition Temperature in VO₂ Thin Films on c-Cut Sapphire Substrates via Strain Variation

Vanadium dioxide (VO₂) 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 VO₂ lattice is found to be dependent on the VO₂ thickness and the VO₂/AZO interface roughness. The semiconductor-to-metal transition (SMT) properties of VO₂ thin films are characterized and the transition temperature (T_c) is successfully tuned by the VO₂ thickness as well as the VO₂/AZO interface roughness. It shows that the T_c of VO₂ decreases with the decrease of film thickness or VO₂/AZO interface roughness. Other SMT properties of the VO₂ films are maintained during the T_c tuning. The results suggest that the strain tuning induced by AZO buffer provides an effective approach for tuning T_c of VO₂ continuously.