Characteristics of phase transition of VO₂films grown on TiO₂substrates with different crystal orientations

Vanadium dioxide (VO₂) films were synthesized on two-side polished titanium dioxide (TiO₂) substrates of five different crystal orientations, (0 0 1), (1 0 0), (1 0 1), (1 1 0), and (1 1 1), through pulsed laser deposition. X-ray diffraction measurements suggested that epitaxial VO₂films with good crystallinity were grown on TiO₂. Transmission electron microscopy measurements showed the thickness of VO₂films to be about 50 nm and revealed the presence of an inter-mixing layer of ~10 nm thickness at the interface between VO₂and TiO₂. A metal-insulator transition (MIT) showing a change in resistance of 3-4 orders of magnitude was observed in all samples. The MIT temperature (T_MI) showed a significant variation with crystal orientation: the highest value of T_MIwas 350 K in VO₂/TiO₂(0 0 1) and the lowest value was 310 K in VO₂/TiO₂(1 1 0), and VO₂films for the (1 1 1), (1 0 1), and (1 0 0) orientations exhibited T_MI~315 K, 330 K, and 340 K, respectively. For infrared light, the change in the optical transmittance by the MIT was about 60%.