Characteristics of phase transition of VO2 films grown on TiO2 substrates 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 VO2 films with good crystallinity were grown on TiO2. Transmission electron microscopy measurements showed the thickness of VO2 films to be about 50 nm and revealed the presence of an inter-mixing layer of ~10 nm thickness at the interface between VO2 and 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 (TMI) showed a significant variation with crystal orientation: the highest value of TMI was 350 K in VO2/TiO2(0 0 1) and the lowest value was 310 K in VO2/TiO2(1 1 0), and VO2 films for the (1 1 1), (1 0 1), and (1 0 0) orientations exhibited TMI ~315 K, 330 K, and 340 K, respectively. For infrared light, the change in the optical transmittance by the MIT was about 60%.