Substrate effects on metal-insulator transition characteristics of rf-sputtered epitaxial VO₂ thin films

We report on synthesis and phase transition characteristics of VO ₂ films grown on various single crystal substrates Al ₂O₃ (0001), TiO₂ (101), TiO₂ (001), and MgF₂ (001). An epitaxial orientation relationship was established for films on Al₂O₃ and TiO₂ from x-ray 2θ-ω coupled scans and scans. Films grown on these substrates exhibit a metal to insulator transition below that for bulk single crystals with accompanying resistance change of 3 to 4 orders of magnitude. Trends in phase transition characteristics with substrate physical properties are analyzed. Postdeposition treatment studies in oxygen and ozone at low temperatures demonstrate that epitaxial VO₂ films on TiO₂ can tolerate oxidation environment better than the films on Al₂O₃. The studies could be of relevance toward further advancing structure-functional property relations in this important material system.