Optimal Oxidation Conditions Using Water Vapor for the Topotactic Formation of High-Quality Vanadium Dioxide Films from Vanadium Sesquioxide Epitaxial Films

Abstract

Vanadium dioxide (VO₂) films, which undergo a metal–insulator transition (MIT) at 68 °C, are promising materials for switching device applications. Topotactic oxidation of vanadium sesquioxide (V₂O₃) epitaxial films yields highly oriented VO₂ films. However, the effect of oxidation conditions on the MIT properties of the resulting VO₂ films has not been thoroughly explored. In this study, we investigated the effects of oxidation conditions, such as oxygen partial pressure, temperature, and time, on the topotactic transformation from V₂O₃ to VO₂ films and fabricated high-quality VO₂ films. Thermodynamic calculations demonstrated that oxidation atmospheres with thermodynamically stable VO₂ can be formed using a gas mixture containing water vapor and hydrogen. Experiments with different oxidation parameters revealed that the optimal oxidation conditions are oxygen partial pressures ranging from 10^–20 to 10^–8 atm, oxidation temperature of 500 °C, and oxidation times exceeding 6 h. Under these conditions, V₂O₃ was topotactically oxidized to VO₂, and the electrical resistance of the resulting VO₂ films changed by 4.7 orders of magnitude across the MIT. This study opens new avenues for fabricating highly sensitive VO₂-based switching devices.