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

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.