Effect of oxygen flow rate on magnetron-sputtering-based preparation and photoelectric properties of vanadium dioxide films

Abstract

Vanadium dioxide (VO₂) exhibits typical metal–semiconductor phase transition properties and undergoes phase transitions with considerable changes in its optical and electrical properties. Numerous studies on VO₂ have been conducted, including those regarding thin-film fabrication, phase transition temperatures, and hysteresis widths. However, despite having a complicated vanadium–oxygen system, vanadium oxides exhibit a single-substance multi-phase characteristic, which inhibits the synthesis of pure VO₂ during preparation, impeding a quantitative analysis. In this study, magnetron sputtering was conducted to produce VO₂ thin films on c-type sapphire substrates at oxygen concentration of 4.5, 6.0, 7.0, 8.0, and 9.0 %. The film samples prepared at 4.5 % oxygen were primarily V₂O₃; at higher oxygen concentration values, the physical phases of the prepared samples were mixed crystals of VO₂ and V₂O₅, which did not exhibit any evident phase transition properties. Specifically, in-situ Raman spectroscopy revealed the transition of the VO₂ monoclinic (M) phase to the rutile (R) phase at 7.0 % oxygen, indicating transmittance variations in the mid-infrared region (2.5–7 µm). The findings demonstrated the effect of oxygen on the electrical and optical properties and surface structures of vanadium oxides under various oxidizing conditions during magnetron sputtering, laying the foundation for the preparation of high-quality VO₂-based thin films.