Tailoring the thermochromic properties of sputter-deposited VO2 films by O2+ ion irradiation

Abstract

Vanadium dioxide (VO2) thin film is a well-known phase transition material showing extensive modification in their physical properties, such as electronic, magnetic, and optical characteristics when the metal–insulator transition (MIT) occurs. Many approaches (including doping, micro-structure, external stress, and defect engineering) can enhance the MIT characteristics of vanadium dioxide thin films. More recently, low-energy ion irradiation has been well-established to modify the electrical, optical, and physical properties of metal oxide thin films. In this paper, the effect of low-energy O2+ ion irradiation on the thermochromic properties of VO2 thin films was investigated. From the temperature-dependent near infrared transmittance measurements, both MIT temperature and thermal hysteresis width of VO2 thin films showed an opposite trend and decreased as the ion fluence increased. The values of solar modulation and luminous transmittance of irradiated VO2 films were significantly altered by introducing low-energy ion irradiation, compared to the pristine VO2 thin films. According to the XPS analyses, the vanadium ion are in mixed of two valence states (V4+ and V5+). Moreover, the concentration of oxygen vacancies in VO2 films increases as the fluence of low-energy O2+ ion increases. Our study concludes that low-energy O2+ ion irradiation is an effective means to optimize the MIT characteristics of VO2 thin films to a certain extent.