Tuning phase transition temperature of VO₂ thin films by annealing atmosphere

A simple new way to tune the optical phase transition temperature of VO₂ films was proposed by only controlling the pressure of oxygen during the annealing process. Vanadium films were deposited on glass by a large-scale magnetron sputtering coating system and then annealed in appropriate oxygen atmosphere to form the VO₂ films. The infrared transmission change (at 2400 nm) is as high as 58% for the VO₂ thin film on the glass substrate, which is very good for tuning infrared radiation and energy saving as smart windows. The phase transition temperature of the films can be easily tuned from an intrinsic temperature to 44.7 °C and 40.2 °C on glass and sapphire by annealing oxygen pressure, respectively. The mechanism is: V³⁺ ions form in the film when under anaerobic conditions, which can interrupt the V⁴⁺ chain and reduce the phase transition temperature. The existence of V³⁺ ions has been observed by x-ray photoelectron spectroscopy (XPS) experiments as proof.