New route for modification of thermochromic properties of vanadium dioxide films via high-energy X-ray irradiation

Abstract To study the effect of high-energy X-ray irradiation on the thermochromic properties of VO 2 films, we prepared VO 2 films on fused silica substrates by direct-current reactive magnetron sputtering and exposed them to X-ray irradiation at various doses in the range of 0–9000 Gy. X-ray diffraction analysis showed that an appropriate irradiation dose (1500 Gy) can enhance the crystallization of VO 2 films, whereas a higher dose (9000 Gy) would reduce the crystallinity slightly. XPS measurement indicated that the VO 2 film irradiated at 1500 Gy had the maximum V 4+ content (71.64%) among the film samples. Moreover, atomic force microscopy and scanning electron microscopy measurements suggested that the VO 2 film samples treated at 1500 Gy had higher surface roughness than other films, possibly owing to the localized annealing effect at lower doses. The visible and infrared transmittance of the irradiated and pristine samples were characterized and analyzed. The results demonstrated that high-energy X-ray irradiation strongly influenced the room-temperature infrared transmittance of the VO 2 films, and the visible transmittance of the films decreased monotonously as the irradiation dose increased owing to the formation of color centers. In addition, the phase transition temperature of the VO 2 film samples increased from 48 °C for the pristine sample to 53 °C for the sample irradiated at 1500 Gy, and then decreased continuously to 43 °C for the sample irradiated at 9000 Gy. These findings provided valuable insight into modification of the thermochromic properties of vanadium dioxide films by X-ray irradiation.