Towards Room Temperature Phase Transition of W-Doped VO Thin Films Deposited by Pulsed Laser Deposition: Thermochromic, Surface, and Structural Analysis.

Vanadium dioxide (VO) with an insulator-to-metal (IMT) transition (∼68 °C) is considered a very attractive thermochromic material for smart window applications. Indeed, tailoring and understanding the thermochromic and surface properties at lower temperatures can enable room-temperature applications. The effect of W doping on the thermochromic, surface, and nanostructure properties of VO thin film was investigated in the present proof. W-doped VO thin films with different W contents were deposited by pulsed laser deposition (PLD) using V/W (+O) and VO/W multilayers. Rapid thermal annealing at 400-450 °C under oxygen flow was performed to crystallize the as-deposited films. The thermochromic, surface chemistry, structural, and morphological properties of the thin films obtained were investigated. The results showed that the V was more surface sensitive and W distribution was homogeneous in all samples. Moreover, the VO acted as a W diffusion barrier during the annealing stage, whereas the V+O environment favored W surface diffusion. The phase transition temperature gradually decreased with increasing W content with a high efficiency of -26 °C per at. % W. For the highest doping concentration of 1.7 at. %, VO showed room-temperature transition (26 °C) with high luminous transmittance (62%), indicating great potential for optical applications.