Aerosol assisted chemical vapour deposition of photochromic tungsten oxide and doped tungsten oxide thin films

Abstract

Thin films of tungsten oxide, titanium doped tungsten oxide and overlayers of titanium oxide/tungsten oxide have been produced by aerosol assisted CVD (AACVD) at 400 °C. The films were crystalline monoclinic WO₃ by XRD, showing strong preferred orientation in the (0 2 0) plane. Films were blue on deposition (WO_3−x; x ≈ 0.1). Fully oxidised yellow WO₃ films were produced by annealing the blue films in air at 500 °C. The annealed films showed a photochromic transition to a coloured blue state when irradiated with 254 nm or 365 nm UV light. The colour change was reversible; the films returned to their original yellow colour when left in the dark, after which the blue colour could be regained by further UV irradiation. The WO₃ and layered WO₃/TiO₂ films showed significant photochromism, while comparable thickness titanium doped WO₃ films showed reduced photochromism, proportional to the level of Ti doping.