Effect of oxygen partial pressure and VO2 content on hexagonal WO3 thin films synthesized by pulsed laser deposition technique

We report on the effect of oxygen partial pressure and vacuum annealing on structural and optical properties of pulsed laser-deposited nanocrystalline WO₃ thin films. XRD results show the hexagonal phase of deposited WO₃ thin films. The crystallite size was observed to increase with increase in oxygen partial pressure. Vacuum annealing changed the transparent as-deposited WO₃ thin film to deep shade of blue color which increases the optical absorption of the film. The origin of this blue color could be due to the presence of oxygen vacancies associated with tungsten ions in lower oxidation states. In addition, the effects of VO₂ content on structural, electrochemical, and optical properties of (WO₃)_1−x (VO₂) _x nanocomposite thin films have also been systematically investigated. Cyclic voltammogram exhibits a modification with the appearance of an extra cathodic peak for VO₂–WO₃ thin film electrode with higher VO₂ content (x ≥ 0.2). Increase of VO₂ content in (WO₃)_1−x (VO₂) _x films leads to red shift in optical band gap.