The effect of heat treatment on physical properties of nanograined (WO3)1–x–(Fe2O3)x thin films

Abstract: Thin films of (WO3)1–x–(Fe2O3)x composition were deposited by thermal evaporation on glass substrates and then all samples were annealed at 200–500 °C in air. Optical properties such as transmittance, reflectance, optical bangap energy, and the optical constants of the “as deposited” and the annealed films were studied using ultraviolet-visible spectrophotometry. It was shown that the annealing process changes the film optical properties which were related to Fe2O3 concentration. Moreover, using X-ray photoelectron spectroscopy, we have indicated that WO3 is stoichiometric, while iron oxide was in both FeO and Fe2O3 compositions so that the FeO composition converted to Fe2O3 after the annealing process. Using atomic force microscopy, it was observed that surface of the “as deposited” films were smooth with a nanometric grain size. The film surface remained unchanged after annealing up to 300 °C. Surface roughness and the grain size of the films with x = 0, 0.05, and 0.75 highly increased at higher annealing temperatures (400 and 500 °C), but were nearly unchanged for medium x-values (0.3 and 0.4). [Copyright &y& Elsevier]