The effect of heat treatment on physical properties of nanograined (WO 3) 1–x–(Fe 2O 3) x thin films

Abstract

Thin films of (WO 3) 1–x–(Fe 2O 3) 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 Fe 2O 3 concentration. Moreover, using X-ray photoelectron spectroscopy, we have indicated that WO 3 is stoichiometric, while iron oxide was in both FeO and Fe 2O 3 compositions so that the FeO composition converted to Fe 2O 3 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).