Effect of annealing on structural and optical properties of WO3 thin films prepared by electron-beam coating

Thin films of WO3 were deposited on glass substrates by the electron-beam evaporation technique. Three annealing temperatures, of 673, 723 and 773 K, were used for different films. Two kinds of annealing were used: in air and under vacuum. The influence of the annealing temperature on the structure and optical properties of the WO3 was studied. The surface morphology of the thin films was investigated by atomic force microscopy, which showed that molecule size depends on the air pressure and the annealing temperature. Spectrophotometric measurements of transmittance and reflectance were carried out in the wavelength range 190-2500 nm. The refractive index, n, and the change in optical density, ΔOD, were found to be dependent on annealing temperature. The energy gap Eg decreased with increasing annealing temperature.