Physical properties characterization of WO3 films grown by hot-filament metal oxide deposition

WO3 is grown by hot-filament metal oxide deposition (HFMOD) technique under atmospheric pressure and an oxygen atmosphere. By X-ray diffraction obtains that WO3 presents mainly monoclinic crystalline phase. The chemical stoichiometry is obtained by X-ray Photoelectron Spectroscopy (XPS). The IR spectrum of the as-grown WO3 presents broad peaks in the range of 1100 to 3600 cm-1. A broad band in the 2200 to 3600 cm-1 region and the peaks sited at 1645 and 1432 cm-1 are well resolved, which are originated from moisture and are assigned to ν(OH) and δ(OH) modes of adsorbed water and the corresponding tungsten oxide vibrations are in infrared region from 400 to 1453 cm-1 and around 3492 cm-1, which correspond to tungsten-oxygen (W-O) stretching, bending and lattice modes. The Raman spectrum shows intense peaks at 801, 710, 262 and 61 cm-1 that are typical Raman peaks of crystalline WO3 (m-phase) that correspond to stretching vibrations of the bridging oxygen, which are assigned to W-O stretching (ν) and W-O bending (δ) modes, respectively. By transmittance measurements obtains that the WO3 band gap can be varied from 2.92 to 3.13 eV in the investigated annealing temperature range.