We studied the effect of annealing temperature on the physical properties of WO3 thin films using different experimental techniques. WO3 has been prepared by hot-filament metal oxide deposition (HFMOD). The films, chemical stoichiometry was determined by X-ray photoelectron spectroscopy (XPS). The monoclinic single-phase nature of the as-deposited films, structure was changed to triclinic structure by annealing them at higher temperatures than 400°C, which has been determined by the X-ray diffraction analysis. By Raman scattering is confirmed the change of crystalline phase, of monoclinic to triclinic, since that lattice vibrational modes of as-deposited WO3 and annealed at 500°C present clearly differences. WO3 band gap energy can be varied from 2.92 to 3.15？eV by annealing WO3 from 0 to 500°C as was obtained by transmittance measurements. The photoluminescence response of the as-deposited film presents three radiative transitions observed at 2.85, 2.41, and 2.04？eV that could be associated with oxygen vacancies; the first one is shifted to higher energies as the annealing temperature is increased due to the change of crystalline phase of the WO3. 1. Introduction Transition metal oxides represent a large family of materials possessing various interesting properties, such as superconductivity, colossal magnetoresistance, and piezoelectricity. Among them, tungsten oxide is of great interest and has been investigated extensively for its distinctive properties. With outstanding electrochromic [1], photochromic [2], gas chromic [3], gas sensor [4], photocatalyst [5], and photoluminescence properties [6], as a result, tungsten oxide has been used to construct “smart-window,” antiglare rear view mirrors for automobiles, nonemissive displays, optical recording devices, solid-state gas sensors, humidity and temperature sensors, biosensors, photonic crystals, and so forth. WO3 thin films can be prepared by various deposition techniques such as thermal evaporation [3, 7], spray pyrolysis [8], sputtering [9], pulsed laser ablation [4], sol-gel coating [10], and chemical vapour deposition [11]. The purpose of this work is to characterize the WO3 layers deposited by hot filament metal oxide deposition (HFMOD) technique, which uses a metallic filament heated in a rarefied oxygen atmosphere [12]. The film is deposited on a substrate positioned near the filament, and the deposition rate is controlled by the filament temperature and the oxygen pressure, after they were annealed at a wide temperature range. This growth technique has some advantages compared to the
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