Effect of Substrate Temperature on the Properties of Sprayed WO3 Thin Films Using Peroxotungstic Acid and Ammonium Tungstate: A Comparative Study
A comparative study on the physicochemical properties of tungsten oxide (WO3) thin films synthesized using peroxotungstic acid (PTA) and ammonium tungstate (AT) by simple spray pyrolysis technique is reported. X-ray diffraction patterns show that the films deposited using both the precursors are polycrystalline with monoclinic crystal structure. The x-ray photoelectron spectroscopy studies confirm that the films are sub-stoichiometric with O/W ratios of 2.93 and 2.87, respectively, for typical PTA and AT films. Tungsten (W) exists in two chemical states, 5+ and 6+. Scanning electron microscopy images show the uniform and dense network of wires in PTA films, while the films deposited using AT possess a porous structure with small grains. Electrical and dielectric studies show that films are highly resistive and possess high dielectric constant. The near ultra-violet, blue, green and weak red emissions due to defects were observed in the photoluminescence studies. Properties of the WO3 thin films reported here are suitable for gas sensor applications. Films deposited using PTA are more functional than those deposited using AT.
KeywordsThin films spray pyrolysis WO3 photoluminescence x-ray photoelectron spectroscopy (XPS) electrical properties
One of the authors, Mr. V.V. Ganbavle is very grateful to UGC, New Delhi, for providing financial support through a UGC-BSR junior research fellowship. This work is partly supported by UGC through financial support under a major research project entitled “Photocatalytic degradation of waste water using sprayed tungsten trioxide (WO3) thin films”, No. 41-869/2012. We acknowledge D. Haranath, CSIR-NPL, New Delhi, for providing PL measurements, and Michael Neumann-Spallart, CNRS France, for discussions and suggestions.
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