Preparation and Characterization of Cubic WO_3 Films

Cubic WO_3 films were prepared by the polymeric precursor method using ammonium metatungstate as precursor and polyethylene glycol as structure-directing agent.The obtained materials were characterized by means of X-ray diffraction(XRD),scanning electron microscope(SEM),energy disperse spectroscope(EDS) and high-resolution transmission electron microscope(HRTEM).The influence of calcination temperature,pH value and substrates on the structure and morphology of films was investigated.The results indicate that the surface morphology of the resulting film on FTO glass has particle of 60 nm in size as cubic WO_3 calcined at 450℃,and the films are smooth and glossy with an uniform thickness of 2.9μm.The structures of all samples on FTO glass annealed at 450-550℃or prepared at the different pH values are cubic WO_3.The particle size of the films decreases with the increase of the pH values.Monoclinic WO_3 is formed when the films are prepared on quartz glass and graphite substrate,indicating that the substrates have apparent influence on the crystal structure of WO_3 thin films.