Structural and gasochromic properties of epitaxial WO3 films prepared by pulsed laser deposition

The structural and gasochromic properties of epitaxial tungsten trioxide (WO3) thin films, prepared by ArF excimer pulsed laser deposition under the controlled oxygen atmosphere, have been investigated. The WO3 films were grown on the α-Al2O3(011¯2) substrates, as the oxygen pressure ranged from 0.57 to 1.20 Pa and the substrate temperature ranged from 432 to 538 °C. The deposited films were characterized by Rutherford backscattering spectroscopy (RBS)/channeling, X-ray diffraction, X-ray pole figures and Raman spectroscopy. RBS and XRD results demonstrated that monoclinic WO3 (0 0 1) films were successfully grown on the α-Al2O3(011¯2) substrates. The crystal quality was improved by increasing both the oxygen pressure and the substrate temperature. Gasochromic coloration in the WO3 films by exposure to diluted hydrogen gas was found to correlate with the crystal quality of the films. The gasochromic coloration was suppressed by the epitaxial growth of the films.