The microstructure and properties of thin WO3 films modified by gold

Direct current magnetron sputtering of a metallic W + Au target or high-frequency magnetron sputtering of WO₃ + Au oxide targets was used to prepare thin (about 100 nm) nanocrystalline WO₃ films with the addition of gold (disperse layers of catalytic gold were additionally deposited on the surface of films). The composition and micromorphology of the surface of films and the electrical and gas sensitive characteristics of nitrogen dioxide sensors were studied to determine the mechanism of the influence of gold on the properties of WO₃ films. The films were shown to contain the β-WO₃ orthorhombic and γ-WO_2.72 monoclinic phases and gold particles. The presence of the nonstoichiometric γ-WO_2.72 phase was shown to increase the concentration of oxygen vacancies in films and decrease the resistance of sensors to 1–2 MΩ. Gold nanoparticles 9–15 nm in size segregated on the surface of semiconductor crystallites and increased the response of sensors to NO₂. The conclusion was drawn that deposited catalytic gold layers increased the response to traces of nitrogen dioxide.