Sensing properties of Pt/Pd activated tungsten oxide films grown by simultaneous radio-frequency sputtering to reducing gases

1 at% platinum activated tungsten oxide (Pt–WO3) and 1 at% palladium activated WO3 (Pd–WO3) films were grown on Al2O3 substrates by a simultaneous radio-frequency sputtering process. The as-sputtered films were thermally treated at 450 °C for 24 h. Phase structure and chemical composition of the as-sputtered and thermally treated films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. Sensing characteristics of the Pt–WO3 and Pd–WO3 films, as well as a pure WO3 film, were characterized with 25–200 ppm H2, 25–200 ppm CO and 0.62–5 ppm NH3 at various working temperatures and relative humidity of target gases. Effects of Pt and Pd on sensing characteristics of the sensors were compared and studied.