Microstructure and enhanced H2S sensing properties of Pt-loaded WO3 thin films

Pt-loaded WO3 thin films were deposited on oxidized Si substrates under various discharge gas pressures at room temperature using reactive magnetron sputtering. Structural characterizations by means of X-ray diffraction and field emission scanning electron microscopy show that the films composed of nano-size grains have a monoclinic structure. The films become more porous as the discharge gas pressure increases due to the decrease in film density and the increase in effective surface area. Gas sensing properties demonstrate that the films show reversible response to H2S with various concentrations. Under the same operating conditions the sensor response increases and the operating temperature at which the maximum response is shown decreases with discharge gas pressure. The highest response of 3512 is obtained for a Pt-loaded porous film deposited at 12 Pa upon exposure to 5 ppm H2S at an operating temperature of 100 °C. Such a high response of a Pt-loaded porous film at a low operating temperature is discussed in relation to the Schottky-barrier-limited transport as well as the chemical mechanism of Pt loading.