Pt/WO ₃ thin films prepared by photochemical metal-organic deposition (PMOD) and its evaluation as carbon monoxide sensor

Pure and 10% Pt-loaded tungsten oxide thin films have been successfully prepared by direct UV irradiation of bis(β-diketonate)dioxotungsten(VI) and Pt(II) precursor complexes spin-coated on Si(1 0 0) substrates. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques were used to analyze the crystal structure and chemical composition of the films before and after heat treatment at 500°C. The results of XRD and AFM analysis showed that the as-photodeposited films are amorphous and have a rougher surface than thermally treated films. Post-annealing of the films in air at 500°C transforms the oxides to a monoclinic WO ₃ phase. Gas sensing tests reveal that annealed 10% Pt/WO ₃ films exhibit a better response than unloaded WO ₃ films towards 20 ppm carbon monoxide at an operating temperature of 350°C. The sensors also posses fast response and recovery characteristics.