Characterization of photochemically grown Pd loaded WO3 thin films and its evaluation as ammonia gas sensor

Abstract

Pd-loaded tungsten oxide thin films have been successfully fabricated by direct UV irradiation of bis(β-diketonate)dioxotungsten(VI) and Pd(II) precursor complexes spin-coated on Si(100) substrates. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to analyze the crystal structure and the chemical composition of the films before and after annealing at 500 °C. The results of XRD and AFM analysis showed that the as-photodeposited films are amorphous whereas thermally treated films present a rougher morphology. Post-annealing of the films in air at 500 °C transforms the oxides to a monoclinic WO3 phase. Annealed 10% Pd/WO3 films exhibited an excellent response towards 50 ppm ammonia gas at an operating temperature of 300 °C. The Pd-loaded sensors presented higher sensitivity and quicker response-recovery rates than unloaded WO3 films.