Synthesis and characterization of thin molybdenum oxide films prepared from molybdenum dioxo tropolonate precursors by photochemical metal-organic deposition (PMOD) and its evaluation as ammonia gas sensors

Abstract

Amorphous non-stoichiometricmolybdenumoxide thin films have been successfully prepared by direct UV irradiation of amorphous films of molybdenum dioxo tropolonate complexes on Si(100) substrates. Photodeposited films were characterized by X-ray photoelectron spectroscopy (XPS) and the surface morphology examined by Atomic ForceMicroscopy (AFM). Itwas found that as-photodeposited films are uniformwith rms surface roughness of 231 nmand contain non-stoichiometric oxides (MoO3 − x). The results of XRD analysis showed that postannealing of the films in air at 350 °C transforms the sub-oxides to α-MoO3 phase with a much smoother surface morphology (rms = 164 nm). Both, the as-photodeposited and annealed MoO3 − x films exhibit good optical quality with transparency in the visible region better than 80%. Gas sensing tests reveal that annealed MoO3 − x films exhibit a better response than as-deposited films towards 50 ppm ammonia at an operating temperature of 350 °C.