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

Amorphous non-stoichiometric molybdenum oxide 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 Force Microscopy (AFM). It was found that as-photodeposited films are uniform with rms surface roughness of 231nm and contain non-stoichiometric oxides (MoO3−x). The results of XRD analysis showed that post-annealing of the films in air at 350°C transforms the sub-oxides to α-MoO3 phase with a much smoother surface morphology (rms=164nm). 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 50ppm ammonia at an operating temperature of 350°C.