NO2 gas sensing properties of sprayed composite porous MoO3-V2O5 thin films

The (MoO3)(1-x)(V2O5)(x) thin films with x = 0.2, 0.4, 0.6 and 0.8 composition are deposited onto the ultrasonically cleaned glass substrates at optimized substrate temperature of 400 degrees C using a simple and inexpensive chemical spray pyrolysis (CSP) deposition method. XRD study shows that the films are polycrystalline with an orthorhombic crystal structure. The layered orthorhombic structure and oxygen vacancy defects in V2O5 and MoO3 are more favorable adsorption sites for gas molecules adsorption on the film surface. For composite (MoO3)(0.4)(V2O5)(0.6) thin film, FE-SEM micrograph shows that the surface area is remarkably increased due to unique microstructure formed by the microsheets. The EDAX study confirms the presence of both molybdenum oxide and vanadium oxide phases in the film. The AFM micrograph shows the higher surface roughness of 27 nm for (MoO3)(0.4)(V2O5)(0.6) thin film. The selectivity study shows that the films are highly selective to NO2 gas. This is due to an unpaired electron in nitrogen which forms the bond with surface oxygen atoms and subsequently, promotes the chemisorption as compared to other gases such as H2S, CO, CO2, NH3 and SO2. For (MoO3)(0.4)(V2O5)(0.6) thin film, 80% response at 200 degrees C toward 100 ppm NO2 gas concentration is observed.