Aerosol assisted chemical vapour deposition of WO3 thin films from tungsten hexacarbonyl and their gas sensing properties

Aerosol assisted chemical vapour deposition (AACVD) reactions of tungsten hexacarbonyl, [ W( CO) 6], in acetone, methanol, acetonitrile and a 50 : 50 mixture of acetone and toluene resulted in the deposition of blue partially reduced WO3-x films which showed preferred orientation along the (0 1 0) direction. Films deposited solely from toluene, however, were composed of a mixture of tungsten metal and W3O. All films could be annealed to yellow randomly orientated crystalline monoclinic WO3. The films deposited from methanol had a morphology comprising of a network of randomly orientated needles, which is strikingly different to the agglomeration of spherical particles observed with the other solvents. The WO3 films functioned as gas sensitive resistors for the detection of NO2. Responses were recorded at minimum concentrations of 1.03 ppm of NO2, significantly exceeding those of commercial screen printed sensors.