A morphological control of tungsten oxide nanowires by thermal evaporation method for sub-ppm NO2 gas sensor application

Controlling the proper geometrical morphology of metal oxide nanowires (NWs) with large surface areas is important for enhancement of gas-sensing performance through the improvement of sensing sites. In this study, we synthesized geometrically controllable tungsten oxide NWs for detection of NO2 at sub-ppm concentrations. Tungsten oxide NWs were grown through the thermal evaporation method using WO3 powders and W foils as precursor and substrates, respectively. Effects of growth conditions on the morphologies and gas-sensing properties of synthesized NWs were investigated. Results revealed that the as-obtained NWs possessed a cross-section of polygonal shapes, and their diameters increased as the growth temperature increased from 950 °C to 1000 °C. However, the NWs formed bundles and generated porous structures as the growth temperature increased up to 1050 °C. The comparative NO2 gas-sensing properties of tungsten oxide NWs synthesized at different growth temperatures indicated that the NWs synthesized at 1050 °C exhibited relatively good NO2 sensing performance at the sub-ppm level because of the formation of porous NW structures. This phenomenon suggested that porous tungsten oxide NWs are effective for highly sensitive NO2 gas sensor applications.