Thermal-oxidative growth of aligned W18O49 nanowire arrays for high performance gas sensor

Abstract

Gas sensors based on aligned arrays of W18O49 nanowires were formed directly via a novel route of in situ thermal oxidation of sputtered W film on the substrate attached patterned Pt electrodes. The well-developed nanowires have diameter of 10–20nm and show roughly aligned morphology. It is found that the duration of oxygen exposure during thermal annealing plays a crucial role to harvest a pure phase of W18O49 nanowire with desired length. The roughly aligned W18O49 nanowires show favourable microstructure for gas adsorption and rapid gas diffusion. The NO2-sensing properties of aligned W18O49 nanowires sensor were evaluated at 50°C up to 200°C over NO2 concentration ranging from 250ppb to 2.5ppm. The results indicate that the W18O49 nanowire arrays sensor exhibits good NO2-sensing performances at its optimal operating temperature of 150°C, especially perfect stability and fast response–recovery characteristics. The reliable interface performance and fast gas adsorption–desorption properties of the directly assembled vertically aligned nanowire array attribute to the superior stability and quick response/recovery. The growth mechanism of aligned W18O49 nanowires is proposed based on the direct SEM observations on the intermediate products, and meanwhile the sensing mechanism of the corresponding sensor is analyzed.