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

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 10-20 nm 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 250 ppb to 2.5 ppm. 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.