Thermal-oxidative growth of aligned W 18 O 49 nanowire arrays for high performance gas sensor

Gas sensors based on aligned arrays of W 18 O 49 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 W 18 O 49 nanowire with desired length. The roughly aligned W 18 O 49 nanowires show favourable microstructure for gas adsorption and rapid gas diffusion. The NO 2 -sensing properties of aligned W 18 O 49 nanowires sensor were evaluated at 50 °C up to 200 °C over NO 2 concentration ranging from 250 ppb to 2.5 ppm. The results indicate that the W 18 O 49 nanowire arrays sensor exhibits good NO 2 -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 W 18 O 49 nanowires is proposed based on the direct SEM observations on the intermediate products, and meanwhile the sensing mechanism of the corresponding sensor is analyzed.