Highly aligned array of W18O49/CuO core-shell nanorods and its promising NO2 sensing properties

Highly ordered geometrical configuration and uniform shell layer are desirable for applications of one-dimensional (1D) core-shell heterostructures in gas sensors. In this work, we put forward a novel preparation of W18O49/CuO core-shell nanorods array with high alignment and uniform shell layer through the induction of shell film sputtering to roughly aligned W18O49-core nanorods. The W18O49-core nanorods with diameter of ∼20 nm were first grown via in-situ thermal oxidation of sputtered W film. Further sputtering-depositon of polycrystalline shell layer of CuO harvests a uniform W18O49/CuO core-shell nanorods array with improved alignment. Thicker shell results in better alignment. The NO2-sensing properties of W18O49/CuO core-shell nanorods array were investigated at room temperature up to 200 °C. It is found that the formation of core-shell heterostructure lowers the optimal operating temperature of W18O49 nanorods sensor from 150 °C to near-room temperature of 50 °C. The presented heteroarray of W18O49/CuO core-shell nanorods is responsive to diluted NO2 gas at ppb level. At 50 °C, it shows satisfactory sensing response to 0.1-1 ppm NO2 gas with excellent dynamic response-recovery characteristics. These results are associated with the unique aligned configuration and the dual modulations of both heterojunction potential barrier at core-shell interface and the conductive carrier-accumulation channel.