Enhanced gas selectivity by p-n type competition of ZnO nanorods with varied CuO shells

In this work, n-ZnO/p-Cu_xO and n-Cu:ZnO/n-Zn:CuO core-shell nanorod (NR) arrays were synthesized by depositing Cu_xO nanoshells with different thickness on surface of ZnO NRs and subsequent annealing. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) show the outer Cu_xO shells were comprised of Cu₂O and CuO nanocrystals before annealing, but they transformed to single-crystalline Zn doped CuO nanoparticles after annealing. X-ray diffraction (XRD) showed the (0002) peaks shift to higher angle after annealing, indicative of diffusion of Cu and replacement of Zn²⁺ by Cu²⁺ ions. Room-temperature Gas-sensing measurements show the n-ZnO/p-Cu_xO core/shell nanostructures with various Cu_xO thicknesses demonstrating enhanced selectivity for different gases by utilizing the competition of inner n-ZnO and outer p-Cu_xO. This work proposes an effective route to synthesize n-ZnO/p-Cu_xO and CZO nanostructures which have great potential in developing room-temperature gas sensors.