Fabrication of CuO ( p )-ZnO ( n ) Core-Shell Nanowires and Their H 2 -Sensing Properties.

Unlike the conventional one-dimensional (1D) core-shell nanowires (NWs) composed of p -type shells and n -type cores, in this work, an inverse design is proposed by depositing n -type ZnO (shell) layers on the surface of p -type CuO (core) NWs, to have a comprehensive understanding of their conductometric gas-sensing kinetics. The surface morphologies of bare and core-shell NWs were investigated by field emission scanning electron microscope (FE-SEM). The ZnO shell layer was presented by overlay images taken by electron dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HRTEM). The pronounced crystalline plane peaks of ZnO were recorded in the compared glancing incident X-ray diffraction (GI-XRD) spectra of CuO and CuO-ZnO core-shell NWs. The ZnO shell layers broaden the absorption curve of CuO NWs in the UV-vis absorption spectra. As a result of the heterostructure formation, the intrinsic p -type sensing behavior of CuO NWs towards 250 and 500 ppm of hydrogen ( H 2 ) switched to n -type due to the deposition of ZnO shell layers, at 400 °C in dry airflow.