Thermal oxidation of Cu nanofilm on three-dimensional ZnO nanorod arrays

Three-dimensional (3D) ZnO-CuO core-shell nanorod arrays have been synthesized by a three-step process on silicon (100) substrates. A hydrothermal method was used to grow 3D ZnO nanorod arrays, followed by deposition of Cu nanofilm using sputtering, which was oxidized subsequently at 400 degrees C to form CuO shell surrounding ZnO nanorod core. The control over oxygen flow and pressure during the Cu nanofilm oxidation was found to improve the uniformity and intactness of CuO shell surrounding ZnO nanorod core. With higher oxygen flow, more conformal CuO thin film coating was achieved on the 3D ZnO nanorods array as a result of more sufficient oxygen access at the bottom portion of ZnO nanorods array. Higher pressure during thermal oxidation favored the formation of non-conformal ZnO-CuO core-shell nanorods and impurity Zn2SiO4 possibly at the interface of ZnO and Si substrate. UV-vis absorption spectroscopy revealed higher absorption efficiency in the visible region in ZnO-CuO core-shell nanorods than in pure ZnO nanorods. The fabricated ZnO-CuO core-shell nanorods could be useful nanoscale building blocks in solar cells and light emitting devices.