Vertically aligned ZnO-ZnGa2O4 core-shell nanowires: from synthesis to optical properties

Dense and vertically aligned ZnO-ZnGa2O4 core-shell nanowires were synthesized in large scale on a-plane sapphire substrates by a simple two-step chemical vapor deposition method. The synthesized ZnO-ZnGa2O4 core-shell nanowires were connected through their base by a thick underlayer of the same material realizing electrical contact of the nanostructured array. X-ray diffraction and transmission electron microscopy analyses of the core-shell nanowires reveal that the ZnO cores and ZnGa2O4 shells of the core-shell nanowires are of single-crystal quality and have aligned crystallographic orientations. The ultraviolet-visible diffuse reflectance spectra of the core-shell nanowires showed two sharp edges corresponding to near-band-edge absorption contributed by the ZnO cores and the ZnGa2O4 shells. Moreover, the room-temperature photoluminescence spectra of the core-shell nanowires gave three UV emission peaks coming from the ZnGa2O4 shells and the ZnO cores. The dense and vertically aligned ZnO-ZnGa2O4 core-shell nanowires showing promising photoelectric properties offer an ideal structure for light harvesting applications such as a photoanode in a photoelectrochemical water splitting cell.