Facile synthesis and enhanced luminescent properties of ZnO/HfO2 core–shell nanowires
The morphological, structural and photoluminescence properties of one-dimensional ZnO/HfO2 core–shell nanowires (NWs) with various thicknesses of HfO2 shell layers are studied in detail in this work. The ZnO NWs have been fabricated by a simple hydrothermal method, which are then coated by thin HfO2 shell layers using atomic layer deposition (ALD). The morphological and structural characterization demonstrates that the HfO2 shells with polycrystalline structures grow on the single-crystalline ZnO NWs conformally. Moreover, the ZnO/HfO2 core/shell NWs show remarkable enhanced ultraviolet (UV) emission with increasing thickness of the HfO2 shell layer compared with bare ZnO NWs. The UV emission intensity for the sample with HfO2 shell thickness of ∼16 nm is about 9 times higher than that of bare ZnO NWs. It mainly results from the decreased surface states by surface passivation of the HfO2 shell layer as well as a typical type-I band alignment in the ZnO/HfO2 core/shell structure. A model is also proposed to explain the evolution of the wide visible emission band with the relatively low intensity of the core/shell structures. Our results suggest that the ZnO/HfO2 core/shell structures have potential applications for high-efficiency optoelectronic devices such as UV light-emitting diodes and lasers.