Hierarchical ZnO Superstructures: Nanoflake-Decorated Nanonail Arrays

By using metallic Zn powders as zinc source, we synthesized unusual hierarchical ZnO superstructures, nanoflake-decorated nanonail arrays, on a large scale via a simple low-temperature thermal evaporation method. The hierarchical superstructures were characterized by using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy as well as selected area electron diffraction. Studies found that both the ZnO nanonails and the decorated ZnO nanoflakes are single-crystals, with the preferred growth orientations along the (001) direction. The possible formation mechanism for the interesting hierarchical superstructures has been discussed. It was found that the deposition of indium films on a Si substrate and the heterogeneous nucleation of ZnO nanoflakes on the main ZnO nanonails play key roles in the fabrication of ZnO superstructures. Moreover, these special hierarchical superstructures showed much strong and complicated photoluminescent emissions in the visible region.