Solution-Based Epitaxial Growth of ZnO Nanoneedles on Single-Crystalline Zn Plates

We report a method for growing aligned single-crystalline ZnO nanoneedles on single-crystalline Zn plates via a solution-phase reaction. An Al film deposited on a Si wafer was immersed and maintained in an aqueous ammonia solution containing Zn ions at 90 °C. After 30 min, the substrate surface was found to be covered with hierarchical ZnO nanoneedles/Zn heterostructures. ZnO nanoneedles evolved epitaxially from the surface of a hexagonal “mother” Zn disk. The mother Zn crystals were thin, hexagonal disks with lateral dimensions on the order of 2−8 μm. The nanoneedles had an average diameter of 100 nm and an average length of 700 nm. The mechanism of formation of the hierarchical ZnO/Zn structures was investigated by characterizing the crystalline nature, morphology, and composition of the synthesized materials as a function of the reaction time. In this way, the evolution of structures could be determined. The role of the Al layer in this method is also discussed. On the basis of the experimental results, we propose a mechanism for the spontaneous growth of such ZnO/Zn heterostructures.