Substrate Atomic-Termination-Induced Anisotropic Growth of ZnO Nanowires/Nanorods by the VLS Process

In the vapor−liquid−solid (VLS) growth of 1D nanostructures, the electronic structure of the substrate surface may critically affect the morphology of the grown nanowires/nanorods. In this paper, using a model system of the Sn-catalyzed growth of ZnO nanostructures on a single-crystal ZnO substrate, we demonstrate the effect of substrate surface termination on nanowire growth. Symmetric nanoribbons have been grown on the nonpolar surfaces of ±(21̄1̄0) (or ±(011̄0)), but the polar surface ±(0001) substrates have asymmetrically grown nanostructures. For the Zn-terminated (0001) substrate surface, uniform, long, and epitaxially aligned nanowires have been grown. For the oxygen-terminated (0001̄) substrate surface, short nanotrunks have been grown. These asymmetrical growth features are related to the atomic termination of the substrate, surface charges, and interface adhesion. These observations provide some insight into the physical chemical process in VLS growth.