Epitaxy of Vertical ZnO Nanorod Arrays on Highly (001)-Oriented ZnO Seed Monolayer by a Hydrothermal Route

A long ZnO nanorod array with good verticality and thin diameter is synthesized from a single solution by the hydrothermal route. Prior to the growth, a ZnO seed layer with the c-axis texturing and the monolayer distribution is deposited on the substrate by a modified sol-gel spin coating process. A molecule adsorption stabilization mechanism is proposed to explain the seed orientation. Factors affecting the ZnO nanorod growth are systematically investigated. The critical conditions for the rod growth are obtained by changing the polyethyleneimine amount and the pH. The results suggest that the verticality of the array depends heavily on the seed orientation. The atomic force microscopy and X-ray diffraction measurements reveal that the crystallinity and the initial strain relaxation determine the growth activation energy and the rod diameter size.