Growth Direction Control of ZnO Nanorods on the Edge of Patterned Indium-Tin Oxide/Aluminum-Doped Zinc Oxide Bilayers

ZnO nanorods were grown on the edge of patterned indium-tin oxide/aluminum-doped zinc oxide (ITO/AZO) bilayers by a hydrothermal method. Since the mask ITO layer covered the AZO seed layer, the ZnO nanorods grew radially on the edge of the AZO seed layer. By etching the as-patterned ITO/AZO bilayers with dilute HCl solution, the under-cut space is created under the ITO layer. We found that the under-cut space is the key for the vertical growth direction of ZnO nanorods on the etched-edge of the AZO seed layer. Only the ZnO nuclei phase exactly in parallel to the substrate can extend out from the under-cut space and provides the (0002) plane for the growth of the vertical ZnO nanorods. Interestingly, we found that the ZnO nanorods grew laterally on the etched-edge of the patterned ITO/AZO bilayers prepared with 400 °C substrate temperature. Due to the higher crystallinity of the AZO seed layer (400 °C), the etched-edge microstructure is different from that of the AZO seed layers prepared at room temperature and 150 °C. As a result, the hexagonal ZnO nuclei phase grown on the etched-edge surface of the AZO seed layer (400 °C) has the (0002) preferred-plane facing the opening of the under-cut space. Therefore, the ZnO nanorods can grow horizontally on the exposed polar c-plane (0002) of the hexagonal ZnO nuclei phase along the substrate. By manipulating the under-cut etching space dimension and the surface microstructure on the etched-edge of the AZO seed layer, the growth direction of ZnO nanorods can be controlled.