Low-temperature hydrothermal growth of ZnO nanorods on sol–gel prepared ZnO seed layers: Optimal growth conditions

Abstract ZnO nanostructures composed of hexagonal ZnO nanorods were prepared by a synthesis of a sol–gel solution (Step I), a spin-coating method producing a ZnO seed layer (Step II), and a hydrothermal method growing ZnO nanorods (Step III). Each step was optimized for the optimal preferred crystal growth of ZnO nanorods standing perpendicular onto ZnO substrates by varying several growth conditions, such as the ratio of zinc acetate dihydrate and monoethanolamine in Step I, preheating and annealing temperatures in Step II, and the volume ratio of zinc acetate dihydrate and NaOH for a precursory solution and the heating temperatures in the hydrothermal method in Step III. The orientation and morphology of both the ZnO seed layer and nanorods were analyzed by using X-ray diffraction and field emission-scanning electron microscopy. Optical and structural properties of ZnO nanostructures were studied by UV–vis and Raman spectroscopy.