Growth of self-aligned ZnO nanorods by hydrothermal process

Abstract

The present paper discuss the growth mechanisms of ZnO nanorods thin-films using the hydrothermal process. This was achieved on a ZnO seed layer prepared by sputtering and spray pyrolysis. ZnO nanorods were prepared using various precursors, including zinc nitrate [Zn(NO3)2.6H2O], zinc chloride [ZnCl2], and zinc acetate [Zn(CH3COO)2.2H2O, to investigate the effect of salt source. The morphological and structural properties of ZnO NRs were investigated using x-ray diffraction (XRD) and a scanning electron microscopy (SEM). The deposited film consist of highly oriented crystalline ZnO NRs along the [002] axis. We found that the seed layer preparation method alters the nanorods alignment. SEM observation revealed that, regardless of the seed layer preparation method, the nature of salt source play a key role in the nanorods size. We concluded that the ZnO nanorods diameter increases in the following order with respect to zinc salt source: ZnAc <zinc nitride <zinc chloride. The mechanism of of ZnO nanorods formation is correlated with bath solution viscosity and surface tension properties. We emphasized that, in a solution with a larger viscosity and surface tension, such as zinc chloride, the motion and transfer towards the substrate, of species participating in ZnO formation, is hindered by the friction force due to the viscosity. When using a solution with lower viscosity and surface tension, such as zinc acetate, the species forming the ZnO nanorods can easily reach the substrate, which leads to a larger nucleation center, yielding low-diameter ZnO nanorods.