Nucleation mechanisms and their influences on characteristics of ZnO nanorod arrays prepared by a hydrothermal method

ZnO nanorod arrays (ZNAs) with various degrees of density and vertical alignment were grown on ZnO/Si substrates by a hydrothermal approach containing ZnO seed layers with designed microstructural characteristics. The nucleation mechanisms of ZNAs and the effect of the seed layers on the density and vertical alignment of ZNAs were systematically studied. Grain size and surface roughness were demonstrated to compete as the dominating characteristics for nucleation resulting in ZNAs with variable density and vertical alignment. Experimental results reveal that the nucleation mechanism of ZNAs switches from grain-boundary nucleation to surface nucleation when the characteristics of the seed layer change from small grains and low surface roughness to large grains and high surface roughness. Grain-boundary nucleation results in ZNAs with high rod density and poor vertical alignment. In contrast, surface-nucleating ZNAs possess low rod density and excellent vertical alignment of rods.