Growth behavior and microstructure evolution of ZnO nanorods grown on Si in aqueous solution

Two substrates, Si and ZnO film-coated Si (ZnO _f /Si), were used to investigate growth behavior and microstructure evolution of single-crystal ZnO nanorods (ZNs) in aqueous solutions at low temperatures. It was found that those ZNs present different growth behavior and characterization. On pure Si substrate, ZNs were scattered over the entire Si substrate with a preferred orientation in the (1 0 0) plane or grown along the [0 1 1̄ 0] direction. HRTEM observation demonstrates that the scattered ZNs exhibit a two-stage growth mechanism with a self-assembly process of ZNs in the later growth stage. In contrast, on ZnO _f /Si, well-aligned ZNs were directly nucleated from ZnO film on Si and grown along the [0 0 0 2] direction. In comparison with the scattered ZNs, a larger aspect ratio (length/width) up to 25-30 was obtained for the well-aligned ZNs. In addition, some planar defects such as stacking faults probably resulted due to faster stacking of a ZnO growth unit in the later growth stage. These observations and findings imply that the growth of the well-aligned ZNs from the solution is not related to the used substrates but strongly influenced by the surface treatment and characteristics on the substrate.