Effects of Preparation Conditions on the Growth of ZnO Nanorod Arrays Using Aqueous Solution Method

Abstract

In this study, ZnO nanorod arrays were synthesized on a seeded substrate using the aqueous solution method. The growth rate, morphology, and crystallinity of ZnO nanorods were controlled by tailoring various process parameters and the [Zn(NO3)2]/[C6H12N4] ratio. A high density of ZnO nanorods with well‐defined hexagonal facets (002) were grown almost vertically over the entire substrate surface in all cases. The largest growth rate of length was observed in the ZnO nanorods grown in solution with a [Zn(NO3)2]/[C6H12N4] ratio in the vicinity of 1, which corresponds to an environment of small excess NH3, or OH− ions, while the change in diameter of the nanorods was insignificant with the [Zn(NO3)2]/[C6H12N4] ratio. In the solution of [Zn(NO3)2]/[C6H12N4]=5, ZnO nanorod arrays with a high concentration of oxygen vacancy were formed, due to the deficiency of C6H12N4 and thus OH− concentration. The average diameter and length of ZnO nanorods increased from 43 to 70 nm and from 65 to 320 nm, respectively, as the precursor concentration was increased from 0.008 to 0.04M. Mechanical stirring of the solution doubles the growth rate and enhances the crystallinity of ZnO nanorods, because stirring reduces the thickness of the Zn2+ depletion layer surrounding the fast‐growing (002) surfaces of ZnO nanorods. Both the radial and the axial dimensions increased almost linearly with the reaction time up to 240 min. The growth rates of diameter and length are 0.21 and 2.16 nm/min, respectively.