A one batch synthetic protocol to produce bi-modal aspect ratio ZnO crystallites

Abstract

We report the formation of ZnO structures with a bimodal distribution of aspect ratios in a one-batch reaction. In this synthesis, low aspect ratio (similar to 10) ZnO microrods were formed in the bulk solution, whereas high aspect ratio (similar to 1000) ZnO nanostructures formed on a ZnO thin film-coated substrate immersed in the bulk solution. The two types of structures were easily separated because the high aspect ratio ZnO nanostructures remained immobilized on the substrate. The distinct aspect ratios suggested that two types of ZnO structures formed by different growth mechanisms in the one-batch reaction. A systematic investigation led to the proposal of a formation mechanism. In the early stages of the reaction, Zn(OH)(2) formed and was converted to ZnO in the bulk solution. The ZnO grew to form low aspect ratio ZnO mircorods via layer-by-layer growth. As the reaction proceeded, precursors were consumed, which decreased the degree of supersaturation. The high aspect ratio ID ZnO nanostructures grew from defects in the ZnO film on the substrate via axial screw dislocation growth at a low degree of supersaturation.