Zinc oxide nanostructures: Experiments probing their transformation to nanorods

Abstract

Due to their high length-to-diameter aspect ratio, ZnO nanorods (ZnO-NRs) are extensively used in different applications. However, how they form is not well understood. Here, we have investigated the formation of ZnO-NR by sequential, temporal evolution of ZnO nanostructures. We observe sphere-like ZnO nanoparticles (ZnO-NP), as early as 5–10 s. Subsequently, these spherical ZnO-NPs aggregate and form short chains, which transform into novel nanocones. This hitherto unseen ZnO nanocones (ZnO-NCs) are hollow on one side and has a pointed end on the other side. Two ZnO-NCs together form individual ZnO-NC pairs. High intrinsic surface energy may have caused a ZnO-NC to pair-up with another adjacent ZnO-NC. Later, each of these paired ZnO-NCs transform into ZnO-NRs. We find that, formation of ZnO-NR follows second-order rate kinetics with respect to zinc precursor and HMTA concentration. Additionally, temperature and HMTA concentration significantly influence the length of ZnO-NR.