Critical Nucleation Effects on the Structural Relationship Between ZnO Seed Layer and Nanowires

Abstract

The effects of the structural morphology of the ZnO thin seed layer composed of nanoparticles grown by dip coating have been investigated on the structural properties of ZnO nanowires grown by chemical bath deposition. It is revealed by scanning electron microscopy that the growth of ZnO nanowires is limited by the mass transport of chemical precursors in solution, leading to the inverse relationship of their average diameter and length with their density. It is shown by transmission electron microscopy and X-ray diffraction measurements that ZnO nanowires epitaxially grow on the seed layer and preferentially nucleate on the free surface of ZnO nanoparticles. The vertical alignment of ZnO nanowires as quantitatively deduced by X-ray pole figures is found to be improved by strengthening the texture of the seed layer along the c axis. Similarly, their density increases, showing that the c polar plane is highly reactive chemically and presents preferential surface nucleation sites. The relationship between the average diameters of ZnO nanoparticles and nanowires is completely driven by the nature of the nucleation site that is strongly dependent upon the growth conditions and upon the structural morphology of the seed layer. The texture, roughness, and porosity of the seed layer are three critical parameters.