Direct solution phase fabrication of ZnO nanostructure arrays on copper at near room temperature

Abstract

Large-scale ZnO nanocone arrays were fabricated by using a [Zn(OH)₄]²⁻ solution consisting of Zn(NO₃)₂·6H₂O and KOH on copper foil at near room temperature (~35 °C). The ZnO nanocones showed aligned growth on the downward surface when the copper foil floated in the solution. However, random growth of block-like microcrystals and microflowers composed of nanocones occurred on the upward surface if the foil was placed in the solution. In the [Zn(OH)₄]²⁻ solution, the growth of ZnO and Zn(OH)₂ was a competitive process, the downward surface and the relatively high growth temperature were beneficial to the formation and growth of ZnO, and the pure and aligned ZnO arrays were obtained on the downward surface at 35 °C. Furthermore, the detailed growth behaviors of the crystals were discussed. We proposed that van der Waals epitaxy and Volmer–Weber growth accompanied by Ostwald ripening controlled the nucleation and growth of ZnO nanocone arrays on the downward surface of the copper foil, while oriented attachment and gravity deposition commanded the morphology on the upward surface in the solution.