Synthesis of ZnO nanotowers controlled by a reagent's vapour pressure

In this work, ZnO nanotowers with layer-by-layer structure were prepared using Zn as a source at 700 °C via the chemical vapour deposition method. In the growth process, the Zn vapour pressure was considered as the crucial factor determining the growth behaviour of reagent species, and a competitive model between axial and lateral growth controlled by Zn vapour pressure was proposed to explain the formation of the tower-shaped structure. Several other experiments were conducted to analyse the growth behaviour under different Zn vapour pressures. Experimental results indicated that decreasing Zn vapour pressure was responsible for the formation of the layer-by-layer structure. A high Zn vapour pressure would induce the formation of a nanotower with large diameter and thin layer, and a low Zn vapour pressure would result in the formation of a nanotower with small diameter and thick layer. These experimental results further confirmed the competitive growth model. Our growth analyses were helpful in understanding the microcosmic growth behaviour of reagent species, which contributed to realizing controlled growth of complex nanostructures in the vapour route. Furthermore, these obtained nanotowers might have potential applications as functional blocks in future nanodevices. (paper)