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Controllable synthesis of branched ZnO/Si nanowire arrays with hierarchical structure

Shengli Huang12*, Qianqian Yang12, Binbin Yu1, Dingguo Li1, Ruisheng Zhao1, Shuping Li1 and Junyong Kang1

Author Affiliations

1 Fujian Provincial Key Lab of Semiconductors and Applications, Department of Physics, Xiamen University, Xiamen, Fujian 361005, People's Republic of China

2 State Key Lab of Silicon Materials, Zhejiang University, Hangzhou 310027, People's Republic of China

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Nanoscale Research Letters 2014, 9:328  doi:10.1186/1556-276X-9-328

Published: 30 June 2014

Abstract

A rational approach for creating branched ZnO/Si nanowire arrays with hierarchical structure was developed based on a combination of three simple and cost-effective synthesis pathways. The crucial procedure included growth of crystalline Si nanowire arrays as backbones by chemical etching of Si substrates, deposition of ZnO thin film as a seed layer by magnetron sputtering, and fabrication of ZnO nanowire arrays as branches by hydrothermal growth. The successful synthesis of ZnO/Si heterogeneous nanostructures was confirmed by morphologic, structural, and optical characterizations. The roles of key experimental parameters, such as the etchant solution, the substrate direction, and the seed layer on the hierarchical nanostructure formation, were systematically investigated. It was demonstrated that an etchant solution with an appropriate redox potential of the oxidant was crucial for a moderate etching speed to achieve a well-aligned Si nanowire array with solid and round surface. Meanwhile, the presence of gravity gradient was a key issue for the growth of branched ZnO nanowire arrays. The substrate should be placed vertically or facedown in contrast to the solution surface during the hydrothermal growth. Otherwise, only the condensation of the ZnO nanoparticles took place in a form of film on the substrate surface. The seed layer played another important role in the growth of ZnO nanowire arrays, as it provided nucleation sites and determined the growing direction and density of the nanowire arrays for reducing the thermodynamic barrier. The results of this study might provide insight on the synthesis of hierarchical three-dimensional nanostructure materials and offer an approach for the development of complex devices and advanced applications.

Keywords:
ZnO/Si nanowire arrays; Hierarchical structure; Chemical etching; Hydrothermal growth