Highly Oriented Plate-like Rod/Tube Arrays of ZnO

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Highly Oriented Plate-like Rod/Tube Arrays of ZnO Ying Dai1, 2, Long Q. Zhou2, Yue L. Sun2 , Wen Chen1, 2 and Yue Zhang3 1 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China 2 School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China 3 Department of Materials Physics, University of Science and Technology Beijing, Beijing 100083, China ABSTRACT Highly oriented plate-like rod/tube arrays of ZnO are synthesized by a solution-based approach at low temperature. The ZnO rod/tube arrays grow oriented vertically on silicon substrate and the intersectant ZnO nanosheets stand on the backbones of ZnO rods/tubes. The constructions of plate-like rod or tube arrays depend on the processing conditions. The growth mechanisms are investigated based on the nucleation and growth process. The initial ZnO film formed on substrate is crucial for the growth of ZnO rods/tubes perpendicular to the substrate. The nanosheets grow around the ZnO rods/tubes by the secondary nucleation and growth process. The ZnO tubes are formed by the etching of the ZnO polar faces. The novel ZnO structures are expected to have great potential for electronics, photoelectronics, sensors, and catalysis etc. INTRODUCTION The control of the morphology and orientation of nano/microstructures on various substrates represents essential tasks to accomplish the future generation of smart and functional devices. In addition, many applications require novel and oriented structures to fulfill the demand of high efficiency and high performance, for instance, microelectronic devices, chemical and biological sensing and diagnosis, photovoltaic, cells, batteries and capacitors, hydrogen storage devices, displays, catalysis, and drug delivery and separation. Attempts have been focused on the synthesis of ordered one-dimensional superstructures and the integration of building blocks into complex functional architectures [1-6]. The current synthetic techniques to obtain ordered nano/microstructure arrays are mainly high temperature deposition [1], replication and template techniques [2], self-assembly through electric/magnetic fields or microchannel networks [3-5] and Langmuir-Blodget technique [6]. However, the direct fabrication of novel structures with large area, orientation and special morphology remains a scientific challenge. Zinc Oxide (ZnO), as an important semiconductor material with a direct wide band gap of 3.37 eV and large exciton binding energy of 60 meV, has been extensively investigated for applications in UV light emitters, transparent electronics, piezoelectric transducers, gas sensors and surface acoustic wave devices [7,8]. Consequently, the properties of ZnO depend on the controlled morphology with crystal size, growth direction, and surface area, etc. Various ZnO novel nano/microstructures have been extensively synthesized by solid-vapor phase growth for

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its simplicity and high-purity [8-10]. To meet the economic a