Growth of catalyst-free high-quality ZnO nanowires by thermal evaporation under air ambient
© Liu et al; licensee Springer. 2012
Received: 22 March 2012
Accepted: 13 April 2012
Published: 13 April 2012
ZnO nanowires have been successfully fabricated on Si substrate by simple thermal evaporation of Zn powder under air ambient without any catalyst. Morphology and structure analyses indicated that ZnO nanowires had high purity and perfect crystallinity. The diameter of ZnO nanowires was 40 to 100 nm, and the length was about several tens of micrometers. The prepared ZnO nanowires exhibited a hexagonal wurtzite crystal structure. The growth of the ZnO nanostructure was explained by the vapor-solid mechanism. The simplicity, low cost and fewer necessary apparatuses of the process would suit the high-throughput fabrication of ZnO nanowires. The ZnO nanowires fabricated on Si substrate are compatible with state-of-the-art semiconductor industry. They are expected to have potential applications in functional nanodevices.
In the past decade, significant interest has emerged in the synthesis of one-dimensional semiconductor materials, such as Si [1–3], SiC [4, 5], GaN [6–8], SnO2  and ZnO [10–13]. Among these nanoscale semiconductors, ZnO has attracted a great deal of attention because of its potential as a large direct band gap semiconductor (Eg is about 3.35 eV at room temperature) with high exciton binding energy (60 meV). It can act as building blocks for nano-FET, nanolasers, photodetectors and gas sensors [8, 14]. In addition, ZnO nanowires have excellent field emission for its good hardness, thermal stability and resistance to oxidation [15, 16].
Recently, many methods have been developed to synthesize ZnO nanowires, for example, carbon thermal reduction [13, 17], chemical vapor deposition [12, 18], physical vapor deposition , electrodeposition , aqueous synthesis  and solvothermal technique . In this paper, we synthesized ZnO nanowires by thermal evaporation without a catalyst under air ambient. The reactions were carried out in a traditional horizontal furnace with one end open at 750°C. The gray-white product was successfully deposited on the Si substrate. The process does not need any metal catalyst, so it avoids catalyst contamination. Furthermore, the simplicity, low cost and fewer necessary apparatuses of the process would suit the high-throughput fabrication of ZnO nanowires.
The as-synthesized products were characterized by X-ray diffraction (XRD) with CuKα radiation (wavelength, λ = 1.5406 Å), field emission scanning electron microscopy (SEM) (Hitachi S-4800, Hitachi Ltd., Tokyo, Japan), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) (JEOL JEM2010F, JEOL Co., Ltd., Beijing, China).
Results and discussion
ZnO nanowires with high purity and perfect crystallinity were fabricated by simple thermal evaporation of pure Zn powders under air ambient without any catalyst. The diameter of the ZnO nanowires was 40 to 100 nm, and the length was about several tens of micrometers. Some aligned ZnO nanowires with smooth surface were also detected. The growth of ZnO nanostructure was explained by the V-S mechanism. The prepared ZnO nanowires exhibited a hexagonal wurtzite crystal structure. The as-fabricated ZnO nanowires are expected to find applications in nanosensors and nanodetectors.
Dr. Ping Liu got her PhD degree in 2010. She has devoted her effort in the research of one-dimensional semiconductor materials for 7 years. Her research interest lies in the fabrication and application of zinc oxide nanowires. She has published her work in several important international journals.
The authors thank the Foundation of He'nan Educational Committee (no. 2011A470015) and the Henan province science and technology tackling key project (no. 102102210444).
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