New method of producing well-aligned ZnO nanorods on a Si-SiO 2 substrate
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Well-aligned ZnO nanorods arrays were fabricated by sintering powder Zn underneath a Si–SiO2 substrate. In this fabrication, ZnO was produced by the displacement reactions between Zn and SiO vapors. We found that these ZnO nanorods grew toward the [0001] direction. The diameter and the alignment of these nanorods strongly depended on the sintering temperature. When the temperature was increased from 740 to 800 °C, the diameter of the rods was increased from 30–70 nm to 300–700 nm, and their alignment was also improved. A model is proposed to describe the formation of these nanorods.
One-dimensional (1D) nanomaterials have attracted a great deal of attention due to their potential in technological applications.1 In particular, ZnO possesses a wide band gap (3.37 eV) and a high exciton binding energy (about 60 meV), which make it a suitable candidate for a room-temperature ultraviolet (UV) laser with low threshold excitation and high emission efficiency. The UV lasing from ZnO thin films and grains has been reported.2,3 The current conventional method of fabricating arrays of ordered 1D ZnO nanorods involves the deposition of ZnO vapor on a sapphire substrate or silicon substrate coated with catalytic Au.1,4,5 Although the size and alignment of the products were claimed to be controllable, the incorporation of metallic impurities was unavoidable in this technique. Other attempts for producing high-quality ZnO nanorod arrays, such as metalorganic chemical vapor deposition (MOCVD)6,7,8 and thermal evaporation of Zn in different environments9,10 have been conducted. In particular, the MOCVD technique used by Park et al. utilized catalyst-free alumina substrate for the deposition of ZnO. They successfully obtained pure and high quality and well-aligned ZnO nanorods6 and nanoneedles.8 However, the MOCVD approach is complex and costly, and it usually involves the use of toxic metalorganic salts and inflammable gases. Thus, the search for simple fabrication method for 1D nanomaterials is still one of the prime issues for investigators. In this paper, we report a novel and low-cost method of preparing well-aligned ZnO nanorod arrays. The process involves the reaction between Zn powder and a Si–SiO 2 substrate. The advantages of this fabrication technique are that the a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0318 2226
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 8, Aug 2004 Downloaded: 18 Mar 2015
process is simple and can be conducted at relatively low temperature with common tube furnace. Moreover, it does not require any catalyst or the establishment of thermal gradient. In this work, well-aligned and pure ZnO nanorods arrays are formed on the Si–SiO2 substrate after the sintering reactions. A model is proposed to describe the growth mechanism of these ZnO nanorods. About 0.2 g Zn powder (97.5% purity, 7 mm from Alfa, Ward Hill, MA) was placed in a quartz crucible. It was then covered with a 2-mm-thick flat substrate. The substrate was prepared by cold
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