Density-controlled growth of aligned ZnO nanowire arrays by seedless chemical approach on smooth surfaces
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A novel ZnO seedless chemical approach for density-controlled growth of ZnO nanowire (NW) arrays has been developed. The density of ZnO NWs is controlled by changing the precursor concentration. Effects of both growth temperature and growth time are also investigated. By this novel synthesis technique, ZnO NW arrays can grow on any substrate (polymer, glass, semiconductor, metal, and more) as long as the surface is smooth. This technique represents a new, low-cost, time-efficient, and scalable method for fabricating ZnO NW arrays for applications in field emission, vertical field effect transistor arrays, nanogenerators, and nanopiezotronics.
I. INTRODUCTION
ZnO nanorod and nanowire (NW) arrays have been extensively studied over the past several years for their potential applications in fabricating electronic, optoelectronic, electrochemical, and electromechanical devices, such as solar cells,1 ultraviolet (UV) lasers,2 piezonanogenerators,3,4 light-emitting diodes,5 and fieldemission devices.6 For many of these applications, it is crucial to synthesize well-aligned NW arrays. A variety of methods have been reported for fabricating arrays of aligned NWs, including vapor phase transport,7,8 metalorganic chemical vapor deposition (MOCVD),9,10 and hydrothermal synthesis. 11,12 However, vapor-phase transport and MOCVD usually require single-crystal substrates and high operation temperature, which are expensive and not compatible with organic substrates for applications in flexible and wearable electronics. Hydrothermal synthesis is a good alternative approach from this purpose, but it usually employs ZnO seeds in the forms of thin films or nanoparticles13–15 or requires an external electrical field to promote the growth of ZnO nanostructures.16,17 In such a case, nanowhiskers would grow densely on the entire substrate with large variation in orientation, which may not meet the needs for nanogenerators,3,4 because it requires well-aligned and wellseparated NWs.18,19 Density-controlled synthesis of oriented arrays of one-dimensional ZnO NWs or nanorods has been achieved by nanosphere lithography,7,20 photolithography21–23 and electron-beam lithography,24,25
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0274 2072
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 8, Aug 2008 Downloaded: 17 May 2014
which are expensive, time consuming, and usually used for small-scale experiments. In this work, we report a chemical approach for achieving density-controlled growth of aligned ZnO NWs arrays without using ZnO seeds, as shown in Fig. 1. By adjusting the precursor concentration, the density of ZnO NW arrays could be controlled within one order of magnitude (number of ZnO NWs per 100 m2) with one NW growing from one spot site. This novel synthesis technique does not require ZnO seeds or external electrical field, and it can be carried out at low temperatures and large scale on any substrate, regardless of whether it is crystalline or amorphous. II. EXPERIMEN
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