Manipulation of ZnO Nanowire by Low-Temperature Solution Approach
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Manipulation of ZnO Nanowire by Low-Temperature Solution Approach Chia-Hsin Lin, Syh-Yuh Cheng, Ren-Jay Lin, Yi-Hui Wang Materials Research Laboratories, Industrial Technology Research Institute, Chutung, Hsin-Chu, 310, Taiwan ABSTRACT A catalyst free, structure-induced heterogeneous nucleation and direct growth of ZnO nanowires on organic and inorganic substrates was prepared by low-temperature solution approach process. The experimental results showed that ZnO nanowires could be directly synthesized upon the concave of substrate without any pre-seeding. In this work ZnO nanowires were grown on both polystyrene bead layer and physical-grinded wafer substrate. ZnO nanowires with a broad aspect ratio of 10-2 ~ 102 was controlled mainly by adjusting of reactant concentration and pH state of solution. A needle-like ZnO nanotip were also prepared by a two-step limited growth condition as a result that tip diameter is several nanometers only, which may be highly in favor of the field emission. Structure-induced heterogeneous nucleation and growth facilitates the fabrication of ZnO nanowires as the potential photoeletronic units in field-emission displays. INTRODUCTION ZnO has been extensively adopted for the electro-optical devices. Recently, some needleshaped ZnO nanowires were reported as candidate for field emitters because of extreme geometry and chemical stability [1-5]. The performance of needle-shaped ZnO nanowires has caught up with carbon nanotube due to extra high aspect ratio as a result of low turn-on field for initial current emission [6,7]. The synthesis of this attractive material has been carried out using various methods including metal vapor deposition (MVD) [1], chemical vapor deposition (CVD) [2,5], and thermal evaporation/condensation [3]. However, these processes were conducted at either extreme high temperature or vacuum conditions. Moreover metal and metal oxide nanoparticles are frequently used as seeding layer, such as Co [1], ZnSe [2], Au [3], NiO [5] and so on. Recently, as-grow ZnO nanowires on Al2O3 was synthesized by a metal catalyst free process, metalorganic vapor-phase epitaxy (MOVPE) [8] because both materials are lattice matched. Prior to grow ZnO nanowire, a thin ZnO buffer layer was necessarily deposited on the surface of substrate. The similar pre-seeding on the substrate were also prepared by depositing 5nm ZnO nanoparticles on ITO substrate, followed by annealing at 300oC [9]. But it may not be suitable for preparing ZnO nanowires on organic substrate. Consideration of soft material for the future application, a low temperature process for the combination of soft matrix and functional nanostructures is now attractively being explored. In this study, a catalyst free process (including metal or pre-seeding ZnO film) for the ZnO nanowires growth was proposed by a low temperature solution approach. Here we prepared a structure-induced heterogeneous nucleation and direct growth of ZnO nanowires on physical-treated substrates in the liquid status under atmospheric enviro
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