Self Seeded ZnO Nanowire Growth by Ultrasonic Spray Assisted Chemical Vapour Deposition
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Self Seeded ZnO Nanowire Growth by Ultrasonic Spray Assisted Chemical Vapour Deposition M. Wei, D. Zhi, and J. L. MacManus-Driscoll Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
ABSTRACT ZnO, which exhibits a direct bandgap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV,is of considerable technological importance because of its potential use in short-wavelength devices, such as ultraviolet (UV) light-emitting diodes and laser diodes. The fabrication and application of 1-D ZnO nanostructures has attracted considerable interest in recent years. In this work, we produced single crystal nanowires of zinc oxide using a novel self-seeded growth using ultrasonic spray assisted chemical vapour deposition, in which a nanocrystalline seed layer was first deposited onto a glass substrate and the nanowires subsequently grown using a different precursor concentration and substrate temperature. The diameter of the nanowires is in the range of 20-80 nm and the length of the wires is as long as 10 µm. The single crystal nature of the nanowires was revealed by high resolution transmission electron microscopy. The formation of liquid droplets due to the reducing atmosphere and the higher temperature during the nanowire growth was found to be the key step of the ZnO nanowire formation.
INTRODUCTION One-dimensional nanostructures, such as nanotubes and nanowires, have received growing interests in recent years [1]. These structures have shown distinct and superior properties over their bulk counterparts due to their small size and large surface-to-volume ratios; they are also promising candidates for realising nanoscaled electronic, optical, and mechanical devices [2]. ZnO, which exhibits a direct band gap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV [3], is of considerable technological importance because of its potential use in short-wavelength devices, such as ultraviolet (UV) light-emitting diodes and laser diodes. The fabrication and application of 1-D ZnO nanostructures have therefore attracted considerable interest in recent years. Notably, ZnO nanowires have been demonstrated in roomtemperature UV lasing [4]. In most of the vapour transport deposition processes, the 1-D ZnO nanostructures were produced at relatively high temperature (>900ºC) and Au is often used as catalyst [4], although other catalysts, such as Co [5] and Sn [6], have also been reported. Low-temperature growth of ZnO nanowire arrays by a physical vapour deposition method has also been reported by Lyu et al, in which predeposited NiO nanoparticles were used as catalyst [7]. Here, we report an ultrasonic spray assisted chemical vapour deposition method, in which ZnO nanowires can grow on top of a nanocrystalline ZnO seed layer. The method is relatively simple, without involving any use of a catalyst, and is a low-temperature process operating in an
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ambient atmosphere. In our approach, a nanocrystalline ZnO seed layer with uniform size dist
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