Liquid–Solid Process for Growing Gold Nanowires on an Indium Tin Oxide Substrate as Excellent Field Emitters

Abstract

Gold nanowires are successfully grown on an ITO substrate by a liquid−solid process. An excellent field emission behavior of the nanowires, as indicated by the field enhancement factor (β) of up to 7585, indicates a significant decrease in energy barrier between the nanowires and the ITO substrate. A single Au nanowire demonstrates a strong emission current up to 800 nA at an applied voltage of 200 V. The outstanding reliability of the nanowires warrants their potential applications as effective electron field emitters and chemical and/or biological sensors in future microelectronics. O ne-dimensional (1-D) nanostructures such as nanowires (NWs), nanotubes, and nanobelts have been widely used for fabrication of electronic and field emission devices. 1−4 Onedimensional noble nanowires possess excellent electrical and thermal conductivity, the very best malleability and ductility, and high chemical inertness property. 5 Au nanostructures have been widely investigated for a century due to its easy fabrication and many possible applications. Takayanagi et al. investigated the behavior of electron transport through 1-D nanoscale Au channels. 6,7 With all of these attractive merits, Au nanomaterials are most promising for applications, such as nanoelectronic interconnects, 6−8 optical transport behavior, 9 chemical sensors, 10 and biomedical or biosensing devices. 11 There are many reports about the synthesis techniques of gold nanostructures such as oxidation reduction, 12,13 electrochemical process, 14,15 or template fabrications. 16 However, the synthesis method employing liquid−solid (L− S) mechanism has yet to be explored. In this study, we report a simple, low-temperature (∼400°C) synthesis method to grow single-crystal Au nanowires on an indium tin oxide (ITO) substrate via the L−S growth process. These nanowires are approximately 100 nm in diameter and 10 μm in length. The field emission characteristics of Au nanowires have been studied, and the results indicate that the Au nanowires have a great potential to be used for field emission and sensor applications. ■ RESULTS AND DISCUSSIONITO substrates are selected for the growth of Au nanowires. A 500 nm Ti thin film to be followed with a 100 nm Au film has been deposited on the ITO by e-beam deposition at a pressure below 10 −6 Torr. We have designed a unique method to grow single-crystal Au nanowires with high aspect ratio through a L− S mechanism. The L−S process takes place in two steps. It starts with the formation of liquid Au−Ti droplets first to be followed by the growth of solid Au nanowires. Figure 1 illustrates a schematic growth model of the singlecrystal Au nanowires form at low temperature on the ITO substrate. Previous investigations of the binary Au−Ti system have shown that Au−Ti solid solution may form above 400°C. 17,18 During the nucleation step, the Au/Ti multilayer transforms and separates tiny Au−Ti nanoparticles having Au concentration close to be ∼99% form on the ITO substrate when the sample is annealed at temperature around 500°C for 60 ...

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