Thin and long silver nanowires self-assembled in ionic liquids as a soft template: electrical and optical properties
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NANO EXPRESS
Open Access
Thin and long silver nanowires self-assembled in ionic liquids as a soft template: electrical and optical properties Min-Hwa Chang, Hyun-Ah Cho, Youn-Soo Kim, Eun-Jong Lee and Jin-Yeol Kim*
Abstract Thin and long silver nanowires were successfully synthesized using the polyvinylpyrrolidone (PVP)-assisted polyol method in the presence of ionic liquids, tetrapropylammonium chloride and tetrapropylammonium bromide, which served as soft template salts. The first step involved the formation of Ag nanoparticles with a diameter of 40 to 50 nm through the reduction of silver nitrate. At the growing stage, the Ag nanoparticles were converted into thin and long one-dimensional wires, with uniform diameters of 30 ± 3 nm and lengths of up to 50 μm. These Ag nanowires showed an electrical conductivity of 0.3 × 105 S/cm, while the sheet resistance of a two-dimensional percolating Ag nanowire network exhibited a value of 20 Ω/sq with an optical transmittance of 93% and a low haze value. Keywords: Silver nanowire; Ionic liquid; Polyol synthesis; Tetrapropylammonium chloride; Tetrapropylammonium bromide; Self-assembly
Background One-dimensional (1-D) metallic nanostructures, namely silver nanowires (Ag NWs), have recently attracted a great deal of attention for their unique electrical, optical, magnetic, and thermal properties as a promising alternative to indium tin oxide (ITO) as an electrode material used in the fabrication of devices such as electronic displays, photonics, and sensors [1-10]. Ag NWs with well-defined shapes such as lengths and diameters are particularly interesting, as they have superior optical and electrical properties, thus making them excellent candidates for transparent electrodes. However, in order to implement the optical and electrical features required for transparent electrodes, there is still a need to develop more effective processes for synthesizing Ag NWs with controllable shapes and sizes, which can be grown continuously up to at least 30 μm in length with 30-nm diameter. Several chemical approaches have been actively explored and developed in order to process Ag into 1-D nanostructures using various physical templates and surface-capping reagents (organic polymers or surfactants) in conjunction with the solution-phase * Correspondence: [email protected] School of Advanced Materials Engineering, Kookmin University, Seoul 136-702, South Korea
polyol process [11-14]. These studies largely focused on controlling the size, shape, crystal structure, and optical/ electrical properties of the Ag NWs. For example, Sun and co-workers [12] developed a solution-based polyol process to prepare single-crystal Ag NWs using polyvinylpyrrolidone (PVP) as a surface-capping reagent. The capping reagents were then evaluated in order to kinetically control the growth rates of the metal surfaces and subsequently induce 1-D growth leading to the formation of NWs. Based on the PVP-assisted polyol method, Xia and co-workers [15,16] also demonstrated a salt-mediated polyol process, using
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