Abstract: One-dimensional (1D) nanowires and nanowire arrays of metal, semiconductor, and conductive polymers have attracted much attention because of their unique electrical, magnetic, optical, and mechanical properties, and their potential application in nanodevices. Although other successful approaches such as vapor±solid and liquid±solid phase methods exist for silicon and other semiconductor nanowires, the most widely used method for fabrication of nanowires and nanowire arrays is still chemical or electrochemical deposition guided by an appropriate porous ahardo template such as anodized alumina, track-etched polycarbonate and mica, carbon nanotubes, zeolite/mesoporous silica, and diblock copolymers. Step edges of freshly cleaved graphite and a conducting quantum well in a semiconductor multilayer prepared by molecular beam epitaxy also have been used as nanowire growth guides. The hard template approach is an effective route to metal, semiconductor, and polymer nanowires; however, most of the templates are tedious to fabricate and dissolution of the template in corrosive media is required to retrieve the nanowires if separate single wires are desired. Surfactant mesophases have proved to be a useful and versatile asofto template for the synthesis of nanostructured materials. For example, syntheses of porous zeolite-type materials using normal (oil in water) surfactant mesophases as a template are well established. Reverse (water in oil) micelles and microemulsions with spherical aqueous microdomains have been used for nanoparticle and sometimes nanowire synthesis (mainly compounds such as BaSO4 and BaCrO4). [21±24] All of the aforementioned syntheses use low surfactant concentrations where liquid-crystalline phases are not present. In contrast, at high surfactant concentrations, homogeneous normal or reverse hexagonal liquid-crystalline phases can be obtained. Attard et al. and others have demonstrated that normal hexagonal liquid crystals can template the synthesis of bulk porous materials and porous metal films by electrodeposition. Very recently, a reverse hexagonal liquid crystal was used as a template to synthesize ZnS nanowires by gamma ray irradiation. The ZnS nanowires so obtained are fairly short (<2 lm) probably due to the random orientation of the reverse hexagonal liquid crystal. In this communication, we demonstrate for the first time fabrication of crystalline silver nanowire arrays with a high aspect ratio by electrodeposition from a reverse hexagonal liquid-crystalline phase containing one-dimensional aqueous channels. We provide evidence that a high electric field during electrodeposition helps align the reverse hexagonal liquidcrystalline phase, which is believed to be essential for production of high aspect ratio crystalline metal nanowires. For growth of silver nanowires, a reverse hexagonal liquidcrystalline phase was first prepared according to the wellknown ternary phase diagram consisting of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT), an oil phase of p-xylene, and water. For our synthesis the water phase was substituted by an aqueous 0.1 M AgNO3 solution. The resulting mixture has the characteristic birefringence of a hexagonal liquid crystal when viewed under a polarized light microscope. The electrodeposition was conducted by using a potentiostat in a two-electrode configuration with the two electrodes narrowly spaced (0.5±1.0 mm) and the aforementioned reverse liquid-crystalline phase as electrolyte. The nanowire product deposited on the cathode substrate (polished stainless steel) was thoroughly washed with ethanol. High-density nanowire arrays were obtained over a short deposition time of 15 min with the nanowires roughly perpendicular to the cathode surface (Fig. 1A). The slight disorder in the nanowire array may arise from the washing process after deposition. After a deposition time of 2 h, nanowires tens of micrometers long were obtained (Fig. 1B). The nanowires were almost parallel (no longer perpendicular) to the electrode surface, most probably due to the washing process after deposition. The high-density nanowire array can be separated into single wires after ultrasonic dispersion in ethanol (Fig. 1C), indicating that the nanowires can be used in a bundle form or as single wires for nanodevices. Figure 2 shows the X-ray diffraction (XRD) pattern of the silver nanowire arrays deposited on a stainless steel substrate. It shows the diffraction peaks with d-spacings of 2.36 , 2.04 , 1.44 , 1.23 , and 1.18 , which are consistent with that of face centered cubic (fcc) Ag metal phase. Energy dispersive X-ray (EDX) analysis shows that the wires are made of pure silver, suggesting that surfactant molecules can be totally removed from the nanowire arrays by a simple washing process. Transmission electron microscopy (TEM) images and electron diffraction of nanowires are shown in Figure 3. Figures 3A and 3B show a bright field (BF) and dark field (DF) image, respectively, of a fragment of a single silver nanowire. The entire crystal is bright in DF mode with operating reflection (11Å1), confirming the single crystal nature of the nanowire. The individual wire is either a single crystal or consists of symmetrically oriented domains that are twinned on {111} planes. The twinned nanowire crystals are made of multiple