Nanostructured materials are one of the most active areas of materials science research. This interest is due to their unique properties (e.g., magnetic, optical, electronic, mechanical) and potential applications.[1] Metallic nanostructured materials, such as metal nanowires and nanoarrays, have potential applications in nanoscale devices, sensors, nonlinear optics, magnetic storage media, and anisotropic conductors. [1,2] Synthetic methods such as electron-beam lithography, step-edge decoration, and templated growth have been developed to prepare metallic nanostructured materials.[3] The templated growth method, which involves confined growth of metallic materials to a template (e.g., a pore) followed by removal of the template, provides a flexible and affordable synthetic route to a large variety of metal nanowires. Examples of such templates include hard templates [4] (e.g., porous alumina films, track-etched polycarbonate films, and mesoporous silica) and soft templates [1a,5] (e.g., liquid-crystalline phases and amphiphilic block copolymers). The hard templating approach is conceptually simple to implement; however, the use of porous alumina or polycarbonate membranes as templates usually results in polycrystalline nanowires or nanowires with large wire diameters (20±1000 nm), which may preclude quantum confinement effects. Surfactant-templated mesoporous silica possesses unique mesoscale pore channels and a controllable pore surface chemistry, which make it an ideal template for the synthesis of metal nanowires.[6±8] Electrodeposition is an efficient and ready technique for depositing metal coatings. In this Communication, we report the fabrication of metal thin films composed of ordered arrays of metal nanowires that are grown electrochemically within silica mesoporous channels. Although syntheses of metal nanowires by chemical reduction of metallic complexes and by chemical vapor infiltration of mesoporous silica pore channels have been reported previously, [8] as-synthesized metal nanowires usually lack macroscopic continuity. In this new method, nanowires are continually grown from the bottom conductive substrate upward until the mesoporous channels are filled. This provides a ready and efficient route to macroscopic, hierarchical metal nanowire thin films. The metal nanowire thin films before and after removal of silica were characterized using X-ray diffraction (XRD). Figure 1 shows the XRD patterns of a mesoporous silica thin film (A) and a silica/metal thin film before (B) and after (C) removal of the silica template. Trace A exhibits a typical one-dimensional hexagonal pattern with an intense (100) diffraction peak with a d-spacing of 67.4 and with a (200) peak of 35.6 . The mesostructured silica after metal deposition (trace B) shows a diffraction pattern similar to that for trace A, except for the expected decrease in the XRD peak intensity at low angles.[8b] The inset shows the XRD pattern of the silica/palladium thin film at higher 2h angles. The presence of the characteristic diffraction ...

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