A template-based electrochemical method for the synthesis of multisegmented metallic nanotubes.

Tubular nanostructures have stimulated extensive research efforts in recent years because of their technological importance in advanced electronic or magnetic devices and prospective applications in catalysis, sensors, and biological separation and transport. To date, various methods including reductive sulfidization, thermal decomposition of precursors, atomic layer deposition (ALD), hydrothermal pyrolysis, galvanic replacement reactions, and surfactantor template-based growth have been developed for the fabrication of such tubular nanostructures. Among them, template-based synthesis using anodic aluminum oxide (AAO) or track-etched polymer membranes has attracted much attention, because it provides several distinct advantages over other approaches. It offers a convenient way for producing structurally uniform nanostructures periodically aligned in template matrices. A wide range of materials including metals, semiconductors, and polymers have been prepared in the form of nanotubes. However, few examples have been reported on the fabrication of metal nanotubes despite their technological importance. The development of a generalized method for the fabrication of aligned metalnanotube arrays remains a challenge. Precise control of the nanotube growth process and formation of well-aligned arrays will greatly assist investigations of their physical properties and their potential use in nanoscale fluidics, chemical and biological separations, sensors, and catalysts. Herein, we report a novel approach for the preparation of metallic nanotubes based on the preferential electrodeposition of a metal along the pore walls of an AAO membrane in the presence of metallic nanoparticles on the wall surfaces (Figure 1). Several reports on the immobilization of metallic nanoparticles on the pore walls of AAO have been published previously. Schmid and co-workers showed that Au nanoparticles can be self-assembled on AAO channels modified with organosilane molecules, which function as molecular anchors binding the nanoparticles. More recently, Rubin-