Creating catalytically active nanoparticles via block copolymer templates for carbon nanotube and silicon nanowire growt
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0921-T01-04
Creating catalytically active nanoparticles via block copolymer templates for carbon nanotube and silicon nanowire growth Jennifer Lu and Danielle Chamberlin Agilent Technologies, 3500 Deer Creek Road, Palo Alto, 94304
Abstract Using solution micelles formed by a block copolymer template, a variety of highly ordered catalytically active transition metal nanoparticles, ranging from single metallic nanoparticles of Fe, Co, Ni and Au to bimetallic nanoparticles such as Ni/Fe with uniform size and periodicity, have been created. These nanoparticles are excellent catalyst systems for the synthesis of carbon nanotubes and silicon nanowires. High quality, small diameter carbon nanotubes and silicon nanowires with narrow size distribution have been successfully produced. Since this block copolymer is fully compatible with conventional top-down photolithography, spatially selective growth of carbon nanotubes and silicon nanowires on a surface or carbon nanotubes suspended across trenches have been achieved using standard semiconductor processing techniques. The ability of the block copolymer template to generate catalyst with adjustable size and composition on a variety of surfaces not only enhance the manufacturability of these 1D nanobuilding blocks but also facilitates studying the growth mechanism. Introduction Carbon nanotubes (CNTs) and semiconductor nanowires have been demonstrated to have exceptional electronic and optoelectronic properties and are being explored in applications including nanoelectronics, nanolasers, nanoscale sensors and nanofluidic devices. (1-5) Since CNTs and semiconducting nanowires are very small, quantum mechanical effects determine their properties. It has been experimentally proven that many of the properties such as electronic and optical properties are highly sensitive to their diameters. (6-7) In the case of CNTs, their properties are not only sensitive to diameter but also geometrical arrangement of carbon atoms as well. The quantization condition along the perimeter determines whether a tube manifests semiconducting or metallic behavior. The lack of a method to fabricate these 1D nanostructures with controlled size at predefined locations prevents realizing their highly touted properties, thus stymies the commercialization of nanotechnology. A block copolymer consists of two or more homopolymers covalently bound together. The inherent immiscibility of these homopolymer segments, coupled with the linkage between them, coerce the block copolymer to attain a variety of nanoscale morphologies. The domain size can easily be tuned by adjusting the total molecular weight. Morphologies can be morphed from spheres to cylinders to lamellae, depending on the volume fraction of each component. These self-assembled morphologies are emerging as scaffolds and templates for the fabrication of nanostructured material. (8-11) In this study, a catalyst-bearing block copolymer has been synthesized by selectively attaching catalyst species onto an existing block copolymer. The catalyst-contain
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