Recent Advances in Methods of Forming Carbon Nanotubes
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Recent Advances in
Methods of Forming Carbon Nanotubes
Jie Liu, Shoushan Fan, and Hongjie Dai Abstract Since their discovery, carbon nanotubes, both single-walled and multiwalled, have been a focus in materials research. Fundamental research and application development hinge on high-quality nanotube materials and controlled routes to their organization and assembly. The aim of this article is to provide updated information on recent progress in the synthesis of carbon nanotubes. Keywords: bulk synthesis, carbon nanotubes, chemical vapor deposition (CVD), multiwalled, single-walled, surface synthesis.
Introduction First discovered in 1991,1 carbon nanotubes are considered to be a new form of carbon material with many unique electrical, mechanical, and chemical properties. They have attracted much attention due to potential applications such as additives for high-strength polymer composites, electrode materials for high-capacity batteries, efficient field-emitters as electron sources, and functional components for nanoscale electronic devices. Over the years, basic research and applications exploration have been greatly accelerated by the synthesis of high-quality nanotube materials. The first growth of high-quality and milligramquantity single-walled carbon nanotubes (SWNTs) by laser ablation2 represented an important milestone that enabled the study of the intrinsic properties of nanotubes. It is clear that future developments in nanotube-based science and technology will rely on the highly controlled synthesis of nanotube materials. Currently, there are four main challenges in the field of nanotube synthesis: (1) the development of low-cost, large-scale processes for the synthesis of high-quality nanotubes, including SWNTs; (2) control over the structure and electronic properties of the produced nanotubes; (3) control over the location and orientation of the produced nanotubes on a flat substrate; and (4) the development of a thorough understanding of the growth mechanism of nanotubes. 244
There have been many review articles3–6 and special issues of journals7–9 in addition to several books10–13 focusing on carbon nanotubes published during the past several years. Recently, activities have increased in theoretical modeling and simulation of carbon nanotubes in order to understand the growth mechanisms from the theoretical perspective.14–18 In this article, we will present an overview of the current state of the art in the synthesis of carbon nanotubes. The preparation of high-quality SWNTs with high yield has been the goal of many research endeavors. So far, arc-discharge,19,20 laser ablation,2 and chemical vapor deposition (CVD) are the three main methods for SWNT production. Arc-discharge and laser ablation were the first methods that allowed synthesis of SWNTs in relatively large (gram) amounts. Both methods involve the condensation of hot gaseous carbon atoms generated from the evaporation of solid carbon. However, the equipment requirements and the large amount of energy consumed by these methods make the
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