Carbon Nanotubes
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Introduction Nanostructured materials have recently attracted the attention of some materials scientists. Because of their unique properties occurring in low-dimensional structures, nanostructured materials are sought for their possible industrial applications. This article introduces a specific nanostructured material, the carbon nanorube—an extremely thin filaments of graphite considered to be a quasi one-dimensional structure, with a simple well-understood atomic structure. Because of these qualities, the carbon nanorube has elicited great interest from diverse fields of basic and technological research. My discovery of carbon nanotubes was inspired by the discovery of C m and its familyx and their mass production.2 The carbon nanotubes were serendipitously found during the examination of fullerene materials by a high-resolution transmission electron microscope (HRTEM).3 Since introducing this technique in 1971,91 have been employing HRTEM to characterize the microscopic structural details of a variety of materials, including carbonaceous materials.4"8 So far, only nanotubes have been revealed with HRTEM. Interest in the carbon nanorube is multifold. Academically the nanotube is an ideal model structure for a quasi onedimensional structure since its known atomic structure makes computer simulations more reliable. It is worthwhile to study both rare structures of graphite— cylindrical forms with a helical arrangement of carbon atom hexagons and flexible graphitic sheets containing topological surface defects. These materials may find practical uses as tough graphite fibers, molecular wires, catalyst supports, molecular adsorbers, and so on. Despite great expectations for carbon nanotubes and extensive efforts to meet such expectations, characterization of carbon nanotubes has been slow compared to fullerene research activity. This is due partly to the inability to synthesize macroscopic quantities of the tubules and to refine them. This article reviews the production, morphologies, and atomic structures of carbon nanotubes as based on TEM observations. From these results a mechanism for tubule growth is discussed
MRS BULLETIN/NOVEMBER 1994
with the hope of developing a tubule massproduction process. Electronic properties of the tubules are also described briefly. Finding Carbon Nanotubes It is possible to image individual C^i molecules using a modern electron microscope, but many of the fundamental problems of the molecule, such as superconductivity of metal-doped Cffl crystals, require techniques beyond TEM. Although crystalline forms of the molecules will provide some conventional crystallographic features such as twins, stacking faults, surface structures, and phase transitions, I have hesitated to enter that area. Instead, I have focused on looking for the formation of fullerene molecules which grow out of a carbon plasma gas. This idea came from my previous experience with spheroidal graphitic particles.4 They comprise nested shells of spherical graphite layers with a Corsize spherical shell at the particl
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