Evidence for glide and rotation defects observed in well-ordered graphite fibers
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M.S. Dresselhaus Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 28 November 1994; accepted 6 March 1995)
New structural features observed in heat-treated vapor-grown carbon fibers (VGCF's), produced by the thermal decomposition of hydrocarbon vapor, are reported using image analysis of the lattice plane structure observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM lattice image of well-ordered graphite fibers (heat-treated VGCF's at 2800 °C) was treated by a two-dimensional fast Fourier transform, showing sharp bright spots associated with the 002 and 100 lattice planes. The heat-treated VGCF's consist of a polygonally shaped shell, and the long and short fringe structures in the TEM lattice image reflect the 002 and 100 lattice planes, respectively. From this analysis, new facts about the lattice structure are obtained visually and quantitatively. The 002 lattice planes remain and are highly parallel to each other along the fiber axis, maintaining a uniform interlayer spacing of 3.36 A. The 100 lattice planes are observed to make several inclined angles with the 002 lattice planes relative to the plane normals, caused by the gliding of adjacent graphene layers. This work visually demonstrates coexistence of the graphitic stacking, as well as the gliding of the adjacent graphene layers, with a gliding angle of about 3-20°. These glide planes are one of the dominant stacking defects in heat-treated VGCF's. On the other hand, turbostratic structural evidence was suggested by AFM observations. The structural model of coexisting graphitic, glide, and turbostratic structures is proposed as a transitional stage to perfect three-dimensional stacking in the graphitization process. These structural features could also occur in common carbons and in carbon nanotubes.
I. INTRODUCTION
The vapor-grown carbon fibers (VGCF's) in this study were obtained by hydrocarbon pyrolysis such as with benzene and with methane, using the catalytic effect of ultrafine metal particles of iron with diameters as small as 50 A. The growth processes, structure, and formation mechanism of VGCF's have been characterized by a variety of techniques, such as electron microscopy, electron diffraction, and x-ray diffraction.1"5 As-prepared vapor-grown carbon fibers have a circular cross section and show a preferred orientation in which networks of carbon planes are arranged like annular rings of a tree, and these carbon planes are parallel to one another along the fiber axis. By heat treatment of VGCF's, graphite fibers of unusually high structural order, high electrical conductivity, high bulk-modulus, and high
a) Permanent
address: Department of Electronics and Computer Science, Nagano National College of Technology, 713 Tokuma, Nagano 381, Japan. J. Mater. Res., Vol. 10, No. 6, Jun 1995 http://journals.cambridge.org
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tensile strength have been prepared.2 The VGCF's
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