STACKING NATURE OF GRAPHENE LAYERS IN CARBON NANOTUBES AND NANOFIBRES

The structure of multilayer carbon nanotubes is studied using digital image analysis to interpret high resolution TEM lattice images contain ing 002 and 100 fringes, in comparision with very thin vapour-grown ca rbon fibres with nanometer-sized diameter (nanofibres). The results sh ow that the stacking of graphene shells in a multilayer nanotube glide with respect to one another, which is in contrast to th: stacking fid elity of three-dimensional graphite. The diffraction patterns derived from the fast Fourier transform of the lattice images yield angles of 0 degrees-17 degrees for the 100 lattice planes relative to the ideal 100 direction. The median inter-shell spacing d(002) between carbon na notubes is also characterized, by using the 100 spacing as an internal standard, and d(002) range from 3.4 to 3.6 Angstrom. The inter-shell spacing d(002) decreases with increasing carbon nanotube diameter, whi ch could be due to a size effect. The so-called vapour-grown carbon fi bres (VGCFs), obtained by pyrolytic decomposition of hydrocarbon, are grown through spontaneous deposition of carbon layers on primarily for med nanotubes. In order to clarify the size effect for layer stacking, very thin VGCFs with diameter similar to 500 Angstrom, named nanofibe rs as well as submicron diameter VGCFs, are compared with carbon nanot ubes, and are discussed in relation with the curvature of graphene lay ers. Some gently pulverized VGCFs with nm as well as mu m size diamete rs possess an exposed carbon nanotube at the core of the broken portio n, suggesting a difference in the stacking structure of the graphene l ayers between the central core nanotube and the outer pyrolytic sectio ns. (C) 1997 Elsevier Science Ltd.