MICROSTRUCTURAL AND ELECTRON SPECTROSCOPIC CHARACTERIZATION OF CARBONNANOSTRUCTURES AND NANOTUBES PRODUCED USING MULTIMETAL CATALYSTS

The microstructure of graphite are discharge soot catalysed with Fe, N i, Co and a mixture of Fe-Ni is investigated. It is shown that as well as single shell nanotubes and nanotube bundles, particles containing random networks of tubules and large diameter short tubules are found. Furthermore, the presence of fullerene nanocrystals directly formed d uring arcing is reported for the first time. The addition of a supplem entary inert metallic element (Ag) to the catalysts, introduced with t he aim of filling the tubules, reduces the nanotube yield significantl y. Particles of Ag of spherical shape are found to be aligned and enca psulated in a carbon envelope. Energy loss spectroscopy carried out in an electron microscope reveals significant variations in the carbon-c arbon bonding of the various soot morphologies which can be related to the formation site during are discharge. Spectra from single shell na notube bundles show an increase in the density of states on the antibo nding pi bands, in agreement with electronic structure calculation pre dicting metallicity. Spectra from spherical soot particles indicate a similarity in the carbon-carbon bond with the C-60/C-70 fullerenes. Im portant variations of the carbon bonding in areas of the nanotube bund les where pentagons are introduced during the growth are also detected . Considering the observed morphologies and yield variations due to va rious catalysts and the presence of Ag, mechanisms contributing to the growth of the observed microstructures are proposed. (C) 1997 Elsevie r Science Ltd. All rights reserved.