Incorporation of nitrogen in carbon nanotubes

Nitrogen-doped carbon nanotubes were obtained by the are-discharge technique in a helium-nitrogen atmosphere and using iron-nickel-cobalt catalysts. The samples were analyzed using spectroscopic techniques (Raman, EELS, Xray photoelectron spectroscopy) and transmission electron microscopy (TEM). Pure helium atmosphere conditions led to bundles of single-wall nanotubes with diameters of similar to1.5 nm. The presence of nitrogen during tube formation produced irregular and thickly textured tubes. TEM micrographs showed that N suppresses the formation of bundles of single-wall nanotubes, giving rise to nested nanofibers. Quantum-chemical calculations were carried out to study the influence of substitutional N on the tube conformation. The calculations show that the combination of hexagons and pentagons at low N concentration produces kinks that account for the irregular shaped nanotubcs. (C) 2002 Elsevier Science B.V. All rights reserved.