NEW GROWING MODES FOR CARBON - MODELIZATION OF LATTICE-DEFECTS, STRUCTURE OF TUBULES AND ONIONS

Topological defects and tubule-to-tubule connections on single-walled carbon nanotubes are examined in the frame of dislocations and Burgers vectors concepts. A tubule is defined by its Burgers vector on the gr aphene triangular Bravais lattice. The 'adjacent pentagon + heptagon d efect', in short '5 circle plus 7', is identified with a dislocation w ith a lattice primitive vector as Burgers vector, i.e. a high-energy-h ighly-mobile defect. It acts as an elementary translational operator o n the triangular array, allowing the description of the set of transfo rmations undergone by a tubule through a single 5 circle plus 7 in ter ms of nearest neighbours jumps. The standard labelling system in use f or tubules is extended into a unified system for tubules anl for chira l and non-chiral icosahedral fullerenes, allowing easy relations betwe en a tubule and the either flat or hemispherical caps able to match it . Interest of these ideas in onions and multi-walled nanotubes is emph asized. (C) 1997 Elsevier Science Ltd.