The role of defects in graphitic structures

The importance of defects in the formation of graphitic structures such as fullerenes, nanotubes, onion-like structures, helically coiled nanotubes and hypothetical periodic structures is analyzed. The structures mentioned above can also present defects which preserve their connectivity and topology. We have calculated the stability of Stone-Wales type defects in different shapes of graphitic structures finding that the energy required for these defects is not very high. * To whom correspondence should be addressed We show that polyhedral graphitic particles can be transformed into quasi-spherical onion-like structures by the introduction of defects preserving the topology. These quasi-spherical onions can be crystalline with symmetry, quasi-crystalline or amorphous with poor symmetry.