Carbon nano architectures containing non-hexagonal rings: necklaces of pearls

The structure of novel forms of carbon nanostructures (Haeckelites) is investigated combining modeling with experimental data. New arguments are given for the existence of a theoretically predicted sp(2) hybridized carbon form, with structure close to that of graphite, called Haeckelite (Terrones et al., Phys. Rev. Lett. 84 (2000) 1716). The major difference between Haeckelite and graphite is given by the regular occurrence of non-hexagonal carbon rings as building blocks of Haeckelite. It is proposed that the necklace of pearls type nanostructures investigated by SEM, TEM and HRTEM, are built of Haeckelite and a structural model which allows a graphitic interlayer spacing for multilayer Haeckelite necklaces is proposed. (C) 2004 Elsevier Ltd. All rights reserved.