Structural properties of Haeckelite nanotubes

The name ‘Haeckelite’ has been proposed to designate a three-fold coordinated network generated by a periodic arrangement of pentagons, hexagons and heptagons (Terrones H et al 2000 Phys. Rev. Lett 84 1716). Starting from a planar Haeckelite array, tubular structures are obtained by applying the same wrapping procedure as for the usual nanotubes, which are rolled up sheets of graphene. This paper is a short review of the structural properties of Haeckelite nanotubes, as investigated by computer molecular modelling. The Haeckelite nanotubes may adopt various shapes, among which coiled structures, doublescrew molecules, corrugated cylinders, and pearl-necklace-like nanotubes are the most spectacular. It is shown that some of these structures may explain exotic forms of C nanostructures revealed by electron microscopy on samples produced experimentally. The identification of the possible Haeckelite structure of a nanotube by electron diffraction and scanning tunnelling microscopy is discussed.