Coiled carbon nanotube structures with supraunitary nonhexagonal to hexagonal ring ratio

By assembling azulene units (fused pentagon-heptagon pairs) and hexagons, and applying specific wrapping rules to these structures resembling some recently-proposed Haeckelite structures [Terrones et al., Phys. Rev. Lett. 84, 1716 (2000)], a large variety of toroidal, coiled, screwlike, and double-helix structures can be generated. In particular, the coiling appears naturally by rolling up stripes made of heptagons, hexagons and pentagons. In the structures examined here, the ratio of nonhexagonal rings to hexagonal units varies from 4: 1 to 4: 3. In the coiled nanotubes produced actually by catalytic chemical vapor deposition, it is not impossible that such a high concentration of nonhexagonal units in the nanotube structure be the result of a fast kinetic leading to metastable states that cannot anneal out due to the low growth temperatures used.