Ring formations from catalytically synthesized carbon nanotubes

Rings of typically 0.5 mu m diameter have been observed with the atomic for ce microscope and the scanning electron microscope in carbon nanotube depos its produced catalytically by thermal decomposition of hydrocarbon gas. The carbon nanotubes are predominantly multiwalled with an average thickness o f 20 nm, which is the typical thickness of the rings as well. The observati ons are discussed in light of the previous discoveries of helical nanotubes in the same material and the observation of rings of similar thickness and diameter (interpreted as toroids) in single wall carbon nanotube material grown by laser vaporization. In our observations, the ring formations can b e interpreted as single turn coils with a short overlap between the beginni ng and end of the coiled nanotube, but the toroidal interpretation cannot b e ruled out. (C) 1999 Elsevier Science B.V. All rights reserved.