Ring formations from catalytically synthesized carbon nanotubes

Rings of typically 0.5 μm diameter have been observed with the atomic force microscope and the scanning electron microscope in carbon nanotube deposits produced catalytically by thermal decomposition of hydrocarbon gas. The carbon nanotubes are predominantly multiwalled with an average thickness of 20 nm, which is the typical thickness of the rings as well. The observations 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 be interpreted as single turn coils with a short overlap between the beginning and end of the coiled nanotube, but the toroidal interpretation cannot be ruled out.