Carbon and metals: a path to single-wall carbon nanotubes

Adding metals to carbon vapor leads to the formation of a rich variety of molecular structures. Examples include endohedral fullerenes, metallocarbohedrenes, metal-carbide nanocrystallites and perhaps most spectacularly, single-wall carbon nanotubes (SWNT). We discovered that pure carbon SWNT catalytically self-assemble when cobalt is covaporized with carbon in a fullerene generator. Third elements added to the metal and carbon can have important effects. Sulfur and bismuth can greatly increase the production efficiency of SWNT, leading to aggregation of SWNT into nanotube bundles or ropes, and can significantly extend the tube diameter distribution. Tubes larger than 5 nm were produced and S increased the mean tube diameter by similar to60%. A different type of 'third atom' effect was recently found at Virginia Tech: adding nitrogen to a scandium/carbon vapor leads to the formation of Sc3N@C-80, a new type of endohedral fullerene. Erbium can substitute for any of the scandium atoms and we have measured the emission spectra and lifetimes of ErmSc3-mN@C-80 (m = 1-3). These were the first emission lifetime measurements reported for light coming from species trapped inside fullerenes. (C) 2002 Elsevier Science B.V. All rights reserved.