We have synthesized single-layer carbon nanotubes by co-vaporizing cobalt with carbon in an arc fullerene
generator and have identified conditions that lead to high yields. The diameter distribution of the tubes and
their morphologies are studied using transmission electron microscopy. For nanotubes produced using cobalt
and carbon, the tube diameters range from 1 to 2 nm with distribution peaks at 1.3 and 1.5 nm. When sulfur
is added to the carbon and cobalt, production of single-layer nanotubes is enhanced and the tubes have a wider
range of diameters (from 1 to 6 nm). The diameter distribution for these nanotubes shows prominent peaks at 1.3 and 1.5 nm and additional maxima at 2.7 and 3.6 nm. Cobalt-containing crystallites, some encapsulated in graphitic polyhedra, are produced with the nanotubes and are found in the soot away from the cathode.