Catalytic effects of heavy metals on the growth of carbon nanotubes and nanoparticles

The effects of bismuth, lead, and tungsten on the cobalt-catalyzed synthesis of single-layer carbon nanotubes and nanoparticles have been studied. When co-vaporized with cobalt in an electric are, bismuth and lead increase the yield of single-layer nanotubes and broaden the range of tube diameters, compared to the case where only cobalt is used. Tungsten is found to reduce the nanotube yield and does not change the tube diameter distribution. Both tungsten and bismuth increase the graphitization of the carbon encapsulating the cobalt particles found in the soot, while lead does not. None of these three heavy metals catalyzes the formation of single-layer nanotubes without a transition metal present.