CRYSTALLINE ROPES OF METALLIC CARBON NANOTUBES

Fullerene single-wall nanotubes (SWNTs) were produced in yields of mor e than 70 percent by condensation of a laser-vaporized carbon-nickel-c obalt mixture at 1200 degrees C. X-ray diffraction and electron micros copy showed that these SWNTs are nearly uniform in diameter and thai t hey self-organize into ''ropes,'' which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice with a lattice constant of 17 an gstroms. The x-ray form factor is consistent with that of uniformly ch arged cylinders 13.8 +/- 0.2 angstroms in diameter. The ropes were met allic, with a single-rope resistivity of <10(-4) ohm-centimeters at 30 0 kelvin. The uniformity of SWNT diameter is attributed to the efficie nt annealing of an initial fullerene tubelet kept open by a few metal atoms; the optimum diameter is determined by competition between the s train energy of curvature of the graphene sheet and the dangling-bond energy of the open edge, where growth occurs. These factors strongly f avor the metallic (10,10) tube with C-5v symmetry and an open edge sta bilized by triple bonds.