Crystalline ropes of metallic carbon nanotubes

Abstract

Fullerene single-wall nanotubes (SWNTs) were produced in yields of more than 70 percent by condensation of a laser-vaporized carbon-nickel-cobalt mixture at 1200°. X-ray diffraction and electron microscopy showed that these SWNTs are nearly uniform in diameter and that they self-organize into 'ropes,' which consist of 100 to 500 SWNTs in a two-dimensional triangular lattice constant of 17 angstroms. The x-ray form factor is consistent with that of uniformly charged cylinders 13.8 ± 0.2 angstroms in diameter. The ropes were metallic, with a single-rope resistivity of <10-4 ohm- centimeters at 300 kelvin. The uniformity of SWNT diameter is attributed to the efficient annealing of an initial fullerene tubelet kept open by a few metal atoms; the optimum diameter is determined by competition between the strain energy of curvature of the graphene sheet and the dangling-bond energy of the open edge, where growth occurs. These factors strongly favor the metallic (10,10) tube with C(5v) symmetry and an open edge stabilized by triple bonds.