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Crystalline Ropes of Metallic Carbon Nanotubes
 

Single-wall fullerene nanotubes (SWNT) have been produced in > 70% yield by
condensation of a laser-vaporized carbon/Ni/Co mixture at 1200oC. X-ray
diffraction and electron microscopy show that the SWNT are nearly uniform
in diameter and self-organize into "ropes" consisting of 100 to 500 SWNT in
a two-dimensional triangular lattice with a lattice constantof 17 angstroms
(Å). The x-ray form factor is consistent with uniformly charged cylinders
13.8 0.2 Å in diameter. The ropes were metallic (single-rope resistivity
10-4 Ohm-cm at 300 Kelvin). Uniformity of SWNT diameter is attributed to
efficient annealing of an initial fullerene tubelet kept open by a few
metal atoms, the optimum being determined by competition between the strain
energy of curvature of the graphene sheet and the dangling bond energy of
the open edge. These factors strongly favor the metallic C5V symmetry tube
(10,10) with an open growth edge stabilized by triple bonds.

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