Crystalline Ropes of Metallic Carbon Nanotubes

TLDR

SWNT diameter uniformity arises from annealing of fullerene tubelets with metal atoms, balancing curvature strain and dangling‑bond energy at the growth edge. SWNTs were synthesized by laser‑vaporizing a carbon‑nickel‑cobalt mixture at 1200 °C, yielding >70 %. The SWNTs form uniform‑diameter ropes of 100–500 tubes arranged in a 17‑Å triangular lattice, exhibit metallic conductivity with single‑rope resistivity below 10⁻⁴ Ω·cm at 300 K, and are dominated by (10,10) C5v tubes stabilized by triple‑bonded open edges.

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 1200degreesC. 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 with a 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 C5v symmetry and an open edge stabilized by triple bonds.