CARBON NANOTUBES WITH SINGLE-LAYER WALLS

Macroscopic quantities of single-layer carbon nanotubes have recently been synthesized by co-condensing atomic carbon and iron group or lant hanide metal vapors in an inert gas atmosphere. The nanotubes consist solely of carbon, sp(2)-bonded as in graphene strips rolled to form cl osed cylinders. The structure of the nanotubes has been studied using high-resolution transmission electron microscopy. Iron group catalysts , such as Co, Fe, and Ni, produce single-layer nanotubes with diameter s typically between 1 and 2 nm and lengths on the order of micrometers . Groups of shorter nanotubes with similar diameters can grow radially from the surfaces of lanthanide carbide nanoparticles that condense f rom the gas phase. if the elements S, Bi, or Pb (which by themselves d o not catalyze nanotube production) are used together with Co, the yie ld of nanotubes is greatly increased and tubules with diameters as lar ge as 6 nm are produced. Single-layer nanotubes are anticipated to hav e novel mechanical and electrical properties, including very high tens ile strength and one-dimensional conductivity. Theoretical calculation s indicate that the properties of single-layer tubes will depend sensi tively on their detailed structure. Other novel structures, including metallic crystallites encapsulated in graphitic polyhedra, are produce d under the conditions that lead to nanotube growth.