Carbon Nanotubes: Electronic Structure and Physical Properties -- Update

Discovered in 1991, carbon nanotubes are molecules of pure carbon having the shape of a long, hollow cylinder with diameter in the nanometer range. More precisely stated, a nanotube is a cylindrical variety of graphite. A single-wall nanotube is just one atomic layer thick, that is, one seamless rolled-up graphene layer. Multiwall nanotubes are composed of several coaxial graphitic layers, with a separation distance of 0.34 nm. The electronic properties of a thick multiwall nanotube resemble those of graphite, which is semimetallic. Remarkably enough, a single-wall nanotube can be a metal or a semiconductor depending on its exact atomic structure. A metallic single-wall nanotube often conducts electrons ballistically, which means that electrons flow through it over long distances (micrometers) without collisions. A semiconducting single-wall nanotube has a band gap of about 0.6 eV, depending on its diameter.