Armchair nanotube

Armchair nanotube is one of the classifications of carbon nanotubes. Carbon nanotubes at the fundamental level are a single sheet of graphite (sp2 hybridization) that is rolled upon itself and connected at the edge. "Armchair" nanotubes correspond to the configuration with no 'twist' in the rolling. Thus, if you were to follow one of the bonds and make alternating left and right turns at the intersections, you would eventually come back to your starting position. In other configurations, following such would cause you to spiral up or down the nanotube following a trajectory more like that of a threaded rod.

One important peculiarity of isolated armchair nanotubes is that they are metallic, meaning that they are good electric conductors. This is in contrast with "zigzag" nanotubes, whose electric behavior is that of a semi-conductor.