Carbon nanotube. Computer illustration showing the molecular structure of carbon nanotubes or buckytubes. Nanotubes are a type of fullerene molecule, a structural form (allotrope) of carbon whose atoms are arranged into interlinking hexagonal and pentagonal rings. Theoretically, a wide range of shapes can be engineered at the molecular level using fullerenes. Such structures could have a wide range of uses in nanotechnology. Atoms are represented as spheres.