Fullerene technology. Computer artwork of spherical and cylindrical fullerenes (buckyballs and carbon nanotubes), illustrating their hexagonal and (in the case of the buckyballs) pentagonal carbon structure. Fullerenes are a structural form (allotrope) of carbon. Theoretically, a wide range of molecular shapes can be engineered at the molecular level using fullerenes. Such structures are being investigated for a wide range of technological and medical uses. Here, the carbon nanotubes have been engineered to have a diameter just large enough to allow buckyballs to pass through them.