Nanotube technology. Computer artwork of two interlinked cylindrical fullerenes (carbon nanotubes), which have been bent to form a circular torus shape. The hexagonal carbon structure of the nanotubes is shown here. 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.