Carbon nanotube, molecular model. This is a macromolecule made entirely of carbon atoms. Most carbon nanotubes are linear and composed of hexagons of carbon. The presence of pentagonal defects" in this structure has given the tube a spiral shape. Carbon nanotubes are a type of fullerene, large structures of carbon atoms which includes the spherical "buckyball", C60. These new materials have remarkable properties. Nanotubes act as semiconductors, which raises the possibility of using them in electronics. They are also extremely strong, and fibres made from nanotubes could find uses in materials and engineering."