Fully collapsed carbon nanotubes

IT has been suggested¹ that the tensile strength of carbon nanotubes² might exceed that of other known fibres because of the inherent strength of the carbon-carbon bond. Calculations of the elastic properties of nanotubes confirm that they are extremely rigid in the axial direction and are most likely to distort perpendicular to the axis^{3, 4}. Carbon nanotubes with localized kinks and bends^{5, 6}, as well as minor radial deformations^7'8, have been observed. Here we report the existence of multi-shelled carbon nanotubes whose overall geometry differs radically from that of a straight, hollow cylinder. Our observations reveal nanotubes that have suffered complete collapse along their length. Theoretical modelling demonstrates that, for a given range of tube parameters, a completely collapsed nanotube is favoured energetically over the more familiar 'inflated' form with a circular cross-section.