Using state-of-the-art classical and quantum simulations, a study was made of the mechanical and electronic response of carbon nanotubes to external deformations, such as strain and bending. In strained nanotubes, the spontaneous formation of double pentagon-heptagon defect pairs was observed. Tubes containing these defects were energetically preferred to uniformly stretched tubes at strains greater than 5%. These defects acted as nucleation centers for the formation of dislocations in the originally ideal graphitic network and constituted the onset of further deformations of the carbon nanotube. In particular, plastic or brittle behaviors could occur depending upon the external conditions and tube symmetry. Also investigated were the effects that the presence of ad-dimers had on strained carbon nanotubes. The main result was the formation of a new class of defects that wrapped themselves around the circumference of the nanotube. These defects were shown to modify the geometrical structure and to induce the formation of nanotube-based quantum dots. Transport properties were computed for various ideal and mechanically deformed carbon nanotubes. High defect densities were shown to affect greatly the transport in individual nanotubes, while small diameter bent armchair nanotubes maintained their basic electrical properties even in the presence of large deformations, with no defects involved.

Mechanical Properties, Defects and Electronic Behavior of Carbon Nanotubes. M.Buongiorno Nardelli, J.L.Fattebert, D.Orlikowski, C.Roland, Q.Zhao, J.Bernholc: Carbon, 2000, 38[11], 1703-11