The folding and tearing of graphitic sheets followed well-defined patterns which seemed to be governed by the formation of sp3-like line defects in the sp2 graphitic network. Studies involving atomic force microscopy and scanning tunneling microscopy revealed that these folds and tears occurred preferentially along the symmetry axes of graphite, and that ‘ripples’ were observed in the curved portions of the folds. Ripples were also seen in deformed carbon nanotubes. They lay along the directions for which sp3-like line defects could form most easily in order to relieve strain. The ab initio molecular orbital calculations indicated that the ripples stabilized the π-electronic energy in the bent structures, with the total energy balance being determined by the amount of nuclear repulsion. These results provided insight into the geometries that graphitic structures would preferentially accommodate, and the properties that might result.

Role of sp3 Defect Structures in Graphite and Carbon Nanotubes. H.Hiura, T.W.Ebbesen, J.Fujita, K.Tanigaki, T.Takada: Nature, 1994, 367[6459], 148-51