Structure of polygonal defects in graphitic carbon sheets

Various polygonal defects which retain the three-bonded character of carbon are proposed as disclinations in graphitic carbon. The n-gonal defects, where n is an integer less than 5, are responsible for forming cones and are less stable than pentagonal defects in a hexagonal network which are responsible for forming spherical fullerenes such as C-60. On the other hand, the n-gonal defects, where n is greater than 6, correspond to negative wedge disclinations on the surface and leads to a negatively curved surface. Using molecular-dynamics simulations, it is found that the surfaces containing 10(deca)-, 11(hendeca)-, or 12(dodeca)-gonal defects are more stable than similarly shaped surfaces containing a multiple number of heptagons. It is also found that the surfaces which contain an n-gonal defect (with a large-n value) with a periodic folding of the surface are stable for some cases. The buckled surface with an 18(octadeca)-gonal defect in particular, which is rolling with surface distortions bending upward and downward three times around the defect, gives a stable structure. Our considerations indicate that complex structures not considered before could possibly exist. The relation of screw dislocations to polygonal defects, and their stability, are also studied.