A class of topological defects in graphene was presented which consisred of a rotating sequence of dislocations that closed upon themselves, forming grain boundary loops that either conserved the number of atoms in the hexagonal lattice or accommodate vacancy or interstitial reconstruction, while leaving no unsatisfied bonds. One grain boundary loop was observed as a “flower” pattern in scanning tunneling microscopy studies of epitaxial graphene grown on SiC(00•1). It was shown that the flower defect has the lowest energy per dislocation core of any known topological defect in graphene, providing a natural explanation for its growth via the coalescence of mobile dislocations.

Grain Boundary Loops in Graphene. E.Cockayne, G.M.Rutter, N.P.Guisinger, J.N.Crain, P.N.First, J.A.Stroscio: Physical Review B, 2011, 83[19], 195425