Closed Line Of dislocations in graphene

Defects are valuables in materials science. They are purported to generate novel physics in unexpected ways. Low dimensional systems are more prone to defects. In graphene, structural defects can exist in zero or one D, called point defect or line defect, respectively. A line defect can have tremendous impact upon the transport properties of graphene. Very common is the dislocations. In this new work[PHYSICAL REVIEW B 83, 195425 (2011)], closed line of dislocations were observed. They look like flowers. They are topologically different from open dislocations. What kind of effects can be expected on electronic properties ? Let's see.

Topological defects can affect the physical properties of graphene in unexpected ways. Harnessing their influence may lead to enhanced control of both material strength and electrical properties. Here we present a class of topological defects in graphene composed of a rotating sequence of dislocations that close on themselves,
forming grain boundary loops that either conserve the number of atoms in the hexagonal lattice or accommodate vacancy or interstitial reconstruction, while leaving no unsatisfied bonds. One grain boundary loop is observed as a “flower” pattern in scanning tunneling microscopy studies of epitaxial graphene grown on SiC(0001).We show 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.