REVIEW ON GRAIN BOUNDARIES IN GRAPHENE. CURVED POLY- AND NANOCRYSTALLINE GRAPHENE STRUCTURES AS NEW CARBON ALLOTROPES

This article briefly summarizes the information now available, from recent experiments, computer simulations and theoretical models, addressing grain boundaries (GBs) in graphene. Special attention is devoted to the structures of GBs in hexagonal crystal lattice of graphene and their description in terms of such point defects as topological dislocations, pentagon-heptagon pairs. Papers are reviewed which deal with both energy characteristics of GBs in graphene and effects of GBs on its mechanical and transport properties. Geometric features of conventional curved carbon allotropes (fullerenes, cones, carbon nanotubes, etc.) and difference in structure between such allotropes and graphene are discussed in terms of topological disclinations (pentagons, heptagons). Also, it is suggested that the presence of GBs with specific defect configurations in graphene can cause formation of its new curved structures that can be treated as new carbon allotropes. Finally, important unsolved problems in fundamental science and applied research of GBs in graphene are outlined.