ABSTRACT
Graphene—a monolayer of covalently bonded carbon atoms—represents a new two-dimensional (2D) material with unique mechanical and physical properties, which are of utmost interest for a wide range of functional and structural applications. Pristine graphene has 2D ideal hexagonal crystal lattice with covalently bonded carbon atoms being located at its nodes. The structure and behavior of defects are sensitive to the form of graphene, which may exist as either a monolayer attached to substrates made of another material or freestanding sheets/membranes. Grain boundaries (GBs) in graphene by definition are line defects that separate graphene grains whose crystal lattices are misoriented relative to each other. Experimental observation of GBs in graphene specimens revealed low-angle tilt boundaries consisting of perfect dislocations, that is, 5–7 defects in hexagonal lattice of graphene. In hexagonal crystal lattice of graphene, pentagons and heptagons represent topological disclinations, that is, point defects associated with rotational symmetry.
