Structural defects in epitaxial graphene layers synthesized on C-terminated 4H-SiC (0001¯) surface—Transmission electron microscopy and density functional theory studies

Abstract

The principal structural defects in graphene multilayers synthesized on the carbon-terminated face of a 4H-SiC (0001¯) substrate were investigated using the high-resolution transmission electron microscopy. The analyzed systems include a wide variety of defected structures such as edge dislocations, rotational multilayers, and grain boundaries. It was shown that graphene layers are composed of grains of the size of several nanometres or larger; they differ in a relative rotation by large angles, close to 30°. The structure of graphene multilayers results from the synthesis on a SiC (0001¯) surface, which proceeds via intensive nucleation of new graphene layers that coalesce under various angles creating an immense orientational disorder. Structural defects are associated with a built-in strain resulting from a lattice mismatch between the SiC substrate and the graphene layers. The density functional theory data show that the high-angular disorder of AB stacked bi-layers is not restoring the hexagonal symmetry of the lattice.