Honeycomb superperiodic pattern and its fine structure near the armchair edge of graphene observed by low-temperature scanning tunneling microscopy

The local electronic structure near a graphene edge was investigated by scanning tunneling microscopy (STM) at low temperature. In addition to the presence of (root 3 x root 3)R30 degrees and honeycomb superperiodic patterns, a fine structure with threefold symmetry was discovered on the individual bright sites in the honeycomb pattern. Electron wave scattering occurring at an armchair edge was confirmed to be responsible for the honeycomb pattern. The fine structure in the honeycomb pattern can be explained by spatial distribution of the local density of states and the following overlap between the atomic orbital of carbon atom and that of STM-tip-end atom, resulting in the threefold-symmetric spatial variation in the tunneling current.