We conducted atomic-scale scanning tunneling microscopy of a graphene nanosheet on graphite. In addition to a rhombus lattice representing the ( √ 3× √ 3)R30 • superstructure, we resolved another quadrangle lattice similar to a rectangle in the sheet. Its lattice size was approximately 0.37×0.22 nm 2 . To clarify the origin of this unique rectangular lattice, the overlap of the √ 3× √ 3 superstructures along the direction of their long diagonals was theoretically examined using a simple model.

more »

... he electron distribution with high energy in the occupied states of armchair-edged graphene nanoribbons (AGNRs) was calculated based on first principles. A rectangular lattice, resembling the one observed experimentally, was found to form on the AGNR under a specific width condition. This finding was also analyzed in terms of Clar's theory and the scattering of electron waves. We propose that wrinkles and adsorbates in graphene play a role similar to an armchair edge, resulting in the √ 3× √ 3 phase. If these local defects are in close proximity, the rhombus phases interact to generate electronic structures predicted for AGNRs. This is probably the reason why a rectangular lattice was imaged on the graphene sheet that is not an ideal AGNR.