Atomic-scale insights into the origin of rectangular lattice in nanographene probed by scanning tunneling microscopy

We conducted atomic-scale scanning tunneling microscopy of a graphene nanosheet on graphite. In addition to rhombus lattice representing the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R{30}^{\ensuremath{\circ}}$ superstructure, we resolved another quadrangle similar rectangle in sheet. Its size was approximately $0.37\ifmmode\times\else\texttimes\fi{}0.22\phantom{\rule{0.16em}{0ex}}\mathrm{n}{\mathrm{m}}^{2}$. To clarify origin this unique rectangular lattice, overlap $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ superstructures along direction their long diagonals theoretically examined using simple model. The electron distribution with high energy occupied states armchair-edged nanoribbons (AGNRs) calculated based first principles. A resembling one observed experimentally, found form AGNR under specific width condition. This finding also analyzed terms Clar's theory and scattering waves. propose that wrinkles adsorbates play role an armchair edge, resulting phase. If these local defects are close proximity, phases interact generate electronic structures predicted for AGNRs. is probably reason why imaged sheet not ideal AGNR.