ELECTRONIC EFFECTS IN SCANNING-TUNNELING-MICROSCOPY - MOIRE PATTERN ON A GRAPHITE SURFACE

We observed by scanning tunneling microscopy (STM) a hexagonal superla ttice on graphite with a period of 66 angstrom. Direct measurement of the angle between lattice vectors confirmed that the superlattice is a Moire pattern caused by a 2.1-degrees rotation of the topmost (0001) plane with respect to the bulk. The STM corrugation of 2.6 angstrom is not due to physical buckling, but to differences in electronic struct ure between AA-stacked, normal AB-stacked, and rhombohedral CAB-stacke d graphite. The high tunneling current of A A-stacked regions is in ag reement with the high density of states at the Fermi level calculated for A A graphite. The Moire pattern changes, both the amplitude and th e shape, with bias voltage. The observation provides a basis for a com parative study of surface electronic structures with different subsurf ace layer configuration, which is a vital test of our understanding of STM.