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

We observed by scanning tunneling microscopy (STM) a hexagonal superlattice 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 structure between AA-stacked, normal AB-stacked, and rhombohedral CAB-stacked graphite. The high tunneling current of A A-stacked regions is in agreement with the high density of states at the Fermi level calculated for A A graphite. The Moire pattern changes, both the amplitude and the shape, with bias voltage. The observation provides a basis for a comparative study of surface electronic structures with different subsurface layer configuration, which is a vital test of our understanding of STM.