A CURRENT IMAGING TUNNELING SPECTROSCOPY STUDY OF LOCALIZED STATES ATTHE FERMI-LEVEL ON CIRCULAR PIT EDGES IN GRAPHITE

Thermal oxidation of the (0001) basal plane of highly oriented pyrolit ic graphite leads to the removal of monoatomic carbon layers from the surface and to the formation of circular pits and steps on the exposed plane. Scanning tunneling microscopy and current imaging tunneling sp ectroscopy are used to study a localized surface state at the Fermi le vel on the circular edges of the pit. The surface state appears as the maximum of the local density of states at 10-50 meV below the Fermi l evel. The appearance of the state does not depend on the orientation o f the step. The explanation for this effect includes the superposition of the two different surface states. The first one is due to the exis tence of an edge in the graphite sheet. The second one is due to fused disclination centers caused by mechanical deformations on the terrace .