SEVERAL LARGE-SCALE SUPERPERIODICITIES ON HIGHLY ORIENTED PYROLYTIC-GRAPHITE OBSERVED BY SCANNING TUNNELING MICROSCOPY

On freshly cleaved highly oriented pyrolytic graphite we observed large-scale superperiodicities by a scanning tunneling microscope at room temperature in air. Several hexagonal superstructures with periods of 30 nm, 4.2 nm, 2.4 nm, and 2.0 nm, respectively, and a strip-like superstructure with a period of 1 nm were obtained. With exception of the largest hexagonal superperiodicity (30 nm spacing), all other superstructures are superimposed on the atomic corrugation of graphite. The origin of these superstructures is not clear vet. We assume that they arise from crystal defects in graphite. The hexagonal superstructure may be caused by the Moire effect due LO the rotational misorientation of the two top layers or of two successive layers near the surface.