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O: Oberflächenphysik

O 22: POSTER II

O 22.71: Poster

Mittwoch, 19. März 1997, 14:15–15:45, AULA

Anomalous superperiodic features observed on graphite in ultra high vacuum with scanning tunneling microscopy — •Jürgen Osing and Igor V. Shvets — Physics Department, Trinity College, Dublin 2, Ireland

An anomalous superperiodic structure (SPS) on highly oriented pyrolytic graphite (HOPG) has been studied using scanning tunneling microscopy (STM). To our knowledge this is the first observation of superperiodic features on the basal plane of graphite in ultra high vacuum (UHV).

The superlattice is of hexagonal symmetry with a periodicity of 82Å ± 4Å and is superimposed on the atomic graphite lattice. The atomic corrugation was measured to be ≈1.2Å, the superperiodic features have a smaller corrugation of 0.7 to 1 Å. These results are not consistent with a moiré pattern caused by the rotation of the surface layer with respect to the underlying bulk since the superperiodic features extend over three monatomic terraces. The superperiodic structures are not caused by a physical buckling on the graphite surface, they can be interpreted as a modulation of the surface charge density because STM images represent a map of the local density of states at surface and tip. The reported results are compared to previous studies on superperiodic features and it is explained why none of the proposed explanations can be applied here.