Anomalous superperiodicity in scanning tunneling microscope images of graphite

An anomalously large periodicity has been observed in scanning tunneling microscope images of a (00.1) graphite sample. The unusual contrast has hexagonal symmetry, a periodicity of 7.7±0.2 nm and is superimposed on the usual a=0.246 nm atomic spacing of graphite. Current-voltage curves recorded in the scanning tunneling spectroscopy mode from the region showing the superperiodicity exhibit slightly more metallic behavior than those from neighboring normal regions. One possible explanation for the observed periodicity is that it is a rotational moiré pattern resulting from the overlap between a misoriented layer of graphite and the underlying graphite single crystal.