Characteristics of the (√3 x √3)R30° superstructure of graphite by scanning tunneling microscopy

The bias-voltage- and the tunneling-current-dependent scanning tunneling microscopy (STM) images of the (root 3 x root 3)R30 degrees superstructure of graphite formed near defects produced by Ar+-irradiation on highly oriented pyrolytic graphite annealed at 1373 K were investigated. The root 3 x root 3)R30 degrees superstructure of graphite is gradually changed to a triangular structure and the area of the superstructure becomes smaller with increasing bias voltage or decreasing tunneling current, namely, with increasing tip-sample distance. This result indicates that the STM image of the (root 3 x root 3)R30 degrees superstructure of graphite mainly depends on the tip-sample distance. It is suggested that the electronic superstructure induced by the defects on the surface of graphite decays faster than the electronic structure of normal graphite in vacuum.