Origin of Anomalous Corrugation Height of STM Images of Graphite

To clarify the origin of the anomalous corrugation height of STM images of a graphite under a constant current mode, we carefully investigated the variation of the tunneling current and forces between the lever and graphite during lateral scans. In the case of an unoxidized Pt lever, the variations of the sample displacement, the lever deflections and the apparent corrugation height were almost independent of the measuring tunneling current. On the other hand, in the case of a slightly oxidized W lever, the variation of the sample displacement, the lever deflection and the apparent corrugation height increased with increasing tunneling current. We also found a tendency that for the W lever, an apparent corrugation height increases monotonously with the increase of the force variation. We concluded that the anomalous corrugation height of STM images of a graphite surface was enhanced by the oxide layer of the tunneling tip.