SITE-SELECTIVE IMAGING IN SCANNING-TUNNELING-MICROSCOPY OF GRAPHITE -THE NATURE OF SITE ASYMMETRY

In the absence of tip-sample mechanical interaction, graphite images s how very different behaviors from those of typical images. Contrary to the current interpretation of site asymmetry, where protrusions in im ages are considered as B-site atoms, we have found that one can select ively image A- or B-site atoms depending on the bias polarity. Further more, the corrugation amplitude is extremely small. If measurements ar e performed under tip-sample mechanical interaction, one observes larg er corrugations and in-phase images at opposite polarities. A new inte rpretation of site asymmetry is proposed.