Correlation of frequency shift discontinuity to atomic positionson a Si(111)7 × 7 surface by noncontact atomic forcemicroscopy

Abstract

We succeeded in obtaining site-dependent frequency-shiftcurves on an atomic scale as a function of the tip-sample surfacedistance between a clean Si(111)7×7 surface and a clean activeSi tip with a dangling bond using noncontact atomic force microscopy(NC-AFM). As a result, we found a discontinuous jump in thefrequency-shift curve measured above active Si adatoms with a danglingbond, in contrast to a continuous frequency-shift curve measured abovegaps between adjacent Si adatoms. These results suggest thepossibility that the NC-AFM can be developed into a kind ofspectroscopic tool, i.e. atomic force spectroscopy, which can measurethe three-dimensional force-related map with true atomic resolution.Furthermore, we succeeded in suppressing the discontinuous jump in thefrequency-shift curve by replacing the clean active Si tip apex with anoxidized inactive Si tip apex. This result suggests the possibilitythat we can control the interaction force between the tip and sampleatoms on an atomic scale by placing a suitable atom on the tip apex.