Atomic-dipole-moment induced local surface potential on Si(111)-(7 × 7) surface studied by non-contact scanning nonlinear dielectric microscopy

We have performed the site-specific, quantitative measurement of a local surface potential induced by atomic dipoles on a Si(111)-(7 × 7) surface by non-contact scanning nonlinear dielectric microscopy (NC-SNDM) combined with an atom-tracking technique. The measured potentials were quantitatively consistent with those estimated by a simultaneous measurement of the tunneling current, which validates a previously proposed hypothetical mechanism that explains the unexpected resemblance between the dipole and time-averaged tunneling current images in NC-SNDM imaging. The results show that an asymmetry arising in the current-voltage characteristics within the tunneling regime is governed by the local surface potential induced by atomic dipoles.