Simultaneous measurement of tunneling current and atomic dipole moment on Si(111)-(7 × 7) surface by noncontact scanning nonlinear dielectric microscopy

Abstract

Non-contact scanning nonlinear dielectric microscopy (NC-SNDM) can resolve the topography and dipole moment distribution of a Si(111)-(7 × 7) surface on an atomic level. We discuss the origin of the atomic contrast in dipole moment images based on simultaneously acquired time-averaged tunneling current images. The dipole moment images are found to have the same characteristics as the simultaneously acquired current images. This similarity between these two images does not originate from circuit crosstalk since it is suppressed by our circuit design that decouples the tip-sample capacitance and the tunneling current. Constant-height images also indicate that the atomic contrast is not artificially caused by feedback crosstalk. These results suggest that the atomic contrast is due to the variation in the tip-sample capacitance caused by modulation of atomic dipole moments by the local density of states of the surface.