Atomic Resolution Studies on Surface Dipoles by Noncontact Scanning Nonlinear Dielectric Microscopy and Potentiometry

Noncontact scanning nonlinear dielectric microscopy (NC-SNDM) is a microwave-based scanning probe microscopy method detecting the variation in the tip-sample capacitance. By detecting the second order nonlinear effect in dielectric polarization, this method enables imaging spontaneous polarization in materials. Although dielectric polarization is a material property formulated in a somewhat macroscopic sense, a series of the measurement results on cleaned semiconductor surfaces suggest that atomic-scale polarization, or atomic dipoles, can be resolved by NC-SNDM. Here we review unique capability of this method and mention its significance in solid state and surface physics. We also explain a novel extension of NC-SNDM, called noncontact scanning nonlinear dielectric potentiometry (NC-SNDP), and its application to the nanoscale evaluation of two-dimensional materials. The results reviewed here show that these methods will be tools for the atomic-scale investigation of surface and interface charge states even in a quantitative way.