SCANNING NONLINEAR DIELECTRIC POTENTIOMETRY: NEW STRATEGY FOR MESURING DIPOLE-INDUCED POTENTIALS IN ATOMIC SCALE Kohei Yamasue and Yasuo Cho Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan Presenting author: Yasuo Cho; yasuocho@riec.tohoku.ac.jp Scanning nonlinear dielectric microscopy (SNDM) has been utilized for imaging spontaneous polarization of a material surface in an atomic-scale 1-3 . Recently, this method has been extended to quantitatively measure potentials induced by spontaneous polarization or permanent dipoles 4 . This extension, called scanning nonlinear dielectric potentiometry (SNDP), is, unlike Kelvin probe force microscopy (KPFM), selectively sensitive to potentials induced by spontaneous polarization rather than those by monopole charges and contact potential differences (CPDs). The feasibility of this method is demonstrated by measuring a Si(111)-(7×7) surface and monolayer graphene on a SiC substrate in atomic resolution. The strategy to measure polarization-induced potentials is to find a dc reference voltage such that the dielectric response of a material surface is symmetric about the deviation from the dc reference. As long as polarization exists on a surface area, the local dielectric response on the area remains asymmetric about the deviation. Conversely, if spontaneous polarization is effectively cancelled by an oppositely-oriented polarization induced by the dc reference field, the response becomes symmetric. The dc voltage to establish the symmetric response gives the polarization-induced potential. In the SNDP method, the existence of asymmetry is detected by measuring the 2nd-order nonlinear response to a sinusoidal modulation field, which results in the emergence of a 1st-order harmonic variation in tip- sample capacitance (∂C/∂V). By using feedback technique for keeping ∂C/∂V at zero while the lateral scan of the surface, a two-dimensional potential map can be acquired. Although SNDP is similar with KPFM in that both use ac field modulation and dc-bias feedback, but they are quite different in the sensitivity to monopole surface charges and CPDs. Since KPFM detects an electrostatic force between the tip and sample, KPFM is sensitive to all of CPDs, monopole charges, and polarization-induced potentials, which generate electric fields between the tip and the surface. In contrast, SNDP does not have sensitivity to CPDs nor monopole charges, because CPDs does not induce ∂C/∂V and the charge-induced polarization is ideally zero in the measurement. In more detail, if a monopole surface charge exists, the electric field from the charge penetrates into the sample and thus induces polarization. The induced polarization cannot be distinguished from spontaneous polarization in general. However, as the tip gets closer to the charge, the electric field in the gap becomes larger but that in the sample smaller, since the tip-sample capacitance becomes much larger than the sample’s capacitance. Ideally, the field exists only in the gap and thus no polarization is induced in the material when the tip is placed near the surface. Since spontaneous polarization or permanent dipoles on surfaces and interfaces are important in understanding electronic structures, transport, and related characteristics, SNDP will be a useful technique to quantitatively evaluate electronic materials and devices. References 1) Y. Cho and R. Hirose, Phys. Rev. Lett. 99, (2007) 186101. 2) D. Mizuno, K. Yamasue, and Y. Cho, Appl. Phys. Lett. 103, (2013) 101601. 3) M. Suzuki et al., Appl. Phys. Lett. 105, (2014), 101603. 4) K. Yamasue and Y. Cho, (under review).