To confirm the performance of noncontact scanning nonlinear dielectric microscopy (NC-SNDM), we attempted to determine the local dipole moment of Si atoms on a cleaned Si (100) surface under UHV conditions. From the topography images, atomically flat terraces, step structures, and defects were clearly recognized, and paired bright spots with a 2×1 symmetry were observed with clear contrast. In addition, we observed the local electric dipole moment distribution of Si atoms on a 2×1 structure. This revealed that the surface is naturally biased with an offset potential of -0.2 V, and the direction of the local dipole moment is upward at dimer sites for bias values above -0.2 V.
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