Atomic scale imaging of TiO₂(100) reconstructed surfaces by noncontact scanning nonlinear dielectric microscopy

We performed noncontact scanning nonlinear dielectric microscopy (NC-SNDM) measurements to investigate both the topography and polarization distribution images of a reconstructed TiO₂(100) surface. To acquire an atomic resolution image of the (110) surface, which is the most stable in TiO ₂, NC-SNDM requires annealing at a temperature higher than that for scanning tunneling microscopy (STM). However, in the case of the (100) surface, we found that annealing at the same temperature as that used for STM was sufficient. The two types of reconstructed surfaces were measured using NC-SNDM. We confirmed we could even achieve NC-SNDM measurements in a dielectric material by reducing the thickness of the specimen and making the specimen nonstoichiometric without any annealing. These results show that NC-SNDM has superb capabilities that STM does not have, including the capability to measure the topography and polarization distribution even in a dielectric material, by inducing polarization near the surface without any means of inducing conductivity.