Koya Ohara

Higher-order nonlinear dielectric microscopy

A higher-order nonlinear dielectric microscopy technique with higher lateral resolution than conventional nonlinear dielectric imaging is investigated. The proposed scheme involves the measurement of higher-order nonlinear dielectric constants, with sensitivity to the first 0.75 nm in depth for LiNbO3 substrate surface. This technique is demonstrated to be very useful for observing surface layers of the order of unit cell thickness on ferroelectric materials.

Non-contact scanning nonlinear dielectric microscopy

Contact-type scanning nonlinear dielectric microscopy (SNDM) can measure the distribution of linear and nonlinear dielectric properties of insulators with sub-nanometre resolution. SNDM, however, has a tip-abrasion problem, and this problem is one of the obstacles in obtaining a high-quality image. In this paper, in order to improve SNDM, we propose a non-contact scanning nonlinear dielectric microscopy (NC-SNDM) which focuses on the nonlinear dielectric signal for controlling the non-contact condition. With the NC-SNDM technique, topographic and SNDM images were obtained successfully. Moreover, from the calculation results, it was confirmed that NC-SNDM has atomic-order sensitivity to the gap between the tip and the specimen.

Quantitative Measurement of Linear and Nonlinear Dielectric Characteristics Using Scanning Nonlinear Dielectric Microscopy

The theory for quantitative measurement of linear and nonlinear dielectric constants using scanning nonlinear dielectric microscopy is explained in this paper. Using this theory, quantitative measurements for linear and nonlinear dielectric constants of dielectric materials were performed successfully.

Observation of the Si(111)7 ? 7 atomic structure using non-contact scanning nonlinear dielectric microscopy

Non-contact scanning nonlinear dielectric microscopy (NC-SNDM) operated under ultra high vacuum (UHV) conditions was developed. This microscopy enables the simultaneous measurement of the topography and dielectric properties of a specimen. For electrically conductive materials, the tunnelling current is also measurable. The atomic structure of Si(111)7 × 7 was successfully resolved using this new SNDM technique. This is the first report on the achievement of atomic resolution in capacitance measurements.

Effect of the surface adsorbed water on the studying of ferroelectrics by scanning nonlinear dielectric microscopy

The effect of adsorbed water on the signal of scanning nonlinear dielectric microscopy (SNDM) is reported. By measuring SNDM image variation under various measurement conditions and by computing the theoretical SNDM signal corresponding to these conditions, we verified that the adsorbed water strongly affects the signal strength, depth sensitivity, and resolution of SNDM. From this study, we find that it is necessary to consider adsorbed water for detailed measurement of the surface polarization state by SNDM. In addition, we also confirmed that the surface paraelectric layer on a LiTaO3 single crystal grows upon heat treatment.

Quantitative Measurement of Linear Dielectric Constant Using Scanning Nonlinear Dielectric Microscopy with Electro-Conductive Cantilever

A quantitative measurement method of the linear dielectric constant using cantilever-type scanning nonlinear dielectric microscopy (SNDM) is reported. Using this method, we succeed in quantitatively measuring the linear dielectric constant distribution of TiO2–Bi2Ti4O11 ceramics with higher resolution than that obtained with needle-type SNDM.

Higher Order Nonlinear Dielectric Imaging Using Scanning Nonlinear Dielectric Microscopy

The higher order nonlinear dielectric imaging technique using scanning nonlinear dielectric microscopy (SNDM) is investigated. The resolution of the higher order nonlinear dielectric imaging is much higher than that of the conventional nonlinear dielectric imaging which detects the lowest order of the nonlinear dielectric constant. It is demonstrated that this higher order imaging is very useful for observing a surface layer with a unit cell scale thickness formed on ferroelectric material.

Theory of scanning nonlinear dielectric microscopy and application to quantitative evaluation

Abstract A theory for scanning nonlinear dielectric microscopy (SNDM) and its application to the quantitative evaluation of the linear and nonlinear dielectric constants of dielectric materials are described. A general theorem for the capacitance variation under an applied electric field is derived and a capacitance variation susceptibility Snl is defined. The results show that the sensitivity of the SNDM probe does not change, even if a tip with a smaller radius is selected to obtain a finer resolution and that SNDM has an atomic scale resolution. Using the theoretical results and the data taken by SNDM, the quantitative linear and nonlinear dielectric properties of several dielectric materials were successfully determined.

New Functions of Scanning Nonlinear Dielectric Microscopy —Higher-Order Measurement and Vertical Resolution—

We investigated new features (functions) of scanning nonlinear dielectric microscopy (SNDM), namely, higher-order nonlinear dielectric imaging and the very high vertical resolution. The resolution of the higher-order nonlinear dielectric imaging is higher than that of the conventional nonlinear dielectric imaging which detects the lowest order of the nonlinear dielectric constant. The very high vertical resolution of SNDM is also reported. These features of the SNDM enable us to obtain a new microscopy for measuring the topography or a new displacement sensor with extremely high sensitivity.

Fundamental Study of Surface Layer on Ferroelectrics by Scanning Nonlinear Dielectric Microscopy.

Distribution and growth of very thin surface layers on ferroelectric materials are investigated by scanning nonlinear dielectric microscopy. This microscopy technique involves the measurement of higher order nonlinear dielectric constants, with depth resolution down to one unit cell order. By changing the order of nonlinearity of the dielectric response, we obtain information about the surface layer on lead zirconate titanate (PZT) thin film and also observe the growth process of a surface paraelectric layer on LiNbO3 single crystal.