Three-dimensional observation of nano-scale ferroelectric domain using scanning nonlinear dielectric microscopy
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0902-T06-04.1
Three-dimensional observation of nano-scale ferroelectric domain using scanning nonlinear dielectric microscopy Yasuo Cho and Tomoyuki Sugihara Research Institute of Electrical Communication, Tohoku University 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan ABSTRACT Three-dimensional domain configuration of multi-domain LiTaO3 is revealed by Scanning Nonlinear Dielectric Microscopy (SNDM). SNDM can measure the polarization components both perpendicular and parallel to the surface of the specimen. These techniques are applied to the both congruent and stoichiometric LiTaO3 crystals. The images obtained by SNDM measurements allow us to confirm the various domain features of LiTaO3 and to understand both similarities and differences between the congruent and stoichiometric compositions.
INTRODUCTION Recently, ferroelectric materials have been applied to various purposes such as surface acoustic wave devices, quasi-phase matching (QPM) devices and ultrahigh-density data storage [1]. In these applications, it is necessary to evaluate the characteristic features of the materials. One of the most important evaluations is to investigate a domain configuration on the nanometer scale because the macroscopic features of ferroelectric-based devices are closely linked to the microscopic domain structure. With this background, there are various techniques to evaluate the ferroelectric domain structure on the basis of the scanning probe microscopy such as scanning nonlinear dielectric microscopy (SNDM), piezoelectric force microscopy [2] and scanning near-field optical microscopy [3]. In the field of microscope, a spatial resolution is quite important factor to distinguish the feature of the microscopy. SNDM has the highest sub-nanometer resolution in the field of microscope for observation of ferroelectric polarization distribution [4]. The basic function of SNDM is to measure the polarization component perpendicular to the surface of the specimen by detecting a nonlinear dielectric constant ε 333 (vertical measurement). Here, we define the z-axis (indicated by the suffix 3) as the polarization direction. Furthermore, it is also possible to measure the polarization component parallel to the surface of the specimen by detecting the nonlinear dielectric constant ε 311 (lateral measurement). In this experiment, these techniques were applied to investigate the domain structure of multi domain LiTaO3 with the both congruent and stoichiometric compositions. By imaging the z-cut plane and the x-cut plane of the multi domain LiTaO3, the apparent figures of the multi domain structures were revealed and interesting phenomena were observed.
PRINCIPLE OF THREE-DIMENSIONAL MEASUREMENT OF POLARIZATION DIRECTION BY SNDM In ferroelectric materials, the sign of the lowest-order component of a nonlinear dielectric
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