Absolute measurement of three-dimensional polarization direction using scanning nonlinear dielectric Microscopy
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Absolute measurement of three-dimensional polarization direction using scanning nonlinear dielectric Microscopy Yasuo Cho, Tomoyuki Sugihara and Hiroyuki Odagawa Research Institute of Electrical Communication, Tohoku University 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan ABSTRACT A technique for measuring the absolute value of the ferroelectric polarization angle using scanning nonlinear dielectric microscopy (SNDM) is proposed and demonstrated. Using the technique, periodically poled lithium niobate (PPLN) with three-dimensional domain structure is observed. The measured polarization angles agreed well with the actual polarization orientations, and allowed precise visualization of the microdomain structure in PPLN. Through this experiment, we confirmed that SNDM is a useful tool for the absolute evaluation of the three-dimensional polarization direction.
INTRODUCTION Ferroelectric materials have been applied to various technologies including SAW devices, piezoelectric actuators and ultra-high density data storage systems [1]. As such, the development of high performance ferroelectric-based piezoelectric materials is a very important subject of research. For example, recently, a large piezoelectric response has been derived from engineered micro domain structures [2]. With this background, it is of primary importance to observe these micro domain structures to determine the physical properties of ferroelectric-based piezoelectric materials. Several researchers have reported various techniques to investigate the domain structure at the surface using scanning probe microscopy [3-13]. One of the most well-known methods for observing polarization distribution is piezoelectric response imaging [3-6]. This technique detects mechanical vibrations of the sample surface based on the piezoelectric response by application of an ac voltage to the tip of a conductive cantilever. In this method, however, measurement of the lateral polarization angle requires rotating the specimen several times to sample around the axis normal to the surface and rescanning the same area in order to evaluate the relative contributions of Px and Py, the lateral polarization components along the x-axis and y-axis, respectively. To provide a more useful method of observing the ferroelectric polarization distribution, we developed a type of Scanning Nonlinear Dielectric Microscopy (SNDM) that was the first successful, purely electrical method of observing the ferroelectric polarization distribution [7-9]. The resolution of this microscopy has been improved up to sub-nanometer order [10], exceeding the resolution of piezoimaging in resolution. [11] Conventional SNDM can measure the polarization component perpendicular to the surface by applying an electric field in the vertical direction. We have proposed and developed a lateral measurement system, which can measure the polarization component parallel to the surface without rotating the sample [12]. In this report, using both vertical and lateral measurements, we demonstrate the absolute me
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