[20a-231A-1~10] 9.1 Dielectrics, ferroelectrics

△ [20a-231A-7] Orientational Correlation between Crystallographic Axis and Ferroelectric Domain Walls in Organic Ferroelectric Thin Films

〇(D)Yohei Uemura¹, Shunto Arai¹, Junya Tsutsumi², Satoshi Matsuoka¹, Reiji Kumai³, Sachio Horiuchi², Tatsuo Hasegawa^1,2 (1.U. Tokyo, 2.AIST FLEC, 3.KEK)

Keywords:organic ferroelectrics, electric field modulation spectrum, domain observation technique of ferroelectrics

Proton-transfer type organic ferroelectrics are novel ferroelectric materials whose spontaneous polarization derives from the order of protons in hydrogen bonds. They are expected to be key materials for the realization of ferroelectric devices with low-voltage operation due to their small coercive electric field (3 - 20 kV/cm). For the device application, it is essential to understand the motion of ferroelectric domain walls in thin films. We have developed a new optical technique to visualize ferroelectric domains named “ferroelectrics field modulation imaging (FFMI)”, which utilizes the change of optical spectrum induced by applied electric field. In contrast to piezoresponse force microscopy (PFM), FFMI can probe the domain structure in depth direction because FFMI detect the transmitted light. In this study, the three-dimensional structure of domain walls was observed by the comparison between FFMI and PFM. In addition, crystal orientation was determined by X-ray structure analysis in order to investigate the orientational correlation between crystallographic axis and ferroelectric domain walls. The result shows that the orientation of domain walls tends to be determined so as to minimize the free energy under the effect of molecular planes and array of hydrogen bonds.