Field Modulation Imaging of Ferroelectric Domains in Molecular Single-Crystal Film

Yohei Uemura, Shunto Arai, Jun’ya Tsutsumi, Satoshi Matsuoka, Hiroyuki Yamada, Reiji Kumai, Sachio Horiuchi, Akihito Sawa, Tatsuo Hasegawa

Many hydrogen-bonded organic ferroelectrics exhibit low-field switching of large spontaneous polarizations. Although the switchable electric dipoles of π-conjugated organic molecules account for the large spontaneous polarizations, their relevant optoelectronic processes have not been used to probe the ferroelectricity. We show that the variation in electro-optic response enables visualization of the ferroelectric domains and domain walls in single-crystal films of a hydrogen-bonded molecular cocrystal. Highly sensitive and rapid visualization is realized by difference optical image sensing between the forward and reverse field applications. We call this technique “ferroelectrics field modulation imaging (FFMI).” The unique optical-probe nature reveals the existence of two types of domain walls showing different three-dimensional orientations within the films; one is roughly perpendicular to the film plane, whereas the other is considerably tilted from the normal to the plane. We explain that both of the domain walls are stabilized to generate substantial neutrality by being directed parallel to the direction of polarization. This study opens a route for exploring the three-dimensional topological nature of domain walls in ferroelectric materials.


Physical Review Applied: