Birefringent Field-Modulation Imaging of Transparent Ferroelectrics

Abstract

Observations of ferroelectric domains and domain walls are essential for understanding ferroelectric switching characteristics. Here, we demonstrate that the use of optical birefringence, coupled with a first-order electro-optic effect (Pockels effect), allows the visualization of ferroelectric domains in transparent ferroelectric materials. We utilize a field-modulation imaging technique, with the use of a complementary metal-oxide-semiconductor (CMOS) area image sensor to detect slight differences in parallel- and crossed-Nicols polarized optical microscopy images between forward- and reverse-electric-field applications. The ferroelectric domains with antiparallel polarizations are clearly discriminated from each other by the sign of the ellipticity modulation of outgoing elliptically polarized light. The observed images are consistent with piezoresponse force microscopy images of transparent single-crystal films of 2-methylbenzimidazole (MBI). The modulation signal at both polarization configurations exhibit clear sign changes in the wavelength dispersion, owing to the anisotropic nature of the MBI films. The unique optical-probe nature also reveals the existence of two types of domain walls with different three-dimensional orientations.