Observation and mobility study of single 180° domain wall using a near-field scanning optical microscope

We have made a direct and nanometer scale observation of single 180° domain walls in 500 μm thick ferroelectric LiTaO₃ by using a collection mode Near-Field Scanning Optical Microscope. We unambiguously identify single domain walls by simultaneously recording nanometer scale topographic and optical images. The polarization rotation of a linear polarized laser beam due to the birefringence at the domain wall is optically imaged with 80-100nm spatial resolution. Next we have made a direct nanometer scale study of the mobility of a single 180° domain wall under a uniform applied electric field using the same technique. The mobility of the domain walls is strongly influenced by sub-surface pinning defects.