Nanometer-scale observation of ferroelectric domains using an apertureless near-field optical microscope

Optical observation of the polarization domain structure of a ferroelectric material (triglycine sulfate) is achieved using a reflection apertureless near-field optical microscope operating with an electrical ac polarization of the tip. By showing that there is no detectable contribution of the converse piezoelectric effect of the sample nor of the electrical forces acting on the tip in the optical signal detected, we explain the observed contrast between domains of opposite polarity by the electro-optic effect. Using the phase of the demodulated optical signal, we image the ferroelectric domain structure with a resolution better than 35 nm.