Ferroelectric domains and domain boundaries observed by scanning force microscopy

Splitting of ferroelectric crystals into domains is a bulk phenomenon. However, many investigation methods rely on observations of intersections of domains or domain boundaries with crystal surfaces. Among them scanning force microscopy promises to be one of the most powerful. In this paper we discuss the different modes of operating the scanning force microscope in order to obtain a contrast between domains with antiparallel polarization. TGS has been chosen as a model material both for its suitable cleavage properties and the wealth of previous knowledge about its domain properties. We have found that antiparallel domains - identified by their lenticular shape - are discernible in both the non-contact mode and the friction force mode of imaging. We offer explanation of the origin of contrast, taking into account forces of topographic origin and those connected with spontaneous polarization. Higher resolution studies made it even possible to evaluate the upper limit of the domain wall thickness at the sample surface : the measured value of 8 nm lies considerably below previous estimations which concern crystal bulk. On the other hand, two neighbouring antiparallel domains cannot be revealed in the contact force mode of operation, indicating that they are terminated by one and the same atomically flat plane. Additionally, contact images are found to reflect the history of the TGS crystal surface.