Imaging domains in BaTiO₃ single crystal nanostructures: comparing information from transmission electron microscopy and piezo-force microscopy

摘要

This article compares and contrasts information obtained, using transmission electron microscopy (TEM) and piezo-force microscopy (PFM), on domain configurations adopted in single crystal lamellae of BaTiO₃, that had been cut directly from bulk using a focused ion beam microscope with top and bottom surfaces parallel to {100}_pseudocubic. Both forms of imaging reveal domain walls parallel to {110}_pseudocubic, consistent with sets of 90° domains with dipoles oriented parallel to the two _pseudocubic directions in the plane of the lamellae. However, the domain width was observed to be dramatically larger using PFM than it was using TEM. This suggests significant differences in the surface energy densities that drive the domain formation in the first place, that could relate to differences in the boundary conditions in the two modes of imaging (TEM samples are imaged under high vacuum, whereas PFM imaging was performed in air). Attempts were made to map local dipole orientations directly, using a form of ‘vector’ PFM. However, information inferred was largely inconsistent with the known crystallography of the samples, raising concern about the levels of care needed for accurate interpretation of PFM images.