报告人：潘晓晴，密歇根大学

报告时间：6月15日上午10：00－11：30

报告地点：清华大学材料院学术报告厅（逸夫技术科学楼2－321）

报告题目：Structure and Dynamics of Ferroelectric Domains

报告摘要：The ability of an electric field to switch the spontaneous polarization in a crystal between energetically degenerate states is the defining characteristic of a ferroelectric and provides the underlying storage mechanism in an important class of nonvolatile memories. This switchable polarization couples with electronic transport properties, surface chemistry, strain, and magnetic order, enabling multifunctional devices. Domain motion and stability is influenced by defects within the ferroelectric as well as by electrical and mechanical boundary conditions. Dislocations, for example, are known to destroy ferroelectric order; neighboring grains and interfaces subject the ferroelectric to localized strain, electric fields, or the screening of electric fields. As advances in ferroelectric synthesis have enabled ferroelectric materials to be integrated with other functionalities with atomic precision, understanding the ferroelectric switching in such increasingly complex structures has come to the fore, requiring improvements in both theory and characterization. In this talk we show that the atomic scale polarization map in ferroelectrics can be determined using aberration-corrected transmission electron microscopy (TEM) owing to the large atomic displacements responsible for the dipole moment. This study reveals how interfaces in complex multidomain geometries lead to the formation of polarization vortices with electric flux closure domains. Using aberration-corrected transmission electron microscopy (TEM) in combination with in-situ scanning probing holder the kinetics and dynamics of ferroelectric switching is followed at millisecond temporal and sub-angstrom spatial resolution. We directly observe localized nucleation events at the interface, domain wall pinning on point defects, and the formation of metastable ferroelectric states localized to the ferroelectric and ferromagnetic interface. These results show how defects and interfaces impede full ferroelectric switching of a thin film.