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Structure and Dynamics of Ferroelectric Domains
Xiaoqing Pan
Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109
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 revealshow interfaces in complex multidomain geometries lead to the formation of polarization vorticeswith 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.
潘晓晴：1982年南京大学物理系本科毕业，1985年获得物理学硕士学位。1987年赴德国萨尔兰德大学学习和研究，1991年获得该校物理学博士，1991-96年为德国马普金属所博士后，1996-2003年为密西根大学材料科学与工程系副教授，2004年起升为教授，并且担任密西根大学电子微束分析实验室主任。长期从事电子显微学、薄膜生长、纳米结构、表面与界面、铁电性、超导性、智能催化等方面研究。近年来主要研究氧化物异质机构及其纳米材料的多铁性及其光电性能，在揭示新型纳米结构的铁电性、透明氧化物半导体特性、超导薄膜材料的结构与性能的关系等方面取得许多国际有重要影响的研究成果。 |
