报告题目：Probing the Structure and Dynamic Behaviors of Nanostructured Materials with Sub-Å Resolution in Real Time
报告人：潘晓晴教授
报告时间：2012年12月21日（周五）15:00-17:00
报告地点：电镜中心会议室（教十一125室）
邀请人：张 泽院士
报告摘要：
As advances in aberration-corrected transmission electron microscopy (TEM) have enabled the determination of the three-dimensional structure of nanostructures and defects with the sub-angstrom resolution, the recent development of in situ holders and environmental cells for TEM allows us to study the dynamic behaviors of materials under applied fields and environments while the atomic structure is imaged directly. In this talk I will show our atomic resolution TEM studies of precious-metal-doped perovskites for automotive exhaust treatment, using a novel gas-cell specimen holder within an aberration-corrected scanning transmission electron microscope. Our observations show that nanometer-scale metal particles tend to precipitate throughout the bulk of the perovskite upon reduction, and most of the metal that participates in the reversible process of metal precipitation/dissolution remain entirely within the perovskite matrix, where it is unavailable for gas-phase catalysis. However, this new understanding, based on recognition of the novel mechanism of self-stabilization, will help further development and eventual implementation of a more sustainable automotive catalyst technology in the future.
I will also show that the atomic scale polarization map in ferroelectrics can be determined using aberration-corrected TEM images 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 a customized in situ scanning probing holder the kinetics and dynamics of ferroelectric switching is followed at millisecond temporal and sub-angstrom spatial resolution in an epitaxial bilayer of an antiferromagnetic ferroelectric (BiFeO3) on a ferromagnetic electrode (La0.7Sr0.3MnO3). We observe localized nucleation events at the electrode interface, domain wall pinning on point defects, and the formation of metastable ferroelectric states localized to the ferroelectric and ferromagnetic interface. These studies show how defects and interfaces impede full ferroelectric switching of a thin film. This highlights the selective roles that specific defect types can play in ferroelectric switching, and illustrates in situ TEM as an ideal platform for their study.
