原子尺度下BiFeO3薄膜中缺陷结构与特性的原位动态研究

BiFeO3(BFO), a well-known room temperature multiferroic with robust ferroelectric and magnetic order, shows its promise for memory applications, sensors and spin electronic devices. The utility of ferroelectrics is derived from a reversible transition between equivalent polar orientation states under an applied electric field （and/or stress）. This is especially important in ferroelectric memory devices scaled down to the nanometre scale to achieve a high data storage density where a single defect may dominate the total switching process. At this feature size, an understanding of the local response and underlying dynamic behaviour of individual domain walls and defects throughout the thickness of the film during the switching process is necessary to engineer reliable ferroelectric devices..Here we propose to use various advanced aberration corrected microscopy and spectroscopy to study the interface properties and dynamic correction between the ferroelectric/ferroeleastic and ferromagnetic domains switching in BiFeO3 thin films to gain insights into the effects of defects in multiferroic thin film heterostructures. Specifically, (1) applying atomic resolution imaging to characterize the atomic structure and quantitatively measure the octahedral distortion; (2) applying differential phase contrast imaging and aberration corrected Lorentz imaging to measure the localized electrical and magnetic fields; (3) by applying in situ electric fields (and/or stress) to switch the ferroelectric and ferroelastic domains, we simultaneously observe the changes of the domains, such as domain nucleation, domain wall propagation, defect pining to domain wall, and domain wall stability. These studies should greatly advance our understanding of the domain dynamics in multiferroic thin films and thereby providing useful information for interface engineering.

BiFeO3（BFO）铁电材料同时具有铁电、铁弹、反铁磁等多种性质，在数据存储、传感器、自旋电子器件方面具有巨大的应用前景。电偶极矩翻转的动力学过程是铁电材料和铁电器件中最为核心的问题。特别地，随着器件尺寸越来越小，单个缺陷的变化都会对器件性能产生不可忽视的影响。对于铁电薄膜材料，研究其缺陷的原子结构与物理性能，特别是外场下缺陷与铁电、铁弹、甚至铁磁畴在动力学上的关联，是我们理解铁电材料极化翻转过程的关键，也是我们改善铁电器件性能和设计新功能器件的前提。. 本项目拟在本单位新购置的球差矫正电镜的基础上，结合球差矫正和原位探测的透射电子显微学技术，利用原位外场（力场、电场）翻转铁电、铁弹、铁磁畴，并结合高能量分辨的电子能量损失振动谱等技术来研究铁电薄膜中的极化翻转与缺陷关联的动力学过程。提出导致铁电材料失效的关键因素，为提高器件性能和设计新功能器件提供依据。

过渡金属氧化物等低维材料中晶格、自旋、电荷等自由度之间的相互作用为实现磁电耦合提供了可能，在类脑计算、传感器、自旋电子器件方面有着巨大的应用前景。磁、电性能和其内部的畴结构以及原子结构息息相关，为了全面理解磁电耦合的机制，提高磁电耦合效率，深入研究材料微观结构，并实现对微观结构的调控至关重要。本项目基于先进透射电子显微镜的多种成像和谱学方法，系统研究了材料界面、畴和畴壁、晶界等微观结构，搭建了原位电学测试系统和原位力学测试系统，实现了对畴和畴壁的外场调控。首先，利用高空间分辨率的球差矫正电镜并结合图像定量化分析技术，研究了多个铁电材料中的微观结构，定量分析了界面、点缺陷、畴壁和晶界的原子结构。然后，基于原位电学和原位力学测试系统，实现了外电场和应力作用下的铁弹畴的可逆转变，并揭示了转变的原了尺度机理。另外，我们探究了透射电镜中的基于固态电解质的原位静电门控技术，揭示了材料的晶格、电荷、自旋与缺陷等相互作用，为铁电铁磁材料的研究提供更多的方法手段，为设计更高效的磁电相关器件提供了实验依据。本项目共发表标注了项目基金号(11904372)论文12篇，其中影响因子大于7的论文9篇，其中包括Infomat 1篇，Advanced Functional Materials 2篇，Small Methods1篇，Nano Research 1篇 ，Applied Physics Letters 1篇等，申请相关专利5项，研究进展入选第68届国际电子器件会议1篇。