Abstract：
Accurately determining local polarization at atomic resolution can unveil the mechanisms by which static and dynamical behaviors of the polarization occur, including domain wall motion, defect interaction, and switching mechanisms, advancing us toward the better control of polarized states in materials. In this work, we explore the potential of atomic-resolution scanning transmission electron microscopy to measure the projected local polarization at the unit cell length scale. ZnO and PbMg1/3Nb2/3O3 are selected as case studies, to identify microscope parameters that can significantly affect the accuracy of the measured projected polarization vector. Different STEM imaging modalities are used to determine the location of the atomic columns, which, when combined with the Born effective charges, allows for the calculation of local polarization. Our results indicate that differentiated differential phase contrast (dDPC) imaging enhances the accuracy of measuring local polarization relative to other imaging modalities, such as annular bright-field or integrated-DPC imaging. For instance, under certain experimental conditions, the projected spontaneous polarization for ZnO can be calculated with 1.4% error from the theoretical value. Furthermore, we quantify the influence of sample thickness, probe defocus, and crystal mis-tilt on the relative errors of the calculated polarization.
摘要：
以原子分辨率准确确定局域极化可以揭示极化发生的静态和动态行为的机制，包括畴壁运动，缺陷相互作用，和交换机制，推动我们更好地控制材料中的极化状态。在这项工作中,我们探索了原子分辨率扫描透射电子显微镜在晶胞长度尺度上测量投影局部极化的潜力。选择ZnO和PbMg1/3Nb2/3O3作为案例研究，识别显微镜参数，可以显着影响测量的投影偏振矢量的精度。不同的STEM成像模式用于确定原子柱的位置，which,当与Born有效指控相结合时，允许计算局部极化。我们的结果表明，微分相衬（dDPC）成像提高了测量局部偏振相对于其他成像方式的准确性。如环形明场或集成DPC成像。例如,在一定的实验条件下,可以计算出ZnO的投影自发极化，其理论值有1.4％的误差。此外，我们量化了样品厚度的影响，探针散焦，和晶体误倾斜对计算偏振的相对误差。
