Wu Lijun, Meng Qingping, Zhu Yimei
Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, USA.
Condensed Matter Physics and Materials Science Division, Brookhaven National Laboratory, Upton, New York 11973, USA.
Ultramicroscopy. 2020 Dec;219:113095. doi: 10.1016/j.ultramic.2020.113095. Epub 2020 Aug 26.
Recent advancement in aberration correction and detector technology opened a door to various applications using 4D-STEM, which yields a diffraction pattern for each scanning position within a crystal unit-cell in scanning transmission electron microscopy (STEM) and generates incredible amounts of data in momentum space. Currently 4D-STEM analysis relies on the center-of-mass of the diffraction patterns in electric field and charge density mapping. It only derives the total projected charge density and is limited to phase objects, e.g. extremely thin samples. Here, we propose a new analytical method to accurately map aspherical valence electron distributions with atom-centered multipolar functions formalism using the whole 4D-STEM dataset. We demonstrate that, with the full dynamical calculations for various sample thicknesses, the method is sensitive not only to the miniscule charge transfer, but also to the atomic site symmetry and aspherical electron orbitals. The process of the refinement is much more robust and reliable than quantitative convergent beam electron diffraction.
像差校正和探测器技术的最新进展为使用4D-STEM的各种应用打开了一扇门，4D-STEM在扫描透射电子显微镜（STEM）中为晶体晶胞内的每个扫描位置产生一个衍射图案，并在动量空间中生成大量数据。目前，4D-STEM分析依赖于电场和电荷密度映射中衍射图案的质心。它只能得出总投影电荷密度，并且仅限于相位物体，例如极薄的样品。在这里，我们提出了一种新的分析方法，使用整个4D-STEM数据集，以原子中心多极函数形式精确映射非球形价电子分布。我们证明，通过对各种样品厚度进行全动态计算，该方法不仅对微小的电荷转移敏感，而且对原子位置对称性和非球形电子轨道也敏感。与定量会聚束电子衍射相比，细化过程更加稳健和可靠。
