Department of Condensed Matter Physics, Tokyo Institute of Technology, 2-12-1-H-51 Oh-okayama, Meguro-ku, Tokyo 152-8551, Japan.
Ultramicroscopy. 2013 Feb;125:43-8. doi: 10.1016/j.ultramic.2012.09.011. Epub 2012 Oct 8.
A through-focus series of annular bright field (ABF) images were observed simultaneously with high-angle annular dark field (HAADF) images of very thin lithium manganese oxide (LiMn₂O₄), a typical cathode material used in lithium ion batteries, using a spherical aberration corrected electron microscope with a 50 pm resolution (R005). The ABF images showed dark dips at the positions of Li and Mn--O atomic columns, which reversed to bright peaks when the defocus sign was changed, as commonly observed in phase contrast images. The optimal defocus for the ABF images was about 2 nm of over-focus, while that for the HAADF images was 2 nm of under-focus for an incident probe with a convergent semi-angle of 30 mrad. These experimental results are interpreted based on a weak-phase-object approximation.
采用分辨率为 50 pm（R005）的球差校正电子显微镜，对锂离子电池中常用的典型正极材料——超薄尖晶石型氧化锂锰（LiMn₂O₄）进行了高角环形暗场（HAADF）与环形明场（ABF）同步聚焦系列像的观察。ABF 图像显示，在 Li 和 Mn--O 原子列的位置有暗陷，改变离焦符号时，这些暗陷会反转成明亮的峰，这与相衬图像中常见的情况相同。ABF 图像的最佳聚焦约为 2nm 的过焦，而对于 HAADF 图像，对于会聚半角为 30mrad 的入射探针，最佳聚焦为 2nm 的欠焦。这些实验结果基于弱相位物体近似进行了解释。
