Li Zhongbo, Biskupek Johannes, Kaiser Ute, Rose Harald
Electron Microscopy Group of Materials Science, University of Ulm, Ulm89081, Germany.
Microsc Microanal. 2022 Mar 7:1-11. doi: 10.1017/S1431927622000289.
The integrated differential phase contrast (IDPC) method is useful for generating the potential map of a thin sample. We evaluate theoretically the potential of IDPC imaging for thick samples by varying the focus at different sample thicknesses. Our calculations show that high defocus values result in enhanced anisotropy of the contrast transfer function (CTF) and uninterpretable images, if a quadrant detector is applied. We further show that applying a multi-sector detector can result in an almost isotropic CTF. By sector number-dependent calculations for both Cc/C3-corrected and C3-corrected scanning transmission electron microscopy (STEM), we show that the increase of detector sectors not only removes the anisotropy of the CTF, but also improves image contrast and resolution. For a proof-of-principle IDPC-STEM (uncorrected) experiment, we realize the functionality of a 12-sector detector from a physical quadrant detector and demonstrate the improvement in contrast and resolution on the example of InGaN/GaN quantum well structure.
积分差分相衬（IDPC）方法对于生成薄样品的电位图很有用。我们通过在不同样品厚度下改变焦点，从理论上评估了IDPC成像对厚样品的适用性。我们的计算表明，如果使用象限探测器，高散焦值会导致对比度传递函数（CTF）的各向异性增强以及图像无法解读。我们进一步表明，应用多扇区探测器可导致几乎各向同性的CTF。通过对Cc/C3校正和C3校正的扫描透射电子显微镜（STEM）进行与扇区数量相关的计算，我们表明探测器扇区数量的增加不仅消除了CTF的各向异性，还提高了图像对比度和分辨率。对于原理验证的IDPC-STEM（未校正）实验，我们从物理象限探测器实现了12扇区探测器的功能，并以InGaN/GaN量子阱结构为例展示了对比度和分辨率的提高。
