Majert S, Kohl H
Physikalisches Institut und Interdisziplinäres Centrum für Elektronenmikroskopie und Mikroanalyse (ICEM), Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
Physikalisches Institut und Interdisziplinäres Centrum für Elektronenmikroskopie und Mikroanalyse (ICEM), Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany.
Ultramicroscopy. 2015 Jan;148:81-86. doi: 10.1016/j.ultramic.2014.09.009. Epub 2014 Oct 8.
Differential phase contrast is a contrast mechanism that can be utilized in the scanning transmission electron microscope (STEM) to determine the distribution of magnetic or electric fields. In practice, several different detector geometries can be used to obtain differential phase contrast. As recent high resolution differential phase contrast experiments with the STEM are focused on ring quadrant detectors, we evaluate the contrast transfer characteristics of different quadrant detector geometries, namely two ring quadrant detectors with different inner detector angles and a conventional quadrant detector, by calculating the corresponding phase gradient transfer functions. For an ideal microscope and a weak phase object, this can be done analytically. The calculated phase gradient transfer functions indicate that the barely illuminated ring quadrant detector setup used for imaging magnetic fields in the specimen reduces the resolution limit to about 2.5Å for an aberration corrected STEM. Our results show that the resolution can be drastically improved by using a conventional quadrant detector instead.
差分相衬是一种可用于扫描透射电子显微镜（STEM）以确定磁场或电场分布的相衬机制。在实际应用中，可以使用几种不同的探测器几何结构来获得差分相衬。由于最近使用STEM进行的高分辨率差分相衬实验主要集中在环形象限探测器上，我们通过计算相应的相位梯度传递函数，评估了不同象限探测器几何结构的相衬传递特性，即两种具有不同内探测器角度的环形象限探测器和一种传统象限探测器。对于理想显微镜和弱相位物体，可以通过解析方法来完成此操作。计算得到的相位梯度传递函数表明，用于对样品中的磁场进行成像的几乎未被照亮的环形象限探测器设置，对于像差校正后的STEM，将分辨率极限降低到了约2.5埃。我们的结果表明，改用传统象限探测器可大幅提高分辨率。
