Radić Dražen, Hilke Sven, Peterlechner Martin, Posselt Matthias, Wilde Gerhard, Bracht Hartmut
University of Münster, Institute of Materials Physics, 48149Münster, Germany.
Helmholtz-Zentrum Dresden-Rossendorf, 01328Dresden, Germany.
Microsc Microanal. 2020 Dec;26(6):1100-1109. doi: 10.1017/S143192762002440X.
Variable-resolution fluctuation electron microscopy (VR-FEM) data from measurements on amorphous silicon and PdNiP have been obtained at varying experimental conditions. Measurements have been conducted at identical total electron dose and with an identical electron dose normalized to the respective probe size. STEM probes of different sizes have been created by variation of the semi-convergence angle or by defocus. The results show that defocus yields a reduced normalized variance compared to data from probes created by convergence angle variation. Moreover, the trend of the normalized variance upon probe size variation differs between the two methods. Beam coherence, which affects FEM data, has been analyzed theoretically using geometrical optics on a multi-lens setup and linked to the illumination conditions. Fits to several experimental beam profiles support our geometrical optics theory regarding probe coherence. The normalized variance can be further optimized if one determines the optimal exposure time for the nanobeam diffraction patterns.
在不同实验条件下，已获得了关于非晶硅和钯镍磷的可变分辨率波动电子显微镜（VR-FEM）测量数据。测量是在相同的总电子剂量下进行的，并且电子剂量相对于各自的探针尺寸进行了归一化处理。通过改变半会聚角或散焦来创建不同尺寸的扫描透射电子显微镜（STEM）探针。结果表明，与通过改变会聚角创建的探针数据相比，散焦产生的归一化方差更小。此外，两种方法在探针尺寸变化时归一化方差的趋势有所不同。利用几何光学在多透镜装置上对影响波动电子显微镜数据的束相干性进行了理论分析，并将其与照明条件联系起来。对几种实验束轮廓的拟合支持了我们关于探针相干性的几何光学理论。如果确定纳米束衍射图案的最佳曝光时间，则归一化方差可以进一步优化。
