The angle-resolved electron scattering is investigated in scanning-transmission electron microscopy (STEM) using a motorised iris aperture placed above a conventional annular detector. The electron intensity scattered into various angle ranges is compared with simulations that were carried out in the frozen-lattice approximation. As figure of merit for the agreement of experiment and simulation we evaluate the specimen thickness which is compared with the thickness obtained from position-averaged convergent beam electron diffraction (PACBED). We find deviations whose strengths depend on the angular range of the detected electrons. As possible sources of error we investigate, for example, the influences of amorphous surface layers, inelastic scattering (plasmon excitation), phonon-correlation within the frozen-lattice approach, and distortions in the diffraction plane of the microscope. The evaluation is performed for four experimental thicknesses and two angle-resolved STEM series under different camera lengths. The results clearly show that especially for scattering angles below 50 mrad, it is mandatory that the simulations take scattering effects into account which are usually neglected for simulating high-angle scattering. Most influences predominantly affect the low-angle range, but also high scattering angles can be affected (e.g. by amorphous surface covering).

中文翻译：

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使用虹膜孔径的角度分辨 STEM：Si 中定量分析的散射贡献和误差来源

在扫描透射电子显微镜 (STEM) 中使用放置在传统环形检测器上方的电动虹膜孔径研究角度分辨电子散射。将散射到不同角度范围内的电子强度与在冻结晶格近似中进行的模拟进行比较。作为实验和模拟一致性的品质因数，我们评估样品厚度，并将其与从位置平均会聚束电子衍射 (PACBED) 获得的厚度进行比较。我们发现偏差的强度取决于检测到的电子的角度范围。作为可能的误差来源，我们研究了无定形表面层的影响、非弹性散射（等离子体激发）、冻结晶格方法中的声子相关性、和显微镜衍射平面的畸变。评估是在不同相机长度下对四种实验厚度和两种角度分辨 STEM 系列进行的。结果清楚地表明，特别是对于低于 50 mrad 的散射角，模拟必须考虑散射效应，而这些效应通常在模拟高角散射时被忽略。大多数影响主要影响低角度范围，但也会影响高散射角度（例如，通过无定形表面覆盖）。模拟必须考虑散射效应，这些效应通常在模拟高角度散射时被忽略。大多数影响主要影响低角度范围，但也会影响高散射角度（例如，通过无定形表面覆盖）。模拟必须考虑散射效应，这些效应通常在模拟高角度散射时被忽略。大多数影响主要影响低角度范围，但也会影响高散射角度（例如，通过无定形表面覆盖）。