Martinez G T, Jones L, De Backer A, Béché A, Verbeeck J, Van Aert S, Nellist P D
Electron Microscopy for Materials Science (EMAT), University of Antwerp, Gronenborgerlaan 171, 2020 Antwerp, Belgium.
Department of Materials, Oxford University, Parks Road, Oxford OX1 3PH, United Kingdom.
Ultramicroscopy. 2015 Dec;159 Pt 1:46-58. doi: 10.1016/j.ultramic.2015.07.010. Epub 2015 Jul 31.
Annular dark-field (ADF) scanning transmission electron microscopy (STEM) has become widely used in quantitative studies based on the opportunity to directly compare experimental and simulated images. This comparison merely requires the experimental data to be normalised and expressed in units of 'fractional beam-current'. However, inhomogeneities in the response of electron detectors can complicate this normalisation. The quantification procedure becomes both experiment and instrument specific, requiring new simulations for the particular response of each instrument's detector, and for every camera-length used. This not only impedes the comparison between different instruments and research groups, but can also be computationally very time consuming. Furthermore, not all image simulation methods allow for the inclusion of an inhomogeneous detector response. In this work, we propose an alternative method for normalising experimental data in order to compare these with simulations that consider a homogeneous detector response. To achieve this, we determine the electron flux distribution reaching the detector by means of a camera-length series or a so-called atomic column cross-section averaged convergent beam electron diffraction (XSACBED) pattern. The result is then used to determine the relative weighting of the detector response. Here we show that the results obtained by this new electron flux weighted (EFW) method are comparable to the currently used method, while considerably simplifying the needed simulation libraries. The proposed method also allows one to obtain a metric that describes the quality of the detector response in comparison with the 'ideal' detector response.
环形暗场（ADF）扫描透射电子显微镜（STEM）已广泛应用于定量研究，因为它能够直接比较实验图像和模拟图像。这种比较只需要将实验数据进行归一化处理，并以“分数束流”为单位表示。然而，电子探测器响应的不均匀性会使这种归一化变得复杂。量化过程因实验和仪器而异，需要针对每个仪器探测器的特定响应以及所使用的每个相机长度进行新的模拟。这不仅阻碍了不同仪器和研究小组之间的比较，而且计算量也非常大。此外，并非所有图像模拟方法都能考虑探测器响应的不均匀性。在这项工作中，我们提出了一种对实验数据进行归一化的替代方法，以便将其与考虑均匀探测器响应的模拟结果进行比较。为了实现这一点，我们通过相机长度系列或所谓的原子柱横截面平均会聚束电子衍射（XSACBED）图案来确定到达探测器的电子通量分布。然后，利用该结果确定探测器响应的相对权重。我们在此表明，通过这种新的电子通量加权（EFW）方法获得的结果与目前使用的方法相当，同时大大简化了所需的模拟库。所提出的方法还允许获得一个指标，用于描述探测器响应与“理想”探测器响应相比的质量。
