Phase contrast STEM for thin samples: Integrated differential phase contrast
Phase contrast STEM for thin samples: Integrated differential phase contrast
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DOI：
10.1016/j.ultramic.2015.10.011
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发表时间：
2016-01-01
期刊：
影响因子：
2.2
通讯作者：
Lazar, Sorin
中科院分区：
文献类型：
--
作者：
Lazic, Ivan;Bosch, Eric G. T.;Lazar, Sorin
自20世纪70年代以来，人们已经知道，会聚束电子衍射（CBED）模式的质心（COM）的运动与样品中的（投影）电场呈线性关系。我们从图像形成的角度重新推导了基于这种运动的扫描透射电子显微镜（STEM）成像技术的对比度传递函数（CIF），并继续基于COM运动的两个组成部分对两幅图像进行二维积分。由此产生的集成COM (iCOM) STEM技术产生的标量图像在样品引起的相移中是线性的，因此在薄样品的局部（投影）静电势场中也是线性的。我们证实，使用具有4象限（4Q）的分段检测器的差分相位对比（DPC） STEM技术可以很好地近似COM运动。像COM一样进行二维积分，我们得到了样品相位近似线性的集成DPC （iDPC）图像。除了导出iCOM和iDPC的ctf外，我们还明确指出了两种相应成像技术的目标，并强调了与COM-、DPC-和（HA） ADF-STEM对应目标的差异。该理论通过模拟得到验证，我们提出了iDPC-STEM技术的第一个实验结果，显示其具有原子分辨率和良好信噪比（SNR）的轻元素和重元素成像能力。(C) 2015 Elsevier By。版权所有。
It has been known since the 1970s that the movement of the center of mass (COM) of a convergent beam electron diffraction (CBED) pattern is linearly related to the (projected) electrical field in the sample. We re-derive a contrast transfer function (CIF) for a scanning transmission electron microscopy (STEM) imaging technique based on this movement from the point of view of image formation and continue by performing a two-dimensional integration on the two images based on the two components of the COM movement. The resulting integrated COM (iCOM) STEM technique yields a scalar image that is linear in the phase shift caused by the sample and therefore also in the local (projected) electrostatic potential field of a thin sample. We confirm that the differential phase contrast (DPC) STEM technique using a segmented detector with 4 quadrants (4Q) yields a good approximation for the COM movement. Performing a two-dimensional integration, just as for the COM, we obtain an integrated DPC (iDPC) image which is approximately linear in the phase of the sample. Beside deriving the CTFs of iCOM and iDPC, we clearly point out the objects of the two corresponding imaging techniques, and highlight the differences to objects corresponding to COM-, DPC-, and (HA) ADF-STEM. The theory is validated with simulations and we present first experimental results of the iDPC-STEM technique showing its capability for imaging both light and heavy elements with atomic resolution and a good signal to noise ratio (SNR). (C) 2015 Elsevier By. All rights reserved.