Speckle Suppression by Decoherence in Fluctuation Electron Microscopy
Speckle Suppression by Decoherence in Fluctuation Electron Microscopy
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DOI：
10.1017/s1431927615015135
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发表时间：
2015-12-01
影响因子：
2.8
通讯作者：
Treacy, Michael M. J.
中科院分区：
文献类型：
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作者：
Rezikyan, Aram;Jibben, Zechariah J.;Treacy, Michael M. J.
我们比较实验波动电子显微镜（FEM）的散斑数据与电子衍射模拟薄无定形碳和硅样品。我们发现，实验散斑强度方差一般比运动学散射理论预测的空间相干照明低一个数量级以上，我们假设退相干，使散射波之间的相位关系随机化，是负责的异常。具体地，位移退相干可以对散斑抑制有很大贡献，特别是在较高的光束能量下。位移退相干出现时，局部结构被重新安排显着的相互作用与光束在曝光过程中。我们还发现，如果把位移退相干和多次散射考虑在内，非晶硅的连续随机网络模型可以解释实验方差数据。这可能解决长期以来X射线和电子衍射研究的径向分布函数之间的差异，从以前的FEM研究得出的结论。退相干可能会影响所有的定量电子成像和衍射研究。它可能有助于所谓的Stobbs因子，其中高分辨率原子柱图像强度严重低于通过与这里观察到的相似因子预测的强度。
We compare experimental fluctuation electron microscopy (FEM) speckle data with electron diffraction simulations for thin amorphous carbon and silicon samples. We find that the experimental speckle intensity variance is generally more than an order of magnitude lower than kinematical scattering theory predicts for spatially coherent illumination.We hypothesize that decoherence, which randomizes the phase relationship between scattered waves, is responsible for the anomaly. Specifically, displacement decoherence can contribute strongly to speckle suppression, particularly at higher beam energies. Displacement decoherence arises when the local structure is rearranged significantly by interactions with the beam during the exposure. Such motions cause diffraction speckle to twinkle, some of it at observable time scales.We also find that the continuous random network model of amorphous silicon can explain the experimental variance data if displacement decoherence and multiple scattering is included in the modeling. This may resolve the longstanding discrepancy between X-ray and electron diffraction studies of radial distribution functions, and conclusions reached from previous FEM studies.Decoherence likely affects all quantitative electron imaging and diffraction studies. It likely contributes to the so-called Stobbs factor, where high-resolution atomic-column image intensities are anomalously lower than predicted by a similar factor to that observed here.