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arXiv 2008.03796cond-mat.mes-hallcond-mat.mtrl-sciphysics.comp-phphysics.ins-det
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从会聚束电子衍射花样全息再现双层二维晶体样品的层间距

Holographic reconstruction of the interlayer distance of bilayer two-dimensional crystal samples from their convergent beam electron diffraction patterns

Tatiana Latychevskaia, Yichao Zou, Colin Robert Woods, Yi Bo Wang, Matthew Holwill, Eric Prestat, Sarah J. Haigh, Kostya S. Novoselov

摘要:

扭转双层膜样品的会聚束电子衍射(CBED)图在其CBED斑点处呈现干涉图样。这种干涉图案可以被视为离轴全息图和散射波的相位,这意味着可以重建层间距离。本研究提供了重建程序的详细方案。此外,我们推导出一个精确的公式,用于重建层间距离从恢复的相位分布,它考虑到不同的化学成分的各个单层。它示出,在CBED点的一个干涉条纹是足够的,以重建层之间的距离,这可以是实际的成像样品与一个相对较小的扭转角或当探测小的样品区域。作为扭转角的函数的重建层间距离的质量进行了研究。在较小的扭转角下,重建的层间距离分布更精确且无伪影。在较大的扭转角下,由于莫尔结构而导致的伪影出现在重建中。提出了一种重建平均层间距的方法。至于分辨率,层间距离可以通过全息方法以0.5 A的精度重建,这比衍射极限分辨率的固有z分辨率好几百倍,如通过测量的k值的扩展所表示的。此外,我们表明,全息CBED成像可以检测到小至0.1 A的层间距离的变化,虽然这种变化的定量重建遭受较大的误差。

英文摘要:

The convergent beam electron diffraction (CBED) patterns of twisted bilayer samples exhibit interference patterns in their CBED spots. Such interference patterns can be treated as off-axis holograms and the phase of the scattered waves, meaning the interlayer distance can be reconstructed. A detailed protocol of the reconstruction procedure is provided in this study. In addition, we derive an exact formula for reconstructing the interlayer distance from the recovered phase distribution, which takes into account the different chemical compositions of the individual monolayers. It is shown that one interference fringe in a CBED spot is sufficient to reconstruct the distance between the layers, which can be practical for imaging samples with a relatively small twist angle or when probing small sample regions. The quality of the reconstructed interlayer distance is studied as a function of the twist angle. At smaller twist angles, the reconstructed interlayer distance distribution is more precise and artefact free. At larger twist angles, artefacts due to the moiré structure appear in the reconstruction. A method for the reconstruction of the average interlayer distance is presented. As for resolution, the interlayer distance can be reconstructed by the holographic approach at an accuracy of 0.5 A, which is a few hundred times better than the intrinsic z-resolution of diffraction limited resolution, as expressed through the spread of the measured k-values. Moreover, we show that holographic CBED imaging can detect variations as small as 0.1 A in the interlayer distance, though the quantitative reconstruction of such variations suffers from large errors.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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