Liu Amelia C Y, Lumpkin Gregory R, Petersen Timothy C, Etheridge Joanne, Bourgeois Laure
Monash Centre for Electron Microscopy and School of Physics, Monash University, Clayton, Victoria, 3800, Australia.
Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales, 2234, Australia.
Acta Crystallogr A Found Adv. 2015 Sep;71(Pt 5):473-82. doi: 10.1107/S2053273315011845. Epub 2015 Jul 9.
The interpretation of angular symmetries in electron nanodiffraction patterns from thin amorphous specimens is examined. It is found that in general there are odd symmetries in experimental electron nanodiffraction patterns. Using simulation, it is demonstrated that this effect can be attributed to dynamical scattering, rather than other divergences from the ideal experimental conditions such as probe-forming lens aberrations and camera noise. The departure of opposing diffracted intensities from Friedel's law in the phase grating formalism is calculated using a general structure factor for disordered materials. On the basis of this, a simple correction procedure is suggested to recover the kinematical angular symmetries, and thus readily interpretable information that reflects the symmetries of the original projected object. This correction is numerically tested using both the phase object and multislice calculations, and is demonstrated to fully recover all the kinematical diffracted symmetries from a simulated atomic model of a metallic glass.
本文研究了来自薄非晶样品的电子纳米衍射图案中角对称性的解释。研究发现，一般来说，实验电子纳米衍射图案中存在奇数对称性。通过模拟表明，这种效应可归因于动态散射，而不是与理想实验条件的其他偏差，如探针形成透镜像差和相机噪声。使用无序材料的一般结构因子，计算了相位光栅形式中反对称衍射强度与弗里德尔定律的偏差。在此基础上，提出了一种简单的校正程序，以恢复运动学角对称性，从而获得易于解释的反映原始投影物体对称性的信息。使用相位物体和多层计算对该校正进行了数值测试，并证明其能够从金属玻璃的模拟原子模型中完全恢复所有运动学衍射对称性。
