Dickerson Joshua L, Russo Christopher J
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
Ultramicroscopy. 2022 Jul;237:113511. doi: 10.1016/j.ultramic.2022.113511. Epub 2022 Mar 19.
A controversy exists as to whether the signal in a high resolution phase contrast electron micrograph of a particle in a thick specimen is the same irrespective of the particle's position along the beam axis. Different conceptions of inelastic scattering and its effects on wave interference have led to radically different expectations about the degree of phase contrast vs. depth. Here we examine the information available from bright field phase contrast images of small crystalline particles on the top or bottom of a thick support. The support is an aluminium foil which has strong plasmon resonances that cause a large proportion of the electron beam to lose energy in transit. Phase contrast micrographs of the atomic lattice of two ensembles of platinum particles were measured in an energy loss window corresponding to the first plasmon resonance. The signal measured for particles on top was equal to that for particles on the bottom of the foil to within a 99% confidence interval, and the measurements exclude other models of depth dependent phase contrast in the literature to >5σ. These observations are consistent with quantum theory which considers dynamical effects as independent of event sequence and is distinct from the "top-bottom effect" observed in amplitude contrast. We thus confirm that phase contrast using inelastically scattered electrons can be obtained equally well from particles within any layer of a thick specimen.
对于厚样品中粒子的高分辨率相衬电子显微照片中的信号，无论粒子沿束轴的位置如何是否相同，存在争议。对非弹性散射及其对波干涉的影响的不同概念导致了对相衬程度与深度关系的截然不同的预期。在这里，我们研究了从厚支撑物顶部或底部的小晶体粒子的明场相衬图像中获得的信息。支撑物是铝箔，它具有强烈的等离子体共振，导致很大一部分电子束在传输过程中损失能量。在对应于第一等离子体共振的能量损失窗口中测量了两组铂粒子原子晶格的相衬显微照片。在99%的置信区间内，顶部粒子的测量信号与箔底部粒子的信号相等，并且这些测量排除了文献中其他深度相关相衬模型超过5σ的情况。这些观察结果与量子理论一致，量子理论认为动力学效应与事件顺序无关，并且与在振幅衬度中观察到的“顶部-底部效应”不同。因此，我们证实，使用非弹性散射电子的相衬可以从厚样品的任何层内的粒子中同样良好地获得。
