The combination of aberration correction and ultra high energy resolution with monochromators has made it possible to record images showing lattice resolution in phonon modes, both with a displaced collection aperture and more recently with an on -axis collection aperture. In practice the objective aperture has to include Bragg reflections that correspond to the observed lattice image spacings, and the specimen has to be sufficiently thick for adequate phonon scattered intensity. There has been controversy as to whether the images with the on axis detector are really a consequence of lattice resolution in a phonon mode or just a transfer of information from an image that was formed by elastically scattered electrons. We present results of calculations based on a theory that includes the possibility of dynamical electron diffraction for both incident and scattered electrons and the full phonon dispersion relation. We show that Umklapp scattering from the second Brillouin Zone back to the first Brillouin Zone is necessary for lattice resolution with the on axis detector and that it is therefore reasonable to attribute the lattice resolution to the phonon scattering.

中文翻译：

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电子显微镜中振动模式的晶格分辨率

像差校正和超高能量分辨率与单色器的结合使得在声子模式下记录显示晶格分辨率的图像成为可能，包括位移收集孔径和最近的同轴收集孔径。在实践中，物镜孔径必须包括与观察到的晶格图像间距相对应的布拉格反射，并且样品必须足够厚以获得足够的声子散射强度。关于轴上检测器的图像是否真的是声子模式中晶格分辨率的结果，还是仅仅是由弹性散射电子形成的图像的信息传递，一直存在争议。我们提供了基于理论的计算结果，该理论包括入射电子和散射电子的动态电子衍射的可能性以及完整的声子色散关系。我们表明，从第二布里渊区返回到第一布里渊区的 Umklapp 散射对于轴上检测器的晶格分辨率是必要的，因此将晶格分辨率归因于声子散射是合理的。