Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA.
J Struct Biol. 2011 Apr;174(1):1-10. doi: 10.1016/j.jsb.2010.12.005. Epub 2010 Dec 21.
Electron microscopy at a resolution of 0.4nm or better requires more careful adjustment of the illumination than is the case at a resolution of 0.8nm. The use of current-axis alignment is not always sufficient, for example, to avoid the introduction of large phase errors, at higher resolution, due to axial coma. In addition, one must also ensure that off-axis coma does not corrupt the data quality at the higher resolution. We particularly emphasize that the standard CTF correction does not account for the phase error associated with coma. We explain the cause of both axial coma and the typically most troublesome component of off-axis coma in terms of the well-known shift of the electron diffraction pattern relative to the optical axis that occurs when the illumination is not parallel to the axis. We review the experimental conditions under which coma causes unacceptably large phase errors, and we discuss steps that can be taken when setting up the conditions of illumination, so as to ensure that neither axial nor off-axis coma is a problem.
电子显微镜在 0.4nm 的分辨率或更高的分辨率下需要比在 0.8nm 的分辨率下更仔细地调整照明。例如，在更高的分辨率下，使用电流轴对准并不总是足以避免由于轴向彗差引起的大相位误差。此外，还必须确保离轴彗差不会在更高的分辨率下破坏数据质量。我们特别强调，标准的 CTF 校正并没有考虑与彗差相关的相位误差。我们根据当照明不平行于轴时，电子衍射图案相对于光轴发生的众所周知的偏移，解释了轴向彗差和离轴彗差中通常最麻烦的分量的原因。我们回顾了彗差导致不可接受的大相位误差的实验条件，并讨论了在设置照明条件时可以采取的步骤，以确保既没有轴向彗差也没有离轴彗差的问题。
