Precise beam-tilt alignment and collimation are required to minimize the phase error associated with coma in high-resolution cryo-EM.
Precise beam-tilt alignment and collimation are required to minimize the phase error associated with coma in high-resolution cryo-EM.
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DOI：
10.1016/j.jsb.2010.12.005
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发表时间：
2011-04
影响因子：
3
通讯作者：
Cheng A
中科院分区：
文献类型：
--
作者：
Glaeser RM;Typke D;Tiemeijer PC;Pulokas J;Cheng A
与分辨率为0.8 nm的情况相比，分辨率为0.4 nm或更高的电子显微镜需要更仔细地调整照明。例如，使用电流轴对准并不总是足以避免由于轴向彗差而在较高分辨率下引入大的相位误差。此外，还必须确保离轴彗差不会破坏较高分辨率下的数据质量。我们特别强调，标准的CTF校正没有考虑到与彗差相关的相位误差。我们根据众所周知的电子衍射图相对于光轴的偏移来解释轴上彗差的原因和离轴彗差的典型的最麻烦的成分，当照明不平行于光轴时发生的偏移。我们回顾了彗差引起不可接受的大相位误差的实验条件，并讨论了设置照明条件时可以采取的步骤，以确保轴向和离轴彗差都不是问题。
Electron microscopy at a resolution of 0.4 nm or better requires more careful adjustment of the illumination than is the case at a resolution of 0.8 nm. 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.