原文由 hunterwang 发表:
常规的TEM成像或衍射操作,大家习惯是调节亮度旋钮让beam过焦还是欠焦?Goodhew说永远让beam处于过焦状态,这样得到beam更平行,总觉得没有道理。实际操作感觉区别不大。不知道各位的习惯是什么?
Rodenburg said:
the system is usually designed in such a way that the illumination is parallel at the specimen when the intensity (C2) knob is high.
http://www.rodenburg.org/guide/t1100.html
Peter Goodhew sadi:
when overfocused, beam convergences substantially because electrons come from only cross-over only
http://www.matter.org.uk/tem/lenses/beam_convergence.htm
个人觉得Rodenburg的解释更合理,见他网页中的ray diagram