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Figure 6
Schematic of BIR. As a static, imperfect, beam-sensitive molecular crystal is illuminated with a parallel beam in a TEM (a), pre-existing bends propagate and local bend angles (represented by θ in the illustration) change. As pictured, its warping is exaggerated and evidence of this warping is detectable both in diffraction-contrast imaging, where bend contours are seen to migrate along a crystal body, and in SAED, where the net orientation of the reciprocal lattice undergoes a change (b)–(c). For particularly beam-sensitive crystals, the set of excited Bragg reflections changes. The directions of these changes are effectively random with respect to the TEM rotation axis, such that if the crystal were rotating as in a MicroED experiment the deviation in net reciprocal lattice orientation would be non-trivial to predict. As electron beam fluence continues to be delivered to the crystal, both diffraction contrast in imaging mode and reflection intensity in diffraction mode gradually decay (d).

IUCrJ
Volume 12| Part 2| March 2025|
ISSN: 2052-2525
https://doi.org/10.1107/S2052252524012132