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Figure 6
Illustrations of Criterion 6[link] for determining the sign of cos ϕ for thick specimens. The examples are simulated CBED patterns from ZnS [137] near a three-beam condition which is located in the centre of each disc. Following the convention in Fig. 1[link], the regions with negative and positive ζh are labelled with equally sized rectangles with dashed (green) and solid (red), respectively. In order to facilitate an inspection, the rectangles are located away from the exact three-beam condition by the same distance. In the simulations, the following values of the three-phase invariant and the thickness were used: (a) ϕ = 2.5°, z = 1720 Å; (b) ϕ = −140°, z = 1980 Å. In the calculation of (a), the three-phase invariant was adopted from the structure itself whereas in the calculations of (b), the three-phase invariant was artificially adjusted in order to produce a situation such that cos ϕ < 0. The same adjustment as in Fig. 5[link] has been performed.

IUCrJ
Volume 5| Part 6| November 2018| Pages 753-764
ISSN: 2052-2525
https://doi.org/10.1107/S2052252518012216