Determination of structure factor phase invariants from non-systematic many-beam effects in convergent-beam patterns

The determination of structure factor phase invariants and magnitudes from non-systematic many-beam effects in convergent-beam patterns is discussed. Non-centrosymmetric semiconductors are investigated with emphasis on the phase problem. Two-dimensional simulations using three or more beams show that a three-phase invariant may be determined from each of the numerous line intersections observed provided the three-beam coupling is non-negligible. The use of two-dimensional energy-filtered patterns for intensity registration is suggested, and an example using this technique is given.