Many-beam Effects on Thickness Fringes in a Silicon Wedge Crystal

Thickness fringes in a silicon wedge crystal are observed with a 1 MeV electron microscope under some different diffraction conditions. Many-beam calculations of the extinction distances are also performed to compare with the observed results. Accidental interactions cause a remarkable decrease in the extinction distances, while systematic interactions give a little effect on these. As for the (220) extinction distances, a systematic eight-beam computation gives only ~ 2 % decrease In comparison with the case of systematic four-beam computation, while a non-systematic eight-beam computation gives ~ 1 7 % decrease. The changes in the observed fringe spadngs due to the variation of the diffraction conditions are consistent with the calculated results. © 1973 Oxford University Press. All rights reserved.