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X‐ray diffracted intensity for double‐reflection channel‐cut Ge monochromators at extremely asymmetric diffraction conditions
Author(s) -
Ferrari Claudio,
Germini Fabrizio,
Korytár Dusan,
Mikulík Petr,
Peverini Luca
Publication year - 2011
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889811001439
Subject(s) - diffraction , optics , bragg's law , total internal reflection , diffraction topography , total external reflection , reflection (computer programming) , refraction , crystal (programming language) , angle of incidence (optics) , materials science , intensity (physics) , x ray crystallography , x ray optics , x ray , physics , computer science , programming language
The width and integrated intensity of the 220 X‐ray double‐diffraction profile and the shift of the Bragg condition due to refraction have been measured in a channel‐cut Ge crystal in an angular range near the critical angle of total external reflection. The Bragg angle and incidence condition were varied by changing the X‐ray energy. In agreement with the extended dynamical theory of X‐ray diffraction, the integrated intensity of the double diffraction remained almost constant, even for the grazing‐incidence condition very close to the critical angle for total external reflection. A broadening of the diffraction profile not predicted by the extended theory of X‐ray diffraction was observed when the Bragg condition was at angles of incidence lower than 0.6°. Plane wave topographs revealed a contrast that could be explained by a slight residual crystal surface undulation of 0.3° due to etching to remove the cutting damage and the increasing effect of refraction at glancing angles close to the critical angle. These findings confirm that highly asymmetric channel‐cut Ge crystals can also work as efficient monochromators or image magnifiers at glancing angles close to the critical angle, the main limitation being the crystal surface preparation.