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On the widths of dislocation images in X‐ray topography under low‐absorption conditions
Author(s) -
Miltat J. E. A.,
Bowen D. K.
Publication year - 1975
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/s0021889875011569
Subject(s) - misorientation , scattering , dislocation , optics , crystal (programming language) , reflection (computer programming) , absorption (acoustics) , x ray , translation (biology) , materials science , computation , azimuth , image (mathematics) , physics , computational physics , condensed matter physics , chemistry , crystallography , mathematics , computer science , algorithm , programming language , grain boundary , gene , microstructure , biochemistry , messenger rna , artificial intelligence
Detailed measurements have been made of dislocation image widths in X‐ray topographs taken under conditions of low absorption (product of linear absorption coefficient and crystal thickness, μ t = 0.15) with a silicon specimen and Mo K α radiation. These have been compared with two theoretical models, the `diffracting‐zone' model involving computation of misorientation gradient contours, and the direct‐image `mosaic' model using calculations of effective misorientation contours. Neither model completely explains the image widths. The diffracting‐zone model, though theoretically more attractive, gives a very poor correlation, probably because of ( a ) severe photographic limitations and ( b ) the uncertainty in the reconstruction of the intermediary image in translation topographs. For a given reflection the direct‐image mosaic model gives a reasonably good prediction of image widths measured at half peak height. However, the widths in different reflections are not self‐consistent; in particular, images in lower‐order reflections are significantly wider than those predicted by the model. This implies that contributions from interbranch scattering (giving an intermediary image component) are more important in lower‐order reflections, and that such contributions are proportional to the widths obtained from misorientation (rather than misorientation gradient) contours.