Streaked speckle in Cu{sub 3}Au coherent x-ray diffraction

Coherent x-ray diffraction from the binary alloy Cu{sub 3}Au has speckled superstructure Bragg reflections due to its antiphase domain structure. For nonspecular superstructure reflections, it is possible to vary the diffraction geometry through a range of incidence and exit angles. Under grazing-exit conditions on a prepared Cu{sub 3}Au(111) thin-film sample, the superstructure speckles are found to become highly elongated and rotated on the detector. A detailed geometrical explanation of this behavior is developed to explain the effect.