Streaked speckle in Cu3Au coherent x-ray diffraction

Coherent x-ray diffraction from the binary alloy Cu3Au has speckled superst ructure Bragg reflections due to its antiphase domain structure. For nonspe cular superstructure reflections, it is possible to vary the diffraction ge ometry through a range of incidence and exit angles. Under grazing-exit con ditions on a prepared Cu3Au(111) thin-film sample, the superstructure speck les are found to become highly elongated and rotated on the detector. A det ailed geometrical explanation of this behavior is developed to explain the effect.