SPECKLE IN COHERENT X-RAY REFLECTIVITY FROM SI(111) WAFERS

We report the observation of x-ray speckle in the reflected beam from Si(lll) wafers illuminated at grazing incidence. An intense coherent 8 -keV x-ray beam was prepared using a wiggler source and multilayer mon ochromator optics. We demonstrate that the speckle patterns are specif ic to the region of the sample that is illuminated. From the trade-off between surface sensitivity and signal as a function of perpendicular momentum transfer. we infer that the speckle is due to the surface mo rphology on a micrometer length scale. We document and explain the evo lution of the speckle patterns from nearly specular at low q(z) to hig hly structured at larger q(z).