X-ray Back-Diffraction Profiles with an Si (111) Plate

A two- and, alternatively, a four-crystal monochromator were used for simultaneous measurements of the profiles backward (h) and forward (o) diffracted by a thin Si (111) crystal plate for diffraction angles up to exactly 90° at DCI-LURE (Orsay). It is shown that the set-up with a four-crystal monochromator allows the characterization of the back-diffraction region for any crystal plate reflection. Asymmetry and full width at half-maximum (FWHM) of the experimental backward-diffraction profiles are analyzed. Possible simultaneous diffractions occurring near 90° incidence, giving extra peaks in the forward-diffracted profiles, are studied. The good contrast of the o-beam profiles suggests that the back-diffracted o beam could be used as a highly monochromatic beam.