X-ray back-diffraction pointing to a target soft inelastic X-ray scattering spectrometer

Full text: Soft X-ray back-diffraction (SXBD), X-ray diffraction at angles near and exactly equal to 90°at low energies (~ 3.2 keV) was carried out at Soft X-rays Spectroscopy (SXS)beamline at Laboratorio Nacional de Luz Sincrotron (LNLS). A high-resolution Si(220) multi-bounce back-diffraction monochromator was designed and constructed for this experiment. An ultra-thin Si(220) crystal (5 μm thick) was used as the sample. This ultra-thin crystal was characterized by profilometry, rocking-curve measurements and X-ray topography prior to the XBD measurements. It is shown that the measured forward-diffracted beam (o-beam) profiles, taken at different temperatures, are in close agreement with profiles predicted by the extended dynamical theory of X-ray diffraction (2-beam case), with the absence of multiple-beam diffraction (MBD). This is an important result for future studies on the basic properties of back-diffracted X-ray beams at energies slightly above the exact XBD condition (extreme condition where XBD is almost extinguished). Also, the results presented here indicate that stressed crystals behave like ideal strain-free crystals when used for low-energy XBD. This is mainly due to the large widths of SXBD profiles, which lead to a low strain sensitivity in the detection of defects. This result opens up new possibilities for mounting spherical analyzer crystals without degrading the energy resolution, at least for low energies. With these results we aspire to build a soft inelastic X-ray scattering spectrometer, where experiments such as element-specific magnetic imaging tools could be explored. (author)