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The Materials Research Collaborative Access Team’s bending magnet beamline (10-BM) at Argonne National Laboratory is being upgraded to deliver a significantly higher photon flux with improved spectral resolution in the 4–32 keV photon energy range. This will allow faster x-ray absorption spectroscopy measurements. The plan is to use an aspherical focusing mirror downstream of the x-ray monochromator to collect and focus a significant part of the vertically collimated horizontally divergent beam. An x-ray mirror surface is typically coated with high-atomic-number elements such as platinum (Pt) to allow high energy photon reflection. The absorption edges of such coating materials, however, introduce experimental complications when performing spectroscopy measurements at energies near those edges. This problem is typically addressed by coating the mirror substrate (typically silicon) with two different materials on two parallel longitudinal stripes. This option, however, is not possible for two-dimensional focusing optics. This paper reports on a multilayer coating over an x-ray mirror that provides high reflectivity over the entire energy range of interest with minimal absorption edges. An acceptable coating was determined using numerical simulations and a pair of flat silicon mirrors were coated and tested: one with a bilayer of Pt (20 nm) and Al2O3 (10 nm), and another with an additional carbon layer (8 nm). The reflectivity of both mirrors was measured and then re-measured after they were both heated to 70° C for 8 hours for a stability test. Experimental results show excellent stability, high reflectivity over the entire 4–32 keV energy range, and the suppression of the Pt absorption edges to below 1% reflectivity.
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