Development of multilayer mirrors for the water window (a region between absorption edges of carbon and oxygen, from 282 to 533 eV) remains quite a challenge. Proposed 25 years ago, the Cr/Sc multilayer provides theoretical reflectivity about 60% at near-normal incidence near the Sc L2,3 edge. However, the maximum measured peak reflectance achieved so far just slightly exceeds 20%. We report on our approach to design highly reflective Cr/Sc-based multilayer coatings using a process of nitridation of chromium during deposition and adding boron carbide as a third material in the multilayer structure. We will report on our strategy of optimisation of the CrN/B4C/Sc multilayer system and discuss the main findings and results. The peak reflectance as high as 32% at 397 eV was measured with this type of coating which proves to be potentially interesting for various water window applications such as x-ray microscopy.
We present here experimental results and modeling of multilayer gratings developed for the EUV spectro-imager abroad Solar-C mission. Periodic Al/Mo/SiC multilayers were optimized and deposited by magnetron sputtering on high groove density lamellar gratings with various depths. All grating samples were characterized before and after multilayer deposition by atomic force microscopy (AFM) and by grazing incidence x-ray reflectometry (GIXR) at 8.05 keV. AFM measurements reveal the surface prole evolution when the number of deposited layers increases. This effect is confirmed with a transmission electron microscope cross-section analysis. The EUV diffraction efficiency of the multilayer gratings was measured by monochromatic synchrotron radiation on the XUV Metrology beamline at SOLEIL Synchrotron. The results are in good agreement with the model simulated by rigorous coupled-wave analysis and using structural parameters determined by AFM and GIXR. The measured near-normal incidence first-order efficiency reaches a maximum of about 9.27%, 6.54%, and 7.18% at wavelengths of 27.3 nm, 21.4 nm, and 19.4 nm respectively.
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