Multilayer x-ray mirrors for the objective crystal spectrometer on the Spectrum Roentgen Gamma satellite

We carried out experiments to determine the optimum parameters for the production of multilayer x-ray mirrors for the lambda equals 4.4 - 7.1 nm range using electron beam evaporation and ion-polishing. We report on the deposition of Co/C and Ni/C coatings, of which we polished the metal layers with Kr+- and Ar+- ions of 300, 500, and 1000 eV. We examined the effect of different polishing parameters on the smoothening of the Co- and Ni-layers. The in-situ reflectivity of lambda equals 3.16 nm during deposition and the ex-situ grazing incidence reflectivity of Cu-K(alpha ) radiation (lambda equals 0.154 nm) were used to analyze the coatings. We found optimum performance of the mirrors when applying polishing for 40 s with 500 eV Kr+-ions at an angle of 20 degrees and an ion beam current of 20 mA. Using these parameters, we produced Co/C multilayer coatings on forty flat super-polished 6 multiplied by 6 cm2 Si (111) crystals for the Objective Crystal Spectrometer on the Russian Spectrum Rontgen Gamma satellite. The coatings on the flight crystals have a period Lambda of 3.95 plus or minus 0.02 nm and a reflectivity of more than 8% averaged over s- and p-polarization over the entire wavelength range of interest. We present a detailed analysis of the coatings on the crystals.