Design and fabrication of high reflectivity Mo/B4C multilayer mirrors

Mo/B4C multilayer is a suitable material combination for high reflectivity mirrors in the soft X-ray wavelength region of 6.7~8.0 nm. The structures of the ideal Mo/B4C multilayer mirrors optimized based on the General Algorithm method (GA) are that the bilayers number is 150, the period is 3.59 nm, the ratio of Mo film thickness to period is 0.41 for the fixed incident of 10°. The reflectivity of such a Mo/B4C multilayer is 33.29％ at first order Bragg reflectivity peak. Mo/B4C multilayers were fabricated with a DC magnetron sputtering coater. All these multilayers were deposited on super-polished silicon substrates, of which the area is about 20 mm×30 mm. The surfacerms roughness of the Si substrate is less than 0.3 nm. The purity of the target materials Mo, B4C and Cr is respectively