Thermal stability of Cr/Sc multilayers for the soft x-ray range
Cr/Sc multilayer mirrors were designed for grazing (30 and 60 degrees) and normal incidence reflection at about 3.16 nm (NKα line) wavelength. The multilayer coatings have been grown on Si-substrates using ion-assisted sputtering deposition. X-ray scattering of CuKα radiation and transmission electron microscopy were used for the characterization of the multilayer interface quality. The reflective properties of the Cr/Sc multilayers were measured with synchrotron radiation at different angles of incidence. Reflectivity values between R = 15% for near normal incidence (θ=5) and R = 29.6% or θ=60 were measured. Multilayer mirrors with periods less than 1.9 nm have amorphous Cr and Sc layers. The transition from amorphous to crystalline Cr and Sc layers takes place for multilayer periods of more than 3.1 nm and results in interface roughness development. The annealing effect in short-period Cr/Sc multilayers was studied in the temperature range from 50°C to 500°C by X-ray scattering and transmission electron microscopy. Structural and phase transformations and the corresponding changes of the optical properties are presented and discussed.