Characterization of sputtered nickel/carbon multilayers with soft-x-ray reflectivity measurements

Several sputtered Ni/C multilayer mirrors with periods between 3.8 and 6.0 nm were investigated with the HASYLAB reflectometer to determine the peak reflectivity and the internal structure of the multilayers. The enhanced reflectivity in the Bragg maximum, especially below 284 eV (carbon K edge), is interesting for practical applications. For both materials (Ni and C), the optical constants were previously obtained from angular-dependent reflectivity measurements. The layer thicknesses, interface roughnesses, and mean thickness errors of multilayer mirrors are obtained from least-squares fits of theoretical reflectivity curves. A model is presented to describe the influence of interface roughness on other parameters obtained from the analysis. All Ni/C multilayers, with Ar as the sputter gas, were produced in the low-pressure triode-assisted sputtering facility of Sincrotrone Trieste.