Boron-carbide barrier layers in scandium-silicon multilayers

Scandium-silicon (Sc/Si) multilayer structures show promise to efficiently reflect 45-50-nm wavelength X-rays at normal incidence. Barrier layers have been added at each interface to minimize the formation and growth of silicide compounds that broaden interfaces and, consequently, cause a change in the layer spacing and loss of reflectivity. Although tungsten (W) is an effective diffusion barrier, its high absorption causes a loss of reflectivity. We now evaluate the use of another refractory material for the barrier layer, boron carbide (B4C), which is a stable ceramic. The multilayer microstructure and its stability are evaluated using microscopy and diffraction methods. It is found that the use of B4C enhances the thermal stability of Sc/Si multilayers to an extent equivalent that offered by W barrier layers with only a few percent reduction in the reflectivity