As nickel and silicon have no absorption edges in the "water window" (2.4-4.4 nm), these materials form suitable components for multilayers to be applied as optical components in this wavelength region. The practical feasibility of using these components is limited by their chemical reactivity, resulting in intermixing at the interfaces. A procedure, based on the application of ion implantation and ion beam mixing, has been developed to produce silicon nitride and nickel silicide layers. As these processes also cause ion etching, an additional reduction of the surface roughness of the layers has been observed.