Neutron reflectivity and interface roughness in Ni/Ti and FeCoV/TiNx supermirrors

Supermirrors based on various multilayer systems such as Ni/Ti and FeCoV/TiNx are used in neutron optical devices. In this paper, we report on investigations carried out in order to understand the influence of interface roughness on the neutron reflectivity. In the case of Ni/Ti mirrors, the measured neutron reflectivity of mirrors having m=3.65 (600 layers) that are prepared under various sputtering conditions shows that the interface roughness of the samples sputtered only in Ar is large. To be specific, the thinner layers have low roughness when compared with thicker layers and only about 150 layers on the top are responsible for the considerable reduction in the reflectivity. In the case of FeCoV/TiNx mirrors, the use of TiGd/TiNx multilayer absorbers show considerable improvement in the performance of the mirrors.