Interfacial roughness of partially correlated metallic multilayers studied by non-specular X-ray reflectivity

Using a two-dimensional image plate detector we measured the non-specular X-ray reflectivity from (Ni-0.81 Fe-0.19)/Au metallic multilayers. The image plate pattern consists of periodic diffuse sheets which arise from the coherence of the roughness between different interfaces, and are strongest at the position of the Bragg peaks. We analyze the expression for the diffuse scattering cross-section derived from the distorted-wave Born approximation and separate the coherent and incoherent contributions, This allows us to determine the interface roughness parameters, assuming it to be self-affine. From the line shape of the diffuse sheets we determine the partial replication of the roughness for different length scales.