Effect of roughness correlation on diffuse intensity in a neutron supermirror

Neutron supermirrors are increasingly important devices for transporting, bending, and focusing neutron beams. Reflected neutrons from a supermirror are divided into specular and off-specular (diffuse) components. The suppression of the diffuse component is important since it causes a serious problem when a supermirror is used in a focusing system for such purposes as small angle scattering measurement. The diffuse intensity can be decreased by more than an order of magnitude by adopting NiC/Ti multilayers instead of conventional Ni/Ti multilayers. In order to obtain insight into the mechanism that controls the diffuse intensity from a supermirror, the crystal structure of Ni and NiC monolayers and the interface structure of Ni/Ti and NiC/Ti multilayers were investigated. Diffuse intensity calculation based on the distorted wave Born approximation revealed that these differences in the structures explain the difference between the diffuse intensity of the Ni/Ti and NiC/Ti supermirrors. (author)