Material design optimization for large-m 11 B 4 C-based Ni/Ti supermirror neutron optics

State-of-the-art Ni/Ti supermirror neutron optics have limited reflected intensity and a restricted neutron energy range due to the interface width. Incorporating low-neutron-absorbing 11 B 4 C enhances reflectivity and allows for thinner layers to be deposited, with which more efficient supermirrors with higher m-values can be realized. However, incorporating 11 B 4 C reduces the optical contrast, limiting the attainable reflectivity at low scattering vectors, making this approach infeasible. This study explores various approaches to optimize the material design of 11 B 4 C-containing Ni/Ti supermirrors to maintain high reflectivity at low scattering vectors and achieve low interface widths at large scattering vectors. The scattering length density contrast versus interface width is investigated for multilayer periods of 30 Å, 48 Å, and 84 Å, for designs involving pure Ni/Ti multilayers, multilayers with 11 B 4 C co-deposited in Ni and Ti layers, multilayers with 11 B 4 C co-deposited only in Ni layers, and multilayers with 11 B 4 C as thin interlayers between Ni and Ti layers. Our results suggest that a depth-graded hybrid material design by incorporating 11 B 4 C inside the Ni and Ti layers, below approximately 26 Å, and introducing 1.5 Å 11 B 4 C interlayers between the thicker Ni and Ti layers can achieve a higher reflectivity than state-of-the-art Ni/Ti multilayers over the entire scattering vector range.