Material design optimization for large-m 11B4C-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 ¹¹B₄C enhances reflectivity and allows for thinner layers to be deposited, with which more efficient supermirrors with higher m-values can be realized. However, incorporating ¹¹B₄C 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 ¹¹B₄C-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 ¹¹B₄C co-deposited in Ni and Ti layers, multilayers with ¹¹B₄C co-deposited only in Ni layers, and multilayers with ¹¹B₄C as thin interlayers between Ni and Ti layers. Our results suggest that a depth-graded hybrid material design by incorporating ¹¹B₄C inside the Ni and Ti layers, below approximately 26 Å, and introducing 1.5 Å ¹¹B₄C 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.