Ni-C/Ti are suitable for the components of neutron supermirrors with high reflectivity because of their excellent optical constant and smoother interfaces compared to Ni/Ti. In this paper, to investigate the mechanism of C doping to the interface, crystallization, and composition of a Ni-C/Ti multilayer with variable Ni-C thickness, four Ni-C/Ti multilayers were prepared by direct current magnetron sputtering, in which the thickness of the Ni-C layers was 1.5 nm, 2.5 nm, 3.5 nm, and 4.5 nm, respectively, and the thickness of the Ti layers was kept at 5 nm. The prepared samples were characterized by XRD, XPS, HRTEM, EDX, and SAED. The XRD and HRTEM results show that Ni-C layers in Ni-C/Ti multilayers translate from amorphous to polycrystal form, with their thickness increasing from 1.5 to 4.5 nm, and the crystallite size in Ni-C layers is equivalent to the layer thickness, respectively. The XPS, SAED, and EDX results illustrate that the enrichment position of C in Ni-C/Ti multilayers evolves from the Ni-C layers to the Ti layers as the respective Ni-C layer thickness increases from 2.5 to 4.5 nm. The enrichment position evolution of C in Ni-C/Ti multilayers could be due to the lower standard Gibbs free energy of TiC (−180.1 KJ/mol) compared with NiTi (−37.3 KJ/mol) and Ni3Ti (−35.9 KJ/mol) at 298 K.

Ru/C multilayer mirrors with a period of 2.5 nm and 150 bilayers were studied under high-temperature annealing and long-term storage. A general increase in the reflectivity was observed after annealing at different temperatures from 300 to 700 °C, during which a maximum enhancement of around 14% was obtained at 600 °C. The highest reflectance measured at 8 keV reached 69% after 600 °C annealing. This was accompanied by a 6% expansion of the layer period, which could be mainly attributed to carbon layers. The surface roughness was not affected by the annealing, whereas the polycrystallization of Ru with crystallographic planes parallel to the layer interfaces was enhanced. Combining the transmission-electron microscopy measurements, it was found that the interdiffusion at the C-on-Ru interface was significantly suppressed. The decreased interdiffusion, enhanced optical contrast, and larger multilayer period were the main reasons for the increased reflectance. The 600 °C annealed Ru/C multilayer remained intact after 13 months of storage in air, which also demonstrated significant temporal stability.