Interface evolution of cosputtering NiC/Ti multilayer for neutron application

Tracking the interfacial evolution in Ni/Ti multilayers is a crucial aspect of fabricating neutron supermirrors. According to the Debye–Waller factor, the reflectivity of neutron supermirrors is modulated by the interface width, which includes interface roughness and diffusion characteristics. Significant effort has been devoted to shrinking the interface width using mixed working gases or targets during the sputtering process. To elucidate the interfacial evolution, NiC/Ti and Ni/Ti multilayers with different periods were fabricated using direct-current magnetron sputtering. The NiC layers were deposited by co-sputtering Ni and C targets. The interfacial structure and evolution within the multilayers were characterized by grazing incident x-ray reflectivity and transmission electron microscopy (TEM), respectively. The Ni layers in the Ni/Ti multilayers underwent a higher degree of crystallization, resulting in rough interfaces. Moreover, TEM images of the Ni/Ti multilayers suggest that the interface diffusion in the Ni-on-Ti layers reduces the interface smoothness. However, C doping suppresses the crystallization of the Ni layer to achieve smoother Ni/Ti interfaces, thereby improving the interface quality.