Effect of argon-nitrogen mixed ambient Ni sputtering on the interface diffusion of Ni/Ti periodic multilayers and supermirrors

Interface roughness and interface diffusion are two very crucial parameters in determining the performances of thin film multilayer devices for applications in X-ray optics, neutron optics, giant magneto resistance devices etc. Preparation of these thin film multilayers with sharp interfaces is a technological challenge and researchers are using different methods to reduce the interface imperfections. It has been observed that by mixing nitrogen with argon in sputtering ambience during deposition of Ni layers, neutron reflectivity of Ni/Ti neutron supermirrors can be improved significantly.To elucidate the physical mechanism behind this observation, two sets of Ni/Ti periodic multilayers have been prepared using an indigenously built in-line magnetron sputtering system, in one set pure Ar has been used in sputtering ambience and in the other set a mixed ambience of Ar + N2 has been used for deposition of Ni layers. Both the sets of multilayers have been thoroughly characterized by specular and diffused Grazing Incidence X-ray Reflectivity, Nuclear Resonance Reaction, X-ray diffraction and Grazing Incidence Extended X-ray Absorption Fine Structure measurements using synchrotron radiation. All the above complementary measurements unambiguously establish that the reason for improved performance of the supermirror deposited with Ar + N2 ambience is the reduction of interface diffusion at Ti-on-Ni interfaces.