Interfacial roughness study of N2 reactive sputtered Ti/Ni neutron supermirrors by neutron reflection technique

Abstract

Neutron supermirror is an important neutron optics component which uses the total reflection principle to transport neutron beams. The formation of interface intermetallics and interface roughness with total multilayer thickness limit the neutron reflectivity performance of Ti/Ni multilayers. The interface roughness of multilayer film was optimized by adjusting the ratio of N₂ when sputtering the Ni layers, which ultimately guided the preparation of Ti/Ni neutron supermirrors with improved reflectivity. Direct current reactive magnetron sputtered samples were prepared with different N₂ ratios. And the surface morphology was studied by atomic force microscope (AFM), which revealed that 10 % N₂ inhibited the roughness growth of film by refining grains. The results of interfacial structure observed by neutron reflectivity were consistent with the AFM, that the average interfacial roughness of the film was minimized at 10 % N₂ ratio. The magnetization strength measured by vibrating sample magnetometer was affected by the number of bilayers and the N₂ ratio of the magnetic material. Finally, the Ni layers were sputtered with 10 % ratio of N₂, which resulted in a 2.7 % reflectivity enhancement compared to m = 2 Ti/Ni supermirror with pure Ar in the q range of 0.03–0.04 Å^-1.