DEVELOPMENT OF NI TI MULTILAYER SUPERMIRRORS FOR NEUTRON OPTICS

Artificial multilayer neutron supermirrors are composed of discrete se ts of bilayer structures based on Ni and Ti layers with graded thickne sses and with high scattering contrast between individual layers. Vari ous samples consisting of NiX(x)/TiY(y) (X = C, N, dry air, Y = H, V) periodic multilayers and supermirrors, as well as NiX(x) and TiY(y). m onolayers were deposited on normal float-glass, borkron glass and on s ilicon substrates using d.c. magnetron sputtering. The structure and s tability of these thin films is the object of a detailed study mainly by means of X-ray diffraction, TEM, AFM and neutron reflectometry. The addition of N to the Ni layers yields a Ni lattice dilatation, a reor ientation of the Ni grains from {111} to {200} parallel to the layer s urface, a reduction of the grain size, a smoothing of the layer surfac es (R(r.m.s) approximately 0.3 nm for d = 10 nm), a sharpening of the multilayer interfaces and an enhancement of the scattering length dens ity (nb = 9.53 x 10(-4) nm-2 for Ni-N). Similar results are obtained w ith C and dry air, which in addition suppress the diffusion of Ni into Ti. The addition of V to the Ti layers shows a smoothing of the layer surfaces and helps to suppress interdiffusion in multilayers, leading also to sharp and stable interfaces. Large neutron supermirrors made of 40 bilayers of Ni-N-O/Ti-V with a reflectivity in the range of 90% to 94% at glancing angles up to more than twice the critical angle of total reflection from an ordinary Ni surface have been achieved and ar e fabricated in mass production.