Diffusion in Ni-Ti multi-layers with periods of 12nm was studied at temperatures ranging from 293 to 743K by means of grazing-angle unpolarized neutron reflectometry. The effective diffusion coefficients of Ni into Ti (table 279), and the corresponding activation energy, were deduced from measurements of the decay of the reflectivity of the first Bragg peak, which arose from nuclear scattering-length density modulations, as a function of isochronal annealing. The diffusion direction was determined by simulating the Kiessig fringes which were located between the total-reflection plateau and the first Bragg peak. Two diffusion regimes, with a transition temperature of about 543K, were observed in this Ni-Ti multi-layer. The corresponding activation energies were 0.21 and 0.43eV, respectively.

M.Mâaza, C.Sella, J.P.Ambroise, M.Kâabouchi, M.Milôche, F.Wehling, M.Groos: Journal of Applied Crystallography, 1993, 26[3], 334-42