Determination of diffusion coefficient D and activation energy Qa of nickel into titanium in Ni-Ti multilayers by grazing-angle neutron reflectometry

Diffusion in Ni–Ti multilayers with periods of 120 Å is studied in the temperature range 293–743 K by grazing‐angle unpolarized neutron reflectometry. The effective diffusion coefficient, Deff, of nickel into titanium and its corresponding activation energy, Qa, are determined by measurement of the decay of the reflectivity of the first Bragg peak, which arises from the nuclear scattering‐length density modulation, as a function of annealing temperature at constant time. The direction of diffusion is determined by simulation of the Kiessig fringes located between the total‐reflection plateau and the first Bragg peak. Two diffusion regimes with a transition temperature Tc≃ 543 K are observed in this Ni–Ti multilayer; the corresponding activation energy values are 0.21 and 0.43 eV, respectively.