DETERMINATION OF DIFFUSION COEFFICIENT-D AND ACTIVATION-ENERGY Q(A) OF NICKEL INTO TITANIUM IN NI-TI MULTILAYERS BY GRAZING-ANGLE NEUTRON REFLECTOMETRY

Diffusion in Ni-Ti multilayers with periods of 120 angstrom is studied in the temperature range 293-743 K by grazing-angle unpolarized neutr on reflectometry. The effective diffusion coefficient, D(eff), of nick el into titanium and its corresponding activation energy, Q(a), are de termined by measurement of the decay of the reflectivity of the first Bragg peak, which arises from the nuclear scattering-length density mo dulation, as a function of annealing temperature at constant time. The direction of diffusion is determined by simulation of the Kiessig fri nges located between the total-reflection plateau and the first Bragg peak. Two diffusion regimes with a transition temperature T(c) congrue nt-to 543 K are observed in this Ni-Ti multilayer; the corresponding a ctivation energy values are 0.21 and 0.43 eV, respectively.