Epitaxial Cu/Ni multilayers are model systems for investigating the early stages (at the nm scale) of interdiffusion and mechanical stress. In this work we present a method that combines both atomistic simulations of the interdiffusion and x-ray diffraction experiments in this system. The aim of this approach is mainly to confirm (or not) the non-fickian interdiffusion mode that is expected in Cu/Ni multilayers. Indeed, due to the large asymmetry of the atomic mobility (Ni atoms diffuse faster in Cu regions than Cu atoms do in Ni ones), a layer-by-layer mode should be observed experimentally [1].
First, by using a one dimensional mean-field diffusion model, we report our simulation results for two extreme cases of diffusion asymmetry: the Fickian mode where the diffusion coefficient is constant (no asymmetry) and the layer-by-layer mode resulting from a strong concentration dependence of the diffusion coefficient. The theoretical angular shift of the spectra and the evolution of peak intensities are calculated for the two different kinetics. Signatures of the layer-by-layer mode are discussed.
Then, the x-ray diffraction experimental results are presented. The samples [Cu3.375 nm /Ni2.25nm] × 25 and [Cu3.521nm/Ni3.521nm] × 25 are made by magnetron sputtering on the MgO substrate and annealed at about 380°C for different time. The resulting experimental data show important trends. The multilayers are coherent and remain so after annealing. From the out of plane scans, we observed a significant change of the relative values of the peak intensity.
From these experimental evolutions of the peak intensities and with the help of our simulations, we attempt to identify the interdiffusion modes that take place in the CuNi multilayers.

Reference: [1] J. M. Roussel, P. Bellon, Phys. Rev. B 73, 085403 (2006).

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