The interdependence between the microstructure of sputter-deposited Ni(111)/Mo(110) superlattices and their elastic behavior was investigated as a function of the bilayer period, Λ. Brillouin light scattering measurements showed that a marked softening of the effective shear modulus occurred upon decreasing Λ to 2nm; where it reached –62%. Ion irradiation was used to trigger stress relaxation and to induce, in a controlled way, interdiffusion and structural changes which permitted investigation of their influence upon the elastic anomaly. At a very low irradiation dose (0.1dpa), the relief of the lattice expansion and associated compressive stresses did not induce any change in the elastic response. This indicated that the elastic behavior of the as-grown multi-layers was not correlated with the presence of elastic strains. Furthermore, a detailed X-ray diffraction analysis showed that the unstrained lattice parameter of Mo layers exhibited a linear dependence upon the interface density. The Ni unstrained lattice parameter remained nearly unchanged over the same Λ-range. This effect could be attributed to the interfacial mixing of a constant amount of Ni (~1.5 monolayers) into the Mo layers, as a consequence of the dynamic segregation of Ni atoms during growth. Thus, the formation of interfacial metastable and supersaturated solid solutions, structurally and mechanically unstable, appeared to be the origin of the huge elastic softening observed in this system. At high ion fluences, when the mixing process became dominant, the present study also provided experimental data on phase transformation in so-called driven alloys, by addressing the issue of the stability of out-of-equilibrium structures under irradiation.

Strain, Interdiffusion and Microstructural Evolution under Ion Irradiation in Ni(111)/Mo(110) Multilayers - Interdependence with Elastic Properties. F.Martin, C.Jaouen, J.Pacaud, G.Abadias, P.Djemia, F.Ganot: Physical Review B, 2005, 71[4], 045422 (14pp)