Elastic characterization of supported and unsupported Ag/Ni superlattices by Brillouin scattering

Elastic properties of Ag/Ni metallic superlattices have been investigated by means of the Brillouin light scattering technique. Measurements have been taken on both unsupported and glass-supported superlattices with periods in the range between 1 and 20 nm, prepared by DC-sputtering. Strong changes in the Rayleigh wave velocity as a function of the period have been observed and related to a softening of the effective elastic constant c₄₄ in proximity of the interfaces. In unsupported samples, 5 μm thick, measurements of a dip in the surface phonon spectrum lead to the selective determination of c ₁₁. This has permitted an estimation of Young´s modulus and a comparison with results obtained by conventional static techniques; no significant period-dependence has been found. In supported specimens, 0.5 μm thick, measurements of up to five acoustic guided modes have also given information on c₁₃ and c₃₃