Interface effects and elastic constants of Ag/Ni superlattices studied by Brillouin scattering

The elastic properties of sputter-deposited Ag/Ni superlattices have been studied by means of the Brillouin light scattering technique. Measurements have been taken on both free-standing and glass-supported superlattices, the former deposited at 100 K, the latter at 300 K. The two effective elastic constants c11 and c44 have been determined on specimens 5 μm thick for different superlattice periods; c44 decreases by almost 40% as the bilayer periodicity decreases from 19 to 1.3 nm, while c11 shows no appreciable variation. Measurements performed on supported specimens, 0.5 μm thick, enabled us to get information also on the constant c33, which exhibits a monotonic increase with period. The elastic anomalies found can be related to the appreciable lattice distortion observed by x-ray diffraction experiments. Both Brillouin scattering and x-ray analysis have shown that the interface quality improves appreciably when the temperature of deposition is lowered from 300 to 100 K.