Raman Scattering in Nb–Cu Metallic Multilayers

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Abstract
Raman scattering by acoustic phonons is investigated in NbCu metallic multilayers grown by magnetron sputtering, with periods ranging from 1.7 to 20.0 nm. For larger‐periodic samples, many peaks which are analogous to those produced by Raman scattering by folded acoustic phonons in periodic superlattices, can be explained by using a perturbation elastic continuum model. On the other hand, in the samples which are layered polycrystals with textures two additional peaks at 158 and 198 cm−1 are observed and attributed to disorder‐activated transverse‐acoustic mode (DATA). The DATA shows an anomalous shift toward lower frequency as a function of film thickness and explains probably anomalies in the Rayleigh wave velocity versus modulated NbCu film thickness.