Raman Scattering by Bulk Phonons in Microcrystalline Silver and Copper via Electronic Surface Excitations

In Raman scattering from cryocondensed metal films one observes the bulk acoustic phonons. This is not caused by the laser field which penetrates the metal, but via the scattering of optically excited intrasurface band electron hole pairs by the phonons. Phonons with wave vector $\mathbf{Q}$ contribute to the Raman signal according to the scattering probability $S\left(\mathbf{q}\right)$ of the image states by surface roughness, where $\mathbf{q}$ is the projection of $\mathbf{Q}$ onto the low index facets having occupied electronic surface states, in the present case mainly of (111) orientation.