Roughness-induced Raman scattering from surface carbon on PbTe

Surface-roughness features on the scale of 0.1-0.3 μm induce enhanced Raman scattering from adsorbed amorphous carbon on PbTe. Analogous to the scattering by adsorbates on metal surfaces, the spectra show a strong continuum extending beyond 3000 ${\mathrm{cm}}^{-1\mathrm{}}$ and no significant polarization dependence. The wavelength dependence of the enhancement exhibits a correlation with the band-structure properties of PbTe. These results are considered an indication that the scattering is due to roughness-induced coupling of the photons to nonvertical interband transitions at the surface. We discuss a possible explanation of the data in terms of a scattering mechanism which relies on the electrostatic interaction between electronic excitations of the substrate and the vibrational modes of the adsorbate.