Brillouin light scattering investigation of cluster-assembled carbon films : acoustic phonon propagation and elastic properties

Phonon propagation and elastic properties of cluster-assembled carbon films were investigated by surface Brillouin scattering. Films of different thicknesses, produced with different precursor cluster mass distributions have been studied. The propagation of surface and bulk acoustic phonons was strongly affected by the film structure at a typical scale of hundreds of nanometers. Absence of phonon propagation and localization effects have been observed in films assembled with large clusters due to surface roughness, whereas small clusters produced smooth films showing well defined Brillouin peaks. The determination of the material density by X-ray reflectivity, made the evaluation of the elastic properties of nanostructured carbon films possible even in presence of a high surface roughness. Numerical calculation of the scattering cross-section led to the estimation of the elasto-optic constants.