Acoustic phonon propagation and elastic properties of cluster-assembled carbon films investigated by Brillouin light scattering - art. no. 085417

We demonstrate that elastic properties of cluster-assembled carbon films ca n be measured by surface Brillouin scattering. We have studied films with d ifferent nano- and mesostructures produced with different precursor cluster mass distributions. In particular, films showing very high and low surface roughness have been compared over a wide range of film thicknesses. We hav e found that the propagation of surface and bulk acoustic phonons is strong ly affected by the film mesostructure. Absence of phonon propagation and lo calization effects have been observed in films assembled with large cluster s due to surface roughness, whereas small clusters produced smooth films sh owing well defined Brillouin peaks. This occurrence, together with the dete rmination of the material density by x-ray reflectivity, made the evaluatio n of the elastic properties of nanostructured carbon films possible. The va lues of the elastic constants, and in particular the anomalous (extremely l ow) value of the Poisson's ratio, suggest that cluster-assembled carbon fil ms are a unique system among different inorganic carbon-based materials.