Measurement of the elastic constants of nanometer-thick films

Reliable measurement of the elastic constants of films of nanometric thickness is needed for the development of several nanotechnologies, but is still an open issue, especially in the case of hard films. We show that by combining surface Brillouin scattering (SBS) and X-ray reflectivity (XRR) measurements, the elastic constants of nanometric supported films can be obtained. The dispersion relations of surface acoustic waves (SAWs) are measured by SBS. The same dispersion relations are computed as functions of substrate properties, and the film thickness, mass density and elastic constants. The film thickness and density are obtained by X-ray reflectivity measurements; the elastic constants are then derived by fitting the computed SAW dispersion relations to the measured ones. We present results obtained on tetrahedral amorphous carbon films, having thickness below 10 nm, deposited on silicon. We show that the elastic constants can be measured also for these ultrathin films.