High accuracy measurement of elastic constants of thin films by surface Brillouin scattering

Elastic properties of thin supported films can be derived From the dispersion relations of surface acoustic waves (SAWs) of layered structures. SAW velocities can be measured by surface Brillouin scattering (SBS), i.e., light scattering by thermally excited SAWs. Since SAW velocities can be computed as functions of the elastic properties of both the film and the substrate, if Elm thickness and density are independently measured the elastic constants can be obtained Fitting the computed velocities to the measured ones, Our data analysis technique is discussed, Accuracy of the measured velocities is crucial: the SBS measurement technique is analyzed, giving quantitative estimates of errors and uncertainties, and discussing procedures to reduce them. Some examples are considered in detail, showing that SBS measurements allow the determination of film elastic constants on films of thickness down to tens of nanometers, with precision ranging from reasonable to very good.