Attenuation of surface phonons in opaque materials measured by Brillouin scattering

We have measured the velocity and attenuation of surface phonons in amorphous Si by Brillouin Scattering. Due to the small wavelength of the probed phonons, the elastic properties of the thin films can be determined without substrate interference. Strong differences in the mean free path are found between “amorphized” and sputtered samples. Temperature and frequency dependence suggest relaxational processes rather than scattering by defects to be responsible for the attenuation.