Evidence for a shear horizontal resonance in supported thin films

We report evidence for a different type of acoustic film excitation, identi fied as a shear horizontal resonance, in amorphous silicon oxynitride films on GaAs substrate. Observation of this excitation has been carried out usi ng surface Brillouin scattering of light. A Green's function formalism is u sed for analyzing the experimental spectra, and successfully simulates the spectral features associated with this mode. The attributes of this mode ar e described, these include its phase velocity which is nearly equal to that of a bulk shear wave propagating parallel to the surface and is almost ind ependent of film thickness and scattering angle, its localization mainly in the film, and its polarization in the shear horizontal direction.