Acoustic Surface Waves and Film Excitations in CaF sub 2 /Si Heterostructures

While the surface Rayleigh phonon is normally the dominant long wavelength acoustic feature for a film on a substrate, the rich spectrum of higher order excitations also offers novel possibilities to probe the interface region. In particular, the Lamb or Sezawa higher order modes consist of shear vertical and longitudinally polarized partial waves whose displacement field propagates parallel to the surface but decays exponentially with distance into the substrate. The dispersion of these different modes should hence allow a self-consistent evaluation of the elastic constants and study of the influence of the interface region on the acoustic properties.