LOCALIZED SURFACE PHONON PROPAGATION IN CAF2 SI(110) HETEROSTRUCTURES/

We have studied experimentally the propagation of the surface phonon m odes in CaF2/Si(110) heterostructures with h = 0, 10 and 200 nm thickn ess by Brillouin light scattering spectroscopy. The angular azimuthal behaviour of the Rayleigh mode was found to be close to that of the ma terial of the substrate in the case with h = 10 nm, and to that of the layer in the case with h = 200 nm. In an h = 200 nm heterostructure f or the azimuthal directions close to [1(1) over bar0$] it was conclude d that the behaviour of the first localized mode is described well by the proper pseudo-surface mode of CaF2 of the (110) plane, whereas hig her-mode (i.e. second, third) velocity values were found to be close t o that of the material of the substrate. Experimental and calculated v elocity values match each other rather well.