RESUMO
Brillouin scattering from surface phonons was used for determining the dispersion curves of guided acoustic modes propagating along piezoelectric ZnO films. Measurements were performed on films of different thicknesses in the range between 20 and 320 nm, deposited by RF magnetron sputtering on Si and SiO(2) substrates. Brillouin spectra from Rayleigh acoustic modes are taken in the backscattering geometry at different incidence angles between 30 degrees and 70 degrees . The experimental data for the ZnO/Si films fit the expected theoretical dispersion curves fairly well for film thicknesses greater than 150 nm, while they appreciably depart from the same curves for smaller thicknesses. This behavior is interpreted in terms of a reduction of the effective elastic constants of the film in a layer near the interface, due to the lattice misfit between the film and the substrate. This effect was not observed in the case of ZnO films deposited on fused quartz substrates.
RESUMO
The change of polarization that is produced on a transmitted light beam by acoustic surface waves propagating on a yz-LiNbO(3) plate is analyzed. When using a crossed polarizer and analyzer for optimizing the signal-to-noise ratio, the best conditions of diffraction efficiency have been found at an angle of incidence approximately equal to -10 degrees .
RESUMO
The light deflection efficiencies of surface acoustic waves propagating on YZ-LiNbO(3) crystal are examined for different geometrical configurations. The optimum one is found to be the back reflection geometry, with S polarization of the impinging light beam, where a figure of ~16% of the total deflected to undeflected light intensity ratio is easily attainable with a surface corrugation amplitude of about 50 A.
