Brillouin scattering determination of the whole set of elastic constants of a single transparent film of hexagonal symmetry

In this work it is shown that the Brillouin light scattering technique can be successfully applied for determining the five effective elastic constants of a single transparent film of hexagonal symmetry, in the micron range of thicknesses. Measurements have been performed on a polycrystalline ZnO film, about 1.3 mu m thick, supported by a Si substrate. A major result of this work is that the elastic constant c 66 is selectively determined for the first time from detection of the shear horizontal mode travelling parallel to the film surface. Similarly, a selective determination of c 11 is attained from observation of the longitudinal mode guided by the film. The three remaining elastic constants, namely c 13 , c 33 , and c 44 , can be then obtained from detection of the Rayleigh surface mode and of the longitudinal bulk wave propagating at different angles from the surface normal.