Elastic properties of nanocrystalline zirconium-silicon-boron thin films

Thin amorphous films of ZrB3 grown on Si(111) substrates by chemical-vapor deposition are, upon annealing at 960 degreesC, transformed to films compos ed of nanocrystallites (6-10 nm extent) with a nominal composition of Zr0.9 Si0.3B3. The independent elastic constants of the layers are determined fro m the dispersion of the surface and pseudo-Sezawa acoustic excitations and reveal large enhancements in the C-11 and C-44 constants accompanying the c onversion of ZrB3 to the nanocrystalline phase. Since the transverse sound velocities of the binary and Zr0.9Si0.3B3 are in near resonance with the so und velocity of Si (V-T(Si)=4.8 km/s), only the Rayleigh surface wave is lo calized to the film while all higher-order acoustic modes are evanescent. D espite the strong decay channels, high-lying excitations with velocities as large as 25 km/s (>V-T(Si)) are observed in Brillouin light scattering. In sight into these acoustic properties is provided by evaluating the elastody namic Green's functions and associated acoustic-mode densities. (C) 2001 Am erican Institute of Physics.