Brillouin light scattering from surface phonons in hexagonal and cubic boron nitride films

Phase velocities of surface acoustic waves in several boron nitride films w ere investigated by Brillouin light scattering. In the case of films with a predominantly hexagonal crystal structure, grown under conditions close to the nucleation threshold of cubic BN, four independent elastic constants h ave been determined from the dispersion of the Rayleigh and the first Sezaw a mode. The large elastic anisotropy of up to c(11)/c(33) = 0.1 is attribut ed to a pronounced texture with the c-axes of the crystallites parallel to the film plane. In the case of cubic BN films, the dispersion of the Raylei gh wave provides evidence for the existence of a more compliant layer at th e substrate-film interface. The observed broadening of the Rayleigh mode is identified to be caused by the film morphology. (C) 2000 Elsevier Science B.V. All rights reserved.