Surface acoustic waves in Ni/V superlattices

We have measured the surface-acoustic-wave velocities in Ni/V superlattices using both Brillouin scattering and surface-acoustic-wave techniques; the results are in good quantitative agreement. These results confirm earlier reports of phonon-velocity softening in bcc/fcc superlattices and prove that this is a general phenomenon, not a consequence of the measurement method. In addition, we describe in detail the ultrasonic measurement technique which allowed measurements to be performed in thin films.