Evaluation of acoustic wave velocity in thin diamond films by thermal measurement

In this report, a new method to evaluate the acoustic wave velocity in thin dielectric films by thermal measurement is proposed and an experimental result for diamond thin film is presented. The principle is to use the relation between the thermal conductivity, the average acoustic wave velocity, and the mean free path of the phonon after measuring the propagating velocity of the thermal wave. This method was applied to a diamond thin film grown on a Si substrate. The evaluated acoustic wave velocity seems very reasonable, but how this is related to the surface acoustic wave velocity of a layered structure such as ZnO/diamond/Si remains to be investigated.