Non-equilibrium acoustic phonon propagation in CVD diamond films

We have studied the mechanism of heat transfer under pursed excitation at l ow temperatures while measuring the propagation of non-equilibrium acoustic phonon packets across a CVD diamond him. Results are presented on the measurements of acoustic phonon packets propag ating across the high quality CVD diamond films with 0.25 and 0.35 mm thick ness. Two types of phonon generator were employed: laser heated Au/Ti films deposited onto the sample, and photoexcited buried implanted layers. A sup erconducting Al-GR-based bolometer served as the phonon detector. The resul ts obtained essentially differ from those for natural diamond: under photoe xcitation of the buried implanted layer the bolometer response times are la rger by an order of magnitude than those for natural diamond, and the shape of response has a clearly pronounced diffusive character. Possible mechani sms of response broadening are discussed, including the scattering of high- frequency phonons at grain boundaries. (C) 2000 Elsevier Science S.A. All r ights reserved.