The role of surface phonon scattering in the growth and decay of frequency-crossing signals

Abstract
Experiments, using the frequency-crossing technique, on phonon thermalisation in an Al2O3 bicrystal indicate that at 2 K and frequencies of around 200 GHz the process occurs predominantly at the surfaces. The high probability (about 1) of inelastic scattering at a fine-ground cylindrical surface is not reduced by annealing in argon at 1775 degrees C nor by a Syton polish followed by a hydrogen anneal at 1200 degrees C. Preliminary information is obtained on the spatial growth of holes in a phonon current as it travels through a resonantly scattering medium.