Propagation and focusing of high-frequency Rayleigh phonons

We report on the experimental observation of high-frequency Rayleigh phonons on Si(001) surfaces. By use of the phonon-imaging technique we can measure the spatial phonon flux distribution of Rayleigh phonons in the Si(001) surface. Since the mean free path of Rayleigh phonons is limited by surface-roughness-induced scattering mainly into bulk phonons, a micro-imaging experiment was performed. As a suitable detector we use ion implanted Si: P bolometers of 18 mu m in diameter and 200 nm in depth, operated at 1 K. To obtain as clean surfaces as possible, the technique of laser annealing in situ was applied. Experimental results showing propagation distances of several hundred micrometers for Rayleigh phonons are presented.