Reentry of the Kapitza anomaly by submonolayers of gold

Perfect surfaces were prepared by laser annealing of Si in situ at an ambient temperature of 1 K. Gold atoms were deposited onto these surfaces by using a laser-evaporation technique. At the same time, the anomalous Kapitza transmission was probed by measuring the phonon reflection at these surfaces. It is found that the Kapitza anomaly is absent at the laser-annealed surfaces. Coverages as low as 0.02 atomic layer of Au, however, restore the anomaly. The anomalous transmission at the Au-covered surfaces increases weakly with phonon frequency. The data are in very good agreement with the defect model of Kinder if a deformation potential of 0.4 eV and an energy-independent density of states are used as parameters.