Surface Phonons

Abstract

The influence of the perturbation of a bulk crystal by a surface is very important. First of all the breaking of bonds induces forces on the surface atoms which tend to reach an equilibrium configuration different from that of the bulk. We have discussed this effect before in the general context of relaxation and reconstruction of surfaces. This modification in the local bonding induces in turn a change in the vibrational properties which can be observed experimentally. It is this effect that we want to analyze here. For this we first recall some basic properties of phonons in solids with a more detailed discussion of phonon dispersion curves in semiconductors. We then consider surface phonons and try to derive some general results by using simple analytical arguments. We discuss as examples recent results obtained on Si(111) 2 × 1 and Si(100). In the last part we analyze phonon-related properties paying special attention to the asymptotic decrease of static displacements away from surfaces which can be directly deduced from the bulk vibrational properties.