Transition from surface vibrations to liquidlike dynamicsat an incompletely melted semiconductor surface

We present results of a first-principles molecular-dynamics simulation of the vibrational spectrum of a model semiconductor surface where, close to the bulk melting temperature (Formula presented), the top bilayer becomes diffusive. The specific example chosen is Ge(111). In place of the ordinary surface vibrations, we obtain a spectrum more akin to that of a confined liquid. In particular, we predict a dramatic decrease in the intensity of high-frequency (bond-stretching) surface mode intensity, associated with a local melting-induced breaking of hard covalent bonds in the top bilayer.