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 TM, 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.

First principles molecular dynamics studies of the low, intermediate, and high temperature phases of Ge(111) are reviewed. The atomic structure and electronic properties of the c(2 × 8) reconstruction, the diffusion of Ge adatoms at the c(2 × 8) → (1 × 1) disordering transition at T ~ 300°C, and the behavior of Ge(111) close to the bulk melting temperature are discussed.