A detailed analysis was made of the surface phonon spectrum, for a Si (111) -surface, based upon a phenomenological model. A Green’s function method was used. After calculating the surface phonons of an ideal surface, including displacement ellipses and attenuation constants, several models for the surface layer force constants were tested. The most interesting feature found from the calculations was a tendency to phonon softening at a k-vector belonging nearly to a (7 x 7) reconstruction. A model was proposed, for the structure of a (7 x 7) cell, obtained by freezing-in the displacements of the soft surface phonon.

Surface Phonons and Reconstruction of a Silicon Surface. W.Goldammer, W.Ludwig, W.Zierau, C.Falter: Surface Science, 1984, 141[1], 139-57