A STUDY OF ATOMIC VIBRATIONS ON SI(001) SB(2X1)/

We have investigated vibrational properties of the Si(001)/Sb(2 x 1) s urface by applying the adiabatic bond-charge model using the recently determined relaxed atomic geometry. We compare the phonon spectrum of this surface in detail with that of the Si(001)(2 x 1) surface present ed in a recent bond-charge model study. We observe that the surface ac oustic phonon modes are mainly localized on the adsorbate layer atoms due to the large mass difference between Sb and Si atoms. Adsorption o f Sb is shown to result in two new peaks in the phonon density of stat es; one below the bulk continuum, and the other near the boundary betw een bulk acoustic and optical states. (C) 1998 Elsevier Science B.V. A ll rights reserved.