Phonon spectroscopy and surface reconstruction

Abstract

The nature of the recently discovered reconstruction of the Ni(100) surface under the influence of a c (2 x 2) carbon overlayer is investigated. A lattice dynamical analysis of the phonon dispersion of Ni(100) surfaces covered with c (2 x 2) overlayers of sulphur and oxygen suggests that the second derivative of the pair potential between the first- and second-layer nickel atoms is very sensitive to the adsorbed species. It is shown that the observed reconstruction pattern with the carbon overlayer follows naturally from the assumption that the second derivative becomes zero or negative for the unreconstructed atom positions. The effect could be an indication of internal strains caused by the adsorbate. Total energy calculations using the Hohenberg— Kohn—Sham density functional scheme on an Al 9 -cluster indeed provide an indication for such strains. A detailed analysis shows further th at the observed reconstruction may also result from an adsorbate-induced compression within the first layer.