Cluster Analysis of the Vibrations of the p(2x2) Oxygen Structure on Ni(100)

摘要

We have used cluster techniques to carry out an analysis of th vibrational spectrum of the p(2x2) oxygen overlayer on Ni(100). A set of harmonic force constants has been determined which yields a best fit to recent experimental data by Ibach, including not only the oxygen mode polarized parallel to the surface, but also the dispersion of both the perpendicular and parallel modes. The most reasonable fit to experiment is achieved when the oxygen is positioned 0.88 A above the four-fold hollow site of the Ni(100) surface (in agreement with other experimental evidence), and the Ni-O bond stretching force is assigned a value of 1.6911 mdyn/A. A significant off-diagonal force constant which couples opposing Ni-O bond stretching coordinates for a given adsorbate atom is necessary to obtain agreement with the frequency of the oxygen mode polarized parallel to the surface. The value of this off-diagonal force constant is f sub Ni-O, Ni-O = 0.3640 mdyn/A.