Surface Lattice Dynamics of Ordered Overlayers on Metals

Abstract

We have performed lattice dynamical calculations on several types of superstructures on the Ni(100), Ni(111) and Ru(00l) surfaces, with the aim of studying the sensitivity of the electron energy-loss data on these surfaces to issues like the adsorption site symmetry [l], the adsorbate and substrate surface phonon and surface resonance dispersion [2], and the extended overlayer symmetry [3]. The model Hamiltonian consists of nearest neighbour pairwise interactions with central forces, although in cases where it is necessary, angle bending interactions have been included. The Fourier transformed Green’s function for the system is constructed and the corresponding equations of motion obtained. The Green’s function hierarchy thus obtained is solved by invoking an exponential ansatz, for the equation representing the motion of the atoms in the bulk of the metal, and by treating those for the motion of the atoms in the surface layers exactly. The phonon spectral density, which is directly related to the electron energy-loss spectrum, is calculated from these exact Green’s functions.