Dynamics of xenon-covered graphite slabs

Abstract

Following our earlier work [I; Phys. Rev. B 23, 4208 (1981)] on the dynamics of the graphite (0001) free surface, we present here a full dynamical calculation of a (0001) graphite slab with registered monolayers of xenon atoms adsorbed on its two surfaces. The xenon-xenon and xenon-carbon interactions are modeled with a Lennard-Jones potential, whereas the carbon-carbon interactions are described by the extended axially symmetric force-constant model introduced in I. Three doubly degenerate surface-mode branches are found which are associated with almost independent vibrations of the xenon layers in the potential field of the substrate. (However, for increasingly long wavelengths the substrate participates more and more in these vibrations which become the rigid-body translations for infinite wavelength.) Other surface modes involve mainly the underlying carbon slab and have their maximum amplitudes in the outer carbon layers. Density-of-states functions of the xenon-covered slabs have also been calculated, in connection with a future evaluation of the thermodynamic properties of this system.