Theory of Surface Optical Phonons on Reconstructed Surfaces

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Abstract
We consider the effect of surface reconstruction on the properties of surface optical phonons, within the framework of a simple model. The model employed is the semi-infinite simple-cubic Montroll-Potts model, with absorbed layer of atoms with mass less than that of atoms in the bulk. The surface layer is assumed to reconstruct into a 2×1 structure. The reconstruction of the surface has two effects. A gap is opened up in the surface-optical-phonon dispersion relation along the new zone boundaries, and some portions of the surface-optical-phonon branches may be admixed with bulk phonons, and thus become virtual surface phonons. Within the model, the width of the virtual levels is studied as a function of the various model parameters.