DYNAMICAL PROPERTIES OF AN ISOLATED STEP

The dynamics for a model system of an isolated infinite step in a surf ace are presented. The model is simple, treating the monatomic step as the interface between two coupled semi-infinite and single semi-infin ite atomic layers. The breakdown of translational symmetry perpendicul ar to the step edge gives rise to several Rayleigh-like branches local ized in the neighbourhood of the step. It is seen that a step may lift the polarization degeneracy of the ordered surface Rayleigh mode alon g the atomic rows parallel to and in the neighbourhood of the step edg e. Typical dispersion curves for these modes along the step edge are g iven with their polarizations. The vibrational Green functions are cal culated for the system, and the spectral densities are presented numer ically for atomic sites that constitute a minimum representative set i n the neighbourhood of the step. A hyperfine resonance structure is ob tained that permits the analysis of the evolution of the dynamics from one half-space to the other.