Abstract
Despite its importance in theoretical studies of surface diffusion there has been limited experimental progress in developing methods to measure the dynamic structure factor S(q,t). In this work we study gases adsorbed on single-crystal surfaces and show that their equilibrium dynamics is measurable in a diffraction experiment through density fluctuations described by the dynamic correlation function . Using a lattice-gas model with nearest-neighbor repulsive interaction, we demonstrate how to separate out the microscopic dynamics caused by diffusion and adsorption-desorption from the form of . Our analytical results show that decays as an exponential with a time constant {tau}(q). Significant deviations from the hydrodynamic dependence of 1/{tau}(q)=D{sub c}q{sup 2} are found with and without desorption. These deviations have important consequences in extracting diffusion constants from experiments. (c) 2000 The American Physical Society.
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