Coverage Dependence Of Diffusion Research Articles

Low-energy electron microscopy of CO/Pt(111) surface diffusion by nonequilibrium coverage profile evolution

The adsorption and diffusion of CO molecules on a Pt(111) surface have been studied using low-energy electron microscopy (LEEM). The explicit relationship between LEEM image intensity and CO coverage that is determined during adsorption is used to characterize nonequilibrium CO coverage profiles that are subsequently prepared by laser-induced thermal desorption. Real-time observations of the temporal evolution of these profiles toward equilibrium uniform coverage distributions are analyzed by predictive and inverse solutions of the diffusion equation. These two methods determine consistently the detrimental effect on diffusion of the laser-induced surface damage that is observed directly with LEEM. The inverse method also provides independent information on the coverage dependence of diffusion with high coverage resolution.

Diffusion and mobility of interacting particles on stepped surfaces

We study the mobility and collective diffusion of mutually interacting adparticles on stepped surfaces through Monte Carlo simulations. We consider the case of nearest-neighbor repulsive interactions and different binding energies at the step edges in the disordered phase. We find that the coverage dependence of diffusion across the steps is sensitive to the adparticle interaction energy. For strong step binding, it is known that the corresponding collective diffusion coefficient D x,c ( θ) has a maximum at a coverage of θ=1/ L for a given step spacing L. We show that this maximum moves to higher coverages with increasing repulsion, strongly enhancing diffusion. For weak step binding, these effects are even more pronounced. We also find that with a given adparticle repulsion, increasing the step binding energy slows down diffusion but does not change the overall coverage dependence of D x,c ( θ). Implications of these findings are briefly discussed.