Effects of quenched impurities on surface diffusion, spreading, and ordering of O/W(110)

Abstract

We study how quenched impurities affect the surface diffusion and ordering of strongly interacting adsorbate atoms on surfaces. To this end, we carry out Monte Carlo simulations for a lattice-gas model of O/W͑110͒, including small concentrations of immobile impurities which block their adsorption sites. We examine the behavior of the diffusion coefficients and order parameters as a function of coverage corresponding to various ordered phases at low temperatures. The effects of impurities are examined under both equilibrium and nonequilibrium conditions, and the results are compared to recent studies on a completely clean surface. We find that even minute impurity concentrations affect the diffusion behavior considerably in equilibrium. The effects are strongest in ordered phases and close to phase boundaries, where quenched impurities lead to a reduction of order, which in turn leads to significant changes in the collective diffusion and phase behavior. As the impurity concentration is increased to a level of a few percent of the total surface area, the reduction in order becomes particularly prominent at high coverages. Further studies under nonequilibrium conditions reveal that nonequilibrium effects are strong in the absence of impurities, while for surfaces covered by impurities the nonequilibrium effects are relatively weaker.

Nonequilibrium effects in diffusion of interacting particles on vicinal surfaces

“…For more complicated cases characterized by a manifold of competing interactions, it would be of great interest to study the influence of steps on adsorbate systems such as the O / W͑110͒ system considered elsewhere. [26][27][28]33,34 Work in this direction is in progress. …”

“…19,[26][27][28] As for nonequilibrium phenomena on stepped surfaces, the previous work 19 has been based on the Langmuir gas model, where the only interaction between adatoms is site exclusion. However, it is remarkable that despite its highly simplified nature, even the Langmuir gas model indicates nonequilibrium to play a major role, causing significant deviations for the coverage dependence of collective diffusion.…”

Model of Uptake of OH Radicals on Nonreactive Solids

“…The analytical description of the surface heterogeneity is very complicated and requires various mathematical approaches. In particular, the role of quenched impurities on the surface kinetics for a large adsorbate coverage (θ > 0.1) was studied by several groups. , In our modeling, we used the simplification that the catalytic surface has active sites with the same values for the heat of adsorption. The adsorption of the radicals occurs on specific sites, such as defect structures on the surface of the crystal .…”

Interplay between steps and nonequilibrium effects in surface diffusion for a lattice-gas model of O∕W(110)

“…We have recently employed the same approach to elucidate the influence of nonequilibrium conditions and impurities on surface diffusion coefficients. 20,23,[34][35][36] The BM method is based on an assumption that, in the long time limit, the coverage profiles ͑x , t͒ along the spreading direction x collapse to a single scaling function when scaled with ͑x / ͱ t͒. Using the transformation = x / ͱ t, we can find D c ͑ ͒ as a solution of the nonlinear diffusion equation as 37…”