Adsorbate lateral interactions and islanding in surface reaction kinetics

M. Silverberg*, A. Ben-Shaul

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

47 Scopus citations

Abstract

The effects of lateral interactions on the kinetics of bimolecular surface reactions are studied for interactions extending to second and third nearest neighbor range. Monte Carlo simulations are performed for a model system of two adsorbates, A and B, which react to form a rapidly desorbing product. The model features both "topological" and "energetic" effects associated with lateral (A-A, A-B and B-B) interactions; the former reflect the non-random (partially ordered) lateral distribution of the adspecies while the latter correspond to the changes in their diffusion and reaction activation barriers. The general kinetic scheme of the simulations consists of three stages: (i) adsorption of A followed by diffusion and (partial) adlayer ordering; (ii) adsorption of B followed by diffusion of A and B and reorganization of the mixed overlayer; (ii) gradual temperature rise, which triggers and enhances the A + B → AB reaction, as in temperature programmed reaction (TPR) experiments. The substrate surface is a regular two-dimensional square lattice. Adsorbate interaction potentials are chosen such that p(2 × 2) A-islands are formed at coverages below 0.25 and are gradually replaced by c(2 × 2) structures at coverages between 0.25 and 0.5. Similarly, due to repulsive A-B interactions, coadsorption of B also induces (at sufficient coverages) the compression of A's from the p(2 × 2) to the c(2 × 2) structure. The choice of the model system has been partly motivated by an experimental study of CO oxidation on Pd(100) (see Stuve et al., Surface Sci. 146 (1984) 155). Although the simulations reveal some of the important features observed experimentally, no attempt is made to reproduce or predict any specific experiment. TPR spectra are calculated for various initial conditions. The pattern of reaction is characterized by two distinct regimes, reflected by two peaks in the TPR spectra: a "contact" regime in which A and B react when forced into close contact with each other (giving rise to a low temperature peak), and a "diffusion" regime in which particles must diffuse towards each other to react. Comparison is made with combined Monte Carlo-lattice gas (Bethe-Peierls) model calculations, showing that such models can be useful for low and moderate coverages.

Original languageEnglish
Pages (from-to)17-43
Number of pages27
JournalSurface Science
Volume214
Issue number1-2
DOIs
StatePublished - 4 Apr 1989

Fingerprint

Dive into the research topics of 'Adsorbate lateral interactions and islanding in surface reaction kinetics'. Together they form a unique fingerprint.

Cite this