F. Bulnes

Study of adsorption of binary mixtures on disordered substrates

The adsorption of binary mixtures on solid heterogeneous substrates is studied by Monte Carlo simulation in the framework of the lattice gas model. The energy of the surface has been modeled by considering two kind of adsorption sites, deep and shallow traps, forming square homogeneous patches of different sizes; these adsorption domains have been distributed either at random or in chessboard-like lattice to obtain simple heterogeneous topographies. The adsorption process has been monitored through total and partial isotherms and differential heats of adsorption corresponding to both species of the mixture, for different values of the parameters involved in the model (lateral interactions, energy gap between deep and shallow patches) and different topographies. A rich variety of behaviors is found and analyzed in the context of the lattice gas theory.

Adsorption and transport of particles in low-dimensional heterogeneous substrates

Abstract Adsorption and collective diffusion of interacting particles on one-dimensional heterogeneous lattices are studied by both Monte Carlo simulation and theoretical modeling (cluster approximation). The heterogeneous substrate is modeled as a chain of adsorptive sites with patchwise topography. Patches of equal size are alternatively distributed with adsorption energies E 1 and E 2 (bivariate patch surface). Equilibrium adsorption properties (adsorption isotherms, mean-square fluctuations of surface coverage, and adsorption heats), as well as surface diffusion (jump and collective diffusion coefficients) are addressed. Both the effect of lateral interaction between adatoms and substrate heterogeneity are considered. The MC results are compared with analytical results from cluster approximation, and the applicability of this latter approach in presence of heterogeneity is discussed.

Monte Carlo simulation of the adsorption of binary gas mixtures on heterogeneous surfaces

The adsorption of a gaseous mixture containing particles A and B was studied via lattice-gas simulations on homogeneous and heterogeneous bivariate surfaces characterized by a chessboard topography of strong and weak adsorbing sites. The effects of lateral interactions among adsorbed particles and of heterogeneity on the adsorption isotherms and differential heats of adsorption were analyzed. The results displayed a rich variety of behaviours and their analysis contributes to the understanding of mixed-gas adsorption at a molecular level.

Surface diffusion on heterogeneous correlated substrates

Abstract The behaviour of the surface diffusion coefficient on an heterogeneous correlated surface is studied in the framework of the lattice-gas model. Using the multivariate adsorptive energy distribution function the statistical properties of the heterogeneous correlated surface can be appropriately described and the effect of the heterogeneity on the collective diffusion coefficient at finite coverage can be analized through a correlation length. Monte Carlo simulation is also performed to test the analytical results.

Adsorption of interacting particles on square, honeycomb and triangular correlated heterogeneous surfaces

Abstract Adsorption of interacting particles on highly correlated heterogeneous surfaces is studied through grand canonical Monte Carlo simulation and the effective substates approximation in the framework of the lattice-gas model. The adsorptive surface potential has been characterized by patches of weak and strong adsorbing sites arranged in a deterministic chessboard structure, with square, triangular or hexagonal geometry. The effects of heterogeneity and nearest-neighbor adsorbate–adsorbate interactions on the adsorption process are analyzed for square, honeycomb and triangular geometries and different patch sizes.

Heterogeneous energetic topographies generated by a diffusional mechanism

In the present paper, we study the main characteristic features of surface energetic topographies generated via the evolution of a single adsorbed particle whose mobility strongly affects the adsorption energy of each visited site. This tracer changes its coordinates by means of activated jumps to nearest-neighbor sites modifying the adsorption energy of each visited site according to a very simple law. Therefore, its evolution on the lattice step-by-step changes the energy surface which in turn allows to obtain an heterogeneous trap substrate from an initially homogeneous lattice. In the framework of the well known surface growth theory, two different quantities (the mean site energy and the energy roughness of the substrate) have been monitored in order to characterize the process. The study of the time dependence of these quantities leads to the determination of the scaling behaviors represented by the scaling exponents. In particular, the obtained values for the scaling exponents suggest that the problem belongs to an unknown universality class.

Adsorption of laterally interacting gas mixtures on homogeneous surfaces

The adsorption of binary mixtures containing particles A and B on homogeneous substrates is studied by Monte Carlo (MC) simulations, quasi-chemical approximation (QCA), and exact counting of states on finite cells (we call this approach cluster approximation, CA). The energies involved in the adsorption model are five: (1)

Energetic Topography in Adsorption onto Heterogeneous Surfaces

\epsilon_A,