Lattice Gas Model For Adsorption Research Articles

Adsorption of triangular-shaped molecules with directional nearest-neighbor interactions on a triangular lattice

Using Monte Carlo and transfer-matrix methods the lattice gas model of adsorption of triangular-shaped molecules on a triangular lattice is studied. The constructed model takes into account the directionality of pairwise nearest-neighbor interactions between the adsorbed molecules. It is shown that a predominant character of "tip-to-tip" attractive interactions w1 always leads to the formation of the honeycomb structure in the adsorption monolayer with local density ρ = 0.66(6). While, the values of "side-to-side" w2 and "tip-to-side" w3 interactions define the structure of close-packed phase. Depending on the values of the interactions the close-packed phase may have: (a) completely disordered structure; (b) frustrated honeycomb structure which is formed by Langmuir like adsorption onto 2D pores of the honeycomb structure; (c) ordered close-packed structure consisted of the molecules which all have the same orientation relative to each other and relative to the surface.

3004 実数型格子ガス法による吸着脱離現象のモデル化(OS-30A 格子ボルツマン・ガス法,OS-30 格子ボルツマン・ガス法)

3004 実数型格子ガス法による吸着脱離現象のモデル化(OS-30A 格子ボルツマン・ガス法,OS-30 格子ボルツマン・ガス法)

Monte Carlo study of linear chain submonolayer structures. Application to Li/W(1 1 2)

The lattice gas model for adsorption of alkaline elements on W(1 1 2) surface is studied by Monte Carlo simulations. The model includes dipole–dipole interaction as well as long-range indirect interaction. The numerical analysis of ground states shows that truncation of the indirect interaction even at 200 Å may change a phase diagram, i.e., new long-periodic phases might occur. The phase diagram for Li/W(1 1 2) is constructed and chain structures (9 × 1), (6 × 1), (4 × 1), (3 × 1), and (2 × 1) are found to be stable at low temperatures. It is shown that the (4 × 1) phase melts through incommensurate phase. Role of thermal fluctuation is discussed by comparison of Monte Carlo results with mean field calculations.

Three-Site Lattice Gas Model for Adsorption of Binary Aromatic Mixtures in Silicalite

Adsorption of the binary benzene/p-xylene mixture in silicalite is studied by means of a generalized version of the homogeneous three-site lattice gas model. The energy parameters found during fitt...

Multilayer adsorption and desorption: Cs and Li on Ru(0001).

We use a multilayer lattice gas model for adsorption and desorption to analyze and simulate desorption data for Li and Cs on Ru(0001) extracting surface binding energies and lateral interactions. The latter are repulsive for the first layer and attractive for subsequent ones. \textcopyright{} 1996 The American Physical Society.

Multilayer adsorption and desorption: Au and Cu on Mo(110)

We use a multilayer lattice gas model for adsorption and desorption to analyze data on Cu Mo(110) and Au Mo(110) extracting surface binding energies and lateral interactions. We establish layer-by-layer growth for the first two layers.

Multilayer adsorption and desorption

A multilayer lattice gas model for adsorption and desorption is formulated and solved using transfer matrix methods. Ramifications of nearest neighbor and next nearest neighbor interactions on equilibrium properties, on the growth modes, and on the desorption kinetics are studied in numerous examples. A variety of adsorbate structures and growth modes is obtained. Mass transfer between the layers can be induced, both under adsorption and desorption conditions.

Lattice-gas model for adsorption on fractally rough surfaces

A lattice-gas model for physical adsorption of a gas on a fractal surface is solved in mean-field approximation. Adsorption isotherms display a rich structure with first and second order transitions. Surface tension and temperature effects are analysed. The possibility of determining the surface fractal dimension on the basis of "monolayer" adsorption measurements is discussed. Results for the multilayer adsorption regime are also presented and compared with recent scaling conjectures.

Adsorption on stepped surfaces: A Monte Carlo simulation

Within the lattice gas model for adsorption on cubic (100) surfaces, the effect of surface steps running along lattice directions is modelled by considering adsorption on terraces L lattice spacings wide, with various types of boundary energies on the right and left edges of the terrace. Both the cases of attractive and of repulsive nearest-neighbor interaction between the adparticles are considered. While adsorption isotherms are not much affected by boundary energies in the repulsive case, a drastic influence of various choices of boundary energies is identified for the case of attractive interactions, where the system separates in phases of low and high coverage, respectively. Then adsorption will occur typically near one of the terrace boundaries, and a “domain wall” separating the high and low coverage phases will run parallel to the steps. A wetting transition is identified between a phase where the domain wall is bound to one of the steps and a phase where it is “unbound”, delocalized in the bulk of the terrace. The phase diagram found in the simulation for this wetting transition agrees with a theoretical prediction due to Abraham. In contrast, for repulsive interactions where the system orders in the c(2 × 2) structure, antiphase boundaries occur which typically run perpendicular to the steps. The generalization of these results to other models as well as the application to experiments is briefly discussed.

Structure and adsorption at gas–solid interfaces: Layering transitions from a continuum theory

Packing effects in liquid-like films, adsorbed from bulk gas at the interface with an attractive solid substrate, may cause the fluid to adopt layer-like structure near the substrate. Such structure is inherent in the lattice gas model of adsorption where it is known to give rise to a sequence of layering transitions at low temperatures, provided the substrate (wall) is sufficiently attractive. We have used a nonlocal density functional theory to describe a continuum fluid near strongly attractive structureless walls. The theory yields oscillatory density profiles arising from packing effects. At low temperatures T (typically 0.5≲T/Tc ≲0.6, where Tc is the bulk critical temperature) the adsorption may increase with pressure in a series of discontinuous jumps, each corresponding to the appearance of a new dense layer in the adsorbed film. The transitions are first order, with very small metastable regions. As in the lattice gas model the transitions exhibit critical points; above the critical temperature of a given layer the adsorption increases smoothly with increasing pressure. However, we anticipate certain qualitative differences between the transitions we observe in the continuum theory and those of the lattice gas model, since the latter overemphasizes the role of hard-core repulsion. Layering transitions also occur for fluids confined in narrow pores. We find that in cylindrical pores the transitions are shifted to lower pressures. Moreover, capillary condensation (the first order transition to a ‘‘liquid’’ that fills the pore) competes with layering resulting in a rapid truncation of the sequence of layering transitions. The implications of our results for the interpretation of adsorption measurements performed near a bulk triple point are discussed and possible surface phase diagrams are suggested.

Evidence for the roughening and wetting transitions in the lattice-gas model of adsorption from Monte Carlo simulations

Evidence for the roughening and wetting transitions in the lattice-gas model of adsorption from Monte Carlo simulations