Effects of adsorbate lateral repulsion on desorption and diffusion kinetics studied by Monte Carlo simulations

Abstract

The effects of adsorbate lateral interactions on the kinetics of surface diffusion and desorption are studied by means of kinetic and thermodynamic Monte Carlo simulations. This study is motivated by recent diffusion and desorption experiments on the NH 3 /Re͑001͒ system, which show that the activation energies of these processes decrease ͑in different fashions͒ with increasing surface coverage, the interactions between the adsorbates are thus assumed to be repulsive. A long range dipole-dipole-like potential is used to simulate both the diffusion and desorption processes. Most calculations are carried out with the interaction range extending up to fourth-order neighbors. Longer ranges are found to barely affect the kinetic behavior. On the other hand, shorter ranges of interaction result in qualitatively and quantitatively different structural ͑thermodynamic phase͒ behaviors and, consequently, in very different kinetics of diffusion and desorption. The model used to calculate diffusion kinetics assumes that the activation barrier to particle diffusion depends, simultaneously, on the local environments of both the initial and the final sites involved in the elementary event of particle jumps. The chemical diffusion coefficient is evaluated based on thermodynamic and kinetic Monte Carlo simulations. It is found to increase with surface coverage, reflecting the repulsive nature of the interactions. Yet, unlike the experimental results, the increase is nonmonotonic but rather, somewhat oscillatory-reflecting the structural phase transitions of the adsorbed layer. The activation energy of desorption is found to decrease by about 15 kcal/mole as the coverage increases from 0 to 1, showing steeper slopes around the coverages corresponding to a perfectly ordered adlayer phase. These results are in satisfactory qualitative and quantitative agreement with experiment. Finally, it is shown that the coverage dependence of the activation barrier to diffusion can be reasonably well evaluated from equilibrium thermodynamic desorption data.

Air pollution effect of SO2 and/or aliphatic hydrocarbons on marble statues in Archaeological Museums

“…All of these phenomena affect the local environment of the adsorbed particles and are thus expected to significantly affect the kinetics of the various surface processes, such as diffusion, desorption, adsorption and/or chemical reaction. In every case, there is a complete correspondence between regions in plots ε = ε(t) and  = Â(t) [24].…”

The influence of long-range lateral interactions on the thermodynamics and kinetics of thermal desorption

“…Comparing the desorption traces for different total adsorbate-adsorbate interaction, (9, 0), (11,0) and (13,0), one observes the expected overall shift due to the different desorption energy…”

“…Desorption curves are shown for the following combinations of (V of the desorption energy on the adsorbate coverage which cannot be described by nearest neighbor interactions, only. In this case, the simulated adlayer structures clearly reflect the actual distribution of the lateral interaction components [11].…”

“…Just like in the experiment, the macroscopic desorption behavior arises from the underlying microscopic atomic or molecular diffusion and desorption processes in the KMC simulation. While KMC simulation is a commonly used method for studying diffusion limited aggregation, structure formation and growth, its application for desorption simulations is a new frontier [3,5,[10][11][12][13][14] -in contrast to equilibrium Monte Carlo simulations which have previously been applied to study desorption in 2D quasi-equilibrium. Our thoroughly tested KMC simulation scheme allows the computation of ab Chemical Physics Letters 379 (2003) 568-573 www.elsevier.com/locate/cplett initio desorption spectra for known adsorbateadsorbate and adsorbate-substrate interaction potentials.…”

Kinetic modelling of heterogeneous catalytic systems

“…By combining nextnearest-neighbour attractive with nearest-neighbour repulsive interactions [172], Bowker and King were able to provide a qualitative explanation for the maximum in the diffusion coefficient with respect to coverage, observed experimentally for O adatoms on W(1 1 0) [181]. Subsequent studies on the diffusion of interacting adsorbates have elaborated on the effect of different types of interactions (attractive, repulsive, nearest-and next-nearest-neighbour) [182][183][184][185], correlated non-monotonic trends of the diffusion coefficient with the phase transitions of the overlayer [186,187], focused on lattices with multiple site types [188][189][190], analysed memory effects in tracer and collective diffusion [191], and investigated the correlation function of fluctuations in the ordered structure of adlayers [192,193].…”