Statistical Thermodynamics and Surface Phase Transitions of Interacting Particles Adsorbed on One-Dimensional Channels Arranged in a Triangular Cross-Sectional Structure

PASINETTI P. M.; ROMÁ F.; RICCARDO J.L.; RAMIREZ PASTOR A. J.

Solid State Phenomena

Trans Technical Publications Ltd.

Lugar: Baech; Año: 2009 vol. 150 p. 73 - 100

Monte Carlo simulations and finite-size scaling analysis have been carried out to studythe critical behavior in a submonolayer lattice-gas, which mimics a nanoporous environment. In thismodel, one-dimensional chains of atoms were arranged in a triangular cross-sectional structure.Two kinds of lateral interaction energies have been considered: (1) wL, interaction energy betweennearest-neighbor particles adsorbed along a single channel and (2) wT, interaction energy betweenparticles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transverseinteractions (wT > 0), where a rich variety of structural orderings are observed in the adlayer,depending on the value of the parameters kBT/wT (kB being the Boltzmann constant) and wL /wT. ForwL /wT = 0, successive planes are uncorrelated, the system is equivalent to the triangular lattice, andthe well-known ( 3 3) × [( 3 3)* × ] ordered phase is found at low temperatures and acoverage, θ, of 1/3 [2/3]. In the more general case (wL /wT ≠ 0), the competition betweeninteractions along a single channel and the transverse coupling between sites in neighboringchannels leads to a three-dimensional adsorbed layer. Consequently, the ( 3 3) × and ( 3 3)* ×structures “propagate” along the channels and new ordered phases appear in the adlayer. Theinfluence of each ordered phase on adsorption isotherms, differential heat of adsorption andconfigurational entropy of the adlayer has been analyzed and discussed in the context of the latticegas theory. Finally, the Monte Carlo technique was combined with the recently reported free energyminimization criterion approach (FEMCA) [F. Romá et al.: Phys. Rev. B Vol. 68 (2003), art. no.205407] to predict the critical temperatures of the surface-phase transformations occurring in theadsorbate. The excellent qualitative agreement between simulated data and FEMCA results allowsus to interpret the physical meaning of the mechanisms underlying the observed transitions.