Surface phase transitions in one-dimensional channels arranged in a triangular cross-sectional structure: Theory and Monte Carlo simulations

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

JOURNAL OF CHEMICAL PHYSICS

American Institute of Physics

Lugar: USA; Año: 2006 vol. 125 p. 214705 - 214713

0021-9606

Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer lattice-gas of interacting monomers adsorbed on one-dimensional channels arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) wL, interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) wT, interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transverse interactions (wT>0), where a rich variety of structural orderings are observed in the adlayer, depending on the value of the parameters kBT/wT (being kB the Boltzmann constant) and wL/wT. For wL/wT=0, successive planes are uncorrelated, the system is equivalent to the triangular lattice, and the well-known (31/2×31/2) [(31/2×31/2)*] ordered phase is found at low temperatures and a coverage, q, of 1/3 [2/3]. In the more general case (wL/wT ¹ 0), a competition between interactions along a single channel and a transverse coupling between sites in neighboring channels leads to a three-dimensional adsorbed layer. Consequently, the (31/2×31/2) and (31/2×31/2)* structures “propagate” along the channels and new ordered phases appear in the adlayer. Each ordered phase is separated from the disordered state by a continuous order-disorder phase transition occurring at a critical temperature, Tc, which presents an interesting dependence with wL/wT. The Monte Carlo technique was combined with the recently reported free energy minimization criterion approach (FEMCA) [F. Romá et al., Phys. Rev. B 68, 205407 (2003)] to predict the critical temperatures of the order-disorder transformation. The excellent qualitative agreement between simulated data and FEMCA results allows us to interpret the physical meaning of the mechanisms underlying the observed transitions.