Ordering and order-disorder phase transition in the (1x1) monolayer chemisorbed on the (111) face of an fcc crystal

TL;DR

This study uses Monte Carlo simulations to explore phase transitions in a monolayer chemisorbed on an fcc (111) surface, revealing multiple stable ordered phases and a transition to disorder driven by temperature and bond fluctuations.

Contribution

It introduces a lattice gas model incorporating bond fluctuations and surface interactions, identifying new stable ordered phases and phase transition behaviors.

Findings

Multiple stable ordered phases identified.

Phase transition from order to disorder observed.

Bond fluctuations significantly influence phase stability.

Abstract

In this paper we have considered a simple lattice gas model of chemisorbed monolayer which allows for the harmonic fluctuations of the bond length between the adsorbate atom and the surface site. The model also involves a short-ranged attractive potential acting between the adsorbed atoms as well as the surface periodic corrugation potential. It has been assumed that the adsorbed atoms are bonded to the uppermost layer of the substrate atoms. In particular, using Monte Carlo simulation method we have focused on the orderings appearing in the dense monolayer formed on the (111) face of an fcc solid. Within the lattice gas limit, the chemisorbed layer forms a (1x1) structure. On the other hand, when the bonds are allowed to fluctuate, three other different ordered phases have been found to be stable in the ground state. One of them has been found to be stable at finite temperatures and to undergo a phase transition to the disordered state. The remaining two ordered states have been found to be stable in the ground state only. At finite temperatures, the ordering has been demonstrated to be destroyed due to large entropic effects.