Abstract
Using Monte Carlo simulation methods in the canonical and grand canonical ensembles, we discuss the melting and the formation of ordered structures of mixed Ar-Xe submonolayer films on graphite. The calculations have been performed using two- as well as three-dimensional models of the systems studied. It is demonstrated that out-of plane motion does not affect the properties of the adsorbed films as long as the total density is not close to the monolayer completion. On the other hand, close to the monolayer completion, the promotion of particles to the second layer considerably affects the properties of mixed films. It has been shown that the mixture exhibits complete mixing in the liquid phase and freezes into solid phases of the structure depending upon the film composition. For submonolayer densities, the melting temperature exhibits non-monotonous changes with the film composition. In particular, the melting temperature initially increases when the xenon concentration increases up to about 20%, then it decreases and reaches minimum for the xenon concentration of about 40%. For still higher xenon concentrations, the melting point gradually increases to the temperature corresponding to pure xenon film. It has been also demonstrated that the topology of phase diagrams of mixed films is sensitive to the composition of adsorbed layers.
Highlights
It is well known [1,2,3,4,5,6,7,8] that monolayer films of both argon and xenon on graphite form incommensurate two-dimensional solid phases at low temperatures
Experimental data [10,11,12,13,14] as well as computer simulations [15, 16] have demonstrated that submonolayer films of argon melt via continuous phase transition at the triple point temperature equal to Tt ≈ 49.7 K [17]
The melting of incommensurate submonolayer films of xenon is of first order [21, 22], and occurs at the triple point temperature of about 100 K
Summary
It is demonstrated that out-of plane motion does not affect the properties of the adsorbed films as long as the total density is not close to the monolayer completion. Close to the monolayer completion, the promotion of particles to the second layer considerably affects the properties of mixed films. It has been shown that the mixture exhibits complete mixing in the liquid phase and freezes into solid phases of the structure depending upon the film composition. The melting temperature exhibits non-monotonous changes with the film composition. For still higher xenon concentrations, the melting point gradually increases to the temperature corresponding to pure xenon film. It has been demonstrated that the topology of phase diagrams of mixed films is sensitive to the composition of adsorbed layers
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