Disordered topography

The description of real adsorption requires to take into account two main effects on the calculation of the thermodynamic quantities lateral ad-ad interactions, and characteristics of the energy surface. In addition, in the case of multicomponent adsorption, different species could "see" different disordered topographies. 

The surface topography is not only found to be important for metals, but also for elemental and compound semiconductors adsorption often occurs preferentially on the incompletely coordinated surface atoms of disordered surfaces, while ordered surfaces are relatively inert. 

Adsorption of binary gas mixtures in the presence of ad-ad interactions is studied through grand canonical Monte Carlo simulation in the framework of the lattice-gas model. The disordered surface has been characterized by patches of shallow and deep sites, arranged in a chessboard-like topography. 

Previous works dealing with disordered surfaces have been dedicated mainly to random, or correlated topographies. In the latter case, the combination of heterogeneity and ad-ad interactions effects produce complex behaviors on the equilibrium properties. An exact statistical mechanical treatment is unfortunately not yet available and, therefore, the theoretical description of adsorption has relied on simplified models. One way of circumventing this complication is the Monte Cado (MC) method, which has demonstrated to be a valuable tool to study surface processes [3,4],... 

To model the substrate we have used the Dual Site-Bond Model (DSBM) [S], which has proved to be useful to analyze topography effects on several molecular processes on heterogeneous surfaces. DSBM provide a statistical description of the disordered media based on two elements sites, and the corresponding saddle points (bonds) the adsorptive energy surface is described by site and bond probability density functions Fs( s) Fb(Eb)- The distribution functions S and B associated to F and Fb are defined by... 

In the following we present a hypothetical mechanism of c.b. formation that explains the universal value Ds 2.6 of c.b. surface topography on atomic length scales. The model is based on physical concepts of disordered surface growth, which were recently applied in many different fields in namre. 

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