CHARACTERIZATION OF ENERGETIC SURFACE HETEROGENEITY BY A DUAL SITE BOND MODEL

A dual site-bond model for the description of correlated heterogeneous surfaces is presented. This model assumes the surface as a network of adsorptive ''sites'' connected by ''bonds' (saddle point energies). S ite and bond energies are statistically described by their energy dist ribution functions and the adsorptive energy surface by the joint site -bond energy distribution which is expressed in terms of a correlation function. The latter is determined by allowing the maximum randomness degree admitted by the ''construction principle''. This principle sta tes that the potential at an adsorptive site must be deeper than that of any bond connected to that site. Energy correlations naturally aris e when site-bond distributions overlap. A topological characterization of these correlations through an energy correlation length is propose d. This correlation length appears as a meaningful physical parameter. A transition between two well-differentiated morphologies of correlat ed elements upon variation of the overlapping degree of site-bond ener gy distribution is found. This fact is analyzed in terms of cluster mo rphology and percolation theory. A simulation procedure to simulate ad equately a site-bond heterogeneous surface is developed.