Voids in the Coverage of Surfaces by Adsorbed Molecules

The adsorption of complex molecules on a solid surface may result in less than full coverage, even at zero temperature, due to molecular adsorption frozen in disorder. For molecules occupying more than one adsorption site, voids are formed in the layer of adsorbed molecules. This raises a question about the degree of coverage of the solid surface by the adsorbed molecules. Monte Carlo computer simulations for different molecule shapes on a binary AB crystal were done to determine the void concentration. The fraction of “uncovered surface area”, βs, and the fraction of the “excess uncovered surface”, βm, are defined and determined. βs is found to be between 0.093 and 0.577 and βm is in the range of 0.093 and 0.155. These values depend on the molecular size and shape. For a different surface, that of AB2 compound, βm is found to be smaller.