DYNAMICS OF MULTILAYER ADSORPTION - A MONTE-CARLO SIMULATION

The growth of an adsorbed film at an initially empty surface which is exposed at time t = 0 to a gas is studied within the framework of a kinetic lattice gas model by Monte Carlo simulation. The model includes an attractive potential V(z) between adsorbed particles at distance z from the surface, V(z) = -A/z3 and a nearest-neighbor attractive interaction between the gas atoms. Several choices of the surface potential depth A, corresponding to different sequence of layering transitions, are considered. The Monte Carlo process assumes random evaporation/condensation events of gas atoms in adsorbed layers close to the surface, while surface diffusion is disregarded. For temperatures T somewhat less than the interfacial roughening temperature T(R) of the considered lattice gas model, the time-dependent coverage theta(t) exhibits distinct steps, representing the adsorption of the first, second, third, etc. layer. This layerwise adsorption kinetics also shows up in the surface excess energy due to the adsorbed layer. At temperatures far below T(R), pronounced metastability of the empty surface as well as hysteresis is observed. On the other hand, for T > T(R) a smooth increase of coverage with time is observed, corresponding to wetting behavior rather than layering. We relate this behavior to the corresponding phase diagrams of the model and briefly discuss pertinent experimental applications.