Generalized model of irreversible multilayer deposition

The multilayer deposition of macromolecular particles, such as colloids and proteins, is often used to form thin film materials. We present a general model of the irreversible multilayer deposition process that accounts for both surface screening and surface restructuring. Particles are modeled as (d + 1)-dimensional hard spheres that deposit sequentially at random positions onto a d-dimensional substrate. A particle is considered irreversibly adsorbed if it lands directly on the surface. If the particle instead lands on a previously placed particle, it will do one of three things (depending upon the extent of "overhang" with respect to the surface or to the contacting particle): adsorb, desorb, or roll towards the surface. We obtain analytical results for the time evolution of the particle density in the first layer in one dimension when surface overhang rules are employed. We use computer simulation to investigate the other cases. We find that the first-layer saturation density is larger when the deposition rules favor rolling and disfavor higher-layer adsorption. The particle density above the surface exhibits oscillations that also show a strong dependence on the deposition rules.