Relaxation effects in random sequential adsorption: application to chemisorption systems

We consider the effect of slow relaxation processes in two models for irreversible chemisorption which incorporate superlattice ordering of the adsorbed layer on a square lattice of adsorption sites. The first model involves adsorption of monomers onto single empty sites, and we the second involves dissociative adsorption of dimers onto diagonally adjacent empty sites, where adsorption in both models occurs subject to the constraint that no adjacent pairs of occupied sites can be created. These adsorption processes produce adlayers comprised of disordered ‘checkerboard’ or c(2×2) domains, adsorption continuing until a non-equilibrium ‘jammed’ state is reached where no further space is available for adsorption. We focus on characterizing the evolution from this jammed state as a result of slow surface diffusion, or slow desorption (or reaction) processes. These relaxation processes open up further adsorption sites which are immediately filled in the presence of continued adsorption. In all cases, evolution involves Lifshitz–Cahn–Allen-type coarsening of the c(2×2) domains.