Discontinuous formation and desorption of clusters during particles adsorption at surfaces

A theoretical model was derived to describe the discontinuous formation and desorption of clusters during particle adsorption at surfaces. Two steps were investigated: (1) time-dependent adsorption, where we found that the initial slope and the limiting magnitude of an adsorption isotherm depend on the clusters' distribution. A higher magnitude of both the adsorption and desorption rates appear to contract the time scale and hence increase the initial slope. Decreasing the geometrical parameter, q, which represents the shape of an adsorbed cluster, enhances the growth of large clusters on the surface. (2) A concentration dependence model shows that the number of adsorbed molecules increases with increases in the value of n (nucleation capacity). Furthermore, higher rates of adsorption provide steeper initial slopes (higher affinity of, molecules to surface). Decreasing q from 2 to 1, i.e. from a circular to a linear cluster formation, slightly decreases the magnitude of the isotherms.