Mechanism of metal droplet nucleation from supersaturated vapor

An analysis of the full nonlinear mechanism of condensation nucleation from a supersaturated vapor suggests that the classical Markovian growth mechanism may not apply to systems, such as metals, that exhibit pronounced magic-numbered clusters. Packing of atoms in concentric layers and/or quantum confinement of valence electrons lead to particular sized metal clusters that are anomalously stable. They are called magic-numbered clusters. Magic-numbered clusters are not explicitly addressed in the Markovian mechanism that assumes that clusters change size by accommodation or evaporation of one monomer at a time. This is a justifiable approximation only if the frequency of all cluster-cluster collisions is negligible compared with the frequency of the succession of monomer-cluster collisions required to produce an equivalent sized cluster to the cluster-cluster collision. Since the stability of magic-numbered clusters increases the likelihood of collisions between clusters, magic-numbered clusters can affect the nucleation mechanism and may have a significant influence on the nucleation rate from supersaturated metal vapors.