Poisson-like height distribution of Ag nanoislands on Si(111) 7x7

The height distribution of Ag(111) islands grown on Si(111) 7x7 was studied using in situ x-ray reflectivity. This noble metal-on-semiconductor system is of particular interest because the islands exhibit an unusual minimum height that is imposed by the quantum confinement of the conduction electrons. For different coverages and temperatures as well as annealing, it was found that the island heights exhibit a variance that is less than the mean by a constant amount. We argue that this behavior is related to Poisson-like statistics with the imposition of the minimum island height. A modified Poisson height distribution model is presented and shown to provide a good description of the experimentally measured island height distributions. The results, which contribute to a better understanding of the nanoscale growth behavior for an important noble metal, are discussed in terms of mobility that leads to taller islands.