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MM: Metall- und Materialphysik

MM 35: Growth

MM 35.3: Vortrag

Donnerstag, 30. März 2006, 15:15–15:30, IFW B

Molecular dynamics simulation of the nucleation and growth of platinum clusters — •Norbert Lümmen and Thomas Kraska — Physical Chemistry, University Cologne, Luxemburger Str. 116, D-50939 Köln, Germany

The formation of platinum clusters in an inert gas aggregation source is investigated by molecular dynamics simulation. At the beginning of the simulation the platinum atoms are in a highly supersaturated vapour state embedded in the carrier gas argon acting as a heat bath. The interactions of the metal atoms are modelled by the commonly used embedded atom method. Once the simulations are started the metastable phase remains for some time until clusters are formed by homogenous nucleation.

The nucleation rates are calculated from the cluster size statistics. Using a correlation of the nucleation rates as function of the supersaturation and the nucleation theorems the critical cluster size as well as the excess energy of the critical clusters are estimated. Also the continuation of the growth process by coalescence is traced in the simulations. In this context it is shown that coalescence can be the cause for a structural transition of a cluster. Even, or rather especially small clusters, which are often at high temperature, can be responsible for such transition.

Further results on the extension of the methodology on the investigation of nano alloy formation of will be reported. This will include the simulation of the formation process itself and the structural analysis of the resulting clusters.