Nucleation of metal clusters by molecular dynamics simulation

Thomas Kraska

University Cologne, Institute for Physical Chemistry, Cologne, Germany

N. Lümmen (Institute of Physics and Technology, University in Bergen, Norway)
T. Kraska (Physical Chemistry, University of Cologne, Germany)

Molecular dynamics simulation is employed for the investigation of the formation of metal clusters in an inert gas aggregation source. Metal atoms are placed in a simulation box on a lattice with distances larger than the interaction range. After the simulation is started the highly supersaturated state exists for some time until clusters are formed by homogeneous nucleation and particle growth. Argon is added as carrier gas in order to mimic the experimental situation. It removes the heat generated during the nucleation. The interactions of the metal atoms are modelled by the embedded atom method while for argon the Lennard Jones potential is used. With this method the homogeneous nucleation in pure Fe, pure Pt, and binary FePt are investigated. 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. The obtained nucleation rates for Fe are consistent with available experimental data. The Pt nucleation rates and the binary nucleation rates also show systematic behaviour. In case of binary nucleation pure Pt nucleation has been observed leading to pure Pt clusters with up to 10 atoms. This effect is attributed to the stronger cohesive energy of Pt compared to Fe.

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