A spherical gold cluster with 6000 atoms, deposited on a graphite surface, is bombarded at an angle of 45° with a smaller gold cluster Au402 with a total energy of 72 keV.
Gold cluster (red) Au6000 hit by Au402 “from below” at its perimeter. The cluster has left the interaction zone of the graphite (blue). Yellow: small Au-clusters not connected to the main-cluster. A series of MD simulations with impact points at different distances „x“ to the deposited cluster show that the cluster only gets sufficient momentum for desorption, if it is hit directly in a small range at it edge. If the projectile impacts into the graphite beside the cluster, not enough energy is transferred for desorption. If the projectile hits the cluster centrally, it is destroyed and only smaller clusters can fly away. The picture on the right shows the resulting translational energy of the desorbed cluster.
Results to be published in: I. Baranov, S. Della-Negra, V. Domaratsky, A. Chemezov, A. Novikov, V. Obnorsky, M. Pautrat, Chr. Anders, H.M. Urbassek, K. Wien, S. Yarmiychuk, E. Zhurkin, Desorption of nanoclusters from gold nanodispersed layers by 72 keV Au400 ions: experiment and molecular dynamics simulation, Nucl. Instr. and Meth. in Phys. Res. B (2008), doi: 10.1016/j.nimb.2008.03.094
All movies are made for the desorption event.
1. Color codes species: yellow: Graphite, blue: Gold
2. Color codes temperature: blue-red: 0 K up to sublimation-temperature of graphite (Ts = 3820 K), purple: above Ts
3. Color codes pressure: blue-red: -30 GPa up to 30 GPa, purple: overflow, dark purple: underflow
To reduce computer-effort the Au-C-Morse-potential is only computed relative to a virtual surface in z-direction. A hemispherical Au6000 cluster is relaxed for 8 ps in the potential of the virtual surface and then each atom is given a velocity in a random direction. For 0.39 eV per atom the cluster does not desorb while for 0.8 eV per atom it lifts off.
15.4.2008 - Dr. C. Anders