Desorption of Gold-Clusters from Graphite – Atomistic surface

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.

Desorbed Cluster

Translational Energy

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

Movies

All movies are made for the desorption event.

1. Color codes species: yellow: Graphite, blue: Gold

View along inpact direction
View along impact path

Species side view
Side view, slab of 10 Å

Top view species
Top view

2. Color codes temperature: blue-red: 0 K up to sublimation-temperature of graphite (Ts = 3820 K), purple: above Ts

Temperature impact direction
View along impact path

Temperature side view
Side view, slab of 10 Å

Temperature Top view
Top view

3. Color codes pressure: blue-red: -30 GPa up to 30 GPa, purple: overflow, dark purple: underflow

Pressure impact direction
View along impact path

Pressure side view
Side view, slab of 10 Å

Pressure top view Max = 30 GPa
Top view:
Max pressure +/- 30 GPa

Pressure top view Max = 10 GPa
Top view:
Max pressure +/- 10 GPa




Desorption of Gold-Clusters from Graphite – Virtual surface

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.

Temperature for cluster with 0.8 eV/atom
0.8 eV/atom
=> Desorption
color code: temperature,
all atoms shown

Temperature for cluster with 0.8 eV/atom Slab -10 10
0.8 eV/atom,
Slab [-10:10] Å,
color code: temperature

Pressure for cluster with 0.8 eV/atom Slab -10 10
0.8 eV/atom,
Slab [-10:10] Å,
color code: pressure

For comparison

Temperature for cluster with 0.39 eV/atom
0.39 eV/atom
=> no Desorption
color code: temperature

Temperature for cluster with 0.8 eV/atom without
0.8 eV/atom
without wall
Slab [-10:10] Å
color code: temperature

Temperature for cluster with 0.8 eV/atom without
0.8 eV/atom
without wall
all atoms shown
color code: temperature



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15.4.2008 - Dr. C. Anders