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 Karl Franzens University Graz

Graz University of Technology 

The morphology of mesoscopic transition metal clusters under oxidizing conditions
Fl. Mitterndorfer
Fakultät für Physik, Univ. Wien
17:15 - 18:15 Tuesday 06 November 2007 KFU

One of the goals of nanoscience is the fundamental understanding of the catalytic properties of
materials. Accordingly, a wealth of experimental and theoretical studies has been dedicated to the
investigation of the interaction of adsorbates with well-defined low-indexed metal surfaces.
However, the catalytic particles used in industrial processes are often applied as small clusters, which
have unique electronic properties. Therefore the knowledge of the morphology of the particles is a
crucial prerequisite for a realistic description. Furthermore, the shape of the clusters will be changed
by the interaction with the surrounding gas, especially for reactive adsorbates such as oxygen.
Although the typical size of these clusters is too large to allow for atomistic modelling, their
equilibrium shape can be estimated from the respective Gibbs free surface energies.
Therefore the adsorption of oxygen has been studied on the low-indexed (111), (100), (110) and
several stepped surfaces of selected late transition metals, namely rhodium, palladium and silver,
with the help of DFT calculations. The calculations have been performed with the Vienna ab-initio
simulation package (VASP), using PAW potentials and the gradient corrected PBE functional. The
adsorption energies at various oxygen coverages give access to the minimal Gibbs free surface
energy for each surface orientation. This quantity in turn can be used for the construction of
equilibrium shape of the cluster depending on the chemical potential of oxygen. Common trends in
the morphological changes of the different metals will be presented.