Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 71: Metal substrates: Epitaxy and growth
O 71.5: Vortrag
Donnerstag, 25. März 2010, 16:00–16:15, H31
Small Pt adatom clusters on Pt(111): When fewer bonds are better than more — •Michael Schmid1, Andreas Garhofer1,2, Josef Redinger1,2, Florian Wimmer1, Philipp Scheiber1, and Peter Varga1 — 1Institut f. Angewandte Physik, TU Wien — 2Center for Computational Materials Science, Wien, Österreich
Bonding of face-centered-cubic metals is usually characterized by a preference for high a coordination number of each atom. In sharp contrast to this picture, we find that small clusters of Pt adatoms on Pt(111) behave differently. Creating a high number of small Pt adatom clusters by pulsed laser deposition at low temperature, we find that up to 1/3 of all clusters are linear chains of Pt atoms with lengths of up to 9 atoms. This finding cannot be explained by a simple diffusion-limited-aggregation model. We have therefore analyzed the binding energies of Pt adatom clusters by density functional theory and found that bonding of such clusters does not follow the rule of “higher coordination is stronger bonding”. Instead, short linear chains are bound more strongly than some more compact configurations, explaining the preference for such structures observed experimentally. We ascribe the unusually low energies of short chains to strong bonding towards atoms at opposite sides, induced by dz2-like orbitals. We have also obtained time-lapse STM movies of diffusing Pt adatoms and their coalescence. The data show no strong long-range interaction between adatoms, which would otherwise provide a different route towards an explanation of the phenomena observed.