Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 69: Symposium: Size-Selected Clusters at Surfaces III
O 69.1: Vortrag
Donnerstag, 28. Februar 2008, 14:00–14:15, MA 042
Size-dependent structure and bonding of Ir clusters on Graphene / Ir(111) — •Carsten Busse1, Alpha T. N’Diaye1, Johann Coraux1, Peter J. Feibelman2, and Thomas Michely1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Sandia National Laboratories, Albuquerque, USA
Small Ir clusters are grown by deposition of Ir onto a graphene moiré on Ir(111) and analyzed using scanning tunneling microscopy (STM). The clusters are arranged in a hexagonal lattice with perfect ordering and exhibit a narrow, tunable size distribution.
The apparent cluster height for monolayer clusters shows a pronounced increase with cluster size from 1.8 Å for trimers to 2.5 Å for 11-clusters. Density functional theory (DFT) calculations rule out a geometric explanation of this effect, so we attribute it to differences in electronic structure. The majority of clusters are stable and immobile at room temperature, but for certain cluster sizes we observe a jiggling motion (trimer to heptamer) or rapid shape changes (tetramer).
For the experimentally observed binding sites of the clusters within the moiré unit cell, DFT reveals that the bonding of the clusters to the substrate induces a rehybridization of the C directly underneath the particles. The bonding changes from a graphene-like (sp2) into a diamond-like (sp3) arrangement, thus explaining the strong binding of the clusters to the substrate.
Work supported in part by the DOE Office of Basic Energy Sciences, Div. of Mat. Sci. and Eng. Sandia is operated by the Lockheed Martin Co. for the U.S. DOE’s NNSA, under contract DE-AC04-94AL85000.