Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 15: Nanostructures at surfaces: Dots, particles, clusters, arrays I
O 15.7: Vortrag
Montag, 14. März 2011, 16:30–16:45, WIL C107
CO induced unpinning of Pt clusters from the Ir(111)/graphene moiré — •Timm Gerber1, Jan Knudsen2, Patrick Stratmann1, Elin Grånäs2, Karina Schulte3, Carsten Busse1, Jesper Andersen2, and Thomas Michely1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Division of Synchrotron Radiation Research, Department of Physics, Lund University , Sweden — 3MAX-Laboratory, Lund University, Sweden
The Stability of catalyst particles under reactive conditions is of crucial importance for their performance and durability. Here we investigated the adsorption of CO and its effect on the stability of Pt-cluster superlattices with a periodicity of 2.5 nm on a graphene layer on Ir(111).
XPS and TPD both suggest that CO adsorbs on-top and preferentially at cluster step edges, but also on cluster facets. Further, upon CO adsorption XPS signals a weakened binding of the Pt clusters to their graphene substrate: the C1s feature characteristic for cluster binding diminishes. For small clusters with an average size below 10 atoms this unpinning implies cluster diffusion and cluster coalescence, as observed dynamically through STM image sequences. Larger clusters with an average size around 20 atoms remain fixed upon room temperature CO adsorption.
To prevent cluster coalescence in the early stages of cluster growth and to obtain the most regular Pt-cluster superlattices the CO partial pressure during Pt deposition should be minimal. Otherwise adsorbed CO causes unpinning and subsequent coalescence of small intermediate clusters already during the growth process.