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O: Oberflächenphysik

O 28: Surface reactions II

O 28.11: Talk

Tuesday, March 28, 2006, 18:15–18:30, WIL C207

SCANNING TUNNELING MICROSCOPY INVESTIGATIONS OF THE STRUCTURAL BASIS FOR CATALYST DEACTIVATION — •S. Marchini, S. Günther, and J. Wintterlin — Ludwig-Maximilians-Universität, Department Chemie, 81377 München, Germany

Deactivation and poisoning is an essential phenomenon in industrial catalysis. A poison can influence both the activity and the selectivity of the catalyst chemically, by modifying the electronic properties of the surface, or physically, by altering the geometry or blocking the active sites of the catalyst. We here present a scanning tunneling microscopy investigation of the formation of a graphitic layer on the Ru(0001) surface. Prolonged annealing of the sample causes carbon segregation from the bulk of the crystal and the formation of a superstructure whose coverage increases up to saturation upon increasing the heating temperature to 1400K. LEED measurements show that the structure is incommensurate (~12.5x12.5) and rotationally aligned to the surface. STM images exhibit a Moiré pattern with a periodicity of 28Å and whose structure could be atomically resolved. The system exhibits an interesting spectroscopic behavior: images taken with different tunneling voltages show strong changes in the way the structure appears, revealing the presence of a composite surface electronic structure.