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O: Fachverband Oberflächenphysik

O 102: Heterogeneous Catalysis on Metals

O 102.1: Hauptvortrag

Donnerstag, 19. März 2020, 10:30–11:00, TRE Phy

Video STM of particle diffusion on crowded surfaces — •Joost Wintterlin — Dept. of Chemistry, University of Munich, Germany

Fast surface diffusion of adsorbed particles is important for catalytic reactions as it randomizes the adsorption layer and determines transport to active sites. However, under reaction conditions a catalyst can be highly covered by particles. One expects that surface diffusion is then no longer a simple hopping of separate particles but that interactions and correlations in the "crowded layer" play a role. Such effects have been investigated by means of variable-temperature high-speed STM. Movies consisting of several 1000 frames were recorded over extended temperature ranges, providing the amount of data necessary for a statistical analysis. The experiments were performed with coadsorbed oxygen atoms and CO molecules on a Ru(0001) surface, which can be seen as a catalytic model system. Individual O atoms surprisingly moved through an ordered layer of CO molecules almost as fast as on the bare surface. It was shown that this high mobility can be understood by a new surface diffusion mechanism in which fast density fluctuations in the CO layer drive the diffusion of the oxygen atoms. Because combinations of similar types of adsorbates are present in many catalytic reactions the mechanism may play a general role.