Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 26: Particles and clusters I

O 26.6: Talk

Tuesday, March 28, 2006, 17:00–17:15, WIL A317

Electronic and geometric structures of Au nanostructures on HOPG studied using XPS and STM — •Ignacio Lopez, Dong Chan Lim, Rainer Dietsche, and Young Dok Kim — Department of Physics, Universität Konstanz. D-78457, Germany

Au nanostructures grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS), and the results were compared with those of Ag on the same substrate. By varying defect densities of HOPG and Au coverages, one can create Au nanoparticles with various sizes. At high Au coverages, it is observed that Au structures significantly desviate from the ideal truncated octahedral structure: the existence of many steps between different Au planes can be observed, most likely due to high activation barriers for the Au atoms on the topmost plane of the Au structures jumping over the step edges down to the next plane. This result implies that the particle growth at room temperature is strongly limited by kinetic factors. Using XPS, much less positive core level shifts of the Au 4f level with decreasing particle size was found, compared to the core level shifts of the Ag 3d level in the similar particle size range on HOPG. Together with our results of the Auger analysis of the Ag data, we suggest that the metal/substrate charge transfer is an important factor to determine the core level shifts of the metal nanoparticles on HOPG, i.e. Ag is (partially) positively charged, whereas Au negatively on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which can play an important role for e.g. heterogeneous catalysis.