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Free keywords:
Ceria/CeO2(111), Au adsorption, binding site, aggregation, fluxionality, scanning tunneling
microscopy
Abstract:
The adsorption of gold has been investigated on crystalline and defect-poor CeO2(111) films by means of low-temperature scanning tunneling microscopy and spectroscopy. At low coverage, individual Au atoms are observed that homogenously distribute on the ceria surface and show no preference for binding at step edges. With increasing exposure, characteristic Au aggregates become visible, such as upright Au dimers, bilayer and trilayer pyramids. These ultrasmall clusters exhibit pronounced fluxionality, i.e. they easily modify their internal shape and binding position during the scanning process. This observation suggests the presence of various iso-energetic Au isomers on the surface as well as a relatively weak metal-oxide interaction. At higher Au exposure, tall 3D deposits develop on the oxide film. Conductance spectroscopy reveals unoccupied state density in the Au clusters in the energy range of the Au 6p levels. Neither the topographic nor the spectroscopic data provide evidence for a charged nature of the Au species, suggesting that Au binds in a neutral charge state on defect-poor CeO2(111).
