Oxidation-Induced Dispersion of Gold on Ru(0001): A Scanning Tunneling Microscopy Study

With scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) we studied the redox properties of Au islands supported on Ru(0001) as a function of the island thickness. Both the size and the height of Au islands on Ru(0001) can be controlled by the density of the oxygen precoverage on ruthenium and the sample temperature during the deposition of gold. The oxidation of the Au islands at 300 K was accomplished by exposing atomic oxygen produced from a thermal gas cracker. Regardless of the lateral size of the three monolayer (ML) thick Au islands, the oxidation leads to a fragmentation into a number of small particles (3–5 nm) whose arrangement reflects the shape of the former intact Au islands. This oxygen-induced dispersion of Au on Ru(0001) is explained by a shoveling process. Quite in contrast, no fragmentation of the 4–5 ML thick Au islands into smaller entities is observed. Rather, the entire Au island transforms into one big particle. From Au 4f core level spectroscopy we provid...