XPS and LEED study of Pd and Au growth on alumina/Cu-Al surface

Metal-insulator-metal system was prepared using the single-crystalline Cu-9at.% Al(1 1 1) support. Oxidation of the substrate under well-controlled conditions at elevated temperature leads to the formation of well-ordered aluminium oxide layer. The Pd-Au topmost layer was prepared by a step-by-step deposition of both metals afterwards on the oxide layer at room temperature. Low energy electron diffraction (LEED) measurement did not confirm epitaxial growth of the metal overlayer and gave only a rise of diffuse background after each deposition step. The growth of Pd-Au overlayer exhibited Stranski-Krastanov mode influenced by intermetallic interaction between those metals. No binding energy shifts were visible for the core-level photoelectron peaks of the substrate and the oxide using X-ray photoelectron spectroscopy (XPS). In contrast, the binding energy shifts of Pd 3d and Au 4f photoelectron levels in both directions were observed during all depositions. Bimetallic interactions between the metals as well as size effects are further discussed.