Properties of the Ce–Pd–Pt(111) overlayer system

Abstract

The Pd–Pt(111) and the Ce–Pd–Pt(111) overlayer systems were studied by X-ray photoelectron spectroscopy and low-energy electron diffraction (LEED). Variations in the work function were measured by ultraviolet photoelectron spectroscopy. The Pd overlayer thicknesses were in the range of 1 to 4 monolayers (MLs). The Ce overlayer thicknesses were in the range is of 0.5 to 1.5 MLs. The interfaces were studied for annealing temperatures up to 700°C. Surface alloying or intermixing of Ce, Pd and Pt was observed. Upon deposition at ambient temperatures, Ce forms an overlayer. During annealing, both Pd and Ce were found to dissolve into the Pt substrate. For a Pd coverage of about 1 ML, the Ce–Pd–Pt(111) system was found to be Pt, terminated after annealing to 700°C. For Pd coverage above 1 ML, both Pd and Pt were found to be present at the surface. Cerium was found to be absent from the top surface layer in both cases.

Keywords:

• overlayer system
• XPS
• LEED
• work function
• surface alloy
• mixed valence

Acknowledgements

This work was supported by the Norwegian Research Council under the “Nanomat” program.