A resonant photoemission study of the Ce and Ce-oxide/Pd(1 1 1) interfaces |
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Authors: | M Škoda J Libra N Tsud L Sedlá?ek KC Prince |
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Institution: | a Charles University, Faculty of Mathematics and Physics, Department of Surface and Plasma Science, V Holešovi?kách 2, 18000 Prague 8, Czech Republic b Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, 16253 Prague 6, Czech Republic c Sincrotrone Trieste, Strada Statale 14, km 163.5, 34012 Basovizza-Trieste, Italy |
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Abstract: | We have investigated the Ce 4f electronic states in the Ce/Pd(1 1 1) and Ce-oxide/Pd(1 1 1) systems, using resonant photoemission (Ce 4d → 4f transitions), and XPS to understand Pd-Ce interactions in ultra thin layers of cerium and ceria deposited on Pd(1 1 1). Cerium deposited on Pd(1 1 1) at room temperature forms surface Ce-Pd alloys with Ce rich character, while a Pd rich Ce-Pd alloy is formed by heating to 700 °C. A modification of the chemical state of Ce can also be seen after oxygen exposure. RPES provides evidence that Ce-oxide layers deposited on Pd(1 1 1) have a CeO2 (Ce4+) character, however a net contribution of the Ce3+ states is also revealed. The Ce3+ states have surface character and are accompanied by oxygen vacancies. Heating to 600 °C causes Ce-oxide reduction. A significant shift of Pd 4d-derived states, induced by Pd 4d and Ce 4f hybridization, was observed. The resonant features in the valence band corresponding to Ce4+, Ce3+ and Ce0 states have been investigated for various Pd−Ce(CeOx) coverages. |
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Keywords: | Resonant photoemission XPS Cerium Cerium oxide Palladium Valence band |
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