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Science 29 July 2005:
Vol. 309. no. 5735, pp. 752 - 755
DOI: 10.1126/science.1111568
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Reports

Electron Localization Determines Defect Formation on Ceria Substrates

Friedrich Esch,1* Stefano Fabris,2 Ling Zhou,3 Tiziano Montini,4,5 Cristina Africh,1,5,6 Paolo Fornasiero,4,5 Giovanni Comelli,1,5,6 Renzo Rosei1,5,6

The high performance of ceria (CeO2) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resolution scanning tunneling microscopy and density functional calculations to unravel the local structure of surface and subsurface oxygen vacancies on the (111) surface. Electrons left behind by released oxygen localize on cerium ions. Clusters of more than two vacancies exclusively expose these reduced cerium ions, primarily by including subsurface vacancies, which therefore play a crucial role in the process of vacancy cluster formation. These results have implications for our understanding of oxidation processes on reducible rare-earth oxides.

1 Laboratorio Nazionale Tecnologie Avanzate e Nanoscienza (TASC)-Istituto Nazionale per la Fisica della Materia (INFM), 34012 Trieste, Italy.
2 Scuola Internazionale Superiore di Studi Avanzati (SISSA) and INFM Democritos National Simulation Center, 34014 Trieste, Italy.
3 Institute of Physical Chemistry and Electrochemistry, University of Hannover, D-30167 Hannover, Germany.
4 Chemistry Department and Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), University of Trieste, 34127 Trieste, Italy.
5 Center of Excellence for Nanostructured Materials (CENMAT), University of Trieste, 34127 Trieste, Italy.
6 Physics Department, University of Trieste, 34127 Trieste, Italy.

* To whom correspondence should be addressed. E-mail: friedrich.esch{at}elettra.trieste.it

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Science. ISSN 0036-8075 (print), 1095-9203 (online)