title: Diffusion Barriers Block Defect Occupation on Reduced CeO_{2}(111).
abstract: Surface defects are believed to govern the adsorption behavior of reducible oxides. We challenge this perception on the basis of a combined scanning-tunneling-microscopy and density-functional-theory study, addressing the Au adsorption on reduced CeO_{2-x}(111). Despite a clear thermodynamic preference for oxygen vacancies, individual Au atoms were found to bind mostly to regular surface sites. Even at an elevated temperature, aggregation at step edges and not decoration of defects turned out to be the main consequence of adatom diffusion. Our findings are explained with the polaronic nature of the Au-ceria system, which imprints a strong diabatic character onto the diffusive motion of adatoms. Diabatic barriers are generally higher than those in the adiabatic regime, especially if the hopping step couples to an electron transfer into the ad-gold. As the population of O vacancies always requires a charge exchange, defect decoration by Au atoms becomes kinetically hindered. Our study demonstrates that polaronic effects determine not only electron transport in reducible oxides but also the adsorption characteristics and therewith the surface chemistry.
authors.affiliation: Instituto de Física Rosario (IFIR, CONICET-UNR) and Facultad de Ciencias Exactas, Ingeniería y Agrimensura (UNR), 2000 Rosario, Argentina.
authors.forename: P G
authors.initials: PG
authors.lastname: Lustemberg
authors.affiliation: Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China.
authors.forename: Y
authors.initials: Y
authors.lastname: Pan
authors.affiliation: Department of Chemistry and London Centre for Nanotechnology, University College London, London WC1H 0AJ, United Kingdom.
authors.forename: B-J
authors.initials: BJ
authors.lastname: Shaw
authors.affiliation: Department of Chemistry and London Centre for Nanotechnology, University College London, London WC1H 0AJ, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Grinter
authors.affiliation: Department of Chemistry and London Centre for Nanotechnology, University College London, London WC1H 0AJ, United Kingdom.
authors.forename: Chi
authors.initials: C
authors.lastname: Pang
authors.affiliation: Department of Chemistry and London Centre for Nanotechnology, University College London, London WC1H 0AJ, United Kingdom.
authors.forename: G
authors.initials: G
authors.lastname: Thornton
authors.affiliation: Departamento de Fisica Teorica de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autonoma de Madrid, 28049 Madrid, Spain.
authors.forename: Rubén
authors.initials: R
authors.lastname: Pérez
authors.affiliation: Instituto de Catálisis y Petroleoquímica (ICP-CSIC), 28049 Madrid, Spain.
authors.forename: M V
authors.initials: MV
authors.lastname: Ganduglia-Pirovano
authors.affiliation: Institute of Physics, Carl von Ossietzky University, 26111 Oldenburg, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Nilius