Au atoms and dimers on the MgO(100) surface: a DFT study of nucleation at defects.

Full Abstract

The adsorption of Au atoms at the surface of MgO and the formation of Au dimers have been studied by means of first principles DFT supercell calculations. Au atoms have been adsorbed on flat MgO terraces and monatomic steps but also at point defects such as oxygen vacancies (F centers) or divacancies. Very low barriers for diffusion of Au atoms on the MgO(100) terraces have been found. Atom diffusion is stopped only at strong binding sites such as the F and F+ centers (adsorption energy E(a) = 3-4 eV), divacancies (E(a) = 2.3 eV), or, to less extent, steps (E(a) = 1.3 eV). The combination of two Au adatoms with formation of a dimer is accompanied by an energy gain, the dimer binding energy, E(b), between 2 and 2.4 eV for all sites considered, with the exception of the paramagnetic F+ center where the gain is negligible (0.3 eV). The dimerization energy on the surface is not too different from the bond strength of Au2 in the gas phase (2.32 eV). Thus, defects sites on MgO do not have a special role in promoting or demoting Au dimerization, while they are essential to trap the diffusing Au atoms or clusters. Calculations on Au3 formed on an F center show that the cluster is fluxional.

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Author information

Author/s: Del Vitto, Annalisa (A); Pacchioni, Gianfranco (G); Delbecq, Françoise (F); Sautet, Philippe (P);

Affiliation: Dipartimento di Scienza dei Materiali, Università Milano-Bicocca, via R. Cozzi 53, I-20125 Milano, Italy.

Journal and publication information

Publication Type: Journal Article

Journal: The journal of physical chemistry. B (J Phys Chem B), published in United States. (Language: eng)

Reference: 2005-Apr; vol 109 (issue 16) : pp 8040-8

Dates: Created 2006/07/20; Completed 2007/09/28;

PMID: 16851939, status: PubMed-not-MEDLINE (last retrieval date: 12/26/2008)

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