Small-Cluster Coexistence

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Science  13 Jun 2008:
Vol. 320, Issue 5882, pp. 1396
DOI: 10.1126/science.320.5882.1396c

When metal clusters are adsorbed on metal oxide surfaces, their properties can change, especially if they interact with defect sites and undergo charge transfer. Simic-Milosevic et al. explored the extent of such charge transfer in a model system, in which magnesium oxide films [three monolayers (MLs) of MgO(001)] were grown on a Ag(001) surface; Au was then deposited at low coverages (0.03 ML) at very low temperatures (5 K), and its structure was studied with a scanning tunneling microscope (STM). Although most of the Au was present as isolated atoms, two types of dimer could be observed that either lay flat on the surface (shown at left) or stood upright. Manipulations with the STM tip could form the flat dimers from the atoms and then convert them to the upright form. Density functional theory calculations indicated that the upright form is more stable and adsorbs as a neutral species onto surface oxygen sites, whereas the flat form is negatively charged and places the Au atoms over Mg. These results show that the spread in energy between different electronic states may be low enough to allow substantial coexistence on a surface. — PDS

J. Am. Chem. Soc. 130, 10.1021/ja8024388 (2008).

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