Concentration of vacancies at metal-oxide surfaces: case study of MgO(100).

We investigate the effects of doping on the formation energy and concentration of oxygen vacancies at a metal-oxide surface, using MgO(100) as an example. Our approach employs density-functional theory, where the performance of the exchange-correlation functional is carefully analyzed, and the functional is chosen according to a condition on density-functional theory ionization energies. The approach is further validated by coupled-cluster calculations, including single, double, and perturbative triple substitutions, for embedded clusters.

A DFT study of PtAu bimetallic clusters adsorbed on MgO/Ag(100) ultrathin films.

We have performed density functional theory calculations on the properties of small PtAu(n) (n = 1-4) bimetallic clusters adsorbed on ultrathin MgO films deposited over the Ag(100) substrate. The PtAu bimetallic clusters show the occurrence of a charge transfer from the MgO/Ag interface to the supported nanoparticle with the formation of cluster anions. The Pt atom, which exhibits a stronger bonding with the oxide film and a higher diffusion barrier compared to Au, acts as a nucleation site for the bimetallic cluster and limits its diffusion on the surface.

A route toward the generation of thermally stable Au cluster anions supported on the MgO surface.

On the basis of experimental evidence and DFT calculations, we propose a simple yet viable way to stabilize and chemically activate gold nanoclusters on MgO. First the MgO surface is functionalized by creation of trapped electrons, (H (+))(e (-)) centers (exposure to atomic H or to H 2 under UV light, deposition of low amounts of alkali metals on partially hydroxylated surfaces, etc.); the second step consists in the self-aggregation of gold clusters deposited from the gas phase.

Observable consequences of formation of Au anions from deposition of Au atoms on ultrathin oxide films.

Charging of metal atoms or clusters on oxide surfaces has important consequences on their chemical and physical properties. Recently it is has been shown that negatively charged gold atoms and clusters form spontaneously from neutral Au atoms deposited on ultrathin MgO films. The formation of anions on the surface remains difficult to prove experimentally.