Interface-stabilized phases of metal-on-oxide nanodots.

The control of the structure of oxide-supported metal nanoparticles is crucial in determining their properties and possible applications. Here, building principles are derived for predicting the epitaxies of metal nanoparticles on square-symmetry oxide surfaces. Unusual phases are found for an appropriate choice of the metal-oxide pair, where nanoparticles with hcp structure are stabilized for fcc metals such as Ni, Pd, and Pt, or for Co in a size range in which Co has typically nonhcp arrangements. These predictions are supported by a comparison with available experimental data on Ni/MgO(100) nanodots, and generalized to a whole class of metal-oxide systems of great potential interest, such as Pd and Pt on CaO, Ni on CoO, and Co on MgO. The atomistic features of the nanoparticles in turn suggest that these materials should possess peculiar properties; in particular, the facets exposed by the nanodots reveal adsorption sites with unusual geometry of possible effect on their catalytic properties, while the destabilization of stacking faults and the structural deformations observed for these particles are expected to influence their magnetic behavior.