The role of interfacial oxygen in the nucleation and stability of Ni nanoclusters at MgO ultrathin films: Insights from STM and first-principles DFT calculations

The interaction between metal nanoclusters and oxide surfaces plays a crucial role in determining the properties of materials for catalytic and electronic applications. Here we present a combined experimental scanning tunnelling microscopy and first-principles calculations study of the nucleation and spatial distribution of Ni nanoclusters grown by deposition of Ni atoms on MgO monolayer films supported on Ag(100) at temperature between 100 K and 300 K. Clusters compatible in size with the magic number 13, 55 and 147 compact icosahedral structures are metallic, but partially oxidized in the contact area with the MgO film. They also show a markedly different spatial distribution with deposition temperature: up to 250 K they sit mainly on flat MgO terraces, while at 300 K they accumulate almost exclusively at the steps. Both effects are caused by the unavoidable presence of oxygen atoms at the MgO/Ag interface, whose concentration decreases dramatically just below room temperature.