Metals on oxides: structure, morphology and interface chemistry

In this paper we review our recent studies on the structure, morphology and interface chemistry of different metal systems on simple rock- salt oxides, providing a basis for the understanding of their properties. Fe on both MgO and NiO grows in the cubic structure with the (001) Fe parallel to ( 001) oxide and [110]Fe parallel to [100] oxide orientation. The Fe/ MgO interface is sharp at the atomic level up to 400 degrees C, thus showing that MgO can allow the growth of 'free standing' Fe films and low-dimensional structures. Submicrometric Fe dots on MgO have been prepared by FIB milling and characterized by the magneto-optical Kerr effect. At the Fe/NiO(001) interface an Fe-Ni body centred tetragonal alloyed phase is formed on top of a two-dimensional FeO layer situated at the interface. The FeO layer presents an expansion of the interplanar distance at the interface and a buckling in the Fe and O atomic positions. The presence of the structurally distorted FeO phase is predicted by ab initio density functional theory calculations to increase the spin magnetic moment of Fe atoms by 0.6 mu B compared to the ideally abrupt interface. A reduction of NiO is also induced by the deposition of (supposedly) inert Au films, which incorporate the metallic Ni atoms. The reduction takes place at the low-coordination sites at the surface of the NiO film. The Co/MgO( 001) system has also been studied. In all the investigated cases, given the lower surface free energy of the oxide surfaces compared to the metal ones, the deposited metals tend to form islands, which coalesce above a few monolayers.