Metals on oxides: structure, morphology and interface chemistry

In this paper we review our recent studies on the structure, morphology andinterface 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 _ (001)oxide and [110]Fe _ [100]oxide orientation.The Fe/MgO interface is sharp at the atomic level up to 400 ◦C, thusshowing that MgO can allow the growth of ‘free standing’ Fe films and lowdimensionalstructures. Submicrometric Fe dots on MgO have been preparedby FIB milling and characterized by the magneto-optical Kerr effect. Atthe Fe/NiO(001) interface an Fe–Ni body centred tetragonal alloyed phase isformed on top of a two-dimensional FeO layer situated at the interface. TheFeO layer presents an expansion of the interplanar distance at the interfaceand a buckling in the Fe and O atomic positions. The presence of thestructurally distorted FeO phase is predicted by ab initio density functionaltheory calculations to increase the spin magnetic moment of Fe atoms by 0.6 μBcompared to the ideally abrupt interface. A reduction of NiO is also induced bythe deposition of (supposedly) inert Au films, which incorporate the metallicNi atoms. The reduction takes place at the low-coordination sites at the surfaceof the NiO film. The Co/MgO(001) system has also been studied. In all theinvestigated cases, given the lower surface free energy of the oxide surfacescompared to the metal ones, the deposited metals tend to form islands, whichcoalesce above a few monolayers.