Experimental and theoretical study of the MgO/Ag(001) interface

We report on a joint experimental and theoretical investigation of the structure of the MgO/Ag(001) interface, with emphasis on the determination of the interfacial distance between the Ag surface and the first MgO(001) plane. Experiments were performed on 1-5 ML thick MgO layers prepared by Mg deposition in a controlled oxygen atmosphere on a sputter-annealed Ag substrate. The intensity angular distribution (IAD) of the Ag LMM Auger emission was measured as a function of the incidence angle of the primary exciting beam, and the interfacial atomic arrangement was determined by modelling the IAD in a single-scattering cluster approximation. The model adopted in theoretical calculations consisted in a two-dimensionally periodic structure composed of a six-layer thick slab of Ag parallel to the (001) face, covered on both sides by one or two epitaxial MgO MLs. An ab initio density functional theory approach was used with different types of exchange-correlation functionals, and full geometry optimisations were performed. It has been found that MgO accommodates on the substrate with O atoms sitting just on top of the Ag atoms, and that the distance between the Ag surface and the first MgO plane is expanded with respect of both Ag and MgO(001) interplanar distances. Experimental and theoretical results both indicate for the interfacial distance a value of 2.39 +/- 0.06 Angstrom. Significant rumpling occurs in the first ML of MgO, that is removed as the overlayer thickness increases. (C) 2002 Elsevier Science B.V. All rights reserved.