Magnesium oxide ultrathin films grown on metal substrates have received considerable attention because of their technological importance in many research fields, such as spintronics and heterogeneous catalysis. The ability to tune and control the band alignment in magnetic tunnel junctions or the cluster/oxide systems in catalytic applications implies a detailed knowledge of the metal/oxide interface electronic structure. The first part of this thesis deals with a photoemission study of the interface electronic structure of ultrathin MgO films on Ag(001) as a function of the oxide thickness. It is shown that the Fermi-level pinning at the interface is essentially controlled by an interfacial dipole governed by an MgO-induced polarization effect. Next, this extended Schottky-Mott model was also invoked to explain the dependence of the Schottky barrier height on the oxide growth conditions. The lowering of the metal/oxide work function induced by the Mg enrichment of the Ag surface region during the growth was demonstrated. Finally, we present a joint experimental-theoretical study of a three monolayer's MgO/Ag(001) system. Combining x-ray excited Auger electron diffraction measurements and multiple-scattering simulations provide a layer-by-layer resolution of the MgKLL Auger electron emissions which has been used to demonstrate the ability to intercalate Mg atoms at the buried interface by post-growth interface engineering. The induced work function changes and large interlayer relaxation at the metal/oxide interface are evidenced and show an excellent agreement with density functional theory calculations.
