Ultrathin oxide films on metals: new physics and new chemistry?

Oxide thin films on metals are now currently used as model systems to study the surface properties of highly insulating oxides by means of electron spectroscopies. However, it has been recently proposed that ultrathin oxide films and oxide-metal interfaces may actually have unprecedented intrinsic chemical-physical properties, because of image potential screening of charge fluctuations and interfacial hybridizational effects. In fact, on-site Coulomb interactions and charge transfer energies in oxide thin films on metals are reduced by as much as a few eV as compared to the bulk values, thus suggesting a large reduction of the conductivity gap and a strong enhancement of the strength of various exchange and superexchange magnetic interactions in thin layers of strongly correlated oxides on metals. Moreover, interfacial oxygen states with strong metallic character have been observed and considered responsible for an unusually high and chemical selective reactivity of oxide-metal interfaces. Some basic ideas and results connected with these intriguing interfacial phenomena will be presented and discussed taking MgO thin films on Ag(100) as a model system. (C) 2001 Elsevier Science B.V. All rights reserved.