Recent advances in experimental techniques make possible nowadays to grow epitaxial films with accurate control of quality and thickness. In the limit of ultrathin thickness, the influence of the film/support interface confers new properties to the combined material, which are exploited in technological applications including microelectronics and magnetic devices.

Less studied are the emerging phenomena occurring at the free surface of the film. We will show how the surface properties of otherwise inert materials, such as simple metal oxides, can be modified when grown in the form of ultrathin films. Our Density Functional Theory (DFT) calculations, combined with experimental evidence, show that adsorbed metal particles and molecules can become spontaneously charged on two-dimensional oxide films grown on metal supports thanks to the electron transfer from the metal support, through the insulating film. The occurrence of the charge transfer is related to the metal work function change induced by the deposited oxide and is then closely related to the nature of the interface. The combination of redox chemistry on the oxide and the interfacial charge transfer give rise to a richer chemistry and catalytic activity in the case of transition metal oxides films.