Properties of oxide ultrathin films on metal supports

Oxide ultrathin films of thickness of a few nanometers and below, grown on metallic substrates, may exhibit peculiar properties that make these systems extremely appealing for new applications in catalysis, microelectronics and gas sensors. The oxide can exist in unusual atomic structures, stabilized at the nanoscale and by the interface, with consequences on the electronic and magnetic properties of the film [1]. Electron transfer through the insulating film leads to the spontaneous charging of adsorbates on the oxide film [2,3], affecting their reactivity and, in some cases, their magnetic properties. The stabilization of these charged species is enhanced by the polarization of the metal substrate and by the structural response (polaronic-like distortion) of the oxide film. These charge transfer phenomena are also related to the relative position of adsorbate and substrate states. For this reason the work function change induced by the oxide is a key factor in determining the occurrence and the direction of the electron flow through the oxide film [4]. [1] L. Giordano, G. Pacchioni,, Acc. Chem. Res. 44, 1244 (2011). [2] G. Pacchioni, L. Giordano, M. Baistrocchi, Phys. Rev. Lett. 94, 226104 (2005). [3] A. Gonchar, T. Risse, H.-J. Freund, L. Giordano, C. Di Valentin, G. Pacchioni, Angew. Chem. Int. Ed. 50, 2635 (2011). [4] L. Giordano, F. Cinquini, G. Pacchioni, Phys. Rev. B 73, 045414 (2006).