Charge transfers at metal/oxide interfaces: a DFT study of formation of K delta+ and Au delta- species on MgO/Ag(100) ultra-thin films from deposition of neutral atoms.
Ultra-thin oxide films grown on a metal substrate and of thickness smaller than 1 nm may exhibit unusual properties with respect to thicker films or single crystal oxide surfaces. In a previous study [G. Pacchioni, L. Giordano and M. Baistrocchi, Phys. Rev. Lett., 2005, 94, 226104] we have suggested that a Au atom adsorbed on a MgO/Mo(100) thin film becomes negatively charged by direct electron tunneling from the Mo metal and that this is related to the low MgO/Mo(100) work function. Here we show, based on periodic DFT supercell calculations, that charge transfer can occur also in the opposite direction by adsorption of electropositive K atoms on MgO/Ag(100) films. We predict the occurrence of a charge transfer also for Au on MgO/Ag(100) films despite the fact that here the work function is 1 eV larger than in MgO/Mo(100). The formation of a layer of adsorbed negative (Au delta-/MgO/Ag) or positive (K delta+/MgO/Ag) adsorbates results in an increase or decrease, respectively, of the MgO/Ag(100) work function as predicted by the classical Gurney model for ionic adsorbates on metal surfaces.
Giordano
Livia
L
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, via Cozzi, 53-20125, Milano, Italy.
Pacchioni
Gianfranco
G
D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D004579:Electron Transport; D006046:Gold / Q000737:chemistry*; D008277:Magnesium Oxide / Q000737:chemistry*; D008567:Membranes, Artificial; D008670:Metals / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010087:Oxides / Q000737:chemistry; D010316:Particle Size; D055672:Static Electricity; D013499:Surface Properties
D008567:Membranes, Artificial; D008670:Metals; D010087:Oxides; D008277:Magnesium Oxide; D006046:Gold