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

摘要

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.