Recent experiments have demonstrated that tiny amounts of Mo impurities give rise to drastic changes in the adsorption characteristic of a wide-gap CaO(001) film. In this scanning tunneling microscopy (STM) and density functional theory paper, we elucidate the underlying mechanism by analyzing the energy levels of the Mo dopants as a function of their oxidation state and depth below the surface. We show that Mo2+ ions in CaO subsurface layers can be reversibly charged and discharged by inducing local band-bending effects with the STM tip. A similar charge switching is not possible for Mo species in a higher oxidation state, as their highest-occupied molecular orbitals are located well below the onset of the CaO conduction band. The easiness of charge switching in Mo2+ ions explains the remarkable chemical properties of doped CaO films, as it renders the material a strong electron donor to adsorbates bound to the oxide surface.
Cui, Y., Nilius, N., Freund, H., Prada, S., Giordano, L., Pacchioni, G. (2013). Controlling the charge state of single Mo dopants in a CaO film. PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS, 88(20), 205421 [10.1103/PhysRevB.88.205421].
Controlling the charge state of single Mo dopants in a CaO film
PRADA, STEFANO;GIORDANO, LIVIA;PACCHIONI, GIANFRANCO
2013
Abstract
Recent experiments have demonstrated that tiny amounts of Mo impurities give rise to drastic changes in the adsorption characteristic of a wide-gap CaO(001) film. In this scanning tunneling microscopy (STM) and density functional theory paper, we elucidate the underlying mechanism by analyzing the energy levels of the Mo dopants as a function of their oxidation state and depth below the surface. We show that Mo2+ ions in CaO subsurface layers can be reversibly charged and discharged by inducing local band-bending effects with the STM tip. A similar charge switching is not possible for Mo species in a higher oxidation state, as their highest-occupied molecular orbitals are located well below the onset of the CaO conduction band. The easiness of charge switching in Mo2+ ions explains the remarkable chemical properties of doped CaO films, as it renders the material a strong electron donor to adsorbates bound to the oxide surface.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.