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Evidence of charge transfer to atomic and molecular adsorbates on graphitic-like ZnO/X(111) (X = Cu, Ag, Au) ultrathin films

preprint
submitted on 15.11.2017 and posted on 15.11.2017 by Ho Viet Thang, Sergio Tosoni, Gianfranco Pacchioni
ZnO bilayers grown on Cu(111), Ag(111), and Au(111) surfaces form graphitic-like flat structures. They belong to the class of two-dimensional materials. We show, by means of density functional theory (DFT) calculations including dispersion, that Au, NO2, and O2 species adsorbed on ZnO/Cu(111) induce a spontaneous net charge transfer (CT) via electron tunneling from the Cu support through the insulating ZnO film, resulting in the formation of negatively charged atomic, Au-, or molecular, NO2- and O2-, adsorbates. We show for the case of gold that the CT is found also for ZnO/Ag(111) and ZnO/Au(111) interfaces. The stabilization of the anionic species is accompanied by a polaronic distortion of the ZnO lattice. Other molecules with low electron affinity such as NO and CO2, on the contrary, do not induce the CT. However, charge transfer and activation of two CO2 molecules to form an oxalate species, [C2O4]2-, is promoted by a single Au anion, and similar catalytic activity is expected for the negatively charged Au clusters. By comparing the properties of the metal supported ZnO films with those of the free-standing ZnO bilayer, we demonstrate the key role of the metal/oxide interface. These results are relevant in the field of methanol synthesis based on ZnO/Cu catalysts where ultrathin layers of ZnO supported on Cu are formed under reaction conditions.

Funding

This work has been supported by Italian MIUR through the PRIN Project 2015K7FZLH SMARTNESS. CINECA-LISA Awards are also acknowledged for the availability of high-performance computing resources.

History

Topic

  • Computational chemistry and modeling

Email Address of Submitting Author

gianfranco.pacchioni@unimib.it

Email Address(es) for Other Author(s)

hvthangbk@gmail.com; sergio.tosoni@unimib.it

Institution

Dipartimento di Scienza dei Materiali, Università Milano

Country

Italy

ORCID For Submitting Author

0000-0002-4749-0751

Declaration of Conflict of Interest

None

Exports