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Infrared Reflection–Absorption Spectroscopy and Density Functional Theory Investigations of Ultrathin ZnO Films Formed on Ag(111)

Research paper by Mie Andersen, Xiaojuan Yu, Matthias Kick, Yuemin Wang, Christof Wöll, Karsten Reuter

Indexed on: 28 Feb '18Published on: 20 Feb '18Published in: Journal of Physical Chemistry C



Abstract

Reactivity at metal-oxide interfaces is of fundamental importance in heterogeneous catalysis. Herein, we report a thorough surface-science study on the growth and chemical activity of ultrathin ZnO films on Ag(111) by grazing-emission X-ray photoelectron spectroscopy and temperature-dependent infrared reflection–absorption spectroscopy using CO as a probe molecule. Compared to bilayer ZnO on Cu [Schott, V.; Angew. Chem. Int. Ed. 2013, 52, 11925–11929], we find a much decreased CO binding energy of 0.24 eV for bilayer ZnO on Ag. Furthermore, the anomalous, substantial red-shift of the CO stretch frequency with respect to the gas phase value identified for ZnO/Cu is absent in the ZnO/Ag system, where we instead report a slightly blue-shifted frequency at 2146 cm–1 for isolated CO molecules. In order to interpret these differences of ZnO thin layer supported on these two coinage metals, we carried out a thorough theoretical analysis using density functional theory calculations employing van der Waals-corrected generalized-gradient-approximation (GGA)-type and hybrid functionals. We show that bilayer ZnO forms a flat graphitic-like structure on Ag in contrast to the previously reported strongly corrugated ZnO film formed on Cu. While our results show that GGA-type functionals cannot in general be applied uncritically for CO adsorption on ZnO, we explicitly validate our results for the ZnO/Ag system by comparison to hybrid functional calculations for selected model systems.

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