Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping

Miroslav Kettner; Tomáš Duchoň; Matthew J Wolf; Jolla Kullgren; Sanjaya D Senanayake; Kersti Hermansson; Kateřina Veltruská; Václav Nehasil

doi:10.1063/1.5109955

Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping

J Chem Phys. 2019 Jul 28;151(4):044701. doi: 10.1063/1.5109955.

Authors

Miroslav Kettner¹, Tomáš Duchoň¹, Matthew J Wolf², Jolla Kullgren², Sanjaya D Senanayake³, Kersti Hermansson², Kateřina Veltruská¹, Václav Nehasil¹

Affiliations

¹ Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic.
² Department of Chemistry-Ångström Laboratory, Uppsala University, Box 538, 751 21 Uppsala, Sweden.
³ Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA.

PMID: 31370552
DOI: 10.1063/1.5109955

Abstract

Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce³⁺ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce⁴⁺ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F^--Ce⁴⁺ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.