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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Chem. | doi: 10.3389/fchem.2019.00212

STM images of anionic defects at CeO2(111) – a simulated reference companion

  • 1Department of Chemistry– Ångström Laboratory, Box 523, 751 20, Uppsala University, Sweden
  • 2School of Science and Technology, Nottingham Trent University, NG11 8NS, Nottingham Trent University, United Kingdom
  • 3Division of Physics and Mathematics/Natural Science Didactics, Box 883, 721 23, Mälardalen University College, Sweden

We present a comprehensive simulated reference companion to the appearance and properties
of plausible candidates for the anionic defects observed in scanning tunnelling microscopy (STM)
experiments on CeO2 (111), a prototypical reducible oxide surface, in order to assist with experi-
mental characterisation. The simulations are based on density functional theory (DFT) and cover
oxygen vacancies, fluorine impurities and hydroxyl groups in the surface and sub-surface layers. In
the surface layer, all three appear as missing spots in the oxygen sublattice in filled state simulated
STM images, but they are distinguishable in empty state images, where surface oxygen vacancies
and hydroxyls appear as, respectively, diffuse and sharp bright features at oxygen sites, while flu-
orine defects appear as triangles of darkened Ce ions. In the sub-surface layer, all three defects
present more complex patterns, with different combinations of brightened oxygen ion triangles
and/or darkened Ce ion triangles, so we provide image maps to support experimental identifica-
tion. We conclude that identification of defects in STM images requires careful comparison of both
filled and empty state images, as well as other properties such as their distributions and diffusion
rates.

Keywords: Simulated STM images, Cerium dioxide (CeO2), Density funcational theory, Anionic defects, Reducible oxide

Received: 07 Jan 2019; Accepted: 18 Mar 2019.

Edited by:

Maria Veronica Ganduglia-Pirovano, Institute of Catalysis and Petrochemistry (ICP), Spain

Reviewed by:

Niklas Nilius, University of Oldenburg, Germany
Joachim Paier, Humboldt University of Berlin, Germany  

Copyright: © 2019 Wolf, Castleton, Hermansson and Kullgren. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Kersti Hermansson, Uppsala University, Department of Chemistry– Ångström Laboratory, Box 523, 751 20, Uppsala, 753 12, Uppsala, Sweden, kersti.hermansson@kemi.uu.se