AUTHOR=Wolf Matthew J. , Castleton Christopher W. M. , Hermansson Kersti , Kullgren Jolla 

TITLE=STM Images of Anionic Defects at CeO2(111)—A Theoretical Perspective

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 7 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00212

DOI=10.3389/fchem.2019.00212

ISSN=2296-2646

ABSTRACT=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.