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R. Bliem:
"Single metal adatoms at the magnetite Fe₃O₄(001) surface; seminartalk";
Vortrag: Seminar Institut für Allgemeine Physik (IAP), TU Wien; 07.06.2016.

Magnetite (Fe3O4) is a widely abundant material with fascinating physical properties,
which form the basis of its various applications, for example in biomedicine,
microelectronics, or catalysis. In heterogeneous catalysis, magnetite is employed as
catalyst material and as support for active particles down to the size of single atoms.
The Fe3O4(001) surface is a particularly promising support material for single-atom
catalysis, since it is known to stabilize single Au adatoms up to 700 K. The stabilizing
property is closely related to the nature of the (√2×√2)R45° surface reconstruction,
which is based on an ordered array of subsurface Fe vacancies and interstitials.
Initially the structural model and its quantitative confirmation using low-energy electron
diffraction, scanning tunneling microscopy (STM) and ab initio thermodynamics will be
presented. Using STM, x-ray photoelectron spectroscopy and density functional theory
(DFT) calculations, the metal adsorption properties will be explained on the basis of
this model, showing that isolated adatoms are the stable phase for a broad selection of
metals at room temperature. Regarding the high-temperature behavior, two classes of
materials can be distinguished: Metals that agglomerate to clusters and those which
form solid solution with magnetite, incorporating into the surface lattice. In the second
part, the presentation will focus on examples of reactive metal adatoms and their
interaction with relevant gases such as CO or O2, studied using STM image sequences
supported by DFT. These examples illustrate the high potential of the system and the
challenges encountered in single-atom catalysis