Resolving the adsorption of molecular O2 on the rutile TiO2(110) surface by noncontact atomic force microscopy

I. Sokolović, M. Reticcioli, M. Čalkovský, M. Wagner, M. Schmid, C. Franchini, U. Diebold, M. Setvín

Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Faculty of Physics and Center for Computational Materials Science, University of Vienna, 1090 Vienna, Austria
Institute of Physical Engineering, Brno University of Technology, 616 69 Brno,Czech Republic
Central European Institute of Technology, Brno University of Technology, 612 00 Brno, Czech Republic
Dipartimento di Fisica e Astronomia, Università di Bologna, 40127 Bologna, Italy
Department of Surface and Plasma Science, Faculty of Mathematics and Physics, CharlesUniversity, 180 00 Prague 8, Czech Republic

Proc. Natl. Acad. Sci. USA 117 (2020) 14827-14837

Interaction of molecular oxygen with semiconducting oxide surfaces plays a key role in many technologies. The topic is difficult to approach both by experiment and in theory, mainly due to multiple stable charge states, adsorption configurations, and reaction channels of adsorbed oxygen species. Here we use a combination of noncontact atomic force microscopy (AFM) and density functional theory (DFT) to resolve O2 adsorption on the rutile TiO2(110) surface, which presents a longstanding challenge in the surface chemistry of metal oxides. We show that chemically inert AFM tips terminated by an oxygen adatom provide excellent resolution of both the adsorbed species and the oxygen sublattice of the substrate. Adsorbed O2 molecules can accept either one or two electron polarons from the surface, forming superoxo or peroxo species. The peroxo state is energetically preferred under any conditions relevant for applications. The possibility of nonintrusive imaging allows us to explain behavior related to electron/hole injection from the tip, interaction with UV light, and the effect of thermal annealing.

Corresponding author: Martin Setvin (setvin at iap_tuwien_ac_at).

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