Interactions of O2 and CO molecules with small electronic polarons on the TiO2 (110) surface

Igor Sokolović (TU Vienna)

Dec 10. 2019, 17:00 — 19:00

Igor Sokolović1, Michele Reticcioli1,2, Martin Čalkovský1, Michael Schmid1, Ulrike Diebold1, Cesare Franchini2, Martin Setvín1 1Institute of Applied Physics, TU Wien, Wiedner Hauptstraße 8-10/134, 1040 Vienna, Austria 2Faculty of Physics, University of Vienna, Sensengasse 8/8, 1090 Vienna, Austria The rutile TiO2 (110) surface has been extensively studied and today is the best understood transitionmetal oxide surface [1]. Recently, the experimental and theoretical focus on this surface has increased due to its polaron-hosting nature [2,3]. The polarons at the reduced TiO2 (110) surface emerge from the localization of two electrons donated by each oxygen vacancy on the 3d orbitals of the subsurface Ti3+ atoms [4]. The precise knowledge of the polaronic ground state of this surface is necessary for explaining many surface phenomena, exemplified by the appearance of a (1×2) reconstruction on a strongly reduced surface [5]. In this presentation, the interaction of the adsorbed molecular CO [6] and O2 [7] species with the polarons is studied by density functional theory modeling as well as experimental non-contact atomic force microscopy and scanning tunneling spectroscopy techniques. Oxygen molecules were experimentally found to chemisorb to the surface in three distinct configurations with atomicallyresolved precision. The CO molecules were found to physisorb to the surface in two geometrically different positions, among which there are three electronically distinct signatures recognized with orbital resolution. The chemisorbed oxygen molecules were calculated to accept the polaronic charge to their 2π* orbitals, allowing them to create chemical bonds to the surface. The nature of the in-gap state characteristic for the clean, reduced, slab is drastically altered in the presence of each adsorbed oxygen species, accompanied by a complete loss of the polaronic distribution at saturation coverage. On the other hand, the weakly bound physisorbed CO molecules do not create chemical bonds. Nevertheless, some of them alter the polaronic ground state by coupling to polarons and making polarons in the surface layer more energetically favorable, which is not the case for the clean, reduced surface . Both studies illustrate the wide scope of polaron interactions in adsorption phenomena on this surface. References: [1] U. Diebold, Surf. Sci. Rep. 48, 53 (2003). [2] M. Reticcioli, U. Diebold, et. al. Handbook of Materials Modeling: Applications: Current and Emerging Materials 1 (2019). [3] M. Setvin, C. Franchini, et. al. Phys. Rev. Lett. 113, 086402 (2014). [4] M. Reticcioli, M. Setvin, Phys. Rev. B 98, 045306 (2018). [5] M. Reticcioli, M. Setvin, Phys. Rev. X 7, 031053 (2017) [6] M. Reticcioli, I. Sokolović, Phys. Rev. Lett. 122, 016805 (2019). [7] I. Sokolović, M. Reticcioli, In preparation

Further Information
ESI Boltzmann Lecture Hall
Associated Event:
Polarons in the 21st Century (Workshop)
Jozef Devreese (U Antwerpen)
Cesare Franchini (U of Vienna)
Georg Kresse (U of Vienna)
Jacques Tempere (U Antwerpen)