Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
Hybrid-Department Seminar
Host: Akitoshi Shiotari

Monday, November 28, 2022, 9:00 am
Prof. Martin Setvin
Charles University, Czech Republic
FHI/IMS-Joint Seminar - Polarons Imaged in Real Space by Combined AFM/STM
Polarons [1] are quasiparticles that form in ionic lattices due to the interaction of excess charges with lattice distortions. This leads to a spatial confinement of the charge and appearance of many novel phenomena. In past decades, polarons turned out to play an important role in electrical transport, optical properties, organic electronics, catalysis, or in exotic materials properties such as colossal magnetoresistance or high-Tc superconductivity.
I will discuss options of studying the polaron properties by scanning probe methods. First, traces of small and large polarons in Scanning tunnelling spectroscopy will be discussed on the prototypical example of TiO2 rutile and anatase [2]. The use of atomic force microscopy brings an option of imaging and manipulating single small polarons; this will be illustrated on examples of hematite Fe2O3 and the KTaO3 perovskite. Last, the options of studying electron transfer between a solid substrate and adsorbed molecules will be illustrated on several systems: CO adsorbed on Rutile TiO2 [3], CO adsorbed on cleaved KTaO3 [4] and  O2 adsorbed on anatase TiO2 [5]. Each case carries distinctly different characteristics for transferring the electron and requires a choice of an appropriate analysis method.

[1]  Franchini, C., Reticcioli, M., Setvin, M. & Diebold, U. Polarons in Materials. Nature Reviews Materials 6, 560-586 (2021).
[2] Setvin, M. et al. A Direct View at Excess Electrons in TiO2 Rutile and Anatase. Phys. Rev. Lett. 113, 086402 (2014).
[3] Reticcioli, M. et al. Interplay between adsorbates and polarons: CO on rutile TiO2(110). Phys. Rev. Lett. 122, 016805 (2019).
[4] Wang, Z. et al. Surface chemistry on a polarizable surface: Coupling of CO with KTaO3(001). Science Advances 8, eabq1433 (2022).
[5] Setvin, M., Hulva, J., Parkinson, G. S., Schmid, M. & Diebold, U. Electron transfer between anatase TiO2 and an O2 molecule directly observed by atomic force microscopy. PNAS 114, E2556-E2562 (2017).

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