Polarons Imaged in Real Space by Combined AFM/STM

FHI/IMS Joint Online Seminar - Hybrid
Date: Nov 28, 2022
Time: 09:00 AM (Local Time Germany)
Speaker: Prof. Martin Setvin
Charles University, Czech Republic
Location: Building G
Room: Seminar Room 2.06
Host: Akitoshi Shiotari

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 O₂molecule directly observed by atomic force microscopy. PNAS 114, E2556-E2562 (2017).

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