Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 4: Electronic Structure of Surfaces I

O 4.4: Vortrag

Montag, 16. März 2015, 11:15–11:30, MA 041

Employing Infrared Reflection Absorption Spectroscopy to Probe Polarons in Photoactive Oxides: TiO₂ and ZnO — •Fabian Bebensee, Hikmet Sezen, Alexei Nefedov, and Christof Wöll — Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), Herrmann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

TiO₂ and ZnO are wide-band gap metal oxides exhibiting various desirable physico-chemical properties, e.g. high photocatalytic activity. In the context of photoexcitations, primarily excitons have been studied including their very recently reported ultrafast formation dynamics.[1] It is important to note that charge carriers generated from dissociation of excitons may be trapped in polaronic states. Consequently, the polaron binding energy becomes crucial for the photocatalytic activity, as this energy is not available to drive the desired reaction. Yet, only very little work has been devoted to these trap states. Here, we report a novel approach to study polarons in metal oxide single crystals by populating these trap states via UV-light irradiation and probe them using infrared reflection absorption spectroscopy (IRRAS). We will present results for TiO₂ (cf. [2]) and ZnO, where a number of previously unobserved bands ascribed to polaronic states appear in the IR-spectra upon irradiation and compare them to theoretical work. Exploiting time-resolved IRRAS, we were able to deduce lifetimes and binding energies of these states experimentally for ZnO.

[1] Deinert, et al., PRL 2014, 113, 057602.

[2] Sezen, et al., Sci Rep 2014, 4, 3808.