| AVS 61st International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS+EN-WeM |
| Session: | Dynamic Processes of Single Atoms and Molecules at Surfaces |
| Presenter: | Fabian Bebensee, Karlsruhe Institute of Technology, Germany |
| Authors: | F. Bebensee, Karlsruhe Institute of Technology, Germany H. Sezen, Karlsruhe Institute of Technology, Germany A. Nefedov, Karlsruhe Institute of Technology C. Wöll, Karlsruhe Institute of Technology |
| Correspondent: | Click to Email |
ZnO is a wide-bandgap metal oxide exhibiting various highly desirable physico-chemical properties, among them high photocatalytic activity. As such, it has been widely studied employing virtually all available techniques over the past 50 years.[1] In the context of photoexcitations, primarily excitons have been studied extensively including their very recently reported ultrafast formation dynamics.[2] In photocatalysis, dissociation of excitons into free electrons and holes takes place and therefore the binding energies of the polaronic states become crucial for the subsequent steps on the way to finally transferring an electron or hole onto an adsorbed molecule. Despite their importance in photochemistry (see recent work on TiO2[3]), very little work has been devoted to these trap states in ZnO. Here, we report a novel approach to study polarons in ZnO single crystal substrates: the polaron traps are populated via UV-light irradiation and then probed using infrared reflection absorption spectroscopy (IRRAS). Upon irradiation, a number of previously unobserved, well-defined and sharp absorption bands appear in the IR-spectra. Among these new features is an absorption-edge like feature that we assign to excitations of electrons from the conduction band into hole polaronic trap states. From their time-dependent intensity, we infer a (temperature-dependent) life time of 25 seconds at 75 K. The implications of these findings for ZnO photochemistry will be discussed.
[1] C. Klingshirn, physica status solidi (b) 2007, 244, 3027-3073.
[2] J.-C. Deinert, D. Wegkamp, M. Meyer, C. Richter, M. Wolf, J. Stähler, Physical Review Letters 2014, 113, 057602.
[3] H. Sezen, M. Buchholz, A. Nefedov, C. Natzeck, S. Heissler, C. Di Valentin, C. Wöll, Sci Rep-Uk 2014, 4, 3808.