Probing electrons in TiO2 polaronic trap states by IR-absorption: evidence for the existence of hydrogenic states.
An important step in oxide photochemistry, the loading of electrons into shallow trap states, was studied using infrared (IR) spectroscopy on both, rutile TiO2 powders and single-crystal, r-TiO2(110) oriented samples. After UV-irradiation or n-doping by exposure to H-atoms broad IR absorption lines are observed for the powders at around 940 cm(-1). For the single crystal substrates, the IR absorption bands arising from an excitation of the trapped electrons into higher-lying final states show additional features not observed in previous work. On the basis of our new, high-resolution data and theoretical studies on the polaron binding energy in rutile we propose that the trap states correspond to polarons and are thus intrinsic in nature. We assign the final states probed by the IR-experiments to hydrogenic states within the polaron potential. Implications of these observations for photochemistry on oxides will be briefly discussed.
Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), 76021 Karlsruhe, Germany.
Hikmet
H
Sezen
Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), 76021 Karlsruhe, Germany.
Maria
M
Buchholz
Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), 76021 Karlsruhe, Germany.
Alexei
A
Nefedov
Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), 76021 Karlsruhe, Germany.
Carsten
C
Natzeck
Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), 76021 Karlsruhe, Germany.
Stefan
S
Heissler
Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, via R. Cozzi 55, 20125 Milano, Italy.
Cristiana
C
Di Valentin
Karlsruhe Institute of Technology (KIT), Institute of Functional Interfaces (IFG), 76021 Karlsruhe, Germany.
Christof
C
Wöll