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O: Fachverband Oberflächenphysik

O 16: Electronic Structure and Spin-Orbit Interaction II

O 16.6: Vortrag

Montag, 31. März 2014, 17:15–17:30, GER 38

The origin of TiO₂ shallow gap states evidenced from resonant photoelectron spectroscopy (RPES) and AFM on anatase single crystal (101) surface, nanocrystalline anatase films and ALD titania ante and post annealing — •Philip Reckers¹, Mariel Dimamay¹, Sara Trost², Thomas Riedl², Thomas Mayer¹, and Wolfram Jaegermann¹ — ¹Technical University of Darmstadt, Surface Science, Germany — ²Wuppertal University, Electronic Devices, Germany

Transparent, conductive and catalytic active TiO₂ with all its polymorphs is of high interest as it is used e.g. for water splitting, in DSSC and OSC. Gap states in TiO₂ play a crucial role as they influence e.g. charge transport and act as recombination centers. We investigated TiO₂ samples with respect to gap states by the use of resonant photoelectron spectroscopy. We detected two different band gap states. Deep gap states (DGS), that are attributed to oxygen defects are found around 1.3 eV and shallow gap states (SGS) are occupied from the Fermi level to about 0.35 eV binding energy. On a single crystal (SC) anatase (101) surface only SGS were detected. DGS and SGS states are observed on sintered nanocrystals (NC). Together with images from AFM we were able to ascribe the SGS to under coordinated Ti sites. The measured DOS fits well to the calculated DOS tailing into the energy gap inherent to NC as 1D line defects of under coordinated Ti sites form at (101) intersections^[1]. Similar defects are located at edges of terraces on SC surfaces that form along the (101) direction. [1]F.Nunzi, F.De Angelis, E.Environ. Sci.,2013,6,4,1221-1229