Level alignment of a prototypical photocatalytic system: Methanol on TiO<sub>2</sub>(110)

Journal Of The American Chemical Society 135, 11429 - 11432 (2013)

Level alignment of a prototypical photocatalytic system: Methanol on TiO2(110)

Annapaola Migani, Duncan J. Mowbray, Amilcare Iacomino, Jin Zhao, Hrvoje Petek, Angel Rubio

Photocatalytic and photovoltaic activity depends on the optimal alignment of electronic levels at the molecule/semiconductor interface. Establishing level alignment experimentally is complicated by the uncertain chemical identity of the surface species. We address the assignment of the occupied and empty electronic levels for the prototypical photocatalytic system of methanol on a rutile TiO2(110) surface. Using many-body quasiparticle techniques we show that the frontier levels measured in ultraviolet photoelectron and two photon photoemission spectroscopy experiments can be assigned with confidence to the molecularly chemisorbed methanol, rather than its decomposition product, methoxy. We find the highest occupied molecular orbital (HOMO) of methoxy is much closer to the valence band maximum, suggesting why methoxy is more photocatalytically active than methanol. We develop a general semi-quantitative model for predicting many-body quasiparticle energies based on the appropriate description of electronic screening within the bulk, molecular or vacuum regions of the wavefunctions at molecule/semiconductor interfaces.

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