title: Level alignment of a prototypical photocatalytic system: methanol on TiO2(110).
abstract: Photocatalytic activity depends on the optimal alignment of electronic levels at the molecule-semiconductor interface. Establishing the 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 consisting of methanol on a rutile TiO2(110) surface. Using many-body quasiparticle (QP) techniques, we show that the frontier levels measured in UV photoelectron and two-photon photoemission spectroscopy experiments can be assigned to molecularly chemisorbed methanol rather than its dissociated product, the methoxy species. We find that the highest occupied molecular orbital of the methoxy species is much closer to the valence band maximum, suggesting why it is more photocatalytically active than the methanol molecule. We develop a general semiquantitative model for predicting many-body QP energies based on the electronic screening within the bulk, molecular, or vacuum regions of the wave functions at molecule-semiconductor interfaces.
authors.affiliation: Nano-Bio Spectroscopy Group and ETSF Scientific Development Center, Departamento de Física de Materiales, Centro de Física de Materiales CSIC-UPV/EHU-MPC and DIPC, Universidad del País Vasco UPV/EHU, E-20018 San Sebastián, Spain. amigani@cin2.es
authors.forename: Annapaola
authors.initials: A
authors.lastname: Migani
authors.forename: Duncan J
authors.initials: DJ
authors.lastname: Mowbray
authors.forename: Amilcare
authors.initials: A
authors.lastname: Iacomino
authors.forename: Jin
authors.initials: J
authors.lastname: Zhao
authors.forename: Hrvoje
authors.initials: H
authors.lastname: Petek
authors.forename: Angel
authors.initials: A
authors.lastname: Rubio
mesh_terms: D002384:Catalysis; D004583:Electrons; D000432:Methanol / Q000737:chemistry*; D008958:Models, Molecular; D055668:Photochemical Processes; D056951:Photoelectron Spectroscopy; D012666:Semiconductors; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: C009495:titanium dioxide; D014025:Titanium; D000432:Methanol