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O: Fachverband Oberflächenphysik

O 79: Electronic Structure of Surfaces: Spectroscopy, Surface States I

O 79.5: Vortrag

Mittwoch, 22. März 2017, 16:15–16:30, WIL C307

Electronic structure of a single crystal BiVO4 photocatalyst measured by angle-resolved photoemission spectroscopy — Mansour Mohammed^1,2, Matthias May², Christoph Janowitz¹, Michael Kanis³, Reinhardt Uecker⁴, Mario Brützmann⁴, Roel van de Krol³, and •Mattia Mulazzi^1,4 — ¹1Humboldt University in Berlin, Institute of Physics, 12489 Berlin, Germany — ²2Assiut University, Department of Physics, Faculty of Science, 71515 Assiut Egypt — ³3Helmoltz Zentrum Berlin für Materialien und Energie, Institute of Solar Fuels, 14109 Berlin, Germany — ⁴4Leibniz Institute for Crystal Growth, 12489 Berlin, Germany

We measured by angle-resolved photoemission at low energy the valence band dispersion of BiVO4. The material, a wide-band gap n-type oxide, is a promising photoanode material for water splitting applications. A solar-to-hydrogen efficiency of ~5% was reached wiht a BiVO4 / double juntion a-Si tandem cell device. The bands measured in ARPES experiments are flat, with only a sizeable dispersion measured in the in-plane directions perpendicular to the (010) axis. We found a weak non-dispersive peak in the forbidden gap indicating localised states, which we attribute to point defects. To determine thee origin of the defects, we compared (for different photon energies) the in-gap peak and top-of-valence-band photoemission intensity ratio to the theoretical Mo and oxygen cross-sections. We found that the theory is in quantitative agreement with the experiment and attributed the in-gap peak to the Mo dopant. We discuss the consequences of the Mo states, which change the size and character of the band gap.