Dresden 2020 – scientific programme
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O: Fachverband Oberflächenphysik
O 56: Poster Session - Nanostructures at Surfaces: Dots, Particles, Clusters
O 56.4: Poster
Tuesday, March 17, 2020, 18:15–20:00, P2/2OG
Electronic structure of a carbon dot monolayer on TiO2(110) — •Jan Beckord1, Matthias Hengsberger1, Andrea Cannizzo2, and Jürg Osterwalder1 — 1Department of Physics, University of Zurich, CH-8057 Zürich — 2Institute of Applied Physics, University of Bern, CH-3012 Bern
Carbon dots are nanometer-sized particles with a carbon core and a functionalized organic shell. Our research focuses on their observed photocatalytic properties: for example, they significantly improve the oxygen evolution reaction at titanium dioxide surfaces under visible light irradiation. To elucidate the electronic structure of this system, we adsorbed a single layer of carbon dots with an average size of 4 nm on a clean rutile TiO2(110) surface from aqueous solution in vacuo. We will present the full characterization of these surfaces using XPS, UPS and 2PPE. Our measurements revealed an increased upward band bending of the n-doped substrate and a lowered work function. A continuum of additional occupied states is found at binding energies between 6 eV and 11 eV due to the various molecular orbitals on the carbon dots, and some more occupied states are observed very close to the Fermi level at binding energies between 1 eV and 3 eV. 2PPE measurements revealed a continuum of unoccupied states as well, which pushes the band gap below 2 eV. These continua of electronic states therefore facilitate exciton generation from visible light, explaining the function of carbon dots as effective photosensitizers. Additionally, we found excellent long-term stability even in ambient air and under strong light, making this system suitable for applications under ambient conditions.