Regensburg 2025 – scientific programme
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O: Fachverband Oberflächenphysik
O 97: Organic Molecules on Inorganic Substrates: Electronic, Optical and Other Properties II
O 97.2: Talk
Friday, March 21, 2025, 10:45–11:00, H6
Beyond the Koopmans’ theorem: Energy-level alignment of PTCDA on BlueP-Au-network on Au(111) — •Maximilian Schaal1, Felix Otto1, Marco Gruenewald1, Roman Forker1, Keisuke Fukutani2, Satoshi Kera2, and Torsten Fritz1 — 1Institute of Solid State Physics, Friedrich Schiller University Jena, Helmholtzweg 5, 07743 Jena, Germany — 2Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan
Koopmans’ theorem is often used to relate the observed spectroscopic features in UP spectra to the orbital energies of molecules calculated by Hartree-Fock calculations. However, this theorem neglects the self-energy (charging energy), which can be as large as 1 eV for molecules in the gas phase [1]. Therefore, the ground state energy levels of the frontier orbitals are not sufficient to describe the energy-level alignment and the initial and final states must be considered [2].
In this study, we present a framework to investigate the energy-level alignment of a monolayer of PTCDA decoupled from the Au(111) surface by a BlueP-Au-network [3]. We have determined the electronic transport and the optical gap using differential reflectance and (low-energy inverse) photoelectron spectroscopy. From these values, we determined the exciton binding energy and the charging energy. Finally, we compared the energy levels of the adsorbed monolayer with measured and calculated quantities of molecules in the gas phase.
[1] Kirchhuebel et al., J. Phys. Chem. C 124 (2020).
[2] Kirchhuebel et al., Phys. Chem. Chem. Phys. 21 (2019).
[3] Gruenewald et al., Phys. Rev. Materials 6 (2022)
Keywords: Energy-level alignment; Decoupling; Blue Phosphorene (BlueP); Perylene-3,4,9,10-tetracarboxylic dianhydride; Exciton binding energy