Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 51: Organic-Inorganic Systems II: Energy Level Alignment

O 51.8: Talk

Wednesday, March 9, 2016, 12:30–12:45, S054

Two-photon photoemission from tetraphenylporphyrins on Ag(100) — •Andrej Classen, Rebecca Pöschel, Gianluca Di Filippo, and Thomas Fauster — Lehrstuhl für Festkörperphysik, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstraße 7, 91058 Erlangen, Germany

Ultrathin films of two different tetraphenylporphyrins (2HTPP and MgTPP) were grown in-situ under UHV-conditions on a well-defined Ag(100) single crystal. The molecules were deposited by evaporation from a home-built Knudsen-cell evaporator. The substrate was kept at room temperature and layer thicknesses range from one monolayer of molecules (1 ML) up to multilayer films (19 ML). We present an investigation of the electronic structure using ultraviolet photoelectron spectroscopy and monochromatic two-photon photoemission (2PPE). The occupied molecular orbitals of 2HTPP and MgTPP were measured using a photon energy of 21.22 eV (HeI-radiation). 2PPE probes the unoccupied molecular orbitals. The combination of both yields a HOMO-LUMO gap of 4.2 eV (MgTPP) and 4.3 eV (2HTPP) in accordance with literature [1]. Taking the measured work function into account, the ionization potential is 5.9 eV (MgTPP) and 6.1 eV (2HTPP) [2]. The electron affinity is 1.7 eV (MgTPP) and 1.8 eV (2HTPP). The 2PPE intensity as a function of photon energy in the range from 3.08 eV to 3.38 eV follows the absorption spectrum (Soret band) of tetraphenylporphyrin.

[1] X. Blase et al., Phys. Rev. B 83, 115103 (2011)

[2] Y. Nakato et al., Chem. Phys. Lett. 39, 358 (1976)