Regensburg 2025 – scientific programme

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O: Fachverband Oberflächenphysik

O 13: Organic Molecules on Inorganic Substrates: Adsorption and Growth

O 13.3: Talk

Monday, March 17, 2025, 15:30–15:45, H8

Optical and Electronic Properties of Epitaxial Lead Phthalocyanine Monolayers and Bilayers on Graphite and Graphene — •Roman Forker, Marco Gruenewald, Matthias Spoddeck, and Torsten Fritz — Friedrich-Schiller-Universität Jena, Institut für Festkörperphysik, Helmholtzweg 5, 07743 Jena, Germany

The optical and electronic properties of the near-infrared absorber lead phthalocyanine (PbPc) on graphitic surfaces are measured by means of differential reflectance spectroscopy (DRS) and scanning tunneling spectroscopy (STS), respectively. This is corroborated by a thorough structural characterization using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED), demonstrating the similarity of the adlayer structures on graphite and graphene substrates. The dielectric function of PbPc monolayers (ML) extracted from our DRS measurements exhibits monomer character, and thus provides evidence that there is no significant electronic coupling between the molecular film and graphite or graphene. From 1 to 2 ML the dielectric function changes drastically, indicating the formation of physical dimers. Concomitantly, for PbPc bilayers the electronic properties are found to be caused by the formation of face-to-face stacked molecules, resulting in a splitting of the dI/dV-features associated with the PbPc HOMO and LUMO upon bilayer formation. Our results are compared to previous photoelectron spectroscopy data of this system, where a similar splitting of the HOMO-related features was reported.

Keywords: optical transitions; dI/dV spectroscopy; fundamental gap; molecular frontier orbitals; dielectric function