Regensburg 2025 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 50: Poster Organic Molecules on Inorganic Substrates: Adsorption and Growth

O 50.9: Poster

Dienstag, 18. März 2025, 18:00–20:00, P2

Structure and charge carrier dynamics of an organic donor/acceptor heterostructure: a LEEM/PEEM study — •Franz Niklas Knoop, Klaus Stallberg, and Winfried Daum — IEPT, TU Clausthal, Germany

We combine low-energy electron microscopy (LEEM) and two-photon photoemission electron microscopy (2P-PEEM) to study the relation between structure and charge carrier dynamics in well-ordered organic donor/acceptor (D/A) heterostructures of para-sexiphenyl (p-6P) and copper-hexadecaphthalocyanine (F₁₆CuPc). While p-6P monolayers deposited on SiO₂ exhibit structural order only on a nanometer scale, p-6P islands in the second layer comprise micrometer sized single-crystalline domains. Using microspot low-energy electron diffraction (µLEED) and dark-field LEEM, on many islands we observe two mirror domains which we attribute to different tilt angles of the p-6P molecules in the second layer. Using µLEED we confirm epitaxial growth of monolayer F₁₆CuPc on SiO₂/p-6P which results in a structurally well-defined organic D/A interface. Especially on p-6P bilayer regions, large single-crystalline F₁₆CuPc domains are observed. With 2P-PEEM we observe increased photoemission from SiO₂/F₁₆CuPc after optical pumping at 810 nm. In contrast, for SiO₂/p-6P/F₁₆CuPc the photoemission signal decreases. Also, the reflectivity for low-energy electrons changes upon optical pumping. We relate these long-lived pump-induced effects to intermolecular charge transfer which is more pronounced for bilayer-p-6P/F₁₆CuPc than for monolayer-p-6P/F₁₆CuPc.

Keywords: LEEM; PEEM; Organic heterostructures; Phthalocyanines