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O: Fachverband Oberflächenphysik

O 12: Organic Molecules at Surfaces 2: Characterization of Organic Monolayers

O 12.4: Talk

Monday, September 5, 2022, 15:45–16:00, S051

Nickel(II) Porphyrins on Metal Surfaces: Oxidation-State Tuning and Formation of a Supramolecular Mixed-Valence Adsorbate Structure — •Jan Herritsch, Qitang Fan, Marie-Irène Albus, Lukas Ruppenthal, Lukas J. Heuplick, Leonard Neuhaus, Tobias Wassermann, and J. Michael Gottfried — Philipps-Universität Marburg

Nickel tetrapyrrole complexes are structurally related to biologically relevant molecules (e.g., F430 cofactor, tunichlorin, nibalamine) and are promising precursors for novel functional interfaces. Here, we report on the influence of the interaction at the metal/organic interface on the electronic structure of a nickel octaethyl porphyrin (Ni(OEP)) monolayer on different coinage metal surfaces studied by XPS, UPS, STM, NEXAFS and LEED. On Ag(111), Ni(OEP) forms a mixed-valent adsorbate phase in which the Ni centers occur in two different oxidation states. The two separate peaks in the Ni 2p XP spectrum indicate that about 40% of the Ni centers are reduced. STM and LEED show an incommensurate superstructure with an ordered arrangement of the metal centers in different oxidation states. Further insights into the valence electronic structure were obtained by UPS and NEXAFS. On the more reactive Cu(111) surface, Ni(OEP) forms a long-range ordered structure in which nickel centers are uniformly reduced; whereas on the most inert Au(111) surface, the oxidation state of the Ni centers remains unaffected by adsorbate interactions.