Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 20: POSTER A

CPP 20.56: Poster

Montag, 24. März 2003, 19:00–21:00, ZEU/250

Optical properties of potassium intercalated PTCDA — •Gonzalo G. Fuentes, Martin Knupfer, and Jörg Fink — Leibniz Institut für Festkörper- und Werkstofforschung

We have studied the electronic structure and the optical properties of potassium-intercalated poly and single crystalline PTCDA by energy loss (EELS) and photoemission spectroscopy. The PTCDA dielectric function (Im {-1/є}) upon intercalation is strongly influenced by the formation of K-PTCDA domains coexisting with non-reacted PTCDA. The electronic structure of K-PTCDA cannot be understood only in terms of charge transfer localized-polaron formation, but additional solid-state effects should be considered. In addition to the polaron-related transitions, we observe a new feature at 0.68 eV in the loss function. We find that such feature is only compatible with a Mott-type excitation due the presence of on-site electron correlation. Moreover, we have found that this excitation is polarized in the direction parallel to the molecular stacks characteristic of the monoclinic α-PTCDA phase, where a close-packing-molecular arrangement and hence large π orbital overlap, are expected. Photoemission spectra of the valence band also confirm the semiconducting character of the K-PTCDA compound.