Berlin 2012 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 44: Poster IV: Thin film photovoltaics; Organic electronics and photovoltaics (jointly with CPP, HL, O); Organic thin films; Trends in atomic layer deposition (Focused session)

DS 44.45: Poster

Freitag, 30. März 2012, 09:30–12:00, Poster E

Interface Effects on Soret Band Excitations in Magnesium-Tetraphenylporphyrin Thin Films observed by Second-Harmonic Generation Spectroscopy — •Jan Metje, Klaus Stallberg, and Winfried Daum — Institute of Energy Research and Physical Technologies, TU Clausthal, Leibnizstr. 4, 38678 Clausthal-Zellerfeld

MgTPP films with thicknesses from 10 to 40 nm evaporated in UHV conditions on fused silica were studied using optical second-harmonic generation (SHG), UV-VIS absorption spectroscopy and AFM. The SHG spectra of the films exhibit two resonances in the spectral region of the Soret band of the molecule (S₀→ S₂) at 2.95 eV and at about 2.7 eV. The 2.95 eV band agrees in energy with that of MgTPP molecules dissolved in benzene, indicating the presence of weakly interacting molecules. The 2.7 eV SHG band is strongly red-shifted with respect to the Soret band of the aggregated bulk molecules of the film, for which our UV-VIS spectra show an absorption band at 2.81 eV. SHG spectra from films deposited on oxidized Si(100) allow us to relate the SHG strength of the porphyrin bands to that of the silicon E₁ interband transitions. The comparatively weak porphyrin SHG signals indicate an interface effect. The low energy of 2.7 eV in comparison to the bulk transition energy points to strongly interacting molecules presumably located at the SiO₂/MgTPP interface.

Work supported by the NTH School for Contacts in Nanosystems