Regensburg 2002 – wissenschaftliches Programm
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SYOH: Organische Halbleiter
SYOH 2: Growth and Characterisation
SYOH 2.3: Vortrag
Montag, 11. März 2002, 11:30–11:45, H37
Vibrational Spectroscopy of Perylene Derivatives: A Comparison between PTCDA and DiMe-PTCDI — •G. Salvan, S. Silaghi, C. Himcinschi, A. Kobitski, T.U. Kampen, R. Scholz, and D.R.T. Zahn — Institut für Physik, Technische Universität Chemnitz, 09107 Chemnitz, Germany
In this contribution we compare the vibrational properties of two perylene derivatives, namely PTCDA (3,4,9,10-perylene-tetracarboxylic-dianhydride) and DiMe-PTCDI (N,N-dimethylperylene-3,4,9,10-bisdicarboximide) determined by Raman and infrared spectroscopy. The experimental data are obtained on thin films deposited by organic molecular beam deposition on passivated GaAs(100) substrates. The differences observed in the spectra of DiMe-PTCDI with respect of PTCDA ones, e.g. the strong shift of infrared-active C=O modes from 1771 down to 1695 cm−1, or the larger amount of splitting for the anhydride stretch mode near 1020 cm−1, are interpreted in terms of chemical trends induced by the different end-groups. The mode assignment was performed using a density functional calculation (Gaussian 98 package) after the geometry optimization of an isolated molecule. The analysis of spectra taken under different experimental geometries, i.e. different angles of incidence and polarization configurations, provides information regarding the molecular orientation. While the PTCDA molecules lye almost flat, DiMe-PTCDI ones have a large inclination angle with respect to the substrate plane.