Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 2: Organische Dünnschichten I

O 2.1: Talk

Friday, March 4, 2005, 10:45–11:00, TU EB301

Investigating the stability of the tetracene/Al₂O₃-interface with high-resolution electron energy loss spectroscopy and LEED — •R. Temirov¹, A. Langner², M. Sokolowski², and F.S. Tautz¹ — ¹International University Bremen, School of Engineering and Science, PO Box 750761, D-28725 Bremen — ²Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, D-53115 Bonn

Surprisingly, fluorescence of tetracene molecules in contact with a sapphire substrate is quenched, in spite of the fact that the high band gap of Al₂O₃ should provide an effective barrier to charge delocalisation [1]. The reappearance of luminescence after annealing thin tetracene layers to 240 K can be explained by a reduction of the tetracene/substrate interaction, either by molecular reorientation or dewetting of the interface. Here we report an HREELS investigation of the interface between thin epitaxial Al₂O₃-layers on Ni₃Al(111) and tetracene. Our experiments show that under the current deposition conditions (thermal evaporation onto a sample at T=80K) at least some tetracene molecules are oriented with their molecular plane parallel to the substrate. The maximized contact area between molecule and substrate may be an important factor in understanding the observed luminescence quenching. Our data also suggest that after annealing, contact area is minimized by the formation of three-dimensional tetracene islands. [1] M. Schneider, E. Umbach, A. Langner, M. Sokolowski, Journal of Luminescence 110, 275-283 (2004).