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O: Oberflächenphysik

O 19: Electronic structure II

O 19.7: Vortrag

Dienstag, 28. März 2006, 12:45–13:00, WIL A317

Organic small bandgap semiconductors: Electronic properties of quaterrylene derivatives on Au(111) — •Robert Franke, Christian Wagner, Sebastian Franke, and Torsten Fritz — Institut für Angewandte Photophysik, George-Bähr-Straße 1, 01069 Dresden

The understanding of the electronic properties of organic thin films is of large interest for their application in novel devices. As the electronic properties of perylene derivatives [1] and other medium-sized planar aromatic molecules [2] have already been studied intensively, we have now investigated larger organic molecules, namely quaterrylene (QT) and quaterrylenebisdicarboximide (QTCDI) on Au(111) in UHV. This class of materials is especially interesting due to their long-wavelength absorption in the NIR.

Ultrathin films of QTCDI and QT were investigated by Tunnelling Spectroscopy. In case of QTCDI we found a HOMO-LUMO gap of about 2.2 eV. This result is in good agreement with our optical measurements of QTCDI on mica where the optical gap is found to be 1.8 eV, indicating an exciton binding energy of about 0.4 eV. For thin QT films we obtained an electronic bandgap of 2.5 eV, which fits nicely to the fact that the smaller QT-molecule is expected to have a larger gap than the larger QTCDI molecule.

[1] M. Toerker, T. Fritz, H. Proehl, R. Gutierrez, F. Großmann, and R. Schmidt PRB 65 (2002) 245422 [2] H. Proehl, M. Toerker, F. Sellam, T. Fritz, and K.Leo PRB 63 (2001) 205409