Regensburg 2004 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

SYOH: Organic and Hybrid Systems for Future Electronics

SYOH 5: Poster

SYOH 5.5: Poster

Donnerstag, 11. März 2004, 18:00–21:00, B

Luminescence quenching of tetracene molecules adsorbed on the sapphir surface — •Andreas Langner and Moritz Sokolowski — Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstr. 12, D-53115 Bonn

A surface usually affects the photolumenescence (PL) of adsorbed molecules. Our aim is to understand the mechanisms which modify the PL, in order to apply PL spectroscopy to learn something about the dynamic processes of molecules on surfaces (e.g., mobility, diffusion, rotation of molecules). So far PL investigations of isolated molecules on well defined surfaces are missing, partly because on metallic surfaces ultrafast quenching occurs and no fluorescence is observable.

However, on surfaces of wide gap insulator materials we expect to obtain PL signal from adsorbed molecules. In particular, we have investigated tetracene evaporated at 100 K on Al₂O₃(0001). The substrate was prepared in UHV by Ar⁺ sputtering and annealing in O₂ at 1200 K. We control the number of adsorbed molecules very accurately by thermal desorption. Contrary to our expectation, no fluorescence is observed for a 0.2 monolayer thick film of presumably isolated molecules. After annealing to 240 K we can measure an increase of the PL signal of the order of three magnitudes, which is probably due to the growth of 3D-tetracene-crystallites. We report the evolution of the PL in dependence of the film thickness and the annealing temperature.