Regensburg 2007 – scientific programme

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DS: Fachverband Dünne Schichten

DS 2: Organic Thin Films II

DS 2.4: Talk

Monday, March 26, 2007, 12:00–12:15, H32

Unusual narrow absorption bands of PTCDA submonolayers on potassium chloride — •Thomas Dienel, Christian Loppacher, Karl Leo, and Torsten Fritz — Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany

Here we report on the first observation of unusually narrow absorption bands of perylene-3,4,9,10-tetracarbxylic-dianhydride (PTCDA) on potassium chloride (KCl(001)) at room temperature. While submonolayers of the same compound deposited on muscovite mica exhibit absorption bands of similar width as in solution spectra [1], the full width at half maximum of a submonolayer PTCDA on KCl(001) is 3 times smaller. The molecular layer starts to crystallize immediately once a thickness of 1 monolayer (ML) is reached, accompanied with the absorption development towards the well-known spectrum of PTCDA crystallites.

As the spectral width is usually caused by inhomogeneous broadening, we are going to present low-temperature AFM measurements, which exhibit a very unusual structure of the PTCDA submonolayers on KCl, where all molecules are commensurately aligned in rows rather than in the common herringbone structure, therefore experiencing the very same local environment. On top of the aggregated islands one observes the herringbone arrangement, as reported for PTCDA islands on potassium bromide (KBr(001)) [2], which confirms nicely the optical assignment of polycrystalline PTCDA.

[1] H. Proehl et al., Phys. Rev. Lett., 2004, 93, 097403

[2] T. Kunstmann et al., Phys. Rev. B, 2005, 71, 121403