Regensburg 2013 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Poster: Organic Semiconductors

CPP 32.11: Poster

Wednesday, March 13, 2013, 16:30–18:30, Poster C

Understanding changes in optical absorption of thin organic films during growth — Ines Trenkmann¹, Christopher Keil², Derck Schlettwein², and •Harald Graaf¹ — ¹nanoMA (Center for nanostructured Materials and Analytics), Chemnitz University of Technology, D-09107 Chemnitz, Germany — ²Institute of Applied Physics, Justus-Liebig-University Giessen, D-35392 Giessen, Germany

The optical absorption of organic thin films changes during growth. Here mainly the lowest energy transition shows a red shift with increasing film thickness. Different explanations are given in the literature: e.g. increasing island sizes leading to larger coupled systems [1] or a change in the ratio between the numbers of molecules in the bulk compared to surface molecules [2]. We investigated three perylene derivatives showing all the expected red shift of the lowest energy transition. They are characterized by different morphologies and growth modes: One shows a layer-by-layer growth and two (an amorphous and a crystalline) show island growth. The shift for the layer-by-layer perylene can be explained by a combination of the two above mentioned explanation. The shift for the first approximately 1.5 monolayers can be understood by a two-dimensional island growth with increase of coupled chromophoric systems. Further film growth lead to an increase of the ratio between the number of molecules in the bulk with respect to the surface molecules. For the other two molecules the experimental results on the red-shift can be explained by a new theoretical model.

[1] Chau et al. J.Phys.Chem 97 (1993) 2699, [2] e.g. Heinemeyer et al. Phys.Rev.Lett. 104 (2010) 257401