Berlin 2008 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 5: Organic Thin Films
DS 5.5: Vortrag
Montag, 25. Februar 2008, 18:45–19:00, H 2013
Reduced intermolecular interaction in organic ultra-thin films of α-NPD: A multi-sample analysis using VUV ellipsometry — •Sukumar Rudra1, Cameliu Himcinschi1, Sindu John Louis1, Marion Friedrich1, Christoph Cobet2, Norbert Esser2, and Dietrich r.t. Zahn1 — 1Technische Universität Chemnitz, Chemnitz, Germany — 2Institute for Analytical Sciences, Berlin, Germany
In situ ellipsometry using synchrotron radiation in the vacuum ultraviolet (VUV) range was employed to study the growth of α-NPD films starting from submonolayer coverage to bulk-like thicknesses. α-NPD was deposited on hydrogen passivated silicon and on ZnO (either Zn side or O side polished) substrates under ultra-high vacuum condition by organic molecular beam deposition. Ellipsometry was used to study the evolution of the dielectric function of the layers as a function of thickness on H-Si. It was found that the VUV absorption maxima of the ultra-thin film in the submonolayer thickness are spectrally blueshifted compared to its bulk counterparts. To confirm the role of the substrate in the blueshift, it was further studied on two different faces of ZnO substrates and the same behaviour was observed even though the shift was reduced compared to that on H-Si. Reduced intermolecular interaction seems to be the dominant reason behind the shift, whereas the substrate dependence is attributed to the changes in the local field due to the different polarizing media.