Berlin 2005 – scientific programme

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DS: Dünne Schichten

DS 18: Optische Spektroskopie dünner Schichten I

DS 18.2: Talk

Monday, March 7, 2005, 15:30–15:45, TU HS110

Ultra-violet ellipsometry of ultra thin organic layers — •Ovidiu D. Gordan¹, C. Himcinschi¹, M. Friedrich¹, C. Cobet², N. Esser², W. Braun³, and D. R. T. Zahn¹ — ¹Institut für Physik, TU Chemnitz, 09107 Chemnitz, Germany — ²ISAS, 12489 Berlin, Germany — ³BESSY GmbH, 12489 Berlin, Germany

Ultra-thin films of tris-(8-hydroxyquinoline)-aluminum(III) (Alq₃) were prepared by organic molecular beam deposition (OMBD) on hydrogen passivated silicon substrates in ultra high vacuum (UHV). In situ ellipsometric measurements were performed at a fixed angle of incidence (68^∘) in the spectral range from 4 to 9.5 eV using synchrotron radiation at BESSY II. For the first time we proved that the dielectric function can be reliably obtained in this range for strong absorbing materials even for sub-monolayer coverage. The results obtained via a complex fitting procedure are compared with direct calculation [1] using the experimental spectra. The absorption bands of a Alq ₃ sub-monolayer coverage are shifted to higher energies compared to the bulk features. In addition, the shape of the extinction coefficient is in very good agreement with calculations employing time-dependent density functional theory.

[1] D. Aspnes-Spectroscopic Ellipsometry of Solids, Chap 15, Optical Properties of Solids New Developments, ed B.Seraphin, North Holland 1976