Berlin 2005 – scientific programme

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DS: Dünne Schichten

DS 22: Optische Spektroskopie dünner Schichten II

DS 22.1: Talk

Tuesday, March 8, 2005, 14:30–14:45, TU HS110

Optical response of a π-conjugated molecular monolayer adsorbed on Si(001): A first-principles study — •Andreas Hermann, Wolf G. Schmidt, and Friedhelm Bechstedt — Institut für Festkörpertheorie und -optik, Friedrich–Schiller–Universität, Max–Wien–Platz 1, 07743 Jena, Germany

Organic functionalization of semiconductor surfaces has become important for developing new semiconductor-based devices. The modification of the surface optical response for the prototypical system of the π-conjugated molecule 9,10–phenanthrenequinone adsorbed on Si(001) is investigated by means of first-principles calculations . Optical properties are calculated within the independent-particle approximation from all-electron wave functions obtained by the projector augmented wave method (PAW). Structural data and Reflectance Anisotropy Spectra (RAS) agree well with recent experimental findings [1,2]. The detailed analysis of the optical signal shows that intramolecular π–π^* transitions as well as adsorption–modified Si bulk states contribute to the surface spectrum. The calculations illustrate the sensitivity of optical spectroscopy to molecular adsorption but demonstrate clearly that a naive interpretation of the spectrum in terms of gas-phase molecular data fails.

[1] L. Fang et al., Surf. Sci. 514, 362 (2002).

[2] C. Hacker and R. J. Hamers, J. Phys. Chem. B 107, 7689 (2003).