Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 27: Organische Dünnschichten I

O 27.5: Vortrag

Donnerstag, 27. März 2003, 12:15–12:30, HSZ/02

Organic functionalization of semiconductor surfaces – A comprehensive first-principle study of Si(001):pyrrole and Si(001):uracil — •Kaori Seino, Wolf G. Schmidt, and Friedhelm Bechstedt — Institut für Festkörpertheorie und Theoretische Optik, Friedrich-Schiller-Universität Jena, Jena, Germany

The formation of organic thin films on semiconductors allows for adding biological and chemical functionality to microelectronics. Because of the many possible interactions within the organic overlayer as well as between the molecules and the semiconductor, however, the present knowledge about the atomistic structure of such interfaces is rather limited. We present an extensive computational study of the Si(001):pyrrole and Si(001):uracil interfaces based on DFT-GGA and ultrasoft pseudopotentials. The structural and electronic properties of the respective interfaces are predicted in dependence on the molecular coverage and the preparation conditions. We find dissociative reactions, leading to the partial fragmentation of the molecule, to be energetically most favored for pyrrole adsorption on Si(001) surface. The lowest energy configuration for monolayer coverage is characterized by pyrrole rings bonded to the surface via Si-N linkage. In co-existence with alternative adsorption geometries where both N and C are bonded to the surface, this structure accounts very well for the available experimental data. The initial bonding configuration of uracil adsorbed on Si(001) is largely determined by electrostatic effects. However, also for uracil we predict a pronounced tendency for molecular fragmentation, leading eventually to oxygen insertion in Si dimers.