Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 24: Postersitzung (Epitaxie und Wachstum, Oxide und Isolatoren, Elektronische Struktur, Oberfl
ächenreaktionen, Adsorption an Oberfl
ächen, Organische Dünnschichten)

O 24.25: Poster

Mittwoch, 26. März 2003, 14:30–17:30, P1

Electronic Excitations of CO Adsorbed on MgO(001) — •Neng-Ping Wang, Michael Rohlfing, Peter Krüger, and Johannes Pollmann — Institut für Festkörpertheorie, Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster

We report ab-initio calculations of the quasiparticle band structure and the optical absorption spectrum of bulk MgO, the MgO(001) surface, and CO molecules adsorbed on MgO(001). Based on the ground-state properties, as obtained from DFT-LDA, the band structure is calculated within the GW approximation. The electron-hole excitations and their optical spectrum result from the Bethe-Salpeter equation, taking the electron-hole interaction into account. For bulk MgO we find a fundamental gap of 7.8 eV. Weakly bound excitons are observed at excitation energies of 7.7 eV in the bulk and 7.5 eV at the MgO(001)-(1×1) surface, respectively. The free CO molecule, on the other hand, is characterized by excitations near 8 eV. The adsorption of one monolayer of CO on MgO(001) affects the electronic properties of the substrate and, even more pronounced, of the molecule. The ionization potential and electron affinity of the molecule change drastically due to the polarizability of the substrate. The electron-hole excitations of the molecule are now in energetic resonance with those of the substrate and are significantly modified, accordingly.