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O: Oberflächenphysik
O 14: Postersitzung (Adsorption an Oberflächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Phasenübergänge, Rastersondentechniken, Struktur und Dynamik reiner Oberflächen)
O 14.47: Poster
Montag, 8. März 2004, 18:00–21:00, Bereich C
Desorption of Atoms from Optically Excited Alkali Halides — •M. Rohlfing1, N.-P. Wang2, P. Krüger2, and J. Pollmann2 — 1School of Engineering and Science, International University Bremen, P.O. Box 750761, 28725 Bremen — 2Institut für Festkörpertheorie, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster
We investigate the emission of halogen atoms from optically excited alkali halides (e.g., KI). To this end we employ an ab-initio approach to the excited states and the corresponding total-energy surfaces. Based on density-functional theory, the electronic correlation effects are treated within many-body perturbation theory (i.e., the GW method and the Bethe-Salpeter equation). This yields the total energy of the system, both in its ground state and in the excited state, as a function of the geometry. As prototype materials KI and KBr are discussed. Our results indicate that at the KI(001) surface, a surface exciton can be excited leading to direct emission of a neutral iodine atom without any desorption barrier. The emission occurs on a sub-picosecond time scale and leads to kinetic energies of the iodine atoms of several 100 meV, in accordance with recent time-of-flight experiments.