Dresden 2003 – wissenschaftliches Programm

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O: Oberflächenphysik

O 9: Adsorption an Oberfl
ächen I

O 9.10: Vortrag

Montag, 24. März 2003, 17:15–17:30, FOE/ANOR

Hydrogen-induced Phase Transition on the Ir(100)-(5×1) Surface — •Peter Landfried, Andreas Schmidt, Lutz Hammer und Klaus Heinz — Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, D-91058 Erlangen

The clean Ir(100) surface is reconstructed with six atomic rows residing in a quasi-hexagonal arrangement on top of every five square unit cells of the substrate. Hydrogen adsorption at low temperatures (< 190 K) does not lift this reconstruction but leads to significant structural modifications within the hexagonal overlayer as judged from considerably altered LEED intensity spectra. At higher adsorption temperatures the surface reconstruction is lifted in a way that excess atomic rows are expelled from the overlayer and form a well-ordered 5×1 adatom structure. Annealing of the low temperature adsorption phase also triggers the phase transition at about 190 K. However, annealing always results in a phase mixture of the adatom structure and the clean reconstructed surface indicating that hydrogen atoms diffuse from reconstructed patches to unreconstructed ones, where they undergo stronger binding. As a consequence, the lifting of the reconstruction stops at a certain stage, when hydrogen supply from the gas phase is missing. Finally, the extent of surface reorganisation appears to depend also on the hydrogen pressure in the gas phase, which points towards a hydrogen dissociation barrier for the clean reconstructed surface and thus some defect-mediated adsorption kinetics.