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O: Oberflächenphysik

O 18: Adsorption an Oberfl
ächen II

O 18.2: Vortrag

Samstag, 5. März 2005, 11:00–11:15, TU EB301

Structure and Stability of the H / Ir (100) Adsorbate System — •Lutz Hammer, Daniel Lerch, Andreas Schmidt, Andreas Klein, Stefan Müller und Klaus Heinz — Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr.7, D-91058 Erlangen

The structure and energetics of hydrogen adsorption on the Ir(100)−1× 1 and −5 × 1 surface phases were studied by LEED, STM and first-principles calculations. For the metastable Ir(100) − 1 × 1 surface ab-initio DFT calculations surprisingly find the bridge site as the energetically stable adsorption site for all H-coverage values considered. A LEED structure analysis performed for this system confirms both this adsorption site and the substrate multilayer relaxation predicted by DFT. For the 5 × 1 − hex-phase, the reconstructed ground state of Ir(100), again an excellent agreement between the geometrical results of LEED and DFT was achieved. For this phase the heat of adsorption for the bridge and hollow site is degenerate and about 0.2 eV less than for the 1× 1-phase. The heat of adsorption values computed for other sites point towards a one-dimensional diffusion of hydrogen on the quasi-hexagonal surface. The structural modifications induced by H can be regarded as a precursor state for the lifting of the reconstruction. As the hydrogen induced 5 × 1 − hex → 1 × 1 deconstruction is kinetically hindered, a new 1× 1-like phase (5 × 1 − H) is formed instead. The bridge site is again the favoured adsorption site, with a heat of adsorption equivalent to that of the 1× 1-phase. Again the structural parameters revealed from LEED and DFT agree in all details.