Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 67: Metal surfaces: Adsorption of H/O and inorganic molecules

O 67.6: Talk

Thursday, March 29, 2012, 11:45–12:00, MA 043

Ordered domain-wall structure of Ir(100)-(2×1)-O — •Pascal Ferstl, Tobias Schmitt, Lutz Hammer, and M. Alexander Schneider — LS f. Festkörperphysik, Universität Erlangen-Nürnberg, Germany

Oxygen adsorption on Ir(100) leads to the formation of a (2×1) superstructure, whereby 0.5 ML of oxygen atoms are adsorbed in bridge positions [1,2]. A recent SXRD study [2] found an additional partial occupation of the hollow sites in the centres of the (2×1) cell by oxygen atoms. This finding is now validated by our STM measurements where we could directly image these extra atoms, which, however, are still very mobile at room temperature.

A slight reduction of the amount of oxygen adsorbed by heating the sample to the onset of oxygen desorption does not depopulate the hollow sites but creates light domain walls perpendicular to the oxygen rows instead. The mutual spacing of the domain walls is rather regular and decreases with coverage eventually leading to a (2×n) superstructure. The occurrence of such a superstructure has been inferred from very early LEED work [3], but its origin remained unclear. We argue that the domain walls already exhibit the hexagonal reconstruction of the clean surface.

[1] K. Johnson et al., J. Chem Phys. 112 (2000) 10460;
D. Sander et al., Phys. Rev. B 81 (2010) 153403;
J. Küppers & H. Michel; Appl. Surf. Sci. 3 (1979) 179