Lowhyphen;energy electron diffraction structural analysis of the (2times;2) oxygen overlayer on the iridium (111) surface

摘要

Exposure of a clean Ir(111) surface at room temperature to approximately 20 L of oxygen produces a sharp (2times;2) LEED pattern. This LEED pattern can be caused by two fundamentally different adsorbate superstructures: ap(2times;2) array of oxygen atoms (onehyphen;quarter monolayer coverage) or three independent, equivalent domains of a (1times;2) superstructure rotated 120deg; with respect to one another (halfhyphen;monolayer coverage). Dynamical calculations have been performed for the three most symmetric adsites on this surface: the onhyphen;top site and the two different types of threefold sites for both thep(2times;2) and the three domains of (1times;2) superstructures. The results show that the oxygen adatoms, either forming ap(2times;2) superstructure or the three domains of (1times;2) superstructure rotated 120deg; with respect to one another, reside on the threefold site directly above a vacancy in the second substrate layer with an interlayer spacing of 1.30 Aring; corresponding to an Irndash;O bond length of 2.04 Aring;.