LOW-ENERGY ELECTRON-DIFFRACTION STRUCTURAL-ANALYSIS OF THE (2X2) OXYGEN OVERLAYER ON THE IRIDIUM(111) SURFACE

Exposure of a clean Ir(111) surface at room temperature to approximately 20 L of oxygen produces a sharp (2 × 2) LEED pattern. This LEED pattern can be caused by two fundamentally different adsorbate superstructures: a p ( 2 × 2 ) array of oxygen atoms (one-quarter monolayer coverage) or three independent, equivalent domains of a (1 × 2) superstructure rotated 120° with respect to one another (half-monolayer coverage). Dynamical calculations have been performed for the three most symmetric adsites on this surface: the on-top site and the two different types of threefold sites for both the p ( 2 × 2 ) and the three domains of (1 × 2) superstructures. The results show that the oxygen adatoms, either forming a p (2 × 2) superstructure or the three domains of (1 × 2) superstructure rotated 120° 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 Å corresponding to an Ir-0 bond length of 2.04 Å. © 1979 American Institute of Physics.