Regensburg 2007 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 66: Nanostructures at Surfaces VI (Surface Reconstructions)

O 66.7: Vortrag

Freitag, 30. März 2007, 11:45–12:00, H36

DFT Studies on Ir(210)-Surface Faceting Induced by Oxygen Adsorption — •Payam Kaghazchi, Timo Jacob, and Matthias Scheffler — Fritz-Haber-Institut der MPG, D-14195 Berlin, Germany

Some atomically rough surfaces show facet formation in presence of strongly interacting adsorbates. STM and LEED studies demonstrated that the initially planar Ir(210) surface becomes faceted when exposed to oxygen and annealed to temperatures above 600K. The facets that form have been identified to have a pyramidal shape showing (311) and (110) faces. While the (311) faces are smooth and unreconstructed the (110) faces are rough and consist of both 1×1 terraces and a stepped double-missing-row superstructure [1]. Using density functional theory calculations together with the ab initio atomistic thermodynamics we studied the adsorption of oxygen on those surfaces, being involved in the facet-formation. In agreement with the experiment our calculated (p,T)-surface phase diagram shows that while at the experimental oxygen partial pressure and temperatures above ≈900K the planar O/Ir(210) surface is stable, at lower temperatures the facets are thermodynamically more stable. Those combine two O/Ir(311) faces and one face of either O/Ir(110)-regular or O/Ir(110)-superstructure. Due to the relatively small difference in stability our calculations support the picture of a coexistance of the regular and the superstructured Ir(110). We are now in the process of investigating contributions from step-edges, kinks and phonons. [1] I. Ermanoski, C. Kim, S. P. Kelty, T. E. Madey, Surf. Sci., 596, 89 (2005).