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O: Fachverband Oberflächenphysik
O 66: Metallic Nanostructures I (on Metals)
O 66.9: Vortrag
Donnerstag, 28. Februar 2008, 14:45–15:00, MA 041
Adsorbate-Induced Faceting of Ir and Re Surfaces — •Payam Kaghazchi, Timo Jacob, and Matthias Scheffler — Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin
Since high-index clean metal surfaces typically have lower surface atom densities and higher surface free energies compared to the close-packed surfaces of the same metal they can be used as the basis for surface reconstruction and facet formation experiments. In this context the group of T.E. Madey at Rutgers University found recently that on Ir(210) and Re(1121) surfaces strongly interacting adsorbates are able to induce the formation of well defined nanostructures after annealing the system at elevated temperatures.
Using density functional theory calculations with the PBE functional and ab initio atomistic thermodynamics we studied the adsorption of oxygen and nitrogen on the different surface orientations, which are involved in the nanostructures on Ir(210) and Re(1121). Constructing the corresponding (p, T)-surface phase diagrams, we find that at experimental pressure conditions (pO2=5· 10−10 atm) above 1100 K for Ir and above 1200 K for Re the planar surfaces are stable, while lowering the temperature stabilizes the nanofacets found experimentally. While on Ir(210) most nanoscale pyramids consist of smooth and unreconstructed planes, some (110) faces show a stepped double-missing row superstructure, which is only stable at higher temperatures (1000 K<T<1100 K). Interestingly, we find that this superstructure only appears at the faceted surface, but turns out to be unstable on a Ir(110) substrate.