Oxygen-Induced Faceting of Ir(210)

Although rough clean metal surfaces usually have higher surface free energies than their closed-packed analogs, adsorbates are able to modify this behavior and cause changes in surface morphology through reconstructions or facet formations. Using different surface sensitive techniques (e.\,g. STM or LEED) Madey {\it et al.} [1] found that Ir(210) shows interesting surface faceting at high oxygen coverages ($\theta>0.5$\,ML). The facets were identified as three-sided nanoscale pyramids with two (311) and one (110) planes. In oder to understand this effect we used density functional theory in combination with the {\it ab initio} atomistic thermodynamics and studied the influence of an oxygen atmosphere on the structure of Ir(210). Assuming an oxygen partial pressure of 1\,atm, it turned out that below $T<1000$\,K the oxygen-covered facets are thermodynamically more stable than non-faceted O/Ir(210). Further heating reverts the substrate structure to planar O/Ir(210). While most nanoscale pyramids consist of smooth and unreconstructed planes, some (110) facets show a complex reconstructed superstructure. Thus, present studies aim on the stability and an atomistic understanding of those structures.\newline [1] I. Ermanoski {\it et al.}, {\it Surf. Sci.} {\bf 549}, 1 (2004).