Oxygen-induced nano-faceting of Ir(210)

The adsorption of oxygen and the nanometer-scale faceting induced by oxygen have been studied on Ir(210). Oxygen is found to chemisorb dissociatively on Ir(210) at room temperature. The molecular desorption process is complex, as revealed by a detailed kinetic analysis of desorption spectra. Pyramid-shaped facets with {311} and (110) orientations are formed on the oxygen-covered Ir(210) surface when annealed to T greater than or equal to 600 K. The surface remains faceted for substrate temperatures T < 850 K. For T > 850 K, the substrate structure reverts to the oxygen-covered (210) planar state and does so reversibly, provided that oxygen is not lost due to desorption or via chemical reactions upon which the planar (210) structure remains. A clean faceted surface was prepared through the use of low temperature surface cleaning methods: using CO oxidation, or reaction of H-2 to form H2O, oxygen can be removed from the surface while preserving ("freezing") the faceted structure. The resulting clean faceted surface remains stable for T < 600 K. For temperatures above this value, the surface irreversibly relaxes to the planar state. (C) 2003 Published by Elsevier B.V.