Oxidation and Reduction of Ir(100) Studied by High-Energy Surface X-ray Diffraction

: The oxidation and reduction of an Ir(100) surface using 2.5, 5, and 10 mbar O 2 partial pressure and a sample temperature of 775 K have been studied by using high-energy surface X-ray di ff raction (HESXRD) which allowed to record large volumes of reciprocal space in short time periods. The complex 3D di ff raction patterns could be disentangled in a stepwise procedure. For the 2.5 mbar experiment the measurements indicate the formation of an Ir(100)-O c(2 × 2) oxygen superstructure along with the onset of epitaxial IrO 2 (110) bulk oxide formation. For the 5 and 10 mbar O 2 partial pressures the formation of additional IrO 2 bulk oxide epitaxies with (100) and (101) orientations as well as of polycrystalline IrO 2 was observed. Upon CO reduction, we found the IrO 2 islands to be reduced into epitaxial and metallic Ir(111) and (221) oriented islands.

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