We present a new investigation of the metastable 1 × 1 and reconstructed 5 × 1 phases of Ir(100) using quantitative low-energy electron diffraction and scanning tunnelling microscopy. It is shown that the 5 × 1 reconstruction of Ir(100) extends up to the fourth layer into the surface. This structural information is retrieved by the use of electron energies up to 600 eV which simultaneously provides an unusually broad database of more than 10.000 eV. Together with an excellent quality of the theory–experiment fit equivalent to an R-factor of RP = 0.144 this allows for rather small error limits of the as many as 17 structural parameters describing the four-layer reconstructed surface. Similar features hold for the 1 × 1 phase which is analysed in parallel. In addition, we present a systematic investigation of the influence of the electron energy range applied and of the allowed depth of reconstruction on the accuracy of the analysis. It appears that for the case of Ir(100)-5 × 1 the structural parameters describing the top two layers are largely independent from the consideration of the reconstruction of deeper layers.

We show that the Ir(100) surface forms a new nanostructure in a self-organized way when its reconstructed equilibrium surface is exposed to hydrogen. Scanning tunneling microscopy and quantitative low-energy electron diffraction retrieve that a long-range ordered superlattice of defect-free Ir chains with average lateral spacing of 1.36 nm and micrometer lengths develops. This can be used as a template for the formation of other nanostructures as is demonstrated.

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For the example of the B2 CoAl(100) surface, we demonstrate that even slight deviations from an ordered alloy's ideal stoichiometry in a subsurface region or in the bulk can drastically affect its surface composition. By experimental surface analysis and first-principles calculations, we show that Co antisite atoms segregate to the very surface, driven by the same strong interactions which enforce order in the bulk. Our findings are consistent with the lack of antisite segregation we found earlier for the much weaker ordering FeAl(100), and resolve contradictory reports for NiAl(100).