K and mixed K + O adlayers on Rh(110)

The evolution of the structure of the adlayers and the substrate during adsorption of K and coadsorption of K and O on Rh(110) is studied by scanning tunneling microscopy and low-energy electron diffraction. The K adsorption at temperature above 450 K leads to consecutive ( 1 × 4 ) , ( 1 × 3 ) , and ( 1 × 2 ) missing-row reconstructions for coverage up to 0.12 ML, which revert back to ( 1 × 3 ) and ( 1 × 4 ) with increasing coverage up to 0.21 ML. The coadsorption of different oxygen amount at T > 450 K and eventually following reduction-reoxidation cycles led to a wealth of coadsorbate structures, all involving substrate missing-row-type reconstructions, some including segmentation of Rh rows along the [ 1 1 ¯ 0 ] direction. The presence of K stabilizes the ( 1 × 2 ) missing-row reconstruction, which facilitates the formation of a great variety of very open ( 10 × 2 ) -type reconstructions at high oxygen coverage, not observed in the single adsorbate systems.