Surface structure and composition of Pt50Rh50(1 1 0): room temperature analysis of the (1 × 3) missing-row reconstruction

The room temperature structure and composition of the clean Pt50Rh50(1 1 0) surface is investigated by low energy ion scattering (LEIS), scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and grazing incidence X-ray diffraction (GIXRD). While Pt25Rh75(1 1 0) reconstructs with a (1 × 2) missing-row structure, Pt50Rh50(1 1 0) exhibits a (1 × 3) structure in analogy with Pt80Fe20(1 1 0) and Pt90Co10(1 1 0). Three missing rows lead to the formation of (1 1 1) facets in which all atomic sites are enriched with platinum. Similarly all sites directly underneath are enriched with Rh leading to oscillation of the Pt concentrations similar to that of (1 1 1) surfaces. These composition changes are accompanied by a marked inwards relaxation of the top row (−10%) and large buckling in layers 3–5. Additionally the atomic positions of the facets are shifted laterally towards the valleys formed by the missing rows. Consistent pictures are derived from LEED, GIXRD, STM and LEIS concerning the composition while some discrepancy––similar to that recorded for pure Pt––are found concerning the interlayer distances between LEED and X-rays.