Temperature-dependent segregation and (1 x 2) missing-row reconstruction of Pt25Rh75(110)

The surface structure and composition of the clean Pt25Rh75(110) surface is investigated by low energy electron diffraction (LEED) and low energy ion scattering (LEIS). For the equilibrated Pt25Rh75(110) surface we observe a (1 x 2) missing-row reconstruction in analogy to the pure Pt(110) surface, and a significant Pt enrichment of the topmost atomic layer (up to 80 at.% Pt). As the same strong surface enrichment in Pt was found in a previous study on the (100) and (111) surface of the same bulk composition, this means that in contrast to Pt-Ni and Pt-Co alloys, for Pt25Rh75 alloys the segregation behavior is not influenced extensively by the surface orientation. In addition to the structure analysis by LEED we performed LEIS experiments to determine the temperature-induced changes of the surface composition and structure. Since the Pt segregation is less pronounced at elevated temperature, the surface reveals a temperature-induced deconstruction of the (1 x 2) structure around 750 degrees C, resulting in an fcc(110) (1 x 1) surface at high temperature. Temperature-dependent measurements further show a hysteresis-like behavior of the top-layer composition, which is attributed to an enhanced Pt segregation on the (1 x 2) reconstructed surface. (C) 1999 Elsevier Science B.V. All rights reserved.