Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 102: Epitaxy and growth: Metals and semiconductors II

O 102.5: Vortrag

Freitag, 18. März 2011, 12:15–12:30, WIL C307

Phase diagrams of two dimensional Pd_xAg_1−x/Pd(111) and Pt_xAg_1−x/Pt(111) surface alloys — •Albert K. Engstfeld¹, Ralf T. Rötter¹, Andreas Bergbreiter¹, Harry E. Hoster^1,2, and R. Jürgen Behm¹ — ¹Institute of Surface Chemistry and Catalysis, Ulm University, D-89069 Ulm, Germany — ²Current address: Technische Universität München, Centre for Electromobility, 50 Nanyang Drive, Singapore 637553

The distribution of Ag and Pd or Pt in Ag_xPd_1−x/Pd(111) and Ag_xPt_1−x/Pt(111) surface alloys was studied by high resolution UHV-STM. The alloys were prepared by evaporating Ag on the respective substrate and subsequent annealing to 800 K. From quantitative 2D atom distributions we can show that AgPt tends towards two dimensional clustering and AgPd towards a ’quasi’ random distribution, with small deviations for low and high coverages. From effective pair interactions, we are able to calculate the surface mixing energy and determine 2D phase diagrams. Furthermore we will elucidate whether the size mismatch or the differences in the intermetallic bonding are the dominant factor for the respective distribution in the surface alloy.