Monotonous concentration profile and reconstruction at Pt 80Fe 20(111): LEED study of a catalyst

Abstract

Low energy electron diffraction (LEED) is used to determine the structure, the composition of the surface region and the substrate order of Pt 80Fe 20(111). The concentration profile is monotonously decreasing in contrast with disordered Pt x Ni 1− x alloys for the concentration oscillates around the bulk value: the top layer, which is buckled (dz 1 = 0.09 ± 0.02 A ̊ ) , is almost pure Pt ( C 1 = 96 ± 4at% Pt); the second and third layers are also enriched with Pt ( C 2 = 84 ± 7%, C 3, = 85 ± 15%). The interlayer very close to the substrate spacing Δd 12 = 0.3 ± 1% and Δd 23 = −0.6 ± 2%. In addition, we show that the concentration profile the geometry can be solved independently: for surface alloys of this type, the composition profile can be extracted in the subsitution disorder approximation with a large gain in computing time.