The structure of the Pt50Ni50(100) surface was investigated by low energy electron diffraction and scanning tunnelling spectroscopy. Superstructures corresponding to 12 x 1 and 19 x 1 reconstructions were observed in the low-energy electron diffraction pattern, and these reconstructions were identified with atomic resolution by scanning tunnelling microscopy. The reconstructed surface layer had a quasi-hexagonal atomic mesh with almost (111) atomic density and was divided into terraces and domains the size of which could be more than a thousand Å. The domains were corrugated with protrusions made up by 5 x 1 sub-units of the quasi-hexagonal mesh and with valleys containing depressed atoms or 2 x 1 subunits. The 12 x 1 and 19 x 1 periodicities were determined by the sequence of valleys; depending on the thermal treatment, one or the other dominated but both generally coexist on the terrace. Owing to the complexity of the structure, low-energy electron diffraction calculations were performed for a simplified model with surface atoms situated in a planar net and uniform quasi-hexagonal meshes. It was found that in both reconstructions the two surface layers were significantly enriched with platinum. The top layer enrichment was consistent with previous Auger measurements.

Reconstruction of the Pt50Ni50(100) Surface - a LEED and STM Study. Y.Gauthier, R.Baudoing-Savois, J.Rundgren, M.Hammar, M.Gothelid: Surface Science, 1995, 327[1-2], 100-20