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The (2 × 1) structure of the two-dimensional nickel silicide surface alloy on Ni(111) was investigated using quantitative low-energy electron diffraction analysis. The unit cell of the determined silicide structure contains one Si and one Ni atom, corresponding to a chemical formula of NiSi. The Si atoms adopt substitutional face-centered cubic hollow sites on the Ni(111) substrate. The Ni–Si bond lengths were determined to be 2.37 and 2.34 A. Both the alloy surface and the underlying first layers of Ni atoms exhibit slight corrugation. The Ni–Si interlayer distance is smaller than the Ni–Ni interlayer distance, which indicates that Si atoms and underlying Ni atoms strongly interact.

We studied the structural transition for silicon adsorption on Ag(111) by using low-energy electron diffraction (LEED) and Auger electron spectroscopy at various substrate temperatures during deposition. We obtained a single phase of the (4 ? 4) structure at 520 K, which was reported as a silicene. At 620 K, the (4 ? 4) structure changed to a high-temperature phase which was determined as by LEED, while in preceding works, it was assigned to a quasi or structure. Although the high-temperature phase had not been observed as a single phase, we obtained LEED patterns with a single phase for it, which enabled us to explain all the diffraction spots on the basis of the kinematic theory including double diffraction. The was obtained by the multiplication of a subunit cell. We concluded that the and phases could instead be represented as a phase, and we proposed a possible atomic model.