Tensor LEED analysis for the Ni(111)-(root 7 x root 7)R19.1 degrees-P surface structure: Comparison with other root 7 systems

A crystallographic analysis is reported using low-energy electron diffraction (LEED) in the tensor LEED approach for the (root 7 x root 7)R19.1 degrees structure formed by 3/7 monolayer of phosphorus at the Ni(111) surface. This surface has a novel structure in which each phosphorus atom bonds to seven neighbouring Ni atoms, four in the top layer and three in the second layer, at an average distance close to 2.39 Angstrom. Formally this reconstruction involves three neighbouring Ni atoms in a triangular arrangement per unit mesh of the original unreconstructed surface being replaced by three phosphorus atoms. A discussion is included of the structural relaxations that occur in this surface as the demands of Ni-P bonding are balanced against those for Ni-Ni and P-P contributions. Comparisons are made with the root 7 reconstructions observed for related systems, including those for P/Rh(111), S/Pd(111) and S/Cu(111). Copyright (C) 1999 John Wiley & Sons, Ltd.