Formation of two-dimensional silicide on Ni(100) surface

Abstract

The initial formation of two-dimensional silicide on a Ni(100) surface was studied by scanning tunneling microscopy in an ultrahigh vacuum. Less than 0.5 ML of Si deposition at 473 K created a two-dimensional Si–Ni mixed layer by displacing the substrate Ni with impinged Si. On a 0.5 ML Si deposited surface, the Si and Ni atoms were alternately aligned in the close-packed directions and formed a -R45° [or c(2 × 2)] structure. For Si deposition beyond 0.5 ML, excess Si did not react with surface Ni up to 573 K; instead, Si islands were formed on the two-dimensional silicide layer. A first-principles total-energy calculation showed preferential alignments of alternating Si and Ni in the directions, and higher formation energies when the embedded Si atoms were more than 0.5 ML. Since the -R45° structure was robust, impinged excess Si atoms did not penetrate the two-dimensional silicide layer and react with the subsurface Ni layer.