Formation and stability of a two-dimensional nickel silicide on Ni(111): An Auger, LEED, STM, and high-resolution photoemission study

摘要

Using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), scanning tunneling microscopy (STM), and high-resolution photoelectron spectroscopy (HR-PES) techniques we have studied the annealing effect of one silicon monolayer deposited at room temperature onto a Ni(111) substrate. The variations of the Si surface concentration, recorded by AES at 300 ℃ and 400 ℃, show at the beginning a rapid Si decrease followed by a slowing down up to a plateau equivalent to about one third of a silicon monolayer. STM images and LEED patterns, both recorded at room temperature just after annealing, reveal the formation of an ordered hexagonal superstructure of (3~(1/2) × 3~(1/2))R30° type. From these observations and from a quantitative analysis of HR-PES data, recorded before and after annealing, we propose that the (3~(1/2) × 3~(1/2))R 30° superstructure corresponds to a two-dimensional Ni_2Si surface silicide.