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

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 [degrees]C and 400 [degrees]C, 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 ([radical]3 x [radical]3)R30[degrees] type. From these observations and from a quantitative analysis of HR-PES data, recorded before and after annealing, we propose that the ([radical]3 x [radical]3)R30[degrees] superstructure corresponds to a two-dimensional Ni sub(2) Si surface silicide.