Reinvestigation of the Ni/Si interface: Spectromicroscopic evidence for multiple silicide phases

Using photoelectron spectromicroscopy we identified the chemical composition of several phases on a morphologically complex interface formed after segregation of dissolved Ni onto the Si(111) surface. Unexpectedly, coexistence of two types of micrometer-sized silicide islands with composition and electronic structure close to NiSi₂ and NiSi phases was found. This finding revises some of the previous schemes about the evolution of the Ni/Si(111) system at high temperatures, which were based exclusively on structural analyses. A formation mechanism supposing anisotropy of the nucleation barrier for disilicide formation is suggested in order to explain the presence of NiSi islands and the preferred 〈110〉 orientation of the NiSi₂ islands.