Heterogeneous and homogeneous nucleation of epitaxial NiSi₂ in [110] Si nanowires

We report here both heterogeneous and homogeneous nucleation of epitaxial silicide of NiSi₂ in Si nanowires grown in [110] direction by in situ observation in high-resolution transmission electron microscopy (TEM). Owing to the excellent lattice match between Si and NiSi₂, a giant epitaxial step of 2-8 nm wide forms at the interface between Si and NiSi₂ during the growth of the latter. The step formation results in two silicide/Si interfaces parallel to each other in TEM observations. Heterogeneous nucleation of NiSi₂ occurs at the intersection where the step meets the interfaces. However, we have also observed the epitaxial growth of NiSi ₂ having a single interface with the Si, i.e., without a giant step. Homogeneous nucleation of NiSi₂ occurs on the single interface. Incubation time of heterogeneous nucleation of NiSi₂ has been measured by high-resolution video to be much shorter than that of homogeneous nucleation. The overall growth rate of NiSi₂ for the case of heterogeneous nucleation is faster than that for the case of homogeneous nucleation. Kinetic analysis of both types of nucleation is presented for a direct comparison in order to have a better understanding of the nucleation events. © 2010 American Chemical Society.