Atomic-scale analysis of CoFe/Cu and CoFe/NiFe interfaces

Internal interfaces in metallic multilayers grown on planar silicon substrates have been chemically analyzed with atomic resolution using three-dimensional atom probe microscopy. The structure studied was a NiFe/CoFe/Cu/CoFe multilayer grown with (111) texture. Atom probe measurements across the NiFe/CoFe interfaces yield widths of $\text{1.1±0.2\hspace{0.05em}}\mathrm{nm}$ for NiFe grown on CoFe and $\text{1.7±0.2\hspace{0.05em}}\mathrm{nm}$ for CoFe grown on NiFe. The widths of interfaces between CoFe and Cu layers vary as well, with values of $\text{0.82±0.10\hspace{0.05em}}\mathrm{nm}$ for CoFe grown on Cu, but only $\text{0.47±0.15\hspace{0.05em}}\mathrm{nm}$ for Cu grown on CoFe. In addition, the Fe concentration is enriched at the interface where Cu is grown on CoFe, and depleted where CoFe is grown on Cu. These results indicate that the Fe segregates to the surface during the deposition of CoFe so that the composition at the top of this layer is Fe rich.