Dependence of interfacial adhesion of Co–P film on its microstructure

The interfacial adhesion between electroplated Co–P films with various microstructures and substrate was thoroughly investigated by the nanoscratch method and transmission electron microscopy. The Co–P films with various P contents exhibited a completely amorphous structure, a nanocrystalline structure or a mixed structure. The experimental data show that the interfacial adhesion of the Co–P films strongly depends on their microstructure and the nanocrystalline film has stronger interfacial adhesion than the amorphous film. The intermetallic Co–Cu phase that forms at the interface between the nanocrystalline Co–P film and the substrate causes the increase of the adhesion strength. In addition, the first-principles calculation shows that the intense exchange coupling between Co(3d74s2) electrons and Cu(3d104s1) electrons results in the formation of the CoCu bond at the interface between the nanocrystalline Co–P film and the substrate and hence increases the interfacial adhesion strength.