The orientation relationships and interfaces of Ag3Sn and Ag4Sn on Ag and a discussion of their formation sequence

The energy of formation of ε-Ag3Sn is 1.62 times that of ζ-Ag4Sn. According to the heterogeneous nucleation theory, the critical nucleus size can be significantly reduced by coherent interfaces. The above interfaces results indicate that the interfacial energies of the ζ-Ag4Sn/Ag and ε-Ag3Sn/Ag interfaces are similar. Therefore ε-Ag3Sn should have a smaller critical nucleus size. Consequently ε-Ag3Sn nucleates first and forms before ζ-Ag4Sn in the Ag/Sn interfacial reaction.