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

The orientation relationships and interfacial planes of the ε-Ag 3 Sn/Ag and ζ-Ag 4 Sn/Ag interfaces have been studied by transmission electron microscopy. Epitaxial Ag thin films were grown on the NaCl (001) and (111) surfaces and Sn was evaporated at various temperatures or by further annealing to form ε-Ag 3 Sn and ζ-Ag 4 Sn. Results showed that both phases have good orientation relationships with Ag on the (111) Ag surface but none on the (001) Ag surface. The energy of formation of ε-Ag 3 Sn is 1.62 times that of ζ-Ag 4 Sn. 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-Ag 4 Sn/Ag and ε-Ag 3 Sn/Ag interfaces are similar. Therefore ε-Ag 3 Sn should have a smaller critical nucleus size. Consequently ε-Ag 3 Sn nucleates first and forms before ζ-Ag 4 Sn in the Ag/Sn interfacial reaction. [ABSTRACT FROM AUTHOR]