Orientation relationships of Au5Sn/Au interfaces and formation sequence of Au5Sn and AuSn at the Au/Sn interface

Abstract The orientation relationships and interfaces between ζ′-Au 5 Sn and Au have been studied by transmission electron microscopy. Epitaxial Au thin films were grown on the single-crystal NaCl surfaces and Sn was evaporated to form ζ′-Au 5 Sn. Results showed that on both the ( 1 ¯ 11 ) Au and (001) Au surfaces the (0001) ζ′ plane is the common interface surface with a common orientation relationship of ( 1 ¯ 100 ) ζ′ //(110) Au , which has a small misfit of 1.9%. The Au atoms have good matches across both interfaces. That δ-AuSn forms before ζ′-Au 5 Sn in the solid-state Au/Sn interfacial reactions was discussed by heterogeneous nucleation theory. Both phases have good orientation relationships to Au and therefore low interfacial energies. Analysis of the interfaces indicated that the ζ′-Au 5 Sn/Au interfacial energies should be less than δ-AuSn/Au, which favors the nucleation of ζ′-Au 5 Sn. However, the energy of formation of δ-AuSn is much larger, about 2.3 times, than that of ζ′-Au 5 Sn by data from references. Therefore δ-AuSn forms before ζ′-Au 5 Sn.