Characterization of the microstructure and phase formation in the Au–In system using transmission electron microscopy

The Au–In system is of both fundamental and technical importance for engineering applications such as microelectronic packaging. The growth mechanism and crystal orientation of the Au and In thin films produced by thermal evaporation on NaCl substrates are studied by transmission electron microscopy (TEM). Like most metals, the growth of both Au and In thin films on single crystals of NaCl follows the Volmer–Weber mode, i.e. formation of metal nuclei first, and then grain growth and coalescence of the particles to form a continuous thin film. In contrast, the growth of In on the Au-coated NaCl substrates follows the Frank–van der Merwe mode, i.e. layer by layer, as a result of strong interactions between Au and In. The formation of AuIn2 phase occurs instantly upon In deposition, and the intermetallic exhibits an epitaxial orientation to the underlayer Au single crystals. In addition, cross-section TEM observation of the Au/In/Au thin sections by ultramicrotomy shows that the AuIn2 intermetallic is brittle.