Interdiffusion behavior at the interfaces between deposits of Au nanoparticles and electronic substrates

This study investigated the interfacial behavior between thiol-stabilized Au nanoparticle (NP) deposits and the commonly used electronic substrates, Cu, Ni and Ag. Instead of sintering or agglomerating, curing at 300°C resulted in either entire or partial melting of the deposited suspension because of the substantially low melting point of the Au NPs due to the nanosize effect; the melting point was measured to be 230-270°C. Thus a liquid-solid reaction might occur between the NP Au deposits and substrates during the thermal process. The elemental depth profiles examined by x-ray photoelectron spectroscopy (XPS) demonstrated that stoichiometric intermetallic phases, likely Cu₃Au and NiAu₃, existed respectively at the Au/Cu and Au/Ni interfaces, while a miscible solid solution of nonstoichiometric layer was found to have emerged at the Au/Ag interface. Also, the chemical shifts of binding energies inspected at the reaction layers reflected the alloying behavior at those interfaces.