Phase transformations of alloyed and core-shell metallic nanoparticles for interconnect applications

In this study, the phase evolution upon heating of thiol-protected NPs of gold, silver and their alloys with various Au/Ag ratios (3:1, 1:1, and 1:3), as well as the phase transitions and oxidation of copper and copper-silver core shell NPs, are monitored by synchrotron radiation XRD. The interactions between ligands and surface atoms of NPs, and their influence on the coalescence and related properties will be reported. The coalescence of thiol-protected AuAg alloy nanoparticle deposits strongly depends on the rivalry between the thermodynamic and kinetic factors, which are respectively due to alloying effect and the ligand/surface atom interactions. With respect to the Cu@Ag nanoparticles, the formation temperatures of both the CuO and Cu₂O were higher than those of pure Cu nanoparticles with similar size by at least 150 °C, due to the protection by thin Ag shell. After being heated to 500°C, discrete Ag nano-nodules on unprotected CuO micron-particles could be observed.