Atomistic Assessment of Melting Point Depression and Enhanced Interfacial Diffusion of Cu in Confinement with AlN

The continuing trend in heterogeneous integration (i.e., miniaturization and diversification of devices and components) requires a fundamental understanding of the phase stability and diffusivity of nanoconfined metals in functional nanoarchitectures, such as nanomultilayers (NMLs). Nanoconfinement effects, such as interfacial melting and anomalous fast interfacial diffusion, offer promising engineering tools to enhance the reaction kinetics at low temperatures for targeted applications in the fields of joining, solid-state batteries, and low-temperature sintering technologies. In the present study, the phase stability and atomic mobility of confined metals in Cu/AlN NMLs were investigated by molecular dynamics, with the interatomic potential compared to the ab initio calculations of the Cu/AlN interface adhesion energy. Simulations of the structural evolution of Cu/AlN nanomultilayers upon heating in dependence on the Cu nanolayer thickness demonstrate the occurrence of interfacial premelting, a melting point depression, as well as extraordinary fast solid-state diffusion of confined Cu atoms along the defective heterogeneous interfaces. The model predictions rationalize recent experimental observations of premelting and anomalous fast interface diffusion of nanoconfined metals in nanostructured Cu/AlN brazing fillers at strikingly low temperatures.