Substrate-induced liquid layering: A new insight into the heterogeneous nucleation of liquid metals

Liquid layering, which is a general phenomenon adjacent to the solid substrates, is less understood for its role in heterogeneous nucleation. In this work, the structural features and dynamics of the liquid Al layers induced by the (0001) sapphire and the (0001) TiB₂ substrates, respectively, are quantitatively compared based on the ab initio molecular dynamics simulations. An almost fully ordered liquid Al layer is observed adjacent to the TiB₂ substrate above the Al melting point, while the liquid layers near the sapphire substrate are weakly ordered with virtually no in-plane translational symmetry. Further liquid layering is facilitated by the ordered liquid layer near the TiB₂ substrate, while impeded by the low in-plane ordering of the liquid layers near the sapphire substrate, resulting in different nucleation behaviors for the two systems. The difference in the liquid layering is caused, in part, by the lower adsorption strength at the sapphire–liquid Al interface than that at the TiB₂–liquid Al interface. Additionally, the compressive stress imposed on the liquid layers seriously hinders the sapphire-induced liquid layering. We conclude from this work that the interfacial adsorption strength and mismatch alter the heterogeneous nucleation by influencing the features of the substrate-induced liquid layering.