Abstract
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.
Highlights
The ordered structures in liquid metals play a critical role in influencing wetting and nucleation behaviors [1,2]
The solid substrates were fully relaxed, until the residual forces fell below 0.01 eV/Å; liquid Al was prepared by melting the solid Al (15 × 15 × 15 supercell) in Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) [43] using the embedded atom model (EAM) potential [44]
A region matching the substrate was selected in the bulk liquid Al obtained from the last step, and the selected liquid Al was re-equilibrated by continuing the molecular dynamics for 1 ps to eliminate the influence of the imposed periodic boundary condition when the surrounding atoms were removed
Summary
The ordered structures in liquid metals play a critical role in influencing wetting and nucleation behaviors [1,2]. These ordered structures may manifest as clusters with unique symmetry (such as the well-assumed icosahedral structure [3]) or quasi-layers [4,5,6,7,8,9]. The former mainly occur in the systems absence of inoculation [3] and the latter have frequently been observed near the atomically smooth surfaces [10,11,12,13]. A further understanding of the substrate-induced liquid layers, in particular the in-plane atomic arrangement, can provide new insights into the heterogeneous nucleation mechanisms [17], and is beneficial to many industrial applications, such as the design of nucleating agents [18]
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