Structural and dynamical properties of heterogeneous solid–liquid Ta–Cu interfaces: A molecular dynamics study

• Orientation dependent ordering is induced in liquid Cu adjacent to solid Ta.
• Intermixing of Cu and Ta as well as prefreezing of Cu are found on Ta (1 0 0).
• Unexpected negative interfacial energy is deduced, as a result of the enhanced ordering of interfacial Cu layers.
• Prefreezing of Cu leads to a double-interface for specific orientation.
• Orientation dependence in structure in turn results in orientation dependence in interfacial energies and other profiles.

Molecular dynamics simulations based on an angular-dependent potential were performed to examine the structural and dynamical properties of chemically heterogeneous solid–liquid interfaces formed between Ta and Cu. Layering is found in liquid Cu adjacent to solid Ta, and its behavior depends on the orientation of the underlying Ta substrate. In the Ta (1 1 0)/Cu interface, layering in Cu extends more than 15 Å away from the interface, and no intermixing or prefreezing is observed. While in the (1 0 0) interface, besides significant layering in Cu, intermixing of Cu and Ta is also seen in the vicinity of the interface. Furthermore, the first layer of Cu is prefrozen, forming a 1 × 1 structure relatively to the underlying Ta; while atoms in other Cu layers are rather mobile. In the (1 1 1) interface, the layering is very weak, extends no more than 6 Å into the liquid, the interfacial alloying is however rather significant. The orientation dependence in interfacial structure in turn leads to orientation dependence in interfacial energy, interfacial width, and diffusivity of atoms adjacent to the interface. Specially, the diffusion coefficients of Cu depend not only on the orientation of the solid substrate, but also on their relative motion with respective to the interface: the in-plane component is greater than the out-of-plane one, which is also found to have a structural origin.