For liquid metal, heterogeneous nucleation is main approach towards the formation of solid crystal. The nucleation potential of a new crystal on substrate was believe to be a function of lattice misfit between new crystal and substrate as stated by conventional nucleation theory. But as we understand, solidification is a liquid/solid transition rather than solid/solid transition, thus the lattice misfit between two crystals are hardly to elaborate the real scenario of nucleation process. The state-of-the-art analytical techniques offer the opportunities tracking the atomic structural evolution adjacent to solid-liquid interface which makes the in-situ analysis on heterogeneous nucleation possible. Our in-situ experimental results indicate that the liquid structure does not have significant difference for the alloy cooling on different cooling rate. The solidification path is mainly decided below liquidus temperature by the growth dynamics of crystal-like clusters. But for different substrates, the nearest neighbor distance of liquid atoms and their coordination number can be tuned through pre-nucleation ordering, either as layer ordering at strong wetting or as 3D pre-nucleation clusters with weak wetting, and lead to various nucleation barrier. Apart from this, the pre-nucleation ordering will be aligned in a preferred orientation by the substrate. The preferred orientation of new crystals matches the atomic structure of the substrate. That’s also the reason why the lattice mismatching, a parameter describing the matching of new crystal with substrate, is still able to predict the nucleation potential of the substrate in a given liquid. Furthermore, the alloying element can also be used to tune the lattice mismatching at the interface through interfacial structural tuning. A close relationship between lattice misfit and nucleation energy barrier will be given according to the observed nucleation interfaces of Al or Al alloys on various nucleation substrates. These findings will extend the understanding on heterogeneous nucleation leading to more effective nucleation tuning approaches in casting foundries, epitaxial growth of functional metal film or even more extensive application areas. 

 KEYWORDS Heterogeneous nucleation, liquid structure, high energy XRD