Liquid layering at heterogeneous solid/liquid interfaces is a general phenomenon, which provides structural templates for nucleation of crystalline phases on potent nucleants. However, its efficacy near poor nucleants is incompletely understood. Here we use a combination of X-ray crystal truncation rod analysis and ab initio molecular dynamics to probe the pre-nucleation liquid layering at the sapphire-aluminium solid/liquid interface. At the sapphire side, a~1.6 aluminium-terminated structure develops, and at the liquid side, two prenucleation layers emerge at 950 K. No more pre-nucleation layer forms with decreasing temperature indicating that nucleation of crystalline aluminium through layer-by-layer atomic adsorption of liquid atoms is not favoured. Instead, the appearance of stochastically-formed nuclei near the substrate is supported by our experiments. Nucleation on poor nucleants is dominated by the stochastic nucleation events which are substantially influenced by the prenucleation layers that determine the surface structure in contact with the nuclei.

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A synchrotron X-Ray scattering method has been explored to probe the interactions at the interface between liquid Al and α-Al2O3. Melting and solidification behaviour has been observed in-situ in Al via collection and indexing of scattering generated at the solid-liquid interface.