Direct observation of in-plane ordering in the liquid at a liquid Al/α-Al2O3(1¯102¯) interface

Wetting behavior at the Al/α-Al2O3 liquid/solid interface is closely correlated with oxygen-induced structural changes at the interface. However, direct experimental evidence for the possible interfacial modifications has been rare. In the present study in situ high-resolution electron microscopy is successfully employed to characterize the structure of the interfaces between liquid Al and α-Al2O3 with [0 0 0 1] and [1¯102¯] surface normal directions at an elevated temperature. We provide evidence for ordering in the liquid (i.e. ordered oxygen-rich liquid interfacial layers) at both interfaces. The liquid at the Al/α-Al2O3(0 0 0 1) interface shows density perturbations in the direction perpendicular to the interface (layering) with a periodicity close to the interplanar distance of the (0 0 0 6) planes of α-Al2O3. On the other hand, the liquid at the Al/α-Al2O3(1¯102¯) interface also reveals layering with an interlayer spacing of ∼0.25 nm and, additionally, with a degree of order occurring within the first few liquid layers (in-plane ordering), the ordered structure of which is similar to Al2O rather than α-Al2O3.