Quantitative analysis of layering and in-plane structural ordering at an alumina–aluminum solid–liquid interface

Real-time observations of Al–Al2O3 dynamic liquid–solid interfaces on the atomic scale indicate the presence of structural ordering in the liquid at the solid–liquid interface. The main problem with direct high resolution transmission electron microscopy (HRTEM) interpretation is that the imaging conditions and aberrations in the imaging system have a significant influence on the contrast in the image, and may lead to inaccurate conclusions about the structure examined. New quantitative results based on using a single image iterative wave function reconstruction are presented. This technique requires only a single experimental image, and allows extraction of reliable and aberration-free structural information from experimental HRTEM micrographs. This numerical phase retrieval method was successful in analysis of the experimental data and allowed, for the first time, direct extraction of quantitative information regarding the degree of ordering (parallel and perpendicular to the interface) at liquid–solid interfaces. The degree of ordering at the Al2O3–Al interface at 750 °C was quantified and both layering and in-plane ordering were found. The layering in the liquid extends to about four to five layers (about 1 nm from the edge of the crystal). The in-plane ordering, which was observed only in the first three layers of the liquid, decays faster than the layering. In addition, the interlayer spacings measured in the liquid indicate that the liquid atoms at the interface are influenced by the structure of the crystal, while further away the ordering of the liquid atoms gradually disappears, until they adopt the characteristics of the bulk liquid.

► In-situ HRTEM of Al–Al2O3 liquid–solid interfaces show ordering in the liquid at the interface.
► Quantitative results using a single image iterative wave function reconstruction are presented.
► Both layering and in-plane ordering exist at the interface at 750 °C.
► Layering extends to 4–5 liquid layers. In-plane ordering exists in the first 3 layers of the liquid.