Template-directed assembly has been shown to yield a broad diversity of highly ordered mesostructures 1,2, which in a few cases exhibit symmetries not present in the native material 3–5. However, this technique has not yet been applied to eutectic materials, which underpin many modern technologies ranging from high-performance turbine blades to solder alloys. Here we use directional solidification of a simple AgCl-KCl lamellar eutectic material within a pillar template to show that interactions of the material with the template lead to the emergence of a set of microstructures that are distinct from the eutectic’s native lamellar structure and the template’s hexagonal lattice structure. By modifying the solidification rate of this material–template system, trefoil, quatrefoil, cinquefoil and hexafoil mesostructures with submicrometre-size features are realized. Phase-field simulations suggest that these mesostructures appear owing to constraints imposed on diffusion by the hexagonally arrayed pillar template. We note that the trefoil and hexafoil patterns resemble Archimedean honeycomb and square–hexagonal–dodecagonal lattices 6, respectively. We also find that by using monolayer colloidal crystals as templates, a variety of eutectic mesostructures including trefoil and hexafoil are observed, the former resembling the Archimedean kagome lattice. Potential emerging applications for the structures provided by templated eutectics include non-reciprocal metasurfaces 7, magnetic spin-ice systems 8,9, and micro- and nano-lattices with enhanced mechanical properties 10,11.
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