Multi‐Step Crystallization of Self‐Organized Spiral Eutectics

Abstract

A method for the solidification of metallic alloys involving spiral self‐organization is presented as a new strategy for producing large‐area chiral patterns with emergent structural and optical properties, with attention to the underlying mechanism and dynamics. This study reports the discovery of a new growth mode for metastable, two‐phase spiral patterns from a liquid metal. Crystallization proceeds via a non‐classical, two‐step pathway consisting of the initial formation of a polytetrahedral seed crystal, followed by ordering of two solid phases that nucleate heterogeneously on the seed and grow in a strongly coupled fashion. Crystallographic defects within the seed provide a template for spiral self‐organization. These observations demonstrate the ubiquity of defect‐mediated growth in multi‐phase materials and establish a pathway toward bottom‐up synthesis of chiral materials with an inter‐phase spacing comparable to the wavelength of infrared light. Given that liquids often possess polytetrahedral short‐range order, our results are applicable to many systems undergoing multi‐step crystallization.

Discovery of Double Helix and Impact on Nanoscale to Mesoscale Crystalline Structures

“…In MgZn 2 , the metastable Laves phase was found to nucleate from the liquid, with screw dislocations that intersected solid–liquid interfaces, thus catalyzing the spiral growth of the two-phase microstructure. 29 In view of the formation of defect-mediated helical dislocations and double helices, it should be interesting to see how the helicity of a screw dislocation affects the chirality of grown crystals and the formation of novel metastable phases. Thus, the discovery of double helix of screw dislocations stands to impact our understanding of crystal growth and the formation of crystalline structures across the nanoscale to mesoscale for next-generation solid-state devices.…”

Morphology and growth habit of a new flux-grown layered semiconductor KBiS2 revealed by diffraction-contrast tomography

“…Secondary and tertiary dendrites can be seen attached to the primary needle crystals that originate from the bottom of the reaction tube, with this convergence most apparent in Figure 3(b). The cross-sectional views of the needles in Figure 3(d) and (e) reveal hollow centers that likely arise from screw-dislocation-driven spiral growth 21,22 when the dislocation strain field energy is balanced by the creation of an internal surface energy.…”

“…14,15 And diffraction contrast tomography can be accomplished even with a laboratory X-ray source (LabDCT) instead of one of the few synchrotron sources. [16][17][18] While the DCT method has been used to map grain orientations (with resolutions around 50 µm) in Ti, 19,20 AlCu, 16 and Zn-Mg alloys, 21 with synchrotron and conventional X-ray tube sources, those studies are on freestanding materials with simple structures.…”

The LaserFIB: new application opportunities combining a high-performance FIB-SEM with femtosecond laser processing in an integrated second chamber

“…Many materials analysis challenges require connecting data across different length scales and analytical modalities to form a comprehensive understanding of the mechanisms at play or to solve a processing challenge (A. Poozhikunnath et al 2019) (Moniri et al 2020). As an example, 3D pore networks in battery electrodes may vary across distances of centimeters to millimeters, while the details of the networks that affect charge and fluid transport depend on the local microstructure down to the nanometer scale (Shearing et al 2012) (Daemi et al 2018).…”