In addition to affecting their functionality, crystal structure and defects play a strong role in directing the growth of nanomaterials. Particularly in the case of asymmetric nanomaterials, defects may play a crucial role in material formation during synthesis. Boerdijk-Coxeter-Bernal (BCB) nanowires are polycrystalline AuAg alloy nanowire structures that demonstrate icosahedral and decahedral packing of tetrahedral subunits (Fig. 1)[1][2]. Although these structures exhibit a chiral crystal structure, their overall morphology is straight. Upon addition of a shell consisting of a single atomic species, the nanowires twist into double helix structures (Fig. 1(d),(e))[2]. While there are many methods to synthesize twisted and helical structures, BCB-based wires offer the advantage in flexibility in choice of the atomic species of the shell, with a variety of FCC metal shells being demonstrated. Here, we present a detailed electron microscopy study of BCB-based twisted and helical nanowires using atomic resolution electron tomography and in-situ microscopy. The proposed mechanism for the massive morphological transition that BCB nanowires undergo is strain release. The observed interior crystal structure determined by tomography can be related to the twisting behavior observed during in-situ studies, relating the crystal structure to the morphological transition in this system. Ultimately, this information can be used to better control the synthesis of these materials for tunable helical nanostructures with desired optoelectronic properties.

Growth mechanisms of metallic helical nanowires: Combined electron tomography and in-situ microscopy study

2019 Fall National Meeting

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