Mesoscale CdTe helices with near-unity enantiomeric excess offer insight into design rules for chiroptical semiconductor materials.

Unique optical, electrical, and mechanical properties of continuous semiconductor helices with nanoscale and mesoscale dimensions represent a previously unexplored materials platform for various applications requiring near-infrared (NIR) optical activity. However, current methods of their synthesis limit the spectrum of chiral geometries, charge transport, and spectral response. Furthermore, the requirements of nearly perfect enantioselectivity, high uniformity, and high yield need to be attained as well. Here, we show that continuous semiconductor helices with tunable spectral response and high monodispersity can be made via self-assembly of semiconductor nanoparticles (NPs). Unraveling the interdependent effects of solvent, pH, ligand density, and coordination bridges between NPs allowed us to maximize the chiral bias for face-to-face particle–particle interactions, control of the geometry of the helices, and increase assembly efficiency by 3 orders of magnitude. The self-limiting nature of NP association results in consistency of their geometries over the entire synthetic ensemble. The helices show chiroptical activity across a broad range of wavelengths from 300 to 1300 nm, and the maximum/sign of their polarization rotation in NIR part can be modulated by varying their pitch. The method described in this study can be extended to chiral semiconductor materials from a variety of other NPs and their combinations.

Rapidly evolving fields of biomedical, energy, and (opto)electronic devices bring forward the need for deformable conductors with constantly rising benchmarks for mechanical properties and electronic conductivity. The search for conductors with improved strength and strain have inspired the multiple studies of nanocomposites and amorphous metals. However, finding conductors that defy the boundaries of classical materials and exhibit simultaneously high strength, toughness, and fast charge transport while enabling their scalable production, remains a difficult materials engineering challenge. Here, composites made from aramid nanofibers (ANFs) and gold nanoparticles (Au NPs) that offer a new toolset for engineering high strength flexible conductors are described. ANFs are derived from Kevlar macrofibers and retain their strong mechanical properties and temperature resilience. Au NPs are infiltrated into a porous, free-standing aramid matrix, becoming aligned on ANFs, which reduces the charge percolation threshold and facilitates charge transport. Further thermal annealing at 300 °C results in the Au-ANF composites with an electrical conductivity of 1.25 × 10 4 S cm −1 combined with a tensile strength of 96 MPa, a Young's modulus of 5.29 GPa, and a toughness of 1.3 MJ m −3 . These para meters exceed those of most of the composite materials, and are comparable to those of amorphous metals but have no volume limitations. The plasmonic optical frequencies characteristic for constituent NPs are present in the composites with ANFs enabling plasmon-based optoelectronic applications.

Nacre-like composites have been investigated typically in the form of coatings or free-standing sheets. They demonstrated remarkable mechanical properties and are used as ultrastrong materials but macroscale fibres with nacre-like organization can improve mechanical properties even further. The fiber form or nacre can, simplify manufacturing and offer new functional properties unknown yet for other forms of biomimetic materials. Here we demonstrate that nacre-like fibres can be produced by shear-induced self-assembly of nanoplatelets. The synergy between two structural motifs—nanoscale brick-and-mortar stacking of platelets and microscale twisting of the fibres—gives rise to high stretchability (>400%) and gravimetric toughness (640 J g−1). These unique mechanical properties originate from the multiscale deformation regime involving solid-state self-organization processes that lead to efficient energy dissipation. Incorporating luminescent CdTe nanowires into these fibres imparts the new property of mechanically tunable circularly polarized luminescence. The nacre-like fibres open a novel technological space for optomechanics of biomimetic composites, while their continuous spinning methodology makes scalable production realistic.