The human body absorbs and loses heat largely through infrared radiation centering around a wavelength of 10 micrometers. However, neither our skin nor the textiles that make up clothing are capable of dynamically controlling this optical channel for thermal management. By coating triacetate-cellulose bimorph fibers with a thin layer of carbon nanotubes, we effectively modulated the infrared radiation by more than 35% as the relative humidity of the underlying skin changed. Both experiments and modeling suggest that this dynamic infrared gating effect mainly arises from distance-dependent electromagnetic coupling between neighboring coated fibers in the textile yarns. This effect opens a pathway for developing wearable localized thermal management systems that are autonomous and self-powered, as well as expanding our ability to adapt to demanding environments.

Cooperative chirality phenomena extensively exist in biomolecular and organic systems via intra- and inter-molecular interactions, but study of inorganic materials has been lacking. Here we report, experimentally and theoretically, cooperative chirality in colloidal cinnabar mercury sulfide nanocrystals that originates from chirality interplay between the crystallographic lattice and geometric morphology at different length scales. A two-step synthetic scheme is developed to allow control of critical parameters of these two types of handedness, resulting in different chiral interplays expressed as observables through materials engineering. Furthermore, we adopt an electromagnetic model with the finite element method to elucidate cooperative chirality in inorganic systems, showing excellent agreement with experimental results. Our study enables an emerging class of nanostructures with tailored cooperative chirality that is vital for fundamental understanding of nanoscale chirality as well as technology applications based on new chiroptical building blocks.

We show that packed, horizontally aligned films of single-walled carbon nanotubes are hyperbolic metamaterials with ultra-subwavelength unit cells and dynamic tunability. Using Mueller-matrix ellipsometry, we characterize the films' doping-level dependent optical properties and find a broadband hyperbolic region tunable in the mid-infrared. To characterize the dispersion of inplane hyperbolic plasmon modes, we etch the nanotube films into nanoribbons with differing widths and orientations relative to the nanotube axis, and we observe that the hyperbolic modes support strong light localization. Agreement between the experiments and theoretical models using the ellipsometry data indicates that the packed carbon nanotubes support bulk anisotropic responses at the nanoscale. Self-assembled films of carbon nanotubes are well suited for applications in thermal emission and photodetection, and they serve as model systems for studying light-matter interactions in the deep subwavelength regime.

We report on the fabrication of three-dimensional (3D) high-Q whispering gallery microcavities on a fused silica chip by femtosecond laser microfabriction, enabled by the 3D nature of femtosecond laser direct writing. The processing mainly consists of formation of freestanding microdisks by femtosecond laser direct writing and subsequent wet chemical etching. CO(2) laser annealing is followed to smooth the microcavity surface. Microcavities with arbitrary tilting angle, lateral and vertical positioning are demonstrated, and the quality (Q)-factor of a typical microcavity is measured to be up to 1.07 × 10(6), which is currently limited by the low spatial resolution of the motion stage used during the laser patterning and can be improved with motion stages of higher resolutions.

Chiral organizations ubiquitously exist in biomaterials via hierarchical assembly of chiral molecules, but assembly of chiral inorganic nanocrystals (NCs) has been lacking. Recent development of cinnabar HgS NCs that can possess precisely engineered chirality originating from both atomic lattice and morphology offers an emerging class of inorganic building blocks to explore their hierarchical assembly. Two different forms of suprastructures, collinear chains and propellers, have been achieved with various chiral HgS NC building blocks via distinct assembly mechanisms. The chiroptical responses of suprastructures are further evaluated both experimentally and theoretically, and are found to uniquely depend on intrinsic chirality of building blocks and their coupling. Our study therefore opens up a gateway to new assembled inorganic suprastructures with desired chiroptical response for wide-ranging functionalities and applications by bottom-up modular approach.

Precise engineering of phonon-phonon (ph-ph) and electron-phonon (e-ph) interactions by materials design is essential for an in-depth understanding of thermal, electrical, and optical phenomena as well as new technology breakthrough governed by fundamental physical laws. Due to their characteristic length scale, the ph-ph and e-ph interactions can be dramatically modified by nanoscale spatial confinement, thus opening up opportunities to finely maneuver underlying coupling processes through the interplay of confined size, fundamental length scale, and interface. We have combined ultrafast optical spectroscopy with a series of well-designed nanoscale core-shell structures possessing precisely tunable interface to demonstrate for the first time unambiguous experimental evidence of coherent interfacial phonon coupling between the core and shell constituents. Such interfacially coupled phonons can be impulsively excited through the e-ph interaction, in which the critical e-ph coupling constant is further shown to be monotonically controlled by tuning the configuration and constituent of core-shell nanostructure. Precise tunability of elemental physics processes through nanoscale materials engineering should not only offer fundamental insights into different materials properties but also facilitate design of devices possessing desirable functionality and property with rationally tailored nanostructures as building blocks.

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van der Waals nanomaterials supporting phonon polariton quasiparticles possess extraordinary light confinement capabilities, making them ideal systems for molecular sensing, thermal emission, and subwavelength imaging applications, but they require defect-free crystallinity and nanostructured form factors to fully showcase these capabilities. We introduce bottom-up-synthesized α-MoO3 structures as nanoscale phonon polaritonic systems that feature tailorable morphologies and crystal qualities consistent with bulk single crystals. α-MoO3 nanoribbons serve as low-loss hyperbolic Fabry–Pérot nanoresonators, and we experimentally map hyperbolic resonances over four Reststrahlen bands spanning the far- and mid-infrared spectral range, including resonance modes beyond the 10th order. The measured quality factors are the highest from phonon polaritonic van der Waals structures to date. We anticipate that bottom-up-synthesized polaritonic van der Waals nanostructures will serve as an enabling high-performance and low-loss platform for infrared optical and optoelectronic applications.