Optical Metamaterials Research Articles

Prescribing DNA origami barrel-directed subtractive patterning of nanoparticles for crystalline superstructure assembly.

Long-range ordered lattices formed by the directed arrangement of colloidal particles hold significant promise for applications such as photonic crystals, plasmonic metamaterials, and semiconductor electronics. Harnessing regioselective interactions through DNA-mediated assembly is a promising approach to advancing colloidal assembly. Despite efforts to engineer microscale patchy particles using sequence-specific binding properties of DNA, controlling patch formation on nanoscale isotropic spherical nanoparticles remains challenging. We demonstrate a subtractive patterning strategy using barrel-shaped DNA origamis (DNA barrels) to selectively block DNA-coated gold nanosphere surfaces and create regiospecific patches. By designing binding positions and geometric parameters of DNA barrels, we achieve controlled accessibility to nanosphere surfaces, forming patchy nanoparticles with tunable patch numbers and sizes. This strategy enables the construction of multidimensional superstructures with well-defined stereo relationships, represented by an unprecedented graphane-like bilayered superlattice. Furthermore, we developed a geometrical model that accounts for anisotropic particle bonding and steric hindrance, elucidating the relationship between architectural outcomes and the structural parameters of DNA-barrel-directed patchy nanoparticles, and enabling reverse engineering designs of potential assembly symmetries. This approach opens new avenues for generating nanoparticle assemblies with distinct symmetries and properties.

Prescribing DNA origami barrel‐directed subtractive patterning of nanoparticles for crystalline superstructure assembly

Long‐range ordered lattices formed by the directed arrangement of colloidal particles hold significant promise for applications such as photonic crystals, plasmonic metamaterials, and semiconductor electronics. Harnessing regioselective interactions through DNA‐mediated assembly is a promising approach to advancing colloidal assembly. Despite efforts to engineer microscale patchy particles using sequence‐specific binding properties of DNA, controlling patch formation on nanoscale isotropic spherical nanoparticles remains challenging. We demonstrate a subtractive patterning strategy using barrel‐shaped DNA origamis (DNA barrels) to selectively block DNA‐coated gold nanosphere surfaces and create regiospecific patches. By designing binding positions and geometric parameters of DNA barrels, we achieve controlled accessibility to nanosphere surfaces, forming patchy nanoparticles with tunable patch numbers and sizes. This strategy enables the construction of multidimensional superstructures with well‐defined stereo relationships, represented by an unprecedented graphane‐like bilayered superlattice. Furthermore, we developed a geometrical model that accounts for anisotropic particle bonding and steric hindrance, elucidating the relationship between architectural outcomes and the structural parameters of DNA‐barrel‐directed patchy nanoparticles, and enabling reverse engineering designs of potential assembly symmetries. This approach opens new avenues for generating nanoparticle assemblies with distinct symmetries and properties.

Localized Effects in Graphene Oxide Systems: A Pathway to Hyperbolic Metamaterials

Graphene oxide (GO) has emerged as a carbon-based nanomaterial providing a different pathway to graphene. One of its most notable features is the ability to partially reduce it, resulting in graphene-like sheets through the elimination of oxygen-including functional groups. In this paper, the effect of localized interactions in an Ag/GO/Au multilayer system was studied to explore its potential for photonic applications. GO was dip-coated onto magnetron-sputtered silver, followed by the deposition of a thin gold film to form an Ag/GO/Au structure. Micro-Raman Spectroscopy, SEM and Variable Angle Ellipsometry (VASE) measurements were performed on the Ag/GO/Au structure. An interesting behavior of the GO deposited on magnetron-sputtered silver with the formation of Ag nanostructures on top of the GO layer is reported. In addition to typical GO bands, Micro-Raman analysis reveals peaks such as the 1478 cm−1 band, indicating a transition from sp3 to sp2 hybridization, confirming the partial reduction of GO. Additionally, calculations based on effective medium theory (EMT) highlight the potential of Ag/GO structures in hyperbolic metamaterials for photonics. The medium exhibits dielectric behavior up to 323 nm, transitions to type I HMM between 323 and 400 nm and undergoes an Epsilon Near Zero and Pole (ENZP) transition at 400 nm, followed by type II HMM behavior.

Optimal azimuthal distribution of thermal emission for efficient radiative cooling.

Directional control of thermal emission to enhance radiative cooling has recently attracted significant attention. However, the ideal emission directionality remains questionable and under-explored. This Letter employs a universal formalism to analyze typical emission patterns and their impact on radiative power, equilibrium temperature, and cooling power. Contrary to intuition, the optimal emission pattern is bipolar rather than unipolar toward the zero-degree zenith angle under conditions of reduced atmospheric transmittance and low non-radiative heat transfer coefficient, which coincides well with the intrinsic emission pattern of epsilon-near-zero (ENZ) optical metamaterials. This study lays a theoretical foundation for ENZ metamaterial applications in radiative cooling and demonstrates the potential for enhancing cooling through directional thermal emission.

Investigating the potential of optical metamaterials with highly dispersive solitons in twin couplers with stochastic perturbations and white noise effects

This study emphasizes a unique contribution as we investigate the dimensionless version of the perturbed stochastic NLSE within an optical metamaterial-designed coupler. We employ Kudryashov's sextic-power law nonlinearity to present this formulation, and, for the first time, we introduce multiplicative white noise using the Ito interpretation. This study aims to bridge the gap in understanding the influence of stochastic effects on optical metamaterials and offers valuable insights for future research in this field. The methods introduced include enhancements to Kudryashov's approach and extensions to the modified sub-ODE technique. These methodologies are leveraged to derive a wide array of solutions, such as bright, dark, singular, and combined solitons, with some solutions presented using Jacobi and Weierstrass elliptic functions. The effectiveness of these methods in addressing various nonlinear partial differential equations is demonstrated through the results. The study further delves into how random noise impacts optical solitons and analyzes soliton behavior when subjected to different conditions. It is observed that white noise plays a crucial role in the formation of optical solitons within the coupler and that these solitons demonstrate highly dispersive properties under specific scenarios. These insights are pivotal for designing and innovating optical metamaterials for diverse technological uses.

Self-Assembly of Colloidal Dumbbell Isomers and Plasmonic Properties for Optical Metamaterials.

In this study, we explore the self-assembly of various colloidal symmetric dumbbell (DB) isomers, including dipole Janus, cis-Janus, trans-Janus, apolar-inward and polar-inward perpendicular Janus, and alternating perpendicular Janus DBs. Using dissipative particle dynamics (DPD) simulations under conditions mimicking experimental setups, we investigate cluster formation driven by emulsion droplet evaporation. Our findings reveal a diverse set of cluster structures, which are in good agreement with experimental and simulation results reported in the literature while also predicting the formation of novel cluster configurations. These structures, characterized by well-defined and predictable patterns, are potentially applicable to creating colloidal molecules and crystals. Furthermore, we examine the dynamics of cluster formation to gain insight into the mechanisms guiding the self-assembly of these diverse colloidal DBs. The study highlights the impact of particle isomerism on the resulting assembly structures. We further select a set of typical nanoclusters obtained, including a tetrahedral cluster, which is the simplest, to study its plasmonic properties. Our findings indicate that increasing the nanoparticle (NP) radius or decreasing the gap between NPs leads to a red shift in the plasmonic resonance wavelength and enhances the resonance strength. We identify critical parameter regions where the electric-dipole and magnetic-dipole resonances can be engineered to achieve negative dielectric permittivity and magnetic permeability, which are essential for developing negative-index metamaterials.

Non-Hermitian ideal Weyl photonic metamaterials and polarization-momentum resolved ultrahigh absorption.

In the past decade, there has been a significant surge of interest in investigating non-Hermitian Hamiltonians, particularly in photonics. The eigenvalues of general non-Hermitian Hamiltonians are complex and possess unique topological features such as exceptional degeneracy. The introduction of non-Hermitian perturbations into Weyl semimetals can transform Weyl points into exceptional rings characterized by multiple topological invariants. However, the ideal realization of Weyl rings within practical three-dimensional structures has remained a significant challenge. In this work, we extend artificial photonic metamaterial structures that can transform ideal Weyl points into non-Hermitian exceptional rings. We show the associated intriguing polarization-momentum ultrahigh absorption, which enables what we believe to be a new device application in non-Hermitian photonics. Our study not only proposes the practical model for ideal non-Hermitian photonic Weyl exceptional rings but also opens the gate of non-Hermitian scattering characterization.

TIME REFRACTION and SPACETIME OPTICS

A review of recent advances in spacetime optics is given, with special emphasis on time refraction. This is a basic optical process, occurring at a temporal discontinuity or temporal boundary, which is able to produce various different effects, such as frequency shifts, energy amplification, time reflection, and photon emission. If, instead of a single discontinuity, we have two reverse temporal boundaries, we can form a temporal beam splitter, where temporal interferences can occur. It will also be shown that, in the presence of an axis of symmetry, such as a magnetic field, the temporal beam splitter can induce a rotation of the initial polarization state, similar to a Faraday rotation. Recent work on time crystals, superluminal fronts, and superfluid light will be reviewed. Time gates based on spacetime optical effects will be discussed. We also mention recent work on optical metamaterials. Finally, the quantum properties of time refraction, which imply the emission of photon from vacuum, are considered, while similar problems in high-energy QED associated with electron–positron pairs are briefly mentioned.

Bixbyite‐Type Zirconium Tantalum Oxynitride Thin Films as Composition‐Tunable High Refractive Index Semiconductors

AbstractMultinary nitrides and oxynitrides offer a range of tunable structural and optoelectronic properties. However, much of this vast compositional space remains to be explored due to the challenges associated with their synthesis. Here, reactive sputter deposition is used to synthesize isostructural polycrystalline zirconium tantalum oxynitride thin films with varying cation ratios and systematically explore their structural and optical properties. All films possess the cubic bixbyite‐type structure and n‐type semiconducting character, as well as composition‐tunable optical bandgaps in the visible range. Furthermore, these compounds exhibit remarkably high refractive indices that exceed a value 2.8 in the non‐absorbing sub‐bandgap region and reach 3.2 at 589 nm for Ta‐rich compositions. Photoemission spectroscopy reveals non‐uniform shifts in electron binding energies that indicate a complex interplay of structural and compositional effects on interatomic bonding. In addition to being high‐index materials, the measured band edge positions of the films align favorably with the water oxidation and reduction potentials. Thus, this tunable materials family offers prospects for diverse optoelectronics application, including for production of photonic metamaterials and for solar water splitting.

Surface Nanopatterning and Structural Coloration of Liquid Metal Gallium Through Hypergravity Nanoimprinting

AbstractNanoscale structuring of gallium‐based liquid metals has emerged as a promising approach for generating unique properties and functionalities in advanced materials and devices. However, their exceptionally high surface tension presents significant challenges for achieving surface nanostructuring using conventional fabrication techniques. Here, a hypergravity nanoimprinting method is introduced, which harnesses horizontal centrifugation to generate hypergravity fields that drive liquid gallium into nanoscale cavities on an elastic polymer stamp surface at subzero temperatures, where it solidifies and preserves imprinted features down to 100 nm lateral resolution. This surpasses previous limits of gallium patterning, enabling phenomena such as iridescent structural colors with a wide range of hues and high saturation. Numerical simulations reveal the intricate fluid dynamic behaviors and interfacial interactions during the imprinting process, providing valuable insights for process optimization and control. By synergistically combining advanced soft lithography techniques with the reversible solid‐liquid phase transition properties of liquid metals, hypergravity nanoimprinting offers a practical nanofabrication approach, facilitating the development of next‐generation nanoscale gallium devices with finely structured nanofeatures across diverse application domains, such as nanoelectronics and photonic metamaterials.

Surface Engineering of Polymeric Colloidal Crystals by Temperature - Pressure Annealing.

Polymer colloidal crystals (PCCs) have been widely explored as acoustic and optical metamaterials and as templates for nanolithography. However, fabrication impurities and fragility of the self-assembled structures are critical bottlenecks for the device's efficiency and applications. We have demonstrated that temperature-assisted pressure [ annealing results in the mechanical strengthening of PCCs, which improves with the annealing temperature. Here, the enhancement of elastic properties and morphological features of self-assembled PCC's is evaluated using Brillouin light scattering and scanning electron microscopy. The pressure-induced effects on the vibrational modes of PCCs are also illustrated at temperatures well below the polymer glass transition. While the PCCs colloid constituents display reversibility, the PCC material is strongly irreversible in the performed thermodynamic cycle. The effective elastic modulus enhances from 0.7GPa for the pristine sample to 0.8GPa, solely by pressure annealing at room temperature. [ annealing at higher temperatures leads to a maximum effective elastic modulus of 1.7GPa, more than twice the value in the pristine sample. Above a cross-over pressure, 725bar at 348K), the PCCs respond elastically and, hence, reversibly to pressure changes.

Photonic-Metamaterial-Based, Near-Field-Enhanced Biosensing Approach for Early Detection of Lung and Ovarian Cancer

Early detection of lung and ovarian cancers relies heavily on identifying tumor biomarkers, but current methods require large blood samples and complex genetic testing. This study presents a novel photonic-metamaterial-based biosensing approach that leverages near-field radiative enhancement to detect cancer biomarkers (CA 125, CEA, and CYFRA 21-1) with high sensitivity. By utilizing structured photonic metamaterials, we optimize specific wavelengths to identify these biomarkers in interstitial fluid, which can be easily collected via minimally invasive microneedle arrays. Integrating near-field interactions with wavelength-selective metamaterials amplifies the thermal response at the nanoscale, allowing for the detection of deficient concentrations of biomarkers. This photonic metamaterial technique provides a faster, more accessible, and affordable alternative to conventional blood-based methods, significantly improving early detection and monitoring of cancer. Ultimately, this approach offers a transformative tool for clinical and research applications in cancer diagnostics.

Macroscopic Monograin Nano-Gyroid Thin Films in 4-inch Scale Through Shear-Rolling and Subsequent Solvent Annealing.

The gyroid structure from self-assembly is highly attractive for optical applications such as photonic crystals and metamaterials. However, due to the direction-dependent nature of these applications, achieving a monograin-level structure over a large area has remained challenging. In this study, the fabrication of unidirectionally oriented anisotropic nanocylinders of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) is reported block copolymer thin films up to a 4-inch scale via a shear-rolling process, followed by solvent annealing to induce phase transition to nearly monograin gyroid structures. Grazing-incidence small-angle X-ray scattering (GISAXS) analysis and cross-sectional scanning electron microscope (SEM) images in the direction parallel to the shear-rolling direction reveal the preferential orientation with the (111) plane onto the YZ axis of the film, while only the (110) plane on the YZ axis of the film is observed in the perpendicular direction, with grain sizes approaching single-grain levels. For metamaterial applications, the PDMS domain is selectively removed, and gold is electroplated to produce monograin gold gyroid films.

Achiral and chiral ligands synergistically harness chiral self-assembly of inorganics.

Chiral structures and functions are essential natural components in biominerals and biological crystals. Chiral molecules direct inorganics through chiral growth of facets or screw dislocation of crystal clusters. As chirality promoters, they initiate an asymmetric hierarchical self-assembly in a quasi-thermodynamic steady state. However, achieving chiral assembly requires a delicate balance between intricate interactions. This complexity causes the roles of achiral-chiral and inorganic components in crystallization to remain ambiguous. Here, we elucidate a definitive mechanism using an achiral-chiral ligand strategy to assemble inorganics into hierarchical, self-organized superstructures. Achiral ligands cluster inorganic building blocks, while chiral ligands impart chiral rotation. Achiral and chiral ligands can flexibly modulate the chirality of superstructures by fully using their competition in coordination chemistry. This dual-ligand strategy offers a versatile framework for engineering chiroptical nanomaterials tailored to optical devices and metamaterials with optical activities across a broad wavelength range, with applications in imaging, detection, catalysis, and sensing.

Synthesis of Chiral Ag, Pd, and Pt Helicoids inside Chiral Silica Mold.

Chiral inorganic nanomaterials hold significant promise for various applications, including enantioselective catalysis, polarization-controlling optical devices, metamaterials, and enantioselective molecular sensors. In our previous work, we presented a method for synthesizing chiral Au 432 helicoid III (Au helicoids) from peptides and amino acids, where helical gaps are intricately arranged with 432 symmetry within single cubic nanoparticles. In this study, we have achieved the fabrication of chiral silica molds through Au etching subsequent to the silica coating of Au helicoids. We demonstrate that these molds serve as geometrically confined reactors capable of producing chiral Ag, Pd, and Pt 432 helicoid III (Ag, Pd, and Pt helicoids). The morphology of the synthesized Ag, Pd, and Pt helicoids closely resembles that of the Au helicoids, exhibiting a superior g-factor compared to other reported chiral structures of each material. Notably, the Ag and Pd helicoids are found to be single-crystalline, with high-index planes exposed within the gaps. We believe that this silica mold-based approach can be generalized to synthesize chiral nanomaterials of various metal and even oxide materials.

Macro-Nanoporous Film with Cauliflower-Shaped Fibers for Highly Efficient Passive Daytime Radiative Cooling.

Passive daytime radiative cooling (PDRC) is a simple and effective cooling approach that does not consume any extra energy just by highly reflecting shortwave sunlight and highly radiating infrared heat through the atmospheric windows. In recent years, the application of photonic coolers and metamaterials for PDRC has been studied. However, they usually have complex processes and high precision requirements, which seriously limit large-scale fabrication. In this paper, a high-performance polyvinylidene difluoride-hexafluoropropylene (PVDF-HFP) PDRC fiber film was prepared by a simple and efficient electrospinning method combined with phase separation, and the obtained PVDF-HFP fibers have a cauliflower-shaped macro-nanoporous structure. The cauliflower-shaped structure provides more scattering sites of the fibers, and the fiber film with the macro-nanoporous morphology has a high scattering ability in the solar region, resulting in a high solar reflectivity of 99.65%. The PVDF-HFP porous film possesses an emissivity of 90.44% in the atmospheric window, and it can reach a maximum cooling temperature of 10.2 °C during the daytime. In addition, the excellent mechanical strength provides a guarantee for its large-scale practical application. This study offers an effective improvement strategy for the spectral performance of polymer fiber films, which is meaningful for green cooling management and reduction of carbon emission.

Proximal High-Index Metamaterials based on a Superlattice of Gold Nanohexagons Targeting the Near-Infrared Band.

Plasmonic nanoparticles can be assembled into a superlattice, to form optical metamaterials, particularly targeting precise control of optical properties such as refractive index (RI). The superlattices exhibit enhanced near-field, given the sufficiently narrow gap between nanoparticles supporting multiple plasmonic resonance modes only realized in proximal environments. Herein, the planar superlattice of plasmonic Au nanohexagons (AuNHs) with precisely controlled geometries such as size, shape, and edge-gaps is reported. The proximal AuNHs superlattice realized over a large area with selective edge-to-edge assembly exhibited the highest-ever-recorded RI values in the near-infrared (NIR) band, surpassing the upper limit of the RI of the natural intrinsic materials (up to 10.04 at λ = 1.5µm). The exceptionally enhanced RI is derived from intensified in-plane surface plasmon coupling across the superlattices. Precise control of the edge-gap of neighboring AuNHs systematically tuned the RI as confirmed by numerical analysis based on the plasmonic percolation model. Furthermore, a 1D photonic crystal, composed of alternating layers of AuNHs superlattices and low-index polymers, is constructed to enhance the selectivity of the reflectivity operating in the NIR band. It is expected that the proximal AuNHs superlattices can be used as new optical metamaterials that can be extended to the NIR range.

Investigation of chirped solutions in optical metamaterials having parabolic law nonlinearity and space-time dispersion

Investigation of chirped solutions in optical metamaterials having parabolic law nonlinearity and space-time dispersion

Inverse design of metamaterial for dual-band infrared camouflage along with dual-band thermal management

The optical metamaterial for infrared camouflage with thermal management is an artificial structure available to not only evade the detection of various thermal imagers operating in distinct infrared wavebands but also ensure the thermal stability of the target. However, designing such an optical metamaterial is challenging due to the necessity to optimize numerous structural parameters simultaneously, especially metamaterials that are compatible with multiple functions. Herein, this paper proposes a novel inverse design method, combining African vultures optimization algorithm (AVOA) with rigorous coupled-wave analysis (RCWA), to design an optical metamaterial capable of achieving infrared camouflage and thermal management compatibly. The proposed metamaterial enables dual-band infrared camouflage for mid-wave infrared (MWIR, 3–5 μm) and long-wave infrared (LWIR, 8–14 μm), along with thermal management through dual-band non-atmospheric windows of 5–8 μm and 14–17 μm. Comparing to other intelligent optimization algorithms, the AVOA is exceptionally efficient, which only takes less time than others to get better results. This work not only provides theoretical guidance to design an optical metamaterial for infrared camouflage with thermal management, but also has the potential to solve the multi-objective optimization problems of multi-band or wide-band radiative modulation.

Non-Foster approach to broadband optical metamaterials based on Lorentzian gain materials

All passive metamaterials are inherently narrowband due to fundamental dispersion-energy constraints, and their dispersive properties are usually approximated by a Lorentz model. However, there are broadband active metamaterials in the radio frequency (RF) regime based on negative capacitors with non-Foster dispersion properties. Non-Foster dispersion is usually considered as an “electronic-engineering trick” that cannot be applied at optical frequencies. Here, we demonstrate that the dispersion relation of a RF non-Foster capacitor is similar to that of an optical gain material described by a Lorentz model. This insight paves the way to realize non-Foster optical metamaterial structures. As the simplest example, we develop a broadband non-Foster optical epsilon-near-zero slab with a 1:10 bandwidth.