High Optical Anisotropy Research Articles

Chiral plasmonic-dielectric coupling enables strong near-infrared chiroptical responses from helicoidal core-shell nanoparticles

Helicoid plasmonic nanoparticles with intrinsic chirality are an emerging class of artificial chiral materials with tailorable properties. The ability to extend their chiroplasmonic responses to the near-infrared (NIR) range is critically important for biomedical and nanophotonic applications, yet the rational design of such materials remains challenging. Herein, a strategy employing chiral plasmon-dielectric coupling is proposed to manipulate the chiroptical responses into the NIR region with high optical anisotropy. Through this strategy, the helicoid Au@Cu2O nanoparticles with structural chirality are designed and synthesized with tunable and enriched NIR chiroptical responses. Specially, a high optical anisotropy (g-factor) with a value of 0.35 is achieved in the NIR region, and multi-band chiroptical behaviors are observed. Spectral and electromagnetic simulations elucidate that strong coupling between chiroplasmonic core and chiral dielectric shell with high refractive index contributes to the rich and strong chiroptical responses, which are related to the interplay between various emerged and enhanced electric and magnetic multipolar resonance modes proved by multipole expansion analysis. Moreover, the helicoid Au@Cu2O nanoparticles display greater polarization rotation capability than the helicoid Au nanoparticles. This work offers mechanistic insights into chiral plasmon-dielectric coupling and suggests a general approach of creating NIR chiroplasmonic materials.

A Highly Optical Anisotropic Hybrid Metal Halide for Modulation and Generation of Polarized Light

AbstractPolarized light is critical for a wide range of applications in modern optics. However, its generation and modulation typically require additional optical comments, which hinders device compactness. Herein, an air‐stable Tin(IV)‐based hybrid metal halide, (C10H9N2O)2SnCl6, composed of [C10H9N2O]+ cations and isolated [SnCl6]2− octahedra is reported. Notably, (C10H9N2O)2SnCl6 exhibits a robust birefringence of 0.50@550 nm that is evidently larger than those of commercially used crystals, which enables efficient modulation of polarized light. Moreover, it possesses a broad polarized blue emission in the range of 374–600 nm with a peak at 426 nm. Theoretical and structural studies reveal that the high optical anisotropy for large birefringence and directly polarized emission of (C10H9N2O)2SnCl6 is ascribed to the cooperative effect of distortion of [SnCl6]2− and high π‐conjugation of [C10H9N2O]+ in parallel arrangement. This work may provide new thoughts on designing and realizing the miniaturization of polarization‐resolved optoelectronic devices.

Bioinspired transparent ultratough birefringent photonic films with engineerable interference colors derived from in-situ synthesis of CaCO3

Chameleons can rapidly modify their coloration by manipulating the arrangement of iridophores encompassing guanine crystals in their dermis, which enables incident light to undergo birefringence. Various biomaterials have been designed to mimic the arrangement of guanine crystals, yet instances of synthesizing bottom-up structures with anisotropy for optical functionality remain rare. In this study, we report a novel two-step gas diffusion method for in-situ synthesis of CaCO3 (Vaterite) within a hydrogel to fabricate a bio-photonic film displaying birefringence interference colors. This strategy enables the successful fabrication of an inorganic–organic photonic film with superior mechanical properties and flexibility, resulting in high transparency, superior toughness, and adjustable optical anisotropy. Through a combination of experiment and simulation results, we elucidated the critical role played by shape factor (distribution) and structural factor (particle size) in producing transmitted interference colors. Finally, the birefringent photonic films prepared using the dot-plate method can function as optical patterns accurately representing the “on”/“off” state within a binary system. This system offers high spatial resolution, excellent repeatability, and precise controllability of optical properties, making it applicable in fields such as information encryption and decrytion. Our study has successfully synthesized photonic material with anisotropic structure though in-situ method while elucidating the underlying mechanism governing their ability to generate transmission interference colors, thus opening up new avenues for transparent flexible polarized optics, imperceptible wearable devices, and advanced information encryption.

Group III (In/Ga)-V (P/As)-VI (S/Se) Monolayers: A New Class of Auxetic Semiconductors with Highly Anisotropic Electronic/Optical/Mechanical/Thermal Properties.

We present a theoretical design of a class of 2D semiconducting materials, namely, group III (In/Ga)-V (P/As)-VI (S/Se) monolayers, whose global-minimum structures are predicted based on the particle swarm optimization method. Electronic structure calculations suggest that all group III-V-VI monolayers exhibit quasi-direct semiconducting characteristics with desirable band gaps ranging from 1.76 to 2.86 eV (HSE06 functional). Moreover, most group III-V-VI monolayers possess highly anisotropic carrier mobilities with large anisotropic ratios (3.4-6 for electrons, 2.2-25 for holes). G0W0+BSE calculations suggest that these monolayers show high optical anisotropy and relatively large exciton binding energies (0.33-0.75 eV), comparable to that (0.5 eV) of MoS2 monolayer. In particular, the GaPS monolayer manifests strikingly anisotropic I-V curves with a large ON/OFF ratio of ∼105 (106 for the GaPS bilayer) and anisotropic lattice thermal conductivity. Furthermore, the GaPS monolayer is predicted to exhibit both in-plane and out-of-plane negative Poisson ratios (NPRs) and prominent anisotropic Young moduli.

Exploring van der Waals materials with high anisotropy: geometrical and optical approaches

The emergence of van der Waals (vdW) materials resulted in the discovery of their high optical, mechanical, and electronic anisotropic properties, immediately enabling countless novel phenomena and applications. Such success inspired an intensive search for the highest possible anisotropic properties among vdW materials. Furthermore, the identification of the most promising among the huge family of vdW materials is a challenging quest requiring innovative approaches. Here, we suggest an easy-to-use method for such a survey based on the crystallographic geometrical perspective of vdW materials followed by their optical characterization. Using our approach, we found As2S3 as a highly anisotropic vdW material. It demonstrates high in-plane optical anisotropy that is ~20% larger than for rutile and over two times as large as calcite, high refractive index, and transparency in the visible range, overcoming the century-long record set by rutile. Given these benefits, As2S3 opens a pathway towards next-generation nanophotonics as demonstrated by an ultrathin true zero-order quarter-wave plate that combines classical and the Fabry–Pérot optical phase accumulations. Hence, our approach provides an effective and easy-to-use method to find vdW materials with the utmost anisotropic properties.

Discovery of a new bimetallic borate with strong optical anisotropy activated by π-conjugated [B2O5] units.

Birefringent materials with high optical anisotropy have been identified as a research hotspot owing to their significant scientific and technological significance in modern optoelectronics for manipulating light polarization. Researchers studying borate systems have discovered that adding π-conjugated units placed in parallel can significantly increase the birefringence of crystalline solids; some examples include [BO3] units, [B2O5] units, and [B3O6] units. However, there are not many borates with strictly parallel configurations of π-conjugated [B2O5] units. In this study, a new bimetallic borate Sr2Cd4(B2O5)3 with near-parallel arrangement of π-conjugated [B2O5] units was discovered. Sr2Cd4(B2O5)3 possesses the maximum number density of [B2O5] units, shortest dihedral angle of [B2O5] units (between the two [BO3]), and largest degree of [CdO6] octahedral distortion among all the currently known Sr-Cd-B-O tetragonal system borates, making it demonstrate a large birefringence of 0.102 at 532 nm. Theoretical analysis proves that π-conjugated [B2O5] anions are the primary source of the large birefringence of Sr2Cd4(B2O5)3.

Surface-Guided Crystallization of Xanthine Derivatives for Optical Metamaterial Applications.

Numerous bio-organisms employ template-assisted crystallization of molecular solids to yield crystal morphologies with unique optical properties that are difficult to reproduce synthetically. Here, a facile procedure is presented to deposit bio-inspired birefringent crystals of xanthine derivatives on a template of single-crystal quartz. Crystalline sheets that are several millimeters in length, several hundred micrometers in width, and 300-600nm thick, are obtained. The crystal sheets are characterized with a well-defined orientation both in and out of the substrate plane, giving rise to high optical anisotropy in the plane parallel to the quartz surface, with a refractive index difference Δn ≈ 0.25 and a refractive index along the slow axis of n ≈ 1.7. It is further shown that patterning of the crystalline stripes with a tailored periodic grating leads to a thin organic polarization-dependent diffractive meta-surface, opening the door to the fabrication of various optical devices from a platform of small-molecule based organic dielectric crystals.

Highly Anisotropic Mechanical Response of the Van der Waals Magnet CrPS4

AbstractSemiconducting van der Waals magnets exhibit a rich physical phenomenology with different collective excitations, as magnons or excitons, that can be coupled, thereby offering new opportunities for optoelectronic, spintronic, and magnonic devices. In contrast with the well‐studied van der Waals magnets CrI3 or Fe3GeTe2, CrPS4 is a layered metamagnet with a high optical and magnon transport anisotropy. Here, the structural anisotropy of CrPS4 above and below the magnetic phase transition is investigated by fabricating nanomechanical resonators. A large anisotropy is observed in the resonance frequency of resonators oriented along the crystalline a‐ and b‐axis, indicative of a lattice expansion along the b‐axis, boosted at the magnetic phase transition, and a rather small continuous contraction along the a‐axis. This behavior in the mechanical response differs from that previously reported in van der Waals magnets, as FePS3 or CoPS3, and can be understood from the quasi‐1D nature of CrPS4. The results pinpoint CrPS4 as a promising material in the field of low‐dimensional magnetism and show the potential of mechanical resonators for unraveling the in‐plane structural anisotropy coupled to the magnetic ordering that, in a broader context, can be extended to studying structural modifications in other 2D materials and van der Waals heterostructures.

Disulfide‐Bridged Dynamic Covalent Triazine Polymer Thin Films by Interface Polymerization: High Refractive Index with Excellent Optical Transparency

AbstractExploring innovative strategies for molecular structuring of dynamic materials that combine self‐correcting intrinsic reversibility with the robustness of covalent bonds, has been a long‐standing objective from applications perspective in fields ranging from molecular engineering to nanotechnology and interfacial science. To establish dynamic covalent chemistry approaches combined with interfacial polymerization, herein, a distinct synthetic approach is reported to develop disulfide‐bridged 2D polymeric C3N3S3 triazine thin‐films by interfacial thiol‐disulfide dynamic exchange process crosslinking tritopic planar 1,3,5‐triazine‐2,4,6‐trithiol molecular tectons via intermolecular disulfide formation in the presence of I2 vapors at the air/water interface under redox condition. The resulting centimeter‐scale polymeric thin‐films are covalently cross‐linked, dynamic in nature, featuring tunable thickness (6–200 nm) and significant morphological variations are realized under the influence of varying reaction time, concentration and types of reducing agents. Notably, C3N3S3 polymer thin films exhibit a transflectance of around 99.5% in the range from 430 to 1800 nm, show high refractive indices (1.730–1.488) and optical anisotropy with uniaxial negative birefringence. The C3N3S3 free‐standing polymer thin‐films can be easily transferred to different substrates or possibly into application‐relevant forms for device fabrications, making this useful from materials application perspective.

Naphthalene-Like Unit That Induces Strong Optical Anisotropy in C10H8NO2Br and C10H8NO2Br·H2O.

Two metal-free birefringent crystals, C10H8BrNO2 and C10H8BrNO2·H2O, which contain a new birefringence-active [C10H8NO2]+ gene, were synthesized via a mild solution evaporation method. In their crystal structures, the π-conjugated naphthalene-like [C10H8NO2]+ groups are basically aligned, which induces high optical anisotropy; i.e., the title compounds exhibit large birefringences of 0.36 and 0.41 at 550 nm according to first-principles calculations. Moreover, the UV-vis-near-IR diffuse-reflectance spectra suggest that they have similar optical band gaps. Structural analysis and theoretical calculations show that the [C10H8NO2]+ unit is responsible for the good optical anisotropy. These results make the naphthalene-like motif a good structural gene to search for new birefringent crystals.

Research of Liquid-Crystal Materials for a High-Performance FFS-TFT Display

A novel liquid-crystal compound of more than 99.95% purity with high performance (such as a high clearing point, large dielectric anisotropy, high optical anisotropy, low viscosity, and large elastic constants) was designed and synthesized according to the fringe-field switching thin-film-transistor-liquid-crystal display requirements (FFS-TFT). Then, a mixed liquid-crystal material suitable for an FFS-TFT display was developed by mixing this compound with other reported compounds, developing a product whose quality was that of the highest level of similar foreign products and which fully met the customer's use requirements (BOE), and thus able to completely replace similar imported materials.

Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics

AbstractTransition metal dichalcogenides (TMDs) attract significant attention due to their exceptional optical, excitonic, mechanical, and electronic properties. Nanostructured multilayer TMDs were recently shown to be highly promising for nanophotonic applications, as motivated by their exceptionally high refractive indices and optical anisotropy. Here, this vision is extended to more sophisticated structures, such as periodic arrays of nanodisks and nanoholes with ultra sharp walls, as well as proof‐of‐concept all‐TMD waveguides and resonators. Specific focus is given to various advanced nanofabrication strategies, including careful selection of resists for electron beam lithography and etching methods, especially for non‐conductiven but relevant for nanophotonic applications substrates, such as SiO2. The specific materials studied here include semiconducting WS2, in‐plane anisotropic ReS2, and metallic TaSe2, TaS2, and NbSe2. The resulting nanostructures can potentially impact several nanophotonic and optoelectronic areas, including high‐index nanophotonics, plasmonics and on‐chip optical circuits. The knowledge of TMD material‐dependent nanofabrication parameters developed here will help broaden the scope of future applications of all‐TMD nanophotonics.

High Performance Polarization-Resolved Photodetectors Based on Intrinsically Stretchable Organic Semiconductors.

Polarization-sensitive photodetectors based on anisotropic semiconductors sense both the intensity and polarization state information without extra optical components. Here, a self-powered organic photodetector (OPD) composed of intrinsically stretchable polymer donor PNTB6-Cl and non-fullerene acceptor Y6 is reported. The PNTB6-Cl:Y6 photoactive film accommodates a remarkable 100% strain without fracture, exhibiting a high optical anisotropy of 1.8 after strain alignment. The resulting OPD not only shows an impressive faint-light detection capability (high spectral responsivity of 0.45 A W-1 and high specific detectivity of 1012 Jones), but also has a high anisotropic responsivity ratio of 1.42 under the illumination of parallel and traversed polarized light. To the best of the authors' knowledge, both the detector performance and polarization features are among the best-performing OPDs and polarization-sensitive photodetectors. As a proof-of-concept, polarization-sensitive OPDs are also utilized to set up a polarimetric imaging system and full-Stokes polarimeter. This work explores the potential of highly stretchable organic semiconductors for state-of-art polarization imaging and spectroscopy applications.

State-of-the-art luminescent materials based on wood veneer with superior strength, transparency, and water resistance

Current energy and luminescent materials utilize polymers to encapsulate fluorescent carbon nanodots and dyes but they usually lack stability and biodegradability. Here, we introduce an alternative wood nanotechnology to produce luminescent films (veneer) with UV resistance and tailorable surface energy. First, fluorescent and transparent wood (FTW) is shown as a support of aggregation-induced fluorescent emission (AIE) by in-situ Hantzsch reaction of acetoacetate delignified wood (AA-DW). Highly aligned cellulose nanofibers present in AA-DW facilitate FTW densification, ensuing exceptional mechanical performance (tensile strength and Young's modulus of up to 422 MPa and 45 GPa, respectively). Simultaneously, the conjugated structures display high transparency (83 %), haze (80 %) and optical anisotropy. The new luminescent system is demonstrated to be biodegradable and effective in optical (fluorescent) windows as well as encrypted films.

A comprehensive DFT evaluation of catalytic and optoelectronic properties of BaTiO3 polymorphs

BaTiO3 exhibits promising photocatalytic characteristics and has the potential to be employed in photocatalytic water splitting and pollutant degradation. Herein, we have investigated the structural, electronic, and optical properties of BaTiO3 in the framework of density functional theory (DFT). The obtained results are found to be consistent with theoretical results. However, using hybrid HSE06 functional, the calculated bandgap values are 3.254, 3.894, 3.694, 3.519, and 3.388 eV corresponding to cubic, rhombohedral, orthorhombic, tetragonal, and hexagonal phase of BaTiO3 polymorphs. This is the first time a DFT calculation touched over the experimental bandgap values of BaTiO3 polymorphs.Electronic band structure analysis revealed that all the BaTiO3 polymorphs exhibit semiconducting character with indirect bandgap except hexagonal structure which possesses direct bandgap. The density of states (DOS), Mulliken bond analysis and charge density distribution indicates considerable hybridization between O-2p and Ti-3d states caused to the formation of upper valence band (VB) and lower conduction band (CB). The wide bandgap and suitable redox potential of BaTiO3 polymorphs will be effective for water splitting as well as breakdown organic contaminants under UV–vis irradiation. The lower electron effective mass of the polymorphs indicates higher electrical conductivity. The energy dependent optical parameters show close agreement with the underlying electronic band structure. The high absorptivity, lower reflectivity and optical anisotropy (orthorhombic and tetragonal) of the polymorphs suggested that these could be a potential candidate for UV based optical device applications as well as to design wave guides, dielectric condensers and optical display devices.

Anisotropic slot waveguides with bulk transition metal dichalcogenides for crosstalk reduction and high-efficiency mode conversion.

Conventional slot waveguides (CSWs) consisting of an isotropic low-index material sandwiched by two high-index silicon wires have been extensively used in functional photonic devices, including chemical sensing, optical modulating, and all-optical signal processing, due to its significantly enhanced electric field perpendicular to the interfaces in the slot layer. However, there are two drawbacks to be improved if the CSWs are used for signal transmission in photonic integrated circuits, including the crosstalk between waveguides and direct butting mode conversion efficiency (MCE) to a silicon (Si)-strip waveguide. In this study, we propose an anisotropic SW with bulk transition metal dichalcogenide (ASWTMD) to relieve the two shortcomings by replacing the isotropic low-index slot layer with a bulk molybdenum disulfide layer having a high refractive index and giant optical anisotropy. We demonstrated the crosstalk reduction (CR) of the proposed ASWTMD by analyzing the mode profile, power confinement, and coupling strength. We also investigated the MCE by examining the mode overlap ratio and power evolution. The proposed ASWTMD shows significant CR and superior MCE for the transverse electric and transverse magnetic modes compared to those of a CSW with a SiO2-slot layer. The present design paves the possible extensibility to other transition metal dichalcogenides (TMDs) for designing state-of-the-art TMD-based photonic devices exploiting their extraordinary optical properties.

Stabilized Synthesis of 2D Verbeekite: Monoclinic PdSe2 Crystals with High Mobility and In-Plane Optical and Electrical Anisotropy.

PdSe2 has a layered structure with an unusual, puckered Cairo pentagonal tiling. Its atomic bond configuration features planar 4-fold-coordinated Pd atoms and intralayer Se-Se bonds that enable polymorphic phases with distinct electronic and quantum properties, especially when atomically thin. PdSe2 is conventionally orthorhombic, and direct synthesis of its metastable polymorphic phases is still a challenge. Here, we report an ambient-pressure chemical vapor deposition approach to synthesize metastable monoclinic PdSe2. Monoclinic PdSe2 is shown to be synthesized selectively under Se-deficient conditions that induce Se vacancies. These defects are shown by first-principles density functional theory calculations to reduce the free energy of the metastable monoclinic phase, thereby stabilizing it during synthesis. The structure and composition of the monoclinic PdSe2 crystals are identified and characterized by scanning transmission electron microscopy imaging, convergent beam electron diffraction, and electron energy loss spectroscopy. Polarized Raman spectroscopy of the monoclinic PdSe2 flakes reveals their strong in-plane optical anisotropy. Electrical transport measurements show that the monoclinic PdSe2 exhibits n-type charge carrier conduction with electron mobilities up to ∼298 cm2 V-1 s-1 and a strong in-plane electron mobility anisotropy of ∼1.9. The defect-mediated growth pathway identified in this work is promising for phase-selective direct synthesis of other 2D transition metal dichalcogenides.

A supramolecular non centrosymmetric 2,6-diaminopyridinium perchlorate salt: Crystal structure and optoelectronic DFT study

The synthesis of a supramolecular hybrid perchlorate salt using the aromatic amine 2,6-diaminopyridine afforded an unexpected crystal structure with non centrosymmetric crystallographic symmetry. The synthesized material with formula (C5H8N3)ClO4 crystallize according to the monoclinic symmetry in the space group P21. The observed supramolecular crystal structure, consisting of only weak interactions in all the three dimensions, built from hydrogen bonds and through Anion…π+ interaction between (ClO4)- tetrahedrons of the mineral part and the aromatic rings of the organic molecules, is rarely observed for similar compounds. The electronic and optical properties are characterized at the theoretical level using DFT; these characterizations demonstrate a moderate direct band gap and a high optical anisotropy. Our results provide the essential information about structural, electronic and optical properties of (C5H8N3)ClO4, which are useful for guiding the future studies.

Process for the catalytic conversion of micro-carbon residue content of heavy hydrocarbon feedstocks and a low surface area catalyst composition for use therein

The synthesis of a supramolecular hybrid perchlorate salt using the aromatic amine 2,6-diaminopyridine afforded an unexpected crystal structure with non centrosymmetric crystallographic symmetry. The synthesized material with formula (C5H8N3)ClO4 crystallize according to the monoclinic symmetry in the space group P21. The observed supramolecular crystal structure, consisting of only weak interactions in all the three dimensions, built from hydrogen bonds and through Anion…π+ interaction between (ClO4)- tetrahedrons of the mineral part and the aromatic rings of the organic molecules, is rarely observed for similar compounds. The electronic and optical properties are characterized at the theoretical level using DFT; these characterizations demonstrate a moderate direct band gap and a high optical anisotropy. Our results provide the essential information about structural, electronic and optical properties of (C5H8N3)ClO4, which are useful for guiding the future studies.

Optical Constants of Several Multilayer Transition Metal Dichalcogenides Measured by Spectroscopic Ellipsometry in the 300–1700 nm Range: High Index, Anisotropy, and Hyperbolicity

Transition metal dichalcogenides (TMDs) attract significant attention due to their remarkable optical and excitonic properties. It was understood already in the 1960s and recently rediscovered that many TMDs possess a high refractive index and optical anisotropy, which make them attractive for nanophotonic applications. However, accurate analysis and predictions of nanooptical phenomena require knowledge of dielectric constants along both in- and out-of-plane directions and over a broad spectral range, information that is often inaccessible or incomplete. Here, we present an experimental study of optical constants from several exfoliated TMD multilayers obtained using spectroscopic ellipsometry in the broad range of 300–1700 nm. The specific materials studied include semiconducting WS2, WSe2, MoS2, MoSe2, and MoTe2, as well as in-plane anisotropic ReS2 and WTe2 and metallic TaS2, TaSe2, and NbSe2. The extracted parameters demonstrate a high index (n up to ∼4.84 for MoTe2), significant anisotropy (n∥ – n⊥ ≈ 1.54 for MoTe2), and low absorption in the near-infrared region. Moreover, metallic TMDs show potential for combined plasmonic–dielectric behavior and hyperbolicity, as their plasma frequency occurs at around ∼1000–1300 nm depending on the material. The knowledge of optical constants of these materials opens new experimental and computational possibilities for further development of all-TMD nanophotonics.