Intrinsic Tunability Research Articles

A Graphene Geometric Diode with the Highest Asymmetry Ratio and Three States Gate‐Tunable Rectification Ability

AbstractGraphene geometric diodes, with applications in THz detection, energy harvesting, and high‐speed rectification, have been previously constrained by graphene quality and geometry feature size. This study presents significant advancements in graphene geometric diodes by employing the h‐BN/monolayer graphene/h‐BN heterojunction and extremely precise electron beam lithography. Two distinct designs of graphene geometric diodes with neck widths of 23 and 26 nm are fabricated, the superior of which demonstrated an asymmetry ratio of 1.97, a zero bias current responsivity of 0.6 A W−1, and a voltage responsivity of 12,000 V W−1, setting new benchmarks for such devices. Integrating this device into a rectification circuit, the experimentally validate that the rectified DC output voltage can be dynamically modulated and even inverted through adjustments to the diode's gate voltage. This behavior aligns seamlessly with graphene's intrinsic tunability of charge carriers, implying promising prospects for the device's application in advanced logic circuits, bidirectional switches, and signal modulation/demodulation techniques.

Tunable optical topological transitions of plasmon polaritons in WTe2 van der Waals films

Naturally existing in-plane hyperbolic polaritons and the associated optical topological transitions, which avoid the nano-structuring to achieve hyperbolicity, can outperform their counterparts in artificial metasurfaces. Such plasmon polaritons are rare, but experimentally revealed recently in WTe2 van der Waals thin films. Different from phonon polaritons, hyperbolic plasmon polaritons originate from the interplay of free carrier Drude response and interband transitions, which promise good intrinsic tunability. However, tunable in-plane hyperbolic plasmon polariton and its optical topological transition of the isofrequency contours to the elliptic topology in a natural material have not been realized. Here we demonstrate the tuning of the optical topological transition through Mo doping and temperature. The optical topological transition energy is tuned over a wide range, with frequencies ranging from 429 cm−1 (23.3 microns) for pure WTe2 to 270 cm−1 (37.0 microns) at the 50% Mo-doping level at 10 K. Moreover, the temperature-induced blueshift of the optical topological transition energy is also revealed, enabling active and reversible tuning. Surprisingly, the localized surface plasmon resonance in skew ribbons shows unusual polarization dependence, accurately manifesting its topology, which renders a reliable means to track the topology with far-field techniques. Our results open an avenue for reconfigurable photonic devices capable of plasmon polariton steering, such as canaling, focusing, and routing, and pave the way for low-symmetry plasmonic nanophotonics based on anisotropic natural materials.

Discovery of a Magnetic Dirac System with a Large Intrinsic Nonlinear Hall Effect.

Magnetic materials exhibiting topological Dirac fermions are attracting significant attention for their promising technological potential in spintronics. In these systems, the combined effect of the spin-orbit coupling and magnetic order enables the realization of novel topological phases with exotic transport properties, including the anomalous Hall effect and magneto-chiral phenomena. Herein, we report experimental signature of topological Dirac antiferromagnetism in TaCoTe2 via angle-resolved photoelectron spectroscopy and first-principles density functional theory calculations. In particular, we find the existence of spin-orbit coupling-induced gaps at the Fermi level, consistent with the manifestation of a large intrinsic nonlinear Hall conductivity. Remarkably, we find that the latter is extremely sensitive to the orientation of the Néel vector, suggesting TaCoTe2 as a suitable candidate for the realization of non-volatile spintronic devices with an unprecedented level of intrinsic tunability.

In situ induced cation-vacancies in metal sulfides as dynamic electrocatalyst accelerating polysulfides conversion for Li-S battery

Cation vacancy engineering is considered to be one of the effective methods to solve the issues of shuttling and sluggish redox kinetics of LiPSs owing to the intrinsic tunability of electronic structure. However, cation vacancies are few studied in the Li-S realm due to their complex and rigid preparation methods. In this work, one-step pyrolysis is reported to in situ introduce Fe-vacancies into iron sulfide (Fe0.96S) as a sulfur host. For this host structure, Fe0.96S is first employed as an adsorbent and catalyst in Li-S system. During the carbonization process, a tight contact structure of Fe0.96S crystal and carbon network (Fe0.96S@C) is in situ constructed, and the carbon layer as a conductor provides smooth electrons transfer pathways for redox reactions. Meanwhile, due to the introduction of Fe-vacancies in FeS crystal, the adsorption capability and catalytic effect for LiPSs have been substantially enhanced. Moreover, the presence of Fe0.96S crystal favors the mobility of electron and diffusion of Li+, which is revealed by the experiments and theoretical calculations. Through synergy respective advantages effect of Fe0.96S and carbon, the Fe0.96S@C-S cathode delivers high-rate capability at 5.0 C and stable long-life performance. Even under a high sulfur loading of 3.5 mg/cm2, the durable cyclic stability is still exhibited with the capacity retention of 93% over 400 cycles at 1.0 C, and the coulombic efficiency is ≥98%. Noting that this strategy greatly simplifies the synthetic process of currently known cation-vacancy materials and furnishes a universal mentality for designing both divinable and astonishing new cation-vacancy materials.

Flexible and Dual‐Tunable Radar Absorber Enabled by Graphene

AbstractFlexible and tunable radar absorbers (RAs) are in great demand both in stealth technologies and electromagnetic delusion for concealment of complex targets such as aircraft and unmanned aerial vehicle from radar detection. As a general approach, conventional lumped components such as varactor diodes and resistors are employed to achieve frequency and/or amplitude tunability of RAs. However, despite the intricate feeding networks and complex fabrication processes, this approach shows great difficulty in integrating the conventional rigid components with flexible substrate. Hence, it is an enormous challenge to realize both dual‐tunable and flexible RAs. Here the authors for the first time design and experimentally characterize a flexible and dual‐tunable RA with independent control of the frequency and amplitude. Most important is that the achieving both amplitude and frequency control is fully based on the tunability of graphene, without any lumped devices and intricate feeding network, and even without any metal involved. Hence, this dual‐tunable RA shows the priority of being flexible, light weight, and environmentally friendly. Although the prototype in this work is operating in microwave spectrum, the tunable functionalities at millimeter or terahertz spectral bands can also be obtained due to the intrinsic tunability of graphene.

Soliton molecules in femtosecond fiber lasers: universal binding mechanism and direct electronic control

Sequences of ultrashort pulses form the basis of extremely precise laser applications ranging from femtosecond spectroscopy, to material microprocessing, to biomedical imaging. Dynamic patterns of temporal solitons—termed “soliton molecules”—inside mode-locked cavities provide yet unexplored means for generating reconfigurable arrangements of ultrashort pulses. Here, we demonstrate the external control of solitonic bound states in widespread erbium-doped fiber lasers via direct electronic modulation of the semiconductor pump source. This straightforward approach allows for switching between discrete soliton doublet states of picosecond separations, employing and relying on laser-intrinsic soliton interactions. We analyze the externally induced dynamics based on real-time switching data acquired by time-stretch dispersive Fourier transform spectroscopy and identify a universal bound-state formation mechanism different from broadly considered models. Owing to the ease of implementation and its intrinsic tunability, our control scheme is readily applicable to various laser platforms enabling, e.g., rapid multipulse measurements and tailored nonlinear light–matter interactions.

Ultrahigh anharmonicity low-permittivity tunable nanocrystalline thin-film BaTi2O5

Electrically tunable dielectric thin films in active circuits and systems are challenged by capacitance-induced delays and impedance matching requiring a lower dielectric constant. Here an approach to increasing the intrinsic tunability of compounds containing TiO6 octahedra by considering the influence of different connectivity among these octahedra is presented. Such connectivity variants in nanocrystalline monoclinic BaTi2O5 thin films enable a two orders of magnitude enhancement in Ti anharmonic interaction, thereby permitting a ≈65% decrease in dielectric constant to 70 at room temperature without sacrificing tunability. Edge-sharing TiO6 octahedra possess a much shorter Ti-Ti distance of only 2.91 Å as compared to the perovskite structure (~4 Å), permitting large field-induced structural re-arrangement and intrinsic tunability.

Realization of a tunable fiber-based double cavity system

Tunable cavities have proven to be highly attractive systems in cavity quantum electrodynamics thanks to their performance and flexibility. The possibility to form a cavity around any emitter while simultaneously spectrally matching the chosen transitions makes these cavities an important tool in photonic quantum technology. In this paper, we report on the experimental realization and theoretical description of a fiber-based resonator with two spatially and spectrally distinct cavity modes. The careful design of the structures was performed via finite-element simulations. Thanks to the intrinsic tunability of the system, one mode can be brought in resonance with the second one, forming a supermode resulting in a hybridized two-mode pattern in the emission spectrum. For its realization, we combine a monolithic bottom cavity, formed by two distributed Bragg reflectors, with a top movable fiber mirror forming an externally tunable cavity mode. When tuning the top cavity in resonance with the monolithic bottom one, the cavity modes exhibit a pronounced anticrossing behavior typical for mode hybridization. Differently from a standard open cavity, when embedding single emitters---in this case, InGaAs quantum dots---in the structure, the Purcell factor is not uniform for each wavelength. Furthermore, we find a strong influence of the simulated Purcell factor, as well as of the measured light extraction, depending on the placement of the emitter in the top or in the bottom cavity. The discussed two-mode cavity could be employed for simultaneously Purcell-enhancing multiple transitions of an emitter while preserving the single-photon nature of the emitters inside the device.

Flower Inspiration: Broad‐Angle Structural Color through Tunable Hierarchical Wrinkles in Thin Film Multilayers

AbstractThe petals of some flowers form hierarchical structures when nano‐scale cuticular ridges overlay bulged epidermal cells. These hierarchical structures can broaden the observable angles of iridescence. The resulting optical effect enhances the foraging efficiency of pollinators. Although efforts have been devoted to mimicking this unique broad‐angle structural color, the intrinsic tunability offered by natural systems to control such a broadened spectrum is still absent in synthetic models. A hierarchical system is developed that provides hierarchical wrinkle‐based structures that tune the observable angles for structural color. Laser diffraction measurements demonstrate that the observable angle of reflectance is broadened in proportion to the square root of the applied compressive strain. The morphology controls the diffraction pattern: the small wrinkles control the diffraction angles and the large wrinkles broaden the observable range. The development of a multi‐mode wrinkling system to produce this broad‐angle structural color only occurs within a limited range of conditions, which are experimentally discovered and theoretically modeled. Without diffractive small wrinkles, single wrinkling modes do not display structural colors. The control of wrinkling modes mimics the tunability of petals, which gives new insight into the natural system and provides a robust foundation for tunable structural color control.

Design and Characterization of Fatty Acid-Based Amino Acid Ester as a New “Green” Hydrophobic Ionic Liquid for Drug Delivery

Ionic liquid (IL) based drug delivery systems have attracted considerable interest owing to their intrinsic tunability and ability to transport small or large molecules through the skin. However, t...

Prestress-controlled asymmetric wave propagation and reciprocity-breaking in tensegrity metastructure

In this letter, prestress is harnessed to break the spatial or/and time wave reciprocity and realize asymmetric elastic wave propagations in the full elastodynamic context. Unlike other asymmetric wave systems that rely on the complicated microstructures or multi-physical coupling, the proposed metastructure is simply constructed with repetitive prismatic tensegrity cells (PTCs) where prestress exists intrinsically. By investigating the prestress-trigged wave mode selection and conversion phenomena with a theoretical model, we developed a new approach to achieve asymmetric elastic wave propagation in the metastructure with modulated prestress distribution in space. Furthermore, by expanding the prestress tuning in both space and time domains, the elastodynamic reciprocity is finally broken in the tensegrity metastructure without introducing nonlinearity or external bias fields to the system. Due to the simple construction and intrinsic tunability, the proposed tensegrity metastructure design can be potentially useful in various applications, such as vibration isolation and elastic wave communication.

Ultra-tunable graphene light source

Free-electron-based light sources have long attracted interest due to their continuous tunability that has been demonstrated to extend across the electromagnetic spectrum from millimetre waves and microwaves through the infrared and visible to ultraviolet and X-ray regions. However this intrinsic tunability, particularly at short wavelengths, usually involves sources that are large and costly. The prospect of a compact, continuously tunable light source with the capability to generate short-wavelength ultraviolet and even X-ray light is an exciting one for many scientific, medical and engineering applications.

Topographic control of open-access microcavities at the nanometer scale.

Open-access optical microcavities are emerging as an original tool for light-matter studies thanks to their intrinsic tunability and the direct access to the maximum of the electric field along with their small mode volume. In this article, we present recent developments in the fabrication of such devices demonstrating topographic control of the micromirrors at the nanometer scale as well as a high degree of reproducibility. Our method takes into account the template shape as well as the effect of the dielectric mirror growth. In addition, we present the optical characterization of these microcavities with effective radii of curvature down to 4.3 µm and mode volume of 16×(λ/2)(3). This work opens the possibility to fully engineer the photonic potential depending on the required properties.

Liquid Crystals as an Active Medium: Novel Possibilities in Plasmonics

AbstractThe peculiar properties of Liquid Crystals (LCs) foster new possibilities in plasmonics. The combination of the intrinsic tunability of LCs with the plasmonic properties of metallic nanoparticles (NPs) provides novel and intriguing features of systems commonly identified as active plasmonics. Being LCs, one of the media whose refractive index can be controlled through the application of external stimuli, they represent a convenient host for enabling plasmonic tunability. On the other hand, the localized plasmonic resonance, typical of NPs, can strongly influence and control the behaviour of LCs. In this paper, we overview several systems of NPs combined with LCs arranged in different configurations. The properties of the resulting systems suggest novel, intriguing outcomes in both fundamental and applied research.

Electromagnetic chirality induced by graphene inclusions in multilayered metamaterials

We theoretically investigate the electromagnetic response of a novel class of multilayered metamaterials obtained by alternating graphene sheets and dielectric layers, the whole structure not exhibiting a plane of reflection symmetry along the stacking direction. We show that the electromagnetic response of the structure is characterized by a magneto-electric coupling described by an effective chiral parameter. Exploiting the intrinsic tunability of graphene–light coupling, we prove that one can tune both the dielectric and the chiral electromagnetic response by varying the graphene chemical potential through external voltage gating.

Reversible Solid State Redox of an Octacyanometallate-Bridged Coordination Polymer by Electrochemical Ion Insertion/Extraction

Coordination polymers have significant potential for new functionality paradigms due to the intrinsic tunability of both their electronic and structural properties. In particular, octacyanometallate-bridged coordination polymers have the extended structural and magnetic diversity to achieve novel functionalities. We demonstrate that [Mn(H2O)][Mn(HCOO)(2/3)(H2O)(2/3)](3/4)[Mo(CN)8]·H2O can exhibit electrochemical alkali-ion insertion/extraction with high durability. The high durability is explained by the small lattice change of less than 1% during the reaction, as evidenced by ex situ X-ray diffraction analysis. The ex situ X-ray absorption spectroscopy revealed reversible redox of the octacyanometallate. Furthermore, the solid state redox of the paramagnetic [Mo(V)(CN)8](3-)/diamagnetic[Mo(IV)(CN)8](4-) couple realizes magnetic switching.

Nanoscale Clustering of Carbohydrate Thiols in Mixed Self-Assembled Monolayers on Gold

Self-assembled monolayers (SAMs) bearing pendant carbohydrate functionality are frequently employed to tailor glycan-specific bioactivity onto gold substrates. The resulting glycoSAMs are valuable for interrogating glycan-mediated biological interactions via surface analytical techniques, microarrays, and label-free biosensors. GlycoSAM composition can be readily modified during assembly by using mixed solutions containing thiolated species, including carbohydrates, oligo(ethylene glycol) (OEG), and other inert moieties. This intrinsic tunability of the self-assembled system is frequently used to optimize bioavailability and antibiofouling properties of the resulting SAM. However, until now, our nanoscale understanding of the behavior of these mixed glycoSAMs has lacked detail. In this study, we examined the time-dependent clustering of mixed sugar + OEG glycoSAMs on ultraflat gold substrates. Composition and surface morphologic changes in the monolayers were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. We provide evidence that the observed clustering is consistent with a phase separation process in which surface-bound glycans self-associate to form dense glycoclusters within the monolayer. These observations have significant implications for the construction of mixed glycoSAMs for use in biosensing and glycomics applications.

Asymmetric Catalysis with Chiral Porous Metal–Organic Frameworks

This paper provides a brief overview of recent progress in the design and synthesis of chiral metal–organic frameworks (CMOFs) and their applications in heterogeneous asymmetric catalysis. Catalytically active CMOFs can be synthesized using two distinct strategies, either by post-synthetic activation of pre-synthesized porous MOFs or by directly linking well-designed catalytically competent bridging ligands with metal ion or metal cluster nodes. Heterogeneous asymmetric catalysis with very high activity and enantioselectivity has been achieved with CMOFs. The intrinsic tunability of CMOFs promises to lead to the design and synthesis of a variety of practically useful heterogeneous asymmetric catalysts for many organic transformations.

Analysis on dielectric response of polar nanoregions in paraelectric phase of relaxor ferroelectrics

Ferroelectric phase shifter is preferred to be used in paraelectric phase due to the demand of low loss. Dielectric response of polar nanoregions was analyzed in the present study, including their characteristics and contributions both to dielectric polarization and tunability. The corresponding dielectric constant of paraelectric phase consists of two parts, intrinsic one and extrinsic one. The former one, which depends on volume fraction of paraelectric phase, was mainly contributed by ionic displacement. The latter one, proportional to the volume specific surface of nanoregions, was mainly contributed by the boundary vibration of polar nanoregions. The possible mechanism of tunability in paraelectric phase consists of intrinsic tunability of polarization of ionic displacement and extrinsic tunability of boundary vibration of polar nanoregions.

Thickness-dependent tunability for Ti-doped K(Ta,Nb)O3 thin films

In this study, the thickness dependence of tunability in Ti-doped K(Ta,Nb)O3 thin films is reported. The films were grown using pulsed laser deposition. Doping with Ti reduces losses via acceptor doping. Measurements of interdigitated electrode devices using K(Ta,Nb)O3 films of varying thickness was used to extract the intrinsic thickness dependence of dielectric response. An intrinsic tunability of 11% at 40 kV/cm is determined for epitaxial films on (001) MgO. The intrinsic tunability is suppressed for films less than 100 nm, suggesting the onset of size effects in the nonlinear dielectric response.