Exotic Materials Research Articles

Stable, Self‐Adhesive, and High‐Performance Graphene‐Oxide‐Modified Flexible Ionogel Thermoelectric Films

AbstractIonic thermoelectric materials have attracted increasing attention because of their high flexibility and high Seebeck coefficient. However, their insufficient thermoelectric performance and long‐standing processing limit their practical applications. To achieve exotic ionic thermoelectric materials, here, a graphene oxide (GO) modified acrylamide ionogel is designed with high thermoelectric performance and flexibility. Detailed structural characterizations confirm that the uniform dispersion of GO particles in the ionogel structure enables a power factor of 753.0 µW m−1 K−2 and a promising ZT value of 0.19. Additionally, the as‐prepared ionic thermoelectric thin film shows excellent flexibility, stretchability, and self‐adhesiveness. An integrated device, assembled by the as‐prepared ionogel films, can generate an optimal output power density of 1.32 mW cm−2 with a temperature difference of 20 K, indicating great potential for wearable electronics. This work provides insight for searching long‐term, high‐performance ionic thermoelectric materials.

Observation of a Brillouin dynamic grating in silicon nitride waveguides

Brillouin enhanced four wave mixing in the form of a Brillouin dynamic grating (BDG) enables a uniquely tunable filter whose properties can be tuned by purely optical means. This makes the BDG a valuable tool in microwave photonics (MWP). BDGs have been studied extensively in fibers, but the only observation in an integrated platform required exotic materials. Unlocking BDG in a standard and mature platform will enable its integration into large-scale circuits. Here, we demonstrate the first observation of a BDG in a silicon nitride (Si3N4) waveguide. We also present a new and optimized design, which will enhance the BDG response of the waveguide, unlocking the path to large-scale integration into MWP circuits.

Nanofabricated high turn-density spiral coils for on-chip electromagneto-optical conversion

Circuit-integrated electromagnets are fundamental building blocks for on-chip signal transduction, modulation, and tunability, with specific applications in environmental and biomedical micromagnetometry. A primary challenge for improving performance is pushing quality limitations while minimizing size and fabrication complexity and retaining spatial capabilities. Recent efforts have exploited highly involved three-dimensional synthesis, advanced insulation, and exotic material compositions. Here, we present a rapid nanofabrication process that employs electron beam dose control for high-turn-density diamond-embedded flat spiral coils; these coils achieve efficient on-chip electromagnetic-to-optical signal conversion. Our fabrication process relies on fast 12.3 s direct writing on standard poly(methyl methacrylate) as a basis for the metal lift-off process. Prototypes with 70 micrometer overall diameters and 49–470 nm interturn spacings with corresponding inductances of 12.3–12.8 nH are developed. We utilize optical micromagnetometry to demonstrate that magnetic field generation at the center of the structure effectively correlates with finite element modeling predictions. Further designs based on our process can be integrated with photolithography to broadly enable optical magnetic sensing and spin-based computation.

An elementary review on basic principles and developments of qubits for quantum computing.

An elementary review on principles of qubits and their prospects for quantum computing is provided. Due to its rapid development, quantum computing has attracted considerable attention as a core technology for the next generation and has demonstrated its potential in simulations of exotic materials, molecular structures, and theoretical computer science. To achieve fully error-corrected quantum computers, building a logical qubit from multiple physical qubits is crucial. The number of physical qubits needed depends on their error rates, making error reduction in physical qubits vital. Numerous efforts to reduce errors are ongoing in both existing and emerging quantum systems. Here, the principle and development of qubits, as well as the current status of the field, are reviewed to provide information to researchers from various fields and give insights into this promising technology.

Radiation-driven thermoacoustic energy conversion in absorbing media

Thermoacoustic engines rely on an instability that can convert heat into an intense acoustic wave — oscillating pressure and velocity. Being heat-driven, thermoacoustic engines are a promising technology for solar energy conversion, potentially cheap, reliable, and robust, with no moving parts and no exotic materials. Herein, we present an as-yet overlooked mode of triggering a thermoacoustic instability in such engines, driven by radiation. This mode of operation can potentially eliminate much of the viscous losses associated with high-amplitude thermoacoustic energy conversion by eliminating the need for a solid, porous medium with which to mediate heat transfer. A theoretical framework is developed for modeling such devices, with a simplified analysis illustrating that any non-uniform, temperature-dependent heat source has the potential to trigger the thermoacoustic instability. It is then further demonstrated that radiation can indeed drive such instability, with numerical results showing that energy conversion is more substantial when the oscillation period is matched with the characteristic radiative heating time of the gas. A limit-cycle analysis indicates that, for a traveling wave acoustic field, potential efficiencies of up to 90% of Carnot’s efficiency may be achieved, with power densities of up to 5 MW/m3. While several of the assumptions made in the model likely result in lower performance for a real system, the analysis demonstrates the great potential offered by this approach, for future development.

Flux-Tunable Josephson Diode Effect in a Hybrid Four-Terminal Josephson Junction.

We investigate the direction-dependent switching current in a flux-tunable four-terminal Josephson junction defined in an InAs/Al two-dimensional heterostructure. The device exhibits the Josephson diode effect with switching currents that depend on the sign of the bias current. The superconducting diode efficiency, reaching a maximum of |η| ≈ 34%, is widely tunable─both in amplitude and sign─as a function of magnetic fluxes and gate voltages. Our observations are supported by a circuit model of three parallel Josephson junctions with nonsinusoidal current-phase relation. With respect to conventional Josephson interferometers, phase-tunable multiterminal Josephson junctions enable large diode efficiencies in structurally symmetric devices, where local magnetic fluxes generated on the chip break both time-reversal and spatial symmetries. Our work presents an approach for developing Josephson diodes with wide-range tunability that do not rely on exotic materials.

Experimental Demonstration of Topological Catalysis for CO2 Electroreduction.

The past decade has witnessed substantial progress in understanding nontrivial band topology and discovering exotic topological materials in condensed-matter physics. Recently, topological physics has been further extended to the chemistry discipline, leading to the emergence of topological catalysis. In principle, the topological effect is detectable in catalytic reactions, but no conclusive evidence has been reported yet. Herein, by precisely manipulating the topological surface state (TSS) of Bi2Se3 nanosheets through thickness control and the application of a magnetic field, we provide direct experimental evidence to illustrate topological catalysis for CO2 electroreduction. With and without the cooperation of TSS, CO2 is mainly reduced into liquid fuels (HCOOH and H2C2O4) and CO, exhibiting high (up to 90% at -1.1 V versus reversible hydrogen electrode) and low Faradaic efficiency (FE), respectively. Theoretically, the product and FE difference can be attributed to the TSS-regulated adsorption of key intermediates and the reduced barrier of the potential-determining step. Our work demonstrates the inherent correlation between band topology and electrocatalysis, paving a new avenue for designing high-performance catalysts.

Advancing Ion Selective Membranes with Micropore Ion Channels in the Interaction Confinement Regime.

Ion exchange membranes allowing the passage of charge-carrying ions have established their critical role in water, environmental, and energy-relevant applications. The design strategies for high-performance ion exchange membranes have evolved beyond creating microphase-separated membrane morphologies, which include advanced ion exchange membranes to ion-selective membranes. The properties and functions of ion-selective membranes have been repeatedly updated by the emergence of materials with subnanometer-sized pores and the understanding of ion movement under confined micropore ion channels. These research progresses have motivated researchers to consider even greater aims in the field, i.e., replicating the functions of ion channels in living cells with exotic materials or at least targeting fast and ion-specific transmembrane conduction. To help realize such goals, we briefly outline and comment on the fundamentals of rationally designing membrane pore channels for ultrafast and specific ion conduction, pore architecture/chemistry, and membrane materials. Challenges are discussed, and perspectives and outlooks are given.

Static and spherically symmetric wormholes in power-law [formula omitted] gravity model

By venturing into gravitational frameworks that extend beyond general relativity (GR), it becomes evident that traversable wormholes (WHs) can conceivably be constructed solely through gravitational means. In GR, the intrinsic degrees of freedom are insufficient for assembling these special kinds of objects without incorporating exotic matter forms. Nevertheless, by stretching gravity into altered frameworks, it becomes possible to satisfy the necessary stability and traversability conditions without relying on such exotic materials. The key concept lies in the view that WH solutions can appear as common features in gravity theories once extra geometrical degrees of freedom are incorporated. Interestingly, we investigate WH solutions in the context of f(R) gravity theory, using a spherically symmetric metric embracing three asymptotically flat regions. More precisely, we are focusing on f(R) gravitational theories formulated in metric formalism, presuming time-independent metric coefficients, and exploiting the well-established Morris–Thorne space–time framework. We thoroughly derived exact solutions for traversable WHs that graciously adhere to energy and pressure constraints, assuming a power-law form for f(R), denoted f(R)=αRn, where α is an arbitrary constant and n is the power-law exponent. Conclusively, our findings open up the possibility of constraining the parameters (α, n, r0) associated with WH solutions. Importantly, we found that the existence of exotic matter was necessary to satisfy the stability and traversability criteria for WHs in all the cases we analyzed.

Integration of a needle valve mechanism with cura slicing software for improved retraction in pellet-based material extrusion

Fused granular fabrication (FGF) is a cost-effective and increasingly popular additive technology that enables the production of parts using a wide range of exotic materials that are not typically available with material extrusion additive manufacturing. This paper presents a novel needle valve approach for flow control in a FGF system that uses flexibly connected screw extruders. The addition of a needle valve to the existing system allows complex travel moves to be performed without stringing, greatly increasing the available part complexity of the printer. The needle valve is actuated by one of the 3D printer’s extruder stepper motors and can be controlled by g-code generated by off-the shelf slicer software. This paper also proposes a mathematical model for predicting the oozing volume of the valve, which is the small quantity of material that escapes through the nozzle during valve actuation. This model is important for calibration and g-code generation, which could be integrated with commercial slicers to use this needle valve design without writing custom code. The model is tested experimentally, and results show a strong correlation between predicted and measured oozing volumes. The performance of the valve is also characterized in terms of flow rate versus needle position. Experiments showed that the needle stroke (the vertical distance that the needle travels between open and closed states of the needle valve) is the most important parameter in minimizing oozing. An optimized stroke of 0.4 mm was used, with a maximum flow rate of 346 mm3/min when using a nozzle inner bore diameter of 0.8 mm. Using the optimized valve parameters, parallel cube structures were printed to demonstrate the reduction of stringing, along with various demonstration parts including a 3Dbenchy benchmark print and a soft robotic actuator. Overall, this study demonstrates that needle valves present a reliable and low-cost approach for controlling the flow of polymer in FGF systems with a remotely connected screw extruder.

Early human occupation of Australia’s eastern seaboard

Secure archaeological evidence for human occupation on the eastern seaboard of Australia before ~ 25,000 years ago has proven elusive. This has prompted some researchers to argue that the coastal margins remained uninhabited prior to 25 ka. Here we show evidence for human occupation beginning between 30 ± 6 and 49 ± 8 ka at Wallen Wallen Creek (WWC), and at Middle Canalpin Creek (MCA20) between 38 ± 8 and 41 ± 8 ka. Both sites are located on the western side of Minjerribah (North Stradbroke Island), the second largest sand island in the world, isolated by rising sea levels in the early Holocene. The earliest occupation phase at both sites consists of charcoal and heavily retouched stone artefacts made from exotic raw materials. Heat-treatment of imported silcrete artefacts first appeared in sediment dated to ~ 30,000 years ago, making these amongst Australia’s oldest dated heat-treated artefacts. An early human presence on Minjerribah is further suggested by palaeoenvironmental records of anthropogenic burning beginning by 45,000 years ago. These new chronologies from sites on a remnant portion of the continental margin confirm early human occupation along Sahul’s now-drowned eastern continental shelf.

The Hopewell Cosmic Airburst Event: A review of the empirical evidence

Abundance peaks in microscopic materials, including meltglass, microspherules, Ni, Ir, and Pt have been found in Native American Hopewell-age cultural strata. This discovery includes micrometeorites (possibly pallasites) recovered from heavily burned strata in two Hopewell villages. This evidence suggests that a prehistoric cosmic airburst/impact event occurred in the Ohio River valley. The peaks in these exotic materials only occur within a dark, charcoal-rich burn layer containing a wide range of Hopewell artifacts, and they are not found above or below the layer. Transgenerational oral histories and possibly two unique airburst-shaped Hopewell earthworks at or near the epicenter suggest that Native Americans living in the Ohio River valley may have been eyewitnesses to the impact event. AMS radiocarbon ages (n = 15) obtained directly from cultural and geological contexts indicate that the airburst/impact event occurred within a 70-year window from 1640-1570 cal BP. The Hopewell culture existed from ~2100-1500 cal BP and suffered a severe decline beginning ~1650 cal BP, suggesting that the proposed impact event occurred near the end of that span. After the proposed event, the hallmarks of the Hopewell culture, such as monumental landscape architecture, the largest geometric earthen enclosures in the world, intricate hilltop water management systems, massive burial mounds, and extensive ceremonial centers, were no longer constructed in the area impacted by the airburst. We propose that this cosmic airburst/impact event catalyzed the economic and sociopolitical decline and reorganization of the Hopewell cultural complex in the Ohio River valley for villages directly affected by the proposed airburst.

Accelerating Exotic Materials Use with Custom Coating Systems

Abstract Custom equipment designed for the deposition of exotic materials allows advanced coating solutions and ceramic matrix composites to be utilized for applications in automotive, aerospace, defense, energy, and the farthest reaches of space. This article describes custom systems for chemical vapor deposition and advanced materials processing.

Dynamics of Cylindrical Collapse in Palatini Gravity

This research explores how filamentary objects behave when they collapse in the presence of exotic material. To accomplish this, we employ Palatini (R, T) theory as a candidate for exotic material. We derive the collapsing equation by enforcing the Darmois junction condition on the collapsed surface boundary. At this boundary, we obtain that the radial pressure is proportionate to the time‐dependent term of the field and is not zero. Lastly, we investigate the correlation between dark matter and gravitational waves and find that exotic terms disrupt the transmission of gravitational waves. It is worthwhile to mention here that our results (in both formalisms, metric approach and Palatini approach) reduce to (R) gravity and general relativity.

High Chern number quantum anomalous Hall effect in monolayer Co3X3SSe (X = Sn, Pb) kagomes.

The high Chern number quantum anomalous Hall effect can offer an ideal platform to develop exotic quantum materials with a dissipationless chiral edge. The investigation of kagome monolayer Co3X3SSe (X = Sn, Pb) materials enables a comprehensive exploration of their structural, magnetoelectric, and topological characteristics through first-principles calculations. The monolayers Co3Sn3SSe and Co3Pb3SSe are classified as kagome ferromagnets, and they exhibit stable perpendicular magnetic anisotropy energy. These materials can achieve the intrinsic high Chern number quantum anomalous Hall effect with C = -3. The band gaps of Co3Sn3SSe and Co3Pb3SSe are 46 and 59 meV, respectively, which are larger than the thermal energy at room-temperature scale. Additionally, our findings demonstrate that both the band gap and magnetic anisotropy energy of the monolayers Co3Sn3SSe and Co3Pb3SSe are sensitive to applied strain. This research presents intriguing and alternative possibilities for advancing intrinsic high Chern number quantum anomalous Hall devices.

Carbon Kagome nanotubes-quasi-one-dimensional nanostructures with flat bands.

In recent years, a number of bulk materials and heterostructures have been explored due their connections with exotic materials phenomena emanating from flat band physics and strong electronic correlation. The possibility of realizing such fascinating material properties in simple realistic nanostructures is particularly exciting, especially as the investigation of exotic states of electronic matter in wire-like geometries is relatively unexplored in the literature. Motivated by these considerations, we introduce in this work carbon Kagome nanotubes (CKNTs)-a new allotrope of carbon formed by rolling up Kagome graphene, and investigate this material using specialized first principles calculations. We identify two principal varieties of CKNTs-armchair and zigzag, and find both varieties to be stable at room temperature, based on ab initio molecular dynamics simulations. CKNTs are metallic and feature dispersionless states (i.e., flat bands) near the Fermi level throughout their Brillouin zone, along with an associated singular peak in the electronic density of states. We calculate the mechanical and electronic response of CKNTs to torsional and axial strains, and show that CKNTs appear to be more mechanically compliant than conventional carbon nanotubes (CNTs). Additionally, we find that the electronic properties of CKNTs undergo significant electronic transitions-with emergent partial flat bands and tilted Dirac points-when twisted. We develop a relatively simple tight-binding model that can explain many of these electronic features. We also discuss possible routes for the synthesis of CKNTs. Overall, CKNTs appear to be unique and striking examples of realistic elemental quasi-one-dimensional materials that may display fascinating material properties due to strong electronic correlation. Distorted CKNTs may provide an interesting nanomaterial platform where flat band physics and chirality induced anomalous transport effects may be studied together.

Predicting Poisson's Ratio: A Study of Semisupervised Anomaly Detection and Supervised Approaches.

Auxetics are a rare class of materials that exhibit a negative Poisson's ratio. The existence of these auxetic materials is rare but has a large number of applications in the design of exotic materials. We build a complete machine learning framework to detect Auxetic materials as well as Poisson's ratio of non-auxetic materials. A semisupervised anomaly detection model is presented, which is capable of separating out the auxetics materials (treated as an anomaly) from an unknown database with an average precision of 0.64. Another regression model (supervised) is also created to predict the Poisson's ratio of non-auxetic materials with an R2 of 0.82. Additionally, this regression model helps us to find the optimal features for the anomaly detection model. This methodology can be generalized and used to discover materials with rare physical properties.

Rationally Designed in-Situ Gelled Polymer-Ceramic Hybrid Electrolyte Enables Superior Performance and Stability in Quasi-Solid-State Lithium-Sulfur Batteries

Despite boasting giant leaps in performance improvement over the years, the current commercial standard, Li-ion batteries, are fast approaching their theoretical limits. Meanwhile, Lithium-Sulfur (Li-S) batteries offering ultra-high theoretical energy density (～2600 Whkg-1), cost-effectiveness, and nontoxicity are being seen as promising alternatives. Despite their plentiful advantages, the practicality of Li-S batteries has been largely stymied by several challenges: a) deleterious polysulfide dissolution and ‘shuttle effect’, b) significant volume change of S cathodes during cycling, c) safety concerns with flammable traditional glyme-based electrolyte, and d) the instability of Li anode. To mitigate these challenges, researchers have explored all-solid-state electrolytes, but their poor Li-ion conductivity, high interfacial impedance, and need for expensive, exotic materials and complex fabrication procedures severely limit their practical application.To overcome these challenges, we propose an in-situ gelled polymer-ceramic hybrid silsesquioxane-based electrolyte system. The gelled matrix, thermally crosslinked post cell fabrication, immobilizes the glyme-based liquid electrolyte and exhibits high liquid-like ionic conductivities (1.03 mS.cm-1), low interfacial impedance, and high oxidative potential (>4.5V vs. Li/Li+) . In this study, in addition to vastly decreased flammability, we report superior Li-ion conductivity compared to state-of-art solid-state Li-S electrolytes. This high ionic conductivity translated to a significantly improved specific capacity of 1050 mAh.gS-1 at 0.2 C, elevated Coulombic efficiencies (>98.5%), and elevated rate kinetics. The gelled electrolytes exhibited stable cycling in a large temperature range (-10oC - 60 oC). Moreover, polysulfide permeation studies and subsequent DFT calculations revealed that the gelled electrolyte exhibited strong chemical absorptivity to lithium polysulfides due to the polar silsesquioxane core, which translated to superior capacity retention (>80% over 200 cycles). Further, post- mortem XPS characterization studies revealed the formation of stable SEI at the anode and cathode, and SEM of cycled anodes showed reduced dendritic formations. Finally, the electrolyte was tested in practical pouch cell architecture, and the cells demonstrated excellent reliability even under mechanical stress. This work successfully reports a robust, rationally designed gelled electrolyte system for developing safe and high-performance quasi-solid state Li-S batteries.

Wavelength Tunable Infrared Perfect Absorption in Plasmonic Nanocrystal Monolayers.

The ability to efficiently absorb light in ultrathin (subwavelength) layers is essential for modern electro-optic devices, including detectors, sensors, and nonlinear modulators. Tailoring these ultrathin films' spectral, spatial, and polarimetric properties is highly desirable for many, if not all, of the above applications. Doing so, however, often requires costly lithographic techniques or exotic materials, limiting scalability. Here we propose, demonstrate, and analyze a mid-infrared absorber architecture leveraging monolayer films of nanoplasmonic colloidal tin-doped indium oxide nanocrystals (ITO NCs). We fabricate a series of ITO NC monolayer films using the liquid-air interface method; by synthetically varying the Sn dopant concentration in the NCs, we achieve spectrally selective perfect absorption tunable between wavelengths of two and five micrometers. We achieve monolayer thickness-controlled coupling strength tuning by varying NC size, allowing access to different coupling regimes. Furthermore, we synthesize a bilayer film that enables broadband absorption covering the entire midwave IR region (λ = 3-5 μm). We demonstrate a scalable platform, with perfect absorption in monolayer films only hundredths of a wavelength in thickness, enabling strong light-matter interaction, with potential applications for molecular detection and ultrafast nonlinear optical applications.

Acoustically Actuated Flow in Microrobots Powered by Axisymmetric Resonant Bubbles

Bubble‐driven microsystems inspired by the therapeutic use of microbubbles under clinical ultrasound actuation offer innovative remote manipulation in biological settings. Ultrasound‐powered microrobots, benefiting from a distribution of vibrating microbubbles (1–100 μm in diameters), exhibit localized fluid flow for self‐propulsion. Microbubbles also contribute to the design of acoustic metamaterials, where distributed actuation of bubbles enables exotic material properties (e.g., negative refractive index). Herein, a metamaterial‐inspired microrobot design, which exploits the streaming induced by the collective oscillation of microbubble arrays (> 10), is reported. Such a large distribution of bubbles offers twofold advantages: a mesoscale microrobot allowing ease of handling and motion at a considerably low acoustic driving pressure of 50 kPa. In this work, the oscillatory amplitude of a single bubble that acts as a unit cell of the metamaterial‐based microrobot is first characterized. Thereon, this amplitude is related to the flow generated by the collective vibration of all the bubbles close to the theoretically predicted resonant frequency of the bubbles. Finally, the hovering motion of the microrobot induced by the streaming and flow‐assisted debris clearance is demonstrated. Such auxiliary functionalities of the microrobot can be useful for applications like contactless sample extraction in inaccessible biological environments.