Metal Layer Research Articles

A new method for synthesis and designing transmissive linear-to-circular polarization converters based on branch line circuit model

ABSTRACT This paper proposes a new design method of a linear-to-circular polarization converter based on the branch line circuit model. The series branches are implemented by dielectric spacers and the shunt branches are implemented by anisotropic admittance sheets. The admittance matrix of the anisotropic admittance sheets is derived by even and odd mode analysis. A unit cell consisting of two metal layers and a dielectric spacer is then designed using an iterative algorithm for operation from 15.5 to 23 GHz. Results indicate that the axial ratio and insertion loss of the designed polarizer are better than 3 and 1.5 dB respectively, for incident angles between ±45°. To validate the simulation results, a waveguide-based test setup is designed and fabricated, with measurement results indicating good agreement with simulations. The proposed method can be potentially applied to design other anisotropic structures such as half-plate polarizers and polarization rotators.

Exploiting Co-C interface and graphitic carbon belts for enhanced structural stability of a porous layered Co-C catalyst for CO2 hydrogenation

Addressing the urgent need for efficient CO2 reduction, a novel Co@C catalyst was synthesized through the pyrolysis of a unique layered metal–organic framework (MOF), featuring tunable thickness, pore sizes. The CO2 hydrogenation performance demonstrates an enhancement by an optimized structure that significantly improves stability, maintaining a 25% CO2 conversion rate over an extended 80-hour period. The catalyst's composite structure exhibits a dual-confinement effect, where the Co-C interface and graphitic carbon belt stabilize Co nanoparticles, preventing sintering during reaction cycles. This study delves into the structural modifications necessary for catalytic optimization in CO2 hydrogenation, offering valuable insights for designing efficient catalysts for CO2 reduction and advancing sustainable energy solutions.

Влияние износа инструмента в процессе физического моделирования шевингования-прикатывания цилиндрических зубчатых колес на параметр шероховатости

The main issues related to the results of an experimental study aimed at modeling of the combined (cutting-deforming) finishing process of a gear processing, i.e. cylindrical gear shaving and rolling, under turning with a special combined cutting-deforming tool, which is a single-tip tool of a cylindrical work, divided into equal working areas. Due to the proprietary exploratory procedure used for prototype process, in one operation of a compact cylindrical work, a gear processing of a sufficiently large batch of horisontal wheels-representatives with average parameters, consisting of several thousand pieces, is simulated on a CNC lathe. The analysis of the results of the experiment was treated, allowing us to obtain information about gear processing of a large batch of gears in laboratory conditions. The roughness parameter of the work on workpiece areas is determined, the boundaries of tool degradation for this parameter are revealed. The revealed pattern of tool degradation appears to be the following: the prevailing wear of the tool occurs along the back surface due to its design feature, i.e. zero angle of its back, aggravated by the technological characteristics of the process (shaving - rolling), in which the back is involved in the surface plastic deformation, in particular, crushing a metal layer under the influence of a significant normal load. This results in frictional load taking place between its back surface and the surface of the proccesed workpiece. Tool degradation along the front surface, accompanied by its tool cutter blunting of its cutting edge, contributes to further deterioration of cutting process conditions (when stock removal of about 0.02 mm), and at the same time increases the proportion of surface plastic deformation (when shaving– rolling). This, as a result, increases the workpiece material share, which should be removed not by cutting, but by surface plastic deformation, thereby further redoubling a wear bit in its back surface.

Tribological and Chemical–Physical Behavior of a Novel Palm Grease Blended with Zinc Oxide and Reduced Graphene Oxide Nano-Additives

The role of industrial lubricants in machinery is to reduce friction and wear between moving components. Due to the United Nations’ tendency to reduce dependency on fossil fuel, a general awareness is strongly driven towards developing more eco-friendly lubricants. Palm oil possesses promising properties, which promote it to be a competitive alternative to the hostile mineral oils. Still, marginal oxidation stability, viscosity, and tribological properties remain critical issues for performance improvement. This paper presents an improved palm grease using reduced graphene oxide (rGO) and zinc oxide (ZnO) nano-additives at different concentrations. Oil and grease samples were tested for viscosity, oxidation stability, pour point, penetration, roll stability, dropping point, churned grease-oil release, copper corrosion, friction, and wear. ZnO additives enhanced the oxidation stability by 60% and shifted the pour point to 6 °C. Adding ZnO and rGO to the palm grease increased the load-carrying capacity between 30% and 60%, respectively, and reduced the friction coefficient by up to 60%. From the wear scar morphologies, it is believed that graphene 2D nanoparticles formed absorption layers which contributed to the increase in load-carrying capacity, while ZnO chemically reacted with the metallic surface layer, forming zinc compounds that resulted in a protective boundary lubricating film.

Dual-Site Doping in Transition Metal Oxide Cathode Enables High-Voltage Stability of Na-Ion Batteries.

Designing cathode materials that effectively enhancing structural stability under high voltage is paramount for rationally enhancing energy density and safety of Na-ion batteries. This study introduces a novel P2-Na0.73K0.03Ni0.23Li0.1Mn0.67O2 (KLi-NaNMO) cathode through dual-site synergistic doping of K and Li in Na and transition metal (TM) layers. Combining theoretical and experimental studies, this study discovers that Li doping significantly strengthens the orbital overlap of Ni (3d) and O (2p) near the Fermi level, thereby regulates the phase transition and charge compensation processes with synchronized Ni and O redox. The introduction of K further adjusts the ratio of Nae and Naf sites at Na layer with enhanced structural stability and extended lattice space distance, enabling the suppression of TM dissolution, achieving a single-phase transition reaction even at a high voltage of 4.4V, and improving reaction kinetics. Consequently, KLi-NaNMO exhibits a high capacity (105 and 120 mAh g-1 in the voltage of 2-4.2V and 2-4.4V at 0.1 C, respectively) and outstanding cycling performance over 300 cycles under 4.2 and 4.4V. This work provides a dual-site doping strategy to employ synchronized TM and O redox with improved capacity and high structural stability via electronic and crystal structure modulation.

A broadband second-order bandpass frequency selective surface for microwave and millimeter wave application.

This paper presents a frequency selective surface (FSS) with a wideband second-order bandpass response in the dual-band of microwave and millimeter wave. The overall structure consists of three layers of metal pattern and two layers of thin dielectric substrate. The top and bottom metal layers have capacitive patches with integrated curled Jerusalem cross slot resonators, while the intermediate metal layer has an inductive grid structure with cross-shaped slot resonators. The incorporated slot resonators play a pivotal role in achieving the desired transmission poles or zeros, which enable a wideband second-order filtering response in the dual-band and a quick roll-off at the passband edges, increasing the efficacy of electromagnetic shielding. To fully investigate the structure's frequency response, an equivalent circuit model of the structure is created, spanning the complete frequency range of 5-50 GHz. Physical samples are created and measured to confirm the suggested approach's efficacy. The passband center frequencies of the FSS are found at f1 = 19.42 GHz and f2 = 42.78 GHz, and the - 3dB bandwidth is 4.34 GHz (17.25-21.59 GHz) and 8.54 GHz (38.51-47.05 GHz), respectively. The simulation results align well with the experimental data. The transmission response rapidly transitions from the passband to the stopband at the passband boundaries.

Design and analysis of K and Ku-band wide-angle polarization-insensitive dual-band perfect metamaterial absorber

This paper presents a polarization-insensitive dual-band metamaterial perfect absorber applied to the Ku and K bands. The proposed dual-band metamaterial absorber (MMA) is a three-layer structure of metal-dielectric-metal. The top metal layer consists of a split circle ring, two intersecting square rings, and a circle ring, the bottom metal layer is made of copper, and the middle dielectric layer is made of FR-4. The simulation results show that the MMA has two absorption peaks at frequencies of 12.06 GHz and 19.07 GHz, with absorption rates of 99.95% and 99.73%, respectively. The MMA exhibits good polarization insensitivity in TE and TM modes. In TE mode, the increase in incident angle significantly broadens the absorption bandwidth. The experimental results verified the dual-band perfect absorption of MMA and the incident angle gain characteristic of TE mode. The proposed dual-band MMA can be applied in related fields such as radar antennas, satellite communication, and sensing.

Simulation of ageing and wear effect on graphene THz passive components using finite element method

In the growing scenario of 2D material-based metamaterials and metasurfaces for Terahertz (THz) applications, assessing the impact of ageing and wear due to environmental stressors on the components’ performance is becoming mandatory to understand the long-term reliability of novel technologies. This paper introduces approaches to assess the ageing and wear effects on THz passive components through numerical simulations. For this purpose, common techniques for introducing 2D materials and thin metal layers in numerical models are discussed. As a case study, this work explores the effects of graphene degradation and reflective metal ageing on the electromagnetic response of a graphene-enhanced reflective grating for THz absorption and modulation by finite element (FE) analysis. The developed FE model is validated against experimental data obtained through THz Time-Domain Spectroscopy. By computing the device’s transmission, reflection, and absorption spectra for degrading graphene and metal conductive properties, this work provides insights into the influence of ageing and wear on THz passive components.

Josephson diode effect in junctions of superconductors with band asymmetric metals

At interfaces connecting two superconductors (SCs) separated by a metallic layer, an electric current is induced when there is a disparity in the phases of the two superconductors. We elucidate this phenomenon based on the weights of the Andreev bound states associated with the states carrying currents in forward and reverse directions. Typically, current phase relation (CPR) in Josephson junctions is an odd function. When time reversal and inversion symmetries are broken at the junction, CPR ceases to be an odd function and the system may exhibit Josephson diode effect. This phenomenon has been studied in spin orbit coupled systems under an external Zeeman field wherein the magnetochiral anisotropy is responsible for the Josephson diode effect. Recently introduced the band asymmetric metal (BAM) model presents a novel avenue, featuring an asymmetric band structure. We investigate DC Josephson effect in SC-BAM-SC junctions and find that band asymmetry can lead to Josephson diode effect and anomalous Josephson effect. We explain the mechanism behind these effects based on interference of plane wave modes within the Bogoliubov de-Genne formalism. We calculate diode effect coefficient for different values of the parameters.

Influence of the configuration of metal sensing layers on the performance of a bimetallic (Ag-Cu) surface plasmon resonance biosensor.

Bimetallic surface plasmon resonance (SPR) sensors have the potential to overcome the drawbacks of individual metals, but the effect of the configuration of the two metallic layers on the performance of the sensors has not been explored. This study examines the influence of different positions of a thin layer of silver in relation to a copper layer on the sensitivity of such a bimetallic SPR sensor. The design of this configuration aims to improve the SPR reflectance curve and strengthen the evanescent electric field to improve the sensor efficiency. Our findings indicate that, by optimizing the architectures of SPR sensors and using a silver-copper bimetallic structure, we can achieve superior performance compared to devices that utilize only silver or copper. The optimized Ag (5 nm)/Cu (55 nm) sensor design, with the best sensitivity of 299.09°/RIU, can detect a change of 0.43°/(gm/dL) for hemoglobin in blood, 0.35°/(gm/dL) for glucose in urine, and 0.1°/(%) for methanol in ethanol. We also demonstrate the importance of signal quality by introducing two new parameters that offer a better quantitative indication of the efficiency of a sensor than is obtained by using only sensitivity.&#xD.

Exploring the potential of Mbenes in energy storage

MBene, a layered metal boride similar to MXene, has garnered significant attention in recent times. Nevertheless, there is still a lack of comprehensive understanding regarding their structure and properties, necessitating further research and investigation. In this study, theoretical calculations were employed first to study the binding energy, band structures and density of states of three MBenes, namely MoB, MgB2, and ZrB2, providing insights into their electronic characteristics. In addition, open circuit voltage (OCV) and adsorption energy were also conducted using the three MBenes as cathode materials for zinc ion batteries, indicating their low ion migration barrier and potential in energy storage application. Subsequently, MoB, MgB2, and ZrB2 were experimentally synthesized using etching or exfoliation method and utilized as cathode materials for zinc ion batteries. Results demonstrates that the specific capacity of MoB is 60 mAh g-1 at 0.1 A g-1. Systematic investigation including kinetics simulation and ex situ XRD suggests the cation insertion mechanism of the MoB electrodes. Building upon these findings, attempts were made to enhance the performance of MoB through the incorporation of 1 T-MoS2 composites, urea molecular intercalation. Notably, the modified composite exhibited a specific capacity exceeding 150 mAh g-1 at 0.1 A g-1, with a stable Coulombic efficiency of 100% after 100 cycles. This study provides novel directions and insights for the research of MBene in the context of aqueous zinc-ion batteries.

Absorption by a Layered Microbolometer Pixel’s Active Element

Microbolometer arrays, i.e., arrays of micro-scale pixels sensing temperature via resistance changes, have proven to be an effective basis for real-time imaging instrumentation in infrared as well as terahertz frequencies. In previous work, a design of THz and IR absorbing nano-laminates of dielectric and metal layers was studied. It was shown via numerical modeling that absorption may be maximized by appropriate choices of thickness, permittivity and conductivity. In this work, an analytical approach to the problem is formulated based on the standard recursive multiple reflection formulas for multi-layered planar structures. The results fully confirm and extend previous numerical work. A previous relationship between wavelength and silicon thickness for maximum absorption, derived numerically for specific parameter combinations, is now generalized in a parametric closed form. The method can be extended to include multiple lossy dielectric layers and may serve as a tool for optimizing the absorption characteristics of more complex layered absorbing structures. This could enhance the sensitivity of the detection scheme of interest, providing benefits in terms of cost, efficiency, precision, and adjustability.

Non-coplanar helimagnetism in the layered van-der-Waals metal DyTe3

Van-der-Waals magnetic materials can be exfoliated to realize ultrathin sheets or interfaces with highly controllable optical or spintronics responses. In majority, these are collinear ferro-, ferri-, or antiferromagnets, with a particular scarcity of lattice-incommensurate helimagnets of defined left- or right-handed rotation sense, or helicity. Here, we report polarized neutron scattering experiments on DyTe3, whose layered structure has highly metallic tellurium layers separated by double-slabs of dysprosium square nets. We reveal cycloidal (conical) magnetic textures, with coupled commensurate and incommensurate order parameters, and probe the evolution of this ground state in a magnetic field. The observations are well explained by a one-dimensional spin model, with an off-diagonal on-site term that is spatially modulated by DyTe3’s unconventional charge density wave (CDW) order. The CDW-driven term couples to antiferromagnetism, or to the net magnetization in an applied magnetic field, and creates a complex magnetic phase diagram indicative of competing interactions in this easily cleavable van-der-Waals helimagnet.

Realizing Ultrathin LiSn Alloy Anode by Tuning the Wettability of Molten Li for High-Energy-Density Batteries.

Despite being heralded as the "holy grail" of anodes for their high theoretical specific capacity, lithium (Li) metal anodes still face practical challenges due to difficulties in fabricating ultrathin Li with controllable thickness and suppressing Li dendrites growth. Herein, we introduce a simple and cost-effective dip-coating method to fabricate ultrathin lithium-tin (LiSn) anode with adjustable thicknesses ranging from 4.5 to 45 μm. The in situ formation of Li22Sn5 alloy improves the wettability of the molten Li, enabling the casting of ultrathin Li metal layers on different substrates. More importantly, the abundant Li22Sn5 lithiophilic sites significantly lower the nucleation overpotential, inducing uniform Li deposition and accelerating the electrochemical reaction at the interface. As a result, the symmetric cell assembled with LiSn-Cu electrodes can cycle stably for more than 120 h with a charge/discharge depth of 50%, which is 1.5 times longer than the lifespan of the pure Li anode. In the full cells paired with NCM cathode, the discharge specific capacity is improved from 13.84 to 70.31 mA h g-1 with the LiSn-Cu anode at 8 C. The LiSn-Cu||NCM full cell realized a high energy density of 724.9 Wh kg-1 at the active material level with an N/P ratio of 1.4.

Comparison of Current Induced Domain Wall Motion Driven by Spin Transfer Torque and by Spin Orbit Torque in Ferrimagnetic GdFeCo Wires

Current-induced domain wall motion (CIDWM) in magnetic wires can be driven by spin transfer torque (STT) originating from transferring angular momentums of spin-polarized conducting electrons to the magnetic DW and can be driven by spin orbit torque (SOT) originating from the spin Hall effect (SHE) in a heavy metal layer and Dzyaloshinsky Moriya (DMI) generated at an interface between a heavy metal layer and a magnetic layer. In this work, we carried out a comparative study of CIDWM driven by STT and by SOT in ferrimagnetic GdFeCo wires with magnetic perpendicular anisotropy based on structures of SiN (10 nm)/GdFeCo (8 nm)/SiN (10 nm) and Pt (5 nm)/GdFeCo (8 nm)/SiN (10 nm). We found that CIDWM driven by SOT exhibited a much lower critical current density (JC), and much higher DW mobility (µDW). Our work might be useful for the realization and the development of low-power and high-speed memory devices.

Understanding the Correlation between Electrochemical Performance and Operating Mechanism of a Co-free Layered-Spinel Composite Cathode for Na-Ion Batteries.

Compositing different crystal structures of layered transition metal oxides (LTMOs) is an emerging strategy to improve the electrochemical performance of LTMOs in sodium-ion batteries. Herein, a cobalt-free P2/P3-layered spinel composite, P2/P3-LS-Na1/2Mn2/3Ni1/6Fe1/6O2 (LS-NMNF), is synthesized, and the synergistic effects from the P2/P3 and spinel phases were investigated. The material delivers an initial discharge capacity of 143 mAh g-1 in the voltage range of 1.5-4.0 V and displays a capacity retention of 73% at the 50th cycle. The material shows a discharge capacity of 72 mAh g-1 at 5C. This superior rate performance by the material could be by virtue of the increased electronic conductivity contribution of the incorporated spinel phase. The charge compensation mechanism of the material is investigated by in operando X-ray absorption spectroscopy (in a voltage range of 1.5-4.5 V vs Na+/Na), which revealed the contribution of all transition metals toward the generated capacity. The crystal structure evolution of each phase during electrochemical cycling was analyzed by in operando X-ray diffraction. Unlike in the case of many reported P2/P3 composite cathode materials and spinel-incorporated cobalt-containing P2/P3 composites, the formation of a P'2 phase at the end of discharge is absent here.

Novel Highly Efficient Buried Gratings for Selective Coupling of SPP Waves onto Single Interfaces

Diffraction gratings have always been used to effectively couple optical radiation within integrated waveguides. This is also valid for plasmonic structures that support Surface Plasmon Polariton (SPP) waves. Traditional gratings usually excite SPP waves at the interface where they are located or, for thin metal nanostrips, at both interfaces. But reducing the thickness of the metal layer in the presence of a grating has the handicap of increasing the tunnelling of light towards the substrate, which means higher losses and reduced coupling efficiency. In this paper, we design and optimize novel gratings buried within the metallic thin films for selective coupling of SPP waves onto individual interfaces. Compared with traditional superficial gratings, the novel buried ones demonstrate higher efficiency and much lower residual tunnelling of light through the coupling structures.

Construction and catalysis role of a kinetic promoter based on lithium-insertion technology and proton exchange strategy for lithium-sulfur batteries

The high theoretical energy density and specific capacity of lithium-sulfur (Li-S) batteries have garnered considerable attention in the prospective market. However, ongoing research on Li-S batteries appears to have encountered a bottleneck, with unresolved key technical challenges such as the significant shuttle effect and sluggish reaction kinetics. This investigation explores the catalytic efficacy of three catalysts for Li-S batteries and elucidates the correlation between their structure and catalytic impacts. The results suggest that the combined utilization of lithium-insertion technology and a proton exchange approach for δ-MnO2 can optimize its electronic structure, resulting in an optimal catalyst (H/Li inserted δ-MnO2, denoted as HLM) for the sulfur reduction reaction. The replacement of Mn sites in δ-MnO2 with Li atoms can enhance the structural stability of the catalyst, while the introduction of H atoms between transition metal layers contributes to the satisfactory catalytic performance of HLM. Theoretical calculations demonstrate that the bond length of Li2S4 adsorbed by the HLM molecule is elongated, thereby facilitating the dissociation process of Li2S4 and enhancing the reaction kinetics in Li-S batteries. Consequently, the Li-S battery utilizing HLM as a catalyst achieves a high areal specific capacity of 4.2 mAh cm−2 with a sulfur loading of 4.1 mg cm−2 and a low electrolyte/sulfur (E/S) ratio of 8 μL mg−1. This study introduces a methodology for designing effective catalysts that could significantly advance practical developments in Li-S battery technology.

Bandpass frequency selective surfaces with fast roll-off characteristics

We propose a bandpass frequency selective surface (FSS) with fast cut-off characteristics and low insertion loss. It consists of a compact high-frequency hybrid compression board with five metal layers, two Rogers RO4003C layers, and two F4B layers. The hierarchical fitting of equivalent circuits is utilized to analyze the FSS, which maintains angular stability for dual-polarized electromagnetic waves at incidence angles of less than 20 degrees. Under normal incidence, transmission amplitudes in the K-band exceed −0.87 dB. Furthermore, the proposed FSS achieves a roll-off rate of 87.6 dB GHz−1, which can be applied in dual-frequency observing systems for millimeter astronomy.

From Simple Packaging Materials to Smart Sensors: Sunlight Exposure Sensing in Bubble Wraps Incorporating a Layered Metal Selenide Photocatalyst

AbstractThis work demonstrates that the packaging material commonly called “bubble wraps” (Aeroplast) can be leveraged to serve as a probe to visible sunlight exposure. This probe relies on a newly developed layered metal selenide photocatalyst with the general formula (DMAH)2xMnxSn3–xSe6 (DMSe‐1) (x = 1.3–1.7; DMAH+ = dimethylammonium), featuring a narrow bandgap of 0.76 eV, in addition to an indicator dye and a reducing agent. The photochemically sensitive probe is introduced into the air‐filled compartments of bubble wraps and undergoes photocatalytic degradation, resulting in a chromatic response to sunlight exposure. The probe's sensitivity to variable irradiation doses can be adjusted by varying the amount of the photocatalyst. The color intensity correlates with the absorbed irradiation dose, allowing for qualitative assessment by the naked eye or quantitative measurement using the RGB color system. The results obtained from the new probe agree with those obtained from standard sunlight pyranometers (r = 0.98), with an average error of <15%. This suggests that beyond their use as protective coatings, bubble wraps can be successfully repurposed as visible light sensors. Furthermore, this study describes the initial use of metal chalcogenides as visible light probes, potentially paving the way for the development of innovative light‐sensitive materials.