Multilayer Phase Research Articles

Thermo-optical and electro-optical tunable dual-band THz absorber based on multi-layer hybrid VO2 phase transition metamaterial

In this paper, a thermo-optical and electro-optical (EO) tunable multifrequency metamaterial THz absorber based on a multi-layer hybrid VO2 transition metamaterial is demonstrated. The reflectivity and transmittivity, and absorptivity of the metamaterial with various geometric parameters are simulated. The simulation results show that the absorptivity reaches 99.4% at an operating frequency of 6.9 THz. The thermo-optical and EO tunable absorption rates are studied by changing the surrounding temperature and bias voltage, respectively. The absorptivity is adjusted from 36.2% to 99.4% and modulation depth is ∼63.5% when the surrounding temperature rises from 294 to 350 K. The EO wavelength tuning coefficient is ∼1690.4 pm/V. The effects of geometric parameters on the absorptivity of the metamaterial absorber are also discussed. The impedance matching theory is used to explain the physical mechanism of absorption characteristics. The proposed metamaterial absorber has potential applications including infrared imaging, thermal emitters, electromagnetic shielding and photodetector, moreover, the research of the thermo-optical and EO tunable absorption characteristics provides a feasible scheme of THz wave modulation and multiplexing.© 2021 Optica Publishing Group under the terms of the Optica Publishing Group Open Access Publishing Agreement.

Densely packed skyrmions stabilized at zero magnetic field by indirect exchange coupling in multilayers

Room-temperature stabilization of skyrmions in magnetic multilayered systems results from a fine balance between several magnetic interactions, namely, symmetric and antisymmetric exchange, dipolar interaction and perpendicular magnetic anisotropy as well as, in most cases, Zeeman through an applied external field. Such field-driven stabilization approach is, however, not compatible with most of the anticipated skyrmion based applications, e.g., skyrmion memories and logic or neuromorphic computing, which motivates a reduction or a cancellation of field requirements. Here, we present a method to stabilize at room-temperature and zero-field, a densely packed skyrmion phase in ferromagnetic multilayers with moderate number of repetitions. To this aim, we finely tune the multilayer parameters to stabilize a dense skyrmion phase. Then, relying on the interlayer electronic coupling to an adjacent bias magnetic layer with strong perpendicular magnetic anisotropy and uniform magnetization, we demonstrate the stabilization of sub-60 nm diameter skyrmions at zero-field with adjustable skyrmion density.

Dielectric Metalens by Multilayer Nanoimprint Lithography and Solution Phase Epitaxy

Metasurfaces have ushered in a huge development for their superior ability in manipulating light properties including phase, amplitude, and polarization, which show great potential as alternatives for the refractive optical devices. Recently, many applications of metasurface including metalens have been proposed and investigated, aiming at substituting their refractive counterparts. However, the commonly used fabrication approaches employ electron‐beam lithography (EBL) followed by dry etching or atomic layer deposition (ALD) of dielectric materials, which are expensive and inefficient. Besides, dry etching of dielectric materials at sub‐100 nm scale with a high aspect ratio is challenging. Herein, a new approach for dielectric metalens fabrication is presented, which combines multilayer nanoimprint lithography and solution phase epitaxy. High aspect ratio ZnO nanopillars with a height‐to‐diameter ratio of over 7:1 are demonstrated. By using the multilayer nanoimprint lithography, increased aspect ratio nanostructures from shallow imprinting molds are obtained. The highly anisotropic growth characteristic enables nanopillars to grow at a height that exceeds the resist thickness. With this ability, ZnO metalenses are fabricated where the height of nanopillar reaches 1.1 μm, achieving a focusing efficiency of 50%. The process is cost‐effective with a high throughput, which can be widely used for many optical applications.

Upgrading Electricity Generation and Electromagnetic Interference Shielding Efficiency via Phase-Change Feedback and Simple Origami Strategy.

Developing ultimate electromagnetic interference (EMI) shielding materials that can simultaneously upgrade the quality of generated electricity and the light-thermal-electric conversion efficiency based on traditional thermoelectric devices is crucially desired. Herein, a series of flexible multilayered phase change films (PCFs) is developed by a simple and novel origami strategy. The PCFs are first reported to improve the light-thermal-electric conversion efficiency by as high as 11.3%. Simultaneously, the PCFs could significantly upgrade the generated electricity on average voltage (27.3%), average current (23.8%), and lasting power outputs by 2010 times from microwatts to milliwatts. Besides, the EMI shielding efficiency of PCFs could be tuned from 39.2 to 71.9 dB by the origami process, the wide-range EMI shielding performance could be suitable for varying occasions. Overall, this work provides a promising solution for both the preparation of multifunctional materials, high-efficiency solar energy harvesting and upgrading electricity generation, which shows broad application prospects in EMI shielding, energy storage, and conversion.

Erratum: Accurate model of the stripe domain phase of perpendicularly magnetized multilayers [Phys. Rev. B 95 , 174423 (2017)

Erratum: Accurate model of the stripe domain phase of perpendicularly magnetized multilayers [Phys. Rev. B <b>95</b> , 174423 (2017)

HRMS-Targeted-DIA methodology for quantification of wastewater-borne pollutants in surface water

A robust method was developed for the quantification of popular and highly occurrence contaminants of emerging concern from wastewater treatment plant effluents and is explained in detail. A homemade multi-layered and multi-sorbent solid phase extraction (SPE) cartridge was used to cover the wide range of polarities of the selected contaminants. A non-discriminant elution protocol was also applied. Liquid chromatography coupled to a high-resolution mass spectrometer (HRMS) Q-Exactive Orbitrap system was used for the separation and detection of the contaminants. A targeted data independent acquisition (DIA) mode with an inclusion list with the exact mass, retention time window and collision energy was tried for the first time obtaining good sensitivity, selectivity and high quality MS2 product ions.•116 compounds of a wide-scope of polarities and physic-chemical properties were validated using a surface water pool matrix.•SPE followed by LCHRMS with a targeted DIA was used for the method validation at three concentration levels 5, 50, 500 μg l-1 in extract.•Good recoveries were obtained between 70 and 120% for the majority of the selected contaminants. Matrix effect, precision, and linearity were also evaluated and results proved the suitability for the method application.

Construction of layered double hydroxide-modified silica integrated multilayer shell phase change capsule with flame retardancy and highly efficient thermoregulation performance

Current energy problems have driven the development of thermal storage technology based on phase change materials (PCMs). However, the leakage and flammability of organic PCMs appeared as troublesome agendas that deserve attention. In this article, the strategy of constructing phase change capsules with paraffin wax (PW) core and multilayer shell was proposed aiming to address the above issues. For the integrated multi-layer shell, silica (SiO2) acts as initial layer to encapsulate the PW core, and then tannic acid (TA) was creatively taken to bridge the subsequent flame retardant layered double hydroxides (LDH) layer on the surface of the silica shell, and polyvinyl alcohol (PVA) layer was further introduced to improve the compatibility of phase change capsules with polymer matrix. Characterization of chemical structure and morphology confirmed that phase change capsules with LDH modified silica multilayer shell (M-EPCMs) was successfully prepared. The results indicated that M-EPCMs, particularly the representative M-EPCM-5, possessed outstanding thermal stability, excellent leak proofness, good thermal regulation performance as well as long-term cycling stability. Importantly, M-EPCM-5 with the thickest LDH layer can self-extinguish when exposed to fire, and especially can keep the integrity of its shell without breakage after being heated at high temperature. Furthermore, the silicone rubber foam (SRF) composite containing M-EPCM-5 can reach UL-94V-1 level, indicating the flame retardancy of SRF matrix was improved significantly. The possible flame retardant mechanism revels that LDH can not only accelerate the formation of dense ceramic protective layer in condensed phase, but also release non-combustible gases (H2O, CO2) in gas phase, thus improving the fire retardancy of M-EPCMs. Therefore, the construction strategy proposed in this article represents a powerful means to improve flame retardancy and prevent leakage of phase change capsules at the same time, which will greatly expand the application scope of PCMs.

Metasurface Radome to Achieve a Wideband High Gain, Low RCS, and Low SLL Antenna

A Phase- and amplitude-adjustable metasurface radome (PAMR) is proposed to achieve a wideband high gain and low radar cross-section (RCS) antenna with arbitrary sidelobe levels (AS-PGMA) at a 9.8 GHz operating frequency. The proposed PAMR is a special multilayer phase gradient metasurface lens whose amplitude distribution is modified based on the Dolph-Tschebyscheff technique. The AS-PGMA simulation results indicate that a high gain, low RCS, and low sidelobe level (SLL) antenna can be achieved over a broad impedance frequency bandwidth of 9.25–10.1 GHz with in-band average values of 17 dB, −7.5dBsm, −20 dB/−27 dB for gain, RCS, and E-/H-plane SLL, which are measured at 9.8 GHz as 17.4 dB, −9dBsm, and −23.02 dB/−27.91 dB, respectively. Additionally, a novel analytical method for calculating the RCS of the proposed PAMR and AS-PGMA is described and verified by measurement and simulation findings. Measurement results show that the E-/H-plane SLL of the AS-PGMA is improved by 12.2 dB/5.1 dB at the operating frequency, respectively, while its gain and RCS reduction are reduced by 1.6 and 2.1 dB, respectively. Moreover, RCS of the AS-PGMA is reduced over an ultrawide bandwidth of 1–20 GHz for orthogonal polarizations. The analysis, simulations, and measurements are all in good agreement.

Phase change materials for battery thermal management of electric and hybrid vehicles: A review

Battery is essential parts of an electric and hybrid electric vehicle. Good amount of heat is generated by charging and discharging actions. For maximum efficiency, reliability of utmost necessary to conserve the optimum temperature by employing a proper battery thermal management system. Uses of Phase Change Materials for thermal management have attracted attention in recent years due to its lightweight, improved energy efficiency, less intricacy and better thermal homogeneity. These materials are a potential substitute for economical, and simple operation. Phase Change Materials could be utilized as active or passive systems, empowering the universal system to nurture near-autonomous performances. This work consists of the discussions on battery thermal management systems using phase change materials, enhancement of Phase Change Materials’ thermal conductivity, thermal management schemes and finally concluding with the application sections. Heat transfer can be augmented by application of Phase Change Materials through thermally conductive particles, metal fin, metal foam and expanded graphite matrix. Newly developed thermal management configurations like multi-layer Phase Change Materials and sandwiches are also outlined. Additionally, a thermal management system merging Phase Change Material cooling via air or liquid is also presented.

Preparasion of layered V4AlC3 MAX phase for highly selective and efficient solvent-free aerobic oxidation of toluene to benzaldehyde

Selective and solvent-free aerobic oxidation of toluene as a volatile organic compound to benzaldehyde is of immense industrial significance, which is limited by harsh chemical conditions. Developing novel catalysts for overcoming this limitation has attracted the interest of researchers. In this work, a highly stable two-dimensional V4AlC3 MAX phase with layered-like polycrystal structures was synthesized successfully. X-ray diffraction, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy were applied to assess the structure of the MAX phase catalyst. Moreover, the morphology of the synthesized MAX phase was studied using scanning electron microscopy and transmittance electron microscopy. The prepared multi-layered V4AlC3 MAX phase represented a high catalytic activity for solvent-free aerobic oxidation of toluene to benzaldehyde. Up to 18.4% conversion and 84.2% selectivity to benzaldehyde was obtained within only 4 h under air pressure condition. Furthermore, the radical-based mechanism of the oxidation was confirmed by electron paramagnetic resonance by following the produced organic free radical species during reactions.

The growth and corrosion mechanism of Zn-based coating on AZ31 magnesium alloys by novel hot-dip process

A Zn-based coating with excellent corrosion resistance was prepared on the surface of AZ31 magnesium alloy by novel hot-dip process. The microstructure, growth process and corrosion mechanism of coatings were investigated. The results show that good metallurgical bonding and integrated multi-layer phase structure were observed in coatings with sufficient immersion time. This multi-layer phase structure is divided roughly into an alloy layer consisting of Zn + Mg2Zn11 + MgZn2 phases and a diffusion layer consisting of MgZn + Mg7Zn3 phase, which is mainly attributed to the diffusion reaction of Zn and Mg atoms and the subsequent solidification. Furthermore, the corrosion resistance of coated AZ31 is dramatically improved, the low frequency value of the coated AZ31 up to 3541 Ω cm2, more than 90 times higher than bare AZ31 which is 38.1 Ω cm2, the icorr of 4 s coating is 1.948 × 10−5 A cm−2, reduced to 6.6% of bare AZ31 which is 2.895 × 10−4 A cm−2. The outstanding corrosion performance is mainly due to an effective barrier to Mg matrix by the dense multi-layer structure and the compact corrosion products.

Can analyte protectants compensate wastewater matrix induced enhancement effects in gas chromatography – mass spectrometry analysis?

This study aimed to investigate the ability of analyte protectants to enhance GC-MS signals and compensate matrix effects for a range of micropollutants in pure standard, effluent, and influent wastewater samples during analysis and detection. Wastewater samples were prepared for analysis using multilayer solid phase extraction for the purpose of extracting sample components with a broad range of physical-chemical properties. The sample extracts were either spiked or not spiked with target compounds and four analyte protectants: 3-ethoxy-1,2-propanediol, D-sorbitol, gluconolactone, and shikimic acid. In this way, it was possible to evaluate the matrix effects of wastewater samples and compare the use of analyte protectants with the conventional correction method of allocating a best matching internal standard to each target compound. A relation was observed between level of wastewater treatment and matrix effects, with the largest effects observed for influent samples and the smallest effects for effluent samples. Compensation of matrix effects with analyte protectants gave comparable results with the conventional correction method of allocating a best matching internal standard to each of the 13 investigated micropollutants. The best overall compensation was observed using analyte protectants and the internal standard correction method in combination.

Chromatic aberration correction in bi-focal augmented reality display by the multi-layer Pancharatnam-Berry phase lens.

Chromatic aberration is a main obstacle for the commercial application of augmented reality displays. The current digital and optical compensation methods of reducing the chromatic aberration suffer from processing time, power consumption or complex design. Here, a simple strategy of chromatic aberration correction in bi-focal augmented reality near-eye display based on multi-layer Pancharatnam-Berry phase lens has been demonstrated and verified by experimental results. The multi-layer Pancharatnam-Berry phase lens, as a part of optical combiner, is fabricated by three liquid crystal polymer phase lenses with central wavelength in red, green, and blue, respectively. The multi-layer Pancharatnam-Berry phase lens can effectively reduce the chromatic aberration in both convex and concave mode of bi-focal augmented reality system, where the color breakup of virtual images captured in bi-focal augmented reality display is significantly alleviated. Comparing to the value of ΔK = 1.3 m-1 in single green Pancharatnam-Berry phase lens, the multi-layer Pancharatnam-Berry phase lens system significantly reduce the ΔK to 0.45 m-1 with reduction of 65.4%, which finally decreases the longitudinal chromatic aberration and improve the quality of images. The proposed broadband multi-layer Pancharatnam-Berry phase lens can benefit augmented reality displays and find widespread application in the near-eye displays.

Modeling of Multi-Layer Phase Change Material in a Triplex Tube under Various Thermal Boundary Conditions

Nowadays, limited energy resources face ever-growing demands of the modern world. One engineering approach to mitigate this problem which has received considerable attention in recent years is using latent heat thermal storage (LHTS) systems, a significant opportunity which is provided by phase change materials (PCMs). In the present study, a numerical investigation was devoted to estimate the simultaneous freezing and melting processes of a double-layer PCM in terms of heat transfer and fluid flow phenomena. A double-pipe cylindrical channel with two compartments, A and B, was considered for locating two PCMs of RT28 and RT35 in various arrangements. The inner and outer walls were exposed to both hot and cold heat transfer fluids (HHTFs and CHTFs, respectively) beginning with solid or liquid initial state, which led to solid–liquid phase change process through PCMs. The numerical simulation was handled by a two-dimensional finite volume method (FVM) with a fixed Rayleigh number of 106 in which conduction and convection heat transfer mechanisms are taken into account. The effects of employing double-layer PCM and their arrangements, inner and outer walls’ boundary conditions, and initial statuses of PCMs are discussed, and the details of the compared results are shown in the form of temperature and liquid fraction variations over time.

Improved mathematical model of apparent permeability: A focused study on free and multilayer adsorptive phase flow

Apparent permeability is the quantification of gas transport in confined pore, which includes the pressure gradient-driven continuous flow (slip flow), the concentration gradient-driven molecular diffusion (Fick's diffusion, Knudsen diffusion) and the chemical gradient-driven surface diffusion. Molecular diffusion of free/adsorbed gas plays an important role in gas transfer, especially in nanopores. Most existing apparent permeability models simply define free gas diffusion as Knudsen diffusion, and surface diffusion as the diffusion of monolayer adsorbed molecules. However, the pore scale-dependent Knudsen diffusion, the molecular diffusion of free gas also includes the pore scale-independent Fick's diffusion. In addition, the empirical formula of surface diffusion coefficient derived from plug core diffusion experiment should be used cautiously, because there are other diffusion regimes involved in the diffusion process in multi-scale pores. In this work, the diffusion mechanisms of adsorbed/free gas were classified. A supercritical multilayer adsorption (SC-DA) model was obtained by fitting the adsorption data of homogeneous nano activated carbon, and the adsorption effect was applied to pore aperture change and surface diffusion, which is suitable for single/multilayer adsorption. Applying the improved surface diffusion flow and free gas diffusion flow into gas transport, a unified mathematical transport model was presented, from which the apparent permeability model was derived. Later, the improved model was verified using the experimental data from the micro-flow permeability of the nanofilms with regular size. Furthermore, the influence of each flow mechanism in nanopores was calculated and compared. The results showed that the gas transport in nanopores is dominated by molecular diffusion, but the contribution of surface diffusion in gas transfer is exaggerated if its diffusion coefficient is not chosen properly.

Mechanochromic Luminescence of Composites Based on (CH3NH3)PbBr3 and Layered HPs: Influence of 2D Components and Interface Multilayered Phases

AbstractThe mechanochromic luminescence (MCL) properties of crystallized powders of composites based on the 3D perovskite MAPbBr3 and one layered (2D) halide perovskite (HP) are reported for three 2D HPs selected for their distinct emission properties: (PEA)2PbBr4 (n=1) narrow emission (HE), (EDBE)PbBr4 (m=2) broad emission (LE) and (BA)2PbBr4 (n=1) dual emission (HE and LE). All composites exhibit sensitive MCL due to the activation of the 3D component emission through energy transfer (ET) from multilayered perovskites formed at the interface. While the excitonic HE band is less affected by the mechanical treatment, LE is quenched in crushed composites, suggesting that it rather originates from the crystal edge/surfaces. Full reversibility of the MCL process is obtained only when the multilayered phases formed at the interface are not stable. The emission of composite thin films, where larger 2D/3D interface areas are present, further support the role of the interfaces in the activation of 3D emission.

Four-function metasurface based on a tri-band integrated meta-atom for full space control of circularly polarized waves

Highly integrated planar meta-devices have attracted much attention in optics and communication, which can achieve multitasking wavefront manipulations at multiple frequencies. Integrated meta-devices can increase data capacity and functional diversity. However, further expansion of functions in integrated devices is still challenging. Here, a multilayer geometric phase metasurface is proposed. The functions are expanded via decoupling the resonance of different layer structures or decoupling its phase modulation. Under circularly polarized (CP) wave incidence, the proposed multifunctional metasurface performs four functions at three distinct frequencies. When left-handed circularly polarized (σ+ CP) waves at 8 GHz is incident from the lower half of space, deflection is realized. When a CP wave with different handedness at 10 GHz is incident from the upper half of space, focusing and diverging lenses are realized, respectively. When σ+ CP waves at 17 GHz is incident from the lower half of space, the reflective holography is realized. We designed, manufactured, and experimentally proved the multifunctional integrated full-space metasurface. The simulation and measurement results are in good agreement, verifying the four-function and tri-band metasurface design strategy. The method proposed in this paper opens up a new opportunity for increasing the information capacity and has application prospects in communication systems, optical storage, and image display.

Unraveling the Highly Complex Nature of Antimony on Pt(111)

AbstractUnderstanding the growth behavior of group‐V elements on metal surfaces provides valuable information that can shed light on the feasibility of tailoring atomically thin monoelemental 2D polymorphs composed of pnictogens on these metallic substrates. Here, by combining scanning tunneling microscopy (STM), low energy electron diffraction and Auger electron spectroscopy measurements under ultra‐high vacuum conditions, a wide variety of Sb reconstructions on single‐crystal Pt(111) are identified and characterized. At Sb coverage of ≈0.2 ML, STM data are compatible with a scenario in which Sb atoms are randomly embedded into the topmost layer of Pt, in a substitutional configuration and without establishing a periodic structure. This disorder is robust against thermal annealing and quenching. Increasing the surface coverage and whether or not the sample is annealed, different well‐ordered Sb phases are formed. The Sb structures synthesized at room temperature without any heating process are best interpreted as surface alloys that involve only the first atomic layer. In contrast, experimental evidence points towards the development of multilayer alloy phases for the annealed samples.

Superconductivity and other phases in graphene multilayers, without twists

1. Isospin magnetism and spin-triplet superconductivity in Bernal bilayer graphene Authors: Haoxin Zhou, Yu Saito, Liam Cohen, William Huynh, Caitlin L. Patterson, Fangyuan Yang, Takashi Taniguchi, Kenji Watanabe, and Andrea F. Young arXiv:2110.11317 2. Superconductivity in rhombohedral trilayer graphene Authors: Haoxin Zhou, Tian Xie, Takashi Taniguchi, Kenji Watanabe, and Andrea F. Young Nature 598, 434–438 […]

Passive Thermal Management in Lithium-Ion Battery Systems via Multilayered Phase Change Materials

With the emerging presence of lithium-ion batteries in aerospace vehicle applications, weight, volume, and safety of lithium-ion battery packs must be addressed with renewed concernment. A thermal runaway event of a single cell can generate temperatures exceeding 600°C, potentially destroying the entire battery pack along with sensitive equipment critical to vehicle operations. If thermal runaway could be contained to a single cell, it would substantially reduce the risk of damage to the vehicle, potentially enabling mission operations to continue. Due to their relatively low mass, low thermal conductivity, versatile formability, and high heat absorption properties, phase change materials (PCM) are a strong candidate for engineering thermal management into lithium-ion battery packs. Herein, seven PCM-based pads, enhanced by novel flame-retardant and intumescent coatings, are evaluated for their ability to prevent thermal runaway propagation. Thermal runaway is initiated via nail penetration in modules of three 11.7Ah, pouch format, NMC lithium-ion cells at 100% SOC, with a pad between each cell. Computational models of the pad samples are developed based on the experimental data, and are also presented in this work.