Dual-layer Structures Research Articles

Flat double-layer metal-only metasurface with polarization-dependent operation in a C/X dual band

In this communication, a dual-band, orthogonal polarization transmission metasurface antenna operating at 6.5 GHz and 9.5 GHz is proposed. The element of this transmitarray is composed of only two identical layers of metal plates, with air medium filling the space between the upper and lower layers. Each layer has four sets of staggered I-slots, thus ensuring dual-frequency orthogonal polarization operation. Moreover the proposed element overcomes the challenge of achieving full 360-degree phase shift in dual-layer metal-only structures without any additional connecting elements. By altering the length of the slots, it can achieve a continuous full 360-degree phase shift while maintaining a transmission amplitude above −2 dB and exhibits co-polarized transmission in both bands. Then a prototype containing 16 × 16 elements is designed and fabricated to verify the feasibility of the design scheme. The measurement results, which are consistent with the simulation, demonstrate that the maximum gains of 24.85 and 27.64 dBi are obtained at 6.4 GHz and 9.4 GHz, with corresponding aperture efficiencies of 23.18% and 20.4% and a 3-dB gain bandwidth of 15.6% and 22.34%. The good transmission coefficients of the element and the dual-band capability make the design a competitive candidate for satellite and high-power applications.

Bioinspired, surfactant-free, dual-layer asymmetric structures based on polysaccharides, gelatin, and tannic acid for potential applications in biomedicine

The formation of dual-layer asymmetric porous structures in surfactant-based systems is significantly influenced by emulsions. Surfactants self-assemble to alter the conformational arrangement of polysaccharides, while gravity disrupts the initial uniformity of the established equilibrium droplet concentration gradient in the emulsion, thus achieving delamination. Specifically, high-speed rotation and non-instantaneous freezing allow the gelatin solution to form two different states of foam layers. The integrated dual-layer asymmetric porous structure, composed of polysaccharides and tannic acid, is constructed with gelatin as a skeleton and surfactant. This innovative approach eliminates the need to consider the toxicity of chemically synthesized surfactants and expands the concept of gelatin utilization. This intriguing structure exhibits a variety of desirable characteristics within 30 days (e.g., tailorable performance, ultrarapid antioxidant activity, efficient antibacterial activity, low differential blood clotting index, and good hemocompatibility and cytocompatibility), suggesting its potential as a valuable reference for applying hierarchical porous structures, thereby offering more formulation flexibility for biomaterials with adjustable properties.

Filtration of a multi-serotype glycoconjugate vaccine drug product through sterilizing grade 0.2/0.22µm pore size filters.

Glycoconjugate vaccines containing multiple serotypes of a bacterial capsular polysaccharide can provide strong immune protection against pathogenic infections. Sterile filtration is an important component of the fill and finish operations in the preparation of these vaccines, with the capacity of the sterile filter limited by membrane fouling. The objective of this study was to examine the performance of a range of commercial 0.2/0.22µm nominal pore size sterilizing grade filters with both single-layer and dual-layer structures during filtration of a glycoconjugate vaccine drug product consisting of four polysaccharide serotypes. The highly asymmetric Millipore Express showed much higher capacity than the more homogeneous filters, with the support structure of the Express acting as a prefilter that was able to remove foulants thereby protecting the small pores in the size-selective skin layer. This behavior was confirmed by performing experiments with different batch prefilters and by examining the location of foulant deposition within the sterile filters using confocal microscopy. These results provide important insights into the factors controlling fouling by these multiserotype vaccines as well as a framework for increasing the capacity of the sterile filter.

On the Importance of MPL Structural Characteristics for PEM Fuel Cell Performance

Gas diffusions layers (GDLs) constitute vital subcomponents of proton exchange membrane fuel cells (PEMFCs) since they participate in all relevant transport processes (gases, vapor, liquid water, electricity and heat).Meanwhile, state-of-the-art GDLs are produced on commercial scale using high volume reel-to-reel (R2R) processes. In almost any case, GDLs are designed as dual-layer structures with a macro-porous carbon fiber-based substrate (backing) and a micro-porous layer (MPL) consisting of carbon particulates bonded with polytetrafluoroethylene (PTFE) binder. A body of scientific work has verified that different aspects of the MPL microstructure and the MPL/macroporous substrate interface play a substantial role in the water management of PEMFCs [1-6].A systematic study was performed based on a singular backing using different MPL types and penetration levels.A simple method to estimate the micro-porous layer penetration in gas diffusion layers based on data obtained from force-deflection behavior of backings and MPL-coated GDLs is proposed. Comparison with SEM and previously published tomographic studies shows that a good estimate for the extent of MPL intrusion into the backing is obtained.MPL loading and penetration is shown to affect different ex-situ GDL properties (in-plane gas permeability, electrical and thermal conductivity) as well as the GDL single cell performance characteristics with respect to humification and high current density operation.Keywords: Gas diffusion layers, Microporous Layer, PEMFC fuel cells Weber, and J. Newman, “Effects of microporous layers in polymer electrolyte fuel cells”, J. Electrochem. Soc. 152, A677-A688 (2005).Lee, R. Yip, P. Antonacci, N. Ge, T. Kotaka, Y. Tabuchi, and A. Bazylak, Synchrotron investigation of microporous layer thickness on liquid water distribution in a PEM fuel cell, J. Electrochem. Soc. 162, F669-F676 (2015).Zhou, S. Shukla, A. Putz, and M. Secanell, “Analysis of the role of the microporous layer in improving polymer electrolyte fuel cell performance”, Electrochim. Acta. 268, 366-382 (2018).Cho, J. Park, H. Oh, K. Min, E. Lee, and J.Y. Jyoung, “Analysis of the transient response and durability characteristics of a proton exchange membrane fuel cell with different micro-porous layer penetration thicknesses”, Appl. Energy 111, 300-309 (2013).T. Gostick, M. A. Ioannidis, M. W. Fowler, and M. D. Pritzker, “On the role of the microporous layer in PEMFC operation.”, Electrochem. Comm. 11, 576-579 (2009).P. Ramasamy, E. C. Kumbur, M. M. Mench, W. Liu, D. Moore, and M. Murthy, “Investigation of macro- and micro-porous layer interaction in polymer electrolyte fuel cells”, Int. J. Hydrogen Energy 33, 3351-3367 (2008).

Characterization of a High-performance PCF-SPR Sensor for Biomedical Applications

Background: Surface plasmon resonance (SPR) based fibre optic sensors are becoming increasingly popular in biomedical applications. However, the sensor performance is degraded because of low sensitivity with inadequate detection accuracy and figure of merit. Objectives: The first objective of this study is to design a D-shaped photonic crystal fibre (PCF) using COMSOL multiphysics. The second objective is to enhance the performance of the designed sensor in terms of sensitivity and detection accuracy using single and dual metal layer structures. In addition, the performance of the proposed sensor is compared with the existing one. Methods: In this study, the performance of the PCF-SPR sensor is improved using a D-shaped photonic crystal fibre (PCF) and two metals as grating layers. The work in this paper is divided into two parts. In the first part, the gold metal layer with optimized thickness is used to achieve good sensitivity. In the second part, the combination of gold and silver dual metal layers with optimized thickness is used to achieve good detection accuracy. Moreover, the performance of the proposed sensor is compared to other published D-shaped PCF sensors. Results: The proposed D-shaped PCF-SPR sensor is designed and simulated using COMSOL multiphysics. The results in terms of sensitivity (S) and detection accuracy (DA) are obtained using a single metal layer and dual metal layers with optimum thickness. Moreover, the transmission coefficient and loss curve have been calculated using different refractive indices of the material. In addition, the simulation results are validated for cancer detection using the proposed sensor. Conclusion: An improvement of the D-shaped PCF sensor for cancer detection is presented in terms of S and DA using single or dual metal layer structures and COMSOL multiphysics. In a single metal layer structure, only gold is used as a grating layer, and the thickness of the grating layer is optimized for achieving high sensitivity. Similarly, a combination of gold and silver is used as the grating layer in the dual metal layer structure for achieving a high DA. Moreover, the obtained results of the proposed PCFSPR sensor are compared with the published results and found that the proposed sensor can be used with a high degree of S and DA for biomedical applications and also can be used in the bio-sensing field.

An MD-based physical characteristics analysis on the PI/EP duo-layer composites, impacting of diamino groups

Owing to the possible interfacial mismatching, the insulation performance in the polyimide-Epoxy (PI-EP) dual-layer composite structures would be reduced. In this paper, molecular dynamics simulations are used to study changes in various key physical characteristics of PI-EP composites agented by diamino groups, as well as the in-depth mechanisms. Particularly, the thermal-dynamics and dielectric characteristics were analyzed. Results indicated that agented by 4,4′-Diaminodiphenyl sulfur (SDA), the glass transition temperature was increased by 5 %, coefficient of thermal conductivity was increased by 18 %, and dielectric permittivity was reduced by 6 %. In addition, the density functional theory based calculations were applied to clarify the effects of diamino groups on the physical characteristics of the duo-layer composite structures, in the scope of electronics and energies. Agented by SDA, the duo-layer PI-EP composite is more suitable for the solid insulation of power electronics transformers.

Electrical Insulation and Radar-Wave Absorption Performances of Nanoferrite/Liquid-Silicone-Rubber Composites.

Novel radar-wave absorption nanocomposites are developed by filling the nanoscaled ferrites of strontium ferroxide (SrFe12O19) and carbonyl iron (CIP) individually into the highly flexible liquid silicone rubber (LSR) considered as dielectric matrix. Nanofiller dispersivities in SrFe12O19/LSR and CIP/LSR nanocomposites are characterized by scanning electronic microscopy, and the mechanical properties, electric conductivity, and DC dielectric-breakdown strength are tested to evaluate electrical insulation performances. Radar-wave absorption performances of SrFe12O19/LSR and CIP/LSR nanocomposites are investigated by measuring electromagnetic response characteristics and radar-wave reflectivity, indicating the high radar-wave absorption is dominantly derived from magnetic losses. Compared with pure LSR, the SrFe12O19/LSR and CIP/LSR nanocomposites represent acceptable reductions in mechanical tensile and dielectric-breakdown strengths, while rendering a substantial nonlinearity of electric conductivity under high electric fields. SrFe12O19/LSR nanocomposites provide high radar-wave absorption in the frequency band of 11~18 GHz, achieving a minimum reflection loss of −33 dB at 11 GHz with an effective absorption bandwidth of 10 GHz. In comparison, CIP/LSR nanocomposites realize a minimum reflection loss of −22 dB at 7 GHz and a remarkably larger effective absorption bandwidth of 3.9 GHz in the lower frequency range of 2~8 GHz. Radar-wave transmissions through SrFe12O19/LSR and CIP/LSR nanocomposites in single- and double-layered structures are analyzed with CST electromagnetic-field simulation software to calculate radar reflectivity for various absorbing-layer thicknesses. Dual-layer absorbing structures are modeled by specifying SrFe12O19/LSR and CIP/LSR nanocomposites, respectively, as match and loss layers, which are predicted to acquire a significant improvement in radar-wave absorption when the thicknesses of match and loss layers approach 1.75 mm and 0.25 mm, respectively.

Transition between growth of dense and porous films: theory of dual-layer SEI.

The formation of passivating films is a common aging phenomenon, for example in weathering of rocks, silicon, and metals. In many cases, a dual-layer structure with a dense inner and a porous outer layer emerges. However, the origin of this dual-layer growth is so far not fully understood. In this work, a continuum model is developed, which describes the morphology evolution of the solid-electrolyte interphase (SEI) in lithium-ion batteries. Transport through the SEI and a growth reaction governed by the SEI surface energies are modelled. In agreement with experiments, this theory predicts that SEI grows initially as a dense film and subsequently as a porous layer. This dynamic phase transition is driven by the slowing down of electron transport as the film thickens. Thereby, the model offers a universal explanation for the emergence of dual-layer structures in passivating films.

An optical fiber temperature/pressure sensor with dual-layer Fabry-Perot cavity structure for sensitivity enhancement

The multiple transfer method was used to fabricate two kinds of dual-layer composite structures for analysing the response of the dual-layer Fabry-Perot cavity structure. It’s proved that the sensitivity can be enhanced more than 20 times by optimizing the film layer parameters and combination methods of the dual layers.

Layered CMOS SPADs for Low Noise Detection of Charged Particles

This paper reports the characterization of SPAD arrays fabricated in a 150 nm CMOS technology in view of applications to the detection of charged particles. The test vehicle contains SPADs with different active area and operated with different quenching techniques, either passive or active. The set of devices under test (DUTs) consists of single-tier chips, about 30 mm2 in area, with dual-tier structures where two chips are face-to-face bump bonded to each other. In the dual-layer structure obtained in this way, the coincidence signal between overlapping SPAD pairs is read out, with a beneficial impact on the dark count noise performance. The DUT characterization was mainly focused on studying the breakdown voltage in the single-layer arrays and the dark count rate (DCR), measured in different working conditions, in both the single- and the dual-layer structures. Comparison between the DCR performance of the two configurations clearly emphasizes the advantage of the coincidence readout architecture.

Laser-cladding and interface evolutions of inconel 625 alloy on low alloy steel substrate upon heat and chemical treatments

Dual-layer structures of inconel 625 (In625) alloy have been deposited by laser-cladding on low alloy steel substrates for corrosion protections at elevated temperatures. Structural and morphological characterizations, before and after treatments in molten salts and/or acidic solutions, reveal absence of corrosions of the In625 layer except for a ~ 2-μm-thick Cr2O3 layer formed on its surface. However, the heat treatments give rise to remarkable δ-Ni3Nb precipitations along with an in-plane lattice shrinkage [i.e., εγ(111) = −0.26%] of the In625 layer; the former are replaced by carbides (i.e., M3C/M23C6) while the latter is increased to εγ(111) = −0.66% when approaching the In625/MS interface. Chemical treatments reveal a much faster material removal from the heat affected zone (HAZ), RHAZ, than those from the base material of the substrate, RS. They also reveal an in-plane lattice expansion [i.e., εγ(111) = 0.31%] of the In625 layer near the interface along with the material removal. In comparison, after the heat treatment, RHAZ became smaller than RS and, meanwhile, the shrunken in-plane lattices do not exhibit any expansions upon the chemical etching. These observations provide evidence that both the carbide precipitations and the local strains play an important role in the interface stability of the laser-cladded In625/Steel structures upon heat and/or chemical corrosions.

Enhanced Luminous Efficacy of White LED with Flat Dual-Layer Remote Phosphor Structure

This paper shows the differences in luminous fluxes of two distinguishing dual-layer remote phosphor structures, Flat Dual-Remote Phosphor (FDRP) and Concave Dual-Remote Phosphor (CDRP). The impact of the distance between the two phosphor layers (d_1) and the distance from the phosphor layer to the LED surface (d_2) on the optical properties of the CDRP is also presented. Specifically, when d_1 and d_2 are varied, the scattering and absorption characteristics of the remote phosphor layer change dramatically, which enormously influences the color uniformity and illumination capability of WLEDs. The concentration of YAG:Ce3+ phosphor also needs to be modified so that the correlated color temperature of WLEDs could be maintained at 8500K when d_1 and d_2 are adjusted. In case d_1 = d_2 = 0, the scattering and absorption in the remote phosphor layer are minimal, leading to the infinitesimal color and luminous flux. When d_1 and d_2 get bigger, the scattering surface increases and that the blue and yellow rays are blended becomes more uniform, leading to the minimum white light deviation as well as the lowest luminous flux. According to the studied results, the lumen output can be maximum at 1020lm if d_1 = 0.08mm or d_2 = 0.63mm while the smallest color deviation occurs when d_1 = 0.64mm or d_2 = 1.35mm. Therefore, the researched results will provide further information for choosing the suitable d_1 and d_2 in order to improve the quality of WLEDs.

The impact of the carrier concentration and recombination current on the p+pn CZTS thin film solar cells

One of the main causes of low performance of Cu2ZnSnS4 (CZTS) based thin film solar cells is its high recombination current. In this paper, the effects of the carrier concentration and recombination current in the CZTS thin film solar cells have been carefully scrutinized. In continue, for comparison and validation, two simulated structures based on the CZTS absorber layer have been reproduced and the influence of the absorber layer defects and carrier concentration has been analyzed. In this work, two different structures using p+-CZTS intermediate layer (between the CZTS absorber layer and Mo back-contact) and dual CZTS layer have been proposed and optimized to decrease recombination and extract the desired photovoltaic parameters. By using and optimizing these structures as p+pn junction, 15.62% and 19.08% efficiencies have been achieved in p+-CZTS intermediate layer and p+pn CZTS dual layer structures, respectively. The highest efficiency of dual absorber based solar cell is achieved when the carrier concentration of the p+-CZTS and p-CZTS absorber layers is 1 × 1018 cm−3 and 5 × 1015 cm−3, respectively. Moreover, the optimum thickness of the p+-CZTS and p-CZTS absorber layers in p+pn CZTS dual layer structure is 1 and 1.5 µm, respectively. Finally, the total recombination current density is reduced to 2.05 mA/cm2.

Tensile and wettability properties of electrospun polycaprolactone coated with pectin/polyaniline composite for drug delivery application

Purpose Over the years, electrical stimulation in drug delivery system holds particular interest in producing spatially and temporally controlled release mechanism. These systems helped in localized doses drugs to be administrated and response efficiently at target site to achieve excellent healing effect in control microenvironment. Extensive research is needed in order to develop versatile electroactive biomaterials in the field of therapeutics applications. This paper aims to discuss this issue. Design/methodology/approach This work reports the development of polycaprolactone (PCL) electrospun coated with pectin/polyaniline (PANi) composite, which has been characterized and whose drug delivery application is ascertained. The composite has been characterized on its mechanical conductivity and wettability properties to evaluate best formulation. The analysis on morphological properties using scanning electron microscope (SEM) confirmed the formation of the dual-layer electro-responsive composite. Findings Among different formulations studied, the pectin/PANi composition (12 percent/3 percent) was found to be an optimized composition with ultimate tensile strength of 55.48±0.65 MPa and modulus strength of 63.30±0.43 MPa with 2.41×10–3 Scm−1 electrical percolation. The hydrophobic PCL electrospun reduced as coating material was introduced on top with optimum of 85.3 percent degree of swelling and water contact angle at 39.17±0.67°. SEM micrograph revealed strong interaction between dual-layer structures with interconnected porous of uniform fibers. Originality/value Overall, these data present a multiangle initial characterization of this novel dual-layer electro-responsive composite for applications in drug delivery. However, additional analysis should be performed in order to provide a clear verification as drug delivery scaffold.

In situ preparation of hierarchically structured dual-layer TiO2 films by E-spray method for efficient dye-sensitized solar cells

Hierarchically-structured mesoporous TiO2 films are prepared by the electrospray (E-spray) method. The microstructures of TiO2 films can be feasibly tuned as spheres or nanocrystalline-mixed spheres, rendering in situ preparation of TiO2 dual-layer. With these dual-layer TiO2 films as photoanode and N719 as sensitizer, the dye-sensitized solar cell achieves a power conversion efficiency (PCE) of 8.96%, which is among the best of N719 devices so far, and constituting up to 19% improvement relative to single-layer TiO2 photoanode based devices. To disclose the mechanism for the improvement, corresponding samples are prepared and investigated by scanning electron microscopy, electrochemical impedance spectroscopy, diffuse reflectance spectra. It was found that the dual-layer photoanode can simultaneously incorporate high dye loading and low charge transfer resistance, leading to high short current density and thus high PCE. Different to other reported dual-layer photoanodes, which often need two or more preparing procedures, only one step is needed in this work. To our best knowledge, it is the first time to employ only one step to in situ prepare photoanodes with dual-layer structures, which greatly simplifies the experimental processes.

Revealing SEI Morphology: In-Depth Analysis of a Modeling Approach

In this article, we present a novel theory for the long term evolution of the solid electrolyte interphase (SEI) in lithium-ion batteries and propose novel validation measurements. Both SEI thickness and morphology are predicted by our model as we take into account two transport mechanisms, i.e., solvent diffusion in the SEI pores and charge transport in the solid SEI phase. We show that a porous SEI is created due to the interplay of these transport mechanisms. Different dual layer SEIs emerge from different electrolyte decomposition reactions. We reveal the behavior of such dual layer structures and discuss its dependence on system parameters. Model analysis enables us to interpret SEI thickness fluctuations and link them to the rate-limiting transport mechanism. Our results are general and independent of specific modeling choices, e.g., for charge transport and reduction reactions.

Improvement in the electrical performance and bias-stress stability of dual-active-layered silicon zinc oxide/zinc oxide thin-film transistor**Projected supported by the National Natural Science Foundation of China (Grant Nos. 61076113 and 61274085), the Natural Science Foundation of Guangdong Province (Grant No. 2016A030313474), and the University Development Fund (Nanotechnology Research Institute, Grant No. 00600009) of the University of Hong Kong, China.

Si-doped zinc oxide (SZO) thin films are deposited by using a co-sputtering method, and used as the channel active layers of ZnO-based TFTs with single and dual active layer structures. The effects of silicon content on the optical transmittance of the SZO thin film and electrical properties of the SZO TFT are investigated. Moreover, the electrical performances and bias-stress stabilities of the single- and dual-active-layer TFTs are investigated and compared to reveal the effects of the Si doping and dual-active-layer structure. The average transmittances of all the SZO films are about 90% in the visible light region of 400 nm–800 nm, and the optical band gap of the SZO film gradually increases with increasing Si content. The Si-doping can effectively suppress the grain growth of ZnO, revealed by atomic force microscope analysis. Compared with that of the undoped ZnO TFT, the off-state current of the SZO TFT is reduced by more than two orders of magnitude and it is 1.5 × 10−12 A, and thus the on/off current ratio is increased by more than two orders of magnitude. In summary, the SZO/ZnO TFT with dual-active-layer structure exhibits a high on/off current ratio of 4.0 × 106 and superior stability under gate-bias and drain-bias stress.

Single-Compound Complementary Split-Ring Resonator for Simultaneously Measuring the Permittivity and Thickness of Dual-Layer Dielectric Materials

This paper presents the design and analysis of a single-compound complementary split-ring resonator (SC-CSRR) that induces two resonance frequencies for simultaneously measuring the thickness and permittivity of dual-layer dielectric structures. Two resonance frequencies were generated using two distinct embedded resonator current lengths in a single complementary split-ring resonator. These two resonance frequency responses were combined to determine the thickness and permittivity of a dual-layer dielectric sample. Methods proposed in this paper were used to analyze the equivalent permittivity relationship, and thus, determine the thickness and permittivity of the material under test. The proposed simple low-cost SC-CSRR measurement method for assessing the permittivity of materials in a compact area was experimentally analyzed and verified in experiments. The experimental results indicated that the average thickness and permittivity measurement errors were 6.26% and 4.63%, respectively, for single-layer samples, and 5.26% and 6.48%, respectively, for dual-layer samples.

Hierarchical decoration of anodic TiO2 nanorods for enhanced photocatalytic degradation properties

In the present work vertically aligned TiO2 nanorods were fabricated by anodization of Al/Ti dual layer structures. Anodization of Al leads to the formation of a porous alumina layer which is used as a template for the growth of TiO2 nanorods. We have studied the characteristics of these nanorods after annealing by high resolution TEM, showing a core–shell structure along the length of the nanorods formed from the expansion of the TiO2 nanorod into the alumina template during growth. Modification of the nanorods by spin coating of a solution of titanium isopropoxide (TIPO) in isopropanol yields enhanced photocatalytic activity up to 12 times due to the increase in surface area, light absorption volume, and the creation of a crystalline coating with an anatase-phase.

Electrical Conduction and Reliability in Dual-Layered Graphene Heterostructure Interconnects

Dual-layer graphene (DLG) interconnects with hexagonal boron nitride ( h -BN) as intercalated insulating layer have been demonstrated. The DLG employs graphene grown by chemical vapor deposition process with h -BN serving as a barrier preventing interlayer scattering, which degrades carrier transport in multilayer graphene. The conductive behavior in dual-layer structures is compared with monolayer graphene and randomly stacked bilayer graphene. Reduced resistance is observed in DLG, which exhibits higher current-carrying capacity and maximum power density. In addition, DLG wire is shown to be robust under constant voltage stressing (10 V) at an elevated temperature (150 °C) with the mean time to failure $\sim 75$ times higher than that of stacked bilayer graphene wires.