Double-layer Surface Research Articles

Mechanical reconfigurable infrared filter for stress sensing applications

In this study, we introduce a novel tunable infrared filter design aimed at stress sensor applications such as health monitoring, advanced robotics and industrial automation. The design utilizes a double-layer plasmonic frequency-selective surface (FSS) of indium tin oxide (ITO) with an aerogel inter-space region. The unique feature of this design is its ability to control the transmission pattern based on the stress exerted, which alters the distance between the two filter layers. Our approach employs both numerical simulations and a simplified model grounded in equivalent circuit theory and the transfer matrix method for accurate transmission pattern estimation where the sensor achieved a sensitivity of 20nm/MPa for average stress of 14MPa and spectrum range (λ>800nm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\lambda >800 nm$$\\end{document}). The work provides an in-depth analysis of how layer dimensions and inter-layer distance influence both transmission and force, taking into account the elastic properties of the inter-space material.

Simulation analysis of a photonic crystal fiber refractive index sensor based on a double-layer film structure and surface plasmon resonance technology

A photonic crystal fiber surface plasmon resonance sensor based on a double-layer membrane structure is designed and analyzed. In the simple sensing structure with only one air hole size, TiO2 and Au layers with specific thicknesses are sequentially coated on the optical fiber to form a double-layer structure. The sensing characteristics of the double-layer membrane structure are studied by the finite element method. Compared to the single-layer membrane structure, the double-layer membrane sensor has significant sensing properties such as a better wavelength sensitivity and a smaller full width at half maximum in the loss spectrum. In the refractive index range between 1.37 and 1.43, the maximum wavelength sensitivity and average wavelength sensitivity of the sensor are 19,900 nm/RIU and 7417 nm/RIU, respectively, and the resolution can be up to 5.03×10−6RIU. The proposed photonic crystal fiber optic sensor achieves high performance with a simpler sensing structure than previous photonic crystal fiber optic sensors, and eliminates the step of polishing, which will greatly reduce the difficulty of actual fabrication and the error due to uneven polishing. The results show that the photonic crystal fiber optic sensor with a double-layer membrane structure has excellent performance. Due to its high sensitivity and resolution, it has great potential for applications in environmental monitoring, biosensing and chemical sensing.

Dispersion control and radiation based on glide-symmetric spoof surface plasmon polaritons

Glide symmetry transmission line (TL) is a highly symmetric TL with characteristics such as reduced frequency dispersion and merged passband. The dispersion characteristics and field distribution of single-layer and double-layer spoof surface plasmon polaritons (SSPPs) unit with glide symmetry are studied in this paper. It is found that the double layer structure with stronger slow wave effect is more suitable for frequency scanning radiation with higher scanning rates. Thus, T-shaped glide symmetric double-layer unit is proposed. Such unit exhibits stronger field confinement and higher degrees of freedom in modulating dispersion characteristics. Besides the basic transmission characteristic, additional radiation characteristic based on such T-shaped glide symmetric double-layer units performs well with continuously beam scanning in a large frequency and angle range. Experimental results agree well with numerical simulations, demonstrating the superior performance of T-shaped glide symmetric double-layer SSPPs. The radiation method of such T-shaped glide symmetric double layer SSPPs can be applied to antenna design, which is conductive to the development of highly compact plasmonic integrated circuits and systems.

Unraveling the role of boron dimers in the electrical anisotropy and superconductivity in boron-doped diamond

We use quantum mechanics (QM) to determine the states formed by B dopants in diamond. We find that isolated B sites prefer to form BB dimers and that the dimers pair up to form tetramers (BBCBB) that prefer to aggregate parallel to the (111) surface in the <110> direction, one double layer below the H-terminated surface double layer. These tetramers lead to metallic character (Mott metal Insulator Transition) with holes in the valence band near the Γ point and electrons in the BBCBB tetramer promoted band along the X direction. Our experiments find very significant anisotropy in the superconductivity for boron-doped diamond thin films prepared with Microwave Plasma Assisted Chemical Vapor Deposition using deuterium-rich plasma. This leads to much higher conductivity in the X direction than the Y direction, as predicted by the QM. This phase transition to the anomalous phase is linked with the emergence of boson quantum entanglement states behaving as a bosonic insulating state. These anisotropic superconducting properties of the diamond film might enable applications such as single-photon detectors. We expect that this formation of a dirty superconductivity state is related to the BBCBB tetramers found in our QM calculations.

Impact Wear Behavior of the Valve Cone Surface after Plasma Alloying Treatment

Valves are prone to wear under harsh environments, such as high temperatures and reciprocating impacts, which has become one of the most severe factors reducing the service life of engines. As a lightweight ceramic, CrN is considered an excellent protective material with high-temperature strength and resistance to wear. In this study, a CrN coating was applied onto the valve cone surface via double-layer glow plasma surface metallurgy technology. The formation process, microstructure, phase composition, hardness, and adhesion strength were analyzed in detail. Impact wear tests were conducted on the valve using a bench test device. The SEM and EDS results showed that the CrN coating evolved from an island-like form to a dense, cell-shaped surface structure. The thickness of the coating was approximately 46 μm and could be divided into a deposition layer and a diffusion layer, from the outer to the inner sections. The presence of element gradients within the diffusion layer proved that the coating and substrate were metallurgically bonded. The adhesion strength of the CrN coating measured via scratch method was as high as 72 N. The average Vickers hardness of the valve cone surface increased from 377.1 HV0.5 to 903.1 HV0.5 following the plasma alloying treatment. After 2 million impacts at 12,000 N and 650 °C, adhesive wear emerged as the primary wear mode of the CrN coating, with an average wear depth of 42.93 μm and a wear amount of 23.49 mg. Meanwhile, the valve substrate exhibited a mixed wear mode of adhesive wear and abrasive wear, with an average wear depth of 118.23 μm and a wear amount of 92.66 mg, being 63.7% and 74.6% higher than those of the coating. Thus, the CrN coating showed excellent impact wear resistance, which contributed to the enhancement of the service life of the valve in harsh environments.

Relation between Double Layer Structure, Capacitance, and Surface Tension in Electrowetting of Graphene and Aqueous Electrolytes.

Deciphering the mechanisms of charge storage on carbon-based materials is pivotal for the development of next-generation electrochemical energy storage systems. Graphene, the building block of graphitic electrodes, is an ideal model for probing such processes on a fundamental level. Herein, we investigate the thermodynamics of the graphene/aqueous electrolyte interface by utilizing a multiscale quantum mechanics-classical molecular dynamics (QM/MD) approach to provide insights into the effect of alkali metal ion (Li+) concentration on the interfacial tension (γSL) of the charged graphene/electrolyte interface. We demonstrate that the dependence of γSL on the applied surface charge exhibits an asymmetric behavior relative to the neutral surface. At the positively charged graphene sheet, the electrowetting response is amplified by electrolyte concentration, resulting in a strongly hydrophilic surface. On the contrary, at negative potential bias, γSL shows a weaker response to the charging of the electrode. Changes in γSL greatly affect the total areal capacitance predicted by the Young-Lippmann equation but have a negligible impact on the simulated total areal capacitance, indicating that the EDL structure is not directly correlated with the wettability of the surface and different interfacial mechanisms drive the two phenomena. The proposed model is validated experimentally by studying the electrowetting response of highly oriented pyrolytic graphite over a wide range of electrolyte concentrations. Our work presents the first combined theoretical and experimental study on electrowetting using carbon surfaces, introducing new conceptual routes for the investigation of wetting phenomena under potential bias.

Fabrication of double imprinted anchor points in cellulose nanocrystals-based hierarchical porous polyHIPEs for selective separation of flavoniods under physiological pH

Previous research had proved that molecular imprinted polymers can be used as separation material for removing Naringin (NRG) from agricultural pomelo wastes effectively. But the adsorption amounts of NRG molecules from traditional MIPs was quite low by using boronic acid as functional monomer because of single affinity interaction. Therefore, we developed the new combination of bifunctional monomers (i.e. low pKa boronate affinity monomer 2,4-difluoro-3-formylphenylboronic acid and dopamine) based on cellulose nanocrystals (CNCs) mixed with polymerized high internal phase emulsion (polyHIPE, PH) through an double layer surface imprinted method. The introduction of polyethylenimine (PEI) can offer abundant anchor units for the growth of more anchor sites to immobilization template molecules. Importantly, largely improved selective adsorption amounts (50.79 μmol g−1), which may be attribute to the fabrication of the uniform growth of double imprinted layers onto the polydopamine (PDA)/boronic acid-based surfaces. In addition, the resulting double recognition molecular imprinted polymers (MIPs) based on hypercrosslinked PH (DR-HCLPH@MIPs) not only exhibited fast adsorption kinetic of NRG molecule, but also possessed excellent selectivity and high adsorption capacities at physiological pH. Meanwhile, the coarse NRG from pomelo waste can be high selectively extracted to 94.74%. Overall, this study provides a versatile approach for fabrication of the sandwich-biscuit-like double imprinting layer porous MIPs for precise identification and ultrafast transport separation of NRG from complex samples.

Residual carbonate karst reservoir reconstructed by karst planation: A case study of Ordovician paleokarst reservoir characterization in Ordos Basin, North China

Based on the global typical karst characteristics reported in recent decades and the latest petroleum and gas exploration results, it is found that the characteristics of the karst reservoirs in the Ordos Basin are dramatically different from those of traditional karst reservoirs, indicating that the main contribution to the formation of the karst reservoirs in the region may not have been karst dissolution. The previous view of the formation mechanism of karst reservoirs suggests that we should think about the formation and development processes of Ordovician karst and the reservoir pores in the Ordos Basin from another perspective. In this investigation of reservoir formation, karstology, geography, sedimentology, and reservoir geology were all utilized. On the basis of the initial understanding of the control of large-scale landforms on the sediments in sedimentary basins, this study focuses more on the dynamic spatial-temporal relationships between the evolutions of the landforms, karsts, and reservoirs. By studying the petrological characteristics, pore filling, karst zonation, and planation model of the weathering crust reservoir in the study area, it has been determined that the primary reservoir space was formed in advance rather than in the supergene dissolution period. A gypsum-containing dolomite flat served as the material foundation for reservoir construction and later karst planation transformation. The penecontemporaneous dissolution dominated the spatial development of the early dolomite reservoir. The traditional karst cycle is actually caused by the erosion of the bottom of the karst floor on the double-layer leveling surface. The karst planation during the Caledonian period played a discontinuous and destructive filling role throughout the entire reservoir zone by changing the diagenetic environment, the main contribution of which was communication between the pores. Therefore, this weathered crust reservoir is actually a residual reservoir controlled by karst planation rather than a traditional karst reservoir. The “sweet spots” are primarily dispersed in the upper portion of the karst slope and the top of the karst residual hillock in the gypsum-containing dolomitic flat environment.

On a stable calculation of the normal to a surface given approximately

The paper proposes a stable method for constructing a normal to a surface given approximately. The normal is calculated as the gradient of the function in the surface equation. As is known, the problem of calculating the derivative is ill-posed. In the paper, an approach is adopted to solving this problem as to the problem of calculating the values of an unbounded operator. To construct its stable solution, the principle of minimum of the smoothing functional in Morozov’s formulation is used. The normal is obtained in the form of a Fourier series in the expansion in terms of eigenfunctions of the Laplace operator in a rectangle with boundary conditions of the second kind. The functional stabilizer uses the Laplacian, which makes it possible to obtain a normal in the form of a Fourier series that converges uniformly to the exact normal vector as the error in the surface definition tends to zero. The resulting approximate normal vector can be used to solve various problems of mathematical physics using surface integrals, normal derivatives, simple and double layer potentials.

Reversible bacteria-killing and bacteria-releasing cotton fabric with anti-bacteria adhesion ability for potential sustainable protective clothing applications

Multifunctional antibacterial surfaces are playing an essential role in various areas. Smart antibacterial materials equipped with switchable “bacteria-killing” and “bacteria-releasing” abilities have been created by scientists. However, most of them are either biologically incompatible, or complex fabricating procedures, or cannot prevent themselves from being attached by bacteria. In this work, a double-layer smart antibacterial surface was created easily by simple surface initiate atom transfer radical polymerization: the upper layer PSBMA provides anti-bacteria adhesion capacity, the NCl bond can show bacteria-killing ability and the under layer PNIPAM can exhibit bacteria-releasing property. Remarkably, the NCl bond can interconvert with the NH bond easily, which allows switching between bacteria-killing and bacteria-releasing. As a result, the functional cotton fabrics can resist about 99.66 % of bacteria attaching, kill nearly 100 % of attached bacteria after 5 min contacting and release about 99.02 % of the formerly attached bacteria. Furthermore, the functional cotton fabric kept excellent anti-bacteria adhesion ability (about 99.27 %) and bacteria-releasing capacity (about 98.30 %) after 9 cycles of re-chlorination. In general, a reversible “bacteria-killing” and “bacteria-releasing” cotton fabric was fabricated with well anti-bacteria adhesion capacity in a simple way, and this smart multifunctional cotton fabric shows a great potential application in reusable protective clothing.

ZnxNi1-xSe2 nanoparticles grown on functionalized nickel foam as binder-free electrocatalysts for HER in acidic and alkaline media

Metal ion doping is considered as an effective approach towards increasing the activity of transition metal selenide-based catalysts for electrocatalytic hydrogen evolution reaction (HER). Herein, we report a one-pot synthesis of Zn doped NiSe2 nanoparticles (ZnxNi1-xSe2, where x = 0.25, 0.50, 0.75) grown on nickel foam (NF) and the efficacy of ZnxNi1-xSe2/NF has been investigated towards electrocatalytic HER. The synthesized materials were systematically characterized and their electrocatalytic HER activity was tested in acidic and alkaline media, among which Zn0.25Ni0.75Se2/NF has demonstrated a relatively higher electrocatalytic performance. Zn0.25Ni0.75Se2/NF required very low overpotentials of 126 mV and 158 mV for HER to attain 10 mA cm−2 current density in 0.5 M H2SO4 and 1 M KOH, respectively. The inherent electrochemical properties such as electrochemical active surface area and double layer capacitance have been measured and Zn0.25Ni0.75Se2/NF has shown superior activity. Also, the binder-free Zn0.25Ni0.75Se2/NF electrocatalyst has illustrated excellent stability during continuous evolution of hydrogen for 12 h in acidic and alkaline medium.

Surface preparation and double layer effect for silane application on electrogalvanized steel

Abstract Silanes are an alternative to replace pretreatments based on Cr(VI) for electrogalvanized steel (ES). As the interaction between the silane and the metal is important to ensure pretreatment efficiency, surface preparation is a critical step. In this sense, the presence of OH groups on the metal surface is essential. In this paper, the surface preparation of ES and a single/double layer application on the corrosion protection afforded by 3-aminopropyltriethoxy silane was studied. The metal surface was cleaned by polishing, electrochemically (employing anodic or cathodic current) or by chemical oxidation. The electrochemical behavior of the cleaned surfaces was analyzed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Afterwards, the hydrolyzed silane was applied in a single or double layer. Coatings were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, EIS and by exposure to the humidity chamber. Coatings applied on ES cleaned by electrochemical anodic processes or chemical oxidation provided the best protective performance due to a lower surface of zinc exposed to the high humidity environment. Double layer coatings improved protection due to more homogeneous and higher Si content, sealing defects and increasing the thickness of the one-layer protection, enhancing the barrier protection of the silane.

Electrochemically Non-Enzymatic Urea Estimation in Human Dialysate Waste Using Indirect NiOOH-Urea Oxidation

Non-enzymatic urea detection in human dialysate offers a sustainable and spontaneous platform for advanced analysis and monitoring. This study investigated urea estimation in dialysate by using an indirect urea oxidation of nickel on nitrogen doped carbon with an incorporation of surface roughness (Rf) and double layer current (Idl). Fascinatingly, the second oxidation peak on (reverse) cathodic scan at 0.42 V vs Ag/AgCl in cyclic voltammetry and the first peak of differential pulse voltammetry (DPV) after background subtraction were evidenced to the exploited NiOOH binding with urea, concurrently with the regeneration of Ni(OH)2. In presence of more urea, the decreasing trends of the oxidation peaks in both techniques were observed and capable of determining urea concentrations in human dialysate. In consideration of actual reaction current, the measured total current after background subtraction in fresh simulated dialysate provides the sensitivity of −5.136 × 10−5 A.mM−1 (R2 = 0.998) and limit of detection of 60.2 μM in 1–5 mM linear range. For validation in patients’ dialysate, the total current peak was normalized by Rf and subtracted from Idl, resulting in excellent urea estimation with recovery percentage between 99.18 and 102.68 in comparison to that of clinical standard, offering future prognostic monitoring and wearable artificial kidney.

Fabrication of the double-layer millimeter wave frequency selective surface by femtosecond laser

With the rapid development of communication technology, frequency selective surface (FSS) operating at higher frequencies is required and it is necessary to design and fabricate new FSS. In this paper, a broadband double-layer FSS is proposed which is composed of one layer of foam, two metal layers, and four layers of substrate. The simulation result shows that a high transmission in the band of 60.03–89.33 GHz (covering the E band) with a relative bandwidth up to 29 % is achieved. In addition, the effects of the key structural parameters, oblique incidence angle, and TE/TM polarization on the transmission performance are further explored. The results indicate that the proposed FSS has good oblique incidence angular stability and polarization insensitivity up to 60°. Finally, the proposed FSS is fabricated by the femtosecond laser and measured by the waveguide method. Experimental results show that the machined sample has high precision and the machining error is within 1 µm, and good agreement between the simulated and measured results is observed. Therefore, the proposed FSS could be used as spatial filters or sub-reflectors of multiband antennas and the corresponding processing method could be extended to other millimeter wave functional devices, such as absorbers, radomes, etc.

Influence of Long-Period Stacked Ordered Phases on Inductive Impedance of Mg-Gd-Y-Zn-Zr-Ag Alloys

In this paper, the influence of long-period stacked ordered (LPSO) phases on the electrochemical impedance spectroscopy (EIS) of a Mg-Gd-Y-Zn-Zr-Ag alloy in 0.9 wt.% NaCl was investigated. The Mg-6Gd-3Y-1Zn-0.5Zr-0.3Ag (wt.%) alloy samples with and without LPSO phases in the grain interior (HOMO and LPSO, respectively) were prepared using different heat treatments. The EIS results showed that both the HOMO and LPSO samples' Nyquist diagrams contained two inductive loops. However, in the Nyquist plots of the LPSO samples, the inductive loops at 1.71-0.67 Hz appeared in the first quadrant rather than the fourth quadrant. Analysis of the fitting parameters illustrated that the abnormal shape of the inductive loops is related to greater values of the surface film capacitance Cf and double layer capacitance Cdl in the LPSO samples. Further investigations through corrosion morphology observation indicated that the greater values of Cf and Cdl in the LPSO samples resulted from the existence of intragranular LPSO phases that created more film-free areas. The above results show that a better understanding of the relationship between the inductive impedance and corrosion morphology of a Mg-6Gd-3Y-1Zn-0.5Zr-0.3Ag alloy in 0.9 wt.% NaCl solution was attained.

Parameter optimization and mechanism research of double-layer variable screen surface vibrating screen

In the vibrating screening operation, each area of the screen surface has a different screening environment, and the material layer thickness, target particle proportion and other parameters of each area are different, which limits the screening efficiency of a vibrating screen with a traditional screen surface. In this paper, a double-deck variable screen surface screening method is proposed to optimize the design of the double-deck screen surface. The relationship between the elements of the screening process, screening parameters and screening efficiency of a double-deck variable screen surface vibrating screen is investigated through DEM numerical simulation. Using the particle swarm algorithm to support the vector regression model for global optimization, the parameters of the double-deck variable screen surface vibrating screen further optimized to obtain screening parameters: screen area A screen hole edge length of 4.7 mm, screen area D screen hole edge length of 2.7 mm, screen area D screen surface inclination angle of 6.3°, amplitude 2.6 mm, vibration frequency of 22.2 Hz, vibration direction angle of 35°, and through the experimental prototype for physical experimental verification.

Knudsen force based double beam MEMS vacuum pressure sensor

Knudsen forces are gas molecular forces, generated due to the presence of a thermal gradient between two surfaces in rarefied gas and can be effectively used for the measurement of low pressures. This work reports on a Knudsen force based micro electro mechanical systems low pressure sensor consisting of two stacked beams of polysilicon—one acting as a heater while the other as a sensor. The structure is fabricated using a double sacrificial layer surface micromachining process. The thermal gradient across the two stacked beams is induced by resistive heating of the heater beam. The effect of using two separate beams for heating and sensing has been investigated at different heater current and the results are compared with the existing works. The provision of two beams has resulted in the sensor functioning at very low pressure of less than 0.1 Pa with an improved sensitivity of 15.5 fF mPa−1.

Catalyst layer formulations for slot-die coating of PEM fuel cell electrodes

The series of electrodes were fabricated by the scalable and manufacturable slot-die coating method for proton exchange membrane fuel cell (PEMFC) application. The inks with different amounts of solids were studied by rheological methods in order to establish a coating window with minimum manufacturing defects. The obtained electrodes were characterized by SEM, AFM, and optical microscopy, which showed that they were uniform and homogeneous with minimum defects. The electrochemical evaluation of the manufactured gas diffusion electrodes (GDE) showed that the main characteristics of the electrodes, like electrochemical surface area, proton resistivity, and double layer capacitance, were found to be close for all samples confirming the reproducibility of the slot-die process. Additionally, we studied the effects of membrane thickness on the performance of the GDE membrane electrode assemblies and determined that a decrease in membrane thickness favored the performance. The obtained results clearly demonstrated the applicability and feasibility of the approach for the Manufacturing of catalyst layers for the fuel cell application with potential for future mass production.

Effect of Oil Contamination on the Behavior of Collapsible Soil

Loessial soil is moisture-sensitive soil susceptible to settle when fully saturated. In this study, efforts were made to investigate the effect of oil pollutants on mechanical behavior of soil. The loess soil was contaminated by 2,4,6,8 and 10% dry weight of lamp oil and gasoline. Atterberg limits, direct shear, unconfined compressive strength (UCS) and scanning electron microscope (SEM) tests were performed to evaluate the behavior of oil-contaminated collapsible soils. The results of Atterberg tests showed that the plasticity of the soil decreased, due to the reduction in the thickness of the absorbed surface layer and double water layer. According to the direct shear test, with increasing contamination up to 10% of lamp oil and gasoline, the cohesion of the soil was decreased from 14.5 kPa to 7.3 kPa and 7 kPa, respectively, which was due to the reduction in soil plasticity and diffuse double-layer. Because of the lubrication of soil particles, the internal friction angle of soil was reduced from 18.5° to 13.6° and 13.9° for 10% lamp oil and gasoline. UCS of contaminated soil increased in low strains due to the apparent cohesion of hydrocarbons and it decreased 31% for gasoline and 53% for lamp oil at high strains due to the softening behavior of the contaminated soil. SEM test revealed that hydrocarbons covered the soil particles and changed the soil fabrication to dispersed skeleton. Generally, collapsible soil contaminated with different lamp oil and gasoline contents showed a decrease in shear strength and UCS with increasing oil content.

Weakly-singular symmetric Galerkin boundary element method in thermoelasticity for the fracture analysis of three-dimensional solids

The Symmetric Galerkin Boundary Element Method has demonstrated significant advantages for the fracture mechanics analysis of three-dimensional solid structures. However, when dealing with structures in thermal environments, strongly-singular domain integrals resulting from the temperature field require meshing of the interior of the domain. In this paper, formulation and implementation of the weakly-singular SGBEM of three-dimensional thermoelastic intact and cracked solids are presented where temperature-induced domain integrals are transformed into boundary integrals. The strong singularity of these temperature-induced integrals is reduced to the weak singularity by exploring the feature of double-layer surface integrals in the SGBEM. Obtained temperature-induced boundary integrals affect only the right-hand-side vector of the SGBEM equation, and therefore the advantages of the SGBEM, such as the symmetry of the stiffness matrix, are retained. Several examples of three-dimensional solids with or without cracks subjected to thermal loadings are presented to validate the developed methods. Advantages and disadvantages of SGBEMs with different temperature-induced boundary integrals are also discussed.