Multiple Layer Structures Research Articles

Regulating the Third Metal to Design and Engineer Multilayered NiFeM (M: Co, Mn, and Cu) Nanofoam Anode Catalysts for Anion‐Exchange Membrane Water Electrolyzers

AbstractAlkaline anion‐exchange membrane water electrolyzers (AEMWEs) for green hydrogen production have received intensive attention due to their feasibility of using earth‐abundant platinum group metal (PGM)‐free catalysts. Herein, the third metal is incorporated into NiFe‐based catalysts to regulate their electronic structures and morphologies, aiming to achieve sufficient oxygen evolution reaction (OER) activity and performance in AEMWEs. The ternary NiFeM (M: Cu, Co, or Mn) catalysts are featured with multiple layered structures and nanofoam network morphologies, consisting of highly OER‐active amorphous Ni‐rich oxide shells and electrically conductive metallic alloy cores. The physical and electronic perturbations to the NiFe induced by a third element lead to a fine‐tuning of the redox ability of the metal sites at the reaction centers, which breaks the scaling relationship between OH* and O* intermediates at the reaction centers. Thus, the unique structural configuration and electronic regulation simultaneously benefit catalytic activity and performance improvements. These NiFeM nanofoam catalysts demonstrated promising anode performance in actual AEMWEs, comparable to the IrO2 reference, especially at high current densities. Notably, using various electrolytes (e.g., KOH solution or pure water) for AEMWEs exhibited a different performance trend among studied NiFeM catalysts, likely due to dynamic changes of catalysts under various OER environments.

Informing directed energy deposition strategies through understanding the evolution of residual stress

Residual stress is a critical concern in directed energy deposition (DED) as it impacts the functional performance of components, in terms of load-bearing capacity and corrosion behavior. In this paper, an analytical model is developed to characterize the temperature distribution, residual stress profiles, and geometric distortions in DED-built components, which enables efficient planning of the DED strategies. The model combines a finite difference method to predict the temperature history, modified Green's functions to quantify thermal stress, and a radial return method to update plastic stress, which features the deposition of materials with heat source movement. The predictions are validated against the temperature, residual stress, and distortion profiles reported in the literature. In the fabrication of multiple-layer thin-wall structures, the model demonstrates a maximum prediction error of 18.2% for the peak temperature at the middle of the deposit-substrate interface and 17.7% for the vertical distortion of the deposit-substrate system. Simulation results from the model provide insights into understanding stress evolution in the deposition and offer guidance in the selection of linear energy density parameters (heat source power and traverse speed) and process planning parameters (idle time and deposition patterns) when designing DED strategies for thin-wall structures. This approach can be implemented in an efficient workflow to optimize the DED technologies for specified residual stress profiles within a component geometry regardless of heat source or material type.

Delaminated MnPS3 with Multiple Layers Coupled with Si Featuring Ultrahigh Detectivity and Environmental Stability for UV Photodetection.

Silicon (Si), the dominant semiconductor in microelectronics yet lacking optoelectronic functionalities in UV regions, has been researched extensively to make revolutionary changes. In this study, the inherent drawback of Si on optoelectronic functionalities in UV regions is potentially overcome through heterostructure coupling of delaminated p-type MnPS3, having bulk, multiple-layer, and few-layer features, with n-type Si. By artificially mimicking the architectures of shrubs with unique UV shading phenomena, the revolutionary multiple-layer MnPS3 structures with staggered stacking configurations trigger outstanding UV photosensing performances, displaying an average EQE value of 1.1 × 103%, average photoresponsivity of 3.1 × 102 A/W, average detectivity of 1.9 × 1014 cm Hz1/2W1-, and average on/off ratio of 1.8 × 103 under 365 nm light. To the best of our knowledge, this is the first attempt toward realizing gate-free MnPS3-based UV photodetectors, while all of the photodetection outcomes are better than those of more sophisticated field-effect transistor (FET) designs, which have remarkable impacts on the practicality and functionality of next-generation UV optoelectronics.

Tunable 3D printed composite metamaterials with negative stiffness

The paper proposes a class of tunable metamaterials that use inclined beams to achieve instability in a rigid system. Three different beam tilt angles, 25°, 45°, and 60°, are evaluated in the form of unit cells using quasi-static compression tests and numerical simulations. Snap-through behavirous are characterised by structural stiffness and buckling load. Periodic and gradient structures are assembled and analysed by arranging the unit cells in rows and columns. Size effect analyses and parametric studies are carried out on various unit-cell arrangements and different beam angles. The proposed metamaterials are manufactured through fused filament fabrication 3D printing technology with a composite material, onyx. The results from experiments, finite element analysis, and analytical models are compared and evaluated. The structural stiffness and buckling load are shown to be positively related to the inclination angle of the tilted beams. The number of rows of unit cells governs the nonlinear mechanical response (number of snap-throughs) of multiple-layered structures. By increasing the number of rows and columns of unit cells, which are less prone to manufacturing defects, the reliability and repeatability of the structural properties of periodic/gradient structures could be improved. A design plot is also provided to predict and tune the snap-through behaviour of multiple-layered structures via beam angles and unit-cell arrangements.

Magneto-Orientated Graphite Double-Layer Homo-Structure with Broadband Microwave Absorption

We utilized magnetic fields as an efficient tool to manipulate the orientation and electromagnetic properties of graphite micro-flakes (GMFs). As a result, we successfully developed a GMF double-layer homo-structure, which shows excellent electromagnetic absorption properties. By tuning the direction of a small magnetic field (850 G), vertical and horizontal aligned GMFs are produced. Their electromagnetic parameters are effectively tailored by this magneto-orientation effect, and the vertical and horizontal aligned GMFs achieve good results in terms of impedance matching and microwave absorption. With the combination of these two magneto-orientated layers, vertically oriented as the surficial impedance matching layer and horizontally oriented as the inner loss layer, we design a GMF-based double-layer homo-structure. After thickness optimization, −38.2 dB minimum reflection loss and 6.4 GHz (11.6–18.0 GHz) absorption bandwidth are achieved. Our findings further emphasize the importance of material orientation freedom and provide a magneto-strategy to design multiple-layer structures and to produce high-performance microwave devices.

Dendronized Hyperbranched Polyethyleneimines with Switchable Thermoresponsiveness and Encapsulation

AbstractHyperbranched polyethyleneimines (PEIs) with multiple layered structures and high density of terminal amino groups have shown great potential for applications in biomedicine, sensors, and catalysis. In this work, a kind of dendronized hyperbranched PEIs (DHPs) is synthesized by modification of PEIs with dendritic oligoethylene glycols (OEGs). These DHPs not only inherit the characteristic thermoresponsive behavior from the OEG dendrons, but also show low cytotoxicity and switchable encapsulation capacities. Their thermoresponsive behavior is found to be mainly dependent on the coverage and amphiphilicity of dendritic OEGs, solution pH, and NaCl concentration. Moreover, DHPs exhibit advantages in thermally‐switchable complexation with guest molecules because of their adjustable crowding effect from the densely packed OEG chains. In addition, these DHPs can also be used as nanoreactors, which can reduce metal ions into metal nanoparticles in a convenient way. In virtue of these peculiarities, it is believed that these dendronized hyperbranched PEIs with smart properties can be used as promising scaffolds in drug‐controlled release and nanoreactors.

A Study of Combined Graphical Acoustic Computing and the Depth Peeling Technique on Acoustic Backscattering of Multiple-Layered Structures

An efficient graphical acoustic computing (GRACO) method is introduced. Referring to the rendering of semi-transparent objects, the depth peeling (DP) technique is compounded with the GRACO method, forming a combined GRACO and DP method (GRACO–DP) to consider the backscattering of multiple-layered structures in which the contributions of inner structures are included. After that, some examples of GRACO and GRACO–DP are tested to evaluate the accuracy and efficiency of such methods. Through the examples of impedance sphere and benchmark models, GRACO can acquire results with higher efficiency and good consistency compared to the traditional KA method. Also, the TS of a pair of circular plates is determined by GRACO, GRACO–DP, and the finite element method (FEM). The results show that GRACO–DP can fit better with the FEM results. Moreover, the TS of a ribbed double shell is predicted by both GRACO and GRACO–DP; the features of a Bragg wave scattered by the periodically arranged inner ribs can be spotted from the result of GRACO–DP.

Validation of Bayesian design for broadband microslit panel absorbers using causal inference.

This paper discusses experimental validations of multilayer microslit panels (MSPs) designed via Bayesian inference to obtain both high sound absorption and wide bandwidth simultaneously. Microslit perforation in thin panels is similar to microperforated panels [Xiang, Fackler, Hou, and Schmitt (2022). J. Acoust. Soc. Am. 151(5), 3094-3103]. MSP absorbers in single-layer configurations are functioning in a limited frequency range. By stacking the MSPs in multiple layered structures, absorbing performance may be widened in frequency ranges while retaining high absorption coefficients. Besides design challenges of multiple MSPs in layered structures to fulfill a practical requirement and minimize fabrication complexity, this paper further discusses challenges in experimental validations when experimental results undesirably deviate from the initial Bayesian design. Causation analysis is applied to the validation efforts where a causal model-based inference effectively provides causal reasoning of fabrication inaccuracies. Along with the causal inference, a causal reasoning conducted in this work can guide corrections due to fabrication inaccuracies during the iterative validation process.

Reduced flow model and transmissibility upscaling in multi-layered faulted reservoirs

We construct a new three-scale model for single phase incompressible flow in faulted rocks containing multiple damage zones. At the finer scale (O(1m)), flow is influenced by the high-contrast layered heterogeneities inherent to the core and adjacent damage zones, which are populated by geological anomalies, such as compaction bands, debris, and fine sediments and joints. In the first stage of the reiterated homogenization procedure, we construct a lower-dimensional reduced model, where the discontinuity is envisioned as (n−1)-dimensional manifold (n=2,3), topologically attached to multiple layered structures, with flow patterns characterized by various jumps in pressure and velocity fields. Subsequently, by aligning the fault with the interface between adjacent simulation cells of a coarse grid, the upscaling of the reduced flow model gives rise to transmissibility multipliers, whose constitutive response stems naturally from the local flow patterns, exhibiting improved accuracy compared to the traditional harmonic mean, inherent to the two-point flux approximation. Computational simulations obtained with the finite element method with localized discontinuous spaces illustrate the ability of the three-scale model to provide further insight into the behavior of the transmissibility multipliers, which capture the effects of fault zone texture upon the flow discretization. The methodology proposed herein shows enormous potential for the development of more accurate transmissibility preprocessors at relatively low computational costs, consequently overcoming the shortcomings of a direct application of the local high-fidelity approach.

Digital light processing 3D printing for microfluidic chips with enhanced resolution via dosing- and zoning-controlled vat photopolymerization

Conventional manufacturing techniques to fabricate microfluidic chips, such as soft lithography and hot embossing process, have limitations that include difficulty in preparing multiple-layered structures, cost- and labor-consuming fabrication process, and low productivity. Digital light processing (DLP) technology has recently emerged as a cost-efficient microfabrication approach for the 3D printing of microfluidic chips; however, the fabrication resolution for microchannels is still limited to sub-100 microns at best. Here, we developed an innovative DLP printing strategy for high resolution and scalable microchannel fabrication by dosing- and zoning-controlled vat photopolymerization (DZC-VPP). Specifically, we proposed a modified mathematical model to precisely predict the accumulated UV irradiance for resin photopolymerization, thereby providing guidance for the fabrication of microchannels with enhanced resolution. By fine-tuning the printing parameters, including optical irradiance, exposure time, projection region, and step distance, we can precisely tailor the penetration irradiance stemming from the photopolymerization of the neighboring resin layers, thereby preventing channel blockage due to UV overexposure or compromised bonding stability owing to insufficient resin curing. Remarkably, this strategy can allow the preparation of microchannels with cross-sectional dimensions of 20 μm × 20 μm using a commercial printer with a pixel size of 10 μm × 10 μm; this is significantly higher resolution than previous reports. In addition, this method can enable the scalable and biocompatible fabrication of microfluidic drop-maker units that can be used for cell encapsulation. In general, the current DZC-VPP method can enable major advances in precise and scalable microchannel fabrication and represents a significant step forward for widespread applications of microfluidics-based techniques in biomedical fields.

Speed limitations of resonant tunneling diode-based photodetectors.

In this work, we study multiple epitaxial layer structures incorporating a resonant tunneling diode photodetector utilizing the In0.53Ga0.47As/InP material system for operation at the near-infrared region of 1.55 and 1.31 micrometers. We study the photodetection speed of response for these devices and the physical limitations affecting their bandwidth. We show that resonant tunneling diode-based photodetectors have bandwidth limitations due to the charge accumulation near the barriers and report on an operating bandwidth reaching up to 1.75 GHz in particular structures, which is the highest number reported for such detectors to the authors' best knowledge.

Effect of Line Width and Wall Count on the Compressive Strength of Single and Functionally Graded Additively Manufactured ABS Gyroid Structure

Additive Manufacturing (AM) has been in the manufacturing industry for more than a decade. It has aided in producing several intricate objects for several purposes. One of the most used techniques in AM is fused deposition modeling (FDM) wherein a plastic filament is heated to its melting point and deposited layer by layer in a build plate to form a 3D model. Acrylonitrile butadiene styrene (ABS) is one of the commonly used filaments because of its relatively good impact resistance and toughness, and workability in 3D printing various structures. The gyroid structure is a self-supporting structure that has a good strength-to-weight ratio. The compressive strength of single and multiple-layered structures of ABS gyroid lattice structure with different line widths, infill densities, and wall counts was observed. A 0.35 line width with an infill density of 25% and wall count of 3 has a compressive strength of 11.94 MPa, material consumption of 1.87 grams, and printing time of 14 min which makes it the most efficient design for single-layered structures. Among three-layered structures, the combination of infill densities of 25% and 35% is the most efficient with 0.45 line width and 3 walls. It has a compressive strength of 15.87 MPa, printing time of 13 min, and material consumption of 2.3 grams. Nowadays, there are limited research articles on AM of a single structure with gradual varying densities as well as the effect of lesser-known printing parameters on the mechanical properties of AM parts. This study aims to aid future research by providing data on single and functionally graded structures with different line widths and wall counts. With the information from this study, future researchers and designers can further optimize printing parameters to make an efficient design that is light and has sufficient mechanical strength to serve a specific function.

Recent deep learning models for diagnosis and health monitoring: A review of research works and future challenges

As an important branch of machine learning, deep learning (DL) models with multiple hidden layer structures have the ability to extract highly representative features from the input. At present, fault detection and diagnosis (FDD) and health monitoring solutions developed based on DL models have received extensive attention in academia and industry along with the rapid improvement of computing power. Therefore, this paper focuses on a comprehensive review of DL model–based FDD and health monitoring schemes in view of common problems of industrial systems. First, brief theoretical backgrounds of basic DL models are introduced. Then, related publications are discussed about the development of DL and graphical models in the industrial context. Afterwards, public data sets are summarized, which are associated with several research papers. More importantly, suggestions on DL model–based diagnosis and health monitoring solutions and future developments are given. Our work will have a positive impact on the selection and design of FDD solutions based on DL and graphical models in the future.

Probing actin coated planar lipid bilayers with light and electricity in a microelectrode cavity array.

Planar lipid bilayers play a central role in nanopore sensing and ion-channel electrophysiology. However, bilayer fragility, especially in the presence of osmotic stress, can limit their application. We have been developing methods to enhance the mechanical properties of planar lipid bilayers with a layered, molecularly thin, minimal actin cortex (MAC). Approaches involve both single- and multiple-layered MAC structures (multi-MACs). In this work, we describe the MAC formation process in the context of different microelectrode cavity array chips (MECA and MECA-opto), as well as on glass-supported bilayers. We explore the response of these bilayers to osmotic stress and report single-molecule level imaging results that reveal the kinetic motion of actin filaments on the bilayer. We also discuss our latest permeability tests at both the single-molecule and macroscopic levels that show that multi-MACs do not significantly block access to the bilayer.

Intermixing behavior of 1.4430 stainless steel and 1.4718 valve steel in in situ alloying using coaxial laser double-wire laser directed energy deposition

Coaxial laser wire directed energy deposition promises a direction-independent buildup of near net shape geometries and surface coatings. Simultaneously introducing two different wire materials into the processing zone enables the production of in situ alloyed or even functionally graded structures. Functionally graded materials and in situ alloyed parts aim to extend the range of materials for development purposes. This work covers the intermixing behavior of two wire materials with greatly differing element contents. Therefore, a multiple diode coaxial laser (DiCoLas) processing head is used consisting of three individually controllable fiber coupled laser diodes with a combined maximum output power of 660 W and a wavelength of 970 nm. Two metal wires, 1.4430 and 1.4718, with a diameter of 0.8 mm are provided simultaneously to the processing zone under an incidence angle of 3.5° to the processing head's middle axis. The DiCoLas processing head enables a stable welding process with good dimensional accuracy of the single welding geometries. Single weld seams and multiple-layer structures are investigated to cover the intermixing behavior for different applications of additive manufacturing. Thermal images of the melting process provide an insight into the melting behavior of the two wire materials and the formation of the weld seam. energy-dispersive x-ray-mappings and line scans display the element distribution of the main alloying elements along the seam cross section. Furthermore, hardness measurements examine the hardness progression along the multiple-layer welding structures showing an even progression of the hardness values over the entire cross section.

Overview of Polyethylene Based Multi-layered Geomembrane Through Blown Extrusion Process

Geomembranes are low-permeable liners used to control the molecular migration in many proven applications. Landfills is most common application in the field of civil and environmental engineering. Geomembrane is the main component in lining system which works as hydraulic barrier. The polyolefins are the basic materials of liner and more commonly polypropylene and polyethylene are preferred. Commercial manufacturing process involves extrusion techniques viz cast extrusion and blown extrusion process. The individual process is designed for multiple layered structures which are then coextruded to lead into a single liner. Typical structure comprises, high to low-density polyethylene (PE) resin, processing aids, stabilisers to retard the degradation through ultra-violet rays, photo-oxidation, and thermal oxidation. The stabilizer is usually used in smaller dosses to avoid degradations which includes, 2 to 3% carbon-black (CB), 0.5 to 1% antioxidants (AO), and plasticizing additives to introduce the flexibility. During the process, components are homogenised in specially designed screws of feeding and mixing zones. The formulated melt is co-extruded through specially designed die of multi-layered structures. The subsequent melt enters in circular die with a certain pressure which leads to bubbled shaped films. The variation in the surface morphology layer structure and layer number are the important technical aspects to alter the required end application. Finally, manufactured geomembrane is qualified as per the international specifications which are governed by geosynthetic research institute (GSI/GRI).

An introduction to terahertz time-domain spectroscopic ellipsometry

In the past, terahertz spectroscopy has mainly been performed based on terahertz time-domain spectroscopy systems in a transmission or a window/prism-supported reflection configuration. These conventional approaches have limitations in regard to characterizing opaque solids, conductive thin films, multiple-layer structures, and anisotropic materials. Ellipsometry is a self-reference characterization technique with a wide adaptability that can be applied for nearly all sample types. However, terahertz ellipsometry has not yet been widely applied, mainly due to the critical requirement it places on the optical setting and the large discrepancy with regard to traditional terahertz spectroscopy and conventional optical ellipsometry. In this Tutorial, we introduce terahertz time-domain spectroscopic ellipsometry from the basic concept, theory, optical configuration, error calibration to characterization methods. Experimental results on silicon wafers of different resistivities are presented as examples. This Tutorial provides key technical guidance and skills for accurate terahertz time-domain spectroscopic ellipsometry.

Fabrication of multi-layered Co3O4/ZnO nanocatalysts for spectroscopic visualization: Effect of spatial positions on CO2 hydrogenation performance

Controlled fabrication of spatial positions of different active sites on catalyst structures is critical to exploring the reaction mechanisms for CO2 hydrogenation. Herein, two isomorphous zeolitic imidazolate frameworks (ZIF-67 and ZIF-8) were used as sacrificial templates to synthesize multi-layered Co3O4/ZnO catalysts with tunable core-shell structures and well-controlled spatial positions. The multi-layered catalysts were then evaluated for the catalytic performance for CO2 hydrogenation. A series of characterization techniques were applied to investigate the morphology and structure of the Co3O4/ZnO composites with different spatial locations. Due to the unique multi-layered structure, the distinct interfacial structures, and the synergistic effects, the resultant core-shell structured Co3O4/ZnO nanocatalysts exhibited significantly enhanced activity as compared to their monometallic counterparts (pure Co3O4 and ZnO). In addition, the ZnO@Co3O4 with Co3O4 as shell showed significantly higher CO2 conversion (25%) than that of Co3O4@ZnO with ZnO as shell (0.82%). Furthermore, in-situ Diffuse Reflection Fourier Transform Infrared Spectroscopy (DRIFTS) analysis suggested that formate (HCOO*) and methoxy (CH3O*) species were the crucial intermediates in the CO2 hydrogenation over the Co3O4/ZnO composite nanocatalysts. However, pure ZnO could not activate the CO2; consequently, the use of the Co3O4/ZnO nanocatalysts derived from multiple-layered ZIFs structures provides new insights into improving the catalytic efficiency of CO2 hydrogenation.

Microstructural evolution and phase transformation in proton-irradiated NiTi films

In the present work, the microstructural characteristics, martensitic transformation behavior, and mechanical performance of NiTi thin films irradiated with different proton fluences were investigated. Multiple-layer structures formed in the NiTi thin films owing to proton irradiation. As the proton fluences were 1.0 × 1015 p/cm2 and 5.0 × 1015 p/cm2, a two-layer structure containing a B2 phase and a B19’ martensite phase was introduced. In addition, thickness of B2 phase layer becomes larger and larger for irradiated NiTi thin films at room temperature, as the proton irradiation fluence increases. With further increasing proton irradiation fluence to 2.0 × 1016 p/cm2, an amorphous layer forms at the outmost layer of NiTi thin film. Moreover, an R phase and GP zones were detected in the interior of the B2 layer. The twin type of B19’ martensite also changed to release the stored elastic energy induced by proton irradiation. The martensite variant related (111‾) type I twins and the substructure of the <011> type II twins gradually evolved into (111) type I twins and (001) compound twins, respectively, with increasing proton irradiation fluence. The formation of a multiple-layer structure resulted in the presence of two endothermic and exothermic peaks corresponding to the B19’ ⇌ B2 martensitic transformation. The introduction of lattice defects was responsible for the reduction in the martensitic transformation temperature. The strength of the irradiated NiTi films was enhanced as a result of dislocation strengthening. However, the introduction of higher density of defects also leads to the deterioration of ductility.

A Secure Cloud Data Sharing Protocol for Enterprise Supporting Hierarchical Keyword Search

Cloud storage becomes the priority for storing and sharing data for enterprise users. Encrypting prior to uploading data to the cloud is the best way to protect business secrets, however, it hinders the convenient operations on plaintexts, such as searching over the cloud data. In addition, employees in an enterprise have multiple layer structures and a higher layer employee should have the privilege to monitor the lower layer employees’ data to check if these users violate the regulation without letting the employees be aware of. Public key encryption with keyword search (PEKS) is a well-known cryptographic primitive suitable for secure cloud storage, which supports keyword search without decryption in public key encryption settings. Unfortunately, no existing PEKS scheme supports the monitoring function without authorization from the sender. To address this issue, we propose a variant of PEKS named Hierarchical Public Key Encryption with Keyword Search (HPEKS) and provide a semi-generic construction utilizing a public key tree (PKTree) and a PEKS scheme. To better suit for the enterprise secret data sharing, we build an advanced HPEKS scheme, named designated-tester decryptable hierarchical public key encryption with keyword search (dDHPEKS), which enjoys stronger security and integrates the public key and symmetric key encryptions. We prove our dDHPEKS scheme secure under the security definition in the random oracle model. Particularly, it satisfies the security against outside offline keyword guessing attacks and furthermore, enjoys the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">transparency</i> property so that the sender does not need to know the internal hierarchy structure of an enterprise in order to share encrypted data to the enterprise. Theoretical evaluation and concrete experiments show that our dDHPEKS scheme has comparable running efficiency with existing PEKS schemes.