Properties Of Layered Structures Research Articles

Catalyst Layer Structure Properties and Electrode Performance with the Addition of Polyethylene Glycol

Reducing the platinum loading in Proton Exchange Membrane Fuel Cells to mitigation costs is of topical interest. Lowering the Pt content beyond critical thresholds has a direct impact on the kinetic conversion efficiency of O2, and result in local oxygen transport resistance in the catalyst layer at high current densities. Improvements in the Pt use efficiency can be achieved by affecting the catalyst layer structure properties with improved Pt dispersion and increased ionomer interface1-3.In this study, we are investigating how the structure properties of the catalyst layer are affected by the addition of polyethylene glycol (PEG) during the ink step. PEG has a high boiling point (>200°C) and is known to have pore forming properties4. It has also been reported to extend the reach of the ionomer and its resulting protonic connectivity. Increasing the porosity in the catalyst layer can increase the triple phase boundaries and reduce interfacial resistances 5.Membrane electrode assemblies (MEAs) have been made with inks containing increasing wt.% PEG. The resulting inks were coated onto membranes to form catalyst layers containing 0.2 mgPt/cm2. The addition of PEG affected the binding of the ionomer and the catalyst, which will likely affect the packing of the agglomerates in the resulting catalyst layer structure. The catalyst layer thickness, surface area and porosity were determined. The coated substrates were assembled into single cells for electrochemical evaluation. The resulting MEAs showed that the inclusion of PEG reduced the kinetic losses at low current density due to improved electronic connectivity between the catalyst and the ionomer. Overall, the performance increased by ≈30mV at 1A/cm2.However, PEG content higher than 3% resulted in a significant decrease in performance in the high current density region. This is due to a higher packing density and therefore higher mass transport resistance with higher PEG content.The inclusion of PEG into the catalyst ink reduced the amount of flammable organic content and improved the MEA performance especially at low current density. Catalyst layer deposition was smoother with reduced cracking. Ultimately, the ambitions for low loading MEAs can be achieved by optimising the structure performance properties in the catalyst layer. PEG is considered a viable candidate for performance enhancement for low loading MEAs, yet a number of practical obstacles were experienced and require some optimization.

Optical scatterings in layered systems

This paper presents a theoretical framework for exploring the optical properties of layered materials. The derived analytical formulas for reflectance and transmittance spectra incorporate vertical valence-state transitions and appropriate boundary conditions for finite-width bulk materials, integrated with the generalized tight-binding model to account for intrinsic interactions and external fields. The study reveals distinct structures in the spectra of multilayer graphene for different stacking layers at low energies (∼0.2–0.8[Formula: see text]eV), attributed to interband transitions at the K point. Furthermore, the high-energy part (≳5[Formula: see text]eV) highlights thickness-dependent plasmon effects characterized by unique resonance frequencies in the optical spectra. These features depend on the dimensionality, interlayer coupling, and electronic structure of the material. This work provides a deeper understanding of the optical properties of layered structures, facilitating their exploration and characterization for diverse applications.

Spin‐Orbit Readout Using Thin Films of Topological Insulator Sb2Te3 Deposited by Industrial Magnetron Sputtering

AbstractDriving a spin‐logic circuit requires the production of a large output signal by spin‐charge interconversion in spin‐orbit readout devices. This should be possible by using topological insulators, which are known for their high spin‐charge interconversion efficiency. However, high‐quality topological insulators have so far only been obtained on a small scale, or with large scale deposition techniques that are not compatible with conventional industrial deposition processes. The nanopatterning and electrical spin injection into these materials have also proven difficult due to their fragile structure and low spin conductance. The fabrication of a spin‐orbit readout device from the topological insulator Sb2Te3 deposited by large‐scale industrial magnetron sputtering on SiO2 is presented. Despite a modification of the Sb2Te3 layer structural properties during the device nanofabrication, a sizeable output voltage is measured that can be unambiguously ascribed to a spin‐charge interconversion process. The results pave the way for the integration of layered van der Waals materials in spin‐logic devices.

Effects of interfacial energy on interfacial strength and work of adhesion in bcc-Fe tilt interfaces: A molecular dynamic study

Interfaces have been observed to play a vital role in improving the mechanical properties of layered structures. Many studies have indicated that at atomic scale, the interfacial energy can significantly influence the interface adhesion and hence, the mechanical properties. To investigate the relationship between the interfacial energy, atomic configuration, and tensile behaviour, we conducted molecular dynamics (MD) simulations of bcc-Fe interfaces. A total of 108 symmetric and asymmetric tilt interfaces on the <100> and <110> axes were constructed to achieve various interfacial energies. It was observed that the interfacial energy was dominated by the coherence of the interfacial atomic configuration. The tensile simulation results showed an approximately linear relationship between the interfacial strength and interfacial energy. This suggests that interfacial energy is the dominant factor. However, a higher variation in the interfacial energy effects on the work of adhesion was observed. This occurred because both interfacial energy and interfacial deformation behaviour affected the work of adhesion. In addition, twinning deformation and interfacial dislocations were observed in the low-energy coherent and high-energy disordered interfaces, respectively. This indicates that the interfacial atomic configuration determines the deformation behaviour, which, in turn, causes the interfacial property variations.

Magnetoelectric Properties of Ni-PZT-Ni Heterostructures Obtained by Electrochemical Deposition of Nickel in an External Magnetic Field

This paper studied the influence of external electric and magnetic fields on the magnetoelectric properties of layered structures of metal-piezoelectric-metal. The structures under study had the shape of a square 4 mm wide and were obtained in two steps: first, by the chemical deposition of nickel with a thickness of 0.5 μm, and then by the electrochemical deposition of nickel with a thickness of 50 μm on each side onto a lead zirconate–lead titanate substrate. Electrochemical deposition was carried out without a magnetic field on both non-polarized and polarized ceramics. Electrochemical deposition was also carried out in a magnetic field on a non-polarized and polarized PZT ceramic substrate. A magnetic field of 500 Oe at electrochemical deposition was applied in all cases in the direction of structure polarization. The maximum ME voltage coefficient 300 mV/(cmOe) was obtained at transverse orientation at bias magnetic field near 20 Oe.

Solving the Problem of Determining the Mechanical Properties of Road Structure Materials Using Neural Network Technologies

Introduction. Determination of mechanical properties of layered structures of highways is an urgent task. This is due, firstly, to the need to control the quality of new sections during the construction of highways. Secondly, to assess the condition of existing roads with the accumulation of damage and defects is of interest. The formation of multiple defects (cracks) changes the averaged viscoelastic properties of the components of the structure, specifically, the surface asphalt-concrete layers. The article discusses the use of neural network technologies to improve the accuracy of the recovery of viscoelastic properties. This approach is based on experimental methods. As an example, we can give the definition of the dynamic deflection of a structure from a falling weight, FWD.Materials and Methods. The elastic modulus of a three-layer structure was determined on the basis of a neural network. To find out the solution accuracy, it was compared to the results of mathematical modeling and experimental data.Results. The experimental and calculated parameters of the elastic modulus of individual layers of the road structure turned out to be very close. The proposed approach to determining the mechanical properties of materials of road structures allowed us to apply the obtained results to examination of the condition of individual elements and the entire road structure.Discussion and Conclusions. The prospects of using artificial intelligence to determine the mechanical properties of layered structures was shown. Further improvement of methods and tools for analyzing the behavior of road structures under dynamic loading will expand existing approaches to assessing the condition of road structures.

Elucidating the Roles of Polyamide Layer Structural Properties in the Permeability–Selectivity Tradeoff Governing Aqueous Separations

Elucidating the Roles of Polyamide Layer Structural Properties in the Permeability–Selectivity Tradeoff Governing Aqueous Separations

Spontaneous Lithiation of Binary Oxides during Epitaxial Growth on LiCoO2.

Epitaxial growth is a powerful tool for synthesizing heterostructures and integrating multiple functionalities. However, interfacial mixing can readily occur and significantly modify the properties of layered structures, particularly for those containing energy storage materials with smaller cations. Here, we show a two-step sequence involving the growth of an epitaxial LiCoO2 cathode layer followed by the deposition of a binary transition metal oxide. Orientation-controlled epitaxial synthesis of the model solid-state-electrolyte Li2WO4 and anode material Li4Ti5O12 occurs as WO3 and TiO2 nucleate and react with Li ions from the underlying cathode. We demonstrate that this lithiation-assisted epitaxy approach can be used for energy materials discovery and exploring different combinations of epitaxial interfaces that can serve as well-defined model systems for mechanistic studies of energy storage and conversion processes.

Enhanced efficiency in hollow core electrospun nanofiber-based organic solar cells

Over the last decade, nanotechnology and nanomaterials have attracted enormous interest due to the rising number of their applications in solar cells. A fascinating strategy to increase the efficiency of organic solar cells is the use of tailor-designed buffer layers to improve the charge transport process. High-efficiency bulk heterojunction (BHJ) solar cells have been obtained by introducing hollow core polyaniline (PANI) nanofibers as a buffer layer. An improved power conversion efficiency in polymer solar cells (PSCs) was demonstrated through the incorporation of electrospun hollow core PANI nanofibers positioned between the active layer and the electrode. PANI hollow nanofibers improved buffer layer structural properties, enhanced optical absorption, and induced a more balanced charge transfer process. Solar cell photovoltaic parameters also showed higher open-circuit voltage (+ 40.3%) and higher power conversion efficiency (+ 48.5%) than conventional architecture BHJ solar cells. Furthermore, the photovoltaic cell developed achieved the highest reported efficiency value ever reached for an electrospun fiber-based solar cell (PCE = 6.85%). Our results indicated that PANI hollow core nanostructures may be considered an effective material for high-performance PSCs and potentially applicable to other fields, such as fuel cells and sensors.

Phonon Properties of Bulk Violet Phosphorus Single Crystals: Temperature and Pressure Evolution

Violet phosphorus, the most stable phosphorus allotrope, has been successfully produced recently. Phonon properties of layered structures are important characteristic features to provide their stru...

Electrical Conductivity and Magnetoresistive Properties of Layered Structures Based on Fe and SiO

Electrical Conductivity and Magnetoresistive Properties of Layered Structures Based on Fe and SiO

Suppression of Anisotropic Heat Conduction in Ion-Substituted Layered Cobalt Oxides

Layered compounds often show the anisotropic transport properties of both electron and phonon; the electrical/thermal conductivity along with the layer is high and the electrical/thermal conductivity perpendicular to the layer is low. For example, layered Na x CoO2, which is known as a promising candidate for oxide thermoelectric material [1], exhibits a rather large thermoelectric power factor along with the CoO2 layer, whereas it shows low electrical conductivity in perpendicular to the CoO2 layer. In addition, the thermal conductivity is large along with the CoO2 layer, whereas it is small in perpendicular to the CoO2 layer. Therefore, the anisotropic electron/phonon transport properties need to be suppressed to improve the thermoelectric figure of merit of Na x CoO2. Here we demonstrate that the anisotropy in thermal conductivity κ of Ax CoO2 (A = Li, Na, Ca, and Sr) can be suppressed by increasing the weight of Ax . We fabricated Ax CoO2 epitaxial films with two different crystallographic orientations with respect to the surface normal to the substrates by the Reactive Solid-Phase Epitaxy method [2,3]. We measured the electrical conductivity σ and thermopower S along with the substrate surface whereas we measured the κ in normal to the substrate surface. We extracted the κ parallel to the layers (κ p) from the comparison of two different crystallographic orientations [4]. The κ p was 3-6 times larger than that perpendicular to the layers (κ v). The κ p decreased with increasing the atomic mass of Ax though κ v was insensitive to it; anisotropy of κ was controlled by substituting heavier Ax -ions [5]. The results of this study will be of great value in understanding fundamental heat transport properties of layered structures as well as developing Ax CoO2 based thermoelectric materials. In addition, the analysis of the anisotropic thermal conductivity used in this study can be applied to other layered materials. [1] I. Terasaki et al., Phys. Rev. B 56, R12685(R) (1997).[2] H. Ohta et al., Cryst. Growth Des. 5, 25 (2005).[3] K. Sugiura, H. Ohta et al., Appl. Phys. Lett. 88, 082109 (2006).[4] K. Sugiura, H. Ohta et al., Appl. Phys. Lett. 94, 152105 (2009).[5] H.J. Cho, H. Ohta et al., Adv. Mater. Interfaces 7, 1901816 (2019). Figure 1

Magnetic Properties of Layered Ferrimagnetic Structures Based on Gd and Transition 3d Metals

Magnetic properties of layered structures based on transition and rare-earth metals (TMs and REMs) such as Fe and Gd have attracted attention of researchers since 1990s. These materials are artificial ferrimagnets with reach magnetic phase diagrams, which make it possible to realize a wide spectrum of predefined properties. In recent years, a new surge of the interest in such systems was evoked by observations of new peculiar dynamic effects in these materials, including optical magnetization reversal and ultrafast motion of domain walls, as well as the possibility of realization of skyrmion magnetic states. In this article, a brief review of the most interesting features of magnetism and magnetic dynamics of layered ferromagnetic TM/REM structures is presented. The results of our investigation concerning Fe/Gd superlattices and the effects of Cr interlayers on their magnetic properties are reported. The surface cant of the magnetization in these structures has been observed directly using the magnetooptical Kerr effect, and the magnetic phase diagram of the system has been obtained. We have analyzed peculiarities of nonuniform modes of magnetic oscillations excited in the Fe/Gd superlattice by the ferromagnetic resonance method. The possibility of sign reversal of the exchange interaction of Fe and Gd layers from antiferromagnetic to ferromagnetic type upon the introduction of Cr interlayers between them has been demonstrated.

Properties of layered structures based on barium titanate

The dielectric properties of the bipolar SrTiO3/BaTiO3/SrTiO3 structures synthesized by pulsed laser sputtering on a single-crystal SrTiO3 substrate doped with Nb with a buffer conducting oxide sublayer of LaSrCoO3 are studied. It is shown that the structure has a transition temperature to the ferroelectric state approximately equal to 320°С. The transition into the polar phase has all the features of a second-order phase transition. The indicated structures are characterized by the presence of an internal field entirely associated with the presence of a substrate.

Simulation of the Formation and Mechanical Properties of Layered Structures with Polymerized Fullerene-Graphene Components

Simulation of the Formation and Mechanical Properties of Layered Structures with Polymerized Fullerene-Graphene Components

(Invited) Understanding Role of Li Substitution at Alkali-Site of NaX[Fe0.5Mn0.5]O2 As Cathode for Sodium Ion Batteries

Sodium ion batteries(SIB) have gained significant attention as next generation of rechargeable batteries based on natural abundance and low cost. Transition metal oxides with layered structure is well known electrode material that have been successfully commercialized in LIB system and have been reported to be one of the promising electrode material for SIBs. Extensive studies have been reported about substitution of various foreign element in the layered structure. Substitution of foreign element could be achieved by substitution at either transition metal site or alkali site. Many studies focused on the composition and substitution at the transition metal site of the layered structure. Here, this study focused on the substitution at the alkali site of layered structure as cathode materials for SIBs. Substitution at alkali site could not only affect the properties of layered structure, but also interfere with intercalation of sodium. In this study, Li was substituted on alkali site of NaXFe0.5Mn0.5O2 as cathode material for SIBs. Although Li have been reported to be substituted at transition metal site in previous literature, Li substitution at alkali site was achieved by varying the ratio between Fe and Mn. Rietveld refinement synchrotron XRD and neutron diffraction patterns, XANES analysis, and ICP analysis were conducted in order to confirm the substitution of Li at alkali site. When Li was substituted at alkali site, it showed improved cycle life and rate capability in spite of decreased interlayer spacing. In situ XRD analysis and DFT calculation was conducted in order to understand the role of Li in structure stability and Na intercalation behavior. The result showed that Li substitution at alkali site stabilized layered structure during charge/discharge process and that Li lowered the energy barrier of Na hopping, leading to improved cycle life and rate capability.

Optimization of fire-related properties in layered structures

In present paper, fire-related properties of materials with multilayered structure are obtained through reverse heat transfer analysis. For this purpose, one-dimensional heat transfer equation including pyrolysis is analyzed to simulate the fire phenomenon of multi-layered solid materials. The fire-related properties can be obtained by optimizing the objective function expressing the difference between the measured values and the results (surface temperature and mass loss rate under constant incident heat flux) obtained by analyzing the considered heat transfer equations. Repulsive particle swarm optimization is used as the optimization technique. The optimized properties of single-, two- and three-layered materials obtained with the assumed properties were compared to the assumed for various incident heat fluxes. Using a cone calorimeter, the surface temperature and mass loss rate were measured over time with three constant heat fluxes applied to three layers of sandwich type material. The fire-related properties of each layer of the sandwich type material were calculated using the measured results. The technique considered in this study can be applied for determining the fire characteristics of multilayered materials is suitable for engineering the necessary properties to predict fire propagation in solid material.

Elastic interphase properties of nanoparticle/epoxy nanocomposites: A molecular dynamics study

The mechanical properties of nanocomposites are significantly influenced by interfacial interactions between nanoparticles and matrix. In this work, the elastic interphase properties of boehmite nanoparticle/epoxy composites are investigated using molecular dynamics simulations. The distinctive feature of this study is the characterization of the interphase properties thanks to the concept of atomic strain, which allows to capture the stiffness gradient at the interphase. The simulation results suggest that the size of the interphase region may not only be determined by the variation of the mass density, but also by an alteration of the polymer network structure close to the particle. A significant increase of the interphase stiffness is observed for a strong chemical bonding between boehmite and epoxy, while purely physical interactions lead to a slight reduction of the interphase stiffness compared to the bulk epoxy stiffness. Finite element analyses of representative volume elements of the nanocomposite show that the homogenized elastic properties are considerably influenced by the elastic interphase properties. The proposed simulation framework not only estimates elastic interphase properties of layered structures, but can be extended for studying the elastic properties of arbitrarily shaped contiguous subsections of molecular models.

Polymer Electrolyte Water Electrolysis: Correlating Porous Transport Layer Structural Properties and Performance: Part I. Tomographic Analysis of Morphology and Topology

In the first paper of this series, the bulk, surface and transport properties of porous transport layer materials (PTL) for polymer electrolyte water electrolysis cells (PEWE) are characterized. A systematic PTL matrix of Ti fiber materials with 3 fiber diameters and 2 nominal porosities as well as a state of the art sintered powder material are investigated to get a better understanding of the governing parameters in electrolysis cells. X-ray tomographic microscopy analysis of ex situ PTL structures and post operando membrane electrode assemblies is performed. On the tomographic structures, bulk (porosity, pore/solid size distributions, fiber orientation), mass transport (diffusivity, permeability, conductivities) and surface parameters (roughness, membrane deformation, PTL surface area and interfacial contact area) are determined. The second paper of this series will correlate the structural parameters with in-depth electrochemical analysis. The new insights into the effect of PTL properties on PEWE performance allow to isolate governing key parameters. From know-how obtained on the fiber based materials fundamental design guidelines for optimization of PTL structures are deduced.

Three-dimensional finite element simulation of Love mode surface acoustic wave in layered structures including ZnO piezoelectric film and diamond substrate

Three-dimensional (3D) finite element method (FEM) was used to simulate the surface acoustic wave (SAW) propagation properties in layered structures including ZnO piezoelectric film and diamond substrate. The excitation conditions of Love mode and Rayleigh mode SAWs are discussed considering the ZnO crystal orientation and the SAW propagation direction which are specified using Euler angles (α, β, γ). The phase velocity and electromechanical coupling coefficient K2 of Love mode SAW in the ZnO/diamond structure are provided as functions of the normalized ZnO layer thickness hZnO/λ and the Euler angles (α, β, γ). The results show that the maximum K2 of 4.26% is reached at hZnO/λ = 0.3 and (α, β, γ) = (0°, 90°, 0°) for Love mode SAW; the associated phase velocity is 3436 m/s and the temperature coefficient of frequency (TCF) value is −26.5 ppm/°C. The TCF properties are greatly improved by adding a SiO2 layer between the ZnO film and the diamond substrate. A zero TCF can be obtained when the normalized SiO2 thickness hSiO2/λ is 0.25 and the hZnO/λ is 0.2, where the corresponding K2 is 3.26% and the phase velocity is 3126 m/s.