Thicknesses Of Constituent Layers Research Articles

Exceptional ductility through interface-constrained grain growth for the ultrafine-scale Ni/Ni-W layered composites

Enhancing the strength of metallic laminates through decreasing the constituent layer thickness from micrometer to nanometer scale is usually accompanied by the degradation of ductility because plastic instability characterized by fatal shear bands inevitably occurs in the early stage of deformation. To overcome the strength-ductility trade-off dilemma, we designed a kind of metallic layered composites (LCs) consisting of nano-grained Ni (grain size: 21–37 nm) and ultrafine nano-grained Ni-W (grain size: 8 nm) constituent layers with layer thickness ranging from microns to tens of nanometers. We found that the strength and ductility of Ni/Ni-W LCs can be simultaneously enhanced by decreasing the layer thickness. Interface-constrained grain growth in the Ni layers with an initial layer thickness of less than 1 μm enhances strain hardening ability. Thus, strain delocalization characterized by the formation of rectangular strain zones instead of crossed micro shear bands appears in the LCs. Based on the above mechanism, we obtained the optimum ratio of the layer thickness to the grain size for the nano-grained Ni layers as about 15:1, which corresponds to Ni0.25/Ni-W0.025 LCs with the highest tensile strength (1.9 GPa) and elongation to failure (5.5 %). These findings may provide a new path for the design principle of metallic LCs with multi-level microstructural and geometrical scales.

Effect of Al2Cu constituent layer thickness discrepancy on the tensile mechanical behavior of Cu/Al2Cu/Al layered composites: a molecular dynamics simulation

Nano-polycrystalline Cu/Al2Cu/Al layered composites with different layer thicknesses d of single-crystal Al2Cu constituent are constructed. The effects of d on the strength and fracture modes of nano-polycrystalline Cu/Al2Cu/Al layered composites are systematically investigated by molecular dynamics simulations. The uniaxial tensile results show that the ultimate strength and fracture mode of the nano-polycrystalline Cu/Al2Cu/Al layered composites do not change monotonically with the change of single crystal Al2Cu constituent layer thickness d, the ultimate strength peaking at d = 2.44 nm, and the toughness reaching the optimum at d = 4.88 nm. The improvement of deformation incompatibility between Cu, Al and Al2Cu components increases the ultimate strength of polycrystalline Cu/Al2Cu/Al laminated composites. Due to the high activity of Cu dislocation and the uniformity of strain distribution of single crystal Al2Cu, the fracture of nano-crystalline Cu/Al2Cu/Al layered composites changes from brittleness to toughness. This study is crucial to establish the organic connection between microstructure and macroscopic properties of Cu/Al layered composites. To provide theoretical basis and technical support for the application of Cu/Al layered composites in high-end fields, such as automotive and marine, aerospace and defense industries.

Intensity of Dynamic Stresses of Longitudinal Shear in a Periodically Layered Composite with Penny-Shaped Cracks

We consider the problem of harmonic torsional loading of an infinite elastic composite formed by alternating plane layers made of two different materials in the presence of a penny-shaped crack in one of the components of periodic structure. By using the integral representations for displacements and stresses in the frequency domain and satisfying the conditions of periodicity and perfect contact on the interfaces, we deduce a system of uncoupled boundary integral equations for the functions of tangential dynamic crack-opening displacement in a two-layered representative element of the composite. We perform the numerical analysis of the mode-III dynamic stress intensity factors in the vicinity of the analyzed crack depending on the wave number, the thicknesses of constituent layers, and the properties of their materials.

Influence of fatigue on superconducting REBCO tapes under repeated cyclic tensile, bending and twisting loads: A simulation-based investigation

The effect of repeated cyclic loading on the superconducting REBCO tape under tensile, bending, and torsional loadings is investigated. The Fatigue Usage Factor (FUS) is calculated for each cyclic loading condition to identify degradation using the Matake criterion. The thicknesses of the tapes' constituent layers are also varied to identify the relative influence of each layer on overall fatigue performance. When the tape was subjected to fatigue-type loading, the thickness of the copper and Hastelloy layers was found to play a significant role. This holds true under tensile, bending, and twisting loading conditions. However, out of the three loading conditions, bending exhibits the greatest variation in FUS value with changes in Hastelloy and copper layer thickness. The maximum value of the fatigue usage factor is observed in the edges of the Hastelloy layer in all three loading cases. It has been found that the properties of the layer material, as well as the adjacent layer, play an important role in determining the fatigue strength of the tape.

Influence of Combined Tension and Torsion on the Performance of REBCO Superconducting Tapes

Rare-earth-barium-copper-oxide (REBCO) coated conductor tapes are promising materials for superconducting cables and wires. Simulation studies of the impact of the mechanical loading on the degradation of superconducting tapes give a better understanding on the role of different geometrical parameters like tape width and thicknesses of constituent layers. In this article, a detailed analysis of combined tensile and torsional loading on REBCO tape is carried out. The results show that the thickness of each constituting layer of the tape influences the ability of the tape to withstand tensile and torsional loads. Although increasing the width of the tape increases the maximum allowable tensile load, it decreases its ability to withstand the torsional load. The angle of twist is increased from 0.18 to 0.72 °/mm, and the maximum applied tensile strain that can be applied is decreased from 0.65% to 0.3%. The maximum allowable angle of twist is decreased from 4 to 0.93 °/mm with the increase in the tape width from 3 to 12 mm under pure torsion. The critical current retention capacity of the tape changes with different geometric parameters of the tape. The findings are useful in determining appropriate values for the thicknesses of each layer and width of the tape corresponding to the magnitude of pure tensile, pure torsional and combined tensile and torsional loads experienced.

Photovoltaic characteristics of ultrathin Cs2CuBiCl6 halide double perovskite based solar cell: theoretical studies

The strenuous task of managing overall stability and environmental hazards associated with regular halide single perovskites draws attention toward halide double perovskite (DP) as an alternative materials. These materials are relatively stable and potentially less-toxic and have been explored for various applications- optoelectronics, electrical, spintronics, etc. This article brings forth the photovoltaic promise of noble metal and pnictogen element based Cs2CuBiCl6 halide DP as an ultrathin absorber in solar cell configured with p-i-n geometry. The numerical simulation of Cs2CuBiCl6 based all-inorganic inverted solar cell configuration exhibits comparable power conversion efficiency of around 17.03% for a 100 nm ultrathin absorber in a single junction cell. We considered microscopic factors like radiative recombination coefficient, neutral and charged defects with their densities, intrinsic heat in the devices, and macroscopic quantity like thickness of constituent layers, including interfacial effect in the device. The simulated device shows better interfacial defect tolerance on either side of the absorber layer, good device tolerance to absorber defect density < 1016 cm−3 and tollerable 0.84% intrinsic heat (Peltier and Joule heat) fraction for the device. This article may provide a way forward for realizing Cs2CuBiCl6 halide DP absorber based solar cell with a predicted open-circuit voltage of 0.91 Volt and short-circuit density of 21.66 mA/cm2.

Enhancing high-temperature tensile properties of Ni/Ni-W laminated composites for MEMS devices

There is an increasing demand for materials with excellent mechanical performance for Micro-Electro-Mechanical System (MEMS) devices serving at elevated temperatures. However, how to enhance the high-temperature strength of the materials without losing their plasticity is a pending problem. Here, the Ni/Ni-W laminated composites with different monolayer thicknesses and the same ratio of the constituent layer thicknesses were fabricated successfully by using the dual-bath electrodeposition technique. The microstructure stability and tensile properties of annealed Ni/Ni-W laminated composites with different monolayer thicknesses were investigated at 400 °C. The results show that the annealed Ni0.5/Ni-W0.05 laminated composites have both high yield strength (450 MPa) and excellent elongation to failure (25.1%) at 400 °C, being superior to that of the monotonic Ni (179 MPa and 17.7%). Such a high strength of the laminated composite at 400 °C results from the contribution of the intrinsically high strength of the Ni-W layers with excellent thermal stability, the thickness-constrained effect on grain growth of Ni layers and the interface coupling effect of heterogeneous structures. The good plasticity may be derived from the heterogeneous laminated structure and the decrease in the constituent layer thickness, providing a good co-deformation ability. Basic mechanisms for the high tensile strength and good plasticity of the Ni/Ni-W laminated composites at 400 °C were analyzed theoretically. The findings reveal a potential strategy to fabricate MEMS components with excellent high-temperature tensile properties through tailoring the microstructure thermal stability and the constituent layer scale.

First-Principles Study of n*AlN/n*ScN Superlattices with High Dielectric Capacity for Energy Storage.

As a paradigm of exploiting electronic-structure engineering on semiconductor superlattices to develop advanced dielectric film materials with high electrical energy storage, the n*AlN/n*ScN superlattices are systematically investigated by first-principles calculations of structural stability, band structure and dielectric polarizability. Electrical energy storage density is evaluated by dielectric permittivity under a high electric field approaching the uppermost critical value determined by a superlattice band gap, which hinges on the constituent layer thickness and crystallographic orientation of superlattices. It is demonstrated that the constituent layer thickness as indicated by larger n and superlattice orientations as in (111) crystallographic plane can be effectively exploited to modify dielectric permittivity and band gap, respectively, and thus promote energy density of electric capacitors. Simultaneously increasing the thicknesses of individual constituent layers maintains adequate band gaps while slightly reducing dielectric polarizability from electronic localization of valence band-edge in ScN constituent layers. The AlN/ScN superlattices oriented in the wurtzite (111) plane acquire higher dielectric energy density due to the significant improvement in electronic band gaps. The present study renders a framework for modifying the band gap and dielectric properties to acquire high energy storage in semiconductor superlattices.

Versatile Sensing Structure: GaP/Au/Graphene/Silicon

A versatile sensing scheme for gas and biomolecule detection has been proposed theoretically using optimized GaP/Au/Graphene/Silicon structures. A Gallium Phosphide (GaP) prism is used as a substrate in the proposed surface plasmon resonance based sensing scheme, which is designed to be in Kretschmann configuration. The thicknesses of different constituent layers have been optimized for the maximum values of the sensitivities of the gas and bio-sensing probes. To delineate the role of the silicon layer, sensing probes without a silicon layer have also been numerically modelled and compared. The present GaP/Au/Graphene/Silicon probes possess higher values of sensitivity for the detection of gas and biomolecules compared to the conventional SPR sensing probes reported in the literature.

Effect of temperature on the deep drawing forming performance of Ti/Al laminates: experimental investigation and finite element analysis

In this study, Ti/Al laminates are deep-drawn at elevated temperatures to investigate the effect of temperature on forming performance using numerical and experimental methods. Equipment for warm deep drawing process in a vacuum atmosphere is developed. The corresponding deep drawing finite element model (FE model) is established and validated by thickness distribution along the drawn cups’ radial direction. Based on the developed FE model, the thickness strain in different temperature is compared. Following this, the process window is established to determine the optimum temperature. The ratio curve of plastic deformation to sliding (D/S curve) during warm deep drawing is established to characterize the sustainable formability of Ti/Al laminates. The results indicated that the maximum limit drawing ratio in 200°C is consistent with the minimum thickness reduction. The safe forming area narrows with the increase of the drawing ratio. The D/S curve is short and presented fluctuations in the middle-temperature section of 150–250°C, as revealed well sustainable formability. Furthermore, the thickness of constituent layers for Ti/Al laminates is measured from micromorphology diagrams and compared. It is observed that the thickness strain of outside layers has more possibility to decline in bottom radius and is higher in flange radius than inner layers.

Evaluation of graded layer in ground granulated blast furnace slag based layered concrete

This paper reports on the generation, properties, and spatial variability of the graded layer in functionally graded concrete (FGC) made using 20, 35, and 50% ground granulated blast furnace slag (GGBFS) as partial replacement of ordinary Portland cement (OPC). Two different layers of concrete, one being OPC based normal concrete and the other being GGBFS blended concrete were used to prepare the FGC specimens. The control concrete specimens were made with a single layer OPC or GGBFS concrete. Excluding the control concrete samples, three types of double-layered cube samples of 150 mm thick were prepared in various combinations of the thickness of constituent layers. These double-layered combinations were 25 mm + 125 mm, 75 mm + 75 mm, and 125 mm + 25 mm thick containing OPC concrete and GGBFS blended concrete respectively. The properties like compressive strength, the interfacial bond between two constituent layers, modulus of elasticity, micro-structure, and graded layer were examined. The formation, thickness, and properties of the graded layer at the interface of constituent layers were evaluated using elastic equations and microstructural studies like scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The investigation was conducted by applying the load parallel and perpendicular to the interface plane between constituent layers. The results showed that the properties of concrete improved in FGC compared to control. Formation of graded layer added value to the FGC. Among the specimens of various thickness combinations, the samples with 75 mm OPC concrete and 75 mm GGBFS concrete showed the best results when the load was applied parallel to the graded layer. Finally, environmental benefit in terms of embodied CO2, energy and cost benefit of the different mix proportion concrete are analysed. Further the effectiveness of FGC is also reported which has huge potential to be used in concrete structure elements.

Effect of surface attrition on hardness on the hardness and wear properties of 304 stainless steels

The occurrence of wear in austenitic stainless steel is inevitably unavoidable due to the presence of high chromium content and other alloying elements that hinder the implementation of surface treatment process. This process is usually use to improve the hardness and wear properties of steels and alloys by diffusing hard protected layer on the surface of the material. This paper investigates the effect of surface attrition on the hardness and wear properties of paste boronized 304 stainless steel. Surface attrition treatment was applied onto the surface of 304 stainless steel before paste boronizing was conducted at temperature of 850°C for 8 hours holding times. The microstructure of the boronized samples before and after surface attrition treatment was then observed and recorded in order to compare the phase constituent and boride layer thickness. The hardness of each phases was then evaluated using Vickers microhardness test and the wear resistance test of both paste boronized sample and surface attrited samples after boronizing was performed using pin on disk test. The microstructure results show that there are presences of both FeB and Fe2B phases on the surface of Pa-B850 and Pa-SB with boride layer thickness improvement of 3 times compared to untreated samples. This lead to enhancement of both hardness and wear resistance of the paste boronized samples due to better protection on the surface of the 304 stainless steel. The improvement of wear and hardness properties of 304 stainless steel could introduce new application that could be exposed to environment containing friction and wear.

Effects of initial stresses on guided wave propagation in multilayered PZT-4/PZT-5A composites: A polynomial expansion approach

Effects of initial stresses on the dispersion curves of Lamb and SH waves in multilayered PZT-4/PZT-5A composites are investigated using the polynomial expansion approach. The piezoelectric layers are considered with arbitrary crystal orientations with a result that only Lamb or SH waves may be transmitted. The problem is solved employing the Legendre polynomial approach that poses the advantages of numerically stability and effectiveness over conventional matrix method. The solution is validated by comparing the wave propagation behavior of piezoelectric materials with those reported in literature, and the convergence properties are examined. Numerical results demonstrate that initial stress has profound influences on the guided wave propagation in multilayered PZT-4/PZT-5A laminates. The phase velocity of Lamb and SH waves increases with initial tensile stresses. In addition, the effects of initial stresses rely on the wave mode and thickness of constituent layers and the stacking sequence of the constituent materials. The results are useful for understanding and optimization of new designs for actuator, electromechanical sensor and acoustic wave devices made of PZT-4/PZT-5A composites.

Topological Phase Buried in a Chalcogenide Superlattice Monitored by Helicity-Dependent Kerr Measurement.

Chalcogenide superlattices (SLs), formed by the alternate stacking of GeTe and Sb2Te3 layers, also referred to as interfacial phase-change memory (iPCM), are a leading candidate for spin-based memory device applications. Theoretically, the iPCM structure has been predicted to form a three-dimensional topological insulator or Dirac semimetal phase depending on the constituent layer thicknesses. Here, we experimentally investigate the topological insulating nature of chalcogenide SLs using a helicity-dependent time-resolved Kerr measurement. The helicity-dependent Kerr signal is observed to exhibit a four-cycle oscillation with π/2 periodicity, suggesting the existence of a Dirac-like cone in some chalcogenide SLs. Furthermore, we found that increasing the thickness of the GeTe layer dramatically changed the periodicity, indicating a phase transition from a Dirac semimetal into a trivial insulator. Our results demonstrate that thickness-tuned chalcogenide SLs can play an important role in the manipulation of topological states, which may open up new possibilities for spintronic devices based on chalcogenide SLs.

All‐Optical Detection of Periodic Structure of Chalcogenide Superlattice Using Coherent Folded Acoustic Phonons

Chalcogenide superlattices (SL) consist of alternately stacked GeTe and Sb2Te3 layers. The structure can act as a 3D topological insulator depending on the constituent layer thicknesses, making the design of the SL period a central issue for advancing chalcogenide SL as potential candidates for spin devices as well as for optimization of the current generation of phase‐change memory devices. Here we explore the periodic structure of chalcogenide SL by observing coherent folded longitudinal acoustic (FLA) phonons excited by femtosecond laser pulse irradiation. The peak frequency of the FLA modes is observed to change upon variation of the thickness of the GeTe layer, which is well reproduced by means of an elastic continuum model. In addition, a new SL structure is unveiled for a sample consisting of thin GeTe and Sb2Te3 layers, which suggests intermixing of Ge atoms. This all‐optical technique based on observation of coherent FLA modes offers a non‐destructive characterization of superlattice structures at atomic resolution.

Small GTPase RIT1 in Mouse Retina; Cellular and Functional Analysis

ABSTRACTPurpose: Ras-like without CAAX 1 (RIT1/Rit) is a member of the Ras subfamily of small GTP-binding proteins with documented roles in regulating neuronal function, including contributions to neurotrophin signaling, neuronal survival, and neurogenesis. The aim of the study was to (1) examine the expression of RIT1 protein in mouse retina and retinal cell types and (2) determine whether RIT1 contributes to retinal ganglion cell (RGC) survival and synaptic stability following excitotoxic stress.Materials and methods: Gene expression and immunohistochemical analysis were used to examine RIT1 expression in the mouse retina. Primary RGC and Müller glia cultures were used to validate novel RIT1 lentiviral RNAi silencing reagents, and to demonstrate that RIT1 loss does not alter RGC morphology. Finally, in vitro glutamate exposure identified a role for RIT1 in the adaptation of RGCs to excitotoxic stress.Results: Gene expression analysis and immunohistochemical studies in whole eyes and primary cell culture demonstrate RIT1 expression throughout the retina, including Müller glia and RGCs. While genetic RIT1 knockout (RIT1-KO) does not affect gross retinal anatomy, including the thickness of constituent retinal layers or RGC cell numbers, RNAi-mediated RIT1 silencing results in increased RGC death and synaptic loss following exposure to excitotoxic stress.Conclusions: RIT1 is widely expressed in the murine retina, including both Müller glia and RGCs. While genetic deletion of RIT1 does not result in gross retinal abnormalities, these studies identify a novel role for RIT1 in the adaptation of RGC to excitotoxic stress, with RIT1 promoting both neuronal survival and the retention of PSD-95+ synapses.

High-Temperature Thermoelectricity in LaNiO3-La2CuO4 Heterostructures.

Transition metal oxides exhibit a high potential for application in the field of electronic devices, energy storage, and energy conversion. The ability of building these types of materials by atomic layer-by-layer techniques provides a possibility to design novel systems with favored functionalities. In this study, by means of the atomic layer-by-layer oxide molecular beam epitaxy technique, we designed oxide heterostructures consisting of tetragonal K2NiF4-type insulating La2CuO4 (LCO) and perovskite-type conductive metallic LaNiO3 (LNO) layers with different thicknesses to assess the heterostructure-thermoelectric property-relationship at high temperatures. We observed that the transport properties depend on the constituent layer thickness, interface intermixing, and oxygen-exchange dynamics in the LCO layers, which occurs at high temperatures. As the thickness of the individual layers was reduced, the electrical conductivity decreased and the sign of the Seebeck coefficient changed, revealing the contribution of the individual layers where possible interfacial contributions cannot be ruled out. High-resolution scanning transmission electron microscopy investigations showed that a substitutional solid solution of La2(CuNi)O4 was formed when the thickness of the constituent layers was decreased.

Fano Resonance by Means of the One-Dimensional Superconductor Photonic Crystals

In the present work, we introduce a study about the reflectance properties of a one-dimensional superconductor photonic crystal in a different manner. Our structure is designed from alternately layers of high-temperature superconducting material (BSCCO) and a conventional superconducting material (Nb) terminated by the dielectric cap layer. The investigated numerical results are essentially based on the basics of the transfer matrix method and the two-fluid model. The numerical results showed the appearance of two sharp peaks, which are referred to Fano and electromagnetic-induced reflectance resonances. Also, we demonstrate the effects of many parameters on the reflectance properties of Fano resonance and the electromagnetic-induced reflectance. The effects of the constituent layer thicknesses, the number of periods, the operating temperature, the angle of incidence, and the refractive index of the dielectric cap layer are all considered. Finally, the effects of hydrostatic pressure on the Fano and EIR resonances are studied and calculated. This structure can play an important role in optical switching devices.

Toward an understanding of post-necking behavior in ultrafine-scale Cu/Ni laminated composites

Cu/Ni laminated composites with the same total thickness of 128µm, but different modulation wavelength λ (the sum of monolayer thickness of constituent layers) of 32µm and 3µm, respectively were prepared using a dual-bath electrodeposition technique. The tensile testing results and the quantitative characterization of strain gradient in the post-necking region of the composites reveal that the λ = 3µm composites have the higher tensile strength and the better strain hardening ability, as well as the stronger resistance to post-necking compared with the λ = 32µm ones. A high density of layer interfaces in the ultrathin laminated composite may play a key role in delaying the development of unstable plastic deformation along the layer thickness direction through periodical strain gradient and a number of geometrically necessary dislocations near the interfaces. Thus, the fatal localized plastic deformation along the through thickness direction has to be spread over along the loading direction, leading to the large neck breadth in the ultrathin laminated composites.

Atomic Layer Deposition and Properties of HfO2-Al2O3 Nanolaminates

Nanocrystalline HfO2:Al2O3 mixture films and nanolaminates were grown by atomic layer deposition at 350°C from metal chloride precursors and water. Formation of metastable HfO2 polymorphs versus monoclinic phase was affected by the relative amount and thickness of constituent oxide layers. The films exhibited saturative magnetization and charge polarization in externally applied fields at room temperature. The films also demonstrated resistive switching behavior with considerable window between low and high resistance states.