Interface Of Different Materials Research Articles

Performance evaluation of 2D MoS2-based solar cells and realization of transparent ultra-thin devices

Molybdenum disulfide (MoS2) is an alternate absorber layer in 2D solar cells owing to its potential of proficient sunlight harvesting. The optimum electrical and optical properties of MoS2 validate it as a suitable photovoltaic absorber material. This work investigates the performance of 2D (and multi-layer) MoS2-based vertically stacked solar cell by numerical simulation process using one dimensional solar cell capacitance simulator (SCAPS). Two device configurations based on Schottky junction (ITO/n-MoS2/Au) and pn junction (ITO/n-MoS2/p-MoS2/Au) have been theoretically analyzed. The feasibility of ultra-thin transparent solar cells is also demonstrated, which is motivating from a technological outlook. Initially, the properties of the active layers are optimized to give the highest performance. The findings are explained on the basis of band alignment between the electrodes and the different layers. The potential barrier developed at the interface of different materials governs the output of the cells. The calculations forecast the material properties, which need to be tuned to fabricate solar cells with enhanced efficiency. After optimization, the highest efficiency obtained for single n-MoS2-based solar cell is 10.22%, while for the pn junction solar cell it is 16.86%. The optimized cells exhibit high open circuit voltages of ∼1.2 V, which is an essential factor for commercial realization of solar cells. Lastly, the performance of transparent solar cells based on thin 2D MoS2 films has been predicted which showcases the efficiency in the range of 0.78%–4.36%. These homo-junction device investigations of solely MoS2 layer along with employment of a strict control on the defects during deposition and fabrication of MoS2-based solar cells can ensure better performance of the device. Thus, it can open ways to develop next generation feasible solar cells with higher power density as compared to existing technology.

Calculation and Application of Ultimate Lateral Friction Resistance of Concrete Piles under Different Soil Layer Materials

In practical engineering applications, it usually gets the expected value of the ultimate side friction of concrete piles by the empirical parameter method. The expected value of the ultimate side friction of concrete piles cannot achieve maximum optimization due to the complexity of formation conditions and the lack of experience of technicians. To accurately obtain the ultimate lateral friction resistance of piles in homogeneous soil layers, optimize the standard value of pile ultimate lateral resistance, ensure construction safety, and save construction costs, the research method combining theoretical derivation and on-site measurement data validation was done in the manuscript. Based on the shear strength of the pile-soil interface of different materials and the shear performance of the soil around the pile, a calculation equation for the standard value of the ultimate lateral friction resistance of concrete piles in different homogeneous soil materials was derived and applied to the equation for calculating the ultimate bearing capacity of foundation pile and the axial force of pile. Finally, based on an engineering example, the calculated results were compared with the measured resultsThe research results show that in thick coarse-grained soil, as the foundation pile is short, the ultimate bearing capacity of a single pile obtained using the calculation equation deduced in this paper is less than that obtained using the empirical equation provided by the national code. In a deep cohesionless homogeneous soil material, the concrete pile shaft axial force calculation using the pile shaft axial force calculation equation deduced in this paper is close to the measured value when the foundation pile bears the ultimate load; the proposed new method has good application value.

Experimental research on mechanical properties of simply composite beam with reactive powdered concrete considering the shear slip effect

To evaluate the effectiveness of reactive powder concrete in practical applications, this study focuses on analyzing the mechanical properties of composite beams reinforced with reactive powder concrete under concentrated forces. By employing the principles of elastic mechanics, an analytical solution is derived for double-layer reactive powder concrete laminated beams subjected to vertical concentrated forces. The obtained deflection curve equation provides valuable insights into the behavior of double-layer laminated beams. The study investigates the stress performance of concrete beams reinforced with reactive powder concrete through static load tests. The tests include ordinary reinforced concrete beams, ordinary concrete reinforced beams, and steel fiber reactive powder concrete reinforced test beams. The experimental results demonstrate that the load capacity of ordinary concrete beams can be significantly improved by strengthening them with RPC. The strain distribution along the height of the section follows the assumption of a flat section, and the failure pattern of the reinforced test beam is similar to that of the ordinary concrete beam. Therefore, it is feasible to predict the results and phenomena of the composite beam by analyzing the stress in an ordinary reinforced concrete beam. Shear slip occurs at the interface of different materials under stress due to the reinforcement layer. The test results also indicate that special attention should be given to the beam body's fulcrum and the shear member's quart.

Water as a contrast agent to quantify surface chemistry and physics using second harmonic scattering and imaging: A perspective

Molecular level interactions that take place at the interface of different materials determine their local electrical, chemical, and mechanical properties. In the case of solid interfaces, this information has traditionally been obtained with experimental techniques that require ultra-high vacuum conditions. However, these methods are not suitable for studying surface chemistry of aqueous interfaces. Recently, an approach emerged for probing such interfaces using interfacial water as a contrast agent. This approach is based on second harmonic generation from water molecules next to a charged interface and can be utilized in both scattering and microscopy geometries. In this Perspective, we explain this approach in more detail and provide examples and comparisons for a diverse set of applications: colloid science and solid state physics, illustrated by silica–water surface chemistry, and biophysics, illustrated by membrane–water–ion channel interactions. Those two diverse applications show that by following the structure of interfacial water, it is possible to extract and quantify important chemical parameters such as surface potential values, structure of the electric double layer, and local dissociation constants that are useful in many different contexts.

Evaluation of Low-Frequency Noise in MOSFETs Used as a Key Component in Semiconductor Memory Devices

Methods for evaluating low-frequency noise, such as 1/f noise and random telegraph noise, and evaluation results are described. Variability and fluctuation are critical in miniaturized semiconductor devices because signal voltage must be reduced in such devices. Especially, the signal voltage in multi-bit memories must be small. One of the most serious issues in metal-oxide-semiconductor field-effect-transistors (MOSFETs) is low-frequency noise, which occurs when the signal current flows at the interface of different materials, such as SiO2/Si. Variability of low-frequency noise increases with MOSFET shrinkage. To assess the effect of this noise on MOSFETs, we must first understand their characteristics statistically, and then, sufficient samples must be accurately evaluated in a short period. This study compares statistical evaluation methods of low-frequency noise to the trend of conventional evaluation methods, and this study’s findings are presented.

(Invited) Surface Analysis of Corrosion Products Built up at Interfaces of Different Nuclear Waste Forms in Near-Field Environment

In this study, we applied a series of surface analysis techniques to explore the structure and chemistry of the corrosion products built up at the interface of different materials, which is relevant to the permanent disposal of world-wide high-level nuclear waste. Metallic alloys, amorphous glass, and crystalline ceramics are typical candidate nuclear waste forms planned for immobilizing and isolating the dangerous radionuclides enriched in the waste. The near-field corrosion interactions between these dissimilar materials are the focus of this study. The experiments were performed by corroding metallic alloys in intimate proximity to glass or ceramics in Cl--containing solutions at 90 oC. The exposed materials were subsequently subjected to comprehensive surface characterization using X-ray photoelectron spectroscopy, scanning transmission electron microscopy, energy dispersive spectroscopy, time-of-flight secondary ion mass spectrometry, and Raman/infrared spectroscopy analysis. The systematic study revealed localized damage on the alloy surface due to crevice corrosion. Interestingly, localized corrosion was also identified on the surface of some glasses and ceramics that were present nearby, while an inhibition effect was observed in other systems. These interactions were found to strongly depend on the type of materials and environment, which led to different corrosion phenomena.

Numerical Simulation and Experimental Confirmation of a Bimetallic Pipe Forming Process.

Most oil and gas is transported by pipeline, and corrosion causes a great threat to the service life of the pipeline; bimetallic pipe, which combines the advantages of good mechanical properties, good corrosion resistance, and relatively low price, is a good choice for high-pressure and corrosion-resistant pipe, but its manufacturing process and stress distribution are more complex than single metal pipe. JCO is a widely used cold forming method for pipes which is named by the shape of the plate in the forming process, i.e. J-shape, C-shape and O-shape, and the forming process is an important parameter that determines the level of imperfections and residual stresses in a pipe, and residual tensile stress will accelerate corrosion failure of the pipe. In this study, the three-dimensional (3D) finite element method (FEM) is used to simulate the pre-bending and JCO forming process of a 2205/X65 bimetallic pipe. The model and the simulated results are validated by digital image correlation (DIC) experimental and the opening width of the formed pipe billet, respectively. The influence factors of the stresses are studied. Further, a two-dimensional (2D) model is established to study the characteristics of bimetallic plate bending and the stress distribution at the interface of different materials, and the results are compared with that of three-dimensional model.

A New Interpretation of Discontinuity Factor

A new interpretation of the discontinuity factor (DF) for scalar flux, partial current, and angular flux is discussed. Conventionally, the DF is considered as the discontinuous condition of scalar flux, partial current, or angular flux at an interface. In the new interpretation, the DF is considered as the refractive index of materials for partial current or angular flux that conserves odd-parity or odd-moment angular flux at an interface of different materials. It is related to the transmission and reflection of partial current or angular flux at an interface where different materials are adjacent. Using the present interpretation, a fundamental issue of neutron balance (i.e., artificial loss or production of neutrons at an interface due to discontinuous condition), which would appear in the conventional interpretation of DF, can be resolved.

Effect of the twisting chirality configuration on the electromechanical behavior of multilayer superconducting tapes

Seeking a geometry that can withstand greater transverse loads based on the electromechanical material properties of high-temperature superconducting (HTS) tape is an effective way of improving the transport performance of HTS cables. The cabling method requires the determination of the optimum twist angle of the HTS tape for withstanding transverse loads. This paper investigates the critical current characteristics of HTS tapes under combined deformation. The limit range of the twist angle under the combined deformation is measured and the optimum twist angle of the HTS tape is determined. The results show that the twisting chirality configuration obviously affects the bending strength of the HTS tape. In the elastic range, increasing the pre-twist angle increases the bending strength of the HTS tape, thereby improving the transport performance. In addition, a numerical model is built to further investigate the effect of the twisting chirality configuration on the electromechanical properties of the HTS tape, and the experimental results are explained. The experimental and simulation results generally agree well, and calculations show that there is always a sharp change in stress at the interface of different materials. These findings explain the mechanism of the effect of the twisting chirality configuration on the mechanical behavior and critical current of the HTS tape. They also provide a reference for cabling methodologies for the HTS cable configuration.

Multi-material modelling for selective laser melting

Selective Laser Melting (SLM) is a powder-bed Additive Manufacturing (AM) process which uses a laser beam to fully melt the powders layer upon layer to build a 3D part. While most studies are conducted on SLM using single material, the application of multi-materials using this technology can offer more advantages than the conventional manufacturing methods. Complex multi-materials parts can be built which conventional manufacturing methods are unable to due to their restriction in design of freedom. However, the SLM process has its own limitations in producing multi-material parts. Since SLM uses a powder bed to build parts, the use of different powder materials in the powder bed will result in contamination of the unused powder, rendering unnecessary wastages. Therefore, using modelling techniques to attain the optimized parameters before conducting the actual experiment to verify its validity will aid in reducing wastages, leading to cost saving. To study the effects of the interface of different materials during the laser scanning, a model was simulated to observe the melting process. An open-source LAMMPS (Large-scale Atomic Molecular Massively Parallel Simulator) software uses Molecular Dynamics (MD) to simulate the melting process. The materials used for the simulations are iron (FE) and aluminum (Al). The modelling is extended to multiple layers to allow the observation of the bonding between layers.

Multi-material topology optimization considering interface behavior via XFEM and level set method

In most of the existing topology optimization studies of multi-material structures, the interface of different materials was assumed to be perfectly bonded. Optimal design based on the perfect-interface assumption may introduce the risk of failure caused by interface debonding. This paper presents an efficient multi-material topology optimization strategy for seeking the optimal layout of structures considering the cohesive constitutive relationship of the interface. Based on the color level set method to describe the topology and the interface, the interface behavior is simulated by combining the extended finite element method (XFEM) and the cohesive model on fixed mesh. This enables modeling of possible separation of material interfaces, and thus provides a more realistic model of multi-material structures. Furthermore, this interface modeling technique avoids the difficulty of re-meshing when tracking the moving cohesive interface positions during the optimization process. In the topology optimization model, the normal velocities defined on the level set points are considered as design variables. In conjunction with the adjoint-variable sensitivity analysis, these design variables are updated by using the mathematical programming approach and then used to interpolate the boundary velocities. These boundary velocities are extrapolated to the whole domain with the fast marching method and used to advance the structural boundary through the Hamilton–Jacobi equation. This topology optimization technique can handle multiple constraints easily in the framework of level set method and at the same time preserve the signed distance property of the level set functions. Two numerical examples are given to demonstrate the effectiveness of the present method. It is also revealed that the optimal design considering interface behavior may exhibit tension/compression non-symmetric topology, in which material interfaces mainly undergo compression.

An analytical method to estimate spatially-varying thermal contact conductances using the reciprocity functional and the integral transform methods: Theory and experimental validation

The increasingly interest in using composite materials in engineering application requires the proper knowledge of the interaction that occurs between their layers. One of these interactions is related to the temperature jump and heat flux through the interface of different materials, known as thermal contact resistance, or its reciprocal, the thermal contact conductance. Methods to estimate thermal contact resistance usually require temperature measurements taken inside the sample (test body) and complicated experimental arrangements. In this work we propose an analytical, non-iterative and non-intrusive method to solve an inverse heat transfer problem in order to estimate a one-dimensional steady-state distribution of the thermal contact conductance, combining the reciprocity functional and the Classical Integral Transform Technique (CITT). This paper is an extension of our previous works, where the solution procedure was developed numerically and required the solution of two linear systems. In this paper, the estimate is reduced to a single algebraic equation. The method was applied to some test cases using simulated measurements and results were compared with the exact solution showing a good agreement between them. A validation involving a double-layered material was also conducted, where an infrared camera was used to measure the temperature non-intrusively. A micromachinery produced flaw was created in the contact between the two materials and, once the temperature measurements were available, the method was able to identify the flaw location in 0.2s using an Intel Atom(TM) CPU N450 1.66GHz.

Unified formulation for modeling heat and fluid flow in complex real industrial equipment

The direct simulation of conjugate heat transfer has recently attracted considerable attention in many industrial applications. However, the underlying physical phenomena are less clear due to the intrinsically interactions occurring at the interface of different materials at different temperatures with the surrounding turbulent gas. To simulate these direct exchanges, here we study a unified multi-material formulation in two and three-dimension. The coupled system is solved using stabilized finite element methods combined with a posteriori error estimator for anisotropic mesh adaptation enhancing the interface representation. Computational results are compared with experimental data in complex 3D industrial setups with up to four different materials. The results have demonstrated that convection, conduction and radiative heat transfer can be simultaneously used and easily applied yielding accurate predictions.

Thermal Stress and Failure Location Analysis for Through Silicon via in 3D Integration

AbstractThrough silicon via (TSV) is the critical structure for three dimensional (3D) integration, which provides vertical interconnection between stacking dies. In TSV structure, large coefficient differences of thermal expansion exist between silicon substrate, dielectric material, and filled metal. Due to the large thermal mismatch, the high thermal stress occurring at the interface of different materials would result in delamination. Therefore, thermal-mechanical reliability is a key issue for 3D integration. In this study, we investigated the thermal-mechanical stress distribution of TSV under the condition of the accelerated thermal cycling loading by finite element analysis based on a 3D model of TSV structure. Due to the thermal expansion, that the TSV structure squeezed the surface area between TSVs at a high temperature resulted in compressive stresses at the surface area between TSVs. Therefore, a proper distance between the stress-sensitive device and the TSV should be kept. The stress analysis shows that the maximum thermal stress occurs in the outside region of TSV interface and in the annular region of TSV at a high temperature and at a low temperature, respectively. This study helps to obtain a clear thermal stress distribution of TSV and possible failure regions can be determined.

Interlayer interaction in general incommensurate atomic layers

We present a general theoretical formulation to describe the interlayer interaction in incommensurate bilayer systems with arbitrary crystal structures. By using the generic tight-binding description, we show that the interlayer coupling, which is highly complex in the real space, can be simply written in terms of generalized Umklapp process in the reciprocal space. The formulation is useful to describe the interaction in the two-dimensional interface of different materials with arbitrary lattice structures and relative orientations. We apply the method to the incommensurate bilayer graphene with a large rotation angle, which cannot be treated as a long-range moiré superlattice, and obtain the quasi band structure and density of states within the first-order approximation.

X-ray reflectivity study of the glass transition temperature of thin films

The glass transition takes place in amorphous materials (like polymers) during heating or cooling, and can be described as reversible transition from a hard and brittle state into a rubber-like state. Although physical properties of the material change significantly during the glass transition, this is not a phase transition of the material. The temperature at which the transition between the glassy and rubbery state occurs is called the glass transition temperature, and this temperature is always lower than the melting temperature. Thermodynamically, the glass transition is associated with transfer of heat between the system and its surrounding and with an abrupt volume change. Previously it was shown that the glass transition temperature of nano-films is different from that of bulk materials [1], which signifies the importance of determining this parameter for such systems. In the current work, we use quick X-ray reflectivity (qXRR) measurements to determine the glass transition temperature of polyvinyl acetate (PVAc). PVAc is rubbery synthetic polymer with the formula (C4H6O2), a density of 1.18 g/cm3, and a glass transition temperature for bulk material of 30oC [2]. Regular X-ray reflectivity measurements are based on θ/2θ scans at grazing incidence and typically require 0.5-1.5 h for a single scan. The qXRR technique is based on simultaneous measurement of the whole angular x-ray reflectivity profile and is suitable for in-situ measurement without moving the sample and/or the x-ray optics. Thus, the qXRR technique allows for very fast measurement of the x-ray reflectivity curves (duration of each scan is typically 0.1–20 sec [3]), which permits studying the time evolution of chemical, thermal, and mechanical changes at the surface and interface of different materials. X-ray reflectivity measurements give information about both density and thickness of thin films, and are suitable for studying glass transition phenomena. Nano-thickness PVAc layers on a Si substrate were examined with the qXRR technique, with x-ray reflectivity scans (each 10-seconds in duration) being recorded while temperature was changed from 20 to 50oC (total of 331 scans over 7 hours and 46 minutes). In the current paper, the experimental setup, the data-processing, and the analysis of the results from the qXRR measurements will be presented.

Covalent attachment of a three-dimensionally printed thermoplast to a gelatin hydrogel for mechanically enhanced cartilage constructs

Hydrogels can provide a suitable environment for tissue formation by embedded cells, which makes them suitable for applications in regenerative medicine. However, hydrogels possess only limited mechanical strength, and must therefore be reinforced for applications in load-bearing conditions. In most approaches the reinforcing component and the hydrogel network have poor interactions and the synergetic effect of both materials on the mechanical properties is not effective. Therefore, in the present study, a thermoplastic polymer blend of poly(hydroxymethylglycolide-co-ε-caprolactone)/poly(ε-caprolactone) (pHMGCL/PCL) was functionalized with methacrylate groups (pMHMGCL/PCL) and covalently grafted to gelatin methacrylamide (gelMA) hydrogel through photopolymerization. The grafting resulted in an at least fivefold increase in interface-binding strength between the hydrogel and the thermoplastic polymer material. GelMA constructs were reinforced with three-dimensionally printed pHMGCL/PCL and pMHMGCL/PCL scaffolds and tested in a model for a focal articular cartilage defect. In this model, covalent bonds at the interface of the two materials resulted in constructs with an improved resistance to repeated axial and rotational forces. Moreover, chondrocytes embedded within the constructs were able to form cartilage-specific matrix both in vitro and in vivo. Thus, by grafting the interface of different materials, stronger hybrid cartilage constructs can be engineered.

Erratum to: Energy Field Simulating of Heat Transfer Capability and Damage Evaluation on an Improved Langmuir Probe

In this paper we proposed a advanced Langmuir probe (LP)—cooling monoblock (CM) model used in Tokamak of controlled thermonuclear fusion, this model adopted several novel designs used for improving the heat transfer capability. In the transient thermal analysis, the effect of conical degree of AL2O3 ceramic barrel on the thermal contact resistance at the interface of different materials has been systematically studied and a reasonable explanation was given for the phenomenon where the increasing of conical degree lead to the decreasing of thermal contact resistance. Moreover the top part of CM of the plasma facing unit was prepared by pyrolytic graphite can make the temperature of LP obviously reduced. Eventually the thermal state of LP during the 400 s pulse are figured out by ANSYS under optimal loading conditions, the calculation results showed the maximum temperature of LP is 2,253°C at 211 s, meanwhile, the basic characteristics for variation of the maximum temperature of LP with the incident heat flux are presented. These results obtained in this work are helpful to reveal the thermal energy state of LP more accurately, reduce the damage on the device, and improve its working stability.

Finite Element Method Used in the Calculation of Earth-Rock Dam Seepage Reflections

This paper analyzes the problems which exist in finite element calculations of the earth dam seepage which is free surface solution, cell subdivision improper, the transformation of the free surface boundary conditions and the permeability coefficient values at the interface of different materials, boundary conditions and other issues. Put forward the corresponding solution. Applies common general finite element software to calculate the seepage. Works in conjunction with a stable levee seepage analysis and get better results.

Optimal Design of Electrostatic Probe via Finite Element Method and Experimental Investigation

Thermal contact resistance (TCR) at the interface of different materials has been systematically investigated with a effective analytical method and appropriate values of TCR are obtained by theoretical calculation with measured parameters. In this paper, a novel optimal design used to decrease TCR in model via increasing the conical degree of AL2O3 ceramic barrel is developed, results indicated the heat transfer capability of Langmuir Probe (LP) can be improved by using this configuration. Numerical simulation of transient-state thermal analysis by ANSYS and experimental investigation have been used to evaluate the thermal state of LP under different analytical conditions, comparison of simulated results with the top-middle part of LP prepared by Pyrolytic Graphite and Carbon Fiber Composite are presented and an explanation of temperature variation based on the changes of the simulated results with the top part of LP designed by different sizes are demonstrated. Many constructive suggestions have been brought forward to define the best suited material, structures and other characteristics in order to produce the type of LP with high performance and practicability.