Thickness Of Top Layer Research Articles

Fluorophore Coupling to Internal Modes of Bragg Gratings

Multilayer structures with two dielectrics having different optical constants and no structural features in the x-y plane can display photonic band gaps (PBGs) and are called one-dimensional photonic crystals (1DPCs). If the top layer thickness is carefully selected, the electromagnetic energy can be trapped at the top surface. These highly enhanced fields are called Bloch surface waves (BSWs). The BSW resonance angles are sensitive to the dielectric constant above the top dielectric layer. As a result, BSW structures have been used for surface plasmon resonance-like measurements without the use of a metal film. However, the emphasis on surface-localized BSWs has resulted in limited interest in fluorophore interactions with other optical modes of 1DPCs or Bragg gratings without the different thickness top layer. Herein, three different fluorescent probes were used to cover the short, center, and long wavelengths of the PBG. We demonstrate efficient coupling of fluorophores to both the BSW and internal modes (IMs) of a 1DPC. Coupling to the IM is expected to be low because of the micron-scale distances between the fluorophores and IM, which exists inside the Bragg gratings. At different wavelengths or observation angles, the IM-coupled emission (IMCE) can occur with the first three modes of the multilayer. This coupling is not dependent on a BSW mode. IMCE was also observed for a monolayer of fluorophore-labeled protein. IMCE enables sensitive detection of surface-bound fluorophores. Applications are anticipated in high sensitivity detection and super-resolution imaging.

Ultrathin TiO2 microfiltration membranes supported on a holey intermediate layer to raise filtration performance

Ultrathin TiO2 microfiltration membranes with thicknesses in the range of 1−7 μm were prepared by coating TiO2 suspensions on purposely designed holey Al2O3 substrates. The effects of the TiO2 top layer thickness on surface roughness, pore size distribution, and thereby on water flux, steady permeate and retention performance of the overall membrane were systematically investigated. The ultrathin TiO2 membrane layer with a thickness of ∼3 μm, surface roughness of ∼109 nm and an average pore size of 87 nm shows the best overall performance. Its pure water flux (2214 Lm−2 h-1 bar-1) at 100 kPa and normalized permeate flux (59 %) after 50-min filtration in a feed solution of 70-nm polystyrene nanospheres (2 ppm) are much higher than those of the control TiO2 membrane (696 Lm−2 h-1 bar-1 and 27 %). The disruptively improved pure water flux and normalized steady permeate flux, without significantly sacrificing the retention performance, are correlated to the unique membrane structural features.

Nondestructive Evaluation of Thermal Barrier Coatings Interface Delamination Using Terahertz Technique Combined with SWT-PCA-GA-BP Algorithm

Thermal barrier coatings (TBCs) are usually subjected to the combined action of compressive stress, tensile stress, and bending shear stress, resulting in the interfacial delamination of TBCs, and finally causing the ceramic top coat to peel off. Hence, it is vital to detect the early-stage subcritical delamination cracks. In this study, a novel hybrid artificial neural network combined with the terahertz nondestructive technology was presented to predict the thickness of interface delamination in the early stage. The finite difference time domain (FDTD) algorithm was used to obtain the raw terahertz time-domain signals of 32 TBCs samples with various thicknesses of interface delamination, not only that, the influence of roughness and the thickness of the ceramic top layer were considered comprehensively when modeling. The stationary wavelet transform (SWT) and principal component analysis (PCA) methods were employed to extract the signal features and reduce the data dimensions before modeling, to make the cumulative contribution rate reach 100%, the first 31 components of the SWT detail data was used as the input data during modeling. Finally, a back propagation (BP) neural network method optimized by the genetic algorithm (GA-BP) was proposed to set up the interface delamination thickness prediction model. As a result, the root correlation coefficient R2 reached over 0.95, the various errors—including the mean square error, mean squared percentage error, and mean absolute percentage error—were less than or equal to 0.53. All these indicators proved that the trained hybrid SWT-PCA-GA-BP model had excellent prediction performance and high accuracy. Finally, this work proposed a novel and convenient interface delamination evaluation method that could also be potentially utilized to evaluate the structural integrity of TBCs.

Fabrication and Corrosion Resistance Evaluation of Novel Epoxy/Oxide Layer (MgO) Coating on Mg Alloy

A protective novel (MgO) oxide layer (with 91.92% corrosion protection efficiency) was successfully applied on Mg–0.4%Ca alloy using protective oxidation at 390°C (without any pre-treatment). Oxide layer coated Mg alloy was then coated with pure epoxy coating (as top coat). This oxide inner barrier layer protected Mg substrate from 3.5wt % NaCl solution when it passes through from epoxy top layer. Lowest anodic current density and highest charge transfer resistance (1118.124 kΩ cm2) and impedance modulus (│Z│) at low frequency substantiated that the existence of thick epoxy top layer which is integrated (via physical anchoring) with the oxide inner barrier layer could considerably reduce the corrosion rate of magnesium substrate in the chloride containing solutions. Moreover, corrosion mechanism for coated Mg–0.4%Ca alloys was then suggested.

Interface formation between Be and W layers depending on its thickness and ordering

In the present work, formation of interfaces in the W/Be layered structures was studied using X-ray photoelectron spectroscopy. Chemical composition and significance of the interfaces depending on the thickness and ordering of beryllium and tungsten layers were investigated by means of the XPS spectra decomposition technique. The formation of tungsten beryllides WBe2 and WBe12 at the W-on-Be and Be-on-W interfaces, respectively, was revealed. The thickness of WBe2 beryllide does not depend on the thickness of a tungsten top layer, whereas WBe12 thickness increases with increasing Be top layer thickness. Additionally, oxidation of a Be layer under a thin W layer was established and possible mechanism underlying this process was proposed.

On-Chip Inductor in 0.18-μm CMOS for Low-Cost Fully Integrated Contactless Powered Sensors

Contactless sensors with CMOS on-chip antennas use only the top thick metal for the polarization antenna due to the low inductance contribution of the bottom (thin) CMOS metals adding only resistance to the antenna. In this letter, a two-layer inductor (thick top metal layer inductor in series with the bottom thin four-layer metal inductor) configuration was proposed for wireless polarization (by electromagnetic induction). The design proposed was simulated and fabricated in a 0.18- $\mu \text{m}$ CMOS process. The on-chip inductor powers a chip with a 1-mW load at a distance of 2 mm coupled with an external wireless power transmitter at 13.5 MHz with a 30-dBm output. The two-layer inductor configuration reduces the area required for the on-chip inductor by 38% and increases the on-chip inductor quality factor by 25% compared with a single-layer configuration, thus reducing the cost of fabricating fully integrated contactless sensors using only CMOS technologies.

Design and optimization of 26.3% efficient perovskite/FeSi2 monolithic tandem solar cell

A multijunction or tandem technique comprising a wide bandgap top cell and a narrow bandgap bottom cell may be a major stepping stone in an attempt to obtain high-efficiency solar cells. However, easier said than done, it takes a lot to correctly optimize the structure of all the involved layers so as to possibly obtain the desired results. In this paper, a perovskite (CH3NH3PbI3)/FeSi2 (p-i-n structure) 2-terminal (2-T) monolithic tandem solar cell is proposed and investigated using AFORS-HET v2.5 1D simulator. A hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon oxide (µc-Si1−xOx:H) tunnel recombination junction is employed to interconnect both perovskite and FeSi2 solar cell for current matching. The influence of both top and bottom absorber layer thickness is analyzed to optimize the device performance. The study reveals an optimized 26.3% efficient perovskite/FeSi2 monolithic tandem solar cell with JSC (21.4 mA cm−2), VOC (1.63 V), and FF (74.86%). The results in this paper suggest FeSi2 material with 0.87 eV bandgap as an alternative for narrow bandgap bottom cell for the perovskite-based tandem solar cells so as to obtain much higher efficiencies.

Determination of Layers’ Thicknesses by Spectral Analysis of Swept-Frequency Measurement Signals

The aim of this study was to investigate the use of swept frequency eddy current testing to measure each layer's thickness in a layered structure. Theoretical inference showed the impedance signal is an integrand of shape function and generalized reflection function. Analytical study indicated that the wavelength to maximize the shape function is an indicator of a probe's thickness measurement ability. Comprehensive investigation revealed the reflection coefficient of a layered structure could be considered a modification of that of a half space. The amount of modification is a logarithmic linear function of plate thickness and thus a characteristic feature for thickness estimation. The frequency response of a double-layered structure depends, in addition to layer-wise thickness and properties, significantly on the relation of the conductivities of the two layers. In order to evaluate two closely attached layers, we introduced a novel variable, the derivative of impedance with respect to log scaled angular frequency. Spectral analysis on impedance or the frequency derivative related quantities, such as extrema of the real or imaginary parts of the variable, suggested it is possible to determine the top layer's thickness using characteristic features taken from high frequency signals, whereas the lower layer's thickness using characteristic features taken from lower frequency signals afterwards. The characteristic quantities derived from spectral analysis are conductivity independent, implying of conductivity independent measurement. The analytical findings were experimentally verified, suggested that it is possible to determine layers' thicknesses by spectral analysis of swept frequency eddy current testing signals.

In-situ study of exchange-bias in interlayer coupled Co/CoO/Co trilayer structure

Exchange bias (EB) properties of Co/CoO/Co trilayer structure with increasing top Co layer thickness has been studied in-situ using magneto-optic Kerr effect (MOKE) and reflection high energy electron diffraction (RHEED). Intermediate native oxide layer (CoO) was prepared by thermal oxidation of the bottom Co layer (Cobot), whereas the trilayer structure was formed by subsequent deposition of another Co layer (Cotop) on top. Two step magnetization reversal of trilayer at room temperature (RT) is observed due to the different coercive field (Hc) contribution of Cobot and Cotop layers. Individual contribution of magnetization reversal of both Co layers at RT as well as field cooled (FC) conditions is separated out by fitting the magnetic hysteresis loops using an adequate mathematical function. Increasing thickness of Cotop on Cobot/CoO bilayer is found to affect EB and Hc of the Cobot layer significantly. With an addition of 4 nm thick Cotop layer, EB corresponding to a Cobot layer is reduced by about 20% when FC to 153 K. Whereas, a further increase in Cotop layer thickness is found to be responsible for the relatively slow reduction in EB. Unusual asymmetric magnetization reversal with single step coherent rotation in descending branch and two step reversal in ascending branch of the loop after field cooling below Néel temperature (TN) was understood in terms of the combined effect of interface induced EB and interlayer coupling (IC) between Cotop and Cobot layers. The present study, where all the measurements are performed in-situ just after each step of deposition on the same film, provided genuine information about the EB in interlayer coupled spin valve like Co, CoO based trilayer structure.

Evaluation of sustainability of microgrid grounding grid design under varying soil conditions through estimation of touch, step voltages and novel methods of earthing

This study examines the sustainability of uniform as well as an optimal grounding grid (GG) design for the microgrid (MG), in terms of variations in the top layer (TL), middle layer (ML), and bottom layer (BL) soil resistivities ( ρ 1 , ρ 2 , and ρ 3 , respectively) along with change in a thickness of TL and ML. GG design is highly dependent on ρ 2 , as it helps in determining the density of conductors at grid extremities. With an increase in ρ 2 , touch voltage (TV) crosses its tolerable limit, but step voltage (SV) remains within its limit. However, with a simultaneous increase in the thickness of ML (MLT), SV also crosses its limit. For ρ 2 higher than ρ 3 , with an increase in MLT, TV, and SV increase, while in the reverse case, they decrease. For the given MLT, ρ 3 is crucial in determining GG burial depth. Validation of results is done by comparing them with the IEEE standard. Also, the optimal compression ratio of GG with an increase in MLT is analysed. TVs can be reduced to a great extent, with the application of distinctive methods of earthing (TT-GG system, TN-S-GG system, and TN-C-S-GG system) in MG. This study also reveals that an increase in GG resistance leads to a reduction in TV.

Numerical study of ultimate bearing capacity of rectangular footing on layered sand

Purpose: The purpose of this study is to investigate the ultimate bearing capacity of the rectangular footing resting over layered sand using finite element method. Design/methodology/approach: Finite element analysis was used to investigate the dimensionless ultimate bearing capacity of the rectangular footing resting on a limited thickness of upper dense sand layer overlying limitless thickness of lower loose sand layer. The friction angle of the upper dense sand layer was varied from 41° to 46° whereas for the lower loose sand layer it was varied from 31° to 36°. Findings: The results reveal that the dimensionless ultimate bearing capacity was found to increase up to an H/W ratio of about 1.75 beyond which the increase was marginal. The results further reveal that the dimensionless ultimate bearing capacity was the maximum for the upper dense and lower loose sand friction angles of 46° and 36°, while it was the lowest for the upper dense and lower loose sands corresponding to the friction angle of 41° and 31°. For H/W = 0.5 and 2, the dimensionless bearing capacity decreases with the increase in the L/W ratio from 0.5 to 6 beyond which the dimensionless ultimate bearing capacity remains constant for all combinations of parameters. The results were presented in nondimensional manner and compared with the previous studies available in literature. Research limitations/implications: The analysis is performed using a ABAQUS 2017 software. The limitation of this study is that only finite element analysis is performed without conducting any experiments in the laboratory. Further the study is conducted only for the vertical loading. Practical implications: This proposed numerical study can be used to predict the ultimate bearing capacity of the rectangular footing resting on layered sand. Originality/value: The present study gives idea about the ultimate bearing capacity of rectangular footing when placed on layered sand (dense sand over loose sand) as well as the effect of thickness of top dense sand layer on the ultimate bearing capacity. The findings could be used to calculate the ultimate bearing capacity of the rectangular footing on layered sand.

INFLUENCE OF TOP LAYER DENSITY AND THICKNESS ON HARDNESS OF TWO-LAYER FLOOR ELEMENTS

INFLUENCE OF TOP LAYER DENSITY AND THICKNESS ON HARDNESS OF TWO-LAYER FLOOR ELEMENTS

Effect of top soil liquefaction potential on the seismic response of the embedded piles

3D model was performed using the ANSYS program to investigate the behaviour of piles embedded in a liquefiable area during earthquakes. The model contained a CPT215 element that has an additional degree of freedom for water pressure. Two components of the movement were employed to the model for EL-CENTRO earthquake, 1940. The results showed good model accuracy compared to the previous tests. When the model was subjected to horizontal movement only, the lateral pile displacement decreased with the increase of top non-liquefiable layer thickness and vice versa. Whereas when both horizontal and vertical component of motions were applied to the model; the lateral pile displacement increased significantly in the case of the top non-liquefiable depth is 3 m only, and the vertical pile displacement increased with the reduction of top layer thickness. The presence of top liquefiable layer is very influential on the lateral pile displacement as it increased by 120%.

The effect of pinned uncompensated moments on the exchange bias in Ni81Fe19/Ni50Mn50/Ni81Fe19 trilayers

In this work, we prepared Ni81Fe19/Ni50Mn50 bilayers and Ni81Fe19/Ni50Mn50/Ni81Fe19 trilayers by magnetron sputtering. In order to determine whether the main contribution to the exchange bias is the ferromagnetic (FM)/antiferromagnetic (AFM) interface effect or the AFM bulk effect, the relationships between the exchange bias field and the top layer thickness, AFM layer and bottom layer were studied. The measured data show that the values of the exchange bias field were much smaller for trilayers than bilayers. This reduction is mainly caused by the thickness of the top Ni81Fe19 layer; the value of the exchange bias field becomes small when the thickness of the top layer is large. It was also observed that the exchange bias field decreases with the thickness of the bottom Ni81Fe19 layer, which is consistent with the top layer thickness dependence. Such a behavior can be explained by the pinned uncompensated moments inside the bulk of the AFM layer. The results indicate that the Ni50Mn50 layer contains a lower amount of pinned uncompensated moments in the Ni81Fe19/Ni50Mn50/Ni81Fe19 trilayer than in the bilayer films, which leads to a reduction in the exchange bias field.

STUDY SIMULATION OF TOP-CELL ON THE PERFORMANCE OF AlxGa1- xAs/Si1-xGexTANDEM SOLAR CELL

In this study, numerical optimization and analysis utilizing AMPS-1D software package of a simple model for tunnel junction (AlGaAs) between the top cell (AlGaAs) and bottom cell (SiGe) of cascade solar cells. The electrical properties and the photovoltaic performance parameters of AlGaAs/SiGe multijunction solar cells .The possible effects of base of the top cell layer thickness and doping level on solar cell performance parameters are addressed. The conversion efficiency of the solar cell has been found to increase significantly with the doping concentration in the range from 1015 to 1017 cm-3 of 19.52% to 31.19% under the AM1.5G spectrum and one sun. These results are very promising for future potential applications in multijunction and high performance AlGaAs/SiGe solar cells technology.

Quantum mechanical analysis of 2D transition metal dichalcogenide material based vertical heterojunction tunnel FET

In this work, a single layer n-doped MoS2 and p-doped WTe2 based vertical heterojunction tunnel FET has been investigated through a well-organized quantum mechanical approach. The key outcome is the design criteria of the device for low subthreshold swing keeping its length as short as possible. Inter-coupled real space model Hamiltonian of the device is formed by introducing the coupling energy of the WTe2 valence band and the MoS2 conduction band in the overlap region. Here, MATLAB based self-consistent analysis is used to numerically solve the device by coupling Schrödinger and Poisson equations taking into account the plane dependence of permittivity in 2D transition metal dichalcogenide materials. For 15 nm channel overlap length and 15 nm gate extension length, a subthreshold slope of as low as 10 mV/decade has been obtained. For 20 nm channel overlap length, an ON current of 18 µA/μm has been obtained as well. The effect of the top gate extension, overlap length, and dielectric layer thickness over the ON and OFF state currents has been explained from the viewpoint of device physics. Thus, the framework presented will help designers to optimize the device for improved performance.

Undrained seismic bearing capacity of strip footings lying on two-layered slopes

Abstract In this study, finite element limit analysis (FELA) is employed to investigate the undrained seismic bearing capacity of strip footings placed on two-layered slopes. Upper bound theorem (UB), lower bound theorem (LB) and adaptive meshing technique were used in parametric studies to investigate the effects of various factors on seismic bearing capacity Ncs and failure mechanism, especially the seismic coefficient kh and the shear strength ratio of top layer and bottom layer cu1/cu2. The angle of the slope β, the absolute strength of top layer cu/γB, horizontal offset distance b and the thickness of top layer D are also taken into consideration. Furthermore, the comparisons between present study and previous studies are provided. Detailed design tables are presented to distinguish the failure patterns and estimate the seismic bearing capacity of slopes under different conditions.

Stability Analysis of Minimum Broken Top Layer Thickness of Rock Drilling Chamber in a Mining Site Based on Midas/GTS

The determination of the reasonable thickness of the top layer of the large- diameter deep-hole stope is one of the important process parameters that must be considered in the high-stage mining recovery. The thickness of the top layer can ensure that the large-diameter deep-hole stope is not easy to collapse after the formation of the empty zone. To ensure the stability of the rock drilling chamber. According to the similar mine experience and mechanical model, the scientific and reasonable top-level safety thickness range is calculated. The three-dimensional numerical simulation of MIDAS/GTS is used to verify and optimize the stability of different top layer thicknesses. From the perspective of displacement and stress, comprehensive simulation analysis is carried out. After comprehensive comparison of angles, the optimal thickness of the top layer is determined to be 9 m.

Cutting of Al/Si bilayer systems: molecular dynamics study of twinning, phase transformation, and cracking

Using the molecular dynamics simulation, we study the cutting of Al/Si bilayer systems. While the plasticity of metals is dominated by dislocation activity, the deformation behavior of Si crystals is governed by phase transformations—here to the amorphous phase. We find that twinning adds as a major deformation mechanism in the cutting of Al crystals. Cutting of Si crystals requires thrust forces that are larger than the cutting forces in order to induce amorphization; in metals, the thrust forces are relatively smaller than the cutting forces. When putting an Al top layer on a Si substrate, the thrust force is reduced; the opposite effect is observed if a Si top layer is put on an Al substrate. Covering an Al substrate with a thin Si top layer has the detrimental effect that the hard Si requires high pressures for cutting; as a consequence, twinning planes with intersecting directions are generated that ultimately lead to cracks in the ductile Al substrate. The crystallinity of the Si chip is strongly changed if an Al substrate is put under the Si top layer: With decreasing thickness of the Si top layer, the Si chip retains a higher degree of crystallinity.

Optimization of the condition for the fabrication of a two-layer integrated skin polyetherimide nanofiltration membrane

Polyetherimide nanofiltration membranes were fabricated by the double-blade casting technique. Throughout this technique, the application of different compositions for the top-layer and sub-layer polymeric solution becomes possible and therefore it could be used as an effective tool for controlling the morphology of the membranes. The preliminary experiments showed that the highest polymer concentration for the sub-layer for obtaining a suitable morphology and low hydraulic resistance and a defect-free selective top-layer is 16 and 19 wt%, respectively. The effect of membrane fabrication parameters i.e. solvent/co-solvent weight ratio in the top-layer (ψ), top-layer casting thickness (δ), and evaporation time (θ) on the performance of the membranes was evaluated and optimized using the RSM method. Twenty experiments were proposed by the RSM design of experiments method. The experiments were done and 20 membranes were fabricated at the proposed conditions. The membranes were evaluated for pure water flux, NaCl and MgSO4 rejection, and flux and porosity. The analysis of variance (ANOVA) indicated that evaporation time had the most significant impact on the flux and rejection, whilst porosity was most affected by top-layer thickness. Finally, two options for the optimization of the fabrication condition were considered. In CASE 1, membrane fabrication parameters were optimized for attaining maximum NaCl rejection and in CASE 2, both flux and NaCl rejection were considered as the targets for optimization. For CASE 1, the best salt rejection was obtained as 25.7 % at a permeate flux of 0.38 L/m2h.bar and in CASE 2, the optimum values for salt rejection and flux were obtained at 13.6 % and 1.47 L/m2h.bar, respectively. Reasonable agreements were observed between the predicted and actual experimental values.