Multilayer Samples Research Articles

Magnetic multilayer edges in Bernal-stacked hexagonal boron nitride

Single-layer $\it{h}$-BN is known to have edges with unique magnetism, however, in the commonly fabricated multilayer $\text{AA}^{\prime}$-$\it{h}$-BN, edge relaxations occur that create interlayer bonds and eliminate the unpaired electrons at the edge. Recently, a robust method of growing the unconventional Bernal-stacked $\it{h}$-BN (AB-$\it{h}$-BN) has been reported. Here, we use theoretical approaches to investigate the nitrogen-terminated zigzag edges in AB-$\it{h}$-BN that can be formed in a controlled fashion using a high-energy electron beam. We find that these "open" edges remain intact in bilayer and multilayer AB-$\it{h}$-BN, enabling researchers potentially to investigate these edge states experimentally. We also investigate the thermodynamics of the spin configurations at the edge by constructing a lattice model that is based on parameters extracted from a set of first-principles calculations. We find that the edge spins in neighboring layers interact very weakly, resulting in a sequence of independent spin chains in multilayer samples. By solving this model using Monte Carlo simulations, we can determine nm-scale correlation lengths at liquid-N$_{2}$ temperatures and lower. At low temperatures, these edges may be utilized in magnetoresistance and spintronics applications.

High‐resolution peak analysis in TOF SIMS data

High mass resolution time‐of‐flight secondary ion mass spectrometry (TOF SIMS) can provide a wealth of chemical information about a sample, but the analysis of such data is complicated by detector dead‐time effects that lead to systematic shifts in peak shapes, positions, and intensities. We introduce a new maximum‐likelihood analysis that incorporates the detector behavior in the likelihood function, such that a parametric spectrum model can be fit directly to as‐measured data. In numerical testing, this approach is shown to be the most precise and lowest‐bias option when compared with both weighted and unweighted least‐squares fitting of data corrected for dead‐time effects. Unweighted least‐squares analysis is the next best, while weighted least‐squares suffers from significant bias when the number of pulses used is small. We also provide best‐case estimates of the achievable precision in fitting TOF SIMS peak positions and intensities and investigate the biases introduced by ignoring background intensity and by fitting to just the intense part of a peak. We apply the maximum‐likelihood method to fit two experimental data sets: a positive‐ion spectrum from a multilayer MoS2 sample and a positive‐ion spectrum from a TiZrNi bulk metallic glass sample. The precision of extracted isotope masses and relative abundances obtained is close to the best‐case predictions from the numerical simulations despite the use of inexact peak shape functions and other approximations. Implications for instrument calibration, incorporation of prior information about the sample, and extension of this approach to the analysis of imaging data are also discussed.

Multilayered electrospinning strategy for increasing the bioaccessibility of lycopene in gelatin-based sub-micron fiber structures

The main drawback of gelatin nano- and sub-micron fibers for delivery of lipophilic compounds such as lycopene is its quick dissolving in the oral phase. Herein, electrospinning is used to design a multilayer sandwich structure to enhance the bioaccessibility of lycopene in the target site, small intestine. For this purpose, the gelatin layers loaded with 0.05 and 0.075% (w/w) lycopene were sandwiched between the two layers of the hydrophobic electrospun proteins of zein. The rheological, physicochemical and bioaccessibility properties of the designed solutions and spun samples were comprehensively studied. The most favorable conditions for electrospinning of each layer were selected and judged by the morphological, fiber diameter distributions, production efficiency and particularly higher protection of lycopene. The encapsulation efficiencies of lycopene for the sandwich samples were measured between 83.97 and 90.51% which is in a highly acceptable level. The FTIR and DSC analyses confirmed the presence of lycopene, suggested its chemical or physicochemical interactions with protein. The improvement in the thermal resistance of encapsulated lycopene was also confirmed by DSC experiment. The release behavior of lycopene was evaluated by Kopcha, Peppas-Sahlin and Korsmeyer-Peppas models in the simulated digestive environments whereby a Fickian diffusion assisted with matrix erosion was observed. The fast and higher release of lycopene in the small intestine phase was also seen, so that the highest bioaccessibility reached to the 16.44% for the multilayered sample loaded with 0.075% (w/w) lycopene. These findings show a promising approach for designing safe delivery systems based on electrospun fibers with higher bioaccessibility for lipophilic compounds.

Laboratory grazing-incidence X-ray fluorescence spectroscopy as an analytical tool for the investigation of sub-nanometer CrSc multilayer water window optics

Efficient multilayer optics for radiation in the water window range are difficult to manufacture due to extremely small layer thicknesses and severe intermixing of elements between the layers. Therefore, adequate analytics and short feedback loops are of utmost importance for manufacturers to improve performance and efficiency. We show the possibility for non-destructive elemental depth profiling with commercial laboratory equipment using four real-life CrSc multilayer samples. Comparative measurements at the laboratory of PTB at the synchrotron radiation facility BESSY II confirm the results and prove the potential of laboratory equipment for the reliable analysis of stratified materials with sub-nanometer layer thicknesses.

Experimental and numerical study on the solar gain and heat loss of typical existing and refurbished German buildings

This communication introduces an experimental setup for investigating the effect of solar radiation on the reduction of transmission heat losses and the steady state thermal conductance of uninsulated and insulated multi-layer wall samples. The setup consists of two adjacent climatic chambers, which share a common wall, in which the multi-layer wall samples are mounted. A solar simulator is applied within the outdoor air climatic chamber, whose radiation spectrum and radiation intensity are approximately equivalent to those of the sun. The first tests have been carried out on a wall sample with a typical structure of existing buildings from the year 1930 in Germany. In addition, a high-performance insulating plaster layer has been applied on a basic test sample (with existing building structure) to replicate and assess the refurbished scenario. Furthermore, a numerical investigation on the transient heat transfer process is carried out by using the simulation software COMSOL Multiphysics®. The experimental results of both uninsulated and insulated wall samples are validated against 1D and 3D models. As seen, the uninsulated wall, whose thermal conductance was experimentally determined to be equal to 1.79 W/(m²K), absorbs a heat flux of 208 W/m² through its external wall surface over a period of 8 hours. A fraction of 9.8 % of the absorbed heat arrives as a gain on the internal wall and reduces the transmission heat losses by 11.7 % over a period of 55 hours. On the other hand, the thermal conductivity of the insulation layer of the refurbished wall sample with micro hollow glass spheres was estimated by a parameter estimation procedure using the 3D model and the obtained experimental data. Using the estimated thermal conductivity, a thermal conductance of 0.42 W/(m²K) has been obtained for the refurbished wall sample.

PSpice modeling of the pulsed electroacoustic method for dispersive polymer sample application.

In space applications, space charge inside dielectric materials can lead to unwanted phenomena such as breakdown and electrostatic discharge. To prevent such incidents, the pulsed electroacoustic (PEA) device is employed to measure the space charge of dielectric samples. Unfortunately, most of the current PEA signal processing methods are inaccurate in studying the dielectric materials that attenuate and disperse the acoustic wave, as well as studying multi-layer or thin samples. A model under the PSpice software is developed in this work with the aim of improving the PEA signal processing. This model is an evolution of previous works, including the attenuation and dispersion of a polymer sample using the nearly local Kramers-Kronig relation. This model of the polymer sample is implemented into PSpice as a frequency dependent transmission line using Branin's method of characteristics model. A comparison of a model simulation and an experimental PEA signal obtained from a PTFE sample is presented.

Investigation on thermal stability of Si0.7Ge0.3/Si stacked multilayer for gate-all-around MOSFETS

In this study, the thermal stability of a Si0.7Ge0.3/Si stacked multilayer for gate-all-around (GAA) MOSFETS is systematically investigated. Rapid thermal annealing (RTA) treatments at temperatures ranging from 800 °C to 1050 °C are performed on the Si0.7Ge0.3/Si stacked multilayer samples. Compared with the as-grown sample, the RTA-treated (800 °C–900 °C) Si0.7Ge0.3/Si stacked multilayer samples attain good crystal quality, a sharp interface between Si0.7Ge0.3 and Si, and minor diffusion of Ge. Furthermore, owing to the rapid diffusion of Ge, the thickness of Si0.7Ge0.3 increases by ∼6 nm and the Ge concentration of Si0.7Ge0.3 reduces by ∼3% as the annealing temperature increases to 950 °C. The interfaces of the Si0.7Ge0.3/Si stacked multilayer disappear and finally behave like a homogeneous SiGe alloy as the annealing temperature further increases to 1000 °C or 1050 °C. Therefore, for thermal stability, the highest tolerable temperature of 900 °C is proposed for the Si0.7Ge0.3/Si stacked multilayer for the fabrication of the GAA device.

Improving electric field controlled magnetism of micron-scale-thickness Fe71Ga17B12 film on Pb(Mg1/3Nb2/3)0.7O3-PbTi0.3O3 by multilayer preparation method

Enhancing electric field controlled magnetism of micron-scale-thickness ferromagnetic film is of great significance to improve the performance of magnetoelectric (ME) sensors, ME tunable inductors and other ME devices. In order to achieve above purpose, multilayer preparation method was proposed and validated by experiment studies on multilayer (Cu(10 nm)/(FeGaB(100 nm)/Cu(5 nm))10) and monolayer (Cu(10 nm)/FeGaB (1000 nm)/Cu(5 nm)) samples, respectively. The results show the electric field controlled magnetism could be enhanced obviously by the multilayer preparation method. Meanwhile, the finite element simulation model was established to analyze possible causes for the improvement of electric field controlled magnetism in multilayer sample. The model revealed that multilayer preparation can reduce the in-plane demagnetizing factor and increase the internal magnetic field of the magnetic materials, thus enhancing electric field controlled magnetism. This work is conducive to the development of micron-scale-thickness films in electric field control of magnetism, which contributes to the application of ferroelectric/ferromagnetic heterostructures in ME devices.

The crashworthiness performance of thin-walled ultralight braided lattice composite columns: Experimental and finite element study

We studied the crashworthiness performance of thin-walled ultralight braided lattice composites (UBLCs) under quasi-static compressive loading experimentally and numerically. The lattice structures were initially preformed on mandrels with various cross-sectional geometries, including circular, octagonal, hexagonal, and rectangular. The effects of cross-section type and perimeter were also investigated. Our results showed that the square-shaped sample exhibited the highest specific absorbed energy (SAE) and absorbed energy per length. We also investigated the effect of the number of lattice layers. The concentric multi-layer samples absorbed more energy than single-layer samples due to interactions between the embedded layers. Furthermore, the crushing force efficiency (CFE) was improved by the use of multi-layer samples. Finite element (FE) modeling was used to predict and analyze the energy absorption behavior of UBLC samples. Both structure buckling and material failure were included in the simulations. The results of the FE simulation were in good agreement with our experimental results. The SAEs of single-layer and multi-layer UBLCs are significantly higher than those of expanded metal tubes. Considering SAE and CFE simultaneously, we can conclude that the energy absorption behavior of UBLC structures is more promising than that of similar tubular lattice structures.

Sputter deposited crystalline V2O5, WO3 and WO3/V2O5 multi-layers for optical and electrochemical applications

Crystalline V2O5, WO3, WO3/V2O5 (bi-layer) and WO3/V2O5/WO3/V2O5 (multi-layer) thin film samples were deposited on fused silica and fluorinated tin oxide coated microscopy glass substrates by reactive dc magnetron sputtering. Structure-property correlation studies were carried out by X-ray diffraction, Raman and X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy and cyclic voltammetry techniques. V2O5 and WO3 layers have orthorhombic and monoclinic crystal structures respectively and their phase formation was confirmed by XPS. Cyclic voltammetry studies were used to determine the electrochemical properties. H+ diffusion coefficient decreases with increase in the voltage scan rate in all samples except for the bi-layer. At each scan rate the highest diffusion coefficient was achieved for multi-layer sample and the values were 7.4 × 10−14 cm2s−1, 2.4 × 10−14 cm2s−1, 1.4 × 10−14 cm2s−1 at scan rates of 10 mVs−1, 100 mVs−1 and 500 mVs−1, respectively. The multi-layer sample has large areal capacitance of 1165 mFcm−2. The study shows that WO3/V2O5/WO3/V2O5 multi-layer sample has significantly enhanced electrochemical properties as compared to the single layer V2O5 and WO3 films.

Molding Wetting by Laser-Induced Nanostructures

The influence of material characteristics—i.e., type or surface texture—to wetting properties is nowadays increased by the implementation of ultrafast lasers for nanostructuring. In this account, we exposed multilayer thin metal film samples of different materials to a femtosecond laser beam at a 1030 nm wavelength. The interaction generated high-quality laser-induced periodic surface structures (LIPSS) of spatial periods between 740 and 790 nm and with maximal average corrugation height below 100 nm. The contact angle (CA) values of the water droplets on the surface were estimated and the values between unmodified and modified samples were compared. Even though the laser interaction changed both the surface morphology and the chemical composition, the wetting properties were predominantly influenced by the small change in morphology causing the increase in the contact angle of ~80%, which could not be explained classically. The influence of both surface corrugation and chemical composition to the wetting properties has been thoroughly investigated, discussed and explained. The presented results clearly confirm that femtosecond patterning can be used to mold wetting properties.

Fourier interferometry of multi-layer sample using wavelength tuning and partially negative window

When measuring the thickness of a transparent plate using wavelength tuning-based phase modulation fringe analysis, the nonlinearity of the phase modulation can cause both a nonuniform phase error and a bias phase error. In this study, a method of eliminating the bias phase error using the characteristic polynomial theory was developed and a flexible 4 N − 1 algorithm, consisting of a partially negative window and a discrete Fourier transform term, was constructed. The behaviors of the 4 N − 1 algorithm were visualized in the frequency domain. The error compensation ability was estimated by comparing it to conventional algorithms. The thickness and surface profile of a lithium niobate wafer were simultaneously measured using a Fizeau interferometer and the proposed 4 N − 1 algorithm. The experimental results showed that the 4 N − 1 algorithm performs better than other algorithms in terms of the repeatability error and suppression of the bias phase error.

Mechanical properties and translucency of a multi-layered zirconia with color gradient for dental applications

In this work, the properties of yttria-stabilized zirconia-based ceramics, Y-TZP containing Fe2O3 as coloring agent were evaluated. Nanoparticled powder of 3Y-TZP (ZrO2 - 3 mol.% Y2O3) doped with different amounts of Fe2O3 (0.002–0.136 wt%) were compacted into monolithical or multilayered samples and sintered at 1475 °C - 2 h. The samples were characterized by X-ray diffraction analysis (XRD), relative density, scanning electron microscope (SEM). Hardness and fracture toughness in the color interface were investigated using the Vickers indentation method and the biaxial flexural strength was determined by the piston on 3 balls method (P–3B). Furthermore, optical parameters were measured using spectrophotometry in regard to sample thickness and Fe2O3 content. The results indicated a good adhesion between layers, proven by indentation cracks randomly growing between different regions, because the powders used produced very similar morphological characteristics. The different amounts of Fe2O3 studied in this work did not interfere in densification, phase composition, or microstructure of the sintered ceramics. The fracture toughness and flexural strength did not significantly change due to the addition of Fe2O3, presenting values close to 7 MPa m1/2 and 1120–1150 MPa, respectively, in all studied compositions. On the other hand, increasing Fe2O3 contents lead to an increase in the hardness of the material (1280–1330 H V), and higher contrast ratios (CR) with a consequent loss of translucency. Color variation (ΔE) depended also on the thickness of the material.

Model-driven directed-energy-deposition process workflow incorporating powder flowrate as key parameter

Process optimization for directed-energy-deposition, an industrial laser-based additive manufacturing technique, is a time-intensive endeavor for manufacturers. Herein we investigate the use of a modified analytical process-model based on powder-bed-fusion techniques, to predict quality build parameters by incorporating the effects of three key parameters: laser-power, scanning-speed, and powder flowrate. Titanium alloy (Ti6Al4V) tracks of varying parameters were built, studied, and used to predict parameters for quality builds used at different parameters. The model agreed well with experimental build quality at powder flowrates less than 6.5 g/min, whereas, higher flowrates created significant unmelted-particle regions, despite optimal parameter predictions. Processing of multi-layer bulk samples revealed that parameters in the optimal range account for relative densities >99%, indicating quality bulk processing parameters. Our results indicate that process modeling with the incorporation of powder feedrate as a key parameter is possible using a commercial laser-based additive manufacturing system.

Thickness determination of metal multilayers by ED-XRF multivariate analysis using Monte Carlo simulated standards

We present the thickness measurement of multilayer samples by X-ray fluorescence (XRF) using calibration curves obtained from simulated spectra through Monte Carlo (MC) algorithm. The XRF is a widespread technique for the analysis of single and multilayer films but the accuracy of quantitative analysis must be increased. Moreover, the use certified standards is not easy to implement due to the high variability of combination and/or concentration in layered samples. The results of this work were compared with fundamental parameter (FP) method and focussed ion beam scanning electron microscopy (FIB-SEM) analysis. The results show good quantitative values even without the use of any standard with known thickness. In addition to having built the calibration curves with a simple univariate approach, also multivariate data analysis was performed to consider multiple variables simultaneously. From the comparison of the obtained results, it can be inferred that the univariate analysis worked well in the case of single layer samples and in the determination of the upper layer in multilayer samples but only multivariate analysis, taking into account the matrix effect of each layer, provided maximum accuracy on each layer of multilayer samples.

High-sensitivity x-ray/optical cross-correlator for next generation free-electron lasers.

We design and realize an arrival time diagnostic for ultrashort X-ray pulses achieving unprecedented high sensitivity in the soft X-ray regime via cross-correlation with a ≈1550 nm optical laser. An interferometric detection scheme is combined with a multi-layer sample design to greatly improve the sensitivity of the measurement. We achieve up to 275% of relative signal change when exposed to 1.6 mJ/cm2 of soft X-rays at 530 eV, more than a hundred-fold improvement in sensitivity as compared to previously reported techniques. The resolution of the arrival time measurement is estimated to around 2.8 fs (rms). The demonstrated X-ray arrival time monitor paves the way for sub-10 fs-level timing jitter at high repetition rate X-ray facilities.

Measurement of thermal transport properties of selected superlattice and thin films using frequency-domain photothermal infrared radiometry

Thermal transport properties in multi-layered semiconductor samples are reported using modulated photothermal infrared radiometry (PTR). The cross-plane thermal conductivity and diffusivity of thin AlxGa(1-x)As layers and AlAs/GaAs superlattices were determined by fitting solutions of the heat equation for multi-layered systems to PTR data. The thermal conductivity of an AlxGa(1-x)As film with x = 0.5 was found to be lower than an AlxGa(1-x)As film with x = 0.33 which is expected as scattering from alloy disorder is maximized for x = 0.5. In addition, it was found that thermal conductivities of AlAs/GaAs superlattices decrease when the superlattice period is decreased for a constant total thickness which is expected since the number of AlAs/GaAs interfaces (which impede thermal transport) increases as the period decreases. The maximum PTR amplitude signal was found to occur when the diffusion length of the thermal wave is on other order of the thickness of the semiconductor layer. The accuracy and applicability of photothermal infrared radiometry to the study of semiconductor multilayer structures are further discussed in the paper.

Properties of gradient polyimide aerogels prepared through layer‐by‐layer assembly

AbstractA series of density gradient polyimide (PI) aerogels were prepared using layer‐by‐layer assembly and radial freezing method. Briefly, a layer of poly(amic acid) (PAA) ammonium salt aqueous solution was first radially frozen. Then, the second layer of PAA ammonium salt (PAS) aqueous solution of different concentration was added on the top of the first PAS layer and radially frozen. A multilayer gradient PAS solid sample could therefore be fabricated by repeating this similar procedure. The density gradient PI aerogels were obtained after freezing drying and final thermal imidization treatment. Each layer of gradient PI aerogels had anisotropic pore structure, which consisted of tube‐like pores along the radial direction and toward the center axis of the cylindrical samples. The compressive strength of five‐layer gradient PI aerogel was higher than that of three‐layer gradient and single‐layer PI aerogels with the same density. The gradient PI aerogels exhibited anisotropic heat transfer behavior in the direction of density gradient, and heat transfer from the higher density side to the lower density side was faster.

Thermal resistance field estimations from IR thermography using multiscale Bayesian inference

ABSTRACT The main goal of this paper is the estimation of thermal resistive fields in multilayer samples using the classical front face flash method as excitation and InfRared Thermography (IRT) as a monitoring sensor. The complete inverse processing of a multilayer analytical model can be difficult due to a lack of sensitivity to certain parameters (layer thickness, depth of thermal resistance, etc.) or processing time. For these reasons, our present strategy proposes a Bayesian inference approach. Using the analytical quadrupole method, a reference model can be calculated for a set of parameters. Then, the Bayesian probabilistic method is used to determine the maximum likelihood probability between the measured data and the reference model. To keep the processing method robust and fast, an automatic selection of the calculation range is proposed. Finally, in the case of a bilayer sample, both the thickness and resistive 3D layers are estimated in less than 2 min for a space and time matrix of 50,000 pixels by 4000 time steps with a reasonable relative error of less than 5%.

Passive membrane sampler for assessing VOCs contamination in unsaturated and saturated media

Passive sampling (PS) is a method employed to detect volatile organic compounds in groundwater and soil gas. This study attempted to manufacture a polydimethylsiloxane (PDMS) dialysis passive sampler for potential application in detecting trichloroethylene (TCE) in aqueous and gaseous phases. The equilibrium time of the passive sampler was initially determined, followed by multilayer passive sampling in a three-dimensional sandbox to construct a tomography of TCE vapor spatial distribution in the vadose zone above the saturated water level. The results indicated that an equilibrium time period of >10 d was required in the aqueous phase containing TCE concentrations ranging from 3 to 25 mg L−1, while an equilibrium time period of >12 d was necessary for TCE vapor concentrations ranging from 2.6–26 mg L−1. Therefore, a 14 d of equilibrium time was suggested for application of this passive sampler in detecting vapor and aqueous phase TCE. After collection of the passive samples from the three-dimensional sandbox, a three dimensional visualization was created, and it was demonstrated to be a reasonable way to simulate a three dimensional TCE distribution. It was confirmed that the passive sampler developed in this study is effective for assessing TCE contamination in the subsurface.