Two-layer Film Research Articles

Improvement of the magnetic properties of Nd–Fe–B/glass two-layer films deposited on Si substrates

In a previous study, the authors developed Nd–Fe–B/glass two-layer films deposited on Si substrates using pulsed laser deposition for micro electro mechanical systems. Here, the fabrication conditions of the films were investigated to determine the optimum conditions that enhance the magnetic properties of the films. The annealing time in the pulse-annealing process conducted after the deposition was set to 4.0 s at Nd contents of 14 at.–16 at.%. Moreover, the effect of the glass/Nd–Fe–B thickness ratio on the magnetic properties was examined. A ratio less than 2 resulted in an increase in (BH)max up to 80 kJ/m3.

Giant Increase of Hardness in Silicon Carbide by Metastable Single Layer Diamond-Like Coating.

Silicon carbide (SiC) is one of the hardest known materials. Its exceptional mechanical properties combined with its high thermal conductivity make it a very attractive material for a variety of technological applications. Recently, it is discovered that two-layer epitaxial graphene films on SiC can undergo a pressure activated phase transition into a sp3 diamene structure at room temperature. Here, it is shown that epitaxial graphene films grown on SiC can increase the hardness of SiC up to 100% at low loads (up to 900µN), and up to 30% at high loads (10mN). By using a Berkovich diamond indenter and nanoindentation experiments, it is demonstrated that the 30% increase in hardness is present even for indentations depths of 175nm, almost three hundred times larger than the graphene film thickness. The experiments also show that the yield point of SiC increases up to 77% when the SiC surface is coated with epitaxial graphene. These improved mechanical properties are explained with the formation of diamene under the indenter's pressure.

Continuous vapor processes in newly laid concrete

This article presents the results of experiments on the physical processes that occur during the hardening process of concrete in dry hot-climatic seasons and the reduction of their negative effects - as well as on the physical and mechanical properties. Under the influence of solar radiation and high temperature, the amount of water in the newly laid concrete mixture begins to evaporate rapidly. As a result of intensive evaporation of water in the concrete mixture from the bottom to the top, interconnected pores are formed, as a result of which the concrete has a defective structure, and this situation leads to a decrease in concrete strength. As a result of dehydration of the concrete mixture, the cement hydration process slows down and may even stop. If the hardening of the concrete is not adequately controlled, its strength may be only 50% of the design strength. The duration of keeping newly laid concrete under polymer films is determined by the construction laboratory, taking into account specific climatic conditions. Covering the concrete surface with inventory thermal insulation coatings (ITVP). These covers are made by pulling two-layer polyethylene film on wooden or metal frames. They can also be folded and assembled. The effectiveness of this method is not very high, it is considered a waste product.

The main heat-technical parameters of solar greenhouses in the southern climate of Uzbekistan

In the article, the main thermal and technical parameters of solar greenhouses in the climatic conditions of the city of Karshi, southern region of Uzbekistan, were studied. The results of the calculation of the heat load of solar greenhouses with different transparent coatings with a useful area of 100 m2 in the conditions of the city of Karshi are presented. According to the calculation results, it was determined that the maximum heat load of the studied semi-cylindrical one-layer film sunken greenhouse is equal to Qhe=50600 W (50.6 kW), and that of the two-layer film greenhouse Qhe=29614 W (29.61 kW) is equal to.

Performance study of an active solar water curtain heating system for Chinese solar greenhouse heating in high latitudes regions

Thermal preservation and heat storage performance cannot be fully realized in the traditional design of the Chinese solar greenhouse (CSG) north wall. To increase greenhouse thermal efficiency and maximize solar energy utilization, researchers have divided greenhouse into the independent solar heating system as well as the independent north wall heat preservation system. The wall-mounted solar heating system used water as a medium with the characteristics of chemical stability, liquidity preference and high specific heat capacity for heat transport and storage have been developed. To explore and create a better suitable greenhouse thermal environment, we proposed an active solar water curtain heating system with a non-woven fabric liner between the two-layer polyethylene film coated with black water-based paint. The greenhouse heating load was estimated based on energy balance theories during the nighttime and the water mass for heat transfer was calculated. Field tests were carried out to verify theories and investigate the thermal performance of the system. The average heat collection ratio was about 80.1 % and 63 % of the stored heat was released at night with the 3.6 °C improvement in interior air temperature and 6.6 % reduction in interior air relative humidity. The heating COP of the system was 12.5 on average and the energy saving rate was 92 %. Besides, the greenhouse with the solar heating system can save energy consumption cost about 348 USD yr−1 as the cost of solar heating system can be repaid in 1.4 years. The system combined the energy balance method to design with more efficient thermal performance, energy conservation, utilization of solar energy and affordable payback period thereby creating a suitable thermal environment in the Chinese solar greenhouse, which is recommended for practical application.

Integrated magnetic resonance technique for the complete analysis of magnetic properties and interlayer interactions in two-layer film heterostructures ferromagnet/nonmagnetic metal

The paper proposes a technique based on the set of angular dependences of the ferromagnetic resonance (FMR) spectra, which makes it possible to quantitatively determine the parameters of all in-plane and out-of-plane magnetic anisotropies, as well as the magnitude of the interlayer interaction in film two-layer ferromagnet/non-magnetic metal (FM/NM) heterostructures. The obtained value of the interlayer interaction, in turn, makes it possible to unambiguously determine the value of the spin-mixing conductance. The effectiveness of the technique was demonstrated using the example of the analysis of a two-layer film heterostructure La0.7Sr0.3MnO3/SrIrO3 (LSMO/SIO). In particular, the temperature dependences of the value of the perpendicular magnetic anisotropy and the magnitude of the FMR resonant field shift, which is determined by the imaginary part of the spin-mixing conductance at the LSMO/SIO interface, are determined.

The Cyclic Stability of Superelasticity in Aged Ti49.3Ni50.7 Single Crystals with Oxide Surface

The cyclic stability of superelasticity in compression in [001]B2-oriented Ti49.3Ni50.7 single crystals is considered in this paper. The crystals were aged at 823 K for 1.0 h in air and helium. It has been experimentally shown that a two-layered surface thin film, consisting of a Ni-free oxide layer and a Ni-rich sublayer, appears after the oxidation at 823 K in air. The surface layers have a weak effect on the forward B2-R-B19’ martensitic transformation temperatures: TR temperature increases by 4 K; Ms and Mf temperatures decrease by 6 K. The oxide layer does not affect either the superelasticity response during fatigue tests or the temperatures of reverse B19’-B2 martensitic transformation. The cracking of the surface oxide layer during fatigue tests was not found in [001]B2-oriented single crystals aged in air. This is contributed by the relaxation of internal stresses. Such internal stresses are caused by both the formation of an oxide layer during aging and the matrix deformation at the stress-induced martensitic transformation. The main relaxation mechanisms of the internal stresses are the oriented growth of Ti3Ni4 precipitation near a thin surface film at aging in air, the formation of dislocations near the precipitation-matrix interface and a fine twinned B19’-martensite at fatigue tests.

Fabrication of binary to quaternary PVDF based flexible composite films and ultrathin sandwich structured quaternary PVDF/CB/g-C3N4/BaFe11.5Al0.5O19 composite films for efficient EMI shielding performance

This work reports the facile fabrication of binary, ternary, and quaternary polymer composite films using combinations of Polyvinylidene fluoride (PVDF), Carbon Black (CB), Graphitic carbon nitride (g-C3N4), and Aluminum doped Barium hexaferrite (BaFe11.5Al0.5O19) nanoplatelets for application as EMI shielding materials at X-band frequency. The excellent total EMI-SE of 47.39 dB in X-band for ultra-small thickness of 0.193 mm was observed for the quaternary PVDF/CB/g-C3N4/BaFe11.5Al0.5O19 composite film. The quaternary composite film was further hot pressed into sandwich-structured two-layer and three-layer composite films. The sandwich and/or multi-layered structure of the PVDF/CB/g-C3N4/BaFe11.5Al0.5O19 composite film improved the EMI shielding performance through multiple reflection loss. With the addition of intact conduction of fillers and multiple-reflection-absorption effect, the multi-layered composite structure attained the best shielding efficiency (SE) of 64.54 dB.

Frictional Energy Dissipation due to Phonon Resonance in Two-Layer Graphene System

The frictional energy dissipation mechanism of a supported two-layer graphene film under the excitation of the model washboard frequency is investigated by molecular dynamics simulations. The results show that two local maxima in the energy dissipation rate occur at special frequencies as the excitation frequency increases from 0.1 to 0.6 THz. By extracting the vibrational density of states of the graphene, it is found that large numbers of phonons with frequencies equal to the excitation frequency are produced. A two-degree of freedom mass-spring model is proposed to explain the molecular dynamics results. Since the washboard frequency for atomically surfaces in wearless dry friction can be analogous to the excitation frequency in the molecular dynamics simulations, our study indicates that the phonon resonance would occur once the washboard frequency is close to the natural frequency of the frictional system, leading to remarkable local maxima in energy dissipation.Graphical Abstract

Nonreciprocal propagation of spin waves in a bilayer magnonic waveguide based on yttrium-iron garnet films

Objectives. Nonreciprocal spin wave effects can manifest themselves in metalized films of ferrite garnets. By studying the dynamics of spin waves in micro- and nano-scale magnetic films, the possibility of using multilayer dielectric films of yttrium iron garnet (YIG) to ensure the manifestation of the nonreciprocity effect is demonstrated. This approach offers advantages compared to the use of a layered YIG/metal structure due to significantly lower spin-wave losses in the two-layer YIG film consisting of layers with different values of magnetization. Such films can be used in logical elements to create controllable Mach-Zehnder interferometers based on magnonic principles. The purpose of this work is to reconcile the concept of nonreciprocal spin-wave propagation of a signal with the simultaneous manifestation of the effects arising from the propagation of spin waves in microwave guides formed by finite-width YIG films.Methods. We used an experimental microwave spectroscopy method based on a vector network analyzer along with a finite difference method to perform a numerical simulation of the dispersion characteristics of spin waves in two-layer magnonic microwave guides. An analytical model was also used to obtain a dispersion equation based on the magnetostatic approximation.Results. Based on measurements of the amplitude and phase responses, the possible coexistence of two frequency ranges for the propagation of a spin-wave signal in a two-layer magnon microwave guide based on a YIG film formed by two layers with different values of saturation magnetization was demonstrated. Regimes of nonreciprocal propagation of a spin-wave signal were revealed. A numerical model was using to study the formation mechanisms of spin wave modes in the spectrum of a two-layer structure formed due to the finite dimensions of the microwave guide. An analytical model was used to evaluate the transformation of the mode spectrum. The experimental data are in good agreement with the results of the proposed numerical and analytical models.Conclusions. The possibility of frequency-selective propagation of spin waves in a magnon microwaveguide consisting of two layers with different saturation magnetization values is demonstrated. Multimode propagation of spin waves can occur inside a two-layer structure in two frequency ranges. At the same time, this process is accompanied by a strong nonreciprocity of spin-wave signal propagation, which manifests itself in a change in the amplitude and phase responses when the direction of the external magnetic field is reversed. The proposed two-layer spin-wave waveguide concept can be used in the manufacture of magnon interconnects and magnon interferometers with the support of multiband regimes of operation.

Demonstration of the model of physicochemical processes in heavy liquid metal cooled reactors in an example of the THEADES experiment simulation

Activities have been currently underway across the world to build heavy liquid metal-cooled reactors. Thus, for example, the ALFRED and BREST-OD-300 reactor designs use lead coolant, while the MYRRHA and CLEAR-I reactors use lead–bismuth coolant. The high corrosive and erosive activity of the coolant requires regulations oxygen concentration (1 ÷ 4E-6 wt.%) and flow velocity (0.5 ÷ 2.5 m/s). Due to the complex geometry of the reactor circulation circuit flow paths, numerical simulation methods are used extensively to justify scheduled modes of operation for liquid metal coolants. Correct justification of the complex oxygen transport processes in liquid metals requires the respective physicochemical computation model, which takes into account the main reactions of oxygen with the coolant and the structural materials.This paper presents a physicochemical model, which includes the following processes: erosion, growth, and dissolution of the two-layer oxide film, coagulation and dissolution of metal oxides in the circuit with subsequent deposition on filtering elements, and inflow from mass transfer apparatuses. StarCCM+, a commercial CFD code, was used as the tool in this study. The physicochemical model was implemented using models of passive impurities, which are used to simulate oxygen transport in the circulation circuit.Capabilities of the presented model were demonstrated based on the results of investigating thermohydraulic and physicochemical processes obtained at the THEADES experimental facility. The duration of the simulation was 1000 h.The distributions of impurity concentrations, increased erosive activity areas, as well as the total amount of oxides deposited on filter and the amount of oxygen entering the circuit have been obtained as a result of the calculations. The surface distribution of the oxide film thickness on the test facility surfaces contacting the coolant has also been calculated. These data can be extrapolated to reactor elements that operate under conditions that are similar to the considered experiment. For example, fuel assemblies.Simulation of thermocouples, as well as taking into account manufacturing technology made it possible to improve the accuracy of calculating the flow’s thermohydraulic characteristics as compared to earlier studies.

Determination of the doping profile of lanthanum impurities in thin-film barium titanate structures

The paper presents a calculation of doping concentration profile in a two-layer barium titanate film, one of the layers of which contains lanthanum impurity. The theoretically predicted distributions were experimentally verified. Influence of the doping profile on the magnitude of the electrocaloric (EC) response of ferroelectric films is assessed by numerical simulation. It is demonstrated that at the same La concentration, the magnitude of the EC effect can change by 40% due to the distribution of the lanthanum concentration in the structure. The results obtained allow optimizing the technological process to ensure the required characteristics of ferroelectric thin films.

Structural-phase inhomogeneity of aluminum films in multilayer systems

The work is devoted to the study of the influence of the sequence of metal layers in two-layer films (Al 0.5% Ni)/Mo and composition SiO2/Si (111) on the phase composition and structural perfection of Al 0.5% Ni films. The samples used in the experiment were two-layer metal films (Al 0.5% Ni)/Mo and Mo/(Al 0.5% Ni), which were deposited on monosilicon substrates of orientation (111) and composition SiO2/Si (111). The influence of the arrangement of metal layers on the phase composition, crystallographic orientation of aluminum grains and their distribution over the thickness of Al 0.5% Ni films has been studied. It is shown that the annealing of the Al/Mo/Al system in an oxygen atmosphere significantly affects the density of oxides on the surface of the aluminum film, which is facilitated by the high affinity of aluminum for oxygen and the polymorphism of its compounds with oxygen in a wide temperature range.

A ratiometric electrochemical DNA-biosensor for detection of miR-141.

A sensitive biosensor for the detection of miR-141has been constructed. The DNA-biosensor is prepared by firstimmobilizing the thiolated methylene blue-labeled hairpin capture probe (MB-HCP) on two-layer nanocomposite film graphene oxide-chitosan@ polyvinylpyrrolidone-gold nanourchin modified glassy carbon electrode. We used the hematoxylin as an electrochemical auxiliary indicator in the second stage to recognize DNA hybridization via the square wave voltammetry (SWV) responses that record the accumulated hematoxylin on electrode surfaces. The morphology and chemical composition of nanocomposite was characterized using TEM, FE-SEM, and FT-IR techniques. Thepreparation stages of the DNA-biosensor were screened by electrochemical impedance spectroscopy and cyclic voltammetry. The proposed DNA-biosensor can distinguish miR-141 from a non-complementary and mismatch sequence. A detection limit of 0.94 fM and a linear range of 2.0 -5.0 × 105 fM were obtained using SWV for miR-141 detection. The working potential for methylene blue and hematoxylin was -0.28 and + 0.15V vs. Ag/AgCl, respectively. The developed biosensor can be successfully used in the early detection of non-small cell lung cancer (NSCLC) by directly measuring miR-141 in human plasma samples. This novel DNA-biosensor is of promise in early sensitive clinical diagnosis of cancers with miR-141 as its biomarker.

Nonreciprocity of Propagation of Exchange-Dipole Spin Waves in Two-Layer Magnetic Films with Crossed Magnetization of the Layers

Nonreciprocity of Propagation of Exchange-Dipole Spin Waves in Two-Layer Magnetic Films with Crossed Magnetization of the Layers

Real-time evolution and characterization of passive films on individual ferrite and austenite phases of duplex stainless steel

The passive film growth process, the composition of passive films, and the electrochemical behavior of ferrite and austenite individual phases on the unbroken surface of 2205 duplex stainless steel (DSS) were investigated by scanning electron microscopy, energy dispersive spectrometry, Kelvin probe force microscopy, magnetic force microscopy, in situ electrochemical atomic force microscopy, and Auger electron spectroscopy depth analysis. The electrochemical characteristics of the α/γ individual phases on the unbroken 2205 DSS surface were similar. The distribution of elements resulted in an element gradient at α/γ phase boundaries with a 2–6-μm width. Three stages of passive film formation were defined: nucleation, rapid growth, and stable growth. An even distribution of alloying elements with a difference in the concentration of Fe and Cr in the barrier layer was observed in the two-layer passive film of α/γ individual phases on the intact 2205 DSS surface. The preferential dissolution occurring on DSS was also discussed.

The Early-Stage Corrosion of Copper Materials in Chloride and Sulfide Solutions: Nanoscale Characterization and The Effect of Microstructure

The microstructures of copper (Cu) materials were investigated by electron backscatter diffraction, showing that electrodeposited (ED) Cu has a homogenous polycrystalline microstructure, while cold spray (CS) Cu has a heterogeneous microstructure with varying grain size, pores, and interfacial splat regions. The corrosion rate was examined by corrosion potential (ECORR) and polarization resistance (Rp) measurements on Cu specimens in solutions containing 0.1 M NaCl + 1 × 10−3 M Na2S. Although the as sprayed CS-Cu was the least corrosion resistant, the corrosion rate of the heat-treated CS-Cu was similar to that of the ED-Cu and wrought Cu (SKB-Cu). Electrochemical behaviours of Cu materials were investigated by either a potentiodynamic scan or a potentiostatic polarization at a more positive potential (E > ECORR) for various experiment durations up to 4 h, showing that the heat-treated CS-Cu, SKB-Cu and ED-Cu exhibited very similar behaviour while the as sprayed CS-Cu showed erratic behavior consistent with a variable surface reactivity. Nanoscale scanning transmission electron microscopy analysis has been performed at the cross-section of an anodically-oxidized CS-Cu specimen, revealing a two-layer film structure, mostly composed of Cu sulfide, with a minor diffusion of sulfur in the local area of an interfacial splat boundary tip.

Capillary instability of a two-layer annular film: an airway closure model

Capillary instability of a two-layer liquid film lining a rigid tube is studied computationally as a model for liquid plug formation and closure of human airways. The two-layer liquid consists of a serous layer, also called the periciliary liquid layer, at the inner side and a mucus layer at the outer side. Together, they form the airway surface liquid lining the airway wall and surrounding an air core. Liquid plug formation occurs due to Plateau–Rayleigh instability when the liquid film thickness exceeds a critical value. Numerical simulations are performed for the entire closure process, including the pre- and post-coalescence phases. The mechanical stresses and their gradients on the airway wall are investigated for physiologically relevant ranges of the mucus-to-serous thickness ratio, the viscosity ratio, and the air–mucus and serous–mucus surface tensions encompassing healthy and pathological conditions of a typical adult human lung. The growth rate of the two-layer model is found to be higher in comparison with a one-layer equivalent configuration. This leads to a much sooner closure in the two-layer model than that in the corresponding one-layer model. Moreover, it is found that the serous layer generally provides an effective protection to the pulmonary epithelium against high shear stress excursions and their gradients. A linear stability analysis is also performed, and the results are found to be in good qualitative agreement with the simulations. Finally, a secondary coalescence that may occur during the post-closure phase is investigated.

Crystallization and silicon carbide formation in two-layer amorphous silicon-carbon films during electron irradiation

It is shown that the irradiation by focused electron beam with electron energy of 10 keV of two-layer amorphous silicon-carbon films 60 nm thick results in films partial crystallization. Moreover, in the irradiated zone the layer of crystalline silicon carbide with luminescent properties is formed. The observed effects are confirmed by methods of Raman spectroscopy and by luminescence spectra Keywords: silicon, carbon, silicon carbide, film, structure, electron beam, Raman spectroscopy.

Кристаллизация и формирование карбида кремния в двухслойных аморфных пленках кремний-углерод при электронном облучении

It is shown that the irradiation by focused electron beam with electron energy of 10 keV of two-layer amorphous silicon-carbon films 60 nm thick results in films partial crystallization. Moreover, in the irradiated zone the layer of crystalline silicon carbide with luminescent properties is formed. The observed effects are confirmed by methods of Raman spectroscopy and by luminescence spectra.