Multilayer Core Research Articles

Interface formation energy, bonding, energy band alignment in α-NaYF4 related core shell models: For future multi-layer core shell luminescence materials

To break through the bottle-neck of quantum yield in upconversion (UC) core-shell system, we elucidated that the energy transfer efficiency in core-shell system had an evident contribution from the charge transfer of interface with related to two factors: (1) band offsets and (2) binding energy area density. These two variables were determined by material intrinsic properties and core-shell thickness ratio. We further unraveled the mechanism of non-radiative energy transfer by charge transfer induced dipole at the interface, based on a quasi-classical derivation from Förster type resonant energy transfer (FRET) model. With stable bonding across the interface, the contributions on energy transfer in both radiative and non-radiative energy transfer should also be accounted together in Auzel's energy transfer (ETU) model in core-shell system. Based on the discussion about interface bonding, band offsets, and formation energies, we figured out the significance of interface bonding induced gap states (IBIGS) that played a significant role for influencing the charge transfer and radiative type energy transfer. The interface band offsets were a key factor in dominating the non-radiative energy transfer, which was also correlated to core-shell thickness ratio. We found that the energy area density with related to core/shell thickness ratio followed the trend of Boltzman sigmoidal growth function. By the physical trend, this work contributed a reference how the multi-layered core-shell structure was formed starting from the very beginning within minimum size. A route was paved towards a systematic study of the interface to unveil the energy transfer mechanism in core-shell systems.

Ionic liquid ultrathin films at the surface of Cu(100) and Au(111).

Monolayer to multilayer ultrathin films of the ionic liquid (IL) 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)amide have been prepared on Au(111) and Cu(100) surfaces using physical vapor deposition. The ion-surface interactions are studied using a combination of scanning tunnel microscopy, as well as ultraviolet and x-ray photoemission spectroscopies. It is found that the IL does not decompose at the surface of the metals, and that the IL interaction with the Cu(100) surface is much stronger than with the Au(111) surface. As a consequence, STM imaging at room temperature results in more stable imaging at the monolayer coverage on Cu(100) than on Au(111), and work function measurements indicate a large interface dipole upon deposition of a monolayer of IL on Cu. Additional IL depositions on the two surfaces result in two distinct behaviors for the IL core levels: a gradual energy shift of the core levels on Au and a set of two well defined monolayer and multilayer core level components found at fixed energies on Cu, due to the formation of a tightly bound monolayer. Finally, it is proposed that the particularly strong cation-Cu interaction leads to stabilization of the anion and prevents its decomposition at the surface of Cu(100).

Significantly improved charge collection and interface injection in 3D BiVO4 based multilayered core-shell nanowire photocatalysts.

It is challenging to design a photocatalyst with high-efficiency light absorption, charge separation and even high-efficiency charge transfer. Here, we report a demonstration by utilizing a three-dimensional multilayered core-shell nanowire array (rGO-ITO@BiVO4) as the composite photocatalyst. The core-shell structure can shorten the length of charge transfer and enhance light absorption through multireflection. RGO with defects can work as the charge transfer medium to improve the hole injection from semiconductor to electrolyte. Associated with the above effects, the Co-pi electrocatalyst modified rGO-ITO@BiVO4 photocatalyst yields a photocurrent of about 6.0 mA cm-2 at 0.6 V vs. Ag/AgCl. Transient-state surface photovoltage measurement shows that the rGO layer can prolong the lifetime of the photogenerated holes through π-π interactions, so that more holes can participate in the water oxidation reaction.

Multilayer core–shell MoS2/CdS nanorods with very high photocatalytic activity for hydrogen production under visible-light excitation and investigation of the photocatalytic mechanism by femtosecond transient absorption spectroscopy

Understanding the structural features and the dynamics and properties of charge carriers in photocatalysts is critical to develop them for practical applications.

Novel and Facile Strategy for Controllable Synthesis of Multilayered Core–Shell Zeolitic Imidazolate Frameworks

Core–shell metal organic framework (MOF) crystals have attracted increasing attention due to their specific structure and remarkable properties. Herein, we demonstrate a facile approach for the synthesis of uniform multilayered core–shell MOF crystals including ZIF-67@ZIF-8@ZIF-67 and ZIF-8@ZIF-67@ZIF-8 for the first time, by adopting the condition for the preparation of relatively larger sized crystals to fabricate the shells on the surface of relatively smaller sized seeds without any auxiliary condition. Compared with the control experiments opposite our strategy, there are two dominant factors determining the successful synthesis: (i) the homological feature between ZIF-8 and ZIF-67 favors the heterogeneous nucleation and continuous crystal growth on the surface of seeds; (ii) by controlling a relatively lower nucleation rate and a longer crystal growth stage, it enables the shell formation on the surface of the seed but avoids other monocomponent crystals generated in solution. In addition, the size ...

Magnetic Silica Bonding Perfluoroalkylsulfonylimide as Reusable Brønsted Acid Catalysts for Cellobiose Hydrolysis

New Bronsted solid acid, magnetic silica-supported perfluoroalkylsulfonylimide group was prepared. The as-synthesized functional siloxane oligomer was used to introduce perfluoroalkylsulfonylimide onto the magnetic core under the assist of TEOS, forming multi-layer core–shell structure, which was confirmed by TEM. The inner silica shell protected the acid-sensitive magnetic core from the corrosion of the strong acid; while the outer silica shell attached acid perfluoroalkylsulfonylimide groups. Good thermal stability (<229 °C) was expectable for the materials by TG analysis. The conclusive acid loadings of 0.61–0.69 mmol/g endowed the materials with efficient catalytic ability for the conversion of cellobiose to glucose (Glu), providing stable 85–91 % Glu yields throughout 3–4 cycles in water at 130 °C.

Damping properties of bi-dimensional sandwich structures with multi-layered frequency-dependent visco-elastic cores

The aim of this paper is to present a finite element model based on first order shear theory (zig-zag approach) to compute the damping characteristics of sandwich structures with multi-layered frequency-dependent viscoelastic cores. The model is validated versus a layerwise finite element model and used to study damping and rigidity of a laminated glass configuration with a multi-layered visco-elastic core composed of acoustic PVB and PVB. It is shown that the rigidity index of the structure (defined as the adimensionalized inverse of the maximal transverse displacement under a static load) evolves linearly with the viscoelastic layers’ thicknesses and quadratically versus elastic layer’s thickness. The first mode damping and resonant frequency show a non monotonous behaviour. In particular, the existence of an optimal faces thickness for damping is shown while a quadratic behaviour of frequency versus acoustic PVB layer thickness is reported.

Modeling and experimental analysis of polypropylene honeycomb multi-layer sandwich composites under four-point bending

The behavior of a simple and innovative multi-layer sandwich panels having a polypropylene honeycomb core has been investigated carefully, theoretically and experimentally. A four-point bending test was performed to detect the mechanical characteristics of the multi-layer core. The experimental results emphasize a better rigidity of the multi-layer structure compared to the weakness displayed by the single-layer configuration. In fact, a small increase in the final weight of the component leads to a significant increase of the mechanical properties. In the second part of this study, analytical and numerical homogenization approaches were developed to compute the effective properties of the single polypropylene honeycomb core. The numerical model complies with the experimental protocol, and the simulation conducted is aiming to reproduce a typical four-point bending test on a polypropylene honeycomb multi-layer sandwich panel. Both numerical and experimental results are presented in details and a good correlation between them is highlighted.

Integrated On-Chip Solenoid Inductors With Nanogranular Magnetic Cores

On-chip integrated solenoid inductors with nanogranular FeCoTiO magnetic cores have been fabricated. Both single-layered and multilayered magnetic cores with different geometries were studied. An inductance of 14.2 nH was achieved when using a multilayered core structure and keeping the device area of 0.14 mm2. The inductance of the magnetic core inductor is $\sim 14$ times that of the air core inductor, and the quality factor is 7.5. The permeability trends calculated from inductance were compared with the permeability spectra of the patterned FeCoTiO films measured by an improved shorted microstrip transmission line perturbation method. Consistent results have been obtained after considering the demagnetization effect of the magnetic core with high permeability.

Free vibration analysis of multilayered composite and soft core sandwich plates resting on Winkler–Pasternak foundations

Free vibration of laminated composite and soft core sandwich plates resting on Winkler–Pasternak foundations using four-variable refined plate theory are presented. The theory accounts for the hyperbolic distribution of the transverse shear strains through the plate thickness, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factors. Equations of motion are derived from the dynamic version of the principle of virtual work. Navier technique is employed to obtain the closed-form solutions of antisymmetric cross-ply, angle-ply, and soft core laminates or soft core sandwich plates resting on elastic foundations. Numerical results obtained using present theory are compared with three-dimensional elasticity solutions and those computed using the first-order and the other higher-order theories. It can be concluded that the proposed theory is not only accurate, but also efficient in predicting the natural frequencies of laminated composite and soft core sandwich plates resting on Winkler–Pasternak foundations.

Novel pH-responsive multilayer magnetic nanoparticles for controlled drug delivery

A multifunctional nanocarrier with multilayer core–shell architecture was prepared by chemical modification of Fe3O4 magnetic nanoparticle (MNPs) with acrolein–styrene–polyethyleneimine (AL–St–PEI) via covalent bonding. MNPs were prepared by co-precipitation method, and then, thiol functionalized (MNPs-SH) were synthesized by treating MNPs with the (3-mercaptopropyl) trimethoxysilane. Subsequently, the copolymerization of St and AL was performed in the presence of the MNPs-SH and butyrolactam by thiol-lactam initiated radical polymerization. Finally, PEI was covalently bounded to the aldehyde groups on the surface of AL–St copolymer. The AL–St–PEI MNPs were investigated by FTIR, XRD, TGA, SEM and TEM. The drug release from AL–St–PEI MNPs was evaluated using doxorubicin as the model anticancer. Furthermore, to determine the effect of drug structure in the release profile from the modified MNPs, some lipophilic model drugs were studied in loading and release study. It was found that the nature of the drugs affect the release profile. The in vitro release modeling demonstrated that doxorubicin release is described by zero-order mechanism while release of lipophilic model drugs is controlled by fickian diffusion.

Flexural performance of sandwich beams with lattice ribs and a functionally multilayered foam core

This study focused on the flexural behavior of an innovative sandwich beams with GFRP skins, lattice ribs, and a functionally multilayered PU foam core (GLF beams). The lattice ribs, consisted of longitudinal and horizontal ribs, were arranged along the longitudinal direction of the beam. Eight beams, involving a control specimen, were tested under four-point bending to validate the effectiveness of the lattice ribs and functionally multilayered foam core for increasing the ultimate bending strength, stiffness and energy dissipation ability. Test results showed that compared to control specimen, a maximum of 143% increase in the ultimate bending strength can be achieved. The energy dissipation ability of the beam was increased greatly by the use of lattice ribs and functionally multilayered foam core. Meanwhile, unlike the conventional sandwich beam, GLF beams failed in a ductile manner. Furthermore, an analytical model was proposed to predict the bending stiffness and ultimate bending strength of GLF beams. The analytical results were agreed well with test results.

Liprotides made of α-lactalbumin and cis fatty acids form core–shell and multi-layer structures with a common membrane-targeting mechanism

α-Lactalbumin (aLA) has been shown to form complexes with oleic acid (OA), which may target cancer cells. We recently showed that aLA and several other proteins all form protein–OA complexes called liprotides with a generic structure consisting of a micellar OA core surrounded by a shell of partially denatured protein. Here we report that a heat treatment and an alkaline treatment method both allow us to prepare liprotide complexes composed of aLA and a range of unsaturated fatty acids (FA), provided the FAs contain cis (but not trans) double bonds. All liprotides containing cis-FA form both small and large species, which all consist of partially denatured aLA, though the overall shape of the species differs. Small liprotides have a simple core–shell structure while the larger liprotides are multi-layered, i.e. they have an additional layer of both FA and aLA surrounding the outside of the core–shell structure. All liprotides can transfer their entire FA content to vesicles, releasing aLA as monomers and softening the lipid membrane. The more similar to OA, the more efficiently the different FAs induce hemolysis. We conclude that aLA can take up and transfer a wide variety of FA to membranes, provided they contain a cis-bond. This highlights liprotides as a general class of complexes where both protein and cis-FA component can be varied without departing from a generic (though sometimes multi-layered) core–shell structure.

Design Strategy for the Multilayer Core–Shell Bioceramics with Controlled Chemistry

New strategies for fabricating multiphase bioceramic porous scaffolds with time‐dependent biodegradation and pore network enlargement are of fundamental importance in the advancement of bioceramics. Here, we developed a one‐step preparation of core–shell bioceramic microspheres (~2 mm in diameter) with single‐ or double‐shell structure through a coaxially aligned multilayer capillary system. The Ca‐phosphate (CaP) and Ca‐silicate (CaSi) ceramic phase distribution could be also adjusted by extruding through different capillaries, and thus the biodegradation rate would be readily tailored over time. When the polystyrene (PS) microbeads of ~15 μm in diameter were premixed into the CaP‐ or CaSi‐containing alginate slurry, the tailorable porous structures could be introduced into the core or different shell layers of the microspheres. These micropores may potentially maximize the permeability for rapid exchange of guest molecules or inorganic ions from the bioceramics. Totally, such strategy is promising because the ceramic phases with different biological properties can be assembled into the core–shell bioceramic microspheres, and thus the macropore structure evolution may be readily manipulated in the closely packed microsphere systems. We believe our gradient hybrid methodology will have potential in various categories of advanced biomaterials of organic–inorganic composites.

Bovine serum albumin assisted synthesis of Fe3O4@C@Mn3O4 multilayer core–shell porous spheres as anodes for lithium ion battery

The novel uniform Fe3O4@C@Mn3O4 multilayer core–shell porous spheres for used in lithium–ion batteries (LIBs) have been synthesized with utilizing bovine serum albumin (BSA) as carbon source by hydrothermal process. Fe3O4 porous spheres are coated by carbon and Mn3O4 nanolayer, when manganese ion and iron ion could be adsorbed on BSA. It is indicated that chelation of protein and metal is constructed between the metal ions and the atom with lone pair electrons on the surface of the protein amino acid. And the chelation is connected by the nitrogen atoms in histidine of BSA and the Fe2+, Mn2+ in the metal ions. As an anode material for LIBs, Fe3O4@C@Mn3O4 core–shell nanostructure particles show a high initial capacity of 1261mAhg−1 at the current density of 0.1C, a reversible capacity of approximately 987mAhg−1 after 200 cycles, which possess excellent cycling stability. The enhanced electrochemical properties are mainly ascribed to the core/shell architecture between the different metal oxides with carbon interlayer, which can effectively improve the electric conductivity, active phase, the synergy between different metal oxides. And also, the porous structure could help anodes for buffering the dramatic volume change of active material for improving electrochemical performance for LIBs.

Homogenized Magnetoelastic Behavior Model for the Computation of Strain Due to Magnetostriction in Transformers

This paper deals with the prediction of the deformation of a multilayer transformer core made of an assembly of anisotropic E-shaped and I-shaped sheets. This magnetomechanical coupled problem is solved by a stepping finite-element method sequential approach: magnetic resolution is followed by mechanical resolution. A 3-D simplified multiscale model describing both magnetic and magnetostrictive anisotropies is used as the constitutive law of the material. The transformer core structure is modeled in 2-D, and a homogenization technique is implemented to take the anisotropic behavior of each layer into consideration and define an average behavior at each element of the finite-element mesh. A three-layer transformer prototype is fabricated with Hi-B grain-oriented iron-silicon alloy. Experimental measurements are carried out and compared with the modeling results. Small discrepancies are observed and discussed.

Integrated Solenoid Inductor with [FeCoSiN/SiN&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;]&lt;sub&gt;18&lt;/sub&gt; Multilayer Magnetic Film for GHz Applications

In this work, we explored the solenoid inductor integrated [FeCoSiN/SiNx]18 multilayer magnetic film as magnetic core used in GHz range. The multilayer magnetic film was employed due to its high resistivity and excellent soft magnetic properties even in GHz range. It was found that this magnetic core material can dramatically increase the performance of the solenoid inductor, which presenting a 10-fold improvement in the inductance and a 23-fold enhancement in the quality factor at 1.67 GHz in comparison to those of the air core solenoid inductor. Besides, an inductance density of 27 nH/mm2 and a self-resonant frequency of 3 GHz were also achieved. The results indicated that the solenoid inductor with multilayer magnetic core showed good high frequency characteristics.

Fabrication of MPEG-b-PMAA capped YVO4:Eu nanoparticles with biocompatibility for cell imaging

A novel nanoparticle with multilayer core–shell architecture for cell imaging is designed and synthesized by coating a fluorescent YVO4:Eu core with a diblock copolymer, MPEG-b-PMAA. The synthesis of YVO4:Eu core, which further makes MPEG-b-PMAA-YVO4:Eu NPs adapt for cell imaging, is guided by the model determined upon the evaluation of pH and CEu%. The PMAA block attached tightly on the YVO4:Eu core forms the inner shell and the MPEG block forms the biocompatible outermost shell. Factors including reaction time, reaction temperature, CEu% and pH are optimized for the preparation of the YVO4:Eu NPs. A precise defined model is established according to analyzing the coefficients of pH and CEu% during the synthesis. The MPEG-b-PMAA-YVO4:Eu NPs, with an average diameter of 24nm, have a tetragonal structure and demonstrate luminescence in the red region, which lies in a biological window (optical imaging). Significant enhancement in luminescence intensity by MPEG-b-PMAA-YVO4:Eu NPs formation is observed. The capping copolymer MPEG-b-PMAA improves the dispersibility of hydrophobic YVO4:Eu NPs in water, making the NPs stable under different conditions. In addition, the biocompatibility MPEG layer reduces the cytotoxicity of the nanoparticles effectively. 95% cell viability can be achieved at the NPs concentration of 800mgL−1 after 24h of culture. Cellular uptake of the MPEG-b-PMAA-YVO4:Eu NPs is evaluated by cell imaging assay, indicating that the NPs can be taken up rapidly and largely by cancerous or non-cancerous cells through an endocytosis mechanism.

Stable dual-wavelength laser combined with gain flattening ML-FMF Bragg grating filter

A stable dual-wavelength laser combined with gain flattening multi-layer few-mode fiber Bragg grating filter was proposed and experimentally demonstrated. The index profile of the multi-layer few-mode fiber was particularly designed to support LP01 and LP11 modes with approximately equal excitation coefficients. And conventional phase-mask fabrication technique was used to inscribe Bragg gratings in the multi-layer few-mode fiber core, which leads to the gain flattening filter. A switchable dual-wavelength laser combined with the gain flattening filter was successfully achieved with simple linear configuration. The lasing wavelengths spacing was 0.39nm. The variation of the central wavelength and intensity fluctuation were as small as 0.01nm and <0.7dBm in both dual-wavelength and single-wavelength operation regions, respectively.

Improved Performance of Integrated Solenoid Fluxgate Sensor Chip Using a Bilayer Co-Based Ribbon Core

In this paper, based on the multiwire core design and microelectromechanical system technology, we report improved performance of a microsolenoid fluxgate sensor by integrating a bilayer core of co-based amorphous ribbon. By means of utilizing integrated multilayer core structure and high permeability amorphous ribbon core material, this paper shows how a high-performance microfluxgate chip with small dimensions can be realized. The fabricated sensors exhibit a best sensitivity of 3165 V/T, a power of 183.2 mW and a linear range of 150 $\mu \text{T}$ at 100 kHz. The noise power density is found to be 0.5 nT/Hz $^{1/2}~1$ Hz and the noise rms level is 2 nT in the frequency range of 25 mHz–10 Hz.