Sandwich Films Research Articles

Silver nanocubes monolayers as a SERS substrate for quantitative analysis

Surface-enhanced Raman scattering (SERS) is a powerful spectroscopic tool in quantitative analysis of molecules, where the substrate plays a critical role in determining the detection performance. Herein, a silver nanocubes/polyelectrolyte/gold film sandwich structure was prepared as a reproducible, high-performance SERS substrate by the water/oil interfacial assembly method. In addition to the hot spots on the nanocubes surface, the edge-to-edge interspace of the Ag nanocubes led to marked enhancement of the SERS intensity, with a limit of detection of 10−11 mol/L and limit of quantitation of 10−10 mol/L for crystal violet. When rhodamine 6G and crystal violet were co-adsorbed on the Ag nanocube surfaces, the characteristic SERS peaks of the two molecules remained well resolved and separated, and the peak intensities varied with the respective concentration, which could be exploited for concurrent detection of dual molecules. Results from this work indicate that organized ensembles of Ag nanocubes can serve as effective SERS substrate can for sensitive analysis for complex molecular systems.

Improving interfacial bonding performance of damping composites by introducing novel sandwich film

ABSTRACT Damping composites with sandwich layer are widely used in the fields of aerospace and high-speed trains. The most fatal defect of traditional damping composites is the poor interfacial adhesion between resin matrix and damping materials. To enhance interfacial bonding performance of traditional damping sandwich composites, the novel glass fiber reinforced damping composites were prepared by designing interfacial reaction between damping polymer and resin matrix. The novel damping materials in this work were fabricated via orthogonal test. The interfacial bonding mechanisms of new type damping sandwich composites were characterized by physical and chemical methods. The maximum shear strength in this paper is 6.2 MPa, which is 81.2% higher than the previous work. It is confirmed that the excellent interfacial bonding property is derived from interfacial chemical interaction between damping polymer and resin matrix according to FTIR and XPS. These results reveal that the novel damping composites possess a broad application potential in aerospace and high-speed trains.

Reduced thermal effect of AZO/Cu/AZO infrared filter film for solar cell

Abstract In this work, infrared filter property of aluminum doped ZnO (AZO) films prepared on glass substrates with different Ar flow rate by magnetron sputtering was studied. Then Cu was chosen to produce AZO/Cu/AZO sandwich films to further improve its infrared filter property for high transmittance within 380–1100 nm and low transmittance within 1100–2500 nm. The results showed that AZO film had a maximum transmittance over 85% in the region between 380 nm and 1100 nm and a lowest transmittance of 29.70% between 1100 nm and 2500 nm. While AZO/Cu/AZO sandwich film had a maximum transmittance of 80.95% between 380 nm and 1100 nm and its minimum transmittance was 14.61% between 1100 nm and 2500 nm. By using AZO/Cu/AZO sandwich glass as a cover of silicon solar cell, its working temperature showed a less increase of 10.61 °C after 3.5 h under an irradiation of 0.42 sun compared with that where a standard glass was used. This was because that Cu greatly increased the carrier concentration in the sandwich that led to a stronger carrier absorption in infrared wavelength region, so that a reduced thermal effect of the solar cell was obtained.

Space charge regulated high-k polymer nanocomposite with a novel sandwich structure

High-k polymer-based nanocomposite is an emerging field that is extensively studied in electronic devices. One of the main challenges in pursuing high permittivity is to reduce the dielectric loss in order to meet various practical applications. In this work, space charge regulated polymer nanocomposite with a novel sandwich structure is reported. In the proposed sandwich structure, the internal layer is a highly insulating BaTiO3@SiO2 (BT@SO)/PVDF nanocomposite film, and the outer layers are the graphite nanosheet (GR)/PVDF composite films. The structure of the sandwich film is carefully revealed. Under the applied electrical field, the sandwich-structured composites possess a high permittivity of 136 and ultralow loss of 0.028 (10 kHz). Consistently, computational study confirms the improved space charge accumulation in the GR/PVDF layer and reveals the mechanism for the high dielectric constant. Both the experimental and computational results demonstrate the significant role of the novel sandwich structure in designing the high-k polymer nanocomposites. This study provides an effective way for the design of high-k materials.

Bifurcation of magnetorheological film–substrate elastomers subjected to biaxial pre-compression and transverse magnetic fields

This work investigates the primary sinusoidal bifurcation wrinkling response of single- and multi-layered magnetorheological elastomer (MRE) film–substrate systems subjected to combined transverse applied magnetic fields and in-plane biaxial pre-compression. A recently proposed continuum model that includes the volume fraction of soft-magnetic particles is employed to analyze the effect of the magnetic properties upon the bifurcation response of the system. The analysis is built in a highly versatile manner using a finite-element discretization approach along the direction of the applied magnetic field and Fourier expansions along the infinite in-plane layer directions. This allows for a seamless investigation of various multi-layered structures. First, we analyze the effect of biaxial pre-compression upon the critical magnetic field for a film–substrate system and for various mechanical stiffness ratios. We observe a kink in the critical magnetic curves and a reflection in the corresponding wave numbers as they cross the equi-biaxial pre-compression regime. Subsequently, we consider a MRE film bonded to a MRE substrate and study the effect of the particle volume fraction ratios in those two parts. As a result, we obtain sharp pattern transitions, i.e., long-to-short wavelength changes with only minor perturbations of the applied pre-compression. The presence of a magnetic substrate changes qualitatively and quantitatively the bifurcation response of the film–substrate system. Finally, we carry out a data-mining exercise to minimize the critical magnetic field at bifurcation by using three different topologies, i.e., a monolayer, a bilayer and a sandwich film. We find that the topologies resembling closely the monolayer one lead to the lowest critical magnetic fields for a given biaxial pre-compression.

Improved polarization and energy density in boron nitride nanosheets/poly(vinylidene fluoride-chlorotrifluoroethylene) nanocomposite with trilayered architecture regulation

A polymer film capacitor with high energy density has attracted great attention in recent decades to fulfil the requirements of miniaturization and light weight for electronics and energy storage systems. The multi-layered nanocomposite exhibits an effective route for developing polymer film with large energy capability due to the advantage of each layer. Here, two sandwich constructions of boron nitride nanosheets (BNNSs)/poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite film were designed to investigate the effects of architecture regulation on energy storage performance, i.e. the nanocomposite serving as an inner layer with pristine films as outer layers, in which the nanocomposite film delivers a strongly polarized behavior and the pristine polymer provides a high breakdown strength. The BNNSs were liquid exfoliated from boron nitride bulk assisted with fluoro hyperbranched copolymer that was adsorbed on the surface of nanosheets via CH-π non-covalent interactions. The presence of fluoro segments improves the compatibility between the nanosheets and the P(VDF-CTFE) matrix. The maximum polarization of 7.9 μC cm−2 at 300 MV m−1 is achieved in the tailored sandwich film, and the discharged energy density of 9.1 J cm−3 is obtained in the current nanocomposite, which benefits from the barrier effect between adjacent layers induced by the redistribution of electric field and emerging charge traps at the interfaces. This sandwich BNNSs/P(VDF-CTFE) nanocomposite provides an insightful prospect for structural design with respect to the advanced application of the polymer film capacitor.

Attractive nanofiber structure based on Cu-Ti/metal sandwich film with excellent electrocatalytic performance for ethanol oxidation

The support materials are an important part of catalysts and they are the dispersant, adhesive, and support for other components. In this study, three types of thin films with different structures were used as the precursor to prepare loading Pd catalysts. The one-step dealloying method was used to prepare a semiconductor nanofiber film (NFF) support material with upward directional growth from the substrate. Pd/NFF and Pd/NiO/NFF loaded Pd catalysts were prepared using NFF as the support material, and the electrochemical catalytic properties for ethanol oxidation in alkaline media were studied. Cyclic votammetry showed that the NFF support material effectively inhibited agglomeration of palladium, increased the number of active sites of Pd, and improved the electrocatalytic properties of Pd for ethanol oxidation. In addition, the Pd/NiO/NFF loaded Pd catalyst obtained by modification with nickel oxide significantly improved the electrocatalytic performance for ethanol oxidation compared with the Pd/NFF loaded Pd catalyst. These results show that NiO is conductive to absorption of oxygen-containing groups on the surface of the catalyst and can further improve the electrocatalytic ability of Pd for ethanol oxidation. All of the above results demonstrate that the support material prepared by the dealloying method has application prospects in load-type catalysts.

Design and preparation of FDLC/Ag/FDLC sandwich films with tunable photoelectric performance

Using Film Wizard™ Optical software, we obtained the optimal structural parameters of the thickness of each film layer of DLC/Ag/DLC sandwich structure through computer simulation. Then, FDLC/Ag/FDLC sandwich films with different Ag layer thicknesses were prepared by magnetron sputtering equipment. The surface of the films was dense, smooth, and had uniform particles. The luminous optical transmittance of the FDLC (30 nm)/Ag (16 nm)/FDLC (40 nm) sandwich films in the visible region reached 76.8%. When the thicknesses of the silver layer were 14, 16, and 18 nm, the Figure of Merit of the sandwich films reached 53.6 × 10−3 Ω−1, 66.3 × 10−3 Ω−1, and 52.8 × 10−3 Ω−1, respectively, and all were high values. These values were significantly better than most other previously reported ones for multilayer film electrodes. The optical band gap of the sandwich films was in the range of 1.61–2.54 eV. The band gap was regulated through the thickness of the Ag layer, and the regulation range was approximately 0.93 eV. This finding showed that the FDLC/Ag/FDLC sandwich films can potentially be applied to transparent electrodes and solar cell films.

Synthesis of Monolayer Gold Nanorings Sandwich Film and Its Higher Surface-Enhanced Raman Scattering Intensity.

Most previous studies relating to surface-enhanced Raman spectroscopy (SERS) signal enhancement were focused on the interaction between the light and the substrate in the x-y axis. 3D SERS substrates reported in the most of previous papers could contribute partial SERS enhancement via z axis, but the increases of the surface area were the main target for those reports. However, the z axis is also useful in achieving improved SERS intensity. In this work, hot spots along the z axis were specifically created in a sandwich nanofilm. Sandwich nanofilms were prepared with self-assembly and Langmuir-Blodgett techniques, and comprised of monolayer Au nanorings sandwiched between bottom Ag mirror and top Ag cover films. Monolayer Au nanorings were formed by self-assembly at the interface of water and hexane, followed by Langmuir-Blodgett transfer to a substrate with sputtered Ag mirror film. Their hollow property allows the light transmitted through a cover film. The use of a Ag cover layer of tens nanometers in thickness was critical, which allowed light access to the middle Au nanorings and the bottom Ag mirror, resulting in more plasmonic resonance and coupling along perpendicular interfaces (z-axis). The as-designed sandwich nanofilms could achieve an overall ~8 times SERS signals amplification compared to only the Au nanorings layer, which was principally attributed to enhanced electromagnetic fields along the created z-axis. Theoretical simulations based on finite-difference time-domain (FDTD) method showed consistent results with the experimental ones. This study points out a new direction to enhance the SERS intensity by involving more hot spots in z-axis in a designer nanostructure for high-performance molecular recognition and detection.

Reduced holey graphene oxide film and carbon nanotubes sandwich structure as a binder-free electrode material for supercapcitor

A novel carbon nanotubes (CNTs) and reduced holey graphene oxide film (RHGOF) sandwich structure has been fabricated to enhance its electrochemical properties. CNTs are grown by a catalyst assisted chemical vapor deposition technique, interpenetrated between the RHGOF layers. A RHGOF/CNTs hybrid film is used as a binder-free supercapacitor electrode. The grown CNTs in the graphene layers structure act as spacers and bridges to increase the counductivity of RHGOF, while the grown CNTs on the surfaces of the graphene contribute to increase the specific surface area of RHGOF. The results demonstrate that the synthesized porous, flexible and binder free hybrid electrode has advantages of higher ion diffusion rate, longer diffusion length and larger ion accessible surface area as compared to the pristine graphene which results in an extra ordinary galvanostatic charge-discharge specific capacitance of 557 F/g at a current density of 0.5 A/g, with excellent rate capabilities and superior cyclic stabilities.

Fabrication and application of flexible AlN piezoelectric film

A fabrication method for high quality flexible aluminum nitride piezoelectric thin films based on micro-nano fabrication technology is reported in this paper. Molybdenum (Mo)/aluminum nitride (AlN)/aluminum (Al) structure was prepared on silicon(100) by sputtering. Then, deep-reactive ion etching technology was used to remove the silicon material used for support, then the Mo/AlN/Al flexible sandwich film was obtained. The full-width at half-maximum of the AlN film (002) peak before and after removal of silicon was only 1.47° and 1.49°, respectively. No obvious cracks in the film under bending conditions were observed with a scanning electron microscope. Capacitance–voltage (C–V) test results showed that the capacitance curve of the sandwich structure was consistent with that of the double-sided Schottky junction. The flexible piezoelectric film with an active area of 2 × 2 mm2 exhibited an average peak-to-peak generated voltage of 0.6 V in energy harvesting tests, which indicates that the method could be used to fabricate high quality flexible energy collectors based on AlN film. The preparation scheme in this paper is compatible with integrated circuit processes and simple to implement, which lays a foundation for the wide application of flexible piezoelectric devices.

Nacre-Inspired Tunable Electromagnetic Interference Shielding Sandwich Films with Superior Mechanical and Fire-Resistant Protective Performance

With the rapidly increasing development of portable device hardware and flexible electronics, ultrathin electromagnetic interference (EMI) shielding films with a combination of high flexibility and excellent mechanical properties are noticeably required. In addition to minimizing the electromagnetic wave pollution problem, the fire hazards caused by accidental electrical leakage or aging are also a cause of extensive concern. Inspired by nacre and sandwich structure, herein, we fabricated for the first time an electrical insulating sandwich-structured film based on Ca ion cross-linked sodium alginate (SA)-montmorillonite (MMT) and Ti3C2Tx MXene through a step-by-step vacuum-assisted filtration process. This novel design strategy not only maintains the inner EMI shielding network but also can act as an excellent fire-resistant barrier to protect the electronic device in case of accidental fire. Compared with the pure Ti3C2Tx layer, such kind of sandwich film can effectively maintain the EMI shielding performance (50.01 dB), dramatically enhance the mechanical properties (84.4 MPa), and exhibit excellent fire-resistant performance. Especially, compared with the film composed of mixture, the EMI shielding effectiveness value is only 55% that of sandwich films. Besides, it functions well under long-term heat aging test at 80 °C. Therefore, this unique design provides a novel EMI material strategy to facilitate its future applications in flexible electronics.

Low Dielectric Loss and Multiferroic Properties in Ferroelectric/Mutiferroic/Ferroelectric Sandwich Structured Thin Films

Bismuth ferrite (BiFeO3) has proven to be promising for a wide variety of microelectric and magnetoelectric devices applications. In this work, a dense (Ba0.65Sr0.35)TiO3(BST)/(Bi0.875Nd0.125)FeO3(BNF)/BST trilayered thin film grown on Pt-coated Si (100) substrates was developed by the rf-sputtering. For comparison, single-layered BNF and BST were also prepared on the same substrates, respectively. The results show that the dielectric loses suppression in BST/BNF/BST trilayered thin films at room temperature but has enhanced ferromagnetic and ferroelectric properties. The remnant polarization (Pr) and coercive electronic field (Ec) were 5.51 μC/cm2 and 18.3 kV/cm, and the remnant magnetization (Mr) and coercive magnetic field (Hc) were 10.1 emu/cm3 and 351 Oe, respectively, for the trilayered film. We considered that the bismuth’s volatilization was limited by BST bottom layers making the Bi/Fe in good station, and the action of BST layer in the charge transfer between BNF thin film and electrode led to the quite low leakage current and enhanced multiferroic property. The origin of the mechanism of the highly enhanced dielectric constant and decreased loss tanδ was discussed.

Band Alignment and Optical Properties of ZnO/Cu/Al2O3 Sandwich Structure Films

Band Alignment and Optical Properties of ZnO/Cu/Al₂O₃ Sandwich Structure Films

High-energy density in Si-based layered nanoceramic/polymer composites based on gradient design of ceramic bandgaps

Abstract It is difficult to simultaneously achieve a high electrical breakdown strength, dielectric permittivity, discharged energy density and charge-discharge efficiency by simply blending electrically conductive nanoparticles with insulating polymers in large-scale preparations. In this work, a family of gradient sandwich-structured Si-based semiconducting nanoparticle/fluoropolymer nanocomposite films with a high breakdown and good energy storage performances was fabricated using a triple solution casting process by fine tuning the type and volume concentration of the Si-based nanofiller used in each layer of the sandwich films. Differing from traditional homogeneous composite films with mono-layered structures, novel inhomogeneous composite films with gradient sandwich structures were fabricated. This fabrication was achieved by implementing a gradient-design strategy used to produce high breakdown layer-by-layer composite dielectrics and the induced polarization tactics used to produce high-permittivity Si-based semiconductor/polymer composite dielectrics. Beta-Si 3 N 4 , alpha-SiC and monocrystalline Si nanoparticles (all ∼100 nm) were introduced into the upper, middle and bottom layers of the fluoropolymer matrices, respectively. The volume concentrations of the Si-based nanofillers in each of the three layers were controlled, and 1 vol% filler in each layer was found to be optimal. In this case, the preferred electric field applied to each layer due to the gradient design could result in the highest breakdown strength (360 MV m −1 ) of the composite. The interface blocking effect present between two adjacent layers might inhibit the electrical tree growth between the two electrodes, contributing to a significantly enhanced breakdown property. As a result, a discharged energy density of 13 J cm −3 and a charge-discharge efficiency of 67% at 350 MV m −1 were obtained. This work might pave the way for the large-scale preparation of high-performance nanocomposite dielectrics based on the interface blocking effect.

Antibody-functionalized reduced graphene oxide films for highly selective capture and purification of aflatoxins

Pyrenylbutyric acid and streptavidin were coupled to films of reduced graphene oxide (rGO) and then conjugated to a biotinylated broad-spectrum monoclonal antibody against aflatoxins (AFs). It is shown that such films can efficiently and selectively capture AFs inculding AFB1, AFB2, AFG1, AFG2, AFM1 and AFM2. The rGO films were characterized by using scanning electron microscopy, energy-dispersive spectroscopy, and raman spectroscopy. The selectivity and purification performance of the antibody-loaded rGO films were investigated. They were applied to the purification of extremely small samples (100μL) of AFs-spiked rabbit serum after enzymatic hydrolysis. The AFs were analyzed by ultra-performance liquid chromatography coupled to tandem mass spectrometry. The limits of detection for the six AFs investigated ranged from 50 to 170pg·mL-1. The average recoveries of AFs in spiked rabbit serum samples ranged from 55% to 75%, with relative standard deviations of less than 9.4%. Graphical abstract Design of a multifunctional sandwich film that consists of a reduced graphene oxide film base, a pyrenylbutyric acid middle layer and a broad-specificity anti-AF monoclonal antibody surface layer. It was successfully applied to the determination of aflatoxins in only 100μL of rabbit serum samples with satisfactory selectivity and acceptable accuracy.

Editorial overview: Food chemistry and biochemistry

Based on the first-principles calculations, the influence of different geometry models on the theoretical results about the electronic properties of LaAlO3/SrTiO3 perovskite heterostructures has been studied. The results show that the superlattice model can indicate n-type conductivity of interfaces, but it is limited to describe the insulator-metal transition of heterostructures. The sandwich and thin film models with the vacuum layer can take into account the surface termination effect on the electronic properties of the interface. The AlO2 or LaO atomic layer as the outmost surface termination is selected during constructing the model, leading to the distinct electronic properties of the heterostructures. The build-in electric filed appears in the AlO2-terminated structure, whereas it does not exist in LaO-terminated structure. Therefore, the AlO2-terminated structure can give a clear description about the insulator-metal transition of heterostructure and the charge transfer mechanism. The build-in electric filed, the atomic rumpling and surface termination effect of perovskite materials codetermine the conductivity of interfaces. The results would be helpful to construct theoretical model and understand the novel electronic properties during investigating other perovskite heterostructures.

Comparison of geometry models in the study of perovskite heterostructures

Based on the first-principles calculations, the influence of different geometry models on the theoretical results about the electronic properties of LaAlO3/SrTiO3 perovskite heterostructures has been studied. The results show that the superlattice model can indicate n-type conductivity of interfaces, but it is limited to describe the insulator-metal transition of heterostructures. The sandwich and thin film models with the vacuum layer can take into account the surface termination effect on the electronic properties of the interface. The AlO2 or LaO atomic layer as the outmost surface termination is selected during constructing the model, leading to the distinct electronic properties of the heterostructures. The build-in electric filed appears in the AlO2-terminated structure, whereas it does not exist in LaO-terminated structure. Therefore, the AlO2-terminated structure can give a clear description about the insulator-metal transition of heterostructure and the charge transfer mechanism. The build-in electric filed, the atomic rumpling and surface termination effect of perovskite materials codetermine the conductivity of interfaces. The results would be helpful to construct theoretical model and understand the novel electronic properties during investigating other perovskite heterostructures.

Laser Shock Peening Application as Alternative Method to Determine the Mechanical Properties of Aluminum

The structural, physical, and mechanical properties of laser-induced shock peening (LSP) of Aluminum before and after depositing films of different metals (Cu, In, and Al) were investigated. The deposition of single and double films was conducted, and the physical property (density), shockwave properties (shock pressure, particle velocity, and shock velocity), mechanical properties (stress, strain, Young's s modulus, and Hardness) were calculated, Young's s modulus measured of aluminum was measured by classical method (Tensile test ) and by LSP technique, and it was found that the measured using LSP is closer to the standard value than classical method .Single film Cu and sandwich Al / Cu deposited on Al substrate showed an enhancement in the mechanical properties rather than other films, while the deposited films of (In, In / Cu, and Al /In) on Al substrate revealed more strain and higher ductility than others.

Electrical Conduction Properties of Sb & Se Co-Doped PbTe Thin Films

Thenanocrystalline Sb & Se co-doped PbTe thin films were prepared by using an integrated physical-chemical approach by evaporating chemically synthesized Sb& Se co-doped PbTenanopowders on glass substrates. The prepared films were analysed by XRD, SEM, EDAX and their results were discussed in detail. The DC electrical conduction mechanism in Al/SbPbTeSe/Al thin film sandwich system at different temperatures (298–423 K) was studied and was found to be Poole-Frenkel type.