Sandwich Films Research Articles

Improved Thermoelectric Performance in Flexible Tellurium Nanowires/Reduced Graphene Oxide Sandwich Structure Hybrid Films

With a high flexibility and an adjustable electronic structure, reduced graphene oxide (RGO) is a potential candidate for flexible thermoelectric materials. Here, we report that flexible RGO/tellurium nanowires (Te NWs)/RGO sandwich structure hybrid films are prepared on glass fabrics through the drop-cast method. The addition of 20 wt.% Te NWs into a RGO matrix remarkably improves the Seebeck coefficient from 15.2 μV/K to 89.7 μV/K while maintaining relatively high electrical conductivity, thus resulting in a one order of magnitude higher power factor value compared with the Te NWs. According to the values of carrier mobility and concentration of hybrid films, the improved thermoelectric properties are presented because of the energy filtering effect on the interfaces in hybrid films. This article suggests that RGO/Te NWs/RGO hybrid films would be promising for fabricating flexible energy sources.

Strong flexible polymer/graphene composite films with 3D saw-tooth folding for enhanced and tunable electromagnetic shielding

Strong flexible polymer/graphene composite films with ideal electromagnetic interference (EMI) shielding are fabricated through constructing a sandwich structure consisting of polyester non-woven fabric as reinforcing interlayer and thermoplastic polyurethane (TPU) composite with high graphene loading as conductive coating layer. The engineered sandwich film (defined as TPU/G film) with graphene loading of ∼20 wt% and total coating thickness of ∼50 μm not only possesses excellent mechanical flexibility and strong strength, but also exhibits qualified bandwidth of shielding effectiveness (SE) ≥ 20 dB as wide as ∼49.1 GHz in a broadband frequency range of 5.4–59.6 GHz. Moreover, saw-tooth folding of the flexible TPU/G films could efficiently enhance the shielding performance, and more conductive folded film with smaller included angle plus longer side would result in much greater SE enhancement along with reduced EM reflection. This finding also realizes the convenient performance regulation of the folded TPU/G films through a simple mechanical deformation, showing promise for tunable EMI shielding.

Effect of annealing temperatures on the turn‐on voltage of organic Schottky diode based on DPP(BTFu) 2

The electrical properties of diketopyrrolopyrrole ethyl-hexylated (DPP(TBFu)2) thin film sandwich structure of the ITO/DPP(TBFu)2/Al configuration for different annealing temperatures ranging from 40 to 130°C is investigated. The current–voltage characteristics showed an excellent rectifying behaviour of the device, and from which the diode parameters were extracted. It is found that all parameters remain constant upon annealing temperatures, with the exception of the turn-on voltage. An increase of the turn-on voltage from an initial value of 1.6–2.08 V is noticed starting from 70 to 100°C, respectively. This fact is attributed to the effect of residual solvent induced defect states that may act as free carriers. Defect states density for the non-annealed and annealed device at 130°C derived from capacitance–voltage measurements is found to correlate well with the turn-on voltage. It is found that annealing the device at 130°C results in a smaller concentration of defect states. In addition, it is also found that the annealing process produces the flat band voltage drop, which has a direct impact on the turn-on voltage.

A Versatile System for High-Throughput In Situ X-ray Screening and Data Collection of Soluble and Membrane-Protein Crystals.

In recent years, in situ data collection has been a major focus of progress in protein crystallography. Here, we introduce the Mylar in situ method using Mylar-based sandwich plates that are inexpensive, easy to make and handle, and show significantly less background scattering than other setups. A variety of cognate holders for patches of Mylar in situ sandwich films corresponding to one or more wells makes the method robust and versatile, allows for storage and shipping of entire wells, and enables automated crystal imaging, screening, and goniometer-based X-ray diffraction data-collection at room temperature and under cryogenic conditions for soluble and membrane-protein crystals grown in or transferred to these plates. We validated the Mylar in situ method using crystals of the water-soluble proteins hen egg-white lysozyme and sperm whale myoglobin as well as the 7-transmembrane protein bacteriorhodopsin from Haloquadratum walsbyi. In conjunction with current developments at synchrotrons, this approach promises high-resolution structural studies of membrane proteins to become faster and more routine.

Influence of NiZn-Ferrite Spacers on Giant Magnetoimpedance Effect in FeNi/Cu/FeNi Nano Films

FeNi/Cu/FeNi sandwich films without and with one or two NiZn-ferrite spacers were prepared by radio frequency magnetron sputtering. The microstructures and magnetic properties of these multilayer films are presented, and the influence of NiZn-ferrite spacers on the giant magnetoimpedance effect has also been studied. An enhanced giant magnetoimpedance effect is observed in the multilayer film with one 65 nm NiZn-ferrite spacer. The highest giant magnetoimpedance ratio in the FeNi/NiZn-ferrite/Cu/FeNi multilayer film reaches up to 36% at 10 MHz, which is a relatively high value for a nanometer thick film. This ratio is about 1.25 times larger than that of the FeNi/Cu/FeNi sandwich film (similar to 16% at 30 MHz), while the giant magnetoimpedance effect is not evidently enhanced in the FeNi/NiZn-ferrite/Cu/NiZn-ferrite/FeNi multilayer film. These results indicate that inserting one NiZn-ferrite spacer to a sandwich film is a simple and effective way to improve the giant magnetoimpedance effect in the nano film system.

Tunable Optical Mode Ferromagnetic Resonance in FeCoB/Ru/FeCoB Synthetic Antiferromagnetic Trilayers under Uniaxial Magnetic Anisotropy

Ferromagnetic resonance (FMR) is one of the most important characteristics of soft magnetic materials, which practically sets the maximum operation speed of these materials. There are two FMR modes in exchange coupled ferromagnet/nonmagnet/ferromagnet sandwich films. The acoustic mode has relatively lower frequency and is widely used in radio‐frequency/microwave devices, while the optical mode is largely neglected due to its tiny permeability even though it supports much higher frequency. Here, a realistic method is reported to enhance the permeability in the optical mode to an applicable level. FeCoB/Ru/FeCoB trilayers are carefully engineered with both uniaxial magnetic anisotropy and antiferromagnetic interlayer exchange coupling. This special magnetic structure exhibits a high optical mode frequency up to 11.28 GHz and a maximum permeability of 200 at resonance. An abnormally low inverse switch field (<200 Oe, less than 1/5 of the single layer) is observed which can effectively switch the system from optical mode with higher frequency into acoustic mode with lower frequency. The optical mode frequency and inverse switch field can be controlled by tailoring the interlayer coupling strengths and the uniaxial anisotropy fields, respectively. The tunable optical mode resonance thus can increase operation frequency while reduce operation field overhead in FMR based devices.

Metanephrine neuroendocrine tumor marker detection by SERS using Au nanoparticle/Au film sandwich architecture.

Neuroendocrine tumors, such as pheochromocytoma or paraganglioma, are dangerous tumors that constitute a potential threat for a large number of patients. Currently, the biochemical diagnosis of neuroendocrine tumors is based on measurement of the direct secretory products of the adrenomedullary-sympathetic system or of their metabolites, such as catecholamines or their metanephrine derivatives, from plasma or urine. The techniques used for analysis of plasma free metanephrines, i.e. high-performance liquid chromatography or high-performance liquid chromatography coupled with mass-spectrometry are technically-demanding and time consuming, which limit their availability. Here we demonstrate a simple, fast and low-cost method for detecting metanephrine by Surface Enhanced Raman Scattering (SERS). The protocol consists in using evaporation-induced self-assembly of gold (Au) nanoparticles incubated with the analyte, on planar gold films. The assembly process produces regions with a dense distribution of both inter-particle gaps and particle-film gaps. Finite-difference time-domain simulations confirm that both kinds of gaps are locations of enhanced electromagnetic fields resulting from inter-particle and particle-film plasmonic coupling, useful for SERS amplification. Metanephrine vibrational bands assignment was performed according to density functional theory calculations. Metanephrine metabolite was detected in liquid at concentration levels lower than previously reported for other similar metabolites. The obtained results demonstrate that the Au nanoparticle/Au film exhibits noticeable SERS amplification of the adsorbed metabolite and can be used in the design of efficient, stable SERS-active substrates for the detection and identification of specific tumor markers.

TiO2/ZnO/TiO2sandwich multi-layer films as a hole-blocking layer for efficient perovskite solar cells

A continuous and compact hole-blocking layer is crucial to prevent photocurrent recombination at the photoanode/electrode interface of high-performance mesostructure perovskite-based solar cells. Novel TiO2/ZnO/TiO2 sandwich multi-layer compact film prepared as hole-blocking layer for perovskite solar cell. Herein, TiO2, ZnO, and TiO2 layers were successfully deposited by spin-coating onto FTO glass substrate in sequence. The fill factor and power conversion efficiency of the perovskite solar cell are remarkably improved by the employment of a TiO2/ZnO/TiO2 sandwich compact layer. Perovskite solar cell based on TiO2/ZnO/TiO2 sandwich film has been observed to exhibit maximum incident-photon-to-current conversion efficiency in the visible region (400–780 nm) and reach a power conversion efficiency of 12.8% under AM1.5G illumination. Copyright © 2016 John Wiley & Sons, Ltd.

Dielectric response of (K0.5Na0.5)NbO3/CoFe2O4/(K0.5Na0.5)NbO3 magnetoelectric sandwich films

ABSTRACTThe sandwich magnetoelectric (K0.5Na0.5)NbO3/CoFe2O4/(K0.5Na0.5)NbO3 films have been fabricated on Ni–5 at.%W RABiTS tape by pulsed laser deposition. The dielectric properties of the films have been investigated. The dielectric tunability of the sandwich films increases initially and then decreases with increasing the bias field. It is suggested that the peak behavior originates from the interfacial polarization, trapping and locking mechanisms. The abnormal dielectric tunability not only has some new physical meanings, but also has potential practical applications in detectors, sensors and so on.

Nonlinear vibration characteristics of graphene/piezoelectric sandwich films under electric loading based on nonlocal elastic theory

This paper reports the result of an investigation into the nonlinear vibration frequencies of graphene/piezoelectric sandwich films under electrical loading based on nonlocal elastic theory by utilizing a global residual harmonic balance method. Based on the Galerkin method and global residual harmonic balance method, the nonlinear resonant frequencies of graphene/piezoelectric sandwich films under electric exciting loads are obtained with a set of factors: the ratio of the oscillating amplitude to the thickness of sandwich films, small scale effect, electric loading exerted on piezoelectric layer, mode number and size length. Results indicate that the electric exciting load enhances the nonlinear resonant frequency of graphene/piezoelectric sandwich films, the nonlinear resonant frequency decreases as the scale effect increases, the scale effect has a more significant effect on higher mode resonant frequency and linear resonant frequency, and the effect of scale on the nonlinear resonant frequency is independent on the electric exciting load and the boundary conditions exerted on the sandwich films.

Antibacterial property of Ag nanoparticle-impregnated N-doped titania films under visible light.

Photocatalysts produce free radicals upon receiving light energy; thus, they possess antibacterial properties. Silver (Ag) is an antibacterial material that disrupts bacterial physiology. Our previous study reported that the high antibacterial property of silver nanoparticles on the surfaces of visible light-responsive nitrogen-doped TiO2 photocatalysts [TiO2(N)] could be further enhanced by visible light illumination. However, the major limitation of this Ag-TiO2 composite material is its durability; the antibacterial property decreased markedly after repeated use. To overcome this limitation, we developed TiO2(N)/Ag/TiO2(N) sandwich films in which the silver is embedded between two TiO2(N) layers. Various characteristics, including silver and nitrogen amounts, were examined in the composite materials. Various analyses, including electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and ultraviolet–visible absorption spectrum and methylene blue degradation rate analyses, were performed. The antibacterial properties of the composite materials were investigated. Here we revealed that the antibacterial durability of these thin films is substantially improved in both the dark and visible light, by which bacteria, such as Escherichia coli, Streptococcus pyogenes, Staphylococcus aureus, and Acinetobacter baumannii, could be efficiently eliminated. This study demonstrated a feasible approach to improve the visible-light responsiveness and durability of antibacterial materials that contain silver nanoparticles impregnated in TiO2(N) films.

Switching the Localized Surface Plasmon Resonance of Single Gold Nanorods with a Phase-Change Material and the Implementation of a Cellular Automata Algorithm Using a Plasmon Particle Array

We investigate the modulation of the localized surface plasmon resonance (LSPR) of a gold nanorod (AuNR) using a GeSbTe film as an active medium. We demonstrate high-contrast switching of LSPR in an AuNR/GST/Au thin film sandwich structure upon phase change. To go beyond this single-particle switching functionality, we consider a plasmon particle system interacting with a phase-change material (PCM) to discuss the possibility of parallel processing devices with memory functionality, exploiting the plasticity and threshold behavior that are inherent characteristics of PCMs. We demonstrate that the temporal and spatial evolution of a plasmon-PCM array system can be equivalent to a cellular automata algorithm.

用粉末靶在玻璃和PI衬底上制备AZO/Ag/AZO薄膜

室温下在玻璃和聚酰亚胺两种不同衬底上,采用射频磁控溅射法溅射掺铝氧化锌(AZO)粉末靶和固体Ag靶,制备了两组AZO/Ag/AZO 3层透明导电薄膜,研究了AZO层厚度对不同衬底3层膜结构和光电性能的影响。结果表明:不同衬底的两组AZO/Ag/AZO薄膜均为多晶膜。当Ag层厚度不变时,随着AZO层厚度的增加,两组薄膜电学性能变化不大,透射峰向长波方向移动。玻璃和PI衬底上制备的AZO(30 nm)/Ag(14 nm)/AZO(30 nm)薄膜,在550 nm处的透光率分别为85%和70%,方块电阻分别为2.6Ω/□和4.6Ω/□。

A MnOOH/nitrogen-doped graphene hybrid nanowires sandwich film for flexible all-solid-state supercapacitors

An all-solid-state SC based on a flexible freestanding MNGHNs/AGO electrode with a volumetric capacitance as high as 26.3 F cm−3 is developed.

Facile synthesis and electrochemical performances of binder-free flexible graphene/acetylene black sandwich film

Graphene/acetylene black sandwich film was fabricated by a simple vacuum filtration procedure using a stable complex suspension of graphene oxide (GO) and acetylene black followed by a hydroiodic acid (HI) immersion process to fully reduce the GO to graphene sheets. The self-restacking of individual graphene sheets were greatly alleviated and electric conductivity was obviously improved using the acetylene black nanoparticles as both effective spacers to expand the inter-layer interval of the individual graphene sheets during the film assembly course and highly conducting bridges to facilitate the electron/ion transfer between the upper and lower graphene sheets. The flexible graphene/acetylene black film was utilized as supercapacitor electrode without additional conductive additives, binders and current collectors, which achieved an obviously higher specific capacitance (ca. 136.6Fg−1 at 0.5Ag−1) and much better specific capacitance retention at high current densities than that of the pure graphene film electrode, indicating that such a novel sandwich film structure allows for a higher charge storage capability. More importantly, the assembled symmetric supercapacitor device displayed a satisfactory specific capacitance of 59.2Fg−1 at 0.1Ag−1, 47.6Fg−1 at 0.5Ag−1 and 42.8Fg−1 at 1Ag−1, and only negligible 4.05% capacitance degradation have been found after 1000 continuous charge-discharge cycles at 0.5Ag−1, revealing outstanding rate capability, excellent electrochemical reversibility and long-term cyclability. These results proved that such a flexible and highly conductive graphene/acetylene black film can be promising electroactive materials in the development of advanced electrochemical energy storage devices.

Viscoelastic response of multilayer polymeric films of linear low-density polyethylene and ethylene vinyl alcohol copolymer

The viscoelastic response of multilayer polymeric films (sandwiches) of linear low-density polyethylene (LLDPE) and ethylene vinyl alcohol (EVOH) copolymer has been experimentally analyzed. We propose an equation to predict the mechanical response of the sandwich films from the data experimentally obtained for the monomaterial films. The equation is based on the hypothesis that the layers independently contribute to the final response and that there are no interfacial effects. The predictive character of the equation permits us to conclude that the response of the sandwich does not significantly depend on the individual layer thickness but only on the volume fraction of the EVOH in the system. More important, we find a strong sensitivity of the response to the processing conditions, which we quantitatively describe. POLYM. ENG. SCI., 55:1960–1968, 2015. © 2014 Society of Plastics Engineers

Spectroelectrochemical and morphological studies of the ageing of silver nanoparticles embedded in ultra-thin perfluorinated sputter deposited films

This paper focuses on the investigation of the ageing behaviour of silver nanoparticle containing polytetrafluoroethylene thin films during exposure to phosphate buffer solution (pH=7.5). In order to investigate the effect of the electrical connection between the silver nanoparticles via a conductive substrate, two kinds of composite films were compared. One model where the nanoparticles are directly deposited on an inert conducting substrate and then covered by an ultra-thin polytetrafluoroethylene like film. In the second case a polytetrafluoroethylene/silver nanoparticle/polytetrafluoroethylene sandwich film was prepared on the same substrate to prevent electrical connection of the silver nanoparticles. Degradation was followed in-situ by means of the combination of ultraviolet–visible spectroscopy and electrochemical impedance spectroscopy. In the case of electrically connected nanoparticles electrochemical Ostwald ripening took place, while this process was not observed for the insulated nanoparticles. The electrochemical impedance spectroscopy studies allowed for the parallel study of the correlated loss of barrier properties. Transmission electron microscopy images of both composite films confirmed the results obtained by means of the in situ electrochemical ultraviolet–visible studies.

Surface enhanced Raman scattering of 4-aminothiophenol sandwiched between Ag nanocubes and smooth Pt substrate: The effect of the thickness of Pt film

Ag nanocubes (NCs)/4-aminothiophenol (p-ATP)/smooth platinum (Pt) film (Ag-NCs @ p-ATP/Pt) sandwich structure is created for surface enhanced Raman scattering (SERS). The proposed sandwich structure is shown to exhibit better performance than the Ag-NCs only as SERS substrate. The dependence of the Raman signal intensity on the thickness of the Pt films is examined. It is shown that the Raman signal increases with the thickness of the Pt films from 42 to 90 nm, suggesting the electromagnetic coupling of the localized surface plasmons of the Ag-NCs with the surface plasmon polaritons of the underneath Pt film, which is confirmed by our numerical simulations. The SERS enhancement factor in Ag-NCs @ p-ATP/Pt is estimated to be (4.1 ± 0.2) × 106 for a Pt film of 90 nm.

Magnetoelectric effect in lead-free sandwich film composed of Co-ferrite and (K0.5Na0.5)NbO3-based ferroelectric

The lead-free multiferroic sandwich film 0.948(K0.5Na0.5)NbO3–0.052LiSbO3/CoFe2O4/0.948(K0.5Na0.5)NbO3–0.052LiSbO3 was fabricated on the Ni–5at%W RABiTS tape by pulsed laser deposition and its room-temperature magnetoelectric (ME) characteristics were investigated. The ME behaviors strongly depended on the magnitude of bias magnetic field and the frequency of driving field. The resonance peak in frequency-dependent ME voltage coefficient was observed and the maximum value of ME voltage coefficient was found to be 1013.9mVcm−1Oe−1. It is a very high value in the lead-free ME film system for the potential use on actuators and sensors, etc.

Ion transport-related resistive switching in film sandwich structures

Resistive switching memories based on ion transport and related electrochemical reactions have been extensively studied for years. To utilize the resistive switching memories for high-performance information storage applications, a thorough understanding of the key information of ion transport process, including the mobile ion species, the ion transport paths, as well as the electrochemical reaction behaviors of these ions should be provided for material and device optimization. Moreover, ion transport is usually accompanied by processes of microstructure modification, phase transition, and energy band structure variation that lead to further modulation of other physical properties, e.g., magnetism, optical emission/absorbance, etc., in the resistive switching materials. Therefore, novel resistive switching memories that are controlled through additional means of magnetic or optical stimulus, or demonstrate extra functionalities beyond information storage, can be made possible via well-defined ion transportation in various switching materials and devices. In this contribution, the mechanism of ion transport and related resistive switching phenomena in thin film sandwich structures is discussed first, followed by a glance at the recent progress in the development of high-performance and multifunctional resistive switching memories. A brief perspective of the ion transport-based resistive switching memories is addressed at the end of this review.