Multilayer Composite Films Research Articles

Composite multilayer films based on polyelectrolytes and in situ‐formed carbon nanostructures with enhanced photoluminescence and conductivity properties

ABSTRACTWe report a facile route for the fabrication of thin composite films based on polyelectrolytes and carbon nanostructures. Composite films were made by layer‐by‐layer assembly of polyelectrolyte multilayers utilizing embedded dextran sulfate (Dex) solution as a carbon source. Raman measurements indicate the formation of carbon nanostructures from the Dex precursor over the whole film. Formation of these nanostructures results in enhanced photoluminescence and an increase in conductivity by two orders of magnitude to about 0.055 S cm−1. The latter corresponds to the level of wide‐gap semiconductors, in contrast to the initial insulating polyelectrolyte film. A distinct peak of photoluminescence of the films is found in the blue region at the wavelength of 450 nm. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47718.

A flexible pressure sensor by induced ordered nano cracks filled with multilayer graphene oxide composite film as a conductive fine-wire network for higher sensitivity

Inspired by the structure of skin, a flexible pressure sensor is proposed here, which consists of a flexible Kapton/polydimethylsiloxane (PDMS) substrate, a sensing structural layer of a fine-wire connected conductive network and a protective layer of PDMS. Notably, cracks, often referred to as defects, were utilized to fabricate the conductive network in this work. The ordered nano cracks were induced by changing the temperature of the patterned photoresist film suddenly to form the regular hexagonal array nano-channel network. Then the Ni/multilayer graphene oxide/Ni sandwich composites were introduced to obtain the conductive fine-wire connected network by electroplating and graphene oxide electrodeposition. When the sensor is under pressure, the strain effect of the bottom Ni network, the change of intermediate multilayer graphene oxide microstructure, and the breaks of electron transport paths owing to the top wrinkled Ni cracking, contribute to the resistance change together. As a result, the fabricated flexible pressure sensor shows a maximum sensitivity as high as 4953.15 kPa−1 at 52.27 kPa. In addition, the sensor has a fast response (47 ms) and good repeatability, which are essential for practical applications. Furthermore, the pressure sensor was demonstrated to have good potential in e-skin application, such as pulse detection, laughter and swallowing movement recognition. This work provides a new and convenient approach to fabricate a conductive network with nanowires by induced cracks.

Atomistically Informed and Dislocation-Based Viscoplasticity Model for Multilayer Composite Thin Films

Nano-scale multilayer composite thin films are potential candidates for coating applications at harsh environments due to their promising mechanical and thermal properties. In this study, a viscoplasticity continuum model based on the plastic flow potential of metal/ceramic nanolayer composites, obtained from molecular dynamics (MD) simulations, is developed to build up a multiscale model bridges atomistic simulation with continuum models for the thin film composites. The model adopts a power law hardening considering confined layer slip (CLS) mechanism and accounts for the evolution of dislocation density based on the statistically stored dislocations and geometrically necessary dislocations. It is then implemented into a finite element code (ls-dyna) to investigate the deformation behavior of nanolayer composites at the macroscale. The deformation behavior of a high strength steel coated with Nb/NbC multilayer is also examined.

Production of high-performance multi-layer fine-fibrous filter material by application of material extrusion–based additive manufacturing

This study addresses a new approach to production of multi-layer fine-fibrous filter material by application of material extrusion–based additive manufacturing (MEB-AM). By the example of polypropylene/copolyamide (PP/CPA), the ability of a fibrous composite structure formation in the initial strands is demonstrated. It is shown that a change in the size of filter grid cells and the extrusion pressure allows control of the diameter of PP fibrils. It is found that multi-layered composite films formed by MEB-AM of the strands retain the structure inherent in the strands. A polypropylene precision filter material has been produced by extraction of a matrix polymer from composite films. The achieved filter retention is about 100% (for the particles of 0.3–1.0 μm in size).

(1 1 0)–textured BaSn0.15Ti0.85O3/Ba0.6Sr0.4TiO3/BaZr0.2Ti0.8O3 multilayers with enhanced tunable performance

BaSn0.15Ti0.85O3/Ba0.6Sr0.4TiO3/BaZr0.2Ti0.8O3 multilayer, BaSn0.15Ti0.85O3/Ba0.6Sr0.4TiO3 and Ba0.6Sr0.4TiO3/BaZr0.2Ti0.8O3 bilayer composite thin films are deliberately grown on Pt-Si substrates by pulsed laser deposition. The multilayers exhibit preferential growth along the (1 1 0) direction and reveal prominently enhanced dielectric tunable performance compared to the previous reported single-layer dielectric tunable thin films, the BaSn0.15Ti0.85O3/Ba0.6Sr0.4TiO3 and Ba0.6Sr0.4TiO3/BaZr0.2Ti0.8O3 bilayers at room temperature. For the multilayers, a large tunability of 71.3% under bias electric field of 400 kV/cm is achieved, while the dielectric loss is 0.0063 and the leak current density is ∼1.0 × 10−10 A/cm2 at 300 kV/cm. Calculation of figure of merit (FoM) shows a large value of 113. Such outstanding properties have suggested that BaSn0.15Ti0.85O3/Ba0.6Sr0.4TiO3/BaZr0.2Ti0.8O3 multilayer composite thin films are excellent candidates for electrically steerable applications.

Characteristics of Sb6Te4/VO2 Multilayer Thin Films for Good Stability and Ultrafast Speed Applied in Phase Change Memory**Supported by the National Natural Science Foundation of China under Grant No 11774438, the Natural Science Foundation of Jiangsu Province under Grant No BK20151172, the Qing Lan Project, the Opening Project of State Key Laboratory of Silicon Materials under Grant No SKL2017-04, the Opening

The Sb6 Te4/VO2 multilayer thin films are prepared by magnetron sputtering and the potential application in phase change memory is investigated in detail. Compared with Sb6 Te4, Sb6 Te4/VO2 multilayer composite thin films have higher phase change temperature and crystallization resistance, indicating better thermal stability and less power consumption. Also, Sb6 Te4/VO2 has a broader energy band of 1.58 eV and better data retention (125°C for 10 y). The crystallization is suppressed by the multilayer interfaces in Sb6 Te4/VO2 thin film with a smaller rms surface roughness for Sb6 Te4/VO2 than monolayer Sb4 Te6. The picosecond laser technology is applied to study the phase change speed. A short crystallization time of 5.21 ns is realized for the Sb6 Te4(2 nm)/VO2 (8 nm) thin film. The Sb6 Te4/VO2 multilayer thin film is a potential and competitive phase change material for its good thermal stability and fast phase change speed.

Investigation of Sb65Se35/Sb multilayer thin films for high speed and high thermal stability application in phase change memory

Sb65Se35/Sb multilayer composite thin films were prepared by depositing the Sb65Se35 and Sb layers alternately. In situ resistance vs. temperature was measured and the crystallization temperature increased with thickening the Sb65Se35 layer in Sb65Se35/Sb thin films. The data retention temperature of 10 years increased greatly from 14 °C of pure Sb to 103 °C of [Sb65Se35(3 nm)/Sb(7 nm)]3. Also, the band gap was broadened and the surface became smoother. X-ray diffraction patterns for the studied materials revealed that Sb and Sb2Se3 phases coexisted in Sb65Se35/Sb thin films. Absorbing the advantages of the fast phase change for Sb, the [Sb65Se35(1 nm)/Sb(9 nm)]5 multilayer thin film had an ultrafast amorphization speed of 1.6 ns. The results indicated that Sb65Se35/Sb multilayer thin film was a potential phase change material for fast speed and good stability.

Multi-layered zinc oxide-graphene composite thin films for selective nitrogen dioxide sensing

In the present work, selective nitrogen dioxide (NO2) sensing characteristics of multi-layered graphene-zinc oxide (G-ZnO) thin films have been demonstrated at 150 °C. The response% of 5 ppm NO2 was measured to be 894% with response and recovery times estimated to be 150 s and 315 s, respectively. In these composite films, the interaction between graphene and zinc oxide is established through X-ray photoelectron spectroscopy in conjunction with the analyses of photoluminescence spectra. Superior NO2 sensing of these films is due to simultaneous chemiadsorption of molecular oxygen and NO2 gases onto graphene and ZnO surfaces, resulting in an appreciable increase in the depletion layer width and thereby the sensor resistance. The sensor responses for other reducing gases (viz., CO, H2, and i-C4H10) are postulated to be due to their catalytic oxidation on the sensor surface, resulting in a decrease in the sensor resistance upon gas exposure. At lower operating temperature, due to the molecular nature of the chemiadsorbed oxygen, poor catalytic oxidation leads to a far lower sensor response for reducing gases as compared to NO2. For mixed NO2 and reducing gas sensing, we have reported that fast Fourier transformation of the resistance transients of all these gases in conjunction with principal component analyses forms a reasonably distinct cluster and, therefore, could easily be differentiated.

High Reliability and Fast‐Speed Phase‐Change Memory Based on Sb70Se30/SiO2 Multilayer Thin Films

Sb70Se30/SiO2 multilayer thin films were applied to improve the thermal stability by RF magnetron sputtering on SiO2/Si (100) substrates. The characteristics of Sb70Se30/SiO2 multilayer thin films were investigated in terms of crystallization temperature, ten years of data retention, and energy bandgap. It is observed that the crystallization temperature, 10‐year data retention, and resistance of Sb70Se30/SiO2 multilayer composite thin films exhibited a higher value, suggesting that Sb70Se30/SiO2 multilayer composite thin films have superior thermal stability. The AFM measurement suggests that the SbSe (1 nm)/SiO (9 nm) multilayer thin films possess a smaller surface roughness (RMS = 0.23 nm). Besides, it was found that the phase‐change time of SbSe (1 nm)/SiO (9 nm) multilayer thin films was shorter than that of GST in the process of crystallization and amorphization.

Densification of chlorine-doped continuous CNT sheet/polyvinylidene fluoride sandwich film and improvement of the mechanical and dielectric properties

The compact structure of a chlorine-doped continuous CNT sheet/polyvinylidene fluoride (Cl-CNT sheet/PVDF) was successfully optimized by means of a hot-press treatment to improve the mechanical and dielectric properties with a high densification degree. Then, the densified Cl-CNT sheet/PVDF dielectric layer was inserted between two PVDF insulating layers to fabricate a sandwich composite. It was found that the dielectric and mechanical properties were effectively enhanced, with a dielectric permittivity of 40.4 (@102 Hz), a dielectric loss of 0.16 (@102 Hz), a tensile strength of 139 MPa, and a tensile modulus of 4.4 GPa under a hot-pressing pressure of 20 MPa. Furthermore, the densified Cl-CNT sheet/PVDF was used as an electrode in a multilayer sandwich composite film, and good performance was obtained. The improvement mechanism was discussed and the studied CNT composite and other dielectric composites were compared. It demonstrates great potential for applications in dielectric and electrode materials to achieve structural and functional integration.

Layer‐by‐layer fabrication of nacre inspired epoxy/MMT multilayered composites

ABSTRACTThe organic–inorganic hybrid multilayered composites are prepared using a unique combination of poly[(o‐cresyl glycidyl ether)‐co‐formaldehyde] (CNER), amino modified montmorillonite (NH2‐MMT), and polyethyleneimine (PEI). This tricomponent composite multilayer PEI(CNER/NH2‐MMT/PEI)n deposited via layer‐by‐layer technique is based upon synergistic combination of covalent and hydrogen bonding. The growth of multilayer was monitored using UV–vis spectroscopy and ellipsometry. When subjected to optical analyses, the prepared multilayered composite films revealed profound optical transmittance ∼83%–87%. The surface morphological analysis by atomic force microscopy and scanning electron microscopy revealed uniform arrangement of organic–inorganic components with relative increase in intensity of elements (C, N, O, Si) as confirmed by X‐ray photoelectron spectroscopy studies. The multilayered composites possess 1.99 GPa hardness making them potential candidate for a number of applications where mechanical strength is desired. Moreover, significant resistance against alkaline and organic solvents at minimal deterioration of circa 0.12% has also been observed for the prepared films. The epoxy clay based thin films being robust, scratch resistant, hydrophilic, chemically inert, and mechanically strong are potential candidates for advanced environmental applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46079.

Giant negative electrocaloric effect in PbZrO3/0.88BaTiO3–0.12Bi(Mg1/2,Ti1/2)O3 multilayered composite ferroelectric thin film for solid-state refrigeration

A giant negative electrocaloric (EC) effect in a PbZrO3/(0.88BaTiO3–0.12 Bi(Mg1/2,Ti1/2)O3) (PZ/(BT-BMT)) multilayered composite ferroelectric (MCFE) thin film which is grown on Pt(111)/Ti/SiO2/Si(100) substrates by the sol-gel method is investigated in this work. The negative EC effect in the PZ/(BMT-BT) MCFE thin film is greatly higher than that in the PZ AFE thin film with an adiabatic temperature change (ATC) ΔT = 1.5 K. The ATC ΔT of the PZ/(BMT-BT) MCFE thin film is −32 K under the applied electric field change ΔE = 1151 kV/cm. The result is conducive to enhance the EC refrigeration efficiency greatly.

Preparation of MgO/Au Multilayer Composite Films and Related Studies on Secondary Electron Emission Effect

MgO thin film has a high secondary electron emission coefficient. However, the accumulation of electric charge on the surface of the thin film will inhibit it. This paper mainly discusses this phenomenon with the method of reactive magnetron sputtering. We prepared a MgO/Au buffer layer by co-sputtering Au in the inner layer of MgO. The experiments show that Au distributes mainly in the gap of the MgO grains. Adding appropriate Au will promote the growth of MgO grains in the longitudinal direction, increase the conductivity of the material, suppress the accumulation of electric charge on the surface, and increase the secondary electron emission coefficient of the thin film. NiO was also used as the transition layer of MgO and substrate in the experiments, so as to increase the adhesion of the MgO films and improve the quality of the thin film. According to the experiment results, the maximum secondary electron emission coefficient of MgOAu multilayer composite film increased by 28.9% compared with that of the pure MgO film. Under the continuous irradiation of 200 eV incoming energy, the decay rate decreased from 35.2% to 30.6% in 1 h.

Voltammetric determination of folic acid at physiological pH values by using a glassy carbon electrode modified with a multilayer composite consisting of polyoxometalate (H8P2Mo16V2O62) and reduced graphene oxide and prepared via layer-by-layer self-assembly and in-situ photoreduction

Vanadium-substituted polyoxometalate clusters of type H8P2Mo16V2O62 and reduced graphene oxide (rGO) were incorporated into a multilayer composite film via combining layer-by-layer self-assembly (using polyethyleneimine) and in-situ UV photoreduction. The growth of the multilayer film was monitored by UV-vis spectroscopy. The UV-induced conversion of graphene oxide to rGO in the multilayer film is due to the photocatalytic activity of P2Mo16V2 and was proven by X-ray photoelectron spectroscopy. The material was placed on a glassy carbon electrode (GCE) where it displayed good electrocatalytic activity towards oxidation of folic acid (FA) as demonstrated by cyclic voltammetry and differential pulse voltammetry. The modified GCE (best operated at a working voltage of 0.75 V vs Ag/AgCl and a scan rate of 50 mV s−1) compared to films containing either P2Mo16V2 or rGO only. The effects of the number of bilayers and of pH values on the electro-oxidation were investigated. The modified GCE was applied to selective determination of FA even in the presence of dopamine (DA) and uric acid (UA) at physiological pH. In fact, the modified GCE may also be applied to the simultaneous determination of DA, UA and FA. The amperometric response to FA increases linearly in the 10 nM to 0.8 mM FA concentration range, with a 0.28 nM detection limit. The sensor was successfully applied to the determination of FA in spiked human serum samples.

Transfer matrix method for four-flux radiative transfer.

We develop a transfer matrix method for four-flux radiative transfer, which is ideally suited for studying transport through multiple scattering layers. The model predicts the specular and diffuse reflection and transmission of multilayer composite films, including interface reflections, for diffuse or collimated incidence. For spherical particles in the diffusion approximation, we derive closed-form expressions for the matrix coefficients and show remarkable agreement with numerical Monte Carlo simulations for a range of absorption values and film thicknesses, and for an example multilayer slab.

The role of PbTiO3 layers in piezoelectric multilayer composite films based on Pb(Mg1/3Nb2/3)O3-PbTiO3

The sharp decrease of the remnant ferroelectric and piezoelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMNT) thin films close to the Morphotropic Phase Boundary (MPB) respect to their corresponding bulk ceramics is a major drawback for their integration in microdevices. In order to take full advantage of the excellent piezoelectric properties of polycrystalline PMNT in thin film form, a multilayer configuration with PbTiO3 (PT) layers is proposed. The PT layers generate an internal electric bias within the PMNT layer, which anchor an induced polarization in it. This results in a significant improvement of the piezoelectric behavior, obtaining remnant piezoelectric coefficients, d33 r, as high as 67pmV−1. The role of the thickness of the PT layers used is discussed, in order to find the optimum configuration for these multilayers.

Effect Research of Phase Thickness Compensation Factor on the Energy Reflectivity of Multi-layer Optical Anti-counterfeiting Composite Film

In this paper, we have given the equation of energy reflectivity, and discussed the designing principle of reflective anti-counterfeiting film for the high reflecting film system made of metal chromium film and symmetric transparent composite film F-P, then using MATLAB programming to draw out the influence curve of the phase thickness compensation factor on the energy reflectivity for12-layer membrane system. Contrasting the curve analysis, we have studied the effect of phase thickness compensation factor on the energy reflectivity of multi-layer composite film.

Composition analysis of oxide films formed on titanium surface under pulsed laser action by method of chemical thermodynamics

A pulsed fiber laser with a wavelength of 1.06 µm was used to treat a commercial pure titanium surface in the air at intensities below the ablation threshold to provide oxide formation. Laser oxidation results are predicted by the chemical thermodynamic method and confirmed by experimental techniques (x-ray diffraction, energy dispersive x-ray spectroscopy). For the first time, the chemical thermodynamic method was used for determining the qualitative and quantitative phase-chemical composition of the compounds formed by a pulsed laser heating of commercial titanium in the air, and its applicability is proven. The simulation shows that multilayered composite film appears on a surface, the lower layers of which consist of Ti2O3 and TiO oxides with the addition of titanium nitride; and the thin upper layer consists of transparent titanium dioxide. Also, the chemical composition of films remains unchanged within a temperature range of 881–2000 K.

Improvement of Surface Morphology and Critical Current Density of YDy 0 . 2 Ba2Cu 3 . 3 O7−δ Thick Films by Inserted RE2O3 Thin Films

Various artificial multilayers consisting of YDy0.2 Ba2Cu3O7−e /RE2O3/YDy0.2Ba2Cu3O7−e films (RE = Y, Gd, Eu, etc.) about 1 μm in a sandwich-type structure are fabricated on oxide-buffered Hastelloy substrates using low-fluorine metalorganic deposition (MOD) method. Superconducting and microscopic performances are studied on composite YDyBaCuO multilayer films with and without intercalated Y2O3, Gd2O3, and Eu2O3 ultrathin films. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) are used to investigate growth orientation and surface morphology, revealing that multiple superconducting YDyBaCuO thin films separated by an ultrathin RE2O3 interlayer have better c-axis orientation, better in-plane and out-plane textures, as well as superior surface morphology. Using this interlayer technology, a significant enhancement of critical current density (J c) both in self-field and under applied magnetic field is obtained.

Bacterial infection microenvironment-responsive enzymatically degradable multilayer films for multifunctional antibacterial properties.

The adhesion of bacteria is one of the most important stages in biofilm formation and bacterial infection. Once bacteria have adhered to a biomaterial surface, it is hard to eliminate them, and bacterial growth and infection are inevitable. In the current study, we have designed and constructed enzymatically degradable (hyaluronic acid/chitosan)n-(hyaluronic acid/polylysine)n ((HA/CHI)n-(HA/PLL)n) composite multilayer films via a layer-by-layer self-assembly method. Spectroscopic ellipsometry and scanning electron microscopy cross section measurements showed the exponential growth behavior of (HA/CHI)10-(HA/PLL)10 multilayer films (∼2 μm). The increased secretion of hyaluronidase and chymotrypsin in the bacterial infection microenvironment led to the fast degradation of the outer (PLL/HA)n multilayer films in the first 24 h. Enzymatic degradation of the multilayer films efficiently reduced the adhesion of both Staphylococcus aureus and Escherichia coli (>99%). Bacterial live/dead staining demonstrated the bactericidal action of the remaining bottom (CHI/HA)n multilayer films against the two kinds of bacteria. In vivo subcutaneous tests on New Zealand white rabbits, wound appearance and histopathology analysis showed that the implantation of composite multilayer film-modified PDMS promoted wound healing and the materials demonstrated a self-defense antibacterial effect. The material demonstrated both anti-adhesive and bactericidal properties and could be used to modify biomedical implants.