Multilayer Composite Films Research Articles

Piezoelectric response of a PZT thin film to magnetic fields from permanent magnet and coil combination

In this study, we report the magnetically induced electric field E3 in Pb(Zr0.57Ti0.43)O3 (PZT) thin films, when they are subjected to both dynamic magnetic induction (magnitude Bac at 45 kHz) and static magnetic induction (Bdc) generated by a coil and a single permanent magnet, respectively. It is found that highest sensitivity to Bdc—\( {{\Delta \left| {E_{3} } \right|} \mathord{\left/ {\vphantom {{\Delta \left| {E_{3} } \right|} {\Delta B_{\text{dc}} }}} \right. \kern-0pt} {\Delta B_{\text{dc}} }} \)—is achieved for the thin film with largest effective electrode. This magnetoelectric (ME) effect is interpreted in terms of coupling between eddy current-induced Lorentz forces (stress) in the electrodes of PZT and piezoelectricity. Such coupling was evidenced by convenient modelling of experimental variations of electric field magnitude with both Bac and Bdc induction magnitudes, providing imperfect open circuit condition was considered. Phase angle of E3 versus Bdc could also be modelled. At last, the results show that similar to multilayered piezoelectric-magnetostrictive composite film, a PZT thin film made with a simple manufacturing process can behave as a static or dynamic magnetic field sensor. In this latter case, a large ME voltage coefficient of \( \alpha = {{\left| {E_{3} } \right|} \mathord{\left/ {\vphantom {{\left| {E_{3} } \right|} {B_{\text{ac}} }}} \right. \kern-0pt} {B_{\text{ac}} }} = 3.55\,{\text{V}}/{\text{cm}}\,{\text{Oe}} \) under Bdc = 0.3 T was found. All these results may provide promising low-cost magnetic energy harvesting applications with microsized systems.

Fabrication of graphene/polyaniline composite multilayer films by electrostatic layer-by-layer assembly

A novel graphene/polyaniline composite multilayer film was fabricated by electrostatic interactions induced layer-by-layer self-assembly technique, using water dispersible and negatively charged chemically converted graphene (CCG) and positively charged polyaniline (PANI) as building blocks. CCG was achieved through partly reduced graphene oxide, which remained carboxyl group on its surface. The remaining carboxyl groups not only retain the dispersibility of CCG, but also allow the growth of the multilayer films via electrostatic interactions between graphene and PANI. The structure and morphology of the obtained CCG/PANI multilayer film are characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, Ultraviolet–visible absorption spectrum (UV–vis), scanning electron microscopy (SEM), Raman spectroscopy and X-Ray Diffraction (XRD). The electrochemical properties of the resulting film are studied using cyclic voltammetry (CV), which showed that the resulting CCG/PANI multilayer film kept electroactivity in neutral solution and showed outstanding cyclic stability up to 100 cycles. Furthermore, the composite film exhibited good electrocatalytic ability toward ascorbic acid (AA) with a linear response from 1×10−4 to 1.2×10−3M with the detect limit of 5×10−6M. This study provides a facile and effective strategy to fabricate graphene/PANI nanocomposite film with good electrochemical property, which may find potential applications in electronic devices such as electrochemical sensor.

Enhanced dielectric properties of amino-modified-CNT/polyimide composite films with a sandwich structure

Novel amino-modified-CNT/polyimide (NH2-MWNT/PI) flexile composite films with a sandwich structure were prepared through step-by-step casting, in which a dielectric layer (NH2-MWNT/PI composites) intercalated between the two insulating layers (pure PI, acting as both the bottom and the top layers). Due to the high capacitance of the dielectric layer and the effective blocking off conductive paths by the insulating layers, the sandwich composite films show a high dielectric constant and ultralow dielectric loss, and the dielectric constants of the composite films are almost frequency independent between 1 and 1000 kHz. It is notable that the NH2-MWNT/PI ratio of the mid-layer markedly influences the dielectric property of the composite film. When the NH2-MWNT content of the mid-layer is 10 wt%, the multi-layer composite film (P-10-P) shows the highest dielectric constant (e′) of 31.3 at 1 kHz, while the dielectric loss (tan δ) of the P-10-P is only 0.0016. Furthermore, the obtained multi-layer composite films have high breakdown strength and maximum energy storage density. The mechanical properties and thermal properties of the composite films were also examined in this work.

Channel cracks in atomic-layer and molecular-layer deposited multilayer thin film coatings

Metal oxide thin film coatings produced by atomic layer deposition have been shown to be an effective permeation barrier. The primary failure mode of such coatings under tensile loads is the propagation of channel cracks that penetrate vertically into the coating films. Recently, multi-layer structures that combine the metal oxide material with relatively soft polymeric layers produced by molecular layer deposition have been proposed to create composite thin films with desired properties, including potentially enhanced resistance to fracture. In this paper, we study the effects of layer geometry and material properties on the critical strain for channel crack propagation in the multi-layer composite films. Using finite element simulations and a thin-film fracture mechanics formalism, we show that if the fracture energy of the polymeric layer is lower than that of the metal oxide layer, the channel crack tends to penetrate through the entire composite film, and dividing the metal oxide and polymeric materials into thinner layers leads to a smaller critical strain. However, if the fracture energy of the polymeric material is high so that cracks only run through the metal oxide layers, more layers can result in a larger critical strain. For intermediate fracture energy of the polymer material, we developed a design map that identifies the optimal structure for given fracture energies and thicknesses of the metal oxide and polymeric layers. These results can facilitate the design of mechanically robust permeation barriers, an important component for the development of flexible electronics.

Composite films of poly(vinyl alcohol)–chitosan–bacterial cellulose for drug controlled release

Mono and multilayer composite films of poly(vinyl alcohol)–chitosan–bacterial cellulose (PVA/chitosan/BC) have been prepared to achieve controlled release of ibuprofen sodium salt (IbuNa) as model drug. The composite films have been characterized by Fourier transformed infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Surface morphology was investigated by scanning electron microscopy (SEM). Equilibrium swelling was measured in water at two different pH values and in vitro release of IbuNa in pH 1.2 and pH 7.4 media was studied. The release experiments revealed that drug release is pH sensitive. The release kinetics of IbuNa could be described by the Fickian model of diffusion with a good agreement. The IbuNa release rate was decreasing for all the films as the BC concentration was increased in the films composition, the decrease being higher for the multilayer films.

Fabrication of a 12-tungstophosphate and cadmium oxide composite film and its properties

A multilayer composite film of the 12-tungstophosphate H3[PW12O40]3− (PW12) and cadmium oxide nanoparticles (CdO) was fabricated on quartz and silicon by the layer-by-layer (LBL) self-assembly method. The film was characterized by UV–vis spectroscopy, atomic force microscopy (AFM) and luminescence spectra. The proposed composite film exhibits higher photocatalytic activity toward methyl orange (MO) solution at pH 3.5, compared to single PW12 and CdO films. The degradation rate was affected by initial concentration of PW12, pH value of MO solution, inorganic ions concentration and type in MO solution. In addition, the composite film displays luminescent property and reversible electrochromic property with fast response time.

A new approach to investigate Li2MnO3and Li(Ni0.5Mn0.3Co0.2)O2mixed phase cathode materials

In this work, cathodes consisting of a Mn–rich electrochemically inactive Li2MnO3 phase and a Li(Ni0.5Mn0.3Co0.2)O2 (NMC) phase are processed by pulsed laser deposition (PLD). Different from the traditional bulk/powder synthesis approach, pure materials of the two phases are either uniformly integrated by co-deposition of the two phases or deposited sequentially as a layered structure, to emulate Li-rich mixed phase cathode materials. A high deposition temperature, 750 °C, was used to grow the films on c-cut sapphire and stainless steel substrates. The films either in a random form or in a more controlled multilayer-type, both show excellent film quality. The multilayer composite films show superior capacity, cycling and rate capabilities, with a capacity of 293 mA h g−1 at 0.05 C. This method gives much better control of the Mn content of the cathode, phase purity and combination schemes, i.e., mixing at the atomic level or embedding Li2MnO3 domains of different sizes in the NMC matrix or both. Moreover, this approach can be applied to screen lithium-rich Mn phase and other novel material combinations in a more controlled and expedient manner.

Laser receptive polyelectrolyte thin films doped with biosynthesized silver nanoparticles for antibacterial coatings and drug delivery applications

We report a simple method to fabricate multifunctional polyelectrolyte thin films to load and deliver the therapeutic drugs. The multilayer thin films were assembled by the electrostatic adsorption of poly (allylamine hydrochloride) (PAH) and dextran sulfate (DS). The silver nanoparticles (Ag NPs) biosynthesized from novel Hybanthus enneaspermus leaf extract as the reducing agent were successfully incorporated into the film. The biosynthesized Ag NPs showed excellent antimicrobial activity against the range of enteropathogens, which could be significantly enhanced when used with commercial antibiotics. The assembled silver nano composite multilayer films showed rupture and deformation when they are exposed to laser. The Ag NPs act as an energy absorption center, locally heat up the film and rupture it under laser treatment. The antibacterial drug, moxifloxacin hydrochloride (MH) was successfully loaded into the multilayer films. The total amount of MH release observed was about 63% which increased to 85% when subjected to laser light exposure. Thus, the polyelectrolyte thin film reported in our study has significant potential in the field of remote activated drug delivery, antibacterial coatings and wound dressings.

Effect of annealing on the structural and microwave magnetic properties of singlelayer and multilayer films of various compositions

The effect of annealing on the structure and microwave magnetic properties of composite single-layer and multilayer films is investigated. It is found that as the threshold annealing temperature is attained, the width of the FMR line increases abruptly, depending on the concentration ratio of metallic alloy and dielectric. It is shown that the FMR line broadening is also associated with the occurrence of and increase in high-frequency modes of absorption. The surfaces of annealed and unannealed films are investigated at various concentrations of metallic alloys and dielectrics using an atomic force microscope. The strong change in the magnetic characteristics after film annealing is associated with a change in surface roughness and inhomogeneity, and in the size distribution of nano- and submicron formations and their spacing.

Magnetoelectric properties of Ba0.8Sr0.2TiO3–CoFe2O4 multilayered composite film via sol–gel method

Ba0.8Sr0.2TiO3–CoFe2O4 (BST–CFO) multilayered composite films were prepared on Pt/Ti/SiO2/Si substrates via a sol–gel method and spin-coating technique. Microstructures, electric property, magnetic property and magnetoelectric (ME) property of the composites were studied. Results show that the composite films calcined at 750 °C have BST and CFO phases and no obvious impurity phases were detected. Further, the composite films exhibit layered structures and a transition layer which is composed of interfacial delamination exists at the interface between BST and CFO layers. Ferroelectric and ferromagnetic properties were simultaneously observed in the films, evidencing the coexistence of the ferroelectric and ferromagnetic properties. Furthermore, the saturation magnetization value of the composite film is lower than that of the pure CFO film derived by the same processing as a result of the effect of the nonferromagnetic BST layers. Also, ferroelectric hysteresis loops reveal that the saturated polarization and remanent polarization of the composite film are lower than those of the pure BST films. In addition, the composite film exhibits a strong ME effect, which makes the composite film attractive for technological applications as devices.

Structural and optical properties of Cu‐doped ZnS nanoparticles formed in chitosan/sodium alginate multilayer films

Chitosan/alginate multilayers were fabricated using a spin-coating method, and ZnS:Cu nanoparticles were generated within the network of two natural polysaccharides, chitosan and sodium alginate. The synthesized nanoparticles were characterized using an X-ray diffractometer (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The results showed that cubic zinc blende-structured ZnS:Cu nanoparticles with an average crystal size of ~ 3 nm were uniformly distributed. UV-vis spectra indicate a large quantum size effect and the absorption edge for the ZnS:Cu nanoparticles slightly shifted to longer wavelengths with increasing Cu ion concentrations. The photoluminescence of the Cu-doped ZnS nanoparticles reached a maximum at a 1% doping level. The ZnS:Cu nanoparticles form and are distributed uniformly in the composite multilayer films with a surface average height of 25 nm.

Stratified rod network model of electrical conductance in ultrathin polymer–carbon nanotube multilayers

The electronic conductance of polymer--carbon nanotube multilayered composite films assembled by the spin-spray layer-by-layer method is investigated. Our measurements show that the film conductance per bilayer ${\ensuremath{\sigma}}_{1}$ vanishes for film thickness below a critical value, and above this threshold it grows logarithmically with the number of polyelectrolyte bilayers ${k}_{\mathrm{l}}$. The results of our experiments are interpreted using a stratified quasi-two-dimensional conducting-network model, in which the junction resistance between nanotubes deposited in different bilayers is a function of the interlayer distance. Using scaling arguments and numerical simulations, we show that the linear dependence of the junction resistance on the layer separation leads to the logarithmic behavior ${\ensuremath{\sigma}}_{1}\ensuremath{\sim}\mathrm{log}{k}_{\mathrm{l}}$ for large ${k}_{\mathrm{l}}$, as observed in our experiments. Properties of our stratified-network model are investigated, and we show that with proper rescaling, different sets of experimental measurements can be collapsed onto a master curve. The overall shape of the master curve is determined by a single dimensionless parameter characterizing the slope of the junction-resistance function.

Determination of Oxytetracycline with a Gold Electrode Modified by Chitosan-Multiwalled Carbon Nanotube Multilayer Films and Gold Nanoparticles

A molecularly imprinted electrochemical sensor was fabricated based on a gold electrode modified by chitosan-multiwalled carbon nanotube composite (CS-MWCNTs) multilayer films and gold nanoparticles (AuNPs) for convenient and sensitive determination of oxytetracycline (OTC). The multilayer of CS-MWCNTs composites and AuNPs were used to augment electronic transmission and sensitivity. The molecularly imprinted polymers (MIPs) were synthesized using OTC as the template molecule and o-phenylenediamine (OPD) as the functional monomer. They were modified on a gold electrode by electropolymerization. The electrochemical behavior of OTC at the imprinted sensor was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), and amperometry. The molecularly imprinted sensor showed high selectivity and excellent stability toward OTC. The linear range was from 3.0 × 10−8 to 8.0 × 10−5 mol/L, with a limit of detection (LOD) of 2.7 × 10−8 mol/L (S/N = 3). The developed sensor showed good recovery in spiked samples analysis.

An electrochromic composite film of Preyssler-type phosphotungstate decorated by AuNPs

A multilayer composite film containing Preyssler-type phosphotungstate K12.5Nal.5[NaP5W30O110]·l5H2O (P5W30) and Au particles (AuNPs) was fabricated by layer-by-layer assembly technology (LBL). The {[PEI/PSS–AuNPs/PEI/P5W30]n} composite film was characterized by scanning electronic microscopic (SEM), UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and cyclic voltammetry (CV) measurements. The electrochemical behavior of the films with and without AuNPs was investigated by cyclic voltammetry and electrochemical impedance spectra, and the composite film showed an enhanced electron transfer rate. The 6 bilayer AuNPs-free film performed color switching from transparent to blue, optical contrast of 10.4%, and an coloration efficiency of 6.99cm2C−1 at 600nm. The 6 bilayer composite film displayed enhanced electrochromic performance with the color switching from claret-red to deeper purple, optical contrast of 27.3% and coloration efficiency of 18.52cm2C−1 at 550nm due to the presence of AuNPs. The contribution of AuNPs gives valuable information for exploring new electrochromic materials.

Fabrication of Sb2Te3 and Bi2Te3 Multilayer Composite Films by Atomic Layer Deposition

Atomic Layer Deposition (ALD) growth of antimony telluride Sb2Te3 and bismuth telluride Bi2Te3 multilayer composite films has been investigated. We have fabricated Sb2Te3 and Bi2Te3 thin films using (trimethylsilyl) telluride ((Me3Si)2Te), bismuth trichloride (BiCl3) and antimony trichloride (SbCl3) as precursors for telluride, bismuth and antimony respectively. Both metal tellurides exhibit Volmer Weber Island growth mode and have characteristic hexagonal crystallites, which are telluride terminated at the surface making chemisorption rather challenging. We found that the presence of OH- bonds at the surface promotes ALD thin film growth by providing suitable nucleation sites and prevents delamination of the hexagonal platelet shaped crystallites. The use of longer exposure times of precursors during the ALD process increases chemisorptions and interface oxidation aids in the creation of nucleation sites. We present surface morphology studies using FE-SEM analysis.

Photoanode characteristics of multi-layer composite BiVO4 thin film in a concentrated carbonate electrolyte solution for water splitting

The improvement of the solar energy conversion efficiency is important for the solar hydrogen production using semiconductor photoelectrodes. In this paper, the photoelectrochemical properties of multi-layer composite photoelectrodes of thin film BiVO4 in various electrolyte solutions were investigated in detail. The improvement of photocurrent and the decrease of onset potential were observed on BiVO4 composite electrodes in carbonate electrolyte solution as well as bare BiVO4 electrode. The LHE (light-harvesting efficiency) and photocurrent were significantly improved by the light trapping structure of the double stacked photoelectrodes. The photocurrent was increased by insertion of an optimum SnO2 intermediate layer. The decrease of resistance at the BiVO4 composite electrodes was observed comparison with the bare BiVO4. In the BiVO4/SnO2/WO3 photoelectrode, the highest IPCE (incident photon to current efficiency) was 53% at 420 nm. The H2 and O2 were evolved stoichiometrically. The maximum value of the applied bias photon-to-current efficiency (ABPE) was 1.35%. The reaction mechanism of carbonate anions, mainly affecting the BiVO4 layer, was discussed.

Structural and optical properties of fullerene-like amorphous carbon with embedded dual-metal nanoparticles

Dual-metal nanoparticles were simultaneously embedded into amorphous carbon (a-C) matrix at room temperature. As-deposited Au/a-C/Fe sandwich composite multilayer films were fabricated by alternating multitarget pulsed laser deposition. More sp2 carbon content, narrower Tauc optical gap and stronger photoluminescence intensity of the amorphous carbon films were observed after metal-embedding. Especially for Au/a-C/Fe sandwich films, the fullerene-like microstructure demonstrated that the dual-metal embedding modulated greatly the intrinsic structure and properties of the a-C films. These results were attributed primarily to the extended state around the metal deep level in the band gap and the narrowing of the π and π∗ band edge states. The metal deep level defects contributed chiefly to non-radiative recombination.

Nd2Fe14B/FeCo Anisotropic Nanocomposite Films with a Large Maximum Energy Product

Anisotropic Nd(2) Fe(14) B/Fe(67) Co(33) nanocomposite thin films are successfully fabricated. The multilayer composite films comprise Nd-rich shell-enveloped Nd(2) Fe(14) B grains and a Fe(67) Co(33) phase. The strong (001) texture of the Nd(2) Fe(14) B grains and the presence of exchange-coupled Fe(67) Co(33) lead to a high remanence and the presence of the Nd-rich shell gives rise to a high coercivity. The unique nanocomposite microstructure provides hints for developing rare-earth-lean high-performance magnets.

Electrochemical and photoelectrocatalytic properties of TaWO6 nanosheet film

TaWO6 nanosheet was assembled into multilayer films by a layer-by-layer deposition technology with polyethylenimine as the linker. UV–vis absorption spectra in the assembly process showed a linear enhancement of absorbance at 238nm per deposition cycle, indicating the successful formation of multilayer composite films, which were converted into polymer-free films by the heat treatment at 400°C for 2h. The bandgap energy and flatband potential of TaWO6 nanosheet were estimated to be 3.48eV and −0.79V vs. Ag/AgCl, respectively. The photoelectrocatalytic degradation of Rhodamine B with the TaWO6 nanosheet electrodes demonstrated that both the oxygen anionic radicals and the dye cationic radical are essential to mineralize the dye under visible-light-driven photocatalytic conditions. It is the first time to investigate the mechanism of photoelectrocatalysis of TaWO6 nanosheet electrode.

Strong magnetoelectric coupling in sol–gel derived multiferroic (Pb0.76Ca0.24)TiO3–CoFe2O4 composite films

A multilayer heterostructure composite thin films consisting of alternating layers (Pb0.76Ca0.24)TiO3 (PCT) and CoFe2O4 (CFO) were grown on Pt/Ti/SiO2/Si(100) substrate by a sol–gel process. X-ray measurements indicated high quality of crystallization of both PCT and CFO layers. The magnetic and ferroelectric properties of the composite were investigated. Well-defined polarization vs. electric field (P–E) and magnetic hysteresis (M-H) loops were obtained. A strong magnetoelectric (ME) response was observed in the sample which was subjected to an alternating magnetic field, and a high ME voltage coefficient αE = 870 mV/Oe cm was obtained for the composite thin films when applied magnetic field parallel to the sample plane.