Multilayer Films Research Articles

Fatigue and tensile behaviour of Ti+TiN+Ti+TiVN multilayer nitride films coated on AZ91 magnesium alloy by closed field unbalanced magnetron sputtering

Despite their extensive use in the automotive and aerospace industries, Mg and Mg alloys, which are light metals, exhibit low fatigue and tensile strength. In this study, transition metal-nitride (TMN) multilayer coatings (Ti+TiN+Ti+TiVN) were coated twice on AZ91 Mg alloy using a Confined Field Unbalanced Magnetron Sputtering (CFUBMS) system to increase fatigue and tensile strength. The structural properties of the films were analyzed by using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometry (EDS) methods, and the mechanical properties were analyzed by rotating bending fatigue and tensile testing machines. Ti+TiN+Ti+TiVN multilayer nitride surface coatings on AZ91 Mg alloys showed a dense and columnar microstructure and according to XRD results (111) was the preferred orientation with the dominant peak. The fatigue limit value of the AZ91 base material was fixed at 60.46 MPa, while it increased to 68.48 MPa after being coated with multilayer nitride. Along with the multilayer nitride coating, the tensile strength increased from 169.98 MPa to 175.43 MPa. As a result, the multilayer hard nitride coating with low surface roughness, which fills the defects, notches, and voids on the surface of the AZ91 base material, increased the fatigue and tensile strength in parallel. Based on the outcomes of the research, the literature has been enriched with an innovative approach through the enhancement of fatigue and tensile strengths by applying a CFUBMS coating to lightweight metals and alloys, such as AZ91, especially in the transportation industry where lightness and dynamic load resistance are essential.

Design and fabrication of a fast-response and low-energy input micro igniter

In this study, we innovatively combine direct ink writing (DIW) and physical vapor deposition (PVD) to fabricate a novel micro igniter with fast-response and low-energy input characteristics. The igniter comprises a 5×5 mm² metal film bridge with gold contact pads. The metallic resistance is fabricated using a series of photolithography, metal deposition, and lift-off processes. After evaluating titanium and chromium as the resistive filament, titanium was selected due to its superior reactivity when in contact with CuO leading to reduced ignition energy. Onto the resistive titanium layer, either thermite multilayer films and/or energetic inks are deposited to achieve a head-to-head comparison of ignition characteristics. We show that igniters powered by (CuO/Ti)5 bilayers and Al/CuO/PVDF as energetic ink demonstrate the equivalent ignition performance as reactive (CuO/Ti)5 multilayered igniter. The ignition delay and ignition energy are below 1 ms and 2 mJ, respectively, while the flash intensity is approximately one decade higher than what is typically achieved with conventional micro-igniters. Furthermore, its ignition behaviour can be readily adjusted by altering the constituents of the fuel/oxidizer or adjusting the ratio of multilayer/inks, thereby allowing for easy adaptation of the micro-igniter to meet the diverse requirements of various applications.

A mechanistic approach to determine the relationship between film structure, electronic properties, and photocatalytic activity of ALD ZnO thin films on glass gibers

Atomic layer deposition (ALD), a high-conformality thin-film deposition technique, offers the opportunity to immobilize photocatalytic materials on high surface area substrates. Textile substrates are inexpensive, easily accessible materials with a fibrous nature, making them high surface area scaffolds for photocatalytic applications. This study applied ZnO thin-film coatings to fabric structures with different numbers of ALD cycles. The effect of coating thickness on the surface and electronic properties of the films and their photocatalytic properties were investigated. SEM, XRD, PL, and UV–Vis were used to examine the surface morphology, crystal structure, defects, and optical properties of the ZnO thin films. As the film thickness increased, the crystal sizes and the number of defects in the structure increased. Contact angle and Hall Effect measurements revealed that these structural defects are present on the surface of the films. Optimum wettability, mobility, and photocatalytic efficiency values were observed in the 15-nm coated samples, resulting in the highest photocatalytic activity and a turning point.

Electrochemical study and structural comparison of Ni electrodepositions on W/Si and Cr/C multilayered structure films

The Ni electrodeposition combined with multilayered structure film is a promising strategy in modern optical manufacturing, while less effort has been devoted to comprehending the electrochemical reaction process, which is essential for their practical applications. In view of this, the initial reduction dynamics and nucleation mechanisms of Ni electrodepositions on multilayer W/Si and Cr/C films were analyzed in this work, and the morphological, crystal, and mechanical characteristics of produced Ni electrodeposits were further determined and compared. The results show that the considerably irregular crystals accompanied by high tensile stress of 119.5 MPa were formed for the Ni electrodeposit on W/Si film, which were mainly attributed to the progressive nucleation process with more severe side reaction of hydrogen evolution. By contrast, the instantaneous nucleation mode with lower reduction resistance were revealed for the Ni electrodeposition on Cr/C film, which presented a comparatively fine–grained texture, less roughness, and smaller stress structure. To summarize, the more stable electrochemical reaction process and improved structure uniformity are obtained for the Ni electrodeposition on metal/C–based film, which offers a theoretical guidance for optimized fabrication of multilayer optical devices in extreme ultraviolet, x-ray, and neutron focusing fields.

Effect of Ag content on the friction and wear properties of electrodeposited self-lubricating Ni–Ag coating

Thin film coatings are required to improve the performance of components to resist harsh environments as the modern industry grows. In this study, Ni–Ag coatings with various Ag content were deposited on the Cu surface using an electrodeposition technique. The Ni–Ag coatings were deposited to enhance the tribological properties of the coatings and increase the service life of the friction-sliding components. Ni–6wt%Ag, Ni–8wt%Ag, and Ni–10wt%Ag coatings were deposited. A solid solution of Ni–Ag was formed in the coatings. As the concentration of NiSO4 decreased in the electrolyte, the content of Ag in the coatings increased with the granular morphological characteristics. The increase in Ag content reduces the coefficient of friction (CoF) on comparing the initial running-in period and is stable after some time. The initial decrease was due to the surface roughness. The CoF and wear rate were low for all Ag contents compared to the copper substrate due to the effect of Ag solid lubricant material in prepared coatings.

Study of Optical Performance and Structure of Yb/Al (1.5 wt.% Si) and Yb/Al (Pure) Multilayers Designed for the 73.6 nm Range

Yb/Al multilayer films exhibit excellent theoretical reflectivity in the 54–90 nm wavelength range. This study attempted to incorporate 1.5% wt.% of Si impurities into Al to suppress the crystallization of Al, reduce interfacial roughness, and enhance the actual reflectivity of the prepared Yb/Al multilayer films. Internal microstructure changes in the film layers before and after Si impurity doping were investigated using GIXRR, AFM, and XRD techniques. The reflectivity of two types of multilayer films, Yb/Al (1.5 wt.% Si) and Yb/Al (pure), was tested to evaluate the effect of Si impurity on film performance. The reflectivity of Yb/Al (1.5 wt.% Si) multilayers compared to Yb/Al (pure) multilayers increased by approximately 4%.

Loading rutin on surfaces by the layer-by-layer assembly technique to improve the oxidation resistance and osteogenesis of titanium implants in osteoporotic rats

The purpose of this study was to construct a rutin-controlled release system on the surface of Ti substrates and investigate its effects on osteogenesis and osseointegration on the surface of implants. The base layer, polyethylenimine (PEI), was immobilised on a titanium substrate. Then, hyaluronic acid (HA)/chitosan (CS)-rutin (RT) multilayer films were assembled on the PEI using layer-by-layer (LBL) assembly technology. We used scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and contact angle measurements to examine all Ti samples. The drug release test of rutin was also carried out to detect the slow-release performance. The osteogenic abilities of the samples were evaluated by experiments on an osteoporosis rat model and MC3T3-E1 cells. The results (SEM, FTIR and contact angle measurements) all confirmed that the PEI substrate layer and HA/CS-RT multilayer film were effectively immobilised on titanium. The drug release test revealed that a rutin controlled release mechanism had been successfully established. Furthermore, the in vitro data revealed that osteoblasts on the coated titanium matrix had greater adhesion, proliferation, and differentiation capacity than the osteoblasts on the pure titanium surface. When MC3T3-E1 cells were exposed to H2O2-induced oxidative stress in vitro, cell-based tests revealed great tolerance and increased osteogenic potential on HA/CS-RT substrates. We also found that the HA/CS-RT coating significantly increased the new bone mass around the implant. The LBL-deposited HA/CS-RT multilayer coating on the titanium base surface established an excellent rutin-controlled release system, which significantly improved osseointegration and promoted osteogenesis under oxidative stress conditions, suggesting a new implant therapy strategy for patients with osteoporosis.

Preparation of high performance thermal conductive composites from aluminum plastic packaging waste via Solid-state Drawing

Aluminum-plastic multilayer films have been widely used as the top-grade packaging material due to their exceptional barrier properties. However, the recycling of aluminum plastic packaging waste (APPW) poses a great challenge. To address this issue, we proposed a facile method for recycling APPW using solid-state drawing technology to produce high performance thermal conductivity composites for the first time. The ultrafine APPW with good processability was obtained by solid-state shear milling (S3M), with a low electrical conductivity of less than 10−12 S/cm. The subsequent solid-state drawing of both the aluminum sheet and polymer chain resulted in the formation of an oriented crystalline structure, with the Al sheet acting as an effective nucleating agent. This resulted in a significant increase in tensile strength for HDPE/APPW (30 %) composites, from 21.4 MPa to 116.1 MPa at the drawing ratio of 5. In addition, the in-plane thermal conductivity of HDPE/APPW (50 %) composites reached an impressive 2.5 W/mK, with the tensile strength of 78.8 MPa. Our findings demonstrate the potential of utilizing APPW for the production of value-added composites without requiring separation, with possible applications in heat management for emerging electrical systems and electronic devices.

Structural properties controlled magnetisation of Ni/Al multilayers sputtered on flexible polymer substrate: Impact of Ni deposition rates

The goal of this work is to determine how the rate of Ni deposition rates affect the structural characteristics that regulate the magnetization of Ni/Al multilayer thin films sputtered on flexible acrylic acetate polymer substrates. The films with a 5[Ni(20 nm)/Al(10 nm)] structure were gradually sputtered as different Ni deposition rates in the total thickness of 150 nm. With an increase in the rate of Ni deposition, the Ni contents increased from 61.5% to 69.6%. And, X-ray diffraction analysis verified that the films featured a face-centered cubic structure with variable peak intensities. Also, the scanning electron microscopy surface morphology analyses revealed that variations in the film surfaces were a result of the deposition rates. For magnetic measurements, the differences in the structural analysis were observed to cause a notable variation in saturation magnetization, MS, and coercivity, HC values. Accordingly, MS values increased consistently between 359.0 and 389.7 emu cm−3, but HC values decreased from around 34–32 to 28 Oe with the increase in Ni deposition rate from 0.02 to 0.10 nm s−1. It is also observed that when the Ni layers are generated at very fast deposition rates, the Ni/Al multilayer films have a high MS/HC ratio, which is significant for magnetic sensors. It has been concluded that the magnetisation of Ni/Al multilayer thin films can be controlled by the structural properties adjusting the Ni deposition rate.

Unveiling the initial oxidation mechanism of a single crystal Ni-based superalloy with pre-deformation

The role of pre-deformation on the initial oxidation mechanism of a single crystal Ni- was revealed. With pre-deformation, the recrystallized grain boundaries and dislocations provided sites for the nucleation of Al2O3 and enhanced the diffusion flux of Al irrespective of γ/γ′ interface, γ′, and γ phase. Ultimately, a thin compact α-Al2O3 layer formed, improving the oxidation resistance. Without pre-deformation, Ni and Al atoms diffused along the γ'/γ interface, however, the Al-flux is insufficient to maintain the growth of Al2O3. As a result, a loose multilayer film formed on the surface, which decreased the oxidation resistance.

Preparation and tribologic properties of Ti and Zr nitride multilayer coatings

This paper focuses on synthesis and characterization of Zr/Ti and Ti/Zr nitride multilayer coatings by magnetron plasma sputtering to enhance the tribologic properties. The synthesis of nitrides was achieved by non-reactive deposition using Ti or Zr nitride targets or by reactive deposition using Ti or Zr targets in the presence of nitrogen. The formation of nitride layers was highlighted by XRD, EDX and XPS investigations, while the tribologic properties were made with HFRR equipment. The tribological study showed that the coefficient of friction and wear scar diameter decrease in multilayer films with zirconium nitride as the upper layer.

Macroscale Ultradurable Anti‐wear Achieved on Graphene‐based Films via Multiphase Combination

Excellent anti‐wear performance, high bearing capacity, and long service life are essential prerequisites for the reliability and durability of Si‐based micro/nano device operation. To improve the anti‐wear property and prolong service life of Si‐based micro/nano devices under high loads, graphene oxide (GO) nanosheets, graphene quantum dots (GQDs) and ionic liquid‐capped GQDs (IL‐GQDs) were used to create three kinds of multilayer films as solid lubricant, that is, single‐component (GO)5, (GO/GQDs)5 and (GO/IL‐GQDs)5 multilayer films. The results showed that (GO/IL‐GQDs)5 composite multilayer possessed excellent wear resistance under a high load of 4 N with the wear rate of 4.9×10‐7 mm3·N‐1·m‐1. The superior anti‐wear performance of (GO/IL‐GQDs)5 composite film is mainly due to the unique 3D structure composed of GO nanosheets alternating with IL‐GQDs. The rigid GO nanosheets play the role in load‐carrying capacity, and the IL‐GQDs could delay the time of structure transformation and reduce the loss rate of transfer film, thereby effectively extending the service life of (GO/IL‐GQDs)5 composite multilayer. Such multilayers are expected to be good solid lubricating films suitable for Si‐based micro/nano devices.This article is protected by copyright. All rights reserved.

Preparation of Eudragit S100-pullulan/hydroxypropyl-β-cyclodextrin complex-Eudragit S100 multilayer nanofiber film for resveratrol colon delivery

Cyclodextrin-based electrospun nanofibers are promising for encapsulating and preserving unstable compounds, but quick dissolution of certain nanofibers hinders their delivery application. In this study, hydroxypropyl-β-cyclodextrin (HPβCD) was used as an effective carrier of resveratrol (RSV) to obtain the RSV/HPβCD inclusion complex (HPIC), which was then incorporated into pullulan nanofibers. For enhancement of RSV release toward colon target, multilayer structure with a pullulan/HPIC film sandwiched between two layers of hydrophobic Eudragit S100 (ES100) nanofibers was employed. The relationship between the superiority of the ES100-pullulan/HPIC-ES100 film and its multilayer structure was verified. The intimate interactions of hydrogen bonds between two adjacent layers enhanced thermal stability, and the hydrophobic outer layers improved water contact resistance. According to release results, multilayer films also showed excellent colon-targeted delivery property and approximately 78.58 % of RSV was observed to release in colon stage. In terms of release mechanism, complex mechanism best described RSV colonic release. Additionally, ES100-pullulan/HPIC-ES100 multilayer films performed higher encapsulation efficiency when compared to the structures without HPIC, which further increased the antioxidant activity and total release amount of RSV. These results suggest a promising strategy for designing safe colonic delivery systems based on multilayer and HPIC structures with superior preservation for RSV.

Perpendicular magnetic anisotropy of Pd/Co2MnSi/AlN/Pd multilayer films

In this paper, the perpendicular magnetic anisotropy（PMA）of Pd/Co2MnSi (CMS)/AlN/Pd multilayer film is studied, which is designed based on the two-interface interaction, the orbital hybridization effect of Pd5d-Co3d electrons at the Pd/CMS interface and the orbital hybridization effect of Co3d-N2p electrons at the CMS/AlN interface. Compared with the Pd/CMS/Pd multilayer film, the PMA of the Pd/CMS/AlN/Pd structure shows significant enhancement with the insertion of the AlN layer. The Hall resistance (RHall) of the Pd/CMS/AlN/Pd structure reached 0.02 Ω (increased by 300 %) and the coercive force (Hc) is 388 Oe (increased by about 76 %). The magnetic anisotropic energy density (Keff) is 0.61Merg/cm3 (increased by about 135 %). The PMA was optimized with the film factor (layer thickness) of Pd(6 nm)/CMS(5 nm)/AlN(6 nm)/Pd(6 nm). The X-Ray Diffraction（XRD）and High Resolution Transmission Electron Microscope（HRTEM）analysis showed that the PMA is affected by the crystallinity and interface quality of multilayer films.

Multimethod cross-sectional characterization approaching the limits of diamond monophase multilayers

Chemical vapour deposited diamond draws significant scientific interest due to its wide range of mechanical and functional properties, which can be easily tuned by the applied deposition conditions. Here, hot filament chemical vapour deposition was used to synthesize four monophase multilayer diamond thin films with individual layer thickness down to ∼ 300 nm. Extensive structural characterization by scanning electron microscopy and Raman spectroscopy on the cross-section confirmed the different diamond morphologies originating from the different applied process parameters of the individual sublayers, where Raman spectroscopy could give a clear distinction between nano- and microcrystalline diamond down to a layer thickness of ∼ 1 μm. Cross-sectional X-ray nanodiffraction identified exclusively the diamond crystal structure throughout the cross-section of the multilayered diamond thin films. Cross-sectional phase and FWHM analysis allowed to discriminate between the diamond morphologies down to ∼ 500 nm, thus identifying the limitations of monophase diamond multilayers. While the microcrystalline diamond sublayers all exhibit pronounced structural gradients expressed in (i) increasing intensity of the 111 Debye-Scherrer ring, (ii) ⟨110⟩ fibre texture, and periodic variations of (iii) grain size and (iv) residual stress, the nanocrystalline diamond sublayers showed no pronounced cross-sectional variations. In summary, the experimental results provide insights into the cross-sectional evolution of microstructure and residual stress and the limitations of monophase multilayered diamond thin films.

Application of multi-layered composite fiber films with enhanced piezoelectric performance in flexible energy harvesting devices

Flexible electronic components such as wearable sensors, energy harvesting devices, and human health monitoring systems based on piezoelectric materials have garnered significant attention within the scientific community. In this study, PZT nanofibers were modified with dopamine hydrochloride prior to their integration into PVDF fibers, serving as piezoelectric reinforcements to enhance the mechanical and piezoelectric characteristics of composite fiber films. Subsequently, a facile hot-pressing method was employed to fabricate multilayered films characterized by a densely packed surface fiber arrangement and a loosely organized internal fiber orientation, which markedly improved the self-supporting ability and fiber density of the electrospun fiber films. A detailed investigation into the micro-morphology, crystallinity, and enhanced piezoelectric properties of the films was conducted. Notably, the composite fiber film containing 6 wt% PZT NFs exhibited a peak piezoelectric coefficient (d33) of 29 pC/N, resulting in an output voltage of 13.8 V. This represents a 2.23-fold enhancement in d33 value and a 4.6-fold increase in output voltage when compared to the pristine PVDF fiber film, which had a d33 of 13 pC/N and an output voltage of 3 V. The power density achieved by the sensor is 0.73 μW/cm2. This performance is underpinned by a high piezoelectric coefficient, outstanding output characteristics, and robust stability, which collectively enhance the sensor's efficacy in various applications. This research presents an effective approach for augmenting the piezoelectric performance of PVDF-based composite films and paves the way for the advancement of piezoelectric energy harvesting applications.

Optimal permeance ratio, flux direction and layer distribution in composite asymmetric membranes composed of sequences of layers obeying real-power flux laws

In this study, the optimal permeance ratio and layers distribution in multilayer membranes and thin films in which each layer obeys the following real-power law: Flux=πi(P1,ini−P2,ini) are determined for any positive real values of ni. Such an exponent has a physical meaning in several cases, such as: diffusion-controlled permeation of hydrogen in metal membranes i) under infinite-dilution conditions (n = 0.5), and ii) under higher-concentration ones (0.5 < n < 1.5), iii) desorption-limited permeation (n = 1) in the same type of membranes, Knudsen-type diffusional mechanism (n = 1) and viscous flow (n = 2) in microporous membranes. Furthermore, n is equal to 4 in radiation-driven thermal flux. The work considers two generic layers of different thicknesses and exponents, for which it is proven the existence of a general optimal permeance ratio π1/π2 maximising the flux ratio, which is found to be equal to the inverse of the ratio between the respective maximum theoretical driving forces that can be established in each layer. Such an optimal permeance ratio is also proven to be a global optimum. Afterwards, we provide a theoretical generalisation of this optimality to whatever types of driving forces. Then, we provide a demonstration that the highest species permeating flux is always established when feeding it from the layer side with the highest exponent independently of the permeance ratio. As an important consequence, to maximise flux, a multilayer membrane/thin film should be fabricated by depositing the layers in cascade according to the ascending or descending exponents, and should be used in a configuration in which the flux flows from the layer with the highest pressure exponent to the layer with the lowest one. It is also shown that there exists an optimal value of the lower exponent n1 that maximizes the flux ratio keeping constant the other parameters. Finally, we showed that a virial-type linear combination of polynomial driving forces can be approximated by the empirical flux law investigated. Overall, our results are valid not only for whatever type of composite membranes and thin films (metallic, ceramic, polymeric and hybrid ones), but also for any sequential system involving a flux of whatever physical entity obeying the aforementioned law, such as heat transfer in the presence of radiation, non-linear electrical resistances and possible others.

CVD growth of large-area, continuous, and defect-free MoS2 multilayer films from solution-cast seed nanoflakes

Defects in transition metal dichalcogenides are among the primary source of their chemical reactivity, including their response to water. The CVD growth of defect-free continuous molybdenum disulfide (MoS2) films has been particularly challenging. In this work, we demonstrate the growth of large-area continuous films of MoS2 using solution-cast MoS2 seed nanoflakes, both with and without the assistance of alkali halide. The MoS2 seed nanoflakes serve as nucleation sites for the in-plane growth of few-layer MoS2, which is accompanied by localized vertical growth of MoS2 particles. For films grown with the combination of seed and NaCl, very low oxygen content was observed together with the stoichiometric ratio of Mo: S being close to the ideal value of 1: 2. These films show humidity-insensitive electrical response over a wide interval (5%–95% RH). This is attributed to very low concentrations of edge and basal-plane defects, leading to low water dissociation and restricted proton transport.

Innovative coaxial high-temperature thin-film sensor with core–shell structure surpassing traditional multilayer films

Innovative coaxial high-temperature thin-film sensor with core–shell structure surpassing traditional multilayer films

Thermal defocus-free Hartmann Wavefront Sensors for monitoring aberrations in Advanced Virgo

Earth-based gravitational waves interferometric detectors are shot-noise limited in the high-frequency region of their sensitivity band. While enhancing the laser input power is the natural solution to improve on the shot noise limit, higher power also increases the optical aberration budget due to the laser absorption in the highly reflective coatings of mirrors, resulting in a drop of the sensitivity of the detector. Advanced Virgo exploits Hartmann Wavefront Sensors (HWSs) to locally measure the absorption-induced optical aberrations by monitoring the optical path length change in the core optics. Despite the very high sensitivity of Hartmann sensors, temperature fluctuations can cause a spurious curvature term to appear in the reconstructed wavefront due to the thermal expansion of the Hartmann plate, that could affect the accuracy of the aberration monitoring. We present the implementation and validation of a control loop to stabilize the Advanced Virgo HWS temperature at the order of ΔT⩽0.01 K, keeping the spurious curvature within the detector’s requirements on wavefront sensing accuracy.