Multilayer Films Research Articles

Layer thickness dependent interface strengthening of nanolayered W/NbMoTaW medium-entropy alloys

In this work, the interface strengthening behavior of nanostructural W/NbMoTaW medium-entropy multilayer films with different W layer thicknesses was studied by a nanoindentation test. Results indicated that the hardness of multilayer films presented a significant size-dependent effect with the decrease of W layer thickness. The multilayer film reached a peak hardness of 19.8 GPa on account of interface strengthening at the critical layer thickness of 10 nm. An amorphous NbMoTaW layer leads to a decrease in hardness of multilayer films when W layer thickness was less than 10 nm. The room temperature toughness of the multilayer films predicted by the hardness/modulus ratio was improved with the decrease of W layer thickness. The size-dependent interface strengthening due to the decreasing W layer thickness and the solid solution strengthening due to the severe lattice distortion of the NbMoTaW layer are the main strengthening mechanisms of the multilayers.

High transparent conductive Mg, Al, and Ga co-doped ZnO multilayer thin films with Cu interlayer: fabrication, structure, and characteristics

Overcoming the challenge of preparing high-transparency and low-resistivity thin films is of great significance for the development of indium-free transparent electrodes. In the present work, high-quality Mg, Al, and Ga co-doped ZnO (MAGZO)/Cu/MAGZO multilayer thin films are deposited on glass by magnetron sputtering. The effects of Cu layer thickness (dCu) on the structural, morphological, optical, and electrical characteristics of the films are investigated in detail. With increasing dCu from 0 to 25 nm, the growth orientation of (002) ZnO crystal weakens, while that of (111) Cu crystal strengthens, and the surface of the films exhibits uniform, low roughness, and defect-free characteristics. Additionally, both the resistivity and the optical transmittance generally decrease with increasing Cu layer thickness. Interestingly, the average visible transmittance has a reverse change as dCu increases from 5 to 11 nm, resulting in the optimal photoelectric performance of the multilayers at dCu = 11 nm: the figure of merit of 9.42 × 10−3 Ω-1 with the resistivity of 1.24 × 10−4 Ω cm and the visible transmittance of 84.2%. Compared with other reported sandwich transparent conductive films, it is found that doping Mg in the oxide layer is the key to improving the overall optoelectronic properties of the multilayers.

A comparative analysis of different surface tribological and electrochemical properties of TiAlN, TiAlSiN, and CrAlN thin film coatings in seawater

Abstract To reveal the wear mechanisms of TiAlN, TiAlSiN, and CrAlN coatings in a seawater environment, the changes in frictional surfaces and the electrochemical characteristics of these coatings were compared and analyzed in this paper. The coatings were deposited on 316L stainless steel surfaces. Tribological tests were investigated using a ball-on-disk tribometer with Si3N4 ceramic balls as the counter material. Although the friction coefficient of 316L stainless steel was the lowest at 0.34, the order of wear rates was 316L stainless steel (7.38×10-5)>TiAlN(5.31×10-6)>TiAlSiN(4.23×10-6)>CrAlN(1.10×10-6) and the electrochemical protective efficiencies of TiAlSiN and CrAlN were both greater than 97%. Seawater penetrated through the grain boundaries of the TiAlN coating, which led to corrosion and delamination failure. Conversely, the grain refinement in TiAlSiN and CrAlN coatings can significantly slow down the penetration of seawater into the coating under frictional pressure, and the oxide lubricating layer formed during the friction process can become an effective barrier to isolate seawater. Therefore, mechanical wear was the main wear form of these two coatings. Additionally, among the oxides formed in the friction, Cr2O3 showed the strongest corrosion resistance, making the CrAlN coating exhibit superior wear resistance and the lowest wear rate in seawater.

Modeling and simulation of self-propagating exothermic reactions in Al/Ni reactive multilayer films and experimental validation

This paper reports the simulation and experimental validation of a MEMS (micro-electro-mechanical systems)-based Al/Ni reactive multilayer films (RMFs). A finite element model of a double V-shaped Al/Ni reactive multilayer films was developed by combining a thermoelectric coupling model with a self-propagating exothermic reaction model. The results show that the reactive multilayer films with a modulation ratio of 3:2 reach the energy peak the fastest under the same voltage excitation, which suggests that the modulation ratio determines the energy level of the reactive multilayer films before 20 μs, thus affects the energy output of the whole ignition process. Al/Ni reactive multilayer films with different modulation ratios were prepared using electron beam evaporation, the results of the ignition experiments showed that the reactive multilayer films with a modulation ratio of 3:2 had larger flames, which agreed with the simulated results. This suggests that calculating the enthalpy changes process of reactive multilayer films by coupling the self-increasing exothermic reaction can be used to analyze the chemical reaction process of the reactive multilayer films at any moment prior to 20 μs and to predict the flame size to some extent. This approach can be extended to other ignition prediction applications for MEMS-based ignitors.

Chitosan/sodium alginate/ethyl cellulose-based multilayer film incorporated with l-ascorbic acid for improved barrier, mechanical, and antioxidant properties

A bioactive multilayer film (ML) loaded with l-Ascorbic acid (AA) was developed using chitosan (CH), sodium alginate (SA), and ethyl cellulose (EC). Various properties of the films, including morphological, hydrophobic, barrier, mechanical, optical, and antioxidant characteristics, were evaluated and compared to those of monolayer films made from each biopolymer. The cross-sectional analysis via scanning electron microscopy revealed the successful preparation of the ML film with layering of the different biopolymers. For the ML film the resulting water contact angle was observed with an average of 73.86° and the film showed water resistant properties as compared to the individual CH and SA films. The ML film showed the lowest water vapor transmission rate (WVTR) at 54.99 g·d−1·m−2 as compared to the individual films. Moreover, the ML film had the highest tensile strength at 0.56 MPa as compared to the mono-layer films including CH, SA, and EC with TS values of 0.33, 0.24 and 0.17 MPa, respectively. Furthermore, the AA-loaded ML film exhibited significantly higher DPPH scavenging activity at 66.20 %. These findings suggest that the ML film, due to its superior barrier, mechanical, and antioxidant properties has the potential for the applications in active food packaging.

Hybrid layer-by-layer assembly of AuNPs/NSF composite for electrochemical detection of miRNA-196a

Detection of microRNA-196a (miRNA-196a) is crucial in cancer research, enabling early diagnosis and providing guidance for individualized treatment. In this work, we employed a naturally occurring negatively charged nano silk fibroin (NSF) with high mechanical properties, biocompatibility, and conductivity to be encapsulated with a positively charged gold nanoparticles (AuNPs) were used as film-forming materials for electrostatic layer-by-layer self-assembly to modify the working electrode of the screen-printed carbon electrode (SPCE). Under the optimized experimental conditions, the uniformly distributed AuNPs on the surface of the multilayer film modified SPCE (AuNPs/NSF)5.5/SPCE combined with the sulfhydryl-modified capture probe cp-DNA through gold-sulfur bonds. Furthermore, miRNA-196a is specifically captured through complementary base pairing to achieve highly sensitive and specific detection. (AuNPs/NSF)5.5/SPCE electrode can detect miRNA-196a in a concentration range of 1.0 × 10−13 to 1.0 × 10−6 M, and the calculated detection limit is 4.63 × 10−14 M when the signal-to-noise ratio is 3. The obtained results showed that the (AuNPs/NSF)5.5/SPCE has excellent selectivity and good stability over time.

Electrochemical lithium-ion insertion/extraction reactions of multilayered graphene with random twist angles.

A multilayer graphene film with random twist angles between layers (TAGr) on SiC(0001̄) shows six pairs of redox peaks for Li+ insertion/extraction reaction. The distributed twisted angle in TAGr regulates Li+ insertion sites, and smaller c-axis expansion (3%) is realized by Li+ insertion.

A High-Sensitivity Fiber Optic Soil Moisture Sensor Based on D-Shaped Fiber and Tin Oxide Thin Film Coatings

We present a high-sensitivity fiber optic soil moisture sensor based on side-polished multimode fibers and lossy mode resonance (LMR). The multimode fibers (MMFs), after side-polishing to form a D-shaped structure, are coated with a single-layer SnO2 thin film by electron beam evaporation with ion-assisted deposition technology. The LMR effect can be obtained when the refractive index of the thin film is positive and greater than its extinction coefficient and the real part of the external medium permittivity. The D-shaped fiber optic soil moisture sensor was placed in soil, allowing moisture to penetrate into the thin film microstructure, and it observed the resonance wavelength shift in LMR spectra to measure the relative humidity change in soil. Meanwhile, an Arduino electronic soil moisture sensing module was used as the experimental control group, with soil relative humidity ranging from 10%RH to 90%RH. We found that the D-shaped fiber with a residual thickness of 93 μm and SnO2 thin film thickness of 450 nm had a maximum sensitivity of 2.29 nm/%RH, with relative humidity varying from 10%RH to 90%RH. The D-shaped fiber also demonstrates a fast response time and good reproducibility.

Sol-gel prepared TiO2 – PMMA composite thin film for high laser induced damage threshold optical coating

We report high-quality TiO2 and TiO2-PMMA composite thin films prepared by sol-gel process for application in optical coatings. The addition of PMMA to the TiO2 sol exhibits significant improvements in the optical quality and morphology of the TiO2 films. A comparison between TiO2 and TiO2-PMMA composite thin films is described with respect to various optical properties and their application in optical coatings for high-energy laser applications. The refractive index and bandgap of TiO2 are tailored by controlling the TiO2 sol: PMMA volume ratio. The refractive index varies in the range of 2.4 to 2.0 at 550 nm by controlling the TiO2: PMMA composition. Incorporation of PMMA leads to reduction in absorption from 1000 ppm to 20 ppm in the composite films, which is attributed to passivation of defect states. In addition, incorporation of PMMA into the TiO2 sol results in the filling of voids and a significant improvement in surface figure (from λ/6 to λ/10) of the composite films. These properties collectively enhance the laser induced damage threshold (LIDT) of 2.1 J/cm2 for TiO2 film to 17 J/cm2 of the TiO2-PMMA composite film. LIDT mechanisms in the films are discussed. Demonstration of antireflection coatings (AR) as well as high reflection coatings (HR) exhibiting wavelength tuning of the reflection peak using TiO2-PMMA composite thin films, is presented. An AR coating @1200 nm with 11.5 J/cm2 LIDT is reported.

Highly reflective ZrC-Cu-based metal matrix composite coatings deposited via cold-spray for laser protection applications

Lasers are very powerful and can produce high temperatures, capable of melting materials when projected with an appropriate power, exposure time, distance, and beam width. High energy lasers are used for attacking enemy aircraft and missiles; however, the same threat is inevitable to the allied aircraft and missiles. Surface coatings have proven to be a viable solution to reduce damage from such laser attacks. In the present work, ZrC-Cu-based highly reflective coatings were deposited on Al-6061 alloy using the cold spray to develop laser damage resistance. Microstructural characterization, XRD, micro-hardness, reflectivity measurements, and laser ablation tests were conducted on the developed materials. The results showed improved ceramic retention and mechanical properties along with minimal porosity in the coating with increasing ZrC content in the feedstock. Additionally, the XRD analysis revealed that Cu-ZrC composite coatings could be produced by cold spray, without decarburisation of ZrC or oxidation of Cu. Owing to the exceptional purity in coatings, highly reflective coatings were obtained. At the target wavelength of 1080 nm, Cu-30 %ZrC composition achieved a remarkable reflectivity of 75 % (85 % of bulk copper). The coatings with compositions of Cu-30 %ZrC, Cu-50 %ZrC and Cu-70 %ZrC remained undamaged under laser irradiation, whereas Cu-85 %ZrC exhibited a laser ablation pit. These findings provide valuable insights into developing optimized ZrC-Cu coatings against laser irradiation.

Structure, Optical and Electrical Properties of Nb(Zn) Doped Sol-Gel ITO Films: Effect of Substrates and Dopants.

We present comparative studies of sol-gel ITO multilayered films undoped and doped with Nb or Zn (4 at.%). The films were obtained by successive depositions of five layers using the dip-coating sol-gel method on microscopic glass, SiO2/glass, and Si substrates. The influence of the type of substrates and dopant atoms on the structure and optical properties of the sol-gel ITO thin films is examined and discussed in detail. XRD patterns of these layers showed a polycrystalline structure with an average crystallite size of <11 nm. Raman spectroscopy confirmed the chemical bonding of dopants with oxygen and showed the absence of crystallized Nb(Zn)-oxide particles, indicated by the XRD pattern. Spectroscopic Ellipsometry and AFM imaging revealed a clear dependence of the optical parameters and surface morphology of the ITO and ITO:Nb(Zn) thin films on the type of substrates and dopants. The analysis of the current-voltage and capacitance-voltage characteristics of the Al/ITO/Si structures revealed the presence of charge carrier traps in the ITO bulk and the ITO-Si interface. The densities of these traps are obtained and the character of the current transport mechanism is established.

Tuning the bandgap and photoluminescence properties of Ge/Al2O3 multilayer thin films using annealing and ion beam irradiation

Abstract The present work reports high energy ion beam irradiation induced modifications in Ge/Al2O3 multilayers (MLs). Ge and Al2O3 multilayer thin films were deposited using the electron beam evaporation technique. Afterward, the as-deposited films were annealed using Rapid thermal annealing (RTA) at different temperatures ranging from 500 to 800°C under high vacuum. At a constant fluence of 5×1012 ions /cm2, the annealed films were subjected to irradiation with 80 MeV Ag ions. X-ray diffraction patterns show the crystalline nature of films that were annealed above 500°C, and the increase in crystallite size of Ge nanocrystals from 4.5 to 5.7 nm is observed for annealed samples. After Ag ion irradiation, the crystallinity of the films deteriorates. The crystallinity and optical bandgap are found to vary with Ag ion irradiation. The band gap of annealed films decreased from 1.1 to 0.97 eV with increase in crystallite size. The band gap of irradiated samples increased than that of pristine films. In addition, photoluminescence (PL) measurements were carried out to investigate the luminescence characteristics of annealed and irradiated multilayer films, and a wide emission band in the visible region was observed. The basic mechanism for tailoring the optical band gap and PL emission using RTA and ion irradiation is discussed.&amp;#xD;&amp;#xD;

Enhanced Optical and Electrical Properties of IGZO/Ag/IGZO for Solar Cell Application via Post-Rapid Thermal Annealing.

In this paper, we optimized IGZO/Ag/IGZO (IAI) multilayer films by post-rapid thermal annealing (RTA) to enhance the electrical conductivity and optical transmittance in visible wavelengths for solar cell applications. Our optimized device showed an average transmittance of 85% in the visible range, with a lowest sheet resistance of 6.03 Ω/□ when annealed at 500 °C for 60 s. Based on these results, we assessed our device with photo-generated short circuit current density (JSC) using a solar cell simulator to confirm its applicability in the solar cell. IAI multilayer RTA at 500 °C for 60 s showed a highest JSC of 40.73 mA/cm2. These results show that our proposed IAI multilayer film, which showed a high optical transparency and electrical conductivity optimized with post RTA, seems to be excellent transparent electrode for solar cell applications.

Convolutional neural network for colorimetric glucose detection using a smartphone and novel multilayer polyvinyl film microfluidic device

Detecting glucose levels is crucial for diabetes patients as it enables timely and effective management, preventing complications and promoting overall health. In this endeavor, we have designed a novel, affordable point-of-care diagnostic device utilizing microfluidic principles, a smartphone camera, and established laboratory colorimetric methods for accurate glucose estimation. Our proposed microfluidic device comprises layers of adhesive poly-vinyl films stacked on a poly methyl methacrylate (PMMA) base sheet, with micro-channel contours precision-cut using a cutting printer. Employing the gold standard glucose-oxidase/peroxidase reaction on this microfluidic platform, we achieve enzymatic glucose determination. The resulting colored complex, formed by phenol and 4-aminoantipyrine in the presence of hydrogen peroxide generated during glucose oxidation, is captured at various glucose concentrations using a smartphone camera. Raw images are processed and utilized as input data for a 2-D convolutional neural network (CNN) deep learning classifier, demonstrating an impressive 95% overall accuracy against new images. The glucose predictions done by CNN are compared with ISO 15197:2013/2015 gold standard norms. Furthermore, the classifier exhibits outstanding precision, recall, and F1 score of 94%, 93%, and 93%, respectively, as validated through our study, showcasing its exceptional predictive capability. Next, a user-friendly smartphone application named “GLUCOLENS AI” was developed to capture images, perform image processing, and communicate with cloud server containing the CNN classifier. The developed CNN model can be successfully used as a pre-trained model for future glucose concentration predictions.

Performance optimization of novel wear-resistant reflective cooling coatings for asphalt pavement

To enhance the wear resistance of traditional asphalt pavement reflective coatings and extend their cooling effect, this study employed Potassium Hexatitanate Whiskers (PHW) as a functional material to manufacture pavement reflective coatings. It was found that PHW exhibited excellent wear resistance though agglomeration resulted in adverse effects. Therefore, untreated PHW (U-PHW) underwent inorganic-organic surface modification to produce modified PHW (M-PHW). The results indicated that M-PHW exhibited excellent optical properties, with a reflectance of 78.9 %. M-PHW exhibited more uniform dispersion in the resin matrix, which significantly enhanced the coating reflectivity. Moreover, the interfacial bonding strength between M-PHW and the resin matrix was significantly improved, enhancing the wear resistance of the coating. Especially with a whisker content of 16 units, the tensile strength of the M-PHW coating reached 96.20 MPa, representing a 43.0 % increase compared to the U-PHW coating, while achieving a maximum outdoor cooling value of 5.6 °C.

Phase transition behavior and electrical properties of C/Sb2Te3 multilayer films on flexible polyimide substrates

Phase change memory has become one of the ideal choices for flexible electronic memory due to its advantages of fast operation speed, high durability and low power consumption. This paper is dedicated to the preparation of C/Sb2Te3 multilayer films on polyimide (PI) substrates for high-performance flexible phase change memory (FPCM). The findings indicate that C/Sb2Te3 multilayer films on PI substrates exhibit superior thermal stability (higher than that of Silicon substrates) and excellent mechanical bending properties (up to 1 × 104 bending cycles). The variations in optical properties, crystal structure, resistance drift and morphology were systematically investigated for the flat state, 5 × 103 bending cycles and 1×104 bending cycles. FPCM devices based on [C (2 nm)/Sb2Te3 (10 nm)]5 multilayer films have been fabricated, which are capable of reversible SET/RESET operation in the flat, bending state and 1 × 103 bending cycles. An electrothermal model of the FPCM device cell based on C/Sb2Te3 was constructed, and the simulation results confirmed its good thermal confinement capability (∼1278 K). This study demonstrates the potential of C/Sb2Te3 multilayer films based on PI substrates in FPCM.

Disappearance of Odd-Even Effects at the Substrate Interface of n-Alkanes.

The physical and chemical properties of organic compounds having alkyl chains are frequently influenced by the parity of the chain length, which is known as the odd-even effect. Understanding the molecular origin of this phenomenon is particularly important for designing materials used in organic thin-film devices. In this work, we focus on thin films of n-alkanes as the simplest model to study the odd-even effect at the substrate interface and analyze the aggregation structure using p-polarized multiple-angle incidence resolution spectrometry in combination with grazing incidence X-ray diffraction. The spectroscopic analysis shows a pronounced odd-even alternation of the molecular tilt angles in the multilayer films. In addition, high-resolution Brewster-angle transmission spectroscopy reveals that the conformation of the methyl group highly depends on whether the carbon number is even or odd. In contrast to the multilayer films, the odd-even effects do not appear in the monolayer films. We demonstrate that, in other words, the interlayer interactions of the molecules are responsible for the odd-even effects. This study also highlights the first identification of the monolayer phase of n-alkanes by using grazing incidence X-ray diffraction in combination with high-resolution infrared spectroscopy. These results not only reveal the molecular origin for the odd-even effect of n-alkanes but also provide analytical techniques for discussing the monolayer structure of various alkylated compounds on a functional group basis.

Thermal stress concentration points and stress mutations in nano-multilayer film structures

In the multilayer film-substrate system, thermal stress concentration and stress mutations cause film buckling, delamination and cracking, leading to device failure. In this paper, we investigated a multilayer film system composed of a substrate and three film layers. The thermal stress distribution inside the structure was calculated by the finite element method, revealing significant thermal stress differences between the layers. This is mainly due to the mismatch of the coefficient of thermal expansion between materials. Different materials respond differently to changes in external temperature, leading to compression between layers. There are obvious thermal stress concentration points at the corners of the base layer and the transition layer, which is due to the sudden change of the shape at the geometric section of the structure, resulting in a sudden increase in local stress. To address this issue, we chamfered the substrate and added an intermediate layer between the substrate and the transition layer to assess whether these modifications could reduce or eliminate the thermal stress concentration points and extend the service life of the multilayer structure. The results indicate that chamfering and adding the intermediate layer effectively reduce stress discontinuities and mitigate thermal stress concentration points, thereby improving interlayer bonding strength.

Nanostructure of TiO\(_{2}\) and WO\(_{3}\) multilayer films deposited on ITO glass for electrochromic enhanced photocatalytic activity

The photocatalytic activity (PA) by electrochromic (EC) enhancement of single and multilayer films of TiO2, WO3, TiO2/WO3, and WO3/TiO2 was investigated. All films were deposited from metal on an ITO glass substrate using direct current (DC) magnetron sputtering via an oblique angle deposition (OAD) technique at 85°. Subsequently, a thermal oxidation (TO) process at 500℃ was applied for the samples to form metal oxide films. The morphology, elemental composition, crystal structure, and optical properties were studied by using field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD), and UV-vis spectroscopy, respectively. The photocatalytic properties were investigated by showing the degradation rate of methylene blue (MB) solution as an organic pollutant that was examined under ultraviolet irradiation of 300 µW∙cm‒2. The film samples were investigated by comparing the pre-color and colored states that were achieved through the EC process. The EC properties of WO3 led to increased charge insertion on the film surface. This observation was further supported by cyclic voltammetry (CV) testing, which revealed a higher current density for the thin film samples. The photodegradation results showed that the samples in the colored state exhibited a significantly higher degradation rate of MB compared to the pre-color state.

Highly stretchable and strain-insensitive multilayered electromagnetic interference shielding films prepared via a simple soaking-infiltration strategy

Stretchable electromagnetic interference (EMI) shielding films are crucial for wearable electronics. However, it is challenging to further endow the EMI shielding films with good stretchability and satisfactory EMI shielding effectiveness (EMI SE) under large strains. Herein, we successfully prepared high-performance stretchable polydimethylsiloxane (PDMS)/single-walled carbon nanotube buckypaper (SWNT BP)/PDMS EMI shielding films with multi-graded conductive networks via a soaking-infiltration strategy. In this multilayered film, infiltration layers of SWNT/PDMS were particularly created between elastic PDMS and brittle SWNT BP. Owing to the multilayered structure and conductivity compensation effects arising from infiltration layers, our EMI shielding films exhibited excellent EMI SE of 34.2 dB with high stretchability of >400 %. The outstanding EMI SE could be well maintained under large strains. At <50 % strain, the relative change in EMI SE (|ΔSE/SE0|) remained consistently below 10 %, while at even 100 % strain, |ΔSE/SE0| was only ∼35 %. Furthermore, we proposed a parallel-series hybrid model to describe electrical conduction in straining films. Due to their excellent conductivity under strain, the films could also serve as stretchable Joule heaters. This work provides a novel and simple approach for constructing strain-insensitive conductive films, with potential applications in stretchable EMI shielding and thermal management.