Multilayer Films Research Articles

Design of Far-Infrared High-Efficiency Polarization-Independent Retroreflective Metasurfaces.

Retroreflective gratings serve as fundamental optical elements in nanophotonics, with polarization-independent diffraction efficiency being one of the critical parameters for assessing their performance. In the far-infrared spectral range, traditional retroreflective gratings typically refer to metal echelette gratings, but their diffraction efficiency cannot approach 100% due to metal absorption. In the visible and near-infrared spectral ranges, metal echelette gratings have gradually been replaced by all-dielectric metasurfaces because dielectric materials exhibit negligible absorption at specific wavelengths. However, there is still a lack of relevant research in the far-infrared range, mainly due to the weak control capability of the existing devices over the polarization-independent phase. Here, we propose a kind of all-dielectric retroreflective metasurface composed of asymmetric pillars and freely tunable aperiodic multilayer films. The pillar structure can achieve polarization insensitivity, and the insufficient modulation capability of the dielectric materials can be compensated for by aperiodic Ge/ZnS films. The designed metasurface achieves the diffraction efficiency by RCWA, with the maximum larger than 99% and the overall reaching 95% (9.3-9.6 µm). We have provided detailed explanations of the design methodology and fabrication process. Our work lays the groundwork for further exploration and application of far-infrared lasers.

Materials’ properties of low temperature deposited Cu/W and Cu/Cr multilayer thin films using high power impulse magnetron sputtering

In this study, copper/tungsten (Cu/W) and copper/chromium (Cu/Cr) multilayers were created by stacking bilayer films in a 3:1 ratio, with layer thicknesses ranging from 400 to 800 nm, deposited on Si (100) substrates using high power impulse magnetron sputtering (HiPIMS). The microstructural and surface properties of these films were examined through x-ray diffraction, atomic force microscopy, and scanning electron microscopy. Electrical properties were assessed using a four-point probe, while mechanical properties were measured via nanoindentation. Both multilayer systems showed a decrease in the hardness accompanied by an increase in the elastic modulus with each stacking bilayer. The Cu/W system experienced a gradual hardness reduction (down to 19%), compared to the Cu/Cr system, which exhibited a similar decrease (14.5%). The Cu/W and Cu/Cr multilayer film samples consistently demonstrate a softer nature compared to their bilayer counterparts due to the influence of the underlying Cu soft layers. A distinctive surface smoothness in these multilayer systems correlates with the elastic modulus in a manner unlike that with hardness. These multilayer films also demonstrated altered electrical resistivity, enhancing our understanding and capabilities in fabricating films with an increased number of layers.

Recycling Polyethylene/Polyamide Multilayer Films with Poly(isoprene-g-Maleic Anhydride) Compatibilizer.

Polymers generally form incompatible mixtures that make the process of recycling difficult, especially the mechanical recycling of mixed plastic waste. One of the most commonly used films in the packaging industry is multilayer films, mainly composed of polyethylene (PE) and polyamide (PA). Recycling these materials with such different molecular structures requires the use of compatibilizers to minimize phase separation and obtain more useful recycled materials. In this work, commercial polyisoprene-graft-maleic anhydride (PI-g-MA) was tested as a compatibilizer for a blend of PE and PA derived from the mechanical recycling of PE/PA multilayer films. Different amounts of PI-g-MA were tested, and the films made with 1.5% PI-g-MA showed the best results in terms of mechanical properties and dart impact. The films were also characterized thermally via thermogravimetric analysis (TG) and differential scanning calorimetry (DSC), using Fourier-transform infrared spectroscopy (FTIR), and morphologically using a scanning electron microscope (SEM). Other parameters, such as tearing and perforation, were analyzed.

Hydrogenolysis of Poly(Ethylene-co-Vinyl Alcohol) and Related Polymer Blends over Ruthenium Heterogeneous Catalysts.

The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste - poly(ethylene-co-vinyl alcohol) (EVOH) and related polymer blends - into alkane products. We report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1-C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in-situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C-C scission reveal that the hydrogenolysis of EVOH is slower than low-density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products.

A Breathable, Stretchable, and Self‐Calibrated Multimodal Electronic Skin Based on Hydrogel Microstructures for Wireless Wearables

AbstractBiomimetic electronic skins (e‐skins) are widely used in wearables, smart prosthesis and soft robotics. However, multimodal e‐skins, especially those based on hydrogels, face multiple challenges for practical applications, involving multi‐sensing signal mutual interference, low breathability and stretchability. Here, a breathable and stretchable multimodal e‐skin with a multilayer film microstructure is developed to achieve self‐calibrated sensing of any two of three stimuli: strain, temperature, and humidity, with minimal crosstalk. Hydrogel fibers with different shapes are designed for strain and temperature sensing modules, and the hydrogel film is developed as a humidity sensing module. The multimodal e‐skin exhibits impressive sensing performance, including a low strain detection limit (0.03%), strain linearity (R2 = 0.990), high‐temperature sensitivity (1.77%/°C), and a wide humidity detection range (33–98% RH). Interestingly, due to the directional anisotropy in strain sensitivity of different shaped fibers, the e‐skin realizes self‐calibrated detection of strain and temperature in different directions. By introducing porous elastomer encapsulation membranes, the breathability and wearing comfort of the e‐skin are attained, while the high stretchability (100% strain) is maintained. Furthermore, a personalized human‐machine interaction system is created by integrating the e‐skin with a wireless circuit to realize real‐time and wireless gesture recognition, physiological signals monitoring, and smart prosthesis.

Wavelength‐Linearly‐Dependent and Polarization‐Sensitive Perfect Absorbers based on Optically Anisotropic Germanium Selenide (GeSe)

AbstractPerfect absorbers, widely utilized in solar energy‐harvesting devices, optical communications, sensors, displays, and filters, achieve 100% light absorption. However, perfect absorbers employing micro/nanostructures encounter challenges such as high cost and complexity in simulation and fabrication. Here, novel wavelength‐linearly‐dependent and polarization‐sensitive perfect absorbers utilizing optically anisotropic germanium selenide (GeSe) are proposed. A simple and cost‐effective GeSe‐SiO2‐Si multilayered optical thin film is constructed and optimized to achieve destructive interference, leading to perfect absorption. The operating wavelength can be linearly tuned from 900 nm to 1300 nm by adjusting the GeSe thickness from 125 nm to 200 nm. Leveraging the significant optical anisotropy, the polarization angle is introduced as an additional parameter to dynamically and finely control the operating wavelength, enabling the creation of polarization‐sensitive perfect absorbers. Experimental results validate the feasibility of fabricating and dynamically modulating the proposed wavelength‐linearly‐dependent and polarization‐sensitive perfect absorbers. This study introduces a novel approach for designing and fabricating reconfigurable perfect absorbers utilizing low‐symmetry materials, facilitating mass production and on‐chip integrated systems.

Fabrication of Electronically Conductive Protein-Heme Nanowires for Power Harvesting.

Electronically conductive protein-based materials can enable the creation of bioelectronic components and devices from sustainable and nontoxic materials, while also being well-suited to interface with biological systems, such as living cells, for biosensor applications. However, as proteins are generally electrical insulators, the ability to render protein assemblies electroactive in a tailorable manner can usher in a plethora of useful materials. Here, an approach to fabricate electronically conductive protein nanowires is presented by aligning heme molecules in proximity along protein filaments, with these nanowires also possessing charge transfer abilities that enable energy harvesting from ambient humidity. The heme-incorporated protein nanowires demonstrate electron transfer over micrometer distances, with conductive atomic force microscopy showing individual nanowires having comparable conductance to other previously characterized heme-based bacterial nanowires. Exposure of multilayer nanowire films to humidity produces an electrical current, presumably through water molecules ionizing carboxyl groups in the filament and creating an unbalanced total charge distribution that is enhanced by the heme. Incorporation of heme and potentially other metal-center porphyrin molecules into protein nanostructures could pave the way for structurally- and electrically-defined protein-based bioelectronic devices.

Analysis of Mechanical and Thermal Properties of Polymer Materials Derived from Recycled Overprinted Metallized PP Films.

Polymer materials and their composites are one of the most frequently used materials in the packaging and food industries. This applies to both disposable and reusable packaging, layered films with barrier properties, as well as densely overprinted polymer films and metallized food wrap films. According to statistical data from Plastics Europe, approximately 40% of processed thermoplastics are used to produce packaging, including single- and multi-layer film packaging. Growing requirements and new EU directives require the use of recycled materials in new products, which is not easy because the properties of recyclates may differ significantly from those of the primary materials with which the former are mixed. This work attempts to analyze the properties of the primary material used to produce a film using the casting method in comparison with the industrial recyclate obtained by the processing of film made of the primary material and then overprinted and metallized. The process of obtaining re-granulates and preparing test samples was presented, and the mechanical, structural, and thermal properties of the tested materials were compared. The conducted research and the obtained results demonstrated the advisability of conducting advanced mechanical recycling, which leads to obtaining re-granulates with repeatable processing properties and thermal and mechanical properties comparable to the original material despite the impurities they contain.

Enhanced Functional Properties for Packaging Applications Using Sodium Alginate/Starch Bilayer and Multilayer Films

Enhanced Functional Properties for Packaging Applications Using Sodium Alginate/Starch Bilayer and Multilayer Films

Deciphering heterogeneous enzymatic surface reactions on xylan using surface plasmon resonance spectroscopy

Xylans' unique properties make it attractive for a variety of industries, including paper, food, and biochemical production. While for some applications the preservation of its natural structure is crucial, for others the degradation into monosaccharides is essential. For the complete breakdown, the use of several enzymes is required, due to its structural complexity. In fact, the specificity of enzymatically-catalyzed reactions is guided by the surface, limiting or regulating accessibility and serving structurally encoded input guiding the actions of the enzymes. Here, we investigate enzymes at surfaces rich in xylan using surface plasmon resonance spectroscopy. The influence of diffusion and changes in substrate morphology is studied via enzyme surface kinetics simulations, yielding reaction rates and constants. We propose kinetic models, which can be applied to the degradation of multilayer biopolymer films. The most advanced model was verified by its successful application to the degradation of a thin film of polyhydroxybutyrate treated with a polyhydroxybutyrate-depolymerase. The herein derived models can be employed to quantify the degradation kinetics of various enzymes on biopolymers in heterogeneous environments, often prevalent in industrial processes. The identification of key factors influencing reaction rates such as inhibition will contribute to the quantification of intricate dynamics in complex systems.

Preparation and tribological properties of the friction induced Mo-based film

The main idea of this study was to utilize the pressure and heat produced in the friction process to make Mo nanoparticles mixed in lubrication oil into the multi-layered tribo-film. An in-house developed reciprocating wear rig was used for the tribo-film deposition and associated tribological tests. By design of experiment, the optimal deposition parameter was obtained. Results indicate that the multi-layered film consists of a Mo-based concrete structure layer and a carbon-based film. The carbon-based film was produced by the dehydrogenation and carbonization of the lubricating oil catalyzed with Mo nanoparticles. The consumption and deposition of the carbon-based film was dynamically balanced during the wear process, resulting in the outstanding tribological performance.

High Permeability in Broadband of Co-sputtered [Fe-Fe20Ni80/Cr]n Multilayer Films

High Permeability in Broadband of Co-sputtered [Fe-Fe20Ni80/Cr]n Multilayer Films

Effect of vacuum atomic oxygen irradiation on tribological properties of MoS2/WC multilayer films

The adaptability of molybdenum disulfide (MoS2) films in space environments is crucial for aerospace applications. However, atomic oxygen (AO) in low Earth orbit can damage the friction and wear performance of MoS2 films, leading to a reduction in the service life of the film. To enhance the resistance of the film to atomic oxygen irradiation, we constructed a nano-multilayer structure composed of MoS2-WC-MoS2. Studies have shown that MoS2/WC multilayer films exhibit an ultra-low friction coefficient of 0.010 due to their (002) preferred orientation. Even after high-dose AO irradiation at 1.84×1020 atoms·cm-2, the film still maintains a friction coefficient of 0.009. This is attributed to the presence of MeOX nanoparticles in the MoS2 transfer film at the friction interface after AO irradiation, and the existence of MeOX nanoparticles plays a key role in maintaining ultra-low friction of the film. These findings are of great significance for extending the service life of molybdenum disulfide films in space environments and enhancing their resistance to atomic oxygen irradiation.

Finite element simulation and experiment of residual stress evolution in MEMS structures

The MEMS device structure is usually formed by the combination of thick film and thin film deposition of many different materials, and the residual stress generated in the process of integration/superposition of different materials has a significant impact on the performance and reliability of the device.In this study, a test structure of a multilayer thin film was designed and processed. Based on this, finite element modeling analysis and reliability experiment, analyze the evolution of residual stress and construct the corresponding theoretical analysis model. The finite element modeling analysis can characterize the evolution and distribution laws of residual stress. The reliability experiment is mainly by carrying out the temperature shock experiment, and measuring the resistance value, resonance frequency and the surface morphology of the device, so as to better reflect the change of residual stress. Through this study, the resonant frequency and surface morphology of the device can reflect the residual stress of the device, which provides help for the test and analysis of the residual stress. To a certain extent, it can help reduce the harm caused by the residual stress in the design and manufacturing process, and improve the performance and reliability of MEMS devices.

Switching Behavior of the Composite Low Dimensional Structural Hybrids of Carbon After UV Exposure

Low dimensional multi structural components of carbon are of great interest currently owing to their applications in developing flexible plastic electronics. In this work, we discuss emergence of different structural hybrids of carbon from as-prepared HiPCO SWCNTs subjecting them to oxidative acid purification and covalent functionalization process. Transmission electron microscopy (TEM) investigations reveal single wall carbon nanotubes (SWCNTs) serve as a building block to obtain multi wall carbon nanotubes (MWCNTs), graphene sheets (GS), carbon nano scrolls (CNS) structures which coexist in the sample. These structures when grafted with polymer binder and spray coated on Si substrate provide highly sustainable thin film coatings that are stable even in adverse space conditions [1]. These CNT and CNS based composite coatings are promising candidates for stray light control space applications exhibiting a low reflectance of the order of 2-3% in the visible spectral range [1]. Electrical switching behaviour of these films were investigated by capturing current(time) (I(t)) response, displaying promising switching character with distinct ON-OFF cycle. These coatings offer opportunities for the development of facile, cost-effective carbon-based devices without going into the nontrivial task of separating different the structures.

Development of multilayer films based on PLA/PBAT and sodium alginate for active packaging

AbstractIn this study, polylactic acid (PLA) and polyadipic acid/butylene terephthalate (PBAT) blend polymer were used as matrix to prepare PLA/PBAT substrate film by twin‐screw extruder. A series of multilayer films were prepared by starch‐based adhesive by loading 1% chitosan (CS), 1% zinc oxide nanoparticles (ZnONPs) or 1% silver nanoparticles (AgNPs) with sodium alginate (SA) as three different coatings. Compared with PLA/PBAT, the combination of adhesive and SA‐based antibacterial coating significantly improved the water vapor barrier, oxygen barrier and mechanical properties of the film, regardless of the type of antibacterial agent. The water vapor transmission of SA‐based AgNPs coating film decreased from the original 5.77 × 10−14 to 3.41 × 10−14 g·cm·cm−2·Pa−1·s−1. The oxygen permeability of SA‐based chitosan coating decreased from the original 74.35 × 10−14 to 6.40 × 10−14 cm3·cm·cm−2·Pa−1·s−1. The tensile strength of the SA‐based AgNPs coating film increased from the original 264.79 to 286.22 MPa. The film is yellow and has good ultraviolet absorption capacity. Membranes doped with CS, ZnONPs or AgNPs inhibited the growth of Escherichia coli and Staphylococcus aureus. Among them, chitosan doped membrane has weak antibacterial activity, AgNPs doped membrane has the best antibacterial activity against E. coli and S. aureus, and has potential application prospects in active packaging.

Design of a multi-physics coupling MEMS pressure sensor

The pressure measurement of explosion shock wave puts forward high requirements on the temperature resistance and response speed of the sensor. In this paper, a multi-physics coupling pressure sensor is designed to meet requirements. The sensor mainly consists of a Fabry-Perot cavity optical fiber sensing unit, a piezoelectric pressure sensing unit and a thermometric resistance temperature measurement module. Firstly, the structure of the sensor is designed. The top and bottom surfaces of the Fabry-Perot cavity are composed of a silicon diaphragm and a quartz glass. The piezoelectric pressure sensing unit is an AlN film including its electrodes. Pt thermometric resistance is developed to realize real-time temperature monitoring. Secondly, the fabrication process of the sensor is discussed, especially three key technologies. An Al film is sputtered to increase the reflectivity of the quartz glass. The SU-8 photoresist is applied to accurately control the thickness of Fabry-Perot cavity. Etching is adopted to work out the graphics of the AlN piezoelectric film. At last, a complete fabrication process of the sensor is described. The fabrication of multilayer films begins with a double-sided polishing silicon wafer, while Fabry-Perot cavity was from a double-sided polishing quartz glass. Then two parts of the sensor are combined to ensure the multi-physics coupling sensor to achieve complete function.

The rooftop cooling potentials of evaporative cooling porous tiles and high reflective coatings in hot and humid regions

Altering the reflectivity and permeability of surfaces in high-density cities is a key approach to mitigate rising urban heat islands. High Reflectance Coatings (HRC) and Evaporative Cooling Porous Tiles (ECPT) offer potential solutions for urban cooling. However, previous studies have mainly focused on roof surface temperatures, neglecting changes in near-roof air temperature. ECPT, a new permeable material, is mostly used in urban pavements and ignoring the underutilized rooftops, with limited research on its cooling effects in these settings. Therefore, this study investigates the impact of HRC and ECPT on near-roof air temperatures in the Pearl River Delta through observational experiments under various weather conditions. The results show that both HRC and ECPT significantly reduce near-roof air temperatures, but their effectiveness decreases above 1.8 m. In rainy conditions, these strategies are less effective due to their dependence on solar radiation. HRC works by reflecting short-wave radiation, while ECPT cools by evaporation. A key advantage of ECPT is its ability to be actively watered, quickly reducing temperatures by 2.14 °C at 0.3 m. This research is valuable for developing urban cooling strategies in high-density areas during extreme temperature conditions.

Neural network analysis of neutron and X-ray reflectivity data incorporating prior knowledge.

Due to the ambiguity related to the lack of phase information, determining the physical parameters of multilayer thin films from measured neutron and X-ray reflectivity curves is, on a fundamental level, an underdetermined inverse problem. This ambiguity poses limitations on standard neural networks, constraining the range and number of considered parameters in previous machine learning solutions. To overcome this challenge, a novel training procedure has been designed which incorporates dynamic prior boundaries for each physical parameter as additional inputs to the neural network. In this manner, the neural network can be trained simultaneously on all well-posed subintervals of a larger parameter space in which the inverse problem is underdetermined. During inference, users can flexibly input their own prior knowledge about the physical system to constrain the neural network prediction to distinct target subintervals in the parameter space. The effectiveness of the method is demonstrated in various scenarios, including multilayer structures with a box model parameterization and a physics-inspired special parameterization of the scattering length density profile for a multilayer structure. In contrast to previous methods, this approach scales favourably when increasing the complexity of the inverse problem, working properly even for a five-layer multilayer model and a periodic multilayer model with up to 17 open parameters.

Research on Dry Chemical Detection TechnologyBased on Reflectance Photometry

In response to the issues of insufficient stability and accuracy in dry chemical detection using reflectance photometry, caused by the divergence and multiple internal reflections of the reflected light signal from the sample and the multilayer dry film test strip, a dry chemical reflectance photometry detection system based on an integrating sphere is designed. Firstly, an integrating sphere device is incorporated to reduce signal divergence and loss, ensuring even detection of the sample's reflected light signal and improving detection stability. Secondly, Light Tools optical simulation analysis is performed, and an integrating sphere detection model is established. Thirdly, the Williams-Clapper equation is employed to correct the error in reflectance density caused by multiple internal reflections, enhancing detection accuracy. Experimental validation demonstrates that the developed integrating sphere-based dry chemical reflectance photometry detection system improves the stability and accuracy of the detection system.