Multilayer Films Research Articles

Nested deep transfer learning for modeling of multilayer thin films

Nested deep transfer learning for modeling of multilayer thin films

Phase-Selective Synthesis of Rhombohedral WS2 Multilayers by Confined-Space Hybrid Metal-Organic Chemical Vapor Deposition.

Rhombohedral polytype transition metal dichalcogenide (TMDC) multilayers exhibit non-centrosymmetric interlayer stacking, which yields intriguing properties such as ferroelectricity, a large second-order susceptibility coefficient χ(2), giant valley coherence, and a bulk photovoltaic effect. These properties have spurred significant interest in developing phase-selective growth methods for multilayer rhombohedral TMDC films. Here, we report a confined-space, hybrid metal-organic chemical vapor deposition method that preferentially grows 3R-WS2 multilayer films with thickness up to 130 nm. We confirm the 3R stacking structure via polarization-resolved second-harmonic generation characterization and the 3-fold symmetry revealed by anisotropic H2O2 etching. The multilayer 3R WS2 shows a dendritic morphology, which is indicative of diffusion-limited growth. Multilayer regions with large, stepped terraces enable layer-resolved evaluation of the optical properties of 3R-WS2 via Raman, photoluminescence, and differential reflectance spectroscopy. These measurements confirm the interfacial quality and suggest ferroelectric modification of the exciton energies.

Photovoltaic effects in BiVO4/ZnTiO3 multilayer films with high fill factor

Bismuth-based semiconductor materials have garnered significant attention because of their appropriate optical bandgap and substantial photoelectric conversion efficiency. Enhancing the photocurrent and fill factor of photovoltaic films is essential for developing high-performance optoelectronic devices. In this study, high-performance BiVO4-ZnTiO3 multilayer films were fabricated using a straightforward sol-gel method, where the incorporation of ZnTiO3 films significantly improved the photovoltaic performance of BiVO4. Through structural design aimed at enhancing light utilization, the BiVO4-ZnTiO3 multilayer film achieved a photocurrent density of 1.9 mA/cm2 at 450 nm, along with a fill factor of 46.8 % in the composite multilayer structure. The improvement in film performance is attributed to the overall multilayer stacking effect. This study offers a novel approach for utilizing bismuth-based semiconductors in optoelectronics.

Phase-changing NIPAM-AM/ATO hydrogels for thermochromic smart windows with highly adaptive solar modulation

Improving the solar regulation and reducing the response temperature of thermochromic smart windows are pivotal importance for energy-saving buildings. However, these two strategies are challenging to be integrated into one window. Herein, a novel composite hydrogel based on N-isopropylacrylamide (NIPAM) doped with antimony-doped tin oxide (ATO) nanoparticles and acrylamide (AM) was developed for producing a high-performance smart window, which successfully achieved enhanced solar energy regulation and reduced response temperature. This smart window was fabricated by combining a reversible thermoresponsive hydrogel (TAH) that acted as a thermochromic material with a ATO multilayer film that performed as a transparent heater. The as-prepared smart window could modulate solar light over a range from ultraviolet (UV) to infrared (IR) radiation and achieved active responses to high-temperature weather. The smart window showed high luminous transmittance (Tlum, 82.92 %) together with an excellent solar modulation performance (ΔTlum = 73.31 %, ΔTIR = 38.26 %, and ΔTsol = 60.74 %), and a lower critical solution temperature of 32 °C. Even after 120 high- and low-temperature cyclic durability tests, the smart windows still exhibited a high solar modulation capability. In outdoor demonstrations, the as-prepared smart window exhibited a promising temperature regulation ability under strong solar irradiation. Therefore, the present universal modification framework provided some insights for the future design of energy-saving windows.

Data-driven investigation of thickness variations in multilayer thin film coatings

Abstract Design and fabrication of multilayer thin film coatings for photonics applications require careful consideration of various parameters such as layer thickness, refractive indices and number of stacks. A growing trend uses machine learning for efficient navigation in the complex parameter space of photonics applications to efficiently extract valuable insights from the extensive datasets and to predict the optical performance. We developed an approach that combines Monte-Carlo and Finite-Difference Time-Domain simulations to model multilayer thin films. After conducting 95 200 runs, the data were analyzed using Neural Network fitting to explore how thickness variations influence the optical performance. An experiment validation on magnetron sputtered coated samples demonstrates the high accuracy of our method in predicting the optical performance of the thin film stacks (R 2 > 0.99), contributing to the understanding and enhancement of photonics stack properties for diverse optical applications using machine learning approaches.

Compact multilayer selective absorbers based on amorphous carbon for solar-thermal conversion

In addressing the energy crisis and climate change, environmentally sustainable materials and structures with heightened absorption and enhanced photothermal conversion efficiency are urgently demanded. In this study, a series of ultrabroadband, omnidirectional, and near-perfect solar radiation absorbers based on amorphous carbon (a-C) were fabricated by magnetron sputtering. These absorbers, featuring 4, 6, and 8-layer compact multilayer thin film structures, exhibited measured absorption of 96.8 %, 96.5 %, and 96.6 % in the range of 300–2500 nm, respectively. The high absorption efficiency delves into the synergistic effects of intrinsic absorption of a-C and enhanced absorption through thin film interference. Through microstructure analysis, the reduced absorption compared to design originates from the optical thickness mismatch caused by the unstable growth rate of a-C. In addition, the absorbers show very slight variations in absorption within 40° and maintain a high absorption of more than 80 % in the incident angle of 60°. For samples with different air annealing temperatures from 100 to 250 °C, the microstructure, morphology, and optical properties were systematically investigated. The appearance of oxygen channels due to surface defects or voids leads to the oxidation reaction of the diffused Ti atoms at high temperature. Notably, the proposed absorber can be fabricated by a lithography-free method, paving a way for large-area application of a-C.

Incommensurate superlattice modulation surviving down to an atomic scale in sputter-deposited Co/Pt(111) epitaxial multilayered films

Incommensurate superlattice modulation surviving down to an atomic scale in sputter-deposited Co/Pt(111) epitaxial multilayered films

Thickness modulation influenced mechanical properties of TiN/(CrVTaTiW)Nx multilayer coatings

A novel TiN/(CrVTaTiW)Nx multilayer coating, consisting of the high-entropy alloy nitride and the binary nitride was prepared by DC magnetron sputtering. Detailed investigation about the microstructure and mechanical attributes of the multilayer films was conducted, with particular emphasis on the influence of high entropy nitride (HEN) modulation layer's thickness. The results reveal that all samples exhibited a face-centred cubic (fcc) crystal structure with a (111) preferred orientation. Notably, the hardness and elastic modulus of multilayer films increase with increase of the HEN layer's thickness. When the thickness of the HEN layer reached 4.8 nm, the hardness and elastic modulus of the TiN/(CrVTaTiW)Nx multilayer reached the maximum values of 25.33 GPa and 311.95 GPa, respectively. These results indicate the key role of the HEN layer as a modulation layer within the coating, ultimately demonstrating the importance of thickness on the structure and properties of TiN/(CrVTaTiW)Nx nanomultilayer films.

Effects and modulation mechanism of crystal structure on residual stress of Cu films used for metallization

Deformation cracking and delamination arising from residual stress are the main challenges for metallization in large-scale integrated circuits. Herein, an ultra-low residual stress Cu film is prepared on amorphous SiO2 by mixed power magnetron sputtering. Compared to conventional Cu films, the residual stress in the film decreases by 1434 times. The nano multi-layer structure produces lower stress and deformation as well as better reliability. The multi-layer Ti underlayer also reduces the residual stress and promotes the low-defect growth of Cu. The lower surface roughness, smaller dislocation density, predominant grain orientations of 〈111〉 and 〈001〉, and more substructures are beneficial to the reduction of residual stress. In addition, interlayer stress cancellation can be achieved by changing the number of 〈111〉 grains. The research on grain growth at the interface of nano multi-layer films reveals an effective means to fabricate films with low residual stress for metallization in integrated circuits.

Preparation process, surface properties and mechanistic study of HVAF-sprayed CoCrFeNiMo0.2 high-entropy alloy coatings

The objective of this study is to develop infrared reflective coatings with excellent service performance in extreme environments, aimed at reducing system energy consumption and enhancing service life. In this work, CoCrFeNiMo0.2 high-entropy alloy (HEA) powder was deposited on the 316 L stainless steel (SS) substrate using High-Velocity Air Fuel (HVAF) thermal spray technology. The microstructure, mechanical properties, infrared reflectivity, and corrosion resistance of the coatings under different spraying parameters were investigated and compared with those of the substrate. Computational Fluid Dynamics (CFD) simulation was employed to analyze the influence of HVAF spraying parameters on flame characteristics and particle flight behavior, providing guidance for optimizing the spraying process and explaining underlying mechanisms. Results demonstrated that adjusting parameters such as propane and air pressure, spraying distance, and powder feed rate could produce dense coatings with <1 % porosity. The microhardness of the coatings was approximately 1.8 times that of the substrate, and the bonding strength between the coating and the substrate is increased to 39.4 MPa. Additionally, the near-infrared reflectivity of the coatings was significantly higher than that of the substrate, with an enhancement of 18.7 %. Coatings sprayed under different parameters exhibited superior passivation and pitting corrosion resistance compared to the substrate in 3.5 wt% NaCl and 1 mol/L HCl solutions. Optimization of spraying parameters further enhanced the protective capability of the passivation film and corrosion resistance. Consequently, CoCrFeNiMo0.2 HEA coatings prepared by HVAF spraying technology demonstrate excellent comprehensive performance, holding promising potential for industrial applications.

Development and evaluation of STRC coating for cooling asphalt pavement and mitigating urban heat island effects

To mitigate the negative impacts of urban heat island (UHI) effects on modern cities, this study developed and evaluated a novel cool coating, solar thermal reflective coatings (STRC), for reducing asphalt pavement temperatures. Firstly, the optical properties were characterized using UV-Vis-NIR spectroscopy, and the thermal performance of eight STRC formulations was assessed using a custom-built testing apparatus. Subsequently, the microstructure and elemental composition were examined using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). Finally, the optimized coating was applied to asphalt concrete, and its long-term performance and stability were confirmed through durability tests, including water immersion test, temperature variation endurance test, and radiation cycle test. The results showed that chromium sesquioxide (Cr₂O₃), a critical pigment of STRC, exhibited a high near-infrared reflectance of 54.76 % and a lower visible reflectance of 10.22 %. Among the eight STRC formulations, STRC5 demonstrated balanced performance with a visible reflectance of 35.69 % and a near-infrared reflectance of 71.85 %. The microstructure of STRC5 was uniform with minimal surface defects. When STRC5 was applied to asphalt concrete, it achieved significant cooling effects, maintaining a mean temperature of 49.51 °C compared to 60.07 °C for uncoated samples, resulting in a maximum temperature difference of 10.56 °C after 4 h of light exposure. Durability test results confirmed the long-term performance and stability as the coating withstood extreme temperature fluctuations from −20 °C to 60 °C and 72 h of water immersion. In conclusion, STRC5 demonstrated great potential to effectively cool asphalt pavement and mitigate UHI effects.

Influence of hyaluronic acid and chitosan molecular weight on the adhesion of circulating tumor cell on multilayer films

CD44 is a cell receptor glycoprotein overexpressed in circulating tumor cells (CTCs), with levels linked to an increase in metastatic capacity of several tumors. Hyaluronic acid (HA), the natural ligand of CD44, has primarily been investigated for tumor cell interaction in self-assembled polyelectrolyte multilayer films, with little attention given to the complementary polycation. In this study, we screened sixteen different polyelectrolyte multilayer assemblies of HA and chitosan (CHI) to identify key assembly parameters and surface properties that control and govern CTCs adhesion. Statistics analysis revealed a major role of CHI molecular weight in the adhesion, followed by its combinatorial response either with HA ionization degree or ionic strength. PM-IRRAS analysis demonstrated a correlation between the orientation of HA carboxyl groups on the film surface and CTCs adhesion, directly impacted by CHI molecular weight. Overall, although CTCs binding onto the surface of multilayer films is primarily driven by HA-CD44 interaction, both chitosan properties and film assembly conditions modulate this interaction. These findings illustrate an alternative to modifying the performance of biomaterials with minimal changes in the composition of multilayer films.

Spin-coating ANF based multilayer symmetric composite films for enhanced electromagnetic interference shielding and thermal management

The demand for flexible composite films with electromagnetic interference (EMI) shielding capabilities is rapidly increasing. Balancing high EMI performance with flexibility and portability has become a critical research focus in practical applications. In this study, an optimized strategy for aramid nanofibers (ANF) films was developed using spin-coating and sol–gel techniques. The resulting film features a smooth surface and excellent mechanical properties. ANF, initially an insulator, was transformed into a conductor through the in-situ polymerization of ion-doped polypyrrole (PPy). Leveraging a multilayer structural strategy, we prepared a symmetric composite film, ANF@PPy-(TA-MXene)-AgNWs-(TA-MXene)-ANF@PPy (PMA), using vacuum-assisted filtration and lamination hot pressing. This film, composed of ANF@PPy (PA) as the matrix, tannic acid (TA) modified MXene, and silver nanowires (AgNWs) as fillers, exhibited multiple shielding mechanisms as electromagnetic wave (EMW) passed through its various layers. This multilayer configuration provides significant flexibility in EMW shielding. Moreover, TA-modified MXene expands the lamellar spacing, enhancing the scattering efficiency of EMWs within the film, and serves as a medium connecting the upper and lower layers. This results in the efficient integration of the multilayer structure, synergistically improving both EMI shielding performance and mechanical properties. When the ratio of PA/MXene/AgNWs was 1:3:1, the film demonstrated optimal properties, including an EMI shielding effectiveness of 70.2 dB, thermal conductivity of 4.62 W/(m•K), and tensile strength of 50.2 MPa. Due to the exceptional EMI shielding and thermal properties of the PMA composite film, it holds great potential for applications in artificial intelligence, wearable heaters, and military equipment.

Formulation and Characterization of Deep Eutectic Solvents and Potential Application in Recycling Packaging Laminates.

Deep Eutectic Solvents (DESs) show promising abilities for the delamination of multilayer packaging films that are used in food packaging and in pharmaceutical blister packs. Due to the complexity of their structure, the recycling of such materials is a challenging task, leading to the easiest or cheapest disposal option of either landfill or incineration. Towards the development of 'green' solvents for efficient waste management and recycling, this research focuses on the preparation of a range of hydrophobic and hydrophilic DESs based on carboxylic acids in combination with various naturally derived aliphatic and aromatic organic compounds as well as amino acids. Chemical and physical characterization of the solvents was undertaken using differential scanning calorimetry, rheometry, and density measurements for the determination of their properties. Subsequently, batches of solvent were tested against different types of consumer packaging to evaluate the ability of the DES to delaminate these structures into their component materials. The laminate packaging waste products tested were Al/PE, PE/Al/PET, Al/PE/paper, and PVC/PE/Al. Separated films were collected and studied to further examine the effect of solvent delamination on the materials. Depending on the DES formulation, the results showed either partial or full delamination of one or more of the packaging materials, albeit there were challenges for certain solvent systems in the context of delivering a broad delamination efficiency. Variables including temperature, agitation rate, mixing time, and solvent ratios were investigated via a Design of Experiments process to assess the effects of these parameters on the delamination outcome. The results showed that the DESs presented in this research can offer an efficient, low-energy, affordable, and green option for the delamination of laminate packaging materials.

Optimizing excited state adsorption and carrier dynamics of metal doped zinc oxide by p-d orbital modulation for efficient reverse saturation absorption

Doping metals can regulate the excited state adsorption and carrier transport efficiency of ZnO through p-d orbital coupling thereby improving its nonlinear performance. Herein, the thin film coatings consisting of ZnO, and M-ZnO (M=Al, Sn, Mg) were synthesized using the magnetron sputtering technique. ZnO exhibited the granular/stick structure, while the metal dopant atoms (M) were incorporated into the ZnO lattice, resulting in a homogeneous distribution. Photoluminescence spectroscopy reveals the quenched defect emission intensity, indicating a decrease in the rate of photo-induced electron-hole pair complexation. Mg exhibits an optimized effect to promote the saturation absorption of ZnO, resulting in the enhancement of the nonlinear absorption (NLA) coefficients for M-ZnO films. Al-ZnO and Sn-ZnO films exhibit reverse saturation absorption. Theoretical simulation shows that the additions of transition metal atoms favor the electron transfer through p-d orbital modulation of ZnO. The p-d hybridization causes the metal-d orbitals to cross the Fermi level and form an electron transport channel, thereby enhancing the excited state absorption, and effectively controlling the NLA process and mechanism. The excited state absorption of the M-ZnO films significantly rises. This research demonstrates that the optimization of excited state absorption through p-d orbital modulation is a highly effective strategy for the development of efficient and superior nonlinear optical absorbers.

Dual-dielectric Fabry-Perot film for visible-infrared compatible stealth and radiative heat dissipation

Multiband camouflage of space satellite to against advanced detection has attracted rising attention. However, the combination of compatible camouflage and radiative heat dissipation for space satellite still remains challenging, which requires low visibility and selective thermal emission in a dark and deep cold background. In this work, a dual dielectric Ge/SiO2 layer embedded Fabry-Perot multilayer film (W/Ge/SiO2/W/SiO2) is proposed for space stealth and heat dissipation. Ge and SiO2 films with appropriate thickness are designed to realize high visible absorption and spectra selective IR emission, simultaneously. The optimized multilayer film achieves a high absorbance (α = 0.983) in visible light (0.38–0.80 μm) for visible stealth, low emissivity (ε3–5 μm = 0.038; ε8–14 μm = 0.200) in atmospheric windows for infrared stealth, and relative high emissivity outside the atmospheric windows (ε5–8 μm = 0.487) for radiative heat dissipation. The simulation results indicate that the coupling of tunneling effect in ultrathin metallic W film and Fabry-Perot resonant is the main contribution to the excellent absorptivity and emissivity tunability. The proposed dual spacers embedded Fabry-Perot multilayer film paves a new way for multispectral camouflage of space satellite and other applications such as solar-thermal conversion, thermal management, energy saving, and detective technologies.

Correlations between adhesion and molecular interactions at buried interfaces of model polymer systems and in commercial multilayer barrier films.

Sum frequency generation vibrational spectroscopy (SFG) was applied to characterize the interfacial adhesion chemistry at several buried polymer interfaces in both model systems and blown multilayer films. Anhydride/acid modified polyolefins are used as tie layers to bond dissimilar polymers in multilayer barrier structures. In these films, the interfacial reactions between the barrier polymers, such as ethylene vinyl alcohol (EVOH) or nylon, and the grafted anhydrides/acids provide covalent linkages that enhance adhesion. However, the bonding strengths vary for different polymer-tie layer combinations. Here, using SFG, we aim to provide a systematic study on four common polymer-tie interfaces, including EVOH/polypropylene-tie, EVOH/polyethylene-tie, nylon/polypropylene-tie, and nylon/polyethylene-tie, to understand how the adhesion chemistry varies and its impact on the measured adhesion. Our SFG studies suggest that adhesion enhancement is driven by a combination of reaction kinetics and the interfacial enrichment of the anhydride/acid, resulting in stronger adhesion in the case of nylon. This observation matches well with the higher adhesion observed in the nylon/tie systems in both lap shear and peel test measurements. In addition, in the polypropylene-tie systems, grafted oligomers due to chain scission may migrate to the interface, affecting the adhesion. These by-products can react or interfere with the barrier-tie chemistry, resulting in reduced adhesion strength in the polypropylene-tie system.

Frictional properties and environmental adaptability of Ti-MoS2/WC multilayer films

Magnetron-sputtered molybdenum disulfide films are extensively utilized as solid lubricating coatings in space applications as a result of their low friction coefficient and minimal contamination. However, MoS2-based films are sensitive to hygrothermal and oxidation environment, and are easily oxidized to form MoO3, which results in high friction and wear of the films, significantly reducing their operational lifespan. Especially when the spacecraft adopts the launching mode of coastal launch or ocean platform, the performance deterioration caused by oxidation of MoS2 films during transportation, storage and launch is more serious. Therefore, to enhance the frictional performance and oxidation resistance of the films in humid and salt spray environments, the Ti-MoS2/WC multilayer films with preferred (002) crystal plane orientation were prepared, achieving a friction coefficient of 0.009 in a vacuum environment and a wear rate of 1.1×10-7 mm3/N∗m. In particular, the film can maintain this extremely low coefficient of friction even after exposure to moisture or salt spray. These findings demonstrate that the dual doping of Ti and WC and the design of multilayer structures enable MoS2 films to achieve outstanding frictional performance and oxidation resistance. This is crucial for designing MoS2 films with excellent environmental adaptability.

Tribological Properties of MoN (Ag‐W)‐MoS2 (W) Multilayer Films in Wide Temperature Range

In nitride films, an enhanced lubrication effect has been achieved through the incorporation of a soft metal element such as Ag. However, at medium and high temperatures, the favorable tribological properties cannot be sustained for an extended period due to the rapid depletion of Ag. To address this issue, a multilayer film design with W element doping is conceived to impede Ag depletion. MoN (Ag‐W)‐MoS2 (W) multilayer films with 4 different layers are prepared, and their tribological properties are systematically characterized across temperatures ranging from 25 to 800 °C. The results indicate that the tribological properties of four different multilayer films vary considerably at different temperatures. The 8‐layer multilayer film exhibits a relatively low friction coefficient that can be maintained at wide‐range temperatures. X‐ray diffractometer patterns are obtained before and after the friction test to elucidate the lubrication phases of different layers within the multilayer films at various temperatures. Additionally, 3D profiles of wear trajectory surfaces are generated, revealing enhanced wear resistance achieved by effectively inhibiting the migration of Ag. The low friction coefficient in multilayer films can be attributed to the oxidation of MoS2 and the generation of new lubrication phases, as confirmed by Raman spectra analysis.

Composite edible film mimicking cell wall based on arabinoxylan, β-glucan and nanocellulose: Microstructural, physico-chemical properties, and preservation effect

To achieve sustainable environmental development, various biodegradable films have been designed to replace plastic films. The cell walls of the wheat bran aleurone layers primarily comprise alternately overlapping arabinoxylan (AX), β-glucan (BG) and small quantities of cellulose and ferulic acid. The differences in their composition can affect their mechanical strength and hydration. Therefore, multilayer films of AX, BG, cellulose nanofibers (CNFs), and free ferulic acid were prepared to simulate the cell walls of wheat aleurone layers, and the effect of different CNF contents on cell walls characteristics was investigated. The microstructure, physical properties, and hydration characteristics of multilayer films were studied using scanning electron microscopy, time-domain nuclear magnetic resonance, and thermogravimetric analysis. The AX/BG/8%CNF multilayer films possessed excellent thermal stability and mechanical properties along with slow moisture diffusion and flowability. When the CNF content within the films was 8%, the polymer composite structure hindered the diffusion of moisture. Inspired by the biological effects of wheat grain cell walls, cellulose multilayer films were used for blueberries preservation, and the decay rate, weight loss index, and respiration rate of blueberries were found to decrease significantly.