Bilayer Films Research Articles

Impact of metal deposition on the optical and interface properties of NiO: growth and characterization of NiO/metal thin bilayer films

Abstract Since transparent conductive oxides (TCOs) provide electrical conductivity together with optical transparency, they have found wide applications in optoelectronic devices and photovoltaics. Among the TCOs, nickel oxide (NiO) is challenging due to its inherent trade-off between transparency and electrical conductivity. To address this challenge, one effective approach is to deposit a metal layer onto NiO thin films. In this work, NiO, NiO/Au, NiO/Ag, and NiO/Cu thin films are prepared by sputtering and thermal evaporation techniques on glass substrates and fully characterized finding the proper film for optoelectronic applications. The electrical and optical properties of the fabricated films are examined by four-point probe measurements and optical spectrometry. According to the obtained results, the NiO/Au, NiO/Ag, and NiO/Cu bilayers show sheet resistance of 200, 338, and 925 Ω sq−1 respectively while their optical bandgaps vary from 3.2 to 3.76 eV. These findings provide valuable insights into the performance of these films, making them potentially viable choices for various optoelectronic applications.

Water Vapor-Impermeable AlON/HfOx Bilayer Films Deposited by Hybrid High-Power Impulse Magnetron Sputtering/Radio-Frequency Magnetron Sputtering Processes

Water vapor-impermeable AlON/HfOx bilayer films were constructed through a hybrid high-power impulse magnetron sputtering (HiPIMS) and radio-frequency magnetron sputtering process (RFMS), applied as an encapsulation of flexible electronics such as organic photovoltaics. The deposition of monolithic and amorphous AlON films through HiPIMS was investigated by varying the duty cycles from 5% to 20%. At an accelerated test condition, 60 °C, and 90% relative humidity, a 100 nm thick monolithic AlON film prepared using a duty cycle of 20% exhibited a low water vapor transmission rate (WVTR) of 0.0903 g m−2 day−1 after testing for 336 h. Furthermore, after introducing a nanocrystalline HfOx film through RFMS, a 214 nm thick AlON/HfOx bilayer film reached the lowest WVTR of 0.0126 g m−2 day−1.

Extraction of two-magnon scattering and detection of inverse spin Hall effect up to 40 GHz in low-damping Fe65Co35/Pt bilayer thin film

Abstract We report an investigation of the inverse spin Hall effect (ISHE), as a measure of the pure spin current (J S ), induced by spin pumping in a Fe65Co35/Pt bilayer using coplanar waveguide ferromagnetic resonance (CPW-FMR) in the in-plane (IP) geometry over the broadband microwave frequency range of 8–40 GHz. From the IP-FMR measurements, the defect-induced two-magnon scattering (TMS) contribution is evaluated by analyzing the frequency dependence of FMR linewidth using Arias and Mills approach [Arias R and Mills D L (1999 Phys. Rev. B 60, 7395), Mills D L and Arias R (2006 Physica B 384 147–151)]. Here, we have determined a very low Gilbert damping constant (α G ) for Fe65Co35 bare film around 1.3 × 10−3, which is essential for the high spin current (>107 A/m2) generation. The enhanced value of α G ≈3.2 × 10−3 obtained for Fe65Co35/Pt bilayer film is due to spin pumping damping, α SP = 1.9 × 10−3, confirmed by the ISHE induced DC voltage (V DC ) signal measured across the edges of Pt layer. Out-of-plane (OP) angular ISHE measurements have been performed to disentangle spin pumping from spin rectification effects in the V DC signal. Further, we evaluated the effective spin-mixing conductance g eff ↑ ↓ = 3.33 × 1019 m−2, which is higher than the values reported in FeCo-alloy-based bilayer systems. The present study aims to detect the J S injected by low-damping Fe65Co35 thin films, leading to the realization of energy-efficient spintronic devices.

Daytime radiative cooling using pattern free metal dielectric coating

Radiative coolers, which dumps the excess heat to the cold outer space by releasing the thermal radiation through the atmospheric window, have offered an alternate and feasible solution to the conventional coolers that are fueled on the electricity produced by either using renewal or non-renewal sources like fossil fuels. Particularly, daytime passive radiative coolers have paved the way for many energy free technology that are used in reducing the temperature of building tops, power plants, and water harvesting. In this, we propose a pattern free and large area scalable bi-layered thin film based daytime radiative cooler. The proposed design illustrates an average reflectivity of 98.5% for the solar spectrum, while showing average emittance of 91% within the atmospheric window (8-13μm). The design consists of thin films of transparent dielectrics such as ZnS or BaF2 placed on top of a thick glass substrate, that is backed by a thin film silver. We theoretically obtained a cooling power of 119 W.m−2 with a temperature reduction of 9 °C below the ambient.

Recyclable Chitosan-Modified Cellulose Fiber Porous Structure for Sensitive and Robust Moisture-Driven Actuators and Automatic Cooling Textiles.

Moisture-driven actuators featuring programmable stimuli-responsiveness and a rapid response have garnered substantial research attention. Cellulose-based actuators face challenges, including prolonged and unstable responsiveness, along with inadequate interfacial bonding. Herein, we developed a bilayer structured moisture actuator by integrating multiscale cellulose fibers with chitosan. The protonated chitosan forms strong electrostatic attractions with negatively charged cellulose nanofibrils (CNF), achieving a robust interfacial interaction. Leveraging the hierarchically porous structure and varying hygroscopicity of microfibrillated cellulose (MFC) and CNF, the film establishes an effective wettability gradient, enabling a stable and rapid moisture actuation performance. The bilayer film exhibits large deformation toward moisture with a bending angle of 60°, a short response time of 12 s, good stability over 50 wetting and drying cycles, and promising recyclability. Harnessing these advantageous properties, the bilayer film was demonstrated for its applications in automatic cooling textiles, contactless electrical switches, and artificial moisture-activated muscles, showing great potential for practical use.

Stretching and Bending Moduli of Bilayer Films Inferred from Wrinkle Patterns

Stretching and Bending Moduli of Bilayer Films Inferred from Wrinkle Patterns

Thickness dependence on dynamical spin injection driven by thermal effects in CoFeB/Pt bilayer

In ferromagnetic metal (FM)/non-magnetic metal (NM) bilayer structures, dynamical spin injection is primarily attributed to spin pumping at the interface. However, thermal effects, such as the spin (dependent) Seebeck effect (S(d)SE) caused by FMR heating effect, are also expected to contribute, particularly farther from the interface within the FM layer. In this study, the detailed mechanism of dynamical spin injection in CoFeB/Pt bilayer films has been investigated. We demonstrate the proper evaluation of the CoFeB thickness dependence of inverse spin Hall voltage by subtracting the signal from single CoFeB system. The dynamical spin injection and FMR heating effect were observed to significantly depend on thickness. Additionally, we separated the contributions of SSE and SdSE by focusing on their diffusion properties and found that SSE is larger than SdSE in the CoFeB/Pt bilayer film.

Controlled Assembly of Lipid Molecules via Regulating Transient Spatial Confinement

The constructs of lipid molecules follow self-assembly, driven by intermolecular interactions, forming stacking of lipid bilayer films. Achieving designed geometry at nano- to micro-levels with packing deviating from the near-equilibrium structure is difficult to achieve due to the strong tendency of lipid molecules to self-assemble. Using ultrasmall (<fL) droplets containing designed molecules, our prior work has demonstrated that molecular assembly, in principle, is governed mainly by transient inter-molecular interactions under their dynamic spatial confinement, i.e., tri-phase boundaries during drying. As a result, the assemblies can deviate, sometimes significantly, from the near-equilibrium structures of self-assembly. The present work applies the approach and concept to lipid molecules using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Taking advantage of the high spatial precision and the minute size of the delivery probe in our combined atomic force microscopy and microfluidic delivery, the transient shape of each liquid droplet is regulated. In doing so, the final geometry of the POPC assemblies has been regulated to the designed geometry with nanometer precision. The results extend the concept of controlled assembly of molecules to amphiphilic systems. The outcomes exhibit high potential in lipid-based biomaterial science and biodevice engineering.

Tunable MXene/WO3 Fabry−Pérot Microcavity Architecture for Bioinspired Soft Electrochromic Actuators with Vivid Colors

AbstractInspired by stimuli‐responsive creatures in nature, developing devices with synergistic color change and deformation will be of great value for realizing the adaptive variants. Yet, integrating adaptive color variation and deformation into a single device remains elusive. Herein, an intriguing electrochromic actuator based on MXene/WO3 bilayer film is developed with Fabry−Pérot (F–P) microcavity, which successfully integrates both functions of reversible deformation and vivid color variations into the same device. Upon applying a small electric field, the ion intercalation/de‐intercalation can synchronously alter the stress distribution and optical absorption of MXene/WO3, resulting in the dual response of electrochromic phenomenon and ultra‐fast deformation with a maximum angle of 95° within 10 s. Moreover, the F–P microcavity architecture with the physical light interaction additionally endows the bilayer film with a bright color gamut and high color tunability (yellow–green, purple, pink, blue, etc.). Furthermore, an asymmetric soft actuator based on MXene/WO3 bilayer film is assembled, which displays robust grasping ability and excellent cycling stability up to 1000 cycles. These findings may open new opportunities for somatosensory soft robots and next‐generation intelligent robots.

Enhanced Energy Density and Charge–Discharge Efficiency of the Bilayer Film over a Broad Temperature Range

Enhanced Energy Density and Charge–Discharge Efficiency of the Bilayer Film over a Broad Temperature Range

Impact of environmental storage conditions on properties and stability of a smart bilayer film

This study aimed to investigate the behavior of smart bilayer films under various temperature and relative humidity (RH). Smart bilayer films were fabricated using sodium alginate with incorporated butterfly pea anthocyanin and agar containing catechin–lysozyme. Cellulose nanospheres were added at concentrations of 0% and 10% w/w of the film and subjected to test at 4 °C and 25 °C, considering different RHs (0%, 50%, and 80%). The results showed that RH had a greater impact on the mechanical properties than temperature, leading to a decrease in tensile strength and an increase in elongation at break with higher RH. The films displayed increased strength but reduced flexibility at low temperatures. Oxygen permeability was negatively affected by increasing RH, while water vapor barrier properties were better at 25 °C than at 4 °C. In terms of color stability, the temperature played a more important role, with both types of smart bilayer films retaining their color stability throughout 14-day storage at 4 °C, even maintaining their ability to change color with pH. However, the films stored at 25 °C exhibited lower color stability and showed potential for color change with varying pH levels, but with lower intensity. The findings of this study demonstrate the significant impact of temperature and RH on the functional properties of smart bilayer films, with and without the addition of cellulose nanospheres. Such smart bilayer films have great potential for various applications, particularly in food packaging, where maintaining color, mechanical, and barrier properties under varying environmental conditions is crucial.

Development of apple pectin/chitosan-based active films integrated with apple polyphenol/hydroxypropyl-β-cyclodextrin inclusion complex for pork preservation

Sustainable bio-based active films are promising alternative materials that can alleviate the growing environmental problems. Apple processing generates a large number of by-products rich in pectin and polyphenols. Herein, we extracted apple pectin (Apec) from apple pomace, developed a multifunctional bilayer film based on Apec and chitosan by incorporating inclusion complex of apple polyphenol and hydroxypropyl-β-cyclodextrin (ICAH). The results showed that the incorporation of ICAH remarkably improved the mechanical strength, barrier properties, and the thermal stability of the films. Meanwhile, the composite films loaded with ICAH exhibited potent antioxidant and antibacterial activities in vitro. Furthermore, a 7-day shelf-life analysis on fresh pork verified that the films were effective in maintaining the pH level (below 6.0), reducing the thiobarbituric acid reactive substance (from 1.18 to 0.63 mg MDA/kg) and total volatile basic nitrogen (from 23.27 to 14.03 mg/100 g), and inhibiting the microbial growth (from 6.83 to 3.74 log CFU/g), thereby obtaining a satisfactory sensory evaluation. The pork wrapped with the films can significantly extend the period of freshness from 4 days to 7 days under refrigeration at 4 °C. The results suggest that the prepared composite films hold promise as an active packaging material for application in pork preservation.

Harnessing the potential of electrospun TiO2 nanofibers and nanoparticles enriched with natural dyes: a path towards affordable aolutions for low-cost electronic devices

Abstract This study evaluates the morphological effects of TiO2 nanoparticles, nanofibers, and a bilayer configuration on electronic devices, such as Dye-Sensitized Solar Cells (DSSCs) and UV sensors. Cost-efficient natural dyes—curcumin, coffee beans, and banana peel—were used as sensitizers for nanomaterial films. TiO2 nanoparticles were synthesized using the sol–gel technique, while nanofibers were produced via electrospinning. Characterization techniques, including Scanning Electron Microscopy (SEM), Energy Dispersive x-ray Spectroscopy (EDS), and x-ray Diffraction (XRD), confirmed the formation and dimensions of the TiO2 nanostructures. UV–visible spectroscopy was used to determine the optical properties of the samples. TiO2 nanofibers and nanoparticles exhibited high surface-area-to-volume ratios, with nanofibers having a diameter of 20 nm and particles measuring 50 nm. A binder-free, low-temperature paste was prepared using TiO2 nanoparticles and nanofibers to develop thin films. The turmeric dye showed peak absorption at 470 nm with a band gap energy of 2.06 eV when loaded on a TiO2 bilayer film. This study aims to develop electronic devices that reduce costs and enhance performance by using low-cost, efficient, and economically viable dyes. TiO2 nanofiber and nanoparticle films show promise for cost-effective and high-performance electronic devices.

Improving TFT Device Performance by Changing the Thickness of the LZTO/ZTO Dual Active Layer.

The primary objective of this research paper is to explore strategies for enhancing the electrical performance of dual active layer thin film transistors (TFTs) utilizing LZTO/ZTO as the bilayer architecture. By systematically adjusting the thickness of the active layers, we achieved significant improvements in the performance of the LZTO/ZTO TFTs. An XPS analysis was performed to elucidate the impact of the varying O2 element distribution ratio within the LZTO/ZTO bilayer thin film on the TFTs performance, which was directly influenced by the modification in the active layer thickness. Furthermore, we utilized atomic force microscopy to analyze the effect of altering the active layer thickness on the surface roughness of the LZTO/ZTO bilayer film and the impact of this roughness on the TFTs electrical performance. Through the optimization of the ZTO active layer thickness, the LZTO/ZTO TFT exhibited an mobility of 10.26 cm2 V-1 s-1 and a switching current ratio of 5.7 × 107, thus highlighting the effectiveness of our approach in enhancing the electrical characteristics of the TFT device.

Inverse-proximity effect and 2D superconductivity of Ta/Au bilayer thin films

This study investigated the inverse-proximity effect (IPE) and two-dimensional (2D) superconductivity in α-phase Ta films and Ta/Au bilayers. These bilayers were deposited onto silicon substrates using a direct current (DC) sputtering system. The findings reveal that higher substrate temperatures and increased film thickness facilitate the formation of α-Ta up to a temperature limit of 300°C, resulting in higher Tc around 3.5–3.7 K. The fundamental superconductivity of α-Ta thin films is similar to that of a conventional s-wave BCS superconductor. The IPE in the Ta/Au bilayer films was observed, where the Tc increases and decreases with the Au overlayer thickness. This behavior was quantitatively described by considering a model accounting for the reduced superconducting fluctuations induced by the highly conductive Au layer. Furthermore, the presence of 2D superconductivity in the Ta film and Ta/Au bilayer was examined through critical field analysis, vortex motions, and Berezinskii-Kosterlitz-Thouless (BKT) transition detection. Finally, the results were summarized in an H-T phase diagram illustrating the presence of IPE and 2D superconductivity in a Ta/Au bilayer. This study provides additional insights into 2D superconductivity within normal/superconductor (N/S) bilayers, laying the groundwork for future research to optimize film properties to align more closely with theoretical expectations.

The Preparation and Characterization of an Alginate–Chitosan-Active Bilayer Film Incorporated with Asparagus (Asparagus officinalis L.) Residue Extract

The agricultural production of asparagus generates a significant number of residues rich in bioactive compounds, most of which are wasted. In this study, active edible films with antioxidant and antibacterial properties for food packaging were developed using ethanolic extracts obtained from asparagus residues. These ethanolic extracts of asparagus residue (AspE) were incorporated (1 y 4 wt%) into sodium alginate (SA) solutions for the preparation of alginate–chitosan (SA/CS) bilayer films using the casting method, and they were characterized by optical, structural, mechanical, and thermal properties. In addition, the total phenolic and flavonoid content, antioxidant activity, and antibacterial activity were determined. The results showed that the SA/CS film with 1% AspE had better optical, structural, mechanical, and thermal properties due to its color, flexibility, and homogeneity. Both films incorporated with AspE exhibited antioxidant and antibacterial activity, with higher activity in the film with 4% AspE. However, this film showed shrinkage and surface irregularities that make its application in food packaging difficult, so the formulation with 1% AspE was considered better for this type of application. This study shows that asparagus residues can be a valuable source of bioactive compounds for the food industry, indicating the potential for the valorization of this agri-food waste.

Bimetallic AgCo Nanoparticle Synthesis via Combinatorial Nanosecond Laser‐Induced Dewetting of Thin Films

Herein, a combinatorial approach is developed to conduct high‐throughput studies on the nanosecond pulsed laser‐induced dewetting phenomenon of bilayer Ag–Co metallic thin films. Laser irradiation results in the spontaneous rupture of these films in nanosecond timescale, forming bimetallic nanoparticles (NPs) through intermediate stages of hole formation and bicontinuous nanostructures. This approach utilizes bilayer thin films with thickness gradients in both Ag and Co layers (referred to as bigradient samples) while maintaining a constant overall thickness. The laser irradiation on such bigradient bilayer films facilitates control on Ag and Co ratio in the thin films, thus enabling material libraries of Ag–Co NPs covering a large compositional variation. The evolution of NPs with a correlation between NP diameter and interparticle spacings is further studied. The study reveals monotonic increase in NP size and interparticle spacing in Co/Ag bilayer arrangement, while an increase and subsequent decrease in the NP size is observed at 50% Ag in Ag/Co bigradient films. A transition from intermediate stage hole formation to bicontinuous nanostructures with changing composition is also observed. These changes in intermediate stage morphologies and dewetting mechanism are attributed to variation of the free energy of the bilayer system dominated by intermolecular interaction forces.

Growth of [001]-oriented polycrystalline Heusler alloy thin films using [001]-textured Ag buffer layer on thermally oxidized Si substrate for spintronics applications

To utilize highly spin-polarized Heusler alloys in practical spintronic devices, the realization of highly textured and structurally ordered polycrystalline thin films under limited annealing temperatures (TA) is critical. Compared to the natural [110]-texture of Heusler alloys, the [001]-texture is considered to be favorable for current-perpendicular-to-plane giant magnetoresistance devices due to the reduced lattice misfit with the face-centered-cubic Ag spacer layers. In this study, we fabricated [001]-oriented polycrystalline Co2FeGa0.5Ge0.5 (CFGG) Heusler alloy films epitaxially grown on a [001]-oriented polycrystalline Ag buffer layer on a thermally oxidized Si substrate, and the microstructure of the [001]-oriented Ag/CFGG bilayer film was investigated in detail. The [001]-oriented Ag films were obtained by introducing N2 into Ar during the sputtering process. The [001]-oriented CFGG films exhibited smooth interfaces, B2 ordering, and a high saturation magnetization close to the theoretical value under relatively low annealing at TA = 300 °C, which are critical for industrial applications such as read heads of hard disk drives.

A high magnetic energy product obtained in hot-deformed Nd-Fe-B magnet by chemical plating Fe-Co bilayer films

This study investigates a novel method, chemical plating, with the goal of integrating nano-sized ferromagnetic materials into hot-deformed Nd-Fe-B magnets, potentially enhancing their magnetic properties. Coating Fe-Co double layers on Nd-Fe-B magnetic powder resulted in a significant improvement in the remanence over 10 %, increasing from 1.37 to 1.45 T, as well as an increase in the maximum magnetic energy product from 45.95 to 52.02 MGOe in hot-deformed Nd-Fe-B magnets. Microstructure observations revealed that the coarse non-oriented grains at the interface of powder ribbons were suppressed and the texture of grain alignment in the interior of powder ribbons was enhanced after the coating of Fe-Co. Additionally, there was a noticeable increase in the concentrations of ferromagnetic elements in intergranular phases. The reduced coarse grain regions, the enhanced grain alignment and the increased ferromagnetic intergranular phases are considered to be the main reasons for the enhancement of remanence and maximum magnetic energy product in hot-deformed magnets.

Development and characterization of bilayer chitosan/alginate cling film reinforced with essential oil based nanocomposite for red meat preservation

With a goal to finding suitable alternatives to plastic packaging in the food industry, we developed a multifunctional bio-based active packaging film to enhance the shelf life of red meat. A chitosan/alginate (Chi + Alg) bilayer film was developed through layer-by-layer (LBL) assembly and an active material i.e. lemongrass nanoemulsion with silver nanoparticles-based nanocomposite (NC1) was loaded into the alginate layer to improve the quality of the bio-based film (Chi + Alg + NC1). The Chi + Alg + NC1 film was characterized in terms of its microstructure, mechanical strength, thermal stability, and antimicrobial activity. Scanning electron microscopy (SEM) revealed a film (22.5 ± 1.44 μm thickness) with a smooth and even surface and a cross-sectional structure. The incorporation of NC1 improves the quality of the film by enhancing its mechanical strength and thermal stability. FT-IR spectra showed the successful interaction between chitosan and alginate in the LBL assembly and the incorporation of NC1 in the alginate layer. The red meat preservation test demonstrated that the shelf life improved when the meat was covered with the fabricated bio-based film. The color of the meat was retained for up to 7 days compared to that of the control (Chi alone and Chi + Alg). Additionally, a reduction in the microbial count in the Chi + Alg + NC1 film was observed, corroborating the shelf-life improvement. In addition to its inherent antimicrobial properties, NC1 induced hydrophilic properties to the film, which further aids in its antimicrobial activity against E. coli. These findings suggest that Chi + Alg + NC1 film could be a potent alternative to plastic packaging and can be used as a cling film to prolong the shelf life of red meat.