Bilayer Structure Research Articles

Micromagnetic modeling of SOT-MRAM dynamics

We present a flexible and efficient approach to modeling the magnetization dynamics in modern SOT-MRAM cells, by coupling charge, spin, and magnetization dynamics in a three-dimensional framework. We expand on existing literature, to obtain spin current boundary conditions for modeling the Rashba-Edelstein effect. We compute the spin–orbit torques originating from both, the spin Hall and Rashba-Edelstein effect, and show that our model can reproduce experimental results for the thickness dependence of the spin torques in an Ir/CoFeB bilayer structure. Furthermore, we verify our approach by simulating magnetization reversal in field-free SOT-MRAM cells, and show that with the inclusion of the interfacial Dzyaloshinskii–Moriya interaction, we obtain domain wall motion similar to previously reported experimental results.

Enhanced critical current density in optimized high-temperature superconducting bilayer thin films

The superconducting and structural properties of bilayer thin films based on YBa2Cu3O 7−x / YBa2Cu3O 7−x +6%BaZrO3 heterstructures have been studied. In a broad range of magnetic field strengths and temperatures, the optimal bilayer film comprises 30% YBCO at the substrate interface and 70% YBCO+6%BZO on the top. The critical current density measured for the optimal bilayer structure is shown to outperform the corresponding single layer films up to almost 60%. The obtained results are comprehensively discussed in the light of our previously published theoretical framework (Rivasto et al 2023 J. Phys.: Condens. Matter 35 075701:1–10). We conclude that the bilayering provides an efficient and easily applicable way to further increase the performance and applicability of high-temperature superconductors in various applications. Consequently, the bilayer films should be seriously considered as candidates for the upcoming generation of coated conductors.

Asymmetric disturbance and permeabilization of bilayer membranes by 3-nm carbon dots

Small-sized fluorescent carbon dots (CDs) are gaining increasing attention in the field of biomedical applications. The environmental and biological compatibility of positively charged CDs has been extensively investigated; however, the potential cytotoxicity caused by negatively and particularly neutrally charged small CDs has been significantly overlooked. In this study, we conducted a comprehensive investigation into the cellular membrane disruption effect of weakly negatively charged 3-nm CDs using a combination of various biophysical techniques. Our findings demonstrate that even at a low concentration of 0.5 μg mL−1, these CDs induce significant perturbations on the cellular membrane, resulting in increased membrane permeability due to asymmetric disruption of the bilayer structure. Furthermore, CDs exhibit distinct mechanisms at different concentrations, including prompt insertion into the bilayer at low concentrations (<20 μg mL−1) and a synergistic effect after a threshold time at high concentrations (e.g., 25–200 μg mL−1). Moreover, these CDs possess specific antibacterial properties against Acinetobacter baumannii (with a minimum inhibitory concentration of 50 μg mL−1) while showing minimal hemolytic or cytotoxic effects on mammalian cells. This study provides comprehensive insights into the biophysical aspects of cellular membrane toxicity caused by small weakly negatively charged CDs and contributes to assessing their potential biomedical applications.

A novel multilayer film based on sodium alginate/k-carrageenan-gelatin incorporated with ZnO nanoparticles and oregano essential oil for active food packing

Multi-layer active food packing films fabricated with outer layer made of sodium alginate (SA) and inner layer made of k-carrageenan (CAR) and gelatin (GEL) contained with oregano essential oil (OEO) and ZnO nanoparticles (ZnO NPs) were developed through layer-by-layer (LBL) assemble method and characterized in this study. The results of fourier transform infrared (FT-IR) demonstrated OEO, ZnO NPs and SA outer layers were successfully incorporated into the multi-layer film system by hydrogen bonding. ZnO NPs significantly improved the mechanical properties, thermal stability, UV resistance and retention of OEO of the films (P < 0.05). Scanning electron microscope (SEM) images clearly showed SA/CAR-GEL-OEO film and SA/CAR-GEL-OEO-ZnO NPs film had a bilayer structure. Noteworthy, the multi-layer films exhibited higher OEO retention compared to the mono-layer films, and compensated the negative effect of ZnO NPs and OEO on the light transmittance while enhancing the UV resistance of the films. The multi-layer films exhibited stronger antioxidant and antibacterial activity than mono-layer films. To summarize, the multi-layer films loaded with OEO and ZnO NPs enhanced antioxidant and antibacterial activities and displayed great potential as active packaging for food preservation.

Evidence for current suppression in superconductor–superconductor bilayers

Superconducting radio frequency (SRF) cavities, which are critical components in many particle accelerators, need to be operated in the Meissner state to avoid strong dissipation from magnetic vortices. For a defect-free superconductor, the maximum attainable magnetic field for operation is set by the superheating field, Bsh , which directly depends on the surface current. In heterostructures composed of different superconductors, the current in each layer depends not only on the properties of the individual material, but also on the electromagnetic response of the adjacent layers through boundary conditions at the interfaces. Three prototypical bilayers [ Nb1−xTixN (50nm)/Nb , Nb1−xTixN (80nm)/Nb , and, Nb1−xTixN (160nm)/Nb ] are investigated here by depth-resolved measurements of their Meissner screening profiles using low energy muon spin rotation (LE-µSR). From fits to a model based on London theory (with appropriate boundary and continuity conditions), a magnetic penetration depth for the thin Nb1−xTixN layers of λNb1−xTixN=182.5(31)nm is found, in good agreement with literature values for the bulk alloy. Using the measured λNb1−xTixN , the maximum vortex-free field, Bmax , of the superconductor-superconductor (SS) bilayer structure was estimated to be 610(40)mT . The strong suppression of the surface current in the Nb1−xTixN layer suggests an optimal thickness of ∼1.4λNb1−xTixN=261(14)nm.

Polar Polymorphism: A New Intermediate Structure toward the Thin-Film Phase in Asymmetric Benzothieno[3,2-b][1]-benzothiophene Derivatives.

Understanding structure and polymorphism is relevant for any organic device optimization, and it is of particular relevance in 7-decyl-2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) since high carrier mobility in Ph-BTBT-10 thin films has been linked to the structural transformation from the metastable thin-film phase to the thermodynamically stable bilayer structure via thermal annealing. We combine here a systematic nanoscale morphological analysis with local Kelvin probe force microcopy (KPFM) that demonstrates the formation of a polar polymorph in thin films as an intermediate structure for thicknesses lower than 20 nm. The polar structure develops with thickness a variable amount of structural defects in the form of individual flipped molecules (point defects) or sizable polar domains, and evolves toward the reported nonpolar thin-film phase. The direct experimental evidence is supported by electronic structure density functional theory calculations. The structure of the film has dramatic effects on the electronic properties, leading to a decrease in the film work function (by up to 1 eV) and a considerable broadening of the occupied molecular orbitals, attributed to electrostatic disorder. From an advanced characterization point of view, KPFM stands out as a valuable tool for evaluating electrostatic disorder and the conceivable emergence of polar polymorphs in organic thin films. The emergence of polar assemblies introduces a critical consideration for other asymmetric BTBT derivatives, which may be pivotal to understanding the structure-property relationships in organic field-effect transistors (OFETs). A precise determination of any polar assemblies close to the dielectric interface is critical for the judicious design and upgrading of high-performance OFETs.

Multifunctional hybrid T-PI-MPS composite coating: Corrosion resistance, low-wear/friction and heat-resistance

Despite methylphenylsiloxane (MPS) possesses heat-resistance and corrosion resistance, the brittleness hinders its widespread application. Herein, the polyimide (PI) and Ti3AlC2 were introduced for modifying MPS, thereby preparing the T-PI-MPS coating. The bilayer structure of surface-enriched MPS and internal-enriched PI was achieved by controlling the addition amount along with the density difference. The results indicate that the T-PI-MPS coating achieved a contact angle of 95.1° and exhibited corrosion resistance to salt spray for 28 days. Compared to PI-MPS, the wear rate of T-PI-MPS was reduced by 85 % and the friction coefficient declined from 0.75 to 0.58. As expected, T-PI-MPS exhibited exceptional excellent heat-resistance. The exceptional performance is attributed to the following three factors: I. the MPS-enriched layer is characterized by a stable SiO chain organization. This structure gives the corrosion resistance and water resistance, and prevents the hydrolytic swelling of PI. II. the PI-enriched layer is constructed from imide bonds, which give the coating superior friction performance due to its high load-bearing capacity. III. the incorporation of Ti3AlC2 plays a role in mitigating internal defects, prolonging the corrosion path, and inhibiting cracks due to its unique nanolayered structure, high temperature resistance, and hardness.

Nonlinear Optical Response Modulated by Lattice Reconstruction in Small‐Angle Twisted Bilayer MoS2

AbstractSubtle perturbations in interlayer twist angles offer a novel investigational avenue for revealing intriguing optical characteristics within the domain of 2D materials. In this study, a homogeneous bilayer structure featuring precisely defined interlayer twist angles is meticulously engineered by stacking monolayer single‐crystal MoS2 in a controlled, layer‐by‐layer manner. Scanning tunneling microscopy (STM) reveals an unexpected lattice reconstruction, particularly at twist angles of ≤ 2°, which induces the emergence of expansive rhombohedral‐stacked large triangular domains. Furthermore, a second‐harmonic generation (SHG) is utilized as a sensitive modality to demonstrate profound transformations in the local electron band structures. By combining the linear spectra with SHG, the change in the C‐exciton optical response in the band‐nesting region of the small‐angle twisted bilayer MoS2 before and after crossing a critical twist angle of 2° is discussed. The study shows that SHG can be used as a nondestructive method to characterize the lattice structure of small‐angle twisted bilayer samples. Furthermore, determining the potential relationship between the lattice reconstruction and the linear and nonlinear spectra further demonstrates the regulatory effect of the interlayer twist angle on the nonlinear optical effects of 2D materials.

Separating the Effects of Band Bending and Covalency in Hybrid Perovskite Oxide Electrocatalyst Bilayers for Water Electrolysis

Testing single crystalline epitaxial thin films as model systems for metal oxide electrocatalysts in the oxygen evolution reaction (OER) enables differentiating the OER descriptors such as crystal facet orientation, surface chemical composition, electronic structure and band bending at the interface to the electrolyte [1,2,3]. We designed single crystalline perovskite oxide bilayer structures to systematically tune the surface electronic structure and the band bending at the electrode/electrolyte interface to understand their role in the OER.The Co−O covalency in perovskite oxide cobaltites such as La1 − x SrxCoO3 is believed to impact the electrocatalytic activity during the OER. Additionally, space charge layers through band bending at the interface to the electrolyte may affect the electron transfer into the electrode, complicating the analysis and identification of true OER activity descriptors. Here, we separate the influence of covalency and band bending in hybrid epitaxial bilayer structures of highly OER-active La0.6Sr0.4CoO3 and undoped and less-active LaCoO3. Ultrathin LaCoO3 capping layers of 2−8 unit cells on La0.6Sr0.4CoO3 show intermediate OER activity between La0.6Sr0.4CoO3 and LaCoO3 evidently caused by the increased surface Co−O covalency compared to single LaCoO3 as detected by X-ray photoelectron spectroscopy. A Mott−Schottky analysis revealed low flat band potentials for different LaCoO3 capping layer thicknesses, indicating that no limiting extended space charge layer exists under OER conditions as all catalyst bilayer films exhibited hole accumulation at the surface [1].The combined X-ray photoelectron spectroscopy and Mott−Schottky analysis of atomically defined bilayer structures thus enables us to differentiate between the influence of the covalency and intrinsic space charge layers, which are indistinguishable in a single physical or electrochemical characterization. Our results emphasize the prominent role of transition metal oxygen covalency in perovskite electrocatalysts and introduce a bilayer approach to fine-tune the surface electronic structure [1].[1] L. Heymann, M. L. Weber, M. Wohlgemuth, M. Risch, R. Dittmann, C. Baeumer, F. Gunkel (2022) Separating the Effects of Band Bending and Covalency in Hybrid Perovskite Oxide Electrocatalyst Bilayers for Water Electrolysis, ACS Appl. Mater. Interfaces[2] M. Wohlgemuth, M. L. Weber, L. Heymann, C. Baeumer, F. Gunkel (2022) Activity-Stability Relationships in Oxide Electrocatalysts for Water Electrolysis, Front. Chem.[3] M. L. Weber, G. Lole, A. Kormanyos, A. Schwiers, L. Heymann, F. D. Speck, T. Meyer, R. Dittmann, S. Cherevko, C. Jooss, C. Baeumer, F. Gunkel, (2022) Atomistic Insights into Activation and Degradation of La0.6Sr0.4CoO3-δ Electrocatalysts under Oxygen Evolution Conditions Figure 1

Propagation and scattering of Rayleigh wave from an interfacial crack in a viscoelastic waveguide layer bonded to a piezoelectric substrate

In this article, the propagation and scattering of Rayleigh wave from an interfacial crack in a bilayer structure, a viscoelastic waveguide layer attached to a piezoelectric substrate, have been examined. The Principle of Superposition is used to formulate the problem. The Fourier transform method and stiffness matrix formulation have been used to arrive at singular integral equations. These singular integral equations are then reduced to a system of linear algebraic equations by applying the Gauss-Jacobi quadrature technique. A parametric study has been examined for phase velocity, attenuation, and dynamic stress intensity factor of mode-I and mode-II at both crack-tip.

Exploring Cyclic Peptide Nanotube Stability Across Diverse Lipid Bilayers and Unveiling Water Transport Dynamics.

Cyclic Peptide Nanotubes (CPNTs) have emerged as compelling candidates for various applications, particularly as nanochannels within lipid bilayers. In this study, the stability of two CPNTs, namely 8 × [(Cys-Gly-Met-Gly)2] and 8 × [(Gly-Leu)4], are comprehensively investigated across different lipid bilayers, including 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), a mixed model membrane (POPE/POPG), and a realistic yeast model membrane. The results demonstrate that both CPNTs maintain their tubular structures in all lipid bilayers, with [(Cys-Gly-Met-Gly)2] showing increased stability over an extended period in these lipid membranes. The insertion of CPNTs shows negligible impact on lipid bilayer properties, including area per lipid, volume per lipid, and bilayer thickness. The study demonstrates that the CPNT preserves its two-line water movement pattern within all the lipid membranes, reaffirming their potential as water channels. The MSD curves further reveal that the dynamics of water molecules inside the nanotube are similar for all the bilayer systems with minor differences that arise due to different lipid environments.

Transitioning Towards Asymmetric Gel Polymer Electrolytes for Lithium Batteries: Progress and Prospects

AbstractThe utilization of liquid electrolytes (LEs) concerns inevitable dendrite growth and safety issues. In contrast, solid polymer electrolytes suffer from unsettled low ionic conductivity and interfacial impedance issues. The intermediary gel polymer electrolytes (GPEs) improve safety by incorporating a sturdy polymer matrix and ionic conductivity as an advantage of percolating LEs responsible for gelation. The overall stability and compatibility of GPEs with different electrode materials depend on the polymers, plasticizers, and precursors utilized. No single polymer has a wide energy gap to exhibit stability against Li metal anodes and oxidative stability against high‐voltage cathodes. Thereafter, symmetric GPEs (SGPEs) possess limitations while simultaneously satisfying the two electrode requirements, which hinders their practical applications. Asymmetric GPEs (ASGPEs) generally comprise a bilayer or gradient structure, wherein the side contacting the cathode is modified to promote oxidative stability for a stable cathode electrolyte interface (CEI). The corresponding side in contact with the anode is modified to be mechanically and chemically compatible with dendritic lithium. Overall, asymmetric structural engineering enables electrode compatibility while maintaining the physical competency of GPEs. Herein, the focus is to summarize the current transition from SGPEs to asymmetric ones, which promotes multifunctionality while overcoming specific constraints associated with the electrodes.

Imaging of Light-Enhanced Extracellular Vesicle-Mediated Delivery of Oxaliplatin to Colorectal Cancer Cells via Laser Ablation, Inductively Coupled Plasma Mass Spectrometry.

Extracellular vesicles (EVs) are lipid bilayer structures released by all cells that mediate cell-to-cell communication via the transfer of bioactive cargo. Because of the natural origin of EVs, their efficient uptake by recipient cells, capacity to stabilize and transport biomolecules and their potential for cell/tissue targeting and preferential uptake by cancer cells, they have enormous potential for bioengineering into improved and targeted drug delivery systems. In this work, we investigated the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) as a tool to measure the loading of platinum-based chemotherapeutic agents. The EV loading of oxaliplatin via co-incubation was demonstrated, and LA-ICP-MS imaging showed greater efficiency of delivery to colorectal cancer cells compared to free oxaliplatin, leading to enhanced cytotoxic effect. Further, the impact of EV co-loading with a porphyrin (C5SHU, known as 'C5') photosensitizer on oxaliplatin delivery was assessed. Fluorescence analysis using nano-flow cytometry showed dose-dependent EV loading as well as a trend towards the loading of larger particles. Exposure of OXA-C5-EV-treated colorectal cancer cells to light indicated that delivery was enhanced by both light exposure and porphyrins, with a synergistic effect on cell viability observed between oxaliplatin, EVs and light exposure after the delivery of the co-loaded EVs. In summary, this work demonstrates the utility of LA-ICP-MS and mass spectrometry imaging in assessing the loading efficiency and cellular delivery of platinum-based therapeutics, which would also be suitable for agents containing other elements, confirms that EVs are more efficient at delivery compared to free drugs, and describes the use of light exposure in optimizing delivery and therapeutic effects of EV-mediated drug delivery both in combination and independently of porphyrin-based photosensitizers.

Observing coalescence of aluminum nanoparticles during burning using aluminum/ammonia perchlorate sandwiched films

To observe the agglomeration, an important parasitic process in metal composite combustion, sandwiched structures with laminates of aluminum (Al) and ammonia perchlorate (AP) layers are prepared and characterized by high-speed macro and microscopic imaging systems with pyrometry. The bilayer structure prepared by electrospraying was confirmed by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) and the composition was confirmed by thermogravimetric analysis/differential thermal calorimetry (TGA/DSC). We found that the burn rate of the Al/AP sandwich films increases with the decrease of bilayer thickness of Al and AP, owing to the shorter diffusion distance between fuel and oxidizer. More importantly, the complete process of the agglomeration/sintering of Al nanoparticles (NPs) is observed in-situ, which demonstrates the different stages of agglomeration process of Al NPs. Temperature measurement from pyrometry reveals the temperature of agglomerates during combustion, consistent with the agglomerate size and burn rate observation. Simple calculations based on “pocket-theory” support the observed changes in agglomeration size with bilayer thickness.

Highly ordered Si-based ZnO/Ag bilayer structure for recyclable SERS substrates with ultra-sensitivity

Compositing semiconductors with noble metal is considered as an effective strategy for improving SERS enhancement attributed to synergistic contribution of LSPR and CT mechanisms. In this work, highly ordered ZnO/Ag bilayer structures on p-type silicon wafers are prepared by photolithography and electrochemical self-assembly. The synergistic effect of EM and CT for SERS enhancement is identified by the Raman, PL spectra and 3D FDTD simulation. Flower-like Ag deposited on coarse ZnO films exhibits high SERS sensitivity. The ultra-low concentration of R6G molecules as low as 10−15 M can be detected, and the EF is estimated to be 8.08 × 1013. Due to the excellent photocatalytic property of ZnO, the bilayer structures possess steady and effective UV-cleaning performance. After being UV irradiated for 10 min, this SERS substrate can be re-used for many times. And the detecting RSD is about 4.11 %. The multi-functional ZnO/Ag bilayer structures with a wide direct bandgap has the prominent capacity to provide an efficient charge transfer path to possess trace detection ability for many probe molecules.

One-step preparation of bi-layer foamed glass-ceramics using asynchronous oxidization of SiC and B4C

Bi-layer foamed glass-ceramic has the advantages of both dense and foamed structure which lead to low bulk density and high mechanical strength. We propose a new one-step method to produce bi-layer foamed glass-ceramic using the asynchronous oxidization of B4C and SiC. The parent glass is prepared by melting-quenching method, followed by foaming through powder sintering route with addition of B4C and SiC. The bi-layer structure and formation of bi-layers are investigated by scanning electron microscope (SEM), X-ray computed tomography, 11B NMR, and high temperature melting observation system (HTMOS). The results show that during the sintering process, the oxidization of B4C in top layer at low temperature forms boron oxide and helps the formation of glass melt in the top layer. The oxidization of SiC at high temperature leads to foaming in the top layer. The prepared bi-layer foamed glass-ceramic has low bulk density of 1.06 g·cm−3 and high flexural strength of 26.15 MPa.

K2RbB8PO16: A Borophosphate with Moderate Birefringence and Deep-Ultraviolet Transmission.

A new borophosphate, K2RbB8PO16 (KRBPO) was synthesized. It exhibits a bilayer structure consisting of two B-O layers with an 18-membered ring (18-MR) joined by [PO4], which is composed of the π-conjugated group [BO3] and non-π-conjugated groups [BO4] and [PO4]. The UV-vis-NIR diffuse reflectance spectroscopy shows that the cutoff edge is less than 200 nm. The calculation indicates that KRBPO exhibits moderate birefringence of 0.057@1064 nm, and the source of birefringence is mainly from the [BO3] groups.

"Sweat-Driven" MXene Composites with Energy-Storage and Thermal-Management Multifunctions: A Platform for Versatile Electronic Skins.

Most exogenous electronic skins (e-skins) currently face challenges of complex structure and poor compatibility with the human body. Utilizing human secretions (e.g., sweat) to develop e-skins is an effective solution strategy. Here, a new kind of "sweat-driven" e-skin is proposed, which realizes energy-storage and thermal-management multifunctions. Through the layer-by-layer assembly of MXene-carbon nanotube (CNT) composite with paper, lightweight and versatile e-skins based on supercapacitors and actuators are fabricated. Long CNTs wrap and entangle MXene nanosheets, enhancing their long-distance conductivity. Furthermore, the CNT network overcomes the structural collapse of MXene in sweat, improving the energy-storage performance of e-skin. The "sweat-driven" all-in-one supercapacitor with a trilayer structure is patternable, which absorbs sweat as electrolyte and harnesses the ions therein to store energy, exhibiting an areal capacitance of 282.3 mF cm-2 and a high power density (2117.8 µW cm-2). The "sweat-driven" actuator with a bilayer structure can be driven by moisture (bending curvature of 0.9 cm-1) and sweat for personal thermal management. Therefore, the paper serves as a separator, actuating layer, patternable layer, sweat extractor, and reservoir. The "sweat-driven" MXene-CNT composite provides a platform for versatile e-skins, which achieve the interaction with humans and offer insights into the development of multifunctional wearable electronics.

Optically triggered AlGaN/GaN semiconductor power transistor with bi-layer anti-reflecting structure

Optically triggered AlGaN/GaN semiconductor power transistor with bi-layer anti-reflecting structure

Biomimetic Electronic Skin through Hierarchical Polymer Structural Design.

Human skin comprises multiple hierarchical layers that perform various functions such as protection, sensing, and structural support. Developing electronic skin (E-skin) with similar properties has broad implications in health monitoring, prosthetics, and soft robotics. While previous efforts have predominantly concentrated on sensory capabilities, this study introduces a hierarchical polymer system that not only structurally resembles the epidermis-dermis bilayer structure of skin but also encompasses sensing functions. The system comprises a polymeric hydrogel, representing the "dermis", and a superimposed nanoporous polymer film, forming the "epidermis". Within the film, interconnected nanoparticles mimic the arrangement of interlocked corneocytes within the epidermis. The fabrication process employs a robust in situ interfacial precipitation polymerization of specific water-soluble monomers that become insoluble during polymerization. This process yields a hybrid layer establishing a durable interface between the film and hydrogel. Beyond the structural mimicry, this hierarchical structure offers functionalities resembling human skin, which includes (1) water loss protection of hydrogel by tailoring the hydrophobicity of the upper polymer film; (2) tactile sensing capability via self-powered triboelectric nanogenerators; (3) built-in gold nanowire-based resistive sensor toward temperature and pressure sensing. This hierarchical polymeric approach represents a potent strategy to replicate both the structure and functions of human skin in synthetic designs.