Ultrathin Bilayer Research Articles

Highly dispersive transmission conditions for a conductive rods-based ultrathin bilayer metastructure

We experimentally demonstrate that the transmission of microwave electromagnetic fields through a bilayer metasurface (BMS) composed of thin conductive rods can abruptly change in a narrow frequency range. A theoretical analysis based on the coupled oscillator model is performed to reveal the physical mechanism behind the frequency-dependent properties of such a structure. Two conditions primarily facilitate the observed high dispersion in the BMS. The first one is the resonant interaction between the incident microwaves and rods, leading to the formation of surface standing waves. These waves with radial electric fields enable the coupling of the near-field of rods in structural layers. The second condition is the complex value of the coupling coefficient between rods of different owing to the delayed interaction process between them. The electromagnetic response here can be effectively controlled by varying the distance between layers and the dielectric properties of the interlayer medium.

Biomimetic amniotic/silicone-based bilayer membrane for corneal tissue engineering

Amniotic membrane (AM) is an effective and widely used dressing in ocular injuries to reconstruct the cornea. Due to its low mechanical strength, high biodegradation rate, and difficult handling, its usage in medical interventions remains challenging. In this study, decellularized AM was covered with an ultrathin layer of Polydimethylsiloxane (PDMS) through a spinning method, which in turn resulted in an ultrathin (less than 80 µm in thickness) bilayer corneal wound dressing membrane with improved mechanical behavior and transparency. The biomechanical, biological, and antibacterial properties of the bilayer membranes were measured both in vitro and in vivo. The optimized microsized membrane was applied on a corneal defect wound created in a rabbit model to evaluate the corneal healing. The results demonstrated a significant decrease in degradation rate, improved mechanical properties, and AM/PDMS transparency compared with AM.Thecorneal transparency improved until 21 days post-surgery inAM/PDMS group. Histological evaluations revealed that AM/PDMS had better epithelial delaminated cell morphology. The results of the RT-PCR showed a significant increase in MMP9, a significant decrease in Col1A1, TGF-β1, TNF-α and IL-6 in both AM and AM/PDMS compared with control wounds. This study suggessts AM/PDMS membrane as an excellent corneal wound dressing.

Tip Growth of Quasi-Metallic Bilayer Graphene Nanoribbons with Armchair Chirality.

Graphene nanoribbons (GNRs), quasi one-dimensional (1D) narrow strips of graphene, have shown promise for high-performance nanoelectronics due to their exceptionally high carrier mobility and structurally tunable bandgaps. However, producing chirality-uniform GNRs on insulating substrates remains a big challenge. Here, we report the successful growth of bilayer GNRs with predominantly armchair chirality and ultranarrow widths (<5 nm) on insulating hexagonal boron nitride (h-BN) substrates using chemical vapor deposition (CVD). The growth of GNRs is catalyzed by transition metal nanoparticles, including Fe, Co, and Ni, through a unique tip-growth mechanism. Notably, GNRs catalyzed by Ni exhibit a high purity (97.3%) of armchair chirality. Electron transport measurements indicate that the ultrathin bilayer armchair GNRs exhibit quasi-metallic behavior. This quasi-metallicity is further supported by density functional theory (DFT) calculations, which reveal a significantly reduced bandgap in bilayer armchair GNRs. The chirality-specific GNRs reported here offer promising advancements for the application of graphene in nanoelectronics.

A-IGZO thin-film transistors with transparent ultrathin Al/Ag bilayer source and drain for active neural interfaces

Electro-optical neural interface technologies based on transparent electronics have been developed to take advantage of both high spatial resolution of optical cellular imaging by microscopes and high temporal resolution of electrical neural recordings. Recently, active-matrix systems based on amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) have been suggested for high-density electrical neural recordings owing to the high mobility and optical transparency of the IGZO. However, conventional metallic source and drain electrodes forming ohmic contacts with the a-IGZO are the limiting factors of the overall system transparency because the electrodes have substantial portions in the TFT structures. In this work, we propose an ultrathin metal bilayer as the transparent source and drain electrodes of the a-IGZO TFTs for fully transparent TFT-based electro-optical neural interfaces. The ultrathin metal bilayer electrodes consist of 2.5–4.5 nm-thick aluminum as a seed layer and 8 nm-thick silver. The ultrathin Al/Ag bilayer suppressed localized surface plasmonic resonance, showing 40–70% of transmittance in the range of 350–700 nm and thus allowing us to observe cultured neurons through the transparent electrodes. We also confirmed that the ultrathin Al/Ag electrodes form decent ohmic contacts to the IGZO, showing width-normalized contact resistance of 2.9 kΩ-cm which is similar to the previously reported other transparent S/D electrodes. The a-IGZO TFTs with the ultrathin Al/Ag showed the highest linear mobility of 3.9 cm2/Vs of in long channels and 0.2–0.64 cm2/Vs in short channels. The gate-bias normalized cut-off frequency was 8–26 kHz/V at Lch = 20 μm, which would be sufficient for recording a wide range of neural signals.

Efficient solid-state infrared-to-visible photon upconversion on atomically thin monolayer semiconductors.

Upconverting infrared light into visible light via the triplet-triplet annihilation process in solid state is important for various applications including photovoltaics, photodetection, and bioimaging. Although inorganic semiconductors with broad absorption and negligible exchange energy loss have emerged as promising alternative to molecular sensitizers, currently, they have exclusively suffered from low efficiency and contained toxic elements in near-infrared (NIR)-to-visible upconversion. Here, we report an ultrathin bilayer film for NIR-to-visible upconversion based on atomically thin two-dimensional (2D) monolayer semiconductors. The atomic flatness and strong light absorption of 2D monolayer semiconductors enable ultrafast energy transfer and robust NIR-to-visible emission with a high upconversion quantum yield (1.1 ± 0.2%) at modest incident power (260 mW cm-2). Increasing layer thickness adversely quenches the upconversion emission, highlighting the 2D advantage. Considering the whole library of 2D semiconductors, the facile large-scale production and the ultrathin solid-state architecture open a new research field for solid-state upconversion applications.

A PECVD fabricated ultra-thin bilayer coating with superior corrosion resistance and low signal loss for high-frequency PCBs

Undesirable high thickness, terrible loss of high-frequency signal and poor adhesion of the traditional coating had plagued the anticorrosive field of high-frequency circuit boards (PCBs). Herein, a novel ultra-thin bilayer anticorrosive coating was manufactured. The initial Poly (butyl acrylate) coating (~30 nm) was firstly fabricated on the PCBs by plasma enhanced chemical vapor deposition (PECVD). Immediately, the Poly (dodecafluoroheptyl methacrylate) coating, as an external protective coating with low surface energy, was fabricated onto the initial Poly (butyl acrylate) coating via a similar approach. The bilayer anticorrosive coating showed the convex structure of bionic lotus leaf, which caused the water contact angle raised from 62.3° to 108.7°. After a 96-hour corrosion test, the circuit of the high-frequency PCBs with the coating (only 250 nm) can be perfectly protected. Simultaneously, the cross-cut test and molecular dynamics simulations showed the coating had an excellent interface adhesion with the PCB substrate. Importantly, compared with the commercial coating, the bilayer anticorrosive coating exhibited little signal loss over a wide frequency range, even up to 0.63 dB (250 nm, 20 GHz). This work provided clear guidance and a strong impetus for the development of corrosion-resistant coating for high-frequency PCBs.

Observation of multiple fractional quanta in a superconducting bilayer disk with a pinhole

The magnetic-flux quantum (Φ0) cannot be generally divided into smaller ones in a usual superconductor. If a subdividing path is present, the science and technology of the superconductor drastically change. In previous studies, we experimentally presented a new, easy way to subdivide Φ0 into smaller quanta (Φf) using an ultrathin Nb bilayer with a through-pinhole (H. Ishizu, H. Yamamori, S. Arisawa, K. Tokiwa, Y. Tanaka, Physica C 595 (2022) 1354029.). However, because of an experimental technical problem, we could not use a higher field to generate more than one Φf. It was not clear if multiples of Φf could be trapped in a pinhole (in a usual superconductor, multiples of Φ0 are trapped in a pinhole). In this study, we observed multiple fractional phase shifts with a direct-current superconducting interference device (SQUID) placed on an ultrathin Nb bilayer disk containing a through-pinhole using an improved modification of an experimental procedure. The phase shift for the SQUID with the bilayer disk is an integer multiple of a basic fractional phase shift divided by 2π. However, we did not observe the fractional phase shift for a SQUID with a single-layer disk. These observations indicate that multiple fractional flux quanta are trapped in the bilayer disk. According to the vortex-molecule model, if the vortex molecule is larger than the bilayer disk, such quanta can be trapped. This is one example of altering a fundamental (universal) physical constant. The SQUID can more sensitively detect Φf than Φ0, rendering the design of novel superconducting electronics possible.

A review on materials, advantages, and challenges in thin film based solid oxide fuel cells

In accomplishment of massive energy demand, the solid oxide fuel cells (SOFCs) have proven as apotheosis candidates due to their high energy conversion efficiencies, low pollution exhaust, fuel flexibility, and environmental friendliness which make these the most promising alternatives to conventional electricity generators. Despite numerous advantages of SOFCs, large-scale industrial applications are yet to be realized owing to their high operating temperatures (800°C-1000°C). To lower the operating temperature, it is crucial to minimize ionic resistances which can be accomplished by reducing the electrolyte thickness to lesser than 5 μm. Therefore, present article embraces a concise review on conventional materials, designs, and generations of SOFCs with their compatibility and drawbacks. The strengths and limitations of conventional and advanced tools for fabricating thin film based SOFCs (TF-SOFCs) as well as the associated properties of electrolytes and electrodes are thoroughly examined, and further route cast is provided to attain better performance. The present review encourages the development of TF-SOFCs using advanced techniques employing ultrathin single and bilayer electrolytes which can have potential to reduce the operating temperature of SOFCs from 450°C to 600°C region and pave the way for global commercialization.

Self-Rolled-Up Aluminum Nitride-Based 3D Architectures Enabled by Record-High Differential Stress.

Aluminum nitride (AlN) continues to kindle considerable interest in various microelectromechanical system (MEMS)-related fields because of its superior optical, mechanical, thermal, and piezoelectric properties. In this study, we use magnetron sputtering to tailor intrinsic stress in AlN thin films from highly compressive (-1200 MPa) to highly tensile (+700 MPa), with a differential stress of 1900 MPa. By monolithically combining the compressive and tensile ultrathin AlN bilayer membranes (20-60 nm) during deposition, perfectly curved three-dimensional (3D) architectures are spontaneously formed upon dry-releasing from the substrate via a 3D MEMS approach: the complementary metal-oxide-semiconductor (CMOS)-compatible strain-induced self-rolled-up membrane (S-RuM) method. The thermal stability of the AlN 3D architectures is examined, and the curvature of S-RuM microtubes and helical structures as a function of the cumulative membrane thickness and stress are characterized experimentally and simulated using a finite-element physiomechanic method. By combining AlN with various materials such as metal (Cu) and silicon nitride (SiNx), AlN-based hybrid S-RuM microtubes with diameters as small as ∼6 μm are demonstrated with a near-unity yield (∼99%). Compared with other stressed thin films for S-RuMs, including PECVD SiNx, magnetron-sputtered AlN-based S-RuMs show better structural controllability and versatility, probably due to the high Young's modulus and stress uniformity. This work establishes the sputtered AlN thin film as a superior stress-configurable S-RuM shell material for high-performance applications in miniaturizing and integrating electronic components beyond those based on other materials such as SiNx. In addition, for the first time, a single-crystal Al1-xScxN/AlN bilayer grown by molecular beam epitaxy is successfully rolled-up with the diameter varying from ∼9 to 14 μm, paving the way for 3D tubular Al1-xScxN piezoelectric devices.

Probing nanomotion of single bacteria with graphene drums.

Motion is a key characteristic of every form of life1. Even at the microscale, it has been reported that colonies of bacteria can generate nanomotion on mechanical cantilevers2, but the origin of these nanoscale vibrations has remained unresolved3,4. Here, we present a new technique using drums made of ultrathin bilayer graphene, where the nanomotion of single bacteria can be measured in its aqueous growth environment. A single Escherichia coli cell is found to generate random oscillations with amplitudes of up to 60 nm, exerting forces of up to 6 nN to its environment. Using mutant strains that differ by single gene deletions that affect motility, we are able to pinpoint the bacterial flagella as the main source of nanomotion. By real-time tracing of changes in nanomotion on administering antibiotics, we demonstrate that graphene drums can perform antibiotic susceptibility testing with single-cell sensitivity. These findings deepen our understanding of processes underlying cellular dynamics, and pave the way towards high-throughput and parallelized rapid screening of the effectiveness of antibiotics in bacterial infections with graphene devices.

Effect of substrate temperature on plasma-enhanced self-assembling formation of high-density FePt nanodots

We formed FePt magnetic nanodots (NDs) by exposing an ultrathin bilayer metal stack on ∼3.0 nm SiO2/Si(100) substrates to a remote H2 plasma (H2-RP) and studied the effect of external heating during the exposure to H2-RP on the formation and magnetic properties of NDs. The ultrathin bilayer with a uniform surface coverage drastically changed to NDs with an areal density as high as ∼3.5 × 1011 cm−2 by exposing to H2-RP with external heating. We also found that NDs formed by the exposure to H2-RP at 400 °C exhibited a perpendicular anisotropy with a perpendicular coercivity of ∼1.5 kOe, reflecting the magneto-crystalline anisotropy of (001)-oriented L10 phase FePt.

High Energy Density Solid State Lithium Metal Batteries Enabled by Sub-5 µm Solid Polymer Electrolytes.

Solid-state batteries (SSBs) are considered as the most promising next-generation high-energy-density energy storage devices due to their ability in addressing the safety concerns from organic electrolytes and enabling energy dense lithium anodes. To ensure the high energy density of SSBs, solid-state electrolytes (SSEs) are required to be thin and light-weight, and simultaneously offer a wide electrochemical window to pair with high-voltage cathodes. However, the decrease of SSE thickness and delicate structure may increase the cell safety risks, which is detrimental for the practical application of SSBs. Herein, to demonstrate a high-energy-density SSB with sufficient safety insurance, an ultrathin (4.2 µm) bilayer SSE with porous ceramic scaffold and double-layer Li+ -conducting polymer, is proposed. The fire-resistant and stiff ceramic scaffold improves the safety capability and mechanical strength of the composite SSE, and the bilayer polymer structure enhances the compatibility of Li metal anode and high-voltage cathodes. The 3D ceramic facilitates Li-ion conduction and regulates Li deposition. Thus, high energy density of 506Wh kg-1 and 1514Wh L-1 is achieved based on LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) cathodes with a low N/P ratio and long lifespan over 3000 h. High-energy-density anode-free cells are further demonstrated.

Effective method of forming and detecting a fractional magnetic flux quantum

We developed a minimal method of forming and detecting a fractional magnetic flux quantum in a two-component superconductor fabricated using an ultra-thin niobium bilayer that sandwiches a Josephson barrier. The fractional quantum created by cooling a bilayer disk in the magnetic field survived after turning off the magnetic field. The survived quantum was confirmed by the change in the critical current of a superconducting quantum interference device (SQUID) placed on the bilayer disk. By replacing a flux qubit with the SQUID, we can use the fractional flux quantum as the flux bias for the flux qubit. This method enables the investigation of fractional quantization and the related topology.

Ultrathin Heterogeneous Inorganic Solid Electrolyte Interphase for Dendrite-Free and Improved Lithium Battery Performance

Next-generation lithium metal batteries are expected to drive the practical applications that require high energy-density storage, such as, portable electronics and electric vehicles. However, the direct use of metallic lithium causes harsh safety issues, low-grade rate, and cycling performances due to unstable solid electrolyte interphase (SEI) and undesired lithium dendrite growth. Here, the ultrathin bilayer of graphite and SiO2 is deposited on Li foil (Graphite.SiO2@Li) using Radio Frequency (R-F) sputtering to address the inherent problem of lithium metal anode. The R-F sputtered electrodes can be cycled for more than 1300 h and 550 h at a current density of 0.5 mA cm-2 and 1 mA cm-2 respectively to reach a capacity of 1 mAh cm-2. Graphite.SiO2@Li anode coupled with Lithium titanate (LTO) and Lithium Nickel Cobalt Manganese oxide (NMC111) reaches higher capacity retention (96.78% and 98.57%) compared to bare Li (92.31% % and 82.73%) respectively. Higher capacity at higher rates and long stable cycling performances with low voltage hysteresis was achieved with the use of graphite.SiO2@Li anode. The graphite layer lowers the impedance, buffers the volume expansion issue, and helps to electrically connect the plated Li with the bulk Li electrode underneath. The higher electrolyte wettability of SiO2 provides much better Li-ion transportation, and ultrathin SiO2 film allows fast Li-ion diffusion and lithiation/delithiation to slow down the growth of Li dendrites. Besides, its high Young’s modulus form robust SEI, the insulating property of SiO2 blocks the electron transport, and chemical stability prevent side reaction with the liquid electrolyte.

Influence of polyethylene terephthalate/ polyamide (PET/PA) bilayer structure on physical and strength-related properties of superpressure angioplasty balloons.

Percutaneous transluminal coronary angioplasty (PTCA), including balloon angioplasty, is a standard clinical invasive treatment for coronary artery disease. The coronary lesion with calcification is difficult to dilate and the prevention of balloon failure is especially important. A novel superpressure balloon was fabricated with bilayered structure of polyethylene terephthalate (PET) and PA12 (polyamide). The structures of bilayer balloon were adjusted to achieve overall excellent performance. Physicochemical, thermal and mechanical properties of bilayer balloons were characterized by X-ray diffraction, differential scanning calorimeter, hydraulic tester and theoretical simulation. Compared with pure PA12 and PET balloons, PA12 outer layer: PET inner layer balloon with layer ratio of 3:7 shows the highest burst stress and relatively low compliance due to an increase in crystallinity and orientation. The produced bilayer balloon proved to possess a small folding dimension thanks to its ultrathin bilayer structure, which is good for crossing cramped vessels. We believe these optimally fabricated bilayer balloons are proved to provide attractive opportunities for preparation, performance enhancement, and practical applications of super-pressure balloon catheters and cryoablation balloons, that will significantly promote the development of percutaneous transluminal coronary angioplasty for clinical applications.

Direct band gap and strong Rashba effect in van der Waals heterostructures of InSe and Sb single layers

Van der Waals heterostructures formed by stacking different types of 2D materials are attracting increasing attention due to new emergent physical properties such as interlayer excitons. Recently synthesized atomically thin indium selenide (InSe) and antimony (Sb) individually exhibit interesting electronic properties such as high electron mobility in the former and high hole mobility in the latter. In this work, we present a first-principles investigation on the stability and electronic properties of ultrathin bilayer heterostructures composed of InSe and Sb single layers. The calculated electronic band structures reveal a direct band gap semiconducting nature of the InSe/Sb heterostructures independent of stacking pattern. Taking spin–orbit coupling (SOC) into account, we find a large Rashba spin splitting at the bottom of conduction band, which originates from the atomic SOC with the symmetry breaking in the heterostructure. The strength of the Rashba spin splitting can be tuned by applying in-plane biaxial strain or an out-of-plane external electric field. The presence of large Rashba spin splitting together with a suitable band gap in InSe/Sb bilayer heterostructures make them promising candidates for spin field-effect transistor and optoelectronic device applications.

High Efficiency Polarization‐Encoded Holograms with Ultrathin Bilayer Spin‐Decoupled Information Metasurfaces

AbstractInformation metasurfaces, including digital coding and programmable metasurfaces, have reformed the design theory of metasurfaces from effective medium to coding pattern, and bridged the physical and digital world. Metasurface hologram has shown great potential in imaging and manipulating electromagnetic waves. In this work, bilayer information metasurfaces are proposed to achieve polarization‐encoded holograms in microwave regime. The designed metasurfaces consist of 3‐bit spin‐decoupled meta‐atoms, which possess ultrathin profiles (0.14λ0) and high cross‐polarization transmittance (over 0.8). The incident wave, which is right‐handed circularly polarized or left‐handed circularly polarized, is encoded with code “0” or “1”. The spin‐decoupled design is combined with diffuse scattering and holographic technology. Based on this, a novel algorithm is proposed to generate coding sequences according to the code of incident wave, to achieve different functionalities for corresponding circularly polarized channels. In this way, polarization‐encoded holograms, including diffuse scattering holograms (code “00”), single channel holograms (code “01” or “10”), and spin‐selective holograms (code “11”), are achieved. Simulated and measured results show that the maximum imaging efficiency can reach up to 65.1%, verifying the high efficiency of this holographic technology. This work is expected to open a way of realizing more complicated and higher efficiency information metasurface holography.

R-F Sputtered Ultrathin Organic/Inorganic Bilayer for Dendrite Free Li Deposition

Lithium metal anodes have attracted great attention due to its high theoretical capacity and low redox potential. However, the notorious reactivity, uncontrolled solid electrolyte interphase (SEI) and undesired results in low battery performance and risk for safety concern. To resolve these problems, radio frequency (R-F) sputtered ultrathin bilayer of graphite and SiO2 ultrathin bilayer on a Li metal was demonstrated, for the first time, as an effective SEI layer. The graphite-SiO2 bilayer modified Li anode showed an improved capacity retention of 98.57% for lithium nickel cobalt manganese oxide cathode (NMC111) and 96.78% for lithium titanate (LTO), compared to bare Li anodes at 82.73% (NMC111) and 92.31% (LTO), respectively. Higher capacity, longer cycling stability and lower voltage hysteresis were obtained with the use of the graphite and SiO2 modified Li anode. Graphite acts as an electrical bridge between the plated Li and Li electrode, which lowers the impedance and buffers the volume expansion during Li plating/stripping. The addition of an ultrathin SiO2 layer facilitates Li diffusion and lithiation/delithiation, provides higher electrolyte affinity, higher chemical stability, and higher Young’s modulus to suppress the Li dendrite growth. This novel technique can open further pathways towards practical realization of use of lithium metal battery (LMB) in high energy density battery technologies such as Li-S and Li-air battery.

A superfast responsive and ultrathin self-constructed bilayer nanoarchitecture for automatic vertical orientation of liquid crystals

Ultrathin bilayer nanoarchitectures are structurally and functionally tunable yet robust, which are hierarchical building blocks with a wide range of applications from flexible displays to wearable optoelectronic devices. Here, we report an unprecedented cost-effective fabrication strategy to construct an ultrathin, superfast responsive, and highly durable bilayer nanoarchitecture for automatic vertical arrangement of liquid crystals (LCs) by using the spontaneous and cooperative self-construction of small mesogenic amphiphiles. The self-constructed bilayer nanoarchitecture is achieved by the simple doping and subsequent in situ self-assembly of a small amount of mesogenic amphiphiles in the confined cell geometry. It is experimentally demonstrated that an ultrathin and rough bilayer nanoarchitecture with vertical nanopillar array formed by surficial hydrogen bonding and cooperative π–π interaction of mesogenic amphiphiles enables an automatic vertical orientation of LC molecules to be realized during self-construction process. In addition, this simple approach provides a superfast responsive and highly reliable nanoarchitecture with a greatly enhanced electro-optical switching performance compared to conventional polyimide alignment layer. The ultrafast response time of 1.5 ms, which is more than ten times faster than that obtained from a conventional alignment layer, and low voltage driving achieving about 33% energy savings are accomplished by our method.

Integrating 2D/2D CdS/α-Fe2O3 ultrathin bilayer Z-scheme heterojunction with metallic β-NiS nanosheet-based ohmic-junction for efficient photocatalytic H2 evolution

Water splitting for hydrogen production on noble metal-free photocatalysts remains a big challenge. Herein, we present for the first time a 2-dimensional/2-dimensional (2D/2D) Z-scheme photocatalyst formed by in situ growing CdS nanosheets on α-Fe2O3 nanosheets. The former was additionally modified with metallic β-NiS cocatalyst, which creates a Ohmic-based heterojunction and functions as hydrogen-evolution sites. The resultant β-NiS-decorated CdS/α-Fe2O3 ultrathin 2D/2D heterojunction showed a remarkable hydrogen production rate of 45 mmol h−1 g−1 and a high quantum efficiency of 46.9 % at 420 nm. The excellent photocatalytic performance is attributed to: (1) intimate and large interfaces between CdS and α-Fe2O3 nanosheets for facilitated charge transfer, (2) promoted charge separation in the Z-scheme heterojunction, and (3) large quantity of Ohmic-junction hydrogen-evolution sites over metallic β-NiS cocatalyst. Overall, this work demonstrates a promising strategy for improving charge dynamics and hydrogen-production efficiency, through rational design and integration of multiple built-in electric fields over 2D semiconductor nanosheets.