Ultrathin Sheets Research Articles

Preparation of nanosphere-interspersed flower-like heterostructure of ZnS/ZnCo2S4@Ni(OH)2 and its application for asymmetric solid-state supercapacitor

Poor conductivity and easy aggregation of the two-dimensional Ni(OH)2 astrict their extensive applications in supercapacitors. In the current study, a nanosphere-interspersed flower-like heterostructure of ZnS/ZnCo2S4@Ni(OH)2 is successfully synthesized by exploiting high conductivity of ZnS/ZnCo2S4 nanosphere which are gown on the ultra-thin sheets of Ni(OH)2 via a solvothermal reaction. ZnS/ZnCo2S4@Ni(OH)2 electrode delivers a remarkable specific capacitance of 2276.9 F/g at 1 A/g, a considerable high-rate capability (1327.5 F/g at 15 A/g), and an excellent cycling stability (retention of 90.4 % at 15 A/g after 5000 cycles). The all-solid-state hybrid supercapacitor (HSC) device is constructed using ZnS/ZnCo2S4@Ni(OH)2 and active carbon as positive and negative electrode active material, respectively. Imposingly, the device manifests high operating potential of 1.6 V, large energy density of 61.4 Wh/kg at power density of 1.0 kW/kg, as well as good stability of 94.5 % retention after 10,000 cycles. This study provides insight into electro-active materials design and construction of heterostructures for high-performance supercapacitors.

Restoring Piezoelectric Properties in 2D Zinc Oxide Nanosheets by Surface Modifications: Implications for Piezoelectric Nanogenerators

Nanoelectronic devices that are self-powered through the conversion of mechanical energy into electronic energy are of great interest for the fields of wearables and medical implants. The ability to find nanomaterials that have piezoelectric properties suitable for nanogenerators can be a challenge. Zinc oxide (ZnO) is a well-known material that has one of the highest piezoelectric tensors among tetrahedrally bonded semiconductors, due to its buckled noncentrosymmetric structure on the (0001) and (0001̅)] surfaces. However, this piezoelectric response is diminished in few-layered two-dimensional (2D) ZnO, as it loses it buckled structure and becomes graphitic. As a consequence, ultrathin 2D ZnO sheets are not suitable for nanoscale devices that rely on a piezoelectric response. In this work, we show that defects, specifically, zinc and oxygen vacancies, and adsorbed oxygen, can restore the wurtzite structure and piezoelectric response of free standing 2D ZnO sheets at specific thicknesses. Using density functional theory calculations, we show that both a 1 monolayer (ML) surface coverage of oxygen and a 25% concentration of zinc vacancies can restore the buckling in few-layer 2D ZnO nanosheets. For a 1.48 nm thick sheet with a 25% Zn vacancy concentration, an e33 value of 1.26 C/m2 can be achieved, which is 120% enhancement compared to the bulk value. These findings provide a methodology for screening piezoelectric properties of other materials and demonstrate that defects can be used to restore the wurtzite structure and dielectric properties of ultrathin 2D ZnO sheets that would allow them to be used in nanoscale piezoelectric devices.

The modified GTN model for fracture of nickel-based superalloys considering size effect and healing effect in pulsed current assisted deformation

Gurson-Tvergaard-Needleman (GTN) model is one of the most famous and classical criterions widely used in modelling the ductile fracture process of metal. However, the existence of grain size effect affects the ductile fracture prediction in micro-scaled plastic deformation of nickel-based superalloy ultrathin sheet. In the pulsed current assisted (Pca) forming process, the current has a healing effect on the micro-void of metal due to the existence of local Joule heat, yet the strain has a promotion on the micro-void growth, and the coupled effect between grain size and electrical field is complicated, which makes it difficult to predict the fracture for the traditional GTN model in Pca forming process. To solve this problem, the authors added pulsed current parameters to the GTN model to describe the healing effect of pulsed current on the voids in the material. The parameters of the GTN model were calibrated by the finite element inverse identification method. The modified GTN model was embedded into Abaqus by VUMAT, and the Backward Euler algorithm was employed to integrate the constitutive equation. The validity of the model was verified by comparing the true stress-strain curves with the simulation results and comparing the void volume fraction (VVF) measured by three-dimensional X-ray computerized tomography (3DCT). The model provides a new method for ductile fracture prediction of multiphase alloys under a discontinuous energy field. Meanwhile, it is confirmed that the behaviour of fracture and necking in the Pca forming process is affected by the coupling effect of pulsed current and grain size effect, which provides a new idea for studying the Pca forming process.

Ultrathin Crystalline Silicon Nano and Micro Membranes with High Areal Density for Low-Cost Flexible Electronics.

Ultrathin crystalline silicon is widely used as an active material for high-performance, flexible, and stretchable electronics, from simple passive and active components to complex integrated circuits, due to its excellent electrical and mechanical properties. However, in contrast to conventional silicon wafer-based devices, ultrathin crystalline silicon-based electronics require an expensive and rather complicated fabrication process. Although silicon-on-insulator (SOI) wafers are commonly used to obtain a single layer of crystalline silicon, they are costly and difficult to process. Therefore, as an alternative to SOI wafers-based thin layers, here, a simple transfer method is proposed for printing ultrathin multiple crystalline silicon sheets with thicknesses between 300nm to 13µm and high areal density (>90%) from a single mother wafer. Theoretically, the silicon nano/micro membrane can be generated until the mother wafer is completely consumed. In addition, the electronic applications of silicon membranes are successfully demonstrated through the fabrication of a flexible solar cell and flexible NMOS transistor arrays.

Investigation on three-stage stamping of micro-channels with titanium ultra-thin sheet used for PEM fuel cell bipolar plates

Investigation on three-stage stamping of micro-channels with titanium ultra-thin sheet used for PEM fuel cell bipolar plates

Unique ion rectifier intermediate enabled by ultrathin vermiculite sheets for high-performance Zn metal anodes

Metallic Zn represents as a primary choice in fabricating various aqueous Zn-ion batteries (ZIBs), however challenging issues including dendrite growth and parasitic reactions at the anode/electrolyte interface, considerably hamper its practical implementation in large-scale energy storage. Herein, we report a low-cost multifunctional ion rectifier (IRT) as an artificial intermediate to reform Zn anode, which can practically eliminate the above issues. The hydrophobic shell (polyvinylidene difluoride) can suppress Zn interfacial corrosion with an inhibition efficiency of 94.8% by repelling water molecules from the bulk electrolyte. Additionally, negatively-charged ion channels inside the zincophilic core (ultrathin vermiculite sheets) induce de-solvating redistribution effect on Zn2+ ions flux, enabling a high ions transference number (0.79) for dendrite-free Zn deposition. This leads to exceptional Zn/Zn2+ reversibility in metallic Zn with IRT stabilization. The remarkable Coulombic efficiency (99.8%, 2000 cycles) for asymmetrical batteries, and a long lifespan (1600 h) with ultrahigh cumulative capacity of 2400 mAh cm−2 for symmetrical batteries, are successfully achieved. More encouragingly, the Zn//NH4V4O10 pouch cell retains 94.3% of its original capacity after 150 cycles at 1 A g−1. We believe that this low-cost and high-efficiency tactic could pave a promising path for anode surface modification.

Synthesis and Self-Assembly of Ultrathin Holey Graphdiyne Nanosheets for Oxygen Reduction Reaction.

Graphdiyne (GDY) is a fascinating graphene-like 2D carbon allotrope comprising sp and sp2 hybridized carbon atoms. However, GDY materials synthesized by solution-phase methods normally come as thick and porous films or amorphous powders with severely disordered stacking modes that obstruct macroscopic applications. Here, a facile and scalable synthesis of ultrathin holey graphdiyne (HGDY) nanosheets is reported via palladium/copper co-catalyzed homocoupling of 1,3,5-triethynylbenzene. The resulting freestanding 2D HGDY self-assembles into 3D foam-like networks which can in situ anchor clusters of palladium atoms on their surfaces. The Pd/HGDY hybrids exhibit high electrocatalytic activity and stability for the oxygen reduction reaction which outperforms that of Pt/C benchmark. Based on the ultrathin graphene-like sheets and their unique 3D interconnected macrostructures, Pd/HGDY holds great promise for practical electrochemical catalysis and energy-related applications.

Gas-phase microactuation using kinetically controlled surface states of ultrathin catalytic sheets

Biological systems convert chemical energy into mechanical work by using protein catalysts that assume kinetically controlled conformational states. Synthetic chemomechanical systems using chemical catalysis have been reported, but they are slow, require high temperatures to operate, or indirectly perform work by harnessing reaction products in liquids (e.g., heat or protons). Here, we introduce a bioinspired chemical strategy for gas-phase chemomechanical transduction that sequences the elementary steps of catalytic reactions on ultrathin (<10nm) platinum sheets to generate surface stresses that directly drive microactuation (bending radii of 700nm) at ambient conditions (T = 20°C; Ptotal = 1atm). When fueled by hydrogen gas and either oxygen or ozone gas, we show how kinetically controlled surface states of the catalyst can be exploited to achieve fast actuation (600ms/cycle) at 20°C. We also show that the approach can integrate photochemically controlled reactions and can be used to drive the reconfiguration of microhinges and complex origami- and kirigami-based microstructures.

Formation mechanism of texture in ultra-thin Fe Si alloy sheet with excellent medium frequency magnetic properties fabricated by multi-stage decarburizing and cold rolling

Formation mechanism of texture in ultra-thin Fe Si alloy sheet with excellent medium frequency magnetic properties fabricated by multi-stage decarburizing and cold rolling

Ultrasonic Vibration-Assisted Stamping of Serpentine Micro-Channel for Titanium Bipolar Plates Used in Proton-Exchange Membrane Fuel Cell.

Metallic bipolar plates (BPPs) are key components in the proton-exchange membrane fuel cell (PEMFC), which can replace traditional fossil fuels as a kind of clean energy. However, these kinds of plates, characterized by micro-channels with a high ratio between depth and width, are difficult to fabricate with an ultra-thin metallic sheet. Then, ultrasonic-vibration-assisted stamping is performed considering the acoustic softening effect. Additionally, the influence of various vibration parameters on the forming quality is analyzed. The experimental results show that ultrasonic vibration can obviously increase the channel depth. Among the vibration parameters, the vibration power has the maximum influence on the depth, the vibration interval time is the second, and the vibration duration time is the last. In addition, the rolling direction will affect the channel depth. When the micro-channels are parallel to the rolling direction, the depth of a micro-channel is the largest. This means that the developed ultrasonic-vibration-assisted stamping process is helpful for improving the forming limitation of micro-channels used for the bipolar plates in PEMFC.

Sequentially bridged MXene platelets for strong high‐temperature EM‐IR bi‐stealth sheets

AbstractCombination of flexible multifunctional stealth technology properties such as electromagnetic (EM) and infrared (IR) stealth is crucial to the development of aerospace, military, and electronic fields, but the synthesis technology still has a significant challenge. Herein, we have successfully designed and synthesized highly flexible MXene@cellulose lamellae/borate ion (MXCB) sheets with strong high‐temperature EM‐IR bi‐stealth through sequential bridging of hydrogen and covalent bonds. The resultant MXCB sheets display high conductivity and good mechanical features such as flexibility, stretchability, fatigue resistance, and ultrasonic damage. MXCB sheets have a high tensile strength of 795 MPa. Furthermore, MXCB sheets with different thicknesses indicate exceptional high‐temperature thermal‐camouflage characteristics. This reduces the radiation temperature of the target object (&gt;300 °C) to 100 °C. The conductivity of MXCB sheet with 3 μm thickness is 6108 S/cm and the EM interference (EMI) shielding value is 39.74 dB. The normalized surface‐specific EMI SE absolute shielding effectiveness (SSE/t) is as high as 39312.78 dB·cm2/g, which remained 99.39% even after 10,000 times repeated folding. These multifunctional ultrathin MXCB sheets can be arranged by vacuum‐assisted induction to develop EM‐IR bi‐stealth sheet.

N-doped/oxygen-deficient Fe2O3−x @PEDOT cruciform nanosheet arrays: Boosting the performance of all-solid-state flexible supercapacitors

As an ideal Faradaic anode material, Fe2O3 is expected to achieve high electrochemical performance in supercapacitors. However, the application of Fe2O3 in supercapacitors is limited by poor conductivity. In this study, first, we synthesized Fe2O3@Poly(3,4-ethylenedioxythiophene) (Fe2O3@PEDOT) composite cruciform nanosheet arrays via a one-step Fe3+-induced growth strategy. Fe2O3 nanoparticles were uniformly confined in ultrathin PEDOT sheets to enhance the dispersibility and conductivity of Fe2O3. Then, oxygen vacancies and nitrogen doping were introduced in Fe2O3 nanoparticles by plasma treatment (N-Fe2O3−x@PEDOT), which further enhanced the conductivity of Fe2O3 and increased the number of active sites. The engineered N-Fe2O3−x@PEDOT composites exhibited a high area capacitance of approximately 751 mF cm−2 at a current density of 1 mA cm−2 and approximately 103 mF cm−2 at 5 mV s−1 for a corresponding symmetric solid-state flexible supercapacitor with a capacitance retention of ∼60% after 5000 cycles.

Preparation of Thermally Conductive Silicone Rubber-Based Ultra-Thin Sheets with Low Thermal Resistance and High Mechanical Properties

Thermally conductive silicone rubber (TCSR)-based thin sheets with low thermal resistance and high electrical insulation properties have been widely used in thermal management applications in the electronic and energy storage fields. The low thermal resistance is mainly attributed to the sheets’ small thickness. In order to further decrease the sheets’ thermal resistance, it is necessary to decrease their thickness. However, the sheets mostly have a thickness of at least 0.20 mm, and it is still a challenge to decrease the thickness to less than 0.10 mm mainly due to the difficulty of smooth calendering through a narrow roll-to-roll gap on calenders. Here, a low-viscosity calendering method has been developed to prepare TCSR-based ultra-thin sheets. The sheets present unprecedentedly small thickness (~0.08 mm), low thermal resistance (0.87 cm2K/W), high tensile strength (~8 MPa), high flexibility, high electrical resistance (&gt;1014 Ω·cm), and high thermal dissipation (&gt;30 °C decrease in LED working temperature). Comparison studies between this new method and the conventional preparation method have been carried out to understand the mechanism of the improvements.

Ultrasonic resonance-based inspection of ultra-thin nickel sheets bonded to silicone

In the field of non-destructive testing (NDT), The detection of bonding defects between ultra-thin metal and silica gel is a difficult problem. In this study, In this study, ultrasonic resonance method was used to evaluate the bonding strength of ultra-thin metal to silica gel bonding structure. The composite parts of ultra-thin nickel sheet and silicon sheet with three different bonding states were studied. The bonding state of nickel sheet and silica gel is different, and the absorption of ultrasound is different. Using the resonance generated by high-frequency ultrasound in ultra-thin nickel sheet, the acoustic attenuation of the combination of ultra-thin nickel sheet and silicon rubber sheet was analyzed by resonance signal, and the bonding state between ultra-thin nickel sheet and silicon rubber sheet was characterized by bonding coefficient. Through experimental comparison, the results showed that the attenuation of ultrasonic signal in the nickel sheet and silicon film with different adhesive states characterize the adhesive state of ultra-thin nickel sheet and silicon film by the bonding coefficient, the bonding coefficient of good parts, weak adhesive parts and debonded parts is reduced successively. By setting an appropriate determination threshold value, the bonding state between the ultra-thin nickel sheet and the silicon film can be accurately determined according to the bonding coefficient obtained by detection.

Influence of α+β solution treatments on Ti65 ultrathin sheets: Silicide precipitation, mechanical behaviour and novel [formula omitted] twinning system

To cope with the urgent demands of the aerospace industry for lightweight and excellent high-temperature performance titanium alloy components, the microstructure evolution, silicide precipitation and mechanical behaviour of a novel high-temperature Ti65 titanium alloy ultrathin sheet with different heat treatments were systematically investigated. Submicron (Ti,Zr)6Si3 silicides are observed after solution treatments followed by air cooling, leading to a decline and significant fluctuations in tensile properties. For furnace cooling samples, (Ti,Zr)5Si3 silicide crossing grain boundaries and (Ti,Zr)6Si3 silicide near grain boundaries are observed after solution treatment at 950 °C. When the solution temperature increases to 1010 °C, the third silicide (Ti,Zr)3Si appears near dislocations. The combined effect of the strong size effect of the alloy ultrathin sheet and silicide precipitation results in great performance fluctuation, sharp drop of ductility and even brittle fracture. In addition, silicide precipitation differs little with various holding time during low-temperature solution treatment. Moreover, novel {101¯1} twins appear after the rolling process at 990 °C and are only inside coarse basal texture α grains, with an axis—angle pair of 65° 〈844¯3〉.

Ultra-Thin SSPP-Based Sheet for Suppressing Microwave Radiated Emission in SiP Modules

System-in-Package (SiP) has been facing the problem of excessive radiation leakage. In this article, a novel technique of absorptive sheet is proposed for suppressing unwanted microwave radiated emission in an advanced high-speed SiP module backed with a heat sink. Different from the conventional periodic resonant structure or absorptive film, the electromagnetic energy is consumed based on the mechanism of spoof surface plasmon polaritons (SSPP) in our design. By adjusting the length of the metallic strip to control its k-dispersion characteristics, the SSPP modes could be excited around one frequency point. Therefore, a relatively wide absorption band is created by arranging stepped strips in arrays on a dielectric medium. According to the electromagnetic distribution in the SiP module, SSPP-based absorptive units are circularly arranged to constitute the complete proposed absorptive sheet with adequate absorption efficiency. From the simulated results, the proposed design can provide 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> absorption performance covering a wide frequency range of 26.3–31.6 GHz, with a substrate thickness of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{L}$</tex-math></inline-formula> /228 and a total thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{L}$</tex-math></inline-formula> /134, where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{L}$</tex-math></inline-formula> is the wavelength at the lowest operating frequency. Finally, the proposed absorptive sheet is fabricated and measured, where measurement results agree well with the simulated ones, which corroborates the feasibility and effectiveness of applying the SSPP-based absorbing techniques for suppressing the radiated emission in microwave and millimeter-wave frequency range in SiP modules.

Real-Time Quality Monitoring of Ultrathin Sheets Edge Welding Based on Microvision Sensing and SOCIFS-SVM

Ultrathin sheets edge welding is a critical technology for aircraft, aerospace, or much high-end equipment manufacturing industrial applications. However, its online quality monitoring is still challenging due to the complicated and multicoupled transport phenomena in the mesoscale molten pool. This article presents an intelligent methodology for real-time monitoring of edge welds forming quality using microvision sensing and support vector machine based on swarm optimized and computationally inexpensive floating selection (SOCIFS-SVM). The clear images of the mesoscale molten pool are continuously acquired by using the passive microvision sensor. Based on the analysis for the dynamic behavior of the mesoscale molten pool and the morphology of the formed edge welds, a robust image processing procedure is developed to extract the single-frame spatial features and interframe correlation features from the microvision image sequence of the molten pool. A Kalman filter is applied to suppress the noise caused by the pulse current, etc. Then, the SOCIFS-SVM-based approach is established to predict three typical types of welding states. Experimental results with multiple groups of different welding parameters show that the proposed method can effectively and robustly identify the lack of fusion, humping, and sound weld with the highest accuracy of 96.09%. In addition, the established model can still achieve mean accuracy of 94.98% for additional untrained data, indicating that the model has strong generalization ability. The proposed real-time quality monitoring method makes online defect diagnosis of ultrathin sheets edge welding possible and provides a basis for online quality closed-loop control.

Mobile Trions in Electrically Tunable 2D Hybrid Perovskites.

2D hybrid perovskites are currently in the spotlight of material research for light-harvesting and -emitting applications. It remains extremely challenging, however, to externally control their optical response due to the difficulties of introducing electrical doping. Here, an approach of interfacing ultrathin sheets of perovskites with few-layer graphene and hexagonal boron nitride into gate-tunable, hybrid heterostructures, is demonstrated. It allows for bipolar, continuous tuning of light emission and absorption in 2D perovskites by electrically injecting carriers to densities as high as 1012 cm-2 . This reveals the emergence of both negatively and positively charged excitons, or trions, with binding energies up to 46meV, among the highest measured for 2D systems. Trions are shown to dominate light emission and propagate with mobilities reaching 200cm2 V-1 s-1 at elevated temperatures. The findings introduce the physics of interacting mixtures of optical and electrical excitations to the broad family of 2D inorganic-organic nanostructures. The presented strategy to electrically control the optical response of 2D perovskites highlights it as a promising material platform toward electrically modulated light-emitters, externally guided charged exciton currents, and exciton transistors based on layered, hybridsemiconductors.

Ag quantum dots decorated ultrathin g-C3N4 nanosheets for boosting degradation of pharmaceutical contaminants: Insight from interfacial electric field induced by local surface plasma resonance

The design of photocatalysts that can generate local surface plasmon resonance effect (LSPR) is expected to be an effective strategy for improving photocatalytic activity. However, the photocatalytic mechanism of interfacial electric field induced by quantum dot plasma is still unclear. Herein, different amount of Ag quantum dots was loaded on ultrathin carbon nitride sheets (Ag/UCN) to construct Schottky junction. The 1:1 Ag/UCN Schottky junction exhibits excellent photocatalytic activity in ofloxacin degradation with 95.2% removal, and is highly stable during four consecutive photocatalytic cycles. Ag/UCN can also effectively mineralize ofloxacin with 65.8% TOC removal, and NH4+, F− and NO3− were detected in the degradation solution of ofloxacin. Moreover, Ag/UCN shows high antibacterial activity and is effective in pharmaceutical wastewater treatment. The enhanced visible-light absorption of Ag/UCN nanocomposites is attributed to the LSPR effect of Ag quantum dots. Finite difference time domain (FDTD) simulations, density functional theory (DFT) calculations and surface potential confirm that the interfacial electric field drives the photogenerated carriers to cross the Schottky barrier, thus effectively accelerating the electron transfer rate at Ag/UCN interface. The photocatalytic mechanism of the interfacial electric field induced by LSPR effect was also revealed, which provides a new insight for design of LSPR-promoted photocatalyst with interfacial electric field induced by quantum dots.

Size effect on the cyclic deformation behavior of superalloy ultrathin sheet: Characterization and multiscale modelling

Superalloy ultrathin sheets have high strength, outstanding oxidation resistance, corrosion resistance and fatigue performance, and its thin-walled components occupy a considerable proportion in aeroengines. In the microforming process of aeroengine thin-walled components, the superalloy ultrathin sheet is often deformed under complex loading states and shows obvious springback. However, the forming and springback laws of superalloy ultrathin sheet in the microforming process are not clear and often affected by size effect. In addition, the existing nonlinear kinematic hardening models cannot accurately forecast the deformation and springback of superalloy ultrathin sheets. To address this issue, the cyclic shearing tests were performed to systemically explore the size effect on Bauschinger effect, permanent softening, transient hardening and work hardening stagnation of superalloy ultrathin sheets under cyclic loading states. The mechanism of size effect on cyclic mechanical response was systematically revealed through microstructure evolution combined with surface layer effect. In addition, a new multiscale cyclic hardening model was proposed based on the Y-U model and size effect on cyclic deformation behavior of superalloy ultrathin sheets. The new multiscale cyclic hardening model coupling surface layer effect and grain boundary strengthening effect was constructed by modeling the relationship between the cyclic mechanical response and size effect. Comparisons between the original Y-U model and the new proposed model on the characterization effect of shear stress-strain curves demonstrated that the proposed cyclic hardening model can accurately present the cyclic deformation behavior. To further verify the prediction capability of the proposed cyclic hardening model, the springback behavior of superalloy ultrathin sheet in U-bending test and hydroforming of seal ring was predicted via the proposed model combined with the decrease of elastic modulus and Yld2000–2d yield criterion, and the predicted results were compared with experimental ones. Comparative research revealed that the proposed cyclic hardening model can accurately describe the cyclic deformation behavior and springback of superalloy ultrathin sheets affected by size effect.