Flexible perovskite light-emitting diodes for display applications and beyond

The flexible perovskite light-emitting diodes(FPeLEDs),which can be expediently integrated to portable and wearable devices,have shown great potential in various applications.The FPeLEDs inherit the unique optical properties of metal halide perovskites,such as tunable bandgap,narrow emission linewidth,high photoluminescence quantum yield,and particularly,the soft nature of lattice.At present,substantial efforts have been made for FPeLEDs with encouraging external quantum efficiency(EQE)of 24.5%.Herein,we summarize the recent progress in FPeLEDs,focusing on the strategy developed for perovskite emission layers and flexible electrodes to facilitate the optoelectrical and mechanical performance.In addition,we present relevant applications of FPeLEDs in displays and beyond.Finally,perspective toward the future development and applications of flexible PeLEDs are also discussed.

Machine Learning‑Enhanced Flexible Mechanical Sensing

To realize a hyperconnected smart society with high productivity,advances in flexible sensing technology are highly needed.Nowadays,flexible sensing technology has witnessed improvements in both the hardware performances of sensor devices and the data processing capabilities of the device’s software.Significant research efforts have been devoted to improving materials,sensing mechanism,and configurations of flexible sensing systems in a quest to fulfill the requirements of future technology.Meanwhile,advanced data analysis methods are being developed to extract useful information from increasingly complicated data collected by a single sensor or network of sensors.Machine learning(ML)as an important branch of artificial intelligence can efficiently handle such complex data,which can be multi-dimensional and multi-faceted,thus providing a powerful tool for easy interpretation of sensing data.In this review,the fundamental working mechanisms and common types of flexible mechanical sensors are firstly presented.Then how ML-assisted data interpretation improves the applications of flexible mechanical sensors and other closely-related sensors in various areas is elaborated,which includes health monitoring,human-machine interfaces,object/surface recognition,pressure prediction,and human posture/motion identification.Finally,the advantages,challenges,and future perspectives associated with the fusion of flexible mechanical sensing technology and ML algorithms are discussed.These will give significant insights to enable the advancement of next-generation artificial flexible mechanical sensing.

Deformable Catalytic Material Derived from Mechanical Flexibility for Hydrogen Evolution Reaction

Deformable catalytic material with excellent flexible structure is a new type of catalyst that has been applied in various chemical reactions,especially electrocatalytic hydrogen evolution reaction(HER).In recent years,deformable catalysts for HER have made great progress and would become a research hotspot.The catalytic activities of deformable catalysts could be adjustable by the strain engineering and surface reconfiguration.The surface curvature of flexible catalytic materials is closely related to the electrocatalytic HER properties.Here,firstly,we systematically summarized self-adaptive catalytic performance of deformable catalysts and various micro–nanostructures evolution in catalytic HER process.Secondly,a series of strategies to design highly active catalysts based on the mechanical flexibility of lowdimensional nanomaterials were summarized.Last but not least,we presented the challenges and prospects of the study of flexible and deformable micro–nanostructures of electrocatalysts,which would further deepen the understanding of catalytic mechanisms of deformable HER catalyst.

Controlled Twill Surface Structure Endowing Nanofiber Composite Membrane Excellent Electromagnetic Interference Shielding

Inspired by the Chinese Knotting weave structure,an electromagnetic interference(EMI)nanofiber composite membrane with a twill surface was prepared.Poly(vinyl alcohol-co-ethylene)(Pva-co-PE)nanofibers and twill nylon fabric were used as the matrix and filter templates,respectively.A Pva-co-PEMXene/silver nanowire(Pva-co-PE-MXene/AgNW,PM_(x)Ag)membrane was successfully prepared using a template method.When the MXene/AgNW content was only 7.4 wt%(PM_(7.4)Ag),the EMI shielding efficiency(SE)of the composite membrane with the oblique twill structure on the surface was 103.9 dB and the surface twill structure improved the EMI by 38.5%.This result was attributed to the pre-interference of the oblique twill structure in the direction of the incident EM wave,which enhanced the probability of the electromagnetic waves randomly colliding with the MXene nanosheets.Simultaneously,the internal reflection and ohmic and resonance losses were enhanced.The PM_(7.4)Ag membrane with the twill structure exhibited both an outstanding tensile strength of 22.8 MPa and EMI SE/t of 3925.2 dB cm^(-1).Moreover,the PM_(x)Ag nanocomposite membranes demonstrated an excellent thermal management performance,hydrophobicity,non-flammability,and performance stability,which was demonstrated by an EMI SE of 97.3%in a high-temperature environment of 140℃.The successful preparation of surface-twill composite membranes makes it difficult to achieve both a low filler content and a high EMI SE in electromagnetic shielding materials.This strategy provides a new approach for preparing thin membranes with excellent EMI properties.

Experimental Study on Mechanism and Shape Characteristics of Suspended Flexible Dam

Hydraulic structures such as groin, longitudinal dike and seawall are common in water conservancy and water transportation engineering projects at home and abroad, which have long been dominated by solid mass structural form. With brush and stone as building materials, this kind of structure has an obvious engineering effect. However, it not only requires huge capital investments, but also has negative impacts on the ecological environment. The suspended flexible dam is an innovative engineering measure, and few theoretical and experimental researches of this type dam can be found at present. This paper studies the mechanism and shape characteristics of this dam and obtains the dynamic equilibrium equation of flexible dam, the float buoyancy expression, and the condition for transformation among three forms of the underwater shape of the dam. The results are valuable in engineering application and can be used as the reference for the future work due to the distinctive design philosophy, the small negative effects on environment and the consistency for sustainable development.

High-areal-capacity/power lithium metal microbattery configuration based on the mechanically flexible,ultra-lightweight,nanocellulose framework

The ubiquitous implementation of integrated microelectronics requires the on-chip power sources featured with the lightweight configuration design,high areal-capacity-loadings as well as facile reaction kinetics that beyond the current available microbattery prototypes.Herein,this study constructs a mechanically flexible,nanocellulose fiber(NCF)reinforced microbattery configuration,which consists of metal-organic frameworks(ZIF-8)modified NCF as the separator(MOF@NCF),the carbonized MOF@NCF as the metallic deposition substrate(c-MOF@NCF)as well as gradient-structured LiFePO4 particles infiltrated in the NCF matrix(LFP@NCF)as the cathode.The film-stacked,integrated NCF-based microbattery prototype not only achieves the facile reaction kinetics with homogenized,dendrite-free Li metal deposition at high-capacity-loadings(2 mAh·cm^(-2)),but also eliminates the necessary use of metallic current collector to maximize the electroactive mass ratio,which therefore enables the high energy density of 6.8 mWh·cm^(-2)at the power output of 1.36 mW·cm^(-2)as well as the robust cyclability upon various geometric flexing states.This study presents a quantum leap towards the facile reaction kinetics and multi-scale interfacial stability for the flexible microbattery construction that based on the sustainable utilization of bio-scaffolds.

Mechanical robust and self-healing flexible perovskite solar cells with efficiency exceeding 23%

Flexible perovskite solar cells(f-PSCs) have experienced rapid advancements due to the light-weight, flexibility, and solution processability of the perovskite materials, which prompted the power conversion efficiency(PCE) to 24.08%. However, f-PSCs still face challenges in terms of mechanical and environmental stability. This is primarily due to their inherent brittleness, the presence of residual tensile strain, and the high density of defects along the boundaries of perovskite grains. To this end, we carefully developed a cross-linkable elastomers 3-[(3-acrylamidopropyl)dimethylammonium] propanoate(ADP) with electrostatic dynamic bond, which could be in-situ cross-linked and coordinate with [Pb I6]4-to regulate the crystallization process of perovskite. The cross-linked elastomers attached to the perovskite grain boundaries could release the remaining tensile strains and mechanical stresses, leading to enhanced stability and flexibility of the f-PSCs. More importantly, the electrostatic interaction between positive and negative groups of cross-linked elastomers and hydrogen bond formation between N–H and C=O accelerate the cross-linking of ADP, endowing the flexible perovskite films with self-healing ability under mild treating conditions(60 °C for 30 min). As a result, the device achieves a remarkable PCE of 23.53%(certified 23.16%). Additionally, the device exhibits impressive mechanical sustainability and durability, retaining over 90% of initial PCE even after undergoing8,000 bending cycles.

An Active Endoscopy Robotic System for Direct Tracheal Inspection

The development of active endoscopy techniques is one important area of medical robot.This paper designed a new flexible and active endoscopy robotic system for direct tracheal inspection.The mobile mechanism of the robot is based on the inchworm movement actuated by pneumatic rubber actuator.There are five air chambers controlled independently,by adjusting pressures in air chambers,the robot can move in a straight mode or in a bending mode.The inspection sensors and some therapy surgery tools can be equipped in the front of the robot.The prototype was made and its mechanical characteristics were analyzed.The robot could move smoothly in a small plastic tube,and the robot is respectable to be used for inspection in human trachea directly.

GHG emission reductions and costs to achieve Kyoto target

Emission projection and marginal abatement cost curves(MACs) are the central components of any assessment of future carbon market, such as CDM (clean development mechanism) potentials, carbon quota price etc. However, they are products of very complex, dynamic systems driven by forces like population growth, economic development, resource endowments, technology progress and so on. The modeling approaches for emission projection and MACs evaluation were summarized, and some major models and their results were compared. Accordingly, reduction and cost requirements to achieve the Kyoto target were estimated. It is concluded that Annex I Parties' total reduction requirements range from 503—1304 MtC with USA participation and decrease significantly to 140—612 MtC after USA's withdrawal. Total costs vary from 21—77 BUSD with USA and from 5—36 BUSD without USA if only domestic reduction actions are taken. The costs would sharply reduce while considering the three flexible mechanisms defined in the Kyoto Protocol with domestic actions' share in the all mitigation strategies drops to only 0—16%.

Multi-Scale Superhydrophobic Anti-Icing Coating for Wind Turbine Blades

As a surface functional material,super-hydrophobic coating has great application potential in wind turbine blade anti-icing,self-cleaning and drag reduction.In this study,ZnO and SiO2 multi-scale superhydrophobic coatings with mechanical flexibility were prepared by embedding modified ZnO and SiO2 nanoparticles in PDMS.The prepared coating has a higher static water contact angle(CA is 153°)and a lower rolling angle(SA is 3.3°),showing excellent super-hydrophobicity.Because of its excellent superhydrophobic ability and micro-nano structure,the coating has good anti-icing ability.Under the conditions of−10
C and 60%relative humidity,the coating can delay the freezing time by 1511S,which is 10.7 times slower than the normal freezing time.More importantly,due to the mechanical properties provided by SiO2 and the synergistic effect of micro-nano particles,the coating has excellent mechanical durability.After 10 wear tests,the contact angle of the coating is still as high as 141°and the rolling angle is 6.8°.This research provides a theoretical reference for the preparation of a mechanically stable coating with a simple preparation process,as well as a basic research on the anti-icing behavior of the coating.

Active Vibration Control of Macroscopically Smart Mechanisms

This paper presents an investigation on the active vibration control of flexible linkage mechanisms featuring piezoceramic actuators and strain gauge sensors. The dynamic equation of the macroscopically smart mechanism is decoupled by means of the complex mode theory. The state-space expression of the controlled system is developed, which includes the system noise and the observation noise. Moreover, a discrete linear quadratic Gaussian （LQG） state feedback controller and a discrete Kalman filter are designed separately. Finally, the proposed method is applied to the on-line vibration control of a macroscopically smart mechanism. The experimental results reveal that the strain amplitude of the flexible link ig suppressed by 80% and the dynamic performance of mechanism has been ameliorated significantly.

Molecular Ferroelastic Induced by Mono-/Double-Protonation Strategy

Molecular ferroelastics with the natural features of mechanical flexibility and switchable spontaneous strain have attracted widespread attention in the scientific community due to their potential applications in tunable gratings,flexible memorizers,strain sensors,and intelligent actuators.However,most designs of molecular ferroelastics remain in the stage of blind exploration,posing a challenge to achieve a functional ferroelastic more effectively.Herein,we have successfully obtained a molecular ferroelastic,[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2)(Me_(2)NH(CH_(2))_(2)NH_(3)=N,N-dimethylethylenediammonium),under the guidance of the mono-/double-protonation strategy.The_double-protonated[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2) undergoes a paraelastic-ferroelastic phase transition with the Aizu notation of 2/mFi at 322 K.Meanwhile,the theoretical calculation and experimental measurement simultaneously show that[Me_(2)NH(CH_(2))_(2)NH_(3)](ReO_(4))_(2) possesses good mechanical flexibility,because its elastic modulus(E)of 8.26 GPa and hardness(H)of 0.45 GPa are smaller than the average values of organic crystals(E of 12.05 GPa and H of 0.5 GPa),which makes it promising to apply in wearable pressure sensors,implantable medical sensors,high-precision tuners,etc.This work further enriches the molecular ferroelastic family and demonstrates that mono-/double-protonation is one of the effective molecular modification strategies for designing ferroelastics.

Two-dimensional materials:From mechanical properties to flexible mechanical sensors

Two-dimensional(2D)materials have great potential in the fields of flexible electronics and photoelectronic devices due to their unique properties derived by special structures.The study of the mechanical properties of 2D materials plays an important role in next-generation flexible mechanical electronic device applications.Unfortunately,traditional experiment models and measurement methods are not suitable for 2D materials due to their atomically ultrathin thickness,which limits both the theoretical research and practical value of the 2D materials.In this review,we briefly summarize the characterization of mechanical properties of 2D materials by in situ probe nanoindentation experiments,and discuss the effect of thickness,grain boundary,and interlayer interactions.We introduce the strain-induced effect on electrical properties and optical properties of 2D materials.Then,we generalize the mechanical sensors based on various 2D materials and their future potential applications in flexible and wearable electronic devices.Finally,we discuss the state of the art for the mechanical properties of 2D materials and their opportunities and challenges in both basic research and practical applications.

Superhydrophobic, mechanically flexible and recyclable reduced graphene oxide wrapped sponge for highly efficient oil/water separation

Water pollution has become an urgent issue for our modem society, and it is highly desirable to rapidly deal with the water pollution without secondary pollution. In this paper, we have prepared a reduced graphene oxide （RGO） wrapped sponge with superhydrophobicity and mechanically flexibility via a facile low-temperature thermal treatment method under a reducing atmosphere. The skeleton of this sponge is completely covered with RGO layers which are closely linked to the skeleton. This sponge has an abundant pore structure, high selectivity, good recyclability, low cost, and outstanding adsorption capacity for floating oil or heavy oil underwater. In addition, this sponge can maintain excellent adsorption performance for various oils and organic solvents over 50 cycles by squeezing, and exhibits extremely high separa- tion efficiencies, up to 6 × 10^6 and 3.6 × 10^6 L·m^-3.h^-1 in non-turbulent and turbulent water/oil systems, respec- tively. This superhydrophobic adsorbent with attractive properties may find various applications, especially in large-scale removal of organic contaminants and oil spill cleanup.

Driving force and structural strength evaluation of a flexible mechanical system with a hydrostatic skeleton

The purpose of this study was to build a flexible mechanical system with a hydrostatic skeleton.The main components of this system are two type flexible bags.One is a structural bag with constant inner pressure.The other is an actuator bag with controlled inner pressure.To design the system,it was necessary to estimate both structural deformation and driving force.Numerical analysis of flexible bags,however,is difficult because of large nonlinear deformation.This study analyzed structural strength and driving force of flexible bags with the nonlinear finite element analysis (FEA) software ABAQUS.The stress concentration dependency on the bag shape is described and the driving force is calculated to include the large deformation.From the analytical results,this study derives an empirical equation of driving force.The validity of the equation was confirmed by condition-changed analyses and experimental results.

Development of Novel Hybrid Hand Formed by a Parallel Wrist and Three Soft-flexible Fingers

A prototype of a novel hybrid hand is developed by combing a parallel wrist with three flexible fingers.Its dynamics model is established,its grabbed forces are measured,and its grabbing performances are analyzed.First,Jacobian and Hessian matrices of the moving platform in the parallel wrist are derived,the kinematics formulas for solving the general velocity and the general acceleration of the moving platform are derived.Second its dynamics model is established for solving the dynamic actuation forces,the dynamic constrained forces of the developed hybrid hand.Third,its simulation mechanism is constructed in Matlab,and the theoretical solutions of the kinematics and the dynamics of the developed hybrid hand are verified to be correct using its simulation mechanism.Finally,when objects with different mass are grabbed by prototype of hybrid hand in different poses,the grabbed forces are measured,and the grabbing performances are discovered and analyzed to verify its merits.

Review of recent progresses on flexible oxide semiconductor thin film transistors based on atomic layer deposition processes

The current article is a review of recent progress and major trends in the field of flexible oxide thin film transistors（TFTs）, fabricating with atomic layer deposition（ALD） processes. The ALD process offers accurate controlling of film thickness and composition as well as ability of achieving excellent uniformity over large areas at relatively low temperatures. First, an introduction is provided on what is the definition of ALD, the difference among other vacuum deposition techniques, and the brief key factors of ALD on flexible devices. Second, considering functional layers in flexible oxide TFT, the ALD process on polymer substrates may improve device performances such as mobility and stability, adopting as buffer layers over the polymer substrate, gate insulators, and active layers. Third, this review consists of the evaluation methods of flexible oxide TFTs under various mechanical stress conditions. The bending radius and repetition cycles are mostly considering for conventional flexible devices. It summarizes how the device has been degraded/changed under various stress types（directions）. The last part of this review suggests a potential of each ALD film, including the releasing stress, the optimization of TFT structure, and the enhancement of device performance. Thus, the functional ALD layers in flexible oxide TFTs offer great possibilities regarding anti-mechanical stress films, along with flexible display and information storage application fields.

Carbonaceous ceramic nanofibrous aerogels for high-temperature thermal superinsulation

Ultralight ceramic aerogels are attractive thermal superinsulating materials,but display a formidable tradeoff between low and high temperature thermal conductivity(κ)due to their low-density features.Embedding carbon species as infrared opacifier in ultralight ceramic aerogels can substantially reduce the thermal radiation heat transfer without compromising the ultralow solid conduction.However,the oxidation resistance of embedded carbon species still remains inadequate to prevent thermal etching at high temperatures.Herein,we report a carbonaceous design and synthesis of ceramic nanofibrous aerogels with amorphous carbon embedded in the yttrium-stabilized zircon nanofibers to achieve a high-temperature thermal superinsulating performance with robust thermomechanical stability.The aerogels display one of the lowestκof 95 mW·m^(−1)·K^(-1)at 1,000℃in air among ultralight material family,as well as robust mechanical flexibility with up to 95%compressive strain,30%non-linear fracture strain,and 99%bending strain,and high thermal stability with ultralow strength degradation less than 1%after sharp thermal shocks(240℃·s^(-1))and working temperature up to 1,200℃.The combined high-temperature thermal superinsulating and thermomechanical properties offer an attractive material system for robust thermal insulation under extreme conditions.

In-plane corrugated cosine honeycomb for 1D morphing skin and its application on variable camber wing

A novel 0-Poisson＇s ratio cosine honeycomb support structure of flexible skin is proposed. Mechanical model of the structure is analyzed with the energy method, finite element method （FEM） and experiments have been performed to validate the theoretical model. The in-plane characteristics of the cosine honeycomb are compared with accordion honeycomb through analytical models and experiments. Finally, the application of the cosine honeycomb on a variable camber wing is studied. Studies show that mechanical model agrees well with results of FEM and experiments. The transverse non-dimensional elastic modulus of the cosine honeycomb increases （decreases） when the wavelength or the wall width increases （decreases）, or when the amplitude decreases （increases）. Compared with accordion honeycomb, the transverse non-dimensional elastic modulus of the cosine honeycomb is smaller, which means the driving force is smaller and the power consumption is less during deformation. In addition, the cosine honeycomb can satisfy the deform- ing requirements of the variable camber wing.

China＇s Approach to Its Exchange Rate Mechanism： Adaptability of BBC Rules

China＇s recent declaration of principles on its exchange rate mechanism has made it very clear that any move should be on China＇s own initiative; such a move should be sustainable and under control. China has adopted gradualism in the exchange rate reform process. On July 21st, 2005, China changed Renminbi （RMB） pariy （appreciation） by 2 percent, signaling the exchange market reform process. This paper is to study the past history of the crawling-peg of RMB on the US dollar with a view of its future reform. The flexibility provided by the crawling-peg still fits well with China＇s status quo. However, the flexible mechanism should follow the trend of China＇s economic development with well-timed parity changes. The extent of the fluctuation band rests upon China＇s ability to maintain its currency stability to counter future speculation and shocks. Only when the market mechanism is restored in China can an equilibrium RMB exchange rate be reached.