Feasible Fabrication Process Research Articles

Capillary reinforcement strategy guided construction of robust oxygen functionalized carbon-based porous foam for highly efficient solar evaporation

Recent research on carbon-based porous foams has made great progress to alleviate global clean water scarcity. However, it is still a challenge to produce carbon-based porous foams with both high evaporation performance and good mechanical property because of weak interface interactions between carbon-based material and matrix. Herein, we report an effective capillary enhancement strategy to construct robust oxygen-functionalized 3D carbon-based porous foams (OCPF) with abundant hydrophilic oxygen-functional groups from oxidized carbon fiber (OCF) and graphite oxide (GO). Owing to capillary enhancement strategy, a robust foam can be obtained, such as compression stress increases by 6–70 times, and compression modulus reaches 0.56–8.01 MPa, and the obtained foam also contains abundant oxygen-functionalized carbon materials to modulate water state. As a result, the optimized OCPFs show a high evaporation rate of ∼ 3.08 kg·m−2·h−1 with an efficiency of ∼ 94 % under one sun irradiation, which can be further raised to 7.89 kg·m−2·h−1 (5 cm height with 3 m·s−1 wind speed). Besides, the OCPFs also exhibit satisfied desalination and purification performance in actual saline water, domestic and industrial sewage, corrosive and oily wastewater. The feasible fabrication process, excellent performances, and potential applications of OCPFs could provide a new insight into the future development of high-performance and durable carbon-based solar evaporators for large-scale practical applications.

Research on pyroelectric enhancement mechanism of PZT thin films and optimization design of infrared detectors

In this paper, the PZT10/90 thin film was successfully deposited on the Pt/TiO2/SiO2/Si substrate using RF magnetron sputtering, and the dielectric and pyroelectric properties of the thin film were measured and characterized. The measurements show that the dielectric constant of the PZT10/90 thin film is further reduced compared to the previously reported PZT30/70 thin films, which is beneficial for improving the figure of merit of the PZT. The dielectric constant and loss tangent of the PZT10/90 thin film are 173 and 0.016 at 1kHz and the pyroelectric coefficient of the thin film is 20 nC·cm-2·K-1 at room temperature. In addition, a pyroelectric infrared detector based on the PZT thin film was designed, a feasible detector fabrication process was proposed, and the structure of the pyroelectric infrared detector was optimized using simulation software based on the finite element method. The developed infrared detector has promising applications in the fields of spectroscopic instruments and smart seekers.

Highly Luminescent and Stable Perovskite Quantum Dots Films for Light‐Emitting Devices and Information Encryption

AbstractThe inherent flexibility and excellent mechanical strength of lead halide perovskite quantum dots (LHP‐QDs) films have attracted much attention in the fields of flexible lighting, displays, non‐planar x‐ray imaging, and wearable optoelectronics. Unfortunately, the complicated synthesis process and poor stability limit its practical applications, hence there is an urgent need to develop a feasible fabrication process for films to attain high device performance. Herein, a molecular level hybridization of bridged polysilsesquioxane (BPSQ) is designed as matrix to harvest both flexibility of organics and stability of inorganics, resulting in improved interfacial compatibility between the CsPbBr3 QDs and the matrix through chemical bond anchoring. The CsPbBr3@3‐aminopropyl‐triethoxysilane (APTES)@BPSQ films showcase bright narrow‐band photoluminescence, with a photoluminescence quantum yield of 61% and a half‐peak full width at half maximum of <17 nm. Notably, these films demonstrate excellent environmental stability, UV resistance, water stability (experiencing only an 18% decrease in luminescence intensity after 168 h of water immersion), and high‐temperature stability (withstanding temperatures up to 500 K). Furthermore, white light‐emitting diodes (WLEDs) and anti‐counterfeiting patterns have been fabricated using CsPbBr3@APTES@BPSQ, highlighting their wide application potential in flexible light‐emitting devices and information encryption.

The Effect of Concentration on PES/NMP System on Flat Sheet Membrane Fabrication and its Performance for CO2 Gas Separation

Carbon dioxide (CO2) capture utilising membrane technology have become the interest of research due to its low carbon footprint, feasible fabrication process and scalability in its operation. In this study, anisotropic polyethersulfone (PES) membrane was fabricated at various concentration ranging from 20 wt% to 35 wt% without the use of any additives. This study revealed that the finger-like structure disappeared with increased polymer dope concentration which was associated with increased viscosity of the dope solution. Moreover, the surface porosity of the membrane also virtually reduced with increased PES concentration as observed with the SEM images. The pure gas permeation test was also consistent with the observed morphology of the membrane. Membrane made with 20 wt% of PES dope solution exhibits the highest gas permeance which was 154.9 GPU at 2 bar while the CO2/nitrogen (N2) and CO2/methane (CH4) ideal selectivity was close to that of Knudsen’s selectivity value. With increased PES concentration, the CO2 gas permeance reduced drastically accompanied by enhancement on the CO2/N2 and CO2/ CH4 ideal selectivity. The critical concentration of PES dope solution obtained by plotting the PES dope concentration against viscosity was 29.4 wt%. With critical concentration of the dope solution, the CO2 permeance was recorded to be 8.1 GPU while the CO2/N2 and CO2/CH4 ideal selectivity were recorded to be 2.13 and 1.48, respectively at the pressure of 2 bar.

Polyimide/Carboxylated Multi-walled Carbon Nanotube Hybrid Aerogel Fibers for Fabric Sensors: Implications for Information Acquisition and Joule Heating in Harsh Environments

Polymeric hybrid sensors have garnered great interest in health monitoring, human–computer interaction, and soft robotics for their lightweight, flexibility, and feasible fabrication process. However, polymeric hybrid sensors suitable for harsh environments remain a considerable challenge, limiting further application. Herein, polyimide (PI)/carboxylated multi-walled carbon nanotube (c-MWCNT) hybrid aerogel fibers with a micro-porous structure were fabricated via wet-spinning and chemical thermal imidization. The fabricated PI/c-MWCNT hybrid aerogel fibers’ conductivity and the change of current in response to the bending degree were tested, in which the relative current change achieved 4.78% with a bending degree of 150°. The fibers possessed a density of 0.41 ± 0.06 g/cm3, a conductivity of 17.8 ± 2.9 μS/m, and a tensile strength of 13.0 ± 1.1 MPa. In addition, they exhibited excellent heat/cold durability, whose decomposition temperature, cold resistance, and service life were 367 °C, −196 °C, and 300 cycles, respectively. Furthermore, the fabric sensor woven with PI/c-MWCNT hybrid aerogel fibers demonstrated two sensitivity stages of stage 1 (S1) = 6.04 and stage 2 (S2) = 0.55 under various pressures. Besides, it could be heated to 62 °C at a voltage of 30 V in 90 s with a changing resistance. The above properties demonstrate that the as-prepared fabric sensor exhibited great application potential for information acquisition and joule heating in harsh environments.

Design and Thermal Analysis of Flexible Microheaters.

With the development of flexible electronics, flexible microheaters have been applied in many areas. Low power consumption and fast response microheaters have attracted much attention. In this work, systematic thermal and mechanical analyses were conducted for a kind of flexible microheater with two different wire structures. The microheater consisted of polyethylene terephthalate (PET) substrate and copper electric wire with graphene thin film as the middle layer. The steady-state average temperature and heating efficiency for the two structures were compared and it was shown that the S-shaped wire structure was better for voltage-controlled microheater other than circular-shaped structure. In addition, the maximum thermal stress for both structures was from the boundary of microheaters, which indicated that not only the wire structure but also the shape of micro heaters should be considered to reduce the damage caused by thermal stress. The influence resulting from the thickness of graphene thin film also has been discussed. In all, the heating efficiency for flexible microheaters can be up to 135 °C/W. With the proposed PID voltage control system, the response time for the designed microheater was less than 10 s. Moreover, a feasible fabrication process flow for these proposed structures combing thermal analysis results in this work can provide some clues for flexible microheaters design and fabrication in other application areas.

Liquid Metal/Wood Anisotropic Conductors for Flexible and Recyclable Electronics

AbstractNext‐generation electronics requiring high performance, recyclability, and low environmental impact are still in its infancy because of limited design strategies and materials. Herein, a facile approach for constructing liquid metal/wood anisotropic (LMWA) conductors via integration of gallium based LMs and delignified flexible wood (DF‐wood) is reported. Using a delignification treatment and a subsequent LM transfer process with patterns, a rigid and electrically insulating wood slice is converted into a flexible wood‐based LM conductor while retaining its original hierarchical porous structure. The LMWA conductor demonstrates a remarkable anisotropic electrical conductivity (σz/σx) on the order of 108. Subsequently, the LMWA conductors are successfully applied as flexible four‐channel tactile sensor, which exhibits excellent tactile sensitivity. Moreover, by immersing in a deep eutectic solvent (DES) composed of choline chloride with oxalic acid to dissolve the LM circuit, recycling of the LM is achieved with efficiency up to 96%. This is the first time that a DES is used to recycle LM, leading to increased economic and environmental viability of these sustainable electronics. The present LMWA conductors, which have the potential for a scalable and feasible fabrication process, substantially extend the scope of next‐generation electronics toward flexible and recyclable systems.

Self-Adaptive 3D Skeleton with Charge Dissipation Capability for Practical Li Metal Pouch Cells

Increased concentration polarization and cell resistance due to aggregation of “dead Li” is one of the main factors that cause capacity decay during cycling of practical lithium metal batteries. Effective strategies that are able to accommodate dynamic volume expansion of “dead Li” is required to solve the above problem. Herein, a compressible 3D skeleton (polyaniline modified melamine foam) is introduced to modify lithium metal anode to self-adapt the volume expansion. Meanwhile, moderate conductivity of this 3D skeleton can induce the “bottom-up” deposition manner of Li and provide electron pathways to exploit the inactive Li in “dead Li”. More importantly, the COMSOL simulations show that the 3D skeleton can effectively dissipate electrons accumulated on the tips of dendritic Li when unwanted Li dendrites contact the 3D skeleton to achieve low local current density. As a result, a Li/Cu cells using this 3D skeleton on the Cu side show long-term stability within 100 cycles under 3.8 mAh/cm2, and Li symmetrical cells using 3D skeleton modified Li foils achieve stable cycling for 2750 h under 5.0 mAh/cm2. The feasible fabrication process enables us to fabricate 0.6 Ah 3D skeleton modified Li/NCM811 pouch cells, which deliver capacity retention of 85% after 80 cycles under practical test protocols.

An Easy‐to‐Fabricate 2.5D Evaporator for Efficient Solar Desalination

AbstractSolar‐driven steam generation, whereby solar energy is harvested to purify water directly, is emerging as a promising approach to mitigate the worldwide water crisis. The scalable application of conventional 3D evaporators is hindered by their complex spatial geometries. A 2.5D structure is a spatial extension of a 2D structure with an addition of a third vertical dimension, achieving both the feasibility of 2D structure and the performance of 3D structure simultaneously. Here, an interconnected open‐pore 2.5D Cu/CuO foam‐based photothermal evaporator capable of achieving a high evaporation rate of 4.1 kg m−2 h−1 under one sun illumination by exposing one end of the planar structure to air is demonstrated. The micro‐sized open‐pore structure of Cu/CuO foam allows it to trap incident sunlight, and the densely distributed blade‐like CuO nanostructures effectively scatter sunlight inside pores simultaneously. The inherent hydrophilicity of CuO and capillarity forces from the porous structure of Cu foam continuously supply sufficient water. Moreover, the doubled working sides of Cu/CuO foam enlarge the exposure area enabling efficient vapor diffusion. The feasible fabrication process and the combined structural features of Cu/CuO foam offer new insight into the future development of solar‐driven evaporators in large‐scale applications with practical durability.

Sn Alloy and Graphite Addition to Enhance Initial Coulombic Efficiency and Cycling Stability of SiO Anodes for Li‐Ion Batteries

Silicon monoxide (SiO) has aroused increased attention as one of the most promising anodes for high‐energy density Li‐ion batteries. To enhance the initial Coulombic efficiencies (ICE) and cycle stability of SiO‐based anodes, a new facile composition and electrode design strategy have been adapted to fabricate a SiO–Sn–Co/graphite (G) anode. It achieves a unique structure where tiny milled SiO–Sn–Co particles are dispersed among two graphite layers. In this hybrid electrode, Sn–Co alloys promoted Li+ extraction kinetics, and the holistic reversibility of SiO and graphite enhanced the electrical conductivity. The SiO–Sn–Co/G electrode delivered an average ICE of 77.6% and a reversible capacity of 640 mAh g−1 at 800 mA g−1, and the capacity retention was above 98% after 100 cycles, which was much higher than that of the SiO with an ICE of 55.3% and a capacity retention of 50%. These results indicated that this was reliable method to improve the reversibility and cycle ability of the SiO anode. Furthermore, based on its easy and feasible fabrication process, it may provide a suitable choice to combine other alloy anodes with the graphite anode.

A high performance InGaN tunnel FET with InN interlayer and polarization-doped source and drain

An InGaN tunneling field-effect transistor (TFET) with a polarization-doped source and drain as well as an InN interlayer (PD-IL TFET) is proposed and investigated by Silvaco-Atlas simulations for the first time. This device features the graded InxGa1−xN source and drain where the ‘In’ fraction increases linearly in the source while it decreases linearly in the drain along the (0001) orientation. The unique design could realize the high PD carrier concentration in source and drain at the same time, benefiting from the nature of the polarization effect in III-Nitride materials. Thus, the random dopant fluctuations caused by conventional physical doping could be avoided effectively. Simulation results show that the PD-IL TFET with a 2 nm thick InN interlayer and ‘In’ fraction of 0.75 could achieve ON-state current (ION) of 74 μA μm−1, ION/IOFF ratio of 1013 and average subthreshold swing of as low as 1 mV dec−1. The effect of InN interlayer thickness and ‘In’ fraction of InxGa1−xN on the electrical characteristics of the PD-IL TFET are investigated and analyzed systematically. In addition, the circuit analysis and the feasible fabrication process issues of the proposed device are also presented and discussed. These results could break a new path to realize TFETs without physical doping in low power electronics applications.

Large modulation of mobile carriers within MoS2 by decoration of molecular dopants to enhance its gas sensing

Large area functional MoS2 thin films are emerging in many opto-electric applications. In this sense, control of charge transfer via molecular decoration to build up a better gas sensing application is a key issue. We have systematically investigated a feasible fabrication process to realize an optimal molecule decoration with tetrafluorotetracyanoquinodimethane (F4TCNQ) on the surface of MoS2. The field effect transistor gas sensors have been improved remarkably to response on NH3 under all range of analyte concentration by two or three orders of magnitude after molecular decoration. All this improvement can be attributed to charge transfer within a three-body system including NH3, F4TCNQ and MoS2. This research may provide insight guidance to develop large scale high-performance gas-sensors and stimulate an interest to future investigate charge transfer mechanism within molecule decorated two-dimensional materials.

Bioinspired Helical Micromotors as Dynamic Cell Microcarriers.

Micromotors have exhibited great potential in multidisciplinary nanotechnology, environmental science, and especially biomedical engineering due to their advantages of controllable motion, long lifetime, and high biocompatibility. Marvelous efforts focusing on endowing micromotors with novel characteristics and functionalities to promote their applications in biomedical engineering have been taken in recent years. Here, inspired by the flagellar motion of Escherichia coli, we present helical micromotors as dynamic cell microcarriers using simple microfluidic spinning technology. The morphologies of micromotors can be easily tailored because of the highly controllable and feasible fabrication process including microfluidic generation and manual dicing. Benefiting from the biocompatibility of the materials, the resultant helical micromotors could be ideal cell microcarriers that are suitable for cell seeding and further cultivation; the magnetic nanoparticle encapsulation imparts the helical micromotors with kinetic characteristics in response to mobile magnetic fields. Thus, the helical micromotors could be applied as dynamic cell culture blocks and further assembled to complex geometrical structures. The constructed structures out of cell-seeded micromotors could find practical potential in biomedical applications as the stack-shaped assembly embedded in the hydrogel may be used for tissue repairing and the tube-shaped assembly due to its resemblance to vascular structures in the microchannel for organ-on-a-chip study or blood vessel regeneration. These features manifest the possibility to broaden the biomedical application scope for micromotors.

Fabrication and performance of CVD diamond cutting tool in micro milling of oxygen-free copper

Chemical vapor deposited (CVD) diamond is a promising material to fabricate micro-cutting tools owing to its ultra-high hardness, Young's modulus, and isotropic characteristics. In this research work, a novel compound process of laser-induced graphitization coupled with precision grinding, was proposed to fabricate CVD diamond micro-milling tool. The diamond-graphite transition behavior and mechanisms were specifically investigated. The microstructure of the graphite layer and the graphite-diamond boundary layer were observed with a scanning electron microscope (SEM) and three-dimensional confocal microscopy. Under laser irradiation, a loose graphite layer and heat-affected layer (defined as boundary layer) were formed on the CVD diamond matrix. Findings have depicted that a thermal conduction process dominated diamond-graphite transition. With decreasing the laser fluence, the thicknesses of both graphite layer and boundary layer were also reduced. The diameter, cutting edge radius, and nose radius of the fabricated CVD diamond micro-milling tool were 0.4 mm, 2.3 μm and 2.5 μm, respectively. The performance of the cutting tool was studied with regard to micro-milling of oxygen-free copper. The performance of the CVD diamond tool was ensured by comparing it with commercially purchased coated cemented carbide tools under identical machining conditions. The resultant forces, machined surface quality, burr formation, and tool failures were investigated. The results have indicated that lower resultant forces, less burr formation, and minimum surface roughness (arithmetic average surface roughness Ra of 53 nm) were obtained with the CVD diamond tool. The failure of the CVD diamond tool was characterized by flaking and flank/rake face wear, while the cemented carbide tool failure was associated with extensive flaking, coating spalling and flank face wear. The experimental study has shown superior performance of the fabricated CVD diamond tool as compared to commercially purchased coated cemented carbide tool. This work validates a feasible fabrication process of CVD diamond micro-milling tool, and a practical micro-machining data using CVD diamond tool.

Bilayer-graphene-coated Si nanoparticles as advanced anodes for high-rate lithium-ion batteries

Silicon is a promising anode material for the next-generation of high-specific-energy lithium-ion batteries (LIBs), but commercial silicon still has difficulty in gaining both high rate capability and long cycle life for practical application due to poor electrical conductivity and an unstable solid electrolyte interface. Here, a simple electrode with bilayer-graphene-coated Si nanoparticles embedded in a porous current collector is adopted and exceptional electrochemical performance is obtained in lithium-ions batteries. A possible mechanism is analyzed from the insight provided from the conductivity balance between electrons and ions. Used as binder-free and additive-free anodes, the Si composite displays good rate capacity (up to 50 A g−1) and cycling stability (3000 cycles with ∼89% capacity retention). Coupled with a possible physical insight, economical and feasible fabrication process, the electrode designs developed are likely to stimulate more opportunities for the next-generation high-specific-energy LIBs with enhanced power. It is further demonstrated that even in a full-cell electrochemical test, it is stable for 260 cycles and 87% capacity retention is achieved.

Characterization of mechanically reinforced electrospun dextrin‐polyethylene oxide sub‐microfiber mats

Dextrin and dextrin‐polyethylene oxide (DEX/PEO) fibers in the submicron range were produced by electrospinning of single and blend polymer solutions. The morphology, intermolecular interactions, and mechanical properties of dextrin microfibers with and without PEO were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, nuclear magnetic resonance spectroscopy, and uniaxial tensile testing. Spectroscopic results confirmed hydrogen bond formation, evidencing dextrin as a molecular entanglement source for fiber mechanical reinforcement. The uniaxial tensile tests demonstrated a synergistic mechanical reinforcement effect that varied with blend composition. Equal weight ratio blends supported a maximum tensile strength with a high elastic modulus and demonstrated to be more elastic and resistant to breaking, even than pristine PEO fibers. Moreover, elastic moduli of blend fiber mats were found to lie within the value range for human skin, thus providing the DEX/PEO meshes with potential applicability as skin tissue scaffolds. This synthesis approach proved the feasible and inexpensive fabrication process of natural‐synthetic polymer hybrid fibers that combine the biocompatibility, biodegradability, and encapsulating capability of dextrin with the mechanical strength and flexibility of PEO for the development of scaffolds for tissue engineering and topical drug delivery applications in skin wound healing. POLYM. ENG. SCI., 59:1778–1786, 2019. © 2019 Society of Plastics Engineers

The Design and Analysis of a Novel Micro Force Sensor Based on Depletion Type Movable Gate Field Effect Transistor

A novel micro force sensor based on depletion type vertically movable gate array field effect transistor (VMGAFET) was developed with cross-axis decoupling structure and eight gate arrays. This novel sensor is able to detect ultra-low force and exhibit high measuring sensitivity. An accurate electrical model was then proposed and compared with a long channel model, which is better adopted in small-sized devices to predict the electrical performance of this sensor. We also developed a mechanical model for the micro force sensor. Finite element method simulations were conducted, and the results were in accordance with the theoretical ones. Then, a feasible fabrication process was illustrated for the proposed sensor. The measuring sensitivity and nonlinearity of the micro force sensor with the proposed structure and dimension parameters are $12.528~\mu \text{A}$ /nN and <1.35%, respectively. These theoretical analyses provide insights into the design of depletion type VMAGFET-based sensor and other kinds of devices based on movable gate field effect transistor or with similar movable structures.

Planar Luneburg Lens Based on the High Impedance Surface for Effective Ku-Band Wave Focusing

In this paper, a planar Ku-band Luneburg lens is designed, fabricated, and measured. Based on the high impedance surface, metamaterial units are designed and arranged in an array with gradient equivalent refractive index to achieve good wave focusing effects in the Ku band. The proposed 2-D lens is superior at its compact size and more feasible fabrication process when compared with the conventional 3-D lens. Both theoretical analysis and measurement results have been provided for a systematic study on this lens’ performance, and good agreement between them has been achieved. Benefiting from flexible beam steering, the proposed lens has helpful applications in estimating the direction of arrival in the passive direction finding system, improving the directive radiation for an antenna, and simulating increased target’s radar cross-section characteristic by adding a reflector.

Simulation Study of a Super-Junction Deep-Trench LDMOS With a Trapezoidal Trench

A super-junction (SJ) deep-trench (DT) lateral double-diffused metal-oxide-semiconductor transistor improved by tilting the DT sidewalls is proposed. The incline of sidewalls introduces some vertically varying charges into the SJ drift regions on both sides of the DT. Therefore, the adverse effect of the DT on the surface electric field distribution is withstood, and the device can approach an ideal state of charge-balance. Simulation results show compared with a conventional device, which has the same drift region concentration and the same size but the perpendicular sidewalls, the proposed device presents a better figure of merit over 2.5 times higher. Besides, a feasible fabrication process for the proposal is presented and discussed.

A pressure sensor with electrostatic self-detecting structure

A piezoresistive pressure sensor with the electrostatic self-detecting structure was developed in the paper, which can solve the issue of low efficiency and time-consuming drawbacks of the traditional method in testing and calibrating the sensor with the specialized equipment. The theoretical model of the composite membrane piezoresistive sensor was established, the analytical model of the electrostatic force driven by an electrostatic voltage was obtained, a feasible fabrication process based on flip-chip process was proposed based on the MEMS processing, the pressure sensor and its detection structure were manufactured to verify the validity of the model in the paper. From the experiment results, it can be verified that the sensitivity of the pressure sensor was 1.77 mV/hPa and the non-linearity was 1.19% respectively. At the same time, the electrostatic force used to test sensor calibration could replace the loaded pressure in the range between 110 and 500 hPa.