MAX/MAB phases are a series of non-van der Waals ternary layered ceramic materials with a hexagonal structure, rich in elemental composition and crystal structure, and embody physical properties of both ceramics and metals. They exhibit great potential for applications in extreme environments such as high temperature, strong corrosion, and irradiation. In recent years, two-dimensional (2D) materials derived from the MAX/MAB phase (MXene and MBene) have attracted enormous interest in the fields of materials physics and materials chemistry and become a new 2D van der Waals material after graphene and transition metal dichalcogenides. Therefore, structural modulation of MAX/MAB phase materials is essential for understanding the intrinsic properties of this broad class of layered ceramics and for investigating the functional properties of their derived structures. In this paper, we summarize new developments in MAX/MAB phases in recent years in terms of structural modulation, theoretical calculation, and fundamental application research and provide an outlook on the key challenges and prospects for the future development of these layered materials.
For the conventional von Neumann based vision systems, the sensing, memory, and processing units are separated. Shuttling of redundant data between separated image sensing, memory, and processing units causes a high latency and energy consumption. To break these limitations, the next-generation neuromorphic visual systems, which integrate light information sensing, memory, and processing, can reduce the data transfer, thus improving their time and energy efficiencies. As the basis of the hardware-implementing of neuromorphic visual systems, optoelectronic artificial synapse devices have been extensively investigated in recent years. By integrating the functions of synaptic devices and light-sensing elements, the optoelectronic artificial synapse devices pave the way for constructing new neuromorphic vision systems with low latency, high energy efficiency and good reliability. Many materials are widely utilized for optoelectronic artificial synapse devices, and operation mechanisms of the present optoelectronic artificial synapse devices mainly include the ionization and dissociation of oxygen vacancy, the trapping/detrapping of photogenerated carriers, the light-induced phase change, and the interaction between light and ferroelectric materials. In this short review, the recent progresses in optoelectronic artificial synapse devices are introduced from the perspectives of their operation mechanisms. Besides, advantages and challenges of the devices are analyzed from the view of operation mechanisms. Finally, the advanced prospect and research aspect of optoelectronic artificial synapse devices are outlined for the application.
In recent years, inspired by the unique operation mode of the human brain, emulation of the perception and computing functions of synapses and neurons by artificial neuromorphic devices has attracted more and more attention. So far, many researches have been reported about neuromorphic transistors (NMT), but most devices are fabricated on rigid substrates. The flexible neuromorphic transistors can not only realize signal transmission and training learning at the same time, but also carry out nonlinear spatio-temporal integration and cooperative regulation of multiple signals. It can also closely fit the soft human skin and withstand the high physiological strain of organs and tissues. More importantly, flexible neuromorphic transistors have unique advantages and application potential in detecting low amplitude signals at physiologically relevant time scales in biological environments due to their designable flexibility and excellent biocompatibility. Flexible neuromorphic transistors have been widely used in electronic skin, artificial vision system, intelligent wearable system, and other fields. At present, it is one of the most important tasks to develop low-power consumption, high-density integrated flexible neuromorphic transistors. In this paper, the research progress of NMT based on different flexible substrates is reviewed. In addition, the bright application prospect of flexible neuromorphic transistors is prospected. This review provides a reference for the development and application of flexible neuromorphic transistors in the future.
Methane is the second greenhouse gas contributing greatly to global warming, about 80 times of CO2. Considering background of global warming and atmospheric methane growth, to catalyze total oxidation of atmospheric methane is of great importance to mitigate greenhouse effects and slow this global warming. However, catalytic oxidation of methane has always been a big challenge due to its high structural stability. In this article, research progress in total oxidation of methane under thermal-, photo- and photothermal-catalysis was reviewed. High temperature in thermal catalysis increases the energy loss and accelerates the deactivation of catalysts speedingly. Therefore, development of catalysts that oxidize methane under moderate temperatures is the main research interests. Photocatalysis provides a way to eliminate methane at ambient conditions with the assistance of solar energy, but the reaction rates are lower than that in thermal catalysis. It is worth mentioning that photothermal catalysis, developed in recent years, can achieve efficiently catalytic total oxidation of methane under mild conditions, showing a high potential application prospect. This article reviews development of three modes of catalysis, analyzes their different reaction mechanisms, advantages and disadvantages under different reaction conditions. Finally, prospects and challenges of this catalytic total oxidation are pointed out, which is expected to provide references for future research on this field.
The analog channel conductance modulation of electrolyte-gated transistors (EGTs) is a desirable property for the emulation of synaptic weight modulation and thus gives them great potential in neuromorphic computing systems. In this work, an all-solid-state electrochemical EGT was introduced with a low channel conductance (~120 nS) using amorphous Nb2O5 and Li-doped SiO2 (LixSiO2) as the channel and gate electrolyte materials, respectively. By adjusting the applied gate voltage pulse parameters, the reversable and nonvolatile modulation of channel conductance were achieved, which was ascribed to reversible intercalation/deintercalation of Li+ ions into/from the Nb2O5 lattice. Essential functionalities of synapses, such as the short-term plasticity (STP), long-term plasticity (LTP), and transformation from STP to LTP, were simulated successfully by conductive channel modulation of the EGTs. Based on these characteristics, a simple associative learning circuit was designed by parallel a resistor between the gate and the source terminals. The Pavlovian dog classical conditioning behavior was simulated based on associative learning circuit, where the resistor represented the unconditioned synapse and shared the gate voltage with EGT according to the proportion of its resistance, and the resistance between gate and source for negative feedback regulation of synaptic weights. These results demonstrate the potential of EGT for artificial synaptic devices and provide an insight into hardware implementation of neuromorphic computing systems.
Silicon carbide (SiC) ceramics, as a high-performance structural-functional integrated material, are widely used in aerospace, nuclear industry and braking system. However, the conventional fabrication methods can not meet the increasing demands for large-scale and complex-structured SiC ceramics, such as engine nozzles, flaps and turbine blades. Binder jetting (BJ) 3D printing technology can overcome the traditional obstacle and provide a novel manufacturing roadmap. Here, we adopted this technique via SiC particle grading, optimized the particle size ratio based on gradation theory, and studied the influence of BJ printing on properties of SiC green body and as-sintered ceramic. For the particle-graded green body after BJ printing, SiC ceramics with a maximum flexural strength of (16.70±0.53) MPa was obtained after one precursor impregnation and pyrolysis (PIP) treatment, whose flexural strength was improved by 116% as compared with that BJ printed from a median diameter of 20 μm. SiC ceramics were further densified using liquid phase siliconization, with the density, flexural strength, elastic modulus, and fracture toughness reaching (2.655±0.001) g/cm3, (285±30) MPa, (243±12) GPa, and (2.54±0.02) MPa·m1/2, respectively. XRD results demonstrated that the sintered SiC ceramics were mainly composed of 3C structured-β-SiC. All results show that high-performance SiC ceramic materials are innovatively prepared by an efficient and reliable method, based on the combined techniques of particle grading, BJ printing, PIP and liquid silicon infiltration.
Memristor, fusing the functions of storage and computing within a single device, is one of the core electronic components to solve the bottleneck of von Neumann architecture. With the unique volatile/non-volatile resistive switching characteristic, memristor can simulate the function of synapses/neurons in brain well. In addition, due to the compatibility with traditional complementary metal-oxide-semiconductor (CMOS) processes, metal-oxide-based memristors have received a lot of attention. In recent years, many kinds of metal-oxide memristors based on single dielectric layer have been proposed. However, there are still some problems such as the instability of switching voltage, fluctuation of high/low resistance state and poor endurance of memristive device. Thus, the researchers have successfully optimized the device performance by introducing the double dielectric layer into the metal-oxide memristors. In this article, we introduce the advantages of double dielectric layers-based metal-oxide memristors, and discuss their mechanism and design of double dielectric layers-based metal-oxide memristors. Eventually, we introduce their potential applications in neuromorphic computing. This review provides some enlightenment on how to design high-performance metal-oxide memristor based on double dielectric layers.
X-ray detection has been widely used in medical imaging, security inspection, and industrial non-destructive tests. Halide perovskite X-ray detectors have attracted increasing attention due to their high sensitivity and low detection limit, but the notorious ion migration leads to poor operational stability. It is reported that the low dimensional structure can effectively suppress the ion migration of perovskites, thus greatly improving the stability of the detectors. This review introduces the working mechanism, key performance parameters of perovskite X-ray detectors, and summarizes the recent progress of low-dimensional perovskite materials and their application in direct X-ray detectors. The relationship between the structural characteristics of low-dimensional perovskite materials and their X-ray detection performance was systematically analyzed. Low-dimensional perovskite is a promising candidate for the preparation of X-ray detectors with both high sensitivity and stability. Further optimization of detection material and device structure, preparation of large-area pixelated imaging devices, and study of working mechanism in-depth of the detector are expected to promote the practical application of perovskite X-ray detectors.
Indium-gallium-zinc-oxide (IGZO)-based electric-double-layer (EDL) transistors have great applications for neuromorphic perception and computing systems because of their low processing temperature, high homogeneity, and plentiful ionic dynamics. However, IGZO-based EDL transistors have problems of high leakage current (>10 nA), high energy consumption and abnormal current spikes, which are the main obstacles to the development of neuromorphic computing systems based on such devices. In this work, a novel IGZO neuromorphic transistor with Al2O3/chitosan stacked gate dielectric was proposed. Compared with the monolayer chitosan gate dielectric transistor, the device with Al2O3/chitosan layer showed low subthreshold swing of 78.3 mV/decade, a low gate leakage current of 1.3 nA (reduced by about 98%), a large hysteresis window of 3.73 V (increased by about 3.4 times), a low excitable postsynaptic current of 0.86 nA (decreased by about 97%) and an energy consumption of 1.7 pJ for a spike event (0.5 V, 20 ms). Additionally, the emulation of spiking synaptic function and the synergistically modulation of the channel current were also realized, and the abnormal current spike caused by high leakage in synaptic plasticity simulation was also effectively avoided. The results suggest that the inserting of high-k dielectric layer can effectively improve the leakage current, energy consumption and performance of neuromorphic devices, which has substantial value for future ultra-low energy consumption neuromorphic perception and computing systems.
Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted widespread attention due to their high power conversion efficiency (PCE) and low manufacturing cost. Although the certified PCE has reached 25.8%, the stability of PSCs under high temperature, high humidity, and continuous light exposure is still significantly inferior to that of traditional cells, which hinders their commercialization. Developing and applying highly stable inorganic hole transport materials (HTMs) is currently one of the effective methods to solve the photo-thermal stability of devices, which can effectively shield water and oxygen from corroding the perovskite absorption layer, thereby avoiding the formation of ion migration channels. This paper outlines the approximate classification and photoelectric properties of inorganic HTMs, introduces relevant research progress, summarizes performance optimization strategies for inorganic HTMs devices, including element doping, additive engineering, and interface engineering, and finally prospects the future development directions. It is necessary to further study the microstructure of inorganic HTMs and their relationship with the performance of PSCs to achieve more efficient and stable PSCs.
Extreme Ultra-Violet (EUV) lithography utilizes Laser Produced Plasma (LPP) technology to generate EUV light with a 13.5 nm wavelength by bombarding tin liquid droplets with high-power lasers. Piezoelectric high-temperature nozzle based on inverse-piezoelectric effect is the key component for obtaining high-frequency tin droplet targets. Here, breakthroughs have been made in the composition design, fine preparation of high-temperature micro piezoelectric ceramic tubes that can withstand temperatures up to 250 ℃, and structure design, fabrication and precise driving control of the piezoelectric high-temperature nozzle. Based on a self-constructed high-temperature tin droplets generation platform, a stable output of high-temperature tin droplet targets with repetition frequency of 20 kHz and diameter of 100 μm is successfully achieved.
With the rise of the third-generation wide-bandgap semiconductors represented by SiC and GaN, power electronic devices are developing rapidly towards high output power and high power density, putting forward higher performance requirements on ceramic substrate materials used for power module packaging. The conventional Al2O3 and AlN ceramics are inadequate for the new generation of power module packaging applications due to low thermal conductivity or poor mechanical properties. In comparison, the newly developed Si3N4 ceramics have become the most potential insulating heat dissipation substrate materials due to its excellent mechanical properties and high thermal conductivity. In recent years, researchers have made a series of breakthroughs in the preparation of high strength and high thermal conductivity Si3N4 ceramics by screening effective sintering additive systems and optimizing the sintering processes. Meanwhile, as the advancement of the engineering application of coppered Si3N4 ceramic substrate, the evaluation of its mechanical, thermal, and electrical properties has become a research hotspot. Starting from the factors affecting thermal conductivity of Si3N4 ceramics, this article reviews the domestic and international research work focused on sintering aids selection and sintering processes improvement to enhance the thermal conductivity of Si3N4 ceramics. In addition, the latest progress in the dielectric breakdown strength of Si3N4 ceramic substrates and the evaluation of properties after being coppered are also systematically summarized and introduced. Based on above progresses and faced challengies, the future development direction of high strength and high thermal conductivity Si3N4 ceramic substrates is prospected.
The exploration of flexible electronic devices with information processing functions of biological neurons is of great significance for the development of intelligent wearable technologies. Due to lack of inherent mechanical flexibility, conventional threshold-switching memristor based on rigid materials that can implement the computing functions of biological neurons is difficult to fulfill the requirements for potential applications in the future. In this work, an intrinsically stretchable threshold-switching memristor was prepared by using silver nanowire-polyurethane composite as the dielectric layer and liquid metal as the electrodes, respectively. Under application of a sweeping voltage, the device exhibited reliable threshold switching characteristics, which was switched from the high resistance state (HRS) to the low resistance state (LRS) during device programming and spontaneously relaxed to the HRS upon voltage application. Further analysis shows that the underlying mechanism can be attributed to the dynamic formation and rupture of discontinuous silver conductive filaments formed between silver nanowires. In the pulse programming mode, memristor device is able to emulate the integration and firing characteristics of biological neurons, suggesting its great potential as an artificial neuron. Moreover, the pulse amplitude and pulse interval modulated neuronal spiking behaviors are successfully replicated using such devices. Under 20% tensile strain, the threshold-switching memristor shows negligible changes in the operating parameters during device switching and neuronal function implementations, suggesting its excellent mechanical flexibility and stability. This work provides important guidelines for the development of high-performance stretchable artificial neuronal devices and next-generation intelligent wearable systems.
SiCf/SiC ceramic matrix composites have excellent prospects in aeroengine applications. Importantly, the interface design becomes a research focus. Multilayered interfaces can effectively improve the oxidation resistance of ceramic matrix composites, while their effect on the mechanical properties and damage mechanism are still unclear. Here, SiCf/SiC minicomposites with BN and (BN/SiC)3 interfaces were fabricated via the chemical vapor infiltration (CVI) method. Then, effect of multilayered interfaces on the failure mechanism of SiCf/SiC composites was evaluated. According to the two kinds of mechanical experiments and acoustic emission (AE) detection, the damage mechanism of minicomposites was analyzed. Results indicate that the minicomposites prepared by CVI have an obvious interface structure and a dense matrix. The maximum load of BN and (BN/SiC)3 minicomposites was 139 and 160 N, respectively. Besides, the two types of minicomposites possess typical load-displacement curves, and the damage processes of composites with different interfacial coatings exhibit various load-acoustic characteristics correspondingly. The AE characteristics of two mechanical loading tests can effectively assess the damage evolution of the minicomposites at each stage. In conclusion, multilayered interfaces can deflect cracks better, delay cracks extending to fibers, and thus improving mechanical properties of SiCf/SiC composites.
As the basic and essential unit of neuromorphic computing system, artificial synaptic devices exhibit great potential in accelerating the high-performance parallel computation, artificial intelligence, and adaptive learning. Among them, electrolyte-gated synaptic transistors (EGSTs) have received increasing attention as the next generation neuromorphic devices owing to its controllable channel conductance. The devices exhibit the abilities of simulating the short-term plasticity (STP) and long-term plasticity (LTP) of the neural synapses. However, most of EGSTs exhibit short persistence for LTP and their channel conductance is difficult to be adjusted due to the rapid self-discharge of the electric double layer. In this work, the EGSTs based on water-induced In2O3 as the channel and chitosan as gate electrolyte were constructed and the O2 plasma treatments were performed. The formation of traps on the channel surface is caused by the O2 plasma treatments, which leads to capturing hydrogen ions at interface of the electrolyte/channel layer, and the device performance exhibits an enlarged hysteresis window, so as to regulate LTP of EGSTs. Biological synaptic functions, including excitatory postsynaptic current (EPSC), paired-pulse facilitation (PPF), STP, and LTP, were mimicked by electrochemical doping and electrostatic coupling effects. Meanwhile, based on the experimentally verified potentiation/depression characteristics of the EGSTs, a three-layer artificial neural network is applied for handwritten digit recognition, and simulation tests can obtain high recognition accuracy of 94.7%. These results reveal that surface plasma treatment is one of the key technologies to affect the device performance, which has great potential in regulating synaptic function of EGSTs.
Two-dimensional (2D) perovskite displays great potential in optoelectronic applications due to its inherent quantum well structure, large exciton binding energy and good stability. However, facile preparation of high-quality 2D perovskite films with low cost remains a huge challenge. In this work, high-quality two-dimensional perovskite (PEA)2PbI4 films were prepared by solution method at low annealing temperature(80 ℃) without other special treatments, and further applied in the field of photodetectors. The results show that this photodetector possessed a low dark current (10-11 A), good responsiveness illuminated at a wavelength of 450 nm (107 mA·W-1), high detection rate (2.05×1012 Jones) and fast response time (250 μs/330 μs). After 1200 s continuous illumination, the device maintains 95% initial photocurrent. In addition, the photocurrent remains almost unchanged after storage for 30 d. This work provides promising strategy to develop stable and high-performance optoelectronic devices.
Multistage pain perception is of great significance for surviving the outside harmful stimuli for organisms. In this work, using a sodium alginate biopolymer electrolyte as neurotransmitter layer, a 5×5 array of junctionless transistoris successfully fabricated for pain perception. The device operates well at low voltage (2 V) with a large current on-off ratio (>104) and on-state current (>10 μA). This coplanar-gate array can not only emulate the important functions of synapses, such as excitatory postsynaptic current, paired-pulse facilitation, and dynamic filtering, but also successfully mimic pain-perception and sensitization abilities of the artificial nociceptor network. Furthermore, this work also successfully emulates the multistage spatio-temporal sensitization in the nociceptor network. Construction of this kind of network system provides a new way for the application of the next-generation neuromorphic brain-like system.
Mimicking of brain perceptual processing mode is of great importance for the design of bionic intelligent perceptual system. On the meantime, adopting functional materials with biocompatibility and biodegradability to construct environment-friendly neuromorphic devices is also an important aspect for synaptic electronics. Here, gelatin/carboxylated chitosan (GEL/C-CS) composite electrolyte film was adopted as gate dielectrics in oxide neuromorphic transistors. Synaptic plasticities, including excitory post synaptic current and paired pulse facilitation, were mimicked on the oxide neuromorphic transistor under different humidities. A quantitative processing method for tactile recognition of objects was proposed based on the spike number dependent synaptic plasticity. An artificial neural network was built in further. Recognition accuracy of MNIST handwritten digits is above 90%. Data from above evaluation show that the proposed GEL/C-CS gated neuromorphic device has a promising application potential in the design of bionic intelligent perceptual systems and brain inspired neuromorphic systems.
Silicon carbide (SiC) has wide application in electric vehicles, rail transit, high voltage power transmission and transformation, photovoltaic, and 5G communication owing to its excellent physical and chemical properties. 8-inch SiC substrate has great potential in reducing unit cost of devices and increasing capacity supply, and has become an important technology development direction of the industry. Recently, Shandong University and Guangzhou Summit Crystal Semiconductor Co., Ltd. have made a major breakthrough in the control of dislocation defects in 8-inch SiC substrates. The 8-inch n-type 4H-SiC single crystal substrate with low dislocation density has been fabricated by physical vapor transport (PVT) method, of which the threading screw dislocation (TSD) density is 0.55 cm-2, and the basal plane dislocation (BPD) density is 202 cm-2.
With rapid development of lithium ion batteries (LIB) and sodium ion batteries (SIB), hard carbon (HC) as new anode material has earned much attention. Besides its rich precursor sources and low cost, HC has higher Li+ storage capacity and better rate performance than graphite for LIB. Furthermore, it is also recognized as the most commercially potential anode material for SIB. However, low initial Coulombic efficiency is a common issue for HC. In addition, it is believed that the specific capacity can be further improved with the clarification of the Li/Na ion storage mechanism. In recent years, many researches on electrochemical mechanism have been conducted with some model assumptions proposed for better understanding the mechanism. This review introduced the structures and preparation approaches of HC as well as its application in LIB and SIB. The advantages, especially in fast charging, coating and other subdivision were discussed, and the different modification strategies such as pore structure design, doping, optimizing interface between electrode and electrolyte were summarized, aiming at the increase of capacity and the improvement of Coulombic efficiency of batteries.
Ceramic-based porous structures not only inherit the excellent properties of dense ceramic materials such as high-temperature resistance, electrical insulation, and chemical stability, but also have unique advantages similar to porous structures, including low density, high specific surface area, and low thermal conductivity. They show great potential in various applications, such as thermal insulation, bone tissue engineering, filtration and pollutants removal, and electronic components. However, there still exist some challenges for shaping complex geometries on the macro- scale and adjusting pore morphologies on the micro- and nano-scale through the conventional preparation strategy of ceramic-based porous structures. In recent decades, researchers have been devoting themselves to developing novel manufacturing techniques for ceramic-based porous structures. The direct-ink-writing 3D printing, as one of the representative additive manufacturing technologies, has become a current research hotspot, rapidly developing a series of mature theories and innovative methodologies for fabricating porous structures. In this work, the conventional strategies and additive manufacturing strategies for obtaining porous structures were firstly summarized. The direct-write assembly processes of pore structures were further introduced in detail, mainly including pseudoplastic ink formulation, solidification strategy, drying, and post-treatment. Meanwhile, the feasibility of direct-ink-writing 3D printing technologies combined with conventional manufacturing strategies in constructing ceramic-based hierarchical pore structures was analyzed emphatically. The new perspectives, developments, and discoveries of direct-ink-writing 3D printing technologies were further summarized in the field of manufacturing complex ceramic-based porous structures. In addition, the developments and challenges in the future were prospected according to the actual application status.
In recent years, organic-inorganic hybrid perovskite solar cells have received a lot of attention for their excellent performance and low manufacturing cost. However, the toxicity of lead in organic-inorganic hybrid perovskite solar cells and instability inhibits its further commercialization. Double perovskite Cs2AgBiBr6 possess excellent stability, low toxicity, long carrier lifetime, and small effective carrier mass, and is considered as a promising photovoltaic material. It has been applied in solar cells and displayed superior performance. However, the power conversion efficiency of Cs2AgBiBr6 perovskite solar cell still lags behind organic-inorganic hybrid perovskite solar cells, and its development faces various challenges. This review firstly introduces the crystal structure and the structural parameters such as tolerance factor of Cs2AgBiBr6. And then, the progress of thin film preparation technologies such as solution processing method, anti-solvent assisted film forming method, vapor deposition processing method, vacuum-assisted film forming method, spray-coating method are summarized, and the advantages and disadvantages of various preparation technologies are discussed. The performance optimization strategies of Cs2AgBiBr6 perovskite solar cells are analyzed from three aspects: element doping, additive engineering, and interface engineering (interface energy level matching and interface defect passivation), and the research progress in recent years is reviewed. Finally, the challenges faced by Cs2AgBiBr6 perovskite solar cells are pointed out, and future research directions are prospected from three aspects: precursor solvent engineering, bandgap engineering, and device degradation mechanism.
As a high-temperature-resistant structural reinforcement material with excellent performance, alumina continuous fiber has been widely used in various fields. However, its large-scale preparation is still a great challenge due to the technical difficulty. Herein, the alumina continuous fibers were prepared using self-made aluminum sol and commercially available silica sol as precursors, in which the microstructure and composition of aluminum sol were studied to reveal their excellent spinnability. Preparation of alumina-based gel continuous fibers with length longer than 1500 m was realized by Sol-Gel combined dry spinning technology. After calcination at 1100 ℃ for 30 min, the continuous ceramic fiber composed of γ-Al2O3 and amorphous SiO2 with the diameter and mean tensile strength of 10 μm and 2.0 GPa was successfully obtained. Microstructure analyses revealed high relative density of the ceramic fibers, in which the γ-Al2O3 nanocrystals with size of 10-20 nm uniformly distributed in amorphous SiO2, resulting in excellent mechanical properties. This preparation process is environment-friendly, simple and controllable, showing great potential in practical application. The test for high temperature resistance revealed that the alumina continuous fiber can work for a long time at 1000 ℃ while it can endure as high as 1300 ℃ for a short-time service.
Semiconductor materials are the core of modern technology development and industrial innovation, with high frequency, high pressure, high temperature, high power, and other high properties under severe conditions or super properties needed by the “double carbon” goal, the new silicon carbide (SiC) and gallium nitride (GaN) as representative of the third generation of semiconductor materials gradually into industrial applications. For the third-generation semiconductor, there are several development directions in its packaging interconnection materials, including high-temperature solder, transient liquid phase bonding materials, conductive adhesives, and low-temperature sintered nano-Ag/Cu, of which nano-Cu, due to its excellent thermal conductivity, low-temperature sintering characteristics, and good processability, has become a new scheme for packaging interconnection, with low cost, high reliability, and scalability. Recently, the trend from material research to industrial chain end-use is pronounced. This review firstly introduces the development overview of semiconductor materials and summarizes the categories of third-generation semiconductor packaging interconnect materials. Then, combined with recent research results, it further focuses on the application of nano-Cu low-temperature sintering in electronic fields such as packaging and interconnection, mainly including the impact of particle size and morphology, surface treatment, and sintering process on the impact of nano-Cu sintered body conductivity and shear properties. Finally, it summarizes the current dilemmas and the difficulties, looking forward to the future development. This review provides a reference for the research on low-temperature sintered copper nanoparticles in the field of interconnect materials for the third-generation semiconductor.
Si anodes hold immense potential in developing high-energy Li-ion batteries. But fast failure due to huge volume change upon Li uptake impedes their application. This work reports a facile yet low-toxic gas fluorination way for yielding F-doped carbon-coated nano-Si anode materials. Coating of nano-Si with F-doped carbon containing high defects can effectively protect Si from huge volume change upon Li storage while facilitating Li+ transport and formation of stable LiF-rich solid electrolyte interphase (SEI). This anode exhibits high capacities of 1540-580 mAh·g-1 at various current rates of 0.2-5.0 A·g-1, while retaining >75% capacity after 200 cycles. This method also addresses the issues of high cost and toxicity of traditional fluorination techniques that use fluorine sources such as XeF2 and F2.
CoFe2O4@zeolite (CFZ) was prepared by using a co-precipitation hydrothermal method and used for synthetic dyes degradation by activating peroxymonosulfate (PMS). Comprehensive characterizations suggest that CoFe2O4 nanoparticles composing porous shell layer is uniformly covered on Na-A zeolite. The specific surface area of CFZ is 107.06 m2/g, three times that of the original zeolite. Since CFZ has a saturation magnetization of 29.0 A·m2·kg-1, it could be separated efficiently by magnetic separation. Catalytic degradation experiments indicate that the removal of methyl orange (MO) in the CFZ/PMS system is much higher than that using CFZ or PMS alone. Under the optimum condition ([MO]=50 mg/L, [PMS]=1.0 mmol/L, 0.2 g/L CFZ, pH 8 and T=25 ℃), MO removal efficiency is up to 97.1%. Effect of various factors, including pH, PMS and CFZ dosage, MO concentration and presence of coexisting anions, on the catalytic performance of CFZ is carefully studied. Reactive oxygen species quenching experiments suggest that 1O2 and O2•- play a dominant role in the degradation process. CFZ shows excellent recycling performance that the MO removal is declined by only 2.4% after 5 cycles. Catalytic degradation mechanism of the CFZ/PMS system is explored in detail.
MXene is a large family of two-dimensional transition metal carbides, nitrides or carbonitrides. Its characteristics (various compositions, two-dimensional atomic layer structures, metallic electrical conduction, active surfaces, etc.) render MXene unique interactions with electromagnetic waves at different frequencies (visible light, infrared, terahertz, microwave, etc.), deriving a variety of electromagnetic functional applications. In the infrared range, MXene has a wide range of infrared radiation properties, and its active surface endows tunable infrared absorption. These features have attracted researchers’ interest in exploring infrared properties of MXene and the corresponding applications in recent years. In this perspective, the intrinsic infrared characteristics and manipulation strategies of different MXenes are systematically summarized, and the research progress of representative infrared applications are briefly introduced, including infrared identification/camouflage, surface plasmon, photothermal conversion, and infrared photodetection. Particularly, the contribution and mechanism of MXene in these applications are discussed. Finally, the outlook for infrared functional applications with MXenes is proposed.
Metallic Li is one of the ideal anodes for high energy density lithium-ion battery due to its high theoretical specific capacity, low reduction potential as well as abundant reserves. However, the application of Li anodes suffer from serious incompatibility with traditional organic liquid electrolyte. Herein, a gel complex electrolyte (GCE) with satisfactory compatibility with metallic Li anode was constructed via in situ polymerization. The double lithium salt system introduced into the electrolyte can cooperate with the polymer component, which broadens electrochemical window of the electrolyte to 5.26 V compared to 3.92 V of commercial electrolyte, and obtains a high ionic conductivity of 1×10-3 S·cm-1 at 30 ℃ as well. Results of morphology characterization and elemental analysis of Li anode surface show that GCE exhibits obvious protective effect on lithium metal under the condition of double lithium salt system, and volume effect and dendrite growth of Li anode are obviously inhibited. At the same time, the lithium metal full battery, assembled with commercial lithium iron phosphate (LiFePO4) cathode material, exhibits excellent cycling stability and rate performance. The capacity retention rate of the battery reaches 92.95 % after 200 cycles at a constant current of 0.2C (1C = 0.67 mA·cm-2) at 25 ℃. This study indicates that the GCE can effectively improve the safety, stability and comprehensive electrochemical performance of lithium-metal battery, which is expected to provide a strategy for universal quasi-solid electrolyte design.
As a reversible, non-volatile, and resistive state mutation information storage and processing device, the resistive switching (RS) memory is expected to solve the inherent physical limitations of the traditional memory and von Neumann bottleneck, and has received widespread attention. Taking advantage of rapid carrier migration characteristics and excellent photoelectric conversion performance, halide perovskite optoelectronic RS memory devices present excellent resistive switching performance. In recent years, researches on storage and computing applications of the halide perovskite RS memory developed unprecedentedly; whereas, the working mechanisms of halide perovskite RS memory still remain unclear. This review analyzes the working mechanism of halide perovskite RS memory, compares the regulation characteristics of conduction filaments (CFs) and energy level matching (ELM), summarizes the constraints of various mechanisms, reveals the repeated formation and dissolution of CFs under light illumination and electric field, as well as Schottky barrier between the perovskite transfer layer and other layer, dominates the On/Off ratio, threshold (Set/Reset) voltage and performance stability of halide perovskite optoelectronic RS memory, and prospects the applications of halide perovskite RS memory in artificial intelligence bionic synapses, in-memory computing, and machine vision.
Hybrid organic-inorganic perovskite solar cells (PSCs) have attracted global attention as one of the most promising photovoltaic materials due to their high efficiency, low energy consumption and low cost. However, non-radiative recombination caused by interface defects severely inhibits the performance of PSCs. To solve this critical issue, the particle size of nickel oxide (NiOx) hole transport layer was reduced to improve the particle size uniformity and achieve efficient hole transport. Furthermore, the antisolvent acting time of the perovskite film was optimized to reduce the interfacial non-radiative recombination and interfacial defect. As a result, the crystalline quality is improved and power conversion efficiency (PCE) of the perovskite solar cells increase from 10.11% to 18.37%. Kelvin probe atomic force microscopy (KPFM) study shows that the contact potential difference (CPD) of the optimized perovskite film in the illumination condition increases by 120.39 mV compared with that under the dark condition. Analysis by piezoelectric atomic force microscopy (PFM) reveals that the ferroelectric polarization of the optimized interfacial perovskite films hardly changes from illumination to dark states, indicating that reducing interfacial defects can decrease the hysteresis effect of the PSCs. It is concluded that optimizing the NiOx hole transport layer and improving the quality of perovskite film can reduce the interface defects, the non-radiative recombination and the hysteresis effect, and improve PCE of perovskite solar cells.
The shoulder of the crystals grown by the Czochralski method is generally inclined, leading to poor quality and difficult processing, which then result in low utilization rate of the grown crystal. Take congruent lithium niobate (CLN) crystal as an example, this study used numerical simulation and experimental method to investigate the thermal field and growth process of flat shoulder crystal growth by the Czochralski method which can well acceptedly overcome the above problems. The result shows that the shape of the solid-liquid interface should be convex toward melt at the stage of shouldering. Temperature gradient near solid-liquid interface can be reduced by lowering the after-heater position (10 mm) to avoid the formation of polycrystalline. Control of the shouldering speed is the main way while control heating power is the accurate way to ensure the trend of shouldering. Accelerating the speed at the initial stage of shouldering (ϕ≤30 mm) and slowdown the speed at the middle and later stage of shouldering (ϕ≥35 mm) can shorten the period of shouldering and avoid defect inclusion. The pulling rate (0-1.5 mm/h) can be changed rapidly (1.5-2 h) without affecting the trend and quality of shouldering by adjusting power with a small amplitude (Δt=10 min, ∆v= 0.2 mm/h). By using these adjusting ways to thermal field and growth process, a series of 3-inch (1 inch=25.4 mm) flat shoulder CLN crystals with good optical homogeneity have been successfully grown.
AgBi2I7 thin film is one of the important candidates for constructing heterojunction ultraviolet photodetectors, due to their great optoelectronic properties and environmental stability. In this study, AgBi2I7 thin films were prepared by solution method and their photodetecting properties were investigated. By optimizing technological parameters such as concentration of the precursor solution and type of solvent (n-butylamine and DMSO), their photodetecting performance were investigated. AgBi2I7 thin films were fabricated on wide-bandgap GaN by optimal scheme to construct an AgBi2I7/GaN heterojunction. The heterojunction has a great selective detection of UVA-ray of which full width at half maximum is about 30 nm. Under 3 V bias and 350 nm UV irradiation, the On/Off ratio of the device exceeds 5 orders of magnitude, achieving a high responsivity of 27.51 A/W and a high detection rate of 1.53×1014 Jones. Therefore, the present research indicates that AgBi2I7 thin films prepared by solution method are promising to be applied to construct high-performance heterojunction ultraviolet photodetectors.
The perovskite-type oxynitride with AB(O,N)3 formula is a new type of functional ceramic materials, which have unique dielectric/magnetic/photocatalytic properties and prospective applications in the field of energy storage and conversion. However, the traditional preparation process takes a long time and the product purity is low. In this study, SrTa(O,N)3 ceramic powder was synthesized and densified by a pressureless spark plasma sintering equipment with urea as nitrogen source and metal oxides as precursors. Effects of heating rate and synthesis temperature on the composition and microstructure of the powder were deeply investigated, and the dielectric properties of the optimized ceramic bulks were characterized. The results show that higher heating rate and moderate synthesis temperature are beneficial to sufficient nitridation, while the SrTa(O,N)3 powder prepared at 100 ℃/min and 1000 ℃ possesses the highest purity (~97% oxynitride phase content) with a particle size distribution of 100-300 nm. Elements of Sr, Ta, O and N are evenly distributed. The optimized densification process is firstly sintering at 1300 ℃, with heating rate of 300 ℃/min, and dwelled for 1 min. After sintering, the density of SrTa(O,N)3 ceramic pellet can reach >94% with a high purity. Dielectric constant and loss tangent of the material are 8349 and 10-4 level at 300 Hz, respectively, which are superior to that reported in the literature. The high dielectric constant prepared in this study is closely related to standard density and purity, because the existence of pores and impurities can reduce the dielectric constant of materials. Therefore, high density and purity are the key factors to obtain excellent dielectric properties of SrTa(O,N)3 oxynitride ceramics.
Carbon-based perovskite solar cells (C-PSCs) play an important role in industrialization research due to their stability and low cost. In this work, high-quality NiOx mesoporous layer was selected as a hole transport layer (HTL) based on MAPbI3 material to enhance the performance of C-PSCs. The effect of preparation methods of the NiOx mesoporous layer on the solar cell performance and the optimum thickness of the NiOx mesoporous layer were investigated. It was found that mesoporous layers prepared by screen-printing process with well-distributed pores facilitated the filling of perovskite (PVK) precursor solution in the underlayer mesoporous scaffold. Finally, an HTL-contained perovskite solar cell with high efficiency and almost negligible hysteresis was achieved, possessing an open-circuit voltage (VOC) of 910 mV, a power conversion efficiency (PCE) of 14.63%, and certified efficiency reached 14.88%. Moreover, PCE of the solar cell displayed outstanding stability after being stored in air for nearly 900 h.
Brain-inspired neuromorphic computing refers to simulation of the structure and functionality of the human brain via the integration of electronic or photonic devices. Artificial synapses are the most abundant computation element in the brain-inspired system. Memristors are considered to be ideal devices for artificial synapse applications because of their high scalability and low power consumption. Based on Ohm’s law and Kirchhoff’s law, memristor crossbar arrays can perform parallel multiply-accumulate operations in situ, leading to analogue computing with greatly improved speed and energy efficiency. Oxides are most widely used in memristors due to the ease of fabrication and high compatibility with CMOS processes. This work reviews the research progress of oxide memristors for brain-inspired computing, mainly focusing on their resistance switching mechanisms, device structures and performances. These devices fall into three categories: electrical memristors, memristors controlled via both electrical and optical stimuli, and all-optically controlled memristors. The working mechanisms of electrical memristors are commonly related to microstructure change and Joule heat that are detrimental to device stability. The device performance can be improved by optimizing device structure and material composition. Tuning the device conductance with optical signals can avoid microstructure change and Joule heat as well as reducing energy consumption, thus making it possible to address the stability problem. In addition, optically controlled memristors can directly response to external light stimulus enabling integrated sensing-computing-memoring within single devices, which are expected to be used for developing next-generation vision sensors. Hence, the realization of all-optically controlled memristors opens a new window for research and applications of memristors.
Bioceramic scaffolds with excellent osteogenesis ability and degradation rate exhibit great potential in bone tissue engineering. Akermanite (Ca2MgSi2O7) has attracted much attention due to its good mechanical property, biodegradability and enhanced bone repair ability. Here, akermanite (Ca2MgSi2O7) scaffolds were fabricated by an extrusion-type 3D printing at room temperature and sintering under an inert atmosphere using printing slurry composed of a silicon resin as polymer precursor, and CaCO3 and MgO as active fillers. Furthermore, the differences in structure, compressive strength, in vitro degradation, and biological properties among akermanite, larnite (Ca2SiO4) and forsterite (Mg2SiO4) scaffolds were investigated. The results showed that the akermanite scaffold is similar to those of larnite and forsterite in 3D porous structure, and its compressive strength and degradation rate were between those of the larnite and forsterite scaffolds, but it showed a greater ability to stimulate osteogenic gene expression of rabbit bone marrow mesenchymal stem cells (rBMSCs) than both larnite and forsterite scaffolds. Hence, such 3D printed akermanite scaffold possesses great potential for bone tissue engineering.
To solve moisture gradients in the conventional drying with controlled temperature and relative humidity, microwave heating was employed to dry wet alumina green bodies shaped by spontaneous coagulation casting. The weight loss, linear shrinkage, surface temperature, and moisture distribution of the green bodies by conventional drying (temperature: 40 ℃; humidity: 60%) and microwave drying were investigated. The time for no further weight loss and shrinkage of the body by microwave drying (power: 250 W) were respectively shortened to 1/6.8 and 1/6 of those by conventional drying. Surface temperature of the green body during the microwave drying increased firstly and then decreased with time, which was strongly correlated with the internal moisture, while the temperature in the conventional drying keeping at 40 ℃. Low-field nuclear-magnetic-resonance (NMR) imaging revealed that the moisture distribution in the green bodies dried by microwave drying was more uniform than that by conventional drying, indicating that drying stress in the former was lower than that in the latter. After sintering at 1550 ℃ for 6 h, alumina ceramics from microwave drying had a higher flexural strength with a smaller deviation than that from conventional drying.