Solution-processed Cu(In,Ga)Se_(2)(CIGS) solar cells suffer from serious carrier recombination and power conversion efficiency(PCE) loss because of the poor film properties and easy formation of defects.Herein, we pro...Solution-processed Cu(In,Ga)Se_(2)(CIGS) solar cells suffer from serious carrier recombination and power conversion efficiency(PCE) loss because of the poor film properties and easy formation of defects.Herein, we propose Ag&Se co-selenization strategy to enhance the crystallization and passivate harmful defects of the CIGS films. The formation of Ag-Se phase during the selenization process enables the formation of large grains and suppresses the deep level defects. It is found that Ag doping can enlarge the depletion region width, lower the Urbach energy and prolong the carrier lifetime. As a result, a champion solution-processed CIGS solar cell presents a high efficiency of 16.48% with the highly improved opencircuit voltage(VOC) of 662 m V and fill factor(FF) of 75.8%. This work provides an efficient strategy to prepare high quality solution-processed CIGS films for high-performance CIGS solar cells.展开更多
Sodium-based dual-ion batteries(SDIBs) have gained tremendous attention due to their virtues of high operating voltage and low cost, yet it remains a tough challenge for the development of ideal anode material of SDIB...Sodium-based dual-ion batteries(SDIBs) have gained tremendous attention due to their virtues of high operating voltage and low cost, yet it remains a tough challenge for the development of ideal anode material of SDIBs featuring with high kinetics and long durability. Herein, we report the design and fabrication of N-doped carbon film-modified niobium sulfur–selenium(NbSSe/NC) nanosheets architecture, which holds favorable merits for Na^(+) storage of enlarged interlayer space, improved electrical conductivity, as well as enhanced reaction reversibility, endowing it with high capacity, high-rate capability and high cycling stability. The combined electrochemical studies with density functional theory calculation reveal that the enriched defects in such nanosheets architecture can benefit for facilitating charge transfer and Na+ adsorption to speed the electrochemical kinetics. The NbSSe/NC composites are studied as the anode of a full SDIBs by pairing the expanded graphite as cathode, which shows an impressively cyclic durability with negligible capacity attenuation over 1000 cycles at 0.5 A g^(-1), as well as an outstanding energy density of 230.6 Wh kg^(-1) based on the total mass of anode and cathode.展开更多
Defects engineering is an effective strategy for manipulating electromagnetic parameters and enhancing electromagnetic wave(EMW)absorption capacity.However,the relationship between them is not clear,especially in soli...Defects engineering is an effective strategy for manipulating electromagnetic parameters and enhancing electromagnetic wave(EMW)absorption capacity.However,the relationship between them is not clear,especially in solid solution structures.In this work,a series of(Cr_(1-x)V_(x))_(2)AlC MAX phase solid solutions with layered structure were prepared via tuning the ratio of Cr and V to explore their EMW absorption performance.The experimental results indicated that the doping of V atoms at the M-site could effectively regulate its impedance matching and EMW absorption properties by introducing appropriate numbers of defects in the crystal,such as twin boundaries,dislocations and lattice distortions.Among them,if Cr:V=3:1,Cr_(1.5)V_(0.5)AlC,as radar absorption materials,could reach a strong reflection loss of-51.8 dB at the frequency of 12.8 GHz under an ultra-thin thickness of 1.3 mm.The reflection loss value could attain-10 dB in a wide frequency range of 2.7-18 GHz and thickness range of 1-5 mm.In addition,after high temperature and acid-alkali immersion treatment,this sample still had good EMW absorption capability,and the effective absorption bandwidth was enhanced from 2.3 to 2.6 GHz after concentrated acid immersion or 3.1 GHz after concentrated alkali immersion.This work has great reference significance for the research and development of high-performance MAX-based EMW absorption materials in harsh environments.展开更多
Up to now, perovskite solar cells(PSCs) have reached a certified 25.5% efficiency. As a promising photo-electric material, the metal halide perovskite possesses many outstanding properties such as tunable bandgap, lon...Up to now, perovskite solar cells(PSCs) have reached a certified 25.5% efficiency. As a promising photo-electric material, the metal halide perovskite possesses many outstanding properties such as tunable bandgap, long diffusion length, high absorption coefficient and carrier mobility. In spite of these remarkable properties, defects are inevitable during the solution processing. Therefore, many efforts have been made to reduce defects in perovskite films and thus improve the performance of devices. Among them,substitution or doping engineering is one of the most studied methods. Meanwhile, due to the poor stability of the organic-inorganic hybrid perovskite and the toxicity of Pb-based perovskite materials, all inorganic perovskite and lead-less or lead-free perovskite have emerged as promising materials. Here,we focus on the defect engineering especially substitutions on different sites in an ABX_(3) structure. The particular attention is devoted towards lead-less or lead-free perovskites, and we discuss several common elements or groups used to partially replace Pb^(2+). It is noted that proper elemental doping at different sites is an important guarantee for obtaining high-performance lead-less or lead-free PSCs.展开更多
Low quality(Q) factor is often the limiting factor for high performance carbon nanotube(CNT) resonators. The most commonly used approach to enhance the Q factor of CNTs is to reduce/eliminate the intrinsic defects.Her...Low quality(Q) factor is often the limiting factor for high performance carbon nanotube(CNT) resonators. The most commonly used approach to enhance the Q factor of CNTs is to reduce/eliminate the intrinsic defects.Herein, we show surprisingly that hole defects of suitable size and position are able to enhance the Q factor of CNT, which strongly contradicts to the common notion that the presence of defects promote intrinsic dissipation via defects dissipation. By analyzing the strain distribution, we find that such abnormal enhancement in Q factor of defected CNT originates from a coupling competition mechanism between the atomic mismatch around defected atoms and the thermoelastic damping. Although the presence of holes will introduce an additional defect dissipation source, suitable holes are capable of reducing the energy dissipation arisen from the thermoelastic damping, through changing the spatial strain field of defected CNT. This coupling competition mechanism provides a new route for designing high performance CNT resonators via defects engineering.展开更多
Kirkendall voids(KVs)at the Cu/Sn interface are a typical failure in integrated circuits,leading to solder joint cracking and electrical disconnection.Although the formation of KVs has been attributed to the differenc...Kirkendall voids(KVs)at the Cu/Sn interface are a typical failure in integrated circuits,leading to solder joint cracking and electrical disconnection.Although the formation of KVs has been attributed to the difference in atomic diffusion rates at the Cu/Sn interface,the role of Cu intrinsic"quality"parameters(crystal defects)in this process remains unclear.This work systematically investigated the effects of Cu crystal defects on KVs:Cu substrates with different lattice defects and grain boundaries were prepared using proprietary electrodeposition additives,and the number of defects was quantitatively characterized by micro-strain,geometric dislocation density,and geometric phase analysis.The thermal aging experiments further showed that the formation of intermetallic compounds and KVs was related to crystal defect energy.When the grain boundary energy was higher than the lattice energy,the additional driving force resulted in short-circuit diffusion,causing local Cu depletion and voids.The lowcrystal-defect samples maintained the local Cu/Sn interdiffusion equilibrium,resulting in fewer voids after 1000 h.This study emphasizes that regulating the crystal defects can reduce KVs and provides a new insight for improving the integrated solder joint's reliability.展开更多
Light absorption, charge separation and surface reaction are considered as the main processes ofphotocatalysis on one semiconductor, and all of them are demonstrated to be related to the defect statesof photocatalysts...Light absorption, charge separation and surface reaction are considered as the main processes ofphotocatalysis on one semiconductor, and all of them are demonstrated to be related to the defect statesof photocatalysts. This paper will choose Ti02 as model photocatalyst to introduce some basic conceptsand strategies related to defects and methods developed to characterize defects in the past decades.Meanwhile, such strategies as hydrogenation and metal/nonmetal doping intoTi02 will be introduced toextend utilization of solar spectrum and/or to provide active sites. On the contrary, the unfavorable effectof defects such as acting as recombination centers of photogenerated carriers will also be introduced.Some typical methods to characterize the properties of defects are summarized, which contain electronparamagnetic resonance （EPR）, photoluminescence technique （PL）, positron annihilation spectroscopy（PAS）, and so on. We do hope that this review will make a revealing effect on understanding to thefunctions of defects as well as construction of efficient photocatalytic systems in the future.展开更多
In order to evaluate the efficacy of low intensity ultrasound and tissue engineering technique to repair segmental bone defects, the rabbit models of 1.5-cm long rabbit radial segmental osteoperiosteum defects were es...In order to evaluate the efficacy of low intensity ultrasound and tissue engineering technique to repair segmental bone defects, the rabbit models of 1.5-cm long rabbit radial segmental osteoperiosteum defects were established and randomly divided into 2 groups. All defects were implanted with the composite of calcium phosphate cement and bone mesenchymal stem cells, and ad- ditionally those in experimental group were subjected to low intensity ultrasound exposure, while those in control group to sham exposure. The animals were killed on the postoperative week 4, 8 and 12 respectively, and specimens were harvested. By using radiography and the methods of biomechanics, histomorphology and bone density detection, new bone formation and material degradation were observed. The results showed that with the prolongation of time after operation, serum alkaline phosphatase （AKP） levels in both groups were gradually increased, especially in experimental group, reached the peak at 6th week （experimental group： 1,26 mmol/L; control group： 0.58 mmol/L）, suggesting the new bone formation in both two group, but the amount of new bone formation was greater and bone repairing capacity stronger in experimental group than in control group. On the 4th week in experimental group, chondrocytes differentiated into woven bone, and on the 12th week, remodeling of new lamellar bone and absorption of the composite material were observed. The mechanical strength of composite material and new born density in experimental group were significantly higher than in control group, indicating that low intensity ultrasound could not only effectively increase the formation of new bone, but also accelerate the calcification of new bone. It was concluded that low intensity ultrasound could evidently accelerate the healing of bone defects repaired by bone tissue engineering.展开更多
As the global population ages,osteoporotic bone fractures leading to bone defects are increasingly becoming a significant challenge in the field of public health.Treating this disease faces many challenges,especially ...As the global population ages,osteoporotic bone fractures leading to bone defects are increasingly becoming a significant challenge in the field of public health.Treating this disease faces many challenges,especially in the context of an imbalance between osteoblast and osteoclast activities.Therefore,the development of new biomaterials has become the key.This article reviews various design strategies and their advantages and disadvantages for biomaterials aimed at osteoporotic bone defects.Overall,current research progress indicates that innovative design,functionalization,and targeting of materials can significantly enhance bone regeneration under osteoporotic conditions.By comprehensively considering biocompatibility,mechanical properties,and bioactivity,these biomaterials can be further optimized,offering a range of choices and strategies for the repair of osteoporotic bone defects.展开更多
Under the background of the rapid development of the national economy, the domestic demand for medium and heavy machinery and equipment is also increasing, especially the demand for the key parts of machinery and equi...Under the background of the rapid development of the national economy, the domestic demand for medium and heavy machinery and equipment is also increasing, especially the demand for the key parts of machinery and equipment. Mechanical parts are required to have higher life, fatigue strength, impact fatigue strength, hardness and other indicators in engineering operation. Carburizing process is widely considered as a practical chemical heat treatment technology. However, there are still many problems in the carburizing process. Taking 20CrMnTi steel gear as an example, this paper briefly introduces the existing problems in carburizing technology and the optimization of key technologies.展开更多
Tissue-engineering bone with porous β-tricalcium phosphate (β-TCP) ceramic and autologous bone marrow mesenchymal stem cells (MSC) was constructed and the effect of this composite on healing of segmental bone defect...Tissue-engineering bone with porous β-tricalcium phosphate (β-TCP) ceramic and autologous bone marrow mesenchymal stem cells (MSC) was constructed and the effect of this composite on healing of segmental bone defects was investigated. 10-15 ml bone marrow aspirates were harvested from the iliac crest of sheep, and enriched for MSC by density gradient centrifugation over a Percoll cushion (1.073 g/ml). After cultured and proliferated, tissue-engineering bones were constructed with these cells seeded onto porous β-TCP, and then the constructs were implanted in 8 sheep left metatarsus defect (25 mm in length) as experimental group. Porous β-TCP only were implanted to bridge same size and position defects in 8 sheep as control group, and 25 mm segmental bone defects of left metatarsus were left empty in 4 sheep as blank group. Sheep were sacrificed on the 6th, 12th, and 24th week postoperatively and the implants samples were examined by radiograph, histology, and biomechanical test. The 4 sheep in blank group were sacrificed on the 24th week postoperatively. The results showed that new bone tissues were observed either radiographic or histologically at the defects of experimental group as early as 6th week postoperatively, but not in control group, and osteoid tissue, woven bone and lamellar bone occurred earlier than in control group in which the bone defects were repaired in “creep substitution” way, because of the new bone formed in direct manner without progression through a cartilaginous intermediate. At the 24th week, radiographs and biomechanical test revealed an almost complete repair of the defect of experimental group, only partly in control group. The bone defects in blank group were non-healing at the 24th week. It was concluded that engineering bones constructed with porous β-TCP and autologous MSC were capable of repairing segmental bone defects in sheep metatarsus beyond “creep substitution” way and making it healed earlier. Porous β-TCP being constituted with autologous MSC may be a good option in healing critical segmental bone defects in clinical practice and provide insight for future clinical repair of segmental defect.展开更多
The development of metal-free carbon catalysts has garnered significant attention as a promising approach to address the challenges of sustainable catalysis,particularly in the replacement of toxic and environmentally...The development of metal-free carbon catalysts has garnered significant attention as a promising approach to address the challenges of sustainable catalysis,particularly in the replacement of toxic and environmentally hazardous mercury-based systems for the coal-based PVC industry.Within a decade of development,the catalytic performance of carbon catalysts has been improved greatly and even shows superiorities over metal catalysts in some cases,which have demonstrated great potential as sustainable alternatives to mercury catalysts.This review provides a comprehensive summary of the recent advancements in carbon catalysts for acetylene hydrochlorination.It encompasses a wide range of aspects,including the identification of active sites from heteroatom doping to intrinsic carbon defects,the various synthetic strategies employed,the reaction and deactivation mechanisms of carbon catalysts,and the current insights into the key challenges that are encountered on the journey from laboratory research to scalable commercialization within the field of carbon catalysts.The review offers foundational insights and practical guidelines for designing green carbon catalysts systems,not only for acetylene hydrochlorination but also for other heterogeneous catalytic reactions.展开更多
Metal-organic frameworks(MOFs)have emerged as promising materials owing to their high surface areas,tunable pore sizes,and diverse functionalities.However,their practical deployment is frequently hindered by intrinsic...Metal-organic frameworks(MOFs)have emerged as promising materials owing to their high surface areas,tunable pore sizes,and diverse functionalities.However,their practical deployment is frequently hindered by intrinsic microporosity and structural fragility.In this review,we systematically analyze recent advancements in MOF etching techniques,which strategically modify framework architectures to enhance mass transport,expose active sites,and improve stability.The discussion encompasses a range of methods―including acid,base,ion,solvent,steam,selective,in-situ,pyrolysis,and physical etching―with emphasis on the underlying mechanisms that govern the formation of hierarchical pore structures,defect engineering,and heterojunction formation.Notably,etching approaches facilitate precise control over crystal morphology and surface chemistry,thereby optimizing MOF performance in catalysis,electrocatalysis,photocatalysis,adsorption,energy storage,sensing,and biomedical applications.We also outline challenges such as etchant toxicity,over-etching risks,and scalability,while highlighting emerging strategies and computational simulations to refine the etching process.Ultimately,this review underscores the transformative impact of etching on MOF properties,paving the way for the design of next-generation multifunctional materials that address critical issues in environmental remediation,energy conversion,and beyond.展开更多
In this study, we constructed tissue-engineered nerves with acellular nerve allografts in Sprague-Dawley rats, which were prepared using chemical detergents-enzymatic digestion and mechanical methods, in combination w...In this study, we constructed tissue-engineered nerves with acellular nerve allografts in Sprague-Dawley rats, which were prepared using chemical detergents-enzymatic digestion and mechanical methods, in combination with bone marrow mesenchymal stem cells of Wistar rats cultured in vitro, to repair 15 mm sciatic bone defects in Wistar rats. At postoperative 12 weeks, electrophysiological detection results showed that the conduction velocity of regenerated nerve after repair with tissue-engineered nerves was similar to that after autologous nerve grafting, and was higher than that after repair with acellular nerve allografts. Immunohistochemical staining revealed that motor endplates with acetylcholinesterase-positive nerve fibers were orderly arranged in the middle and superior parts of the gastrocnemius muscle; regenerated nerve tracts and sprouted branches were connected with motor endplates, as shown by acetylcholinesterase histochemistry combined with silver staining. The wet weight ratio of the tibialis anterior muscle at the affected contralateral hind limb was similar to the sciatic nerve after repair with autologous nerve grafts, and higher than that after repair with acellular nerve allografts. The hind limb motor function at the affected side was significantly improved, indicating that acellular nerve allografts combined with bone marrow mesenchymal stem cell bridging could promote functional recovery of rats with sciatic nerve defects.展开更多
The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been...The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.展开更多
In this work, hydrogen absorption and the permeation behavior of the passive layer formed on zircaloy-4 are in- vestigated. Potentiodynamic polarization, Mott-Schottky analysis, electrochemical impedance spectroscopy,...In this work, hydrogen absorption and the permeation behavior of the passive layer formed on zircaloy-4 are in- vestigated. Potentiodynamic polarization, Mott-Schottky analysis, electrochemical impedance spectroscopy, and Raman scattering spectroscopy are employed to characterize the passive defects before and after hydrogen permeation. It is found that the nanoscale passive ZrO2 films play an important role in the resistance against corrosion; hydrogen impingement, however, reduces the passive impedance towards hydrothermal oxidation. The increase of defects （vacancies） in passive film is probably attributed to the degradation. We believe that this finding will provide valuable insight into the understanding of the corrosion mechanism of zircaloys used in light water reactors.展开更多
The positron annihilation lifetimes and the Doppler broadening by slow positron beam are measured in thin Fe films with thickness 500 nm, a thin Hf film with thickness 100 nm, and the bilayer Fe (50 nm)/Hf (50 nm) on ...The positron annihilation lifetimes and the Doppler broadening by slow positron beam are measured in thin Fe films with thickness 500 nm, a thin Hf film with thickness 100 nm, and the bilayer Fe (50 nm)/Hf (50 nm) on quartz glass substrate. We have analyzed the behavior in vacancy-type defects in each layer through some deposition temperatures and annealing. It is observed that the thin Fe film, the thin Hf film, and the bilayer Fe (50 nm)/Hf (50 nm) already contain many vacancy-type defects. We have investigated the change of densities of the vacancy-carbon complex and the small vacancy-cluster with carbons, through solid-state amorphization of Fe (50 nm)/Hf (50 nm) bilayer.展开更多
Microspheres containing nerve growth factor for sustained release were prepared by a compound method, and implanted into chitosan conduits to repair 10-mm defects on the right buccal branches of the facial nerve in ra...Microspheres containing nerve growth factor for sustained release were prepared by a compound method, and implanted into chitosan conduits to repair 10-mm defects on the right buccal branches of the facial nerve in rabbits. In addition, chitosan conduits combined with nerve growth factor or normal saline, as well as autologous nerve, were used as controls. At 90 days post-surgery, the muscular atrophy on the right upper lip was more evident in the nerve growth factor and normal sa- line groups than in the nerve growth factor-microspheres and autologous nerve groups. Electro- physiological analysis revealed that the nerve conduction velocity and amplitude were significantly higher in the nerve growth factor-microspheres and autologous nerve groups than in the nerve growth factor and normal saline groups. Moreover, histological observation illustrated that the di- ameter, number, alignment and myelin sheath thickness of myelinated nerves derived from rabbits were higher in the nerve growth factor-microspheres and autologous nerve groups than in the nerve growth factor and normal saline groups. These findings indicate that chitosan nerve conduits com- bined with microspheres for sustained release of nerve growth factor can significantly improve facial nerve defect repair in rabbits.展开更多
基金National Natural Science Foundation of China (62104061, 62074052, 61974173 and 52072327)。
文摘Solution-processed Cu(In,Ga)Se_(2)(CIGS) solar cells suffer from serious carrier recombination and power conversion efficiency(PCE) loss because of the poor film properties and easy formation of defects.Herein, we propose Ag&Se co-selenization strategy to enhance the crystallization and passivate harmful defects of the CIGS films. The formation of Ag-Se phase during the selenization process enables the formation of large grains and suppresses the deep level defects. It is found that Ag doping can enlarge the depletion region width, lower the Urbach energy and prolong the carrier lifetime. As a result, a champion solution-processed CIGS solar cell presents a high efficiency of 16.48% with the highly improved opencircuit voltage(VOC) of 662 m V and fill factor(FF) of 75.8%. This work provides an efficient strategy to prepare high quality solution-processed CIGS films for high-performance CIGS solar cells.
基金financially supported by the National key Research & Development Program of China (2022YFE0115900, 2021YFA1501500)the National Natural Science Foundation of China (Nos. 22225902, U22A20436, 22209185)+3 种基金the CAS-Commonwealth Scientific and Industrial Research Organization (CSIRO) Joint Research Projects (121835KYSB20200039)the Joint Fund of the Yulin University and the Dalian National Laboratory for Clean Energy (Grant. YLUDNL Fund 2021011)Fujian Province Central Government Guides to Science and Technology Development Special Project (No. 2022L3024)Natural Science Foundation of Fujian Province, China (No. 2021J02020)。
文摘Sodium-based dual-ion batteries(SDIBs) have gained tremendous attention due to their virtues of high operating voltage and low cost, yet it remains a tough challenge for the development of ideal anode material of SDIBs featuring with high kinetics and long durability. Herein, we report the design and fabrication of N-doped carbon film-modified niobium sulfur–selenium(NbSSe/NC) nanosheets architecture, which holds favorable merits for Na^(+) storage of enlarged interlayer space, improved electrical conductivity, as well as enhanced reaction reversibility, endowing it with high capacity, high-rate capability and high cycling stability. The combined electrochemical studies with density functional theory calculation reveal that the enriched defects in such nanosheets architecture can benefit for facilitating charge transfer and Na+ adsorption to speed the electrochemical kinetics. The NbSSe/NC composites are studied as the anode of a full SDIBs by pairing the expanded graphite as cathode, which shows an impressively cyclic durability with negligible capacity attenuation over 1000 cycles at 0.5 A g^(-1), as well as an outstanding energy density of 230.6 Wh kg^(-1) based on the total mass of anode and cathode.
基金financially supported by the National Natural Science Foundation of China(Nos.52275187 and 52202364)Natural Science Foundation of Henan(No.232300421135)+1 种基金Fundamental Research Funds for the Universities of Henan Province(No.NSFRF200101)Henan Postdoctoral Foundation(No.202101035)。
文摘Defects engineering is an effective strategy for manipulating electromagnetic parameters and enhancing electromagnetic wave(EMW)absorption capacity.However,the relationship between them is not clear,especially in solid solution structures.In this work,a series of(Cr_(1-x)V_(x))_(2)AlC MAX phase solid solutions with layered structure were prepared via tuning the ratio of Cr and V to explore their EMW absorption performance.The experimental results indicated that the doping of V atoms at the M-site could effectively regulate its impedance matching and EMW absorption properties by introducing appropriate numbers of defects in the crystal,such as twin boundaries,dislocations and lattice distortions.Among them,if Cr:V=3:1,Cr_(1.5)V_(0.5)AlC,as radar absorption materials,could reach a strong reflection loss of-51.8 dB at the frequency of 12.8 GHz under an ultra-thin thickness of 1.3 mm.The reflection loss value could attain-10 dB in a wide frequency range of 2.7-18 GHz and thickness range of 1-5 mm.In addition,after high temperature and acid-alkali immersion treatment,this sample still had good EMW absorption capability,and the effective absorption bandwidth was enhanced from 2.3 to 2.6 GHz after concentrated acid immersion or 3.1 GHz after concentrated alkali immersion.This work has great reference significance for the research and development of high-performance MAX-based EMW absorption materials in harsh environments.
基金financially supported by the National Key Research and Development Program of China (Grant No.2018YFB2202900)the National Natural Science Foundation of China (Grant Nos. 52192610, 61704131)+3 种基金the Key Research and Development Program of Shaanxi Province (Grant No. 2020GY-310)the Joint Research Funds of Department of Science&Technology of Shaanxi Province and Northwestern Polytechnical University (Grant No. 2020GXLH-Z-018)the Fundamental Research Funds for the Central Universitiesthe Innovation Fund of Xidian University。
文摘Up to now, perovskite solar cells(PSCs) have reached a certified 25.5% efficiency. As a promising photo-electric material, the metal halide perovskite possesses many outstanding properties such as tunable bandgap, long diffusion length, high absorption coefficient and carrier mobility. In spite of these remarkable properties, defects are inevitable during the solution processing. Therefore, many efforts have been made to reduce defects in perovskite films and thus improve the performance of devices. Among them,substitution or doping engineering is one of the most studied methods. Meanwhile, due to the poor stability of the organic-inorganic hybrid perovskite and the toxicity of Pb-based perovskite materials, all inorganic perovskite and lead-less or lead-free perovskite have emerged as promising materials. Here,we focus on the defect engineering especially substitutions on different sites in an ABX_(3) structure. The particular attention is devoted towards lead-less or lead-free perovskites, and we discuss several common elements or groups used to partially replace Pb^(2+). It is noted that proper elemental doping at different sites is an important guarantee for obtaining high-performance lead-less or lead-free PSCs.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51605172 and 51775201)the Natural Science Foundation of Hubei Province (Grant No. 2016CFB191)+1 种基金the Fundamental Research Funds for the Central Universities (Grant No. 2015MS014)the Hong Kong Scholars Program (No. XJ2020043)。
文摘Low quality(Q) factor is often the limiting factor for high performance carbon nanotube(CNT) resonators. The most commonly used approach to enhance the Q factor of CNTs is to reduce/eliminate the intrinsic defects.Herein, we show surprisingly that hole defects of suitable size and position are able to enhance the Q factor of CNT, which strongly contradicts to the common notion that the presence of defects promote intrinsic dissipation via defects dissipation. By analyzing the strain distribution, we find that such abnormal enhancement in Q factor of defected CNT originates from a coupling competition mechanism between the atomic mismatch around defected atoms and the thermoelastic damping. Although the presence of holes will introduce an additional defect dissipation source, suitable holes are capable of reducing the energy dissipation arisen from the thermoelastic damping, through changing the spatial strain field of defected CNT. This coupling competition mechanism provides a new route for designing high performance CNT resonators via defects engineering.
基金financially supported by the National Natural Science Foundation of China(Nos.62274172 and 62304143)High-level Talent Innovation and Entrepreneurship Plan of Shenzhen Key Technology Research and Development Team Funding Application(No.JSGGKQTD20221101115650008)+2 种基金Shenzhen-Hong Kong-Macao Science and Technology Plan Project(Category C)(No.SGDX20220530111004028)Macao Science and Technology Development Fund(FDCT)for funding(No.0013/2024/RIB1)the Multi-Year Research Grant(MYRG)from University of Macao(Nos.MYRG-GRG2023-00140-IAPME-UMDF and MYRG-GRG2024-00206-IAPME)
文摘Kirkendall voids(KVs)at the Cu/Sn interface are a typical failure in integrated circuits,leading to solder joint cracking and electrical disconnection.Although the formation of KVs has been attributed to the difference in atomic diffusion rates at the Cu/Sn interface,the role of Cu intrinsic"quality"parameters(crystal defects)in this process remains unclear.This work systematically investigated the effects of Cu crystal defects on KVs:Cu substrates with different lattice defects and grain boundaries were prepared using proprietary electrodeposition additives,and the number of defects was quantitatively characterized by micro-strain,geometric dislocation density,and geometric phase analysis.The thermal aging experiments further showed that the formation of intermetallic compounds and KVs was related to crystal defect energy.When the grain boundary energy was higher than the lattice energy,the additional driving force resulted in short-circuit diffusion,causing local Cu depletion and voids.The lowcrystal-defect samples maintained the local Cu/Sn interdiffusion equilibrium,resulting in fewer voids after 1000 h.This study emphasizes that regulating the crystal defects can reduce KVs and provides a new insight for improving the integrated solder joint's reliability.
基金financially supported by the Basic Research Program of China(973 Program,No.2014CB239403)the National Natural Science Foundation of China(Nos.21633009,21373210,21522306)the priority support from the“Hundred Talents Program”of Chinese Academy of Sciences
文摘Light absorption, charge separation and surface reaction are considered as the main processes ofphotocatalysis on one semiconductor, and all of them are demonstrated to be related to the defect statesof photocatalysts. This paper will choose Ti02 as model photocatalyst to introduce some basic conceptsand strategies related to defects and methods developed to characterize defects in the past decades.Meanwhile, such strategies as hydrogenation and metal/nonmetal doping intoTi02 will be introduced toextend utilization of solar spectrum and/or to provide active sites. On the contrary, the unfavorable effectof defects such as acting as recombination centers of photogenerated carriers will also be introduced.Some typical methods to characterize the properties of defects are summarized, which contain electronparamagnetic resonance （EPR）, photoluminescence technique （PL）, positron annihilation spectroscopy（PAS）, and so on. We do hope that this review will make a revealing effect on understanding to thefunctions of defects as well as construction of efficient photocatalytic systems in the future.
文摘In order to evaluate the efficacy of low intensity ultrasound and tissue engineering technique to repair segmental bone defects, the rabbit models of 1.5-cm long rabbit radial segmental osteoperiosteum defects were established and randomly divided into 2 groups. All defects were implanted with the composite of calcium phosphate cement and bone mesenchymal stem cells, and ad- ditionally those in experimental group were subjected to low intensity ultrasound exposure, while those in control group to sham exposure. The animals were killed on the postoperative week 4, 8 and 12 respectively, and specimens were harvested. By using radiography and the methods of biomechanics, histomorphology and bone density detection, new bone formation and material degradation were observed. The results showed that with the prolongation of time after operation, serum alkaline phosphatase （AKP） levels in both groups were gradually increased, especially in experimental group, reached the peak at 6th week （experimental group： 1,26 mmol/L; control group： 0.58 mmol/L）, suggesting the new bone formation in both two group, but the amount of new bone formation was greater and bone repairing capacity stronger in experimental group than in control group. On the 4th week in experimental group, chondrocytes differentiated into woven bone, and on the 12th week, remodeling of new lamellar bone and absorption of the composite material were observed. The mechanical strength of composite material and new born density in experimental group were significantly higher than in control group, indicating that low intensity ultrasound could not only effectively increase the formation of new bone, but also accelerate the calcification of new bone. It was concluded that low intensity ultrasound could evidently accelerate the healing of bone defects repaired by bone tissue engineering.
基金supported by the National Natural Science Foundation of China(Nos.82160419 and 82302772)Guizhou Basic Research Project(No.ZK[2023]General 201)。
文摘As the global population ages,osteoporotic bone fractures leading to bone defects are increasingly becoming a significant challenge in the field of public health.Treating this disease faces many challenges,especially in the context of an imbalance between osteoblast and osteoclast activities.Therefore,the development of new biomaterials has become the key.This article reviews various design strategies and their advantages and disadvantages for biomaterials aimed at osteoporotic bone defects.Overall,current research progress indicates that innovative design,functionalization,and targeting of materials can significantly enhance bone regeneration under osteoporotic conditions.By comprehensively considering biocompatibility,mechanical properties,and bioactivity,these biomaterials can be further optimized,offering a range of choices and strategies for the repair of osteoporotic bone defects.
文摘Under the background of the rapid development of the national economy, the domestic demand for medium and heavy machinery and equipment is also increasing, especially the demand for the key parts of machinery and equipment. Mechanical parts are required to have higher life, fatigue strength, impact fatigue strength, hardness and other indicators in engineering operation. Carburizing process is widely considered as a practical chemical heat treatment technology. However, there are still many problems in the carburizing process. Taking 20CrMnTi steel gear as an example, this paper briefly introduces the existing problems in carburizing technology and the optimization of key technologies.
基金This project was supported by national high technology re search and development program of China ( 863 Program,2001AA216031), key technologies research and developmentprogram of Beijing (H020920050031).
文摘Tissue-engineering bone with porous β-tricalcium phosphate (β-TCP) ceramic and autologous bone marrow mesenchymal stem cells (MSC) was constructed and the effect of this composite on healing of segmental bone defects was investigated. 10-15 ml bone marrow aspirates were harvested from the iliac crest of sheep, and enriched for MSC by density gradient centrifugation over a Percoll cushion (1.073 g/ml). After cultured and proliferated, tissue-engineering bones were constructed with these cells seeded onto porous β-TCP, and then the constructs were implanted in 8 sheep left metatarsus defect (25 mm in length) as experimental group. Porous β-TCP only were implanted to bridge same size and position defects in 8 sheep as control group, and 25 mm segmental bone defects of left metatarsus were left empty in 4 sheep as blank group. Sheep were sacrificed on the 6th, 12th, and 24th week postoperatively and the implants samples were examined by radiograph, histology, and biomechanical test. The 4 sheep in blank group were sacrificed on the 24th week postoperatively. The results showed that new bone tissues were observed either radiographic or histologically at the defects of experimental group as early as 6th week postoperatively, but not in control group, and osteoid tissue, woven bone and lamellar bone occurred earlier than in control group in which the bone defects were repaired in “creep substitution” way, because of the new bone formed in direct manner without progression through a cartilaginous intermediate. At the 24th week, radiographs and biomechanical test revealed an almost complete repair of the defect of experimental group, only partly in control group. The bone defects in blank group were non-healing at the 24th week. It was concluded that engineering bones constructed with porous β-TCP and autologous MSC were capable of repairing segmental bone defects in sheep metatarsus beyond “creep substitution” way and making it healed earlier. Porous β-TCP being constituted with autologous MSC may be a good option in healing critical segmental bone defects in clinical practice and provide insight for future clinical repair of segmental defect.
文摘The development of metal-free carbon catalysts has garnered significant attention as a promising approach to address the challenges of sustainable catalysis,particularly in the replacement of toxic and environmentally hazardous mercury-based systems for the coal-based PVC industry.Within a decade of development,the catalytic performance of carbon catalysts has been improved greatly and even shows superiorities over metal catalysts in some cases,which have demonstrated great potential as sustainable alternatives to mercury catalysts.This review provides a comprehensive summary of the recent advancements in carbon catalysts for acetylene hydrochlorination.It encompasses a wide range of aspects,including the identification of active sites from heteroatom doping to intrinsic carbon defects,the various synthetic strategies employed,the reaction and deactivation mechanisms of carbon catalysts,and the current insights into the key challenges that are encountered on the journey from laboratory research to scalable commercialization within the field of carbon catalysts.The review offers foundational insights and practical guidelines for designing green carbon catalysts systems,not only for acetylene hydrochlorination but also for other heterogeneous catalytic reactions.
基金the financial support of the National Natural Science Foundation of China(Nos.22308296)。
文摘Metal-organic frameworks(MOFs)have emerged as promising materials owing to their high surface areas,tunable pore sizes,and diverse functionalities.However,their practical deployment is frequently hindered by intrinsic microporosity and structural fragility.In this review,we systematically analyze recent advancements in MOF etching techniques,which strategically modify framework architectures to enhance mass transport,expose active sites,and improve stability.The discussion encompasses a range of methods―including acid,base,ion,solvent,steam,selective,in-situ,pyrolysis,and physical etching―with emphasis on the underlying mechanisms that govern the formation of hierarchical pore structures,defect engineering,and heterojunction formation.Notably,etching approaches facilitate precise control over crystal morphology and surface chemistry,thereby optimizing MOF performance in catalysis,electrocatalysis,photocatalysis,adsorption,energy storage,sensing,and biomedical applications.We also outline challenges such as etchant toxicity,over-etching risks,and scalability,while highlighting emerging strategies and computational simulations to refine the etching process.Ultimately,this review underscores the transformative impact of etching on MOF properties,paving the way for the design of next-generation multifunctional materials that address critical issues in environmental remediation,energy conversion,and beyond.
基金financially sponsored by the Natural Science Foundation of Liaoning Province,No.201102135
文摘In this study, we constructed tissue-engineered nerves with acellular nerve allografts in Sprague-Dawley rats, which were prepared using chemical detergents-enzymatic digestion and mechanical methods, in combination with bone marrow mesenchymal stem cells of Wistar rats cultured in vitro, to repair 15 mm sciatic bone defects in Wistar rats. At postoperative 12 weeks, electrophysiological detection results showed that the conduction velocity of regenerated nerve after repair with tissue-engineered nerves was similar to that after autologous nerve grafting, and was higher than that after repair with acellular nerve allografts. Immunohistochemical staining revealed that motor endplates with acetylcholinesterase-positive nerve fibers were orderly arranged in the middle and superior parts of the gastrocnemius muscle; regenerated nerve tracts and sprouted branches were connected with motor endplates, as shown by acetylcholinesterase histochemistry combined with silver staining. The wet weight ratio of the tibialis anterior muscle at the affected contralateral hind limb was similar to the sciatic nerve after repair with autologous nerve grafts, and higher than that after repair with acellular nerve allografts. The hind limb motor function at the affected side was significantly improved, indicating that acellular nerve allografts combined with bone marrow mesenchymal stem cell bridging could promote functional recovery of rats with sciatic nerve defects.
文摘The effects of Sr addition and pressure increase on the microstructure and casting defects of a low-pressure die cast （LPDC） AISi7Mg0.3 alloy have been studied. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes and the amount of porosity occurring at different Sr levels and pressure parameters. The results indicate that an increase in the filling pressure induces lower heat dissipation of the liquid close to the die/core surfaces, with the formation of slightly greater dendrite arms and coarser eutectic Si particles. On the other hand, the increase in the Sr level leads to finer microstructural scale and eutectic Si. The analysed variables, within the experimental conditions, do not affect the morphology of eutectic Si particles. Higher applied pressure and Sr content generate castings with lower amount of porosiW. However, as the filling pressure increases the flow of metal inside the die cavity is more turbulent, leading to the formation of oxide films and cold shots. In the analysed range of experimental conditions, the design of experiment methodology and the analysis of variance have been used to develop statistical models that accurately predict the average size of secondary dendrite arm spacing and the amount of porosity in the low-pressure die cast AISiTMg0.3 alloy.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB610501)the Funds from the State Key Laboratory of Surface and Chemistry,China(Grant No.SPC 201102)the Reactor Fuel and Materials Laboratory,China(Grant No.STRFML-2013-05)
文摘In this work, hydrogen absorption and the permeation behavior of the passive layer formed on zircaloy-4 are in- vestigated. Potentiodynamic polarization, Mott-Schottky analysis, electrochemical impedance spectroscopy, and Raman scattering spectroscopy are employed to characterize the passive defects before and after hydrogen permeation. It is found that the nanoscale passive ZrO2 films play an important role in the resistance against corrosion; hydrogen impingement, however, reduces the passive impedance towards hydrothermal oxidation. The increase of defects （vacancies） in passive film is probably attributed to the degradation. We believe that this finding will provide valuable insight into the understanding of the corrosion mechanism of zircaloys used in light water reactors.
文摘The positron annihilation lifetimes and the Doppler broadening by slow positron beam are measured in thin Fe films with thickness 500 nm, a thin Hf film with thickness 100 nm, and the bilayer Fe (50 nm)/Hf (50 nm) on quartz glass substrate. We have analyzed the behavior in vacancy-type defects in each layer through some deposition temperatures and annealing. It is observed that the thin Fe film, the thin Hf film, and the bilayer Fe (50 nm)/Hf (50 nm) already contain many vacancy-type defects. We have investigated the change of densities of the vacancy-carbon complex and the small vacancy-cluster with carbons, through solid-state amorphization of Fe (50 nm)/Hf (50 nm) bilayer.
基金supported by the National Natural Science Foundation of China,No.30872898,81371116the Natural Science Foundation of Beijing,No.7132173
文摘Microspheres containing nerve growth factor for sustained release were prepared by a compound method, and implanted into chitosan conduits to repair 10-mm defects on the right buccal branches of the facial nerve in rabbits. In addition, chitosan conduits combined with nerve growth factor or normal saline, as well as autologous nerve, were used as controls. At 90 days post-surgery, the muscular atrophy on the right upper lip was more evident in the nerve growth factor and normal sa- line groups than in the nerve growth factor-microspheres and autologous nerve groups. Electro- physiological analysis revealed that the nerve conduction velocity and amplitude were significantly higher in the nerve growth factor-microspheres and autologous nerve groups than in the nerve growth factor and normal saline groups. Moreover, histological observation illustrated that the di- ameter, number, alignment and myelin sheath thickness of myelinated nerves derived from rabbits were higher in the nerve growth factor-microspheres and autologous nerve groups than in the nerve growth factor and normal saline groups. These findings indicate that chitosan nerve conduits com- bined with microspheres for sustained release of nerve growth factor can significantly improve facial nerve defect repair in rabbits.
