Tantalum thin films with different thicknesses varying from 50nm to 600nm were deposited on Si substrates by radio frequency magnetron sputtering as functions of deposition temperature(Ts) and bias voltage(Ub). Surfac...Tantalum thin films with different thicknesses varying from 50nm to 600nm were deposited on Si substrates by radio frequency magnetron sputtering as functions of deposition temperature(Ts) and bias voltage(Ub). Surface roughness and its dynamic evolution behavior were quantitatively investigated by using atomic force microscopy(AFM). With increasing Ts from 300K to 600K, surface roughness Rrms and dynamic exponent β decreases gradually. With the increase of Ub from 0V to -150V, Rrms and β first decrease and then increase. The dependence of Ts and Ub on the film surface evolution has been discussed in terms of surface diffusion, mound growth, and ion impinging effect.展开更多
Laser-driven inertial confinement fusion(ICF)diagnostics play a crucial role in understanding the complex physical processes governing ICF and enabling ignition.During the ICF process,the interaction between the high-...Laser-driven inertial confinement fusion(ICF)diagnostics play a crucial role in understanding the complex physical processes governing ICF and enabling ignition.During the ICF process,the interaction between the high-power laser and ablation material leads to the formation of a plasma critical surface,which reflects a significant portion of the driving laser,reducing the efficiency of laser energy conversion into implosive kinetic energy.Effective diagnostic methods for the critical surface remain elusive.In this work,we propose a novel optical diagnostic approach to investigate the plasma critical surface.This method has been experimentally validated,providing new insights into the critical surface morphology and dynamics.This advancement represents a significant step forward in ICF diagnostic capabilities,with the potential to inform strategies for enhancing the uniformity of the driving laser and target surface,ultimately improving the efficiency of converting laser energy into implosion kinetic energy and enabling ignition.展开更多
In order to reveal the evolution mechanism of repaired morphology and the material's migration mechanism on the crack surface in the process of CO_(2) laser repairing surface damage of fused silica optics, two mul...In order to reveal the evolution mechanism of repaired morphology and the material's migration mechanism on the crack surface in the process of CO_(2) laser repairing surface damage of fused silica optics, two multi-physics coupling mathematical models with different scales are developed, respectively. The physical problems, such as heat and mass transfer,material phase transition, melt flow, evaporation removal, and crack healing, are analyzed. Studies show that material ablation and the gasification recoil pressure accompanying the material splash are the leading factors in forming the Gaussian crater with a raised rim feature. The use of low-power lasers for a long time can fully melt the material around the crack before healing, which can greatly reduce the size of the residual air layer. Combined with the experimental research, the methods to suppress the negative factors(e.g., raised rim, deposited debris, air bubbles) in the CO_(2) laser repairing process are proposed.展开更多
Contact electrification(CE)is a pretty common phenomenon,but still is poorly understood.The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity.In th...Contact electrification(CE)is a pretty common phenomenon,but still is poorly understood.The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity.In this paper,the CE between metals and polymers is systematically studied,which shows the evolution of surfaces is accompanied by variations of CE outputs.The variations of CE charge quantity are closely related to the creep and deformation of the polymer and metal surfaces.Then the relationship between CE and polymer structures is put forward,which is essentially determined by the electronegativity of elements and the functional groups in the polymers.The effects of load and contact frequency on the CE process and outputs are also investigated,indicating the increase of CE charge quantity with load and frequency.Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer,both of which are believed to have an influence on each other.The findings advance our understanding of the mechanism of CE between metal and polymers,and provides insights into the performance of CE-based application in various conditions,which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.展开更多
Nanowires are fantastic nanostructures for designing new functional devices because of their extraordinary properties.However,nanowires usually suffer pronounced size and surface effects with decreasing diameter size....Nanowires are fantastic nanostructures for designing new functional devices because of their extraordinary properties.However,nanowires usually suffer pronounced size and surface effects with decreasing diameter size.Whether their structure and thermal stability can still fill the requirements of practical applications is a critical issue to be figured out.Herein,Te nanowires with diameters ranging from sub-10 to over 80 nm are used as samples to probe into this issue.In situ heating experiments are performed on these Te nanowires using an aberration-corrected transmission electron microscopy combined with a chip-based heating holder.It is found that Te nanowires suffer sublimation at elevated temperatures rather than melting,showing sizedependent sublimation scenarios.The Te nanowires with diameter smaller than 20 nm sublimate below 205℃,while the larger ones with diameter around 85 nm require a higher temperature of around 225℃.During sublimation-induced shape evolution,the interfacial wetting equilibrium and crystal orientations play critical roles,leading to the formation of spherical surfaces or featured facets at the free surfaces.A mean contact angle of 107.5°is determined at the C-Te interface when the crystalline Te nanowires stay in a quasi-liquid equilibrium state.However,once the crystalline feature is overwhelming,e.g.,at moderate temperatures,the(1011),(1120),and(1010)facets govern the free surface,despite the wetting condition at the interfaces.展开更多
Subject Code:E01With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Profs.Ding Yi(丁轶)and Luo Jun(罗俊)from the School of Materials Science and Eng...Subject Code:E01With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Profs.Ding Yi(丁轶)and Luo Jun(罗俊)from the School of Materials Science and Engineering,Tianjin University of Technology and Prof.Liu Limin(刘利民)from Beijing展开更多
Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface s...Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.展开更多
To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low alloy steel for serv...To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low alloy steel for service performance,four multistage machining processes were applied to the 45Cr Ni Mo VA steel,including the Rough Turning process(RT),RT+the Finish Turning process(FRT),FRT+the Grinding process(GFRT)and RT+the Finish Turning process on dry cutting condition(FRT0).The result showed that the FRT process’s average low-cycle torsional fatigue life increased by 50%when it evolved from the RT process.The lower surface roughness of R1.3μm caused the total strain energy to increase by 163.8 Pa mm/mm instead of the unchanged strain energy density,and the crack feature evolved from some specific bulges to flat shear plane characteristics.When the GFRT process evolved from the FRT process,its average fatigue life increased by 1.45 times,compared with the RT process.Plastic strain amplitude decreased by 21%,and the strain energy density decreased by 4%due to more considerable compressive residual stress(-249 MPa).Plastic deformation layer depth had a consistent tendency with surface roughness.In this paper,surface integrity evolutions on cyclic characteristics and fatigue behaviour have also been explained.A fatigue life prediction model based on the energy method for machined surface integrity is proposed.展开更多
The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam （IPIB） irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses...The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam （IPIB） irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses, the surface morphology of titanium alloy in a spatial scale of μm exhibits an obvious smoothening trend. The mechanism of this phenomenon is explained by the mass transfer caused by the surface tension of molten metal. Hydrodynamic simulation with a combination of the finite element method and the level set method reveals that the change in curvature on the molten surface leads to uneven distribution of surface tension. Mass transfer is caused by the relief of surface tension, and meanwhile a flattening trend in the surface morphology evolution is achieved.展开更多
A midlatitude squall line passed over the array of the Cooperative Convective Precipitation Experiment (CCOPE) on 1 August 1981. The structure and evolution of the squall line, and the correlations of the storm with s...A midlatitude squall line passed over the array of the Cooperative Convective Precipitation Experiment (CCOPE) on 1 August 1981. The structure and evolution of the squall line, and the correlations of the storm with surface thermodynamics and kinematic fields are investigated, mainly by using radar and surface mesonet data in CCOPE. The storm-wide precipitation efficiency is also estimated.The squall line was of an obvious process of metabolism. Thirty-four cells formed successively in front of the primary storm and eventually merged into it during the period 1700-2010 MDT. The newest cells formed near surface equivalent potential temperature maxima, and near surface moisture flux convergence zones or / and the 'temperature break lines'. The thunderstorm rainfall, with the precipitation efficiency of 54%, lags 25-30 min behind the moisture flux convergence on the average.展开更多
The oxygen evolution reaction(OER)has become the barrier of the development and application of next-generation sustainable energy systems due to its extremely sluggish reaction kinetics.One of the fundamental challeng...The oxygen evolution reaction(OER)has become the barrier of the development and application of next-generation sustainable energy systems due to its extremely sluggish reaction kinetics.One of the fundamental challenges is to develop cost-effective and high-efficiency electrocatalysts.Elucidating the dynamic structure evolution of catalysts at electrode-electrolyte interfaces during the reaction is of vital importance for understanding how to activate and sustain electrocatalytic performance.To this end,in situ techniques are invaluable for identifying the active centers together with monitoring the key intermediates under operating conditions.In this review,the latest advances on several cutting-edge in situ methods for characterizing the structure evolution process of OER electrocatalysts are comprehensively summarized.Significantly,a brief overview of active motifs and robust structures during electrocatalysis is provided using multiple in situ correlative techniques,which will contribute to establishing the essential structure-performance relationships and updating the understanding of electrocatalytic mechanisms at unprecedented atomic-scale levels under realistic working conditions.Finally,key challenges and perspectives in this emerging field are highlighted for promoting the design of promising electrocatalysts towards efficient oxygen-associated electrocatalysis and electrosynthesis.展开更多
Polymer gears are increasingly replacing metal gears in applications with low to medium torque.Traditionally,polymer gears have been manufactured using injection molding,but additive manufacturing(AM)is becoming incre...Polymer gears are increasingly replacing metal gears in applications with low to medium torque.Traditionally,polymer gears have been manufactured using injection molding,but additive manufacturing(AM)is becoming increasingly common.Among the different types of polymer gears,nylon gears are particularly popular.However,there is currently very limited understanding of the wear resistance of nylon gears and of the impact of the manufacturing method on gear wear performance.The aims of this work are(a)to study the wear process of nylon gears made using the conventional injection molding method and two popularly used AM methods,namely,fused deposition modeling and selective laser sintering,(b)to compare and understand the wear performance by monitoring the evolution of the gear surfaces of the teeth,and(c)to study the effect of wear on the gear dynamics by analyzing gearbox vibration signals.This article presents experimental work,data analysis of the wear processes using molding and image analysis techniques,as well as the vibration data collected during gear wear tests.It also provides key results and further insights into the wear performance of the tested nylon gears.The information gained in this study is useful for better understanding the degradation process of additively manufactured nylon gears.展开更多
An optical glass array lens is an optical element arranged periodically to achieve imaging,light equalization,focusing,diffusion,collimation,sensing,and other functions.Precision glass molding offers high production e...An optical glass array lens is an optical element arranged periodically to achieve imaging,light equalization,focusing,diffusion,collimation,sensing,and other functions.Precision glass molding offers high production efficiency,simple operation,high replication resolution,and low batch cost,which make it an effective method for the fabrication of glass array lenses.This study used D-K9 optical glass to research the precision molding of ring array lenses.The effects of varying molding temperatures,pressures,and times on the evolution of filling ratio and surface roughness(S_(a))were investigated.Stress evolution and residual stress distribution in the lens during the glass molding process were studied via numerical simulation.The results indicate that molding temperature and molding pressure played crucial roles in determining the filling ratio and surface quality of the molded glass lens.At molding conditions of 590°C/1 kN/30 s,the filling ratios and S_(a)of the molded glass ring array were approximately 99.5%and 11 nm,respectively.The maximum residual stress was observed near the surface edge of the molded glass array lens.This work provides effective guidance for the fabrication of glass array lenses.展开更多
Tungsten,a leading candidate for plasma-facing materials(PFM) in future fusion devices,will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions.In the past two decades,ex...Tungsten,a leading candidate for plasma-facing materials(PFM) in future fusion devices,will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions.In the past two decades,experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering,thermal and other properties of tungsten,posing a serious danger to the performance and lifetime of tungsten and the steadystate operation of plasma.In this article,we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles,surface morphology,and property changes of tungsten exposed to low-energy helium plasma.The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.展开更多
Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice,including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal str...Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice,including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal structures,emergency landing of aircrafts at sea as well as impact of ultra-cold droplets and ice lumps under aviation conditions.In this paper, a two dimensional (2-D) solver for Navier-Stokes equations is developed and applied in the numerical simulation of the impact on a rigid plate by a liquid square. The computational domain is discretized by Finite Volume Method (FVM). The Volume of Fluid (VOF) technique is used to track the free surface and the PiecewiseLinear Interface Construction (PLIC) is used for reconstruction. The Continuum Surface Force (CSF) model is used to account for the surface tension. The convective term and the diffusive term are upwind and centrally differenced respectively. The Inner Doubly Iterative Efficient Algorithm for Linked Equations (IDEAL) is used to decouple the pressure and velocity. Based on the proposed techniques, collapse of water column is simulated and convergence study is performed for the validation of the numerical solver. Then the impact of a free falling liquid body is simulated, and the effect of volume and initial height of the liquid body is analyzed. In addition, the impact on a plate with a liquid layer is also simulated to study the effect of falling height on a liquid floor.展开更多
Under intensive electric current, exposed aluminum interconnects undergo surface evolution driven by electromigration. The evolution of the surface morphology induces fluctuations in electric field. When the surface ...Under intensive electric current, exposed aluminum interconnects undergo surface evolution driven by electromigration. The evolution of the surface morphology induces fluctuations in electric field. When the surface diffusivity is inhomogeneous, surface damage appears under electric current as a combination of stationary solution and transients. The experimental observations confirm the above theoretical predictions and raise the reliability issue of electromigration in polycrystalline interconnects.展开更多
Evolution of surface morphology and optical characteristics of 1.3-μm In0.5Ga0.5As/GaAs quantum dots （QDs） grown by molecular beam epitaxy （MBE） are investigated by atomic force microscopy （AFM） and photolumine...Evolution of surface morphology and optical characteristics of 1.3-μm In0.5Ga0.5As/GaAs quantum dots （QDs） grown by molecular beam epitaxy （MBE） are investigated by atomic force microscopy （AFM） and photoluminescence （PL）. After deposition of 16 monolayers （ML） of In0.5Ga0.5As, QDs are formed and elongated along the [120] direction when using sub-ML depositions, while large size InGaAs QDs with better uniformity are formed when using ML or super-ML depositions. It is also found that the larger size QDs show enhanced PL efficiency without optical nonlinearity, which is in contrast to the elongated QDs.展开更多
This paper presents a systematic study of the growth mechanism for Pd nanobars synthesized by reducing Na_(2)PdCl_(4) with L-ascorbic acid in an aqueous solution in the presence of bromide ions as a capping agent.Tran...This paper presents a systematic study of the growth mechanism for Pd nanobars synthesized by reducing Na_(2)PdCl_(4) with L-ascorbic acid in an aqueous solution in the presence of bromide ions as a capping agent.Transmission electron microscopy(TEM)and high-resolution TEM analyses revealed that the growth at early stages of the synthesis was dominated by particle coalescence,followed by shape focusing via recrystallization and further growth via atomic addition.We also investigated the detailed surface structure of the nanobars using aberration-corrected scanning TEM and found that the exposed{100}surfaces contained several types of defects such as an adatom island,a vacancy pit,and atomic steps.Upon thermal annealing,the nanobars evolved into a more thermodynamically favored shape with enhanced truncation at the corners.展开更多
Correlating dynamic structural transformation of catalysts with the surface intermediate species under operating conditions is critical for updating the understanding of structure–performance relationships.Here,we pr...Correlating dynamic structural transformation of catalysts with the surface intermediate species under operating conditions is critical for updating the understanding of structure–performance relationships.Here,we probe the electrochemical potentialdependent surface structures and adsorbed intermediates on PtRu binary alloy nanocatalysts to revisit its synergistic mechanisms for CO electrooxidation enhanced activity.In-situ spectral characteristics by using modified shell-isolated nanoparticle-enhanced Raman spectroscopy,show that in acidic solution,when the potential is positively scanned from 0.1 V to 1.5 V relative to reversible hydrogen electrode(RHE),the surface of the alloy catalyst evolves from metallic PtRu to adsorbed oxygen gradually covering and accumulating on Ru sites(denoted as PtRuO_(x),x≤2),forming segregated RuO_(2),and finally forming a threedimensional oxide layer(denoted as 3D PtRuO_(4)).Moreover,molecular evidence associated with periodic density functional theory calculations reveals that electronic effects promote ruthenium to become more oxidizable and oxophilic.In particular,we found here that ^(*)O and ^(*)OH at surface RuO_(x) sites are highly efficient CO oxidation active species in comparison to the same entities adsorbed on metallic Ru sites.This work sheds light on the complex surface dynamic process of practical Pt-based binary nanocatalysts and improves the understanding of synergistic mechanism for the development of fuel cell devices.展开更多
Lunar dust, the finest fraction of lunar regolith, has undergone important space weathering on the Moon. It not only serves as a record of the evolution of the lunar surface environment and the modification of mineral...Lunar dust, the finest fraction of lunar regolith, has undergone important space weathering on the Moon. It not only serves as a record of the evolution of the lunar surface environment and the modification of mineral properties, but also influences the lunar surface environment through dust transport. Our current understanding of the properties and transport mechanisms of lunar dust on the lunar surface, however, remains limited. With rapid development of lunar exploration, it is necessary to further study the problem and meet the need of future lunar exploration missions. The lunar surface is the primary environmental space where uncrewed lunar rover activity, crewed lunar exploration, and lunar base construction take place. The lunar dust will distribute in such a space area due to electrostatic lifting and impacted sputtering, which will pose a threat to lunar surface exploration activities. In addition, lunar dust transport is closely related to lunar horizon glow, lunar swirl, and lunar magnetic anomaly. Understanding the properties and transport mechanisms of lunar dust is key to comprehending the formation of these scientific phenomena. Therefore, a systematic and in-depth investigation of lunar dust properties and dust transport patterns is urgently required to advance lunar science and implement lunar exploration projects. In this study, we summarize the physical and chemical properties of lunar dust and our understanding of dust transport on the lunar surface, identify remaining challenges and issues in the study of lunar dust, and offer perspectives on this research field.展开更多
文摘Tantalum thin films with different thicknesses varying from 50nm to 600nm were deposited on Si substrates by radio frequency magnetron sputtering as functions of deposition temperature(Ts) and bias voltage(Ub). Surface roughness and its dynamic evolution behavior were quantitatively investigated by using atomic force microscopy(AFM). With increasing Ts from 300K to 600K, surface roughness Rrms and dynamic exponent β decreases gradually. With the increase of Ub from 0V to -150V, Rrms and β first decrease and then increase. The dependence of Ts and Ub on the film surface evolution has been discussed in terms of surface diffusion, mound growth, and ion impinging effect.
基金supported by the National Natural Science Foundation of China(NSFC)(12074399,12204500 and 12004403)the Key Projects of Intergovernmental International Scientific and Technological Innovation Cooperation(2021YFE0116700)+1 种基金the Shanghai Natural Science Foundation(20ZR1464400)the Shanghai Sailing Program(22YF1455300).
文摘Laser-driven inertial confinement fusion(ICF)diagnostics play a crucial role in understanding the complex physical processes governing ICF and enabling ignition.During the ICF process,the interaction between the high-power laser and ablation material leads to the formation of a plasma critical surface,which reflects a significant portion of the driving laser,reducing the efficiency of laser energy conversion into implosive kinetic energy.Effective diagnostic methods for the critical surface remain elusive.In this work,we propose a novel optical diagnostic approach to investigate the plasma critical surface.This method has been experimentally validated,providing new insights into the critical surface morphology and dynamics.This advancement represents a significant step forward in ICF diagnostic capabilities,with the potential to inform strategies for enhancing the uniformity of the driving laser and target surface,ultimately improving the efficiency of converting laser energy into implosion kinetic energy and enabling ignition.
基金supported by the National Natural Science Foundation of China (Nos. 51775147 and 51705105)Science Challenge Project (No. TZ2016006-0503-01)Young Elite Scientists Sponsorship Program by CAST (No. 2018QNRC001)。
文摘In order to reveal the evolution mechanism of repaired morphology and the material's migration mechanism on the crack surface in the process of CO_(2) laser repairing surface damage of fused silica optics, two multi-physics coupling mathematical models with different scales are developed, respectively. The physical problems, such as heat and mass transfer,material phase transition, melt flow, evaporation removal, and crack healing, are analyzed. Studies show that material ablation and the gasification recoil pressure accompanying the material splash are the leading factors in forming the Gaussian crater with a raised rim feature. The use of low-power lasers for a long time can fully melt the material around the crack before healing, which can greatly reduce the size of the residual air layer. Combined with the experimental research, the methods to suppress the negative factors(e.g., raised rim, deposited debris, air bubbles) in the CO_(2) laser repairing process are proposed.
基金supported by the National Natural Science Foundation of China(Grant Nos.52075249,51505217,51435008,and 51705247)。
文摘Contact electrification(CE)is a pretty common phenomenon,but still is poorly understood.The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity.In this paper,the CE between metals and polymers is systematically studied,which shows the evolution of surfaces is accompanied by variations of CE outputs.The variations of CE charge quantity are closely related to the creep and deformation of the polymer and metal surfaces.Then the relationship between CE and polymer structures is put forward,which is essentially determined by the electronegativity of elements and the functional groups in the polymers.The effects of load and contact frequency on the CE process and outputs are also investigated,indicating the increase of CE charge quantity with load and frequency.Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer,both of which are believed to have an influence on each other.The findings advance our understanding of the mechanism of CE between metal and polymers,and provides insights into the performance of CE-based application in various conditions,which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.
基金supported by the National Natural Science Foundation of China(Nos.52071077 and 11774050)the National Key R&D Program of China(No.2017YFA0305500)the Fundamental Research Funds for the Central Universities.
文摘Nanowires are fantastic nanostructures for designing new functional devices because of their extraordinary properties.However,nanowires usually suffer pronounced size and surface effects with decreasing diameter size.Whether their structure and thermal stability can still fill the requirements of practical applications is a critical issue to be figured out.Herein,Te nanowires with diameters ranging from sub-10 to over 80 nm are used as samples to probe into this issue.In situ heating experiments are performed on these Te nanowires using an aberration-corrected transmission electron microscopy combined with a chip-based heating holder.It is found that Te nanowires suffer sublimation at elevated temperatures rather than melting,showing sizedependent sublimation scenarios.The Te nanowires with diameter smaller than 20 nm sublimate below 205℃,while the larger ones with diameter around 85 nm require a higher temperature of around 225℃.During sublimation-induced shape evolution,the interfacial wetting equilibrium and crystal orientations play critical roles,leading to the formation of spherical surfaces or featured facets at the free surfaces.A mean contact angle of 107.5°is determined at the C-Te interface when the crystalline Te nanowires stay in a quasi-liquid equilibrium state.However,once the crystalline feature is overwhelming,e.g.,at moderate temperatures,the(1011),(1120),and(1010)facets govern the free surface,despite the wetting condition at the interfaces.
文摘Subject Code:E01With the support by the National Natural Science Foundation of China,a collaborative study by the research groups led by Profs.Ding Yi(丁轶)and Luo Jun(罗俊)from the School of Materials Science and Engineering,Tianjin University of Technology and Prof.Liu Limin(刘利民)from Beijing
基金supported by the National Basic Research Program of China (No. 2011CB605602)
文摘Polyacrylonitrile （PAN） based carbon fibers with different surface morphology were electrochemically treated in 3 wt% NH4HCO3 aqueous solution with current density up to 3.47 A/m 2 at room temperature, and surface structures, surface morphology and residual mechanical properties were characterized. The crystallite size （La） of carbon fibers would be interrupted due to excessive electrochemical etching, while the crystallite spacing （d（002）） increased as increasing current density. The disordered structures on the surface of carbon fiber with rough surface increased at the initial oxidation stage and then removed by further electrochemical etching, which resulting in continuous increase of the extent of graphitization on the fiber surface. However, the electrochemical etching was beneficial to getting ordered morphology on the surface for carbon fiber with smooth surface, especially when the current density was lower than 1.77 A/m 2 . The tensile strength and tensile modulus could be improved by 17.27% and 5.75%, respectively, and was dependent of surface morphology. The decreasing density of carbon fibers probably resulted from the volume expansion of carbon fibers caused by the abundant oxygen functional groups intercalated between the adjacent graphite layers.
基金National Natural Science Foundation of China(No.52075042)。
文摘To explore the evolution mechanism of multistage machining processes and torsional fatigue behaviour based on strain energy for the first time and provide process optimization of axis parts of low alloy steel for service performance,four multistage machining processes were applied to the 45Cr Ni Mo VA steel,including the Rough Turning process(RT),RT+the Finish Turning process(FRT),FRT+the Grinding process(GFRT)and RT+the Finish Turning process on dry cutting condition(FRT0).The result showed that the FRT process’s average low-cycle torsional fatigue life increased by 50%when it evolved from the RT process.The lower surface roughness of R1.3μm caused the total strain energy to increase by 163.8 Pa mm/mm instead of the unchanged strain energy density,and the crack feature evolved from some specific bulges to flat shear plane characteristics.When the GFRT process evolved from the FRT process,its average fatigue life increased by 1.45 times,compared with the RT process.Plastic strain amplitude decreased by 21%,and the strain energy density decreased by 4%due to more considerable compressive residual stress(-249 MPa).Plastic deformation layer depth had a consistent tendency with surface roughness.In this paper,surface integrity evolutions on cyclic characteristics and fatigue behaviour have also been explained.A fatigue life prediction model based on the energy method for machined surface integrity is proposed.
基金Supported by the National Natural Science Foundation of China under Grant No 1175012the China Postdoctoral Science Foundation under Grant No 2016M600897the National Science and Technology Major Project of the Ministry of Science and Technology of China under Grant No 2013ZX04001-071
文摘The hydrodynamic effects of molten surface of titanium alloy on the morphology evolution by intense pulsed ion beam （IPIB） irradiation are studied. It is experimentally revealed that under irradiation of IPIB pulses, the surface morphology of titanium alloy in a spatial scale of μm exhibits an obvious smoothening trend. The mechanism of this phenomenon is explained by the mass transfer caused by the surface tension of molten metal. Hydrodynamic simulation with a combination of the finite element method and the level set method reveals that the change in curvature on the molten surface leads to uneven distribution of surface tension. Mass transfer is caused by the relief of surface tension, and meanwhile a flattening trend in the surface morphology evolution is achieved.
文摘A midlatitude squall line passed over the array of the Cooperative Convective Precipitation Experiment (CCOPE) on 1 August 1981. The structure and evolution of the squall line, and the correlations of the storm with surface thermodynamics and kinematic fields are investigated, mainly by using radar and surface mesonet data in CCOPE. The storm-wide precipitation efficiency is also estimated.The squall line was of an obvious process of metabolism. Thirty-four cells formed successively in front of the primary storm and eventually merged into it during the period 1700-2010 MDT. The newest cells formed near surface equivalent potential temperature maxima, and near surface moisture flux convergence zones or / and the 'temperature break lines'. The thunderstorm rainfall, with the precipitation efficiency of 54%, lags 25-30 min behind the moisture flux convergence on the average.
基金supported by the National Natural Science Foundation of China(W2412038 and 22241202)the Start-up Fund for the Youth Innovation Talent Project(KY2060000248)+2 种基金the International Partnership Program of Chinese Academy of Sciences(123GJHZ2024102FN)the Natural Science Foundation of Anhui Province(2508085QA016)the China Postdoctoral Science Foundation(GZC20241632 and 2025T180253)。
文摘The oxygen evolution reaction(OER)has become the barrier of the development and application of next-generation sustainable energy systems due to its extremely sluggish reaction kinetics.One of the fundamental challenges is to develop cost-effective and high-efficiency electrocatalysts.Elucidating the dynamic structure evolution of catalysts at electrode-electrolyte interfaces during the reaction is of vital importance for understanding how to activate and sustain electrocatalytic performance.To this end,in situ techniques are invaluable for identifying the active centers together with monitoring the key intermediates under operating conditions.In this review,the latest advances on several cutting-edge in situ methods for characterizing the structure evolution process of OER electrocatalysts are comprehensively summarized.Significantly,a brief overview of active motifs and robust structures during electrocatalysis is provided using multiple in situ correlative techniques,which will contribute to establishing the essential structure-performance relationships and updating the understanding of electrocatalytic mechanisms at unprecedented atomic-scale levels under realistic working conditions.Finally,key challenges and perspectives in this emerging field are highlighted for promoting the design of promising electrocatalysts towards efficient oxygen-associated electrocatalysis and electrosynthesis.
文摘Polymer gears are increasingly replacing metal gears in applications with low to medium torque.Traditionally,polymer gears have been manufactured using injection molding,but additive manufacturing(AM)is becoming increasingly common.Among the different types of polymer gears,nylon gears are particularly popular.However,there is currently very limited understanding of the wear resistance of nylon gears and of the impact of the manufacturing method on gear wear performance.The aims of this work are(a)to study the wear process of nylon gears made using the conventional injection molding method and two popularly used AM methods,namely,fused deposition modeling and selective laser sintering,(b)to compare and understand the wear performance by monitoring the evolution of the gear surfaces of the teeth,and(c)to study the effect of wear on the gear dynamics by analyzing gearbox vibration signals.This article presents experimental work,data analysis of the wear processes using molding and image analysis techniques,as well as the vibration data collected during gear wear tests.It also provides key results and further insights into the wear performance of the tested nylon gears.The information gained in this study is useful for better understanding the degradation process of additively manufactured nylon gears.
基金supported by a Shenzhen-Hong Kong-Macao Technology Research Programme from Shenzhen Science and Technology Innovation Committee(Project No.SGDX20220530110804030)the Research and Innovation Office of The Hong Kong Polytechnic University(Project code.BBR8 and BBX5)Postdoctoral Matching Fund Scheme(1-W340).
文摘An optical glass array lens is an optical element arranged periodically to achieve imaging,light equalization,focusing,diffusion,collimation,sensing,and other functions.Precision glass molding offers high production efficiency,simple operation,high replication resolution,and low batch cost,which make it an effective method for the fabrication of glass array lenses.This study used D-K9 optical glass to research the precision molding of ring array lenses.The effects of varying molding temperatures,pressures,and times on the evolution of filling ratio and surface roughness(S_(a))were investigated.Stress evolution and residual stress distribution in the lens during the glass molding process were studied via numerical simulation.The results indicate that molding temperature and molding pressure played crucial roles in determining the filling ratio and surface quality of the molded glass lens.At molding conditions of 590°C/1 kN/30 s,the filling ratios and S_(a)of the molded glass ring array were approximately 99.5%and 11 nm,respectively.The maximum residual stress was observed near the surface edge of the molded glass array lens.This work provides effective guidance for the fabrication of glass array lenses.
基金supported by National Natural Science Foundation of China(No.11905071)the National MCF Energy R&D Program(No.2018YFE0308103)
文摘Tungsten,a leading candidate for plasma-facing materials(PFM) in future fusion devices,will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions.In the past two decades,experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering,thermal and other properties of tungsten,posing a serious danger to the performance and lifetime of tungsten and the steadystate operation of plasma.In this article,we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles,surface morphology,and property changes of tungsten exposed to low-energy helium plasma.The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.
基金This study was financially supported by the Equipment Pre-Research Field Foundation(Grant Nos.61402100201,6142204180408,and 6142407180108)the National Natural Science Foundation of China(Grant Nos.51579052 and 51679045).
文摘Fluids and structures impact is one of the common phenomena in nature, and it widely exists in engineering practice,including ship hydrodynamic slamming, wave impact on offshore platforms, plunging wave on coastal structures,emergency landing of aircrafts at sea as well as impact of ultra-cold droplets and ice lumps under aviation conditions.In this paper, a two dimensional (2-D) solver for Navier-Stokes equations is developed and applied in the numerical simulation of the impact on a rigid plate by a liquid square. The computational domain is discretized by Finite Volume Method (FVM). The Volume of Fluid (VOF) technique is used to track the free surface and the PiecewiseLinear Interface Construction (PLIC) is used for reconstruction. The Continuum Surface Force (CSF) model is used to account for the surface tension. The convective term and the diffusive term are upwind and centrally differenced respectively. The Inner Doubly Iterative Efficient Algorithm for Linked Equations (IDEAL) is used to decouple the pressure and velocity. Based on the proposed techniques, collapse of water column is simulated and convergence study is performed for the validation of the numerical solver. Then the impact of a free falling liquid body is simulated, and the effect of volume and initial height of the liquid body is analyzed. In addition, the impact on a plate with a liquid layer is also simulated to study the effect of falling height on a liquid floor.
文摘Under intensive electric current, exposed aluminum interconnects undergo surface evolution driven by electromigration. The evolution of the surface morphology induces fluctuations in electric field. When the surface diffusivity is inhomogeneous, surface damage appears under electric current as a combination of stationary solution and transients. The experimental observations confirm the above theoretical predictions and raise the reliability issue of electromigration in polycrystalline interconnects.
基金supported by the National Natural Science Foundation of China(No.10734060)the National Basic Research Program of China(No.2006CB921504)
文摘Evolution of surface morphology and optical characteristics of 1.3-μm In0.5Ga0.5As/GaAs quantum dots （QDs） grown by molecular beam epitaxy （MBE） are investigated by atomic force microscopy （AFM） and photoluminescence （PL）. After deposition of 16 monolayers （ML） of In0.5Ga0.5As, QDs are formed and elongated along the [120] direction when using sub-ML depositions, while large size InGaAs QDs with better uniformity are formed when using ML or super-ML depositions. It is also found that the larger size QDs show enhanced PL efficiency without optical nonlinearity, which is in contrast to the elongated QDs.
基金This work was supported in part by the Natural Science Foundation(No.DMR-0804088)startup funds from Washington University in St.Louis.P.H.C.C.was also partially supported by the Fulbright Program and the Brazilian Ministry of Education(CAPES).Part of the work was performed at the Nano Research Facility(NRF),a member of the National Nanotechnology Infrastructure Network(NNIN),which is supported by the National Science Foundation(No.ECS-0335765).
文摘This paper presents a systematic study of the growth mechanism for Pd nanobars synthesized by reducing Na_(2)PdCl_(4) with L-ascorbic acid in an aqueous solution in the presence of bromide ions as a capping agent.Transmission electron microscopy(TEM)and high-resolution TEM analyses revealed that the growth at early stages of the synthesis was dominated by particle coalescence,followed by shape focusing via recrystallization and further growth via atomic addition.We also investigated the detailed surface structure of the nanobars using aberration-corrected scanning TEM and found that the exposed{100}surfaces contained several types of defects such as an adatom island,a vacancy pit,and atomic steps.Upon thermal annealing,the nanobars evolved into a more thermodynamically favored shape with enhanced truncation at the corners.
基金supported by the Zhejiang Provincial Natural Science Foundation of China(LQ21B030010 and LQ24B030014)the National Natural Science Foundation of China(22102150,22172146,22303085,21872126 and 21573198)。
文摘Correlating dynamic structural transformation of catalysts with the surface intermediate species under operating conditions is critical for updating the understanding of structure–performance relationships.Here,we probe the electrochemical potentialdependent surface structures and adsorbed intermediates on PtRu binary alloy nanocatalysts to revisit its synergistic mechanisms for CO electrooxidation enhanced activity.In-situ spectral characteristics by using modified shell-isolated nanoparticle-enhanced Raman spectroscopy,show that in acidic solution,when the potential is positively scanned from 0.1 V to 1.5 V relative to reversible hydrogen electrode(RHE),the surface of the alloy catalyst evolves from metallic PtRu to adsorbed oxygen gradually covering and accumulating on Ru sites(denoted as PtRuO_(x),x≤2),forming segregated RuO_(2),and finally forming a threedimensional oxide layer(denoted as 3D PtRuO_(4)).Moreover,molecular evidence associated with periodic density functional theory calculations reveals that electronic effects promote ruthenium to become more oxidizable and oxophilic.In particular,we found here that ^(*)O and ^(*)OH at surface RuO_(x) sites are highly efficient CO oxidation active species in comparison to the same entities adsorbed on metallic Ru sites.This work sheds light on the complex surface dynamic process of practical Pt-based binary nanocatalysts and improves the understanding of synergistic mechanism for the development of fuel cell devices.
基金supported by the National Natural Science Foundation of China(No.41931077)the Strategic Priority Program of CAS(No.XDB41020300)+2 种基金the Guizhou Provincial Science and Technology Projects(No.GZ2019SIG)the National Natural Science Foundation of China(L2224032)the Chinese Academy of Sciences(XK2022DXC004).
文摘Lunar dust, the finest fraction of lunar regolith, has undergone important space weathering on the Moon. It not only serves as a record of the evolution of the lunar surface environment and the modification of mineral properties, but also influences the lunar surface environment through dust transport. Our current understanding of the properties and transport mechanisms of lunar dust on the lunar surface, however, remains limited. With rapid development of lunar exploration, it is necessary to further study the problem and meet the need of future lunar exploration missions. The lunar surface is the primary environmental space where uncrewed lunar rover activity, crewed lunar exploration, and lunar base construction take place. The lunar dust will distribute in such a space area due to electrostatic lifting and impacted sputtering, which will pose a threat to lunar surface exploration activities. In addition, lunar dust transport is closely related to lunar horizon glow, lunar swirl, and lunar magnetic anomaly. Understanding the properties and transport mechanisms of lunar dust is key to comprehending the formation of these scientific phenomena. Therefore, a systematic and in-depth investigation of lunar dust properties and dust transport patterns is urgently required to advance lunar science and implement lunar exploration projects. In this study, we summarize the physical and chemical properties of lunar dust and our understanding of dust transport on the lunar surface, identify remaining challenges and issues in the study of lunar dust, and offer perspectives on this research field.
