Dissimilar friction stir welding（FSW） between aluminum and magnesium alloy was performed, using various tool rotational speed（TRS） at a ？xed travel speed, with tool offset to aluminum to investigate the formation...Dissimilar friction stir welding（FSW） between aluminum and magnesium alloy was performed, using various tool rotational speed（TRS） at a ？xed travel speed, with tool offset to aluminum to investigate the formation of intermetallic compounds（IMCs） in the banded structure（BS） zone and their effect on mechanical properties. Large quantities of IMCs, in the form of alternating bands of particles or lamellae, were found in the BS zone, where drastic material intermixing occurred during FSW. The BS microstructural characters in terms of the morphology of the bands and the quantity and distribution of IMC particles varied with TRS. All welds exhibited brittle fracture mode with their fracture paths propagating mainly in/along the IMCs in the BS. It is shown that these BS microstructural characters have significant effect on the mechanical properties of the joints. Suggestions on tailoring the BS microstructure were proposed for improving the strength of the BS zone and the final mechanical properties of the Al/Mg FSW joints.展开更多
The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission ...The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission electron microscope, and electron probe microanalyzer, the segregation characteristics of alloying elements in cast billet and their relationship with hot-rolled plate banded structure were revealed.The formation causes of an abnormal banded structure and the elimination methods were analyzed.Results indicate the serious positive segregation of C, Cr, and Mn alloy elements in the billet.Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200℃, and the spacing of the element aggregation area increased, but the segregation index of alloy elements decreased.Obvious alloying element segregation characteristics are present in the banded structure of the hot-rolled plate.This distinct white band is composed of martensitic phases.The formation of this abnormal pearlite–martensite banded structure is due to the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements.Under the air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.展开更多
Banded structure is a common harmful microstructure for low carbon microalloyed steel,which seriously shortens the service life of processed parts.In order to study the effect of oxide metallurgy on improving banded s...Banded structure is a common harmful microstructure for low carbon microalloyed steel,which seriously shortens the service life of processed parts.In order to study the effect of oxide metallurgy on improving banded structure,the Ti-Zr deoxidized low carbon microalloyed steel that can play the oxide metallurgical role of inclusion was chosen as the research object,and the inclusion characteristics,microstructure and transverse and longitudinal mechanical properties after hot rolling were analyzed.The results showed the inclusion number density increased in all experimental steels after hot rolling,and a large number of long strip inclusions with aspect ratio greater than 3 appeared along the rolling direction.In addition,after hot rolling,there were element segregation bands in the experimental steels,and granular bainite bands were formed in the element enrichment zone.However,the intragranular ferrite generated in the cooling process destroyed the continuity of granular bainite bands,so that the microstructure anisotropy indexes of experimental steels were small.The mechanical properties analysis showed that the anisotropy of performance was mainly reflected in plasticity and toughness in the experimental steels.Among them,the difference ratio of elongation,section shrinkage and impact energy of No.2 steel was 1.69%,3.87% and 1.69%,respectively,which were less than those of No.1 steel and No.3 steel.The anisotropy of microstructure and mechanical properties of No.2 steel that full played the role of oxide metallurgy were improved,and the banded structure control of low carbon microalloyed steel can be realized by oxide metallurgy technology.展开更多
At the end of May 2008,a massive bloom of macroalgae occurred in the western Yellow Sea off China and lasted for nearly two months,and annual blooms have occurred since then on. During bloom period,the surface-driftin...At the end of May 2008,a massive bloom of macroalgae occurred in the western Yellow Sea off China and lasted for nearly two months,and annual blooms have occurred since then on. During bloom period,the surface-drifting macroalgae have showed an interesting pattern dominated by a banded structure,and the distance between neighboring bands ranged from hundreds of meters to about 6 km with a peak at 1–1.5 km,which is an order of higher than the scale of Langmuir circulation of 50–100 m. In order to explain this new phenomenon,ocean current data obtained from a Doppler current profiler off Qingdao was used to implement stability analysis. By numerically solving the resulting differential Orr-Sommerfeld equation,the secondary circulation induced from the instability of the Emkan current was found to fit well with the observed spatial scale of the surface-drifting macroalgae’s banded structure. As the wind driven Emkan current exist universally in the global ocean,it is reasonable to conclude that the banded structure with kilometers distance between adjoining bands is ubiquitous. We found a new circulation in the upper ocean which is important for exchange of energy,materials and gas between the upper ocean and subsurface layer.展开更多
Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among th...Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).展开更多
Photoelectrocatalytic(PEC)seawater splitting as a green and sustainable route to harvest hydrogen is attractive yet hampered by low activity of photoanodes and unexpected high selectivity to the corrosive and toxic ch...Photoelectrocatalytic(PEC)seawater splitting as a green and sustainable route to harvest hydrogen is attractive yet hampered by low activity of photoanodes and unexpected high selectivity to the corrosive and toxic chlorine.Especially,it is full of challenges to unveil the key factors influencing the selectivity of such complex PEC processes.Herein,by regulating the energy band and surface structure of the anatase TiO_(2) nanotube array photoanode via nitrogen-doping,the seawater PEC oxidation shifts from Cl^(-)oxidation reaction(ClOR)dominant on the TiO_(2) photoanode(61.6%)to oxygen evolution reaction(OER)dominant on the N-TiO_(2) photoanode(62.9%).Comprehensive investigations including operando photoelectrochemical FTIR and DFT calculations unveil that the asymmetric hydrogen-bonding water at the N-TiO_(2) electrode/electrolyte interface enriches under illumination,facilitating proton transfer and moderate adsorption strength of oxygen-intermediates,which lowers the energy barrier for the OER yet elevates the energy barrier for the ClOR,resulting to a promoted selectivity towards the OER.The work sheds light on the underlying mechanism of the PEC water oxidation processes,and highlights the crucial role of interfacial water on the PEC selectivity,which could be regulated by controlling the energy band and the surface structure of semiconductors.展开更多
The electronic structure,elasticity,and magnetic properties of the Mn_(2)XIn(X=Fe,Co)full-Heusler compounds are comprehensively investigated via first-principles calculations.The calculated elastic constants indicate ...The electronic structure,elasticity,and magnetic properties of the Mn_(2)XIn(X=Fe,Co)full-Heusler compounds are comprehensively investigated via first-principles calculations.The calculated elastic constants indicate that both Mn_(2)FeIn and Mn_(2)Co In possess ductility.At the optimal lattice constants,the magnetic moments are found to be 1.40μB/f.u.for Mn_(2)FeIn and 1.69μB/f.u.for Mn_(2)CoIn.Under the biaxial strain ranging from-2%to 5%,Mn_(2)FeIn demonstrates a remarkable variation in the spin polarization,spanning from-2%to 74%,positioning it as a promising candidate for applications in spintronic devices.Analysis of the electronic structure reveals that the change in spin polarization under strain is due to the shift of the spin-down states at the Fermi surface.Additionally,under biaxial strain,the magnetic anisotropy of Mn_(2)FeIn undergoes a transition of easy-axis direction.Utilizing second-order perturbation theory and electronic structure analysis,the variation in magnetic anisotropy with strain can be attributed to changes of d-orbital states near the Fermi surface.展开更多
Photoelectrochemical water oxidation(PEC-WO)as a green and sustainable route to produce H_(2)O_(2)has attracted extensive attentions.However,water oxidation to H_(2)O_(2)via a 2e^(-) pathway is thermodynamically more ...Photoelectrochemical water oxidation(PEC-WO)as a green and sustainable route to produce H_(2)O_(2)has attracted extensive attentions.However,water oxidation to H_(2)O_(2)via a 2e^(-) pathway is thermodynamically more difficult than to O_(2)via a 4e^(-)pathway.Herein,with a series of BiVO_(4)-based photoanodes,the decisive factors determining the PEC activity and selectivity are elucidated,combining a comprehensive experimental and theoretical investigations.It is discovered that the ZnO/BiVO_(4)photoanode(ZnO/BVO)forms a Type-Ⅱheterojunction in energy level alignment.The accelerated photogenerated charge separation/transfer dynamics generates denser surface holes and higher surface photovoltage.Therefore,the activity of water oxidation reaction is promoted.The selectivity of PEC-WO to H_(2)O_(2)is found to be potential-dependent,i.e.,at the lower potentials(PEC-dominated),surface hole density determines the selectivity;and at the higher potentials(electrochemical-dominated),surface reaction barriers govern the selectivity.For the ZnO/BVO heterojunction photoanode,the higher surface hole density facilitates the generation of OH·and the subsequent OH·/OH·coupling to form H_(2)O_(2),thus rising up with potentials;at the higher potentials,the 2-electron pathway barrier over ZnO/BVO surface is lower than over BVO surface,which benefits from the electronic structure regulation by the underlying ZnO alleviating the over-strong adsorption of^(*)OH on BVO,thus,the two-electron pathway to produce H_(2)O_(2)is more favored than on BVO surface.This work highlights the crucial role of band energy structure of semiconductors on both PEC reaction activity and selectivity,and the knowledge gained is expected to be extended to other photoeletrochemical reactions.展开更多
This work is intended to solve the least squares semidefinite program with a banded structure. A limited memory BFGS method is presented to solve this structured program of high dimension.In the algorithm, the inverse...This work is intended to solve the least squares semidefinite program with a banded structure. A limited memory BFGS method is presented to solve this structured program of high dimension.In the algorithm, the inverse power iteration and orthogonal iteration are employed to calculate partial eigenvectors instead of full decomposition of n × n matrices. One key feature of the algorithm is that it is proved to be globally convergent under inexact gradient information. Preliminary numerical results indicate that the proposed algorithm is comparable with the inexact smoothing Newton method on some large instances of the structured problem.展开更多
The performance of the photodetector is significantly impacted by the inherent surface faults in GaAs nanowires(NWs).We combined three-dimensional(3D)gallium arsenide nanowires with zero-dimensional(0D)WS_(2) quantum ...The performance of the photodetector is significantly impacted by the inherent surface faults in GaAs nanowires(NWs).We combined three-dimensional(3D)gallium arsenide nanowires with zero-dimensional(0D)WS_(2) quantum dot(QDs)materials in a simple and convenient way to form a heterogeneous structure.Various performance enhancements have been realized through the formation of typeⅡenergy bands in heterostructures,opening up new research directions for the future development of photodetector devices.This work successfully fabricated a high-sensitivity photodetector based on WS_(2)QDs/GaAs NWs heterostructure.Under 660 nm laser excitation,the photodetector exhibits a responsivity of 368.07 A/W,a detectivity of 2.7×10^(12)Jones,an external quantum efficiency of 6.47×10^(2)%,a low-noise equivalent power of 2.27×10^(-17)W·Hz^(-1/2),a response time of 0.3 s,and a recovery time of 2.12 s.This study provides a new solution for the preparation of high-performance GaAs detectors and promotes the development of optoelectronic devices for GaAs NWs.展开更多
SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe.However,excessive hole carrier concentration in SnTe results in an extremely lo...SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe.However,excessive hole carrier concentration in SnTe results in an extremely low Seebeck coefficient and high thermal conductivity,which makes it exhibit relatively inferior thermoelectric properties.In this work,the thermoelectric performance of p-type SnTe is enhanced through regulating its energy band structures and reducing its electronic thermal conductivity by combining Bi doping with CdSe alloying.First,the carrier concentration of SnTe is successfully suppressed via Bi doping,which significantly decreases the electronic thermal conductivity.Then,the convergence and flattening of the valence bands by alloying CdSe effectively improves the effective mass of SnTe while restraining its carrier mobility.Finally,a maximum figure of merit(ZT) of~ 0.87 at 823 K and an average ZT of~ 0.51 at 300-823 K have been achieved in Sn_(0.96)Bi_(0.04)Te-5%CdSe.Our results indicate that decreasing the electronic thermal conductivity is an effective means of improving the performance of thermoelectric materials with a high carrier concentration.展开更多
So far,a clear understanding about the relationship of variable energy band structure with the corresponding charge-discharge process of energy storage materials is still lacking.Here,using optical spectroscopy(red-gr...So far,a clear understanding about the relationship of variable energy band structure with the corresponding charge-discharge process of energy storage materials is still lacking.Here,using optical spectroscopy(red-green-blue(RGB)value,reflectivity,transmittance,UV-vis,XPS,UPS)to studyα-Co(OH)_(2) electrode working in KOH electrolyte as the research object,we provide direct experimental evidence that:(1)The intercalation of OH-ions will reduce the valence/conduction band(VB and CB)and band gap energy(Eg)values;(2)The deintercalation of OH-ions corresponds with the reversion of VB,CB and E_(g) to the initial values;(3)The color of Co(OH)_(2) electrode also exhibit regular variations in RGB value during the charge-discharge process.展开更多
Materials with kagome lattices have attracted significant research attention due to their nontrivial features in energy bands.We theoretically investigate the evolution of electronic band structures of kagome lattices...Materials with kagome lattices have attracted significant research attention due to their nontrivial features in energy bands.We theoretically investigate the evolution of electronic band structures of kagome lattices in response to uniaxial strain using both a tight-binding model and an antidot model based on a periodic muffin-tin potential.It is found that the Dirac points move with applied strain.Furthermore,the flat band of unstrained kagome lattices is found to develop into a highly anisotropic shape under a stretching strain along y direction,forming a partially flat band with a region dispersionless along ky direction while dispersive along kx direction.Our results shed light on the possibility of engineering the electronic band structures of kagome materials by mechanical strain.展开更多
Band structure analysis holds significant importance for understanding the optoelectronic characteristics of semiconductor structures and exploring their potential applications in practice. For quantum well structures...Band structure analysis holds significant importance for understanding the optoelectronic characteristics of semiconductor structures and exploring their potential applications in practice. For quantum well structures, the energy of carriers in the well splits into discrete energy levels due to the confinement of barriers in the growth direction. However, the discrete energy levels obtained at a fixed wave vector cannot accurately reflect the actual energy band structure. In this work, the band structure of the type-II quantum wells is reanalyzed. When the wave vectors of the entire Brillouin region(corresponding to the growth direction) are taken into account, the quantized energy levels of the carriers in the well are replaced by subbands with certain energy distributions. This new understanding of the energy bands of low-dimensional structures not only helps us to have a deeper cognition of the structure, but also may overturn many viewpoints in traditional band theories and serve as supplementary to the band theory of low-dimensional systems.展开更多
Directional solidification experiments on Pb-Bi peritectic alloys were carried out at very low growth rate （v=0.5 μm/s） and high temperature gradient （G=35 K/mm） in an improved Bridgman furnace. The banding struc...Directional solidification experiments on Pb-Bi peritectic alloys were carried out at very low growth rate （v=0.5 μm/s） and high temperature gradient （G=35 K/mm） in an improved Bridgman furnace. The banding structures were observed in both hypoperitectic and hyperperitectic compositions （Pb-xBi, x=26%, 28%, 30% and 34%）. Tree-like primary α phase in the center of the sample surrounded by the peritectic β phase matrix was also observed, resulting from the melt convection. The banding microstructure, however, is found to be transient after the tree-like structure and only the peritectic phase forms after a few bands. Composition variations in the banding structure are measured to determine the nucleation undercooling for both α and β phases. In a finite length sample, convection is shown to lead only to the transient formation of bands. In this transient banding regime, only a few bands with a variable width are formed, and this transient banding process can occur over a wide range of compositions inside the two-phase peritectic region.展开更多
The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 n...The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 nm diameter,hexagonal,single crystals,sintering at,e.g.,350℃,results,initially,in merger of neighboring particles,followed by individual molecular motion on the substrate and the formation of folded chain,lamellar single crystals andspherulites,and on-edge ribbons.It is suggested these structures develop,with time,in the mesomorphic“melt”.Sintering ofthe bulk resin yields extended chain,band structures,as well as folded chain lamellae;end-surface to end-surface merger,possibly by end-to-end polymerization,occurs with increasing time.展开更多
Due to the weak interlayer interactions,the binary Ⅲ-Ⅵ chalcogenides Ga Se can exist in several distinct polymorphs.Among them,the so-called β-and ε-phases simultaneously exhibit favorable total energies and moder...Due to the weak interlayer interactions,the binary Ⅲ-Ⅵ chalcogenides Ga Se can exist in several distinct polymorphs.Among them,the so-called β-and ε-phases simultaneously exhibit favorable total energies and moderate band gaps,which offer a good platform to explore their thermoelectric properties.Here,we demonstrate by first-principles calculations that the two systems have very similar band structures and phonon dispersions,despite different stacking sequences between adjacent layers.Interestingly,the lattice thermal conductivity of ε-GaSe is obviously lower than that of β-GaSe,which is inherently tied to stronger lattice anharmonicity caused by bonding heterogeneity.Besides,both systems exhibit higher p-type power factors due to doubly degenerate bands with weaker dispersions around the valence band maximum.As a consequence,a significantly enhanced p-type figure-of-merit of 2.1 can be realized at 700 K along the out-of-plane direction of theε-phase.展开更多
The capacity to predict X-ray transition and K-edge energies in dense finite-temperatur plasmas with high precision is of primary importance for atomic physics of matter under extreme conditions.The dual characteristi...The capacity to predict X-ray transition and K-edge energies in dense finite-temperatur plasmas with high precision is of primary importance for atomic physics of matter under extreme conditions.The dual characteristics of bound and continuum states in dense matter are modeled by a valence-band-like structure in a generalized ion-sphere approach with states that are either bound,free,or mixed.The self-consistent combination of this model with the Dirac wave equations of multielectron bound states allows one to fully respect the Pauli principle and to take into account the exact nonlocal exchange terms.The generalized method allows very high precision without implication of calibration shifts and scaling parameters and therefore has predictive power.This leads to new insights in the analysis of various data.The simple ionization model representing the K-edge is generalized to excitation–ionization phenomena resulting in an advanced interpretation of ionization depression data in near-solid-density plasmas.The model predicts scaling relations along the isoelectronic sequences and the existence of bound M-states that are in excellent agreement with experimental data,whereas other methods have failed.The application to unexplained data from compound materials also gives good agreement without the need to invoke any additional assumptions in the generalized model,whereas other methods have lacked consistency.展开更多
Two-dimensional(2D)ferrovalley materials with valley-dependent Hall effect have attracted great interest due to their significant applications in spintronics.In this paper,by using first-principles computational simul...Two-dimensional(2D)ferrovalley materials with valley-dependent Hall effect have attracted great interest due to their significant applications in spintronics.In this paper,by using first-principles computational simulations,we predict that the ScBrCl monolayer is a 2D ferrovalley material with valley-dependent multiple Hall effects.After calculations,we found that the ScBrCl monolayer has excellent thermodynamic stability and kinetic stability,and has a high magnetic transition temperature.When the magnetization direction is turned from in-plane to out-of-plane,a large valley polarization of 44 meV can be generated.In particular,under 5.1%–5.3%tensile strain conditions,ScBrCl monolayer can achieve quantum anomalous Hall effect,and further prove its existence through non-zero Chern number and non-trivial edge state.Our discovery enriches the research on valley-dependent Hall effect and promotes the potential application of 2D Janus monolayer in valley electronics.展开更多
Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phen...Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phenomena,has so far been predominantly determined by fitting Landau-level spectra.Here,by characterizing the electronic capacitance,we reveal unprecedented details of its band structure:the energy shift between the heavy-and light-mass band edges in the conduction band is much larger than that in the valence band.Their responses to displacement fields are also distinct:while the former increases monotonically and significantly,the latter first decreases and then increases slightly.Our results suggest that the interlayer interactions and hopping parameters are more complex than previously expected,calling for precise measurements of band structures in various multilayer van der Waals systems.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51204108)the National Research Foundation for Doctoral Program of Higher Education of China(Grant No.20120073120120)+1 种基金the Shanghai Committee of Science and Technology(Grant No.11ZR1418100)the Research Foundation of Shanghai Academy of Spaceflight Technology-Shanghai Jiao Tong University Joint Research Center for Advanced Spaceflight Technology(Grant No.USCAST2012-12)
文摘Dissimilar friction stir welding（FSW） between aluminum and magnesium alloy was performed, using various tool rotational speed（TRS） at a ？xed travel speed, with tool offset to aluminum to investigate the formation of intermetallic compounds（IMCs） in the banded structure（BS） zone and their effect on mechanical properties. Large quantities of IMCs, in the form of alternating bands of particles or lamellae, were found in the BS zone, where drastic material intermixing occurred during FSW. The BS microstructural characters in terms of the morphology of the bands and the quantity and distribution of IMC particles varied with TRS. All welds exhibited brittle fracture mode with their fracture paths propagating mainly in/along the IMCs in the BS. It is shown that these BS microstructural characters have significant effect on the mechanical properties of the joints. Suggestions on tailoring the BS microstructure were proposed for improving the strength of the BS zone and the final mechanical properties of the Al/Mg FSW joints.
文摘The effect of Cr/Mn segregation on the abnormal banded structure of high carbon bearing steel was studied by reheating and hot rolling.With the use of an optical microscope, scanning electron microscope, transmission electron microscope, and electron probe microanalyzer, the segregation characteristics of alloying elements in cast billet and their relationship with hot-rolled plate banded structure were revealed.The formation causes of an abnormal banded structure and the elimination methods were analyzed.Results indicate the serious positive segregation of C, Cr, and Mn alloy elements in the billet.Even distribution of Cr/Mn elements could not be achieved after 10 h of heat preservation at 1200℃, and the spacing of the element aggregation area increased, but the segregation index of alloy elements decreased.Obvious alloying element segregation characteristics are present in the banded structure of the hot-rolled plate.This distinct white band is composed of martensitic phases.The formation of this abnormal pearlite–martensite banded structure is due to the interaction between the undercooled austenite transformation behavior of hot-rolled metal and the segregation of its alloying elements.Under the air cooling after rolling, controlling the segregation index of alloy elements can reduce or eliminate the abnormal banded structure.
基金supported by the Shaanxi Natural Science Basic Research Program(No.2023-JC-QN-0376)the National Natural Science Foundation of China(Nos.52074207 and 51874081).
文摘Banded structure is a common harmful microstructure for low carbon microalloyed steel,which seriously shortens the service life of processed parts.In order to study the effect of oxide metallurgy on improving banded structure,the Ti-Zr deoxidized low carbon microalloyed steel that can play the oxide metallurgical role of inclusion was chosen as the research object,and the inclusion characteristics,microstructure and transverse and longitudinal mechanical properties after hot rolling were analyzed.The results showed the inclusion number density increased in all experimental steels after hot rolling,and a large number of long strip inclusions with aspect ratio greater than 3 appeared along the rolling direction.In addition,after hot rolling,there were element segregation bands in the experimental steels,and granular bainite bands were formed in the element enrichment zone.However,the intragranular ferrite generated in the cooling process destroyed the continuity of granular bainite bands,so that the microstructure anisotropy indexes of experimental steels were small.The mechanical properties analysis showed that the anisotropy of performance was mainly reflected in plasticity and toughness in the experimental steels.Among them,the difference ratio of elongation,section shrinkage and impact energy of No.2 steel was 1.69%,3.87% and 1.69%,respectively,which were less than those of No.1 steel and No.3 steel.The anisotropy of microstructure and mechanical properties of No.2 steel that full played the role of oxide metallurgy were improved,and the banded structure control of low carbon microalloyed steel can be realized by oxide metallurgy technology.
基金The National Natural Science Foundation of China under contract No.41821004the National Program on Global Change and Air-Sea Interaction under contract No.GASI-IPOVAI-05.
文摘At the end of May 2008,a massive bloom of macroalgae occurred in the western Yellow Sea off China and lasted for nearly two months,and annual blooms have occurred since then on. During bloom period,the surface-drifting macroalgae have showed an interesting pattern dominated by a banded structure,and the distance between neighboring bands ranged from hundreds of meters to about 6 km with a peak at 1–1.5 km,which is an order of higher than the scale of Langmuir circulation of 50–100 m. In order to explain this new phenomenon,ocean current data obtained from a Doppler current profiler off Qingdao was used to implement stability analysis. By numerically solving the resulting differential Orr-Sommerfeld equation,the secondary circulation induced from the instability of the Emkan current was found to fit well with the observed spatial scale of the surface-drifting macroalgae’s banded structure. As the wind driven Emkan current exist universally in the global ocean,it is reasonable to conclude that the banded structure with kilometers distance between adjoining bands is ubiquitous. We found a new circulation in the upper ocean which is important for exchange of energy,materials and gas between the upper ocean and subsurface layer.
基金supported by the National Nature Science Foundation of China[Grant Nos.92365204 and 12274298(Z.K.Liu)]the National Key R&D program of China[Grant No.2022YFA1604400/03(Z.K.Liu)]Zhangjiang Laboratory(Y.M.Zhang).The authors thank BL02B at the Shanghai Synchrotron Radiation Facility supported by the National Natural Science Foundation of China(Contract No.11227902).
文摘Fe-based superconductors represent a fascinating class of materials,extensively studied for their complex interplay of superconductivity,magnetism,spin density waves,and nematicity,along with the interactions among these orders.An intriguing yet unexplained phenomenon observed in Fe-based superconductors is the emergence of superconductivity below 25K in the non-superconducting parent compound SrFe_(2)As_(2)following exposure to water at its surface.In this study,we employed in situ angle-resolved photoemission spectroscopy and low-energy electron diffraction to meticulously examine the electronic structure evolution of SrFe_(2)As_(2)upon in situ water dosing.Our findings indicate that water dosing markedly attenuates the spin density wave phase and surface Sr reconstruction while preserving the nematic order in SrFe_(2)As_(2).Furthermore,we detected an enhancement in the spectral weight of bands near the Fermi level.Our observations highlight the critical role of the intricate interplay among various orders induced by water dosing,which effectively modifies the band structure and favors the emergence of superconductivity in SrFe_(2)As_(2).
文摘Photoelectrocatalytic(PEC)seawater splitting as a green and sustainable route to harvest hydrogen is attractive yet hampered by low activity of photoanodes and unexpected high selectivity to the corrosive and toxic chlorine.Especially,it is full of challenges to unveil the key factors influencing the selectivity of such complex PEC processes.Herein,by regulating the energy band and surface structure of the anatase TiO_(2) nanotube array photoanode via nitrogen-doping,the seawater PEC oxidation shifts from Cl^(-)oxidation reaction(ClOR)dominant on the TiO_(2) photoanode(61.6%)to oxygen evolution reaction(OER)dominant on the N-TiO_(2) photoanode(62.9%).Comprehensive investigations including operando photoelectrochemical FTIR and DFT calculations unveil that the asymmetric hydrogen-bonding water at the N-TiO_(2) electrode/electrolyte interface enriches under illumination,facilitating proton transfer and moderate adsorption strength of oxygen-intermediates,which lowers the energy barrier for the OER yet elevates the energy barrier for the ClOR,resulting to a promoted selectivity towards the OER.The work sheds light on the underlying mechanism of the PEC water oxidation processes,and highlights the crucial role of interfacial water on the PEC selectivity,which could be regulated by controlling the energy band and the surface structure of semiconductors.
基金Project supported by the Fundamental Research Funds for the Provincial Universities of Zhejiang Province,China(Grant No.GK229909299001-05)Zhejiang Provincial Public Welfare Projects of China(Grant No.LGG22F030017)。
文摘The electronic structure,elasticity,and magnetic properties of the Mn_(2)XIn(X=Fe,Co)full-Heusler compounds are comprehensively investigated via first-principles calculations.The calculated elastic constants indicate that both Mn_(2)FeIn and Mn_(2)Co In possess ductility.At the optimal lattice constants,the magnetic moments are found to be 1.40μB/f.u.for Mn_(2)FeIn and 1.69μB/f.u.for Mn_(2)CoIn.Under the biaxial strain ranging from-2%to 5%,Mn_(2)FeIn demonstrates a remarkable variation in the spin polarization,spanning from-2%to 74%,positioning it as a promising candidate for applications in spintronic devices.Analysis of the electronic structure reveals that the change in spin polarization under strain is due to the shift of the spin-down states at the Fermi surface.Additionally,under biaxial strain,the magnetic anisotropy of Mn_(2)FeIn undergoes a transition of easy-axis direction.Utilizing second-order perturbation theory and electronic structure analysis,the variation in magnetic anisotropy with strain can be attributed to changes of d-orbital states near the Fermi surface.
基金financially supported by the National Natural Science Foundation of China(22478211,22179067,22372017)the Major Fundamental Research Program of Natural Science Foundation of Shandong Province(ZR2022ZD10)。
文摘Photoelectrochemical water oxidation(PEC-WO)as a green and sustainable route to produce H_(2)O_(2)has attracted extensive attentions.However,water oxidation to H_(2)O_(2)via a 2e^(-) pathway is thermodynamically more difficult than to O_(2)via a 4e^(-)pathway.Herein,with a series of BiVO_(4)-based photoanodes,the decisive factors determining the PEC activity and selectivity are elucidated,combining a comprehensive experimental and theoretical investigations.It is discovered that the ZnO/BiVO_(4)photoanode(ZnO/BVO)forms a Type-Ⅱheterojunction in energy level alignment.The accelerated photogenerated charge separation/transfer dynamics generates denser surface holes and higher surface photovoltage.Therefore,the activity of water oxidation reaction is promoted.The selectivity of PEC-WO to H_(2)O_(2)is found to be potential-dependent,i.e.,at the lower potentials(PEC-dominated),surface hole density determines the selectivity;and at the higher potentials(electrochemical-dominated),surface reaction barriers govern the selectivity.For the ZnO/BVO heterojunction photoanode,the higher surface hole density facilitates the generation of OH·and the subsequent OH·/OH·coupling to form H_(2)O_(2),thus rising up with potentials;at the higher potentials,the 2-electron pathway barrier over ZnO/BVO surface is lower than over BVO surface,which benefits from the electronic structure regulation by the underlying ZnO alleviating the over-strong adsorption of^(*)OH on BVO,thus,the two-electron pathway to produce H_(2)O_(2)is more favored than on BVO surface.This work highlights the crucial role of band energy structure of semiconductors on both PEC reaction activity and selectivity,and the knowledge gained is expected to be extended to other photoeletrochemical reactions.
基金supported by the National Natural Science Foundation of China under Grant No.11601318。
文摘This work is intended to solve the least squares semidefinite program with a banded structure. A limited memory BFGS method is presented to solve this structured program of high dimension.In the algorithm, the inverse power iteration and orthogonal iteration are employed to calculate partial eigenvectors instead of full decomposition of n × n matrices. One key feature of the algorithm is that it is proved to be globally convergent under inexact gradient information. Preliminary numerical results indicate that the proposed algorithm is comparable with the inexact smoothing Newton method on some large instances of the structured problem.
文摘The performance of the photodetector is significantly impacted by the inherent surface faults in GaAs nanowires(NWs).We combined three-dimensional(3D)gallium arsenide nanowires with zero-dimensional(0D)WS_(2) quantum dot(QDs)materials in a simple and convenient way to form a heterogeneous structure.Various performance enhancements have been realized through the formation of typeⅡenergy bands in heterostructures,opening up new research directions for the future development of photodetector devices.This work successfully fabricated a high-sensitivity photodetector based on WS_(2)QDs/GaAs NWs heterostructure.Under 660 nm laser excitation,the photodetector exhibits a responsivity of 368.07 A/W,a detectivity of 2.7×10^(12)Jones,an external quantum efficiency of 6.47×10^(2)%,a low-noise equivalent power of 2.27×10^(-17)W·Hz^(-1/2),a response time of 0.3 s,and a recovery time of 2.12 s.This study provides a new solution for the preparation of high-performance GaAs detectors and promotes the development of optoelectronic devices for GaAs NWs.
基金financially supported by the National Natural Science Foundation of China (Nos.52102234 and 51972094)the High-level Talents Research Initiation Project of Hebei University (No.521000981421)Hebei Province Introduced Overseas Student Funding Project (No.C20210313)。
文摘SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe.However,excessive hole carrier concentration in SnTe results in an extremely low Seebeck coefficient and high thermal conductivity,which makes it exhibit relatively inferior thermoelectric properties.In this work,the thermoelectric performance of p-type SnTe is enhanced through regulating its energy band structures and reducing its electronic thermal conductivity by combining Bi doping with CdSe alloying.First,the carrier concentration of SnTe is successfully suppressed via Bi doping,which significantly decreases the electronic thermal conductivity.Then,the convergence and flattening of the valence bands by alloying CdSe effectively improves the effective mass of SnTe while restraining its carrier mobility.Finally,a maximum figure of merit(ZT) of~ 0.87 at 823 K and an average ZT of~ 0.51 at 300-823 K have been achieved in Sn_(0.96)Bi_(0.04)Te-5%CdSe.Our results indicate that decreasing the electronic thermal conductivity is an effective means of improving the performance of thermoelectric materials with a high carrier concentration.
基金supported by the National Natural Science Foundation of China(Nos.51972146,52072150).
文摘So far,a clear understanding about the relationship of variable energy band structure with the corresponding charge-discharge process of energy storage materials is still lacking.Here,using optical spectroscopy(red-green-blue(RGB)value,reflectivity,transmittance,UV-vis,XPS,UPS)to studyα-Co(OH)_(2) electrode working in KOH electrolyte as the research object,we provide direct experimental evidence that:(1)The intercalation of OH-ions will reduce the valence/conduction band(VB and CB)and band gap energy(Eg)values;(2)The deintercalation of OH-ions corresponds with the reversion of VB,CB and E_(g) to the initial values;(3)The color of Co(OH)_(2) electrode also exhibit regular variations in RGB value during the charge-discharge process.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11904261 and 11904259).
文摘Materials with kagome lattices have attracted significant research attention due to their nontrivial features in energy bands.We theoretically investigate the evolution of electronic band structures of kagome lattices in response to uniaxial strain using both a tight-binding model and an antidot model based on a periodic muffin-tin potential.It is found that the Dirac points move with applied strain.Furthermore,the flat band of unstrained kagome lattices is found to develop into a highly anisotropic shape under a stretching strain along y direction,forming a partially flat band with a region dispersionless along ky direction while dispersive along kx direction.Our results shed light on the possibility of engineering the electronic band structures of kagome materials by mechanical strain.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61991441 and 62004218)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB01000000)Youth Innovation Promotion Association Chinese Academy of Sciences (Grant No. 2021005)。
文摘Band structure analysis holds significant importance for understanding the optoelectronic characteristics of semiconductor structures and exploring their potential applications in practice. For quantum well structures, the energy of carriers in the well splits into discrete energy levels due to the confinement of barriers in the growth direction. However, the discrete energy levels obtained at a fixed wave vector cannot accurately reflect the actual energy band structure. In this work, the band structure of the type-II quantum wells is reanalyzed. When the wave vectors of the entire Brillouin region(corresponding to the growth direction) are taken into account, the quantized energy levels of the carriers in the well are replaced by subbands with certain energy distributions. This new understanding of the energy bands of low-dimensional structures not only helps us to have a deeper cognition of the structure, but also may overturn many viewpoints in traditional band theories and serve as supplementary to the band theory of low-dimensional systems.
基金Project (20110491492) supported by the China Postdoctoral Science FoundationProject (20114BAB216017) supported by the Natural Science Foundation of Jiangxi Province, ChinaProject (GJJ12035) supported by the Science Foundation of the Educational Department of Jiangxi Province, China
文摘Directional solidification experiments on Pb-Bi peritectic alloys were carried out at very low growth rate （v=0.5 μm/s） and high temperature gradient （G=35 K/mm） in an improved Bridgman furnace. The banding structures were observed in both hypoperitectic and hyperperitectic compositions （Pb-xBi, x=26%, 28%, 30% and 34%）. Tree-like primary α phase in the center of the sample surrounded by the peritectic β phase matrix was also observed, resulting from the melt convection. The banding microstructure, however, is found to be transient after the tree-like structure and only the peritectic phase forms after a few bands. Composition variations in the banding structure are measured to determine the nucleation undercooling for both α and β phases. In a finite length sample, convection is shown to lead only to the transient formation of bands. In this transient banding regime, only a few bands with a variable width are formed, and this transient banding process can occur over a wide range of compositions inside the two-phase peritectic region.
文摘The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 nm diameter,hexagonal,single crystals,sintering at,e.g.,350℃,results,initially,in merger of neighboring particles,followed by individual molecular motion on the substrate and the formation of folded chain,lamellar single crystals andspherulites,and on-edge ribbons.It is suggested these structures develop,with time,in the mesomorphic“melt”.Sintering ofthe bulk resin yields extended chain,band structures,as well as folded chain lamellae;end-surface to end-surface merger,possibly by end-to-end polymerization,occurs with increasing time.
基金supported by the National Natural Science Foundation of China(Grant Nos.62074114 and 12474019)。
文摘Due to the weak interlayer interactions,the binary Ⅲ-Ⅵ chalcogenides Ga Se can exist in several distinct polymorphs.Among them,the so-called β-and ε-phases simultaneously exhibit favorable total energies and moderate band gaps,which offer a good platform to explore their thermoelectric properties.Here,we demonstrate by first-principles calculations that the two systems have very similar band structures and phonon dispersions,despite different stacking sequences between adjacent layers.Interestingly,the lattice thermal conductivity of ε-GaSe is obviously lower than that of β-GaSe,which is inherently tied to stronger lattice anharmonicity caused by bonding heterogeneity.Besides,both systems exhibit higher p-type power factors due to doubly degenerate bands with weaker dispersions around the valence band maximum.As a consequence,a significantly enhanced p-type figure-of-merit of 2.1 can be realized at 700 K along the out-of-plane direction of theε-phase.
基金supported by the NSFC under Grant Nos.11374315 and 12074395the Invited Scientist Program of CNRS at Ecole Polytechnique,Palaiseau,France。
文摘The capacity to predict X-ray transition and K-edge energies in dense finite-temperatur plasmas with high precision is of primary importance for atomic physics of matter under extreme conditions.The dual characteristics of bound and continuum states in dense matter are modeled by a valence-band-like structure in a generalized ion-sphere approach with states that are either bound,free,or mixed.The self-consistent combination of this model with the Dirac wave equations of multielectron bound states allows one to fully respect the Pauli principle and to take into account the exact nonlocal exchange terms.The generalized method allows very high precision without implication of calibration shifts and scaling parameters and therefore has predictive power.This leads to new insights in the analysis of various data.The simple ionization model representing the K-edge is generalized to excitation–ionization phenomena resulting in an advanced interpretation of ionization depression data in near-solid-density plasmas.The model predicts scaling relations along the isoelectronic sequences and the existence of bound M-states that are in excellent agreement with experimental data,whereas other methods have failed.The application to unexplained data from compound materials also gives good agreement without the need to invoke any additional assumptions in the generalized model,whereas other methods have lacked consistency.
基金Project supported by the National Natural Science Foundation of China(Grant No.52173283).
文摘Two-dimensional(2D)ferrovalley materials with valley-dependent Hall effect have attracted great interest due to their significant applications in spintronics.In this paper,by using first-principles computational simulations,we predict that the ScBrCl monolayer is a 2D ferrovalley material with valley-dependent multiple Hall effects.After calculations,we found that the ScBrCl monolayer has excellent thermodynamic stability and kinetic stability,and has a high magnetic transition temperature.When the magnetization direction is turned from in-plane to out-of-plane,a large valley polarization of 44 meV can be generated.In particular,under 5.1%–5.3%tensile strain conditions,ScBrCl monolayer can achieve quantum anomalous Hall effect,and further prove its existence through non-zero Chern number and non-trivial edge state.Our discovery enriches the research on valley-dependent Hall effect and promotes the potential application of 2D Janus monolayer in valley electronics.
基金supported by the National Natural Science Foundation of China(Grant Nos.123B1037 and 12274402)the National Key Research and Development Program of China(Grant No.2024YFA1409700).
文摘Tetralayer graphene has shown several interesting properties such as tunable Lifshitz transitions,helical edge states,and high-temperature anomalous Hall effects.The band structure,which directly relates to these phenomena,has so far been predominantly determined by fitting Landau-level spectra.Here,by characterizing the electronic capacitance,we reveal unprecedented details of its band structure:the energy shift between the heavy-and light-mass band edges in the conduction band is much larger than that in the valence band.Their responses to displacement fields are also distinct:while the former increases monotonically and significantly,the latter first decreases and then increases slightly.Our results suggest that the interlayer interactions and hopping parameters are more complex than previously expected,calling for precise measurements of band structures in various multilayer van der Waals systems.
