Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often ope...Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream(d) is short. It transits to the diffuse mode with increasing d. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer,which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy,plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing d. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.展开更多
In the H-mode experiments conducted on the Experimental Advanced Superconducting Tokamak(EAST),fluctuations induced by the so-called edge localized modes(ELMs)are captured by a high-speed vacuum ultraviolet(VUV)imagin...In the H-mode experiments conducted on the Experimental Advanced Superconducting Tokamak(EAST),fluctuations induced by the so-called edge localized modes(ELMs)are captured by a high-speed vacuum ultraviolet(VUV)imaging system.Clear field line-aligned filamentary structures are analyzed in this work.Ion transport induced by ELM filaments in the scrape-off layer(SOL)under different discharge conditions is analyzed by comparing the VUV signals with the divertor probe signals.It is found that convective transport along open field lines towards the divertor target dominates the parallel ion particle transport mechanism during ELMs.The toroidal mode number of the filamentary structure derived from the VUV images increases with the electron density pedestal height.The analysis of the toroidal distribution characteristics during ELM bursts reveals toroidal asymmetry.The influence of resonance magnetic perturbation(RMP)on the ELM size is also analyzed using VUV imaging data.When the phase difference of the coil changes periodically,the widths of the filaments change as well.Additionally,the temporal evolution of the ELMs on the VUV signals provides rise time and decay time for each single ELM event,and the results indicate a negative correlation trend between these two times.展开更多
The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasm...The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.展开更多
We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a pea...We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity （FLSC）. FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped （x = 0.10） compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.展开更多
The plasma behavior of filamentary barrier discharges in helium is simulated using a twodimensional（2D） particle-in-cell/Monte Carlo model. Four different phases have been suggested in terms of the development of th...The plasma behavior of filamentary barrier discharges in helium is simulated using a twodimensional（2D） particle-in-cell/Monte Carlo model. Four different phases have been suggested in terms of the development of the discharge： the Townsend phase; the space-charge dominated phase; the formation of the cathode layer, and the extinguishing phase. The spatialtemporal evolution of the particle densities, velocities of the charged particles, electric fields, and surface charges has been demonstrated. Our simulation provides insights into the underlying mechanism of the discharge and explains many dynamical behaviors of dielectric barrier discharge（DBD） filaments.展开更多
It is shown that a single-particle wave function Ψ, obtained (Landau, 1930) as a solution of the Schr?dinger equation (for a charged particle in a homogeneous magnetic field), and an operator relation of?(or equation...It is shown that a single-particle wave function Ψ, obtained (Landau, 1930) as a solution of the Schr?dinger equation (for a charged particle in a homogeneous magnetic field), and an operator relation of?(or equation?) lead to the dynamic description of one-dimensional many-particle quantum filamentary states. Thus, one can overcome the problem, connected with the finding of many-body wave function as solution of the Schr?dinger equation with a very tangled Hamiltonian for multi-body system. An effect of nonlocality appears. The dependence of the linear density of particles on the magnetic field and on the number of particles in the one- dimension filamentary multiparticle quantum structure is calculated.展开更多
The analysis of the filamentary structure of the cosmo as well as that of the internal structure of the polar ice suggests the development of models based on three-dimensional(3D)point processes.A point process,regard...The analysis of the filamentary structure of the cosmo as well as that of the internal structure of the polar ice suggests the development of models based on three-dimensional(3D)point processes.A point process,regarded as a random measure,can be expressed as a sum of Delta Dirac measures concentrated at some random points.The integration with respect to the point process leads the continuous wavelet transform of the process itself.As possible mother wavelets,we propose the application of the Mexican hat and the Morlet wavelet in order to implement the scale-angle energy density of the process,depending on the dilation parameter and on the three angles which define the direction in the Euclidean space.Such indicator proves to be a sensitive detector of any variation in the direction and it can be successfully implemented to study the isotropy or the filamentary structure in 3D point patterns.展开更多
Cu-Ag filamentary microcomposites with different Ag contents were prepared by cold drawing and intermediate heat treatments. The microstructure characterization and filamentary distribution were observed for two-phase...Cu-Ag filamentary microcomposites with different Ag contents were prepared by cold drawing and intermediate heat treatments. The microstructure characterization and filamentary distribution were observed for two-phase alloys under different conditions. The effect of heavy drawing strain on the microstructure evolution of Cu-Ag alloys was investigated. The results show that the microstructure components consist of Cu dendrites, eutectic colonies and secondary Ag precipitates in the alloys containing 6%-24% （mass fraction） Ag. With the increase in Ag content, the eutectic colonies in the microstructure increase and gradually change into a continuous net-like distribution. The Cu dendrites, eutectic colonies and secondary Ag precipitates are elongated in an axial direction and developed into the composite filamentary structure during cold drawing deformation. The eutectic colonies tend to evolve into filamentary bundles. The filamentary diameters decrease with the increase in drawing strain degree for the two-phase alloys, in particular for the alloys with low Ag content. The reduction in filamentary diameters becomes slow once the drawing strain has exceeded a certain level.展开更多
In this article,the bunched transport of photoexcited carriers in a GaAs photoconductive semiconductor switch(PCSS)with interdigitated electrodes is investigated under femtosecond laser excitation.Continuous outputs f...In this article,the bunched transport of photoexcited carriers in a GaAs photoconductive semiconductor switch(PCSS)with interdigitated electrodes is investigated under femtosecond laser excitation.Continuous outputs featuring high gain are obtained for single shots and at 1 kHz by varying the optical excitation energy.An ensemble three-valley Monte Carlo simulation is utilized to investigate the transient characteristics and the dynamic process of photoexcited carriers.It demonstrates that the presence of a plasma channel can be attributed to the bunching of high-density electron–hole pairs,which are transported in the form of a highdensity filamentary current.The results provide a picture of the evolution of photoexcited carriers during transient switching.A photoinduced heat effect is analyzed,which reveals the related failure mechanism of GaAs PCSS at various repetition rates.展开更多
Resistive random-access memory(RRAM)is a promising technology to develop nonvolatile memory and artificial synaptic devices for brain-inspired neuromorphic computing.Here,we have developed a STO:Ag/SiO_(2) bilayer bas...Resistive random-access memory(RRAM)is a promising technology to develop nonvolatile memory and artificial synaptic devices for brain-inspired neuromorphic computing.Here,we have developed a STO:Ag/SiO_(2) bilayer based memristor that has exhibited a filamentary resistive switching with stable endurance and long-term data retention ability.The memristor also exhibits a tunable resistance modulation under positive and negative pulse trains,which could fully mimic the potentiation and depression behavior like a bio-synapse.Several synaptic plasticity functions,including long-term potentiation(LTP)and long-term depression(LTD),paired-pulsed facilitation(PPF),spike-rate-dependent-plasticity(SRDP),and post-tetanic potentiation(PTP),are faithfully implemented with the fabricated memristor.Moreover,to demonstrate the feasibility of our memristor synapse for neuromorphic applications,spike-timedependent plasticity(STDP)is also investigated.Based on conductive atomic force microscopy observations and electrical transport model analyses,it can be concluded that it is the controlled formation and rupture of Ag filaments that are responsible for the resistive switching while exhibiting a switching ratio of~10;along with a good endurance and stability suitable for nonvolatile memory applications.Before fully electroforming,the gradual conductance modulation of Ag/STO:Ag/SiO_(2)/p^(++)-Si memristor can be realized,and the working mechanism could be explained by the succeeding growth and contraction of Ag filaments promoted by a redox reaction.This newly fabricated memristor may enable the development of nonvolatile memory and realize controllable resistance/weight modulation when applied as an artificial synapse for neuromorphic computing.展开更多
A tangential fast visible camera has been set up in EAST tokamak for the study of edge MHD instabilities such as ELM. To determine the 3-D information from CCD images, Tsai＇s two-stage technique was utilized to calib...A tangential fast visible camera has been set up in EAST tokamak for the study of edge MHD instabilities such as ELM. To determine the 3-D information from CCD images, Tsai＇s two-stage technique was utilized to calibrate the high-speed camera imaging system for ELM study. By applying tiles of the passive stabilizers in the tokamak device as the calibration pattern, transformation parameters for transforming from a 3-D world coordinate system to a 2-D image coordinate system were obtained, including the rotation matrix, the translation vector, the focal length and the lens distortion. The calibration errors were estimated and the results indicate the reliability of the method used for the camera imaging system. Through the calibration, some information about ELM filaments, such as positions and velocities were obtained from images of H-mode CCD videos.展开更多
A study of the evolution of the pulse width in homogeneous dielectric barrier dis- charge at atmospheric pressure with helium as the working gas is reported by using a one- dimensional fluid model. In this paper, a ne...A study of the evolution of the pulse width in homogeneous dielectric barrier dis- charge at atmospheric pressure with helium as the working gas is reported by using a one- dimensional fluid model. In this paper, a new computational method is presented to estimate the pulse width through calculating the time interval between the breakdown voltage and the extinguishing voltage. The effects on the discharge characteristics of the applied voltage and exci- tation frequency are studied based on the computational data. The results of the simulation show that the pulse width is observed to be narrower and the time intervals between two consecutive current pulses decrease with increasing amplitude and excitation frequency, which indicates that the homogeneous discharge is susceptible to the filamentary mode. The simulation results support the conclusion that in order to restrain the transition from the glow mode to filamentary mode, the applied voltage and excitation frequency should be kept within an appropriate range.展开更多
The homogeneous dielectric barrier discharge （DBD） in atmospheric air between two symmetric-columnar copper electrodes with epoxy plates as the dielectric barriers is generated using a us pulse high voltage power su...The homogeneous dielectric barrier discharge （DBD） in atmospheric air between two symmetric-columnar copper electrodes with epoxy plates as the dielectric barriers is generated using a us pulse high voltage power supply. The discharge characteristics are studied by measurement of its electrical discharge parameters and observation of its light emission phenom- ena, and the main discharge parameters of the homogenous DBD, such as discharge current and average discharge power, are calculated. Results show that the discharge generated is a homogeneous one with one larger single current pulse of about 2 #s duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two elec- trodes. The influences of applied voltage amplitude, air gap distance and barrier thickness on the transition of discharge modes are studied. With the increase of air gap distance, the discharge will transit from homogeneous mode to filamentary mode. The higher the thickness of dielectric barriers, the larger the air gap distance for generating the homogeneous discharge mode. The average discharge power increases non-linearly with increasing applied voltage amplitude, and decreases non-linearly with the increase of air gap distance and barrier thickness. In order to generate stable and homogeneous DBD with high discharge power, thin barriers distance should be used, and higher applied voltage amplitude should be applied to small air gap.展开更多
A pseudoglow discharge behaviour is achieved at a 2.0-mm dielectric-dielectric electrode gap in pure helium under atmospheric pressure. An experimental study of the pseudoglow discharges is presented. The electrical c...A pseudoglow discharge behaviour is achieved at a 2.0-mm dielectric-dielectric electrode gap in pure helium under atmospheric pressure. An experimental study of the pseudoglow discharges is presented. The electrical characteristics and the discharge photos of the pseudoglow discharges are analyzed and discussed. The current-voltage parameters of the pseudoglow dis- charges are considered in regard to the influence on their behaviour.展开更多
The results of research on the adsorption characteristics of materials based on fibrous carbon (CNF) are considered in this paper. It is shown that changing the conditions and procedure of CNF modifying namely specifi...The results of research on the adsorption characteristics of materials based on fibrous carbon (CNF) are considered in this paper. It is shown that changing the conditions and procedure of CNF modifying namely specific adsorption surface, volume of the pore space, and parameters of the pore structure it became possible ultimately to vary in a wide range the adsorption characteristics of obtained materials.展开更多
Ultralow-power non-volatile memristors are key elements in electronics.Generally,power reduction of memristors compromises data retention,a challenge known as the“power-retention dilemma,”due to the stochastic forma...Ultralow-power non-volatile memristors are key elements in electronics.Generally,power reduction of memristors compromises data retention,a challenge known as the“power-retention dilemma,”due to the stochastic formation of conductive dendrites in resistive-switching materials.Here,we report the results of conductive dendrite engineering in single-crystalline two-dimensional(2D)dielectrics in which directional control of filamentary distribution is possible.We find that the single-vacancy density(nSV)of single-crystalline hexagonal boron nitride(h-BN)plays an essential role in regulating conductive dendrite growth,supported by scanning joule expansion microscopy(SJEM).With optimized nSV,random dendrite growth is largely limited,and electrons hop between the neighboring Ag nanoclusters in vertical channels.The corresponding model was established to probe the relationship between nSV and memristor operating voltage.The conductive channel confinement in the vertical orientation contributes to long-retention non-volatile memristors with ultralow switch voltages(set:26 mV;reset:135 mV),excellent power efficiency(4 fW standby and a switching energy of 72 pJ)while keeping a high on/off resistance ratio of 108.Even at a record-low compliance current of 10 nA,memristors retains very robust nonvolatile,multiple resistive states with an operating voltage less than 120 mV(the per-transition power low as 900 pW).展开更多
Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transit...Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transition elements,following the cuprate and iron-pnictide superconductors.However,there are several critical questions that have been perplexing the scientificommunity:(1)What factors contribute to the inconsistent reproducibility of the experimental results?(2)What is the fundamental nature of pressure-induced superconductivity:bulk or nonbulk(filamentary-like)(3)Where is the superconducting phase located within the sample if it is filamentary-like(4)Is the oxygen content important for the development and stabilization of superconductivity?In this study,we employ comprehensive high-pressure techniques to address these questions.Through our modulated ac susceptibility measurements,we are the firs to fin that the superconductivity in this nickelate is filamentary-like Our scanning transmission electron microscopy investigations suggest that the filamentary-lik superconductivity most likely emerges at the interface between La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10)phases.By tuning the oxygen content of polycrystalline La_(3)Ni_(2)O_(7),we also fin that it plays vital role in the development and stabilization of superconductivity in this material.The upper and lower bounds on the oxygen content are 7.35 and 6.89,respectively.Our results provide not only new insights into the puzzling issues regarding this material,but also significan information that will enable a better understanding of its superconductivity.展开更多
Nonvolatile memory devices based on filamentary resistance switching （KS） are among the frontrunners to fuel future devices and sensors of the internet of things （IoT） era. The capability of many two distinctive r...Nonvolatile memory devices based on filamentary resistance switching （KS） are among the frontrunners to fuel future devices and sensors of the internet of things （IoT） era. The capability of many two distinctive resistive states in response to an external electrical stimulus has been demonstrated. Through years of selection, cells based on the drift of metal ions, namely conductive-bridge memory devices, have shown a wide range of applications with nanosecond switching speeds, nanometer scalability, high-density, and low power-consumption. However, for low （sub-10-~A） current operation, a critical challenge is still represented by programming variability and by the stability of the conductive filament over time. Here, by introducing the concept of reverse filament growth （RFG）, we managed to control the structural reconfiguration of the conductive filament inside a memory cell with significant enhancements of each of the aforementioned properties. A first-in-class Cu-based switching device is demonstrated, with a dedicated stack that enabled us to systematically trigger RFG, thus tuning the device＇s properties. Along with nanosecond switching speeds, we achieved an endurance of up to 106 cycles with a 102 read window, with outstanding disturb immunity and optimal stability of the filament over time. Furthermore, by tuning the filament＇s shape, an excellent control of multi-level bit operations was achieved. Thus, this device offers high flexibility in memory applications.展开更多
Three-dimensional(3D)conductive structures significantly reduce flexible circuit complexity and enhance circuit integration.Direct extrusion printing technology offers the advantages of various material applicability ...Three-dimensional(3D)conductive structures significantly reduce flexible circuit complexity and enhance circuit integration.Direct extrusion printing technology offers the advantages of various material applicability and high flexibility for fabricating filamentary interconnects.The printing resolution is,however,highly dependent on the needle size.A micro-printing method was proposed based on fluid drawing to fabricate freestanding 3D conductive structures.The delicate structure is drawn out under the tension when printing.The printing material is a high-viscosity ink composed of silver nanoparticles(AgNPs)and polyvinylpyrrolidone(PVP).The viscosity is controlled by evaporating the ink’s solvent for drawing prints.This unique printing method utilizes a single needle,controlled by precise air pressure and speed,to construct 3D filamentary structures with varied wire widths.The 3D conductive structures exhibit superior structural retention and enhanced conductivity by thermal treatment.The drawing printing method has been successfully implemented on flexible circuits,including light-emitting diode(LED)arrays,thermal imaging displays,and multivibrator circuits.This work establishes a novel paradigm for flexible electronics manufacturing through fluid-drawing printing,achieving unprecedented customization and compatibility in fabricating 3D interconnects.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.51977057,11875121,and 11805013)the Natural Science Foundation of Hebei Province,China (Grant Nos.A2020201025 and A2022201036)+2 种基金the Funds for Distinguished Young Scientists of Hebei Province,China (Grant No.A2012201045)the Natural Science Interdisciplinary Research Program of Hebei University (Grant No.DXK202011)the Postgraduate’s Innovation Fund Project of Hebei University (Grant No.HBU2022bs004)。
文摘Plasma jet has extensive application potentials in various fields, which normally operates in a diffuse mode when helium is used as the working gas. However, when less expensive argon is used, the plasma jet often operates in a filamentary mode. Compared to the filamentary mode, the diffuse mode is more desirable for applications. Hence, many efforts have been exerted to accomplish the diffuse mode of the argon plasma jet. In this paper, a novel single-needle argon plasma jet is developed to obtain the diffuse mode. It is found that the plasma jet operates in the filamentary mode when the distance from the needle tip to the central line of the argon stream(d) is short. It transits to the diffuse mode with increasing d. For the diffuse mode, there is always one discharge pulse per voltage cycle, which initiates at the rising edge of the positive voltage. For comparison, the number of discharge pulse increases with an increase in the peak voltage for the filamentary mode. Fast photography reveals that the plasma plume in the filamentary mode results from a guided positive streamer,which propagates in the argon stream. However, the plume in the diffuse mode originates from a branched streamer, which propagates in the interfacial layer between the argon stream and the surrounding air. By optical emission spectroscopy,plasma parameters are investigated for the two discharge modes, which show a similar trend with increasing d. The diffuse mode has lower electron temperature, electron density, vibrational temperature, and gas temperature compared to the filamentary mode.
基金supported in part by the National Key R&D Program of China(Nos.2019YFE03080200,2022YFE03030001 and 2022YFE03050003)National Natural Science Foundation of China(Nos.12075284,12075283 and 12175277)。
文摘In the H-mode experiments conducted on the Experimental Advanced Superconducting Tokamak(EAST),fluctuations induced by the so-called edge localized modes(ELMs)are captured by a high-speed vacuum ultraviolet(VUV)imaging system.Clear field line-aligned filamentary structures are analyzed in this work.Ion transport induced by ELM filaments in the scrape-off layer(SOL)under different discharge conditions is analyzed by comparing the VUV signals with the divertor probe signals.It is found that convective transport along open field lines towards the divertor target dominates the parallel ion particle transport mechanism during ELMs.The toroidal mode number of the filamentary structure derived from the VUV images increases with the electron density pedestal height.The analysis of the toroidal distribution characteristics during ELM bursts reveals toroidal asymmetry.The influence of resonance magnetic perturbation(RMP)on the ELM size is also analyzed using VUV imaging data.When the phase difference of the coil changes periodically,the widths of the filaments change as well.Additionally,the temporal evolution of the ELMs on the VUV signals provides rise time and decay time for each single ELM event,and the results indicate a negative correlation trend between these two times.
基金Project(51975017) supported by the National Natural Science Foundation of ChinaProject(KZ202110005012) supported by the Scientific Research Project of Beijing Educational Committee+1 种基金ChinaProject(2018YFB1107500) supported by the National Key R&D Program of China。
文摘The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.
基金supported by the National Basic Research Program of China(Grant Nos.2012CB821400,2012CB921302,and 2015CB921303)the National Natural Science Foundation of China(Grant Nos.11274237,91121004,51228201,11004238,and 11374011)
文摘We present magnetotransport studies on a series of BaFe2_xNixAs2 （0.03 〈 x 〈 0.10） single crystals. In the un- derdoped （x = 0.03） non-superconducting sample, the temperature-dependent resistivity exhibits a peak at 22 K, which is associated with the onset of filamentary superconductivity （FLSC）. FLSC is suppressed by an external magnetic field in a manner similar to the suppression of bulk superconductivity in an optimally-doped （x = 0.10） compound, suggesting the same possible origin as the bulk superconductivity. Our magnetoresistivity measurements reveal that FLSC persists up to the optimal doping and disappears in the overdoped regime where the long-range antiferromagnetic order is completely suppressed, pointing to a close relation between FLSC and the magnetic order.
基金sponsored by National Natural Science Foundation of China under Grant Nos.11505044,11405042 and 11421064the Natural Science Foundation of Hebei Province under Grant No.A2016201066+1 种基金the Research Foundation of Education Bureau of Hebei province under Grant No.BJ2016006the Midwest Universities Comprehensive Strength Promotion Project
文摘The plasma behavior of filamentary barrier discharges in helium is simulated using a twodimensional（2D） particle-in-cell/Monte Carlo model. Four different phases have been suggested in terms of the development of the discharge： the Townsend phase; the space-charge dominated phase; the formation of the cathode layer, and the extinguishing phase. The spatialtemporal evolution of the particle densities, velocities of the charged particles, electric fields, and surface charges has been demonstrated. Our simulation provides insights into the underlying mechanism of the discharge and explains many dynamical behaviors of dielectric barrier discharge（DBD） filaments.
文摘It is shown that a single-particle wave function Ψ, obtained (Landau, 1930) as a solution of the Schr?dinger equation (for a charged particle in a homogeneous magnetic field), and an operator relation of?(or equation?) lead to the dynamic description of one-dimensional many-particle quantum filamentary states. Thus, one can overcome the problem, connected with the finding of many-body wave function as solution of the Schr?dinger equation with a very tangled Hamiltonian for multi-body system. An effect of nonlocality appears. The dependence of the linear density of particles on the magnetic field and on the number of particles in the one- dimension filamentary multiparticle quantum structure is calculated.
文摘The analysis of the filamentary structure of the cosmo as well as that of the internal structure of the polar ice suggests the development of models based on three-dimensional(3D)point processes.A point process,regarded as a random measure,can be expressed as a sum of Delta Dirac measures concentrated at some random points.The integration with respect to the point process leads the continuous wavelet transform of the process itself.As possible mother wavelets,we propose the application of the Mexican hat and the Morlet wavelet in order to implement the scale-angle energy density of the process,depending on the dilation parameter and on the three angles which define the direction in the Euclidean space.Such indicator proves to be a sensitive detector of any variation in the direction and it can be successfully implemented to study the isotropy or the filamentary structure in 3D point patterns.
基金Project (No. 50671092) supported by the National Natural Science Foundation of China
文摘Cu-Ag filamentary microcomposites with different Ag contents were prepared by cold drawing and intermediate heat treatments. The microstructure characterization and filamentary distribution were observed for two-phase alloys under different conditions. The effect of heavy drawing strain on the microstructure evolution of Cu-Ag alloys was investigated. The results show that the microstructure components consist of Cu dendrites, eutectic colonies and secondary Ag precipitates in the alloys containing 6%-24% （mass fraction） Ag. With the increase in Ag content, the eutectic colonies in the microstructure increase and gradually change into a continuous net-like distribution. The Cu dendrites, eutectic colonies and secondary Ag precipitates are elongated in an axial direction and developed into the composite filamentary structure during cold drawing deformation. The eutectic colonies tend to evolve into filamentary bundles. The filamentary diameters decrease with the increase in drawing strain degree for the two-phase alloys, in particular for the alloys with low Ag content. The reduction in filamentary diameters becomes slow once the drawing strain has exceeded a certain level.
基金supported in part by National Natural Science Foundation of China(Nos.51877177 and 52007152)in part by the Scientific Research Program Funded by Shaanxi Provincial Education Department(Nos.21JP085 and 21JP088)+3 种基金the Youth Innovation Team of Shaanxi Universitiesin part by the Natural Science Basic Research Plan of Shaanxi Province(Nos.2021JZ-48 and 2020JM-462)in part by Fellowship of China Postdoctoral Science Foundation(No.2021M702639)in part by Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology(No.SKL2020KF01)。
文摘In this article,the bunched transport of photoexcited carriers in a GaAs photoconductive semiconductor switch(PCSS)with interdigitated electrodes is investigated under femtosecond laser excitation.Continuous outputs featuring high gain are obtained for single shots and at 1 kHz by varying the optical excitation energy.An ensemble three-valley Monte Carlo simulation is utilized to investigate the transient characteristics and the dynamic process of photoexcited carriers.It demonstrates that the presence of a plasma channel can be attributed to the bunching of high-density electron–hole pairs,which are transported in the form of a highdensity filamentary current.The results provide a picture of the evolution of photoexcited carriers during transient switching.A photoinduced heat effect is analyzed,which reveals the related failure mechanism of GaAs PCSS at various repetition rates.
基金financially supported by the National Science Funds for Excellent Young Scholars of China(no.61822106)the Natural Science Foundation of China(no.U19A2070)。
文摘Resistive random-access memory(RRAM)is a promising technology to develop nonvolatile memory and artificial synaptic devices for brain-inspired neuromorphic computing.Here,we have developed a STO:Ag/SiO_(2) bilayer based memristor that has exhibited a filamentary resistive switching with stable endurance and long-term data retention ability.The memristor also exhibits a tunable resistance modulation under positive and negative pulse trains,which could fully mimic the potentiation and depression behavior like a bio-synapse.Several synaptic plasticity functions,including long-term potentiation(LTP)and long-term depression(LTD),paired-pulsed facilitation(PPF),spike-rate-dependent-plasticity(SRDP),and post-tetanic potentiation(PTP),are faithfully implemented with the fabricated memristor.Moreover,to demonstrate the feasibility of our memristor synapse for neuromorphic applications,spike-timedependent plasticity(STDP)is also investigated.Based on conductive atomic force microscopy observations and electrical transport model analyses,it can be concluded that it is the controlled formation and rupture of Ag filaments that are responsible for the resistive switching while exhibiting a switching ratio of~10;along with a good endurance and stability suitable for nonvolatile memory applications.Before fully electroforming,the gradual conductance modulation of Ag/STO:Ag/SiO_(2)/p^(++)-Si memristor can be realized,and the working mechanism could be explained by the succeeding growth and contraction of Ag filaments promoted by a redox reaction.This newly fabricated memristor may enable the development of nonvolatile memory and realize controllable resistance/weight modulation when applied as an artificial synapse for neuromorphic computing.
基金supported by National Natural Science Foundation of China(No.11275047)the National Magnetic Confinement Fusion Science Program of China(No.2013GB102000)
文摘A tangential fast visible camera has been set up in EAST tokamak for the study of edge MHD instabilities such as ELM. To determine the 3-D information from CCD images, Tsai＇s two-stage technique was utilized to calibrate the high-speed camera imaging system for ELM study. By applying tiles of the passive stabilizers in the tokamak device as the calibration pattern, transformation parameters for transforming from a 3-D world coordinate system to a 2-D image coordinate system were obtained, including the rotation matrix, the translation vector, the focal length and the lens distortion. The calibration errors were estimated and the results indicate the reliability of the method used for the camera imaging system. Through the calibration, some information about ELM filaments, such as positions and velocities were obtained from images of H-mode CCD videos.
基金supported by National Natural Science Foundation of China(No.51077089)
文摘A study of the evolution of the pulse width in homogeneous dielectric barrier dis- charge at atmospheric pressure with helium as the working gas is reported by using a one- dimensional fluid model. In this paper, a new computational method is presented to estimate the pulse width through calculating the time interval between the breakdown voltage and the extinguishing voltage. The effects on the discharge characteristics of the applied voltage and exci- tation frequency are studied based on the computational data. The results of the simulation show that the pulse width is observed to be narrower and the time intervals between two consecutive current pulses decrease with increasing amplitude and excitation frequency, which indicates that the homogeneous discharge is susceptible to the filamentary mode. The simulation results support the conclusion that in order to restrain the transition from the glow mode to filamentary mode, the applied voltage and excitation frequency should be kept within an appropriate range.
基金supported by National Natural Science Foundation of China(No.50707012)Opening Project of State Key Laboratory of Electrical Insulation and Power Equipment in Xi'an Jiaotong University of China(No.EIPE11205)"Qing Lan Project" of Jiangsu Province,China
文摘The homogeneous dielectric barrier discharge （DBD） in atmospheric air between two symmetric-columnar copper electrodes with epoxy plates as the dielectric barriers is generated using a us pulse high voltage power supply. The discharge characteristics are studied by measurement of its electrical discharge parameters and observation of its light emission phenom- ena, and the main discharge parameters of the homogenous DBD, such as discharge current and average discharge power, are calculated. Results show that the discharge generated is a homogeneous one with one larger single current pulse of about 2 #s duration appearing in each voltage pulse, and its light emission is radially homogeneous and covers the entire surface of the two elec- trodes. The influences of applied voltage amplitude, air gap distance and barrier thickness on the transition of discharge modes are studied. With the increase of air gap distance, the discharge will transit from homogeneous mode to filamentary mode. The higher the thickness of dielectric barriers, the larger the air gap distance for generating the homogeneous discharge mode. The average discharge power increases non-linearly with increasing applied voltage amplitude, and decreases non-linearly with the increase of air gap distance and barrier thickness. In order to generate stable and homogeneous DBD with high discharge power, thin barriers distance should be used, and higher applied voltage amplitude should be applied to small air gap.
文摘A pseudoglow discharge behaviour is achieved at a 2.0-mm dielectric-dielectric electrode gap in pure helium under atmospheric pressure. An experimental study of the pseudoglow discharges is presented. The electrical characteristics and the discharge photos of the pseudoglow discharges are analyzed and discussed. The current-voltage parameters of the pseudoglow dis- charges are considered in regard to the influence on their behaviour.
文摘The results of research on the adsorption characteristics of materials based on fibrous carbon (CNF) are considered in this paper. It is shown that changing the conditions and procedure of CNF modifying namely specific adsorption surface, volume of the pore space, and parameters of the pore structure it became possible ultimately to vary in a wide range the adsorption characteristics of obtained materials.
基金support from NSFC(92264106,62090034,62104214,62122067,and 62261160574)the Research Grant Council of Hong Kong(CRS_PolyU502/22)+2 种基金the National Key R&D Program(2022YFA1204303)the NSFC of Zhejiang Province(DT23F0401 and DT23F040008)the Young Elite Scientists Sponsorship Program by CAST(2021QNRC001).
文摘Ultralow-power non-volatile memristors are key elements in electronics.Generally,power reduction of memristors compromises data retention,a challenge known as the“power-retention dilemma,”due to the stochastic formation of conductive dendrites in resistive-switching materials.Here,we report the results of conductive dendrite engineering in single-crystalline two-dimensional(2D)dielectrics in which directional control of filamentary distribution is possible.We find that the single-vacancy density(nSV)of single-crystalline hexagonal boron nitride(h-BN)plays an essential role in regulating conductive dendrite growth,supported by scanning joule expansion microscopy(SJEM).With optimized nSV,random dendrite growth is largely limited,and electrons hop between the neighboring Ag nanoclusters in vertical channels.The corresponding model was established to probe the relationship between nSV and memristor operating voltage.The conductive channel confinement in the vertical orientation contributes to long-retention non-volatile memristors with ultralow switch voltages(set:26 mV;reset:135 mV),excellent power efficiency(4 fW standby and a switching energy of 72 pJ)while keeping a high on/off resistance ratio of 108.Even at a record-low compliance current of 10 nA,memristors retains very robust nonvolatile,multiple resistive states with an operating voltage less than 120 mV(the per-transition power low as 900 pW).
基金supported by the National Key Research and Development Program of China(Grant Nos.2022YFA1403900 and 2021YFA1401800)the NSF of China(Grant Nos.U2032214,12122414,12104487,and 12004419)+2 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB25000000)support from the Youth Innovation Promotion Association of the CAS(2019008)supported by the Synergetic Extreme Condition User Facility(SECUF)。
文摘Signatures of superconductivity near 80 K have recently been discovered in single crystals of La_(3)Ni_(2)O_(7)under pressure,which makes it a new candidate for high-temperature superconductors dominated by 3d transition elements,following the cuprate and iron-pnictide superconductors.However,there are several critical questions that have been perplexing the scientificommunity:(1)What factors contribute to the inconsistent reproducibility of the experimental results?(2)What is the fundamental nature of pressure-induced superconductivity:bulk or nonbulk(filamentary-like)(3)Where is the superconducting phase located within the sample if it is filamentary-like(4)Is the oxygen content important for the development and stabilization of superconductivity?In this study,we employ comprehensive high-pressure techniques to address these questions.Through our modulated ac susceptibility measurements,we are the firs to fin that the superconductivity in this nickelate is filamentary-like Our scanning transmission electron microscopy investigations suggest that the filamentary-lik superconductivity most likely emerges at the interface between La_(3)Ni_(2)O_(7)and La_(4)Ni_(3)O_(10)phases.By tuning the oxygen content of polycrystalline La_(3)Ni_(2)O_(7),we also fin that it plays vital role in the development and stabilization of superconductivity in this material.The upper and lower bounds on the oxygen content are 7.35 and 6.89,respectively.Our results provide not only new insights into the puzzling issues regarding this material,but also significan information that will enable a better understanding of its superconductivity.
文摘Nonvolatile memory devices based on filamentary resistance switching （KS） are among the frontrunners to fuel future devices and sensors of the internet of things （IoT） era. The capability of many two distinctive resistive states in response to an external electrical stimulus has been demonstrated. Through years of selection, cells based on the drift of metal ions, namely conductive-bridge memory devices, have shown a wide range of applications with nanosecond switching speeds, nanometer scalability, high-density, and low power-consumption. However, for low （sub-10-~A） current operation, a critical challenge is still represented by programming variability and by the stability of the conductive filament over time. Here, by introducing the concept of reverse filament growth （RFG）, we managed to control the structural reconfiguration of the conductive filament inside a memory cell with significant enhancements of each of the aforementioned properties. A first-in-class Cu-based switching device is demonstrated, with a dedicated stack that enabled us to systematically trigger RFG, thus tuning the device＇s properties. Along with nanosecond switching speeds, we achieved an endurance of up to 106 cycles with a 102 read window, with outstanding disturb immunity and optimal stability of the filament over time. Furthermore, by tuning the filament＇s shape, an excellent control of multi-level bit operations was achieved. Thus, this device offers high flexibility in memory applications.
基金supported by the National Natural Science Foundation of China(Grant No.U24A20137,52475587,52103224,52405610)Science and Technology Program of Liaoning Province(2023JH1/10400044)+1 种基金Natural Science Foundation of Ningbo Municipality(2022J008)Fundamental Research Funds for the Central Universities(DUT23RC(3)051,DUT24RC(3)048)。
文摘Three-dimensional(3D)conductive structures significantly reduce flexible circuit complexity and enhance circuit integration.Direct extrusion printing technology offers the advantages of various material applicability and high flexibility for fabricating filamentary interconnects.The printing resolution is,however,highly dependent on the needle size.A micro-printing method was proposed based on fluid drawing to fabricate freestanding 3D conductive structures.The delicate structure is drawn out under the tension when printing.The printing material is a high-viscosity ink composed of silver nanoparticles(AgNPs)and polyvinylpyrrolidone(PVP).The viscosity is controlled by evaporating the ink’s solvent for drawing prints.This unique printing method utilizes a single needle,controlled by precise air pressure and speed,to construct 3D filamentary structures with varied wire widths.The 3D conductive structures exhibit superior structural retention and enhanced conductivity by thermal treatment.The drawing printing method has been successfully implemented on flexible circuits,including light-emitting diode(LED)arrays,thermal imaging displays,and multivibrator circuits.This work establishes a novel paradigm for flexible electronics manufacturing through fluid-drawing printing,achieving unprecedented customization and compatibility in fabricating 3D interconnects.
