Rational reconstruction of oxygen evolution reaction(OER)precatalysts and performance index of OER catalysts are crucial but still challenging for universal water electrolysis.Herein,we develop a double-cation etching...Rational reconstruction of oxygen evolution reaction(OER)precatalysts and performance index of OER catalysts are crucial but still challenging for universal water electrolysis.Herein,we develop a double-cation etching strategy to tailor the electronic structure of NiMoO_(4),where the prepared NiMoO_(4) nanorods etched by H_(2)O_(2) reconstruct their surface with abundant cation deficiencies and lattice distortion.Calculation results reveal that the double cation deficiencies can make the upshift of d-band center for Ni atoms and the active sites with better oxygen adsorption capacity.As a result,the optimized sample(NMO-30M)possesses an overpotential of 260 mV at 10 mA cm−2 and excellent long-term durability of 162 h.Importantly,in situ Raman test reveals the rapid formation of high-oxidation-state transition metal hydroxide species,which can further help to improve the catalytic activity of NiMoO_(4) in OER.This work highlights the influence of surface remodification and shed some light on activating catalysts.展开更多
To fully release the potential of wide bandgap(WBG)semiconductors and achieve high energy density and efficiency,a carbonyl iron soft magnetic composite(SMC)with an easy plane-like structure is prepared.Due to this st...To fully release the potential of wide bandgap(WBG)semiconductors and achieve high energy density and efficiency,a carbonyl iron soft magnetic composite(SMC)with an easy plane-like structure is prepared.Due to this structure,the permeability of the composite increases by 3 times(from 7.5 to 21.5)at 100 MHz compared with to the spherical carbonyl iron SMC,and the permeability changes little at frequencies below 100 MHz.In addition,the natural resonance frequency of the composite shifts to higher frequencies at 1.7 GHz.The total core losses of the composites at 10,20,and 30 m T are80.0,355.3,and 810.7 m W/cm^(3),respectively,at 500 k Hz.Compared with the spherical carbonyl iron SMC,the core loss at500 k Hz is reduced by more than 60%.Therefore,this kind of soft magnetic composite with an easy plane-like structure is a good candidate for unlocking the potential of WBG semiconductors and developing the next-generation power electronics.展开更多
The development of e cient earth-abundant electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions(ORR, OER, and HER) is important for future energy conversion and energy storage devic...The development of e cient earth-abundant electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions(ORR, OER, and HER) is important for future energy conversion and energy storage devices, for which both rechargeable Zn–air batteries and water splitting have raised great expectations. Herein, we report a single-phase bimetallic nickel cobalt sulfide((Ni,Co)S_2) as an e cient electrocatalyst for both OER and ORR. Owing to the synergistic combination of Ni and Co, the(Ni,Co)S_2 exhibits superior electrocatalytic performance for ORR, OER, and HER in an alkaline electrolyte, and the first principle calculation results indicate that the reaction of an adsorbed O atom with a H_2O molecule to form a *OOH is the potential limiting step in the OER. Importantly, it could be utilized as an advanced air electrode material in Zn–air batteries, which shows an enhanced charge–discharge performance(charging voltage of 1.71 V and discharge voltage of 1.26 V at 2 mA cm^(-2)), large specific capacity(842 mAh g_(Zn)^(-1) at 5 mA cm^(-2)), and excellent cycling stability(480 h). Interestingly, the(Ni,Co)S_2-based Zn–air battery can e ciently power an electrochemical water-splitting unit with(Ni,Co)S_2 serving as both the electrodes. This reveals that the prepared(Ni,Co)S_2 has promising applications in future energy conversion and energy storage devices.展开更多
One approach to accelerate the stagnant kinetics of both the oxygen reduction and evolution reactions(ORR/OER)is to develop a rationally designed multiphase nanocomposite,where the functions arising from each of the c...One approach to accelerate the stagnant kinetics of both the oxygen reduction and evolution reactions(ORR/OER)is to develop a rationally designed multiphase nanocomposite,where the functions arising from each of the constituent phases,their interfaces,and the overall structure are properly controlled.Herein,we successfully synthesized an oxygen electrocatalyst consisting of Ni nanoparticles purposely interpenetrated into mesoporous NiO nanosheets(porous Ni/NiO).Benefiting from the contributions of the Ni and NiO phases,the well-established pore channels for charge transport at the interface between the phases,and the enhanced conductivity due to oxygen-deficiency at the pore edges,the porous Ni/NiO nanosheets show a potential of 1.49 V(10 mA cm^-2)for the OER and a half-wave potential of 0.76 V for the ORR,outperforming their noble metal counterparts.More significantly,a Zn-air battery employing the porous Ni/NiO nanosheets exhibits an initial charging-discharging voltage gap of 0.83 V(2 mA cm^-2),specific capacity of 853 mAh gZn^-1 at 20 mA cm^-2,and long-time cycling stability(120 h).In addition,the porous Ni/NiO-based solid-like Zn-air battery shows excellent electrochemical performance and flexibility,illustrating its great potential as a next-generation rechargeable power source for flexible electronics.展开更多
Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnet...Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnetic properties by transmission electron microscopy, selective area electron diffraction, x-ray diffraction, and vibrating sample magnetometer. X-ray diffraction patterns reveal that both as-deposited nanowire arrays films exhibit face-centred cubic structure. Magnetic measurements indicate that the easy magnetization direction of Co/Cu multilayer nanowire arrays films on Ag substrate is perpendicular to the long axis of nanowire, whereas the easy magnetization direction of the sample with Cu substrate is parallel to the long axis of nanowire. The change of easy magnetization direction attributed to different substrates, and the magnetic properties of the nanowire arrays are discussed.展开更多
Soft magnetic composites(SMCs)are effective as magnetic powder cores in an inductor.Due to high saturation magnetization,large magnetocrystalline anisotropy and high operating frequency of M(metal)-RE(rear earth)soft ...Soft magnetic composites(SMCs)are effective as magnetic powder cores in an inductor.Due to high saturation magnetization,large magnetocrystalline anisotropy and high operating frequency of M(metal)-RE(rear earth)soft magnetic composites,it is possible to miniaturize inductor cores by reducing total loss,especially eddy current loss and excess loss at high frequencies.In this article,the characteristics of Ce_(2)Fe_(17)N_(3)/α-Fe(CFN/F)loss per volume and effective permeability reaching a high frequency of 3 MHz are investigated.The biphase CFN/F composite exhibits a high permeability of 16 at 70 MHz,which is two times greater than that of pure Ce_(2)Fe_(17)N_(3)(CFN)powders.The total loss is as low as 545 mW/cm^(3)at 3 MHz and 6 mT.The direct current(DC)-bias properties have a percent of permeability exceeding 65% at H=7960 A/m.This phenomenon indicates that our material has a higher working frequency and lower core loss than other materials;the biphase CFN/F structure is a promising and efficient approach for developing the miniaturized radio frequency(RF)inductor core.展开更多
We propose a renormalization group(RG)theory of eigen microstates,which are introduced in the statistical ensemble composed of microstates obtained from experiments or computer simulations.A microstate in the ensemble...We propose a renormalization group(RG)theory of eigen microstates,which are introduced in the statistical ensemble composed of microstates obtained from experiments or computer simulations.A microstate in the ensemble can be considered as a linear superposition of eigen microstates with probability amplitudes equal to their eigenvalues.Under the renormalization of a factor b,the largest eigenvalueσ1 has two trivial fixed points at low and high temperature limits and a critical fixed point with the RG relationσb1=bβ/νσ1,whereβandνare the critical exponents of order parameter and correlation length,respectively.With the Ising model in different dimensions,it has been demonstrated that the RG theory of eigen microstates is able to identify the critical point and to predict critical exponents and the universality class.Our theory can be used in research of critical phenomena both in equilibrium and non-equilibrium systems without considering the Hamiltonian,which is the foundation of Wilson’s RG theory and is absent for most complex systems.展开更多
We report on the experimental investigation of the properties of the eigenvalues and wavefunctions and the fluctuation properties of the scattering matrix of closed and open billiards, respectively, of which the class...We report on the experimental investigation of the properties of the eigenvalues and wavefunctions and the fluctuation properties of the scattering matrix of closed and open billiards, respectively, of which the classical dynamics undergoes a transition from integrable via almost integrable to fully chaotic. To realize such a system, we chose a billiard with a 60° sector shape of which the classical dynamics is integrable, and introduced circular scatterers of varying number, size,and position. The spectral properties of generic quantum systems of which the classical counterpart is either integrable or chaotic are universal and well understood. If, however, the classical dynamics is pseudo-integrable or almost-integrable,they exhibit a non-universal intermediate statistics, for which analytical results are known only in a few cases, e.g., if it corresponds to semi-Poisson statistics. Since the latter is, above all, clearly distinguishable from those of integrable and chaotic systems, our aim was to design a billiard with these features which indeed is achievable by adding just one scatterer of appropriate size and position to the sector billiard. We demonstrated that, while the spectral properties of almostintegrable billiards are sensitive to the classical dynamics, this is not the case for the distribution of the wavefunction components, which was analyzed in terms of the strength distribution, and the fluctuation properties of the scattering matrix which coincide with those of typical, fully chaotic systems.展开更多
NiFe204 (NFO)/ZnO composite nanoparticles with different ZnO components were investigated, which were pre- pared by a simple wet chemical route method. The magnetoelectric coupling between magnetostriction from NFO ...NiFe204 (NFO)/ZnO composite nanoparticles with different ZnO components were investigated, which were pre- pared by a simple wet chemical route method. The magnetoelectric coupling between magnetostriction from NFO and piezoelectricity from ZnO was induced by the surface coating NFO nanoparticles of ZnO layer, NFO/ZnO composite showed ferroelectric properties and the remanent electric polarization reached 0.08 μC/cm. Moreover, the changes of resistance at different room temperatures reached about 2% under 3 T magnetic fields comparing with that of zero mag- netic fields. Furthermore, multiferroic NFO/ZnO resulted in enhancement of microwave absorption due to magnetoelectric coupling.展开更多
Classical-quantum correspondence has been an intriguing issue ever since quantum theory was proposed. The search- ing for signatures of classically nonintegrable dynamics in quantum systems comprises the interesting f...Classical-quantum correspondence has been an intriguing issue ever since quantum theory was proposed. The search- ing for signatures of classically nonintegrable dynamics in quantum systems comprises the interesting field of quantum chaos. In this short review, we shall go over recent efforts of extending the understanding of quantum chaos to relativistic cases. We shall focus on the level spacing statistics for two-dimensional massless Dirac billiards, i.e., particles confined in a closed region. We shall discuss the works for both the particle described by the massless Dirac equation (or Weyl equation) and the quasiparticle from graphene. Although the equations are the same, the boundary conditions are typically different, rendering distinct level spacing statistics.展开更多
Transparent conductive Al-doped ZnO (AZO) thin films are prepared on normal glass substrates by the sol-gel spin coating method. The effects of drying conditions, annealing temperature and cooling rate on the struct...Transparent conductive Al-doped ZnO (AZO) thin films are prepared on normal glass substrates by the sol-gel spin coating method. The effects of drying conditions, annealing temperature and cooling rate on the structural, electrical and optical properties of AZO films are investigated by x-ray diffraction, scanning electron microscopy, the four-point probe method and UV-VIS spectrophotometry, respectively. The deposited films show a hexagonal wurtzite structure and high preferential c-axis orientation. As the drying temperature increases from 100℃ to 300℃ the resistivity of AZO films decreases dramatically. In contrast to the annealed films cooled in a furnace and in air, the resistivity of the annealed film which is cooled at -15℃is greatly reduced. Increasing the cooling rate dramatically increases the electrical conductivity of AZO films.展开更多
Carbon nanotubes(CNTs)were grown into anodic aluminum oxide(AAO)channels by chemical vapor deposition(CVD)using C2H2/N2mixtures as feeding gas,which can be used as field emitters.The bottom surface of AAO template was...Carbon nanotubes(CNTs)were grown into anodic aluminum oxide(AAO)channels by chemical vapor deposition(CVD)using C2H2/N2mixtures as feeding gas,which can be used as field emitters.The bottom surface of AAO template was etched slightly and the tips of CNTs were explored as the field emission arrays which were uniform and vertical.Field emission characterization showed a low turn-on field about 3.25 V/m and high emission current about 30 mA/cm2with the electric field about 4 V/m.These superior field emission characteristics could be attributed to low density of vertical CNTs and higher conductivity of the substrate.展开更多
Self-powered chaos signal generator is potentially useful in future medical system,such as low cost portable human healthy monitor and treatment without external power source.For both functional and power unit,the pow...Self-powered chaos signal generator is potentially useful in future medical system,such as low cost portable human healthy monitor and treatment without external power source.For both functional and power unit,the power level of electric energy generator and consumption is a key factor for self-powered system.In this paper,we have investigated the power consumption of three typical output modes of a simple chaos circuit.Analytical analysis for power consumption of fixed output mode is obtained for evaluating the power characteristics of chaos signal generator.Numerical calculations are given for predicting the power characteristics of periodical and chaotic output modes.This study is important for not only understanding the power consumption of chaos signal generator,but also guiding new self-powered chaos signal generator design.展开更多
A Zn-air battery is a potential next-generation energy storage device owing to its extremely high theoretical energy density. Currently, it is important to explore non-precious metal electrocatalysts with high electro...A Zn-air battery is a potential next-generation energy storage device owing to its extremely high theoretical energy density. Currently, it is important to explore non-precious metal electrocatalysts with high electroactivity and stability in the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for the development of Zn-air batteries. In this work, porous(Ni,Co)Se2 nanosheets were synthesized by selenizing Ni Co2O4 nanosheets. By regulating the conductivity and morphology of the sample, the prepared porous(Ni,Co)Se2 nanosheets show enhanced electrocatalytic activity for OER and ORR compared to Ni Co2O4 nanosheets. The aqueous Zn-air battery using porous(Ni,Co)Se2 nanosheets as the air cathode exhibits superior charge and discharge performance(1.98 V for charging and 1.17 V for discharging), high specific capacity(770 m Ah/g), and excellent cycle stability(140 h). These results indicate that the porous(Ni,Co)Se2 nanosheets are suitable as a bifunctional electrocatalyst for future Zn-air batteries.展开更多
Slave-particle method is a powerful tool to tackle the correlation effect in quantum many-body physics. Although it has been successfully used to comprehend various intriguing problems, such as Mott metal-insulator tr...Slave-particle method is a powerful tool to tackle the correlation effect in quantum many-body physics. Although it has been successfully used to comprehend various intriguing problems, such as Mott metal-insulator transition and Kondo effect, there is still no convincing theory so far on the availability and limitation of this method. The abuse of slave-particle method may lead to wrong physics. As the simplest slave-particle method, Z2 slave spin, which is widely applied to many strongly correlated problems, is highly accessible and researchable. In this work, we will uncover the nature of the Z2 slave-spin method by studying a two-site Hubbard model. After exploring aspects of properties of this toy model, we make a comparative analysis of the results obtained by three methods:(i) slave-spin method on mean-field level,(ii) slave-spin method with gauge constraint, and(iii) the exact solution as a benchmark. We find that, protected by the particle-hole symmetry, the slave-spin mean-field method can recover the static properties of ground state exactly at half filling. Furthermore, in the parameter space where both U and T are small enough, the slave-spin mean-field method is also reliable in calculating the dynamic and thermal dynamic properties. However, when U or T is considerably large, the mean-field approximation gives ill-defined behaviors, which result from the unphysical states in the enlarged Hilbert space.These findings lead to our conclusion that the accuracy of slave particle can be guaranteed if we can exclude all unphysical states by enforcing gauge constraints. Our work demonstrates the promising prospect of slave-particle method in studying complex strongly correlated models with specific symmetry or in certain parameter space.展开更多
For a quantum system with multiple degrees of freedom or subspaces, loss of coherence in a certain subspace is intimately related to the enhancement of entanglement between this subspace and another one. We investigat...For a quantum system with multiple degrees of freedom or subspaces, loss of coherence in a certain subspace is intimately related to the enhancement of entanglement between this subspace and another one. We investigate intra-particle entanglement in two-dimensional mesoscopic systems, where an electron has both spin and orbital degrees of freedom and the interaction between them is enabled by Rashba type of spin-orbit coupling. The geometric shape of the scattering region can be adjusted to produce a continuous spectrum of classical dynamics with different degree of chaos. Focusing on the spin degree of freedom in the weak spin-orbit coupling regime, we find that classical chaos can significantly enhance spin-orbit entanglement at the expense of spin coherence. Our finding that classical chaos can be beneficial to intra-particle entanglement may have potential applications such as enhancing the bandwidth of quantum communications.展开更多
lectro-optic modulators are key components in data communication,microwave photonics,and quantum photonics.Modulation bandwidth,energy efficiency,and device dimension are crucial metrics of modulators.Here,we provide ...lectro-optic modulators are key components in data communication,microwave photonics,and quantum photonics.Modulation bandwidth,energy efficiency,and device dimension are crucial metrics of modulators.Here,we provide an important direction for the miniaturization of electro-optic modulators by reporting on ultracompact topological modulators.A topological interface state in a one-dimensional lattice is implemented on a thin-film lithium-niobate integrated platform.Due to the strong optical confinement of the interface state and the peaking enhancement of the electro-optic response,a topological cavity with a size of 1.6×140μm^(2)enables a large modulation bandwidth of 104 GHz.The first topological modulator exhibits the most compact device size compared to reported LN modulators with bandwidths above 28 GHz,to the best of our knowledge.100 Gb/s non-return-to-zero and 100 Gb/s four-level pulse amplitude modulation signals are generated.The switching energy is 5.4 fJ/bit,owing to the small electro-optic mode volume and low capacitance.The topological modulator accelerates the response time of topological photonic devices from the microsecond order to the picosecond order and provides an essential foundation for the implementation of large-scale lithium-niobate photonic integrated circuits.展开更多
For the materials that simultaneously exhibit piezoelectric and semiconductor properties,such as wurtzite Zn O,Ga N and In N,as well as two-dimensional single Mo S2,piezoelectric charges induced by externally applied ...For the materials that simultaneously exhibit piezoelectric and semiconductor properties,such as wurtzite Zn O,Ga N and In N,as well as two-dimensional single Mo S2,piezoelectric charges induced by externally applied strain can tune/control carrier transport at a metal-semiconductor contact or semiconductor junction,which is named piezotronic effect.Metal-semiconductor-metal piezotronic transistors are key piezotronic nanodevices for electromechanical applications,and they are typical nonlinear elements.In this paper,a simplified current-voltage analysis solution of piezotronic transistors is developed,which can be used for circuit design and simulation.Furthermore,the typical nonlinear circuit:Chua's circuit based on piezotronic transistors is simulated.We find that the output signal of the piezotronic transistor circuit can be switched and changed asymmetrically by externally applied strain.This study provides insight into the nonlinear properties of the piezotronic transistor,as well as guidance for piezotronic transistor nonlinear circuit application.展开更多
基金supported by the National Natural Science Foundation of China(No.12004146)Natural Science Foundation of Gansu Province,China(Nos.20JR5RA303 and 20JR10RA648)the Fundamental Research Funds for the Central Universities(No.LZUMMM2022007).
文摘Rational reconstruction of oxygen evolution reaction(OER)precatalysts and performance index of OER catalysts are crucial but still challenging for universal water electrolysis.Herein,we develop a double-cation etching strategy to tailor the electronic structure of NiMoO_(4),where the prepared NiMoO_(4) nanorods etched by H_(2)O_(2) reconstruct their surface with abundant cation deficiencies and lattice distortion.Calculation results reveal that the double cation deficiencies can make the upshift of d-band center for Ni atoms and the active sites with better oxygen adsorption capacity.As a result,the optimized sample(NMO-30M)possesses an overpotential of 260 mV at 10 mA cm−2 and excellent long-term durability of 162 h.Importantly,in situ Raman test reveals the rapid formation of high-oxidation-state transition metal hydroxide species,which can further help to improve the catalytic activity of NiMoO_(4) in OER.This work highlights the influence of surface remodification and shed some light on activating catalysts.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10404011 and 50401018, and the Project for New Century Excellent Talents (NCET) in University.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11574122 and 51731001)Joint Fund of Equipment Pre-Research and Ministry of Education,China(Grant No.6141A02033242)。
文摘To fully release the potential of wide bandgap(WBG)semiconductors and achieve high energy density and efficiency,a carbonyl iron soft magnetic composite(SMC)with an easy plane-like structure is prepared.Due to this structure,the permeability of the composite increases by 3 times(from 7.5 to 21.5)at 100 MHz compared with to the spherical carbonyl iron SMC,and the permeability changes little at frequencies below 100 MHz.In addition,the natural resonance frequency of the composite shifts to higher frequencies at 1.7 GHz.The total core losses of the composites at 10,20,and 30 m T are80.0,355.3,and 810.7 m W/cm^(3),respectively,at 500 k Hz.Compared with the spherical carbonyl iron SMC,the core loss at500 k Hz is reduced by more than 60%.Therefore,this kind of soft magnetic composite with an easy plane-like structure is a good candidate for unlocking the potential of WBG semiconductors and developing the next-generation power electronics.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11474137 and 11674143)Program for Changjiang Scholars and Innovative Research Team in University (IRT 16R35)+1 种基金the Fundamental Research Funds for the Central Universities (Grant Nos. LZUMMM2018017, lzujbky-2018-121)the support of Ministry of Education (MOE2016-T2-2-138,Singapore),for research conducted at the National University of Singapore
文摘The development of e cient earth-abundant electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions(ORR, OER, and HER) is important for future energy conversion and energy storage devices, for which both rechargeable Zn–air batteries and water splitting have raised great expectations. Herein, we report a single-phase bimetallic nickel cobalt sulfide((Ni,Co)S_2) as an e cient electrocatalyst for both OER and ORR. Owing to the synergistic combination of Ni and Co, the(Ni,Co)S_2 exhibits superior electrocatalytic performance for ORR, OER, and HER in an alkaline electrolyte, and the first principle calculation results indicate that the reaction of an adsorbed O atom with a H_2O molecule to form a *OOH is the potential limiting step in the OER. Importantly, it could be utilized as an advanced air electrode material in Zn–air batteries, which shows an enhanced charge–discharge performance(charging voltage of 1.71 V and discharge voltage of 1.26 V at 2 mA cm^(-2)), large specific capacity(842 mAh g_(Zn)^(-1) at 5 mA cm^(-2)), and excellent cycling stability(480 h). Interestingly, the(Ni,Co)S_2-based Zn–air battery can e ciently power an electrochemical water-splitting unit with(Ni,Co)S_2 serving as both the electrodes. This reveals that the prepared(Ni,Co)S_2 has promising applications in future energy conversion and energy storage devices.
基金the National Natural Science Foundation of China(Grant Nos.11474137,11674143)the Fundamental Research Funds for the Central Universities(Grant No.Lzujbky-2019-cd02).
文摘One approach to accelerate the stagnant kinetics of both the oxygen reduction and evolution reactions(ORR/OER)is to develop a rationally designed multiphase nanocomposite,where the functions arising from each of the constituent phases,their interfaces,and the overall structure are properly controlled.Herein,we successfully synthesized an oxygen electrocatalyst consisting of Ni nanoparticles purposely interpenetrated into mesoporous NiO nanosheets(porous Ni/NiO).Benefiting from the contributions of the Ni and NiO phases,the well-established pore channels for charge transport at the interface between the phases,and the enhanced conductivity due to oxygen-deficiency at the pore edges,the porous Ni/NiO nanosheets show a potential of 1.49 V(10 mA cm^-2)for the OER and a half-wave potential of 0.76 V for the ORR,outperforming their noble metal counterparts.More significantly,a Zn-air battery employing the porous Ni/NiO nanosheets exhibits an initial charging-discharging voltage gap of 0.83 V(2 mA cm^-2),specific capacity of 853 mAh gZn^-1 at 20 mA cm^-2,and long-time cycling stability(120 h).In addition,the porous Ni/NiO-based solid-like Zn-air battery shows excellent electrochemical performance and flexibility,illustrating its great potential as a next-generation rechargeable power source for flexible electronics.
基金Supported by the Doctorial Start-up Fund of Lanzhou University and the National Natural Science Foundation of China under Grant Nos 10404011 and 50401018.
基金supported by the National Natural Science Foundation of China (Grant Nos 10404011 and 50401018)the Program for New Century Excellent Talents (NCET) in University
文摘Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnetic properties by transmission electron microscopy, selective area electron diffraction, x-ray diffraction, and vibrating sample magnetometer. X-ray diffraction patterns reveal that both as-deposited nanowire arrays films exhibit face-centred cubic structure. Magnetic measurements indicate that the easy magnetization direction of Co/Cu multilayer nanowire arrays films on Ag substrate is perpendicular to the long axis of nanowire, whereas the easy magnetization direction of the sample with Cu substrate is parallel to the long axis of nanowire. The change of easy magnetization direction attributed to different substrates, and the magnetic properties of the nanowire arrays are discussed.
基金Project supported by the National Key R&D Program of China(2021YFB3501302)Joint Fund of Equipment Pre-Researchthe Ministry of Science and Technology of China(6141A02033242)。
文摘Soft magnetic composites(SMCs)are effective as magnetic powder cores in an inductor.Due to high saturation magnetization,large magnetocrystalline anisotropy and high operating frequency of M(metal)-RE(rear earth)soft magnetic composites,it is possible to miniaturize inductor cores by reducing total loss,especially eddy current loss and excess loss at high frequencies.In this article,the characteristics of Ce_(2)Fe_(17)N_(3)/α-Fe(CFN/F)loss per volume and effective permeability reaching a high frequency of 3 MHz are investigated.The biphase CFN/F composite exhibits a high permeability of 16 at 70 MHz,which is two times greater than that of pure Ce_(2)Fe_(17)N_(3)(CFN)powders.The total loss is as low as 545 mW/cm^(3)at 3 MHz and 6 mT.The direct current(DC)-bias properties have a percent of permeability exceeding 65% at H=7960 A/m.This phenomenon indicates that our material has a higher working frequency and lower core loss than other materials;the biphase CFN/F structure is a promising and efficient approach for developing the miniaturized radio frequency(RF)inductor core.
基金supported by the National Natural Science Foundation of China(Grant No.12135003)。
文摘We propose a renormalization group(RG)theory of eigen microstates,which are introduced in the statistical ensemble composed of microstates obtained from experiments or computer simulations.A microstate in the ensemble can be considered as a linear superposition of eigen microstates with probability amplitudes equal to their eigenvalues.Under the renormalization of a factor b,the largest eigenvalueσ1 has two trivial fixed points at low and high temperature limits and a critical fixed point with the RG relationσb1=bβ/νσ1,whereβandνare the critical exponents of order parameter and correlation length,respectively.With the Ising model in different dimensions,it has been demonstrated that the RG theory of eigen microstates is able to identify the critical point and to predict critical exponents and the universality class.Our theory can be used in research of critical phenomena both in equilibrium and non-equilibrium systems without considering the Hamiltonian,which is the foundation of Wilson’s RG theory and is absent for most complex systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11775100,11775101,and 11961131009)
文摘We report on the experimental investigation of the properties of the eigenvalues and wavefunctions and the fluctuation properties of the scattering matrix of closed and open billiards, respectively, of which the classical dynamics undergoes a transition from integrable via almost integrable to fully chaotic. To realize such a system, we chose a billiard with a 60° sector shape of which the classical dynamics is integrable, and introduced circular scatterers of varying number, size,and position. The spectral properties of generic quantum systems of which the classical counterpart is either integrable or chaotic are universal and well understood. If, however, the classical dynamics is pseudo-integrable or almost-integrable,they exhibit a non-universal intermediate statistics, for which analytical results are known only in a few cases, e.g., if it corresponds to semi-Poisson statistics. Since the latter is, above all, clearly distinguishable from those of integrable and chaotic systems, our aim was to design a billiard with these features which indeed is achievable by adding just one scatterer of appropriate size and position to the sector billiard. We demonstrated that, while the spectral properties of almostintegrable billiards are sensitive to the classical dynamics, this is not the case for the distribution of the wavefunction components, which was analyzed in terms of the strength distribution, and the fluctuation properties of the scattering matrix which coincide with those of typical, fully chaotic systems.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51671099,11374131,and 51501081)
文摘NiFe204 (NFO)/ZnO composite nanoparticles with different ZnO components were investigated, which were pre- pared by a simple wet chemical route method. The magnetoelectric coupling between magnetostriction from NFO and piezoelectricity from ZnO was induced by the surface coating NFO nanoparticles of ZnO layer, NFO/ZnO composite showed ferroelectric properties and the remanent electric polarization reached 0.08 μC/cm. Moreover, the changes of resistance at different room temperatures reached about 2% under 3 T magnetic fields comparing with that of zero mag- netic fields. Furthermore, multiferroic NFO/ZnO resulted in enhancement of microwave absorption due to magnetoelectric coupling.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11005053,11135001,and 11375074)the Air Force Office of Scientific Research (Grant No. FA9550-12-1-0095)the Office of Naval Research (Grant No. N00014-08-1-0627)
文摘Classical-quantum correspondence has been an intriguing issue ever since quantum theory was proposed. The search- ing for signatures of classically nonintegrable dynamics in quantum systems comprises the interesting field of quantum chaos. In this short review, we shall go over recent efforts of extending the understanding of quantum chaos to relativistic cases. We shall focus on the level spacing statistics for two-dimensional massless Dirac billiards, i.e., particles confined in a closed region. We shall discuss the works for both the particle described by the massless Dirac equation (or Weyl equation) and the quasiparticle from graphene. Although the equations are the same, the boundary conditions are typically different, rendering distinct level spacing statistics.
文摘Transparent conductive Al-doped ZnO (AZO) thin films are prepared on normal glass substrates by the sol-gel spin coating method. The effects of drying conditions, annealing temperature and cooling rate on the structural, electrical and optical properties of AZO films are investigated by x-ray diffraction, scanning electron microscopy, the four-point probe method and UV-VIS spectrophotometry, respectively. The deposited films show a hexagonal wurtzite structure and high preferential c-axis orientation. As the drying temperature increases from 100℃ to 300℃ the resistivity of AZO films decreases dramatically. In contrast to the annealed films cooled in a furnace and in air, the resistivity of the annealed film which is cooled at -15℃is greatly reduced. Increasing the cooling rate dramatically increases the electrical conductivity of AZO films.
基金supported by China National Funds for Distinguished Young Scientists(Grant No.61125101)the Science and Technology on Vacuum&Cryogenics Technology and Physics Laboratory
文摘Carbon nanotubes(CNTs)were grown into anodic aluminum oxide(AAO)channels by chemical vapor deposition(CVD)using C2H2/N2mixtures as feeding gas,which can be used as field emitters.The bottom surface of AAO template was etched slightly and the tips of CNTs were explored as the field emission arrays which were uniform and vertical.Field emission characterization showed a low turn-on field about 3.25 V/m and high emission current about 30 mA/cm2with the electric field about 4 V/m.These superior field emission characteristics could be attributed to low density of vertical CNTs and higher conductivity of the substrate.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2013-35)Beijing Municipal Commission of Science and Technology(Grant No.Z131100006013005)
文摘Self-powered chaos signal generator is potentially useful in future medical system,such as low cost portable human healthy monitor and treatment without external power source.For both functional and power unit,the power level of electric energy generator and consumption is a key factor for self-powered system.In this paper,we have investigated the power consumption of three typical output modes of a simple chaos circuit.Analytical analysis for power consumption of fixed output mode is obtained for evaluating the power characteristics of chaos signal generator.Numerical calculations are given for predicting the power characteristics of periodical and chaotic output modes.This study is important for not only understanding the power consumption of chaos signal generator,but also guiding new self-powered chaos signal generator design.
基金supported by the National Natural Science Foundation of China (Grant nos.11474137)the Fundamental Research Funds for the Central Universities (Grant nos.LZUMMM2018017,lzujbky-2018-121)+1 种基金Key Research and Development Plan of Gansu Province (No.18YF1GA088)Scientific research project of colleges and universities in gansu province (No.2018A-205)
文摘A Zn-air battery is a potential next-generation energy storage device owing to its extremely high theoretical energy density. Currently, it is important to explore non-precious metal electrocatalysts with high electroactivity and stability in the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for the development of Zn-air batteries. In this work, porous(Ni,Co)Se2 nanosheets were synthesized by selenizing Ni Co2O4 nanosheets. By regulating the conductivity and morphology of the sample, the prepared porous(Ni,Co)Se2 nanosheets show enhanced electrocatalytic activity for OER and ORR compared to Ni Co2O4 nanosheets. The aqueous Zn-air battery using porous(Ni,Co)Se2 nanosheets as the air cathode exhibits superior charge and discharge performance(1.98 V for charging and 1.17 V for discharging), high specific capacity(770 m Ah/g), and excellent cycle stability(140 h). These results indicate that the porous(Ni,Co)Se2 nanosheets are suitable as a bifunctional electrocatalyst for future Zn-air batteries.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674139,11704166,and 11834005)the Fundamental Research Funds for the Central Universities,ChinaProgram for Changjiang Scholars and Innovative Research Team in University,China(Grant No.IRT-16R35)
文摘Slave-particle method is a powerful tool to tackle the correlation effect in quantum many-body physics. Although it has been successfully used to comprehend various intriguing problems, such as Mott metal-insulator transition and Kondo effect, there is still no convincing theory so far on the availability and limitation of this method. The abuse of slave-particle method may lead to wrong physics. As the simplest slave-particle method, Z2 slave spin, which is widely applied to many strongly correlated problems, is highly accessible and researchable. In this work, we will uncover the nature of the Z2 slave-spin method by studying a two-site Hubbard model. After exploring aspects of properties of this toy model, we make a comparative analysis of the results obtained by three methods:(i) slave-spin method on mean-field level,(ii) slave-spin method with gauge constraint, and(iii) the exact solution as a benchmark. We find that, protected by the particle-hole symmetry, the slave-spin mean-field method can recover the static properties of ground state exactly at half filling. Furthermore, in the parameter space where both U and T are small enough, the slave-spin mean-field method is also reliable in calculating the dynamic and thermal dynamic properties. However, when U or T is considerably large, the mean-field approximation gives ill-defined behaviors, which result from the unphysical states in the enlarged Hilbert space.These findings lead to our conclusion that the accuracy of slave particle can be guaranteed if we can exclude all unphysical states by enforcing gauge constraints. Our work demonstrates the promising prospect of slave-particle method in studying complex strongly correlated models with specific symmetry or in certain parameter space.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11775101 and 11422541)the US Office of Naval Research(Grant No.N00014-16-1-2828)
文摘For a quantum system with multiple degrees of freedom or subspaces, loss of coherence in a certain subspace is intimately related to the enhancement of entanglement between this subspace and another one. We investigate intra-particle entanglement in two-dimensional mesoscopic systems, where an electron has both spin and orbital degrees of freedom and the interaction between them is enabled by Rashba type of spin-orbit coupling. The geometric shape of the scattering region can be adjusted to produce a continuous spectrum of classical dynamics with different degree of chaos. Focusing on the spin degree of freedom in the weak spin-orbit coupling regime, we find that classical chaos can significantly enhance spin-orbit entanglement at the expense of spin coherence. Our finding that classical chaos can be beneficial to intra-particle entanglement may have potential applications such as enhancing the bandwidth of quantum communications.
基金This work was supported in part by the Key Technologies Research and Development Program under Grant 2020YFB2206101the National Natural Science Foundation of China(NSFC)under Grant 62035016/61975115/61835008.
文摘lectro-optic modulators are key components in data communication,microwave photonics,and quantum photonics.Modulation bandwidth,energy efficiency,and device dimension are crucial metrics of modulators.Here,we provide an important direction for the miniaturization of electro-optic modulators by reporting on ultracompact topological modulators.A topological interface state in a one-dimensional lattice is implemented on a thin-film lithium-niobate integrated platform.Due to the strong optical confinement of the interface state and the peaking enhancement of the electro-optic response,a topological cavity with a size of 1.6×140μm^(2)enables a large modulation bandwidth of 104 GHz.The first topological modulator exhibits the most compact device size compared to reported LN modulators with bandwidths above 28 GHz,to the best of our knowledge.100 Gb/s non-return-to-zero and 100 Gb/s four-level pulse amplitude modulation signals are generated.The switching energy is 5.4 fJ/bit,owing to the small electro-optic mode volume and low capacitance.The topological modulator accelerates the response time of topological photonic devices from the microsecond order to the picosecond order and provides an essential foundation for the implementation of large-scale lithium-niobate photonic integrated circuits.
基金supported by the Natural Science Foundation of Gansu Province,China(Grant No.145RJZA226)Fundamental Research Funds for the Central Universities(Grant No.lzujbky-2013-35)Beijing Municipal Commission of Science and Technology(Grant Nos.Z131100006013005 and Z131100006013004)
文摘For the materials that simultaneously exhibit piezoelectric and semiconductor properties,such as wurtzite Zn O,Ga N and In N,as well as two-dimensional single Mo S2,piezoelectric charges induced by externally applied strain can tune/control carrier transport at a metal-semiconductor contact or semiconductor junction,which is named piezotronic effect.Metal-semiconductor-metal piezotronic transistors are key piezotronic nanodevices for electromechanical applications,and they are typical nonlinear elements.In this paper,a simplified current-voltage analysis solution of piezotronic transistors is developed,which can be used for circuit design and simulation.Furthermore,the typical nonlinear circuit:Chua's circuit based on piezotronic transistors is simulated.We find that the output signal of the piezotronic transistor circuit can be switched and changed asymmetrically by externally applied strain.This study provides insight into the nonlinear properties of the piezotronic transistor,as well as guidance for piezotronic transistor nonlinear circuit application.