Effects of electron temperature on dielectric function and localization of laser beams in underdense collisional plasmas are investigated. Simulation results show that the electron temperature has a strong effect on t...Effects of electron temperature on dielectric function and localization of laser beams in underdense collisional plasmas are investigated. Simulation results show that the electron temperature has a strong effect on the dielectric constant and the laser beam localization. It is observed that due to the influence of the electron temperature, the dielectric function presents some interesting and complicated nonlinear variations, and gives rise to the laser beam lo- calization. Moreover, the amplitudes of the beam width and the beam intensity are subjected to continuously oscillatory variation in the region of localization. In addition, the effects of several parameters on the dielectric function and the beam localization are discussed.展开更多
The wavelength-dependent and frequency-dependent dielectric function of wurtzite-GaN is cMculated totally from fundamental parameters such as the lattice constant using Waiter's ab initio model. The errors occurring ...The wavelength-dependent and frequency-dependent dielectric function of wurtzite-GaN is cMculated totally from fundamental parameters such as the lattice constant using Waiter's ab initio model. The errors occurring in the cMculation are carefully reduced by/inear interpolation of energy data. The Kramers-Kronig transform of the real part of greater range is obtained by extrapolation of the reM part. The calculation is time-consuming but meaningful The long-wave results are similar to the experimental data of the photon and are useful for related investigation of properties of wide-gap semiconductors such as electron scattering like the Auger recombination and impact ionization.展开更多
Using the generalized viscoelastic fluid model, we derive the dielectric response function in a strongly coupled dusty magnetoplasma which reveals two different dust acoustic(DA) wave modes in the hydrodynamic and k...Using the generalized viscoelastic fluid model, we derive the dielectric response function in a strongly coupled dusty magnetoplasma which reveals two different dust acoustic(DA) wave modes in the hydrodynamic and kinetic limits. The effects of the strong interaction of dust grains and the external magnetic on these DA modes, as well as on the shear wave are examined. It is found that both the real and imaginary parts of DA waves are significantly modified in strongly coupled dusty magnetoplasmas. The implications of our results to space and laboratory dusty plasmas are briefly discussed.展开更多
The features of the band structures of woodpile three-dimensional (3D) photonic crystals composed of plasma and function dielectric constituents, referred to as function plasma photonic crystals (FPPCs), are theor...The features of the band structures of woodpile three-dimensional (3D) photonic crystals composed of plasma and function dielectric constituents, referred to as function plasma photonic crystals (FPPCs), are theoretically studied by a modified plane wave expansion method, and the formulas for computing the band structures are derived. The arrangement for the proposed FPPCs is that the function dielectric columns are surrounded by plasma, and the embedded dielectric columns are stacked according to the woodpile lattices, which are arrayed with facecentered-tetragonal symmetry. The relative permittivity of function dielectric rods depends on the function coefficient and space coordinates. The relationships between the parameters for inserted function dielectric rods and plasma and the band structures are also investigated. The computed results illustrate that the obtained PBG can be tuned by those parameters as mentioned above. Compared to dielectric-air PCs, function dielectric PCs and plasma dielectric PCs with the same topology, a wider bandwidth of the photonic band gap can be observed in the proposed FPPCs. The calculated results also show us another alternative way to realize reconfigurable applications with 3D FPPCs.展开更多
Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , are proposed and studied numerically. The band gaps structures of the photonic c...Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , are proposed and studied numerically. The band gaps structures of the photonic crystals for TE and TM waves are different from the two-dimensional conventional photonic crystals. Some absolute band gaps and semiDirac points are found. When the medium column radius and the function form of the dielectric constant are modulated, the numbers, width, and position of band gaps are changed, and the semi-Dirac point can either occur or disappear. Therefore,the special band gaps structures and semi-Dirac points can be achieved through the modulation on the two-dimensional function photonic crystals. The results will provide a new design method of optical devices based on the two-dimensional function photonic crystals.展开更多
This paper reports that in the quantization of electromagnetic field in the dielectrics, the wave equation with regard to the Green function is analytically solved by a direct integral method for a quadratic continuou...This paper reports that in the quantization of electromagnetic field in the dielectrics, the wave equation with regard to the Green function is analytically solved by a direct integral method for a quadratic continuous nonlinear absorptive dielectric medium. The quantization of the electromagnetic field in such a nonlinear absorptive dielectric is carried out for which the material dielectric function is assumed as a separable variable about the frequency and the space coordinate. The vacuum field fluctuations for different spatial continuous variations of dielectric function are numerically calculated, which shows that the present result is self-consistent.展开更多
A collector with high perveance,efficient recu-peration,and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex.To optimize the collection efficiency of the collector,a ...A collector with high perveance,efficient recu-peration,and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex.To optimize the collection efficiency of the collector,a simulation program,based on the Monte Carlo simulations,was developed in the world’s first attempt to calculate the electron collection efficiency.In this program,the backscattering electrons and secondary electrons generated on the collector surface are calculated using a Monte Carlo approach,and all electron trajectories in the collector region are tracked by the Runge–Kutta method.In this paper,the features and structure of our program are described.The backscattering electron yields,with various collector surface materials,are calculated using our pro-gram.Moreover,the collector efficiencies for various col-lector structures and electromagnetic fields are simulated and optimized.The measurement results of the collection efficiency of the HIAF collector prototype and the CSRm synchrotron are also reported.These experimental results were in good agreement with the simulation results of our program.展开更多
Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm^-1. Eight infrared-active phonon ...Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm^-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the (LO-TO)1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgA1204 can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.展开更多
Lithium(Li)metal batteries(LMBs)can potentially deliver much higher energy density but remain plagued by uncontrollable Li plating with dendrite growth,unstable interfaces,and highly abundant excess Li(>50 mAh·...Lithium(Li)metal batteries(LMBs)can potentially deliver much higher energy density but remain plagued by uncontrollable Li plating with dendrite growth,unstable interfaces,and highly abundant excess Li(>50 mAh·cm^(-2)).Herein,different from the artificial layer or three-dimensional(3D)matrix host constructions,various dielectric polymers are initially well-comprehensively investigated from experimental characterizations to theoretical simulation to evaluate their functions in modulating Li ion distribution.As a proof of concept,a 3D interwoven high dielectric functional polymer(HDFP)nanofiber network with polar C-F dipole moments electrospun on copper(Cu)foil is designed,realizing uniform and controllable Li deposition capacity up to 5.0 mAh·cm^(-2),thereby enabling stable Li plating/stripping cycling over 1400 h at 1.0 mA·cm^(-2).More importantly,under the highcathode loading(~3.1 mAh·cm^(-2))and only 0.6×excess Li(N/P ratio of 1.6),the full cells retain capacity retention of 97.4%after 200 cycles at 3.36 mA·cm^(-2)and achieve high energy density(297.7 Wh·kg^(-1)at cell-level)under lean electrolyte conditions(15μL),much better than ever-reported literatures.Our work provides a new direction for designing high dielectric polymer coating toward high-retention-rate practical Li full batteries.展开更多
The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies (denoted as VFe, VBi, and Vo, respectively) are investigated using the first-prin...The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies (denoted as VFe, VBi, and Vo, respectively) are investigated using the first-principles density functional theory plus U calculations. It is revealed that the structural distortions associated with those vacancies impose significant influences on the total density of state and magnetic behaviors. The existence of VBi favors the excitation of the O2p state into the band gap at 0.4 eV, while the O2p and Fe3d orbitals are co-excited into the band gap around 0.45 eV in VFe- Consequently, a giant net magnetic moment of 1.96 P-B is generated in VFe, and a relatively small moment of 0.13 P-B is induced in VBi, whereas Vo seems magnetically inactive. The giant magnetic moment generated in VFe originates from the suppression of the spatially modulated antiferromagnetic spin structure. Furthermore, VFe and VBi have strong influences on dielectric function, and induce some strong peaks to occur in the lower energy level. In contrast, VO has a small effect.展开更多
We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg0.25Zn0.75O. The calculation is carried out in a-axis and c-axis str...We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg0.25Zn0.75O. The calculation is carried out in a-axis and c-axis strain changing in the range from 0.3 to -0.2 in intervals of 0.1. The results calculated from density of states show that the bottom of conduction band is always dominated by Zn 4s and the top of valence band is always dominated by O 2p in a-axis and c-axis strain. Zn 4s will shift to higher energy range when a-axis strain changes in the range from 0.3 to 0, and then shift to lower energy range when a-axis strain changes in the range from 0 to -0.2. But Zn 4s will always shift to higher energy range when c-axis strain changes in the range from 0.3 to -0.2. The variations of band gap calculated from band structure and absorption spectra are also investigated, which are consistent with the results obtained from density of states. In addition, we analyse and discuss the imaginary part of the dielectric function ε2.展开更多
The anisotropic properties of 1T- and 2H-TaS2 axe investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exh...The anisotropic properties of 1T- and 2H-TaS2 axe investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exhibit anisotropic properties and the calculated electronic specific-heat coefficient γ of 2H-TaS2 accords well with the existing experimental value. The anisotropic frequency-dependent dielectric functions including the effect of the Drude term are analysed, where the ε^xx(ω) spectra corresponding to the electric field E perpendicular to the z axis show excellent agreement with the measured results except for the ε1^xx(ω) of 1T-TaS2 below the energy level of 2.6 eV which is due to the lack of the enough CDW information for reference in our calculation. Furthermore, based on the values of optical effective mass ratio P of 1T and 2H phases it is found that the anisotropy in 2H-TaS2 is stronger than that in 1T-TaS2.展开更多
We present first principles calculations of optical properties of binary semiconductor compounds TlBr and TlCl.Dependences of dielectric function,reflectivity and refractive index on hydrostatic pressure are calculate...We present first principles calculations of optical properties of binary semiconductor compounds TlBr and TlCl.Dependences of dielectric function,reflectivity and refractive index on hydrostatic pressure are calculated using self-consistent scalar relativistic full potential linear augmented plane wave method(FP-LAPW) within a generalized gradient approximation(GGA).They are compared with previous calculations and experimental measurements.Good agreements are found.展开更多
We present structural,magnetic and optical characteristics of Zn_(1-x)TM_xTe(TM = Mn,Fe,Co,Ni and x = 6.25%),calculated through Wien2 k code,by using full potential linearized augmented plane wave(FP-LAPW) techn...We present structural,magnetic and optical characteristics of Zn_(1-x)TM_xTe(TM = Mn,Fe,Co,Ni and x = 6.25%),calculated through Wien2 k code,by using full potential linearized augmented plane wave(FP-LAPW) technique.The optimization of the crystal structures have been done to compare the ferromagnetic(FM) and antiferromagnetic(AFM) ground state energies,to elucidate the ferromagnetic phase stability,which further has been verified through the formation and cohesive energies.Moreover,the estimated Curie temperatures T_c have demonstrated above room temperature ferromagnetism(RTFM) in Zn_(1-x)TM_xTe(TM =Mn,Fe,Co,Ni and x= 6.25%).The calculated electronic properties have depicted that Mn- and Co-doped ZnTe behave as ferromagnetic semiconductors,while half-metallic ferromagnetic behaviors are observed in Fe- and Ni-doped ZnTe.The presence of ferromagnetism is also demonstrated to be due to both the p-d and s-d hybridizations between the host lattice cations and TM impurities.The calculated band gaps and static real dielectric constants have been observed to vary according to Penn's model.The evaluated band gaps lie in near visible and ultraviolet regions,which make these materials suitable for various important device applications in optoelectronic and spintronic.展开更多
The AC-electronic and dielectric properties of different phthalocyanine films (ZnPc, CuPc, FePc, and H2Pc) were investigated over a wide range of temperature. Both real and imaginary parts of the dielectric constant...The AC-electronic and dielectric properties of different phthalocyanine films (ZnPc, CuPc, FePc, and H2Pc) were investigated over a wide range of temperature. Both real and imaginary parts of the dielectric constant (ε = ε1 - ε2) were found to be influenced by temperature and frequency. Qualitatively the behavior was the same for those compounds; however, the central atom, film thickness, and the electrode type play an important role in the variation of their values. The relaxation time, r, was strongly frequency-dependent at all temperatures and low frequencies, while a weak dependency is observed at higher frequencies. The relaxation activation energy was derived from the slopes of the fitted lines of In r and the reciprocal of the temperature (l/T). The values of the activation energy were accounted for the hopping process at low temperatures, while a thermally activated conduction process was dominant at higher temperatures. The maximum barrier height, Wm, was found to be temperature and frequency dependent for all phthalocyanine compounds. The value Wm depends greatly on the nature of the central atom and electrode material type. The correlated barrier hopping model was found to be the appropriate mechanism to describe the charge carrier's transport in phthalocyanine films.展开更多
The dielectric function of some phthalocyanine compounds (ZnPc, H2Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ca, vari...The dielectric function of some phthalocyanine compounds (ZnPc, H2Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ca, varies strongly with frequency and temperature. The frequency dependence was expressed as: ε1 = Aε^n, where the index, n, assumes negative values (n 〈 0). In addition, the imaginary part of the dielectric constant, ε2, is also frequency and temperature dependent. Data analysis confirmed that ε2 = Bo)m with values of m less than zero. At low frequencies and all temperatures, a strong dependence is observed, while at higher frequencies, a moderate dependence is obvious especially for the Au-electrode sample. Qualitatively, the type of electrode material had little effect on the behavior of the dielectric constant but did affect its value. Analysis of the AC conductivity dependence on frequency at different temperatures indicated that the correlated barrier hopping (CBH) model is the most suitable mechanism for the AC conduction behavior. Maximum barrier height, W, has been estimated for ZnPc with different electrode materials (Au and AI), and had values between 0.10 and 0.9 eV. For both electrode types, the maximum barrier height has strong frequency dependence at high frequency and low temperatures. The relaxation time, r, for ZnPc and FePc films increases with decreasing frequency. The activation energy was derived from the slopes of r versus 1/T curves. At low temperatures, an activation energy value of about 0.01 eV and 0.04 eV was estimated for ZnPc and FePc, respectively. The low values of activation energy suggest that the hopping of charge carriers between localized states is the dominant mechanism.展开更多
The electronic structures and dielectric properties of TiO_(2)-graphene composites are studied using pseudo-potential density functional theory.It is shown that interfacial charge transfer properties of graphene/TiO_(...The electronic structures and dielectric properties of TiO_(2)-graphene composites are studied using pseudo-potential density functional theory.It is shown that interfacial charge transfer properties of graphene/TiO_(2)are influenced by the atomic type on TiO_(2)surface.The interfacial interaction of graphene with Ti-terminated surface is so strong that it causes a buckling structural graphene,and the titanium atomic d electrons are transferred obviously from TiO_(2)to graphene.It is revealed that dielectric properties of the composites are greatly affected by both band structures and electronic transitions.Compared with bulk TiO_(2),dielectric constants of TiO_(2)-graphene composites are significantly improved.展开更多
The optical properties of α-BeH2 in an Orthorhombic crystal structure with the space group (Ibam) are investigated. We have calculated the optical properties including dielelectric function, refractive index and exti...The optical properties of α-BeH2 in an Orthorhombic crystal structure with the space group (Ibam) are investigated. We have calculated the optical properties including dielelectric function, refractive index and extinction coefficient, using density functional approach. A theoretical explanation of the relationship between the dielectric function and other optical constants has been provided. Furthermore, the real and imaginary components of the dielectric function have been examined. The effects of the exchange-correlation potentials (GGA and GGA + U) applied on this compound’s absorption peaks and edges have also been investigated. It was found that using the GGA + U approximation caused the conduction band to shift, which in turn caused the initial absorption peak to shift.展开更多
For single-walled carbon nanotubes(SWCNTs)with a length of 1-50μm,the surface plasmon-polariton(SPP)resonance is within the terahertz frequency range;therefore,SWCNT lattices can be used to design frequency-selective...For single-walled carbon nanotubes(SWCNTs)with a length of 1-50μm,the surface plasmon-polariton(SPP)resonance is within the terahertz frequency range;therefore,SWCNT lattices can be used to design frequency-selective surface(FSS).A numerical model of electromagnetic wave diffraction on a two-dimensional periodic SWCNT lattice can be described by an integro-differential equation of the second-order with respect to the surface current along SWCNT.The equation can be solved by the Bubnov-Galerkin method.Frequency dependence of reflecting and transmitting electromagnetic waves for FSSs near the SPP resonance is studied numerically.It is shown that the resonances are within the lowerfrequency part of the terahertz range.We also estimate the relaxa-tion frequency of an individual SWCNT and demonstrate the applic-ability of the Kubo formula for graphene conductivity to array of strips similar in size to SWCNTs under consideration.展开更多
A new solar selective absorbing coating of Mo/NiAlN/NiAlON/SiO_2 multilayer was prepared on stainless steel(SS) substrates by magnetron sputtering for solar thermal power applications. The optical constants and thickn...A new solar selective absorbing coating of Mo/NiAlN/NiAlON/SiO_2 multilayer was prepared on stainless steel(SS) substrates by magnetron sputtering for solar thermal power applications. The optical constants and thickness of individual layers were simulated using the Scout software based on the experimentally measured reflectance and transmittance spectra of individual layers. The coating of Mo/NiAlN/NiAlON/SiO_2 with an ideal solar absorptance(α) of 0.945 in the solar spectrum range was designed via the optical constants of each layer in the Scout software. The Mo/NiAlN/NiAlON/SiO_2 coating was deposited via the optimized layer thickness. A good spectral selectivity with absorptance(α=0.936) and emittance(ε=0.09, T=80 ℃) was obtained. This method, which incorporates the optical simulation with the related experiments, provides a convenient approach to obtain the ideal solar selective absorbing coatings.展开更多
基金Project supported by the Autonomous Innovation Fund,China (Grant Nos.0109012922 and 0109012926)the Youth Foundation of Department of Education of Hubei Province,China (Grant No.Q20101602)
文摘Effects of electron temperature on dielectric function and localization of laser beams in underdense collisional plasmas are investigated. Simulation results show that the electron temperature has a strong effect on the dielectric constant and the laser beam localization. It is observed that due to the influence of the electron temperature, the dielectric function presents some interesting and complicated nonlinear variations, and gives rise to the laser beam lo- calization. Moreover, the amplitudes of the beam width and the beam intensity are subjected to continuously oscillatory variation in the region of localization. In addition, the effects of several parameters on the dielectric function and the beam localization are discussed.
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFB0400102the National Basic Research Program of China under Grant Nos 2012CB3155605,2013CB632804,2014CB340002 and 2015CB351900+7 种基金the National Natural Science Foundation of China under Grant Nos 61574082,61210014,61321004,61307024 and 51561165012the High Technology Research and Development Program of China under Grant No 2015AA017101the Tsinghua University Student Research Training Projects under Grant No 1611T0157the Tsinghua University Initiative Scientific Research Program under Grant Nos 2013023Z09N and 2015THZ02-3the Open Fund of the State Key Laboratory on Integrated Optoelectronics under Grant No IOSKL2015KF10the CAEP Microsystem and THz Science and Technology Foundation under Grant No CAEPMT201505the Science Challenge Project under Grant No JCKY2016212A503the Guangdong Province Science and Technology Program under Grant No 2014B010121004
文摘The wavelength-dependent and frequency-dependent dielectric function of wurtzite-GaN is cMculated totally from fundamental parameters such as the lattice constant using Waiter's ab initio model. The errors occurring in the cMculation are carefully reduced by/inear interpolation of energy data. The Kramers-Kronig transform of the real part of greater range is obtained by extrapolation of the reM part. The calculation is time-consuming but meaningful The long-wave results are similar to the experimental data of the photon and are useful for related investigation of properties of wide-gap semiconductors such as electron scattering like the Auger recombination and impact ionization.
文摘Using the generalized viscoelastic fluid model, we derive the dielectric response function in a strongly coupled dusty magnetoplasma which reveals two different dust acoustic(DA) wave modes in the hydrodynamic and kinetic limits. The effects of the strong interaction of dust grains and the external magnetic on these DA modes, as well as on the shear wave are examined. It is found that both the real and imaginary parts of DA waves are significantly modified in strongly coupled dusty magnetoplasmas. The implications of our results to space and laboratory dusty plasmas are briefly discussed.
基金funded by the Postdoctoral Foundation of Jiangsu Province (No. 1501016A)China Postdoctoral Science Foundation (No. 2015M581790)the Special Grade China Postdoctoral Science Foundation (No. 2016T90455)
文摘The features of the band structures of woodpile three-dimensional (3D) photonic crystals composed of plasma and function dielectric constituents, referred to as function plasma photonic crystals (FPPCs), are theoretically studied by a modified plane wave expansion method, and the formulas for computing the band structures are derived. The arrangement for the proposed FPPCs is that the function dielectric columns are surrounded by plasma, and the embedded dielectric columns are stacked according to the woodpile lattices, which are arrayed with facecentered-tetragonal symmetry. The relative permittivity of function dielectric rods depends on the function coefficient and space coordinates. The relationships between the parameters for inserted function dielectric rods and plasma and the band structures are also investigated. The computed results illustrate that the obtained PBG can be tuned by those parameters as mentioned above. Compared to dielectric-air PCs, function dielectric PCs and plasma dielectric PCs with the same topology, a wider bandwidth of the photonic band gap can be observed in the proposed FPPCs. The calculated results also show us another alternative way to realize reconfigurable applications with 3D FPPCs.
基金Project supported by the National Natural Science Foundations of China(Grant No.61275047)the Research Project of Chinese Ministry of Education(Grant No.213009A)the Scientific and Technological Development Foundation of Jilin Province,China(Grant No.20130101031JC)
文摘Two-dimensional function photonic crystals, in which the dielectric constants of medium columns are the functions of space coordinates , are proposed and studied numerically. The band gaps structures of the photonic crystals for TE and TM waves are different from the two-dimensional conventional photonic crystals. Some absolute band gaps and semiDirac points are found. When the medium column radius and the function form of the dielectric constant are modulated, the numbers, width, and position of band gaps are changed, and the semi-Dirac point can either occur or disappear. Therefore,the special band gaps structures and semi-Dirac points can be achieved through the modulation on the two-dimensional function photonic crystals. The results will provide a new design method of optical devices based on the two-dimensional function photonic crystals.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10574010 and 10974010)Beijing Commission of Education (Grant No. 1010005466903)
文摘This paper reports that in the quantization of electromagnetic field in the dielectrics, the wave equation with regard to the Green function is analytically solved by a direct integral method for a quadratic continuous nonlinear absorptive dielectric medium. The quantization of the electromagnetic field in such a nonlinear absorptive dielectric is carried out for which the material dielectric function is assumed as a separable variable about the frequency and the space coordinate. The vacuum field fluctuations for different spatial continuous variations of dielectric function are numerically calculated, which shows that the present result is self-consistent.
基金This work was supported by the International Partnership Program of the Chinese Academy of Sciences(No.113462KYSB20170051)the National Natural Science Foundation of China(No.11575264)the National Key R&D Program of China(No.2019YFA0405400).
文摘A collector with high perveance,efficient recu-peration,and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex.To optimize the collection efficiency of the collector,a simulation program,based on the Monte Carlo simulations,was developed in the world’s first attempt to calculate the electron collection efficiency.In this program,the backscattering electrons and secondary electrons generated on the collector surface are calculated using a Monte Carlo approach,and all electron trajectories in the collector region are tracked by the Runge–Kutta method.In this paper,the features and structure of our program are described.The backscattering electron yields,with various collector surface materials,are calculated using our pro-gram.Moreover,the collector efficiencies for various col-lector structures and electromagnetic fields are simulated and optimized.The measurement results of the collection efficiency of the HIAF collector prototype and the CSRm synchrotron are also reported.These experimental results were in good agreement with the simulation results of our program.
基金Project supported by the National Natural Science Foundation of China (Grant No 10474128) and Chinese Academy of Sciences.
文摘Near-normal incident infrared reflectivity spectra of (100) MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm^-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the (LO-TO)1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgA1204 can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.
基金This work was financial supported by the National Natural Science Foundation of China(Nos.51877132,52003153,and 22005186)the Program of Shanghai Academic Research Leader(No.21XD1401600).
文摘Lithium(Li)metal batteries(LMBs)can potentially deliver much higher energy density but remain plagued by uncontrollable Li plating with dendrite growth,unstable interfaces,and highly abundant excess Li(>50 mAh·cm^(-2)).Herein,different from the artificial layer or three-dimensional(3D)matrix host constructions,various dielectric polymers are initially well-comprehensively investigated from experimental characterizations to theoretical simulation to evaluate their functions in modulating Li ion distribution.As a proof of concept,a 3D interwoven high dielectric functional polymer(HDFP)nanofiber network with polar C-F dipole moments electrospun on copper(Cu)foil is designed,realizing uniform and controllable Li deposition capacity up to 5.0 mAh·cm^(-2),thereby enabling stable Li plating/stripping cycling over 1400 h at 1.0 mA·cm^(-2).More importantly,under the highcathode loading(~3.1 mAh·cm^(-2))and only 0.6×excess Li(N/P ratio of 1.6),the full cells retain capacity retention of 97.4%after 200 cycles at 3.36 mA·cm^(-2)and achieve high energy density(297.7 Wh·kg^(-1)at cell-level)under lean electrolyte conditions(15μL),much better than ever-reported literatures.Our work provides a new direction for designing high dielectric polymer coating toward high-retention-rate practical Li full batteries.
基金supported by the National Natural Science Foundation of China(Grant Nos.51101063,51072061,and 51172067)the Natural Science Foundation of Guangdong Province,China(Grant No.S2011040003205)
文摘The electronic structure, magnetism, and dielectric functions of BiFeO3 with intrinsic vacancies, including Bi-, Fe-, and O-vacancies (denoted as VFe, VBi, and Vo, respectively) are investigated using the first-principles density functional theory plus U calculations. It is revealed that the structural distortions associated with those vacancies impose significant influences on the total density of state and magnetic behaviors. The existence of VBi favors the excitation of the O2p state into the band gap at 0.4 eV, while the O2p and Fe3d orbitals are co-excited into the band gap around 0.45 eV in VFe- Consequently, a giant net magnetic moment of 1.96 P-B is generated in VFe, and a relatively small moment of 0.13 P-B is induced in VBi, whereas Vo seems magnetically inactive. The giant magnetic moment generated in VFe originates from the suppression of the spatially modulated antiferromagnetic spin structure. Furthermore, VFe and VBi have strong influences on dielectric function, and induce some strong peaks to occur in the lower energy level. In contrast, VO has a small effect.
基金supported by doctor start-up fund of Bohai University (Grant No KJ2007005)
文摘We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg0.25Zn0.75O. The calculation is carried out in a-axis and c-axis strain changing in the range from 0.3 to -0.2 in intervals of 0.1. The results calculated from density of states show that the bottom of conduction band is always dominated by Zn 4s and the top of valence band is always dominated by O 2p in a-axis and c-axis strain. Zn 4s will shift to higher energy range when a-axis strain changes in the range from 0.3 to 0, and then shift to lower energy range when a-axis strain changes in the range from 0 to -0.2. But Zn 4s will always shift to higher energy range when c-axis strain changes in the range from 0.3 to -0.2. The variations of band gap calculated from band structure and absorption spectra are also investigated, which are consistent with the results obtained from density of states. In addition, we analyse and discuss the imaginary part of the dielectric function ε2.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 90503005 and 50472097), the State Key Development Program for Basic Research of China (Grant No 2005CB623603), Knowledge Innovation Program of Chinese Academy of Sciences, and Director Grants of Hefei Institutes of Physical Sciences. Acknowledgment Part of the calculations were performed at the Centre for Computational Science, Hefei Institute of Physics China.
文摘The anisotropic properties of 1T- and 2H-TaS2 axe investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exhibit anisotropic properties and the calculated electronic specific-heat coefficient γ of 2H-TaS2 accords well with the existing experimental value. The anisotropic frequency-dependent dielectric functions including the effect of the Drude term are analysed, where the ε^xx(ω) spectra corresponding to the electric field E perpendicular to the z axis show excellent agreement with the measured results except for the ε1^xx(ω) of 1T-TaS2 below the energy level of 2.6 eV which is due to the lack of the enough CDW information for reference in our calculation. Furthermore, based on the values of optical effective mass ratio P of 1T and 2H phases it is found that the anisotropy in 2H-TaS2 is stronger than that in 1T-TaS2.
文摘We present first principles calculations of optical properties of binary semiconductor compounds TlBr and TlCl.Dependences of dielectric function,reflectivity and refractive index on hydrostatic pressure are calculated using self-consistent scalar relativistic full potential linear augmented plane wave method(FP-LAPW) within a generalized gradient approximation(GGA).They are compared with previous calculations and experimental measurements.Good agreements are found.
基金the University of the Punjab, Lahore for financial support through faculty research grant program
文摘We present structural,magnetic and optical characteristics of Zn_(1-x)TM_xTe(TM = Mn,Fe,Co,Ni and x = 6.25%),calculated through Wien2 k code,by using full potential linearized augmented plane wave(FP-LAPW) technique.The optimization of the crystal structures have been done to compare the ferromagnetic(FM) and antiferromagnetic(AFM) ground state energies,to elucidate the ferromagnetic phase stability,which further has been verified through the formation and cohesive energies.Moreover,the estimated Curie temperatures T_c have demonstrated above room temperature ferromagnetism(RTFM) in Zn_(1-x)TM_xTe(TM =Mn,Fe,Co,Ni and x= 6.25%).The calculated electronic properties have depicted that Mn- and Co-doped ZnTe behave as ferromagnetic semiconductors,while half-metallic ferromagnetic behaviors are observed in Fe- and Ni-doped ZnTe.The presence of ferromagnetism is also demonstrated to be due to both the p-d and s-d hybridizations between the host lattice cations and TM impurities.The calculated band gaps and static real dielectric constants have been observed to vary according to Penn's model.The evaluated band gaps lie in near visible and ultraviolet regions,which make these materials suitable for various important device applications in optoelectronic and spintronic.
文摘The AC-electronic and dielectric properties of different phthalocyanine films (ZnPc, CuPc, FePc, and H2Pc) were investigated over a wide range of temperature. Both real and imaginary parts of the dielectric constant (ε = ε1 - ε2) were found to be influenced by temperature and frequency. Qualitatively the behavior was the same for those compounds; however, the central atom, film thickness, and the electrode type play an important role in the variation of their values. The relaxation time, r, was strongly frequency-dependent at all temperatures and low frequencies, while a weak dependency is observed at higher frequencies. The relaxation activation energy was derived from the slopes of the fitted lines of In r and the reciprocal of the temperature (l/T). The values of the activation energy were accounted for the hopping process at low temperatures, while a thermally activated conduction process was dominant at higher temperatures. The maximum barrier height, Wm, was found to be temperature and frequency dependent for all phthalocyanine compounds. The value Wm depends greatly on the nature of the central atom and electrode material type. The correlated barrier hopping model was found to be the appropriate mechanism to describe the charge carrier's transport in phthalocyanine films.
文摘The dielectric function of some phthalocyanine compounds (ZnPc, H2Pc, CuPc, and FePc) were investigated by analyzing the measured capacitance and loss tangent data. The real part of the dielectric constant, ca, varies strongly with frequency and temperature. The frequency dependence was expressed as: ε1 = Aε^n, where the index, n, assumes negative values (n 〈 0). In addition, the imaginary part of the dielectric constant, ε2, is also frequency and temperature dependent. Data analysis confirmed that ε2 = Bo)m with values of m less than zero. At low frequencies and all temperatures, a strong dependence is observed, while at higher frequencies, a moderate dependence is obvious especially for the Au-electrode sample. Qualitatively, the type of electrode material had little effect on the behavior of the dielectric constant but did affect its value. Analysis of the AC conductivity dependence on frequency at different temperatures indicated that the correlated barrier hopping (CBH) model is the most suitable mechanism for the AC conduction behavior. Maximum barrier height, W, has been estimated for ZnPc with different electrode materials (Au and AI), and had values between 0.10 and 0.9 eV. For both electrode types, the maximum barrier height has strong frequency dependence at high frequency and low temperatures. The relaxation time, r, for ZnPc and FePc films increases with decreasing frequency. The activation energy was derived from the slopes of r versus 1/T curves. At low temperatures, an activation energy value of about 0.01 eV and 0.04 eV was estimated for ZnPc and FePc, respectively. The low values of activation energy suggest that the hopping of charge carriers between localized states is the dominant mechanism.
基金supported by NSFC(Grant No.21171138)the National Key Basic Research Program of China(Grant No.2012CB720904)the Key Project in the National Science and Technology Pillar Program of China(Grant No.2010BAK67B12).
文摘The electronic structures and dielectric properties of TiO_(2)-graphene composites are studied using pseudo-potential density functional theory.It is shown that interfacial charge transfer properties of graphene/TiO_(2)are influenced by the atomic type on TiO_(2)surface.The interfacial interaction of graphene with Ti-terminated surface is so strong that it causes a buckling structural graphene,and the titanium atomic d electrons are transferred obviously from TiO_(2)to graphene.It is revealed that dielectric properties of the composites are greatly affected by both band structures and electronic transitions.Compared with bulk TiO_(2),dielectric constants of TiO_(2)-graphene composites are significantly improved.
文摘The optical properties of α-BeH2 in an Orthorhombic crystal structure with the space group (Ibam) are investigated. We have calculated the optical properties including dielelectric function, refractive index and extinction coefficient, using density functional approach. A theoretical explanation of the relationship between the dielectric function and other optical constants has been provided. Furthermore, the real and imaginary components of the dielectric function have been examined. The effects of the exchange-correlation potentials (GGA and GGA + U) applied on this compound’s absorption peaks and edges have also been investigated. It was found that using the GGA + U approximation caused the conduction band to shift, which in turn caused the initial absorption peak to shift.
基金Russian Foundation for Basic Research(RFBR),project number 21-52-15034。
文摘For single-walled carbon nanotubes(SWCNTs)with a length of 1-50μm,the surface plasmon-polariton(SPP)resonance is within the terahertz frequency range;therefore,SWCNT lattices can be used to design frequency-selective surface(FSS).A numerical model of electromagnetic wave diffraction on a two-dimensional periodic SWCNT lattice can be described by an integro-differential equation of the second-order with respect to the surface current along SWCNT.The equation can be solved by the Bubnov-Galerkin method.Frequency dependence of reflecting and transmitting electromagnetic waves for FSSs near the SPP resonance is studied numerically.It is shown that the resonances are within the lowerfrequency part of the terahertz range.We also estimate the relaxa-tion frequency of an individual SWCNT and demonstrate the applic-ability of the Kubo formula for graphene conductivity to array of strips similar in size to SWCNTs under consideration.
基金National Natural Science Foundation of China (No.51172012 and No.51472017)State Key Lab of Advance Metals and Materials (2014-ZD03)Foundation of Beijing Municipal Science & Technology Commission
文摘A new solar selective absorbing coating of Mo/NiAlN/NiAlON/SiO_2 multilayer was prepared on stainless steel(SS) substrates by magnetron sputtering for solar thermal power applications. The optical constants and thickness of individual layers were simulated using the Scout software based on the experimentally measured reflectance and transmittance spectra of individual layers. The coating of Mo/NiAlN/NiAlON/SiO_2 with an ideal solar absorptance(α) of 0.945 in the solar spectrum range was designed via the optical constants of each layer in the Scout software. The Mo/NiAlN/NiAlON/SiO_2 coating was deposited via the optimized layer thickness. A good spectral selectivity with absorptance(α=0.936) and emittance(ε=0.09, T=80 ℃) was obtained. This method, which incorporates the optical simulation with the related experiments, provides a convenient approach to obtain the ideal solar selective absorbing coatings.