bluuebunny/crossref_metadata_2025 huggingface dataset:
Internuclear-distance dependence of nonsequential double ionization of H2 in different alignments
Authors: Tong Ai-Hong  , Liao Qing  , Zhou Yue-Ming  , Lu Pei-Xiang  ,   Wuhan National Laboratory for Optoelectronics, School of Optoelectronic Science and Engineering, Huazhong University of Science and Technology,Wuhan 430074,China
Published: December 2020

Using a three-dimensional classical ensemble, we have investigated the internuclear distance (R) dependence of nonsequential double ionization (NSDI) of H2 molecules. In all alignments, as R increases, the double ionization (DI) rate first increases and then decreases, and it reaches its maxima when R is 4a.u.. The dependence of NSDI of H2 on R weakens as the angle between molecular axis and laser polarization(φ) increases. When φ is zero, the NSDI of H2 provides rich correlation patterns, which is strongly dependent on R. When φ is π/2, the correlation patterns are similar for different values of R and recollisions play a more important role in DI process. These results indicate that molecular structure has an important influence on NSDI of diatomic molecules.
Low-energy isomers and isomerization of water cluster (H2O)6
Authors: Che Xiao-Fang  , Chen Hong-Shan  ,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

(H2O)6 is the smallest water cluster to form three-dimensional(3-D) structure, and there exist a few low-energy isomers. The stability of the isomers and the isomerization process are studied by ab initio calculations. The difference in energy between the ring structure and the most stable prism is 0.31 eV, which is the energy of one hydrogen bond. The isomerization process of water clusters corresponds to the breaking and/or the reforming of hydrogen bonds. For (H2O)6, the isomerization among the low-energy structures involves the breaking or the reforming of only one hydrogen bond, and the energy barriers separating the isomers range from 0.07—0.21 eV.
Numerical study of three-dimensional isotropic left-handed metamaterials at visible frequencies
Authors: Gong Bo-Yi  , Zhou Xin  , Zhao Xiao-Peng  ,   Smart Materials Laboratory, Northwestern Polytechnical University, Xi’an 710129 , China
Published: December 2020

In this paper, we design a three-dimensional isotropic left-handed metamaterial (LHM) composed of sphere-thorn shaped cells at visible frequencies. Adopting the metallic Drude's principle, we simulate and study its transmission properties for the incident plane electromagnetic wave. The dimension of unit cell here is far below the resonant wavelength, and thus the effective medium theory is well satisfied. With appropriate geometric parameters, this structure can realize negative refractive index with simultaneous negative permittivity and permeability at visible frequencies. The LHM proposed in this paper has advantages of simplicity and isotropy, moreover, our numerical model provides a new method for 'top-to-bottom’approach to preparing visible three-dimensional metamaterials.
Experimental and theoretical investigations of spatial dark solitons in nonlocal nonlinear medium
Authors: Zhou Luo-Hong  , Gao Xing-Hui  , Yang Zhen-Jun  , Lu Da-Quan  , Guo Qi  , Cao Wei-Wen  , Hu Wei  ,   Laboratory of Photonic Information Technology, South China Normal University, Guangzhou 510631, China
Published: December 2020

In this paper, we investigate spatial dark solitons in nonlocal nonlinear media. Based on the nonlocal nonlinear Schrödinger equation and the diffusion equation, the numerical solutions with different propagation constants are obtained by using the Newton iterative method. And it is found that there exist dark soliton solutions .and the relation between the width of dark soliton and the degree of nonlocality for any propagation constant under arbitrary nonlocal degrees different propagation constants. In experiments, we observe the formation of the spatial dark solitons in the solution of dye. The influence of Gaussian background on dark solitons is also discussed, and the numerical results are in agreement with the experimental results.
Study of holographic characteristics of TiO2 nanoparticles dispersed resisting shrinkage photopolymer
Authors: Zhao Lei  , Wang Long-Ge  , Hu Bin  , Huang Ming-Ju  ,   (1)Institute of Photon and Optoelectronics Technique, College of Physics and Electronics, Henan University, Kaifeng 475004, China; (2)Key Lab For Special Functional Materials, Ministry of Education, Henan University, Kaifeng 475004, China
Published: December 2020

Holographic recording characteristics of the hydrophilic TiO2-nanoparticle-dispersed polyvinyl alcohol/acrylamide-based thick photopolymer are studied. The experimental results show that not only the volume shrinkage during the holographic exposure can be suppressed by the inclusion of the nanoparticles, but also the diffraction efficiency and other performance parameters can be improved in the hydrophilic TiO2-nanoparticles dispersed photopolymer compared with those traditional samples. There exists an optimum concentration of TiO2-nanoperticals, in which the maximum diffraction efficiency can reach 92.3%, the maximum refractive index modulation arrives at 2.09×10-3, and the volume shrinkage reduces to 0.80%.
Acoustic metamaterial with split hollow spheres
Authors: Ding Chang-Lin  , Zhao Xiao-Peng  , Hao Li-Mei  , Zhu Wei-Ren  ,   Department of Applied Physics, Northwestern Polytechnical University, Xi’ an 710129, China
Published: December 2020

We propose an acoustic metamaterial (AM) composed of local resonant split hollow sphere (SHS). The results of numerical simulation and acoustic experiment show that the effective modulus of the AM with SHS is negative. To further investigate the intrinsic resonant mechanism of the SHS, we study the transmission of the AM by adjusting the geometry sizes of the SHS, such as the diameter of split hole and the diameter of hollow sphere. It is found that the geometry sizes of SHS will greatly affect the frequency of transmission dip, say, the resonant frequency. Moreover, we investigate the effects of the arrangement in AM on transmission feature. When the lattice constant and the number of SHSs change, the frequency range of resonance in the single-layer AM keeps unchanged. However, the resonant intensity of AM becomes stronger with the increase of the number of SHSs in single layer and the number of SHS layers.
Ratcheting thermal conduction in one-dimensional homogeneous Morse lattice systems
Authors: Gao Xiu-Yun  , Zheng Zhi-Gang  ,   Department of Physics, Beijing Normal University, Beijing 100875, China
Published: December 2020

The ratchet effect in heat conductions of one-dimensional Morse lattices is studied when the system is located between two averagely isothermal reserviors, of which one keeps the temperature constant and the other is periodically modulated in temperature,and their temperatures averaged over a long time are equal to each other. Unidirectional heat current can be observed when one of the heat baths is periodically modulated in temperature. The efficiency and the direction of heat conduction can be rectified and controlled by adjusting the frequency and the amplitude of the modulation. An interesting non-stationary negative thermal conductivity, i.e., a reversed heat flow against the temperature gradient, is found in an appropriate region of frequency of the modulation. A heat wave scheme in revealing the spatiotemporal behavior of the heat conduction is proposed to study the this phenomenon. The influence of the parameters of the Morse lattice on the directional heat current is investigated, and so this provides theoretical support for practical applications.
Dynamic modeling of flexible beam with considering shear deformation in non-inertial reference frame
Authors: He Xing-Suo  , Song Ming  , Deng Feng-Yan  ,   Department of Engineering Mechanics, Northwestern Polytechnical University, Xi’an 710072, China
Published: December 2020

In this paper, the effect of shear deformation is considered into flexural deflection of the geometrically nonlinear deformation of a flexible beam. Then, considering the coupling effect of deformation in to the extensional and flexural deflection, the second-order coupling terms of deformation in two displacement fields are developed and the axial inertial force and transverse distributed force are considered. The finite element method is used for the system discretization and the coupling dynamic equations of flexible beam are obtained by Lagrange’s equations. In this way, the new governing differential equations of the beam in the geometrically non-linear kinematics of deformation are derived. Numerical examples of a flexible beam are studied to analyze the effect of shear deformation on the dynamic character and to investigate the coupling effect. Furthermore, from this present method, a moving Timoshenko beam can also produce the dynamic stiffening phenomenon and some new properties can be shown.
A new approach to the construction of Lagrangians and Hamiltonians for one-dimensional dissipative systems with variable coefficients
Authors: Ding Guang-Tao  ,   The Collega of Physics and Electronic Information, Anhui Normal University, Wuhu 241000, China
Published: December 2020

A new approach to the construction of Lagrangian and Hamiltonian for a second-order differential equation is presented. By writing the second-order equation in the first-order form and constructing first-order Lagranian corresponding to the set of the first-order equations, the second-order Lagrangian and Hamiltionian are deduced from the first-order Lagrangian directly. By using the above method the first-order ane the second-order Lagrangians and the Hamiltonians for some of dissipative and dissipative-like systems are obtained. The advantage of the approach is discussed. Four examples are given to illustrate the applications of the results.
Numerical study on uniformity of electron cyclotron resonance plasma density
Authors: Gao Bi-Rong  , Liu Yue  ,   School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Based on drift-diffusion approximation and under axis-symmetric assumption, a two-dimensional(2D) fluid model is established for the plasma in the chamber of electron cyclotron resonance plasma source. A finite difference method is used for self-consistent numerically simulating the model. Numerical results of uniformity evolution of plasma density are obtained. From the analysis of the numerical results, the effects of background gas pressure, microwave power and current in magnetic field coil on uniformity of the plasma density are studied. The results shows that during the initial ionization, the uniformity of electron density is better than that of ion density. During the later ionization, the uniformity of ion density is better than that of electron density. As background gas pressure increases, the uniformities of both electron and ion densities increase, and the uniformity of ion density increases faster. As microwave power increases, the uniformities of both electron and ion densities increase with almost the same rates. As current in magnetic field coil increases, the uniformities of both electron and ion densities increase at almost the same rates. However, when the current in magnetic field coil becomes big enough, the uniformities of both electron and ion densities decrease at almost of same rates.
Spectral diagnostics of electron density of plasma torch at atmospheric pressure
Authors: Dong Li-Fang  , Liu Wei-Yuan  , Yang Yu-Jie  , Wang Shuai  , Ji Ya-Fei  ,   College of Physics Science and Technology, Hebei University, Baoding 071002, China
Published: December 2020

An atmospheric pressure plasma torch is generated with a hollowneedle-to-plate dielectric barrier discharge and the electron densities in the inside and at the surface of the plasma torch are measured by optical emission spectroscopy (OES). A plasma torch with 1cm long is generated in atmospheric ambient when argon gas is introduced through the hollwneedle. The Stark broadenings of Hα and ArⅠ(696.54 nm) lines, which are decomposed from the experimental profiles by using deconvolution method, are used to estimate the corresponding electron densities. The electron densities are 1.0×1015 cm－3 and 3.78×1015 cm－3 corresponding to the Stark broadening of Hα and ArⅠ(696.54 nm) lines, respectively. The electron density calculated from the Stark broadening of Hα is the same as that at the surface of the plasma because Hα line originates from the dissociation and the excitation of H\-2O at the plasma torch surface where argon can meet with atmosphere. While the electron density calculated from the Stark broadening of ArⅠ(696.54 nm)line is the same as that in the insid of plasma.
Study of far-field directivity of optical dipole antenna
Authors: Jiang Shuang-Feng  , Kong Fan-Min  , Li Kang  , Gao Hui  ,   School of Information Science and Engineering, Shandong University, Jinan 250100, China
Published: December 2020

By simulating the field distributions of two optical dipole antenna models with the finite-difference time-domain (FDTD) method, the variation regularity of their far-field radiation with their length increasing and the factors which can influence their far-field directivity are studied. The results show that the variation regularity of optical dipole antenna is analogous to that of classic symmetrical dipole antenna. But in the far-field directivity plot of optical dipole antenna, side-lobes occur much more quickly, owing to the existence of high-order localized surface plasmon modes. These results hold a significant promise of improving the performance of optical antennas.
The Bohm criterion of plasma sheath with different species
Authors: Ni Zhi-Xiang  , Zhao Xiao-Yun  , Duan Ping  , Liu Jin-Yuan  ,   (1)College of Physics Science and Technology, Dalian University, Dalian 116622, China; (2)School of Physics and Electronics, Fuyang Teachers College, Fuyang 236041, China; (3)School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, China
Published: December 2020

A fluid model has been used to study the Bohm criterion of the plasma sheath with different species. The charge particle includes electrons, ions, negative ions and secondary electrons from the wall striked by the electrons. Numerical calculation results are obtained through quasi-Newton method. It is found that secondary electron emission(SEE) can increase the critical ion Mach number of the plasma sheath. The critical ion Mach number decreases with the increase of the temperature of the electrons emitted. Negative ions reduce this critical number. In addition, it is obvious that the SEE affects the ion Mach number when the density of negative ions is small, but the ion Mach number is mainly affected by negative ions when the density of negative ions is high in the presence of secondary electron emission and negative ions.
Quantitative analysis of chrome in soil samples usinglaser-induced breakdown spectroscopy
Authors: Lu Cui-Ping  , Liu Wen-Qing  , Zhao Nan-Jing  , Liu Li-Tuo  , Chen Dong  , Zhang Yu-Jun  , Liu Jian-Guo  ,   Key Laboratory of Environment Optics and Technology, Anhui Province Laboratory of Environment Optics MonitoringTechnology,Anhui Institute of Optics and Fine Mechanics,Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

We quantitatively analyze the content of element Cr in the national standard soil samples by the method of plasma atomic emission spectroscopy, through using Nd:YAG (Wavelength:1064 nm) laser as an excitation source to induce soil plasma in ambient environment of the laboratory. The calibration curve of element Cr is measured by studying the characteristics of laser-induced breakdown spectroscopy of element Cr in soil under optimal conditions. The experimental results demonstrate that the element content (60—400)×10-6 and the spectral line intensity are in good linear relation, and the relative standard deviation of element analysis of concentration measurement from the standard value is 7.89%. The relative deviation of the quantitative analytic result from the standard value is 5.3%, and the detection limit of Cr in soil is 16.3×10-6. The relative deviation by the internal standard method is 2.7%, which indicates that the internal standard method can improve the accuracy of the measurement. Using the same type of soil to achieve the calibration curves, the relative deviation by the quantitative analysis is 8%.
X-ray continuum spectra for diagnosing plasma temperaturein aluminum wire array Z-pinches
Authors: Meng Shi-Jian  , Li Zheng-Hong  , Qin Yi  , Ye Fan  , Xu Rong-Kun  ,   Institute of Nuclear Physics and Chemistry, Mianyang 621900, China
Published: December 2020

Time-integrated X-ray continuum spectra measured with spherical bent quartz crystal and CCD in aluminum wire array Z-pinches, provide electron temperature by fitting the continuum slope. More data obtained for fitting and markedly reduced influence of line radiation by removing the data superimposed with line spectra, make the temperature in hot core region of plasma more reliable. In experiment of shot No. 09076, the core temperature is around 250 eV, ranging from 241 eV to 258 eV at a 95% confidence level.
Localized surface plasmon resonance propertiesof elliptical gold nanotubes
Authors: Cong Chao  , Wu Da-Jian  , Liu Xiao-Jun  ,   School of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

The effects of ellipse shape, polarization direction of incident light, shell thickness, and dielectric constants of core and embedding medium on the localized surface plasmon resonance (LSPR) of elliptical gold nanotube have been investigated by the Finite Difference Time Domain (FDTD) method. When the semimajor axis is fixed, it is found that with the increase of the semiminor axis of the ellipse the extinction peak of the gold nanotube has a red-shift. With the increase of the angle between the incident polarization and the semimajor axis, the extinction peak has a red-shift. With the shell thickness decreasing, the extinction peak of gold nanotube also has a red-shift. Furthermore, we also find that the increase of the dielectric constant for core or embedding medium will induce a red-shift of LSPR in gold nanotube. The change of the extinction peak is ascribed to the plasmon hybridization and the competition between the variations of conduction and oscillation electrons.
Effect of temperature on motion of misfit dislocation in γ/γ'interface of a Ni-based single-crystal superalloy:molecular dynamic simulations
Authors: Xie Hong-Xian  , Yu Tao  , Liu Bo  ,   (1)Central Iron and Steel Research Institute, Beijing 100081, China; (2)School of Mechanical Engineering, Hebei University of Technology, Tianjin 300132, China
Published: December 2020

The effect of temperature on motion of misfit dislocation in the γ/γ' interface of a Ni-based superalloy is studied in periodic simulation cells subjected to an applied shear stress. The simulation results show that no matter what temperature is, the motion of misfit dislocation occurs through the nucleation and the propagation of the double kink; at low temperature, the interaction of the misfit dislocation facilitates the motion of the misfit dislocation; on the contrary, at higher temperature, it can obstruct the motion of the misfit dislocation, and improves the mechanical properties of nickel-base superalloys.
Effect of doping concentration in p+ deep well on charge sharing in 90nm CMOS technology
Authors: Liu Fan-Yu  , Liu Heng-Zhu  , Liu Bi-Wei  , Liang Bin  , Chen Jian-Jun  ,   Computer School, National University of Defense Technology, Changsha 410073,China
Published: December 2020

This paper deals with the effect of doping concentration in p+ deep well on charge sharing in 90nm dual well CMOS technology. TCAD simulation results show doping concentration in p+ deep well has a more significant effect on charge sharing in PMOS tube than in NMOS tube. By increasing doping concentration of p+ deep well appropriately, the charge sharing in PMOS can be restrained effectively, which is useful for reinforcing the charge sharing.
Sound velocity and shock melting of low porosity aluminum
Authors: Song Ping  , Wang Qing-Song  , Dai Cheng-Da  , Cai Ling-Cang  , Zhang Yi  , Weng Ji-Dong  ,   National Key Laboratory for Shock Wave and Detonation Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Shock loading-release is performed on the porous aluminum with micropore and porosity m=1.04. Time-resolved interfacial velocity between the porous aluminum and LiF window is measured with diatance interferometer system for any reflector (DISAR) under five pressures ranging from 53 GPa to 99 GPa . From the interfacial velocity, the Euler longitudinal sound velocities under five pressures and the bulk sound velocities under 53 GPa, 72 GPa and 91 GPa are obtained. The melting pressure of the material is about 81 GPa. The poisson ratio before shock melting is about 0.37. From the analysis, the existence of the micropore in the material reduces the the shock melting obviously. So, its induced anharmonic effect cannot be neglected. Considering anharmonic effect into the equation of state, the anharmonic parameter is calculated to be about 30.
Computational analysis of double-bubble ultrasonic cavitation
Authors: Lu Yi-Gang  , Wu Xiong-Hui  ,   School of Physics, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Double-bubble ultrasonic cavitation dynamic differential equation obtained from superposition principle is normalized. MATLAB is used to analyse the effects of bubble linearity, double-bubble distance, sound frequency, sound pressure amplitude on cavitation process. Bifrequency ultrasound is introduced into the equation under discussion in this article. The calculation results show that bubble linearity is a main factor, which determines cavitation characteristics. The effect of sound pressure is strongest, and the frequency effect is the next strongest. Double bubble interactions affect cavitation characteristics to a certain extent, which reduces with distance increasing. Bifrequency ultrasound has a limited effect on cavitation characteristics, and it turns biggest when two component pressure amplitudes are equal.
First principles study on half-metallic ferromagnetismof ternary compounds ZnVSe
Authors: Nie Zhao-Xiu  , Wang Feng  , Cheng Zhi-Mei  , Liu Gao-Bin  , Wang Xin-Qiang  ,   (1)College of Elementary Education, Chongqing Normal University, Chongqing 400700, China; (2)College of Physics, Chongqing University, Chongqing 400044, China
Published: December 2020

We have calculated the electronic structure of ZnVSe2 by the method of first-principles plane wave pseudopotential (PWP) with density functional theory (DFT) combined with generalized gradient approximation (GGA), such as spin polarized energy band structure, density of states, Mulliken population, magnetic moments and so on. The calculation results show that ternary compound ZnVSe2 is a half-metallic ferromagnet that shows significant ferromagnetism, its half-metallic energy band gap reaches 0.443 eV. The electron spin polarization is as high as almost 100%, and therefore, ZnVSe2 may be a useful material for spintronics.
Study of La0.67Ca0.33MnO3(001) thin film surfacestructure using scanning tunneling microscopy
Authors: Liu Kai  , Wang Bing  ,   Hefei National Laboratory for Physical Sciences at the Microscale, Universityof Science and Technology of China, Hefei 230026, China
Published: December 2020

La0.67Ca0.33MnO3(001) thin films have been grown with pulsed laser deposition method, and the surface structures and electronic states have been characterized using scanning tunneling microscopy/spectroscopy (STM/STS). In the Mn-O terminated surface, insulating ( 2 × 2 )R45° reconstruction surface and metallic (1×1) reconstruction surface are observed. In the (La,Ca)-O terminated surface, the surface presents the stripe structure. The results obtained from the variable temperature STM/STS show that the ( 2 × 2 )R45° reconstructed surface persists in insulating phase in a temperature range of 144—300 K, which may shield the signal of possible insulator-metal transition occurred in bulk in STS measurements.
Effect of magnetic filtering coil current on the tribology propertyof tetrahedral amorphous carbon films
Authors: Han Liang  , Yang Li  , Yang Lamaocao  , Wang Yan-Wu  , Zhao Yu-Qing  ,   School of Electronic and Information Engineering,Xian JiaoTong University, Xian 710049, China
Published: December 2020

Tetrahedral amorphous carbon (ta-C) films are deposited on single crystalline silicon with filtered cathodic vacuum arc by changing the magnetic filtering coil current from 5 A to 13 A. Visible Raman measurements show that the content of the sp3 hybridization decreases with magnetic filtering coil current increasing, and it deereased down to a minimum value as the coil currew increases up to 13 A. The surface morphology is investigated by atomic force microscope (AFM), and the surface roughness (RMS) of the film increases with the current of magnetic filtering coil increasing from 0.13 to 0.38, The friction test indicates that the minimum of friction coefficient is about 0.08 when the magnetic filtering coil current is 5 A. The friction coefficient increases when the magnetic filtering coil current is 7A. But the friction coefficient decreases again down to 0.1 with magnetic filtering coil current inereasing from 7 A to 13 A.
Study of high frequency characteristics of metallic-pole-planar slow wave structure
Authors: Shi Zong-Jun  , Yang Zi-Qiang  , Hou Jun  , Lan Feng  , Liang Zheng  ,   Research Institute of High Energy Electronics, University of Electronic Science and Technology of China, Chengdu 610054,China
Published: December 2020

The discrete metallic-pole-planar slow wave structure (SWS) is introduced in this paper, and the high frequency characteristics are studied. And procedures based on three-dimensional finite-difference time-domain (3-D FDTD) arithmetic are used to calculate the dispersive characteristics of the new SWS, and HFSS simulation software is used to analyze the coupling impedance. Results show the high frequency characteristics of the pole structure not only have a general similarity in comparison with these of the grating, but also have itself advantages. For the electrons moving between multiple poles of the structure, the interaction impedances are symmetry; relatively thick electron beams can efficiently interact with the high-frequency field while it used as the high frequency system of vacuum electronic devices. This kind of SWS is promising to lower the starting current density and have better efficiency than the traditional grating SWS. According to the results, a sub-millimeter radiation source driven by the multiple beams can be designed at a low operating current density.
Band structures of zigzag graphene nanoribbons
Authors: Wang Xue-Mei  , Liu Hong  ,   Department of Physics and Science, Nanjing Normal University, Nanjing 210046, China
Published: December 2020

Based on the π-electron tight-binding model, for zigzag graphene nanoribbons(ZGNRs) the influence of boundary structure on band structure, specially the electrons of the valence band and the conductor band near the Fermi level, are studied in detail. We investigate the band structures and the distributions of electrons of different atoms in a unit cell of the valence band near the Fermi level of ZGNRs with seven reasonable boundary structures. We find NN-ZGNRs with no dangling atoms on both edges, DN-ZGNRs with dangling atoms only on one edge, SPP-ZGNRs and ASPP-ZGNRs each with pentagons on both two edges and being metallic, DD-ZGNRs with dangling atoms on both two edges, PN-ZGNRs each with a defective structure of pentagons on one edge and no dangling atoms on the other edge, PD-ZGNRs with a pentagon on one edge and dangling atoms on the other edge being semiconducting, and the energy gap being inversely proportional to the width of nanoribbons. But for DD-ZGNRs and PD-ZGNRs, the energy gaps quickly reduce to zero with the increase of width; for PN-ZGNRs, the energy gaps decrease exponentially to a limited value of 0.154 eV. It is found that different boundary structures have different effects on the distribution of electrons in the valence band near the Fermi level. And the probability for electrons staying in the atoms on two edges of nanoribbons is relatively large.
First principles study on substitution behavior and alloying effects of Nb in Ni3Al
Authors: Li Ai-Hong  , Mu Yan-Qing  , Yang Wei-Ming  , Hou Hua  , Han Pei-De  , Zhang Su-Ying  , Huang Zhi-Wei  , Zhao Yu-Hong  ,   (1)College of Materials Science and Engineering, North University of China, Taiyuan 030051, China; (2)College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China; (3)College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

By using the first-principles plane-wave pseudopotential method based on the density functional theory, substitution behavior and alloying effect of Nb in Ni3Al are studied. The analyses of the formation enthalpies,the cohesive energies and the densities of states of systems with different substitution behaviors show that Nb prefers to occupy the Al site. The site preference is determined primarily by the electronic structure, and the calculated result is in good agreement with the experimental result. In order to further study the site preference, the occupied sites are divided into being of relaxed distribution and unrelaxed distribution, which are two different distributions. The calculations of total energy, the formation enthalpy, the cohesive energy and the density of states of system indicate that Nb has a preference for unrelaxed distribution. In order to study the alloying effect of Nb in Ni3Al, the calculations of cohesive energy, density of states of system and electronic charge density indicate that Nb in Ni3Al could increase the stability of the alloy. The study also indicates that the limited solubility of Nb in Ni3Al lie between6.25at % and 12.5at %.
Frist principles study of effect of high Al doping concentrationof p-type ZnO on electric conductivity performance
Authors: Hou Qing-Yu  , Zao Chun-Wang  , Li Ji-Jun  , Wang Gang  ,   College of Sciences, Inner Mongolia University of Technology, Hohhot 010051, China
Published: December 2020

We optimize the geometric structure and calculate total densities of states, band structures, the relative number of electrons and mobility ratios of electrons of ZnO mode established at different concentrations of Al, in the condition of high concentration of Al heavily doped ZnO semiconductor at low temperature, by adopting the ab-initio study of plane wave ultra-soft pseudo potential technique based on the density function theory (DFT). It is found that the relative number of electrons increases, but the mobility ratio of electrons of ZnO decreases, with the concentration of Al increasing. On the contrary, the lower the Al doping concentration, the stronger the conductivity of ZnOis. The conductivity is compared. We can draw a conclusion that the conductivity of ZnO semiconductor decreases with Al doping concentration increasing. The calculation results are consistent with the change trend of experiments with Al concentrations exceeding o.z, i.e., x≥0.02.
Magnetic properties and excited states of thegraphene quantum dots
Authors: Gao Shuang-Hong  , Ren Zhao-Yu  , Guo Ping  , Zheng Ji-Ming  , Du Gong-He  , Wan Li-Juan  , Zheng Lin-Lin  ,   Institute of Photon-Technology, Northwest University, Xian 710069, China
Published: December 2020

We use the density functional theory B3LYP/6-31G(d) to study the graphene quantum dots with zigzag edges. The result shows that the ground states of different size graphene quantum dots are all ferromagnetic spin-triplet states. The magnetic properties orignate both from the boundary carbon atom occuping protruding position, and from the carbon atom with unpaired electron. On the whole, the energy gap of other structures decreases with the increase of the number of benzene rings as excepted for the structure of 6b, and the system energy gap decreases significantly by the added charges. In addition, using time-dependent density functional theory (TD-DFT), the excited states of the triangular structure composed of six carbon rings which have an energy gap is 3.83 eV are calculated, and the results show that the 17th excited state has the greatest excitation strength, the excitation energy is 3.93 eV, corresponding to a wavelength of 315.8 nm, close to experimental result.
Structural, magnetic and half-metallic properties of CoFeMnSi alloys
Authors: Zhao Jing-Jing  , Qi Xin  , Liu En-Ke  , Zhu Wei  , Qian Jin-Feng  , Li Gui-Jiang  , Wang Wen-Hong  , Wu Guang-Heng  ,   (1)School of Science, Beijing University of Chemical Technology, Beijing 100029, China; (2)State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Compared with the experiment results,the atomic moment of Co50Fe25-xMnxSi25 dependending on composition and half-metalic of these alloys have been investigated by GGA + U method. It has been found that with the increase of Mn content, Co50Fe25-xMnxSi25 alloys always maintain a high ordered L21 structure and the total moment of these alloys decrease linearly which is mainly attribute to the reduction of Co atomic moment. It has also been found that with the increase of Mn content,Co50Fe25-xMnxSi25 alloys maintain 100% spin polarization and Fermi level move from the edge of the energy gap to the middle of the energy gap while the gap-width has changed.
First-principles study of magnetism and electronic structureof Sb-containing half-Heusler alloys
Authors: Wang Yu-Mei  , Pei Hui-Xia  , Ding Jun  , Wen Li-Wei  ,   (1)Department of Physis and Electronic Engineering, Zhoukou Normal University, Zhoukou 466001,China; (2)National Laboratory for condensed Matter Physics, Institute of Physic, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Using the first-principles density functional theory, we calculate the crystal structures, magnetisms and electronic structures of Sb-containing half-Heusler alloys XYSb(X=Ni, Pd, Pt; Y=Mn, Cr). The calculation results show that alloy NiMnSb is half-metal and the others are metals at equilibrium lattice constant. The contribution of the spin magnetic moment of Y element to the total moment is largest for all alloys. It is found that the Fermi level of the minority spin band shifts closer to the bottom of spin-down conduction band with atomic number of X element reducing. The Fermi level moves up due to the compressive strain, away from p bands of Sb atom. Under the compresive stress, PtMnSb, PdMnSb and NiCrSb can induce metal half-metal transitions.
Competition between band filling effect and band-gap renormalization effect in GaAs
Authors: Teng Li-Hua  , Wang Xia  , Lai Tian-Shu  ,   (1)School of Mathematics and physics, Qingdao University of Scienced and Technology, Qingdao 266061 China; (2)State Key laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275, China
Published: December 2020

Time-resolved linearly polarized pump-probe spectroscopy is used to investigate carrier relaxation dynamics in instrinsic GaAs. Absorption saturation and absorption enhancement are observed. It is found that the absorption saturation can be observed obviously when the photon energy is smaller than 1.549eV, otherwise, the absorption enhancement can be observed at a carrier density of 2×1017 cm-3. When the carrier density is above 7×1016 cm-3, the absorption enhancement increases rather than decreases with delay time. The simulation results with consideration of the competition between band filling effect and band-gap renormalization effect are in good agreement with our experimental results. With the band filling effect and band-gap renormalization effect considered, we develop a new analytical model to retrieve the carrier lifetime.
Preparation of graphene on different-polarity 6H-SiC substrates and the study of their electronic structures
Authors: Li Li-Min  , Pan Hai-Bin  , Yan Wen-Sheng  , Xu Peng-Shou  , Wei Shi-Qiang  , Chen Xiu-Fang  , Xu Xian-Gang  , Kang Chao-Yang  , Tang Jun  ,   (1)National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029,China; (2)State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
Published: December 2020

The epitaxial graphene (EG) layers are grown on Si-terminated 6H-SiC (0001) substrates and C-terminated 6H-SiC (000 1 - ) substrates separately by thermal annealing in an ultrahigh vacuum chamber. Low energy electron diffraction(LEED) and synchrotron radiation photoelectron spectroscopy(SRPES) are used to in-situ study the synthesis process, and the prepared samples are characterized by Raman spectrum, and near edge X-ray absorption fine structure(XANEX). The results show that we have successfully prepared high-quality EG layers on the two polar surfaces of 6H-SiC. The comparisons studies indicate that Si terminated EG is highly oriented while C terminated EG is anisotropic, and that the interface interaction similar to that of C-sp3 bond of diamond exists on the Si terminated EG, the interaction between the epitaxial film and substrate is stronger, while on the C terminated EG there is no such interaction, and the interaction between the epitaxial film and substrate is weaker.
Fabrication method improvement and superconducting property investigation of single domain GdBCO bulk superconductors
Authors: Li Guo-Zheng  , Yang Wan-Min  ,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

Top seeded infiltration and growth method (TSIG) is improved by adopting a new liquid source and novel configuration. And single-domain Gd-Ba-Cu-O (GdBCO) bulk superconductors are successfully prepared using the improved method. Experimental observations on the morphology and the microstructure show that the samples exhibit good texture and homogeneous distribution of fine Gd2BaCuO5 (Gd-211) inclusions. Superconductive measurements reveal that the sample exhibits high superconducting transition temperature, self-field critical current density, and strong levitation force. In addition, the improved method can be used to simplify the process flow, shorten the experimental cycle, and hance the stability of the process, thus reducing the experimental difficulties. The results lay a good foundation for the batch production of large single domain bulks.
Magnetic properties and exchange bias effect of nano-structure Co x Fe3-x O4 porous microspheres
Authors: Lv Qing-Rong  , Fang Qing-Qing  , Liu Yan-Mei  ,   School of Physics and Materials Science, Anhui University, Anhui Key Laboratory of Information Materials and Devices, Hefei 230039, China
Published: December 2020

Nano-structure CoxFe3-xO4 porous microspheres are synthesized in ethylene glycol (EG) solution, using FeCl3·6H2O, CoCl2·6H2O and NH4Ac as the starting materials through solvothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are used to characterize the structures of synthesized products. The results show that monodisperse CoxFe3-xO4porous microspheres with polycrystal structures are assembled by nanoparticles, and the average diameters is about 300 nm. The magnetic properties are evaluated with a vibrating sample magnetometer (VSM). The results indicate that the saturation magnetization ( Ms) and the Curie temperature (Tc) first increase and then decrease, and the coercivity (Hc) increase with the increase of Co2+ content. According to the hysteresis loops at different temperatures, CoxFe3-xO4 porous microspheres possess remarkable exchange bias effects at low temperatures.
Volume and interface absorptions of single layer
Authors: Lu Jiang-Tao  , Cheng Xin-Bin  , Shen Zheng-Xiang  , Jiao Hong-Fei  , Zhang Jin-Long  , Ma Bin  , Ding Tao  , Liu Yong-Li  , Bao Gang-Hua  , Wang Xiao-Dong  , Ye Xiao-Wen  , Wang Zhan-Shan  ,   Institute of Precision Optical Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

The volume absorptions and the interface absorptions of SiO2 and HfO2 single layers are studied using the thermal lens method. Based on the fact that electric field distributions in single layers are different when the films are illuminated from the coating side and substrate side, an equation is given to calculate volume and interface absorptions of single layers. Half wave HfO2 and SiO2 single layers are prepared by electron beam evaporation method. With the absorption data measured by thermal lens technique, we separate the volume absoption from the interface absorption for these two single layers. The results show that interface absorption is non negligible when the absorption of film approaches to a ppm level. Additionally, the HfO2 single layer shows bigger volume and interface absorptions than SiO2 single layer.
Characteristics of Nb2O5 thin films deposited by ion beam sputtering
Authors: Yuan Wen-Jia  , Zhang Yue-Guang  , Shen Wei-Dong  , Ma Qun  , Liu Xu  ,   State Key Laboratory of Modern Optical Instrumentation, Zhejiang University,Hangzhou 310027, China
Published: December 2020

Optical properties, stress and microstructure of Nb2O5 thin films prepared by ion beam sputtering (IBS) are investigated, and the effects of assist ion beam energy and ion current on characteristics of Nb2O5 thin films are systematically discussed. The results show that with different parameters of assisted ion source, the refractive index changes from 2.310 to 2.276 and residual stress varies from -281MPa to -152 MPa. The extinction coefficient of Nb2O5 can be under 10-4, and the surface is very smooth in an optimum deposition condition. Thin films deposited by IBS exhibit better optical properties and microstructures than those deposited by ion assisted deposition (IAD).
Optical properties of exciton and charged exciton in undoped ZnSe/BeTe type-Ⅱ quantum wells under high magnetic fields
Authors: Zheng Yu-Jun  , Xu Xian-Gang  , Ji Zi-Wu  ,   (1)School of Physics, Shandong University, Jinan 250100, China; (2)State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
Published: December 2020

We report on the magnetic field (up to 53 T) dependence of photoluminescence (PL) spectra occurring as a spacially direct optical transition of the ZnSe layer in undoped ZnSe/BeTe/ZnSe type-II quantum structures at a low temperature (4.2 K). With magnetic field increasing, the PL intensity (IX) of exciton (X) shows an oscillation feature opposite to the PL intensity (IX－) of charged exciton (X－). As IX- increases, IX decreases, but as IX－ decreases, IX increases. In all fields, the oscillation behaviour shows a periodic change approximately with magnetic field interval. The results are attributed to the periodic resonance of the Fermi level with the Landau level, which results in the modulation of the density of states of the 2DEG system at the Fermi energy.
Tri-color luminescence glass under long-wavelength ultraviolet excitation
Authors: Liu Zi-Jun  , Yang Lv-Yun  , Dai Neng-Li  , Li Jin-Yan  ,   Wuhan National Laboratory for Optoelectronics, College of Optoelectronic Science and Engineering,Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

In this paper we report on a new kind of tri-color luminescence glass which can be excited efficiently by long-wavelength ultraviolet. These samples are prepared by melting silicon-borate raw material co-doped with Ce3+/Mn2+, Ce3+/Tb3+ and Eu2+, respectively. Among these doped ions, Mn2+, Tb3+ and Eu2+ are activators and Ce3+ is sensibilizer. Because the sencibilzer can provide energy for activator so the intense tri-color luminescence can be obtained by long-wavelength ultraviolet excitation. At the same time, the role of Al in the fluorescence enhancement, the energy transfer process, and the control of the ions valence are discussed.
Enhancing electric fields around nanospheresby parallel clapboards
Authors: Zhang Zhi-Dong  , Xiong Zu-Hong  , Zhang Zhong-Yue  , Wang Hong-Yan  , Li Xue-Lian  ,   (1)Institute of High temperature and High Pressure Physics, Southwest Jiaotong University, Chengdu 610031, China; (2)School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

Nanospheres are widely used as the substrates for surface enhanced Raman scattering (SERS). In order to further enhance the electric fields around nanospheres and improve the SERS intensity, in this paper, we introduce a novel nanostructure which is composed of a couple of parallel clapboards and a clamped nanosphere. The discrete dipole approximation calculation results indicate that when the parallel clapboards are used, the electric fields around the nanosphere are much enhanced. Therefore, the nanospheres clamped by parallel clapboards may work well as the SERS substrates. In addition, the effects of the structural parameters of parallel clapboards are also investigated.
Comparison between gradient-doping and uniform-doping GaN photocathodes
Authors: Du Xiao-Qing  , Wang Xiao-Hui  , Chang Ben-Kang  , Qian Yun-Sheng  , Gao Pin  , Zhang Yi-Jun  , Guo Xiang-Yang  ,   (1)College of Optoelectronic Engineering, Chongqing University, Chongqing 400030, China; (2)Institute of Electronic Engineering and Optoelectronic Technology, Nanjing University of Science & Technology, Nanjing 210094, China
Published: December 2020

In order to enhance the quantum efficiencies of negative electron affinity (NEA) GaN photocathodes, gradient-doping reflection-mode GaN photocathodes are grown by metal organic chemical vapor deposition (MOCVD)at doping concentrations of 1×1018cm-3, 4×1017cm-3, 2×1017cm-3 and 6×1016cm-3 from the body to the surface, with the thickness of each doping region being about 45nm and the total thickness of GaN 180 nm. The gradient-doping GaN photocathodes are activated in an ultra-high vacuum system and are compared with two kinds of uniform-doping GaN photocathodes whose thicknesses are both 150 nm and doping concentrations are 1.6×1017cm-3 and 3×1018cm-3 separately. The results show that both the photocurrent growth rate and the maximum photocurrent of the gradient-doping GaN photocathodes are greater than those of the uniform-doping GaN in the Cs/O activation process, and the multi-test system measured maximum quantum efficiency of the gradient-doping NEA GaN photocathode is about 56% which is as high as the double of the uniform-doping. Calculations show that the energy band bendings of the gradient-doping GaN photocathodes are 0.024eV, 0.018eV and 0.031eV from the body to the surface, a larger electron drift and diffusion length are gained due to the built-in electric field formed by the energy band bending, because of the 0.073eV total energy band bending the photoelectrons reaching the surface have higher energies and pass through the surface barrier more easily. Therefore the gradient-doping NEA GaN photocathodes have greater quantum efficiencies.