bluuebunny/crossref_metadata_2025 huggingface dataset:
Xylene gas sensing performance of Au nanoparticlesloaded WO3 nanoflowers
Authors: Li Dong-Ke , He Bing-Yan , Chen Kun-Quan , Pi Ming-Yu , Cui Yu-Ting , Zhang Ding-Ke ,   School of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China
Published: December 2020

Pure and Au nanoparticles loaded WO3 nanoflowers are synthesized by the hydrothermal method.The structures and morphologies of the as-prepared products are characterized by X-ray diffraction (XRD),scanning electron microswcope (SEM), and transmission electron microscope (TEM). The gas sensing performance of the Au/WO3 sensor to xylene is investigated. The Au content and the operating temperature are first optimized. It is found that WO3 with 0.4 μL Au nanoparticles shows the highest sensitivity at an operating temperature of 250 ℃. Compared with pure WO3, Au(0.4)/WO3 possesses fast response/recovery speed and high target gas selectivity. Its sensitivity to 100 ppm xylene is 29.5. Meanwhile, the practical detection limitation is as low as 0.5 ppm. Finally, the mechanism of Au/WO3 gas sensing is also proposed and discussed. Au nanoparticles loaded WO3 nanoflowers are considered to be a promising sensing material for detecting xylene pollutants.
Interaction between borophene and graphene on a nanoscale
Authors: Chen Yong , Li Rui ,   School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

The interface dynamic behavior of borophene is one of the issues that need investigating for its applications. In this paper, the interaction between graphene and borophene, h-BN is investigated. The results show that the interactions between C atoms and B atoms are weaker than those between C atoms and N atoms when graphene slides on h-BN substrate. The corrugation of interface potential between graphene and borophene is smaller than between graphene and h-BN, which implies smaller friction. Moreover, the pull-out force in the simulation system including graphene and borophene is smaller than the interaction between graphene and h-BN, which indicates a weaker boundary effect. Therefore, borophene promises to exhibit an excellent tribological behavior in application.
TM01 dominant mode coaxial virtual cathode oscillator with feedback construction
Authors: Zhang Yun-Jian , Ding En-Yan ,   Science and Technology on High Power Microwave Laboratory, Mianyang 621900, China,   Key Laboratory of Science and Technology on Complex Electromagnetic Environment, Mianyang 621900, China,   Institute of Applied Electronics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Virtual cathode oscillator, as a kind of space-charge high-power microwave source, has an output microwave mode that is generally an admixture of TM01 mode and TE11 mode. The analysis of the resonator in the anode mesh shows that when the transmission of the anode mesh is high, it is easy to produce strong reflected electron beam, forming a conical quasi-resonator structure, thus enhances the output of TE11 mode. When the transmission of the anode mesh is low, the beam intensity of the reflected electron beam can be weakened due to the absorption of the metal mesh, and the TE11 mode can be suppressed, so the output mode is mainly TM01 mode. In this paper, a feedback coaxial virtual cathode oscillator is investigated with the use of numerical simulation and experimental data analysis. The feedback coaxial virtual cathode oscillator is formed by closing the end of the anode mesh through a metal plate and changing the path of the reflected electron beam from the metal mesh to the gap between cathode and anode. The particle in cell method is used in the numerical simulation of the virtual cathode oscillator, and the impedance of the 400 kV diode is about 13 Ω under a voltage of 400 kV. After the optimal design by numerical simulation, the average output microwave power from the virtual cathode oscillator is 1.5 GW, and the frequency of the microwave is about 4.2 GHz, which is basically consistent with the theoretical calculation results. In this new kind of virtual cathode oscillator, the distribution of reflected electrons is modified by the feedback sheet on the anode mesh, the output high power microwave pattern is demonstrated to be dominated by TM01 mode. The microwave power obtained in the experiment is measured by the array antenna power density integration method. For axisymmetric mode, a receiving antenna array is formed by placing multiple receiving antennas on one side of the axis of the antenna pattern. The power densities of different angles on the horizontal circumference with the phase center of the transmitting antenna are measured, the average power density of two adjacent points is multiplied by the area of the spherical belt between these two points, and then the resulting power is added by the power between the adjacent two points, thereby obtaining the total radiation power. With this method, the microwave power is 850 MW with frequency 4.1 GHz and pulse width 30 ns under slaving voltage 400 kV.
Comparative study of n-GaN transition group refractory metal Ohmic electrode
Authors: He Tian-Li , Wei Hong-Yuan , Li Cheng-Ming , Li Geng-Wei ,   School of Science, China University of Geoscience, Beijing 100083, China,   Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Ohmic contact is directly related to the performance of GaN device and is one of the important factors affecting device performance. In recent years, many research groups have studied the electrode materials and annealing conditions of n-type GaN Ohmic contacts. In this paper, the ohmic contact properties and structural characteristics of the Hf/Al electrode of a transition group metal refractory metal Hf system under different annealing conditions are studied, and compared with those of the Ti-based ohmic contact Ti/Al electrode. The specific contact resistivity of each electrode is measured by a dot-type transmission line model, and the structural characteristics of the electrode are analyzed by using an Auger electron spectrometer which can be analyzed in depth. The results show that the Hf/Al electrode under the same annealing condition exhibits superior ohmic contact performance compared with the conventional Ti/Al electrode. At the same time, the lowest specific contact resistivity of the Hf/Al electrode annealed in an N2 atmosphere at a low temperature of 650 ℃ for 60 s is 4.28×10–5 Ω·cm2. The in-depth analysis of Auger electron spectrum shows that the Hf/Al electrode has a solid phase reaction with the n-type GaN material. In addition, the cross section of each electrode is observed by auger electron spectroscopy. In the Hf/Al electrode sample, the metal-semiconductor interface does not show voids after annealing. This situation occurs at the sample interface where the Ti/Al electrode is annealed at 650 ℃ for 60 s in N2 atmosphere and annealed at 850 ℃ for 30 s in N2 atmosphere. This is one of the reasons why the Hf/Al electrode sample has a lower specific contact resistivity. At the same time, the surface of Hf/Al electrode and Ti/Al electrode annealed at 850 ℃ are characterized by using scanning electron microscope. It is found that the surfaces of both electrodes subject to high temperature annealing show a similar granular rough surface, and this rough surface has a certain influence on the electrical properties of the GaN device. The rough surface formed by the electrode under such high temperature annealing conditions is an urgent problem to be solved in the future research. In summary, the study in this paper indicates the use of Hf/Al to form an ohmic contact with n-type GaN under a low temperature annealing condition.
Enhanced near field focus steering of rectangular nanoslit metasurface structure
Authors: Li Xin , Wu Li-Xiang , Yang Yuan-Jie ,   Department of Physics, University of Electronic Science And Technology of China, Chengdu 610054, China
Published: December 2020

 Surface plasmon polaritons (SPPs) are electromagnetic excitations propagating along the metal-dielectric interface. The SPPs excited by the metal micro/nano structures have the ability to manipulate the light on a subwavelength scale. The SPPs are of interest to researchers for its excellent subwavelength field confinement and local field enhancement. So far, the SPPs have found numerous applications in optical tweezers, biological sensors, and near-field holographic imaging, due to its subwavelength focusing.

 In order to achieve enhanced near field subwavelength focusing, we propose a metasurface structure in this paper, which is composed of rectangular nanoslit circular arrays and multilayer annular slits. The function of the inner ring arrays is to excite SPPs and the outer ring slits is to enhance focusing. The electric field expression of SPP is studied analytically and theoretically, and then the principle of rectangular nanoslit to excite SPP and the inner ring array structure to generate central focusing are explained. The parameters of the structure are optimized, and the focusing characteristics of the metasurface structure under different polarization light are studied by using the finite difference time domain method. Furthermore, we explain the principle of the external structure enhancing focusing by introducing the theory of Fresnel zone plate and depth modulation. The analytical expressions and simulations show that when the incident polarized light has a wavelength of 980 nm, the focal spot having a full width at half maximum of about 650 nm, and the distribution of the coupled field can be approximately expressed by the first kind Bessel function. Compared with the former single circular array structure, the composite structure proposed in this paper has a good effect of both enhancing the central focusing and inhibiting the outer field divergence, and the center focal spot intensity is doubled. In addition, the electric field excited by the arbitrary linearly polarized light is also discussed, the electric field satisfies the form of the polarization angle sinusoidal function multiplied by a Bessel function.
 The research results of our study have some applications in subwavelength light modulation, near-field imaging, optical tweezers, and subwavelength scale optical information processing and so on.
Influence of trap characteristics on DC surface flashover performance of low density polyethylene in vacuum
Authors: Nie Yong-Jie , Zhao Xian-Ping , Li Sheng-Tao ,   Electric Power Research Institute, Yunnan Power Gird Co., Ltd., Kunming  650217, China,   State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi’an 710049, China
Published: December 2020

Surface flashover is the primary limitation to the development of power system and the increase of voltage level. Previous work has proved that the trap can greatly influence flashover performances, but the relationship between trap parameters and surface flashover voltage is not clear. In the paper, we study the effects of crystallization behavior, microstructure, and trap parameters on DC surface flashover performance of semi-crystallinity polymer through adding phenolphthalein which is regarded as nucleating agent in low density polyethylene (LDPE). Micro-IR spectroscopy result proves that phenolphthalein exactly exists in LDPE/phenolphthalein composite. Differential scanning calorimeter (DSC) and scanning electron microscope (SEM) are used to investigate the effect of nucleating agent (phenolphthalein) on crystallinity behavior and microstructure of LDPE, and their results indicate that the phenolphthalein modification greatly changes the crystallization behavior of LDPE. The SEM results show that the spherulite size of LDPE decreases and is distributed more uniformly with the increase of phenolphthalein concentration. The DSC results show that the crystallinity and lamella thickness increase. Thermally stimulated depolarization current (TSDC) is used to characterize the trap parameters of LDPE/phenolphthalein composites. The TSDC results indicate that the shallow trap level (γ peak) increases from 0.19 eV to 0.65 eV and the deep trap (α peak) increases from 0.81 eV to 0.99 eV with the increase of phenolphthalein concentration. Relationship between microstructure and trap parameters shows that the smaller spherulite size indicates the deeper trap level (for LDPE, the trap level increases from 0.81 eV to 0.99 eV when the spherulite size decreases from 23.2 μm to 14.9 μm), and larger crystallinity means smaller trap density (for LDPE, the trap density decreases from 1404 pC to 612 pC when the crystallinity increases from 34.51% to 43.25%). The DC surface flashover performance increases with the increase of phenolphthalein concentration, and reaches a highest value: when the concentration is 1 wt%, the highest value is increased by 48.42%. Finally, it is concluded that the microstructure of semi-crystallinity polymerinfluences the trap parameters, which affects the surface flashover performance through affecting the carrier transport process in the development process of surface flashover. The trap level and trap density play complementary, cooperation and mutual transformation roles in improving the surface flashover performances as indicated by the analysis of the " U-shaped” relationship between trap parameters and flashover voltage.
Large-range electric field sensor based on parity-time symmetry cavity structure
Authors: Fang Yun-Tuan , Wang Yu-Ya , Xia Jing ,   School of Computer Science and Telecommunication Engineering, Jiangsu University, Zhenjiang 212013, China,   Jiangsu Key Laboratory of Security Tech. for Industrial Cyberspace, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

In order to solve the technical problem of the traditional electric field sensor limited by its measurement range, a parity-time (PT) symmetric microcavity structure doped by electro-optical medium is designed, and a new electric field sensing mechanism is proposed. The transfer matrix method is used to calculate the transmission spectrum of the structure. A unique amplified defect mode is found. The peak value and wavelength position of the defect mode vary with the external electric field. The same electric field can be measured by using two mechanisms. One is to detect the change of the defect mode peak value, and the other is to measure the change of the defect mode wavelength position. The measurement range is limited only by the breakdown field value of the electro-optical medium, which can range from 0 to 0.06 V/nm, covering almost any possible electric field environment. For the peak-value sensing mechanism, the sensitivity range is 38.042—47.558 (nm/V); for the wavelength position sensing mechanism, the sensitivity range is 18.357—18.642 (nm2/V), and the average resolution in the measurement range is 0.00925 V/nm.
Estimating structure and geoacoustic parameters of sub-bottom by using spatial characteristics of ocean ambient noise in shallow water
Authors: Li He , Guo Xin-Yi , Ma Li ,   Key Laboratory of Underwater Acoustics Environment, Institute of Acoustics, Chinese Academy of Science, Beijing 100190, China,   University of Chinese Academy of Science, Beijing 100049, China
Published: December 2020

The field of ocean ambient noise contains numerous information about the water column, especially the information about the sub-bottom. The geoacoustics parameters of sub-bottom are very important factors influencing the spatial characteristics of ocean ambient noise field. For different layered structures of the sub-bottom, the bottom-loss shows different critical angles according to sound speed of each layer, while the structure of interference fringe is dependent on the thickness of the sediment. Flux theory of ocean ambient noise proposed by Harrison is used in this paper. Using this theory, the curve of bottom-loss can be extracted by computing the ratio between the energy of the upward wave and the downward wave. From the ideal reflection coefficient, the influence of sound speed, density and attenuation coefficient on reflection coefficient are discussed in the situation of the sub-bottom of acoustic half space, while the reflection coefficient of 1 layer of sediment is simplified. Initially, the reflection coefficient is the sum of sound waves reflect from the sub-bottom transmitted from the same source at the same angle. Only the first two terms are reserved, so that the mechanism of the interference fringe can be easily discussed. The structure of interference fringe can be explained which is affected by the thickness of the sediment. The curve of bottom-loss oscillates periodically with the increase of the thickness of the sub-bottom. Also by the reciprocity principle, the interference fringe of the reflection coefficient can be explained by considering the sound transmitted from two point sources at the surface of the sea. In this way the same result can be obtained as that from the method of simplification. The result of the experiment in China Yellow Sea shows that the information about the reflection coefficient of the sub-bottom can be extracted by the vertical azimuth spectrum of ocean ambient noise. In this way, the critical angle can be obtained, so that the sound speed of the sub-bottom can be estimated by using Snell law. The structure of the interference fringe is also contained in the bottom-loss curve estimated by ocean ambient noise. Therefore the layered structure, sound speed and the thickness of the layer of the sub-bottom can be estimated.
Imaging through coda wave interferometryvia sparse reconstruction
Authors: Zhang Tao , Hou Hong , Bao Ming ,   Key Laboratory of Ocean Acoustics and Sensing, Ministry of Industry and Information Technology, School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China,   Key Laboratory of Noise and Vibration Research, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The coda wave interferometry is widely used in the fields of geophysics and material science. As an extension of coda wave interferometry, imaging through coda wave interferometry is a technique to obtain the spatial distribution of small velocity perturbations within a scattering medium by using time lapse and sensitivity kernels in the diffusion approximation. However, imaging through coda wave interferometry is essentially an undetermined problem without definite solution, resulting in some difficulties in accurately locating small velocity perturbations within a scattering medium. Meanwhile, compressed sensing has been used in many physical imaging systems in recent years. In this paper, we present an imaging method through coda wave interferometry to solve aforementioned problems by using sparse reconstruction algorithm which is involved in compressed sensing theory. The sparsity of velocity perturbation in its space distribution is taken into account in the proposed method. Firstly, the undetermined equation for inversion imaging is established based on the time-lapse data obtained by coda wave interferometry and the sensitivity kernel matrix in the diffusion approximation. Secondly, the inversion equation is reconstructed by using the sparse transformation within the framework of compressed sensing theory. Finally, the minimization of l1 norm is solved by the compressed sensing reconstruction algorithm, and the imaginary part for the spatial distribution of velocity perturbations is subsequently obtained. This method can accurately capture the spatial locations and ranges of both single velocity perturbation and multiple velocity perturbations in scattering medium with high computational efficiency. The numerical simulations are compared with the results from the existing linear least squares method, demonstrating that the proposed method can avoid the complex parameter determination operation, thus greatly improving the accuracy of inversion images, and also significantly reducing the calculating time.
Two-dimensional distribution expressions of micro-prism on bottom surface of partial integrated light guide plate
Authors: Zhang Xu-Lin , Yang Wei , Luo Tong-Zheng , Huang Yan-Yan , Lei Lei , Li Gui-Jun , Xu Ping ,   College of Physics and Optoelectronic Engineering, Institute of Micro-Nano Photoelectronic Technology, Shenzhen University, Shenzhen 518060, China
Published: December 2020

The design of the microstructure distribution on the bottom surface of the partial integrated light guide plate (PILGP) is one of the key factors to improve the luminance uniformity of the partial integrated backlight module (BLM). In this paper, the two-dimensional micro-prism expressions on the bottom surface of the small-sized PILGP are presented. The two-dimensional micro-prism expressions make the micro-prisms spread out on a two-dimensional scale of the bottom surface of the PILGP. By fitting and analyzing a large number of simulation data, the relationship expressions between the coefficients of the two-dimensional micro-prism expressions and the structural parameters of the PILGP are established. The above expressions are directly applied to the two-dimensional distribution design of micro-prism on the bottom surface of small-sized PILGPs with different structural parameters. Without the help of the designers’ experience and the multiple simulations of the software, the average value of luminance uniformity in the partial integrated BLMs is obtained to be 84.94%. The simulation results show that the two-dimensional micro-prism expressions and coefficient relation-expressions presented in this paper have important application value. Take the 5-inch partial integrated BLM for example. The two-dimensional distribution of the micro-prism on the bottom surface of the PILGP with high luminance uniformity can be obtained directly by using the above expressions. By fine-tuning the coefficients of two-dimensional micro-prism expressions, calculated by the coefficient relation-expressions, the utilization of light energy, illuminance uniformity and luminance uniformity of the partial integrated BLM respectively reach 90.69%, 88.02% and 92.17%, which meet the practical requirements. The optimization and design time of the partial integrated BLM are both greatly saved. Further, the two-dimensional micro-prism expressions on the bottom surface of the PILGP are analyzed and the physical mechanism is explained reasonably. This work is of significance for the distribution design of the microstructures on the surface of the LGP.
Numerical investigation on interaction mechanisms between flow field and electromagnetic field for nonequilibrium inductively coupled plasma
Authors: Yu Ming-Hao ,   School of Mechanical and Precision Instrument Engineering, Xi’an University of Technology, Xi’an 710048, China
Published: December 2020

In this paper, the inductively coupled plasma (ICP) wind tunnel, which is widely used in the development of thermal protection system for reentry vehicle in the aerospace field, is studied. The distribution properties and the interaction mechanism of the flow field and electromagnetic field are investigated by numerically solving the multi-physics fields coupling among the flow field, electromagnetic field, thermodynamic field and turbulent field. In the numerical simulation, the thermochemical non-equilibrium plasma magneto-hydrodynamic model is used to accurately simulate the high-frequency discharge, Joule heating, energy conversion, and internal energy exchange of air ICP. Finally, the distribution of electron temperature, particle number density, Lorentz force, Joule heating rate, velocity, pressure and electric field strength of air plasma are obtained through the multi-physics field coupling calculation. The results show that the plasma flow is in a thermodynamic non-equilibrium state near the torch wall in the induction coil region and that the Lorentz force plays an important role in controlling the momentum transfer. A strong eddy flow occurs between the inlet and the second turn of the inductive coil. The eddy flow has a close relationship with the negative pressure gradient and the electromagnetic heating phenomenon in the induction coil region. The radial Lorentz force is always negative. This indicates that the free electrons are generated near the wall due to the fact that the skin effect are always subjected to a force making them move to the central axis of the ICP torch. The maximum value of the radial Lorentz force is 3.95 times higher than that of the axial Lorentz. This indicates that the momentum transfer is predominantly radial. The Joule heating effect of the air particles is also affected by the radial Lorentz force. The maximum value of EI is 2.9 times larger than the real part of electric field, ER. The positive EI is generated by the free electrons inside the plasma. The number density of free electrons reaches a maximum value at a distance of 5.5 mm far from the inner wall surface of the torch below the second induction coil. 91% of N2 are dissociated into atomic N near the central axis. The maximum electron and translational temperature simulated in this paper are 9921 K and 8507 K, respectively.
Theoretical study of laser cooling of potassium chloride anion
Authors: Wan Ming-Jie , Luo Hua-Feng , Yuan Di , Li Song ,   School of Physics and Electronic Engineering, Yibin University, Yibin 644007, China,   College of Chemistry & Chemical Engineering, Yibin University, Yibin 644007, China,   School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou 434023, China
Published: December 2020

The potential energy curves and transition dipole moments (TDMs) for three Λ-S states (X2Σ+, A2Π, and B2Σ+) of potassium chloride anion (KCl–) are investigated by using multi-reference configuration interaction (MRCI) method. The def2-AQZVPP-JKFI of K atom and AV5Z-DK all-electron basis set of Cl atom are used in all calculations. The Davidson correction, core-valence (CV) correction, and spin-orbit coupling effect (SOC) are also considered. In the complete active self-consistent field (CASSCF) calculations, eight molecular orbitals are selected as active orbitals, which includ K 4s4p and Cl 3s3p shells; K 3p shell is closed orbital, and the remaining shells (K 1s2s3s and Cl 1s2s2p) are frozen orbitals. In the MRCI+Q calculations, K 3p shell is used for the CV correction. There are 15 electrons in the correlation energy calculations. Then, their spectroscopic parameters, Einstein coefficients, Franck-Condon factors, and radiative lifetimes are obtained by solving the radial Schrödinger equation. The spectroscopic properties and transition properties for the Ω states are predicted. Highly diagonally distributed Franck-Condon factor f00 values for the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 transition are 0.8816 and 0.8808, respectively. And the short radiative lifetimes for the (2)1/2 and (1)3/2 excited states are also obtained, i.e. τ[(2)1/2] = 45.7 ns and τ[(1)3/2] = 45.5 ns, which can ensure laser cooling of KCl– anion rapidly. The results indicate that the (2)1/2↔(1)1/2 and (1)3/2↔(1)1/2 quasicycling transitions are suitable to the building of laser cooling projects. For driving the (2)1/2↔(1)1/2 transition, a main pump laser (λ00) and two repumping lasers (λ10 and λ21) are required. Their wavelengths are λ00 = 1065.77 nm, λ10 = 1090.13 nm and λ21 = 1087.76 nm. For driving the (1)3/2↔(1)1/2 transition, the wavelengths are λ00 = 1064.24 nm, λ10 = 1088.54 nm, and λ21 = 1086.17 nm. The cooling wavelengths of KCl- anion for two transitions are both deep in the infrared range. Finally, the Doppler temperature and recoil temperature for two transitions are also calculated, respectively. The Doppler temperatures for (2)1/2↔(1)1/2 and (1)3/2(1)1/2 transitions are 83.57 μK and 83.93 μK, and the recoil temperatures for two transitions are 226 nK and 227 nK, respectively. for two transitions are 226 nK and 227 nK, respectively.
Isostructural phase transition of fcc Ce: Molecular dynamics simulations
Authors: Diwu Min-Jie , Hu Xiao-Mian ,   Graduate School, China Academy of Engineering Physics, Beijing 100088, China,   National Laboratory of Computational Physics, Beijing Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
Published: December 2020

Ce is a rare earth element in the periodic table. In the range of low temperature and low pressure, there are two face-centered-cubic (FCC) phases (α-Ce and γ-Ce) and a double-hexagonal-close-packed phase (β-Ce) for metallic Ce. At ambient temperature and about 0.7 GPa pressure, Ce undergoes γ→α phase transition with a volume shrink of 14%–17% discontinuously. In this paper, an embedded-atom method (EAM) potential compatible for α-Ce and γ-Ce was developed. This EAM potential has been employed to study several basic properties of cerium in these two FCC phases, such as equilibrium lattice constants, cohesive energies, and elastic constants. These results showed good accordance with experiments and first principle calculations. The lattice defects have been studied with the formation energy calculations of vacancies, interstitials, surfaces, stacking faults, and twinning defects in α-Ce and γ-Ce lattice. The lattice dynamics of α-Ce and γ-Ce have been analyzed using our EAM potential. The lattice vibrational entropy was calculated and plotted as functions of temperature for each phases. The vibrational entropy change across the α-γ phase transition showed to be ~0.67 kB per atom at ambient temperature. Using molecular dynamics simulation with our EAM potential, several isotherms and radial distribution functions were calculated. These isotherms and radial distribution functions demonstrate a first order phase transition between two FCC structures, corresponding to α-Ce and γ-Ce, with a critical point sets at Tc≈550 K and Pc≈1.21 GPa. Thus the newly developed EAM potential could provide a reasonable description of FCC Ce and its α-γ phase transition within the scale of classical molecular dynamics simulation.
Graphene plasmon enhanced infrared spectroscopy
Authors: Wu Chen-Chen , Guo Xiang-Dong , Hu Hai , Yang Xiao-Xia , Dai Qing ,   Division of Nanophotonics, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Infrared spectroscopy can accurately reflect the information of molecular vibration, and it is an important technology to characterize the composition and structure of materials. However, since the interaction between nanomaterials and infrared light is very weak due to the significant size mismatch, it is challenging to obtain the spectral information of nanomaterials in the field of infrared spectroscopy. The plasmon is a collective electron oscillation on the surface of the material inducing by the incident light, and it has excellent light field confinement, which can significantly enhance the interaction between light and nanomaterials. Graphene plasmon has prominent properties, such as high light field confinement, dynamic adjustment, and low intrinsic attenuation. Therefore it is an important solution to enhance the infrared absorption of nanomaterials. This article systematically introduces the infrared plasmon materials system. Then it summarizes the characteristics of graphene plasmon and their advantages on surface enhanced infrared spectroscopy, and it emphasizes the recent important researches and applications of graphene plasmon enhanced infrared spectroscopy in the world, including single molecular layer biochemical detection, gas identification, refractive index sensing, etc. Further prospects for the development and potential applications of graphene plasmon enhanced infrared spectroscopy are also demonstrated.
Theoretical analysis and simulation of W-band sheet beam extended interaction klystron amplifier
Authors: Zeng Zao-Jin , Ma Qiao-Sheng , Hu Lin-Lin , Jiang Yi , Hu Peng , Lei Wen-Qiang , Ma Guo-Wu , Chen Hong-Bin ,   Institute of Applied Electronics, China  Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The sheet beam extended interaction klystron is an important kind of millimeter-wave and sub-millimeter-wave vacuum electron device, which has extensive applications such as in high resolution radar, imaging system, satellite communication and precision guided missiles. Compared with conventional pencil beam klystron, the sheet beam extended interaction klystron, in which a thin rectangular sheet beam is used, can generate higher power by obtaining higher current and reducing space-charge-effect of electron beam. Kinematical theory and space charge wave theory are extensively used to analyze the bunching process of electrons. Kinematical theory is precise when electron beam is especially small because the influence of space charge effect is ignored, while space charge wave theory is accurate when the modulation of electron beam is small since it is based on the premise of small amplitude. Electron flow oscillatory theory is a compromise between kinematical theory and space charge wave theory, which adapts to the bigger modulation of electron beam than space charge wave theory, while it is inaccurate in the case of big bunching parameter. Based on electron flow oscillatory theory under the small signal condition, the influence of electron beam on standing wave electric field of 2π mode in a three-gap cavity is analyzed, and the expressions of beam loading conductance and beam loading susceptance in a three-gap cavity are obtained. The influences of plasma frequency, transit angle of single gap and transit angle of drift on the interaction of beam and wave in a three-gap cavity are discussed. The results show that space-charge-effect of beam is unbeneficial to the interaction between beam and wave, otherwise beam loading conductance and beam loading susceptance fluctuate with the increasing of transit angle of single gap and transit angle of drift. A W-band sheet beam extended interaction klystron is designed by theoretical analysis and 3D PIC software. The output power of 5773 W at 94.47 GHz is obtained with an efficiency of 8.46%, a gain of 37.6 dB and a 3 dB bandwith of about 140 MHz, when beam voltage is 19.5 kV, current is 3.5 A and focus magnetic field is 0.85 T. This research is important for the engineering of the W-band sheet beam extended interaction klystron amplifier.
Influence of dispersion and impurity on double-parameter asymmetric Gaussian quantum dot qubit
Authors: Han Chao ,   College of Physics and Electronic Information, Inner Mongolia University for Nationalities, Tongliao 028043, China,   Institute of Condensed Matter Physics, Hebei Normal University of Science and Technology, Qinhuangdao 066004, China
Published: December 2020

Selecting the double-parameter asymmetric Gaussian (AG) potential to describe the confinement effect of electrons in a quantum dot, the ground state and the first excited state energy eigenvalues and eigenfunctions of the three-body interaction system that are composed of the electrons, the impurity and the longitudinal optical phonon are derived by using the Lee-Low-Pines unitary transformation and the Pekar-type variational method, and the two-level structure required for a qubit is constructed. The influences of material parameters such as the dispersion coefficient, dielectric constant (DC) ratio, and electron-phonon coupling (EPC) constant on the probability density and the oscillation period of electron in the AG potential qubit are investigated. Based on the Fermi gold rule and the even-order approximation, the effects of the DC ratio, the dispersion coefficient and the EPC constant on the qubit decoherence are studied. And then the influences of the dispersion coefficient, the DC ratio and the EPC constant on the phase rotation manipulation of the qubit sphere are discussed. Numerical results show that the dispersion coefficient, the DC ratio and EPC constant of the medium have both advantages and disadvantages for the formation and information storage of qubits. The probability density of electrons in quantum dot qubits decreases with DC ratio increasing and exhibits significant oscillations as the well width of the AG potential decreases; the oscillation period of the qubit decreases with the well depth of the AG potential or the DC ratio increasing; the decoherence time increases with DC ratio or dispersion coefficient increasing; the phase rotation quality factor increases with DC ratio or dispersion coefficient increasing. Using the double-parameter AG potential to describe the confinement of electrons in quantum dot will better reflect the quantization properties of qubit. Increasing the dispersion coefficient or the DC ratio of the material is beneficial to not only the phase rotation manipulation of the qubit sphere, but also improving the coherence of the quantum dot qubit. The results of this paper can be used for reference in the experimental work on the constructing and manipulating of the quantum dot qubits.
Fano resonances in symmetric gold nanorod trimers
Authors: Li Ai-Yun , Zhang Xing-Fang , Liu Feng-Shou , Yan Xin , Liang Lan-Ju ,   School of Opt-Electronic Engineering, Zaozhuang University, Zaozhuang 277160, China,   Laboratory of Optoelectronic Information Processing and Display of Shandong, Zaozhuang 277160, China
Published: December 2020

A symmetrical gold nanorod trimer structure consisting of a short center nanorod and two long nanorods on both sides is proposed. The scattering spectra, electromagnetic field and current density vector distributions across the central cross section of the nanorod trimer are calculated by the finite difference time domain method, and the effects of structural parameters and dielectric environment on Fano resonance characteristics are theoretically investigated in detail. The results show that the Fano resonance can be generated mainly due to the interference between the bonding electric dipole mode in lower energy and the antibonding electric dipole mode or antiphase magnetic dipole mode in higher energy. The Fano dip is blue-shifted with the decrease in the short nanorod length, the size of whole trimer structure with constant displacement, or the refractive index of dielectric medium in the gaps between the central nanorod and two side nanorods; the resonance intensity on both sides of the Fano dip also changes. Meanwhile, the bonding mode on the red side of the Fano dip is gradually dominated by the electric dipole mode of two side nanorods, and the spectral intensity increases, while the antibonding mode on the blue side gradually evolves into the short nanorod-dominated antiphase magnetic dipole mode, and the spectral intensity becomes weaker. The increase in the inter-rod spacing also leads the Fano dip to be blue-shifted, and a similar change in the spectral intensity occurs on both sides of the Fano dip, due to the degeneration of bonding and antibonding modes caused by the decrease of near-field coupling between the short nanorod and two side nanorods, which finally degenerate into the electric dipole modes generated by the short nanorod or the two side nanorods, respectively. In addition, the Fano dip is insensitive to the change of the side nanorod length, but the relative resonance intensity on both sides of the Fano dip also changes. Furthermore, it is found that the spectral contrast ratio of the Fano resonance first increases and then decreases by varying the above-mentioned structural parameters or dielectric environment. These results are expected to be used for guiding the design of Fano controllable nanostructures and also for developing the applications of specific micro-nano photonics.
Self-repairing process of defect graphene under metal atom catalysis
Authors: Wang Lu-Kuo , Duan Fang-Li ,   State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing 400030, China
Published: December 2020

Single-atom catalysts play a crucial role in repairing defective graphene, but the existing research on the single-atom catalysts focuses on the reduction of energy barriers. The unique repairing behavior of the single-atom catalysts in the graphene-healing process and the different repair mechanisms between different catalyst atoms have not been studied in depth. In this paper, the molecular dynamics simulation is used to study the the self-repairing process of defective graphene in the presence of Ni and Pt atoms. By changing the system temperature, multiple sets of simulations are obtained. By observing the atomistic structure obtained at the end of the simulations, the different catalytic repair effects are studied. We calculate the variation of 5, 6 and 7-member rings of graphene in the repair process, it is found that at the appropriate temperatures (1600 K and 2000 K), Ni atom shows stronger catalytic repair capability than Pt atom, and as the temperature increases, the repair effect on defects is also improved. By comparing with the repair process without metal atoms, we find that the effect of metal atoms is significant especially in repairing the carbon chain. To figure out the reason, some typical structure evolutions are simulated. The simulations show that when Ni atom can capture carbon chains at 1600 K, Pt atom needs higher temperature at least 2000 K. Apart from that, Ni and Pt atoms respectively lead to local structural transformations of " jump from the ring” and " bond breakage”. This may be the reason why the 5, 6, and 7-membered rings in the final structure of Pt catalytic system are less than those of Ni catalytic system at 1600 K and 2000 K. In addition, we map the migration route of metal atoms and calculate the migration distance. By observing the different migration behaviors of the two metal atoms in and out of the plane, the different catalytic mechanisms are further studied. The research results in this paper conduce to understanding the catalytic mechanism of metal atoms in the repair of defective graphene. It is of theoretical significance for selecting the external conditions and catalysts for the repairing of defective graphene.
Application prospect of metal-oxide-semiconductor silicon light emitting devices in integrated circuits
Authors: Zhang Ning , Xu Kai-Kai , Chen Yan-Xu , Zhu Kun-Feng , Zhao Jian-Ming , Yu Qi ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China,   Science and Technology on Analog Integrated Circuits Laboratory, Chongqing 400060, China
Published: December 2020

Photonic interconnects have potentials to break increasingly severe energy efficiency and bandwidth density bottlenecks of electrical interconnect in scaled complementary metal oxide semiconductor (CMOS) integrated circuits, leading to the emergence of optoelectronic integrated circuits (OEICs) that utilize electronic and photonic devices together in a synergistic way to achieve better performance than those based on pure electronic device technology. By reviewing the progresses of Si-based light-emitting device, the schematic of MOS-like light source integrated with waveguides and the following photodetector is analyzed for its availability. It is believed that on-chip optical interconnects could be achieved by standard CMOS technology successfully with the speed as fast as the velocity of light, supplying propulsions for nest-generation OEICs.
Temperature and stress sensing characteristics of symmetrically fused tapered fiber grating
Authors: Tu Xing-Hua , Zhao Yi-Chao ,   Research Center of Optoelectronic Sensing Engineering, School of Electronic and Optical Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
Published: December 2020

The stress-sensitive and temperature-insensitive characteristics of the tapered fiber grating can be used effectively to suppress the cross-sensitive problem of temperature and stress. In this paper, a fiber grating with a symmetric double-cone shape is proposed, which is made by using a fused taper technology. The theoretical model of sensing characteristics is established and analyzed by the transfer matrix method. Firstly, the factors affecting the change of radon coefficient are studied, and the relationship between the radon coefficient and the amount of grate length change is obtained, and then the spectral characteristics of the symmetric fused-tapered fiber grating are analyzed to discuss the origin of dense modulation at the short wavelength of the spectrum. The effects of temperature and stress on the reflection spectrum of symmetrically fused-tapered fiber grating are studied, and the relationship between the corresponding center wavelength and spectral bandwidth is obtained. In order to solve the problem of low stress sensitivity of the fiber grating, a scheme is presented that the radius difference of the optical fiber in the sensing cone region is enhanced by using polymer to coat the tapered area. Finally, a fused taper technology is used to prepare the symmetrically molten fiber grating, and verify the correctness of theoretical simulation in experiment, indicating that its stress sensitivity is 0.11391 nm/N. Firstly, the ripple coefficient of the symmetrically fused-tapered fiber grating is linearly related to the amount of change in the length of the grating. Secondly, because the grating cycle is small at the end of the symmetrically melt-pull-cone fiber-optic grating, and the reflectivity is less than 1, the left-hand transmission light and the right-hand reflected light will produce interference, so the spectral short wavelength will present dense modulation phenomenon. Thirdly, the center wavelength shifts to long wavelength region and the reflection bandwidth is broadened as stress is raised, and the center wavelength and reflection bandwidth are both linearly changed with the applied stress. Finally, the center wavelength shifts to long wavelength region as the temperature rises gradually, and the effect on the spectral bandwidth can be ignored. The stress sensitivity of the fiber grating increases hundreds of times by increasing the difference in fiber optic grating radius in the sensing tapered area, and the stress sensitivity can be further improved by increasing the fused taper variation of the grating. The spectral bandwidth of the symmetrical fused tapered fiber grating is only sensitive to stress but not to temperature. The characteristics can be used to realize the double-parameter measurement of temperature and stress.