bluuebunny/crossref_metadata_2025 huggingface dataset:
Two-dimensional hexagonal boron nitride based memristor
Authors: Wu Quan-Tan  , Shi Tuo  , Zhao Xiao-Long  , Zhang Xu-Meng  , Wu Fa-Cai  , Cao Rong-Rong  , Long Shi-Bing  , Lü Hang-Bing  , Liu Qi  , Liu Ming  ,   Key Laboratory of Microelectronic Devices and Integrated Technology, Institute of Microelectronics of Chinese Academy of Sciences, Beijing 100029, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Hexagonal boron nitride (h-BN) based resistive switching device is fabricated with the multilayer h-BN film serving as an active material. The device shows the coexistence of forming-free and self-compliance bipolar resistive switching behavior with reproducible switching endurance and long retention time. Moreover, the device in pulse mode shows analog resistive switching characteristics, i.e. the resistance states can be continuously tuned by successive voltage pulses. This suggests that the device is also capable of mimicking the synaptic weight changes in neuromorphic systems.
Preparation, structure configuration, physical properties and applications of borophene and two-dimensional alkaline-earth metal boride nanomaterials
Authors: Guo Ze-Kun  , Tian Yan  , Gan Hai-Bo  , Li Zi-Juan  , Zhang Tong  , Xu Ning-Sheng  , Chen Jun  , Chen Huan-Jun  , Deng Shao-Zhi  , Liu Fei  ,   Guangdong Key Laboratory of Display Materials and Technologies, State Key Laboratory of Optoelectronic Materials and Technology, School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

With the rise of graphene, two-dimensional nanomaterials have been significantly developed in recent years. As novel two-dimensional nanostructures, borophene and alkaline-earth metal boride two-dimensional materials have received much attention because of their unique physical and chemical properties, such as high Fermi velocities, high electron mobilities, large Young's moduli, high transparencies, negative Poisson's ratios and high chemical stabilities. This paper focuses on the researches of the fabrication techniques, structure configurations, properties and applications of borophene and two-dimensional alkaline-earth metal boride nanomaterials. Firstly, the current preparation methods and structure configurations of borophene are summarized. Secondly, the possible structures and fabrication techniques of two-dimensional alkaline-earth metal boride nanomaterials are introduced in detail. Thirdly, the physical properties of borophene and two-dimensional alkaline-earth metal boride nanomaterials are investigated. Finally, the most promising application areas of borophene and two-dimensional alkaline-earth metal boride nanomaterials in the future are predicted.
High performance graphene Hall sensors
Authors: Huang Le  , Zhang Zhi-Yong  , Peng Lian-Mao  ,   Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
Published: December 2020

The state-of-the-art graphene Hall elements and integrated circuits are reviewed. By optimizing the growth and transfer of graphene and the micro-fabrication process of Hall sensor, graphene Hall elements and integrated circuits outperform conventional Hall sensors in many aspects. Graphene Hall elements exhibit better sensitivities, resolutions, linearities and temperature stabilities than commercialized Hall elements. Through developing a set of passivation processes, the stabilities of graphene Hall elements are improved. Besides, the flexible magnetic sensing and multifunctional detection applications based on graphene are demonstrated. In addition, graphene/silicon hybrid Hall integrated circuits are realized. By developing a set of low temperature processes (below 180℃), graphene Hall elements are monolithically integrated onto the passivation layer of silicon complementary metal oxide semiconductor chip. This work demonstrates that graphene possesses significant performance advantages in Hall magnetic sensing and potentially practical applications.
Simulation and analysis of sensing modes of in-fiber interferometer
Authors: Li Li-Jun  , Ma Qian  , Cao Mao-Yong  , Gong Shun-Shun  , Li Wen-Xian  , Guo Xiao-Li  , Liu Yi-Lin  , Xu Lin  , Liu Qian  ,   College of Electronics, Communication and Physics, Shandong University of Science and Technology, Qingdao 266590, China;,   College of Electrical Engineering and Automation, Shandong University of Science and Technology, Qingdao 266590, China;,   State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology, Shandong University of Science and Technology, Qingdao 266590, China
Published: December 2020

The cladding mode of the in-fiber interference sensor relates to the externally sensing physical quantity, so the investigation of the cladding mode is very important for designing and improving the sensing performance of the sensor. By using the finite difference beam propagation method, the interference spectra of the sensors with different lengths and different core-to-core diameter ratios are simulated. Its spatial frequency spectrum is obtained through Fourier transform. The effective refractive index of the dominant cladding mode can be obtained through analyzing its spatial frequency spectrum. Its corresponding cladding mode order can be determined through substituting the values of the effective refractive index into the dispersion equation of sensing optical fiber. The simulation results show that the number and the order of the cladding modes both increase with sensing part fiber length increasing. The interference spectrum becomes dense according to the superposition of multi order cladding mode interferences. Its free spectral space of the sensor output interference spectrum becomes small. With the variations of the input fiber and sensing fiber core-to-core diameter ratio, the power distributions among the modes change obviously. The increase of core-to-core diameter ratio can increase the number and order of the cladding modes.
Landau critical velocity of spin-orbit-coupled Bose-Einstein condensate across quantum phase transition
Authors: He Li  , Yu Zeng-Qiang  ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China;,   Institute of Theoretical Physics, Shanxi University, Taiyuan 030006, China
Published: December 2020

An impurity immersed in a superfluid can move without friction when its velocity is below a critical value. This phenomenon can be explained by the famous Landau criterion, according to which, the critical velocity is determined by the elementary excitation spectrum of the superfluid. Landau critical velocity has been measured in the isotropic superfluid, such as the liquid He-Ⅱ and the Bose-Einstein condensates of dilute atomic gases, where the onset of dissipation is due to the creation of roton and phonon, respectively. The recent realization of synthetic spin-orbit coupling in quantum gas opens up possibilities for the study of novel superfluidity with ultracold atoms. To date, a specific type of spin-orbit coupling, which is generated by a pair of Raman laser beams, has been achieved in a Bose-Einstein condensate of 87Rb experimentally. Remarkably, the excitation spectrum of this system is anisotropic and can be feasibly tuned by the external laser field. While the anisotropic dynamics has been observed experimentally, the critical velocity has not been measured so far. It is a conventional wisdom that in an anisotropic superfluid, the critical velocity is determined by the excitation spectrum in the moving direction of the impurity. However, this is not always the case. In this work, we investigate the motion of a point-like impurity in a spin-orbit-coupled condensate with the spin-dependent interatomic interaction. In the vicinity of the quantum phase transition between the plane-wave (PW) phase and the zero-momentum (ZM) phase, the onset of the dissipation is due to the emission of a phonon, and the Landau critical velocity vc depends on the anisotropic sound velocity. While the sound velocity varies smoothly across the PW-ZM phase transition, the critical velocity in the direction perpendicular to the axis of spin-orbit coupling exhibits a sudden jump at the phase boundary. The value of vc on the PW phase side of the transition is generally smaller than the one on the ZM phase side, and the jump amplitude of vc is an increasing function of the spin-dependent interaction strength. Beyond the critical velocity, the energy dissipation rate of the impurity is explicitly calculated via a perturbation approach. The discontinuity of vc at the phase boundary can be clearly seen from the dissipation curves, which can be measured through the heating of the condensate. Our prediction can be tested in the current experiments with ultracold atoms.
Accurate analysis of magnetic force of bi-stable cantilever vibration energy harvesting system with the theory of magnetizing current
Authors: Zhang Yu-Yang  , Leng Yong-Gang  , Tan Dan  , Liu Jin-Jun  , Fan Sheng-Bo  ,   School of Mechanical Engineering, Tianjin University, Tianjin 300350, China
Published: December 2020

In the study of piezoelectric cantilever energy harvesting system, a bi-stable nonlinear cantilever with magnets added to the structure has a wider frequency band response and a higher energy output efficiency. Hence, the calculation accuracy of the magnetic force on which the potential function and dynamics of the system depend is essential to predicting the output response and energy harvesting effect. In this work, we use a shape function to describe the relation between the deflections of an arbitrary point and the free-end point on the beam, and then calculate the trace and deflection angle of the beam's free-end by integrating the entire slope of the cantilever beam. The magnetic force is consequently derived from the magnets' real-time relative positions and postures by using the magnetizing current method. With comprehensively considering the axial magnetic force and the lateral magnetic force, the simulation results demonstrate that when the displacement of the magnet at the end of the beam is large enough, the directions of axial and lateral magnetic force change from repulsive to attractive, which leads to a large veer of the resultant magnetic force across two quadrants. So, it means that a smaller interval between magnets may not cause a larger deflection of the beam, and the magnetic force existing as attractive force could diminish the well space of potential function (that is, the distance between two equilibrium positions of the system). The experimental data in this work are nicely consistent with the simulation results. And in this work, we also make a comparison of the simulation results with those from our method and existing method, showing that the accuracy of the proposed method is much higher than that from the existing calculation method, especially in the scenario where the magnet at the end of the beam is far from the horizontal axis.
Topological phase transitions caused by a simple rotational operation in two-dimensional acoustic crystals
Authors: Wang Jian  , Wu Shi-Qiao  , Mei Jun  ,   School of Physics, South China University of Technology, Guangzhou 510641, China
Published: December 2020

We design a two-dimensional acoustic crystal (AC) to obtain topologically protected edge states for sound waves. The AC is composed of a triangular array of a complex unit cell consisting of two identical triangle-shaped steel rods arranged in air. The steel rods are placed on the vertices of the hexagonal unit cell so that the whole lattice possesses the C6v symmetry. We show that by simply rotating all triangular rods around their respective centers by 180 degrees, a topological phase transition can be achieved, and more importantly, such a transition is accomplished with no need of changing the fill ratios or changing the positions of the rods. Interestingly, the achieved topologically nontrivial band gap has a very large frequency width, which is really beneficial to future applications. The topological properties of the AC are rooted in the spatial symmetries of the eigenstates. It is well known that there are two doubly-degenerate eigenstates at the point for a C6v point group, and they are usually called the p and d states in electronic system. By utilizing the spatial symmetries of the p and d states in the AC, we can construct the pseudo-time reversal symmetry which renders the Kramers doubling in this classical system. We find pseudospin states in the interface between topologically trivial and nontrivial ACs, where anticlockwise (clockwise) rotational behaviors of time-averaged Poynting vectors correspond to the pseudospin-up (pseudospin-down) orientations of the edge states, respectively. These phenomena are very similar to the real spin states of quantum spin Hall effect in electronic systems. We also develop an effective Hamiltonian for the associated bands to characterize the topological properties of the AC around the Brillouin zone center by the kp perturbation method. We calculate the spin Chern numbers of the ACs, and reveal the inherent link between the band inversion and the topological phase transition. With full-wave simulations, we demonstrate the one-way propagation of sound waves along the interface between topologically distinct ACs, and demonstrate the robustness of the edge states against different types of defects including bends, cavity and disorder. Our design provides a new way to realize acoustic topological effects in a wide frequency range spanning from infrasound to ultrasound. Potential applications and acoustic devices based on our design are expected, so that people can manipulate and transport sound waves in a more efficient way.
Topological phonons and phonon Hall effects
Authors: Xing Yu-Heng  , Xu Xi-Fang  , Zhang Li-Fa  ,   School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

The combination of topology and physics is a new field of physics development in recent decades. It is not only active in quantum field theory and high energy physics, but also widely exists in condensed matter physics, including quantum (anomalous, spin) Hall effect and topological insulators (superconductors) etc. Phonon, as the main carrier of heat transport in the crystal, recently, due to the discovery of various phonon devices, phonons has been widely concerned by scientist. In this paper, we introduce the topological properties of phonons and the phonon hall effect. We have reviewed the related physical research progress of phonon hall effect, phonon valley hall effect and so on, which are generated by breaking the time reversal symmetry, spatial inversion symmetry, both breaking the time and spatial inversion symmetry. Finally, the application of topology in other acoustic systems is briefly introduced, and the future development direction is discussed too.
Subwavelength topological valley-spin states in the space-coiling acoustic metamaterials
Authors: Zheng Sheng-Jie  , Xia Bai-Zhan  , Liu Ting-Ting  , Yu De-Jie  ,   State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha 410082, China
Published: December 2020

Phononic crystals possess Dirac linear dispersion bands. In the vicinity of Dirac cones, phononic crystals exhibit topological properties which have good application prospects in control of acoustic waves. Up to now, the topological edge states of phononic crystals, based on the band structures arising from the Bragg scattering, cannot realize low-frequency sound waves by the topologically protected one-way edge transmission. In this paper, by introducing the space-coiling structure, a space-coiling phononic metamaterial with C3v symmetry is designed. At the K (K') points of the Brillouin zone, the bands linearly cross to a subwavelength Dirac degenerated cones. With a rotation of the acoustic metamaterials, the mirror symmetry will be broken and the Dirac degenerated cones will be reopened, leading to subwavelength topological phase transition and subwavelength topological valley-spin states. Lastly, along the topological interface between acoustic metamaterials with different topological valley-spin states, we successfully observe the phononic topologically valley-spin transmission. The subwavelength Dirac conical dispersion and the subwavelength topological valley-spin state breakthrough the limitation of the geometric dimension of the phononic topological insulator, and provide a theoretical basis for the application of the phononic topologically robust transmission in a subwavelength scale.
Continuous variable quantum entanglement at 1.34 m
Authors: Ma Ya-Yun  , Feng Jin-Xia  , Wan Zhen-Ju  , Gao Ying-Hao  , Zhang Kuan-Shou  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China;,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Continuous variable (CV) quantum entanglement is a fundamental resource of CV quantum communication and quantum computation. It is useful in a wide variety of applications, including quantum teleportation, quantum dense coding, quantum key distribution, and high-precision quantum measurement. In this paper, we generate CV quantum entanglement at a telecommunication wavelength of 1342 nm by using a nondegenerate optical parametric amplifier (NOPA) with a type-Ⅱ periodically poled KTiOPO4 (PPKTP) crystal. A home-made continuous-wave single-frequency dual-wavelength (671 nm and 1342 nm) Nd:YVO4/LiB3O5 laser is achieved with output powers of 1.5 W (671 nm) and 1.3 W (1342 nm). Then a mode cleaner (MC1) with a fineness of 400 and linewidth of 0.75 MHz and a mode cleaner MC2 with a fineness of 400 and linewidth of 0.75 MHz are used to filter the noises of laser at 1342 nm and 671 nm, respectively. By using MCs, the intensity noise of laser reaches a shot noise level (SNL) for analysis frequencies higher than 1.0 MHz, and the phase noise of laser reaches an SNL for analysis frequencies higher than 1.3 MHz. Utilizing this kind of low noise single-frequency 671 nm laser as a pump, a doubly-resonant optical parametric oscillator with a threshold of 325 mW is realised. When the low noise single-frequency 1342 nm laser is injected as a signal and the relative phase between the pump and injected signal is locked to , the NOPA is operated at deamplification. After optimizing the temperature of the type-Ⅱ PPKTP crystal and at a pump power of 260 mW, Einstein-Podolsky-Rosen (EPR)-entangled beams with quantum correlation of 3.0 dB for both the amplitude and phase quadratures are experimentally generated. The strength of EPR-entangled beams is relatively low. It is maybe due to the low nonlinear conversion efficiency and large absorption of the type-Ⅱ PPKTP crystal at 671 nm and 1342 nm. The generated CV quantum entanglement at 1.34 m has lower transmission loss and smaller phase diffusion effect in a silica fiber. The research contributes to a high quality quantum source for the CV quantum communication based on existing telecommunication fiber networks.
Effect of plasma grating roughness on high-order harmonic generation
Authors: Li Xia-Zhi  , Zou De-Bin  , Zhou Hong-Yu  , Zhang Shi-Jie  , Zhao Na  , Yu De-Yao  , Zhuo Hong-Bin  ,   College of Science, National University of Defence Technology, Changsha 410073, China;,   IFSA Collaborative Innovation Center, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

Extreme ultra-violet (XUV) light and soft X-ray are widely used to detect the microscopic structure and observe the ultra-fast physical process. It is found that high order harmonic with the frequency as high as that of the waterwindow waves and the pulse duration as short as attosecond can be obtained in the laser-plasma interaction. Due to these features, high order harmonic (HH) is a promising alternative to generating ultra-short XUV light and X-ray. Recently, HHs have been observed in the experiments. However, the frequency spectrum is not complete compared with the results predicted theoretically and numerically. It might relate to the damage of the grating target surface by a long laser repulse. In this article, the effect of target surface roughness on the high order generation (HHG) in the interaction between ultra-intense laser pulse and grating targets is investigated by surface current model and particle-in-cell simulations. We find that both the spatial and spectral domains of harmonics are modulated by the periodical structure of the grating due to the optical interference. The roughness on the surface significantly distorts the modulation effect and leads to different radiation angle and spectral distributions. For the ideal grating, only harmonics satisfying matching condition in a certain direction can be enhanced and the radiation power is restricted in the direction nearly parallel to the target surface. When the surface roughness of the grating target is considered, the matching condition is not valid and the harmonics are scattered into the direction away from the target surface. Comparing with the ideal grating target, most of the harmonic energy is concentrated in the low order harmonics and the intensities of the harmonics decrease rapidly with increasing HH order when surface roughness is considered. The results show good consistence with the phenomena observed in previous experiments and provide the technical reference for exploring the future applications of HHs and HHG.
Magneto-electronic properties of zigzag graphene nanoribbons doped with triangular boron nitride segment
Authors: Zhang Hua-Lin  , Sun Lin  , Han Jia-Ning  ,   School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410114, China
Published: December 2020

In this paper, magneto-electronic properties of zigzag graphene nanoribbons (ZGNR) doped with triangular boron nitride (BN) segments are investigated by using first-principles method based on density functional theory. It is shown that in the nonmagnetic state, the ZGNRs doped with triangular BN segments at different positions are metals. In the ferromagnetic state, with the impurities moving from one edge of the nanoribbon to the other edge, a transition is caused from a spin metal to a spin half-metal, and then to spin semiconductor, and as long as the impurity is not on the edge of the nanoribbon, the doped ZGNR is always spin half-metal. In the antiferromagnetic state, the ZGNR doped in the middle of the nanoribbon is spin metal, while the ZGNR doped on the edge of the nanoribbon has no antiferromagnetic state. The electronic structures of the ZGNRs doped with BN segments at different positions are explained by the difference in charge density. The binding energies of doped ZGNRs are negative, thus the structures of the doped ZGNRs are stable. As the impurity moves from position P1 to position P5, the binding energy decreases gradually. When the impurity is located at position P5, the binding energy of ZGNR is smallest, and the structure of ZGNR is most stable. When the impurity doped in the middle of the nanoribbon, the antiferromagnetic state is the ground state, while the impurity is doped on the edge of the nanoribbon, the ferromagnetic state is the ground state. These obtained results are of significance for developing electronic nanodevices based on graphene.
First-principles study of absorption mechanism of hydrogen on W20O58 (010) surface
Authors: Jiang Ping-Guo  , Wang Zheng-Bing  , Yan Yong-Bo  , Liu Wen-Jie  ,   School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
Published: December 2020

With the development of modern industrial technology, tungsten products prepared from traditional tungsten powder cannot meet the demands of industry. However, the properties of tungsten products produced from ultra-fine tungsten powder have been greatly improved:they have high strength, high toughness, and low metal plasticity-brittle transition temperature. Hence, it is necessary to carry out theoretical research of the micro-adsorption dynamics during hydrogen reduction of W20O58, which is beneficial to synthetizing ultra-fine tungsten powder. In this article, to comprehend the crystal characteristics of W20O58 (010) surface and provide the theoretical reaction law for hydrogen reduction on W20O58 (010) surface, the absorption mechanism of H2 molecule on W20O58 (010) surface is studied by the first-principles calculation based on density functional theory in a plane wave pseudo-potential framework. The results show that the indirect band gap of W20O58 is 0.8 eV, indicating that it has metallic characteristic. The W20O58 (010) surface has different terminations, i.e., WO-terminated (010) surface and O-terminated (010) surface. After the geometrical optimization of the two surfaces, the W–O bond length and bond angle of W–O–W are both changed. In addition, six absorption configurations of H2 on W20O58 (010) surface, including WO-L-O1c, WO-V-O1c, WO-L-O2c, WO-V-O2c, O-L-O1c and O-V-O1c, are chosen to be investigated. The calculation results show that the WO-L-O1c, WO-V-O1c and WO-L-O2c absorption system are unstable, while the WO-V-O2c, O-L-O1c and O-V-O1c absorption configuration are stable. When H2 molecule is dissociated into two H atoms, the absorption energies of the three stable configurations are-1.164 eV,-1.021 eV and-3.11 eV, respectively. It is obvious that the O-V-O1c absorption configuration is the most stable one. The analysis of density of states reveals that the 1s state of H atom interacts with the 2p and 2s states of O atom. The outermost O1c atom of O-terminated (010) surface contains an unsaturated bond, which results in the formation of bonding between two H atoms and O1c atom. As a result, an H2O molecule is formed and an oxygen vacancy on the surface is generated after absorption reaction. By combining experimental observations with simulation calculations, the mechanism of hydrogen reduction of W20O58 can be revealed from a microscopic view.
Progress of Cu2O/ZnO oxide heterojunction solar cells
Authors: Chen Xin-Liang  , Chen Li  , Zhou Zhong-Xin  , Zhao Ying  , Zhang Xiao-Dan  ,   Tianjin Key Laboratory of Photo-electronic Thin Film Devices and Technology, Institute of Photo-electronic Thin Film Devices and Technology, Nankai University, Tianjin 300071, China
Published: December 2020

Recent progress of low cost Cu2O/ZnO hetero-junction solar cells is reviewed in this paper. The Cu2O used as an absorbing layer in photovoltaic cells is a direct bandgap semiconductor, exhibiting natural p-type conductivity. The source material of Cu2O-based solar cells is abundant and environmentally friendly. The main device structure of Cu2O/ZnO solar cells presents a planar and nano-wire/nano-rod configuration. The nanostructured Cu2O architecture conduces to charge collection in the device. The planar Cu2O absorbing layer with large grain size, achieved through the thermal oxidation of Cu sheets, exhibits high quality of the Cu2O/ZnO solar cells. The interface buffer layer (like i-ZnO, a-ZTO and Ga2O3) and back surface field (BSF, such as p+-Cu2O) can effectively improve energy band alignment match and increase carrier transport. The Cu2O paired with a 10-nm-thick Ga2O3 layer provides a nearly ideal conduction band offset and thus reduces the interface recombination. The Ga2O3 is a highly suitable buffer layer for enhancing the Voc (Voc value reaches 1.2 V) and conversion efficiency of Cu2O-based solar cells. The p+-Cu2O like N-doped Cu2O (Cu2O:N) and Na-doped Cu2O (Cu2O:Na) can reduce back-contact resistance and create an electron-reflecting back surface field in the Cu2O based solar cells. When a p-type Cu2O: Na acts as an absorbing layer and a zinc-germanium-oxide (Zn1-xGex-O) thin film is used as an n-type layer (buffer), Cu2O hetero-junction solar cell with the device structure MgF2/Al-doped ZnO (ZnO:Al)/Zn0.38Ge0.62-O/Cu2O:Na shows an efficiency of 8.1%. The oxide hetero-junction solar cells have a great potential application in the future photovoltaic field.
Characteristics of granular sheet of dense granular jet oblique impact
Authors: Wang Yue  , Li Wei-Feng  , Shi Zhe-Hang  , Liu Hai-Feng  , Wang Fu-Chen  ,   Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Thchonlogy, Shanghai 200237, China;,   Shanghai Engineering Reaearch Center of Coal Gasification, East China University of Science and Thchonlogy, Shanghai 200237, China
Published: December 2020

Dense granular impinging jets widely exist in natural flow phenomena and industrial processes, such as the rapid heating, cooling or drying, and gasification. It is important to investigate the factors influencing the flow patterns of dense granular impinging jets and reveal the evolution rules of the flow patterns. The dynamic behaviors of the dense granular impinging jets are experimentally studied by a high-speed camera and image processing software of Image J. The effects of the particle diameter, the granular jet velocity (u0) and the solid content of the granular jet (xp) on flow pattern of the granular impinging jet are investigated. Two flow regimes of the dense granular impinging jets, i.e., the liquid-like granular film and the scattering pattern, are identified. The results show that with the increase of the particle diameter and the granular jet velocity, both the solid content of the granular jet and the inter-particle collision frequency decrease, which results in the transition of granular sheet to scattering pattern. With the increase of granular jet velocity, the opening angle of the granular sheet from the side view increases, while the opening angle from the front view increases first and sharply decreases later. The results also show that with the increase of the granular jet velocity, the liquid-like granular film becomes unstable and a non-axisymmetric oscillation appears. And the amplitude and frequency of the liquid-like granular film increase with granular jet velocity increasing, and are significantly affected by particle diameter. The interesting behaviors of the liquid-like surface waves are observed on the granular sheet. The surface waves become remarkable with the increase of the granular jet velocity, and their propagating velocities normalized by the granular jet velocity vary from 0.7 to 0.9. The waves propagating on the granular sheet may emerge, which will reduce the frequencies of the surface waves and increase the surface wavelengths. The results also show that the oscillation frequency of the granular film nearly equals the pulsation frequency of the granular jet. It is indicated that the gas-solid interaction inside the nozzle increases with granular jet velocity increasing, and causes the instability of the granular jet, resulting in the non-axisymmetric oscillation on the granular sheet consequently. The results in this paper present significant knowledge of the dense granular impinging jets and also provide some principles for the applications in dense granular impinging jets in industrial processes.
First-principles study on the optical properties of Fe-doped GaN
Authors: Jia Wan-Li  , Zhou Miao  , Wang Xin-Mei  , Ji Wei-Li  ,   School of Science, Xi'an University of Technology, Xi'an 710048, China
Published: December 2020

Using hybrid density functional theory, we investigate the structural, electronic and optical properties of pristine GaN and Fe-doped GaN with a Fe concentration of 12.5%. Specifically, we first analyze the crystal lattice constant, band structure, and density of states, respectively. Then we predict the dielectric function, absorption coefficient, refractive index, reflectivity, energy-loss spectrum and extinction coefficient. Finally, we analyze the influences of the doping of Fe element on the photoelectric property of Fe doped systems. The calculated lattice constants for perfect GaN are a=b=3.19 Å, c=5.18 Å, which are in good agreement with the experimental values. Furthermore, we find that the doping of Fe element has little effect on the structural properties of GaN. The Band gap of pristine GaN is predicted to be 3.41 eV, very close to the experimental value of 3.39 eV. The band gap of Fe doped GaN (12.5%) significantly decreases to 3.06 eV. By comparing the densities of states of the systems with and without Fe doping, it is found that Fe-3 d state is mainly responsible for the decrease of band gap. The calculated static dielectric constant of perfect GaN is 5.74, and it increases to 6.20 after incorporating the Fe element. The results about the imaginary part of dielectric function show that two equal-strength perfect GaN peaks are observed to be at 6.81 eV and 10.85 eV. The first peak is closely related to the direction transition from the valence band top to the conduction band bottom. Furthermore, it is also observed that a peak is located at 4.04 eV in the low energy, which can be understood as resulting from the electron transition inside the valence band. The optical absorption edge of the intrinsic GaN is 3.25 eV, corresponding to the transition energy. The reason why this energy is smaller than the bandgap is because the electronic band gap equals the sum of optical bandgap and exciton energy. However, the maximum absorption coefficients of these two systems both occur at 13.80 eV in energy. The refractive index for intrinsic system is 2.39, and it increases to 2.48 after doping the Fe element. It is found from the energy-loss spectrum that the maximum energy-loss is at 20.02 eV for a perfect system, while it is at 18.96 eV for a doped system. Additionally, we obtain the reliable reflectivity and excitation coefficient. In conclusion, our calculated results provide a well theoretical basis for the theoretical research on the co-doping of Fe element and other elements. The analyses on the Fe-doped GaN high-voltage photoconductive switch materials and devices also provide a powerful theoretical basis and experimental support in the future research.
Influence of eikonal-initial-state on ionization of atom by proton
Authors: Chen Zhan-Bin  , Ma Kun  ,   College of Science, Hunan University of Technology, Zhuzhou 412007, China;,   School of Information Engineering, Huangshan University, Huangshan 245041, China
Published: December 2020

Apart from its fundamental importance, ionization phenomenon of atoms by impact of energetic charged particles has practical applications in various kinds of plasmas, in radiation physics and in the study of penetration of charged particles through matter. Compared with other processes, this particular reaction helps to reveal many details about the dynamical process and the level population, and, in fact, can provide a new insight into and a promising route to studying the e-p interactions in the presence of Coulomb field. The development of ion sources producing multiply charged ions and of antiproton beams allow us to change the potentials and hence the whole final momentum distribution. A great variety of experimental conditions allowed by changing the projectile charge and velocity constitute a stringent test for theory. The continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximation model has emerged as a reliable method to compute cross sections for different projectile/target combinations from intermediate to high non-relativistic impact energies. This model is of the first order in a distorted-wave series. It takes into account the long-range behaviour of the Coulomb potential and includes the distortion of the target states in both the initial and final channels. In the present work, the single different cross sections (SDCS), double different cross sections (DDCS), and total cross sections for single ionization of 1s, 2s and 2p shell of Ne atom by impact of proton are calculated in the framework of continuum-distorted-wave (CDW) method and the CDW-EIS approximation model, respectively. The influence of the eikonal-initial-state on the cross section, and the mechanism of the proton-atom collision ionization are discussed in detail. Moreover, the structures of the SDCS and DDCS of each shell are studied and the ionization mechanism of soft collision, electron capture to the continuum state, binary encounter collision are demonstrated. Our results show that for the 2p shell of Neon, as the incident proton energy increases, the region of the SDCS becomes larger and the soft ionization turns dominant in the low energy region. The eikonal-initial-state effect on the cross section is obvious in the lower energy region, yet smaller as the incident energy increases. These effects on the DDCS are greater than on the SDCS. The present CDW-EIS and CDW results are compared with the experimental data available in the energy range of 1-5000 keV/u for H+ on Ne in the literature, showing that they are quantitatively in good agreement. In general, the CDW-EIS describes well the multiple ionization above 50 keV/u, showing a clear tendency to coalesce with the CDW at high energies.
Radiation effect and degradation mechanism in 65 nm CMOS transistor
Authors: Ma Wu-Ying  , Yao Zhi-Bin  , He Bao-Ping  , Wang Zu-Jun  , Liu Min-Bo  , Liu Jing  , Sheng Jiang-Kun  , Dong Guan-Tao  , Xue Yuan-Yuan  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Xi'an 710024, China;,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Radiation effect of deep submicron semiconductor device has been extensively studied in recent years. However, fewer researches laid emphasis on the degradation characterization induced by total ionizing dose (TID) damage in nano-device. The purpose of this paper is to analyze the TID effect on the 65 nm commercial complementary metal oxide semiconductor transistor. The n-type and p-type metal oxide semiconductor field effect transistors (NMOSFET and PMOSFET) with different sizes are irradiated by 60Co γ rays at 50 rad (Si)/s, and TID is about 1 Mrad (Si). Static drain-current ID versus gate-voltage VG electrical characteristics are measured with semiconductor parameter measurement equipment. The irradiation bias of NMOSFET is as follows:the ON state is under gate voltage VG=+1.32 V, drain voltage VD is equal to source voltage VS (VD=VS=0), and the OFF state is under drain voltage VD=+1.32 V, gate voltage VG is equal to source voltage VS (VG=VS=0). The irradiation bias of PMOSFET is follows:the ON state is under gate voltage VG=0 V, drain voltage VD is equal to source voltage VS (VD=VS=1.32 V), and the OFF state is under VD=VG=VS=+1.32 V. The experimental results show that the negative shifts in the threshold voltage are observed in PMOSFET after irradiation. Besides, for PMOSFET the degradation of the ON state during radiation is more severe than that of the OFF state, whereas comparatively small effect are present in NMOSFET. Through experimental data and theoretical analysis, we find that the changes in the characteristics of the irradiated devices are attributed to the building up of positive oxide charges in the light doped drain (LDD) spacer oxide, rather than shallow trench isolation oxide degradation. The positive charges induced by TID in PMOSFET LDD spacer oxide will lead to the change of hole concentration in channel, which causes the threshold voltage to shift. What is more, the difference in electric field in the LDD spacer is the main reason for the difference in the radiation response between the two radiation bias conditions. Radiation-enabled technology computer aided design used to establish two-dimensional mode of the transistor. The simulation results of ID-VG curves are in good agreement with the experimental results. Combining theoretical analysis and numerical simulation, the radiation sensitive regions and the damage physical mechanism and radiation sensitivity regions of PMOSFETs are given. This work provides the helpful theory guidance and technical supports for the radiation hardening of the nano-devices used in the radiation environments.
Compressed sensing based fast method of solving the electromagnetic scattering problems for threedimensional conductor targets
Authors: Ding Ya-Hui  , Sun Yu-Fa  , Zhu Jin-Yu  ,   School of Electronics and Information Engineering, Anhui University, Hefei 230601, China
Published: December 2020

The method of moments is one of the most commonly used algorithms for analyzing the electromagnetic scattering problems of conductor targets. However, it is difficult to solve the matrix equation when analyzing the electromagnetic scattering problem of the electric large target. In recent years, the theory of the compressed sensing was introduced into the method of moments to improve the computation efficiency. The random selected impedance matrix is used as a measurement matrix, and the excitation voltage is used as a measurement value when using compressed sensing theory. The recovery algorithm is used to solve the induced current of target. The method can avoid the inverse problem of matrix equation and improve the computational efficiency of the method of moments, but it can be applied only to 2-dimensional or 2.5-dimensional target. The application of compressed sensing needs to know the sparse basis of the current in advance, but the induced current of three-dimensional target which is expressed by an Rao-Wilton-Glisson basis function is not sparse on the commonly used sparse basis, such as discrete cosine transform basis and discrete wavelet basis. To solve this problem, a method of combining compressed sensing with characteristic basis functions is proposed to analyze the electromagnetic scattering problem of three-dimensional conductor target in this paper. The characteristic basis function method is an improved method of moments. The target is divided into several subdomains, the main characteristic basis functions are comprised of current bases arising from the self-interactions within the subdomain, and the secondary characteristic basis functions are obtained from the mutual coupling effects of the rest of the subdomains. Then a reduction matrix is constructed to reduce the order of matrix equation, and the current can be expressed by the characteristic basis function and its weighting coefficient. In the method presented in this paper, the weighting coefficient is considered as a sparse vector to be solved when the characteristic basis function is used as sparse basis. The number of weighting coefficients is less than the number of unknown ones, so it can be obtained from the compressed sensing recovery algorithm. At the same time, the generalized orthogonal matching pursuit algorithm is used as the recovery algorithm to speed up the recovery process. Finally, the proposed method is used to calculate the radar cross sections of a PEC sphere, nine discrete PEC targets and a simple missile model. The numerical results validate the accuracy and efficiency of the method.
Separate estimation of laser micro-Doppler parameters based on maximum likelihood schemes
Authors: Guo Li-Ren  , Hu Yi-Hua  , Wang Yun-Peng  , Xu Shi-Long  ,   State Key Laboratory of Pulsed Power Laser Technology, College of Electronic Engineering, National University of Defense Technology, Hefei 230037, China;,   Anhui Province Key Laboratory of Electronic Restriction Technology, College of Electronic Engineering, National University of Defense Technology, Hefei 230037, China
Published: December 2020

Laser micro-Doppler (MD) effect is capable of obtaining obvious modulation in weak vibration detection. It helps to estimate target micro-motion parameters with high precision, which may extend the application field of MD to subtle identification and recognition. In laser detection, the multiple scattering points in the field of view will generate the single-channel multi-component (SCMC) signal. Moreover, the micro-Doppler features of each component will be overlapped in the time-frequency domain because of the similar micro-motion parameters. The overlapped SCMC signal makes the estimation of the MD parameters a very difficult problem, and there has been no good method so far. In this paper, a separate parameter estimator based on the maximum likelihood framework is proposed to deal with this underdetermined problem. First, the detailed period scanning method is presented to improve the estimation accuracy of micro-motion frequency from the singular value ratio (SVR) spectrum. Further, the amplitude ratio information of each component is extracted from the SVR spectrum. Then, the closed-form expressions of the maximum likelihood estimation (MLE) for the remaining micro-motion parameters are derived, where the mean likelihood estimation is used to approximate to the performance of MLE. The high nonlinearity and multi-peak distribution shape of the likelihood function (LF) in laser MD signal will lead to incorrect estimation result. To this end, a new LF based on the energy spectrum characteristics is designed. The new LF acts as a smoothing filter to the probability density function, through which the ideal PDF distribution form that has only one smooth peak is obtained. With this modification, the requirements for the initialization are reduced and the robustness in low SNR situation is increased. The Markov chain Monte Carlo sampling is employed to implement the MLE. The Gibbs method is chosen to solve the multi-dimensional parametric problems, and the detailed process is listed. In the end, the simulation results prove the feasibility and high efficiency of the proposed method. The accuracy of parameter estimation reaches the Cramer-Rao boundary. The inverse Radon transform is used as a comparison with the experiment, and the results show the precise estimation advantage of the presented method.