bluuebunny/crossref_metadata_2025 huggingface dataset:
D-brane interaction, the open string pair production and its enhancement plus its possible detection
Authors: Lu Jian-Xin , Zhang Nan ,   Peng Huanwu Center for Fundamental Theory, The Interdisciplinary Center for Theoretical Study, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

This review article reports the recent studies, based on a series of publications by one of the present authors along with his collaborators, regarding the interaction between two D-branes, the open string pair production and its possible enhancement in Type II superstring theories. Specifically, computed is the interaction amplitude between two D-branes, placed parallel at a separation, with each carrying a general worldvolume constant flux, and discussed are the amplitude properties, say, the repulsive or attractive nature of the interaction. When at least one of the D-branes carries an electric flux, the interaction amplitude can have an imaginary part, reflecting the instability of the underlying system via the open string pair production. The decay rate and the pair production rate are both computed. In addition, the enhancement of the latter is found when the added electric and magnetic fluxes are correlated in both magnitude and direction in a certain manner. In particular, when one of the branes is D3 and the other is D1, the corresponding pair production rate becomes large enough to be tested in an earthbound laboratory. Note that the pair production rate is related to the brane separation along the direction transverse to both branes, therefore, to the extra-dimensions with respect to the brane observer. So if the underlying string theory is relevant and the D3 can be taken as our own 4-dimensional world, measuring, say, the electric current due to the pair production and comparing it against the added electric and magnetic fields to see if the measurements agree with the prediction of the computations. This can be used to verify the existence of extra-dimensions. Further, this provides also a potential new means to test the underlying string theory without the need of compactifying it to four dimensions.
Electrodynamic characteristics of λ-DNA molecule translocating through the microfluidic channel port studied with single molecular fluorescence imaging technology
Authors: Wang Qiong , Wang Kai-Ge , Meng Kang Kang , Sun Dan , Han Tong Yu , Gao Ai-Hua ,   National Center for International Research of Photoelectric Technology and Nano-Functional Materials and Application, State Key Laboratory of Cultivation Base for Photoelectric Technology and Functional Materials, Laboratory of Photoelectric Technology of Shaanxi Province, Institute of Photonics and Photon-Technology, Northwest University, Xi’an 710069, China,   School of Physics, Northwestern University, Xi’an 710069, China
Published: December 2020

Manipulating a single DNA molecule and effectively introducing it into and exporting micro-nano-fluidic channels are prerequisites for the functional DNA biochips. And it is the key to the precise separation and screening of different DNA molecules by the micro-/nanochannel system that accurately understanding the movement characteristics and dynamic mechanism of DNA molecules moving near the channel port. In this paper, the electrodynamic characteristics of λ-DNA molecule entering into/leaving off a 50 μm channel port driven by the electric field force are systematically investigated and analyzed by the single molecule fluorescence microscopy. The experimental results indicated that there were the maximum (Emax) and minimum (Emin) thresholds of the applied electric field intensity, and only when the field intensity E meets Emin ≤ E ≤ Emax, the single λ-DNA molecule could successfully enter into the trans port and exit out of the cis port; when the electric field intensity was less than the minimum threshold, E ≤ Emin, λ-DNA molecules could not enter the trans port; when the electric field intensity was greater than the maximum threshold, Emax ≤ E, λ-DNA molecules could move into the microchannel through the trans port, but not exit out of the cis port. When λ-DNA molecule migrated toward the cis port along the channel, the movement state was changed, some new phenomena were observed, e.g. the translocation direction was reversed, reciprocated, or even rotated; moreover, the DNA molecules were easy to adhere to the channel wall. In addition, when the electric field intensity enhanced, the distance between the position where DNA molecular direction reversing and the cis port was increased. Based on the microfluidic electrodynamics, the physical mechanism of the velocities and translocation states of single λ-DNA molecule passing microchannel port was preliminarily analyzed. The results of this study have certain practical guiding significance for the development of gene chip laboratory and DNA molecular sensors based on the micro/nanochannel fluidic system.
Axial driving characteristics of water in rotating black phosphorus nanotubes
Authors: Zhang Zhong-Qiang , Fan Jin-Wei , Zhang Fu-Jian , Cheng Guang-Gui , Ding Jian-Ning ,   Institute of Intelligent Flexible Mechatronics, Jiangsu University, Zhenjiang 212013, China,   Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164, China
Published: December 2020

Since the advent of two-dimensional materials, the micro/nano technology has been greatly developed, and the design of micro/nano fluid devices has become an important research area. As a new two-dimensional material, the black phosphorus (BP) has attracted wide attention because of its excellent properties such as anisotropy, and it has been applied to many areas. In this paper, the axial motion properties of water molecules in the rotating black phosphorus nanotube (BPNT) are studied by the molecular dynamics method. The results show that water molecules in the rotating chiral BPNT can move along the axis, and the moving direction of water molecules is determined by the rotating direction of the nanotube. The velocity of water molecules and the resultant force of water molecules received from the nanotube in the axial direction increase with the angular velocity increasing. The friction coefficient and slip characteristics of the water-BP interface are calculated by using the Couette flow model, and it is clarified that the natural anisotropic microstructure on the surface of BP is the essential reason for the axial motion of water molecules in the rotating BPNT. Besides, we construct a model of filling water molecules between two BPNTs. It is found that the axial movement of water molecules between two nanotubes will be enhanced when the internal and external tube rotate simultaneously. The radius of the nanotubes will also affect the directional motion of the water molecules. Specifically, at the same angular velocity of BPNTs, with the increase of the radius, the axial motion velocity of water molecules in the BPNT will decrease, while the force received from the BPNT will increase. The axial motion of water molecules in the double-walled BPNT is little different from that in the single-walled BPNT, which proves that the number of layers has no significant influence on the driving effect of water molecules. The influence of temperature on the motion properties of water molecules depends on the coupling effect of pressure and temperature in the tube on the convection-solid interface friction coefficient. When the temperature is lower than the normal temperature, the axial velocity of water molecules and the force exerted by the BPNT will increase with the increase of temperature, and when the temperature reaches the normal temperature, it will become stable. The results will provide a theoretical basis for the study of the flow characteristics of the fluid in BPNTs and the application of the fluid drive devices based on BPNTs.
Atmospheric CO2 column concentration retrieval based on high resolution laser heterodyne spectra and evaluation method of system measuring error
Authors: Sun Chun-Yan , Wang Gui-Shi , Zhu Gong-Dong , Tan Tu , Liu Kun , Gao Xiao-Ming ,   Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China,   University of Science and Technology of China, Hefei 230026, China,   School of Electronic Engineering, Huainan Normal University, Huainan 232038, China
Published: December 2020

In this paper, a near-infrared laser heterodyne spectrometer developed by the laboratory is used to investigate the inversion of greenhouse gas column concentration and approximately evaluate the system measurement errors based on the optimal estimation algorithm. Firstly, the spectral database and the calculation results from the reference forward model are compared with the ground-based FTIR results, thereby selecting the detection window, the corresponding laser and detector. Secondly, the optimal estimation concentration inversion algorithm based on the reference forward model is established, and the Levenberg-Marquardt (LM) iterative method is adopted to realize the inversion of the concentration and vertical distribution profile of atmospheric CO2 column in the whole layer, and the long-term observation comparative experiment is carried out to verify the feasibility of this algorithm. Finally, by simulating the selected detection window spectrum in different white noise, the approximate corresponding relationship between the system signal-noise-ratio (SNR) and CO2 column concentration measuring error is eventually obtained. This research is an indispensable theoretical calculation part of the detection system and will conduce to improving the application of laser heterodyne technology in atmospheric observations.
Phase field crystal simulation of effect of misorientation angle on low-angle asymmetric tilt grain boundary dislocation motion
Authors: Qi Ke-Wu , Zhao Yu-Hong , Tian Xiao-Lin , Peng Dun-Wei , Sun Yuan-Yang , Hou Hua ,   Material Science and Engineering Institute, North University of China, Taiyuan 030051, China
Published: December 2020

Grain boundary affects the microstructure of metal material, and thus further its macroscopic properties. As is well known, under the action of applied stress, the grain boundary migrates. The structures and arrangements of grain boundary dislocations at different misorientation angles are very different, which affects the macrophysical and chemical properties of metal crystal. Therefore, it is of great theoretical and practical significance to study the dislocation structure and reaction mechanism of grain boundary under different misorientations for further studying the material properties.The phase field crystal method is used to simulate the low-angle asymmetric tilt grain boundary structure and dislocation motion on a nanoscale. From the perspective of the change of the position of the grain boundary dislocation motion under the applied stress and the change of the free energy of the crystal system, the influences of the misorientation angle on the low-angle asymmetric tilt grain boundary structure and the motion of the grain boundary dislocation are analyzed. The results show that the types of dislocation pairs of low-angle asymmetric tilt grain boundaries at different misorientation angles are the same. With the increase of misorientation angle, the grain boundary dislocation pairs increase, and n1n2 and n4n5 type dislocation pairs are more easily formed at the grain boundaries. Under the action of applied stress, the initial movement states of the grain boundary dislocation pairs at different misorientation angles are all climbing along the grain boundaries. As the system energy accumulates, the larger the misorientation angle is, the more the number of decomposed grain boundary dislocation pairs decomposed will be, and only in the dislocation pairs of n1n2 and n4n5 type there occurs decomposition reaction. There are four stages in the free energy curve of the low-angle asymmetric tilt grain boundary system at different misorientation angles, which correspond to the dislocation pairs climbing, dislocation pairs sliding and decomposition, dislocation pairs reaction to form single crystal, and the free energy rising process of the system. Further research shows that as the misorientation angle increases, the time for the single crystal system formed by the dislocation of grain boundary pairs to annihilate is required to be long.
Numerical design of frequency-split Weyl points in Weyl metamaterial
Authors: Zhou Xiao-Xi , Hu Chuan-Deng , Lu Wei-Xin , Lai Yun , Hou Bo ,   Collaborative Innovation Center of Suzhou Nano Science and Technology, School of Physical Science and Technology, Soochow University, Suzhou 215006, China,   Shenzhen Fantwave Tech. Co., Ltd., Shenzhen 518000, China,   National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

Weyl semimetal has the massless and chiral low-energy electronic excitation charateristic, and its quasi-particle behavior can be described by Weyl equation, and may lead to appealing transport properties, such as Fermi arc surface state, negative magnetic resistance, chiral Landau level, etc. By analogous with Weyl semimetal, one has realized Weyl point degeneracy of electromagnetic wave in an ideal Weyl metamaterial. In this article, by breaking the mirror symmetry of the saddle-shaped meta-atom structure, we theoretically investigate chirality-dependent split and shift effect of Weyl point frequencies which would otherwise be identical. The frequency shift can be tuned by the symmetry-broken intensity. Finally, we study the Fermi arc surface state connecting two Weyl points on \begin{document}$\left\langle {001} \right\rangle $\end{document} crystal surface.
Measurement of magnetic field of capacitor-coil target using proton radiography
Authors: Han Bo , Liang Ya-Qiong ,   Department of Astronomy, Beijing Normal University, Beijing 100875, China,   School of Logistic, Beijing Wuzi University, Beijing 101149, China
Published: December 2020

Proton radiography is a widely used method to diagnose the electromagnetic field of plasma. When protons pass through the electromagnetic field of plasma, they are deflected by Lorentz force and redistributed on the recorder. How to reconstruct electromagnetic field from the experimental result is an open problem. In this paper, we take the laser-driven capacitor-coil target for example to introduce and compare particle tracing and flux analysis, which are two widely used methods in proton radiography experiment to reconstruct the magnetic field. The capacitor-coil target is an important method to generate strong magnetic field in laser plasma experiment, where the strong current flows in the coil and its producing magnetic field may be larger than kilotesla. Firstly, the theoretical magnetic fields of capacitor-coil target are calculated with current being 10 kA and 50 kA. Secondly, the Geant4 is used to simulate the proton radiographs, where protons with 7.5 MeV pass through the target and the theoretical magnetic field is recorded. Thirdly, the theoretical proton radiographs are analyzed by the flux analysis method, and two magnetic fields are reconstructed. Finally, the theoretical magnetic fields are compared with the reconstructed ones, and the advantages and disadvantages of these two methods are analyzed. Particle tracing rebuilds the geometry distribution of proton source, plasma magnetic field and recorder in experiment, and it needs few assumptions. However, it strongly relies on accurate calculation of theoretical magnetic field and proton trajectory, and it requires to change the magnetic field over and over to achieve a closest result to the experimental proton radiograph. Meanwhile, particle tracing method consumes a lot of computation sources. The flux analysis directly reconstructs the magnetic field from experimental proton radiograph. However, it is only applicable to the case of weak magnetic field, and the error becomes larger for the case of stronger magnetic field. A dimensionless parameter μ is used to estimate the deflection of proton in the magnetic field, which measures the amount of deflection per unit length in the interaction region. The flux analysis method is applicable to the \begin{document}$\mu\ll 1$\end{document} regime. Additionally, the target may absorb the proton when the energy of proton is low and produces shadow on the proton radiograph, which leads to some difference between the original magnetic field and the reconstructed result.
Magnetopolaron-state lifetime and qubit decoherence in donor-center quantum dots with the electromagnetic field
Authors: Bai Xu-Fang , Chen Lei ,   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

Recently, the measurement scheme of quantum dot qubit decocoherence quantized by the longitudinal optical (LO) phonon spontaneous emission rate has attracted the attention and discussion of many researchers. However, it is not difficult to see that the above-mentioned measurement scheme still has some insufficient and imperfect aspects that are to be studied urgently. Considering from the physical mechanism, the essence of the above scheme is to quantify the decoherence time of qubit by using the excited state decay time or excited state lifetime of the polaron. However, so far, there is little research on how the ground state decay time and ground state lifetime of two-state polaron affect the coherence of qubit. There is no doubt that this is an equally important research topic. This is because, firstly, for the coherence of the quantum state of polaron, both the decay of the excited state and the decay of the ground state will destroy or attenuate the qubit coherence, secondly, the transition rate of the two-state polaron from the ground state to the excited state after absorbing an LO phonon is also a function quantifying the qubit decoherence time of two-state system of which the inverse is called the ground state decay time or the ground state lifetime. It may be called a measure of qubit decoherence time quantized by the ground state decay time or ground state lifetime of polaron. In this article, the ground-state and excited-state energy and wave function of the magnetopolaron in a donor-center quantum dot with asymmetric Gaussian potential are derived by Lee-Low-Pines transformation and Pekar-type variational methodd, and then the two-level structure for a qubit is constructed. The measure of qubit decoherence time of quantum dots quantified by ground state decay time of two-state polaron is established, which is compared with the well-known measure of qubit decoherence time of quantum dots quantified by polaron excited state decay time, and their physical mechanisms are revealed. By studying the influence of dielectric constant ratio, electro-phonons coupling constant, temperature and electromagnetic field on the ground state lifetime of magnetopolaron in the donor-center quantum dots with asymmetric Gaussian potential, the influences of material properties, temperature, electromagnetic field and other environmental factors on qubit decoherence of quantum dots are revealed, thereby revealing the mechanism of qubit decoherence caused by LO phonon effect.
Study on the ground state properties and excitation properties of C18 under different external electric fields
Authors: Li Shi-Xiong , Chen De-Liang , Zhang Zheng-Ping , Long Zheng-Wen , Qin Shui-Jie ,   School of Physics and Electronic Science, Guizhou Education University, Guiyang 550018, China,   College of Big Data and Information Engineering, Guizhou University, Guiyang 550025, China,   College of physics, Guizhou University, Guiyang 550025, China,   Key Laboratory of Photoelectron Technology and Application, Guizhou University, Guiyang 550025, China
Published: December 2020

In this work, density functional theory method with the ωB97XD/def2-TZVP level is carried out to investigate the ground state structures, energy, electronic structures, aromaticity, infrared and Raman spectra of cyclo[18]carbon under different external electric field in the x, y and z direction of cyclo[18]carbon molecule. The excitation properties (the first 48 excited states containing excited energies, excited wavelengths and oscillator strengths) of cyclo[18]carbon are calculated by the time-dependent density functional theory method (TD-ωB97XD) with the def2-TZVP basis set under the same external electric field. The results show that cyclo[18]carbon can be elongated in the x or y direction under the electric field, and some C-C bond lengths can be elongated or shortened under the electric field. Meanwhile, the calculated results show that electric dipole moment is proved to be increasing with the increase of the external field intensity, but the total energy and LUMO-HOMO gap are proved to decrease with the increase of external field intensity. Moreover, addition of electric field can modify the electron delocalization and molecular aromaticity, such as external electric field in z direction can lower the electron delocalization and molecular aromaticity and external electric field in x or y direction can enhance the electron delocalization and molecular aromaticity. The addition of electric field can modify the infrared spectra, such as shift of vibrational frequencies and strengthening of infrared peaks. Furthermore, the calculated results indicate that the external electric field has significant effects on the excitation properties of cyclo[18]carbon. The increase of the electric field intensity can lead to the redshift of transition wavelengths (such as the first excited state). With the change of the electric field intensity, the stronger excited state (with the bigger oscillator strength) can become weak (with the small oscillator strength) or optically inactive (with the oscillator strength of zero). Meanwhile, the weak or optically inactive excited state can become stronger excited state by the external field. The ground state properties and excitation properties of cyclo[18]carbon can be modified by the external electric field. Our works can provide theoretical guidance for the application of cyclo[18]carbon in the nanotechnology such as molecular device.
Slowly spreading propagation characteristics of flying electromagnetic toroid
Authors: Wang Ren , Liu Sheng , Zhang Mo-Ran , Wang Bing-Zhong ,   Institute of Applied Physics, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

As a new kind of electromagnetic pulses with finite energy, the flying electromagnetic toroid (FET), also called as the flying electromagnetic doughnut, has significant potential applications, such as the excitation of anapole non-radiation mode and the acceleration of charged particles. To show the propagation characteristic of FET, the spatial distribution and spectrum characteristic of the transverse and longitudinal components of FET and its topology evolution in the propagation process are discussed in this paper. Without loss of generality, we theoretically research the longitudinal field and transverse field of the transverse magnetic (TM) FET based on the real part of FET’s propagation equations. The field distribution, topology, and spectrum when the FET propagates to different positions can be calculated by assigning corresponding values to the time variable in FET’s propagation equations, therefore, the propagation characteristics of FET can be studied accurately in theory. The magnetic field of TM FET is distributed into rings in the plane vertical to the propagation direction and the electric field of TM FET is rotated around the magnetic field, which means the FET has a hypertorus topology. All the field components of FET are rotationally symmetric in the plane vertical to the propagation direction. The FET’s center is the maximum position of the longitudinal electric field component and the null position of the transverse electric and magnetic field components. Maximum values of FET’s longitudinal field are always located on the central line of FET’s propagation path and decrease gradually in the propagation process. Different from the longitudinal field, the maximum value of FET’s transverse field gradually moves away from FET’s center. The theoretical research indicates that the FET spreads quite slowly in its early propagation state and spreads linearly after propagating a long distance, which has the slowly spreading propagation characteristic even in the so-called focused range with stable toroidal topological structure. The further spectrum analysis shows that the high-frequency components spread less than the low-frequency components and the high-frequency components play a vital role in the topology retention of FET in the focused range, which may provide a basis for the generation and application of FET. At present, the theoretical research on FET’s characteristics is increasingly improved. To apply the attractive characteristics of FET in actual systems, it is necessary to actually generate FET. Therefore, the generation method of FET should become the next research emphasis.
Theoretical study on ignition of titanium alloy under high temperature friction condition
Authors: Liang Xian-Ye , Mi Guang-Bao , Li Pei-Jie , Huang Xu , Cao Chun-Xiao ,   Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China,   Institute of Titanium Alloy, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China,   Key Laboratory on Advanced Titanium Alloys of AECC, Beijing 100095, China
Published: December 2020

Combustion of titanium alloy is a typical catastrophic failure of modern aeroengine. The abnormal friction between compressor rotor and stator is the main ignition source. A thermal theory model with friction heat source of titanium alloy is established based on the theory of heterogeneous ignition. The corresponding equation of critical temperature and ignition delay time are derived. The difference between the frictional ignition model and the classic model is discussed. The concept of critical heat generation temperature is proposed. The difference from the heterogeneous ignition model, and the effects of friction coefficient, oxygen concentration, flow velocity, contact radius and flame retardant layer thickness on the ignition parameters are analyzed. The research result shows that when the instantaneous temperature of the contact surface is lower than the critical heat temperature, the heat generation process is dominated by frictional heat, and when the temperature is higher than the critical heat temperature, the heat generation process is dominated by chemical reaction heat, that reducing the coefficient of friction can dramatically increase the critical temperature, but the change of friction coefficient has very little effect on the ignition delay time which can be ignored, that the critical temperature decreases significantly with the increase of oxygen concentration and the decrease of flow velocity. When the oxygen concentration increases from 21% to 42% and the flow velocity decreases from 310 m/s to 50 m/s, the critical temperature decreases by about 213 K and 197 K, respectively. The relative error between the experimental result and the theoretical result is 8.3%, which verifies the reliability of the model. The contact area has an effect on friction heat generation, reaction heat generation, and surface heat dissipation, and has a great influence on the critical temperature. The critical temperature decreases exponentially with contact radius increasing. When the contact radius increases to 0.007 m, the ignition temperature of the titanium alloy and its flame retardant layer are 899 K and 988 K, respectively. The increase of the thickness of flame retardant layer can effectively improve the critical temperature and ignition delay time. The critical temperature of titanium alloy with flame retardant layer is increased by about 172 K, and the ignition delay time is increased by about 3 s.
Fast structured illumination three-dimensional color microscopic imaging method based on Hilbert-transform
Authors: Qian Jia , Dang Shi-Pei , Zhou Xing , Dan Dan , Wang Zhao-Jun , Zhao Tian-Yu , Liang Yan-Sheng , Yao Bao-Li , Lei Ming ,   State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China,   School of Optoelectronics, University of Chinese Academy of Sciences, Beijing 100049, China,   School of Science, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

As a wide-field microscopy, structured illumination microscopy (SIM) enables super-resolution and three-dimensional (3D) imaging. It has recently received lots of attention due to the advantages of high spatial resolution, short image recording time, and less photobleaching and phototoxicity. The SIM has found numerous important applications in time-lapse imaging of living tissues and cellular structures in the field of biomedical science. Color information is an important physical quantity describing the characteristics of living creatures and reflects the differences in its microstructure and optical property to some extent. Although HSV (hue, saturation, value) color space based structured illumination full-color 3D optical sectioning technique can recover the full color information on the surface of the samples without color distortion. However, for each optical sectioning, three raw images with fixed phase shift are required to calculate the sectioning images by the rootmean square (RMS) algorithm. This will dramatically increase the data acquisition time and data storage space, especially for a large-scaled sample that needs image stitching strategy. The image processing progress operated in HSV color space need to run the RMS algorithm three times in each channel of HSV space for every section, and transform the images between RGB (red-green-blue) space and HSV space twice. This will absolutely extend the data processing time and put forward higher requirements for computer hardware and software for data storage and processing. To this end, in this paper, a fast 3D color optical sectioning SIM algorithm based on Hilbert-transform is proposed. The Hilbert-transform has proved to be a powerful tool in digital signal and image processing and has successfully applied to the SIM. Here, only two raw images with structured illumination are needed to reconstruct a full-color optical sectioned image for each slice. This fast 3D color sectioning method has the advantage of insensitivity to phase-shift error and has better adaptability to noise, high quality color sectioning images can be obtained under the phase-shift error or noise disturbed environment. The image acquisition data are reduced by 1/3 and the color optical sectioning reconstruction time is saved by about 28%, this new method effectively improves the efficiency and speed for 3D color imaging and will bring a wider application range for SIM.
A compact model of shield-gate trench MOSFET based on BSIM4
Authors: Jiang Yi-Xun , Qiao Ming , Gao Wen-Ming , He Xiao-Dong , Feng Jun-Bo , Zhang Sen , Zhang Bo ,   State Key Laboratory of Electronic Thin Film and Integrated Devices, University of Electronic Science and Technology of China, Chendu 610054, China,   CSMC Technologies Corporation, Wuxi 214028, China
Published: December 2020

Shield-gate trench MOSFET in a low-to-medium voltage range (12－250 V) plays a key role in the power conversion market due to its low power loss caused by the sheild-gate structure. In order to eliminate the faults resulting from the parasitic effects of the device and improve the conversion efficiency, the device model is indispensable in designing a circuit system. In this paper, a compact model of shield-gate trench MOSFET based on BSIM4 is proposed, including the DC model and the capacitance model. In the DC model, the basic MOSFET structure uses BSIM4, and the equivalent resistances of the basic MOSFET in series are divided into three parts. The equivalent resistance model of JFET region is established by using the electric potential difference between both ends for the first time, and the equivalent resistance model of electron diffusion region is also introduced, in order to solve the problem of current error caused by neglecting the source potential of JFET region. The equivalent resistance between drain and JFET region and the equivalent resistance of electron diffusion region both prove to be constant. In the capacitance model based on BSIM4, the model of shield-gate to drain capacitance is added to the model of drain to source capacitance, and the voltage bias between drain and gate in the model of gate to drain capacitance is modified into the potential difference between the node at the end of the gate-drift overlap region and the gate. Poisson equations are used to solve the electric potential of this node. Furthermore, the gate oxide thickness factor k1, the shield-gate oxide thickness factor k2, the equivalent length of gate-drift overlap Lovequ and the equivalent length of shield-gate LSHequ are introduced to redefine the position of gate and shield-gate, thereby simplifying the Poisson equations and ensuring the smoothness of the potential curve of the node. Comparison of the data from the simulation by using Verilog-A program with the test results from the experimental platform shows that the model simulation results fit well with the test data, Therefore, the proposed model is verified.
Novel phenomena in flatband photonic structures: from localized states to real-space topology
Authors: Xia Shi-Qiang , Tang Li-Qin , Xia Shi-Qi , Ma Ji-Na , Yan Wen-Chao , Song Dao-Hong , Hu Yi , Xu Jing-Jun , Chen Zhi-Gang ,   TEDA Institute of Applied Physics, School of Physics, Nankai University, Tianjin 300457, China,   School of Physics, Henan Normal University, Xinxiang 453007, China,   Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan 030006, China
Published: December 2020

In recent years, flatband systems have aroused considerable interest in different branches of physics, from condensed-matter physics to engineered flatband structures such as in ultracold atoms, various metamaterials, electronic materials, and photonic waveguide arrays. Flatband localization, as an important phenomenon in solid state physics, is of broad interest in the exploration of many fundamental physics of many-body systems. We briefly review the recent experimental advances in light localization in engineered flatband lattices, with the emphasis on the optical induction technique of various photonic lattices and unconventional flatband states. The photonic lattices, established by various optical induction techniques, include quasi-one-dimensional diamond lattices and two-dimensional super-honeycomb, Lieb and Kagome lattices. Nontrivial flatband line states, independent of linear superpositions of conventional compact localized states, are demonstrated in photonic Lieb and super-honeycomb lattices, and they can be considered as an indirect illustration of the non-contractible loop states. Furthermore, we discuss alternative approaches to directly observing the non-contractible loop states in photonic Kagome lattices. These robust loop states are direct manifestation of real-space topology in such flatband systems. In this paper we do not intend to comprehensively account the vast flatband literature, but we briefly review the relevant work on photonic lattices mainly from our group. We hope that the mentioned concepts and techniques can be further explored and developed for subsequent applications in other structured photonic media such as photonic crystals, metamaterials, and other synthetic nanophotonic materials.
Research progress of terahertz semiconductor optical frequency combs
Authors: Liao Xiao-Yu , Cao Jun-Cheng , Li Hua ,   Key Laboratory of Terahertz Solid State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Science, Shanghai 200050, China,   Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Optical frequency comb consists of a series of equally spaced and highly stable frequency lines. Due to the advantages of the ultra-high frequency stability and ultra-low phase noise, the optical frequency combs have important applications in high precision spectroscopy, imaging, communications, etc. In the terahertz frequency range, semiconductor-based electrically pumped terahertz quantum cascade lasers have the characteristics of high output power and wide frequency coverage, and are the ideal candidates for generating terahertz optical frequency combs. In this article, we first briefly introduce the research progress of the optical frequency comb in the communication and the mid-infrared bands. Then we mainly review the research progress of the optical frequency combs based on the terahertz semiconductor quantum cascade laser (QCL) operating in free-running, active frequency stabilization and passive frequency stabilization modes. In free running mode, the terahertz QCL frequency comb is mainly limited by the large group velocity dispersion which results in a small comb bandwidth. Therefore, the dispersion compensation is one of the important methods to stabilize the optical frequency comb and broaden the spectral bandwidth. At present, the active frequency stabilization mode is a relatively matured method to realize the optical frequency combs in terahertz QCLs. In this article, we also detail the methods and applications of terahertz QCL dual-comb operations, including on-chip dual-comb and dual-comb spectroscopy. Compared with the Fourier transform infrared spectroscopy and time domain spectroscopy, the terahertz dual-comb spectroscopy has advantages in fast data acquisition (real-time) and high spectral resolution. The emergence of the dual-comb technique not only verifies the concept of optical frequency combs, but also further promotes the applications of frequency combs.
Preparation, doping modulation and field emission properties of square-shaped GaN nanowires
Authors: Yang Meng-Qi , Ji Yu-Hang , Liang Qi , Wang Chang-Hao , Zhang Yue-fei , Zhang Ming , Wang Bo , Wang Ru-Zhi ,   College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China,   School of Physics, Beihang University, Beijing 100191, China,   Institute and Beijing Key Laboratory of Solid Microstructure and Properties, Beijing University of Technology, Beijing 100124, China
Published: December 2020

GaN nanomaterials, as one of the most important third-generation semiconductor materials, have attracted wide attention. In this study, GaN nanowires with square cross section were successfully prepared by microwave plasma chemical vapor deposition system. The diameters of nanowires are from 300 to 500 nm and the lengths from 15 to 20 μm. The results show that the cross section of nanowires could be transformed from triangle into square by adjusting the ratio of Mg to Ga in source materials. X-ray diffraction(XRD)result indicate that the structure of GaN nanowires are agree with the hexagonal wurtzite. X-ray photoelectron spectroscopy (XPS) rusult show that a certain amount of Mg and O impurities incoporated in the square-shaped GaN nanowires. Transmission electron microscopy (TEM) result suggested that square-shaped GaN nanowires had high crystallinity with a growth direction of [\begin{document}$0\bar 110$\end{document}]. The ratio of source materials- and time-depented growth mechanism was also studied. It was suggested that the transformation of the cross section from triangle to square structure should be derived from the growth mechanism change from vapor-liquid-solid(VLS)process to vapor-solid(VS)process. The doped Mg increased the growth rate of the nanowires sidewalls, which led to a symmetrically growth of GaN nanowires along the twin boundaries. GaN nanowires gradually transformed to square structure by auto-catalytic growth. Moreover, the property of field emission were further investigated. The results showed that the turn-on electric field of square-shaped GaN nanowires was 5.2 V/m and a stable field emission property at high electric field. This research provides a new method for the preparation of square-shaped GaN nanowires and a prospective way for the design and fabrication of novel nano-scale devices.
Second harmonic generation of two-dimensional layered materials: characterization, signal modulation and enhancement
Authors: Zeng Zhou-Xiao-Song , Wang Xiao , Pan An-Lian ,   Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, School of Physics and Electronic Science, Hunan University, Changsha 410082, China,   Key Laboratory for Micro-Nano Physics and Technology of Hunan Province, State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Materials Science and Engineering, Hunan University, Changsha 410082, China
Published: December 2020

Two-dimensionl (2D) layered transition metal dichalcogenides (TMDCs) have received great attention in integrated on-chip photonic and photoelectric applications due to their unique physical properties including indirect-to-direct optical bandgap transition, broad bandgap from visible band to near-infrared band, as well as their excellent optoelectric properties derived from the 2D confinement. Recently, with the in-depth study of their fundament nonlinear optical properties, these 2D layered TMDCs have displayed significant potential applications in nonlinear optical devices. In this review, we focus on recent research progress of second harmonic generation (SHG) studies of TMDCs. Firstly, we briefly introduce the basic theory of nonlinear optics (mainly about SHG). Secondly, the several intrinsic SHG relative properties in TMDCs including layer dependence, polarization dependence, exciton resonance effect, valley selection rule are discussed. Thirdly, the latest SHG modulation and enhancement studies are presented, where the electric field, strain, plasmonic structure and micro-cavity enhancement are covered. Finally, we will summarize and give a perspective of possible research direction in the future. We believe that a more in-depth understanding of the SHG process in 2D layered TMDCs as well as the material structure and modulation effects paves the way for further developing the ultra-thin, multifunctional 2D nonlinear optical devices.
129Xeq+ induced near-infrared light and X-ray emission at Cu surface
Authors: Zhang Xiao-An , Mei Ce-Xiang , Zhang Ying , Liang Chang-Hui , Zhou Xian-Ming , Zeng Li-Xia , Li Yao-Zong , Liu Yu , Xiang Qian-Lan , Meng Hui , Wang Yi-Jun ,   Ion Beam and Optical Physical Joint Laboratory of Xianyang Normal University and Institute of Modern Physics, Chinese Academy of Sciences, Xianyang 712000, China,   Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
Published: December 2020

During the interaction of highly charged ions with solid target in the energy region near the Bohr velocity, the potential energy of the projectiles will be deposited on a nanometer-scale target surface within the time on the order of femtoseconds. That will lead the target atoms to be ionized into ions and the ions to be excited, resulting in the multiple ionization states and the complex configuration of energy levels. The de-excitation radiations of these levels cover the radiations from near-infrared spectral line to X-ray. Investigation of these spectral lines is significant for investigating the mechanism of such an interaction, diagnosing plasma and studying astrophysics. The experimental results show that the near-infrared spectral lines and X-ray spectra are produced by the 129Xeq+ (q = 21, 23, 25, 27) with kinetic energy of 1360 keV and 129Xe20+ with kinetic energy of 4 MeV impacting on the Cu surface, separately. The experiment is carried out in the National Laboratory of Heavy Ion Research Facility in Lanzhou, HIRFL. The beam intensity is on the order of nA. The highly charged ions capture the electrons of the Cu target and thus being neutralized in a femtosecond time. The energy of the highly charged ions is deposited on the target surface, and the target atoms are excited or ionized, resulting in the transition between complex configurations, such as the dipole forbidden transition (magnetic dipole and quadrupole transition) and magnetic dipole transition of the Cu22+. The infrared spectral lines of the atoms and ions from deexcitation radiation are measured. With the 4 MeV 129Xe20+ ions impacting on solid Cu surfsce, the X-rays are measured, such as, the magnetic dipole deexcitation radiation transition of Cu22+, the X-rays of the L1 edge transition and Lβ3 of the Cu I, Lη and Lβ3 X-rays of the Xe ions. The results show that during the neutrilization of highly charged Xe ions with lower energy above the Cu surface, the infrared lines are mainly from the deexcitation of the incident ions and the ionized or excited target atoms. The increasing trend of the the single ion fluorescence yield of the infrared spectral line is the same as that of the potential energy of the projectile. The characteristic L X-rays of the Xe atom are emitted by the second generation of hollow atoms formed below the surface.
Mechanical failures in solid-state lithium batteries and their solution
Authors: Liang Yu-Hao , Fan Li-Zhen ,   Institute of Advanced Materials and Technology, Beijing University of Science and Technology, Beijing 100083, China
Published: December 2020

The mechanical properties of electrode materials and solid-state electrolytes in solid-state batteries (SSBs) have an important influence on the mechanical stabilties of SSBs. Mechanical failures in SSBs on different scales and in different components will occur once the stress inside SSBs exceeds the materials’ strengths, which seriously deteriorates the electrochemical performances of SSBs. From the perspective of stabilizing the mechanical stabilities of SSBs, in this review we describe the influences of the mechanical properties of each component in SSBs on the mechanical stabilites of SSBs, and we analyze the factors that affect the mechanical properties of materials. In addition, we also discuss the mechanical failures of SSBs during cycle, including electrode materials’ or solid-state electrolytes’ fractures, electrode-electrolyte contact losses, and short-circuits due to lithium dendrites. Finally, we summarize some common strategies to mitigate the mechanical failures in SSBs, and look forward to the future research directions in this field. Overall, the mechanical failures in SSBs and their strategies discussed in this review will help researchers build SSBs with higher energy density, longer life and higher safety.