bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance characteristics of a novel high-efficientgraphene thermionic power device
Authors: Liao Tian-Jun , Lin Bi-Hong , Wang Yu-Hui ,   Department of Physics and Energy, Chongqing University of Technology, Chongqing 400054, China,   Department of Physics, Huaqiao University, Xiamen 361021, China
Published: December 2020

According to the theories of the solid physics and irreversible thermodynamics, the performance characteristics of a novel high-efficient graphene thermionic power device (TPD) are studied. The temperature of the cathode plate and anode plate are determined by solving the energy balance equation of hot and cold sides of the TPD. The effects of the output voltage and the work function of the cathode on the volt-ampere characteristics of the TPD and the temperature of the two electrodes are analyzed to determine the parametric characteristics of the TPD at the maximum power density and efficiency. The power density and efficiency are compromised, and the parametric optimal designs are given. The influence of the temperature of heat source at high temperature on optimization performance is analyzed. The results obtained here can provide theoretical guidance for developing the thermionic energy conversion devices.
Inversion for acoustic parameters of plastic polymer target in water
Authors: Zhou Yan-Ling , Fan Jun , Wang Bin ,   Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

The high-precision molding capability of complex surfaces and structures makes three-dimensional (3D) printing technology more widely used in underwater acoustic models and structural molding. The plastic polymer material, as the main material in the field of 3D printing, possesses the acoustic parameters that are directly related to the acoustic properties of 3D printed underwater acoustic models and structures. Based on the Rayleigh normal series solution for the acoustic scattering of underwater target and the mechanism analysis of the low-frequency resonance which is associated with subsonic Rayleigh waves on the solid plastic polymer spheres, the sensitivity characteristics of the resonance frequency and amplitude to the wave velocity and attenuation coefficient are obtained at low frequencies. It is shown that the transverse wave velocity and the transverse wave attenuation coefficient both have high inversion accuracy at low values of ka, where a is the radius of elastic sphere, as they are quite sensitive to the backscattering resonance frequency and amplitude, respectively. In the frequency band of interest, the backscattering resonance frequency is almost independent of attenuation coefficient. Considering the inversion accuracy, the longitudinal wave velocity and transverse wave velocity are inverted by the resonance frequency separately. Based on these characteristics, the cyclic search method is used to establish an acoustic parameter inversion method for plastic polymer materials, in which the frequency and amplitude of backscattering resonance peak are used as cost functions. Finally, the backscattering acoustic scattering experiment on a solid typical plastic polymer PMMA (methyl methacrylate-acrylic) sphere is conducted in the tank. The experimental results about the backscattering target strength varying with the frequency are in good agreement with the simulation results in a frequency range of 5–20 kHz. The simulation parameters such as the longitudinal wave velocity, transverse wave velocity and attenuation coefficient are obtained by the previously established inversion method. Therefore, the acoustic parameter inversion method provides reliable acoustic parameters for 3D printed underwater acoustic model and structure performance prediction for plastic polymer materials.
Recent progress in polarization-sensitive photodetectors based on low-dimensional semiconductors
Authors: Wei Zhong-Ming , Xia Jian-Bai ,   State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Polarized photodetection technology has good application value in the fields of remote sensing imaging, environmental monitoring, medical detection and military equipment. Polarized photodetectors based on low-dimensional materials can use the natural anisotropy of materials to detect polarized information. Some two-dimensional materials have strong in-plane anisotropy due to their low-symmetrical crystal structure, such as black-phosphorus, black-arsenic, ReS2, GaTe, GeSe, GeAs, and TiS3. These anisotropic two-dimensional materials are appropriate for the working medium of polarized photodetectors. Numerous researchs focused on polarized photodetectors with different materials and device structures and our works are introduced. Polarized photodetectors based on such low-dimensional materials have realized a broadband photodetection, including ultraviolet, visible, and infrared lights.
Spectroscopic studies of plasmons in topological materials
Authors: Wang Chong , Xing Qiao-Xia , Xie Yuan-Gang , Yan Hu-Gen ,   Department of Physics, Fudan University, Shanghai 200438, China
Published: December 2020

Plasmonics plays an important role in the development of nanophotonics, which allows breaking diffraction limit and controlling light in deep-subwavelength scale due to the strong interaction between light and free carriers. Noble metals and 2-dimensional electron gas have been the main platforms for studying plasmonics over the past decade. The metal-based plasmonic devices have exhibited great potential in various applications, including integrated photonic systems, biological sensing, super-resolution imaging and surface-enhanced Raman scattering, etc. Because of the high carrier density, plasmons of noble metals are realized in the near-infrared to visible frequency range. With the rapid development of new materials, many other plasmonic materials are discovered to exhibit new properties. One example is the graphene plasmons working in the mid-infrared and terahertz spectral range, which exhibit strong field confinement and frequency tunability due to the massless Dirac fermions and other exotic electrical and optical properties. Recently, topological materials, the band structures of which are composed of cones with linear dispersion like in graphene, are discovered, such as the topological insulators, Dirac semimetals, Weyl semimetals and nodal line semimetals, providing another platform to study the Dirac plasmons. Such linear dispersion results in small electron mass and unique carrier density dependence of plasmons. In addition, topological materials possess a tremendous amount of exotic electron properties, such as the ultrahigh mobility, topological surface states and chiral anomaly in Weyl semimetals, etc. Many of these electronic properties can be inherited by the collective oscillation of free electrons, promising new possibility for plasmonics. Here, the experimental observations of plasmons in topological insulators and topological semimetals are reviewed, with special focus on the studies based on electron energy loss spectrum and Fourier transform infrared spectroscopy. At the end, other topological materials with potential for hosting 2D plasmons are discussed. This review provides an overview of plasmons in topological semimetals and may stimulate further quest of more exotic features for plasmons.
Progress of the study on carrier scattering mechanisms of silicon/germanium field effect transistors
Authors: Zhao Yi , Li Jun-Kang , Zheng Ze-Jie ,   College of Electronic Engineering and Information Science, Zhejiang University, Hangzhou 310027, China,   Zhijiang Laboratory, Hangzhou 310000, China
Published: December 2020

As the feature size of Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) continues to decrease, large numbers of new problems appear. Techniques such as strain project, new channel materials and new device structures are considered by academics and industry to be effective ways to continue to improve device performance. In this paper, the scattering mechanism of carriers in the device channel is studied from three aspects: strain technique, new channel material and new structure device: (1) strain technique: Biaxial tensile strain can change carrier distribution among different energy levels, which affects Coulomb scattering and Coulomb mobility. Furthermore, from the TEM image, it is found that biaxial tensile reduces the channel surface roughness for Si nMOSFET, leading an enhancement of electron mobility. However, no such similar phenomena were observed in pMOSFET. Based on this, a new method for calculating the mobility of MOSFET surface roughness scattering using TEM image has been proposed. (2) New channel material: In the germanium (Ge) transistors with different crystal faces, the scattering mechanisms of electron under high field conditions are different. The phonon scattering dominates the Ge(100) transistor, while the surface roughness scattering dominates the Ge(110), (111) transistors. This result is quite different from Si MOSFET. Therefore, a unified model for the scattering mechanism of electron in Ge nMOSFET has been proposed. In SiGe transistors, alloy scattering mainly play a role in the region with relatively small effective electric field (Eeff). The strength of alloy scattering would be weakened in high field and could be decreased by reducing the thickness of SiGe layer. (3) New structure devices: In ultra-thin body germanium (GeOI) transistors, carrier transport is influenced by high- k /channel interfaces, as well as Ge channel/buried oxide (BOX) interface. As the Ge layer thickness decreases, carrier distribution is closer to the interfaces, which intensifies Coulomb scattering and surface roughness scattering. As a result, the mobility in GeOI transistor decreases as the thickness scaling. In addition, the distribution of electron in different energy valleys changes with the thickness decrease in Ge layer, which affects the scattering of electrons. When the Ge film is lower than 10 nm, a part of electron in the L valley will move to the Γ valley, causing the decrease of electron effective mass and increasing the electron mobility.
Effect of structure parameters on performance of N-polar GaN/InAlN high electron mobility transistor
Authors: Liu Yan-Li , Wang Wei , Dong Yan , Chen Dun-Jun , Zhang Rong , Zheng You-Dou ,   School of Information and Electronic Engineering, Shandong Technology and Business University, Yantai 264005, China,   School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
Published: December 2020

Based on the drift-diffusion transport model, Fermi-Dirac statistics and Shockley-Read-Hall recombination model, the effect of the structure parameters on the performance of N-polar GaN/InAlN high electron mobility transistor is investigated by self-consistently solving the Schrodinger equation, Poisson equation and carrier continuity equation. The results indicate that the saturation current density of the device increases and the threshold voltage shifts negatively with GaN channel thickness increasing from 5 nm to 15 nm and InAlN back barrier thickness increasing from 10 nm to 40 nm. The maximum transconductance decreases with GaN channel thickness increasing or InAlN back barrier thickness decreasing. The change trends of the various performance parameters become slow gradually with the increase of the thickness of the GaN channel layer and InAlN back barrier layer. When the GaN channel thickness is beyond 15 nm or the InAlN back barrier thickness is more than 40 nm, the saturation current, the threshold voltage and the maximum transconductance tend to be stable. The influence of the structure parameter on the device performance can be mainly attributed to the dependence of the built-in electric field, energy band structure and the two-dimensional electron gas (2DEG) on the thickness of the GaN channel layer and InAlN back barrier layer. The main physical mechanism is explained as follows. As the GaN channel thickness increases from 5 nm to 15 nm, the bending of the energy band in the GaN channel layer is mitigated, which means that the total built-in electric field in this layer decreases. However, the potential energy drop across this GaN channel layer increases, resulting in the fact that the quantum well at the GaN/InAlN interface becomes deeper. So the 2DEG density increases with GaN channel thickness increasing. Furthermore, the saturation current density of the device increases and the threshold voltage shifts negatively. Moreover, due to the larger distance between the gate and the 2DEG channel, the capability of the gate control of the high electron mobility transistor decreases. Similarly, the depth of the GaN/InAlN quantum well increases with InAlN back barrier thickness increasing from 10 nm to 40 nm, which results in the increase of the 2DEG concentration. Meanwhile, the electron confinement in the quantum well is enhanced. Therefore the device saturation current and the maximum transconductance increase with InAlN back barrier thickness increasing.
Phase control and stabilization in attosecond beamline with fast Fourier transform
Authors: Jiang Yu-Jiao , Gao Yi-Tan , Huang Pei , Zhao Kun , Xu Si-Yuan , Zhu Jiang-Feng , Fang Shao-Bo , Teng Hao , Hou Xun , Wei Zhi-Yi ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi’an 710071, China,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China,   Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China
Published: December 2020

With the unveiling of molecular and atomic dynamics, scientists crave finer and faster tools to communicate with the microworld. Attosecond pump-probe enjoys its reputation as the fastest camera, hinting ultrafast movements in the delay graph. To employ this camera, the stability and delay control should have very great accuracy comparable to the camera resolution. It is also of significant importance for stabilizing the carrier envelope phase (CEP) in few-cycle laser field. When dealing with a huge quantity of data, conventional Fourier transform algorism is challenging in high-speed control. Here we put forward the efficient calculation method, fast Fourier transform (FFT) algorism in Mach-Zehnder interferometer for arm length locking and f-2f for CEP locking. In the interferometer locking, 532 nm continuous wave laser is used in the Mach-Zehnder interferometer, and the phase of the FFT term corresponding to the delay between the two arms of the interferometer serves as a feedback signal on piezo transducer (PZT) in the delay line to reduce the change of the arm length. In the CEP control experiment, data to be analyzed are the f-2f spectrum interference fringes recorded by the spectrometer. The CEP values are obtained from the first order of FFT module output of the integrated spectrum interference fringes, and a labview program examines the relative phase drift and sends a feedback voltage signal to the PZT through the proportion integration differentiation module to compensate slow CEP drift after the chirped pulse amplification system by changing the insert length of a prism pair. The results show that the root mean square (RMS) of the arm length difference is 1.24 nm (4.1 attosecond for light to travel) per meter in the interferometer locking over 12 h, and the RMS of CEP is 227 mrad under 3 ms integration time in the CEP locking over 20 min. These results are able to meet the requirement of the accuracy for attosecond pulse generation and attosecond pump-probe experiments. We also use FFT to stabilize the CEP and relative time simultaneously in the waveform synthesis for 8 h (Huang P, Fang S, Gao Y, Zhao K, Hou X, Wei Z 2019 Appl. Phys. Lett. 115 031102), the phase-locking system results in a CEP stability of 280 mrad and a relative time stability of 110 as at a repetition rate of 1 kHz. These results imply that the FFT is versatile and reliable in ultrafast control.
Current collapse suppression in AlGaN/GaN high electron mobility transistor with groove structure
Authors: Liu Jing , Wang Lin-Qian , Huang Zhong-Xiao ,   Department of Electronic Engineering, Xi’an University of Technology, Xi’an 710048, China
Published: December 2020

Due to the excellent properties of GaN, such as wide band gap, high electron mobility, high saturation speed, and high breakdown electric field, AlGaN/GaN high electron mobility transistor (HEMT) possesses highly promising applications in the fields of high power, radio frequency, and high temperature applications. However, they are still subjected to the influence of current collapse which strangles its development. Based on the double-pulse technique, the effect of GaN buffer layer trap on the current collapse of AlGaN/GaN HEMT is studied. The results show that the electric field peak at the gate edge is one of the main causes of current collapse. The channel electrons are trapped by the buffer trap under the peak electric field. Because the response speed of the trap in the buffer layer is slow, the channel can not be turned on immediately after the gate voltage has jumped to 0 V, which leads the current to collapse. In this paper, the new structure is proposed by introducing a groove structure in the barrier layer. The channel two-dimensional electron gas is modulated by the groove structure, which influences the channel electric field of AlGaN/GaN HEMT device, reduces the electric field peak at the gate edge, and improves the current collapse effect of the device. Comparing with the traditional AlGaN/GaN HEMT, the inhibition effect of the new device structure on current collapse is increased by 22.30%. The length and height of the groove structure are the critical parameters to affect the new HEMT performance. The optimal parameters of length and hight show that when the length of the groove is 1 μm and the height is 0.01 μm, the current collapse of HEMT and its performance are significantly improved.
Research progress of coupling theory of metal surface plasmon
Authors: Zhu Xu-Peng , Zhang Shi , Shi Hui-Min , Chen Zhi-Quan , Quan Jun , Xue Shu-Wen , Zhang Jun , Duan Hui-Gao ,   School of Physics Science and Technology, Lingnan Normal University, Zhanjiang 524048, China,   College of Mechanical and Vehicle Engineering, Hunan University, Changsha 410082, China,   School of Mechanical and Electric Engineering, Guangzhou University, Guangzhou 510006, China
Published: December 2020

Metal surface plasmon is a collective oscillation effect of free electrons at the micro-nanostructure surface under the stimulation of incident light. Since the corresponding oscillating electric field is strongly bound below the sub-wavelength scale, it can be used as an information carrier for future micro-nano photonic circuit and device, and can also be used to enhance the interaction between light and matter on a micro-nano scale, such as surface enhanced photoluminescence, Raman scattering, nonlinear signal generation, surface enhanced catalysis, photothermal conversion, photovoltaic conversion, etc. How to theoretically understand the unique optical behavior dominated by the plasmon oscillation mode is one of the hot research spots in the field of surface plasmon photonics. In recent years, the theory of surface plasmon has been continuously improved with the support of a large number of experimental researches. In this paper, we first systematically summarize the optical behaviors and properties of metal under the excitation of incident electromagnetic waves, and then briefly describe the plasmonic modes existing in the metal and their corresponding physical natures, the oscillation dynamics process and the currently prevailing surface plasmon coupling theories. We hope that this paper can provide a theoretical basis for those researchers who have just dabbled in the field of surface plasmons and help them to master the relevant basic knowledge quickly.
Topological invariant in quench dynamics
Authors: Yang Chao , Chen Shu ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   Yangtze River Delta Physics Research Center, Liyang  213300, China
Published: December 2020

In this review, we give a brief review on the recent progress in the theoretical research of quench dynamics in topological band systems. Beginning with two band models, we introduce conception of dynamical Chern number and give the connection between the dynamical Chern number and topological invariant in the corresponding equilibrium systems. Then by studying the 1 + 1 dimensional parent Hamiltonian, we show the complete dynamical classification of Altland-Zirnbauer classes, and show the crossing of entanglement spectrum as a feature of dynamical bulk edge correspondence. Furthermore, we consider the impact of the disorder and band dispersion. At last, we show the experimental simulation of dynamical Chern number by a superconducting qubit system.
Topological and non-reciprocal phenomena in elastic waves and heat transport of phononic systems
Authors: Wang Zi , Zhang Dan-Mei , Ren Jie ,   China-EU Joint Center for Nanophononics, Shanghai Key Laboratory of Special Articial Microstructure Materials and Technology, Center for Phononics and Thermal Energy Science, School of Physics Sciences and Engineering, Tongji University, Shanghai 200092, China
Published: December 2020

Phonon is a quasi-particle excitation after the second quantization of lattice vibration. In the phonon framework, we can describe mechanics, elastic wave and thermal phenomena in solid uniformly. With the development of our understanding about solid state systems, phonon has become an important method to control device in solid state, which can be seen as a supplement and replacement for electronics and photonics. Among them, the modulation of elastic wave and heat conduction in phonon system has great theoretical and practical value. Elastic wave as an information carrier has the potential to construct new chip elements, while manipulating thermal phonon as an energy carrier can achieve the goal of energy transformation and device optimization. These fields have developed rapidly in recent years. A large number of novel materials such as thermal diodes, elastic meta-materials, thermal meta-materials, and heat pumping devices have been predicted and obtained. These developments are inseparable from the application of the concept of "topology" to phonon systems and the realization of non-reciprocal devices on various scales. In this paper, the topological and nonreciprocal phenomena in phonon systems are tentatively summarized. Besides, the latest research results are introduced and the development trend is prospected. The non-reciprocity of elastic wave and heat flow realized by time-dependent driving is reviewed with emphasis. This method has a great flexibility and can be similarly applied to multi-component systems on all scales.
Observation of planar Hall effect in topological semimetal ZrSiSe device
Authors: Wei Bo-Yuan , Bu Hai-Jun , Zhang Shuai , Song Feng-Qi ,   Center of Artificial Microstructure Science and Technology Innovation, National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

Planar Hall effect(PHE) is a newly emerging experimental tool to detect chiral anomaly and nontrivial Berry curvature in topological semimetals, as chiral-anomaly-induced negative magnetoresistance is sensitive to the angle between magnetic field B and current I. Here we demonstrate the PHE in a topological nodal-line semimetal ZrSiSe device by electric transport measurement. According to our analysis, we conclude that the PHE results from the trivial anisotropic magnetoresistance (AMR). We argue that there is no inevitability between PHE and chiral anomaly, and some other mechanisms can induce PHE. This work indicates that PHE cannot be considered as evidence of chiral anomaly and one may seek for non-topological origin in such studies.
Optical properties of topological semimetals
Authors: Xu Bing , Qiu Zi-Yang , Yang Run , Dai Yao-Min , Qiu Xiang-Gang ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
Published: December 2020

Topological semimetal represents a novel quantum phase of matter, which exhibits a variety of fascinating quantum phenomena. This class of materials not only have potential applications in electronic devices, but also represent one of the hottest topics in the field of quantum materials. According to the band structure of these materials in the three-dimensional momentum space, topological semimetals can be classified into Dirac semimetals, Weyl semimetals and nodal-line semimetals. Extensive studies on these materials have been conducted using various techniques. For example, angle-resolved photoemission spectroscopy (ARPES) has directly observed the Fermi arc that connects two Weyl points with opposite chiralities in the surface states of Weyl semimetals; the Dirac points, Weyl points as well as the Dirac nodal line in the bulk states have also been revealed by soft X-ray ARPES; the observation of negative magnetoresistance in transport measurements has been taken as the evidence for the chiral anomaly in Weyl and Dirac semimetals; the chirality of the Weyl fermions have been detected by measuring the photocurrent in response of circularly polarized light; in addition, strong second harmonic generation and THz emission have been observed, indicating strong non-linear effects of Weyl semimetals. Infrared spectroscopy is a bulk-sensitive technique, which not only covers a very broad energy range (meV to several eV), but also has very high energy resolution (dozens of µeV). Investigations into the optical response of these materials not only help understand the physics of the topological phase and explore novel quantum phenomena, but also pave the way for future studies and applications in optics. In this article, we introduce the optical studies on several topological semimetals, including Dirac, Weyl and nodal-line semimetals.
Progress on topological nodal line and nodal surface
Authors: Wang Shan-Shan , Wu Wei-Kang , Yang Sheng-Yuan ,   School of Physics, Southeast University, Nanjing 211189, China,   Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore 487372, Singapore
Published: December 2020

Electronic band crossing can not only form zero-dimensional nodal points, but also one dimensional nodal lines and two dimensional nodal surfaces. These topological band features have been attracting significant research interest, as they may lead to many special physical properties. In this article, we review the progress in this field, including the conceptual development, the character and classification of these nodal structures, and the material realization.
Scanning tunneling microscopy study on two-dimensional topological insulators
Authors: Zhang Zhi-Mo , Zhang Wen-Hao , Fu Ying-Shuang ,   School of Physics , Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Topological state is a rapidly emerging branch of condensed matter physics in recent years, among which two-dimensional topological insulators (2D TIs) have attracted wide attentions due to their great potential in basic research and applications. The 2D TI has insulating bulk state and conductive edge state. Its edge state is protected by time inversion symmetry and will not be backscattered by weak disordered impurities on the boundaries, thus forming a dissipationless edge conductive channel. Compared with 3D TIs, the edge state of 2D TIs can only propagate in two directions, meaning stronger anti-interference with robustness, thus is of great significance for the development of advanced integrated circuits with low energy consumption. Among many experimental methods for studying two-dimensional materials, scanning tunneling microscopy is a surface-sensitive tool with high atomic and energy resolution to locally detect the electronic structure of the material surface. By detecting the edge state of 2D materials in real space, it is particularly suitable for characterizing their topological properties. This paper traces the research progress of 2D TIs, and illustrates their spectroscopic evidences to resolve the nontrivial properties of the one-dimensional edge states. Combined with theoretical calculations, the topological edge states are verified to reside within the bulk energy gap, as well as being localized in the vicinity of step boundaries with a specific spatial distribution in real space. Finally, we discuss the tunability and manipulations of 2D topological materials through structural and external fields, which show promising prospects for applications in future spintronics and energy-saving devices.
Exploration of Majorana bound states in topological superconductors
Authors: Liang Qi-Feng , Wang Zhi , Kawakami Takuto , Hu Xiao ,   Department of Physics, Shaoxing University, Shaoxing 312000, China,   Department of Physics, Sun Yet-San University, Guangzhou 510275, China,   Department of Physics, Graduate School of Science, Osaka University, Osaka 565-0871, Japan,   International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba 305-0044, Japan,   Kavli Institute for Theoretical Physics, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Majorana bound states are considered useful for realizing topological quantum computation since they obey the non-Abelian quantum statistics. Recent experiments have provided evidences for their existence in some superconducting systems, triggering significant interests from scientists in the field of condensed matter physics and related materials science. In this article, we briefly review the basic concepts and recent developments in the study of Majorana bound states. We first discuss about the origin of the nontrivial topology in superconducting systems within the Bogoliubov-de Gennes mean-field scheme. Then we show the construction of Majorana quasiparticle excitations from an electronic state, and the realization of non-Abelian statistics based on position exchanges of the Majorana bound states hosted in superconductivity vortices. Afterwards we talk about specific one-dimensional and two-dimensional topological superconductors, and propose possible experimental methods for detecting Majorana bound states and operating the Majorana qubits. In particular, a quantum device for Majorana braiding without moving vortices is introduced. Finally, perspectives of the study on Majorana bound states are provided.
Ge Schottky diode for improving energy conversion efficiency of the receiver of microwave wireless power transfer
Authors: Li Yu-Chen , Chen Hang-Yu , Song Jian-Jun ,   School of Electrical and Control Engineering, Xi’an University of Science and Technology, Xi’an 710054, China,   School of Microelectronics, Xidian University, Xi’an 710071, China
Published: December 2020

Microwave wireless power transfer(MWPT) can break through the restriction of transmission line to transmit electrical energy, which is conducive to dealing with power supply in complex scenarios, and has a very large application prospect. Energy conversion efficiency is an important parameter of MWPT. Hence, researchers are focus on improving the conversion efficiency of MWPT from different ways. Schottky diode is the core component of the rectifier circuit, which determines the limit of the energy conversion efficiency. However, the research involving the design of Schottky diode has rarely reported. In this paper, a GeOI folded space charge region Schottky diode is proposed. The space charge region of the proposed Schottky diode is composed of two parts: the vertical space charge region and the horizontal space charge region. So the capacitor is also divided into two parts, namely the vertical capacitor and the lateral capacitor. In the device model, these two capacitors are in series. So the total capacitance will be reduced. This article establishes its capacitance model and completes the optimization of device material parameters and structure parameters. The designed device parameters are as follows: the doping concentration of the heavily doped buffer layer on the left side of the Ge material is 2 × 1020 cm–3 to form Ohm contact, the doping concentration of the lightly doped region on the right side is 3.8 × 1017 cm–3, the thickness of the folded region is 0.2 μm, the Schottky metal is Wu, the width of metal is 8 μm, and the length of metal is 2 μm. We use the proposed Schottky diode as the core rectifier to simulate the rectifier circuit by using ADS, in which the SPICE parameters of the proposed Schottky diode was extract using Cadence Model Editor. When the input energy is 24.5 dBm, the energy conversion efficiency reached 75.4%. Compared with the conventional schottky diode, the energy conversion efficiency is significantly improved. The study of the proposed Schottky diodes can provide valuable reference for improving the energy conversion efficiency of microwave wireless energy transmission.
Energy fluence measurement for pulse hard X-ray
Authors: Su Zhao-Feng , Lai Ding-Guo , Qiu Meng-Tong , Xu Qi-Fu , Ren Shu-Qing ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi’an 710024, China
Published: December 2020

Pulsed high-energy fluence X-ray source is based on the “Flash II” accelerator. It can be used to carry out effect vulnerability and sensitivity test of unit level system generated electromagnetic pulse (SGEMP). The energy fluence of pulsed hard X-ray is a main parameter of the equipment beam. At present, theoretical calculation method is widely used. Energy fluence can be calculated according to the dose, energy spectrum and energy absorption coefficient of each energy segment.

The principle measuring energy fluence of pulsed hard X-ray by total absorption method is introduced. The photoelectric cell with lutetium silicate (LSO) scintillator is selected as a core component of the detection system, and the measurement system is developed. It is composed of scintillation detector, LSO scintillator, dimmer film, photon collimator, visible light shielding material, power supply and signal collecting system. The conversion coefficient between the incident photon energy and the waveform parameter is calibrated by a standard X-ray source.

The energy fluence measurement experiment is carried out with the high-energy beam source of the “Flash II” accelerator as an experimental platform. In order to meet the requirements of the effect test experiments, the series diode structure is used in the accelerator for forming a high strength and large area uniform X-ray source. In the experiment, the LiF TLD is located in the front of the phototube and used to monitor the dose. According to the measured waveform, the actual energy of the incident photons is calculated. Combined with the receiving area of incident photons, the energy fluence of pulsed hard X-ray is calculated. The average measured value is 35.9 mJ/cm2 in 5 consecutive experiments. Energy fluence calculated from the measured dose and energy spectrum is 39.8 mJ/cm2. The results of the two methods are compared.

It can be found that the experimental result is about 9.8% smaller than the theoretical value. The reasons are as follows. According to the law of exponential decay of rays in matter, in fact, the scintillator cannot absorb all the rays, and some of the rays can penetrate through, the energy of these rays cannot be detected, and thus giving rise to small experimental value. Due to the limited energy point of quasi-monoenergetic source, the sensitivity under the mean photon energy is taken as the sensitivity of the detector, and therefore there is a certain degree of uncertainty.

The successful application of the measurement technology provides a good experimental method for the following similar research, and can also provide a reference for X-ray intensity analysis.
Significant enhancement of the performance of dye-sensitized solar cells with photoelectrode co-doped graphene and hybrid SiO2@Au nanostructure
Authors: Zhang Yuan , Chen Chen , Li Mei-Ya , Luoshan Mengdai ,   School of Information Engineering, Hubei Minzu University, Enshi 445000, China,   School of Physics and Technology, Wuhan University, Wuhan 430072, China,   School of Science, Hubei University of Technology, Wuhan 430068, China
Published: December 2020

Attributed to facile fabrication, low production costs and outstanding photoelectric properties, dye-sensitized solar cells (DSCs) have attracted widespread attention in recent years. In order to achieve better photoelectric conversion efficiency of the DSCs, a series of TiO2 nanocomposite photoanodes co-doped with different amounts of hybrid SiO2@Au nanostructures and certain amount of graphene are prepared by a mechanical ball milling method. The influence of SiO2@Au nanostructures and graphene on the performance of the photoanodes and their DSCs were investigated. The Au nanoparticles can remarkably enhance the short-circuit current density (Jsc) due to the local surface plasmon resonance effect of the noble metal nanoparticles. As a unique two-dimensional material, graphene has several amazing characteristics, such as high specific surface area and excellent conductivity. Studies showed that by introducing both SiO2@Au nanostructures and graphene, the light-absorbing, electron mobility and dye loading of the photoanodes were remarkably increased. Experimental results indicated that in comparison with those DSCs based with pure TiO2 photoanode, the DSCs with photoanodes incorporated with SiO2@Au nanostructures and graphene showed the optimal performance with short-circuit current density (Jsc) of 15.59 mA/cm2 and photoelectric conversion efficiency (PCE) of 6.68%, increasing significantly by 15.67% and 8.8%, respectively. This significant enhancement in Jsc and PCE of DSCs are mainly attributed to the increase in light-absorption and dye-loading of the photoanodes due to the hybrid SiO2@Au nanostructures and graphene.
Numerical study on discharge characteristics in ultra-high frequency band modulated by pulses with electrodes covered by barriers
Authors: Gao Shu-Han , Wang Xu-Cheng , Zhang Yuan-Tao ,   School of Electrical Engineering, Shandong University, Jinan 250061, China
Published: December 2020

Pulse-modulated discharge is an effective way to improve the stability of radio-frequency (rf) discharges. Previous studies have shown that with the power frequency increasing to the ultra-high frequency (UHF) band, the introduction of pulse modulation in rf discharges will bring about new discharge behaviors. In this paper, the fluid model is adopted to numerically investigate the new discharge characteristics in dielectric barrier discharges (DBDs) with the rf frequency larger than 500 MHz. A very large current peak occurs in the first positive and negative half cycle during the power-on phase, respectively. The spatial structure of electric field is given to further understand the underpinning physics of the large current peaks. Furthermore, the effects of duty cycle, modulation frequency and voltage modulation rates on the large current peaks are examined based on the computational data. This numerical study will deepen the understanding of DBDs modulated by pulses in the UHF band.
A hybrid model for photovoltaic power prediction of both convolutional and long short-term memory neural networks optimized by genetic algorithm
Authors: Wang Chen-Yang , Duan Qian-Qian , Zhou Kai , Yao Jing , Su Min , Fu Yi-Chao , Ji Jun-Yang , Hong Xin , Liu Xue-Qin , Wang Zhi-Yong ,   Chongqing Key Laboratory of Green Energy Materials Technology and Systems, School of Science, Chongqing University of Technology, Chongqing 400054, China,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

Photovoltaic power generation is affected by weather and geographical environment, showing fluctuations and random multi-interference, and its output power is easy to change with changes in external factors. Therefore, the prediction of output power is crucial to optimize the grid-connected operation of photovoltaic power generation and reduce the impact of uncertainty. This paper proposes a hybrid model of both convolutional neural network (CNN) and long short-term memory neural network (LSTM) based on genetic algorithm (GA) optimization (GA-CNN-LSTM). First, the CNN module is used to extract the spatial features of the data, and then the LSTM module is used to extract the temporal features and nearby hidden states. Optimizing the hyperparameter weights and bias values of the LSTM training network through GA. At the initial stage, the historical data is normalized, and all features were analyzed by grey relational degree. Important features are extracted to reduce the computational complexity of the data. Then, the GA-optimized CNN-LSTM hybrid neural network model (GA-CNN-LSTM) is applied for photovoltaic power prediction experiment. The GA-CNN-LSTM model was compared with the single neural network models such as CNN and LSTM, and the CNN-LSTM hybrid neural network model without GA optimization. Under the Mean Absolute Percentage Error index, the GA-CNN-LSTM algorithm proposed in this paper reduces the error by 1.537% compared with the ordinary single neural network model, and 0.873% compared with the unoptimized CNN-LSTM hybrid neural network algorithm model. From the perspective of training and test running time, the GA-CNN-LSTM model takes a little longer than the single neural network model, but the disadvantage is not obvious. To sum up, the performance of GA-CNN-LSTM model for photovoltaic power predicting is better.
Field effect transistor photodetector based on two dimensional SnSe2
Authors: Meng Xian-Cheng , Tian He , An Xia , Yuan Shuo , Fan Chao , Wang Meng-Jun , Zheng Hong-Xing ,   School of Electronic and Information Engineering, Hebei University of technology, Tianjin 300401, China
Published: December 2020

Two dimensional materials have been attracting intensive interest due to their unique physical and optoelectronic properties. As an emerging two dimensional materials, SnSe2 have shown a considerable potential for next-generation electronic and optoelectronic. Herein, SnSe2 bulk crystals have been prepared by a chemical vapour transport method with high purity tin and selenium powder as precursors. Then SnSe2 multilayers has been successfully prepared by a micromechanical exfoliation method from the SnSe2 bulk crystals. The phase structures and elemental composition of the bulk crystal are investigated using an X-Ray diffractometer, an X-ray photoelectrons spectrometer and a Raman spectrometer. And the morphologies are observed using an optical microscope, an atomic force microscope and a transmission electron microscope. The measurement results show that the SnSe2 bulks are single crystals with a high crystallization and purity. The SnSe2 multilayers have a size of 25–35 μm and a thickness of 1.4 nm. To detect the electronic and photoresponse characteristics of the SnSe2 multilayers, a field effect transistor based on such SnSe2 are fabricated via a photolithographic-pattern-transfer method. The transistor has a smooth surface without wrinkles and bubbles, and also has a good contact with Au electrodes. The transistor shows a linear output characteristic and an obvious rectification. The on/off ratio of the device is 47.9 and the electron mobility is 0.25 cm2·V–1·s–1. As a photodetector, the field effect transistor exhibits obvious photoresponse to three visible lights with the wavelengths of 405, 532, and 650 nm. As the lasers are turned on and the device is under illuminations of three visible lights, the current increase rapidly to a saturation state. Then as the lasers are switched off, the current decrease and recover to the original state. The drain-source current can alternate between high and low states rapidly and reversibly, which demonstrates photoresponse characteristics of the devices are stable and sensible. Notably, it shows a strongest response to the 405 nm light at an intensity of 5.4 mW/cm2 with a high responsivity of 19.83 A/W, a good external quantum efficiency of 6.07 × 103%, a normalized detectivity of 4.23 × 1010 Jones, and a fast response time of 23.8 ms. The results of this work demonstrate that layered SnSe2 can be a suitable and excellent candidate for visible light photodetector and has a huge potential for high-performance optoelectronic devices.
Thick yet tough TiN coatings deposited by filter cathode vacuum arc technology
Authors: Zhang Zhi-Qiang , Liao Bin , Ou Yi-Xiang , Zhang Feng-Shou , Zhang Xu , Shen Yong-Qing , Chen Shu-Nian , Hua Qing-Song , He Guang-Yu , Ouyang Xiao-Ping ,   College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China,   Beijing Radiation Center, Beijing 100875, China,   Science and Technology on Plasma Dynamics Laboratory, Air Force Engineering University, Xi’an 710038, China
Published: December 2020

There are some high requirements for mechanical property to protective coatings of turbojet engine compressor blades as the appearance of extreme service conditions. The hard coating with high toughness, good adhesion, good wear resistance and excellent load carrying capacity is a potential coating for extreme service conditions in the future. Thick yet tough TiN hard coatings were successfully deposited on 304L stainless steel substrates by magnetic filtered cathodic vacuum arc technology. The morphology, structure and properties of the coatings were studied by SEM and XRD, etc.The results show that the continuous growth of TiN coatings attributed to periodic high energy ion bombardment which can suppress the large grain size and reduce the internal stress. The thickness of TiN coating can reach to 50 μm and the deposition rate was close to 0.2 μm/min. At the same time, the stable non stoichiometric TiN0.9 can be formed by controlling the constant N2 flow rate, which can improve the toughness of TiN coatings. All TiN ciatings belong to superhard coating and the max value of hardness and modulus of elasticity were 38.24 GPa and 386.53 GPa respectively. TiN coatings have good adhesion and excellent toughness.The highest  \begin{document}$ H/E^{*} $\end{document} and \begin{document}$ H^3/E^{*2} $\end{document} rate of TiN coating can reach to 0.0989 and 0.3742. Thick yet tough TiN hard coatings have excellent wear resistance with the lowest friction coefficient of 0.26.