bluuebunny/crossref_metadata_2025 huggingface dataset:
Research progress of semiconductor up-conversion single photon detection technology
Authors: Bai Peng  , Zhang Yue-Heng  , Shen Wen-Zhong  ,   Key Laboratory of Artificial Structures and Quantum Control, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China;,   Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
Published: December 2020

Quantum communication technology has achieved remarkable progress and development in recent years, and the single photon detector, as the receiving terminal, plays a vital role in communication systems. In this paper, we focus on the current mainstream semiconductor-based single photon detectors and review their device principle, operating mode, advantages and disadvantages. Besides, the research progress of a novel semiconductor near-infrared single photon detection technology (USPD) is introduced. The feasibility and superiority of the USPD device are demonstrated from the basic principle, device structure and key performance indicators of USPD, and the latest spatial optical coupling experiment results of the USPD are also given. The design principle of the USPD device is to utilize Si multiplication layer of the Si SPAD as a multiplication layer instead of InP in conventional InGaAs-SPAD. The Si-SPAD has a much lower dark count rate and afterpulsing effect because of high-quality material of Si. Such a characteristic design of USPD can suppress the afterpulsing probability to the same level as that of the Si-SPAD and enables it to operate in the free-running regime without sacrificing photon detection efficiency. For the same reason, the dark count rate (DCR) of USPD is also very low. The operating mechanism of USPD is to convert the infrared photons into near-infrared or visible photons and the emitted near-infrared photons can be detected by a Si SPAD, which provides us with a new idea for single photon detection.
Topological phase transitions in square-octagon lattice with Rashba spin-orbit coupling
Authors: Yang Yuan  , Chen Shuai  , Li Xiao-Bing  ,   1. Zhangjiagang Campus, Jiangsu University of Science and Technology, Zhangjiagang 215600, China;,   2. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

Motivated by the square-octagon lattice which supports topological phases over a wide range of parameters and a number of interesting quantum phase transitions in the phase diagram when considering the intrinsic spin-orbit coupling, we investigate the topological phase transitions in the isotropic square-octagon lattice combining the effects of both spin-orbit couplings and exchange field. The inversion symmetry and time-reversal symmetry are broken when both Rashba spin-orbit coupling and exchange field are present. The Z2 index is not applicable for quantum spin Hall systems without time-reversal symmetry, but the spin Chern number remains valid even in the absence of time-reversal symmetry. Therefore, we use the Chern number and spin Chern number to describe the topological properties of the system. We explore that a variety of topologically nontrivial states appear with changing the exchange field, including time-reversal-symmetry-broken quantum spin Hall states and quantum anomalous Hall states. The phase transition between these topological phases is accompanied by the closing of band gaps. Interestingly, the quantum spin Hall effect described by nonzero spin Chern number is found to remain intact when the time-reversal symmetry is broken. Furthermore, the variation of the amplitude of the exchange field and filling factor drive interesting topological phase transitions from the time-reversal-symmetry-broken quantum spin Hall phase to spin-filtered quantum anomalous Hall phase. A spin-filtered quantum anomalous Hall phase is characterized by the presence of edge states with only one spin component, which provides an interesting route towards quantum spin manipulation. We also present the band structures, edge state wave functions, and spin polarizations of the different topological phases in the system. It is demonstrated that the energy spectra of edge states are in good agreement with the topological characterization based on the Chern number and spin Chern number. In particular, we observe that gapless edge states can appear in a time-reversal-symmetry-broken quantum spin Hall system, but the corresponding spin spectrum gap remains open on the edges. Recently, an important functional material ZnO with quasi square-octagon lattice has been found experimentally. Consequently, the results found in our work are helpful for understanding the property of square-octagon lattice and studying the real materials with square-octagon structure.
Interaction between Sso7d and DNA studied by single-molecule technique
Authors: Teng Cui-Juan  , Lu Yue  , Ma Jian-Bing  , Li Ming  , Lu Ying  , Xu Chun-Hua  ,   Key Laboratory of Soft Matter Physics, 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
Published: December 2020

Each organism has its own set of chromatin proteins to protect the stable structure of DNA and thus maintain the stability of genes. Sso7d is a small nonspecific DNA-binding protein from the hyperthermophilic archaea Sulfolobus solfataricus. This protein has high thermal and acid stability. It stabilizes dsDNA and constrains negative DNA supercoils. Besides, the Sso7d binds in a minor groove of DNA and causes a sharp kink in DNA. By observing the interaction between chromatin protein and DNA structure, we can understand the function and mechanism of chromatin protein. Sulfolobus solfataricus can survive at high temperature. To understand why the DNA of Sulfolobus solfataricus retains activity at high temperature, we investigate the interaction between Sso7d and DNA by atomic force microscope (AFM) and magnetic tweezers. Atomic force microscope and magnetic tweezers are advanced single molecule experimental tools that can be used to observe the interaction between individual molecules. The experimental result of AFM reveals the process of interaction between Sso7d and DNA. The DNA structure changes at a different concentration of Sso7d and depends on reaction time. At a relatively low concentration of Sso7d, DNA strand forms a kink structure. When the concentration of Sso7d is increased, DNA loops appear. Finally, DNA becomes a dense nuclear structure at a high concentration of Sso7d. If the time of the interaction between Sso7d and DNA is increased, DNA structure tends to be more compact. These results indicate that high concentration of Sso7d is important for the compact structure of DNA. We design an experiment to find out the formation of the looped structure on DNA. Moreover, we measure the angle of kinked DNA and compared it with previous result. Through the experiment of magnetic tweezers, we measure the forces of unfolding the double-stranded DNA complexed with Sso7d at different concentrations. The experimental results show that the binding between Sso7d and DNA increases the force of unfolding the double-stranded DNA. The binding energy between Sso7d and dsDNA is 3.1kBT which is calculated from experimental data. It indicates that DNA base pairs are more stable when chromatin protein Sso7d exists. These results can explain the survival of Sulfolobus in high temperature environment.
Role of impurities in modifying isotope scaling law of ion temperature gradient turbulence driven transport in tokamak
Authors: Shen Yong  , Dong Jia-Qi  , Xu Hong-Bing  ,   Southwestern Institute of Physics, Chengdu 610041, China;,   Institute for Fusion Theory and Simulation, Zhejiang Universtiy, Hangzhou 310013, China
Published: December 2020

Tokamak experiments show that the plasma empirical energy confinement scaling law varies with plasma ion mass (Ai) in a certain range under conditions of different plasma parameters or different devices. In order to understand such a modification of the empirical energy confinement scaling law, the isotope mass dependence of ion temperature gradient (ITG, including impurity modes) turbulence driven transport in the presence of tungsten impurity ions in tokamak plasma is studied by employing the gyrokinetic theory. The effect of heavy (tungsten) impurity ions on ITG and impurity mode is revealed to modify significantly the isotope mass dependence and effective charge effect. As the charge number of impurity ions (Z) or impurity charge concentration (fz) changes, the theoretical scaling law of ITG turbulence transport varies substantially in a relatively large range. The maximum growth rate of ITG mode scales as Mi-0.48 -0.12, whilst that of impurity mode scales as Mi-0.46 -0.3. Here, Mi is the mass number of primary ion in the plasma. In both cases the fitting index with Mi deviates further away from -0.5 when impurity charge concentration fz increases. The isotope mass dependence of ITG turbulence gradually weakens when the effective charge number Zeff increases. The isotope mass dependence of impurity mode turbulence also weakens with Zeff increasing for the same impurity ion charge number (Z). In contrast, the isotope mass dependence gradually strengthens with effective charge number Zeff increasing for the same impurity charge concentration (fz). On average, the maximum growth rates of impurity mode scale roughly as max~Mi-0.35Zeff1.5 and max~Mi-0.4Zeff1, respectively, for Zeff 3 and Zeff 3. The reason for the deviation of isotope scaling law from the normal case is investigated deliberately, and it is demonstrated that the isotope scaling index deviates from -0.5 more or less due to the fact that the impurity species, charge number and impurity concentrations vary in a certain range. These results demonstrate that it is impossible to deduce a unique isotope scaling law due to the variety of micro-instabilities and various plasma parameter regimes in tokamak plasma, which is consistent with the experimental observations. These results may contribute to the transport study involving heavy (tungsten) impurity ions in ITER discharge scenario investigation.
Microbubble oscillation induced acoustic micromixing in microfluidic device
Authors: Zhao Zhang-Feng  , Zhang Wen-Jun  , Niu Li-Li  , Meng Long  , Zheng Hai-Rong  ,   Key Laboratory of E & M, Ministry of Education and Zhejiang Province, Zhejiang University of Technology, Hangzhou 310014, China;,   Paul C Lauterbur Research Center for Biomedical Imaging, Institute of Biomedical and Health Engineering, Shenzhen
Published: December 2020

Microfluidic is of great significance for biomedical research and chemical engineering. The mixing of liquids is an essential and necessary procedure for the sample preparation. Due to the low Reynolds number, laminar flow is dominant in a microfluidic channel and it is difficult to mix the fluids in the microchannel quickly and effectively. To improve the mixing efficiency of the liquids in microfluidic channels, we develop an acoustic mixer based on single microbubble oscillation. By designing the cylinder structure on the bottom surface, when the fluid flows through cylinder structure with a diameter of 40 m, the microbubble can be generated by the surface tension of the liquid. The device is fabricated by using standard soft lithography and the replica moulding technique, ensuring the stability and repeatability of the mixing. A piezoelectric transducer (PZT) with a resonant frequency of 165 kHz is attached to the polydimethylsiloxane microfluidic device on the glass substrate by ultrasound coupling gel. When the microbubble is excited by the PZT at a resonant frequency of 165 kHz, microbubble oscillates immediately. To verify whether ultrasound can induce microbubble cavitation, a passive cavitation detection system is established. The results show that the higher harmonics can be detected, indicating that the stable cavitation occurs. The microstreaming induced by the oscillating microbubble disturbs the fluid dramatically, achieving the mixture of liquids. Particle image velocimetry method is utilized to characterize the microstreaming, and a pair of counter-rotating vortices in the microchannel is detected. Furthermore, to test the performance of the device, the deionized water and rhodamine B are injected into the Y-shape microchannel. Relative mixing index is used to quantitatively analyze the mixing performance by measuring the grayscale values of the optical images. The results indicate that with the increase of the input power, mixing time can be shortened correspondingly. When the input power is 14.76 W, the mixing process is ultrafast, within 37.5 ms the high mixing uniformity can be achieved to be 92.7%. With the advantages of simple design, high efficient and ultrafast mixing, and low power consumption, this oscillating microbubble-based acoustic micromixer may provide a powerful tool for various biochemical studies and applications.
In situ transmission electron microscopy studies on nanomaterials and HfO2-based storage nanodevices
Authors: Li Chao  , Yao Yuan  , Yang Yang  , Shen Xi  , Gao Bin  , Huo Zong-Liang  , Kang Jin-Feng  , Liu Ming  , Yu Ri-Cheng  ,   Laboratory of Advanced Materials and Electron Microscopy, Beijing National Laboratory of 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;,   School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China;,   Key Laboratory of Microelectronics Device and Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China
Published: December 2020

Advanced transmission electron microscopy combined with in situ techniques provides powerful ability to characterize the dynamic behaviors of phase transitions, composition changes and potential variations in the nanomaterials and devices under external electric field. In this paper, we review some important progress, in this field, of the explanation of structural transition path caused by the Joule heating in C60 nanowhikers, the clarification of electron storage position in charge trapping memory and the direct evidences of the oxygen vacancy channel and the conductive filament formation in resistive random access memory. These studies could improve an understanding of the basic mechanism of nanomaterial and device performance, and also demonstrate the diversity of the functions of transmission electron microscopy in microelectronic field.
Refractive index sensor and filter of metal-insulator-metal waveguide based on ring resonator embedded by cross structure
Authors: Qi Yun-Ping  , Zhang Xue-Wei  , Zhou Pei-Yang  , Hu Bing-Bing  , Wang Xiang-Xian  ,   Engineering Research Center of Gansu Province for Intelligent Information Technology and Application, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China;,   School of Science, Lanzhou University of Technology, Lanzhou 730050, China
Published: December 2020

Continuous improvement in nanofabrication and nano-characterization capabilities have changed projections about the role that metals could play in developing the new optical devices. Surface plasmon polaritons are evanescent waves that propagate along a metal-dielectric interface. They can be laterally confined below the diffraction limit by using subwavelength metal structures, rendering them attractive to the development of miniaturized optical devices. A surface plasmon polariton refractive index sensor and filter which consist of two metal-insulator-metal (MIM) waveguides coupled to each other by a ring resonator embedded by cross structure are proposed. And the transmission characteristics of surface plasmon polaritons are studied in our proposed structure. The transmission properties of such a structure are simulated by the finite element method, and the eigenvalue wavelengths of the ring resonator are calculated theoretically. The sensing characteristics of such a structure are systematically analyzed by investigating the transmission spectrum. The results show that there are three resonance peaks in the transmission spectrum, that is, three resonance modes corresponding to the eigenvalue solutions of the first, second and third-order Bessel eigen-function equations, and each of which has a linear relationship with the refractive index of the material under sensing. Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity (S) as high as 1500 nm/RIU, and the corresponding sensing resolution is 1.3310-4 RIU. More importantly, it is sensitive to none of the parameters of our proposed structure, which means that the sensitivity of the sensor is immune to the fabrication deviation. In addition, by the resonant theory of ring resonator, we find a linear relationship between the resonance wavelength and the radius of ring resonator. So the resonance wavelength can be easily manipulated by adjusting the radius and refractive index. In addition, the positions of transmission peaks can be easily modulated by changing the radius of the ring, which can be used to design band-pass filter for a large wavelength range. Moreover, the transmission intensity and the transmission bandwidth decrease as spacing distance between the MIM waveguide and ring cavity increases. These results would be helpful in designing the refractive index sensor of high-sensitivity and band-pass filters, and have guiding significance for biological sensor applications.
Effect of silver film roughness on imaging property of BaTiO3 microsphere
Authors: Wang Jian-Guo  , Yang Song-Lin  , Ye Yong-Hong  ,   Department of Physics, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

Due to the Abbe diffraction limit, the resolution of a traditional optical microscopy is limited to about half of the illumination wavelength. Recent studies show that super-resolution imaging through dielectric microsphere has emerged as a simple imaging technique to overcome the diffraction limit under the illumination of white light. However, for imaging through microsphere, sometimes it is needed to enhance the reflection of a sample by depositing a metallic thin film on the top of the sample. Metallic thin films with different surface roughness have different optical properties. However, the effect caused by the surface roughness of a metallic film on microsphere imaging is rarely studied. In this paper, we study the effects of silver films with different surface roughness deposited on the surfaces of samples on the imaging properties of BaTiO3 (BTG) microspheres. Silver thin films are deposited respectively at evaporation rates of 1.5-3 Å/s and 5-10 Å/s, and the surface roughness values (root mean square (RMS) values) of the obtained silver films are about 3.23 nm and 6.80 nm, respectively. Using a BTG microsphere to observe a sample with a silver film deposited on its surface, we find that the surface roughness of the silver film will affect the imaging resolution and the range of focal image position (RFIP) of the BTG microsphere. When we use a 15-μm-diameter BTG microsphere to observe a 250-nm-diameter microsphere array and 580-nm-diameter microsphere array, the RFIP of the BTG microsphere increases with the RMS of the silver film increasing from 3.23 to 6.80 nm. Moreover, a 200-nm-diameter microsphere array can also be clearly discerned. The simulation results obtained by the commercial software COMSOL show that when the surface of a microsphere array sample is deposited with a rough silver film, the electric field intensity is enhanced not only in the gaps between adjacent microspheres, but also on the silver particles due to the excitation of localized surface plasmons. We propose that the scattering effect and the local electric field intensity enhancement caused by the rough silver film allow more high-frequency information of the sample to be coupled into the BTG microsphere, and thus improving the resolution and RFIP of the microsphere. As the imaging law of microsphere imaging still needs to be explored, our research work will be helpful in further revealing the mechanism in microsphere imaging.
Research progress of materials and devices for room-temperature Na-ion batteries
Authors: Lu Ya-Xiang  , Zhao Cheng-Long  , Rong Xiao-Hui  , Chen Li-Quan  , Hu Yong-Sheng  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Among various electrochemical energy storage technologies, room-temperature Na-ion batteries (NIBs) are regarded as ideal candidates in large-scale energy storage field due to advantages of abundant resources and low material cost in addition to their characteristics of high energy density and long cycle life. Since 2011, the Institute of Physics, Chinese Academy of Sciences (IOP-Chinese Academy of Sciences) has devoted to developing the cost-effective and environmental-safe NIBs, and attained many original achievements in the research of cathode, anode and electrolyte materials, and also developed Na-ion pouch cells with capacities of 1 Ah. For instance, the highly reversible Cu2+/Cu3+ redox was discovered for the first time and the low cost Na-Cu-Fe-Mn-O layered oxide cathodes have been designed accordingly; the anthracite-derived carbon anodes have been exploited via a simple one-step carbonization process with a high performance-to-price ratio; a new type of NaFSI sodium salt was first used in the non-aqueous carbonate electrolyte to significantly improve the performance of electrode materials, etc. This review summarizes the important progress and breakthroughs achieved in IOP-Chinese Academy of Sciences for materials and devices of NIBs. We hope that these contributions conduce to realizing the industrialization of NIBs.
Magnetoelectric heterostructure and device application
Authors: Yang Na-Na  , Chen Xuan  , Wang Yao-Jin  ,   School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

The magnetoelectric (ME) heterostructure is composed of ferromagnetic and ferroelectric materials. The heterostructural ME effect originates from piezoelectric effect in the ferroelectric component and magnetostrictive effect in the ferromagnetic component. The magnetoelectric heterostructure has higher magnetoelectric coupling coefficient and lower dielectric loss than the particulate composites, and thus leading to several promising applications such as in the magnetic field sensors, the energy harvesters, antenna and memory devices. In this paper, we review the recent research progress in ME heterostructure for device applications, and present a development course of ME heterostructure. Finally, we also summarize the challenges of developing the ME heterostructure and point out its perspectives.
High pressure synthesis and physical properties of multiferroic materials with multiply-ordered perovskite structure
Authors: Zhou Long  , Wang Xiao  , Zhang Hui-Min  , Shen Xu-Dong  , Dong Shuai  , Long You-Wen  ,   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;,   Department of Physics, Southeast University, Nanjing 211189, China
Published: December 2020

Perovskite is one of the most important material systems for magnetoelectric multiferroic study. However, multiferroic is not expected to occur in a cubic perovskite on account of the highly symmetric crystal structure. Besides, magnetoelectric multiferroics with large ferroelectric polarization and strong magnetoelectric coupling have not been found to occur simultaneously in a single-phase multiferroic material discovered so far, challenging to the potential applications of this kind of material. Here we briefly review two multiferroic materials with multiply-ordered perovskite structure synthesized under high pressure and high temperature conditions. In the cubic perovskite LaMn3Cr4O12, we observed spin-induced ferroelectric polarization, providing the first example where ferroelectric takes place in a cubic perovskite material. In another multiply-ordered provskite BiMn3Cr4O12, type-I and type-Ⅱ multiferroic phases successively developed when cooled. It provides a rare example where two different types of multiferroic phases occur subsequently so that both large polarization and strong magnetoelectric effect are achieved in a single-phase material. In addition, since double ferroelectric phases take place in BiMn3Cr4O12, one can obtain four different polarization states by adopting different poling procedures, thus opening up a new way for generating multifunctional spintronics and multistate storage devices.
Hydrogen adsorption mechanism on single-layer MoSe2 for hydrogen evolution reaction: First-principles study
Authors: Xu Zi-Wei  , Shi Chang-Shuai  , Zhao Guang-Hui  , Wang Ming-Yuan  , Liu Gui-Wu  , Qiao Guan-Jun  ,   School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013, China
Published: December 2020

Based on the first-principles of the density functional theory, the Gibbs free energies (△GH0) of the hydrogen adsorption on the 2H-phase molybdenum diselenide monolayer (MoSe2) with different active sites and hydrogen coverage rates are calculated. The calculated results reveal that several ideal adsorbed rates and sites are very close to those at thermoneutral state (△GH0~0). To compare their catalytic ability in the hydrogen evolution reaction (HER), the exchange current density (i0) as a function of △GH0 is calculated as a volcano curve. Two sites located at the top of volcano curve present higher exchange current densities than that of Pt catalyst. The charge transfers and the bonding details of the two edge-hydrogen-adsorptions (Mo edge and Se edge) are analyzed by the charge density difference and electronegativity as the associated structures and relative △GH0 are further explained. It is found that the localized charge transfer distributed uniformly between the hydrogen atoms and the adsorption sites can facilitate the catalytic ability of HER. For this reason, the catalytic ability of HER for the Se edge is more stable than that of Mo edge with less sensitivity to the absorption sites and hydrogen coverage rates. Based on the first-principles molecular dynamics (MD) simulation, finally, the influences of the thermal motion on the two kinds of structures of hydrogen adsorption at the higher temperature are explored, with the critical temperature for the hydrogen desorption as well as the atomistic dynamics discovered. It is worth mentioning that during the structure optimization and MD simulation, the edge deformation and reconstruction are discovered, respectively, which indicates that the ideal edge of MoSe2 may not be the most stable structure, which will change with the external conditions. This theoretic study reveals the atomistic mechanisms of the hydrogen adsorption and desorption of the single-layer 2H-phase MoSe2 at different temperatures, with the edge lattice deformation and reconstruction discovered, which can deepen our insights into the HER mechanisms near the edges of the 2H-phase MoSe2 at different temperatures and provide theoretic guidelines for designing the high-efficient and low-cost catalyst in the HER through tuning the MoSe2 edges.
Formation mechanism of coherent rainbows
Authors: Sun Tian-Jiao  , Qian Xuan  , Shang Ya-Xuan  , Liu Jian  , Wang Kai-You  , Ji Yang  ,   State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China;,   College of Materials Science and Opto-Electronic Technology, School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Focusing white laser into samples, many colorful rings (coherent rainbows) come out. Such phenomena have been observed in many materials like water, acetone, absolute ethyl alcohol, soft drink and other liquids, and ice, colored glass, plastics, wax and other solids. From the center of the coherent rainbows to the outer side, the distance between neighboring rings becomes larger and larger. The coherent rainbow is an interference effect, whose optical path difference is induced by locally heating the material with the laser beam. Especially, the coherent rainbows from colored glass in reflection mode can be described with a simple formula, with which simulated results fit the observed interference pattern very well. Several possible mechanisms like nonlinear optical effect, thermal lens effect and self-phase modulation effect are excluded.
Recent progress of improper ferroelectricity in perovskite oxides
Authors: Zhao Guo-Dong  , Yang Ya-Li  , Ren Wei  ,   Department of Physics, College of Sciences, Materials Genome Institute, International Centre for Quantum and Molecular Structures, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai 200444, China
Published: December 2020

Perovskite oxides show many potential applications in the research fields of emerging materials and devices for electronics, information and communication because of their rich functionalities, e.g. magnetic, ferroelectric, multiferroic, mechanical and optical properties. Among them, ferroelectricity is currently being studied intensively due to the existence of many different mechanisms, and the coupling with magnetism and strain. In contrast to the proper ferroelectricity in which the polarization is the main order parameter as the driving force, the improper ferroelectricity possesses the ferroelectric polarization that becomes a secondary order parameter induced by other orders. In this review, we focus on the inorganic perovskite oxides to summarize the recent research progress of the improper ferroelectricity in general, but we review the magnitude of polarization, and the generation mechanism of improper ferroelectricity in perovskite superlattice, double perovskite structures and a specific SmFeO3 single crystal possessing antiferromagnetic domain walls in particular. This review will hopefully provide routes to systematically understanding the improper ferroelectricity.
Retrieval and uncertainty analysis of stochastic parameter in atmospheric boundary layer model
Authors: Yan Bing  , Huang Si-Xun  , Feng Jing  ,   College of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China;,   Center for Computational Science and Finance, Shanghai University of Finance and Economics, Shanghai 200433, China
Published: December 2020

The eddy viscosity is an important parameter in the atmospheric boundary layer meteorology, and we usually cannot determine their exact values by direct measurements, but we can only obtain an approximate range by indirect approximate method. In this paper, the eddy viscosity in the stochastic general Ekman momentum approximation model is used for the retrieval research and uncertainty analysis. The main purpose of retrieval is to reduce the uncertainty and narrow the approximate range of eddy viscosity. First, the polynomial chaos-ensemble Kalman filter and the wind observations are used for eddy viscosity retrieval and uncertainty reduction. The main idea of this method is to replace the Monte-Carlo method with polynomial chaos in the uncertainty quantification of ensemble Kalman filter, and thusavoiding the consumption of computing resources brought by massive samples. The goal of uncertainty quantification is to investigate the effect of uncertainty in the eddy viscosity on the model and to subsequently provide a reliable distribution of simulation results. Then two numerical experiments are implemented, i.e. experiment I in which the eddy viscosity is assumed to be constant, and experiment Ⅱ in which the eddy viscosity is assumed to be a vertically varying random parameter. The uncertainty of eddy viscosity in experiment I is reduced quickly, at the same time the mean of eddy viscosity can converge to a reference value. The effect in experiment Ⅱ is also remarkable after 16 data assimilation steps. These results show that the polynomial chaos-ensemble Kalman filter is an effective and fast method of solving the posterior distribution of eddy viscosity and reducing the uncertainty of eddy viscosity. Finally, we calculate the prior distribution of wind speed according to the prior distribution of eddy viscosity and identify the heavy uncertainty area in wind speed. The results indicate that the posterior distribution of eddy viscosity solved with wind observations in the big uncertainty area is more accurate, which provides an important guidance for selecting the location of observation points.
Non-ionization energy loss of proton in different regions in SiC
Authors: Shen Shuai-Shuai  , He Chao-Hui  , Li Yong-Hong  ,   School of Nuclear Science and Technology, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Silicon carbide (SiC), as a representative of the third-generation semiconductor materials, is widely used in some fields which may suffer strong radiation such as in the cases of military affairs, aerospace and reactor. SiC possesses the superior radiation-resistance characteristic. However, SiC under the proton irradiation generate a lot of defects, resulting in degradation of device performance and even complete loss of its function. Therefore, the study on the irradiation damage to SiC under proton irradiation possesses important significance. A large number of studies have shown that for most of electronic devices and different types of incident particles, the degradation of device performance caused by displacement damage is linearly dependent on non-ionizing energy loss (NIEL), so the displacement damage can be evaluated by NIEL. In this work, the Monte Carlo software Geant4 is used to simulate the relationship between NIEL and proton energy, and the variation of NIEL with the depth of the material and the contribution of different types of primary recoil atoms to the total NIEL are also studied. The NIEL simulation results show that the NIEL in SiC material is less than that in Si and Ga semiconductor material under the same proton irradiation, proving that the stability and the radiation-resistance of SiC are stronger. The simulation results of NIEL at different depths show that the most serious damage regions of the material under different energy protons are diverse. Under the irradiation of low energy proton, the most serious region of the displacement damage occurs at the end of the proton range. With the increase of proton energy, the worst damage region of material will gradually move from the end of the proton range to the surface of SiC material. According to the contribution of different types of primary recoil atoms to the total NIEL, when the energy of the incident proton is low, the displacement damage of the proton in the SiC is mainly caused by 28Si and 12C, and the damage caused by 28Si is obviously higher than that by 12C. As the energy of proton increases, the 28Si and 12C are still the main causes of Bragg peak of the NIEL at the end of the proton range, but the number of ions generated by nuclear reactions increases accordingly, and the displacement damage caused by these ions increases in the shallow area of SiC, leading the surface of the material to be the worst damaged region. The combination of the two factors caused the most serious damage region moves from the end of the proton range to the surface of the material with the increase of proton energy. The results of this study are useful for the application of SiC devices to irradiation environment.
Effect of oxygen vacancy defect on leakage current of PbTiO3 ferroelectric thin film
Authors: She Yan-Chao  , Zhang Wei-Xi  , Wang Ying  , Luo Kai-Wu  , Jiang Xiao-Wei  ,   Department of Physics and Electronic Engineering, Tongren University, Tongren 554300, China;,   School of Physics and Optoelectronics, Xiangtan University, Xiangtan 411105, China
Published: December 2020

Ferroelectric (FE) materials have been extensively applied to the multifunctional electronic devices, particularly the FE memories due to their excellent physical properties. The FE memory is a kind of nonvolatile memory device, and it could overcome the shortcomings of the traditional memory. But the development of the FE memory is very slow due to the FE failure problem. However, with the continuous decrease of the thickness of FE thin film, when it reaches microns or nanometers in magnitude, the leakage current is the main cause of the FE failure of FE thin film. The leakage current of FE thin film is directly related to whether the FE memory is applicable, and it has been the hot spot of scientific researches. There are still a lot of factors influencing the FE memory leakage current except for the thickness of the film, such as interface, processing temperature, defect, domain wall, etc. Of these factors, the defect and domain wall are the most common and the most probable. In this paper, the first-principle calculation method through combining the density function theory with the nonequilibrium Green's function is used to systematically study the influence of oxygen vacancy defect on the leakage current of the FE thin film. The doping with four kinds of Cu, Al, V, and Fe cations is used to regulate and control the leakage current of the FE thin PbTiO3 film caused by the oxygen vacancy defects. We investigate the leakage current induced by oxygen vacancies in PbTiO3 films, and the doped PbTiO3 thin FE films having oxygen vacancies. It is found that Fe and Al doping will increase the leakage current of oxygen vacancy defects of FE thin films, while the Cu and V doping significantly reduce the leakage current of oxygen vacancy defects of FE thin films. This is because the Cu and V doping have obvious pinning effect on oxygen vacancy defect. In addition, we find that the oxygen vacancies are pinned by Cu and V atoms due to the fact that the formation energy of oxygen vacancies can be remarkably reduced. So Cu and V doping in PbTiO3 not only induce the leakage current but also improve the fatigue resistance of the FE thin film induced by oxygen vacancies. Moreover, since the ionic radius of V is closer to the ionic radius of Ti than the ionic radius of Cu, V is easier to implement doping to suppress the leakage current caused by the oxygen vacancy defects. These conclusions are of important theoretical significance and application value for improving the performance of FE thin films and their FE memories.
Broadband absorbent materials based on topology optimization design
Authors: Mo Man-Man  , Ma Wu-Wei  , Pang Yong-Qiang  , Chen Run-Hua  , Zhang Xiao-Mei  , Liu Zhao-Tang  , Li Xiang  , Guo Wan-Tao  ,   Luoyang Ship Material Research Institute, Luoyang 471023, China;,   Jiangsu Saibo Space Science and Technology Co., Ltd, Nanjing 210000, China
Published: December 2020

In this paper, we present a kind of broadband absorbent material. The broadband absorbent material is designed based on topology optimization and tested. The optimizing of metamaterials with a genetic algorithm has become one of the most effective methods of designing metamaterials in recent years. An integral system with interactive simulation of MATLAB and CST Microwave Studio is developed, and the main program of genetic algorithm is written in MATLAB; with simulation and computation in CST the metamaterial is optimized by a genetic algorithm with power of global optimization. Vacuum assistant resin infusion process is a new cost-effective and high-performance process. The proposed radar absorbent material possesses a sandwich structure, which consists of transparent composite skin panel, resistive metasurface, polyurethane foam and reflective composite skin panel. The transparent composite skin panel is low-dielectric-constant glass fiber reinforced composite, which has excellent physical properties and weather resistant property. The core material is composed of low density polyurethane foam and metamaterials, which can well meet the requirements for weight reduction and the invisibility. The reflective composite skin panel is a low-resistance carbon fiber reinforced composite, which prevents the electromagnetic waves from transmitting and also provides electrical boundary conditions for metamaterial. Simulation and test results indicate that the reflectivity of the radar absorbent material is less than-12 dB in a range of 2-18 GHz. Because of the symmetrical structure design of the resistance film, the radar absorbent material is polarization-independent. We preliminarily produce a batch of radar absorbent materials and test their various performances. Such a radar absorbent material has a strong absorption and other properties such as light quality, high temperature resistance, low temperature resistance, humidity resistance and corrosion resistance. The radar absorbent material which has been widely used in the engineering field is easy to achieve the compatibility of absorption, mechanical properties and environmental performance. Compared with previous design method, the topology optimization design is simple in programming operation, good in generality, and short in design periode. The radar absorbent materials owns strong application value.
Coherent terahertz radiation via ultrafast manipulation of spin currents in ferromagnetic heterostructures
Authors: Zhang Shun-Nong  , Zhu Wei-Hua  , Li Ju-Geng  , Jin Zuan-Ming  , Dai Ye  , Zhang Zong-Zhi  , Ma Guo-Hong  , Yao Jian-Quan  ,   Department of Physics, Shanghai University, Shanghai 200444, China;,   Department of Optical Science and Engineering, Fudan University, Shanghai 200082, China;,   STU & SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China;,   College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300110, China
Published: December 2020

The development of efficient terahertz (THz) radiation sources is driven by the scientific and technological applications. To date, as far as the radiation of THz pulses is concerned, the widely used methods are biased semiconductor, electro-optical crystal and air plasma, which are excited separately by femtosecond laser pulses. The mechanisms involved in these THz sources are photo-carrier acceleration, second order nonlinear effect, and plasma oscillations, respectively. Here, we report the generation of coherent THz radiation in the designed ferromagnetic/non-magnetic metallic W/CoFeB/Pt and Ta/CoFeB/Pt trilayers on SiO2 substrates, excited separately by ultrafast laser pulses. The transient THz electric field is fully inverted when the magnetization is reversed, which indicates a strong connection between THz radiation and spin order of the sample. We present the THz radiation results of the bilayers, CoFeB/W, CoFeB/Pt and CoFeB/Ta, which are comprised of the trilayer heterostructures used in our experiments. We find that all experimental results are in good agreement with the results from the inversed spin-Hall effect (ISHE) mechanism. Owing to the ISHE, the transient spin current converts into a transient transverse charge current, which launches the THz electromagnetic wave. In our experiments, W or Ta has an opposite spin Hall angle to Pt. Therefore, the amplitude of the THz emission can be increased by a constructive superposition of two charge currents in metallic layers. Our results indicate that the peak-values of the THz radiation covering the 0-2.5 THz range from W/CoFeB/Pt and Ta/CoFeB/Pt are stronger than that from 0.5 mm thick ZnTe (110) crystal, under very similar excitation conditions. Finally, we investigate the dependence of peak-to-peak values for two different heterostructures on the pump fluence. The saturations of THz pulse at pump fluences of~0.47 mJ/cm2 and~0.61 mJ/cm2 are found for W/CoFeB/Pt and Ta/CoFeB/Pt heterostructures, respectively. The saturation can be generally attributed to the spin accumulation effect and laser-induced thermal effect. Our results indicate that the spin accumulation effect, by which the density of spin-polarized electrons is restricted in a non-magnetic metallic layer, is slightly less pronounced for Ta/CoFeB/Pt system at high fluences. Our findings provide a new pathway for fabricating the spintronic THz emitter, which is comparable to the conventional nonlinear optical crystals.
Generation and applications of non-diffraction beam
Authors: Liu Hui-Long  , Hu Zong-Hua  , Xia Jing  , Lü Yan-Fei1\2  ,   School of Physics and Astronomy, Yunnan University, Kunming 650500, China;,   Key laboratory of Astroparticle Physics of Yunnan Province, Kunming 650500, China
Published: December 2020

In recent years, with the development of laser technology, various non-diffraction beams each with a central spot unchanged after a long distance propagation, have been generated, they being the Bessel beam, higher Bessel beam, Mathieu beam, higher Mathieu beam, cosine beam, parabolic beam, and Airy beam. Diffraction-free beams are widely used in laser drilling, laser precision alignment, optical precision control, optical micromanipulation, optical communication, plasma guidance, light bullet, synthesis of autofocusing beam, nonlinear optics, etc.
In this paper, the expressions, generation methods and corresponding experimental results of the various non-diffraction beams are presented. There are many ways to generate the Bessel beam, they being circular slit, computed hologram, spherical aberration lens, resonant cavity, axicon, and metasurface. The main methods of generating the non-diffraction beams are summarized, and each method is analyzed in depth from the cost of the system, and then some suggestions for improving and perfecting are made. For the generation of non-diffraction beams, the passive methods are used most to convert other beams into corresponding non-diffraction beams by optical components. Due to the low damage threshold and high cost of optical components, the power, energy and beam quality of a non-diffracting beam will be limited. How to generate a high-power, high-beam quality non-diffracting beam will be a hot research spot.
Diffractionless beams have attracted a great deal of interest due to their unique non-diffraction, transverse-accelerating (or self-bending) and self-healing property. Transverse-accelerating property refers to that non-diffraction beams propagate along a parabola trajectory. The diffractionless beams' propagation trajectory control method implemented by changing system parameters is simple and easily successful, but cannot reverse acceleration direction, and its controlling range is limited. The self-healing property means that the non-diffraction beam tends to reform during propagation in spite of severe perturbations imposed. Both the Airy beam and the Bessel beam exhibit self-healing properties during propagation. And non-diffraction beams have potential applications in many fields. In atmosphere, such as in optical communication, non-diffracting beam exhibits more resilience against perturbations.
Finally, brief summary and outlook of non-diffraction beams playing important roles in future study, and their application prospects are presented. In addition to Airy beam and Bessel beam, for other non-diffraction beams due to the complexity of the beams themselves, by comparison, their applications are investigated very little, so the applications in Mathieu beam, cosine beam, and parabolic beam will be a hot research spot.