bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrically controlled quantum spin Hall in narrow zigzag graphene nanoribbon
Authors: Liu Na  , Hu Bian  , Wei Hong-Peng  , Liu Hong  ,   School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China;,   No.1 High School of Tongling, Tongling 244000, China
Published: December 2020

Using the tight binding Kane-Mele model including the self-consistent on-site Coulomb interactions (O-CIs), we study the influence of transverse electric field in the narrow zigzag graphene nanoribbon (ZGNR) plane on the edge band structure in order to investigate the way to control the type of quantum spin Hall (QSH) system in the ZGNR. The theoretical results show that when applying weak electric field intensity, the direction of electric field can adjust these two spin-down edge bands moving along the different directions in one-dimensional q space, which leads to the two different types of degenerative breakdown of two pure spin-down edge states at q=0.5. When applying positive electric field the energy of spin-down edge band at edge site 1 is higher than that at edge site 8. On the contrary, when applying negative electric field the energy of spin-down edge band at edge site 8 is higher than that at edge site 1. It shows that we can use the direction of electric field to control the two spin-down edge currents occurring at two different energies. Further, when the electric field intensity increases above 0.69 V/nm, the increased large band gap between the two spin-down edge bands leads to the inversion of these two spin-down edge bands. That is to say, there is a spin-down band gap, however, there is not a band gap for spin-up edge band in the region of spin-down band gap. Thus the system becomes half-metallic, and the QSH does not belong in the type B any longer. Specially, when the electric field intensity reaches 1.17 V/nm in the region of spin-down band gap, the pure spin-up edge state appears at q=0.5, which shows that the strong pure spin-up edge current along the edge site 8 can occur. With increasing the intensity of electric field, the QSH system undergoes three processes from the type B to the type C. When the electric field intensity is more than 1.42 V/nm, the two spin-up edge bands also present band inversion and turn into the conduction band and the valence band, respectively. Thus the system becomes semiconducting and the QSH system does not belong in the type C, ordinary quantum Hall system. Finally, according to the results discussed above, we can expect that using the direction and the intensity of the transverse electric field in plane we can adjust the properties of edge current, and control the type of QSH system varying from the type B to the type C.
Dzyaloshinsky-Moriya interaction in -(Zn, Cr)S(111) surface: First principle calculations
Authors: Li Xiao-Ying  , Huang Can  , Zhu Yan  , Li Jin-Bin  , Fan Ji-Yu  , Pan Yan-Fei  , Shi Da-Ning  , Ma Chun-Lan  ,   College of Science, Nanjing University of Aeronautics and Astronautics, Najing 210006, China;,   School of Mathematics and Physics, Suzhou University of Science and Technology, Suzhou 215009, China
Published: December 2020

According to density functional theory calculations, we elucidate the atomic and electronic structure of -(Zn, Cr)S(111) surface. The magnetic interaction between Cr atoms is via S atoms close to the Cr layer. This interaction is shown by the analysis of spin charge contour plot and partial density of states (DOS) of each atom. The DOSs of other S atoms are non magnetic and have no magnetic exchange with the Cr layer. E(q) and E(-q) are the dispersions between energy E and wave vector q of spin spiral in the opposite directions. They are calculated with generalized Bloch equations and all the magnetic moments of Cr atoms are arranged in the plane perpendicular to the -(Zn, Cr)S(111) film. The differences between E(q) and E(-q) are caused by the interface of -(Zn, Cr)S(111), where the symmetry of space perpendicular to the film is broken. Effective Heisenberg exchange interaction (HBI) and Dzyaloshinsky-Moriya interaction (DMI) parameters between different neighbors (Ji and di) are derived by well fitting the ab initio spin spiral dispersion E(q) to HBI with DMI model and E(q)-E(-q) to DMI model, respectively. The J2 plays a major role with a large negative value of -9.04 meV. The J1 is about 2/5 of J2, and J3 is about 1/4 of J2 with positive value. The DMI d1 is -0.53 meV, and d2 is 0.07 meV. With these HBI parameters, E(0) is the largest one at which -(Zn, Cr)S(111) has no ferromagnetic interface. The E(q) has its lowest energy with the q at M=b1/2 in the first Brillouin zone. Hence, -(Zn, Cr)S(111) is an M-type antiferromagnetic (AFM) material. In this type of AFM configuration, magnetic moments of Cr atom in a line along b2 are parallel to each other, and antiparallel to the magnetic moments in adjacent lines. The E(q) at K=b1/2+ b2/2 is almost as large as that at point. The value of DMI parameter d1 is about 1/5 of that on Co/Pt3 interface and 1/2 of Co/graphene. However, it is a negative number, which shows the clockwise chirality. The -(Zn, Cr)S(111) interface has obvious DMI, and skyrmion may be formed at this transition-metal/semiconductor (TM/S) interface. It is a good option to search for DMI in different kinds of TM/S heterojunctions. The material that combines the advantage of heterojunction, and DMI may have new magnetic phenomenon, which is usefulfor the magnetic storage. This paper enriches the research on DMI.
Method of picking up carbon nanotubes inside scanning electron microscope
Authors: Yang Quan  , Ma Li  , Yang Bin  , Ding Hui-Yang  , Chen Tao  , Yang Zhan  , Sun Li-Ning  , Toshio Fukuda  ,   School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China;,   Robotics and Microsystems Center, Soochow University, Suzhou 215021, China;,   Intelligent Robotics Institute, School of Mechatronic Engineering, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

In this paper a promising method of recognizing spatial contact state between carbon nanotubes (CNTs) and atomic force microscope (AFM) probe inside scanning electron microscope (SEM) is proposed. The CNTs can be picked up simply and effectively by van der Waals force without knowing depth information of SEM images by using this method. And a micro-nanorobotic manipulation system with 16 DOFs, which allows the automatic pick-up of CNTs based on visual feedback, is presented. The micro-nanorobotic manipulators are assembled into 4 units with 4 DOFs individually. Namely, a manipulator has 4 DOFs i.e., three linear motions and a rotational motion. Manipulators are actuated by picomotors with better than 30 nm linear resolution and less than 1 micro-rad rotary resolution. The van der Waals force mechanics model between CNTs and AFM probe in the picking up manuplation is established. In reality, the van der Waals force is the main attractive force under the vacuum condition inside SEM when the influence of staticelectricity is ignored. It is shown that the van der Waals force under horizontal (sphere-plane) contact model is significantly larger with appropriate overlapping length. Though the positions in both x and y directions of the CNTs and AFM cantilever are acquired, the relative positions of those two objects in the z direction remain unclear. In the gradually ascending process of AFM cantilever to contact the CNTs, the CNTs abruptly drop on the surface of AFM probe due to the van der Waals force. According to the relative coordinate system of SEM visual feedback images, the detection of contact state between carbon nanotubes and AFM probe are completed by using the inclination changing value of fitting line. The experimental results suggest that the abrupt contact between CNTs and AFM probe happens when the inclination changing value of the regression line is found to be 3.0263. The spatial contact state between carbon nanotubes and AFM probe includes line contact (Model a) and point contact (Model b, Model c). Then the dynamic difference method is introduced to identify the spatial contact model of CNTs and AFM probe. The results demonstrate that contact model of CNTs and AFM probe is line contact when the dynamic difference is approximately zero. The position of carbon nanotubes is corrected by moving AFM cantilever automatically underneath the CNTs. The picking-up of CNTs from substrate under line contact model is completed by choosing the optimum contact angle, contact length and pickup speed.
The quantum field model for treasury forward interest rate
Authors: Lei Li-Mei  , Feng Ling  ,   School of Economics and Management, Fuzhou University, Fuzhou 350002, China
Published: December 2020

With the further reform of interest rate liberalization and the increasing of interest rate derivatives, it becomes more important and urgent to model the forward rate accurately and rationally in China. In this paper, we use the quantum field theory in econophysics, which can effectively incorporate the incomplete correlations between forward interest rates with different maturities, to model the Chinese treasury bond instantaneous forward rates. Firstly, we start with the correlation structure of the instantaneous change of treasury forward rates, one of the most important variables for a quantum field, during the period from January 4, 2011 to December 30, 2016, then apply the quantum field theory to model the actual market evolution of the treasury instantaneous forward rates directly. Secondly, we also use the mainstream two-factor Heath-Jarrow-Morton (HJM) model commonly used in financial industry, which requires the particular form of forward rate volatility functions to be set in advance, to model the treasury instantaneous forward rates, then compare the results with those of the quantum field model. The empirical results show that the quantum field model based on stiff action provides a fitting accuracy of 63.23% for actual treasury bond instantaneous forward rate, but this fitting accuracy increases to 92.67% for the quantum field model with taking into account the psychological perceptive remaining time, which is also superior to the classic optimal two-factor HJM model with a fitting accuracy of 69.02%. Finally, the optimal parameters estimated are respectively substituted into the forward interest rate update equations of the quantum field model with the psychological perception time in mind and the classical two-factor HJM model to conduct the back testing of forward rates with one hundred maturities, from January 3, 2017 to December 30, 2017. From the results of average instantaneous forward rate, root mean square error and Theil inequality coefficient, we can see the superiority of using the quantum field theory to model the term structure of treasury forward rates compared with traditionally used two-factor HJM model in financial industry. In conclusion, the quantum field model we constructed, is more consistent with the actual situation, and all the parameters estimated by this model are obtained directly from the market data, without making any assumption of the specific form of forward rate volatility function, thus greatly improving the accuracy of applying the quantum field theory to finance. These findings are not only of great theoretic and practical significance for applying the quantum field theory to pricing those financial products linked to treasury bonds and for managing its relevant interest rate risk, but also have reference value for quantitatively analyzing banks and finance companies in financial field, and also for practitioners in the field of fixed-income securities.
Tunable bandgaps in novel two-dimensional piezoelectric phononic crystal slab
Authors: Liao Tao  , Sun Xiao-Wei  , Song Ting  , Tian Jun-Hong  , Kang Tai-Feng  , Sun Wei-Bin  ,   School of Mathematics and Physics, Lanzhou Jiaotong University, Lanzhou 730070, China
Published: December 2020

One of the outstanding challenges in phononic crystal development is the ability to achieve bandgap tunability in a low frequency range. The introduction of piezoelectric materials into phononic crystals is an attractive technique for actively controlling the bandgaps, which is reliable, economical and light in weight. Phononic crystal possesses an artificial periodic composite structure whose elastic constant, density and sound velocity change periodically. When the elastic wave passes through a phononic crystal, special dispersion curve is formed due to the interaction among periodically arranged materials. In order to study the tunability of phononic crystal bandgap, we propose a novel two-dimensional piezoelectric phononic crystal structure possessing a wider complete bandgap, which is composed of piezoelectric materials with hard coatings periodically connected by four thin bars. The dispersion relation, transmission spectrum and displacement field are studied by using the finite element method in combination with the Bloch theorem. Numerical results show that the frequency of the first complete bandgap of the new designed phononic crystal slab is lower and the band width is enlarged by a factor of 5 compared with the band width of the traditional binary phononic crystal. Instead of changing the geometry or orientation of the phononic crystal units or inclusions, electrical boundary conditions are used to actively control the frequency bandgap. The boundary condition for electrical open circuit and short circuit are considered in this paper. With different electrical boundary conditions imposed on the surfaces of the piezoelectric inclusions, multiple complete bandgaps can be controlled actively, which means that the new designed phononic crystal structure can adapt to the vibration and noise reduction requirements under different vibration environments. The effect of piezoelectric effect on the band structure is investigated as well. The piezoelectric effect has a great influence on the band structure, with the increase of the piezoelectric constant, a part of bands move to high-frequency and the other part of the bands are kept at the original position, which means that the piezoelectric effect is of benefit to the opening of the complete bandgap. Furthermore, according to the tunability of the bandgap, the switchable piezoelectric phononic crystal slab waveguide is analyzed. Calculation shows that the electrical boundary defects can result in defect bands existing in the complete band gap, and the elastic wave energy flows can be limited by changing the applied electrical boundary conditions. This investigation is conducive to controlling the bandgaps and also reveals potential applications in designing the sensing system and different piezoelectric devices.
Development of novel high-resolution electron energy loss spectroscopy and related studies on surface excitations
Authors: Zhu Xue-Tao  , Guo Jian-Dong  ,   State Key Laboratory for Surface Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   Beijing National Laboratory for Condensed Matter Physics, Beijing 100190, China
Published: December 2020

High-resolution electron energy loss spectroscopy (HREELS) is a powerful technique to probe vibrational and electronic excitations at solid surfaces. A monochromatic electron beam incident on the crystal surface may interact with the vibrations of adsorbed molecules, surface phonons or electronic excitations before being back-scattered. By analyzing the energy and momentum of the scattered electrons, we can obtain the information about the chemical bonds, lattice dynamics, occupation of electronic states, and surface plasmons. However the application of traditional HREELS to dispersion analyses is restricted by its point-by-point measurement of the energy loss spectrum for each momentum. Recently, a new strategy for HREELS was realized by utilizing a specially designed lens system with a double-cylindrical monochromator combined with a commercial Scienta hemispherical electron energy analyzer, which can be used to simultaneously measure the energy and momentum of the scattered electrons. The new system possesses improved momentum resolution, high detecting efficiency and high sampling density with no loss in energy resolution. The new HREELS system was employed to study the mechanism of the superconductivity enhancement at FeSe/SrTiO3 interface. By surface phonon measurements on samples with different film thickness, it is revealed that the electric field associated with phonon modes of SrTiO3 substrate can penetrate into FeSe film and interact with the electrons therein, playing the key role in the superconductivity enhancement. The surface collective modes of three-dimensional topological insulator was also studied by using this new HREELS system. A highly unusual acoustic plasmon mode is revealed on the surface of a typical three-dimensional topological insulator Bi2Se3. This mode exhibits an almost linear dispersion to the second Brouillion zone center without reflecting lattice periodicity, and it remains prominent over a large momentum range, with unusually weak damping unseen in any other system. This observation indicates that the topological protection exists not only in single-particle topological states but also in their collective excitations. The application of the new HREELS system with the ability to measure large momentum range with high-efficiency, will definitely promote the development of related researches on condensed matter physics.
Design of dual-band-pass frequency selective structure based on spoof surface plasmon polariton
Authors: Wang Chao  , Li Yong-Feng  , Shen Yang  , Feng Mao-Chang  , Wang Jia-Fu  , Ma Hua  , Zhang Jie-Qiu  , Qu Shao-Bo  ,   Department of Basic Sciences, Air Force Engineering University, Xi'an 710051, China
Published: December 2020

In this paper, a method of designing the frequency selective structure based on spoof surface plasmon polariton (SSPP) is proposed and demonstrated. According to the applications in different working bands, the designed frequency selective surface (FSS) and metallic fishbone structure array can be combined together to form a new frequency selective structure and satisfy the requirements for practical applications. Meanwhile, a dual-band-pass frequency selective structure with the property of steep cut-off frequency and high-efficiency transmission and inhibition is designed by using this method. The dual-band-pass frequency selective structure is composed of a metallic fishbone structure array and two identical FSSs. The metallic fishbone structure based on SSPP coupling can form a broadband high-efficiency transmission below the cut-off frequency of SSPP on the metallic fishbone structure. When a dual-band-pass FSS is loaded to this metallic fishbone structure array, a dual-band-pass frequency selective structure can be achieved. To improve the impedance matching of the dual-band-pass frequency selective structure, two identical FSSs are respectively loaded to the top and bottom sides of the metallic fishbone structure array. The simulated transmissivities of the dual-band-pass frequency selective structure exceed-0.5 dB in two frequency ranges:3.0-4.1 GHz and 10.5-10.9 GHz. The simulated transmissivities are lower than-10 dB in other frequency ranges:4.7-9.2 GHz and 12.1-18 GHz. The simulated transmissivities are even below-20 dB from 12.4 GHz to 15.5 GHz. The electromagnetic waves can be efficiently transmitted in the passband and restrained in the stopband. Then the dual-band-pass frequency selective structure is fabricated by using the printed circuit board technique and measured in the anechoic chamber. The measured results indicate that the real property of the dual-band-pass frequency selective structure is consistent with the simulated property and this method of designing the frequency selective structure is feasible. After filling the lightweight foam into the gap of the metallic fishbone structure, the mechanical loading property can be highly improved. Therefore, we can realize the design of combined structural and functional performance.
Excited charge-transfer organics with multiferroicity
Authors: Yuan Guo-Liang  , Li Shuang  , Ren Shen-Qiang  , Liu Jun-Ming  ,   School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;,   Department of Mechanical and Aerospace Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260, USA;,   Department of Physics, Nanjing University, Nanjing 210046, China
Published: December 2020

Multiferroics, showing simultaneous electric and magnetic degree of freedom, has aroused increasing interest due to tailored multiferroic properties and magneto-electric coupling for shaping the development of energy-efficient multifunctional devices. Now, the multiferroics can be classified as two groups:1) inorganic multiferroics, which can be single-phase, multi-phases oxide multiferroic or multiferroic heterojunction and 2) organic counterpart, which is mostly determined by instinct charge-transfer behavior. But it is difficult to find the polarization and the magnetization co-exist in a single-phase oxide multiferroic material, and their coupling range in the multiferroic heterojunction is only several atomic layers, which limits the applications. As a result, more and more different types of organic multiferroics have been studied. Some organic complexes can display dual ferroelectric and ferromagnetic properties at ambient temperature, e.g. thiophene-fullerene donor-acceptor charge-transfer networks. The organic charge-transfer complex is based on electron donor (D+) and acceptor (A-) assembly. D+A- are long-range ordering, the excitons have s lifetime and 1/2 spin, which contributes to the room temperature ferroelectricity and ferromagnetism. The excitons can be excited by external magnetic field, electric field, illumination and stress, and eventually influence the polarization, magnetization and magnetoelectric coupling coefficient. However, there are still many problems to be solved, i.e., searching for new charge-transfer systems and preparing supramolecular co-crystal with ordered molecular chain, further improving magnetoelectric properties; developing the heterojunction technology and epitaxial growth of organic ferroelectric or ferromagnetic systems on excited organic films, which is expected to greatly improve their magnetoelectric coupling effects; inventing more new charge transport organic multiferroic devices to extend the application scope of new multiferroic devices in actual industrial production. Generally speaking, the organic charge-transfer complexes not only greatly enrich the room temperature multiferroics materials, but also provide the technical basis for developing the new multifunctional electronic devices.
Skyrmions-based magnetic racetrack memory
Authors: Liang Xue  , Zhao Li  , Qiu Lei  , Li Shuang  , Ding Li-Hong  , Feng You-Hua  , Zhang Xi-Chao  , Zhou Yan  , Zhao Guo-Ping  ,   College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610101, China;,   School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen 518172, China;,   Collaborative Innovation Center for Shanxi Advanced Permanent Materials and Technology, Linfen 041004, China
Published: December 2020

Magnetic skyrmions are topologically stable spin configurations with small size, which can be driven into motion by a small current. They are widely regarded as building blocks for next-generation magnetic storage. The main advantage of skyrmions lies in their particular dynamic behaviors, especially in their ability to move stably in racetrack under the action of small spin-polarized currents. The writing, driving and reading methods of skyrmions in racetrack are reviewed in detail in this paper, including the most recent research findings. The review focuses on the most commonly used driving method, i.e., driving skyrmions by applying spin-polarized currents. The clogging and annihilation of skyrmions in racetrack are analyzed, with the skyrmion Hall effect discussed which may lead skyrmion signals to lose. Methods to avoid skyrmion Hall effect are introduced and hence the optimized designs for skyrmion-based racetrack are also reviewed. Finally, some challenges of skyrmion-based racetrack memory are discussed.
Crystal structures and physical properties of novel 4d/5d based superconductors
Authors: Song Yan-Peng  , Chen Hong-Xiang  , Guo Jian-Gang  , Chen Xiao-Long  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

The interplay among spin, orbital and lattice in a strongly-correlated electron system attracts a lot of attention in the community of condensed matter physics. The competition and collaboration of these effects result in multiple ground states, such as superconductivity, quantum criticality state, topological phase transition, metallic-insulating transition, etc. As is well known, the spin-orbital coupling is an interaction between the spin angular moment and orbit angular moment. In quantum mechanics, the spin-orbital coupling can be described as an additional interaction in the Hamitonian. For a compound containing heavy elements, the spin-orbital interaction becomes nontrival and can influence the ground states. For instance, in 4d/5d based superconductors, the superconducting pairing mechanism might be significantly different from that of conventional Bardeen-Cooper-Schrieffer superconductor. In this paper, we will summarize the structures and physical properties of several typical 4d/5d transition metal-based superconductors and discuss the intrinsic relationship between them. Importantly, the strength of anionic covalent bonds can determine the phase transition and superconductivity, which will be highlighted here.
Terahertz photoconductivity in InAs/GaSb based quantum well system
Authors: Wei Xiang-Fei  , He Rui  , Zhang Gang  , Liu Xiang-Yuan  ,   School of Electrical and Photoelectronic Engineering, West Anhui University, Lu'an 237012, China
Published: December 2020

Great attention has been paid to the terahertz (THz) technology due to its potential applications, in which THz radiation source and detector with excellent performances at the room temperature are most desired. The semi-classical Boltzmann equation is employed to study the response of electrons and holes to the electromagnetic radiation field in InAs/GaSb based type Ⅱ quantum well system (QWS). The balance equation method is used to solve the Boltzmann equation, and the influences of the structure of the QWS on the photoconductivity is studied in detail to reveal the mechanism of the photoconductivity in the QWS. The photoconductivity is influenced by the carrier density, the subband energy of the carriers and the coupling of the wavefunctions which can be modulated conveniently by the structure of the QWS. In this study, our attention focuses on the influence of the structure of the QWS on the conductivity. When the width of the InAs layer and the GaSb layer are both 8 nm, a sharp peak in photoconductivity is observed at about 0.2 THz due to the electron transition in different layers. The strength of the peak decreases slightly with the increase of the temperature, and a red shift is observed. However, the photoconductivity is not sensitive to the temperature and has good performances at relatively high temperatures up to the room temperature, which indicates that the InAs/GaSb based type-Ⅱ QWS can be used as a THz photoelectric device at room temperature.
Total ionizing dose effect of ferroelectric random access memory under Co-60 gamma rays and electrons
Authors: Qin Li  , Guo Hong-Xia  , Zhang Feng-Qi  , Sheng Jiang-Kun  , Ouyang Xiao-Ping  , Zhong Xiang-Li  , Ding Li-Li  , Luo Yin-Hong  , Zhang Yang  , Ju An-An  ,   Department of Material Science and Engineer, Xiangtan University, Xiangtan 411105, China;,   Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Ferroelectric random access memory (FeRAM) has superior features such as low power consumption, short write access time, low voltage, high tolerance to radiation. Data about the total ionizing dose (TID) radiation effects of FeRAM have not been rich in the literature so far. Experimental study of the ionizing radiation effect of FeRAM is carried out based on Co-60 γ rays and 2 MeV electrons. And the TID radiation damages to the FeRAM in the dynamic biased, static biased and unbiased case are studied. The direct current and alternating current parameters are tested by J-750. The test results indicate that the stored information about the memory cell has no change before failure, the ferroelectric capacitors are still able to hold the data. Accordingly, the TID failure of the FeRAM should be mainly ascribed to the poor TID hardness of the peripheral complementary metal oxide semiconductor circuits. Besides, three types of electric fields from three working conditions can result in different generation and recombination rates of electronhole pairs. For static biased case, the internal electric field in the FeRAM is constant. It can lead to high net production of the electronhole pairs and a great number of trapped charges. Hence the radiation damage in the static biased case is most serious. With the increase of the total radiation dose, the electrical parameters of FeRAM have different degradations. Part of the parameters that can be detected by J-750, may lapse before they are detected online. Standby current, operating power supply current, leakage current and output low voltage are radiationsensitive parameters of FeRAM through analyzing the test data. And, other parameters, which have slight changes, have small effect on the degradation of the device. Furthermore, the electron accelerator is used in electron irradiation experiment. By comparing the results of the two kinds of radiation tests, it is discovered that the electrons tend to cause lighter TID degradation than Co-60 γ rays because of the high density of electrons in the electron irradiation environment and low net production rate of electronhole pairs. In addition, the electrons have weaker penetration than Co-60 γ rays due to low energy. The device packaging, the upper metal layers can also influence the experimental result of electron irradiation. The above conclusions provide a reference value for the total dose effect of FeRAM and will be of great significance for studying the radiation hardening of FeRAM.
Disintegration, functionalization and drug-delivery application of nanodiamond
Authors: Qin Shi-Rong  , Zhao Qi  , Cheng Zhen-Guo  , Su Li-Xia  , Shan Chong-Xin  ,   School of Physical Engineering, Zhengzhou University, Zhengzhou 450000, China;,   School of Basic Medical Sciences, Zhengzhou University, Zhengzhou 450052, China
Published: December 2020

In recent years, with the rapid development of nanomedicine, the nanomaterials for bio-medical applications have received much attention. Although there are a variety of nanomaterials such as lipid, carbon nanotube, etc. that have been studied as drug carrier, they are restricted by the potential toxicity and high cost of production. So, it is necessary to find a good alternative for the future drug delivery applications. Detonation nanodiamond, as an important carbon nanomaterial, possesses many excellent properties such as facile functionalization, large specific surface area, low toxicity and high chemical stability and so on, which make them advantageous in bio-medical applications over many other nanomaterials. In this work, the carboxyl functionalized and well-dispersed nanodiamond (ND-COOH) is obtained through disintegration and chemical modification, and then the functionalized nanodiamond is characterized by transmission electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, etc. to analyze its morphology and structure and the toxicity. Besides, the drug loading and release properties are also examined. The ND-COOH exhibits high zeta potential in aqueous solution, which enables them adsorb doxorubicin (dox) molecules onto the surface through electrostatic interaction, and the maximal loading reaches to 325 μg/mg, which is higher than most of reported results. It is because the bond between dox and ND-COOH origins from the electrostatic attraction between negatively charged-COO- on the ND and positively charged–NH3 in the dox. So, when the drug compounds are dispersed into low pH environment, the high H+ concentration would promote the transformation of –COO- into –COOH, which would weaken the electrostatic attraction between ND and dox and hence accelerate the drug release. This leads a drug release to reach 85% in pH 5.0 PBS and less than 40% in pH 7.4 PBS, exhibiting interesting pH-responsive drug release behavior. Finally, the toxicity and in vitro cancer cell killing results of ND-COOH and ND-dox preliminarily show that in the concentration range from 0 to 150 μg/mL, the functionalized ND-COOH does not inhibit the viability of SGC-7901 cells, exhibiting low toxicity. In contrast, the ND-dox shows obvious cytotoxicity towards SGC-7901 cells by strongly inhibiting their viability to lower than 40% in 150 μg/mL group. This work details and systematically discusses the disintegration, functionalization, drug loading and release properties of ND, which would be significant in promoting the biomedical application of ND.
Flow and mixing in shock-accelerated elliptic helium gas cylinder process
Authors: Li Dong-Dong  , Wang Ge  , Zhang Bin  ,   College of Aerospace and Civil Engineering, Harbin Engineering University, Harbin 150001, China;,   School of Aeronautics and Astronautics, Shanghai Jiao Tong University, Shanghai 201100, China
Published: December 2020

In shock bubble interaction (SBI), the baroclinic vorticity generated by misalignment of pressure and density gradient will lead to flow instability which promotes the mixing between the bubbles and surrounding gas. A numerical study on the flow and mixing of shock-accelerated elliptic helium cylinder with the surrounding air is presented in this study. To well simulate the SBI, compressible multi-component two-dimensional Navier-Stokes equations are solved by combining with double-flux model and five-order weighted essentially non-oscillatory scheme. Both the wave system evolution and the interface deformation are clearly illustrated by using the present numerical method. Quantitatively, the length scales of distorted interface, compressibility of helium cylinder, circulation, and total mixing rates of helium are measured and compared to investigate the mixing mechanism and structure effect of the helium cylinder. It is found that the evolution of elliptic interface is closely related to its shape. In the case of elliptic gas cylinder shock-accelerated along major axis, the most remarkable feature is the air jet which grows constantly with time and penetrates the downstream interface boundary, forming two independent vortices. The penetration speed of the air jet is found to increase with ellipse eccentricity increasing. In addition, like the case of the circular helium cylinder, typical free-precursor irregular shock wave refraction occurs when incident shock wave passes through the interface. In the case of shock-accelerated elliptic gas cylinder along minor axis, a distinct flat structure appears due to the shock compression during the evolution of interface, and then vorticity concentrates at the two ends of the ellipses, which finally bends the interface severely. Simple regular shock wave refraction occurs in the large frontal area of the helium cylinder. These features also grow intensely with the eccentricity of the initial elliptic interface increasing. The distinct morphologies of these elliptic interfaces also lead to the different behaviors of the interface features including the length and height. The comprehensive analysis shows that for the elliptic helium cylinder, the structure effect not only affects the interface evolution in a length-scale manner but also plays a role in their mixing process. The mixing rate of helium cylinder shocked along the major axis is significantly superior to that along the minor axis.
Quantum metrology with atom and light correlation
Authors: Feng Xiao-Tian  , Yuan Chun-Hua  , Chen Li-Qing  , Chen Jie-Fei  , Zhang Ke-Ye  , Zhang Wei-Ping  ,   Department of Physics, School of Physics and Material Science, East China Normal University, Shanghai 200241, China;,   Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

The measurement of physical quantities and measurement units standard promote the development of metrology. Especially, the developments of laser interference and atomic frequency standard bring a revolutionary leap for metrology. Many precision measurement techniques have been proposed and experimentally demonstrated, such as gravitational wave measurements and laser gyroscopes based on laser interferometry, and atomic clocks and atomic gyroscopes based on the atom interferometry. Recently, a new branch of science, quantum metrology, has grown up to further explore and exploit the quantum techniques for precision measurement of physical quantities.#br#This paper will focus on recent developments in quantum metrology and interference based on coherence and correlation of light and atom. Firstly, we briefly review the development of metrology. Then, we introduce our own researches in recent years, including quantum-correlation SU(1,1) optical interferometer based on four wave mixing process in atomic vapor and the atom-light hybrid interferometer based on Raman scattering in atomic vapor.#br#Interferometer is a powerful tool to measure physical quantities sensitive to the inference wave with high precision, and has been widely used in scientific research, industry test, navigation and guidance system. For example, the laser interferometer is able to measure optical phase sensitive quantities, including length, angular velocity, gravitational wave and so on. Meanwhile, the atom interferometer is sensitive to the change of atomic phase caused by the light, gravity, electric and magnetic fields. As a new type of interferometry, the atom-light hybrid interferometer, is sensitive to both the optical phase and atomic phase. Furthermore, SU(1,1) interferometer and nonlinear atom-light hybrid interferometer have the ability to beat the standard quantum limit of phase sensitivity. Quantum interference technology, whose phase measurement accuracy can break through the limit of standard quantum limit, is the core of quantum metrology and quantum measurement technology.
First principle study on atomic structure of La65X35(X=Ni, Al) metallic glasses
Authors: Liu Qi  , Guan Peng-Fei  ,   Division of Materials and Energy, Beijing Computational Science Research Center, Beijing 100193, China
Published: December 2020

The atomic-level structure of metallic glasses (MGs) is one of the most fundamental and challenging topics in condensed matter physics. Unlike crystalline metals or alloys, the MGs are lacking in a well-defined description of structure order, which is a major obstruction for relating its structure to physical properties. Obviously, it is vitally important to have an in-depth understanding of the atomic packing scheme in MGs. Due to the limitations of experimental characterization methods, it is hard to obtain the atomic packing scheme of MGs in experiment. Computational simulation on an atomic scale has become an important method of characterizing the atomic structure of MGs. The La-based LaNiAl glass forming system is well-known for its good glass-forming ability, distinctive relaxation peak that is well separated from relaxation, and liquid-liquid transition at a temperature around 1000 K. Many efforts have been made to investigate these novel properties. However, the atomic structure of this system is rarely studied. In this paper, the atomic structure evolution from liquids to glass states in La-based binary MGs La65Ni35 and La65Al35 are studied via ab initio molecular dynamics based on the density functional theory. The local structures are systematically analyzed by the radical distribution function, partial radical distribution function (PRDF), Voronoi tessellation method, and bond-type method in Honeycutt-Andersen. The results indicate that the PRDF of NiNi is much weaker than that of AlAl, which indicates the NiNi avoidance in La65Ni35. The major peaks of PRDFs are always smaller than the sum of efficient radius of the two kinds of atoms, especially for LaNi pairs. Atomic structure of the two systems are coincident with dense atomic packing scheme and the difference between major Voronoi polyhedron types (0, 3, 6, 0 for La65Ni35 and 0, 2, 8, 1, 0, 2, 8, 0 for La65Al35) in local structures is controlled by their ratio of solute to solvent atomic size. The high five-fold local symmetry structure gradually increases in both systems with the decrease of temperature, which validates its pivotal part in hindering crystallization. The electronic structure is studied with the partial density of states. It is found that the significant bond-shortening between La and Ni is due to the strong hybridization between Ni-3d and La-5d electrons and this result may play a key role in understanding composition related structure and properties in MGs.
Influence of laser-generated perturbations on hypersonic boundary-layer stability
Authors: Liu Xiao-Lin  , Yi Shi-He  , Niu Hai-Bo  , Lu Xiao-Ge  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In this paper, the boundary layer flow stability is investigated experimentally in a 7° half-angle straight cone under the condition of Mach number 6 and unit Reynolds number 3.1×106/m. Expanded shock wave generated by focusing laser in a limit space is used as the small artificial disturbance, and the influence of the laser-generated perturbation on the stability of the hypersonic boundary layer is analyzed. In the experiment, the wall fluctuation pressure is measured by the high-frequency pressure sensors whose response frequencies each reach a value on the order of megahertz. Through the short time Fourier transformation and power spectrum density analysis of the pressure data, the results show that when the laser-generated perturbation is added to the flow field, the position of the second mode wave advances and the amplitude of the disturbance wave greatly increases. Within the same flow range, the laser focusing on disturbance pushes the disturbance wave in the boundary layer from the linear development phase into the nonlinear development state. The laser-generated perturbation has a significant effect on the promotion of the development of disturbance waves in the boundary layer. At the same time, laser-generated perturbation that has different influences on the boundary layer when it focuses on different positions. When the laser focus disturbance focuses on the location X=100 mm, the amplitude of the disturbance wave with a frequency of 90 kHz in the boundary layer grows fastest, and the amplitude magnification at the position of X=500 mm is 3.81. When the laser perturbation is added to the free flow in front of the cone, the frequency of the disturbance wave with the fastest amplitude increase speed greatly decreases to 73 kHz. In the same range, the amplitude magnification is 4.51 times. It can be seen that when the laser focuses on the free stream upstream from the cone, its effect on the disturbance wave in the boundary layer is more significant.
Electric field driven magnetic switching in nanoscale multiferroic heterostructures
Authors: Song Xiao  , Gao Xing-Sen  , Liu Jun-Ming  ,   Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China;,   National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
Published: December 2020

Recently, there has been a surge of research interest in the electric field control of magnetism due to its promising application in spintronic and memory devices, which has become a hot topic in the field of multiferroic research. In current spintronic technology, magnetic reversal is usually driven by a large electric current via current generated magnetic field or spin-torque effect to write/erase a magnetic bit, and thus producing large power consumption and heat dissipation. While using insulating multiferroic materials, the reversal of magnetization can be triggered by applying an electric field instead of current, hence dramatically reducing the energy consumption and heat dissipation. With the current miniature trend in microelectronic technology, it is very essential to explore the electric field driven magnetic reversal (EFMS) behaviours in a micro/nanometer scale. In this article we briefly review the new progress in the field of EFMS based on multiferroic heterostructures, including some new features arising from size reduction, as well as some recent experimental and theoretical advances towards nanoscale EFMS, e.g. strain-mediated coupling, or spin exchange coupling in BiFeO3-based heterostructures, and their associated mechanisms. Finally, some key challenges in developing future EFMS based magnetoelectric devices, and some prospects for future research are also discussed.