bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of fitting methods for laser-triggered ultrafast magnetization dynamics in diluted magnetic semiocnductor (Ga, Mn)As film
Authors: Li Hang  , Zhang Xin-Hui  ,   State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

Laser-triggered magnetization dynamics for diluted magnetic semiconductor (Ga, Mn)As has drawn great attention in recent years, aiming at studying the ultrafast manipulation of collective spin excitations towards spintronic information processing. In this work, different fitting methods for time-resolved magneto-optical Kerr (TR-MOKE) study of the laser-triggered magnetization dynamics in a diluted magnetic semiconductor (Ga, Mn)As are analyzed and compared. It is known that the exponentially damped cosine harmonic function and the numerical simulation based on Landau-Lifshitz-Gilbert (LLG) equation are usually applied to fit the laser-induced magnetization dynamics from TR-MOKE measurements. Under the specified experimental conditions, it is sometimes hard to fit the TR-MOKE response well with single-mode uniform precession by using the exponentially damped cosine harmonic function. Although the fitting with multiple precession frequencies may usually show much better fitting results, the numerical simulation based on LLG equation reveals that the multi-frequency precessional modes are caused by the superposition of three-dimensional trajectories of magnetization precession with different contributions from the in-plane and out-of-plane magneto-optical response in (Ga, Mn)As. Thus, the multi-frequency precessional modes obtained by adopting the fitting method with exponentially damped cosine harmonic function could be the fake ones. Meanwhile, it is important to note that though the LLG equation can be used to fit the macroscopic magnetization precession well with single frequency, the contribution of pulse-like background response from photo-generated polarized carriers at the above-bandgap excitation is strongly superimposed on the magnetization precession response, and the pulse-like background response cannot be described by LLG equation. Thus one should be cautious of applying LLG equation only to fit the entire TR-MOKE signal, especially when the excitation energy is above the band gap of (Ga, Mn)As. One may combine both fitting methods, namely, fitting with the exponentially damped cosine harmonic function and the LLG simulation by considering both the in-plane and out-of-plane magneto-optical response of (Ga, Mn)As film in order to properly fit the laser-triggered magnetization dynamic response from TR-MOKE measurements. The proper handling of fitting methods helps to extract the dynamic magnetic parameters correctly and to further understand the physical mechanisms for triggering the ultrafast manipulation of collective spin dynamics. This is fundamentally important for developing novel spintronics based on diluted magnetic semiconductor (Ga, Mn)As.
High-efficiency ultra-wideband polarization conversion metasurfaces based on split elliptical ring resonators
Authors: Yu Ji-Bao  , Ma Hua  , Wang Jia-Fu  , Feng Ming-De  , Li Yong-Feng  , Qu Shao-Bo  ,   School of Science, Air Force Engineering University, Xi'an 710051, China;,   State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Polarization state of electromagnetic waves plays a significant role in the fields of signal transmission and sensitive measurements. High-efficiently manipulating and controlling polarization state by two-dimensional flat metamaterials over a wider bandwidth has been turned into hot issues in recent years. A polarization conversion metasurface based on the split elliptical ring resonator is designed, simulated, and experimentally validated in the microwave regime. The proposed metasurface can convert a linear polarization state into its orthogonal one with a high efficiency for an ultra-wide band. Theoretically, the mechanism of polarization conversion is explained by the theoretical models of high-impedance surface and multi-plasmonic resonances. The metasurface has a strong anisotropy, which behaves as a high-impedance surface, and serves as a metal sheet in orthogonal orientation in the vicinity of the resonant frequencies. The reflection phase has a delay of π for one of the two electric field components and remains unchanged for the other. As a result, the polarization angle of the synthesized reflection electric field rotates by π/2. The fourth-order plasmonic resonances are generated by the electric and magnetic resonances, which contribute to the bandwidth expansion of cross-polarization reflection. Numerically, by means of simulation and analysis on the axial ratio and flare angle of the split elliptical ring resonators, the influences of these structure parameters on the bandwidth and efficiency of the polarization conversion are clarified. And then the design method of multi-peaks and wideband polarization conversion metasurfaces with split elliptic ring resonators is proposed for different kinds of applications. Experimentally, the geometry is implemented within the currently available printing circuit techniques, and a free space method is adopted to measure the scattering coefficients. A polarization conversion ratio of the fabricated sample is larger than 85% at a relative bandwidth of 104.5%, and approximately 100% of the polarization conversion ratio can be achieved around the resonant frequencies. Experimental results are in good consistency with the simulation results. Compared with the anterior polarization conversion metasurfaces, the proposed metasurface broadens the cross-polarization bandwidth greatly with little efficiency expenses. These works provide beneficial guidance for manipulating and controlling polarization states of electromagnetic waves, and have potential applications in modern radar and communication systems, signal detection systems, and sensitivity measurement systems, etc.
Effects of nuclear reactions between protons and metal interconnect overlayers on single event effects of micro/nano scaled static random access memory
Authors: Zhao Wen  , Guo Xiao-Qiang  , Chen Wei  , Qiu Meng-Tong  , Luo Yin-Hong  , Wang Zhong-Ming  , Guo Hong-Xia  ,   State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024, China
Published: December 2020

Since metal interconnect overlayers are central components of micro/nano scaled static random access memory (SRAM), the effects of their presence on proton-induced single-event susceptibility are noteworthy. Geant4 is used to calculate the kinds and probabilities of secondary particles existing in bulk silicon, which are produced from nuclear reactions between protons of different energies (30, 100, 200 and 500 MeV) and micro/nano scaled SRAM. The probabilities of secondary particles with Z≥30 in different overlays are compared with one another; the particles are chiefly coming from nuclear reactions between 500 MeV protons and the SRAM topped with interconnect overlayers. In addition, the kinds and ranges of the secondary particles with high LETs (linear energy transfers) are also analyzed. Results show that there is an increase in the production of secondary particles with Z≥30 due to the presence of metal interconnect overlayers and the rise of proton energy. The secondary particles with Z>60 in bulk silicon are generated by proton interactions with tungsten. As another consequence of the interactions, the secondary particles with 30≤Z≤50 are produced, the probability of which is higher as the proton energy increases. The maximum LET for the secondary particles with 30≤Z≤50 is about 37 MeV·cm2/mg and the corresponding range is several microns, which may induce single event latch-up in micro/nano scaled SRAM with well depths on the order of microns. Results obtained support the theoretic analysis of proton-induced single event effects of aerospace devices in space radiation environment.
Comprehensive evaluation method in the cooling mode of large-scale hydro-generators
Authors: Teng Qi-Zhi  , Tan Xin  , Wu Zi-Yu  , Shen Jun  , Wang Hai-Feng  ,   School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China;,   Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, China;,   Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

With the development of large-scale hydro-generators, large hydro-generator cooling technology is increasingly demanded. Different cooling method will not only affect the structure of hydro-generators, also it will affect the energy consumption and reliability of the generators. The commonly large-scale hydro-generator cooling method includes: air cooling, water cooling, and evaporative cooling methods. This paper analyzes the principle of the three cooling methods and describes qualitatively the advantages and disadvantages of them. The air cooling hydro-generator structure is simple, but the generator operating temperature is high; the water-cooling method has a certain superior in cooling performance, but it requires more auxiliary equipments, and has higher equipment failure rates. The evaporative cooling method is a recently developed cooling technique. It not only has a remarkable cooling effect, but also can decrease the equipment failure rates and the cost of maintenance. In order to build a comprehensive model to assess the three hydro-generator cooling methods, this paper proposes a comprehensive evaluation method based on AHP. The method includes 11 indexes of resource consumption, energy consumption and reliability to assess the influence of cooling ways. The energy saving influence of all the 11 indicators are calculated by using the AHP comprehensive evaluation. Finally, comparison between a 400 MW air cooling and an evaporative cooling hydro-generators at Lijiaxia hydropower Station are made using the proposed method. Evaluation results indicate that in terms of daily operation, the energy saving of the evaporative cooling hydro-generator can be more than 300 tons standard coal equivalent per year as compared with that of air cooling generator. In terms of maintenance, the evaporative cooling method can save more than 5000 tons of standard coal equivalent per year. The comprehensive evaluation results show that the evaporative cooling method is significantly better than the air cooling. It can be seen that the proposed evaluation method may quantitatively calculate the merits of hydro-generator caused by cooling method, which provides guidance to select and improve cooling method of hydro-generator.
self-similarity of Rydberg hydrogen atom in parallel electric and magnetic fields
Authors: Li Hong-Yun  , Yin Yan-Yan  , Wang Qing  , Wang Li-Fei  ,   School of Science, Shandong Jiaotong University, Jinan 250357, China
Published: December 2020

Using the semi-classical methods, the self-similarity structure of Rydberg hydrogen atom in parallel electric and magnetic fields is analysed in this paper. Based on the Hamiltonian canonical equations, all the escape orbits are found, and the escape time and the initial launch angle of every escape orbit can be derived. The self-similarity structure of escape time plot is found by studying the relationship between the escape time and the initial launch angle of electron in parallel electric and magnetic fields. The relationship between the self-similarity structure and escape orbits is also established through the study of the escape orbits in the escape time plot. The regularity of escape orbits in self-similarity structure is found and the corresponding escape orbits in self-similarity structure plots meet the law of (-o)k. According to this rule, the self-similarity structure can be easily found, and the rule is applicable to other research system. Moreover, the influences of scaled energy and scaled magnetic field are analyzed in detail. It is presented that the dynamic behavior of the Rydberg hydrogen atom is sensitively controlled by scaled energy and scaled magnetic field. Different scaled energies or scaled magnetic fields can lead to different escape behaviors of electron. It is also found that the self-similarity structure is present not in all cases. When scaled energy or scaled magnetic field is small, the escape time plot is simple, and no self-similarity structure is observed. When scaled energy or scaled magnetic field increases, self-similarity structure appears accordingly and the system becomes complicated. When scaled energy or scaled magnetic field changes, the self-similarity region also changes. For a given scaled magnetic field, with the increase of scaled energy, self-similarity region shifts toward the bigger initial launch angle, while self-similarity region shifts toward the smaller initial launch angle with the increase of scaled magnetic field for a given scaled energy.
Incoherent broadband cavity enhanced absorption spectroscopy for measurements of atmospheric HONO
Authors: Duan Jun  , Qin Min  , Fang Wu  , Ling Liu-Yi  , Hu Ren-Zhi  , Lu Xue  , Shen Lan-Lan  , Wang Dan  , Xie Pin-Hua  , Liu Jian-Guo  , Liu Wen-Qing  ,   Anhui Institute of Optics and Fine Mechanics, Key Laboratory of Environmental Optics and Technology, Chinese Academy of Sciences, Hefei 230031, China;,   Institute of Electric and Information Technology, Anhui University of Science and Technology, Huainan 232001, China;,   School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

We report the development of an incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) based on an ultraviolet light emitting diode (UV-LED), and the IBBCEAS instrument is used for simultaneously measuring of the atmospheric HONO and NO2. The cavity-enhanced method is characterized by high sensitivity and spatial resolution. The incoherent broadband light is focused into a high-finesse optical cavity, two highly reflecting mirrors form the ends of the cavity, and the light is then trapped between the two highly reflecting mirrors, resulting in long photon residence time and long optical path length. The effects of the Rayleigh scattering of the gases in the cavity and stability of the UV-LED light source were discussed in this paper. The reflectivity of the highly reflecting mirror was calibrated by the difference of Rayleigh scattering of He and N2, and the optimum averaging time of the IBBCEAS instrument was confirmed to be 320 s by the Allan variance analysis. Detection limits (1) of 0.22 ppb for HONO and 0.45 ppb for NO2 were achieved with an optimum acquisition time of 320 s. In order to test the accuracy of measured results by the IBBCEAS instrument, concentrations of HONO and NO2 were recorded during about continuous three days by the IBBCEAS instrument and compared with the results obtained by a different optical absorption spectroscopy (DOAS) instrument. The results of HONO show a linear correction factor (R2) of 0.917, in a slope of 0.897 with an offset of 0.13 ppb; NO2 concentration measured by the IBBCEAS instrument accords well with the result obtained by the DOAS instrument, with a linear correlation of R2 = 0.937, in a slope of 0.914 with an offset of-0.17 ppb.
Broadband anomalous reflector based on cross-polarized version phase gradient metasurface
Authors: Fan Ya  , Qu Shao-Bo  , Wang Jia-Fu  , Zhang Jie-Qiu  , Feng Ming-De  , Zhang An-Xue  ,   Science College, Air Force Engineering University, Xi'an 710051, China;,   Key Laboratory of Electronics Materials Research of Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China;,   School of Electronics and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Phase gradient meatsurface (PGM) is a new way to control reflective beam and refractive beam. By means of PGM, wave-fronts can be controlled in a more freedom way. The generalized Snell's law was put forward first by Nanfang Yu et al. [Yu N F, Genevet P, Kats M A, Aieta F, Tetienne J P, Capasso F, Gaburro Z 2011 Science 333 334] to describe the anomalous refraction on PGM. Anomalous refraction and out-of-plane reflection were then demonstrated using PGM composed of V-shaped nanoantennas. As deeper research about PGM, many reflective PGMs are also proposed. Typical examples are the reflective PGM using H-shaped resonators by Lei Zhou's group and using split-ring resonators by Shaobo Qu's group, both acting as high-efficiency surface wave couplers. However phase gradient of most PGMs above are achieved in a narrow-band and cannot change the polarizations. Anomalous reflection can only be realized in a certain narrow-band, and anomalous reflective angles cannot be precisely predicted. In this paper, a polarized conversion metasurface based on double-circular metallic resonator is first designed. The conversion successfully achieves ultra-wideband cross-polarization for linearly-polarized waves within a broadband of 12.2 GHz (from 7.9-20.1 GHz) with more than 99% cross-polarized reflectance. On the premise of high efficiency, reflective phase can be regulated by changing geometrical parameter of double-circular metallic structure. Then a broadband one-dimensional dispersive phase gradient metasurface comprised of six unit cells periodically arrayed above substrate is designed and fabricated. The PGM can perfectly achieve anomalous reflection. Measured result about its specular reflectivity is in good agreement with simulated result. Moreover, the measurement results of E-field distribution and anomalous reflective angle nearly accord with simulation results. Anomalous reflective angle is precisely predicted based on the generalized Snell's law. Both simulation and experiment verify that the PGM can make incident waves efficiently coupled as surface waves from 8.9-10 GHz and anomalously reflected in a range from 10 GHz to 18.1 GHz.
Four-wave-mixing generated by femto-second laser pumping based on graphene coated microfiber structure
Authors: Feng Qiu-Yan  , Yao Bai-Cheng  , Zhou Jin-Hao  , Xia Han-Ding  , Fan Meng-Qiu  , Zhang Li  , Wu Yu  , Rao Yun-Jiang  ,   Key Laboratory of Optical Fiber Sensing and Communication, Ministry of Education, School of Communication and Information Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China;,   State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China;,   School of Optoelectronic Information, University of Electronic Science and Technology of China, Chengdu 610054, China
Published: December 2020

Nonlinear optics researches of graphene-based four waves mixing (FWM) effect are important for a new generation of photonic devices. Compared with the ordinary graphene materials, the P-doped graphene based hybrid waveguide structure is more conducive to the simulating of the third-order nonlinear effect in low power due to its smaller transmission loss. In this work, we propose a P-doped graphene coated microfiber hybrid waveguide structure for femto-second laser pumping excited FWM. By the simulations, we analyze the HE11 mode distribution and the effective refractive index of the silica microfiber and P-doped graphene coated microfiber hybrid waveguide with different fiber diameters at a wavelength of ～1550 nm. We also implement the fabrication processing and characterize this P-doped graphene coated microfiber hybrid waveguide. In the experiments, we utilize a femto-second laser as the pump laser with a peak power up to kW. As the graphene material and the microfiber contribute to the nonlinearity, the cascade FWM could be obtained. Experimental results demonstrate that when the peak power of the injection pump is fixed at 1.03 kW, by adjusting the detuning in wavelength to the length less than 10.0nm, there are four sets of frequency components that can be observed. In the present paper, we provide the relationship among the detuning in wavelength, the pump power and the the power of stokes peak. These results indicate that under the condition of a few nanometer detuning wavelength, when the pump power is fixed at 14.1 dBm and the detuning wavelength is 6.7 nm, there are second order stokes light and the second order anti-stokes light, which can be observed, here the obtained conversion efficiency is up to-60 dB, which can be improved by optimizing the waveguide structure and increasing the pump power. Meanwhile, this FWM processing is also fast due to the fast pumping laser.#br#The simulation and experimental results demonstrate that this P-doped graphene coated microfiber hybrid structure has the advantages of highly nonlinearity, compact size and withstanding high power ultrafast laser, showing the important research value and potential applications in fields based on ultrafast optics, such as multi-wavelength laser, phase-sensitive amplification, comb filters and all-optical regeneration.
Experimental analysis of auditory mechanism of neural phase-locking based on sample entropy
Authors: Zhu Li  , Deng Juan  , Wu Jian-Hua  , Zhou Nan-Run  ,   School of Information Engineering, Nanchang University, Nanchang 330031, China;,   Institute of Biomedical Engineering, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin 300192, China
Published: December 2020

Phase-locking is a physical phenomenon that refers to a system response which is synchronized with a specific phase of the periodic stimulus. The auditory neural phase-locking plays an important role in revealing the basic neural mechanism of auditory cognition and improving auditory perception. In the existing auditory researches, psychophysical and amplitude spectral methods are mainly adopted. However, those two methods cannot differentiate the envelope-related auditory response from the temporal-fine-structure-related auditory response, and cannot reveal the neural phase-locking mechanism directly either. In this study, a phase locking value (PLV), based on sample entropy, bootstrapping and discrete Fourier transform, is proposed for analyzing the temporal-fine-structure-related frequency following response (FFRT). The proposed PLV is applied to computing neural and physical data. Two electroencephalography experiments are carried out. Results show that the sample entropy of FFRT's PLV is significantly greater than that of FFRE's PLV, and the two PLVs are orthogonal and independent. Thus, the PLVs of FFRE and FFRT reveal the auditory phase-locking mechanisms effectively. In addition, the response to fundamental frequency is mainly attributed to the envelope-related phase locking. And human auditory capability of phase locking to the envelope of the unresolved frequency is superior to the capability of phase-locking to the envelope of the resolved frequency. Moreover, in the case of missing fundamental frequency, the distortion product is the mixture of FFRE in various auditory neural paths. Also, FFRE concentrates at the low harmonic frequencies, while FFRT concentrates at the mid and high order harmonic frequencies. Therefore, the auditory neural phase-locking is related to the frequency resolution of sound. In conclusion, the proposed method overcomes some disadvantages of existing FFR analyses, making it beneficial to exploring auditory neural mechanisms.
A new free energy model for predicting the qual-biaxial tests of dielectric elastomers
Authors: Jiang Shi-Ming  ,   School of Aerospace Engineering and Applied Mechanics of Tongji University, Shanghai 200092, China
Published: December 2020

Dielectric elastomeric actuators (DEAs) have been intensely studied in the recent decades. Their attractive features include large deformation(380%), large energy density(3.4 J/g), light weight, fast response( 1 ms), and high efficiency (80%-90%). They can be used in medical devices, space robotices and energy harvesters. The core part of DEAs is a dielectric elastomeric film with two electordes. When pre-stretched forces are exerted on the film in plane direction and voltage is applied across its thickness, the film achieves a large deformation. Usually the effect of electric field is described by Maxwell stress E2, and the effect of mechanical field is described by free energy function models (such as Neo-Hookean model, Arruda-Boyce model and Gent model). There are deviations in varying degree between every models and tests of dielectric elastomer. No model works perfectly.
In the present paper, a new free energy function model is given to reduce the deviation. According to the main models above, an undetermined parameter C(1, 2) is introduced. and i (W/i)= C( 1, 2)(i2- 1-2 2-2), pi = C( 1, 2)( pi2- p1-2p2-2)(i/ pi), i = 1, 2, are assumed. The new i ( W/i) and pi are substituted into the equation of equilibrium of dielectric elastomer film pi + E2 = i ( W/i), i = 1, 2. Under equal-biaxial pre-stretched condition, P1 = P2 = P, p1 = p2 = p, C(1, 2) = C(). The parameter C()= (V2/t0)2/( 2- -4-( p- p-4)(/ p)) is obtained. Through analysing the test results of VHB4905 which contains a series of equal-biaxial pre-stretched tests, the data (, C()) are obtained from the test data (, V). C() =a + beI1-3, (I1 = 12 + 22 + 32) can be determined by data points (, C()). By computing the integral of i ( W/i)= a + beI1-3)(i2- 1-2 2-2), i = 1, 2, a new free energy function W = (a/2)(I1-3) + b[eI1-3(I1-3-1) + 1] (the new model) is achieved.
The test results of VHB4905 are fitted by Neo-Hookean, Gent model and the new model. Neo-Hookean model fits well only in small deformation. Gent model fits well only in small-middle deformation, and does not work well when stretch 3.5. The new model fits well in small, middle and large deformation. It is better than Neo-Hookean and Gent model. The new model can give big support in the study of dielectric elastomer materials and structure property, and can be used in engineering practice effectively.
Numerical investigation on drag reduction with hydrophobic surface by lattice Boltzmann method
Authors: Zhang Ya  , Pan Guang  , Huang Qiao-Gao  ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

In recent years, hydrophobic surface has attracted much attention for its potential applications in flow drag reduction. This article focuses on the drag reduction mechanism of hydrophobic surface by the multi-relaxation-time scheme and the Shan-Chen multiphase model of lattice Boltzmann method. At first, we validate our method through the multiphase cases of wall adhesion effect and the single-phase cases of flow around a square column, showing that the results from our method are in good consistence with those in previous literature. Then, we simulate and analyze the typical problem of flow around a square column with hydrophobic surface while Reynolds number is 100, in order to investigate the influences of contact angle and gas holdup of the inlet flow on drag coefficient and lift coefficient. The simulation results show that for a given contact angle, hydrophobic surface is capable of reducing drag when gas holdup of the inlet flow is in a certain range; otherwise, drag coefficient will increase. With an appropriate gas holdup of the inlet flow, both drag coefficient and lift coefficient will decrease as the contact angle becomes larger. Finally, we compare gas holdup contours and the corresponding streamline patterns under different drag coefficients. Analyses suggest that the increases of drag coefficient and lift coefficient are related to the gas mass shedding near the square column wall where the eddy forms. Increasing the gas holdup of the inflow is properly conducible to reducing the gas mass shedding and also both drag coefficient and lift coefficient greatly if contact angle is too large. However, if the near-wall gas holdup is saturated, it will aggravate the instability of gas holdup and change the near-wall gas holdup a little, which makes drag coefficient increase slightly. When gas holdup of the inlet flow is appropriate, the near-wall gas holdup becomes steadier with a larger contact angle. Through analysis we note that for hydrophobic surface, the key factor of drag reduction is to keep the near-wall gas layer stable, with which the effect of drag reduction becomes better as the contact angle becomes larger. However, the larger the contact angle, the more sensitive to the change of gas holdup both drag coefficient and lift coefficient are, so it is not recommended to adopt the hydrophobic surface with very large contact angle. With the analysis of the gas holdup near hydrophobic surface with different contact angles, in this article we put forward a new approach to the further exploration of the drag reduction mechanism of hydrophobic surface.
Tuning the electronic property of monolayer MoS2 adsorbed on metal Au substrate: a first-principles study
Authors: Zhang Li-Yong  , Fang Liang  , Peng Xiang-Yang  ,   State Key Laboratory of High Performance Computing, National University of Defense Technology, Changsha 410072, China;,   School of Computer, National University of Defense Technology, Changsha 410072, China;,   School of Physics and Optoelectronics Xiangtan University, Xiangtan 411005, China
Published: December 2020

Using first principles calculations within density functional theory, we investigate the electronic property of a single-layer MoS2 adsorbed on Au. All the quantities are calculated using the Vienna ab initio simulation package. Calculations are performed using the projector augmented wave method with the Perdew-Burke-Ernzerhof functional and a kinetic energy cutoff of 400 eV. The atomic plane and its neighboring image are separated by a 15 Å vacuum layer. The k-meshes for the structure relaxation and post analysis are 9×9×1 and 19×19×1, respectively. The spin-orbit coupling is considered in the calculation. The research includes the binding energy, the band structure, density of states (DOS) and electric charge difference density. Three contact modes between MoS2 (0001) and Au (111) are considered. When the atom S layer and the atom Au layer on the contacting interface have the same structure, the minimum binding energy and distance between MoS2 (0001) and Au(111) are 2.2 eV and 2.5 Å respectively. The minimum binding energy confirms that the absorption is unstable. The band structure demonstrates that the MoS2-Au contact nature is of the Schottky-barrier type, and the barrier height is 0.6 eV which is bigger than MoS2-Sc contact. By comparison with other metal contacts such as Ru(0001), Pd(111) and Ir(111), the dependence of the barrier height on the work function difference exhibits a Fermi-level pinning. But the MoS2 is so thin that the Fermi-level pinning must be very small. Maybe there is a metal induced gap state. DOS points out that the Au substrate has no influence on the covalent bond between Mo and S. The influence of the Au substrate is that it shifts the DOS of monolayer MoS2 left on the axis. The change of DOS results in the increases of electron concentration and electric conductivity. Other calculation points out that Ti substrate can excite more electrons. Electric charge density difference demonstrates that there are a few electric charges that transfer on the contact interface. The conducting path of monolayer MoS2 may emerge at the interface between Au and MoS2. In summary, the Au electrode is not the best electrode in the MoS2 device. The Ti electrode can excite more electrons from MoS2. The work function of Sc electrode is close to the affine of MoS2. The Fermi energy level of graphene can be tuned by external voltage. So the Ti, Sc and graphene will be the better electrodes for MoS2 device. Results of this study may provide a theoretical basis for single-layer MoS2 transistor and guidance for its applications.
Complete three-dimensional reduced surface field super junction lateral double-diffused metal-oxide-semiconductor field-effect transistor with semi-insulating poly silicon
Authors: Cao Zhen  , Duan Bao-Xing  , Yuan Xiao-Ning  , Yang Yin-Tang  ,   Key Laboratory of the Ministry of Education for Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

Lateral double-diffused metal-oxide-semiconductor field-effect transistor (LDMOS) is a key device for the power integrated circuit (PIC) and high voltage integrated circuit (HVIC) technologies. In order to break through the limit relation of 2.5 power between breakdown voltage (BV) and specific on-resistance (Ron,sp) for the traditional LDMOS, and improve the driving capability for the PIC by reducing the power consumption, the new SJ-LDMOS with the semi-insulating poly silicon (SIPOS SJ-LDMOS) is proposed in this paper for the first time, to the best of the authors' knowledge. In order to take full advantage of super junction concept, the SIPOS layer is used for SJ-LDMOS to achieve the effect of the complete three-dimensional reduced surface field (3D-RESURF) for the SJ-LDMOS. The substrate assisted depletion is effectively eliminated by the buffer layer under the super junction. The overall performances of the SIPOS SJ-LDMOS are improved by the uniform and high resistance of the SIPOS layer. The surface electric field is modulated to be uniform by the electric field modulation effect due to the SIPOS layer covering the field oxide. The higher BV would be achieved for the more uniform surface electric field because of the increased average lateral electric field. The BV for the unit length of the drift region is improved to 19.4 V/μupm. The SIPOS SJ-LDMOS along the 3D are subjected to the electric field modulation by the SIPOS layer, which achieves the complete 3D-RESURF effect, thus the drift region with the high concentration can be depleted completely to obtain the high BV. Moreover, in the on-state the majority carrier accumulation can be formed in the drift region of the SIPOS SJ-LDMOS due to the SIPOS layer, so that the specific on-resistance decreases further. In virtue of the ISE simulation, by optimizing the SIPOS layer of the proposed SIPOS SJ-LDMOS, the results show that the specific on-resistance of the SIPOS SJ-LDMOS is 20.87 mΩ·cm2 with a breakdown voltage of 388 V, which is less than 31.14 mΩ·cm2 for the N-buffer SJ-LDMOS with a breakdown voltage of 287 V, and far less than 71.82 mΩ·cm2 for the conventional SJ-LDMOS with a breakdown voltage of only 180 V with the same drift length.
Spin-polarization of organic molecules at the ferromagnetic surface
Authors: Yi Ding  , Wu Zhen  , Yang Liu  , Dai Ying  , Xie Shi-Jie  ,   School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
Published: December 2020

Study on organic/ferromagnetic interface is helpful for understanding the effects of magnetoresistance in organic spin-valve, because one of the reasons of leading to this phenomenon is due to the spin injection at the interface. However, the interactions at the organic/ferromagnetic interface are complicated and full of possibilities, and the effects are still under debate till now. One possible cause is that the adsorption of organic molecules on the ferromagnetic surface is random, which leads to various adsorbing configurations. Therefore, in this paper we select some typical adsorbing configurations of benzene/Co system to reveal the effect of spin-polarization of organic molecules at the ferromagnetic surface by using first-principles calculations. It is obtained that the spin degenerated electronic states of benzene molecule will be broken due to the coupling between the 3d electrons of Co atoms and the 2p electrons of benzene molecule. The density of states at the Fermi level becomes spin related and a spin polarization appears in the benzene molecule. For both of the configurations T1T2 and T1H12, from the projected density of states we can find that the majority-spin electrons of the benzene molecule is oriented in opposition to the direction of the ferromagnetic electrode at the Fermi level, which means that the organic molecules filter and reverse the original spin direction of the injected electrons from the ferromagnetic electrode. As mentioned above, the adsorbing configurations are different, so we consider three kinds of configurations with different adsorbing distances for further studying the spin polarization at the interface. On the basis of the configuration T1T2, distances of 2.0 Å, 2.2 Å and 2.4 Å are studied, where 2.0 Å is the equilibrium position we obtained with full relaxation. It should be noted that we do not relax the geometric structure of the system in this part of study. It is found that the spin polarization is sensitively dependent on the distance between benzene and Co surface. The spin-polarization near the Fermi level even changes its direction from positive to negative with the increase of the distance in such a small range. Our studies reflect the complexity of organic molecule/ferromagnetic electrode interfaces, and enrich the understanding of this field.
Shock plasticity design of brittle material
Authors: Jiang Tai-Long  , Yu Yin  , Huan Qiang  , Li Yong-Qiang  , He Hong-Liang  ,   School of Sciences, Northeastern University, Shenyang 110819, China;,   National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The mechanical properties of a material are closely related to its internal micro-structure. Enhancing shock plasticity by designing appropriate micro-structure will help to slow down or delay shock failure of brittle material. In this paper, we put forward a method of designing and improving shock plasticity of brittle material by implanting specific micro-voids. A lattice-spring model is adopted, which can represent mechanical properties of brittle materials quantitatively. Simulations reveal how the arrangement modes of micro-voids can affect the shock response of brittle material. By implanting randomly arranged voids, porous brittle material has significantly higher shock plasticity than dense brittle material and the design of the regular arrangement mode of voids will help to enhance the shock plasticity further. The dominant mechanism corresponding to the void collapse in the shocked brittle material is shear slip caused by shear stress concentration, which features the occurrence of shear cracks around the voids. Features of mesoscopic deformation in the sample with 5% porosity indicate that the shock plasticity of porous brittle material comes from the volume shrinkage deformation caused by void collapse and the slippage and rotation deformation caused by extension of shear cracks. The inter-permeation of voids and volume shrinkage deformation play a leading role in the sample with regularly arranged voids. While the shear cracks extends over long distance, slippage and rotation deformation take place dominantly in the sample with randomly arranged voids. The two samples with different arrangement modes of voids both have three stages of response in the Hugoniot stress-strain curves in this paper, i. e., linear elasticity stage, collapse deformation stage, and slippage and rotation deformation stage. The sample with higher porosity has a higher shock plasticity than the sample with lower porosity. When the samples have the same porosity, the collapse deformation stage makes greater contribution to the overall shock plasticity if voids are regularly arranged, while the slippage and rotation deformation stage make greater contribution to the overall shock plasticity if the voids are randomly arranged. The principle of enhancing shock plasticity of brittle material by arranging voids regularly in this paper provides physical knowledge for the designing and preparing new types of brittle materials, thereby helping to prevent the function failure induced by shock in brittle material.
Thermo-vacuum state in a negative binomial optical field and its application
Authors: Wan Zhi-Long  , Fan Hong-Yi  ,   Department of Materials Science and Engineering, University of Science and Technology of China, Heifei 230026, China;,   School of Mathematical and Chemical Ind ustry, Changzhou Institute of Technology, Changzhou 213002, China
Published: December 2020

The core of optical field theory at finite temperature is how to introduce the thermo-vacuum state which is the basis of comprehensive investigation of electromagnetic field by virtue of quantum statistic method. Based on the spirit of thermo-field dynamics initiated by Takahashi and Umezawa, we first employ the integration method within the ordered product of operators to search for thermo-vacuum state for the optical negative binomial state (NBS)s=s+1(1-)n|n,+,+,which takes the form of pure negative binomial state. The newly found thermo-vacuum state brings convenience for evaluating the Wigner function of NBS and the fluctuation of photon numbers in NBS.
Quantum pseudocritical point in the unbounded quasiperiodic transverse field Ising chain
Authors: Zhang Zhen-Jun  , Li Wen-Juan  , Zhu Xuan  , Xiong Ye  , Tong Pei-Qing  ,   College of Science, Hohai University, Nanjing 210098, China;,   Primary Education Department, Changsha Normal University, Changsha 410100, China;,   Department of Basic Courses , Jiangsu Jiankang Vocational College, Nanjing 210029, China;,   School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China;,   Jiangsu Key Laboratory for Numerical Simulation of Large Scale Complex Systems, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

We study the quantum pseudocritical points in the unbounded quasiperiodic transverse field Ising chain of finite-size systematically. Firstly, we study the derivatives of averaged magnetic moment and the averaged concurrence with transverse fields. Both of them show two visible peaks, with are nearly not raised when the length of chain is increased. Moreover, the places where the peaks occur in the transverse field are obviously different from that of the quantum phase transition point in the thermodynamic limit. These results are very different from those of the bounded quasiperiodic transverse field Ising chain and the disordered transverse field Ising chain. Then, we analyze the origin of the two visible peaks. For that we study the derivative of magnetic moment for each spin with transverse field. For all spins, the single magnetic moment only show one peak. However, the places where the peaks occur are not random. The peaks always occur in two regions. Thus, the derivatives of averaged magnetic moment reveal two peaks. Furthermore, we study the probability distribution of the pseudocritical points through finding out the peaks of the single magnetic moment in 1000 samples. The distribution is not Guassian. This result is obviously different from that of the disordered case. Besides, the pseudocritical points nearly do not occur at the quantum phase transition point. Finally, we analyze the origin of the pseudocritical points. For that we study the relationship between the spin places and the corresponding places of pseudocritical points. It is found that the pseudocritical points are caused by the two groups that exist in the nearest neighboring interactions of the unbounded quasiperiodic structure. When a spin is in one group, this group will decide the probable place of the pseudocritical point. Through this study, we find that although the quantum phase transition behaviors of the unbounded quasiperiodic transverse field Ising chain and the disordered transverse field Ising chain belong to the same universal class in the thermodynamic limit, the thermodynamic behaviors of the two Ising chains are very different as in finite sizes. The differences are caused by the special structure in the unbounded quasiperiodic system.
Research on the asphericity error elimination of the invariant of magnetic gradient tensor
Authors: Lü Jun-Wei  , Chi Cheng  , Yu Zhen-Tao  , Bi Bo  , Song Qing-Shan  ,   Department of Control Engineering, Naval Aeronautical and Astronautical University, Yantai 264001, China;,   Institute of Remote Sensing, Naval Submarine Academy, Qingdao 266001, China;,   Department of Armament, The 91213th Unit of PLA, Yantai 264001, China
Published: December 2020

Real-time, point-by-point localization of magnetic targets such as ferrous unexploded ordnance can be achieved by the cube magnetic gradiometer system designed by the Naval Surface Warfare Center. The localization method uses the Frobenius norm of the magnetic gradient tensor to calculate the location of the magnetic target. This method assumes that the potential field of the Frobenius norm of the magnetic gradient tensor is a prefect sphere. But the Frobenius norm of the magnetic gradient tensor has an asphericity parameter, and its potential field is an ellipsoid, which can cause asphericity error. Since the current localization method can be affected seriously by the asphericity error, an improved method is proposed in this paper to eliminate the asphericity error. The improved method is based on a new invariant, which does not contain asphericity parameter. The new invariant can be obtained by the combination of the Frobenius norm and eigenvalues of the magnetic gradient tensor. In detail the procedure is as follows: first, the magnetic gradient tensor of the center point of the regular hexahedron's six planes can be measured by the cube magnetic gradiometer system, then these eigenvalues can be calculated and combined according to a certain relationship to eliminate the asphericity parameter, then the new invariants of the six planes can be obtained, and the spatial gradient of the new invariant can be calculated from the six new invariants, then the localization of the magnetic target can be calculated from the spatial gradient of the new invariant. This improved method can overcome the asphericity error effectively, and it can be used for real-time, point-by-point localization and detection of unexploded ordnance. Simulation experiments show that the localization error of the improved method is much smaller than that of the original method, the average relative error can be reduced by 10.9%. The improved method can be deployed on the highly maneuverable platform. The platform motion will not be constrained, and the improved method will be made more effectively in detection and localization of the magnetic targets. Thus the improved method can be widely applied in naval mines localization, mineral exploration, ferrous resources exploration, moving magnetic target tracking, and other fields.