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CN 11-5639/O4
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  • Theoretical analysis of the coupling between Feshbach states and hyperfine excited states in the creation of 23Na40K molecule

    Ya-Xiong Liu(刘亚雄), Bo Zhao(赵博)
    Chin. Phys. B 2020, 29 (2): 023103
    We present an intensive study of the coupling between different Feshbach states and the hyperfine levels of the excited states in the adiabatic creation of 23Na40K ground-state molecules. We use coupled-channel method to calculate the wave function of the Feshbach molecules, and give the short-range...

     
  • Triphenylene adsorption on Cu(111) and relevant graphene self-assembly

    Qiao-Yue Chen(陈乔悦), Jun-Jie Song(宋俊杰), Liwei Jing(井立威), Kaikai Huang(黄凯凯), Pimo He(何丕模), Hanjie Zhang(张寒洁)
    Chin. Phys. B 2020, 29 (2): 026801
    Investigations on adsorption behavior of triphenylene (TP) and subsequent graphene self-assembly on Cu(111) were carried out mainly by using scanning tunneling microscopy (STM). At monolayer coverage, TP molecules formed a long-range ordered adsorption structure on Cu(111) with an uniform orientatio...

     
  • Breakdown voltage enhancement in GaN channel and AlGaN channel HEMTs using large gate metal height

    Zhong-Xu Wang(王中旭), Lin Du(杜林), Jun-Wei Liu(刘俊伟), Ying Wang(王颖), Yun Jiang(江芸), Si-Wei Ji(季思蔚), Shi-Wei Dong(董士伟), Wei-Wei Chen(陈伟伟), Xiao-Hong Tan(谭骁洪), Jin-Long Li(李金龙), Xiao-Jun Li(李小军), Sheng-Lei Zhao(赵胜雷), Jin-Cheng Zhang(张进成), Yue Hao(郝跃)
    Chin. Phys. B 2020, 29 (2): 027301
    A large gate metal height technique is proposed to enhance breakdown voltage in GaN channel and AlGaN channel high-electron-mobility-transistors (HEMTs). For GaN channel HEMTs with gate-drain spacing LGD=2.5 μm, the breakdown voltage VBR increases from 518 V to 582 V by increasing gate metal height ...

     
Chin. Phys. B  
  Chin. Phys. B--2020, Vol.29, No.2
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TOPICAL REVIEW—High-throughput screening and design of optoelectronic materials

Designing solar-cell absorber materials through computational high-throughput screening

Xiaowei Jiang(江小蔚), Wan-Jian Yin(尹万健)
Chin. Phys. B, 2020, 29 (2): 028803 doi: 10.1088/1674-1056/ab6655
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Although the efficiency of CH3NH3PbI3 has been refreshed to 25.2%, stability and toxicity remain the main challenges for its applications. The search for novel solar-cell absorbers that are highly stable, non-toxic, inexpensive, and highly efficient is now a viable research focus. In this review, we summarize our recent research into the high-throughput screening and materials design of solar-cell absorbers, including single perovskites, double perovskites, and materials beyond perovskites. BaZrS3 (single perovskite), Ba2BiNbS6 (double perovskite), HgAl2Se4 (spinel), and IrSb3 (skutterudite) were discovered to be potential candidates in terms of their high stabilities, appropriate bandgaps, small carrier effective masses, and strong optical absorption.
TOPICAL REVIEW—Optical field manipulation

Research progress of femtosecond surface plasmon polariton

Yulong Wang(王玉龙), Bo Zhao(赵波), Changjun Min(闵长俊), Yuquan Zhang(张聿全), Jianjun Yang(杨建军), Chunlei Guo(郭春雷), Xiaocong Yuan(袁小聪)
Chin. Phys. B, 2020, 29 (2): 027302 doi: 10.1088/1674-1056/ab6717
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As the combination of surface plasmon polariton and femtosecond laser pulse, femtosecond surface plasmon polariton has both nanoscale spatial resolution and femtosecond temporal resolution, and thus provides promising methods for light field manipulation and light-matter interaction in extreme small spatiotemporal scales. Nowadays, the research on femtosecond surface plasmon polariton is mainly concentrated on two aspects: one is investigation and characterization of excitation, propagation, and dispersion properties of femtosecond surface plasmon polariton in different structures or materials; the other one is developing new applications based on its unique properties in the fields of nonlinear enhancement, pulse shaping, spatiotemporal super-resolved imaging, and others. Here, we introduce the research progress of properties and applications of femtosecond surface plasmon polariton, and prospect its future research trends. With the further development of femtosecond surface plasmon polariton research, it will have a profound impact on nano-optoelectronics, molecular dynamics, biomedicine and other fields.
TOPICAL REVIEW—Overcoming doping bottleneck in widegap semiconductors

Growth and doping of bulk GaN by hydride vapor phase epitaxy

Yu-Min Zhang(张育民), Jian-Feng Wang(王建峰), De-Min Cai(蔡德敏), Guo-Qiang Ren(任国强), Yu Xu(徐俞), Ming-Yue Wang(王明月), Xiao-Jian Hu(胡晓剑), Ke Xu(徐科)
Chin. Phys. B, 2020, 29 (2): 026104 doi: 10.1088/1674-1056/ab65b9
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Doping is essential in the growth of bulk GaN substrates, which could help control the electrical properties to meet the requirements of various types of GaN-based devices. The progresses in the growth of undoped, Si-doped, Ge-doped, Fe-doped, and highly pure GaN by hydride vapor phase epitaxy (HVPE) are reviewed in this article. The growth technology and precursors of each type of doping are introduced. Besides, the influence of doping on the optical and electrical properties of GaN are presented in detail. Furthermore, the problems caused by doping, as well as the methods to solve them are also discussed. At last, highly pure GaN is briefly introduced, which points out a new way to realize high-purity semi-insulating (HPSI) GaN.
TOPICAL REVIEW—Advanced calculation & characterization of energy storage materials & devices at multiple scale

Review on electrode-level fracture in lithium-ion batteries

Bo Lu(吕浡), Chengqiang Ning(宁成强), Dingxin Shi(史定鑫), Yanfei Zhao(赵炎翡), Junqian Zhang(张俊乾)
Chin. Phys. B, 2020, 29 (2): 026201 doi: 10.1088/1674-1056/ab6841
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Fracture occurred in electrodes of the lithium-ion battery compromises the integrity of the electrode structure and would exert bad influence on the cell performance and cell safety. Mechanisms of the electrode-level fracture and how this fracture would affect the electrochemical performance of the battery are of great importance for comprehending and preventing its occurrence. Fracture occurring at the electrode level is complex, since it may involve fractures in or between different components of the electrode. In this review, three typical types of electrode-level fractures are discussed: the fracture of the active layer, the interfacial delamination, and the fracture of metallic foils (including the current collector and the lithium metal electrode). The crack in the active layer can serve as an effective indicator of degradation of the electrochemical performance. Interfacial delamination usually follows the fracture of the active layer and is detrimental to the cell capacity. Fracture of the current collector impacts cell safety directly. Experimental methods and modeling results of these three types of fractures are concluded. Reasonable explanations on how these electrode-level fractures affect the electrochemical performance are sorted out. Challenges and unsettled issues of investigating these fracture problems are brought up. It is noted that the state-of-the-art studies included in this review mainly focus on experimental observations and theoretical modeling of the typical mechanical damages. However, quantitative investigations on the relationship between the electrochemical performance and the electrode-level fracture are insufficient. To further understand fractures in a multi-scale and multi-physical way, advancing development of the cross discipline between mechanics and electrochemistry is badly needed.

Advanced characterization and calculation methods for rechargeable battery materials in multiple scales

Xin-Yan Li(李欣岩), Su-Ting Weng(翁素婷), Lin Gu(谷林)
Chin. Phys. B, 2020, 29 (2): 028801 doi: 10.1088/1674-1056/ab65ba
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The structure-activity relationship of functional materials is an everlasting and desirable research question for material science researchers, where characterization and calculation tools are the keys to deciphering this intricate relationship. Here, we choose rechargeable battery materials as an example and introduce the most representative advanced characterization and calculation methods in four different scales: real space, energy, momentum space, and time. Current research methods to study battery material structure, energy level transition, dispersion relations of phonons and electrons, and time-resolved evolution are reviewed. From different views, various expression forms of structure and electronic structure are presented to understand the reaction processes and electrochemical mechanisms comprehensively in battery systems. According to the summary of the present battery research, the challenges and perspectives of advanced characterization and calculation techniques for the field of rechargeable batteries are further discussed.

Pair distribution function analysis: Fundamentals and application to battery materials

Xuelong Wang(王雪龙), Sha Tan(谭莎), Xiao-Qing Yang(杨晓青), Enyuan Hu(胡恩源)
Chin. Phys. B, 2020, 29 (2): 028802 doi: 10.1088/1674-1056/ab6656
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Battery materials are of vital importance in powering a clean and sustainable society. Improving their performance relies on a clear and fundamental understanding of their properties, in particular, structural properties. Pair distribution function (PDF) analysis, which takes into account both Bragg scattering and diffuse scattering, can probe structures of both crystalline and amorphous phases in battery materials. This review first introduces the principle of PDF, followed by its application in battery materials. It shows that PDF is an effective tool in studying a series of key scientific topics in battery materials. They range from local ordering, nano-phase quantification, anion redox reaction, to lithium storage mechanism, and so on.
SPECIAL TOPIC—Advanced calculation & characterization of energy storage materials & devices at multiple scale

Revealing the inhomogeneous surface chemistry on the spherical layered oxide polycrystalline cathode particles

Zhi-Sen Jiang(蒋之森), Shao-Feng Li(李少锋), Zheng-Rui Xu(许正瑞), Dennis Nordlund, Hendrik Ohldag, Piero Pianetta, Jun-Sik Lee, Feng Lin(林锋), Yi-Jin Liu(刘宜晋)
Chin. Phys. B, 2020, 29 (2): 026103 doi: 10.1088/1674-1056/ab6585
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The hierarchical structure of the composite cathodes brings in significant chemical complexity related to the interfaces, such as cathode electrolyte interphase. These interfaces account for only a small fraction of the volume and mass, they could, however, have profound impacts on the cell-level electrochemistry. As the investigation of these interfaces becomes a crucial topic in the battery research, there is a need to properly study the surface chemistry, particularly to eliminate the biased, incomplete characterization provided by techniques that assume the homogeneous surface chemistry. Herein, we utilize nano-resolution spatially-resolved x-ray spectroscopic tools to probe the heterogeneity of the surface chemistry on LiNi0.8Mn0.1Co0.1O2 layered cathode secondary particles. Informed by the nano-resolution mapping of the Ni valance state, which serves as a measurement of the local surface chemistry, we construct a conceptual model to elucidate the electrochemical consequence of the inhomogeneous local impedance over the particle surface. Going beyond the implication in battery science, our work highlights a balance between the high-resolution probing the local chemistry and the statistical representativeness, which is particularly vital in the study of the highly complex material systems.
SPECIAL TOPIC—Strong-field atomic and molecular physics

Numerical simulations of strong-field processes in momentum space

Yan Xu(徐彦), Xue-Bin Bian(卞学滨)
Chin. Phys. B, 2020, 29 (2): 023202 doi: 10.1088/1674-1056/ab6553
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The time-dependent Schrödinger equation (TDSE) is usually treated in the real space in the textbook. However, it makes the numerical simulations of strong-field processes difficult due to the wide dispersion and fast oscillation of the electron wave packets under the interaction of intense laser fields. Here we demonstrate that the TDSE can be efficiently solved in the momentum space. The high-order harmonic generation and above-threshold ionization spectra obtained by numerical solutions of TDSE in momentum space agree well with previous studies in real space, but significantly reducing the computation cost.
GENERAL

Bäcklund transformations, consistent Riccati expansion solvability, and soliton-cnoidal interaction wave solutions of Kadomtsev-Petviashvili equation

Ping Liu(刘萍), Jie Cheng(程杰), Bo Ren(任博), Jian-Rong Yang(杨建荣)
Chin. Phys. B, 2020, 29 (2): 020201 doi: 10.1088/1674-1056/ab5eff
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The famous Kadomtsev-Petviashvili (KP) equation is a classical equation in soliton theory. A Bäcklund transformation between the KP equation and the Schwarzian KP equation is demonstrated by means of the truncated Painlevé expansion in this paper. One-parameter group transformations and one-parameter subgroup-invariant solutions for the extended KP equation are obtained. The consistent Riccati expansion (CRE) solvability of the KP equation is proved. Some interaction structures between soliton-cnoidal waves are obtained by CRE and several evolution graphs and density graphs are plotted.

Performance analysis of continuous-variable measurement-device-independent quantum key distribution under diverse weather conditions

Shu-Jing Zhang(张淑静), Chen Xiao(肖晨), Chun Zhou(周淳), Xiang Wang(汪翔), Jian-Shu Yao(要建姝), Hai-Long Zhang(张海龙), Wan-Su Bao(鲍皖苏)
Chin. Phys. B, 2020, 29 (2): 020301 doi: 10.1088/1674-1056/ab5efd
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The effects of weather conditions are ubiquitous in practical wireless quantum communication links. Here in this work, the performances of atmospheric continuous-variable measurement-device-independent quantum key distribution (CV-MDI-QKD) under diverse weather conditions are analyzed quantitatively. According to the Mie scattering theory and atmospheric CV-MDI-QKD model, we numerically simulate the relationship between performance of CV-MDI-QKD and the rainy and foggy conditions, aiming to get close to the actual combat environment in the future. The results show that both rain and fog will degrade the performance of the CV-MDI-QKD protocol. Under the rainy condition, the larger the raindrop diameter, the more obvious the extinction effect is and the lower the secret key rate accordingly. In addition, we find that the secret key rate decreases with the increase of spot deflection distance and the fluctuation of deflection. Under the foggy condition, the results illustrate that the transmittance decreases with the increase of droplet radius or deflection distance, which eventually yields the decrease in the secret key rate. Besides, in both weather conditions, the increase of transmission distance also leads the secret key rate to deteriorate. Our work can provide a foundation for evaluating the performance evaluation and successfully implementing the atmospheric CV-MDI-QKD in the future field operation environment under different weather conditions.

Unified approach to various quantum Rabi models witharbitrary parameters

Xiao-Fei Dong(董晓菲), You-Fei Xie(谢幼飞), Qing-Hu Chen(陈庆虎)
Chin. Phys. B, 2020, 29 (2): 020302 doi: 10.1088/1674-1056/ab6555
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A general approach is proposed to the quantum Rabi model and its several variants within the extended coherent states. The solutions to all these models including the anisotropy and the nonlinear Stark coupling are then obtained in an unified way. The essential characteristics such as the possible first-order phase transition can be detected analytically. This approach can be easily applied to the recent experiments with various tunable parameters without much additional effort, so it should be very helpful to the analysis of the experimental data.

Interference properties of two-component matter wave solitons

Yan-Hong Qin(秦艳红), Yong Wu(伍勇), Li-Chen Zhao(赵立臣), Zhan-Ying Yang(杨战营)
Chin. Phys. B, 2020, 29 (2): 020303 doi: 10.1088/1674-1056/ab65b7
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Wave properties of solitons in a two-component Bose-Einstein condensate are investigated in detail. We demonstrate that dark solitons in one of components admit interference and tunneling behavior, in sharp contrast to the scalar dark solitons and vector dark solitons. Analytic analyses of interference properties show that spatial interference patterns are determined by the relative velocity of solitons, while temporal interference patterns depend on the velocities and widths of two solitons, differing from the interference properties of scalar bright solitons. Especially, for an attractive interactions system, we show that interference effects between the two dark solitons can induce some short-time density humps (whose densities are higher than background density). Moreover, the maximum hump value is remarkably sensitive to the variation of the solitons' parameters. For a repulsive interactions system, the temporal-spatial interference periods of dark-bright solitons have lower limits. Numerical simulation results suggest that interference patterns for the dark-bright solitons are more robust against noises than bright-dark solitons. These explicit interference properties can be used to measure the velocities and widths of solitons. It is expected that these interference behaviors can be observed experimentally and can be used to design matter wave soliton interferometer in vector systems.

Quantifying non-classical correlations under thermal effects in a double cavity optomechanical system

Mohamed Amazioug, Larbi Jebli, Mostafa Nassik, Nabil Habiballah
Chin. Phys. B, 2020, 29 (2): 020304 doi: 10.1088/1674-1056/ab65b6
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We investigate the generation of quantum correlations between mechanical modes and optical modes in an optomechanical system, using the rotating wave approximation. The system is composed of two Fabry-Pérot cavities separated in space; each of the two cavities has a movable end-mirror. Our aim is the evaluation of entanglement between mechanical modes and optical modes, generated by correlations transfer from the squeezed light to the system, using Gaussian intrinsic entanglement as a witness of entanglement in continuous variables Gaussian states, and the quantification of the degree of mixedness of the Gaussian states using the purity. Then, we quantify nonclassical correlations between mechanical modes and optical modes even beyond entanglement by considering Gaussian geometric discord via the Hellinger distance. Indeed, entanglement, mixdness, and quantum discord are analyzed as a function of the parameters characterizing the system (thermal bath temperature, squeezing parameter, and optomechanical cooperativity). We find that, under thermal effect, when entanglement vanishes, purity and quantum discord remain nonzero. Remarkably, the Gaussian Hellinger discord is more robust than entanglement. The effects of the other parameters are discussed in detail.

Monogamy and polygamy relations of multiqubit entanglement based on unified entropy

Zhi-Xiang Jin(靳志祥), Cong-Feng Qiao(乔从丰)
Chin. Phys. B, 2020, 29 (2): 020305 doi: 10.1088/1674-1056/ab6720
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Monogamy relation is one of the essential properties of quantum entanglement, which characterizes the distribution of entanglement in a multipartite system. By virtual of the unified-(q,s) entropy, we obtain some novel monogamy and polygamy inequalities in general class of entanglement measures. For the multiqubit system, a class of tighter monogamy relations are established in term of the α-th power of unified-(q,s) entanglement for α≥1. We also obtain a class of tighter polygamy relations in the β-th (0≤β≤1) power of unified-(q,s) entanglement of assistance. Applying these results to specific quantum correlations, e.g., entanglement of formation, Renyi-q entanglement of assistance, and Tsallis-q entanglement of assistance, we obtain the corresponding monogamy and polygamy relations. Typical examples are presented for illustration. Furthermore, the complementary monogamy and polygamy relations are investigated for the α-th (0≤α≤q 1) and β-th (β≥1) powers of unified entropy, respectively, and the corresponding monogamy and polygamy inequalities are obtained.

Influence of the Earth's rotation on measurement of gravitational constant G with the time-of-swing method

Jie Luo(罗杰), Tao Dong(董涛), Cheng-Gang Shao(邵成刚), Yu-Jie Tan(谈玉杰), Hui-Jie Zhang(张惠捷)
Chin. Phys. B, 2020, 29 (2): 020401 doi: 10.1088/1674-1056/ab6584
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In the measurement of the Newtonian gravitational constant G with the time-of-swing method, the influence of the Earth's rotation has been roughly estimated before, which is far beyond the current experimental precision. Here, we present a more complete theoretical modeling and assessment process. To figure out this effect, we use the relativistic Lagrangian expression to derive the motion equations of the torsion pendulum. With the correlation method and typical parameters, we estimate that the influence of the Earth's rotation on G measurement is far less than 1 ppm, which may need to be considered in the future high-accuracy experiments of determining the gravitational constant G.

Effect of system-reservoir correlations on temperature estimation

Wen-Li Zhu(朱雯丽), Wei Wu(吴威), Hong-Gang Luo(罗洪刚)
Chin. Phys. B, 2020, 29 (2): 020501 doi: 10.1088/1674-1056/ab5fc0
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In many previous temperature estimation schemes, the temperature of a sample is directly read out from the final steady state of a quantum probe, which is coupled to the sample. However, in these studies, information of correlations between system (the probe) and reservoir (the sample) is usually eliminated, leading the steady state of the probe is a canonical equilibrium state with respect solely to system's Hamiltonian. To explore the influence of system-reservoir correlations on the estimation precision, we investigate the equilibration dynamics of a spin interacting with a finite temperature bosonic reservoir. By incorporating an intermediate harmonic oscillator or a collective coordinate into the spin, the system-reservoir correlations can be correspondingly encoded in a Gibbs state of an effective Hamilton, which is size consistent with the original bare spin. Extracting information of temperature from this corrected steady state, we find the effect of the system-reservoir correlations on the estimation precision is highly sensitive to the details of the spectral density function of the measured reservoir.

Quantum-classical correspondence and mechanical analysis ofa classical-quantum chaotic system

Haiyun Bi(毕海云), Guoyuan Qi(齐国元), Jianbing Hu(胡建兵), Qiliang Wu(吴启亮)
Chin. Phys. B, 2020, 29 (2): 020502 doi: 10.1088/1674-1056/ab6205
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Quantum-classical correspondence is affirmed via performing Wigner function and a classical-quantum chaotic system containing random variables. The classical-quantum system is transformed into a Kolmogorov model for force and energy analysis. Combining different forces, the system is divided into two categories: conservative and non-conservative, revealing the mechanical characteristic of the classical-quantum system. The Casimir power, an analysis tool, is employed to find the key factors governing the orbital trajectory and the energy cycle of the system. Detailed analyses using the Casimir power and an energy transformation uncover the causes of the different dynamic behaviors, especially chaos. For the corresponding classical Hamiltonian system when Planck's constant ħ→0, the supremum bound of the system is derived analytically. Difference between the classical-quantum system and the classical Hamiltonian system is displayed through trajectories and energies. Quantum-classical correspondences are further demonstrated by comparing phase portrait, kinetic, potential and Casimir energies of the two systems.

The effect of phase fluctuation and beam splitter fluctuation on two-photon quantum random walk

Zijing Zhang(张子静), Feng Wang(王峰), Jie Song(宋杰), Yuan Zhao(赵远)
Chin. Phys. B, 2020, 29 (2): 020503 doi: 10.1088/1674-1056/ab6654
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In the optical quantum random walk system, phase fluctuation and beam splitter fluctuation are two unavoidable decoherence factors. These two factors degrade the performance of quantum random walk by destroying coherence, and even degrade it into a classical one. We propose a scheme for the simulation of quantum random walk using phase shifters, tunable beam splitters, and photodetectors. This proposed scheme enables us to analyze the effect of phase fluctuation and beam splitter fluctuation on two-photon quantum random walk. Furthermore, it is helpful to guide the control of phase fluctuation and beam splitter fluctuation in the experiment.

Bifurcation and chaos characteristics of hysteresis vibration system of giant magnetostrictive actuator

Hong-Bo Yan(闫洪波), Hong Gao(高鸿), Gao-Wei Yang(杨高炜), Hong-Bo Hao(郝宏波), Yu Niu(牛禹), Pei Liu(刘霈)
Chin. Phys. B, 2020, 29 (2): 020504 doi: 10.1088/1674-1056/ab65b4
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Chaotic motion and quasi-periodic motion are two common forms of instability in the giant magnetostrictive actuator (GMA). Therefore, in the present study we intend to investigate the influences of the system damping coefficient, system stiffness coefficient, disc spring cubic stiffness factor, and the excitation force and frequency on the output stability and the hysteresis vibration of the GMA. In this regard, the nonlinear piezomagnetic equation, Jiles-Atherton hysteresis model, quadratic domain rotation model, and the GMA structural dynamics are used to establish the mathematical model of the hysteresis vibration system of the GMA. Moreover, the multi-scale method and the singularity theory are used to determine the co-dimensional two-bifurcation characteristics of the system. Then, the output response of the system is simulated to determine the variation range of each parameter when chaos is imposed. Finally, the fourth-order Runge-Kutta method is used to obtain the time domain waveform, phase portrait and Poincaré mapping diagrams of the system. Subsequently, the obtained three graphs are analyzed. The obtained results show that when the system output is stable, the variation range of each parameter can be determined. Moreover, the stability interval of system damping coefficient, system stiffness coefficient, and the coefficient of the cubic stiffness term of the disc spring are obtained. Furthermore, the stability interval of the exciting force and the excitation frequency are determined.

Optimization of laser focused atomic deposition by channeling

Jie Chen(陈杰), Jie Liu(刘杰), Li Zhu(朱立), Xiao Deng(邓晓), Xinbin Cheng(陈鑫彬), Tongbao Li(李同保)
Chin. Phys. B, 2020, 29 (2): 020601 doi: 10.1088/1674-1056/ab631c
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Laser focused atomic deposition is a unique and effective way to fabricate highly accurate pitch standards in nanometrology. However, the stability and repeatability of the atom lithography fabrication process remains a challenging problem for massive production. Based on the atom-light interaction theory, channeling is utilized to improve the stability and repeatability. From the comparison of three kinds of atom-light interaction models, the optimal parameters for channeling are obtained based on simulation. According to the experimental observations, the peak to valley height of Cr nano-gratings keeps stable when the cutting proportion changes from 15% to 50%, which means that the channeling shows up under this condition. The channeling proves to be an effective method to optimize the stability and repeatability of laser focused Cr atomic deposition.

Doppler radial velocity detection based on Doppler asymmetric spatial heterodyne spectroscopy technique for absorption lines

Yin-Li Kuang(况银丽), Liang Fang(方亮), Xiang Peng(彭翔), Xin Cheng(程欣), Hui Zhang(张辉), En-Hai Liu(刘恩海)
Chin. Phys. B, 2020, 29 (2): 020701 doi: 10.1088/1674-1056/ab5fc3
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Doppler asymmetric spatial heterodyne spectroscopy (DASH) technique has developed rapidly in passive Doppler-shift measurements of atmospheric emission lines over the last decade. With the advantages of high phase shift sensitivity, compact, and rugged structure, DASH is proposed to be used for celestial autonomous navigation based on Doppler radial velocity measurement in this work. Unlike atmospheric emission lines, almost all targeted lines in the research field of deep-space exploration are the absorption lines of stars, so a mathematical model for the Doppler-shift measurements of absorption lines with a DASH interferometer is established. According to the analysis of the components of the interferogram received by the detector array, we find that the interferogram generated only by absorption lines in a passband can be extracted and processed by a method similar to the approach to studying the emission lines. In the end, numerical simulation experiments of Doppler-shift measurements of absorption lines are carried out. The simulation results show that the relative errors of the retrieved speeds are less than 0.7% under ideal conditions, proving the feasibility of measuring Doppler shifts of absorption lines by DASH instruments.

A method for calibrating the confocal volume of a confocal three-dimensional micro-x-ray fluorescence setup

Peng Zhou(周鹏), Xin-Ran Ma(马欣然), Shuang Zhang(张爽), Tian-Xi Sun(孙天希), Zhi-Guo Liu(刘志国)
Chin. Phys. B, 2020, 29 (2): 020702 doi: 10.1088/1674-1056/ab671c
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The measurement of the confocal volume of a confocal three-dimensional micro-x-ray fluorescence (3D-XRF) setup is a key step in the field of confocal 3D-XRF analysis. With the development of x-ray facilities and optical devices, 3D-XRF analysis with a micro confocal volume will create a great potential for 2D and 3D microstructural analysis and accurate quantitative analysis. However, the classic measurement method of scanning metal foils of a certain thickness leads to inaccuracy. A method for calibrating the confocal volume is proposed in this paper. The new method is based on the basic content of the textbook, and the theoretical results and the feasibility are given in detail for the 3D-XRF mono-chromatic x-ray condition and the poly-chromatic x-ray condition. We obtain a set of experimental confirmation using the poly-chromatic x-ray tube in the laboratory. It is proved that the sensitivity factor of the 3D-XRF can be directly and accurately obtained in a real calibration process.

Multiple Lagrange stability and Lyapunov asymptotical stability of delayed fractional-order Cohen-Grossberg neural networks

Yu-Jiao Huang(黄玉娇), Xiao-Yan Yuan(袁孝焰), Xu-Hua Yang(杨旭华), Hai-Xia Long(龙海霞), Jie Xiao(肖杰)
Chin. Phys. B, 2020, 29 (2): 020703 doi: 10.1088/1674-1056/ab6716
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This paper addresses the coexistence and local stability of multiple equilibrium points for fractional-order Cohen-Grossberg neural networks (FOCGNNs) with time delays. Based on Brouwer's fixed point theorem, sufficient conditions are established to ensure the existence of Πi=1n(2Ki+1) equilibrium points for FOCGNNs. Through the use of Hardy inequality, fractional Halanay inequality, and Lyapunov theory, some criteria are established to ensure the local Lagrange stability and the local Lyapunov asymptotical stability of Πi=1n(Ki+1) equilibrium points for FOCGNNs. The obtained results encompass those of integer-order Hopfield neural networks with or without delay as special cases. The activation functions are nonlinear and nonmonotonic. There could be many corner points in this general class of activation functions. The structure of activation functions makes FOCGNNs could have a lot of stable equilibrium points. Coexistence of multiple stable equilibrium points is necessary when neural networks come to pattern recognition and associative memories. Finally, two numerical examples are provided to illustrate the effectiveness of the obtained results.
ATOMIC AND MOLECULAR PHYSICS

Molecular opacities of low-lying states of oxygen molecule

Gui-Ying Liang(梁桂颖), Yi-Geng Peng(彭裔耕), Rui Li(李瑞), Yong Wu(吴勇), Jian-Guo Wang(王建国)
Chin. Phys. B, 2020, 29 (2): 023101 doi: 10.1088/1674-1056/ab5fb6
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The X3Σg-, A'3u, A3Σu+, 13Πg, and B3Σu- electronic states of oxygen molecule (O2) are calculated by the multiconfiguration self-consisted filed (MRCI) + Q method with the scalar relativistic correction and core-valence correlation correction. The obtained spectroscopic constants of the low-lying bound states are in excellent agreement with measurements. Based on the accurately calculated structure parameters, the opacities of the oxygen molecule at the temperatures of 1000 K, 2000 K, 2500 K, and 5000 K under a pressure of 100 atm (1 atm=1.01325×105 Pa) and the partition functions between 10 K and 104 K are obtained. It is found that with the increase of temperature, the opacities for transitions in a long wavelength range are enlarged because of the larger population on excited electronic states at the higher temperatures.

HfN2 monolayer: A new direct-gap semiconductor with high and anisotropic carrier mobility

Yuan Sun(孙源), Bin Xu(徐斌), Lin Yi(易林)
Chin. Phys. B, 2020, 29 (2): 023102 doi: 10.1088/1674-1056/ab610b
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Searching for two-dimensional (2D) stable materials with direct band gap and high carrier mobility has attracted great attention for their electronic device applications. Using the first principles calculations and particle swarm optimization (PSO) method, we predict a new 2D stable material (HfN2 monolayer) with the global minimum of 2D space. The HfN2 monolayer possesses direct band gap (~1.46 eV) and it is predicted to have high carrier mobilities (~103 cm2·V-1·s-1) from deformation potential theory. The direct band gap can be well maintained and flexibly modulated by applying an easily external strain under the strain conditions. In addition, the newly predicted HfN2 monolayer possesses good thermal, dynamical, and mechanical stabilities, which are verified by ab initio molecular dynamics simulations, phonon dispersion and elastic constants. These results demonstrate that HfN2 monolayer is a promising candidate in future microelectronic devices.

Theoretical analysis of the coupling between Feshbach states and hyperfine excited states in the creation of 23Na40K molecule Hot!

Ya-Xiong Liu(刘亚雄), Bo Zhao(赵博)
Chin. Phys. B, 2020, 29 (2): 023103 doi: 10.1088/1674-1056/ab6314
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We present an intensive study of the coupling between different Feshbach states and the hyperfine levels of the excited states in the adiabatic creation of 23Na40K ground-state molecules. We use coupled-channel method to calculate the wave function of the Feshbach molecules, and give the short-range wave function of triplet component. The energies of the hyperfine excited states and the coupling strength between the Feshbach states and the hyperfine excited states are calculated. Our results can be used to prepare a specific hyperfine level of the rovibrational ground state to study the ultracold collisions involving molecules.

Thermodynamic and structural properties of polystyrene/C60 composites: A molecular dynamics study

Junsheng Yang(杨俊升), Ziliang Zhu(朱子亮), Duohui Huang(黄多辉), Qilong Cao(曹启龙)
Chin. Phys. B, 2020, 29 (2): 023104 doi: 10.1088/1674-1056/ab6312
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To tailor properties of polymer composites are very important for their applications. Very small concentrations of nanoparticles can significantly alter their physical characteristics. In this work, molecular dynamics simulations are performed to study the thermodynamic and structural properties of polystyrene/C60 (PS/C60) composites. The calculated densities, glass transition temperatures, and coefficient of thermal expansion of the bulk PS are in agreement with the experimental data available, implying that our calculations are reasonable. We find that the glass transition temperature Tg increases accordingly with an added concentration of C60 for PS/C60 composites. However, the self-diffusion coefficient D decreases with increase of addition of C60. For the volumetric coefficients of thermal expansion (CTE) of bulk PS and PS/C60 composites, it can be seen that the CTE increases with increasing content of C60 above Tg (rubbery region). However, the CTE decreases with increasing content of C60 below Tg (glassy region).

Effect of isotope on state-to-state dynamics for reactive collision reactions O(3P)+H2+→OH++H and O(3P)+H2+→OH+H+ in ground state 12A" and first excited 12A' potential energy surfaces

Juan Zhao(赵娟), Ting Xu(许婷), Lu-Lu Zhang(张路路), Li-Fei Wang(王立飞)
Chin. Phys. B, 2020, 29 (2): 023105 doi: 10.1088/1674-1056/ab6554
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We carry out quantum scattering dynamics and quasi-classical trajectory (QCT) calculations for the O+H2+ reactive collision in the ground (12A') and first excited (12A') potential energy surface. We calculate the reaction probabilities of O+H2+(v=0,j=0)→OH++H and O+H2+(v=0,j=0)→OH+H+ reaction for total angular momentum J=0. The results calculated by QCT are consistent with those from quantum mechanical wave packet. Using the QCT method, we generate in the center-of-mass frame the product state-resolved integral cross-sections (ICSs); two commonly used generalized polarization-dependent differential cross-sections (PDDCSs), (2π/σ)(dσ00/dωt), (2π/σ)(dσ20/dωt); and three angular distributions of the product rotational vectors, P(θr ), P(φr ), and P(θr,φr). We discuss the influence on the scalar and vector properties of the potential energy surface, the collision energy, and the isotope mass. Since there are deep potential wells in these two potential energy surfaces, their kinetic characteristics are similar to each other and the isotopic effect is not obvious. However, the well depths and configurations of the two potential energy surfaces are different, so the effects of isotopic substitution on the integral cross-section and the rotational polarization of product are different.

Phase jump in resonance harmonic emission driven by strong laser fields

Yuan-Yuan Zhao(赵媛媛), Di Zhao(赵迪), Chen-Wei Jiang(蒋臣威), Ai-Ping Fang(方爱平), Shao-Yan Gao(高韶燕), Fu-Li Li(李福利)
Chin. Phys. B, 2020, 29 (2): 023201 doi: 10.1088/1674-1056/ab5fbf
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We present a theoretical investigation of the multiphoton resonance dynamics in the high-order-harmonic generation (HHG) process driven by a strong driving continuous wave (CW) field along with a weak control harmonic field. The Floquet theorem is employed to provide a nonperturbative and exact treatment of the interaction between a quantum system and the combined laser field. Multiple multiphoton-transition paths for the harmonic emission are coherently summed. The phase information about paths can be extracted via the Fourier transform analysis of the harmonic signals which oscillate as a function of the relative phase between driving and control fields. Phase jumps are observed when sweeping across the resonance by varying the frequency or intensity of the driving field. The phase variation as a function of driving frequency at a fixed intensity and as a function of the intensity at a fixed driving frequency allows us to determine the intensity dependence of the transition energy of quantum systems.

Enhanced optical molasses cooling for Cs atoms with largely detuned cooling lasers

Di Zhang(张迪), Yu-Qing Li(李玉清), Yun-Fei Wang(王云飞), Yong-Ming Fu(付永明), Peng Li(李鹏), Wen-Liang Liu(刘文良), Ji-Zhou Wu(武寄洲), Jie Ma(马杰), Lian-Tuan Xiao(肖连团), Suo-Tang Jia(贾锁堂)
Chin. Phys. B, 2020, 29 (2): 023203 doi: 10.1088/1674-1056/ab5fc6
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We report a detailed study of the enhanced optical molasses cooling of Cs atoms, whose large hyperfine structure allows to use the largely red-detuned cooling lasers. We find that the combination of a large frequency detuning of about -110 MHz for the cooling laser and a suitable control for the powers of the cooling and repumping lasers allows to reach a cold temperature of ~5.5 μK. We obtain 5.1×107 atoms with the number density around 1×1012 cm-3. Our result gains a lower temperature than that got in other experiments, in which the cold Cs atoms with the temperature of ~10 μK have been achieved by the optical molasses cooling.

Comparative study on atomic ionization in bicircular laser fields by length and velocity gauges S-matrix theory

Hong Xia(夏宏), Xin-Yan Jia(贾欣燕), Xiao-Lei Hao(郝小雷), Li Guo(郭丽), Dai-He Fan(樊代和), Gen-Bai Chu(储根柏), Jing Chen(陈京)
Chin. Phys. B, 2020, 29 (2): 023204 doi: 10.1088/1674-1056/ab610c
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Ionization of atoms in counter-rotating and co-rotating bicircular laser fields is studied using the S-matrix theory in both length and velocity gauges. We show that for both the bicircular fields, ionization rates are enhanced when the two circularly polarized lights have comparable intensities. In addition, the curves of ionization rate versus the field amplitude ratio of the two colors for counter-rotating and co-rotating fields coincide with each other in the length gauge case at the total laser intensity 5×1014 W/cm2, which agrees with the experimental observation. Moreover, the degree of the coincidence between the ionization rate curves of the two bicircular fields decreases with the increasing field amplitude ratio and decreasing total laser intensity. With the help of the ADK theory, the above characteristics of the ionization rate curves can be well interpreted, which is related to the transition from the tunneling to multiphoton ionization mechanism.

Theoretical investigations of collision dynamics of cytosine by low-energy (150-1000 eV) proton impact

Zhi-Ping Wang(王志萍), Feng-Shou Zhang(张丰收), Xue-Fen Xu(许雪芬), Chao-Yi Qian(钱超义)
Chin. Phys. B, 2020, 29 (2): 023401 doi: 10.1088/1674-1056/ab6313
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Using a real-space real-time implementation of time-dependent density functional theory coupled to molecular dynamics (TDDFT-MD) nonadiabatically, we theoretically study both static properties and collision process of cytosine by 150-1000 eV proton impact in the microscopic way. The calculated ground state of cytosine accords well with experiments. It is found that proton is scattered in any case in the present study. The bond break of cytosine occurs when the energy loss of proton is larger than 22 eV and the main dissociation pathway of cytosine is the breaks of C1N2 and N8H10. In the range of 150 eV≤Ek≤360 eV, when the incident energy of proton increases, the excitation becomes more violent even though the interaction time is shortened. While in the range of 360 eV < Ek ≤q 1000 eV, the excitation becomes less violent as the incident energy of proton increases, indicating that the interaction time dominates mainly. We also show two typical collision reaction channels by analyzing the molecular ionization, the electronic density evolution, the energy loss of proton, the vibration frequency and the scattering pattern detailedly. The result shows that the loss of electrons can decrease the bond lengths of C3N8 and C5N6 while increase the bond lengths of C4H11, C5H12 and C4C5 after the collision. Furthermore, it is found that the peak of the scattering angle shows a little redshift when compared to that of the loss of kinetic energy of proton.

Vibrational effects on electron momentum distributionsof outer valence orbitals of benzene

Yu Zhang(张钰), Shanshan Niu(牛珊珊), Yaguo Tang(唐亚国), Yichun Wang(王忆纯), Xu Shan(单旭), Xiangjun Chen(陈向军)
Chin. Phys. B, 2020, 29 (2): 023402 doi: 10.1088/1674-1056/ab671b
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The outer valence electron momentum distributions of benzene are reinvestigated with theoretical calculations involving the vibrational effects. The results are compared with recent experimental measurements [Phys. Rev. A 98 042705 (2018)]. The significant discrepancies between theories and experiments in previous works have now been interpreted quantitatively, indicating that the vibrational motion in benzene molecule has noticeable influence on its electron momentum distributions.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Oxide-aperture-dependent output characteristics of circularly symmetric VCSEL structure

Wen-Yuan Liao(廖文渊), Jian Li(李健), Chuan-Chuan Li(李川川), Xiao-Feng Guo(郭小峰), Wen-Tao Guo(郭文涛), Wei-Hua Liu(刘维华), Yang-Jie Zhang(张杨杰), Xin Wei(韦欣), Man-Qing Tan(谭满清)
Chin. Phys. B, 2020, 29 (2): 024201 doi: 10.1088/1674-1056/ab5fbd
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The influence of oxidation aperture on the output characteristics of the circularly symmetric vertical-cavity-surface-emitting laser (VCSEL) structure is investigated. To do so, VCSELs with different oxide aperture sizes are simulated by the finite-difference time-domain (FDTD) method. The relationships among the field distribution of mode superposition, mode wavelength, output spectra, and far-field divergence with different oxide apertures are obtained. Further, VCSELs respectively with oxide aperture sizes of 2.7 μm, 4.4 μm, 5.9 μm, 7 μm, 8 μm, 9 μm, and 18.7 μm are fabricated and characterized. The maximum output power increases from 2.4 mW to 5.7 mW with oxide aperture increasing from 5.9 μm to 9 μm. Meanwhile, the wavelength tuning rate decreases from 0.93 nm/mA to 0.375 nm/mA when the oxide aperture increases from 2.7 μm to 9 μm. The thermal resistance decreases from 2.815 ℃/mW to 1.015 ℃/mW when the oxide aperture increases from 4.4 μm to 18.7 μm. It is demonstrated theoretically and experimentally that the wavelength spacing between adjacent modes increases with the augment of the injection current and the spacing becomes smaller with the oxide aperture increasing. Thus it can be reported that the aperture size can effectively reduce the mode overlaying but at the cost of the power decreasing and the wavelength tuning rate and thermal resistance increasing.

A hybrid method of solving near-zone composite eletromagnetic scattering from targets and underlying rough surface

Xi-Min Li(李西敏), Jing-Jing Li(李晶晶), Qian Gao(高乾), Peng-Cheng Gao(高鹏程)
Chin. Phys. B, 2020, 29 (2): 024202 doi: 10.1088/1674-1056/ab5ef9
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For composite electromagnetic (EM) scattering from rough surface and target above it in near-field condition, modified shooting and bouncing ray (SBR) method and integral equation method (IEM), which are analytic methods combined with two-scale model for rough surface, are proposed to solve the composite near-field scattering problems. And the modified method is verified in effectiveness and accuracy by comparing the simulation results with measured results. Finally, the composite near-fielding scattering characteristics of a slanted plane and rough water surface below are obtained by using the proposed methods, and the dynamic tendency of composite scattering characteristics versus near-fielding distance is analyzed, which may have practical contribution to engineering programs in need of radar targets near-field characteristics under extra-low-altitude conditions.

Dynamically adjustable asymmetric transmission and polarization conversion for linearly polarized terahertz wave

Tong Li(李彤), Fang-Rong Hu(胡放荣), Yi-Xian Qian(钱义先), Jing Xiao(肖靖), Long-Hui Zhang(张隆辉), Wen-Tao Zhang(张文涛), Jia-Guang Han(韩家广)
Chin. Phys. B, 2020, 29 (2): 024203 doi: 10.1088/1674-1056/ab5ef8
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The asymmetric transmission (AT) and polarization conversion of terahertz (THz) wave play a vital role in future THz communication, spectrum, and information processing. Generally, it is very difficult and complicated to actively control the AT of electromagnetic (EM) wave by using traditional devices. Here, we theoretically demonstrate a stereo-metamaterial (stereo-MM) consisting of a layer of metal structure and a layer of phase transition structure with a polyimide spacer in between. The performance of the device is simulated by using the finite-integration-technology (FIT). The results show that the AT and polarization conversion of linearly polarized wave can be dynamically controlled in a range of 1.0 THz-1.6 THz when the conductivity σ of vanadium dioxide (VO2) is changed under the external stimulation. This study provides an example of actively controlling of the AT and polarization conversion of the EM wave.

Compressed ghost imaging based on differential speckle patterns

Le Wang(王乐), Shengmei Zhao(赵生妹)
Chin. Phys. B, 2020, 29 (2): 024204 doi: 10.1088/1674-1056/ab671a
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We propose a compressed ghost imaging scheme based on differential speckle patterns, named CGI-DSP. In the scheme, a series of bucket detector signals are acquired when a series of random speckle patterns are employed to illuminate an unknown object. Then the differential speckle patterns (differential bucket detector signals) are obtained by taking the difference between present random speckle patterns (present bucket detector signals) and previous random speckle patterns (previous bucket detector signals). Finally, the image of object can be obtained directly by performing the compressed sensing algorithm on the differential speckle patterns and differential bucket detector signals. The experimental and simulated results reveal that CGI-DSP can improve the imaging quality and reduce the number of measurements comparing with the traditional compressed ghost imaging schemes because our scheme can remove the environmental illuminations efficiently.

Enhancement effect of cumulative second-harmonic generation by closed propagation feature of circumferential guided waves

Guang-Jian Gao(高广健), Ming-Xi Deng(邓明晰), Ning Hu(胡宁), Yan-Xun Xiang(项延训)
Chin. Phys. B, 2020, 29 (2): 024301 doi: 10.1088/1674-1056/ab628d
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On the basis of second-order perturbation approximate and modal expansion approach, we investigate the enhancement effect of cumulative second-harmonic generation (SHG) of circumferential guided waves (CGWs) in a circular tube, which is inherently induced by the closed propagation feature of CGWs. An appropriate mode pair of primary- and double-frequency CGWs satisfying the phase velocity matching and nonzero energy flux is selected to ensure that the second harmonic generated by primary CGW propagation can accumulate along the circumference. Using a coherent superposition of multi-waves, a model of unidirectional CGW propagation is established for analyzing the enhancement effect of cumulative SHG of primary CGW mode selected. The theoretical analyses and numerical simulations performed directly demonstrate that the second harmonic generated does have a cumulative effect along the circumferential direction and the closed propagation feature of CGWs does enhance the magnitude of cumulative second harmonic generated. Potential applications of the enhancement effect of cumulative SHG of CGWs are considered and discussed. The theoretical analysis and numerical simulation perspective presented here yield an insight previously unavailable into the physical mechanism of the enhancement effect of cumulative SHG by closed propagation feature of CGWs in a circular tube.

Avalanching patterns of irregular sand particles in continual discrete flow

Ren Han(韩韧), Yu-Feng Zhang(张宇峰), Ran Li(李然), Quan Chen(陈泉), Jing-Yu Feng(冯靖禹), Ping Kong(孔平)
Chin. Phys. B, 2020, 29 (2): 024501 doi: 10.1088/1674-1056/ab65b8
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We investigate the flow patterns of irregular sand particles under avalanching mode in a rotating drum by using the spatial filtering velocimetry technique. By exploring the variations of velocity distribution of granular flow, we find a type of avalanching pattern of irregular sand particles which is similar to that of spherical particles flow. Due to the fact that the initial position of avalanche in this pattern locates at the middle of the drum and the avalanche propagates toward the edge area gradually, we named it as mid-to-edge avalanching pattern. Furthermore, we find another avalanching pattern which slumps from the edge and propagates toward the opposite edge of the flow surface, named as edge-to-edge pattern. By analyzing the temporal and spatial characteristics of these two types of avalanching patterns, we discover that these two types of avalanche patterns are caused by that the avalanching particles constantly perturb the axial adjacent particles. Thus, the particles on the flow surface are involved in avalanching sequentially in order of the axial distance from the initial position.

Quantitative temperature imaging at elevated pressures and in a confined space with CH4/air laminar flames by filtered Rayleigh scattering

Bo Yan(闫博), Li Chen(陈力), Meng Li(李猛), Shuang Chen(陈爽), Cheng Gong(龚诚), Fu-Rong Yang(杨富荣), Yun-Gang Wu(吴运刚), Jiang-Ning Zhou(周江宁), Jin-He Mu(母金河)
Chin. Phys. B, 2020, 29 (2): 024701 doi: 10.1088/1674-1056/ab5f00
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Laminar methane/air premixed flames at different pressures in a newly developed high-pressure laminar burner are studied through Cantera simulation and filtered Rayleigh scattering (FRS). Different gas component fractions are obtained through the detailed numerical simulations. And this approach can be used to correct the FRS images of large variations in a Rayleigh cross section in different flame regimes. The temperature distribution above the flat burner is then presented without stray light interference from soot and wall reflection. Results also show that the extent of agreement with the single point measurement by the thermocouple is <6%. Finally, this study concludes that the relative uncertainty of the presented filtered Rayleigh scattering diagnostics is estimated to be below 10% in single-shot imaging.

Effects of square micro-pillar array porosity on the liquid motion of near surface layer

Xiaoxi Qiao(乔小溪), Xiangjun Zhang(张向军), Ping Chen(陈平), Yu Tian(田煜), Yonggang Meng(孟永钢)
Chin. Phys. B, 2020, 29 (2): 024702 doi: 10.1088/1674-1056/ab5fba
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The influence rules of square micro-pillar array porosity on the liquid motion characteristics of the near-surface layer are investigated by quartz crystal microbalance (QCM). QCM is a powerful and promising technique in studying the interfacial behavior, which exhibits great advantages in investigating the effects of surface microstructure, roughness, and array. In our experiments, three different arrays with the same height of about 280 nm and center distance of 200 μm, but different diameters of about 78 μm, 139 μm, and 179 μm are investigated. The results indicate that when the surface array has a large porosity, its influence on the liquid motion of the near surface layer is slight, thus resulting in a small increase of half-bandwidth variation due to the additional friction energy dissipation. When the surface array has a small porosity, the array tends to make the liquid film trapped in the array oscillating with the substrate, then there may be a layer of liquid film behaving like rigid film, and it also will make the liquid motion near the array layer more complicated. Thus for the #3 surface with a small porosity, both the absolute values of frequency shift |Δf3| and half-bandwidth variation ΔΓ3 increase obviously. The experimental results show good consistence with the theoretical model of Daikhin and Urbakh. This study sheds light on understanding the influence mechanism of surface array porosity on the liquid motion of near-surface layer.

Shape reconstructions and morphing kinematics of an eagle during perching manoeuvres

Di Tang(唐迪), Dawei Liu(刘大伟), Hai Zhu(朱海), Xipeng Huang(黄喜鹏), Zhongyong Fan(范忠勇), Mingxia Lei(雷鸣霞)
Chin. Phys. B, 2020, 29 (2): 024703 doi: 10.1088/1674-1056/ab610a
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The key to high manoeuvre ability in bird flight lies in the combined morphing of wings and tail. The perching of a wild Haliaeetus Albicilla without running or wing flapping is recorded and investigated using a high-speed digital video. A shape reconstruction method is proposed to describe wing contours and tail contours during perching. The avian airfoil geometries of the Aquila Chrysaetos are extracted from noncontact surface measurements using a ROMBER 3D laser scanner. The wing planform, chord distribution and twist distribution are fitted in convenient analytical expressions to obtain a 3D wing geometry. A three-jointed arm model is proposed to associate with the 3D wing geometry, while a one-joint arm model is proposed to describe the kinematics of tail. Therefore, a 3D bird model is established. The perching sequences of the wild eagle are recaptured and regenerated with the proposed 3D bird model. A quasi-steady aerodynamic model is applied in the aerodynamic predictions, a four-step Adams-Bashforth method is used to calculate the ordinary differential equations, thus a BFGS based optimization method is established to predict the perching motions.

Dynamic evolution of vortex structures induced bytri-electrode plasma actuator

Bo-Rui Zheng(郑博睿), Ming Xue(薛明), Chang Ge(葛畅)
Chin. Phys. B, 2020, 29 (2): 024704 doi: 10.1088/1674-1056/ab671f
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Plasma flow control is a new type of active flow control approach based on plasma pneumatic actuation. Dielectric barrier discharge (DBD) actuators have become a focus of international aerodynamic research. However, the practical applications of typical DBDs are largely restricted due to their limited discharge area and low relative-induced velocity. The further improvement of performance will be beneficial for engineering applications. In this paper, high-speed schlieren and high-speed particle image velocimetry (PIV) are employed to study the flow field induced by three kinds of plasma actuations in a static atmosphere, and the differences in induced flow field structure among typical DBD, extended DBD (EX-DBD), and tri-electrode sliding discharge (TED) are compared. The analyzing of the dynamic evolution of the maximum horizontal velocity over time, the velocity profile at a fixed horizontal position, and the momentum and body force in a control volume reveals that the induced velocity peak value and profile velocity height of EX-DBD are higher than those of the other two types of actuation, suggesting that EX-DBD actuation has the strongest temporal aerodynamic effect among the three types of actuations. The TED actuation not only can enlarge the plasma extension but also has the longest duration in the entire pulsed period and the greatest influence on the height and width of the airflow near the wall surface. Thus, the TED actuation has the ability to continuously influencing a larger three-dimensional space above the surface of the plasma actuator.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Nonlinear simulation of multiple toroidal Alfvén eigenmodes in tokamak plasmas

Xiao-Long Zhu(朱霄龙), Feng Wang(王丰), Zheng-Xiong Wang(王正汹)
Chin. Phys. B, 2020, 29 (2): 025201 doi: 10.1088/1674-1056/ab610e
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Nonlinear evolution of multiple toroidal Alfvén eigenmodes (TAEs) driven by fast ions is self-consistently investigated by kinetic simulations in toroidal plasmas. To clearly identify the effect of nonlinear coupling on the beam ion loss, simulations over single-n modes are also carried out and compared with those over multiple-n modes, and the wave-particle resonance and particle trajectory of lost ions in phase space are analyzed in detail. It is found that in the multiple-n case, the resonance overlap occurs so that the fast ion loss level is rather higher than the sum loss level that represents the summation of loss over all single-n modes in the single-n case. Moreover, increasing fast ion beta βh can not only significantly increase the loss level in the multiple-n case but also significantly increase the loss level increment between the single-n and multiple-n cases. For example, the loss level in the multiple-n case for βh=6.0% can even reach 13% of the beam ions and is 44% higher than the sum loss level calculated from all individual single-n modes in the single-n case. On the other hand, when the closely spaced resonance overlap occurs in the multiple-n case, the release of mode energy is increased so that the widely spaced resonances can also take place. In addition, phase space characterization is obtained in both single-n and multiple-n cases.

Discharge simulation and volt-second consumption analysis during ramp-up on the CFETR tokamak

Cheng-Yue Liu(刘成岳), Bin Wu(吴斌), Jin-Ping Qian(钱金平), Guo-Qiang Li(李国强), Ya-Wei Hou(侯雅巍), Wei Wei(韦维), Mei-Xia Chen(陈美霞), Ming-Zhun Lei(雷明准), Yong Guo(郭勇)
Chin. Phys. B, 2020, 29 (2): 025202 doi: 10.1088/1674-1056/ab610d
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The plasma current ramp-up is an important process for tokamak discharge, which directly affects the quality of the plasma and the system resources such as volt-second consumption and plasma current profile. The China Fusion Engineering Test Reactor (CFETR) ramp-up discharge is predicted with the tokamak simulation code (TSC). The main plasma parameters, the plasma configuration evolution and coil current evolution are given out. At the same time, the volt-second consumption during CFETR ramp-up is analyzed for different plasma shaping times and different plasma current ramp rates dIP/dt with/without assisted heating. The results show that the earlier shaping time and the faster plasma current ramp rate with auxiliary heating will enable the volt-second to save 5%-10%. At the same time, the system ability to provide the volt-second is probably 470 V·s. These simulations will give some reference to engineering design for CFETR to some degree.

Directional motion of dust particles at different gear structuresin a plasma

Chao-Xing Dai(戴超星), Chao Song(宋超), Zhi-Xiang Zhou(周志向), Wen-Tao Sun(孙文涛), Zhi-Qiang Guo(郭志强), Fu-Cheng Liu(刘富成), Ya-Feng He(贺亚峰)
Chin. Phys. B, 2020, 29 (2): 025203 doi: 10.1088/1674-1056/ab6109
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Directional motion of dust particles in a dusty plasma ratchet is observed experimentally. The dusty plasma ratchet consists of two concentric gears with asymmetric sawtooth. It is found that the sawtooth number affects the directional motion of dust particles along the saw channel. With the increase of the sawtooth number, the particle velocity increases firstly and then decreases, and there is an optimum number of the sawtooth which could induce fast rotation of dust particles. The velocities of dust particles change as they are flowing along the saw channel. We also explore the force acting on the dust particle experimentally.

The E×B drift instability in Hall thruster using 1D PIC/MCC simulation

Zahra Asadi, Mehdi Sharifian, Mojtaba Hashemzadeh, Mahmood Borhani Zarandi, Hamidreza Ghomi Marzdashti
Chin. Phys. B, 2020, 29 (2): 025204 doi: 10.1088/1674-1056/ab6719
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The E×B drift instability is studied in Hall thruster using one-dimensional particle in cell (PIC) simulation method. By using the dispersion relation, it is found that unstable modes occur only in discrete bands in k space at cyclotron harmonics. The results indicate that the number of unstable modes increases by increasing the external electric field and decreases by increasing the radial magnetic field. The ion mass does not affect the instability wavelength. Furthermore, the results confirm that there is an instability with short wavelength and high frequency. Finally, it is shown that the electron and ion distribution functions deviate from the initial state and eventually the instability is saturated by ion trapping in the azimuthal direction. Also for light mass ion, the frequency and phase velocity are very high that could lead to high electron mobility in the axial direction.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Geant4 simulation of proton-induced single event upset in three-dimensional die-stacked SRAM device

Bing Ye(叶兵), Li-Hua Mo(莫莉华), Tao Liu(刘涛), Jie Luo(罗捷), Dong-Qing Li(李东青), Pei-Xiong Zhao(赵培雄), Chang Cai(蔡畅), Ze He(贺泽), You-Mei Sun(孙友梅), Ming-Dong Hou(侯明东), Jie Liu(刘杰)
Chin. Phys. B, 2020, 29 (2): 026101 doi: 10.1088/1674-1056/ab5fc4
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Geant4 Monte Carlo simulation results of the single event upset (SEU) induced by protons with energy ranging from 0.3 MeV to 1 GeV are reported. The SEU cross section for planar and three-dimensional (3D) die-stacked SRAM are calculated. The results show that the SEU cross sections of the planar device and the 3D device are different from each other under low energy proton direct ionization mechanism, but almost the same for the high energy proton. Besides, the multi-bit upset (MBU) ratio and pattern are presented and analyzed. The results indicate that the MBU ratio of the 3D die-stacked device is higher than that of the planar device, and the MBU patterns are more complicated. Finally, the on-orbit upset rate for the 3D die-stacked device and the planar device are calculated by SPACE RADIATION software. The calculation results indicate that no matter what the orbital parameters and shielding conditions are, the on-orbit upset rate of planar device is higher than that of 3D die-stacked device.

Composition effect on elastic properties of model NiCo-based superalloys

Weijie Li(李伟节), Chongyu Wang(王崇愚)
Chin. Phys. B, 2020, 29 (2): 026102 doi: 10.1088/1674-1056/ab6204
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NiCo-based superalloys exhibit higher strength and creep resistance over conventional superalloys. Compositional effects on elastic properties of the γ and γ' phases in newly-developed NiCo-based superalloys were investigated by first-principles calculation combined with special quasi-random structures. The lattice constant, bulk modulus, and elastic constants vary linearly with the Co concentration in the NiCo solution. In the selected (Ni, Co)3(Al, W) and (Ni, Co)3(Al, Ti) model γ' phase, the lattice constant, and bulk modulus show a linear trend with alloying element concentrations. The addition of Co, Ti, and W can regulate lattice mismatch and increase the bulk modulus, simultaneously. W-addition shows excellent performance in strengthening the elastic properties in the γ' phase. Systems become unstable with higher W and Ni contents, e.g., (Ni0.75Co0.25)3(Al0.25 W0.75), and become brittle with higher W and Co addition, e.g., Co3(Al0.25 W0.75). Furthermore, Co, Ti, and W can increase the elastic constants on the whole, and such high elastic constants always correspond to a high elastic modulus. The anisotropy index always corresponds to the nature of Young's modulus in a specific direction.

Doping effects on the stacking fault energies of the γ' phase in Ni-based superalloys

Weijie Li(李伟节), Chongyu Wang(王崇愚)
Chin. Phys. B, 2020, 29 (2): 026401 doi: 10.1088/1674-1056/ab6203
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The doping effects on the stacking fault energies (SFEs), including the superlattice intrinsic stacking fault and superlattice extrinsic stacking fault, were studied by first principles calculation of the γ' phase in the Ni-based superalloys. The formation energy results show that the main alloying elements in Ni-based superalloys, such as Re, Cr, Mo, Ta, and W, prefer to occupy the Al-site in Ni3Al, Co shows a weak tendency to occupy the Ni-site, and Ru shows a weak tendency to occupy the Al-site. The SFE results show that Co and Ru could decrease the SFEs when added to fault planes, while other main elements increase SFEs. The double-packed superlattice intrinsic stacking fault energies are lower than superlattice extrinsic stacking fault energies when elements (except Co) occupy an Al-site. Furthermore, the SFEs show a symmetrical distribution with the location of the elements in the ternary model. A detailed electronic structure analysis of the Ru effects shows that SFEs correlated with not only the symmetry reduction of the charge accumulation but also the changes in structural energy.

High pressure and high temperature induced polymerization of C60 quantum dots

Shi-Hao Ruan(阮世豪), Chun-Miao Han(韩春淼), Fu-Lu Li(李福禄), Bing Li(李冰), Bing-Bing Liu(刘冰冰)
Chin. Phys. B, 2020, 29 (2): 026402 doi: 10.1088/1674-1056/ab6657
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We synthesized C60 quantum dots (QDs) with a uniform size by a modified ultrasonic process and studied its polymerization under high pressure and high temperature (HPHT). Raman spectra showed that a phase assemblage of a dimer (D) phase (62 vol%) and a one-dimensional chain orthorhombic (O) phase (38 vol%) was obtained at 1.5 GPa and 300 °C. At 2.0 GPa and 430 °C, the proportion of the O phase increased to 46 vol%, while the corresponding D phase decreased to 54 vol%. Compared with bulk and nanosized C60, C60 QDs cannot easily form a high-dimensional polymeric structure. This fact is probably caused by the small particle size, orientation of the disordered structure of C60 QDs, and the barrier of oxide function groups between C60 molecules. Our studies enhance the understanding of the polymerization behavior of low-dimension C60 nanomaterials under HPHT conditions.

Triphenylene adsorption on Cu(111) and relevant graphene self-assembly Hot!

Qiao-Yue Chen(陈乔悦), Jun-Jie Song(宋俊杰), Liwei Jing(井立威), Kaikai Huang(黄凯凯), Pimo He(何丕模), Hanjie Zhang(张寒洁)
Chin. Phys. B, 2020, 29 (2): 026801 doi: 10.1088/1674-1056/ab6583
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Investigations on adsorption behavior of triphenylene (TP) and subsequent graphene self-assembly on Cu(111) were carried out mainly by using scanning tunneling microscopy (STM). At monolayer coverage, TP molecules formed a long-range ordered adsorption structure on Cu(111) with an uniform orientation. Graphene self-assembly on the Cu(111) substrate with TP molecules as precursor was achieved by annealing the sample, and a large-scale graphene overlayer was successfully captured after the sample annealing up to 1000 K. Three different Moiré patterns generated from relative rotational disorders between the graphene overlayer and the Cu(111) substrate were observed, one with 4° rotation between the graphene overlayer and the Cu(111) substrate with a periodicity of 2.93 nm, another with 7° rotation and 2.15 nm of the size of the Moiré supercell, and the third with 10° rotation with a periodicity of 1.35 nm.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Molecular dynamics simulation of atomic hydrogen diffusion in strained amorphous silica

Fu-Jie Zhang(张福杰), Bao-Hua Zhou(周保花), Xiao Liu(刘笑), Yu Song(宋宇), Xu Zuo(左旭)
Chin. Phys. B, 2020, 29 (2): 027101 doi: 10.1088/1674-1056/ab5fc5
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Understanding hydrogen diffusion in amorphous SiO2 (a-SiO2), especially under strain, is of prominent importance for improving the reliability of semiconducting devices, such as metal-oxide-semiconductor field effect transistors. In this work, the diffusion of hydrogen atom in a-SiO2 under strain is simulated by using molecular dynamics (MD) with the ReaxFF force field. A defect-free a-SiO2 atomic model, of which the local structure parameters accord well with the experimental results, is established. Strain is applied by using the uniaxial tensile method, and the values of maximum strain, ultimate strength, and Young's modulus of the a-SiO2 model under different tensile rates are calculated. The diffusion of hydrogen atom is simulated by MD with the ReaxFF, and its pathway is identified to be a series of hops among local energy minima. Moreover, the calculated diffusivity and activation energy show their dependence on strain. The diffusivity is substantially enhanced by the tensile strain at a low temperature (below 500 K), but reduced at a high temperature (above 500 K). The activation energy decreases as strain increases. Our research shows that the tensile strain can have an influence on hydrogen transportation in a-SiO2, which may be utilized to improve the reliability of semiconducting devices.

Simulation of GaN micro-structured neutron detectors for improving electrical properties

Xin-Lei Geng(耿昕蕾), Xiao-Chuan Xia(夏晓川), Huo-Lin Huang(黄火林), Zhong-Hao Sun(孙仲豪), He-Qiu Zhang(张贺秋), Xing-Zhu Cui(崔兴柱), Xiao-Hua Liang(梁晓华), Hong-Wei Liang(梁红伟)
Chin. Phys. B, 2020, 29 (2): 027201 doi: 10.1088/1674-1056/ab671e
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Nowadays, the superior detection performance of semiconductor neutron detectors is a challenging task. In this paper, we deal with a novel GaN micro-structured neutron detector (GaN-MSND) and compare three different methods such as the method of modulating the trench depth, the method of introducing dielectric layer and p-type inversion region to improve the width of depletion region (W). It is observed that the intensity of electric field can be modulated by scaling the trench depth. On the other hand, the electron blocking region is formed in the detector enveloped with a dielectric layer. Furthermore, the introducing of p-type inversion region produces new p/n junction, which not only promotes the further expansion of the depletion region but also reduces the intensity of electric field produced by main junction. It can be realized that all these methods can considerably enhance the working voltage as well as W. Of them, the improvement on W of GaN-MSND with the p-type inversion region is the most significant and the value of W could reach 12.8 μm when the carrier concentration of p-type inversion region is 1017 cm-3. Consequently, the value of W is observed to improve 200% for the designed GaN-MSND as compared with that without additional design. This work ensures to the researchers and scientific community the fabrication of GaN-MSND having superior detection limit in the field of intense radiation.

Breakdown voltage enhancement in GaN channel and AlGaN channel HEMTs using large gate metal height Hot!

Zhong-Xu Wang(王中旭), Lin Du(杜林), Jun-Wei Liu(刘俊伟), Ying Wang(王颖), Yun Jiang(江芸), Si-Wei Ji(季思蔚), Shi-Wei Dong(董士伟), Wei-Wei Chen(陈伟伟), Xiao-Hong Tan(谭骁洪), Jin-Long Li(李金龙), Xiao-Jun Li(李小军), Sheng-Lei Zhao(赵胜雷), Jin-Cheng Zhang(张进成), Yue Hao(郝跃)
Chin. Phys. B, 2020, 29 (2): 027301 doi: 10.1088/1674-1056/ab5fb9
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A large gate metal height technique is proposed to enhance breakdown voltage in GaN channel and AlGaN channel high-electron-mobility-transistors (HEMTs). For GaN channel HEMTs with gate-drain spacing LGD=2.5 μm, the breakdown voltage VBR increases from 518 V to 582 V by increasing gate metal height h from 0.2 μm to 0.4 μm. For GaN channel HEMTs with LGD=7 μm, VBR increases from 953 V to 1310 V by increasing h from 0.8 μm to 1.6 μm. The breakdown voltage enhancement results from the increase of the gate sidewall capacitance and depletion region extension. For Al0.4Ga0.6N channel HEMT with LGD=7 μm, VBR increases from 1535 V to 1763 V by increasing h from 0.8 μm to 1.6 μm, resulting in a high average breakdown electric field of 2.51 MV/cm. Simulation and analysis indicate that the high gate metal height is an effective method to enhance breakdown voltage in GaN-based HEMTs, and this method can be utilized in all the lateral semiconductor devices.

A simple tight-binding approach to topological superconductivity in monolayer MoS2

H Simchi
Chin. Phys. B, 2020, 29 (2): 027401 doi: 10.1088/1674-1056/ab6552
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Monolayer molybdenum disulfide (MoS2) has a honeycomb crystal structure. Here, with considering the triangular sublattice of molybdenum atoms, a simple tight-binding Hamiltonian is introduced (derived) for studying the phase transition and topological superconductivity in MoS2 under uniaxial strain. It is shown that spin-singlet p+ip wave phase is a topological superconducting phase with nonzero Chern numbers. When the chemical potential is greater (smaller) than the spin-orbit coupling (SOC) strength, the Chern number is equal to four (two) and otherwise it is equal to zero. Also, the results show that, if the superconductivity energy gap is smaller than the SOC strength and the chemical potential is greater than the SOC strength, the zero energy Majorana states exist. Finally, we show that the topological superconducting phase is preserved under uniaxial strain.

Time-dependent photothermal characterization on damage of fused silica induced by pulsed 355-nm laser with high repetition rate

Chun-Yan Yan(闫春燕), Bao-An Liu(刘宝安), Xiang-Cao Li(李香草), Chang Liu(刘畅), Xin Ju(巨新)
Chin. Phys. B, 2020, 29 (2): 027901 doi: 10.1088/1674-1056/ab671d
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Time-dependent damage to fused silica induced by high frequency ultraviolet laser is investigated. Photothermal spectroscopy (PTS) and optical microscopy (OM) are utilized to characterize the evolution of damage pits with irradiation time. Experimental results describe that in the pre-damage stage of fused silica sample irradiated by 355-nm laser, the photothermal spectrum signal undergoes a process from scratch to metamorphism due to the absorption of laser energy by defects. During the visible damage stage of fused silica sample, the photothermal spectrum signal decreases gradually from the maximum value because of the aggravation of the damage and the splashing of the material. This method can be used to estimate the operation lifetime of optical elements in engineering.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Atomically flat surface preparation for surface-sensitive technologies

Cen-Yao Tang(唐岑瑶), Zhi-Cheng Rao(饶志成), Qian-Qian Yuan(袁茜茜), Shang-Jie Tian(田尚杰), Hang Li(李航), Yao-Bo Huang(黄耀波), He-Chang Lei(雷和畅), Shao-Chun Li(李绍春), Tian Qian(钱天), Yu-Jie Sun(孙煜杰), Hong Ding(丁洪)
Chin. Phys. B, 2020, 29 (2): 028101 doi: 10.1088/1674-1056/ab6586
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Surface-sensitive measurements are crucial to many types of researches in condensed matter physics. However, it is difficult to obtain atomically flat surfaces of many single crystals by the commonly used mechanical cleavage. We demonstrate that the grind-polish-sputter-anneal method can be used to obtain atomically flat surfaces on topological materials. Three types of surface-sensitive measurements are performed on CoSi (001) surface with dramatically improved quality of data. This method extends the research area of surface-sensitive measurements to hard-to-cleave alloys, and can be applied to irregular single crystals with selective crystalline planes. It may become a routine process of preparing atomically flat surfaces for surface-sensitive technologies.

High sensitive pressure sensors based on multiple coating technique

Rizwan Zahoor, Chang Liu(刘畅), Muhammad Rizwan Anwar, Fu-Yan Lin(林付艳), An-Qi Hu(胡安琪), Xia Guo(郭霞)
Chin. Phys. B, 2020, 29 (2): 028102 doi: 10.1088/1674-1056/ab6721
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A multi-coating technique of reduced graphene oxide (RGO) was proposed to increase the sensitivity of paper-based pressure sensors. The maximum sensitivity of 17.6 kPa-1 under the 1.4 kPa was achieved. The electrical sensing mechanism is attributed to the percolation effect. Such paper pressure sensors were applied to monitor the motor vibration, which indicates the potential of mechanical flaw detection by analyzing the waveform difference.

A numerical study on pattern selection in crystal growth by using anisotropic lattice Boltzmann-phase field method

Zhaodong Zhang(张兆栋), Yuting Cao(曹宇婷), Dongke Sun(孙东科), Hui Xing(邢辉), Jincheng Wang(王锦程), Zhonghua Ni(倪中华)
Chin. Phys. B, 2020, 29 (2): 028103 doi: 10.1088/1674-1056/ab6718
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Pattern selection during crystal growth is studied by using the anisotropic lattice Boltzmann-phase field model. In the model, the phase transition, melt flows, and heat transfer are coupled and mathematically described by using the lattice Boltzmann (LB) scheme. The anisotropic streaming-relaxation operation fitting into the LB framework is implemented to model interface advancing with various preferred orientations. Crystal pattern evolutions are then numerically investigated in the conditions of with and without melt flows. It is found that melt flows can significantly influence heat transfer, crystal growth behavior, and phase distributions. The crystal morphological transition from dendrite, seaweed to cauliflower-like patterns occurs with the increase of undercoolings. The interface normal angles and curvature distributions are proposed to quantitatively characterize crystal patterns. The results demonstrate that the distributions are corresponding to crystal morphological features, and they can be therefore used to describe the evolution of crystal patterns in a quantitative way.

Effects of buried oxide layer on working speed of SiGe heterojunction photo-transistor

Xian-Cheng Liu(刘先程), Jia-Jun Ma(马佳俊), Hong-Yun Xie(谢红云), Pei Ma(马佩), Liang Chen(陈亮), Min Guo(郭敏), Wan-Rong Zhang(张万荣)
Chin. Phys. B, 2020, 29 (2): 028501 doi: 10.1088/1674-1056/ab5f01
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The effects of buried oxide (BOX) layer on the capacitance of SiGe heterojunction photo-transistor (HPT), including the collector-substrate capacitance, the base-collector capacitance, and the base-emitter capacitance, are studied by using a silicon-on-insulator (SOI) substrate as compared with the devices on native Si substrates. By introducing the BOX layer into Si-based SiGe HPT, the maximum photo-characteristic frequency ft, opt of SOI-based SiGe HPT reaches up to 24.51 GHz, which is 1.5 times higher than the value obtained from Si-based SiGe HPT. In addition, the maximum optical cut-off frequency fβ, opt, namely its 3-dB bandwidth, reaches up to 1.13 GHz, improved by 1.18 times. However, with the increase of optical power or collector current, this improvement on the frequency characteristic from BOX layer becomes less dominant as confirmed by reducing the 3-dB bandwidth of SOI-based SiGe HPT which approaches to the 3-dB bandwidth of Si-based SiGe HPT at higher injection conditions.

Memristor-based vector neural network architecture

Hai-Jun Liu(刘海军), Chang-Lin Chen(陈长林), Xi Zhu(朱熙), Sheng-Yang Sun(孙盛阳), Qing-Jiang Li(李清江), Zhi-Wei Li(李智炜)
Chin. Phys. B, 2020, 29 (2): 028502 doi: 10.1088/1674-1056/ab65b5
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Vector neural network (VNN) is one of the most important methods to process interval data. However, the VNN, which contains a great number of multiply-accumulate (MAC) operations, often adopts pure numerical calculation method, and thus is difficult to be miniaturized for the embedded applications. In this paper, we propose a memristor based vector-type backpropagation (MVTBP) architecture which utilizes memristive arrays to accelerate the MAC operations of interval data. Owing to the unique brain-like synaptic characteristics of memristive devices, e.g., small size, low power consumption, and high integration density, the proposed architecture can be implemented with low area and power consumption cost and easily applied to embedded systems. The simulation results indicate that the proposed architecture has better identification performance and noise tolerance. When the device precision is 6 bits and the error deviation level (EDL) is 20%, the proposed architecture can achieve an identification rate, which is about 92% higher than that for interval-value testing sample and 81% higher than that for scalar-value testing sample.
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