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Chin. Phys. B  
  Chin. Phys. B--2019, Vol.28, No.10
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TOPICAL REVIEW—CALYPSO structure prediction methodology and its applications to materials discovery

Cluster structure prediction via CALYPSO method

Yonghong Tian, Weiguo Sun, Bole Chen, Yuanyuan Jin, Cheng Lu
Chin. Phys. B 2019, 28 (10): 103104 ;  doi: 10.1088/1674-1056/ab4274
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Cluster science as a bridge linking atomic molecular physics and condensed matter inspired the nanomaterials development in the past decades, ranging from the single-atom catalysis to ligand-protected noble metal clusters. The corresponding studies not only have been restricted to the search for the geometrical structures of clusters, but also have promoted the development of cluster-assembled materials as the building blocks. The CALYPSO cluster prediction method combined with other computational techniques have significantly stimulated the development of the cluster-based nanomaterials. In this review, we will summarize some good cases of cluster structure by CALYPSO method, which have also been successfully identified by the photoelectron spectra experiments. Beginning with the alkali-metal clusters, which serve as benchmarks, a series of studies are performed on the size-dependent elemental clusters which possess relatively high stability and interesting chemical physical properties. Special attentions are paid to the boron-based clusters because of their promising applications. The NbSi12 and BeB16 clusters, for example, are two classic representatives of the silicon- and boron-based clusters, which can be viewed as building blocks of nanotubes and borophene. This review offers a detailed description of the structural evolutions and electronic properties of medium-sized pure and doped clusters, which will advance fundamental knowledge of cluster-based nanomaterials and provide valuable information for further theoretical and experimental studies.

Discovery of superhard materials via CALYPSO methodology

Shuangshuang Zhang, Julong He, Zhisheng Zhao, Dongli Yu, Yongjun Tian
Chin. Phys. B 2019, 28 (10): 106104 ;  doi: 10.1088/1674-1056/ab4179
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The study of superhard materials plays a critical role in modern industrial applications due to their widespread applications as cutting tools, abrasives, exploitation drills, and coatings. The search for new superhard materials with superior performance remains a hot topic and is mainly considered as two classes of materials:(i) the light-element compounds in the B-C-N-O(-Si) system with strong and short covalent bonds, and (ii) the transition-element light-element compounds with strong covalent bonds frameworks and high valence electron density. In this paper, we review the recent achievements in the prediction of superhard materials mostly using the advanced CALYPSO methodology. A number of novel, superhard crystals of light-element compounds and transition-metal borides, carbides, and nitrides have been theoretically identified and some of them account well for the experimentally mysterious phases. To design superhard materials via CALYPSO methodology is independent of any known structural and experimental data, resulting in many remarkable structures accelerating the development of new superhard materials.

The CALYPSO methodology for structure prediction

Qunchao Tong, Jian Lv, Pengyue Gao, Yanchao Wang
Chin. Phys. B 2019, 28 (10): 106105 ;  doi: 10.1088/1674-1056/ab4174
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Structure prediction methods have been widely used as a state-of-the-art tool for structure searches and materials discovery, leading to many theory-driven breakthroughs on discoveries of new materials. These methods generally involve the exploration of the potential energy surfaces of materials through various structure sampling techniques and optimization algorithms in conjunction with quantum mechanical calculations. By taking advantage of the general feature of materials potential energy surface and swarm-intelligence-based global optimization algorithms, we have developed the CALYPSO method for structure prediction, which has been widely used in fields as diverse as computational physics, chemistry, and materials science. In this review, we provide the basic theory of the CALYPSO method, placing particular emphasis on the principles of its various structure dealing methods. We also survey the current challenges faced by structure prediction methods and include an outlook on the future developments of CALYPSO in the conclusions.

Pressure-induced new chemistry

Jianyan Lin, Xin Du, Guochun Yang
Chin. Phys. B 2019, 28 (10): 106106 ;  doi: 10.1088/1674-1056/ab3f91
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It has long been recognized that the valence electrons of an atom dominate the chemical properties, while the inner-shell electrons or outer empty orbital do not participate in chemical reactions. Pressure, as a fundamental thermodynamic variable, plays an important role in the preparation of new materials. More recently, pressure stabilized a series of unconventional stoichiometric compounds with new oxidation states, in which the inner-shell electrons or outer empty orbital become chemically active. Here, we mainly focus on the recent advances in high-pressure new chemistry including novel chemical bonding and new oxidation state, identified by first-principles swarm intelligence structural search calculations. The aim of this review is to provide an up-to-date research progress on the chemical bonding with inner-shell electrons or outer empty orbital, abnormal interatomic charge transfer, hypervalent compounds, and chemical reactivity of noble gases. Personal outlook on the challenge and opportunity in this field are proposed in the conclusion.

Geoscience material structures prediction via CALYPSO methodology

Andreas Hermann
Chin. Phys. B 2019, 28 (10): 106107 ;  doi: 10.1088/1674-1056/ab43bc
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Many properties of planets such as their interior structure and thermal evolution depend on the high-pressure properties of their constituent materials. This paper reviews how crystal structure prediction methodology can help shed light on the transformations materials undergo at the extreme conditions inside planets. The discussion focuses on three areas:(i) the propensity of iron to form compounds with volatile elements at planetary core conditions (important to understand the chemical makeup of Earth's inner core), (ii) the chemistry of mixtures of planetary ices (relevant for the mantle regions of giant icy planets), and (iii) examples of mantle minerals. In all cases the abilities and current limitations of crystal structure prediction are discussed across a range of example studies.

High-pressure electrides: From design to synthesis

Biao Wan, Jingwu Zhang, Lailei Wu, Huiyang Gou
Chin. Phys. B 2019, 28 (10): 106201 ;  doi: 10.1088/1674-1056/ab3f95
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Electrides are unique ionic compounds that electrons serve as the anions. Many electrides with fascinating physical and chemical properties have been discovered at ambient condition. Under pressure, electrides are also revealed to be ubiquitous crystal morphology, enriching the geometrical topologies and electronic properties of electrides. In this Review, we overview the formation mechanism of high-pressure electrides (HPEs) and outline a scheme for exploring new HPEs from pre-design, CALYPSO assisted structural searches, indicators for electrides, to experimental synthesis. Moreover, the evolution of electronic dimensionality under compression is also discussed to better understand the dimensional distribution of anionic electrons in HPEs.

The role of CALYPSO in the discovery of high-Tc hydrogen-rich superconductors

Wenwen Cui, Yinwei Li
Chin. Phys. B 2019, 28 (10): 107104 ;  doi: 10.1088/1674-1056/ab4253
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Hydrogen-rich compounds are promising candidates for high-Tc or even room-temperature superconductors. The search for high-Tc hydrides poses a major experimental challenge because there are many known hydrides and even more unknown hydrides with unusual stoichiometries under high pressure. The combination of crystal structure prediction and first-principles calculations has played an important role in the search for high-Tc hydrides, especially in guiding experimental synthesis. Crystal structure AnaLYsis by Particle Swarm Optimization (CALYPSO) is one of the most efficient methods for predicting stable or metastable structures from the chemical composition alone. This review summarizes the superconducting hydrides predicted using CALYPSO. We focus on two breakthroughs toward room-temperature superconductors initiated by CALYPSO:the prediction of high-Tc superconductivity in compressed hydrogen sulfide and lanthanum hydrides, both of which have been confirmed experimentally and have set new record Tc values. We also address the challenges and outlook in this field.

Recent progress on the prediction of two-dimensional materials using CALYPSO

Cheng Tang, Gurpreet Kour, Aijun Du
Chin. Phys. B 2019, 28 (10): 107306 ;  doi: 10.1088/1674-1056/ab41ea
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In recent years, structure design and predictions based on global optimization approach as implemented in CALYPSO software have gained great success in accelerating the discovery of novel two-dimensional (2D) materials. Here we highlight some most recent research progress on the prediction of novel 2D structures, involving elements, metal-free and metal-containing compounds using CALYPSO package. Particular emphasis will be given to those 2D materials that exhibit unique electronic and magnetic properties with great potentials for applications in novel electronics, optoelectronics, magnetronics, spintronics, and photovoltaics. Finally, we also comment on the challenges and perspectives for future discovery of multi-functional 2D materials.
SPECIAL TOPIC—Recent advances in thermoelectric materials and devices

Dynamic and inner-dressing control of four-wave mixing in periodically-driven atomic system

Yuan-Yuan Li, Li Li, Yun-Zhe Zhang, Lei Zhang
Chin. Phys. B 2019, 28 (10): 104201 ;  doi: 10.1088/1674-1056/ab3b52
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Four-wave-mixing (FWM) process is examined by using density matrix formalism in a periodically-driven atomic medium. Numerical result shows that FWM signals can be controlled by selecting different dynamic parameters of the probe field and strengths of the inner-dressing fields. It is also shown that the controllable FWM process is dominantly influenced by the evolution of atomic population difference and two-photon coherence. This dynamic and inner-dressing control of FWM is probably used for optimizing the optical nonlinear process and information processing.

Proof-of-principle experimental demonstration of quantum secure imaging based on quantum key distribution

Yi-Bo Zhao, Wan-Li Zhang, Dong Wang, Xiao-Tian Song, Liang-Jiang Zhou, Chi-Biao Ding
Chin. Phys. B 2019, 28 (10): 104203 ;  doi: 10.1088/1674-1056/ab3e66
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We present a quantum secure imaging (QSI) scheme based on the phase encoding and weak+vacuum decoy-state BB84 protocol of quantum key distribution (QKD). It allows us to implement a computational ghost imaging (CGI) system with more simplified equipment and reconstructed algorithm by using a digital micro-mirror device (DMD) to preset the specific spatial distribution of the light intensity. What is more, the quantum bit error rate (QBER) and the secure key rate analytical functions of QKD are used to see through the intercept-resend jamming attacks and ensure the authenticity of the imaging information. In the experiment, we obtained the image of the object quickly and efficiently by measuring the signal photon counts with a single-photon detector (SPD), and achieved a secure key rate of 571.0 bps and a secure QBER of 3.99%, which is well below the lower bound of QBER of 14.51%. Besides, our imaging system uses a laser with invisible wavelength of 1550 nm, whose intensity is as low as single-photon, that can realize weak-light imaging and is immune to the stray light or air turbulence, thus it will become a better choice for quantum security radar against intercept-resend jamming attacks.

Numerical investigation on coherent mid-infrared supercontinuum generation in chalcogenide PCFs with near-zero flattened all-normal dispersion profiles

Jie Han, Sheng-Dong Chang, Yan-Jia Lyu, Yong Liu
Chin. Phys. B 2019, 28 (10): 104204 ;  doi: 10.1088/1674-1056/ab3f25
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We design a novel all-normal flat near-zero dispersion chalcogenide photonic crystal fiber (PCF) for generating mid-infrared (MIR) supercontinuum (SC). The proposed PCF with a core made of As2Se3 glass and uniform air holes in the cladding is selectively filled with As2S5 glass. By carefully engineering the PCF with an all-normal flat near-zero dispersion profile, the anomalous-dispersion soliton effect is reduced, thus enabling broadband highly coherent SC to be generated. We also investigate the influence of the pulse parameters on the SC generation. Broadband SC covering 1.4 μm-10 μm with perfect coherence is achieved by pumping the proposed 3-cm-long PCF with 3-μm 100-fs pulses. The results provide a potential all-fiber realization of the broadband coherent MIR-SC.

Second-order interference of two independent photons with different spectra

Yu Zhou, Jian-Bin Liu, Huai-Bin Zheng, Hui Chen, Fu-Li Li, Zhuo Xu
Chin. Phys. B 2019, 28 (10): 104205 ;  doi: 10.1088/1674-1056/ab3f23
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The second-order interference of two independent photons with different spectra in a Shih-Alley/Hong-Ou-Mandel interferometer is studied in Feynman's path integral theory. There is a second-order interference pattern for photons with different spectra if the photons are indistinguishable for the employed detection system. The conditions to observe the second-order temporal beating with photons of different spectra are analyzed. The influence of the response time of the detection system on the observed second-order interference pattern is also discussed. It is a direct result of that measurement in quantum mechanics is dependent on the employed measuring apparatus. The results are helpful to understand the physics of two-photon interference in different schemes.

Polymer/silica hybrid waveguide Y-branch power splitter with loss compensation based on NaYF4: Er3+, Yb3+ nanocrystals

Yue-Wu Fu, Tong-He Sun, Mei-Ling Zhang, Xu-Cheng Zhang, Fei Wang, Da-Ming Zhang
Chin. Phys. B 2019, 28 (10): 104206 ;  doi: 10.1088/1674-1056/ab3f24
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A polymer waveguide Y-branch power splitter with loss compensation is proposed based on NaYF4:Er3+, Yb3+ nanocrystals prepared by a high temperature thermal decomposition method. The Y-branch power splitter is designed as a structure of embedded waveguide, and its core material is nanocrystals-doped SU-8. The insertion loss of the device is~15 dB. For an input signal power of 0.05 mW and a pump power of 267.7 mW, the two branches with 5.81-dB and 5.41-dB loss compensations at 1530 nm are achieved respectively. A polymer waveguide Y-branch power splitter with loss compensation has an important research significance.

Properties of multi-Gaussian Schell-model beams carrying an edge dislocation propagating in oceanic turbulence

Da-Jun Liu, Yao-Chuan Wang, Gui-Qiu Wang, Hong-Ming Yin, Hai-Yang Zhong
Chin. Phys. B 2019, 28 (10): 104207 ;  doi: 10.1088/1674-1056/ab3f21
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Based on the theory of coherence, the model of multi-Gaussian Schell-model (MGSM) beams carrying an edge dislocation generated by the MGSM source is introduced. The analytical cross-spectral density of MGSM beams carrying an edge dislocation propagating in oceanic turbulence is derived, and used to study the evolution properties of the MGSM beams carrying an edge dislocation. The results indicate that the MGSM beam carrying an edge dislocation propagating in oceanic turbulence will evolve from the profile with two intensity peaks into a flat-topped beam caused by the MGSM source, and the beam will evolve into the Gaussian-like beam due to the influences of oceanic turbulence in the far field. As the propagation distance increases, the MGSM beam carrying an edge dislocation propagating in oceanic turbulence with the larger rate of dissipation of mean-squared temperature (χT) and ratio of temperature to salinity contribution to the refractive index spectrum (ε) or the smaller rate of dissipation of kinetic energy per unit mass of fluid (ξ) evolves into the flat-topped beam or a Gaussian beam faster.

Extraordinary transmission and reflection in PT-symmetric two-segment-connected triangular optical waveguide networks with perfect and broken integer waveguide length ratios

Jia-Ye Wu, Xu-Hang Wu, Xiang-Bo Yang, Hai-Ying Li
Chin. Phys. B 2019, 28 (10): 104208 ;  doi: 10.1088/1674-1056/ab3f92
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By adjusting the waveguide length ratio, we study the extraordinary characteristics of electromagnetic waves propagating in one-dimensional (1D) parity-time-symmetric (PT-symmetric) two-segment-connected triangular optical waveguide networks with perfect and broken integer waveguide length ratios respectively. It is found that the number and the corresponding frequencies of the extremum spontaneous PT-symmetric breaking points are dependent on the waveguide length ratio. Near the extremum breaking points, ultrastrong extraordinary transmissions are created and the maximal can arrive at, respectively, 2.4079×1014 and 4.3555×1013 in both kinds of networks. However, bidirectional invisibility can only be produced by the networks with broken integer waveguide length ratio, whose mechanism is explained in detail from the perspective of photonic band structure. The findings of this work can be useful optical characteristic control in the fabrication of PT-symmetric optical waveguide networks, which possesses great potential in designing optical amplifiers, optical energy saver devices, and special optical filters.

Low insertion loss silicon-based spatial light modulator with high reflective materials outside Fabry-Perot cavity

Li-Fei Tian, Ying-Xin Kuang, Zhong-Chao Fan, Zhi-Yong Li
Chin. Phys. B 2019, 28 (10): 104209 ;  doi: 10.1088/1674-1056/ab427c
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The extinction ratio and insertion loss of spatial light modulator are subject to the material problem, thus limiting its applications. One reflection-type silicon-based spatial light modulator with high reflective materials outside the Fabry-Perot cavity is demonstrated in this paper. The reflectivity values of the outside-cavity materials with different film layer numbers are simulated. The reflectivity values of 6-pair Ta2O5/SiO2 films at 1550 nm are experimentally verified to be as high as 99.9%. The surfaces of 6-pair Ta2O5/SiO2 films are smooth:their root-mean-square roughness values are as small as 0.53 nm. The insertion loss of the device at 1550 nm is only 1.2 dB. The high extinction ratio of the device at 1550 nm and 11 V is achieved to be 29.7 dB. The spatial light modulator has a high extinction ratio and low insertion loss for applications.

Multi-objective strategy to optimize dithering technique for high-quality three-dimensional shape measurement

Ning Cai, Zhe-Bo Chen, Xiang-Qun Cao, Bin Lin
Chin. Phys. B 2019, 28 (10): 104210 ;  doi: 10.1088/1674-1056/ab427b
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Dithering optimization techniques can be divided into the phase-optimized technique and the intensity-optimized technique. The problem with the former is the poor sensitivity to various defocusing amounts, and the problem with the latter is that it cannot enhance phase quality directly nor efficiently. In this paper, we present a multi-objective optimization framework for three-dimensional (3D) measurement by utilizing binary defocusing technique. Moreover, a binary patch optimization technique is used to solve the time-consuming issue of genetic algorithm. It is demonstrated that the presented technique consistently obtains significant phase performance improvement under various defocusing amounts.

Single event upset on static random access memory devices due to spallation, reactor, and monoenergetic neutrons

Xiao-Ming Jin, Wei Chen, Jun-Lin Li, Chao Qi, Xiao-Qiang Guo, Rui-Bin Li, Yan Liu
Chin. Phys. B 2019, 28 (10): 104212 ;  doi: 10.1088/1674-1056/ab4175
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This paper presents new neutron-induced single event upset (SEU) data on the SRAM devices with the technology nodes from 40 nm to 500 nm due to spallation, reactor, and monoenergetic neutrons. The SEU effect is investigated as a function of incident neutron energy spectrum, technology node, byte pattern and neutron fluence rate. The experimental data show that the SEU effect mainly depends on the incident neutron spectrum and the technology node, and the SEU sensitivity induced by low-energy neutrons significantly increases with the technology downscaling. Monte-Carlo simulations of nuclear interactions with device architecture are utilized for comparing with the experimental results. This simulation approach allows us to investigate the key parameters of the SEU sensitivity, which are determined by the technology node and supply voltage. The simulation shows that the high-energy neutrons have more nuclear reaction channels to generate more secondary particles which lead to the significant enhancement of the SEU cross-sections, and thus revealing the physical mechanism for SEU sensitivity to the incident neutron spectrum.

Theoretical framework for geoacoustic inversion by adjoint method

Yang Wang, Xiao-Feng Zhao
Chin. Phys. B 2019, 28 (10): 104301 ;  doi: 10.1088/1674-1056/ab3f93
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Traditional geoacoustic inversions are generally solved by matched-field processing in combination with meta-heuristic global searching algorithms which usually need massive computations. This paper proposes a new physical framework for geoacoustic retrievals. A parabolic approximation of wave equation with non-local boundary condition is used as the forward propagation model. The expressions of the corresponding tangent linear model and the adjoint operator are derived, respectively, by variational method. The analytical expressions for the gradient of the cost function with respect to the control variables can be formulated by the adjoint operator, which in turn can be used for optimization by the gradient-based method.

Evolution of real contact area during stick-slip movement observed by total reflection method

Zhijun Luo, Baojiang Song, Jingyu Han, Shaoze Yan
Chin. Phys. B 2019, 28 (10): 104601 ;  doi: 10.1088/1674-1056/ab3f1f
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We build an experiment system based on total reflection (TR) method to observe the evolution of real contact area of polymethyl methacrylate (PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959. Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement:the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs, the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.

Stabilized seventh-order dissipative compact scheme for two-dimensional Euler equations

Jia-Xian Qin, Ya-Ming Chen, Xiao-Gang Deng
Chin. Phys. B 2019, 28 (10): 104701 ;  doi: 10.1088/1674-1056/ab3f26
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We derive in this paper a time stable seventh-order dissipative compact finite difference scheme with simultaneous approximation terms (SATs) for solving two-dimensional Euler equations. To stabilize the scheme, the choice of penalty coefficients for SATs is studied in detail. It is demonstrated that the derived scheme is quite suitable for multi-block problems with different spacial steps. The implementation of the scheme for the case with curvilinear grids is also discussed. Numerical experiments show that the proposed scheme is stable and achieves the design seventh-order convergence rate.

Numerical simulation on dynamic behaviors of bubbles flowing through bifurcate T-junction in microfluidic device

Liang-Yu Wu, Ling-Bo Liu, Xiao-Tian Han, Qian-Wen Li, Wei-Bo Yang
Chin. Phys. B 2019, 28 (10): 104702 ;  doi: 10.1088/1674-1056/ab3f27
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Based on the volume of fluid (VOF) method, a numerical model of bubbles splitting in a microfluidic device with T-junction is developed and solved numerically. Various flow patterns are distinguished and the effects of bubble length, capillary number, and diameter ratio between the mother channel and branch are discussed. The break-up mechanism is explored in particular. The results indicate that the behaviors of the bubbles can be classified into two categories:break-up and non-break. Under the condition of slug flowing, the branches are obstructed by the bubbles that the pressure difference drives the bubbles into break-up state, while the bubbles that retain non-break state flow into an arbitrary branch under bubbling flow condition. The break-up of the short bubbles only occurs when the viscous force from the continuous phase overcomes the interfacial tension. The behavior of the bubbles transits from non-break to break-up with the increase of capillary number. In addition, the increasing of the diameter ratio is beneficial to the symmetrical break-up of the bubbles.

Construction of an Hα diagnostic system and its application to determine neutral hydrogen densities on the Keda Torus eXperiment

Junfeng Zhu, Tao Lan, Ge Zhuang, Tijian Deng, Jie Wu, Hangqi Xu, Chen Chen, Sen Zhang, Jiaren Wu, Yiming Zu, Hong Li, Jinlin Xie, Ahdi Liu, Zixi Liu, Zhengwei Wu, Hai Wang, Xiaohui Wen, Haiyang Zhou, Chijin Xiao, Weixing Ding, Wandong Liu
Chin. Phys. B 2019, 28 (10): 105201 ;  doi: 10.1088/1674-1056/ab427a
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A 10-channel Hα diagnostic system has been designed with the rapid response rate of 300 kHz, spatial resolution of about 40 mm, and overlap between adjacent channels of about 3%, and it has been implemented successfully on Keda Torus eXperiment (KTX), a newly constructed, reversed field pinch (RFP) experimental device at the University of Science and Technology of China (USTC). This diagnostic system is a very important tool for the initial KTX operations. It is compact, with an aperture slit replacing the traditional optical lens system. A flexural interference filter is designed to prevent the center wavelength from shifting too much as the increase of angle from vertical incidence. To eliminate the stray light, the interior of the system is covered with the black aluminum foil having a very high absorptivity. Using the Hα emission data, together with the profiles of electron temperature and density obtained from the Langmuir probe, the neutral density profiles have been calculated for KTX plasmas. The rapid response rate and good spatial resolution of this Hα diagnostic system will be beneficial for many studies in RFP plasma physics.

The inverse Bremsstrahlung absorption in the presence of Maxwellian and non-Maxwellian electrons

Mehdi Sharifian, Fatemeh Ghoveisi, Leila Gholamzadeh, Narges Firouzi Farrashbandi
Chin. Phys. B 2019, 28 (10): 105202 ;  doi: 10.1088/1674-1056/ab4173
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Inverse Bremsstrahlung absorption (IBA) of an intense laser field in plasma containing Maxwellian and non-Maxwellian (with Kappa and q-nonextensive distribution functions) electrons is studied analytically. Our results show that IBA decreases with an increase in temperature at high intensities and a decrease in plasma density for all kinds of distribution functions. Another striking result is that IBA is independent of the laser intensity at low intensity but is dependent on it when the intensity is going to rise. Also, it could be find that the behavior of the absorption as the function of laser intensity for the Kappa distribution with κ=10 at low intensity is close to that for the Maxwellian distribution, but at high intensity it is close to that in the presence of q-nonextensive electrons with q=0.9. These results provide insights into the inverse Bremsstrahlung absorption in the laser-plasma interactions.

Defects and electrical properties in Al-implanted 4H-SiC after activation annealing

Yi-Dan Tang, Xin-Yu Liu, Zheng-Dong Zhou, Yun Bai, Cheng-Zhan Li
Chin. Phys. B 2019, 28 (10): 106101 ;  doi: 10.1088/1674-1056/ab3cc2
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The defects and electrical properties in Al-implanted 4H-SiC after activation annealing (1600 ℃-1800 ℃) are investigated. High temperature annealing can reduce the ion implantation-induced damage effectively, but it may induce extended defects as well, which are investigated by using Rutherford backscattering spectroscopy (RBS/C), secondary ion mass spectroscopy (SIMS), and transmission electron microscopy (TEM) analyses. According to the ratio of the channeled intensity to the random intensity in the region just below the surface scattering peak (Xmin) and RBS/C analysis results, the ion implantation-induced surface damages can be effectively reduced by annealing at temperatures higher than 1700 ℃, while the defects near the bottom of the ion-implanted layer cannot be completely annealed out by high temperature and long time annealing process, which is also demonstrated by SIMS and TEM analyses. Referring to the defect model and TEM analyses, an optimized annealing condition can be achieved through balancing the generation and elimination of carbon vacancies in the ion implanted layers. Furthermore, the electrical and surface properties are also analyzed, and the hole concentration, mobility, and resistivity are obtained through the Hall effect. The optimized activation annealing conditions of 1800 ℃/5 min are achieved, under which the lower defects and acceptable electrical properties are obtained.

First principles study of interactions of oxygen-carbon-vacancy in bcc Fe

Yuan You, Mu-Fu Yan, Ji-Hong Yan, Gang Sun, Chao Wang
Chin. Phys. B 2019, 28 (10): 106102 ;  doi: 10.1088/1674-1056/ab3a8f
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Behaviors of C or O in bcc Fe and interactions of C-O and oxygen-carbon-vacancy (O-C-□) are investigated by first principles calculations. Octahedral interstitial site is the most stable position for an O atom in bcc Fe. The migration energy of an O atom in bcc Fe is 0.46 eV. The strength of O-Fe (1nn) bond (0.32) is slightly greater than that of Fe-Fe metallic bond (0.26). Repulsive interactions of C-C, O-O, and C-O exist in bcc Fe. When the concentration of FIA (FIA refers to C or O) is relatively high, a vacancy can attract four FIAs and form stable FIAs-□ complex.

Physical properties of ternary thallium chalcogenes Tl2MQ3 (M=Zr, Hf; Q=S, Se, Te) via ab-initio calculations

Engin Ateser, Oguzhan Okvuran, Yasemin Oztekin Ciftci, Haci Ozisik, Engin Deligoz
Chin. Phys. B 2019, 28 (10): 106301 ;  doi: 10.1088/1674-1056/ab427d
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We have reported a first principles study of structural, mechanical, electronic, and thermoelectric properties of the monoclinic ternary thallium chalcogenes Tl2MQ3 (M=Zr, Hf; Q=S, Se, Te). The electronic band structure calculations confirm that all compounds exhibit semiconductor character. Especially, Tl2ZrTe3 and Tl2HfTe3 can be good candidates for thermoelectric materials, having narrow band gaps of 0.169 eV and 0.21 eV, respectively. All of the compounds are soft and brittle according to the second-order elastic constant calculations. Low Debye temperatures also support the softness. We have obtained the transport properties of the compounds by using rigid band and constant relaxation time approximations in the context of Boltzmann transport theory. The results show that the compounds could be considered for room temperature thermoelectric applications (ZT~0.9).

Phosphine-free synthesis of FeTe2 nanoparticles and self-assembly into tree-like nanoarchitectures

Hongyu Wang, Min Wu, Yixuan Wang, Hao Wang, Xiaoli Huang, Xinyi Yang
Chin. Phys. B 2019, 28 (10): 106401 ;  doi: 10.1088/1674-1056/ab3b51
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Manipulating the self-assembly of transition metal telluride nanocrystals (NCs) creates opportunities for exploring new properties and device applications. Iron ditelluride (FeTe2) has recently emerged as a new class of magnetic semiconductor with three-dimensional (3D) magnetic ordering and narrow band gap structure, yet the self-assembly of FeTe2 NCs has not been achieved. Herein, the tree-like FeTe2 nanoarchitectures with orthorhombic crystal structure have been successfully synthesized by hot-injection solvent thermal approach using phosphine-free Te precursor. The morphology, size, and crystal structure have been investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and powder x-ray diffraction (XRD). We study the formation process of tree-like FeTe2 NCs according to trace the change of the sample morphology with the reaction time. It was found that the FeTe2 nanoparticles show oriented aggregation and self-assembly behavior with the increase of reaction time, which is attributed to size-dependent magnetism properties of the samples. The magnetic interaction is thought to be the driving force of nanoparticle self-organization.

Expansion dynamics of a spherical Bose-Einstein condensate

Rui-Zong Li, Tian-You Gao, Dong-Fang Zhang, Shi-Guo Peng, Ling-Ran Kong, Xing Shen, Kai-Jun Jiang
Chin. Phys. B 2019, 28 (10): 106701 ;  doi: 10.1088/1674-1056/ab4177
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We experimentally and theoretically observe the expansion behaviors of a spherical Bose-Einstein condensate. A rubidium condensate is produced in an isotropic optical dipole trap with an asphericity of 0.037. We measure the variation of the condensate size in the expansion process after switching off the trap. The free expansion of the condensate is isotropic, which is different from that of the condensate usually produced in the anisotropic trap. We derive an analytic solution of the expansion behavior based on the spherical symmetry, allowing a quantitative comparison with the experimental measurement. The interaction energy of the condensate is gradually converted into the kinetic energy during the expansion and after a long time the kinetic energy saturates at a constant value. We obtain the interaction energy of the condensate in the trap by probing the long-time expansion velocity, which agrees with the theoretical calculation. This work paves a way to explore novel quantum states of ultracold gases with the spherical symmetry.

Highly reliable and selective ethanol sensor based on α-Fe2O3 nanorhombs working in realistic environments

Wenjun Yan, Xiaomin Zeng, Huan Liu, Chunwei Guo, Min Ling, Houpan Zhou
Chin. Phys. B 2019, 28 (10): 106801 ;  doi: 10.1088/1674-1056/ab3af1
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A highly reliable and selective ethanol gas sensor working in realistic environments based on alpha-Fe2O3 (α-Fe2O3) nanorhombs is developed. The sensor is fabricated by integrating α-Fe2O3 nanorhombs onto a low power microheater based on micro-electro-mechanical systems (MEMS) technology. The α-Fe2O3 nanorhombs, prepared via a solvothermal method, is characterized by transmission electron microscopy (TEM), Raman spectroscopy, x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The sensing performances of the α-Fe2O3 sensor to various toxic gases are investigated. The optimum sensing temperature is found to be about 280 ℃. The sensor shows excellent selectivity to ethanol. For various ethanol concentrations (1 ppm-20 ppm), the response and recovery times are around 3 s and 15 s at the working temperature of 280 ℃, respectively. Specifically, the α-Fe2O3 sensor exhibits a response shift less than 6% to ethanol at 280 ℃ when the relative humidity (RH) increases from 30% to 70%. The good tolerance to humidity variation makes the sensor suitable for reliable applications in Internet of Things (IoT) in realistic environments. In addition, the sensor shows great long-term repeatability and stability towards ethanol. A possible gas sensing mechanism is proposed.


Electronic properties of size-dependent MoTe2/WTe2 heterostructure

Jing Liu, Ya-Qiang Ma, Ya-Wei Dai, Yang Chen, Yi Li, Ya-Nan Tang, Xian-Qi Dai
Chin. Phys. B 2019, 28 (10): 107101 ;  doi: 10.1088/1674-1056/ab3b53
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Lateral two-dimensional (2D) heterostructures have opened up unprecedented opportunities in modern electronic device and material science. In this work, electronic properties of size-dependent MoTe2/WTe2 lateral heterostructures (LHSs) are investigated through the first-principles density functional calculations. The constructed periodic multi-interfaces patterns can also be defined as superlattice structures. Consequently, the direct band gap character remains in all considered LHSs without any external modulation, while the gap size changes within little difference range with the building blocks increasing due to the perfect lattice matching. The location of the conduction band minimum (CBM) and the valence band maximum (VBM) will change from P-point to Γ-point when m plus n is a multiple of 3 for A-mn LHSs as a result of Brillouin zone folding. The bandgap located at high symmetry Γ-point is favourable to electron transition, which might be useful to optoelectronic device and could be achieved by band engineering. Type-Ⅱ band alignment occurs in the MoTe2/WTe2 LHSs, for electrons and holes are separated on the opposite domains, which would reduce the recombination rate of the charge carriers and facilitate the quantum efficiency. Moreover, external biaxial strain leads to efficient bandgap engineering. MoTe2/WTe2 LHSs could serve as potential candidate materials for next-generation electronic devices.

Hubbard model on an anisotropic checkerboard lattice at finite temperatures: Magnetic and metal-insulator transitions

Hai-Di Liu
Chin. Phys. B 2019, 28 (10): 107102 ;  doi: 10.1088/1674-1056/ab4279
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We study magnetic and Mott transitions of the Hubbard model on the geometrically frustrated anisotropic checkerboard lattice at half filling using cellular dynamical mean-field theory. Phase diagrams over a wide area of the parameter space are obtained by varying the interparticle interaction strength, geometric frustration strength, and temperature. Our results show that frustration and thermal fluctuations play a competing role against the interactions and in general favor a metallic phase without antiferromagnetic order. Due to their interplay, the system exhibits competition between antiferromagnetic insulator, antiferromagnetic metal, paramagnetic insulator, and paramagnetic metal phases in the intermediate-interaction regime. In the strong-interaction limit, which reduces to the Heisenberg model, our result is consistent with previous studies.

Negative transconductance effect in p-GaN gate AlGaN/GaN HEMTs by traps in unintentionally doped GaN buffer layer

Mei Ge, Qing Cai, Bao-Hua Zhang, Dun-Jun Chen, Li-Qun Hu, Jun-Jun Xue, Hai Lu, Rong Zhang, You-Dou Zheng
Chin. Phys. B 2019, 28 (10): 107301 ;  doi: 10.1088/1674-1056/ab3e00
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We investigate the negative transconductance effect in p-GaN gate AlGaN/GaN high-electron-mobility transistor (HEMT) associated with traps in the unintentionally doped GaN buffer layer. We find that a negative transconductance effect occurs with increasing the trap concentration and capture cross section when calculating transfer characteristics. The electron tunneling through AlGaN barrier and the reduced electric field discrepancy between drain side and gate side induced by traps are reasonably explained by analyzing the band diagrams, output characteristics, and the electric field strength of the channel of the devices under different trap concentrations and capture cross sections.

Optical response of an inverted InAs/GaSb quantum well in an in-plane magnetic field

Xiaoguang Wu
Chin. Phys. B 2019, 28 (10): 107302 ;  doi: 10.1088/1674-1056/ab3c29
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The optical response of an inverted InAs/GaSb quantum well is studied theoretically. The influence of an in-plane magnetic field that is applied parallel to the quantum well is considered. This in-plane magnetic field will induce a dynamical polarization even when the electric field component of the external optical field is parallel to the quantum well. The electron-electron interaction in the quantum well system will lead to the de-polarization effect. This effect is found to be important and is taken into account in the calculation of the optical response. It is found that the main feature in the frequency dependence of the velocity-velocity correlation function remains when the velocity considered is parallel to the in-plane magnetic field. When the direction of the velocity is perpendicular to the in-plane magnetic field, the de-polarization effect will suppress the oscillatory behavior in the corresponding velocity-velocity correlation function. The in-plane magnetic field can change the band structure of the quantum well drastically from a gapped semiconductor to a no-gapped semi-metal, but it is found that the distribution of the velocity matrix elements or the optical transition matrix elements in the wave vector space has the same two-tadpole topology.

Observation of hopping transitions for delocalized electrons by temperature-dependent conductance in siliconjunctionless nanowire transistors

Yang-Yan Guo, Wei-Hua Han, Xiao-Song Zhao, Ya-Mei Dou, Xiao-Di Zhang, Xin-Yu Wu, Fu-Hua Yang
Chin. Phys. B 2019, 28 (10): 107303 ;  doi: 10.1088/1674-1056/ab3e68
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We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics. There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data, which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance gm peak in Vg1 and valley in Vg2. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages Vg1 and Vg2. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.

Enhanced spin-dependent thermopower in a double-quantum-dot sandwiched between two-dimensional electron gases

Feng Chi, Zhen-Guo Fu, Liming Liu, Ping Zhang
Chin. Phys. B 2019, 28 (10): 107305 ;  doi: 10.1088/1674-1056/ab3f98
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We study the spin-dependent thermopower in a double-quantum-dot (DQD) embedded between the left and right two-dimensional electron gases (2DEGs) in doped quantum wells under an in-plane magnetic field. When the separation between the DQD is smaller than the Fermi wavelength in the 2DEGs, the asymmetry in the dots' energy levels leads to pronounced quantum interference effects characterized by the Dicke line-shape of the conductance, which are sensitive to the properties of the 2DEGs. The magnitude of the thermopower, which denotes the generated voltage in response to an infinitesimal temperature difference between the two 2DEGs under vanishing charge current, will be obviously enhanced by the Dicke effect. The application of the in-plane magnetic field results in the polarization of the spin-up and spin-down conductances and thermopowers, and enables an efficient spin-filter device in addition to a tunable pure spin thermopower in the absence of its charge counterpart.

Magnetic vortex gyration mediated by point-contact position

Hua-Nan Li, Zi-Wei Fan, Jia-Xin Li, Yue Hu, Hui-Lian Liu
Chin. Phys. B 2019, 28 (10): 107503 ;  doi: 10.1088/1674-1056/ab4277
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Micromagnetic simulation is employed to study the gyration motion of magnetic vortices in distinct permalloy nanodisks driven by a spin-polarized current. The critical current density for magnetic vortex gyration, eigenfrequency, trajectory, velocity and the time for a magnetic vortex to obtain the steady gyration are analyzed. Simulation results reveal that the magnetic vortices in larger and thinner nanodisks can achieve a lower-frequency gyration at a lower current density in a shorter time. However, the magnetic vortices in thicker nanodisks need a higher current density and longer time to attain steady gyration but with a higher eigenfrequency. We also find that the point-contact position exerts different influences on these parameters in different nanodisks, which contributes to the control of the magnetic vortex gyration. The conclusions of this paper can serve as a theoretical basis for designing nano-oscillators and microwave frequency modulators.

Cascaded plasmonic nanorod antenna for large broadband local electric field enhancement

Dou Zhang, Zhong-Jian Yang, Jun He
Chin. Phys. B 2019, 28 (10): 107802 ;  doi: 10.1088/1674-1056/ab3f99
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We propose a cascaded plasmonic nanorod antenna for large broadband electric near-field enhancement. The structure has one big gold nanorod on each side of a small two-wire antenna which consists of two small gold nanorods. For each small nanorod, the enhanced and broadened optical response can be obtained due to the efficient energy transfer from its adjacent big nanorod through strong plasmonic near-field coupling. Thus, the electric field intensity of the cascaded antenna is significantly larger and broader than that of the individual small two-wire antenna. The resonant position, field intensity enhancement, and spectral width of the cascaded antenna are highly tunable by varying the geometry of the system. The quantum efficiency of the cascaded antenna is also greatly enhanced compared with that of the small antenna. Our results are important for the applications in field-enhanced spectroscopy.

Photoluminescence properties of blue and green multiple InGaN/GaN quantum wells

Chang-Fu Li, Kai-Ju Shi, Ming-Sheng Xu, Xian-Gang Xu, Zi-Wu Ji
Chin. Phys. B 2019, 28 (10): 107803 ;  doi: 10.1088/1674-1056/ab4046
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The photoluminescence (PL) properties of blue multiple InGaN/GaN quantum well (BMQW) and green multiple InGaN/GaN quantum well (GMQW) formed on a single sapphire substrate are investigated. The results indicate that the peak energy of GMQW-related emission (PG) exhibits more significant “S-shaped” dependence on temperature than that of BMQW-related emission (PB), and the excitation power-dependent carrier-scattering effect is observed only in the PG emission; the excitation power-dependent total blue-shift (narrowing) of peak position (line-width) for the PG emission is more significant than that for the PB emission; the GMQW shows a lower internal quantum efficiency than the BMQW. All of these results can be attributed to the fact that the GMQW has higher indium content than the BMQW due to its lower growth temperature and late growth, and the higher indium content in the GMQW induces a more significant compositional fluctuation, a stronger quantum confined Stark effect, and more non-radiative centers.

Effect of AlN coating on hydrogen permeability and surface structure of VT6 alloy by vacuum arc ion plating

Zi-Yi Ding
Chin. Phys. B 2019, 28 (10): 108101 ;  doi: 10.1088/1674-1056/ab3a8e
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We study the absorption of hydrogen of metal by the permeability method. With the help of the gas reaction controller (GRC), the absorptive capacity of hydrogen, which is a function of time, temperature and pressure, can be recorded. The effect of the performance of the hydrogen permeability of AlN coating on the titanium alloy surface structure is studied. In the research, the AlN is selected to be added to the titanium alloy sample VT6, and the properties of the titanium alloy are investigated, and the hydrogen absorption rate of the coating is calculated by performing the hydrogen saturation of the test sample. The results show that under 600 ℃ the AlN film reduces the hydrogen absorption rate of titanium alloy and improves the surface properties of VT6 alloy.

Effect of sintering temperature on luminescence properties of borosilicate matrix blue-green emitting color conversion glass ceramics

Qiao-Yu Zheng, Yang Li, Wen-Juan Wu, Ming-Ming Shi, Bo-Bo Yang, Jun Zou
Chin. Phys. B 2019, 28 (10): 108102 ;  doi: 10.1088/1674-1056/ab3f97
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The color conversion glass ceramics which were made of borosilicate matrix co-doped (SrBaSm)Si2O2N2:(Eu3+Ce3+) blue-green phosphors were prepared by two-step method in co-sintering. The change in luminescence properties and the drift of chromaticity coordinates (CIE) of the (SrBaSm)Si2O2N2:(Eu3+Ce3+) blue-green phosphors and the color conversion glass ceramics were studied in the sintering temperature range from 600 ℃ to 800 ℃. The luminous intensity and internal quantum yield (QY) of the blue-green phosphors and glass ceramics decreased with the sintering temperature increasing. When the sintering temperature increased beyond 750 ℃, the phosphors and the color conversion glass ceramics almost had no peak in photoluminescence (PL) and excitation (PLE) spectra. The results showed that the blue-green phosphors had poor thermal stability at higher temperature. The lattice structure of the phosphors was destroyed by the glass matrix and the Ce3+ in the phosphors was oxidized to Ce4+, which further caused a decrease in luminescent properties of the color conversion glass ceramics.

Flexible rGO/Fe3O4 NPs/polyurethane film with excellent electromagnetic properties

Wei-Qi Yu, Yi-Chen Qiu, Hong-Jun Xiao, Hai-Tao Yang, Ge-Ming Wang
Chin. Phys. B 2019, 28 (10): 108103 ;  doi: 10.1088/1674-1056/ab4041
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Large-area and flexible reduced graphene oxide (rGO)/Fe3O4 NPs/polyurethane (PU) composite films are fabricated by a facile solution-processable method. The monolayer assembly of Fe3O4 nanoparticles with a high particle-stacking density on the graphene oxide (GO) sheets is achieved by mixing two immiscible solutions of Fe3O4 nanoparticles in hexane and GO in dimethylformide (DMF) by a mild sonication. The x-ray diffraction and Raman spectrum confirm the reduced process of rGO by a simple thermal treatment. The permittivity value of the composite in a frequency range of 0.1 GHz-18 GHz increases with annealing temperature of GO increasing. For 5-wt% rGO/Fe3O4 NPs/PU, the maximum refection loss (RL) of over -35 dB appears at 4.5 GHz when the thickness of film increases to 5 mm. The rGO/Fe3O4 NPs/PU film, exhibiting good electromagnetic properties over GHz frequency range, could be a potential candidate as one of microwave absorption materials in flexible electronic devices.

Parameter identification and state-of-charge estimation approach for enhanced lithium-ion battery equivalent circuit model considering influence of ambient temperatures

Hui Pang, Lian-Jing Mou, Long Guo
Chin. Phys. B 2019, 28 (10): 108201 ;  doi: 10.1088/1674-1056/ab3af5
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It is widely accepted that the variation of ambient temperature has great influence on the battery model parameters and state-of-charge (SOC) estimation, and the accurate SOC estimation is a significant issue for developing the battery management system in electric vehicles. To address this problem, in this paper we propose an enhanced equivalent circuit model (ECM) considering the influence of different ambient temperatures on the open-circuit voltage for a lithium-ion battery. Based on this model, the exponential-function fitting method is adopted to identify the battery parameters according to the test data collected from the experimental platform. And then, the extended Kalman filter (EKF) algorithm is employed to estimate the battery SOC of this battery ECM. The performance of the proposed ECM is verified by using the test profiles of hybrid pulse power characterization (HPPC) and the standard US06 driving cycles (US06) at various ambient temperatures, and by comparing with the common ECM with a second-order resistance capacitor. The simulation and experimental results show that the enhanced battery ECM can improve the battery SOC estimation accuracy under different operating conditions.

Analysis of non-uniform hetero-gate-dielectric dual-material control gate TFET for suppressing ambipolar nature and improving radio-frequency performance

Hui-Fang Xu, Jian Cui, Wen Sun, Xin-Feng Han
Chin. Phys. B 2019, 28 (10): 108501 ;  doi: 10.1088/1674-1056/ab3a8b
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A tunnel field-effect transistor (TFET) is proposed by combining various advantages together, such as non-uniform gate-oxide layer, hetero-gate-dielectric (HGD), and dual-material control-gate (DMCG) technology. The effects of the length of non-uniform gate-oxide layer and dual-material control-gate on the on-state, off-state, and ambipolar currents are investigated. In addition, radio-frequency performance is studied in terms of gain bandwidth product, cut-off frequency, transit time, and transconductance frequency product. Moreover, the length of non-uniform gate-oxide layer and dual-material control-gate are optimized to improve the on-off current ratio and radio-frequency performances as well as the suppression of ambipolar current. All results demonstrate that the proposed device not only suppresses ambipolar current but also improves radio-frequency performance compared with the conventional DMCG TFET, which makes the proposed device a better application prospect in the advanced integrated circuits.

Opto-electromechanically induced transparency in a hybrid opto-electromechanical system

Hui Liu, Li-Guo Qin, Li-Jun Tian, Hong-Yang Ma
Chin. Phys. B 2019, 28 (10): 108502 ;  doi: 10.1088/1674-1056/ab3af2
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We study opto-electromechanically induced transparency in a hybrid opto-electromechanical system made up of an optical cavity tunneling-coupled to an opto-mechanical cavity, which is capacitively coupled to a charged mechanical oscillator by a charged and moveable mechanical cavity mirror as an interface. By studying the effects of the different parameters on the output field, we propose a scheme to modulate the opto-electromechanically induced transparency (OEMIT). Our results show that the OEMIT with the transparency windows from single to double to triple can be modulated by changing the tunneling, opto-mechanical and electrical couplings. In addition, the explanation of the OEMIT with multi-windows is given by the energy level diagram based on quantum interference. Our investigation will provide an optimal platform to manipulate the transmission of optical field via microfabricated opto-electromechanical device.

Designing of spin filter devices based on zigzag zinc oxide nanoribbon modified by edge defect

Bao-Rui Huang, Fu-Chun Zhang, Yan-Ning Yang, Zhi-Yong Zhang, Wei-Guo Wang
Chin. Phys. B 2019, 28 (10): 108503 ;  doi: 10.1088/1674-1056/ab3b50
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The spin-dependent electronic transport properties of a zigzag zinc oxide (ZnO) nanoribbon are studied by using density functional theory with non-equilibrium Green's functions. We calculate the spin-polarized band structure, projected density of states, Bloch states, and transmission spectrum of the ZnO nanoribbon. It is determined that all Bloch states are located at the edge of the ZnO nanoribbon. The spin-up transmission eigenchannels are contributed from Zn 4s orbital, whereas the spin-down transmission eigenchannels are contributed from Zn 4s and O 2p orbitals. By analyzing the current-voltage curves for the opposite spins of the ZnO nanoribbon device, negative differential resistance (NDR) and spin filter effect are observed. Moreover, by constructing the ZnO nanoribbon modified by the Zn-edge defect, the spin-up current is severely suppressed because of the destruction of the spin-up transmission eigenchannels. However, the spin-down current is preserved, thus resulting in the perfect spin filter effect. Our results indicate that the ZnO nanoribbon modulated by the edge defect is a practical design for a spin filter.

Quantitative heterogeneity and subgroup classification based on motility of breast cancer cells

Ling Xiong, Yanping Liu, Ruchuan Liu, Wei Yuan, Gao Wang, Yi He, Jianwei Shuai, Yang Jiao, Xixiang Zhang, Weijing Han, Junle Qu, Liyu Liu
Chin. Phys. B 2019, 28 (10): 108701 ;  doi: 10.1088/1674-1056/ab3af4
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Cancer cell motility and its heterogeneity play an important role in metastasis, which is responsible for death of 90% of cancer patients. Here, in combination with a microfluidic technique, single-cell tracking, and systematic motility analysis, we present a rapid and quantitative approach to judge the motility heterogeneity of breast cancer cells MDA-MB-231 and MCF-7 in a well-defined three-dimensional (3D) microenvironment with controllable conditions. Following this approach, identification of highly mobile active cells in a medium with epithelial growth factor will provide a practical tool for cell invasion and metastasis investigation of multiple cancer cell types, including primary cells. Further, this approach could potentially become a speedy (~hours) and efficient tool for basic and clinical diagnosis.

Theory and method of dual-energy x-ray grating phase-contrast imaging

Feng Rong, Yan Gao, Cui-Juan Guo, Wei Xu, Wei Xu
Chin. Phys. B 2019, 28 (10): 108702 ;  doi: 10.1088/1674-1056/ab3f1d
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The principle of dual-energy x-ray grating phase-contrast imaging (DEPCI) is clarified by using the theory of x-ray interference and Fresnel diffraction. A new method of retrieving phase from the two interferograms is proposed for DEPCI, and its feasibility is verified via simulation. Finally, the proposed method applied to DEPCI experiment demonstrates the effectiveness of the method. This paper lays the theoretical foundation for performance optimization of DEPCI and the further integration of DEPCI and computed tomography.

Benefit community promotes evolution of cooperation in prisoners' dilemma game

Jianwei Wang, Jialu He, Fengyuan Yu, Wei Chen, Rong Wang, Ke Yu
Chin. Phys. B 2019, 28 (10): 108703 ;  doi: 10.1088/1674-1056/ab3f1e
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Exploring the emergence and maintenance of cooperation in social dilemma is valuable and it arises considerable concerns of many researchers. In this paper, we propose a mechanism to promote cooperation, called benefit community, in which cooperators linking together form a common benefit community and all their payoffs obtained from game are divided coequally. The robustness of conclusions is tested for the PDG (prisoners' dilemma game) on square lattice and WS small world network. We find that cooperation can be promoted by this typical mechanism, especially, it can diffuse and prevail more easily and rapidly on the WS small world network than it on the square lattice, even if a big temptation to defect b. Our research provides a feasible direction to resolve the social dilemma.

Theoretical analyses of stock correlations affected by subprime crisis and total assets: Network properties and corresponding physical mechanisms

Shi-Zhao Zhu, Yu-Qing Wang, Bing-Hong Wang
Chin. Phys. B 2019, 28 (10): 108901 ;  doi: 10.1088/1674-1056/ab3f22
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In the field of statistical mechanics and system science, it is acknowledged that the financial crisis has a profound influence on stock market. However, the influence of total asset of enterprise on stock quote was not considered in the previous studies. In this work, a modified cross-correlation matrix that focuses on the influence of total asset on stock quote is introduced into the analysis of the stocks collected from Asian and American stock markets, which is different from the previous studies. The key results are obtained as follows. Firstly, stock is more greatly correlated with big asset than with small asset. Secondly, the higher the correlation coefficient among stocks, the larger the eigenvector is. Thirdly, in different periods, like the pre-subprime crisis period and the peak of subprime crisis period, Asian stock quotes show that the component of the third eigenvector of the cross-correlation matrix decreases with the asset of the enterprise decreasing. Fourthly, by simulating the threshold network, the small network constructed by 10 stocks with large assets can show the large network state constructed by 30 stocks. In this research we intend to fully explain the physical mechanism for understanding the historical correlation between stocks and provide risk control strategies in the future.
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