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Chin. Phys. B  
  Chin. Phys. B--2017, Vol.26, No.9
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Improved control for distributed parameter systems with time-dependent spatial domains utilizing mobile sensor—actuator networks

Jian-Zhong Zhang, Bao-Tong Cui, Bo Zhuang
Chin. Phys. B 2017, 26 (9): 090201;  doi: 10.1088/1674-1056/26/9/090201
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A guidance policy for controller performance enhancement utilizing mobile sensor-actuator networks (MSANs) is proposed for a class of distributed parameter systems (DPSs), which are governed by diffusion partial differential equations (PDEs) with time-dependent spatial domains. Several sufficient conditions for controller performance enhancement are presented. First, the infinite dimensional operator theory is used to derive an abstract evolution equation of the systems under some rational assumptions on the operators, and a static output feedback controller is designed to control the spatial process. Then, based on Lyapunov stability arguments, guidance policies for collocated and non-collocated MSANs are provided to enhance the performance of the proposed controller, which show that the time-dependent characteristic of the spatial domains can significantly affect the design of the mobile scheme. Finally, a simulation example illustrates the effectiveness of the proposed policy.

Geometry and thermodynamics of smeared Reissner-Nordström black holes in d-dimensional AdS spacetime

Bo-Bing Ye, Ju-Hua Chen, Yong-Jiu Wang
Chin. Phys. B 2017, 26 (9): 090202;  doi: 10.1088/1674-1056/26/9/090202
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We construct a family of d-dimensional Reissner-Nordström-AdS black holes inspired by noncommutative geometry. The density distribution of the gravitational source is determined by the dimension of space, the minimum length of spacetime l, and other parameters (e.g., n relating to the central matter density). The curvature of the center and some thermodynamic properties of these black holes are investigated. We find that the center of the source is nonsingular for n≥ 0 (under certain conditions it is also nonsingular for -2 ≤ n < 0), and the properties at the event horizon, including the Hawking temperature, entropy, and heat capacity, are regular for n >-2. Due to the presence of l, there is an exponentially small correction to the usual entropy.

Stochastic responses of tumor—immune system with periodic treatment

Dong-Xi Li, Ying Li
Chin. Phys. B 2017, 26 (9): 090203;  doi: 10.1088/1674-1056/26/9/090203
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We investigate the stochastic responses of a tumor-immune system competition model with environmental noise and periodic treatment. Firstly, a mathematical model describing the interaction between tumor cells and immune system under external fluctuations and periodic treatment is established based on the stochastic differential equation. Then, sufficient conditions for extinction and persistence of the tumor cells are derived by constructing Lyapunov functions and Ito's formula. Finally, numerical simulations are introduced to illustrate and verify the results. The results of this work provide the theoretical basis for designing more effective and precise therapeutic strategies to eliminate cancer cells, especially for combining the immunotherapy and the traditional tools.

Invariants-based shortcuts for fast generating Greenberger—Horne—Zeilinger state among three superconducting qubits

Jing Xu, Lin Yu, Jin-Lei Wu, Xin Ji
Chin. Phys. B 2017, 26 (9): 090301;  doi: 10.1088/1674-1056/26/9/090301
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As one of the most promising candidates for implementing quantum computers, superconducting qubits (SQs) are adopted for fast generating the Greenberger-Horne-Zeilinger (GHZ) state by using invariants-based shortcuts. Three SQs are separated and connected by two coplanar waveguide resonators (CPWRs) capacitively. The complicated system is skillfully simplified to a three-state system, and a GHZ state among three SQs is fast generated with a very high fidelity and simple driving pulses. Numerical simulations indicate the scheme is insensitive to parameter deviations. Besides, the robustness of the scheme against decoherence is discussed in detail.

Cancelable remote quantum fingerprint templates protection scheme

Qin Liao, Ying Guo, Duan Huang
Chin. Phys. B 2017, 26 (9): 090302;  doi: 10.1088/1674-1056/26/9/090302
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With the increasing popularity of fingerprint identification technology, its security and privacy have been paid much attention. Only the security and privacy of biological information are insured, the biological technology can be better accepted and used by the public. In this paper, we propose a novel quantum bit (qbit)-based scheme to solve the security and privacy problem existing in the traditional fingerprint identification system. By exploiting the properties of quantum mechanics, our proposed scheme, cancelable remote quantum fingerprint templates protection scheme, can achieve the unconditional security guaranteed in an information-theoretical sense. Moreover, this novel quantum scheme can invalidate most of the attacks aimed at the fingerprint identification system. In addition, the proposed scheme is applicable to the requirement of remote communication with no need to worry about its security and privacy during the transmission. This is an absolute advantage when comparing with other traditional methods. Security analysis shows that the proposed scheme can effectively ensure the communication security and the privacy of users' information for the fingerprint identification.

A high-fidelity memory scheme for quantum data buses

Bo-Yang Liu, Wei Cui, Hong-Yi Dai, Xi Chen, Ming Zhang
Chin. Phys. B 2017, 26 (9): 090303;  doi: 10.1088/1674-1056/26/9/090303
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A novel quantum memory scheme is proposed for quantum data buses in scalable quantum computers by using adjustable interaction. Our investigation focuses on a hybrid quantum system including coupled flux qubits and a nitrogen-vacancy center ensemble. In our scheme, the transmission and storage (retrieval) of quantum state are performed in two separated steps, which can be controlled by adjusting the coupling strength between the computing unit and the quantum memory. The scheme can be used not only to reduce the time of quantum state transmission, but also to increase the robustness of the system with respect to detuning caused by magnetic noises. In comparison with the previous memory scheme, about 80% of the transmission time is saved. Moreover, it is exemplified that in our scheme the fidelity could achieve 0.99 even when there exists detuning, while the one in the previous scheme is 0.75.

Determination of the thermal noise limit in test of weak equivalence principle with a rotating torsion pendulum

Wen-Ze Zhan, Jie Luo, Cheng-Gang Shao, Di Zheng, Wei-Ming Yin, Dian-Hong Wang
Chin. Phys. B 2017, 26 (9): 090401;  doi: 10.1088/1674-1056/26/9/090401
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Thermal noise is one of the most fundamental limits to the sensitivity in weak equivalence principle test with a rotating torsion pendulum. Velocity damping and internal damping are two of many contributions at the thermal noise, and which one mainly limits the torsion pendulum in low frequency is difficult to be verified by experiment. Based on the conventional method of fast Fourier transform, we propose a developed method to determine the thermal noise limit and then obtain the precise power spectrum density of the pendulum motion signal. The experiment result verifies that the thermal noise is mainly contributed by the internal damping in the fiber in the low frequency torsion pendulum experiment with a high vacuum. Quantitative data analysis shows that the basic noise level in the experiment is about one to two times of the theoretical value of internal damping thermal noise.

Stochastic bifurcations of generalized Duffing-van der Pol system with fractional derivative under colored noise

Wei Li, Mei-Ting Zhang, Jun-Feng Zhao
Chin. Phys. B 2017, 26 (9): 090501;  doi: 10.1088/1674-1056/26/9/090501
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The stochastic bifurcation of a generalized Duffing-van der Pol system with fractional derivative under color noise excitation is studied. Firstly, fractional derivative in a form of generalized integral with time-delay is approximated by a set of periodic functions. Based on this work, the stochastic averaging method is applied to obtain the FPK equation and the stationary probability density of the amplitude. After that, the critical parameter conditions of stochastic P-bifurcation are obtained based on the singularity theory. Different types of stationary probability densities of the amplitude are also obtained. The study finds that the change of noise intensity, fractional order, and correlation time will lead to the stochastic bifurcation.

A generalized model of TiOx-based memristive devices andits application for image processing

Jiangwei Zhang, Zhensen Tang, Nuo Xu, Yao Wang, Honghui Sun, Zhiyuan Wang, Liang Fang
Chin. Phys. B 2017, 26 (9): 090502;  doi: 10.1088/1674-1056/26/9/090502
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Memristive technology has been widely explored, due to its distinctive properties, such as nonvolatility, high density, versatility, and CMOS compatibility. For memristive devices, a general compact model is highly favorable for the realization of its circuits and applications. In this paper, we propose a novel memristive model of TiOx-based devices, which considers the negative differential resistance (NDR) behavior. This model is physics-oriented and passes Linn's criteria. It not only exhibits sufficient accuracy (IV characteristics within 1.5% RMS), lower latency (below half the VTEAM model), and preferable generality compared to previous models, but also yields more precise predictions of long-term potentiation/depression (LTP/LTD). Finally, novel methods based on memristive models are proposed for gray sketching and edge detection applications. These methods avoid complex nonlinear functions required by their original counterparts. When the proposed model is utilized in these methods, they achieve increased contrast ratio and accuracy (for gray sketching and edge detection, respectively) compared to the Simmons model. Our results suggest a memristor-based network is a promising candidate to tackle the existing inefficiencies in traditional image processing methods.

Recursion-transform method and potential formulae of the m×n cobweb and fan networks

Zhi-Zhong Tan
Chin. Phys. B 2017, 26 (9): 090503;  doi: 10.1088/1674-1056/26/9/090503
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In this paper, we made a new breakthrough, which proposes a new Recursion-Transform (RT) method with potential parameters to evaluate the nodal potential in arbitrary resistor networks. For the first time, we found the exact potential formulae of arbitrary m×n cobweb and fan networks by the RT method, and the potential formulae of infinite and semi-infinite networks are derived. As applications, a series of interesting corollaries of potential formulae are given by using the general formula, the equivalent resistance formula is deduced by using the potential formula, and we find a new trigonometric identity by comparing two equivalence results with different forms.

ADC border effect and suppression of quantization error in the digital dynamic measurement

Li-Na Bai, Hai-Dong Liu, Wei Zhou, Yong Zhang, Hong-Qi Zhai, Zhen-Jian Cui, Ming-Ying Zhao, Xiao-Qian Gu, Bei-Ling Liu, Li-Bei Huang
Chin. Phys. B 2017, 26 (9): 090601;  doi: 10.1088/1674-1056/26/9/090601
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The digital measurement and processing is an important direction in the measurement and control field. The quantization error widely existing in the digital processing is always the decisive factor that restricts the development and applications of the digital technology. In this paper, we find that the stability of the digital quantization system is obviously better than the quantization resolution. The application of a border effect in the digital quantization can greatly improve the accuracy of digital processing. Its effective precision has nothing to do with the number of quantization bits, which is only related to the stability of the quantization system. The high precision measurement results obtained in the low level quantization system with high sampling rate have an important application value for the progress in the digital measurement and processing field.

Microwave coherent manipulation of cold atoms in optically induced fictitious magnetic traps on an atom chip

Feng Zhou, Xiao Li, Min Ke, Jin Wang, Ming-Sheng Zhan
Chin. Phys. B 2017, 26 (9): 090701;  doi: 10.1088/1674-1056/26/9/090701
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We propose a novel on-chip platform for controlling and manipulating cold atoms precisely and coherently. The scheme is achieved by producing optically induced fictitious magnetic traps (OFMTs) with 790 nm (for 87Rb) circularly polarized laser beams and state-dependent potentials simultaneously for two internal atomic states with microwave coplanar waveguides. We carry out numerical calculations and simulations for controlled collisional interactions between OFMTs and addressable single atoms' manipulation on our designed hybrid atom chips. The results show that our proposed platform is feasible and flexible, which has wide applications including collisional dynamics investigation, entanglement generation, and scalable quantum gates implementation.

Elastic strain response in the modified phase-field-crystal model

Wenquan Zhou, Jincheng Wang, Zhijun Wang, Yunhao Huang, Can Guo, Junjie Li, Yaolin Guo
Chin. Phys. B 2017, 26 (9): 090702;  doi: 10.1088/1674-1056/26/9/090702
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To understand and develop new nanostructure materials with specific mechanical properties, a good knowledge of the elastic strain response is mandatory. Here we investigate the linear elasticity response in the modified phase-field-crystal (MPFC) model. The results show that two different propagation modes control the elastic interaction length and time, which determine whether the density waves can propagate or not. By quantitatively calculating the strain field, we find that the strain distribution is indeed extremely uniform in case of elasticity. Further, we present a detailed theoretical analysis for the orientation dependence and temperature dependence of shear modulus. The simulation results show that the shear modulus reveals strong anisotropy and the one-mode analysis provides a good guideline for determining elastic shear constants until the system temperature falls below a certain value.

Pressure-induced phase transition of B-type Y2O3

Qian Zhang, Xiang Wu, Shan Qin
Chin. Phys. B 2017, 26 (9): 090703;  doi: 10.1088/1674-1056/26/9/090703
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The synthesized monoclinic (B-type) phase of Y2O3 has been investigated by in situ angle-dispersive x-ray diffraction in a diamond anvil cell up to 44 GPa at room temperature. A phase transition occurs from monoclinic (B-type) to hexagonal (A-type) phase at 23.5 GPa and these two phases coexist even at the highest pressure. Parameters of isothermal equation of state are V0=69.0(1) Å3, K0=159(3) GPa, K0'=4 (fixed) for the B-type phase and V0=67.8(2) Å3, K0=156(3) GPa, K0'=4 (fixed) for the A-type phase. The structural anisotropy increases with increasing pressure for both phases.

Theoretical study of spin-forbidden cooling transitions of indium hydride using ab initio methods

Yun-Guang Zhang, Hua Zhang, Ge Dou
Chin. Phys. B 2017, 26 (9): 093101;  doi: 10.1088/1674-1056/26/9/093101
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The feasibility of spin-forbidden cooling of the InH molecule is investigated based on ab initio quantum chemistry calculations. The potential energy curves for the X1Σ0++, a3Π0-, a3Π0+, a3Π1, a3Π2, A1Π1, 13Σ0-+, and 13Σ1+ states of InH are obtained based on multi-reference configuration interaction plus the Davidson corrections method. The calculated spectroscopic constants are in good agreement with the available experimental data. In addition, the influences of the active space and spin-orbit coupling effects on the potential energy curves and spectroscopic constants are also studied. For Re of a3Π0-, a3Π0+, a3Π1, and a3Π2 states, the error from large active space is small. The potential energy curve of the A1Π1 state is not smooth for small active space. The spin-orbit coupling effects have great influences on the potential well depth and equilibrium internuclear distance of the A1Π state. The Franck-Condon factors and radiative lifetimes are obtained on the basis of the transition dipole moments of the a3Π0+→X1Σ0++,a3Π1→X1Σ0++,and A1Π1→X1Σ0++ transitions. Our calculation indicates that the a3Π1(v'=0)→X1Σ0++(v=0) transition provides a highly diagonally distributed Franck– Condon factor and a short radiative lifetime for the a3Π1 state, which can ensure rapid and efficient laser cooling of InH. The proposed laser drives a3Π0+→X1Σ0++ transitions by using three wavelengths.

First-principles study of solute diffusion in Ni3Al

Shaohua Liu, Zi Li, Chongyu Wang
Chin. Phys. B 2017, 26 (9): 093102;  doi: 10.1088/1674-1056/26/9/093102
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Using first-principles calculations in combination with Wagner-Schottky and kinetic Monte Carlo methods, the diffusion behaviors of solutes via various vacancy-mediated diffusion mechanisms in L12 γ'-Ni3Al were investigated. The formation energies of the point defects and the migration energies for solutes were calculated. Adding alloying elements can decrease the defect-formation energies of Nim Al, increase the defect-formation energies of AlNi, and have little effect on the formation energy of VNi. The migration energies of solutes are related with the site preference and the diffusion mechanism. The diffusion coefficients of Ni, Al, and solutes were calculated, and the concentration of antisite defects plays a crucial role in the elemental diffusion.

Relativistic and distorted wave effects on Xe 4d electron momentum distributions

Minfu Zhao, Xu Shan, Shanshan Niu, Xiangjun Chen
Chin. Phys. B 2017, 26 (9): 093103;  doi: 10.1088/1674-1056/26/9/093103
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The relativistic and distorted wave effects are investigated for the electron momentum distributions of Xe 4d electrons. The theoretical results show good agreements with the experimental data measured previously with electron momentum spectroscopy. The distorted wave effect and the relativistic effect are found to play important roles in the low and high momentum regions, respectively.

Effect of grain boundary structures on the behavior of He defects in Ni: An atomistic study

H F Gong, Y Yan, X S Zhang, W Lv, T Liu, Q S Ren
Chin. Phys. B 2017, 26 (9): 093104;  doi: 10.1088/1674-1056/26/9/093104
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We investigated the effect of grain boundary structures on the trapping strength of HeN (N is the number of helium atoms) defects in the grain boundaries of nickel. The results suggest that the binding energy of an interstitial helium atom to the grain boundary plane is the strongest among all sites around the plane. The HeN defect is much more stable in nickel bulk than in the grain boundary plane. Besides, the binding energy of an interstitial helium atom to a vacancy is stronger than that to a grain boundary plane. The binding strength between the grain boundary and the HeN defect increases with the defect size. Moreover, the binding strength of the HeN defect to the Σ3(112)[110] grain boundary becomes much weaker than that to other grain boundaries as the defect size increases.

Thermodynamic properties of ZnSe under pressure and with variation in temperature

Najm Ul Aarifeen, A Afaq
Chin. Phys. B 2017, 26 (9): 093105;  doi: 10.1088/1674-1056/26/9/093105
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The thermodynamic properties of ZnSe are obtained by using quasi-harmonic Debye model embedded in Gibbs-code for pressure range 0-10 GPa and for temperature range 0-1000 K. Helmholtz free energy, internal energy, entropy, Debye temperature, and specific heat are calculated. The thermal expansion coefficient along with Grüneisen parameter are also calculated at room temperature for the pressure range. It is found that internal energy is pressure dependent at low temperature, whereas entropy and Helmholtz free energy are pressure sensitive at high temperature. At ambient conditions, the obtained results are found to be in close agreement to available theoretical and experimental data.

Lattice stability and the effect of Co and Re on the ideal strength of Ni: First-principles study of uniaxial tensile deformation

Minru Wen, Chong-Yu Wang
Chin. Phys. B 2017, 26 (9): 093106;  doi: 10.1088/1674-1056/26/9/093106
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Using first-principles density functional calculations, lattice stability of γ-Ni under [001], [110], and [111] uniaxial tensions and the effect of alloying elements Co and Re on the uniaxial tensile behavior of γ-Ni were studied in this paper. With elastic constants and phonon spectra calculations, we examined the mechanical stability and phonon stability of Ni during the uniaxial tensions along the three characteristic directions. The results show that the mechanical stability and phonon stability of a lattice occurs before the maximum stress-strain point under the [001] and [111] tension, respectively. The effects of Co and Re on the ideal tensile strength of γ-Ni show a significant directivity: Co and Re have little effect on the stresses in [001] and [111] directions, but increases the ideal strength of the system in the weakest uniaxial tensile direction. Moreover, the strengthening effect of Re is significantly better than that of Co. By further analyzing electronic structure, it is found that the effect of alloying elements on the uniaxial tensile behavior of γ-Ni comes from their interactions with host atoms.

First principles study and comparison of vibrational and thermodynamic properties of XBi (X= In, Ga, B, Al)

Raheleh Pilevar Shahri, Arsalan Akhtar
Chin. Phys. B 2017, 26 (9): 093107;  doi: 10.1088/1674-1056/26/9/093107
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In the present work, vibrational and thermodynamic properties of XBi (X=B, Al, Ga, In) compounds are compared and investigated. The calculation is carried out using density functional theory (DFT) within the generalized gradient approximation (GGA) in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory (DFPT) as implemented in Quantum ESPRESSO (QE) code. Thermodynamic properties involving phonon density of states (DOS) and specific heat at constant volume are investigated using quasi-harmonic approximation (QHA) package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm-1, 150 cm-1, 300 cm-1, and 150 cm-1, respectively. For all compounds, the three acoustic modes near the gamma point have a linear behavior. CV is a function of T3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected.

Isolated attosecond pulse generation with few-cycle two-color counter-rotating circularly polarized laser pulses

Jin-Song Wu, Zheng-Mao Jia, Zhi-Nan Zeng
Chin. Phys. B 2017, 26 (9): 093201;  doi: 10.1088/1674-1056/26/9/093201
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Most of the schemes for generating isolated attosecond pulses (IAP) are sensitive to the carrier-envelope phase (CEP) of the driving lasers. We propose a scheme for generating IAP using two-color counter-rotating circularly polarized (TC-CRCP) laser pulses. The results demonstrate that the dependence of the IAP generation on CEP stability is largely reduced in this scheme. IAP can be generated at most of CEPs. Therefore, the experiment requirements become lower.

Optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis

Zhi-Chao Ding, Jie Yuan, Hui Luo, Xing-Wu Long
Chin. Phys. B 2017, 26 (9): 093301;  doi: 10.1088/1674-1056/26/9/093301
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A model of an optical pumping nuclear magnetic resonance system rotating in a plane parallel to the quantization axis is presented. Different coordinate frames for nuclear spin polarization vector are introduced, and theoretical calculation is conducted to analyze this model. We demonstrate that when the optical pumping nuclear magnetic resonance system rotates in a plane parallel to the quantization axis, it will maintain a steady state with respect to the quantization axis which is independent of rotational speed and direction.


Design of double-layer active frequency-selective surface with PIN diodes for stealth radome

Bin Deng, Jian Chen
Chin. Phys. B 2017, 26 (9): 094101;  doi: 10.1088/1674-1056/26/9/094101
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An experimental double-layer active frequency-selective surface (AFSS) for stealth radome is proposed. The AFSS is a planar structure which is composed of a fixed frequency-selective surface (FSS), a PIN diodes array, and a DC bias network. The AFSS elements incorporating switchable PIN diodes are discussed. By means of controlling the DC bias network, it is possible to switch the frequency response for reflecting and transmitting. Measured and simulated data validate that when the incidence angle varies from 0° to 30° the AFSS produces more than -11.5 dB isolation across 6-18 GHz when forward biased. The insertion loss (IL) is less than 0.5 dB across 10-11 GHz when reverse biased.

Reduced technique for modeling electromagnetic immunity on braid shielding cable bundles

Pei Xiao, Ping-An Du, Bao-Lin Nie, Dan Ren
Chin. Phys. B 2017, 26 (9): 094102;  doi: 10.1088/1674-1056/26/9/094102
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In this paper, an efficient multi-conductor simplification technique is proposed to model the electromagnetic immunity on cable bundles within a braid shielding structure over a large frequency range. By grouping together the conductors based on the knowledge of Z-Smith chart, the required computation time is markedly reduced and the complexity of modeling the completely shielding cable bundles is significantly simplified with a good accuracy. After a brief description of the immunity problems in shielding structure, a six-phase procedure is detailed to generate the geometrical characteristics of the reduced cable bundles. Numerical simulation is carried out by using a commercial software CST to validate the efficiency and advantages of the proposed approach. The research addressed in this paper is considered as a simplified modeling technique for the electromagnetic immunity within a shielding structure.

A linear-to-circular polarization converter based on I-shapedcircular frequency selective surfaces

Jia-Liang Wu, Bao-Qin Lin, Xin-Yu Da, Kai Wu
Chin. Phys. B 2017, 26 (9): 094201;  doi: 10.1088/1674-1056/26/9/094201
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In this paper, a linear-to-circular polarization converter using a three-layer frequency selective surface based on I-shaped circular structure resonant is presented and investigated. Numerical simulations exhibit that when the normal y-polarized waves impinge on this device propagating towards +z direction, the two orthogonal components of the transmitted waves have a 90° phase difference as well as the nearly equal amplitudes at the resonant frequency of 7.04 GHz, which means that the left-hand circular polarization is realized in transmission. For validating the proposed design, a prototype which consists of 25×25 elements has been designed, manufactured and measured. The measured results are in good agreement with the simulated ones, showing that the polarization conversion transmission is over -3 dB in the frequency range of 5.22-8.08 GHz and the axial ratio is below 3 dB from 5.86 GHz to 7.34 GHz.

Orbital angular momentum density and spiral spectra of Lorentz-Gauss vortex beams passing through a single slit

Zhi-Yue Ji, Guo-Quan Zhou
Chin. Phys. B 2017, 26 (9): 094202;  doi: 10.1088/1674-1056/26/9/094202
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Based on the Hermite-Gaussian expansion of the Lorentz distribution and the complex Gaussian expansion of the aperture function, an analytical expression of the Lorentz-Gauss vortex beam with one topological charge passing through a single slit is derived. By using the obtained analytical expressions, the properties of the Lorentz-Gauss vortex beam passing through a single slit are numerically demonstrated. According to the intensity distribution or the phase distribution of the Lorentz-Gauss vortex beam, one can judge whether the topological charge is positive or negative. The effects of the topological charge and three beam parameters on the orbital angular momentum density as well as the spiral spectra are systematically investigated respectively. The optimal choice for measuring the topological charge of the diffracted Lorentz-Gauss vortex beam is to make the single slit width wider than the waist of the Gaussian part.

Fabrication and characterization of ultra-low noise narrow and wide band Josephson parametric amplifiers Hot!

Keqiang Huang, Qiujiang Guo, Chao Song, Yarui Zheng, Hui Deng, Yulin Wu, Yirong Jin, Xiaobo Zhu, Dongning Zheng
Chin. Phys. B 2017, 26 (9): 094203;  doi: 10.1088/1674-1056/26/9/094203
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We have fabricated two types of lumped-element Josephson parameter amplifiers (JPAs) by using a multilayer micro-fabrication process involving wet etching of Al films. The first type is a narrow band JPA which shows typical gain above 14 dB in a bandwidth around 35 MHz. The second type is a wideband JPA which is coupled to an input 50 Ω transmission line via an impedance transformer that changes the impedance from about 15 Ω on the non-linear resonator side to 50 Ω on the input transmission line side. The wideband JPA could operate in a 200 MHz range with a gain higher than 14 dB. The amplifiers were used for superconducting qubit readout. The results showed that the signal to noise ratio and hence the readout fidelity were improved significantly.

Super-resolution and super-sensitivity of entangled squeezed vacuum state using optimal detection strategy

Jiandong Zhang, Zijing Zhang, Longzhu Cen, Shuo Li, Yuan Zhao, Feng Wang
Chin. Phys. B 2017, 26 (9): 094204;  doi: 10.1088/1674-1056/26/9/094204
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Interference metrology is a method for achieving high precision detection by phase estimation. The phase sensitivity of a traditional interferometer is subject to the standard quantum limit, while its resolution is constrained by the Rayleigh diffraction limit. The resolution and sensitivity of phase measurement can be enhanced by using quantum metrology. We propose a quantum interference metrology scheme using the entangled squeezed vacuum state, which is obtained using the magic beam splitter, expressed as |ψ > = (|ξ>|0 > + ≤ |0 > ≤|ξ>)/√2+2/coshr, such as the N00N state. We derive the phase sensitivity and the resolution of the system with Z detection, project detection, and parity detection. By simulation and analysis, we determine that parity detection is an optimal detection method, which can break through the Rayleigh diffraction limit and the standard quantum limit.

Phase estimation of phase shifts in two arms for an SU(1,1) interferometer with coherent and squeezed vacuum states

Qian-Kun Gong, Dong Li, Chun-Hua Yuan, Ze-Yu Qu, Wei-Ping Zhang
Chin. Phys. B 2017, 26 (9): 094205;  doi: 10.1088/1674-1056/26/9/094205
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We theoretically study the quantum Fisher information (QFI) of the SU(1,1) interferometer with phase shifts in two arms by coherent ⊗ squeezed vacuum state input, and give the comparison with the result of phase shift only in one arm. Different from the traditional Mach-Zehnder interferometer, the QFI of single-arm case for an SU(1,1) interferometer can be slightly higher or lower than that of two-arm case, which depends on the intensities of the two arms of the interferometer. For coherent ⊗ squeezed vacuum state input with a fixed mean photon number, the optimal sensitivity is achieved with a squeezed vacuum input in one mode and the vacuum input in the other.

Er3+,Yb3+:glass-Co2+:MgAl2O4 diffusion bonded passively Q-switched laser

Yan Zou, Yong-Ling Hui, Jin-Lu Cai, Na Guo, Meng-Hua Jiang, Hong Lei, Qiang Li
Chin. Phys. B 2017, 26 (9): 094206;  doi: 10.1088/1674-1056/26/9/094206
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A Co2+:spinel passively Q-switched erbium-ytterbium-phosphate glass bonded laser pumped at 940 nm is reported. A pulse energy of 210 μJ, a peak power over 70 kW, and beam quality M2 parameter of 1.2 are obtained under a pump power of 235 mW. An unbonded laser output experiment with the same dimension of the active material and the saturable absorber as the bonded laser output experiment is carried out. The reason why the output in the bonded laser is improved is determined.

Retrieval of high-order susceptibilities of nonlinear metamaterials

Zhi-Yu Wang, Jin-Peng Qiu, Hua Chen, Jiong-Jiong Mo, Fa-Xin Yu
Chin. Phys. B 2017, 26 (9): 094207;  doi: 10.1088/1674-1056/26/9/094207
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Active metamaterials embedded with nonlinear elements are able to exhibit strong nonlinearity in microwave regime. However, existing S-parameter based parameter retrieval approaches developed for linear metamaterials do not apply in nonlinear cases. In this paper, a retrieval algorithm of high-order susceptibilities for nonlinear metamaterials is derived. Experimental demonstration shows that, by measuring the power level of each harmonic while sweeping the incident power, high-order susceptibilities of a thin-layer nonlinear metamaterial can be effectively retrieved. The proposed approach can be widely used in the research of active metamaterials.

Structural deformation of nitro group of nitromethane molecule in liquid phase in an intense femtosecond laser field

Chang Wang, Hong-lin Wu, Yun-fei Song, Yan-qiang Yang
Chin. Phys. B 2017, 26 (9): 094208;  doi: 10.1088/1674-1056/26/9/094208
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The structural deformation of NO2 group induced by an intense femtosecond laser field of liquid nitromethane (NM) molecule is detected by time- and frequency-resolved coherent anti-Stokes Raman spectroscopy (CARS) technique with the intense pump laser. Here, we present the mechanism of molecular alignment and deformation. The CARS spectra and its FFT spectra of liquid NM show that the NO2 torsional mode couples with the CN symmetric stretching mode and that the NO2 group undergoes ultrafast structural deformation with a relaxation time of 195 fs. The frequency of the NO2 torsional mode in liquid NM (50.8±0.3 cm-1) at room temperature is found. Our results prove the structural deformation of two groups in liquid NM molecule occur simultaneously in the intense laser field.

Odd-even harmonic emission from asymmetric molecules: Identifying the mechanism

Jianguo Chen, Shujuan Yu, Yanpeng Li, Shang Wang, Yanjun Chen
Chin. Phys. B 2017, 26 (9): 094209;  doi: 10.1088/1674-1056/26/9/094209
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We study odd-even high-order harmonic generation (HHG) from oriented asymmetric molecules HeH2+ numerically and analytically. The variational method is used to improve the analytical description of the ground-state wave function for the asymmetric system, with which the ground-state-continuum-state transition dipole is evaluated. The comparison between the odd-even HHG spectra and the improved dipoles allows us to identify and clarify the complex generation mechanism of odd-even harmonics from asymmetric molecules, providing deep insights into the relation between the odd-even HHG and the asymmetric molecular orbital.

Electro-optical properties of high birefringence liquid crystal compounds with isothiocyanate and naphthyl group

Zeng-Hui Peng, Qi-Dong Wang, Shao-Xin Wang, Li-Shuang Yao, Yong-Gang Liu, Li-Fa Hu, Zhao-Liang Cao, Quan-Quan Mu, Cheng-Liang Yang, Li Xuan
Chin. Phys. B 2017, 26 (9): 094210;  doi: 10.1088/1674-1056/26/9/094210
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Liquid crystal (LC) compound with isothiocyanate and naphthyl group is an attractive high birefringence LC material, and can be used in optical devices. In this paper, the electro-optical properties of a series of this type of LC compounds were investigated. The melting points and enthalpy values of these LC compounds were higher than those of corresponding compounds with the phenyl group. These compounds exhibited high birefringence with a maximum value of 0.66. Fluorine substitution in the molecular almost does not affect the birefringence value. When these LC compounds with the naphthyl group were dissolved in a commercial LC mixture, the electro-optical properties depending on temperature were investigated. In the low-temperature region, LC mixtures with the naphthyl-group LC compounds exhibited higher viscosity than pure commercial LCs. In the high-temperature region, viscosity values very closely approached each other. When response performance was investigated, figure-of-merit (FoM) values were measured. The FoM values of LC mixtures containing LC compounds with naphthyl group were lower than those of reference benzene LCs in the low-temperature region. However, in the high-temperature region, the results were reversed. These isothiocyanate LC compounds with naphthyl group can be applied in special fast-response LC device, particularly the ones used under high-temperature conditions.

Optical and defect properties of S-doped and Al-doped GaSe crystals

Chang-Bao Huang, Hai-Xin Wu, You-Bao Ni, Zhen-You Wang, Shi-Jing Chen
Chin. Phys. B 2017, 26 (9): 094211;  doi: 10.1088/1674-1056/26/9/094211
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S-doped and Al-doped GaSe crystals are promising materials for their applications in nonlinear frequency conversion devices. The optical and defect properties of pure, S-doped, and Al-doped GaSe crystals were studied by using photoluminescence (PL) and Fourier transform infrared spectroscopy (FT-IR). The micro-topography of (0001) face of these samples was observed by using scanning electron microscope (SEM) to investigate the influence of the doped defects on the intralayer and interlayer chemical bondings. The doped S or Al atoms form the SSe0 or AlGa+1 substitutional defects in the layer GaSe structure, and the positive center of AlGa+1 could induce defect complexes. The incorporations of S and Al atoms can change the optical and mechanical properties of the GaSe crystal by influencing the chemical bonding of the layer structure. The study results may provide guidance for the crystal growth and further applications of S-doped and Al-doped GaSe crystals.

A scheme for Sagnac-effect quantum enhancement with Fock state light input

Kun Chen, Shu-Xin Chen, De-Wei Wu, Chun-Yan Yang, Qiang Miao
Chin. Phys. B 2017, 26 (9): 094212;  doi: 10.1088/1674-1056/26/9/094212
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Sagnac effect enhancement can improve optical gyro precision. For a certain input intensity, we suggest that the other input port of beam splitter (BS) should be fed with some quantum light to break through shot noise limit (SNL) to improve Sagnac effect without increasing radiation-pressure noise (NRP). We design a Sagnac effect quantum enhancement criterion (SQEC) to judge whether some quantum light can enhance Sagnac effect and present a Sagnac effect enhancement scheme that utilizing Fock state light and parity measurement technique to extract the output phase. The results of the theoretical analysis show that the maximum sensitivity can be reached at θ = 0, and the phase precision can break through SNL and even achieve Heisenberg limit (HL). When the Fock state average photon number n is far less than coherent state, the minimum measurable angular rate is improved with √2n+1 times, which can deduce shot noise and increase NRP little.

Wideband dispersion removal and mode separation of Lamb waves based on two-component laser interferometer measurement

Yan-Feng Xu, Wen-Xiang Hu
Chin. Phys. B 2017, 26 (9): 094301;  doi: 10.1088/1674-1056/26/9/094301
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Ultrasonic Lamb waves are considered as a sensitive and effective tool for nondestructive testing and evaluation of plate-like or pipe-like structures. The nature of multimode and dispersion causes the wave packets to spread, and the modes overlap in both time and frequency domains as they propagate through the structures. By using a two-component laser interferometer technique, in combination with a priori knowledge of the dispersion characteristics and wave structure information of Lamb wave modes, a two-component signal processing technique is presented for implementing dispersion removal and mode separation simultaneously for two modes mixture signals of Lamb waves. The proposed algorithm is first processed and verified using synthetic Lamb wave signals. Then, the two-component displacements test experiment is conducted using different aluminum plate samples. Moreover, we confirm the effectiveness and robustness of this method.

Magneto-elastic dynamics and bifurcation of rotating annular plate

Yu-Da Hu, Jiang-Min Piao, Wen-Qiang Li
Chin. Phys. B 2017, 26 (9): 094302;  doi: 10.1088/1674-1056/26/9/094302
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In this paper, magneto-elastic dynamic behavior, bifurcation, and chaos of a rotating annular thin plate with various boundary conditions are investigated. Based on the thin plate theory and the Maxwell equations, the magneto-elastic dynamic equations of rotating annular plate are derived by means of Hamilton's principle. Bessel function as a mode shape function and the Galerkin method are used to achieve the transverse vibration differential equation of the rotating annular plate with different boundary conditions. By numerical analysis, the bifurcation diagrams with magnetic induction, amplitude and frequency of transverse excitation force as the control parameters are respectively plotted under different boundary conditions such as clamped supported sides, simply supported sides, and clamped-one-side combined with simply-another-side. Poincaré maps, time history charts, power spectrum charts, and phase diagrams are obtained under certain conditions, and the influence of the bifurcation parameters on the bifurcation and chaos of the system is discussed. The results show that the motion of the system is a complicated and repeated process from multi-periodic motion to quasi-period motion to chaotic motion, which is accompanied by intermittent chaos, when the bifurcation parameters change. If the amplitude of transverse excitation force is bigger or magnetic induction intensity is smaller or boundary constraints level is lower, the system can be more prone to chaos.

Interaction between infinitely many dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal

Guan-Ting Liu, Li-Ying Yang
Chin. Phys. B 2017, 26 (9): 094601;  doi: 10.1088/1674-1056/26/9/094601
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By means of analytic function theory, the problems of interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are studied. The analytic solutions of stress fields of the interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are obtained. They indicate that the stress concentration occurs at the dislocation source and the tip of the crack, and the value of the stress increases with the number of the dislocations increasing. These results are the development of interaction among the finitely many defects of quasicrystals, which possesses an important reference value for studying the interaction problems of infinitely many defects in fracture mechanics of quasicrystal.

Tungsten ion source under double-pulse laser ablation system

Ahmed Asaad I Khalil, Ashraf I Hafez, Mahmoud E Elgohary, Mohamed A Morsy
Chin. Phys. B 2017, 26 (9): 095201;  doi: 10.1088/1674-1056/26/9/095201
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New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd:YAG laser beams (266+1064 nm) are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laser wavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.

Rotation of a single vortex in dusty plasma

Jia Yan, Fan Feng, Fu-Cheng Liu, Ya-Feng He
Chin. Phys. B 2017, 26 (9): 095202;  doi: 10.1088/1674-1056/26/9/095202
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A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex.

Interactions of ion acoustic multi-soliton and rogue wave with Bohm quantum potential in degenerate plasma

M S Alam, M G Hafez, M R Talukder, M Hossain Ali
Chin. Phys. B 2017, 26 (9): 095203;  doi: 10.1088/1674-1056/26/9/095203
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This work investigates the interactions among solitons and their consequences in the production of rogue waves in an unmagnetized plasmas composing non-relativistic as well as relativistic degenerate electrons and positrons, and inertial non-relativistic helium ions. The extended Poincaré-Lighthill-Kuo (PLK) method is employed to derive the two-sided Korteweg-de Vries (KdV) equations with their corresponding phase shifts. The nonlinear Schrödinger equation (NLSE) is obtained from the modified KdV (mKdV) equation, which allows one to study the properties of the rogue waves. It is found that the Fermi temperature and quantum mechanical effects become pronounced due to the quantum diffraction of electrons and positrons in the plasmas. The densities and temperatures of the helium ions, degenerate electrons and positrons, and quantum parameters strongly modify the electrostatic ion acoustic resonances and their corresponding phase shifts due to the interactions among solitons and produce rogue waves in the plasma.

Understanding hydrogen plasma processes based on the diagnostic results of 2.45 GHz ECRIS at Peking University

Wen-Bin Wu, Hai-Tao Ren, Shi-Xiang Peng, Yuan Xu, Jia-Mei Wen, Jiang Sun, Ai-Lin Zhang, Tao Zhang, Jing-Feng Zhang, Jia-Er Chen
Chin. Phys. B 2017, 26 (9): 095204;  doi: 10.1088/1674-1056/26/9/095204
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Optical emission spectroscopy (OES), as a simple in situ method without disturbing the plasma, has been performed for the plasma diagnosis of a 2.45 GHz permanent magnet electron cyclotron resonance (PMECR) ion source at Peking University (PKU). A spectrum measurement platform has been set up with the quartz-chamber electron cyclotron resonance (ECR) ion source [Patent Number: ZL 201110026605.4] and experiments were carried out recently. The electron temperature and electron density inside the ECR plasma chamber have been measured with the method of line intensity ratio of noble gas. Hydrogen plasma processes inside the discharge chamber are discussed based on the diagnostic results. What is more, the superiority of the method of line intensity ratio of noble gas is indicated with a comparison to line intensity ratio of hydrogen. Details will be presented in this paper.

Radiative divertor behavior and physics in Ar seeded plasma on EAST

Jingbo Chen, Yanmin Duan, Zhongshi Yang, Liang Wang, Kai Wu, Kedong Li, Fang Ding, Hongmin Mao, Jichan Xu, Wei Gao, Ling Zhang, Jinhua Wu, Guang-Nan Luo, EAST Team
Chin. Phys. B 2017, 26 (9): 095205;  doi: 10.1088/1674-1056/26/9/095205
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To investigate the radiative divertor behavior and physics for the scenario of impurity seeded plasma in ITER, the radiative divertor experiments with argon (Ar) seeding under ITER-like tungsten divertor condition were carried out during recent EAST campaigns. The experimental results reveal the high efficiency of reducing heat load and particle flux onto the divertor targets owing to increased radiation by Ar seeding. We achieve detached plasmas in these experiments. The inner-outer divertor asymmetry reduces after Ar seeding. Impurities, such as Ar, C, Li, and W, exist in the entire space of the vacuum chamber during EAST operations, and play important roles in power exhausting and accelerating the plasma detachment process. It is remarkable that the contamination of the core plasma is observed using Ar seeding owing to the sputtering of plasma facing components (PFCs), particularly when Ar impurity is injected from the upper tungsten divertor.

Initial growth and microstructure feature of Ag films prepared by very-high-frequency magnetron sputtering

Yue Zhang, Chao Ye, Xiang-Ying Wang, Pei-Fang Yang, Jia-Min Guo, Su Zhang
Chin. Phys. B 2017, 26 (9): 095206;  doi: 10.1088/1674-1056/26/9/095206
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The initial growth and microstructure feature of Ag films formation were investigated, which were prepared by using the very-high-frequency (VHF) (60 MHz) magnetron sputtering. Because of the moderate energy and very low flux density of ions impinging on the substrate, the evolutions of initial growth for Ag films formation were well controlled by varying the sputtering power. It was found that the initial growth of Ag films followed the island (Volmer-Weber, VW) growth mode, but before the island nucleation, the adsorption of Ag nanoparticles and the formation of Ag clusters dominated the growth. Therefore, the whole initial stages of Ag films formation included the adsorption of nanoparticles, the formation of clusters, the nucleation by the nanoparticles and clusters simultaneously, the islands formation, and the coalescence of islands.


Synthesis and magnetotransport properties of Bi2Se3 nanowires Hot!

Kang Zhang, Haiyang Pan, Zhongxia Wei, Minhao Zhang, Fengqi Song, Xuefeng Wang, Rong Zhang
Chin. Phys. B 2017, 26 (9): 096101;  doi: 10.1088/1674-1056/26/9/096101
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Bi2Se3, as a three-dimensional topological insulator, has attracted worldwide attention for its unique surface states which are protected by time-reversal symmetry. Here we report the synthesis and characterization of high-quality single-crystalline Bi2Se3 nanowires. Bi2Se3 nanowires were synthesized by chemical vapor deposition (CVD) method via gold-catalyzed vapor-liquid-solid (VLS) mechanism. The structure and morphology were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. In magnetotransport measurements, the Aharonov-Bohm (AB) effect was observed in a nanowire-based nanodevice, suggesting the existence of surface states in Bi2Se3 nanowires.

Ionizing radiation effect on single event upset sensitivity of ferroelectric random access memory

Jia-Nan Wei, Hong-Xia Guo, Feng-Qi Zhang, Yin-Hong Luo, Li-Li Ding, Xiao-Yu Pan, Yang Zhang, Yu-Hui Liu
Chin. Phys. B 2017, 26 (9): 096102;  doi: 10.1088/1674-1056/26/9/096102
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The impact of ionizing radiation effect on single event upset (SEU) sensitivity of ferroelectric random access memory (FRAM) is studied in this work. The test specimens were firstly subjected to 60Co γ-ray and then the SEU evaluation was conducted using 209Bi ions. As a result of TID-induced fatigue-like and imprint-like phenomena of the ferroelectric material, the SEU cross sections of the post-irradiated devices shift substantially. Different trends of SEU cross section with elevated dose were also found, depending on whether the same or complementary test pattern was employed during the TID exposure and the SEU measurement.

Direct measurement and analysis of total ionizing dose effect on 130 nm PD SOI SRAM cell static noise margin

Qiwen Zheng, Jiangwei Cui, Mengxin Liu, Dandan Su, Hang Zhou, Teng Ma, Xuefeng Yu, Wu Lu, Qi Guo, Fazhan Zhao
Chin. Phys. B 2017, 26 (9): 096103;  doi: 10.1088/1674-1056/26/9/096103
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In this work, the total ionizing dose (TID) effect on 130 nm partially depleted (PD) silicon-on-insulator (SOI) static random access memory (SRAM) cell stability is measured. The SRAM cell test structure allowing direct measurement of the static noise margin (SNM) is specifically designed and irradiated by gamma-ray. Both data sides' SNM of 130 nm PD SOI SRAM cell are decreased by TID, which is different from the conclusion obtained in old generation devices that one data side's SNM is decreased and the other data side's SNM is increased. Moreover, measurement of SNM under different supply voltages (Vdd) reveals that SNM is more sensitive to TID under lower Vdd. The impact of TID on SNM under data retention Vdd should be tested, because Vdd of SRAM cell under data retention mode is lower than normal Vdd. The mechanism under the above results is analyzed by measurement of I-V characteristics of SRAM cell transistors.

Strain rate and cold rolling dependence of tensile strength and ductility in high nitrogen nickel-free austenitic stainless steel

Gui-Xun Sun, Yue Jiang, Xiao-Ru Zhang, Shi-Cheng Sun, Zhong-Hao Jiang, Wen-Quan Wang, Jian-She Lian
Chin. Phys. B 2017, 26 (9): 096104;  doi: 10.1088/1674-1056/26/9/096104
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The tensile strength and ductility of a high nitrogen nickel-free austenitic stainless steel with solution and cold rolling treatment were investigated by performing tensile tests at different strain rates and at room temperature. The tensile tests demonstrated that this steel exhibits a significant strain rate and cold rolling dependence of the tensile strength and ductility. With the increase of the strain rate from 10-4 s-1 to 1 s-1, the yield strength and ultimate tensile strength increase and the uniform elongation and total elongation decrease. The analysis of the double logarithmic stress-strain curves showed that this steel exhibits a two-stage strain hardening behavior, which can be well examined and analyzed by using the Ludwigson equation. The strain hardening exponents at low and high strain regions (n2 and n1) and the transition strain (εL) decrease with increasing strain rate and the increase of cold rolling RA. Based on the analysis results of the stress-strain curves, the transmission electron microscopy characterization of the microstructure and the scanning electron microscopy observation of the deformation surfaces, the significant strain rate and cold rolling dependence of the strength and ductility of this steel were discussed and connected with the variation in the work hardening and dislocation activity with strain rate and cold rolling.

Theoretical study on the structural, mechanical, electronic properties and QTAIM of CrB4 as a hard material

Xiao-Hong Li, Hong-Ling Cui, Rui-Zhou Zhang
Chin. Phys. B 2017, 26 (9): 096201;  doi: 10.1088/1674-1056/26/9/096201
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Using the first-principles calculations based on spin density functional theory (DFT), we investigate the structure, elastic properties, and electronic structure of Pnnm-CrB4. It is found that Pnnm-CrB4 is thermodynamically and mechanically stable. The calculated elastic properties such as the bulk modulus, shear modulus, Young's modulus, and Poisson's ratio indicate that CrB4 is an incompressible material. Vicker's hardness of Pnnm-CrB4 is estimated to be 26.3 GPa, which is in good agreement with the experimental values. The analysis of the investigated electronic properties shows that Pnnm-CrB4 has the metallic character and there exist strong B-B and Cr-B bonds in the compound, which are further confirmed by Bader's quantum theory of atoms in molecules (QTAIM). Thermodynamic properties are also investigated.

First-principles investigations on the mechanical, thermal,electronic, and optical properties of the defect perovskites Cs2SnX6 (X= Cl, Br, I)

Hai-Ming Huang, Zhen-Yi Jiang, Shi-Jun Luo
Chin. Phys. B 2017, 26 (9): 096301;  doi: 10.1088/1674-1056/26/9/096301
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The mechanical properties, thermal properties, electronic structures, and optical properties of the defect perovskites Cs2SnX6 (X=Cl, Br, I) were investigated by first-principles calculation using PBE and HSE06 hybrid functional. The optic band gaps based on HSE06 are 3.83 eV for Cs2SnCl6, 2.36 eV for Cs2SnBr6, and 0.92 eV for Cs2SnI6, which agree with the experimental results. The Cs2SnCl6, Cs2SnBr6, and Cs2SnI6 are mechanically stable and they are all anisotropic and ductile in nature. Electronic structures calculations show that the conduction band consists mainly of hybridization between the halogen p orbitals and Sn 5s orbitals, whereas the valence band is composed of the halogen p orbitals. Optic properties indicate that these three compounds exhibit good optical absorption in the ultraviolet region, and the absorption spectra red shift with the increase in the number of halogen atoms. The defect perovskites are good candidates for probing the lead-free and high power conversion efficiency of solar cells.

Effect of ballistic electrons on ultrafast thermomechanical responses of a thin metal film

Qi-lin Xiong, Xin Tian
Chin. Phys. B 2017, 26 (9): 096501;  doi: 10.1088/1674-1056/26/9/096501
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The ultrafast thermomechanical coupling problem in a thin gold film irradiated by ultrashort laser pulses with different electron ballistic depths is investigated via the ultrafast thermoelasticity model. The solution of the problem is obtained by solving finite element governing equations. The comparison between the results of ultrafast thermomechanical coupling responses with different electron ballistic depths is made to show the ballistic electron effect. It is found that the ballistic electrons have a significant influence on the ultrafast thermomechanical coupling behaviors of the gold thin film and the best laser micromachining results can be achieved by choosing the specific laser technology (large or small ballistic range). In addition, the influence of simplification of the ultrashort laser pulse source on the results is studied, and it is found that the simplification has a great influence on the thermomechanical responses, which implies that care should be taken when the simplified form of the laser source term is applied as the Gaussian heat source.

First-principles study of helium clustering at initial stage in ThO2

Kuan Shao, Han Han, Wei Zhang, Chang-Ying Wang, Yong-Liang Guo, Cui-Lan Ren, Ping Huai
Chin. Phys. B 2017, 26 (9): 097101;  doi: 10.1088/1674-1056/26/9/097101
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The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site (OIS). As the concentration of He atoms in ThO2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect (SD) configurations (SD1, SD2, and SD3). When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD1. Large He clusters, such as a He hexamer, are also stable in the SDs.

Voltage-controlled Kosterlitz-Thouless transitions and various kinds of Kondo behaviors in a triple dot device

Yong-Chen Xiong, Jun Zhang, Wang-Huai Zhou, Amel Laref
Chin. Phys. B 2017, 26 (9): 097102;  doi: 10.1088/1674-1056/26/9/097102
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The transport property and phase transition for a parallel triple dot device are studied by adopting Wilson's numerical renormalization group technique, focusing on the effects of level spacings between neighboring dot sites. By keeping dot 2 at the half-filled level and tuning the level differences, it is demonstrated that the system transits from local spin quadruplet to triplet and doublet sequently, and three kinds of Kondo peaks at the Fermi surface could be found, which are separated by two Kosterlitz-Thouless type quantum phase transitions and correspond to spin-3/2, spin-1, and spin-1/2 Kondo effect, respectively. To obtain a detailed understanding of these problems, the charge occupation, the spin-spin correlation, the transmission coefficient, and the temperature-dependent magnetic moment are shown, and necessary physical arguments are given.

Magnetpolaron effect in two-dimensional anisotropic parabolic quantum dot in a perpendicular magnetic field

Kang-Kang Ju, CuiXian Guo, Xiao-Yin Pan
Chin. Phys. B 2017, 26 (9): 097103;  doi: 10.1088/1674-1056/26/9/097103
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We study the two-dimensional weak-coupling Fröhlich polaron in a completely anisotropic quantum dot in a perpendicular magnetic field. By performing a unitary transformation, we first transform the Hamiltonian into a new one which describes an anisotropic harmonic oscillator with new mass and trapping frequencies interacting with the same phonon bath but with different interaction form and strength. Then employing the second-order Rayleigh-Schrödinger perturbation theory, we obtain the polaron correction to the ground-state energy. The magnetic field and anisotropic effects on the polaron correction to the ground-state energy are discussed.

Parasitic source resistance at different temperatures for AlGaN/AlN/GaN heterostructure field-effect transistors

Yan Liu, Zhao-Jun Lin, Yuan-Jie Lv, Peng Cui, Chen Fu, Ruilong Han, Yu Huo, Ming Yang
Chin. Phys. B 2017, 26 (9): 097104;  doi: 10.1088/1674-1056/26/9/097104
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The parasitic source resistance (RS) of AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) is studied in the temperature range 300-500 K. By using the measured RS and both capacitance-voltage (C-V) and current-voltage (I-V) characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field (PCF) scattering exhibits a significant impact on RS at the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.

Effects of Mn substitution on thermoelectric properties of CuIn1-xMnxTe2

Pengfei Luo, Li You, Jiong Yang, Juanjuan Xing, Jiye Zhang, Chenyang Wang, Xinluo Zhao, Jun Luo, Wenqing Zhang
Chin. Phys. B 2017, 26 (9): 097201;  doi: 10.1088/1674-1056/26/9/097201
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CuIn1-xMnxTe2 samples have been synthesized by a melt-annealing method. The x-ray powder diffraction (XRD) analysis shows that the CuIn1-xMnxTe2 samples crystallize in the chalcopyrite phase. Mn doping can effectively optimize the electrical properties and accordingly improve the power factor. The room temperature electrical conductivity of doped CuInTe2 increases by several orders of magnitude due to substituting In with Mn. In addition, a large reduction in thermal conductivity is achieved through the enhanced phonon scattering via Mn-related point defects and precipitates. Therefore, an enhanced average ZT value up to 0.34 is achieved for sample CuIn0.925Mn0.075Te2, which is 41% higher than that of the pristine CuInTe2.

Ultrafast interlayer photocarrier transfer in graphene-MoSe2 van der Waals heterostructure Hot!

Xin-Wu Zhang, Da-Wei He, Jia-Qi He, Si-Qi Zhao, Sheng-Cai Hao, Yong-Sheng Wang, Li-Xin Yi
Chin. Phys. B 2017, 26 (9): 097202;  doi: 10.1088/1674-1056/26/9/097202
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We report the fabrication and photocarrier dynamics in graphene-MoSe2 heterostructures. The samples were fabricated by mechanical exfoliation and manual stacking techniques. Ultrafast laser measurements were performed on the heterostructure and MoSe2 monolayer samples. By comparing the results, we conclude that photocarriers injected in MoSe2 of the heterostructure transfer to graphene on an ultrafast time scale. The carriers in graphene alter the optical absorption coefficient of MoSe2. These results illustrate the potential applications of this material in optoelectronic devices.

Inverted organic solar cells with solvothermal synthesized vanadium-doped TiO2 thin films as efficient electron transport layer

Mehdi Ahmadi, Sajjad Rashidi Dafeh, Samaneh Ghazanfarpour, Mohammad Khanzadeh
Chin. Phys. B 2017, 26 (9): 097203;  doi: 10.1088/1674-1056/26/9/097203
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We investigated the effects of using different thicknesses of pure and vanadium-doped thin films of TiO2 as the electron transport layer in the inverted configuration of organic photovoltaic cells based on poly (3-hexylthiophene) P3HT: [6-6] phenyl-(6) butyric acid methyl ester (PCBM). 1% vanadium-doped TiO2 nanoparticles were synthesized via the solvothermal method. Crystalline structure, morphology, and optical properties of pure and vanadium-doped TiO2 thin films were studied by different techniques such as x-ray diffraction, scanning electron microscopy, transmittance electron microscopy, and UV-visible transmission spectrum. The doctor blade method which is compatible with roll-2-roll printing was used for deposition of pure and vanadium-doped TiO2 thin films with thicknesses of 30 nm and 60 nm. The final results revealed that the best thickness of TiO2 thin films for our fabricated cells was 30 nm. The cell with vanadium-doped TiO2 thin film showed slightly higher power conversion efficiency and great Jsc of 10.7 mA/cm2 compared with its pure counterpart. In the cells using 60 nm pure and vanadium-doped TiO2 layers, the cell using the doped layer showed much higher efficiency. It is remarkable that the external quantum efficiency of vanadium-doped TiO2 thin film was better in all wavelengths.

Application of real space Kerker method in simulating gate-all-around nanowire transistors with realistic discrete dopants

Chang-Sheng Li, Lei Ma, Jie-Rong Guo
Chin. Phys. B 2017, 26 (9): 097301;  doi: 10.1088/1674-1056/26/9/097301
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We adopt a self-consistent real space Kerker method to prevent the divergence from charge sloshing in the simulating transistors with realistic discrete dopants in the source and drain regions. The method achieves efficient convergence by avoiding unrealistic long range charge sloshing but keeping effects from short range charge sloshing. Numerical results show that discrete dopants in the source and drain regions could have a bigger influence on the electrical variability than the usual continuous doping without considering charge sloshing. Few discrete dopants and the narrow geometry create a situation with short range Coulomb screening and oscillations of charge density in real space. The dopants induced quasi-localized defect modes in the source region experience short range oscillations in order to reach the drain end of the device. The charging of the defect modes and the oscillations of the charge density are identified by the simulation of the electron density.

Polaron effects in cylindrical GaAs/AlxGa1-xAs core-shell nanowires

Hui Sun, Bing-Can Liu, Qiang Tian
Chin. Phys. B 2017, 26 (9): 097302;  doi: 10.1088/1674-1056/26/9/097302
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By the fractal dimension method, the polaron properties in cylindrical GaAs/AlxGa1-xAs core-shell nanowire are explored. In this study, the polaron effects in GaAs/AlxGa1-xAs core-shell nanowire at different values of shell width and aluminum concentration are discussed. The polaron binding energy, polaron mass shift and fractal dimension parameter are numerically worked out each as a function of core radius. The calculation results show that the binding energy and mass shift of the polaron first increase and then decrease as the core radius increases, forming their corresponding maximum values for different aluminum concentrations at a given shell width. Polaron problems in the cylindrical GaAs/AlxGa1-xAs core-shell nanowire are solved simply by using the fractal dimension method to avoid complex and lengthy calculations.

Tunneling field effect transistors based on in-plane and vertical layered phosphorus heterostructures

Shenyan Feng, Qiaoxuan Zhang, Jie Yang, Ming Lei, Ruge Quhe
Chin. Phys. B 2017, 26 (9): 097401;  doi: 10.1088/1674-1056/26/9/097401
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Tunneling field effect transistors (TFETs) based on two-dimensional materials are promising contenders to the traditional metal oxide semiconductor field effect transistor, mainly due to potential applications in low power devices. Here, we investigate the TFETs based on two different integration types: in-plane and vertical heterostructures composed of two kinds of layered phosphorous (β-P and δ-P) by ab initio quantum transport simulations. NDR effects have been observed in both in-plane and vertical heterostructures, and the effects become significant with the highest peak-to-valley ratio (PVR) when the intrinsic region length is near zero. Compared with the in-plane TFET based on β-P and δ-P, better performance with a higher on/off current ratio of ~106 and a steeper subthreshold swing (SS) of ~23 mV/dec is achieved in the vertical TFET. Such differences in the NDR effects, on/off current ratio and SS are attributed to the distinct interaction nature of the β-P and δ-P layers in the in-plane and vertical heterostructures.

Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni48-xCo2Mn38+xSn12 (x = 0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys

Ishfaq Ahmad Shah, Najam ul Hassan, Abdur Rauf, Jun Liu, Yuanyuan Gong, Guizhou Xu, Feng Xu
Chin. Phys. B 2017, 26 (9): 097501;  doi: 10.1088/1674-1056/26/9/097501
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An investigation on the magnetostructural transformation and magnetocaloric properties of Ni48-xCo2Mn38+xSn12 (x=0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys is carried out. With the partial replacement of Ni by Mn in the Ni48Co2Mn38Sn12 alloy, the electron concentration decreases. As a result, the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite. Thus, the samples with x=1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature. The structural transformation can be induced not only by the temperature, but also by the magnetic field. Accompanied by the magnetic-field-induced magnetostructural transformation, a considerable magnetocaloric effect is observed. With the increase of x, the maximum entropy change decreases, but the effective magnetic cooling capacity increases.

Nonvolatile control of transport and magnetic properties in magnetoelectric heterostructures by electric field

Qian Li, Dun-Hui Wang, Qing-Qi Cao, You-Wei Du
Chin. Phys. B 2017, 26 (9): 097502;  doi: 10.1088/1674-1056/26/9/097502
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Nonvolatile manipulation of transport and magnetic properties by external electric field is significant for information storage. In this study, we investigate the electric field control of resistance and magnetization in a magnetoelectric heterostructure comprising an electronic phase-separated La0.325Pr0.3Ca0.375MnO3 (LPCMO) thin film and a ferroelectric (011)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) substrate. In a room-temperature poled sample, the metal-to-insulator transition temperature of an LPCMO film increases and the resistance decreases with variation in the effect of the remnant strain. Meanwhile, the increase in the magnetization of the sample is observed as well. This effect would be beneficial for the development of novel storage devices with low power consumption.

Magnetic properties of AlN monolayer doped with group 1A or 2A nonmagnetic element: First-principles study

Ruilin Han, Xiaoyang Chen, Yu Yan
Chin. Phys. B 2017, 26 (9): 097503;  doi: 10.1088/1674-1056/26/9/097503
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The electronic structure, magnetic properties, and mechanism of magnetization in two-dimensional (2D) aluminum nitride (AlN) monolayer doped with nonmagnetic elements of group 1A (Li, Na, K) or group 2A (Be, Mg, Ca) were systematically investigated using first-principles studies. Numerical results reveal that the total magnetic moments produced by group 1A and group 2A nonmagnetic doping are 2.0μB and 1.0μB per supercell, respectively. The local magnetic moments of the three N atoms around the doping atom are the primary moment contributors for all these doped AlN monolayers. The p orbital of the dopant atom contributes little to the total magnetic moment, but it influences adjacent atoms significantly, changing their density of states distribution, which results in hybridization among the p orbitals of the three closest N atoms, giving rise to magnetism. Moreover, the doped AlN monolayer, having half-metal characteristics, is a likely candidate for spintronic applications. When two group 1A or group 2A atoms are inserted, their moments are long-range ferromagnetically coupled. Remarkably, the energy of formation shows that, if the monolayer has been grown under N-rich conditions, substitution of a group 2A atom at an Al site is easier than substitution of a group 1A atom.

Large tunable FMR frequency shift by magnetoelectric coupling in oblique-sputtered Fe52.5Co22.5B25.0/PZN-PT multiferroic heterostructure

Zhi-Peng Shi, Xiao-Min Liu, Shan-Dong Li
Chin. Phys. B 2017, 26 (9): 097601;  doi: 10.1088/1674-1056/26/9/097601
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In this study, we observe a strong inverse magnetoelectric coupling in Fe52.5Co22.5B25.0/PZN-PT multiferroic heterostructure, which produces large electric field (E-field) tunability of microwave magnetic properties. With the increase of the E-field from 0 to 8 kV/cm, the magnetic anisotropy field Heff is dramatically enhanced from 169 to 600 Oe, which further leads to a significant enhancement of ferromagnetic resonance frequency from 4.57 to 8.73 GHz under zero bias magnetic field, and a simultaneous decrease of the damping constant α from 0.021 to 0.0186. These features demonstrate that this multiferroic composite is a promising candidate for fabricating E-field tunable microwave components.

Electronic structure and photoluminescence property of a novel white emission phosphor Na3MgZr(PO4)3:Dy3+ for warm white light emitting diodes

Ge Zhu, Zhuo-Wei Li, Chuang Wang, Fa-Guang Zhou, Yan Wen, Shuang-Yu Xin
Chin. Phys. B 2017, 26 (9): 097801;  doi: 10.1088/1674-1056/26/9/097801
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To explore suitable single-phase white emission phosphors for warm white light emitting diodes, a series of novel phosphors Na3MgZr(PO4)3:xDy3+ (0≤ x≤ 0.03) is prepared, and their phase purities as well as photoluminescence properties are discussed in depth via x-ray diffraction structure refinement and photoluminescence spectrum measurement. The electronic structure properties of the Na3MgZr(PO4)3 host are calculated. The results reveal that Na3MgZr(PO4)3 possesses a direct band gap with a band gap value of 4.917 eV. The obtained Na3MgZr(PO4)3:Dy3+ phosphors are all well crystallized in trigonal structure with space group R3c, which has strong absorption around 365 nm and can generate warm white light emissions peaking at 487, 576, and 673 nm upon ultraviolet excitation, which are attributed to the transitions from 4F9/2 to 6H15/2, 6H13/2, and 6H11/2 of Dy3+ ions, respectively. The optimal doping content, critical distance, decay time, and Commission International de L'Eclairage (CIE) chromaticity coordinates are investigated in Dy3+ ion-doped Na3MgZr(PO4)3. The thermal quenching analysis shows that Na3MgZr(PO4)3:Dy3+ has a good thermal stability, and the thermal activation energy is calculated. The performances of Na3MgZr(PO4)3:Dy3+ make it a potential single-phase white emission phosphor for warm white light emitting diode.

Optical response of tunable terahertz plasmon in a grating-gated graphene transistor

Bo Yan, Jingyue Fang, Shiqiao Qin, Yongtao Liu, Li Chen, Shuang Chen, Renbing Li, Zhen Han
Chin. Phys. B 2017, 26 (9): 097802;  doi: 10.1088/1674-1056/26/9/097802
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Tunable terahertz plasmon in a graphene-based device with a grating serving as a top gate is studied. Transmission spectra exhibit a distinct peak in the terahertz region when the terahertz electric field is perpendicular to the grating fingers. Our results show that the extinction in the transmission of single-layer graphene shields beyond 80%. Electronic results further show that the graphene plasmon can be weakly adjusted by tuning the gate voltage. Theoretical calculation also implies that the plasmon frequency of graphene can fall into the terahertz region of 1-2 THz by improving the sustaining ability and capacitance of the top gate.

A synthetic semi-empirical physical model of secondary electron yield of metals under E-beam irradiation

Guo-Bao Feng, Wan-Zhao Cui, Na Zhang, Meng Cao, Chun-Liang Liu
Chin. Phys. B 2017, 26 (9): 097901;  doi: 10.1088/1674-1056/26/9/097901
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Calculations of secondary electron yield (SEY) by physical formula can hardly accord with experimental results precisely. Simplified descriptions of internal electron movements in the calculation and complex surface contamination states of real sample result in notable difference between simulations and experiments. In this paper, in order to calculate SEY of metal under complicated surface state accurately, we propose a synthetic semi-empirical physical model. The processes of excitation of internal secondary electron (SE) and movement toward surface can be simulated using this model. This model also takes into account the influences of incident angle and backscattering electrons as well as the surface gas contamination. In order to describe internal electronic states accurately, the penetration coefficient of incident electron is described as a function of material atom number. Directions of internal electrons are set to be uniform in each angle. The distribution of internal SEs is proposed by considering both the integration convergence and the cascade scattering process. In addition, according to the experiment data, relationship among desorption gas quantities, sample ultimate temperature and SEY is established. Comparing with experiment results, this synthetic semi-empirical physical model can describe the SEY of metal better than former formulas, especially in the aspect of surface contaminated states. The proposed synthetic semi-empirical physical model and presented results in this paper can be helpful for further studying SE emission, and offer an available method for estimating and taking advantage of SE emission accurately.

Synthesis of diamonds in Fe—C systems using nitrogen and hydrogen co-doped impurities under HPHT

Shi-Shuai Sun, Zhi-Hui Xu, Wen Cui, Xiao-Peng Jia, Hong-An Ma
Chin. Phys. B 2017, 26 (9): 098101;  doi: 10.1088/1674-1056/26/9/098101
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In this study, we investigate the effect of nitrogen and hydrogen impurities on colors, morphologies, impurity structures and synthesis conditions of diamond crystals in Fe-C systems with C3N6H6 additives at pressures in the range 5.0-6.5 GPa and temperatures of 1400-1700 ℃ in detail. Our results reveal that the octahedron diamond nucleation in a Fe-C system is evidently inhibited by co-doped N-H elements, thereby resulting in the increase of minimum pressure and temperature of diamond synthesis by spontaneous nucleation. The octahedron diamond crystals synthesized from a pure Fe-C system are colorless, while they become green in the system with C3N6H6 additive. The surface defects of diamond will deteriorate when the nitrogen and hydrogen atoms simultaneously incorporate in the diamond growth environment in the Fe-C system. We believe that this study will provide some important information and be beneficial for the deep understanding of the crystallization of diamonds from different component systems.

Silicon quantum dots delivered phthalocyanine for fluorescence guided photodynamic therapy of tumor

Jiao-Jiao Liu, Qi Chang, Mei-Mei Bao, Bing Yuan, Kai Yang, Yu-Qiang Ma
Chin. Phys. B 2017, 26 (9): 098102;  doi: 10.1088/1674-1056/26/9/098102
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Imaging-guided cancer therapy provides a simultaneous tumor imaging and treatment, which helps to eliminate the excessive toxicity to the healthy tissues. For this purpose, multifunctional probes capable of both imaging and curing are needed. In this work, we synthesize water-soluble silicon quantum dots (Si QDs) smaller than 5 nm. Such Si QDs are used for delivering the hydrophobic drug phthalocyanine (Pc). The as-prepared Si/Pc nanocomposite particles show efficient transmembrane delivery into cells and feasible biocompatibility. Moreover, these composite particles emit dual-channel fluorescence signals even after cellular internalization and demonstrate robust photostability in the Si channel. More interestingly, the Si/Pc composite particles show efficient photodynamic therapy effects against tumors both in vitro and in vivo.

Crystalline silicon surface passivation investigated by thermal atomic-layer-deposited aluminum oxide

Cai-Xia Hou, Xin-He Zheng, Rui Jia, Ke Tao, San-Jie Liu, Shuai Jiang, Peng-Fei Zhang, Heng-Chao Sun, Yong-Tao Li
Chin. Phys. B 2017, 26 (9): 098103;  doi: 10.1088/1674-1056/26/9/098103
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Atomic-layer-deposited (ALD) aluminum oxide (Al2O3) has demonstrated an excellent surface passivation for crystalline silicon (c-Si) surfaces, as well as for highly boron-doped c-Si surfaces. In this paper, water-based thermal atomic layer deposition of Al2O3 films are fabricated for c-Si surface passivation. The influence of deposition conditions on the passivation quality is investigated. The results show that the excellent passivation on n-type c-Si can be achieved at a low thermal budget of 250 ℃given a gas pressure of 0.15 Torr. The thickness-dependence of surface passivation indicates that the effective minority carrier lifetime increases drastically when the thickness of Al2O3 is larger than 10 nm. The influence of thermal post annealing treatments is also studied. Comparable carrier lifetime is achieved when Al2O3 sample is annealed for 15 min in forming gas in a temperature range from 400 ℃to 450 °C. In addition, the passivation quality can be further improved when a thin PECVD-SiNx cap layer is prepared on Al2O3, and an effective minority carrier lifetime of 2.8 ms and implied Voc of 721 mV are obtained. In addition, several novel methods are proposed to restrain blistering.

Material microstructures analyzed by using gray level Co-occurrence matrices

Yansu Hu, Zhijun Wang, Xiaoguang Fan, Junjie Li, Ang Gao
Chin. Phys. B 2017, 26 (9): 098104;  doi: 10.1088/1674-1056/26/9/098104
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The mechanical properties of materials greatly depend on the microstructure morphology. The quantitative characterization of material microstructures is essential for the performance prediction and hence the material design. At present, the quantitative characterization methods mainly rely on the microstructure characterization of shape, size, distribution, and volume fraction, which related to the mechanical properties. These traditional methods have been applied for several decades and the subjectivity of human factors induces unavoidable errors. In this paper, we try to bypass the traditional operations and identify the relationship between the microstructures and the material properties by the texture of image itself directly. The statistical approach is based on gray level Co-occurrence matrix (GLCM), allowing an objective and repeatable study on material microstructures. We first present how to identify GLCM with the optimal parameters, and then apply the method on three systems with different microstructures. The results show that GLCM can reveal the interface information and microstructures complexity with less human impact. Naturally, there is a good correlation between GLCM and the mechanical properties.

Performance enhancement of CMOS terahertz detector by drain current

Xingxing Zhang, Xiaoli Ji, Yiming Liao, Jingyu Peng, Chenxin Zhu, Feng Yan
Chin. Phys. B 2017, 26 (9): 098401;  doi: 10.1088/1674-1056/26/9/098401
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In this paper, we study the effect of the drain current on terahertz detection for Si metal-oxide semiconductor field-effect transistors (MOSFETs) both theoretically and experimentally. The analytical model, which is based on the small-signal equivalent circuit of MOSFETs, predicts the significant improvement of the voltage responsivity Rv with the bias current. The experiment on antennas integrated with MOSFETs agrees with the analytical model, but the Rv improvement is accompanied first by a decrease, then an increase of the low-noise equivalent power (NEP) with the applied current. We determine the tradeoff between the low-NEP and high-Rv for the current-biased detectors. As the best-case scenario, we obtained an improvement of about six times in Rv without the cost of a higher NEP. We conclude that the current supply scheme can provide high-quality signal amplification in practical CMOS terahertz detection.

Modulation depth of series SQUIDs modified by Josephson junction area

Jie Liu, He Gao, Gang Li, Zheng Wei Li, Kamal Ahmada, Zhang Ying Shan, Jian She Liu, Wei Chen
Chin. Phys. B 2017, 26 (9): 098501;  doi: 10.1088/1674-1056/26/9/098501
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The superconducting quantum interference device (SQUID) amplifier is widely used in the field of weak signal detection for its low input impedance, low noise, and low power consumption. In this paper, the SQUIDs with identical junctions and the series SQUIDs with different junctions were successfully fabricated. The Nb/Al-AlOx/Nb trilayer and input Nb coils were prepared by asputtering equipment. The SQUID devices were prepared by a sputtering and the lift-off method. Investigations by AFM, OM and SEM revealed the morphology and roughness of the Nb films and Nb/Al-AlOx/Nb trilayer. In addition, the current-voltage characteristics of the SQUID devices with identical junction and different junction areas were measured at 2.5 K in the He3 refrigerator. The results show that the SQUID modulation depth is obviously affected by the junction area. The modulation depth obviously increases with the increase of the junction area in a certain range. It is found that the series SQUID with identical junction area has a transimpedance gain of 58 Ω approximately.

Improved high-frequency equivalent circuit model based on distributed effects for SiGe HBTs with CBE layout

Ya-Bin Sun, Xiao-Jin Li, Jin-Zhong Zhang, Yan-Ling Shi
Chin. Phys. B 2017, 26 (9): 098502;  doi: 10.1088/1674-1056/26/9/098502
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In this paper, we present an improved high-frequency equivalent circuit for SiGe heterojunction bipolar transistors (HBTs) with a CBE layout, where we consider the distributed effects along the base region. The actual device structure is divided into three parts: a link base region under a spacer oxide, an intrinsic transistor region under the emitter window, and an extrinsic base region. Each region is considered as a two-port network, and is composed of a distributed resistance and capacitance. We solve the admittance parameters by solving the transmission-line equation. Then, we obtain the small-signal equivalent circuit depending on the reasonable approximations. Unlike previous compact models, in our proposed model, we introduce an additional internal base node, and the intrinsic base resistance is shifted into this internal base node, which can theoretically explain the anomalous change in the intrinsic bias-dependent collector resistance in the conventional compact model.

Impact of Al addition on the formation of Ni germanosilicide layers under different temperature annealing

Xiao-Ran Meng, Yun-Xia Ping, Wen-Jie Yu, Zhong-Ying Xue, Xing Wei, Miao Zhang, Zeng-Feng Di, Bo Zhang, Qing-Tai Zhao
Chin. Phys. B 2017, 26 (9): 098503;  doi: 10.1088/1674-1056/26/9/098503
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Solid reactions between Ni and relaxed Si0.7Ge0.3 substrate were systematically investigated with different Al interlayer thicknesses. The morphology, composition, and micro-structure of the Ni germanosilicide layers were analyzed with different annealing temperatures in the appearance of Al. The germanosilicide layers were characterized by Rutherford backscattering spectrometry, cross-section transmission electron microscopy, scan transmission electron microscopy, and secondary ion mass spectroscopy. It was shown that the incorporation of Al improved the surface and interface morphology of the germanosilicide layers, enhanced the thermal stabilities, and retarded the Ni-rich germanosilicide phase to mono germanosilicide phase. With increasing annealing temperature, Al atoms distributed from the Ni/Si0.7Ge0.3 interface to the total layer of Ni2Si0.7Ge0.3, and finally accumulated at the surface of NiSi0.7Ge0.3. We found that under the assistance of Al atoms, the best quality Ni germanosilicide layer was achieved by annealing at 700 ℃ in the case of 3 nm Al.

Intrinsic relationship between photoluminescence and electrical characteristics in modulation Fe-doped AlGaN/GaN HEMTs

Jianfei Li, Yuanjie Lv, Changfu Li, Ziwu Ji, Zhiyong Pang, Xiangang Xu, Mingsheng Xu
Chin. Phys. B 2017, 26 (9): 098504;  doi: 10.1088/1674-1056/26/9/098504
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The photoluminescence (PL) and electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) with different Fe doping concentrations in the GaN buffer layers were studied. It was found that, at low Fe doping concentrations, the introduction of Fe atoms can result in a downward shift of the Fermi level in the GaN buffer layer, since the Fe atoms substitute Ga and introduce an FeGa3+/2+ acceptor level. This results in a decrease in the yellow luminescence (YL) emission intensity accompanied by the appearance of an infrared (IR) emission, and a decrease in the off-state buffer leakage current (BLC). However, a further increase in the Fe doping concentration will conversely result in the upward shift of the Fermi level due to the incorporation of O donors under the large flow rate of the Fe source. This results in an increased YL emission intensity accompanied by a decrease in the IR emission intensity, and an increase in the BLC. The intrinsic relationship between the PL and BLC characteristics is expected to provide a simple and effective method to understand the variation of the electrical characteristic in the modulation Fe-doped HEMTs by optical measurements.

Experimental and simulation studies of single-event transient in partially depleted SOI MOSFET

Wei-Wei Yan, Lin-Chun Gao, Xiao-Jing Li, Fa-Zhan Zhao, Chuan-Bin Zeng, Jia-Jun Luo, Zheng-Sheng Han
Chin. Phys. B 2017, 26 (9): 098505;  doi: 10.1088/1674-1056/26/9/098505
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In this study, we investigate the single-event transient (SET) characteristics of a partially depleted silicon-on-insulator (PDSOI) metal-oxide-semiconductor (MOS) device induced by a pulsed laser.We measure and analyze the drain transient current at the wafer level. The results indicate that the body-drain junction and its vicinity are more SET sensitive than the other regions in PD-SOI devices.We use ISE 3D simulation tools to analyze the SET response when different regions of the device are hit. Then, we discuss in detail the characteristics of transient currents and the electrostatic potential distribution change in devices after irradiation. Finally, we analyze the parasitic bipolar junction transistor (p-BJT) effect by performing both a laser test and simulations.

Performance of dual-band short- or mid-wavelength infrared photodetectors based on InGaAsSb bulk materials and InAs/GaSb superlattices

Yao-yao Sun, Yue-xi Lv, Xi Han, Chun-yan Guo, Zhi Jiang, Hong-yue Hao, Dong-wei Jiang, Guo-wei Wang, Ying-qiang Xu, Zhi-chuan Niu
Chin. Phys. B 2017, 26 (9): 098506;  doi: 10.1088/1674-1056/26/9/098506
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In this paper, we demonstrate bias-selectable dual-band short- or mid-wavelength infrared photodetectors based on In0.24Ga0.76As0.21Sb0.79 bulk materials and InAs/GaSb type-II superlattices with cutoff wavelengths of 2.2 μm and 3.6 μ m, respectively. At 200 K, the short-wave channel exhibits a peak quantum efficiency of 42% and a dark current density of 5.93×10-5 A/cm2 at 500 mV, thereby providing a detectivity of 1.55×1011 cm·Hz1/2/W. The mid-wave channel exhibits a peak quantum efficiency of 31% and a dark current density of 1.22×10-3 A/cm2 at -300 mV, thereby resulting in a detectivity of 2.71×1010 cm·Hz1/2/W. Moreover, we discuss the band alignment and spectral cross-talk of the dual-band n-i-p-p-i-n structure.

Lowering the driving voltage and improving the luminance of blue fluorescent organic light-emitting devices by thermal annealing a hole injection layer of pentacene

Jian Gao, Qian-Qian Yu, Juan Zhang, Yang Liu, Ruo-Fei Jia, Jun Han, Xiao-Ming Wu, Yu-Lin Hua, Shou-Gen Yin
Chin. Phys. B 2017, 26 (9): 098507;  doi: 10.1088/1674-1056/26/9/098507
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We chose pentacene as a hole injection layer (HIL) to fabricate the high performance blue fluorescent organic light-emitting devices (OLEDs). We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120 °C. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120 ℃ annealed pentacene film and n-doped electron transport layer (ETL) presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.

Gas-sensor property of single-molecule device: F2 adsorbing effect

Zong-Liang Li, Jun-Jie Bi, Ran Liu, Xiao-Hua Yi, Huan-Yan Fu, Feng Sun, Ming-Zhi Wei, Chuan-Kui Wang
Chin. Phys. B 2017, 26 (9): 098508;  doi: 10.1088/1674-1056/26/9/098508
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The single thiolated arylethynylene molecule with 9,10-dihydroanthracene core (denoted as TADHA) possesses pronounced negative differential conductance (NDC) behavior at lower bias regime. The adsorption effects of F2 molecule on the current and NDC behavior of TADHA molecular junctions are studied by applying non-equilibrium Green's formalism combined with density functional theory. The numerical results show that the F2 molecule adsorbed on the benzene ring of TADHA molecule near the electrode can dramatically suppresses the current of TADHA molecular junction. When the F2 molecule adsorbed on the conjugated segment of 9,10-dihydroanthracene core of TADHA molecule, an obviously asymmetric effect on the current curves induces the molecular system showing apparent rectifier behavior. However, the current especially the NDC behavior have been significantly enlarged when F2 addition reacted with triple bond of TADHA molecule.

Spin-dependent transport characteristics of nanostructures based on armchair arsenene nanoribbons

Kai-Wei Yang, Ming-Jun Li, Xiao-Jiao Zhang, Xin-Mei Li, Yong-Li Gao, Meng-Qiu Long
Chin. Phys. B 2017, 26 (9): 098509;  doi: 10.1088/1674-1056/26/9/098509
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By employing non-equilibrium Green's function combined with the spin-polarized density-functional theory, we investigate the spin-dependent electronic transport properties of armchair arsenene nanoribbons (aAsNRs). Our results show that the spin-metal and spin-semiconductor properties can be observed in aAsNRs with different widths. We also find that there is nearly 100% bipolar spin-filtering behavior in the aAsNR-based device with antiparallel spin configuration. Moreover, rectifying behavior and giant magnetoresistance are found in the device. The corresponding physical analyses have been given.

Heat transfer enhancement in MOSFET mounted on different FR4 substrates by thermal transient measurement

Norazlina M S, Dheepan Chakravarthii M K, Shanmugan S, Mutharasu D, Shahrom Mahmud
Chin. Phys. B 2017, 26 (9): 098901;  doi: 10.1088/1674-1056/26/9/098901
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Miniaturization of electronic package leads to high heat density and heat accumulation in electronics device, resulting in short life time and premature failure of the device. Junction temperature and thermal resistance are the critical parameters that determine the thermal management and reliability in electronics cooling. Metal oxide field effect transistor (MOSFET) is an important semiconductor device for light emitting diode-integrated circuit (LED IC) driver application, and thermal management in MOSFET is a major challenge. In this study, investigations on thermal performance of MOSFET are performed for evaluating the junction temperature and thermal resistance. Suitable modifications in FR4 substrates are proposed by introducing thermal vias and copper layer coating to improve the thermal performance of MOSFET. Experiments are conducted using thermal transient tester (T3ster) at 2.0 A input current and ambient temperature varying from 25 ℃to 75 °C. The thermal parameters are measured for three proposed designs: FR4 with circular thermal vias, FR4 with single strip of copper layer and embedded vias, and FR4 with I-shaped copper layer, and compared with that of plain FR4 substrate. From the experimental results, FR4I-shaped shows promising results by 33.71% reduction in junction temperature and 54.19% reduction in thermal resistance. For elevated temperature, the relative increases in junction temperature and thermal resistance are lower for FR4I-shaped than those for other substrates considered. The introduction of thermal vias and copper layer plays a significant role in thermal performance.

Analysis of dynamic features in intersecting pedestrian flows

Hai-Rong Dong, Qi Meng, Xiu-Ming Yao, Xiao-Xia Yang, Qian-Ling Wang
Chin. Phys. B 2017, 26 (9): 098902;  doi: 10.1088/1674-1056/26/9/098902
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This paper focuses on the simulation analysis of stripe formation and dynamic features of intersecting pedestrian flows. The intersecting flows consist of two streams of pedestrians and each pedestrian stream has a desired walking direction. The model adopted in the simulations is the social force model, which can reproduce the self-organization phenomena successfully. Three scenarios of different cross angles are established. The simulations confirm the empirical observations that there is a stripe formation when two streams of pedestrians intersect and the direction of the stripes is perpendicular to the sum of the directional vectors of the two streams. It can be concluded from the numerical simulation results that smaller cross angle results in higher mean speed and lower level of speed fluctuation. Moreover, the detailed pictures of pedestrians' moving behavior at intersections are given as well.

Collective motion of active particles in environmental noise

Qiu-shi Chen, Ming Ji
Chin. Phys. B 2017, 26 (9): 098903;  doi: 10.1088/1674-1056/26/9/098903
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We study the collective motion of active particles in environmental noise, where the environmental noise is caused by noise particles randomly diffusing in two-dimensional space. We show that active particles in a noisy environment can self organize into three typical phases: polar liquid, band, and disordered gas states. In our model, the transition between band and disordered gas states is discontinuous. Giant number fluctuation is observed in the polar liquid phase. We also compare our results with the Vicsek model and show that the interaction with noise particles can stabilize the band state to very low noise condition. This band structure could recruit most of the active particles in the system, which greatly enhances the coherence of the system. Our findings of complex collective behaviors in environmental noise help us to understand how individuals modify their self-organization by environmental factors, which may further contribute to improving the design of collective migration and navigation strategies.

Temperature dependence of heat conduction coefficient in nanotube/nanowire networks

Kezhao Xiong, Zonghua Liu
Chin. Phys. B 2017, 26 (9): 098904;  doi: 10.1088/1674-1056/26/9/098904
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Studies on heat conduction are so far mainly focused on regular systems such as the one-dimensional (1D) and two-dimensional (2D) lattices where atoms are regularly connected and temperatures of atoms are homogeneously distributed. However, realistic systems such as the nanotube/nanowire networks are not regular but heterogeneously structured, and their heat conduction remains largely unknown. We present a model of quasi-physical networks to study heat conduction in such physical networks and focus on how the network structure influences the heat conduction coefficient κ. In this model, we for the first time consider each link as a 1D chain of atoms instead of a spring in the previous studies. We find that κ is different from link to link in the network, in contrast to the same constant in a regular 1D or 2D lattice. Moreover, for each specific link, we present a formula to show how κ depends on both its link length and the temperatures on its two ends. These findings show that the heat conduction in physical networks is not a straightforward extension of 1D and 2D lattices but seriously influenced by the network structure.

Air breakdown induced by the microwave with two mutually orthogonal and heterophase electric field components

Pengcheng Zhao, Lixin Guo
Chin. Phys. B 2017, 26 (9): 099201;  doi: 10.1088/1674-1056/26/9/099201
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The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.

Relationship measurement between ac-Stark shift of 40Ca+ clock transition and laser polarization direction

Hong-Fang Song, Shao-Long Chen, Meng-Yan Zeng, Yao Huang, Hu Shao, Yong-Bo Tang, Hua Guan, Ke-Lin Gao
Chin. Phys. B 2017, 26 (9): 099501;  doi: 10.1088/1674-1056/26/9/099501
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Ac-Stark shift of atom levels is caused by an ac-electromagnetic field. As an electromagnetic wave, laser light does induce ac-Stark shift. It is proved experimentally that if the light is linearly polarized, the dynamic polarizability changes with polarization direction. The polarization direction of the linearly-polarized laser is tuned by 720°, and the ac-Stark shifts of the 4S1/2, m= 1/2→3D5/2, m= 1/2 clock transitions in 40Ca+ are measured in steps of 10°. The frequency shifts change with laser polarization in a periodical manner and have values opposite to each other.

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