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Chin. Phys. B  
  Chin. Phys. B--2015, Vol.24, No.2
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Conservation laws of the generalized short pulse equation

Zhang Zhi-Yong, Chen Yu-Fu
Chin. Phys. B 2015, 24 (2): 020201;  doi: 10.1088/1674-1056/24/2/020201
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We show that the generalized short pulse equation is nonlinearly self-adjoint with differential substitution. Moreover, any adjoint symmetry is a differential substitution of nonlinear self-adjointness, and vice versa. Consequently, the general conservation law formula is constructed and new conservation laws for some special cases are found.

Self-adjusting entropy-stable scheme for compressible Euler equations

Cheng Xiao-Han, Nie Yu-Feng, Feng Jian-Hu, Luo Xiao-Yu, Cai Li
Chin. Phys. B 2015, 24 (2): 020202;  doi: 10.1088/1674-1056/24/2/020202
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In this work, a self-adjusting entropy-stable scheme is proposed for solving compressible Euler equations. The entropy-stable scheme is constructed by combining the entropy conservative flux with a suitable diffusion operator. The entropy has to be preserved in smooth solutions and be dissipated at shocks. To achieve this, a switch function, which is based on entropy variables, is employed to make the numerical diffusion term be automatically added around discontinuities. The resulting scheme is still entropy-stable. A number of numerical experiments illustrating the robustness and accuracy of the scheme are presented. From these numerical results, we observe a remarkable gain in accuracy.

Containment consensus with measurement noises and time-varying communication delays

Zhou Feng, Wang Zheng-Jie, Fan Ning-Jun
Chin. Phys. B 2015, 24 (2): 020203;  doi: 10.1088/1674-1056/24/2/020203
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In this paper, we consider the containment consensus control problem for multi-agent systems with measurement noises and time-varying communication delays under directed networks. By using stochastic analysis tools and algebraic graph theory, we prove that the followers can converge to the convex hull spanned by the leaders in the sense of mean square if the allowed upper bound of the time-varying delays satisfies a certain sufficient condition. Moreover, the time-varying delays are asymmetric for each follower agent, and the time-delay-dependent consensus condition is derived. Finally, numerical simulations are provided to illustrate the effectiveness of the obtained theoretical results.

Response of a Duffing—Rayleigh system with a fractional derivative under Gaussian white noise excitation

Zhang Ran-Ran, Xu Wei, Yang Gui-Dong, Han Qun
Chin. Phys. B 2015, 24 (2): 020204;  doi: 10.1088/1674-1056/24/2/020204
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In this paper, we consider the response analysis of a Duffing-Rayleigh system with fractional derivative under Gaussian white noise excitation. A stochastic averaging procedure for this system is developed by using the generalized harmonic functions. First, the system state is approximated by a diffusive Markov process. Then, the stationary probability densities are derived from the averaged Itô stochastic differential equation of the system. The accuracy of the analytical results is validated by the results from the Monte Carlo simulation of the original system. Moreover, the effects of different system parameters and noise intensity on the response of the system are also discussed.

From fractional Fourier transformation to quantum mechanical fractional squeezing transformation

Lv Cui-Hong, Fan Hong-Yi, Li Dong-Wei
Chin. Phys. B 2015, 24 (2): 020301;  doi: 10.1088/1674-1056/24/2/020301
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By converting the triangular functions in the integration kernel of the fractional Fourier transformation to the hyperbolic function, i.e., tanα→tanhα,sinα→sinhα, we find the quantum mechanical fractional squeezing transformation (FrST) which satisfies additivity. By virtue of the integration technique within the ordered product of operators (IWOP) we derive the unitary operator responsible for the FrST, which is composite and is made of eiπa*a/2 and exp[ia/2(a2+a*2)]. The FrST may be implemented in combinations of quadratic nonlinear crystals with different phase mismatches.

Unified treatment of the bound states of the Schiöberg and the Eckart potentials using Feynman path integral approach

A. Diaf
Chin. Phys. B 2015, 24 (2): 020302;  doi: 10.1088/1674-1056/24/2/020302
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We obtain analytical expressions for the energy eigenvalues of both the Schiöberg and Eckart potentials using an approximation of the centrifugal term. In order to determine the l-states solutions, we use the Feynman path integral approach to quantum mechanics. We show that by performing nonlinear space-time transformations in the radial path integral, we can derive a transformation formula that relates the original path integral to the Green function of a new quantum solvable system. The explicit expression of bound state energy is obtained and the associated eigenfunctions are given in terms of hypergeometric functions. We show that the Eckart potential can be derived from the Schiöberg potential. The obtained results are compared to those produced by other methods and are found to be consistent.

Two-electron quantum ring in short pulses

Poonam Silotia, Rakesh Kumar Meena, Vinod Prasad
Chin. Phys. B 2015, 24 (2): 020303;  doi: 10.1088/1674-1056/24/2/020303
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The response of a two-electron quantum ring system to the short laser pulses of different shapes in the presence of external static electric field is studied. The variation of transition probabilities of the two-electron quantum ring from ground state to excited states with a number of parameters is shown and explained. The energy levels and wavefunctions of the system in the presence of static electric field are found by solving the time-independent Schrödinger equation numerically by the finite difference method. The shape of the pulse plays a dominant role on the dynamics.

Quantum communication for satellite-to-ground networks with partially entangled states

Chen Na, Quan Dong-Xiao, Pei Chang-Xing, Yang-Hong
Chin. Phys. B 2015, 24 (2): 020304;  doi: 10.1088/1674-1056/24/2/020304
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To realize practical wide-area quantum communication, a satellite-to-ground network with partially entangled states is developed in this paper. For efficiency and security reasons, the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network. Based on this point, an efficient and secure quantum communication scheme with partially entangled states is presented. In our scheme, the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states. Thus, the security of quantum communication is guaranteed. The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices. Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high. In addition, the auxiliary quantum bit provides a heralded mechanism for successful communication. Based on the critical components that are presented in this article an efficient, secure, and practical wide-area quantum communication can be achieved.

Time-bin-encoding-based remote states generation of nitrogen-vacancy centers through noisy channels

Su Shi-Lei, Chen Li, Guo Qi, Wang Hong-Fu, Zhu Ai-Dong, Zhang Shou
Chin. Phys. B 2015, 24 (2): 020305;  doi: 10.1088/1674-1056/24/2/020305
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We design proposals to generate a remote Greenberger-Horne-Zeilinger (GHZ) state and a W state of nitrogen-vacancy (NV) centers coupled to microtoroidal resonators (MTRs) through noisy channels by utilizing time-bin encoding processes and fast-optical-switch-based polarization rotation operations. The polarization and phase noise induced by noisy channels generally affect the time of state generation but not its success probability and fidelity. Besides, the above proposals can be generalized to n-qubit between two or among n remote nodes with success probability unity under ideal conditions. Furthermore, the proposals are robust for regular noise-changeable channels for the n-node case. This method is also useful in other remote quantum information processing tasks through noisy channels.

Concrete quantum tunneling spectrum of Schwarzschild black holes

Chen Si-Na, Zhang Jing-Yi
Chin. Phys. B 2015, 24 (2): 020401;  doi: 10.1088/1674-1056/24/2/020401
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In this paper, a canonical ensemble model for black hole quantum tunneling radiation is introduced. We find that the probability distribution function is the same as the emission rate of a spherical shell in the Parikh-Wilczek tunneling framework. With this model, the probability distribution function corresponding to the emission shell system is calculated. Therefore, the concrete quantum tunneling spectrum of the Schwarzschild black hole is obtained.

Applications of modularized circuit designs in a new hyper-chaotic system circuit implementation

Wang Rui, Sun Hui, Wang Jie-Zhi, Wang Lu, Wang Yan-Chao
Chin. Phys. B 2015, 24 (2): 020501;  doi: 10.1088/1674-1056/24/2/020501
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Modularized circuit designs for chaotic systems are introduced in this paper. Especially, a typical improved modularized design strategy is proposed and applied to a new hyper-chaotic system circuit implementation. In this paper, the detailed design procedures are described. Multisim simulations and physical experiments are conducted, and the simulation results are compared with Matlab simulation results for different system parameter pairs. These results are consistent with each other and they verify the existence of the hyper-chaotic attractor for this new hyper-chaotic system.

Complex dynamics analysis of impulsively coupled Duffing oscillators with ring structure

Jiang Hai-Bo, Zhang Li-Ping, Yu Jian-Jiang
Chin. Phys. B 2015, 24 (2): 020502;  doi: 10.1088/1674-1056/24/2/020502
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Impulsively coupled systems are high-dimensional non-smooth systems that can exhibit rich and complex dynamics. This paper studies the complex dynamics of a non-smooth system which is unidirectionally impulsively coupled by three Duffing oscillators in a ring structure. By constructing a proper Poincaré map of the non-smooth system, an analytical expression of the Jacobian matrix of Poincaré map is given. Two-parameter Hopf bifurcation sets are obtained by combining the shooting method and the Runge-Kutta method. When the period is fixed and the coupling strength changes, the system undergoes stable, periodic, quasi-periodic, and hyper-chaotic solutions, etc. Floquet theory is used to study the stability of the periodic solutions of the system and their bifurcations.

Recursion-transform approach to compute the resistance of a resistor network with an arbitrary boundary Hot!

Tan Zhi-Zhong
Chin. Phys. B 2015, 24 (2): 020503;  doi: 10.1088/1674-1056/24/2/020503
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We consider a profound problem of two-point resistance in the resistor network with a null resistor edge and an arbitrary boundary, which has not been solved before because the Green's function technique and the Laplacian matrix approach are invalid in this case. Looking for the exact solutions of resistance is important but difficult in the case of the arbitrary boundary since the boundary is a wall or trap which affects the behavior of a finite network. In this paper, we give a general resistance formula that is composed of a single summation by using the recursion-transform method. Meanwhile, several interesting results are derived by the general formula. Further, the current distribution is given explicitly as a byproduct of the method.

Antagonistic formation motion of cooperative agents

Lu Wan-Ting, Dai Ming-Xiang, Xue Fang-Zheng
Chin. Phys. B 2015, 24 (2): 020504;  doi: 10.1088/1674-1056/24/2/020504
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This paper investigates a new formation motion problem of a class of first-order multi-agent systems with antagonistic interactions. A distributed formation control algorithm is proposed for each agent to realize the antagonistic formation motion. A sufficient condition is derived to ensure that all of the agents make an antagonistic formation motion in a distributed manner. It is shown that all of the agents can be spontaneously divided into several groups and that agents in the same group collaborate while agents in different groups compete. Finally, a numerical simulation is included to demonstrate our theoretical results.

Computer simulation of the bombardment of a copper film on graphene with argon clusters

A. Y. Galashev, O. R. Rakhmanova
Chin. Phys. B 2015, 24 (2): 020701;  doi: 10.1088/1674-1056/24/2/020701
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The process of graphene cleaning of a copper film by bombarding it with Ar13 clusters is investigated by the molecular dynamics method. The kinetic energies of the clusters are 5, 10, 20, and 30 eV and the incident angles are θ = 90°, 75°, 60°, 45°, and 0°. It is obtained that the cluster energy should be in the interval 20 eV-30 eV for effective graphene cleaning. There is no cleaning effect at vertical incidence (θ = 0°) of Ar13 clusters. The bombardments at 45° and 90° incident angles are the most effective on a moderate and large amount of deposited copper, respectively.

Estimation of spatially distributed processes using mobile sensor networks with missing measurements

Jiang Zheng-Xian, Cui Bao-Tong
Chin. Phys. B 2015, 24 (2): 020702;  doi: 10.1088/1674-1056/24/2/020702
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This paper investigates the estimation problem for a spatially distributed process described by a partial differential equation with missing measurements. The randomly missing measurements are introduced in order to better reflect the reality in the sensor network. To improve the estimation performance for the spatially distributed process, a network of sensors which are allowed to move within the spatial domain is used. We aim to design an estimator which is used to approximate the distributed process and the mobile trajectories for sensors such that, for all possible missing measurements, the estimation error system is globally asymptotically stable in the mean square sense. By constructing Lyapunov functionals and using inequality analysis, the guidance scheme of every sensor and the convergence of the estimation error system are obtained. Finally, a numerical example is given to verify the effectiveness of the proposed estimator utilizing the proposed guidance scheme for sensors.

Onsager principle as a tool for approximation

Masao Doi
Chin. Phys. B 2015, 24 (2): 020505;  doi: 10.1088/1674-1056/24/2/020505
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Onsager principle is the variational principle proposed by Onsager in his celebrated paper on the reciprocal relation. The principle has been shown to be useful in deriving many evolution equations in soft matter physics. Here the principle is shown to be useful in solving such equations approximately. Two examples are discussed: the diffusion dynamics and gel dynamics. Both examples show that the present method is novel and gives new results which capture the essential dynamics in the system.

The influence of ablation products on the ablation resistance of C/C-SiC composites and the growth mechanism of SiO2 nanowires

Li Xian-Hui, Yan Qing-Zhi, Mi Ying-Ying, Han Yong-Jun, Wen Xin, Ge Chang-Chun
Chin. Phys. B 2015, 24 (2): 026103;  doi: 10.1088/1674-1056/24/2/026103
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Ablation under oxyacetylene torch with heat flux of 4186.8 (10% kW/m2 for 20 s was performed to evaluate the ablation resistance of C/C-SiC composites fabricated by chemical vapor infiltration (CVI) combined with liquid silicon infiltration (LSI) process. The results indicated that C/C-SiC composites present a better ablation resistance than C/C composites without doped SiC. The doped SiC and the ablation products SiO2 derived from it play key roles in ablation process. Bulk quantities of SiO2 nanowires with diameter of 80 nm-150 nm and length of tens microns were observed on the surface of specimens after ablation. The growth mechanism of the SiO2 nanowires was interpreted with a developed vapor-liquid-solid (VLS) driven by the temperature gradient.


Selection of quantum path in high-order harmonics and isolated sub-100 attosecond generation in few-cycle spatially inhomogeneous laser fields

Ge Xin-Lei, Du Hui, Wang Qun, Guo Jing, Liu Xue-Shen
Chin. Phys. B 2015, 24 (2): 023201;  doi: 10.1088/1674-1056/24/2/023201
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We theoretically study the selection of the quantum path in high-order harmonics (HHG) and isolated attosecond pulse generation from a one-dimensional (1D) model of a H2+ molecule in few-cycle inhomogeneous laser fields. We show that the inhomogeneity of the laser fields play an important role in the HHG process. The cutoff of the harmonics can be extended remarkably, and the harmonic spectrum becomes smooth and has fewer modulations. We investigate the time-frequency profile of the time-dependent dipole, which shows that the short quantum path is enhanced and the long quantum path disappears in spatially inhomogeneous fields. The semi-classical three-step model is also applied to illustrate the physical mechanism of HHG. The influence of driving field carrier-envelop phase (CEP) on HHG is also discussed. By superposing a series of properly selected harmonics, an isolated attosecond pulse (IAP) with duration 53 as can be obtained by a 15-fs, 1600-nm laser pulse with the parameter ε=0.0013 (ε is the parameter that determines the order of inhomogeneity of the laser field).

Responsive mechanism of 2-(2'-hydroxyphenyl)benzoxazole-based two-photon fluorescent probes for zinc and hydroxide ions

Zhang Yu-Jin, Zhang Qiu-Yue, Ding Hong-Juan, Song Xiu-Neng, Wang Chuan-Kui
Chin. Phys. B 2015, 24 (2): 023301;  doi: 10.1088/1674-1056/24/2/023301
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Response theory is used to investigate one- and two-photon absorption (TPA) as well as the emission properties of a series of potential zinc ion and pH sensitive materials containing 2-(2'-hydroxyphenyl)benzoxazole (HPBO) end groups. Special emphasis is placed on the evolution of their optical properties upon combining with zinc ions or deprotonation. Our calculated results indicate that upon combining with zinc ions or deprotonation, these HPBO derivatives show drastic changes in their one-photon absorption (OPA), emission, and TPA properties. Moreover, the mechanisms of the probes are analyzed and found to be an intramolecular charge transfer. These compounds are thus proved to be excellent candidates for two-photon fluorescent zinc and pH probes.

Uniform stable conformal convolutional perfectly matched layer for enlarged cell technique conformal finite-difference time-domain method

Wang Yue, Wang Jian-Guo, Chen Zai-Gao
Chin. Phys. B 2015, 24 (2): 024101;  doi: 10.1088/1674-1056/24/2/024101
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Based on conformal construction of physical model in a three-dimensional Cartesian grid, an integral-based conformal convolutional perfectly matched layer (CPML) is given for solving the truncation problem of the open port when the enlarged cell technique conformal finite-difference time-domain (ECT-CFDTD) method is used to simulate the wave propagation inside a perfect electric conductor (PEC) waveguide. The algorithm has the same numerical stability as the ECT-CFDTD method. For the long-time propagation problems of an evanescent wave in a waveguide, several numerical simulations are performed to analyze the reflection error by sweeping the constitutive parameters of the integral-based conformal CPML. Our numerical results show that the integral-based conformal CPML can be used to efficiently truncate the open port of the waveguide.

Influence of the illumination coherency and illumination aperture on the ptychographic iterative microscopy

Liu Cheng, Zhu Jian-Qiang, John Rodenburg
Chin. Phys. B 2015, 24 (2): 024201;  doi: 10.1088/1674-1056/24/2/024201
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While ptychography is an algorithm based on coherent illumination, satisfactory reconstructions can still be generated in most experiments, even though the radiation sources that are used are not ideally coherent. The underlying physics of this phenomenon is that the diffraction patterns of partially coherent illumination can be treated as those of purely coherent illumination by altering the intensities of the diffracted beams relative to their real values. On the other hand, due to the inconsistency in the altering interference among all the diffraction beams, noise/distortion is always involved in the reconstructed images. Furthermore, for a weak object, the noise/distortion in the reconstruction can be mostly reduced by using a highly curved beam for illumination in the data recording and forcing the dark field diffraction to be zero in the reconstruction.

Phase modulation pseudocolor encoding ghost imaging

Duan De-Yang, Zhang Lu, Du Shao-Jiang, Xia Yun-Jie
Chin. Phys. B 2015, 24 (2): 024202;  doi: 10.1088/1674-1056/24/2/024202
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We present a ghost imaging scheme that can obtain a good pseudocolor image of black-and-white objects. The essential idea is to use a multi-wavelength thermal light source and the phase modulation pseudocolor encoding technique, which overcomes the disadvantages of other methods involved spatial filtering. Therefore, the pseudocolor ghost image achieved by this imaging scheme is better than that obtained by other methods in terms of brightness, color, and signal-to-noise ratio.

Comparison of two absorption imaging methods to detect cold atoms in magnetic trap

Wang Yan, Hu Zhao-Hui, Qi Lu
Chin. Phys. B 2015, 24 (2): 024203;  doi: 10.1088/1674-1056/24/2/024203
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Two methods of absorption imaging to detect cold atoms in a magnetic trap are implemented for a high-precision cold atom interferometer. In the first method, a probe laser which is in resonance with a cycle transition frequency is used to evaluate the quantity and distribution of the atom sample. In the second method, the probe laser is tuned to an open transition frequency, which stimulates a few and constant number of photons per atom. This method has a shorter interaction time and results in absorption images which are not affected by the magnetic field and the light field. We make a comparison of performance between these two imaging methods in the sense of parameters such as pulse duration, light intensity, and magnetic field strength. The experimental results show that the second method is more reliable when detecting the quantity and density profiles of the atoms. These results fit well to the theoretical analysis.

Photon counting statistics of V-type three-level systems: The effects of the field fluctuations

Peng Yong-Gang, Zheng Yu-Jun
Chin. Phys. B 2015, 24 (2): 024204;  doi: 10.1088/1674-1056/24/2/024204
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We investigate the influence of the field fluctuations to the emission photons of V-type three-level systems. The emission intensity I and Mandel's Q parameter show stochastic resonance with respect to the pure dephasing constant γp. The amplitude fluctuation of the field causes these systems to lose their coherence. On the other hand, the amplitude fluctuation provides a new interference method for these systems. The quantum beats are shown in the orthogonal system.

Position-dependent property of resonant dipole—dipole interaction mediated by localized surface plasmon of an Ag nanosphere

Xu Dan, Wang Xiao-Yun, Huang Yong-Gang, Ouyang Shi-Liang, He Hai-Long, He Hao
Chin. Phys. B 2015, 24 (2): 024205;  doi: 10.1088/1674-1056/24/2/024205
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We use the photon Green-function method to study the quantum resonant dipole-dipole interaction (RDDI) induced by an Ag nanosphere (ANP). As the distance between the two dipoles increases, the RDDI becomes weaker, which is accompanied by the influence of the higher-order mode of the ANP on RDDI declining more quickly than that of the dipole mode. Across a broad frequency range (above 0.05 eV), the transfer rate of the RDDI is nearly constant since the two dipoles are fixed at the proper position. In addition, this phenomenon still exists for slightly different radius of the ANPs. We find that the frequency corresponding to the maximum transfer rate of RDDI exhibits a monotonic decrease by moving away one dipole as the other dipole and the ANP are kept fixed. In addition, the radius of ANP has little effect on this. When the two dipoles are far from the ANP, the maximum transfer rate of the RDDI takes place at the frequency of the dipole mode. In contrast, when the two dipoles are close to the ANP, the higher-order modes come into effect and they will play a leading role in the RDDI if they match the transition frequency of the dipole. Our results may be used in a biological detector and have a certain guiding significance for further application.

Frequency-locking and threshold current-lowering effects of a quantum cascade laser and an application in gas detection field

Chen Wei-Gen, Wan Fu, Zou Jing-Xin, Gu Zhao-Liang, Zhou Qu
Chin. Phys. B 2015, 24 (2): 024206;  doi: 10.1088/1674-1056/24/2/024206
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In this paper, the frequency-locking and threshold current-lowering effects of a quantum cascade laser are studied and achieved. Combined with cavity-enhanced absorption spectroscopy, the noninvasive detection of H2 with a prepared concentration of 500 ppm in multiple dissolved gases is performed and evaluated. The high frequency selectivity of 0.0051 cm-1 at an acquisition time of 1 s allows the sensitive detection of the (1-0) S(1) band of H2 with a high accuracy of (96.53± 0.29)% and shows that the detection limit to an absorption line of 4712.9046 cm-1 is approximately (17.26± 0.63) ppm at an atmospheric pressure and a temperature of 20 ℃.

A novel method of evaluating large mode area fiber design by brightness factor

Zhang Hai-Tao, Chen Dan, Ren Hai-Cui, Yan Ping, Gong Ma-Li
Chin. Phys. B 2015, 24 (2): 024207;  doi: 10.1088/1674-1056/24/2/024207
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A novel evaluation term and a more reasonable criterion, which is described by a new parameter of brightness factor for active large mode area fiber design, are presented. The brightness factor evaluation method is based on the transverse mode competition mechanism in fiber lasers and amplifiers. The brightness factor can be seen as a description of fiber general property since it can represent the output laser brightness of the fiber laser system and because of its ability to resist the nonlinear effect. A core-doped active large pitch fiber with a core diameter of 190 μ and a mode-field diameter of 180 μm is designed by this method, and the designed fiber allows effective single-mode operation.

Theoretical analysis of the mode coupling induced by heat of large-pitch micro-structured fibers

Zhang Hai-Tao, Chen Dan, Hao Jie, Yan Ping, Gong Ma-Li
Chin. Phys. B 2015, 24 (2): 024208;  doi: 10.1088/1674-1056/24/2/024208
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In this paper, a theoretical model to analyze the mode coupling induced by heat, when the fiber amplifier works at high power configuration, is proposed. The model mainly takes into consideration the mode field change due to the thermally induced refractive index change and the coupling between modes. A method to predict the largest average output power of fiber is also proposed according to the mode coupling theory. The largest average output power of a large pitch fiber with a core diameter of 190 μm and an available pulse energy of 100 mJ is predicted to be 540 W, which is the highest in large mode field fibers.

Optimal oxide-aperture for improving the power conversion efficiency of VCSEL arrays

Wang Wen-Juan, Li Chong, Zhou Hong-Yi, Wu Hua, Luan Xin-Xin, Shi Lei, Guo Xia
Chin. Phys. B 2015, 24 (2): 024209;  doi: 10.1088/1674-1056/24/2/024209
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The maximum power conversion efficiencies of the top-emitting, oxide-confined, two-dimensional integrated 2×2 and 4×4 vertical-cavity surface-emitting laser (VCSEL) arrays with the oxide-apertures of 6 μm, 16 μm, 19 μm, 26 μm, 29 μm, 36 μm, 39 μm, and 46 μm are fabricated and characterized, respectively. The maximum power conversion efficiencies increase rapidly with the augment of oxide-aperture at the beginning and then decrease slowly. A maximum value of 27.91% at an oxide-aperture of 18.6 μm is achieved by simulation. The experimental data are well consistent with the simulation results, which are analyzed by utilizing an empirical model.

Power-induced polarization switching and bistability characteristics in 1550-nm VCSELs subjected to orthogonal optical injection

Chen Jian-Jun, Xia Guang-Qiong, Wu Zheng-Mao
Chin. Phys. B 2015, 24 (2): 024210;  doi: 10.1088/1674-1056/24/2/024210
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The polarization switching (PS) and polarization bistability (PB) characteristics of a 1550-nm vertical-cavity surface-emitting laser (VCSEL) subjected to orthogonal optical injection are systematically investigated. The simulated results show that the PS and polarization-resolved nonlinear dynamical states of the VCSEL are critically dependent on the changing paths of the injected power. The polarization dynamics for different scanning directions of the injected power is presented to explain the polarization evolution during the formation of PS. In the case of forward scanning injected power, with the increase of frequency detuning level between the VCSEL and the injected light, the injected power required for PS gradually increases for negative frequency detuning but exhibits fluctuations for positive frequency detuning. In the case of reversely scanning injected power, the injected power required for PS displays fluctuant changes within the whole frequency detuning range. Specifically, PS may disappear under certain negative frequency detuning and large bias current. Furthermore, the hysteresis width as a function of the frequency detuning is calculated, and the regions for the appearance and disappearance of PB have been determined in the parameter space of the bias current and frequency detuning.

Theoretical study of the optical gain characteristics of a Ge1-xSnx alloy for a short-wave infrared laser

Zhang Dong-Liang, Cheng Bu-Wen, Xue Chun-Lai, Zhang Xu, Cong Hui, Liu Zhi, Zhang Guang-Ze, Wang Qi-Ming
Chin. Phys. B 2015, 24 (2): 024211;  doi: 10.1088/1674-1056/24/2/024211
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Optical gain characteristics of Ge1-xSnx are simulated systematically. With an injection carrier concentration of 5×1018/cm3 at room temperature, the maximal optical gain of Ge0.922Sn0.078 alloy (with n-type doping concentration being 5×1018/cm3) reaches 500 cm-1. Moreover, considering the free-carrier absorption effect, we find that there is an optimal injection carrier density to achieve a maximal net optical gain. A double heterostructure Ge0.554Si0.289Sn0.157/Ge0.922Sn0.078/Ge0.554Si0.289Sn0.157 short-wave infrared laser diode is designed to achieve a high injection efficiency and low threshold current density. The simulation values of the device threshold current density Jth are 6.47 kA/cm2 (temperature: 200 K, and λ =2050 nm), 10.75 kA/cm2 (temperature: 200 K, and λ =2000 nm), and 23.12 kA/cm2 (temperature: 300 K, and λ =2100 nm), respectively. The results indicate the possibility to obtain a Si-based short-wave infrared Ge1-xSnx laser.

Very low threshold operation of quantum cascade lasers

Yan Fang-Liang, Zhang Jin-Chuan, Yao Dan-Yang, Liu Feng-Qi, Wang Li-Jun, Liu Jun-Qi, Wang Zhan-Guo
Chin. Phys. B 2015, 24 (2): 024212;  doi: 10.1088/1674-1056/24/2/024212
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A strain-compensated InP-based quantum cascade laser (QCL) structure emitting at 4.6 μm is demonstrated, based on a two-phonon resonant design and grown by solid-source molecular beam epitaxy (MBE). By optimizing the growth parameters, a very high quality heterostructure with the lowest threshold current densities ever reported for QCLs was fabricated. Threshold current densities as low as 0.47 kA/cm2 in pulsed operation and 0.56 kA/cm2 in continuous-wave (cw) operation at 293 K were achieved for this state-of-the-art QCL. A minimum power consumption of 3.65 W was measured for the QCL, uncooled, with a high-reflectivity (HR) coating on its rear facet.

A 23.75-GHz frequency comb with two low-finesse filtering cavities in series for high resolution spectroscopy

Hou Lei, Han Hai-Nian, Wang Wei, Zhang Long, Pang Li-Hui, Li De-Hua, Wei Zhi-Yi
Chin. Phys. B 2015, 24 (2): 024213;  doi: 10.1088/1674-1056/24/2/024213
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A laser frequency comb with several tens GHz level is demonstrated, based on a Yb-doped femtosecond fiber laser and two low-finesse Fabry-Pérot cavities (FPCs) in series. The original 250-MHz mode-line-spacing of the source comb is filtered to 4.75 GHz and 23.75 GHz, respectively. According to the multi-beam interferences theory of FPC, the side-mode suppression rate of FPC schemes is in good agreement with our own theoretical results from 27 dB of a single FPC to 43 dB of paired FPCs. To maintain long-term stable operation and determine the absolute frequency mode number in the 23.75-GHz comb, the Pound-Drever-Hall (PDH) locking technology is utilized. Such stable tens GHz frequency combs have important applications in calibrating astronomical spectrographs with high resolution.

Tandem-pumped 1120-nm actively Q-switched fiber laser

Wang Jian-Hua, Hu Jin-Meng, Zhang Shi-Qiang, Chen Lu-Lu, Fang Yong, Feng Yan, Li Zhi
Chin. Phys. B 2015, 24 (2): 024214;  doi: 10.1088/1674-1056/24/2/024214
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We report on a tandem-pumped actively Q-switched fiber laser system emitting at 1120 nm. Parasitic oscillation is challenging in Yb-doped Q-switched 1120-nm fiber laser, which is suppressed by pumping with a fiber laser at 1018 nm. At least four times improvement in output peak power is demonstrated in a single laser setup with 1018-nm fiber laser pumping instead of 976-nm laser diode pumping. This is, to the best of our knowledge, the first demonstration of a tandem-pumped Q-switched fiber laser.

1.12-W Q-switched Yb:KGW laser based on transmission-type Bi2Se3 saturable absorber

Liu Jing-Hui, Tian Jin-Rong, Hu Meng-Ting, Xu Run-Qin, Dou Zhi-Yuan, Yu Zhen-Hua, Song Yan-Rong
Chin. Phys. B 2015, 24 (2): 024215;  doi: 10.1088/1674-1056/24/2/024215
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We present a passively Q-switched Yb:KGW laser based on a transmission-type saturable absorber of topological insulator: Bi2Se3. The saturable absorber is prepared on a 0.17-mm glass substrate and can translate intra-cavity for best performance nearly without influence on the laser mode. At a maximum pump power of 13.7 W, the central wavelength, pulse duration, repetition rate, and pulse energy of Q-switched pulse are 1043 nm, 1.5 μs, 175.4 kHz, 6.39 μJ, respectively. The maximum output power is 1.12 W. To our knowledge, this is the highest average output power from passively Q-switched lasers with topological insulator saturable absorbers.

Walk-off reduction, using an external optical plate and Bessel—Gaussian interaction

Masoume Mansouri, Mohsen Askarbioki, Saeed Ghavami Sabouri, Alireza Khorsandi
Chin. Phys. B 2015, 24 (2): 024216;  doi: 10.1088/1674-1056/24/2/024216
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To reduce the walk-off angle of the extraordinary third-harmonic ultraviolet wave at 355 nm generated by type Ⅱ KTiOPO4 and type I β-BaB2O4 optical crystals, and the Gaussian output beam of a Q-switched Nd:YAG laser, a simple theoretical model was developed based on a rotatable BK7 plate of variable thickness. By rotating the plate up to 35° along the beam direction, we reduced the walk-off angle up to ~ 13%. The same phenomenon is predicted by the model, confirming the performance of the model. It is found that, due to the walk-off effect, the intensity profile of the third-harmonic generation beam is slightly degraded. To compensate for the observed phenomena and further reduce the walk-off, we used a combination of a convex lens and an axicon to transform the beam profile of the interacting fundamental and second-harmonic generation waves to the zero-order Bessel-Gaussian form. As a result, the walk-off is decreased to ~ 48.81 mrad, providing ~ 30% relative reduction. By using the same BK7 plate rotated up to 35° along the third-harmonic beam direction, the walk-off angle is further reduced to 38.9 mrad. Moreover, it is observed that the beam profile of the emerged Bessel-Gaussian third-harmonic generation beam remains unchanged with no degradation.

Fiber laser pumped burst-mode operated picosecond mid-infrared laser

Wei Kai-Hua, Jiang Pei-Pei, Wu Bo, Chen Tao, Shen Yong-Hang
Chin. Phys. B 2015, 24 (2): 024217;  doi: 10.1088/1674-1056/24/2/024217
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We demonstrate a compact periodically poled MgO-doped lithium niobate (MgO:PPLN)-based optical parametric oscillator (OPO) quasi-synchronously pumped by a fiber laser system with burst-mode operation. The pump source is a peak-power-selectable pulse-multiplied picosecond Yb fiber laser. The chirped pulses from a figure of eight-cavity mode-locked fiber laser seed are narrowed to a duration of less than 50 ps using an FBG reflector and a circulator. The narrowed pulses are directed to pass through a pulse multiplier and to form pulse bunches, each of which is composed of 13 sub-pulses. The obtained pulse bunches are amplified by two-stage fiber pre-amplifiers: one-stage is core-pumped and the other is cladding-pumped. A fiberized acousto-optic modulator is inserted to control the pulse repetition rate (PRR) of the pulse bunches before they are power-amplified in the final amplifier stage with a large mode area (LMA) PM Yb-doped fiber. The maximum average powers from the final amplifier are 85 W, 60 W, and 45 W, respectively, corresponding to the PRR of 2.72 MHz, 1.36 MHz, and 0.68 MHz. The amplified pulses are directed to pump an MgO:PPLN-based optical parametric oscillator (OPO). A maximum peak power at 3.45 μm is obtained approximately to be 8.4 kW. Detailed performance characteristics are presented.

Correction of temperature influence on the wind retrieval from a mobile Rayleigh Doppler lidar

Zhao Ruo-Can, Xia Hai-Yun, Dou Xian-Kang, Sun Dong-Song, Han Yu-Li, Shangguan Ming-Jia, Guo Jie, Shu Zhi-Feng
Chin. Phys. B 2015, 24 (2): 024218;  doi: 10.1088/1674-1056/24/2/024218
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A mobile Rayleigh Doppler lidar based on double-edge technique is implemented for simultaneously observing wind and temperature at heights of 15 km-60 km away from ground. Before the inversion of the Doppler shift due to wind, the Rayleigh response function should be calculated, which is a convolution of the laser spectrum, Rayleigh backscattering function, and the transmission function of the Fabry-Perot interferometer used as the frequency discriminator in the lidar. An analysis of the influence of the temperature on the accuracy of the line-of-sight winds shows that real-time temperature profiles are needed because the bandwidth of the Rayleigh backscattering function is temperature-dependent. An integration method is employed in the inversion of the temperature, where the convergence of this method and the high signal-to-noise ratio below 60 km ensure the accuracy and precision of the temperature profiles inverted. Then, real-time and on-site temperature profiles are applied to correct the wind instead of using temperature profiles from a numerical prediction system or atmosphere model. The corrected wind profiles show satisfactory agreement with the wind profiles acquired from radiosondes, proving the reliability of the method.

Influences of excitation power and temperature on photoluminescence in phase-separated InGaN quantum wells

Wang Qiang, Ji Zi-Wu, Wang Fan, Mu Qi, Zheng Yu-Jun, Xu Xian-Gang, Lü Yuan-Jie, Feng Zhi-Hong
Chin. Phys. B 2015, 24 (2): 024219;  doi: 10.1088/1674-1056/24/2/024219
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The photoluminescence (PL) properties of a green and blue light-emitting InGaN/GaN multiple quantum well structure with a strong phase separated into quasi-quantum dots (QDs) and an InGaN matrix in the InGaN epilayer are investigated. The excitation power dependences of QD-related green emissions (PD) and matrix-related blue emissions (PM) in the low excitation power range of the PL peak energy and line-width indicate that at 6 K both PM and PD are dominated by the combined action of Coulomb screening and localized state filling effect. However, at 300 K, PM is dominated by the non-radiative recombination of the carriers in the InGaN matrix, while PD is influenced by the carriers transferred from the shallower QDs to deeper QDs by tunnelling. This is consistent with the excitation power dependence of the PL efficiency for the emission.

ATR-FTIR spectroscopic studies on density changes of fused silica induced by localized CO2 laser treatment

Zhang Chuan-Chao, Zhang Li-Juan, Liao Wei, Yan Zhong-Hua, Chen Jing, Jiang Yi-Lan, Wang Hai-Jun, Luan Xiao-Yu, Ye Ya-Yun, Zheng Wan-Guo, Yuan Xiao-Dong
Chin. Phys. B 2015, 24 (2): 024220;  doi: 10.1088/1674-1056/24/2/024220
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The surface density changes of the central region of the sites treated by using the CO2 laser-based non-evaporative damage mitigation for fused silica are investigated by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The ATR-FTIR peak shifts of the treated sites of fused silica are monitored to determine the changes of the corresponding density. For the quenching treated sites, the surface density is increased by (0.24± 0.01)% compared with the initial density but the laser annealing by the exposure of a power ramp down after damage mitigation effectively suppresses the structural changes of treated sites, which could reduce the increase of the corresponding density to (0.08± 0.01)%. The results provide sufficient evidence that the laser annealing by a power ramp down after damage mitigation has a positive effect on the control of the structural change induced by CO2 laser-based damage mitigation.

First-principles study of structure and nonlinear optical properties of CdHg(SCN)4 crystal

Zhang Peng, Kong Chui-Gang, Zheng Chao, Wang Xin-Qiang, Ma Yue, Feng Jin-Bo, Jiao Yu-Qiu, Lu Gui-Wu
Chin. Phys. B 2015, 24 (2): 024221;  doi: 10.1088/1674-1056/24/2/024221
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The geometric structure, electronic structure, and optical properties of CdHg(SCN)4 crystal are calculated by using the density functional perturbation theory and Green function screening Coulomb interaction approximation. The band gap of CdHg(SCN)4 crystal is calculated to be 3.198 eV, which is in good agreement with the experimental value 3.265 eV. The calculated second-order nonlinear optical coefficients are d14=1.2906 pm/V and d15=5.0928 pm/V, which are in agreement with the experimental results (d14=(1.4± 0.6) pm/V and d15=(6.0± 0.9) pm/V). Moreover, it is found that the contribution to the valence band mainly comes from Cd-4d, Hg-5d states, and the contributions to the valence band top and the conduction band bottom predominantly come from C-2p, N-2p, and S-3p states. The second-order nonlinear optical effect of CdHg(SCN)4 crystal results mainly from the internal electronic transition of (SCN)-.

Exciplex formation and electroluminescent absorption in ultraviolet organic light-emitting diodes

Zhang Qi, Zhang Hao, Zhang Xiao-Wen, Xu Tao, Wei Bin
Chin. Phys. B 2015, 24 (2): 024222;  doi: 10.1088/1674-1056/24/2/024222
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We investigated the formation of exciplex and electroluminescent absorption in ultraviolet organic light-emitting diodes (UV OLEDs) using different heterojunction structures. It is found that an energy barrier of over 0.3 eV between the emissive layer (EML) and adjacent transport layer facilitates exciplex formation. The electron blocking layer effectively confines electrons in the EML, which contributes to pure UV emission and enhances efficiency. The change in EML thickness generates tunable UV emission from 376 nm to 406 nm. In addition, the UV emission excites low-energy organic function layers and produces photoluminescent emission. In UV OLED, avoiding the exciplex formation and averting light absorption can effectively improve the purity and efficiency. A maximum external quantum efficiency of 1.2% with a UV emission peak of 376 nm is realized.

Controlling an acoustic wave with a cylindrically-symmetric gradient-index system

Zhang Zhe, Li Rui-Qi, Liang Bin, Zou Xin-Ye, Cheng Jian-Chun
Chin. Phys. B 2015, 24 (2): 024301;  doi: 10.1088/1674-1056/24/2/024301
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We present a detailed theoretical description of wave propagation in an acoustic gradient-index system with cylindrical symmetry and demonstrate its potential to numerically control acoustic waves in different ways. The trajectory of an acoustic wave within the system is derived by employing the theory of geometric acoustics, and the validity of the theoretical descriptions is verified numerically by using the finite element method simulation. The results show that by tailoring the distribution function of the refractive index, the proposed system can yield a tunable manipulation of acoustic waves, such as acoustic bending, trapping, and absorbing.

Study of acoustic bubble cluster dynamics using a lattice Boltzmann model

Mahdi Daemi, Mohammad Taeibi-Rahni, Hamidreza Massah
Chin. Phys. B 2015, 24 (2): 024302;  doi: 10.1088/1674-1056/24/2/024302
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The search for the development of a reliable mathematical model for understanding bubble dynamics behavior is an ongoing endeavor. A long list of complex phenomena underlies the physics of this problem. In the past decades, the lattice Boltzmann method has emerged as a promising tool to address such complexities. In this regard, we have applied a 121-velocity multiphase lattice Boltzmann model to an asymmetric cluster of bubbles in an acoustic field. A problem as a benchmark is studied to check the consistency and applicability of the model. The problem of interest is to study the deformation and coalescence phenomena in bubble cluster dynamics, as well as the screening effect on an acoustic multi-bubble medium. It has been observed that the LB model is able to simulate the combination of the three aforementioned phenomena for a bubble cluster as a whole and for every individual bubble in the cluster.

Homogenization theory for designing graded viscoelastic sonic crystals

Qu Zhao-Liang, Ren Chun-Yu, Pei Yong-Mao, Fang Dai-Ning
Chin. Phys. B 2015, 24 (2): 024303;  doi: 10.1088/1674-1056/24/2/024303
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In this paper, we propose a homogenization theory for designing graded viscoelastic sonic crystals (VSCs) which consist of periodic arrays of elastic scatterers embedded in a viscoelastic host material. We extend an elastic homogenization theory to VSC by using the elastic-viscoelastic correspondence principle and propose an analytical effective loss factor of VSC. The results of VSC and the equivalent structure calculated by using the finite element method are in good agreement. According to the relation of the effective loss factor to the filling fraction, a graded VSC plate is easily and quickly designed. Then, the graded VSC may have potential applications in the vibration absorption and noise reduction fields.

Pulse decomposition-based analysis of PAT/TAT error caused by negative lobes in limited-view conditions

Liu Liang-Bing, Tao Chao, Liu Xiao-Jun, Li Xian-Li, Zhang Hai-Tao
Chin. Phys. B 2015, 24 (2): 024304;  doi: 10.1088/1674-1056/24/2/024304
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Pulse decomposition has been proven to be efficient to analyze complicated signals and it is introduced into the photo-acoustic and thermo-acoustic tomography to eliminate reconstruction distortions caused by negative lobes. During image reconstruction, negative lobes bring errors in the estimation of acoustic pulse amplitude, which is closely related to the distribution of absorption coefficient. The negative lobe error degrades imaging quality seriously in limited-view conditions because it cannot be offset so well as in full-view conditions. Therefore, a pulse decomposition formula is provided with detailed deduction to eliminate the negative lobe error and is incorporated into the popular delay-and-sum method for better reconstructing the image without additional complicated computation. Numerical experiments show that the pulse decomposition improves the image quality obviously in the limited-view conditions, such as separating adjacent absorbers, discovering a small absorber despite disturbance from a big absorber nearby, etc.

Short-pulse high-power microwave breakdown at high pressures

Zhao Peng-Cheng, Liao Cheng, Feng Ju
Chin. Phys. B 2015, 24 (2): 025101;  doi: 10.1088/1674-1056/24/2/025101
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The fluid model is proposed to investigate the gas breakdown driven by a short-pulse (such as a Gaussian pulse) high-power microwave at high pressures. However, the fluid model requires specification of the electron energy distribution function (EEDF); the common assumption of a Maxwellian EEDF can result in the inaccurate breakdown prediction when the electrons are not in equilibrium. We confirm that the influence of the incident pulse shape on the EEDF is tiny at high pressures by using the particle-in-cell Monte Carlo collision (PIC-MCC) model. As a result, the EEDF for a rectangular microwave pulse directly derived from the Boltzmann equation solver Bolsig+ is introduced into the fluid model for predicting the breakdown threshold of the non-rectangular pulse over a wide range of pressures, and the obtained results are very well matched with those of the PIC-MCC simulations. The time evolution of a non-rectangular pulse breakdown in gas, obtained by the fluid model with the EEDF from Bolsig+, is presented and analyzed at different pressures. In addition, the effect of the incident pulse shape on the gas breakdown is discussed.

Landau damping in a bounded magnetized plasma column

H. Zakeri-Khatir, F. M. Aghamir
Chin. Phys. B 2015, 24 (2): 025201;  doi: 10.1088/1674-1056/24/2/025201
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The damping decrement of Landau damping and the effect of thermal velocity on the frequency spectrum of a propagating wave in a bounded plasma column are investigated. The magnetized plasma column partially filling a cylindrical metallic tube is considered to be collisionless and non-degenerate. The Landau damping is due to the thermal motion of charge carriers and appears whenever the phase velocity of the plasma waves exceeds the thermal velocity of carriers. The analysis is based on a self-consistent kinetic theory and the solutions of the wave equation in a cylindrical plasma waveguide are presented using Vlasov and Maxwell equations. The hybrid mode dispersion equation for the cylindrical plasma waveguide is obtained through the application of appropriate boundary conditions to the plasma-vacuum interface. The dependence of Landau damping on plasma parameters and the effects of the metallic tube boundary on the dispersion characteristics of plasma and waveguide modes are investigated in detail through numerical calculations.

Relativistic degenerate effects of electrons and positrons on modulational instability of quantum ion acoustic waves in dense plasmas with two polarity ions

Liu Tie-Lu, Wang Yun-Liang, Lu Yan-Zhen
Chin. Phys. B 2015, 24 (2): 025202;  doi: 10.1088/1674-1056/24/2/025202
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The nonlinear propagation of quantum ion acoustic wave (QIAW) is investigated in a four-component plasma composed of warm classical positive ions and negative ions, as well as inertialess relativistically degenerate electrons and positrons. A nonlinear Schrödinger equation is derived by using the reductive perturbation method, which governs the dynamics of QIAW packets. The modulation instability analysis of QIAWs is considered based on the typical parameters of the white dwarf. The results exhibit that both in the weakly relativistic limit and in the ultrarelativistic limit, the modulational instability regions are sensitively dependent on the ratios of temperature and number density of negative ions to those of positive ions respectively, and on the relativistically degenerate effect as well.

Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons

Chen Zhao-Quan, Yin Zhi-Xiang, Xia Guang-Qing, Hong Ling-Li, Hu Ye-Lin, Liu Ming-Hai, Hu Xi-Wei, A. A. Kudryavtsev
Chin. Phys. B 2015, 24 (2): 025203;  doi: 10.1088/1674-1056/24/2/025203
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Atmospheric lower-power pulsed microwave argon cold plasma jets are obtained by using coaxial transmission line resonators in ambient air. The plasma jet plumes are generated at the end of a metal wire placed in the middle of the dielectric tubes. The electromagnetic model analyses and simulation results suggest that the discharges are excited resonantly by the enhanced electric field of surface plasmon polaritons. Moreover, for conquering the defect of atmospheric argon filamentation discharges excited by 2.45-GHz of continued microwave, the distinctive patterns of the plasma jet plumes can be maintained by applying different gas flow rates of argon gas, frequencies of pulsed modulator, duty cycles of pulsed microwave, peak values of input microwave power, and even by using different materials of dielectric tubes. In addition, the emission spectrum, the plume temperature, and other plasma parameters are measured, which shows that the proposed pulsed microwave plasma jets can be adjusted for plasma biomedical applications.

Experimental and modeling researches of dust particles in the HL-2A tokamak

Huang Zhi-Hui, Yan Long-Wen, Tomita Yukihiro, Feng Zhen, Cheng Jun, Hong Wen-Yu, Pan Yu-Dong, Yang Qing-Wei, Duan Xu-Ru, HL-2A Team
Chin. Phys. B 2015, 24 (2): 025204;  doi: 10.1088/1674-1056/24/2/025204
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The investigation of dust particle characteristics in fusion devices has become more and more imperative. In the HL-2A tokamak, the morphologies and compositions of dust particles are analyzed by using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) with mapping. The results indicate that the sizes of dust particles are in a range from 1 μm to 1 mm. Surprisingly, stainless steel spheres with a diameter of 2.5 μm-30 μm are obtained. The production mechanisms of dust particles include flaking, disintegration, agglomeration, and arcing. In addition, dynamic characteristics of the flaking dust particles are observed by a CMOS fast framing camera and simulated by a computer program. Both of the results display that the ion friction force is dominant in the toroidal direction, while the centrifugal force is crucial in the radial direction. Therefore, the visible dust particles are accelerated toriodally by the ion friction force and migrated radially by the centrifugal force. The averaged velocity of the grain is on the order of ~ 100 m/s. These results provide an additional supplement for one of critical plasma-wall interaction (PWI) issues in the framework of the International Thermonuclear Experimental Reactor (ITER) programme.

Characterization of plasma current quench during disruption in EAST tokamak

Chen Da-Long, Granetz Robert, Shen Biao, Yang Fei, Qian Jin-Ping, Xiao Bing-Jia
Chin. Phys. B 2015, 24 (2): 025205;  doi: 10.1088/1674-1056/24/2/025205
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A preliminary analysis of plasma current quenching is presented in this paper based on the disruption database. It demonstrates that 26.8% of discharges have been disrupted in the last 2012 campaign, in addition, the plasma disruptive rate grows with the increase of plasma current. The best-fit linear and instantaneous plasma current quench rate is extracted from the recent EAST disruptions, showing that an 80%-30% interval of the maximum plasma current is well fit for the EAST device. The lowest area-normalized current quench time is 3.33 ms/m2 with the estimated plasma electron temperature being 7.3 eV~9.5 eV. In the disruption case the maximum eddy current goes up to 400 kA, and a fraction of currents are respectively driven on the upper and lower outer plate with nearly 100 MPa-200 MPa stress in the leg.

Quartic coupling and its effect on wetting behaviors in nematic liquid crystals

Zeng Ming-Ying, Holger Merlitz, Wu Chen-Xu
Chin. Phys. B 2015, 24 (2): 026101;  doi: 10.1088/1674-1056/24/2/026101
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Based on the fact that rubbed groove patterns also affect the anchoring of liquid crystals at substrates, a quartic coupling is included in constructing the surface energy for a liquid crystal cell. The phase diagram and the wetting behaviors of the liquid crystal cell, bounded by surfactant-laden interfaces in a magnetic field perpendicular to the substrate are discussed by taking the quartic coupling into account. The nematic order increases at the surface while it decreases in the bulk as a result of the introduction of quartic substrate-liquid crystal coupling, indicating that the groove anchoring makes the liquid crystal molecules align more orderly near the substrate than away from it. This causes a different wetting behavior: complete wetting.

Dynamics of a ± 1/2 defect pair in a confined geometry: A thin hybrid aligned nematic cell

Lu Li-Xia, Zhang Zhi-Dong
Chin. Phys. B 2015, 24 (2): 026102;  doi: 10.1088/1674-1056/24/2/026102
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Confined geometry can change the defect structure and its properties. In this paper, we investigate numerically the dynamics of a dipole of ± 1/2 parallel wedge disclination lines in a confined geometry: a thin hybrid aligned nematic (HAN) cell, based on the Landau-de Gennes theory. When the cell gap d is larger than a critical value of 12ζ (where ζ is the characteristic length for order-parameter change), the pair annihilates. A pure HAN configuration without defect is formed in an equilibrium state. In the confined geometry of d ≤ 12ζ, the diffusion process is discovered for the first time and an eigenvalue exchange configuration is formed in an equilibrium state. The eigenvalue exchange configuration is induced by different essential reasons. When 10ζ <d ≤ 12ζ, the two defects coalesce and annihilate. The biaxial wall is created by the inhomogeneous distortion of the director, which results in the eigenvalue exchange configuration. When d ≤ 10ζ, the defects do not collide and the eigenvalue exchange configuration originates from the biaxial seeds concentrated at the defects.

Effect of twin boundary on nanoimprint process of bicrystal Al thin film studied by molecular dynamics simulation

Xie Yue-Hong, Xu Jian-Gang, Song Hai-Yang, Zhang Yun-Guang
Chin. Phys. B 2015, 24 (2): 026201;  doi: 10.1088/1674-1056/24/2/026201
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The effects of a twin boundary (TB) on the mechanical properties of two types of bicrystal Al thin films during the nanoimprint process are investigated by using molecular dynamics simulations. The results indicate that for the TB direction parallel to the imprinting direction, the yield stress reaches the maximum for the initial dislocation nucleation when the mould directly imprints to the TB, and the yield stress first decreases with the increase of the marker interval and then increases. However, for the TB direction perpendicular to the imprinting direction, the effect of the TB location to the imprinting forces is very small, and the yield stress is greater than that with the TB direction parallel to the imprinting direction. The results also demonstrate that the direction of the slip dislocations and the deformation of the thin film caused by spring-back are different due to various positions and directions of the TB.

Effects of in-plane stiffness and charge transfer on thermal expansion of monolayer transition metal dichalcogenide Hot!

Wang Zhan-Yu, Zhou Yan-Li, Wang Xue-Qing, Wang Fei, Sun Qiang, Guo Zheng-Xiao, Jia Yu
Chin. Phys. B 2015, 24 (2): 026501;  doi: 10.1088/1674-1056/24/2/026501
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The temperature dependence of lattice constants is studied by using first-principles calculations to determine the effects of in-plane stiffness and charge transfer on the thermal expansions of monolayer semiconducting transition metal dichalcogenides. Unlike the corresponding bulk material, our simulations show that monolayer MX2 (M=Mo and W; X=S, Se, and Te) exhibits a negative thermal expansion at low temperatures, induced by the bending modes. The transition from contraction to expansion at higher temperatures is observed. Interestingly, the thermal expansion can be tailored regularly by alteration of the M or X atom. Detailed analysis shows that the positive thermal expansion coefficient is determined mainly by the in-plane stiffness, which can be expressed by a simple relationship. Essentially the regularity of this change can be attributed to the difference in charge transfer between the different elements. These findings should be applicable to other two-dimensional systems.

Coadsorption of gold with chlorine on CeO2 (111) surfaces: A first principles study

Lu Zhan-Sheng, He Bing-Ling, Ma Dong-Wei, Yang Zong-Xian
Chin. Phys. B 2015, 24 (2): 026801;  doi: 10.1088/1674-1056/24/2/026801
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To investigate the effects of chlorine on the Au/ceria catalysts, the adsorption of gold or chlorine and their coadsorpiton on the stoichiometric and partially reduced CeO2 (111) surfaces are studied from the first principles. It is found that the adsorption of Au is significantly enhanced by the chlorine preadsorption on the stoichiometric CeO2 (111) surface; while on the partially reduced CeO2 (111) surface, the preadsorbed chlorine inhabits the oxygen vacancy (which is the preferred adsorption site for gold), leading to a CeOCl phase and the dramatical weakening of the Au adsorption. Therefore, chlorine on the CeO2 (111) surface can affect the Au adsorption thus the activity of the Au/CeO2 catalyst.

Effect of the thickness of InGaN interlayer on a-plane GaN epilayer

Wang Jian-Xia, Wang Lian-Shan, Zhang Qian, Meng Xiang-Yue, Yang Shao-Yan, Zhao Gui-Juan, Li Hui-Jie, Wei Hong-Yuan, Wang Zhan-Guo
Chin. Phys. B 2015, 24 (2): 026802;  doi: 10.1088/1674-1056/24/2/026802
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In this paper, we use the a-plane InGaN interlayer to improve the property of a-plane GaN. Based on the a-InGaN interlayer, a template exhibits that a regular, porous structure, which acts as a compliant effect, can be obtained to release the strain caused by the lattice and thermal mismatch between a-GaN and r-sapphire. We find that the thickness of InGaN has a great influence on the growth of a-GaN. The surface morphology and crystalline quality both are first improved and then deteriorated with increasing the thickness of the InGaN interlayer. When the InGaN thickness exceeds a critical point, the a-GaN epilayer peels off in the process of cooling down to room temperature. This is an attractive way of lifting off a-GaN films from the sapphire substrate.

Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values

Ma Xiao-Hua, Zhang Ya-Man, Wang Xin-Hua, Yuan Ting-Ting, Pang Lei, Chen Wei-Wei, Liu Xin-Yu
Chin. Phys. B 2015, 24 (2): 027101;  doi: 10.1088/1674-1056/24/2/027101
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In this paper, the off-state breakdown characteristics of two different AlGaN/GaN high electron mobility transistors (HEMTs), featuring a 50-nm and a 150-nm GaN thick channel layer, respectively, are compared. The HEMT with a thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage (BVoff). Device simulation indicates that thickening the channel increases the drain-induced barrier lowering (DIBL) but reduces the lateral electric field in the channel and buffer underneath the gate. The increase of BVoff in the thick channel device is due to the reduction of the electric field. These results demonstrate that it is necessary to select an appropriate channel thickness to balance DIBL and BVoff in AlGaN/GaN HEMTs.

Localization correction to the anomalous Hall effect in amorphous CoFeB thin films

Ding Jin-Jun, Wu Shao-Bing, Yang Xiao-Fei, Zhu Tao
Chin. Phys. B 2015, 24 (2): 027201;  doi: 10.1088/1674-1056/24/2/027201
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An obvious weak localization correction to anomalous Hall conductance (AHC) in very thin CoFeB film is reported. We find that both the weak localization to AHC and the mechanism of the anomalous Hall effect are related to the CoFeB thickness. When the film is thicker than 3 nm, the side jump mechanism dominates and the weak localization to AHC vanishes. For very thin CoFeB films, both the side jump and skew scattering mechanisms contribute to the anomalous Hall effect, and the weak localization correction to AHC is observed.

Influence of interface within the composite barrier on the tunneling electroresistance of ferroelectric tunnel junctions with symmetric electrodes

Wang Pin-Zhi, Zhu Su-Hua, Pan Tao, Wu Yin-Zhong
Chin. Phys. B 2015, 24 (2): 027301;  doi: 10.1088/1674-1056/24/2/027301
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The interface with a pinned dipole within the composite barrier in a ferroelectric tunnel junction (FTJ) with symmetric electrodes is investigated. Different from the detrimental effect of the interface between the electrode and barrier in previous studies, the existence of an interface between the dielectric SrTiO3 slab and ferroelectric BaTiO3 slab in FTJs will enhance the tunneling electroresistance (TER) effect. Specifically, the interface with a lower dielectric constant and larger polarization pointing to the ferroelectric slab favors the increase of TER ratio. Therefore, interface control of high performance FTJ can be achieved.

Transport mechanism of reverse surface leakage current in AlGaN/GaN high-electron mobility transistor with SiN passivation

Zheng Xue-Feng, Fan Shuang, Chen Yong-He, Kang Di, Zhang Jian-Kun, Wang Chong, Mo Jiang-Hui, Li Liang, Ma Xiao-Hua, Zhang Jin-Cheng, Hao Yue
Chin. Phys. B 2015, 24 (2): 027302;  doi: 10.1088/1674-1056/24/2/027302
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The transport mechanism of reverse surface leakage current in the AlGaN/GaN high-electron mobility transistor (HEMT) becomes one of the most important reliability issues with the downscaling of feature size. In this paper, the research results show that the reverse surface leakage current in AlGaN/GaN HEMT with SiN passivation increases with the enhancement of temperature in the range from 298 K to 423 K. Three possible transport mechanisms are proposed and examined to explain the generation of reverse surface leakage current. By comparing the experimental data with the numerical transport models, it is found that neither Fowler-Nordheim tunneling nor Frenkel-Poole emission can describe the transport of reverse surface leakage current. However, good agreement is found between the experimental data and the two-dimensional variable range hopping (2D-VRH) model. Therefore, it is concluded that the reverse surface leakage current is dominated by the electron hopping through the surface states at the barrier layer. Moreover, the activation energy of surface leakage current is extracted, which is around 0.083 eV. Finally, the SiN passivated HEMT with a high Al composition and a thin AlGaN barrier layer is also studied. It is observed that 2D-VRH still dominates the reverse surface leakage current and the activation energy is around 0.10 eV, which demonstrates that the alteration of the AlGaN barrier layer does not affect the transport mechanism of reverse surface leakage current in this paper.

Improved performance of AlGaN/GaN HEMT by N2O plasma pre-treatment

Mi Min-Han, Zhang Kai, Zhao Sheng-Lei, Wang Chong, Zhang Jin-Cheng, Ma Xiao-Hua, Hao Yue
Chin. Phys. B 2015, 24 (2): 027303;  doi: 10.1088/1674-1056/24/2/027303
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The influence of an N2O plasma pre-treatment technique on characteristics of AlGaN/GaN high electron mobility transistor (HEMT) prepared by using a plasma-enhanced chemical vapor deposition (PECVD) system is presented. After the plasma treatment, the peak transconductance (gm) increases from 209 mS/mm to 293 mS/mm. Moreover, it is observed that the reverse gate leakage current is lowered by one order of magnitude and the drain current dispersion is improved in the plasma-treated device. From the analysis of frequency-dependent conductance, it can be seen that the trap state density (DT) and time constant (τT) of the N2O-treated device are smaller than those of a non-treated device. The results indicate that the N2O plasma pre-pretreatment before the gate metal deposition could be a promising approach to enhancing the performance of the device.

Morphology-controlled preparation of tungsten oxide nanostructures for gas-sensing application

Qin Yu-Xiang, Liu Chang-Yu, Liu Yang
Chin. Phys. B 2015, 24 (2): 027304;  doi: 10.1088/1674-1056/24/2/027304
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A novel three-dimensional (3D) hierarchical structure and a roughly oriented one-dimensional (1D) nanowire of WO3 are selectively prepared on an alumina substrate by an induced hydrothermal growth method. Each hierarchical structure is constructed hydrothermally through bilateral inductive growth of WO3 nanowire arrays from a nanosheet preformed on the substrate. Only roughly oriented 1D WO3 nanowire can be obtained from a spherical induction layer. The analyses show that as-prepared 1D nanowire and 3D hierarchical structures exhibit monoclinic and hexagonal phases of WO3, respectively. The gas-sensing properties of the nanowires and the hierarchical structure of WO3, which include the variations of their resistances and response times when exposed to NO2, are investigated at temperatures ranging from room temperature (20 ℃) to 250 ℃ over 0.015 ppm-5 ppm NO2. The hierarchical WO3 behaves as a p-type semiconductor at room temperature, and shows p-to-n response characteristic reversal with the increase of temperature. Meanwhile, unlike the 1D nanowire, the hierarchical WO3 exhibits an excellent response characteristic and very good reversibility and selectivity to NO2 gas at room temperature due to its unique microstructure. Especially, it is found that the hierarchical WO3-based sensor is capable of detecting NO2 at a ppb level with ultrashort response time shorter than 5 s, indicating the potential of this material in developing a highly sensitive gas sensor with a low power consumption.

Synthesis and electrical properties of In2O3(ZnO)m superlattice nanobelt

Tang Xin-Yue, Gao Hong, Wu Li-Li, Wen Jing, Pan Si-Ming, Liu Xin, Zhang Xi-Tian
Chin. Phys. B 2015, 24 (2): 027305;  doi: 10.1088/1674-1056/24/2/027305
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One-dimensional (1D) In2O3(ZnO)m superlattice nanobelts are synthesized by a chemical vapor deposition method. The formation of the In2O3(ZnO)m superlattice is verified by the high-resolution transmission electron microscopy images. The typical zigzag boundaries could be clearly observed. An additional peak at 614 cm-1 is found in the Raman spectrum, which may correspond to the superlattice structure. The study about the electrical transport properties reveals that the In2O3(ZnO)m nanobelts exhibit peculiar nonlinear I-V characteristics even under the Ohmic contact measurement condition, which are different from the Ohmic behaviors of the In-doped ZnO nanobelts. The photoelectrical measurements show the differences in the photocurrent property between them, and their transport mechanisms are also discussed.

Evolution of the 128-cm-1 Raman phonon mode with temperature in Ba(Fe1-xCox)2As 2 (x = 0.065 and 0.2) Hot!

Yang Yan-Xing, Gallais Yann, Fang Zhi-Hao, Shi Jing, Xiong Rui
Chin. Phys. B 2015, 24 (2): 027401;  doi: 10.1088/1674-1056/24/2/027401
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We report electronic Raman scattering measurements on Ba(Fe1-xCox)2As2 (x = 0.065 and 0.2) single crystals with Raman shifts from 9 cm-1 up to 600 cm-1 in the symmetry of B1g with respect to 1 Fe unit cell. When the crystals are cooled down, the evident quasielastic peaks of Raman spectra occur only in the crystal with x = 0.065, which is due to the contribution of orbital ordering between xz and yz Fe 3d orbitals, as we reported in another work. Here, we analyze the Eg phonon at 128 cm-1, which has the same function form of its Raman tensors as those of xz and yz Fe 3d orbitals in these two crystals respectively. Unlike their electronic continuums, no anomalies are found in the Eg phonons of these two samples, which simply follows the expressions corresponding to the anharmonic phonon decay into acoustic phonons with the same frequencies and opposite momenta. Our results indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping and there is not any indication of coupling between charge nematicity and Eg phonon mode from our experimental results, which is consistent with the results in our previous work.

Quantum phase transition and Coulomb blockade effect in triangular quantum dots with interdot capacitive and tunnel couplings

Xiong Yong-Chen, Wang Wei-Zhong, Yang Jun-Tao, Huang Hai-Ming
Chin. Phys. B 2015, 24 (2): 027501;  doi: 10.1088/1674-1056/24/2/027501
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The quantum phase transition and the electronic transport in a triangular quantum dot system are investigated using the numerical renormalization group method. We concentrate on the interplay between the interdot capacitive coupling V and the interdot tunnel coupling t. For small t, three dots form a local spin doublet. As t increases, due to the competition between V and t, there exist two first-order transitions with phase sequence spin-doublet-magnetic frustration phase-orbital spin singlet. When t is absent, the evolutions of the total charge on the dots and the linear conductance are of the typical Coulomb-blockade features with increasing gate voltage. While for sufficient t, the antiferromagnetic spin correlation between dots is enhanced, and the conductance is strongly suppressed for the bonding state is almost doubly occupied.

Schwinger-boson approach to anisotropy ferrimagnetic chain with bond alternation

Li Yin-Xiang, Chen Bin
Chin. Phys. B 2015, 24 (2): 027502;  doi: 10.1088/1674-1056/24/2/027502
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We use the Schwinger-boson approach to study the anisotropy ferrimagnetic spin-(1/2,1) chain with bond alternation. Based on the effect of bond alternation δ, we obtain energy gap, free energy, and specific heat, respectively. The specific heat with larger bond alternation (δ>0.7) displays a peak at low temperature. Based on the effect of XXZ anisotropy parameter Δ, we present excited spectrums, free energy, and specific heat, respectively.

Room-temperature ferromagnetism with high magnetic moment in Cu-doped AlN single crystal whiskers

Jiang Liang-Bao, Liu Yu, Zuo Si-Bin, Wang Wen-Jun
Chin. Phys. B 2015, 24 (2): 027503;  doi: 10.1088/1674-1056/24/2/027503
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Ferromagnetism is investigated in high-quality Cu-doped AlN single crystal whiskers. The whiskers exhibit room-temperature ferromagnetism with a magnetic moment close to the results from first-principles calculations. High crystallinity and low Cu concentrations are found to be indispensable for high magnetic moments. The difference between the experimental and theoretical moment values is explored in terms of the influence of nitrogen vacancies. The calculated results demonstrate that nitrogen vacancies can reduce the magnetic moments of Cu atom.

Effects of growing conditions on the electric and magnetic properties of strained La2/3Sr1/3MnO3 thin films

Lu Hai-Xia, Wang Jing, Shen Bao-Gen, Sun Ji-Rong
Chin. Phys. B 2015, 24 (2): 027504;  doi: 10.1088/1674-1056/24/2/027504
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We investigate the growing condition dependences of magnetic and electric properties of the La2/3Sr1/3MnO3 thin films grown on SrTiO3 (001) substrates. With reducing the film thickness and growth pressure, the Curie temperature (TC) drops off, and the magnetism and metallicity are suppressed. At an appropriate deposition temperature, we can obtain the best texture and remarkably enhance the magnetic and electrical properties. However, the resistivity of film cannot be modulated by changing the dc current and green light intensity. This result may be induced by the coherent strains in the epitaxially grown film due to its lattice mismatching that of the SrTiO3 substrate. Furthermore, we show that the relations between the magnetism and the resistivity for the typical films with different thickness values. For the 13.4-nm-thick film, the R-T curve presents two transition behaviors: insulator-to-metal and metal-to-insulator in the cooling process: the former corresponds to magnetic transition, and the later correlates with thermal excitation conduction.

Magnetization reversal process in Fe/Si (001) single-crystalline film investigated by planar Hall effect

Ye Jun, He Wei, Hu Bo, Tang Jin, Zhang Yong-Sheng, Zhang Xiang-Qun, Chen Zi-Yu, Cheng Zhao-Hua
Chin. Phys. B 2015, 24 (2): 027505;  doi: 10.1088/1674-1056/24/2/027505
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A planar Hall effect (PHE) is introduced to investigate the magnetization reversal process in single-crystalline iron film grown on a Si (001) substrate. Owing to the domain structure of iron film and the characteristics of PHE, the magnetization switches sharply in an angular range of the external field for two steps of 90° domain wall displacement and one step of 180° domain wall displacement near the easy axis, respectively. However, the magnetization reversal process near the hard axis is completed by only one step of 90° domain wall displacement and then rotates coherently. The magnetization reversal process mechanism near the hard axis seems to be a combination of coherent rotation and domain wall displacement. Furthermore, the domain wall pinning energy and uniaxial magnetic anisotropy energy can also be derived from the PHE measurement.

Hole transporting material 5, 10, 15-tribenzyl-5H-diindolo[3, 2-a:3',2'-c]-carbazole for efficient optoelectronic applications as an active layer

Zheng Yan-Qiong, William J. Potscavage Jr, Zhang Jian-Hua, Wei Bin, Huang Rong-Juan
Chin. Phys. B 2015, 24 (2): 027801;  doi: 10.1088/1674-1056/24/2/027801
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In order to explore the novel application of the transparent hole-transporting material 5,10,15-tribenzyl-5H-diindolo[3,2-a:3',2'-c]-carbazole (TBDI), in this article TBDI is used as an active layer but not a buffer layer in a photodetector (PD), organic light-emitting diode (OLED), and organic photovoltaic cell (OPV) for the first time. Firstly, the absorption and emission spectra of a blend layer comprised of TBDI and electron-transporting material bis-(2-methyl-8-quinolinate) 4-phenylphenolate (BAlq) are investigated. Based on the absorption properties, an organic PD with a peak absorption at 320 nm is fabricated, and a relatively-high detectivity of 2.44×1011 cm·Hz1/2/W under 320-nm illumination is obtained. The TBDI/tris (8-hydroxyquinoline) aluminum (Alq3) OLED device exhibits a comparable external quantum efficiency and current efficiency to a traditional 4, 4-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD)/Alq3 OLED. A C70-based Schottky junction with 5 wt%-TBDI yields a power conversion efficiency of 5.0%, which is much higher than 1.7% for an α -NPD-based junction in the same configuration. These results suggest that TBDI has some promising properties which are in favor of the hole-transporting in Schottky junctions with a low-concentration donor.

Elastic, dielectric, and piezoelectric characterization of 0.92Pb(Zn1/3Nb2/3)O3-0.08PbTiO3 single crystal by Brillouin scattering

Fang Shao-Xi, Tang Dong-Yun, Chen Zhao-Ming, Zhang Hua, Liu Yu-Long
Chin. Phys. B 2015, 24 (2): 027802;  doi: 10.1088/1674-1056/24/2/027802
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In this paper, a complete set of elastic, piezoelectric, and dielectric constants of high-quality tetragonal poled 0.92Pb(Zn1/3Nb2/3)O3-0.08PbTiO3 single crystal grown by the modified flux method is determined using high-resolution Brillouin scattering. A comparison is made between the results obtained by a hybrid method combining ultrasonic and resonant techniques and the results obtained by the Brillouin scattering. The elastic, piezoelectric, and dielectric constants obtained by the two methods are similar. The Brillouin spectrum consists of one longitudinal and two transverse acoustic phonon modes, and the variations of the Brillouin shifts, the full widths at half maximum, and the scattering intensities of these modes with scattering angle θ are investigated. In particular, the transverse acoustic phonon mode at the low-frequency becomes markedly soft from 28.2 GHz to 18.4 GHz and broadens gradually with the increase of θ, while its intensity decreases gradually as compared with that of the original one. The possible origins of the results are discussed.

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with Fe3O4 particles

Geng Xin, He Da-Wei, Wang Yong-Sheng, Zhao Wen, Zhou Yi-Kang, Li Shu-Lei
Chin. Phys. B 2015, 24 (2): 027803;  doi: 10.1088/1674-1056/24/2/027803
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In order to investigate the impedance matching properties of microwave absorbers, the ternary nanocomposites of GO/PANI/Fe3O4 (GPF) are prepared via a two-step method, GO/PANI composites are synthesized by dilute polymerization in the presence of aniline monomer and GO, and GO/PANI/Fe3O4 is prepared via a co-precipitation method. The obtained nanocomposites are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), respectively. The microwave absorbability reveals enhanced microwave absorption properties compared with GO, PANI, and GO/PANI. The maximum reflection loss of GO/PANI/Fe3O4 is up to -27 dB at 14 GHz with its thickness being 2 mm, and its absorption bandwidths exceeding -10 dB are more than 11.2 GHz with its thickness values being in the range from 1.5 mm-4 mm. It provides that GO/PANI/Fe3O4 can be used as an attractive candidate for microwave absorbers.

High-frequency properties of oil-phase-synthesized ZnO nanoparticles

Ding Hao-Feng, Yang Hai-Tao, Liu Li-Ping, Ren Xiao, Song Ning-Ning, Shen Jun, Zhang Xiang-Qun, Cheng Zhao-Hua, Zhao Guo-Ping
Chin. Phys. B 2015, 24 (2): 027804;  doi: 10.1088/1674-1056/24/2/027804
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Monodispersive ZnO nanoparticles each with a hexagonal wurtzite structure are facilely prepared by the high-temperature organic phase method. The UV-visible absorption peak of ZnO nanoparticles presents an obvious blue-shift from 385 nm of bulk ZnO to 369 nm. Both the real part and the image part of the complex permittivity of ZnO nanoparticles from 0.1 GHz to 10 GHz linearly decrease without obvious resonance peak appearing. The real parts of intrinsic permittivity of ZnO nanoparticles are about 5.7 and 5.0 at 0.1 GHz and 10 GHz respectively, and show an obvious size-dependent behavior. The dielectric loss angle tangent (tanδ) of ZnO nanoparticles with a different weight ratio shows a different decreasing law with the increase of frequency.

Temperature effect on the electronic structure of Nb:SrTiO3 (100) surface

Zhang Shuang-Hong, Wang Jia-Ou, Qian Hai-Jie, Wu Rui, Zhang Nian, Lei Tao, Liu Chen, Kurash Ibrahim
Chin. Phys. B 2015, 24 (2): 027901;  doi: 10.1088/1674-1056/24/2/027901
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The effect of temperature on the electronic structure of Nb-doped SrTiO3 (100) surface is investigated by high-resolution synchrotron radiation photoemission spectroscopy. According to the x-ray photoemission spectroscopy (XPS) results, at an annealing temperature of less than 700 ℃, the adsorbed carbon and hydroxyl on the STO surface could be removed, to expose the fresh intrinsic surface with a constant ratio of Ti/O. It is obvious that the STO would be doped by Ca+ impurities of bulks and O vacancies in the surface after annealing at 920 ℃ for one hour.

Defect reduction in GaAs/Si film with InAs quantum-dot dislocation filter grown by metalorganic chemical vapor deposition

Wang Jun, Hu Hai-Yang, Deng Can, He Yun-Rui, Wang Qi, Duan Xiao-Feng, Huang Yong-Qing, Ren Xiao-Min
Chin. Phys. B 2015, 24 (2): 028101;  doi: 10.1088/1674-1056/24/2/028101
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The growth of GaAs epilayers on silicon substrates with multiple layers of InAs quantum dots (QDs) as dislocation filters by metalorganic chemical vapor deposition (MOCVD) is investigated in detail. The growth conditions of single and multiple layers of QDs used as dislocation filters in GaAs/Si epilayers are optimized. It is found that the insertion of a five-layer InAs QDs into the GaAs buffer layer effectively reduces the dislocation density of GaAs/Si film. Compared with the dislocation density of 5×107 cm-2 in the GaAs/Si sample without QDs, a density of 2×106 cm-2 is achieved in the sample with QD dislocation filters.

Influence of substrate bias voltage on the microstructure of nc-SiOx:H film

Li Hui-Min, Yu Wei, Xu Yan-Mei, Ji Yun, Jiang Zhao-Yi, Wang Xin-Zhan, Li Xiao-Wei, Fu Guang-Sheng
Chin. Phys. B 2015, 24 (2): 028102;  doi: 10.1088/1674-1056/24/2/028102
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Amorphous silicon oxide containing nanocrystalline silicon grain (nc-SiOx:H) films are prepared by a plasma-enhanced chemical vapor deposition technique at different negative substrate bias voltages. The influence of the bias voltage applied to the substrate on the microstructure is investigated. The analysis of x-ray diffraction spectra evidences the in situ growth of nanocrystalline Si. The grain size can be well controlled by varying the substrate bias voltage, and the largest size is obtained at 60 V. Fourier transform infrared spectra studies on the microstructure evolutions of the nc-SiOx:H films suggest that the absorption peak intensities, which are related to the defect densities, can be well controlled. It can be attributed to the fact that the negative bias voltage provides a useful way to change the energies of the particles in the deposition process, which can provide sufficient driving force for the diffusion and movement for the species on the growing surface and effectively passivate the dangling bonds. Also the larger grain size and lower band gap, which will result in better photosensitivity, can also be obtained with a moderate substrate bias voltage of 60 V.

Effects of annealing temperature on shape transformation and optical properties of germanium quantum dots

Alireza Samavati, Z. Othaman, S. K. Ghoshal, M. K. Mustafa
Chin. Phys. B 2015, 24 (2): 028103;  doi: 10.1088/1674-1056/24/2/028103
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The influences of thermal annealing on the structural and optical features of radio frequency (rf) magnetron sputtered self-assembled Ge quantum dots (QDs) on Si (100) are investigated. Preferentially oriented structures of Ge along the (220) and (111) directions together with peak shift and reduced strain (4.9% to 2.7%) due to post-annealing at 650 ℃ are discerned from x-ray differaction (XRD) measurement. Atomic force microscopy (AFM) images for both pre-annealed and post-annealed (650 ℃) samples reveal pyramidal-shaped QDs (density ~ 0.26×1011 cm-2) and dome-shape morphologies with relatively high density ~ 0.92 ×1011 cm-2, respectively. This shape transformation is attributed to the mechanism of inter-diffusion of Si in Ge interfacial intermixing and strain non-uniformity. The annealing temperature assisted QDs structural evolution is explained using the theory of nucleation and growth kinetics where free energy minimization plays a pivotal role. The observed red-shift ~ 0.05 eV in addition to the narrowing of the photoluminescence peaks results from thermal annealing, and is related to the effect of quantum confinement. Furthermore, the appearance of a blue-violet emission peak is ascribed to the recombination of the localized electrons in the Ge-QDs/SiO2 or GeOx and holes in the ground state of Ge dots. Raman spectra of both samples exhibit an intense Ge-Ge optical phonon mode which shifts towards higher frequency compared with those of the bulk counterpart. An experimental Raman profile is fitted to the models of phonon confinement and size distribution combined with phonon confinement to estimate the mean dot sizes. A correlation between thermal annealing and modifications of the structural and optical behavior of Ge QDs is established. Tunable growth of Ge QDs with superior properties suitable for optoelectronic applications is demonstrated.

Influence of colloidal particle transfer on the quality of self-assembling colloidal photonic crystal under confined condition

Zhao Yong-Qiang, Li Juan, Liu Qiu-Yan, Dong Wen-Jun, Chen Ben-Yong, Li Chao-Rong
Chin. Phys. B 2015, 24 (2): 028104;  doi: 10.1088/1674-1056/24/2/028104
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The relationship between colloidal particle transfer and the quality of colloidal photonic crystal (CPC) is investigated by comparing colloidal particle self-assembling under the vertical channel (VC) and horizontal channel (HC) conditions. Both the theoretical analyses and the experimental measurements indicate that crystal quality depends on the stability of mass transfer. For the VC, colloidal particle transfer takes place in a stable laminar flow, which is conducive to forming high-quality crystal. In contrast, it happens in an unstable turbulent flow for the HC. Crystals with cracks and an uneven surface formed under the HC condition can be seen from the images of a field emission scanning electron microscope (SEM) and a three-dimensional (3D) laser scanning microscope (LSM), respectively.

Baseline optimization of SQUID gradiometer for magnetocardiography

Li Hua, Zhang Shu-Lin, Qiu Yang, Zhang Yong-Sheng, Zhang Chao-Xiang, Kong Xiang-Yan, Xie Xiao-Ming
Chin. Phys. B 2015, 24 (2): 028501;  doi: 10.1088/1674-1056/24/2/028501
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SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements. An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance. By placing several magnetometers at different heights along the vertical direction, we could simultaneously obtain the synthetic gradiometers with different baselines. By using the traditional signal-to-noise ratio (SNR) as a performance index, we successfully obtain an optimal baseline for the magnetocardiography (MCG) measurement in a magnetically shielded room (MSR). Finally, we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR. The SNR about 38 dB is obtained in the recorded MCG signal.

One-dimensional breakdown voltage model of SOI RESURF lateral power device based on lateral linearly graded approximation

Zhang Jun, Guo Yu-Feng, Xu Yue, Lin Hong, Yang Hui, Hong Yang, Yao Jia-Fei
Chin. Phys. B 2015, 24 (2): 028502;  doi: 10.1088/1674-1056/24/2/028502
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A novel one-dimensional (1D) analytical model is proposed for quantifying the breakdown voltage of a reduced surface field (RESURF) lateral power device fabricated on silicon on an insulator (SOI) substrate. We assume that the charges in the depletion region contribute to the lateral PN junctions along the diagonal of the area shared by the lateral and vertical depletion regions. Based on the assumption, the lateral PN junction behaves as a linearly graded junction, thus resulting in a reduced surface electric field and high breakdown voltage. Using the proposed model, the breakdown voltage as a function of device parameters is investigated and compared with the numerical simulation by the TCAD tools. The analytical results are shown to be in fair agreement with the numerical results. Finally, a new RESURF criterion is derived which offers a useful scheme to optimize the structure parameters. This simple 1D model provides a clear physical insight into the RESURF effect and a new explanation on the improvement in breakdown voltage in an SOI RESURF device.

Nonlinear properties of the lattice network-based nonlinear CRLH transmission lines

Wang Zheng-Bin, Wu Zhao-Zhi, Gao Chao
Chin. Phys. B 2015, 24 (2): 028503;  doi: 10.1088/1674-1056/24/2/028503
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The nonlinear properties of lattice network-based (LNB) composite right-/left-handed transmission lines (CRLH TLs) with nonlinear capacitors are experimentally investigated. Harmonic generation, subharmonic generation, and parametric excitation are clearly observed in an unbalanced LNB CRLH TL separately. While the balanced design of the novel nonlinear TL shows that the subharmonic generation and parametric processes can be suppressed, and almost the same power level of the higher harmonics can be achieved over a wide bandwidth range, which are difficult to find in conventional CRLH TLs.

Mapping an on-chip terahertz antenna by a scanning near-field probe and a fixed field-effect transistor

Lü Li, Sun Jian-Dong, Roger A. Lewis, Sun Yun-Fei, Wu Dong-Min, Cai Yong, Qin Hua
Chin. Phys. B 2015, 24 (2): 028504;  doi: 10.1088/1674-1056/24/2/028504
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In the terahertz (THz) regime, the active region for a solid-state detector usually needs to be implemented accurately in the near-field region of an on-chip antenna. Mapping of the near-field strength could allow for rapid verification and optimization of new antenna/detector designs. Here, we report a proof-of-concept experiment in which the field mapping is realized by a scanning metallic probe and a fixed AlGaN/GaN field-effect transistor. Experiment results agree well with the electromagnetic-wave simulations. The results also suggest a field-effect THz detector combined with a probe tip could serve as a high sensitivity THz near-field sensor.

Energy transfer ultraviolet photodetector with 8-hydroxyquinoline derivative-metal complexes as acceptors

Wu Shuang-Hong, Li Wen-Lian, Chen Zhi, Li Shi-Bin, Wang Xiao-Hui, Wei Xiong-Bang
Chin. Phys. B 2015, 24 (2): 028505;  doi: 10.1088/1674-1056/24/2/028505
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We choose 8-hydroxyquinoline derivative-metal complexes (Beq, Mgq, and Znq) as the acceptors (A) and 4,4',4”-tri-(2-methylphenyl phenylamino) triphenylaine (m-MTDATA) as the donor (D) respectively to study the existing energy transfer process in the organic ultraviolet (UV) photodetector (PD), which has an important influence on the sensitivity of PDs. The energy transfer process from D to A without exciplex formation is discussed, differing from the working mechanism of previous PDs with Gaq [Zisheng Su, Wenlian Li, Bei Chu, Tianle Li, Jianzhuo Zhu, Guang Zhang, Fei Yan, Xiao Li, Yiren Chen and Chun-Sing Lee 2008 Appl. Phys. Lett. 93 103309)] and REq [J. B. Wang, W. L. Li, B. Chu, L. L. Chen, G. Zhang, Z. S. Su, Y. R. Chen, D. F. Yang, J. Z. Zhu, S. H. Wu, F. Yan, H. H. Liu, C. S. Lee 2010 Org. Electron. 11 1301] used as an A material. Under 365-nm UV irradiation with an intensity of 1.2 mW/cm2, the m-MTDATA:Beq blend device with a weight ratio of 1:1 shows a response of 192 mA/W with a detectivity of 6.5×1011 Jones, which exceeds those of PDs based on Mgq (146 mA/W) and Znq (182 mA/W) due to better energy level alignment between m-MTDATA/Beq and lower radiative decay. More photophysics processes of the PDs involved are discussed in detail.

Stretching instability of intrinsically curved semiflexible biopolymers: A lattice model approach

Zhou Zi-Cong, Lin Fang-Ting, Chen Bo-Han
Chin. Phys. B 2015, 24 (2): 028701;  doi: 10.1088/1674-1056/24/2/028701
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We apply a Monte Carlo simulation method to lattice systems to study the effect of an intrinsic curvature on the mechanical property of a semiflexible biopolymer. We find that when the intrinsic curvature is sufficiently large, the extension of a semiflexible biopolymer can undergo a first-order transition at finite temperature. The critical force increases with increasing intrinsic curvature. However, the relationship between the critical force and the bending rigidity is structure-dependent. In a triangle lattice system, when the intrinsic curvature is smaller than a critical value, the critical force increases with the increasing bending rigidity first, and then decreases with the increasing bending rigidity. In a square lattice system, however, the critical force always decreases with the increasing bending rigidity. In contrast, when the intrinsic curvature is greater than the critical value, the larger bending rigidity always results in a larger critical force in both lattice systems.

Controlling cooperativity of a metastable open system coupled weakly to a noisy environment

Victor I. Teslenko, Oleksiy L. Kapitanchuk, Zhao Yang
Chin. Phys. B 2015, 24 (2): 028702;  doi: 10.1088/1674-1056/24/2/028702
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The notion of cooperativity comprises a specific characteristic of a multipartite system concerning its ability to demonstrate a sigmoidal-type response of varying sensitivities to input stimuli in transitions between states under controlled conditions. From a statistical physics viewpoint, in this work we attempt to describe the cooperativity by the stability of a metastable open system with respect to irreversibility. To treat the evolution of a system weakly coupled to the environment in a kinetic framework, we consider two fluctuating energy levels of different dimensionalities, initial population of one level, reversible transitions of population between the levels, and irreversible depopulation of another level. An average is made over level fluctuations and environment vibrations so that an inter-level transition rate can be obtained accounting for the influences of external control on level position and dimensionality. It is found that the cooperativity of the two-level system is bounded approximately between 0.736 and unity, with the lower bound indicating worsening system stability.

Fast parallel algorithm for three-dimensional distance-driven model in iterative computed tomography reconstruction

Chen Jian-Lin, Li Lei, Wang Lin-Yuan, Cai Ai-Long, Xi Xiao-Qi, Zhang Han-Ming, Li Jian-Xin, Yan Bin
Chin. Phys. B 2015, 24 (2): 028703;  doi: 10.1088/1674-1056/24/2/028703
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The projection matrix model is used to describe the physical relationship between reconstructed object and projection. Such a model has a strong influence on projection and backprojection, two vital operations in iterative computed tomographic reconstruction. The distance-driven model (DDM) is a state-of-the-art technology that simulates forward and back projections. This model has a low computational complexity and a relatively high spatial resolution; however, it includes only a few methods in a parallel operation with a matched model scheme. This study introduces a fast and parallelizable algorithm to improve the traditional DDM for computing the parallel projection and backprojection operations. Our proposed model has been implemented on a GPU (graphic processing unit) platform and has achieved satisfactory computational efficiency with no approximation. The runtime for the projection and backprojection operations with our model is approximately 4.5 s and 10.5 s per loop, respectively, with an image size of 256×256×256 and 360 projections with a size of 512×512. We compare several general algorithms that have been proposed for maximizing GPU efficiency by using the unmatched projection/backprojection models in a parallel computation. The imaging resolution is not sacrificed and remains accurate during computed tomographic reconstruction.

Multiple optical trapping based on high-order axially symmetric polarized beams

Zhou Zhe-Hai, Zhu Lian-Qing
Chin. Phys. B 2015, 24 (2): 028704;  doi: 10.1088/1674-1056/24/2/028704
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Multiple optical trapping with high-order axially symmetric polarized beams (ASPBs) is studied theoretically, and a scheme based on far-field optical trapping with ASPBs is first proposed. The focused fields and the corresponding gradient forces on Rayleigh dielectric particles are calculated for the scheme. The calculated results indicate that multiple ultra-small focused spots can be achieved, and multiple nanometer-sized particles with refractive index higher than the ambient can be trapped simultaneously near these focused spots, which are expected to enhance the capabilities of traditional optical trapping systems and provide a solution for massive multiple optical trapping of nanometer-sized particles.

Changing characteristics and spatial differentiation of spring precipitation in Southwest China during 1961-2012

Liu Hong-Lan, Zhang Qiang, Zhang Jun-Guo, Hu Wen-Chao, Guo Jun-Qin, Wang Sheng
Chin. Phys. B 2015, 24 (2): 029201;  doi: 10.1088/1674-1056/24/2/029201
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In this study, we analyze spring precipitation from 92 meteorological stations spanning between 1961 and 2012 to understand temporal-spatial variability and change of spring precipitation over Southwest China. Various analysis methods are used for different purposes, including empirical orthogonal function (EOF) analysis and rotated EOF (REOF) for analyzing spatial structure change of precipitation anomaly, and the Mann-Kendall testing method to determine whether there were abrupt changes during the analyzed time span. We find that the first spatial mode of the precipitation has a domain uniform structure; the second is dominated by a spatial dipole; and the third contains five variability centers. The 2000s is the decade with the largest amount of precipitation while the 1990s is the decade with the smallest amount of precipitation. The year-to-year difference of that region is large: the amount of the largest precipitation year doubles that of the smallest precipitation year. We also find that spring precipitation in Southwest China experienced a few abrupt changes: a sudden increase at 1966, a sudden decrease at 1979, and a sudden increase at 1995. We speculate that the spring precipitation will increase gradually in the next two decades.
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