中国物理B

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Consecutive induction melting of nickel-based superalloy in electrode induction gas atomization

峰山, 夏敏, 葛昌纯

2017 (6): 60201-060201. doi: 10.1088/1674-1056/26/6/060201

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The crucible-free electrode induction melting gas atomization (EIGA) technology is an advanced technology for preparing ultra-clean nickel-based superalloy powders. One of the key issues for fabricating powders with high quality and yield is the consecutive induction melting of a superalloy electrode. The coupling of a superalloy electrode and coil, frequency, output power, and heat conduction are investigated to improve the controllable electrode induction melting process. Numerical simulation results show that when the coil frequency is 400 kHz, the output power is 100 kW, superalloy liquid flow with a diameter of about 5 mm is not consecutive. When the coil frequency is reduced to 40 kHz, the output power is 120 kW, superalloy liquid flow is consecutive, and its diameter is about 7 mm.

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Determination of the vapor-liquid transition of square-well particles using a novel generalized-canonical-ensemble-based method

赵亮, 徐顺, 涂育松, 周昕

2017 (6): 60202-060202. doi: 10.1088/1674-1056/26/6/060202

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The square-well (SW) potential is one of the simplest pair potential models and its phase behavior has been clearly revealed, therefore it has become a benchmark for checking new theories or numerical methods. We introduce the generalized canonical ensemble (GCE) into the isobaric replica exchange Monte Carlo (REMC) algorithm to form a novel isobaric GCE-REMC method, and apply it to the study of vapor-liquid transition of SW particles. It is validated that this method can reproduce the vapor-liquid diagram of SW particles by comparing the estimated vapor-liquid binodals and the critical point with those from the literature. The notable advantage of this method is that the unstable vapor-liquid coexisting states, which cannot be detected using conventional sampling techniques, are accessed with a high sampling efficiency. Besides, the isobaric GCE-REMC method can visit all the possible states, including stable, metastable or unstable states during the phase transition over a wide pressure range, providing an effective pathway to understand complex phase transitions during the nucleation or crystallization process in physical or biological systems.

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Solvability of a class of PT-symmetric non-Hermitian Hamiltonians: Bethe ansatz method

M Baradaran,H Panahi

2017 (6): 60301-060301. doi: 10.1088/1674-1056/26/6/060301

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We use the Bethe ansatz method to investigate the Schrödinger equation for a class of PT-symmetric non-Hermitian Hamiltonians. Elementary exact solutions for the eigenvalues and the corresponding wave functions are obtained in terms of the roots of a set of algebraic equations. Also, it is shown that the problems possess sl(2) hidden symmetry and then the exact solutions of the problems are obtained by employing the representation theory of sl(2) Lie algebra. It is found that the results of the two methods are the same.

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Approximate energies and thermal properties of a position-dependent mass charged particle under external magnetic fields

M Eshghi,H Mehraban,S M Ikhdair

2017 (6): 60302-060302. doi: 10.1088/1674-1056/26/6/060302

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We solve the Schrödinger equation with a position-dependent mass (PDM) charged particle interacted via the superposition of the Morse-plus-Coulomb potentials and is under the influence of external magnetic and Aharonov-Bohm (AB) flux fields. The nonrelativistic bound state energies together with their wave functions are calculated for two spatially-dependent mass distribution functions. We also study the thermal quantities of such a system. Further, the canonical formalism is used to compute various thermodynamic variables for second choosing mass by using the Gibbs formalism. We give plots for energy states as a function of various physical parameters. The behavior of the internal energy, specific heat, and entropy as functions of temperature and mass density parameter in the inverse-square mass case for different values of magnetic field are shown.

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Generating EPR-entangled mechanical state via feeding finite-bandwidth squeezed light

伊程前, 伊珍, 谷文举

2017 (6): 60303-060303. doi: 10.1088/1674-1056/26/6/060303

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Einstein-Podolski-Rosen (EPR) entanglement state is achievable by combining two single-mode position and momentum squeezed states at a 50:50 beam-splitter (BS). We investigate the generation of the EPR entangled state of two vibrating membranes in a ring resonator, where clockwise (CW) and counter-clockwise (CCW) travelling-wave modes are driven by lasers and finite-bandwidth squeezed lights. Since the optomechanical coupling depends on the location of the membranes, CW and CCW can couple to the symmetric and antisymmetric combination of mechanical modes for a suitable arrangement, which corresponds to a 50:50 BS mixing. Moreover, by employing the red-detuned driving laser and tuning the central frequency of squeezing field blue detuned from the driving laser with a mechanical frequency, the squeezing property of squeezed light can be perfectly transferred to the mechanical motion in the weak coupling regime. Thus, the BS mixing modes can be position and momentum squeezed by feeding the appropriate squeezed lights respectively, and the EPR entangled mechanical state is obtained. Moreover, cavity-induced mechanical cooling can further suppress the influence of thermal noise on the entangled state.

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Performance analysis of quantum access network using code division multiple access model

胡林曦, 杨灿, 何广强

2017 (6): 60304-060304. doi: 10.1088/1674-1056/26/6/060304

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A quantum access network has been implemented by frequency division multiple access and time division multiple access, while code division multiple access is limited for its difficulty to realize the orthogonality of the code. Recently, the chaotic phase shifters were proposed to guarantee the orthogonality by different chaotic signals and spread the spectral content of the quantum states. In this letter, we propose to implement the code division multiple access quantum network by using chaotic phase shifters and synchronization. Due to the orthogonality of the different chaotic phase shifter, every pair of users can faithfully transmit quantum information through a common channel and have little crosstalk between different users. Meanwhile, the broadband spectra of chaotic signals efficiently help the quantum states to defend against channel loss and noise.

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Realization of quantum permutation algorithm in high dimensional Hilbert space

陈东旭, 刘瑞丰, 张沛, 王云龙, 李宏荣, 高宏, 李福利

2017 (6): 60305-060305. doi: 10.1088/1674-1056/26/6/060305

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Quantum algorithms provide a more efficient way to solve computational tasks than classical algorithms. We experimentally realize quantum permutation algorithm using light's orbital angular momentum degree of freedom. By exploiting the spatial mode of photons, our scheme provides a more elegant way to understand the principle of quantum permutation algorithm and shows that the high dimension characteristic of light's orbital angular momentum may be useful in quantum algorithms. Our scheme can be extended to higher dimension by introducing more spatial modes and it paves the way to trace the source of quantum speedup.

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Fast generating W state of three superconducting qubits via Lewis-Riesenfeld invariants

于琳, 徐晶, 吴金雷, 计新

2017 (6): 60306-060306. doi: 10.1088/1674-1056/26/6/060306

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We propose a scheme for a fast generating three-qubit W state in a superconducting system by using a technique of shortcuts to adiabaticity, Lewis-Riesenfeld invariants. Three identical superconducting qubits (SQs) are connected by two coplanar waveguide resonators (CPWRs) capacitively. Under a certain limit condition, we convert the complicated SQ system into a simple three-state system. By designing experimentally accessible harmonic pulses, a three-SQ W state is implemented with quite short operation time and high fidelity. Numerical simulations prove that the scheme is robust against the parameter deviation. In addition, we also give detailed discussion about the scheme robustness against decoherence.

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Multi-copy entanglement purification with practical spontaneous parametric down conversion sources

张帅帅, 祁舒, 周澜, 盛宇波

2017 (6): 60307-060307. doi: 10.1088/1674-1056/26/6/060307

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Entanglement purification is to distill the high quality entanglement from the low quality entanglement with local operations and classical communications. It is one of the key technologies in long-distance quantum communication. We discuss an entanglement purification protocol (EPP) with spontaneous parametric down conversion (SPDC) sources, in contrast to previous EPP with multi-copy mixed states, which requires ideal entanglement sources. We show that the SPDC source is not an obstacle for purification, but can benefit the fidelity of the purified mixed state. This EPP works for linear optics and is feasible in current experiment technology.

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Superconducting phase qubits with shadow-evaporated Josephson junctions

宿非凡, 刘伟洋, 徐晖凯, 邓辉, 李志远, 田野, 朱晓波, 郑东宁, 吕力, 赵士平

2017 (6): 60308-060308. doi: 10.1088/1674-1056/26/6/060308

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We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device (SQUID) detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μ² are fabricated for the qubit, in which the number of the decoherence-causing two-level systems (TLS) residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T₁ and dephasing time T_φ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.

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Gravitational quasi-normal modes of static R² Anti-de Sitter black holes

马洪, 李瑾

2017 (6): 60401-060401. doi: 10.1088/1674-1056/26/6/060401

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In this paper, we study the gravitational quasi-normal modes (QNMs) for a static R² black hole (BH) in Anti-de Sitter (AdS) spacetime. The corresponding master equation of odd parity is derived and the QNMs are evaluated by the Horowitz and Hubeny method. Meanwhile the stability of such BH is also discussed through the temporal evolution of the perturbation field. Here we mainly consider the coefficient λ, which is related to the radius of AdS black hole, on the QNMs of the R² AdS BH. The results show that the Re(ω) and |Im(ω)| of the QNMs increase together as |λ| increases for a given angular momentum number l. That indicates with a larger value of |λ| the corresponding R² AdS BH returns to stable much more quickly. The dynamic evolution of the perturbation field is consistent with the results derived by the Horowitz and Hubeny method. Since in the conformal field theory the QNMs can reflect its approach to equilibrium, so our related results could be referential to studies of the AdS/CFT conjecture. The relationship between λ and the properties of the static R² BH might be helpful for the development of R² gravitational theory.

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Equilibrium dynamics of the sub-Ohmic spin-boson model under bias

郑大川, 同宁华

2017 (6): 60501-060501. doi: 10.1088/1674-1056/26/6/060501

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Using the bosonic numerical renormalization group method, we studied the equilibrium dynamical correlation function C(ω) of the spin operator σ_z for the biased sub-Ohmic spin-boson model. The small-ω behavior C(ω)∝ω^s is found to be universal and independent of the bias ε and the coupling strength α (except at the quantum critical point α=α_c and ε=0). Our NRG data also show C(ω)∝χ²ω^s for a wide range of parameters, including the biased strong coupling regime (ε≠0 and α > α_c), supporting the general validity of the Shiba relation. Close to the quantum critical point α_c, the dependence of C(ω) on α and ε is understood in terms of the competition between ε and the crossover energy scale ω₀^* of the unbiased case. C(ω) is stable with respect to ε for ε≪ε^*. For ε≫ε^*, it is suppressed by ε in the low frequency regime. We establish that ε^*∝(ω₀^*)^1/θ holds for all sub-Ohmic regime 0≤s < 1, with θ=2/(3s) for 0 < s≤1/2 and θ=2/(1+s) for 1/2 < s < 1. The variation of C(ω) with α and ε is summarized into a crossover phase diagram on the α-ε plane.

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Dynamical correlation functions of the quadratic coupling spin-Boson model

郑大川, 同宁华

2017 (6): 60502-060502. doi: 10.1088/1674-1056/26/6/060502

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The spin-boson model with quadratic coupling is studied using the bosonic numerical renormalization group method. We focus on the dynamical auto-correlation functions C_O(ω), with the operator Ô taken as σ_x, σ_z, and X, respectively. In the weak-coupling regime α < α_c, these functions show power law ω-dependence in the small frequency limit, with the powers 1+2s, 1+2s, and s, respectively. At the critical point α=α_c of the boson-unstable quantum phase transition, the critical exponents y_O of these correlation functions are obtained as y_{σ_x}=y_{σ_z}=1-2s and y_X=-s, respectively. Here s is the bath index and X is the boson displacement operator. Close to the spin flip point, the high frequency peak of C_{σ_x}(ω) is broadened significantly and the line shape changes qualitatively, showing enhanced dephasing at the spin flip point.

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Attempt to generalize fractional-order electric elements to complex-order ones

司刚全, 刁利杰, 朱建伟, 雷妤航, 张彦斌

2017 (6): 60503-060503. doi: 10.1088/1674-1056/26/6/060503

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The complex derivative D^α±jβ, with α, β∈R+ is a generalization of the concept of integer derivative, where α=1, β=0. Fractional-order electric elements and circuits are becoming more and more attractive. In this paper, the complex-order electric elements concept is proposed for the first time, and the complex-order elements are modeled and analyzed. Some interesting phenomena are found that the real part of the order affects the phase of output signal, and the imaginary part affects the amplitude for both the complex-order capacitor and complex-order memristor. More interesting is that the complex-order capacitor can do well at the time of fitting electrochemistry impedance spectra. The complex-order memristor is also analyzed. The area inside the hysteresis loops increases with the increasing of the imaginary part of the order and decreases with the increasing of the real part. Some complex case of complex-order memristors hysteresis loops are analyzed at last, whose loop has touching points beyond the origin of the coordinate system.

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Anisotropic total variation minimization approach in in-line phase-contrast tomography and its application to correction of ring artifacts

冀东江, 渠刚荣, 胡春红, 刘宝东, 简建波, 郭晓坤

2017 (6): 60701-060701. doi: 10.1088/1674-1056/26/6/060701

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In-line phase-contrast computed tomography (IL-PC-CT) imaging is a new physical and biochemical imaging method. IL-PC-CT has advantages compared to absorption CT when imaging soft tissues. In practical applications, ring artifacts which will reduce the image quality are commonly encountered in IL-PC-CT, and numerous correction methods exist to either pre-process the sinogram or post-process the reconstructed image. In this study, we develop an IL-PC-CT reconstruction method based on anisotropic total variation (TV) minimization. Using this method, the ring artifacts are corrected during the reconstruction process. This method is compared with two methods:a sinogram preprocessing correction technique based on wavelet-FFT filter and a reconstruction method based on isotropic TV. The correction results show that the proposed method can reduce visible ring artifacts while preserving the liver section details for real liver section synchrotron data.

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Visibility enhancement in two-dimensional lensless ghost imaging with true thermal light

陈希浩, 燕玲, 吴炜, 孟少英, 吴令安, 孙志斌, 王超, 翟光杰

2017 (6): 60702-060702. doi: 10.1088/1674-1056/26/6/060702

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We report an experimental demonstration of two-dimensional (2D) lensless ghost imaging with true thermal light. An electrodeless discharge lamp with a higher light intensity than the hollow cathode lamp used before is employed as a light source. The main problem encountered by the 2D lensless ghost imaging with true thermal light is that its coherence time is much shorter than the resolution time of the detection system. To overcome this difficulty we derive a method based on the relationship between the true and measured values of the second-order optical intensity correlation, by which means the visibility of the ghost image can be dramatically enhanced. This method would also be suitable for ghost imaging with natural sunlight.

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Theoretical investigation on radiation tolerance of M_n+1AX_n phases

殷克迪, 张西通, 黄庆, 薛建明

2017 (6): 60703-060703. doi: 10.1088/1674-1056/26/6/060703

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Ternary M_n+1AX_n phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, M_n+1AX_n materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different M_n+1AX_n (MAX) phases in terms of electronic structure, including the density of states (DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds, thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between M_n+1AC_n and M_n+1AN_n due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti₃AlC₂ to Ti₂AlC (Ti₃AlC₂ and Ti₂AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other M_n+1AX_n phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.

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Optical sensors based on the NiPc–CoPc composite films deposited by drop casting and under the action of centrifugal force

Noshin Fatima,Muhammad M Ahmed,Khasan S Karimov,Zubair Ahmad,Fahmi Fariq Muhammad

2017 (6): 60704-060704. doi: 10.1088/1674-1056/26/6/060704

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In this study, solution processed composite films of nickel phthalocyanine (NiPc) and cobalt phthalocyanine (CoPc) are deposited by drop casting and under centrifugal force. The films are deposited on surface-type inter-digitated silver electrodes on ceramic alumina substrates. The effects of illumination on the impedance and capacitance of the NiPc-CoPc composite samples are investigated. The samples deposited under centrifugal force show better conductivity than the samples deposited by drop casting technique. In terms of impedance and capacitance sensitivities the samples fabricated under centrifugal force are more sensitive than the drop casting samples. The values of impedance sensitivity (S_z) are equal to (-1.83) MΩ·cm²/mW and (-5.365) MΩ·cm²/mW for the samples fabricated using drop casting and under centrifugal force, respectively. Similarly, the values of capacitance sensitivity (S_c) are equal to 0.083 pF·cm²/mW and 0.185 pF·cm²/mW for the samples fabricated by drop casting and under centrifugal force. The films deposited using the different procedures could potentially be viable for different operational modes (i.e., conductive or capacitive) of the optical sensors. Both experimental and simulated results are discussed.

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Design and characterization of a 3D encapsulation with silicon vias for radio frequency micro-electromechanical system resonator

赵继聪, 袁泉, 王凤祥, 阚骁, 韩国威, 孙玲, 孙海燕, 杨晋玲, 杨富华

2017 (6): 60705-060705. doi: 10.1088/1674-1056/26/6/060705

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In this paper, we present a three-dimensional (3D) vacuum packaging technique at a wafer level for a radio frequency micro-electromechanical system (RF MEMS) resonator, in which low-loss silicon vias is used to transmit RF signals. Au-Sn solder bonding is adopted to provide a vacuum encapsulation as well as electrical conductions. A RF model of the encapsulation cap is established to evaluate the parasitic effect of the packaging, which provides an effective design solution of 3D RF MEMS encapsulation. With the proposed packaging structure, the signal-to-background ratio (SBR) of 24 dB is achieved, as well as the quality factor (Q-factor) of the resonator increases from 8000 to 10400 after packaging. The packaged resonator has a linear frequency-temperature (f-T) characteristic in a temperature range between 0℃ and 100℃. And the package shows favorable long-term stability of the Q-factor over 200 days, which indicates that the package has excellent hermeticity. Furthermore, the average shear strength is measured to be 43.58 MPa among 10 samples.

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Co-focus experiment of segmented mirror

李斌, 于文豪, 陈莫, 唐金龙, 鲜浩

2017 (6): 60706-060706. doi: 10.1088/1674-1056/26/6/060706

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In this paper, an active optics and co-focus experimental system of segmented mirror is built. Firstly, a support structure of segmented mirror is designed and it is verified by simulation to meet the requirement for the experimental system of segmented mirror. In this system, the large de-focus and tilt/tip errors of the segmented mirror are adjusted by observing the density and contrast of interference fringes based on isoclinic interference theory until the defocus and tilt/tip errors are in the detective range of the Shack-Hartmann. Then, the Shack-Hartmann is used to measure them and they are adjusted by actuators. The actuators are controlled by active optics to realize the closed-loop adjustment and maintenance for fine co-focus of segmented mirror. And the interference fringes are utilized to verify the detective precision of Shack-Hartmann. After the co-focus fine-tuning of the segmented mirror, the tilt/tip residual surface error is better than 0.01λ RMS; the defocus residual surface error is better than 0.01λ RMS.

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Structural optimization of Au-Pd bimetallic nanoparticles with improved particle swarm optimization method

邵桂芳, 朱梦, 上官亚力, 李文然, 张灿, 王玮玮, 李玲

2017 (6): 63601-063601. doi: 10.1088/1674-1056/26/6/063601

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Due to the dependence of the chemical and physical properties of the bimetallic nanoparticles (NPs) on their structures, a fundamental understanding of their structural characteristics is crucial for their syntheses and wide applications. In this article, a systematical atomic-level investigation of Au-Pd bimetallic NPs is conducted by using the improved particle swarm optimization (IPSO) with quantum correction Sutton-Chen potentials (Q-SC) at different Au/Pd ratios and different sizes. In the IPSO, the simulated annealing is introduced into the classical particle swarm optimization (PSO) to improve the effectiveness and reliability. In addition, the influences of initial structure, particle size and composition on structural stability and structural features are also studied. The simulation results reveal that the initial structures have little effects on the stable structures, but influence the converging rate greatly, and the convergence rate of the mixing initial structure is clearly faster than those of the core-shell and phase structures. We find that the Au-Pd NPs prefer the structures with Au-rich in the outer layers while Pd-rich in the inner ones. Especially, when the Au/Pd ratio is 6:4, the structure of the nanoparticle (NP) presents a standardized Pd_coreAu_shell structure.

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Difference scattering field properties between periodic defect particles and three-dimensional slightly rough optical surface

葛城显, 吴振森, 白靖, 巩蕾

2017 (6): 64201-064201. doi: 10.1088/1674-1056/26/6/064201

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Based on the practical situation of nondestructive examination, the calculation model of the composite scattering is established by using a three-dimensional half-space finite difference time domain, and the Monte Carlo method is used to solve the problem of the optical surface with roughness in the proposed scheme. Moreover, the defect particles are observed as periodic particles for a more complex situation. In order to obtain the scattering contribution of defects inside the optical surface, a difference radar cross section is added into the model to analyze the selected calculations on the effects of numbers, separation distances, different depths and different materials of defects. The effects of different incident angles are also discussed. The numerical results are analyzed in detail to demonstrate the best position to find the defects in the optical surface by detecting in steps of a fixed degree for the incident angle.

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Effect of atmospheric turbulence on entangled orbital angular momentum three-qubit state

闫香, 张鹏飞, 张京会, 冯晓星, 乔春红, 范承玉

2017 (6): 64202-064202. doi: 10.1088/1674-1056/26/6/064202

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The entangled orbital angular momentum (OAM) three photons propagating in Kolmogorov weak turbulence are investigated. Here, the single phase screen model is used to study the entanglement evolution of OAM photons. The results indicate that the entangled OAM three-qubit state with higher OAM modes will be more robust against turbulence. Furthermore, it is found that the entangled OAM three-qubit state has a higher overall transmission for small OAM values.

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Investigation of the nonlinear CPT spectrum of ⁸⁷Rb and its application for large dynamic magnetic measurement

徐迟, 王时光, 胡勇, 冯焱颖, 王力军

2017 (6): 64203-064203. doi: 10.1088/1674-1056/26/6/064203

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The coherent population trapping (CPT) phenomenon has found widespread application in quantum precision measurements. Various designs based on the narrow resonant spectrum corresponding to the linear Zeeman effect have been demonstrated to achieve high performance. In this article, the nonlinear Zeeman split of the CPT spectrum of ⁸⁷Rb in the lin||lin setup is investigated. We observe re-split phenomenon for both magnetic sensitive and magnetic insensitive CPT resonant lines at a large magnetic field. The re-split in the magnetic sensitive lines raises a practical problem to magnetometers worked in the lin||lin setup while the other one shows a good potential for applications in large magnetic field. We propose a design based on the nonlinear split of the magnetic insensitive lines and test its performance. It provides a much larger measurement range compared to the linear one, offering an option for atomic magnetometers where a large dynamic range is preferred.

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Enhanced thermal stability of VCSEL array by thermoelectric analysis-based optimization of mesas distribution

钟础宇, 张星, 刘迪, 宁永强, 王立军

2017 (6): 64204-064204. doi: 10.1088/1674-1056/26/6/064204

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The thermal stability of a vertical-cavity surface-emitting laser (VCSEL) array is enhanced by redesigning the mesa arrangement. Based on a thermoelectric coupling three-dimensional (3D) finite-element model, an optimized VCSEL array is designed. The effects of this optimization are studied experimentally. Power density characteristics of VCSEL arrays with different mesa configuration are obtained under different thermal stress in which the optimized device shows improved performance. Optimized device also shows better stability from measured spectra and calculated thermal resistances. The experimental results prove that our simulation model and optimization is instructive for VCSEL array design.

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Enhancement of multiple four-wave mixing via cascaded fibers with discrete dispersion decreasing

李嘉宝, 孔令杰, 肖晓晟, 杨昌喜

2017 (6): 64205-064205. doi: 10.1088/1674-1056/26/6/064205

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Cascaded fiber geometry with the dispersion of each fiber decreasing is proposed to enhance the multiple four-wave mixing (FWM) generation. The first fiber with relatively large dispersion initiates and accelerates the expansion of multiple FWM, and the second fiber with small dispersion would allow the phase-matching process (thus the spectrum broadening) to keep going. Numerical and experimental results show that with this geometry not only multiple FWM expansion can be accelerated, but also the efficiency of multiple FWM products can be effectively improved with shorter fibers.

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Optical pulse evolution in the presence of a probe light in CW-pumped nonlinear fiber

陈伟, 张学亮, 胡晓阳, 宋章启, 孟洲

2017 (6): 64206-064206. doi: 10.1088/1674-1056/26/6/064206

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We investigate theoretically and numerically the evolutions of optical pulses in the time domain due to modulation instability (MI), where CW pump accompanied with a probe is used as the input of nonlinear fiber. As the fiber length increases, we show that it exhibits beat frequency between the pump and the probe first when the probe lies outside the MI resonance region, and then gradually transforms into a pulse train resulting from spontaneous MI rather than induced MI. However, the regular pulse train is easier to generate in the whole fiber if the probe exists in MI resonance region, and the period of the pulse train is inversely proportional to the frequency spacing between the pump and the probe. It is emphasized that the pulse period can be adjusted only when the probe is in MI resonance region. The numerical simulations are in agreement with the theoretical results. The obtained results are guidable for generating and manipulating the optical pulse train in the fiber.

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Wavelength modulation spectroscopy for measurements of gas parameters in combustion field

屈东胜, 洪延姬, 王广宇, 潘虎

2017 (6): 64207-064207. doi: 10.1088/1674-1056/26/6/064207

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A novel wavelength modulation spectroscopy sensor for studying gas properties near 1.4 μm is developed, validated and used in a direct-connect supersonic combustion test facility. In this sensor there are two H₂O transitions near 7185.60 cm^-1 and 7454.45 cm^-1 that are used to enable the measurements along the line-of-sight. According to an iterative algorithm, the gas pressure, temperature and species mole fraction can be measured simultaneously. The new sensor is used in the isolator and extender of the supersonic combustion test facility. In the isolator, the sensor resolves the transient and measured pressure, temperature and H₂O mole fraction with accuracies of 2.5%, 8.2%, and 7.2%, respectively. Due to the non-uniform characteristic in the extender, the measured results cannot precisely characterize gas properties, but they can qualitatively describe the distinctions of different zones or the changes or fluctuations of the gas parameters.

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Generation of femtosecond laser pulses at 263 nm by K₃B₆O₁₀Cl crystal

张宁华, 方少波, 何鹏, 黄杭东, 朱江峰, 田文龙, 吴红萍, 潘世烈, 滕浩, 魏志义

2017 (6): 64208-064208. doi: 10.1088/1674-1056/26/6/064208

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The third harmonic generation (THG) of a linear cavity Ti:sapphire regenerative amplifier by use of a K₃B₆O₁₀Cl (KBOC) crystal is studied for the first time. Output power up to 5.9 mW is obtained at a central wavelength of 263 nm, corresponding to a conversion efficiency of 4.5% to the second harmonic power. Our results show a tremendous potential for nonlinear frequency conversion into the deep ultraviolet range with the new crystal and the output laser power can be further improved.

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Design of tunable surface mode waveguide based on photonic crystal composite structure using organic liquid

张兰兰, 刘伟, 李萍, 杨曦, 曹旭

2017 (6): 64209-064209. doi: 10.1088/1674-1056/26/6/064209

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With the method of replacing the surface layer of photonic crystal with tubes, a novel photonic crystal composite structure used as a tunable surface mode waveguide is designed. The tubes support tunable surface states. The tunable propagation capabilities of the structure are investigated by using the finite-difference time-domain. Simulation results show that the beam transmission distributions of the composite structure are sensitive to the frequency range of incident light and the surface morphology which can be modified by filling the tubes with different organic liquids. By adjusting the filler in tubes, the T-shaped, Y-shaped, and L-shaped propagations can be realized. The property can be applied to the tunable surface mode waveguide. Compared with a traditional single function photonic crystal waveguide, our designed structure not only has a small size, but also is a tunable device.

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Adaptive optimization on ultrasonic transmission tomography-based temperature image for biomedical treatment

朱昀浩, 袁杰, 程茜, 王学鼎, 陶超, 刘晓峻, 徐冠

2017 (6): 64301-064301. doi: 10.1088/1674-1056/26/6/064301

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Hyperthermia has proven to be beneficial to treating superficial malignancies, particularly chest wall recurrences of breast cancer. During hyperthermia, monitoring the time-temperature profiles in the target and surrounding areas is of great significance for the effect of therapy. An ultrasound-based temperature imaging method has advantages over other approaches. When the temperature around the tumor is calculated by using the propagation speed of ultrasound, there always exist overshoot artifacts along the boundary between different tissues. In this paper, we present a new method combined with empirical mode decomposition (EDM), similarity constraint, and continuity constraint to optimize the temperature images. Simulation and phantom experiment results compared with those from our previously proposed method prove that the EMD-based method can build a better temperature field image, which can adaptively yield better temperature images with less computation for assistant medical treatment control.

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Density and temperature reconstruction of a flame-induced distorted flow field based on background-oriented schlieren (BOS) technique

郭广明, 刘洪

2017 (6): 64701-064701. doi: 10.1088/1674-1056/26/6/064701

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An experimental system based on the background-oriented schlieren (BOS) technique is built to reconstruct the density and temperature distribution of a flame-induced distorted flow field which has a density gradient. The cross-correlation algorithm with sub-pixel accuracy is introduced and used to calculate the background-element displacement of a disturbed image and a fourth-order difference scheme is also developed to solve the Poisson equation. An experiment for a disturbed flow field caused by a burning candle is performed to validate the built BOS system and the results indicate that density and temperature distribution of the disturbed flow field can be reconstructed accurately. A notable conclusion is that in order to make the reconstructed results have a satisfactory accuracy, the inquiry step length should be less than the size of the interrogation window.

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Equation of state for warm dense lithium: A first principles investigation

龙飞沄, 刘海涛, 李大芳, 颜君

2017 (6): 65101-065101. doi: 10.1088/1674-1056/26/6/065101

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The quantum molecular dynamics based on the density functional theory has been adopted to simulate the equation of state for the shock compressed lithium. In contrary to some earlier experimental measurement and theoretical simulation, there is not any evidence of the ‘kink’ in the Hugoniot curve in our accurate simulation. Throughout the shock compression process, only a simple solid-to-liquid melting behavior is demonstrated, instead of complicated solid-solid phase transitions. Moreover, the x-ray absorption near-edge spectroscopy has been predicted as a feasible way to diagnose the structural evolution of warm dense lithium in this density region.

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Simulations of the effects of density and temperature profile on SMBI penetration depth based on the HL-2A tokamak configuration

吴雪科, 李会东, 王占辉, 冯灏, 周雨林

2017 (6): 65201-065201. doi: 10.1088/1674-1056/26/6/065201

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Using the trans-neut module of the BOUT++ code, we study how the fueling penetration depth of supersonic molecular beam injection (SMBI) is affected by plasma density and temperature profiles. The plasma densities and temperatures in L-mode are initialized to be a set of linear profiles with different core plasma densities and temperatures. The plasma profiles are relaxed to a set of steady states with different core plasma densities or temperatures. For a fixed gradient, the steady profiles are characterized by the core plasma density and temperature. The SMBI is investigated based on the final steady profiles with different core plasma densities or temperatures. The simulated results suggest that the SMB injection will be blocked by dense core plasma and high-temperature plasma. Once the core plasma density is set to be N_i0=1.4N₀ (N₀=1×10¹⁹ m^-3) it produces a deeper penetration depth. When N_i0 is increased from 1.4N₀ to 3.9N₀ at intervals of 0.8N₀, keeping a constant core temperature of T_e0=725 eV at the radial position of ψ=0.65}, the penetration depth gradually decreases. Meanwhile, when the density is fixed at N_i0=1.4N₀ and the core plasma temperature T_e0 is set to 365 eV, the penetration depth increases. The penetration depth decreases as T_e0 is increased from 365 eV to 2759 eV. Sufficiently large N_i0 or T_e0 causes most of the injected molecules to stay in the scrape-off-layer (SOL) region, lowering the fueling efficiency.

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Drift vortices in inhomogeneous collisional dusty magnetoplasma

杨建荣, 吕岿, 许磊, 毛杰键, 刘希忠, 刘萍

2017 (6): 65202-065202. doi: 10.1088/1674-1056/26/6/065202

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For the sake of investigating the drift coherent vortex structure in an inhomogeneous dense dusty magnetoplasma, using the quantum hydrodynamic model a nonlinear controlling equation is deduced when the collision effect is considered. New vortex solutions of the electrostatic potential are obtained by a special transformation method, and three evolutive cases of monopolar vortex chains with spatial and temporal distribution are analyzed by representative parameters. It is found that the collision frequency, particle density, drift velocity, dust charge number, electron Fermi wavelength, quantum correction, and quantum parameter are all influencing factors of the vortex evolution. Compared to the uniform dusty system, the vortex solutions of the inhomogeneous system present richer spatial evolution and physical meaning. These results may explain corresponding vortex phenomena and support beneficial references for the dense dusty plasma atmosphere.

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Generation of high quality ion beams through the stable radiation pressure acceleration of the near critical density target

洪学仁, 周伟军, 谢柏松, 杨阳, 王莉, 田建民, 唐荣安, 段文山

2017 (6): 65203-065203. doi: 10.1088/1674-1056/26/6/065203

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In order to generate high quality ion beams through the stable radiation pressure acceleration (RPA) of the near critical density (NCD) target, we propose a new type of target where an ultra-thin high density (HD) layer is attached to the front surface of an NCD target, which has a preferable self-supporting property in the RPA experiments than the ultra-thin foil target. It is found that in one-dimensional particle-in-cell (PIC) simulation, by the block of the HD layer in the new target, there emerges the hole-boring process rather than propagation in the NCD layer when the intense laser pulse impinges on this target. As a result, a typical RPA structure that the compressed electron layer overlaps the ion layer as a whole is formed and a high quality ion beam is obtained, e.g., a circularly polarized laser pulse with normalized amplitude a₀=120 impinges on this new target and a 1.2 GeV monoenergetic ion beam is generated through the RPA of the NCD layer. Similar results are also found in the two-dimensional PIC simulation.

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Modeling and optimization of the multichannel spark discharge

张志波, 吴云, 贾敏, 宋慧敏, 孙正中, 李应红

2017 (6): 65204-065204. doi: 10.1088/1674-1056/26/6/065204

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This paper reports a novel analytic model of this multichannel spark discharge, considering the delay time in the breakdown process, the electric transforming of the discharge channel from a capacitor to a resistor induced by the air breakdown, and the varying plasma resistance in the discharge process. The good agreement between the experimental and the simulated results validated the accuracy of this model. Based on this model, the influence of the circuit parameters on the maximum discharge channel number (MDCN) is investigated. Both the input voltage amplitude and the breakdown voltage threshold of each discharge channel play a critical role. With the increase of the input voltage and the decrease of the breakdown voltage, the MCDN increases almost linearly. With the increase of the discharge capacitance, the MDCN first rises and then remains almost constant. With the increase of the circuit inductance, the MDCN increases slowly but decreases quickly when the inductance increases over a certain value. There is an optimal value of the capacitor connected to the discharge channel corresponding to the MDCN. Finally, based on these results, to shorten the discharge time, a modified multichannel discharge circuit is developed and validated by the experiment. With only 6-kV input voltage, 31-channels discharge is achieved. The breakdown voltage of each electrode gap is larger than 3 kV. The modified discharge circuit is certain to be widely used in the PSJA flow control field.

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Comparison benchmark between tokamak simulation code and TokSys for Chinese Fusion Engineering Test Reactor vertical displacement control design

仇庆来, 肖炳甲, 郭勇, 刘磊, 汪悦航

2017 (6): 65205-065205. doi: 10.1088/1674-1056/26/6/065205

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Vertical displacement event (VDE) is a big challenge to the existing tokamak equipment and that being designed. As a Chinese next-step tokamak, the Chinese Fusion Engineering Test Reactor (CFETR) has to pay attention to the VDE study with full-fledged numerical codes during its conceptual design. The tokamak simulation code (TSC) is a free boundary time-dependent axisymmetric tokamak simulation code developed in PPPL, which advances the MHD equations describing the evolution of the plasma in a rectangular domain. The electromagnetic interactions between the surrounding conductor circuits and the plasma are solved self-consistently. The TokSys code is a generic modeling and simulation environment developed in GA. Its RZIP model treats the plasma as a fixed spatial distribution of currents which couple with the surrounding conductors through circuit equations. Both codes have been individually used for the VDE study on many tokamak devices, such as JT-60U, EAST, NSTX, DIII-D, and ITER. Considering the model differences, benchmark work is needed to answer whether they reproduce each other's results correctly. In this paper, the TSC and TokSys codes are used for analyzing the CFETR vertical instability passive and active controls design simultaneously. It is shown that with the same inputs, the results from these two codes conform with each other.

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Numerical study on the discharge characteristics and nonlinear behaviors of atmospheric pressure coaxial electrode dielectric barrier discharges

张定宗, 王艳辉, 王德真

2017 (6): 65206-065206. doi: 10.1088/1674-1056/26/6/065206

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The discharge characteristics and temporal nonlinear behaviors of the atmospheric pressure coaxial electrode dielectric barrier discharges are studied by using a one-dimensional fluid model. It is shown that the discharge is always asymmetrical between the positive pulses and negative pulses. The gas gap severely affects this asymmetry. But it is hard to acquire a symmetrical discharge by changing the gas gap. This asymmetry is proportional to the asymmetric extent of electrode structure, namely the ratio of the outer electrode radius to the inner electrode radius. When this ratio is close to unity, a symmetrical discharge can be obtained. With the increase of frequency, the discharge can exhibit a series of nonlinear behaviors such as period-doubling bifurcation, secondary bifurcation and chaotic phenomena. In the period-doubling bifurcation sequence the period-n discharge becomes more and more unstable with the increase of n. The period-doubling bifurcation can also be obtained by altering the discharge gas gap. The mechanisms of two bifurcations are further studied. It is found that the residual quasineutral plasma from the previous discharges and corresponding electric field distribution can weaken the subsequent discharge, and leads to the occurrence of bifurcation.

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Effect of driving frequency on the structure of silicon grown on Ag (111) films by very-high-frequency magnetron sputtering

郭佳敏, 叶超, 王响英, 杨培芳, 张苏

2017 (6): 65207-065207. doi: 10.1088/1674-1056/26/6/065207

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The effect of driving frequency on the structure of silicon grown on Ag (111) film is investigated, which was prepared by using the very-high-frequency (VHF) (40.68 MHz and 60 MHz) magnetron sputtering. The energy and flux density of the ions impinging on the substrate are also analyzed. It is found that for the 60-MHz VHF magnetron sputtering, the surface of silicon on Ag (111) film exhibits a small cone structure, similar to that of Ag (111) film substrate, indicating a better microstructure continuity. However, for the 40.68-MHz VHF magnetron sputtering, the surface of silicon on Ag (111) film shows a hybrid structure of hollowed-cones and hollowed-particles, which is completely different from that of Ag (111) film. The change of silicon structure is closely related to the differences in the ion energy and flux density controlled by the driving frequency of sputtering.

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Serrated magnetic properties in metallic glass by thermal cycle

李明哲, 丁大伟, 董帮少, 周少雄, 汪卫华

2017 (6): 66101-066101. doi: 10.1088/1674-1056/26/6/066101

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Fe-based metallic glasses (MGs) with excellent soft magnetic properties are applicable in a wide range of electronic industry. We show that the cryogenic thermal cycle has a sensitive effect on soft magnetic properties of Fe₇₈Si₉B₁₃ glassy ribbon. The values of magnetic induction (or magnetic flux density) B and coercivity H_c show fluctuation with increasing number of thermal cycles. This phenomenon is explained as thermal-cycle-induced stochastically structural aging or rejuvenation which randomly fluctuates magnetic anisotropy and, consequently, the magnetic induction and coercivity. Overall, increasing the number of thermal cycles improves the soft magnetic properties of the ribbon. The results could help understand the relationship between relaxation and magnetic property, and the thermal cycle could provide an effective approach to improving performances of metallic glasses in industry.

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Label-free tungsten disulfide quantum dots as a fluorescent sensing platform for highly efficient detection of copper (II) ions

赵宣, 何大伟, 王永生, 胡音, 付晨, 李雪

2017 (6): 66102-066102. doi: 10.1088/1674-1056/26/6/066102

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A fluorescent probe for the sensitive and selective determination of copper ion (Cu²⁺) is presented. It is based on the use of tungsten disulfide quantum dots (WS₂ QDs) which is independent of the pH of solution and emits strong blue fluorescence. Copper ions could cause aggregation of the WS₂ QDs and lead to fluorescence quenching of WS₂ QDs. The change of fluorescence intensity is proportional to the concentration of Cu²⁺, and the limit of detection is 0.4 μM. The fluorescent probe is highly selective for Cu²⁺ over some potentially interfering ions. These results indicate that WS₂ QDs, as a fluorescent sensing platform, can meet the selective requirements for biomedical and environmental application.

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Electronic and thermoelectric properties of Mg₂Ge_xSn_1-x (x=0.25, 0.50, 0.75) solid solutions by first-principles calculations

李开跃, 鲁勇, 黄艳, 邵晓红

2017 (6): 66103-066103. doi: 10.1088/1674-1056/26/6/066103

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The electronic structure and thermoelectric (TE) properties of Mg₂Ge_xSn_1-x (x=0.25, 0.50, 0.75) solid solutions are investigated by first-principles calculations and semi-classical Boltzmann theory. The special quasi-random structure (SQS) is used to model the solid solutions, which can produce reasonable band gaps with respect to experimental results. The n-type solid solutions have an excellent thermoelectric performance with maximum zT values exceeding 2.0, where the combination of low lattice thermal conductivity and high power factor (PF) plays an important role. These values are higher than those of pure Mg₂Sn and Mg₂Ge. The p-type solid solutions are inferior to the n-type ones, mainly due to the much lower PF. The maximum zT value of 0.62 is predicted for p-type Mg₂Ge_0.25Sn_0.75 at 800 K. The results suggest that the n-type Mg₂Ge_xSn_1-x solid solutions are promising mid-temperature TE materials.

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Effects of pressure on structural, electronic, and mechanical properties of α, β, and γ uranium

张慧杰, 李世娜, 郑晶晶, 李卫东, 王保田

2017 (6): 66104-066104. doi: 10.1088/1674-1056/26/6/066104

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The first-principles methods have been employed to calculate the structural, electronic, and mechanical properties of the α, β, and γ phases of uranium under pressure up to 100 GPa. The electronic structure has been viewed in forms of density of states and band structure. The mechanical stability of metal U in the α, β, and γ phases have been examined. The independent elastic constants, polycrystalline elastic moduli, as well as Poisson's ratio have been obtained. Upon compression, the elastic constants, elastic moduli, elastic wave velocities, and Debye temperature of α phase are enhanced pronouncedly. The value of B/G illustrates that α and γ phases are brittle in ground state.

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Stability, elastic anisotropy, and electronic properties of Ca₂C₃

张权, 魏群, 闫海燕, 朱轩民, 张军琴, 贾晓菲, 姚荣辉

2017 (6): 66201-066201. doi: 10.1088/1674-1056/26/6/066201

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The systematic investigations of the mechanical, elastic, and electronic properties, and stability of the newly synthesized monoclinic C2/m-Ca₂C₃ are performed, based on the first-principles calculations. Ca₂C₃ is found to be mechanically and dynamically stable only from 0 GPa to 24 GPa. The elastic anisotropy studies show that Ca₂C₃ exhibits the elastic anisotropy increasing with the augment of pressure. Furthermore, using the HSE06 hybrid functional, the electronic properties of Ca₂C₃ under pressure are calculated. The structure can be regarded as a quasi-direct band gap semiconductor, and the pressure-induced direct-indirect band gap transition is studied in detail.

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Unraveling the effect of uniaxial strain on thermoelectric properties of Mg₂Si: A density functional theory study

Kulwinder Kaur,Ranjan Kumar

2017 (6): 66401-066401. doi: 10.1088/1674-1056/26/6/066401

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In this work, the effect of uniaxial strain on electronic and thermoelectric properties of magnesium silicide using density functional theory (DFT) and Boltzmann transport equations has been studied. We have found that the value of band gap increases with tensile strain and decreases with compressive strain. The variations of electrical conductivity, Seebeck coefficient, electronic thermal conductivity, and power factor with temperatures have been calculated. The Seebeck coefficient and power factor are observed to be modified strongly with strain. The value of power factor is found to be higher in comparison with the unstrained structure at 2% tensile strain. We have also calculated phonon dispersion, phonon density of states, specific heat at constant volume, and lattice thermal conductivity of material under uniaxial strain. The phonon properties and lattice thermal conductivity of Mg₂Si under uniaxial strain have been explored first time in this report.

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Direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene via van der Pauw geometry

马瑞松, 郇庆, 吴良妹, 严佳浩, 张余洋, 鲍丽宏, 刘云圻, 杜世萱, 高鸿钧

2017 (6): 66801-066801. doi: 10.1088/1674-1056/26/6/066801

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We report the direct measurements of conductivity and mobility in millimeter-sized single-crystalline graphene on SiO₂/Si via van der Pauw geometry by using a home-designed four-probe scanning tunneling microscope (4P-STM). The gate-tunable conductivity and mobility are extracted from standard van der Pauw resistance measurements where the four STM probes contact the four peripheries of hexagonal graphene flakes, respectively. The high homogeneity of transport properties of the single-crystalline graphene flake is confirmed by comparing the extracted conductivities and mobilities from three setups with different geometry factors. Our studies provide a reliable solution for directly evaluating the entire electrical properties of graphene in a non-invasive way and could be extended to characterizing other two-dimensional materials.

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Study of structural and magnetic properties of Fe₈₀P₉B₁₁ amorphous alloy by ab initio molecular dynamic simulation

朱力, 王寅岗, 曹成成, 孟洋

2017 (6): 67101-067101. doi: 10.1088/1674-1056/26/6/067101

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The structural and magnetic properties of Fe₈₀P₉B₁₁ amorphous alloy are investigated through ab initio molecular dynamic simulation. The structure evolution of Fe₈₀P₉B₁₁ amorphous alloy can be described in the framework of topological fluctuation theory, and the fluctuation of atomic hydrostatic stress gradually decreases upon cooling. The left sub peak of the second peak of Fe-B partial pair distribution functions (PDFs) becomes pronounced below the glass transition temperature, which may be the major reason why B promotes the glass formation ability significantly. The magnetization mainly originates from Fe 3d states, while small contribution results from metalloid elements P and B. This work may be helpful for developing Fe-based metallic glasses with both high saturation flux density and glass formation ability.

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Anisotropic and mutable magnetization in Kondo lattice CeSb₂

张云, 朱燮刚, 胡丙锋, 谭世勇, 谢东华, 冯卫, 刘琴, 张文, 刘瑜, 宋海峰, 罗丽珠, 张政军, 赖新春

2017 (6): 67102-067102. doi: 10.1088/1674-1056/26/6/067102

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We have systematically studied the behaviors of the resistivity and magnetization of CeSb₂ single crystals as a function of temperature and external field. Four anomalies in the resistivity/magnetization-versus-temperature curves are observed at low magnetic field. They are located at 15.5 K, 11.5 K, 9.5 K, and 6.5 K, corresponding to the paramagnetic-magnetically ordered state (MO), MO-antiferromagnetic (AFM), AFM-AFM, and AFM-ferromagnetic (FM) transitions, respectively. The anomaly at 9.5 K is only visible with H||[010] by magnetic susceptibility measurements, indicating that the AFM-AFM transition only happens along[010] direction in ab-plane. The four magnetic transitions are strongly suppressed by high external field. Finally, the field-temperature phase diagrams of CeSb₂ with different orientations of the applied field in ab-plane are constructed and indicate the highly anisotropic nature of the magnetization of CeSb₂.

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First-principles investigation of the effects of strain on elastic, thermal, and optical properties of CuGaTe₂

薛丽, 任一鸣, 何俊荣, 徐四六

2017 (6): 67103-067103. doi: 10.1088/1674-1056/26/6/067103

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Based on the density functional theory, the influences of strain on structural, elastic, thermal and optical properties of CuGaTe₂ are discussed in detail. It is found that the tensile strain on CuGaTe₂ is beneficial to the decrease of lattice thermal conductivity by reducing the mean sound velocity and Debye temperature. Moreover, all strained and unstrained CuGaTe₂ exhibit rather similar optical characters. But the tensile strain improves the ability to absorb sunlight in the visible range. These research findings can give hints for designing thermoelectric and photovoltaic devices.

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Spin-filter effect and spin-polarized optoelectronic properties in annulene-based molecular spintronic devices

马志远, 李莹, 宋贤江, 杨致, 徐利春, 刘瑞萍, 刘旭光, 胡殿印

2017 (6): 67201-067201. doi: 10.1088/1674-1056/26/6/067201

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Using Fe, Co or Ni chains as electrodes, we designed several annulene-based molecular spintronic devices and investigated the quantum transport properties based on density functional theory and non-equilibrium Green's function method. Our results show that these devices have outstanding spin-filter capabilities and exhibit giant magnetoresistance effect, and that with Ni chains as electrodes, the device has the best transport properties. Furthermore, we investigated the spin-polarized optoelectronic properties of the device with Ni electrodes and found that the spin-polarized photocurrents can be directly generated by irradiating the device with infrared, visible or ultraviolet light. More importantly, if the magnetization directions of the two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents.

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Transport properties in monolayer-bilayer-monolayer graphene planar junctions

储开龙, 王孜博, 周娇娇, 江华

2017 (6): 67202-067202. doi: 10.1088/1674-1056/26/6/067202

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The transport study of graphene based junctions has become one of the focuses in graphene research. There are two stacking configurations for monolayer-bilayer-monolayer graphene planar junctions. One is the two monolayer graphene contacting the same side of the bilayer graphene, and the other is the two-monolayer graphene contacting the different layers of the bilayer graphene. In this paper, according to the Landauer-Büttiker formula, we study the transport properties of these two configurations. The influences of the local gate potential in each part, the bias potential in bilayer graphene, the disorder and external magnetic field on conductance are obtained. We find the conductances of the two configurations can be manipulated by all of these effects. Especially, one can distinguish the two stacking configurations by introducing the bias potential into the bilayer graphene. The strong disorder and the external magnetic field will make the two stacking configurations indistinguishable in the transport experiment.

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Flexible electrically pumped random lasing from ZnO nanowires based on metal-insulator-semiconductor structure

阙妙玲, 王贤迪, 彭轶瑶, 潘曹峰

2017 (6): 67301-067301. doi: 10.1088/1674-1056/26/6/067301

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Flexible electrically pumped random laser (RL) based on ZnO nanowires is demonstrated for the first time to our knowledge. The ZnO nanowires each with a length of 5 μm and an average diameter of 180 nm are synthesized on flexible substrate (ITO/PET) by a simple hydrothermal method. No obvious visible defect-related-emission band is observed in the photoluminescence (PL) spectrum, indicating that the ZnO nanowires grown on the flexible ITO/PET substrate have few defects. In order to achieve electrically pumped random lasing with a lower threshold, the metal-insulator-semiconductor (MIS) structure of Au/SiO₂/ZnO on ITO/PET substrate is fabricated by low temperature process. With sufficient forward bias, the as-fabricated flexible device exhibits random lasing, and a low threshold current of ~11.5 mA and high luminous intensity are obtained from the ZnO-based random laser. It is believed that this work offers a case study for developing the flexible electrically pumped random lasing from ZnO nanowires.

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Tunable charge density wave in TiS₃ nanoribbons

黄策, 张恩泽, 袁翔, 王伟懿, 刘彦闻, 张成, 凌霁玮, 刘姗姗, 修发贤

2017 (6): 67302-067302. doi: 10.1088/1674-1056/26/6/067302

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Recently, modifications of charge density wave (CDW) in two-dimensional (2D) show intriguing properties in quasi-2D materials such as layered transition metal dichalcogenides (TMDCs). Optical, electrical transport measurements and scanning tunneling microscopy uncover the enormous difference on the many-body states when the thickness is reduced down to monolayer. However, the CDW in quasi-one-dimensional (1D) materials like transition metal trichalcogenides (TMTCs) is yet to be explored in low dimension whose mechanism is likely distinct from their quasi-2D counterparts. Here, we report a systematic study on the CDW properties of titanium trisulfide (TiS₃). Two phase transition temperatures were observed to decrease from 53 K (103 K) to 46 K (85 K) for the bulk and <15-nm thick nanoribbon, respectively, which arises from the increased fluctuation effect across the chain in the nanoribbon structure, thereby destroying the CDW coherence. It also suggests a strong anisotropy of CDW states in quasi-1D TMTCs which is different from that in TMDCs. Remarkably, by using back gate of -30 V~70 V in 15-nm device, we can tune the second transition temperature from 110 K (at -30 V) to 93 K (at 70 V) owing to the altered electron concentration. Finally, the optical approach through the impinging of laser beams on the sample surface is exploited to manipulate the CDW transition, where the melting of the CDW states shows a strong dependence on the excitation energy. Our results demonstrate TiS₃ as a promising quasi-1D CDW material and open up a new window for the study of collective phases in TMTCs.

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Structural, elastic, and vibrational properties of phase H: A first-principles simulation

吕超甲, 刘雷, 高阳, 刘红, 易丽, 庄春强, 李营, 杜建国

2017 (6): 67401-067401. doi: 10.1088/1674-1056/26/6/067401

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Phase H (MgSiO₄H₂), one of the dense hydrous magnesium silicates (DHMSs), is supposed to be vital to transporting water into the lower mantle. Here the crystal structure, elasticity and Raman vibrational properties of the two possible structures of phase H with Pm and P2/m symmetry under high pressures are evaluated by first-principles simulations. The cell parameters, elastic and Raman vibrational properties of the Pm symmetry become the same as the P2/m symmetry at~30 GPa. The symmetrization of hydrogen bonds of the Pm symmetry at~30 GPa results in this structural transformation from Pm to P2/m. Seismic wave velocities of phase H are calculated in a range from 0 GPa to 100 GPa and the results testify the existence and stability of phase H in the lower mantle. The azimuthal anisotropies for phase H are A_P0=14.7%, A_S0=21.2% (P2/m symmetry) and A_P0=16.4%, A_S0=27.1% (Pm symmetry) at 0 GPa, and increase to A_P30=17.9%, A_S30=40.0% (P2/m symmetry) and A_P30=19.2%, A_S30=37.8% (Pm symmetry) at 30 GPa. The maximum V_P direction for phase H is[101] and the minimum direction is[110]. The anisotropic results of seismic wave velocities imply that phase H might be a source of seismic anisotropy in the lower mantle. Furthermore, Raman vibrational modes are analyzed to figure out the effect of symmetrization of hydrogen bonds on Raman vibrational pattern and the dependence of Raman spectrum on pressure. Our results may lead to an in-depth understanding of the stability of phase H in the mantle.

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Transition from tunneling regime to local point contact realized on Ba_0.6K_0.4Fe₂As₂ surface

侯兴元, 揭云印, 巩靖, 沈冰, 子海, 李春红, 任聪, 单磊

2017 (6): 67402-067402. doi: 10.1088/1674-1056/26/6/067402

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Using scanning tunneling spectroscopy, we studied the transition from tunneling regime to local point contact on the iron-based superconductor Ba_0.6K_0.4Fe₂As₂. By gradually reducing the junction resistance, a series of spectra were obtained with the characteristics evolving from single-particle tunneling into Andreev reflection. The spectra can be well fitted to the modified Blonder-Tinkham-Klapwijk (BTK) model and exhibit significant changes of both spectral broadening and orbital selection due to the formation of point contact. The spatial resolution of the point contact was estimated to be several nanometers, providing a unique way to study the inhomogeneity of unconventional superconductors on such a scale.

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Kosterlitz-Thouless transition, spectral property and magnetic moment for a two-dot structure with level difference

熊永臣, 周望怀, 张俊, 南楠

2017 (6): 67501-067501. doi: 10.1088/1674-1056/26/6/067501

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By means of the numerical renormalization group method, we study the phase transition, the spectral property, and the temperature-dependent magnetic moment for a parallel double dot system with level difference, where the dot energies are kept symmetric to the half-filled level. A Kosterlitz-Thouless (KT) transition between local spin triplet and singlet is found. In the triplet regime, the local spin is partially screened by the conduction leads and spin-1 Kondo effect is realized. While for the singlet, the Kondo peak is strongly suppressed and the magnetic moment decreases to 0 at a definite low temperature. We attribute this KT transition to the breaking of the reflection symmetry, resulting from the difference of the charge occupations of the two dots. To understand this KT transition and related critical phenomena, detailed scenarios are given in the transmission coefficient and the magnetic moment, and an effective Kondo model refers to the Rayleigh-Schrödinger perturbation theory is used.

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Effects of Pr substitution on the hydrogenating process and magnetocaloric properties of La_1-xPr_xFe_11.4Si_1.6H_y hydrides

许磊, 赵金良, 杨静洁, 张红国, 刘丹敏, 岳明, 蒋毅坚

2017 (6): 67502-067502. doi: 10.1088/1674-1056/26/6/067502

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In this paper, we study the effects of Pr substitution on the hydrogenating process and magnetocaloric properties of La_1-xPr_xFe_11.4Si_1.6H_y hydrides. The powder x-ray diffraction patterns of the La_1-xPr_xFe_11.4Si_1.6 and its hydrides show that each of the alloys is crystallized into the single phase of cubic NaZn₁₃-type structure. There are hydrogen-absorbing plateaus under 0.4938 MPa and 0.4882 MPa in the absorbing curves for the La_0.8Pr_0.2Fe_11.4Si_1.6 and La_0.6Pr_0.4Fe_11.4Si_1.6 compounds. The releasing processes lag behind the absorbing process, which is obviously different from the coincidence between absorbing and releasing curves of the LaFe_11.4Si_1.6 compound. The remnant hydrogen content for La_0.6Pr_0.4Fe_11.4Si_1.6 is significantly more than that for La_0.8Pr_0.2Fe_11.4Si_1.6 after hydrogen desorption, indicating that more substitutions of Pr for La are beneficial to retaining more hydrogen atoms in the alloys. The values of maximum magnetic entropy change are 14.91 J/kg·K and 17.995 J/kg·K for La_0.8Pr_0.2Fe_11.4Si_1.6H_0.13 and La_0.6Pr_0.4Fe_11.4Si_1.6H_0.87, respectively.

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Low temperature ferromagnetic properties of CdS and CdTe thin films

王东明, 王德亮

2017 (6): 67503-067503. doi: 10.1088/1674-1056/26/6/067503

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The magnetic property in a material is induced by the unpaired electrons. This can occur due to defect states which can enhance the magnetic moment and the spin polarization. In this report, CdS and CdTe thin films are grown on FTO glass substrates by chemical bath deposition and close-spaced sublimation, respectively. The magnetic properties, which are introduced from oxygen states, are found in CdS and CdTe thin films. From the hysteresis loop of magnetic moment it is revealed that CdS and CdTe thin films have different kinds of magnetic moments at different temperatures. The M-H curves indicate that from 100 K to 350 K, CdS and CdTe thin films show paramagnetism and diamagnetism, respectively. A superparamagnetic or a weakly ferromagnetic response is found at 5 K. It is also observed from ZFC/FC curves that magnetic moments decrease with temperature increasing. Spin polarized density functional calculation for spin magnetic moment is also carried out.

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Influences of different oxidants on characteristics of La₂O₃/Al₂O₃ nanolaminates deposited by atomic layer deposition

樊继斌, 刘红侠, 段理, 张研, 于晓晨

2017 (6): 67701-067701. doi: 10.1088/1674-1056/26/6/067701

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A comparative study of two kinds of oxidants (H₂O and O₃) with the combination of two metal precursors (TMA and La(ⁱPrCp)₃) for atomic layer deposition (ALD) La₂O₃/Al₂O₃ nanolaminates is carried out. The effects of different oxidants on the physical properties and electrical characteristics of La₂O₃/Al₂O₃ nanolaminates are studied. Initial testing results indicate that La₂O₃/Al₂O₃ nanolaminates could avoid moisture absorption in the air after thermal annealing. However, moisture absorption occurs in H₂O-based La₂O₃/Al₂O₃ nanolaminates due to the residue hydroxyl/hydrogen groups during annealing. As a result, roughness enhancement, band offset variation, low dielectric constant and poor electrical characteristics are measured because the properties of H₂O-based La₂O₃/Al₂O₃ nanolaminates are deteriorated. Addition thermal annealing effects on the properties of O₃-based La₂O₃/Al₂O₃ nanolaminates indicate that O₃ is a more appropriate oxidant to deposit La₂O₃/Al₂O₃ nanolaminates for electron devices application.

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Improved photovoltaic effects in Mn-doped BiFeO₃ ferroelectric thin films through band gap engineering

阎堂柳, 陈斌, 刘钢, 牛瑞鹏, 尚杰, 高双, 薛武红, 金晶, 杨九如, 李润伟

2017 (6): 67702-067702. doi: 10.1088/1674-1056/26/6/067702

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As a low-bandgap ferroelectric material, BiFeO₃ has gained wide attention for the potential photovoltaic applications, since its photovoltaic effect in visible light range was reported in 2009. In the present work, Bi(Fe, Mn)O₃ thin films are fabricated by pulsed laser deposition method, and the effects of Mn doping on the microstructure, optical, leakage, ferroelectric and photovoltaic characteristics of Bi(Fe, Mn)O₃ thin films are systematically investigated. The x-ray diffraction data indicate that Bi(Fe, Mn)O₃ thin films each have a rhombohedrally distorted perovskite structure. From the light absorption results, it follows that the band gap of Bi(Fe, Mn)O₃ thin films can be tuned by doping different amounts of Mn content. More importantly, photovoltaic measurement demonstrates that the short-circuit photocurrent density and the open-circuit voltage can both be remarkably improved through doping an appropriate amount of Mn content, leading to the fascinating fact that the maximum power output of ITO/BiFe_0.7Mn_0.3O₃/Nb-STO capacitor is about 175 times higher than that of ITO/BiFeO₃/Nb-STO capacitor. The improvement of photovoltaic response in Bi(Fe, Mn)O₃ thin film can be reasonably explained as being due to absorbing more visible light through bandgap engineering and maintaining the ferroelectric property at the same time.

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Giant low-frequency magnetoelectric torque (MET) effect in polyvinylidene-fluoride (PVDF)-based MET device

郑春蕾, 刘宜伟, 詹清峰, 巫远招, 李润伟

2017 (6): 67703-067703. doi: 10.1088/1674-1056/26/6/067703

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A polyvinylidene-fluoride (PVDF)-based magnetoelectric torque (MET) device is designed with elastic layer sandwiched by PVDF layers, and low-frequency MET effect is carefully studied. It is found that elastic modulus and thickness of the elastic layer have great influences on magnetoelectric (ME) voltage coefficient (α_ME) and working range of frequency in PVDF-based MET device. The decrease of the modulus and thickness can help increase the α_ME. However, it can also reduce the working range in the low frequency. By optimizing the parameters, the giant α_ME of 320 V/cm·Oe (1 Oe=79.5775 A·m^-1) at low frequency (1 Hz) can be obtained. The present results may help design PVDF-based MET low-frequency magnetic sensor with improved magnetic sensitivity in a relative large frequency range.

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Hybrid temperature effect on a quartz crystal microbalance resonator in aqueous solutions

李强, 谷宇, 谢斌

2017 (6): 67704-067704. doi: 10.1088/1674-1056/26/6/067704

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The quartz crystal microbalance (QCM) is an important tool that can sense nanogram changes in mass. The hybrid temperature effect on a QCM resonator in aqueous solutions leads to unconvincing detection results. Control of the temperature effect is one of the keys when using the QCM for high precision measurements. Based on the Sauerbrey's and Kanazawa's theories, we proposed a method for enhancing the accuracy of the QCM measurement, which takes into account not only the thermal variations of viscosity and density but also the thermal behavior of the QCM resonator. We presented an improved Sauerbrey equation that can be used to effectively compensate the drift of the QCM resonator. These results will play a significant role when applying the QCM at the room temperature.

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Combined effect of light intensity and temperature on the magnetic resonance linewidth in alkali vapor cell with buffer gas

高阳, 董海峰, 王翔, 王笑菲, 尹凌霄

2017 (6): 67801-067801. doi: 10.1088/1674-1056/26/6/077801

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One of the peculiar phenomenons in non-zero magnetic resonance magnetometer is that, with the increase of the temperature, the magnetic resonance linewidth is narrowed at first instead of broadened due to the increasing collision rate. The magnetometer usually operates at the narrowest linewidth temperature to obtain the best sensitivity. Here, we explain this phenomenon quantitatively considering the nonlinear of the optical pumping in the cell and did experiments to verify this explanation. The magnetic resonance linewidth is measured using one amplitude-modulated pump laser and one continuous probe laser. The field is along the direction orthogonal to the plane of pump and probe beams. We change the temperature from 53℃ to 93℃ and the pumping light from 0.1 mW to 2 mW. The experimental results agree well with the theoretical calculations.

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Different angle-resolved polarization configurations of Raman spectroscopy: A case on the basal and edge plane of two-dimensional materials

刘雪璐, 张昕, 林妙玲, 谭平恒

2017 (6): 67802-067802. doi: 10.1088/1674-1056/26/6/067802

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Angle-resolved polarized Raman (ARPR) spectroscopy can be utilized to assign the Raman modes based on crystal symmetry and Raman selection rules and also to characterize the crystallographic orientation of anisotropic materials. However, polarized Raman measurements can be implemented by several different configurations and thus lead to different results. In this work, we systematically analyze three typical polarization configurations:1) to change the polarization of the incident laser, 2) to rotate the sample, and 3) to set a half-wave plate in the common optical path of incident laser and scattered Raman signal to simultaneously vary their polarization directions. We provide a general approach of polarization analysis on the Raman intensity under the three polarization configurations and demonstrate that the latter two cases are equivalent to each other. Because the basal plane of highly ordered pyrolytic graphite (HOPG) exhibits isotropic feature and its edge plane is highly anisotropic, HOPG can be treated as a modelling system to study ARPR spectroscopy of two-dimensional materials on their basal and edge planes. Therefore, we verify the ARPR behaviors of HOPG on its basal and edge planes at three different polarization configurations. The orientation direction of HOPG edge plane can be accurately determined by the angle-resolved polarization-dependent G mode intensity without rotating sample, which shows potential application for orientation determination of other anisotropic and vertically standing two-dimensional materials and other materials.

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Super scattering phenomenon in active spherical nanoparticles

刘昌宇, 解亚明, 王治国

2017 (6): 67803-067803. doi: 10.1088/1674-1056/26/6/067803

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Localized surface electromagnetic resonances in spherical nanoparticles with gain are investigated by using the Mie theory. Due to the coupling between the gain and resonances, super scattering phenomenon is raised and the total scattering efficiency is increased by over six orders of magnitude. The dual frequency resonance induced by the electric dipole term of the particle is observed. The distributions of electromagnetic field and the Poynting vector around nanoparticles are provided for better understanding different multipole resonances. Finally, the scattering properties of active spherical nanoparticles are investigated when the sizes of nanoparticles are beyond the quasi-static limit. It is noticed that more high-order multipole resonances can be excited with the increase of the radius. Besides, all resonances dominated by multipole magnetic terms can only appear in dielectric materials.

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Temperature-dependent photoluminescence of size-tunable ZnAgInSe quaternary quantum dots

丁琪, 张晓松, 李岚, 徐建萍, 周平, 董晓菲, 晏明

2017 (6): 67804-067804. doi: 10.1088/1674-1056/26/6/067804

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Colloidal ZnAgInSe (ZAISe) quantum dots (QDs) with different particle sizes were obtained by accommodating the reaction time. In the previous research, photoluminescence (PL) of ZAISe QDs only could be tuned by changing the composition. In this work the size-tunable photoluminescence was observed successfully. The red shift in the photoluminescence spectra was caused by the quantum confinement effect. The time-resolved photoluminescence indicated that the luminescence mechanisms of the ZAISe QDs were contributed by three recombination processes. Furthermore, the temperature-dependent PL spectra were investigated. We verified the regular change of temperature-dependent PL intensity, peak energy, and the emission linewidth of broadening for ZAISe QDs. According to these fitting data, the activation energy (ΔE) of ZAISe QDs with different nanocrystal sizes was obtained and the stability of luminescence was discussed.

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Graphene/Mo₂C heterostructure directly grown by chemical vapor deposition

邓荣轩, 张浩然, 张燕辉, 陈志蓥, 隋妍萍, 葛晓明, 梁逸俭, 胡诗珂, 于广辉, 姜达

2017 (6): 67901-067901. doi: 10.1088/1674-1056/26/6/067901

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Graphene-based heterostructure is one of the most attractive topics in physics and material sciences due to its intriguing properties and applications. We report the one-step fabrication of a novel graphene/Mo₂C heterostructure by using chemical vapor deposition (CVD). The composition and structure of the heterostructure are characterized through energy-dispersive spectrometer, transmission electron microscope, and Raman spectrum. The growth rule analysis of the results shows the flow rate of methane is a main factor in preparing the graphene/Mo₂C heterostructure. A schematic diagram of the growth process is also established. Transport measurements are performed to study the superconductivity of the heterostructure which has potential applications in superconducting devices.

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Influence of adatom migration on wrinkling morphologies of AlGaN/GaN micro-pyramids grown by selective MOVPE

陈杰, 黄溥曼, 韩小标, 潘郑州, 钟昌明, 梁捷智, 吴志盛, 刘扬, 张佰君

2017 (6): 68101-068101. doi: 10.1088/1674-1056/26/6/068101

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GaN micro-pyramids with AlGaN capping layer are grown by selective metal-organic-vapor phase epitaxy (MOVPE). Compared with bare GaN micro-pyramids, AlGaN/GaN micro-pyramids show wrinkling morphologies at the bottom of the structure. The formation of those special morphologies is associated with the spontaneously formed AlGaN polycrystalline particles on the dielectric mask, owing to the much higher bond energy of Al-N than that of Ga-N. When the sizes of the polycrystalline particles are larger than 50 nm, the uniform source supply behavior is disturbed, thereby leading to unsymmetrical surface morphology. Analysis reveals that the scale of surface wrinkling is related to the migration length of Ga adatoms along the AlGaN {1101} facet. The migration properties of Al and Ga further affect the distribution of Al composition along the sidewalls, characterized by the μ-PL measurement.

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Different effect of NiMnCo or FeNiCo on the growth of type-IIa large diamonds with Ti/Cu as nitrogen getter

李尚升, 张贺, 宿太超, 胡强, 胡美华, 龚春生, 马红安, 贾晓鹏, 李勇, 肖宏宇

2017 (6): 68102-068102. doi: 10.1088/1674-1056/26/6/068102

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In order to synthesize high-quality type-IIa large diamond, the selection of catalyst is very important, in addition to the nitrogen getter. In this paper, type-IIa large diamonds are grown under high pressure and high temperature (HPHT) by using the temperature gradient method (TGM), with adopting Ti/Cu as the nitrogen getter in Ni₇₀Mn₂₅Co₅ (abbreviated as NiMnCo) or Fe₅₅Ni₂₉Co₁₆ (abbreviated FeNiCo) catalyst. The values of nitrogen concentration (N_c) in both synthesized high-quality diamonds are less than 1 ppm, when Ti/Cu (1.6 wt%) is added in the FeNiCo or Ti/Cu (1.8 wt%) is added in the NiMnCo. The difference in solubility of nitrogen between both catalysts at HPHT is the basic reason for the different effect of Ti/Cu on eliminating nitrogen. The nitrogen-removal efficiency of Ti/Cu in the NiMnCo catalyst is less than in the FeNiCo catalyst. Additionally, a high-quality type-IIa large diamond size of 5.0 mm is obtained by reducing the growth rate and keeping the nitrogen concentration of the diamond to be less than 1 ppm, when Ti/Cu (1.6 wt%) is added in the FeNiCo catalyst.

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Anomalous temperature dependence of photoluminescence spectra from InAs/GaAs quantum dots grown by formation-dissolution-regrowth method

杨冠卿, 张世著, 徐波, 陈涌海, 王占国

2017 (6): 68103-068103. doi: 10.1088/1674-1056/26/6/068103

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Two kinds of InAs/GaAs quantum dot (QD) structures are grown by molecular beam epitaxy in formation-dissolution-regrowth method with different in-situ annealing and regrowth processes. The densities and sizes of quantum dots are different for the two samples. The variation tendencies of PL peak energy, integrated intensity, and full width at half maximum versus temperature for the two samples are analyzed, respectively. We find the anomalous temperature dependence of the InAs/GaAs quantum dots and compare it with other previous reports. We propose a new energy band model to explain the phenomenon. We obtain the activation energy of the carrier through the linear fitting of the Arrhenius curve in a high temperature range. It is found that the GaAs barrier layer is the major quenching channel if there is no defect in the material. Otherwise, the defects become the major quenching channel when some defects exist around the QDs.

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Magnesium incorporation efficiencies in Mg_xZn_1-xO films on ZnO substrates grown by metalorganic chemical vapor deposition

胡启昌, 丁凯

2017 (6): 68104-068104. doi: 10.1088/1674-1056/26/6/068104

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We investigate the magnesium (Mg) incorporation efficiencies in Mg_xZn_1-xO films on c-plane Zn-face ZnO substrates by using metalorganic chemical vapor deposition (MOCVD) technique. In order to deposit high quality Mg_xZn_1-xO films, atomically smooth epi-ready surfaces of the hydrothermal grown ZnO substrates are achieved by thermal annealing in O₂ atmosphere and characterized by atomic force microscope (AFM). The AFM, scanning electron microscope (SEM), and x-ray diffraction (XRD) studies demonstrate that the Mg_xZn_1-xO films each have flat surface and hexagonal wurtzite structure without phase segregation at up to Mg content of 34.4%. The effects of the growth parameters including substrate temperature, reactor pressure and VI/II ratio on Mg content in the films are investigated by XRD analysis based on Vegard's law, and confirmed by photo-luminescence spectra and x-ray photoelectron spectroscopy as well. It is indicated that high substrate temperature, low reactor pressure, and high VI/II ratio are good for obtaining high Mg content.

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A low cost composite quasi-solid electrolyte of LATP, TEGDME, and LiTFSI for rechargeable lithium batteries

黄杰, 彭佳悦, 凌仕刚, 杨琪, 邱纪亮, 卢嘉泽, 郑杰允, 李泓, 陈立泉

2017 (6): 68201-068201. doi: 10.1088/1674-1056/26/6/068201

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The composite quasi solid state electrolytes (CQSE) is firstly synthesized with quasi solid state electrolytes (QSE) and lithium-ion-conducting material Li_1.4Al_0.4Ti_1.6(PO₄)₃ (LATP), and the QSE consists of[LiG4][TFSI] with fumed silica nanoparticles. Compared with LATP, CQSE greatly improves the interface conductance of solid electrolytes. In addition,it has lower liquid volume relative to QSE. Although the liquid volume fraction of CQSE drops to 60%, its conductivity can also reach 1.39×10^-4 s/cm at 20℃. Linear sweep voltammetry (LSV) is conducted on each composite electrolyte. The results show the possibility that CQSE has superior electrochemical stability up to 5.0 V versus Li/Li⁺¹. TG curves also show that composite electrolytes have higher thermal stability. In addition, the performance of Li/QSE/LiMn₂O₄ cells and Li/CQSE/LiMn₂O₄ is evaluated and shows good electrochemical characteristics at 60℃.

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Synthesis and characterization of NaAlSi₂O₆ jadeite under 3.5 GPa

李刚, 王健, 李亚东, 陈宁, 陈良超, 郭龙锁, 赵亮, 苗辛原, 马红安, 贾晓鹏

2017 (6): 68202-068202. doi: 10.1088/1674-1056/26/6/068202

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The high pressure and high temperature (HPHT) method is successfully used to synthesize jadeite in a temperature range of 1000℃-1400℃ under a pressure of 3.5 GPa. The initial raw materials are Na₂SiO₃·9H₂O and Al₂(SiO₃)₃. Through the HPHT method, the amorphous glass material is entirely converted into crystalline jadeite. We can obtain the good-quality jadeite by optimizing the reaction pressure and temperature. The measurements of x-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and Raman scattering indicate that the properties of synthesized jadeite at 1260℃ under 3.5 GPa are extremely similar to those of the natural jadeite. What is more, the results will be valuable for understanding the formation process of natural jadeite. This work also reveals the mechanism for metamorphism of magma in the earth.

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Reversal current observed in micro-and submicro-channel flow under non-continuous DC electric field

段一飞, 马宏伟, 高泽阳, 王凯歌, 赵伟, 孙聃, 王归仁, 李俊杰, 白晋涛, 顾长志

2017 (6): 68203-068203. doi: 10.1088/1674-1056/26/6/068203

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In practical applications of biochips and bio-sensors, electrokinetic mechanisms are commonly employed to manipulate and analyze the characteristics of single bio-molecules. To accurately and flexibly control the movement of single molecule within micro-/submicro-fluidic channels, the characteristics of current signals at the initial stage of the flow are systematically studied based on a three-electrode system. The current response of micro-/submicro-fluidic channels filled with different electrolyte solutions in non-continuous external electric field are investigated. It is found, there always exists a current reversal phenomenon, which is an inherent property of the current signals in micro/submicro-fluidics Each solution has an individual critical voltage under which the steady current value is equal to zero The interaction between the steady current and external applied voltage follows an exponential function. All these results can be attributed to the overpotentials of the electric double layer on the electrodes. These results are helpful for the design and fabrication of functional micro/nano-scale fluidic sensors and biochips.

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Correction of failure in antenna array using matrix pencil technique

S U Khan,M K A Rahim

2017 (6): 68401-068401. doi: 10.1088/1674-1056/26/6/068401

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In this paper a non-iterative technique is developed for the correction of faulty antenna array based on matrix pencil technique (MPT). The failure of a sensor in antenna array can damage the radiation power pattern in terms of sidelobes level and nulls. In the developed technique, the radiation pattern of the array is sampled to form discrete power pattern information set. Then this information set can be arranged in the form of Hankel matrix (HM) and execute the singular value decomposition (SVD). By removing nonprincipal values, we obtain an optimum lower rank estimation of HM. This lower rank matrix corresponds to the corrected pattern. Then the proposed technique is employed to recover the weight excitation and position allocations from the estimated matrix. Numerical simulations confirm the efficiency of the proposed technique, which is compared with the available techniques in terms of sidelobes level and nulls.

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Helicase activity and substrate specificity of RecQ5β

尤菁, 徐雅楠, 李辉, 吕袭明, 李伟, 王鹏业, 窦硕星, 奚绪光

2017 (6): 68701-068701. doi: 10.1088/1674-1056/26/6/068701

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RecQ5β is an essential DNA helicase in humans, playing important roles in DNA replication, repair, recombination and transcription. The unwinding activity and substrate specificity of RecQ5β is still elusive. Here, we used stopped-flow kinetic method to measure the unwinding and dissociation kinetics of RecQ5β with several kinds of DNA substrates, and found that RecQ5β could well unwind ss/dsDNA, forked DNA and Holiday junction, but was compromised in unwinding blunt DNA and G-quadruplex. Rec5β has the preferred unwinding specificity for certain DNA substrates containing the junction point, which may improve the binding affinity and unwinding activity of RecQ5β. Moreover, from a comparison with the truncated RecQ5β^1-467, we discovered that the C-terminal domain might strongly influence the unwinding activity and binding affinity of RecQ5β. These results may shed light on the physiological functions and working mechanisms of RecQ5β helicase.

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A damping boundary condition for atomistic-continuum coupling

张杰, 朱洪涛, 张亮, 苏利红, 邓关宇, 王辉

2017 (6): 68702-068702. doi: 10.1088/1674-1056/26/6/068702

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The minimization of spurious wave reflection is a challenge in multiscale coupling due to the difference of spatial resolution between atomistic and continuum regions. In this study, a new damping condition is presented for eliminating spurious wave reflection at the interface between atomistic and continuum regions. This damping method starts by a coarse-fine decomposition of the atomic velocity based on the bridging scale method. The fine scale velocity of the atoms in the damping region is reduced by applying nonlinear damping coefficients. The effectiveness of this damping method is verified by one-and two-dimensional simulations.

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Cooperative impulsive formation control for networked uncertain Euler-Lagrange systems with communication delays

陈亮名, 李传江, 孙延超, 马广富

2017 (6): 68703-068703. doi: 10.1088/1674-1056/26/6/068703

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This paper investigates the cooperative formation problem via impulsive control for a class of networked Euler-Lagrange systems. To reduce the energy consumption and communication frequency, the impulsive control method and cooperative formation control approach are combined. With the consideration of system uncertainties and communication delays among agents, neural networks-based adaptive technique is used for the controller design. Firstly, under the constraint that each agent interacts with its neighbors only at some sampling moments, an adaptive neural-networks impulsive formation control algorithm is proposed for the networked uncertain Euler-Lagrange systems without communication delays. Using Lyapunov stability theory and Laplacian potential function in the graph theory, we conclude that the formation can be achieved by properly choosing the constant control gains. Further, when considering communication delays, a modified impulsive formation control algorithm is proposed, in which the extended Halanay differential inequality is used to analyze the stability of the impulsive delayed dynamical systems. Finally, numerical examples and performance comparisons with continuous algorithm are provided to illustrate the effectiveness of the proposed methods.

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Dissociation of H₂ on Mg-coated B₁₂C₆N₆

马丽, 金雪玲, 杨慧慧, 王小霞, 杜宁, 陈宏善

2017 (6): 68801-068801. doi: 10.1088/1674-1056/26/6/068801

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The dissociation of H₂ molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to determine the kinetics of the regeneration of the storage material. In this paper, we investigate the hydrogen adsorption and dissociation on Mg-coated B₁₂C₆N₆. The B₁₂C₆N₆ is an electron deficient fullerene, and Mg atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The preferred binding sites for Mg atoms are the B₂C₂ tetragonal rings. The positive charge quantity on the Mg atom is 1.50 when a single Mg atom is coated on a B₂C₂ ring. The stable dissociation products are determined and the dissociation processes are traced. Strong orbital interaction between the hydrogen and the cluster occurs in the process of dissociation, and H₂ molecule can be easily dissociated. We present four dissociation paths, and the lowest energy barrier is only 0.11 eV, which means that the dissociation can take place at ambient temperature.

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Influence of interface states, conduction band offset, and front contact on the performance of a-SiC: H(n)/c-Si(p) heterojunction solar cells

乔治, 冀建利, 张彦立, 刘虎, 李同锴

2017 (6): 68802-068802. doi: 10.1088/1674-1056/26/6/068802

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P-type silicon heterojunction (SHJ) solar cells with a-SiC:H(n) emitters were studied by numerical computer simulation in this paper. The influence of interface states, conduction band offset, and front contact on the performance of a-SiC:H(n)/c-Si(p) SHJ solar cells was investigated systematically. It is shown that the open circuit voltage (V_oc) and fill factor (FF) are very sensitive to these parameters. In addition, by analyzing equilibrium energy band diagram and electric field distribution, the influence mechanisms that interface states, conduction band offset, and front contact impact on the carrier transport, interface recombination and cell performance were studied in detail. Finally, the optimum parameters for the a-SiC:H(n)/c-Si(p) SHJ solar cells were provided. By employing these optimum parameters, the efficiency of SHJ solar cell based on p-type c-Si was significantly improved.

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O₃ fast and simple treatment-enhanced p-doped in Spiro-MeOTAD for CH₃NH₃I vapor-assisted processed CH₃NH₃PbI₃ perovskite solar cells

贾恩东, 娄茜, 周春兰, 郝维昌, 王文静

2017 (6): 68803-068803. doi: 10.1088/1674-1056/26/6/068803

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We demonstrate a simple and fast post-deposition treatment with high process compatibility on the hole transport material (HTM) Spiro-MeOTAD in vapor-assisted solution processed methylammonium lead triiodide (CH₃NH₃PbI₃)-based solar cells. The prepared Co-doped p-type Spiro-MeOTAD films are treated by O₃ at room temperature for 5 min, 10 min, and 20 min, respectively, prior to the deposition of the metal electrodes. Compared with the traditional oxidation of Spiro-MeOTAD films overnight in dry air, our fast O₃ treatment of HTM at room temperature only needs just 10 min, and a relative 40.3% increment in the power conversion efficiency is observed with respect to the result of without-treated perovskite solar cells. This improvement of efficiency is mainly attributed to the obvious increase of the fill factor and short-circuit current density, despite a slight decrease in the open-circuit voltage. Ultraviolet photoelectron spectroscopy (UPS) and Hall effect measurement method are employed in our study to determine the changes of properties after O₃ treatment in HTM. It is found that after the HTM is exposed to O₃, its p-type doping level is enhanced. The enhancement of conductivity and Hall mobility of the film, resulting from the improvement in p-doping level of HTM, leads to better performances of perovskite solar cells. Best power conversion efficiencies (PCEs) of 13.05% and 16.39% are achieved with most properly optimized HTM via CH₃NH₃I vapor-assisted method and traditional single-step method respectively.

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