Chin. Phys. B

Coexisting hidden attractors in a 4D segmented disc dynamo with one stable equilibrium or a line equilibrium

Jianghong Bao(鲍江宏), Dandan Chen(陈丹丹)

Chin. Phys. B, 2017, 26 (8): 080201. DOI: 10.1088/1674-1056/26/8/080201

Abstract ( 697 )

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This paper introduces a four-dimensional (4D) segmented disc dynamo which possesses coexisting hidden attractors with one stable equilibrium or a line equilibrium when parameters vary. In addition, by choosing an appropriate bifurcation parameter, the paper proves that Hopf bifurcation and pitchfork bifurcation occur in the system. The ultimate bound is also estimated. Some numerical investigations are also exploited to demonstrate and visualize the corresponding theoretical results.

Simulations of solitary waves of RLW equation by exponential B-spline Galerkin method

Melis Zorsahin Gorgulu, Idris Dag, Dursun Irk

Chin. Phys. B, 2017, 26 (8): 080202. DOI: 10.1088/1674-1056/26/8/080202

Abstract ( 890 )

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In this paper, an approximate function for the Galerkin method is composed using the combination of the exponential B-spline functions. Regularized long wave equation (RLW) is integrated fully by using an exponential B-spline Galerkin method in space together with Crank-Nicolson method in time. Three numerical examples related to propagation of single solitary wave, interaction of two solitary waves and wave generation are employed to illustrate the accuracy and the efficiency of the method. Obtained results are compared with some early studies.

Topology optimization using the improved element-free Galerkin method for elasticity

Yi Wu(吴意), Yong-Qi Ma(马永其), Wei Feng(冯伟), Yu-Min Cheng(程玉民)

Chin. Phys. B, 2017, 26 (8): 080203. DOI: 10.1088/1674-1056/26/8/080203

Abstract ( 831 )

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The improved element-free Galerkin (IEFG) method of elasticity is used to solve the topology optimization problems. In this method, the improved moving least-squares approximation is used to form the shape function. In a topology optimization process, the entire structure volume is considered as the constraint. From the solid isotropic microstructures with penalization, we select relative node density as a design variable. Then we choose the minimization of compliance to be an objective function, and compute its sensitivity with the adjoint method. The IEFG method in this paper can overcome the disadvantages of the singular matrices that sometimes appear in conventional element-free Galerkin (EFG) method. The central processing unit (CPU) time of each example is given to show that the IEFG method is more efficient than the EFG method under the same precision, and the advantage that the IEFG method does not form singular matrices is also shown.

Exact solution of the generalized Kemmer oscillator

Zi-Long Zhao(赵子龙), Chao-Yun Long(龙超云), Zheng-Wen Long(隆正文), Ting Xu(徐渟)

Chin. Phys. B, 2017, 26 (8): 080301. DOI: 10.1088/1674-1056/26/8/080301

Abstract ( 674 )

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In the present work, the generalized Kemmer oscillator was introduced in one dimension. It is shown that the exact solutions of generalized Kemmer oscillator with some appropriate choices of the interactions f(x) have been obtained by using the Nikiforov-Uvarov (NU) method. Moreover, several interesting cases are discussed.

Conditions on converting coherence into entanglement

Lian-Wu Yang(杨连武), Yun-Jie Xia(夏云杰)

Chin. Phys. B, 2017, 26 (8): 080302. DOI: 10.1088/1674-1056/26/8/080302

Abstract ( 650 )

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The present studies show that any nonzero amount of coherence of a system can be converted into entanglement between the system and an incoherent ancillary system via incoherent operations. According to this conclusion, we study the process of converting coherence into entanglement via a unitary operation where the initial ancillary system is of different quantum state. We find that some other conditions should be satisfied in converting coherence into entanglement. We also study the conditions of coherence consumption of converting coherence into entanglement.

Determining spatial structures of ion crystals by simulated annealing method Suggested by editors

Wen-Bo Wu(武文博), Chun-Wang Wu(吴春旺), Jian Li(李剑), Bao-Quan Ou(欧保全), Yi Xie(谢艺), Wei Wu(吴伟), Ping-Xing Chen(陈平形)

Chin. Phys. B, 2017, 26 (8): 080303. DOI: 10.1088/1674-1056/26/8/080303

Abstract ( 731 )

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Calculating the spatial structures of ion crystals is important in ion-trapped quantum computation. Here we demonstrate that the simulated annealing method is a powerful tool to evaluate the structures of ion crystals. By calculating equilibrium positions of 10 ions under harmonic potential and those of 120 ions under anharmonic potential, both with the standard procedure and simulated annealing method, we find that the standard procedure to evaluate spatial structures is complicated and may be inefficient in some cases, and that the simulated annealing method is more favorable.

Tunable ground-state solitons in spin-orbit coupling Bose-Einstein condensates in the presence of optical lattices

Huafeng Zhang(张华峰), Fang Chen(陈方), Chunchao Yu(郁春潮), Lihui Sun(孙利辉), Dahai Xu(徐大海)

Chin. Phys. B, 2017, 26 (8): 080304. DOI: 10.1088/1674-1056/26/8/080304

Abstract ( 762 )

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Properties of the ground-state solitons, which exist in the spin-orbit coupling (SOC) Bose-Einstein condensates (BEC) in the presence of optical lattices, are presented. Results show that several system parameters, such as SOC strength, lattice depth, and lattice frequency, have important influences on properties of ground state solitons in SOC BEC. By controlling these parameters, structure and spin polarization of the ground-state solitons can be effectively tuned, so manipulation of atoms may be realized.

Effect of gravity gradient in weak equivalence principle test Suggested by editors

Jia-Hao Xu(徐家豪), Cheng-Gang Shao(邵成刚), Jie Luo(罗杰), Qi Liu(刘祺), Lin Zhu(邾琳), Hui-Hui Zhao(赵慧慧)

Chin. Phys. B, 2017, 26 (8): 080401. DOI: 10.1088/1674-1056/26/8/080401

Abstract ( 857 )

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A high accuracy test of the weak equivalence principle (WEP) is of great scientific significance no matter whether its result is positive. We analyze the gravity gradient effect which is a main systematic error source in the test of WEP. The result shows that the uncompensated gravity gradient effect from the coupling term of the dominated gravity gradient multipole moment component q₂₁ and the relative multipole field component Q₂₁ contributes to an uncertainty of 1×10^-11 on the Eötvös parameter. We make a Q₂₁ compensation to reduce the effect by about 20 times, and the limit of the test precision due to this coupling is improved to a level of a part in 10¹³.

Modified Chapman-Enskog expansion: A new way to treat divergent series

Zhen-Su She(佘振苏)

Chin. Phys. B, 2017, 26 (8): 080501. DOI: 10.1088/1674-1056/26/8/080501

Abstract ( 862 )

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The resolution by Chen and Sun of divergent Chapman-Enskog expansion problem will not only build a unified foundation for non-equilibrium dynamics modeling at all Mach number and Knudsen number, but also shed light to a large class of difficult theoretical problems involving divergent expansion on strong nonlinearity.

Identifying the closeness of eigenstates in quantum many-body systems Suggested by editors

Hai-bin Li(李海彬), Yang Yang(杨扬), Pei Wang(王沛), Xiao-guang Wang(王晓光)

Chin. Phys. B, 2017, 26 (8): 080502. DOI: 10.1088/1674-1056/26/8/080502

Abstract ( 819 )

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We propose a quantity called modulus fidelity to measure the closeness of two quantum pure states. We use it to investigate the closeness of eigenstates in one-dimensional hard-core bosons. When the system is integrable, eigenstates close to their neighbor or not, which leads to a large fluctuation in the distribution of modulus fidelity. When the system becomes chaos, the fluctuation is reduced dramatically, which indicates all eigenstates become close to each other. It is also found that two kind of closeness, i.e., closeness of eigenstates and closeness of eigenvalues, are not correlated at integrability but correlated at chaos. We also propose that the closeness of eigenstates is the underlying mechanism of eigenstate thermalization hypothesis (ETH) which explains the thermalization in quantum many-body systems.

Dynamic analysis and fractional-order adaptive sliding mode control for a novel fractional-order ferroresonance system Suggested by editors

Ningning Yang(杨宁宁), Yuchao Han(韩宇超), Chaojun Wu(吴朝俊), Rong Jia(贾嵘), Chongxin Liu(刘崇新)

Chin. Phys. B, 2017, 26 (8): 080503. DOI: 10.1088/1674-1056/26/8/080503

Abstract ( 773 )

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Ferroresonance is a complex nonlinear electrotechnical phenomenon, which can result in thermal and electrical stresses on the electric power system equipments due to the over voltages and over currents it generates. The prediction or determination of ferroresonance depends mainly on the accuracy of the model used. Fractional-order models are more accurate than the integer-order models. In this paper, a fractional-order ferroresonance model is proposed. The influence of the order on the dynamic behaviors of this fractional-order system under different parameters n and F is investigated. Compared with the integral-order ferroresonance system, small change of the order not only affects the dynamic behavior of the system, but also significantly affects the harmonic components of the system. Then the fractional-order ferroresonance system is implemented by nonlinear circuit emulator. Finally, a fractional-order adaptive sliding mode control (FASMC) method is used to eliminate the abnormal operation state of power system. Since the introduction of the fractional-order sliding mode surface and the adaptive factor, the robustness and disturbance rejection of the controlled system are enhanced. Numerical simulation results demonstrate that the proposed FASMC controller works well for suppression of ferroresonance over voltage.

Multi-phase field simulation of grain growth in multiple phase transformations of a binary alloy Suggested by editors

Li Feng(冯力), Beibei Jia(贾北北), Changsheng Zhu(朱昶胜), Guosheng An(安国升), Rongzhen Xiao(肖荣振), Xiaojing Feng(冯小静)

Chin. Phys. B, 2017, 26 (8): 080504. DOI: 10.1088/1674-1056/26/8/080504

Abstract ( 758 )

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This work establishes a temperature-controlled sequence function, and a new multi-phase-field model, for liquid-solid-solid multi-phase transformation by coupling the liquid-solid phase transformation model with the solid-solid phase transformation model. Taking an Fe-C alloy as an example, the continuous evolution of a multi-phase transformation is simulated by using this new model. In addition, the growth of grains affected by the grain orientation of the parent phase (generated in liquid-solid phase transformation) in the solid-solid phase transformation is studied. The results show that the morphology of ferrite grains which nucleate at the boundaries of the austenite grains is influenced by the orientation of the parent austenite grains. The growth rate of ferrite grains which nucleate at small-angle austenite grain boundaries is faster than those that nucleate at large-angle austenite grain boundaries. The difference of the growth rate of ferrites grains in different parent phase that nucleate at large-angle austenite grain boundaries, on both sides of the boundaries, is greater than that of ferrites nucleating at small-angle austenite grain boundaries.

Fiber-based joint time and frequency dissemination via star-shaped commercial telecommunication network

Yi-Bo Yuan(袁一博), Bo Wang(王波), Li-Jun Wang(王力军)

Chin. Phys. B, 2017, 26 (8): 080601. DOI: 10.1088/1674-1056/26/8/080601

Abstract ( 691 )

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A fiber-based, star-shaped joint time and frequency dissemination scheme is demonstrated. By working in cooperation with the existing commercial telecommunication network. Our scheme enables the frequency, time, and digital data networks to be integrated together and could represent an ideal option of interconnection among scientific institutions. The compensation functions of the time and frequency transfer scheme are set at the client nodes. The complexity of the central node is thus reduced, and future expansion by the addition of further branches will be accomplished more easily. During a performance test in which the ambient temperature fluctuation is 30 ℃/day, timing signal dissemination stability is achieved to be approximately ± 50 ps along 25-km-long fiber spools. After calibration, a timing signal synchronization accuracy of 100 ps is also realized. The proposed scheme offers an option of the construction of large-scale fiber-based frequency and time transfer networks.

Raman sideband cooling of rubidium atoms in optical lattice Suggested by editors

Chun-Hua Wei(魏春华), Shu-Hua Yan(颜树华)

Chin. Phys. B, 2017, 26 (8): 080701. DOI: 10.1088/1674-1056/26/8/080701

Abstract ( 799 )

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We develop a simple and practical scheme to apply sideband cooling to a cloud of rubidium atoms. A sample containing 4×10⁷⁰ ⁸⁷Rb is trapped in a far red detuned optical lattice. Through optimizing the relevant parameters, i.e., laser detuning, magnetic field, polarization, and duration time, a temperature around 1.5 μK and phase space density close to 1/500 are achieved. Compared with polarization gradient cooling, the temperature decreases by around one order of magnitude. This technique could be used in high precision measurement such as atomic clocks and atom interferometer. It could also serve as a precooling means before evaporation cooling in a dipole trap, and may be a promising method of achieving quantum degeneracy with purely optical means.

Effective transport of passive particles induced by chiral-active particles in microchannel Suggested by editors

Yunfeng Hua(华昀峰), Linli He(何林李), Linxi Zhang(章林溪)

Chin. Phys. B, 2017, 26 (8): 080702. DOI: 10.1088/1674-1056/26/8/080702

Abstract ( 685 )

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Transport of passive particles induced by chiral-active particles in microchannel is investigated by using the overdamped Langevin dynamics simulation in a two-dimensional model system. Due to the chirality of active particles and special structure of microchannel, effective ratchet transport of passive particles is achieved. Effective transport of passive particles depends on the width of microchannel (d), the density (ρ), and the angular velocity (ω) of chiral-active particles. There exist optimal parameters for d and ω at which the transport efficiency for passive particles takes its maximal value. This investigation can help us understand the necessity of active motion for living systems to maintain a number of vital processes such as materials transport inside cells and the foraging dynamics of mobile organisms.

A numerical Hartree self-consistent field calculation of an autoionization resonance parameters for a doubly excited 2s², 3s², and 4s² states of He atom with a complex absorbing potential

Tsogbayar Tsednee, Danny L Yeager

Chin. Phys. B, 2017, 26 (8): 083101. DOI: 10.1088/1674-1056/26/8/083101

Abstract ( 687 )

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The self-consistent Hartree-Fock equation for the He atom is solved using the pseudospectral method. The Feshbach-type autoionization resonance parameters for doubly excited 2s², 3s², and 4s² ¹S states of He have been determined by adding a complex absorbing potential to the Hamiltonian. The Riss-Meyer iterative and Padé extrapolation methods are applied to obtain reliable values for the autoionization resonance parameters, which are compared to previous results in the literature.

Responsive mechanism of three novel hypochlorous acid fluorescent probes and solvent effect on their sensing performance

Yong Zhou(周勇), Yun-Kun Wang(王云坤), Xiao-Fei Wang(王晓菲), Yu-Jin Zhang(张玉瑾), Chuan-Kui Wang(王传奎)

Chin. Phys. B, 2017, 26 (8): 083102. DOI: 10.1088/1674-1056/26/8/083102

Abstract ( 810 )

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Optical properties and responsive mechanisms of three newly synthesized fluorescent probes for hypochlorous acid (HOCl) are investigated by employing time-dependent density functional theory. The computational results show that the absorption and emission properties of these probes change obviously when they react with hypochlorous acid. It is found that the probe FHZ has the best performance according to the probing behavior. Moreover, the responsive mechanisms of the probes are studied by analyzing the distributions of molecular orbitals and charge transfer, which are shown as the photon-induced electron transfer (PET) for FHZ and the intramolecular charge transfer (ICT) for the other two probes. Specially, solvent effect on optical properties of the probe FHZ before and after reaction is studied within the polarizable continuum model (PCM). It is shown that performance of the probe depends crucially on the solvent polarity. Our computational results agree well with the experimental measurement, and provide information for design of efficient two-photon fluorescent probes.

Geometries, stabilities, and electronic properties analysis in In_nNi^{(0, ±1)} clusters: Molecular modeling and DFT calculations

Shun-Ping Shi(史顺平), Chuan-Yu Zhang(张传瑜), Xiao-Feng Zhao(赵晓凤), Xia Li(李侠), Min Yan(闫珉), Gang Jiang(蒋刚)

Chin. Phys. B, 2017, 26 (8): 083103. DOI: 10.1088/1674-1056/26/8/083103

Abstract ( 584 )

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Density functional theory (DFT) with the B3LYP method and the SDD basis set is selected to investigate In_nNi, In_nNi^-, and In_nNi⁺ (n=1-14) clusters. For neutral and charged systems, several isomers and different multiplicities are studied with the aim to confirm the most stable structures. The structural evolution of neutral, cationic, and anionic In_nNi clusters, which favors the three-dimensional structures for n=3-14. The main configurations of the In_nNi isomers are not affected by adding or removing an electron, the order of their stabilities is also nearly not affected. The obtained binding energy exhibits that the Ni-doped In₁₃ cluster is the most stable species of all different sized clusters. The calculated fragmentation energy and the second-order energy difference as a function of the cluster size exhibit a pronounced even-odd alternation phenomenon. The electronic properties including energy gap (E_g), adiabatic electron affinity (AEA), vertical electron detachment energy (VDE), adiabatic ionization potential energy (AIP), and vertical ionization potential energy (VIP) are studied. The total magnetic moments show that the different magnetic moments depend on the number of the In atoms for charged In_nNi. Additionally, the natural population analysis of In_nNi^{(0, ±1)} clusters is also discussed.

Wetting and coalescence of the liquid metal on the metal substrate Suggested by editors

Zhen-Yang Zhao(赵珍阳), Tao Li(李涛), Yun-Rui Duan(段云瑞), Zhi-Chao Wang(王志超), Hui Li(李辉)

Chin. Phys. B, 2017, 26 (8): 083104. DOI: 0.1088/1674-1056/26/8/083104

Abstract ( 469 )

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Molecular dynamics (MD) simulations are performed to investigate the wettability of liquid metal on the metal substrate. Results show that there exists different wettability on the different metal substrates, which is mainly determined by the interaction between the liquid and the substrate. The liquid metal is more likely to wet the same kind of metal substrate, which attracts the liquid metal to one side on the hybrid substrate. Exchanging the liquid metal and substrate metal has no effect on the wettability between these two metals. Moreover, the study of metal drop coalescing indicates that the metal substrate can significantly affect the coalescence behavior, in which the changeable wettability of liquid metal plays a predominant role. These studies demonstrate that the wetting behavior of liquid metal can be controlled by choosing the suitable metal substrate.

Polarization control of multi-photon absorption under intermediate femtosecond laser field

Wenjing Cheng(程文静), Pei Liu(刘沛), Guo Liang(梁果), Ping Wu(吴萍), Tianqing Jia(贾天卿), Zhenrong Sun(孙真荣), Shian Zhang(张诗按)

Chin. Phys. B, 2017, 26 (8): 083201. DOI: 10.1088/1674-1056/26/8/083201

Abstract ( 817 )

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It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light-matter interaction. Previous studies mainly focused on the multi-photon absorption control in the weak field. In this paper, we further explore the polarization control behavior of multi-photon absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the second-order perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect (e.g., four-photon absorption) can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and four-photon transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization.

Photoassociation spectra of ultracold ⁸⁵Rb₂ molecule in 0_u⁺ long range state near the 5S_1/2+5P_1/2 asymptote Suggested by editors

Guodong Zhao(赵国栋), Dianqiang Su(苏殿强), Zhonghua Ji(姬中华), Tengfei Meng(孟腾飞), Yanting Zhao(赵延霆), Liantuan Xiao(肖连团), Suotang Jia(贾锁堂)

Chin. Phys. B, 2017, 26 (8): 083301. DOI: 10.1088/1674-1056/26/8/083301

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We investigate the high resolution photoassociation spectra of ⁸⁵Rb₂ molecules in 0_u⁺ long range state below the (5S_1/2 + 5P_1/2) asymptote. The ⁸⁵Rb atomic samples are trapped in a dark magneto-optical trap (MOT) and prepared in the dark state. With the help of trap loss technique, we obtain considerable photoassociation spectroscopy with rovibrational resolution, some of which have never been observed before. The observed spectrum is fitted by a rigid rotation model, and the rotational constants of ultracold ⁸⁵Rb₂ molecule in long range 0_u⁺ are obtained for different vibrational states. By applying the LeRoy-Bernstein method, we assign the vibrational quantum numbers and derive C₃ coefficient, which is used to obtain the potential energy curve.

Ultraviolet discharges from a radio-frequency system for potential biological/chemical applications

Joseph Ametepe, Sheng Peng, Dennis Manos

Chin. Phys. B, 2017, 26 (8): 083302. DOI: 10.1088/1674-1056/26/8/083302

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In this work, we describe a new electrode-less radio-frequency (RF) excitation technique for generating excimers in the vacuum ultraviolet (VUV) and ultraviolet (UV) spectral regions for potential biological/chemical applications. Spectra data of Xe₂^*, XeI^*, and KrI^* generated by this new technique are presented. Optical efficiency of the lamp system ranges from 3% to 6% for KrI^*, 7% to 13% for XeI^*, and 15% to 20% for Xe₂^*. Also, results of irradiating E-coli with XeI^* discharge from this lamp system is presented to show one of the promising applications of such electrode-less apparatus. This new RF lamp system offers an interesting addition to the already existing technologies for generating VUV and UV light for various biological, physical, and chemical processes especially those requiring large area for high productivity.

The impact of vibrational wave function on low energy electron vibrational scattering from nitrogen molecule

Jia Fu(付佳), Hao Feng(冯灏), Yi Zhang(张燚)

Chin. Phys. B, 2017, 26 (8): 083401. DOI: 10.1088/1674-1056/26/8/083401

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The vibrational wave function of the target theoretically plays an important role in the calculation of vibrational excitation cross sections. By a careful study of the differential cross sections resulting from different vibrational wave functions we find that cross sections are susceptible to vibrational wave functions. Minor changes in the vibration wave function may cause a significant change in the cross section. Even more surprising is that by selecting a few numbers of potential models (which determine the vibrational wave functions) we can often calculate the differential scattering cross section in much closer agreement with experiment in the framework of body-frame vibrational close-coupling theory, which suggest that an accurate potential energy may play a more important role in scattering than we thought before.

Effect of Ni and vacancy concentration on initial formation of Cu precipitate in Fe-Cu-Ni ternary alloys by molecular dynamics simulation

Ke Liu(刘珂), Li-Juan Hu(胡丽娟), Qiao-Feng Zhang(张巧凤), Yao-Ping Xie(谢耀平), Chao Gao(高超), Hai-Ying Dong(董海英), Wan-Yi Liang(梁婉怡)

Chin. Phys. B, 2017, 26 (8): 083601. DOI: 10.1088/1674-1056/26/8/083601

Abstract ( 719 )

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In the present work, the effects of Ni atoms and vacancy concentrations (0.1%, 0.5%, 1.0%) on the formation process of Cu solute clusters are investigated for Fe-1.24%Cu-0.62%Ni alloys by molecular dynamics (MD) simulations. The presence of Ni is beneficial to the nucleation of Cu precipitates and has little effect on coarsening rate in the later stage of aging. This result is caused by reducing the diffusion coefficient of Cu clusters and the dynamic migration of Ni atoms. Additionally, there are little effects of Ni on Cu precipitates as the vacancy concentration reaches up to 1.0%, thereby explaining the embrittlement for reactor pressure vessel (RPV) steel. As a result, the findings can hopefully provide the important information about the essential mechanism of Cu cluster formation and a better understanding of ageing phenomenon of RPV steel. Furthermore, these original results are analyzed with a simple model of Cu diffusion, which suggests that the same behavior could be observed in Cu-containing alloys.

Three-dimensional hexapole focusing of pulsed molecular beam for state selection

Yi Ke(柯毅), Xiao-Bing Deng(邓小兵), Zhong-Kun Hu(胡忠坤)

Chin. Phys. B, 2017, 26 (8): 083701. DOI: 10.1088/1674-1056/26/8/083701

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We theoretically investigate three-dimensional (3D) focusing of pulsed molecular beam using a series of hexapoles with different orientations. Transversely oriented hexapoles provide both the transverse and longitudinal focusing force and a longitudinally oriented one provides only the transverse force. The hexapole focusing position are designed to realize the simultaneous focusing in three directions. The additional longitudinal focusing compared with the conventional hexapole can suppress the effect of chromatic aberration induced by the molecular longitudinal velocity spread, thus improving the state-selection purity as well as the beam density. Performance comparison of state selection between this 3D focusing hexapole and a conventional one is made using numerical trajectory simulations, choosing CHF₃ molecules as a tester. It is confirmed that our proposal can improve the state-selection purity from 68.2% to 96.1% and the beam density by a factor of 2.3.

Cascaded third-harmonic-generation converter based on a single ADP crystal

Hong-Wei Qi(亓宏伟), Yu-Xiang Sun(孙玉祥), Zheng-Ping Wang(王正平), Xu-Zhao Zhang(张栩朝), Fa-Peng Yu(于法鹏), Xun Sun(孙洵), Xin-Guang Xu(许心光), Xian Zhao(赵显)

Chin. Phys. B, 2017, 26 (8): 084201. DOI: 10.1088/1674-1056/26/8/084201

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Based on a specially designed optical structure, an efficient cascaded third-harmonic-generation (THG) output of a 1064-nm, pico-seconds pulse laser is successively realized by using an NH₄H₂PO₄(ADP) crystal that acts as the second-harmonic-generation component and sum-frequency-generation component. The maximum THG output is 1.61 mJ, and the highest conversion efficiency from 1064 nm to 355 nm reaches 35%, which are obviously superior to the results obtained using a KDP crystal under the same circumstance. The further phase-matching analysis indicates that this THG configuration of ADP crystal can be applied to various fundamental wavelengths in a range of 1 μ-1.1 μm. Compared with the previously reported KDP THG converter, which is based on a similar principle, the present ADP THG converter is favorable for large-energy, high-efficiency operation because of the larger effective nonlinear optical coefficient d_eff and higher laser damage threshold.

Resonantly driven exciton Rabi oscillation in single quantum dots emitting at 1300 nm Suggested by editors

Yong-Zhou Xue(薛永洲), Ze-Sheng Chen(陈泽升), Hai-Qiao Ni(倪海桥), Zhi-Chuan Niu(牛智川), De-Sheng Jiang(江德生), Xiu-Ming Dou(窦秀明), Bao-Quan Sun(孙宝权)

Chin. Phys. B, 2017, 26 (8): 084202. DOI: 10.1088/1674-1056/26/8/084202

Abstract ( 722 )

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We report on the resonance fluorescence (RF) from single InAs quantum dots (QDs) emitting at the telecom band of 1300 nm. The InAs/GaAs QDs are embedded in a planar optical microcavity and the RF is measured by an orthogonal excitation-detection geometry for deeply suppressing the residual laser scattering. An ultra-weak He-Ne laser is necessary to be used as a gate laser for obtaining RF. Rabi oscillation with more than one period is observed through the picosecond (ps) pulsed laser excitation. The resonant control of exciton opens up new possibilities for realizing the on-demand single photon emission and quantum manipulation of solid-state qubits at telecom band.

Diode-pumped laser performance of Tm:Sc₂SiO₅ crystal at 1971 nm

Bin Liu(刘斌), Li-He Zheng(郑丽和), Qing-Guo Wang(王庆国), Jun-Fang Liu(刘军芳), Liang-Bi Su(苏良碧), Hui-Li Tang(唐慧丽), Jie Liu(刘杰), Xiu-Wei Fan(范秀伟), Feng Wu(吴锋), Ping Luo(罗平), Heng-Yu Zhao(赵衡煜), Jiao-Jiao Shi(施佼佼), Nuo-Tian He(何诺天), Na Li(李纳), Qiu Li(李秋), Chao Guo(郭超), Xiao-Dong Xu(徐晓东), Zhan-Shan Wang(王占山), Jun Xu(徐军)

Chin. Phys. B, 2017, 26 (8): 084203. DOI: 10.1088/1674-1056/26/8/084203

Abstract ( 708 )

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The 4-at.% Tm:Sc₂SiO₅(Tm:SSO) crystal is successfully obtained by the Czochralski method. The optical properties and thermal conductivity of the crystal are investigated. The broad continuous wave (CW) laser output of (100)-cut Tm:SSO with the dimensions of 3 mm×3 mm×3 mm under laser diode (LD)-pumping is realized. The full width at half maximum (FWHM) of the laser emitting reaches up to 21 nm. The laser threshold of Tm:SSO is measured to be 0.43 W. Efficient diode-pumped CW laser performance of Tm:SSO is demonstrated with a slope efficiency of 25.9% and maximum output power of 934 mW.

Boundary normal pressure-based electrical conductivity reconstruction for magneto-acoustic tomography with magnetic induction

Ge-Pu Guo(郭各朴), He-Ping Ding(丁鹤平), Si-Jie Dai(戴思捷), Qing-Yu Ma(马青玉)

Chin. Phys. B, 2017, 26 (8): 084301. DOI: 10.1088/1674-1056/26/8/084301

Abstract ( 817 )

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As a kind of multi-physics imaging approach integrating the advantages of electrical impedance tomography and ultrasound imaging with the improved spatial resolution and image contrast, magneto-acoustic tomography with magnetic induction (MAT-MI) is demonstrated to have the capability of electrical impedance contrast imaging for biological tissues with conductivity differences. By being detected with a strong directional transducer, abrupt pressure change is proved to be generated by the gradient of the induced Lorentz force along the force direction at conductivity boundary. A simplified boundary normal pressure (BNP)-based conductivity reconstruction algorithm is proposed and the formula for conductivity distribution inside the object with the clear physical meaning of pressure derivative, is derived. Numerical simulations of acoustic pressure and conductivity reconstruction are conducted based on a 2-layer eccentric cylindrical phantom model using Hilbert transform. The reconstructed two-dimensional conductivity images accord well with the model, thus successfully making up the deficiency of only imaging conductivity boundary in traditional MAT-MI. The proposed method is also demonstrated to have a spatial resolution of one wavelength. This study provides a new method of reconstructing accurate electrical conductivity and suggests the potential applications of MAT-MI in imaging biological tissues with conductivity difference.

Noether symmetry and conserved quantity for dynamical system with non-standard Lagrangians on time scales

Jing Song(宋静), Yi Zhang(张毅)

Chin. Phys. B, 2017, 26 (8): 084501. DOI: 10.1088/1674-1056/26/8/084501

Abstract ( 637 )

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This paper focuses on studying the Noether symmetry and the conserved quantity with non-standard Lagrangians, namely exponential Lagrangians and power-law Lagrangians on time scales. Firstly, for each case, the Hamilton principle based on the action with non-standard Lagrangians on time scales is established, with which the corresponding Euler-Lagrange equation is given. Secondly, according to the invariance of the Hamilton action under the infinitesimal transformation, the Noether theorem for the dynamical system with non-standard Lagrangians on time scales is established. The proof of the theorem consists of two steps. First, it is proved under the infinitesimal transformations of a special one-parameter group without transforming time. Second, utilizing the technique of time-re-parameterization, the Noether theorem in a general form is obtained. The Noether-type conserved quantities with non-standard Lagrangians in both classical and discrete cases are given. Finally, an example in Friedmann-Robertson-Walker spacetime and an example about second order Duffing equation are given to illustrate the application of the results.

Ultrasound wave propagation in glass-bead packing under isotropic compression and uniaxial shear Suggested by editors

Zhi-Gang Zhou(周志刚), Yi-Min Jiang(蒋亦民), Mei-Ying Hou(厚美瑛)

Chin. Phys. B, 2017, 26 (8): 084502. DOI: 10.1088/1674-1056/26/8/084502

Abstract ( 827 )

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The axial-stress dependence of sound wave velocity in granular packing is experimentally investigated with tri-axial and uni-axial devices. Preparing samples by repetitive loadings and unloadings in a range of 20 kPa-1000 kPa, we find that the axial-stress dependence of sound wave velocity approaches the Hertz scaling with an exponent of 1/6 for large axial stresses (> 400 kPa). Weak deviation from the Hertz scaling is seen at low stresses. Repetitive axial loadings slightly reduce this deviation, and sound velocities increase nonlinearly approaching some saturated values. Velocities for uni-axial case are found slightly to be bigger than those for tri-axial isotropic compression case. These effects are discussed in the frameworks of granular solid hydrodynamics (GSH) and effective medium theory (EMT), which indicate that they cannot be explained with density nor Janssen ratio only. Dissipation occurring during wave propagation may be a non-negligible factor.

X-ray tomography study on the structure of the granular random loose packing Suggested by editors

Yi Xing(邢义), Yu-Peng Qiu(邱宇鹏), Zhi Wang(王智), Jia-Chao Ye(叶佳超), Xiang-Ting Li(李向亭)

Chin. Phys. B, 2017, 26 (8): 084503. DOI: 10.1088/1674-1056/26/8/084503

Abstract ( 665 )

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Random loose packing is the minimum-density granular packing which can maintain mechanical stability. In this study, x-ray tomography is used to investigate the internal structure of an isotropically prepared random loose packing through a special apparatus to minimize the effect of gravity. It is found that the minimum packing density is around 0.587. The microscopic structural analysis of the packing is also carried out.

Required width of exit to avoid the faster-is-slower effect in highly competitive evacuation Suggested by editors

Yu-Chun Zhang(张玉春), Jian Ma(马剑), You-Liang Si(司有亮), Tong Ran(冉桐), Fan-Yu Wu(吴凡雨), Guo-Yuan Wang(王国元), Peng Lin(林鹏)

Chin. Phys. B, 2017, 26 (8): 084504. DOI: 10.1088/1674-1056/26/8/084504

Abstract ( 668 )

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A group of competitive people escaping through an exit could lead to the formation of a deadlock, which significantly increases the evacuation time. Such a phenomenon is called the faster-is-slower effect (FIS) and it has been experimentally verified in different systems of particles flowing through an opening. In this paper, the numerical simulation based on discrete element method (DEM) is adopted to study a group of highly competitive people through an exit of varying widths. The FIS effect is observed for a narrow exit whilst it is not observed for the exit wide enough to accommodate two people through it side-by-side. Experimental validation of such a phenomenon with humans is difficult due to ethical issues. The mouse is a kind of self-driven and soft-body creature and it exhibits selfish behaviour under stressed conditions. Particles flowing through an opening in different systems, such as pedestrian flow, animal flow, silo flow, etc. have similar characteristics. Therefore, experimental study is conducted by driving mice to escape through an exit of different widths at varying levels of stimulus. The escape time through a narrow exit (i.e., 2 cm) increases obviously with the increase of stimulus level but it is quite opposite to a wider exit (i.e., 4 cm). The FIS effect is avoided for an exit wide enough to accommodate two mice passing through it side-by-side. The study illustrates that FIF effect could be effectively prevented for an exit when its width is twice the size of particles.

A multicomponent multiphase lattice Boltzmann model with large liquid-gas density ratios for simulations of wetting phenomena Suggested by editors

Qing-Yu Zhang(张庆宇), Dong-Ke Sun(孙东科), Ming-Fang Zhu(朱鸣芳)

Chin. Phys. B, 2017, 26 (8): 084701. DOI: 10.1088/1674-1056/26/8/084701

Abstract ( 824 )

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A multicomponent multiphase (MCMP) pseudopotential lattice Boltzmann (LB) model with large liquid-gas density ratios is proposed for simulating the wetting phenomena. In the proposed model, two layers of neighboring nodes are adopted to calculate the fluid-fluid cohesion force with higher isotropy order. In addition, the different-time-step method is employed to calculate the processes of particle propagation and collision for the two fluid components with a large pseudo-particle mass contrast. It is found that the spurious current is remarkably reduced by employing the higher isotropy order calculation of the fluid-fluid cohesion force. The maximum spurious current appearing at the phase interfaces is evidently influenced by the magnitudes of fluid-fluid and fluid-solid interaction strengths, but weakly affected by the time step ratio. The density ratio analyses show that the liquid-gas density ratio is dependent on both the fluid-fluid interaction strength and the time step ratio. For the liquid-gas flow simulations without solid phase, the maximum liquid-gas density ratio achieved by the present model is higher than 1000:1. However, the obtainable maximum liquid-gas density ratio in the solid-liquid-gas system is lower. Wetting phenomena of droplets contacting smooth/rough solid surfaces and the dynamic process of liquid movement in a capillary tube are simulated to validate the proposed model in different solid-liquid-gas coexisting systems. It is shown that the simulated intrinsic contact angles of droplets on smooth surfaces are in good agreement with those predicted by the constructed LB formula that is related to Young's equation. The apparent contact angles of droplets on rough surfaces compare reasonably well with the predictions of Cassie's law. For the simulation of liquid movement in a capillary tube, the linear relation between the liquid-gas interface position and simulation time is observed, which is identical to the analytical prediction. The simulation results regarding the wetting phenomena of droplets on smooth/rough surfaces and the dynamic process of liquid movement in the capillary tube demonstrate the quantitative capability of the proposed model.

Turbulence modulation model for gas-particle flow based on probability density function approach

Lu Wang(王路), Jiang-rong Xu(徐江荣)

Chin. Phys. B, 2017, 26 (8): 084702. DOI: 10.1088/1674-1056/26/8/084702

Abstract ( 637 )

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The paper focuses on the turbulence modulation problem in gas-particle flow with the use of probability density function (PDF) approach. By means of the PDF method, a general statistical moment turbulence modulation model without considering the trajectory difference between two phases is derived from the Navier-Stokes equations. A new turbulence production term induced by the dispersed-phase is analyzed and considered. Furthermore, the trajectory difference between two media is taken into account. Subsequently, a new k-ε turbulence modulation model in dilute particle-laden flow is successfully set up. Then, the changes to several terms, including the turbulence production, dissipation, and diffusion terms, are well described consequently. The promoted model provides a more probable explanation for the modification of particles on the turbulence. Finally, we applied the model to simulate a gas-particle turbulence flow case in a wall jet, and found that the simulation results agree well with the experimental data.

Comparison between AlN and Al₂O₃ ceramics applied to barrier dielectric of plasma actuator

Dong-Liang Bian(卞栋梁), Yun Wu(吴云), Min Jia(贾敏), Chang-Bai Long(龙昌柏), Sheng-Bo Jiao(焦胜博)

Chin. Phys. B, 2017, 26 (8): 084703. DOI: 10.1088/1674-1056/26/8/084703

Abstract ( 645 )

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This paper reports the material characterization and performance evaluation of an AlN ceramic based dielectric barrier discharge (DBD) plasma actuator. A conventional Al₂O₃ ceramic is also investigated as a control. The plasma images, thermal characteristics and electrical properties of the two actuators are compared and studied. Then, with the same electrical operating parameters (12-kV applied voltage and 11-kHz power frequency), variations of the surface morphologies, consumed power and induced velocities are recorded and analyzed. The experimental results show that the AlN actuator can produce a more uniform discharge while the discharge of the Al₂O₃ actuator is easier to become filamentary. The later condition leads to higher power consumption and earlier failure due to electrode oxidation. In the plasma process, the power increment of the AlN actuator is higher than that of the Al₂O₃ actuator. The induced velocity is also influenced by this process. Prior to aging, the maximum induced velocity of the AlN actuator is 4.2 m/s, which is about 40% higher than that of the Al₂O₃actuator. After 120-min plasma aging, the maximum velocity of the aged AlN actuator decreases by 27.8% while the Al₂O₃ actuator registers a decrease of 25%.

Mechanism of controlling turbulent channel flow with the effect of spanwise Lorentz force distribution

Yang Han(韩洋), Hui Zhang(张辉), Bao-Chun Fan(范宝春), Jian Li(李健), Dai-Wen Jiang(江代文), Zi-Jie Zhao(赵子杰)

Chin. Phys. B, 2017, 26 (8): 084704. DOI: 10.1088/1674-1056/26/8/084704

Abstract ( 778 )

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A direct numerical simulation (DNS) is performed to investigate the control effect and mechanism of turbulent channel flow with the distribution of spanwise Lorentz force. A sinusoidal distribution of constant spanwise Lorentz force is selected, of which the control effects, such as flow characters, mean Reynolds stress, and drag reductions, at different parameters of amplitude A and wave number k_x are discussed. The results indicate that the control effects vary with the parameter A and k_x. With the increase of A, the drag reduction rate D_r first increases and then decreases rapidly at low k_x, and slowly at high k_x. The low drag reduction (or even drag increase) is due to a weak suppression or even the enhancements of the random velocity fluctuation and mean Reynolds stress. The efficient drag reduction is due to the quasi-streamwise vortex structure induced by Lorentz force, which contributes to suppressing the random velocity fluctuation and mean Reynolds stress, and the negative vorticity improves the distribution of streamwise velocity. Therefore, the optimal control effect with a drag reduction of up to 58% can be obtained.

Energetic-ion excited internal kink modes with weak magnetic shear in q₀ >1 tokamak plasmas Suggested by editors

Wen-Ming Chen(陈文明), Xiao-Gang Wang(王晓钢), Xian-Qu Wang(王先驱), Rui-Bin Zhang(张瑞斌)

Chin. Phys. B, 2017, 26 (8): 085201. DOI: 10.1088/1674-1056/26/8/085201

Abstract ( 903 )

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The energetic particle driven internal kink mode is investigated in this paper for q₀ > 1 tokamak plasma with weak magnetic shear. With the effect of energetic particles, the m/n = 1/1 internal mode structure in tokamak plasma does not appear as a rigid step-function when safety factor passes through q= 1 rational surface. It is found that even when the rational surface is removed, the mode may be still unstable under the low magnetic shear condition if the energetic particle drive is strong enough; with the low shear region of safety factor profile widening, the mode becomes more unstable with its growth-rate increasing. Furthermore, we find that the existence of the q = 1 rational surface does not have a significant effect on the stability of the plasma if energetic particles are present, which is very different from the scenarios of the ideal-MHD modes.

Surface plasmon-enhanced dual-band infrared absorber for VO_x-based microbolometer application

Qi Li(李琦), Bing-qiang Yu(于兵强), Zhao-feng Li(李兆峰), Xiao-feng Wang(王晓峰), Zi-chen Zhang(张紫辰), Ling-feng Pan(潘岭峰)

Chin. Phys. B, 2017, 26 (8): 085202. DOI: 10.1088/1674-1056/26/8/085202

Abstract ( 726 )

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We propose a periodic structure as an extra absorption layer (i.e., absorber) based on surface plasmon resonance effects, enhancing dual-band absorption in both middle wavelength infrared (MWIR) and long wavelength infrared (LWIR) regions. Periodic gold disks are selectively patterned onto the top layer of suspended SiN/VO₂/SiN sandwich-structure. We employ the finite element method to model this structure in COMSOL Multiphysics including a proposed method of modulating the absorption peak. Simulation results show that the absorber has two absorption peaks at wavelengths λ =4.8 μ and λ =9 μm with the absorption magnitudes more than 0.98 and 0.94 in MWIR and LWIR regions, respectively. In addition, the absorber achieves broad spectrum absorption in LWIR region, in the meanwhile, tunable dual-band absorption peaks can be achieved by variable heights of cavity as well as diameters and periodicity of disk. Thus, this designed absorber can be a good candidate for enhancing the performance of dual band uncooled infrared detector, furthermore, the manufacturing process of cavity can be easily simplified so that the reliability of such devices can be improved.

Surface enhancement of molecular ion H₂⁺ yield in a 2.45-GHz electron-cyclotron resonance ion source Suggested by editors

Yuan Xu(徐源), Shi-Xiang Peng(彭士香), Hai-Tao Ren(任海涛), Ai-Lin Zhang(张艾霖), Tao Zhang(张滔), Jing-Feng Zhang(张景丰), Jia-Mei Wen(温佳美), Wen-Bin Wu(武文斌), Zhi-Yu Guo(郭之虞), Jia-Er Chen(陈佳洱)

Chin. Phys. B, 2017, 26 (8): 085203. DOI: 10.1088/1674-1056/26/8/085203

Abstract ( 608 )

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High current hydrogen molecular ion beam is obtained with a specially designed stainless steel liner permanent magnet 2.45-GHz electron-cyclotron resonance (ECR) ion source (PMECR II) at Peking University (PKU). To further understand the physics of the hydrogen generation process inside a plasma chamber, theoretical and experimental investigations on the liner material of the plasma chamber in different running conditions are carried out. Several kinds of materials, stainless steel (SS), tantalum (Ta), quartz, and aluminum (Al) are selected in our study. Experimental results show that stainless steel and tantalum are much better than others in H₂⁺ generation. During the experiment, an increasing trend in H₂⁺ fraction is observed with stainless steel liner after O₂ discharge inside the ion source. Surface analyses show that the roughness change on the surface after O₂ discharge may be responsible for this phenomenon. After these studies, the pure current of H₂⁺ ions can reach 42.3 mA with a fraction of 52.9%. More details are presented in this paper.

Fast parallel Grad-Shafranov solver for real-time equilibrium reconstruction in EAST tokamak using graphic processing unit

Yao Huang(黄耀), Bing-Jia Xiao(肖炳甲), Zheng-Ping Luo(罗正平)

Chin. Phys. B, 2017, 26 (8): 085204. DOI: 10.1088/1674-1056/26/8/085204

Abstract ( 836 )

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To achieve real-time control of tokamak plasmas, the equilibrium reconstruction has to be completed sufficiently quickly. For the case of an EAST tokamak experiment, real-time equilibrium reconstruction is generally required to provide results within 1ms. A graphic processing unit (GPU) parallel Grad-Shafranov (G-S) solver is developed in P-EFIT code, which is built with the CUDA^TM architecture to take advantage of massively parallel GPU cores and significantly accelerate the computation. Optimization and implementation of numerical algorithms for a block tri-diagonal linear system are presented. The solver can complete a calculation within 16 μs with 65×65 grid size and 27 μs with 129×129 grid size, and this solver supports that P-EFIT can fulfill the time feasibility for real-time plasma control with both grid sizes.

Favourable scenarios established by SMBI for the realization of the ELMy H-mode at HL-2A

Zheng-Ying Cui(崔正英), Yuan Xu(徐媛), Bei-Bin Feng(冯北滨), Yu-Hong Xu(许宇鸿), Xuan-Tong Ding(丁玄同), Xiao-Quan Ji(季小全), Yong-Gao Li(李永高), Zhong-Bing Shi(石中兵), Wu-Lv Zhong(钟武律), Min Jiang(蒋敏), Shao-Dong Song(宋绍栋), Jun Cheng(程均), Jin-Ming Gao(高金明), Jian-Yong Cao(曹建勇), Chun-Feng Dong(董春凤), Kai Zhang(张凯), Cheng-Yuan Chen(陈程远), Mei Huang(黄梅), Qing-Wei Yang(杨青巍), Xu-Ru Duan(段旭如), HL-2A Team

Chin. Phys. B, 2017, 26 (8): 085205. DOI: 10.1088/1674-1056/26/8/085205

Abstract ( 652 )

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The ELMy H-mode plasmas realized with the supersonic molecular beam injection (SMBI) are studied in relation to the energy confinement and the heating power for the L-H transition (P_L-H) in the HL-2A tokamak. A database is assembled for this study based on the ELMy H-mode discharges during the experimental campaigns in the period 2009-2013 at the HL-2A tokamak. The statistical results show that the SMBI is favourable for reaching the H-mode by reducing the heating power at the L-H transition and for the H-mode performance by improving the energy confinement compared with the ordinary gas puffing (GP). The reduction of P_L-H is about 20% when the density is low, and the energy confinement enhancement factor of H_H98y2=τ_E/τ_th,98y2 ≈ 1.5 is achieved with the SMBI. Note that in the database the density dependence of P_L-H is non-monotonic with the n_e,min ≈ 3×10¹⁹m^-3 at which the P_L-H is minimum. Most of P_L-H data are on the low density branch where the P_L-H increases with the decrease in density. The minimum of the P_L-H in HL-2A is comparable to the ITPA multi-machine threshold power scaling P_{thr_scal08}. The physics behind the reduction of the P_L-H with the SMBI is also investigated in relation to the change of the density gradient at the plasma edge, the gas fuelling efficiency, and the recycling.

Laser-induced convenient fabrication of CdS nanocages with super-adsorption capability for methyl blue solution

Le Liu(刘乐), Lin-Lin Xu(徐林林), Hua Zhang(张华), Ming Chen(陈明)

Chin. Phys. B, 2017, 26 (8): 085206. DOI: 10.1088/1674-1056/26/8/085206

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We report on the successful synthesis of cadmium sulfide (CdS) nanocages by laser ablation of bulk Cd target in thioacetamide (TAA) solution. The CdS nanocages exhibit obvious interior hollow spaces and distinctive porous-shell structures. After laser ablation of Cd target in liquid condition, the unique structure should be attributed to the initial formation of Cd micro-gas bubble via a model of micro-explosive boiling model. Surprisingly, the obtained CdS nanocages can provide a super-adsorption of methyl blue (MB) solution. The maximum adsorption capacity reaches up to 11813.3 mg/g, which is much higher than that reported in many previous researches. Without using any complicated stabilizers or soft directing agents, the pure CdS nanocages fabricated by laser ablation will serve as advanced absorbents in further research.

Characteristics of helium DC plasma jets at atmospheric pressure with multiple cathodes Suggested by editors

Cheng Wang(王城), Zelong Zhang(张泽龙), Haichao Cui(崔海超), Weiluo Xia(夏维珞), Weidong Xia(夏维东)

Chin. Phys. B, 2017, 26 (8): 085207. DOI: 10.1088/1674-1056/26/8/085207

Abstract ( 730 )

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A novel DC plasma torch with multiple cathodes is developed for generating laminar, transitional and turbulent plasma jets. The jet's characteristics, including jet appearance, voltage fluctuation, thermal efficiency, specific enthalpy, and distributions of temperature, pressure, and velocity, are experimentally investigated. The results show that as the gas flow rate increases, the plasma jet transforms first from the laminar state to the transitional state and second to the turbulent state. Compared with the transitional/turbulent jet, the laminar jet possesses not only a better stability and a longer high-temperature zone but also a higher average/core temperature and a higher specific enthalpy at the nozzle's outlet. With the change of jet states from the laminar to the turbulent flow, the core pressure and velocity at the nozzle's outlet increase, while the decaying rates of temperature/pressure/velocity along the jet's axial direction increase sharply. Furthermore, applications of laminar, transitional and turbulent jets for zirconia spray coating are described. The test results indicate that the long laminar jet is favorable for the deposition of a high-quality coating because the powder particles injected into the laminar jet may have better heating and lower kinetic energy.

Density functional study on the pressure profile of the inhomogeneous fluid mixture

Yanshuang Kang(康艳霜), Yanmei Kang(康艳梅), Zongli Sun(孙宗利), Yushan Li(李玉山), Shanshan Tan(檀姗姗)

Chin. Phys. B, 2017, 26 (8): 086101. DOI: 10.1088/1674-1056/26/8/086101

Abstract ( 644 )

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By using the statistical mechanics, the pressure tensor for the multi component fluid mixture is derived. With the help of the classical density functional theory, profiles of the pressure components are calculated, and the influence of the total volume fraction, ratio of volume fraction, and size asymmetry on the pressure are studied. In addition, our results show that for the mixture confined in the hard cavity, the pressure shows a discontinuity near the cavity wall. However, in the soft cavity condition, the discontinuity disappears.

Experimental design to measure the anchoring energy on substrate surface by using the alternating-current bridge

Hui-Ming Hao(郝慧明), Yao-Yao Liu(刘瑶瑶), Ping Zhang(张平), Ming-Lei Cai(蔡明雷), Xiao-Yan Wang(王晓燕), Ji-Liang Zhu(朱吉亮), Wen-Jiang Ye(叶文江)

Chin. Phys. B, 2017, 26 (8): 086102. DOI: 10.1088/1674-1056/26/8/086102

Abstract ( 624 )

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The anchoring property of the substrate surface of liquid crystal cells plays an important role in display and nondisplay fields. This property directly affects the deformation of liquid crystal molecules to change the phase difference through liquid crystal cells. In this paper, a test method based on the alternating-current bridge is proposed to determine the capacitance of liquid crystal cells and thus measure the anchoring energy of the substrate surface. The anchoring energy can be obtained by comparing the capacitance-voltage curves of twisted nematic liquid crystal cells with different anchoring properties in experimental and theoretical results simulated on the basis of Frank elastic theory. Compared with the other methods to determine the anchoring energy, our proposed method requires a simple treatment of liquid crystal cells and allows easy and high-accuracy measurements, thereby expanding the test ideas on the performance parameters of liquid crystal devices.

Electronic, optical, and mechanical properties of BN, AlN, and InN with zinc-blende structure under pressure

A R Degheidy, E B Elkenany

Chin. Phys. B, 2017, 26 (8): 086103. DOI: 10.1088/1674-1056/26/8/086103

Abstract ( 686 )

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In this work, the electronic, optical, and mechanical properties of BN, AlN, and InN under the action of pressure are calculated. For each of these compounds, the energy band structure, band gaps (E_g^L, E_g^Γ,E_g^X), refractive index (n), dielectric constants (ε_∞, ε₀), elastic constants (C₁₁, C₁₂,C₄₄), and relevant parameters such as bulk (B_u), shear (S_h), and Young's (Y₀) moduli are studied, and other important parameters such as bond-stretching (α), bond-bending (β) force constant, internal-strain parameter (ζ), effective charges (e_T^*, Z^*), anisotropy factor (I_s), Poisson's ratio (P_o), Cauchy ratio (C_a), the ductility index (μ_D), and linear compressibility (C₀) are also calculated. The effects of pressure on all studied properties are investigated. Our results are in good agreement with the available experimental and theoretical data for BN, AlN, and InN.

Study on irradiation-induced defects in GaAs/AlGaAs core-shell nanowires via photoluminescence technique

Li-Ying Tan(谭立英), Fa-Jun Li(黎发军), Xiao-Long Xie(谢小龙), Yan-Ping Zhou(周彦平), Jing Ma(马晶)

Chin. Phys. B, 2017, 26 (8): 086201. DOI: 10.1088/1674-1056/26/8/086201

Abstract ( 510 )

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To gain a physical insight into the radiation effect on nanowires (NWs), the time resolved photoluminescence (TRPL) technique is used to investigate the carrier dynamic behaviors in GaAs/AlGaAs core-shell NWs before and after 1-MeV proton irradiation with fluences ranging from 1.0×10¹² cm^-2 to 3.0×10¹³ cm^-2. It is found that the degradations of spectral peak intensity and minority carrier lifetime show similar trends against irradiation fluence, which is closely related to the displacement defects induced by irradiation. We also find that the proton irradiation-induced defects behave as Shockley-Read-Hall (SRH) recombination center trapping free carriers. Finally, the defect concentration could be estimated through measuring the minority carrier lifetime.

Proton radiation effect on GaAs/AlGaAs core-shell ensemble nanowires photo-detector

Li-Ying Tan(谭丽英), Fa-Jun Li(黎发军), Xiao-Long Xie(谢小龙), Yan-Ping Zhou(周彦平), Jing Ma(马晶)

Chin. Phys. B, 2017, 26 (8): 086202. DOI: 10.1088/1674-1056/26/8/086202

Abstract ( 644 )

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We demonstrate that the GaAs/AlGaAs nanowires (NWs) ensemble is fabricated into photo-detectors. Current-voltage (I-V) characteristics are measured on GaAs/AlGaAs core-shell ensemble NW photo-detectors at room-temperature before and after 1-MeV proton irradiation with fluences from 1.0×10¹³ cm^-2 to 5.0×10¹⁴ cm^-2. The degradation of photocurrent suggests that the point defects induced by proton radiation could cause both carrier lifetime and carrier mobility to decrease synchronously. Comparing with a GaAs quantum well, the degradations of light and dark current for the irradiated NWs photo-detector indicate that NWs material is a preferable potential candidate for space applications.

Elastic, vibrational, and thermodynamic properties of Sr₁₀(PO₄)₆F₂and Ca₁₀(PO₄)₆F₂ from first principles Suggested by editors

Xianggang Kong(孔祥刚), Zhihong Yuan(袁志红), You Yu(虞游), Tao Gao(高涛), Shenggui Ma(马生贵)

Chin. Phys. B, 2017, 26 (8): 086301. DOI: 10.1088/1674-1056/26/8/086301

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The electronic, elastic, vibrational, and thermodynamic properties of Sr₁₀(PO₄)₆F₂(Sr-FAP) and Ca₁₀(PO₄)₆F₂(Ca-FAP) are systematically investigated by the first-principles calculations. The calculated electronic band structure indicates that the Sr-FAP and Ca-FAP are insulator materials with the indirect band gap of 5.273 eV and 5.592 eV, respectively. The elastic constants are obtained by the “stress-strain” method, and elastic modulus are further evaluated and discussed. The vibrational properties, including the phonon dispersion curves, the phonon density of states, the Born effective charge, and associated longitudinal optical and transverse optical (LO-TO) splitting of optical modes, as well as the phonon frequencies at zone-center are obtained within the linear-response approach. Substitution of Ca by Sr causes phonon frequencies to shift to lower values as expected due to the mass effect. Additionally, some phonon-related thermodynamic properties, such as Helmholtz free energy F, internal energy E, entropy S, and specific heat C_V of Sr-FAP and Ca-FAP are predicted with the harmonic approximation. The present calculated results of two apatites are consistent with the reported experimental and theoretical results.

Structural and optical properties of thermally reduced graphene oxide for energy devices

Ayesha Jamil, Faiza Mustafa, Samia Aslam, Usman Arshad, Muhammad Ashfaq Ahmad

Chin. Phys. B, 2017, 26 (8): 086501. DOI: 10.1088/1674-1056/26/8/086501

Abstract ( 709 )

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Natural intercalation of the graphite oxide, obtained as a product of Hummer's method, via ultra-sonication of water dispersed graphite oxide has been carried out to obtain graphene oxide (GO) and thermally reduced graphene oxide (RGO). Here we report the effect of metallic nitrate on the oxidation properties of graphite and then formation of metallic oxide (MO) composites with GO and RGO for the first time. We observed a change in the efficiency of the oxidation process as we replaced the conventionally used sodium nitrate with that of nickel nitrate Ni(NO₃)₂, cadmium nitrate Cd(NO₃)₂, and zinc nitrate Zn(NO₃)₂. The structural properties were investigated by x-ray diffraction and observed the successful formation of composite of MO-GO and MO-RGO (M = Zn, Cd, Ni). We sought to study the effect on the oxidation process through optical characterization via UV-Vis spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. Moreover, Thermo Gravimetric Analysis (TGA) was carried out to confirm >90% weight loss in each process thus proving the reliability of the oxidation cycles. We have found that the nature of the oxidation process of graphite powder and its optical and electrochemical characteristics can be tuned by replacing the sodium nitrate (NaNO₃) by other metallic nitrates as Cd(NO₃)₂, Ni(NO₃)₂, and Zn(NO₃)₂. On the basis of obtained results, the synthesized GO and RGO may be expected as a promising material in antibacterial activity and in electrodes fabrication for energy devices such as solar cell, fuel cell, and super capacitors.

Quench dynamics of ultracold atoms in one-dimensional optical lattices with artificial gauge fields

Xiaoming Cai(蔡小明)

Chin. Phys. B, 2017, 26 (8): 086701. DOI: 10.1088/1674-1056/26/8/086701

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We study the quench dynamics of noninteracting ultracold atoms loaded in one-dimensional (1D) optical lattices with artificial gauge fields, which are modeled by lattices with complex hopping coefficients. After suddenly changing the hopping coefficient, time evolutions of the density distribution, momentum distribution, and mass current at the center are studied for both finite uniform systems and trapped systems. Effects of filling factor, system size, statistics, harmonic trap, and phase difference in hopping are identified, and some interesting phenomena show up. For example, for a finite uniform fermionic system shock and rarefaction wave plateaus are formed at two ends, whose wave fronts move linearly with speed equaling to the maximal absolute group velocity. While for a finite uniform bosonic system the whole density distribution moves linearly at the group velocity. Only in a finite uniform fermionic system there can be a constant quasi-steady-state current, whose amplitude is decided by the phase difference and filling factor. The quench dynamics can be tested in ultracold atoms with minimal modifications of available experimental techniques, and it is a very interesting and fundamental example of the transport phenomena and the nonequilibrium dynamics.

Thermo-controllable self-assembled structures of single-layer 4, 4"-diamino-p-terphenyl molecules on Au (110) ^Hot!

Junhai Ren(任俊海), Deliang Bao(包德亮), Li Dong(董立), Lei Gao(高蕾), Rongting Wu(武荣庭), Linghao Yan(闫凌昊), Aiwei Wang(王爱伟), Jiahao Yan(严佳浩), Yeliang Wang(王业亮), Shixuan Du(杜世萱), Qing Huan(郇庆), Hongjun Gao(高鸿钧)

Chin. Phys. B, 2017, 26 (8): 086801. DOI: 10.1088/1674-1056/26/8/086801

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Here we report the thermo-controllable self-assembled structures of single-layer 4, 4"-diamino-p-terphenyl (DAT) molecules on Au (110), which are investigated by scanning tunneling microscopy (STM) combined with density functional theory (DFT) based calculations. With the deposition of monolayer DAT molecules on Au (110) and subsequent annealing at 100 ℃, all DAT molecules adsorb on a (1×5) reconstructed surface with a ladder-like structure. After annealing the sample at about 200 ℃, STM images show three distinct domains, including DAT molecules on a (1×3) reconstructed surface, dehydrogenated molecules with two hydrogen atoms detached from one amino group (-2H-DAT) on a (1×5) reconstructed surface and dehydrogenated molecules with four hydrogen atoms detached from two amino groups (-4H-DAT) on a (1×3) reconstructed surface through N-Au bonds. Furthermore, after annealing the sample to 350 ℃, STM image shows only one self-assembled structure with -4H-DAT molecules on a (1×3) reconstructed surface. Relative STM simulations of different self-assembled structures show excellent agreements with the experimental STM images at different annealing temperatures. Further DFT calculations on the dehydrogenation process of DAT molecule prove that the dehydrogenation barrier on a (1×5) reconstructed surface is lower than that on (1×3) one, which demonstrate the experimental results that the formation temperature of a (1×3) reconstructed surface is higher than that of a (1×5) one.

Direct characterization of boron segregation at random and twin grain boundaries

Xiang-Long Li(李向龙), Ping Wu(吴平), Rui-Jie Yang(杨锐杰), Shi-Ping Zhang(张师平), Sen Chen(陈森), Xue-Min Wang(王学敏), Xiu-Lan Huai(淮秀兰)

Chin. Phys. B, 2017, 26 (8): 086802. DOI: 10.1088/1674-1056/26/8/086802

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Boron distribution at grain boundaries in hot-deformed nickel is directly characterized by the time-of-flight secondary ion mass spectrometry. The segregations of boron are observed at both the random and twin grain boundaries. Two types of segregations at random grain boundaries are observed. The first type of segregation has a high intensity and small width. Its formation is attributed to the incorporating of dislocations into the moving grain boundaries. The second type of segregation arises from the cooling induced segregation at the dislocations associated with the grain boundaries. The segregation at twin boundary is similar to the second type of segregation at random grain boundaries.

Optical properties of anatase and rutile TiO₂ studied by GGA+U

Jinping Li(李金平), Songhe Meng(孟松鹤), Liyuan Qin(秦丽媛), Hantao Lu(陆汉涛)

Chin. Phys. B, 2017, 26 (8): 087101. DOI: 10.1088/1674-1056/26/8/087101

Abstract ( 687 )

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The optical properties of thermally annealed TiO₂ samples depend on their preparation process, and the TiO₂ thin films usually exist in the form of anatase or rutile or a mixture of the two phases. The electronic structures and optical properties of anatase and rutile TiO₂ are calculated by means of a first-principles generalized gradient approximation (GGA) +U approach. By introducing the Coulomb interactions on 3d orbitals of Ti atom (U^d) and 2p orbitals of O atom (U^p), we can reproduce the experimental values of the band gap. The optical properties of anatase and rutile TiO₂ are obtained by means of the GGA+U method, and the results are in good agreement with experiments and other theoretical data. Further, we present the comparison of the electronic structure, birefringence, and anisotropy between the two phases of TiO₂. Finally, the adaptability of the GGA+U approach has been discussed.

Visible light absorption of (Fe, C/N) co-doped NaTaO₃: DFT+U Suggested by editors

Peng-Li Tian(田鹏莉), Zhen-Yi Jiang(姜振益), Xiao-Dong Zhang(张小东), Bo Zhou(周波), Ya-Ru Dong(董亚茹), Rui Liu(刘睿)

Chin. Phys. B, 2017, 26 (8): 087102. DOI: 10.1088/1674-1056/26/8/087102

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The effects of Fe-C/N co-doping on the electronic and optical properties of NaTaO₃ are studied with density functional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable. The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C (N) atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO₃ are well positioned for the feasibility of hydrogen production by water splitting. The Fe-C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe-N co-doping due to the different locations of impurity energy levels originating from their p-d hybridization effect.

Uniaxial strain-modulated electronic structures of CdX (X=S, Se, Te) from first-principles calculations: A comparison between bulk and nanowires

Linlin Xiang(相琳琳), Shenyuan Yang(杨身园)

Chin. Phys. B, 2017, 26 (8): 087103. DOI: 10.1088/1674-1056/26/8/087103

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Using first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX (X=S, Se, Te) bulk and nanowires (NWs) under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {1010} facets have heavy hole (HH)-like valence band maximum (VBM) states, while NWs with {1120} facets have crystal hole (CH)-like VBM states. The external uniaxial strain induces an HH-CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH-CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum (CBM) of NWs shows a linear relation with the CBM-HH energy difference, the same as the bulk material.

Modulating the properties of monolayer C₂N: A promising metal-free photocatalyst for water splitting Suggested by editors

Song Yu(俞松), Yong-Chao Rao(饶勇超), Xiang-Mei Duan(段香梅)

Chin. Phys. B, 2017, 26 (8): 087301. DOI: 10.1088/1674-1056/26/8/087301

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Photocatalytic water splitting has gained increasing attention, since it utilizes renewable resources, such as water and solar energy, to produce hydrogen. Using the first-principles density functional theory, we investigate the properties of the single layer C₂N which was successfully synthesized. We reveal that monolayer C₂N has a substantial direct band gap of 2.45 eV. To regulate its band gap, four different nonmetal elements (B, O, P, and S) on the cation and anion sites are considered. Among them, B-doped N site is the most effective one, with the lowest formation energy and a band gap of 2.01 eV. P-doped N site is the next, with a band gap of 2.08 eV, though its formation energy is higher. The band alignments with respect to the water redox levels show that, for these two dopings, the thermodynamic criterion for the overall water splitting is satisfied. We therefore predict that B- or P-doped C₂N, with an appropriate band gap and an optimal band-edge position, would be a promising photocatalyst for visible-light water splitting.

High-efficiency organic light-emitting diodes based on ultrathin blue phosphorescent modification layer

Yun-Ke Zhu(朱云柯), Jian Zhong(钟建), Shu-Ying Lei(雷疏影), Hui Chen(陈辉), Shuang-Shuang Shao(邵双双), Yu Lin(林宇)

Chin. Phys. B, 2017, 26 (8): 087302. DOI: 10.1088/1674-1056/26/8/087302

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Yellow organic light-emitting devices (YOLEDs) with a novel structure of ITO/MoO₃(5 nm)/NPB(40 nm)/TCTA(15 nm)/CBP:(tbt)₂Ir(acac)(x%)(25 nm)/FIrpic(y nm)/TPBi(35 nm)/Mg:Ag are fabricated. The ultrathin blue phosphorescent bis[(4,6-difluorophenyl)-pyridi-nato-N,C2\prime ](picolinate) iridium (III) (FIrpic) layer is regarded as a high-performance modification layer. By adjusting the thickness of FIrpic and the concentration of (tbt)₂Ir(acac), a YOLED achieves a high luminance of 41618 cd/m², power efficiency of 49.7 lm/W, current efficiency of 67.3 cd/A, external quantum efficiency (EQE) of 18%, and a low efficiency roll-off at high luminance. The results show that phosphorescent material of FIrpic plays a significant role in improving YOLED performance. The ultrathin FIrpic modification layer blocks excitons in EML. In the meantime, the high triplet energy of FIrpic (2.75 eV) alleviates the exciton energy transport from EML to FIrpic.

Optical anisotropy and the direction of polarization of exciton emissions in a semiconductor quantum dot:Effect of heavy- and light-hole mixing

Ranber Singh, Rajiv Kumar, Vikramjeet Singh

Chin. Phys. B, 2017, 26 (8): 087303. DOI: 10.1088/1674-1056/26/8/087303

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The dependence of the directions of polarization of exciton emissions, fine structure splittings (FSS), and polarization anisotropy on the light- and heavy-hole (LH-HH) mixing in semiconductor quantum dots (QDs) is investigated using a mesoscopic model. In general, all QDs have a four-fold exciton ground state. Two exciton states have directions of polarization in the growth-plane, while the other two are along the growth direction of the QD. The LH-HH mixing does affect the FSS and polarization anisotropy of bright exciton states in the growth-plane in the low symmetry QDs (e.g., C_2V, C_S, C₁), while it has no effect on the FSS and polarization anisotropy in high symmetry QDs (e.g., C_3V, D_2d). When the hole ground state is pure HH or LH, the bright exciton states in the growth-plane are normal to each other. The LH-HH mixing affects the relative intensities and directions of bright exciton states in the growth-plane of the QD. The polarization anisotropy of exciton emissions in the growth-plane of the QD is independent of the phase angle of LH-HH mixing but strongly depends on the magnitude of LH-HH mixing in low symmetry QDs.

Stress-induced leakage current characteristics of PMOS fabricated by a new multi-deposition multi-annealing technique with full gate last process

Yanrong Wang(王艳蓉), Hong Yang(杨红), Hao Xu(徐昊), Weichun Luo(罗维春), Luwei Qi(祁路伟), Shuxiang Zhang(张淑祥), Wenwu Wang(王文武), Jiang Yan(闫江), Huilong Zhu(朱慧珑), Chao Zhao(赵超), Dapeng Chen(陈大鹏), Tianchun Ye(叶甜春)

Chin. Phys. B, 2017, 26 (8): 087304. DOI: 10.1088/1674-1056/26/8/087304

Abstract ( 934 )

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In the process of high-k films fabrication, a novel multi deposition multi annealing (MDMA) technique is introduced to replace simple post deposition annealing. The leakage current decreases with the increase of the post deposition annealing (PDA) times. The equivalent oxide thickness (EOT) decreases when the annealing time(s) change from 1 to 2. Furthermore, the characteristics of SILC (stress-induced leakage current) for an ultra-thin SiO₂/HfO₂ gate dielectric stack are studied systematically. The increase of the PDA time(s) from 1 to 2 can decrease the defect and defect generation rate in the HK layer. However, increasing the PDA times to 4 and 7 may introduce too much oxygen, therefore the type of oxygen vacancy changes.

Thermal stability and data retention of resistive random access memory with HfO_x/ZnO double layers Suggested by editors

Yun-Feng Lai(赖云锋), Fan Chen(陈凡), Ze-Cun Zeng(曾泽村), Pei-Jie Lin(林培杰), Shu-Ying Cheng(程树英), Jin-Ling Yu(俞金玲)

Chin. Phys. B, 2017, 26 (8): 087305. DOI: 10.1088/1674-1056/26/8/087305

Abstract ( 618 )

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As an industry accepted storage scheme, hafnium oxide (HfO_x) based resistive random access memory (RRAM) should further improve its thermal stability and data retention for practical applications. We therefore fabricated RRAMs with HfO_x/ZnO double-layer as the storage medium to study their thermal stability as well as data retention. The HfO_x/ZnO double-layer is capable of reversible bipolar switching under ultralow switching current (< 3 μA) with a Schottky emission dominant conduction for the high resistance state and a Poole-Frenkel emission governed conduction for the low resistance state. Compared with a drastically increased switching current at 120 ℃ for the single HfO_x layer RRAM, the HfO_x/ZnO double-layer exhibits excellent thermal stability and maintains neglectful fluctuations in switching current at high temperatures (up to 180 ℃), which might be attributed to the increased Schottky barrier height to suppress current at high temperatures. Additionally, the HfO_x/ZnO double-layer exhibits 10-year data retention @85 ℃ that is helpful for the practical applications in RRAMs.

A facile and efficient dry transfer technique for two-dimensional Van der Waals heterostructure ^Hot!

Li Xie(谢立), Luojun Du(杜罗军), Xiaobo Lu(卢晓波), Rong Yang(杨蓉), Dongxia Shi(时东霞), Guangyu Zhang(张广宇)

Chin. Phys. B, 2017, 26 (8): 087306. DOI: 10.1088/1674-1056/26/8/087306

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Two-dimensional (2D) Van der Waals heterostructures have aroused extensive concerns in recent years. Their fabrication calls for facile and efficient transfer techniques for achieving well-defined structures. In this work, we report a simple and effective dry transfer method to fabricate 2D heterostructures with a clean interface. Using Propylene Carbonate (PC) films as stamps, we are able to pick up various 2D materials flakes from the substrates and unload them to the receiving substrates at an elevated temperature. Various multilayer heterostructures with ultra-clean interfaces were fabricated by this technique. Furthermore, the 2D materials can be pre-patterned before transfer so as to fabricate desired device structures, demonstrating a facile way to promote the development of 2D heterostructures.

Performance improvement of InGaN/GaN multiple quantum well visible-light photodiodes by optimizing TEGa flow

Bin Li(黎斌), Shan-Jin Huang(黄善津), Hai-Long Wang(王海龙), Hua-Long Wu(吴华龙), Zhi-Sheng Wu(吴志盛), Gang Wang(王钢), Hao Jiang(江灏)

Chin. Phys. B, 2017, 26 (8): 087307. DOI: 10.1088/1674-1056/26/8/087307

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The performance of an InGaN/GaN multiple quantum well (MQW) based visible-light Schottky photodiode (PD) is improved by optimizing the source flow of TEGa during InGaN QW growth. The samples with five-pair InGaN/GaN MQWs are grown on sapphire substrates by metal organic chemical vapor deposition. From the fabricated Schottky-barrier PDs, it is found that the smaller the TEGa flow, the lower the reverse-bias leakage is. The photocurrent can also be enhanced by depositing the InGaN QWs with using lower TEGa flow. A high responsivity of 1.94 A/W is obtained at 470 nm and -3-V bias in the PD grown with optimized TEGa flow. Analysis results show that the lower TEGa flow used for depositing InGaN may lead to superior crystalline quality with improved InGaN/GaN interface, and less structural defects related non-radiative recombination centers formed in the MQWs.

Progressive current degradation and breakdown behavior in GaN LEDs under high reverse bias stress Suggested by editors

Linna Zhao(赵琳娜), Peihong Yu(于沛洪), Zixiang Guo(郭子骧), Dawei Yan(闫大为), Hao Zhou(周浩), Jinbo Wu(吴锦波), Zhiqiang Cui(崔志强), Huarui Sun(孙华锐), Xiaofeng Gu(顾晓峰)

Chin. Phys. B, 2017, 26 (8): 087308. DOI: 10.1088/1674-1056/26/8/087308

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The progressive current degradation and breakdown behaviors of GaN-based light emitting diodes under high reverse-bias stress are studied by combining the electrical, optical, and surface morphology characterizations. The current features a typical “soft breakdown” behavior, which is linearly correlated to an increase of the accumulative number of electroluminescence spots. The time-to-failure for each failure site approximately obeys a Weibull distribution with slopes of about 0.67 and 4.09 at the infant and wear-out periods, respectively. After breakdown, visible craters can be observed at the device surface as a result of transient electrostatic discharge. By performing focused ion beam cuts coupled with scan electron microscope, we observed a local current shunt path in the surface layer, caused by the rapid microstructure deterioration due to significant current heating effect, consistent well with the optical beam induced resistance change observations.

Investigation of Zn_1-xCd_xO films bandgap and Zn_1-xCd_xO/ZnO heterojunctions band offset by x-ray photoelectron spectroscopy

Jie Chen(陈杰), Xue-Min Wang(王雪敏), Ji-Cheng Zhang(张继成), Hong-Bu Yin(尹泓卜), Jian Yu(俞健), Yan Zhao(赵妍), Wei-Dong Wu(吴卫东)

Chin. Phys. B, 2017, 26 (8): 087309. DOI: 10.1088/1674-1056/26/8/087309

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A series of Zn_1-xCd_xO thin films have been fabricated on sapphire by pulsed-laser deposition (PLD), successfully. To investigate the effect of Cd concentration on structural and optical properties of Zn_1-xCd_xO films, x-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), and x-ray photoelectron spectroscopy (XPS) are employed to characterize the films in detail. The XRD pattern indicates that the Zn_1-xCd_xO thin films have high single-orientation of the c axis. The energy bandgap values of ZnCdO thin films decrease from 3.26 eV to 2.98 eV with the increasing Cd concentration (x) according to the (αhν)²-hν curve. Furthermore, the band offsets of Zn_1-xCd_xO/ZnO heterojunctions are determinated by XPS, indicating that a type-I alignment takes place at the interface and the value of band offset could be tuned by adjusting the Cd concentration.

Electronic transport properties of single-wall boron nanotubes

Xinyue Dai(代新月), Yi Zhou(周毅), Jie Li(李洁), Lishu Zhang(张力舒), Zhenyang Zhao(赵珍阳), Hui Li(李辉)

Chin. Phys. B, 2017, 26 (8): 087310. DOI: 10.1088/1674-1056/26/8/087310

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Electronic transport properties of single-wall boron nanotube (BNT) with different chiralities, diameters, some of which are encapsulated with silicon, germanium, and boron nanowires are theoretically studied. The results indicate that the zigzag (3, 3) BNT has more electronic transmission channels than the armchair (5, 0) BNT because of its unique structure distortion. Nanowires encapsulated in the BNT can enhance the conductance of the BNT to some extent by providing a significant electronic transmission channel to the BNT. The effect of the structure of nanowires and the diameter of BNTs on the transport properties has also been discussed. The results of this paper can enrich the knowledge of the electron transport of the BNT and provide theoretical guidance for subsequent experimental study.

Improvement of green InGaN-based LEDs efficiency using a novel quantum well structure Suggested by editors

Yangfeng Li(李阳锋), Yang Jiang(江洋), Junhui Die(迭俊珲), Caiwei Wang(王彩玮), Shen Yan(严珅), Ziguang Ma(马紫光), Haiyan Wu(吴海燕), Lu Wang(王禄), Haiqiang Jia(贾海强), Wenxin Wang(王文新), Hong Chen(陈弘)

Chin. Phys. B, 2017, 26 (8): 087311. DOI: 10.1088/1674-1056/26/8/087311

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The green light emitting diodes (LEDs) have lower quantum efficiency than LEDs with other emission wavelengths in the visible spectrum. In this research, a novel quantum well structure was designed to improve the electroluminescence (EL) of green InGaN-based LEDs. Compared with the conventional quantum well structure, the novel structure LED gained 2.14 times light out power (LOP) at 20-mA current injection, narrower FWHM and lower blue-shift at different current injection conditions.

Total ionizing radiation-induced read bit-errors in toggle magnetoresistive random-access memory devices

Yan Cui(崔岩), Ling Yang(杨玲), Teng Gao(高腾), Bo Li(李博), Jia-Jun Luo(罗家俊)

Chin. Phys. B, 2017, 26 (8): 087501. DOI: 10.1088/1674-1056/26/8/087501

Abstract ( 642 )

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The 1-Mb and 4-Mb commercial toggle magnetoresistive random-access memories (MRAMs) with 0.13 μm and 0.18-μm complementary metal-oxide-semiconductor (CMOS) process respectively and different magnetic tunneling junctions (MTJs) are irradiated with a Cobalt-60 gamma source. The electrical functions of devices during the irradiation and the room temperature annealing behavior are measured. Electrical failures are observed until the dose accumulates to 120-krad (Si) in 4-Mb MRAM while the 1-Mb MRAM keeps normal. Thus, the 0.13-μm process circuit exhibits better radiation tolerance than the 0.18-μm process circuit. However, a small quantity of read bit-errors randomly occurs only in 1-Mb MRAM during the irradiation while their electrical function is normal. It indicates that the store states of MTJ may be influenced by gamma radiation, although the electrical transport and magnetic properties are inherently immune to the radiation. We propose that the magnetic Compton scattering in the interaction of gamma ray with magnetic free layer may be the origin of the read bit-errors. Our results are useful for MRAM toward space application.

Effects of Zr substitution on structural, morphological, and magnetic properties of bismuth iron oxide phases

A Asif, M Hassan, S Riaz, S Naseem, S S Hussain

Chin. Phys. B, 2017, 26 (8): 087502. DOI: 10.1088/1674-1056/26/8/087502

Abstract ( 744 )

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The present study involves co-precipitation method to grow un-doped and Zr-doped bismuth iron oxide with x_Zr = 0.10-0.30. The molar solutions of ferric chloride (FeCl₃), zirconyle chloride (ZrOCl₂), and bismuth chloride (BiCl₃) are prepared in distilled water, and are allowed to react with sodium hydroxide (NaOH). The synthesized powders are then converted into pellets, which are sintered at 500 ℃ for two hours in a muffle furnace. X-ray diffraction (XRD) shows multi-phase formation in un-doped and Zr doped samples. Scanning electron microscope (SEM) depicts layered structure at low Zr concentration x_Zr = 0.10, while uniform surface with smaller grains and voids is observed at x_Zr = 0.20, but at x_Zr = 0.30, cracks and voids become prominent. The ferromagnetic nature of the un-doped sample is observed by vibrating sample magnetometer (VSM), while paramagnetic behavior appears due to Zr doping. The ferromagnetism in un-doped sample is lost by Zr doping, which is due to the formation of additional Fe-O-Zr bonds that induce paramagnetic behavior.

Improvement of the high-κ/Ge interface thermal stability using an in-situ ozone treatment characterized by conductive atomic force microscopy

Ji-Bin Fan(樊继斌), Xiao-Jiao Cheng(程晓姣), Hong-Xia Liu(刘红侠), Shu-Long Wang(王树龙), Li Duan(段理)

Chin. Phys. B, 2017, 26 (8): 087701. DOI: 10.1088/1674-1056/26/8/087701

Abstract ( 573 )

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In this work, an in-situ ozone treatment is carried out to improve the interface thermal stability of HfO₂/Al₂O₃ gate stack on germanium (Ge) substrate. The micrometer scale level of HfO₂/Al₂O₃ gate stack on Ge is studied using conductive atomic force microscopy (AFM) with a conductive tip. The initial results indicate that comparing with a non in-situ ozone treated sample, the interface thermal stability of the sample with an in-situ ozone treatment can be substantially improved after annealing. As a result, void-free surface, low conductive spots, low leakage current density, and relative high breakdown voltage high-κ/Ge are obtained. A detailed analysis is performed to confirm the origins of the changes. All results indicate that in-situ ozone treatment is a promising method to improve the interface properties of Ge-based three-dimensional (3D) devices in future technology nodes.

Synergistic effects of electrical and optical excitations on TiO₂ resistive device Suggested by editors

Qi Mao(毛奇), Wei-Jian Lin(林伟坚), Ke-Jian Zhu(朱科建), Yang Meng(孟洋), Hong-Wu Zhao(赵宏武)

Chin. Phys. B, 2017, 26 (8): 087702. DOI: 10.1088/1674-1056/26/8/087702

Abstract ( 623 )

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The influences of electrical and optical excitations on the conductivity characteristic are investigated in bulk and edge devices of ITO/TiO₂/ITO structure. Driven by the electrical and optical stimuli independently, the conductivity relaxation behaviors of the pristine resistive state (PRS) are observed and ascribed to the electron trapping and the oxygen transport processes. For a resistive switching (RS) device, the conductance change under optical illumination is about two orders of magnitude smaller than the conductance change corresponding to the variation of background current due to the emergence of a great number of oxygen vacancies in the RS device. With the illumination being off, the conductance slowly decays, which suggests that the oxygen diffusion process dominates the conductance relaxation. The difference in conductance relaxation between the bulk and edge devices indicates that the oxygen exchange plays a critical role in the relaxation process of conductivity. The synergistic effects of both electrical and optical excitations on the RS devices could be used for novel applications in integrated optoelectronic memory devices.

Propagations of Rayleigh and Love waves in ZnO films/glass substrates analyzed by three-dimensional finite element method

Yan Wang(王艳), Ying-Cai Xie(谢英才), Shu-Yi Zhang(张淑仪), Xiao-Dong Lan(兰晓东)

Chin. Phys. B, 2017, 26 (8): 087703. DOI: 10.1088/1674-1056/26/8/087703

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Propagation characteristics of surface acoustic waves (SAWs) in ZnO films/glass substrates are theoretically investigated by the three-dimensional (3D) finite element method. At first, for (1120) ZnO films/glass substrates, the simulation results confirm that the Rayleigh waves along the [0001] direction and Love waves along the [1100] direction are successfully excited in the multilayered structures. Next, the crystal orientations of the ZnO films are rotated, and the influences of ZnO films with different crystal orientations on SAW characterizations, including the phase velocity, electromechanical coupling coefficient, and temperature coefficient of frequency, are investigated. The results show that at appropriate h/λ, Rayleigh wave has a maximum k² of 2.4% in (90°, 56.5°, 0°) ZnO film/glass substrate structure; Love wave has a maximum k² of 3.81% in (56°, 90°, 0°) ZnO film/glass substrate structure. Meantime, for Rayleigh wave and Love wave devices, zero temperature coefficient of frequency (TCF) can be achieved at appropriate ratio of film thickness to SAW wavelength. These results show that SAW devices with higher k² or lower TCF can be fabricated by flexibly selecting the crystal orientations of ZnO films on glass substrates.

Shape controllable synthesis and enhanced upconversion photoluminescence of β-NaGdF₄:Yb³⁺, Er³⁺ nanocrystals by introducing Mg²⁺

Yong-Xin Yang(杨永馨), Zheng Xu(徐征), Su-Ling Zhao(赵谡玲), Zhi-Qin Liang(梁志琴), Wei Zhu(朱薇), Jun-Jie Zhang(张俊杰)

Chin. Phys. B, 2017, 26 (8): 087801. DOI: 10.1088/1674-1056/26/8/087801

Abstract ( 643 )

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Different concentrations of Mg²⁺-doped hexagonal phase NaGdF₄:Yb³⁺, Er³⁺ nanocrystals (NCs) were synthesized by a modified solvothermal method. Successful codoping of Mg²⁺ ions in upconversion nanoparticles (UCNPs) was supported by XRD, SEM, EDS, and PL analyses. The effects of Mg²⁺ doping on the morphology and the intensity of the upconversion (UC) emission were discussed in detail. It turned out that with the concentration of Mg²⁺ increasing, the morphology of the nanoparticles turn to change gradually and the UC emission was increasing gradually as well. Notably the UC fluorescence intensities of Er³⁺ were gradually improved owing to the codoped Mg²⁺ and then achieved a maximum level as the concentration of Mg²⁺ ions was 60 mol% from the amendment of the crystal structure of β -NaGdF₄:Yb³⁺, Er³⁺ nanoparticles. Moreover, the UC luminescence properties of the rare-earth (Yb³⁺, Er³⁺ ions codoped NaGdF4 nanocrystals were investigated in detail under 980-nm excitation.

Studies on the polycrystalline silicon/SiO₂ stack as front surface field for IBC solar cells by two-dimensional simulations Suggested by editors

Shuai Jiang(姜帅), Rui Jia(贾锐), Ke Tao(陶科), Caixia Hou(侯彩霞), Hengchao Sun(孙恒超), Zhiyong Yu(于志泳), Yongtao Li(李勇滔)

Chin. Phys. B, 2017, 26 (8): 087802. DOI: 10.1088/1674-1056/26/8/087802

Abstract ( 728 )

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Interdigitated back contact (IBC) solar cells can achieve a very high efficiency due to its less optical losses. But IBC solar cells demand for high quality passivation of the front surface. In this paper, a polycrystalline silicon/SiO₂ stack structure as front surface field to passivate the front surface of IBC solar cells is proposed. The passivation quality of this structure is investigated by two dimensional simulations. Polycrystalline silicon layer and SiO₂ layer are optimized to get the best passivation quality of the IBC solar cell. Simulation results indicate that the doping level of polycrystalline silicon should be high enough to allow a very thin polycrystalline silicon layer to ensure an effective passivation and small optical losses at the same time. The thickness of SiO₂ should be neither too thin nor too thick, and the optimal thickness is 1.2 nm. Furthermore, the lateral transport properties of electrons are investigated, and the simulation results indicate that a high doping level and conductivity of polycrystalline silicon can improve the lateral transportation of electrons and then the cell performance.

Theoretical investigation of optical properties and band gap engineering for Zn_1-xTM_xTe(TM=Fe, Co) alloys by modified Becke—Johnson potential

Q Mahmood, M Yaseen, M Hassan, Shahid M Ramay, Asif Mahmood

Chin. Phys. B, 2017, 26 (8): 087803. DOI: 10.1088/1674-1056/26/8/087803

Abstract ( 620 )

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The direct band gap ZnTe with transition metal (TM) impurities plays a vital role in optoelectronic and spintronic applications. In the present study, we use the advanced modified Becke-Johnson (mBJ) functional for performing the structural computations and detailed investigations of the optical characters in Zn_1-xTM_xTe (TM=Fe, Co) alloys with 0 ≤ x ≤1. By employing the FP-LAPW method, we determine various optical parameters for the ternary alloys and for the end binaries. The calculated static dielectric constants and optical band gaps for Zn_1-xTM_xTe (TM=Fe, Co) have an inverse relation that verifies the Penn model. We find that the static dielectric constant is nearly equal to the square of the static refractive index, and both increase with TM content. Furthermore, we also find a slight shift of peaks to a higher energy region with increasing TM concentration. The decreasing band gap and high value of the absorption in the visible region of electromagnetic spectrum make these alloys suitable for photonic and solar cell applications.

Horizontal InAs nanowire transistors grown on patterned silicon-on-insulator substrate Suggested by editors

Wang Zhang(张望), Wei-Hua Han(韩伟华), Xiao-Song Zhao(赵晓松), Qi-Feng Lv(吕奇峰), Xiang-Hai Ji(季祥海), Tao Yang(杨涛), Fu-Hua Yang(杨富华)

Chin. Phys. B, 2017, 26 (8): 088101. DOI: 10.1088/1674-1056/26/8/088101

Abstract ( 662 )

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High-density horizontal InAs nanowire transistors are fabricated on the interdigital silicon-on-insulator substrate. Hexagonal InAs nanowires are uniformly grown between face-to-face (111) vertical sidewalls of neighboring Si fingers by metal-organic chemical vapor deposition. The density of InAs nanowires is high up to 32 per group of silicon fingers, namely an average of 4 nanowires per micrometer. The electrical characteristics with a higher on/off current ratio of 2×10⁵ are obtained at room temperature. The silicon-based horizontal InAs nanowire transistors are very promising for future high-performance circuits.

Exploring the role of inhibitory coupling in duplex networks Suggested by editors

Cui-Yun Yang(杨翠云), Guo-Ning Tang(唐国宁), Hai-Ying Liu(刘海英)

Chin. Phys. B, 2017, 26 (8): 088201. DOI: 10.1088/1674-1056/26/8/088201

Abstract ( 710 )

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The electrical coupling of myocytes and fibroblasts can play a role in inhibiting electrical impluse propagation in cardiac muscle. To understand the function of fibroblast-myocyte coupling in the aging heart, the spiral-wave dynamics in the duplex networks with inhibitory coupling is numerically investigated by the Bär-Eiswirth model. The numerical results show that the inhibitory coupling can change the wave amplitude, excited phase duration and excitability of the system. When the related parameters are properly chosen, the inhibitory coupling can induce local abnormal oscillation in the system and the Eckhaus instability of the spiral wave. For the dense inhibitory network, the maximal decrement (maximal increment) in the excited phase duration can reach 24.3%(13.4%), whereas the maximal decrement in wave amplitude approaches 28.1%. Upon increasing the inhibitory coupling strength, the system excitability is reduced and even completely suppressed when the interval between grid points in the inhibitory network is small enough. Moreover, the inhibitory coupling can lead to richer phase transition scenarios of the system, such as the transition from a stable spiral wave to turbulence and the transition from a meandering spiral wave to a planar wave. In addition, the self-sustaining planar wave, the unique meandering of spiral wave and inward spiral wave are observed. The physical mechanisms behind the phenomena are analyzed.

Gas treatment protection of metallic lithium anode ^Hot!

Wen-jun Li(李文俊), Quan Li(李泉), Jie Huang(黄杰), Jia-yue Peng(彭佳悦), Geng Chu(褚赓), Ya-xiang Lu(陆雅翔), Jie-yun Zheng(郑杰允), Hong Li(李泓)

Chin. Phys. B, 2017, 26 (8): 088202. DOI: 10.1088/1674-1056/26/8/088202

Abstract ( 710 )

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The effects of different coating layers on lithium metal anode formed by reacting with different controlled atmospheres (argon, CO₂-O₂(2:1), N₂, and CO₂-O₂-N₂(2:1:3)) have been investigated. The obtained XRD, second ion mass spectroscopy (SIMS), and scanning probe microscope (SPM) results demonstrate the formation of coating layers composed of Li₂CO₃, Li₃N, and the mixture of them on lithium tablets, respectively. The Li/Li symmetrical cell and Li/S cell are assembled to prove the advantages of the protected lithium tablet on electrochemical performance. The comparison of SEM and SIMS characterizations before/after cycles clarifies that an SEI-like composition formed on the lithium tablets could modulate the interfacial stabilization between the lithium foil and the ether electrolyte.

Anisotropic transport of microalgae Chlorella vulgaris in microfluidic channel

Nur Izzati Ishak, S V Muniandy, Vengadesh Periasamy, Fong-Lee Ng, Siew-Moi Phang

Chin. Phys. B, 2017, 26 (8): 088203. DOI: 10.1088/1674-1056/26/8/088203

Abstract ( 551 )

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In this work, we study the regional dependence of transport behavior of microalgae Chlorella vulgaris inside microfluidic channel on applied fluid flow rate. The microalgae are treated as spherical naturally buoyant particles. Deviation from the normal diffusion or Brownian transport is characterized based on the scaling behavior of the mean square displacement (MSD) of the particle trajectories by resolving the displacements in the streamwise (flow) and perpendicular directions. The channel is divided into three different flow regions, namely center region of the channel and two near-wall boundaries and the particle motions are analyzed at different flow rates. We use the scaled Brownian motion to model the transitional characteristics in the scaling behavior of the MSDs. We find that there exist anisotropic anomalous transports in all the three flow regions with mixed sub-diffusive, normal and super-diffusive behavior in both longitudinal and transverse directions.

Molecular dynamics simulation of the response of bi-disperse polyelectrolyte brushes to external electric fields

Fen Zhang(张芬), Huan-Da Ding(丁欢达), Chao Duan(段超), Shuang-Liang Zhao(赵双良), Chao-Hui Tong(童朝晖)

Chin. Phys. B, 2017, 26 (8): 088204. DOI: 10.1088/1674-1056/26/8/088204

Abstract ( 705 )

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Langevin dynamics simulations have been performed to investigate the response of bi-disperse and strong polyacid chains grafted on an electrode to electric fields generated by opposite surface charges on the polyelectrolyte (PE)-grafted electrode and a second parallel electrode. Simulation results clearly show that, under a negative external electric field, the longer grafted PE chains are more strongly stretched than the shorter ones in terms of the relative change in their respective brush heights. Whereas under a positive external electric field, the grafted shorter chains collapse more significantly than the longer ones. It was found that, under a positive external electric field, the magnitude of the total electric force acting on one shorter PE chain is larger than that on one longer PE chain, or vice versa. The effects of smeared and discrete charge distributions of grafted PE chains on the response of PE brushes to external electric fields were also examined.

The coupling effect of air-bridges on broadband spiral inductors in SiC-based MMIC technology

Jia-Xin Zheng(郑佳欣), Xiao-Hua Ma(马晓华), Yang Lu(卢阳), Bo-Chao Zhao(赵博超), Heng-Shuang Zhang(张恒爽), Meng Zhang(张濛), Li-Xiang Chen(陈丽香), Qing Zhu(朱青), Yue Hao(郝跃)

Chin. Phys. B, 2017, 26 (8): 088401. DOI: 10.1088/1674-1056/26/8/088401

Abstract ( 730 )

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The coupling effect of air-bridges on broadband spiral inductors in SiC-based MMIC technology has been investigated deeply. The fabricated 1-nH spiral inductor on SiC substrate demonstrates a self-resonant frequency of 51.6 GHz, with a peak Q-fact of 12.14 at 22.1 GHz. From the S-parameters measurements, the exponential decay phenomenon is observed for L, Q-factor, and SRF with the air-bridge height decreasing, and an analytic expression is concluded to exactly fit the measured data which can be used to predict the performance of the spiral inductor. All the coefficients in the formula have specific meaning. By means of establishing the lumped model, the parasitic coupling capacitance of the air-bridge has been extracted and presents the exponential decay with the air-bridge heights decreasing which indicates that this capacitor is directly related to the coupling effect of the air-bridge. Through the electromagnetic field distribution simulation, the details of the electric field around the air-bridge have been presented which demonstrate the formation and the variation principles of the coupling effect.

Impact of energy straggle on proton-induced single event upset test in a 65-nm SRAM cell

Bing Ye(叶兵), Jie Liu(刘杰), Tie-Shan Wang(王铁山), Tian-Qi Liu(刘天奇), Jie Luo(罗捷), Bin Wang(王斌), Ya-Nan Yin(殷亚楠), Qing-Gang Ji(姬庆刚), Pei-Pei Hu(胡培培), You-Mei Sun(孙友梅), Ming-Dong Hou(侯明东)

Chin. Phys. B, 2017, 26 (8): 088501. DOI: 10.1088/1674-1056/26/8/088501

Abstract ( 796 )

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This paper presents a simulation study of the impact of energy straggle on a proton-induced single event upset (SEU) test in a commercial 65-nm static random access memory cell. The simulation results indicate that the SEU cross sections for low energy protons are significantly underestimated due to the use of degraders in the SEU test. In contrast, using degraders in a high energy proton test may cause the overestimation of the SEU cross sections. The results are confirmed by the experimental data and the impact of energy straggle on the SEU cross section needs to be taken into account when conducting a proton-induced SEU test in a nanodevice using degraders.

Three-dimensional simulation of fabrication process-dependent effects on single event effects of SiGe heterojunction bipolar transistor

Jin-Xin Zhang(张晋新), Chao-Hui He(贺朝会), Hong-Xia Guo(郭红霞), Pei Li(李培), Bao-Long Guo(郭宝龙), Xian-Xiang Wu(吴宪祥)

Chin. Phys. B, 2017, 26 (8): 088502. DOI: 10.1088/1674-1056/26/8/088502

Abstract ( 763 )

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The fabrication process dependent effects on single event effects (SEEs) are investigated in a commercial silicon-germanium heterojunction bipolar transistor (SiGe HBT) using three-dimensional (3D) TCAD simulations. The influences of device structure and doping concentration on SEEs are discussed via analysis of current transient and charge collection induced by ions strike. The results show that the SEEs representation of current transient is different from representation of the charge collection for the same process parameters. To be specific, the area of C/S junction is the key parameter that affects charge collection of SEE. Both current transient and charge collection are dependent on the doping of collector and substrate. The base doping slightly influences transient currents of base, emitter, and collector terminals. However, the SEEs of SiGe HBT are hardly affected by the doping of epitaxial base and the content of Ge.

An investigation of ionizing radiation damage in different SiGe processes

Pei Li(李培), Mo-Han Liu(刘默寒), Chao-Hui He(贺朝会), Hong-Xia Guo(郭红霞), Jin-Xin Zhang(张晋新), Ting Ma(马婷)

Chin. Phys. B, 2017, 26 (8): 088503. DOI: 10.1088/1674-1056/26/8/088503

Abstract ( 807 )

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Different SiGe processes and device designs are the critical influences of ionizing radiation damage. Based on the different ionizing radiation damage in SiGe HBTs fabricated by Huajie and an IBM SiGe process, quantitatively numerical simulation of ionizing radiation damage was carried out to explicate the distribution of radiation-induced charges buildup in KT9041 and IBM SiGe HBTs. The sensitive areas of the EB-spacer and isolation oxide of KT9041 are much larger than those of the IBM SiGe HBT, and the distribution of charge buildup in KT9041 is several orders of magnitude greater than that of the IBM SiGe HBT. The result suggests that the simulations are consistent with the experiment, and indicates that the geometry of the EB-spacer, the area of the Si/SiO₂ interface and the isolation structure could be contributing to the different ionizing radiation damage.

A theoretical and experimental evaluation of III-nitride solar-blind UV photocathode

Bin Ren(任彬), Hui Guo(郭晖), Feng Shi(石峰), Hong-Chang Cheng(程宏昌), Hui Liu(刘晖), Jian Liu(刘健), Zhi-Hui Shen(申志辉), Yan-Li Shi(史衍丽), Pei Liu(刘培)

Chin. Phys. B, 2017, 26 (8): 088504. DOI: 10.1088/1674-1056/26/8/088504

Abstract ( 637 )

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We have developed a superior solar-blind ultraviolet (UV) photocathode with an Al_xGa_1-xN photocathode (x ～ 0.45) in semi-transparent mode, and assessed spectra radiant sensitivity related to practical use. Before being grown over a basal plane sapphire substrate by low-pressure metal organic chemical vapor deposition (MOCVD), a reasonable design was made to the photocathode epitaxy structure, focusing on the Al_xGa_1-xN: Mg active layer, then followed by a comprehensive analysis of the structural and optical characterization. The spectra radiant sensitivity is peaked of 41.395 mA/W at wavelength 257 nm and then decreases by about 3 to 4 decades at 400 nm demonstrating the ability of this photocathode for solar-blind application prospects.

Bloom's syndrome protein unfolding G-quadruplexes in two pathways Suggested by editors

Zhen-Ye Zhao(赵振业), Chun-Hua Xu(徐春华), Jing Shi(史婧), Jing-Hua Li(李菁华), Jian-Bing Ma(马建兵), Qi Jia(贾棋), Dong-Fei Ma(马东飞), Ming Li(李明), Ying Lu(陆颖)

Chin. Phys. B, 2017, 26 (8): 088701. DOI: 10.1088/1674-1056/26/8/088701

Abstract ( 752 )

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The Bloom helicase (BLM) gene product encodes a DNA helicase that functions in homologous recombination repair to prevent genomic instability. BLM is highly active in binding and unfolding G-quadruplexes (G4), which are non-canonical DNA structures formed by Hoogsteen base-pairing in guanine-rich sequences. Here we use single-molecule fluorescence resonance energy transfer (smFRET) to study the molecular mechanism of BLM-catalysed G4 unfolding and show that BLM unfolds G4 in two pathways. Our data enable us to propose a model in which the HRDC domain functions as a regulator of BLM, depending on the position of the HRDC domain of BLM in action: when HRDC binds to the G4 sequence, BLM may hold G4 in the unfolded state; otherwise, it may remain on the unfolded G4 transiently so that G4 can refold immediately.

Optimization of wide band mesa-type enhanced terahertz photoconductive antenna at 1550 nm Suggested by editors

Jian-Xing Xu(徐建星), Jin-Lun Li(李金伦), Si-Hang Wei(魏思航), Ben Ma(马奔), Yi Zhang(张翼), Yu Zhang(张宇), Hai-Qiao Ni(倪海桥), Zhi-Chuan Niu(牛智川)

Chin. Phys. B, 2017, 26 (8): 088702. DOI: 10.1088/1674-1056/26/8/088702

Abstract ( 754 )

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A mesa-type enhanced InGaAs/InAlAs multilayer heterostructure (MLHS) terahertz photoconductive antenna (PCA) at 1550 nm is demonstrated on an InP substrate. The InGaAs/InAlAs superlattice multilayer heterostructures are grown and studied with different temperatures and thickness ratios of InGaAs/InAlAs. The PCAs with different gap sizes and pad sizes are fabricated and characterized. The PCAs are evaluated as THz emitters in a THz time domain spectrometer and we measure the optimized THz bandwidth in excess of 2 THz.

Degradation behavior of electrical properties of GaInAs (1.0 eV) and GaInAs (0.7 eV) sub-cells of IMM4J solar cells under 1-MeV electron irradiation

Yan-Qing Zhang(张延清), Ming-Xue Huo(霍明学), Yi-Yong Wu(吴宜勇), Cheng-Yue Sun(孙承月), Hui-Jie Zhao(赵慧杰), Hong-Bin Geng(耿洪滨), Shuai Wang(王帅), Ru-Bin Liu(刘如彬), Qiang Sun(孙强)

Chin. Phys. B, 2017, 26 (8): 088801. DOI: 10.1088/1674-1056/26/8/088801

Abstract ( 736 )

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In this work the degradation effects of the Ga_0.7In_0.3As (1.0 eV) and Ga_0.42In_0.58As (0.7 eV) sub-cells for IMM4J solar cells are investigated after 1-MeV electron irradiation by using spectral response and photoluminescence (PL) signal amplitude analysis, as well as electrical property measurements. The results show that, compared with the electrical properties of traditional single junction (SJ) GaAs (1.41 eV) solar cell, the electrical properties (such as I_sc, V_oc, and P_max) of the newly sub-cells degrade similarly as a function of Φ, where Φ represents the electron fluence. It is found that the degradation of V_oc is much more than that of I_sc in the irradiated Ga_0.42In_0.58As (0.7 eV) cells due to the additional intrinsic layer, leading to more serious damage to the space charge region. However, of the three types of SJ cells with the gap widths of 0.7, 1.0, and 1.4 eV, the electric properties of the Ga_0.7In_0.3As (1.0 eV) cell decrease largest under each irradiation fluence. Analysis on the spectral response indicates that the J_sc of the Ga_0.7In_0.3As (1.0 eV) cell also shows the most severe damage. The PL amplitude measurements qualitatively confirm that the degradation of the effective minority carrier life-time (τ_eff) in the SJ Ga_0.7In_0.3As cells is more drastic than that of SJ GaAs cells during the irradiation. Thus, the output current of Ga_0.7In_0.3As sub-cell should be controlled in the irradiated IMM4J cells.

The robustness of sparse network under limited attack capacity

Xiao-Juan Wang(王小娟), Mei Song(宋梅), Lei Jin(金磊), Zhen Wang(王珍)

Chin. Phys. B, 2017, 26 (8): 088901. DOI: 10.1088/1674-1056/26/8/088901

Abstract ( 692 )

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The paper studies the robustness of the network in terms of the network structure. We define a strongly dominated relation between nodes and then we use the relation to merge the network. Based on that, we design a dominated clustering algorithm aiming at finding the critical nodes in the network. Furthermore, this merging process is lossless which means the original structure of the network is kept. In order to realize the visulization of the network, we also apply the lossy consolidation to the network based on detection of the community structures. Simulation results show that compared with six existed centrality algorithms, our algorithm performs better when the attack capacity is limited. The simulations also illustrate our algorithm does better in assortative scale-free networks.

Elastic properties of CaCO₃ high pressure phases from first principles Suggested by editors

Dan Huang(黄丹), Hong Liu(刘红), Ming-Qiang Hou(侯明强), Meng-Yu Xie(谢梦雨), Ya-Fei Lu(鹿亚飞), Lei Liu(刘雷), Li Yi(易丽), Yue-Ju Cui(崔月菊), Ying Li(李营), Li-Wei Deng(邓力维), Jian-Guo Du(杜建国)

Chin. Phys. B, 2017, 26 (8): 089101. DOI: 10.1088/1674-1056/26/8/089101

Abstract ( 747 )

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Elastic properties of three high pressure polymorphs of CaCO₃ are investigated based on first principles calculations. The calculations are conducted at 0 GPa-40 GPa for aragonite, 40 GPa-65 GPa for post-aragonite, and 65 GPa-150 GPa for the P2₁/c-h-CaCO₃ structure, respectively. By fitting the third-order Birch-Murnaghan equation of state (EOS), the values of bulk modulus K₀ and pressure derivative K₀' are 66.09 GPa and 4.64 for aragonite, 81.93 GPa and 4.49 for post-aragonite, and 56.55 GPa and 5.40 for P2₁/c-h-CaCO₃, respectively, which are in good agreement with previous experimental and theoretical data. Elastic constants, wave velocities, and wave velocity anisotropies of the three high-pressure CaCO₃ phases are obtained. Post-aragonite exhibits 25.90%-32.10% V_P anisotropy and 74.34%-104.30% V_S splitting anisotropy, and P2₁/c-h-CaCO₃shows 22.30%-25.40% V_P anisotropy and 42.81%-48.00% V_S splitting anisotropy in the calculated pressure range. Compared with major minerals of the lower mantle, CaCO₃ high pressure polymorphs have low isotropic wave velocity and high wave velocity anisotropies. These results are important for understanding the deep carbon cycle and seismic wave velocity structure in the lower mantle.

Revisit to frozen-in property of vorticity

Shuai Yang(杨帅), Qun-Jie Zuo(左群杰), Shou-Ting Gao(高守亭)

Chin. Phys. B, 2017, 26 (8): 089201. DOI: 10.1088/1674-1056/26/8/089201

Abstract ( 554 )

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Considering some simple topological properties of vorticity vector, the frozen-in property of vorticity herein is revisited. A vortex line, as is analogous to velocity vector along a streamline, is defined as such a coincident material (curve) line that connects many material fluid elements, on which the local vorticity vector for each fluid element is also tangent to the vortex line. The vortex line evolves in the same manner as the material line that it is initially associated with. The vortex line and the material line are both oriented to the same directions, and evolve with the proportional magnitude, just like being ‘frozen’ or ‘glued’ to the material elements of the fluid under the barotropic assumption. To relax the limits of incompressible and barotropic atmosphere, the frozen-in property is further derived and proved in the baroclinic case. Then two effective usages are given as examples. One is the derivation of potential vorticity conservation from the frozen-in property in both barotropic and baroclinic atmospheres, as a theory application, and the other is used to illuminate the vorticity generation and growth in ideal cases and real severe weather process, e.g., in squall line, tornado, and other severe convection weather with vortex. There is no necessity to derive vorticity equation, and this method is very intuitive to explain vorticity development qualitatively, especially for fast analysis for forecasters. Certainly, by investigating the evolution of vortex line, it is possible to locate the associated line element vector and its development on the basis of the frozen-in property of vorticity. Because it is simple and visualized, it manifests broad application prospects.

Error analysis and optimal design of polarization calibration unit for solar telescope

Jun-Feng Hou(侯俊峰), Dong-Guang Wang(王东光), Yuan-Yong Deng(邓元勇), Ying-Zi Sun(孙英姿), Zhi-Yong Zhang(张志勇)

Chin. Phys. B, 2017, 26 (8): 089501. DOI: 10.1088/1674-1056/26/8/089501

Abstract ( 632 )

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Polarization calibration unit (PCU) has become an indispensable element for solar telescopes to remove the instrumental polarization; the polarimetric accuracy of calibration depends strongly on the properties of PCU. In the paper, we analyze the measurement errors induced by PCU based on polarized light theory and find that the imperfections of the waveplate generate the main calibration errors. An optimized calibration method is proposed to avoid the effects from waveplate imperfections, and a numerical simulation is given to evaluate the polarization accuracy by analyzing the relation between calibration error and intensity instability. The work is very important for solar telescopes with high polarization precision up to 10^-4 I_c.

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