中国物理B

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Complex dynamical behaviors of compact solitary waves in the perturbed mKdV equation

殷久利, 邢倩倩, 田立新

2014 (8): 80201-080201. doi: 10.1088/1674-1056/23/8/080201

摘要 ( 844 )

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In this paper, we give a detailed discussion about the dynamical behaviors of compact solitary waves subjected to the periodic perturbation. By using the phase portrait theory, we find one of the nonsmooth solitary waves of the mKdV equation, namely, a compact solitary wave, to be a weak solution, which can be proved. It is shown that the compact solitary wave easily turns chaotic from the Melnikov theory. We focus on the sufficient conditions by keeping the system stable through selecting a suitable controller. Furthermore, we discuss the chaotic threshold for a perturbed system. Numerical simulations including chaotic thresholds, bifurcation diagrams, the maximum Lyapunov exponents, and phase portraits demonstrate that there exists a special frequency which has a great influence on our system; with the increase of the controller strength, chaos disappears in the perturbed system. But if the controller strength is sufficiently large, the solitary wave vibrates violently.

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Model-based predictive controller design for a class of nonlinear networked systems with communication delays and data loss

安宝冉, 刘国平

2014 (8): 80202-080202. doi: 10.1088/1674-1056/23/8/080202

摘要 ( 677 )

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This paper discusses the model-based predictive controller design of networked nonlinear systems with communication delay and data loss. Based on the analysis of the closed-loop networked predictive control systems, the model-based networked predictive control strategy can compensate for communication delay and data loss in an active way. The designed model-based predictive controller can also guarantee the stability of the closed-loop networked system. The simulation results demonstrate the feasibility and efficacy of the proposed model-based predictive controller design scheme.

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Improved locality-sensitive hashing method for the approximate nearest neighbor problem

陆颖华, 马廷淮, 钟水明, 曹杰, 王新, Abdullah Al-Dhelaan

2014 (8): 80203-080203. doi: 10.1088/1674-1056/23/8/080203

摘要 ( 635 )

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In recent years, the nearest neighbor search (NNS) problem has been widely used in various interesting applications. Locality-sensitive hashing (LSH), a popular algorithm for the approximate nearest neighbor problem, is proved to be an efficient method to solve the NNS problem in the high-dimensional and large-scale databases. Based on the scheme of p-stable LSH, this paper introduces a novel improvement algorithm called randomness-based locality-sensitive hashing (RLSH) based on p-stable LSH. Our proposed algorithm modifies the query strategy that it randomly selects a certain hash table to project the query point instead of mapping the query point into all hash tables in the period of the nearest neighbor query and reconstructs the candidate points for finding the nearest neighbors. This improvement strategy ensures that RLSH spends less time searching for the nearest neighbors than the p-stable LSH algorithm to keep a high recall. Besides, this strategy is proved to promote the diversity of the candidate points even with fewer hash tables. Experiments are executed on the synthetic dataset and open dataset. The results show that our method can cost less time consumption and less space requirements than the p-stable LSH while balancing the same recall.

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Multi-symplectic method for the coupled Schrödinger-KdV equations

张弘, 宋松和, 周炜恩, 陈绪栋

2014 (8): 80204-080204. doi: 10.1088/1674-1056/23/8/080204

摘要 ( 673 )

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In this paper, we present a multi-symplectic Hamiltonian formulation of the coupled Schrödinger-KdV equations (CSKE) with periodic boundary conditions. Then we develop a novel multi-symplectic Fourier pseudospectral (MSFP) scheme for the CSKE. In numerical experiments, we compare the MSFP method with the Crank-Nicholson (CN) method. Our results show high accuracy, effectiveness, and good ability of conserving the invariants of the MSFP method.

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Discrete event model-based simulation for train movement on a single-line railway

徐小明, 李克平, 杨立兴

2014 (8): 80205-080205. doi: 10.1088/1674-1056/23/8/080205

摘要 ( 557 )

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The aim of this paper is to present a discrete event model-based approach to simulate train movement with the considered energy-saving factor. We conduct extensive case studies to show the dynamic characteristics of the traffic flow and demonstrate the effectiveness of the proposed approach. The simulation results indicate that the proposed discrete event model-based simulation approach is suitable for characterizing the movements of a group of trains on a single railway line with less iterations and CPU time. Additionally, some other qualitative and quantitative characteristics are investigated. In particular, because of the cumulative influence from the previous trains, the following trains should be accelerated or braked frequently to control the headway distance, leading to more energy consumption.

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A feedback control method for the stabilization of a nonlinear diffusion system on a graph

于欣, 许超, 林群

2014 (8): 80206-080206. doi: 10.1088/1674-1056/23/8/080206

摘要 ( 574 )

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In this paper, we consider the internal stabilization problems of FitzHugh-Nagumo (FHN) systems on the locally finite connected weighted graphs, which describe the process of signal transmission across axons in neurobiology. We will establish the proper condition on the weighted Dirichlet-Laplace operator on a graph such that the nonlinear FHN system can be stabilized exponentially and globally only using internal actuation over a sub-domain with a linear feedback form.

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New operator-ordering identities and associative integration formulas of two-variable Hermite polynomials for constructing non-Gaussian states

范洪义, 王震

2014 (8): 80301-080301. doi: 10.1088/1674-1056/23/8/080301

摘要 ( 564 )

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For directly normalizing the photon non-Gaussian states (e.g., photon added and subtracted squeezed states), we use the method of integration within an ordered product (IWOP) of operators to derive some new bosonic operator-ordering identities. We also derive some new integration transformation formulas about one- and two-variable Hermite polynomials in complex function space. These operator identities and associative integration formulas provide much convenience for constructing non-Gaussian states in quantum engineering.

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A sufficient and necessary criterion for separability of bipartite quantum states

赵慧, 于欣玉

2014 (8): 80302-080302. doi: 10.1088/1674-1056/23/8/080302

摘要 ( 624 )

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A sufficient and necessary criterion for separability of bipartite quantum states is presented. We construct a class of mixed states in 2⊗ k quantum systems and in 3⊗ k quantum systems, respectively and show that these states are separable if and only if they are positive partial transpositions.

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Security of a practical semi-device-independent quantum key distribution protocol against collective attacks

汪洋, 鲍皖苏, 李宏伟, 周淳, 李源

2014 (8): 80303-080303. doi: 10.1088/1674-1056/23/8/080303

摘要 ( 669 )

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Similar to device-independent quantum key distribution (DI-QKD), semi-device-independent quantum key distribution (SDI-QKD) provides secure key distribution without any assumptions about the internal workings of the QKD devices. The only assumption is that the dimension of the Hilbert space is bounded. But SDI-QKD can be implemented in a one-way prepare-and-measure configuration without entanglement compared with DI-QKD. We propose a practical SDI-QKD protocol with four preparation states and three measurement bases by considering the maximal violation of dimension witnesses and specific processes of a QKD protocol. Moreover, we prove the security of the SDI-QKD protocol against collective attacks based on the min-entropy and dimension witnesses. We also show a comparison of the secret key rate between the SDI-QKD protocol and the standard QKD.

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An autobias control system for the electro–optic modulator used in a quantum key distribution system

陈文芬, 魏正军, 郭莉, 侯丽燕, 王赓, 王金东, 张智明, 郭建平, 刘颂豪

2014 (8): 80304-080304. doi: 10.1088/1674-1056/23/8/080304

摘要 ( 741 )

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In a quantum key distribution system, it is crucial to keep the extinction ratio of the coherent pulses stable. This means that the direct current bias point of the electro-optic modulator (EOM) used for generating coherent pulses must be locked. In this paper, an autobias control system based on a lock-in-amplifier for the EOM is introduced. Its drift information extracting theory and control method are analyzed comprehensively. The long term drift of the extinction ratio of the coherent pulses is measured by a single photon detector, which indicates that the autobias control system is effective for stabilizing the bias point of the EOM.

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Entanglement concentration for W-type entangled coherent states

盛宇波, 刘炯, 赵圣阳, 王磊, 周澜

2014 (8): 80305-080305. doi: 10.1088/1674-1056/23/8/080305

摘要 ( 740 )

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An entangled coherent state (ECS) is one type of entanglement, which is widely discussed in the application of quantum information processing (QIP). In this paper, we propose an entanglement concentration protocol (ECP) to distill the maximally entangled W-type ECS from the partially entangled W-type ECS. In the ECP, we adopt the balanced beam splitter (BS) to make the parity check measurement. Our ECP is quite different from the conventional ECPs. After performing the ECP, not only can we obtain the maximally entangled ECS with some success probability, but also we can increase the amplitude of the coherent state. Therefore, it is especially useful in long-distance quantum communication, if the photon loss is considered.

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Control of fractional chaotic and hyperchaotic systems based on a fractional order controller

李天增, 王瑜, 罗懋康

2014 (8): 80501-080501. doi: 10.1088/1674-1056/23/8/080501

摘要 ( 643 )

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We present a new fractional-order controller based on the Lyapunov stability theory and propose a control method which can control fractional chaotic and hyperchaotic systems whether systems are commensurate or incommensurate. The proposed control method is universal, simple, and theoretically rigorous. Numerical simulations are given for several fractional chaotic and hyperchaotic systems to verify the effectiveness and the universality of the proposed control method.

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Solid-state resonant tunneling thermoelectric refrigeration in the cylindrical double-barrier nanostructure

刘念, 罗小光, 章毛连

2014 (8): 80502-080502. doi: 10.1088/1674-1056/23/8/080502

摘要 ( 716 )

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A solid-state thermoelectric refrigerator with a cylindrical InP/InAs/InP double-barrier heterostructure is proposed. Based on the ballistic electron transport and the asymmetrical transmission, we derive the expressions of the performance parameters of this refrigerator. The cooling rate rather than the coefficient of performance is affected by the area of the inner cylinder. Then through the numerical simulation, a triangular cooling rate region is found with respect to the chemical potential and bias voltage; further, that it is because of the small full width at half maximum of the transmission resonance and the linear relationship between the energy position of resonance and the bias voltage. These tunable results might supply some guide to the cooling in tiny components or devices.

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Stochastic resonance in an over-damped linear oscillator

林丽烽, 田艳, 马洪

2014 (8): 80503-080503. doi: 10.1088/1674-1056/23/8/080503

摘要 ( 694 )

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For an over-damped linear system subjected to both parametric excitation of colored noise and external excitation of periodically modulated noise, and in the case that the cross-correlation intensity between noises is a time-periodic function, we study the stochastic resonance (SR) in this paper. Using the Shapiro-Loginov formula, we acquire the exact expressions of the first-order and the second-order moments. By the stochastic averaging method, we obtain the analytical expression of the output signal-to-noise ratio (SNR). Meanwhile, we discuss the evolutions of the SNR with the signal frequency, noise intensity, correlation rate of noise, time period, and modulation frequency. We find a new bona fide SR. The evolution of the SNR with the signal frequency presents periodic oscillation, which is not observed in a conventional linear system. We obtain the conventional SR of the SNR with the noise intensity and the correlation rate of noise. We also obtain the SR in a wide sense, in which the evolution of the SNR with time period modulation frequency presents periodic oscillation. We find that the time-periodic modulation of the cross-correlation intensity between noises diversifies the stochastic resonance phenomena and makes this system possess richer dynamic behaviors.

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Double coherence resonance of the FitzHugh–Nagumo neuron driven by harmonic velocity noise

宋艳丽

2014 (8): 80504-080504. doi: 10.1088/1674-1056/23/8/080504

摘要 ( 718 )

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The effect of noise frequency on the FitzHugh-Nagumo neuron is investigated by the use of the harmonic velocity noise, which has a direct frequency parameter and no zero frequency part of the power spectrum. It is shown that the neuron has the resonance characteristic strongly responding to the noise with a certain frequency at fixed power, and there is double coherence resonance related to the frequency and the intensity. If the harmonic velocity noise lacks low frequency ingredients, there is no synchronization between the frequency of the neuron and that of the noise. Thus the low frequency part of the noise plays an important role in creating the synchronization.

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Evacuation of pedestrians from a hall by game strategy update

王浩楠, 陈栋, 盘薇, 薛郁, 何红弟

2014 (8): 80505-080505. doi: 10.1088/1674-1056/23/8/080505

摘要 ( 924 )

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In this paper, a cellular automaton model considering game strategy update is proposed to study the pedestrian evacuation in a hall. Pedestrians are classified into two categories, i.e., cooperators and defectors, and they walk to an exit according to their own strategy change. The conflicts that two or three pedestrians try to occupy the same site at the same time are investigated in the Game theory model. Based on it, the relationship between the pedestrian flow rate and the evacuation time as well as the variation of cooperative proportion against evacuation time is investigated from the different initial cooperative proportions under the influence of noise. The critical value of the noise is found when there is a small number of defectors in the initial time. Moreover, the influences of the initial cooperative proportion and strength of noise on evacuation are discussed. The results show that the lower the initial cooperative proportion as well as the bigger the strength of noise, the longer the time it takes for evacuation.

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Influence of chirality on the thermal conductivity of single-walled carbon nanotubes

冯雅, 祝捷, 唐大伟

2014 (8): 83101-083101. doi: 10.1088/1674-1056/23/8/083101

摘要 ( 756 )

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The influence of chirality on the thermal conductivity of single-walled carbon nanotubes (SWNTs) is discussed in this paper, using a non-equilibrium molecular dynamics (NEMD) method. The tube lengths of the SWNTs studied here are 20, 50, and 100 nm, respectively, and at each length the relationship between chiral angle and thermal conductivity of a SWNT is revealed. We find that if the tube length is relatively short, the influence of chirality on the thermal conductivity of a SWNT is more obvious and that a SWNT with a larger chiral angle has a greater thermal conductivity. Moreover, the thermal conductivity of a zigzag SWNT is smaller than that of an armchair one. As the tube length becomes longer, the thermal conductivity increases while the influence of chirality on the thermal conductivity decreases.

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Semi-classical explanation for the dissociation control of H₂⁺

贾正茂, 曾志男, 李儒新, 徐至展

2014 (8): 83201-083201. doi: 10.1088/1674-1056/23/8/083201

摘要 ( 688 )

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A semi-classical model is utilized to explain the dissociation control of the hydrogen molecular ion (H₂⁺). By analyzing the curve of the dissociation asymmetry parameter as a function of the time delay between the exciting and steering pulses, we find that the dissociation control is dependent not only on the peak intensity and direction of the electric field of the steering pulse, but also on the peak intensity of the exciting pulse.

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Electromagnetic wave absorbing properties and hyperfine interactions of Fe-Cu-Nb-Si-B nanocomposites

韩满贵, 郭韦, 吴燕辉, 刘明, Magundappa L. Hadimani

2014 (8): 83301-083301. doi: 10.1088/1674-1056/23/8/083301

摘要 ( 655 )

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The Fe-Cu-Nb-Si-B alloy nanocomposite containing two ferromagnetic phases (amorphous phase and nanophase phase) is obtained by properly annealing the as-prepared alloys. High resolution transmission electron microscopy (HR-TEM) images show the coexistence of these two phases. It is found that Fe-Si nanograins are surrounded by the retained amorphous ferromagnetic phase. Mössbauer spectroscopy measurements show that the nanophase is the D0₃-type Fe-Si phase, which is employed to find the atomic fractions of resonant ⁵⁷Fe atoms in these two phases. The microwave permittivity and permeability spectra of Fe-Cu-Nb-Si-B nanocomposite are measured in the frequency range of 0.5 GHz-10 GHz. Large relative microwave permeability values are obtained. The results show that the absorber containing the nanocomposite flakes with a volume fraction of 28.59% exhibits good microwave absorption properties. The reflection loss of the absorber is less than -10 dB in a frequency band of 1.93 GHz-3.20 GHz.

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A simple encapsulation method for organic optoelectronic devices

孙倩倩, 安桥石, 张福俊

2014 (8): 83302-083302. doi: 10.1088/1674-1056/23/8/083302

摘要 ( 738 )

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The performances of organic optoelectronic devices, such as organic light emitting diodes and polymer solar cells, have rapidly improved in the past decade. The stability of an organic optoelectronic device has become a key problem for further development. In this paper, we report one simple encapsulation method for organic optoelectronic devices with a parafilm, based on ternary polymer solar cells (PSCs). The power conversion efficiencies (PCE) of PSCs with and without encapsulation decrease from 2.93% to 2.17% and from 2.87% to 1.16% after 168-hours of degradation under an ambient environment, respectively. The stability of PSCs could be enhanced by encapsulation with a parafilm. The encapsulation method is a competitive choice for organic optoelectronic devices, owing to its low cost and compatibility with flexible devices.

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Production of CH (A²Δ) by multi-photon dissociation of (CH₃)₂CO, CH₃NO₂, CH₂Br₂, and CHBr₃ at 213 nm

李胜强, 许亮, 陈扬骎, 邓联忠, 印建平

2014 (8): 83701-083701. doi: 10.1088/1674-1056/23/8/083701

摘要 ( 589 )

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In order to realize electrostatic Stark deceleration of CH radicals and study cold chemistry, the fifth harmonic of a YAG laser is used to prepare CH (A²Δ) molecules through using the multi-photon dissociation of (CH₃)₂CO, CH₃NO₂, CH₂Br₂, and CHBr₃ at ~213 nm. The CH product intensity is measured by using the emission spectrum of CH (A²Δ→X²Π). The dependence of fluorescence intensity on laser power is studied, and the probable dissociation channels are analyzed. The relationship between the fluorescence intensity and some parameters, such as the temperature of the beam source, stagnation pressure, and the time delay between the opening of pulse valve and the photolysis laser, are also studied. The influence of three different carrier gases on CH signal intensity is investigated. The vibrational and rotational temperatures of the CH (A²Δ) product are obtained by comparing experimental data with the simulated ones from the LIFBASE program.

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High refractive index sensitivity sensing in gold nanoslit arrays

袁浚, 阚强, 耿照新, 解意洋, 王春霞, 陈弘达

2014 (8): 84201-084201. doi: 10.1088/1674-1056/23/8/084201

摘要 ( 723 )

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The extraordinary optical transmission (EOT) phenomenon of nano-periodic aperture array in metallic film has been widely investigated and used in biosensors. The surface plasmon resonance and cavity mode in some periodic nanostructures, such as nanohole and nanoslit, cause EOTs at certain wavelengths. This resonance wavelength is sensitive to the refractive index on the surface of periodic nanostructures. Therefore, the metallic nanostructures are expected to be good sensing elements. The sensing performances of gold nanoslit arrays are experimentally and theoretically investigated. Three-dimensional finite difference time domain (FDTD) simulations are utilized to explore their transmission spectra and steady-state field intensity distributions. The electron beam evaporation, electron beam lithography, and ion milling are applied to the gold nanoslit arrays with different widths and periods. The sensing performances of the gold nanoslit array are characterized via transmission spectra in four kinds of refractive index samples. The highest sensitivity reaches 726 nm/RIU when the width of the gold nanoslit array is 38.5 nm.

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Relation between Airy beams and triple-cusp beams

任志君, 李晓东, 金洪震, 陈晨, 吴疆苗

2014 (8): 84202-084202. doi: 10.1088/1674-1056/23/8/084202

摘要 ( 539 )

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Airy beams and triple-cusp beams are two kinds of accelerating beams. The propagation characteristics and internal topological structures of accelerating Airy beams are well understood because of the developed mathematical theory about Airy function. However, limited information is available about the optical characteristics of accelerating triple-cusp beams. In this work, the relationship between Airy beams and triple-cusp beams is examined theoretically and experimentally. Results reveal some important optical characteristics of triple-cusp beams based on the optical characteristics of Airy beams. These findings are expected to provide a foundation for future applications of triple-cusp beams.

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Electronic and optical properties of TiO₂ and its polymorphs by Z-scan method

S. Divya, V P N Nampoori, P Radhakrishnan, A Mujeeb

2014 (8): 84203-084203. doi: 10.1088/1674-1056/23/8/084203

摘要 ( 689 )

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TiO₂ is a material which has attracted considerable attention from the scientific community for its innumerable properties. TiO₂ is known to exist in nature in three different crystalline structures: rutile, anatase, and brookite. Anatase and rutile TiO₂ films have been widely characterized for their potential applications in solar cells, self-cleaning coatings, and photocatalysis. In the present report, the third-order nonlinear susceptibilities of TiO₂ and its polymorphs, anatase, and rutile, prepared by the sol-gel technique followed by heat treatment are investigated using the Z-scan technique at a wavelength of 532 nm with a duration of 7 ns. Imaginary and real values of χ⁽³⁾ for amorphous, anatase, and rutile are also calculated and found to be 5× 10^-19 m²/V², 27× 10^-19 m²/V², 19× 10^-19 m²/V², respectively. It is found that the values of the optical constants of amorphous TiO₂ after heat treatment vary considerably. It is assumed that this could be due to the variation in the electronic structure of TiO₂ synchronous with the formation of its polymorphs, anatase, and rutile. Amorphous TiO₂ is marked by the localization of the tail states near the band gap, whereas its crystalline counterparts are characterized by completely delocalized tail states.

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Large phase shift of spatial soliton in lead glass by cross-phase modulation in pump-signal geometry

寿倩, 刘东文, 张翔, 胡巍, 郭旗

2014 (8): 84204-084204. doi: 10.1088/1674-1056/23/8/084204

摘要 ( 644 )

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We investigate the co-propagation of a strong pump beam and a weak signal beam in lead glass, and find that the large phase shift of the strongly nonlocal spatial optical soliton (SNSOS) can be realized via cross-phase modulation. The theoretical study suggests a synchronous propagation of the pump SNSOS and the signal SNSOS under the required initial condition. A π-phase shift of the signal SNSOS is experimentally obtained by changing the power of the pump SNSOS by about 13 mW around the soliton critical power, which agrees qualitatively with our theoretical prediction. The ratio of the phase shift rate of the signal SNSOS to that of the pump SNSOS shows a close match to the reciprocal of the ratio between their wavelengths.

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A new kind of superimposing morphology for enhancing the light scattering in thin film silicon solar cells：Combining random and periodic structure

黄振华, 张建军, 倪牮, 王昊, 赵颖

2014 (8): 84205-084205. doi: 10.1088/1674-1056/23/8/084205

摘要 ( 615 )

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In this article, a new type of superimposing morphology comprised of a periodic nanostructure and a random structure is proposed for the first time to enhance the light scattering in silicon-based thin film solar cells. According to the framework of the Reyleigh-Sommerfeld diffraction algorithm and the experimental results of random morphologies, we analyze the light-scattering properties of four superimposing morphologies and compare them with the individual morphologies in detail. The results indicate that the superimposing morphology can offer a better light trapping capacity, owing to the coexistence of the random scattering mechanism and the periodic scattering mechanism. Its scattering property will be dominated by the individual nanostructures whose geometrical features play the leading role.

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Multipole resonance in the interaction of a spherical Ag nanoparticle with an emitting dipole

刘加东, 宋峰, 张俊, 刘淑静, 王凤箫, 王立超

2014 (8): 84206-084206. doi: 10.1088/1674-1056/23/8/084206

摘要 ( 639 )

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The effect of multipole resonance in the interaction between a spherical metallic nanoparticle (MNP) and an emitting dipole is studied with the Mie theory. The results show that the absorption peak of the MNP with respect to the field of the emitting dipole is blue-shifted with the decrease of the spacing between MNP and emitting dipole due to the enhanced multipole resonance. At a short distance, the enhanced multipole terms of scattering are not obvious compared with the dipole term. For the decay rate of the emitting dipole, multipole resonance brings about the enhancement of it largely at short spacing. For the radiative decay rate, the behavior is quite different. The dipole term is dominant at a short spacing, and the multipole term is dominant at a larger spacing.

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Heralded linear optical quantum Fredkin gate based on one auxiliary qubit and one single photon detector

朱畅华, 曹鑫, 权东晓, 裴昌幸

2014 (8): 84207-084207. doi: 10.1088/1674-1056/23/8/084207

摘要 ( 731 )

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Linear optical quantum Fredkin gate can be applied to quantum computing and quantum multi-user communication networks. In the existing linear optical scheme, two single photon detectors (SPDs) are used to herald the success of the quantum Fredkin gate while they have no photon count. But analysis results show that for non-perfect SPD, the lower the detector efficiency, the higher the heralded success rate by this scheme is. We propose an improved linear optical quantum Fredkin gate by designing a new heralding scheme with an auxiliary qubit and only one SPD, in which the higher the detection efficiency of the heralding detector, the higher the success rate of the gate is. The new heralding scheme can also work efficiently under a non-ideal single photon source. Based on this quantum Fredkin gate, large-scale quantum switching networks can be built. As an example, a quantum Beneš network is shown in which only one SPD is used.

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Experimental study on the Stokes effect in disordered birefringent microstructure fibers

赵原源, 周桂耀, 李建设, 张志远, 韩颖

2014 (8): 84208-084208. doi: 10.1088/1674-1056/23/8/084208

摘要 ( 874 )

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In this paper, a 120-fs pulse transmission experiment is carried out using disordered birefringent microstructure fibers with cladding ventages. Through this experiment, it is found for the first time that remarkable Stokes and anti-Stokes waves can also be produced when the central wavelength of the incident pulse is in the normal dispersion regime of the microstructure fiber. The generation of the two waves can be explained by the four-wave mixing phase matching theory. Properties of the two waves under the action of femtosecond laser pulses with different parameters are studied. The results show that the central wavelength of anti-Stokes waves and Stokes waves produced under the two orthogonal polarization states shift by 63 nm and 160 nm, respectively. The strengths and central positions of the two waves in birefringent fibers can be controlled by adjusting the phase match condition and the polarization directions of incident pulses.

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Broadband energy harvesting via magnetic coupling between two movable magnets

樊康旗, 徐春辉, 王卫东, 方阳

2014 (8): 84501-084501. doi: 10.1088/1674-1056/23/8/084501

摘要 ( 787 )

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Harvesting energy from ambient mechanical vibrations by the piezoelectric effect has been proposed for powering microelectromechanical systems and replacing batteries that have a finite life span. A conventional piezoelectric energy harvester (PEH) is usually designed as a linear resonator, and suffers from a narrow operating bandwidth. To achieve broadband energy harvesting, in this paper we introduce a concept and describe the realization of a novel nonlinear PEH. The proposed PEH consists of a primary piezoelectric cantilever beam coupled to an auxiliary piezoelectric cantilever beam through two movable magnets. For predicting the nonlinear response from the proposed PEH, lumped parameter models are established for the two beams. Both simulation and experiment reveal that for the primary beam, the introduction of magnetic coupling can expand the operating bandwidth as well as improve the output voltage. For the auxiliary beam, the magnitude of the output voltage is slightly reduced, but additional output is observed at off-resonance frequencies. Therefore, broadband energy harvesting can be obtained from both the primary beam and the auxiliary beam.

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Heat transfer analysis in the flow of Walters’B fluid with a convective boundary condition

T. Hayat, Sadia Asad, M. Mustafa, Hamed H. Alsulami

2014 (8): 84701-084701. doi: 10.1088/1674-1056/23/8/084701

摘要 ( 662 )

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Radiative heat transfer in the steady two-dimensional flow of Walters' B fluid with a non-uniform heat source/sink is investigated. An incompressible fluid is bounded by a stretching porous surface. The convective boundary condition is used for the thermal boundary layer problem. The relevant equations are first simplified under usual boundary layer assumptions and then transformed into a similar form by suitable transformations. Explicit series solutions of velocity and temperature are derived by the homotopy analysis method (HAM). The dimensionless velocity and temperature gradients at the wall are calculated and discussed.

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Simulation of fluid-structure interaction in a microchannel using the lattice Boltzmann method and size-dependent beam element on a graphics processing unit

Vahid Esfahanian, Esmaeil Dehdashti, Amir Mehdi Dehrouye-Semnani

2014 (8): 84702-084702. doi: 10.1088/1674-1056/23/8/084702

摘要 ( 598 )

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Fluid-structure interaction (FSI) problems in microchannels play a prominent role in many engineering applications. The present study is an effort toward the simulation of flow in microchannel considering FSI. The bottom boundary of the microchannel is simulated by size-dependent beam elements for the finite element method (FEM) based on a modified couple stress theory. The lattice Boltzmann method (LBM) using the D2Q13 LB model is coupled to the FEM in order to solve the fluid part of the FSI problem. Because of the fact that the LBM generally needs only nearest neighbor information, the algorithm is an ideal candidate for parallel computing. The simulations are carried out on graphics processing units (GPUs) using computed unified device architecture (CUDA). In the present study, the governing equations are non-dimensionalized and the set of dimensionless groups is exhibited to show their effects on micro-beam displacement. The numerical results show that the displacements of the micro-beam predicted by the size-dependent beam element are smaller than those by the classical beam element.

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Compound sawtooth in EAST LHCD plasma：An experimental study

徐立清, 胡立群, 陈开云, 李妙辉

2014 (8): 85201-085201. doi: 10.1088/1674-1056/23/8/085201

摘要 ( 610 )

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A compound sawtooth with an incomplete relaxation was observed in EAST's lower hybrid current drive (LHCD) plasma. The sub-crash phase of the compound sawtooth corresponds to a longer-lasting and slower-growing 1/1 mode. Based on the two-dimensional (2D) SXR tomography, the time-dependent 2D image of a compound sawtooth crash is obtained. The island produced during a resistive internal kink mode is observed in the all crash phases of the compound sawtooth. The destabilization of 1/1 long-lasting saturated 1/1 mode is related to the current driven by the LHCD near the q=1 surface.

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Simulation of nanoparticle coagulation in radio-frequency capacitively coupled C₂H₂ discharges

刘相梅, 李奇楠, 徐翔

2014 (8): 85202-085202. doi: 10.1088/1674-1056/23/8/085202

摘要 ( 586 )

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A self-consistent fluid model is employed to investigate the coagulation stage of nanoparticle formation, growth, charging, and transport in a radio-frequency capacitively coupled parallel-plate acetylene (C₂H₂) discharge. In our simulation, the distribution of neutral species across the electrode gap is determined by mass continuity, momentum balance, and energy balance equations. Since a thermal gradient in the gas temperature induced by the flow of the neutral gas, a careful study of the thermophoretic force on the spatial distribution of the nanoparticle density profiles is indispensable. In the present paper, we mainly focus on the influences of the gas flow rate, voltage, and gas pressure on the spatial distribution of the nanoparticle density. It appears that the resulting density profile of the 10-nm particles experiences a significant shift towards the upper showerhead electrode once the neutral equations are applied, and a serious shift is observed when increasing the gas flow rate. Thus, the flow of neutral gas can strongly influence the spatial distribution of the particles in the plasma.

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Shadowgraph investigation of plasma shock wave evolution from Al target under 355-nm laser ablation

刘天航, 郝作强, 高勋, 刘泽昊, 林景全

2014 (8): 85203-085203. doi: 10.1088/1674-1056/23/8/085203

摘要 ( 857 )

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The propagation of a plasma shock wave generated from an Al target surface ablated by a nanosecond Nd:YAG laser operating at 355 nm in air is investigated at the different focusing positions of the laser beam by using a time-resolved shadowgraph imaging technique. The results show that in the case of a target surface set at the off-focus position, the condition of the focal point behind or in front of the target surface greatly influences the evolution of an Al plasma shock wave, and an ionization channel forms in the case of the focal point set in front of the target surface. Moreover, it is found that the shadowgraph with the evolution time around 100 ns shows that a protrusion appears at the front tip of the shock wave if the focal point is at the target surface. In addition, the calculated results of the expanding velocity of the shock wave front, the mass density, and pressure just behind the shock wave front are presented based on the shadowgraphs.

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Synthesis of boron, nitrogen co-doped porous carbon from asphaltene for high-performance supercapacitors

周颖, 王道龙, 王春雷, 金新新, 邱介山

2014 (8): 86101-086101. doi: 10.1088/1674-1056/23/8/086101

摘要 ( 974 )

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Oxidized asphaltene (OA), a thermosetting material with plenty of functional groups, is synthesized from asphaltene (A) using HNO₃/H₂SO₄ as the oxidizing agent. Boron, nitrogen co-doped porous carbon (BNC-OA) is prepared by carbonization of the mixture of boric acid and OA at 1173 K in an argon atmosphere. X-ray photoelectron spectroscopy (XPS) characterization reveals that the BNC-OA has a nitrogen content of 3.26 at.% and a boron content of 1.31 at.%, while its oxidation-free counterpart (BNC-SA) has a nitrogen content of 1.61 at.% and a boron content of 3.02 at.%. The specific surface area and total pore volume of BNC-OA are 1103 m²·g^-1 and 0.921 cm³·g^-1, respectively. At a current density of 0.1 A·g^-1, the specific capacitance of BNC-OA is 335 F·g^-1 and the capacitance retention can still reach 83% at 1 A·g^-1. The analysis shows that the superior electrochemical performance of the BNC-OA is attributed to the pseudocapacitance behavior of surface heteroatom functional groups and an abundant pore-structure. Boron, nitrogen co-doped porous carbon is a promising electrode material for supercapacitors.

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Enhanced photoluminescence of CdSe quantum dots by the coupling of Ag nanocube and Ag film

蒋童童, 邵伟佳, 尹乃强, 刘玲, 宋江鲁奇, 朱立新, 许小亮

2014 (8): 86102-086102. doi: 10.1088/1674-1056/23/8/086102

摘要 ( 960 )

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The coupling of local surface plasmon (LSP) of nanoparticle and surface plasmon (SP) mode produced by metal film can lead to the enhanced electromagnetic field, which has an important application in enhancing the fluorescence of quantum dots (QDs). Herein, the Ag nanocube and Ag film are used to enhance the fluorescence of CdSe QDs. The enhancement is found to relate to the sizes of the Ag nanocube and the thickness of the Ag film. Moreover, we also present the fluorescence enhancement caused by only SP. The result shows that the coupling between metal nanoparticles and metal film can realize larger field enhancement. Numerical simulation verifies that a nanocube can localize a strong electric field around its corner. All the results indicate that the fluorescence of QDs can be efficiently improved by optimizing the parameters of Ag film and Ag cubes.

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Two-coupled structural modulations in charge-density-wave state of SrPt₂As₂ superconductor

王莉, 王臻, 施洪龙, 陈震, 蒋复国, 田焕芳, 杨槐馨, 房爱芳, 王楠林, 李建奇

2014 (8): 86103-086103. doi: 10.1088/1674-1056/23/8/086103

摘要 ( 610 )

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Transmission electron microscopy (TEM) study of SrPt₂As₂ reveals two incommensurate modulations appearing in the charge-density-wave (CDW) state below T_CDW ≈ 470 K. These two structural modulations can be well explained in terms of condensations of two-coupled phonon modes with wave vectors of q₁= 0.62a^* on the a^*-b^* plane and q₂= 0.23a^* on the a^*-c^* plane. The atomic displacements occur along the b-axis direction for q₁ and along the c-axis direction for q₂, respectively. Moreover, the correlation between q₁ and q₂ can be generally written as q₁= (q₂+a^*)/2 in the CDW state, suggesting the presence of essential coupling between q₁ and q₂. A small fraction of Ir doping on the Pt site in Sr(Pt_1-xIr_x)₂As₂ (x ≤ 0.06) could moderately change these CDW modulations and also affect their superconductivities.

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Simulation of temporal characteristics of ion-velocity susceptibility to single event upset effect

耿超, 习凯, 刘天奇, 古松, 刘杰

2014 (8): 86104-086104. doi: 10.1088/1674-1056/23/8/086104

摘要 ( 681 )

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Using a Monte Carlo simulation tool of the multi-functional package for SEEs Analysis (MUFPSA), we study the temporal characteristics of ion-velocity susceptibility to the single event upset (SEU) effect, including the deposited energy, traversed time within the device, and profile of the current pulse. The results show that the averaged dposited energy decreases with the increase of the ion-velocity, and incident ions of ²⁰⁹Bi have a wider distribution of energy deposition than ¹³²Xe at the same ion-velocity. Additionally, the traversed time presents an obvious decreasing trend with the increase of ion-velocity. Concurrently, ion-velocity certainly has an influence on the current pulse and then it presents a particular regularity. The detailed discussion is conducted to estimate the relevant linear energy transfer (LET) of incident ions and the SEU cross section of the testing device from experiment and simulation and to critically consider the metric of LET.

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Microwave ferromagnetic properties of as-deposited Co₂FeSi Heusler alloy films prepared by oblique sputtering

曹晓琴, 李山东, 蔡志义, 杜洪磊, 薛倩, 高小洋, 谢施名

2014 (8): 86201-086201. doi: 10.1088/1674-1056/23/8/086201

摘要 ( 690 )

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The Co₂FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co₂FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe-330 Oe (1 Oe=79.5775 A·m^-1), and low coercivities in a range of 5 Oe-28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co₂FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.

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Study on lattice vibrational properties and Raman spectra of Bi₂Te₃ based on density-functional perturbation theory

冯松科, 李双明, 傅恒志

2014 (8): 86301-086301. doi: 10.1088/1674-1056/23/8/086301

摘要 ( 639 )

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We present a variational density-functional perturbation theory (DFPT) to investigate the lattice dynamics and vibrational properties of single crystal bismuth telluride material. The phonon dispersion curves and phonon density of states (DOS) of the material were obtained. The phonon dispersions are divided into two fields by a phonon gap. In the lower field, atomic vibrations of both Bi and Te contribute to the DOS. In the higher field, most contributions come from Te atoms. The calculated Born effective charges and dielectric constants reveal a great anisotropy in the crystal. The largest Born effective charge generates a significant dynamic charge transferring along the c axis. By DFPT calculation, the greatest LO-TO splitting takes place in the infrared phonon modes and reaches 1.7 THz in the Brillouin zone center. The Raman spectra and peaks corresponding to respective atomic vibration modes were found to be in good agreement with the experimental data.

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Decline of nucleation in the heating process with a high heating rate

杨高林, 林鑫, 宋梦华, 胡桥, 汪志太, 黄卫东

2014 (8): 86401-086401. doi: 10.1088/1674-1056/23/8/086401

摘要 ( 668 )

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The effect of the heating rate on the nucleation of metallic glass in a rapid heating process starting from the glass transition temperature is investigated. The critical nucleus radius increases with the increase of the temperature of the undercooling liquid. If the increment rate of the critical nucleus radius, owing to the heating process, is higher than the growth rate of the nuclei, the nuclei generated at the low temperature will become the embryos at the high temperature. This means that the high heating rate can make no nucleation happen in the heating process. In consideration of the interfacial energy, the growth rate of the nuclei increases with the increase of their size and the growth rate of the critical nucleus is zero. Thus, the lower heating rate can also make the nuclei decline partially. Finally, this theory is used to analyze the nucleation process during laser remelting metallic glass.

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Influence of defects in SiC (0001) on epitaxial graphene

郭钰, 郭丽伟, 芦伟, 黄郊, 贾玉萍, 孙伟, 李治林, 王逸非

2014 (8): 86501-086501. doi: 10.1088/1674-1056/23/8/086501

摘要 ( 649 )

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Defects in silicon carbide (SiC) substrate are crucial to the properties of the epitaxial graphene (EG) grown on it. Here we report the effect of defects in SiC on the crystalline quality of EGs through comparative studies of the characteristics of the EGs grown on SiC (0001) substrates with different defect densities. It is found that EGs on high quality SiC possess regular steps on the surface of the SiC and there is no discernible D peak in its Raman spectrum. Conversely, the EG on the SiC with a high density of defects has a strong D peak, irregular stepped morphology and poor uniformity in graphene layer numbers. It is the defects in the SiC that are responsible for the irregular stepped morphology and lead to the small domain size in the EG.

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Dye-sensitized solar cells：Atomic scale investigation of interface structure and dynamics

马薇, 张帆, 孟胜

2014 (8): 86801-086801. doi: 10.1088/1674-1056/23/8/086801

摘要 ( 674 )

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Recent progress in dye-sensitized solar cells (DSC) research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto TiO₂, ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron-hole recombination. Advanced experimental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and opportunities for further improvement of dye solar cells are presented.

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Adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co (200)：A first-principles density-functional study

乔靓, 王淑敏, 张晓明, 胡小颖, 曾毅, 郑伟涛

2014 (8): 86802-086802. doi: 10.1088/1674-1056/23/8/086802

摘要 ( 798 )

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First-principles calculations based on density functional theory are used to investigate the adsorptions and diffusions of carbon atoms on the surface and in the subsurface of Co (200). The preferred site for the carbon atom on the surface is the hollow site, and the preferred site in the subsurface is the octahedral site. There is charge transfer from the surface to the adsorbed carbon atom, and for the most favorable adsorbed structure the charge transfer is largest. Moreover, the energy barriers for the diffusions of carbon atoms on the surface and from the surface into the subsurface and then back to the surface are calculated in detail. The results indicate that the energy barrier for the diffusion of carbon atoms on the surface is comparable to that from the subsurface to the surface. The results imply that both the direct surface nucleation and the surface segregation from Co bulk can be observed in the chemical vapor deposition growth of graphene on Co (200) substrate, which can gain a new insight into the growth mechanism of graphene.

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Electronic structures and optical properties of Ⅲ_A-doped wurtzite Mg_0.25Zn_0.75O

郑树文, 何苗, 李述体, 章勇

2014 (8): 87101-087101. doi: 10.1088/1674-1056/23/8/087101

摘要 ( 632 )

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The energy band structures, density of states, and optical properties of Ⅲ_A-doped wurtzite Mg_0.25Zn_0.75O (Ⅲ_A=Al, Ga, In) are investigated by a first-principles method based on the density functional theory. The calculated results show that the optical bandgaps of Mg_0.25Zn_0.75O:Ⅲ_A are larger than those of Mg_0.25Zn_0.75O because of the Burstein-Moss effect and the bandgap renormalization effect. The electron effective mass values of Mg_0.25Zn_0.75O:Ⅲ_A are heavier than those of Mg_0.25Zn_0.75O, which is in agreement with the previous experimental result. The formation energies of MgZnO:Al and MgZnO:Ga are smaller than that of MgZnO:In, while their optical bandgaps are larger, so MgZnO:Al and MgZnO:Ga are suitable to be fabricated and used as transparent conductive oxide films in the ultra-violet (UV) and deep UV optoelectronic devices.

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Theory of phonon-modulated electron spin relaxation time based on the projection–reduction method

Nam Lyong Kang, Sang Don Choi

2014 (8): 87102-087102. doi: 10.1088/1674-1056/23/8/087102

摘要 ( 577 )

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This paper introduces a new method for a formula for electron spin relaxation time of a system of electrons interacting with phonons through phonon-modulated spin-orbit coupling using the projection-reduction method. The phonon absorption and emission processes as well as the photon absorption and emission processes in all electron transition processes can be explained in an organized manner, and the result can be represented in a diagram that can provide intuition for the quantum dynamics of electrons in a solid. The temperature (T) dependence of electron spin relaxation times (T₁) in silicon is T₁∝ T^-1.07 at low temperatures and T₁∝ T^-3.3 at high temperatures for acoustic deformation constant P_ad=1.4× 10⁷ eV and optical deformation constant P_od=4.0×10¹⁷ eV/m. This means that electrons are scattered by the acoustic deformation phonons at low temperatures and optical deformation phonons at high temperatures, respectively. The magnetic field (B) dependence of the relaxation times is T₁∝ B^-2.7 at 100 K and T₁∝ B^-2.3 at 150 K, which nearly agree with the result of Yafet, T₁∝ B^-3.0～ B^-2.5.

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Investigations of the half-metallic behavior and the magnetic and thermodynamic properties of half-Heusler CoMnTe and RuMnTe compounds：A first-principles study

T. Djaafri, A. Djaafri, A. Elias, G. Murtaza, R. Khenata, R. Ahmed, S. Bin Omran, D. Rached

2014 (8): 87103-087103. doi: 10.1088/1674-1056/23/8/087103

摘要 ( 689 )

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First-principles spin-polarized density functional theory (DFT) investigations of the structural, electronic, magnetic, and thermodynamics characteristics of the half-Heusler, CoMnTe and RuMnTe compounds are carried out. Calculations are accomplished within a state of the art full-potential (FP) linearized (L) augmented plane wave plus a local orbital (APW+lo) computational approach framed within DFT. The generalized gradient approximation (GGA) parameterized by Perdew, Burke, and Ernzerhof (PBE) is implemented as an exchange correlation functional as a part of the total energy calculation. From the analysis of the calculated electronic band structure as well as the density of states for both compounds, a strong hybridization between d states of the higher valent transition metal (TM) atoms (Co, Ru) and lower valent TM atoms of (Mn) is observed. Furthermore, total and partial density of states (PDOS) of the ground state and the results of spin magnetic moments reveal that these compounds are both stable and ideal half-metallic ferromagnetic. The effects of the unit cell volume on the magnetic properties and half-metallicity are crucial. It is worth noting that our computed results of the total spin magnetic moments, for CoMnTe equal to 4 μB and 3 μB per unit cell for RuMnTe, nicely follow the rule μ_tot=Z_t-18. Using the quasi-harmonic Debye model, which considers the phononic effects, the effecs of pressure P and temperature T on the lattice parameter, bulk modulus, thermal expansion coefficient, Debye temperature, and heat capacity for these compounds are investigated for the first time.

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An improved EEHEMT model for kink effect on AlGaN/GaN HEMT

曹梦逸, 卢阳, 魏家行, 陈永和, 李卫军, 郑佳欣, 马晓华, 郝跃

2014 (8): 87201-087201. doi: 10.1088/1674-1056/23/8/087201

摘要 ( 915 )

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In this paper, a new current expression based on both the direct currect (DC) characteristics of the AlGaN/GaN high election mobility transistor (HEMT) and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the AlGaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of I-V, S-parameter, and radio frequency (RF) large-signal characteristics are compared for a self-developed on-wafer AlGaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-μm wide (Such an AlGaN/GaN HEMT is denoted as AlGaN/GaN HEMT (10× 125 μm)). The improved large signal model simulates the I-V characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data.

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Valley selection rule in a Y-shaped zigzag graphene nanoribbon junction

张林, 汪军

2014 (8): 87202-087202. doi: 10.1088/1674-1056/23/8/087202

摘要 ( 660 )

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The valley valve effect was predicted in a straight zigzag graphene nanoribbon (ZGR) p/n junction. In this work, we address a possible valley selection rule in a Y-shaped ZGR junction. By modeling the system as a three-terminal device and calculating the conductance spectrum, we found that the valley valve effect could be preserved in the system and the Y-shaped connection does not mix the valley index or the pseudoparities of quasiparticles. It is also shown that the Y-shaped ZGR device can be used to separate spins in real space according to the unchanged valley valve effect. Our finding might pave a way to manipulate and detect spins in a multi-terminal graphene-based spin device.

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Synthesis and electrical conductivity of nanocrystalline tetragonal FeS

曾树林, 王辉宪, 董成

2014 (8): 87203-087203. doi: 10.1088/1674-1056/23/8/087203

摘要 ( 742 )

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A convenient method for synthesis of tetragonal FeS using iron powder as iron source, is reported. Nanocrystalline tetragonal FeS samples were successfully synthesized by reacting metallic iron powder with sodium sulfide in acetate buffer solution. The obtained sample is single-phase tetragonal FeS with lattice parameters a = 0.3767 nm and c =0.5037 nm, as revealed by X-ray diffraction. The sample consists of flat nanosheets with lateral dimensions from 20 nm up to 200 nm and average thickness of about 20 nm. We found that tetragonal FeS is a fairly good conductor from the electrical resistivity measurement on a pellet of the nanosheets. The temperature dependence of conductivity of the pellet was well fitted using an empirical equation wherein the effect of different grain boundaries was taken into consideration. This study provides a convenient, economic way to synthesize tetragonal FeS in a large scale and reports the first electrical conductivity data for tetragonal FeS down to liquid helium temperature.

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Phase transformation in Mg–Sb₃Te thin films

李军建, 王国祥, 陈益敏, 沈祥, 聂秋华, 吕业刚, 戴世勋, 徐铁锋

2014 (8): 87301-087301. doi: 10.1088/1674-1056/23/8/087301

摘要 ( 717 )

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Mg-doped Sb₃Te films are proposed to improve the performance of phase-change memory (PCM). We prepare Mg-doped Sb₃Te films and investigate their crystallization behaviors, structural, optical and electrical properties. We find that Mg-doping can increase the crystallization temperature, enhance the activation energy, and improve the 10-year data retention of Sb₃Te. Especially Mg_25.19(Sb₃Te)_74.81 shows higher T_c (～ 190 ℃) and larger E_a (～ 3.49 eV), which results in a better data retention maintaining for 10 yr at ～ 112 ℃. Moreover R_a/R_c value is also improved. These excellent properties make Mg-Sb-Te material a promising candidate for the phase-change memory (PCM).

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Stability and electronic structure studies of LaAlO₃/SrTiO₃ (110) heterostructures

杜颜伶, 王春雷, 李吉超, 徐攀攀, 张新华, 刘剑, 苏文斌, 梅良模

2014 (8): 87302-087302. doi: 10.1088/1674-1056/23/8/087302

摘要 ( 675 )

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The first-principles calculations are employed to investigate the stability, magnetic, and electrical properties of the oxide heterostructure of LaAlO₃/SrTiO₃ (110). By comparing their interface energies, it is obtained that the buckled interface is more stable than the abrupt interface. This result is consistent with experimental observation. At the interface of LaAlO₃/SrTiO₃ (110) heterostructure, the Ti-O octahedron distortions cause the Ti t_{m 2g} orbitals to split into the two-fold degenerate d_xz/d_yz and nondegenerate d_xy orbitals. The former has higher energy than the latter. The partly filled two-fold degenerate t_2g orbitals are the origin of two-dimensional electron gas, which is confined at the interface. Lattice mismatch between LaAlO₃ and SrTiO₃ leads to ferroelectric-like lattice distortions at the interface, and this is the origin of spin-splitting of Ti 3d electrons. Hence the magnetism appears at the interface of LaAlO₃/SrTiO₃ (110).

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Fano-like resonance characteristics of asymmetric Fe₂O₃@Au core/shell nanorice dimer

王彬兵, 周骏, 张昊鹏, 陈金平

2014 (8): 87303-087303. doi: 10.1088/1674-1056/23/8/087303

摘要 ( 704 )

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A geometrical configuration of Fe₂O₃/Au core-shell nanorice dimer is proposed and its multipolar plasmon Fano-like resonance characteristics are theoretically investigated by generalizing the plasmon hybridization model of individual nanorice to the bright and dark modes of the nanorice dimer. Under the irradiation of polarization light, the extinction spectra of the nanorice dimer are numerically simulated by using the finite element method (FEM). Our studies show that the Fano-like resonance of the nanorice dimer results in an asymmetric line shape of the Fano dip in the extinction spectrum which can be controlled by varying the structure parameters of the nanorice dimer. Meanwhile, there is a giant field enhancement at the gap between the two nanorices on account of the plasmonic coupling in the nanorice dimer. The aforementioned two characteristics of the nanorice dimer are useful for plasmon-induced transparency and localized surface plasmon resonance sensors.

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Bipolar resistance switching in the fully transparent BaSnO₃-based memory device

张婷, 殷江, 赵高峰, 张伟风, 夏奕东, 刘治国

2014 (8): 87304-087304. doi: 10.1088/1674-1056/23/8/087304

摘要 ( 542 )

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The fully transparent indium-tin-oxide/BaSnO₃/F-doped SnO₂ devices that show a stable bipolar resistance switching effect are successfully fabricated. In addition to the transmittance being above 87% for visible light, an initial forming process is unnecessary for the production of transparent memory. Fittings to the current-voltage curves reveal the interfacial conduction in the devices. The first-principles calculation indicates that the oxygen vacancies in cubic BaSnO₃ will form the defective energy level below the bottom of conduction band. The field-induced resistance change can be explained based on the change of the interfacial Schottky barrier, due to the migration of oxygen vacancies in the vicinity of the interface. This work presents a candidate material BaSnO₃ for the application of resistive random access memory to transparent electronics.

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A two-dimensional fully analytical model with polarization effect for off-state channel potential and electric field distributions of GaN-based field-plated high electron mobility transistor

毛维, 佘伟波, 杨翠, 张超, 张进成, 马晓华, 张金风, 刘红侠, 杨林安, 张凯, 赵胜雷, 陈永和, 郑雪峰, 郝跃

2014 (8): 87305-087305. doi: 10.1088/1674-1056/23/8/087305

摘要 ( 627 )

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In this paper, we present a two-dimensional (2D) fully analytical model with consideration of polarization effect for the channel potential and electric field distributions of the gate field-plated high electron mobility transistor (FP-HEMT) on the basis of 2D Poisson's solution. The dependences of the channel potential and electric field distributions on drain bias, polarization charge density, FP structure parameters, AlGaN/GaN material parameters, etc. are investigated. A simple and convenient approach to designing high breakdown voltage FP-HEMTs is also proposed. The validity of this model is demonstrated by comparison with the numerical simulations with Silvaco-Atlas. The method in this paper can be extended to the development of other analytical models for different device structures, such as MIS-HEMTs, multiple-FP HETMs, slant-FP HEMTs, etc.

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Spin-excited states and rectification in an organic spin rectifier

左梦莹, 胡贵超, 李营, 任俊峰, 王传奎

2014 (8): 87306-087306. doi: 10.1088/1674-1056/23/8/087306

摘要 ( 707 )

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Spin-excited states in an asymmetric magnetic organic co-oligomer diode are investigated theoretically. The results demonstrate that the structural asymmetry of the co-oligomer is modulated by the spin-excited states, which is embodied in the wave functions of the eigenstates as well as the spin density wave. By calculating the transport property, a robust spin-current rectification concomitant with a charge-current rectification is observed in all spin-excited states. However, the current through the diode is suppressed distinctly by the spin-excited states, while the rectification ratios may be reduced or enhanced depending on the bias and the excited spins. The intrinsic mechanism is analyzed from the spin-dependent transmission combined with the change of molecular eigenstates under bias. Finally, the temperature-induced spin excitation is simulated. Significant rectification behavior is obtained even at room temperature.

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Forward and reverse electron transport properties across a CdS/Si multi-interface nanoheterojunction

李勇, 王伶俐, 王小波, 闫玲玲, 苏丽霞, 田永涛, 李新建

2014 (8): 87307-087307. doi: 10.1088/1674-1056/23/8/087307

摘要 ( 699 )

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The electron transport behavior across the interface plays an important role in determining the performance of optoelectronic devices based on heterojunctions. Here through growing CdS thin film on silicon nanoporous pillar array, an untraditional, nonplanar, and multi-interface CdS/Si nanoheterojunction is prepared. The current density versus voltage curve is measured and an obvious rectification effect is observed. Based on the fitting results and model analyses on the forward and reverse conduction characteristics, the electron transport mechanism under low forward bias, high forward bias, and reverse bias are attributed to the Ohmic regime, space-charge-limited current regime, and modified Poole-Frenkel regime respectively. The forward and reverse electrical behaviors are found to be highly related to the distribution of interfacial trap states and the existence of localized electric field respectively. These results might be helpful for optimizing the preparing procedures to realize high-performance silicon-based CdS optoelectronic devices.

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Topological quantum-phase coherence in full counting statistics of transport electrons with two-body interaction

郭小芳, 薛海斌, 梁九卿

2014 (8): 87308-087308. doi: 10.1088/1674-1056/23/8/087308

摘要 ( 538 )

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The full counting statistics of electron transport through two parallel quantum dots with antiparallel magnetic fluxes is investigated as a probe to detect the topological quantum-phase coherence (TQPC), which results in the characteristic oscillation of the zero-frequency cumulants including the shot noise and skewness. We show explicitly the phase transition of cumulant spectrum-patterns induced by the topology change of electron path-loops while the pattern period, which depends only on the topology (or Chern number), is robust against the variation of Coulomb interaction and interdot coupling strengths. Most importantly we report for the first time on a new type of TQPC, which is generated by the two-particle interaction and does not exist in the single-particle wave function interference. Moreover, the accurately quantized peaks of Fano-factor spectrum, which characterize the super- and sub-Poissonian shot noises, are of fundamental importance in technical applications similar to the superconducting quantum interference device.

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In-plane optical spectral weight redistribution in the optimally doped Ba_0.6K_0.4Fe₂As₂ superconductor

许兵, 戴耀民, 肖宏, R. P. S. M. Lobo, 邱祥冈

2014 (8): 87401-087401. doi: 10.1088/1674-1056/23/8/087401

摘要 ( 617 )

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We performed detailed temperature-dependent optical measurements on optimally doped Ba_0.6K_0.4Fe₂As₂ single crystal. We examine the changes of the in-plane optical conductivity spectral weight in the normal state and the evolution of the superconducting condensate in the superconducting state. In the normal state, the low-frequency spectral weight shows a metallic response with an arctan (T) dependence, indicating a T-linear scattering rate behavior for the carriers. A high energy spectral weight transfer associated with the Hund's coupling occurs from the low frequencies below 4000 cm^-1～ 5000 cm^-1 to higher frequencies up to at least 10⁴ cm^-1. Its temperature dependence analysis suggests that the Hund's coupling strength is continuously enhanced as the temperature is reduced. In the superconducting state, the FGT sum rule is conserved according to the spectral weight estimation within the conduction bands, only about 40% of the conduction bands participates in the superconducting condensate indicating that Ba_0.6K_0.4Fe₂As₂ is in dirty limit.

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Fabrication and properties of the meander nanowires based on ultra-thin Nb films

赵璐, 金贻荣, 李洁, 邓辉, 郑东宁

2014 (8): 87402-087402. doi: 10.1088/1674-1056/23/8/087402

摘要 ( 672 )

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We report the fabrication and the study of superconducting properties of ultra-thin Nb superconducting meander nanowires, which can be used as superconducting nanowire single-photon detectors (SNSPDs). The ultra-thin (about 7-nm thick) Nb films are patterned into micro-bridges, and 100-nm wide meander nanowires by using e-beam lithography (EBL). The average transition temperature (T_c) of the nanowires is about 4.8 K and the critical current density j_c is about 2.8× 10⁶ A/cm². Superconducting characteristics of the specimens at different applied magnetic fields up to 8 T (parallel or perpendicular to the specimen) are systematically investigated. The normalized temperature t (=T/T_c) dependences of the parallel critical field (H_c||) for both the micro-bridge and the meander nanowire are almost the same, following the Ginzburg and Landau (GL) formalism for ultra-thin films. However, in perpendicular field and in the vicinity of T_c (>0.95T_c), the critical field H_c⊥ of the nanowire exhibits a down-turn curvature nonlinear temperature dependence while the micro-bridge displays a linear temperature dependence. The nonlinear behavior of H_c⊥ in the nanowire is believed to be due to the fact that in the vicinity of T_c the coherence length becomes larger than the line width. Additionally, the localization of carriers in the nanowire could also contribute to the nonlinear behavior. The resistive transitions could be described by the phase-slip model for quasi-one-dimensional system. Moreover, the hysteresis in I-V curve of the meander nanowires can be illustrated by a simple model of localized normal hotspot maintained by Joule heating.

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Exchange interaction between vortex and antivortex

柳艳, 李化南, 胡勇, 杜安

2014 (8): 87501-087501. doi: 10.1088/1674-1056/23/8/087501

摘要 ( 553 )

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The dynamic properties of interacting vortex-antivortex pairs in thin film are studied by analytical calculations. Analytical expressions for the magnetization vector distribution of vortex-antivortex pairs and the trivortex states are given. The magnetic states of the vortices are treated as having rigid structures, i.e., the vortex maintains its spin distribution when moving. The trajectories of the vortex cores are calculated by the Thiele's equation. It is found that the vortex-antivortex pair rotates around each other when they have opposite polarities, however, vortex and antivortex cores move along straight lines when they have the same polarity. The frequency of the rotation decreases with increasing the distance between the two cores of vortex-antivortex pair, and it has a lower value when a third vortex is introduced.

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Magnetic field control of ferroelectric polarization and magnetization of LiCu₂O₂ compound

齐岩, 杜安

2014 (8): 87502-087502. doi: 10.1088/1674-1056/23/8/087502

摘要 ( 676 )

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A spin model of LiCu₂O₂ compound with ground state of ellipsoidal helical structure is adopted. Taking into account the interchain coupling and exchange anisotropy, we investigate the magnetoelectric properties in a rotating magnetic field and perform the Monte Carlo simulation on a two-dimensional lattice. A prominent anisotropic response is observed in both the magnetization curve and the polarization curve, qualitatively coinciding with the behaviors that are detected in the experiment. In addition, the influences of the magnetic field with various magnitudes on polarization are also explored and analyzed in detail. As the magnetic field increases, a much smoother polarization of angle dependence is exhibited, indicating the strong correlation between the magnetic and ferroelectric orders.

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Large coercivity and unconventional exchange coupling in manganese-oxide-coated manganese–gallium nanoparticles

冯俊宁, 刘伟, 耿殿禹, 马嵩, 余涛, 赵晓天, 代志明, 赵新国, 张志东

2014 (8): 87503-087503. doi: 10.1088/1674-1056/23/8/087503

摘要 ( 589 )

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The microstructures and magnetic properties of nanoparticles, each composed of an antiferromagnetic (AFM) manganese-oxide shell and a ferromagnetic-like core of manganese-gallium (MnGa) compounds, are studied. The core-shell structure is confirmed by transmission electron microscope (TEM). The ferromagnetic-like core contains three kinds of MnGa binary compounds, i.e., ferrimagnetic (FI) D0₂₂-type Mn₃Ga, ferromagnetic (FM) Mn₈Ga₅, and AFM D0₁₉-type Mn₃Ga, of which the first two correspond respectively to a hard magnetic phase and to a soft one. Decoupling effect between these two phases is found at 1ow temperature, which weakens gradually with increasing temperature and disappears above 200 K. The exchange bias (EB) effect is observed simultaneously, which is caused by the exchange coupling between the AFM shell and FM-like core. A large coercivity of 6.96 kOe (1 Oe = 79.5775 A·m^-1) and a maximum EB value of 0.45 kOe are achieved at 300 K and 200 K respectively.

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Influence of magnetic layer thickness on [Fe₈₀Ni₂₀–O/SiO₂]_n multilayer thin films

魏建清, 耿昊, 徐磊, 王来森, 陈远志, 岳光辉, 彭栋梁

2014 (8): 87504-087504. doi: 10.1088/1674-1056/23/8/087504

摘要 ( 802 )

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In the present work, a series of [Fe₈₀Ni₂₀-O/SiO₂]_n multilayer thin films is fabricated using a reactive magnetron sputtering equipment. The thickness of SiO₂ interlayer is fixed at 3 nm, while the thickness values of Fe₈₀Ni₂₀-O magnetic films range from 10 nm to 30 nm. All films present obvious in-plane uniaxial magnetic anisotropy. With increasing the Fe₈₀Ni₂₀-O layer thickness, the saturation magnetization increases slightly and the coercivity becomes larger due to the enlarged grain size, which could weaken the soft magnetic property. The results of high frequency magnetic permeability characterization show that films with thin magnetic layer are more suitable for practical applications. When the thickness of Fe₈₀Ni₂₀-O layer is 10 nm, the multilayer film exhibits the most comprehensive high-frequency magnetic property with a real permeability of 300 in gigahertz range.

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The spin dynamics of the random transverse Ising chain with a double-Gaussian disorder

刘中强, 姜素蓉, 孔祥木

2014 (8): 87505-087505. doi: 10.1088/1674-1056/23/8/087505

摘要 ( 609 )

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The dynamical properties of one-dimensional random transverse Ising model (RTIM) with a double-Gaussian disorder is investigated by the recursion method. Based on the first twelve recurrences derived analytically, the spin autocorrelation function (SAF) and associated spectral density at high temperature were obtained numerically. Our results indicate that when the standard deviation σ_J (or σ_B) of the exchange couplings J_i (or the random transverse fields B_i) is small, no long-time tail appears in the SAF. The spin system undergoes a crossover from a central-peak behavior to a collective-mode behavior, which is the dynamical characteristics of RTIM with the bimodal disorder. However, when σ_J (or σ_B) is large enough, the system exhibits similar dynamics behaviors to those of the RTIM with the Gaussian disorder, i.e., the system exhibits an enhanced central-peak behavior for large σ_J or a disordered behavior for large σ_B. In this instance, SAFs exhibit a similar long-time tail, i.e., C(t)～ t^-2 for large t. Similar properties are obtained when J_i (or B_i) satisfy the double-exponential distribution or the double-uniform distribution. Besides, when both the standard deviations and the mean values of the exchange couplings are small, the effects of the Gaussian random bonds may drive the system undergo two crossovers from a triplet state to a doublet state, and then to a collective-mode state.

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Magnetic interaction in the metamaterial/magnet system

M. K. Alqadi, F. Y. Alzoubi

2014 (8): 87506-087506. doi: 10.1088/1674-1056/23/8/087506

摘要 ( 570 )

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The stability of the magnetic dipole and the metamaterial with negative permeability are investigated. Analytical expressions of the interaction force and stiffness of the magnetic line and metamaterial with negative permeability are derived. The repulsive force between the magnetic line and the metamaterial exceeds the value of the maximum force in the magnet-superconductor system.

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Rational doping for zinc oxide and its influences on morphology and optical properties

夏玉静, 管自生, 贺涛

2014 (8): 87701-087701. doi: 10.1088/1674-1056/23/8/087701

摘要 ( 575 )

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Zinc oxide (ZnO) nanopowders doped with different metal ions (Me, Me = Sn⁴⁺, In³⁺, Mn²⁺, and Co²⁺) are prepared by a simple sol-gel method. Influences of the ion doping on morphology and optical properties of the resulting Zn_xMe_yO are investigated by scanning electron microscopy, X-ray diffraction, UV-vis absorption spectrum, and photoluminescence. The morphology of ZnO can be tailored by ion doping, which is closely related not only to the ionic radii and electronegativities of the doped ions, but also to their oxidation states and electron configurations. The optical band gap and photoluminescence of ZnO can also be modulated by ion doping, which results from a combination of different effects, Burstein-Moss, band tail, charge compensation, sp-d exchange, non-radiative recombination, and blocking barrier. This may offer us a viable approach to tuning the (optical) properties of ZnO-based materials via rational ion doping.

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Effect of structural parameters of Gaussian repaired pit on light intensity distribution inside KH₂PO₄ crystal

肖勇, 陈明君, 程健, 廖威, 王海军, 李明全

2014 (8): 87702-087702. doi: 10.1088/1674-1056/23/8/087702

摘要 ( 645 )

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KH₂PO₄ (KDP) crystal with excellent optical properties is a very important element of inertial confinement fusion (ICF) device. However, KDP crystal surface micro-defects severely reduce the crystal laser damage threshold, affecting the crystal service life. In this paper, Gaussian repaired pit is used to replace the crystal surface micro-defects, in order to improve the laser damage resistance of the KDP crystal with surface micro-defects. At first, the physical model of Gaussian repaired pit is built by Fourier model method, and the accuracy of the method is analyzed. It is found that the calculation error can be reduced by increasing the product of the width-period ratio and the truncation constant of the repaired pit. The calculation results about the physical model of Gaussian repaired pit show that the light intensity distribution within the crystal is symmetrical, and there are evidently enhanced light intensity regions in the crystal. Meanwhile, the maximum relative intensity inside the KDP crystal decreases gradually with the increase of the width of the Gaussian repaired pit. Secondly, the Gaussian repaired pits with different widths and the same depth of 20 μm are processed by micro-milling. Their surfaces are very smooth and present the ductile cutting state under the microscope. Finally, the laser damage threshold of the Gaussian repaired pits on the surface of the KDP crystal sample is measured by a 3ω, 6-ns laser. The results show that the maximum threshold of the Gaussian repaired pits is 3.12 J/cm², which is 60% higher than the threshold of initial damage point, and the laser damage threshold increases with the increase of the width of the Gaussian repaired pit.

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Three-dimensional noble-metal nanostructure：A new kind of substrate for sensitive, uniform, and reproducible surface-enhanced Raman scattering

田翠锋, 尤红军, 方吉祥

2014 (8): 87801-087801. doi: 10.1088/1674-1056/23/8/087801

摘要 ( 721 )

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Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique for highly sensitive structural detection of low concentration analyte. The SERS activities largely depend on the topography of the substrate. In this review, we summarize the recent progress in SERS substrate, especially focusing on the three-dimensional (3D) noble-metal substrate with hierarchical nanostructure. Firstly, we introduce the background and general mechanism of 3D hierarchical SERS nanostructures. Then, a systematic overview on the fabrication, growth mechanism, and SERS property of various noble-metal substrates with 3D hierarchical nanostructures is presented. Finally, the applications of 3D hierarchical nanostructures as SERS substrates in many fields are discussed.

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Thickness dependence of the optical constants of oxidized copper thin films based on ellipsometry and transmittance

宫俊波, 董伟乐, 代如成, 王中平, 张增明, 丁泽军

2014 (8): 87802-087802. doi: 10.1088/1674-1056/23/8/087802

摘要 ( 759 )

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Thin oxidized copper films in various thickness values are deposited onto quartz glass substrates by electron beam evaporation. The ellipsometry parameters and transmittance in a wavelength range of 300 nm-1000 nm are collected by a spectroscopic ellipsometer and a spectrophotometer respectively. The effective thickness and optical constants, i.e., refractive index n and extinction coefficient k, are accurately determined by using newly developed ellipsometry combined with transmittance iteration method. It is found that the effective thickness determined by this method is close to the physical thickness and has obvious difference from the mass thickness for very thin film due to variable density of film. Furthermore, the thickness dependence of optical constants of thin oxidized Cu films is analyzed.

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Raman scattering in In/InO_x core–shell structured nanoparticles

王萌, 田野, 张建明, 郭传飞, 张心正, 刘前

2014 (8): 87803-087803. doi: 10.1088/1674-1056/23/8/087803

摘要 ( 877 )

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The properties of Raman phonons are very important due to the fact that they can availably reflect some important physical information. An abnormal Raman peak is observed at about 558 cm^-1 in In film composed of In/InO_x core-shell structured nanoparticles, and the phonon mode stays very stable when the temperature changes. Our results indicate that this Raman scattering is attributed to the existence of incomplete indium oxide in the oxide shell.

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Thermal effect of Ge₂Sb₂Te₅ in phase change memory device

李俊焘, 刘波, 宋志棠, 任堃, 朱敏, 徐佳, 任佳栋, 冯高明, 任万春, 童浩

2014 (8): 87804-087804. doi: 10.1088/1674-1056/23/8/087804

摘要 ( 628 )

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In the fabrication of phase change random access memory (PRAM) devices, high temperature thermal processes are inevitable. We investigate the thermal stability of Ge₂Sb₂Te₅ (GST) which is a prototypical phase change material. After high temperature process, voids of phase change material exist at the interface between Ge₂Sb₂Te₅ and substrate in the initial open memory cell. This lower region of Ge₂Sb₂Te₅ is found to be a Te-rich phase change layer. Phase change memory devices are fabricated in different process conditions and examined by scanning electron microscopy and energy dispersive X-ray. It is found that hot-chuck process, nitrogen-doping process, and lower temperature inter-metal dielectric (IMD) deposition process can ease the thermal impact of line-GST PRAM cell.

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The engineering of doxorubicin-loaded liposome-quantum dot hybrids for cancer theranostics

田博文, Wafa' T. Al-Jamal, Kostas Kostarelos

2014 (8): 87805-087805. doi: 10.1088/1674-1056/23/8/087805

摘要 ( 778 )

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Many studies have recently attempted to develop multifunctional nanoconstructs by integrating the superior fluorescence properties of quantum dots (QD) with therapeutic capabilities into a single vesicle for cancer theranostics. Liposome-quantum dot (L-QD) hybrid vesicles have shown promising potential for the construction of multifunctional nanoconstructs for cancer imaging and therapy. To fulfil such a potential, we report here the further functionalization of L-QD hybrid vesicles with therapeutic capabilities by loading anticancer drug doxorubicin (Dox) into their aqueous core. L-QD hybrid vesicles are first engineered by the incorporation of TOPO-capped, CdSe/ZnS QD into the lipid bilayers of DSPC:Chol:DSPE-PEG₂₀₀₀, followed by Dox loading using the pH-gradient technique. The loading efficiency of Dox into L-QD hybrid vesicles is achieved up to 97%, comparable to liposome control. All these evidences prove that the incorporation of QD into the lipid bilayer does not affect Dox loading through the lipid membrane of liposomes using the pH-gradient technique. Moreover, the release study shows that Dox release profile can be modulated simply by changing lipid composition. In conclusion, the Dox-loaded L-QD hybrid vesicles presented here constitute a promising multifunctional nanoconstruct capable of transporting combinations of therapeutic and diagnostic modalities.

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A tunable infrared plasmonic polarization filter with asymmetrical cross resonator

陈曦曜, 钟远刚, 蒋俊贞, 曾夏辉, 傅平, 邱怡申, 李晖

2014 (8): 87806-087806. doi: 10.1088/1674-1056/23/8/087806

摘要 ( 681 )

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A tunable infrared plasmonic polarization filter is proposed and investigated in this paper. The filter is based on the sandwich absorption structure which consists of three layers. The top layer is an array of asymmetrical cross resonator. The middle and bottom layers are dielectric spacer and metal film respectively. By absorbing specific wavelength of the incident light perfectly, the reflection spectrum of the structure shows filter performance. The calculated results show that the absorption wavelength is strongly dependent on the length of branch of the asymmetrical cross resonator which is parallel to the light polarization and independent of the length of the vertical one. Therefore, the asymmetrical cross resonator filter structure opens the way for freely tuning the filtering wavelength for a different light polarization. We can fix a resonant wavelength (absorption wavelength) corresponding to one polarization and change the resonant wavelength for the other polarization by adjusting the corresponding branch length of the asymmetrical cross resonator, or change the two resonant wavelengths of both two polarizations at the same time.

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Synthesis of Au nanorods in a low pH solution via seed-media method

马晓, 冯晋阳, 游芳芳, 马娟, 赵修建, 王木琴

2014 (8): 87807-087807. doi: 10.1088/1674-1056/23/8/087807

摘要 ( 623 )

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The gold (Au) nanorods with various aspect ratios are obtained by a seed-media method in low pH growth solution. Transmission electron microscopy (TEM) and UV-visible spectrophotometry are utilized to characterize the Au nanorods, and the longitudinal absorption peak positions of Au nanorods show different shifting trends of the growth evolutions in various low pH (1～ 3) solutions. Other influential factors on the shape of Au nanorod are also systematically studied under low pH reaction condition. The positions of longitudinal peak shift between 600 nm and 900 nm, with the aspect ratios of Au nanorods varying from 2 to 5 both in the simulation and experimental results. The simulation results are in agreement with experimental ones.

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Microwave-promoted pure host phase for red emission CaS：Eu²⁺ phosphor from single CaSO₄ precursor and the photoluminescence property

马健, 陆启飞, 王延泽, 卢志娟, 孙亮, 董晓菲, 王达健

2014 (8): 87808-087808. doi: 10.1088/1674-1056/23/8/087808

摘要 ( 524 )

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We report a novel approach to obtaining a classical blue-green excitable CaS:Eu²⁺ phosphor with desired red emission by microwave (MW) firing procedure in the absence of adding elemental sulphur. The disturbing effect of MW electromagnetic field on decomposition of CaSO₄ into CaS activated by europium is distinctly observed to give pure host phase without adding any elemental sulphur and carbon. The host phase evolution is observed to be highly dependent on the variation of applied MW power from X-ray diffraction (XRD) patterns and the corresponding photoluminescence (PL), and a maximum PL intensity at 1100 W of MW power is acquired for the obtained purer host phase. The non-thermal and non-equilibrium effects by MW are revealed to correlate with the interaction between polar structure of the host and applied electromagnetic field. The results demonstrate an optional procedure to prepare this red-emitting phosphor in an effective, environment-friendly and scalable approach for phosphor production in the application of bio-illumination for plant cultivation and artificial photosynthesis.

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Concentration effect of the near-infrared quantum cutting of 1788-nm luminescence of Tm³⁺ ion in (Y_1-xTm_x)₃Al₅O₁₂ powder phosphor

陈晓波, 李崧, 丁贤林, 杨小冬, 刘泉林, 高燕, 孙萍, 杨国建

2014 (8): 87809-087809. doi: 10.1088/1674-1056/23/8/087809

摘要 ( 668 )

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In the present paper, the concentration effect of near-infrared quantum cutting of Tm³⁺ ion in (Y_1-xTm_x)₃Al₅O₁₂ powder phosphor is studied by means of experiments and calculations. In addition, the absorption spectra, visible-to-nearinfrared excitation and emission spectra, and fluorescence lifetimes are measured. It is found that (Y_1-xTm_x)₃Al₅O₁₂ powder phosphor has a strong four-photon near-infrared quantum cutting luminescence of 1788.0-nm ³F₄ →³H₆ fluorescence of Tm³⁺ ion, when excited by 357.0-nm light. It is also found that the up-limit of the four-photon near-infrared quantum cutting luminescence efficiency of (Y_0.700Tm_0.300)₃Al₅O₁₂ powder phosphor is approximately 302.19%. To the knowledge of the authors, this is the first time that a near-infrared quantum cutting efficiency up-limit exceeding 300% has been reported. The results of this manuscript are valuable in aiding the probing of the new generation Ge solar cell.

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Effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition

王维颖, 金鹏, 刘贵鹏, 李维, 刘斌, 刘兴昉, 王占国

2014 (8): 87810-087810. doi: 10.1088/1674-1056/23/8/087810

摘要 ( 808 )

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The effect of high-temperature annealing on AlN thin film grown by metalorganic chemical vapor deposition was investigated using atomic force microscopy, Raman spectroscopy, and deep ultra-violet photoluminescence (PL) with the excitation wavelength as short as ～ 177 nm. Annealing experiments were carried out in either N₂ or vacuum atmosphere with the annealing temperature ranging from 1200 ℃ to 1600 ℃. It is found that surface roughness reduced and compressive strain increased with the annealing temperature increasing in both annealing atmospheres. As to optical properties, a band-edge emission peak at 6.036 eV and a very broad emission band peaking at about 4.7 eV were observed in the photoluminescence spectrum of the as-grown sample. After annealing, the intensity of the band-edge emission peak varied with the annealing temperature and atmosphere. It is also found that a much stronger emission band ranging from 2.5 eV to 4.2 eV is superimposed on the original spectra by annealing in either N₂ or vacuum atmosphere. We attribute these deep-level emission peaks to the V_AL-O_{m N} complex in the AlN material.

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Effect of NaCl doped into Bphen layer on the performance of tandem organic light-emitting diodes

肖志慧, 吴晓明, 华玉林, 毕文涛, 王丽, 张欣, 辛利文, 印寿根

2014 (8): 87811-087811. doi: 10.1088/1674-1056/23/8/087811

摘要 ( 641 )

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To improve the performance of tandem organic light-emitting diodes (OLEDs), we study the novel NaCl as n-type dopant in Bphen:NaCl layer. By analyzing their relevant energy levels and carrier transporting characteristics, we discuss the mechanisms of the effective charge generation layer (CGL) of Bphen:NaCl (6 wt%)/MoO₃. In addition, we use the Bphen:NaCl (20 wt%) layer as the electron injection layer (EIL) combining the CGL to further improve the performance of tandem device. For this tandem device, the maximal current efficiency of 9.32 cd/A and the maximal power efficiency of 1.93 lm/W are obtained, which are enhanced approximately by 2.1 and 1.1 times compared with those of the single-emissive-unit device respectively. We attribute this improvement to the increase of electron injection ability by introducing of Bphen:NaCl layer. Moreover, the CGL is almost completely transparent in the visible light region, which is also important to achieve an efficient tandem OLEDs.

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Introduction to ChinaNANO 2013

魏志祥, 朱星

2014 (8): 88101-088101. doi: 10.1088/1674-1056/23/8/088101

摘要 ( 649 )

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Silicon nanoparticles have attracted great attention in the past decades because of their intriguing physical properties, active surface state, distinctive photoluminescence, and biocompatibility. In this review, we present some recent progress in preparation methodologies, surface functionalization approaches of silicon nanoparticles. Further, their promising applications in the fields of energy and electronic engineering are introduced.

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Silicon nanoparticles：Preparation, properties, and applications

常欢, 孙树清

2014 (8): 88102-088102. doi: 10.1088/1674-1056/23/8/088102

摘要 ( 682 )

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Silicon nanoparticles have attracted great attention in the past decades because of their intriguing physical properties, active surface state, distinctive photoluminescence and biocompatibility. In this review, we present some of the recent progress in preparation methodologies and surface functionalization approaches of silicon nanoparticles. Further, their promising applications in the fields of energy and electronic engineering are introduced.

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Growth of threaded AlN whiskers by a physical vapor transport method

王军, 赵萌, 左思斌, 王文军

2014 (8): 88103-088103. doi: 10.1088/1674-1056/23/8/088103

摘要 ( 718 )

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Threaded aluminum nitride (AlN) whiskers are grown by a physical vapor transport method in a radio-frequency induction heating furnace. The resultant whiskers are characterized by X-ray diffraction, Raman scattering, scanning electron microscopy, transmission electron microscopy and photoluminescence. The analysis shows that the whiskers are single-crystalline, wurtzite AlN. The threaded AlN whiskers are 0.5 μm～ 100 μm in diameter and several millimeters in length in the fiber direction, and have lots of tiny sawteeth on the surface. The morphology of this threaded AlN whisker is beneficial for bonding when the whisker is used in composite. The growth of the whiskers is dominated by the vapor-solid (VS) mechanism, and the particular morphology might result from an oscillating condition produced in the radio-frequency induction heating furnace.

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Complete coverage of reduced graphene oxide on silicon dioxide substrates

HuangJHuang Jingfeng, Melanie Larisika, Chen Hu, Steve Faulkner, Myra A. Nimmo, Christoph Nowak, Alfred Tok Iing Yoong

2014 (8): 88104-088104. doi: 10.1088/1674-1056/23/8/088104

摘要 ( 695 )

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Reduced graphene oxide (RGO) has the advantage of an aqueous and industrial-scale production route. No other approaches can rival the RGO field effect transistor platform in terms of cost (< US$1) and portability (millimetre scale). However the large deviations in the electrical resistivity of this fabricated material prevent it from being used widely. After an ethanol chemical vapor deposition (CVD) post-treatment to graphene oxide with ethanol, carbon islets are deposited preferentially at the edges of existing flakes. With a 2-h treatment, the standard deviation in electrical resistance of the treated chips can be reduced by 99.95%. Thus this process could enable RGO to be used in practical electronic devices.

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Templated synthesis of highly ordered mesoporous cobalt ferrite and its microwave absorption properties

力国民, 王连成, 徐耀

2014 (8): 88105-088105. doi: 10.1088/1674-1056/23/8/088105

摘要 ( 637 )

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Based on the nanocasting strategy, highly ordered mesoporous CoFe₂O₄ is synthesized via the‘two-solvent’impregnation method using a mesoporous SBA-15 template. An ordered two-dimensional (P6mm) structure is preserved for the CoFe₂O₄/SBA-15 composite after the nanocasting. After the SBA-15 template is dissolved by NaOH solution, a mesoporous structure composed of aligned nanoparticles can be obtained, and the P6mm structure of the parent SBA-15 is preserved. With a high specific surface area (above 90 m²/g) and ferromagnetic behavior, the obtained material shows potential in light weight microwave absorption application. The minimum reflection loss (RL) can reach -18 dB at about 16 GHz with a thickness of 2 mm and the corresponding absorption bandwidth is 4.5 GHz.

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Properties of passive nano films on zircaloy-4 affected by defects induced by hydrogen permeation

顾俊骥, 凌云汉, 张瑞谦, 戴训, 白新德

2014 (8): 88106-088106. doi: 10.1088/1674-1056/23/8/088106

摘要 ( 577 )

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In this work, hydrogen absorption and the permeation behavior of the passive layer formed on zircaloy-4 are investigated. Potentiodynamic polarization, Mott-Schottky analysis, electrochemical impedance spectroscopy, and Raman scattering spectroscopy are employed to characterize the passive defects before and after hydrogen permeation. It is found that the nanoscale passive ZrO₂ films play an important role in the resistance against corrosion; hydrogen impingement, however, reduces the passive impedance towards hydrothermal oxidation. The increase of defects (vacancies) in passive film is probably attributed to the degradation. We believe that this finding will provide valuable insight into the understanding of the corrosion mechanism of zircaloys used in light water reactors.

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Quantum transport characteristics in single and multiple N-channel junctionless nanowire transistors at low temperatures

王昊, 韩伟华, 马刘红, 李小明, 杨富华

2014 (8): 88107-088107. doi: 10.1088/1674-1056/23/8/088107

摘要 ( 644 )

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Single and multiple n-channel junctionless nanowire transistors (JNTs) are fabricated and experimentally investigated at variable temperatures. Clear current oscillations caused by the quantum-confinement effect are observed in the curve of drain current versus gate voltage acquired at low temperatures (10 K-100 K) and variable drain bias voltages (10 mV-90 mV). Transfer characteristics exhibit current oscillation peaks below flat-band voltage (V_FB) at temperatures up to 75 K, which is possibly due to Coulomb-blocking from quantum dots, which are randomly formed by ionized dopants in the just opened n-type one-dimensional (1D) channel of silicon nanowires. However, at higher voltages than V_FB, regular current steps are observed in single-channel JNTs, which corresponds to the fully populated subbands in the 1D channel. The subband energy spacing extracted from transconductance peaks accords well with theoretical predication. However, in multiple-channel JNT, only tiny oscillation peaks of the drain current are observed due to the combination of the drain current from multiple channels with quantum-confinement effects.

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Effects of graphene defects on Co cluster nucleation and intercalation

徐文焱, 黄立, 阙炎德, 林晓, 王业亮, 杜世萱, 高鸿钧

2014 (8): 88108-088108. doi: 10.1088/1674-1056/23/8/088108

摘要 ( 757 )

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Four kinds of defects are observed in graphene grown on Ru (0001) surfaces. After cobalt deposition at room temperature, the cobalt nanoclusters are preferentially located at the defect position. By annealing at 530 ℃, cobalt atoms intercalate at the interface of Graphene/Ru (0001) through the defects. Further deposition and annealing increase the sizes of intercalated Co islands. This provides a method of controlling the arrangement of cobalt nanoclusters and also the density and the sizes of intercalated cobalt islands, which would find potential applications in catalysis industries, magnetism storage, and magnetism control in future information technology.

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Phase field crystal study of the crystallization modes within the two-phase region

杨涛, 张静, 龙建, 龙清华, 陈铮

2014 (8): 88109-088109. doi: 10.1088/1674-1056/23/8/088109

摘要 ( 667 )

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Using the phase field crystal approach, the crystallization process within the liquid-solid coexistence region is investigated for a square lattice on an atomic scale. Two competing growth modes, i.e., the diffusion-controlled growth through long-range atomic migration in liquid and the diffusionless growth through local atom rearrangement, which give rise to two completely different crystallization behaviors, are compared. In the diffusion-controlled regime, the interface migrates in a layerwise manner, leading to a gradual change of crystal morphology from truncated square to four-fold symmetric dendrite with the increase of driving force. For the diffusionless growth mode, a single crystal with no significant density change occupies the whole system at a faster rate while exhibiting a small growth anisotropy. The competition between these two modes is also discussed from the key input of the phase field crystal model: the correlation function.

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Nucleation of GaSb on GaAs (001) by low pressure metal-organic chemical vapor deposition

王连锴, 刘仁俊, 杨皓宇, 吕游, 李国兴, 张源涛, 张宝林

2014 (8): 88110-088110. doi: 10.1088/1674-1056/23/8/088110

摘要 ( 666 )

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The initial growth stage of GaSb on GaAs (001) by low pressure metal-organic chemical vapor deposition (MOCVD) is investigated. The dependence of the nucleation on growth temperature, growth pressure, and vapor V/Ⅲ ratio is studied by means of atomic force microscopy. The nucleation characteristics include the island density, size, and size uniformity distribution. The nucleation mechanism is discussed by the effects of growth temperature, growth pressure, and vapor V/Ⅲ ratio on the density, size, and size uniformity of GaSb islands. With the growth temperature increasing from 500 ℃ to 610 ℃ and the growth pressure increasing from 50 mbar to 1000 mbar (1 mbar = 10⁵ Pa), the island density first increases and then decreases; with the V/Ⅲ ratio increasing from 0.5 to 3, the trend is contrary.

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Annealing effect of platinum-incorporated nanowires created by focused ion/electron-beam-induced deposition

方靖岳, 秦石乔, 张学骜, 刘东青, 常胜利

2014 (8): 88111-088111. doi: 10.1088/1674-1056/23/8/088111

摘要 ( 655 )

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Focused ion-beam-induced deposition (FIBID) and focused electron-beam-induced deposition (FEBID) are convenient and useful in nanodevice fabrication. Since the deposition is from the organometallic platinum precursor, the conductive lines directly written by focused ion-beam (FIB) and focused electron-beam (FEB) are carbon-rich materials. We discuss an alternative approach to enhancing the platinum content and improving the conductivity of the conductive leads produced by FIBID and FEBID, namely an annealing treatment. Annealing in pure oxygen at 500 ℃ for 30 min enhances the platinum content values from ～ 18% to 30% and ～ 50% to 90% of FIBID and FEBID, respectively. Moreover, we find that thin films will be formed in the FIBID and FEBID processes. The annealing treatment is helpful to avoid the current leakage caused by these thin films. A single electron transistor is fabricated by FEBID and the current-voltage curve shows the Coulomb blockade effect.

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Epitaxial growth of Ge_1-xSn_x films with x up to 0.14 grown on Ge (00l) at low temperature

陶平, 黄磊, Cheng H H, 王焕华, 吴小山

2014 (8): 88112-088112. doi: 10.1088/1674-1056/23/8/088112

摘要 ( 674 )

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We characterize the structures of Ge_1-xSn_x films with x up to 0.14 grown on Ge (00l) by molecular-beam epitaxy at low temperature. The results show that Ge_1-xSn_x films are fully strained even at high Sn composition. The in-plane lattice parameters remain exactly the same as that of the substrate. Depth sensitivity analysis of the lattice parameters indicates that the strains of the epitaxial films are all in homogeneity. The films are fully strained. Poisson ratios, the force constants for the bonds between Ge and Sn are estimated and discussed in the present paper. Raman results show Ge-Ge, Ge-Sn, Sn-Sn vibrational modes. The Sn-Sn bond aggregation may respond to the high quality of our films. The fully strained epitaxy films with high content of Sn may be useful in designing the high quality GeSn films.

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Modeling for V-O₂ reactive sputtering process using a pulsed power supply

王涛, 于贺, 董翔, 蒋亚东, 陈超, 胡锐麟

2014 (8): 88113-088113. doi: 10.1088/1674-1056/23/8/088113

摘要 ( 573 )

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In this article, we present a time-dependent model that enables us to describe the dynamic behavior of pulsed DC reactive sputtering and predict the film compositions of VO_x prepared by this process. In this modeling, the average current J is replaced by a new parameter of J_eff. Meanwhile, the four species states of V, V₂O₃, VO₂, and V₂O₅ in the vanadium oxide films are taken into consideration. Based on this work, the influences of the oxygen gas supply and the pulsed power parameters including the duty cycle and frequency on film compositions are discussed. The model suggests that the time to reach process equilibrium may vary substantially depending on these parameters. It is also indicated that the compositions of VO_x films are quite sensitive to both the reactive gas supply and the duty cycle when the power supply works in pulse mode. The‘steady-state’balance values obtained by these simulations show excellent agreement with the experimental data, which indicates that the experimentally obtained dynamic behavior of the film composition can be explained by this time-dependent modeling for pulsed DC reactive sputtering process. Moreover, the computer simulation results indicate that the curves will essentially yield oscillations around the average value of the film compositions with lower pulse frequency.

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Large-scale photonic crystals with inserted defects and their optical properties

李超荣, 李娟, 杨虎, 赵永强, 吴艳, 董文钧, 陈本永

2014 (8): 88114-088114. doi: 10.1088/1674-1056/23/8/088114

摘要 ( 538 )

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Deliberately introducing defects into photonic crystals is an important way to functionalize the photonic crystals. We prepare a special large-scale three-dimensional (3D) photonic crystal (PC) with designed defects by an easy and low-cost method. The defect layer consists of photoresist strips or air-core strips. Field emission scanning electron microscopy (FESEM) shows that the 3D PC is of good quality and the defect layer is uniform. Different defect states shown in the ultraviolet-visible spectra are induced by the photoresist strip layer and air-core strip layer. The special large-scale 3D PC can be tested for integrated optical circuits, and the defects can act as optical waveguides.

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Nonlinear dynamic characteristics and optimal control of a giant magnetostrictive film-shaped memory alloy composite plate subjected to in-plane stochastic excitation

竺致文, 张庆昕, 许佳

2014 (8): 88201-088201. doi: 10.1088/1674-1056/23/8/088201

摘要 ( 585 )

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The nonlinear dynamic characteristics and optimal control of a giant magnetostrictive film (GMF)-shaped memory alloy (SMA) composite plate subjected to in-plane stochastic excitation are studied. GMF is prepared based on an SMA plate, and combined into a GMF-SMA composite plate. The Van der Pol item is improved to explain the hysteretic phenomena of GMF and SMA, and the nonlinear dynamics model of a GMF-SMA composite cantilever plate subjected to in-plane stochastic excitation is developed. The stochastic stability of the system is analyzed, and the steady-state probability density function of the dynamic response of the system is obtained. The condition of stochastic Hopf bifurcation is discussed, the reliability function of the system is provided, and then the probability density of the first-passage time is given. Finally, the stochastic optimal control strategy is proposed by the stochastic dynamic programming method. Numerical simulation shows that the stability of the trivial solution varies with bifurcation parameters, and stochastic Hopf bifurcation appears in the process; the system's reliability is improved through stochastic optimal control, and the first-passage time is delayed. A GMF-SMA composite plate combines the advantages of GMF and SMA, and can reduce vibration through passive control and active control effectively. The results are helpful for the engineering applications of GMF-SMA composite plates.

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Complete eigenmode analysis of a ladder-type multiple-gap resonant cavity

张长青, 阮存军, 赵鼎, 王树忠, 杨修东

2014 (8): 88401-088401. doi: 10.1088/1674-1056/23/8/088401

摘要 ( 768 )

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A theoretical model is developed for calculating the eigenmodes of the multi-gap resonant cavity. The structure of concern is a kind of ladder-type circuit, offering the advantages of easy fabrication, high characteristic impedance (R/Q), and thermal capacity in the millimeter wave to THz regime. The eigenfunction expansion method is used to establish the field expressions for the gaps and the coupling region. Then, the match conditions at the interface are employed, which leads to a group of complicate boundary equations in the form of an infinite series. To facilitate the mathematical treatments and perform a highly efficient calculation, these boundary equations are transformed into the algebraic forms through the matrix representations. Finally, the concise dispersion equation is obtained. The roots of the dispersion equation include both the axial modes in the gaps, which include the fundamental and the high-order modes, and the cavity modes in the coupling region. Extensive numerical results are presented and the behaviors of the multi-gap resonant cavity are examined.

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Analysis of the injection-locked magnetron with a mismatched circulator

岳松, 张兆传, 高冬平

2014 (8): 88402-088402. doi: 10.1088/1674-1056/23/8/088402

摘要 ( 586 )

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Based on the scatter matrix of the four-port lossless mismatched circulator, the phase differential equation of the injection-locked magnetron is derived by comparing different effects of the mismatched and perfect circulator on the injection ratio. Besides, the locking range of the injection-locked magnetron with the mismatched circulator is deduced by functional operation. In addition, the phase differential equation and the locked bandwidth of the injection-locked system with a mismatched circulator are compared with those of the small injection-ratio case with a perfect circulator. The influence of the circulator reflection coefficient on the injection-locked magnetron is also analyzed by numerical calculation. Theoretical analysis shows that the decrement of the locked bandwidth is less than 1% and decrement of the stable phase difference is less than 1.2% when the reflection coefficient is less than 0.1.

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Comparison between N₂ and O₂ anneals on the integrity of an Al₂O₃/Si₃N₄/SiO₂/Si memory gate stack

褚玉琼, 张满红, 霍宗亮, 刘明

2014 (8): 88501-088501. doi: 10.1088/1674-1056/23/8/088501

摘要 ( 880 )

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In this paper the endurance characteristics and trap generation are investigated to study the effects of different post-deposition anneals (PDAs) on the integrity of an Al₂O₃/Si₃N₄/SiO₂/Si memory gate stack. The flat-band voltage (V_fb) turnarounds are observed in both the programmed and erased states of the N₂-PDA device. In contrast, this turnaround is observed only in the erased state of the O₂-PDA device. The V_fb in the programmed state of the O₂-PDA device keeps increasing with increasing program/erase (P/E) cycles. Through the analyses of endurance characteristics and the low voltage round-trip current transients, it is concluded that in both kinds of device there are an unknown type of pre-existing characteristic deep traps and P/E stress-induced positive oxide charges. In the O₂-PDA device two extra types of trap are also found: the pre-existing border traps and the P/E stress-induced negative traps. Based on these four types of defects we can explain the endurance characteristics of two kinds of device. The switching property of pre-existing characteristic deep traps is also discussed.

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Chemical mechanical planarization of Ge₂Sb₂Te₅ using IC1010 and Politex reg pads in acidic slurry

何敖东, 刘波, 宋志棠, 王良咏, 刘卫丽, 冯高明, 封松林

2014 (8): 88502-088502. doi: 10.1088/1674-1056/23/8/088502

摘要 ( 722 )

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In the paper, chemical mechanical planarization (CMP) of Ge₂Sb₂Te₅(GST) is investigated using IC1010 and Politex reg pads in acidic slurry. For the CMP with blank wafer, it is found that the removal rate (RR) of GST increases with the increase of pressure for both pads, but the RR of GST polished using IC1010 is far more than that of Politex reg. To check the surface defects, GST film is observed with an optical microscope (OM) and scanning electron microscope (SEM). For the CMP with Politex reg, many spots are observed on the surface of the blank wafer with OM, but no obvious spots are observed with SEM. With regard to the patterned wafer, a few stains are observed on the GST cell, but many residues are found on other area with OM. However, from SEM results, a few residues are observed on the GST cell, more dielectric loss is revealed about the trench structure. For the CMP with IC1010, the surface of the polished blank wafer suffers serious scratches found with both OM and SEM, which may result from a low hardness of GST, compared with those of IC1010 and abrasives. With regard to the patterned wafer, it can achieve a clean surface and almost no scratches are observed with OM, which may result from the high-hardness SiO₂ film on the surface, not from the soft GST film across the whole wafer. From the SEM results, a clean interface and no residues are observed on the GST surface, and less dielectric loss is revealed. Compared with Politex reg, the patterned wafer can achieve a good performance after CMP using IC1010.

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A SQUID gradiometer module with large junction shunt resistors

邱阳, 刘超, 张树林, 张国峰, 王永良, 李华, 曾佳, 孔祥燕, 谢晓明

2014 (8): 88503-088503. doi: 10.1088/1674-1056/23/8/088503

摘要 ( 898 )

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A dual-washer superconducting quantum interference device (SQUID) with a loop inductance of 350 pH and two on-washer integrated input coils is designed according to conventional niobium technology. In order to obtain a large SQUID flux-to-voltage transfer coefficient, the junction shunt resistance is selected to be 33 Ω. A vertical SQUID gradiometer module with a baseline of 100 mm is constructed by utilizing such a SQUID and a first-order niobium wire-wound antenna. The sensitivity of this module reaches about 0.2 fT/(cm·Hz^1/2) in the white noise range using a direct readout scheme, i.e., the SQUID is directly connected to an operational amplifier, in a magnetically shielded room. Some magnetocardiography (MCG) measurements with a sufficiently high signal-to-noise ratio (SNR) are demonstrated.

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A novel high performance TFS SJ IGBT with a buried oxide layer

张金平, 李泽宏, 张波, 李肇基

2014 (8): 88504-088504. doi: 10.1088/1674-1056/23/8/088504

摘要 ( 710 )

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A novel high performance trench field stop (TFS) superjunction (SJ) insulated gate bipolar transistor (IGBT) with a buried oxide (BO) layer is proposed in this paper. The BO layer inserted between the P-base and the SJ drift region acts as a barrier layer for the hole-carrier in the drift region. Therefore, conduction modulation in the emitter side of the SJ drift region is enhanced significantly and the carrier distribution in the drift region is optimized for the proposed structure. As a result, compared with the conventional TFS SJ IGBT (Conv-SJ), the proposed BO-SJ IGBT structure possesses a drastically reduced on-state voltage drop (V_ce(on)) and an improved tradeoff between V_ce(on) and turn-off loss (E_off), with no breakdown voltage (BV) degraded. The results show that with the spacing between the gate and the BO layer W_o=0.2 μm, the thickness of the BO layer L_o=0.2 μm, the thickness of the drift region L_d=90 μm, the half width and doping concentration of the N- and P-pillars W_n=W_p=2.5 μm and N_n=N_p=3× 10¹⁵ cm^-3, the V_ce(on) and E_off of the proposed structure are 1.08 V and 2.81 mJ/cm² with the collector doping concentration N_c=1× 10¹⁸ cm^-3 and 1.12 V and 1.73 mJ/cm² with N_c=5× 10¹⁷ cm^-3, respectively. However, with the same device parameters, the V_ce(on) and E_off for the Conv-SJ are 1.81 V and 2.88 mJ/cm² with N_c=1× 10¹⁸ cm^-3 and 1.98 V and 2.82 mJ/cm² with N_c=5× 10¹⁷ cm^-3, respectively. Meanwhile, the BV of the proposed structure and Conv-SJ are 1414 V and 1413 V, respectively.

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Estimation of pulsed laser-induced single event transient in a partially depleted silicon-on-insulator 0.18-μm MOSFET

毕津顺, 曾传滨, 高林春, 刘刚, 罗家俊, 韩郑生

2014 (8): 88505-088505. doi: 10.1088/1674-1056/23/8/088505

摘要 ( 739 )

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In this paper, we investigate the single event transient (SET) occurring in partially depleted silicon-on-insulator (PDSOI) metal-oxide-semiconductor (MOS) devices irradiated by pulsed laser beams. Transient signal characteristics of a 0.18-μm single MOS device, such as SET pulse width, pulse maximum, and collected charge, are measured and analyzed at wafer level. We analyze in detail the influences of supply voltage and pulse energy on the SET characteristics of the device under test (DUT). The dependences of SET characteristics on drain-induced barrier lowering (DIBL) and the parasitic bipolar junction transistor (PBJT) are also discussed. These results provide a guide for radiation-hardened deep sub-micrometer PDSOI technology for space electronics applications.

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Realization of a broadband terahertz wavelength-selective coupling based on five-core fibers

李绪友, 于莹莹, 孙波, 何昆鹏

2014 (8): 88701-088701. doi: 10.1088/1674-1056/23/8/088701

摘要 ( 631 )

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We propose a novel kind of wavelength-selective coupling for the terahertz range based on solid five-core fiber (FCF). The performances of coupling, propagation characteristics, and confinement loss properties are numerically investigated by using a full vector beam propagation method (BPM). Simulation results show that it is possible to realize a broadband wavelength-selective coupling. The coupling length can reach 1.913 cm, and the confinement loss is better than 1.965× 10^-4 cm^-1. Furthermore, a parameter, the power difference, is defined, and it numerically demonstrates the working performance of the wavelength-selective coupler; that is, when the power difference is better than -15 dB, the frequency located in the range of 0.76 THz-1.00 THz is separated relatively well from the frequency of 0.3 THz. Finally, the effect of the structural parameter on the working performance of the coupler is also investigated. We show that the performance optimization is possible by appropriately tuning the core diameter, and the tunabilities of frequency and bandwidth are possible by appropriately tuning the pitch. The wavelength-selective coupler is of potential application for optical fiber sensing and communication in terahertz wavelength division multiplexer fields.

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A study of multi-trapping of tapered-tip single fiber optical tweezers

梁佩博, 雷皎洁, 刘志海, 张羽, 苑立波

2014 (8): 88702-088702. doi: 10.1088/1674-1056/23/8/088702

摘要 ( 669 )

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We develop a pair of tapered-tip single fiber optical tweezers, and study its multi-trapping characteristic. The finite difference time domain method is employed to simulate the trapping force characteristic of this pair of single fiber optical tweezers, and the results show that the number of trapped particles depends on the refractive index and the size of the particles. The trapping force of this pair of tapered-tip single fiber optical tweezers is calibrated by the experimental method, and the experimental results are consistent with the theoretical calculation results. The multi-trapping capability realized by the tapered-tip single fiber optical tweezers will be practical and useful for applications in biomedical research fields.

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Colloidal monolayer self-assembly and its simulation via cellular automaton model

吴以治, 陈晨, 许小亮, 刘赟夕, 邵伟佳, 尹乃强, 张文婷, 柯佳鑫, 方啸天

2014 (8): 88703-088703. doi: 10.1088/1674-1056/23/8/088703

摘要 ( 743 )

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A wafer-scale colloidal monolayer consisting of SiO₂ spheres is fabricated by a method combining spin coating and thermal treatment for the first time. Moreover, a new cellular automaton model describing the self-assembly process of the colloidal monolayer is introduced. Rather than simulate molecular self-assembly to establish the most energetically favored position, we reconstruct the self-assembly of the colloidal monolayer by adjusting several simple transition rules of a cellular automaton. This model captures the main self-assembly characteristics of SiO₂ spheres, including experimental processing time, morphology, and some statistics. It possesses the advantage of less calculation and higher efficiency, paving a new way to simulate a mesoscopic system.

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Functionalization of carbon nanotubes/graphene by polyoxometalates and their enhanced photo-electrical catalysis

张双双, 刘荣基, 张光晋, 谷战军

2014 (8): 88801-088801. doi: 10.1088/1674-1056/23/8/088801

摘要 ( 771 )

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Carbon nanotubes and graphene are carbon-based materials, which possess not only unique structure but also properties such as high surface area, extraordinary mechanical properties, high electronic conductivity, and chemical stability. Thus, they have been regarded as an important material, especially for exploring a variety of complex catalysts. Considerable efforts have been made to functionalize and fabricate carbon-based composites with metal nanoparticles. In this review, we summarize the recent progress of our research on the decoration of carbon nanotubes/graphene with metal nanoparticles by using polyoxometalates as key agents, and their enhanced photo-electrical catalytic activities in various catalytic reactions. The polyoxometalates play a key role in constructing the nanohybrids and contributing to their photo-electrical catalytic properties.

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High microwave absorption performances for single-walled carbon nanotube-epoxy composites with ultra-low loadings

梁嘉杰, 黄毅, 张帆, 李宁, 马延风, 李飞飞, 陈永胜

2014 (8): 88802-088802. doi: 10.1088/1674-1056/23/8/088802

摘要 ( 683 )

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Microwave-absorbing polymeric composites based on single-walled carbon nanotubes (SWNTs) are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption performances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites (1.3-mm thickness) with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appropriate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.

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Photoinduced degradation of organic solar cells with different microstructures

路春希, 闫鹏, 王金泽, 刘爱民, 宋德, 江潮

2014 (8): 88803-088803. doi: 10.1088/1674-1056/23/8/088803

摘要 ( 663 )

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An in situ measurement setup is established to investigate the photoinduced degradation effects in a controllable inert gas ambient environment for the two different microstructures of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyricacid methyl ester (PCBM) bulk-heterojunction organic solar cells. The two devices are fabricated with the solvent vapor drying process followed by a thermal annealing (vapor drying device) and only a normal thermal annealing process (control device), respectively. Their power conversion efficiencies (PCEs) and aging features are compared. Their different degradation behaviors in light absorption are confirmed. In addition, irradiation-induced changes in both nanostructure and surface morphology of the P3HT:PCBM blend films treated with two different fabrication processes are observed through scanning electron microscopy and atomic force microscopy. Aggregated bulbs are observed at the surfaces for control devices after light irradiation for 50 h, while the vapor drying devices exhibit smooth film surfaces, and the corresponding device features are not easy to degrade under the aging measurement. Thus the devices having solvent vapor drying and thermal annealing show better device stabilities than those having only the thermal annealing process.

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Modeling walking behavior of pedestrian groups with floor field cellular automaton approach

陆丽丽, 任刚, 王炜, 王义

2014 (8): 88901-088901. doi: 10.1088/1674-1056/23/8/088901

摘要 ( 789 )

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Walking in groups is very common in a realistic walking environment. An extended floor field cellular automaton (CA) model is therefore proposed to describe the walking behavior of pedestrian groups. This model represents the motion of pedestrian groups in a realistic way. The simulation results reveal that the walking behavior of groups has an important but negative influence on pedestrian flow dynamics, especially when the density is at a high level. The presence of pedestrian groups retards the emergence of lane formation and increases the instability of operation of pedestrian flow. Moreover, the average velocity and volume of pedestrian flow are significantly reduced due to the group motion. Meanwhile, the parameter-sensitive analysis suggests that pedestrian groups should make a compromise between efficient movement and staying coherent with a certain spatial structure when walking in a dense crowd.

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An effective method to improve the robustness of small-world networks under attack

张争珍, 许文俊, 曾上游, 林家儒

2014 (8): 88902-088902. doi: 10.1088/1674-1056/23/8/088902

摘要 ( 607 )

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In this study, the robustness of small-world networks to three types of attack is investigated. Global efficiency is introduced as the network coefficient to measure the robustness of a small-world network. The simulation results prove that an increase in rewiring probability or average degree can enhance the robustness of the small-world network under all three types of attack. The effectiveness of simultaneously increasing both rewiring probability and average degree is also studied, and the combined increase is found to significantly improve the robustness of the small-world network. Furthermore, the combined effect of rewiring probability and average degree on network robustness is shown to be several times greater than that of rewiring probability or average degree individually. This means that small-world networks with a relatively high rewiring probability and average degree have advantages both in network communications and in good robustness to attacks. Therefore, simultaneously increasing rewiring probability and average degree is an effective method of constructing realistic networks. Consequently, the proposed method is useful to construct efficient and robust networks in a realistic scenario.

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An approach to estimating and extrapolating model error based on inverse problem methods：towards accurate numerical weather prediction

胡淑娟, 邱春雨, 张利云, 黄启灿, 于海鹏, 丑纪范

2014 (8): 89201-089201. doi: 10.1088/1674-1056/23/8/089201

摘要 ( 563 )

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Model error is one of the key factors restricting the accuracy of numerical weather prediction (NWP). Considering the continuous evolution of the atmosphere, the observed data (ignoring the measurement error) can be viewed as a series of solutions of an accurate model governing the actual atmosphere. Model error is represented as an unknown term in the accurate model, thus NWP can be considered as an inverse problem to uncover the unknown error term. The inverse problem models can absorb long periods of observed data to generate model error correction procedures. They thus resolve the deficiency and faultiness of the NWP schemes employing only the initial-time data. In this study we construct two inverse problem models to estimate and extrapolate the time-varying and spatial-varying model errors in both the historical and forecast periods by using recent observations and analogue phenomena of the atmosphere. Numerical experiment on Burgers' equation has illustrated the substantial forecast improvement using inverse problem algorithms. The proposed inverse problem methods of suppressing NWP errors will be useful in future high accuracy applications of NWP.

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Test particle simulations of resonant interactions between energetic electrons and discrete, multi-frequency artificial whistler waves in the plasmasphere

常珊珊, 倪彬彬, 赵正予, 顾旭东, 周晨

2014 (8): 89401-089401. doi: 10.1088/1674-1056/23/8/089401

摘要 ( 560 )

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Modulated high frequency (HF) heating of the ionosphere provides a feasible means of artificially generating extremely low frequency (ELF)/very low frequency (VLF) whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency artificially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ～ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval (Δf) of the discrete, multi-frequency waves. We find that there is a threshold value of Δf for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to Δf (proportional to the frequency components N_w) when Δf is below the threshold value but it remains unchanged with increasing Δf when Δf is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the 'effective frequency band'. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electrons in the plasmasphere by artificial ELF/VLF whistler waves can be achieved.

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The mass limit of white dwarfs with strong magnetic fields in general relativity

文德华, 刘荷蕾, 张向东

2014 (8): 89501-089501. doi: 10.1088/1674-1056/23/8/089501

摘要 ( 588 )

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Recently, U. Das and B. Mukhopadhyay proposed that the Chandrasekhar limit of a white dwarf could reach a new high level (2.58 M_⊙) if a superstrong magnetic field were considered (Das U and Mukhopadhyay B 2013 Phys. Rev. Lett. 110 071102), where the structure of the strongly magnetized white dwarf (SMWD) is calculated in the framework of Newtonian theory (NT). As the SMWD has a far smaller size, in contrast with the usual expectation, we found that there is an obvious general relativistic effect (GRE) in the SMWD. For example, for the SMWD with a one Landau level system, the super-Chandrasekhar mass limit in general relativity (GR) is approximately 16.5% lower than that in NT. More interestingly, the maximal mass of the white dwarf will be first increased when the magnetic field strength keeps on increasing and reaches the maximal value M=2.48 M_⊙ with B_D=391.5. Then if we further increase the magnetic fields, surprisingly, the maximal mass of the white dwarf will decrease when one takes the GRE into account.

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