中国物理B

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Improved control of distributed parameter systems using wireless sensor and actuator networks: An observer-based method

江正仙, 崔宝同, 楼旭阳, 庄波

2017 (4): 40201-040201. doi: 10.1088/1674-1056/26/4/040201

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In this paper, the control problem of distributed parameter systems is investigated by using wireless sensor and actuator networks with the observer-based method. Firstly, a centralized observer which makes use of the measurement information provided by the fixed sensors is designed to estimate the distributed parameter systems. The mobile agents, each of which is affixed with a controller and an actuator, can provide the observer-based control for the target systems. By using Lyapunov stability arguments, the stability for the estimation error system and distributed parameter control system is proved, meanwhile a guidance scheme for each mobile actuator is provided to improve the control performance. A numerical example is finally used to demonstrate the effectiveness and the advantages of the proposed approaches.

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Carlson iterating rational approximation and performance analysis of fractional operator with arbitrary order

何秋燕, 余波, 袁晓

2017 (4): 40202-040202. doi: 10.1088/1674-1056/26/4/040202

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The performance analysis of the generalized Carlson iterating process, which can realize the rational approximation of fractional operator with arbitrary order, is presented in this paper. The reasons why the generalized Carlson iterating function possesses more excellent properties such as self-similarity and exponential symmetry are also explained. K-index, P-index, O-index, and complexity index are introduced to contribute to performance analysis. Considering nine different operational orders and choosing an appropriate rational initial impedance for a certain operational order, these rational approximation impedance functions calculated by the iterating function meet computational rationality, positive reality, and operational validity. Then they are capable of having the operational performance of fractional operators and being physical realization. The approximation performance of the impedance function to the ideal fractional operator and the circuit network complexity are also exhibited.

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Consensus of multiple autonomous underwater vehicles with double independent Markovian switching topologies and timevarying delays

严浙平, 刘一博, 周佳加, 张伟, 王璐

2017 (4): 40203-040203. doi: 10.1088/1674-1056/26/4/040203

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A new method in which the consensus algorithm is used to solve the coordinate control problems of leaderless multiple autonomous underwater vehicles (multi-AUVs) with double independent Markovian switching communication topologies and time-varying delays among the underwater sensors is investigated. This is accomplished by first dividing the communication topology into two different switching parts, i.e., velocity and position, to reduce the data capacity per data package sent between the multi-AUVs in the ocean. Then, the state feedback linearization is used to simplify and rewrite the complex nonlinear and coupled mathematical model of the AUVs into a double-integrator dynamic model. Consequently, coordinate control of the multi-AUVs is regarded as an approximating consensus problem with various time-varying delays and velocity and position topologies. Considering these factors, sufficient conditions of consensus control are proposed and analyzed and the stability of the multi-AUVs is proven by Lyapunov-Krasovskii theorem. Finally, simulation results that validate the theoretical results are presented.

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Physical interpretation of Planck's constant based on the Maxwell theory

张东才

2017 (4): 40301-040301. doi: 10.1088/1674-1056/26/4/040301

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The discovery of the Planck relation is generally regarded as the starting point of quantum physics. Planck's constant h is now regarded as one of the most important universal constants. The physical nature of h, however, has not been well understood. It was originally suggested as a fitting constant to explain the black-body radiation. Although Planck had proposed a theoretical justification of h, he was never satisfied with that. To solve this outstanding problem, we use the Maxwell theory to directly calculate the energy and momentum of a radiation wave packet. We find that the energy of the wave packet is indeed proportional to its oscillation frequency. This allows us to derive the value of Planck's constant. Furthermore, we show that the emission and transmission of a photon follows the all-or-none principle. The “strength” of the wave packet can be characterized by ζ, which represents the integrated strength of the vector potential along a transverse axis. We reason that ζ should have a fixed cut-off value for all photons. Our results suggest that a wave packet can behave like a particle. This offers a simple explanation to the recent satellite observations that the cosmic microwave background follows closely the black-body radiation as predicted by Planck's law.

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Experimentally testing Hardy's theorem on nonlocality with entangled mixed states

樊代和, 戴茂春, 郭伟杰, 韦联福

2017 (4): 40302-040302. doi: 10.1088/1674-1056/26/4/040302

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Hardy's theorem on nonlocality has been verified by a series of experiments with two-qubit entangled pure states. However, in this paper we demonstrate the experimental test of the theorem by using the two-photon entangled mixed states. We first investigate the generic logic in Hardy's proof of nonlocality, which can be applied for arbitrary two-qubit mixed polarization entangled states and can be reduced naturally to the well-known logic tested successfully by the previous pure state experiments. Then, the optimized violations of locality for various experimental parameters are delivered by the numerical method. Finally, the logic argued above for testing Hardy's theorem on nonlocality is demonstrated experimentally by using the mixed entangled-photon pairs generated via pumping two type-I BBO crystals. Our experimental results shows that Hardy's proof of nonlocality can also be verified with two-qubit polarization entangled mixed states, with a violation of about 3.4 standard deviations.

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Continuous variable quantum key distribution

李永民, 王旭阳, 白增亮, 刘文元, 杨申申, 彭堃墀

2017 (4): 40303-040303. doi: 10.1088/1674-1056/26/4/040303

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Quantum key distribution enables unconditionally secure key distribution between two legitimate users. The information-theoretic security is guaranteed by the fundamental laws of quantum physics. Initially, the quantum key distribution protocol was proposed based on the qubits. Later on, it was found that quantum continuous variables can also be exploited for this target. The continuous variable quantum key distribution can build upon standard telecommunication technology and exhibits a higher secret key rate per pulse at a relatively short distance due to the possibility of encoding more than 1 bit per pulse. In this article, we review the current status of the continuous variable quantum key distribution research, including its basic principle, experimental implementations, security and future directions; the experimental progress in this field made by our group is also presented.

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Spherical reconciliation for a continuous-variable quantum key distribution

卢钊, 史建红, 李风光

2017 (4): 40304-040304. doi: 10.1088/1674-1056/26/4/040304

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Information reconciliation is a significant step for a continuous-variable quantum key distribution (CV-QKD) system. We propose a reconciliation method that allows two authorized parties to extract a consistent and secure binary key in a CV-QKD protocol, which is based on Gaussian-modulated coherent states and homodyne detection. This method named spherical reconciliation is based on spherical quantization and non-binary low-density parity-check (LDPC) codes. With the suitable signal-to-noise ratio (SNR) and code rate of non-binary LDPC codes, spherical reconciliation algorithm has a high efficiency and can extend the transmission distance of CV-QKD.

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Bidirectional multi-qubit quantum teleportation in noisy channel aided with weak measurement

杨光, 廉保旺, 聂敏, 金娇

2017 (4): 40305-040305. doi: 10.1088/1674-1056/26/4/040305

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Recently, bidirectional quantum teleportation has attracted a great deal of research attention. However, existing bidirectional teleportation schemes are normally discussed on the basis of perfect quantum environments. In this paper, we first put forward a bidirectional teleportation scheme to transport three-qubit Greenberger-Horne-Zeilinger (GHZ) states based on controled-not (CNOT) operation and single-qubit measurement. Then, we generalize it to the teleportation of multi-qubit GHZ states. Further, we discuss the influence of quantum noise on our scheme by the example of an amplitude damping channel, then we obtain the fidelity of the teleportation. Finally, we utilize the weak measurement and the corresponding reversing measurement to protect the quantum entanglement, which shows an effective enhancement of the teleportation fidelity.

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Correction of cosine oscillation to the improved correlation method of estimating the amplitude of gravitational background signal

巫伟皇, 田苑, 薛超, 罗杰, 邵成刚

2017 (4): 40401-040401. doi: 10.1088/1674-1056/26/4/040401

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In the measurement of G with the angular acceleration method, the improved correlation method developed by Wu et al. (Wu W H, Tian Y, Luo J, Shao C G, Xu J H and Wang D H 2016 Rev. Sci. Instrum. 87 094501) is used to accurately estimate the amplitudes of the prominent harmonic components of the gravitational background signal with time-varying frequency. Except the quadratic slow drift, the angular frequency of the gravitational background signal also includes a cosine oscillation coming from the useful angular acceleration signal, which leads to a deviation from the estimated amplitude. We calculate the correction of the cosine oscillation to the amplitude estimation. The result shows that the corrections of the cosine oscillation to the amplitudes of the fundamental frequency and second harmonic components obtained by the improved correlation method are within respective errors.

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Fiber-based multiple access timing signal synchronization technique

袁一博, 王波, 高超, 王力军

2017 (4): 40601-040601. doi: 10.1088/1674-1056/26/4/040601

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A fiber-based, multiple access timing signal synchronization scheme is demonstrated. By coupling out the bidirectional transmission signals, a highly stable timing signal can be recovered at arbitrary points along the fiber with the help of the loop delay message broadcasted via ethernet from the local module. The experiment is carried out on a 30-km fiber placed in a temperature-controlled box. In one-day period, when the round trip fiber transfer delay fluctuation is 60 ns, the fluctuations of the stabilized timing signal from the download and the remote modules were only ± 125 ps and ± 100 ps, respectively. Also, the system error caused by transmission path asymmetry and thermal drift is calibrated, and a 100-ps magnitude synchronization accuracy is realized. This method could provide new insights into the construction of a fiber-based time transfer network.

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Noise analysis of grating-based x-ray differential phase-contrast imaging with angular signal radiography

鲍园, 高昆, 吴朝, 卫晨希, 昝贵彬, 朱佩平, 田扬超

2017 (4): 40602-040602. doi: 10.1088/1674-1056/26/4/040602

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X-ray phase-contrast imaging is one of the novel techniques, and has potential to enhance image quality and provide the details of inner structures nondestructively. In this work, we investigate quantitatively signal-to-noise ratio (SNR) of grating-based x-ray phase contrast imaging (GBPCI) system by employing angular signal radiography (ASR). Moreover, photon statistics and mechanical error that is a major source of noise are investigated in detail. Results show the dependence of SNR on the system parameters and the effects on the extracted absorption, refraction and scattering images. Our conclusions can be used to optimize the system design for upcoming practical applications in the areas such as material science and biomedical imaging.

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Modeling and analysis for the image mapping spectrometer

袁艳, 丁晓铭, 苏丽娟, 王婉悦

2017 (4): 40701-040701. doi: 10.1088/1674-1056/26/4/040701

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The snapshot image mapping spectrometer (IMS) has advantages such as high temporal resolution, high throughput, compact structure and simple reconstructed algorithm. In recent years, it has been utilized in biomedicine, remote sensing, etc. However, the system errors and various factors can cause cross talk, image degradation and spectral distortion in the system. In this research, a theoretical model is presented along with the point response function (PRF) for the IMS, and the influence of the mirror tilt angle error of the image mapper and the prism apex angle error are analyzed based on the model. The results indicate that the tilt angle error causes loss of light throughput and the prism apex angle error causes spectral mixing between adjacent sub-images. The light intensity on the image plane is reduced to 95% when the mirror tilt angle error is increased to ±100" (≈0.028°). The prism apex error should be controlled within the range of 0-36" (0.01°) to ensure the designed number of spectral bands, and avoid spectral mixing between adjacent images.

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Semiclassical investigation of Coulomb focusing effects in atomic above-threshold ionization with elliptically polarized laser fields

王传亮, 夏立新, 姚洪斌, 李文亮

2017 (4): 43201-043201. doi: 10.1088/1674-1056/26/4/043201

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We investigate atomic above-threshold ionization in elliptically polarized strong laser fields with a semiclassical approach. With increasing laser intensity, the Coulomb focusing (CF) effects are found to become stronger in both parallel and perpendicular directions with respect to the polarization plane. The dependence of CF effects on tunnel exit, initial transverse momentum distribution and laser electric field is analyzed. It was revealed that the effects of tunnel exit are most prominent with variation of the laser intensity, and the other two factors both play non-negligible roles. Our results provide a deeper insight to the recent experiments of Coulomb asymmetry [Shafir D, et al., 2013 Phys. Rev. Lett. 111 023005 and Li M, et al., 2013 Phys. Rev. Lett. 111 023006].

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The effect of field modulation on the vibrational population of the photoassociated NaK and its dynamics

王玉, 岳大光, 周旭聪, 郭雅慧, 孟庆田

2017 (4): 43202-043202. doi: 10.1088/1674-1056/26/4/043202

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This paper presents calculation results for the photoassociation of a NaK molecule with a two-color modulated laser and gives a detailed analysis about them. For the two-step photoassociation process in intense fields, the effect of two-color modulated laser parameters, such as relative phase, envelope period, and laser intensity, on the population of the molecular electronic state can be obtained by solving the time-dependent Schrödinger equation through the quantum wave packet method. The numerical simulation shows not only that the influence of laser parameters on the vibrational distribution presents some regularity, but also that a higher population in the ground electronic state can be realized through adjusting these laser parameters.

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Off-site trimer superfluid on a one-dimensional optical lattice

范二女, 张万舟

2017 (4): 43701-043701. doi: 10.1088/1674-1056/26/4/043701

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The Bose-Hubbard model with an effective off-site three-body tunneling, characterized by jumps towards one another, between one atom on a site and a pair atoms on the neighborhood site, is studied systematically on a one-dimensional (1D) lattice, by using the density matrix renormalization group method. The off-site trimer superfluid, condensing at momentum k=0, emerges in the softcore Bose-Hubbard model but it disappears in the hardcore Bose-Hubbard model. Our results numerically verify that the off-site trimer superfluid phase derived in the momentum space from [Phys. Rev. A 81, 011601(R) (2010)] is stable in the thermodynamic limit. The off-site trimer superfluid phase, the partially off-site trimer superfluid phase and the Mott insulator phase are found, as well as interesting phase transitions, such as the continuous or first-order phase transition from the trimer superfluid phase to the Mott insulator phase. Our results are helpful in realizing this novel off-site trimer superfluid phase by cold atom experiments.

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Common-mode noise rejection using fringe-locking method in WEP test by simultaneous dual-species atom interferometers

邓小兵, 段小春, 毛德凯, 周敏康, 邵成刚, 胡忠坤

2017 (4): 43702-043702. doi: 10.1088/1674-1056/26/4/043702

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We theoretically investigate the application of the fringe-locking method (FLM) in the dual-species quantum test of the weak equivalence principle (WEP). With the FLM, the measurement is performed invariably at the midfringe, and the extraction of the phase shift for atom interferometers is linearized. For the simultaneous interferometers, this linearization enables a good common-mode rejection of vibration noise, which is usually the main limit for high precision WEP tests of the dual-species kind. We note that this method also allows for an unbiased determination of the gravity accelerations difference, which meanwhile is ready to be implemented.

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Computational and experimental verification of a wide-angle metamaterial absorber

陈超, 王君

2017 (4): 44101-044101. doi: 10.1088/1674-1056/26/4/044101

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A metamaterial absorber is computed numerically and measured experimentally in a 150-THz~300-THz range. The measured absorber achieves high absorption rate for both transverse electric (TE) and transverse magnetic (TM) polarizations at large angles of incidence. An absorption sensor scheme is proposed based on the measured absorber and the variations of surrounding media. Different surrounding media are applied to the surface of the absorption sensor (including air, water, and glucose solution). Measured results show that high figure of merit (FOM) values are obtained for different surrounding media. The proposed sensor does not depend on the substrate, which means that it can be transplanted to different sensing platforms conveniently.

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Compressing ultrafast electron pulse by radio frequency cavity

裴敏洁, 齐大龙, 齐迎朋, 贾天卿, 张诗按, 孙真荣

2017 (4): 44102-044102. doi: 10.1088/1674-1056/26/4/044102

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An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale. The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width, and therefore limit the temporal resolution of the high brightness electron pulse. Here in this work, we design an ultrafast electron diffraction system, and utilize a radio frequency cavity to realize the ultrafast electron pulse compression. We experimentally demonstrate that the stretched electron pulse width of 14.98 ps with an electron energy of 40 keV and the electron number of 1.0×10⁵ can be maximally compressed to about 0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity. We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single- and multi-pulse measurements by considering radiofrequency field time jitter, electron pulse time jitter and their relative time jitter. We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency. These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.

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Investigation of three-pulse photon echo in thick crystal using finite-difference time-domain method

马秀荣, 徐林, 常世元, 张双根

2017 (4): 44201-044201. doi: 10.1088/1674-1056/26/4/044201

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This paper investigates the phenomenon of three-pulse photon echo in thick rare-earth ions doped crystal whose thickness is far larger than 0.002 cm which is adopted in previous works. The influence of thickness on the three-pulse photon echo's amplitude and efficiency is analyzed with the Maxwell-Bloch equations solved by finite-difference time-domain method. We demonstrate that the amplitude of three-pulse echo will increase with the increasing of thickness and the optimum thickness to generate three-pulse photon echo is 0.3 cm for Tm³⁺:YAG when the attenuation of the input pulse is taken into account. Meanwhile, we find the expression 0.09exp(α'L), which is previously employed to describe the relationship between echo's efficiency and thickness, should be modified as 1.3·0.09exp(2.4·α'L ight) with the propagation of echo considered.

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Tunable second harmonic generation from a Kerr-lens mode-locked Yb: YCa₄O(BO₃)₃ femtosecond laser

高子叶, 朱江峰, 吴正茂, 魏志义, 于浩海, 张怀金, 王继扬

2017 (4): 44202-044202. doi: 10.1088/1674-1056/26/4/044202

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We experimentally demonstrated a diode-pumped Kerr-lens mode-locked femtosecond (fs) laser with a self-frequency doubling Yb:YCa₄O(BO₃)₃ crystal. Sub-40 fs laser pulses were directly generated from the oscillator without extracavity compression. The central wavelength was tunable from 1039 nm to 1049 nm with a typical bandwidth of 35 nm and an average output power of 53 mW. For the first time, a self-frequency doubled second harmonic green laser with tunable range from 519 nm to 525 nm was observed.

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1.5-MHz repetition rate passively Q-switched Nd: YVO₄ laser based on WS₂ saturable absorber

王茜, 李璐, 李金萍, 王勇刚

2017 (4): 44203-044203. doi: 10.1088/1674-1056/26/4/044203

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A transmission-type tungsten disulfide (WS₂)-based saturable absorber (SA) is fabricated and applied to passively Q-switched Nd:YVO₄ laser. The WS₂ nanosheets are deposited on a quartz substrate by the vertical evaporation method. By inserting the WS₂ SA into the plano-concave laser cavity, we achieve 153-ns pulses with an average output power of 1.19 W at 1064 nm. To the best of our knowledge, both of them are the best results among those obtained by the Q-switched solid-state lasers with WS₂-based absorbers. The repetition rate ranges from 1.176 MHz to 1.578 MHz. As far as we know, it is the first time that MHz level Q-switched pulses have been generated in all solid state lasers based on low-dimensional materials so far.

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Autler-Townes spectroscopy of high-lying state by phase conjugate six-wave mixing

白金海, 李建军, 吴令安, 傅盘铭, 王如泉, 左战春

2017 (4): 44204-044204. doi: 10.1088/1674-1056/26/4/044204

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An Autler-Townes (AT) spectroscopy based on phase conjugate six-wave mixing (SWM) is proposed to detect AT doublet of high-lying state in a Doppler-broadened cascade four-level system. It is found that the SWM spectrum is dependent strongly on the ratios between the magnitudes of the wave vectors. We discuss how the Doppler broadening affects the SWM spectrum from a time-domain viewpoint and find that, due the atomic motion, the atomic polarizations acquire different phases for atoms with different velocities as time evolves. The Doppler free SWM spectrum can be obtained only when the atomic polarization can be rephasing again at certain time after the interactions of all the incident fields.

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Optical nonlinearities of tetracarbonyl-chromium triphenyl phosphine complex

M D Zidan,A W Allaf,A Allahham,A AL-Zier

2017 (4): 44205-044205. doi: 10.1088/1674-1056/26/4/044205

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The new tetracarbonyl–chromium-triphenyl phosphine complex was synthesized and characterized using ultraviolet (UV)-visible, Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) techniques. The characterization results confirm the molecular structure of the new complex. The z-scan measurements were done by diode laser [continuous wave (CW)] to estimate the nonlinear optical parameter (χ³). The results led to calculate three parameters: the ground-state cross sections (σ_g), the excited-state cross sections (σ_ex), and thermo-optic coefficient of the new complex. This study indicated that our complex is a suitable for photonic applications.

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Laser phase effect on asymmetric harmonic distribution in H₂⁺

冯立强, 李文亮, 刘辉

2017 (4): 44206-044206. doi: 10.1088/1674-1056/26/4/044206

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The laser phase effect on the spatial distribution of the molecular high-order harmonic generation (MHHG) spectrum from H₂⁺ is theoretically investigated through solving the Non-Bohn-Oppenheimer (NBO) time-dependent Schrödinger equation (TDSE). The results are shown as follows. (i) The generated harmonics from the two nuclei each present an asymmetric distribution. Particularly, when the laser phases are chosen from 0.0π to 0.6π and from 1.7π to 2.0π, the contribution from the negative-H plays a main role in harmonic generation. When the laser phases are chosen from 0.7π to 1.6π, the contribution from the positive-H to the harmonic generation is remarkably enhanced and becomes greater than that from the negative-H. The electron localization, the time-frequency analyses of the harmonic spectrum and the time-dependent wave function are shown to explain the asymmetric harmonic distribution in H₂⁺, which provides us with a method to control the electron motion in molecules. (ii) As the pulse duration increases, the asymmetric distributions of the MHHG in two H nuclei decrease. (iii) Isotope investigation shows that the asymmetric harmonic distribution can be reduced by introducing the heavy nucleus (i.e., D₂⁺).

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Optical properties of Mg²⁺, Yb³⁺, and Ho³⁺ tri-doped LiNbO₃ crystals

代丽, 刘春蕊, 谭超, 阎哲华, 徐玉恒

2017 (4): 44207-044207. doi: 10.1088/1674-1056/26/4/044207

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A series of LiNbO₃ crystals tri-doped with Mg²⁺, Yb³⁺, and Ho³⁺ are grown by the conventional Czochraski technique. The concentrations of Mg²⁺, Yb³⁺, and Ho³⁺ ions in Mg:Yb:Ho:LiNbO₃ crystals are measured by using an inductively coupled plasma atomic emission spectrometry. The x-ray diffraction is proposed to determine the lattice constant and analyze the internal structure of the crystal. The light-induced scattering of Mg:Yb:Ho:LiNbO₃ crystal is quantitatively described via the threshold effect of incident exposure energy flux. The exposure energy (E_r) is calculated to discuss the optical damage resistance ability. The exposure energy of Mg(7 mol):Yb:Ho:LiNbO₃ crystal is 709.17 J/cm², approximately 425 times higher than that of the Mg(1 mol):Yb:Ho:LiNbO₃ crystal in magnitude. The blue, red, and very intense green bands of Mg:Yb:Ho:LiNbO₃ crystal are observed under the 980-nm laser excitation to evaluate the up-conversion emission properties. The dependence of the emission intensity on pumping power indicates that the up-conversion emission is a two-photon process. The up-conversion emission mechanism is discussed in detail. This study indicates that Mg:Yb:Ho:LiNbO₃ crystal can be applied to the fabrication of new multifunctional photoluminescence devices.

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Numerical study on characteristic of two-dimensional metal/dielectric photonic crystals

宗易昕, 夏建白, 武海斌

2017 (4): 44208-044208. doi: 10.1088/1674-1056/26/4/044208

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An improved plan-wave expansion method is adopted to theoretically study the photonic band diagrams of two-dimensional (2D) metal/dielectric photonic crystals. Based on the photonic band structures, the dependence of flat bands and photonic bandgaps on two parameters (dielectric constant and filling factor) are investigated for two types of 2D metal/dielectric (M/D) photonic crystals, hole and cylinder photonic crystals. The simulation results show that band structures are affected greatly by these two parameters. Flat bands and bandgaps can be easily obtained by tuning these parameters and the bandgap width may reach to the maximum at certain parameters. It is worth noting that the hole-type photonic crystals show more bandgaps than the corresponding cylinder ones, and the frequency ranges of bandgaps also depend strongly on these parameters. Besides, the photonic crystals containing metallic medium can obtain more modulation of photonic bands, band gaps, and large effective refractive index, etc. than the dielectric/dielectric ones. According to the numerical results, the needs of optical devices for flat bands and bandgaps can be met by selecting the suitable geometry and material parameters.

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DEM simulation of granular segregation in two-compartment system under zero gravity

王文广, 周志刚, 宗谨, 厚美瑛

2017 (4): 44501-044501. doi: 10.1088/1674-1056/26/4/044501

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In this paper, granular segregation in a two-compartment cell in zero gravity is studied numerically by DEM simulation. In the simulation using a virtual window method we find a non-monotonic flux, a function which governs the segregation. A parameter is used to quantify the segregation. The effect of three parameters: the total number of particles N, the excitation strength Γ, and the position of the window coupling the two compartments, on the segregation and the waiting time τ are investigated. It is found that the segregation observed in zero gravity exists and does not depend on the excitation strength Γ. The waiting time τ, however, depends strongly on Γ: the higher the Γ, the lower the waiting time τ. The simulation results are important in guiding the SJ-10 satellite microgravity experiments.

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The interaction between a screw dislocation and a wedge-shaped crack in one-dimensional hexagonal piezoelectric quasicrystals

姜丽娟, 刘官厅

2017 (4): 44601-044601. doi: 10.1088/1674-1056/26/4/044601

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Based on the fundamental equations of piezoelasticity of quasicrystal material, we investigated the interaction between a screw dislocation and a wedge-shaped crack in the piezoelectricity of one-dimensional hexagonal quasicrystals. Explicit analytical solutions are obtained for stress and electric displacement intensity factors of the crack, as well as the force on dislocation. The derivation is based on the conformal mapping method and the perturbation technique. The influences of the wedge angle and dislocation location on the image force are also discussed. The results obtained in this paper can be fully reduced to some special cases already available or deriving new ones.

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Research on the jet characteristics of the deflector-jet mechanism of the servo valve

延皓, 王凤聚, 李长春, 黄静

2017 (4): 44701-044701. doi: 10.1088/1674-1056/26/4/044701

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In view of the complicated structure of the deflector-jet mechanism, a mathematical model based on the turbulent jet flow theory in the deflector-jet amplifier is proposed. Considering the energy transformation and momentum variation, an equation of the flow velocity distribution at the key fluid region is established to describe the morphological changes of the fluid when it passes through the deflector and jets into the receiver. Moreover, the process is segmented into four stages. According to the research results, the oil enters the deflector and impinges with the side wall. Then one part of the oil's flow velocity decreases and a high pressure zone is formed by the oil accumulation, the other part of the oil reverses out of the deflector along the side wall. Prior to entering the receiver, the flow is a kind of plane impinging jet. Virtually, the working pressure of the receiver is generated by the impact force, while the high speed fluid flows out of the receiver and forms a violent vortex, which generates negative pressure and causes the oil to be gasified. Compared with the numerical simulation results, the turbulent jet model that can effectively describe the characteristics of the deflector-jet mechanism is accurate. In addition, the calculation results of the prestage pressure characteristic have been verified by experiments.

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Variation of passivation behavior induced by sputtered energetic particles and thermal annealing for ITO/SiO_x/Si system

高明, 杜汇伟, 杨洁, 赵磊, 徐静, 马忠权

2017 (4): 45201-045201. doi: 10.1088/1674-1056/26/4/045201

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The damage on the atomic bonding and electronic state in a SiO_x(1.4-2.3 nm)/c-Si(150 μm) interface has been investigated. This occurred in the process of depositing indium tin oxide (ITO) film onto the silicon substrate by magnetron sputtering. We observe that this damage is caused by energetic particles produced in the plasma (atoms, ions, and UV light). The passivation quality and the variation on interface states of the SiO_x/c-Si system were mainly studied by using effective minority carrier lifetime (τ_eff) measurement as a potential evaluation. The results showed that the samples' τ_eff was reduced by more than 90% after ITO formation, declined from 107 μs to 5 μs. Following vacuum annealing at 200℃, the τ_eff can be restored to 30 μs. The components of Si to O bonding states at the SiO_x/c-Si interface were analyzed by x-ray photoelectron spectroscopy (XPS) coupled with depth profiling. The amorphous phase of the SiO_x layer and the “atomistic interleaving structure” at the SiO_x/c-Si interface was observed by a transmission electron microscope (TEM). The chemical configuration of the Si-O fraction within the intermediate region is the main reason for inducing the variation of Si dangling bonds (or interface states) and effective minority carrier lifetime. After an appropriate annealing, the reduction of the Si dangling bonds between SiO_x and near the c-Si surface is helpful to improve the passivation effect.

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Mode transition in dusty micro-plasma driven by pulsed radio-frequency source in C₂H₂/Ar mixture

刘相梅, 李瑞, 郑亚辉

2017 (4): 45202-045202. doi: 10.1088/1674-1056/26/4/045202

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Physical qualities of dusty plasma in the pulsed radio-frequency C₂H₂/Ar microdischarges are carefully investigated by a one-dimensional hydrodynamic model and aerosol dynamics model. Since the thermophoretic force has a great effect on the nanoparticle density spatial distribution, the neutral gas energy equation is taken into accounted. The effects of pulse parameters (dust ratio, modulation frequency) on the nanoparticle formation and growth process are mainly discussed. The calculation results show that, as the duty ratio increases, the mode transition from the sheath oscillation (α regime) to the secondary electron heating (γ regime) occurred, which is quite different from the conventional pulsed discharge. Moreover, the effect of modulation frequency on the width of sheath and plasma density is analyzed. Compared with the H₂CC^- ions, the modulation frequency effect on the nanoparticles density becomes more prominent.

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Analysis of the Zeeman effect on D_α spectra on the EAST tokamak

高伟, 黄娟, 吴承瑞, 许棕, 侯玉梅, 金钊, 陈颖杰, 张鹏飞, 张凌, 吴振伟

2017 (4): 45203-045203. doi: 10.1088/1674-1056/26/4/045203

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Based on the passive spectroscopy, the D_α atomic emission spectra in the boundary region of the plasma have been measured by a high resolution optical spectroscopic multichannel analysis (OSMA) system in EAST tokamak. The Zeeman splitting of the D_α spectral lines has been observed. A fitting procedure by using a nonlinear least squares method was applied to fit and analyze all polarization π and ±σ components of the D_α atomic spectra to acquire the information of the local plasma. The spectral line shape was investigated according to emission spectra from different regions (e.g., low-field side and high-field side) along the viewing chords. Each polarization component was fitted and classified into three energy categories (the cold, warm, and hot components) based on different atomic production processes, in consistent with the transition energy distribution by calculating the gradient of the D_α spectral profile. The emission position, magnetic field intensity, and flow velocity of a deuterium atom were also discussed in the context.

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Theoretical prediction of new C-Si alloys in C2/m-20 structure

徐向阳, 柴常春, 樊庆扬, 杨银堂

2017 (4): 46101-046101. doi: 10.1088/1674-1056/26/4/046101

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We study structural, mechanical, and electronic properties of C₂₀, Si₂₀ and their alloys (C₁₆Si₄, C₁₂Si₈, C₈Si₁₂, and C₄Si₁₆) in C2/m structure by using density functional theory (DFT) based on first-principles calculations. The obtained elastic constants and the phonon spectra reveal mechanical and dynamic stability. The calculated formation enthalpy shows that the C-Si alloys might exist at a specified high temperature scale. The ratio of B/G and Poisson's ratio indicate that these C-Si alloys in C2/m-20 structure are all brittle. The elastic anisotropic properties derived by bulk modulus and shear modulus show slight anisotropy. In addition, the band structures and density of states are also depicted, which reveal that C₂₀, C₁₆Si₄, and Si₂₀ are indirect band gap semiconductors, while C₈Si₁₂ and C₄Si₁₆ are semi-metallic alloys. Notably, a direct band gap semiconductor (C₁₂Si₈) is obtained by doping two indirect band gap semiconductors (C₂₀ and Si₂₀).

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Influence of high pulsed magnetic field on tensile properties of TC4 alloy

李桂荣, 王芳芳, 王宏明, 郑瑞, 薛飞, 程江峰

2017 (4): 46201-046201. doi: 10.1088/1674-1056/26/4/046201

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The tensile tests of TC4 alloy are carried on electronic universal testing machine in the synchronous presence of high pulsed magnetic field (HPMF) parallel to the axial direction. The effects of magnetic induction intensity (B=0, 1 T, 3 T, and 5 T) on elongation (δ) of TC4 alloy are investigated. At 3 T, the elongation arrives at a maximum value of 12.41%, which is enhanced by 23.98% in comparison with that of initial sample. The elongation curve shows that 3 T is a critical point. With B increasing, the volume fraction of α phase is enhanced from 49.7% to 55.9%, which demonstrates that the HPMF can induce the phase transformation from β phase to α phase. Furthermore, the magnetic field not only promotes the orientation preference of crystal plane along the slipping direction, but also has the effect on increasing the dislocation density. The dislocation density increases with the enhancement of magnetic induction intensity and the 3-T parameter is ascertained as a turning point from increase to decrease tendency. When B is larger than 3 T, the dislocation density decreases with the enhancement of B. The influence of magnetic field is analyzed on the basis of magneto-plasticity effect. The high magnetic field will enhance the dislocation strain energy and promote the state conversion of radical pair generated between the dislocation and obstacles from singlet into triplet state, in which is analyzed the phenomenon that the dislocation density is at an utmost with B=3 T. Finally, the inevitability of optimized 3-T parameter is further discussed on a quantum scale.

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High-pressure dynamic, thermodynamic properties, and hardness of CdP₂

冯世全, 王伶俐, 姜晓旭, 李海宁, 程新路, 苏磊

2017 (4): 46301-046301. doi: 10.1088/1674-1056/26/4/046301

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Using a pseudopotential plane-waves method, we calculate the phonon dispersion curves, thermodynamic properties, and hardness values of α-CdP₂ and β-CdP₂ under high pressure. From the studies of the phonon property and enthalpy difference curves, we discuss a phase transform from β-CdP₂ to α-CdP₂ in a pressure range between 20 GPa and 25 GPa. Then, the thermodynamic properties, Debye temperatures, and heat capacities are investigated at high pressures. What is more, we employ a semiempirical method to evaluate the pressure effects on the hardness for these two crystals. The results show that the hardness values of both α-CdP₂ and β-CdP₂ increase as pressure is increased. The influence mechanism of the pressure effect on the hardness of CdP₂ is also briefly discussed.

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Lattice dynamics properties of chalcopyrite ZnSnP₂: Density-functional calculations by using a linear response theory

虞游, 董玉静, 沈艳红, 赵国栋, 郑小林, 盛佳南

2017 (4): 46302-046302. doi: 10.1088/1674-1056/26/4/046302

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We present a first-principles study of the structural, dielectric, and lattice dynamical properties for chalcopyrite semiconductor ZnSnP₂. The structural properties are calculated using a plane-wave pseudopotential method of density-functional theory. A linear response theory is used to derive Born effective charge tensors for each atom, dielectric constants in low and high frequency limits, and phonon frequencies. We calculate all zone-center phonon modes, identify Raman and infrared active modes, and report LO-TO splitting of the infrared modes. The results show an excellent agreement with experiment and propose several predictive behaviors.

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The electronic, optical, and thermodynamical properties of tetragonal, monoclinic, and orthorhombic M₃N₄ (M=Si, Ge, Sn): A first-principles study

陈东, 程科, 齐蓓影

2017 (4): 46303-046303. doi: 10.1088/1674-1056/26/4/046303

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A detailed study of the M₃N₄ (M=Si, Ge, Sn) nitrides in their tetragonal, monoclinic and orthorhombic phases has been performed with the plane-wave pseudo-potential method combined with the quasi-harmonic approximation, including the phononic effects. We rationalize the main puzzle, i.e., the fundamental properties of these phases are unclear, by calculating the crystal structures, density of states, and optical properties. The direct band gaps of t-Ge₃N₄, m-Si₃N₄, and o-Ge₃N₄ benefit the opto-electrical properties. t-, m-, and o-Si₃N₄ can be used as refractive materials while m-M₃N₄ (M=Si, Ge, Sn) are optically transparent in the visible light region. Our results improve the understanding of the detailed electronic structures of all compounds, as well as the influences of electronic structure on their stabilities. Furthermore, we find that thermodynamic quantities are sensitive to structures and, therefore, depend on various temperature and pressure conditions.

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High pressure electrical transport behavior in SrF₂ nanoplates

崔晓岩, 胡廷静, 王婧姝, 张俊凯, 李雪飞, 杨景海, 高春晓

2017 (4): 46401-046401. doi: 10.1088/1674-1056/26/4/046401

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The charge transport behavior of strontium fluoride nanocrystals has been investigated by in situ impedance measurement up to 35 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in SrF₂ nanocrystals include both F^- ions and electrons. In the Fm3m phase, pressure makes the electronic transport easier, while makes it more difficult in the Pnma phase. The defects at grain boundaries dominate the electronic transport process. Pressure could make the charge-discharge processes in the Fm3m phase much easier, but make it more difficult in the Pnma phase.

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Low-temperature phase transformation of CZTS thin films

赵蔚, 杜霖元, 刘林林, 孙亚利, 柳志伟, 滕晓云, 谢娟, 刘匡, 于威, 傅广生, 高超

2017 (4): 46402-046402. doi: 10.1088/1674-1056/26/4/046402

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The low temperature phase transformation in the Cu₂ZnSnS₄ (CZTS) films was investigated by laser annealing and low temperature thermal annealing. The Raman measurements show that a-high-power laser annealing could cause a red shift of the Raman scattering peaks of the kesterite (KS) structure and promotes the formation of the partially disordered kesterite (PD-KS) structure in the CZTS films, and the low-temperature thermal annealing only shifts the Raman scattering peak of KS phase by several wavenumber to low frequency and the broads Raman peaks in the low frequency region. Moreover, the above two processes were reversible. The Raman analyses of the CZTS samples prepared under different process show that the PD-KS structure tends to be found at low temperatures and low sulfur vapor pressures. Our results reveal that the control of the phase structure in CZTS films is feasible by adjusting the preparation process of the films.

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Superfluidity of coherent light in self-focusing nonlinear waveguides

成泽

2017 (4): 46701-046701. doi: 10.1088/1674-1056/26/4/046701

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We establish the superfluidity theory of coherent light in waveguides made of nonlinear polar crystals. It is found that the pairing state of photons in a nonlinear polar crystal is the photonic superfluid state. The photon-photon interaction potential is an attractive effective interaction by exchange of virtual optical phonons. In the traveling-wave pairing state of photons, the photon number is conserved, which is similar to the Bose-Einstein condensation (BEC) state of photons. In analogy to the BCS-BEC crossover theory of superconductivity, we derive a set of coupled order parameter and number equations, which determine the solution of the traveling-wave superfluid state of photons. This solution gives the critical velocity of light in a self-focusing nonlinear waveguide. The most important property of the photonic superfluid state is that the system of photon pairs evolves without scattering attenuations.

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Superexchange-mediated magnetization dynamics with ultracold alkaline-earth atoms in an optical lattice

朱少兵, 钱军, 王育竹

2017 (4): 46702-046702. doi: 10.1088/1674-1056/26/4/046702

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Superexchange and inter-orbital spin-exchange interactions are key ingredients for understanding (orbital) quantum magnetism in strongly correlated systems and have been realized in ultracold atomic gases. Here we study the spin dynamics of ultracold alkaline-earth atoms in an optical lattice when the two exchange interactions coexist. In the superexchange interaction dominating regime, we find that the time-resolved spin imbalance shows a remarkable modulated oscillation, which can be attributed to the interplay between local and nonlocal quantum mechanical exchange mechanisms. Moreover, the filling of the long-lived excited atoms affects the collapse and revival of the magnetization dynamics. These observations can be realized in state-dependent optical lattices combined with the state-of-the-art advances in optical lattice clock spectroscopy.

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Icephobic performance on the aluminum foil-based micro-/nanostructured surface

陈宇, 刘桂成, 姜磊, 金志永, 叶锋, 李重基, 王磊, 王波

2017 (4): 46801-046801. doi: 10.1088/1674-1056/26/4/046801

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The research of superhydrophobic materials has attracted many researchers' attention due to its application value and prospects. In order to expand the serviceable range, people have investigated various superhydrophobic materials. The simple and easy preparation method has become the focus for superhydrophobic materials. In this paper, we present a program for preparing a rough surface on an aluminum foil, which possesses excellent hydrophobic properties after the treatment with low surface energy materials at high vacuum. The resulting contact angle is larger than 160°, and the droplet cannot freeze on the surface above -10℃. Meanwhile, the modified aluminum foil with the thickness of less than 100 μm can be used as an ideal flexible applied material for superhydrophobicity/anti-icing.

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Effect of deposited temperatures of the buffer layer on the band offset of CZTS/In₂S₃ heterostructure and its solar cell performance

俞金玲, 郑重明, 董丽美, 程树英, 赖云锋, 郑巧, 周海芳, 贾宏杰, 张红

2017 (4): 46802-046802. doi: 10.1088/1674-1056/26/4/046802

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The effect of the deposition temperature of the buffer layer In₂S₃ on the band alignment of CZTS/In₂S₃ heterostructures and the solar cell performance have been investigated. The In₂S₃ films are prepared by thermal evaporation method at temperatures of 30, 100, 150, and 200℃, respectively. By using x-ray photoelectron spectroscopy (XPS), the valence band offsets (VBO) are determined to be -0.28 ±0.1, -0.28±0.1, -0.34±0.1, and -0.42±0.1 eV for the CZTS/In₂S₃ heterostructures deposited at 30, 100, 150, and 200℃, respectively, and the corresponding conduction band offsets (CBO) are found to be 0.3±0.1, 0.41±0.1, 0.22±0.1, and 0.01±0.1 eV, respectively. The XPS study also reveals that inter-diffusion of In and Cu occurs at the interface of the heterostructures, which is especially serious at 200℃ leading to large amount of interface defects or the formation of CuInS₂ phase at the interface. The CZTS solar cell with the buffer layer In₂S₃ deposited at 150℃ shows the best performance due to the proper CBO value at the heterostructure interface and the improved crystal quality of In₂S₃ film induced by the appropriate deposition temperature. The device prepared at 100℃ presents the poorest performance owing to too high a value of CBO. It is demonstrated that the deposition temperature is a crucial parameter to control the quality of the solar cells.

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Ab initio study on the anisotropy of mechanical behavior and deformation mechanism for boron carbide

李君, 徐爽, 张金咏, 刘立胜, 刘齐文, 佘武昌, 傅正义

2017 (4): 47101-047101. doi: 10.1088/1674-1056/26/4/047101

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The mechanical properties and deformation mechanisms of boron carbide under a-axis and c-axis uniaxial compression are investigated by ab initio calculations based on the density functional theory. Strong anisotropy is observed. Under a-axis and c-axis compression, the maximum stresses are 89.0 GPa and 172.2 GPa respectively. Under a-axis compression, the destruction of icosahedra results in the unrecoverable deformation, while under c-axis compression, the main deformation mechanism is the formation of new bonds between the boron atoms in the three-atom chains and the equatorial boron atoms in the neighboring icosahedra.

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First principles investigation of protactinium-based oxide-perovskites for flexible opto—electronic devices

Nazia Erum,Muhammad Azhar Iqbal

2017 (4): 47102-047102. doi: 10.1088/1674-1056/26/4/047102

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The structural, elastic, mechanical, electronic, and optical properties of KPaO₃ and RbPaO₃ compounds are investigated from first-principles calculations by using the WIEN2k code in the frame of local density approximation (LDA) and generalized gradient approximation (GGA). The calculated ground state quantities, such as lattice constant (a₀), ground state energy (E), bulk modulus (B), and their pressure derivative (B_p) are in reasonable agreement with the present analytical and previous theoretical results and available experimental data. Based on several elastic and mechanical parameters, the structural stability, hardness, stiffness and the brittle and ductile behaviors are discussed, which reveal that protactinium-based oxide series of perovskites is mechanically stable and possesses weak resistance to shear deformation compared with resistance to unidirectional compression while flexible and covalent behaviors are dominated in them. The analysis of band profile through Trans-Blaha modified Becke-Johnson (TB-mBJ) potential highlights the underestimation of bandgap with traditional density functional theory (DFT) approximation. Specific contribution of electronic states is investigated by means of total and partial density of states and it can be evaluated that both compounds are (Γ-Γ) direct bandgap semiconductors. All fundamental optical properties are analyzed while attention is paid to absorption and reflection spectra to explore extensive absorptions and reflections of these compounds in high frequency regions. The present method represents an influential approach to calculating the whole set of elastic, mechanical, and opto-electronic parameters, which would conduce to the understanding of various physical phenomena and empower the device engineers to implement these materials in flexible opto-electronic applications.

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Electric current-induced giant electroresistance in La_0.36Pr_0.265Ca_0.375MnO₃ thin films

孙颖慧, 赵永刚, 王荣明

2017 (4): 47103-047103. doi: 10.1088/1674-1056/26/4/047103

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The electroresistance (ER) of La_0.36Pr_0.265Ca_0.375MnO₃ (LPCMO) epitaxial thin film was studied under various dc currents. The current effect was compared for the unpatterned film and patterned microbridge with a width of 50 μm. The value of ER in the unpatterned LPCMO film could reach 0.54 under a 1-mA current, which is much higher than ER under 1 mA for the patterned weak phase-separated La_0.67Ca_0.33MnO₃ and La_0.85Sr_0.15MnO₃ microbridges with 50-μm width. More interestingly, for the patterned LPCMO microbridge, the maximum of ER can reach 0.6 under a small current of 100 μA. The results were explained by considering the coexistence of ferromagnetic metallic phase with the charge-ordered phase, and the variation of the phase separation with electric current.

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Investigation of the surface orientation influence on 10-nm double gate GaSb nMOSFETs

邸绍岩, 沈磊, 伦志远, 常鹏鹰, 赵凯, 卢朓, 杜刚, 刘晓彦

2017 (4): 47201-047201. doi: 10.1088/1674-1056/26/4/047201

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The performance of double gate GaSb nMOSFETs with surface orientations of (100) and (111) are compared by deterministically solving the time-dependent Boltzmann transport equation (BTE). Results show that the on-state current of the device with (111) surface orientation is almost three times larger than the (100) case due to the higher injection velocity. Moreover, the scattering rate of the (111) device is slightly lower than that of the (100) device.

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The origin of spin current in YIG/nonmagnetic metal multilayers at ferromagnetic resonance

康韵, 钟海, 郝润润, 胡树军, 康仕寿, 刘国磊, 张引, 王向荣, 颜世申, 吴勇, 于淑云, 韩广兵, 姜勇, 梅良模

2017 (4): 47202-047202. doi: 10.1088/1674-1056/26/4/047202

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Spin pumping in yttrium-iron-garnet (YIG)/nonmagnetic-metal (NM) layer systems under ferromagnetic resonance (FMR) conditions is a popular method of generating spin current in the NM layer. A good understanding of the spin current source is essential in extracting spin Hall angle of the NM and in potential spintronics applications. It is widely believed that spin current is pumped from precessing YIG magnetization into NM layer. Here, by combining microwave absorption and DC-voltage measurements on thin YIG/Pt and YIG/NM₁/NM₂ (NM₁=Cu or Al, NM₂=Pt or Ta), we unambiguously showed that spin current in NM, instead of from the precessing YIG magnetization, came from the magnetized NM surface (in contact with thin YIG), either due to the magnetic proximity effect (MPE) or from the inevitable diffused Fe ions from YIG to NM. This conclusion is reached through analyzing the FMR microwave absorption peaks with the DC-voltage peak from the inverse spin Hall effect (ISHE). The voltage signal is attributed to the magnetized NM surface, hardly observed in the conventional FMR experiments, and was greatly amplified when the electrical detection circuit was switched on.

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Decoupling technique of patch antenna arrays with shared substrate by suppressing near-field magnetic coupling using magnetic metamaterials

柳兆堂, 王甲富, 屈绍波, 张介秋, 马华, 徐卓, 张安学

2017 (4): 47301-047301. doi: 10.1088/1674-1056/26/4/047301

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In this paper, we propose the decoupling technique of patch antenna array by suppressing near-field magnetic coupling (NFMC) using magnetic metamaterials. To this end, a highly-integrated magnetic metamaterials, the substrate-integrated split-ring resonator (SI-SRR), is firstly proposed to achieve negative permeability at the antenna operating frequency. By integrating SI-SRR in between two closely spaced antennas, magnetic fields are blocked in the shared substrate due to negative permeability of SI-SRR, reducing NFMC between the two antennas. To verify the technique, a prototype was fabricated and measured. The measured results demonstrated that the isolation can be enhanced by more than 17 dB even when the gap between the two patch antennas is only about 0.067λ. Due to high integration, this technique provides an effective alternative to high-isolation antenna array.

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Enhancement of Förster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices

王子君, 赵娟, 周畅, 祁一歌, 于军胜

2017 (4): 47302-047302. doi: 10.1088/1674-1056/26/4/047302

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Fluorescence/phosphorescence hybrid white organic light-emitting devices (WOLEDs) based on double emitting layers (EMLs) with high color stability are fabricated. The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence (TADF) layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone (DMAC-DPS) and an ultrathin non-doped yellow phosphorescence layer employing bis[2-(4-tertbutylphenyl)benzothiazolato-N,C2'] iridium (acetylacetonate) ((tbt)₂Ir(acac)). Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline (Bphen) and 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBi) are selected as the electron transporting layer (ETL), and the thickness of yellow EML is adjusted to optimize device performance. The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l'Eclairage (CIE) coordinates variation of (0.017, 0.009) at a luminance ranging from 52 cd/m² to 6998 cd/m². The TPBi-based device yields a high efficiency with a maximum external quantum efficiency (EQE), current efficiency, and power efficiency of 10%, 21.1 cd/A, and 21.3 lm/W, respectively. The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer, so that Förster energy transfer (FRET) from DMAC-DPS to (tbt)₂Ir(acac) is dominant, which is beneficial to keep the color stable. The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.

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Etching mask optimization of InAs/GaSb superlattice mid-wavelength infared 640×512 focal plane array

郝宏玥, 向伟, 王国伟, 徐应强, 韩玺, 孙瑶耀, 蒋洞微, 张宇, 廖永平, 魏思航, 牛智川

2017 (4): 47303-047303. doi: 10.1088/1674-1056/26/4/047303

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In this paper we focused on the mask technology of inductively coupled plasma (ICP) etching for the mesa fabrication of infrared focal plane arrays (FPA). By using the SiO₂ mask, the mesa has higher graphics transfer accuracy and creates less micro-ripples in sidewalls. Comparing the IV characterization of detectors by using two different masks, the detector using the SiO₂ hard mask has the R₀A of 9.7×10⁶ Ω·cm², while the detector using the photoresist mask has the R₀A of 3.2×10² Ω·cm² in 77 K. After that we focused on the method of removing the remaining SiO₂ after mesa etching. The dry ICP etching and chemical buffer oxide etcher (BOE) based on HF and NH₄F are used in this part. Detectors using BOE only have closer R₀A to that using the combining method, but it leads to gaps on mesas because of the corrosion on AlSb layer by BOE. We finally choose the combining method and fabricated the 640×512 FPA. The FPA with cutoff wavelength of 4.8 μm has the average R₀A of 6.13×10⁹ Ω·cm² and the average detectivity of 4.51×10⁹ cm·Hz^1/2·W^-1 at 77 K. The FPA has good uniformity with the bad dots rate of 1.21% and the noise equivalent temperature difference (NEDT) of 22.9 mK operating at 77 K.

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Quantum transport through a Z-shaped silicene nanoribbon

A Ahmadi Fouladi

2017 (4): 47304-047304. doi: 10.1088/1674-1056/26/4/047304

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In this work, the electronic transport properties of Z-shaped silicene nanoribbon (ZsSiNR) structure are investigated. The calculations are based on the tight-binding model and Green's function method in Landauer-Büttiker formalism, in which the electronic density of states (DOS), transmission probability, and current-voltage characteristics of the system are calculated, numerically. It is shown that the geometry of the ZsSiNR structure can play an important role to control the electron transport through the system. It is observed that the intensity of electron localization at the edges of the ZsSiNR decreases with the increase of the spin-orbit interaction (SOI) strength. Also, the semiconductor to metallic transition occurs by increasing the SOI strength. The present theoretical results may be useful to design silicene-based devices in nanoelectronics.

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A novel enhancement mode AlGaN/GaN high electron mobility transistor with split floating gates

王辉, 王宁, 蒋苓利, 林新鹏, 赵海月, 于洪宇

2017 (4): 47305-047305. doi: 10.1088/1674-1056/26/4/047305

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A novel enhancement-mode AlGaN/GaN high electron mobility transistor (HEMT) is proposed and studied. Specifically, several split floating gates (FGs) with negative charges are inserted to the conventional MIS structure. The simulation results revealed that the V_th decreases with the increase of polarization sheet charge density and the tunnel dielectric (between FGs and AlGaN) thickness, while it increases with the increase of FGs sheet charge density and blocking dielectric (between FGs and control gate) thickness. In the case of the same gate length, the V_th will left shift with decreasing FG length. More interestingly, the split FGs could significantly reduce the device failure probability in comparison with the single large area FG structure.

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Improvement of reverse blocking performance in vertical power MOSFETs with Schottky-drain-connected semisuperjunctions

毛维, 王海永, 王晓飞, 杜鸣, 张金风, 郑雪峰, 王冲, 马晓华, 张进成, 郝跃

2017 (4): 47306-047306. doi: 10.1088/1674-1056/26/4/047306

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To enhance the reverse blocking capability with low specific on-resistance, a novel vertical metal-oxide-semiconductor field-effect transistor (MOSFET) with a Schottky-drian (SD) and SD-connected semisuperjunctions (SD-D-semi-SJ), named as SD-D-semi-SJ MOSFET is proposed and demonstrated by two-dimensional (2D) numerical simulations. The SD contacted with the n-pillar exhibits the Schottky-contact property, and that with the p-pillar the Ohmic-contact property. Based on these features, the SD-D-semi-SJ MOSFET could obviously overcome the great obstacle of the ineffectivity of the conventional superjunctions (SJ) or semisuperjunctions (semi-SJ) for the reverse applications and achieve a satisfactory trade-off between the reverse breakdown voltage (BV) and the specific on-resistance (R_onA). For a given pillar width and n-drift thickness, there exists a proper range of n-drift concentration (N), in which the SD-D-semi-SJ MOSFET could exhibit a better trade-off of R_onA-BV compared to the predication of SJ MOSFET in the forward applications. And what is much valuable, in this proper range of N, the desired BV and good trade-off could be achieved only by determining the pillar thickness, with the top assist layer thickness unchanged. Detailed analyses have been carried out to get physical insights into the intrinsic mechanism of R_onA-BV improvement in SD-D-semi-SJ MOSFET. These results demonstrate a great potential of SD-D-semi-SJ MOSFET in reverse applications.

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Review of flexible and transparent thin-film transistors based on zinc oxide and related materials

张永晖, 梅增霞, 梁会力, 杜小龙

2017 (4): 47307-047307. doi: 10.1088/1674-1056/26/4/047307

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Flexible and transparent electronics enters into a new era of electronic technologies. Ubiquitous applications involve wearable electronics, biosensors, flexible transparent displays, radio-frequency identifications (RFIDs), etc. Zinc oxide (ZnO) and relevant materials are the most commonly used inorganic semiconductors in flexible and transparent devices, owing to their high electrical performances, together with low processing temperatures and good optical transparencies. In this paper, we review recent advances in flexible and transparent thin-film transistors (TFTs) based on ZnO and relevant materials. After a brief introduction, the main progress of the preparation of each component (substrate, electrodes, channel and dielectrics) is summarized and discussed. Then, the effect of mechanical bending on electrical performance is highlighted. Finally, we suggest the challenges and opportunities in future investigations.

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Recent progress of ZnMgO ultraviolet photodetector

杨佳霖, 刘可为, 申德振

2017 (4): 47308-047308. doi: 10.1088/1674-1056/26/4/047308

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The ultra-violet (UV) detection has a wide application in both civil and military fields. ZnO is recognized as one of ideal materials for fabricating the UV photodetectors due to its plenty of advantages, such as wide bandgap, low cost, being environment-friendly, high radiation hardness, etc. Moreover, the alloying of ZnO with MgO to make ZnMgO could continually increase the band gap from ~3.3 eV to ~7.8 eV, which allows both solar blind and visible blind UV radiation to be detected. As is well known, ZnO is stabilized in the wurtzite structure, while MgO is stabilized in the rock salt structure. As a result, with increasing the Mg content, the crystal structure of ZnMgO alloy will change from wurtzite structure to rock salt structure. Therefore, ZnMgO photodetectors can be divided into three types based on the structures of alloys, namely, wurtzite-phase, cubic-phase and mixed-phase devices. In this paper, we review recent development and make the prospect of three types of ZnMgO UV photodetectors.

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Structural, electronic, and optical properties of hexagonal and triangular SiC NWs with different diameters

李彦景, 李亚林, 李树龙, 龚裴, 房晓勇

2017 (4): 47309-047309. doi: 10.1088/1674-1056/26/4/047309

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Silicon carbide (SiC) is a wideband gap semiconductor with great application prospects, and the SiC nanomaterials have attracted more and more attention because of their unique photoelectric properties. According to the first-principles calculations, we investigate the effects of diameter on the electronic and optical properties of triangular SiC NWs (T-NWs) and hexagonal SiC NWs (H-NWs). The results show that the structure of H-NWs is more stable than T-NWs, and the conduction band bottom of H-NWs is more and more deviated from the valence band top, while the conduction band bottom of T-NWs is closer to the valence band top. What is more, H-NWs and T-NWs have anisotropic optical properties. The result may be helpful in developing the photoelectric materials.

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Density-functional theory study on the electronic properties of laves phase superconductor CaIr₂

张奕, 陶向明, 谭明秋

2017 (4): 47401-047401. doi: 10.1088/1674-1056/26/4/047401

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In this work we have used density-functional theory methods such as full-potential local orbital minimum basis (FPLO) and ELK-flapw to study the electronic structure of newly discovered Laves phase superconductor CaIr₂. The calculation of density of states (DOS) indicates that the bands near Fermi level are mostly occupied by the d-electrons of iridium. The simulation of de Haas-van Alphen (dHvA) effect has been performed by using Elk code to check the Fermi surface topology. The results show that there exist four Fermi surfaces in CaIr₂, including two electron-type and two hole-type surfaces. The optical response properties of CaIr₂ have been calculated in the dipole-transition approximations combined with including intra-band Drude-like terms. In the optical spectrum σ (ω) shows that the crossover from intra-band to inter-band absorption occur near 1.45 eV. Further analysis on the electron energy loss spectra (EELS) matches the conclusion from that of optical conductivity σ (ω).

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Macroscopic resonant tunneling in an rf-SQUID flux qubit under a single-cycle sinusoidal driving

史建新, 许伟伟, 孙国柱, 陈健, 康琳, 吴培亨

2017 (4): 47402-047402. doi: 10.1088/1674-1056/26/4/047402

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We experimentally demonstrate the observation of macroscopic resonant tunneling (MRT) phenomenon of the macroscopic distinct flux states in a radio frequency superconducting quantum interference device (rf-SQUID) under a single-cycle sinusoidal driving. The population of the qubit exhibits interference patterns corresponding to resonant tunneling peaks between states in the adjacent potential wells. The dynamics of the qubit depends significantly on the amplitude, frequency, and initial phase of the driving signal. We do the numerical simulations considering the intra-well and inter-well relaxation mechanism, which agree well with the experimental results. This approach provides an effective way to manipulate the qubit population by adjusting the parameters of the external driving field.

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Dynamics of vortex-antivortex pair in a superconducting thin strip with narrow slits

何安, 薛存, 周又和

2017 (4): 47403-047403. doi: 10.1088/1674-1056/26/4/047403

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In the framework of phenomenological time-dependent Ginzburg-Landau (TDGL) formalism, the dynamical properties of vortex-antivortex (V-Av) pair in a superconductor film with a narrow slit was studied. The slit position and length can have a great impact not only on the vortex dynamical behavior but also the current-voltage (I-V) characteristics of the sample. Kinematic vortex lines can be predominated by the location of the slit. In the range of relatively low applied currents for a constant weak magnetic field, kinematic vortex line appears at right or left side of the slit by turns periodically. We found such single-side kinematic vortex line cannot lead to a jump in the I-V curve. At higher applied currents the phase-slip lines can be observed at left and right sides of the slit simultaneously. The competition between the vortex created at the lateral edge of the sample and the V-Av pair in the slit will result in three distinctly different scenarios of vortex dynamics depending on slit length: the lateral vortex penetrates the sample to annihilate the antivortex in the slit; the V-Av pair in the slit are driven off and expelled laterally; both the lateral vortex and the slit antivortex are depinned and driven together to annihilation in the halfway.

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Control of spins in a nano-sized magnet using electric-current

文宏玉, 夏建白

2017 (4): 47501-047501. doi: 10.1088/1674-1056/26/4/047501

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With the development of spintronics, spin-transfer torque control of magnetic properties receives considerable attention. In this paper the Landau-Lifshitz-Gilbert equation including the torque term is used to investigate the magnetic moment dynamics in the free layer of the ferromagnet/non-magnetic/ferromagnet (FM1/N/FM2) structures. It is found that the reverse critical time τ_c decreases with the current increasing. The critical time τ_c as a function of current for the perpendicular and parallel easy magnetic axes are the same. The critical time τ_c increases with the damping factor α increasing. In the case of large current the influence of the damping factor α is smaller, but in the case of little torque the critical time τ_c increases greatly with the damping increasing. The direction of the magnetization in the fixed layer influences the critical time, when the angle between the magnetization and the z direction changes from 0.1π to 0.4π, the critical time τ_c decreases from 26.7 to 15.6.

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Study on the dielectric properties of Mg-doped NaBiTi₆O₁₄ ceramics

陈勇, 薛思敏, 骆迁, 苏虎音, 陈琪, 黄镇, 徐玲芳, 曹万强, 黄兆祥

2017 (4): 47701-047701. doi: 10.1088/1674-1056/26/4/047701

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With the interest in using lead-free materials to replace lead-containing materials increasing, the use of Na_0.5Bi_0.5TiO₃ (NBT) has come into our sight. We studied the composition of NBT and found that NaBiTi₆O₁₄ ceramics can be compositionally tuned by Mg-doping on the Ti-site to optimize the dielectric properties. In this study, Mg-doped NaBiTi₆O₁₄ (NaBi(Ti_0.98Mg_0.02)₆O_14-δ) ceramics were prepared by a conventional mixed oxide route at different sintering temperatures, and their dielectric properties have been studied at a wide temperature range. X-ray diffraction (XRD) patterns of the NBT-based ceramics indicate that all samples have a pure phase without any secondary impurity phase. The experimental data show that after Mg-doping, the relative permittivity and dielectric loss become lower at 1040, 1060, and 1080℃ except 1020℃ and at different frequencies from 10 kHz, 100 kHz to 1 MHz. Take 1060℃ for example, when the sintering temperature is 1060℃ at 1 MHz, the minimum relative permittivity of NaBiTi₆O₁₄ is 32.9 and the minimum dielectric loss is 0.01417, the relative permittivity of NaBi(Ti_0.98Mg_0.02)₆O_14-δ under the same condition is 25.8 and the dielectric loss is 0.000104. We explored the mechanism of Mg-doping and surprisingly found that the dielectric property of NaBi(Ti_0.98Mg_0.02)₆O_14-δ becomes better owing to Mg-doping. Thus, NaBi(Ti_0.98Mg_0.02)₆O_14-δ can be used in microwave ceramics and applied to new energy materials.

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Recent progress of the native defects and p-type doping of zinc oxide

汤琨, 顾书林, 叶建东, 朱顺明, 张荣, 郑有炓

2017 (4): 47702-047702. doi: 10.1088/1674-1056/26/4/047702

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Zinc oxide (ZnO) is a compound semiconductor with a direct band gap and high exciton binding energy. The unique property, i.e., high efficient light emission at ultraviolet band, makes ZnO potentially applied to the short-wavelength light emitting devices. However, efficient p-type doping is extremely hard for ZnO. Due to the wide band gap and low valence band energy, the self-compensation from donors and high ionization energy of acceptors are the two main problems hindering the enhancement of free hole concentration. Native defects in ZnO can be divided into donor-like and acceptor-like ones. The self-compensation has been found mainly to originate from zinc interstitial and oxygen vacancy related donors. While the acceptor-like defect, zinc vacancy, is thought to be linked to complex shallow acceptors in group-VA doped ZnO. Therefore, the understanding of the behaviors of the native defects is critical to the realization of high-efficient p-type conduction. Meanwhile, some novel ideas have been extensively proposed, like double-acceptor co-doping, acceptor doping in iso-valent element alloyed ZnO, etc., and have opened new directions for p-type doping. Some of the approaches have been positively judged. In this article, we thus review the recent (2011-now) research progress of the native defects and p-type doping approaches globally. We hope to provide a comprehensive overview and describe a complete picture of the research status of the p-type doping in ZnO for the reference of the researchers in a similar area.

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ZnO-based deep-ultraviolet light-emitting devices

卢英杰, 史志锋, 单崇新, 申德振

2017 (4): 47703-047703. doi: 10.1088/1674-1056/26/4/047703

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Deep-ultraviolet (DUV) light-emitting devices (LEDs) have a variety of potential applications. Zinc-oxide-based materials, which have wide bandgap and large exciton binding energy, have potential applications in high-performance DUV LEDs. To realize such optoelectronic devices, the modulation of the bandgap is required. This has been demonstrated by the developments of Mg_xZn_1-xO and Be_xZn_1-xO alloys for the larger bandgap materials. Many efforts have been made to obtain DUV LEDs, and promising successes have been achieved continuously. In this article, we review the recent progress of and problems encountered in the research of ZnO-based DUV LEDs.

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Structural characterization of Al_0.55Ga_0.45N epitaxial layer determined by high resolution x-ray diffraction and transmission electron microscopy

徐庆君, 刘斌, 张士英, 陶涛, 谢自力, 修向前, 陈敦军, 陈鹏, 韩平, 张荣, 郑有炓

2017 (4): 47801-047801. doi: 10.1088/1674-1056/26/4/047801

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Structural characteristics of Al_0.55Ga_0.45N epilayer were investigated by high resolution x-ray diffraction (HRXRD) and transmission electron microscopy (TEM); the epilayer was grown on GaN/sapphire substrates using a high-temperature AlN interlayer by metal organic chemical vapor deposition technique. The mosaic characteristics including tilt, twist, heterogeneous strain, and correlation lengths were extracted by symmetric and asymmetric XRD rocking curves as well as reciprocal space map (RSM). According to Williamson-Hall plots, the vertical coherence length of AlGaN epilayer was calculated, which is consistent with the thickness of AlGaN layer measured by cross section TEM. Besides, the lateral coherence length was determined from RSM as well. Deducing from the tilt and twist results, the screw-type and edge-type dislocation densities are 1.0×10⁸ cm^-2 and 1.8×10¹⁰ cm^-2, which agree with the results observed from TEM.

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Fabrication of crystalline selenium microwire

彭帅, 唐国武, 孙敏, 刘旺旺, 单秀杰, 钱奇, 陈东丹, 张勤远, 杨中民

2017 (4): 48101-048101. doi: 10.1088/1674-1056/26/4/048101

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A method of fabricating selenium (Se) microwire is demonstrated. A multimaterial fiber with amorphous selenium (a-Se) core and multicomponent phosphate glass cladding is drawn by using a conventional optical fiber drawing technique. Then the a-Se core of the fiber is crystallized by a post thermal process at 150℃. After the multicomponent phosphate glass cladding is stripped from the multimaterial fiber by marinating the fiber in HF acid solution, a crystalline selenium (c-Se) microwire with high uniformity and smooth surface is obtained. Based on microstructure measurements, the c-Se microwire is identified to consist of most hexagonal state particles and very few trigonal state whiskers. The good photoconduction property of c-Se microwire with high quality and longer continuous length makes it possible to apply to functional devices and arrays.

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Two-dimensional polyaniline nanosheets via liquid-phase exfoliation

范苏娜, 刘仁威, 马瑞松, 于陕升, 李明, 郑伟涛, 胡书新

2017 (4): 48102-048102. doi: 10.1088/1674-1056/26/4/048102

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Two-dimensional (2D) organic nanomaterials are fascinating because of their unique properties and pentential applications in future optoelectronic devices. Polyaniline (PANI) has attracted much attention for its high conductivity, good environmental stability and unusual doping chemistry. We report on liquid-phase exfoliation of layered PANI films grown by electrochemical polymerization. Atomic force microscopy images demonstrate that few- or even mono-layer PANI nanosheets can be fabricated. The PANI nanosheets can be transferred onto a variety of surfaces, providing a promising route to their incorporation into a variety of devices for further studies and various applications.

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Large scale and controllable preparation of W₂C nanorods or WC nanodots with peroxidase-like catalytic activity

任晓娜, 夏敏, 燕青芝, 葛昌纯

2017 (4): 48103-048103. doi: 10.1088/1674-1056/26/4/048103

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W₂C nanorods or WC nanodots are prepared via an easy, shape-controllable and large-scale preparation technique. Results reveal that each of the W₂C nanorods and WC nanodots has a peroxidase-like activity. Besides, the peroxidase-like activity of W₂C is the first time to be demonstrated. The catalytic efficiency of W₂C nanorods is much higher than that of WC nanodots and chemical condition range of W₂C can be wider than that of WC, which indicates that W₂C is likely to be used as artificial mimetic peroxidase or in-situ amplified colorimetric immunoassay.

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Interface states study of intrinsic amorphous silicon for crystalline silicon surface passivation in HIT solar cell

肖友鹏, 魏秀琴, 周浪

2017 (4): 48104-048104. doi: 10.1088/1674-1056/26/4/048104

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Intrinsic hydrogenated amorphous silicon (a-Si:H) film is deposited on n-type crystalline silicon (c-Si) wafer by hot-wire chemical vapor deposition (HWCVD) to analyze the amorphous/crystalline heterointerface passivation properties. The minority carrier lifetime of symmetric heterostructure is measured by using Sinton Consulting WCT-120 lifetime tester system, and a simple method of determining the interface state density (D_it) from lifetime measurement is proposed. The interface state density (D_it) measurement is also performed by using deep-level transient spectroscopy (DLTS) to prove the validity of the simple method. The microstructures and hydrogen bonding configurations of a-Si:H films with different hydrogen dilutions are investigated by using spectroscopic ellipsometry (SE) and Fourier transform infrared spectroscopy (FTIR) respectively. Lower values of interface state density (D_it) are obtained by using a-Si:H film with more uniform, compact microstructures and fewer bulk defects on crystalline silicon deposited by HWCVD.

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Combined effects of headgroup charge and tail unsaturation of lipids on lateral organization and diffusion of lipids in model biomembranes

陈晓洁, 梁清

2017 (4): 48701-048701. doi: 10.1088/1674-1056/26/4/048701

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Lateral organization and dynamics of lipids in plasma membranes are crucial for several cellular processes such as signal transduction across the membrane and still remain elusive. In this paper, using coarse-grained molecular dynamics simulation, we theoretically study the combined effects of headgroup charge and tail unsaturation of lipids on the lateral organization and diffusion of lipids in ternary lipid bilayers. In neutral ternary lipid bilayers composed of saturated lipids, unsaturated lipids, and cholesterols, under the conditions of given temperature and components, the main factor for the phase separation is the unsaturation of unsaturated lipids and the bilayers can be separated into liquid-ordered domains enriched in saturated lipids and cholesterols and liquid-disordered domains enriched in unsaturated lipids. Once the headgroup charge is introduced, the electrostatic repulsion between the negatively charged lipid headgroups will increase the distance between the charged lipids. We find that the lateral organization and diffusion of the lipids in the (partially) charged ternary lipid bilayers are determined by the competition between the headgroup charge and the unsaturation of the unsaturated lipids. In the bilayers containing unsaturated lipids with lower unsaturation, the headgroup charge plays a crucial role in the lateral organization and diffusion of lipids. The headgroup charge may make the lipid domains unstable and even can suppress phase separation of the lipids in some systems. However, in the bilayers containing highly unsaturated lipids, the lateral organization and diffusion of lipids are mainly dominated by the unsaturation of the unsaturated lipids. This work may provide some theoretical insights into understanding the formation of nanosized domains and lateral diffusion of lipids in plasma membranes.

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Design and optimization of carbon nanotube/polymer actuator by using finite element analysis

张薇, 陈鲁倬, 张健敏, 黄志高

2017 (4): 48801-048801. doi: 10.1088/1674-1056/26/4/048801

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In recent years, actuators based on carbon nanotube (CNT) or graphene demonstrate great potential applications in the fields of artificial muscles, smart switches, robotics, and so on. The electrothermal and photothermal bending actuators based on CNT/graphene and polymer composites show large bending actuations, which are superior to traditional thermal-driven actuators. However, the influence of material parameters (thickness, temperature change, etc.) on the actuation performance needs to be further studied, because it is a critical point to the design and fabrication of high-performance actuators. In this work, finite element analysis (FEA) is employed to simulate the actuation performance of CNT/polymer actuator, which has a bilayer structure. The main focus of this work is to design and to optimize material parameters by using computational method. FEA simulation results show that each layer thickness of actuator has an important influence on the actuation deformation. A maximum curvature of 2.7 cm^-1 is obtained by simulation, which is much larger than most of the actuator curvature reported in previous experiments. What is more, larger temperature change and larger difference of coefficient of thermal expansion (CTE) between two layers will result in larger bending actuation. This study is expected to provide valuable theoretical reference for the design and realization of CNT-based thermal actuator with ultra-large actuation performance.

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A simulation study on p-doping level of polymer host material in P3HT: PCBM bulk heterojunction solar cells

Hossein Movla,Mohammad Babazadeh

2017 (4): 48802-048802. doi: 10.1088/1674-1056/26/4/048802

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In this study, we investigate the influence of doping on the charge transfer and device characteristics parameters in the bulk heterojunction solar cells based on poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM). Organic semiconductors are also known to be not pure and they have defects and impurities, some of them are being charged and act as p-type or n-type dopants. Calculations of the solar cell characteristics parameters versus the p-doping level have been done at three different n-dopings (N_d) that consist of 5×10¹⁷ cm^-3, 10¹⁸ cm^-3, and 5×10¹⁸ cm^-3. We perform the analysis of the doping concentration through the drift-diffusion model, and calculate the current and voltage doping dependency. We find that at three different n-dopant levels, optimum p-type doping is about N_p=6×10¹⁸ cm^-3. Simulation results have shown that by increasing doping level, V_oc monotonically increases by doping. Cell efficiency reaches its maximum at somewhat higher doping as FF has its peak at N_p=3×10¹⁸ cm^-3. Moreover, this paper demonstrates that the optimum value for the p-doping is about N_p=6×10¹⁸ cm^-3 and optimum value for n-dopant is N_d=10¹⁸ cm^-3, respectively. The simulated results confirm that doping considerably affects the performance of organic solar cells.

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