Vol. 65, No. 6 (2016)

Fabrication of triboelectric nanogenerator with textured surface and its electric output performance
Cheng Guang-Gui, Zhang Wei, Fang Jun, Jiang Shi-Yu, Ding Jian-Ning, Noshir S. Pesika, Zhang Zhong-Qiang, Guo Li-Qiang, Wang Ying
2016, 65 (6): 060201. doi: 10.7498/aps.65.060201
Abstract +
Contact electrification between insulators, manifesting as static or triboelectricity is a well-known effect. The triboelectric nanogenerator (TENG) which is based on the contact triboelectricification and electrostatic induction provides a promising route for harvesting ambient mechanical energy and converting it into electric energy. The TENG which is due to its unique properties such as simple structures, low cost, high electric density etc., can offset or even replace the traditional power source for small portable electronics, sensors and so on. So far, the influence of factors on the output performance of TENG is still trapped in unsettled questions and under debate. In this paper, we prepare several textured polydimethylsiloxane (PDMS) films with micro rod array by model method and fabricate a TENG with a size of 2222 mm. The electric generation can be achieved with a cycled process of contact and separation between a polymer and metal electrode (PDMS and aluminum respectively in this study). Several influences as the surface structure and external load on the electrical output of the TENG are systematically studied by integrating use of experimenal tests and ANSYS simulation. Results show that the existence of micro rod array on the PDMS films effectively enlarges the contact area and provides more surfaces for charge storage and hence improve the output performance of TENG. When keeping the external load constant, the output increases with decreasing distance between micro rods. When the external load is 5 N and the distance is 15 m, the average output voltage and current as high as 88 V and 15 A can be achieved respectively, which is 1.5 times higher than the output generated when the distance is 50 m. The electrical output increases quasilinearly with the increase of the external load. Simulation results show that the micro rods of PDMS films are mainly compressed by normal load, which results in a bigger diameter of micro rods. The deformations of PDMS substrate leads to the lateral friction between the micro rods and the upper electrode, which produces more charges because of the friction. For 5 N normal load, the deformations of PDMS substrate and micro rods contribute to the sum of displacement vector and the deformations along Z-axis are 32.7 m and 21.3 m respectively, and are 4.96 and 5.04 times higher than the deformation at the load of 1 N. All the results in an enlarging surface area and the larger output correspondingly. Not only does this work present a new type of generator with micro rods on the PDMS surface, which can be an effective method to improve the electrical output of TENG, but also offers a unique point of view for further understanding of the working principle of TENG.
Resonance transmission of one-dimensional quantum walk with phase defects
Wang Dan-Dan, Li Zhi-Jian
2016, 65 (6): 060301. doi: 10.7498/aps.65.060301
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In this paper, the resonance transmission of discrete time quantum walk is studied when it walks on one-dimensional lattice in which two-phase defects or a piece of phase defects exists. The quasi energy of discrete time quantum walk has a unique dispersion relation with the momentum, from which we first discuss the wave velocity direction versus the values of momentum, and distinguish the incident wave and the reflected wave. The gap between two energy bands depends on the parameters of coincident operator, so the phase defects, which break down the translation invariance of quantum walk on uniform lattices, can be regarded as an analogue of quantum potential. Then we use the condition of energy conversion at the boundary points to obtain the transmission rate and discuss its variation with the incident momentum for different strengths and widths of defects in detail. The multiple resonant peaks are observed due to the enhanced interference effect. Different resonant behaviors are shown when the strength of defect is less or greater than /2, correspondingly the resonances occur in a wide region of incident momentum or the sharp resonant peaks appear at discrete values of momentum. Under the condition of strong defect strength, i.e., approaching to , the qualitative relation between the number of resonant peaks and the widths of defect region is given. The number of resonant peaks is 2(N-1) when the two phase defects are located at N sites symmetric about the origin, while the number is 2N when a piece of phase defects is located at -N to N sites. In the case of a piece of phase defects, we also present the phase diagram in parameter space of (k, ) to show the discrete time of quantum walk propagating or tunneling through the defect region. In terms of this phase diagram, the variations of transmission rate with the incident momentum are reasonably explained. One special phenomenon is that the quantum walk is almost totally reflected in the tunneling case except for =/2 and k being slightly off -/2. Moreover, this behavior seems little affecting the defect strength, just similar to a classical particle. As a result of this research, we hope to deepen the insight of the quantum walk and provide methods to control the spreading of quantum walk through artificial defects.


Three wire toroidal magnetic guide based on the vertical leads and ac current modulation
Cheng Jun, Zhang Jing-Fang, Xu Xin-Ping, Jiang Xiao-Jun, Li Xiao-Lin, Zhang Hai-Chao, Wang Yu-Zhu
2016, 65 (6): 060302. doi: 10.7498/aps.65.060302
Abstract +
A new scheme to create a closed toroidal magnetic waveguide for deBroglie wave on a single layer atom chip is proposed and there is no zero magnetic field along the guide center. The guide is a two-dimensional magnetic trap for trapping weak-field seeking states of atoms with a magnetic dipole moment. The designed wire structure on the atom chip consists of three concentric and isometric ring wires, and six vertical current leads of the three ring wires. By using the through silicon via technology, the current leads can be made perpendicular to the atom chip surface instead of being generally arranged side by side on the chip surface. Compared with the general wiring way, the vertical lead way has two advantages. One is that each ring wire gap caused by the current leads is substantially smaller than the distance between the ring wires, which permits the generation of a closed toroidal magnetic guide near the atom chip surface when dc currents are supplied to the three ring wires. The other is that the distance between two leads of each ring wire is considerably reduced, resulting in the fact that the magnetic perturbation of the leads to the whole toroidal magnetic guide is negligible. We numerically calculate the magnetic field distribution generated by our wire layout when dc currents are applied, and it is shown that a closed and tight toroidal magnetic guide is formed near the atom chip surface. However, there are zero magnetic fields existing along the center of the toroidal guide, which leads to Majorana spin flips from trapped magnetic substate to an un-trapped magnetic sub-state. According to the time-orbiting-potential principle, we propose an ac current modulation method, which is simple and stable, to reduce the atom losses and suppress the atomic decoherence in the toroidal magnetic guide. We deduce the ac current expressions for the case of three isometric infinite straight wires and apply the ac modulation current expressions directly to our three ring wire structure. The numerical calculation results show that the closed toroidal guide does no longer have zero magnetic fields near the magnetic field minimum, and that the magnetic field fluctuation of the guide is smaller. Based on the vertical leads and ac current modulation, the closed toroidal wave guide with no zero magnetic field along the guide center can be generated near the atom chip surface. This scheme has important scientific significance and engineering value for developing the cold atomic chip gyroscope.
Generation of low-frequency squeezed states
Liu Zeng-Jun, Zhai Ze-Hui, Sun Heng-Xin, Gao Jiang-Rui
2016, 65 (6): 060401. doi: 10.7498/aps.65.060401
Abstract +
Squeezed state of light is an important resource of optical measuerments below the shot noise limit and has been used to improve measurement sensitivity in many areas such as gravitational wave detection, especially in audio frequency region. Compared with the high-frequency squeezed states, the generation of the low-frequency squeezed states is more difficult, because it is limited by several technical noise sources. In this paper we report the observation of more than 2 dB of vacuum squeezing at 1064 nm in the gravitational-wave detection band down to 3 kHz with a double-resonant optical parametric oscillator (OPO). The OPO has a configuration of linear cavity consisting of an input coupling mirror with a transmission of 11% at 532 nm and an output coupling mirror with the transmission of 12% at 1064 nm. The nonlinear materials in the OPO is type-I periodically poled potassium titanyl phosphate (PPKTP) crystal which is chosen for this experiment due to its higher nonlinearity, broader phase matching temperature, and smaller photo-thermal effect. The OPO is pumped by the light of 532 nm from Nd: YVO4/KTP solid-state laser of maximum optical power 3 W. To avoid various noise coupled from the seed beam, the OPO is seeded by vacuum fluctuations instead of coherent field at the fundamental wavelength (1064 nm). A Pound-Drever-Hall (PDH) locking scheme is used to lock the OPO cavity length with the signal derived from the reflected pump beam, so as to lock the pump field and also lock the fundamental field. To make both the pump and seed beams resonant simultaneously, the temperature of the PPKTP is carefully adjusted. The squeezed state can be detected on a homodyne detection by interfering it with the local oscillator (LO) and detected by a balanced detector with two photodiodes (EXT500 T) but having the same quantum efficiency of 86% at 1064 nm. The subsequent electronic noise is analyzed with a low-frequency spectrum analyzer, which shows that the audio noise sources from lab enviroment, locking quality, escape efficiency, propagation loss, homodyne efficiency and detection efficiency have effect on the squeezing pruced by an OPO.
Stochastic resonance of a linear harmonic oscillator with non-linear damping fluctuation
Tian Yan, He Gui-Tian, Luo Mao-Kang
2016, 65 (6): 060501. doi: 10.7498/aps.65.060501
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Although non-linear noise exists far more widely in actual systems than linear noise, the study on non-linear noise is far from meeting the needs of practical situations as yet. The phenomenon of stochastic resonance (SR) is a non-linear cooperative effect which is jointly produced by signal, noise, and system, obviously, it is closely related to the nature of the noise. As a result, the non-linear nature of the non-linear noise has an inevitable impact on the dynamic behavior of a system, so it is of great significance to study the non-linear noise's influence on the dynamic behavior of the system. The linear harmonic oscillator is the most basic model to describe different phenomena in nature, and the quadratic noise is the most basic non-linear noise. In this paper, we consider a linear harmonic oscillator driven by an external periodic force and a quadratic damping fluctuation. For the proposed model, we focus on the effect of non-linear nature of quadratic fluctuation on the system's resonant behavior. Firstly, by the use of the Shapiro-Loginov formula and the Laplace transform technique, the analytical expressions of the first moment and the steady response amplitude of the output signal are obtained. Secondly, by studying the impacts of noise parameters and system intrinsic frequency, the non-monotonic behaviors of the steady response amplitude are found. Finally, numerical simulations are presented to verify the effectiveness of the analytical result. According to the research, we have the following conclusions: (1) The steady response amplitude is a non-monotonic function of coefficients of the quadratic damping fluctuation. Furthermore, the non-linear damping fluctuation is easier to contribute the system's enhancing response to the external periodic signal than the linear fluctuation. (2) The evolution of the steady response amplitude versus noise intensity presents more resonant behaviors. One-peak SR phenomenon and double-peak SR phenomenon are observed at different values of coefficients of the quadratic noise, particularly, the SR phenomenon disappears at the positive quadratic coefficient of the quadratic noise. (3) The evolution of the steady response amplitude versus the system intrinsic frequency presents true resonance, i. e. the phenomenon of resonance appears when the external signal frequency is equal to the system intrinsic frequency. True resonance is not observed in the linear harmonic oscillator driven by a linear damping fluctuation as yet. In conclusion, all the researches show that the non-linear nature of non-linear noise plays a key role in system's resonant behavior, in addition, the non-linear damping fluctuation is conductive to the detection and frequency estimation of weak periodic signal.
General robust stability controller design method for a class of hopf bifurcation systems
Lu Jin-Bo, Hou Xiao-Rong, Luo Min
2016, 65 (6): 060502. doi: 10.7498/aps.65.060502
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For the nonlinear Hopf bifurcation system, the change of bifurcation parameter has an important influence on the state of the system. In order to control the Hopf bifurcations of the nonlinear dynamic system, the parameter values of bifurcation points in the system need to be found out before controller designing. However, due to uncertainties of the system structure and parameters in the nonlinear system, or disturbance, it is difficult to determine the bifurcation point precisely. So it is a good way of designing a robust controller near the bifurcation point. Although, lots of works have discussed the robust control of a Hopf bifurcation in a nonlinear dynamic system, the solutions are not satisfactory and there are still many problems. The controller is always designed for some special system. Its structure is usually complex, not general, and the design process is complicated. And before controller design, the value of bifurcation point must be solved accurately.In this paper, a parametric robust stability controller design method is proposed for a class of polynomial form Hopf bifurcation systems. Using this method, it is not necessary to solve the exact values of the bifurcation parameter, it is only needed to determine the bifurcation parameter range. The designed controller includes a system state polynomial; its structure is general, simple and keeps the equilibrium of the original system unchanged. By using the Hurwitz criterion, the system stability constraints for bifurcation parameter boundaries are obtained at equilibrium, and they are described by algebraic inequalities. Cylindrical algebraic decomposition is applied to calculate the stability region of the controller parameters. And then, in the region, parameters of the robust controller can be calculated to make the dynamic system stable. In this paper, the Lorenz system without disturbance is used as an example to show the designing process of the method, and then the controller of the van der Pol oscillator system with disturbance is designed by this method as an engineering application. Simulations of the two systems are given to demonstrate that the proposed controller designing method can be effectively applied to the robust stability control of the Hopf bifurcation systems.
Parameter identification for fractional-order multi-scroll chaotic systems based on original dual-state transition algorithm
Wang Cong, Zhang Hong-Li
2016, 65 (6): 060503. doi: 10.7498/aps.65.060503
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Parameter estimation for fractional-order chaotic systems is a multi-dimensional optimization problem, which is one of the important issues in fractional-order chaotic control and synchronization. With the orthogonal learning strategies and the original dual learning mechanism, the original dual-state transition algorithm is proposed for solving the problem of parameter estimation in fractional-order chaotic systems. The orthogonal learning strategy is presented which can increase the diversity of initial population and improve the convergence ability. And the original dual learning mechanism is presented which can increase the space ability of states, and also can improve the search capability of the algorithm. In the process of identification, we adopt Radau IIA method to solve the fractional-order differential equation. The simulation of the fractional-order multi-scroll chaotic systems with or without noise is conducted and the results demonstrate the e?ectiveness, robustness, and versatility of the proposed algorithm.
Research on high sensitivity detection of carbon monoxide based on quantum cascade laser and quartz-enhanced photoacoustic spectroscopy
Ma Yu-Fei, He Ying, Yu Xin, Yu Guang, Zhang Jing-Bo, Sun Rui
2016, 65 (6): 060701. doi: 10.7498/aps.65.060701
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Quartz-enhanced photoacoustic spectroscopy (QEPAS) technology was invented lately. Therefore it is an innovative method for trace gas detection compared with other existing technologies. In this paper, trace gas detection for carbon monoxide (CO) based on QEPAS technology is demonstrated. In order to realize high sensitive detection, a novel mid-infrared, state-of-art 4.6 m high power, continuous wave (CW), distributed feedback (DFB) quantum cascade laser (QCL) with single mode output is used as the laser exciting source. Therefore, the strongest absorption of fundamental frequency band of CO is achieved. Using the wavelength modulation spectroscopy and the 2nd harmonic detection, the influence of laser wavelength modulation depth on QEPAS signal level is investigated. Two important parameters of Q-factor and resonant frequency for quartz tuning fork as a function of gas pressure are measured. After optimization of the modulation depth of laser wavelength, the gas pressure of CO:N2 gas mixture and the improving speed of the V-R relaxation rate through the addition of water vapor, a minimum detection limit (MDL) of 1.95 parts per billion by volume (ppbv) for CO at gas pressure of 500 Torr and modulation depth of 0.2 cm-1 is achieved with a 1 sec acquisition time and the addition of 2.6% water vapor in the analyzed gas mixture. Finally, the influence of level lifetime of the targeted gas on QEPAS signal amplitude is investigated by comparison of CO QEPAS sensor performance using two different CO absorption lines of R(5) and R(6) located at 2165.6 cm-1 and 2169.2 cm-1respectively. The expression of the QEPAS signal amplitude is modified by adding the level lifetime parameter for a better precision.
Algorithm researches for efficient global tallying in criticality calculation of Monte Carlo method
ShangGuan Dan-Hua, Deng Li, Li Gang, Zhang Bao-Yin, Ma Yan, Fu Yuan-Guang, Li Rui, Hu Xiao-Li
2016, 65 (6): 062801. doi: 10.7498/aps.65.062801
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Based on the research of the uniform fission site algorithm, the uniform tally density algorithm and the uniform track number density algorithm are proposed and compared with the original uniform fission site algorithm in this paper for seeking high performance of global tallying in Monte Carlo criticality calculation. Because reducing the largest uncertainties to an acceptable level simply by running a large number of neutron histories is often prohibitively expensive, the researches are indispensable for the calculation to reach the goal of practical application (the so called 95/95 standard). Using the global volume-averaged cell flux tally and energy deposition tally of the pin-by-pin model of Dayawan nuclear reactor as two examples, these new algorithms show better results. Although the uniform tally density algorithm has the best performance, the uniform track number density algorithm still has the advantage of being applicable to any type of tally, which is based on the track length estimator without any modification. All the algorithms are realized in a recently developed parallel Monte Carlo particle transport code JMCT.
Study on the virtual source calibration technology based on the volume of radioactive gas source
Tian Zi-Ning, Chen Wei, Han Bin, Tian Yan-Jie, Liu Wen-Biao, Feng Tian-Cheng, Ouyang Xiao-Ping
2016, 65 (6): 062901. doi: 10.7498/aps.65.062901
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The calibration methods for the radioactive Kr and Xe gases produce the key data for the judgment of nuclear fission reaction, whose accurate measurement has always been a difficult problem in operation for a long time. In order to obtain the accuracy, it is very important to calibrate the efficiencies of these gas sources, especially for proficiency test exercise of the laboratory, to analyze the CTBT samples of radioactive xenon, which are used to judge the nuclear test of the country and the measurement system. The relative measurement method has not realized in the experimental calibration, and the Monte Carlo method has large uncertainty also. Therefore, a new measurement method and experimental technology is needed. In order to avoid the above shortcomings, we need to develop a source-less efficient calibration method based on the virtual point source (VPS). In the past, it was suggested that for point sources placed on the symmetry axis, a Ge(Li) or an HPGe cylindrical detector can be changed to an virtual point detector (VPD), where all -ray interactions are considered to occur. This is not a real physical model but only a mathematical description. Aiming at the VPD, we put forward an innovative approach and define the concept of VPS. But, the concept is introduced in a volume source. In this concept, it is assumed that the total photons emission has occurred in a distance within the source described, and it is from the whole source to an imaginary point. If there is really a point located on the symmetry axis of the detector, whose efficiency is similar to that of the whole real volume source, the geometrical considerations used in calibrations of the source will be much simpler. The calibration process of the VPS is: firstly, a standard point source is placed at different position on the symmetry axis to obtain its full-energy peak efficiency. Secondly, the relationship between the height and the efficiency can be established. The position of the VPS can be deduced according to the full-energy peak efficiency of the volume source. Finally, a standard point source, instead of a volume source, is placed at the virtual point position to finish the efficiency calibration work. In this study, the LabSOCS software is used to simulate the detection efficiencies including different volumes of gas source and point source at different points on the symmetry axis. According to the calculated data, a function relationship between the volume of gas source and the virtual point source position is established. It has been proved theoretically that the volume of gas source and the virtual point location have a good linear relationship. This provides a new way in theory to solve the virtual source calibration technology. The VPS efficiency calibration technology is very important in the field of verification of nuclear test-ban, nuclear emergency measurement and environmental radioactivity measurement.
The chemical bond properties and ferroelectricity studies of SrBi4Ti4O15
Xiao Xiao-Hong, Li Shi-Chun
2016, 65 (6): 063101. doi: 10.7498/aps.65.063101
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Spontaneous polarization as the most immediate parameter in ferroelectricity is always an emphasis in ferroelectric research. Some ferroelectric microscopic theory such as Berry-phase method and first principles calculation are used to study the spontaneous polarization of perovskite type ferroelectrics. SrBi4Ti4O15 is a typical bismuth layered structure ferroelectric, the complexity of its crystal structure makes the ferroelectric research more difficult. This study, from the perspective of chemical bond, analyzes the relationship between the chemical bond properties and the spontaneous polarization, and further explores the atomic bonding state in ferroelectric crystal and its impact on ferroelectricity.By starting from the crystal structure data of SrBi4Ti4O15, the atomic local cluster structure including bond length, atomic coordination situation and the number of atoms in a crystal structure unit are obtained by the atomic environment calculation (AEC). Calculation results show that there are 13 atomic local cluster structures in SrBi4Ti4O15. Then combined with the crystal decomposition method, the SrBi4Ti4O15crystal is decomposed into 38 pseudo-binary crystals, and each pseudo-binary crystal corresponds to a chemical bond. Accordding to the dielectric theory of chemical bond that used in binary crystal, chemical bond properties such as the number of effective valence electron, the effective valence electron density and the bond ionicity are calculated. Through improvement of the bond dipole moment model, the relationship among bond dipole moment, bond properties, and bond parameter is established, and the bond dipole moment of each bond in SrBi4Ti4O15 is calculated.The spontaneous polarization of an ferroelectric can be approximated as the superposition of the spontaneous polarization of various chemical bonds in the crystal, where the spontaneous polarization of chemical bond is due to the bond dipole moment. Based on the traditional polarization theory, the spontaneous polarization can be expressed as the average bond dipole moment per unit volume, and considering the number of molecules in unit cell (Z) and the atomic site occupation factor (SOF), the correlation between bond dipole moment and spontaneous polarization of the bismuth layered ferroelectrics is established. On the basis of this, the calculated spontaneous polarization along a axis in the ferroelectric SrBi4Ti4O15 is 28.03 C/cm2.This study simplifies the complex crystal research by AEC and crystal decomposition method, and studies the ferroelectricity of the bismuth layered ferroelectrics from the viewpoint of chemical bond. The bond dipole moment as the bridge in this study for connecting spontaneous polarization with chemical bond properties, which is a new micro study method in macro-properties of bismuth layered ferroelectrics. Based on this method, the spontaneous polarization of other relevant ferroelectrics such as orthogonal SrBi2Ta2O9, orthogonal Bi4Ti3O12, and tetragonal SrBi4Ti4O15 are calculated, all the results are in good agreement with the experimental values and other theoretically calculated values.
Potential energy curves and spectroscopic properties of GeS molecules: in ground states and low-lying excited states
Huang Duo-Hui, Wan Ming-Jie, Wang Fan-Hou, Yang Jun-Sheng, Cao Qi-Long, Wang Jin-Hua
2016, 65 (6): 063102. doi: 10.7498/aps.65.063102
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The potential energy curves (PECs) for ground state (X1+) and five low-lying electronic states (11-, 11, A1, 15+, 25+) of the GeS molecule have been studied by multi-reference configuration interaction (MRCI) plus Davidson correction (+Q) with all-electron basis set aug-cc-pv5Z. Results show that the 25+ state is an unstable repulsive state, and the others are bound states, and the six electronic states are dissociated along the same channel, Ge(3P)+S(3P). The adiabatic transition energy Te equilibrium bond length Re, dissociation energy De, harmonic frequency e, anharmonic constant exe, and equilibrium dipole moments are obtained by fitting the PECs for the X1+, 11-, 11, A1 and 15+ states. While Re is 2.034 , De 5.728 eV, e 571.73 cm-1, exe 1.6816 cm-1, the equilibrium dipole moment is 1.9593 Debye for the ground state. The values of Te are 25904.81, 26209.22, 32601.19, 43770.26 cm-1 for 11, 11, A1 and 15+ states, respectively; the values of Re are 2.313, 2.322, 2.188, 2.8790 for 11, 11, A1 and 15+ states, respectively; the values of De are 2.524, 2.487, 1.694, 0.3036 eV for 11-, 11, A1 and 15+ states, respectively; the values of e are 358.90, 353.08, 376.32, 134.96 cm-1 for 11-, 11, A1 and 15+ states, respectively; the values of exe are 1.2421, 1.2151, 1.6608, 1.9095 cm-1 for 11, 11, A1 and 15+ states, respectively, and the values of equilibrium dipole moments are 1.3178, 1.4719, 1.5917, -1.9785 Debye for 11-, 11, A1 and 15+ states, respectively. By solving the radial Schrdinger equation of nuclear motion, the 30 vibration levels and 30 inertial rotation constants (J=0) for X1+, 11-, 11, A1 and 15+ states are also obtained, and all of are in good agreement with the available experimental and other theoretical values.
Study of high-order harmonic generation in crystals exposed to laser fields
Guan Zhong, Li Wei, Wang Guo-Li, Zhou Xiao-Xin
2016, 65 (6): 063201. doi: 10.7498/aps.65.063201
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Crystal structures are very different from the atomic structure in the gaseous state, so the high-order harmonic generation (HHG) from the crystal irradiated by an in intense laser is also different from that of an atom exposed to a strong laser field. By simulating the dynamics of a single active electron in periodic potentials based on the expansion method of the basis functions, we study the HHG in crystals and find, in certain wave lengths and intensity of the laser, that solid harmonic generation exhibits the characteristics of double plateaus. After analyzing the induced electric current of laser field, which is the source of HHG in the crystal, we find that the first plateau of HHG arises chiefly from the electric current between the lowest conduction band and the valence band (electron-hole recollision), and the second plateau is predominantly due to electric current between higher conduction bands and the valence band (electron-hole recollision). The cutoff energies of the two plateaus vary approximately linearly with the laser field strength. Furthermore, by considering the crystal driven by the few-cycle laser pulse, the cutoff energy of the second plateau changes monotonously with carrier-envelope phases. Based on this phenomenon, it can be a way to measure the carrier-envelope phases of the few-cycle laser pulse. Finally, we study further the HHG from crystals driven by the chirped laser and find that it has a great influence on the HHG, and the second plateau of HHG is sensitive to the chirp parameter. According to this phenomenon, we propose a novel way that is capable of greatly improving the emission efficiency of the second plateau by changing the chirp parameter of the driving laser.
Detection optical vortex topological charges with monocyclic multistage intensity distribution
Zhang Hao, Chang Chen-Liang, Xia Jun
2016, 65 (6): 064101. doi: 10.7498/aps.65.064101
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Generation and application of the vortex beams are part of the hot topics in the optical field. In connection with the limited detection range of topological charge, we introduce a novel monocyclic multistage intensity distribution, which is generated by the coaxial superposition of two vortex beams with different topological charge numbers which have the same radius of ring in the focal plane of fraunhofer diffraction. This novel intensity distribution which is achieved by computer generated hologram is a new application of sidelobe-modulated optical vortices. The detection range of topological charge is expanded to 128 by two detection constants consisting of segments and radius in the monocyclic multistage intensity distribution method. We study the generation and distribution characteristics of monocyclic multistage intensity distribution in the focal plane of fraunhofer diffraction theoretically and experimentally to generate the qualified monocyclic multistage intensity distribution using a spatial light modulator. Excellent agreement between theoretical and experimental results is observed. The study indicates that two orbital angular momenta of vortex beams can be accurately determined by the segments and radius determined in the monocyclic multistage intensity distribution method. The method is immune to harassments from alignment and phase matching between the beams and optical elements, and has a large detection range, which is enlarged one order of magnitude compared with the previous way of detecting topological charges with sidelobe-modulated optical vortices. Our method provides a more large detection range of topological charge, which enables the vortex beams as the information carriers to carry more data in communication. Therefore, this method possesses research potential and applicability in future free-space optical communication.
Single-pixel remote imaging based on Walsh-Hadamard transform
Li Ming-Fei, Mo Xiao-Fan, Zhao Lian-Jie, Huo Juan, Yang Ran, Li Kai, Zhang An-Ning
2016, 65 (6): 064201. doi: 10.7498/aps.65.064201
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Single-pixel imaging has become a topic of intense interest amongst theoreticians and experimentalists in recent years, and is still attracting great attention due to its potential applications in biomedical imaging, remote sensing, defence monitoring, etc. Two main fields should be involved in single-pixel imaging scheme: single-pixel camera and computational quantum imaging, which are proposed in the year 2006 and 2008, respectively. Although these two single-pixel imaging schemes belong to different research fields, they are nearly identical in the realization setup and using the similar image recovering algorithm. The single-pixel camera scheme is mainly based on compressive sensing algorithms, which can recover the image with about 30 percent measurements of its total pixels (raster scan method), but need the prior knowledge of the image. While the computational quantum imaging method usually recovers the image by using the second-order correlation function, which is computational fast but need more measurements to retrieve a high quality image. Thus, both the methods mentioned above are time consuming. In this paper, a single-pixel imaging scheme based on Walsh-Hadamard transform is proposed and is demonstrated both theoretically and experimentally. The retrieving times of different algorithms are discussed and compared with each other. An image of 10241024 pixels can be acquired around 1 second with our method while it will take 8 seconds by using TVAL3 algorithm on the general computer in our numerical simulation experiment. It is also experimentally demonstrated that the nature targets from 500 meters to 5000 meters away are acquired, with pixels of 128128 and in the waveband of 350-900 nm, and the speed of the imaging frame rate is achieved at 0.5 frame per second. The differences and commons between single-pixel imaging and computational quantum imaging are also discussed in this article. It is found that the Walsh-Hadamard transform we proposed is stable and can be sufficiently saving the imaging time of the single-pixel imaging schemes while maintaining a high imaging quality. Moreover, the single-pixel remote imaging scheme can be used in other wave band such as infrared and micro wave imaging, or will be useful in the case when the array detector technique is difficult to meet the requirements such as the sensitivity or the volume. And our scheme proposed here can make the single-pixel imaging technique step further toward its real applications.
A highly sensitive chemosensor for solution based on organic semiconductor laser gain media
Chi Lang, Fei Hong-Tao, Wang Teng, Yi Jian-Peng, Fang Yue-Ting, Xia Rui-Dong
2016, 65 (6): 064202. doi: 10.7498/aps.65.064202
Abstract +
Laser has been widely applied in the scientific and engineering areas including communications, medical treatment, industry, and military due to its extremely strict monochromaticity, high coherence and high energy density. Organic laser based on solution processable polymer gain media has attracted considerable attention in various applications due to its easy fabrication, compact system and flexibility. At present, the chemosensors based on organic semiconductor laser have been widely developed. It has been reported to achieve solution monitoring by organic DFB (distributed feedback) laser. Although the method has its own advantages, there are still many operability and craftsmanship problems to be resolved. In this paper we introduce a new type of the real-time monitoring for various solution. The monitor is realized by using amplified spontaneous emission (ASE) from optically pumped organic semiconductor gain media. The gain media comprising blends of poly(9, 9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(3-hexylthiophene) (P3HT) at a ratio of 15:85 wt.% is dissolved into toluene (25 mg/mL). Thin films (90 nm thickness) of P3HT/F8BT are obtained by spin coating (2000 rpm) from solution onto pre-cleaned quartz substrates. The P3HT/F8BT film demonstrates the absorption peak at 471 nm, the PL peak at 622 nm, and the ASE peak at 661 nm with FWHM (full-width-at-half-maximum) linewidth of ~ 10 nm under the stripe laser pumping. The thin films are, then, covered by droplet of solution to form planar waveguide structure with variable effective refractive index. Upon analyte binding, a change in refractive index at the P3HT/F8BT film surface results in a change in the effective refractive index of the planar waveguide and in turn induces shift of the ASE mode wavelength and variation of ASE threshold of the organic gain media. The changes in ASE wavelength and threshold can be monitored for sensing. The red shift of 4.5 nm in the ASE spectrum is from 661 to 665.5 nm and the threshold increases from 0.579 J/pulse to 1.447 J/pulse which can be detected with the concentration of sodium chloride increasing from 0 to 25 wt.% in pure water. Our experimental results show that this method is easy to detect the concentration grads of 1 wt.% sodium chloride solution. The measurement sensitivity of solution reaches 97.8 nm/RIU (refractive index unit), and accuracy reaches 141.9 nm/RIU. Furthermore, we demonstrate that the chemosensor could be used for detecting different kinds of solution in the same concentration. The ASE peak position and threshold display clearly different when the droplet 10 wt.% sodium, chloride solution and hydromel solution onto P3HT/F8BT film. Our study suggests that the organic gain media films have potentiality to be developed as a high sensitivity and high accuracy chemosensor to detect solution due to the high sensitivity of the ASE peak position and threshold to the refractive index of the solution.
Light intensity distribution of high-power laser beams on target plane under different focus system of 22 beam array
Sun Xiao-Yan, Lei Ze-Min, Lu Xing-Qiang, Lü Feng-Nian, Zhang Zhen, Fan Dian-Yuan
2016, 65 (6): 064203. doi: 10.7498/aps.65.064203
Abstract +
Large aperture high-power laser drivers usually focus the high power laser beams in 22 quads to the target chamber center in order to increase the light intensity on the target plane. The large aperture wedged focus lenses are the core components in the focus system of quadruplets of beams, and it is thought possible to use four two-dimensional off-axis wedged focus lenses as four sub-lenses to make up a larger aperture wedged focus lens in form to focus the four beams. Given that the large aperture two-dimensional off-axis wedged focus lenses are processed and used difficultly, the wedged focus lenses are divided into three categories: the two-dimensional off-axis wedged focus lenses, the one-dimensional off-axis wedged focus lenses, and the non-off-axis wedged focus lenses. On the basis of the three modes of the wedged focus lenses and the corresponding specific incidence angles of each sub-beam, the three focus schemes for the 22 beam array are put forward to comparatively research the light intensity distribution on the target plane. Research results show that from a perspective of the coherence among the four sub-beams, the phase factors of each sub-beam respectively introducing by the three focus systems with the two-dimensional off-axis, one-dimensional off-axis, and non-off-axis wedged focus lenses are asymmetric, asymmetric and symmetric inside each sub-beam, and symmetric, asymmetric and symmetric among the four sub-beams. Therefore, the wave front consistency of the four sub-beams decreases in the order of the focus systems with the non-off-axis, two-dimensional off-axis, and one-dimensional off-axis wedged focus lenses. The focus schemes with the non-off-axis wedged focus lenses for 22 beam array can get the narrowest main-lobe, the strongest peak-value intensity, the highest energy concentration ratio on the target plane, followed by the one-dimensional off-axis and two-dimensional off-axis wedged focus lenses. The off-axis mode of the wedged focus lenses not only increases the complexity in the course of processing and using, but also increases the main-lobe size, decreases the peak-value intensity and the energy concentration ratio, which obtains a weaker focusing characteristics than that of the non-off-axis mode of the wedged focus lenses. Research results can provide an important reference for the design of the focus system in the target area of high-power laser drivers.
Research on coherent anti-Stokes Raman scattering microscopy
Liu Shuang-Long, Liu Wei, Chen Dan-Ni, Qu Jun-Le, Niu Han-Ben
2016, 65 (6): 064204. doi: 10.7498/aps.65.064204
Abstract +
In this paper, we analyze the process of coherent anti-Stokes Raman scattering (CARS) based on quantum theory and set up a traditional point-scanning CARS microscope. With this microscope, high-contrast images of polystyrene microspheres are obtained. By scanning polystyrene beads with 110 nm diameter, we reconstruct the point spread faction (PSF) of the system. And the full width at half maximum (FWHM) of the PSF shows a lateral resolution about 600 nm, which is larger than the theoretical value (~ 300 nm). Therefore, we propose several resolution-improvement approaches, which lay a strong foundation for the realization of nano-CARS microscopy.
Research of the influence of non-spherical ellipsoid particle parameter variation on polarization characteristic of light
Zhang Su, Peng Jie, Zhan Jun-Tong, Fu Qiang, Duan Jin, Jiang Hui-Lin
2016, 65 (6): 064205. doi: 10.7498/aps.65.064205
Abstract +
There are many non-spherical particles in the sand-dust and carbonaceous environment of the natural world, but this kind of particles are in most cases approximated by the spheres in the description of the transmission process, which cannot reflect the actual state of the transmission through the particles. For this reason, on the basis of polarization characteristic of spherical particles, a further research is made on the polarization characteristic with different refractive index, effective radius, particle shape, and other parameters of ellipsoid particles. When the non-polarized light is used as the incident light, the T-matrix method is applied to the simulation of the transmission process of the non-spherical particles, and the power-law size distribution is used to describe the size distribution condition of the particles, which is the most effective method to show the whole process of light scattering through non-spherical particles. With this method, the polarization characteristic after the transmission of the ellipsoid particles and the polarization differences between the ellipsoid and spherical particles can be obtained, and at the same time the examples of the sand-dust, marine and carbonaceous aerosols are given to show the validity of the results. Simulation results show that the smaller the real part of the refractive index and the larger the image nary part of the refractive index, the less obvious the polarization character differences between the ellipsoid and spherical particles are. When the effective radius of particle increases, the DOP (degree of polarization) variation of the spherical particles is more obvious than the non-spherical particles, and the maximum values are at the positions of the scattering angles 150 and 120 respectively. When the particle shape is different, the differences between the ellipsoid at diverse vertical-to-horizontal ratio and spherical particles are not obvious if the scattering angle is less than 60, and when the vertical-to-horizontal ratio of the ellipsoid particle is reciprocal, the polarization character of the two kinds of particles becomes the same. Through the analysis above, in the process of transmission, in most circumstances the ellipsoid particles cannot be approximated by spherical particles for computation, and the parameters of the refractive index, effective radius, shape of the ellipsoid particles can all influence the polarization character.
Preparation and characterization of self-cleaning and anti-reflection ZnO-SiO2 nanometric films
Guo Zhao-Long, Zhao Hai-Xin, Zhao Wei
2016, 65 (6): 064206. doi: 10.7498/aps.65.064206
Abstract +
Unlike the general anti-reflection and self-cleaning film such as SiO2 and TiO2-SiO2, the ZnO-SiO2 nanometric film used as a substrate of excellent transparency in visible region and effective photo-catalytic self-cleaning under UV illumination is seldom studied in the application as a substrate; however, it has a lot of advantages including high transmittance and low refractivity. In this paper, a self-cleaning and anti-reflection ZnO-SiO2 nanometric film is successfully fabricated by using a sol-gel dip-coating method. The morphology, crystal structure, surface microstructure and light transmittance of the obtained products are characterized by techniques such as TEM, SAD, XRD, SEM, DTA and UV-vis. Photo-catalytic degradation of the methylene blue (MB) in aqueous solution is used as probe reaction to evaluate the photo-catalytic activity of ZnO-SiO2 nanometric film. The TEM images reveal that the as-prepared ZnO nanoparticles are spherical grains with diameters of 12-20 nm, the average grain diameter is about 14.51 nm. ZnO nanoparticles obtained are of hexagonal wurtzite structure revealed by XRD pattern and there exist no other diffraction peaks, Furthermore, the SAD results show that ZnO microstructurs have good crystallinity. In addition, the ZnO grain size is about 14.41 nm by using the Scherrer formula calculation, which is consistent with the TEM results by the Gauss simulation. The UV-vis spectra reveal that the ultraviolet characteristic absorption peak of ZnO-SiO2 composite films is located at 368 nm and 375 nm after annealing at different temperatures such as 300℃ and 450℃, corresponding to the band gaps of 3.37 eV and 3.31 eV, respectively. It is highly consistent with that obtained from pure ZnO nanoparticles. Increasing the annealing temperature results in a lower refractive index and the increases of the porosity in of the ZnO-SiO2 composite films. It has a uniformly refractive index value about 1.23-1.25 and a high porosity value about 50.3-54.7% when the annealing temperature is 450 ℃. Experimental results show that the ZnO-SiO2 composite film can enhance the light transmittance of the quartz substrate, due to its lower reflective index and higher porosity. Compared with the quartz substrate, the average optical transmission rate of the quartz glass coated with ZnO-SiO2composite films is increased by about 4.17% at 400-800 nm, which favors greatly anti-reflection characteristics in a wide spectrum range. Meanwhile, the ZnO-SiO2 composite films are found to be efficient for photo-catalytically degradation of methylene blue dye under UV illumination, which favors greatly the self-cleaning function.
High efficiency all-optical diode based on hexagonal lattice photonic crystal waveguide
Liu Yun-Feng, Liu Bin, He Xing-Dao, Li Shu-Jing
2016, 65 (6): 064207. doi: 10.7498/aps.65.064207
Abstract +
A high efficiency all-optical diode based on 2D hexagonal lattice photonic crystal (PC) waveguide is proposed. The structure is asymmetrically coupled by a high Q factor micro-cavity-containing nonlinear Kerr medium and a F-P cavity in PC waveguide. The transmission properties are numerically investigated by finite-difference time-domain (FDTD) method. Because of interference between the two cavities, the structure can achieve the function of forward transmission and backward cut-off under a suitable light intensity. For light incidence close to the direction of micro-cavity, nonlinear Kerr effect of micro-cavity can be excited by a certain light intensity. Then the resonant frequency of Fano cavity will change and forward incidence becomes transmission from reflective state. But for light incidence away from the direction of micro-cavity, the field distribution is asymmetric due to the asymmetric structure, so backward incidence needs stronger incidence light to excite Kerr effect and keeps reflective state. This design of all-optical diode has many advantages, including high maximum transmittance, high transmittance contrast ratio, low power threshold, and ease of integration, and so on.
Study on bending losses of few-mode optical fibers
Zheng Xing-Juan, Ren Guo-Bin, Huang Lin, Zheng He-Ling
2016, 65 (6): 064208. doi: 10.7498/aps.65.064208
Abstract +
With the rapid increase of the capacity of optical fiber transmission system, the mode division multiplexing (MDM) transmission system using few-mode fibers (FMFs) (which provides the multi-channel multiplexing, high efficiency of frequency spectrum, and low nonlinear effects) becomes a research focus to upgrade the capacity of the optical communication. In this paper, an analytical expression of bending loss for each high-order mode of parabolic-index FMFs is deduced based on the perturbation theory and verified by finite element method. Based on this expression, the influence of four key structure parameters of trench-assisted parabolic-index FMFs: i.e. the radius of fiber core, the distance between core and trench, the width of trench, and the refractive index difference of trench, on the bending loss performance are discussed in detail. It is found that, firstly, the sensitivity of the bending loss increases with the increase of mode order of FMFs. Secondly, the smaller the core radius, the smaller the bending loss of each mode-order is, since small core radius leads to a smaller effective mode area, which is beneficial for saving power leakage. Additionally, the effective mode area of LP02 mode is lower than that of LP21 mode, while the bending loss of LP02 mode is higher than that of LP21 mode, this observation is different from other mode-orders. Thirdly, an optimized distance between trench and core for each high-order mode is also investigated for obtaining minimum bending loss, which plays an important role in controlling the bending performance of FMFs. So the higher the mode-order, the smaller the optimized distance between core and trench is, and this observation could be used to optimize the bending loss of the fiber. With the increase of the distance between the core and trench, the effective mode area of high-order mode increases quickly at first, then it is approximately unaltered. The distance between the core and trench is a key factor that influences both the bending loss and the effective mode area of each mode. Finally, the bending loss of each mode decreases with the increase of the width of trench around the fiber core or the refractive index difference of trench. These results are helpful for understanding the mechanism of bending loss for FMFs and are of significance for designing and manufacturing of few-mode bend-insensitive fibers, especially for the optimization of the bending loss of specific high-order mode.
Acoustic scattering from elastic target buried in water-sand sediment
Hu Zhen, Fan Jun, Zhang Pei-Zhen, Wu Yu-Shuang
2016, 65 (6): 064301. doi: 10.7498/aps.65.064301
Abstract +
Acoustic scattering from objects buried in water-sand sediment is the foundation of target detection and identification. It is also a research hotspot in areas of acoustic scattering while the domestic research on scattered field from buried targets is not deep. This paper deduces an approximate Green's function of acoustic scattering from targets buried in water-sand sediment, which describes clearly the whole physical process during the propagation of scattered waves. Next, on basis of geometric acoustics, the corresponding Helmholtz-Kirchhoff formula of integration is presented. Complicated integration of the full wave number spectral representation of the Green's function is avoided by employing approximate formula derived from the method of ray acoustics. As a result of neglecting the influence from lateral waves, the Helmholtz-Kirchhoff integral given applies to supercritical incidence case. The function of COMSOL Multiphysics software is expanded by writing this formula of integration into it. By means of finite-element method, numerical calculation models for two-dimensional axisymmetric targets are established on the software platform. The proposed model built in free field is verified through comparing numerical results obtained with the Rayleigh method which has been validated in previous research achievements of acoustics. The target strength of buried elastic solid sphere is calculated under different conditions in order to analyze the change regularity of buried scattered field. We provide a summary about the law of target strength of the elastic sphere varying with frequency, buried depth, and the attenuation of sand. Finally, we conduct acoustic scattering experiments in free space and shallow buried conditions and process the data with the method of isolation and identification of resonance to separate eliastic echoes from reverberation echo and specular echo. Results from the experiment of free field show that components of the scattered wave should include Rayleigh waves and whispering gallery waves. The processed data of objects buried inside layered fluid media indicate that characteristics of resonance spectra can be used to identify and detect the target effectively while echo signal is not available for identification of target. The proposed technique is verified through the comparison of data from total scattered field between experiment and theoretical prediction. This study has important guiding significance for detecting and identifying targets embedded within layered acoustic media in practical applications.
Studies on the mechanism of acoustic pulse train and full transmission
Cao Song-Hua, Wu Jiu-Hui, Wang Yu, Hou Ming-Ming, Li Jing
2016, 65 (6): 064302. doi: 10.7498/aps.65.064302
Abstract +
Critical phenomenon in a one-dimensional periodic stratified structure with time-varying elastic modulus functions is found out for acoustic waves. By using the classical separation of variables method to solve the one-dimensional wave equation, and taking the time-varying elastic modulus functions into consideration, a critical value can be found of the varying amplitude of the time-varying elastic modulus functions. Near the critical value, due to the alternation of the characteristic exponent, the reflectivity of the one-dimensional periodic stratified structure changes in essence. Below or at the critical value, the incident wave can be converted into a periodic and millisecond pulse train, particularly when the varying amplitude is at the critical value. In addition, the layer number can be up to 16. Under these circumstances, complete pulse train of 0 or 1 is generated with respect to time; in the end, when above the critical value, the reflectivity decreases rapidly to 0 within 50 milliseconds, indicating that, at one moment, the incident wave can be totally transferred through the structure as if the stratified structure becomes transparent, which means a modulational transparency. In conclusion, by altering the varying amplitude of the time-varying elastic modulus functions, three different phenomena are generated. These excellent properties could find potential applications of one-dimensional periodic stratified structure in the acoustic transducer and the control of the acoustic wave.
Study of highway lane-changing model under rain weather
Zhang Wei-Hua, Yan Ran, Feng Zhong-Xiang, Wang Kun
2016, 65 (6): 064501. doi: 10.7498/aps.65.064501
Abstract +
Rainfall decreases road adhesion coefficient and sight distance of drivers, these can easily lead to traffic accidents which affect the road traffic efficiency. To study the vehicle lane-changing behavior under rainfall conditions, the adhesion coefficient parameter and drivers' reaction delay time parameter are introduced into the safety distance model. Based on the relationship between rainfall intensity and the water film thickness as well as the relationship among the road adhesion coefficient, water film thickness, and vehicle speed, the influence of rainfall on the road adhesion coefficient is quantified. And based on the relationship between visibility distance under rainfall condition and safe distance upon stopping sight distance, the influence of rainfall on drivers' reaction delay time is quantified. Therefore, the safety distance is different under different rainfall conditions and vehicle speed, it no longer is a fixed value like in other lane-changing models by quantifying the two parameters. The improved lane-changing model is established by considering the influence of the speed difference on vehicle lane-changing behavior; the speed difference is not only existing between the research vehicle and the adjacent lane vehicle ahead, but also between the research vehicle and the adjacent lane after the car. And the safety distance model including the two parameters is embedded in the improved lane-changing model by the lane-changing rules. For the three-lane traffic, the lane-changing rules which take into consideration the safety distance and the speed difference are established respectively for each lane, and the simulation analysis is conducted using cellular automata based on the above mentioned rules. Simulation results show that in the medium density the lane-changing rates in the rain condition are significantly lower compared with sunny days, the biggest drop is about 25%. Through comparison and analysis of the space-time diagrams and the speed-time curve of one vehicle at different traffic density on rain days and sunny days, the improved model redisplays the phenomenon of free flow, free flow into dynamic blocking flow in the absence of external cause, and the phenomenon of vehicles stopping and going under blocking flow. In the medium and high densities, the rain causes more traffic congestion, and the frequency and duration of traffic congestion in space-time diagram increase accordingly; the low speed and the speed of zero state increase gradually in the speed-time curve.
Numerical simulation on weld line development of injection molding in mold cavity with inserts
Li Qiang, Li Wu-Ming
2016, 65 (6): 064601. doi: 10.7498/aps.65.064601
Abstract +
A gas-liquid two-phase model for a viscoelastic fluid is proposed and used to simulate and predict the behavior of melt welding in injection molding process, in which the extended pom-pom (XPP) model and cross-WLF viscosity model combined with Tait state equation are used to describe the constitutive relationship and viscosity change of the viscoelastic melt in this paper, respectively. Meanwhile, the coupled level-set and volume-of-fluid (CLSVOF) method is employed to capture the melt front, and the immersed boundary method is applied to the simulation of the polymer melt flows with the aid of a shaped level-set function to describe and treat the irregular mold cavities. A finite volume method on non-staggered grid is used to solve the mass, momentum, and energy conservation equations. Firstly, the benchmark problem of the single shear flow is simulated to verify the validity of the CLSVOF method. Then, the non-isothermal filling process of the viscoelastic fluid based on the XPP model in a mold with square inset is simulated, and the behavior of the weld line devolopment in the filling process is shown and compared with the experimental result. Finally, it is to simulate the evolution processes of the melt front interface and weld line in a mold with the circular notched inset; and the linear stress-optical rule is adopted to calculate the flow-induced birefringence. Numerical results show that the numerical model proposed in this paper can be employed to simulate the non-isothermal filling process in complex mold cavity and to capture the weld line automatically. Because of the complexity of polymer melt flows, the flow-induced stress increases quickly near the weld line region and then decreases gradually until reaching the mold cavity wall. The maximum value of the flow-induced stress appears at some point after the insert. The distributions of physical quantities, such as pressure and temperature in the mold, are given during the mold filling process. Moreover, it is also discussed the influence of melt and mold temperatures on the solidified layer thickness. The higher the melt or mold temperature, the thinner the solidified layer is. Thus, raising the melt or the mold temperature will improve or remove the weld line in melt filling process.
Low frequency band gaps and vibration reduction properties of a multi-frequency locally resonant phononic plate
Wu Jian, Bai Xiao-Chun, Xiao Yong, Geng Ming-Xin, Yu Dian-Long, Wen Ji-Hong
2016, 65 (6): 064602. doi: 10.7498/aps.65.064602
Abstract +
A multi-frequency locally resonant (LR) phononic plate is proposed in this paper. The phononic plate consists of periodic arrays of multiple double-cantilevered thin beams attached to a thin homogeneous plate. This proposed phononic plate is simplified and modeled using a plane wave expansion method to enable the calculation of flexural wave band structures. The band gap behavior of the phononic plate is analyzed comprehensively. In addition, an experimental specimen is fabricated using a square aluminum plate with a thickness of 0.9 mm and an area of 840 mm840 mm, and attached to the specimens as periodic arrays of two types of double-cantilevered thin beams made of the same material as the host plate. And the specimen is measured by using a scanning laser Doppler vibrometer to verify the theoretical predictions of band gaps. Investigations of this paper yield the following findings and conclusions: (1) Due to the interaction of low-frequency vibrational modes of attached multiple double-cantilevered beams and flexural vibration of the host plate, the proposed multi-frequency LR phononic plate can exhibit multiple low-frequency flexural wave band gaps (stop bands). It is also found that the band gaps of a multi-frequency LR phononic plate, especially those appearing in a lower frequency range, are generally narrower than that of a single-frequency LR phononic plate with the same type of double-cantilevered beams. (2) The frequency location of band gaps moves to higher frequency range when the thickness of the double-cantilevered beams is increased, or when the length of the double-cantilevered beams is decreased. It is also shown that a very small variation of the thickness (e. g., 0.1 mm) may lead to significant changes of frequency position of the band gaps. (3) When the width of the double-cantilevered beams is enlarged or the number of the double-cantilevered beams is increased, the lower band gap edge will move to a lower frequency range, while the upper band gap edge will move to a higher frequency range. This implies that the bandwidth of the band gaps is broadened. However, at the same time, it is shown that the central frequencies of the band gaps remain almost unchanged. (4) Experimental measurements of the fabricated specimen evidence the existence of two low frequency band gaps, and confirm that the flexural plate vibrations are significantly reduced in the predicted band gaps.
Analysis of the magnetohydrodynamic heat shield system for hypersonic vehicles
Li Kai, Liu Wei-Qiang
2016, 65 (6): 064701. doi: 10.7498/aps.65.064701
Abstract +
During hypersonic flight, the weakly-ionized plasma layer post shock can be utilized for flow control by externally applying a magnetic field. The Lorentz force, which is induced by the interaction between the ionized air and the magnetic field, decelerates the flow in the shock layer. Consequently, the thickness of the shock layer is increased and the convective heat flux can be mitigated. This so-called magnetohydrodynamic (MHD) heat shield system has been proved to be effective in heat flux mitigation by many researchers.Different from the dipole magnet conventionally used in previous researches on MHD heat shield, a normal columned solenoid-based MHD thermal protection system model is built in this paper. The present numerical analysis is mainly based on the low magneto-Reynolds MHD model, which neglects the induction magnetic field. Hall effect and the ion-slip effect are also neglected here because an insulating wall is assumed. With these hypothesis, a series of axisymmetric simulations on the flow field of Japanese Orbital Reentry Experimental Capsule (OREX) are performed to analyze the influence of different externally applied magnetic fields on the efficiency of MHD thermal protection. First, based on the dipole magnet field, the influence of magnetic induction density is analyzed. Second, differences between the efficiency of MHD thermal protection under three types of magnetic field, namely dipole magnet, solenoid magnet, and uniform magnet field are compared. Finally, the influence of the geometric parameters of solenoid magnet on the MHD thermal protection is analyzed. Results show that, saturation effect exists in the process of MHD heat flux mitigation and it confines the effectiveness of MHD heat shield system. Thermal protection capabilities under three types of magnetic field are ranked from weak to strong as dipole magnet, solenoid magnet, and uniform magnet field. Under the same magnetic induction intensity at the stagnation point, first, the increase of solenoid radius improves its effectiveness in MHD thermal protection; second, the influence of solenoid length on the efficiency of MHD thermal protection is weak, indicating that the solenoid length can be optimized with the remaining two factors, namely the exciting current density and the total weight of solenoid magnet. Finally, the closer distance between the solenoid and stagnation point has negative influence on MHD thermal protection for the stagnation and the shoulder area of the reentry capsule.
A simple and effective simulation for electrical conductivity of warm dense titanium
Fu Zhi-Jian, Jia Li-Jun, Xia Ji-Hong, Tang Ke, Li Zhao-Hong, Quan Wei-Long, Chen Qi-Feng
2016, 65 (6): 065201. doi: 10.7498/aps.65.065201
Abstract +
A linear mixture rule has been used to calculate the electrical conductivity of warm dense titanium plasmas in the density and temperature ranges of 10-510 gcm-3 and 1043104 K, in which the interactions among electrons, atoms, and ions are considered systemically. In the first place, the coupling and degeneracy parameters of titanium plasma are shown as a function of density and temperature in the warm dense range. The warm dense titanium plasmas span from weakly coupled, nondegenerate region to strongly coupled, degenerate domain in the whole density and temperature regime. The titanium plasma becomes strongly coupled plasma at higher than 0.22 gcm-3 and almost in the whole temperature range where the coupling parameter ii 1. In particular, the Coulomb interactions become stronger at higher than 0.56 gcm-3 where 10 ii 216. At the same time, the titanium plasma is in the degenerate regime at higher than 0.35 gcm-3 where the degeneracy parameter 1, and is in the nondegenerate or partial degenerate regime at lower than 0.35 gcm-3 where 1. The influence of temperature on the coupling and degeneracy parameters is less than that of the density, and the plasma composition is calculated by the nonideal Saha equation felicitously. Thus the ionization degree decreases with increasing density at lower density, which is due to the thermal ionization in that regime where the free electrons have sufficiently high thermal energy. Meanwhile, the ionization degree increases with the increase of density at higher than 0.1 gcm-3, in which the pressure ionization takes place in the region where the electrons have sufficiently high density and the collisions increase rapidly. There is a minimum for the ionization degree at about 0.1 gcm-3, while the maximum ionization degree reaches 4 at 10 gcm-3. In the whole temperature regime, the titanium plasma is mostly in the partial plasma domain at lower than 1 gcm-3, and becomes completely ionized at higher than 1 gcm-3. The calculated conductivity is in reasonable agreement with the experimental data. At a fixed temperature, there is a minimum in each of the ionization curves at lower than 3104 K. And the position of the minimum is shifted towards decreasing density with increasing temperature. The conductivity monotonously increases as the density increases at a temprature of 3104 K. At a constant density, the conductivity increases with increasing temperature for lower than 0.56 gcm-3, while it decreases with increasing temperature for higher than 0.56 gcm-3. This behavior is connected with the nonmetal to metal transition in a dense plasma regime. So the nonmetal to metal transition in dense titanium plasma occurs at about 0.56 gcm-3 and its corresponding electrical conductivity is 1.5105 -1m-1. Finally, the contour of electrical conductivity of titanium plasma is shown as a function of density and temperature in the whole range. Its electrical conductivity spans a range from 103 to 106 -1m-1. It can be seen that the titanium plasma gradually approaches the semiconducting regime as temperature increases. When the order of magnitude of the electrical conductivity reaches 105 -1m-1, the plasma almost becomes conducting fluid in the higher density range. This also demonstrates that a nonmetal-metal transition has taken place in the warm dense titanium plasma.
Plasma distribution properties of vacuum ribbon-like cathodic arc plasma fliter and Raman studies of diamond-like carbon films perpared by it
Li Liu-He, Liu Hong-Tao, Luo Ji, Xu Yi
2016, 65 (6): 065202. doi: 10.7498/aps.65.065202
Abstract +
As is well known, most filtered cathodic vacuum arc deposition technology adopts filters with various geometries to remove macro particles in the last three decades, but almost all of them have a circular cross-section. Compared with the traditional toroidal duct filters, the rectangular graphite cathodic arc source can have a larger area which can be an arc source of a ribbon-like cathodic arc plasma filter, which has a higher coating efficiency due to its larger area arc source and may be more suitable for a larger scale industrial production. Thus, the research on the plasma distribution properties within the vacuum ribbon-like cathodic arc plasma filter is of great significance. In this paper, a rectangular graphite cathodic arc source is used to produce the ribbon-like cathodic arc plasma. Within the filter, a 90 curved magnetic duct with a rectangular cross-section is used as the arc filter. The ribbon-like cathodic arc plasma is transmitted from cathode to the deposition area along the magnetic line produced by external coils. A Faraday cup ion energy analyzer and a Langmuir probe are used to characterize the distribution properties of the filtered plasma at 15 places on the exit plane. Ion energies and ion density at these positions are obtained. For the special retrograde motion of the cathode spot on the rectangular target surface, the ion energies and ion density data are not stable. In order to obtain representative values, the net results are the average value of 3 measurements. Diamond-like carbon (DLC) films are deposited by the ribbon-like cathodic arc plasma filter at the same exit plane and their structures are characterized by Raman shift. To compare the distinctness of the 15 Raman spectrums, each Raman spectrum of the DLC films is normalized and shown in a figure. Meanwhile, the thicknesses of all the DLC films are measured by step profiler. Results show that the ion energies are of Maxwell distributions at all the 15 places on the exit plane. The ion energies vary from 0 to 60 eV, most being in the range from 20 to 30 eV. The arc voltage is 30 eV, which exactly coincides with the ion energies. While Raman spectra of the DLC films show an obvious correspondence relationship with the ion energies as well as the ion density and the DLC film thickness. The nano-hardness of the DLC films lies in a range of 25-43 GPa. Although the ion energies, ion density, DLC film thickness and nano-hardness are slightly different at different locations, they are not significant. Owing to the relatively evenly distributed properties of the ribbon-like arc plasma this may open great opportunities for a large area filtered arc deposition technique.
Electronic structure and magnetic properties of MnTe from first-principles calculations
Wang Bu-Sheng, Liu Yong
2016, 65 (6): 066101. doi: 10.7498/aps.65.066101
Abstract +
Based on density functional theory (DFT) together with the projector augmented wave (PAW) method, we systematically investigate the structural, magnetic and electronic properties of the chalcogenide MnTe in six competing structures: rocksalt (RS), cesiun-chloride (CC), zinc-blende (ZB), wurtzite (WZ), iron-silicide (IS) and nickel-arsenide (NA). The ground state of MnTe is completely determined. And the structural parameters, magnetic properties, bulk modulus, phase transition pressure, and the density of states are studied, too. The density of states shows that MnTe in RS, CC and IS structures are antiferromagnetic conductors, and MnTe in WZ, ZB and NA are antiferromagnetic semiconductors. These results provide us the possibility to apply them to the spintronics of antiferromagnetic systems.
Characterization of dislocation loops in hydrogen-ion irradiated vanadium
Cui Li-Juan, Gao Jin, Du Yu-Feng, Zhang Gao-Wei, Zhang Lei, Long Yi, Yang Shan-Wu, Zhan Qian, Wan Fa-Rong
2016, 65 (6): 066102. doi: 10.7498/aps.65.066102
Abstract +
Vanadium alloys are considered as the candidate materials for structure application in fusion reactors because of their low radiation-induced activation, high resistance to radiation damage, high thermal conduction, and low thermal expansion coefficient. Before these materials, which will be exposed to high-flux hydrogen and helium isotopes, may be safely used in fusion device much more data based on irradiation damage are required. The study of dislocation loops in vanadium is designed to indicate the mechanism of void growing under irradiation. The mechanism is that different types of dislocation loops have different bias which represent their abilities to absorb point defects. It is possible to explain the irradiation swelling performance in the material with the bias of loops. The thin disks samples used in this experiment are made of pure vanadium and vanadium alloy (V-4Cr-4Ti) by twin-jet electro-polishing. Electrolyte of H2SO4-CH3OH (1 : 6 by volume) at -20 ℃ is used in a current of 80~120 mA. To get a clear view of dislocation loops, the SRIM code is used to simulate the implantation of hydrogen ions into vanadium. The ion irradiation is carried out to a dose of 51016H+/cm2, at an energy of 30 keV. Microstructure observations are performed on a Tecnai G2 F20 (transmission electron microscope, TEM) at an accelerating voltage of 200 kV. The Burger's vectors and nature of the dislocation loops formed in pure vanadium by hydrogen implantation are confirmed by TEM. This experiment has focused on as many as 76 dislocation loops, lots of images are taken under different diffraction conditions from the same areas of interest. Results show that most of the dislocation loops have a Burger's vectors of 1/2111 (90%), and a few of 110. No loops with b= 100 loops can be found in this study. The nature of dislocation loops is determined by the inside-outside method. The number of the dislocation loops that can make sure of their nature is 29, and all of them are conformed to be interstitial type, their habit planes are from {110} to {112}. No vacancy type loops are found. The density and average size of dislocation loops in vanadium and vanadium alloy are also analysed. Compared with the pure vanadium, the loops in vanadium alloy of V-4Cr-Ti are formed in a smaller size and higher number density. As a future work the difference of the loops nature between pure vanadium and vanadium-based alloys should be investigated to illustrate their behaviour of irradiation swelling.
A molecular dynamics simulation of thermodynamic properties of 1, 3, 5-triamino-2, 4, 6-trinitrobenzene under high pressure and high temperature
Fan Hang, Nie Fu-De, Long Yao, Chen Jun
2016, 65 (6): 066201. doi: 10.7498/aps.65.066201
Abstract +
Equation of states and thermodynamic properties of insensitive high explosive 1, 3, 5-triamino-2, 4, 6-trinitrobenzene (TATB) are investigated by using molecular dynamics simulation, where an all-atom force field for TATB developed by Richard H. Gee and isothermal-isobaric molecular dynamics (NPT-MD) methods are used. Results obtained include thermal expansion coefficient, elastic constants, tensile modulus, and debye frequency under high temperature and high pressure. The volume coefficient of thermal expansion for crystalline TATB is calculated in a temperature range of 200 to 500 K and at atmospheric pressure. The result, 35.910-5 K-1, is in general agreements with the experimental results. Results of elastic constants show that the crystalline TATB is an orthotropic material. The calculated elastic constants decrease with increasing temperature in the range from 0 to 450 K, while increase as the pressure increases from 0 to 50 GPa. And the bulk modulus at 300 K is 11.32 GPa, which is in good agreement with the available experimental results. Results obtained above have been compared with available experimental data, and also discussed in relation to the previous calculations. The above results are better than existing ones gained by others. In addition, the elastic anisotropy becomes lower with increasing temperature or pressure. As the temperature goes up to 400 K, the lattice becomes unstable. The sound speed and Debye frequency are calculated by using the data of elastic constants at different pressures. This provides a theoretical basis to calculate the anisotropic thermal conductivity for crystalline TATB.
Heredity of icosahedrons: a kinetic parameter related to glass-forming abilities of rapidly solidified Cu56Zr44 alloys
Deng Yong-He, Wen Da-Dong, Peng Chao, Wei Yan-Ding, Zhao Rui, Peng Ping
2016, 65 (6): 066401. doi: 10.7498/aps.65.066401
Abstract +
To explore the origin of glassy transition and glass-forming abilities (GFAs) of transition metal-transition metal (TM-TM) alloys from the microstructural point of view, a series of molecular dynamics (MD) simulation for the rapid solidification processes of liquid Cu56Zr44alloys at various cooling rates and pressures P are performed by using a LAMPS program. On the basis of Honeycutt-Andersen (H-A) bond-type index (ijkl), we propose an extended cluster-type index (Z, n/(ijkl)) method to characterize and analyze the microstructures of the alloy melts as well as their evolution in the rapid solidification. It is found that the majority of local atomic configurations in the rapidly solidified alloy are (12 12/1551) icosahedra, as well as (12 8/1551 2/1541 2/1431) and (12 2/1441 8/1551 2/1661) defective icosahedra, but no relationship can be seen between their number N(300 m K) and the glassy transition temperature Tg of rapidly solidified Cu56Zr44alloys. By an inverse tracking of atom trajectories from low temperatures to high temperatures the configuration heredity of icosahedral clusters in liquid is discovered to be an intrinsic feature of rapidly solidified alloys; the onset of heredity merely emerges in the super-cooled liquid rather than the initial alloy melt. Among these the (12 12/1551) standard icosahedra inherited from the super-cooled liquids at Tm-Tg is demonstrated to play a key role in the formation of Cu56Zr44 glassy alloys. Not only is their number N300 KTgP inherited from Tg to 300 K closely related to the GFA of rapidly solidified Cu56Zr44alloys, but a good correspondence of the onset temperatures of heredity (Tonset) with the reduced glass transition temperature (Trg= Tg/Tm) can be also observed. As for the influence of and P on the glassy transition, a continuous tracking of descendible icosahedra reveals that the high GFA of rapidly solidified Cu56Zr44 alloys caused by big and P can be attributed to their elevated inheritable fraction (fp and ftotal) above Tg.
Influence of defect states on proton conductivity of Y-doped BaZrO3
Yang Yi-Bin, Gong Yu, Liu Cai-Lin, Luo Yang-Ming, Chen Ping
2016, 65 (6): 066701. doi: 10.7498/aps.65.066701
Abstract +
Nuclear energy is a promising new energy to solve energy crisis. Separation and purification of hydrogen isotopes play an important role in the developing and utilizing of nuclear energy. BaZrO3-based oxide is an effective material for the separation and purification of hydrogen isotopes. In this paper, a series of BaZr1-xYxO3- (0 x 0.3) are synthesized by high-temperature solid state reaction method. The raw materials are calcined at 1200 ℃ for 5 h in air. Then the calcined powder is consolidated by an isostatic press and sintered at 1500 ℃ for 48 h in air, using a furnace equipped with aluminum oxide heater. Phase purity and phase structure of the obtained BaZr1-xYxO3- are analyzed by XRD. Results show that the structures of the BaZr1-xYxO3- are consistent with the BaZrO3 diffraction pattern (JCPDS 06-399). The Y ions are already incorporated into the lattice of BaZrO3, and the maximum doping concentration of Y rangs from 0.24 to 0.26. Besides, the proton conductivity of Y-doped BaZrO3 is determined under hydrogen atmosphere by the electrochemical impedance spectroscopy (EIS). Experiments show that the BaZr1-xYxO3- with 20 mol% Y has the highest conductivity of 0.0015 S/cm at 600 ℃ which is higher than that of the BaZrO3 matrix material by two orders of magnitude. As the concentration of Y increases, the strain in the crystal structure of BaZrO3 increases, which may be created by the defect of Y-doped BaZrO3. In order to reveal the mechanism of proton conduction in Y-doped BaZrO3, the influence of defect types on proton conduction is also investigated via photoluminescence (PL) and thermoluminescence (TL). For the BaZrO3 matrix, an asymmetrical broad emission peak at 350 to 650 nm occurs in PL with an excitation light of 334 nm. Analysis of Gaussian decomposition shows that the asymmetrical broad emission peak is created by two kinds of different oxygen vacancies (Vo..), which are beneficial to proton conduction. Interestingly, when BaZrO3 is doped with Y, a new emission peak P1 at 388 nm appears owing to the negatively charged YZr' of proton-trapping-type defects, which is harmful to the proton conduction in general. TL analysis shows that the number of YZr' increases and the depth of the trap reduce, as the Y concentration increases in BaZr1-xYxO3- (x=0, 0.05, 0.1, 0.2). Although the YZr' is noxious for the proton conduction, the proton conductivity of BaZr1-xYxO3- (x=0, 0.05, 0.1, 0.2) can be improved via the increase of the release ability of proton trapping as the depth of trap is reduced.
Defects and thermoelectric performance of ternary chalcopyrite CuInTe2-based semiconductors doped with Mn
Wang Hong-Xiang, Ying Peng-Zhan, Yang Jiang-Feng, Chen Shao-Ping, Cui Jiao-Lin
2016, 65 (6): 067201. doi: 10.7498/aps.65.067201
Abstract +
In thermoelectric (TE) semiconductors, there are three physical parameters that govern the TE performance (i.e. Seebeck coefficient (), electrical conductivity (), and thermal conductivity ()); they are interrelated, hence it is hard to optimize them simultaneously. In order to improve the TE performance, we need to further explore new materials. Ternary chalcopyrite (diamond-like) I-III-VI2 semiconductors (Eg = 1:02 eV) are new materials of the TE family, which have potential in conversion between heat and electricity. Since in the ternary chalcopyrite structure, such as Cu(Ag) MTe2, there is an inherent Coulomb attraction between charged defects MCu(Ag)2+ and 2VCu(Ag)- (a native defect pair, i.e., metal M-on-Cu or Ag antisites and two Cu or Ag vacancies), hence the electronic and structural properties can easily be tailored if these two defects, along with the creation of other defects, are modified through the introduciton of foreign elements. Besides, the ternary I-III-VI2 compounds often show tetragonal distortion because 0.25, = c/2a 1 (here and are the anion position displacement parameters, and a and c are the lattice parameters), and the cationanion distances are not equal (dCuTedInTe). Any occupation by foreign elements in the cation sites of I-III-VI2 will cause the redistribution of bond charges between I-VI and III-VI, thus leading to a tiny adjustment of the crystal structure and altering the phonon scattering behavior. In this work, we substitute Mn for Cu in the chalcopyrite CuInTe2 and prepare the Cu-poor Cu1-xInMnxTe2 semiconductors. Investigations of Z-ray patterns after Rietveld refinement reveal that Mn prefers In to Cu lattice sites for low Mn content (x 0.1), thus creating MnIn- as an active acceptor, and improving the carrier concentration (n) and electrical conductivity as Mn content increases. However, Mn can either occupy In or Cu sites simultaneously when x 0.1, and generate both the donor defect MnCu+ and the acceptor defect MnIn-. In this case, annihilation may occur between these two defects, allowing the reduction in both the defect and carrier concentrations. Because of the annihilation between the two defects, two values (|| = |-0.25| and ||= |-1.0|) reduce, this only yields a subtle change in the difference between mean cation-anion distance (RInTe-RCuTe), indicating a small distortion tendency in lattice structure as Mn content increases. Because of this, there is a limited enhancement in lattice thermal conductivity (L) at high temperatures. As a consequence, we attain an optimal TE performance at a certain Mn content (x = 0.05) with the dimensionless figure of merit (ZT) ZT = 0.84 at 810.0 K, which is about twice as much as that of Mn-free CuInTe2.
Dynamics of polarons in organic conjugated polymers with impurity ions
Liu Jun-Juan, Wei Zeng-Jiang, Chang Hong, Zhang Ya-Lin, Di Bing
2016, 65 (6): 067202. doi: 10.7498/aps.65.067202
Abstract +
Based on the one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model, and using the molecular dynamics method, we discuss the dynamics of electron and hole polarons under the influence of impurity potentials and the distance between impurities. Under an external electric field, the electron or hole polaron can move along the polymer chain with a steady velocity. When the polarons collide with impurities, the velocities of the polarons would be affected by the impurity potentials and the distance between the impurities. 1) Firstly, at a fixed impurity potential strength, the average velocities of the electron and hole polarons as a function of the distance (2-16 times the lattice constant) between impurities have been discussed in polymers. It is found that the average velocities of the electron and hole polarons increase with increasing distance between impurities. It is worth noting that the average velocities of the electron polarons are greater than those of the hole polarons, which results from the fact that the electron and hole polarons have different coulomb interactions with the impurity ions. That is to say, the coulomb repulsion is shown between the electron polarons and impurity ions, which is similar to the potential barriers; while the coulomb attraction appears between the hole polaron and impurity ions, which is similar to a potential well. However, as the distance between the impurity ions becomes large enough, the average speeds of the electron and hole polarons almost remain the same, and show just a few small oscillation. This is due to the different distances between impurity ions which generate the different superposition effects of barrier or potential well on the electron and hole polarons. 2) Next, with a fixed distance between the two impurity ions, we find that with the increase of impurity potential strength, the average velocities of the electron and hole polarons decrease. And the decrease of the average speed of the hole polaron is more obvious. It can be explained as follows: the coulomb attraction interactions between the hole polaron and impurity ions can obviously enhance the localization of the hole polaron. While the coulomb repulsion interactions between electron polaron and impurity ions can only make the electron polaron undergo a small shift in the polymer chain, so that the localization of it is almost unchanged. In view of the average speed of the polaron being closely related to the localization of the polaron, the change of the average speed of the hole polaron is more obvious. The results above may provide some theoretical basis for understanding the conduction properties in doped polymers.


White light emitting diode based on quantum dots and MEH-PPV
Sun Li-Zhi, Zhao Su-Ling, Xu Zheng, Yin Hui-Li, Zhang Cheng-Wen, Long Zhi-Juan, Hong Xiao-Xia, Wang Peng, Xu Xu-Rong
2016, 65 (6): 067301. doi: 10.7498/aps.65.067301
Abstract +
The white light emitting diode (LED) devices, in which blue-emitting quantum dots doped in the polymer of poly [2-methoxy-5-(2-ethylhexyloxy)-1, 4-phenylene vinylene] (MEH-PPV) serve as the active layer, have been fabricated in a nitrogen-filled glove box; the devices have the structure of ITO/PEDOT/MEH-PPV:QDs(B)/LiF/Al. After a systematical investigation, we report the effect of different quantum dots (QDs) doping concentration (mass fraction) on the electroluminescent spectrum, current density, brightness, CIE coordinates of the devices and atomic force microscopy (AFM) characterizations of the emitting layer. With the increase of QDs doping concentration, we find that the QDs luminance intensity of the controlling devices continues to grow. When the QDs doping concentration is 40%, the normal white light emission is obtained in the devices. The CIE coordinates of the white QD-LED are (0.35, 0.32), which are close to the balanced white coordinates. Besides, we also fabricate the non-doped devices, in which the structure is ITO/PEDOT/MEH-PPV/QDs(B)/LiF/Al. After finishing the active layer's preparation, the morphology of the films are investigated by AFM. By comparing the analysis, the doped system has a lower level on the root mean squared roughness. In addition, the doped devices demonstrate a superior performance, and exhibit a low turn-on voltage and a high maximum value of luminance.
Study on hysteresis characteristics of magnetic domain rotation in Tb0.3Dy0.7Fe2 alloy
Yan Bai-Ping, Zhang Cheng-Ming, Li Li-Yi, Lü Fu-Zai, Deng Shuang
2016, 65 (6): 067501. doi: 10.7498/aps.65.067501
Abstract +
In this paper, the rotation effects of magnetic domain with different pre-compressive stress and basic magnetic field in the Tb0.3Dy0.7Fe2 alloy have been studied, the curves of magnetization induced by the rotation of magnetic domains are calculated, and the hysteresis characteristics of magnetization in the process of piezomagnetic and magnetoelastic effects are summarized. Based on the minimal value principle of three-dimensional Stoner-Wolhfarth (S-W) model, the total free energy of magnetostrictive particles (including magneto-crystal line anisotropy energy, stress-induced anisotropy energy, and magnetic field energy) is calculated, the curve of free energy is plotted as a function of domain rotation angle for various compressive stresses and magnetic fields. Then, the values of rotation angle for the magnetic domains in the eight easy axial directions 111 are given, and the summation values of magnetization induced by the rotations of magnetic domain angle are analyzed, the hysteresis characteristics and the hysteresis loops of magnetic domain rotations are calculated and discussed. All the above results indicate that the rotations of magnetic domains in the TbDyFe alloy have hysteresis and transition effects in its piezomagnetic and magnetoelastic processes, and the hysteresis effect of magnetization is always induced by the irreversible transitions of domain angle rotation. Due to the load of magnetic field and compressive stress, the angle of the eight easy axial domains 111 will rotate to the more suitable free energy directions, the reversible and irreversible transitions of domain rotation appear in this rotation, and irreversible transition will induce a larger value of changes in the magnetization existing as a hysteresis loop. Also, In the piezomagnetic effect, magnetization hysteresis loop appears with the load of basic magnetic field, and the increase of magnetic field will help to enhance its hysteresis loop and lead to the hysteresis curve deflected toward the greater compressive stress direction. Thirdly, the hysteresis effects of magnetic domain rotation have two important critical magnetic fields in the magnetoelastic process: the magnetostrictive materials will have different domain rotation paths and hysteresis curve in different basic magnetic fields, and the value of critical field will be influenced by the load of pre-compressive stress. Lastly, the experimental testing is used to verify the model and calculations, and the test results of magnetic remanence are in good agreement with the calculated results, especially in the larger values of pre-compressive stress loads. The above computations have a significance for perfecting magnetic domain deflection model and the results are helpful for designing and analyzing of magnetosrictive materials in application.
Research on mechanism of carbon transformation in the preparation of polycrystalline diamond by melt infiltration and growth method under high pressures
Hu Qiang, Jia Xiao-Peng, Li Shang-Sheng, Su Tai-Chao, Hu Mei-Hua, Fang Chao, Zhang Yue-Wen, Li Gang, Liu Hai-Qiang, Ma Hong-An
2016, 65 (6): 068101. doi: 10.7498/aps.65.068101
Abstract +
Recently, a variety of carbon materials can be turned into pure polycrystalline diamond directly without any additives under extreme high pressures and high temperatures (pressure above 13 GPa and temperature above 2000 ℃). Polycrystalline diamond shows a broad application prospect because of its superior performance. However, it is difficult to realize the industrialization of pure polycrystalline diamond on current high pressure equipment due to the high synthetic conditions. The focus of our work is that the synthesis of pure polycrystalline diamond can be realized in the same synthesis range of single diamond produced from the solvent metal (pressure below 6 GPa and temperature below 1500 ℃). The carbon materials can precipitate from the solution in a form of diamond, and fill into the gaps between the diamond particles. According to some domestic scholars' researches on polycrystalline diamond, the solvent method can reduce the high temperature and high pressure conditions on which carbon may transform into diamond directly, and precipitate from the solution in the form of diamond into the gaps between diamond particles. Through a deep study of the approach, the low addition content, even pure polycrystalline diamond without gaps can be prepared. In this paper we have prepared pure polycrystalline diamonds under relatively lower conditions (the pressure being below 6 GPa and the temperature below 1500 ℃) by the method that the metal solution layer infiltrates into the gaps between the pure diamond particles and then the diamond particles will grow up. We also carry out a research on the mechanism of carbon transformation in the preparation of polycrystalline diamond. Compared with the traditional method of powder mixing technology, the melt infiltration and growth method is more advantageous to prepare high abrasive resistance and high density pure polycrystalline diamond.In order to prepare pure flawless polycrystalline diamonds without additives by China-type large volume cubic high-pressure apparatus (CHPA) (SPD-61200), we study thoroughly on the melt infiltration and growth method under high pressures; and this provides a theoretical guidance for pure polycrystalline diamond synthesis. In this paper, polycrystalline diamond is prepared by melt infiltration and growth method at pressures below 6 GPa and temperatures below 1500 ℃. Mechanism research of carbon transformation is made under high pressure and high temperature (HPHT). Through the analyses of optical microscope, X-ray diffraction, and field emission scanning electron microscope measurements, graphitization occurs on the surface of diamond in the procedure of metal solution infiltrating, and then the generated graphite quickly change into diamond-like carbon under HPHT. Meanwhile, the morphology of diamond particles changes distinctly in the syntheses process. From the analysis of experimental phenomena, carbon may undergo three transformations in the preparation: 1) graphite is generated due to the graphitization on the surface of diamond particles, which is caused by the metal solution infiltrating; 2) the generated graphite quickly fills into the gap with the form of diamond-like carbon during the sintering stage; 3) the diamond-like carbon is dissolved in a metal solution, and then precipitates between particles in the form of diamond. The mechanism research on carbon source transformation plays an important guiding role in the industrialization of no-additive, no-gap pure polycrystalline diamond preparation.
The first-principles study on the interaction of Ni with the yttria-stabilized zirconia and the activity of the interface
Dong Shan, Zhang Yan-Xing, Zhang Xi-Lin, Xu Xiao-Pei, Mao Jian-Jun, Li Dong-Lin, Chen Zhi-Ming, Ma Kuan, Fan Zheng-Quan, Wei Dan-Dan, Yang Zong-Xian
2016, 65 (6): 068201. doi: 10.7498/aps.65.068201
Abstract +
Solid oxide fuel cell (SOFC) is expected to be a crucial technology in future power generation due to its advantages of high efficiency, fuel adaptability, all-solid state, modular assembly, and low pollution. The Ni/YSZ (yttrium-stabilized zirconia) cermet is the most popular anode material in SOFCs. However, a major problem is that it can be easily oxidized, thus resulting in the decline of long-term stability and activity as an anode catalyst. A better performance of the Ni/YSZ cermet can be obtained by improving its microstructure as well as the Ni distribution in it. Interactions between Ni and the yttria-stabilized zirconia (YSZ) (111) or oxygen-enriched YSZ(111) (YSZ+O) surface are studied in terms of the first-principles method based on the density functional theory with particular focus put on the activity of the Ni atom at the interface. The geometric and electronic structures of CO and O2 on the Ni1 (the single Ni atom)/YSZ and Ni1/YSZ+O surfaces are also studied. It is found that the Ni atom tends to be adsorbed to O sites and away from the Y atoms on both the surfaces. The most favorable adsorption site is the oxygen vacancy, which has an adsorption energy of 2.85 eV. Compared with YSZ, the single Ni atom loses 1.06 electrons and is oxidized as Ni+ on YSZ+O, which produces a strong interaction between the Ni atom and YSZ+O. Strong adsorption is mainly attributed to the interaction between Ni 3d and Ou 2p orbitals. And the oxidation of Ni can lead to the decrease of electrocatalytic activity of the Ni catalyst. The d-band DOS (density of states) peaks of the Ni1/YSZ+O are lower than that of the Ni1/YSZ, and the corresponding d-band centers are shifted away from the Fermi level to lower energy with the d value of -3.69 eV; therefore the CO and O2 adsorption is weakened. While the adsorption energy for CO on the Ni1/YSZ+O (0.42 eV) is much lower than that on the Ni1/YSZ surface (1.78 eV). In addition, the adsorbed CO gains 0.07 electrons, less than those on the Ni1/YSZ surface (0.34 e). The adsorption energy of O2 on Ni1/YSZ+O also decreases (0.34 eV) and gains fewer electrons (0.24 e) as compared with the corresponding values (2.57 eV, 1.15 eV) on Ni1/YSZ. Results would improve our understanding on the mechanism of oxidation of Ni on the Ni/YSZ anode of SOFCs and would be of great importance for designing highly active catalysts used for fuel cells.
Single event upsets sensitivity of low energy proton in nanometer static random access memory
Luo Yin-Hong, Zhang Feng-Qi, Wang Yan-Ping, Wang Yuan-Ming, Guo Xiao-Qiang, Guo Hong-Xia
2016, 65 (6): 068501. doi: 10.7498/aps.65.068501
Abstract +
Low-energy protons are able to generate enough energy through direct ionization to cause a high single event upset cross section as the feature size of semiconductor devices shrinks. It poses a large challenge on the present proton single event modeling test technique and the space upset rate prediction method. Experimental study of proton single event effect in three different feature sizes of static random access memory (SRAM) (i.e. 65 nm, 90 nm, and 250 nm) is carried out based on domestic low-energy proton accelerators and also the foreign middle-high proton accelerators. Complete cross section curves of proton single event upset from low energy to high energy are acquired. Test results show that single event upset cross section below 1 MeV proton is up to three orders of magnitude higher than the saturation cross section of high-energy proton in nanometer SRAM. However, single event upset is not observed for protons below 3 MeV in 250 nm SRAM, and no single event multiple-cell upsets occur for protons below 1 MeV in 90 nm and 65 nm SRAM. The accurate geometrical structure model of composite sensitive volume is constructed through the combination of test data with device information, and calibrated further by single event test data of low-LET heavy ion and high-energy proton. Simulation results based on the model and Monte-Carlo calculation can reveal the root cause of low-proton single event upset cross section peak. Proton single event upsets are only caused through direct ionization of protons below 1 MeV. When low-energy protons pass through the multiple metallization and passivation layers of the device, the energy spectrum is broadened near the Bragg peak of the proton direct ionization, and the energy is deposited concentratedly into the sensitive volume through direct ionization. When the proton energy is too high or too low, the energy can not be deposited effectively into the sensitive volume through direct ionization. The energy spectrum straggling of low-energy protons due to the use of degrader has a large influence on the height and width of the single event upset cross section peak. Moreover, the contribution of low protons to the space proton single event upset rate is predicted for GEO orbit environment in the worst day environment. It shows that the direct ionization from low energy dominates the proton single event upset rate in the space in 65 nm SRAM. With the development of device technology, the critical charge of single event upset will be further reduced; and to the single event upset from low proton direct ionization more attention must be paid in the study and evaluation of single event effect.
Study on evaporation from alloys used in microwave vacuum electron devices
Liu Yan-Wen, Wang Xiao-Xia, Lu Yu-Xin, Tian Hong, Zhu Hong, Meng Ming-Feng, Zhao Li, Gu Bing
2016, 65 (6): 068502. doi: 10.7498/aps.65.068502
Abstract +
The development of modern satellite communication technologies is imposing higher demands on the lifetime and reliability of the microwave vacuum electronic devices, which directly depend on the evaporation properties of the extensively used Monel and stainless steel. Therefore, it is of vital importance to study the evaporation properties of these two types of metallic materials. For the first time, as far as we know, this paper proposes to study the evaporation properties of metallic materials using time-of-flight mass spectrometer (TOFMS). The components and the contents of the vacuum background, the evaporants from the Monel and from the stainless steel have been measured using the TOFMS, respectively. After the pressure of the measurement chamber is below 4.010-8 Pa, the TOFMS is used for the metallic materials working at different temperatures. They are respectively acquired when the Monel and stainless steel are at room temperature on operate between 750 to 900 ℃ under a pressure of 1.010-6 Pa. The measurements are carried out rapidly and in high sensitivity. As disclosed by the measurements, Mn and Cu began to evaporate when the Monel and the stainless steel are heated to 800 ℃, which is still far below the melting points of the two alloys (1243 ℃ and 1080 ℃). When the Monel and the stainless steel are further heated to 900 ℃, the evaporation of Mn, Cu, and Cr becomes quite considerable. Once the evaporated Mn, Cu, or Cr deposit on the ceramics for the insulation in an electron gun, its insulation will be deteriorated. Hence, the Monel and the stainless steel are not suitable to be use as the components in cathode electron guns, especially those used in the devices that are to work a long lifetime in high vacuum. Moreover, the Monel and the stainless steel are not suitable for used as the components that are often under the electron bombardment, e.g., anodes and collectors, either. The SEM images and XRD of the heat treated surface structures of the Monel and the stainless steel in ultrahigh vacuum (1.010-6 Pa) have also been studied. On heating at 900 ℃ for 30 and 120 min the surface structure and composition change remarkably and a significant reduction in Mn and Cr is visible, and also a large number of holes and crystal boundaries emerge on the surfaces of the two metallic alloys. With increasing heating time, the boundaries will grow larger and larger. As a result, the strength of the two metallic materials becomes weaker and gas permeation and leakage even occur. Therefore, it can be concluded that the components made from Monel and stainless steel, especially those with thin walls, should not be heated to high temperatures in ultrahigh vacuum for a long time. The above phenomena are analyzed in detail theoretically and the proper and feasible application methods of the metallic materials are explored in device design and technological process control. These works are expected to contribute to the prolonging of the lifetimes of the satellites, and will lead to tremendous economic benefits.
Spin transport properties for iron-doped zigzag-graphene nanoribbons interface
Deng Xiao-Qing, Sun Lin, Li Chun-Xian
2016, 65 (6): 068503. doi: 10.7498/aps.65.068503
Abstract +
By using the first-principles method based on the density-functional theory, the spin transport properties for the systems consisting of iron-doped zigzag-edged graphene nanoribbons (ZGNRs) with iron doping at the interface, where the connection is realized between electrodes and the central scattering region, are investigated theoretically. The ribbon widths of ZGNRs are four zigzag C chains (4 ZGNRs), and the length of scattering region is N unit cells (here, N=4, 6, 8, 10). Results show that -spin current is obviously greater than the -spin current under the ferromagnetic (FM) configuration, which is the spin filtering effect. The reason of spin filtering effect cames from two aspects: a) The symmetry-dependent transport properties which arise from different coupling rules between the up and * subbands around the Fermi level, that are dependent on the wave-function symmetry of the two subbands; b) the distribution of molecular orbit within the bias windows, location, or delocalization. While for antiferromagnetic (AFM) spin state, both and spin currents are very small and both the positive and negative bias regions originate from the existence of band gap; therefore, no obvious spin filtering effect can be obtained. For antiparallel (AP) magnetism configuration, spin filtering effect also can be obtained at high bias. Next, we also investigate the other models: the ribbon width of ZGNRs is five (six) zigzag C chains, namely, 5 ZGNRs (6 ZGNRs), and the scattering region is 6 unit cells length. The currents in 6 ZGNRs are less than that of 5 ZGNRs obviously, and this difference is revealed to arise from different couplings between the conducting subbands around the Fermi level, which is dependent on the symmetry of the systems. However, both of the two models show the similar characteristic: spin filtering effect. The spin current is obviously greater than the -spin current with the whole bias under the ferromagnetic (FM) configuration, The analysis on the electronic structure, transmission spectra, the molecular projected self-consistent Hamiltonian (MPSH) which have been modified by the electrodes, local density (LDOS) and the spin density give an insight into the observed results for the systems. These results indicate that the iron doping at interface between electrodes and central scattering region for ZGNRs can modulate effectively the spin electrons. It is of important significance for developing high spin polarization filtering device based on GNRs.
Exploring new opening-up membrane vesicles of two holes by using the relaxation method
Kong Xiang-Bo, Zhang Shao-Guang
2016, 65 (6): 068701. doi: 10.7498/aps.65.068701
Abstract +
Due to the discovery and study of opening-up lipid vesicles, the theoretical analysis and numerical calculation have aroused increasing interests of researchers. In the previous study, Suezaki and Umeda gave the opening-up vesicles near the spherical vesicles, such as the dish and cup shapes with one hole, and the tube and funnel shapes with two holes. These shapes are found at relatively low values of reduced, relaxed area difference a0. However, what are the stable shapes for high values of a0 is not known. Kang et al. found solutions of opening up dumbbell shapes with one hole. Whether or not there exist dumbbell shapes with two holes, and the phase transformation behavior between them remains unknown. The purpose of this paper is to explore a new kind of two-hole dumbbell shaped lipid vesicles and phase transformations between this kind of vesicle and previously found vesicles. Based on the area-difference-elasticity model, this paper tries to explore new solutions of the Euler-Lagrange equations of the opening-up membrane vesicles which meet the boundary conditions by using the relaxation method. A new branch of solution of dumbbell shapes with two holes is found. The phase transformations of closed dumbbell shapes and opening-up dumbbell shapes with one hole and two holes are studied in detail. To explore whether these shapes could be found in experiments, the energy of the cup, tube, and funnel shaped vesicles are also compared with the opening-up dumbbell shapes. It is found that at high values of a0, all the cup, tube, and funnel shapes will transform into closed spherical vesicles. So the energy of new opening-up dumbbell vesicles can be compared to that of closed spherical vesicles and closed dumbbell vesicles. It is found that the dumbbell shapes with one hole and two holes all have stable regions, implying that it is possible for these open dumbbells to be observed. Since the distance in the functional space is too far between the open dumbbell shapes and spherical vesicles, experimental test is needed to verify whether the dumbbell shapes with two holes will evolve continuously to the closed dumbbell shapes or to the closed spherical vesicles. It has been noticed that for relatively small values of a0, two holes vesicles may exhibit symmetrical tube shapes and asymmetric funnel shapes between which the phase transformation is continuous, because the funnel solutions bifurcate from the tube solutions. In order to check whether there exist asymmetric opening-up dumbbell shapes with two holes and the similar bifurcation behavior, a thorough search is made in the parameter space. So far no asymmetric dumbbell shape with two holes is found.


Quaternary sulphides Cu2Zn(Ti, Zr, Hf)S4, the new type of photovoltaic materials
Fan Wei, Zeng Zhi
2016, 65 (6): 068801. doi: 10.7498/aps.65.068801
Abstract +
Based on the first-principles electronic-structure method, we study the electronic structures, optical properties, and the structural stabilities of the quaternary sulphides Cu2Zn(Ti, Zr, Hf) S4, which are obtained via substituting Ti, Zr, and Hf elements for Sn elements in Cu2ZnSnS4 (CTZS). It is well known that the photovoltaic efficiency of CZTS(Se) will be improved if the Se atoms partially substitute S atoms in CZTS. Our results show that the valence-band top of CZTSe shifts to lower energy and accesses to the valence-band top of Cu(InGa) Se2 (CIGS). Similar to CZTSe, the valenceband tops of Cu2Zn(Ti, Zr, Hf) S4 also shift to lower energies and access to the top of valence-band of CIGS. The high photovoltaic efficiency requires the smooth changes of the valence-band top and energy gap from the window material and the buffer layer to the light-absorption layer. Thus we predict that the photovoltaic efficiency will be improved if Sn atoms are substituted, even partially, by Ti, Zr, Hf atoms in CZTS, just like Se atoms substituting S atoms in CZTS. To obtain some reliable results, we perform the calculations both of PBE functional and HSE06 functional. The changes of valence-band tops from window materials to the light-absorbed materials are similar for PBE functional and HSE06 functional. The absolute values of the valence-band tops with HSE06 are lower in energies compared with PBE functional and the gaps obtained from HSE06 are larger than the gaps from PBE. We also calculate the optical properties of different light-absorbed materials including CZTiS, CZZrS, CZHfS, CZTS and CIGS, in which we mainly focus on the reflectance of different layers from the vacuum to the light-absorbed materials, from the window layers to the buffer layers and from the buffer layers to the light-absorbed layers. For the window layers we consider the ZnO and TiO2, and for the buffer layer we consider the CdS, In2S3, ZnSe and ZnS, etc. respectively. The high-performance solar cell requires low reflectance between the window layer and the buffer layer, the buffer layer and the light-absorbed layer so as to ensure more light transmit to the light-absorbed layer. Our results of reflectance show that ZnO(TiO2)/In2S3(ZnSe)/PVM are possible multilayer structures, with PVM (photovoltaic materials) =CZTS, CIGS, CZTiS, CZZrS, CZHfS. If we replace CdS buffer layer with other n-type semiconductors, the material of the window layer must be replaced accordingly with new materials to reach the lower reflectance. The structural stability of photovoltaics is an important topic in the application of photovoltaics. Our results show that CZTiS, CZZrS and CZHfS are structure-stable at zero temperature in terms of the calculated elastic properties and phonon vibration spectrum. Based on the elastic constants and Poisson-ratio, similar to CdTe, CIGS and CZTS, the CZTiS, CZZrS and CZHfS are ductile materials suitable to be used as the flexible solar cell. Additionally, we have performed the molecular-dynamics simulations at some finite temperatures (100, 800 and 1200 K respectively), calculated the pair-distribution functions and angle-distribution functions. As comparison, we also perform the corresponding molecular dynamics simulations of CZTS and ZnS. Our results show that the structural stabilities of CZTiS, CZZrS, and CZHfS are close to those of CZTS and ZnS. This means that once CZTiS, CZZrS and CZHfS are obtained experimentally, they will be stable. In summary, the novel photovoltaic materials CZTiS, CZZrS and CZHfS studied in detail in this work are potentially the high-performance photovoltaic materials for the solar cell application in the near future.