Table of contents

    05 August 2018, Volume 27 Issue 8 Previous issue    Next issue
    A target group tracking algorithm based on a hybrid sensor network
    Chun Zhang(张淳)
    Chin. Phys. B, 2018, 27 (8):  080101.  DOI: 10.1088/1674-1056/27/8/080101
    Abstract ( 624 )   HTML   PDF (866KB) ( 191 )  
    Traditional tracking algorithms based on static sensors have several problems. First, the targets only occur in a part of the interested area; however, a large number of static sensors are distributed in the area to guarantee entire coverage, which leads to wastage of sensor resources. Second, many static sensors have to remain in active mode to track the targets, which causes an increase of energy consumption. To solve these problems, a target group tracking algorithm based on a hybrid sensor network is proposed in this paper, which includes static sensors and mobile sensors. First, an estimation algorithm is proposed to estimate the objective region by static sensors, which work in low-power sensing mode. Second, a movement algorithm based on sliding windows is proposed for mobile sensors to obtain the destinations. Simulation results show that this algorithm can reduce the number of mobile sensors participating in the tracking task and prolong the network lifetime.
    Power control and channel allocation optimization game algorithm with low energy consumption for wireless sensor network
    Xiao-Chen Hao(郝晓辰), Jin-Shuo Liu(刘金硕), Li-Xia Xie(解力霞), Bai Chen(陈白), Ning Yao(姚宁)
    Chin. Phys. B, 2018, 27 (8):  080102.  DOI: 10.1088/1674-1056/27/8/080102
    Abstract ( 595 )   HTML   PDF (2399KB) ( 170 )  
    In a wireless sensor network (WSN), the energy of nodes is limited and cannot be charged. Hence, it is necessary to reduce energy consumption. Both the transmission power of nodes and the interference among nodes influence energy consumption. In this paper, we design a power control and channel allocation game model with low energy consumption (PCCAGM). This model contains transmission power, node interference, and residual energy. Besides, the interaction between power and channel is considered. The Nash equilibrium has been proved to exist. Based on this model, a power control and channel allocation optimization algorithm with low energy consumption (PCCAA) is proposed. Theoretical analysis shows that PCCAA can converge to the Pareto Optimal. Simulation results demonstrate that this algorithm can reduce transmission power and interference effectively. Therefore, this algorithm can reduce energy consumption and prolong the network lifetime.
    Radiating frequency of three-loop mesoscopic LC circuit with mutual inductance obtained by IEO method
    Hong-yi Fan(范洪义), Ze Wu(吴泽)
    Chin. Phys. B, 2018, 27 (8):  080301.  DOI: 10.1088/1674-1056/27/8/080301
    Abstract ( 600 )   HTML   PDF (346KB) ( 140 )  
    Instead of normally tackling electric circuits by virtue of the Kirchhoff's theorem whose aim is to derive voltage, electric current, and electric impedence, our aim in this paper is to derive the characteristic frequency of a three-loop mesoscopic LC circuit with three mutual inductances, e.g., for the radiating frequency of the three-loop LC oscillator, we adopt the invariant eigen-operator (IEO) method to realize our aim.
    Dynamical effects of switching a super-critical well potential on pair creation from a vacuum
    Qiang Wang(王强), Qin-Zhi Xia(夏勤智), Jie Liu(刘杰), Li-Bin Fu(傅立斌)
    Chin. Phys. B, 2018, 27 (8):  080302.  DOI: 10.1088/1674-1056/27/8/080302
    Abstract ( 700 )   HTML   PDF (844KB) ( 127 )  

    The dynamical effects on electron-positron pair creation from a vacuum caused by the switching processes of a super-critical well potential are investigated in detail. The results show that only when the switching on and switching off time both increase will the final pair yield converge to the integer of embedded bound states nearly exponentially. But a single adiabatic switching on or switching off cannot lead to an integer pair yield. If the potential is turned on abruptly, associated with the discrete and embedded bound states, there is multi-frequency oscillation around the pair number's saturation. The slowly switching on can suppress the amplitude of this oscillation and reduce the final pair yield. The switching off can also reduce the final pair number in the same order of magnitude. The evolution of a single-pair number shows a robust long range correlation between particle and antiparticle. For an adiabatic switching case, the single-pair dominates the early pair creation, their upper limit value is equal to the integer, and these single-pairs will totally disentangle during the switching off.

    Quantum pseudodots under the influence of external vector and scalar fields
    M Eshghi, S M Ikhdair
    Chin. Phys. B, 2018, 27 (8):  080303.  DOI: 10.1088/1674-1056/27/8/080303
    Abstract ( 578 )   HTML   PDF (2231KB) ( 172 )  
    We study the spherical quantum pseudodots in the Schrödinger equation by using the pseudo-harmonic plus harmonic oscillator potentials considering the effect of the external electric and magnetic fields. The finite energy levels and the wave functions are calculated. Furthermore, the behavior of the essential thermodynamic quantities such as, the free energy, the mean energy, the entropy, the specific heat, the magnetization, the magnetic susceptibility, and the persistent currents are also studied by using the characteristic function. Our analytical results are found to be in good agreement with the other works. The numerical results on the energy levels as well as the thermodynamic quantities have also been given.
    Dynamic quantum secret sharing protocol based on two-particle transform of Bell states
    Yu-Tao Du(杜宇韬), Wan-Su Bao(鲍皖苏)
    Chin. Phys. B, 2018, 27 (8):  080304.  DOI: 10.1088/1674-1056/27/8/080304
    Abstract ( 574 )   HTML   PDF (421KB) ( 657 )  
    To solve the problems of updating sub-secrets or secrets as well as adding or deleting agents in the quantum secret sharing protocol, we propose a two-particle transform of Bell states, and consequently present a novel dynamic quantum secret sharing protocol. The new protocol can not only resist some typical attacks, but also be more efficient than the existing protocols. Furthermore, we take advantage of the protocol to establish the dynamic secret sharing of a quantum state protocol for two-particle maximum entangled states.
    Controlling a sine wave gating single-photon detector by exploiting its filtering loophole
    Lin-Xi Feng(冯林溪), Mu-Sheng Jiang(江木生), Wan-Su Bao(鲍皖苏), Hong-Wei Li(李宏伟), Chun Zhou(周淳), Yang Wang(汪洋)
    Chin. Phys. B, 2018, 27 (8):  080305.  DOI: 10.1088/1674-1056/27/8/080305
    Abstract ( 736 )   HTML   PDF (4326KB) ( 166 )  
    GHz single-photon detector (SPD) is a crucial part in the practical high speed quantum key distribution (QKD) system. However, any imperfections in a practical QKD system may be exploited by an eavesdropper (Eve) to collect information about the key without being discovered. The sine wave gating SPD (SG-SPD) based on InGaAs/InP avalanche photodiode, one kind of practical high speed SPD, may also contain loopholes. In this paper, we study the principle and characteristic of the SG-SPD and find out the filtering loophole of the SG-SPD for the first time. What is more, the proof-of-principle experiment shows that Eve could blind and control Bob's SG-SPD by exploiting this loophole. We believe that giving enough attention to this loophole can improve the practical security of the existing QKD system.
    Concept study of measuring gravitational constant using superconducting gravity gradiometer
    Xing Bian(边星), Ho Jung Paik, Martin Vol Moody
    Chin. Phys. B, 2018, 27 (8):  080401.  DOI: 10.1088/1674-1056/27/8/080401
    Abstract ( 551 )   HTML   PDF (3164KB) ( 191 )  

    Newton's gravitational constant G is the least known fundamental constant of nature. Since Cavendish made the first measurement of G with a torsion balance over two hundred years ago, the best results of G have been obtained by using torsion balances. However, the uncorrected anelasticity of torsion fibers makes the results questionable. We present a new method of G measurement by using a superconducting gravity gradiometer constructed with levitated test masses, which is free from the irregularities of mechanical suspension. The superconducting gravity gradiometer is rotated to generate a centrifugal acceleration that nulls the gravity field of the source mass, forming an artificial planetary system. This experiment has a potential accuracy of G better than 10 ppm.

    Correlation method estimation of the modulation signal in the weak equivalence principle test
    Jie Luo(罗杰), Liang-Cheng Shen(沈良程), Cheng-Gang Shao(邵成刚), Qi Liu(刘祺), Hui-Jie Zhang(张惠捷)
    Chin. Phys. B, 2018, 27 (8):  080402.  DOI: 10.1088/1674-1056/27/8/080402
    Abstract ( 617 )   HTML   PDF (510KB) ( 161 )  

    In a test of the weak equivalence principle (WEP) with a rotating torsion pendulum, it is important to estimate the amplitude of the modulation signal with high precision. We use a torsional filter to remove the free oscillation signal and employ the correlation method to estimate the amplitude of the modulation signal. The data analysis of an experiment shows that the uncertainties of amplitude components of the modulation signal obtained by the correlation method are in agreement with those due to white noise. The power spectral density of the modulation signal obtained by the correlation method is about one order higher than the thermal noise limit. It indicates that the correlation method is an effective way to estimate the amplitude of the modulation signal and it is instructive to conduct a high-accuracy WEP test.

    Topological classification of periodic orbits in Lorenz system
    Chengwei Dong(董成伟)
    Chin. Phys. B, 2018, 27 (8):  080501.  DOI: 10.1088/1674-1056/27/8/080501
    Abstract ( 725 )   HTML   PDF (2057KB) ( 189 )  
    We systematically investigate the periodic orbits of the Lorenz flow up to certain topological length. As an alternative to Poincaré section map analysis, we propose a new approach for establishing one-dimensional symbolic dynamics based on the topological structure of the orbit. A newly designed variational method is stable numerically for cycle searching, and two orbital fragments can be used as basic building blocks for initialization. The topological classification based on the entire orbital structure is revealed to be effective. The deformation of periodic orbits with the change of parameters provides a chart to the periods of cycles. The current research may provide a methodology for finding and systematically classifying periodic orbits in other similar chaotic flows.
    Double compound combination synchronization among eight n-dimensional chaotic systems
    Gamal M Mahmoud, Tarek M Abed-Elhameed, Ahmed A Farghaly
    Chin. Phys. B, 2018, 27 (8):  080502.  DOI: 10.1088/1674-1056/27/8/080502
    Abstract ( 620 )   HTML   PDF (5766KB) ( 216 )  
    Depending on double compound synchronization and compound combination synchronization, a new kind of synchronization is introduced which is the double compound combination synchronization (DCCS) of eight n-dimensional chaotic systems. This kind may be considered as a generalization of many types of synchronization. In the communication, based on many of drive and response systems, the transmitted and received signals will be more secure. Using the Lyapunov stability theory and nonlinear feedback control, analytical formulas of control functions are obtained to insure our results. The corresponding analytical expression and numerical treatment are used to show the validity and feasibility of our proposed synchronization scheme. The eight memristor-based Chua oscillators are considered as an example. Other examples can be similarly investigated. The proposed synchronization technique is supported using the MATLAB simulation outcomes. We obtain the same results of numerical treatment of our synchronization using simulation observations of our example.
    Phase transitions of the five-state clock model on the square lattice
    Yong Chen(陈勇), Zhi-Yuan Xie(谢志远), Ji-Feng Yu(余继锋)
    Chin. Phys. B, 2018, 27 (8):  080503.  DOI: 10.1088/1674-1056/27/8/080503
    Abstract ( 793 )   HTML   PDF (445KB) ( 187 )  

    Using the tensor renormalization group method based on the higher-order singular value decomposition, we have studied the phase transitions of the five-state clock model on the square lattice. The temperature dependence of the specific heat indicates the system has two phase transitions, as verified clearly by the correlation function at three representative temperatures. By calculating the magnetic susceptibility, we obtained only the upper critical temperature as Tc2=0.9565(7). Investigating the fixed-point tensor, we precisely locate the transition temperatures at Tc1=0.9029(1) and Tc2=0.9520(1), consistent well with the Monte Carlo and the density matrix renormalization group results.

    Transport of velocity alignment particles in random obstacles
    Wei-jing Zhu(朱薇静), Xiao-qun Huang(黄小群), Bao-quan Ai(艾保全)
    Chin. Phys. B, 2018, 27 (8):  080504.  DOI: 10.1088/1674-1056/27/8/080504
    Abstract ( 465 )   HTML   PDF (750KB) ( 140 )  
    We numerically investigate the trapping behaviors of aligning particles in two-dimensional (2D) random obstacles system. Under the circumstances of the effective diffusion rate and the average velocity tend to zero, particles are in trapped state. In this paper, we examine how the system parameters affect the trapping behaviors. At the large self-propelled speed, the ability of nematic particles escape from trapping state is enhancing rapidly, in the meanwhile the polar and free particles are still in trapped state. For the small rotation diffusion coefficient, the polar particles circle around (like vortices) the obstacles and here particles are in trapped state. Interestingly, only the partial nematic particles are trapped in the confined direction and additional particles remain flowing. In the free case, the disorder particle-particle collisions impede the motion in each other's directions, leading the free particles to be trapped. At the large rotation diffusion coefficient, the ordered motion of aligning particles disappear, particles fill the sample evenly and are self-trapped around obstacles. As the particles approach the trapping density due to the crowding effect the particles become so dense that they impede each other's motion. With the increasing number of obstacles, the trajectories of particles are blocked by obstacles, which obstruct the movement of particles. It is worth noting that when the number of the obstacles are large enough, once the particles are trapped, the system is permanently absorbed into a trapped state.
    Efficient image encryption scheme with synchronous substitution and diffusion based on double S-boxes
    Xuan-Ping Zhang(张选平), Rui Guo(郭瑞), Heng-Wei Chen(陈恒伟), Zhong-Meng Zhao(赵仲孟), Jia-Yin Wang(王嘉寅)
    Chin. Phys. B, 2018, 27 (8):  080701.  DOI: 10.1088/1674-1056/27/8/080701
    Abstract ( 571 )   HTML   PDF (3662KB) ( 240 )  
    Single or multiple S-boxes are widely used in image encryption schemes, and in many image encryption schemes the asynchronous encryption structure is utilized, which separates the processes of substitution and diffusion. In this paper, we analyze the defects of this structure based on the example of an article and crack it using a simpler method. To address the defects of the asynchronous encryption structure, a novel encryption scheme is proposed, in which the structure of synchronous substitution and diffusion based on double S-boxes is utilized, so the processes of substitution and diffusion are combined together and the attackers cannot crack the cryptosystem by any of the processes. The simulation results and security analysis show that the proposed encryption scheme is safer and more efficient to expediently use in the real-time system.
    Calibration and data restoration of light field modulated imaging spectrometer
    Li-Juan Su(苏丽娟), Qiang-Qiang Yan(严强强), Yan Yuan(袁艳), Shi-Feng Wang(王世丰), Yu-Jian Liu(刘宇健)
    Chin. Phys. B, 2018, 27 (8):  080702.  DOI: 10.1088/1674-1056/27/8/080702
    Abstract ( 595 )   HTML   PDF (1348KB) ( 184 )  

    A light field modulated imaging spectrometer (LFMIS) can acquire the spatial-spectral datacube of targets of interest or a scene in a single shot. The spectral information of a point target is imaged on the pixels covered by a microlens. The pixels receive spectral information from different spectral filters to the diffraction and misalignments of the optical components. In this paper, we present a linear spectral multiplexing model of the acquired target spectrum. A calibration method is proposed for calibrating the center wavelengths and bandwidths of channels of an LFMIS system based on the liner-variable filter (LVF) and for determining the spectral multiplexing matrix. In order to improve the accuracy of the restored spectral data, we introduce a reconstruction algorithm based on the total least square (TLS) approach. Simulation and experimental results confirm the performance of the spectrum reconstruction algorithm and validate the feasibility of the proposed calibrating scheme.

    Configuration interaction calculations on the spectroscopic and transition properties of magnesium chloride
    Dong-lan Wu(伍冬兰), Cheng-quan Lin(林成泉), Yu-feng Wen(温玉锋), An-dong Xie(谢安东), Bing Yan(闫冰)
    Chin. Phys. B, 2018, 27 (8):  083101.  DOI: 10.1088/1674-1056/27/8/083101
    Abstract ( 565 )   HTML   PDF (751KB) ( 246 )  
    The potential energy curves (PECs) of 14 Λ-S states for magnesium chloride (MgCl) have been calculated by using multi-reference configuration interaction method with Davidson correction (MRCI+Q). The core-valence correlation (CV), scalar relativistic effect, and spin-orbit coupling (SOC) effect are considered in the electronic structure computations. The spectroscopic constants of X2Σ+ and A2Π states have been obtained, which are in good agreement with the existing theoretical and experimental results. Furthermore, other higher electronic states are also characterized. The permanent dipole moments (PDMs) of Λ-S states and the spinorbit (SO) matrix elements between Λ-S states are also computed. The results indicate that the abrupt changes of PDMs and the SO matrix elements are attributed to the avoided crossing between the states with the same symmetry. The SOC effect is taken into account with Breit-Pauli operator, which makes the 14 Λ-S states split into 30 Ω states, and leads to a double-well potential of the Ω=(3)1/2 state. The energy splitting for the A2Π is calculated to be 53.61 cm-1 and in good agreement with the experimental result 54.47 cm-1. The transition dipole moments (TDMs), Franck-Condon factors (FCFs), and the corresponding radiative lifetimes of the selected transitions from excited Ω states to the ground state X2Σ+1/2 have been reported. The computed radiative lifetimes τν' of low-lying excites Ω states are all on the order of 10 ns. Finally, the feasibility of laser cooling of MgCl molecule has been analyzed.
    Forbidden transition properties of fine-structure 2p3 4S3/2-2p3 2D3/2,5/2 for nitrogen-like ions
    Xiao-Kang He(何晓康), Jian-Peng Liu(刘建鹏), Xiang Zhang(张祥), Yong Shen(沈咏), Hong-Xin Zou(邹宏新)
    Chin. Phys. B, 2018, 27 (8):  083102.  DOI: 10.1088/1674-1056/27/8/083102
    Abstract ( 893 )   HTML   PDF (472KB) ( 207 )  

    Based on relativistic wave functions from multiconfiguration Dirac-Hartree-Fock and configuration interaction calculations, E2 and M1 transition probabilities of 2p3 4S3/2-2p3 2D3/2,5/2 are investigated in the nitrogen-like sequence with 7 ≤ Z ≤ 16. The contributions of the electron correlations, Breit interaction, and the quantum electrodynamic (QED) effects on the transition properties are analyzed. The present results can be used for diagnosing plasma. In addition, several N-like ions can also be recommended as a promising candidate for a highly charged ion (HCI) clock with a quality factor (Q) of transition as high as 1020.

    A simulation study of water property changes using geometrical alteration in SPC/E
    Ming-Ru Li(李明儒), Nan Zhang(张楠), Feng-Shou Zhang(张丰收)
    Chin. Phys. B, 2018, 27 (8):  083103.  DOI: 10.1088/1674-1056/27/8/083103
    Abstract ( 690 )   HTML   PDF (1110KB) ( 197 )  
    We present a systematic investigation of the impact of changing the geometry structure of the SPC/E water model by performing a series of molecular dynamic simulations at 1 bar (1 bar=105 Pa) and 298.15 K. The geometric modification includes altering the H-O-H angle range from 90° to 115° and modifying the O-H length range from 0.90 Å to 1.10 Å in the SPC/E model. The former is achieved by keeping the dipole moment constant by modifying the O-H length, while in the latter only the O-H length is changed. With the larger bond length and angle, we find that the liquid shows a strong quadrupole interaction and high tetrahedral structure order parameter, resulting in the enhancement of the network structure of the liquid. When the bond length or angle is reduced, the hydrogen bond lifetime and self-diffusion constant decrease due to the weakening of the intermolecular interaction. We find that modifying the water molecular bond length leading to the variation of the intermolecular interaction strength is more intensive than changing the bond angle. Through calculating the average reduced density gradient and thermal fluctuation index, it is found that the scope of vdW interaction with neighbouring water molecules is inversely proportional to the change of the bond length and angle. The effect is mainly due to a significant change of the hydrogen bond network. To study the effect of water models as a solvent whose geometry has been modified, the solutions of ions in different solvent environments are examined by introducing NaCl. During the dissolving process, NaCl ions are ideally dissolved in SPC/E water and bond with natural water more easily than with other solvent models.
    Relativistic R-matrix calculations for L-shell photoionization cross sections of C Ⅱ
    Lu-You Xie(颉录有), Qian-Qian Man(满倩倩), Jian-Guo Wang(王建国), Yi-Zhi Qu(屈一至), Chen-Zhong Dong(董晨钟)
    Chin. Phys. B, 2018, 27 (8):  083201.  DOI: 10.1088/1674-1056/27/8/083201
    Abstract ( 566 )   HTML   PDF (695KB) ( 181 )  
    The photoionization cross section of the ground state 2s22p 2P1/2o and the first excited state 2s22p 2P3/2o of C Ⅱ ions are systematically calculated using the fully relativistic R-matrix code DARC. The detailed resonances are presented and identified for the photon energy ranging from threshold (24.38 eV) up to 41.5 eV where the L-shell (2p, 2s) photoionization process is dominant. In the calculations, the relativistic effect and electronic correlation effect are well considered. It is found that the relativistic effect is very important for the light atomic system CⅡ, which accounts for experimentally observed fine structure resonance peaks. A careful comparison is made between the present results and the experimental values, and also other theoretical data available in the literature, showing that good agreement is obtained for the resonance peaks.
    Simultaneous study of the lower order harmonic and photoelectron emission from an atom in intense laser pulse
    Yan Yan(闫妍), Fu-Ming Guo(郭福明), Jun Wang(王俊), Ji-Gen Chen(陈基根), Yu-Jun Yang(杨玉军)
    Chin. Phys. B, 2018, 27 (8):  083202.  DOI: 10.1088/1674-1056/27/8/083202
    Abstract ( 620 )   HTML   PDF (3701KB) ( 185 )  
    We simultaneously investigate variations of a low order harmonic and photoelectron emission with an incident laser intensity by solving the time-dependent Schrödinger equation in a momentum space. It can be found that, the intensity of low order harmonic and photoelectron are gradually enhanced with the increase of the laser intensity, when the laser frequency is not in resonance with the transition frequency between the laser-induced high excited states and the ground state. If the resonance occurs, the intensity of the lower order harmonic is reduced and the interference can be observed in the lower order photoelectron spectra.
    Theoretical study on twisted intramolecular charge transfer of 1-aminoanthraquinone in different solvents
    Si-Mei Sun(孙四梅), Song Zhang(张嵩), Chao Jiang(江超), Xiao-Shan Guo(郭小珊), Yi-Hui Hu(胡义慧)
    Chin. Phys. B, 2018, 27 (8):  083401.  DOI: 10.1088/1674-1056/27/8/083401
    Abstract ( 492 )   HTML   PDF (588KB) ( 166 )  
    The twisted intramolecular charge transfer and the excited state relaxation of 1-aminoanthraquinone (1-NH2-AQ) in different solvents are investigated using quantum chemical calculations in this paper. The geometries of the ground state are optimized both in gas and solvents based on the high-level ab initio calculations, the lowest excited singlet state geometry is optimized only in gas for simplicity. An intramolecular charge transfer property is substantiated by the large change of dipole moments between the S0 and S1 states. The mechanism of twisted intramolecular charge transfer is proposed by the conformational relaxation on the potential surface of the S1 state. Quantum chemical calculations present that internal conversion and intersystem crossing are important approaches to the ultrafast deactivation of the S1 state via the twisting of the amino group. The smaller energy difference between the S0 and S1 state shows that the internal conversion process is much faster in a polar solvent than in a nonpolar solvent. Energy intersections between the T2 and S1 state in cyclohexane and dioxane indicate a faster intersystem crossing process in them than in ethanol. These theoretical results agree well with the previous experimental results. Energy barriers are predicted on the potential surface of the S1 state, and they have a positive correlation to solvent viscosity, and the timescale of twisted intra-molecular charge transfer in dioxane is predicted to be longer than in cyclohexane and ethanol.
    Structural evolutions and electronic properties of AunGd (n=6-15) small clusters: A first principles study
    Han-Xing Zhang(张汉星), Chao-Hao Hu(胡朝浩), Dian-Hui Wang(王殿辉), Yan Zhong(钟燕), Huai-Ying Zhou(周怀营), Guang-Hui Rao(饶光辉)
    Chin. Phys. B, 2018, 27 (8):  083601.  DOI: 10.1088/1674-1056/27/8/083601
    Abstract ( 610 )   HTML   PDF (1663KB) ( 150 )  
    Structural, electronic, and magnetic properties of AunGd (n=6-15) small clusters are investigated by using first principles spin polarized calculations and combining with the ab-initio evolutionary structure simulations. The calculated binding energies indicate that after doping a Gd atom AunGd cluster is obviously more stable than a pure Aun+1 cluster. Au6Gd with the quasiplanar structure has a largest magnetic moment of 7.421 μB. The Gd-4f electrons play an important role in determining the high magnetic moments of AunGd clusters, but in Au6Gd and Au12Gd clusters the unignorable spin polarized effects from the Au-6s and Au-5d electrons further enhance their magnetism. The HOMO-LUMO (here, HOMO and LUMO stand for the highest occupied molecular orbital, and the lowest unoccupied molecular orbital, respectively) energy gaps of AunGd clusters are smaller than those of pure Aun+1 clusters, indicating that AunGd clusters have potential as new catalysts with enhanced reactivity.
    Ultra-thin circularly polarized lens antenna based on single-layered transparent metasurface
    Kaiyue Liu(刘凯越), Guangming Wang(王光明), Tong Cai(蔡通), Wenlong Guo(郭文龙), Yaqiang Zhuang(庄亚强), Gang Liu(刘刚)
    Chin. Phys. B, 2018, 27 (8):  084101.  DOI: 10.1088/1674-1056/27/8/084101
    Abstract ( 654 )   HTML   PDF (3371KB) ( 301 )  
    Circularly polarized (CP) lens antenna has been applied to numerous wireless communication systems based on its unique advantages such as high antenna gain, low manufacturing cost, especially stable data transmission between the transmitter and the receiver. Unfortunately, current available CP lens antennas mostly suffer from high profile, low aperture efficiency as well as complex design. In this paper, we propose an ultra-thin CP lens antenna based on the designed single-layered Pancharatnam-Berry (PB) transparent metasurface with focusing property. The PB metasurface exhibits a high transmissivity, which ensures a high efficiency of the focusing property. Launched the metasurface with a CP patch antenna at its focal point, a low-profile lens antenna is simulated and measured. The experimental results show that our lens antenna exhibits a series of advantages including high radiation gain of 20.7 dB, aperture efficiency better than 41.3%, and also narrow half power beam width (HPBW) of 13° at about 14GHz. Our finding opens a door to realize ultra-thin transparent metasurface with other functionalities or at other working frequencies.
    Rapid measurement of transmission matrix with the sequential semi-definite programming method
    Zhenfeng Zhang(张振峰), Bin Zhang(张彬), Qi Feng(冯祺), Huimei He(何惠梅), Yingchun Ding(丁迎春)
    Chin. Phys. B, 2018, 27 (8):  084201.  DOI: 10.1088/1674-1056/27/8/084201
    Abstract ( 693 )   HTML   PDF (1103KB) ( 158 )  

    This paper puts forward for the first time a combined transmission matrix (TM) method to measure the monochromatic TM of scattering media without a reference beam. This method can be named a sequential semi-definite programming method which combines the sequential algorithm and the semi-definite programming method. Firstly, each part of the TM is calculated respectively in proper sequence. Then every part of TM is combined to form a complete TM in accordance with a certain rule. The phase modulation of the incident light is achieved by using a high speed digital mirror device with the superpixel method. We have experimentally demonstrated that the incident light field is focused at the target through scattering media using the measured TM to optimize the wavefront of the incident light. Compared with the semi-definite programming method, our method takes less computational time and occupies less memory space. The sequential semi-definite programming method shows potential applications in imaging through biological tissues.

    Cavity-induced ATS effect on a superconducting Xmon qubit
    Xueyi Guo(郭学仪), Hui Deng(邓辉), Jianghao Ding(丁江浩), Hekang Li(李贺康), Pengtao Song(宋鹏涛), Zhan Wang(王战), Luhong Su(苏鹭红), Yanjun Liu(刘彦军), Zhongcheng Xiang(相忠诚), Jie Li(李洁), Yirong Jin(金贻荣), Yuxi Liu(刘玉玺), Dongning Zheng(郑东宁)
    Chin. Phys. B, 2018, 27 (8):  084202.  DOI: 10.1088/1674-1056/27/8/084202
    Abstract ( 934 )   HTML   PDF (2781KB) ( 188 )  

    We couple a ladder-type three-level superconducting artificial atom to a cavity. Adjusting the artificial atom to make the cavity be resonant with the two upper levels, we then probe the lower two levels of the artificial atom. When driving the cavity to a coherent state, the probe spectrum shows energy level splitting induced by the quantized electromagnetic field in the cavity. This splitting size is related to the coupling strength between the cavity and the artificial atom and, thus, is fixed after the sample is fabricated. This is in contrast to the classical Autler-Townes splitting of a three-level system in which the splitting is proportional to the driving amplitude, which can be continuously changed. Our experiment results show the difference between the classical microwave driving field and the quantum field of the cavity.

    Three-mode optomechanical system for angular velocity detection
    Kai Li(李凯), Sankar Davuluri, Yong Li(李勇)
    Chin. Phys. B, 2018, 27 (8):  084203.  DOI: 10.1088/1674-1056/27/8/084203
    Abstract ( 673 )   HTML   PDF (1847KB) ( 182 )  

    We propose a scheme for measuring the angular velocity of absolute rotation using a three-mode optomechanical system in which one mode of the two-dimensional (2D) mechanical resonator is coupled to an optical cavity. When the total system rotates, the Coriolis force acting on the 2D mechanical resonator due to the absolute rotation will affect the mechanical motion and thus change the phase of the output field from the cavity. The angular velocity of the absolute rotation can be estimated by monitoring the spectrum of the output field from the cavity via homodyne measurement. The minimum measurable angular velocity, which is determined by the noise spectrum, is calculated. The working range of the gyroscope for measuring angular velocity is discussed.

    Tripartite continuous-variable entanglement of NOPA system
    Chao-Ying Zhao(赵超樱), Cheng-Mei Zhang(张成梅)
    Chin. Phys. B, 2018, 27 (8):  084204.  DOI: 10.1088/1674-1056/27/8/084204
    Abstract ( 498 )   HTML   PDF (594KB) ( 164 )  
    We investigate the fundamental limits to the achievable tripartite continuous-variable (CV) entanglement criterion of a generalized V1 criterion. Our numerical simulation results show that the non-degenerate eigenvalues do effect the performances of the estimated minimum variances. From below the threshold to above the threshold, with the increase of the pump parameter, the tripartite CV entanglement gradually disappears. The different off-diagonal elements seriously distort the weights for entanglement. We can obtain a good tripartite CV entanglement by appropriately controlling the values of off-diagonal elements εij.
    High power external-cavity surface-emitting laser with front and end pump
    Lidan Jiang(蒋丽丹), Renjiang Zhu(朱仁江), Maohua Jiang(蒋茂华), Dingke Zhang(张丁可), Yuting Cui(崔玉亭), Peng Zhang(张鹏), Yanrong Song(宋晏蓉)
    Chin. Phys. B, 2018, 27 (8):  084205.  DOI: 10.1088/1674-1056/27/8/084205
    Abstract ( 586 )   HTML   PDF (615KB) ( 209 )  
    High power optically pumped vertical-external-cavity surface-emitting lasers with front and end pump are reported. The gain chip consists of 15 repeats of In0.26GaAs/GaAsP0.02 multiple quantum wells and 30 pairs of Al0.2GaAs/Al0.98GaAs distributed Bragg reflectors. The maximum output power of 3 W, optical-to-optical conversion efficiency of 22.4%, and slope efficiency of 29.8% are obtained with 5-℃ heatsink temperature under the front pump, while the maximum output power of 1.1 W, optical-to-optical conversion efficiency of 23.2%, and slope efficiency of 30.8% are reached with 5-℃ heatsink temperature under the end pump. Influences of thermal effects on the output power of the laser with front and end pump are discussed.
    SPECIAL TOPIC—Nanophotonics
    Reduced graphene oxide as saturable absorbers for erbium-doped passively mode-locked fiber laser
    Zhen-Dong Chen(陈振东), Yong-Gang Wang(王勇刚), Lu Li(李璐), Rui-Dong Lv(吕瑞东), Liang-Lei Wei(韦良雷), Si-Cong Liu(刘思聪), Jiang Wang(王江), Xi Wang(王茜)
    Chin. Phys. B, 2018, 27 (8):  084206.  DOI: 10.1088/1674-1056/27/8/084206
    Abstract ( 829 )   HTML   PDF (924KB) ( 399 )  

    We demonstrate a nanosecond mode-locked erbium-doped fiber laser (EDFL) based on a reduced graphene oxide (RGO) saturable absorber (SA). The RGO SA is prepared by depositing the graphene oxide (GO) on fluorine mica through thermal reduction of GO. A scanning electron microscope (SEM), Raman spectrometer, and x-ray photoelectron spectroscopy (XPS) are adopted to analyze the RGO characteristics. The results show that the reduction degree of graphene oxide is very high. By embedding the RGO SA into the EDFL cavity, a stable mode-locked fiber laser is achieved with a central wavelength of 1567.29 nm and repetition rate of 12.66 MHz. The maximum output power and the minimum pulse duration are measured to be 18.22 mW and 1.38 ns respectively. As far as we know, the maximum output power of 18.22 mW is higher than those of other nanosecond mode-locked oscillators reported. Such a nanosecond pulse duration and megahertz repetition rate make this mode-locked erbium-doped fiber laser a suitable seed oscillator for high-power applications and chirped pulse amplifications.

    Construction of two-qubit logical gates by transmon qubits in a three-dimensional cavity
    Han Cai(蔡涵), Qi-Chun Liu(刘其春), Chang-Hao Zhao(赵昌昊), Ying-Shan Zhang(张颖珊), Jian-She Liu(刘建设), Wei Chen(陈炜)
    Chin. Phys. B, 2018, 27 (8):  084207.  DOI: 10.1088/1674-1056/27/8/084207
    Abstract ( 602 )   HTML   PDF (770KB) ( 238 )  
    We report the implementation of qubit-qubit coupling in a three-dimensional (3D) cavity, using the exchange of virtual photons, to realize logical operations. We measure single photon and multi-photon transitions in this qubit-qubit coupling system and obtain its energy avoided-crossing spectrum. With ac-Stark effect, fast control of the qubits is achieved to tune the effective coupling on and off and the state-swap gate √SWAP is successfully constructed. Moreover, using two-photon transition between the ground state and doubly excited states, a kind of two-photon Rabi-like oscillation is observed. A quarter period of this oscillation corresponds to the logical gate √bSWAPP, which is used for generating Bell states. √bSWAPP and √iSWAP are the foundations of future preparation of two-qubit Bell states and realization of CNOT gate.
    Research progress of third-order optical nonlinearity of chalcogenide glasses
    Xiao-Yu Zhang(张潇予), Fei-Fei Chen(陈飞飞), Xiang-Hua Zhang(章向华), Wei Ji(季伟)
    Chin. Phys. B, 2018, 27 (8):  084208.  DOI: 10.1088/1674-1056/27/8/084208
    Abstract ( 555 )   HTML   PDF (510KB) ( 270 )  
    Chalcogenide glasses (ChGs) are a promising candidate for applications in nonlinear photonic devices. In this paper, we review the research progress of the third-order optical nonlinearity (TONL) of ChGs from the following three aspects:chemical composition, excitation condition, and post processing. The deficiencies in previous studies and further research of the TONL property of ChGs are also discussed.
    Enhancement and modulation of terahertz radiation by multi-color laser pulses
    Min-Jie Pei(裴敏洁), Chen-Hui Lu(卢晨晖), Xian-Wei Wang(王宪位), Zhen-Rong Sun(孙真荣), Shi-An Zhang(张诗按)
    Chin. Phys. B, 2018, 27 (8):  084209.  DOI: 10.1088/1674-1056/27/8/084209
    Abstract ( 634 )   HTML   PDF (469KB) ( 155 )  
    We study theoretically intense terahertz radiation from multi-color laser pulse with uncommon frequency ratios. Comparing the two-color laser scheme, of which the uncommon frequency ratio should be set to be a specific value, we show that by using multi-color harmonic laser pulses as the first pump component, the lasers as the second pump component can be adjusted in a continuous frequency range. Moreover, these multi-color laser pulses can effectively modulate and enhance the terahertz radiation, and the terahertz yield increases with the increase of the wavelength of the uncommon pump component and is stable to the laser relative phase. Finally, we utilize the electron densities and velocities of ionization events to illustrate the physical mechanism of the intense terahertz generation.
    Influences of adsorptions of some inorganic molecules on electronic, optical, and thermodynamic properties of Mg12O12 nanocage: A computational approach
    Asghar Mohammadi Hesari, Hamid Reza Shamlouei
    Chin. Phys. B, 2018, 27 (8):  084210.  DOI: 10.1088/1674-1056/27/8/084210
    Abstract ( 570 )   HTML   PDF (7924KB) ( 152 )  
    According to density functional theory, we investigate the effects of BF3, BF4, BCl3, AlF3, AlCl3, AlBr3, BeF3, GaF3, GaCl3, GaBr3, NO3, BS2, BSO, BO2, F2, PF5, PCl5, and ASF5 molecules on the geometric, electronic, linear, and nonlinear optical properties of an Mg12O12 nanocage. The thermodynamic stability and feasibility of the adsorption process are investigated by analyzing the free energy. It is shown that the adsorptions of almost all molecules on the Mg12O12 surface are exothermic. The calculations of the polarizability of these nanoclusters show that among the studied molecules, BeF3 has the largest influence on the polarizability value (α≈315 a.u., the unit a.u. is short for atomic unit). The static first hyperpolarizability (β0) value is increased in the presence of these superhalogens. This increase is greatest for BeF3 and BF4 of which the highest value of the first hyperpolarizability (β0≈5775 a.u.) is related to a BeF3_c(e@Mg12O12) nanocluster. The adsorption position is a key to estimating the value of increasing the first hyperpolarizability.
    SPECIAL TOPIC—Nanophotonics
    MoS2 saturable absorber prepared by chemical vapor deposition method for nonlinear control in Q-switching fiber laser
    Meng-Li Liu(刘孟丽), Yu-Yi OuYang(欧阳毓一), Huan-Ran Hou(侯焕然), Ming Lei(雷鸣), Wen-Jun Liu(刘文军), Zhi-Yi Wei(魏志义)
    Chin. Phys. B, 2018, 27 (8):  084211.  DOI: 10.1088/1674-1056/27/8/084211
    Abstract ( 618 )   HTML   PDF (1266KB) ( 239 )  

    Due to the remarkable carrier mobility and nonlinear characteristic, MoS2 is considered to be a powerful competitor as an effective optical modulated material in fiber lasers. In this paper, the MoS2 films are prepared by the chemical vapor deposition method to guarantee the high quality of the crystal lattice and uniform thickness. The transfer of the films to microfiber and the operation of gold plated films ensure there is no heat-resistant damage and anti-oxidation. The modulation depth of the prepared integrated microfiber-MoS2 saturable absorber is 11.07%. When the microfiber-MoS2 saturable absorber is used as a light modulator in the Q-switching fiber laser, the stable pulse train with a pulse duration of 888 ns at 1530.9 nm is obtained. The ultimate output power and pulse energy of output pulses are 18.8 mW and 88 nJ, respectively. The signal-to-noise ratio up to 60 dB indicates the good stability of the laser. This work demonstrates that the MoS2 saturable absorber prepared by the chemical vapor deposition method can serve as an effective nonlinear control device for the Q-switching fiber laser.

    Tunable graphene-based mid-infrared band-pass planar filter and its application
    Somayyeh Asgari, Hossein Rajabloo, Nosrat Granpayeh, Homayoon Oraizi
    Chin. Phys. B, 2018, 27 (8):  084212.  DOI: 10.1088/1674-1056/27/8/084212
    Abstract ( 667 )   HTML   PDF (2731KB) ( 325 )  
    We have designed and proposed the edge modes supported by graphene ribbons and the planar band-pass filter consisting of graphene ribbons coupled to a graphene ring resonator by using the finite-difference time-domain numerical method. Simulation results show that the edge modes improve the electromagnetic coupling between devices. This structure works as a novel, tunable mid-infrared band-pass filter. Our studies will benefit the fabrication of planar, ultra-compact nano-scale devices in the mid-infrared region. A power splitter consisting of two output ribbons that is useful in photonic integrated devices and circuits is also designed and simulated. These devices are useful for designing ultra-compact planar devices in photonic integrated circuits.
    Analysis of resonance asymmetry phenomenon in resonator integrated optic gyro
    Yao Fei(费瑶), Yu-Ming He(何玉铭), Xiao-Dong Wang(王晓东), Fu-Hua Yang(杨富华), Zhao-Feng Li(李兆峰)
    Chin. Phys. B, 2018, 27 (8):  084213.  DOI: 10.1088/1674-1056/27/8/084213
    Abstract ( 781 )   HTML   PDF (514KB) ( 190 )  
    Resonator integrated optic gyro (RIOG) is a high-accuracy gyroscope based on the Sagnac effect. The waveguide-type ring resonator is a key rotation sensing element in the RIOG. An asymmetric resonance line shape is found in the optic resonator. These asymmetries will induce offset errors when the phase modulation spectroscopy technique (PMST) is applied to the RIOG. The polarization errors and the difference among normal mode losses are found to be the two main sources of resonance asymmetry in an experiment. These sources are fully investigated and their contributions to the offset errors are compared. The analysis shows that proper modulation frequencies in clockwise (CW) and counterclockwise (CCW) directions can reduce an RIOG bias error. A transmissive resonator is recommended to obtain a better resonance line shape.
    SPECIAL TOPIC—Nanophotonics
    Sb2Te3 mode-locked ultrafast fiber laser at 1.93 μm
    Jintao Wang(王金涛), Jinde Yin(尹金德), Tingchao He(贺廷超), Peiguang Yan(闫培光)
    Chin. Phys. B, 2018, 27 (8):  084214.  DOI: 10.1088/1674-1056/27/8/084214
    Abstract ( 836 )   HTML   PDF (5413KB) ( 272 )  

    Ultrafast pulse generation was demonstrated in thulium doped fiber laser mode locked by magnetron sputtering deposited Sb2Te3 with the modulation depth, non-saturable loss, and saturable intensity of 38%, 31.2%, and 3.3 MW/cm2, respectively. Stable soliton pulses emitting at 1930.07 nm were obtained with pulse duration of 1.24 ps, a 3-dB spectral bandwidth of 3.87 nm, an average output power of 130 mW, and signal-to-noise ratio (SNR) of 84 dB. To our knowledge, this is the first demonstration of Sb2Te3-based SA in fiber lasers at 2-μm regime.

    Generation and evolution of multiple operation states in passively mode-locked thulium-doped fiber laser by using a graphene-covered-microfiber
    Xiao-Fa Wang(王小发), Jun-Hong Zhang(张俊红), Xiao-Ling Peng(彭晓玲), Xue-Feng Mao(毛雪峰)
    Chin. Phys. B, 2018, 27 (8):  084215.  DOI: 10.1088/1674-1056/27/8/084215
    Abstract ( 524 )   HTML   PDF (2655KB) ( 185 )  
    Using graphene-covered-microfiber (GCM) as a saturable absorber, the generation and evolution of multiple operation states are proposed and demonstrated in passively mode-locked thulium-doped fiber laser. The microfiber was fabricated using the flame brushing method to an interaction length of~1.2 cm with a waist diameter of~10 μm. Graphene layers were grown on copper foils by chemical vapor deposition and transferred onto the polydimethylsiloxane (PDMS) to form a PDMS/graphene film, which allowed light-graphene interaction via evanescent field. With the increase of the pump power from 1.25 W to 2.15 W, five different lasing regimes, including continuous-wave, conventional soliton mode-locking, multi-soliton mode-locking, a period of transition, and noise-like mode-locking, were achieved in a fiber ring cavity. To the best of our knowledge, it is the first report of the generation and evolution of multiple operation states by covering graphene on the microfiber in the 2-μm region. The results demonstrate that GCM can be a promising method for fabricating all fiber SA, and the switchable operation states can provide more portability in complex application domain.
    Lamb wave signal selective enhancement by an improved design of meander-coil electromagnetic acoustic transducer
    Wen-Xiu Sun(孙文秀), Guo-Qiang Liu(刘国强), Hui Xia(夏慧), Zheng-Wu Xia(夏正武)
    Chin. Phys. B, 2018, 27 (8):  084301.  DOI: 10.1088/1674-1056/27/8/084301
    Abstract ( 575 )   HTML   PDF (1400KB) ( 157 )  
    In this paper, we investigate a method of selectively enhancing the single mode signal of a Lamb wave by using a meander-coil electromagnetic acoustic transducer (EMAT) with a new magnetic configuration. We use the Lamb antisymmetric (A0) mode and symmetric (S0) mode as an example for analysis. The analytical expression of the magnitude of the spatial Fourier transform of the Lorentz force generated by different meander coils is used to determine the optimal driving frequency for single mode generation. The numerical calculation is used to characterize the new magnetic configuration and the conventional EMAT magnet. Experimental examinations of each meander coil in combination with the conventional and new magnetic configuration show that the Lamb wave signal can be selectively enhanced by choosing the appropriate driving frequency and coil parameters through using the improved meander-coil EMAT.
    Interaction between encapsulated microbubbles: A finite element modelling study
    Chen-Liang Cai(蔡晨亮), Jie Yu(于洁), Juan Tu(屠娟), Xia-Sheng Guo(郭霞生), Pin-Tong Huang(黄品同), Dong Zhang(章东)
    Chin. Phys. B, 2018, 27 (8):  084302.  DOI: 10.1088/1674-1056/27/8/084302
    Abstract ( 563 )   HTML   PDF (2266KB) ( 223 )  
    Theoretical studies on the multi-bubble interaction are crucial for the in-depth understanding of the mechanism behind the applications of ultrasound contrast agents (UCAs) in clinics. A two-dimensional (2D) axisymmetric finite element model (FEM) is developed here to investigate the bubble-bubble interactions for UCAs in a fluidic environment. The effect of the driving frequency and the bubble size on the bubble interaction tendency (viz., bubbles' attraction and repulsion), as well as the influences of bubble shell mechanical parameters (viz., surface tension coefficient and viscosity coefficient) are discussed. Based on FEM simulations, the temporal evolution of the bubbles' radii, the bubble-bubble distance, and the distribution of the velocity field in the surrounding fluid are investigated in detail. The results suggest that for the interacting bubble-bubble couple, the overall translational tendency should be determined by the relationship between the driving frequency and their resonance frequencies. When the driving frequency falls between the resonance frequencies of two bubbles with different sizes, they will repel each other, otherwise they will attract each other. For constant acoustic driving parameters used in this paper, the changing rate of the bubble radius decreases as the viscosity coefficient increases, and increases first then decreases as the bubble shell surface tension coefficient increases, which means that the strength of bubble-bubble interaction could be adjusted by changing the bubble shell visco-elasticity coefficients. The current work should provide a powerful explanation for the accumulation observations in an experiment, and provide a fundamental theoretical support for the applications of UCAs in clinics.
    Experimental and numerical study on energy dissipation in freely cooling granular gases under microgravity
    Wen-Guang Wang(王文广), Mei-Ying Hou(厚美瑛), Ke Chen(陈科), Pei-Dong Yu(虞培东), Matthias Sperl
    Chin. Phys. B, 2018, 27 (8):  084501.  DOI: 10.1088/1674-1056/27/8/084501
    Abstract ( 656 )   HTML   PDF (2457KB) ( 147 )  

    Energy dissipation is one of the most important properties of granular gas, which makes its behavior different from that of molecular gas. In this work we report our investigations on the freely-cooling evolution of granular gas under microgravity in a drop tower experiment, and also conduct the molecular dynamics (MD) simulation for comparison. While our experimental and simulation results support Haff's law that the kinetic energy dissipates with time t as E(t)~(1+t/τ)-2, we modify τ by taking into account the friction dissipation during collisions, and study the effects of number density and particle size on the collision frequency. From the standard deviation of the measured velocity distributions we also verify the energy dissipation law, which is in agreement with Haff's kinetic energy dissipation.

    A new kind of hairpin-like vortical structure induced by cross-interaction of sinuous streaks in turbulent channel
    Jian Li(李健), Gang Dong(董刚), Hui Zhang(张辉), Zhengshou Chen(陈正寿), Zhaode Zhang(张兆德)
    Chin. Phys. B, 2018, 27 (8):  084701.  DOI: 10.1088/1674-1056/27/8/084701
    Abstract ( 627 )   HTML   PDF (3247KB) ( 152 )  
    This work is motivated by previous experimental and numerical studies which reveal that the hairpin vortex could be formed by the interaction between spanwise adjacent low-speed streaks. To prove that such an interaction mechanism is still applicable in the normal direction, two sinuous low-speed streaks with the same streamwise phase are set to be in the upper half and bottom half of a small size channel, respectively, and their evolution and interaction are investigated by direct numerical simulation. A new kind of hairpin-like vortical structure, distributed in the normal direction and straddled across both halves of the channel, is found during the cross-interaction process of the low-speed streaks. The influence of such a normal-distributed hairpin-like vortex (NHV) on the turbulent statistical regularity is also revealed. It is observed that the NHV can lead to a sudden surge of wall skin friction, but the value of the normal velocity as well as the streamwise and spanwise vorticity sharply decrease to zero in the center of the channel.
    Walking of spider on water surface studied from its leg shadows
    Yelong Zheng(郑叶龙), Hongyu Lu(鲁鸿宇), Jile Jiang(蒋继乐), Dashuai Tao(陶大帅), Wei Yin(尹维), Yu Tian(田煜)
    Chin. Phys. B, 2018, 27 (8):  084702.  DOI: 10.1088/1674-1056/27/8/084702
    Abstract ( 633 )   HTML   PDF (699KB) ( 140 )  
    Different from sculling forward of water striders with their hairy water-repellent legs, water spiders walked very quickly on water surfaces. By using a shadow method, the walking of water spiders had been studied. The three-dimensional trajectories and the supporting forces of water spider legs during walking forward were achieved. Results showed that the leg movement could be divided into three phases:slap, stroke, and retrieve. Employing an effective strategy to improving walking efficiency, the sculling legs supported most of its body weight while other legs were lifted to reduce the lateral water resistance, which was similar to the strategy of water striders. These findings could help guiding the design of water walking robots with high efficiency.
    Theoretical analysis on deflagration-to-detonation transition
    Yun-Feng Liu(刘云峰), Huan Shen(沈欢), De-Liang Zhang(张德良), Zong-Lin Jiang(姜宗林)
    Chin. Phys. B, 2018, 27 (8):  084703.  DOI: 10.1088/1674-1056/27/8/084703
    Abstract ( 540 )   HTML   PDF (772KB) ( 148 )  
    The study on deflagration-to-detonation transition (DDT) is very important because this mechanism has relevance to safety issues in industries, where combustible premixed gases are in general use. However, the quantitative prediction of DDT is one of the major unsolved problems in combustion and detonation theory to date. In this paper, the DDT process is studied theoretically and the critical condition is given by a concise theoretical expression. The results show that a deflagration wave propagating with about 60% Chapman-Jouguet (CJ) detonation velocity is a critical condition. This velocity is the maximum propagating velocity of a deflagration wave and almost equal to the sound speed of combustion products. When this critical condition is reached, a CJ detonation is triggered immediately. This is the quantitative criteria of the DDT process.
    Observation of double pseudowaves in an ion-beam-plasma system
    Zi-An Wei(卫子安), Jin-Xiu Ma(马锦秀), Kai-Yang Yi(弋开阳)
    Chin. Phys. B, 2018, 27 (8):  085201.  DOI: 10.1088/1674-1056/27/8/085201
    Abstract ( 807 )   HTML   PDF (1046KB) ( 149 )  

    Pseudowaves, known as burst-ion signals, which are different from plasma normal modes, exist frequently in ion-wave excitation experiments when launching the waves by applying a pulsed voltage to a negatively biased grid. In previous experiments, only one kind of the pseudowave was observed. In this paper, we report the observation and identification of double pseudowaves in an ion-beam-plasma system. These pseudowaves originate from two ion groups:the burst of the beam ions and the burst of the background ions. It was observed that the burst of the background ions was in the case of high ion beam energy, while the burst of the beam ions was in the case of low ion beam energy. By observing the dependence of the signal velocities on the characteristics of the excitation voltage, these pseudowaves can be identified. It was also observed that the burst ion signal originating from the background ions can interact with slow beam mode and that originating from the beam ions can interact with fast beam mode.

    Factors affecting improvement of fluorescence intensity of quartet and doublet state of NO diatomic molecule excited by glow discharge
    Ahmed Asaad I Khalil, Reem Al-Tuwirqi, Mohammed A Gondal, Noura Al-Suliman
    Chin. Phys. B, 2018, 27 (8):  085202.  DOI: 10.1088/1674-1056/27/8/085202
    Abstract ( 614 )   HTML   PDF (3596KB) ( 149 )  

    We report on the observation of new fluorescence emission spectral transitions obtained from NO diatomic molecule in the region from ultraviolet (UV) to near infrared (NIR) in a low power glow discharge system. This glow discharge electronic excitation populates different quartet and doublet states of NO in its proximity such as the A2Σ (υ=2), b4Σ- (υ=3), B2Π (υ=4), and X2Π (υ=33-32) states. Due to inter-system crossing, emission lines originating from these levels to lower lying states are recorded and spectral line assignments are performed. The observed systems include b4Σ--a4Π, B2Π-a4Π, a4Π-X2Π, A2Σ-X2Π, X2Π-X2Π (33-15), X2Π-X2Π (33-17), X2Π-X2Π (33-20), and X2Π-X2Π (33-18). This new information will conduce to the better understanding of the interesting features of NO molecule. Such parameters that affect the recording of low density of NO molecules are also discussed In addition to the factors such as the time evolution, argon gas concentration relative to NO mixture, the percentage of NO molecular gas concentration, discharge electric current signals and discharge applied voltage are studied. Those factors would enhance the fluorescence signal intensity of NO molecules. The recent results might be significant as reference data for optimizing the glow discharge spectrometer and diagnostics of NO gas.

    Properties of long light filaments in natural environment
    Shi-You Chen(陈式有), Hao Teng(滕浩), Xin Lu(鲁欣), Zong-Wei Shen(沈忠伟), Shuang Qin(秦爽), Wen-Shou Wei(魏文寿), Rong-Yi Chen(陈荣毅), Li-Ming Chen(陈黎明), Yu-Tong Li(李玉同), Zhi-Yi Wei(魏志义)
    Chin. Phys. B, 2018, 27 (8):  085203.  DOI: 10.1088/1674-1056/27/8/085203
    Abstract ( 520 )   HTML   PDF (1412KB) ( 142 )  

    The multiple filamentation of terawatt femtosecond (fs) laser pulses is experimentally studied in a natural environment. A more than 30-m long plasma filament with a millimeter diameter is formed by the collimated fs laser pulse freely propagating in an open atmosphere. This study provides the first quantitative experimental data about the electron density of a long range light filament in the atmosphere. The electron density of such a filament is quantitatively detected by using an electric method, showing that it is at the 1011-cm-3 level.

    Influence of channel length on discharge performance of anode layer Hall thruster studied by particle-in-cell simulation
    Xi-Feng Cao(曹希峰), Hui Liu(刘辉), Wen-Jia Jiang(蒋文嘉), Zhong-Xi Ning(宁中喜), Run Li(黎润), Da-Ren Yu(于达仁)
    Chin. Phys. B, 2018, 27 (8):  085204.  DOI: 10.1088/1674-1056/27/8/085204
    Abstract ( 580 )   HTML   PDF (2048KB) ( 183 )  
    Hall thruster has the advantages of simple structure, high specific impulse, high efficiency, and long service life, and so on. It is suitable for spacecraft attitude control, North and South position keeping, and other track tasks. The anode layer Hall thruster is a kind of Hall thruster. The thruster has a longer anode area and a relatively short discharge channel. In this paper, the effect of the channel length on the performance of the anode layer Hall thruster is simulated by the PIC simulation method. The simulation results show that the change of the channel length has significant effect on the plasma parameters, such as potential and plasma density and so on. The ionization region mainly concentrates at the hollow anode outlet position, and can gradually move toward the channel outlet as the channel length decreases. The collision between the ions and the wall increases with the channel length increasing. So the proper shortening of the channel length can increase the life of the thruster. Besides, the results show that there is a best choice of the channel length for obtaining the best performance. In this paper, thruster has the best performance under a channel length of 5 mm.
    Electrical and thermal characterization of near-surface electrical discharge plasma actuation driven by radio frequency voltage at low pressure
    Zhen Yang(杨臻), Hui-Min Song(宋慧敏), Di Jin(金迪), Min Jia(贾敏), Kang Wang(王康)
    Chin. Phys. B, 2018, 27 (8):  085205.  DOI: 10.1088/1674-1056/27/8/085205
    Abstract ( 556 )   HTML   PDF (2954KB) ( 152 )  
    The electrical and thermal characterization of near-surface electrical discharge plasma driven by radio frequency voltage are investigated experimentally in this paper. The influences of operating pressure, electrode distance, and duty cycle on the discharge are studied. When pressure reaches 60 Torr (1 Torr=1.33322×102 Pa) the transition from diffuse glow mode to constricted mode occurs. With the operating pressure varying from 10 Torr to 60 Torr, the discharge energy calculated from the charge-voltage (Q-V) Lissajous figure decreases rapidly, while it remains unchanged between 60 Torr and 460 Torr. Under certain experimental conditions, there exists an optimized electrode distance (8 mm). As the duty cycle of applied voltage increases, the voltage-current waveforms and Q-V Lissajous figures show no distinct changes.
    Similarity principle of microwave argon plasma at low pressure
    Xiao-Yu Han(韩晓宇), Jun-Hong Wang(王均宏), Mei-E Chen(陈美娥), Zhan Zhang(张展), Zheng Li(李铮), Yu-Jian Li(李雨键)
    Chin. Phys. B, 2018, 27 (8):  085206.  DOI: 10.1088/1674-1056/27/8/085206
    Abstract ( 583 )   HTML   PDF (901KB) ( 205 )  
    In order to validate the similarity principle of microwave breakdown, a two-dimensional (2D) fluid model of low-pressure microwave argon plasma is established and solved by the finite-element method. Proportional conditions are used in this model to build three different breakdown processes that meet the premise of a similarity principle, and these breakdown processes are called “similar cases” in this paper. Similar cases have proportionately sized breakdown regions, where the ratio of frequency of incident microwave f to gas pressure p (f/p), and the reduced field E/p in them are kept the same. All the important physical parameters such as electron density, electron temperature, and reduced electric field can be obtained from the simulation of this model. The results show that the parameters between similar cases are in constant ratio without changing with time, which means that the similarity principle is also valid in microwave breakdown.
    SPECIAL TOPIC—Nanophotonics
    Sputtered gold nanoparticles enhanced quantum dot light-emitting diodes
    Abida Perveen, Xin Zhang(张欣), Jia-Lun Tang(汤加仑), Deng-Bao Han(韩登宝), Shuai Chang(常帅), Luo-Gen Deng(邓罗根), Wen-Yu Ji(纪文宇), Hai-Zheng Zhong(钟海政)
    Chin. Phys. B, 2018, 27 (8):  086101.  DOI: 10.1088/1674-1056/27/8/086101
    Abstract ( 733 )   HTML   PDF (3859KB) ( 238 )  

    Surface plasmonic effects of metallic particles have been known to be an effective method to improve the performances of light emitting didoes. In this work, we report the sputtered Au nanoparticles enhanced electroluminescence in inverted quantum dot light emitting diodes (ITO/Au NPs/ZnMgO/QDs/TFB/PEDOT:PSS/Al). By combining the time-resolved photoluminescence, transient electroluminescence, and ultraviolet photoelectron spectrometer measurements, the enhancement of the internal field enhanced exciton coupling to surface plasmons and the electron injection rate increasing with Au nanoparticles' incorporation can be explained. Phenomenological numerical calculations indicate that the electron mobility of the electron transport layer increases from 1.39×10-5 cm2/V·s to 1.91×10-5 cm2/V·s for Au NPs modified device. As a result, the maximum device luminescence is enhanced by 1.41 fold (from 14600 cd/cm2 to 20720 cd/cm2) and maximum current efficiency is improved by 1.29 fold (from 3.12 cd/A to 4.02 cd/A).

    Synthesis of Pr-doped ZnO nanoparticles: Their structural, optical, and photocatalytic properties
    Jun-Lian Chen(陈军联), Neena Devi, Na Li(李娜), De-Jun Fu(付德君), Xian-Wen Ke(柯贤文)
    Chin. Phys. B, 2018, 27 (8):  086102.  DOI: 10.1088/1674-1056/27/8/086102
    Abstract ( 769 )   HTML   PDF (1078KB) ( 323 )  

    Undoped and praseodymium-doped zinc oxide (Pr-doped ZnO) (with 2.0-mol%-6.0-mol% Pr) nanoparticles as sunlight-driven photocatalysts are synthesized by means of co-precipitation with nitrates followed by thermal annealing. The structure, morphology, and chemical bonding of the photocatalysts are studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray emission spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR), respectively. The optical properties are studied by photoluminescence (PL) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). We find that Pr doping does not change the crystallinity of ZnO; but it reduces the bandgap slightly, and restrains the recombination of the photogenerated electron-hole pairs. The photocatalytic performance of the photocatalysts is investigated by the photodegradation reaction of 10-mg/L rhodamine B (RhB) solution under simulated sunlight irradiation, showing a degradation rate of 93.75% in ZnO doped with 6.0-mol% Pr.

    Influences of total ionizing dose on single event effect sensitivity in floating gate cells
    Ya-Nan Yin(殷亚楠), Jie Liu(刘杰), Qing-Gang Ji(姬庆刚), Pei-Xiong Zhao(赵培雄), Tian-Qi Liu(刘天奇), Bing Ye(叶兵), Jie Luo(罗捷), You-Mei Sun(孙友梅), Ming-Dong Hou(侯明东)
    Chin. Phys. B, 2018, 27 (8):  086103.  DOI: 10.1088/1674-1056/27/8/086103
    Abstract ( 527 )   HTML   PDF (1134KB) ( 197 )  
    The influences of total ionizing dose (TID) on the single event effect (SEE) sensitivity of 34-nm and 25-nm NAND flash memories are investigated in this paper. The increase in the cross section of heavy-ion single event upset (SEU) in memories that have ever been exposed to TID is observed, which is attributed to the combination of the threshold voltage shifts induced by γ-rays and heavy ions. Retention errors in floating gate (FG) cells after heavy ion irradiation are observed. Moreover, the cross section of retention error increases if the memory has ever been exposed to TID. This effect is more evident at a low linear energy transfer (LET) value. The underlying mechanism is identified as the combination of the defects induced by γ-rays and heavy ions, which increases the possibility to constitute a multi-trap assisted tunneling (m-TAT) path across the tunnel oxide.
    First principles study on lattice vibration and electrical properties of layered perovskite Sr2M2O7 (M=Nb, Ta)
    Xing Liu(刘星), Hui-Qing Fan(樊慧庆)
    Chin. Phys. B, 2018, 27 (8):  086104.  DOI: 10.1088/1674-1056/27/8/086104
    Abstract ( 601 )   HTML   PDF (1919KB) ( 186 )  

    In this paper, we performed calculations to investigate the dielectric, piezoelectric properties, Born effective charge (BEC), and spontaneous polarization of Sr2M2O7, the method used in our study was a well-known density functional theory based on first-principles. The optimized results were in good agreement with previous experiments and calculations, which indicates that our calculated method is reasonable. The research we have done suggested that greater piezoelectric components of Sr2Nb2O7 were e31 and e33, and the contributions were derived from the A1. By studying the Born effective charge, it could be seen that the valence of ions changed, and the O of Sr2Nb2O7 were most obviously that caused by the covalent character of ions and the hybridization of O-2p and Nb-4d. The spontaneous polarization of Sr2Nb2O7 in the[001] direction is 25 μC/cm2, while for Sr2Ta2O7, there was no spontaneous polarization in the paraelectric state. Finally, the effect of pressure on the piezoelectric properties were also investigated, the polarization of Sr2Nb2O7 decreased linearly with the increase after pressure. All our preliminary results throw light on the nature of dielectric, piezoelectric properties, Born effective charge, and spontaneous polarization of Sr2M2O7, it was helpful for experimental research, the development of new materials, and future applications.

    Unconventional lattice dynamics in few-layer h-BN and indium iodide crystals Hot!
    Gan Hu(胡干), Jian-Qi Huang(黄建啟), Ya-Ning Wang(王雅宁), Teng Yang(杨腾), Bao-Juan Dong(董宝娟), Ji-Zhang Wang(王吉章), Bo Zhao(赵波), Sajjad Ali(阿里·萨贾德), Zhi-Dong Zhang(张志东)
    Chin. Phys. B, 2018, 27 (8):  086301.  DOI: 10.1088/1674-1056/27/8/086301
    Abstract ( 916 )   HTML   PDF (3952KB) ( 595 )  

    Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increasing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional (2D) systems, few-layer h-BN and indium iodide (InI). We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the competition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.

    First-principles study of the (CuxNi1-x)3Sn precipitations with different structures in Cu-Ni-Sn alloys
    Guang-Wei Peng(彭广威), Xue-Ping Gan(甘雪萍), Zhou Li(李周), Ke-Chao Zhou(周科朝)
    Chin. Phys. B, 2018, 27 (8):  086302.  DOI: 10.1088/1674-1056/27/8/086302
    Abstract ( 602 )   HTML   PDF (2527KB) ( 173 )  
    The structural parameters, the formation energies, and the elastic and thermodynamic properties of the (CuxNi1-x)3Sn phase with different structures are studied by the virtual crystal approximation (VCA) and super-cell (SC) methods. The lattice constants, formation energies, and elastic constants obtained by SC and VCA are generally consistent with each other. It can be inferred that the VCA method is suitable for (CuxNi1-x)3Sn ordered phase calculation. The calculated results show that the equilibrium structures of Cu3Sn and Ni3Sn are D0a and D019 respectively. (CuxNi1-x)3Sn-D03 with various components are the metastable phase at temperature of 0 K, just as D022 and L12. With the temperature increase, the free energy of the D03 is lower than those of D022 and L12, and D022 and L12 eventually turn into D03 in the aging process. The (CuxNi1-x)3Sn-D022 is first precipitated in a solid solution because its structure and cell volume are most similar to those of a solid solution matrix. The L12 and the D022 possess better mechanical stability than the D03. Also, they may play a more important role in the strengthening of Cu-Ni-Sn alloys. This study is valuable for further research on Cu-Ni-Sn alloys.
    The effect of dislocations on the thermodynamic properties of Ta single crystal under high pressure by molecular dynamics simulation
    Yalin Li(李亚林), Jun Cai(蔡军), Dan Mo(莫丹), Yandong Wang(王沿东)
    Chin. Phys. B, 2018, 27 (8):  086401.  DOI: 10.1088/1674-1056/27/8/086401
    Abstract ( 685 )   HTML   PDF (1253KB) ( 280 )  

    The thermodynamic properties of Ta metal under high pressure are studied by molecular dynamics simulation. For dislocation-free Ta crystal, all the thermodynamic properties considered are in good agreement with the results from experiments or higher level calculations. If dislocations are included in the Ta crystal, it is found that as the dislocation density increases, the hydrostatic pressure at the phase transition point of bcc→hcp and hcp→fcc decreases, while the Hugoniot temperature increases. Meanwhile, the impact pressure at the elastic-plastic transition point is found to depend on the crystallographic orientation of the pressure. As the dislocation density increases, the pressure of the elastic-plastic transition point decreases rapidly at the initial stage, then gradually decreases with the increase of the dislocation density.

    Liquid phase epitaxy magnetic garnet films and their applications
    Yi-Heng Rao(饶毅恒), Huai-Wu Zhang(张怀武), Qing-Hui Yang(杨青慧), Dai-Nan Zhang(张岱南), Li-Chuan Jin(金立川), Bo Ma(马博), Yu-Juan Wu(吴玉娟)
    Chin. Phys. B, 2018, 27 (8):  086701.  DOI: 10.1088/1674-1056/27/8/086701
    Abstract ( 714 )   HTML   PDF (7162KB) ( 372 )  
    Liquid phase epitaxy (LPE) is a mature technology. Early experiments on single magnetic crystal films fabricated by LPE were focused mainly on thick films for microwave and magneto-optical devices. The LPE is an excellent way to make a thick film, low damping magnetic garnet film and high-quality magneto-optical material. Today, the principal challenge in the applied material is to create sub-micrometer devices by using modern photolithography technique. Until now the magnetic garnet films fabricated by LPE still show the best quality even on a nanoscale (about 100 nm), which was considered to be impossible for LPE method.
    Analysis of meniscus beneath metastable droplets and wetting transition on micro/nano textured surfaces
    Yanjie Li(李艳杰), Xiangqin Li(李香琴), Tianqing Liu(刘天庆), Weiguo Song(宋伟国)
    Chin. Phys. B, 2018, 27 (8):  086801.  DOI: 10.1088/1674-1056/27/8/086801
    Abstract ( 543 )   HTML   PDF (801KB) ( 172 )  
    The expressions of interface free energy (IFE) of composite droplets with meniscal liquid-air interface in metastable state on micro/nano textured surfaces were formulated. Then the parameters to describe the meniscus were determined based on the principle of minimum IFE. Furthermore, the IFE barriers and the necessary and sufficient conditions of drop wetting transition from Cassie to Wenzel were analyzed and the corresponding criteria were formulated. The results show that the liquid-air interface below a composite droplet is flat when the post pitches are relatively small, but in a shape of curved meniscus when the piteches are comparatively large and the curvature depends on structural parameters. The angle between meniscus and pillar wall is just equal to the supplementary angle of intrinsic contact angle of post material. The calculations also illustrate that Cassie droplets will transform to Wenzel state when post pitch is large enough or when drop volume is sufficiently small. The opposite transition from Wenzel to Cassie state, however, is unable to take place spontaneously because the energy barrier is always positive. Finally, the calculation results of this model are well consistent with the experimental observations in literatures for the wetting transition of droplets from Cassie to Wenzel state.
    Fabrication of seeded substrates for layer transferrable silicon films
    Ji-Zhou Li(李纪周), Wei Zhang(张伟), Jing-Yuan Yan(鄢靖源), Cong Wang(王聪), Hong-Fei Chen(陈宏飞), Xiao-Yuan Chen(陈小源), Dong-Fang Liu(刘东方)
    Chin. Phys. B, 2018, 27 (8):  086802.  DOI: 10.1088/1674-1056/27/8/086802
    Abstract ( 692 )   HTML   PDF (2529KB) ( 146 )  
    The layer transfer process is one of the most promising methods for low-cost and highly-efficient solar cells, in which transferrable mono-crystalline silicon thin wafers or films can be produced directly from gaseous feed-stocks. In this work, we show an approach to preparing seeded substrates for layer-transferrable silicon films. The commercial silicon wafers are used as mother substrates, on which periodically patterned silicon rod arrays are fabricated, and all of the surfaces of the wafers and rods are sheathed by thermal silicon oxide. Thermal evaporated aluminum film is used to fill the gaps between the rods and as the stiff mask, while polymethyl methacrylate (PMMA) and photoresist are used as the soft mask to seal the gap between the filled aluminum and the rods. Under the joint resist of the stiff and soft masks, the oxide on the rod head is selectively removed by wet etching and the seed site is formed on the rod head. The seeded substrate is obtained after the removal of the masks. This joint mask technique will promote the endeavor of the exploration of mechanically stable, unlimitedly reusable substrates for the kerfless technology.
    The properties of surface nanobubbles formed on different substrates
    Zheng-Lei Zou(邹正磊), Nan-Nan Quan(权楠楠), Xing-Ya Wang(王兴亚), Shuo Wang(王硕), Li-Min Zhou(周利民), Jun Hu(胡钧), Li-Juan Zhang(张立娟), Ya-Ming Dong(董亚明)
    Chin. Phys. B, 2018, 27 (8):  086803.  DOI: 10.1088/1674-1056/27/8/086803
    Abstract ( 703 )   HTML   PDF (1376KB) ( 152 )  

    The properties and stability of the reported surface nanobubbles are related to the substrate used and the generation method. Here, we design a series of experiments to study the influence of the hydrophobicity of the substrate and the production method on the formation and properties of nanobubbles. We choose three different substrates, dodecyltrichlorosilane (DTS) modified silicon, octadecyltrichlorosilane (OTS) modified silicon, and highly oriented pyrolytic graphite (HOPG) as nanobubble substrates, and two methods of ethanol-water exchange and 4-℃ cold water to produce nanobubbles. It is found that using ethanol-water exchange method could produce more and larger nanobubbles than the 4-℃ cold water method. The contact angle of nanobubbles produced by ethanol-water exchange depends on the hydrophobicity of substrates, and decreases with the increase of the hydrophobicity of substrates. More interestingly, nanoscopic contact angle approaches the macroscopic contact angle as the hydrophobicity of substrates increases. It is believed that these results would be very useful to understand the stability of surface nanobubbles.

    High quality PdTe2 thin films grown by molecular beam epitaxy Hot!
    En Li(李恩), Rui-Zi Zhang(张瑞梓), Hang Li(李航), Chen Liu(刘晨), Geng Li(李更), Jia-Ou Wang(王嘉鸥), Tian Qian(钱天), Hong Ding(丁洪), Yu-Yang Zhang(张余洋), Shi-Xuan Du(杜世萱), Xiao Lin(林晓), Hong-Jun Gao(高鸿钧)
    Chin. Phys. B, 2018, 27 (8):  086804.  DOI: 10.1088/1674-1056/27/8/086804
    Abstract ( 955 )   HTML   PDF (1224KB) ( 625 )  

    PdTe2, a member of layered transition metal dichalcogenides (TMDs), has aroused significant research interest due to the coexistence of superconductivity and type-Ⅱ Dirac fermions. It provides a promising platform to explore the interplay between superconducting quasiparticles and Dirac fermions. Moreover, PdTe2 has also been used as a substrate for monolayer antimonene growth. Here in this paper, we report the epitaxial growth of high quality PdTe2 films on bilayer graphene/SiC(0001) by molecular beam epitaxy (MBE). Atomically thin films are characterized by scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), low-energy electron diffraction (LEED), and Raman spectroscopy. The band structure of 6-layer PdTe2 film is measured by angle-resolved photoemission spectroscopy (ARPES). Moreover, our air exposure experiments show excellent chemical stability of epitaxial PdTe2 film. High-quality PdTe2 films provide opportunities to build antimonene/PdTe2 heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.

    Dirac states from px,y orbitals in the buckled honeycomb structures: A tight-binding model and first-principles combined study
    Shi-Ru Song(宋士儒), Ji-Hui Yang(杨吉辉), Shi-Xuan Du(杜世萱), Hong-Jun Gao(高鸿钧), Boris I Yakobson
    Chin. Phys. B, 2018, 27 (8):  087101.  DOI: 10.1088/1674-1056/27/8/087101
    Abstract ( 524 )   HTML   PDF (1367KB) ( 413 )  

    Dirac states composed of px,y orbitals have been reported in many two-dimensional (2D) systems with honeycomb lattices recently. Their potential importance has aroused strong interest in a comprehensive understanding of such states. Here, we construct a four-band tight-binding model for the px,y-orbital Dirac states considering both the nearest neighbor hopping interactions and the lattice-buckling effect. We find that px,y-orbital Dirac states are accompanied with two additional narrow bands that are flat in the limit of vanishing π bonding, which is in agreement with previous studies. Most importantly, we analytically obtain the linear dispersion relationship between energy and momentum vector near the Dirac cone. We find that the Fermi velocity is determined not only by the hopping through π bonding but also by the hopping through σ bonding of px,y orbitals, which is in contrast to the case of pz-orbital Dirac states. Consequently, px,y-orbital Dirac states offer more flexible engineering, with the Fermi velocity being more sensitive to the changes of lattice constants and buckling angles, if strain is exerted. We further validate our tight-binding scheme by direct first-principles calculations of model-materials including hydrogenated monolayer Bi and Sb honeycomb lattices. Our work provides a more in-depth understanding of px,y-orbital Dirac states in honeycomb lattices, which is useful for the applications of this family of materials in nanoelectronics.

    Investigations on mesa width design for 4H-SiC trench super junction Schottky diodes
    Xue-Qian Zhong(仲雪倩), Jue Wang(王珏), Bao-Zhu Wang(王宝柱), Heng-Yu Wang(王珩宇), Qing Guo(郭清), Kuang Sheng(盛况)
    Chin. Phys. B, 2018, 27 (8):  087102.  DOI: 10.1088/1674-1056/27/8/087102
    Abstract ( 837 )   HTML   PDF (1573KB) ( 286 )  
    Mesa width (WM) is a key design parameter for SiC super junction (SJ) Schottky diodes (SBD) fabricated by the trench-etching-and-sidewall-implant method. This paper carries out a comprehensive investigation on how the mesa width design determines the device electrical performances and how it affects the degree of performance degradation induced by process variations. It is found that structures designed with narrower mesa widths can tolerant substantially larger charge imbalance for a given BV target, but have poor specific on-resistances. On the contrary, structures with wider mesa widths have superior on-state performances but their breakdown voltages are more sensitive to p-type doping variation. Medium WM structures (~2 μ) exhibit stronger robustness against the process variation resulting from SiC deep trench etching. Devices with 2-μ mesa width were fabricated and electrically characterized. The fabricated SiC SJ SBDs have achieved a breakdown voltage of 1350 V with a specific on-resistance as low as 0.98 mΩ·cm2. The estimated specific drift on-resistance by subtracting substrate resistance is well below the theoretical one-dimensional unipolar limit of SiC material. The robustness of the voltage blocking capability against trench dimension variations has also been experimentally verified for the proposed SiC SJ SBD devices.
    SPECIAL TOPIC—Nanophotonics
    Transverse localization of Tamm plasmon in metal-DBR structure with disordered layer
    Deng-Ju He(何登举), Wei-Li Zhang(张伟利), Rui Ma(马瑞), Shan-Shan Wang(王珊珊), Xiao-Min Wu(吴小敏), Yun-Jiang Rao(饶云江)
    Chin. Phys. B, 2018, 27 (8):  087301.  DOI: 10.1088/1674-1056/27/8/087301
    Abstract ( 855 )   HTML   PDF (1453KB) ( 312 )  

    Transverse localization of the optical Tamm plasmon (OTP) is studied in a metal-distributed Bragg reflector (DBR) structure with a one-dimensional disordered layer embedded at the interface between the metal and the DBR. The embedded disordered layer induces multiple scattering and interference of light, forming the light localization in the transverse direction. This together with the formation of Tamm plasmonic modes at the metal-DBR interface (i.e., the confinement of light in the longitudinal direction), gives birth to the so called transverse-localized Tamm plasmon. It is shown that for both transverse electric (TE) and transverse magnetic (TM) polarized light injection, the excited transverse-localized Tamm plasmon broadens and splits the dispersion curve due to spatial incoherence in the transverse direction, thus proving the stronger light confinement especially in the TE polarized injection. By adding the gain medium, specific random lasing modes are observed. The proposed study could be an efficient way of trapping and locally enhancing light on a subwavelength scale, which is useful in applications of random lasers, optical sensing, and imaging.

    Giant Goos-Hänchen shifts of waveguide coupled long-range surface plasmon resonance mode
    Qi You(游琪), Jia-Qi Zhu(祝家齐), Jun Guo(郭珺), Lei-Ming Wu(吴雷明), Xiao-Yu Dai(戴小玉), Yuan-Jiang Xiang(项元江)
    Chin. Phys. B, 2018, 27 (8):  087302.  DOI: 10.1088/1674-1056/27/8/087302
    Abstract ( 700 )   HTML   PDF (787KB) ( 235 )  

    A hybrid structure based on a planar waveguide (PWG) mode coupling a long-range surface plasmon resonance (LRSPR) mode is proposed to enhance the GH shift. Both the PWG mode and LRSPR mode can be in strong resonance, and these two modes can be coupled together due to the normal-mode splitting. The largest GH shift of PWG-coupled LRSPR structure is 4156 times that of the incident beam, which is 23 times and 3.6 times that of the surface plasmon resonance (SPR) structure and the LRSPR structure, respectively. As a GH shift sensor, the highest sensitivity of 4.68×107λ is realized in the coupled structure. Compared with the sensitivity of the traditional SPR structure, the sensitivity of our structure is increased by more than 2 orders, which theoretically indicates that the proposed configuration can be applied to the field of high-sensitivity sensors in the future.

    Optoelectronic properties of bottom gate-defined in-plane monolayer WSe2 p-n junction
    Di Liu(刘頔), Xiao-Zhuo Qi(祁晓卓), Kuei-Lin Chiu(邱奎霖), Takashi Taniguchi, Xi-Feng Ren(任希锋), Guo-Ping Guo(郭国平)
    Chin. Phys. B, 2018, 27 (8):  087303.  DOI: 10.1088/1674-1056/27/8/087303
    Abstract ( 546 )   HTML   PDF (2359KB) ( 237 )  

    Monolayer transition-metal dichalcogenides (TMDs) are considered to be fantastic building blocks for a wide variety of optical and optoelectronic devices such as sensors, photodetectors, and quantum emitters, owing to their direct band gap, transparency, and mechanical flexibility. The core element of many conventional electronic and optoelectronic devices is the p-n junction, in which the p- and n-types of the semiconductor are formed by chemical doping in different regions. Here, we report a series of optoelectronic studies on a monolayer WSe2 in-plane p-n photodetector, demonstrating a low-power dissipation by showing an ambipolar behavior with a reduced threshold voltage by a factor of two compared with the previous results on a lateral electrostatically doped WSe2 p-n junction. The fabrication of the device is based on a polycarbonates (PC) transfer technique and hence no electron-beam exposure induced damage to the monolayer WSe2 is expected. Upon optical excitation, the photodetector demonstrates a photoresponsivity of 0.12 mA·W-1 and a maximum external quantum efficiency of 0.03%. Our study provides an alternative platform for a flexible and transparent two-dimensional photodetector, from which we expect to further promote the development of next-generation optoelectronic devices.

    Effect of Au/Ni/4H-SiC Schottky junction thermal stability on performance of alpha particle detection
    Xin Ye(叶鑫), Xiao-Chuan Xia(夏晓川), Hong-Wei Liang(梁红伟), Zhuo Li(李卓), He-Qiu Zhang(张贺秋), Guo-Tong Du(杜国同), Xing-Zhu Cui(崔兴柱), Xiao-Hua Liang(梁晓华)
    Chin. Phys. B, 2018, 27 (8):  087304.  DOI: 10.1088/1674-1056/27/8/087304
    Abstract ( 588 )   HTML   PDF (735KB) ( 160 )  
    Au/Ni/n-type 4H-SiC Schottky alpha particle detectors are fabricated and annealed at temperatures between 400℃ and 700℃ to investigate the effects of thermal stability of the Schottky contact on the structural and electrical properties of the detectors. At the annealing temperature of 500℃, the two nickel silicides (i.e., Ni31Si12 and Ni2Si) are formed at the interface and result in the formation of an inhomogeneous Schottky barrier. By increasing the annealing temperature, the Ni31Si12 transforms into the more stable Ni2Si. The structural evolution of the Schottky contact directly affects the electrical properties and alpha particle energy resolutions of the detectors. A better energy resolution of 2.60% is obtained for 5.48-MeV alpha particles with the detector after being annealed at 600℃. As a result, the Au/Ni/n-type 4H-SiC Schottky detector shows a good performance after thermal treatment at temperatures up to 700℃.
    Quantum spin Hall insulators in chemically functionalized As (110) and Sb (110) films
    Xiahong Wang(王夏烘), Ping Li(李平), Zhao Ran(冉召), Weidong Luo(罗卫东)
    Chin. Phys. B, 2018, 27 (8):  087305.  DOI: 10.1088/1674-1056/27/8/087305
    Abstract ( 672 )   HTML   PDF (1591KB) ( 132 )  
    We propose a new type of quantum spin Hall (QSH) insulator in chemically functionalized As (110) and Sb (110) film. According to first-principles calculations, we find that metallic As (110) and Sb (110) films become QSH insulators after being chemically functionalized by hydrogen (H) or halogen (Cl and Br) atoms. The energy gaps of the functionalized films range from 0.121 eV to 0.304 eV, which are sufficiently large for practical applications at room temperature. The energy gaps originate from the spin-orbit coupling (SOC). The energy gap increases linearly with the increase of the SOC strength λ/λ0. The Z2 invariant and the penetration depth of the edge states are also calculated and studied for the functionalized films.
    Behavior of fractional quantum Hall states in LLL and 1LL with in-plane magnetic field and Landau level mixing: A numerical investigation Hot!
    Lin-Peng Yang(杨林鹏), Qi Li(李骐), Zi-Xiang Hu(胡自翔)
    Chin. Phys. B, 2018, 27 (8):  087306.  DOI: 10.1088/1674-1056/27/8/087306
    Abstract ( 894 )   HTML   PDF (847KB) ( 235 )  

    By exactly solving the effective two-body interaction for a two-dimensional electron system with layer thickness and an in-plane magnetic field, we recently found that the effective interaction can be described by the generalized pseudopotentials (PPs) without the rotational symmetry. With this pseudopotential description, we numerically investigate the behavior of the fractional quantum Hall (FQH) states both in the lowest Landau level (LLL) and first excited Landau level (1LL). The enhancements of the 7/3 FQH state on the 1LL for a small tilted magnetic field are observed when layer thickness is larger than some critical values, while the gap of the 1/3 state in the LLL monotonically reduced with increasing the in-plane field. From the static structure factor calculation, we find that the systems are strongly anisotropic and finally enter into a stripe phase with a large tilting. With considering the Landau level mixing correction on the two-body interaction, we find the strong LL mixing cancels the enhancements of the FQH states in the 1LL.

    Multi-carrier transport in ZrTe5 film
    Fangdong Tang(汤方栋), Peipei Wang(王培培), Peng Wang(王鹏), Yuan Gan(甘远), Le Wang(王乐), Wei Zhang(张威), Liyuan Zhang(张立源)
    Chin. Phys. B, 2018, 27 (8):  087307.  DOI: 10.1088/1674-1056/27/8/087307
    Abstract ( 430 )   HTML   PDF (1333KB) ( 252 )  

    Single-layered zirconium pentatelluride (ZrTe5) has been predicted to be a large-gap two-dimensional (2D) topological insulator, which has attracted particular attention in topological phase transitions and potential device applications. Herein, we investigated the transport properties in ZrTe5 films as a function of thickness, ranging from a few nm to several hundred nm. We determined that the temperature of the resistivity anomaly peak (Tp) tends to increase as the thickness decreases. Moreover, at a critical thickness of~40 nm, the dominating carriers in the films change from n-type to p-type. A comprehensive investigation of Shubnikov-de Hass (SdH) oscillations and Hall resistance at variable temperatures revealed a multi-carrier transport tendency in the thin films. We determined the carrier densities and mobilities of two majority carriers using the simplified two-carrier model. The electron carriers can be attributed to the Dirac band with a non-trivial Berry phase π, while the hole carriers may originate from surface chemical reaction or unintentional doping during the microfabrication process. It is necessary to encapsulate the ZrTe5 film in an inert or vacuum environment to potentially achieve a substantial improvement in device quality.

    SPECIAL TOPIC—Nanophotonics
    Black phosphorus-based field effect transistor devices for Ag ions detection
    Hui-De Wang(王慧德), David K Sang, Zhi-Nan Guo(郭志男), Rui Cao(曹睿), Jin-Lai Zhao(赵劲来), Muhammad Najeeb Ullah Shah, Tao-Jian Fan(范涛健), Dian-Yuan Fan(范滇元), Han Zhang(张晗)
    Chin. Phys. B, 2018, 27 (8):  087308.  DOI: 10.1088/1674-1056/27/8/087308
    Abstract ( 694 )   HTML   PDF (2698KB) ( 330 )  

    Black phosphorus (BP), an attractive two-dimensional (2D) semiconductor, is widely used in the fields of optoelectronic devices, biomedicine, and chemical sensing. Silver ion (Ag+), a commonly used additive in food industry, can sterilize and keep food fresh. But excessive intake of Ag+ will harm human health. Therefore, high sensitive, fast and simple Ag+ detection method is significant. Here, a high-performance BP field effect transistor (FET) sensor is fabricated for Ag+ detection with high sensitivity, rapid detection speed, and wide detection concentration range. The detection limit for Ag+ is 10-10 mol/L. Testing time for each sample by this method is 60 s. Besides, the mechanism of BP-FET sensor for Ag+ detection is investigated systematically. The simple BP-FET sensor may inspire some relevant research and potential applications, such as providing an effective method for the actual detection of Ag+, especially in witnessed inspections field of food.

    Characterization of ion irradiated silicon surfaces ablated by laser-induced breakdown spectroscopy
    T Iqbal, M Abrar, M B Tahir, M Seemab, A Majid, S Rafique
    Chin. Phys. B, 2018, 27 (8):  087401.  DOI: 10.1088/1674-1056/27/8/087401
    Abstract ( 576 )   HTML   PDF (4135KB) ( 136 )  
    Low energy metallic ions, generated by a Q-switched Nd:YAG laser (1064-nm wavelength, 10-mJ energy, 9-nm~12-ns-pulse width, 1011 W/cm2 intensity) irradiated on a silicon substrate to modify various properties, such as electrical, morphological, and structural modifications. Thomson parabola technique is used to calculate the energy of these metallic ions whereas the electrical conductivity is calculated with the help of Four-point probe. Interestingly circular tracks forming chain like damage trails are produced via these energetic ions which are carefully examined by optical microscopy. It is observed that excitation, ionization, and cascade collisions are responsible for surface modifications of irradiated samples. Four-point probe analysis revealed that the electrical conductivity of substrate has reduced with increasing trend of atomic number of irradiated metallic ions (Al, Ti, Cu, and Au). The x-ray diffraction analysis elucidated the crystallographic changes leading to reduction of grain size of N-type silicon substrate, which is also associated with the metallic ions used. The decreasing trend of conductivity and grain size is due to thermal stresses, scattering effect, structural imperfections, and non-uniform conduction of energy absorbed by substrate atoms after the ion irradiation.
    Nonlinear uniaxial pressure dependence of the resistivity in Sr1-xBaxFe1.97Ni0.03As2 Hot!
    Hui-Can Mao(毛慧灿), Dong-Liang Gong(龚冬良), Xiao-Yan Ma(马肖燕), Hui-Qian Luo(罗会仟), Yi-Feng Yang(杨义峰), Lei Shan(单磊), Shi-Liang Li(李世亮)
    Chin. Phys. B, 2018, 27 (8):  087402.  DOI: 10.1088/1674-1056/27/8/087402
    Abstract ( 903 )   HTML   PDF (4743KB) ( 179 )  

    Nematic order and its fluctuations have been widely found in iron-based superconductors. Above the nematic order transition temperature, the resistivity shows a linear relationship with the uniaxial pressure or strain along the nematic direction and the normalized slope is thought to be associated with nematic susceptibility. Here we systematically studied the uniaxial pressure dependence of the resistivity in Sr1-xBaxFe1.97Ni0.03As2, where nonlinear behaviors are observed near the nematic transition temperature. We show that it can be well explained by the Landau theory for the second-order phase transitions considering that the external field is not zero. The effect of the coupling between the isotropic and nematic channels is shown to be negligible. Moreover, our results suggest that the nature of the magnetic and nematic transitions in Sr1-xBaxFe2As2 is determined by the strength of the magnetic-elastic coupling.

    Typicality at quantum-critical points Hot!
    Lu Liu(刘录), Anders W Sandvik, Wenan Guo(郭文安)
    Chin. Phys. B, 2018, 27 (8):  087501.  DOI: 10.1088/1674-1056/27/8/087501
    Abstract ( 604 )   HTML   PDF (2852KB) ( 258 )  

    We discuss the concept of typicality of quantum states at quantum-critical points, using projector Monte Carlo simulations of an S=1/2 bilayer Heisenberg antiferromagnet as an illustration. With the projection (imaginary) time τ scaled as τ=aLz, L being the system length and z the dynamic critical exponent (which takes the value z=1 in the bilayer model studied here), a critical point can be identified which asymptotically flows to the correct location and universality class with increasing L, independently of the prefactor a and the initial state. Varying the proportionality factor a and the initial state only changes the cross-over behavior into the asymptotic large-L behavior. In some cases, choosing an optimal factor a may also lead to the vanishing of the leading finite-size corrections. The observation of typicality can be used to speed up simulations of quantum criticality, not only within the Monte Carlo approach but also with other numerical methods where imaginary-time evolution is employed, e.g., tensor network states, as it is not necessary to evolve fully to the ground state but only for sufficiently long times to reach the typicality regime.

    Micromagnetism simulation on effects of soft phase size on Nd2Fe14B/α–Fe nanocomposite magnet with soft phase imbedded in hard phase
    Yu-Qing Li(李玉卿), Ming Yue(岳明), Yi Peng(彭懿), Hong-Guo Zhang(张红国)
    Chin. Phys. B, 2018, 27 (8):  087502.  DOI: 10.1088/1674-1056/27/8/087502
    Abstract ( 631 )   HTML   PDF (3012KB) ( 234 )  
    In this study, micromagnetism simulation by using finite difference method is carried out on the Nd2Fe14B/α-Fe nanocomposite magnet with soft phase imbedded in hard phase. The effects of soft magnetic phase size (S) on the magnetic properties and magnetic reversal modes are systematically analyzed. As S increases from 1 nm to 48 nm, the remanence (Jr) increases, while the coercivity (Hci) decreases, leading to the result that the magnetic energy product[(BH)max] first increases slowly, and then decreases rapidly, peaking at S=24 nm with the (BH)max of 72.9 MGOe (1 MGOe=7.95775 kJ·m-3). Besides, with the increase of S, the coercivity mechanism of the nanocomposite magnet changes from nucleation to pinning. Furthermore, by observing the magnetic moment evolution in demagnetization process, the magnetic reversal of the soft phase in the nanocomposite magnet can be divided into three modes with the increase of S:coherent rotation (S < 3 nm), quasi-coherent rotation (3 nm ≤ qslant S < 36 nm), and the vortex-like rotation (S ≥ 36 nm).
    Detailed electronic structure of three-dimensional Fermi surface and its sensitivity to charge density wave transition in ZrTe3 revealed by high resolution laser-based angle-resolved photoemission spectroscopy
    Shou-Peng Lyu(吕守鹏), Li Yu(俞理), Jian-Wei Huang(黄建伟), Cheng-Tian Lin(林成天), Qiang Gao(高强), Jing Liu(刘静), Guo-Dong Liu(刘国东), Lin Zhao(赵林), Jie Yuan(袁洁), Chuang-Tian Chen(陈创天), Zu-Yan Xu(许祖彦), Xing-Jiang Zhou(周兴江)
    Chin. Phys. B, 2018, 27 (8):  087503.  DOI: 10.1088/1674-1056/27/8/087503
    Abstract ( 915 )   HTML   PDF (3800KB) ( 245 )  

    The detailed information of the electronic structure is the key to understanding the nature of charge density wave (CDW) order and its relationship with superconducting order in the microscopic level. In this paper, we present a high resolution laser-based angle-resolved photoemission spectroscopy (ARPES) study on the three-dimensional (3D) hole-like Fermi surface around the Brillouin zone center in a prototypical quasi-one-dimensional CDW and superconducting system ZrTe3. Double Fermi surface sheets are clearly resolved for the 3D hole-like Fermi surface around the zone center. The 3D Fermi surface shows a pronounced shrinking with increasing temperature. In particular, the quasiparticle scattering rate along the 3D Fermi surface experiences an anomaly near the charge density wave transition temperature of ZrTe3 (~63 K). The signature of electron-phonon coupling is observed with a dispersion kink at~20 meV; the strength of the electron-phonon coupling around the 3D Fermi surface is rather weak. These results indicate that the 3D Fermi surface is also closely connected to the charge-density-wave transition and suggest a more global impact on the entire electronic structure induced by the CDW phase transition in ZrTe3.

    Effect of flash thermal annealing by pulsed current on rotational anisotropy in exchange-biased NiFe/FeMn film
    Zhen Wang(王振), Shi-Jie Tan(谭士杰), Jun Li(李俊), Bo Dai(代波), Yan-Ke Zou(邹延珂)
    Chin. Phys. B, 2018, 27 (8):  087504.  DOI: 10.1088/1674-1056/27/8/087504
    Abstract ( 479 )   HTML   PDF (1620KB) ( 197 )  
    In this paper, Ta/[NiFe(15 nm)/FeMn(10 nm)]/Ta exchange-biased bilayers are fabricated by magnetron sputtering, and their static and dynamic magnetic properties before and after rapid annealing treatment with pulsed current are characterized by using a vibrating sample magnetometer (VSM) and a vector network analyzer (VNA), respectively. The exchange bias field He and static anisotropy field Hksta decrease from 118.45 Oe (1 Oe=79.5775 A·m-1) and 126.84 Oe at 0 V to 94.75 Oe and 102.31 Oe at 90 V, respectively, with increasing capacitor voltage, which supplies pulsed current to heat the sample. The effect of flash thermal annealing by pulsed current on the rotational anisotropy (Hrot), the difference value between static and dynamic magnetic anisotropy, is investigated particularly. The highest Hrot is obtained in the sample annealing with 45-V capacitor (3300 μF) voltage. According to the anisotropic magnetoresistance measurements, it can be explained by the fact that the temperature of the sample is around the blocking temperature of the exchange bias system (Tb) at 45 V, the critical temperature where the formation of more unstable antiferromagnetic grains occurs.
    High uniformity and forming-free ZnO-based transparent RRAM with HfOx inserting layer
    Shi-Jian Wu(吴仕剑), Fang Wang(王芳), Zhi-Chao Zhang(张志超), Yi Li(李毅), Ye-Mei Han(韩叶梅), Zheng-Chun Yang(杨正春), Jin-Shi Zhao(赵金石), Kai-Liang Zhang(张楷亮)
    Chin. Phys. B, 2018, 27 (8):  087701.  DOI: 10.1088/1674-1056/27/8/087701
    Abstract ( 785 )   HTML   PDF (2296KB) ( 197 )  

    The impacts of HfOx inserting layer thickness on the electrical properties of the ZnO-based transparent resistance random access memory (TRRAM) device were investigated in this paper. The bipolar resistive switching behavior of a single ZnO film and bilayer HfOx/ZnO films as active layers for TRRAM devices was demonstrated. It was revealed that the bilayer TRRAM device with a 10-nm HfOx inserted layer had a more stable resistive switching behavior than other devices including the single layer device, as well as being forming free, and the transmittance was more than 80% in the visible region. For the HfOx/ZnO devices, the current conduction behavior was dominated by the space-charge-limited current mechanism in the low resistive state (LRS) and Schottky emission in the high resistive state (HRS), while the mechanism for single layer devices was controlled by ohmic conduction in the LRS and Poole-Frenkel emission in the HRS.

    Optical polarization response at gold nanosheet edges probed by scanning near-field optical microscopy
    Zhuan-Fang Bi(毕篆芳), Mu Yang(杨沐), Guang-Yi Shang(商广义)
    Chin. Phys. B, 2018, 27 (8):  087801.  DOI: 10.1088/1674-1056/27/8/087801
    Abstract ( 629 )   HTML   PDF (1459KB) ( 161 )  
    Optical properties of metallic edge-like structures known as knife-edges are a topic of interest and possess potential applications in enhanced Raman scattering, optical trapping, etc. In this work, we investigate the near-field optical polarization response at the edge of a triangular gold nanosheet, which is synthesized by a wet chemical method. A homemade scanning near-field optical microscope (SNOM) in collection mode is adopted, which is able to accurately locate its probe at the edge during experiments. An uncoated straight fiber probe is used in the SNOM, because it still preserves the property of light polarization though it has the depolarization to some extent. By comparing near-field intensities at the edge and glass substrate, detected in different polarization directions of incident light, the edge-induced depolarization is found, which is supported by the finite differential time domain (FDTD) simulated results. The depolarized phenomenon in the near-field is similar to that in the far-field.
    High-performance lens antenna using high refractive index metamaterials
    Lai-Jun Wang(王来军), Qiao-Hong Chen(陈巧红), Fa-Long Yu(余发龙), Xi Gao(高喜)
    Chin. Phys. B, 2018, 27 (8):  087802.  DOI: 10.1088/1674-1056/27/8/087802
    Abstract ( 684 )   HTML   PDF (2337KB) ( 178 )  
    In this paper, a high refractive index metamaterial (HRM), whose element is composed of bilayer square patch (BSP) spaced by a dielectric plate, is proposed. By reducing the thickness of the dielectric plate and the gap between adjacent patches, the BSP can effectively enhance capacitive coupling and simultaneously suppress diamagnetic response, which significantly increases the refractive index of the proposed metamaterial. Furthermore, the high refractive index region is far away from the resonant region of the metamaterial, resulting in broadband. Based on these characteristics of BSP, a gradient refractive index (GRIN) lens with thin thickness (0.34λ0, where λ0 is the wavelength at 5.75 GHz) is designed. By using this lens, we then design a circularly polarized horn antenna with high performance. The measurement results show that the 3-dB axial ratio bandwidth is 34.8% (4.75 GHz~6.75 GHz) and the antenna gain in this frequency range is increased by an average value of 3.4 dB. The proposed method opens up a new avenue to design high-performance antenna.
    Modulated thermal transport for flexural and in-plane phonons in double-stub graphene nanoribbons
    Chang-Ning Pan(潘长宁), Meng-Qiu Long(龙孟秋), Jun He(何军)
    Chin. Phys. B, 2018, 27 (8):  088101.  DOI: 10.1088/1674-1056/27/8/088101
    Abstract ( 772 )   HTML   PDF (3571KB) ( 167 )  

    Thermal transport properties are investigated for out-of-plane phonon modes (FPMs) and in-plane phonon modes (IPMs) in double-stub graphene nanoribbons (GNRs). The results show that the quantized thermal conductance plateau of FPMs is narrower and more easily broken by the double-stub structure. In the straight GNRs, the thermal conductance of FPMs is higher in the low temperature region due to there being less cut-off frequency and more low-frequency excited modes. In contrast, the thermal conductance of IPMs is higher in the high temperature region because of the wider phonon energy spectrum. Furthermore, the thermal transport of two types of phonon modes can be modulated by the double-stub GNRs, the thermal conductance of FPMs is less than that of IPMs in the low temperatures, but it dominates the contribution to the total thermal conductance in the high temperatures. The modulated thermal conductance can provide a guideline for designing high-performance thermal or thermoelectric nanodevices based on graphene.

    Effect of FeS doping on large diamond synthesis in FeNi–C system
    Jian-Kang Wang(王健康), Shang-Sheng Li(李尚升), Quan-Wei Jiang(蒋全伟), Yan-Ling Song(宋艳玲), Kun-Peng Yu(于昆鹏), Fei Han(韩飞), Tai-Chao Su(宿太超), Mei-Hua Hu(胡美华), Qiang Hu(胡强), Hong-An Ma(马红安), Xiao-Peng Jia(贾晓鹏), Hong-Yu Xiao(肖宏宇)
    Chin. Phys. B, 2018, 27 (8):  088102.  DOI: 10.1088/1674-1056/27/8/088102
    Abstract ( 560 )   HTML   PDF (1599KB) ( 202 )  

    The large single-crystal diamond with FeS doping along the (111) face is synthesized from the FeNi-C system by the temperature gradient method (TGM) under high-pressure and high-temperature (HPHT). The effects of different FeS additive content on the shape, color, and quality of diamond are investigated. It is found that the (111) face of diamond is dominated and the (100) face of diamond disappears gradually with the increase of the FeS content. At the same time, the color of the diamond crystal changes from light yellow to gray-green and even gray-yellow. The stripes and pits corrosion on the diamond surface are observed to turn worse. The effects of FeS doping on the shape and surface morphology of diamond crystal are explained by the number of hang bonds in different surfaces of diamond. It can be shown from the test results of the Fourier transform infrared (FTIR) spectrum that there exists an S element in the obtained diamond. The N element content values in different additive amounts of diamond are calculated. The XPS spectrum results demonstrate that our obtained diamond contains S elements that exist in S-C and S-C-O forms in a diamond lattice. This work contributes to the further understanding and research of FeS-doped large single-crystal diamond characterization.

    Growth of high-quality perovskite (110)-SrIrO3 thin films using reactive molecular beam epitaxy
    Kai-Li Zhang(张凯莉), Cong-Cong Fan(樊聪聪), Wan-Ling Liu(刘万领), Yu-Feng Wu(吴宇峰), Xiang-Le Lu(卢祥乐), Zheng-Tai Liu(刘正太), Ji-Shan Liu(刘吉山), Zhong-Hao Liu(刘中灏), Da-Wei Shen(沈大伟)
    Chin. Phys. B, 2018, 27 (8):  088103.  DOI: 10.1088/1674-1056/27/8/088103
    Abstract ( 737 )   HTML   PDF (3101KB) ( 270 )  

    Recently, 5d transition metal iridates have been reported as promising materials for the manufacture of exotic quantum states. Apart from the semimetallic ground states that have been observed, perovskite SrIrO3 is also predicted to have a lattice-symmetrically protected topological state in the (110) plane due to its strong spin-orbit coupling and electron correlation. Compared with non-polar (001)-SrIrO3, the especial polarity of (110)-SrIrO3 undoubtedly adds the difficulty of fabrication and largely impedes the research on its surface states. Here, we have successfully synthesized high-quality (110)-SrIrO3 thin films on (110)-SrTiO3 substrates by reactive molecular beam epitaxy for the first time. Both reflection high-energy electron diffraction patterns and x-ray diffraction measurements suggest the expected orientation and outstanding crystallinity. A (1×2) surface reconstruction driven from the surface instability, the same as that reported in (110)-SrTiO3, is observed. The electric transport measurements uncover that (110)-SrIrO3 exhibits a more prominent semimetallic property in comparison to (001)-SrIrO3.

    SPECIAL TOPIC—Nanophotonics
    Novel graphene enhancement nanolaser based on hybrid plasmonic waveguides at optical communication wavelength
    Zhengjie Xu(徐政杰), Jun Zhu(朱君), Wenju Xu(徐汶菊), Deli Fu(傅得立), Cong Hu(胡聪), Frank Jiang
    Chin. Phys. B, 2018, 27 (8):  088104.  DOI: 10.1088/1674-1056/27/8/088104
    Abstract ( 874 )   HTML   PDF (1375KB) ( 291 )  

    Surface plasmon polariton (SPP) nanolaser, which can achieve an all-optical circuit, is a major research topic in the field of micro light source. In this study, we examine a novel SPP graphene nanolaser in an optoelectronic integration field. The proposed nanolaser consists of metallic silver, two-dimensional (2D) graphene and high refractive index semiconductor of indium gallium arsenide phosphorus. Compared with other metals, Ag can reduce the threshold and propagation loss. The SPP field, excited by coupling Ag and InGaAsP, can be enhanced by the 2D material of graphene. In the proposed nanolaser, the maximum value of propagation loss is approximately 0.055 dB/μ, and the normalized mode area is constantly less than 0.05, and the best threshold can achieve 3380 cm-1 simultaneously. Meanwhile, the proposed nanolaser can be fabricated by conventional materials and work in optical communication (1550 nm), which can be easily achieved with current nanotechnology. It is also an important method that will be used to overcome the challenges of high speed, miniaturization, and integration in optoelectronic integrated technology.

    A lattice Boltzmann-cellular automaton study on dendrite growth with melt convection in solidification of ternary alloys
    Dong-Ke Sun(孙东科), Zhen-Hua Chai(柴振华), Qian Li(李谦), Guang Lin(林光)
    Chin. Phys. B, 2018, 27 (8):  088105.  DOI: 10.1088/1674-1056/27/8/088105
    Abstract ( 702 )   HTML   PDF (2301KB) ( 183 )  

    A lattice Boltzmann (LB)-cellular automaton (CA) model is employed to study the dendrite growth of Al-4.0 wt%Cu-1.0 wt%Mg alloy. The effects of melt convection, solute diffusion, interface curvature, and preferred growth orientation are incorporated into the coupled model by coupling the LB-CA model and the CALPHAD-based phase equilibrium solver, PanEngine. The dendrite growth with single and multiple initial seeds was numerically studied under the conditions of pure diffusion and melt convection. Effects of initial seed number and melt convection strength were characterized by new-defined solidification and concentration entropies. The numerical result shows that the growth behavior of dendrites, the final microstructure, and the micro-segregation are significantly influenced by melt convection during solidification of the ternary alloys. The proposed solidification and concentration entropies are useful characteristics bridging the solidification behavior and the microstructure evolution of alloys.

    Influence of dopant concentration on electrical quantum transport behaviors in junctionless nanowire transistors
    Liu-Hong Ma(马刘红), Wei-Hua Han(韩伟华), Xiao-Song Zhao(赵晓松), Yang-Yan Guo(郭仰岩), Ya-Mei Dou(窦亚梅), Fu-Hua Yang(杨富华)
    Chin. Phys. B, 2018, 27 (8):  088106.  DOI: 10.1088/1674-1056/27/8/088106
    Abstract ( 738 )   HTML   PDF (2083KB) ( 195 )  
    We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation. Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorus-doped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.
    Size effect of Si particles on the electrochemical performances of Si/C composite anodes
    Bonan Liu(刘柏男), Hao Lu(陆浩), Geng Chu(褚赓), Fei Luo(罗飞), Jieyun Zheng(郑杰允), Shimou Chen(陈仕谋), Hong Li(李泓)
    Chin. Phys. B, 2018, 27 (8):  088201.  DOI: 10.1088/1674-1056/27/8/088201
    Abstract ( 727 )   HTML   PDF (3369KB) ( 245 )  

    A series of Si/C composites were fabricated based on pitch and Si powders with particle sizes of 30, 100, 500, and 3000 nm. The size effects of the Si particles in the Si/C composites were investigated for lithium-ion battery anodes. The nanoscale Si and Si/C composites exhibited good capacity retentions. Scanning electron microscopy showed that exterior and interior cracks emerging owing to volume expansion as well as parasitic reactions with the electrolyte could well explain the performance failure.

    Improved electrochemical performances of high voltage LiCoO2 with tungsten doping
    Jie-Nan Zhang(张杰男), Qing-Hao Li(李庆浩), Quan Li(李泉), Xi-Qian Yu(禹习谦), Hong Li(李泓)
    Chin. Phys. B, 2018, 27 (8):  088202.  DOI: 10.1088/1674-1056/27/8/088202
    Abstract ( 710 )   HTML   PDF (1392KB) ( 415 )  

    The effects of tungsten W doping and coating on the electrochemical performance of LiCoO2 cathode are comparatively studied in this work. The amount of modification component is as low as 0.1 wt% and 0.3 wt% respectively. After 100 cycles between 3.0 V-4.6 V, 0.1 wt% W doping provides an optimized capacity retention of 72.3%. However, W coating deteriorates battery performance with capacity retention of 47.8%, even lower than bare LiCoO2 of 55.7%. These different electrochemical performances can be attributed to the surface aggregation of W between doping and coating methods. W substitution is proved to be a promising method to develop high voltage cathodes. Practical performance relies on detailed synthesis method.

    Molecular dynamics simulations on the dynamics of two-dimensional rounded squares
    Zhang-lin Hou(侯章林), Ying Ju(句颖), Yi-wu Zong(宗奕吾), Fang-fu Ye(叶方富), Kun Zhao(赵坤)
    Chin. Phys. B, 2018, 27 (8):  088203.  DOI: 10.1088/1674-1056/27/8/088203
    Abstract ( 829 )   HTML   PDF (4583KB) ( 204 )  

    The collective motion of rounded squares with different corner-roundness ζ is studied by molecular dynamics (MD) simulation in this work. Three types of translational collective motion pattern are observed, including gliding, hopping and a mixture of gliding and hopping. Quantitatively, the dynamics of each observed ordered phase is characterized by both mean square displacement and van Hove functions for both translation and rotation. The effect of corner-roundness on the dynamics is further studied by comparing the dynamics of the rhombic crystal phases formed by different corner-rounded particles at a same surface fraction. The results show that as ζ increases from 0.286 to 0.667, the translational collective motion of particles changes from a gliding-dominant pattern to a hopping-dominant pattern, whereas the rotational motion pattern is hopping-like and does not change in its type, but the rotational hopping becomes much more frequent as ζ increases (i.e., as particles become more rounded). A simple geometrical model is proposed to explain the trend of gliding motion observed in MD simulations.

    Calculation and analysis of unbalanced magnetic pulls of different stator winding setups in static eccentric induction motor
    Yang Zhou(周洋), Xiaohua Bao(鲍晓华), Mingna Ma(马明娜), Chunyu Wang(王春雨)
    Chin. Phys. B, 2018, 27 (8):  088401.  DOI: 10.1088/1674-1056/27/8/088401
    Abstract ( 548 )   HTML   PDF (1331KB) ( 214 )  

    In large-scale electric machines, unbalanced magnetic pull (UMP) caused by eccentricity usually results in stator-rotor rub, so it is necessary to investigate the amplitude and the influencing factors. This paper takes the squirrel-cage induction motor as an example. A magnetic loop model of an induction motor is established by an analytical method. The impact of stator winding setup (parallel branch and pole pairs) on each magnetomotive force (MMF) and unbalanced magnetic pull is analyzed. Using the finite element simulation method, the spatial and time distribution of flux density of the rotor outer circle under static eccentricity is obtained, and the unbalanced magnetic pull calculation caused by static eccentricity is completed. The conclusion of the influence of stator winding on the size of unbalanced magnetic pull provides reliable gist for motor noise and vibration analysis, and especially provides an important reference for large induction motor design.

    A snapback-free TOL-RC-LIGBT with vertical P-collector and N-buffer design
    Weizhong Chen(陈伟中), Yao Huang(黄垚), Lijun He(贺利军), Zhengsheng Han(韩郑生), Yi Huang(黄义)
    Chin. Phys. B, 2018, 27 (8):  088501.  DOI: 10.1088/1674-1056/27/8/088501
    Abstract ( 680 )   HTML   PDF (800KB) ( 221 )  

    A reverse-conducting lateral insulated-gate bipolar transistor (RC-LIGBT) with a trench oxide layer (TOL), featuring a vertical N-buffer and P-collector is proposed. Firstly, the TOL enhances both of the surface and bulk electric fields of the N-drift region, thus the breakdown voltage (BV) is improved. Secondly, the vertical N-buffer layer increases the voltage drop VPN of the P-collector/N-buffer junction, thus the snapback is suppressed. Thirdly, the P-body and the vertical N-buffer act as the anode and the cathode, respectively, to conduct the reverse current, thus the inner diode is integrated. As shown by the simulation results, the proposed RC-LIGBT exhibits trapezoidal electric field distribution with BV of 342.4 V, which is increased by nearly 340% compared to the conventional RC-LIGBT with triangular electric fields of 100.2 V. Moreover, the snapback is eliminated by the vertical N-buffer layer design, thus the reliability of the device is improved.

    Damage effects and mechanism of the silicon NPN monolithic composite transistor induced by high-power microwaves
    Hui Li(李慧), Chang-Chun Chai(柴常春), Yu-Qian Liu(刘彧千), Han Wu(吴涵), Yin-Tang Yang(杨银堂)
    Chin. Phys. B, 2018, 27 (8):  088502.  DOI: 10.1088/1674-1056/27/8/088502
    Abstract ( 557 )   HTML   PDF (1160KB) ( 201 )  
    A two-dimensional model of the silicon NPN monolithic composite transistor is established for the first time by utilizing the semiconductor device simulator, Sentaurus-TCAD. By analyzing the internal distributions of electric field, current density, and temperature of the device, a detailed investigation on the damage process and mechanism induced by high-power microwaves (HPM) is performed. The results indicate that the temperature elevation occurs in the negative half-period and the temperature drop process is in the positive half-period under the HPM injection from the output port. The damage point is located near the edge of the base-emitter junction of T2, while with the input injection it exists between the base and the emitter of T2. Comparing these two kinds of injection, the input injection is more likely to damage the device than the output injection. The dependences of the damage energy threshold and the damage power threshold causing the device failure on the pulse-width are obtained, and the formulas obtained have the same form as the experimental equations, which demonstrates that more power is required to destroy the device if the pulse-width is shorter. Furthermore, the simulation result in this paper has a good coincidence with the experimental result.
    Time-dependent crosstalk effects for image sensors with different isolation structures
    Lei Shen(沈磊), Li-Qiao Liu(刘力桥), Hao Hao(郝好), Gang Du(杜刚), Xiao-Yan Liu(刘晓彦)
    Chin. Phys. B, 2018, 27 (8):  088503.  DOI: 10.1088/1674-1056/27/8/088503
    Abstract ( 587 )   HTML   PDF (1402KB) ( 223 )  
    Photo-generated carriers may diffuse into the adjacent cells to form the electrical crosstalk, which is especially noticeable after the pixel cell size has been scaled down. The electrical crosstalk strongly depends on the structure and electrical properties of the photosensitive areas. In this work, time-dependent crosstalk effects considering different isolation structures are investigated. According to the different depths of photo-diode (PD) and isolation structure, the transport of photo-generated carriers is analyzed with different regions in the pixel cell. The evaluation of crosstalk is influenced by exposure time. Crosstalk can be suppressed by reducing the exposure time. However, the sensitivity and dynamic range of the image sensor need to be considered as well.
    SPECIAL TOPIC—Nanophotonics
    Improved carrier injection and confinement in InGaN light-emitting diodes containing GaN/AlGaN/GaN triangular barriers
    Li-Wen Cheng(程立文), Jian Ma(马剑), Chang-Rui Cao(曹常锐), Zuo-Zheng Xu(徐作政), Tian Lan(兰天), Jin-Peng Yang(杨金彭), Hai-Tao Chen(陈海涛), Hong-Yan Yu(于洪岩), Shu-Dong Wu(吴曙东), Shun Yao(尧舜), Xiang-Hua Zeng(曾祥华), Zai-Quan Xu(徐仔全)
    Chin. Phys. B, 2018, 27 (8):  088504.  DOI: 10.1088/1674-1056/27/8/088504
    Abstract ( 794 )   HTML   PDF (799KB) ( 241 )  

    In this study, an InGaN lighting-emitting diode (LED) containing GaN/AlGaN/GaN triangular barriers is proposed and investigated numerically. The simulation results of output performance, carrier concentration, and radiative recombination rate indicate that the proposed LED has a higher output power and an internal quantum efficiency, and a lower efficiency droop than the LED containing conventional GaN or AlGaN barriers. These improvements mainly arise from the modified energy bands, which is evidenced by analyzing the LED energy band diagram and electrostatic field near the active region. The modified energy bands effectively improve carrier injection and confinement, which significantly reduces electron leakage and increases the rate of radiative recombination in the quantum wells.

    Weighted total variation using split Bregman fast quantitative susceptibility mapping reconstruction method
    Lin Chen(陈琳), Zhi-Wei Zheng(郑志伟), Li-Jun Bao(包立君), Jin-Sheng Fang(方金生), Tian-He Yang(杨天和), Shu-Hui Cai(蔡淑惠), Cong-Bo Cai(蔡聪波)
    Chin. Phys. B, 2018, 27 (8):  088701.  DOI: 10.1088/1674-1056/27/8/088701
    Abstract ( 691 )   HTML   PDF (2763KB) ( 202 )  
    An ill-posed inverse problem in quantitative susceptibility mapping (QSM) is usually solved using a regularization and optimization solver, which is time consuming considering the three-dimensional volume data. However, in clinical diagnosis, it is necessary to reconstruct a susceptibility map efficiently with an appropriate method. Here, a modified QSM reconstruction method called weighted total variation using split Bregman (WTVSB) is proposed. It reconstructs the susceptibility map with fast computational speed and effective artifact suppression by incorporating noise-suppressed data weighting with split Bregman iteration. The noise-suppressed data weighting is determined using the Laplacian of the calculated local field, which can prevent the noise and errors in field maps from spreading into the susceptibility inversion. The split Bregman iteration accelerates the solution of the L1-regularized reconstruction model by utilizing a preconditioned conjugate gradient solver. In an experiment, the proposed reconstruction method is compared with truncated k-space division (TKD), morphology enabled dipole inversion (MEDI), total variation using the split Bregman (TVSB) method for numerical simulation, phantom and in vivo human brain data evaluated by root mean square error and mean structure similarity. Experimental results demonstrate that our proposed method can achieve better balance between accuracy and efficiency of QSM reconstruction than conventional methods, and thus facilitating clinical applications of QSM.
    Individual identification using multi-metric of DTI in Alzheimer's disease and mild cognitive impairment
    Ying-Teng Zhang(张应腾), Shen-Quan Liu(刘深泉)
    Chin. Phys. B, 2018, 27 (8):  088702.  DOI: 10.1088/1674-1056/27/8/088702
    Abstract ( 619 )   HTML   PDF (3196KB) ( 242 )  

    Accurate identification of Alzheimer's disease (AD) and mild cognitive impairment (MCI) is crucial so as to improve diagnosis techniques and to better understand the neurodegenerative process. In this work, we aim to apply the machine learning method to individual identification and identify the discriminate features associated with AD and MCI. Diffusion tensor imaging scans of 48 patients with AD, 39 patients with late MCI, 75 patients with early MCI, and 51 age-matched healthy controls (HCs) are acquired from the Alzheimer's Disease Neuroimaging Initiative database. In addition to the common fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity metrics, there are two novel metrics, named local diffusion homogeneity that used Spearman's rank correlation coefficient and Kendall's coefficient concordance, which are taken as classification metrics. The recursive feature elimination method for support vector machine (SVM) and logistic regression (LR) combined with leave-one-out cross validation are applied to determine the optimal feature dimensions. Then the SVM and LR methods perform the classification process and compare the classification performance. The results show that not only can the multi-type combined metrics obtain higher accuracy than the single metric, but also the SVM classifier with multi-type combined metrics has better classification performance than the LR classifier. Statistically, the average accuracy of the combined metric is more than 92% for all between-group comparisons of SVM classifier. In addition to the high recognition rate, significant differences are found in the statistical analysis of cognitive scores between groups. We further execute the permutation test, receiver operating characteristic curves, and area under the curve to validate the robustness of the classifiers, and indicate that the SVM classifier is more stable and efficient than the LR classifier. Finally, the uncinated fasciculus, cingulum, corpus callosum, corona radiate, external capsule, and internal capsule have been regarded as the most important white matter tracts to identify AD, MCI, and HC. Our findings reveal a guidance role for machine-learning based image analysis on clinical diagnosis.

    Electronic states and molecular orientation of ITIC film
    Ying-Ying Du(杜莹莹), De-Qu Lin(林德渠), Guang-Hua Chen(陈光华), Xin-Yuan Bai(白新源), Long-Xi Wang(汪隆喜), Rui Wu(吴蕊), Jia-Ou Wang(王嘉鸥), Hai-Jie Qian(钱海杰), Hong-Nian Li(李宏年)
    Chin. Phys. B, 2018, 27 (8):  088801.  DOI: 10.1088/1674-1056/27/8/088801
    Abstract ( 672 )   HTML   PDF (647KB) ( 188 )  
    ITIC is the milestone of non-fullerene small molecule acceptors used in organic solar cells. We study the electronic states and molecular orientation of ITIC film using photoelectron spectroscopy and x-ray absorption spectroscopy. The negative integer charge transfer energy level is determined to be 4.00±0.05 eV below the vacuum level, and the ionization potential is 5.75±0.10 eV. The molecules predominantly have the face-on orientation on inert substrates as long as the surfaces of the substrates are not too rough. These results provide the physical understanding of the high performance of ITIC-based solar cells, which also afford implications to design more advanced photovoltaic small molecules.
    Nanoforest-like CdS/TiO2 heterostructure composites: Synthesis and photoelectrochemical application
    Shi Su(苏适), Jinwen Ma(马晋文), Wanlong Zuo(左万龙), Jun Wang(汪俊), Li Liu(刘莉), Shuang Feng(冯爽), Tie Liu(刘铁), Wuyou Fu(付乌有), Haibin Yang(杨海滨)
    Chin. Phys. B, 2018, 27 (8):  088802.  DOI: 10.1088/1674-1056/27/8/088802
    Abstract ( 682 )   HTML   PDF (2207KB) ( 174 )  

    In this study, TiO2 nanoforest films consisting of nanotubes have been synthesized by a simple hydrothermal method and a subsequent sintering technique. The hydrothermal reaction time is important for the controlling of the nanotube diameter and the specific surface area of holistic TiO2 films. When the hydrothermal process reaction time is up to 8 hours, the diameter of the nanotube is about 10 nm, and the specific surface area of TiO2 nanoforest films reaches the maximum. CdS nanoparticles are synthesized on TiO2 nanoforest films by the successive ionic layer adsorption and reaction (SILAR) technique. The transmission electron microscope (TEM) and energy dispersive x-ray spectroscopy (EDX) mapping results verify that TiO2/CdS heterostructures are realized. A significant red-shift of the absorption edge from 380 nm to 540 nm can be observed after the pure TiO2 film is sensitized by CdS nanoparticles. Under irradiation of light, the current density of the optimal TiO2/CdS photoanode is 2.30 mA·cm-2 at 0 V relative to the saturated calomel electrode (SCE), which is 6 times stronger than that of the pure TiO2 photoanode. This study suggests that the TiO2 nanoforest consisting of interlinked pony-size nanotubes is a promising nanostructure for photoelectrochemical.

    Evacuation flow of pedestrians considering compassion effect
    Yu-Zhang Chen(陈煜章), Ming Li(李明), Rui Jiang(姜锐), Mao-Bin Hu(胡茂彬)
    Chin. Phys. B, 2018, 27 (8):  088901.  DOI: 10.1088/1674-1056/27/8/088901
    Abstract ( 797 )   HTML   PDF (1130KB) ( 174 )  
    By means of game theory, the effect of compassion mechanism on the evacuation dynamics of pedestrians from a room is studied based on a cellular automaton model. Pedestrians can choose to cooperate or defect in a snowdrift game during the movement. With the compassion mechanism, pedestrians share their payoff to the poorest peer when several pedestrians compete for the same empty cell. Simulation results show that the escape time grows with fear degree r of the snowdrift game, and the compassion mechanism will have a different effect on the system compared with the situation of a spatial game with fixed population. By payoff redistribution, the compassion can help the minor strategy to survive. When the fear degree r is large, the compassion can sustain the cooperative behavior, and spontaneously decreases the escape time. When the fear degree r is small, the compassion will decrease the cooperation frequency, and slightly increase the escape time. The phenomenon is explained by the evolution and competition of defectors and cooperators in the system. Finally, the effect of initial cooperator proportion, the effect of two exits, and the effect of “Richest-Following” strategy, and the effect of initial density are also discussed.
ISSN 1674-1056   CN 11-5639/O4
, Vol. 27, No. 8

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