Table of contents

    05 June 2019, Volume 28 Issue 6 Previous issue    Next issue
    Simulation of the influence of imperfections on dynamical decoupling of a superconducting qubit
    Ying-Shan Zhang(张颖珊), Jian-She Liu(刘建设), Chang-Hao Zhao(赵昌昊), Yong-Cheng He(何永成), Da Xu(徐达), Wei Chen(陈炜)
    Chin. Phys. B, 2019, 28 (6):  060201.  DOI: 10.1088/1674-1056/28/6/060201
    Abstract ( 653 )   HTML   PDF (1238KB) ( 272 )  

    Dynamical decoupling is widely used in many quantum computing systems to combat decoherence. In a practical superconducting quantum system, imperfections can plague decoupling performance. In this work, imperfections in a superconducting qubit and its control system are modeled via modified Hamiltonian and collapse operator. A master equation simulation is carried out on the qubit under 1/f environment noise spectrum. The average dephasing rate of qubit is extracted to characterize the impact of different imperfections on the decoupling from dephasing. We find that the precision of pulse position, on-off ratio, and filtering effect are most critical. Bounded pulses have weaker impact, while variation in pulse width and qubit relaxation are insignificant. Consequently, alternative decoupling protocols, jitter mitigation, cascaded mixers, and pulse shaping can be conducive to the performance of decoupling. This work may assist the analysis and optimization of dynamical decoupling on noisy superconducting quantum systems.

    Atom interferometers with weak-measurement path detectors and their quantum mechanical analysis
    Zhi-Yuan Li(李志远)
    Chin. Phys. B, 2019, 28 (6):  060301.  DOI: 10.1088/1674-1056/28/6/060301
    Abstract ( 919 )   HTML   PDF (818KB) ( 278 )  

    According to the orthodox interpretation of quantum physics, wave-particle duality (WPD) is the intrinsic property of all massive microscopic particles. All gedanken or realistic experiments based on atom interferometers (AI) have so far upheld the principle of WPD, either by the mechanism of the Heisenberg's position-momentum uncertainty relation or by quantum entanglement. In this paper, we propose and make a systematic quantum mechanical analysis of several schemes of weak-measurement atom interferometer (WM-AI) and compare them with the historical schemes of strong-measurement atom interferometer (SM-AI), such as Einstein's recoiling slit and Feynman's light microscope. As the critical part of these WM-AI setups, a weak-measurement path detector (WM-PD) deliberately interacting with the atomic internal electronic quantum states is designed and used to probe the which-path information of the atom, while only inducing negligible perturbation of the atomic center-of-mass motion. Another instrument that is used to directly interact with the atomic center-of-mass while being insensitive to the internal electronic quantum states is used to monitor the atomic center-of-mass interference pattern. Two typical schemes of WM-PD are considered. The first is the micromaser-cavity path detector, which allows us to probe the spontaneously emitted microwave photon from the incoming Rydberg atom in its excited electronic state and record unanimously the which-path information of the atom. The second is the optical-lattice Bragg-grating path detector, which can split the incoming atom beam into two different directions as determined by the internal electronic state and thus encode the which-path information of the atom into the internal states of the atom. We have used standard quantum mechanics to analyze the evolution of the atomic center-of-mass and internal electronic state wave function by directly solving Schrödinger's equation for the composite atom-electron-photon system in these WM-AIs. We have also compared our analysis with the theoretical and experimental studies that have been presented in the previous literature. The results show that the two sets of instruments can work separately, collectively, and without mutual exclusion to enable simultaneous observation of both wave and particle nature of the atoms to a much higher level than the historical SM-AIs, while avoiding degradation from Heisenberg's uncertainty relation and quantum entanglement. We have further investigated the space-time evolution of the internal electronic quantum state, as well as the combined atom-detector system and identified the microscopic origin and role of quantum entanglement, as emphasized in numerous previous studies. Based on these physics insights and theoretical analyses, we have proposed several new WM-AI schemes that can help to elucidate the puzzling physics of the WPD of the atoms. The principle of WM-AI scheme and quantum mechanical analyses made in this work can be directly extended to examine the principle of WPD for other massive particles.

    Spin squeezing in Dicke-class of states with non-orthogonal spinors
    K S Akhilesh, K S Mallesh, Sudha, Praveen G Hegde
    Chin. Phys. B, 2019, 28 (6):  060302.  DOI: 10.1088/1674-1056/28/6/060302
    Abstract ( 596 )   HTML   PDF (684KB) ( 150 )  

    The celebrated Majorana representation is exploited to investigate spin squeezing in different classes of pure symmetric states of N qubits with two distinct spinors, namely the Dicke-class of states. On obtaining a general expression for spin squeezing parameter, the variation of squeezing for different configurations is studied in detail. It is shown that the states in the Dicke-class, characterized by two-distinct non-orthogonal spinors, exhibit squeezing.

    Steady-state entanglement and heat current of two coupled qubits in two baths without rotating wave approximation
    Mei-Jiao Wang(王美姣), Yun-Jie Xia(夏云杰)
    Chin. Phys. B, 2019, 28 (6):  060303.  DOI: 10.1088/1674-1056/28/6/060303
    Abstract ( 635 )   HTML   PDF (595KB) ( 201 )  
    We study the steady-state entanglement and heat current of two coupled qubits, in which two qubits are connected with two independent heat baths (IHBs) or two common heat baths (CHBs). We construct the master equation in the eigenstate representation of two coupled qubits to describe the dynamics of the total system and derive the solutions in the steady-state with stronger coupling regime between two qubits than qubit-baths. We do not make the rotating wave approximation (RWA) for the qubit-qubit interaction, and so we are able to investigate the behaviors of the system in both the strong coupling regime and the weak coupling regime, respectively. In an equilibrium bath, we find that the entanglement decreases with the bath temperature and energy detuning increasing under the strong coupling regime. In the weak coupling regime, the entanglement increases with coupling strength increasing and decreases with the bath temperature and energy detuning increasing. In a nonequilibrium bath, the entanglement without RWA is useful for entanglement at lower temperatures. We also study the heat currents of the two coupled qubits and their variations with the energy detuning, coupling strength and low temperature. In the strong (weak) coupling regime, the heat current increases (decreases) with coupling strength increasing when the temperature of one bath is lower (higher) than the other, and the energy detuning leads to a positive (negative) effect when the temperature is low (high). In the weak coupling regime, the variation trend of heat current is opposite to that of coupling strength for the IHB case and the CHB case.
    Entropy squeezing for three-level atom interacting with a single-mode field
    Fei-Fan Liu(刘非凡), Mao-Fa Fang(方卯发), Xiong Xu(许雄)
    Chin. Phys. B, 2019, 28 (6):  060304.  DOI: 10.1088/1674-1056/28/6/060304
    Abstract ( 853 )   HTML   PDF (671KB) ( 231 )  

    The entropy squeezing for a three-level atom interacting with a single-model field is studied. A general definition of entropy squeezing for three-level atom is given according to entropic uncertainty relation of three-level system, and the calculation formalism of entropy is derived for a cascade three-level atom. By using numerical calculation, the entropy squeezing properties of a cascade three-level atom are examined. Our results show that, three-level atom can generate obvious entropy squeezing effect via choosing appropriate superposition state of three-level atom. Our results are meaningful for preparing three-level system information resources with ultra-low quantum noise.

    Simulation and measurement of millimeter-wave radiation from Josephson junction array
    Xin Zhang(张鑫), Sheng-Hui Zhao(赵生辉), Li-Tian Wang(王荔田), Jian Xing(邢建), Sheng-Fang Zhang(张胜芳), Xue-Lian Liang(梁雪连), Ze He(何泽), Pei Wang(王培), Xin-Jie Zhao(赵新杰), Ming He(何明), Lu Ji(季鲁)
    Chin. Phys. B, 2019, 28 (6):  060305.  DOI: 10.1088/1674-1056/28/6/060305
    Abstract ( 767 )   HTML   PDF (615KB) ( 183 )  
    We report the circuit simulations and experiments of millimeter-wave radiation from a high temperature superconducting (HTS) bicrystal Josephson junction (BJJ) array. To study the effects of junction characteristic parameters on radiation properties, new radiation circuit models are proposed in this paper. The series resistively and capacitively shunted junction (RCSJ) models are packaged into a Josephson junction array (JJA) model in the simulation. The current-voltage characteristics (IVCs) curve and radiation peaks are simulated and analyzed by circuit models, which are also observed from the experiment at liquid nitrogen temperature. The experimental radiation linewidth and power are in good agreement with simulated results. The presented circuit models clearly demonstrate that the inconsistency of the JJA will cause a broad linewidth and a low detected power. The junction radiation properties are also investigated at the optimal situation by circuit simulation. The results further confirm that the consistent JJA characteristic parameters can successfully narrow the radiation linewidth and increase the power of junction radiation.
    Group consensus of multi-agent systems subjected to cyber-attacks
    Hai-Yun Gao(高海云), Ai-Hua Hu(胡爱花), Wan-Qiang Shen(沈莞蔷), Zheng-Xian Jiang(江正仙)
    Chin. Phys. B, 2019, 28 (6):  060501.  DOI: 10.1088/1674-1056/28/6/060501
    Abstract ( 687 )   HTML   PDF (577KB) ( 280 )  

    In this paper, we investigate the group consensus for leaderless multi-agent systems. The group consensus protocol based on the position information from neighboring agents is designed. The network may be subjected to frequent cyber-attacks, which is close to an actual case. The cyber-attacks are assumed to be recoverable. By utilizing algebraic graph theory, linear matrix inequality (LMI) and Lyapunov stability theory, the multi-agent systems can achieve group consensus under the proposed control protocol. The sufficient conditions of the group consensus for the multi-agent networks subjected to cyber-attacks are given. Furthermore, the results are extended to the consensus issue of multiple subgroups with cyber-attacks. Numerical simulations are performed to demonstrate the effectiveness of the theoretical results.

    Domain walls and their interactions in a two-component Bose-Einstein condensate
    Ling-Zheng Meng(孟令正), Yan-Hong Qin(秦艳红), Li-Chen Zhao(赵立臣), Zhan-Ying Yang(杨战营)
    Chin. Phys. B, 2019, 28 (6):  060502.  DOI: 10.1088/1674-1056/28/6/060502
    Abstract ( 610 )   HTML   PDF (3562KB) ( 171 )  

    We investigate domain wall excitations in a two-component Bose-Einstein condensate with two-body interactions and pair-transition effects. It is shown that domain wall excitations can be described exactly by kink and anti-kink excitations in each component. The domain wall solutions are given analytically, which exist with different conditions compared with the domain wall reported before. Bubble-droplet structure can be also obtained from the fundamental domain wall, and their interactions are investigated analytically. Especially, domain wall interactions demonstrate some striking particle transition dynamics. These striking transition effects make the domain wall admit quite different collision behavior, in contrast to the collision between solitons or other nonlinear waves. The collisions between kinks induce some phase shift, which makes the domain wall change greatly. Their collisions can be elastic or inelastic with proper combination of fundamental domain walls. These characters can be used to manipulate one domain wall by interacting with other ones.

    Thermal characterization of GaN heteroepitaxies using ultraviolet transient thermoreflectance
    Kang Liu(刘康), Jiwen Zhao(赵继文), Huarui Sun(孙华锐), Huaixin Guo(郭怀新), Bing Dai(代兵), Jiaqi Zhu(朱嘉琦)
    Chin. Phys. B, 2019, 28 (6):  060701.  DOI: 10.1088/1674-1056/28/6/060701
    Abstract ( 753 )   HTML   PDF (952KB) ( 213 )  
    Thermal transport properties of GaN heteroepitaxial structures are of critical importance for the thermal management of high-power GaN electronic and optoelectronic devices. Ultraviolet (UV) lasers are employed to directly heat and sense the GaN epilayers in the transient thermoreflectance (TTR) measurement, obtaining important thermal transport properties in different GaN heterostructures, which include a diamond thin film heat spreader grown on GaN. The UV TTR technique enables rapid and non-contact thermal characterization for GaN wafers.
    Investigation of copper sulfate pentahydrate dehydration by terahertz time-domain spectroscopy
    Yuan-Yuan Ma(马媛媛), Hao-Chong Huang(黄昊翀), Si-Bo Hao(郝思博), Wei-Chong Tang(汤伟冲), Zhi-Yuan Zheng(郑志远), Zi-Li Zhang(张自力)
    Chin. Phys. B, 2019, 28 (6):  060702.  DOI: 10.1088/1674-1056/28/6/060702
    Abstract ( 611 )   HTML   PDF (644KB) ( 180 )  

    Copper sulfate pentahydrate is investigated by terahertz time-domain spectroscopy. It is shown that the terahertz absorption coefficients are correlated with the particle size of the samples, as well as the heating rates of the ambient temperature. Furthermore, the water molecules of copper sulfate pentahydrate can be quantitatively characterized due to the high sensitivity of the terahertz wave to water molecules. Based on such results, the status of water incorporated in mineral opal is also characterized using terahertz time-domain spectroscopy. It indicates that terahertz technology can be considered as an efficient method to detect the dehydration of minerals.

    Digitally calibrated broadband dual-comb gases absorption spectral measurements
    Xinyi Chen(陈馨怡), Weipeng Zhang(张伟鹏), Haoyun Wei(尉昊赟), Yan Li(李岩)
    Chin. Phys. B, 2019, 28 (6):  060703.  DOI: 10.1088/1674-1056/28/6/060703
    Abstract ( 690 )   HTML   PDF (1458KB) ( 170 )  

    From the perspective of error compensation in the sampling process, a digital calibration algorithm was studied for the processing of spectral data in dual-comb spectroscopy. In this algorithm, dynamic adaptation to phase fluctuations maintained constant measurement results of spectral line positions and intensities. A mode-resolved broadband absorption spectrum was obtained over the full-spectral range of the comb with a Hertz linewidth of radio frequency comb mode. The measured spectrum spanned over 10 THz, which covered the multiplexed absorption regions of mixed gases, such as CO2 and N2O. The calibrated interferograms were also capable of direct coherent averaging in the time domain. The transmittance obtained deviated from the theoretical calculation by no more than 2% in the whole spectral span.

    Negativity of Wigner function and phase sensitivity of an SU(1,1) interferometer
    Chun-Li Liu(刘春丽), Li-Li Guo(郭丽丽), Zhi-Ming Zhang(张智明), Ya-Fei Yu(於亚飞)
    Chin. Phys. B, 2019, 28 (6):  060704.  DOI: 10.1088/1674-1056/28/6/060704
    Abstract ( 659 )   HTML   PDF (565KB) ( 181 )  

    Both the negativity of Wigner function and the phase sensitivity of an SU(1,1) interferometer are investigated in this paper. In the case that the even coherent state and squeezed vacuum state are input into the interferometer, the Heisenberg limit can be approached with parity detection. At the same time, the negativity volume of Wigner function of detection mode comes entirely from the input state and varies periodically with the encoding phase. In addition, the negativity volume of Wigner function is positively correlated with the phase sensitivity of the SU(1,1) interferometer. The positive correlation may mean that the non-classicality indicated by negative Wigner function is a kind of resource that can verify some related research results of phase estimation.

    Structure, conductivity, and ion emission properties of RbAg4I5 solid electrolyte film prepared by pulsed laser deposition
    Jun-Lian Chen(陈军联), Wen-Bin Zuo(左文彬), Xian-Wen Ke(柯贤文), Alexander B Tolstoguzov, Can-Xin Tian(田灿鑫), Neena Devi, Ranjana Jha, Gennady N Panin, De-Jun Fu(付德君)
    Chin. Phys. B, 2019, 28 (6):  060705.  DOI: 10.1088/1674-1056/28/6/060705
    Abstract ( 609 )   HTML   PDF (937KB) ( 238 )  

    We fabricated a silver ion emitter based on the solid state electrolyte film of RbAg4I5 prepared by pulsed laser deposition. The RbAg4I5 target for PLD process was mechano-chemically synthesized by high-energy ball milling in Ar atmosphere using β-AgI and RbI as raw materials. The ion-conducting properties of RbAg4I5 were studied by alternating current (AC) impedance spectroscopy and the ionic conductivity at room temperature was estimated 0.21 S/m. The structure, morphology, and elemental composition of the RbAg4I5 film were investigated. The Ag+ ion-conducting property of the prepared superioni-conductor film was exploited for ion-beam generation. The temperature and accelerating voltage dependences of the ion current were studied. Few nA current was obtained at the temperature of 196 ℃ and the accelerating voltage of 10 kV.

    New measurement of thick target yield for narrow resonance at Ex=9.17 MeV in the 13C(p, γ)14N reaction
    Yong-Le Dang(党永乐), Fu-Long Liu(刘伏龙), Guang-Yong Fu(付光永), Di Wu(吴笛), Chuang-Ye He(贺创业), Bing Guo(郭冰), Nai-Yan Wang(王乃彦)
    Chin. Phys. B, 2019, 28 (6):  060706.  DOI: 10.1088/1674-1056/28/6/060706
    Abstract ( 821 )   HTML   PDF (657KB) ( 212 )  

    High energy γ-rays can be used in many fields, such as nuclear waste transmutation, flash photographics, and astrophysics. The 13C(p, γ)14N resonance reaction was used to generate high energy and mono-energetic γ-rays in this work. The thick-target yield of the 9.17-MeV γ-ray from the resonance in this reaction was determined to be (4.7±0.4)×10-9γ/proton, which was measured by a HPGe detector. Meanwhile, the angular distribution of 9.17-MeV γ-ray was also determined. The absolute efficiency of HPGe detector was calibrated using 56Co and 152Eu sources with known radioactive activities and calculated by GEANT4 simulation.

    Photo-transmutation based on resonance γ-ray source
    Guang-Yong Fu(付光永), Yong-Le Dang(党永乐), Fu-Long Liu(刘伏龙), Di Wu(吴笛), Chuang-Ye He(贺创业), Nai-Yan Wang(王乃彦)
    Chin. Phys. B, 2019, 28 (6):  060707.  DOI: 10.1088/1674-1056/28/6/060707
    Abstract ( 443 )   HTML   PDF (541KB) ( 160 )  

    High intensity γ-ray source can be obtained through resonance reaction induced by protons. In this work, the possibility of using such high intensity MeV-range γ-ray source to transmute nuclear waste is investigated through Mont Carlo simulation. 197Au(γ,n)196Au experiment is performed to obtain the transmutation rate and compared with the simulation result. If the current of the proton beam is 10 mA at the resonance energy of 441 keV, with the γ photons emitted from 7Li(p, γ)8Be, then the corresponding transmutation yield for 129I in 2π direction can reach 9.4×109 per hour. The result is compared with that of LCS γ-ray source.

    Photoelectron imaging of resonance-enhanced multiphoton ionization and above-threshold ionization of ammonia molecules in a strong 800-nm laser pulse
    Le-Le Song(宋乐乐), Ya-Nan Sun(孙亚楠), Yan-Hui Wang(王艳辉), Xiao-Chun Wang(王晓春), Lan-Hai He(赫兰海), Si-Zuo Luo(罗嗣佐), Wen-Hui Hu(胡文惠), Qiu-Nan Tong(佟秋男), Da-Jun Ding(丁大军), Fu-Chun Liu(刘福春)
    Chin. Phys. B, 2019, 28 (6):  063201.  DOI: 10.1088/1674-1056/28/6/063201
    Abstract ( 675 )   HTML   PDF (1036KB) ( 171 )  

    In this work, we mainly investigate the NH3 molecular multiphoton ionization process by using the photoelectron velocity map imaging technique. Under the condition of femtosecond laser (wavelength at 800 nm), the photoelectron images are detected. The channel switching and above-threshold ionization (ATI) effect are also confirmed. The kinetic energy spectrum (KES) and the photoelectron angular distributions (PADs) are obtained through the anti-Abel transformation from the original images, and then three ionization channels are confirmed successfully according to the Freeman resonance effect in a relatively low laser intensity region. In the excitation process, the intermediate resonance Rydberg states are C~1A'1 (6+2 photons process), B~1E" (6+2 photons process) and C~1A'1 (7+2 photons process), respectively. At the same time, we also find that the photoelectron angular distributions are independent of laser intensity. In addition, the electrons produced by different processes interfere with each other and they can produce a spider-like structure. We also find ac-Stark movement according to the Stark-shift-induced resonance effect when the laser intensity is relatively high.

    Quantal studies of sodium 3p←3s photoabsorption spectra perturbed by ground lithium atoms
    N Lamoudi, F Talbi, M T Bouazza, M Bouledroua, K Alioua
    Chin. Phys. B, 2019, 28 (6):  063202.  DOI: 10.1088/1674-1056/28/6/063202
    Abstract ( 529 )   HTML   PDF (740KB) ( 122 )  

    The pressure broadening in the far wings, where the sodium Na (3p←3s) resonance line is perturbed by ground lithium Li (2s) atoms, has been theoretically analyzed. The NaLi potential-energy curves and the transition dipole moments are constructed by using a reliable ab initio data points to carry out the reduced-absorption coefficients kr(ν,T). This quantum-mechanical investigation have demonstrated that the NaLi profile spectra show a satellite future in the red wing at wavelength λ=685 nm in the temperature range 4000 K-1.8×104 K. The computation could also exhibit a second satellite, in the blue wing, near the wavelength λ=574 nm beyond 6000 K and a third peak located at λ=490 nm which begins to appear at 1.8×104 K.

    Charge-state populations for the neon-XFEL system
    Ping Deng(邓萍), Gang Jiang(蒋刚)
    Chin. Phys. B, 2019, 28 (6):  063203.  DOI: 10.1088/1674-1056/28/6/063203
    Abstract ( 534 )   HTML   PDF (565KB) ( 151 )  

    The interaction between neon and x-ray free-electron lasers with different laser parameters is systematically studied by solving a set of coupled rate equations. As an example, the evolution of 1s12s22p6 configuration is given under different incident photon numbers, pulse widths, and photon energies. We have also determined all of the charge-state populations as a function of three laser pulse parameters by averaging over time. The result shows that the variations of these charge-state populations demonstrate a pattern when the pulse width is shorter than 10 fs:some of the charge-states decrease rapidly, while the others rise but remain relatively constant for pulse width larger than 10 fs. The variation of the average charge with three parameters has also obtained. The average charge decreases for a pulse width shorter than 10 fs but remains basically unchanged for a pulse width longer than 10 fs.

    Hydrogen sulphide detection using near-infrared diode laser and compact dense-pattern multipass cell
    Xing Tian(田兴), Yuan Cao(曹渊), Jia-Jin Chen(陈家金), Kun Liu(刘锟), Gui-Shi Wang(王贵师), Xiao-Ming Gao(高晓明)
    Chin. Phys. B, 2019, 28 (6):  063301.  DOI: 10.1088/1674-1056/28/6/063301
    Abstract ( 737 )   HTML   PDF (1807KB) ( 192 )  

    Sub-ppmv level detection of hydrogen sulphide (H2S) using a 1.578-μm distributed feedback tunable diode laser combining with wavelength modulation spectroscopy and second harmonic detection scheme is reported. A home-developed novel compact dense-pattern multipass gas cell with an effective optical path length of 29.37 m is used to improve sensitivity and reduce sample volume. Detection parameters are optimized, including modulation frequency and amplitude. The analysis of Allan variance shows that a minimum detectable concentration 60 ppbv is obtained with a lock-in time constant of 10 ms, and a detection limit of 13 ppbv can be achieved by average in 300 s. The demonstrated H2S sensor has a strong penitential application in natural gas process for regulating and controlling H2S concentration.

    Non-adiabatic quantum dynamical studies of Na(3p)+HD(ν=1, j=0)→NaH/NaD+D/H reaction
    Yue-Pei Wen(温月佩), Bayaer Buren(布仁巴雅尔), Mao-Du Chen(陈茂笃)
    Chin. Phys. B, 2019, 28 (6):  063401.  DOI: 10.1088/1674-1056/28/6/063401
    Abstract ( 754 )   HTML   PDF (1839KB) ( 103 )  

    Non-adiabatic dynamical calculations are carried out for the Na(3p)+HD(ν=1, j=0)→NaH/NaD+D/H reaction on the diabatic potential energy surfaces of Wang et al. (Sci. Rep. 2018, 8, 17960) by using the time-dependent wave packet method. The state-to-state integral cross sections and differential cross sections of two reaction channels (NaH/NaD+D/H) are calculated for collision energy up to 0.4 eV. The cross section branching ratio indicates that the dominant reaction channel changes from NaD+H to NaH+D when the collision energy is larger than 0.227 eV. The products from two reaction channels both prefer to form in vibrationally cold but rotationally hot states, and they both tend to forward scattering.

    Axial magnetic field effect in numerical analysis of high power Cherenkov free electron laser
    F Bazouband, B Maraghechi
    Chin. Phys. B, 2019, 28 (6):  064101.  DOI: 10.1088/1674-1056/28/6/064101
    Abstract ( 584 )   HTML   PDF (5756KB) ( 178 )  

    Cherenkov free electron laser (CFEL) is simulated numerically by using the single particle method to optimize the electron beam. The electron beam is assumed to be moving near the surface of a flat dielectric slab along a growing radiation. The set of coupled nonlinear differential equations of motion is solved to study the electron dynamics. For three sets of parameters, in high power CFEL, it is found that an axial magnetic field is always necessary to keep the electron beam in the interaction region and its optimal strength is reported for each case. At the injection point, the electron beam's distance above the dielectric surface is kept at a minimum value so that the electrons neither hit the dielectric nor move away from it to the weaker radiation fields and out of the interaction region. The optimal electron beam radius and current are thereby calculated. This analysis is in agreement with two previous numerical studies for a cylindrical waveguide but is at odds with analytical treatments of a flat dielectric that does not use an axial magnetic field. This is backed by an interesting physical reasoning.

    Characterization of focusing performance of spiral zone plates with fractal structure
    Hua-Ping Zang(臧华平), Cheng-Long Zheng(郑程龙), Zi-Wen Ji(吉子雯), Quan-Ping Fan(范全平), Lai Wei(魏来), Yong-Jie Li(李永杰), Kai-Jun Mu(牧凯军), Shu Chen(陈述), Chuan-Ke Wang(王传珂), Xiao-Li Zhu(朱效力), Chang-Qing Xie(谢常青), Lei-Feng Cao(曹磊峰), Er-Jun Liang(梁二军)
    Chin. Phys. B, 2019, 28 (6):  064201.  DOI: 10.1088/1674-1056/28/6/064201
    Abstract ( 593 )   HTML   PDF (3863KB) ( 153 )  

    We propose an efficient method of generating a vortex beam with multi-foci by using a fractal spiral zone plate (FSZP), which is designed by combining fractal structure with a spiral zone plate (SZP) in the squared radial coordinate. The theoretical analysis reveals that the number of foci that embed vortices is significantly increased as compared with that obtained by using a conventional SZP. Furthermore, the influence of topological charge on the intensity distribution in focal plane is also discussed in detail. For experimental investigation, an FSZP with topological charge p=1 and 6.4 mm diameter is fabricated by using a photo-etching technique. The calibration indicates that the focusing performances of such a kind of zone plane (ZP) accord well with simulations, thereby providing its potential applications in multi-dimensional optical manipulation and optical imaging technology.

    Fast Fourier single-pixel imaging based on Sierra-Lite dithering algorithm
    Zhen-Yu Liang(梁振宇), Zheng-Dong Cheng(程正东), Yan-Yan Liu(刘严严), Kuai-Kuai Yu(于快快), Yang-Di Hu(胡洋頔)
    Chin. Phys. B, 2019, 28 (6):  064202.  DOI: 10.1088/1674-1056/28/6/064202
    Abstract ( 780 )   HTML   PDF (1134KB) ( 211 )  

    The single-pixel imaging (SPI) technique is able to capture two-dimensional (2D) images without conventional array sensors by using a photodiode. As a novel scheme, Fourier single-pixel imaging (FSI) has been proven capable of reconstructing high-quality images. Due to the fact that the Fourier basis patterns (also known as grayscale sinusoidal patterns) cannot be well displayed on the digital micromirror device (DMD), a fast FSI system is proposed to solve this problem by binarizing Fourier pattern through a dithering algorithm. However, the traditional dithering algorithm leads to low quality as the extra noise is inevitably induced in the reconstructed images. In this paper, we report a better dithering algorithm to binarize Fourier pattern, which utilizes the Sierra-Lite kernel function by a serpentine scanning method. Numerical simulation and experiment demonstrate that the proposed algorithm is able to achieve higher quality under different sampling ratios.

    Fe: ZnSe laser pumped by a 2.93-μm Cr, Er: YAG laser
    Ying-Yi Li(李英一), Tong-Yu Dai(戴通宇), Xiao-Ming Duan(段小明), Chun-Fa Guo(郭春发), Li-Wei Xu(徐丽伟), You-Lun Ju(鞠有伦)
    Chin. Phys. B, 2019, 28 (6):  064203.  DOI: 10.1088/1674-1056/28/6/064203
    Abstract ( 833 )   HTML   PDF (687KB) ( 125 )  

    We demonstrated an Fe:ZnSe laser pumped by a 2.93-μm Cr, Er:YAG laser at liquid nitrogen and room temperature in single-shot free-running operation for the first time. The xenon flash lamp pumped Cr, Er:YAG laser had a maximum single pulse energy of 1.414 J, and the threshold and slope efficiency were 141.70 J and 0.70% which were respectively reduced by 29.3% and increased by 52.2% compared with the Er:YAG laser. At liquid nitrogen temperature of 77 K, the maximum single pulse energy of the Fe:ZnSe laser was 197.6 mJ, corresponding to a slope efficiency of 13.4%. The central wavelength and full width at half maximum (FWHM) linewidth were 4037.4 nm and 122.0 nm, respectively. At room temperature, the laser generated a maximum single pulse energy of 3.5 mJ at the central wavelength of 4509.6 nm with an FWHM linewidth of 171.5 nm.

    Supercontinuum generation of highly nonlinear fibers pumped by 1.57-μm laser soliton
    Song-Tao Fan(樊松涛), Yan-Yan Zhang(张颜艳), Lu-Lu Yan(闫露露), Wen-Ge Guo(郭文阁), Shou-Gang Zhang(张首刚), Hai-Feng Jiang(姜海峰)
    Chin. Phys. B, 2019, 28 (6):  064204.  DOI: 10.1088/1674-1056/28/6/064204
    Abstract ( 778 )   HTML   PDF (1083KB) ( 184 )  

    Highly nonlinear fibers (HNLFs) are crucial components for supercontinuum (SC) generation with laser solution. However, it is difficult to exactly estimate the structure of produced SC according to material parameters. To give a guideline for choosing and using HNLFs for erbium-fiber-based optical applications, we demonstrate SC generation in five types of HNLFs pumped by 1.57-μm laser solitons. All five fibers output a SC exceeding 1000 nm. Three different SC formation processes were observed in the experiment. By comparing optical parameters of these fibers, we find the zero dispersion wavelength (ZDW) of fiber has an important influence on the SC structure and energy distribution for a given pump source.

    Monolithic all-fiber mid-infrared supercontinuum source based on a step-index two-mode As2S3 fiber
    Jinmei Yao(姚金妹), Bin Zhang(张斌), Jing Hou(侯静)
    Chin. Phys. B, 2019, 28 (6):  064205.  DOI: 10.1088/1674-1056/28/6/064205
    Abstract ( 717 )   HTML   PDF (1458KB) ( 140 )  

    We demonstrate efficient supercontinuum generation extending into mid-infrared spectral range by pumping a two-mode As2S3 fiber in the normal dispersion regime. The As2S3 fiber is fusion spliced to the pigtail of a near-infrared supercontinuum pump source with ultra-low splicing loss of 0.125 dB, which enables a monolithic all-fiber mid-infrared supercontinuum source. By two-mode excitation and mixed-mode cascaded stimulated Raman scattering, a supercontinuum spanning from 1.8 μm to 4.2 μm is obtained. Over 70% of the supercontinuum power is converted to wavelengths beyond 2.4 μm. This is the first experimental report with respect to the multimode mid-infrared supercontinuum generation in a step-index two-mode chalcogenide fiber.

    Analysis of third and one-third harmonic generation in lossy waveguides
    Jianyu Zhang(张剑宇), Yunxu Sun(孙云旭), Qinghai Song(宋清海)
    Chin. Phys. B, 2019, 28 (6):  064206.  DOI: 10.1088/1674-1056/28/6/064206
    Abstract ( 543 )   HTML   PDF (760KB) ( 120 )  

    A comprehensive study on the requirements for the highly efficient third harmonic generation (THG) and its inverse process, one-third harmonic generation (OTHG), in lossy waveguides is proposed. The field intensity restrictions for both THG and OTHG caused by loss are demonstrated. The effective relative phase ranges, supporting the positive growth of signal fields of THG and OTHG are shrunken by the loss. Furthermore, it turns out that the effective relative phase ranges depend on the intensities of the interacting fields. At last, a modified definition of coherent length in loss situation, which evaluates the phase matching degree more precisely, is proposed by incorporating the shrunken relative phase range and the nonlinear phase mismatch. These theoretical analysis are valuable for guiding the experimental designs for highly efficient THG and OTHG.

    Energetic few-cycle pulse compression in gas-filled hollow core fiber with concentric phase mask
    Yu Zhao(赵钰), Zhi-Yuan Huang(黄志远), Rui-Rui Zhao(赵睿睿), Ding Wang(王丁), Yu-Xin Leng(冷雨欣)
    Chin. Phys. B, 2019, 28 (6):  064207.  DOI: 10.1088/1674-1056/28/6/064207
    Abstract ( 469 )   HTML   PDF (2924KB) ( 140 )  

    The compression of high-energy, linearly polarized pulses in a gas-filled hollow core fiber (HCF) by using a concentric phase mask is studied theoretically. Simulation results indicate that using a properly designed concentric phase mask, a 40-fs input pulse centered at 800 nm with energy up to 10.0 mJ can be compressed to a full width at half maximum (FWHM) of less than 5 fs after propagating through a neon-filled HCF with a length of 1 m and diameter of 500 μ with a transmission efficiency of 67%, which is significantly higher than that without a concentric phase mask. Pulses with energy up to 20.0 mJ can also be efficiently compressed to less than 10 fs with the concentric phase mask. The higher efficiency due to the concentric phase mask can be attributed to the redistribution of the transverse intensity profile, which reduces the effect of ionization. The proposed method exhibits great potential for generating few-cycle laser pulse sources with high energy by the HCF compressor.

    High-performance waveguide-integrated Ge/Si avalanche photodetector with small contact angle between selectively epitaxial growth Ge and Si layers
    Xiao-Qian Du(杜小倩), Chong Li(李冲), Ben Li(黎奔), Nan Wang(王楠), Yue Zhao(赵越), Fan Yang(杨帆), Kai Yu(余凯), Lin Zhou(周琳), Xiu-Li Li(李秀丽), Bu-Wen Cheng(成步文), Chun-Lai Xue(薛春来)
    Chin. Phys. B, 2019, 28 (6):  064208.  DOI: 10.1088/1674-1056/28/6/064208
    Abstract ( 705 )   HTML   PDF (856KB) ( 287 )  

    Step-coupler waveguide-integrated Ge/Si avalanche photodetector (APD) is based on the vertical multimode interference (MMI), enhancing light scattering towards the Ge active region and creating mirror images of optical modes close to the Ge layer. However, there are two ineluctable contact angels between selectively epitaxial growth Ge and Si layers and selectively epitaxial growth Si and Si substrate, which has an effect on the coupling efficiency and the absorption of the photodetector. Therefore, step-coupled Ge/Si avalanche photodetectors with different step lengths are designed and fabricated. It is found that responsivity of APDs with step-coupler-length of 3.0 μm is 0.51 A/W at -6 V, 21% higher than that of 1.5 μm, which matches well with simulation absorption. The multiplication gain factor is as high as 50, and the maximum gain-bandwidth product reaches up to 376 GHz.

    Macadam's theory in RGB laser display
    Guan Wang(王贯), Yuhua Yang(杨雨桦), Tianhao Dong(董天浩), Chun Gu(顾春), Lixin Xu(许立新), Zhongcan Ouyang(欧阳钟灿), Zuyan Xu(许祖彦)
    Chin. Phys. B, 2019, 28 (6):  064209.  DOI: 10.1088/1674-1056/28/6/064209
    Abstract ( 647 )   HTML   PDF (628KB) ( 131 )  

    We have developed Macadam's theory to deal with RGB laser display, which can well describe the color gamut display system varying with the laser bandwidth. By calculating the volume of Rösch-Macadam color solid of laser display system under the Rec.2020 standard, we can obtain that the volume of chromatic stereoscopic at 30-nm laser spectral linewidth is about 90% of that at 1 nm laser spectral linewidth, which is important in laser display system to trade off the color gamut and the suppression of laser speckles. Moreover, we can also calculate the color gamut volume with different primary numbers and different primary wavelengths.

    Internal and near-surface fields for a chiral sphere under arbitrary laser beam illumination
    Bi-Da Su(苏必达), Ming-Jun Wang(王明军), Yue Peng(彭月), Su-Hui Yang(杨苏辉), Hua-Yong Zhang(张华永)
    Chin. Phys. B, 2019, 28 (6):  064210.  DOI: 10.1088/1674-1056/28/6/064210
    Abstract ( 581 )   HTML   PDF (4720KB) ( 202 )  

    A general scheme for the investigation of scattering by a chiral sphere under arbitrary monochromatic laser beam illumination is presented. The scattered and internal fields are expanded by using appropriate spherical vector wave functions, and their expansion coefficients are determined by the boundary conditions and the projection method. Targeting multiple incidence forms such as Gaussian beam, Hermite-Gaussian beam, doughnut mode beam and zero-order Bessel beam, the influence and propagation of near-surface intensity field for a chiral sphere are analyzed. These properties are very important for studying the properties of chiral media, and for manipulating the optical tweezers and super-resolution imaging of particles.

    Infrared cooling properties of cordierite
    Si-Heng Chen(陈思衡), Xiao-Xiong Wang(王晓雄), Guang-Di Nie(乜广弟), Qi Liu(刘奇), Jin-Xia Sui(隋金霞), Chao Song(宋超), Jian-Wei Zhu(朱建伟), Jie Fu(付洁), Jun-Cheng Zhang(张君诚), Xu Yan(闫旭), Yun-Ze Long(龙云泽)
    Chin. Phys. B, 2019, 28 (6):  064401.  DOI: 10.1088/1674-1056/28/6/064401
    Abstract ( 565 )   HTML   PDF (1456KB) ( 180 )  

    Cordierite (Mg2Al4Si5O18) is known for its good thermal shock resistance and it is widely used to improve thermal shock properties of materials. We found that cordierite has good infrared heat dissipation performance. This performance provides an additional means of heat dissipation to assist in the cooling of the metal surface. Spectroscopic tests show that cordierite reflects sunlight in the visible range and emits infrared in the far infrared range, making it potential candidate as an infrared radiative cooling material for daytime use.

    Uniformity principle of temperature difference field in heat transfer optimization
    Xue-Tao Cheng(程雪涛), Xin-Gang Liang(梁新刚)
    Chin. Phys. B, 2019, 28 (6):  064402.  DOI: 10.1088/1674-1056/28/6/064402
    Abstract ( 474 )   HTML   PDF (474KB) ( 131 )  

    The uniformity principle of temperature difference field is very useful in heat exchanger analyses and optimizations. In this paper, we analyze some other heat transfer optimization problems in the thermal management system of spacecrafts, including the cooling of thermal components, the one-stream series-wound heat exchanger network, the volume-to-point heat conduction problem, and the radiative heat transfer optimization problem, and have found that the uniformity principle of temperature difference field also holds. When the design objectives under the given constraints are achieved, the distributions of the temperature difference fields are uniform. The principle reflects the characteristic of the distribution of potential in the heat transfer optimization problems. It is also shown that the principle is consistent with the entransy theory. Therefore, although the principle is intuitive and phenomenological, the entransy theory can be the physical basis of the principle.

    Three-dimensional thermal illusion devices with arbitrary shape
    Xingwei Zhang(张兴伟), Xiao He(何晓), Linzhi Wu(吴林志)
    Chin. Phys. B, 2019, 28 (6):  064403.  DOI: 10.1088/1674-1056/28/6/064403
    Abstract ( 661 )   HTML   PDF (4355KB) ( 151 )  

    Since the concept of invisible cloak was proposed by Pendry and Leonhardt in 2006, many researchers have applied the theory of coordinate transformation to thermodynamics and overcome the complexity of inhomogeneous and anisotropic of material parameters. However, only two-dimensional (2D) thermal illusion devices are researched recently. According to this situation, our study focuses on three-dimensional (3D) thermal illusion devices including shrinker (or invisible cloak), concentrator, amplifier, reshaper, and rotator with arbitrary shape in a general way. In this paper, the corresponding material parameters of thermal illusion devices mentioned above are derived based on the theory of transformation thermodynamics and the simulated results agree well with the theoretical derivations. In addition, the conventional invisible cloak just controls the temperature gradient rather than the temperature value which is more concerned in physical applications. Here, we find that the temperature value of the cloaked object can be controlled by adjusting the location of the original point of the coordinate system.

    Effects of thiocyanate anions on switching and structure of poly(N-isopropylacrylamide) brushes
    Xin-Jun Zhao(赵新军), Zhi-Fu Gao(高志福)
    Chin. Phys. B, 2019, 28 (6):  064701.  DOI: 10.1088/1674-1056/28/6/064701
    Abstract ( 448 )   HTML   PDF (614KB) ( 122 )  

    In this work, we investigate the effects of thiocyanate anions on the switching and the structure of poly (N-isopropylacrylamide) (PNIPAM) brushes using a molecular theory. Our model takes into consideration the PNIPAM-anion bonds, the electrostatic effects and their explicit coupling to the PNIPAM conformations. It is found that at low thiocyanate anion concentration, as the anion concentration of thiocyanate increases, thiocyanate anions are more associated with PNIPAM chains through the PNIPAM-anion bonds, which contributes to stronger electrostatic repulsion and leads to an increase of lower critical solution temperature (LCST). By analyzing the average volume fractions of PNIPAM brushes, it is found that the PNIPAM brush presents a plateau structure. Our results show that the thiocyanate anions promote phase segregation due to the PNIPAM-anion bonds and the electrostatic effect. According to our model, the reduction of LCST can be explained as follows:at high thiocyanate anion concentration, with the increase of thiocyanate concentration, more ion bindings occurring between thiocyanate anions and PNIPAM chains will result in the increase of the hydrophobicity of PNIPAM chains; when the increase of electrostatic repulsion is insufficient to overcome the hydrophobic interaction of PNIPAM chains, it will lead to the reduction of brush height and LCST at high thiocyanate anion concentration. Our theoretical results are consistent with the experimental observations, and provide a fundamental understanding of the effects of thiocyanate on the LCST of PNIPAM brushes.

    Flow characteristics of supersonic gas passing through a circular micro-channel under different inflow conditions
    Guang-Ming Guo(郭广明), Qin Luo(罗琴), Lin Zhu(朱林), Yi-Xiang Bian(边义祥)
    Chin. Phys. B, 2019, 28 (6):  064702.  DOI: 10.1088/1674-1056/28/6/064702
    Abstract ( 570 )   HTML   PDF (9222KB) ( 167 )  

    Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a micro-flow is the direct simulation Monte Carlo (DSMC) method, which is used in this paper to investigate primary flow properties of supersonic gas in a circular micro-channel for different inflow conditions, such as free stream at different altitudes, with different incoming Mach numbers, and with different angles of attack. Simulation results indicate that the altitude and free stream incoming Mach number have a significant effect on the whole micro-channel flow field, whereas the angle of attack mainly affects the entrance part of micro-channel flow field. The fundamental mechanism behind the simulation results is also presented. With the increase of altitude, thr free stream would be partly prevented from entering into micro-channel. Meanwhile, the gas flow in micro-channel is decelerated, and the increase in the angle of attack also decelerates the gas flow. In contrast, gas flow in micro-channel is accelerated as free stream incoming Mach number increases. A noteworthy finding is that the rarefaction effects can become very dominant when the free stream incoming Mach number is low. In other words, a free stream with a larger incoming velocity is able to reduce the influence of the rarefaction effects on gas flow in the micro-channel.

    Relationship between characteristic lengths and effective Saffman length in colloidal monolayers near a water-oil interface
    Na Li(李娜), Wei Zhang(张伟), Wei Chen(陈唯)
    Chin. Phys. B, 2019, 28 (6):  064703.  DOI: 10.1088/1674-1056/28/6/064703
    Abstract ( 620 )   HTML   PDF (4895KB) ( 131 )  

    The hydrodynamic interactions (HIs) in colloidal monolayers are strongly influenced by the boundary conditions and can be directly described in terms of the cross-correlated diffusion of the colloid particles. In this work, we experimentally measured the cross-correlated diffusion in colloidal monolayers near a water-oil interface. The characteristic lengths of the system were obtained by introducing an effective Saffman length. The characteristic lengths of a particle monolayer near a water-oil interface were found to be anisotropic in the longitudinal and transverse directions. From these characteristic lengths, the master curves of cross-correlated diffusion are obtained, which universally describe the HIs near a liquid-liquid interface.

    Studies of flow field characteristics during the impact of a gaseous jet on liquid-water column
    Jian Wang(王健), Wen-Jun Ruan(阮文俊), Hao Wang(王浩), Li-Li Zhang(张莉莉)
    Chin. Phys. B, 2019, 28 (6):  064704.  DOI: 10.1088/1674-1056/28/6/064704
    Abstract ( 670 )   HTML   PDF (1569KB) ( 178 )  

    Both experimental and numerical studies were presented on the flow field characteristics in the process of gaseous jet impinging on liquid-water column. The effects of the impinging process on the working performance of rocket engine were also analyzed. The experimental results showed that the liquid-water had better flame and smoke dissipation effect in the process of gaseous jet impinging on liquid-water column. However, the interaction between the gaseous jet and the liquid-water column resulted in two pressure oscillations with large amplitude appearing in the combustion chamber of the rocket engine with instantaneous pressure increased by 17.73% and 17.93%, respectively. To analyze the phenomena, a new computational method was proposed by coupling the governing equations of the MIXTURE model with the phase change equations of water and the combustion equation of propellant. Numerical simulations were carried out on the generation of gas, the accelerate gas flow, and the mutual interaction between gaseous jet and liquid-water column. Numerical simulations showed that a cavity would be formed in the liquid-water column when gaseous jet impinged on the liquid-water column. The development speed of the cavity increased obviously after each pressure oscillation. In the initial stage of impingement, the gaseous jet was blocked due to the inertia effect of high-density water, and a large amount of gas gathered in the area between the nozzle throat and the gas-liquid interface. The shock wave was formed in the nozzle expansion section. Under the dual action of the reverse pressure wave and the continuously ejected high-temperature gas upstream, the shock wave moved repeatedly in the nozzle expansion section, which led to the flow of gas in the combustion chamber being blocked, released, re-blocked, and re-released. This was also the main reason for the pressure oscillations in the combustion chamber.

    The universal characteristic water content of aqueous solutions Hot!
    Xiao Huang(黄晓), Ze-Xian Cao(曹则贤), Qiang Wang(王强)
    Chin. Phys. B, 2019, 28 (6):  065101.  DOI: 10.1088/1674-1056/28/6/065101
    Abstract ( 752 )   HTML   PDF (424KB) ( 284 )  

    Raman measurements at room temperature reveal a characteristic concentration for a series of aqueous solutions of electrolytes, through which O-H stretching vibration of H2O or dilute HDO obviously changes their concentration dependence. This characteristic concentration is very consistent with another, through which the solutions undergo an abrupt change in their glass-forming ability. Interestingly, the molar ratio of water to solute at these two consistent concentration points is almost solute-type independent and about twice the hydration number of solutes. We suggest that just when the concentration increases above this characteristic concentration, bulk-like free water disappears in aqueous solutions and all water molecules among closely-packed hydrated solutes exhibit the characteristics of confined water.

    Quantum density functional theory studies of structural, elastic, and opto-electronic properties of ZMoO3 (Z=Ba and Sr) under pressure
    Saad Tariq, A A Mubarak, Saher Saad, M Imran Jamil, S M Sohail Gilani
    Chin. Phys. B, 2019, 28 (6):  066101.  DOI: 10.1088/1674-1056/28/6/066101
    Abstract ( 620 )   HTML   PDF (12389KB) ( 220 )  

    In continuation of our recent report on molybdates[Appl. Phys. A 124, 44 (2018)], the structural, electronic, elastic, and optical properties of ZMoO3 (Z=Ba and Sr) molybdates are investigated under pressure (10 GPa-50 GPa) comprehensively by deploying the density functional theory. Our investigations show that the studied compounds exhibit stable cubic phase with metallic attributes. The thermodynamic parameters such as enthalpy of formation, Debye, and melting temperatures of the compounds are observed to increase with pressure. While the Grüninsen parameter and the coefficient of super-plastic deformation decrease as the pressure increases. Mechanical properties elucidate an increase in measured values of hardness, bulk, shear, and young's moduli with pressure. Our results suggest that the studied compounds are useful in high pressure optoelectronic devices. The optical properties of BaMoO3 (BMO) and SrMoO3 (SMO) are computed for the radiation of up to 35 eV. The present compounds show beneficial optical applications in the anti-reflection coating, lenses, and the high avoiding solar heating applications in the variant applied pressure.

    Nanosheet-structured B4C with high hardness up to 42 GPa
    Chang-Chun Wang(王常春), Le-Le Song(宋乐乐)
    Chin. Phys. B, 2019, 28 (6):  066201.  DOI: 10.1088/1674-1056/28/6/066201
    Abstract ( 599 )   HTML   PDF (1328KB) ( 168 )  

    High-quality bulk boron carbide (B4C) is successfully prepared at high pressure and high temperature (HPHT) by using B4C powder as a precursor. The as-synthesized B4C possesses a nanosheet structure with a thickness value of 15 nm and a length of several dozen micrometers. Its Vickers hardness value and fracture toughness value are 42.4 GPa and 4.51 MPa·m1/2, respectively, which are superior to those of B4C obtained from spark plasma sintering due to its high densification and nanosheet structure. Additionally, it shows good property of oxidation resistance. In air, its oxidation resistance temperature is 1100 ℃ which is higher than that of diamond under the same test condition.

    Theoretical analysis of cross-plane lattice thermal conduction in graphite
    Yun-Feng Gu(顾云风)
    Chin. Phys. B, 2019, 28 (6):  066301.  DOI: 10.1088/1674-1056/28/6/066301
    Abstract ( 612 )   HTML   PDF (2039KB) ( 147 )  

    A theoretical analysis of the cross-plane lattice thermal conduction in graphite is performed by using first-principles calculations and in the single-mode relaxation time approximation. The out-of-plane phonon acoustic mode ZA and optical mode ZO' have almost 80% and 20% of contributions to cross-plane heat transfer, respectively. However, these two branches have a small part of total specific heat above 300 K. Phonons in the central 16% of Brillouin zone contribute 80% of cross-plane transport. If the group velocity angle with respect to the graphite layer normal is less than 30circ, then the contribution is 50% at 300 K. The ZA phonons with long cross-plane mean free path are focused in the cross-plane direction, and the largest mean free path is on the order of several micrometers at room temperature. The average value of cross-plane mean free path at 300 K is 112 nm for ZA phonons with group velocity angle with respect to the layer normal being less than 15circ. The average value is dropped to 15 nm when phonons of all branches in the whole Brillouin zone are taken into account, which happens because most phonons have small or even no contributions.

    Calculation of the infrared frequency and the damping constant (full width at half maximum) for metal organic frameworks
    M Kurt, H Yurtseven, A Kurt, S Aksoy
    Chin. Phys. B, 2019, 28 (6):  066401.  DOI: 10.1088/1674-1056/28/6/066401
    Abstract ( 520 )   HTML   PDF (1110KB) ( 177 )  

    The ρ(NH2) infrared (IR) frequencies and the corresponding full width at half maximum (FWHM) values for (CH3)2NH2FeM(HCOO)6 (DMFeM, M=Ni, Zn, Cu, Fe, and Mg) are analyzed at various temperatures by using the experimental data from the literature. For the analysis of the IR frequencies of the ρ (NH2) mode which is associated with the structural phase transitions in those metal structures, the temperature dependence of the mode frequency is assumed as an order parameter and the IR frequencies are calculated by using the molecular field theory. Also, the temperature dependence of the IR frequencies and of the damping constant as calculated from the models of pseudospin (dynamic disorder of dimethylammonium (DMA+) cations)-phonon coupling (PS) and of the energy fluctuation (EF), is fitted to the observed data for the wavenumber and FWHM of the ρ (NH2) IR mode of the niccolites studied here. We find that the observed behavior of the IR frequencies and the FWHM of this mode can be described adequately by the models studied for the crystalline structures of interest. This method of calculating the frequencies (IR and Raman) and FWHM of modes which are responsible for the phase transitions can also be applied to some other metal organic frameworks.

    Pressure-induced isostructural phase transition in α-Ni(OH)2 nanowires
    Xin Ma(马鑫), Zhi-Hui Li(李志慧), Xiao-Ling Jing(荆晓玲), Hong-Kai Gu(顾宏凯), Hui Tian(田辉), Qing Dong(董青), Peng Wang(王鹏), Ran Liu(刘然), Bo Liu(刘波), Quan-Jun Li(李全军), Zhen Yao(姚震), Bing-Bing Liu(刘冰冰)
    Chin. Phys. B, 2019, 28 (6):  066402.  DOI: 10.1088/1674-1056/28/6/066402
    Abstract ( 705 )   HTML   PDF (2533KB) ( 231 )  

    High pressure structural phase transition of monoclinic paraotwayite type α-Ni(OH)2 nanowires with a diameter of 15 nm-20 nm and a length of several micrometers were studied by synchrotron x-ray diffraction (XRD) and Raman spectra. It is found that the α-Ni(OH)2 nanowires experience an isostructural phase transition associated with the amorphization of the H-sublattice of hydroxide in the interlayer spaces of the two-dimensional crystal structure at 6.3 GPa-9.3 GPa. We suggest that the isostructural phase transition can be attributed to the amorphization of the H-sublattice. The bulk moduli for the low pressure phase and the high pressure phase are 41.2 (4.2) GPa and 94.4 (5.6) GPa, respectively. Both the pressure-induced isostructural phase transition and the amorphization of the H-sublattice in the α-Ni(OH)2 nanowires are reversible upon decompression. Our results show that the foreign anions intercalated between the α-Ni(OH)2 layers play important roles in their structural phase transition.

    Real-space observation on standing configurations of phenylacetylene on Cu (111) by scanning probe microscopy
    Jing Qi(戚竞), Yi-Xuan Gao(高艺璇), Li Huang(黄立), Xiao Lin(林晓), Jia-Jia Dong(董佳家), Shi-Xuan Du(杜世萱), Hong-Jun Gao(高鸿钧)
    Chin. Phys. B, 2019, 28 (6):  066801.  DOI: 10.1088/1674-1056/28/6/066801
    Abstract ( 529 )   HTML   PDF (3441KB) ( 162 )  

    The adsorption configurations of molecules adsorbed on substrates can significantly affect their physical and chemical properties. A standing configuration can be difficult to determine by traditional techniques, such as scanning tunneling microscopy (STM) due to the superposition of electronic states. In this paper, we report the real-space observation of the standing adsorption configuration of phenylacetylene on Cu (111) by non-contact atomic force microscopy (nc-AFM). Deposition of phenylacetylene at 25 K shows featureless bright spots in STM images. Using nc-AFM, the line features representing the C-H and C-C bonds in benzene rings are evident, which implies a standing adsorption configuration. Further density functional theory (DFT) calculations reveal multiple optimized adsorption configurations with phenylacetylene breaking its acetylenic bond and forming C-Cu bond(s) with the underlying copper atoms, and hence stand on the substrate. By comparing the nc-AFM simulations with the experimental observation, we identify the standing adsorption configuration of phenylacetylene on Cu (111). Our work demonstrates an application of combining nc-AFM measurements and DFT calculations to the study of standing molecules on substrates, which enriches our knowledge of the adsorption behaviors of small molecules on solid surfaces at low temperatures.

    Formation and preferred growth behavior of grooved seed silicon substrate for kerfless technology
    Jing-Yuan Yan(鄢靖源), Yong-Wei Wang(王勇炜), Yong-Ming Guo(郭勇明), Wei Zhang(张伟), Cong Wang(王聪), Bao-Li An(安保礼), Dong-Fang Liu(刘东方)
    Chin. Phys. B, 2019, 28 (6):  066802.  DOI: 10.1088/1674-1056/28/6/066802
    Abstract ( 608 )   HTML   PDF (1427KB) ( 142 )  

    Kerfless technology is a promising alternative for reducing cost and providing flexible thin crystals in silicon-based semiconductors. In this work we propose a protruded seed substrate technology to prepare flexible monocrystalline Si thin film economically. Grooved seed substrate is fabricated by using SiNx thin film as a mask for the wet-etching and thermal oxidation process. After the SiNx layer on the wedged strip is removed by hot phosphoric acid, the pre-defined structured substrate is achieved with the top of the strip serving as the seed site where there is no oxide layer. And a preferred growth of epitaxial Si on the substrate is performed by introducing an intermittent feed method for silicon source gas. The technique in this paper obviously enhances the mechanical stability of the seed structure and the growth behavior on the seed sites, compared with our previous techniques, so this technique promises to be used in the industrial fabrication of flexible Si-based devices.

    Nonlocal effect on resonant radiation force exerted on semiconductor coupled quantum well nanostructures
    Jin-Ke Zhang(张金珂), Ting-Ting Zhang(张婷婷), Yu-Liang Zhang(张玉亮), Guang-Hui Wang(王光辉), Dong-Mei Deng(邓冬梅)
    Chin. Phys. B, 2019, 28 (6):  066803.  DOI: 10.1088/1674-1056/28/6/066803
    Abstract ( 660 )   HTML   PDF (562KB) ( 120 )  

    Based on the microscopic nonlocal optical response theory, the resonant radiation force exerted on a semiconductor-coupled quantum well nanostructure (CQWN), induced by the nonlocal interaction between lasers and electrons in conduction bands, is investigated for two different polarized states. The numerical results show that the spatial nonlocality of optical response can cause a radiation shift (blue-shift) for the spectrum of the resonant radiation force, which is dependent on the CQWN width ratio, the barrier height, and polarized states sensitively. It is also confirmed that the resonant radiation force is steerable by the incident and polarized directions of incident light. This work may provide an advantageous method for detecting internal quantum properties of nanostructures, and open novel and raising possibilities for optical manipulation of nano-objects using laser-induced radiation force.

    Temperature-dependent subband mobility characteristics in n-doped silicon junctionless nanowire transistor
    Ya-Mei Dou(窦亚梅), Wei-Hua Han(韩伟华), Yang-Yan Guo(郭仰岩), Xiao-Song Zhao(赵晓松), Xiao-Di Zhang(张晓迪), Xin-Yu Wu(吴歆宇), Fu-Hua Yang(杨富华)
    Chin. Phys. B, 2019, 28 (6):  066804.  DOI: 10.1088/1674-1056/28/6/066804
    Abstract ( 620 )   HTML   PDF (600KB) ( 117 )  

    We have investigated the temperature-dependent effective mobility characteristics in impurity band and conduction subbands of n-doped silicon junctionless nanowire transistors. It is found that the electron effective mobility of the first subband in 2-fold valleys is higher than that of the second subband in 4-fold valleys. There exists a maximum value for the effective subband mobilities at low temperatures, which is attributed to the increase of thermally activated electrons from the ionized donors in the impurity band. The experimental results indicate that the effective subband mobility is temperature-dependent on the electron interactions by thermal activation, impurity scattering, and intersubband scattering.

    Magnetotransport properties of graphene layers decorated with colloid quantum dots
    Ri-Jia Zhu(朱日佳), Yu-Qing Huang(黄雨青), Jia-Yu Li(李佳玉), Ning Kang(康宁), Hong-Qi Xu(徐洪起)
    Chin. Phys. B, 2019, 28 (6):  067201.  DOI: 10.1088/1674-1056/28/6/067201
    Abstract ( 603 )   HTML   PDF (754KB) ( 178 )  

    The hybrid graphene-quantum dot devices can potentially be used to tailor the electronic, optical, and chemical properties of graphene. Here, the low temperature electronic transport properties of bilayer graphene decorated with PbS colloid quantum dots (CQDs) have been investigated in the weak or strong magnetic fields. The presence of the CQDs introduces additional scattering potentials that alter the magnetotransport properties of the graphene layers, leading to the observation of a new set of magnetoconductance oscillations near zero magnetic field as well as the high-field quantum Hall regime. The results bring about a new strategy for exploring the quantum interference effects in two-dimensional materials which are sensitive to the surrounding electrostatic environment, and open up a new gateway for exploring the graphene sensing with quantum interference effects.

    Time-dependent first-principles study of optical response of BaTiO3 quantum dots coupled with silver nanowires
    Bo-Xun Han(韩博逊), Hong Zhang(张红)
    Chin. Phys. B, 2019, 28 (6):  067301.  DOI: 10.1088/1674-1056/28/6/067301
    Abstract ( 434 )   HTML   PDF (1704KB) ( 139 )  

    All-inorganic perovskite quantum dots (QDs) have drawn much attention due to their prominent quantum-size effects and highly tunable optical properties. Tuning the size of perovskite QDs is attractive for many potential applications. For instance, smaller QDs exhibit more evident quantum properties than larger QDs, but present a blue-shifted spectrum, which limits their applications. Here, we conduct a systematically theoretical analysis about the optical response and plasmon resonance of comparatively small barium titanate quantum dots (BTO-QDs) coupled with silver (Ag) nanowires based on time-dependent density functional theory (TDDFT). Our results show that the silver nanowires can induce an intense optical response respectively in the infrared and visible region to eliminate the spectrum-shift. Furthermore, the absorption spectrum and plasmon resonance can be effectively modified by either altering the position of the silver nanowires or changing the thickness of the BTO-QDs. More importantly, these two methods can act simultaneously, this maybe provide a new approach to implementing the quantum control.

    Analysis of displacement damage effects on bipolar transistors irradiated by spallation neutrons
    Yan Liu(刘岩), Wei Chen(陈伟), Chaohui He(贺朝会), Chunlei Su(苏春垒), Chenhui Wang(王晨辉), Xiaoming Jin(金晓明), Junlin Li(李俊霖), Yuanyuan Xue(薛院院)
    Chin. Phys. B, 2019, 28 (6):  067302.  DOI: 10.1088/1674-1056/28/6/067302
    Abstract ( 633 )   HTML   PDF (1403KB) ( 134 )  

    Displacement damage induced by neutron irradiation in China Spallation Neutron Source (CSNS) is studied on bipolar transistors with lateral PNP, substrate PNP, and vertical NPN configurations, respectively. Comparison of the effects on different type transistors is conducted based on displacement damage factor, and the differences are analyzed through minority carrier lifetime calculation and structure analysis. The influence of CSNS neutrons irradiation on the lateral PNP transistors is analyzed by the gate-controlled method, including the oxide charge accumulation, surface recombine velocity, and minority carrier lifetime. The results indicate that the total ionizing dose in CSNS neutron radiation environment is negligible in this study. The displacement damage factors based on 1-MeV equivalent neutron flux of different transistors are consistent between Xi'an pulse reactor (XAPR) and CSNS.

    Neutral excitation and bulk gap of fractional quantum Hall liquids in disk geometry
    Wu-Qing Yang(杨武庆), Qi Li(李骐), Lin-Peng Yang(杨林鹏), Zi-Xiang Hu(胡自翔)
    Chin. Phys. B, 2019, 28 (6):  067303.  DOI: 10.1088/1674-1056/28/6/067303
    Abstract ( 749 )   HTML   PDF (1147KB) ( 212 )  

    For the numerical simulation of the fractional quantum Hall (FQH) effects on a finite disk, the rotational symmetry is the only symmetry that is used in diagonalizing the Hamiltonian. In this work, we propose a method of using the weak translational symmetry for the center of mass of the many-body system. With this approach, the bulk properties, such as the energy gap and the magneto-roton excitation are consistent with those in the closed manifolds like the sphere and torus. As an application, we consider the FQH phase and its phase transition in the fast rotated dipolar fermions. We thus demonstrate the disk geometry having versatility in analyzing the bulk properties beside the usual edge physics.

    Method of evaluating interface traps in Al2O3/AlGaN/GaN high electron mobility transistors
    Si-Qin-Gao-Wa Bao(包斯琴高娃), Xiao-Hua Ma(马晓华), Wei-Wei Chen(陈伟伟), Ling Yang(杨凌), Bin Hou(侯斌), Qing Zhu(朱青), Jie-Jie Zhu(祝杰杰), Yue Hao(郝跃)
    Chin. Phys. B, 2019, 28 (6):  067304.  DOI: 10.1088/1674-1056/28/6/067304
    Abstract ( 849 )   HTML   PDF (591KB) ( 198 )  

    In this paper, the interface states of the AlGaN/GaN metal-insulator-semiconductor (MIS) high electron mobility transistors (HEMTs) with an Al2O3 gate dielectric are systematically evaluated. By frequency-dependent capacitance and conductance measurements, trap density and time constant at Al2O3/AlGaN and AlGaN/GaN interface are determined. The experimental results reveal that the density of trap states and the activation energy at the Al2O3/AlGaN interface are much higher than at the AlGaN/GaN interface. The photo-assisted capacitance-voltage measurements are performed to characterize the deep-level traps located near mid-gap at the Al2O3/AlGaN interface, which indicates that a density of deep-level traps is lower than the density of the shallow-level states.

    Aging mechanism of GaN-based yellow LEDs with V-pits
    Tian-Ran Zhang(张天然), Fang Fang(方芳), Xiao-Lan Wang(王小兰), Jian-Li Zhang(张建立), Xiao-Ming Wu(吴小明), Shuan Pan(潘栓), Jun-Lin Liu(刘军林), Feng-Yi Jiang(江风益)
    Chin. Phys. B, 2019, 28 (6):  067305.  DOI: 10.1088/1674-1056/28/6/067305
    Abstract ( 656 )   HTML   PDF (1504KB) ( 191 )  

    GaN-based yellow light-emitting diodes (LEDs) on Si substrates are aged at a direct current density of 50 A/cm2 for 500 h. After the aging process, it can be found that the LEDs have a stable electrical property but their light output power is decayed by 4.01% at 35 A/cm2. Additionally, the aging mechanism of GaN-based yellow LED is analyzed. It is found that the decay of light output power may be attributed to the following two reasons:one is the increase of Shockley-Rrad-Hall recombination and the other is the change of the transport path of holes via V-pits after aging, which may induce the radiative recombination current to decrease. In this paper, not only the aging mechanism of GaN-based yellow LED is investigated, but also a new possible research direction in LED aging is given.

    Crystal structures and sign reversal Hall resistivities in iron-based superconductors Lix(C3H10N2)0.32FeSe (0.15 < x < 0.4) Hot!
    Rui-Jin Sun(孙瑞锦), Shi-Feng Jin(金士锋), Jun Deng(邓俊), Mu-Nan Hao(郝木难), Lin-Lin Zhao(赵琳琳), Xiao Fan(范晓), Xiao-Ning Sun(孙晓宁), Jian-Gang Guo(郭建刚), Lin Gu(谷林)
    Chin. Phys. B, 2019, 28 (6):  067401.  DOI: 10.1088/1674-1056/28/6/067401
    Abstract ( 567 )   HTML   PDF (6543KB) ( 285 )  

    Heavy electron-doped FeSe-derived materials have attracted attention due to their uncommon electronic structures with only ‘electron pockets’, and they are different from other iron-based superconductors. Here, we report the crystal structures, superconductivities and normal state properties of two new Li-doped FeSe-based materials, i.e., Li0.15(C3H10N2)0.32FeSe (P-4) and Lix(C3H10N2)0.32FeSe (P4/nmm, 0.25 < x < 0.4) with superconducting transition temperatures ranging from 40 K to 46 K. The determined crystal structures reveal a coupling between Li concentration and the orientation of 1,3-diaminopropane molecules within the largely expanded FeSe layers. Superconducting fluctuations appear in the resistivity of the two superconductors and are fitted in terms of the quasi two-dimensional (2D) Lawrence-Doniach model. The existence of a crossing point and scaling behavior in the T-dependence of diamagnetic response also suggests that the two superconductors belong to the quasi-2D system. Interestingly, with the increase of temperature, a sign of Hall coefficient (RH) reversing from negative to positive is observed at~185 K in both phases, suggesting that ‘hole pockets’ emerge in these electron-doped FeSe materials. First principle calculations indicate that the increase in FeSe layer distance will lift up a ‘hole band’ associated with dx2-y2 character and increase the hole carriers. Our findings suggest that the increase in two dimensionalities may lead to the sign-reversal Hall resistivity in Lix(C3H10N2)0.32FeSe at high temperature.

    Enhancing superconductivity of ultrathin YBa2Cu3O7-δ films by capping non-superconducting oxides
    Hai Bo(薄海), Tianshuang Ren(任天爽), Zheng Chen(陈峥), Meng Zhang(张蒙), Yanwu Xie(谢燕武)
    Chin. Phys. B, 2019, 28 (6):  067402.  DOI: 10.1088/1674-1056/28/6/067402
    Abstract ( 680 )   HTML   PDF (1070KB) ( 288 )  

    In this study, we have explored the ways to fabricate and optimize high-quality ultrathin YBa2Cu3O7-δ (YBCO) films grown on single-crystal (001) SrTiO3 substrates. Nearly atomic-flat YBCO films are obtained by pulsed laser deposition. Our result shows that the termination of SrTiO3 has only a negligible effect on the properties of YBCO. In contrast, we found that capping a non-superconducting oxide layer can generally enhance the superconductivity of YBCO. PrBa2Cu3O7, La2CuO4, LaMnO3, SrTiO3, and LaAlO3 have been examined as capping layers, and the minimum thickness of superconducting YBCO with capping is~2 unit cells-3 unit cells. This result might be useful in constructing good-performance YBCO-based field effect devices.

    TOPICAL REVIEW—Topological superconductors
    Topological superconductivity in a Bi2Te3/NbSe2 heterostructure: A review
    Hao Zheng(郑浩), Jin-Feng Jia(贾金锋)
    Chin. Phys. B, 2019, 28 (6):  067403.  DOI: 10.1088/1674-1056/28/6/067403
    Abstract ( 1083 )   HTML   PDF (2028KB) ( 547 )  

    Topological superconductors carry globally protected gapless boundary excitations, which are robust under local perturbations, and thus exhibit both fundamental and applicational importance. An unconventional pairing with p-wave symmetry, such as a nontrivial topology in the superconductor's wavefunction, is required to generate a non-zero Berry phase. Until now, the Bi2Te3/2H-NbSe2 heterostructure has proven to be a practical way to realize a topological superconductor in real materials. This complex system, where odd numbers of spin-momentum locked Dirac cone surface states on the topological insulator Bi2Te3 become superconducting, induced by the proximate effect from the underlying s-wave superconductor 2H-NbSe2, realizes an effective two-dimensional (2D) spinless px + i py topological superconductor. In this review article, we summarize the recent experimental progress of the successful synthesis of Bi2Te3/2H-NbSe2 heterostructures using molecular beam epitaxy, determining the thickness limit of the heterostructure, detecting the long thought Majorana quasiparticle inside a magnetic vortex core state by means of scanning tunneling microscopy and demonstration of the unique spatial and spin properties of a Majorana zero mode.

    Critical behavior and magnetocaloric effect in magnetic Weyl semimetal candidate Co2-xZrSn
    Tianlin Yu(于天麟), Xiaoyun Yu(余骁昀), En Yang(杨恩), Chang Sun(孙畅), Xiao Zhang(张晓), Ming Lei(雷鸣)
    Chin. Phys. B, 2019, 28 (6):  067501.  DOI: 10.1088/1674-1056/28/6/067501
    Abstract ( 632 )   HTML   PDF (808KB) ( 239 )  

    We investigate the critical exponents and magnetocaloric effect of Co2-xZrSn polycrystal. The Co2-xZrSn undergoes a second-order ferromagnetism phase transition around the Curie temperature of Tc~280 K. The critical behavior in the vicinity of the magnetic phase transition has been investigated by using modified Arrott plot and Kouvel-Fisher methods. The obtained critical exponents, β, γ, and δ can be well described by the scaling theory. The determined exponents of Co2-xZrSn obey the mean-field model with a long-range magnetic interaction. In addition, the maximum magnetic entropy change -ΔSMmax of Co2-xZrSn is about 0.57 J·kg-1·K-1 and the relative cooling power (RCP) is 14.68 J·kg-1 at 50 kOe (1 Oe=79.5775 A·m-1).

    Fabrication and characterization of one-port surface acoustic wave resonators on semi-insulating GaN substrates
    Xue Ji(吉雪), Wen-Xiu Dong(董文秀), Yu-Min Zhang(张育民), Jian-Feng Wang(王建峰), Ke Xu(徐科)
    Chin. Phys. B, 2019, 28 (6):  067701.  DOI: 10.1088/1674-1056/28/6/067701
    Abstract ( 647 )   HTML   PDF (1232KB) ( 177 )  

    One-port surface acoustic wave resonators (SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy (HVPE) and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between[1120] GaN and[1100] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film (~1%) reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8-μ Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.

    Gradient refractive structured NiCr thin film absorber for pyroelectric infrared detectors
    Yunlu Lian(练芸路), He Yu(于贺), Zhiqing Liang(梁志清), Xiang Dong(董翔)
    Chin. Phys. B, 2019, 28 (6):  067801.  DOI: 10.1088/1674-1056/28/6/067801
    Abstract ( 634 )   HTML   PDF (898KB) ( 128 )  

    A gradient refractive structured NiCr film that has a high extinction coefficient at far infrared range (8-μm-24 μm) is presented as an absorber for pyroelectric infrared detectors. The absorber features high absorption efficiency due to the low reflection off the structured surface and high absorption across the film thickness. The refractive index and extinction coefficient are extracted using spectroscopic ellipsometry. It is found that the single NiCr film exhibits an increasing refractive index as the gas atmosphere pressure increases, hence the three-layer gradient NiCr absorber can be fabricated by adjusting the gas atmosphere pressure during sputtering deposition. Essential Macleod software has been used to generate an efficient film structure design and the calculations show similar absorptance trend compared to the experimental measurement result. The results indicate that the gradient refractive structured metal thin film absorber can provide high absorption for applications in thermal sensing.

    Structural stability and vibrational characteristics of CaB6 under high pressure
    Mingkun Liu(刘明坤), Can Tian(田灿), Xiaoli Huang(黄晓丽), Fangfei Li(李芳菲), Yanping Huang(黄艳萍), Bingbing Liu(刘冰冰), Tian Cui(崔田)
    Chin. Phys. B, 2019, 28 (6):  068101.  DOI: 10.1088/1674-1056/28/6/068101
    Abstract ( 635 )   HTML   PDF (1147KB) ( 142 )  

    In situ Raman spectroscopy and x-ray diffraction measurements are used to explore the structural stability of CaB6 at high pressures and room temperature. The results show no evidence of structural phase transitions up to at least 40 GPa. The obtained equation of state with smooth pressure dependencies yields a zero-pressure isothermal bulk modulus B0=170 (5) GPa, which agrees well with the previous measurements. The frequency shifts for A1g, Eg, and T2g vibrational modes of polycrystalline CaB6 are obtained with pressure uploading. As the pressure increases, all the vibration modes have smooth monotonic pressure dependence. The Grüneisen parameter of Eg modes is the largest, indicating its largest dependence on the volume of a crystal lattice.

    Direct deposition of graphene nanowalls on ceramic powders for the fabrication of a ceramic matrix composite Hot!
    Hai-Tao Zhou(周海涛), Da-Bo Liu(刘大博), Fei Luo(罗飞), Ye Tian(田野), Dong-Sheng Chen(陈冬生), Bing-Wei Luo(罗炳威), Zhang Zhou(周璋), Cheng-Min Shen(申承民)
    Chin. Phys. B, 2019, 28 (6):  068102.  DOI: 10.1088/1674-1056/28/6/068102
    Abstract ( 760 )   HTML   PDF (1519KB) ( 340 )  

    Uniform mixing of ceramic powder and graphene is of great importance for producing ceramic matrix composite. In this study, graphene nanowalls (GNWs) are directly deposited on the surface of Al2O3 and Si3N4 powders using chemical vapor deposition system to realize the uniform mixing. The morphology and the initial stage of the growth process are investigated. It is found that the graphitic base layer is initially formed parallel to the powder surface and is followed by the growth of graphene nanowalls perpendicular to the surface. Moreover, the lateral length of the graphene sheet could be well controlled by tuning the growth temperature. GNWs/Al2O3 powder is consolidated by using sparking plasma sintering method and several physical properties are measured. Owing to the addition of GNWs, the electrical conductivity of the bulk alumina is significantly increased.

    Fluorescence spectra of colloidal self-assembled CdSe nano-wire on substrate of porous Al2O3/Au nanoparticles
    Xin Zhang(张欣), Li-Ping Shao(邵丽萍), Man Peng(彭嫚), Zhong-Chen Bai(白忠臣), Zheng-Ping Zhang(张正平), Shui-Jie Qin(秦水介)
    Chin. Phys. B, 2019, 28 (6):  068103.  DOI: 10.1088/1674-1056/28/6/068103
    Abstract ( 549 )   HTML   PDF (1337KB) ( 158 )  

    We present a self-assembly method to prepare array nano-wires of colloidal CdSe quantum dots on a substrate of porous Al2O3 film modified by gold nanoparticles. The photoluminescence (PL) spectra of nanowires are in situ measured by using a scanning near-field optical microscopy (SNOM) probe tip with 100-nm aperture on the scanning near-field optical microscope. The results show that the binding sites from the edge of porous Al2O3 nanopores are combined with the carboxyl of CdSe quantum dots' surface to form an array of CdSe nanowires in the process of losing background solvent because of the gold nanoparticles filling the nano-holes of porous Al2O3 film. Compared with the area of non-self-assembled nano-wire, the fluorescence on the Al2O3/Au/CdSe interface is significantly enhanced in the self-assembly nano-wire regions due to the electron transfer conductor effect of the gold nanoparticles' surface. In addition, its full width at half maximum (FWHM) is also obviously widened. The method of enhancing fluorescence and energy transfer can widely be applied to photodetector, photocatalysis, optical display, optical sensing, and biomedical imaging, and so on.

    Spin glassy behavior and large exchange bias effect in cubic perovskite Ba0.8Sr0.2FeO3-δ
    Yu-Xuan Liu(刘宇轩), Zhe-Hong Liu(刘哲宏), Xu-Bin Ye(叶旭斌), Xu-Dong Shen(申旭东), Xiao Wang(王潇), Bo-Wen Zhou(周博文), Guang-Hui Zhou(周光辉), You-Wen Long(龙有文)
    Chin. Phys. B, 2019, 28 (6):  068104.  DOI: 10.1088/1674-1056/28/6/068104
    Abstract ( 616 )   HTML   PDF (1770KB) ( 196 )  

    A single-phase iron oxide Ba0.8Sr0.2FeO3-δ with a simple cubic perovskite structure in Pm-3m symmetry is successfully synthesized by a solid-state reaction method in O2 flow. The oxygen content is determined to be about 2.81, indicating the formation of mixed Fe3+ and Fe4+ charge states with a disorder fashion. As a result, the compound shows small-polaron conductivity behavior, as well as spin glassy features arising from the competition between the ferromagnetic interaction and the antiferromagnetic interaction. Moreover, the competing interactions also give rise to a remarkable exchange bias effect in Ba0.8Sr0.2FeO2.81, providing an opportunity to use it in spin devices.

    Influence of carbon coating on the electrochemical performance of SiO@C/graphite composite anode materials
    Hao Lu(陆浩), Junyang Wang(汪君洋), Bonan Liu(刘柏男), Geng Chu(褚赓), Ge Zhou(周格), Fei Luo(罗飞), Jieyun Zheng(郑杰允), Xiqian Yu(禹习谦), Hong Li(李泓)
    Chin. Phys. B, 2019, 28 (6):  068201.  DOI: 10.1088/1674-1056/28/6/068201
    Abstract ( 770 )   HTML   PDF (2186KB) ( 225 )  

    Silicon monoxide (SiO) has been considered as one of the most promising anode materials for next generation high-energy-density Li-ion batteries (LiBs) thanks to its high theoretical capacity. However, the poor intrinsic electronic conductivity and large volume change during lithium intercalation/de-intercalation restrict its practical applications. Fabrication of SiO/C composites is an effective way to overcome these problems. Herein, a series of micro-sized SiO@C/graphite (SiO@C/G) composite anode materials, with designed capacity of 600 mAh·g-1, are successfully prepared through a pitch pyrolysis reaction method. The electrochemical performance of SiO@C/G composite anodes with different carbon coating contents of 5 wt%, 10 wt%, 15 wt%, and 35 wt% is investigated. The results show that the SiO@C/G composite with 15-wt% carbon coating content exhibits the best cycle performance, with a high capacity retention of 90.7% at 25 ℃ and 90.1% at 45 ℃ after 100 cycles in full cells with LiNi0.5Co0.2Mn0.3O2 as cathodes. The scanning electron microscope (SEM) and electrochemistry impedance spectroscopy (EIS) results suggest that a moderate carbon coating layer can promote the formation of stable SEI film, which is favorable for maintaining good interfacial conductivity and thus enhancing the cycling stability of SiO electrode.

    Improved electrochemical performance of Li(Ni0.6Co0.2Mn0.2)O2 at high charging cut-off voltage with Li1.4Al0.4Ti1.6(PO4)3 surface coating Hot!
    Yi Wang(王怡), Bo-Nan Liu(刘柏男), Ge Zhou(周格), Kai-Hui Nie(聂凯会), Jie-Nan Zhang(张杰男), Xi-Qian Yu(禹习谦), Hong Li(李泓)
    Chin. Phys. B, 2019, 28 (6):  068202.  DOI: 10.1088/1674-1056/28/6/068202
    Abstract ( 1197 )   HTML   PDF (1143KB) ( 836 )  

    Li(Ni0.6Co0.2Mn0.2)O2 has been surface-modified by the lithium-ion conductor Li1.4Al0.4Ti1.6(PO4)3 via a facile mechanical fusion method. The annealing temperature during coating process shows a strong impact on the surface morphology and chemical composition of Li(Ni0.6Co0.2Mn0.2)O2. The 600-℃ annealed material exhibits the best cyclic stability at high charging cut-off voltage of 4.5 V (versus Li+/Li) with the capacity retention of 90.9% after 100 cycles, which is much higher than that of bare material (79%). Moreover, the rate capability and thermal stability are also improved by Li1.4Al0.4Ti1.6(PO4)3 coating. The enhanced performance can be attributed to the improved stability of interface between Li(Ni0.6Co0.2Mn0.2)O2 and electrolyte by Li1.4Al0.4Ti1.6(PO4)3 modification. The results of this work provide a possible method to design reliable cathode materials to achieve high energy density and long cycle life.

    Hard carbons derived from pine nut shells as anode materials for Na-ion batteries Hot!
    Hao Guo(郭浩), Kai Sun(孙凯), Yaxiang Lu(陆雅翔), Hongliang Wang(王洪亮), Xiaobai Ma(马小柏), Zhengyao Li(李正耀), Yong-Sheng Hu(胡勇胜), Dongfeng Chen(陈东风)
    Chin. Phys. B, 2019, 28 (6):  068203.  DOI: 10.1088/1674-1056/28/6/068203
    Abstract ( 739 )   HTML   PDF (2543KB) ( 222 )  

    Hard carbons as promising anode materials for Na-ion batteries (NIBs) have captured extensive attention because of their low operation voltage, easy synthesis process, and competitive specific capacity. However, there are still several disadvantages, such as high cost and low initial coulombic efficiency, which limit their large-scale commercial applications. Herein, pine nut shells (PNSs), a low-cost biomass waste, are used as precursors to prepare hard carbon materials. Via a series of washing and heat treatment procedures, a pine nut shell hard carbon (PNSHC)-1400 sample has been obtained and delivers a reversible capacity of around 300 mAh/g, a high initial coulombic efficiency of 84%, and good cycling performance. These excellent Na storage properties indicate that PNSHC is one of the most promising candidates of hard carbon anodes for NIBs.

    Development of 0.5-V Josephson junction array devices for quantum voltage standards
    Lanruo Wang(王兰若), Jinjin Li(李劲劲), Wenhui Cao(曹文会), Yuan Zhong(钟源), Zhonghua Zhang(张钟华)
    Chin. Phys. B, 2019, 28 (6):  068501.  DOI: 10.1088/1674-1056/28/6/068501
    Abstract ( 919 )   HTML   PDF (809KB) ( 172 )  

    The design, fabrication, and the characterization of a 0.5-V Josephson junction array device are presented for the quantum voltage standards in the National Institute of Metrology (NIM) of China. The device consists of four junction arrays, each of which has 1200 3-stacked Nb/NbxSi1-x/Nb junctions and an on-chip superconducting microwave circuit which is mainly a power divider enabling each Josephson array being loaded with an equal amount of microwave power. A direct current (dc) quantum voltage of about 0.5 V with a~1 -mA current margin of the 1st quantum voltage step is obtained. To further prove the quality of NIM device, a comparison between the NIM device with the National Institute of Standards and Technology (NIST) programmable Josephson voltage standard (PJVS) system device is conducted. The difference of the reproduced 0.5-V quantum voltage between the two devices is about 0.55 nV, which indicates good agreement between the two devices. With the homemade device, we have realized a precise and applicable 0.5-V applicable-level quantum voltage.

    Dark count rate and band to band tunneling optimization for single photon avalanche diode topologies
    Taha Haddadifam, Mohammad Azim Karami
    Chin. Phys. B, 2019, 28 (6):  068502.  DOI: 10.1088/1674-1056/28/6/068502
    Abstract ( 540 )   HTML   PDF (6731KB) ( 167 )  

    This paper proposes two optimal designs of single photon avalanche diodes (SPADs) minimizing dark count rate (DCR). The first structure is introduced as p+/pwell/nwell, in which a specific shallow pwell layer is added between p+ and nwell layers to decrease the electric field below a certain threshold. The simulation results show on average 19.7% and 8.5% reduction of p+/nwell structure's DCR comparing with similar previous structures in different operational excess bias and temperatures respectively. Moreover, a new structure is introduced as n+/nwell/pwell, in which a specific shallow nwell layer is added between n+ and pwell layers to lower the electric field below a certain threshold. The simulation results show on average 29.2% and 5.5% decrement of p+/nwell structure's DCR comparing with similar previous structures in different operational excess bias and temperatures respectively. It is shown that in higher excess biases (about 6 volts), the n+/nwell/pwell structure is proper to be integrated as digital silicon photomultiplier (dSiPM) due to low DCR. On the other hand, the p+/pwell/nwell structure is appropriate to be utilized in dSiPM in high temperatures (above 50 ℃) due to lower DCR value.

    Research on SEE mitigation techniques using back junction and p+ buffer layer in domestic non-DTI SiGe HBTs by TCAD
    Jia-Nan Wei(魏佳男), Chao-Hui He(贺朝会), Pei Li(李培), Yong-Hong Li(李永宏)
    Chin. Phys. B, 2019, 28 (6):  068503.  DOI: 10.1088/1674-1056/28/6/068503
    Abstract ( 614 )   HTML   PDF (1876KB) ( 141 )  

    In this paper we investigate two techniques for single event effect (SEE) mitigation by using back junction and p+ buffer layer in non-deep trench isolation (DTI) domestic silicon-germanium heterojunction bipolar transistors (SiGe HBTs) based on technology computer aided design (TCAD) simulation. The effectiveness of the two mitigation techniques and the influence of various structure parameters are investigated. Simulation results indicate that the two techniques are more effective in reducing collector charge collection induced by heavy ions striking at positions outside the collector-substrate (C-S) junction where charge collection is dominated by diffusion. By properly adjusting the parameters, charge collection of events outside the C-S junction can be reduced by more than an order of magnitude, while charge collection of events in the device center is halved without affecting the direct current (DC) and alternating current (AC) characteristics of the SiGe HBTs.

    Design and fabrication of 10-kV silicon-carbide p-channel IGBTs with hexagonal cells and step space modulated junction termination extension
    Zheng-Xin Wen(温正欣), Feng Zhang(张峰), Zhan-Wei Shen(申占伟), Jun Chen(陈俊), Ya-Wei He(何亚伟), Guo-Guo Yan(闫果果), Xing-Fang Liu(刘兴昉), Wan-Shun Zhao(赵万顺), Lei Wang(王雷), Guo-Sheng Sun(孙国胜), Yi-Ping Zeng(曾一平)
    Chin. Phys. B, 2019, 28 (6):  068504.  DOI: 10.1088/1674-1056/28/6/068504
    Abstract ( 691 )   HTML   PDF (1521KB) ( 269 )  

    10-kV 4H-SiC p-channel insulated gate bipolar transistors (IGBTs) are designed, fabricated, and characterized in this paper. The IGBTs have an active area of 2.25 mm2 with a die size of 3 mm×3 mm. A step space modulated junction termination extension (SSM-JTE) structure is introduced and fabricated to improve the blocking performance of the IGBTs. The SiC p-channel IGBTs with SSM-JTE termination exhibit a leakage current of only 50 nA at -10 kV. To improve the on-state characteristics of SiC IGBTs, the hexagonal cell (H-cell) structure is designed and compared with the conventional interdigital cell (I-cell) structure. At an on-state current of 50 A/cm2, the voltage drops of I-cell IGBT and H-cell IGBT are 10.1 V and 8.3 V respectively. Meanwhile, on the assumption that the package power density is 300 W/cm2, the maximum permissible current densities of the I-cell IGBT and H-cell IGBT are determined to be 34.2 A/cm2 and 38.9 A/cm2 with forward voltage drops of 8.8 V and 7.8 V, respectively. The differential specific on-resistance of I-cell structure and H-cell structure IGBT are 72.36 mΩ·cm2 and 56.92 mΩ·cm2, respectively. These results demonstrate that H-cell structure silicon carbide IGBT with SSM-JTE is a promising candidate for high power applications.

    Theoretical study of overstretching DNA-RNA hybrid duplex
    Dong-Ni Yang(杨东尼), Zhen-Sheng Zhong(钟振声), Wen-Zhao Liu(刘文钊), Thitima Rujiralai, Jie Ma(马杰)
    Chin. Phys. B, 2019, 28 (6):  068701.  DOI: 10.1088/1674-1056/28/6/068701
    Abstract ( 604 )   HTML   PDF (1050KB) ( 220 )  

    DNA-RNA hybrid (DRH) plays important roles in many biological processes. Here, we use a thermodynamic theory to analyze the free energy and unpeeling properties of the overstretching transition for the DRH molecule and compare the results with double-helix DNA. We report that the RNA strand of DRH is easier to get unpeeled than the DNA strand while the difficulty in unpeeling the double helix DNA lies in between. We also investigate the sequence effect, such as GC content and purine content, on the properties of unpeeling the DRH. Further, to study the temperature effect, the force-temperature phase diagram of DRH and DNA are calculated and compared. Finally, using a kinetic model, we calculate the force-extension curves in the DRH stretching and relaxation process under different pulling rates and temperatures. Our results show that both pulling rate and temperature have important influences on the stretching and relaxation kinetics of unpeeling the DRH. Putting all these results together, our work provides a comprehensive view of both the thermodynamics and kinetics in DRH overstretching.

    Uncovering offline event similarity of online friends by constructing null models
    Wenkuo Cui(崔文阔), Jing Xiao(肖婧), Ting Li(李婷), Xiaoke Xu(许小可)
    Chin. Phys. B, 2019, 28 (6):  068901.  DOI: 10.1088/1674-1056/28/6/068901
    Abstract ( 563 )   HTML   PDF (970KB) ( 121 )  

    The emergence of Event-based Social Network (EBSN) data that contain both social and event information has cleared the way to study the social interactive relationship between the virtual interactions and physical interactions. In existing studies, it is not really clear which factors affect event similarity between online friends and the influence degree of each factor. In this study, a multi-layer network based on the Plancast service data is constructed. The the user's events belongingness is shuffled by constructing two null models to detect offline event similarity between online friends. The results indicate that there is a strong correlation between online social proximity and offline event similarity. The micro-scale structures at multi-levels of the Plancast online social network are also maintained by constructing 0k-3k null models to study how the micro-scale characteristics of online networks affect the similarity of offline events. It is found that the assortativity pattern is a significant micro-scale characteristic to maintain offline event similarity. Finally, we study how structural diversity of online friends affects the offline event similarity. We find that the subgraph structure of common friends has no positive impact on event similarity while the number of common friends plays a key role, which is different from other studies. In addition, we discuss the randomness of different null models, which can measure the degree of information availability in privacy protection. Our study not only uncovers the factors that affect offline event similarity between friends but also presents a framework for understanding the pattern of human mobility.

ISSN 1674-1056   CN 11-5639/O4
, Vol. 28, No. 6

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