中国物理B

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Enhancement of water self-diffusion at super-hydrophilic surface with ordered water

于晓萌, 齐崇海, 王春雷

2018 (6): 60101-060101. doi: 10.1088/1674-1056/27/6/060101

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It has been well acknowledged that molecular water structures at the interface play an important role in the surface properties, such as wetting behavior or surface frictions. Using molecular dynamics simulation, we show that the water self-diffusion on the top of the first ordered water layer can be enhanced near a super-hydrophilic solid surface. This is attributed to the fewer number of hydrogen bonds between the first ordered water layer and water molecules above this layer, where the ordered water structures induce much slower relaxation behavior of water dipole and longer lifetime of hydrogen bonds formed within the first layer.

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Multiple Darboux-Bäcklund transformations via truncated Painlevé expansion and Lie point symmetry approach

刘帅君, 唐晓艳, 楼森岳

2018 (6): 60201-060201. doi: 10.1088/1674-1056/27/6/060201

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For a given truncated Painlevé expansion of an arbitrary nonlinear Painlevé integrable system, the residue with respect to the singularity manifold is known as a nonlocal symmetry, called the residual symmetry, which is proved to be localized to Lie point symmetries for suitable prolonged systems. Taking the Korteweg-de Vries equation as an example, the n-th binary Darboux-Bäcklund transformation is re-obtained by the Lie point symmetry approach accompanied by the localization of the n-fold residual symmetries.

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Distance-based formation tracking control of multi-agent systems with double-integrator dynamics

吴梓杏, 孙金生, 王希铭

2018 (6): 60202-060202. doi: 10.1088/1674-1056/27/6/060202

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This paper addresses the distance-based formation tracking problem for a double-integrator modeled multi-agent system (MAS) in the presence of a moving leader in d-dimensional space. Under the assumption that the state of leader can be obtained over fixed graphs, a distributed distance-based control protocol is designed for each double-integrator follower agent. The protocol consists of three terms:a gradient function term, a velocity consensus term, and a leader tracking term. Different shape stabilizing functions proposed in the literature can be applied to the gradient function term. The proposed controller allows all agents to both achieve the desired shape and reach the same velocity with moving leader by controlling the distances and velocity. Finally, we analyze the local asymptotic stability of the equilibrium set with center manifold theory. We validate the effectiveness of our approach through two examples.

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Stochastic evolutionary public goods game with first and second order costly punishments in finite populations

全吉, 储育青, 刘伟, 王先甲, 阳修康

2018 (6): 60203-060203. doi: 10.1088/1674-1056/27/6/060203

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We study the stochastic evolutionary public goods game with punishment in a finite size population. Two kinds of costly punishments are considered, i.e., first-order punishment in which only the defectors are punished, and second-order punishment in which both the defectors and the cooperators who do not punish the defective behaviors are punished. We focus on the stochastic stable equilibrium of the system. In the population, the evolutionary process of strategies is described as a finite state Markov process. The evolutionary equilibrium of the system and its stochastic stability are analyzed by the limit distribution of the Markov process. By numerical experiments, our findings are as follows. (i) The first-order costly punishment can change the evolutionary dynamics and equilibrium of the public goods game, and it can promote cooperation only when both the intensity of punishment and the return on investment parameters are large enough. (ii) Under the first-order punishment, the further imposition of the second-order punishment cannot change the evolutionary dynamics of the system dramatically, but can only change the probability of the system to select the equilibrium points in the “C+P” states, which refer to the co-existence states of cooperation and punishment. The second-order punishment has limited roles in promoting cooperation, except for some critical combinations of parameters. (iii) When the system chooses “C+P” states with probability one, the increase of the punishment probability under second-order punishment will further increase the proportion of the “P” strategy in the “C+P” states.

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Frequency response range of terahertz pulse coherent detection based on THz-induced time-resolved luminescence quenching

张曼, 杨振刚, 刘劲松, 王可嘉, 龚姣丽, 汪盛烈

2018 (6): 60204-060204. doi: 10.1088/1674-1056/27/6/060204

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It has been proposed previously that the coherent detection of a terahertz (THz) pulse can be achieved based on the time-resolved luminescence quenching. In this paper, we investigate the frequency response range of this novel detection technology by simulating the motion of carriers in gallium arsenide (GaAs) by the ensemble Monte Carlo method. At room temperature, for a direct-current (DC) voltage of 20 kV/cm applied to the semiconductor (GaAs) and sampling time of 140 fs, the luminescence quenching phenomena induced by terahertz pulses with different center frequencies are studied. The results show that the quenching efficiency is independent of the THz frequency when the frequency is in a range of 0.1 THz-4 THz. However, when the frequency exceeds 4 THz, the efficiency decreases with the increase of frequency. Therefore, the frequency response range is 0.1 THz-4 THz. Moreover, when the sampling time is changed to 100 fs, the frequency response range is extended to be approximately 0.1 THz-5.6 THz. This study of the frequency-dependent characteristics of the luminescence response to the THz pulse can provide a theoretical basis for the exploration of THz detection technology.

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Growth mode of helium crystal near dislocations in titanium

张宝玲, 王保文, 苏雪, 宋小勇, 李敏

2018 (6): 60205-060205. doi: 10.1088/1674-1056/27/6/060205

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The helium bubble structure and growth modes near dislocations in titanium are studied using the molecular dynamics method. A helium crystal with an HCP structure in titanium is found to have a lattice constant of 1.977 Å at 0 K. On either side of the slip plane, helium bubbles form in the (001) plane, but they are in different growth modes. On the side of the slip plane with full atomic layers, helium bubbles grow toward the slip plane and easily cross the slip plane. In the growth process, the position of the top surface of the helium bubble remains almost unchanged. On the other side of the slip plane, the helium bubble grows initially toward the dislocation core, but it is difficult to cross the slip plane, which results in growth in the opposite direction upon reaching the slip plane.

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Monogamy quantum correlation near the quantum phase transitions in the two-dimensional XY spin systems

秦猛, 任中洲, 张欣

2018 (6): 60301-060301. doi: 10.1088/1674-1056/27/6/060301

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We investigate the role of quantum correlation around the quantum phase transitions by using quantum renormalization group theory. Numerical analysis indicates that quantum correlation as well as quantum nonlocality can efficiently detect the quantum critical point in the two-dimensional XY systems. The nonanalytic behavior of the first derivative of quantum correlation is observed at the critical point as the size of the model increases. Furthermore, we discuss the quantum correlation distribution in this system based on the square of concurrence (SC) and square of quantum discord (SQD). The monogamous properties of SC and SQD are obtained. Particularly, we prove that the quantum critical point can also be achieved by monogamy score.

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Quantum speed-up capacity in different types of quantum channels for two-qubit open systems

吴薇, 刘辛, 王超

2018 (6): 60302-060302. doi: 10.1088/1674-1056/27/6/060302

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A potential acceleration of a quantum open system is of fundamental interest in quantum computation, quantum communication, and quantum metrology. In this paper, we investigate the “quantum speed-up capacity” which reveals the potential ability of a quantum system to be accelerated. We explore the evolutions of the speed-up capacity in different quantum channels for two-qubit states. We find that although the dynamics of the capacity is varying in different kinds of channels, it is positive in most situations which are considered in the context except one case in the amplitude-damping channel. We give the reasons for the different features of the dynamics. Anyway, the speed-up capacity can be improved by the memory effect. We find two ways which may be used to control the capacity in an experiment:selecting an appropriate coefficient of an initial state or changing the memory degree of environments.

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Quantum estimation of detection efficiency with no-knowledge quantum feedback

谢东, 徐春玲

2018 (6): 60303-060303. doi: 10.1088/1674-1056/27/6/060303

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We investigate that no-knowledge measurement-based feedback control is utilized to obtain the estimation precision of the detection efficiency. We show that no-knowledge measurement is the optimal way to estimate the detection efficiency. The higher precision can be achieved for the lower or larger detection efficiency. It is found that no-knowledge feedback can be used to cancel decoherence. No-knowledge feedback with a high detection efficiency can perform well in estimating frequency and detection efficiency parameters simultaneously; simultaneous estimation is better than independent estimation given by the same probes.

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Classical-driving-assisted coherence dynamics and its conservation

高德营, 高强, 夏云杰

2018 (6): 60304-060304. doi: 10.1088/1674-1056/27/6/060304

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We investigate the quantum coherence and quantum entanglement dynamics of a classical driven single atom coupled to a single-mode cavity. It is shown that the transformation between the atomic coherence and the atom-field entanglement exists, and can be improved by adjusting the classical driving field. The joint evolution of two identical single-body systems is also studied. The results show the quantum coherence transfers among composite subsystems, and the coherence conservation of composite subsystems is obtained. Moreover, the classical driving field can be used to suppress the decay of the coherence and entanglement, owing to considering the leaky cavity. The non-Markovian dynamics of the system is also discussed finally.

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Demonstration of quantum permutation parity determine algorithm in a superconducting qutrit

戴坤哲, 赵鹏, 李蒙蒙, 谭新生, 于海峰, 于扬

2018 (6): 60305-060305. doi: 10.1088/1674-1056/27/6/060305

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A quantum algorithm provides a new way in solving certain computing problems and usually faster than classical algorithms. Here we report an implementation of a quantum algorithm to determine the parity of permutation in a single three-dimensional (3D) superconducting transmon qutrit system. The experiment shows the capacity to speed up in a qutrit, which can also be extended to a multi-level system for solving high-dimensional permutation parity determination problem.

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Electronic and magnetic properties of semihydrogenated, fully hydrogenated monolayer and bilayer MoN₂ sheets

佘彦超, 魏昭, 罗开武, 李勇, 张云, 张蔚曦

2018 (6): 60306-060306. doi: 10.1088/1674-1056/27/6/060306

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Based on density functional theory, we investigate the electronic and magnetic properties of semi-hydrogenated, fully hydrogenated monolayer and bilayer MoN₂. We find that the AB stacking bilayer MoN₂ exhibits ferromagnetic coupling of intralayer and antiferromagnetic coupling of interlayer, however, the ground states of the semi-hydrogenated, fully hydrogenated monolayer and AA stcaking bilayer MoN₂ are nonmagnetic. The fully hydrogenated system has a quasi-direct band-gap of 2.5 eV, which has potential applications in light-emitting diode and photovoltaics. The AB stacking bilayer MoN₂ shows the Dirac cone at K point in BZ around Fermi energy. Furthermore, the interlayer of the AB stacking bilayer MoN₂ is subjected to a weak van der Waals force, while the interlayer of the AA stacking forms N-N covalent bond.

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Topologically protected edge gap solitons of interacting Bosons in one-dimensional superlattices

郭西华, 徐天赋, 刘承师

2018 (6): 60307-060307. doi: 10.1088/1674-1056/27/6/060307

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We comprehensively investigate the nontrivial states of an interacting Bose system in a cosine potential under the open boundary condition. Our results show that there exists a kind of stable localized state:edge gap solitons. We argue that the states originate from the eigenstates of independent edge parabolas. In particular, the edge gap solitons exhibit a nonzero topological-invariant behavior. The topological nature is due to the connection of the present model to the quantized adiabatic particle transport problem. In addition, the composition relations between the gap solitons and the extended states are also discussed.

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General series expression of eddy-current impedance for coil placed above multi-layer plate conductor

雷银照

2018 (6): 60308-060308. doi: 10.1088/1674-1056/27/6/060308

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This paper presents a closed expression of the layered-plate factor used to calculate the coil eddy-current impedance over the multi-layer plate conductor. By using this expression, the general series of eddy-current impedance can be written directly without solving the undetermined constant equations. The series expression is easy to use for theoretical analysis and programming. Experimental results show that calculated values and measured values are in agreement. As an application, when the bottom layer of the layered plate is a non-ferromagnetic thin layer conductor and the product of the thickness and conductivity of the layer remains unchanged, using the layered-plate factor expression proposed in this paper, it can be theoretically predicted that the eddy-current impedance curves corresponding to different thin layer thickness values will coincide.

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Dynamic characteristics in an external-cavity multi-quantum-well laser

颜森林

2018 (6): 60501-060501. doi: 10.1088/1674-1056/27/6/060501

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This paper outlines our studies of bifurcation, quasi-periodic road to chaos and other dynamic characteristics in an external-cavity multi-quantum-well laser with delay optical feedback. The bistable state of the laser is predicted by finding theoretically that the gain shifts abruptly between two values due to the feedback. We make a linear stability analysis of the dynamic behavior of the laser. We predict the stability scenario by using the characteristic equation while we make an approximate analysis of the stability of the equilibrium point and discuss the quantitative criteria of bifurcation. We deduce a formula for the relaxation oscillation frequency and prove theoretically that this formula function relates to the loss of carriers transferring between well regime and barrier regime, the feedback level, the delayed time and the other intrinsic parameters. We demonstrate the dynamic distribution and double relaxation oscillation frequency abruptly changing in periodic states and find the multi-frequency characteristic in a chaotic state. We illustrate a road to chaos from a stable state to quasi-periodic states by increasing the feedback level. The effects of the transfers of carriers and the escaping of carriers on dynamic behavior are analyzed, showing that they are contrary to each other via the bifurcation diagram. Also, we show another road to chaos after bifurcation through changing the linewidth enhancement factor, the photon loss rate and the transfer rate of carriers.

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The heat and work of quantum thermodynamic processes with quantum coherence

苏山河, 陈劲夫, 马宇翰, 陈金灿, 孙昌璞

2018 (6): 60502-060502. doi: 10.1088/1674-1056/27/6/060502

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Energy is often partitioned into heat and work by two independent paths corresponding to the change in the eigenenergies or the probability distributions of a quantum system. The discrepancies of the heat and work for various quantum thermodynamic processes have not been well characterized in literature. Here we show how the work in quantum machines is differentially related to the isochoric, isothermal, and adiabatic processes. We prove that the energy exchanges during the quantum isochoric and isothermal processes are simply depending on the change in the eigenenergies or the probability distributions. However, for a time-dependent system in a non-adiabatic quantum evolution, the transitions between the different quantum states representing the quantum coherence can affect the essential thermodynamic properties, and thus the general definitions of the heat and work should be clarified with respect to the microscopic generic time-dependent system. By integrating the coherence effects in the exactly-solvable dynamics of quantum-spin precession, the internal energy is rigorously transferred as the work in the thermodynamic adiabatic process. The present study demonstrates that the quantum adiabatic process is sufficient but not necessary for the thermodynamic adiabatic process.

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Chemical structure of grain-boundary layer in SrTiO₃ and its segregation-induced transition: A continuum interface approach

顾辉

2018 (6): 60503-060503. doi: 10.1088/1674-1056/27/6/060503

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Grain-boundary (GB) structures are commonly imaged as discrete atomic columns, yet the chemical modifications are gradual and extend into the adjacent lattices, notably the space charge, hence the two-dimensional defects may also be treated as continuum changes to extended interfacial structure. This review presents a spatially-resolved analysis by electron energy-loss spectroscopy of the GB chemical structures in a series of SrTiO₃ bicrystals and a ceramic, using analytical electron microscopy of the pre-C_s-correction era. It has identified and separated a transient layer at the model Σ5 grain-boundaries (GBs) with characteristic chemical bonding, extending the continuum interfacial approach to redefine the GB chemical structure. This GB layer has evolved under segregation of iron dopant, starting from subtle changes in local bonds until a clear transition into a distinctive GB chemistry with substantially increased titanium concentration confined within the GB layer in 3-unit cells, heavily strained, and with less strontium. Similar segregated GB layer turns into a titania-based amorphous film in SrTiO₃ ceramic, hence reaching a more stable chemical structure in equilibrium with the intergranular Ti₂O₃ glass also. Space charge was not found by acceptor doping in both the strained Σ5 and amorphous GBs in SrTiO₃ owing to the native transient nature of the GB layer that facilitates the transitions induced by Fe segregation into novel chemical structures subject to local and global equilibria. These GB transitions may add a new dimension into the structure-property relationship of the electronic materials.

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Superconducting membrane mechanical oscillator based on vacuum-gap capacitor

李永超, 戴欣, 江俊良, 潘佳政, 魏兴雨, 卢亚鹏, 卢盛, 涂学凑, 孙国柱, 吴培亨

2018 (6): 60701-060701. doi: 10.1088/1674-1056/27/6/060701

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Using the diluted S1813 UV photoresist as a sacrificial layer, we successfully fabricate a superconducting suspended parallel-plate capacitor, in which the top layer of aluminum film acts as a membrane mechanical resonator. Together with a superconducting octagonal spiral inductor, this parallel-plate capacitor constitutes a superconducting microwave resonator. At mK temperature, the transmission characteristic and spectrum of the microwave resonator are measured. Sideband frequencies caused by the vibration of the membrane mechanical resonator are clearly demonstrated. By down-converting with a mixer, the dependence of fundamental frequency and its harmonics on the input microwave power are clearly demonstrated, which is consistent with the numerical simulation.

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Cryogenic amplifier with low input-referred voltage noise calibrated by shot noise measurement

杨伍昊, 危健

2018 (6): 60702-060702. doi: 10.1088/1674-1056/27/6/060702

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A low-noise cryogenic amplifier for the bandwidth from 100 kHz to 2 MHz with commercially available components is presented. The amplifier is mounted on the cold finger of our home-made liquid helium dipstick. The input impedance of the amplifier is 2 kΩ. The input-referred voltage noise of the amplifier at approximately 2 MHz is around 1 nV/√Hz. We demonstrate the performance of the amplifier by measuring shot noise on the Al/AlO_x/Al tunneling junction with resistance about 17 kΩ at liquid helium temperature.

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Baseline optimization for scalar magnetometer array and its application in magnetic target localization

樊黎明, 郑权, 康曦元, 张晓峻, 康崇

2018 (6): 60703-060703. doi: 10.1088/1674-1056/27/6/060703

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Generally, a magnetic target can be described with six parameters, three describing the position and three describing the magnetic moment. Due to a lack of sufficient components from one magnetometer, we need more than one magnetometer when locating the magnetic target. Thus, a magnetometer array should be designed. The baseline of the array is an important factor that affects the localization accuracy of the target. In this paper, we focus on the localization of a static target by using a scalar magnetometer array. We present the scalar magnetometer array with a cross-shaped structure. We propose a method of determining the optimal baseline according to the parameters of the magnetometer and detection requirements. In the method, we use the traditional signal-to-noise ratio (SNR) as a performance index, and obtain the optimal baseline of the array by using the Monte Carlo method. The proposed method of determining the optimal baseline is verified in simulation. The arrays with different baselines are used to locate a static magnetic target. The results show that the location performance is better when using the array with the optimal baseline determined by the proposed method.

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Determination of static dipole polarizabilities of Yb atom

唐志明, 于艳梅, 董晨钟

2018 (6): 63101-063101. doi: 10.1088/1674-1056/27/6/063101

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We determine the static values of the scalar and tensor dipole polarizabilities of the ground, 6s6p³P₀^o, and 6s6p³P₁^o states of the Yb atom. These results can be useful in many experiments undertaken using this atom. We employed a combined configuration interaction (CI) method and a second-order many-body perturbation theory (MBPT) to evaluate energies and electric dipole (E1) matrix elements of many low-lying excited states of the above atom. These values are compared with the other available theoretical calculations and experimental values. By combining these E1 matrix elements with the experimental excitation energies, we estimate the dominant valence correlation contributions to the dipole polarizabilities of the above states. The core contribution is obtained from the finite field approach. We also compare these values with the other theoretical results as there are no precise experimental values that are available for these properties.

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Structure, stability, catalytic activity, and polarizabilities of small iridium clusters

Francisco E Jorge, José R da Costa Venâncio

2018 (6): 63102-063102. doi: 10.1088/1674-1056/27/6/063102

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At the second order Douglas-Kroll-Hess (DKH2) level, the B3PW91 functional in conjunction with the relativistic all-electron basis set of valence triple zeta quality plus polarization functions are employed to compute bond lengths, dissociation energies, vertical ionization potentials, and the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gaps of the small iridium clusters (Ir_n, n ≤ 8). These results are compared with the experimental and theoretical data available in the literature. Our results confirm the theoretical predictions made by Feng et al. about the catalytic activities of the Ir₄ and Ir₆ clusters. From the optimized geometries, DKH2 calculations of static electric mean dipole polarizabilities and polarizability anisotropies are also carried out. It is the first time that the polarizabilities of small iridium clusters have been studied. For n ≤ 4, the mean dipole polarizabilities per atom present an odd-even oscillatory behavior, whereas from Ir₅ to Ir₈, they decrease with the cluster size increasing. The dependence of the polarizability anisotropy on the structure symmetry of the iridium cluster is verified.

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Effect of nickel segregation on CuΣ9 grain boundary undergone shear deformations

刘湘月, 张红, 程新路

2018 (6): 63103-063103. doi: 10.1088/1674-1056/27/6/063103

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Impurity segregation at grain boundary (GB) can significantly affect the mechanical behaviors of polycrystalline metal. The effect of nickel impurity segregated at Cu GB on the deformation mechanism relating to loading direction is comprehensively studied by atomic simulation. The atomic structures and shear responses of CuΣ9(114) <110> and Σ9(221) <110> symmetrical tilt grain boundary with different quantities of nickel segregation are analyzed. The results show that multiple accommodative evolutions involving GB gliding, GB shear-coupling migration, and dislocation gliding can be at play, where for the[221] shear of Σ9(114) <110> the segregated GBs tend to maintain their initial configurations and a segregated GB with a higher impurity concentration is more inclined to be a dislocation emission source while maintaining the high mechanical strength undergone plastic deformation for the[114] shear of Σ9(221) <110>. It is found that the nickel segregated GB exerts a cohesion enhancement effect on Cu under deformation:strong nickel segregation increases the work of separation of GB, which is proved by the first-principles calculations.

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Single and double Auger decay of 4f-ionized mercury including cascade and direct processes

马玉龙, 周福阳, 刘振旗, 屈一至

2018 (6): 63201-063201. doi: 10.1088/1674-1056/27/6/063201

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Single (SA) and double (DA) Auger decay including cascade and direct processes are investigated for Hg 4f^-1 with multiconfiguration Dirac-Fock method and two-step approaches, i.e., knockout and shakeoff mechanisms. Due to the computational effort, only the major transitions are considered to describe the SA and DA decays for the Hg⁺ ions with complex electronic configurations. In order to estimate the Auger transition energies and amplitudes, the reference configuration sets producing the configuration state functions are carefully chosen for balancing electron correlations among the successive singly, doubly and triply ionized mercury. The Auger rates and electron spectra, DA probabilities as well as the populations of the final Hg³⁺ states are obtained. Our results well explain the recent experimental data about the 4f hole states of Hg[Palaudoux J et al., Phys. Rev. A 91 012513 (2015)], and could provide guidance for further studies on complex atoms. Particularly for the DA decay, the contributions of the direct processes, which are neglected in their calculations, are found to be important, accounting for as high as about 38% and 34% of the total DA decays for the 4f_7/2^-1 and 4f_5/2^-1, respectively.

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Demonstration of superadiabatic population transfer in superconducting qubit

李蒙蒙, 谭新生, 戴坤哲, 赵鹏, 于海峰, 于扬

2018 (6): 63202-063202. doi: 10.1088/1674-1056/27/6/063202

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We implemented the superadiabatic population transfer within the nonadiabatic regime in a two-level superconducting qubit system. To realize the superadiabatic procedure, we added an additional term in the Hamiltonian, introducing an auxiliary counter-diabatic field to cancel the nonadiabatic contribution in the evolution. Based on the superadiabatic procedure, we further demonstrated quantum Phase and NOT gates. These operations, which possess both of the fast and robust features, are promising for quantum information processing.

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Enhanced ionization of vibrational hot carbon disulfide molecules in strong femtosecond laser fields

左万龙, 吕航, 梁红静, 单石敏, 马日, 闫冰, 徐海峰

2018 (6): 63301-063301. doi: 10.1088/1674-1056/27/6/063301

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By using a heated molecular beam in combination with a time-of-flight mass spectrometer, we experimentally study the ionization of vibrational-hot carbon disulfide (CS₂) molecules irradiated by a linearly polarized 800-nm 50-fs strong laser field. The ion yields are measured in a laser intensity range of 7.0×10¹² W/cm²-1.5×10¹⁴ W/cm² at different molecular temperatures of up to 1400 K. Enhanced ionization yield is observed for vibrationally excited CS₂ molecules. The results show that the enhancement decreases as the laser intensity increases, and exhibits non-monotonical dependence on the molecular temperature. According to the calculated potential energy curves of the neutral and ionic electronic states of CS₂, as well as the theoretical models of molecular strong-field ionization available in the literature, we discuss the mechanism of the enhanced ionization of vibrational-hot molecules. It is indicated that the enhanced ionization could be attributed to both the reduced ionization potential with vibrational excitation and the Frank-Condon factors between the neutral and ionic electronic states. Our study paves the way to understanding the effect of nuclear motion on the strong-field ionization of molecules, which would give a further insight into theoretical and experimental investigations on the interaction of polyatomic molecules with strong laser fields.

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Dynamics of the CH₄+O(³P)→CH₃(ν=0)+OH(ν'=0) reaction

蒋仲安, 彭亚, 陈举师, 兰桂, 林浩宇

2018 (6): 63401-063401. doi: 10.1088/1674-1056/27/6/063401

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The dynamics of the ground-state reaction of CH₄+O(³P) → CH₃(ν=0) +OH(ν'=0) have attracted a great deal of attention both theoretically and experimentally. This rapid communication represents extensive quasi-classical trajectory calculations of the vibrational distributions on a unique full-dimensional ab initio potential energy surface for the title reaction, at the collision energy of relevance to previous crossed molecular beam experiments. The surface is constructed using the all electrons coupled-cluster singles and doubles approach plus quasi-perturbative triple excitations with optimized basis sets. A modified Shepard interpolation method is also employed for the construction. Good agreement between our calculations and the available experimental results has been achieved, opening the door for accurate dynamics on this surface.

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Investigations of the dielectronic recombination of phosphorus-like tin at CSRm

许鑫, 汪书兴, 黄忠魁, 汶伟强, 汪寒冰, 徐天衡, 啜晓亚, 豆丽君, 徐卫青, 陈重阳, 李传莹, 王建国, 师应龙, 董晨钟, 冒立军, 殷达钰, 李杰, 马晓明, 杨建成, 原有进, 马新文, 朱林繁

2018 (6): 63402-063402. doi: 10.1088/1674-1056/27/6/063402

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The electron-ion recombination for phosphorus-like ¹¹²Sn³⁵⁺ has been measured at the main cooler storage ring of the Heavy Ion Research Facility in Lanzhou, China, employing an electron-ion merged-beams technique. The absolute total recombination rate coefficients for electron-ion collision energies from 0 eV-14 eV are presented. Theoretical calculations of recombination rate coefficients were performed using the Flexible Atomic Code to compare with the experimental results. The contributions of dielectronic recombination and trielectronic recombination on the experimental rate coefficients have been identified with the help of the theoretical calculation. The present results show that the trielectronic recombination has a substantial contribution to the measured electron-ion recombination spectrum of ¹¹²Sn³⁵⁺. Although a reasonable agreement is found between the experimental and theoretical results the precise calculation of the electron-ion recombination rate coefficients for M-shell ions is still challengeable for the current theory.

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Orienting the future of bio-macromolecular electron microscopy

孙飞

2018 (6): 63601-063601. doi: 10.1088/1674-1056/27/6/063601

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With 40 years of development, bio-macromolecule cryo-electron microscopy (cryo-EM) has completed its revolution in terms of resolution and currently plays a highly important role in structural biology study. According to different specimen states, cryo-EM involves three specific techniques:single-particle analysis (SPA), electron tomography and sub-tomogram averaging, and electron diffraction. None of these three techniques have realized their full potential for solving the structures of bio-macromolecules and therefore need additional development. In this review, the current existing bottlenecks of cryo-EM SPA are discussed with theoretical analysis, which include the air-water interface during specimen cryo-vitrification, bio-macromolecular conformational heterogeneity, focus gradient within thick specimens, and electron radiation damage. Furthermore, potential solutions of these bottlenecks worthy of further investigation are proposed and discussed.

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Overrun phenomenon and neutron yield in Coulomb explosion of deuterated alkane clusters driven by intense laser field

李洪玉, 黄美东, 康明, 李德军

2018 (6): 63602-063602. doi: 10.1088/1674-1056/27/6/063602

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By using a simplified Coulomb explosion model, the laser-driven Coulomb explosion processes of three deuterated alkane clusters, i.e., deuterated methane (CD₄)_N, ethane (C₂D₆)_N and propane (C₃D₈)_N clusters are simulated numerically. The overrun phenomenon that the deuterons overtake the carbon ions inside the expanding clusters, as well as the dependence of the energetic deuterons and fusion neutron yield on cluster size, is discussed in detail. Researches show that the average kinetic energy of deuterons and neutron yield generated in the Coulomb explosion of (C₂D₆)_N cluster are higher than those of (CD₄)_N cluster with the same size, in qualitative agreement with the reported conclusions from the experiments of (C₂H₆)_N and (CH₄)_N clusters. It is indicated that (C₂D₆)_N clusters are superior to (CD₄)_N clusters as a target for the laser-induced nuclear fusion reaction to achieve a higher neutron yield. In addition, by comparing the relevant data of (C₃D₈)_N cluster with those of (C₂D₆)_N cluster with the same size, it is theoretically concluded that (C₃D₈)_N clusters with a larger competitive parameter might be a potential candidate for improving neutron generation. This will provide a theoretical basis for target selection in developing experimental schemes on laser-driven nuclear fusion in the future.

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Optimization of endcap trap for single-ion manipulation

钱源, 方长达人, 黄垚, 管桦, 高克林

2018 (6): 63701-063701. doi: 10.1088/1674-1056/27/6/063701

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Potential distribution is an important characteristic for evaluating the performance of an ion trap. Here, we analyze and optimize the potential distribution of an endcap ion trap for single-ion trapping.We obtain an optimal endcap radius of 225 μm-250 μm, endcap-shield gap of~250 μm, and inter-endcap distance of 540 μm-590 μm. The simulation method for analysis can also be applied to other ion traps, which is useful for improving the design and assembly of ion traps.

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Propagation of acoustic waves in a fluid-filled pipe with periodic elastic Helmholtz resonators

郁殿龙, 沈惠杰, 刘江伟, 尹剑飞, 张振方, 温激鸿

2018 (6): 64301-064301. doi: 10.1088/1674-1056/27/6/064301

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Helmholtz resonators are widely used to reduce noise in a fluid-filled pipe system. It is a challenge to obtain low-frequency and broadband attenuation with a small sized cavity. In this paper, the propagation of acoustic waves in a fluid-filled pipe system with periodic elastic Helmholtz resonators is studied theoretically. The resonance frequency and sound transmission loss of one unit are analyzed to validate the correctness of simplified acoustic impedance. The band structure of infinite periodic cells and sound transmission loss of finite periodic cells are calculated by the transfer matrix method and finite element software. The effects of several parameters on band gap and sound transmission loss are probed. Further, the negative bulk modulus of periodic cells with elastic Helmholtz resonators is analyzed. Numerical results show that the acoustic propagation properties in the periodic pipe, such as low frequency, broadband sound transmission, can be improved.

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Reversed rotation of limit cycle oscillation and dynamics of low-intermediate-high confinement transition

曹丹丹, 弯峰, 侯雅娟, 桑海波, 谢柏松

2018 (6): 65201-065201. doi: 10.1088/1674-1056/27/6/065201

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The dynamics of the confinement transition from L mode to H mode (LH) is investigated in detail theoretically via the extended three-wave coupling model describing the interaction of turbulence and zonal flow (ZF) for the first time. Thereinto, turbulence is divided into a positive-frequency (PF) wave and a negative-frequency (NF) one, and the gradient of pressure is added as the auxiliary energy for the system. The LH confinement transition is observed for a sufficiently high input energy. Moreover, it is found that the rotation direction of the limit cycle oscillation (LCO) of PF wave and pressure gradient is reversed during the transition. The mechanism is illustrated by exploring the wave phases. The results presented here provide a new insight into the analysis of the LH transition, which is helpful for the experiments on the fusion devices.

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Measurements of argon metastable density using the tunable diode laser absorption spectroscopy in Ar and Ar/O₂

韩道满, 刘永新, 高飞, 刘文耀, 徐军, 王友年

2018 (6): 65202-065202. doi: 10.1088/1674-1056/27/6/065202

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Densities of Ar metastable states 1s₅ and 1s₃ are measured by using the tunable diode laser absorption spectroscopy (TDLAS) in Ar and Ar/O₂ mixture dual-frequency capacitively coupled plasma (DF-CCP). We investigate the effects of high-frequency (HF, 60 MHz) power, low-frequency (LF, 2 MHz) power, and working pressure on the density of Ar metastable states for three different gas components (0%, 5%, and 10% oxygen mixed in argon). The dependence of Ar metastable state density on the oxygen content is also studied at different working pressures. It is found that densities of Ar metastable states in discharges with different gas components exhibit different behaviors as HF power increases. With the increase of HF power, the metastable density increases rapidly at the initial stage, and then tends to be saturated at a higher HF power. With a small fraction (5% or 10%) of oxygen added in argon plasma, a similar change of the Ar metastable density with HF power can be observed, but the metastable density is saturated at a higher HF power than in the pure argon discharge. In the DF-CCP, the metastable density is found to be higher than in a single frequency discharge, and has weak dependence on LF power. As working pressure increases, the metastable state density first increases and then decreases, and the pressure value, at which the density maximum occurs, decreases with oxygen content increasing. Besides, adding a small fraction of oxygen into argon plasma will significantly dwindle the metastable state density as a result of quenching loss by oxygen molecules.

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Fractional Stokes-Einstein relation in TIP5P water at high temperatures

任淦, 桑革

2018 (6): 66101-066101. doi: 10.1088/1674-1056/27/6/066101

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Fractional Stokes-Einstein relation described by D~(τ/T ight)^ξ is observed in supercooled water, where D is the diffusion constant, τ the structural relaxation time, T the temperature, and the exponent ξ≠-1. In this work, the Stokes-Einstein relation in TIP5P water is examined at high temperatures within 400 K-800 K. Our results indicate that the fractional Stokes-Einstein relation is explicitly existent in TIP5P water at high temperatures, demonstrated by the two usually adopted variants of the Stokes-Einstein relation, D~τ^-1and D~T/τ, as well as by D~T/η, where η is the shear viscosity. Both D~τ^-1 and D~T/τ are crossed at temperature T_x=510 K. The D~τ^-1 is in a fractional form as D~τ^ξ with ξ=-2.09 for T ≤ T_x and otherwise ξ=-1.25. The D~T/τ is valid with ξ=-1.01 for T ≤ T_x but in a fractional form for T> T_x. The Stokes-Einstein relation D~T/η is satisfied below T_x=620 K but in a fractional form above T_x. We propose that the breakdown of D~T/η may result from the system entering into the super critical region, the fractional forms of D~τ^-1 and D~T/τ are due to the disruption of the hydration shell and the local tetrahedral structure as well as the increase of the shear viscosity.

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Jamming of packings of frictionless particles with and without shear

郑文, 张世允, 徐宁

2018 (6): 66102-066102. doi: 10.1088/1674-1056/27/6/066102

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By minimizing the enthalpy of packings of frictionless particles, we obtain jammed solids at desired pressures and hence investigate the jamming transition with and without shear. Typical scaling relations of the jamming transition are recovered in both cases. In contrast to systems without shear, shear-driven jamming transition occurs at a higher packing fraction and the jammed solids are more rigid with an anisotropic force network. Furthermore, by introducing the macro-friction coefficient, we propose an explanation of the packing fraction gap between sheared and non-sheared systems at fixed pressure.

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Li adsorption on monolayer and bilayer MoS₂ as an ideal substrate for hydrogen storage

张诚, 唐少龙, 邓明森, 都有为

2018 (6): 66103-066103. doi: 10.1088/1674-1056/27/6/066103

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Based on the first-principles plane wave calculations, we show that Li adsorbed on monolayer and bilayer MoS₂ forming a uniform and stable coverage can serve as a high-capacity hydrogen storage medium, and Li-coated MoS₂ can be recycled by operations at room temperature due to Li having strength binding, big separation and is stable against clustering. The full Li coverage MoS₂ system (2*2 hexagonal MoS₂ supercell) can reach up to eight H₂ molecules on every side, corresponding to the gravimetric density of hydrogen storage up to 4.8 wt% and 2.5 wt% in monolayer and bilayer MoS₂, respectively. The adsorption energies of hydrogen molecules are in the range of 0.10eV/H₂-0.25 eV/H₂, which are acceptable for reversible H₂ adsorption/desorption near ambient temperature. In addition, compared with light metals decorated low dimension carbon-based materials, the sandwiched structure of MoS₂ exhibits the greatly enhanced binding stability of Li atoms as well as slightly decreased Li-Li interaction and thus avoids the problem of metal clustering. It is interesting to note that the Li atom apart from the electrostatic interaction, acts as a bridge of hybridization between the S atoms of MoS₂ and adsorbed H₂ molecules. The encouraging results show that such light metals decorated with MoS₂ have great potential in developing high performance hydrogen storage materials.

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Effects of temperature and point defects on the stability of C15 Laves phase in iron: A molecular dynamics investigation

王昊, 高宁, 吕广宏, 姚仲文

2018 (6): 66104-066104. doi: 10.1088/1674-1056/27/6/066104

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Molecular dynamics simulations are used to investigate the stabilities of C15 Laves phase structures subjected to temperature and point defects. The simulations based on different empirical potentials show that the bulk perfect C15 Laves phase appears to be stable under a critical temperature in a range from 350 K to 450 K, beyond which it becomes disordered and experiences an abrupt decrement of elastic modulus. In the presence of both vacancy and self-interstitial, the bulk C15 Laves phase becomes unstable at room temperature and prefers to transform into an imperfect body centered cubic (BCC) structure containing free vacancies or vacancy clusters. When a C15 cluster is embedded in BCC iron, the annihilation of interstitials occurs due to the presence of the vacancy, while it exhibits a phase transformation into a (1/2)<111> dislocation loop due to the presence of the self-interstitial.

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Mechanisms of atmospheric neutron-induced single event upsets in nanometric SOI and bulk SRAM devices based on experiment-verified simulation tool

雷志锋, 张战刚, 恩云飞, 黄云

2018 (6): 66105-066105. doi: 10.1088/1674-1056/27/6/066105

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In this paper, a simulation tool named the neutron-induced single event effect predictive platform (NSEEP²) is proposed to reveal the mechanism of atmospheric neutron-induced single event effect (SEE) in an electronic device, based on heavy-ion data and Monte-Carlo neutron transport simulation. The detailed metallization architecture and sensitive volume topology of a nanometric static random access memory (SRAM) device can be considered to calculate the real-time soft error rate (RTSER) in the applied environment accurately. The validity of this tool is verified by real-time experimental results. In addition, based on the NSEEP², RTSERs of 90 nm-32 nm silicon on insulator (SOI) and bulk SRAM device under various ambient conditions are predicted and analyzed to evaluate the neutron SEE sensitivity and reveal the underlying mechanism. It is found that as the feature size shrinks, the change trends of neutron SEE sensitivity of bulk and SOI technologies are opposite, which can be attributed to the different MBU performances. The RTSER of bulk technology is always 2.8-64 times higher than that of SOI technology, depending on the technology node, solar activity, and flight height.

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Non-monotonic dependence of current upon i-width in silicon p-i-n diodes

庞正鹏, 王欣, 陈健, 杨盼, 张洋, 田永辉, 杨建红

2018 (6): 66106-066106. doi: 10.1088/1674-1056/27/6/066106

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Silicon p-i-n diodes with different i-region widths are fabricated and tested. It is found that the current shows the non-monotonic behavior as a function of i-region width at a bias voltage of 1.0 V. In this paper, an analytical model is presented to explain the non-monotonic behavior, which mainly takes into account the diffusion current and recombination current contributing to the total current. The calculation results indicate that the concentration ratio of p-region to n-region plays a crucial role in the non-monotonic behavior, and the carrier lifetime also has a great influence on this abnormal phenomenon.

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Scanning transmission electron microscopy: A review of high angle annular dark field and annular bright field imaging and applications in lithium-ion batteries

仝毓昕, 张庆华, 谷林

2018 (6): 66107-066107. doi: 10.1088/1674-1056/27/6/066107

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Scanning transmission electron microscopy (STEM) has been shown as powerful tools for material characterization, especially after the appearance of aberration-corrector which greatly enhances the resolution of STEM. High angle annular dark field (HAADF) and annular bright field (ABF) imaging of the aberration-corrected STEM are widely used due to their high-resolution capabilities and easily interpretable image contrasts. However, HAADF mode of the STEM is still limited in detecting light elements due to the weak electron-scattering power. ABF mode of the STEM could detect light and heavy elements simultaneously, providing unprecedented opportunities for probing unknown structures of materials. Atomic-level structure investigation of materials has been achieved by means of these imaging modes, which is invaluable in many fields for either improving properties of materials or developing new materials. This paper aims to provide a introduction of HAADF and ABF imaging techniques and reviews their applications in characterization of cathode materials, study of electrochemical reaction mechanisms, and exploring the effective design of lithium-ion batteries (LIBs). The future prospects of the STEM are also discussed.

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Impressive self-healing phenomenon of Cu₂ZnSn(S, Se)₄ solar cells

于晴, 石将建, 张朋朋, 郭林宝, 闵雪, 罗艳红, 吴会觉, 李冬梅, 孟庆波

2018 (6): 66108-066108. doi: 10.1088/1674-1056/27/6/066108

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A study of the self-healing phenomenon of Cu₂ZnSn(S, Se)₄ (CZTSSe) solar cells has shown more than 10% enhancement in cell performance after storage at room temperature for a week, with a significant improvement in the open-circuit photovoltage (V_oc) and fill factor (FF). In addition, up to 10.45% power conversion efficiency (PCE) has been achieved. No obvious change in crystallinity, crystal phase, optical absorption or elemental distribution in the CZTSSe films was detected on examining the x-ray diffraction (XRD) pattern, Raman spectrum, ultraviolet-visible (UV-Vis), and TOF-SIMS. Further investigations on the charge carrier concentration, charge radiative recombination, and band structure suggest that the enhancement in PCE stems mainly from a reduction in deep defects of the CZTSSe semiconductor film.

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Pressure-induced enhancement of optoelectronic properties in PtS₂

袁亦方, 张志涛, 王伟科, 周永惠, 陈绪亮, 安超, 张冉冉, 周颖, 顾川川, 李亮, 李新建, 杨昭荣

2018 (6): 66201-066201. doi: 10.1088/1674-1056/27/6/066201

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PtS₂, which is one of the group-10 transition metal dichalcogenides, attracts increasing attention due to its extraordinary properties under external modulations as predicted by theory, such as tunable bandgap and indirect-to-direct gap transition under strain; however, these properties have not been verified experimentally. Here we report the first experimental exploration of its optoelectronic properties under external pressure. We find that the photocurrent is weakly pressure-dependent below 3 GPa but increases significantly in the pressure range of 3 GPa-4 GPa, with a maximum~6 times higher than that at ambient pressure. X-ray diffraction data shows that no structural phase transition can be observed up to 26.8 GPa, which indicates a stable lattice structure of PtS₂ under high pressure. This is further supported by our Raman measurements with an observation of linear blue-shifts of the two Raman-active modes to 6.4 GPa. The pressure-enhanced photocurrent is related to the indirect-to-direct/quasi-direct bandgap transition under pressure, resembling the gap behavior under compression strain as predicted theoretically.

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Phase transition and near-zero thermal expansion of Zr_0.5Hf_0.5VPO₇

王俊平, 陈庆东, 李赛磊, 纪延俊, 穆文英, 冯伟伟, 曾高杰, 刘友文, 梁二军

2018 (6): 66501-066501. doi: 10.1088/1674-1056/27/6/066501

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The Zr_0.5Hf_0.5VPO₇ is successfully synthesized by the solid-state method with near-zero thermal expansion. Powder x-ray diffraction (XRD), Raman spectroscopy, thermal dilatometry, and scanning electron microscopy (SEM) are used to investigate the structure, the phase transition, and the coefficient of thermal expansion (CTE) of Zr_0.5Hf_0.5VPO₇. The investigation results show that the samples are of the single cubic type with a space group of Pa3 at room temperature (RT). It can be inferred that the superstructure is transformed from the 3×3×3 superstructure to the 1×1×1 ideal crystal in a temperature range between 310 K and 323 K. The CTE is measured by a dilatometer to be 0.59×10^-6 K^-1 (310 K-673 K). The values of intrinsic (XRD) and extrinsic (dilatometric) thermal expansion are both near zero. The results show that Zr_0.5Hf_0.5VPO₇ has near-zero thermal expansion behavior over a wide temperature range.

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Towards dynamic structure of biological complexes at atomic resolution by cryo-EM

张凯

2018 (6): 66801-066801. doi: 10.1088/1674-1056/27/6/066801

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Cryo-electron microscopy makes use of transmission electron microscopy to image vitrified biological samples and reconstruct their three-dimensional structures from two-dimensional projections via computational approaches. After over 40 years of development, this technique is now reaching its zenith and reforming the research paradigm of modern structural biology. It has been gradually taking over X-ray crystallography as the mainstream method. In this review, we briefly introduce the history of cryo-EM, recent technical development and its potential power to reveal dynamic structures. The technical barriers and possible approaches to tackle the upcoming challenges are discussed.

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Lorentz transmission electron microscopy studies on topological magnetic domains

彭丽聪, 张颖, 左淑兰, 何敏, 蔡建旺, 王守国, 魏红祥, 李建奇, 赵同云, 沈保根

2018 (6): 66802-066802. doi: 10.1088/1674-1056/27/6/066802

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Lorentz transmission electron microscopy (TEM) is a powerful tool to study the crystal structures and magnetic domain structures in correlation with novel physical properties. Nanometric topological magnetic configurations such as vortices, bubbles, and skyrmions have received enormous attention from the viewpoint of both fundamental science and potential applications in magnetic logic and memory devices, in which understanding the physical properties of magnetic nanodomains is essential. In this review article, several magnetic imaging methods in Lorentz TEM including the Fresnel and Foucault modes, electron holography, and differential phase contrast (DPC) techniques are discussed, where the novel properties of topological magnetic domains are well addressed. In addition, in situ Lorentz TEM demonstrates that the topological domains can be efficiently manipulated by electric currents, magnetic fields, and temperatures, exhibiting novel phenomena under external fields, which advances the development of topological nanodomain-based spintronics.

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Cryo-ET bridges the gap between cell biology and structural biophysics

程小芳, 王睿, 沈庆涛

2018 (6): 66803-066803. doi: 10.1088/1674-1056/27/6/066803

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Cryo-electron tomography (cryo-ET) is a cutting-edge technology providing three-dimensional in situ ultra-structural information of macromolecular machineries, organelles, and eukaryotic cells in their native environment at an unprecedented level of detail. Cryo-ET enables the direct observation of dynamic macromolecular architectures of bio-samples in their naturally occurring physiological state, without any harmful artifacts introduced by heavy metal staining, dehydration, and chemical fixation, which occur in traditional transmission electron microscopy. Over decades, cryo-ET has been providing insights into numerous aspects of cellular biology by revealing the pristinely preserved ultra-structures of different cellular components comprising the crowded and complex environment of the cell, thus, bridging the gap between cellular biology and structural biophysics. In this paper, we review the fundamentals of this technique, its recent advances in optics, detection devices, and computational algorithms. The enhancement of our understanding of structural cellular biology by combining these improvements, when integrated with other methods, such as cryo-focused ion beam milling, correlative light and electron microscopy, is discussed via a few examples from research groups worldwide. We also believe that cryo-ET applications in cell biology continue to provide fundamental insights into the field, revolutionizing structural biology itself.

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Explicit forms of zero modes in symmetric interacting Kitaev chain without and with dimerization

王一鸣, 李志聃, 韩强

2018 (6): 67101-067101. doi: 10.1088/1674-1056/27/6/067101

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The fermionic and bosonic zero modes of the one-dimensional (1D) interacting Kitaev chain at the symmetric point are unveiled. The many-body structures of the Majorana zero modes in the topological region are given explicitly by carrying out a perturbation expansion up to infinite order. We also give the analytic expressions of the bosonic zero modes in the topologically trivial phase. Our results are generalized to the hybrid fermion system comprised of the interacting Kitaev model and the Su-Schrieffer-Heeger (SSH) model, in which we show that these two types of zero modes can coexist in a certain region of its phase diagram.

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The structural, electronic, and optical properties of organic-inorganic mixed halide perovskites CH₃NH₃Pb(I_1-y X_y)₃ (X=Cl, Br)

姜淼, 邓乃航, 王丽, 谢海明, 仇永清

2018 (6): 67102-067102. doi: 10.1088/1674-1056/27/6/067102

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Methylammmonium lead iodide perovskites (CH₃NH₃PbI₃) have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH₃NH₃Pb(I_1-yX_y)₃ (X=Cl, Br; y=0, 0.33, 0.67). Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl^-/Br^- at I^-. Electronic structure calculations indicate that the valance band maximum (VBM) is mainly governed by the halide p orbitals and Pb 6s orbitals, Pb 6p orbitals contribute the conduction band minimum (CBM) and doping does not change the direct semiconductor material. The organic cation[CH₃NH₃]⁺ does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y=0 (0.793 eV) to y=0.33 (0.953 eV) then to y=0.67 (1.126 eV). The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.

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Magnetic interactions in a proposed diluted magnetic semiconductor (Ba_1-xK_x)(Zn_1-yMn_y)₂P₂

杨焕成, 刘凯, 卢仲毅

2018 (6): 67103-067103. doi: 10.1088/1674-1056/27/6/067103

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By using first-principles electronic structure calculations, we have studied the magnetic interactions in a proposed BaZn₂P₂-based diluted magnetic semiconductor (DMS). For a typical compound Ba(Zn_0.944Mn_0.056)₂P₂ with only spin doping, due to the superexchange interaction between Mn atoms and the lack of itinerant carriers, the short-range antiferromagnetic coupling dominates. Partially substituting K atoms for Ba atoms, which introduces itinerant hole carriers into the p orbitals of P atoms so as to link distant Mn moments with the spin-polarized hole carriers via the p-d hybridization between P and Mn atoms, is very crucial for the appearance of ferromagnetism in the compound. Furthermore, applying hydrostatic pressure first enhances and then decreases the ferromagnetic coupling in (Ba_0.75K_0.25)(Zn_0.944Mn_0.056)₂P₂ at a turning point around 15 GPa, which results from the combined effects of the pressure-induced variations of electron delocalization and p-d hybridization. Compared with the BaZn₂As₂-based DMS, the substitution of P for As can modulate the magnetic coupling effectively. Both the results for BaZn₂P₂-based and BaZn₂As₂-based DMSs demonstrate that the robust antiferromagnetic (AFM) coupling between the nearest Mn-Mn pairs bridged by anions is harmful to improving the performance of these Ⅱ-Ⅱ-V based DMS materials.

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Complex alloying effect on thermoelectric transport properties of Cu₂Ge(Se_1-xTe_x)₃

王瑞峰, 戴璐, 闫艳慈, 彭坤岭, 卢旭, 周小元, 王国玉

2018 (6): 67201-067201. doi: 10.1088/1674-1056/27/6/067201

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To enhance the thermoelectric performance of Cu₂GeSe₃, a series of Te-alloyed samples Cu₂Ge(Se_1-xTe_x)₃ are synthesized and investigated in this work. It is found that the lattice thermal conductivity is reduced drastically for x=0.1 sample, which may be attributed to the point defects introduced by alloying. However, for samples with x ≥ 0.2, the lattice thermal conductivity increases with increasing x, which is related to a less distorted structure. The structure evolution, together with the change in carrier concentration, also leads to a systemically change in electrical properties. Finally, a zT of 0.55@750 K is obtained for the sample with x=0.3, about 62% higher than that for the pristine sample.

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How to characterize capacitance of organic optoelectronic devices accurately

于浩淼, 何鋆

2018 (6): 67202-067202. doi: 10.1088/1674-1056/27/6/067202

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The selection of circuit model (i.e., parallel or series model) is critical when using a capacitance-frequency and capacitance-voltage technique to probe properties of organic materials and physical processes of organic optoelectronic devices. In the present work, capacitances of ITO/Alq₃/Al and ITO/CuPc/Al are characterized by series and parallel model, respectively. It is found that the large series resistance comes from the ITO electrode and results in the inapplicability of the parallel model to measuring the capacitances of organic devices at high frequencies. An equivalent circuit model with consideration of the parasitical inductance of cables is constructed to derive the capacitance, and actual capacitance-frequency spectra of Alq₃ and CuPc devices are obtained. Further investigation of temperature-dependent capacitance-frequency and capacitance-voltage characteristics indicates that CuPc and Al form the Schottky contact, the density and ionization energy of impurities in CuPc are obtained. Moreover, more practical guidelines for accurate capacitance measurement are introduced instead of the impedance magnitude, which will be very helpful for the organic community to investigate capacitance-related characteristics when dealing with various organic optoelectronic devices.

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Electrical controllable spin valves in a zigzag silicene nanoribbon ferromagnetic junction

张林

2018 (6): 67203-067203. doi: 10.1088/1674-1056/27/6/067203

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We propose two possible spin valves based on a zigzag silicene nanoribbon (ZSR) ferromagnetic junction. By using the Landauer-Bütikker formula, we calculate the spin-resolved conductance spectrum of the system and find that the spin transport is crucially dependent on the band structure of the ZSR tuned by a perpendicular electric field. When the ZSR is in the topological insulator phase under a zero electric field, the low-energy spin transport and its ON and OFF states in the tunneling junction mainly rely on the valley valve effect and the edge state of the energy band, which can be electrically modulated by the Fermi level, the spin-orbit coupling, and the local magnetization. When a nonzero perpendicular electric field is applied, the ZSR is a band insulator with a finite energy gap, the spin switch phenomenon is still preserved in the device and it does not come from the valley valve effect, but from the energy gap opened by the perpendicular electric field. The proposed device might be designed as electrical tunable spin valves to manipulate the spin degree of freedom of electrons in silicene.

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Room-temperature large photoinduced magnetoresistance in semi-insulating gallium arsenide-based device

何雄, 孙志刚

2018 (6): 67204-067204. doi: 10.1088/1674-1056/27/6/067204

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It is still a great challenge for semiconductor based-devices to obtain a large magnetoresistance (MR) effect under a low magnetic field at room temperature. In this paper, the photoinduced MR effects under different intensities of illumination at room temperature are investigated in a semi-insulating gallium arsenide (SI-GaAs)-based Ag/SI-GaAs/Ag device. The device is subjected to the irradiation of light which is supplied by light-emitting diode (LED) lamp beads with a wavelength in a range of about 395 nm-405 nm and the working power of each LED lamp bead is about 33 mW. The photoinduced MR shows no saturation under magnetic fields (B) up to 1 T and the MR sensitivity S (S=MR/B) at low magnetic field (B=0.001 T) can reach 15 T^-1. It is found that the recombination of photoinduced electron and hole results in a positive photoinduced MR effect. This work implies that a high photoinduced S under a low magnetic field may be obtained in a non-magnetic semiconductor device with a very low intrinsic carrier concentration.

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Enhanced photoresponse performance in Ga/Ga₂O₃ nanocomposite solar-blind ultraviolet photodetectors

崔书娟, 梅增霞, 侯尧楠, 陈全胜, 梁会力, 张永晖, 霍文星, 杜小龙

2018 (6): 67301-067301. doi: 10.1088/1674-1056/27/6/067301

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In the present work, we explore the solar-blind ultraviolet (UV) photodetectors (PDs) with enhanced photoresponse, fabricated on Ga/Ga₂O₃ nanocomposite films. Through pre-burying metal Ga layers and thermally post-annealing the laminated Ga₂O₃/Ga/Ga₂O₃ structures, Ga/Ga₂O₃ nanocomposite films incorporated with Ga nanospheres are obtained. For the prototype PD, it is found that the photocurrent and photoresponsivity will first increase and then decrease monotonically with the thickness of the pre-buried Ga layer increasing. Each of all PDs shows a spectrum response peak at 260 nm, demonstrating the ability to detect solar-blind UV light. Adjustable photoresponse enhancement factors are achieved by means of the surface plasmon in the nanocomposite films. The PD with a 20 nm thick Ga interlayer exhibits the best solar-blind UV photoresponse characteristics with an extremely low dark current of 8.52 pA at 10-V bias, a very high light-to-dark ratio of~8×10⁵, a large photoresponsivity of 2.85 A/W at 15-V bias, and a maximum enhancement factor of~220. Our research provides a simple and practical route to high performance solar-blind UV PDs and potential applications in the field of optoelectronics.

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Resonant surface plasmons of a metal nanosphere treated as propagating surface plasmons

方蔚瑞, 田小锐

2018 (6): 67302-067302. doi: 10.1088/1674-1056/27/6/067302

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On the assumption that the resonant surface plasmons on a spherical nanoparticle are formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match with those of the surface plasmons on a semi-infinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave.

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Improved performance of Au nanocrystal nonvolatile memory by N₂-plasma treatment on HfO₂ blocking layer

王尘, 许怡红, 陈松岩, 李成, 汪建元, 黄巍, 赖虹凯, 郭榕榕

2018 (6): 67303-067303. doi: 10.1088/1674-1056/27/6/067303

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The N₂-plasma treatment on a HfO₂ blocking layer of Au nanocrystal nonvolatile memory without any post annealing is investigated. The electrical characteristics of the MOS capacitor with structure of Al-TaN/HfO₂/SiO₂/p-Si are also characterized. After N₂-plasma treatment, the nitrogen atoms are incorporated into HfO₂ film and may passivate the oxygen vacancy states. The surface roughness of HfO₂ film can also be reduced. Those improvements of HfO₂ film lead to a smaller hysteresis and lower leakage current density of the MOS capacitor. The N₂-plasma is introduced into Au nanocrystal (NC) nonvolatile memory to treat the HfO₂ blocking layer. For the N₂-plasma treated device, it shows a better retention characteristic and is twice as large in the memory window than that for the no N₂-plasma treated device. It can be concluded that the N₂-plasma treatment method can be applied to future nonvolatile memory applications.

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Electronic transport properties of Co cluster-decorated graphene

蔡超逸, 陈剑豪

2018 (6): 67304-067304. doi: 10.1088/1674-1056/27/6/067304

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Interactions of magnetic elements with graphene may lead to various electronic states that have potential applications. We report an in-situ experiment in which the quantum transport properties of graphene are measured with increasing cobalt coverage in continuous ultra-high vacuum environment. The results show that e-beam deposited cobalt forms clusters on the surface of graphene, even at low sample temperatures. Scattering of charge carriers by the absorbed cobalt clusters results in the disappearance of the Shubnikov-de Haas (SdH) oscillations and the appearance of negative magnetoresistance (MR) which shows no sign of saturation up to an applied magnetic field of 9 T. We propose that these observations could originate from quantum interference driven by cobalt disorder and can be explained by the weak localization theory.

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Enhanced transient photovoltaic characteristics of core-shell ZnSe/ZnS/L-Cys quantum-dot-sensitized TiO₂ thin-film

李葵英, 任伦, 沈同德

2018 (6): 67305-067305. doi: 10.1088/1674-1056/27/6/067305

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Photoanodic properties greatly determine the overall performance of quantum-dot-sensitized solar cells (QDSCs). In the present report, the microdynamic behaviors of carriers in the nanocomposite thin-film, a ZnSe QD-sensitized mesoporous La-doped nano-TiO₂ thin-film, as a potential candidate for photoanode, are probed via nanosecond transient photovoltaic (TPV) spectroscopy. The results confirm that the L-Cys ligand has a dual function serving as a stabilizer and molecular linker. Large quantities of interface states are located at the energy level with a photoelectric threshold of 1.58 eV and a quantum well (QW) depth of 0.67 eV. This QW depth is approximately 0.14 eV deeper than the depth of QW buried in the ZnSe QDs, and a deeper QW results in a higher quantum confinement energy. A strong quantum confinement effect of the interface state may be responsible for the excellent TPV characteristics of the photoanode. For example, the peak intensity of the TPV response of the QD-sensitized thin-film lasts a long time, from 9.40×10^-7 s to 2.96×10^-4 s, and the end time of the PTV response of the QD-sensitized thin-film is extended by approximately an order of magnitude compared with those of the TiO₂ substrate and the QDs. The TPV characteristics of the QD-sensitized thin-film change from p-type to n-type for the QDs before and after sensitizing. These properties strongly depend on the extended diffusion length of the photogenerated carries and the reduced recombination rate of photogenerated electron-hole pairs, resulting in prolonged carrier lifetime and an increased level of electron injection into the TiO₂ thin-film substrate.

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Nodeless superconductivity in a quasi-two-dimensional superconductor AuTe₂Se_4/3

贾小雨, 俞云杰, 陈旭, 郭建刚, 应天平, 何兰坡, 陈小龙, 李世燕

2018 (6): 67401-067401. doi: 10.1088/1674-1056/27/6/067401

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We performed ultra-low temperature thermal conductivity measurements on the single crystal of a new gold-based quasi-two-dimensional superconductor AuTe₂Se_4/3, which has a superconducting transition temperature T_c=2.70 K. A negligible residual linear term κ₀/T in zero magnetic field is observed, which suggests fully gapped superconducting state. Furthermore, the field dependence of κ₀/T is similar to that of the multi-band s-wave superconductor BaFe_1.9Ni_0.1As₂ at low field. These results reveal multiple nodeless superconducting gaps in this interesting quasi-two-dimensional superconductor with Berezinsky-Kosterlitz-Thouless topological transition.

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Enhancement of off-state characteristics in junctionless field effect transistor using a field plate

王斌, 张鹤鸣, 胡辉勇, 史小卫

2018 (6): 67402-067402. doi: 10.1088/1674-1056/27/6/067402

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In this paper, a novel junctionless field effect transistor (JLFET) is proposed. In the presence of a field plate between gate and drain, the gate-induced drain leakage (GIDL) effect is suppressed due to the decrease of lateral band-to-band tunneling probability. Thus, the off-state current I_off, which is mainly provided by the GIDL current, is reduced. Sentaurus simulation shows that the I_off of the new optimized JLFET is reduced by~2 orders and its sub-threshold swing can reach 76.8 mV/decade with little influence on its on-state current I_on, so its I_on/I_off ratio is improved by 2 orders of magnitude compared with that of the normal JLFET. Optimization of device parameters such as Φ_fps (the work difference between field plate and substrate) and L_FP (the length of field plate), is also discussed in detail.

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Superconductivity of bilayer titanium/indium thin film grown on SiO₂/Si (001)

莫钊洪, 路超, 刘毅, 冯卫, 张云, 张文, 谭世勇, 张宏俊, 郭春煜, 汪小冬, 王亮, 杨蕊竹, 任忠国, 朱燮刚, 熊忠华, 安琪, 赖新春

2018 (6): 67403-067403. doi: 10.1088/1674-1056/27/6/067403

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Bilayer superconducting films with tunable transition temperature (T_c) are a critical ingredient to the fabrication of high-performance transition edge sensors. Commonly chosen materials include Mo/Au, Mo/Cu, Ti/Au, and Ti/Al systems. Here in this work, titanium/indium (Ti/In) bilayer superconducting films are successfully fabricated on SiO₂/Si (001) substrates by molecular beam epitaxy (MBE). The success in the epitaxial growth of indium on titanium is achieved by lowering the substrate temperature to -150℃ during indium evaporation. We measure the critical temperature under a bias current of 10 μA, and obtain different superconducting transition temperatures ranging from 645 mK to 2.7 K by adjusting the thickness ratio of Ti/In. Our results demonstrate that the transition temperature decreases as the thickness ratio of Ti/In increases.

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Current-induced synchronized magnetization reversal of two-body Stoner particles with dipolar interaction

孙周洲, 杨玉, J Schliemann

2018 (6): 67501-067501. doi: 10.1088/1674-1056/27/6/067501

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We investigate magnetization reversal of two-body uniaxial Stoner particles, by injecting spin-polarized current through a spin-valve structure. The two-body Stoner particles perform synchronized dynamics and can act as an information bit in computer technology. In the presence of magnetic dipole-dipole interaction (DDI) between the two particles, the critical switching current I_c for reversing the two dipoles is analytically obtained and numerically verified in two typical geometric configurations. The I_c bifurcates at a critical DDI strength, where I_c can decrease to about 70% of the usual value without DDI. Moreover, we also numerically investigate the magnetic hysteresis loop, magnetization self-precession, reversal time and synchronization stability phase diagram for the two-body system in the synchronized dynamics regime.

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Voltage control of magnetization switching and dynamics

文宏玉, 夏建白

2018 (6): 67502-067502. doi: 10.1088/1674-1056/27/6/067502

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The voltage controlled magnetic switching effect is verified experimentally. The Landau-Lifshitz-Gilbert (LLG) equation is used to study the voltage controlled magnetic switching. It is found that the initial values of magnetic moment components are critical for the switching effect, which should satisfy a definite condition. The external magnetic field which affects only the oscillation period should be comparable to the internal magnetic field. If the external magnetic field is too small, the switching effect will disappear. The precessions of m_x and m_y are the best for the tilt angle of the external magnetic field θ_t=0°, i.e., the field is perpendicular to the sample plane.

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Machine learning technique for prediction of magnetocaloric effect in La(Fe, Si/Al)₁₃-based materials

张博, 郑新奇, 赵同云, 胡凤霞, 孙继荣, 沈保根

2018 (6): 67503-067503. doi: 10.1088/1674-1056/27/6/067503

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Data-mining techniques using machine learning are powerful and efficient for materials design, possessing great potential for discovering new materials with good characteristics. Here, this technique has been used on composition design for La(Fe,Si/Al)₁₃-based materials, which are regarded as one of the most promising magnetic refrigerants in practice. Three prediction models are built by using a machine learning algorithm called gradient boosting regression tree (GBRT) to essentially find the correlation between the Curie temperature (T_C), maximum value of magnetic entropy change ((Δ S_M)_max), and chemical composition, all of which yield high accuracy in the prediction of T_C and (Δ S_M)_max. The performance metric coefficient scores of determination (R²) for the three models are 0.96, 0.87, and 0.91. These results suggest that all of the models are well-developed predictive models on the challenging issue of generalization ability for untrained data, which can not only provide us with suggestions for real experiments but also help us gain physical insights to find proper composition for further magnetic refrigeration applications.

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Transition intensity calculation of Yb: YAG

张洪波, 张庆礼, 王星, 孙贵花, 王小飞, 张德明, 孙敦陆

2018 (6): 67801-067801. doi: 10.1088/1674-1056/27/6/067801

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The Yb:YAG is an excellent high-average power and ultra-short pulse laser crystal. Transition intensity parameters A_tp^k and Huang-Rhys factors are fitted to its emission spectrum by the full-profile fitting method. Calculated results indicate that the emission spectrum of Yb:YAG at cryogenic temperature consists of three pure electron state transitions and two phonon-assisted transitions, one vibronic transition releases one-phonon of 3 cm^-1, and the other vibronic transition absorbs one-phonon of 22 cm^-1. At 300 K, the phonon assisted transition of 3 cm^-1 turns into two-or more-phonon assisted transitions. The procedure absorbing phonon can reduce the thermal load of Yb:YAG and improve the laser efficiency, which may be one of the reasons why Yb:YAG has excellent performance. The emission bands of Yb:YAG are broadened thermally, and the peak values decrease by several times. The emission cross sections of Yb:YAG determined by Fuchtbauer-Ladenburg (F-L) formula are remarkably different from those calculated with A_tp^k, which indicates that it is necessary for a laser material to determine its transition intensity parameters A_tp^k in order to reasonably evaluate the laser performance.

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Variable angle spectroscopic ellipsometry and its applications in determining optical constants of chalcogenide glasses in infrared

韦宁宁, 杨振, 潘宏波, 张凡, 刘永兴, 王荣平, 沈祥, 戴世勋, 聂秋华

2018 (6): 67802-067802. doi: 10.1088/1674-1056/27/6/067802

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The principle of variable angle spectroscopic ellipsometry (VASE) and the data analysis models, as well as the applications of VASE in the characterization of chalcogenide bulk glasses and thin films are reviewed. By going through the literature and summarizing the application scopes of various analysis models, it is found that a combination of various models, rather than any single data analysis model, is ideal to characterize the optical constants of the chalcogenide bulk glasses and thin films over a wider wavelength range. While the reliable optical data in the mid-and far-infrared region are limited, the VASE is flexible and reliable to solve the issues, making it promising to characterize the optical properties of chalcogenide glasses.

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Free-standing, curled and partially reduced graphene oxide network as sulfur host for high-performance lithium-sulfur batteries

陈辉亮, 肖卓建, 张楠, 肖仕奇, 夏晓刚, 席薇, 王艳春, 周维亚, 解思深

2018 (6): 68101-068101. doi: 10.1088/1674-1056/27/6/068101

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Lithium-sulfur (Li-S) batteries have received more and more attention because of higher specific capacity and energy density of sulfur than current lithium-ion batteries. However, the low electrical conductivity of sulfur and its discharge product, and also the high dissolution of polysulfides restrict the Li-S battery practical applications. To improve their performances, in this work, we fabricate a novel free-standing, curled and partially reduced graphene oxide (CPrGO for short) network and combine it with sulfur to form a CPrGO-S composite as a cathode for Li-S battery. With sulfur content of 60 wt%, the free-standing CPrGO-S composite network delievers an initial capacity of 988.9 mAh·g^-1. After 200 cycles, it shows a stable capacity of 841.4 mAh·g^-1 at 0.2 C, retaining about 85% of the initial value. The high electrochemical performance demonstrates that the CPrGO-S network has great potential applications in energy storage system. Such improved properties can be ascribed to the unique free-standing and continous CPrGO-S network which has high specific surface area and good electrical conductivity. In addition, oxygen-containing groups on the partially reduced graphene oxide are beneficial to preventing the polysulfides from dissolving into electrolyte and can mitigate the “shuttle effect”.

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Wider frequency domain for negative refraction index in a quantized composite right-left handed transmission line

吴奇宣, 赵顺才

2018 (6): 68102-068102. doi: 10.1088/1674-1056/27/6/068102

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The refraction index of the quantized lossy composite right-left handed transmission line (CRLH-TL) is deduced in the thermal coherence state. The results show that the negative refraction index (herein the left-handedness) can be implemented by the electric circuit dissipative factors(i.e., the resistances R and conductances G) in a higher frequency band (1.446 GHz ≤ ω ≤ 15 GHz), and flexibly adjusted by the left-handed circuit components (C_l, L_l) and the right-handed circuit components (C_r, L_r) at a lower frequency (ω=0.995 GHz). The flexible adjustment for left-handedness in a wider bandwidth will be significant for the microscale circuit design of the CRLH-TL and may make the theoretical preparation for its compact applications.

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In situ growth of different numbers of gold nanoparticles on MoS₂ with enhanced electrocatalytic activity for hydrogen evolution reaction

赵宣, 何大伟, 王永生, 付晨

2018 (6): 68103-068103. doi: 10.1088/1674-1056/27/6/068103

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Producing hydrogen through a hydrogen evolution reaction (HER) by splitting water at the suitable overpotential is a great alternative to solving the problems of environmental pollution and the energy crisis. Molybdenum sulfide (MoS₂) has attracted extensive attention as one of the most promising catalytic materials for HER. In this work, we design a facile method to in situ grow gold nanoparticles (AuNPs) on MoS₂. Different numbers of AuNPs with MoS₂ are used to find the best catalytic activity. Due to the larger active surface area and higher conductivity of the Au-MoS₂ composites, all the Au-MoS₂ composites exhibit more enhanced HER electroactivity than pure MoS₂. In brief, the new material architecture exhibits optimized HER activity with a low onset overpotential of 0.12 V, low Tafel slope of 0.163 V·dec^-1, and an excellent stability in acidic solution.

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Effect of substrate curvature on thickness distribution of polydimethylsiloxane thin film in spin coating process

闫英, 周平, 张尚雄, 郭晓光, 郭东明

2018 (6): 68104-068104. doi: 10.1088/1674-1056/27/6/068104

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The polymer spin coating is critical in flexible electronic manufaction and micro-electro-mechanical system (MEMS) devices due to its simple operation, and uniformly coated layers. Some researchers focus on the effects of spin coating parameters such as wafer rotating speed, the viscosity of the coating liquid and solvent evaporation on final film thickness. In this work, the influence of substrate curvature on film thickness distribution is considered. A new parameter which represents the edge bead effect ratio (r_e) is proposed to investigate the influence factor of edge bead effect. Several operation parameters including the curvature of the substrate and the wafer-spin speed are taken into account to study the effects on the film thickness uniformity and edge-bead ratio. The morphologies and film thickness values of the spin-coated PDMS films under various substrate curvatures and coating speeds are measured with laser confocal microscopy. According to the results, both the convex and concave substrate will help to reduce the edge-bead effect significantly and thin film with better surface morphology can be obtained at high spin speed. Additionally, the relationship between the edge-bead ratio and the thin film thickness is like parabolic curve instead of linear dependence. This work may contribute to the mass production of flexible electronic devices.

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Tuning hybrid liquid/solid electrolytes by lowering Li salt concentration for lithium batteries

杨伟, 王启迪, 雷宇, 万子裴, 秦磊, 余唯, 刘如亮, 翟登云, 李泓, 李宝华, 康飞宇

2018 (6): 68201-068201. doi: 10.1088/1674-1056/27/6/068201

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Hybrid liquid/solid electrolytes (HLSEs) consisting of conventional organic liquid electrolyte (LE), polyacrylonitrile (PAN), and ceramic lithium ion conductor Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) are proposed and investigated. The HLSE has a high ionic conductivity of over 2.25×10^-3 S/cm at 25℃, and an extended electrochemical window of up to 4.8 V versus Li/Li⁺. The Li|HLSE|Li symmetric cells and Li|HLSE|LiFePO₄ cells exhibit small interfacial area specific resistances (ASRs) comparable to that of LE while much smaller than that of ceramic LAGP electrolyte, and excellent performance at room temperature. Bis(trifluoromethane sulfonimide) salt in HLSE significantly affects the properties and electrochemical behaviors. Side reactions can be effectively suppressed by lowering the concentration of Li salt. It is a feasible strategy for pursuing the high energy density batteries with higher safety.

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Electrical field-driven ripening profiles of colloidal suspensions

王子瑞, 温维佳, 刘雳宇

2018 (6): 68301-068301. doi: 10.1088/1674-1056/27/6/068301

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Electrorheological (ER) fluid is a type of smart fluid whose shear yield stress relies on the external electrical field strength. The transition of ER fluid microstructure driven by the electrical field is the reason why viscosity changes. Experimentally, the transparent electrodes are used to investigate the column size distribution where an external electric field is applied to a colloidal suspension, i.e., ER fluid is increased. The coarsening profile of ER suspensions is strongly related to electrical field strength, but it is insensitive to particle size. In addition, in a low field range the shear stress corresponding to the mean column diameter is studied and they are found to satisfy a power law. However, this dependence is invalid when the field strength surpasses a threshold value.

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Tunable circularly-polarized turnstile-junction mode converter for high-power microwave applications

王晓玉, 樊玉伟, 舒挺, 袁成卫, 张强

2018 (6): 68401-068401. doi: 10.1088/1674-1056/27/6/068401

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Frequency tunability has become a subject of concern in the field of high-power microwave (HPM) source research. However, little information about the corresponding mode converter is available. A tunable circularly-polarized turnstile-junction mode converter (TCTMC) for high-power microwave applications is presented in this paper. The input coaxial TEM mode is transformed into TE₁₀ mode with different phase delays in four rectangular waveguides and then converted into a circularly-polarized TE₁₁ circular waveguide mode. Besides, the rods are added to reduce or even eliminate the reflection. The innovations in this study are as follows. The tunning mechanism is added to the mode converter, which can change the effective length of rectangular waveguide and the distance between the rods installed upstream and the closest edge of the rectangular waveguide, thus improving the conversion efficiency and bandwidth. The conversion efficiency of TCTMC can reach above 98% over the frequency range of 1.42 GHz-2.29 GHz, and the frequency tunning bandwidth is about 47%. Significantly, TCTMC can obtain continuous high conversion efficiency of different frequency points with the change of tuning mechanism.

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Characterization of barrier-tunable radio-frequency-SQUID for Maxwell's demon experiment

李刚, Suman Dhamala, 李浩, 刘建设, 陈炜

2018 (6): 68501-068501. doi: 10.1088/1674-1056/27/6/068501

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We present the design, fabrication, and characterization of a barrier-tunable superconducting quantum interference device (SQUID) qubit for the study of Maxwell's demon experiment. In this work, a compound Josephson junction (CJJ) radio-frequency (RF)-SQUID qubit with an overdamped resistively shunted direct-current (DC)-SQUID magnetometer is used to continuously monitor the state of the qubit. The circuit is successfully fabricated with the standard Nb/Al-AlO_x/Nb trilayer process of our laboratory and characterized in a low noise measurement system, which is capable of measuring coherent dynamics of superconducting qubits, in an Oxford dilution refrigerator. All circuit parameters are determined accurately by fitting experimental data to theoretical analysis and simulation, which allows us to make a quantitative comparison between the results of the experiment and theory.

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Compact wide stopband superconducting bandpass filter using modified spiral resonators with interdigital structure

吴荻, 魏斌, 李博, 郭旭波, 卢新祥, 曹必松

2018 (6): 68502-068502. doi: 10.1088/1674-1056/27/6/068502

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In this study, we propose a novel resonator that is composed of a modified spiral with an embedded interdigital capacitor. A large ratio of the first spurious frequency to the fundamental resonant frequency is obtained, which is suitable for the design of filters with wide stopbands, and the circuit size is considerably reduced by embedding the interdigital structure in the spiral. For demonstration, a compact four-pole high temperature superconducting (HTS) filter with a center frequency of 568 MHz is designed and fabricated on double-sided YBCO film with a size of 11.4 mm×8.0 mm. The filter measurement shows excellent performance with an out-of-band rejection level better than 60.9 dB up to 3863 MHz.

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Compact high-order quint-band superconducting band-pass filter

吴荻, 魏斌, 陆喜龙, 卢新祥, 郭旭波, 曹必松

2018 (6): 68503-068503. doi: 10.1088/1674-1056/27/6/068503

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In this paper, we present a compact quint-band superconducting filter operating at 2.4, 3.5, 4.7, 5.3, and 5.9 GHz. Matching junctions with different impedance branch lines are used to connect a dual-band sub-filter with a tri-band sub-filter and to reduce the channel interactions. The quint-band filter design is divided into two sections to determine the controllable frequencies and bandwidths, while ensuring compact size and reducing design complexity. The filter is fabricated on double-sided YBCO film deposited on an MgO substrate with a size of 26 mm×19 mm. The measured results match well with the simulations.

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Degradation of current-voltage and low frequency noise characteristics under negative bias illumination stress in InZnO thin film transistors

王黎, 刘远, 耿魁伟, 陈雅怡, 恩云飞

2018 (6): 68504-068504. doi: 10.1088/1674-1056/27/6/068504

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The instabilities of indium-zinc oxide thin film transistors under bias and/or illumination stress are studied in this paper. Firstly, illumination experiments are performed, which indicates the variations of current-voltage characteristics and electrical parameters (such as threshold voltage and sub-threshold swing) are dominated by the stress-induced ionized oxygen vacancies and acceptor-like states. The dependence of degradation on light wavelength is also investigated. More negative shift of threshold voltage and greater sub-threshold swing are observed with the decrease of light wavelength. Subsequently, a negative bias illumination stress experiment is carried out. The degradation of the device is aggravated due to the decrease of recombination effects between ionized oxygen vacancies and free carriers. Moreover, the contributions of ionized oxygen vacancies and acceptor-like states are separated by using the mid-gap method. In addition, ionized oxygen vacancies are partially recombined at room temperature and fully recombined at high temperature. Finally, low-frequency noise is measured before and after negative bias illumination stress. Experimental results show few variations of the oxide trapped charges are generated during stress, which is consistent with the proposed mechanism.

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Physics-based analysis and simulation model of electromagnetic interference induced soft logic upset in CMOS inverter

刘彧千, 柴常春, 张宇航, 史春蕾, 刘阳, 樊庆扬, 杨银堂

2018 (6): 68505-068505. doi: 10.1088/1674-1056/27/6/068505

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The instantaneous reversible soft logic upset induced by the electromagnetic interference (EMI) severely affects the performances and reliabilities of complementary metal-oxide-semiconductor (CMOS) inverters. This kind of soft logic upset is investigated in theory and simulation. Physics-based analysis is performed, and the result shows that the upset is caused by the non-equilibrium carrier accumulation in channels, which can ultimately lead to an abnormal turn-on of specific metal-oxide-semiconductor field-effect transistor (MOSFET) in CMOS inverter. Then a soft logic upset simulation model is introduced. Using this model, analysis of upset characteristic reveals an increasing susceptibility under higher injection powers, which accords well with experimental results, and the influences of EMI frequency and device size are studied respectively using the same model. The research indicates that in a range from L waveband to C waveband, lower interference frequency and smaller device size are more likely to be affected by the soft logic upset.

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Integration of a field-effect-transistor terahertz detector with a diagonal horn antenna

李想, 孙建东, 张志鹏, V V Popov, 秦华

2018 (6): 68506-068506. doi: 10.1088/1674-1056/27/6/068506

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Efficient coupling of terahertz electromagnetic wave with the active region in a terahertz detector is required to enhance the optical sensitivity. In this work, we demonstrate direct integration of a field-effect-transistor (FET) terahertz detector chip at the waveguide port of a horn antenna. Although the integration without a proper backshot is rather preliminary, the noise-equivalent power is greatly reduced from 2.7 nW/Hz^1/2 for the bare detector chip to 76 pW/Hz^1/2 at 340 GHz. The enhancement factor of about 30 is confirmed by simulations revealing the effective increase in the energy flux density seen by the detector. The simulation further confirms the frequency response of the horn antenna and the on-chip antennas. A design with the detector chip fully embedded within a waveguide cavity could be made to further enhance the coupling efficiency.

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Interaction between human telomeric G-quadruplexes characterized by single molecule magnetic tweezers

王一舟, 侯锡苗, 车海鹏, 肖雪, 奚绪光, 窦硕星, 王鹏业, 李伟

2018 (6): 68701-068701. doi: 10.1088/1674-1056/27/6/068701

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Human telomeric G-quadruplex plays a crucial role in regulating the genome stability. Despite extensive studies on structures and kinetics of monomeric G-quadruplex, the interaction between G-quadruplexes is still in debate. In this work, we employ magnetic tweezers to investigate the folding and unfolding kinetics of two contiguous G-quadruplexes in 100-mM K⁺ buffer. The interaction between G-quadruplexes and the consequent effect on the kinetics of G-quadruplex are revealed. The linker sequence between G-quadruplexes is further found to play an important role in the interaction between two G-quadruplexes. Our results provide a high-resolution insight into kinetics of multimeric G-quadruplexes and genome stability.

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Detection of finger interruptions in silicon solar cells using photoluminescence imaging

张磊, 梁鹏, 朱慧时, 韩培德

2018 (6): 68801-068801. doi: 10.1088/1674-1056/27/6/068801

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Finger interruptions are common problems in screen printed solar cells, resulting in poor performance in efficiency because of high effective series resistance. Electroluminescence (EL) imaging is typically used to identify interrupted fingers. In this paper, we demonstrate an alternative method based on photoluminescence (PL) imaging to identify local series resistance defects, with a particular focus on finger interruptions. Ability to detect finger interruptions by using PL imaging under current extraction is analyzed and verified. The influences of external bias control and illumination intensity on PL images are then studied in detail. Finally, in comparison with EL imaging, the using of PL imaging to identify finger interruptions possesses the prominent advantages:in PL images, regions affected by interrupted fingers show higher luminescence intensity, while regions affected by recombination defects show lower luminescence intensity. This inverse signal contrast allows PL imaging to more accurately identify the defect types.

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