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Chin. Phys. B  
  Chin. Phys. B--2015, Vol.24, No.8
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Hamiltonian structure, Darboux transformation for a soliton hierarchy associated with Lie algebra so(4, C)

Wang Xin-Zeng, Dong Huan-He
Chin. Phys. B 2015, 24 (8): 080201;  doi: 10.1088/1674-1056/24/8/080201
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In this paper, we first introduce a Lie algebra of the special orthogonal group, g=so(4, C), whose elements are 4×4 trace-free, skew-symmetric complex matrices. As its application, we obtain a new soliton hierarchy which is reduced to AKNS hierarchy and present its bi-Hamiltonian structure and Liouville integrability. Furthermore, for one of the equations in the resulting hierarchy, we construct a Darboux matrix T depending on the spectral parameter λ.

New solutions from nonlocal symmetry of the generalized fifth order KdV equation

Liu Xi-Zhong, Yu Jun, Ren Bo
Chin. Phys. B 2015, 24 (8): 080202;  doi: 10.1088/1674-1056/24/8/080202
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The nonlocal symmetry of the generalized fifth order KdV equation (FOKdV) is first obtained by using the related Lax pair and then localizing it in a new enlarged system by introducing some new variables. On this basis, new Bäcklund transformation is obtained through Lie's first theorem. Furthermore, the general form of Lie point symmetry for the enlarged FOKdV system is found and new interaction solutions for the generalized FOKdV equation are explored by using a symmetry reduction method.

Harmonic signal extraction from noisy chaotic interference based on synchrosqueezed wavelet transform

Wang Xiang-Li, Wang Wen-Bo
Chin. Phys. B 2015, 24 (8): 080203;  doi: 10.1088/1674-1056/24/8/080203
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For the harmonic signal extraction from chaotic interference, a harmonic signal extraction method is proposed based on synchrosqueezed wavelet transform (SWT). First, the mixed signal of chaotic signal, harmonic signal, and noise is decomposed into a series of intrinsic mode-type functions by synchrosqueezed wavelet transform (SWT) then the instantaneous frequency of intrinsic mode-type functions is analyzed by using of Hilbert transform, and the harmonic extraction is realized. In experiments of harmonic signal extraction, the Duffing and Lorenz chaotic signals are selected as interference signal, and the mixed signal of chaotic signal and harmonic signal is added by Gauss white noises of different intensities. The experimental results show that when the white noise intensity is in a certain range, the extracting harmonic signals measured by the proposed SWT method have higher precision, the harmonic signal extraction effect is obviously superior to the classical empirical mode decomposition method.

Fractional-order LβCα filter circuit network

Hong Zheng, Qian Jing, Chen Di-Yi, Herbert H. C. Iu
Chin. Phys. B 2015, 24 (8): 080204;  doi: 10.1088/1674-1056/24/8/080204
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In this paper we introduce the new fundamentals of the conventional LC filter circuit network in the fractional domain. First, we derive the general formulae of the impedances for the conventional and fractional-order filter circuit network. Based on this, the impedance characteristics and phase characteristics with respect to the system variables of the filter circuit network are studied in detail, which shows the greater flexibility of the fractional-order filter circuit network in design. Moreover, from the point of view of the filtering property, we systematically study the effects of the filter units and fractional orders on the amplitude–frequency characteristics and phase–frequency characteristics. In addition, numerical tables of the cut-off frequency are presented. Finally, two typical examples are presented to promote the industrial applications of the fractional-order filter circuit network. Numerical simulations are presented to verify the theoretical results introduced in this paper.

Inverse problem of quadratic time-dependent Hamiltonians

Guo Guang-Jie, Meng Yan, Chang Hong, Duan Hui-Zeng, Di Bing
Chin. Phys. B 2015, 24 (8): 080301;  doi: 10.1088/1674-1056/24/8/080301
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Using an algebraic approach, it is possible to obtain the temporal evolution wave function for a Gaussian wave-packet obeying the quadratic time-dependent Hamiltonian (QTDH). However, in general, most of the practical cases are not exactly solvable, for we need general solutions of the Riccatti equations which are not generally known. We therefore bypass directly solving for the temporal evolution wave function, and study its inverse problem. We start with a particular evolution of the wave-packet, and get the required Hamiltonian by using the inverse method. The inverse approach opens up a new way to find new exact solutions to the QTDH. Some typical examples are studied in detail. For a specific time-dependent periodic harmonic oscillator, the Berry phase is obtained exactly.

Wave–particle duality in a Raman atom interferometer

Jia Ai-Ai, Yang Jun, Yan Shu-Hua, Hu Qing-Qing, Luo Yu-Kun, Zhu Shi-Yao
Chin. Phys. B 2015, 24 (8): 080302;  doi: 10.1088/1674-1056/24/8/080302
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We theoretically investigate the wave–particle duality based on a Raman atom interferometer, via the interaction between the atom and Raman laser, which is similar to the optical Mach–Zehnder interferometer. The wave and which-way information are stored in the atomic internal states. For the φ-π-π/2 type of atom interferometer, we find that the visibility (V) and predictability (P) still satisfy the duality relation, P2+V2 ≤ 1.

Decay of N-qubit GHZ states in Pauli channels

Chen Xiao-Yu, Wang Ting-Ting
Chin. Phys. B 2015, 24 (8): 080303;  doi: 10.1088/1674-1056/24/8/080303
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An N-qubit Greenberger–Horne–Zeilinger (GHZ) state has many applications in various quantum information tasks and can be realized in different experimental schemes. A GHZ diagonal state evolves to another GHZ diagonal state in independent parallel Pauli channels. We give the explicit expression of the resultant GHZ diagonal state in terms of the initial state and channel parameters. If the initial state is a pure N qubit GHZ state or a three-qubit GHZ diagonal state admits a condition, the full separability criterion of the Pauli noisy state is equivalent to positive partial transpose (PPT) criterion. Thus the fully separable condition follows.

Population dynamics of excited atoms in non-Markovian environments at zero and finite temperature

Zou Hong-Mei, Fang Mao-Fa
Chin. Phys. B 2015, 24 (8): 080304;  doi: 10.1088/1674-1056/24/8/080304
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The population dynamics of a two-atom system, which is in two independent Lorentzian reservoirs or in two independent Ohmic reservoirs respectively, where the reservoirs are at zero temperature or finite temperature, is studied by using the time-convolutionless master-equation method. The influences of the characteristics and temperature of a non-Markovian environment on the population of the excited atoms are analyzed. We find that the population trapping of the excited atoms is related to the characteristics and the temperature of the non-Markovian environment. The results show that, at zero temperature, the two atoms can be effectively trapped in the excited state both in the Lorentzian reservoirs and in the Ohmic reservoirs. At finite temperature, the population of the excited atoms will quickly decay to a nonzero value.

An optimized encoding method for secure key distribution by swapping quantum entanglement and its extension

Gao Gan
Chin. Phys. B 2015, 24 (8): 080305;  doi: 10.1088/1674-1056/24/8/080305
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Song [Song D 2004 Phys. Rev. A 69 034301] first proposed two key distribution schemes with the symmetry feature. We find that, in the schemes, the private channels which Alice and Bob publicly announce the initial Bell state or the measurement result through are not needed in discovering keys, and Song's encoding methods do not arrive at the optimization. Here, an optimized encoding method is given so that the efficiencies of Song's schemes are improved by 7/3 times. Interestingly, this optimized encoding method can be extended to the key distribution scheme composed of generalized Bell states.

Faithful deterministic secure quantum communication and authentication protocol based on hyperentanglement against collective noise

Chang Yan, Zhang Shi-Bin, Yan Li-Li, Han Gui-Hua
Chin. Phys. B 2015, 24 (8): 080306;  doi: 10.1088/1674-1056/24/8/080306
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Higher channel capacity and security are difficult to reach in a noisy channel. The loss of photons and the distortion of the qubit state are caused by noise. To solve these problems, in our study, a hyperentangled Bell state is used to design faithful deterministic secure quantum communication and authentication protocol over collective-rotation and collective-dephasing noisy channel, which doubles the channel capacity compared with using an ordinary Bell state as a carrier; a logical hyperentangled Bell state immune to collective-rotation and collective-dephasing noise is constructed. The secret message is divided into several parts to transmit, however the identity strings of Alice and Bob are reused. Unitary operations are not used.

Decoherence in optimized quantum random-walk search algorithm

Zhang Yu-Chao, Bao Wan-Su, Wang Xiang, Fu Xiang-Qun
Chin. Phys. B 2015, 24 (8): 080307;  doi: 10.1088/1674-1056/24/8/080307
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This paper investigates the effects of decoherence generated by broken-link-type noise in the hypercube on an optimized quantum random-walk search algorithm. When the hypercube occurs with random broken links, the optimized quantum random-walk search algorithm with decoherence is depicted through defining the shift operator which includes the possibility of broken links. For a given database size, we obtain the maximum success rate of the algorithm and the required number of iterations through numerical simulations and analysis when the algorithm is in the presence of decoherence. Then the computational complexity of the algorithm with decoherence is obtained. The results show that the ultimate effect of broken-link-type decoherence on the optimized quantum random-walk search algorithm is negative.

Two-color laser modulation of magnetic Feshbach resonances

Li Jian, Liu Yong, Huang Yin, Cong Shu-Lin
Chin. Phys. B 2015, 24 (8): 080308;  doi: 10.1088/1674-1056/24/8/080308
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We investigate the two-color laser modulation of the magnetically induced Feshbach resonance. The two-color laser is nearly resonant with an optical bound-to-bound transition at the resonance position. The analytical formula of scattering length is obtained by solving the Heisenberg equation. The scattering length can be modified by changing the Rabi frequencies or optical field frequency. By choosing the suitable optical parameters, the two-body loss coefficient K2 can be greatly reduced compared to the usual single optical scheme.

The stability of Majorana fermion in correlated quantum wire

Zhang De-Ping, Tian Guang-Shan
Chin. Phys. B 2015, 24 (8): 080401;  doi: 10.1088/1674-1056/24/8/080401
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In this paper, we investigate the effect of the Coulomb interaction between electrons on the stability of Majorana fermion in a heterostructure of s-wave superconductor and quantum wire. In particular, by using the bosonization method and the renormalization group technique, we show that interplay between the so-called umklapp electron–electron scattering process and the superconducting proximity effect plays an extremely important role in determining the phase diagram of the system. We find that, at half-filling, the strong umklapp scattering process suppresses not only the superconducting pairing interaction and hence, destabilizes Majorana fermion in the quantum wire, but aslo results in a Mott insulating state. However, if the proximity effect is sufficiently strong, the topological superconducting phase can still survive and support Majorana fermion in the heterostructure. Furthermore, the existence of a critical Luttinger liquid phase is also found in a narrow region of parameters.

Chaotic dynamics and its analysis of Hindmarsh–Rose neurons by Shil'nikov approach

Wei Wei, Zuo Min
Chin. Phys. B 2015, 24 (8): 080501;  doi: 10.1088/1674-1056/24/8/080501
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In this paper, the relationship between external current stimulus and chaotic behaviors of a Hindmarsh–Rose (HR) neuron is considered. In order to find out the range of external current stimulus which will produce chaotic behaviors of an HR neuron, the Shil'nikov technique is employed. The Cardano formula is taken to obtain the threshold of the chaotic motion, and series solution to a differential equation is utilized to obtain the homoclinic orbit of HR neurons. This analysis establishes mathematically the value of external current input in generating chaotic motion of HR neurons by the Shil'nikov method. The numerical simulations are performed to support the theoretical results.

Fractional-order systems without equilibria: The first example of hyperchaos and its application to synchronization

Donato Cafagna, Giuseppe Grassi
Chin. Phys. B 2015, 24 (8): 080502;  doi: 10.1088/1674-1056/24/8/080502
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A challenging topic in nonlinear dynamics concerns the study of fractional-order systems without equilibrium points. In particular, no paper has been published to date regarding the presence of hyperchaos in these systems. This paper aims to bridge the gap by introducing a new example of fractional-order hyperchaotic system without equilibrium points. The conducted analysis shows that hyperchaos exists in the proposed system when its order is as low as 3.84. Moreover, an interesting application of hyperchaotic synchronization to the considered fractional-order system is provided.

Secure communication based on spatiotemporal chaos

Ren Hai-Peng, Bai Chao
Chin. Phys. B 2015, 24 (8): 080503;  doi: 10.1088/1674-1056/24/8/080503
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In this paper, we propose a novel approach to secure communication based on spatiotemporal chaos. At the transmitter end, the state variables of the coupled map lattice system are divided into two groups: one is used as the key to encrypt the plaintext in the N-shift encryption function, and the other is used to mix with the output of the N-shift function to further confuse the information to transmit. At the receiver end, the receiver lattices are driven by the received signal to synchronize with the transmitter lattices and an inverse procedure of the encoding is conducted to decode the information. Numerical simulation and experiment based on the TI TMS320C6713 Digital Signal Processor (DSP) show the feasibility and the validity of the proposed scheme.

Molecular modeling of oscillating GHz electric field influence on the kinesin affinity to microtubule

H. R. Saeidi, S. S. Setayandeh, A. Lohrasebi
Chin. Phys. B 2015, 24 (8): 080701;  doi: 10.1088/1674-1056/24/8/080701
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Kinesin is a microtubule-associated motor protein which can respond to the external electric field due to its polarity. Using a molecular dynamics simulation method, the effect of such a field on the affinity of kinesin to the αβ-tubulin is investigated in this study. To consider kinesin affinity, the system is exposed to an electric field of 0.03 V/nm with frequency values of 1, 2,..., 9, and 10 GHz. It is found that the applied electric field can change kinesin affinity to the microtubule. These changes could perturb the normal operation of kinesin, such as the processive motility of kinesin on the microtubule.

Design and fabrication of structural color by local surface plasmonic meta-molecules

Ma Ya-Qi, Shao Jin-Hai, Zhang Ya-Feng, Lu Bing-Rui, Zhang Si-Chao, Sun Yan, Qu Xin-Ping, Chen Yi-Fang
Chin. Phys. B 2015, 24 (8): 080702;  doi: 10.1088/1674-1056/24/8/080702
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In this paper, we propose a new form of nanostructures with Al film deposited on a patterned dielectric material for generating structural color, which is induced by local surface plasmonic resonant (LSPR) absorption in sub-wavelength-indented hole/ring arrays. Unlike other reported results obtained by using focus ion beam (FIB) to create metallic nanostructures, the nano-sized hole/ring arrays in Al film in this work are replicated by high resolution electron beam lithography (EBL) combined with self-aligned metallization. Clear structural color is observed and systematically studied by numerical simulations as well as optical characterizations. The central color is strongly related to the geometric size, which provides us with good opportunities to dye the colorless Al surface by controlling the hole/ring dimensions (both diameter and radius), and to open up broad applications in display, jewelry decoration, green production of packing papers, security code, and counterfeits prevention.

Piecewise spectrally band-pass for compressive coded aperture spectral imaging

Qian Lu-Lu, Lü Qun-Bo, Huang Min, Xiang Li-Bin
Chin. Phys. B 2015, 24 (8): 080703;  doi: 10.1088/1674-1056/24/8/080703
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Coded aperture snapshot spectral imaging (CASSI) has been discussed in recent years. It has the remarkable advantages of high optical throughput, snapshot imaging, etc. The entire spatial-spectral data-cube can be reconstructed with just a single two-dimensional (2D) compressive sensing measurement. On the other hand, for less spectrally sparse scenes, the insufficiency of sparse sampling and aliasing in spatial-spectral images reduce the accuracy of reconstructed three-dimensional (3D) spectral cube. To solve this problem, this paper extends the improved CASSI. A band-pass filter array is mounted on the coded mask, and then the first image plane is divided into some continuous spectral sub-band areas. The entire 3D spectral cube could be captured by the relative movement between the object and the instrument. The principle analysis and imaging simulation are presented. Compared with peak signal-to-noise ratio (PSNR) and the information entropy of the reconstructed images at different numbers of spectral sub-band areas, the reconstructed 3D spectral cube reveals an observable improvement in the reconstruction fidelity, with an increase in the number of the sub-bands and a simultaneous decrease in the number of spectral channels of each sub-band.

Spectral properties of endohedrally confined helium atom

Fang Shuai-Shuai, Qiao Hao-Xue
Chin. Phys. B 2015, 24 (8): 083101;  doi: 10.1088/1674-1056/24/8/083101
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Based on the B-spline basis method, the properties of the helium atom confined inside an endohedral environment, such as buckminster fullerene, are studied. In our calculations, the endohedral environment is a parabolic potential well. In this situation, the phenomenon of “mirror collapse” is exhibited for energy levels of a confined helium atom. The “giant resonance” of oscillator strength of the dipole transition emerges with the variation of depth of the confining well. The physical mechanisms of these phenomena are analyzed in this paper.

Electric dipole moment function and line intensities for the ground state of carbon monxide

Chen Hua-Jun, Wu Jie, Liu Hao, Cheng Xin-Lu
Chin. Phys. B 2015, 24 (8): 083102;  doi: 10.1088/1674-1056/24/8/083102
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An accurate electric dipole moment function (EDMF) is obtained for the carbon monoxide (CO) molecule (X1Σ+) by fitting the experimental rovibrational transitional moments. Additionally, an accurate ab initio EDMF is found using the highly accurate, multi-reference averaged coupled-pair functional (ACPF) approach with the basis set, aug-cc-pV6Z, and a finite-field with ± 0.005 a.u. (The unit a.u. is the abbreviation of atomic unit). This ab initio EDMF is very consistent with the fitted ones. The vibrational transition matrix moments and the Herman–Wallis factors, calculated with the Rydberg–Klein–Rees (RKR) potential and the fitted and ab initio EDMFs, are compared with experimental measurements. The consistency of these line intensities with the high-resolution transmission (HITRAN) molecular database demonstrates the improved accuracy of the fitted and ab initio EDMFs derived in this work.

Electron impact excitation of helium atom

Han Xiao-Ying, Zeng De-Ling, Gao Xiang, Li Jia-Ming
Chin. Phys. B 2015, 24 (8): 083103;  doi: 10.1088/1674-1056/24/8/083103
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A method to deal with the electron impact excitation cross sections of an atom from low to high incident energies are presented. This method combines the partial wave method and the first Born approximation (FBA), i.e., replacing the several lowest partial wave cross sections of the total cross sections within FBA by the corresponding exact partial wave cross sections. A new set of codes are developed to calculate the FBA partial wave cross sections. Using this method, the convergent e–He collision cross sections of optical-forbidden and optical-allowed transitions at low to high incident energies are obtained. The calculation results demonstrate the validity and efficiency of the method.

State-to-state quantum dynamics of the N(4S)+H2 (X1Σ+)→NH(X3-)+H(2S) reaction and its reaction mechanism analysis

Zhang Jing, Gao Shou-Bao, Wu Hui, Meng Qing-Tian
Chin. Phys. B 2015, 24 (8): 083104;  doi: 10.1088/1674-1056/24/8/083104
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Quantum state-to-state dynamics of the N(4S)+H2 (X1Σ+)→NH(X3-)+H(2S) reaction is reported in an accurate novel potential energy surface constructed by Zhai et al. (2011 J. Chem. Phys. 135 104314). The time-dependent wave packet method, which is implemented on graphics processing units, is used to calculate the differential cross sections. The influences of the collision energy on the product state-resolved integral cross sections and total differential cross sections are calculated and discussed. It is found that the products NH are predominated by the backward scattering due to the small impact parameter collisions, with only minor components being forward and sideways scattered, and have an inverted rotational distribution and no inversion in vibrational distributions; both rebound and stripping mechanisms exist in the case of high collision energies.

Photodetachment of H- near a hard wall with arbitrary laser polarization direction

Azmat Iqbal, A. Afaq
Chin. Phys. B 2015, 24 (8): 083201;  doi: 10.1088/1674-1056/24/8/083201
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The photodetachment of H- near a hard wall is investigated with linear polarized laser light travelling in arbitrary direction θL with respect to the z axis. An analytical formula for the total cross section is derived using semi-classical closed orbit theory, which consists of two terms, i.e., the smooth background term and the oscillatory term with an extra factor 2(θL). This factor controls oscillations in the total photodetachment cross section. The amplitude of oscillation is maximum at θL=0 when the laser polarization direction is perpendicular to the wall and it approaches zero at θL=π/2 when the laser polarization direction is parallel to the wall. It is also observed that the total cross section depends on the source–wall distance and it reduces to a free space case when the wall is at infinite distance from the source.

Optically pumped quantum MxMR magnetometer with high oscillating magnetic field

Ding Zhi-Chao, Yuan Jie, Wang Zhi-Guo, Yang Kai-Yong, Luo Hui
Chin. Phys. B 2015, 24 (8): 083202;  doi: 10.1088/1674-1056/24/8/083202
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A dip of the transverse component of the magnetic moment as a function of resonance frequency-detuning will emerge when the intensity of oscillating magnetic field exceeds a specific value, which is demonstrated theoretically and experimentally. The linewidth of magnetic-resonance signal can be much smaller than when the MxMR magnetometer operates on condition that the intensity of oscillating magnetic field is smaller than this specific value, and the MxMR magnetometer can possess a much higher signal-to-noise ratio. The experimental result shows that the sensitivity of MxMR magnetometer can be improved by an order of magnitude under this condition.

Branching ratios of autoionization from Eu 4f76p1/26d [J] autoionizing states

Yan Jun-Gang, Shen Li, Liang Hong-Rui, Dai Chang-Jian
Chin. Phys. B 2015, 24 (8): 083203;  doi: 10.1088/1674-1056/24/8/083203
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The autoionization branching ratios from Eu 4f76p1/26d [J] autoionizing states to its 4f76s+ (9So), 4f76s+ (7So), and 4f75d+ (9Do) final ionic states are investigated with the combination of the three-step laser excitation and the velocity-map imaging technique. These different autoionizing states are excited via 4f76s6d 8DJ [J = 5/2, 7/2, and 9/2] intermediate states, respectively. The experimental photoelectron images are obtained, from which energy distributions of ejected electrons are achieved with the mathematical transformation. Furthermore, the energy dependence of the branching ratio is investigated within the autoionization resonance, by which population inversion is observed as an important characteristic. The J-dependence is also studied systematically. The validity of the well-known isolated core excitation technique used for obtaining the autoionization spectrum is also studied.

Study on the A2Π3/2u, B2Δ3/2u, and X2Π3/2g states of Cl2+ including its isotopologues

Wu Ling, You Su-Ping, Shao Xu-Ping, Chen Gang-Jin, Ding Ning, Wang You-Mei, Yang Xiao-Hua
Chin. Phys. B 2015, 24 (8): 083301;  doi: 10.1088/1674-1056/24/8/083301
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Adopting the experimentally available vibrational constants in a recent analysis of the strong perturbation between the A2Π3/2u and B2Δ3/2u states of Cl2+ in the A–X band system [Gharaibeh et al. 2012 J. Chem. Phys. 137 194317], an unambiguous vibrational assignment of the bands reported previously is carried out. The equilibrium rotational constants Be and αe of the X2Π3/2g and A2Π3/2u states for 35Cl2+ and 35Cl37Cl+ and those of the B2Δ3/2u state for 35Cl2+ are obtained by fitting the experimental values of Bv. In addition, the values of Be and αe of these three states for the minor isotopologues 35Cl37Cl+ and 37Cl2+ are predicted by employing the isotopic effect. The values of equilibrium internuclear distance Re of the three states for the three isotopologues are calculated as well.

Atomic motion in the magneto–optical trap consisting of partially spatially coherent laser

Zhang Bao-Wu, Wang Zhao-Ying, Kong De-Long, Lin Qiang
Chin. Phys. B 2015, 24 (8): 083701;  doi: 10.1088/1674-1056/24/8/083701
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Rb atom motion in a magneto–optical trap (MOT) consisting of a partially spatially coherent laser (PSCL) is investigated theoretically. The spatial coherence of the laser is controlled by the electro–optic crystal. The instantaneous spatial distribution of the dissipative force induced by the PSCL on an Rb atom is varying with time stochastically. The simulated results indicate that compared with a fully coherent laser, the spatial coherent laser has effects on the atomic trajectories; however, the capture velocity and the escape velocity are kept the same. The main reason is that the spatial coherence of the laser fluctuates temporally and spatially, but the average photon scattering rate varies little, which makes the total number of atoms and the atomic density distribution unchanged.

Compensating for excess micromotion of ion crystals

Du Li-Jun, Chen Ting, Song Hong-Fang, Chen Shao-Long, Li Hai-Xia, Huang Yao, Tong Xin, Guan Hua, Gao Ke-Lin
Chin. Phys. B 2015, 24 (8): 083702;  doi: 10.1088/1674-1056/24/8/083702
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A new method of compensating for the excess micromotion along two directions in three-dimensional Coulomb crystals is reported in this paper; this method is based on shape control and optical imaging of a Coulomb crystal in a sectioned linear ion trap. The characteristic parameters, such as the ion numbers, temperatures, and geometric factors of different ion crystals are extracted from the images and secular motion excitation spectra. The method of controlling the shape of the ion crystals can be used in cold ion experiments, such as sympathetically cooling, structural phase transitions, and selective-control of ions, etc.

Switchable multi-wavelength fiber laser based on modal interference

Ma Lin, Sun Jiang, Qi Yan-Hui, Kang Ze-Xin, Jian Shui-Sheng
Chin. Phys. B 2015, 24 (8): 084201;  doi: 10.1088/1674-1056/24/8/084201
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A comb fiber filter based on modal interference is proposed and demonstrated in this paper. Here two cascaded up-tapers are used to excite the cladding mode, and a core-offset jointing point is used to act as an interference component. Experimental results show that this kind of structure possesses a comb filter property in a range of the C-band. The measured extinction ratio is better than 12 dB with an insertion loss of about 11 dB. A switchable multi-wavelength erbium-doped fiber laser based on this novel comb filter is demonstrated. By adjusting the polarization controller, the output laser can be switched among single-, dual-, and three-wavelengths with a side mode suppression ratio of better than 45 dB.

Characteristic of femtosecond laser-pulsed digital holography

Shi Bing-Chuan, Wang Xiao-Lei, Guo Wen-Gang, Song Li-Pei
Chin. Phys. B 2015, 24 (8): 084202;  doi: 10.1088/1674-1056/24/8/084202
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Digital holography can be applied to ultrafast detection when a femtosecond laser pulse is used. In this paper, the interference process of two femtosecond laser pulses is studied and the recording process of the femtosecond laser pulsed digital hologram is simulated. Holograms at different recording angles are generated by integrating the instantaneous interference field. By analyzing the distribution of the reconstructed phase error, the characteristics of femtosecond laser pulsed digital holography are discussed.

Strong violations of locality by testing Bell's inequality with improved entangled-photon systems

Wang Yao, Fan Dai-He, Guo Wei-Jie, Wei Lian-Fu
Chin. Phys. B 2015, 24 (8): 084203;  doi: 10.1088/1674-1056/24/8/084203
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Bell's theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell's inequality. Therefore, the violation of Bell's inequality (BI) has been regarded as one of the robust evidences of quantum mechanics. Until now, BI has been tested by many experiments, but the maximal violation (i.e., Cirel'son limit) has never been achieved. By improving the design of entangled sources and optimizing the measurement settings, in this work we report the stronger violations of the Clauser–Horne–Shimony–Holt (CHSH)-type Bell's inequality. The biggest value of Bell's function in our experiment reaches to a significant one: S=2.772± 0.063, approaching to the so-called Cirel'son limit in which the Bell function value is S=2√2. Further improvement is possible by optimizing the entangled-photon sources.

Double transmission peaks electromagnetically induced transparency induced by simultaneously exciting the electric and magnetic resonance in one unit cell

Liu Si-Yuan, Zheng Bu-Sheng, Li Hai-Ming, Liu Xiao-Chun, Liu Shao-Bin
Chin. Phys. B 2015, 24 (8): 084204;  doi: 10.1088/1674-1056/24/8/084204
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In this paper, we investigate a metamaterial formed by a planar array of a metallic L-shaped structure and a cut wire (CW), which behaves as an analogue of the electromagnetically induced transparency (EIT). The double transmission peaks are formed by the destructive interference of two bright-modes and a quasi-dark mode. The two bright-modes are respectively excited by the L-shaped structure and CW. The unit structure itself performs a quasi-dark mode. The group refractive indexes are over 20 in the first transmission peak, and 117 in the second transmission peak, thus offering potential applications in slow light devices. Finally, all the above characteristics are achieved in just one simple unit cell.

Plasma induced by pulsed laser and fabrication of silicon nanostructures

Hang Wei-Qi, Dong Tai-Ge, Wang Gang, Liu Shi-Rong, Huang Zhong-Mei, Miao Xin-Jian, Lv Quan, Qin Chao-Jian
Chin. Phys. B 2015, 24 (8): 084205;  doi: 10.1088/1674-1056/24/8/084205
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It is interesting that in preparing process of nanosilicon by pulsed laser, the periodic diffraction pattern from plasmonic lattice structure in the Purcell cavity due to interaction between plasmons and photons is observed. This kind of plasmonic lattice structure confined in the cavity may be similar to the Wigner crystal structure. Emission manipulation on Si nanostructures fabricated by the plasmonic wave induced from pulsed laser is studied by using photoluminescence spectroscopy. The electronic localized states and surface bonding are characterized by several emission bands peaked near 600 nm and 700 nm on samples prepared in oxygen or nitrogen environment. The electroluminescence wavelength is measured in the telecom window on silicon film coated by ytterbium. The enhanced emission originates from surface localized states in band gap due to broken symmetry from some bonds on surface bulges produced by plasmonic wave in the cavity.

Passive harmonic mode-locking of Er-doped fiber laser using CVD-grown few-layer MoS2 as a saturable absorber

Xia Han-Ding, Li He-Ping, Lan Chang-Yong, Li Chun, Deng Guang-Lei, Li Jian-Feng, Liu Yong
Chin. Phys. B 2015, 24 (8): 084206;  doi: 10.1088/1674-1056/24/8/084206
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Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide (MoS2) saturable absorber (SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition (CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible MoS2 SA. The 20th harmonic mode-locked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio (SMSR) of 36.1 dB. The results confirm that few-layer MoS2 can serve as an effective SA for mode-locked fiber lasers.

Effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier

Song Rui, Lei Cheng-Min, Chen Sheng-Ping, Wang Ze-Feng, Hou Jing
Chin. Phys. B 2015, 24 (8): 084207;  doi: 10.1088/1674-1056/24/8/084207
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The effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier is investigated theoretically and experimentally. The complex Ginzburg–Landau equation and adaptive split-step Fourier method are used to simulate the propagation of pulses with different pulse widths in the fiber amplifier, and the results show that a longer pulse is more profitable in near-infrared supercontinuum generation if the central wavelength of the input laser lies in the normal dispersion region of the gain fiber. A four-stage master oscillator power amplifier configuration is adopted and the output spectra under picosecond and nanosecond input pulses are compared with each other. The experimental results are in good accordance with the simulations which can provide some guidance for further optimization of the system.

Compact, temperature-stable multi-gigahertz passively modelocked semiconductor disk laser

Song Yan-Rong, Guoyu He-Yang, Zhang Peng, Tian Jin-Rong
Chin. Phys. B 2015, 24 (8): 084208;  doi: 10.1088/1674-1056/24/8/084208
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We present a compact passively mode-locked semiconductor disk laser at 1045 nm. The gain chip without any post processing consists of 16 compressively strained InGaAs symmetrical step quantum wells in the active region. 3-GHz repetition rate, 4.9-ps pulse duration, and 30-mW average output power are obtained with 1.4 W of 808-nm incident pump power. The temperature stability of the laser is demonstrated to have an ideal shift rate of 0.035 nm/K of the lasing wavelength.

Optical coherence transfer over 50-km spooled fiber with frequency instability of 2×10-17 at 1 s

Ma Chao-Qun, Wu Li-Fei, Jiang Yan-Yi, Yu Hong-Fu, Bi Zhi-Yi, Ma Long-Sheng
Chin. Phys. B 2015, 24 (8): 084209;  doi: 10.1088/1674-1056/24/8/084209
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We demonstrate coherent transfer of an ultra-stable optical frequency at 192.8 THz over 50-km spooled fiber. Random phase noise induced by environmental disturbance through fiber is detected and suppressed by feeding a correctional signal into an acousto-optic modulator. After being compensated, the fiber-induced frequency instability is 2×10-17 at 1-s averaging time and reaches 8×10-20 after 16 h. The noise floor of the compensation system could be as low as 2×10-18 at 1-s averaging time.

Evolution of dark solitons in the presence of Ramangain and self-steepening effect

Yu Yu, Jia Wei-Guo, Yan Qing, Menke Neimule, Zhang Jun-Ping
Chin. Phys. B 2015, 24 (8): 084210;  doi: 10.1088/1674-1056/24/8/084210
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Based on the equation satisfied by optical pulse that is a slowly varying function, the higher-order nonlinear Schrödinger equation (NLSE) including Raman gain and self-steepening effect is deduced in detail, and a new Raman gain function is defined. By using the split-step Fourier method, the influence of the combined effect between Raman gain and self-steepening on the propagation characteristic of dark solitons is simulated in the isotropic fiber. The results show that gray solitons can be symmetrically formed by high order dark soliton, however self-steepening effect will inhibit the formation mechanism through the phenomenon that gray solitons are produced only in the trailing edge of the central black soliton. Meanwhile, the Raman gain changes the propagation characteristic of optical soliton and inhibits the self-steepening effect, resulting in the broadening of pulse width and the decreasing of pulse offset.

Control over hysteresis curves and thresholds of optical bistability in different semiconductor double quantum wells

Hamedi H R, Mehmannavaz M R, Afshari Hadi
Chin. Phys. B 2015, 24 (8): 084211;  doi: 10.1088/1674-1056/24/8/084211
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The effects of optical field on the phenomenon of optical bistability (OB) are investigated in a K-type semiconductor double quantum well (SDQW) under various parametric conditions. It is shown that the OB threshold can be manipulated by increasing the intensity of coupling field. The dependence of the shift of OB hysteresis curve on probe wavelength detuning is then explored. In order to demonstrate controllability of the OB in this SDQW, we compare the OB features of three different configurations which could arise in this SDQW scheme, i.e., K-type, Y-type, and inverted Y-type systems. The controllability of this semiconductor nanostructure medium makes the presented OB scheme more valuable for applications in all-optical switches, information storage, and logic circuits of all optical information processing.

Optimizational 6-bit all-optical quantization with soliton self-frequency shift and pre-chirp spectral compression techniques based on photonic crystal fiber

Li Sha, Wang Jian-Ping, Kang Zhe, Yu Chong-Xiu
Chin. Phys. B 2015, 24 (8): 084212;  doi: 10.1088/1674-1056/24/8/084212
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In this paper, we optimize a proposed all-optical quantization scheme based on soliton self-frequency shift (SSFS) and pre-chirp spectral compression techniques. A 10m-long high-nonlinear photonic crystal fiber (PCF) is used as an SSFS medium relevant to the power of the sampled optical pulses. Furthermore, a 10m-long dispersion flattened hybrid cladding hexagonal-octagonal PCF (6/8-PCF) is utilized as a spectral compression medium to further enhance the resolution. Simulation results show that 6-bit quantization resolution is still obtained when a 100m-long dispersion-increasing fiber (DIF) is replaced by a 6/8-PCF in spectral compression module.

Estimation of random errors for lidar based on noise scale factor

Wang Huan-Xue, Liu Jian-Guo, Zhang Tian-Shu
Chin. Phys. B 2015, 24 (8): 084213;  doi: 10.1088/1674-1056/24/8/084213
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Estimation of random errors, which are due to shot noise of photomultiplier tube (PMT) or avalanche photodiode (APD) detectors, is very necessary in lidar observation. Due to the Poisson distribution of incident electrons, there still exists a proportional relationship between standard deviation and square root of its mean value. Based on this relationship, noise scale factor (NSF) is introduced into the estimation, which only needs a single data sample. This method overcomes the distractions of atmospheric fluctuations during calculation of random errors. The results show that this method is feasible and reliable.

Comparison between iterative wavefront control algorithm and direct gradient wavefront control algorithm for adaptive optics system

Cheng Sheng-Yi, Liu Wen-Jin, Chen Shan-Qiu, Dong Li-Zhi, Yang Ping, Xu Bing
Chin. Phys. B 2015, 24 (8): 084214;  doi: 10.1088/1674-1056/24/8/084214
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Among all kinds of wavefront control algorithms in adaptive optics systems, the direct gradient wavefront control algorithm is the most widespread and common method. This control algorithm obtains the actuator voltages directly from wavefront slopes through pre-measuring the relational matrix between deformable mirror actuators and Hartmann wavefront sensor with perfect real-time characteristic and stability. However, with increasing the number of sub-apertures in wavefront sensor and deformable mirror actuators of adaptive optics systems, the matrix operation in direct gradient algorithm takes too much time, which becomes a major factor influencing control effect of adaptive optics systems. In this paper we apply an iterative wavefront control algorithm to high-resolution adaptive optics systems, in which the voltages of each actuator are obtained through iteration arithmetic, which gains great advantage in calculation and storage. For AO system with thousands of actuators, the computational complexity estimate is about O(n2)~ O(n3) in direct gradient wavefront control algorithm, while the computational complexity estimate in iterative wavefront control algorithm is about O(n)~ (O(n)3/2), in which n is the number of actuators of AO system. And the more the numbers of sub-apertures and deformable mirror actuators, the more significant advantage the iterative wavefront control algorithm exhibits.

Effects of core position of locally resonant scatterers on low-frequency acoustic absorption in viscoelastic panel

Zhong Jie, Wen Ji-Hong, Zhao Hong-Gang, Yin Jian-Fei, Yang Hai-Bin
Chin. Phys. B 2015, 24 (8): 084301;  doi: 10.1088/1674-1056/24/8/084301
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Locally resonant sonic materials, due to their ability to control the propagation of low-frequency elastic waves, have become a promising option for underwater sound absorption materials. In this paper, the finite element method is used to investigate the absorption characteristics of a viscoelastic panel periodically embedded with a type of infinite-long non-coaxially cylindrical locally resonant scatterers (LRSs). The effect of the core position in the coating layer of the LRS on the low-frequency (500 Hz–3000 Hz) sound absorption property is investigated. With increasing the longitudinal core eccentricity e, there occur few changes in the absorptance at the frequencies below 1500 Hz, however, the absorptance above 1500 Hz becomes gradually better and the valid absorption (with absorptance above 0.8) frequency band (VAFB) of the viscoelastic panel becomes accordingly broader. The absorption mechanism is revealed by using the displacement field maps of the viscoelastic panel and the steel slab. The results show two typical resonance modes. One is the overall resonance mode (ORM) caused by steel backing, and the other is the core resonance mode (CRM) caused by LRS. The absorptance of the viscoelastic panel by ORM is induced mainly by the vibration of the steel slab and affected little by core position. On the contrary, with increasing the core eccentricity, the CRM shifts toward high frequency band and decouples with the ORM, leading to two separate absorption peaks and the broadened VAFB of the panel.

Direct numerical simulation of viscoelastic-fluid-based nanofluid turbulent channel flow with heat transfer

Yang Juan-Cheng, Li Feng-Chen, Cai Wei-Hua, Zhang Hong-Na, Yu Bo
Chin. Phys. B 2015, 24 (8): 084401;  doi: 10.1088/1674-1056/24/8/084401
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Our previous experimental studies have confirmed that viscoelastic-fluid-based nanofluid (VFBN) prepared by suspending nanoparticles in a viscoelastic base fluid (VBF, behaves drag reduction at turbulent flow state) can reduce turbulent flow resistance as compared with water and enhance heat transfer as compared with VBF. Direct numerical simulation (DNS) is performed in this study to explore the mechanisms of heat transfer enhancement (HTE) and flow drag reduction (DR) for the VFBN turbulent flow. The Giesekus model is used as the constitutive equation for VFBN. Our previously proposed thermal dispersion model is adopted to take into account the thermal dispersion effects of nanoparticles in the VFBN turbulent flow. The DNS results show similar behaviors for flow resistance and heat transfer to those obtained in our previous experiments. Detailed analyses are conducted for the turbulent velocity, temperature, and conformation fields obtained by DNSs for different fluid cases, and for the friction factor with viscous, turbulent, and elastic contributions and heat transfer rate with conductive, turbulent and thermal dispersion contributions of nanoparticles, respectively. The mechanisms of HTE and DR of VFBN turbulent flows are then discussed. Based on analogy theory, the ratios of Chilton–Colburn factor to friction factor for different fluid flow cases are investigated, which from another aspect show the significant enhancement in heat transfer performance for some cases of water-based nanofluid and VFBN turbulent flows.

On the ascent of infinite dimensional Hamiltonian operators

Wu De-Yu, Chen Alatancang
Chin. Phys. B 2015, 24 (8): 084601;  doi: 10.1088/1674-1056/24/8/084601
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In this paper, the ascent of 2×2 infinite dimensional Hamiltonian operators and a class of 4×4 infinite dimensional Hamiltonian operators are studied, and the conditions under which the ascent of 2×2 infinite dimensional Hamiltonian operator is 1 and the ascent of a class of 4×4 infinite dimensional Hamiltonian operators that arises in study of elasticity is 2 are obtained. Concrete examples are given to illustrate the effectiveness of criterions.

A novel method of evaluating the lift force on the bluff body based on Noca's flux equation

Sui Xiang-Kun, Jiang Nan
Chin. Phys. B 2015, 24 (8): 084701;  doi: 10.1088/1674-1056/24/8/084701
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The influence of experimental error on lift force evaluated by Noca's flux equation is studied based on adding errors into the direct numerical simulation data for flow past cylinder at Re=100. As Noca suggested using the low-pass filter to get rid of the high-frequency noise in the evaluated lift force, we verify that his method is inapplicable for dealing with the dataset of 1% experimental error, although the precision is acceptable in practice. To overcome this defect, a novel method is proposed in this paper. The average of the lift forces calculated by using multiple control volume is taken as the evaluation before applying the low-pass filter. The method is applied to an experimental data for flow past a cylinder at approximately Re=900 to verify its validation. The results show that it improves much better on evaluating the lift forces.

Reactive oxygen species in plasma against E. coli cells survival rate

Zhou Ren-Wu, Zhang Xian-Hui, Zong Zi-Chao, Li Jun-Xiong, Yang Zhou-Bin, Liu Dong-Ping, Yang Si-Ze
Chin. Phys. B 2015, 24 (8): 085201;  doi: 10.1088/1674-1056/24/8/085201
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In this paper, we report on the contrastive analysis of inactivation efficiency of E. coli cells in solution with different disinfection methods. Compared with the hydrogen peroxide solution and the ozone gas, the atmospheric-pressure He plasma can completely kill the E. coli cells in the shortest time. The inactivation efficiency of E. coli cells in solution can be well described by using the chemical reaction rate model. X-ray photoelectron spectroscopy (XPS) analysis shows that the C–O or C=O content of the inactivated E. coli cell surface by plasma is predominantly increased, indicating the quantity of oxygen-containing species in plasma is more than those of two other methods, and then the C–C or C–H bonds can be broken, leading to the etching of organic compounds. Analysis also indicates that plasma-generated species can play a crucial role in the inactivation process by their direct reactions or the decompositions of reactive species, such as ozone into OH radicals in water, then reacting with E. coli cells.

Particle-in-cell simulation for different magnetic mirror effects on the plasma distribution in a cusped field thruster

Liu Hui, Chen Peng-Bo, Zhao Yin-Jian, Yu Da-Ren
Chin. Phys. B 2015, 24 (8): 085202;  doi: 10.1088/1674-1056/24/8/085202
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Magnetic mirror used as an efficient tool to confine plasma has been widely adopted in many different areas especially in recent cusped field thrusters. In order to check the influence of magnetic mirror effect on the plasma distribution in a cusped field thruster, three different radii of the discharge channel (6 mm, 4 mm, and 2 mm) in a cusped field thruster are investigated by using Particle-in-Cell Plus Monte Carlo (PIC-MCC) simulated method, under the condition of a fixed axial length of the discharge channel and the same operating parameters. It is found that magnetic cusps inside the small radius discharge channel cannot confine electrons very well. Thus, the electric field is hard to establish. With the reduction of the discharge channel's diameter, more electrons will escape from cusps to the centerline area near the anode due to a lower magnetic mirror ratio. Meanwhile, the leak width of the cusped magnetic field will increase at the cusp. By increasing the magnetic field strength in a small radius model of a cusped field thruster, the negative effect caused by the weak magnetic mirror effect can be partially compensated. Therefore, according to engineering design, the increase of magnetic field strength can contribute to obtaining a good performance, when the radial distance between the magnets and the inner surface of the discharge channel is relatively big.

Extended x-ray absorption fine structure study of MnFeP0.56Si0.44 compound

Li Ying-Jie, Haschaolu W, Wurentuya, Song Zhi-Qiang, Ou Zhi-Qiang, Tegus O, Nakai Ikuo
Chin. Phys. B 2015, 24 (8): 086101;  doi: 10.1088/1674-1056/24/8/086101
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The MnFeP0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a =b = 5.9823(0) Å and c = 3.4551(1) Å and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 Å and 4.01 Å in the ferromagnetic state to 2.61 Å and 3.96 Å in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 Å–2.73 Å below the Curie temperature and 2.68 Å–2.75 Å above it.

Irradiation effects of graphene and thin layer graphite induced by swift heavy ions Hot!

Zeng Jian, Liu Jie, Zhang Sheng-Xia, Zhai Peng-Fei, Yao Hui-Jun, Duan Jing-Lai, Guo Hang, Hou Ming-Dong, Sun You-Mei
Chin. Phys. B 2015, 24 (8): 086103;  doi: 10.1088/1674-1056/24/8/086103
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Graphene and thin graphite films deposited on SiO2/Si are irradiated by swift heavy ions (209Bi, 9.5 MeV/u) with the fluences in a range of 1011 ions/cm2–1012 ions/cm2 at room temperature. Both pristine and irradiated samples are investigated by Raman spectroscopy. For pristine graphite films, the "blue shift" of 2D bond and the "red shift" of G bond with the decrease of thickness are found in the Raman spectra. For both irradiated graphene and thin graphite films, the disorder-induced D peak and D' peak are detected at the fluence above a threshold Φth. The thinner the film, the lower the Φth is. In this work, the graphite films thicker than 60 nm reveal defect free via the absence of a D bond signal under the swift heavy ion irradiation till the fluence of 2.6×1012 ions/cm2. For graphite films thinner than 6 nm, the area ratios between D peak and G peak increase sharply with reducing film thickness. It concludes that it is much easier to induce defects in thinner films than in thicker ones by swift heavy ions. The intensities of the D peak and D' peak increase with increasing ion fluence, which predicts the continuous impacting of swift heavy ions can lead to the increasing of defects in samples. Different defect types are detected in graphite films of different thickness values. The main defect types are discussed via the various intensity ratios between the D peak and D' peak (HD/HD').

Analytical model for describing ion guiding through capillaries in insulating polymers

Liu Shi-Dong, Zhao Yong-Tao, Wang Yu-Yu, Stolterfoht N, Cheng Rui, Zhou Xian-Ming, Xu Hu-Shan, Xiao Guo-Qing
Chin. Phys. B 2015, 24 (8): 086104;  doi: 10.1088/1674-1056/24/8/086104
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An analytical description for guiding of ions through nanocapillaries is given on the basis of previous work. The current entering into the capillary is assumed to be divided into a current fraction transmitted through the capillary, a current fraction flowing away via the capillary conductivity and a current fraction remaining within the capillary, which is responsible for its charge-up. The discharging current is assumed to be governed by the Frenkel–Poole process. At higher conductivities the analytical model shows a blocking of the ion transmission, which is in agreement with recent simulations. Also, it is shown that ion blocking observed in experiments is well reproduced by the analytical formula. Furthermore, the asymptotic fraction of transmitted ions is determined. Apart from the key controlling parameter (charge-to-energy ratio), the ratio of the capillary conductivity to the incident current is included in the model. Differences resulting from the nonlinear and linear limits of the Frenkel–Poole discharge are pointed out.

Accurate calculations of the high-pressure elastic constants based on the first-principles

Wang Chen-Ju, Gu Jian-Bing, Kuang Xiao-Yu, Yang Xiang-Dong
Chin. Phys. B 2015, 24 (8): 086201;  doi: 10.1088/1674-1056/24/8/086201
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The energy term corresponding to the first order of the strain in Taylor series expansion of the energy with respect to strain is always ignored when high-pressure elastic constants are calculated. Whether the modus operandi would affect the results of the high-pressure elastic constants is still unsolved. To clarify this query, we calculate the high-pressure elastic constants of tantalum and rhenium when the energy term mentioned above is considered and neglected, respectively. Results show that the neglect of the energy term corresponding to the first order of the strain indeed would influence the veracity of the high-pressure elastic constants, and this influence becomes larger with pressure increasing. Therefore, the energy term corresponding to the first-order of the strain should be considered when the high-pressure elastic constants are calculated.

First-principles verification of CuNNi3 and ZnNNi3 as phonon mediated superconductors

Chen Jian-Yong, Wang Xing
Chin. Phys. B 2015, 24 (8): 086301;  doi: 10.1088/1674-1056/24/8/086301
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Very recently, a new Ni-based antiperovskite nitride superconductor CuNNi3 has been successfully synthesized. We investigate the electronic structures, phonon dispersions, and electron–phonon interactions of CuNNi3 and the isostructual ZnNNi3 by first-principles approach. By analyzing the Eliashberg function we obtain the superconducting transition temperature Tc 3.16 K (3.53 K), which is in good agreement with corresponding experimental Tc 3.2 K (3 K) for CuNNi3 (ZnNNi3). They can be verified as conventional phonon-mediated superconductors.

Bending-induced phase transition in monolayer black phosphorus

Pan Dou-Xing, Wang Tzu-Chiang, Guo Wan-Lin
Chin. Phys. B 2015, 24 (8): 086401;  doi: 10.1088/1674-1056/24/8/086401
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Bending-induced phase transition in monolayer black phosphorus is investigated through first principles calculations. By wrapping the layer into nanotubes along armchair and zigzag directions with different curvatures, it is found that phase transitions of the tubes occur when radius of curvature is smaller than 5 Å in bending along the zigzag direction, while the tubes remain stable along the armchair direction. Small zigzag tubes with odd numbered monolayer unit cells tend to transfer toward armchair-like phases, but the tubes with even numbered monolayer unit cells transfer into new complex bonding structures. The mechanism for the bending-induced phase transition is revealed by the comprehensive analyses of the bending strain energies, electron density distributions, and band structures. The results show significant anisotropic bending stability of black phosphorus and should be helpful for its mechanical cleavage fabrication in large size.

Surface-charge-governed electrolyte transport in carbon nanotubes

Xue Jian-Ming, Guo Peng, Sheng Qian
Chin. Phys. B 2015, 24 (8): 086601;  doi: 10.1088/1674-1056/24/8/086601
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The transport behavior of pressure-driven aqueous electrolyte solution through charged carbon nanotubes (CNTs) is studied by using molecular dynamics simulations. The results reveal that the presence of charges around the nanotube can remarkably reduce the flow velocity as well as the slip length of the aqueous solution, and the decreasing of magnitude depends on the number of surface charges and distribution. With 1-M KCl solution inside the carbon nanotube, the slip length decreases from 110 nm to only 14 nm when the number of surface charges increases from 0 to 12 e. This phenomenon is attributed to the increase of the solid–liquid friction force due to the electrostatic interaction between the charges and the electrolyte particles, which can impede the transports of water molecules and electrolyte ions. With the simulation results, we estimate the energy conversion efficiency of nanofluidic battery based on CNTs, and find that the highest efficiency is only around 30% but not 60% as expected in previous work.

Improvement of variational approach in an interacting two-fermion system

Liu Yan-Xia, Ye Jun, Li Yuan-Yuan, Zhang Yun-Bo
Chin. Phys. B 2015, 24 (8): 086701;  doi: 10.1088/1674-1056/24/8/086701
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A more reasonable trial ground state wave function is constructed for the relative motion of an interacting two-fermion system in a one-dimensional (1D) harmonic potential. At the boundaries both the wave function and its first derivative are continuous and the quasi-momentum is determined by a more practical constraint condition which associates two variational parameters. The upper bound of the ground state energy is obtained by applying the variational principle to the expectation value of the Hamiltonian of relative motion on the trial wave function. The resulted energy and wave function show better agreement with the analytical solution than the original proposal.

Contact angle hysteresis in electrowetting on dielectric

Zhao Rui, Liu Qi-Chao, Wang Ping, Liang Zhong-Cheng
Chin. Phys. B 2015, 24 (8): 086801;  doi: 10.1088/1674-1056/24/8/086801
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Contact angle hysteresis (CAH) is one of the significant physical phenomena in electrowetting on dielectric (EWOD). In this work, a theoretical model is proposed to characterize electrowetting evolution on substrates with CAH, and the relationship among apparent contact angle, potential, and some other parameters is quantified. And this theory is also validated experimentally. The results indicate that our theory and equation based on energy balance succeed in describing the electrowetting response of potential with significant contact angle hysteresis. The CAH in EWOD, ranging from 0o to about 20o in electrowetting cycle, increases with the increase of voltage and climbs up to about 20o when voltage is increased to about 38 V, and then decreases to zero with the further increase of voltage.

Structured dark-field imaging for single nano-particles

Chen Jian, Gao Kun, Wang Zhi-Li, Yun Wen-Bing, Wu Zi-Yu
Chin. Phys. B 2015, 24 (8): 086804;  doi: 10.1088/1674-1056/24/8/086804
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In this work, we extensively describe and demonstrate the structured dark-field imaging (SDFI). SDFI is a newly proposed x-ray microscopy designed for revealing the fine features below Rayleigh resolution, in which different orders of scattered x-ray photons are collected by changing the numerical aperture of the condenser. Here, the samples of single particles are discussed to extend the scope of the SDFI technique reported in a previous work (Chen J, Gao K, Ge X, et al. 2013 Opt. Lett. 38 2068). In addition, the details of the newly invented algorithm are explained, which is able to calculate the intensity of any pixel on the image plane rapidly and reliably.

Indenter size effect on the reversible incipient plasticity of Al (001) surface: Quasicontinuum study

Tang Dan, Shao Yu-Fei, Li Jiu-Hui, Zhao Xing, Qi Yang
Chin. Phys. B 2015, 24 (8): 086805;  doi: 10.1088/1674-1056/24/8/086805
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Indenter size effect on the reversible incipient plasticity of Al (001) surface is studied by quasicontinuum simulations. Results show that the incipient plasticity under small indenter, the radius of which is less than ten nanometers, is dominated by a simple planar fault defect that can be fully removed after withdrawal of the indenter; otherwise, irreversible incipient plastic deformation driven by a complex dislocation activity is preferred, and the debris of deformation twins, dislocations, and stacking fault ribbons still remain beneath the surface when the indenter has been completely retracted. Based on stress distributions calculated at an atomic level, the reason why the dislocation burst instead of a simple fault ribbon is observed under a large indenter is the release of the intensely accumulated shear stress. Finally, the critical load analysis implies that there exists a reversible-irreversible transition of incipient plasticity induced by indenter size. Our findings provide a further insight into the incipient surface plasticity of face-centered-cubic metals in nano-sized contact issues.

Silicene: from monolayer to multilayer–A concise review

Li Hui, Fu Hui-Xia, Meng Sheng
Chin. Phys. B 2015, 24 (8): 086102;  doi: 10.1088/1674-1056/24/8/086102
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Silicene, a newly isolated silicon allotrope with a two-dimensional (2D) honeycomb lattice structure, is predicted to have electronic properties similar to those of graphene, including the existence of signature Dirac fermions. Furthermore, the strong spin–orbit interaction of Si atoms potentially makes silicene an experimentally accessible 2D topological insulator. Since 2012, silicene films have been experimentally synthesized on Ag (111) and other substrates, motivating a burst of research on silicene. We and collaborators have employed STM investigations and first principles calculations to intensively study the structure and electronic properties of silicene films on Ag (111), including monolayer, bilayer, and multilayer silicenes, as well as hydrogenation of silicene.

A review of the growth and structures of silicene on Ag (111)

Wu Ke-Hui
Chin. Phys. B 2015, 24 (8): 086802;  doi: 10.1088/1674-1056/24/8/086802
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Ag (111) is currently the most often used substrate for growing silicene films. Silicene forms a variety of different phases on the Ag (111) substrate. However, the structures of these phases are still not fully understood so far. In this brief review we summarize the growth condition and resulting silicene phases on Ag (111), and discuss the most plausible structural model and electronic property of individual phases. The existing debates on silicene on Ag (111) system are clarified as mush as possible.

Fabrication and properties of silicene and silicene–graphene layered structures on Ir (111)

Meng Lei, Wang Ye-Liang, Zhang Li-Zhi, Du Shi-Xuan, Gao Hong-Jun
Chin. Phys. B 2015, 24 (8): 086803;  doi: 10.1088/1674-1056/24/8/086803
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Silicene, a two-dimensional (2D) honeycomb structure similar to graphene, has been successfully fabricated on various substrates. This work will mainly review the syntheses and the corresponding properties of silicene and silicene–graphene layered structures on Ir (111) substrates. For silicene on Ir (111), the buckled (√3×√3) silicene/(√7×√7) Ir (111) configuration and its electronic structure are fully discussed. For silicene–graphene layered structures, silicene layer can be constructed underneath graphene layer by an intercalation method. These results indicate the possibility of integrating silicene with graphene and may link up with potential applications in nanoelectronics and related areas.

Chemical modification of silicene

Wang Rong, Xu Ming-Sheng, Pi Xiao-Dong
Chin. Phys. B 2015, 24 (8): 086807;  doi: 10.1088/1674-1056/24/8/086807
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Silicene is a two-dimensional (2D) material, which is composed of a single layer of silicon atoms with sp2–sp3 mixed hybridization. The sp2–sp3 mixed hybridization renders silicene excellent reactive ability, facilitating the chemical modification of silicene. It has been demonstrated that chemical modification effectively enables the tuning of the properties of silicene. We now review all kinds of chemical modification methods for silicene, including hydrogenation, halogenation, organic surface modification, oxidation, doping and formation of 2D hybrids. The effects of these chemical modification methods on the geometrical, electronic, optical, and magnetic properties of silicene are discussed. The potential applications of chemically modified silicene in a variety of fields such as electronics, optoelectronics, and magnetoelectronics are introduced. We finally envision future work on the chemical modification of silicene for further advancing the development of silicene.

Silicene spintronics–A concise review

Wang Yang-Yang, Quhe Ru-Ge, Yu Da-Peng, Lü Jin
Chin. Phys. B 2015, 24 (8): 087201;  doi: 10.1088/1674-1056/24/8/087201
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Spintronics involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. The fascinating spin-resolved properties of graphene motivate numerous researchers to study spintronics in graphene and other two-dimensional (2D) materials. Silicene, the silicon analog of graphene, is considered to be a promising material for spintronics. Here, we present a review of theoretical advances with regard to spin-dependent properties, including the electric field-and exchange field-tunable topological properties of silicene and the corresponding spintronic device simulations.

Modulation of electronic properties with external fields in silicene-based nanostructures

Li Geng, Zhao Yin-Chang, Zheng Rui, Ni Jun, Wu Yan-Ning
Chin. Phys. B 2015, 24 (8): 087302;  doi: 10.1088/1674-1056/24/8/087302
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This work reviews our recent works about the density functional theory (DFT) calculational aspects of electronic properties in silicene-based nanostructures with the modulation of external fields, such as electric field, strain, etc. For the two-dimensional (2D) silicene-based nonostructures, the magnetic moment of Fe-doped silicene shows a sharp jump at a threshold electric field, which indicates a good switching effect, implying potential applications as a magnetoelectric (ME) diode. With the electric field, the good controllability and sharp switching of the magnetism may offer a potential applications in the ME devices. For the one-dimensional (1D) nanostructures, the silicene nanoribbons with sawtooth edges (SSiNRs) are more stable than the zigzag silicene nanoribbons (ZSiNRs) and show spin-semiconducting features. Under external electric field or uniaxial compressive strain, the gapless spin-semiconductors are gained, which is significant in designing qubits for quantum computing in spintronics. The superlattice structures of silicene-based armchair nanoribbons (ASiSLs) is another example for 1D silicene nanostructures. The band structures of ASiSLs can be modulated by the size and strain of the superlattices. With the stain increased, the related energy gaps of ASiSLs will change, which are significantly different with that of the constituent nanoribbons. The results suggest potential applications in designing quantum wells.

Growth mechanism and modification of electronic and magnetic properties of silicene

Liu Hong-Sheng, Han Nan-Nan, Zhao Ji-Jun
Chin. Phys. B 2015, 24 (8): 087303;  doi: 10.1088/1674-1056/24/8/087303
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Silicene, a monolayer of silicon atoms arranged in a honeycomb lattice, has been undergoing rapid development in recent years due to its superior electronic properties and its compatibility with mature silicon-based semiconductor technology. The successful synthesis of silicene on several substrates provides a solid foundation for the use of silicene in future microelectronic devices. In this review, we discuss the growth mechanism of silicene on an Ag (111) surface, which is crucial for achieving high quality silicene. Several critical issues related to the electronic properties of silicene are also summarized, including the point defect effect, substrate effect, intercalation of alkali metal, and alloying with transition metals.

Silicene on substrates: A theoretical perspective

Zhong Hong-Xia, Quhe Ru-Ge, Wang Yang-Yang, Shi Jun-Jie, Lü Jin
Chin. Phys. B 2015, 24 (8): 087308;  doi: 10.1088/1674-1056/24/8/087308
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Silicene, as the silicon analog of graphene, is successfully fabricated by epitaxially growing it on various substrates. Like free-standing graphene, free-standing silicene possesses a honeycomb structure and Dirac-cone-shaped energy band, resulting in many fascinating properties such as high carrier mobility, quantum spin Hall effect, quantum anomalous Hall effect, and quantum valley Hall effect. The existence of the honeycomb crystal structure and the Dirac cone of silicene is crucial for observation of its intrinsic properties. In this review, we systematically discuss the substrate effects on the atomic structure and electronic properties of silicene from a theoretical point of view, especially with emphasis on the changes of the Dirac cone.

Electronic structure of silicene

L. C. Lew Yan Voon
Chin. Phys. B 2015, 24 (8): 087309;  doi: 10.1088/1674-1056/24/8/087309
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In this topical review, we discuss the electronic structure of free-standing silicene by comparing results obtained using different theoretical methods. Silicene is a single atomic layer of silicon similar to graphene. The interest in silicene is the same as for graphene, in being two-dimensional and possessing a Dirac cone. One advantage of silicene is due to its compatibility with current silicon electronics. Both empirical and first-principles techniques have been used to study the electronic properties of silicene. We will provide a brief overview of the parameter space for first-principles calculations. However, since the theory is standard, no extensive discussion will be included. Instead, we will emphasize what empirical methods can provide to such investigations and the current state of these theories. Finally, we will review the properties computed using both types of theories for free-standing silicene, with emphasis on areas where we have contributed. Comparisons to graphene is provided throughout.

Silicene transistors–A review

Quhe Ru-Ge, Wang Yang-Yang, Lü Jin
Chin. Phys. B 2015, 24 (8): 088105;  doi: 10.1088/1674-1056/24/8/088105
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Free standing silicene is a two-dimensional silicon monolayer with a buckled honeycomb lattice and a Dirac band structure. Ever since its first successful synthesis in the laboratory, silicene has been considered as an option for post-silicon electronics, as an alternative to graphene and other two-dimensional materials. Despite its theoretical high carrier mobility, the zero band gap characteristic makes pure silicene impossible to use directly as a field effect transistor (FET) operating at room temperature. Here, we first review the theoretical approaches to open a band gap in silicene without diminishing its excellent electronic properties and the corresponding simulations of silicene transistors based on an opened band gap. An all-metallic silicene FET without an opened band gap is also introduced. The two chief obstacles for realization of a silicene transistor are silicene's strong interaction with a metal template and its instability in air. In the final part, we briefly describe a recent experimental advance in fabrication of a proof-of-concept silicene device with Dirac ambipolar charge transport resembling a graphene FET, fabricated via a growth-transfer technique.


Domain boundaries in silicene: Density functional theory calculations on electronic properties

Xiao Hong-Jun, Zhang Li-Zhi, Du Shi-Xuan, Gao Hong-Jun
Chin. Phys. B 2015, 24 (8): 086806;  doi: 10.1088/1674-1056/24/8/086806
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By using density functional theory (DFT)-based first-principles calculations, the structural stability and electronic properties for two kinds of silicene domain boundaries, forming along armchair edge and zigzag edge, have been investigated. The results indicate that a linkage of tetragonal and octagonal rings (4|8) appears along the armchair edge, while a linkage of paired pentagonal and octagonal rings (5|5|8) appears along the zigzag edge. Different from graphene, the buckling properties of silicene lead to two mirror symmetrical edges of silicene line-defect. The formation energies indicate that the 5|5|8 domain boundary is more stable than the 4|8 domain boundary. Similar to graphene, the calculated electronic properties show that the 5|5|8 domain boundaries exhibit metallic properties and the 4|8 domain boundaries are half-metal. Both domain boundaries create the perfect one-dimensional (1D) metallic wires. Due to the metallic properties, these two kinds of nanowires can be used to build the silicene-based devices.

Comparison of electronic structure between monolayer silicenes on Ag (111)

Chun-Liang Lin, Ryuichi Arafune, Maki Kawai, Noriaki Takagi
Chin. Phys. B 2015, 24 (8): 087307;  doi: 10.1088/1674-1056/24/8/087307
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The electronic structures of monolayer silicenes (4×4 and √13×√13R13.9o) grown on Ag (111) surface are studied by scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations. While both phases have similar electronic structures around the Fermi level, significant differences are observed in the higher energy unoccupied states. The DFT calculations show that the contributions of Si 3pz orbitals to the unoccupied states are different because of their different buckled configurations.

Antiferromagnetic and topological states in silicene: A mean field study

Liu Feng, Liu Cheng-Cheng, Yao Yu-Gui
Chin. Phys. B 2015, 24 (8): 087503;  doi: 10.1088/1674-1056/24/8/087503
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It has been widely accepted that silicene is a topological insulator, and its gap closes first and then opens again with increasing electric field, which indicates a topological phase transition from the quantum spin Hall state to the band insulator state. However, due to the relatively large atomic spacing of silicene, which reduces the bandwidth, the electron–electron interaction in this system is considerably strong and cannot be ignored. The Hubbard interaction, intrinsic spin orbital coupling (SOC), and electric field are taken into consideration in our tight-binding model, with which the phase diagram of silicene is carefully investigated on the mean field level. We have found that when the magnitudes of the two mass terms produced by the Hubbard interaction and electric potential are close to each other, the intrinsic SOC flips the sign of the mass term at either K or K' for one spin and leads to the emergence of the spin-polarized quantum anomalous Hall state.

Low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene

Hu Bo
Chin. Phys. B 2015, 24 (8): 087101;  doi: 10.1088/1674-1056/24/8/087101
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Based on semiclassical Boltzamnn transport theory in random phase approximation, we develop a theoretical model to investigate low-temperature carrier transport properties in relatively high doped bilayer graphene. In the presence of both electron–hole puddles and band gap induced by charged impurities, we calculate low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene. Our calculated conductivity results are in excellent agreement with published experimental data in all compensated gate voltage regime of study by using potential fluctuation parameter as only one free fitting parameter, indicating that both electron–hole puddles and band gap induced by charged impurities play an important role in carrier transport. More importantly, we also find that the conductivity not only depends strongly on the total charged impurity density, but also on the top layer charged impurity density, which is different from that obtained by neglecting the opening of band gap, especially for bilayer graphene with high top layer charged impurity density.

Spin pumping through magnetic impurity effect Hot!

Deng Wei-Yin, Sheng Li, Xing Ding-Yu
Chin. Phys. B 2015, 24 (8): 087202;  doi: 10.1088/1674-1056/24/8/087202
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We propose a simple adiabatic quantum spin pump to generate pure spin current. The spin pump is driven by an ac gate voltage and a time-dependent magnetic impurity potential. It is found that the total pumped spin per cycle exhibits oscillations, whose magnitude decays exponentially with changing strength of the impurity potential. The proposed method may be useful for spintronic applications.

Tunable multiple plasmon resonances and local field enhancement of nanocrescent/nanoring structure

Wang Bin-Bing, Zhou Jun, Chen Dong, Fang Yun-Tuan, Chen Ming-Yang
Chin. Phys. B 2015, 24 (8): 087301;  doi: 10.1088/1674-1056/24/8/087301
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According to the plasmon hybridization theory, the plasmon resonance characteristics of the gold nanocrescent/nanoring (NCNR) structure are systematically investigated by the finite element method. It is found that the extinction spectra of NCNR structure exhibit multiple plasmon resonance peaks, which could be attributed to the result of the plasmon couplings between the multipolar plasmon modes of nanocrescent and the dipolar, quadrupolar, hexapolar, octupolar, decapolar plasmon modes of nanoring. By changing the geometric parameters, the intense and separate multiple plasmon resonance peaks are obtained and can be tuned in a wide wavelength range. It is further found that the plasmon coupling induces giant multipole electric field enhancements around the tips of the nanocrescent. The tunable and intense multiple plasmon resonances of NCNR structure may provide effective applications in multiplex biological sensing.

Charge trapping behavior and its origin in Al2O3/SiC MIS system

Liu Xin-Yu, Wang Yi-Yu, Peng Zhao-Yang, Li Cheng-Zhan, Wu Jia, Bai Yun, Tang Yi-Dan, Liu Ke-An, Shen Hua-Jun
Chin. Phys. B 2015, 24 (8): 087304;  doi: 10.1088/1674-1056/24/8/087304
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Charge trapping behavior and its origin in Al2O3/SiC MOS structure are investigated by analyzing the capacitance–voltage (C–V) hysteresis and the chemical composition of the interface. The C–V hysteresis is measured as a function of oxide thickness series for an Al2O3/SiC MIS capacitor. The distribution of the trapped charges, extracted from the C–V curves, is found to mainly follow a sheet charge model rather than a bulk charge model. Therefore, the electron injection phenomenon is evaluated by using linear fitting. It is found that most of the trapped charges are not distributed exactly at the interface but are located in the bulk of the Al2O3 layers, especially close to the border. Furthermore, there is no detectable oxide interface layer in the x-ray photoelectron spectroscope (XPS) and transmission electron microscope (TEM) measurements. In addition, Rutherford back scattering (RBS) analysis shows that the width of the Al2O3/SiC interface is less than 1 nm. It could be concluded that the charge trapping sites in Al2O3/SiC structure might mainly originate from the border traps in Al2O3 film rather than the interface traps in the interfacial transition layer.

Hetero-epitaxy of Lg=0.13-μm metamorphic AlInAs/GaInAs HEMT on Si substrates by MOCVD for logic applications

Huang Jie, Li Ming, Zhao Qian, Gu Wen-Wen, Lau Kei-May
Chin. Phys. B 2015, 24 (8): 087305;  doi: 10.1088/1674-1056/24/8/087305
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In this work, a hetero-epitaxial Al0.49In0.51As/Ga0.47In0.53As metamorphic high electron mobility transistor (mHEMT) grown by metal–organic chemical vapor deposition (MOCVD) on p-type silicon substrate has been successfully demonstrated. A novel AlGaAs/AlAs period multiple quantum well (MQW) composite buffer scheme is developed to effectively tune the leakage current from the buffer layer. The quantized room-temperature Hall mobility of the two-dimensional electron gas (2DEG) is larger than 7800 cm2/V·s, with an average sheet carrier density of 4.6×1012 cm-2. Two-stage electron beam (EB) lithography technology by a JBX-6300 e-beam lithography system is developed to realize a 0.13-μm mHEMT device on Si substrate. A maximum transconductance Gm of up to 854 mS/mm is achieved, and is comparable to that of mHEMT technology on GaAs substrate with the same dimension. The fT and fmax are 135 GHz and 120 GHz, respectively.

Influence of the AlGaN barrier thickness on polarization Coulomb field scattering in an AlGaN/AlN/GaN heterostructure field-effect transistor

Lv Yuan-Jie, Feng Zhi-Hong, Gu Guo-Dong, Yin Jia-Yun, Fang Yu-Long, Wang Yuan-Gang, Tan Xin, Zhou Xing-Ye, Lin Zhao-Jun, Ji Zi-Wu, Cai Shu-Jun
Chin. Phys. B 2015, 24 (8): 087306;  doi: 10.1088/1674-1056/24/8/087306
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In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field (PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility. Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness. This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect.

Evolution of structure and magnetic properties in PrCo5 magnet for high energy ball milling in ethanol

Li Zhu-Bai, Lan Jian-Ting, Zhang Xue-Feng, Liu Yan-Li, Li Yong-Feng
Chin. Phys. B 2015, 24 (8): 087501;  doi: 10.1088/1674-1056/24/8/087501
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High energy ball milling (HEBM) is employed to produce nano-sized grains and particles. In this paper, the structure and magnetic properties are investigated in PrCo5 alloy for HEBM in an ethanol milling medium. With the increase of milling time, the grain size reduces and the coercivity increases. For a milling time of less than 30 min, the hysteresis loop of the aligned sample is very different from that of the un-aligned sample and it does not show a large decrease in magnetization slope, indicating a relatively good alignment of easy axes in particles due to the fact that the texture is nearly well preserved. However, when the milling time is further prolonged, the textured structure deteriorates in the powders. Even though exchange coupling exists between grains within the particle, the magnetic properties are exchange-decoupled between particles and the dipolar interaction results in a negative value of δ m in the whole range of the magnetic field.

Magnetization plateaus and frequency dispersion of hysteresis on frustrated dipolar array

Zhang You-Tian
Chin. Phys. B 2015, 24 (8): 087502;  doi: 10.1088/1674-1056/24/8/087502
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Competings or frustrated interactions are common for condensed matter systems. In consideration of the effect of dipole–dipole interaction, the static properties of square lattice spin systems are investigated using the Wang–Landau algorithm. The dynamic hysteresis is also simulated using the Monte Carlo (MC) method. The step-like magnetization under a DC magnetic field and two distinct peaks in hysteresis dispersion under an AC magnetic field are observed. Then, the formation of the properties of the frustrated dipolar array are discussed.

Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with gold nanoparticles

Fu Chen, He Da-Wei, WangYong-Sheng, Fu Ming, Geng Xin, Zhuo Zu-Liang
Chin. Phys. B 2015, 24 (8): 087801;  doi: 10.1088/1674-1056/24/8/087801
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A composite of graphene/PANI/GAunano is synthesized using the co-blend method. The morphologies and microstructures of samples are examined by transition electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Moreover, the microwave absorption properties of both graphene/PANI and GO/PANI/GAunano composites are investigated in a microwave frequency band from 1 GHz to 18 GHz. The maximum reflection loss (RL) of GO/PANI/GAunano with a thickness of 2 mm is up to-24.61 dB at 15.45 GHz, and the bandwidth corresponding to RL at-10 dB can reach 4.08 GHz (from 13.92 GHz to 18.00 GHz) for a 2-mm-thick layer. The electromagnetic data demonstrate that GO/PANI/GAunano can be used as an attractive candidate for microwave absorbers.

Influence of Al3+ doping on the energy levels and thermal property of the 3.5MgO·0.5MgF2·GeO2:Mn4+ red-emitting phosphor

Yuan Lin-lin, Zhang Xiao-Song, Xu Jian-Ping, Sun Jian, Jin Han, Liu Xiao-Juan, Li Lin-Lin, Li Lan
Chin. Phys. B 2015, 24 (8): 087802;  doi: 10.1088/1674-1056/24/8/087802
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A series of Al3+-doped 3.5MgO·0.5MgF2·GeO2:Mn4+ red-emitting phosphors is synthesized by high temperature solid-state reaction. The broad excitation band at 300 nm-380 nm, resulting from the 4A24T1 transition of Mn4+, exhibits a blue shift with the increase of Al2O3 content. The observation of the decreased Mn4+-O2- distance is explained by the crystal field theory. The temperature-dependent photoluminescence spectra with various amounts of Al2O3 content are comparatively measured and the calculation shows that the activation energy increases up to 0.41 eV at the Al2O3 content of 0.1 mol. The maximum phonon densities of state for these samples are calculated from Raman spectra and they are correlated with the thermal properties.

Photoluminescence of rare-earth ion (Eu3+, Tm3+, and Er3+)-doped and co-doped ZnNb2O6 for solar cells

Gao Sen-Pei, Qian Yan-Nan, Wang Biao
Chin. Phys. B 2015, 24 (8): 087803;  doi: 10.1088/1674-1056/24/8/087803
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Visible converted emissions produced at an excitation of 286 nm in ZnNb2O6 ceramics doped with rare-earth ions (RE = Eu3+, Tm3+, Er3+ or a combination of these ions) were investigated with the aim of increasing the photovoltaic efficiency of solar cells. The structure of RE:ZnNb2O6 ceramics was confirmed by x-ray diffraction patterns. The undoped ZnNb2O6 could emit a blue emission under 286-nm excitation, which is attributed to the self-trapped excitons' recombination of the efficient luminescence centers of edge-shared NbO6 groups. Upon 286-nm excitation, Eu:ZnNb2O6, Tm:ZnNb2O6, and Er:ZnNb2O6 ceramics showed blue, green, and red emissions, which correspond to the transitions of 5D07FJ (J = 1-4) (Eu3+), 1G43H6 (Tm3+), and 2H11/2/4S3/24I15/2 (Er3+), respectively. The calculated CIE chromaticity coordinates of Eu:ZnNb2O6, Tm:ZnNb2O6, and Er:ZnNb2O6 are (0.50, 0.31), (0.14, 0.19), and (0.29, 0.56), respectively. RE ionco- doped ZnNb2O6 showed a combination of characteristic emissions. The chromaticity coordinates of Eu/Tm:ZnNb2O6, Eu/Er:ZnNb2O6, and Tm/Er:ZnNb2O6 were calculated to be (0.29, 0.24), (0.45, 0.37), and (0.17, 0.25).


Theoretical study of the effects of vacancy and oxygen impurity on Ti2GaC

Chen Jun-Jun, Duan Ji-Zheng, Zhao Da-Qiang, Zhang Jian-Rong, Yang Yang, Duan Wen-Shan
Chin. Phys. B 2015, 24 (8): 088101;  doi: 10.1088/1674-1056/24/8/088101
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This paper presents the mono-vacancy formation and migration energies of each element Ti, Ga, and C in the MAX phase Ti2GaC, which are obtained by first principles calculations. We also calculate the formation energies of oxygen substituting for Ti, Ga, and C and two formation energies of oxygen interstitial in different sites. The results show that the formation energy of oxygen substituting for Ti is the highest, and the formation energies of the O substitution for Ga atoms decrease as the oxygen concentration increases. The two different formation energies of one oxygen interstitial show that the stable site for the oxygen interstitial is at the center of the triangle composed by three Ga atoms. The effects of vacancy, oxygen substitution, and the interstitial on the electronic properties of Ti2GaC are also discussed in light of the density of states and the electron charge density.

A superhigh discharge capacity induced by a synergetic effect between high-surface-area carbons and a carbon paper current collector in a lithium–oxygen battery

Luo Guang-Sheng, Huang Shi-Ting, Zhao Ning, Cui Zhong-Hui, Guo Xiang-Xin
Chin. Phys. B 2015, 24 (8): 088102;  doi: 10.1088/1674-1056/24/8/088102
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This paper invesitages the synergetic effect between high-surface-area carbons, such as Ketjan Black (KB) or Super P (SP) carbon materials, and low-surface-area carbon paper (CP) current collectors and it also examines their influence on the discharge performance of nonaqueous Li–O2 cells. Ultra-large specific discharge capacities are found in the KB/CP cathodes, which are much greater than those observed in the individual KB or CP cathodes. Detailed analysis indicates that such unexpectedly large capacities result from the synergetic effect between the two components. During the initial discharges of KB or SP materials, a large number of superoxide radical (O2·-) species in the electrolytes and Li2O2 nuclei at the CP surfaces are formed, which activate the CP current collectors to contribute considerable capacities. These results imply that CP could be a superior material for current collectors in terms of its contribution to the overall discharge capacity. On the other hand, we should be careful to calculate the specific capacities of the oxygen cathodes when using CP as a current collector; i.e., ignoring the contribution from the CP may cause overstated discharge capacities.

Path integral Monte Carlo study of (H2)n@C70 (n=1,2,3)

Hao Yan, Zhang Hong, Cheng Xin-Lu
Chin. Phys. B 2015, 24 (8): 088103;  doi: 10.1088/1674-1056/24/8/088103
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The path integral Monte Carlo (PIMC) method is employed to study the thermal properties of C70 with one, two, and three H2 molecules confined in the cage, respectively. The interaction energies and vibrationally averaged spatial distributions under different temperatures are calculated to evaluate the stabilities of (H2)n@C70 (n=1, 2, 3). The results show that (H2)2@C70 is more stable than H2@C70. The interaction energy slowly changes in a large temperature range, so temperature has little effect on the stability of the system. For H2@C70 and (H2)2@C70, the interaction energies keep negative; however, when three H2 molecules are in the cage, the interaction energy rapidly increases to a positive value. This implies that at most two H2 molecules can be trapped by C70. With an increase of temperature, the peak of the spatial distribution gradually shifts away from the center of the cage, but the maximum distance from the center of H2 molecule to the cage center is much smaller than the average radius of C70.

Effects of Fe additive on diamond crystallization from carbonyl nickel powders-C system under HPHT condition

Li Yong, Jia Xiao-Peng, Feng Yun-Guang, Fang Chao, Fan Li-Juan, Li Ya-Dong, Zeng Xiang, Ma Hong-An
Chin. Phys. B 2015, 24 (8): 088104;  doi: 10.1088/1674-1056/24/8/088104
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In this paper, diamond crystallization from carbonyl nickel powders-C and carbonyl nickel powders+Fe–C systems are investigated in detail at a pressure of 6.0 GPa and temperatures ranging from 1410 ℃–to 1435 ℃ by temperature gradient growth. The effects of Fe additive on the crystal morphology are discussed in the diamond crystallization process. Furthermore, Fourier infrared measurement results indicate that the spectrum of the diamond obtained from Ni+Fe–C system after annealing treatment is nearly consistent with that of natural diamond crystal. We believe that this study is of benefit to a further understanding of the growth mechanism of natural diamond.

Molecular dynamics simulation on generalized stacking fault energies of FCC metals under preloading stress

Zhang Liang, Lü Cheng, Tieu Kiet, Zhao Xing, Pei Lin-Qing, Michal Guillaume
Chin. Phys. B 2015, 24 (8): 088106;  doi: 10.1088/1674-1056/24/8/088106
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Molecular dynamics (MD) simulations are performed to investigate the effects of stress on generalized stacking fault (GSF) energy of three fcc metals (Cu, Al, and Ni). The simulation model is deformed by uniaxial tension or compression in each of [111], [11-2], and [1-10] directions, respectively, before shifting the lattice to calculate the GSF curve. Simulation results show that the values of unstable stacking fault energy (γusf), stable stacking fault energy (γsf), and unstable twin fault energy (γutf) of the three elements can change with the preloaded tensile or compressive stress in different directions. The ratio of γsf/γusf, which is related to the energy barrier for full dislocation nucleation, and the ratio of γutf/γusf, which is related to the energy barrier for twinning formation are plotted each as a function of the preloading stress. The results of this study reveal that the stress state can change the energy barrier of defect nucleation in the crystal lattice, and thereby can play an important role in the deformation mechanism of nanocrystalline material.

Microwave dielectric properties of Nextel-440 fiber fabrics with pyrolytic carbon coatings in the temperature range from room temperature to 700 ℃

Song Hui-Hui, Zhou Wan-Cheng, Luo Fa, Qing Yu-Chang, Chen Ma-Lin
Chin. Phys. B 2015, 24 (8): 088107;  doi: 10.1088/1674-1056/24/8/088107
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Pyrolytic carbon (PyC) coatings are deposited on the Nextel-440 fiber fabrics by chemical vapor deposition (CVD). The dielectric properties of the Nextel-440 fiber fabrics with PyC coatings (Nextel-440/PyC) are investigated in a temperature range from room temperature to 700 ℃ in X-band. Compared with the permittivity of the original Nextel-440 received, the complex permittivity of the Nextel-440/PyC (the real part ε' and the imaginary part ε"), is significantly improved: ε' of the Nextel-440/PyC has a positive temperature coefficient, in contrast, ε" of the Nextel-440/PyC exhibits a negative temperature coefficient. Moreover, the reflection loss in units of dB is calculated. The results indicate that the microwave absorbing properties of the Nextel-440/PyC coatings is enhanced at 700 ℃ compared with that at lower temperatures.

Switching mechanism for TiO2 memristor and quantitative analysis of exponential model parameters

Wang Xiao-Ping, Chen Min, Shen Yi
Chin. Phys. B 2015, 24 (8): 088401;  doi: 10.1088/1674-1056/24/8/088401
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The memristor, as the fourth basic circuit element, has drawn worldwide attention since its physical implementation was released by HP Labs in 2008. However, at the nano-scale, there are many difficulties for memristor physical realization. So a better understanding and analysis of a good model will help us to study the characteristics of a memristor. In this paper, we analyze a possible mechanism for the switching behavior of a memristor with a Pt/TiO2/Pt structure, and explain the changes of electronic barrier at the interface of Pt/TiO2. Then, a quantitative analysis about each parameter in the exponential model of memristor is conducted based on the calculation results. The analysis results are validated by simulation results. The efforts made in this paper will provide researchers with theoretical guidance on choosing appropriate values for (α, β, χ, γ) in this exponential model.

Effects of back gate bias on radio-frequency performance in partially depleted silicon-on-inslator nMOSFETs

Lü Kai, Chen Jing, Luo Jie-Xin, He Wei-Wei, Huang Jian-Qiang, Chai Zhan, Wang Xi
Chin. Phys. B 2015, 24 (8): 088501;  doi: 10.1088/1674-1056/24/8/088501
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The effects of back gate bias (BGEs) on radio-frequency (RF) performances in PD SOI nMOSFETs are presented in this paper. Floating body (FB) device, T-gate body-contact (TB) device, and tunnel diode body-contact (TDBC) device, of which the supply voltages are all 1.2 V, are compared under different back gate biases by different figures of merit, such as cut-off frequency (fT), maximum frequency of oscillation (fmax), etc. Because of the lack of a back gate conducting channel, the drain conductance (gd) of TDBC transistor shows a smaller degradation than those of the others, and the trans-conductance (gm) of TDBC is almost independent of back gate bias. The values of fT of TDBC are also kept nearly constant under different back gate biases. However, RF performances of FB and TB each show a significant degradation when the back gate bias is larger than ~ 20 V. The results indicate that TDBC structures could effectively improve the back gate bias in RF performance.

Single-event response of the SiGe HBT in TCAD simulations and laser microbeam experiment

Li Pei, Guo Hong-Xia, Guo Qi, Zhang Jin-Xin, Xiao Yao, Wei Ying, Cui Jiang-Wei, Wen Lin, Liu Mo-Han, Wang Xin
Chin. Phys. B 2015, 24 (8): 088502;  doi: 10.1088/1674-1056/24/8/088502
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In this paper the single-event responses of the silicon germanium heterojunction bipolar transistors (SiGe HBTs) are investigated by TCAD simulations and laser microbeam experiment. A three-dimensional (3D) simulation model is established, the single event effect (SEE) simulation is further carried out on the basis of SiGe HBT devices, and then, together with the laser microbeam test, the charge collection behaviors are analyzed, including the single event transient (SET) induced transient terminal currents, and the sensitive area of SEE charge collection. The simulations and experimental results are discussed in detail and it is demonstrated that the nature of the current transient is controlled by the behaviors of the collector–substrate (C/S) junction and charge collection by sensitive electrodes, thereby giving out the sensitive area and electrode of SiGe HBT in SEE.

Low frequency noise and radiation response in the partially depleted SOI MOSFETs with ion implanted buried oxide

Liu Yuan, Chen Hai-Bo, Liu Yu-Rong, Wang Xin, En Yun-Fei, Li Bin, Lu Yu-Dong
Chin. Phys. B 2015, 24 (8): 088503;  doi: 10.1088/1674-1056/24/8/088503
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Low frequency noise behaviors of partially depleted silicon-on-insulator (PDSOI) n-channel metal-oxide semiconductors (MOS) transistors with and without ion implantation into the buried oxide are investigated in this paper. Owing to ion implantation-induced electron traps in the buried oxide and back interface states, back gate threshold voltage increases from 44.48 V to 51.47 V and sub-threshold swing increases from 2.47 V/dec to 3.37 V/dec, while electron field effect mobility decreases from 475.44 cm2/V·s to 363.65 cm2/V·s. In addition, the magnitude of normalized low frequency noise also greatly increases, which indicates that the intrinsic electronic performances are degenerated after ion implantation processing. According to carrier number fluctuation theory, the extracted flat-band voltage noise power spectral densities in the PDSOI devices with and without ion implantation are equal to 7×10-10 V2·Hz-1 and 2.7×10-8 V2·Hz-1, respectively, while the extracted average trap density in the buried oxide increases from 1.42×1017 cm-3·eV-1 to 6.16×1018 cm-3·eV-1. Based on carrier mobility fluctuation theory, the extracted average Hooge's parameter in these devices increases from 3.92×10-5 to 1.34×10-2 after ion implantation processing. Finally, radiation responses in the PDSOI devices are investigated. Owing to radiation-induced positive buried oxide trapped charges, back gate threshold voltage decreases with the increase of the total dose. After radiation reaches up to a total dose of 1 M·rad(si), the shifts of back gate threshold voltage in the SOI devices with and without ion implantation are-10.82 V and-31.84 V, respectively. The low frequency noise behaviors in these devices before and after radiation are also compared and discussed.

Influence of white light illumination on the performance of a-IGZO thin film transistor under positive gate-bias stress

Tang Lan-Feng, Yu Guang, Lu Hai, Wu Chen-Fei, Qian Hui-Min, Zhou Dong, Zhang Rong, Zheng You-Dou, Huang Xiao-Ming
Chin. Phys. B 2015, 24 (8): 088504;  doi: 10.1088/1674-1056/24/8/088504
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The influence of white light illumination on the stability of an amorphous InGaZnO thin film transistor is investigated in this work. Under prolonged positive gate bias stress, the device illuminated by white light exhibits smaller positive threshold voltage shift than the device stressed under dark. There are simultaneous degradations of field-effect mobility for both stressed devices, which follows a similar trend to that of the threshold voltage shift. The reduced threshold voltage shift under illumination is explained by a competition between bias-induced interface carrier trapping effect and photon-induced carrier detrapping effect. It is further found that white light illumination could even excite and release trapped carriers originally exiting at the device interface before positive gate bias stress, so that the threshold voltage could recover to an even lower value than that in an equilibrium state. The effect of photo-excitation of oxygen vacancies within the a-IGZO film is also discussed.

Theoretical study of interactions between striated cylindrical particles and membrane Hot!

Wang Jing-Jing, Feng Jia-Wei, Ren Chun-Lai
Chin. Phys. B 2015, 24 (8): 088701;  doi: 10.1088/1674-1056/24/8/088701
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The interaction of nanoparticles with cell membranes is of great importance because of their potential biomedical applications. In this paper, we investigate the adhesion of stripe-patterned cylinders to a fluid membrane with a full consideration of the Helfrich free energy. Three situations are considered: one striated cylindrical particle, two pure cylindrical particles, and two Janus cylindrical particles. It is found that, with the adhesion of a single sparse striated cylinder, there are a variety of steady-states with energy barriers and the stable state is determined by the pattern of the cylinder. However, when the particle is densely striped, it has no effect on the stable state. By comparing the wrapping degree of two cylindrical particles with that of a single cylindrical particle, we find that two pure cylindrical particles can promote or suppress their interaction with the membrane under different situations. However, two Janus cylindrical particles can only inhibit their interaction with the membrane. Besides, this interaction is related to a first-order transition which is a shallow-to-deep wrapping transition for two pure cylinders while it is a shallow-to-half wrapping transition for two Janus cylinders. Furthermore, the position where the transition happens as a function of adhesion energy is given for fixed membrane tension and the precondition of the transition is presented.

Stability of focal adhesion enhanced by its inner force fluctuation

Mao Zhi-Xiu, Chen Xiao-Feng, Chen Bin
Chin. Phys. B 2015, 24 (8): 088702;  doi: 10.1088/1674-1056/24/8/088702
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Cells actively sense and respond to mechanical signals from the extracellular matrix through focal adhesions. By representing a single focal adhesion as a cluster of slip bonds, it has been demonstrated that the cluster often became unstable under fluctuated forces. However, an unusual case was also reported, where the stability of the cluster might be substantially enhanced by a fluctuated force with a relatively low fluctuation frequency and high fluctuation amplitude. Such an observation cannot be explained by the conventional fracture theory of fatigue. Here, we intensively investigate this intriguing observation by carrying out systematic parametric studies. Our intensive simulation results indicate that stability enhancement of this kind is in fact quite robust, which can be affected by the stochastic features of a single bond and the profile of the fluctuated forces such as the average value of bond force. We then suggest that the fluctuation of traction force within a focal adhesion might enhance its stability in a certain way.

Theoretical investigation on generating terahertz radiation from gas plasma induced by three-color ultrashort lasers

Wang Cheng-Liang, Yang Zhen-Gang, Liu Jin-Song, Wang Sheng-Lie, Wang Ke-Jia
Chin. Phys. B 2015, 24 (8): 088703;  doi: 10.1088/1674-1056/24/8/088703
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Generation of intense broadband terahertz (THz) waves from gas plasma induced by tri-color ultrashort (fundamental (ω), second harmonic (2ω), and third harmonic (3ω)) laser pulses is theoretically investigated. Simulation results show that the 3ω laser pulse can greatly enhance or suppress the generation of THz wave at different values of relative phase (θ3) between the 3ω and ω fields. Moreover, the polarities of the generated THz waves can be controlled by changing θ3, with the relative phase θ2 (between the 2ω and ω fields) fixed to be a certain value. All of our results show that θ3 plays a key role in the generation process, which promises to control the intensity as well as the polarity of gas plasma-induced THz radiation.

Effect of focused ultrasound stimulation at different ultrasonic power levels on the local field potential power spectrum

Yuan Yi, Lu Cheng-Biao, Li Xiao-Li
Chin. Phys. B 2015, 24 (8): 088704;  doi: 10.1088/1674-1056/24/8/088704
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Local field potential (LFP) signals of the rat hippocampus were recorded under noninvasive focused ultrasound stimulation (FUS) with different ultrasonic powers. The LFP mean absolute power was calculated with the Welch algorithm at the delta, theta, alpha, beta, and gamma frequency bands. The experimental results demonstrate that the LFP mean absolute power at different frequency bands increases as the ultrasound power increases.

Establishment, maintenance, and re-establishment of the safe and efficient steady-following state

Pan Deng, Zheng Ying-Ping
Chin. Phys. B 2015, 24 (8): 088901;  doi: 10.1088/1674-1056/24/8/088901
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We present an integrated mathematical model of vehicle-following control for the establishment, maintenance, and re-establishment of the previous or new safe and efficient steady-following state. The hyperbolic functions are introduced to establish the corresponding mathematical models, which can describe the behavioral adjustment of the following vehicle steered by a well-experienced driver under complex vehicle following situations. According to the proposed mathematical models, the control laws of the following vehicle adjusting its own behavior can be calculated for its moving in safety, efficiency, and smoothness (comfort). Simulation results show that the safe and efficient steady-following state can be well established, maintained, and re-established by its own smooth (comfortable) behavioral adjustment with the synchronous control of the following vehicle's velocity, acceleration, and the actual following distance.

Oscillatory Shannon entropy in the process of equilibration of nonequilibrium crystalline systems

A. Giri, Nilangshu K. Das, P. Barat
Chin. Phys. B 2015, 24 (8): 088902;  doi: 10.1088/1674-1056/24/8/088902
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We present a study of the equilibration process of some nonequilibrium crystalline systems by means of molecular dynamics simulation technique. The nonequilibrium conditions are achieved in the systems by randomly defining velocity components of the constituent atoms. The calculated Shannon entropy from the probability distribution of the kinetic energy among the atoms at different instants during the process of equilibration shows oscillation as the system relaxes towards equilibrium. Fourier transformations of these oscillating Shannon entropies reveal the existence of Debye frequency of the concerned system.

A study of the early warning signals of abrupt change in the Pacific decadal oscillation

Wu Hao, Hou Wei, Yan Peng-Cheng, Zhang Zhi-Sen, Wang Kuo
Chin. Phys. B 2015, 24 (8): 089201;  doi: 10.1088/1674-1056/24/8/089201
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In recent years, the phenomenon of a critical slowing down has demonstrated its major potential in discovering whether a complex dynamic system tends to abruptly change at critical points. This research on the Pacific decadal oscillation (PDO) index has been made on the basis of the critical slowing down principle in order to analyze its early warning signal of abrupt change. The chaotic characteristics of the PDO index sequence at different times are determined by using the largest Lyapunov exponent (LLE). The relationship between the regional sea surface temperature (SST) background field and the early warning signal of the PDO abrupt change is further studied through calculating the variance of the SST in the PDO region and the spatial distribution of the autocorrelation coefficient, thereby providing the experimental foundation for the extensive application of the method of the critical slowing down phenomenon. Our results show that the phenomenon of critical slowing down, such as the increase of the variance and autocorrelation coefficient, will continue for six years before the abrupt change of the PDO index. This phenomenon of the critical slowing down can be regarded as one of the early warning signals of an abrupt change. Through calculating the LLE of the PDO index during different times, it is also found that the strongest chaotic characteristics of the system occurred between 1971 and 1975 in the early stages of an abrupt change (1976), and the system was at the stage of a critical slowing down, which proves the reliability of the early warning signal of abrupt change discovered in 1970 from the mechanism. In addition, the variance of the SST, along with the spatial distribution of the autocorrelation coefficient in the corresponding PDO region, also demonstrates the corresponding relationship between the change of the background field of the SST and the change of the PDO.
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