Table of contents

05 August 2015, Volume 24 Issue 8 Previous issue    Next issue

GENERAL

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Hamiltonian structure, Darboux transformation for a soliton hierarchy associated with Lie algebra so(4, C) Wang Xin-Zeng (王新赠), Dong Huan-He (董焕河) Chin. Phys. B, 2015, 24 (8):  080201.  DOI: 10.1088/1674-1056/24/8/080201 Abstract ( 957 )   HTML   PDF (231KB) ( 340 )   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.

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New solutions from nonlocal symmetry of the generalized fifth order KdV equation Liu Xi-Zhong (刘希忠), Yu Jun (俞军), Ren Bo (任博) Chin. Phys. B, 2015, 24 (8):  080202.  DOI: 10.1088/1674-1056/24/8/080202 Abstract ( 750 )   HTML   PDF (205KB) ( 7234 )   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.

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Harmonic signal extraction from noisy chaotic interference based on synchrosqueezed wavelet transform Wang Xiang-Li (汪祥莉), Wang Wen-Bo (王文波) Chin. Phys. B, 2015, 24 (8):  080203.  DOI: 10.1088/1674-1056/24/8/080203 Abstract ( 602 )   HTML   PDF (1544KB) ( 5081 )   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.

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Fractional-order LβCα filter circuit network Hong Zheng (洪铮), Qian Jing (钱晶), Chen Di-Yi (陈帝伊), Herbert H. C. Iu Chin. Phys. B, 2015, 24 (8):  080204.  DOI: 10.1088/1674-1056/24/8/080204 Abstract ( 436 )   HTML   PDF (2437KB) ( 374 )   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.

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Inverse problem of quadratic time-dependent Hamiltonians Guo Guang-Jie (郭光杰), Meng Yan (孟艳), Chang Hong (常虹), Duan Hui-Zeng (段会增), Di Bing (邸冰) Chin. Phys. B, 2015, 24 (8):  080301.  DOI: 10.1088/1674-1056/24/8/080301 Abstract ( 554 )   HTML   PDF (308KB) ( 337 )   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.

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Wave–particle duality in a Raman atom interferometer Jia Ai-Ai (贾爱爱), Yang Jun (杨俊), Yan Shu-Hua (颜树华), Hu Qing-Qing (胡青青), Luo Yu-Kun (罗玉昆), Zhu Shi-Yao (朱诗尧) Chin. Phys. B, 2015, 24 (8):  080302.  DOI: 10.1088/1674-1056/24/8/080302 Abstract ( 673 )   HTML   PDF (223KB) ( 331 )   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.

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Decay of N-qubit GHZ states in Pauli channels Chen Xiao-Yu (陈小余), Wang Ting-Ting (王婷婷) Chin. Phys. B, 2015, 24 (8):  080303.  DOI: 10.1088/1674-1056/24/8/080303 Abstract ( 697 )   HTML   PDF (927KB) ( 269 )   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.

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Population dynamics of excited atoms in non-Markovian environments at zero and finite temperature Zou Hong-Mei (邹红梅), Fang Mao-Fa (方卯发) Chin. Phys. B, 2015, 24 (8):  080304.  DOI: 10.1088/1674-1056/24/8/080304 Abstract ( 575 )   HTML   PDF (272KB) ( 292 )   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.

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An optimized encoding method for secure key distribution by swapping quantum entanglement and its extension Gao Gan (高干) Chin. Phys. B, 2015, 24 (8):  080305.  DOI: 10.1088/1674-1056/24/8/080305 Abstract ( 707 )   HTML   PDF (173KB) ( 313 )   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.

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Faithful deterministic secure quantum communication and authentication protocol based on hyperentanglement against collective noise Chang Yan (昌燕), Zhang Shi-Bin (张仕斌), Yan Li-Li (闫丽丽), Han Gui-Hua (韩桂华) Chin. Phys. B, 2015, 24 (8):  080306.  DOI: 10.1088/1674-1056/24/8/080306 Abstract ( 669 )   HTML   PDF (288KB) ( 436 )   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.

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Decoherence in optimized quantum random-walk search algorithm Zhang Yu-Chao (张宇超), Bao Wan-Su (鲍皖苏), Wang Xiang (汪翔), Fu Xiang-Qun (付向群) Chin. Phys. B, 2015, 24 (8):  080307.  DOI: 10.1088/1674-1056/24/8/080307 Abstract ( 750 )   HTML   PDF (271KB) ( 310 )   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.

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Two-color laser modulation of magnetic Feshbach resonances Li Jian (李健), Liu Yong (刘勇), Huang Yin (黄寅), Cong Shu-Lin (丛书林) Chin. Phys. B, 2015, 24 (8):  080308.  DOI: 10.1088/1674-1056/24/8/080308 Abstract ( 607 )   HTML   PDF (415KB) ( 284 )   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.

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The stability of Majorana fermion in correlated quantum wire Zhang De-Ping (张德平), Tian Guang-Shan (田光善) Chin. Phys. B, 2015, 24 (8):  080401.  DOI: 10.1088/1674-1056/24/8/080401 Abstract ( 688 )   HTML   PDF (384KB) ( 312 )   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.

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Chaotic dynamics and its analysis of Hindmarsh–Rose neurons by Shil'nikov approach Wei Wei (魏伟), Zuo Min (左敏) Chin. Phys. B, 2015, 24 (8):  080501.  DOI: 10.1088/1674-1056/24/8/080501 Abstract ( 578 )   HTML   PDF (440KB) ( 248 )   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.

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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 Abstract ( 665 )   HTML   PDF (1490KB) ( 508 )   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.

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Secure communication based on spatiotemporal chaos Ren Hai-Peng (任海鹏), Bai Chao (白超) Chin. Phys. B, 2015, 24 (8):  080503.  DOI: 10.1088/1674-1056/24/8/080503 Abstract ( 530 )   HTML   PDF (584KB) ( 385 )   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.

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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 Abstract ( 523 )   HTML   PDF (1427KB) ( 394 )   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.

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Design and fabrication of structural color by local surface plasmonic meta-molecules Ma Ya-Qi (马亚琪), Shao Jin-Hai (邵金海), Zhang Ya-Feng (张亚峰), Lu Bing-Rui (陆冰睿), Zhang Si-Chao (张思超), Sun Yan (孙艳), Qu Xin-Ping (屈新萍), Chen Yi-Fang (陈宜方) Chin. Phys. B, 2015, 24 (8):  080702.  DOI: 10.1088/1674-1056/24/8/080702 Abstract ( 762 )   HTML   PDF (683KB) ( 325 )   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.

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Piecewise spectrally band-pass for compressive coded aperture spectral imaging Qian Lu-Lu (钱路路), Lü Qun-Bo (吕群波), Huang Min (黄旻), Xiang Li-Bin (相里斌) Chin. Phys. B, 2015, 24 (8):  080703.  DOI: 10.1088/1674-1056/24/8/080703 Abstract ( 678 )   HTML   PDF (970KB) ( 537 )   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.

ATOMIC AND MOLECULAR PHYSICS

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Spectral properties of endohedrally confined helium atom Fang Shuai-Shuai (方帅帅), Qiao Hao-Xue (乔豪学) Chin. Phys. B, 2015, 24 (8):  083101.  DOI: 10.1088/1674-1056/24/8/083101 Abstract ( 545 )   HTML   PDF (2636KB) ( 248 )   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.

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Electric dipole moment function and line intensities for the ground state of carbon monxide Chen Hua-Jun (陈华君), Wu Jie (吴杰), Liu Hao (刘浩), Cheng Xin-Lu (程新路) Chin. Phys. B, 2015, 24 (8):  083102.  DOI: 10.1088/1674-1056/24/8/083102 Abstract ( 784 )   HTML   PDF (420KB) ( 253 )   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.

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Electron impact excitation of helium atom Han Xiao-Ying (韩小英), Zeng De-Ling (曾德灵), Gao Xiang (高翔), Li Jia-Ming (李家明) Chin. Phys. B, 2015, 24 (8):  083103.  DOI: 10.1088/1674-1056/24/8/083103 Abstract ( 479 )   HTML   PDF (526KB) ( 377 )   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.

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State-to-state quantum dynamics of the N(4S)+H2 (X1Σ+)→NH(X3∑-)+H(2S) reaction and its reaction mechanism analysis Zhang Jing (张静), Gao Shou-Bao (高守宝), Wu Hui (吴慧), Meng Qing-Tian (孟庆田) Chin. Phys. B, 2015, 24 (8):  083104.  DOI: 10.1088/1674-1056/24/8/083104 Abstract ( 699 )   HTML   PDF (544KB) ( 348 )   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.

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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 Abstract ( 659 )   HTML   PDF (269KB) ( 345 )   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.

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Optically pumped quantum Mx–MR magnetometer with high oscillating magnetic field Ding Zhi-Chao (丁志超), Yuan Jie (袁杰), Wang Zhi-Guo (汪之国), Yang Kai-Yong (杨开勇), Luo Hui (罗晖) Chin. Phys. B, 2015, 24 (8):  083202.  DOI: 10.1088/1674-1056/24/8/083202 Abstract ( 742 )   HTML   PDF (345KB) ( 357 )   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 Mx–MR magnetometer operates on condition that the intensity of oscillating magnetic field is smaller than this specific value, and the Mx–MR magnetometer can possess a much higher signal-to-noise ratio. The experimental result shows that the sensitivity of Mx–MR magnetometer can be improved by an order of magnitude under this condition.

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Branching ratios of autoionization from Eu 4f76p1/26d [J] autoionizing states Yan Jun-Gang (闫俊刚), Shen Li (沈礼), Liang Hong-Rui (梁洪瑞), Dai Chang-Jian (戴长建) Chin. Phys. B, 2015, 24 (8):  083203.  DOI: 10.1088/1674-1056/24/8/083203 Abstract ( 568 )   HTML   PDF (433KB) ( 187 )   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.

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Study on the A2Π3/2u, B2Δ3/2u, and X2Π3/2g states of Cl2+ including its isotopologues Wu Ling (吴玲), You Su-Ping (尤素萍), Shao Xu-Ping (邵旭萍), Chen Gang-Jin (陈钢进), Ding Ning (丁宁), Wang You-Mei (汪友梅), Yang Xiao-Hua (杨晓华) Chin. Phys. B, 2015, 24 (8):  083301.  DOI: 10.1088/1674-1056/24/8/083301 Abstract ( 617 )   HTML   PDF (226KB) ( 210 )   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.

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Atomic motion in the magneto–optical trap consisting of partially spatially coherent laser Zhang Bao-Wu (张宝武), Wang Zhao-Ying (王兆英), Kong De-Long (孔德龙), Lin Qiang (林强) Chin. Phys. B, 2015, 24 (8):  083701.  DOI: 10.1088/1674-1056/24/8/083701 Abstract ( 593 )   HTML   PDF (336KB) ( 270 )   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.

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Compensating for excess micromotion of ion crystals Du Li-Jun (杜丽军), Chen Ting (陈婷), Song Hong-Fang (宋红芳), Chen Shao-Long (陈邵龙), Li Hai-Xia (李海霞), Huang Yao (黄垚), Tong Xin (童昕), Guan Hua (管桦), Gao Ke-Lin (高克林) Chin. Phys. B, 2015, 24 (8):  083702.  DOI: 10.1088/1674-1056/24/8/083702 Abstract ( 639 )   HTML   PDF (2012KB) ( 358 )   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.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Switchable multi-wavelength fiber laser based on modal interference Ma Lin (马林), Sun Jiang (孙将), Qi Yan-Hui (齐艳辉), Kang Ze-Xin (康泽新), Jian Shui-Sheng (简水生) Chin. Phys. B, 2015, 24 (8):  084201.  DOI: 10.1088/1674-1056/24/8/084201 Abstract ( 534 )   HTML   PDF (563KB) ( 376 )   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.

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Characteristic of femtosecond laser-pulsed digital holography Shi Bing-Chuan (石炳川), Wang Xiao-Lei (王晓雷), Guo Wen-Gang (郭文刚), Song Li-Pei (宋丽培) Chin. Phys. B, 2015, 24 (8):  084202.  DOI: 10.1088/1674-1056/24/8/084202 Abstract ( 529 )   HTML   PDF (2007KB) ( 419 )   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.

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Strong violations of locality by testing Bell's inequality with improved entangled-photon systems Wang Yao (王尧), Fan Dai-He (樊代和), Guo Wei-Jie (郭伟杰), Wei Lian-Fu (韦联福) Chin. Phys. B, 2015, 24 (8):  084203.  DOI: 10.1088/1674-1056/24/8/084203 Abstract ( 604 )   HTML   PDF (617KB) ( 427 )   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.

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Double transmission peaks electromagnetically induced transparency induced by simultaneously exciting the electric and magnetic resonance in one unit cell Liu Si-Yuan (刘思源), Zheng Bu-Sheng (郑步生), Li Hai-Ming (李海明), Liu Xiao-Chun (刘晓春), Liu Shao-Bin (刘少斌) Chin. Phys. B, 2015, 24 (8):  084204.  DOI: 10.1088/1674-1056/24/8/084204 Abstract ( 753 )   HTML   PDF (698KB) ( 359 )   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.

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Plasma induced by pulsed laser and fabrication of silicon nanostructures Hang Wei-Qi (黄伟其), Dong Tai-Ge (董泰阁), Wang Gang (王刚), Liu Shi-Rong (刘世荣), Huang Zhong-Mei (黄忠梅), Miao Xin-Jian (苗信建), Lv Quan (吕泉), Qin Chao-Jian (秦朝建) Chin. Phys. B, 2015, 24 (8):  084205.  DOI: 10.1088/1674-1056/24/8/084205 Abstract ( 615 )   HTML   PDF (636KB) ( 326 )   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.

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Passive harmonic mode-locking of Er-doped fiber laser using CVD-grown few-layer MoS2 as a saturable absorber Xia Han-Ding (夏汉定), Li He-Ping (李和平), Lan Chang-Yong (兰长勇), Li Chun (李春), Deng Guang-Lei (邓光磊), Li Jian-Feng (李剑峰), Liu Yong (刘永) Chin. Phys. B, 2015, 24 (8):  084206.  DOI: 10.1088/1674-1056/24/8/084206 Abstract ( 711 )   HTML   PDF (513KB) ( 546 )   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.

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Effect of pulse width on near-infrared supercontinuum generation in nonlinear fiber amplifier Song Rui (宋锐), Lei Cheng-Min (雷成敏), Chen Sheng-Ping (陈胜平), Wang Ze-Feng (王泽锋), Hou Jing (侯静) Chin. Phys. B, 2015, 24 (8):  084207.  DOI: 10.1088/1674-1056/24/8/084207 Abstract ( 653 )   HTML   PDF (442KB) ( 277 )   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.

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Compact, temperature-stable multi-gigahertz passively modelocked semiconductor disk laser Song Yan-Rong (宋晏蓉), Guoyu He-Yang (郭于鹤洋), Zhang Peng (张鹏), Tian Jin-Rong (田金荣) Chin. Phys. B, 2015, 24 (8):  084208.  DOI: 10.1088/1674-1056/24/8/084208 Abstract ( 594 )   HTML   PDF (684KB) ( 365 )   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.

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Optical coherence transfer over 50-km spooled fiber with frequency instability of 2×10-17 at 1 s Ma Chao-Qun (马超群), Wu Li-Fei (吾利飞), Jiang Yan-Yi (蒋燕义), Yu Hong-Fu (于洪浮), Bi Zhi-Yi (毕志毅), Ma Long-Sheng (马龙生) Chin. Phys. B, 2015, 24 (8):  084209.  DOI: 10.1088/1674-1056/24/8/084209 Abstract ( 728 )   HTML   PDF (318KB) ( 359 )   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.

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Evolution of dark solitons in the presence of Ramangain and self-steepening effect Yu Yu (于宇), Jia Wei-Guo (贾维国), Yan Qing (闫青), Menke Neimule (门克内木乐), Zhang Jun-Ping (张俊萍) Chin. Phys. B, 2015, 24 (8):  084210.  DOI: 10.1088/1674-1056/24/8/084210 Abstract ( 608 )   HTML   PDF (6337KB) ( 847 )   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.

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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 Abstract ( 706 )   HTML   PDF (1050KB) ( 286 )   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.

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Optimizational 6-bit all-optical quantization with soliton self-frequency shift and pre-chirp spectral compression techniques based on photonic crystal fiber Li Sha (李莎), Wang Jian-Ping (王建萍), Kang Zhe (康哲), Yu Chong-Xiu (余重秀) Chin. Phys. B, 2015, 24 (8):  084212.  DOI: 10.1088/1674-1056/24/8/084212 Abstract ( 771 )   HTML   PDF (1643KB) ( 882 )   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.

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Estimation of random errors for lidar based on noise scale factor Wang Huan-Xue (王欢雪), Liu Jian-Guo (刘建国), Zhang Tian-Shu (张天舒) Chin. Phys. B, 2015, 24 (8):  084213.  DOI: 10.1088/1674-1056/24/8/084213 Abstract ( 666 )   HTML   PDF (299KB) ( 506 )   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.

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Comparison between iterative wavefront control algorithm and direct gradient wavefront control algorithm for adaptive optics system Cheng Sheng-Yi (程生毅), Liu Wen-Jin (刘文劲), Chen Shan-Qiu (陈善球), Dong Li-Zhi (董理治), Yang Ping (杨平), Xu Bing (许冰) Chin. Phys. B, 2015, 24 (8):  084214.  DOI: 10.1088/1674-1056/24/8/084214 Abstract ( 649 )   HTML   PDF (2244KB) ( 546 )   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.

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Effects of core position of locally resonant scatterers on low-frequency acoustic absorption in viscoelastic panel Zhong Jie (钟杰), Wen Ji-Hong (温激鸿), Zhao Hong-Gang (赵宏刚), Yin Jian-Fei (尹剑飞), Yang Hai-Bin (杨海滨) Chin. Phys. B, 2015, 24 (8):  084301.  DOI: 10.1088/1674-1056/24/8/084301 Abstract ( 639 )   HTML   PDF (442KB) ( 309 )   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.

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Direct numerical simulation of viscoelastic-fluid-based nanofluid turbulent channel flow with heat transfer Yang Juan-Cheng (阳倦成), Li Feng-Chen (李凤臣), Cai Wei-Hua (蔡伟华), Zhang Hong-Na (张红娜), Yu Bo (宇波) Chin. Phys. B, 2015, 24 (8):  084401.  DOI: 10.1088/1674-1056/24/8/084401 Abstract ( 686 )   HTML   PDF (1996KB) ( 470 )   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.

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On the ascent of infinite dimensional Hamiltonian operators Wu De-Yu (吴德玉), Chen Alatancang (陈阿拉坦仓) Chin. Phys. B, 2015, 24 (8):  084601.  DOI: 10.1088/1674-1056/24/8/084601 Abstract ( 536 )   HTML   PDF (191KB) ( 210 )   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.

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A novel method of evaluating the lift force on the bluff body based on Noca's flux equation Sui Xiang-Kun (隋相坤), Jiang Nan (姜楠) Chin. Phys. B, 2015, 24 (8):  084701.  DOI: 10.1088/1674-1056/24/8/084701 Abstract ( 509 )   HTML   PDF (877KB) ( 246 )   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.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Reactive oxygen species in plasma against E. coli cells survival rate Zhou Ren-Wu (周仁武), Zhang Xian-Hui (张先徽), Zong Zi-Chao (宗子超), Li Jun-Xiong (李俊雄), Yang Zhou-Bin (杨周斌), Liu Dong-Ping (刘东平), Yang Si-Ze (杨思泽) Chin. Phys. B, 2015, 24 (8):  085201.  DOI: 10.1088/1674-1056/24/8/085201 Abstract ( 684 )   HTML   PDF (848KB) ( 601 )   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.

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Particle-in-cell simulation for different magnetic mirror effects on the plasma distribution in a cusped field thruster Liu Hui (刘辉), Chen Peng-Bo (陈蓬勃), Zhao Yin-Jian (赵隐剑), Yu Da-Ren (于达仁) Chin. Phys. B, 2015, 24 (8):  085202.  DOI: 10.1088/1674-1056/24/8/085202 Abstract ( 679 )   HTML   PDF (705KB) ( 446 )   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.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Extended x-ray absorption fine structure study of MnFeP0.56Si0.44 compound Li Ying-Jie (李英杰), Haschaolu W (哈斯朝鲁), Wurentuya (乌仁图雅), Song Zhi-Qiang (宋志强), Ou Zhi-Qiang (欧志强), Tegus O (特古斯), Nakai Ikuo (中井生央) Chin. Phys. B, 2015, 24 (8):  086101.  DOI: 10.1088/1674-1056/24/8/086101 Abstract ( 747 )   HTML   PDF (524KB) ( 284 )   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.

TOPICAL REVIEW—Silicene

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Silicene: from monolayer to multilayer–A concise review Li Hui (李晖), Fu Hui-Xia (付会霞), Meng Sheng (孟胜) Chin. Phys. B, 2015, 24 (8):  086102.  DOI: 10.1088/1674-1056/24/8/086102 Abstract ( 770 )   HTML   PDF (1241KB) ( 1297 )   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.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Irradiation effects of graphene and thin layer graphite induced by swift heavy ions Hot! Zeng Jian (曾健), Liu Jie (刘杰), Zhang Sheng-Xia (张胜霞), Zhai Peng-Fei (翟鹏飞), Yao Hui-Jun (姚会军), Duan Jing-Lai (段敬来), Guo Hang (郭航), Hou Ming-Dong (侯明东), Sun You-Mei (孙友梅) Chin. Phys. B, 2015, 24 (8):  086103.  DOI: 10.1088/1674-1056/24/8/086103 Abstract ( 668 )   HTML   PDF (1153KB) ( 461 )   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').

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Analytical model for describing ion guiding through capillaries in insulating polymers Liu Shi-Dong (刘世东), Zhao Yong-Tao (赵永涛), Wang Yu-Yu (王瑜玉), Stolterfoht N, Cheng Rui (程锐), Zhou Xian-Ming (周贤明), Xu Hu-Shan (徐瑚珊), Xiao Guo-Qing (肖国青) Chin. Phys. B, 2015, 24 (8):  086104.  DOI: 10.1088/1674-1056/24/8/086104 Abstract ( 476 )   HTML   PDF (324KB) ( 199 )   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.

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Accurate calculations of the high-pressure elastic constants based on the first-principles Wang Chen-Ju (王臣菊), Gu Jian-Bing (顾建兵), Kuang Xiao-Yu (邝小渝), Yang Xiang-Dong (杨向东) Chin. Phys. B, 2015, 24 (8):  086201.  DOI: 10.1088/1674-1056/24/8/086201 Abstract ( 691 )   HTML   PDF (280KB) ( 362 )   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.

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First-principles verification of CuNNi3 and ZnNNi3 as phonon mediated superconductors Chen Jian-Yong (陈建勇), Wang Xing (王星) Chin. Phys. B, 2015, 24 (8):  086301.  DOI: 10.1088/1674-1056/24/8/086301 Abstract ( 715 )   HTML   PDF (1295KB) ( 545 )   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.

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Bending-induced phase transition in monolayer black phosphorus Pan Dou-Xing (潘斗兴), Wang Tzu-Chiang (王自强), Guo Wan-Lin (郭万林) Chin. Phys. B, 2015, 24 (8):  086401.  DOI: 10.1088/1674-1056/24/8/086401 Abstract ( 730 )   HTML   PDF (1754KB) ( 646 )   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.

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Surface-charge-governed electrolyte transport in carbon nanotubes Xue Jian-Ming (薛建明), Guo Peng (郭鹏), Sheng Qian (盛倩) Chin. Phys. B, 2015, 24 (8):  086601.  DOI: 10.1088/1674-1056/24/8/086601 Abstract ( 463 )   HTML   PDF (965KB) ( 411 )   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.

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Improvement of variational approach in an interacting two-fermion system Liu Yan-Xia (刘彦霞), Ye Jun (叶君), Li Yuan-Yuan (李源远), Zhang Yun-Bo (张云波) Chin. Phys. B, 2015, 24 (8):  086701.  DOI: 10.1088/1674-1056/24/8/086701 Abstract ( 683 )   HTML   PDF (305KB) ( 238 )   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.

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Contact angle hysteresis in electrowetting on dielectric Zhao Rui (赵瑞), Liu Qi-Chao (刘启超), Wang Ping (王评), Liang Zhong-Cheng (梁忠诚) Chin. Phys. B, 2015, 24 (8):  086801.  DOI: 10.1088/1674-1056/24/8/086801 Abstract ( 652 )   HTML   PDF (250KB) ( 358 )   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.

TOPICAL REVIEW—Silicene

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A review of the growth and structures of silicene on Ag (111) Wu Ke-Hui (吴克辉) Chin. Phys. B, 2015, 24 (8):  086802.  DOI: 10.1088/1674-1056/24/8/086802 Abstract ( 772 )   HTML   PDF (4864KB) ( 733 )   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.

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Fabrication and properties of silicene and silicene–graphene layered structures on Ir (111) Meng Lei (孟蕾), Wang Ye-Liang (王业亮), Zhang Li-Zhi (张理智), Du Shi-Xuan (杜世萱), Gao Hong-Jun (高鸿钧) Chin. Phys. B, 2015, 24 (8):  086803.  DOI: 10.1088/1674-1056/24/8/086803 Abstract ( 770 )   HTML   PDF (4787KB) ( 1756 )   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.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Structured dark-field imaging for single nano-particles Chen Jian (陈健), Gao Kun (高昆), Wang Zhi-Li (王志立), Yun Wen-Bing (云文兵), Wu Zi-Yu (吴自玉) Chin. Phys. B, 2015, 24 (8):  086804.  DOI: 10.1088/1674-1056/24/8/086804 Abstract ( 438 )   HTML   PDF (355KB) ( 294 )   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.

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Indenter size effect on the reversible incipient plasticity of Al (001) surface: Quasicontinuum study Tang Dan (唐丹), Shao Yu-Fei (邵宇飞), Li Jiu-Hui (李久会), Zhao Xing (赵星), Qi Yang (祁阳) Chin. Phys. B, 2015, 24 (8):  086805.  DOI: 10.1088/1674-1056/24/8/086805 Abstract ( 536 )   HTML   PDF (534KB) ( 276 )   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.

SPECIAL TOPIC—Silicene

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Domain boundaries in silicene: Density functional theory calculations on electronic properties Xiao Hong-Jun (肖红君), Zhang Li-Zhi (张礼智), Du Shi-Xuan (杜世萱), Gao Hong-Jun (高鸿钧) Chin. Phys. B, 2015, 24 (8):  086806.  DOI: 10.1088/1674-1056/24/8/086806 Abstract ( 507 )   HTML   PDF (1608KB) ( 888 )   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.

TOPICAL REVIEW—Silicene

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Chemical modification of silicene Wang Rong (王蓉), Xu Ming-Sheng (徐明生), Pi Xiao-Dong (皮孝东) Chin. Phys. B, 2015, 24 (8):  086807.  DOI: 10.1088/1674-1056/24/8/086807 Abstract ( 846 )   HTML   PDF (13800KB) ( 567 )   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.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Low-temperature charged impurity scattering-limited conductivity in relatively high doped bilayer graphene Hu Bo (胡波) Chin. Phys. B, 2015, 24 (8):  087101.  DOI: 10.1088/1674-1056/24/8/087101 Abstract ( 709 )   HTML   PDF (244KB) ( 400 )   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.

TOPICAL REVIEW—Silicene

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Silicene spintronics–A concise review Wang Yang-Yang (王洋洋), Quhe Ru-Ge (屈贺如歌), Yu Da-Peng (俞大鹏), Lü Jin (吕劲) Chin. Phys. B, 2015, 24 (8):  087201.  DOI: 10.1088/1674-1056/24/8/087201 Abstract ( 681 )   HTML   PDF (7004KB) ( 705 )   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.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Spin pumping through magnetic impurity effect Hot! Deng Wei-Yin (邓伟胤), Sheng Li (盛利), Xing Ding-Yu (邢定钰) Chin. Phys. B, 2015, 24 (8):  087202.  DOI: 10.1088/1674-1056/24/8/087202 Abstract ( 932 )   HTML   PDF (271KB) ( 259 )   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.

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Tunable multiple plasmon resonances and local field enhancement of nanocrescent/nanoring structure Wang Bin-Bing (王彬兵), Zhou Jun (周骏), Chen Dong (陈栋), Fang Yun-Tuan (方云团), Chen Ming-Yang (陈明阳) Chin. Phys. B, 2015, 24 (8):  087301.  DOI: 10.1088/1674-1056/24/8/087301 Abstract ( 793 )   HTML   PDF (709KB) ( 342 )   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.

TOPICAL REVIEW—Silicene

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Modulation of electronic properties with external fields in silicene-based nanostructures Li Geng (李庚), Zhao Yin-Chang (赵银昌), Zheng Rui (郑蕊), Ni Jun (倪军), Wu Yan-Ning (吴言宁) Chin. Phys. B, 2015, 24 (8):  087302.  DOI: 10.1088/1674-1056/24/8/087302 Abstract ( 523 )   HTML   PDF (5750KB) ( 689 )   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.

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Growth mechanism and modification of electronic and magnetic properties of silicene Liu Hong-Sheng (柳洪盛), Han Nan-Nan (韩楠楠), Zhao Ji-Jun (赵纪军) Chin. Phys. B, 2015, 24 (8):  087303.  DOI: 10.1088/1674-1056/24/8/087303 Abstract ( 888 )   HTML   PDF (3965KB) ( 928 )   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.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Charge trapping behavior and its origin in Al2O3/SiC MIS system Liu Xin-Yu (刘新宇), Wang Yi-Yu (王弋宇), Peng Zhao-Yang (彭朝阳), Li Cheng-Zhan (李诚瞻), Wu Jia (吴佳), Bai Yun (白云), Tang Yi-Dan (汤益丹), Liu Ke-An (刘可安), Shen Hua-Jun (申华军) Chin. Phys. B, 2015, 24 (8):  087304.  DOI: 10.1088/1674-1056/24/8/087304 Abstract ( 537 )   HTML   PDF (520KB) ( 293 )   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.

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Hetero-epitaxy of Lg=0.13-μm metamorphic AlInAs/GaInAs HEMT on Si substrates by MOCVD for logic applications Huang Jie (黄杰), Li Ming (黎明), Zhao Qian (赵倩), Gu Wen-Wen (顾雯雯), Lau Kei-May (刘纪美) Chin. Phys. B, 2015, 24 (8):  087305.  DOI: 10.1088/1674-1056/24/8/087305 Abstract ( 694 )   HTML   PDF (574KB) ( 401 )   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.

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Influence of the AlGaN barrier thickness on polarization Coulomb field scattering in an AlGaN/AlN/GaN heterostructure field-effect transistor Lv Yuan-Jie (吕元杰), Feng Zhi-Hong (冯志红), Gu Guo-Dong (顾国栋), Yin Jia-Yun (尹甲运), Fang Yu-Long (房玉龙), Wang Yuan-Gang (王元刚), Tan Xin (谭鑫), Zhou Xing-Ye (周幸叶), Lin Zhao-Jun (林兆军), Ji Zi-Wu (冀子武), Cai Shu-Jun (蔡树军) Chin. Phys. B, 2015, 24 (8):  087306.  DOI: 10.1088/1674-1056/24/8/087306 Abstract ( 720 )   HTML   PDF (361KB) ( 351 )   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.

SPECIAL TOPIC—Silicene

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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 Abstract ( 710 )   HTML   PDF (1520KB) ( 374 )   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.

TOPICAL REVIEW—Silicene

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Silicene on substrates: A theoretical perspective Zhong Hong-Xia (钟红霞), Quhe Ru-Ge (屈贺如歌), Wang Yang-Yang (王洋洋), Shi Jun-Jie (史俊杰), Lü Jin (吕劲) Chin. Phys. B, 2015, 24 (8):  087308.  DOI: 10.1088/1674-1056/24/8/087308 Abstract ( 573 )   HTML   PDF (7810KB) ( 496 )   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.

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Electronic structure of silicene L. C. Lew Yan Voon (刘祿昌) Chin. Phys. B, 2015, 24 (8):  087309.  DOI: 10.1088/1674-1056/24/8/087309 Abstract ( 525 )   HTML   PDF (3664KB) ( 1761 )   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.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Evolution of structure and magnetic properties in PrCo5 magnet for high energy ball milling in ethanol Li Zhu-Bai (李柱柏), Lan Jian-Ting (兰剑亭), Zhang Xue-Feng (张雪峰), Liu Yan-Li (刘艳丽), Li Yong-Feng (李永峰) Chin. Phys. B, 2015, 24 (8):  087501.  DOI: 10.1088/1674-1056/24/8/087501 Abstract ( 651 )   HTML   PDF (417KB) ( 305 )   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.

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Magnetization plateaus and frequency dispersion of hysteresis on frustrated dipolar array Zhang You-Tian (张又天) Chin. Phys. B, 2015, 24 (8):  087502.  DOI: 10.1088/1674-1056/24/8/087502 Abstract ( 672 )   HTML   PDF (2681KB) ( 628 )   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.

SPECIAL TOPIC—Silicene

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Antiferromagnetic and topological states in silicene: A mean field study Liu Feng (刘峰), Liu Cheng-Cheng (刘铖铖), Yao Yu-Gui (姚裕贵) Chin. Phys. B, 2015, 24 (8):  087503.  DOI: 10.1088/1674-1056/24/8/087503 Abstract ( 973 )   HTML   PDF (1310KB) ( 479 )   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.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Synthesis and microwave absorption properties of graphene-oxide(GO)/polyaniline nanocomposite with gold nanoparticles Fu Chen (付晨), He Da-Wei (何大伟), WangYong-Sheng (王永生), Fu Ming (富鸣), Geng Xin (耿欣), Zhuo Zu-Liang (卓祖亮) Chin. Phys. B, 2015, 24 (8):  087801.  DOI: 10.1088/1674-1056/24/8/087801 Abstract ( 792 )   HTML   PDF (676KB) ( 1069 )   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.

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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 (苑琳琳), Zhang Xiao-Song (张晓松), Xu Jian-Ping (徐建萍), Sun Jian (孙健), Jin Han (金含), Liu Xiao-Juan (刘晓娟), Li Lin-Lin (李霖霖), Li Lan (李岚) Chin. Phys. B, 2015, 24 (8):  087802.  DOI: 10.1088/1674-1056/24/8/087802 Abstract ( 742 )   HTML   PDF (860KB) ( 684 )   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 4A2 → 4T1 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.

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Photoluminescence of rare-earth ion (Eu3+, Tm3+, and Er3+)-doped and co-doped ZnNb2O6 for solar cells Gao Sen-Pei (高森沛), Qian Yan-Nan (钱艳楠), Wang Biao (王彪) Chin. Phys. B, 2015, 24 (8):  087803.  DOI: 10.1088/1674-1056/24/8/087803 Abstract ( 689 )   HTML   PDF (558KB) ( 467 )   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 5D0→7FJ (J = 1-4) (Eu3+), 1G4 → 3H6 (Tm3+), and 2H11/2/4S3/2 → 4I15/2 (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).

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Theoretical study of the effects of vacancy and oxygen impurity on Ti2GaC Chen Jun-Jun (陈俊俊), Duan Ji-Zheng (段济正), Zhao Da-Qiang (赵大强), Zhang Jian-Rong (张建荣), Yang Yang (杨阳), Duan Wen-Shan (段文山) Chin. Phys. B, 2015, 24 (8):  088101.  DOI: 10.1088/1674-1056/24/8/088101 Abstract ( 484 )   HTML   PDF (671KB) ( 322 )   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.

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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 (罗广生), Huang Shi-Ting (黄诗婷), Zhao Ning (赵宁), Cui Zhong-Hui (崔忠慧), Guo Xiang-Xin (郭向欣) Chin. Phys. B, 2015, 24 (8):  088102.  DOI: 10.1088/1674-1056/24/8/088102 Abstract ( 502 )   HTML   PDF (2782KB) ( 293 )   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.

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Path integral Monte Carlo study of (H2)n@C70 (n=1,2,3) Hao Yan (郝妍), Zhang Hong (张红), Cheng Xin-Lu (程新路) Chin. Phys. B, 2015, 24 (8):  088103.  DOI: 10.1088/1674-1056/24/8/088103 Abstract ( 724 )   HTML   PDF (384KB) ( 304 )   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.

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Effects of Fe additive on diamond crystallization from carbonyl nickel powders-C system under HPHT condition Li Yong (李勇), Jia Xiao-Peng (贾晓鹏), Feng Yun-Guang (冯云光), Fang Chao (房超), Fan Li-Juan (樊丽娟), Li Ya-Dong (李亚东), Zeng Xiang (曾祥), Ma Hong-An (马红安) Chin. Phys. B, 2015, 24 (8):  088104.  DOI: 10.1088/1674-1056/24/8/088104 Abstract ( 815 )   HTML   PDF (1372KB) ( 430 )   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.

TOPICAL REVIEW—Silicene

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Silicene transistors–A review Quhe Ru-Ge (屈贺如歌), Wang Yang-Yang (王洋洋), Lü Jin (吕劲) Chin. Phys. B, 2015, 24 (8):  088105.  DOI: 10.1088/1674-1056/24/8/088105 Abstract ( 3089 )   HTML   PDF (3834KB) ( 1300 )   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.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Molecular dynamics simulation on generalized stacking fault energies of FCC metals under preloading stress Zhang Liang (张亮), Lü Cheng (吕程), Tieu Kiet, Zhao Xing (赵星), Pei Lin-Qing (裴林清), Michal Guillaume Chin. Phys. B, 2015, 24 (8):  088106.  DOI: 10.1088/1674-1056/24/8/088106 Abstract ( 544 )   HTML   PDF (807KB) ( 2146 )   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.

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Microwave dielectric properties of Nextel-440 fiber fabrics with pyrolytic carbon coatings in the temperature range from room temperature to 700 ℃ Song Hui-Hui (宋荟荟), Zhou Wan-Cheng (周万城), Luo Fa (罗发), Qing Yu-Chang (卿玉长), Chen Ma-Lin (陈马林) Chin. Phys. B, 2015, 24 (8):  088107.  DOI: 10.1088/1674-1056/24/8/088107 Abstract ( 814 )   HTML   PDF (388KB) ( 321 )   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.

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Switching mechanism for TiO2 memristor and quantitative analysis of exponential model parameters Wang Xiao-Ping (王小平), Chen Min (陈敏), Shen Yi (沈轶) Chin. Phys. B, 2015, 24 (8):  088401.  DOI: 10.1088/1674-1056/24/8/088401 Abstract ( 610 )   HTML   PDF (618KB) ( 587 )   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.

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Effects of back gate bias on radio-frequency performance in partially depleted silicon-on-inslator nMOSFETs Lü Kai (吕凯), Chen Jing (陈静), Luo Jie-Xin (罗杰馨), He Wei-Wei (何伟伟), Huang Jian-Qiang (黄建强), Chai Zhan (柴展), Wang Xi (王曦) Chin. Phys. B, 2015, 24 (8):  088501.  DOI: 10.1088/1674-1056/24/8/088501 Abstract ( 510 )   HTML   PDF (291KB) ( 385 )   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.

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Single-event response of the SiGe HBT in TCAD simulations and laser microbeam experiment Li Pei (李培), Guo Hong-Xia (郭红霞), Guo Qi (郭旗), Zhang Jin-Xin (张晋新), Xiao Yao (肖尧), Wei Ying (魏莹), Cui Jiang-Wei (崔江维), Wen Lin (文林), Liu Mo-Han (刘默寒), Wang Xin (王信) Chin. Phys. B, 2015, 24 (8):  088502.  DOI: 10.1088/1674-1056/24/8/088502 Abstract ( 646 )   HTML   PDF (1147KB) ( 344 )   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.

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Low frequency noise and radiation response in the partially depleted SOI MOSFETs with ion implanted buried oxide Liu Yuan (刘远), Chen Hai-Bo (陈海波), Liu Yu-Rong (刘玉荣), Wang Xin (王信), En Yun-Fei (恩云飞), Li Bin (李斌), Lu Yu-Dong (陆裕东) Chin. Phys. B, 2015, 24 (8):  088503.  DOI: 10.1088/1674-1056/24/8/088503 Abstract ( 527 )   HTML   PDF (508KB) ( 327 )   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.

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Influence of white light illumination on the performance of a-IGZO thin film transistor under positive gate-bias stress Tang Lan-Feng (汤兰凤), Yu Guang (于广), Lu Hai (陆海), Wu Chen-Fei (武辰飞), Qian Hui-Min (钱慧敏), Zhou Dong (周东), Zhang Rong (张荣), Zheng You-Dou (郑有炓), Huang Xiao-Ming (黄晓明) Chin. Phys. B, 2015, 24 (8):  088504.  DOI: 10.1088/1674-1056/24/8/088504 Abstract ( 815 )   HTML   PDF (398KB) ( 972 )   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.

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Theoretical study of interactions between striated cylindrical particles and membrane Hot! Wang Jing-Jing (王晶晶), Feng Jia-Wei (冯佳伟), Ren Chun-Lai (任春来) Chin. Phys. B, 2015, 24 (8):  088701.  DOI: 10.1088/1674-1056/24/8/088701 Abstract ( 628 )   HTML   PDF (367KB) ( 236 )   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.

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Stability of focal adhesion enhanced by its inner force fluctuation Mao Zhi-Xiu (毛志秀), Chen Xiao-Feng (陈笑风), Chen Bin (陈彬) Chin. Phys. B, 2015, 24 (8):  088702.  DOI: 10.1088/1674-1056/24/8/088702 Abstract ( 646 )   HTML   PDF (665KB) ( 266 )   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.

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Theoretical investigation on generating terahertz radiation from gas plasma induced by three-color ultrashort lasers Wang Cheng-Liang (王成亮), Yang Zhen-Gang (杨振刚), Liu Jin-Song (刘劲松), Wang Sheng-Lie (汪盛烈), Wang Ke-Jia (王可嘉) Chin. Phys. B, 2015, 24 (8):  088703.  DOI: 10.1088/1674-1056/24/8/088703 Abstract ( 678 )   HTML   PDF (860KB) ( 300 )   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.

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Effect of focused ultrasound stimulation at different ultrasonic power levels on the local field potential power spectrum Yuan Yi (袁毅), Lu Cheng-Biao (路承彪), Li Xiao-Li (李小俚) Chin. Phys. B, 2015, 24 (8):  088704.  DOI: 10.1088/1674-1056/24/8/088704 Abstract ( 663 )   HTML   PDF (2073KB) ( 479 )   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.

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Establishment, maintenance, and re-establishment of the safe and efficient steady-following state Pan Deng (潘登), Zheng Ying-Ping (郑应平) Chin. Phys. B, 2015, 24 (8):  088901.  DOI: 10.1088/1674-1056/24/8/088901 Abstract ( 526 )   HTML   PDF (361KB) ( 203 )   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.

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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 Abstract ( 496 )   HTML   PDF (9574KB) ( 326 )   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.

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A study of the early warning signals of abrupt change in the Pacific decadal oscillation Wu Hao (吴浩), Hou Wei (侯威), Yan Peng-Cheng (颜鹏程), Zhang Zhi-Sen (张志森), Wang Kuo (王阔) Chin. Phys. B, 2015, 24 (8):  089201.  DOI: 10.1088/1674-1056/24/8/089201 Abstract ( 490 )   HTML   PDF (665KB) ( 655 )   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.