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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2012, 29 (7)   Published: 02 July 2012
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GENERAL

Symmetry Groups and Gauss Kernels of the Schrödinger Equations with Potential Functions

KANG Jing, QU Chang-Zheng
Chin. Phys. Lett. 2012, 29 (7): 070301 doi: 10.1088/0256-307X/29/7/070301
Full Text: [PDF 461 KB] (621)
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We study the Gauss kernels for a class of (2+1)-dimensional linear Schrödinger equations with potential functions. The relationship between the Lie point symmetries and Gauss kernels for the Schrödinger equations is established. It is shown that a classical integral transformation of the Gauss kernel can be generated by a proper Lie point symmetry admitted by the equation. Then we can recover the Gauss kernels for the Schrödinger equations by performing the inverse integral transformation.

Discontinuity of the Measurement-Induced Nonlocality Evolution

XU Guo-Fu, TONG Dian-Min
Chin. Phys. Lett. 2012, 29 (7): 070302 doi: 10.1088/0256-307X/29/7/070302
Full Text: [PDF 498 KB] (236)
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A novel resource, i.e. measurement-induced nonlocality, was proposed by Luo and Fu [Phys. Rev. Lett. 106 (2011) 120401]. It can directly reflect the usefulness of quantum nonlocality in quantum protocols. We investigate the dynamics of measurement-induced nonlocality by exactly solving a model which consists of two independent atoms each subject to a zero-temperature muti-mode cavity. We find that the dynamics of measurement-induced nonlocality is discontinuity under some special conditions. The reason for this phenomenon is the constraint of the von Neumann measurements which do not disturb the reduced density operator. We also find the sudden death phenomenon and the sudden birth phenomenon.

Exact Solutions to the Two-Dimensional Spatially Inhomogeneous Cubic-Quintic Nonlinear Schrödinger Equation with an External Potential

CHEN Jun-Chao, ZHANG Xiao-Fei, LI Biao, CHEN Yong
Chin. Phys. Lett. 2012, 29 (7): 070303 doi: 10.1088/0256-307X/29/7/070303
Full Text: [PDF 2076 KB] (431)
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We investigate the two-dimensional spatially inhomogeneous cubic-quintic nonlinear Schrödinger equation with different external potentials. In the absence of external potential or in the presence of harmonic potential, the number of localized nonlinear waves is associated not only with the boundary condition but also with the singularity of inhomogeneous cubic-quintic nonlinearities; while in the presence of periodic external potential, the periodic inhomogeneous cubic-quintic nonlinearities, together with the boundary condition, support the periodic solutions with an arbitrary number of circular rings in every unit. Our results may stimulate new matter waves in high-dimensional Schrödinger equations with spatially modulated nonlinearities.

Quasi-exactly Solvable Cases of the N-Dimensional Symmetric Quartic Anharmonic Oscillator

PAN Feng, XIE Ming-Xia, SHI Chang-Liang, J. P. DRAAYER
Chin. Phys. Lett. 2012, 29 (7): 070304 doi: 10.1088/0256-307X/29/7/070304
Full Text: [PDF 485 KB] (290)
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The O(N) invariant quartic anharmonic oscillator is shown to be exactly solvable if the interaction parameter satisfies special conditions. The problem is directly related to that of a quantum double well anharmonic oscillator in an external field. A finite dimensional matrix equation for the problem is constructed explicitly, along with analytical expressions for some excited states in the system. The corresponding Niven equations for determining the polynomial solutions for the problem are given.

Multi-particle Entanglement Generation Using Quantum-Dot Spin and Optical Microcavity System

ZHANG Chuan-Lin, WANG Chuan, CAO Cong, ZHANG Ru
Chin. Phys. Lett. 2012, 29 (7): 070305 doi: 10.1088/0256-307X/29/7/070305
Full Text: [PDF 460 KB] (329)
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We propose an efficient multi-particle entanglement generation protocol using a quantum dot and optical micro-cavity coupled system. Multi-electron spins may become entangled by the interaction between the electrons and the single photons. The entanglement success probability relies on the coupling strength and the cavity leakage, which is also discussed.

Testing Quantum Entanglement with Local Measurement

XIE Qing, WU Xian-Xin, DING Xiang-Mao, YANG Wen-Li, YUE Rui-Hong, FAN Heng
Chin. Phys. Lett. 2012, 29 (7): 070306 doi: 10.1088/0256-307X/29/7/070306
Full Text: [PDF 481 KB] (238)
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We propose to detect quantum entanglement by a condition of local measurements. We find that this condition can efficiently detect the pure entangled states for both discrete and continuous variable systems. It does not depend on interference of decoherence from noise and detection loss in some systems, which allows a loophole-free test in real experiments. In particular, it is a necessary condition for the violation of some generalized Bell inequalities.

Thermodynamics of the Bardeen Regular Black Hole

M. Akbar, Nema Salem, S. A. Hussein
Chin. Phys. Lett. 2012, 29 (7): 070401 doi: 10.1088/0256-307X/29/7/070401
Full Text: [PDF 415 KB] (258)
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We deal with the thermodynamic properties of the Bardeen regular black hole with reference to their respective horizons. It is argued here that the expression of the heat capacity at horizons is positive in one parameter region and negative in the other, and between them the heat capacity diverges where the black hole undergoes the second-order phase transition.

Wavelet Phase Synchronization of Fractional-Order Chaotic Systems

CHEN Feng, XIA Lei, LI Chun-Guang
Chin. Phys. Lett. 2012, 29 (7): 070501 doi: 10.1088/0256-307X/29/7/070501
Full Text: [PDF 711 KB] (382)
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Nowadays, fractional-order systems are attracting more and more attention. There are several ways available for analyzing fractional-order systems, among which wavelet transform is an efficient method for analyzing system dynamics in both time and frequency domains. We investigate the wavelet phase synchronization employing wavelet transform to explore the phase synchronization behaviors of fractional-order chaotic oscillators. We analyze in detail the synchronization behaviors with changes to the coupling strength, the central frequency Ω0, and the time scale of the wavelet.

A Novel Super-High Resolution Phase Comparison Approach

YU Jian-Guo, ZHOU Wei, DU Bao-Qiang, DONG Shao-Feng, FAN Qiao-Yan
Chin. Phys. Lett. 2012, 29 (7): 070601 doi: 10.1088/0256-307X/29/7/070601
Full Text: [PDF 490 KB] (302)
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With the improvement of the accuracy of atomic frequency standard and satellite navigation, the high-resolution phase comparison method is necessary. Using the phase synchronous detection principle, a super-high resolution phase comparison method between frequency standards is proposed based on the greatest common factor frequency, phase group processing and a common frequency source and so on. This method is mainly dependent on the stability of the common frequency standard and its frequency. The ±1 count error can be eliminated effectively. Therefore, higher than 1 ps resolution can be easily reached with a simple instrument. Experimental results show higher than 10−15/h precision can be obtained in the long-term frequency standard comparison and the measuring precision can reach 10−17 for several days of comparison.

Enhanced Gas Sensing Properties of Aligned Porous SnO2 Nanofibers

ZHAO Yan, HE Xiu-Li, LI Jian-Ping, JIA Jian, GAO Xiao-Guang
Chin. Phys. Lett. 2012, 29 (7): 070701 doi: 10.1088/0256-307X/29/7/070701
Full Text: [PDF 1996 KB] (381)
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Aligned porous SnO2 nanofibers are obtained by electrospinning with the collector of parallel wedge-shaped electrodes and then by oxygen plasma treatment and annealing. The morphology and crystal structure of the fibers are analyzed by scanning electron microscopy and x-ray diffraction, and the effects of the morphology and alignment on ethanol sensing properties of the fibers are investigated. The results show that the porous SnO2 fibers with an average diameter of tens of nanometers can be deposited orderly on the micro-hotplate with the auxiliary electrodes. The aligned porous fibers exhibit higher sensitivity and faster response compared with randomly oriented ones at the operating temperature of 300°C.

Label-Free and Real-Time Detection of Antigen-Antibody Capture Processes Using the Oblique-Incidence Reflectivity Difference Technique

HE Li-Ping, DAI Jun, SUN Yue, WANG Jing-Yi, LÜ Hui-Bin, WANG Shu-Fang, JIN Kui-Juan, ZHOU Yue-Liang, YANG Guo-Zhen
Chin. Phys. Lett. 2012, 29 (7): 070702 doi: 10.1088/0256-307X/29/7/070702
Full Text: [PDF 534 KB] (133)
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We successfully label-free and real-time detect the capture processes of human immunoglobulin G (IgG)/goat anti-human IgG and mouse IgG/goat anti-mouse IgG antigen-antibody pairs with different concentrations using the oblique-incidence reflectivity difference (OIRD) method, and obtain the interaction kinetics curves and the interaction times. The experimental results prove that the OIRD method is a promising technique for label-free and real-time detection of the biomolecular interaction processes and achieving the quantitative information of interaction kinetics.

Lateral Resolution and Signal to Noise Ratio in Electrostatic Force Detection Based on Scanning Probe Microscopy

ZHANG Dong-Dong, WANG Xiao-Wei, WANG Rui, WANG Sheng-Nan, CHENG Zhi-Hai, QIU Xiao-Hui
Chin. Phys. Lett. 2012, 29 (7): 070703 doi: 10.1088/0256-307X/29/7/070703
Full Text: [PDF 810 KB] (197)
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The lateral resolution (LR) and signal-to-noise ratio (SNR) are the essential factors in the applications of scanning probe microscopy in quantitative measurement of surface charge distribution, potential profile, and dielectric properties. We use a model system to comprise Au nanoparticles (NPs) embedded in a polystyrene (PS) matrix to study the effects of various experimental parameters, such as modulation bias voltage, tip-sample distance, and actual tip shape, on the electrostatic interactions between the tips and samples. The results show that LR and SNR decrease when the tip-sample distance increases, while SNR increases with tip modulation voltage. LR is less sensitive to tip modulation voltage, but shows complex dependence on the sample geometric structure. In combination with a numerical simulation based on the integral capacitance model, the electrostatic force interaction between tip and sample was quantitatively analyzed.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Pair Production in an Intense Laser Pulse: The Effect of Pulse Length

REN Na, WANG Jia-Xiang, LI An-Kang, WANG Ping-Xiao
Chin. Phys. Lett. 2012, 29 (7): 071201 doi: 10.1088/0256-307X/29/7/071201
Full Text: [PDF 800 KB] (233)
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Production of positron-electron (e+e) pairs in an intense laser pulse is investigated by solving the Dirac equation with analytical and numerical methods. We observe that the probability of the pair production will firstly decrease slowly as the pulse length τ becomes shortened. Then it will increase until τ is reduced to the Compton time τc=ħ/(mec)1.29×10−21 s and finally decrease exponentially to zero. Hence, for a prominent pair production, we not only require that the electric field strength should be higher than the the Schwinger critical value Ecr=m2c3/()≈1.32×1016 V/cm, but also that the pulse duration τ should be larger than τc. The latter is shown to be related to momentum requirement for the transition. For fields with different pulse lengths, the phase and chirp influences upon the pair production are also explored.

Radiative Dileptonic Decays Bs→l+lγ in the TC2 Model

ZHANG Jiao, YUE Chong-Xing
Chin. Phys. Lett. 2012, 29 (7): 071301 doi: 10.1088/0256-307X/29/7/071301
Full Text: [PDF 629 KB] (219)
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We investigate the radiative dileptonic decays Bs→l+lγ (l=e, μ and τ) in the framework of the topcolor-assisted technicolor (TC2) model. The contributions of the new particles predicted by this model to the branching ratios and the forward-backward asymmetry (AFB) of these decays are considered. It is found that the values of their branching ratios are greater than the standard model (SM) predictions by several times up to one order of magnitude and |AFB| can also be enhanced by several times in a wide range of the parameter space.

Weak Decays of First Radial Excited Dq(2S) and Bq(2S) States

WANG Zhi-Hui, WANG Guo-Li, ZHANG Jin-Mei, WANG Tian-Hong
Chin. Phys. Lett. 2012, 29 (7): 071401 doi: 10.1088/0256-307X/29/7/071401
Full Text: [PDF 520 KB] (158)
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We study the exclusive semileptonic and nonleptonic decays of the first radial excited heavy-light pseudoscalars Dq(2S) and Bq(2S) (q=u, d, s) with the improved Bethe–Salpeter (B-S) method which takes into account the relativistic effects in wave functions and transition matrix elements.
NUCLEAR PHYSICS

Transition from Electric Rotation to Chiral Mode in 135Nd

QI Bin, LI Jian, WANG Shou-Yu, ZHANG Jing, ZHANG Shuang-Quan
Chin. Phys. Lett. 2012, 29 (7): 072101 doi: 10.1088/0256-307X/29/7/072101
Full Text: [PDF 594 KB] (181)
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With the inputs from the relativistic mean field approach, the observed energy spectra and electromagnetic properties are well reproduced for the yrast band of odd-A nucleus 135Nd by the particle rotor model. Based on the analysis of the angular momentum components, it is further illustrated that this yrast band contains two stages of rotational mode, i.e., the electric rotation for low-spin region and chiral mode for high-spin region.

Methodological Study on Change in Half Life of 210Po Embedded in a Metallic Medium at Ultra-Low Temperature

DONG Ke-Jun, JIANG Shan, HE Ming, HE Xian-Wen, RUAN Xiang-Dong, GUAN Yong-Jing, LIN De-Yu, YUAN Jian, WU Shao-Yong
Chin. Phys. Lett. 2012, 29 (7): 072301 doi: 10.1088/0256-307X/29/7/072301
Full Text: [PDF 550 KB] (186)
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It has been claimed that the half-life of radioactive nuclides embedded in metals may be significantly affected by the screening of quasi-free electrons provided by the metals, especially at the cryogenic temperature. We determine the α-decay half-life values of 210Po in high purity metallic bismuth at 4.2 K and 293 K. The results show that the α-decay half-life of 210Po at T=4.2 K is about (24 ±8)% shorter than that at room temperature.

Dependence of Elliptic Flow on Transverse Momentum in √sNN=200 GeV Au-Au and √sNN=2.76 TeV Pb-Pb Collisions

LI Bao-Chun, FU Yuan-Yuan, WANG Li-Li, WANG Er-Qin, WEN Xin-Jian, LIU Fu-Hu
Chin. Phys. Lett. 2012, 29 (7): 072501 doi: 10.1088/0256-307X/29/7/072501
Full Text: [PDF 654 KB] (160)
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We investigate the dependence of elliptic flows v2 on transverse momentum PT for charged hadrons produced in nucleus-nucleus collisions at high energy by using a multi-source thermal model, where the contribution of source interactions is considered. Our calculated results are approximately in agreement with the experimental data over a wider PT range from the PHENIX and ALICE collaborations. It is found that the expansion factor increases linearly with the impact parameter from most central (0–5%) to mid-peripheral (35–40%) collisions.
ATOMIC AND MOLECULAR PHYSICS

Angle-Dependent Irradiation of C4 in Femtosecond Laser Pulses

WANG Zhi-Ping ZHANG Feng-Shou, ZHU Yun, XIE Guan-Hao
Chin. Phys. Lett. 2012, 29 (7): 073101 doi: 10.1088/0256-307X/29/7/073101
Full Text: [PDF 839 KB] (161)
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We study the angle-dependent irradiation of linear C4 in the strong femtosecond laser pulses with the help of time-dependent local density approximation applied to valence electrons, coupled non-adiabatically to molecular dynamics of ions. It is found that the excitation of C4 including the electrons and ions has a strong relation to the angle between the laser polarization and the internuclear axis of C4. The ionization yield decreases when the angle ranges from 0 to π/2. A clear suppression in the ionization yield is found when the laser polarization is perpendicular to the internuclear axis of C4. We track the dynamic motion of ionized C4 even in the relaxation time. It shows that the ionized C4 keeps on oscillating without fragmenting after the irradiation in different cases, while it is more excited when the laser polarization is along the internuclear axis. Furthermore, it is found that the change of the ELF takes place mainly in the xy plane and xz plane and the electron ejection mainly comes from the middle two atoms for the θ=0 case.

Energy-Crossing and Its Effect on Lifetime of the 4s24p 2P3/2 Level for Highly Charged Ga-Like Ions

FAN Jian-Zhong, ZHANG Deng-Hong, CHANG Zhi-Wei, SHI Ying-Long, DONG Chen-Zhong
Chin. Phys. Lett. 2012, 29 (7): 073102 doi: 10.1088/0256-307X/29/7/073102
Full Text: [PDF 590 KB] (178)
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The multi-configuration Dirac–Fock method is employed to calculate the energy levels and transition probabilities for the electric dipole allowed (E1) and forbidden (M1, E2) lines for the 4s24p, 4s4p2 and 4s24d configurations of highly charged Ga-like ions from Z=68–95. The lifetimes of the 4s24p 2P3/2 level of the ground configuration are also derived. Based on our calculations, it is found that the energy level of the 4s24p 2P3/2 is higher than that of the 4s4p24P1/2 for the high-Z Ga-like ions with Z≥74, so as to generate an energy crossing at Z=74. The effect of the energy crossing is important to the calculation of the 4s24p 2P3/2 level lifetime for Ga-like ions with Z≥74.

Detached Electron Spectra from H near a Partially Reflecting Spherical Surface

Muhammad Haneef, Saleh Mohammad, Jehan Akbar, Suneela Arif, Muhammad Zahir, Humayun Khan
Chin. Phys. Lett. 2012, 29 (7): 073201 doi: 10.1088/0256-307X/29/7/073201
Full Text: [PDF 505 KB] (273)
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The photodetachment of a hydrogen negative ion (H) near a partially reflecting surface with a spherical shape is investigated by a theoretical imaging method. Analytical expressions for the detached electron flux and total photodetachment cross section are derived. It is found that two parameters, i.e. curvature radius rc and reflection parameter K, control the photodetachment spectra. Furthermore, these parameters can be used for the classification, identification and revelation of minor details like curvature of different types of surfaces.

Superradiant Laser with Ultra-Narrow Linewidth Based on 40Ca

WANG Yan-Fei, CHEN Jing-Biao
Chin. Phys. Lett. 2012, 29 (7): 073202 doi: 10.1088/0256-307X/29/7/073202
Full Text: [PDF 461 KB] (389)
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An experiment setup for narrow linewidth superradiant laser based on the mechanism of an active optical clock is proposed with optical lattice trapped 40Ca. We obtain the threshold pumping rate analytically and deduce the linewidth of the superradiant laser in a bad cavity regime. The proposed laser has an extremely narrow linewidth at millihertz level and a power level of order 10−9 W.

Coherent Control of Lithium Atom by Adiabatic Rapid Passage with Chirped Microwave Pulses

JIANG Li-Juan, ZHANG Xian-Zhou, MA Huan-Qiang, XIA Li-Hua, JIA Guang-Rui
Chin. Phys. Lett. 2012, 29 (7): 073203 doi: 10.1088/0256-307X/29/7/073203
Full Text: [PDF 672 KB] (199)
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Using the time-dependent multilevel approach and the B-spline technique, populations of Rydberg lithium atoms in chirped microwave pulses are demonstrated. Firstly the populations of two energy levels are controlled by the microwave pulse parameters. Secondly the atoms experience the consequence 70s-71p-72s-73p-74s in a microwave field using optimized microwave field parameters. It is shown that the coherent control of the population transfer in the microwave field from the initial to the target states can be accomplished by optimizing the microwave field parameters.

Exact Quantum-Scattering Study of the D(2S)+DS(2Π) Reaction

LV Shuang-Jiang, ZHANG Pei-Yu, HE Guo-Zhong
Chin. Phys. Lett. 2012, 29 (7): 073401 doi: 10.1088/0256-307X/29/7/073401
Full Text: [PDF 801 KB] (213)
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The quantum scattering dynamics calculations are carried out for the exchange and abstraction processes in the D(2S)+DS(2Π) reaction by the time-dependent wave-packet (TDWP) method. These calculations are based on the high-quality ab initio potential energy surface of the reacting system. The reaction probabilities and integral cross sections are obtained in the collision energy (Ecol) range of 0.0–2.0 eV for the reactant DS initially in the ground state and the first vibrationally excited state. We take the Coriolis coupling (CC) effect into account and present the comparison between the CC and the centrifugal sudden (CS) approximation calculation. The dynamics results show that the initial vibrational excitation of DS enhances both abstraction and exchange processes except that it has little effect on the abstraction cross section in the high energy region.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Comparison of Small-Scale Actively and Passively Q-Switched Eye-Safe Intracavity Optical Parametric Oscillators at 1.57 µm

MIAO Jie-Guang, PAN Yu-Zhai, QU Shi-Liang
Chin. Phys. Lett. 2012, 29 (7): 074201 doi: 10.1088/0256-307X/29/7/074201
Full Text: [PDF 511 KB] (262)
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The first experimental comparison between the actively and passively Q-switched intracavity optical parametric oscillators (IOPOs) at 1.57 µm driven by a small-scale diode-pumped Nd:YVO4 laser are thoroughly presented. It is found that the performances of the two types of IOPOs are complementary. The actively Q-switched IOPO features a shorter pulse duration, a higher peak power, and a superior power and pulse stability. However, in terms of compactness, operation threshold and conversion efficiency, passively Q-switched IOPOs are more attractive. It is further indicated that the passively Q-switched IOPO at 1.57 µm is a promising and cost-effective eye-safe laser source, especially at the low and moderate output levels. In addition, instructional improvement measures for the two types of IOPOs are also summarized.

Numerical Approximations to the Solution of Ray Tracing through the Crystalline Lens

A. Yildirim, A. Gökdoğan, M. Merdan, V. Lakshminarayanan
Chin. Phys. Lett. 2012, 29 (7): 074202 doi: 10.1088/0256-307X/29/7/074202
Full Text: [PDF 439 KB] (425)
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An approximate analytical solution in the form of a rapidly convergent series for tracing light rays through an inhomogeneous graded index medium is developed, using the multi-step differential transform method based on the classical differential transformation method. Numerical results are compared to those obtained by the fourth-order Runge–Kutta method to illustrate the precision and effectiveness of the proposed method. Results are given in explicit and graphical forms.

Controllable Dual-Wavelength Fiber Laser

LI Zhen, ZHOU Jun, HE Bing, LIU Hou-Kang, LIU Chi, WEI Yun-Rong, DONG Jing-Xing, LOU Qi-Hong
Chin. Phys. Lett. 2012, 29 (7): 074203 doi: 10.1088/0256-307X/29/7/074203
Full Text: [PDF 420 KB] (316)
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We demonstrate a controllable dual-wavelength fiber laser which contains a master laser and a slave laser. The master laser is a kind of ring cavity laser which can be injected into by the slave laser. The output laser wavelength is controlled by injected power of the slave laser; both single- and dual-wavelength operation can be achieved. Under free running, the master laser generates 1064 nm laser output. Here the slave laser is a 1072 nm fiber laser. The 1064 nm and 1072 nm laser coexist in output spectrum for relatively low injected power. Dual-wavelength and power-ratio-tunable operation can be achieved. If the injected power of the slave laser is high enough, the 1064 nm laser is extinguished automatically and there is only 1072 nm laser output.

Numerical Study of Plasmonic Modes in Hexagonally Arranged Metal Nanowire Array

YAN Hao-Zhe, PENG Jing-Gang, LI Jin-Yan, YANG Lü-Yun
Chin. Phys. Lett. 2012, 29 (7): 074204 doi: 10.1088/0256-307X/29/7/074204
Full Text: [PDF 814 KB] (264)
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A plasmonic waveguide containing hexagonally arranged parallel metallic nanowires with hexagonal cross sections embedded in a silica fiber is proposed and discussed. According to simulations of surface plasmon polariton eigenmodes at varying geometrical transverse parameters, we obtain comprehensive mode characteristics, including field mode distribution, effective refractive index, propagation length, and lateral mode radius, thus allowing us to investigate the precise trade-off between propagation length and confinement, which is very important in designing plasmonic waveguides of different applications. This waveguide is also proved to be robust against fabrication imperfections, which makes its manufacture and practical applicability feasible.

Dual-Peak Bragg Gratings Inscribed in an All-Solid Photonic Bandgap Fiber for Sensing Applications

ZHANG Ji-Huang, LIU Ning-Liang, WANG Ying, JI Ling-Ling, LU Pei-Xiang
Chin. Phys. Lett. 2012, 29 (7): 074205 doi: 10.1088/0256-307X/29/7/074205
Full Text: [PDF 723 KB] (286)
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Bragg gratings are inscribed in an all-solid photonic bandgap fiber by use of femtosecond laser irradiation. Dual-peak structure is observed in the transmission spectrum of the induced grating, which is formed by the coupling between the forward-propagating fundamental core mode and the backward-propagating core mode or supermode. Sensing characteristics of the device are investigated experimentally by employing strain and temperature tests, and similar behavior is obtained for both resonant peaks. The strain and temperature sensitivities are 0.968pm/μϵ and 12.01pm/°C, and 0.954pm/μϵ and 12.04pm/°C, for the two peaks, respectively. This device would find potential applications in real optical fiber sensing without extra reference gratings.

A Compact Setup of Saturated Absorption Spectroscopy for Diode Laser Frequency Stabilization

ZHANG Xian, HUANG Kai-Kai, XU Hao, XU Zhou-Xiang, LI Nan, LU Xuan-Hui
Chin. Phys. Lett. 2012, 29 (7): 074206 doi: 10.1088/0256-307X/29/7/074206
Full Text: [PDF 662 KB] (295)
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A novel setup of saturated absorption spectroscopy (SAS) is presented. It is based on laser reflections at surfaces of a sample vapor cell. It only needs one cell and one photodiode and is more compact than conventional setups of SAS. Its spectrum is similar to a conventional SAS. The frequency stabilization performance of an external-cavity diode laser with this setup is investigated. A frequency stability of 1.1×10-11 is achieved at an averaging time of 60 s in the Allen variance measurements.

Application of Optical Kerr Gate with SrTiO3 Crystal in Acquisition of Gated Spectra from a Supercontinuum

YAN Li-He, JIA Sen, SI Jin-Hai, MATSUO Shigeki, CHEN Feng, HOU Xun
Chin. Phys. Lett. 2012, 29 (7): 074207 doi: 10.1088/0256-307X/29/7/074207
Full Text: [PDF 1568 KB] (307)
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We investigate the optical Kerr effect of SrTiO3 (STO) crystal, of which the nonlinear response time was measured to be less than 200 fs, while the nonlinear refractive index is estimated to be 2.16×10-15 cm2/W. Using the optical Kerr gate (OKG) technique with an STO crystal as the Kerr medium, we obtain narrow-bandwidth and symmetric gated spectra from a supercontinuum generated in distilled water by a femtosecond laser. The experimental results show superiority compared with the gated spectra obtained using OKG with CS2 as the Kerr medium, demonstrating that STO crystal is a promising OKG medium.

Experimental Realization of a Magnetically Tunable Cavity in a Gyromagnetic Photonic Crystal

LIAN Jin, FU Jin-Xin, GAN Lin, LI Zhi-Yuan
Chin. Phys. Lett. 2012, 29 (7): 074208 doi: 10.1088/0256-307X/29/7/074208
Full Text: [PDF 1001 KB] (200)
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We theoretically and experimentally study the cavity modes in a gyromagnetic photonic crystal (GPC). Because the permeability of gyromagnetic material relies on the dc magnetic field exerted upon it, the band gap of the GPC is supposed to be tunable. Based on this, it is expected that the cavity mode in the GPC is also tunable under the variation of dc magnetic fields. The relation between the frequency of the cavity mode and exerted dc magnetic field is theoretically investigated. Furthermore, we measure the frequency variation of the cavity mode in the GPC and demonstrate the tunable property of GPC cavity.

Enhanced and Tunable Spin Hall Effect of Light upon Reflection of One-Dimensional Photonic Crystal with a Defect Layer

LING Xiao-Hui, LUO Hai-Lu, TANG Ming, WEN Shuang-Chun
Chin. Phys. Lett. 2012, 29 (7): 074209 doi: 10.1088/0256-307X/29/7/074209
Full Text: [PDF 981 KB] (257)
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We show that the spin Hall effect of light upon reflection of one-dimensional photonic crystal with a defect layer can be enhanced significantly with a spin-dependent transverse displacement of the beam centroid of several wavelengths of light which is much larger than those reported previously, for horizontal- and vertical-polarization incidence. Under the condition of abrupt phase changes of reflection coefficients however, the spin Hall effect of light could be completely suppressed. Further, we demonstrate that, by tuning the optical parameters of the defect layer, the spin Hall effect of light upon reflection can be switchable for any incident angle and polarization of incidence.

Electromagnetic Wave Propagation over Oil-Covered Sea Surface

YANG Chao, JIN Wei, GUO Li-Xin
Chin. Phys. Lett. 2012, 29 (7): 074210 doi: 10.1088/0256-307X/29/7/074210
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An exhaustive analysis of electromagnetic wave propagation over an oil-covered sea surface in an evaporation duct environment is studied in comparison with those of the oil-free sea surface. Instead of using the traditional rms height formula, which only considers the oil-free sea surface, we reduce the rms height of a one-dimensional oil-covered sea surface based on the Pierson–Moskowitz sea spectrum. Then, the electromagnetic wave propagation over the oil-covered sea surface in an evaporation duct environment with different wind speeds and frequencies is discussed by the parabolic equation for a fully oil-covered sea surface. In addition, the influence of the fractional filling factor on the electromagnetic wave propagation over non-fully oil-covered sea surface is also investigated. The results show that the oil film can reduce the sea surface roughness and strengthen the trapping effect in an evaporation duct environment.

Resonance Cavities in Parallel-Hetero Perturbation Photonic Crystal Waveguide Structures

WANG Chen, LI Zhi-Yuan
Chin. Phys. Lett. 2012, 29 (7): 074211 doi: 10.1088/0256-307X/29/7/074211
Full Text: [PDF 818 KB] (260)
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We design a series of W1 waveguide-like parallel-hetero cavities (PHCs) made from the combination of parallel-hetero perturbation (PHP) waveguides and photonic crystal waveguides and investigate their optical properties. Spectral properties are calculated numerically using the three-dimensional finite-difference time-domain method. The resonant frequencies and quality factors are obtained for each type of PHC and comparisons are made among different types of PHC, which is helpful for predicting and understanding the properties of PHC and designing PHC based high-performance cavities. The PHCs can broaden the category of cavity design and find interesting applications in integrated optical devices and solid state lasers.

Resolution for Forward and Phase-Conjugate Degenerate Four-Wave Mixing in Hot Atomic Media

CHENG Xue-Mei, CHEN Hao-Wei, WANG Jian, MIAO Yi-Zhu, YIN Xun-Li, REN Zhao-Yu, BAI Jin-Tao
Chin. Phys. Lett. 2012, 29 (7): 074212 doi: 10.1088/0256-307X/29/7/074212
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Resolutions of degenerate four-wave mixing with forward and phase-conjugate configurations (FDFWM and PCDFWM) are investigated and compared theoretically and experimentally in hot rubidium (Rb) atomic vapor. The theoretical simulations indicate that PCDFWM is of much higher resolution than FDFWM. The resolution of PCDFWM is less dependent on Doppler broadening. The experimental results are in good agreement with the theoretical expectation. PCDFWM can resolve the hyperfine transitions and crossover resonances of 87Rb which cannot be achieved by FDFWM. Additionally, with sample temperature increasing, the linewidth of FDFWM spectrum obviously broadens. In comparison, no obvious broadening can be observed in the PCDFWM spectrum.

Evolution of Slow Dual Steady-State Optical Solitons in a Cold Three-State Medium

SUN Jian-Qiang, LI Hao-Chen, GU Xiao-Yan
Chin. Phys. Lett. 2012, 29 (7): 074213 doi: 10.1088/0256-307X/29/7/074213
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The generalized nonlinear Schrödinger equation, which describes the evolution of dual steady-state optical solitons in a cold three-state medium, is written as the Hamiltonian symplectic structure. The symplectic method is applied to investigate evolution of dual steady-state optical solitons. By adjusting the initial pulses, the saturation parameter variables and the distances of optical solitons, the different behaviors of dual steady-state optical solitons are analyzed.

Estimation of the Maximum Output Power of Double-Clad Photonic Crystal Fiber Laser

CHEN Yue-E, WANG Yong, QU Xi-Long
Chin. Phys. Lett. 2012, 29 (7): 074214 doi: 10.1088/0256-307X/29/7/074214
Full Text: [PDF 393 KB] (258)
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Compared with traditional optical fiber lasers, double-clad photonic crystal fiber (PCF) lasers have larger surface-area-to-volume ratios. With an increase of output power, thermal effects may severely restrict output power and deteriorate beam quality of fiber lasers. We utilize the heat-conduction equations to estimate the maximum output power of a double-clad PCF laser under natural-convection, air-cooling, and water-cooling conditions in terms of a certain surface-volume heat ratio of the PCF. The thermal effects hence define an upper power limit of double-clad PCF lasers when scaling output power.

High-Power High-Temperature Continuous-Wave Operation of Quantum Cascade Laser at λ∼4.6 µm without Lateral Regrowth

LIANG Ping, LIU Feng-Qi**, ZHANG Jin-Chuan, WANG Li-Jun, LIU Jun-Qi, WANG Zhan-Guo
Chin. Phys. Lett. 2012, 29 (7): 074215 doi: 10.1088/0256-307X/29/7/074215
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High-power quantum cascade lasers (λ=4.6 µm ) working in continuous wave (cw) up to 90°C are presented. The material was grown by solid-source molecular beam epitaxy and processed into narrow conventional ridge geometry without lateral regrowth. High cw output power of 850 mW at 10°C and more than 200 mW at 90°C were obtained with threshold current densities of 1.34 and 2.47 kA/cm2, respectively, for a high-reflectivity-coated 12-µm -wide and 3-mm-long laser.

Nonlocal Imaging by Conditional Averaging of Random Reference Measurements Hot!

LUO Kai-Hong, HUANG Bo-Qiang, ZHENG Wei-Mou, WU Ling-An
Chin. Phys. Lett. 2012, 29 (7): 074216 doi: 10.1088/0256-307X/29/7/074216
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We report the nonlocal imaging of an object by conditional averaging of the random exposure frames of a reference detector, which only sees the freely propagating field from a thermal light source. A bucket detector, synchronized with the reference detector, records the intensity fluctuations of an identical beam passing through the object mask. These fluctuations are sorted according to their values relative to the mean, then the reference data in the corresponding time-bins for a given fluctuation range are averaged, to produce either positive or negative images. Since no correlation calculations are involved, this correspondence imaging technique challenges our former interpretations of "ghost" imaging. Compared with conventional correlation imaging or compressed sensing schemes, both the number of exposures and computation time are greatly reduced, while the visibility is much improved. A simple statistical model is presented to explain the phenomenon.

Enhancement Effect of Patterning Resolution Induced by an Aluminum Thermal Conduction Layer with AgInSbTe as a Laser Thermal Lithography Film

LI Hao, WANG Rui, GENG Yong-You, WU Yi-Qun, WEI Jing-Song
Chin. Phys. Lett. 2012, 29 (7): 074401 doi: 10.1088/0256-307X/29/7/074401
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We employ an aluminum (Al) film as a thermal conduction layer under the laser thermal lithography AgInSbTe phase-change film to improve the patterning resolution in laser thermal lithography. The patterns were fabricated by laser writing and wet-etching. The laser writing was conducted by a setup where the laser wavelength and the numerical aperture of the converging lens were 405 nm and 0.90, respectively. The wet-etching was carried out in a 17wt% ammonium sulfide solution. Experimental results indicate that the patterning resolution enhancement induced by an Al thermal conduction layer is more than 20% compared with that of the samples without an Al thermal conduction layer. The analysis reveals that the resolution-enhancing effect may be due to the changes of heat diffusion directions induced by the Al thermal conduction layer.

Breakdown of Energy Equipartition in Vibro-Fluidized Granular Media in Micro-Gravity Hot!

CHEN Yan-Pei, Pierre Evesque, HOU Mei-Ying
Chin. Phys. Lett. 2012, 29 (7): 074501 doi: 10.1088/0256-307X/29/7/074501
Full Text: [PDF 567 KB] (318)
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We present a micro-gravity experimental study of intermediate number density vibro-fluidized inelastic spheres in a rectangular container. Local velocity distributions are investigated, and are found to deviate measurably from a symmetric distribution for the velocity component of the vibrating direction when dividing particles along the vibration direction into several bins. This feature does not exist in the molecular gas. We further study the hydrodynamic profiles of pressures p and temperatures T in positive and negative components, such as py+ and py and Ty+ and Ty, in accordance with the sign of velocity components of the vibrating direction. Along vibration direction, granular media are found to be not only inhomogeneous and anisotropic, but also different greatly in positive and negative components. Energy equipartition breaks down in this case.

Aspherical Oscillation of Two Interacting Bubbles in an Ultrasound Field

LIANG Jin-Fu, CHEN Wei-Zhong, SHAO Wei-Hang, QI Shui-Bao
Chin. Phys. Lett. 2012, 29 (7): 074701 doi: 10.1088/0256-307X/29/7/074701
Full Text: [PDF 536 KB] (201)
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Based on the perturbation theory and Bernoulli equation, equations of aspherical oscillation of two interacting bubbles are derived. This system is then used for the numerical investigation of the deformation of the two bubbles' surfaces in a spherical ultrasound field in liquid. We find that the details of the aspherical oscillation of two bubbles are shown by the analysis of a2(t) and b2(t) that describe the surface deformation of bubbles 1 and 2, respectively.

Marangoni Bifurcation Flow in a Microchannel T-Junction and Its Micropumping Effect: A Computational Study

PAN Zhen-Hai, WANG Hao, YANG Zhen
Chin. Phys. Lett. 2012, 29 (7): 074702 doi: 10.1088/0256-307X/29/7/074702
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We discuss a bifurcation phenomenon of Marangoni flow in a microchannel T-junction and its novel unidirectional pumping effect. The T-junction is formed by a main channel connected with a liquid reservoir and a side channel outlet to the atmosphere. A volatizing meniscus is formed in the side channel and Marangoni convections are generated due to the non-uniform evaporation on the meniscus. It is found for weak evaporations (Ma < 270) the Marangoni convections are symmetrical. However, for intense evaporations (Ma >270), the initial inward symmetrical Marangoni convection becomes unstable and converted into one single vortex flow. Moreover, the single vortex induces a steady unidirectional flow in the main channel, acting like a pump.

Dynamics Evolution Investigation of Mack Mode Instability in a Hypersonic Boundary Layer by Bicoherence Spectrum Analysis

HAN Jian, JIANG Nan
Chin. Phys. Lett. 2012, 29 (7): 074703 doi: 10.1088/0256-307X/29/7/074703
Full Text: [PDF 928 KB] (208)
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The instability of a hypersonic boundary layer on a cone is investigated by bicoherence spectrum analysis. The experiment is conducted at Mach number 6 in a hypersonic wind tunnel. The time series signals of instantaneous fluctuating surface-thermal-flux are measured by Pt-thin-film thermocouple temperature sensors mounted at 28 stations on the cone surface along streamwise direction to investigate the development of the unstable disturbances. The bicoherence spectrum analysis based on wavelet transform is employed to investigate the nonlinear interactions of the instability of Mack modes in hypersonic laminar boundary layer transition. The results show that wavelet bicoherence is a powerful tool in studying the unstable mode nonlinear interaction of hypersonic laminar-turbulent transition. The first mode instability gives rise to frequency shifts to higher unstable modes at the early stage of hypersonic laminar-turbulent transition. The modulations subsequently lead to the second mode instability occurrence. The second mode instability governs the last stage of instability and final breakdown to turbulence with multi-scale disturbances growth.

Numerical Simulation of Thermocapillary-Buoyant Convection in an Annular Pool under Various Gravity Levels

ZHOU Xiao-Ming, HUANG Hu-Lin
Chin. Phys. Lett. 2012, 29 (7): 074704 doi: 10.1088/0256-307X/29/7/074704
Full Text: [PDF 805 KB] (152)
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Thermocapillary-buoyant convection in an annular two-layer system under various gravity levels is investigated, in which the level set method is employed to capture the interface, and the continuum surface force tension model is used to simulate the Marangoni effect. The results show that, under the influence of the Marangoni effect, the interface bulges out near the outer wall and bulges in near the inner wall. The flow pattern consists of static convective cells, but a transition of flow pattern occurs as the gravity level increases. The interface deformability decreases with increasing gravity level, and the change rate of deformability is the largest as the gravity level varies from 0.001g to 0.01g.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Usage of Displaced Current in Langmuir Probe Measurement

MING Zhang-Jian, LI Hong, CHEN Zhi-Peng, LUO Chen, XIE Jin-Lin, LAN Tao, LIU A-Di, LIU Wan-Dong
Chin. Phys. Lett. 2012, 29 (7): 075201 doi: 10.1088/0256-307X/29/7/075201
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We investigate the possibility of the usage of displaced current in Langmuir probe measurement theoretically and experimentally. The displaced current flows through the self-generated or artificial capacitance of the reference electrode under an alternative sweep voltage. It can increase the total current afforded by the reference electrode, and eliminate the interference deriving from the finite plasma sheath resistance of the reference electrode. The results in both theory and experiment lead to the conclusion that the usage of displaced current is valid and more efficient with a floating probe method. This method is applied in some harsh plasma environments when the grounded chamber wall can easily be contaminated by the dielectric.

Effects of an Electric Field on the Cylindrical Dust Acoustic Wave in Magnetized Complex Plasmas

B. Farokhi, M. Eghbali
Chin. Phys. Lett. 2012, 29 (7): 075202 doi: 10.1088/0256-307X/29/7/075202
Full Text: [PDF 573 KB] (235)
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Stability of a dust acoustic wave in cylindrical complex plasmas is investigated. Effects of a static magnetic field (axial) and an electric field (radial) on the propagation of a low frequency wave are studied. The linear dispersion relations of rotational modes and breathing modes are derived. When a dusty plasma is confined in a finite region, the void behavior is observed at high speed rotation. Vivid structures of different-mode-number solutions are illustrated.

Deactivation of Enterococcus Faecalis Bacteria by an Atmospheric Cold Plasma Brush

CHEN Wei, HUANG Jun, DU Ning, LIU Xiao-Di, LV Guo-Hua, WANG Xing-Quan, ZHANG Guo-Ping, GUO Li-Hong, YANG Si-Ze
Chin. Phys. Lett. 2012, 29 (7): 075203 doi: 10.1088/0256-307X/29/7/075203
Full Text: [PDF 1056 KB] (288)
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An atmospheric cold plasma brush suitable for large area and low-temperature plasma-based sterilization is designed and used to treat enterococcus faecalis bacteria. The results show that the efficiency of the inactivation process by helium plasma is dependent on applied power and exposure time. After plasma treatments, the cell structure and morphology changes can be observed by scanning electron microscopy. Optical emission measurements indicate that reactive species such as O and OH play a significant role in the sterilization process.

Study on the Resistive Wall Instability Driven by Plasma Flow

LI Li, LIU Yue
Chin. Phys. Lett. 2012, 29 (7): 075204 doi: 10.1088/0256-307X/29/7/075204
Full Text: [PDF 1154 KB] (199)
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A slab model with a uniform plasma flow and magnetic field along the slab is carried out to study the resistive wall instability driven by longitudinal plasma flow. All solutions of complex frequency in the dispersion relation of this system are calculated numerically, and the results indicate that there are three eigen modes in this system. One of them is the normal stable plasma mode; another one is the resistive wall instability driven by plasma flow, which can be excited when the flow exceeds critical velocity, and can be stabilized when the flow increases sufficiently. At the same time, the last mode similar to the K-H mode will become unstable.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Collision Energy Dependence of Defect Formation in Graphene

MAO Fei, ZHANG Chao, ZHANG Yan-Wen, ZHANG Feng-Shou
Chin. Phys. Lett. 2012, 29 (7): 076101 doi: 10.1088/0256-307X/29/7/076101
Full Text: [PDF 742 KB] (298)
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Molecular dynamics simulations are performed using an empirical potential to simulate the collision process of an energetic carbon atom hitting a graphene sheet. According to the different impact locations within the graphene sheet, the incident threshold energies of different defects caused by the collision are determined to be 22 eV for a single vacancy, 36 eV for a divacancy, 60 eV for a Stone-Wales defect, and 65 eV for a hexavacancy. Study of the evolution and stability of the defects formed by these collisions suggests that the single vacancy reconstructs into a pentagon pair and the divacancy transforms into a pentagon-octagon-pentagon configuration. The displacement threshold energy in graphene is investigated by using the dynamical method, and a reasonable value 22.42 eV is clarified by eliminating the heating effect induced by the collision.

Unsteady Cavitating Flow around a Hydrofoil Simulated Using the Partially-Averaged Navier–Stokes Model

JI Bin, LUO Xian-Wu, WU Yu-Lin, XU Hong-Yuan
Chin. Phys. Lett. 2012, 29 (7): 076401 doi: 10.1088/0256-307X/29/7/076401
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Numerical simulations of unsteady cavitating flow around a NACA66-mod hydrofoil were performed using the partially-averaged Navier–Stokes method with different values of the resolution control parameters (fk=1.0–0.2, fϵ=1). With decreasing fk, the predicted cavitating flow becomes unsteady as the time-averaged turbulent viscosity at the rear part of the attached cavity is gradually reduced. For fk=0.9 and 0.8, the cavity becomes unstable and its length dramatically expands and shrinks, but the calculation fails to predict the vapor cloud shedding behavior observed experimentally. With smaller fk less than 0.7, the cloud shedding behavior is simulated numerically and the predicted cavity shedding frequency increases. With fk=0.2, the whole cavitating flow evolution can be reasonably reproduced including the cavity growth/destabilization observed previously. The re-entrant flow along the suction surface of the hydrofoil is the main trigger to cause the vapor cloud shedding. The wall pressure along the hydrofoil surface oscillates greatly due to the dynamic cavity shedding. Comparing the simulations and experiments, it is confirmed that for the PANS method, resolution control parameters of fk=0.2 and fϵ=1 are recommended for numerical simulations of unsteady cavitating flows. Thus, the present study shows that the PANS method is an effective approach for predicting unsteady cavitating flow over hydrofoils.

Growth, Mechanical and Thermal Properties of Bi4Si3O12 Single Crystals

SHEN Hui, XU Jia-Yue, PING Wei-Jie, HE Qing-Bo, ZHANG Yan, JIN Min, JIANG Guo-Jian
Chin. Phys. Lett. 2012, 29 (7): 076501 doi: 10.1088/0256-307X/29/7/076501
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Bi4Si3O12 (BSO) is an excellent scintillation crystal, and is becoming the desirable candidate for dual-readout calorimeters in high-energy physics. In this work, high quality BSO crystals are successfully grown by the modified Bridgman method. For the first time, its mechanical and thermal properties are investigated and compared with those of the famous scintillation crystal Bi4Ge3O12 (BGO). The Vickers hardness and fracture toughness of BSO crystal are higher than those of BGO crystal. Its specific heat, thermal diffusivity and thermal conductivity are measured to be 0.319 J⋅gK-1, 1.54 mm2⋅s-1 and 3.29 W⋅m-1K-1 at 298 K, respectively. The average thermal expansion coefficient is calculated to be 7.07×10-6 K-1 from 300 to 1173 K. Compared with BGO crystal, BSO crystal possesses larger specific heat, thermal conductivity and smaller thermal expansion. These results indicate that BSO crystals possess better mechanical and thermal properties, which will benefit its practical applications.

Metalorganic Chemical Vapor Deposition Growth of InAs/GaSb Superlattices on GaAs Substrates and Doping Studies of P-GaSb and N-InAs

LI Li-Gong, LIU Shu-Man, LUO Shuai, YANG Tao, WANG Li-Jun, LIU Feng-Qi, YE Xiao-Ling, XU Bo, WANG Zhan-Guo
Chin. Phys. Lett. 2012, 29 (7): 076801 doi: 10.1088/0256-307X/29/7/076801
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InAs/GaSb type-II superlattices (SLs), Zn-doped GaSb and Si-doped InAs were grown on semi-insulating (001) GaAs substrates by metalorganic chemical vapor deposition. X-ray diffraction reveals that complete strain compensation between the SLs and the GaSb buffer layer is achieved in our SL samples. The relationship between the hole concentration p in GaSb and the diethylzinc (DEZn) flow rate is p∝[DEZn]0.57. The electron concentration in InAs does not show good linearity with the SiH4 flow rate. The growth rate of the p-GaSb epilayer is decreased as the DEZn mole fraction increases, while the growth rate of the n-InAs epilayer is weakly dependent on the SiH4 flow rate.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Optimal Electron Density Mechanism for Hydrogen on the Surface and at a Vacancy in Tungsten

LIU Yue-Lin, GAO An-Yuan, LU Wei, ZHOU Hong-Bo, ZHANG Ying
Chin. Phys. Lett. 2012, 29 (7): 077101 doi: 10.1088/0256-307X/29/7/077101
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In terms of first-principles investigation of H-tungsten (W) interaction, we reveal a generic optimal electron density mechanism for H on W(110) surface and at a vacancy in W. Both the surface and vacancy internal surface can provide a quantitative optimal electron density of ∼0.10 electron/Å3 for H binding to make H stability. We believe that such a mechanism is also applicable to other surfaces such as W(100) surface because of the (100) surface also providing an optimal electron density for H binding, and further likely actions on other metals.

Different Roles of a Boron Substitute for Carbon and Silicon in β-SiC

ZHOU Yan, WANG Kun, FANG Xiao-Yong, HOU Zhi-Ling, JIN Hai-Bo, CAO Mao-Sheng
Chin. Phys. Lett. 2012, 29 (7): 077102 doi: 10.1088/0256-307X/29/7/077102
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The first-principles numerical simulation is employed to calculate the effect of replacement of carbon and silicon with boron on the electronic structure and optical properties of β-SiC. Mulliken analysis shows that the B impurity bond lengths shrink in the case of BSi, while they expand with reference to BC. In addition, BSi contains C–C, Si–Si and B–Si bonds. The calculated results show that the two systems of BC and BSi apply different dispersion. BC is in accordance with the Lorentz dispersion theory while BSi follows the Drude dispersion theory. Theoretic analysis and quantitative calculation are used for conductivity spectra in the infrared region.

Low Bias Negative Differential Resistance with Large Peak-to-Valley Ratio in a BDC60 Junction

REN Hua, LIANG Wei, ZHAO Peng, LIU De-Sheng
Chin. Phys. Lett. 2012, 29 (7): 077301 doi: 10.1088/0256-307X/29/7/077301
Full Text: [PDF 1575 KB] (205)
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Based on nonequilibrium Green's function method and density functional theory calculations, we investigate theoretically the electronic transport properties of 1,4-bis(fullero[c]pyrrolidinl-yl)benzene (BDC60). A low bias negative differential resistance with the peak-to-valley ratio as high as 305.41 is obtained. The observed negative differential resistance is explained in terms of the evolution of the transmission spectra, molecular projected self-consistent Hamiltonian states and molecular projected energy levels with applied bias.

Controllable Excitation of Surface Plasmons in End-to-Trunk Coupled Silver Nanowire Structures

ZHU Yin, WEI Hong, YANG Peng-Fei, XU Hong-Xing
Chin. Phys. Lett. 2012, 29 (7): 077302 doi: 10.1088/0256-307X/29/7/077302
Full Text: [PDF 1132 KB] (190)
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In branched nanowire structures, the controllable excitation of surface plasmons is investigated by both experiments and simulations. By focusing the excitation light at the junction between the main wire and the branch wire, surface plasmons can be selectively launched to propagate to different output terminals, depending on the polarization of the excitation light. The parameters influencing the plasmon excitation and thus emission behavior are investigated, including the branch angle, the position of the branch and the nanowire radius. The different polarization dependence of the output light is determined by the surface plasmon modes selectively excited in the junction through end-excitation or/and gap-excitation manners. For the branch wire, when the branch angle is small, the end-excitation is dominant, which makes the branched wire behave like an individual nanowire. With the increase of the branch angle, the coupling between the branch wire end and the primary wire trunk is increased, which influences the plasmon excitation in the branch wire as evidenced by the rotation of the polarization angle for maximum output. For the primary wire, the SP excitation is dependent on the branch angle, position of the junction along the primary wire, and the radii of the nanowires. The results may be important for the design of a controllable surface plasmon launcher, one of the functional components in surface-plasmon-based nanophotonic circuits.

Alternating-Current Transport Properties in Nd0.7Sr0.3MnO3 Ceramic with Secondary Phases

CHEN Shun-Sheng, YANG Chang-Ping, LUO Xiao-Jing, Medvedeva I V
Chin. Phys. Lett. 2012, 29 (7): 077303 doi: 10.1088/0256-307X/29/7/077303
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Nd0.7Sr0.3MnO3 ceramics with secondary phases were prepared by ball-milling and post heat- treatment at 1623 K for 3, 7 and 13 h, respectively. The results from x-ray diffraction and energy dispersed spectroscopy show that some secondary phases are introduced and grow gradually with sintering time. These secondary phases have significant effects on the ac transport. For all the samples, the real part of impedance (Zr ) decreases with increasing frequency and the Zr peak moves to a higher temperature. Interestingly, for a given frequency the Zr peak decreases with sintering time. However, for samples B and C which were sintered for a longer time than sample A, an additional Zr peak appears at a higher temperature and gradually increases with sintering time. The reposition of trapped charges in phase/grain boundaries or secondary phases is supposed to be responsible for the unusual relaxation process.

Influence of Temperature and Frequency on Dielectric Permittivity and ac Conductivity of Au/SnO2/n-Si (MOS) Structures

R. Ertuğrul, A. Tataroğlu
Chin. Phys. Lett. 2012, 29 (7): 077304 doi: 10.1088/0256-307X/29/7/077304
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The complex dielectric permittivity (ϵ=ϵ'-jϵ") and ac conductivity (σac) of Au/SnO2/n-Si (MOS) structures are studied using capacitance (C) and conductance (G(ω)) measurements in a wide temperature range of 125–400 K for six different frequency values. It is observed that the C and G(ω) values decrease with the increasing frequency, while they increase with the increasing temperature. The observed nature of the C is due to the inability of the dipoles to orient in a rapidly varying electric field. The experimental values of the dielectric constant ϵ', dielectric loss ϵ", loss tangent tanδ and σac are found to be strong functions of frequency and temperature. The values of the ϵ' and ϵ" are found to decrease with the increasing frequency and increase with the increasing temperature. The σac is found to increase with the increasing frequency and temperature. Activation energy (Ea), from the Arrhenius plot, is studied to discuss the conduction mechanism in a MOS structure.

Controllable Negative Differential Resistance Behavior of an Azobenzene Molecular Device Induced by Different Molecule-Electrode Distances

FAN Zhi-Qiang, ZHANG Zhen-Hua, QIU Ming, DENG Xiao-Qing, TANG Gui-Ping
Chin. Phys. Lett. 2012, 29 (7): 077305 doi: 10.1088/0256-307X/29/7/077305
Full Text: [PDF 649 KB] (223)
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We report the ab initio calculations of transport behaviors of an azobenzene molecular device which is similar to the experimental configurations. The calculated results show that the transport behaviors of the device are sensitive to the molecule-electrode distance and the currents will drop rapidly when the molecule-electrode distance changes from 1.7 Åto 2.0 Å. More interestingly, the negative differential resistance behavior can be found in our device. Nevertheless, it is not the inherent property of an azobenzene molecular device but an effect of the molecule-electrode distance. Detailed analyses of the molecular projected self-consistent Hamiltonian states and the transmission spectra of the system reveal the physical mechanism of these behaviors.

Synthesis of ITO Nanoparticles Prepared by the Degradation of Sulfide Method

Majid. Farahmandjou
Chin. Phys. Lett. 2012, 29 (7): 077306 doi: 10.1088/0256-307X/29/7/077306
Full Text: [PDF 672 KB] (794)
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Indium tin oxide (ITO) nanoparticles are synthesized by the two-degradation sulfide and liquid-phase co-precipitation method under the given conditions with solutions of InCl3⋅4H2O and SnCl4⋅5H2O in the presence of ethylendyamine. The sample powders were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses after heat treatments. The SEM results show that the size of the ITO particles prepared by the co-precipitation method is decreased to 100 nm, whereas the size of the ITO prepared by degradation of sulfide increases to 1 µm after heat treatment. The XRD results reveal that the size of crystallite ITO particles is increased with increasing annealing temperature. Finally the intensity ratio of I400/I222 has an increase of 29.07% for ITO prepared by the co-precipitation method.

Electron Transport through Magnetic Superlattices with Asymmetric Double-Barrier Units in Graphene

HUO Qiu-Hong, WANG Ru-Zhi, YAN Hui
Chin. Phys. Lett. 2012, 29 (7): 077307 doi: 10.1088/0256-307X/29/7/077307
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We investigate the transport properties through magnetic superlattices with asymmetric double-barrier units in monolayer graphene. In N-periodic asymmetric double-barrier units, there is (N−1)-fold resonant peak splitting for transmission, but the splitting is (2N−1)-fold in N-periodic symmetric units. The transmission depends not only on the value of incident wavevectors but also on the value and the direction of transverse wavevectors. This renders the structure's efficient wavevector filters. In addition, the conductance of standard electrons with a parabolic energy spectrum is suppressed more strongly than that of Dirac electrons, whereas the resonances are more pronounced for Dirac electrons than for standard ones.

Polarization-Selective Collimation Effect with a Reflective Plasmonic Cavity

MAO Fei-Long, XIE Jin-Jin, FAN Qing-Yan, ZHANG Li-Jian, AN Zheng-Hua
Chin. Phys. Lett. 2012, 29 (7): 077308 doi: 10.1088/0256-307X/29/7/077308
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We report that a metal-dielectric-metal cavity with a perforated top metallic film shows a remarkable polarization-selective collimation effect through reflection on the perforated film. According to simulations, such plasmonic cavities can achieve nearly perfect absorption (R<1.5%) of a transverse magnetic (TM) wave at an optimized incident angle while nearly perfect reflection (R∼100%) at normal incidence. A very wide incident angle range (approximately 15°–65°) is found to exhibit a high absorption ratio exceeding over 70%. In contrast, for a transverse electric (TE) wave, the plasmonic cavities remain highly reflective (R∼100%) regardless of the incident angles. We elucidate that this polarization- and angle-dependent behavior arises from an even-order (N=2) horizontal Fabry–Pérot (FP) resonant mode inside the plasmonic cavity. This effect may find potential applications for angle filtering of polarized divergent light beams in optics.

First Principle Study of the Electronic Properties of 3C-SiC Doped with Different Amounts of Ni

DOU Yan-Kun, QI Xin, JIN Hai-Bo, CAO Mao-Sheng, Usman Zahid, HOU Zhi-Ling
Chin. Phys. Lett. 2012, 29 (7): 077701 doi: 10.1088/0256-307X/29/7/077701
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The electronic properties of 3C-SiC doped with different contents of Ni are investigated by using first-principles calculations. It is observed that the non-filled impurity energy levels in the band-gap region increase with increasing Ni content, which subsequently results in an enhancement of electrical conductivity of 3C-SiC. This enhancement in conductivity is verified by the conductivity spectrum in which new peaks appear in the middle-infrared region, visible region, and middle-ultraviolet region. It is further observed that the width and intensity of these newly appeared peaks increase with the increase of Ni content. The electronic density of states exhibits the peaks crossing the Fermi level, which favors the electronic transitions and proves Ni-doped 3C-SiC to be a half-metallic semiconductor. Through the analysis of electron density difference and Mulliken overlap population, it is found that the covalent bonds are formed between Ni and near-by C atoms. These features confirm that the Ni-doped 3C-SiC semiconductor is a promising material for device applications in modern day electronics.

Can Hydrogen be Incorporated inside Silicon Nanocrystals?

NI Zhen-Yi, PI Xiao-Dong, YANG De-Ren
Chin. Phys. Lett. 2012, 29 (7): 077801 doi: 10.1088/0256-307X/29/7/077801
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Hydrogen is omnipresent during the synthesis and processing of silicon nanocrystals (Si NCs). It is generally assumed that the incorporation of hydrogen leads to the passivation of Si dangling bonds at the NC surface. However, it is also speculated that hydrogen may be incorporated inside Si NCs. In this work the formation energy and probability of hydrogen in its three configurations, i.e., hydrogen molecules, bond-centered atomic hydrogen, and antibonding atomic hydrogen, are calculated to rigorously evaluate the incorporation of hydrogen inside Si NCs. We find that hydrogen cannot be incorporated inside Si NCs with a diameter of a few nanometers at temperatures up to 1500 K.

Abnormal Temperature Dependence of Coercivity in Cobalt Nanowires

FAN Xiu-Xiu, HU Hai-Ning, ZHOU Shi-Ming, YANG Mao, DU Jun, SHI Zhong
Chin. Phys. Lett. 2012, 29 (7): 077802 doi: 10.1088/0256-307X/29/7/077802
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Co nanowire arrays have been fabricated into anodic aluminum oxide templates at 20°C by dc electrodeposition. It is shown that Co nanowires fabricated at lower and higher growth voltages have a hexagonal close packing (hcp) structure with preferred [100] orientation along the nanowire axis and a face-centered cubic (fcc) structure with preferred [220] orientation, respectively. With increasing growth voltage, the room-temperature coercivity along the nanowire axis is enhanced gradually. For fcc Co nanowires, the coercivity increases monotonically with increasing temperature while for hcp Co nanowires, a minimal coercivity is obtained along both parallel-to-axis and perpendicular-to-axis orientations with the temperature rising from 50 K to 390 K. The abnormal temperature dependence of the coercivity can be attributed to the competition between the shape anisotropy and magnetocrystalline anisotropy as a function of temperature.

Growth-induced Stacking Faults of ZnO Nanorods Probed by Spatial Resolved Cathodoluminescence

XIE Yong, JIE Wan-Qi, WANG Tao, WIEDENMANN Michael, NEUSCHL Benjamin, MADEL Manfred, WANG Ya-Bin, FENEBERG Martin, THONKE Klaus
Chin. Phys. Lett. 2012, 29 (7): 077803 doi: 10.1088/0256-307X/29/7/077803
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Low density ZnO nanorods are grown by modified chemical vapor deposition on silicon substrates using gold as a catalyst. We use high resolution photoluminescence spectroscopy to gain the optical properties of these nanorods in large scale. The as-grown samples show sharp near-band-gap luminescence with a full width at half maximum of bound exciton peaks at about 300 µeV, and the ratio of ultraviolet/yellow luminescence larger than 100. Highly spatial and spectral resolved scanning electron microscope-cathodoluminescence is performed to excite the ZnO nanorods in single rods or different positions of single rods with the vapour-solid growth mechanism. The bottom of the nanorod has a 3.31-eV luminescence, which indicates that basal plane stacking faults are related to the defects that are created at the first stage of growth due to the misfit between ZnO and Si.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Ultrathin Carbon Films Prepared by Negative Cluster-Beam Technology

ZHANG Zao-Di, WANG Ze-Song, WANG Shi-Xu, FU De-Jun
Chin. Phys. Lett. 2012, 29 (7): 078101 doi: 10.1088/0256-307X/29/7/078101
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We develop a miniaturized chamber installed on a tandetron accelerator into which negative ions of small carbon clusters are transported. Negative clusters C1− C10 are obtained with beam currents of 1–104 nA at energies of 10–20 keV. C2 beams of 0.2 µA are used to directly deposit carbon films on SiO2/Si substrates. Formation of ultrathin carbon films are demonstrated by Raman scattering, which reveals the evolution of the graphitic peak (1550 cm−2) with deposition time.

Betavoltaic Battery Conversion Efficiency Improvement Based on Interlayer Structures

LI Da-Rang, JIANG Lan, YIN Jian-Hua, TAN Yuan-Yuan, LIN Nai
Chin. Phys. Lett. 2012, 29 (7): 078102 doi: 10.1088/0256-307X/29/7/078102
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Significant differences among the doping densities of PN junctions in semiconductors cause lattice mismatch and lattice defects that increase the recombination current of betavoltaic batteries. This extensively decreases the open circuit voltage and the short current, which results in low conversion efficiency. This study proposes P+PINN+-structure based betavoltaic batteries by adding an interlayer to typical PIN structures to improve conversion efficiency. Numerical simulations are conducted for the energy deposition of beta particles along the thickness direction in semiconductors. Based on this, 63Ni-radiation GaAs batteries with PIN and P+PINN+ structures are designed and fabricated to experimentally verify the proposed design. It turns out that the conversion efficiency of the betavoltaic battery with the proposed P+PINN+ structure is about 1.45 times higher than that with the traditional PIN structure.

Effect of Grain Boundary on Spinodal Decomposition Using the Phase Field Crystal Method

YANG Tao, CHEN Zheng, ZHANG Jing, DONG Wei-Ping, WU Lin
Chin. Phys. Lett. 2012, 29 (7): 078103 doi: 10.1088/0256-307X/29/7/078103
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Spinodal decomposition (SD) with different grain boundaries (GBs) is investigated on the atomic scale using the novel phase field crystal model. It is demonstrated that the decomposition process is initiated by precipitating one phase with a larger lattice constant in the tension region at the GBs and the other one with a smaller lattice constant in the compression region. As the phase separation proceeds, the dislocations comprising the low-angle GBs migrate toward the compositional domain boundaries to relieve the coherent strain energy, and eventually become randomly distributed in the coarsening regime of SD, which leads to the disappearance of the low-angle GBs. For high-angle GBs, the location of GBs remains unchanged, while the atoms rearrange along the GBs to fit the stress field arising from compositional inhomogeneity.

Influence of Dry Etching Damage on the Internal Quantum Efficiency of Nanorod InGaN/GaN Multiple Quantum Wells

YU Zhi-Guo, CHEN Peng YANG Guo-Feng, LIU Bin, XIE Zi-Li, XIU Xiang-Qian, WU Zhen-Long, XU Feng, XU Zhou, HUA Xue-Mei, HAN Ping, SHI Yi ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2012, 29 (7): 078501 doi: 10.1088/0256-307X/29/7/078501
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The influence of dry etching damage on the internal quantum efficiency of InGaN/GaN nanorod multiple quantum wells (MQWs) is studied. The samples were etched by inductively coupled plasma (ICP) etching via a self-assembled nickel nanomask, and examined by room-temperature photoluminescence measurement. The key parameters in the etching process are rf power and ICP power. The internal quantum efficiency of nanorod MQWs shows a 5.6 times decrease substantially with the rf power increasing from 3 W to 100 W. However, it is slightly influenced by the ICP power, which shows 30% variation over a wide ICP power range between 30 W and 600 W. Under the optimized etching condition, the internal quantum efficiency of nanorod MQWs can be 40% that of the as-grown MQW sample, and the external quantum efficiency of nanorod MQWs can be about 4 times that of the as-grown one.

Gate-Recessed AlGaN/GaN MOSHEMTs with the Maximum Oscillation Frequency Exceeding 120 GHz on Sapphire Substrates

KONG Xin, WEI Ke, LIU Guo-Guo, LIU Xin-Yu
Chin. Phys. Lett. 2012, 29 (7): 078502 doi: 10.1088/0256-307X/29/7/078502
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Gate-recessed AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors (MOSHEMTs) on sapphire substrates are fabricated. The devices with a gate length of 160 nm and a gate periphery of 2×75 µm exhibit two orders of magnitude reduction in gate leakage current and enhanced off-state breakdown characteristics, compared with conventional HEMTs. Furthermore, the extrinsic transconductance of an MOSHEMT is 237.2 mS/mm, only 7% lower than that of Schottky-gate HEMT. An extrinsic current gain cutoff frequency fT of 65 GHz and a maximum oscillation frequency fmax of 123 GHz are deduced from rf small signal measurements. The high fmax demonstrates that gate-recessed MOSHEMTs are of great potential in millimeter wave frequencies.

Thermoluminescence Response of Germanium-Doped Optical Fibers to X-Ray Irradiation

M. A. Saeed, N. A. Fauzia, I. Hossain, A. T. Ramli, B. A. Tahir
Chin. Phys. Lett. 2012, 29 (7): 078701 doi: 10.1088/0256-307X/29/7/078701
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We present the characteristics of the thermoluminescence (TL) response of Ge-doped optical fibers with various energies and exposures of photon irradiation. To investigate the Ge-doped SiO2 as an efficient TL material, the TL responses are compared with commercially available standard TLD100 media. The Ge-doped optical fiber and TLD100 are placed in gelatin capsules and irradiated with x-ray using a Toshiba model KXO-15R x-ray generator. The Ge-doped fiber and TLD-100 show linear response as a function of current and time using x-ray photon of energy 60, 80 and 100 kV. When irradiated with 60, 80 and 100 kV x-ray energy at various currents (mA), tube distance (cm) and exposure time (second) ranges, TLD100 media provide a TL yield up to two times that of Ge-doped fibers. The energy response of the Ge-doped fibers is linear and similar over the 60–100 kV energy range, and its sensitivity is 0.39±0.05 of the TLD100 media. The glow curves of TLD 100 and doped optical fiber are also compared.

A Poly-(3-Hexylthiophene) (P3HT)/[6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PCBM) Bilayer Organic Solar Cell Fabricated by Airbrush Spray Deposition

CHEN Zheng, DENG Zhen-Bo, ZHOU Mao-Yang, LÜ Zhao-Yue, DU Hai-Liang, ZOU Ye, YIN Yue-Hong, LUN Jian-Chao
Chin. Phys. Lett. 2012, 29 (7): 078801 doi: 10.1088/0256-307X/29/7/078801
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Airbrush spray deposition is applied to fabricate a bilayer heterojunction solar cell based on P3HT/PCBM. This solar cell device shows an open-circuit voltage of 0.36 V, a short circuit current density of 6.76 mA/cm2, a conversion efficiency of 0.74%, and a fill factor of 30.4%. The results demonstrate that airbrush spray deposition is an effective method to fabricate multilayer or other complex polymer-based organic solar cells. Although spin-coated bulk heterojunction devices have better performance than the airbrushed ones, the airbrush is indeed feasible as a low-cost yet simple process. It is noteworthy that such preliminary results of the airbrush spray solar cell is unoptimized and thus its performance can be further improved with the development of this technology. Furthermore, this method itself has huge potential as it can be used for other polymer-based organic thin film devices.

Response Surface Analysis of Crowd Dynamics during Tawaf

Zarita Zainuddin, Lim Eng Aik
Chin. Phys. Lett. 2012, 29 (7): 078901 doi: 10.1088/0256-307X/29/7/078901
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A refined cellular automata model is applied to simulate the crowd movement of Muslim pilgrims performing the Tawaf ritual within the Al-Haram Mosque in Mecca. The results from the simulation are obtained and the influence of the predictor variables of the evacuation process (pedestrian flow and Tawaf duration) on the responses (pedestrian density, average walking speed, and cumulative evacuee) is investigated using response surface methodology (RSM). The average results from the experiments with an rms error less than 0.5 are obtained from the RSM. Its performance indicates that the RSM possesses excellent predictive ability for the model evacuation study, because both the experimental and the predicted values agree well with the results obtained in this study.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Laser Interferometer Used for Satellite–Satellite Tracking: an On-Ground Methodological Demonstration

LI Yu-Qiong, LUO Zi-Ren, LIU He-Shan, DONG Yu-Hui, JIN Gang
Chin. Phys. Lett. 2012, 29 (7): 079501 doi: 10.1088/0256-307X/29/7/079501
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A Chinese satellite gravity mission called SAGM (Space Advanced Gravity Measurements) is now taken into consideration. To meet its designed requirement, the measurement precision of the laser ranging system used to measure the inter-satellite distance change has to be better than 100 nm/Hz1/2 within a broad bandwidth from 0.1 mHz to 1 Hz. An equal arm heterodyne Mach–Zehnder interferometer has been built on ground to demonstrate the measurement principle of a laser ranging system, which potentially can be used for both SAGM and future GW (gravitational wave) space antennas. Because of the equal arm length, the laser frequency noise has been significantly suppressed in the interferometer. Thus, the sensitivity better than 1 nm/Hz1/2 in a frequency range of 0.15 mHz–0.375 Hz has been achieved. The result shows that the proposed methodology has very promising feasibility to meet the requirements of SAGM and of GW space antennas as well.

Cosmological Constant Dominated Transit Universe from the Early Deceleration Phase to the Current Acceleration Phase in Bianchi-V Spacetime

YADAV Anil Kumar
Chin. Phys. Lett. 2012, 29 (7): 079801 doi: 10.1088/0256-307X/29/7/079801
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We present the transition of the universe from the early decelerating phase to the current accelerating phase with viscous fluid and time-dependent cosmological constant Λ as a source of matter in Bianchi-V spacetime. To study the transit behaviour of the universe, we assume the scale factor as an increasing function of time, which generates a time-dependent deceleration parameter (DP). The study reveals that the cosmological term does not change its fundamental nature for ξ=const and ξ=ξ(t), where ξ is the coefficient of bulk viscosity. The Λ(t) is found to be positive and is a decreasing function of time. The same behavior was observed during recent supernovae observations. The physical behaviour of the universe is discussed in detail.
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