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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2014, 31 (4)   Published: 25 March 2014
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GENERAL

Numerical Simulation of Rogue Waves by the Local Discontinuous Galerkin Method

CAI Wen-Jun, WANG Yu-Shun, SONG Yong-Zhong
Chin. Phys. Lett. 2014, 31 (4): 040201 doi: 10.1088/0256-307X/31/4/040201
Full Text: [PDF 2139 KB] (238)
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We study rogue waves described by nonlinear Schrödinger equations. Such wave solutions are so different from conventional soliton solutions that classic methods such as the Crank–Nicolson scheme cannot work for these cases. Fortunately, we find that the local discontinuous Galerkin method equipped with Dirichlet boundary conditions can simulate rogue waves very well. Several numerical examples are presented to show such interesting wave solutions.

Thermal Entanglement in the Spin-S Heisenberg XYZ Model

LI Hu, LI Da-Chuang, WANG Xian-Ping, YANG Ming, CAO Zhuo-Liang
Chin. Phys. Lett. 2014, 31 (4): 040301 doi: 10.1088/0256-307X/31/4/040301
Full Text: [PDF 620 KB] (86)
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The thermal entanglement in the spin-S Heisenberg XYZ model is studied in detail by using the entanglement measure of negativity. The effects of spin on the thermal entanglement, the threshold temperature, the critical uniform external magnetic field, the nonuniform external magnetic field and the entanglement extremum are discussed, respectively. It is shown that with increasing spin, the entanglement will increase, and then decrease slowly. In addition, we find that entanglement will approach a constant Nc with the increase of DM interaction, the constant increases with the increase of spin, and both the threshold temperature Tc and critical uniform external magnetic field Bc will increase with the increasing spin. Thus high-spin system can inhibit the influence of the external environment better.

Manipulating Single-Photon Transport Properties in an Asymmetrical Waveguide Coupled to a Whispering-Gallery Resonator Containing a Two-Level Atom

ZHOU Tao, ZANG Xiao-Fei, XU Dan-Hua
Chin. Phys. Lett. 2014, 31 (4): 040302 doi: 10.1088/0256-307X/31/4/040302
Full Text: [PDF 543 KB] (58)
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A hybrid system containing an asymmetrical waveguide coupled to a whispering-gallery resonator embedded with a two-level atom is designed to investigate single-photon transport properties. The transmission and reflection amplitudes are obtained via the discrete coordinates approach. Numerical simulation demonstrates that a tri-frequency photon attenuator is realized by controlling the couplings between the asymmetrical waveguide and the whispering-gallery resonator. The phase shift, group delay and dissipation effects of the transmitted single-photon are also discussed.

Separability Criterion for Bipartite States and Its Generalization to Multipartite Systems

HUANG Jie-Hui, HU Li-Yun, WANG Lei, ZHU Shi-Yao
Chin. Phys. Lett. 2014, 31 (4): 040303 doi: 10.1088/0256-307X/31/4/040303
Full Text: [PDF 449 KB] (40)
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A group of symmetric operators are introduced to carry out the separability criterion for bipartite and multipartite quantum states. All the symmetric operators, represented by a symmetric matrix with only two nonzero elements, and their arbitrary linear combinations are found to be entanglement witnesses. By using these symmetric operators, Wootters' separability criterion for two-qubit states can be generalized to bipartite and multipartite systems in arbitrary dimensions.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Finite Size Effect on the in-Medium Chiral Condensate at Finite Density

XIA Cheng-Jun, PENG Guang-Xiong, HOU Jia-Xun
Chin. Phys. Lett. 2014, 31 (4): 041101 doi: 10.1088/0256-307X/31/4/041101
Full Text: [PDF 674 KB] (26)
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The in-medium quark condensate is studied with an equivalent quark mass approach that has the advantage of no need for extra assumptions on the current mass derivatives of model parameters with respect to the quark current mass. It is found that the ratio of the quark condensate in a medium to that in a vacuum depends not only on density but also on the finite size. With decreasing volume, it decreases to a minimum, and then saturates at a radius of about 1 fm. The condensate approaches to its bulk value when the volume becomes infinitely large, and it decreases linearly with increasing density if the density is extremely low.

The Scalar Photon Light-Cone Distribution Amplitude in the Instanton Vacuum Model of QCD

MO Xin, LIU Jue-Ping
Chin. Phys. Lett. 2014, 31 (4): 041102 doi: 10.1088/0256-307X/31/4/041102
Full Text: [PDF 616 KB] (20)
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Based on the principle of the Lorentz covariance, the transition matrix elements from an off-shell photon state to the vacuum are parameterized by the light-cone photon distribution amplitudes (DAs). Both the scalar off-shell photon light-cone DA and the corresponding coupling are calculated in the instanton vacuum model of quantum chromodynamics (QCD), and their explicit analytical expressions and the numerical results are given. The results for the other chiral-odd light-cone photon DAs and their couplings are presented as well.
NUCLEAR PHYSICS

Quasi Random Phase Approximation Predictions on Two-Neutrino Double Beta Decay Half-Lives to the First 2+ State

S. Unlu
Chin. Phys. Lett. 2014, 31 (4): 042101 doi: 10.1088/0256-307X/31/4/042101
Full Text: [PDF 460 KB] (20)
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Two-neutrino double beta decay (2νββ) half-lives to the first excited state are calculated in the framework of quasi random phase approximation. The quadrupole transition probabilities and the 2νββ decay amplitudes to the final ground states are reproduced by using adjustable parameters. The obtained half-lives are compared with the corresponding experimental data.

High-Spin States in the Odd-Odd Nucleus 92Nb

WU Yi-Heng, LU Jing-Bin, LUO Peng-Wei, LI Guang-Sheng, LI Hong-Wei, WU Xiao-Guang, HE Chuang-Ye, ZHENG Yun, MA Ke-Yan, YANG Dong, LI Cong-Bo, HU Shi-Peng, LIU Jia-Jian, WANG Jin-Long, YAO Shun-He, CHEN Qi-Ming, ZHONG Jian
Chin. Phys. Lett. 2014, 31 (4): 042102 doi: 10.1088/0256-307X/31/4/042102
Full Text: [PDF 576 KB] (25)
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High spin states of the odd-odd nucleus 92Nb are investigated using the 82Se (14N, 4n)92Nb reaction at a beam energy of 54 MeV. The level scheme of the 92Nb was extended up to Jπ=(16+) at about 7.3 MeV and Jπ=(21) at about 9.7 MeV. According to systematic analyses and a comparison with the neighboring nucleus, the higher spin states could be interpreted by the multi-particle excitations in the π(f5/2,p3/2,p1/2,g9/2)⊗ν(p1/2,g9/2,d5/2, g7/2) configuration space.
ATOMIC AND MOLECULAR PHYSICS

The Inversionless Amplification in a Tripod System of 87Rb Atoms in a Magneto-optical Trap

SUN Zhen, JIA Feng-Dong, LV Shuang-Fei, RUAN Ya-Ping, QING Bo, XUE Ping, XU Xiang-Yuan, DAI Xing-Can, ZHONG Zhi-Ping
Chin. Phys. Lett. 2014, 31 (4): 043201 doi: 10.1088/0256-307X/31/4/043201
Full Text: [PDF 806 KB] (30)
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The probe transmission spectra around the atomic transition 52S1/2,F=2→52P3/2,F'=2 of 87Rb are measured in a magneto-optical trap by adding a coupling field around the atomic transition 52S1/2,F=2→52P3/2,F'=2. The inversionless amplification is observed in the spectrum over the atomic transition 52S1/2,F=2→52P3/2,F'=2. The tripod electromagnetically induced transparency is proposed to account for the amplification feature, in which population distributions among these related atomic levels play an important role.

Carrier Envelope Phase Effect of a Long Duration Pulse in the Low Frequency Region

ZHAO Xi, YANG Yu-Jun, LIU Xue-Shen, WANG Bing-Bing
Chin. Phys. Lett. 2014, 31 (4): 043202 doi: 10.1088/0256-307X/31/4/043202
Full Text: [PDF 575 KB] (27)
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Using the characteristic of small energy difference between two high Rydberg states, we theoretically investigate the carrier envelope phase (CEP) effect in a bound-bound transition of an atom in a low-frequency long laser pulse with tens of optical cycles. Particularly, we first prepare a Rydberg state of a hydrogen-like atom by a laser field with the resonant frequency between this state and the ground state. Then by using a low-frequency long laser pulse interacting with this Rydberg atom, we calculate the population of another Rydberg state nearby this Rydberg state at the end of the laser pulse and find that the population changes dramatically with the CEP of the low-frequency pulse. This CEP effect is attributed to the interference between the positive-frequency and negative-frequency components in one-photon transition. These results may provide a method to measure the CEP value of a long laser pulse with low frequency.

Optimized Degenerate Bose–Fermi Mixture in Microgravity: DSMC Simulation of Sympathetic Cooling

LUAN Tian, JIA Tao, CHEN Xu-Zong, MA Zhao-Yuan
Chin. Phys. Lett. 2014, 31 (4): 043401 doi: 10.1088/0256-307X/31/4/043401
Full Text: [PDF 614 KB] (20)
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Applying the direct simulation Monte Carlo (DSMC) method developed for the cold atom system, we explore the possibility of a high-efficiency sympathetic cooling process between 87Rb and 40K without gravitational force in an optical trap. The relation between the pre-cooling of Bosons and the sympathetic cooling efficiency is also studied. We find that the absence of gravitational force is beneficial to the process of sympathetic cooling. Furthermore, an inefficient pre-cooling process will in fact hamper the creation of Fermi degenerate gases. This suggests the advantages of sympathetic cooling in microgravity.

Simulation and Optimization of Miniature Ring-Endcap Ion Traps

CAO Jian, TONG Xin, CUI Kai-Feng, SHANG Jun-Juan, SHU Hua-Lin, HUANG Xue-Ren
Chin. Phys. Lett. 2014, 31 (4): 043701 doi: 10.1088/0256-307X/31/4/043701
Full Text: [PDF 630 KB] (50)
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With the decrease in dimension of ion traps employed in optical frequency standards and precision spectroscopy, the sensitivity of trapping behavior to trap geometry is more and more prominent. We present a guide for the design and construction of a miniature trap for a single ion confinement, and propose an optimized combination of rring/rendcap0.5 and z0≈r0 within the range of r0=0.7±0.2 mm. Compared with the trap used by Huang et al. [Phys. Rev. A 84 (2011) 053841], the design can lead to an increase in trap pseudo-potential of more than 20% and a reduction on potential anharmonicity of more than 90%. The improvements make the trap closer to an ideal hyperboloidal trap to confine a single ion tightly with the benefit of weaker micro-motion. Considering the imperfection of electrodes machining and traps alignment, we also demonstrate the importance of trap symmetry, especially on two endcap electrodes.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Distributed Field Rotator Composed of Isolated Components

LIU Guo-Chang, LI Chao, SHAO Jin-Jin, FANG Guang-You
Chin. Phys. Lett. 2014, 31 (4): 044101 doi: 10.1088/0256-307X/31/4/044101
Full Text: [PDF 1065 KB] (42)
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Transformation optics offers remarkable control over electromagnetic fields and has recently opened an exciting gateway to design 'field rotator devices'. We propose a distributed field rotator with open windows based on composite transformation optics, which consists of a central circular region and several isolated components. The number, position and size of the components can be controlled freely by the design purpose. Full-wave simulations are performed to demonstrate its function, which is equivalent to a classic field rotator. However, such a distributed rotator makes it much easier to access and make use of the rotated field in the central region, compared to the closed classic field rotator, especially in the case of 3D situations.

A Compact High Power Laser-Diode Side-Pumped Tm,Ho:YAG Laser Nearly at Room Temperature with Intracavity Tm:YAG Laser

ZHANG Chao, DU Shi-Feng, NIU Yan-Xiong, WANG Cai-Li, WANG Zhi-Chao, XU Jia-Lin, BO Yong, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2014, 31 (4): 044201 doi: 10.1088/0256-307X/31/4/044201
Full Text: [PDF 488 KB] (26)
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We report a compact high power Tm,Ho:YAG laser nearly at room temperature. The laser-diode side-pumped Tm:YAG and Tm,Ho:YAG laser modules are operated in the same cavity. The laser yields 37.34 W of continuous wave output power under the temperature of 6 °C, corresponding to a maximum slope efficiency of 16.7% when the output power lies from 5.1 W to 27.0 W. This is the first report on the combined Tm:YAG and Tm,Ho:YAG lasers for obtaining high power 2.1 μm laser.

A Linearly-Polarized Cesium Vapor Laser with Fundamental Mode Output and Low Threshold

LI Zhi-Yong, TAN Rong-Qing, HUANG Wei, XU Cheng
Chin. Phys. Lett. 2014, 31 (4): 044202 doi: 10.1088/0256-307X/31/4/044202
Full Text: [PDF 608 KB] (18)
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We report a cesium vapor laser with fundamental mode output and a wavelength of 894 nm. The laser is pumped by a laser diode array with an external cavity of a holographic grating by using Littrow's structure. A slope efficiency of 22.4% is obtained by using a pumping source with a linewidth of 0.26 nm and 80 kPa methane as the buffer gas. The threshold pumping power is 1.56 W.

Effect of Wavefront Properties on Numerical Aperture of Fresnel Hologram in Incoherent Holographic Microscopy

WAN Yu-Hong, MAN Tian-Long, CHEN Hao, JIANG Zhu-Qing, WANG Da-Yong
Chin. Phys. Lett. 2014, 31 (4): 044203 doi: 10.1088/0256-307X/31/4/044203
Full Text: [PDF 2260 KB] (30)
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Fresnel incoherent correlation holographic (FINCH) microscopy is a recently developed new technique, which employs a spatial light modulator (SLM) as the beam splitter. Light originating from the same object point is split into two beams by the wavefront-division phase mask displayed on SLM, and a Fresnel-zone plate-like hologram is formed by the interference of the two beams. The numerical aperture NAH of the recorded Fresnel hologram is introduced as a comprehensive parameter for evaluating the imaging characteristics in the FINCH scheme. The effect of wavefront properties on NAH of the hologram is investigated theoretically in the sense of optimizing imaging resolution. The variation trends of NAH are described and an optimal NAH is achieved by implementing an appropriate phase mask for a given recording distance between SLM and CCD; thus optimized imaging resolution and signal-to-noise ratio are demonstrated experimentally.

Enhanced Impurity-Free Intermixing Bandgap Engineering for InP-Based Photonic Integrated Circuits

CUI Xiao, ZHANG Can, LIANG Song, ZHU Hong-Liang, HOU Lian-Ping
Chin. Phys. Lett. 2014, 31 (4): 044204 doi: 10.1088/0256-307X/31/4/044204
Full Text: [PDF 541 KB] (17)
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Impurity-free intermixing of InGaAsP multiple quantum wells (MQW) using sputtering Cu/SiO2 layers followed by rapid thermal processing (RTP) is demonstrated. The bandgap energy could be modulated by varying the sputtering power and time of Cu, RTP temperature and time to satisfy the demands for lasers, modulators, photodetector, and passive waveguides for the photonic integrated circuits with a simple procedure. The blueshift of the bandgap wavelength of MQW is experimentally investigated on different sputtering and annealing conditions. It is obvious that the introduction of the Cu layer could increase the blueshift more greatly than the common impurity free vacancy disordering technique. A maximum bandgap blueshift of 172 nm is realized with an annealing condition of 750°C and 200 s. The improved technique is promising for the fabrication of the active/passive optoelectronic components on a single wafer with simple process and low cost.

Wavelength-Tunable Rectangular Pulse Dissipative Soliton Operation of an Erbium-Doped Mode-Locked Fiber Laser

HU Xue-Juan, GUO Chun-Yu, RUAN Shuang-Chen
Chin. Phys. Lett. 2014, 31 (4): 044205 doi: 10.1088/0256-307X/31/4/044205
Full Text: [PDF 633 KB] (40)
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The wavelength-tunable rectangular pulse dissipative soliton (DS) is experimentally demonstrated, for the first time to the best of our knowledge, in an erbium-doped figure-of-eight fiber laser based on the nonlinear amplifying loop mirror mode-locked technique. The proposed rectangular pulse DS fiber laser can operate in the wavelength-tunable mode-locked state from 1573.5 nm to 1594.6 nm with the rotation of the polarization controllers. The achieved output wavelengths are 1573.5 nm, 1576.3 nm, 1586.8 nm, 1590.4 nm and 1594.6 nm, respectively. The pulse widths of the rectangular pulse can also be tuned from ∼8 ns to ∼24 ns by adjusting the pump power. The fundamental repetition rate of the rectangular pulse DS is 1.154 MHz and the output power is 6.14 mW (at 1594.6 nm).

Four-Channel 1.55-µm DFB Laser Array Monolithically Integrated with a 4×1 Multimode-Interference Combiner Based on Nanoimprint Lithography

CHEN Xin, ZHAO Jian-Yi, ZHOU Ning, HUANG Xiao-Dong, LIU Wen
Chin. Phys. Lett. 2014, 31 (4): 044206 doi: 10.1088/0256-307X/31/4/044206
Full Text: [PDF 852 KB] (24)
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A monolithically integrated four-channel λ/4 phase shift distributed feedback (DFB) laser array with a 4×1 multimode interference combiner is designed and fabricated using nanoimprint lithography. The threshold currents of the lasers are less than 10 mA, which are as good as a discrete DFB laser. Moreover, the side-mode suppression ratio is also better than 50 dB. The channel space is about 200 GHz for dense wavelength division multiplexing applications in an 1.55 μm system.

Analysis of the Attenuation Characteristics of an Elastic Wave Due to the Wave-Induced Fluid Flow in Fractured Porous Media

WANG Ding, WANG Li-Ji, ZHANG Mei-Gen
Chin. Phys. Lett. 2014, 31 (4): 044301 doi: 10.1088/0256-307X/31/4/044301
Full Text: [PDF 481 KB] (31)
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A theoretical model is presented to describe the elastic wave propagation characteristics in porous media of periodically arranged fractures. The effects of fracture geometric parameters on a compressional wave (p-wave) are considered through analysis of the wave induced fluid flow (WIFF) process between the fractures and the background media. The diffusion equation in porous media is used to reveal how the entire diffusion process affects the wave propagation. When the thickness proportion of fractures tends to 0 and 1, the WIFF does not take place almost between fractures and background matrix porosity, and therefore the media elasticity modulus is perfectly elastic. When the fracture thickness fraction achieves a certain value, the peak of the attenuation curve reaches the maximum value at a particular frequency, which is controlled by the fluid mass conservation and stress continuity conditions on each fracture boundary. That is, the inter-coupling of fluid diffusion between the adjacent layers is important for waves attenuation. Physically speaking, the dissipation of a wave is associated with the fluid flux essentially.

Surface Oscillation and Flow Structure of a Liquid Bridge under Small Vibration

LIANG Ru-Quan, Kawaji Masahiro
Chin. Phys. Lett. 2014, 31 (4): 044701 doi: 10.1088/0256-307X/31/4/044701
Full Text: [PDF 992 KB] (19)
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A three-dimensional direct numerical simulation is carried out to predict the surface oscillation and flow structure of isothermal liquid bridges of 5 cSt silicone oil held vertically between solid disks. By subjecting liquid bridges to various horizontal vibrations, the surface resonance frequencies are clearly determined numerically and compared well with the existing analytical model predictions. The investigation on the flow structure inside the liquid bridge reveals, for the first time, the flow structure and the existence of transversal vortices inside the liquid bridge when a horizontal vibration is applied.

On the Second Harmonic Generation through Bell–Plesset Effects in Cylindrical Geometry

GUO Hong-Yu, YU Xiao-Jin, WANG Li-Feng, YE Wen-Hua, WU Jun-Feng, LI Ying-Jun
Chin. Phys. Lett. 2014, 31 (4): 044702 doi: 10.1088/0256-307X/31/4/044702
Full Text: [PDF 525 KB] (19)
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Generation of the second harmonic initiated by Bell–Plesset effects in a cylindrical geometry is studied analytically. For an initial single-mode velocity perturbation, the second-order mode-coupling formula is obtained by expanding the perturbation displacement and velocity potential up to the second-order accuracy. It is found that the initially symmetric interface evolves into a significant bubble-spike asymmetric pattern. The second-order solutions clearly show that the amplitude of the spike grows faster than that of the bubble. The temporal evolutions of the amplitudes of the bubble and spike are dependent on the interface velocity V0. The larger interface velocity leads to the smaller amplitude of the perturbation at an arbitrary interface position in a cylindrically convergent geometry.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Design of an Indirect-Drive Pulse Shape for ∼1.6 MJ Inertial Confinement Fusion Ignition Capsules

WANG Li-Feng, WU Jun-Feng, YE Wen-Hua, FAN Zheng-Feng, HE Xian-Tu
Chin. Phys. Lett. 2014, 31 (4): 045201 doi: 10.1088/0256-307X/31/4/045201
Full Text: [PDF 585 KB] (29)
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We present a design of indirect-drive pulse shape for inertial confinement fusion ignition capsules using laser energy 1.6 MJ with a moderate gain (∼10) on the Shenguang IV laser facility. The trade-off fuel compression (pressure) for resistance to the hydrodynamic instability (HI) in the recent high-foot (HF) implosion campaign [Dittrich T R et al Phys. Rev. Lett. 112 (2014) 055002] is recovered. The proposed design modifies the "main" pulse shape, which features a decompression-recompression step for the fuel shell resulting in higher areal density than that of the "simple" HF design, and thereby approaches the conditions required for ignition avoiding at the expense of more laser energy while holding the HI under control.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Synergistic Effect of Triple Ion Beams on Radiation Damage in CLAM Steel

YUAN Da-Qing, ZHENG Yong-Nan, ZUO Yi, FAN Ping, ZHOU Dong-Mei, ZHANG Qiao-Li, MA Xiao-Qiang, CUI Bao-Qun, CHEN Li-Hua, JIANG Wei-Sheng, WU Yi-Can, HUANG Qun-Ying, PENG Lei, CAO Xing-Zhong, WANG Bao-Yi, WEI Long, ZHU Sheng-Yun
Chin. Phys. Lett. 2014, 31 (4): 046101 doi: 10.1088/0256-307X/31/4/046101
Full Text: [PDF 706 KB] (23)
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The synergistic effect of triple ion beams is investigated by simultaneous and sequential irradiations of gold, hydrogen and helium ions on the low activation martensitic steel (CLAM) developed in China. The depth profile measurements of the positron annihilation Doppler broadening S parameter are carried out as a function of slow-positron beam energy to examine the produced radiation damage. The synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage is clearly observed. In the preset case ,this effect suppresses the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters.

Dislocation Dissociation Strongly Influences on Frank–Read Source Nucleation and Microplasticy of Materials with Low Stacking Fault Energy

HUANG Min-Sheng, ZHU Ya-Xin, LI Zhen-Huan
Chin. Phys. Lett. 2014, 31 (4): 046102 doi: 10.1088/0256-307X/31/4/046102
Full Text: [PDF 551 KB] (33)
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The influence of dislocation dissociation on the evolution of Frank–Read (F-R) sources is studied using a three-dimensional discrete dislocation dynamics simulation (3D-DDD). The classical Orowan nucleation stress and recently proposed Benzerga nucleation time models for F-R sources are improved. This work shows that it is necessary to introduce the dislocation dissociation scheme into 3D-DDD simulation, especially for simulations on micro-plasticity of small sized materials with low stacking fault energy.

Crystallization Kinetics Study on Magnetron-Sputtered Amorphous TiAl Alloy Thin Films

SHUI Lu-Yu, YAN Biao
Chin. Phys. Lett. 2014, 31 (4): 046103 doi: 10.1088/0256-307X/31/4/046103
Full Text: [PDF 855 KB] (13)
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Crystallization kinetics of magnetron-sputtered amorphous TiAl alloy thin films is investigated by differential scanning calorimetry through isothermal analysis and non-isothermal analysis. In non-isothermal analysis, the Kissinger method and the Ozawa method are used to calculate the apparent activation energy and local activation energy, respectively, in the crystallization processes of amorphous TiAl thin films. Furthermore, the crystallization mechanism is discussed from the investigation of the Avrami exponent by isothermal analysis. In addition, x-ray diffraction is utilized to reveal the grain orientation and evolution during the crystallization of TiAl thin films.

Theoretical Investigations of the Physical Properties of Cd1−xCaxO Ternary Alloys

S. Labidi, A. Lakel, M. Labidi, R. Bensalem
Chin. Phys. Lett. 2014, 31 (4): 046104 doi: 10.1088/0256-307X/31/4/046104
Full Text: [PDF 668 KB] (30)
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The structural, electronic and thermodynamic properties of Cd1−xCaxO ternary alloys are calculated using the first principles calculations performed within the framework of density functional theory. The exchange correlation potential for structural properties is calculated by the standard generalized gradient approximation (GGA) of Perdew et al., while for the electronic properties, the modified Becke-Johnson (MBJ) scheme is also applied. A deviation of the lattice constants from Vegard's law and bulk modulus from linear concentration dependence (LCD) are observed for the alloys. In addition, the thermodynamic stability of the alloys is investigated by calculating the critical temperatures of alloys.

Ab-Initio Study of Cobalt Impurity Effects on Phonon Spectra, Mechanical and Thermal Properties of Single Wall Carbon Nanotube (5,0)

H. Tashakori, B. Khoshnevisan, F. Kanjouri
Chin. Phys. Lett. 2014, 31 (4): 046301 doi: 10.1088/0256-307X/31/4/046301
Full Text: [PDF 595 KB] (21)
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We use density functional perturbation theory based on the pseudo-potential to calculate the phonon spectrum, phonon density of states, specific heat capacity and mechanical properties of pristine and cobalt doped (5,0) single wall carbon nanotube (CNT). In the calculations, we consider one Co atom in the center of the unit cell of the tube and it is shown that the pristine (5,0) CNT is nonmagnetic while the Co-doped tube becomes magnetic. Young's modulus for both systems is about 1 TPa (after Co-doping it goes slightly higher) and the Poisson ratio for the pristine tube becomes quite a bit larger than the doped one. On the other hand, the calculated value of radial breath mode for the pristine CNT is in good agreement with the experimental reports while after Co-doping it is increased. In addition, heat capacity of the doped CNT is reduced, which leads to some important empirical applications.

Optical Constants of SiO2 Films Deposited on Si Substrates

JI Yi-Qin, JIANG Yu-Gang, LIU Hua-Song, WANG Li-Shuan, LIU Dan-Dan , JIANG Cheng-Hui, FAN Rong-Wei, CHEN De-Ying
Chin. Phys. Lett. 2014, 31 (4): 046401 doi: 10.1088/0256-307X/31/4/046401
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SiO2 films were deposited on single-crystalline silicon substrates by ion beam sputtering technology. Optical constants of SiO2 films are calculated from spectroscopic ellipsometry data, transmittance spectra and reflectance spectra by WVASE32 software, and the best fitted method is obtained for calculating optical constants of dielectric materials in the ultraviolet-visible-infrared (UV-VIS-IR) range. In the UV-VIS-NIR spectral range, refractive indices of SiO2 films are calculated separately by both ellipsometry data and reflectance spectra, and the obtained results are almost the same. Complex dielectric functions of SiO2films in the IR spectral range are accurately calculated with infrared transmission spectra using the GenOsc model. The obtained accuracy complex refractive index of SiO2 films in the wavelength region from 0.19 μm to 25 μm is of great importance for the design of high quality coatings, such as ultra-low loss coating.

Mechanisms Causing Ballistic Thermal Rectification

DING Xing, MING Yi
Chin. Phys. Lett. 2014, 31 (4): 046601 doi: 10.1088/0256-307X/31/4/046601
Full Text: [PDF 386 KB] (29)
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The mechanism causing the ballistic thermal rectification in the harmonic system is analytically studied. Using the conceptual model of a dephasing probe, we obtain that phase breaking is unnecessary to realize the ballistic thermal rectification. However, it can change the strength of rectification. Asymmetric phonon-phonon interaction inducing the energy exchange of the normal mode of vibration is necessary to realize the ballistic thermal rectification. Moreover, the quantum statistics of phonons in at least one thermal reservoir is crucial to guarantee the asymmetric phonon-phonon interaction.

High-Efficiency Phosphorescent White Organic Light-Emitting Diodes with Stable Emission Spectrum Based on RGB Separately Monochromatic Emission Layers

ZHANG Zhi-Qiang, LIU Yi-Peng, DAI Yan-Feng, CHEN Jiang-Shan, MA Dong-Ge, ZHANG Hong-Mei
Chin. Phys. Lett. 2014, 31 (4): 046801 doi: 10.1088/0256-307X/31/4/046801
Full Text: [PDF 647 KB] (35)
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Highly efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable emission spectra are successfully fabricated by using an RGB three-color separately monochromatic emission layer (EML) structure. The EML consists of a sequence of bis(2-methyldibenzo[f, h]quinoxaline) (acetylacetonate) iridium (III) (Ir(MDQ)(acac)) doped tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as the red emission layer, iridium, tris(2-phenylpyidine)(Ir(ppy)) doped TCTA as the green emission layer and iridium(III) [bis(4, 6-difuorophenyl)-pyridinato-N, C2']picolinate (FIrpic) doped a mixed-host of TCTA and tris(4-carbazoyl-9-ylphenyl)amine (26DCz PPy) as the blue emission layer. Without using any out-coupling techniques, the resulting WOLEDs achieve a power efficiency of 42 lm/W at 100 cd/m2, and 34 lm/W at 1000 cd/m2. The WOLEDs also show excellent spectrum stability with bias voltages, remaining the Commission Internationale de L'Eclairage coordinates at (0.44, 0.43) from 1000 cd/m2 to 10000 cd/m2 and the color rendering index is as high as over 80. We contribute the stable emission spectrum to the RGB separate EML structure that successfully suppresses the undesired competition between host-guest energy transfer and direct exciton formation on emissive dopants by effectively controlling the position of exciton recombination region.

Growth and Morphology of Magnetron-Sputtered TiAl Alloy Thin Films Studied by Atomic Force Microscopy

SHUI Lu-Yu, YAN Biao
Chin. Phys. Lett. 2014, 31 (4): 046802 doi: 10.1088/0256-307X/31/4/046802
Full Text: [PDF 520 KB] (13)
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At the aim of investigating the growth mechanism and morphology evolution of magnetron-sputtered TiAl alloy thin films, we observe the films deposited for different times and find out the variation by atomic force microscopy. Nucleation mechanism and growth kinetics are studied by dynamic scaling, obtained from the morphology evolution of as-deposited TiAl thin films with different growth times. As a result, we demonstrate that the process of film growth goes through three stages, divided by three different growth exponents. The three growth exponents are β1=0.52±0.01, β2=0.71±0.01, and β3=0.17±0.02, respectively. With the deposition time varying from 2 min to 10 min, the roughness exponent α fluctuates in the range 0.61–1.16.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Molecular Dynamics Simulation of Xe Behavior in U-Mo Alloys Fuel

XIAO Hong-Xing, TANG Rui, TIAN Xiao-Feng, LONG Chong-Sheng
Chin. Phys. Lett. 2014, 31 (4): 047101 doi: 10.1088/0256-307X/31/4/047101
Full Text: [PDF 1117 KB] (22)
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Classical molecular dynamics simulations are used to investigate the fission gas Xe behavior in a U-Mo alloy fuel matrix. The embedded atom method potential proposed by Smirnova et al. is used to describe the U-Mo-Xe system. The results show that the initial configuration of interstitial Xe atoms in U-Mo alloys is very instable and has a strong tendency to get together and to form a Xe bubble by ejecting the adjacent U atoms and Mo atoms from their former normal lattice sites. The pressure in Xe bubbles is initially quite high and then drops with increasing Xe concentration obviously. The matrix swelling of U-Mo alloys associated with the Xe bubble growth follows approximately a linear relationship with the ratio of Xe to U at low Xe concentration while the rate of swelling increases rapidly at high Xe concentration. The simulation results are in good agreement with the experimental data. The recovery of the damaged structure in the U-Mo alloys matrix is also investigated. It is shown that a damaged structure cannot be recovered completely after a system is relaxed for a long time while still having lots of defects.

Optoelectronic Properties, Elastic Moduli and Thermoelectricity of SrAlGa: An Ab Initio Study

Roshan Ali, G. Murtaza, Y. Takagiwa, R. Khenata, Haleem Uddin, H. Ullah, S. A. Khan
Chin. Phys. Lett. 2014, 31 (4): 047102 doi: 10.1088/0256-307X/31/4/047102
Full Text: [PDF 685 KB] (43)
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Half-Heusler compounds are an impressive class of materials with a huge potential for different applications such as in future energy, especially in the fields of thermoelectrics and solar cells. We present ab initio total energy calculations within the modified Becke–Johnson generalized gradient approximation (mBJ-GGA) to obtain the physical properties of SrAlGa compounds. The structural, elastic, acoustic, electronic, chemical bonding, optical, and thermoelectric properties are calculated and compared with the available calculation data. The SrAlGa is found to be a small-band-gap (0.125–0.175 eV) material, suitable for thermoelectric applications with a relatively high Seebeck coefficient. Also, SrAlGa has the potential in the optoelectronic applications due to high optical conductivity and reflectivity in the infrared and visible region of electromagnetic spectra.

Effects of the Antiferromagnetic Spin Coupling and Interdot Coulomb Repulsion on Kondo Effects in Serial Double Quantum Dots

LI Zeng-Peng, WU Shao-Quan, ZHAO Guo-Ping
Chin. Phys. Lett. 2014, 31 (4): 047201 doi: 10.1088/0256-307X/31/4/047201
Full Text: [PDF 1179 KB] (11)
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We theoretically study the effects of the antiferromagnetic (AF) spin coupling and the interdot Coulomb repulsion on the Kondo effects in serial double quantum dots by means of the slave-boson mean-field approximation. Our results indicate that in the weak coupling regime, the AF spin coupling strengthens the Kondo resonance, while the interdot Coulomb repulsion suppresses them for the equilibrium case. In the non-equilibrium case, the AF spin coupling strengthens the Kondo resonance only when J>2.5TK0, while the interdot Coulomb repulsion does not suppress Kondo peaks. In the strong coupling regime, the bias voltage has no effects on the Kondo resonance in this system, and the AF spin coupling increases the height of Kondo peaks only when J<2.5TK0. However, the inter-dot Coulomb repulsion suppresses the spin Kondo effect, which induces the orbit Kondo effect. Moreover, the relevant underlying physics of these problems are discussed.

Effect of the Minimal Length on the Thermodynamics of Ultra-Relativistic Ideal Fermi Gas

ZHANG Xiu-Ming, SUN Jiu-Xun, YANG Li
Chin. Phys. Lett. 2014, 31 (4): 047301 doi: 10.1088/0256-307X/31/4/047301
Full Text: [PDF 461 KB] (16)
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Based on the generalized uncertainty principle, the thermodynamics of Fermi gas in high density, high pressure and high temperature are calculated. As the temperature and density increases, the energy and entropy becomes saturated and the pressure blows up without any bound. Using the conservation equation of the Robertson–Walker cosmology, we find that, when the energy exceeds the EH=β0−1/2c2Mp, the expansion cannot be driven by the photon gas and the fermion gas. This requires some new physical mechanism related to quantum gravity, such as tachyons and dilatons.

Surface Plasmon Resonance and Raman Scattering Activity of the Au/AgxO/Ag Multilayer Film

ZHONG Yu-Ting, CHENG Zi-Qiang, MA Liang, WANG Jia-Hong, HAO Zhong-Hua, WANG Qu-Quan
Chin. Phys. Lett. 2014, 31 (4): 047302 doi: 10.1088/0256-307X/31/4/047302
Full Text: [PDF 677 KB] (26)
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The nanostructured Au/AgxO/Ag sandwich multilayer films on quartz substrates are prepared by the magnetron sputtering method. The morphology, plasmon resonance and surface enhanced Raman scattering (SERS) activities of the multilayer films are studied. The resonant absorption wavelength of localized surface plasmon is tuned in a wide range from 618 nm to 993 nm by controlling the density of nanoparticles of Au and Ag. The SERS activity of the Au/AgxO/Ag multilayer films are enhanced over ∼10 times compared with those of bare Ag and bare Au films. These properties may find a potential application in biosensor and bioimaging.

The Edge Magnetization and Strip Phase of Graphene Quantum Dots with Long-Range Coulomb Interaction

LI Ning, ZHU Wen-Huan, LIANG Qi, DING Guo-Hui
Chin. Phys. Lett. 2014, 31 (4): 047303 doi: 10.1088/0256-307X/31/4/047303
Full Text: [PDF 846 KB] (21)
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We investigate the magnetism and optical absorption properties of charge neutral hexagonal graphene quantum dots (GQDs) terminated with zigzag edges by using a tight-binding Hubbard type model for the π electrons. Within the Hartree–Fock approximation and taking into account the long-range Coulomb interaction, our calculation yields a ferromagnetic ground state with magnetic moments localized on the edges for GQDs, and also gives an antiferromagnetism state with the energy very close to the ferromagnetism ground state. We find that both the ferromagnetic and the antiferromagnetic states have stripe patterned charge density distributions as a result of the long-range Coulomb interaction. The optical conductivity for GQDs has an energy gap in the low frequency regime in contrast to the bulk neutral graphene sheet where a universal constant is approached.

Critical-Current Degeneration Dependence on Axial Strain of Bi-based Superconducting Multi-filamentary Composite Tapes

GAO Pei-Feng, WANG Xing-Zhe
Chin. Phys. Lett. 2014, 31 (4): 047401 doi: 10.1088/0256-307X/31/4/047401
Full Text: [PDF 562 KB] (15)
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Superconducting materials are always severely restricted in practical engineering applications due to their carrying-current degradation under mechanical loads. Based on Ekin's exponential model and Weibull's distribution function, we propose an empirical degradation model for describing the mechanical deformation influence on the critical-current of Bi-based superconducting multi-filamentary composite tapes under axial loading. The critical currents of superconducting tapes depending on the axial strain are investigated analytically. It is shown that the predictions by the developed degradation model agree with the experimental data, in the processes of axial mechanical loading and unloading on the samples. The effect of the critical tension and compression damage strains on the normalized critical currents is also discussed.

Switching Behavior Induced by Electric and Magnetic Fields in (La0.73Bi0.27)0.67Ca0.33MnO3

WANG Ye-Shuai, XIA Nian-Ming, ZUO Hua-Kun, SHEN Yi-Ning, XIA Zheng-Cai
Chin. Phys. Lett. 2014, 31 (4): 047501 doi: 10.1088/0256-307X/31/4/047501
Full Text: [PDF 738 KB] (29)
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Both electric and magnetic field-induced switching behaviors between a high resistive state and a low resistive one are observed in (La0.73Bi0.27)0.67Ca0.33MnO3. The effects of magnetoresistance and electric-resistance suggest that the applied electric field and magnetic field greatly tune the percolative paths in the phase-separated system. According to the experimental results, the switching behaviors may come from the coexistence of the charge ordering state, and localized and freedom ferromagnetic states, in which the external field destroys partially the localized ferromagnetic states and charge ordering leads to the ferromagnetic state growth, which causes a switch between a high resistive state and low resistive one. This makes the doped manganite a good system for both electric and magnetic field sensor materials.

An Enhanced Photoelectric Conversion Efficiency of n-Type Crystalline Silicon p–n Junctions Using a Ferroelectric Passivation Layer

LI Zi-Zhen, TANG Rong-Sheng, WANG Xiao-Feng, ZHENG Fen-Gang
Chin. Phys. Lett. 2014, 31 (4): 047701 doi: 10.1088/0256-307X/31/4/047701
Full Text: [PDF 972 KB] (17)
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A multilayered structure consisting of ferroelectric Pb(Zr,Ti)O3 (PZT) film is deposited by sputtering on the crystalline silicon p-n junction without any buffer layer. The photovoltaic output of the p-n junction is greatly enhanced due to the usage of In2O3:Sn(ITO)/PZT as top surface passivation layers. The short circuit current and photoelectric conversion efficiency of the p-n junction with ITO/PZT ferroelectric films increase about four and six times, respectively, compared with those without any passivation layers. Improvement in the passivated device is mainly attributed to the built-in field at the ITO/PZT interface.

Electromagnetic and Microwave Absorption Properties of Fe Coating on SiC with Metal Organic Chemical Vapor Reaction

LIU Yuan, LIU Xiang-Xuan, WANG Xuan-Jun, WEN Wu
Chin. Phys. Lett. 2014, 31 (4): 047702 doi: 10.1088/0256-307X/31/4/047702
Full Text: [PDF 806 KB] (15)
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SiC−Fe composites are prepared by metal organic chemical vapor deposition (MOCVD) using silicon carbide (SiC) and iron pentacarbonyl (Fe(CO)5) as the precursors. The structure and morphology analyses demonstrate that the Fe nanoparticles have been deposited on the surface of the SiC particles. In terms of reflection loss (RL), the absorbing frequency band (AFB, the value of RL <−10 dB), and the matching thickness (tm), SiC-Fe composites show the best performances: minimum RL of -31.6 dB with tm=2.0 mm at 15.1 GHz, AFB of 12.9–17.3 GHz, indicating that Fe-doped SiC by MOCVD can significantly improve the electromagnetic properties of SiC and that SiC-Fe composites could be used as an effective microwave absorption material.

Temperature-Dependent Photoluminescence of Silicon Nanoporous Pillar Array

LI Yong, WANG Xiao-Bo, FAN Zhi-Qiang, LI Xin-Jian
Chin. Phys. Lett. 2014, 31 (4): 047801 doi: 10.1088/0256-307X/31/4/047801
Full Text: [PDF 1434 KB] (21)
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Silicon nanoporous pillar array (Si-NPA) is a micron-nanometer hierarchical structure which might be used as functional substrates for constructing optoelectronic nanodevices. This makes understanding the photoluminescence (PL) from Si-NPA important. We measure the PL of Si-NPA in the range of 11–300 K. By analyzing the evolution of the peak energy and intensity with temperature, the ultraviolet, blue, orange and red PL bands from Si-NPA are attributed to the radiative recombination through the deep-levels in silicon oxide, oxygen-related defect states in silicon nanocrystallites (nc-Si), band-to-band transition within nc-Si, and surface/interface states of nc-Si or between nc-Si and SiOx, respectively. At least two non-radiative recombination processes, which are activated at different temperature ranges, are proposed for the PL intensity variation with temperature. These results might provide strong foundations for designing and constructing optoelectronic devices based on silicon nanostructures.

Giant Birefringence in Layered Compound LaOBiS2

WANG Hai
Chin. Phys. Lett. 2014, 31 (4): 047802 doi: 10.1088/0256-307X/31/4/047802
Full Text: [PDF 622 KB] (21)
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Birefringent crystals (BFCs) have been extensively used in imaging spectrometers, laser devices, and optical components. Seeking new BFCs is important for both fundamental research and industrial applications. Employing first-principles density functional theory, we find that LaOBiS2 (space group: P4/nmm) appearing in the parent phase of the recently discovered BiS2-superconductor exhibits superior birefringence with a maximum value of 2.94, which is 13.4 times larger than the extensively used YVO4 (0.22). Furthermore, LaOBiS2 is an indirect semiconductor with a band gap of 0.9 eV, which is suitable for optical applications. The origin of giant inherent birefringence is also discussed.

Improvement of the Injection and Transport Characteristics of Electrons in Organic Light-Emitting Diodes by Utilizing a NaCl N-Doped Layer

XIAO Zhi-Hui, WU Xiao-Ming, HUA Yu-Lin, WANG Li, BI Wen-Tao, BAI Juan-Juan, MU Xue, YIN Shou-Gen
Chin. Phys. Lett. 2014, 31 (4): 047803 doi: 10.1088/0256-307X/31/4/047803
Full Text: [PDF 521 KB] (21)
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The injection and transport characteristics of electrons are enhanced by using sodium chloride (NaCl) as an n-type dopant doped into a 4,7-diphnenyl-1, 10-phe-nanthroline (Bphen) electron-transporting layer, which improves the performance of organic light-emitting diodes (OLEDs). Meanwhile, a NaCl-doped Bphen layer can effectively influence electrical characteristics of the devices, and significantly improve the current and power efficiency. The turn-on voltage and the operation voltage of the optimal device are decreased drastically from 6.5 V and 10.8 V to 3.3 V and 5 V, respectively, compared with those of the reference device. The maximum current efficiency and power efficiency of the optimal device are 7.0 cd/A and 4.4 lm/W at the current density of 16.70 mA/cm2, which are about 1.7 and 4 times higher than those of the reference device, respectively. Moreover, the enhancement of the injection and transport ability for electrons is attributed not only to the reduced energy barrier between Al cathode and Bphen, but also to the increased mobility of electrons by the doping effect of NaCl. Therefore, both the electron injection and transport ability are enhanced, which improve the carrier balance in OLEDs and lead to the better device efficiency.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

The near-Surface Region of Cubic Boron Nitride Single Crystal from the Li3N-hBN System

GUO Xiao-Fei, XU Bin, WEN Zhen-Xing, FAN Xiao-Hong, TIAN Bin
Chin. Phys. Lett. 2014, 31 (4): 048101 doi: 10.1088/0256-307X/31/4/048101
Full Text: [PDF 1994 KB] (16)
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Cubic boron nitride single crystals are synthesized with lithium nitride as a catalyst under high pressure and high temperature. The main phases in the near-surface region, which around the single crystal are determined as a mixture of hexagonal boron nitride (hBN), cubic boron nitride (cBN) and lithium boron nitride (Li3BN2). High resolution transmission electron microscopy examinations show that there exist lots of nanometer-sized cubic boron nitride nuclei in this region. The interface phase structures of cubic boron nitride crystal and its near-surface region are investigated by means of transmission electron microscopy. The growth mechanism of cubic boron nitride crystal is analyzed briefly. It is supposed that Li3BN2 impels the direct conversion of hBN to cBN as a real catalyst, and cBN is homogeneously nucleated in the molten state under high pressure and high temperature.

Direct Laser Writing Facility for Fabrication of Submicron Mask

ZHU Feng, MA Jian-Yong
Chin. Phys. Lett. 2014, 31 (4): 048102 doi: 10.1088/0256-307X/31/4/048102
Full Text: [PDF 521 KB] (20)
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Direct laser writing technique has become a well-established, multi-functional and flexible method for fabricating high quality diffractive optical elements. We propose and build a maskless direct laser writing system with the ability to produce a sub-micron feature size. The high precision lithography is realized by using the astigmatic autofocus method. The minimum feature size of the system, breaking through the diffraction limit with the chromium layer, can achieve 300 nm with the 405 nm blue laser. A 50×50 mm2 chromium grating mask with a period of 1 μm and line width of 300 nm is fabricated. This facility will be useful for the fabrication of large-scale submicron diffraction optical elements in the future.

Impact of CHF3 Plasma Treatment on AlGaN/GaN HEMTs Identified by Low-Temperature Measurement

DU Yan-Dong, HAN Wei-Hua, YAN Wei, YANG Fu-Hua
Chin. Phys. Lett. 2014, 31 (4): 048501 doi: 10.1088/0256-307X/31/4/048501
Full Text: [PDF 665 KB] (20)
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We investigate the impact of CHF3 plasma treatment on the performance of AlGaN/GaN HEMT (F−HEMT) by a temperature-dependent measurement in the thermal range from 6 K to 295 K. The temperature dependence of the transconductance characteristics in F-HEMT declares that the Coulomb scattering and the optical phonon scattering are effectively enhanced by the fluorine ions in the AlGaN layer. The fluorine ions not only provide immobile negative charges to deplete 2DEG, but also enhance the Schottky barrier height of the metal gate. Thermal activation of the carrier traps induced by CHF3 plasma for F-HEMT contributes to the negative shift of the threshold voltage by -3.4 mV/°C with the increasing temperature. The reverse gate-leakage current of F-HEMT is decreased by more than two-order magnitude in comparison with that of conventional AlGaN/GaN HEMT (C-HEMT) without fluorine ions.

Spin Polarization Properties of Na Doped Meridianal Tris(8-Hydroxyquinoline) Aluminum Studied by First Principles Calculations

REN Jun-Feng, YUAN Xiao-Bo, HU Gui-Chao
Chin. Phys. Lett. 2014, 31 (4): 048502 doi: 10.1088/0256-307X/31/4/048502
Full Text: [PDF 618 KB] (16)
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We theoretically investigate the electronic structure and spin polarization properties of Na-doped meridianal tris(8-hydroxyquinoline) aluminum (Alq3) by first principles calculations. It is found that the spin density is distributed mainly in the Alq3 part in the Alq3:Na complex. Electron charge transfer takes place from the Na atom to the Alq3 molecule, which induces asymmetric changing of the molecule bond lengths, thus the spin density distribution becomes asymmetric. Spin polarization of the complex originates from the preferable filling of the spin-split nitrogen and carbon p-orbitals because of the different bond length changes of the Alq3 molecule upon Na doping.

Effect of Electronic Polarization to Human α-Thrombin

DUAN Li-Li, LI Zong-Chao, HE Xiang, ZHANG Qing-Gang
Chin. Phys. Lett. 2014, 31 (4): 048701 doi: 10.1088/0256-307X/31/4/048701
Full Text: [PDF 1237 KB] (8)
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The polarized protein-specific charges (PPC) of human α-thrombin (thrombin) and its inhibitor (L86) are made possible by employing the recently developed molecular fractionation with conjugate caps approach incorporated the Poisson–Boltzmann model. Molecular dynamics (MD) simulations of thrombin have been carried out to investigate the dynamics and stability of the thrombin-inhibitor using PPC and AMBER charges respectively. Detailed analysis and comparison of MD results show that the PPC can correctly describe the polarized state of the thrombin and L86. Especially, the root-mean-square deviation of backbone atoms and the hydrogen bonds using PPC are more stable than the AMBER charge. The present results indicate that protein polarization plays critical roles in maintaining the compact structure of thrombin.

Locking Function of a Key Residue in Kinesin's Gating Mechanism

GENG Yi-Zhao, ZHANG Hui, JI Qing, YAN Shi-Wei
Chin. Phys. Lett. 2014, 31 (4): 048702 doi: 10.1088/0256-307X/31/4/048702
Full Text: [PDF 1177 KB] (18)
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In kinesin's mechanochemical cycle, ATP's binding to the nucleotide-free leading head is exquisitely gated so that futile hydrolysis is effectively avoided. Experiments show that, when both kinesin heads bind to a microtubule, ATP cannot bind to kinesin's leading head when the neck linker (NL) of this head has a backward orientation. How NL's backward orientation is maintained needs understanding on a structural basis. By using steered molecular dynamics and mutation simulations, we investigate the backward-pointing conformation of the leading head's NL under different inter-head tensions. We find that the NL cannot keep in a strict backward orientation solely by the inter-head tension. LYS325 (amino acid sequence in 2KIN) has an assistant locking function which locks the NL and β0 to the β-domain. This locking function has an enhanced positive cooperation with the inter-head tension. When the inter-head tension is weakened, this locking function can be broken, resulting in a loose backward orientation of the NL. The difference between the strict and loose backward orientation of the NL might be a crucial factor in the gating mechanism. These results are consistent with relevant experiments and proposals.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Hadronic Scenarios for Gamma-Ray Emission from Three Supernova Remnants Interacting with Molecular Clouds

YU Huan, FANG Jun, ZHANG Li
Chin. Phys. Lett. 2014, 31 (4): 049801 doi: 10.1088/0256-307X/31/4/049801
Full Text: [PDF 546 KB] (19)
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GeV γ-rays detected with the large area telescope on board the Fermi Gamma-ray space telescope in the direction of HB21, MSH 17-39 and G337.0-0.1 have been recently reported. The three supernova remnants (SNRs) show interactions with molecular clouds, and they are effective gamma-ray emitters as the relativistic protons accelerated by the SNR shocks inelastically colliding with the dense gas in the clouds. The origin of the observed γ-rays for the three remnants is investigated in the scenario of the diffusive shock acceleration. In the model, a part of the SNR shock transmits into the nearby molecular clouds, and the shock velocity is greatly reduced. As a result, a shock with a relatively low Alfvén Mach number is generated, and the spectra of the accelerated protons and theγ-ray photons produced via proton-proton interaction can be obtained. The results show that the observed γ-ray spectra for the three SNRs interacting with the molecular clouds can be reproduced. It can be concluded that the hadronic origin of the γ-rays for the three SNRs is approved, and the ability of SNR shocks to accelerate protons is also supported.
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