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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2014, 31 (10)   Published: 22 September 2014
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GENERAL

Selective Tunneling Dynamics of Bosons with Effective Three-Particle Interactions

NIU Zhen-Xia, XUE Ju-Kui
Chin. Phys. Lett. 2014, 31 (10): 100301 doi: 10.1088/0256-307X/31/10/100301
Full Text: [PDF 1278 KB] (292)
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The selective coherent destruction of tunneling (CDT) of ultracold Bose gas with three-particle interactions in a modulated double-well potential is discussed. It is shown that the effects of two- and three-particle interactions on the dynamics of the selective CDT are strongly coupled and the three-particle interactions significantly modify the selective CDT. For weak three-particle interactions, an upper bound of the boson number for realizing the selective CDT exists and the region of boson number for realizing the selective CDT is enlarged (reduced) with repulsive (attractive) three-particle interactions. For strong three-particle interactions, the boson number in the system for realizing the selective CDT not only has an upper bound, but also has a lower bound. The results are confirmed by numerical simulations.

Spontaneous Emission of a Two-Level Static Atom Coupling with Electromagnetic Vacuum Fluctuations Outside a High-Dimensional Einstein Gauss-Bonnet Black Hole

ZHANG Ming, YANG Zhan-Ying, YUE Rui-Hong
Chin. Phys. Lett. 2014, 31 (10): 100401 doi: 10.1088/0256-307X/31/10/100401
Full Text: [PDF 502 KB] (95)
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Using the generalized formalism of Dalibard, Dupont-Roc and Cohen-Tannoudji we investigate the spontaneous excitation of a static atom interacting with electromagnetic vacuum fluctuations outside an Einstein Gauss-Bonnet black hole in d-dimensions. It shows that spontaneous excitation does not occur in a Boulware vacuum, while exists in an Unruh vacuum and Hartle–Hawking vacuum. As to the total rate of change of the atomic energy, it does not receive the contribution from the coupling constant of the Gauss–Bonnet term at spatial infinity, only the dimensional parameter has the contribution to it. Near the event horizon, both the coupling constant and the dimension p contribute to the total rate of change of the atomic energy in all three kinds of vacuum. We discuss the contribution of the coupling constant and dimensional factor to the results in three different kinds of spacetime lastly.

Paths to Synchronization on Complex Networks with External Drive

ZOU Ying-Ying, LI Hai-Hong
Chin. Phys. Lett. 2014, 31 (10): 100501 doi: 10.1088/0256-307X/31/10/100501
Full Text: [PDF 849 KB] (92)
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We investigate the dynamics of the Kuramoto model on complex networks with part of the oscillators subjected to an external drive. It is found that the mutual synchronization is attracted to the drive when the frequency of the drive is close to the mean frequency of oscillators and, otherwise, mutual synchronization coexists with the driven synchronization. We also find that the synchronization between the mutual synchronization and the driven synchronization is dependent on the network topology when the coupling strength among oscillators is far away from the global synchronization in the absence of the drive. The transition is continuous on Erdös-Rényi networks while it is discontinuous on scale free networks.

The Heisenberg Model after an Interaction Quench

ZHOU Zong-Li, LI Min, YE Jian, LI Dong-Peng, LOU Ping, ZHANG Guo-Shun
Chin. Phys. Lett. 2014, 31 (10): 100502 doi: 10.1088/0256-307X/31/10/100502
Full Text: [PDF 437 KB] (52)
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In accordance with the recent experimental progress of the controllable spin-spin interactions, the Heisenberg model after an interaction quench is discussed. The Hamiltonian of the system out of equilibrium is introduced and treated by the flow equation method. As a result, the spectrum and zero-point spin deviation are obtained with the help of time-evolved operators. Additionally, other methods are applied to verify the results in mathematics. It is found that the observables show an oscillating behavior. The feasible experimental scheme of the concerned scenario is also mentioned.

Accurate Evaluation of Microwave-Leakage-Induced Frequency Shifts in Fountain Clocks

FANG Fang, LIU Kun, CHEN Wei-Liang, LIU Nian-Feng, SUO Rui, LI Tian-Chun
Chin. Phys. Lett. 2014, 31 (10): 100601 doi: 10.1088/0256-307X/31/10/100601
Full Text: [PDF 506 KB] (48)
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We report theoretical calculations of the transition probability errors introduced by microwave leakage in Cs fountain clocks, which will shift the clock frequency. The results show that the transition probability errors are affected by the Ramsey pulse amplitude, the relative phase between the Ramsey field and the leakage field, and the asymmetry of the leakage fields for the upward and downward passages. This effect is quite different for the leakage fields presenting below the Ramsey cavity and above the Ramsey cavity. The leakage-field-induced frequency shifts of the NIM5 fountain clock in different cases are measured. The results are consistent with the theoretical calculations, and give an accurate evaluation of the leakage-field-induced frequency shifts, as distinguished from other microwave-power-related effects for the first time.

Verification and Application of the Border Effect in Precision Measurement

ZHOU Wei, LI Zhi-Qi, BAI Li-Na, XUAN Zong-Qiang, CHEN Fa-Xi, YU Jian-Guo, GAO Jian-Ning, MIAO Miao, DONG Shao-Feng, SONG Hui-Min, WEI Zhong, YE Yun-Xia
Chin. Phys. Lett. 2014, 31 (10): 100602 doi: 10.1088/0256-307X/31/10/100602
Full Text: [PDF 565 KB] (50)
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Detection resolution is crucial for improvement of the measurement precision in the device and instrument. Because of the limited resolution, a fuzzy area with the truth-value as its center is found during the detection. The finding for improving the measurement precision by the border of fuzzy area is first introduced. The higher resolution can be captured by the higher resolution stability which makes the different detection results of the inner and outer fuzzy area on the border reflected more sensitively between the measure and the reference quantity. The system resolution obtained only depends on the stability of measurement resolution, which is much better than the measurement resolution itself. Based on the finding, the measurement precision can be improved two or three orders of magnitude. The finding can be used in various kinds of high precision measurement.

Mechanism and Simulation of Generating Pulsed Strong Magnetic Field

YANG Xian-Jun, WANG Shuai-Chuang, DENG Ai-Dong, GU Zhuo-Wei, LUO Hao
Chin. Phys. Lett. 2014, 31 (10): 100702 doi: 10.1088/0256-307X/31/10/100702
Full Text: [PDF 509 KB] (56)
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A strong magnetic field (over 1000 T) was recently experimentally produced at the Academy of Engineering Physics in China. The theoretical methods, which include a simple model and MHD code, are discussed to investigate the physical mechanism and dynamics of generating the strong magnetic field. The analysis and simulation results show that nonlinear magnetic diffusion contributes less as compared to the linear magnetic diffusion. This indicates that the compressible hydrodynamic effect and solid imploding compression may have a large influence on strong magnetic field generation.
NUCLEAR PHYSICS

Simulation and Characterization of Aluminium Three-Dimensional Resonator for Quantum Computation

ZHAO Hu, LI Tie-Fu, LIU Qi-Chun, LIU Jian-She, CHEN Wei
Chin. Phys. Lett. 2014, 31 (10): 102101 doi: 10.1088/0256-307X/31/10/102101
Full Text: [PDF 987 KB] (58)
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We present the simulation and characterization of several aluminium three-dimensional (3D) resonators, which can be used for superconducting quantum computation. By changing the conductivity of the aluminium in a high frequency structure simulator, the loaded quality factor at room temperature and base temperature (20 mK) can be simulated. From S21 measurement, we can characterize the properties of the resonators. The simulated and experimental results can be fitted well by exponential equations.

Tensor Force Effect on Shape Coexistence of N=28 Neutron-Rich Isotones

WANG Yan-Zhao, GU Jian-Zhong, YU Guo-Liang, HOU Zhao-Yu
Chin. Phys. Lett. 2014, 31 (10): 102102 doi: 10.1088/0256-307X/31/10/102102
Full Text: [PDF 526 KB] (39)
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The tensor force effect on potential energy surfaces of the N=28 neutron-rich isotones is investigated by using the deformed Skyrme–Hartree–Fock–Bogoliubov approach with the T22 interaction. It is found that, without the tensor force, 40Mg and 46Ar have prolate and spherical ground states, respectively. The ground states of 42Si and 44S are oblate. The shape coexistence in 40Mg, 42Si and 44S is evident. However, the ground state deformations of these isotones are not changed and the shape coexistence in 42Si and 44S vanishes when the tensor force is switched on. Taking 42Si as an example, the disappearance of the shape coexistence is understood by analyzing the tensor force effect on the shell correction energies.

Geometric Scaling in New Combined Hadron-Electron Ring Accelerator Data

ZHOU Xiao-Jiao, QI Lian, KANG Lin, ZHOU Dai-Cui, XIANG Wen-Chang
Chin. Phys. Lett. 2014, 31 (10): 102401 doi: 10.1088/0256-307X/31/10/102401
Full Text: [PDF 572 KB] (20)
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We study the geometric scaling in the new combined data of the hadron-electron ring accelerator by using the Golec-Biernat–Wüsthoff model. It is found that the description of the data is improved once the high accurate data are used to determine the model parameters. The value of x0 extracted from the fit is larger than the one from the previous study, which indicates a larger saturation scale in the new combined data. This makes more data located in the saturation region, and our approach is more reliable. This study lets the saturation model confront such high precision new combined data, and tests geometric scaling with those data. We demonstrate that the data lie on the same curve, which shows the geometric scaling in the new combined data. This outcome seems to support that the gluon saturation would be a relevant mechanism to dominate the parton evolution process in deep inelastic scattering, due to the fact that the geometric scaling results from the gluon saturation mechanism.

Nucleon Emission Number as a Probe of Isospin-Dependent N–N Cross Section in Photonuclear Reactions

GUO Wen-Jun, HUANG Jiang-Wei, YONG Gao-Chan, ZHANG Xiao-Ji, ZHANG Ao
Chin. Phys. Lett. 2014, 31 (10): 102501 doi: 10.1088/0256-307X/31/10/102501
Full Text: [PDF 588 KB] (44)
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Based on the modified isospin-dependent quantum molecular dynamics model, the number of emitted nucleons in a photonuclear reaction is studied with different symmetry potentials and different isospin-dependent nucleon-nucleon (N–N) collision cross sections. It is found that the number of emitted nucleons is sensitive to the isospin-dependent nucleon-nucleon cross section when the photon's energy is higher than 150 MeV, while it is insensitive to symmetry potential. The number of emitted neutrons is more sensitive to N–N collision cross sections than that of protons. It is realized that the number of emitted neutrons can be used as a sensitive probe to extract the information of the isospin-dependent N–N cross section at high energy photonuclear reactions.
ATOMIC AND MOLECULAR PHYSICS

Polarization Transfer in the 2p3/2 Photoionization of Magnesium-Like Ions

MA Kun, DONG Chen-Zhong, XIE Lu-You, QU Yi-Zhi
Chin. Phys. Lett. 2014, 31 (10): 103201 doi: 10.1088/0256-307X/31/10/103201
Full Text: [PDF 742 KB] (36)
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The inner-shell 2p3/2 ionization of Mg-like Fe14+, Cd36+, W62+ and U80+ ions by linear polarized light and the subsequent radiative decay are studied theoretically with the multiconfiguration Dirac–Fock (MCDF) method and the density matrix theory. Special attention is paid to exploring the influence of the polarization properties of the incident photon and the non-dipole term which arises from the multipole expansion of the electron-photon interaction on the properties of the subsequent x-ray radiation. The results show that there is a linear relationship between the degree of linear polarization of the radiative decay and ones of the incident light, which can be used for diagnosing the polarization of a light source. In addition, with the increasing photon energies, the non-dipole contribution to the alignment of the residual ions, the degree of linear polarization, as well as the angular distribution of the radiative decay following the inner-shell photoionization will also be increased.

Electron Dynamics of Atoms in Parallel Electric and Magnetic Fields

YANG Hai-Feng, GAO Wei, CHENG Hong, LIU Hong-Ping
Chin. Phys. Lett. 2014, 31 (10): 103202 doi: 10.1088/0256-307X/31/10/103202
Full Text: [PDF 522 KB] (33)
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Through an analysis of the nearest neighbor level spacing statistics for atoms in parallel electric and magnetic fields, we investigate the evolution of the electron dynamics as electric field strength increases. In the 'inter-l mixing' predominant region, the electron shows complex dynamics while in the 'inter-n mixing' predominant region, its dynamics behaves in a relatively stable way and the characteristic quantity ξ shows a slight oscillation. Comparing the dynamics for hydrogen and barium, we find that the core effect makes the main contribution to the chaotic behavior in non-hydrogen atoms.

Determination of Atomic Number Densities of 87Rb and 3He Based on Absorption Spectroscopy

ZHENG Hui-Jie, QUAN Wei, LIU Xiang, CHEN Yao, LU Ji-Xi
Chin. Phys. Lett. 2014, 31 (10): 103203 doi: 10.1088/0256-307X/31/10/103203
Full Text: [PDF 515 KB] (20)
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The atomic number densities of 87Rb vapor and surrounding gas 3He in a sealed cubic cell were measured by sweeping the absorption line and fitting the experimental data with a Lorentzian profile. The absorption was carried out around the D1 transition at different temperatures. We compare our results for the number density for87Rb with the previous methods and calculate the fractional error to be less than 5% as well as the error for 3He between this work and the density obtained from the filling procedure to be no more than 4.2% at 370 K. In addition, we discuss the factors that contribute to the error, among which the cell temperature plays the most important role.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

High-Precision Two-Dimensional Atom Localization in a Cascade-Type Atomic System

CHEN Jing-Dong, FANG Yu-Hong, ZHANG Ting
Chin. Phys. Lett. 2014, 31 (10): 104201 doi: 10.1088/0256-307X/31/10/104201
Full Text: [PDF 746 KB] (39)
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We investigate the behavior of two-dimensional (2D) atom localization in a three-level cascade-type atomic system via measuring the probe absorption. It is found that the precision of the atom localization can be improved by adjusting probe detuning and coupling a coherent coupling field and standing-wave fields to the same atomic transition. Remarkably, a single localization peak can be obtained by adjusting appropriate system parameters, and some corresponding explanations are also given.

Contributions of the Two Nuclei to the Harmonic Generation in H+2 Molecules

PEI Ya-Nan, MIAO Xiang-Yang
Chin. Phys. Lett. 2014, 31 (10): 104202 doi: 10.1088/0256-307X/31/10/104202
Full Text: [PDF 899 KB] (33)
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The separate contributions of the two nuclei in H+2 to the harmonic generation are investigated by numerically solving the time-dependent Schrödinger equation. The results show that the diverse electron distributions around the two nuclei under the effect of a laser field lead to different contributions of the two nuclei to the harmonic generation in different times, i.e., the contribution mainly comes from nucleus A around the (n+0.5) optical cycle while from nucleus B around the n optical cycle. By means of the time-frequency distributions and the coupled electron nuclear wave-packet density distributions, the physical mechanism is discussed in detail.

High-Power High-Efficiency Laser Power Transmission at 100 m Using Optimized Multi-Cell GaAs Converter

HE Tao, YANG Su-Hui, Miguel Ángel Muñoz, ZHANG Hai-Yang, ZHAO Chang-Ming, ZHANG Yi-Chen, XU Peng
Chin. Phys. Lett. 2014, 31 (10): 104203 doi: 10.1088/0256-307X/31/10/104203
Full Text: [PDF 1738 KB] (44)
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A high-power high-efficiency laser power transmission system at 100 m based on an optimized multi-cell GaAs converter capable of supplying 9.7 W of electricity is demonstrated. An IV testing system integrated with a data acquisition circuit and an analysis software is designed to measure the efficiency and the IV characteristics of the laser power converter (LPC). The dependencies of the converter's efficiency with respect to wavelength, laser intensity and temperature are analyzed. A diode laser with 793 nm of wavelength and 24 W of power is used to test the LPC and the software. The maximum efficiency of the LPC is 48.4% at an input laser power of 8 W at room temperature. When the input laser power is 24 W (laser intensity of 60000 W/m2), the efficiency is 40.4% and the output voltage is 4 V. The overall efficiency from electricity to electricity is 11.6%.

Optimization of the Monopole Acoustic Transducer for Logging-while-Drilling

FU Lin, WANG Dong, WANG Xiu-Ming
Chin. Phys. Lett. 2014, 31 (10): 104301 doi: 10.1088/0256-307X/31/10/104301
Full Text: [PDF 670 KB] (24)
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A new design idea for a monopole acoustic transducer which increases the frequency band and improves electromechanical performance is proposed with a focus on the lowest order of the radial and flexural modes. Numerical modeling of the resonance frequencies and electrical conductance are conducted with respect to the dimensions and material parameters of the proposed transducer. The transmitting voltage response level with respect to the density and velocity of the fluid media is calculated. The numerical simulation is validated through experiments. The frequency band and the electromechanical performance of the monopole acoustic transducer can be optimized by the given methods concluded from the numerical results.

Guided Wave Propagation in a Gold Electrode Film on a Pb(Mg1/3Nb2/3)O3–33%PbTiO3 Ferroelectric Single Crystal Substrate

HUANG Nai-Xing, LÜ Tian-Quan, ZHANG Rui, WANG Yu-Ling, CAO Wen-Wu
Chin. Phys. Lett. 2014, 31 (10): 104302 doi: 10.1088/0256-307X/31/10/104302
Full Text: [PDF 982 KB] (15)
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Dispersion relations of Love mode acoustic guided waves propagation in Pb(Mg1/3Nb2/3)O3–33%PbTiO3 (PMN-0.33 PT) single crystal with a gold electrode film are calculated. There is no cross coupling among Love wave modes, which is conducive to eliminating the cross interference between modes. The general formula is derived to precisely measure the thickness of the electrode. More acoustic energy would be concentrated inside the electrode with the increase of film thickness for a given frequency. Compared with the PZT-5 ceramic, [001]c poled PMN-33%PT single crystal has a slower attenuation of the amplitude of the acoustic guided wave. Therefore, single crystal is extremely suitable for making low loss acoustic wave devices with a high operating frequency.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Repetitive 'Snakes' and Their Damping Effect on Core Toroidal Rotation in EAST Plasmas with Multiple H–L–H Transitions

XU Li-Qing, HU Li-Qun, CHEN Kai-Yun, LI Chang-Zheng, LI Er-Zhong, ZHAO Jin-Long, SHENG Xiu-Li, ZHANG Ji-Zong, MAO Song-Tao
Chin. Phys. Lett. 2014, 31 (10): 105201 doi: 10.1088/0256-307X/31/10/105201
Full Text: [PDF 687 KB] (30)
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Repetitive impurity snake modes are observed after H–L mode transitions (high to low confinement modes) in EAST plasmas exhibiting multiple H–L–H transitions. Such snake modes are observed to lower the core plasma toroidal rotation. A critical impurity strength factor associated with snake-mode formation is estimated to be as high as αZ,c =nZ,c Z2/ne0.75. These observations have implications for ITER H-mode sustainability when the heating power is only slightly above the H-mode power threshold.

Mode Transition of Vacuum Arc Discharge and Its Effect on Ion Current

LAN Chao-Hui, LONG Ji-Dong, ZHENG Le, PENG Yu-Fei, LI Jie, YANG Zhen, DONG Pan
Chin. Phys. Lett. 2014, 31 (10): 105202 doi: 10.1088/0256-307X/31/10/105202
Full Text: [PDF 510 KB] (22)
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The mode transition of a pulsed vacuum arc discharge, which is from vacuum surface flashover to non-surface vacuum breakdown or vice versa, is studied by simply adjusting a trigger resistor. This approach provides a possibility to research the transition discharge process. Since the transition process is smooth and controllable, the transition mechanism and its effect on the performance of an ion source can be investigated via various diagnosis experiments. The experimental results show that the mode transition occurs when the resistance is in the range of 0–10 Ω. With the mode transition from surface flashover to non-surface vacuum breakdown, the vacuum arc discharge becomes more intense and the ion current produced by the Ti cathode ion source increases by two times. The related physical mechanism is also discussed in detail.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Chemical Composition Dependent Elastic Strain in AlGaN Epilayers

WANG Huan, YAO Shu-De
Chin. Phys. Lett. 2014, 31 (10): 106101 doi: 10.1088/0256-307X/31/10/106101
Full Text: [PDF 587 KB] (25)
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Systematic investigations are performed on a set of AlxGa1−xN/GaN heterostructures grown by metalorganic chemical vapor deposition on sapphire (0001). The Al composition x is determined by Rutherford backscattering. By using high resolution x-ray diffraction and the channeling scan around an off-normal <1213> axis in {1010} plane of the AlGaN layer, the tetragonal distortion eT caused by the elastic strain in the epilayer is determined. The results show that eT in the high-quality AlGaN layers is dramatically influenced by the Al content.

Effect of Indium and Antimony Doping on SnS Photoelectrochemical Solar Cells

Sunil H. Chaki, Mahesh D. Chaudhary, M. P. Deshpande
Chin. Phys. Lett. 2014, 31 (10): 106102 doi: 10.1088/0256-307X/31/10/106102
Full Text: [PDF 777 KB] (51)
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Single crystals of pure SnS, indium (In) and antimony (Sb) doped SnS are grown by the direct vapor transport technique. Two doping concentrations of 5 at.% and 15 at.% are employed for both In and Sb dopants. In total, five samples are studied, i.e., pure SnS, 5 at.% In-doped SnS, 15 at.% In-doped SnS, 5 at.% Sb-doped SnS and 15 at.% Sb-doped SnS single crystals. The energy dispersive analysis of x-ray (EDAX) and x-ray diffraction (XRD) analysis show that all the five as-grown single crystal samples possess near perfect stoichiometry and orthorhombic structure, respectively. The doping of In and Sb in SnS is established from the EDAX data and from the shift in the peak positions in XRD. Photoelectrochemical (PEC) solar cells are fabricated by using the as-grown single crystal samples along with iodine/iodide electrolytes. Mott–Schottky plots for different compositions of iodine/iodide electrolytes show that 0.025 M I2+1 M NaI+2 M Na2SO4+0.5 M H2SO4 will be the most suitable electrolyte. Study of efficiency (η) and fill factor for different intensities of illuminations at room temperature is carried out for the five samples. The In-doped SnS single crystals show better PEC efficiency than the undoped and Sb-doped SnS single crystals.

Equivalent Trap Energy Level Extraction for SiGe Using Gate-Induced-Drain-Leakage Current Analysis

LIU Chang, YU Wen-Jie, ZHANG Bo, XUE Zhong-Ying, WU Wang-Ran, ZHAO Yi, ZHAO Qing-Tai
Chin. Phys. Lett. 2014, 31 (10): 106103 doi: 10.1088/0256-307X/31/10/106103
Full Text: [PDF 536 KB] (29)
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The gate-induced-drain-leakage of MOSFETs is analyzed to better understand the sub-threshold swing degradation of SiGe tunnel field-effect transistors and their band-to-band tunneling mechanism. The numerical model of the analysis is elaborated. Equivalent trap energy levels are extracted for Si and strained SiGe. It is found that the equivalent trap energy level in SiGe is shallower than that in Si.

Effective Dielectric Properties of Au-ZnS and Au-ZnO Plasmonics Nanocomposites in the Terahertz Regime

A. Zolanvar, H. Sadeghi, A. Ranjgar
Chin. Phys. Lett. 2014, 31 (10): 106201 doi: 10.1088/0256-307X/31/10/106201
Full Text: [PDF 492 KB] (37)
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Composite materials based on plasmonic nanoparticles allow building metamaterials with very large effective permittivity (positive or negative). Moreover, if clustered or combined with other nanoparticles, it is also possible to generate effective magnetic permeability (positive or negative), and an ad-hoc design would result in the generation of double negative materials, and therefore backward wave propagation. In this work, the optical properties such as the effective permittivity, permeability and refractive index of Au-ZnS and Au-ZnO nanocomposites in a broad frequency range are studied. The enhancement is attributed to energy transfer from ZnS or ZnO to Au followed by a large local electromagnetic field on or near the surface of the Au nanoparticles. Local surface plasmon resonance could be the key reason for this enhancement. The surface plasmon, in response to changes in the refractive index of the local environment, also depends on the type of metal through the bulk plasma wavelength and the nano-particle compositions and geometry.

Mechanical and Vibrational Properties of ZnS with Wurtzite Structure: A First-Principles Study

YU You, CHEN Chun-Lin, ZHAO Guo-Dong, ZHENG Xiao-Lin, ZHU Xing-Hua
Chin. Phys. Lett. 2014, 31 (10): 106301 doi: 10.1088/0256-307X/31/10/106301
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We perform a first-principles study of the mechanical and vibrational properties of ZnS with a wurtzite structure. The calculated elastic constants by using a pseudopotential plane-wave method agree well with the experimental data and with the previous theoretical works. Based on the elastic constants and their related parameters, the crystal mechanical stability is discussed. Calculations of the zone-center optical-mode frequencies including longitudinal-optical/transverse-optical splitting, by using the density functional perturbation theory, are reported. All optical modes are identified, especially B1 modes, and agree with Raman measurements.

A Kinetic Transition from Low to High Fragility in Cu-Zr Liquids

BI Qing-Ling, LÜ Yong-Jun
Chin. Phys. Lett. 2014, 31 (10): 106401 doi: 10.1088/0256-307X/31/10/106401
Full Text: [PDF 593 KB] (28)
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Researchers have reported that Cu-Zr liquids are kinetically strong at the best glass-forming compositions. Here we systematically study the temperature dependence of viscosity and diffusion of Cu-Zr liquids using molecular dynamics simulations, and the results illustrate that the better glass formers are actually more fragile close to the glass transition. There is a kinetic transition from low to high fragility when the optimal glass-forming liquids are quenched into glass states. This transition is associated with the more rapid decrease of the excess entropy of the liquids above and close to the glass transition temperature, Tg, compared to other compositions. Accompanied by the transition to high fragility, peaks in the thermal expansivity and specific heat are observed at the optimal compositions. Furthermore, the Stokes–Einstein relation is examined over a wide composition range for Cu-Zr alloys, and the results indicate that glass-forming ability closely correlates with dynamical heterogeneity.

A Source for the Excellent Floating Ability of a Water Strider

LIU Shuang, LIU Zhan-Wei, SHI Wen-Xiong
Chin. Phys. Lett. 2014, 31 (10): 106801 doi: 10.1088/0256-307X/31/10/106801
Full Text: [PDF 798 KB] (21)
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A water strider's floating mechanism is of significance for the design of new biomimetic robots. However, the explanation of this mechanism has not been fully comprehended due to a lack of effective experimental methods. We describe a novel transmission speckle correlation technique, which is used to determine the deformation of liquid surfaces caused by a resting water strider, as well as a calculation of the resulting forces in the vertical direction. Furthermore, the variation of the liquid surface morphology at different times in the process of a water strider being unconscious has been measured and analyzed. The results show that the wax material secreted by water striders is a vital source for the excellent floating ability of a water strider, and that the effective time of the wax is less than 2 h.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

The Effect of the Semiconductive Screen on Space Charge Suppression in Cross-Linked Polyethylene

LI Lin, HAN Bai, SONG Wei, WANG Xuan, LEI Qing-Quan
Chin. Phys. Lett. 2014, 31 (10): 107301 doi: 10.1088/0256-307X/31/10/107301
Full Text: [PDF 741 KB] (31)
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The space charge distributions of cross-linked polyethylene (XLPE) with Borouge's BorlinkTM semiconductive screen type LE0550 and LE0595 from a pulsed electro-acoustic method are obtained. The contact interface morphology at the semiconductive screen and the structure of XLPE near the interface are characterized. The dielectric spectrum and the conductivity current of XLPE with the different semiconductive electrodes are compared. The semiconductive screen changes the structure and the dielectric characteristic of XLPE near the contact interface, which may be the main reason for space charge suppression in XLPE with Borouge's type LE0550 semiconductive screen.

Perfect Spin-Filtering in 4H-TAHDI-Based Molecular Devices: the Effect of N-Substitution

WU Qiu-Hua, ZHAO Peng, LIU De-Sheng
Chin. Phys. Lett. 2014, 31 (10): 107302 doi: 10.1088/0256-307X/31/10/107302
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Based on the non-equilibrium Green's function formalism and spin-polarized density functional theory calculations, we investigate the spin transport properties of HDI and terahydrotetraazahexacene diimide (4H-TAHDI) with two ferromagnetic zigzag-edge graphene nanoribbon electrodes. Compared with HDI, four carbon atoms in the hexacene part of 4H-TAHDI are substituted by nitrogen atoms. The results show that the nitrogen substitution can improve significantly the spin-filtering performance and 4H-TAHDI can be used as a perfect spin filter. Our study indicates that suitable chemical substitution is a possible way to realize high-efficiency spin filters.

A Forming-Free Bipolar Resistive Switching in HfOx-Based Memory with a Thin Ti Cap

PANG Hua, DENG Ning
Chin. Phys. Lett. 2014, 31 (10): 107303 doi: 10.1088/0256-307X/31/10/107303
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The electroforming process of Ti/HfOx stacked RRAM devices is removed via the combination of low temperature atomic layer deposition and post metal annealing. The Pt/Ti/HfOx/Pt RRAM devices show a forming-free bipolar resistive switching behavior. By x-ray photoelectron emission spectroscopy analysis, it is found that there are many oxygen vacancies and nonlattice oxygen pre-existing in the HfOx layer that play a key role in removing the electroforming process. In addition, when the thickness ratio of the Ti and HfOx layer is 1, the uniformity of the switching parameters of Pt/Ti/HfOx/Pt devices is significantly improved. The OFF/ON window maintains about 100 at the read voltage of 0.1 V.

Enhanced Current Carrying Capability of Au-ZnSe Nanowire-Au Nanostructure via High Energy Electron Irradiation

TAN Yu, WANG Yan-Guo
Chin. Phys. Lett. 2014, 31 (10): 107304 doi: 10.1088/0256-307X/31/10/107304
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To enhance the performance of nanoelectronics based on Au-ZnSe nanowire (NW)-Au (M-S-M) nanostructure, the effect of irradiation of the high energy electron beam emitted from the electron gun of a transmission electron microscope operated at 200 kV on the current carrying capability of M-S-M nanostructure is investigated in situ. Focusing the high energy electron beam on a Au electrode, the current carrying capability of the M-S-M nanostructure can be enhanced significantly with respect to the case of the electron beam being switched off. In this case, the electrons in the electrode are excited by the incident high energy electron and can freely tunnel through the Schottky barriers at the metal-semiconductor NW (M-S) nanocontacts, which can effectively reduce Joule heat dissipation and remarkably improve the current carrying capability of M-S-M nanostructure due to the fact that the current carrying capability highly depends on the Joule heating effect of Schottky barriers at M-S nanocontacts.

Magnetic and Ferroelectric Properties of BiCrO3 from First-Principles Calculations

DING Jun, KANG Xiu-Bao, WEN Li-Wei, LI Hai-Dong, ZHANG Jian-Min
Chin. Phys. Lett. 2014, 31 (10): 107501 doi: 10.1088/0256-307X/31/10/107501
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The electronic, magnetic, and ferroelectric properties of BiCrO3 in C2/c and R3c structure are investigated by first principles calculations. It is found that the easy magnetization axis in C2/c structure is along the b axis, the magnetic order in R3c structure is G-type antiferromagnetic and the easy magnetization axis is along the rhombohedral [111] direction. Berry phase theory predicts that the R3c structure of BiCrO3 has a large spontaneous polarization of 73.9 μC/cm2 along the rhombohedral [111] direction.

Local Piezoresponse and Thermal Behavior of Ferroelastic Domains in Multiferroic BiFeO3 Thin Films by Scanning Piezo-Thermal Microscopy

YU Hui-Zhu, CHEN Hong-Guang, XU Kun-Qi, ZHAO Kun-Yu, ZENG Hua-Rong, LI Guo-Rong
Chin. Phys. Lett. 2014, 31 (10): 107701 doi: 10.1088/0256-307X/31/10/107701
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A dual probe, i.e., high resolution scanning piezo-thermal microscopy, is developed and employed to characterize the local piezoresponse and thermal behaviors of ferroelastic domains in multiferroic BiFeO3 thin films. Highly inhomogeneous piezoelectric responses are found in the thin film. A remarkably local thermal transformation across ferroelastic domain walls is clearly demonstrated by the quantitative 3Ω signals related to thermal conductivity. Different polarization oriented ferroelastic domains are found to exhibit different local thermal responses. The underlying mechanism is possibly associated with the inhomogeneous stress distribution across the ferroelastic domain walls, leading to different phonons scattering contributions in the BiFeO3 thin film.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

A C-Band Internally-Matched High Efficiency GaN Power Amplifier

MA Xiao-Hua, WEI Jia-Xing, CAO Meng-Yi, LU Yang, ZHAO Bo-Chao, DONG Liang, WANG Yi, HAO Yue
Chin. Phys. Lett. 2014, 31 (10): 108401 doi: 10.1088/0256-307X/31/10/108401
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We present a design and realization of a high efficiency C-Band (5.2 GHz–5.8 GHz) internally-matched gallium nitride (GaN) power amplifier (PA). To reduce power dissipation and to achieve high efficiency, both input and output matching networks, along with 2nd-harmonic modulation circuits, are designed accurately according to the source and load optimum impedances extracted by source-pull and load-pull measurements. The PA realizes an excellent rf performance under a pulsed condition, demonstrating a maximum output power of 52.2 dBm (164 W) with at least 13.5 dB gain in the frequency range from 5.2 GHz to 5.8 GHz (10% relative bandwidth). At the same time, a power-added efficiency (PAE) of 69.4% is observed at 5.6 GHz and over 65.0% throughout the whole bandwidth. The PAE is the state-of-art performance for C-band GaN high-electron-mobility transistor PA with such high output power, to the best of our knowledge.

High-Pressure Water-Vapor Annealing for Enhancement of a-Si:H Film Passivation of Silicon Surface

GUO Chun-Lin, WANG Lei, ZHANG Yan-Rong, ZHOU Hai-Feng, LIANG Feng, YANG Zhen-Hui, YANG De-Ren
Chin. Phys. Lett. 2014, 31 (10): 108501 doi: 10.1088/0256-307X/31/10/108501
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We investigate the effect of amorphous hydrogenated silicon (a-Si:H) films passivated on silicon surfaces based on high-pressure water-vapor annealing (HWA). The effective carrier lifetime of samples reaches the maximum value after 210°C, 90 min HWA. Capacitance-voltage measurement reveals that the HWA not only greatly reduces the density of interface states (Dit), but also decreases the fixed charges (Qfixed) mainly caused by bulk defects. The change of hydrogen and oxygen in the film is measured by a spectroscopic ellipsometer and a Fourier-transform infrared (FTIR) spectrometer. All these results show that HWA is a useful method to improve the passivation effect of a-Si:H films deposited on silicon surfaces.

Optical Performance of N-Face AlGaN Ultraviolet Light Emitting Diodes

YU Hong-Ping, LI Shi-Bin, ZHANG Peng, WU Shuang-Hong, WEI Xiong-Bang, WU Zhi-Ming, CHEN Zhi
Chin. Phys. Lett. 2014, 31 (10): 108502 doi: 10.1088/0256-307X/31/10/108502
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The optical property and injection efficiency of N-face AlGaN based ultraviolet light emitting diodes (UV-LEDs) are studied and compared with Ga-face AlGaN based UV-LEDs. A staircase electron injector is introduced in the N-face AlGaN based UV-LED. The electroluminescence spectra, power-current performance curves, energy band diagrams, carrier concentration and radiative recombination rate are numerically calculated. The results indicate that the N-face UV-LED has a better optical performance than the Ga-face UV-LED, and the injection efficiency is enhanced owing to the fact that the staircase electron injector is available for UV-LEDs.

High Performance Long Wavelength Superlattice Photodetectors Based on Be Doped Absorber Region

ZHOU Yi, CHEN Jian-Xin, XU Zhi-Cheng, WANG Fang-Fang, XU Qing-Qing, XU Jia-Jia, BAI Zhi-Zhong, JIN Chuan, HE Li
Chin. Phys. Lett. 2014, 31 (10): 108503 doi: 10.1088/0256-307X/31/10/108503
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The effect of Be doping on the quantum efficiency and the dark current of InAs/GaSb long-wavelength infrared superlattice photodetectors grown by molecular-beam epitaxy on GaSb substrates are reported. A significant improvement of quantum efficiency (QE) with p-type doping is demonstrated. Our results show that Be doping level at 2.5×1015 cm3 gives the highest quantum efficiency of product 28%. We also demonstrate that the increased QE is not only resulted from the longer minority carrier diffusion length, but also the p-n junction location change. Finally, the result also shows that the sample with a doping density of 2.5×1015 cm3 has the largest D* as 8.68×1010 cm⋅Hz1/2⋅W−1, which is almost five times D* of the non-intentionally doped one.

Non-Volatile Threshold Adaptive Transistors with Embedded RRAM

DEND Ning, JIA Hong-Yang, WU Wei, WU Hua-Qiang
Chin. Phys. Lett. 2014, 31 (10): 108504 doi: 10.1088/0256-307X/31/10/108504
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We propose a novel nonvolatile threshold adaptive transistor (TAT) for neuromorphic circuits. The threshold adaptive transistor is achieved by embedding a resistive random-access memory (RRAM) material stack between the gate electrode and gate dielectric. During operation, the embedded RRAM device is kept at a high resistance state, which makes it act as a nonvolatile capacitor. The threshold could be nonlinearly adjusted by the voltage pulses applied on the gate of the transistor. We quantitatively estimate the range of the capacitance variation of the RRAM device. The threshold voltage of the TAT is simulated and shows expected variation. The simulated output of an inverter using a TAT shows a nonlinear adaptive behavior.

Junctionless Coplanar-Gate Oxide-Based Thin-Film Transistors Gated by Al2O3 Proton Conducting Films on Paper Substrates

WU Guo-Dong, ZHANG Jin, WAN Xiang
Chin. Phys. Lett. 2014, 31 (10): 108505 doi: 10.1088/0256-307X/31/10/108505
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Nanogranular Al2O3 films deposited by plasma-enhanced chemical vapor deposition show a high proton conductivity of ∼1.25 × 10−4 S/cm and a huge electric-double-layer (EDL) capacitance of ∼4.8 μF/cm2 at room temperature. Using nanogranular Al2O3 proton conducting films as gate dielectrics, junctionless indium-zinc-oxide (IZO) thin-film transistors (TFTs) with a coplanar-gate configuration are fabricated. The unique feature of such junctionless TFTs is that the channel and source/drain electrodes are the same thin IZO film without any source/drain junction. Due to the strong EDL capacitive coupling triggered by mobile protons in nanogranular Al2O3, these TFTs show a low-voltage operation of 1.5 V and a high performance with a large field-effect mobility (>18 cm2/V⋅s), a small subthreshold swing (<130 mV/decade) and a high current on/off ratio (>106). Our results demonstrate that such junctionless TFTs gated by Al2O3 proton conducting films have great potential applications in low-power and low-cost electronics.
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