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Volume 31 Issue 2
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GENERAL
Quantum Speed Limit of a Photon under Non-Markovian Dynamics
XU Zhen-Yu, ZHU Shi-Qun
Chin. Phys. Lett. 2014, 31 (2): 020301 .   DOI: 10.1088/0256-307X/31/2/020301
Abstract   PDF(pc) (571KB) ( 635 )
Quantum speed limit (QSL) time under noise has drawn considerable attention in real quantum computational processes. Though non-Markovian noise is found to be able to accelerate quantum evolution for a damped Jaynes–Cummings model, in this work we show that non-Markovianity will slow down the quantum evolution of an experimentally controllable photon system. As an application, QSL time of a photon can be controlled by regulating the relevant environment parameter properly, which nearly reaches the currently available photonic experimental technology.
Quasi-Topological Cosmology from Emergence of Cosmic Space
Ahmad Sheykhi
Chin. Phys. Lett. 2014, 31 (2): 020401 .   DOI: 10.1088/0256-307X/31/2/020401
Abstract   PDF(pc) (412KB) ( 266 )
We show that one can always derive the Friedmann equation of an (n+1)-dimensional Friedmann–Robertson–Walker universe in cubic quasi-topological gravity, by determining the difference between the bulk and the apparent horizon degrees of freedom in a region of space. We also generalize the study to the higher-order quasi-topological gravity, and extract the corresponding Friedmann equation in this theory by using the same approach.
Effect of Time Delay on Binary Signal Detection via a Bistable System
ZENG Ling-Zao, LIU Bing-Yang, XU Yi-Da, LI Jian-Long
Chin. Phys. Lett. 2014, 31 (2): 020501 .   DOI: 10.1088/0256-307X/31/2/020501
Abstract   PDF(pc) (453KB) ( 371 )
The effect of time delay on binary signal detection via a bistable system in the presence of white or colored Gaussian noise is investigated. By defining the bit error rate based on the solution of the approximated Fokker–Planck equation, the detector performance is investigated theoretically and is verified by Monte Carlo simulation. It is shown that, when the system parameter or noise intensity is optimally chosen, the increasing time delay generally improves the system performance. It is also shown that it is more difficult to accurately predict the system performance with a larger time delay and correlation time. This may inspire more thorough investigations in cooperative effects of a nonlinear system and time delay on signal processing.
Non-Gaussian Colored Noise Optimized Spatial Coherence of a Hodgkin–Huxley Neuronal Network
SUN Xiao-Juan, LU Qi-Shao
Chin. Phys. Lett. 2014, 31 (2): 020502 .   DOI: 10.1088/0256-307X/31/2/020502
Abstract   PDF(pc) (791KB) ( 330 )
We numerically study how non-Gaussian colored noise affects the spatial coherence of a Hodgkin–Huxley neuronal network. From the simulation results, we find that there exists some intermediate noise intensities, correlation time of the colored noise, and the deviation from Gaussian colored noise, for which an ordered pattern with a characteristic spatial frequency of the system comes forth in a resonant manner. Namely, under certain conditions, spatial coherence of the studied neuronal network can be optimized by the non-Gaussian colored noise, which indicates the occurrence of spatial coherence resonance.
An Improved Local Weighted Linear Prediction Model for Chaotic Time Series
QU Jian-Ling, WANG Xiao-Fei, QIAO Yu-Chuan, GAO Feng, DI Ya-Zhou
Chin. Phys. Lett. 2014, 31 (2): 020503 .   DOI: 10.1088/0256-307X/31/2/020503
Abstract   PDF(pc) (685KB) ( 501 )
Previous research working on local prediction state with some unsuitable neighbor points (such as false points and pseudo-false neighbor points) are the main source of errors of local prediction and these unsuitable neighbors cannot be eliminated entirely. Therefore, an improved local weighted linear prediction model based on local integrated correlation, which can reduce the influence of the residual unsuitable neighbors, is proposed to predict chaotic time series in our study. Simulation results show that the performance of the improved model is superior to the other local prediction models in the prediction of chaotic time series without and with additive white Gaussian noise.
Berezinskii–Kosterlitz–Thouless Transition in a Two-Dimensional Random-Bond XY Model on a Square Lattice
DENG Yi-Bo, GU Qiang
Chin. Phys. Lett. 2014, 31 (2): 020504 .   DOI: 10.1088/0256-307X/31/2/020504
Abstract   PDF(pc) (614KB) ( 367 )
We perform Monte Carlo simulations to study the two dimensional random-bond XY model on a square lattice. Two kinds of bond randomness with the coupling coefficient obeying the Gaussian or uniform distribution are discussed. It is shown that the two kinds of disorders lead to similar thermodynamic behaviors if their variances take the same value. This result implies that the variance can be chosen as a characteristic parameter to evaluate the strength of the randomness. In addition, the Berezinskii–Kosterlitz–Thouless transition temperature decreases as the variance increases and the transition can even be destroyed as long as the disorder is strong enough.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Pair Production of the Doubly Charged Leptons via Electroweak Vector Boson Fusion at the Large Hadron Collider
YU You, YUE Chong-Xing, XIA Yun
Chin. Phys. Lett. 2014, 31 (2): 021201 .   DOI: 10.1088/0256-307X/31/2/021201
Abstract   PDF(pc) (532KB) ( 279 )
Pair production of the doubly charged leptons X±± via vector boson fusion (γγ, and WW) at the large hadron collider is studied. Our numerical results show that the cross section via fusion is very small. For the center-of-mass energy √s=14 TeV and MX=200–650 GeV, the values of the cross sections σγγ and σww are in the ranges of 5.2 fb–0.04 fb and 20.2 fb–1.2 fb, respectively.
NUCLEAR PHYSICS
The Hydrodynamic Description for the Pseudorapidity Distributions of the Charged Particles Produced in Pb–Pb Collisions at LHC Energy
ZHANG Hai-Li, JIANG Zhi-Jin, JIANG Guan-Xiang
Chin. Phys. Lett. 2014, 31 (2): 022501 .   DOI: 10.1088/0256-307X/31/2/022501
Abstract   PDF(pc) (601KB) ( 284 )
The charged particles produced in nucleus-nucleus collisions are classified into two parts. One is from the hot and dense matter created in collisions with the evolution dominated by revised Landau hydrodynamics, and the other is from leading particles. The rapidity distributions of these two parts of the particles are presented, which are then compared with the experimental measurements carried out by a CERN-LHC-ALICE collaboration in Pb–Pb collisions at √sNN=2.76 TeV. The theoretical results are consistent with the experimental data.
Energy Gain Investigation in Fast Ignition ICF with Electron Ignition Beam by Changing Fuel Characteristics
Moosavi Mohadeseh, Ahmadi Masoume, Ghasemizad Abbas
Chin. Phys. Lett. 2014, 31 (2): 022801 .   DOI: 10.1088/0256-307X/31/2/022801
Abstract   PDF(pc) (532KB) ( 517 )
Fast ignition is a method in inertial confinement fusion (ICF) in which an ignition spark in pre-compression fuel is formed by an ultra-intense laser beam. In applying this method, a hot spot is built by relative electrons which are produced by the ultra-intense laser beam. For a better understanding, a fuel energy gain curve based on density is drawn and it can be observed that the ignition by an electron beam has the maximum energy gain. The maximum energy gain has been observed in equimolar DT fuel with a density of 500 g/cm3 and in fuel with tritium (10%) with a density of 1000 g/cm3.
ATOMIC AND MOLECULAR PHYSICS
High-l Rydberg States' Interference Using a Double-Pulse Electric Field
CHEN Jie, ZHANG Hao, BAO Shan-Xia, WANG Li-Mei, ZHANG Lin-Jie, LI Chang-Yong, ZHAO Jian-Ming, JIA Suo-Tang
Chin. Phys. Lett. 2014, 31 (2): 023201 .   DOI: 10.1088/0256-307X/31/2/023201
Abstract   PDF(pc) (668KB) ( 358 )
The interference behavior of high-l Rydberg states is investigated in external fields. We prepare high-l states from an initial excited ns Cs Rydberg state by applying one electric-field pulse. The interference between the initial ns state and the high-l states is investigated by two time-delayed short electric-field pulses. The state selective field ionization technique is used to measure the transfer ratio versus the field pulses parameters. The visibility of interference is defined to describe interference and the results show that a relative long duration of electric-field pulse will weaken the interference.
Electron Impact Excitations and Linear Polarization for 1s2 1S0–1s2p 3,1P1 Lines of Fe24+ Ions under Screened Coulomb Interactions
JIANG Jun, DONG Chen-Zhong, XIE Lu-You
Chin. Phys. Lett. 2014, 31 (2): 023401 .   DOI: 10.1088/0256-307X/31/2/023401
Abstract   PDF(pc) (663KB) ( 303 )
Electron impact excitation cross sections from the ground state to the individual magnetic sublevels of 1s2p 3,1P1 states in high-temperature dense plasmas are calculated for highly charged He?like Fe24+ions by using a fully relativistic distorted?wave method. The Debye?Hückel screening model is used to screen the projectile electron from the nucleus and target electrons. The linear polarization degrees for these lines are obtained. It is found that the cross sections at all incident energies decrease with the increase of the screening for these excitations. The influence of screening on linear polarization degrees of the 1P1 line is very small. The linear polarization degrees of 3P1 line decrease sharply at low incident energy with the increase of the screening.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Three-Dimensional Photon Control in Membrane-Stack Photonic Crystals
ZHOU Xing-Ping, SHU Jing
Chin. Phys. Lett. 2014, 31 (2): 024201 .   DOI: 10.1088/0256-307X/31/2/024201
Abstract   PDF(pc) (876KB) ( 346 )
We design two novel waveguides in membrane-stack photonic crystals and obtain their dispersion characteristics by the three-dimensional (3D) plane wave-expansion method. The 3D photon control phenomena are demonstrated, in which light is incident on the crystal and is bent both horizontally and vertically. Then light is split into two and is finally emitted from the other side of the crystal. A 3D splitter is realized. We also present a nanocavity to trap photons. With waveguides of different directions and nanocavities, the arbitrary 3D photon manipulation has been demonstrated.
Optical Transparency Induced by Periodic Modulation in a Passive Optical Coupler
LUO Xiao-Bing, LIU Rong-Xuan, LIU Ming-Hua, YU Xiao-Guang, WU Dong-Lan, HU Qiang-Lin
Chin. Phys. Lett. 2014, 31 (2): 024202 .   DOI: 10.1088/0256-307X/31/2/024202
Abstract   PDF(pc) (718KB) ( 330 )
We propose a scheme for the realization of optical transparency by using a periodically modulated optical coupler with losses in one waveguide. We discover that the increase of the transparency can be achieved only by varying the parameters of modulation, and such modulation-enhanced transmission is the consequence of phase transition of the quasi-energy spectrum. Our findings offer an efficient way to manipulate light transmission in realistic dissipative systems.
High Power 1060 nm Distributed Feedback Semiconductor Laser
ZHAI Teng, TAN Shao-Yang, LU Dan, WANG Wei, ZHANG Rui-Kang, JI Chen
Chin. Phys. Lett. 2014, 31 (2): 024203 .   DOI: 10.1088/0256-307X/31/2/024203
Abstract   PDF(pc) (554KB) ( 317 )
A GaAs based high power distributed feedback (DFB) semiconductor laser with a second-order grating has been demonstrated. An output power of 150 mW at an injection current of 350 mA is realized with a 1-mm cavity length. With a new design of the waveguide structure, the DFB laser maintains a stable single longitudinal mode around 1060 nm with a side mode suppression ratio of larger than 50 dB.
Wildly Tunable, High-Efficiency MgO:PPLN Mid-IR Optical Parametric Oscillator Pumped by a Yb-Fiber Laser
LIU Shan-De, WANG Zhao-Wei, ZHANG Bai-Tao, HE Jing-Liang, HOU Jia, YANG Ke-Jian, WANG Rui-Hua, LIU Xun-Min
Chin. Phys. Lett. 2014, 31 (2): 024204 .   DOI: 10.1088/0256-307X/31/2/024204
Abstract   PDF(pc) (598KB) ( 494 )
We demonstrate a wildly tunable, high-efficiency mid-infrared (mid-IR) output-coupled single resonant optical parametric oscillator (OC-SRO) pumped by a Yb-fiber laser. The compact mid-infrared source employs a 50-mm-long, multi-grating MgO-doped periodically poled lithium niobate (MgO-PPLN) crystal, providing as much as 1.73 W idler power at 3.012 μm, and 1.27 W signal power at 1645 nm, corresponding to an overall conversion efficiency of 41.7% and a slope efficiency of 77.9%. In particular, the mid-infrared output power of 1.03 W and 0.67 W are obtained at 3.7 μm and 3.9 μm, respectively, with an optical-to-optical conversion efficiency of 14.3% and 9.3%. Furthermore, the idler light is tunable from 3 μm to 3.9 μm by changing the periods from 31 to 28.5 μm, with the output power >1 W over 78% of the tuning range. Our experimental results are pump power limited and further mid-IR power and conversion efficiency could be obtained with a suitable high-power pump source. The total OC-SRO output power rms at 2.6 W is about 0.6% during 2 h measurement.
A 5.9-mJ 500-Hz Electro-Optic Q-Switched 1053 nm Nd:LiLuF4 Laser
YANG Qi, ZHU Xiao-Lei, LU Ting-Ting, MA Jian, HANG Yin, CHEN Wei-Biao
Chin. Phys. Lett. 2014, 31 (2): 024205 .   DOI: 10.1088/0256-307X/31/2/024205
Abstract   PDF(pc) (653KB) ( 291 )
An efficient and high power 1053 nm electro-optic Q-switched Nd:LiLuF4 laser, end-pumped by two fiber coupled laser diodes at wavelength 806 nm, is reported for the first time. With an incident pump power of 24.4 W, the maximum laser output power of 7.3 W is achieved in free-running mode, and the optical conversion efficiency is 29.8%. For the Q-switched operation, the shortest pulse width of 17 ns is obtained at the pulse repetition rate of 500 Hz, corresponding to the pulse energy of 5.9 mJ with the peak power of 0.35 MW.
Distributed Qutrit–Qutrit Entanglement through Laser-Driven Resonant Interaction
WU Huai-Zhi, YANG Zhen-Biao
Chin. Phys. Lett. 2014, 31 (2): 024206 .   DOI: 10.1088/0256-307X/31/2/024206
Abstract   PDF(pc) (906KB) ( 328 )
We propose to deterministically realize the qutrit–qutrit maximal entanglement for two atoms held in separate cavities coupled by an optical resonator. We study such a system in the resonant regime and show that the laser-driven resonant dynamics allow for the fast and robust creation of qutrit–qutrit entanglement.
A Hertz-Linewidth Ultrastable Diode Laser System for Clock Transition Detection of Strontium Atoms
LI Ye, LIN Yi-Ge, WANG Qiang, WANG Shao-Kai, ZHAO Yang, MENG Fei, LIN Bai-Ke, CAO Jian-Ping, LI Tian-Chu, FANG Zhan-Jun, ZANG Er-Jun
Chin. Phys. Lett. 2014, 31 (2): 024207 .   DOI: 10.1088/0256-307X/31/2/024207
Abstract   PDF(pc) (635KB) ( 406 )
The frequencies of two 698 nm external cavity diode lasers (ECDLs) are locked separately to two independently located ultrahigh finesse optical resonant cavities with the Pound–Drever–Hall technique. The linewidth of each ECDL is measured to be 4.6 Hz by their beating and the fractional frequency stability below 5×10?15 between 1 s to 10 s averaging time. Another 698 nm laser diode is injection locked to one of the cavity-stabilized ECDLs with a fixed frequency offset for power amplification while maintaining its linewidth and frequency characteristics. The frequency drift is 1 Hz/s measured by a femtosecond optical frequency comb based on erbium fiber. The output of the injection slave laser is delivered to the magneto-optical trap of a Sr optical clock through a 10-m-long single mode polarization maintaining fiber with an active fiber noise cancelation technique to detect the clock transition of Sr atoms.
High-Energy Rectangular Pulse Dissipative Soliton Generation in a Long-Cavity Sigma-Shaped Configuration Mode-Locked Fiber Laser
YANG Jin-Hui, GUO Chun-Yu, RUAN Shuang-Chen, OUYANG De-Qin, LIN Huai-Qin, WU Yi-Ming
Chin. Phys. Lett. 2014, 31 (2): 024208 .   DOI: 10.1088/0256-307X/31/2/024208
Abstract   PDF(pc) (674KB) ( 393 )
The high-energy rectangular pulse dissipative soliton (DS) is achieved in a long-cavity sigma-shaped configuration erbium-doped fiber laser. A long fiber is inserted in the linear arm of the sigma-shaped configuration to extend the resonator length twice, which effectively improves the pulse energy. The nonlinear polarization rotation technique is employed to realize the mode-locked state. Stable rectangular pulses with pulse energy of 421.22 nJ are obtained at the pump power of 620 mW. To the best of our knowledge, this high pulse energy is a new record of the rectangular pulse mode-locked DS fiber lasers.
A Method of Measuring the In Situ Seafloor Sound Speed using Two Receivers with Warping Transformation
LI Feng-Hua, ZHANG Bo, GUO Yong-Gang
Chin. Phys. Lett. 2014, 31 (2): 024301 .   DOI: 10.1088/0256-307X/31/2/024301
Abstract   PDF(pc) (523KB) ( 257 )
We present a method of measuring the in situ superficial seafloor sound speed by using two receivers deployed vertically in sediment, based on the dispersion characteristic of normal modes in shallow water. Warping transformation is adopted to extract the first normal mode from the broadband propagation signals. Some experimental results which could validate the method are shown. One of the advantages of the method is that the seafloor sound speed can be solved directly from the relative vertical transmission loss of the first normal mode without the exact priori information of the environmental parameters such as the sound speed profile, the water-column depth and the source location.
In Vivo Magnetic Particle Targeting by Local Gradient Field of Interstitial Seeds Magnetized in an Ex Vivo Uniform Field
LI Xiao-Qiang, ZHENG Lu, WANG Xu-Fei
Chin. Phys. Lett. 2014, 31 (2): 024701 .   DOI: 10.1088/0256-307X/31/2/024701
Abstract   PDF(pc) (1003KB) ( 173 )
The possibility of in vivo magnetic particle targeting by the locally induced gradient field of interstitial ferromagnetic implants, magnetized in an ex vivo uniform field, is evaluated by a modelling analysis. A simplified 3D model analogous to a torso size, with a continuous laminar flow through the volume with the typical velocity and viscosity values of in vivo blood flow and a ferromagnetic seed inserted in the volume center vertical to the flow, is used to evaluate the magnetic particle capturing efficiency by the seed, which is magnetized in a uniform field. The initial modelling results indicate that for 1–10 μm iron oxide particles transporting with a blood flow of 0.5–5 mm/s, the seeds of tungsten steel, magnet steel and cast cobalt all present an effective particle capturing efficiency, which shows a fast initial increase and a slow saturation with the increasing magnetic field, a quasilinear increase with the increasing particle size, and a nonlinear decrease with the increasing blood velocity.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
The Burst Time Duration in Micropillar Deformation
ZHANG Xu, SHANG Fu-Lin
Chin. Phys. Lett. 2014, 31 (2): 026401 .   DOI: 10.1088/0256-307X/31/2/026401
Abstract   PDF(pc) (507KB) ( 508 )
Plastic flow of single crystal micropillars proceeds through a sequence of intermittent burst slips. The burst time durations are investigated based on an extended theoretical model which incorporates the observed power-law distribution of burst sizes in compression experiments of micropillars. The results show that the burst time durations exhibit a powerlaw behavior with an exponential cutoff, suggesting the same scaling behaviors as the burst sizes. In addition, the predicted scaling exponent is found to converge to a value of 1.6. It is demonstrated that our results are consistent with the experimental data.
Ultrathin Carbon Nanotubes for Efficient Energy Storage: a First-Principles Study
WANG Xue-Qing, WANG Yu-Sheng, WANG Yu-Cang, WANG Fei, SUN Qiang, JIA Yu
Chin. Phys. Lett. 2014, 31 (2): 026801 .   DOI: 10.1088/0256-307X/31/2/026801
Abstract   PDF(pc) (903KB) ( 243 )
On the basis of first-principles density functional calculations, the present study sheds theoretical insight on ultrathin carbon nanotube (UCNT) and hydrogenated ultrathin carbon nanotube (HUCNT) for use as potential materials not only for Li-ion battery anode but also for high-capacity hydrogen storage. The highest Li storage capacities in UCNT and HUCNT can be of LiC4 and LiC4H2, respectively, which are higher than that in graphite and LiC6. Binding between Li (Ca) atoms and these materials are found to be enhanced considerably. Each Li (Ca) atom may bind multi-hydrogen molecules, and the adsorption energies are ideally suited for storing hydrogen under ambient conditions, and the predicted weight percentage of molecular hydrogen are in the range of 6.4–12 wt% exceeding the target set by the United States Department of Energy.
Surface Morphology of GaAs/In0.3Ga0.7As in an Elastic Field of Static Point Defects
WU Ping-Ping, GAO Fang-Liang, ZHANG Shu-Guang, LI Guo-Qiang
Chin. Phys. Lett. 2014, 31 (2): 026802 .   DOI: 10.1088/0256-307X/31/2/026802
Abstract   PDF(pc) (887KB) ( 335 )
The surface morphology InGaAs layers with In composition of 0.3 on GaAs (001) substrates are simulated by the phase field method. We investigate the influence of the strain field induced by static point defects on surface morphology of the InGaAs thin film. Our simulation demonstrates that the rms roughness of the thin film surface is strongly dependent on the density and magnitude of the randomly distributed point defects. Point defects near the thin film surface can produce a relatively large change of the surface morphology. The influences of thin film thickness on the surface morphology with different defect distributions are illustrated in the simulations. Additionally, a combination of experiment and theory is used to examine the influence of the defect density and magnitude on the surface morphology and roughness.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Enhanced Output Power of Near-Ultraviolet Light-Emitting Diodes by p-GaN Micro-Rods
WANG Dong-Sheng, ZHANG Ke-Xiong, LIANG Hong-Wei, SONG Shi-Wei, YANG De-Chao, SHEN Ren-Sheng, LIU Yang, XIA Xiao-Chuan, LUO Ying-Min, DU Guo-Tong
Chin. Phys. Lett. 2014, 31 (2): 027101 .   DOI: 10.1088/0256-307X/31/2/027101
Abstract   PDF(pc) (1133KB) ( 571 )
Near-ultraviolet (UV) InGaN/AlGaN light-emitting diodes (LEDs) are grown by low-pressure metal-organic chemical vapor deposition. The scanning electronic microscope image shows that the p-GaN micro-rods are formed above the interface of p-AlGaN/p-GaN due to the rapid growth rate of p-GaN in the vertical direction. The p-GaN micro-rods greatly increase the escape probability of photons inside the LED structure. Electroluminescence intensities of the 372 nm UV LED lamps with p-GaN micro rods are 88% higher than those of the flat surface LED samples.
Phonon-Limited Electron Mobility in Single-Layer MoS2
ZENG Lang, XIN Zheng, CHEN Shao-Wen, DU Gang, KANG Jin-Feng, LIU Xiao-Yan
Chin. Phys. Lett. 2014, 31 (2): 027301 .   DOI: 10.1088/0256-307X/31/2/027301
Abstract   PDF(pc) (609KB) ( 697 )
The dynamics of electron transport in single-layer MoS2 is simulated by employing the single particle Monte Carlo method. Acoustic phonon scattering, optical phonon scattering and Fr?hlich scattering are taken into account. It is found that the electron mobility decreases from 806 cm2/V?s for a transverse electrical field of 103 V/m to 426/112 cm2/V?s for a transverse electrical field of 105/107 V/m. Further detailed analysis on carrier dynamics reveals that the low field mobility is dominated by the acoustic phonon scattering while the role of optical phonon scattering is to relax the electron energy below the optical phonon energy by efficient energy relaxation through optical phonon emission. Only when the transverse electrical field is larger than 106 V/m, the mobility can be determined by the optical phonon scattering, leading to a strong mobility degradation.
Observation of Dynamic Behavior in YBa2Cu3O7−δ/La0.88Ca0.12MnO3 Using Femtosecond Optical Pulses
PENG Lin, CAI Chuan-Bing, LIU Yong-Sheng
Chin. Phys. Lett. 2014, 31 (2): 027401 .   DOI: 10.1088/0256-307X/31/2/027401
Abstract   PDF(pc) (615KB) ( 268 )

Ultrafast pump-optical probe spectroscopy is used to analyze the carrier dynamic behavior in YBa2Cu3O7−δ/La0.88 Ca0.12MnO3 (YBCO/LCMO) heterostructure. The change in reflectivity ΔR/R is induced and is probed by using pulses of 120 fs duration and photon energy 1.55 eV from a Ti:sapphire laser. For higher laser power fluence (such as 0.5 mJ/cm2), the time evolution in transient reflectivity change ΔR/R exhibits three long relaxation processes. We extract the characteristic relaxation time of the different processes by fitting the data and obtain the long characteristic relaxation time which indicates the enhanced proximity effect of the YBCO/LCMO.

Towards a Mechanism Underlying the Stability of the Tetragonal CuO Phase: Comparison with NiO and CoO by Hybrid Density Functional Calculation
WANG Fang-Fang, WEI Peng-Yue, DING Xue-Yong, XING Xian-Ran, CHEN Xing-Qiu
Chin. Phys. Lett. 2014, 31 (2): 027402 .   DOI: 10.1088/0256-307X/31/2/027402
Abstract   PDF(pc) (658KB) ( 433 )
By means of hybrid density functional theory, we interpret the stability mechanism of the tetragonal CuO phase, which was synthesized using the pulsed laser deposition. The orbital ordering resulted from the crystal field splitting is found to be favorable for the d9 electronic configuration of the Cu2+ ion, yielding two possible metastable tetragonal phases (c/a < 1 and c/a > 1) of CuO. A detailed comparison is also performed with the ideal rock-salt compounds CoO and NiO.
Magnetic Properties of Co-Doped TiO2 Films Grown on TiN Buffered Silicon Substrates
XIA Yu-Qian, SUN Lei, XU Hao, HAN Jing-Wen, ZHANG Yi-Bo, WANG Yi, ZHANG Sheng-Dong
Chin. Phys. Lett. 2014, 31 (2): 027501 .   DOI: 10.1088/0256-307X/31/2/027501
Abstract   PDF(pc) (725KB) ( 266 )
Co-doped TiO2 thin films are grown on TiN buffered silicon substrates by the pulsed laser deposition method and then hydrogenated. Transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy measurements have shown that the TiN buffer layer can suffer a 400°C deposition temperature and prevent the growth of silicon dioxide on silicon. After that, the room temperature ferromagnetism behaviors are observed in the hydrogenated samples, which are measured by the alternating gradient magnetometer. X-ray photoelectron spectroscopy and x-ray absorption fine structure measurements have revealed the existence of cobalt clusters. According to the material analysis, the magnetic behavior after hydrogenation is suggested to be induced by the enhancement of cobalt clusters.
Controlling Factors of the Electric Field at the Triple Junction
LIU Yang, HUANG Xu-Dong, FENG Yu-Jun, HE Hong-Liang
Chin. Phys. Lett. 2014, 31 (2): 027701 .   DOI: 10.1088/0256-307X/31/2/027701
Abstract   PDF(pc) (670KB) ( 816 )
The metal-dielectric-vacuum junction is defined as the triple junction owned enhanced electric field, thus this special region is regarded as the location where primary electrons emission is favored. For electron emission, triple junction could affect both the flashover breakdown of insulators and the electron emission property of ferroelectric cathodes. In this study, we theoretically investigate the electric field enhancement in the triple-junction region. It is found that the key parameter to determine the field enhancement is the taper angle of the electrode and the relative permittivity of the dielectric. In addition, we first deduce the accurate expression of the electric field in this special region. The controlling parameters for determining the field enhancement are discussed in detail. We also discover the way to reduce the electric field of this region through simulation. The current analysis would be useful for both the electron emission enhancement and the issue of flashover breakdown.
Band Alignment and Band Gap Characterization of La2O3 Films on Si Substrates Grown by Radio Frequency Magnetron Sputtering
LIU Qi-Ya, FANG Ze-Bo, JI Ting, LIU Shi-Yan, TAN Yong-Sheng, CHEN Jia-Jun, ZHU Yan-Yan
Chin. Phys. Lett. 2014, 31 (2): 027702 .   DOI: 10.1088/0256-307X/31/2/027702
Abstract   PDF(pc) (584KB) ( 512 )
La2O3 films are grown on Si (100) substrates by the radio-frequency magnetron sputtering technique. The band alignment of the La2O3/Si heterojunction is analyzed by the x-ray photoelectron spectroscopy. The valence-band and the conduction-band offsets of La2O3 films to Si substrates are found to be 2.40±0.1 and 1.66±0.3 eV, respectively. Based on O 1s energy loss spectrum analysis, it can be noted that the energy gap of La2O3 films is 5.18±0.2 eV, which is confirmed by the ultra-violet visible spectrum. According to the suitable band offset and large band gap, it can be concluded that La2O3 could be a promising candidate to act as high-k gate dielectrics.
Analysis of Intrinsic Degradation Mechanism in Organic Light-Emitting Diodes by Impedance Spectroscopy
ZHENG Rui, HUANG Wen-Bo, XU Wei, CAO Yong
Chin. Phys. Lett. 2014, 31 (2): 027703 .   DOI: 10.1088/0256-307X/31/2/027703
Abstract   PDF(pc) (1318KB) ( 1590 )
The organic light-emitting diodes (OLEDs) in the sandwiched structures ITO/poly[3,4-ethylenedioxythiopene] (PEDOT)/poly[9,9-dioctylfluorene-co-4,7-di-2-thienyl-2,1,3-benzothiadiazole] (PFO-DBT15)/Ba/Al are fabricated. We use impedance measurements to investigate the degradation of aged OLEDs. A detailed analysis of the impedance spectra as functions of frequency and dc bias yields information about the injection of the interfacial electrode and the transport properties of emissive layer changes. Morphology differences between degraded and undegraded devices can also be observed by a scanning electron microscope. We perform comparative studies of the impedance spectroscopy (IS) of undegraded and degraded devices by both experiment and simulation approaches to explain the degradation mechanism for OLEDs. The IS of the undegraded device can be well understood by simply adopting the conventional RC equivalent circuits. For the degraded device, however, the successful model of the impedance spectroscopy results needs to take into account the more complicated situations, and we adopt a constant phase element to meet the experimental and simulated data and discuss the reasons caused by the problem.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
GaN Films Grown on Si (111) Substrates Using a Composite Buffer with Low Temperature AlN Interlayer
FANG Yu-Tao, JIANG Yang, DENG Zhen, ZUO Peng, CHEN Hong
Chin. Phys. Lett. 2014, 31 (2): 028101 .   DOI: 10.1088/0256-307X/31/2/028101
Abstract   PDF(pc) (1594KB) ( 370 )
A GaN interlayer between low temperature (LT) AlN and high temperature (HT) AlN is introduced to combine HT AlN, LT AlN and composition-graded AlGaN as a novel buffer layer for GaN films grown on Si (111) substrates. The crystal quality, surface morphology and strain state of the GaN film with this new buffer are compared with those of GaN grown on a conventional buffer structure. By changing the thickness of LT AlN, the crystal quality is optimized and the crack-free GaN film is obtained. The in-plane strain in the GaN film can be changed from tensile to compressive strain with the increase in LT AlN thickness.
Electronic Structures of Carbon-Based Kagomé Lattices
ZHANG Dong, LIN Liang-Zhong, ZHU Jia-Ji
Chin. Phys. Lett. 2014, 31 (2): 028102 .   DOI: 10.1088/0256-307X/31/2/028102
Abstract   PDF(pc) (904KB) ( 316 )
A structurally stable two-dimensional carbon allotrope of graphene is studied theoretically based on the first-principles calculations. This allotrope can be formed by inserting acetylene and diacetylene fragments into β-graphyne. The calculations on structure and electronic energy spectra show that the carbon Kagomé lattice is a structurally stable semimetal with the Dirac cones below the Fermi surface, in contrast to the Dirac points at the Fermi surface in intrinsic graphene.
Influence of ITO, Graphene Thickness and Electrodes Buried Depth on LED Thermal-Electrical Characteristics Using Numerical Simulation
XUE Sheng-Jie, FANG Liang, LONG Xing-Ming, LU Yi, WU Fang, LI Wan-Jun, ZUO Jia-Qi, ZHANG Shu-Fang
Chin. Phys. Lett. 2014, 31 (2): 028501 .   DOI: 10.1088/0256-307X/31/2/028501
Abstract   PDF(pc) (725KB) ( 257 )
Finite elements methods are used to investigate the thermal?electrical characteristics of gallium?nitride (GaN) light-emitting diodes (LEDs) with different transparent conductive layers (TCLs) and buried depths of electrodes, where the transparent conductive layers include indium tin oxide (ITO), graphene (Gr) and the combination of them (ITO/Gr). The optimal material parameters and the precision and accuracy of the simulation model are validated. Moreover, the parameters' sensitivity analysis is carried out as well. The results indicate that the LED with the TCL of a 100-nm ITO or 4-layer Gr has a good thermal-electrical performance from the viewpoint of the maximum temperature and the current density deviation of multiple quantum well (MQW), where the maximum temperature occurs at the n-Pad rather than p-Pad. The compound TCL with a 20-nm ITO and 3-layer Gr reaches a thermal-electrical performance better than that of a 100-nm ITO or 4-layer Gr. Moreover, their maximum temperatures decrease about -0.43% and 1.21%, and the current density uniformities increase up to -6.09% and 17.41%, respectively. Furthermore, when the electrode buried depth is 0.51 μm, the thermal-electrical performance of the GaN LEDs can be further improved.
Sensing Characteristics of Shear-Mode AlN Solidly Mounted Resonators with a Silicone Microfluidic System in Viscous Media
XIONG Juan, GUO Peng, SUN Xi-Liang, WANG Sheng-Fu, HU Ming-Zhe, GU Hao-Shuang
Chin. Phys. Lett. 2014, 31 (2): 028502 .   DOI: 10.1088/0256-307X/31/2/028502
Abstract   PDF(pc) (739KB) ( 350 )
AlN solidly mounted resonators with silicone microfluidic systems vibrating in shear mode are fabricated and characterized. The fabrication process is compatible with integrated circuits and the c-axis tilted AlN films are deposited, which allow in-liquid operation through excitation of the shear mode. The silicone microfluidic system is mounted on top of the sensor chip to transport the analyses and confine the flow to the active area. The properties of sensor operation in air, deionized water, ethanol, isopropanol, 80% glycol aqueous solution, glycol, and olive oil are characterized. The effects of different viscosities on the resonance frequency shift and Q-factor of the sensor have been discussed. The sensitivity and Q value in glycol of the sensor are 1.52 MHz cm2/μg and around 60, respectively. The results indicate the potential of a highly sensitive microfluidic sensor system for the applications in viscous media.
The Distinguished Charge-Trapping Capability of the Memory Device with Al2O3-Cu2O Composite as the Charge Storage Layer
LU Jian-Xin, OU Xin, LAN Xue-Xin, CAO Zheng-Yi, LIU Xiao-Jie, LU Wei, GONG Chang-Jie, XU Bo, LI Ai-Dong, XIA Yi-Dong, YIN Jiang, LIU Zhi-Guo
Chin. Phys. Lett. 2014, 31 (2): 028503 .   DOI: 10.1088/0256-307X/31/2/028503
Abstract   PDF(pc) (925KB) ( 227 )
A memory device Si/Al2O3/Al2O3-Cu2O/Al2O3/Pt is fabricated by using atomic layer deposition and rf-magnetron sputtering techniques. The memory device including the composite of Al2O3 and Cu2O as the charge storage layer shows a distinguished charge trapping capability. At a working voltage of ±11 V a memory window of 9.22 V is obtained. The x-ray photoelectron spectroscopic study shows a shoulder from Cu2+ ions around the peak of Cu1+ ions. It is suggested that the charge-trapping mechanism should be attributed to the defect states formed by the inter-diffusion at the interface of two oxides.
Effects of pH on Oxaliplatin-Induced Condensation of Single DNA Molecules
ZHANG Hong-Yan, JI Chao, LIU Yu-Ru, LI Wei, LI Hui, DOU Shuo-Xing, WANG Wei-Chi, ZHANG Ling-Yun, XIE Ping, WANG Peng-Ye
Chin. Phys. Lett. 2014, 31 (2): 028701 .   DOI: 10.1088/0256-307X/31/2/028701
Abstract   PDF(pc) (545KB) ( 257 )
By using magnetic tweezers, atomic force microscope and mass spectrometry, we study the effects of pH on oxaliplatin-induced DNA condensation, the DNA persistence length, the amounts of micro-loops and of oxaliplatin bound to DNA. It is found that the DNA condensation degree, the amounts of micro-loops and of oxaliplatin bound to DNA increase with the decrease in the pH value while the DNA persistence length has an opposite behavior. The observed effects may be related to the drug resistance of cancer cells.
Laminated Polymer Solar Cells with PEDOT:PSS Film as Anode
HOU Teng, LIANG Chun-Jun, ZHANG Fu-Jun, HE Zhi-Qun, SUN Kai
Chin. Phys. Lett. 2014, 31 (2): 028801 .   DOI: 10.1088/0256-307X/31/2/028801
Abstract   PDF(pc) (673KB) ( 290 )
A prefabricated conductive polymer film of polymer poly(3,4-ethylenedioxy-thiophene):poly (styrene-sulfonate) (PEDOT:PSS) is developed and is used as the anode in an inverted polymer solar cell (PSC) through a lamination process. The geometry structure of the PSC is indium tin oxide/interface layer/P3HT:PCBM/PEDOT:PSS. The PEDOT:PSS electrode is 5 μm and the sheet resistance is 10 Ω/sq. The device fabrication process is vacuum-free and extremely simple. Lithium carbonate (Li2CO3) and cesium carbonate (Cs2CO3) are used as the cathode interface layers, respectively, and the result shows that Li2CO3 can enhance the open-circuit voltage (Voc) and fill factor distinctly, and the power conversion efficiency (PCE) can reach 2.1%.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Reconstruction of New Holographic Chaplygin Gas Model with Viscosity
WU Ya-Bo, TONG Hai-Dan, YANG Hao, LU Jian-Bo, ZHAO Yue-Yue, LU Jun-Wang, ZHANG Xue
Chin. Phys. Lett. 2014, 31 (2): 029801 .   DOI: 10.1088/0256-307X/31/2/029801
Abstract   PDF(pc) (530KB) ( 242 )
We investigate the interacting new holographic dark energy (HDE) with viscosity. Specifically, we not only study the dynamical evolutions of the new HDE with viscosity and the influences of viscosity as well as the coupling constant on the equation of state for the new HDE, but also establish the correspondence between the new HDE with viscosity and variable generalized Chaplygin gas (VGCG) models in the flat Friedmann–Robertson–Walker universe. Furthermore, we also reconstruct the potential and the dynamics of VGCG as the scalar field. By analysis we show that for the new holographic Chaplygin gas model, if the related parameters to the potential satisfy some constraints, the accelerated expansion can be achieved. These research results can reduce to the ones without viscosity.
40 articles