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Volume 28 Issue 7
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Two New Fourth-Order Three-Stage Symplectic Integrators
LI Rong, WU Xin**
Chin. Phys. Lett. 2011, 28 (7): 070201 .   DOI: 10.1088/0256-307X/28/7/070201
Abstract   PDF(pc) (664KB) ( 611 )
Two new fourth-order three-stage symplectic integrators are specifically designed for a family of Hamiltonian systems, such as the harmonic oscillator, mathematical pendulum and lattice φ4 model. When the nonintegrable lattice φ4 system is taken as a test model, numerical comparisons show that the new methods have a great advantage over the second-order Verlet symplectic integrators in the accuracy of energy, become explicitly better than the usual non-gradient fourth-order seven-stage symplectic integrator of Forest and Ruth, and are almost equivalent to a fourth-order seven-stage force gradient symplectic integrator of Chin. As the most important advantage, the new integrators are convenient for solving the variational equations of many Hamiltonian systems so as to save a great deal of the computational cost when scanning a lot of orbits for chaos.
Quantum Stackelberg Duopoly in a Noninertial Frame
Salman Khan**, M. Khalid Khan
Chin. Phys. Lett. 2011, 28 (7): 070202 .   DOI: 10.1088/0256-307X/28/7/070202
Abstract   PDF(pc) (502KB) ( 534 )
We study the influence of the Unruh effect on quantum Stackelberg duopoly. It is shown that the acceleration of a noninertial frame strongly affects the payoffs of the firms. The validation of the subgame perfect Nash equilibrium is limited to a particular range of acceleration of the noninertial frame. The benefit of the initial state entanglement in the quantum form of the duopoly in the inertial frame is adversely affected by the acceleration. The duopoly can become a follower advantage only in a small region of the acceleration.
Numerical Simulation of Hyperbolic Gradient Flow with Pressure
LI Dong **, XIE Zheng, YI Dong-Yun
Chin. Phys. Lett. 2011, 28 (7): 070203 .   DOI: 10.1088/0256-307X/28/7/070203
Abstract   PDF(pc) (1577KB) ( 386 )
We propose a numerical algorithm for hyperbolic gradient flow with pressure for the initial value problem and boundary value problem on a compact manifold to investigate the influence of pressure on the evolution of the manifold. In particular, we simulate the behavior of a cotangent vector field on compact submanifolds in R3, and show that shock waves are generated.
Coevolution of Structure and Strategy Promoting Fairness in the Ultimatum Game
DENG Li-Li, TANG Wan-Sheng**, ZHANG Jian-Xiong
Chin. Phys. Lett. 2011, 28 (7): 070204 .   DOI: 10.1088/0256-307X/28/7/070204
Abstract   PDF(pc) (687KB) ( 510 )
We try to figure out how the structure evolution and strategy evolution commonly affect the emergence of fair behaviors in the ultimatum game under a complex network framework. By allowing the players to change their neighbors in the network as well as their strategies, several experiments have been conducted. Results of the simulations show that the coevolution has substantial impacts on the resulting outcomes for the strategy adopted as well as the ultimate structure. With increasing structure updating rate, players offer more in the ultimatum game, but players will offer less with increasing strategy updating rate. In particular, the ratio of structure updating to strategy updating also affects the emergence of fairness substantially because the larger the ratio, the more the players offer. In addition, the mutation in strategies plays a promoting role in the emergence of fairness. Moreover, the initial random network is evolved into the structure with small-world effects. By comparison with the traditional models of static structures, we show that allowing the network structure and strategy to coevolve generally promotes the emergence of fairness.
A Probability Measure for Entanglement of Pure Two-Qubit Systems and a Useful Interpretation for Concurrence
Abbass Sabour, Mojtaba Jafarpour**
Chin. Phys. Lett. 2011, 28 (7): 070301 .   DOI: 10.1088/0256-307X/28/7/070301
Abstract   PDF(pc) (422KB) ( 465 )
A new probability measure for the quantification of entanglement of pure states is introduced. Numerical computations indicate that the derived measure is equal to concurrence, up to the precision of the computer program used. Hence it also provides a physical interpretation for concurrence.
Photon Counting Optical Time Domain Reflectometry Applying a Single Photon Modulation Technique
WANG Xiao-Bo, WANG Jing-Jing, HE Bo, XIAO Lian-Tuan**, JIA Suo-Tang
Chin. Phys. Lett. 2011, 28 (7): 070302 .   DOI: 10.1088/0256-307X/28/7/070302
Abstract   PDF(pc) (697KB) ( 1184 )
Photon-counting optical time domain reflectometry (v-OTDR) is typically used in a mode with spatial resolution in the centimeter range. Here we demonstrate a 1550 nm v-OTDR system to optimize the discriminate voltage of a single photon avalanche detector using a single photon modulation and demodulation technique, which shows obvious improvement in the signal intensity. The intensity of signal is doubled when the discriminator voltage is optimized from 184 mV to 162 mV.
Energy Spectra of the Harmonic Oscillator in a Generalized Noncommutative Phase Space of Arbitrary Dimension
LIN Bing-Sheng**, HENG Tai-Hua
Chin. Phys. Lett. 2011, 28 (7): 070303 .   DOI: 10.1088/0256-307X/28/7/070303
Abstract   PDF(pc) (424KB) ( 679 )
We use the invariant eigen-operator method to study the higher-dimensional harmonic oscillator in a type of generalized noncommutative phase space, and obtain the explicit expression of the energy spectra of the noncommutative harmonic oscillator in arbitrary dimension. It is found that the energy spectra of the higher-dimensional noncommutative harmonic oscillator are equal to the sum of the energy spectra of some 1D harmonic oscillators and some 2D noncommutative harmonic oscillators. We believe that the properties of the harmonic oscillator may reflect some essence of the noncommutative phase space.
Feasibility of Double-Click Attack on a Passive Detection Quantum Key Distribution System
ZHANG Peng**, LI Chao,
Chin. Phys. Lett. 2011, 28 (7): 070304 .   DOI: 10.1088/0256-307X/28/7/070304
Abstract   PDF(pc) (489KB) ( 585 )
An eavesdropper (Eve) can exploit all the imperfections of a practical quantum key distribution (QKD) system to obtain some information about the secret key, no matter whether these imperfections are from the physical layer or from the post-processing layer. We propose a possible attack on a passive detection QKD system based on the imperfection from the software layer. The analysis shows that Eve can obtain all the information about the key without being discovered.
Quantum Computing via Singlet-Triplet Spin Qubits in Nanowire Double Quantum Dots
XUE Peng
Chin. Phys. Lett. 2011, 28 (7): 070305 .   DOI: 10.1088/0256-307X/28/7/070305
Abstract   PDF(pc) (613KB) ( 429 )
We propose a new structure for quantum computing via spin qubits with high fidelity. Each spin qubit corresponds to two electrons in a nanowire double quantum dot, with the singlet and one of the triplets as the logical qubit states. The entangling gate is effected by virtual charge dipole transitions. We include noise to show the feasibility of this scheme under current experimental conditions.
Quantum Discord Dynamics of Two Atoms Interacting with Two Quantized Field Modes through a Raman Interaction with Phase Decoherence
QIAN Yi, XU Jing-Bo**
Chin. Phys. Lett. 2011, 28 (7): 070306 .   DOI: 10.1088/0256-307X/28/7/070306
Abstract   PDF(pc) (505KB) ( 421 )
We investigate the quantum discord dynamics of two effective two-level atoms independently interacting with two quantized field modes through a Raman interaction in the presence of phase decoherence. The influence of the phase decoherence and detuning on the evolution of the quantum discord and entanglement between two atoms is discussed. It is found that the quantum discord is more robust than the entanglement under the phase decoherence, and the amount of discord and entanglement between two atoms can be increased by adjusting the detuning.
Efficient Phase-Encoding Quantum Key Generation with Narrow-Band Single Photons
YAN Hui, **, ZHU Shi-Liang, DU Sheng-Wang
Chin. Phys. Lett. 2011, 28 (7): 070307 .   DOI: 10.1088/0256-307X/28/7/070307
Abstract   PDF(pc) (531KB) ( 391 )
We propose an efficient phase-encoding quantum secret key generation scheme with heralded narrow-band single photons. The key information is carried by the phase modulation directly on the single-photon temporal waveform. We show that when the technique is applied to the conventional single photon phase-encoding BB84 and differential phase shift (DPS) quantum key distribution schemes, the key generation efficiencies can be improved by factors of 2 and 3, respectively. For N(≥3)−period DPS systems, the key generation efficiency can be improved by a factor of N. The technique is suitable for quantum-memory-based long-distance fiber communication systems.
Experimental Demonstration of Largeness in Bipartite Entanglement Sudden Death
PENG Liang, HUANG Yun-Feng**, LI Li, LIU Bi-Heng, LI Chuan-Feng**, GUO Guang-Can
Chin. Phys. Lett. 2011, 28 (7): 070308 .   DOI: 10.1088/0256-307X/28/7/070308
Abstract   PDF(pc) (672KB) ( 435 )
Quantum coherence is the most distinct feature of quantum mechanics. However, inevitable decoherence processes will finally destroy it and make the "Schrödinger's cat" invisible in our classical world. In this "quantum-to-classical transition", the so-called "largeness" plays a critical role. We experimentally study the largeness phenomena in the bipartite entanglement decay process through a depolarizing channel with two-photon entangled states generated from a spontaneous parametric down-conversion source. Our experiment demonstrates how the speed of entanglement decay and the time when "entanglement sudden death" happens depend on the size of the system exposed to the environment noise.
Measurement of the Speed of Gravity
Chin. Phys. Lett. 2011, 28 (7): 070401 .   DOI: 10.1088/0256-307X/28/7/070401
Abstract   PDF(pc) (445KB) ( 624 )
From the Liénard–Wiechert potential in both the gravitational field and the electromagnetic field, it is shown that the propagation speed of gravitational field (waves) can be tested by comparing the measured speed of gravitational force with the measured speed of Coulomb force.
Chaos in Kundt Type-III Spacetimes
Department of Physics, Eastern Mediterranean University, G. Magosa, N. Cyprus, Mersin 0, Turkey
Chin. Phys. Lett. 2011, 28 (7): 070402 .   DOI: 10.1088/0256-307X/28/7/070402
Abstract   PDF(pc) (505KB) ( 383 )
We consider geodesic motion in a particular Kundt type-III spacetime in which the Einstein–Yang–Mills equations admit the solutions. On a particular surface as constraint, we project the geodesics into the (x,y) plane and treat the problem as a two-dimensional one. Our numerical study shows that chaotic behavior emerges under reasonable conditions.
Generalized Second Law of Thermodynamics in Wormhole Geometry with Logarithmic Correction
Faiz-ur-Rahman, Salahuddin, M. Akbar**
Chin. Phys. Lett. 2011, 28 (7): 070403 .   DOI: 10.1088/0256-307X/28/7/070403
Abstract   PDF(pc) (444KB) ( 1167 )
We construct various cases for validity of the generalized second law (GSL) of thermodynamics by assuming the logarithmic correction to the horizon entropy of an evolving wormhole. It is shown that the GSL is always respected for α0 ≤0, whereas for α0>0 the GSL is respected only if πr2A+/ℏ<α.
Ground-State Density Profiles of One-Dimensional Bose Gases with Anisotropic Transversal Confinement
HAO Ya-Jiang
Chin. Phys. Lett. 2011, 28 (7): 070501 .   DOI: 10.1088/0256-307X/28/7/070501
Abstract   PDF(pc) (583KB) ( 409 )
We investigate the ground-state density distributions of interacting one-dimensional Bose gases with anisotropic transversal confinement. Combining the exact ground state energy density of homogeneous Bose gases with local density approximation, we determine the density distribution in each interacting regime for different anisotropic parameters. It is shown that the transversal anisotropic parameter changes the density distribution obviously, and the observed density profiles on each orientation exhibit a difference of a factor.
Enhanced Total Ionizing Dose Susceptibility in Narrow Channel Devices
LIU Zhang-Li, **, HU Zhi-Yuan, ZHANG Zheng-Xuan, SHAO Hua, NING Bing-Xu, BI Da-Wei, CHEN Ming, ZOU Shi-Chang
Chin. Phys. Lett. 2011, 28 (7): 070701 .   DOI: 10.1088/0256-307X/28/7/070701
Abstract   PDF(pc) (964KB) ( 373 )
Total ionizing dose effects of different transistor sizes in a 0.18 µm technology are studied by 60Co γ-ray irradiation. Significant threshold voltage shift is observed for the narrow channel devices, which is called the radiation induced narrow channel effect (RINCE). A charge sharing model is introduced to understand the phenomenon. The devices' characteristic degradations after irradiation, such as threshold voltage shift, increase in on-state current under different drain biases and substrate biases, are discussed in detail. Radiation induced oxide trapped charge at the edges of shallow trench isolation plays an important role in the RINCE. Narrow channel devices are susceptible to the total ionizing dose effect.
Micro Humidity Sensor with High Sensitivity and Quick Response/Recovery Based on ZnO/TiO2 Composite Nanofibers
XU Lei, WANG Rui**, XIAO Qi, ZHANG Dan, LIU Yong
Chin. Phys. Lett. 2011, 28 (7): 070702 .   DOI: 10.1088/0256-307X/28/7/070702
Abstract   PDF(pc) (1869KB) ( 647 )
ZnO/TiO2 composite nanofibers are synthesized by an electrospinning method and characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A micro humidity sensor is fabricated by spinning the precursors of these nanofibers on a ceramic substrate with Ag-Pd interdigitated electrodes. Humidity sensing investigation reveals that this micro sensor offers high sensitivity and quick response/recovery at an operating frequency of 100 Hz. The corresponding impedance changes more than four orders of magnitude within the whole humidity range from 10% to 90% relative humidity (RH), and the response and recovery times are about 4 and 12 s, respectively. The maximum hysteresis is around 2% RH. The humidity sensing mechanism is also discussed based on the nanofiber structure and morphology.
AMS Measurement of 53Mn at CIAE
DONG Ke-Jun, HE Ming, LI Chao-Li, HU Hao, LIU Guang-Shan, CHEN Zhi-Gang, LI Zhen-Yu, WU Shao-Yong, LIU Jian-Cheng, YOU Qu-Bo, JIN Chun-Sheng, WANG Xiang-Gao, SHEN Hong-Tao, GUAN Yong-Jing, YUAN Jian, JIANG Shan**
Chin. Phys. Lett. 2011, 28 (7): 070703 .   DOI: 10.1088/0256-307X/28/7/070703
Abstract   PDF(pc) (547KB) ( 371 )
The long-lived isotope 53Mn cosmogenically produced in situ is a very useful indicator for geochronological dating. A new 53Mn accelerator−mass-spectrometry (AMS) measurement method is developed based on the HI-13 Tandem Accelerator and ΔE−Q3D detection system at China Institute of Atomic Energy. The performance of 53Cr isobar separation and suppression is tested by a series of 53Mn standards and commercial MnO samples. The results show that the ΔE−Q3D detection system brought about an overall suppression factor of more than 107 for the interfering isobar 53Cr.
Hamiltonian of Green–Schwarz IIB Superstring Theory in AdS3×S3 Background
KE San-Min, **, WANG Chun, WANG Zhan-Yun, JIANG Ke-Xia, SHI Kang-Jie
Chin. Phys. Lett. 2011, 28 (7): 071101 .   DOI: 10.1088/0256-307X/28/7/071101
Abstract   PDF(pc) (495KB) ( 310 )
We parameterize the Green–Schwarz IIB superstring in the AdS3×S3 background under the light cone gauge by the method of Metsaev and Tseytlin in AdS3 and by the method of Rahmfeld and Rajaraman in S3. After some calculation, we obtain the corresponding Maurer–Cartan 1−forms and the action. Then we fix two bosonic variables x+ and y5=σ, perform the partial Legendre transformation of the remaining bosonic variables, and find a Lagrangian that is linear in velocity after eliminating the metric of the world sheet. We also give the Hamiltonian and prove that the system is local and the Poisson bracket of the theory can be well defined. Using these results, one can further study the properties of solution space, solution transformation and the structure of the flat current algebra of the superstring in the AdS3×S3 background.
A Primary Study of Heavy Baryons ΛQ, ΣQ, ΞQ and ΩQ
ZHAO Qiao-Yan, ZHANG Dan**, ZHANG Qiu-Yang
Chin. Phys. Lett. 2011, 28 (7): 071201 .   DOI: 10.1088/0256-307X/28/7/071201
Abstract   PDF(pc) (463KB) ( 351 )
We perform a preliminary study of the 1/2+ and 3/2+ ground−state baryons containing a heavy quark in the framework of the chiral SU(3) quark model. By using the calculus of variations, masses of ΛQ, ΣQ, ΞQ, ΩQ, ΣQ*, ΞQ* and ΩQ*, where Q means c or b quark, are calculated. By taking reasonable model parameters, the numerical results of established heavy baryons are generally in agreement with the experimental data available, except that those of ΞQ are somewhat heavier. For Ωb with undetermined experimental mass and unobserved Ξb*, Ωb*, reasonable theoretical predictions are obtained. Interactions inside baryons are also discussed.
The Decay Rate of J/ψ to Λc+øverlineΣ+ in and beyond the Standard Model
KE Hong-Wei**, CHEN Ya-Zheng, LI Xue-Qian
Chin. Phys. Lett. 2011, 28 (7): 071301 .   DOI: 10.1088/0256-307X/28/7/071301
Abstract   PDF(pc) (506KB) ( 345 )
ã With rapid growth of the database of the BES III and the proposed super flavor factory, measurement of the rare J/ψ decays may be feasible, especially the weak decays into baryon final states. In this work, we study the decay rate of J/ψ to Λc+øverline Σ+ in the standard model (SM) and physics beyond the SM (here we use the unparticle model as an example). The quark−pair-creation model is employed to describe the creation of a pair of qq from a vacuum. We find that the rate of J/ψ→Λc+Σ+ is of the order of 10−10 in the SM, whereas the contribution of the unparticle is too small to be substantial. Therefore if a large branching ratio is observed, it must be due to new physics beyond the SM, but by no means the unparticle.
Cooling of Hyperonic Neutron Stars with Antikaons
DING Wen-Bo**, YU Zi, LIU Yu-Hui
Chin. Phys. Lett. 2011, 28 (7): 072601 .   DOI: 10.1088/0256-307X/28/7/072601
Abstract   PDF(pc) (783KB) ( 336 )
We discuss the impact of hyperons on the neutrino emitting and the gross cooling features of neutron stars with K and K0 condensations. The results show that hyperons change the density ranges of the direct Urca process with nucleons and the Urca processes of K and K0 condensations, as well as the values of neutrino emissivity. Moreover, interactions between hyperons and antikaons make the neutrino luminosity complicated. It is found that various hyperons play different roles in neutron stars. For massive stars, Σ hyperons make the cooling slower. However, Λ can hardly change the cooling history but it reduces the mass of neutron stars.
Power Test of the Ladder IH-RFQ Accelerator at Peking University
LU Yuan-Rong, CHEN Wei, NIE Yuan-Cun**, LIU Ge, GAO Shu-Li, ZENG Hong-Jin, YAN Xue-Qing, CHEN Jia-Er
Chin. Phys. Lett. 2011, 28 (7): 072901 .   DOI: 10.1088/0256-307X/28/7/072901
Abstract   PDF(pc) (2377KB) ( 355 )
A 104-MHz ladder interdigital-H radio frequency quadrupole accelerator (T-IH-RFQ) is developed for applying RFQs to heavy ion implantation and accelerator-based mass spectroscopy in recent years at the Institute of Heavy Ion Physics, Peking University. It could accelerate ions with a mass-to-charge ratio of less than 14, from 2.9 keV/u to 35.7 keV/u within a length of 1.1 m. The T-IH-RFQ cavity operating at H21(0) mode was constructed successfully. Based on a well designed rf power feeding system, the cavity was cold measured and tested with high rf power. In the case of cold measurement, the rf properties were obtained using a vector network analyzer with the help of a perturbation capacitor. During a high power test, the inter−electrode voltage was derived from the energy spectrum of x-rays measured by a high purity Ge detector. The results show that the specific shunt impedance of the T-IH-RFQ cavity reaches 178 kΩm, which could meet the requirements of beam dynamics design.
Magic Wavelength of an Optical Clock Transition of Barium
YU Geng-Hua, , ZHONG Jia-Qi, , LI Run-Bing, WANG Jin, ZHAN Ming-Sheng, **
Chin. Phys. Lett. 2011, 28 (7): 073201 .   DOI: 10.1088/0256-307X/28/7/073201
Abstract   PDF(pc) (658KB) ( 589 )
Similar to most of the other alkaline earth elements, barium atoms can be candidates for optical clocks, thus the magic wavelength for an optical lattice is important for the clock transition. We calculate the magic wavelength of a possible clock transition between 6s2 1S0 and 6s5d3D2 states of barium atoms. Our theoretical result shows that there are three magic wavelengths 615.9 nm, 641.2 nm and 678.8 nm for a linearly polarized optical lattice laser for barium.
Laser-Focused Atomic Deposition for Nanascale Grating
MA Yan**, LI Tong-Bao, WU Wen, XIAO Yi-Li, ZHANG Ping-Ping, GONG Wei-Gang
Chin. Phys. Lett. 2011, 28 (7): 073202 .   DOI: 10.1088/0256-307X/28/7/073202
Abstract   PDF(pc) (1226KB) ( 411 )
Laser-focused atomic deposition is a technique with which nearly resonant light is used to pattern an atom beam. To solve the problem that the result of laser-cooled atoms cannot be monitored during the 30-min depositing time, we present a three-hole mechanically precollimated aperture apparatus. A 425 nm laser light standing wave is used to focus a beam of chromium atoms to fabricate the nanoscale grating. The period of the grating is 213±0.1 nm, the height is 4 nm and the full width at half miximum is 64±6 nm.
Analytical Research on Rotation-Vibration Multiphoton Absorption of Diatomic Molecules in Infrared Laser Fields
FENG Hai-Ran**, CHENG Jie, YUE Xian-Fang, ZHENG Yu-Jun, DING Shi-Liang
Chin. Phys. Lett. 2011, 28 (7): 073301 .   DOI: 10.1088/0256-307X/28/7/073301
Abstract   PDF(pc) (908KB) ( 402 )
The multiphoton rotation-vibration energy absorption of diatomic molecules in infrared laser fields is analytically studied using the algebraic approach. The analytical expression of the rotation-vibration transition probability is given. The long-time average absorbed energy spectra and the average number of photons absorbed by the molecule are discussed. The results show that both molecular orientation and molecular anharmonicity are important factors in the rotation-vibration multiphoton absorption.
Water Vapor Interference Correction in a Non Dispersive Infrared Multi-Gas Analyzer
SUN You-Wen, LIU Wen-Qing**, ZENG Yi, WANG Shi-Mei, HUANG Shu-Hua, XIE Pin-Hua, YU Xiao-Man
Chin. Phys. Lett. 2011, 28 (7): 073302 .   DOI: 10.1088/0256-307X/28/7/073302
Abstract   PDF(pc) (1072KB) ( 647 )
We demonstrate an effective method to eliminate the interfering effect of water vapor in a non-dispersive infrared multi-gas analyzer. The response coefficients of water vapor at each filter channel are measured from the humidity of the ambient air. Based on the proposed method, the water vapor interference is corrected with the measured response coefficients. By deducting the absorbance of each filter channel related to water vapor, the measuring precision of the analyzer is improved significantly and the concentration retrieval correlation accuracy of each target gas is more than 99%.
Integral and Momentum Cross Sections for Electron Elastic and Vibrational Excitation Scattering with Nitrogen in the Energy Range 5–30eV
ZENG Yang-Yang, FENG Hao**, SUN Wei-Guo, **
Chin. Phys. Lett. 2011, 28 (7): 073401 .   DOI: 10.1088/0256-307X/28/7/073401
Abstract   PDF(pc) (521KB) ( 348 )
Integral and momentum transfer cross sections are calculated in the energy range from 5 to 30 eV and compared with other calculated and measured data. The overall agreement between our present results and various theoretical and experimental results are obtained. The present results are obtained by solving integrodifferential body-frame vibrational close-coupling equations. Distributed spherical Gaussian correlation-polarization model potentials with high-order terms and exact exchange effects in a single-configuration Slater determinant are used. The analytic Born completion method is also used to calculate high-order scattering matrix elements.
An Optimum Method for a Grooved 2D Planar Ion Trap Design
JI Wei-Bang, WAN Jin-Yin, CHENG Hua-Dong, LIU Liang**
Chin. Phys. Lett. 2011, 28 (7): 073701 .   DOI: 10.1088/0256-307X/28/7/073701
Abstract   PDF(pc) (505KB) ( 448 )
We investigate an effective grooved 2D ion chip design and optimize the ratio between the size of the rf electrodes and the groove. We calculate the optimal size of the groove using the analytical model, which was introduced by House, and the optimum result is obtained. We also obtain the simulated scattering points with the finite element analysis method. The analytical curve and simulated scattering points are coincident with each other. It is shown that this analytical model also fits for the grooved planar ion chip. Thus the optimum grooved 2D planar ion chip design could be obtained. It is effective for scalable quantum information processing.
An Approximate Analytical Propagation Formula for Gaussian Beams through a Cat-Eye Optical Lens under Large Incidence Angle Condition
ZHAO Yan-Zhong**, SUN Hua-Yan, ZHENG Yong-Hui
Chin. Phys. Lett. 2011, 28 (7): 074101 .   DOI: 10.1088/0256-307X/28/7/074101
Abstract   PDF(pc) (962KB) ( 720 )
Based on the generalized diffraction integral formula and the idea that the angle misalignment of the cat-eye optical lens can be transformed into the displacement misalignment, an approximate analytical propagation formula for Gaussian beams through a cat-eye optical lens under large incidence angle condition is derived. Numerical results show that the diffraction effect of the apertures of the cat-eye optical lens becomes stronger along with the increase in incidence angle. The results are also compared with those from using an angular spectrum diffraction integral and experiment to illustrate the applicability and validity of our theoretical formula. It is shown that the approximate extent is good enough for the application of a cat-eye optical lens with a radius of 20 mm and a propagation distance of 100 m, and the approximate extent becomes better along with the increase in the radius of the cat-eye optical lens and the propagation distance.
An All-Fiber Gas Raman Light Source Based on a Hydrogen-Filled Hollow-Core Photonic Crystal Fiber Pumped with a Q-Switched Fiber Laser
CHEN Xiao-Dong, , MAO Qing-He**, SUN Qing, ZHAO Jia-Sheng, LI Pan, FENG Su-Juan
Chin. Phys. Lett. 2011, 28 (7): 074201 .   DOI: 10.1088/0256-307X/28/7/074201
Abstract   PDF(pc) (2695KB) ( 483 )
A gas Raman light source based on a H2−filled hollow-core photonic-crystal-fiber cell with a Q-switched fiber laser followed by a fiber amplifier as the Raman pump source is demonstrated. The Stokes frequency-shift lasing line is observed at 1135.7 nm with the Q-switched pump pulses at 1064.7 nm. Our experimental results show that the generated Stokes pulse is much narrower than the pump pulse, and the generated Stokes pulse duration is increased with the single pulse energy for the same duration pump pulses. For the 125 ns pump pulses with a repetition rate of 5 kHz, the Raman threshold pump energy and the conversion efficiency at the Raman threshold are 2.13 µJ and 9.82%. Moreover, by choosing narrower pump pulses, the Raman threshold pump energy may be reduced and the conversion efficiency may be improved.
A Compact and Highly Efficient Silicon-Based Asymmetric Mach–Zehnder Modulator with Broadband Spectral Operation
ZHOU Liang, LI Zhi-Yong**, XIAO Xi, XU Hai-Hua, FAN Zhong-Chao, HAN Wei-Hua, YU Yu-De, YU Jin-Zhong
Chin. Phys. Lett. 2011, 28 (7): 074202 .   DOI: 10.1088/0256-307X/28/7/074202
Abstract   PDF(pc) (1246KB) ( 467 )
An asymmetric Mach–Zehnder electro-optic modulator is demonstrated by using a silicon-based p-i-n diode embedded in compact 200 µm long phase shifters. The measured figure of merit VπL=0.23 Vmm shows highly efficient modulation by the device, and an open eye−diagram at 3.2 Gbit/s confirmed its fast electro-optic response. Integrated with the grating coupler, the device exhibits a broad operational wavelength range of 70 nm with a uniform 18 dB extinction ratio covering the C−band and part L-band of optical communication.
Room-Temperature Continuous-Wave Operation of a Tunable External Cavity Quantum Cascade Laser
ZHANG Jin-Chuan, , WANG Li-Jun**, LIU Wan-Feng, LIU Feng-Qi, YIN Wen, LIU Jun-Qi, LI Lu, WANG Zhan-Guo
Chin. Phys. Lett. 2011, 28 (7): 074203 .   DOI: 10.1088/0256-307X/28/7/074203
Abstract   PDF(pc) (1179KB) ( 788 )
A room-temperature cw operation of a tunable external cavity (EC) quantum cascade laser (QCL) at an emitting wavelength of 4.6 µm is presented. Strain−compensation combined with two-phonon resonance in an active region design promises low threshold current density. A very low threshold current density of 1.47 kA/cm2 for an EC−QCL operated in cw mode is realized. Single-mode cw operation with a side-mode suppression ratio of 20 dB and a wide tuning range of over 110 cm-1 are achieved. Moreover, an even wider tuning range of over 135 cm−1 is obtained in pulsed mode at room temperature.
An Optical 2×4 90° Hybrid Based on a Birefringent Crystal for a Coherent Receiver in a Free-Space Optical Communication System
HOU Pei-Pei, ZHI Ya-Nan**, ZHOU Yu, SUN Jian-Feng, LIU Li-Ren
Chin. Phys. Lett. 2011, 28 (7): 074204 .   DOI: 10.1088/0256-307X/28/7/074204
Abstract   PDF(pc) (767KB) ( 794 )
The design and fabrication of an optical 2×4 90° hybrid based on birefringent crystals for a coherent receiver in a free−space optical communication system are presented. For the quadrature receiver, two pairs of 180° phase−shift outputs are obtained and one pair has a phase difference of 90° with respect to the other. The 90° hybrid comprises two pairs of stacked birefringent plates, a phase retardation plate and an analyser birefringent plate. The testing results measured by the heterodyne method verify that the 2×4 optical 90° hybrid can work correctly and effectively. The phase compensation and further optimization schemes are also proposed.
Laser Cleaning Techniques for Removing Surface Particulate Contaminants on Sol-Gel SiO2 Films
ZHANG Chun-Lai, LI Xi-Bin, WANG Zhi-Guo**, LIU Chun-Ming, XIANG Xia, LV Hai-Bing, YUAN Xiao-Dong, ZU Xiao-Tao
Chin. Phys. Lett. 2011, 28 (7): 074205 .   DOI: 10.1088/0256-307X/28/7/074205
Abstract   PDF(pc) (1230KB) ( 623 )
Dry laser cleaning (DLC) and laser shockwave cleaning (LSC) are used to remove the particulate contamination from SiO2 sol−gel optical films. The results show that the LSC with a shockwave initiated by plasma formation under a focused laser beam pulse offers much better efficiency than DLC. Silica particles up to 10 µm on SiO2 films can be removed without substrate damage at a gap distance of 0.5 mm, and a more uniform surface microstructure can be obtained after LSC. Furthermore, it is demonstrated that the transmittance of contaminated SiO2 films can be restored to the as-deposited value after the LSC on dispersed-particle zones. LSC has potential applications in engineering-oriented large components.
Complex Spectra Structure of an Attosecond Pulse Train Driven by Sub-5-fs Laser Pulses
YUN Chen-Xia, TENG Hao**, ZHANG Wei, WANG Li-Feng, ZHAN Min-Jie, HE Xin-Kui, WANG Bing-Bing, WEI Zhi-Yi**
Chin. Phys. Lett. 2011, 28 (7): 074206 .   DOI: 10.1088/0256-307X/28/7/074206
Abstract   PDF(pc) (556KB) ( 393 )
We present the observation of the additional spectral components between the odd order harmonics in the harmonic spectrum generated from argon gas driven by sub-5-fs laser pulses. The theoretical analysis shows that the asymmetric laser field in both spatial and temporal domains leads to this complicated spectrum structure of high order harmonics.
A Special Sampling Structure with an Arbitrary Equivalent-Phase-Shift for Semiconductor Lasers and Multiwavelength Laser Arrays
ZHOU Ya-Ting, **, SHI Yue-Chun, LI Si-Min, LIU Sheng-Chun, CHEN Xiang-Fei**
Chin. Phys. Lett. 2011, 28 (7): 074207 .   DOI: 10.1088/0256-307X/28/7/074207
Abstract   PDF(pc) (816KB) ( 462 )
A method used to introduce an arbitrary equivalent-phase-shift (EPS) into an asymmetric sampled Bragg grating (SBG) is reported. Under the same structural parameters except for the sampling pattern, the asymmetric SBG offers better performance than that of a normal SBG structure for keeping single-longitudinal-mode (SLM) operation. This is because the proposed sampling pattern can suppress the 0th-order light resonance due to the mismatch between the two different grating sections along the whole SBG. This method can be used to design and fabricate semiconductor lasers and multiwavelength laser arrays (MLAs) with the required EPS at high yield and low cost.
High-Efficiency Supercontinuum Generation at 12.8W in an All-Fiber Device
WANG Yan-Bin**, HOU Jing**, CHEN Zi-Lun, CHEN Sheng-Ping, SONG Rui, LI Ying, YANG Wei-Qiang, LU Qi-Sheng
Chin. Phys. Lett. 2011, 28 (7): 074208 .   DOI: 10.1088/0256-307X/28/7/074208
Abstract   PDF(pc) (995KB) ( 417 )
We report 12.8 W supercontinuum generation with a high optical-to-optical conversion efficiency of up to 85% in an all-fiber device. This is achieved by using an all-fiber picosecond master oscillator power amplifier laser, which has an output pigtail double clad fiber, to pump a 3-m photonic crystal fiber with the core at one end enlarged by adiabatically collapsing two inner layers of air holes while keeping other holes open. Our experimental results show that the short-wavelength generation is due to dispersive wave trapping by redshifted solitons.
Voltage-Controlled Scattering of Single Photons in a One-Dimensional Waveguide
LUO Ya-Qin**, SONG Yan-Yan, GU Ling-Ming, LANG Jia-Hong, MA Xiao-San
Chin. Phys. Lett. 2011, 28 (7): 074209 .   DOI: 10.1088/0256-307X/28/7/074209
Abstract   PDF(pc) (1016KB) ( 539 )
We investigate theoretically the voltage-controlled single-photon transport properties in a one-dimensional waveguide. The transmission and reflection amplitudes are obtained by a full quantum-mechanical approach. It is revealed that one can control the single photon transmitted or reflected by adjusting the bias voltage. This scheme may have applications in the design of optoelectronic devices.
Acousto-Optic Q-Switched Operation Ho:YAP Laser Pumped by a Tm-Doped Fiber Laser
ZHOU Ren-Lai**, JU You-Lun, WANG Wei, ZHU Guo-Li, WANG Yue-Zhu
Chin. Phys. Lett. 2011, 28 (7): 074210 .   DOI: 10.1088/0256-307X/28/7/074210
Abstract   PDF(pc) (1514KB) ( 449 )
We report on the acousto-optic Q-switched operation of a Ho:YAP laser double-passed pumped by an all-fiber Tm-doped fiber laser. The output characteristics of the Ho:YAP laser are studied at pulse repetition frequencies of 1, 2, 5 and 10 kHz. The shortest pulse width, the maximum pulse energy and the highest peak power are measured to be 17 ns, 1.71 mJ and 71.25 kW, respectively. The output wavelength is centered at 2115.96 nm with a bandwidth of about 1.5 nm. The beam quality factor M2=2.41±0.03 at the output power of 3.54 W was measured by using the traveling knife-edge method.
Noise Suppression of a Single Frequency Fiber Laser
LIU Kui, CUI Shu-Zhen, ZHANG Hai-Long, ZHANG Jun-Xiang, GAO Jiang-Rui**
Chin. Phys. Lett. 2011, 28 (7): 074211 .   DOI: 10.1088/0256-307X/28/7/074211
Abstract   PDF(pc) (809KB) ( 744 )
We present an experimental demonstration of fiber laser noise suppression by the mode cleaner. The intensity noise of a single frequency fiber laser is suppressed near the shot noise limit after a sideband frequency of 3 MHz. Two series mode cleaners are used to improve the noise suppression. The noise reduction is over 27 dB at 3 MHz.
Spectrum Analysis of a Pulsed Photon Source Generated from Periodically Poled Lithium Niobate
FANG Bin, LIU Bi-Heng, HUANG Yun-Feng**, SHI Bao-Sen, GUO Guang-Can
Chin. Phys. Lett. 2011, 28 (7): 074212 .   DOI: 10.1088/0256-307X/28/7/074212
Abstract   PDF(pc) (1927KB) ( 481 )
We present a theoretical and experimental study on the bandwidth of parametric down-converted photons generated from periodically poled lithium niobate (PPLN) crystal pumped by a pulsed laser. By comparison of crystals with different lengths and pump beams of different bandwidths, we demonstrate that the bandwidth of down-converted photons will increase for a broader bandwidth of pump pulse and decrease for a longer crystal, but the influence of crystal length will become weaker along with increase of both crystal length and pump pulse bandwidth. Especially under the conditions of our experiment, the bandwidth almost remains unchanged for longer crystals when pumped by a femtosecond laser. This may be helpful for schemes in which pulsed lasers are used to pump PPLN crystals.
Dipole Solitons in Nonlinear Media with an Exponential-Decay Nonlocal Response
YANG Zhen-Jun, MA Xue-Kai, ZHENG Yi-Zhou, GAO Xing-Hui, LU Da-Quan, HU Wei**
Chin. Phys. Lett. 2011, 28 (7): 074213 .   DOI: 10.1088/0256-307X/28/7/074213
Abstract   PDF(pc) (791KB) ( 470 )
By applying the variational approach, the analytical expression of dipole solitons is obtained in nonlinear media with an exponential-decay nonlocal response. The relations of the soliton power versus the propagation constant and the soliton width are given. Some numerical simulations are carried out. The results show that the analytical expression is in excellent agreement with the numerical results for the strongly nonlocal case.
Narrowband Biphoton Generation with Four-Wave Mixing in a Far-Detuning Three-Level System
CHEN Peng, ZHOU Shu-Yu, XU Zhen, DUAN Ya-Fan, CUI Guo-Dong, HONG Tao, WANG Yu-Zhu**
Chin. Phys. Lett. 2011, 28 (7): 074214 .   DOI: 10.1088/0256-307X/28/7/074214
Abstract   PDF(pc) (638KB) ( 488 )
Non-classical paired photons are generated by a four-wave mixing process in a far-detuning three-level system with cold atoms. A violation of the Cauchy–Schwartz inequality of a factor of 310 is observed. This phenomenon shows that paired photons have a non-classical correlation. The experimental results are compared with theoretical results obtained using perturbation theory. The oscillation frequencies of the two-photon intensity correlation functions are in reasonable agreement with the effective Rabi frequencies of the coupling laser. However, we find that the dephasing rates (or decay rates) observed are far larger than the theoretical values.
Two Schemes for Generating Efficient Terahertz Waves in Nonlinear Optical Crystals with a Mid-Infrared CO2 Laser
RAO Zhi-Ming, WANG Xin-Bing**, LU Yan-Zhao, ZUO Du-Luo, WU Tao
Chin. Phys. Lett. 2011, 28 (7): 074215 .   DOI: 10.1088/0256-307X/28/7/074215
Abstract   PDF(pc) (624KB) ( 454 )
Terahertz wave generation is explored on the basis of difference frequency generation in nonlinear optical crystals with a mid-infrared CO2 laser. The phase−matching angle and the grating period of periodically inverted GaAs in the 100–1000 µm (0.3–3 THz) range are also investigated on the basis of the surface-emitted difference frequency generation. It is found that two schemes of phase-matching-applied collinear phase matching and phase-matching-applied non-collinear phase matching are efficient to obtain THz waves.
Photocurrent Effect in Reverse-Biased p-n Silicon Waveguides in Communication Bands
ZHAO Yong, XU Chao, WANG Wan-Jun, ZHOU Qiang, HAO Yin-Lei, YANG Jian-Yi, WANG Ming-Hua, JIANG Xiao-Qing**
Chin. Phys. Lett. 2011, 28 (7): 074216 .   DOI: 10.1088/0256-307X/28/7/074216
Abstract   PDF(pc) (799KB) ( 502 )
The photocurrent effect in reverse biased p-n silicon waveguides at wavelength 1550 nm is experimentally investigated. The photocurrent, which is mainly related to surface-state absorption, defect-state absorption and/or two-photon absorption, is more than 0.08 µA/mm under 8 V reverse biasing and 0.75 mW irradiation. The responsivity of a silicon waveguide with length of 4500 µm achieves 0.5 mA/W. Moreover, the enhancement of the photocurrent effect under the electric field is discussed.
Nonadiabatic Effects of Atomic Coherence on Laser Intensity Fluctuations in Electromagnetically Induced Transparency
XU Qing, HU Xiang-Ming**
Chin. Phys. Lett. 2011, 28 (7): 074217 .   DOI: 10.1088/0256-307X/28/7/074217
Abstract   PDF(pc) (955KB) ( 345 )
In an electromagnetically induced transparency system, the atoms have long-lived coherence compared to the cavity lifetime and interact nonadiabatically with the laser fields. We show that the high frequency fluctuations of both the intensities and the intensity difference can be squeezed below the shot noise limit due to the nonadiabatic effects. This noise squeezing can be used to enhance the precision in the short time measurements based on the intensities or the intensity difference.
Broadband Response of Second Harmonic Generation in a Two-Dimensional Quasi-Random Quasi-Phase-Matching Structure
MA Dong-Li, REN Ming-Liang, LI Zhi-Yuan**
Chin. Phys. Lett. 2011, 28 (7): 074218 .   DOI: 10.1088/0256-307X/28/7/074218
Abstract   PDF(pc) (1656KB) ( 352 )
The broadband response of second harmonic generation (SHG) is experimentally observed in a two-dimensional (2D) quasi-random quasi-phase-matching (QPM) structure. A nonlinear conversion efficiency of more than 50% is obtained. Due to the line-type distribution of the reciprocal vector, the second harmonic wave (SHW) covering a broad frequency band is efficiently radiated in the shape of one single spot or three spots instead of a stripe. This is believed to be favorable for its practical application and paves the way for the use of ultrahigh-bandwidth light sources and devices in modern optical technologies.
Tolerance on Tilt Error for the Incoherent Combination of Fiber Lasers in a Real Environment
TAO Ru-Mao, SI Lei, MA Yan-Xing, ZOU Yong-Chao, ZHOU Pu*
Chin. Phys. Lett. 2011, 28 (7): 074219 .   DOI: 10.1088/0256-307X/28/7/074219
Abstract   PDF(pc) (632KB) ( 448 )
We present a detailed study on the tolerance on tilt error for the incoherent combination of fiber lasers propagating in a real environment and analyze the influence of fill factor, mechanical jitter and atmospheric turbulence on tilt tolerance. Numerical results show that the tolerance on tilt error is independent of the fill factor and decreases with an increase in mechanical jitter or turbulence intensity.
Kerr-Lens Self-Mode-Locked Laser Characteristics of Yb:Lu2SiO5 Crystal
LIU Jie**, YANG Ji-Min, WANG Wei-Wei, ZHENG Li-He, SU Liang-Bi, XU Jun
Chin. Phys. Lett. 2011, 28 (7): 074220 .   DOI: 10.1088/0256-307X/28/7/074220
Abstract   PDF(pc) (735KB) ( 503 )
A diode-pumped Kerr-lens self-mode-locked laser is achieved by using Yb: Lu2SiO5 (Yb:LSO) crystal without additional components. Under the incident pump power of 14.44 W, a self-mode-locked output power of 2.98 W is obtained in the five-mirror cavity, corresponding to an optical-optical efficiency of 20.6%. Pulses as short as 8.2 ps are realized at 1059 nm, with the corresponding pulse energy and peak power of 28.9 nJ and 3.5 kW, respectively. A pair of SF10 prisms are inserted into the laser cavity to compensate for the group velocity dispersion. The pulse width is compressed to 2.2 ps with an average output power of 1.25 W.
Time-Domain Second-Harmonic Generation of Primary Lamb-Wave Propagation in an Elastic Plate
DENG Ming-Xi**, XIANG Yan-Xun, LIU Liang-Bing
Chin. Phys. Lett. 2011, 28 (7): 074301 .   DOI: 10.1088/0256-307X/28/7/074301
Abstract   PDF(pc) (2538KB) ( 454 )
We present an experimental observation of the generation of the time-domain second harmonic by propagation of the primary Lamb-wave tone-burst. For a case where the phase velocity matching between the primary and the double frequency Lamb waves is satisfied but the group velocity matching between them is not, our observation clearly shows that the duration of the time-domain second-harmonic tone-burst, as well as its integrated amplitude, increases with the increasing propagation distance. This experimental result is consistent with the theoretical prediction and demonstrates that group velocity matching is not absolutely necessary for the generation of the cumulative time-domain second harmonic by primary Lamb-wave propagation.
Boundary Layer Flow and Heat Transfer over an Exponentially Shrinking Sheet
Krishnendu Bhattacharyya
Chin. Phys. Lett. 2011, 28 (7): 074701 .   DOI: 10.1088/0256-307X/28/7/074701
Abstract   PDF(pc) (555KB) ( 2835 )
An analysis is made to study boundary layer flow and heat transfer over an exponentially shrinking sheet. Using similarity transformations in exponential form, the governing boundary layer equations are transformed into self-similar nonlinear ordinary differential equations, which are then solved numerically using a very efficient shooting method. The analysis reveals the conditions for the existence of steady boundary layer flow due to exponential shrinking of the sheet and it is found that when the mass suction parameter exceeds a certain critical value, steady flow is possible. The dual solutions for velocity and temperature distributions are obtained. With increasing values of the mass suction parameter, the skin friction coefficient increases for the first solution and decreases for the second solution.
Simultaneous Effects of MHD and Thermal Radiation on the Mixed Convection Stagnation-Point Flow of a Power-Law Fluid
T. Hayat, M. Mustafa**, S. Obaidat
Chin. Phys. Lett. 2011, 28 (7): 074702 .   DOI: 10.1088/0256-307X/28/7/074702
Abstract   PDF(pc) (604KB) ( 518 )
Magnetohydrodynamic (MHD) mixed convection stagnation-point flow and heat transfer of power-law fluids towards a stretching surface is investigated. The homotopy analysis method (HAM) is used in finding the series solution for a nonlinear problem. Closed form solutions for velocity and temperature fields are presented in the limiting cases. Graphical results are shown. It is found that velocity and temperature are decreasing functions of power law index. Numerical computations for shear stress coefficient and local Nusselt number are reported. The present results are also compared with the existing numerical solution in a limiting sense.
Emission Lines of Boron, Carbon, Oxygen and Iron in Tokamak Plasma
DI Long, SHI Jian-Rong, WANG Shou-Jun, DONG Quan-Li, ZHAO Jing, LI Yu-Tong, FU Jia, WANG Fu-Di, SHI Yue-Jiang, WAN Bao-Nian, ZHAO Gang**, ZHANG Jie,
Chin. Phys. Lett. 2011, 28 (7): 075201 .   DOI: 10.1088/0256-307X/28/7/075201
Abstract   PDF(pc) (1759KB) ( 1057 )
The emission lines of B, C, O and Fe in tokamak plasma are reported. The spectra are compared with those calculated by the CHIANTI code, which is based on the collisional-radiative models with a large amount of accurate atomic data. General agreement is obtained between the results of experiment and computation. Most of the lines in the spectra are identified, and the relative number density ratios of B, C, O and Fe are determined. It is found that the processes of line formation in our experiment are similar to those in the stellar coronae. The line-averaged electron density of the tokamak plasma is measured by the HCN laser, indicating a good agreement with the theoretical prediction by the density-dependent line ratio of Fe XXI.
Nonlinear Plasma Dynamics in Electron Heating of Asymmetric Capacitive Discharges with a Fluid Sheath Model
DAI Zhong-Ling, WANG You-Nian**
Chin. Phys. Lett. 2011, 28 (7): 075202 .   DOI: 10.1088/0256-307X/28/7/075202
Abstract   PDF(pc) (745KB) ( 413 )
A fluid radio-frequency (rf) sheath model coupled to an equivalent circuit method is adopted to describe the nonlinear series resonance effects due to nonlinear interaction of plasma bulk and sheath in asymmetric capacitive discharges. With the fluid sheath model, we can determine self-consistently the relationship between the instantaneous potential drop across the rf sheath and the instantaneous sheath thickness. The numerical results demonstrate that the self-excitation of the plasma series resonance significantly enhances both ohmic heating and stochastic heating. Also, we observe that the effects of nonlinear series resonance increases the total power dissipation by factors of 2–5 for low pressure capacitive plasmas. Furthermore, we find that the largest harmonic is about 13 for the plasma current.
Dust Acoustic Rotation Modes in Magnetized Complex Plasmas
B. Farokhi, ** F. Amini, M. Eghbali
Chin. Phys. Lett. 2011, 28 (7): 075203 .   DOI: 52.27.Lw, 52.35.-g, 52.35.Lv
Abstract   PDF(pc) (1307KB) ( 366 )
A theoretical investigation is made of the low-frequency electrostatic modes in a cylindrical system and in magnetized dusty plasmas. The linear dispersion relation of the rotational modes is derived. We discuss the difference between the magnetized and unmagnetized modes. When the dusty plasma is confined in a finite region, the void behavior is observed at high speed rotation. Vivid structures of different mode number solutions are illustrated.
Role of Jeans Instability in Multi-Component Quantum Plasmas in the Presence of Fermi Pressure
S. Ali Shan, **, A. Mushtaq
Chin. Phys. Lett. 2011, 28 (7): 075204 .   DOI: 10.1088/0256-307X/28/7/075204
Abstract   PDF(pc) (459KB) ( 473 )
The quantum hydrodynamic model is employed to investigate the effects of gravitational potential on multi-component dusty plasmas. The effects of Fermi temperature ratios of ions to electrons (TFi/TFe) and positrons to electrons (TFp/TFe) have been calculated and presented graphically. It is observed that an increase in the Fermi temperature ratios of ions to electrons and positrons to electrons stabilizes the Jeans instability as the mode phase speed increases with these ratios. In the absence of the statistical effects due to Fermi pressure, the dispersion is weak. The stability criteria are calculated for each case separately.
A Modified Third-Order Semi-Discrete Central-Upwind Scheme for MHD Simulation
JI Zhen, **, ZHOU Yu-Fen, HOU Tian-Xiang
Chin. Phys. Lett. 2011, 28 (7): 075205 .   DOI: 10.1088/0256-307X/28/7/075205
Abstract   PDF(pc) (634KB) ( 480 )
The Kurganov scheme is a third-order semi-discrete central numerical algorithm. The high solution of the scheme is ensured by a piecewise quadratic non-oscillatory reconstruction which consists of the cell-average data. We employ a modification of the smooth limiter of reconstruction in a simple way. The modified limiter possesses rigorous positivity and the reformulation does not change the non-oscillatory property of reconstruction. In order to explore the potential capability of application of the modified Kurganov scheme to magnetohydrodynamics (MHD) and resistive magnetohydrodynamics (RMHD) equations, two numerical problems are simulated in two dimensions (2D). These numerical simulations demonstrate that the modified Kurganov scheme keeps high precision and has stable reliable results for MHD and RMHD applications.
Strong Coupling between Propagating and Localized Surface Plasmons in Plasmonic Cavities
LI Ming-Zhu, AN Zheng-Hua**, ZHOU Lei, MAO Fei-Long, WANG Heng-Liang
Chin. Phys. Lett. 2011, 28 (7): 075206 .   DOI: 10.1088/0256-307X/28/7/075206
Abstract   PDF(pc) (5464KB) ( 638 )
Au/GaAs/Au plasmonic cavities with a periodic hole array perforated in the top Au layer are studied. Propagating surface plasmons (PSPs) and localized surface plasmons (LSPs) associated with the rectangle hole shapes are found to interact and highly hybridize in the cavity structure, which eventually determines the resonance properties of the cavities. An anticrossing of resonance frequencies in the reflection spectra is observed when the frequency of PSPs approaches that of LSPs, demonstrating the strong coupling between SPPs and LSPs in the tri-layer plasmonic cavities. This work may provide hints to the plasmonic cavity design for light-harvesting optoelectronic applications.
High Pressure X-Ray Diffraction Study of a Grossular–Andradite Solid Solution and the Bulk Modulus Variation along this Solid Solution
FAN Da-Wei**, WEI Shu-Yi, LIU Jing, LI Yan-Chun, XIE Hong-Sen
Chin. Phys. Lett. 2011, 28 (7): 076101 .   DOI: 10.1088/0256-307X/28/7/076101
Abstract   PDF(pc) (883KB) ( 423 )
In-situ angle-dispersive x-ray diffraction measurements on three samples of Gr14An84, Gr34An64 and Gr63An34 were performed by using a diamond anvil cell instrument with synchrotron radiation at the Beijing Synchrotron Radiation Facility at up to 13.7 GPa. A least−square fit of the pressure-volume to the Birch–Murnaghan equation of state, when fixed K'0=4.0 yields bulk modulus values of K0=166±2, 168±3, 173±2 GPa for Gr14An84, Gr34An64 and Gr63An34, respectively. The bulk modulus increases from 166±2 GPa for Gr14An84 and to 173±2 GPa for Gr63An34 with the increasing An content. Furthermore, by linear interpolation, the bulk modulus of the Gr−An binary system as a function of An content can be expressed as K0(GPa) =176.9(9)−0.12(1)XAn (R2=0.987).
Theoretical Hardness of Zr3N4 Films
GAO Fa-Ming
Chin. Phys. Lett. 2011, 28 (7): 076102 .   DOI: 10.1088/0256-307X/28/7/076102
Abstract   PDF(pc) (510KB) ( 435 )
The structures, energetics and properties for orthohombic Zr3N4 and cubic Zr3N4 are calculated by first−principles calculations. The agreement between the predicted properties with available experimental data is excellent. The cubic phase has a smaller volume (by 11.2%) and a slightly higher total energy (by 0.3 eV/pair), in comparison to the orthohombic phase. We elucidate the effects of stress on hardness of Zr3N4 films. The results show that the hardness of c−Zr3N4 increases up to 23% as the stress increases to 15 GPa.
High-Order Elastic Constants and Anharmonic Properties of NaBH4: First-Principles Calculations
ZHANG Xiao-Dong, JIANG Zhen-Yi**, ZHOU Bo, HOU Zhu-Feng, HOU Yu-Qing
Chin. Phys. Lett. 2011, 28 (7): 076201 .   DOI: 10.1088/0256-307X/28/7/076201
Abstract   PDF(pc) (579KB) ( 638 )
We present theoretical studies for second- and third-order elastic constants in NaBH4 based on ab initio calculations. Our calculated second−order elastic constants agree well with available experimental results. The anharmonic properties of NaBH4 , such as pressure derivative of the second−order elastic constants and the Grüneisen constants for long-wavelength acoustic mode γ(q,j), are characterized using the third-order elastic constants.
Anisotropic Diffusion Evolution of Vacancies Created by Oxygen Etching on a Si Surface
WANG Shu-Hua, CAI Qun**
Chin. Phys. Lett. 2011, 28 (7): 076801 .   DOI: 10.1088/0256-307X/28/7/076801
Abstract   PDF(pc) (1394KB) ( 396 )
We report the diffusion behavior of dimer vacancies on a Si(100)-(2×1) surface by using ultrahigh−vacuum scanning tunneling microscopy. The dimer vacancies are created by oxygen etching of Si atoms at elevated temperatures. By annealing the sample at 600–750°C, the dimer vacancies uniformly distribute on the terrace nucleate to form larger elongated voids of one atomic layer deep. The long axis of these voids is parallel to the Si dimer rows. During annealing, the surface morphology evolves in a way dominantly caused by the anisotropic diffusion of the dimer vacancies. A difference of diffusion barriers of 0.17±0.09 eV is obtained between the [110] and [110] directions.
Scanning Tunneling Spectroscopy of Metal Phthalocyanines on a Au(111) Surface with a Ni Tip
JIA Zhi-Chun, HU Zhen-Peng, ZHAO Ai-Di, LI Zhen-Yu, LI Bin**
Chin. Phys. Lett. 2011, 28 (7): 076802 .   DOI: 10.1088/0256-307X/28/7/076802
Abstract   PDF(pc) (2202KB) ( 827 )
Scanning tunneling spectroscopy of metal phthalocyanines (MPc) adsorbed on a Au(111) surface with a Ni(111) scanning tunneling microscopy tip is simulated on the basis of first-principles calculations and a modified Bardeen approximation. Local d orbital symmetry matching between the molecule and the Ni tip brings obvious negative differential resistance (NDR) phenomena, of which, bias voltage and resonant orbitals can be tuned sensitively by the central ion of the molecule. Different dependences of the NDR peak on the tip−molecule distance at two bias polarities and rectifying phenomena are also interpreted in terms of specific structures of 3d orbitals of the adsorbed MPc and Ni tip.
Growth of Graphene Nanoribbons and Carbon Onions from Polymer
GUO Xiao-Song, LU Bing-An, XIE Er-Qing**
Chin. Phys. Lett. 2011, 28 (7): 076803 .   DOI: 10.1088/0256-307X/28/7/076803
Abstract   PDF(pc) (2413KB) ( 620 )
Graphene nanoribbons and carbon onions are directly prepared by electron beam irradiation of polyacrylonitrile and expanded polystyrene nanofibers, respectively. By controlling the irradiation process in a high resolution transmission electron microscope, the number of layers of the graphene nanoribbons, as well as the dimension of the carbon onions, can be controlled. It is found that the initial diameter of the nanofiber has a strong effect on the final results. A mechanism is proposed to explain the transformation of polymer nanofibers to carbon nanostructures under electron beam irradiation. This supposes that the polymer nanofibers are first carbonized and then graphitized as a result of the high energy electrons. According to the mechanism, it is believed that all polymer nanofibers could be carbonized and then converted to graphene nanoribbons by proper electron beam irradiation.
Electronic Structure and Optical Properties of SrBi2A2O9(A=Nb,Ta)
ZHAO Na, WANG Yue-Hua**, ZHAO Xin-Yin, ZHANG Min, GONG Sai
Chin. Phys. Lett. 2011, 28 (7): 077101 .   DOI: 10.1088/0256-307X/28/7/077101
Abstract   PDF(pc) (1476KB) ( 619 )
The first-principles calculation is performed to investigate the energy band structures, density of states (DOS) and optical properties of SrBi2A2O9 (A=Nb,Ta), by using density functional theory (DFT) with the generalized gradient approximation (GGA). The results show that the band−gap of SrBi2Nb2O9 is smaller than that of SrBi2Ta2O9, and that there are strong hybridizations of A−O bands, which play very important roles in the electronic properties and optical responses of SrBi2A2O9. SrBi2Ta2O9 stimulates much higher photocatalytic activity than SrBi2Nb2O9, which is due to its suitable crystal structure.
Effects of an Intense Laser Field and Hydrostatic Pressure on the Intersubband Transitions and Binding Energy of Shallow Donor Impurities in a Quantum Well
U. Yesilgul**, F. Ungan, E. Kasapoglu, H. Sari, I. Sö, kmen
Chin. Phys. Lett. 2011, 28 (7): 077102 .   DOI: 10.1088/0256-307X/28/7/077102
Abstract   PDF(pc) (902KB) ( 400 )
We have calculated the intersubband transitions and the ground-state binding energies of a hydrogenic donor impurity in a quantum well in the presence of a high-frequency laser field and hydrostatic pressure. The calculations are performed within the effective mass approximation, using a variational method. We conclude that the laser field amplitude and the hydrostatic pressure provide an important effect on the electronic and optical properties of the quantum wells. According to the results obtained from the present work, it is deduced that (i) the binding energies of donor impurity decrease as the laser field increase, (ii) the binding energies of donor impurity increase as the hydrostatic pressure increase, (iii) the intersubband absorption coefficients shift toward lower energies as the hydrostatic pressure increases, (iv) the magnitude of absorption coefficients decrease and also shift toward higher energies as the laser field increase. It is hopeful that the obtained results will provide important improvements in device applications.
Zener Tunneling in One-Dimensional Organic Semiconductors at Finite Temperature
LIU Wen, CHENG Jie, ZHANG Ming-Hua, LIU De-Sheng, **
Chin. Phys. Lett. 2011, 28 (7): 077103 .   DOI: 10.1088/0256-307X/28/7/077103
Abstract   PDF(pc) (2480KB) ( 406 )
Zener tunneling at finite temperature in one-dimensional organic semiconductors under an external electric field is studied within the framework of a tight-binding model. The temperature effect is simulated by the introduction of random forces to lattice motion. It is found that the critical field strength of Zener tunneling decreases with the increasing temperature. Under sufficiently high electric field, dielectric breakdown occurs, which is characterized by the irreversibility of the energy gap.
CMOS Compatible Nonvolatile Memory Devices Based on SiO2/Cu/SiO2 Multilayer Films
WANG Yan, LIU Qi, LV Hang-Bing, LONG Shi-Bing, ZHANG Sen, LI Ying-Tao, LIAN Wen-Tai, YANG Jian-Hong**, LIU Ming
Chin. Phys. Lett. 2011, 28 (7): 077201 .   DOI: 10.1088/0256-307X/28/7/077201
Abstract   PDF(pc) (808KB) ( 578 )
We systematically investigate the resistive switching characteristics of SiO2 films with a Cu/SiO2/Cu/SiO2/Pt multilayer structure. The device exhibits good resistive switching performances, including a high ON/OFF resistance ratio (>103), good retention characteristic (>104s), satisfactory switching endurance (>200 cycles), a fast programming speed (<100 ns) and a high device yield (∼100%). Considering these results, SiO2-based memories have highly promising applications for nonvolatile memory devices.
Enhancement-Mode AlGaN/GaN High Electron Mobility Transistors Using a Nano-Channel Array Structure
LIU Sheng-Hou, CAI Yong**, GONG Ru-Min, WANG Jin-Yan, ZENG Chun-Hong, SHI Wen-Hua, FENG Zhi-Hong, WANG Jing-Jing, YIN Jia-Yun, Cheng P. Wen, QIN Hua, ZHANG Bao-Shun
Chin. Phys. Lett. 2011, 28 (7): 077202 .   DOI: 10.1088/0256-307X/28/7/077202
Abstract   PDF(pc) (945KB) ( 1029 )
A nano-channel array (NCA) structure is applied to realize enhancement-mode (E-mode) AlGaN/GaN high-electron mobility transistors (HEMTs). The fabricated NCA-HEMT, consisting of 1000 channels connected in parallel with a channel width of 64 nm, shows a threshold voltage of 0.15 V and a subthreshold slope of 78 mV/dec, compared to 3.92 V and 99 mV/dec for a conventional HEMT (C-HEMT), respectively. Both the NCA-HEMT and C-HEMT show similar gate leakage current, indicating no significant degradation in gate leakage characteristics for the NCA-HEMT. The surrounding-field effect and relieved polarization contribute to the very large positive threshold voltage shift, while the work function difference makes it positive.
Crystalline, Optical and Electrical Properties of NiZnO Thin Films Fabricated by MOCVD
WANG Jin, WANG Hui, ZHAO Wang, MA Yan, LI Wan-Cheng, XIA Xiao-Chuan, SHI Zhi-Feng, ZHAO Long, ZHANG Bao-Lin, DONG Xin**, DU Guo-Tong
Chin. Phys. Lett. 2011, 28 (7): 077301 .   DOI: 10.1088/0256-307X/28/7/077301
Abstract   PDF(pc) (1083KB) ( 607 )
NiZnO thin films are grown on c-plane sapphire substrates by using a photo-assisted metal organic chemical vapor deposition (MOCVD) system. The effect of the Ni content on the crystalline, optical and electrical properties of the films are researched in detail. The NiZnO films could retain a basic wurtzite structure when the Ni content is less than 0.18. As Ni content increases, crystal quality degradation could be observed in the x-ray diffraction patterns and a clear red shift of the absorption edge can be observed in the transmittance spectrum. Furthermore, the donor defects in the NiZnO film can be compensated for effectively by increasing the Ni content. The change of Ni content has an important effect on the properties of NiZnO films.
Magnetostrictions and Magnetic Properties of Nd-Fe-B and SrFe12O19
CHEN Hai-Ying, ZHANG Yan, YANG Yun-Bo, CHEN Xue-Gang, LIU Shun-Quan, WANG Chang-Sheng, YANG Ying-Chang, YANG Jin-Bo, **
Chin. Phys. Lett. 2011, 28 (7): 077501 .   DOI: 10.1088/0256-307X/28/7/077501
Abstract   PDF(pc) (1376KB) ( 636 )
The magnetostrictions of polycrystalline Nd-Fe-B and Sr-ferrite at different temperatures are reinvestigated using a strain gauge rotating-sample method. It is found that the magnetostriction λs of Nd−Fe-B is +52×10−6, and that of Sr-ferrite is 25×10-6 under a magnetic field of 8 T at room temperature. The maximum energy product (BH)max of the Nd-Fe-B magnet is improved when the powders are magnetically aligned perpendicular to the pressing direction, whereas that of the Sr-ferrite magnet is better when the powders are aligned parallel to the pressing direction. These experimental results suggest that the magnetostriction can generate compressive strain anisotropy resulting from the inverse effect of the magnetostriction. Thus, the magnetization of materials with a negative coefficient of magnetostriction are easier to be aligned normal to the stress direction, while for the materials with a positive coefficient of magnetostriction, the magnetization is easier to be aligned along the stress direction. Therefore, the magnetostriction anisotropy can be used to improve the alignment of the magnetic powders as well as the performance of the magnets.
Peripheral Ferroelectric Domain Switching and Polarization Fatigue in Nonvolatile Memory Elements of Continuous Pt/SrBi2Ta2O9/Pt Thin-Film Capacitors
CHEN Min-Chuan, JIANG An-Quan**
Chin. Phys. Lett. 2011, 28 (7): 077701 .   DOI: 10.1088/0256-307X/28/7/077701
Abstract   PDF(pc) (972KB) ( 368 )
We verify the domain sideway motion around the peripheral regions of the crossed capacitors of top and bottom electrode bars without electrode coverage. To avoid the crosstalk problem between adjacent memory cells, the safe distance between adjacent elements of Pt/SrBi2Ta2O9/Pt thin−film capacitors is estimated to be 0.156 µm. Moreover, the fatigue of Pt/SrBi2Ta2O9/Pt thin-film capacitors is independent of the individual memory size due to the absence of etching damage.
Sol-Gel Template Synthesis and Photoluminescence Properties of (Pb0.5Sr0.5)TiO3 Nanotube Arrays
JIANG Yan-Ping, **, WANG Yu, CHAN Lai Wa Helen, TANG Xin-Gui, ZHOU Yi-Chun**
Chin. Phys. Lett. 2011, 28 (7): 077702 .   DOI: 10.1088/0256-307X/28/7/077702
Abstract   PDF(pc) (1126KB) ( 365 )
Lead strontium titanate (Pb0.5Sr0.5)TiO3 (PST) nanotube arrays are prepared by a sol-gel and spin-coating process using an anodic aluminium oxide template. The structure and morphology of the as-prepared sample are characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the as-prepared PST sample possesses a perovskite structure with a relatively uniform diameter of about 200 nm. Photoluminescence (PL) spectrum of the sample shows emission bands centered at about 2.87 eV at room temperature, which consists of three intense emission sub-bands at 3.02, 2.87 and 2.76 eV, respectively. The energy corresponding to the central PL peak is lower than the band-gap energy (3.2 eV) of PST bulk materials, which may originate from the size effect of the PST nanotube arrays. The multi-peaks in the PL spectrum may be attributed to the radiative recombination of trapped electrons and holes in tail and gap states induced by local defect and oxygen vacancies. The Raman scattering spectrum of the PST nanotube arrays, which are obviously broadened in comparison with the bulk materials, show that their phonon modes are in agreement with those allowed in the tetragonal phase.
Photo- and Electro-Luminescence at 1.54µm from Er3+ in SiC:Er2O3 Films and Structures
YIN Yang, RAN Guang-Zhao**, ZHANG Bin, QIN Guo-Gang**
Chin. Phys. Lett. 2011, 28 (7): 077801 .   DOI: 10.1088/0256-307X/28/7/077801
Abstract   PDF(pc) (756KB) ( 851 )
SiC:Er2O3 films with different ratios of SiC to SiC:Er2O3 are deposited on p−type Si substrates by the magnetron co-sputtering technique, which was fully compatible with current Si processing technologies. Intense room temperature 1.54 µm photoluminescence (PL) from Er3+ ions in the SiC:Er2O3 films is observed and the PL intensity at 1.54 µm is enhanced by about 40 times with increasing Er concentration in the films from 0.8 to 22 at.% under both direct and indirect excitations. The 1.54 µm electroluminescence from the structure of indium tin oxide (ITO)/n+ −Si/SiC:Er2O3/p−Si with suitable ratios of SiC to SiC:Er2O3 is measured under forward biases.
Bias Effects on the Growth of Helium-Containing Titanium Films
ZHANG Li-Ran, DENG Ai-Hong, **, YANG Dong-Xu, ZHOU Yu-Lu, HOU Qing, SHI Li-Qun, ZHONG Yu-Rong, WANG Bao-Yi
Chin. Phys. Lett. 2011, 28 (7): 077802 .   DOI: 10.1088/0256-307X/28/7/077802
Abstract   PDF(pc) (632KB) ( 344 )
Helium-containing titanium films were prepared on Si substrates with various biases applied by magnetron sputtering under stable He/Ar ambiance. Rutherford backscattering and elastic recoil detection analyses are used to measure the thickness of the He-Ti films and the helium depth profile, respectively. Experiments of x-ray diffraction and variable energy positron annihilation spectroscopy are carried out to investigate the microstructures of titanium films and the corresponding helium-related defects developed. The behavior of the implanted He, the microstructure of the He-Ti film and the formation of He-related defects all are affected by the substrate biases applied.
Infrared Luminescent Properties of a Pr-Doped KBr Submicron Rod
WEI Feng-Wei, ZHANG Xiao-Song**, LI Lan, XU Jian-Ping, ZHOU Yong-Liang, LIU Pei
Chin. Phys. Lett. 2011, 28 (7): 077803 .   DOI: 10.1088/0256-307X/28/7/077803
Abstract   PDF(pc) (1244KB) ( 442 )
KBr:Pr with a submicron rod structure is successfully synthesized by a solid-state reaction using absolute alcohol as the abrasive. X-ray diffraction, scanning electron microscopy, photoluminescence spectra and fluorescence decay curves are used to characterize the resulting materials. The influences of Pr3+ dopant concentration on the luminescence and lifetime are discussed. Furthermore, luminescent measurements show that KBr:Pr has a high emission intensity compared with other Pr-doped matrixes, which is related to the low phonon energy of KBr. The results suggest that the phonon energy of the host is important in determining the luminescent efficiency.
Crystal Growth in Al72.9Ge27.1 Alloy Melt under Acoustic Levitation Conditions
YAN Na, DAI Fu-Ping, WANG Wei-Li, WEI Bing-Bo**
Chin. Phys. Lett. 2011, 28 (7): 078101 .   DOI: 10.1088/0256-307X/28/7/078101
Abstract   PDF(pc) (2346KB) ( 420 )
The nonequilibrium solidification of liquid Al72.9Ge27.1 hypoeutectic alloy is accomplished by using single−axis acoustic levitation. A maximum undercooling of 112 K (0.16TL) is obtained for the alloy melt at a cooling rate of 50 K/s. The primary (Al) phase displays a morphological transition from coarse dendrite under a normal conditions to equiaxed grain under acoustic levitation. In the (Al)+(Ge) eutectic, the (Ge) phase exhibits a conspicuous branched growth morphology. Both the primary (Al) dendrites and (Al)+(Ge) eutectics are well refined and the solute content of the primary (Al) phase is extended under acoustic levitation. The calculated and experimental results indicate that the solute trapping effect becomes more intensive with the enhancement of bulk undercooling.
Fabrication of Hinged Mirrors Using a Strain-Driven Self-Assembly Method on a GaAs Substrate
ZHOU Yan, WANG Hai-Long**, MA Chuan-He, GONG Qian, FENG Song-Lin
Chin. Phys. Lett. 2011, 28 (7): 078102 .   DOI: 10.1088/0256-307X/28/7/078102
Abstract   PDF(pc) (763KB) ( 432 )
Hinged mirror arrays are widely utilized for display applications and optical communication. They can be fabricated by an self-assembly technique using the strain in lattice-mismatched epitaxial layers. A multilayer structure including a strain-compensated layer, a digital alloy sacrificial layer and a strain bilayer, is grown by molecular-beam epitaxy. Self-assembly hinged mirrors on a GaAs substrate have been successfully fabricated by photolithography and selective etching. The hinge fabrication method with a strain bilayer is simple and flexible. Structures formed by multiple hinged plates will enable the self-assembly of more complex three-dimensional microstructures.
A Facile Method for Synthesizing TiO2 Sea-Urchin-Like Structures and Their Applications in Solar Energy Harvesting
WANG Wen-Hui**, WANG Wen-Zhong, XU Hong-Xing
Chin. Phys. Lett. 2011, 28 (7): 078103 .   DOI: 10.1088/0256-307X/28/7/078103
Abstract   PDF(pc) (1312KB) ( 422 )
We present a new method to prepare TiO2 sea−urchin-like structures, which involves the initial formation of tubular nanostructures and subsequent self-assembly of the nanotubes into micrometer-scale sea-urchin-like structures. We also investigate the important role of alkali aqueous conditions in the preparation of TiO2 sea−urchin-like structures. This facile and cost-effective approach provides a new route for the preparation of self-assembled TiO2 structures. In addition, the performance of the as−synthesized TiO2 sea-urchin-like structures as the active layer of an efficient solar energy harvester is also studied and discussed.
Structural Analysis of In xGa1−xN/GaN MQWs by Different Experimental Methods
DING Bin-Beng, PAN Feng, FENG Zhe-Chuan, FA Tao, CHENG Feng-Feng, YAO Shu-De**
Chin. Phys. Lett. 2011, 28 (7): 078201 .   DOI: 10.1088/0256-307X/28/7/078201
Abstract   PDF(pc) (1141KB) ( 486 )
Structural properties of InxGa1−xN/GaN multi-quantum wells (MQWs) grown on sapphire by metal organic chemical vapor deposition are investigated by synchrotron radiation x-ray diffraction (SRXRD), Rutherford backscattering/channelling (RBS/C) and high-resolution transmission electron microscopy. The sample consists of eight periods of InxGa1−xN/GaN wells of 2.1 nm thickness and 8.5 nm thickness of GaN barrier, and the results are very close, which verifies the accuracy of the three methods. The indium content in InxGa1−xN/GaN MQWs by SRXRD and RBS/C is estimated, and results are in general the same. By RBS/C random spectra, the indium atomic lattice substitution rate is 94.0%, indicating that almost all indium atoms in InxGa1−xN/GaN MQWs are at substitution, that the indium distribution of each layer in InxGa1−xN/GaN MQWs is very homogeneous and that the InxGa1−xN/GaN MQWs have a very good crystalline quality. It is not accurate to estimate indium content in InxGa1−xN/GaN MQWs by photoluminescence (PL) spectra, because the result from the PL experimental method is very different from the results by the SRXRD and RBS/C experimental methods.
Demonstration of a High Open-Circuit Voltage GaN Betavoltaic Microbattery
CHENG Zai-Jun, SAN Hai-Sheng**, CHEN Xu-Yuan, **, LIU Bo, FENG Zhi-Hong
Chin. Phys. Lett. 2011, 28 (7): 078401 .   DOI: 10.1088/0256-307X/28/7/078401
Abstract   PDF(pc) (861KB) ( 1218 )
A high open-circuit voltage betavoltaic microbattery based on a GaN p-i-n diode is demonstrated. Under the irradiation of a 4×4 mm2 planar solid 63Ni source with an activity of 2 mCi, the open−circuit voltage Voc of the fabricated single 2×2 mm2 cell reaches as high as 1.62 V, the short−circuit current density Jsc is measured to be 16nA/cm2. The microbattery has a fill factor of 55%, and the energy conversion efficiency of beta radiation into electricity reaches to 1.13%. The results suggest that GaN is a highly promising potential candidate for long-life betavoltaic microbatteries used as power supplies for microelectromechanical system devices.
Restabilizing Mechanisms after the Onset of Thermal Instability in Bipolar Transistors
CHEN Liang**, ZHANG Wan-Rong, XIE Hong-Yun, JIN Dong-Yue, DING Chun-Bao, FU Qiang, WANG Ren-Qing, XIAO Ying, ZHAO Xin
Chin. Phys. Lett. 2011, 28 (7): 078501 .   DOI: 10.1088/0256-307X/28/7/078501
Abstract   PDF(pc) (581KB) ( 412 )
The restabilizing mechanisms after the onset of thermal instability in bipolar transistors are studied by theoretical analyses, computer simulations and experimental measurements. Restability conditions are described by novel analytical formulae. Furthermore, the expression of collect current in the second fly-back point is given for the first time. The effects of emitter ballast resistance, collector-emitter voltage and thermal resistance on restabilization mechanisms are expressed and investigated.
Numerical Simulation of 4H-SiC Metal Semiconductor Field Transistors
Kuang-Po HSUEH**, Shih-Tzung SU, Jun ZENG
Chin. Phys. Lett. 2011, 28 (7): 078502 .   DOI: 10.1088/0256-307X/28/7/078502
Abstract   PDF(pc) (437KB) ( 393 )
This work simulates the performance of 4H-SiC MESFETs and establishes the optimum device structure for dc and rf applications that operate at high voltages. Devices with various channel doping, buffer layer doping, recess thickness, gate-to-drain spacing and temperatures of operation are considered. The simulation results reveal that a p-type buffer layer of 5×1015 cm−3 and a channel layer of 1×1017 cm−3 yield favorable results. The cut-off frequency is 22.53 GHz, the maximum transconductance is 50.55 mS/mm, the drain saturation current is 239.76 mA/mm and the breakdown voltage is 70.40 V. The breakdown voltages increase to 90.2 V as the gate-to-drain spacing increases to 1 µm. Based on these simulation results, new 4H-SiC MESFET designs can be calibrated.
Optical Gain Analysis of Graded InGaN/GaN Quantum-Well Lasers
Seoung-Hwan Park**, Yong-Tae Moon, Jeong Sik Lee, Ho Ki Kwon, Joong Seo Park, Doyeol Ahn
Chin. Phys. Lett. 2011, 28 (7): 078503 .   DOI: 10.1088/0256-307X/28/7/078503
Abstract   PDF(pc) (910KB) ( 587 )
Optical properties of graded InGaN/GaN quantum well (QW) lasers are analyzed as improved gain media for laser diodes emitting near 500 nm. These results are compared with those of conventional InGaN/GaN QW structures. The heavy-hole effective mass around the topmost valence band is found to nearly not be affected by the inclusion of the graded layer. The graded InGaN/GaN QW structure shows a much larger matrix element than the conventional InGaN/GaN QW structure. The radiative current density dependences of the optical gain are similar to each other. However, the graded QW structure is expected to have lower threshold current density than the conventional QW structure because the former has a lower threshold carrier density than the latter.
Significant Improvement of Organic Thin-Film Transistor Mobility Utilizing an Organic Heterojunction Buffer Layer
PAN Feng, QIAN Xian-Rui, HUANG Li-Zhen, WANG Hai-Bo, YAN Dong-Hang**
Chin. Phys. Lett. 2011, 28 (7): 078504 .   DOI: 10.1088/0256-307X/28/7/078504
Abstract   PDF(pc) (1346KB) ( 476 )
High-mobility vanadyl phthalocyanine (VOPc)/5,5"'−bis(4-fluorophenyl)-2,2':5',2":5",2"'−quaterthiophene (F2-P4T) thin-film transistors are demonstrated by employing a copper hexadecafluorophthalocyanine (F16CuPc)/copper phthalocyanine (CuPc) heterojunction unit, which are fabricated at different substrate temperatures, as a buffer layer. The highest mobility of 4.08 cm2/Vs is achieved using a F16CuPc/CuPc organic heterojunction buffer layer fabricated at high substrate temperature. Compared with the random small grain-like morphology of the room-temperature buffer layer, the high-temperature organic heterojunction presents a large-sized fiber-like film morphology, resulting in an enhanced conductivity. Thus the contact resistance of the transistor is significantly reduced and an obvious improvement in device mobility is obtained.
An Analytical Avalanche Multiplication Model for Partially Depleted Silicon-on-Insulator SiGe Heterojunction Bipolar Transistors
XU Xiao-Bo**, ZHANG He-Ming
Chin. Phys. Lett. 2011, 28 (7): 078505 .   DOI: 10.1088/0256-307X/28/7/078505
Abstract   PDF(pc) (512KB) ( 399 )
An analytical expression for avalanche multiplication of a novel vertical SiGe partially depleted heterojunction bipolar transistor (HBT) on a thin silicon-on-insulator (SOI) layer is obtained, considering vertical and horizontal impact ionization effects. The avalanche multiplication is found to be dependent on the collector width and doping concentration, and shows kinks with the increase of reverse base-collector bias, which is quite different from that of a conventional bulk HBT. The model is consistent with the experimental and simulation data and is found to be significant for the design and simulation of 0.13 µm millimeter wave SiGe SOI BiCMOS technology.
Constrained Traffic of Particles on Complex Networks
MENG Qing-Kuan**, ZHU Jian-Yang
Chin. Phys. Lett. 2011, 28 (7): 078901 .   DOI: 10.1088/0256-307X/28/7/078901
Abstract   PDF(pc) (536KB) ( 393 )
We study the traffic of particles on complex networks under constraints. The constraints we propose are the different interactions between particles and the limited capability of node holding particles. We give the grand partition function of the system and find the distributions of particles at the dynamically balanced point. Then, we investigate the internal relations among the theories of classical statistics, quantum statistics and the zero range process. Finally, we find the finite temperature of Bose–Einstein condensation. Numerical results verify our theoretical expectations.
Direct Urca Processes with Hyperons in Cooling Neutron Stars
XU Yan, LIU Guang-Zhou**, WU Yao-Rui, ZHU Ming-Feng, YU Zi, WANG Hong-Yan, ZHAO En-Guang
Chin. Phys. Lett. 2011, 28 (7): 079701 .   DOI: 10.1088/0256-307X/28/7/079701
Abstract   PDF(pc) (776KB) ( 406 )
In the relativistic mean field approximation, the relativistic energy losses of the direct Urca processes with nucleons (N-DURCA) and hyperons (Y-DURCA) are studied in the degenerate baryon matter of neutron stars. We investigate the effects of hyperon degrees of freedom and the Y-DURCA processes on the N-DURCA processes, and the total neutrino emissivity of neutron star matter. The results show that the existence of hyperons decreases the abundance of protons and leptons, and can sharply suppress the neutrino emissivity of the N-DURCA processes.
90 articles