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Volume 28 Issue 8
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GENERAL
Solving Method for the Single-Kink Soliton Solution to a Disturbed Coupled Burgers System
YAO Jing-Su**, CHEN Li-Hua, WEN Zhao-Hui, MO Jia-Qi, **
Chin. Phys. Lett. 2011, 28 (8): 080201 .   DOI: 10.1088/0256-307X/28/8/080201
Abstract   PDF(pc) (417KB) ( 566 )
We study a class of disturbed coupled Burgers systems. The approximate single-kink soliton solution is obtained by using the asymptotic method.
Geometric Phase for a Qutrit-Qubit Mixed-Spin System
ZHANG Ai-Ping**, QIANG Wen-Chao, LING Ya-Wen, XIN Hong, YANG Yong-Ming
Chin. Phys. Lett. 2011, 28 (8): 080301 .   DOI: 10.1088/0256-307X/28/8/080301
Abstract   PDF(pc) (853KB) ( 450 )
We study the geometric phase of a qutrit-qubit mixed-spin system in an external homogeneous magnetic field. Both the spin-spin interaction strength J and the external magnetic field B can affect the geometric phase of the system. In addition, we consider the negativity of the composite system. The relationship between the negativity and the geometric phase is obtained. Finally, we calculate the geometric phase for a thermal mixed state and show how the geometric phase depends on the rescaled coupling parameter and temperature. In the limit T→0, we can recover the result of the ground state. This analysis has some implications in realistic implementations of geometric quantum computation.
Implementation of Quantum Private Queries Using Nuclear Magnetic Resonance
WANG Chuan, **, HAO Liang, ZHAO Lian-Jie
Chin. Phys. Lett. 2011, 28 (8): 080302 .   DOI: 10.1088/0256-307X/28/8/080302
Abstract   PDF(pc) (404KB) ( 371 )
We present a modified protocol for the realization of a quantum private query process on a classical database. Using one-qubit query and CNOT operation, the query process can be realized in a two-mode database. In the query process, the data privacy is preserved as the sender would not reveal any information about the database besides her query information, and the database provider cannot retain any information about the query. We implement the quantum private query protocol in a nuclear magnetic resonance system. The density matrix of the memory registers are constructed.
N−Qubit W State of Spatially Separated Atoms via Fractional Adiabatic Passage
ZHENG An-Shou, **, LIU Ji-Bing, CHEN Hong-Yun
Chin. Phys. Lett. 2011, 28 (8): 080303 .   DOI: 10.1088/0256-307X/28/8/080303
Abstract   PDF(pc) (547KB) ( 410 )
An alternative scheme is presented to realize an N−qubit W state with distant atoms trapped in spatially separated optical cavities coupled by optical fibers via a fractional adiabatic passage. The present scheme is tolerant to device parameter nonuniformity and does not need to accurately control the experimental time by employing the fractional stimulated Raman adiabatic passage. In addition, the excited states of atoms are adiabatically eliminated and no additional qubit is required. Cavity decay, fiber losses and atomic spontaneous emission can all be greatly suppressed in the present scheme.
Feasibility for Testing the Equivalence Principle with Optical Readout in Space
GAO Fen, ZHOU Ze-Bing**, LUO Jun
Chin. Phys. Lett. 2011, 28 (8): 080401 .   DOI: 10.1088/0256-307X/28/8/080401
Abstract   PDF(pc) (477KB) ( 428 )
A concept of testing the equivalence principle with optical readout in space (TEPO) has been proposed [J. Jpn. Soc. Microgravity Appl. 25 (2008) 423]. We further discuss the feasibility of TEPO using LISA (laser interferometer space antenna) Pathfinder technologies, such as a heterodyne interferometer, an inertial sensor, drag-free control and discharge technique, and determine that the equivalence principle could be tested at 8×10−17 with one day integration.
Pseudo-Random Sequences Generated by a Class of One-Dimensional Smooth Map
WANG Xing-Yuan**, QIN Xue, XIE Yi-Xin
Chin. Phys. Lett. 2011, 28 (8): 080501 .   DOI: 10.1088/0256-307X/28/8/080501
Abstract   PDF(pc) (5645KB) ( 488 )
We extend a class of a one-dimensional smooth map. We make sure that for each desired interval of the parameter the map's Lyapunov exponent is positive. Then we propose a novel parameter perturbation method based on the good property of the extended one-dimensional smooth map. We perturb the parameter r in each iteration by the real number xi generated by the iteration. The auto-correlation function and NIST statistical test suite are taken to illustrate the method's randomness finally. We provide an application of this method in image encryption. Experiments show that the pseudo-random sequences are suitable for this application.
Size Model of Critical Temperature for Grain Growth in Nano V and Au
LU Yun-Bin, LIAO Shu-Zhi**, PENG Hao-Jun, ZHANG Chun, ZHOU Hui-Ying, XIE Hao-Wen, OUYANG Yi-Fang, ZHANG Bang-Wei,
Chin. Phys. Lett. 2011, 28 (8): 080502 .   DOI: 10.1088/0256-307X/28/8/080502
Abstract   PDF(pc) (588KB) ( 445 )
The intrinsic thermodynamical factors that dominate the stability of nanocrystallines are investigated through the microcosmic process of grain growth. The results suggest that nanocrystallines grows at a certain temperature and the critical temperature is determined by the vacancy formation energy and diffusion activation energy of the nanocrystallines. Based on the hypothesis, a simple model is proposed to predict the size-dependent critical temperature of grain growth. Within this model, we investigate the thermal stability of nanocrystallines V and Au, compared with the results available. It is shown that the critical temperature decreases with decreasing size, showing an evident size effect. The research reveals that the thermal stability is dependent on the energetic state of the nanocrystallines and the mobility of the inner atoms.
Feasibility of Extreme Ultraviolet Active Optical Clock
ZHUANG Wei, CHEN Jing-Biao**
Chin. Phys. Lett. 2011, 28 (8): 080601 .   DOI: 10.1088/0256-307X/28/8/080601
Abstract   PDF(pc) (496KB) ( 486 )
We propose an experimental scheme of vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) optical frequency standards with noble gas atoms. Considering metastable state 3P2 noble atoms pumped by a conventional discharging method, the atomic beam is collimated with transverse laser cooling at the metastable state and enters into the laser cavity in the proposed setup. Due to stimulated emission from the metasable state to the ground state inside the laser cavity consisting of VUV reflection coating mirrors, our calculations show that with enough population inversion to compensate for the cavity loss, an active optical frequency standard at VUV and XUV is feasible.
Micropore Structure Representation of Sandstone in Petroleum Reservoirs Using an Atomic Force Microscope
BAI Yong-Qiang**, ZHU Xing, WU Jun-Zheng, BAI Wen-Guang
Chin. Phys. Lett. 2011, 28 (8): 080701 .   DOI: 10.1088/0256-307X/28/8/080701
Abstract   PDF(pc) (1834KB) ( 676 )
The pore structure of sandstone in an oil reservoir is investigated using atomic force microscopy (AFM). At nanoscale resolution, AFM images of sandstone show us the fine structure. The real height data of images display the three-dimensional space structure of sandstone effectively. The three-dimensional analysis results show that the AFM images of sandstone have unique characteristics that, like fingerprints, can identify different structural properties of sandstones. The results demonstrate that AFM is an effective method used to represent original sandstone in petroleum reservoirs, and may help geologists to appreciate the sandstone in oil reservoirs fully.
Room-Temperature NH Gas Sensor Based on Hydrothermally Grown ZnO Nanorods
WEI Ang, WANG Zhao, PAN Liu-Hua, LI Wei-Wei, XIONG Li, DONG Xiao-Chen**, HUANG Wei**
Chin. Phys. Lett. 2011, 28 (8): 080702 .   DOI: 10.1088/0256-307X/28/8/080702
Abstract   PDF(pc) (1089KB) ( 965 )
A NH3 gas sensor based on a ZnO nanorod array is fabricated by hydrothermal decomposition on a Au electrode. The as−grown ZnO nanorods have uniform diameter distribution and good crystal structure, shown by scanning electron microscopy, x-ray diffraction, high resolution transmission electron microscopy and photoluminescence emission characterizations. The gas sensing results show that the ZnO nanorod-based device responds well to ammonia gas at room temperature (sensitivity S is about 8).
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Analysis of Mass Difference of the π and ρ with Bethe–Salpeter Equation
WANG Zhi-Gang**
Chin. Phys. Lett. 2011, 28 (8): 081201 .   DOI: 10.1088/0256-307X/28/8/081201
Abstract   PDF(pc) (474KB) ( 375 )
The one-pion exchange force in addition to the one-gluon exchange force is taken into account to study the mass difference of the π and ρ mesons with the Bethe–Salpeter equation. After projecting the Bethe–Salpeter equation into a simple form, it can be seen explicitly that the bound energy |Eπ|≫|Eρ|.
Lattice QCD Study of the σ Meson
FU Zi-Wen**
Chin. Phys. Lett. 2011, 28 (8): 081202 .   DOI: 10.1088/0256-307X/28/8/081202
Abstract   PDF(pc) (762KB) ( 429 )
We study the σ meson in 2+1 flavor full quantum chromodynamics (QCD) with sufficiently light u and d quarks. The point−to-point correlator is measured for the σ channel in the “Asqtad” improved staggered fermion formulation. Particular attention is paid to its disconnected diagram and bubble contribution. After chiral extrapolation, we obtain the σ mass with 706±53 MeV, which is close to the observed σ meson within error, and is heavier than the ππ threshold. The simulations are carried out with MILC 2+1 flavor gauge configurations at lattice spacing of a≈0.15 fm.
Large Dimuon Asymmetry and a Non-Universal Z Boson in the BsBs System
CHANG Qin, WANG Ru-Min, XU Yuan-Guo, CUI Xiao-Wei
Chin. Phys. Lett. 2011, 28 (8): 081301 .   DOI: 10.1088/0256-307X/28/8/081301
Abstract   PDF(pc) (699KB) ( 382 )
Motivated by recently observed anomalously large dimuon charge asymmetry in neutral B decays reported by the D0 collaboration, we study the effects of a family of non-universal Z bosons for possible solutions. The fitting results for the Z parameters are presented under the constraints from the D0 result for asls and UTfit results for CBs and φBs in two limiting scenarios for left− and right-handed b-s-Z couplings. We find the couplings BsbL and BsbR are rigorously bounded but not excluded, which means that the anomalies in the BsBs system could be moderated simultaneously within a non-universal Z model. Numerically, a new weak phase φLs ∼−60° (80°) in scenario I or 30°(10°) in scenario II is crucial to moderate the large dimuon charge asymmetry.
Effect of Excited and Fourth Generation Leptons in Lepton Flavor Violating μ → e- Decay
S. C. �, nan**
Chin. Phys. Lett. 2011, 28 (8): 081401 .   DOI: 10.1088/0256-307X/28/8/081401
Abstract   PDF(pc) (571KB) ( 338 )
We study the lepton flavor violating μ →e- decay induced by the mediation of heavy leptons, such as the excited and fourth generation leptons. Effects of these leptons in μ →e- decay are examined. It is found that the branching ratio of this decay is very sensitive to excited and fourth generation leptons. Furthermore, we obtain the bounds on model parameters by using the current experimental limit of this decay.
NUCLEAR PHYSICS
Singly and Doubly Charged Projectile Fragments in Nucleus-Emulsion Collisions at Dubna Energy in the Framework of the Multi-Source Model
WANG Er-Qin, LIU Fu-Hu**, Magda A. Rahim, S. Fakhraddin, SUN Jian-Xin,
Chin. Phys. Lett. 2011, 28 (8): 082501 .   DOI: 10.1088/0256-307X/28/8/082501
Abstract   PDF(pc) (1042KB) ( 436 )
The multiplicity distributions of projectile fragments emitted in interactions of different nuclei with emulsion are studied by using a multi-source model. Our calculated results show that the projectile fragments can be described by the model and each source contributes an exponential distribution. As the weighted sum of the folding result of many exponential distributions, a multi-component Erlang distribution is used to describe the experimental data. The relationship between the height (or width) of the distribution and the mass of the incident projectile, as well as the dependence of projectile fragments on target groups, are investigated too.
Comparison of Fission Induced by Protons and Pions
Zafar Yasin*, M. Ikram Shahzad
Chin. Phys. Lett. 2011, 28 (8): 082502 .   DOI: 10.1088/0256-307X/28/8/082502
Abstract   PDF(pc) (651KB) ( 360 )
We compare the properties of fission induced by protons and pions. Three different methodologies are used to make this comparison. First, it is shown that pion-induced fission cross sections are not much different in magnitude from proton-induced fission cross sections at the same beam kinetic energy. Secondly, across the pion-nucleon (3,3) resonance so prominent with free nucleons, it has been observed that there is no significant change in the reaction mechanism in the case of pions. Thirdly, it is noted that an empirical expression used for evaluations of proton-induced fission cross sections is also valid for positive pion-induced fission cross sections, at least for actinide nuclei. Fission cross sections computed using a cascade-exciton model code for 209Bi and 238U are also compared with the experimental data available.
Measurement of Cross Sections for the 10B(n,α)7Li Reaction at 4.0 and 5.0MeV Using an Asymmetrical Twin Gridded Ionization Chamber
ZHANG Guo-Hui**, LIU Xiang, LIU Jia-Ming, XUE Zhi-Hua, WU Hao, CHEN Jin-Xiang
Chin. Phys. Lett. 2011, 28 (8): 082801 .   DOI: 10.1088/0256-307X/28/8/082801
Abstract   PDF(pc) (6059KB) ( 479 )
Cross sections of the 10B(n,α)7Li reaction (including the total, the “leaking” alpha, forward alpha and backward alpha parts) at En =4.0 and 5.0 MeV were measured using an asymmetrical twin gridded ionization chamber and two back−to-back 10B samples. Measurements were performed at the 4.5 MV Van de Graaff accelerator of Peking University. Monoenergetic neutrons were produced through the 2H(d,n)3He reaction with a deuterium gas target. Absolute neutron flux was determined by a 238U sample set inside the gridded ionization chamber and a BF3 long counter was employed as a neutron flux monitor and for normalization. The present results are compared with previous measurements and evaluations.
Effects of Electron Flow Current Density on Flow Impedance of Magnetically Insulated Transmission Lines
HE Yong*, ZOU Wen-Kang, SONG Sheng-Yi
Chin. Phys. Lett. 2011, 28 (8): 082901 .   DOI: 10.1088/0256-307X/28/8/082901
Abstract   PDF(pc) (441KB) ( 364 )
In modern pulsed power systems, magnetically insulated transmission lines (MITLs) are used to couple power between the driver and the load. The circuit parameters of MITLs are well understood by employing the concept of flow impedance derived from Maxwell's equations and pressure balance across the flow. However, the electron density in an MITL is always taken as constant in the application of flow impedance. Thus effects of electron flow current density (product of electron density and drift velocity) in an MITL are neglected. We calculate the flow impedances of an MITL and compare them under three classical MITL theories, in which the electron density profile and electron flow current density are different from each other. It is found that the assumption of constant electron density profile in the calculation of the flow impedance is not always valid. The electron density profile and the electron flow current density have significant effects on flow impedance of the MITL. The details of the electron flow current density and its effects on the operation impedance of the MITL should be addressed more explicitly by experiments and theories in the future.
ATOMIC AND MOLECULAR PHYSICS
Quasi-Classical Trajectory Calculations of Reaction Stereodynamics of H+OH( v = 0, j = 0)H2+O(3 P )
ZHAO Li, SUN Ping, LIU Chao-Zhuo*
Chin. Phys. Lett. 2011, 28 (8): 083101 .   DOI: 10.1088/0256-307X/28/8/083101
Abstract   PDF(pc) (821KB) ( 399 )
In order to study the vector properties, especially the correlation between the reagents and the products, of the title reaction, the quasi-classical trajectory calculations on the 3A' and 3A" potential energy surfaces (PESs) have been performed. The results indicate that the product rotational angular momentum j' is aligned and oriented perpendicular to the scattering plane on both PESs. The rotational polarization behaviors of the product H2 with different collision energies are shown for the two PESs. The alignment effect tends to become weaker with the increasing collision energy. The product H2 mainly tends to the backward scattering on the two PESs at low collision energy. However, there exists a switch from backward scattering to the sideways one on the 3A" PES with increasing collision energy. The differences are reasonably explained with the characteristics of the two PESs.
Product Rotational Polarization in the Li+HF ( v=0, j=0) Reaction and Its Isotopic Variants
CHENG Jie, YUE Xian-Fang**
Chin. Phys. Lett. 2011, 28 (8): 083102 .   DOI: 10.1088/0256-307X/28/8/083102
Abstract   PDF(pc) (1573KB) ( 404 )
Product rotational polarization in the title reactions is investigated by employing the quasi-classical trajectory method. An accurate ground 12A' potential energy surface [J. Chem. Phys. 107 (1997) 10085] and a collision energy of 110 meV are adopted in these calculations. The commonly used rotational alignment parameter A0(2) and the three angular distributions P(θr), P(φr), and P(θrr) (θr and φr being the polar angles of the product angular momentum) are computed in the c.m. frame to gain insight into the product rotational alignment and orientation. It is found that the product rotational angular momentum prefers not only to align perpendicular to the reagent relative velocity vector k but also orientate along the negative y axis, which is successfully interpreted by an impulsive mode. The isotope mass effect on the product rotational polarization is also revealed and discussed.
Intensity and Polarization Effects in Short-Pulse Multiphoton Ionization of Xenon
KANG Hui-Peng, **, WANG Chuan-Liang, LIN Zhi-Yang, CHEN Yong-Ju, WU Ming-Yan, QUAN Wei, LIU Hong-Ping, LIU Xiao-Jun***
Chin. Phys. Lett. 2011, 28 (8): 083201 .   DOI: 10.1088/0256-307X/28/8/083201
Abstract   PDF(pc) (740KB) ( 346 )
We present photoelectron spectra (PES) of xenon subject to ultrashort intense laser pulses at 400 nm. The intensity-dependent PES exhibit the dominance of ac-Stark-shifted multiphoton resonances in a multiphoton ionization process. A distinct difference in the spectra with different laser polarization states (i.e., linearly and circularly polarized states) is revealed and can be understood in terms of the quantum selection rule, which restricts the angular momentum of states that may shift into multiphoton resonances. Furthermore, the intensity dependence of the resonance-enhanced electron yield is analyzed in the context of multiphoton Landau–Zener theory. The model calculation results considering the focal volume effect are in good agreement with the experimental observation.
Relative Phase Dependence of Double Ionization in a Synthesized Laser Pulse
WANG Yuan-Sheng, XIA Chang-Long, GUO Jing**, LIU Xue-Shen**
Chin. Phys. Lett. 2011, 28 (8): 083202 .   DOI: 10.1088/0256-307X/28/8/083202
Abstract   PDF(pc) (1787KB) ( 346 )
We investigate the double ionization process of a three-dimensional model atom interacting with a synthesized laser pulse and explore the mechanism of non-sequential double ionization varying with the value of relative phase. The result shows that the recollision probability decreases when the value of the relative phase increases. The momentum spectra of electrons in the sequential ionization region are also illustrated.
Radiation-Induced Nano-Explosions at the Solid Surface: Near Surface Radiation Damage in CR-39 Polymer
Mukhtar Ahmed Rana*
Chin. Phys. Lett. 2011, 28 (8): 083203 .   DOI: 10.1088/0256-307X/28/8/083203
Abstract   PDF(pc) (660KB) ( 493 )
New measurements of fission fragment and alpha particle induced surface damage in the most sensitive and commonly used nuclear track detector CR-39 are presented here. Precisely designed and optimized exposure and chemical etching experiments are employed to unfold the structure of radiation induced surface damage (RISD). Delay in the startup of the chemical etching of latent tracks or surface radiation damage is measured and is found to contain important information about the structure of the surface damage. Simple atomic scale pictures of RISD and its chemical etching are developed in an empirical manner. Theoretical model and experimental findings coherently compose a realistic picture of early or femtosecond evolution of RISD.
Investigation of Linear Tetra-Atomic Negative Ion by Photodetached-Electron Spectra
A. Rahman, Iftikhar Ahmad, **, A. Afaq, M. Haneef, H. J. Zhao
Chin. Phys. Lett. 2011, 28 (8): 083301 .   DOI: 10.1088/0256-307X/28/8/083301
Abstract   PDF(pc) (467KB) ( 378 )
Photodetachment spectra from a linear tetra-atomic negative ion is investigated by treating the detached-electron wave function quantum mechanically. A plane polarized laser light, perpendicular to the axis of the ion, is used to detach the electron from the ion. Analytical expressions for the electron flux and total photodetachment cross section are derived. The electron flux on screen shows strong-energy-dependent oscillations with different frequencies. The total cross section of the tetra-atomic negative ion reduces the cross section of mono-atomic, diatomic and triatomic negative ions for high energy photons, while for low energy photons it becomes four times the cross section of mono-atomic negative ions.
Two-Fermion Scattering on Momentum-Representation in a Trap and Their Periodic Phenomena
FANG Yi-Zhong**, HE Yan-Zhang
Chin. Phys. Lett. 2011, 28 (8): 083401 .   DOI: 10.1088/0256-307X/28/8/083401
Abstract   PDF(pc) (535KB) ( 318 )
Under the control of the prepared initial state, two-body scattering of trapped neutral fermions is studied theoretically. Since the fermions collide inside the trap frequently, the effect of atom-atom interaction can be accumulated. On the momentum-representation, we find the presence of periodic probability density, which is much longer than that of bosons. The measurement and details of this periodic phenomenon might be valid information about weak interactions among neutral particles.
Photoassociative Production and Detection of Ultracold Polar RbCs Molecules
JI Zhong-Hua, ZHANG Hong-Shan, WU Ji-Zhou, YUAN Jin-Peng, ZHAO Yan-Ting**, MA Jie, WANG Li-Rong, XIAO Lian-Tuan, JIA Suo-Tang
Chin. Phys. Lett. 2011, 28 (8): 083701 .   DOI: 10.1088/0256-307X/28/8/083701
Abstract   PDF(pc) (882KB) ( 462 )
We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85Rb and 133Cs atoms in a dual−species, forced dark magneto-optical trap. The formed electronically excited RbCs molecules correlated to the Rb(5S1/2)+Cs(6P1/2) dissociation limit are observed by trap loss spectroscopy. Following the decay of these excited RbCs* molecules, the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser, which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Proton Acceleration with Double-Layer Targets in the Radiation Pressure Dominant Regime
XIA Chang-Quan**, DENG Ai-Hua, LIU Li, WANG Wen-Tao, LU Hai-Yang, WANG Cheng, LIU Jian-Sheng
Chin. Phys. Lett. 2011, 28 (8): 084101 .   DOI: 10.1088/0256-307X/28/8/084101
Abstract   PDF(pc) (2506KB) ( 855 )
Acceleration of protons by a circularly polarized laser pulse irradiating on a double-layer target is investigated by a theoretical model and particle-in-cell simulations. The target is made up of a heavy ion layer coated with a proton layer on the rear surface. The results show that when the first layer is transparent induced by the hole-boring effect, the whole proton layer is accelerated by the transmitted laser pulse to high energy with low energy spread. The quality of the proton beam generated from a double-layer target is better than that from a single-layer target. The improvement is attributed to the flat top structure of the electrostatic field caused by the electrons injected into the second layer. It is easier to control the spectrum quality by using a double-layer target rather than using a single-layer one when the radiation pressure acceleration is dominant.
Design of a Novel Polarized Beam Splitter Based on a Two-Dimensional Photonic Crystal Resonator Cavity
ZHANG Xuan, CHEN Shu-Wen, LIAO Qing-Hua**, YU Tian-Bao, LIU Nian-Hua, HUANG Yong-Zhen
Chin. Phys. Lett. 2011, 28 (8): 084201 .   DOI: 10.1088/0256-307X/28/8/084201
Abstract   PDF(pc) (1174KB) ( 511 )
We propose and analyze a novel ultra-compact polarization beam splitter based on a resonator cavity in a two-dimensional photonic crystal. The two polarizations can be separated efficiently by the strong coupling between the microcavities and the waveguides occurring around the resonant frequency of the cavities. The transmittance of two polarized light around 1.55 µm can be more than 98.6%, and the size of the device is less than 15 µm×13 µm, so these features will play an important role in future integrated optical circuits.
Single Mode Condition and Power Fraction of Air-Cladding Total Refractive Guided Porous Polymer Terahertz Fibers
JING Lei, **, YAO Jian-Quan,
Chin. Phys. Lett. 2011, 28 (8): 084202 .   DOI: 10.1088/0256-307X/28/8/084202
Abstract   PDF(pc) (633KB) ( 575 )
We investigate the single-mode condition and power fraction of an air cladding total internal reflection (TIR) guided porous polymer THz fiber. It is shown that the single mode condition and a high fraction of power in air holes cannot be simultaneously met in porous fibers. Employing the V parameter and the Lorentz–Lorenz formula, we analyze this problem theoretically.
Optical Noise Analysis in Dual-Resonator Structural Micro-Optic Gyro
YU Huai-Yong, **, ZHANG Chun-Xi, FENG Li-Shuang, HONG Ling-Fei, WANG Jun-Jie,
Chin. Phys. Lett. 2011, 28 (8): 084203 .   DOI: 10.1088/0256-307X/28/8/084203
Abstract   PDF(pc) (3636KB) ( 620 )
A novel micro resonator optic gyroscope comprising a dual-resonator structure is proposed. This design radically eliminates the noise induced by Rayleigh backscattering, the Kerr effect and polarization coupling. The configuration of the micro optic gyroscope (MOG) is given and described. Three methods are applied to suppress the optical noises in the system and to theoretically analyze the performance improvement. Experiments are carried out on both dual-resonator and single-resonator MOGs, which show the resonance depth improvement from 0.7477 to 0.9173 in the present MOG dual-resonator configuration.
Diode-Pumped Soliton and Non-Soliton Mode-Locked Yb:GYSO Lasers
HE Jin-Ping, LIANG Xiao-Yan**, LI Jin-Feng, ZHENG Li-He, SU Liang-Bi, XU Jun
Chin. Phys. Lett. 2011, 28 (8): 084204 .   DOI: 10.1088/0256-307X/28/8/084204
Abstract   PDF(pc) (545KB) ( 396 )
Diode-pumped soliton and non-soliton mode-locked Yb:(Gd1−xYx)2SiO5 (x = 0.5) lasers are demonstrated. Pulses as short as 1.4 ps are generated for the soliton mode−locked operation, with a pair of SF10 prisms as the negative dispersion elements. The central wavelength is 1056 nm and the repetition rate is 48 MHz. For the non-soliton mode locking, the output power could achieve 1.2 W, and the pulse width is about 20 ps. The critical pulse energy in the soliton-mode locked operation against the Q-switched mode locking is much lower than the critical pulse energy in the non-soliton mode-locked operation.
Optical Properties of BDK-Doped Highly Photosensitive Sol-Gel Hybrid Film
XU Ming**, SHEN Wei-Dong**, ZHANG Yue-Guang, ZHEN Hong-Yu, LIU Xu
Chin. Phys. Lett. 2011, 28 (8): 084205 .   DOI: 10.1088/0256-307X/28/8/084205
Abstract   PDF(pc) (1012KB) ( 436 )
A new organic-inorganic hybrid material doped with BDK that exhibits a large photo-induced change in optical properties is prepared by the sol-gel method. The photosensitivity of the film under ultraviolet irradiation is investigated with various exposure times. An increase in refractive index from 1.558 to 1.592 at λ = 550 nm is observed together with a 57.3% expansion in physical thickness. The film's optical thickness exhibits an exponential change with the irradiation time. The photo-decomposition of BDK organic groups confirmed by the infrared absorption spectrum contributes to the photosensitive mechanism. A first example of photo-patterning is finally presented by direct light writing.
Large-Mode-Area Double-Cladding Photonic Crystal Fiber Laser in the Watt Range at 980nm
LI Ping-Xue**<\sup>, , ZHANG Xue-Xia, LIU Zhi, CHI Jun-Jie
Chin. Phys. Lett. 2011, 28 (8): 084206 .   DOI: 10.1088/0256-307X/28/8/084206
Abstract   PDF(pc) (567KB) ( 507 )
We report on a quasi-three-level large-mode-area double-clad Yb-doped fiber laser that adopts a linear cavity consisting of a 0° fiber end and a cavity mirror. Two kinds of Yb−doped photonic crystal fiber (PCF) with different inner-clads (170 µm and 200 µm) and absorption coefficients (4.5 dB/m and 3 dB/m) are used as the gain media. By optimizing the structure and elements of the cavity, maximum output powers of 1.24 W and 1.1 W were yielded with optical conversion efficiencies of 7.8% and 6.8% when the fiber lengths were 25 cm and 40 cm with 170 µm and 200 µm inner-claddings, respectively.
A High Power Single Frequency Diode Side-Pumped Nd:YAG Ring Laser
XIE Shi-Yong, **, BO Yong, XU Jia-Lin, WANG Zhi-Chao, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan
Chin. Phys. Lett. 2011, 28 (8): 084207 .   DOI: 10.1088/0256-307X/28/8/084207
Abstract   PDF(pc) (853KB) ( 458 )
We demonstrate a high-power single-frequency diode-side pumped Nd:YAG laser at 1064 nm. A bow-tie ring cavity configuration comprising two plane and two curved mirrors with two-rod birefringence compensation is employed. The influence of length Lx between two curved mirrors on output power and beam quality is investigated theoretically and experimentally while the separation of the flat mirrors is set to be 656 mm and the fold angle is 10°. When the pump powers are 358, 343 and 329 W at 808 nm, the maximal output powers of 31.9, 26 and 14.1 W are obtained with beam quality factors M2 = 1.41, 1.12 and 1.20 for Lx = 205, 215 and 230 mm, respectively.
Third-Order Optical Nonlinearities of Squarylium Dyes with Benzothiazole Donor Groups Measured Using the Picosecond Z-Scan Technique
LI Zhong-Yu**, XU Song, CHEN Zi-Hui, ZHANG Fu-Shi, KASATANI Kazuo
Chin. Phys. Lett. 2011, 28 (8): 084208 .   DOI: 10.1088/0256-307X/28/8/084208
Abstract   PDF(pc) (686KB) ( 463 )
Third-order optical nonlinearities of two squarylium dyes with benzothiazole donor groups (BSQ1 and BSQ2) in chloroform solution are measured by a picosecond Z-scan technique at 532 nm. It is found that the two compounds show the saturation absorption and nonlinear self-focus refraction effect. The molecular second hyperpolarizabilities are calculated to be 7.46×10−31 esu and 5.01×10−30 esu for BSQ1 and BSQ2, respectively. The large optical nonlinearities of squarylium dyes can be attributed to their rigid and intramolecular charge transfer structure. The difference in γ values is attributed to the chloro group of benzene rings of BSQ2 and the one−photon resonance effect. It is found that the third-order nonlinear susceptibilities of two squarylium dyes are mainly determined by the real parts of χ(3), and the large optical nonlinearities of studied squarylium dyes can be attributed to the nonlinear refraction.
Reduction of the Far-Field Divergence Angle of an 850nm Multi-Leaf Holey Vertical Cavity Surface Emitting Laser
ZHOU Kang**, XU Chen, XIE Yi-Yang, ZHAO Zhen-Bo, LIU Fa, SHEN Guang-Di
Chin. Phys. Lett. 2011, 28 (8): 084209 .   DOI: 10.1088/0256-307X/28/8/084209
Abstract   PDF(pc) (1603KB) ( 1388 )
By introducing multi-leaf sectorial holes into an oxidation confined 850 nm vertical cavity surface emitting laser (VCSEL), the far-field divergence angle is reduced. The finite-difference time-domain method is used to simulate the far-field pattern of the multi-leaf holey VCSEL with different etching depths and different shapes of the oxide aperture in diameter R. Based on the simulation result, we design and fabricate a multi−leaf holey VCSEL and its divergence angle is only 6°. The experimental results agree well with the theoretical predication.
Light Scattering of Rough Orthogonal Anisotropic Surfaces with Secondary Most Probable Slope Distributions
LI Hai-Xia, CHENG Chuan-Fu**
Chin. Phys. Lett. 2011, 28 (8): 084210 .   DOI: 10.1088/0256-307X/28/8/084210
Abstract   PDF(pc) (6520KB) ( 317 )
We study the light scattering of an orthogonal anisotropic rough surface with secondary most probable slope distribution. It is found that the scattered intensity profiles have obvious secondary maxima, and in the direction perpendicular to the plane of incidence, the secondary maxima are oriented in a curve on the observation plane, which is called the orientation curve. By numerical calculation of the scattering wave fields with the height data of the sample, it is validated that the secondary maxima are induced by the side face element, which constitutes the prismoid structure of the anisotropic surface. We derive the equation of the quadratic orientation curve. Experimentally, we construct the system for light scattering measurement using a CCD. The scattered intensity profiles are extracted from the images at different angles of incidence along the orientation curves. The experimental results conform to the theory.
Experimental Observation of Near-Field Deterioration Induced by Stimulated Rotational Raman Scattering in Long Air Paths
WANG Jing, ZHANG Xiao-Min, HAN Wei, LI Fu-Quan, ZHOU Li-Dan**, FENG Bin, XIANG Yong
Chin. Phys. Lett. 2011, 28 (8): 084211 .   DOI: 10.1088/0256-307X/28/8/084211
Abstract   PDF(pc) (3945KB) ( 395 )
We report the experimental investigation of a stimulated rotational Raman scattering effect in long air paths on SG-III TIL, with a 1053 nm, 20-cm-diameter, linearly polarized, 3 ns flat-topped laser pulse. An intense speckle pattern of near field with thickly dotted hot spots is observed at the end of propagation with an intensity-length product above 17 TW/cm. The Stokes developing from the scattering of the laser beam by quantum fluctuations is characterized by a combination of high spatial frequency components. The observed speckle pattern with small-diameter hot spots results from the combination of the nonlinear Raman amplification and the linear diffraction propagation effect of the Stokes with a noise pattern arising from the spontaneous Raman scattering. A new promising suppression concept based on the special characteristic of the Stokes, called active and selective filtering of Stokes, is proposed.
Compact 2×2 Multi-Mode Interference Couplers with Uneven Splitting-Ratios Based on Silicon Nanowires
ZHOU Jing-Tao**, SHEN Hua-Jun, YANG Cheng-Yue, LIU Huan-Ming, TANG Yi-Dan, LIU Xin-Yu
Chin. Phys. Lett. 2011, 28 (8): 084212 .   DOI: 10.1088/0256-307X/28/8/084212
Abstract   PDF(pc) (697KB) ( 481 )
Two types of uneven splitting-ratio 2×2 multi−mode interference (MMI) couplers based on silicon nanowires are designed, fabricated and characterized. The splitting ratios are 85:15 and 72:28, respectively. The devices have compact sizes and low excess losses. The footprints of the rectangular MMI region are only about 3 µm×18 µm and 3 µm×14 µm, and the minimum excess losses (ELs) are 1.30 dB and 0.82 dB. The measured splitting−ratios are consistent with the designed values. Based on their performance, these 2×2 MMI couplers are suitable candidates for the coupling section of microring resonators where a large resonance bandwidth is required for high speed signal processing. The uneven splitting capability also provides a convenient way to further optimize the Q factor and the bandwidth of the resonator.
Measurement of Temperature Change in Nonlinear Optical Materials by Using the Z-Scan Technique
DONG Shu-Guang, YANG Jun-Yi, SHUI Min, YI Chuan-Xiang, LI Zhong-Guo, SONG Ying-Lin**
Chin. Phys. Lett. 2011, 28 (8): 084213 .   DOI: 10.1088/0256-307X/28/8/084213
Abstract   PDF(pc) (1586KB) ( 663 )
Spatial and temporal changes of temperature in a novel polymer are investigated by using the Z−scan technique under ns laser pulse excitation. According to the open aperture Z−scan experimental results, the nonlinear absorption coefficient of the polymer is determined. By solving the diffusion equation of heat conduction induced by optical absorption, the spatial and temporal changes in temperature are obtained. This change in temperature drives the photo-acoustic and electromagnetic wave propagating in the polymer and induces the change in refractive index, which serves as a negative lens, and the closed aperture Z−scan shows a peak and valley profile. Based on the numerical calculation, we achieve a good fit to the closed-aperture Z−scan curve with an optimized nonlinear refractive index. This consistency attests the existence of temperature change in the solution, and the Z-scan technique is suitable to investigate this change in temperature.
A Digital Phase Lock Loop for an External Cavity Diode Laser
WANG Xiao-Long, TAO Tian-Jiong, CHENG Bing, WU Bin, XU Yun-Fei, WANG Zhao-Ying, LIN Qiang**
Chin. Phys. Lett. 2011, 28 (8): 084214 .   DOI: 10.1088/0256-307X/28/8/084214
Abstract   PDF(pc) (616KB) ( 914 )
A digital optical phase lock loop (OPLL) is implemented to synchronize the frequency and phase between two external cavity diode lasers (ECDL), generating Raman pulses for atom interferometry. The setup involves all-digital phase detection and a programmable digital proportional-integral-derivative (PID) loop in locking. The lock generates a narrow beat-note linewidth below 1 Hz and low phase-noise of 0.03 rad2 between the master and slave ECDLs. The lock proves to be stable and robust, and all the locking parameters can be set and optimized on a computer interface with convenience, making the lock adaptable to various setups of laser systems.
Nondestructive Characterization of Quantitative Bonding Strength at a Bonded Solid-Solid Interface
CHEN Jian-Jun, ZHANG De, MAO Yi-Wei, CHENG Jian-Chun
Chin. Phys. Lett. 2011, 28 (8): 084301 .   DOI: 10.1088/0256-307X/28/8/084301
Abstract   PDF(pc) (599KB) ( 347 )
We propose a nondestructive method to characterize the quantitative bonding strength at a bonded solid-solid interface by a contact acoustic nonlinearity (CAN) microscope. The principle of the CAN microscope is briefly described. The vibration amplitude of the incident focusing wave at the bonded interface is calculated, the standard bonding strength with a complete bonding state is established by the tension test, and the CAN parameter is calibrated. The quantitative contour of bonding strength at the interface could be obtained. The experimental contours of two samples are also presented.
Simultaneous Measurements of Harmonic Waves at Fatigue-Cracked Interfaces
Hyunjo Jeong**, Dan Barnard
Chin. Phys. Lett. 2011, 28 (8): 084302 .   DOI: 10.1088/0256-307X/28/8/084302
Abstract   PDF(pc) (499KB) ( 450 )
Nonlinear harmonic waves generated at cracked interfaces are investigated theoretically and experimentally. A compact tension specimen is fabricated and the amplitude of the transmitted wave is analyzed as a function of position along the fatigued crack surface. In order to measure as many nonlinear harmonic components as possible, broadband lithium niobate (LiNbO3) transducers are employed together with a calibration technique for making absolute amplitude measurements with fluid−coupled receiving transducers. Cracked interfaces are shown to generate high acoustic nonlinearities, which are manifested as harmonics in the power spectrum of the received signal. The first subharmonic f/2 and the second harmonic 2f waves are found to be dominant nonlinear components for an incident toneburst signal of frequency f. To explain the observed nonlinear behavior, a partially closed crack is modeled by planar half interfaces that can account for crack parameters, such as crack opening displacement and crack surface conditions. The simulation results show reasonable agreement with the experimental results.
MHD Flow of an Oldroyd-B Fluid through a Porous Space Induced by Sawtooth Pulses
Masood Khan*, Zeeshan
Chin. Phys. Lett. 2011, 28 (8): 084701 .   DOI: 10.1088/0256-307X/28/8/084701
Abstract   PDF(pc) (477KB) ( 371 )
We investigate the unsteady magnetohydrodynamic (MHD) flow of an Oldroyd-B fluid through a porous space induced by sawtooth pulses. The fluid is assumed to be electrically conducting in the presence of a transverse uniform magnetic field. The porous space is taken into account using modified Darcy's law for the Oldroyd-B fluid. Exact solutions of the governing problem are obtained by using the Laplace transform method. The effects of the magnetic parameter, the permeability of the porous space and the elasticity parameter of the fluid are studied on the flow characteristics.
Dual Solutions in Unsteady Stagnation-Point Flow over a Shrinking Sheet
Krishnendu Bhattacharyya**
Chin. Phys. Lett. 2011, 28 (8): 084702 .   DOI: 10.1088/0256-307X/28/8/084702
Abstract   PDF(pc) (521KB) ( 948 )
An analysis is made to study the dual nature of solution of unsteady stagnation-point flow due to a shrinking sheet. Using similarity transformations, the governing boundary layer equations are transformed into the self-similar nonlinear ordinary differential equations. The transformed equations are solved numerically using a very efficient shooting method. The study reveals the conditions of existence, uniqueness and non-existence of unsteady similarity solution. The dual solutions for velocity distribution exist for certain values of velocity ratio parameter (c/a), and the increment in the unsteadiness parameter A increases the range of c/a where solution exists. Also, with increasing A, the skin friction coefficient increases for the first solution and decreases for the second.
Experimental Investigation of Flow Drag and Turbulence Intensity of a Channel Flow with Rough Walls
ZHANG Hui-Qiang, LU Hao, WANG Bing**, WANG Xi-Lin
Chin. Phys. Lett. 2011, 28 (8): 084703 .   DOI: 10.1088/0256-307X/28/8/084703
Abstract   PDF(pc) (985KB) ( 659 )
Turbulent flow over rough walls is investigated through acoustic doppler velocimeter measurements. Smooth rods with a diameter of 6 mm are used as roughness elements. The rods are arranged at the channel bottom wall in three ways: longitudinally (along the flow direction); transversely (orthogonally to flow direction); and mesh-shaped (in a staggered mesh). The transverse roughness elements produce higher disturbance and flow drag than longitudinal roughness. Both turbulence intensity and flow drag for mesh-shaped roughness are not significantly different from those of transverse roughness, indicating that the transverse roughness elements mainly affect turbulence characteristics. Both turbulence intensity and flow drag are greatest for transverse rough walls at w/k=7; likewise, both increase with decreasing w/k for longitudinal rough walls. Compared with channel flow over a smooth wall, the turbulence intensity increases considerably, while the flow drag only increases slightly when w/k is small for the three arrangements. This is beneficial for enhancing heat transfer and mixing in channel flows with relatively small flow resistance.
Instability Criterion of One-Dimensional Detonation Wave with Three-Step Chain Branching Reaction Model
TENG Hong-Hui**, JIANG Zong-Lin
Chin. Phys. Lett. 2011, 28 (8): 084704 .   DOI: 10.1088/0256-307X/28/8/084704
Abstract   PDF(pc) (427KB) ( 368 )
One-dimensional detonation waves are simulated with the three-step chain branching reaction model, and the instability criterion is studied. The ratio of the induction zone length and the reaction zone length may be used to decide the instability, and the detonation becomes unstable with the high ratio. However, the ratio is not invariable with different heat release values. The critical ratio, corresponding to the transition from the stable detonation to the unstable detonation, has a negative correlation with the heat release. An empirical relation of the Chapman–Jouguet Mach number and the length ratio is proposed as the instability criterion.
MHD Boundary Layer Flow of Dilatant Fluid in a Divergent Channel with Suction or Blowing
Krishnendu Bhattacharyya**, G. C. Layek
Chin. Phys. Lett. 2011, 28 (8): 084705 .   DOI: 10.1088/0256-307X/28/8/084705
Abstract   PDF(pc) (494KB) ( 896 )
An analysis is carried out to study a steady magnetohydrodynamic (MHD) boundary layer flow of an electrically conducting incompressible power-law non-Newtonian fluid through a divergent channel. The channel walls are porous and subjected to either suction or blowing of equal magnitude of the same kind of fluid on both walls. The fluid is permeated by a magnetic field produced by electric current along the line of intersection of the channel walls. The governing partial differential equation is transformed into a self-similar nonlinear ordinary differential equation using similarity transformations. The possibility of boundary layer flow in a divergent channel is analyzed with the power-law fluid model. The analysis reveals that the boundary layer flow (without separation) is possible for the case of the dilatant fluid model subjected to suitable suction velocity applied through its porous walls, even in the absence of a magnetic field. Further, it is found that the boundary layer flow is possible even in the presence of blowing for a suitable value of the magnetic parameter. It is found that the velocity increases with increasing values of the power-law index for the case of dilatant fluid. The effects of suction/blowing and magnetic field on the velocity are shown graphically and discussed physically.
A Low Voltage Driven Digital-Droplet-Transporting-Chip by Electrostatic Force
GAO An-Ran, LIU Xiang, GAO Xiu-Li, LI Tie**, GAO Hua-Min, ZHOU Ping, WANG Yue-Lin
Chin. Phys. Lett. 2011, 28 (8): 084706 .   DOI: 10.1088/0256-307X/28/8/084706
Abstract   PDF(pc) (926KB) ( 611 )
A low-voltage-driven digital-droplet-transporting chip with an open structure is designed, fabricated and characterized. The digital microfluidic chip is fabricated by the silicon planar process. Using only a single electrode panel, the droplet on the chip can be manipulated by electrostatic force under a dc driving voltage. The actuation principle is proposed and verified by the experiment. The experimental results show that the minimum driving voltage decreases as the thickness of the dielectric layer decreases. The driving voltage for a 3 µL deionized (DI) water droplet is reduced to 15 V in air and 13.5 V in oil by employing a thin dielectric layer of 600 nm with a high dielectric constant and a coating hydrophobic layer on the top. The DI water droplets are also demonstrated to be transported in two dimensions smoothly in a programmable manner, and the maximum transport speed reaches 96 mm/s. The droplets of normal saline, a solution of 0.9 wt% NaCl, are also successfully manipulated on the chip.
Peristaltic Motion of Power-Law Fluid with Heat and Mass Transfer
T. Hayat, **, S. Hina, Awatif A. Hendi
Chin. Phys. Lett. 2011, 28 (8): 084707 .   DOI: 10.1088/0256-307X/28/8/084707
Abstract   PDF(pc) (556KB) ( 733 )
The effects of wall properties and heat and mass transfer on the peristalsis in a power-law fluid are investigated. The solutions for the stream function, temperature, concentration and heat transfer coefficient are obtained. The axial velocity, temperature and mass concentration are studied for different emerging parameters.
Direct Numerical Simulation of Particle Migration in a Simple Shear Flow
LV Hong, TANG Sheng-Li**, ZHOU Wen-Ping
Chin. Phys. Lett. 2011, 28 (8): 084708 .   DOI: 10.1088/0256-307X/28/8/084708
Abstract   PDF(pc) (3282KB) ( 606 )
Motion of a rectangular particle in a two-dimensional vertical shear flow of Newtonian fluid and viscoelastic fluid with different parameters is studied using the finite element arbitrary Lagrangian–Eulerian domain method. The results show that the centerline of the channel is a stable equilibrium position for the neutrally buoyant rectangular particle in a vertical shear flow. Inertia causes the particle to migrate towards the centerline of the channel. In addition, a critical elasticity number exists. When the elasticity number is below the critical value, the rectangular particle migrates to the centerline; otherwise the centerline of the channel is apparently no longer a global attractor of trajectories of the particle.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Preliminary Investigation of a Dielectric Barrier Discharge Lamp in Open Air at Atmospheric Pressure
LIU Feng, WANG Wei-Wei, CHANG Xi-Jiang, LIANG Rong-Qing**
Chin. Phys. Lett. 2011, 28 (8): 085201 .   DOI: 10.1088/0256-307X/28/8/085201
Abstract   PDF(pc) (5099KB) ( 689 )
A dielectric barrier discharge (DBD) lamp is investigated by using sinusoidal power with a 10 kHz frequency in open air at atmospheric pressure. With increasing applied voltages, the different discharge phenomena appear. At relatively low voltages, the discharge states are general stochastic filamentary discharges with weak light. However, at relatively high voltages, the walls of quartz tubes are heated sharply by plasma, and then the dazzling light is emitted very quickly to form the DBD Lamp, corresponding to the low maintaining voltage that is lower than the ignited voltage. The discharge state or mode of the DBD lamp that corresponds to the glow discharge is deduced according to the wave form of the circuit current, which is evidently different from the filamentary discharges. Under these conditions, the spectrum of the DBD lamp is continuous in the range 400–932 nm, which is scanned in the range 300–932 nm. It is also shown that there is another discharge state or mode that is different from the traditional filamentary discharges. Therefore, it is concluded that the discharge state or mode of the DBD lamp is a glow discharge.
Shock-Timing Experiment Using a Two-Step Radiation Pulse with a Polystyrene Target
WANG Feng**, PENG Xiao-Shi, JIAO Chun-Ye, LIU Shen-Ye, JIANG Xiao-Hua, DING Yong-Kun
Chin. Phys. Lett. 2011, 28 (8): 085202 .   DOI: 10.1088/0256-307X/28/8/085202
Abstract   PDF(pc) (801KB) ( 338 )
A shock-timing experiment plays an important role in inertial confinement fusion studies, and the timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. We present an experimental observation of a shock wave driven by a two-step radiation pulse in a polystyrene target. The experiment is carried out at Shen Guang III Yuan Xing (SGIIIYX) laser facility in China, and the generation and coalescence of the two shock waves, originating from each of the two radiation steps, is clearly seen with two velocity interferometers. This two-shock-wave coalescence is also simulated by the radioactive hydrodynamic code of a multi-1D program. The experimental measurements are compared with the simulations and quite good agreements are found, with relatively small discrepancies in shock timing.
Magnetic Fluid Flows in Porous Media*
LI Ming-Jun**, CHEN Liang
Chin. Phys. Lett. 2011, 28 (8): 085203 .   DOI: 10.1088/0256-307X/28/8/085203
Abstract   PDF(pc) (445KB) ( 514 )
The seepage law under a magnetic field is obtained by up-scaling the flow at the pore scale of rigid porous media, and the macroscopic equivalent model is also obtained. It is proved that the macroscopic mass flow depends on the macroscopic magnetic force and the gradients of pressure and of magnetic pressure, as Zahn and Rosensweig have described in their experiments. The permeability tensor is symmetric and positive.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Mechanical Property Evaluation of GaAs Crystal for Solar Cells
JIN Min**, FANG Yong-Zheng, SHEN Hui, JIANG Guo-Jian, WANG Zhan-Yong, XU Jia-Yue
Chin. Phys. Lett. 2011, 28 (8): 086101 .   DOI: 10.1088/0256-307X/28/8/086101
Abstract   PDF(pc) (988KB) ( 940 )
The mechanical properties of Si-doped (111) GaAs crystal for solar cells are investigated by means of a microindentation technique. Vickers' microhardness Hv exhibits a nonlinear relationship with the applied load. In the range of 0.1–1 kg, Hv is decreased from 5.59 GPa to 5.03 GPa. Such a phenomenon is explained on the basis of indenter penetration. The Hv value can effectively be presumed by Kick's law, and Meyer's index n is calculated to be 1.90. For the fracture toughness Kc of the GaAs crystal, it also displays nonlinear behavior related to the applied load, which is caused by energy dissipation during the development process of cracks on the wafer.
Effect of Iodine Additive on Thermostability of Bulk Amorphous Sulfur Prepared by Rapid Compression
LIN Sheng-Xiong, LIU Xiu-Ru**, SHAO Chun-Guang, SHEN Ru, HONG Shi-Ming
Chin. Phys. Lett. 2011, 28 (8): 086102 .   DOI: 10.1088/0256-307X/28/8/086102
Abstract   PDF(pc) (3582KB) ( 498 )
Bulk amorphous sulfur (a-S) with 1 mol% of phosphorus, selenium and iodine additives and bulk amorphous pure sulfur samples were prepared by rapidly compressing the melts to 2 GPa within 20 ms. The results of x-ray diffraction, differential scanning calorimetry and in situ wide angle x-ray scattering of the recovered samples are presented and discussed. In the iodine doping case, obvious inhibiting effects on the crystallization and the melting process under high temperatures occurred, as well as on the structure relaxation of a-S at room temperature, suggesting that the thermal stability of amorphous sulfur is remarkably improved by the introduction of iodine additives.
Hole Mobility of Molecular β-Copper Phthalocyanine Crystal
S. Pengmanayol, T. Osotchan, M. Suewattana, N. Ingadapa, J. Girdpun
Chin. Phys. Lett. 2011, 28 (8): 086103 .   DOI: 10.1088/0256-307X/28/8/086103
Abstract   PDF(pc) (586KB) ( 1150 )
A Monte Carlo approach is used to estimate hole mobilities in molecular β−copper phthalocyanine (CuPc) crystal for different applied electric field directions. Due to the crystal symmetry, the twelve neighboring molecules in the three-dimensional crystal are selected in the hopping rate calculation. Density functional theory is employed to derive the molecular interaction between the central and neighboring molecules for various applied electric fields. The derived molecular hopping rate is applied to 80 × 80 × 80 lattice sites under periodic boundary conditions. In order to achieve accurate statistics, each calculation includes 6561 particles with more than 10000 hopping steps under an applied electric field of 0.5–3.5 MV/cm. The results indicate that the molecular hopping strongly depends on the molecular orientation and neighboring sites related to the applied electric field direction. The estimated carrier mobility can be described by the percentage occupation in each neighboring site and the obtained hole mobility value is in the same range of the measured values of single crystal CuPc. The calculated mobility for applied electric field along the c crystal axis exhibits the highest values while the mobility along the b axis has the smallest value.
A Novel Large Moment Antiferromagnetic Order in K0.8Fe1.6Se2 Superconductor
BAO Wei**, HUANG Qing-Zhen, CHEN Gen-Fu, M. A. Green, WANG Du-Ming, HE Jun-Bao, QIU Yi-Ming,
Chin. Phys. Lett. 2011, 28 (8): 086104 .   DOI: 10.1088/0256-307X/28/8/086104
Abstract   PDF(pc) (1052KB) ( 825 )
The discovery of cuprate high TC superconductors has inspired the search for unconventional superconductors in magnetic materials. A successful recipe has been to suppress long−range order in a magnetic parent compound by doping or high pressure to drive the material towards a quantum critical point. We report an exception to this rule in the recently discovered potassium iron selenide. The superconducting composition is identified as the iron vacancy ordered K0.83(2)Fe1.64(1)Se2 with TC above 30 K. A novel large moment 3.31 μB/Fe antiferromagnetic order that conforms to the tetragonal crystal symmetry has an unprecedentedly high ordering temperature TN≈559 K for a bulk superconductor. Staggeringly polarized electronic density of states is thus suspected, which would stimulate further investigation into superconductivity in a strong spin-exchange field under new circumstances.
Hydrogenic-Donor Impurity States in GaAs/Al xGa 1−xAs Quantum Dots in the Presence of an Electric Field
PAN Jiang-Hong, LIU Li-Zhe, LIU Min**
Chin. Phys. Lett. 2011, 28 (8): 086201 .   DOI: 10.1088/0256-307X/28/8/086201
Abstract   PDF(pc) (834KB) ( 849 )
We report a calculation of binding energy of the ground state of a hydrogenic donor in a quantum cylindrical GaAs dot surrounded by Ga1−xAlxAs with finite confinement potentials, in the presence of a uniform electric field applied parallel to the dot axis. The binding energy increases inchmeal as the radius of the dot decreases until a maximum value for a certain value of the quantum dot radii, then begins to drop quickly. Results for the binding energies and electronic wave function density of the hydrogenic-donor as functions of the impurity position, dot thickness and applied electric field are also presented.
FMAA-MS Investigation into Ni68Fe32 Nanoalloy with Sample Length Less than 30mm
LI Ping-Yun, CAO Zhen-Hua, JIANG Zhong-Hao, MENG Xiang-Kang**
Chin. Phys. Lett. 2011, 28 (8): 086401 .   DOI: 10.1088/0256-307X/28/8/086401
Abstract   PDF(pc) (923KB) ( 360 )
An investigation into the properties of nanocrystalline (NC) materials with sample lengths less than 30 mm seems to be a challenge by using conventional mechanical spectroscopy (MS). We use a newly developed frequency modulation acoustic attenuation mechanical spectroscopy (FMAA-MS) to investigate phase transition in Ni68Fe32 NC alloy (22 nm) where the length of the sample is 10 mm. An internal friction peak accompanied by an abrupt increase in resonant frequency occurs at 641 K, which originates from order-disorder phase transition, confirmed by a vibrating sample magnetometer and differential scanning calorimetry.
Stability of TiO2 and Al2O3 Nanofluids
WANG Xian-Ju, LI Hai, LI Xin-Fang, WANG Zhou-Fei**, LIN Fang
Chin. Phys. Lett. 2011, 28 (8): 086601 .   DOI: 10.1088/0256-307X/28/8/086601
Abstract   PDF(pc) (861KB) ( 2317 )
Aiming at the dispersion stability of nanofluids, we investigate the absorbency and the zeta potential of TiO2 and Al2O3 nanofluids under different pH values and different dispersant concentrations. The results show that in the mass fraction 0.05% alumina and 0.01% titanium dioxide nanosuspensions, the absolute value of the zeta potential and the absorbency of the two nanofluids with sodium dodecyl sulfate (SDS) dispersant are the highest at an optimal pH (pHAl2O3≈6.0, pHTiO2≈9.5) and that there is a good correlation between absorbency and zeta potential: the higher the absolute value of the zeta potential is, the greater the absorbency is, and the better the stability of the system is. The optimizing concentrations for SDS are 0.10% and 0.14%, respectively, at which the two nanofluids have the best dispersion results. The calculated DLVO interparticle interaction potentials verify the experimental results of the pH effect on the stability behavior.
Elimination of the Coherent Artifact in a Pump-Probe Experiment by Directly Detecting the Background-Free Diffraction Signal
LIU Hui, ZHANG Hang, SI Jin-Hai**, YAN Li-He, CHEN Feng, HOU Xun
Chin. Phys. Lett. 2011, 28 (8): 086602 .   DOI: 10.1088/0256-307X/28/8/086602
Abstract   PDF(pc) (1658KB) ( 758 )
The influence of the coherent artifact in a semiconductor Ga-doped ZnO film on femtosecond pump-probe measurement is studied. The coherent artifact mixed into the pump-probe signal can be directly inspected by detecting the background-free first-order diffraction signal induced by the interference between the pump and probe pulses. Experimental results show that by varying the polarization angle or adjusting the relative intensity between the pump and probe pulses, the coherent artifact can be eliminated from the pump-probe measurement.
Spectral Resolution Improvement of Mo/Si Multilayers
WU Wen-Juan**, WANG Zhan-Shan, ZHU Jing-Tao, ZHANG Zhong, WANG Feng-Li, CHEN Ling-Yan, ZHOU Hong-Jun, HUO Tong-Lin
Chin. Phys. Lett. 2011, 28 (8): 086801 .   DOI: 10.1088/0256-307X/28/8/086801
Abstract   PDF(pc) (1224KB) ( 388 )
Theoretically, the spectral resolution of a multilayer can be improved through a combination of utilizing high reflectance orders and by decreasing the thickness of the scattering layer. We fabricate Mo/Si multilayers in the first, second, third, fourth and fifth reflectance orders with Mo layer thicknesses of 3.0 nm and 2.0 nm, respectively, using direct current magnetron sputtering. The structure of the multilayers is characterized with a grazing angle x-ray diffractometer (XRD). Then the reflectivity of the multilayers is measured in a synchrotron radiation facility. The results show that the spectral resolution increases with the increasing reflectance order and with the decreasing Mo layer thickness. The highest spectral resolution is improved to 117.5 in the 5th order for dMo=2 nm, where the reflectivity is 18%.
Structural and Electronic Properties of Sulfur-Passivated InAs(001) ( 2×6 ) Surface
LI Deng-Feng **, GUO Zhi-Cheng, LI Bo-Lin, DONG Hui-Ning, XIAO Hai-Yan
Chin. Phys. Lett. 2011, 28 (8): 086802 .   DOI: 10.1088/0256-307X/28/8/086802
Abstract   PDF(pc) (1137KB) ( 806 )
The structural and electronic properties of S-passivated InAs(001)-(2×6) and InAs(001)−(2×1) surfaces are studied by first−principles total-energy calculations. Based on the calculated adsorption energies and electronic properties, we propose that the reconstruction of a S-treated InAs(001) surface should be InAs(001)–(2×6)S rather than InAs(001)−(2×1)S. This is similar to the adsorption behavior of S on a GaAs(001) surface. The Fermi level of an InAs(001)−(2×6)S surface exists above the conduction band minimum by 371 meV and the energy gap becomes 0.145 eV smaller than the clean surface. A strong surface electron accumulation layer is formed and downward band bending is increased, which is in good agreement with recent experiments.
Electrical, Structural and Interfacial Characterization of HfO2 Films on Si Substrates
TAN Ting-Ting**, LIU Zheng-Tang, LI Yan-Yan
Chin. Phys. Lett. 2011, 28 (8): 086803 .   DOI: 10.1088/0256-307X/28/8/086803
Abstract   PDF(pc) (943KB) ( 793 )
Hafnium oxide films are deposited on Si (100) substrates by means of rf magnetron sputtering. The interfacial structure is studied using high-resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS), and the electrical properties of the Au/ HfO2/Si stack are analyzed by frequency−dependent capacitance-voltage (CVf) measurements. The amorphous interfacial layer between HfO2 and the Si substrate is observed by the HRTEM method. From the results of XPS, the interfacial layer comprises hafnium silicate and silicon oxide. For CVf measurements, the CV plots show a peak at a low frequency and the change in frequency has effects on the intensity of the peak. As expected, rapid thermal annealing can passivate the interface states of the HfO2/Si stack.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Dynamics of Exciton Diffusion in PVK:Phosphorescent Materials/Al Hetero-Structures
YANG Shao-Peng**, HUANG Da, GE Da-Yong, LIU Bo-Ya, WANG Li-Shun, FU Guang-Sheng
Chin. Phys. Lett. 2011, 28 (8): 087101 .   DOI: 10.1088/0256-307X/28/8/087101
Abstract   PDF(pc) (1200KB) ( 1201 )
Exciton quenching dynamics in a polymer PVK doped with FirPic, Ir(piq)2(acac) and Ir(ppy)3 phosphorescent guest materials, respectively, due to the presence of metal films is analyzed using time−resolved photoluminescence. The quenching is directly governed by radiationless energy transfer to the metal and is further enhanced by diffusion of excitons into the depletion region of the exciton population at the polymer/metal interface. The influence of polymer layer thickness on the luminescence decay is described by a one-dimensional diffusion model. The energy transfer distance and exciton diffusion length are 10 nm, 9 nm, 15 nm and 29.3 nm, 30.1 nm, 30.9 nm for PVK doped with phosphorescent guest materials FirPic, Ir(piq)2(acac) and Ir(ppy)3, respectively. This can disentangle the contributions from direct energy transfer to the metal and exciton migration to the exciton quenching process. The lengths of the exciton quenching region of the three doping systems are 39.3 nm, 39.1 nm and 45.9 nm, respectively.
Growth and Properties of Blue and Amber Complex Light Emitting InGaN/GaN Multi-Quantum Wells
XIE Zi-Li**, ZHANG Rong, LIU Bin, XIU Xiang-Qian, SU Hui, LI Yi, HUA Xue-Mei, ZHAO Hong, CHEN Peng, HAN Ping, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2011, 28 (8): 087102 .   DOI: 10.1088/0256-307X/28/8/087102
Abstract   PDF(pc) (795KB) ( 632 )
Blue-red complex light emitting InGaN/GaN multi-quantum well (MQW) structures are fabricated by metal organic chemical vapor deposition (MOCVD). The structures are grown on a 2-inch diameter (0001) oriented (c−face) sapphire substrate, which consists of an approximately 2-µm−thick GaN template and a five-period layer consisting of a 4.9-nm-thick In0.18Ga0.82N well layer and a GaN barrier layer. The surface morphology of the MQW structures is observed by an atomic force microscope (AFM), which indicates the presence of islands of several tens of nanometers in height on the surface. The high resolution x−ray diffraction (XRD) θ/2θ scan is carried out on the symmetric (0002) of the InGaN/GaN MQW structures. At least four order satellite peaks presented in the XRD spectrum indicate that the thickness and alloy compositions of the individual quantum wells are repeatable throughout the active region. Besides the 364 nm GaN band edge emission, two main emissions of blue and amber light from these MQWs are found, which possibly originate from the carrier recombinations in the InGaN/GaN QWs and InGaN quasi-quantum dots embedded in the QWs.
Electronic Properties of Boron Nanotubes under Uniaxial Strain: a DFT study
PAN Li-Jun, JIA Yu, **, SUN Qiang, HU Xing
Chin. Phys. Lett. 2011, 28 (8): 087103 .   DOI: 10.1088/0256-307X/28/8/087103
Abstract   PDF(pc) (1608KB) ( 845 )
Electronic structures of a uniaxially stretched boron nanotube (BNT) are studied by the density functional theory (DFT) and compared with a zigzag single-walled carbon nanotube (CNT). It is verified that modifications of the electronic band structures of CNTs may be classified into three patterns depending on their helicity under the applied strain up to 20%. However, for the BNT, the partial boron bonds will be broken as the applied strain is more than 10%, indicating its poor deformation ability as compated with CNTs. Moreover, the band gap of the BNT keeps or converts to zero regardless of its chirality as the applied strain increases, which is drastically distinct from the CNT. The special behavior of the BNT implies a potential application as an excellent stress sensor.
Current Transport in Copper Schottky Contacts to a−Plane/ c−Plane n-Type MoSe2
C. K. Sumesh**, K. D. Patel, V. M. Pathak, R. Srivastav
Chin. Phys. Lett. 2011, 28 (8): 087201 .   DOI: 10.1088/0256-307X/28/8/087201
Abstract   PDF(pc) (565KB) ( 423 )
We identically prepared Cu-nMoSe2 (a−plane) and Cu-nMoSe2 (c−plane) Schottky barrier diodes (SBDs) on the same n-type MoSe2 single crystal. The effective Schottky barrier heights (SBHs) and ideality factors were obtained from the current−voltage-temperature (IVT) characteristics. The barrier height and ideality factor, estimated from the conventional thermionic emission model by assuming a Gaussian barrier distribution, are highly dependent on temperature. A notable deviation from the theoretical Richardson constant value is also observed in the conventional Richardson plot. The decrease in the experimental barrier height ΦB0 and an increase in the ideality factor n with a decrease in temperature have been explained on the basis of barrier height inhomogeneities at the metal−semiconductor interface. It is proven that the presence of a distribution of barrier heights is responsible for the apparent decrease of the zero bias barrier height. The voltage dependence of the standard deviation causes the increase of the ideality factor at low temperatures. The value of the Richardson constant obtained without considering the inhomogeneous barrier heights is much closer than the theoretical value. The Cu-nMoSe2 (a−plane) Schottky diode shows better results in comparison with the nMoSe2 (c-plane) Schottky diode.
Leakage Current and Photovoltaic Properties in a Bi2Fe4O9/Si Heterostructure
JIN Ke-Xin**, LUO Bing-Cheng, ZHAO Sheng-Gui, WANG Jian-Yuan, CHEN Chang-Le
Chin. Phys. Lett. 2011, 28 (8): 087301 .   DOI: 10.1088/0256-307X/28/8/087301
Abstract   PDF(pc) (909KB) ( 537 )
A heterostructure composed of a Bi2Fe4O9 film and an n−type Si substrate is fabricated. The characteristics of leakage current density versus electric field are investigated and the leakage current density is about 6×10−6 A/cm2 at an electric field of 200 kV/cm at 300 K. A strong photovoltaic effect is observed when the heterostructure is exposed to a laser pulse with a wavelength of 532 nm and a power of 6 mW/mm2. It is found that the peak photovoltages initially increase with decreasing temperature, followed by a decrease at T<210 K. These results reveal that the heterostructure is a promising candidate for photovoltaic devices that are compatible with Si integrated circuits.
Oscillations of Low-Field Magnetoresistivity of Two-Dimensional Electron Gases in Al0.22Ga0.78N/GaN Heterostructures in a Weak Localization Region
HAN Kui, TANG Ning**, DUAN Jun-Xi, LU Fang-Chao, LIU Yu-Chi, SHEN Bo**, ZHOU Wen-Zheng, LIN Tie, SUN Lei, YU Guo-Lin, CHU Jun-Hao
Chin. Phys. Lett. 2011, 28 (8): 087302 .   DOI: 10.1088/0256-307X/28/8/087302
Abstract   PDF(pc) (814KB) ( 410 )
Low-field magnetotransport properties of two-dimensional electron gases (2DEGs) are investigated in Al0.22Ga0.78N/GaN heterostructures. By means of a tilting magnetic field, unexpected oscillations of magnetoresistivity are observed in a weak localization region. Qualitative understanding based on Altshuler–Aronov–Spivak oscillations is proposed for the case of interface disorder in Al0.22Ga0.78N/GaN heterostructures.
Transformation from AA to AB-Stacked Bilayer Graphene on α−SiO2 under an Electric Field
LIU Yan, AO Zhi-Min**, WANG Tao**, WANG Wen-Bo, SHENG Kuang, YU Bin,
Chin. Phys. Lett. 2011, 28 (8): 087303 .   DOI: 10.1088/0256-307X/28/8/087303
Abstract   PDF(pc) (954KB) ( 1429 )
The energetic and electronic structure of bilayered graphene (BLG) with AA stacking arrangement on a SiO2 substrate is investigated in the presence of an electric field F of different intensities by ab initio density functional calculations. The AA−stacked bilayer graphene is stable on the SiO2 substrate in the absence of an electric field. However, as F increases, the AA-stacked bilayer graphenes are gradually shifted with each other and finally transfers into AB-stacked bilayer graphenes. The bandgap is accordingly changed.
Rectifying Characteristics and Transport Behavior in a Schottky Junction of CaCu 3Ti4O12 and Pt
CHEN Cong, NING Ting-Yin, WANG Can**, ZHOU Yue-Liang, ZHANG Dong-Xiang, WANG Pei, MING Hai, YANG Guo-Zhen
Chin. Phys. Lett. 2011, 28 (8): 087304 .   DOI: 10.1088/0256-307X/28/8/087304
Abstract   PDF(pc) (1058KB) ( 392 )
CaCu3Ti4O12 (CCTO) thin films were fabricated on ITO−covered MgO (100) substrates. The rectification characteristics were observed in the CCTO capacitance structure with Pt top electrodes at temperatures ranging from 150 K to 330 K, which are attributed to the formation of a Schottky junction between n-type semiconducting CCTO and Pt due to the difference of their work functions. At low forward-bias voltage, the current-voltage characteristics of the Schottky junction follow J=JsD exp[qV/(k0T)]. A strong decrease in ideality factor with the increasing temperature is obtained by linear fitting at the low bias voltage.
Influence of Fluorine on the Conductivity and Oxidation of Silicon Nanomembranes after Hydrofluoric Acid Treatment
ZHAO Xiang-Fu**, HAN Ping, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2011, 28 (8): 087305 .   DOI: 10.1088/0256-307X/28/8/087305
Abstract   PDF(pc) (741KB) ( 510 )
After immersion in hydrofluoric acid, the sheet resistance of a 220-nm-thick silicon nanomembrane, measured in dry air by van der Pauw method, drops around two orders of magnitude initially, then increases and reaches the level of a sample with a native oxide surface in about one month. The surface component and oxidation rate are also characterized by x-ray photo electronic spectroscopy measurement. Fluorine is found to play a significant role in improving conductivity and has no apparent influence on the oxidation rate after hydrofluoric acid treatment.
Dipolar and Quadrupolar Modes of SiO2/Au Nanoshell Enhanced Light Trapping in Thin Film Solar Cells
BAI Yi-Ming**, WANG Jun, CHEN Nuo-Fu, YAO Jian-Xi, ZHANG Xing-Wang, YIN Zhi-Gang, ZHANG Han, HUANG Tian-Mao
Chin. Phys. Lett. 2011, 28 (8): 087306 .   DOI: 10.1088/0256-307X/28/8/087306
Abstract   PDF(pc) (844KB) ( 740 )
Dipolar and quadrupolar resonance wavelengths of SiO2/Au nanoshell surface plasmons are designed at 560 nm to enhance the light trapping in thin film solar cells. In order to quantitatively describe the light trapping effect, the forward−scattering efficiency (FSE) and the light trapping efficiency (LTE) are proposed by considering the light scattering direction of SiO2/Au nanoshells. Based on the Mie theory, the FSE and the LTE are calculated for SiO2/Au nanoshells of different dimensions, and the contributions of the dipolar and quadrupolar modes to the light trapping effect are analyzed in detail. When the surface coverage of nanoshells is 5%, the LTEs are 21.7% and 46.9% for SiO2/Au nanoshells with sizes of (31 nm, 69 nm) and (53 nm, 141 nm), respectively. The results indicate that the SiO2/Au nanoshell whose quadrupolar mode peak is designed to the strongest solar energy flux density of the solar spectrum facilitates the further enhancement of light harvesting in thin film solar cells.
Influence of Magnetic Scattering and Interface Transparency on Superconductivity Based on a Ferromagnet/Superconductor Heterostructure
PENG Lin**, LIU Yong-Sheng, CAI Chuan-Bing, ZHANG Jin-Cang
Chin. Phys. Lett. 2011, 28 (8): 087401 .   DOI: 10.1088/0256-307X/28/8/087401
Abstract   PDF(pc) (897KB) ( 337 )
We investigate an antiferromagnet/ferromagnet/superconductor/ferromagnet (AF/F/S/F) spin-valve system with nanoscopic scale, described by Usadel equations in the dirty limit. The results show that the superconducting characteristics in the system strongly depend not only on the mutual orientation and thickness of two ferromagnetic layers, but also on the interface transparency and the magnetic scattering. The superconducting critical temperature can exhibit three types of characteristic behaviors with a variation of interface transparency. In particular, the reentrance phenomenon of the superconductivity is observed at the interface transparency γB ξnf =7.1, while the reentrance phenomenon disappears in the presence of magnetic scattering. In addition, it is also found that the introduction of magnetic scattering results in the decrease of the spin-valve effect. The obtained results could provide some practical recommendations for the spin-valve effect in experimental observation.
Structural, Electronic and Optical Properties of BiAl xGa1−xO3 (x=0, 0.25, 0.5 and 0.75)
GONG Sai, WANG Yue-Hua**, ZHAO Xin-Yin, ZHANG Min, ZHAO Na, DUAN Yi-Feng
Chin. Phys. Lett. 2011, 28 (8): 087402 .   DOI: 10.1088/0256-307X/28/8/087402
Abstract   PDF(pc) (2100KB) ( 1520 )
A first principles study using the full potential linearized augmented plane wave (FP-LAPW) method is applied to study the structural, electronic and optical properties of BiAlxGa1−xO3. The results show that the alloys become markedly hard as the Al concentration increases. The calculated structural parameters are in good agreement with the experimental data. The band structure and density of states are obtained, which indicate that BiAlxGa1−xO3 has an indirect band gap. Moreover, the optical properties are calculated and analyzed in detail. It is proposed that BiAlxGa1−xO3 is a promising dielectric material.
Fabrication of High-Quality Niobium Superconducting Tunnel Junctions
XU Qin-Yin, CAO Chun-Hai, LI Meng-Yue, JIANG Yi, ZHA Shi-Tong, KANG Lin, XU Wei-Wei, CHEN Jian**, WU Pei-Heng
Chin. Phys. Lett. 2011, 28 (8): 087403 .   DOI: 10.1088/0256-307X/28/8/087403
Abstract   PDF(pc) (1189KB) ( 534 )
For high-quality superconducting tunnel junctions (STJs), it is necessary to reduce leakage current as much as possible. We describe the fabrication of niobium STJs using the selective niobium (Nb) etching process and various ways to minimize the leakage current. The experiment shows that the leakage current mainly comes from shorts in the tunnel barrier layer rather than those around the junction edges. Through systematic analysis of the thin film stress, surface morphology and modified junction structures, we fabricate high-quality Nb STJs with a gap voltage of 2.8 mV and a leakage current at 1 mV as low as 8.1% and 0.023% at 4.2 K and 0.3 K, respectively.
Magnetic Performance of a Nanocomposite Permanent Material
LIU Min**, HAN Guang-Bing, GAO Ru-Wei
Chin. Phys. Lett. 2011, 28 (8): 087501 .   DOI: 10.1088/0256-307X/28/8/087501
Abstract   PDF(pc) (525KB) ( 299 )
We build a sandwiched structure model in which the intergranular phase (IP) is homogeneously distributed between soft and hard magnetic grains, and gives a continuously anisotropic expression of the coupling part under the assumption that the IP weakens the intergrain exchange-coupling interaction. Based on the idea that the hardening mechanism is of the pinning type, we calculate the effect of the IP's thickness d and its anisotropy constant K1(0) on the intrinsic coercivity of a nanocomposite permanent material. The calculated results indicate that the domain wall goes twice through irreversible domain wall displacement during the process of moving from soft to hard magnetic grains, and the intrinsic coercivity increases with increasing d, but decreases with increasing K1(0). When d and K1(0) take 2 nm and 0.7Kh, respectively, with Kh being the anisotropy constant in the inner part of the hard magnetic grain, the calculated intrinsic coercivity is in good agreement with the experimental data.
Piezoresponse Force Microscopy Imaging of Ferroelectric Domains in Bi(Zn1/2Ti1/2)O3−Pb(Mg1/3Nb2/3)O3−PbTiO3 Piezoelectric Ceramics
LIU Li-Ming, ZENG Hua-Rong**, CAO Zhen-Zhu, LENG Xue, ZHAO Kun-Yu, LI Guo-Rong, YIN Qing-Rui
Chin. Phys. Lett. 2011, 28 (8): 087701 .   DOI: 10.1088/0256-307X/28/8/087701
Abstract   PDF(pc) (1445KB) ( 415 )
Bismuth zinc titanate dopied lead magnesium niobate-lead titanate [Bi(Zn1/2Ti1/2)O3−Pb(Mg1/3Nb2/3)O3−PbTiO3 (BZT-PMN-PT)] piezoelectric ceramics are synthesized by the conventional solid state reaction method. Ferroelectric domain structures and the evolutionary behavior of BZT-PMN-PT ceramics under an external in-plane electric field are investigated by piezoresponse force microscopy (PFM). It is found that the BZT doping has a significant effect on the domain configurations and the domain kinetic behavior of the piezoelectric BZT-PMN-PT solid solution ceramics. Microdomains embedded in the macrodomains, induced by the BZT dopant in the solid solution ceramics, are clearly observed by PFM and their volume increases with increasing amounts of BZT doping. The microdomains of BZT-PMN-PT piezoelectric ceramics exhibit better domain dynamic behavior stability than macrodomains under an external in-plane electric field.
Femtosecond Pulse Propagation in a Symmetric Gap Surface Plasmon Polariton Waveguide
LU Zhi-Xin, YU Li, **, LIU Bing-Can, , ZHANG Kai, SONG Gang,
Chin. Phys. Lett. 2011, 28 (8): 087801 .   DOI: 10.1088/0256-307X/28/8/087801
Abstract   PDF(pc) (713KB) ( 405 )
We investigate the effect of a symmetric gap surface plasmon polariton (SPP) waveguide on ultrashort pulses with a central wavelength of 850 nm and a width of 20 fs using the finite-difference time-domain method. The length of the waveguide is 560 nm. Linear and nonlinear dielectrics are chosen to be the core layers whose thicknesses are set to be 20, 50, 100 and 200 nm, respectively. The results show that for the linear case, strong coupling of the SPP mode can lead to the pulse tailing phenomenon and spectrum compression due to waveguide resonance. For the nonlinear case, the output pulse is broadened and the fluctuation is more complex than the input pulse and can induce the spectrum splitting as well. The smaller the thickness of the core layer is, the more distinct the pulse distortion is, which may be due to the combined effects of dispersion, waveguide resonance and self-phase modulation.
Fast Modification of Microdischarge Emission Bands by Fracture of Sugar
Sergej Aman**, Juergen Tomas, A. Streletskii
Chin. Phys. Lett. 2011, 28 (8): 087802 .   DOI: 10.1088/0256-307X/28/8/087802
Abstract   PDF(pc) (444KB) ( 482 )
Intensive light pulses with widths of about 10 ns were observed during the crack propagation by cleavage of crystalline sugar at atmospheric pressure. The observed light pulses were caused by a sequence of gas microdischarges (MDs). The pulses were detected in the UV/VIS and NIR wavelength ranges. First the light pulses appear in the UV/VIS wavelength range, and then after a delay of about 0.4–1.2 ns in the NIR wavelength range. This characteristic feature of MDs can be used for the characterization of crack propagation.
Temperature-Induced Phase Transition of In2O3 from a Rhombohedral Structure to a Body-Centered Cubic Structure
YANG Lin-Hong, DONG Hong-Xing, SUN Zheng, SUN Liao-Xin, SHEN Xue-Chu, CHEN Zhang-Hai**
Chin. Phys. Lett. 2011, 28 (8): 087803 .   DOI: 10.1088/0256-307X/28/8/087803
Abstract   PDF(pc) (1993KB) ( 474 )
We report an experimental study on the temperature-induced phase transition of three-dimensional nanosheet-based flower-like microspheres (NBFMs) of In2O3. Using InOOH as precursor, rhombohedral−In2O3 NBFMs are fabricated. Temperature−induced phase transition of In2O3 NBFMs from a rhombohedral (rh) structure to a body−centered cubic (bcc) structure is examined by Raman spectroscopy and x-ray diffraction. The critical phase transition temperature is found to be about 500 °C. Photoluminescence (PL) spectra of In2O3 are measured before annealing and after annealing at different temperatures. The PL spectral results provide further evidence for the phase transition, confirming the fabrication of bcc−In2O3 NBFMs via a simple annealing method.
Optical Temperature Sensor Using Infrared-to-Visible-Frequency Upconversion in Er 3+/Yb 3+−Codoped Bi3TiNbO9 Ceramics
CHEN Heng-Zhi, YANG Bin**, SUN Yan, ZHANG Ming-Fu, WANG Zhu, ZHANG Rui, ZHANG Zhi-Guo, CAO Wen-Wu,
Chin. Phys. Lett. 2011, 28 (8): 087804 .   DOI: 10.1088/0256-307X/28/8/087804
Abstract   PDF(pc) (942KB) ( 862 )
An optical temperature sensor based on infrared-to-visible upconversion emission in Er3+/Yb3+ co−doped Bi3TiNbØ9 (BTN) ceramics is reported. The fluorescence intensity ratio of the green upconversion photoluminescence (UC−PL) around 524 nm and 545 nm depends on temperature. The operating temperature range and the maximum sensitivity of Er3+/Yb3+ co−doped Bi3TiNbO9 ceramics are 123–693 K and 0.0032 K−1, respectively. BTN:Er3+/Yb3+ ceramic has good thermal, physical and chemical stability, great UC−PL intensity and low cost fabrication. The results imply that Er3+/Yb3+ co−doped Bi3TiNbO9 ceramic is promising for applications in wide-temperature-range sensors.
Raman and Mid-IR Spectral Analysis of the Atacamite-Structure Hydroxyl/Deuteroxyl Nickel Chlorides Ni2(OH/D)3Cl
LIU Xiao-Dong, **, Hagihala Masato, ZHENG Xu-Guang, **, MENG Dong-Dong, GUO Qi-Xin
Chin. Phys. Lett. 2011, 28 (8): 087805 .   DOI: 10.1088/0256-307X/28/8/087805
Abstract   PDF(pc) (1376KB) ( 452 )
Vibrational spectra (Raman 4000–95 cm−1 and mid-IR 4000–400 cm−1) of the atacamite-structure Ni2(OH)3Cl, including a rarely reported kind of asymmetric trimetric hydrogen bond, as a member of the geometrically frustrated material series and its deuteride Ni2(OD)3Cl are, to the best of our knowledge, reported for the first time and analyzed at room temperature. Through a comparative study of four spectra according to their crystal structural parameters, we assign OH stretching modes v(OH) in a functional group region (3700–3400 cm−1) and their deformation modes δ(NiOH/D) in the correlation peak region (900–600 cm−1) with the corresponding mode frequency ratios ωv(OD)/ωv(OH)73% and ωδ(NiOD)/ωδ(NiOH)75%, and further self−consistently suggest Ni-O and Ni-Cl related modes in the fingerprint region (500–200 cm−1 and 200–0 cm−1, respectively) by use of the unified six-ligand NiO5Cl and NiO4Cl2 frames. This report may contribute to the spectral analysis of other hydroxyl transition-metal halides and to the understanding of the fundamental physics of their exotic magnetic geometrical frustration property from the spectral changes around the corresponding low transition temperatures.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Floating Zone Growth and Thermionic Emission Property of Single Crystal CeB6
BAO Li-Hong, ZHANG Jiu-Xing**, ZHOU Shen-Lin, ZHANG Ning, XU Hong
Chin. Phys. Lett. 2011, 28 (8): 088101 .   DOI: 10.1088/0256-307X/28/8/088101
Abstract   PDF(pc) (2339KB) ( 612 )
Large-sized and high-quality cerium hexaboride (CeB6) single crystals are successfully grown by the optical floating zone method. The structure, chemical composition and thermionic emission properties of the crystal are characterized by x−ray diffraction, x-ray fluorescence and emission measurements, respectively. Based on the observation of single crystal diffraction, the relative density of feed rods has a great effect on the quality of the grown crystal. The thermionic emission measurement results show that the emission current density of the single crystal is 47.1 A/cm2 at 1873 K with an applied voltage of 1 kV, which is about two times larger than the value for polycrystalline samples. The single crystal possesses excellent emission current stability. Therefore, it is expected that CeB6 single crystal is a very promising material for thermionic cathode applications.
Modeling of PZT Ferroelectric Ceramic Depolarization Driven by Shock Stress
LAN Chao-Hui**, PENG Yu-Fei LONG Ji-Dong, WANG Qiang, WANG Wen-Dou
Chin. Phys. Lett. 2011, 28 (8): 088301 .   DOI: 10.1088/0256-307X/28/8/088301
Abstract   PDF(pc) (890KB) ( 552 )
Shock-induced phase transition of ferroelectric ceramic PZT 95/5 causes elastic stiffening and depolarization, releasing stored electrostatic energy into the load circuit. We develop a model to describe the response of the PZT ferroelectric ceramic and implement it into simulation codes. The model is based on the phenomenological theory of phase transition dynamics and takes into account the effects of the self-generated intensive electrical field and stress. Connected with the discharge model and external circuit, the whole transient process of PZT ceramic depoling can be investigated. The results show the finite transition velocity of the ferroelectric phase and the double wave structure caused by phase transition. Simulated currents are compared with the results from experiments with shock pressures varying from 0.4 to 2.8 GPa.
Double-Teeth-Shaped Plasmonic Waveguide Electro-Optical Switches
ZHU Jia-Hu, HUANG Xu-Guang**, MEI Xian
Chin. Phys. Lett. 2011, 28 (8): 088501 .   DOI: 10.1088/0256-307X/28/8/088501
Abstract   PDF(pc) (701KB) ( 688 )
An electro-optical switch based on a plasmonic T-shaped waveguide structure with a double-teeth-shaped waveguide filled with 4-dimethylamino-N-methyl-4-stilbazolium tosylate is proposed and numerically investigated. The Finite-difference time domain simulation results reveal that the structure can operate as a circuit switch by controlling the external voltages V1 and/or V2. The proposed structure can also operate as a variable optical attenuator, which can continuously attenuate the power of a light beam from 6 dB to 30 dB by an external electrical field. The structure is of small size of a few hundred nanometers. Our results may open a possibility to construct nanoscale high-density photonic integration circuits.
Spin Filtering in a Nanowire Superlattice by Dresselhause Spin-Orbit Coupling
Samad Javidan*
Chin. Phys. Lett. 2011, 28 (8): 088502 .   DOI: 10.1088/0256-307X/28/8/088502
Abstract   PDF(pc) (487KB) ( 443 )
An InAs/GaSb nanowire superlattice using GaAs for the impure layers is proposed. Dresselhaus spin-orbit coupling eliminates spin degeneracy, induces one miniband in the superlattices to split into two minibands and leads to complete spin polarization and excellent filtering by optimizing the well and barrier widths and GaAs layer distances.
Electronic Properties of the N2C4 Cluster of DNA
WANG Yong-Juan **, CHENG Jie, YUE Xian-Fang
Chin. Phys. Lett. 2011, 28 (8): 088701 .   DOI: 10.1088/0256-307X/28/8/088701
Abstract   PDF(pc) (386KB) ( 361 )
The electronic density of state and atomic magnetic moment of the N2C4 cluster of DNA bases are studied. The results show that there are at least two metastable states around the ground state. The electronic structures of those states are found to differ from each other. The cluster exhibits semiconductor properties and antiferromagnetism in the ground state, while it exhibits ferromagnetism and metal properties in the metastable state.
Estimating RNA Loop Entropies Using a New Nucleobase Model and Sequential Monte Carlo Method
LIN Hui**, ZHANG Jian**
Chin. Phys. Lett. 2011, 28 (8): 088702 .   DOI: 10.1088/0256-307X/28/8/088702
Abstract   PDF(pc) (1031KB) ( 310 )
We report a new scheme that is designed to accurately and efficiently compute the entropy of RNA loops. The scheme is based on a new RNA nucleobase discrete state (RNAnbds) model and a Sequential Monte Carlo (SMC) method. The novelty of the RNAnbds model is that it directly represents the conformation of the RNA nucleobases, instead of the RNA backbones. To test the performance of this new scheme, we calculate the entropies for RNA hairpin loops and compare the results with the exact computational values obtained by an enumeration strategy and with the experimental data. It is found that the SMC method gives almost indistinguishable results from enumerations for short loops. For long hairpin loops, it also provides a good estimation that agrees with experiments.
Viscoelastic Characteristics of Fins, Muscle and Skin in Crucian Carp (Carassius Auratus) Described by the Fractional Zener Model
CHEN Ming, JIA Lai-Bing, YIN Xie-Zhen**
Chin. Phys. Lett. 2011, 28 (8): 088703 .   DOI: 10.1088/0256-307X/28/8/088703
Abstract   PDF(pc) (985KB) ( 559 )
Fish are supposed to be able to adapt to various underwater environments. The mechanical properties of the body of a fish is of essential importance in order to explore the source of high efficiency during fish swimming. We investigate the viscoelastic properties of the fins, muscle and skin of Crucian carp (carassius auratus). A fractional Zener model is used to fit the relaxation force and the results show that the model can describe the relaxation process well. With a Fourier transform, we discuss the response functions of the fins, muscle and skin of Crucian carp under the external excitation of a harmonic force. Comparison of these results with the cruising frequency of Crucian carp shows that the dissipation due to internal viscoelasticity during cruising is small.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Non-Markovian and Non-Perturbative Entanglement Dynamics of Biomolecular Excitons
LIU Zhi-Qiang, LIANG Xian-Ting**
Chin. Phys. Lett. 2011, 28 (8): 089201 .   DOI: 10.1088/0256-307X/28/8/089201
Abstract   PDF(pc) (881KB) ( 431 )
We investigate the entanglement dynamics of two coupled chromophore pairs embedded in a protein-solvent environment. The non-Markovian and non-perturbative hierarchical expansion technique is used in the solution of the quantum dynamics. The spectral distribution function of the bath is set with the Drude–Lorentz form. It is shown that the evolutions of the entanglement described by the measures of negativity and concurrence are in agreement with each other. They decay to zero in a short time and the sudden death and sudden birth can be observed in the process of the evolutions of the entanglement.
Department of Physics and Institute of Modern Physics, Ningbo University, Ningbo 315211
ZHANG Shao-Hua, **, FENG Xue-Shang, WANG Yi, YANG Li-Ping,
Chin. Phys. Lett. 2011, 28 (8): 089601 .   DOI: 10.1088/0256-307X/28/8/089601
Abstract   PDF(pc) (1045KB) ( 379 )
The evolutionary process of magnetic reconnection under solar coronal conditions is investigated with our recently developed 2.5D adaptive mesh refinement (AMR) resistive magneto hydrodynamics (MHD) model. We reveal the successive fragmentation and merging of plasmoids in a long-thin current sheet with Lundquist number Rm=5.0×104. It is found that several big magnetic islands are formed eventually, with many slow-mode shocks bounding around the outflow regions. The multi-scale hierarchical-like structures of the magnetic reconnection are well resolved by the model and the AMR technique of the model can capture many fine pictures (e.g., the near-singular diffusion regions) of the development and simultaneously it can save a great deal of computing resources.
PSR J1614-2230 May Include Hyperons
YU Zi**, DING Wen-Bo, BAO Tmurbagan, LIU Ning-Ning
Chin. Phys. Lett. 2011, 28 (8): 089701 .   DOI: 10.1088/0256-307X/28/8/089701
Abstract   PDF(pc) (1131KB) ( 379 )
In the framework of the relativistic mean field theory, it is found that recently discovered PSR J1614-2230 with mass of 1.97±0.04Mʘ may include hyperons when the weakly interacting light boson (WILB) is considered. To describe PSR J1614−2230 with the equation of state (EOS) including hyperons, the characteristic scale of the WILB (g2/μ2) should lie in the range of 13–46 (24–46) GeV−2 with the weak (strong) hyperon-hyperon (YY) interaction. The measurements of inertial momentum and the total neutrino luminosity of the neutron star could be used to further constrain the characteristic scale of the WILB. Before more stringent constraint on the WILB is given, the mass measurement of the neutron star could not exclude any soft EOS.
Fermi γ-Ray Pulsars: Spectral and Generation Order Parameters
CAI Yan, A. Taani**, WANG Wei, ZHAO Yong-Heng, ZHANG Cheng-Min
Chin. Phys. Lett. 2011, 28 (8): 089702 .   DOI: 10.1088/0256-307X/28/8/089702
Abstract   PDF(pc) (748KB) ( 353 )
We examine the theory of generation order parameters. Three kinds of generation order parameters are introduced, which describe the production of high-energy γ photons in a cascade process scenario. We find a correlation between the average power−law photon index Γ and spin−down rate .P in 38 common FERMI γ−ray pulsars, and find that the third generation order parameter, which implies that the magnetic field may have the most significant effect on the high-energy γ photon absorption in the cascade processes, is the best one. The statistical work shows that the theory of generation order parameters can be applied to describe the the γ-ray pulsar radiation mechanisms in the cascade processes.
Original Articles
Inflation and Singularity of a Bianchi Type-VII0 Universe with a Dirac Field in the Einstein–Cartan Theory
HUANG Zeng-Guang**, FANG Wei, , LU Hui-Qing,
Chin. Phys. Lett. 2011, 28 (8): 089801 .   DOI: 10.1088/0256-307X/28/8/089801
Abstract   PDF(pc) (445KB) ( 329 )
We discuss Bianchi type-VII0 cosmology with a Dirac field in the Einstein–Cartan (E−C) theory and obtain the equations of the Dirac and gravitational fields in the E-C theory. A Bianchi type-VII0 inflationary solution is found. When 3S2/16−σ2 > 0, the Universe may avoid singularity.
Locally Rotationally Symmetric Bianchi Type-II Magnetized String Cosmological Model with Bulk Viscous Fluid in General Relativity
Atul Tyagi*, Keerti Sharma
Chin. Phys. Lett. 2011, 28 (8): 089802 .   DOI: 10.1088/0256-307X/28/8/089802
Abstract   PDF(pc) (379KB) ( 449 )
The locally rotationally symmetric Bianchi type-II magnetized string cosmological model with bulk viscous fluid is investigated. The magnetic field is due to an electric current produced along the x−axis. Thus the magnetic field is in the yz plane and F23 is the only non−vanishing component of electromagnetic field tensor Fij. To obtain the deterministic model in terms of cosmic time t, we have assumed the condition ξθ=const, where ξ is the coefficient of bulk viscosity and θ is the expansion in the model.
Bianchi Type-I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in the Bimetric Theory of Gravitation
N. P. Gaikwad**, M. S. Borkar, S. S. Charjan
Chin. Phys. Lett. 2011, 28 (8): 089803 .   DOI: 10.1088/0256-307X/28/8/089803
Abstract   PDF(pc) (444KB) ( 419 )
We investigate the Bianchi type-I massive string magnetized barotropic perfect fluid cosmological model in Rosen's bimetric theory of gravitation with and without a magnetic field by applying the techniques used by Latelier (1979, 1980) and Stachel (1983). To obtain a deterministic model of the universe, it is assumed that the universe is filled with barotropic perfect fluid distribution. The physical and geometrical significance of the model are discussed. By comparing our model with the model of Bali et al. (2007), it is realized that there are no big-bang and big-crunch singularities in our model and T=0 is not the time of the big bang, whereas the model of Bali et al. starts with a big bang at T=0. Further, our model is in agreement with Bali et al.(2007) as time increases in the presence, as well as in the absence, of a magnetic field.
99 articles