Chin. Phys. Lett.

Volume 25 Issue 7

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Multisoliton Solutions for the Isospectral and Nonisospectral BKP Equation with Self-Consistent Sources

DENG Shu-Fang

Chin. Phys. Lett. 2008, 25 (7): 2331-2334 .

Abstract

PDF(pc) (101KB) ( 802 )

The isospectral and nonisospectral BKP equation with self-consistent sources is derived to study the linear problem of the BKP system. The bilinear form of the nonisospectral BKP equation with self-consistent sources is given and the N-soliton solutions are obtained with the Hirota method and Pfaffian technique, respectively.

Original Articles

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An Explicit Scheme for the KdV Equation

WANG Hui-Ping, WANG Yu-Shun, HU Ying-Ying

Chin. Phys. Lett. 2008, 25 (7): 2335-2338 .

Abstract

PDF(pc) (222KB) ( 1909 )

A new explicit scheme for the Korteweg--de Vries (KdV) equation is proposed. The scheme is more stable than the Zabusky--Kruskal scheme and the multi-symplectic six-point scheme. When used to simulate the collisions of multi-soliton, it does not show the nonlinear instabilities and un-physical oscillations.

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A New Method for Constructing Travelling Wave Solutions to the modified Benjamin--Bona--Mahoney Equation

WANG Jun-Mao, ZHANG Miao, ZHANG Wen-Liang, ZHANG Rui, HAN Jia-Hua

Chin. Phys. Lett. 2008, 25 (7): 2339-2341 .

Abstract

PDF(pc) (197KB) ( 755 )

We present a new method to find the exact travelling wave solutions of nonlinear evolution equations, with the aid of the symbolic computation. Based on this method, we successfully solve the modified Benjamin--Bona--Mahoney equation, and obtain some new solutions which can be expressed by trigonometric functions and hyperbolic functions. It is shown that the proposed method is direct, effective and can be used for many other nonlinear evolution equations in mathematical physics.

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Application of Symplectic Algebraic Dynamics Algorithm to Circular Restricted Three-Body Problem

LU Wei-Tao, ZHANG Hua, WANG Shun-Jin

Chin. Phys. Lett. 2008, 25 (7): 2342-2346 .

Abstract

PDF(pc) (330KB) ( 1286 )

Symplectic algebraic dynamics algorithm (SADA) for ordinary differential equations is applied to solve numerically the circular restricted three-body problem (CR3BP) in dynamical astronomy for both stable motion and chaotic motion. The result is compared with those of Runge--Kutta algorithm and symplectic algorithm under the fourth order, which shows that SADA has higher accuracy than the others in the long-term calculations of the CR3BP.

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Generation of Long-Distance Entanglement in Spin System

XI Xiao-Qiang, LIU Wu-Ming

Chin. Phys. Lett. 2008, 25 (7): 2346-2349 .

Abstract

PDF(pc) (138KB) ( 851 )

We propose two schemes to produce long-distance entanglement in a spin chain. The first is based on a controllable interaction system, one starts from an entangled kernel and adds weaken interaction spins to the boundary sites step by step, then the entanglement will be extended longer and longer and its value is equal to that of its kernel. The second is based on a uniform interaction (J) system with a bulk magnetic field (B) that is absent for the boundary qubits, as long as B/J>5, one can obtain near perfect long distance entanglement. Ultra-low temperature is needed in both schemes.

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Numerical Simulation of Bell Inequality's Violation Using Optical Transverse Modes in Multimode Waveguides

FU Jian, GAO Shu-Juan

Chin. Phys. Lett. 2008, 25 (7): 2350-2353 .

Abstract

PDF(pc) (840KB) ( 790 )

We numerically demonstrate that `mode-entangled states' based on the transverse modes of classical optical fields in multimode waveguides violate Bell's inequality. Numerically simulating the correlation measurement scheme of Bell's inequality, we obtain the normalized correlation functions of the intensity fluctuations for the two entangled classical fields. By using the correlation functions, the maximum violations of Bell's inequality are obtained. This implies that the two classical fields in the mode-entangled states, although spatially separated, present a nonlocal correlation.

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Efficient Quantum Secure Direct Communication with Authentication

LIU Wen-Jie, , CHEN Han-Wu, LI Zhi-Qiang, LIU Zhi-Hao

Chin. Phys. Lett. 2008, 25 (7): 2354-2357 .

Abstract

PDF(pc) (527KB) ( 654 )

Two protocols of quantum direct communication with authentication [Phys. Rev. A 73 (2006) 042305] were recently indicated to be insecure against the authenticator Trent attacks [Phys. Rev. A 75 (2007) 026301]. We present two efficient protocols by using four Pauli operations, which are secure against inner Trent attacks as well as outer Eve attacks. Finally, we generalize them to multiparty quantum direction communication.

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Decoy State Quantum Key Distribution with Odd Coherent State

SUN Shi-Hai, GAO Ming, DAI Hong-Yi, CHEN Ping-Xing, LI Cheng-Zu

Chin. Phys. Lett. 2008, 25 (7): 2358-2361 .

Abstract

PDF(pc) (125KB) ( 748 )

We propose a decoy state quantum key distribution scheme with odd coherent state which follows sub-Poissonian distributed photon count and has low probability of the multi-photon event and vacuum event in each pulse. The numerical calculations show that our scheme can improve efficiently the key generation rate and secure communication distance. Furthermore, only one decoy state is necessary to approach to the perfect asymptotic limit with infinite decoy states in our scheme, but at least two decoy states are needed in other scheme.

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Remote Generation of Entanglement for Individual Atoms via Optical Fibres

GUO Yan-Qing, ZHONG Hai-Yang, ZHANG Ying-Hui, SONG He-Shan

Chin. Phys. Lett. 2008, 25 (7): 2362-2365 .

Abstract

PDF(pc) (136KB) ( 590 )

The generation of atomic entanglement is discussed in a system that atoms are trapped in separate cavities which are connected via optical fibres. Two distant atoms can be projected to Bell-state by synchronized turning off of the local laser fields and then performing a single quantum measurement by a distant controller. The distinct advantage of this scheme is that it works in a regime where Δ≈>>g, which makes the scheme insensitive to cavity strong leakage. Moreover, the fidelity is not affected by atomic spontaneous emission.

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Class of Unlockable Bound Entangled States and Their Applications

DIAO Da-Sheng, ZHANG Cheng-Jie, ZHANG Yong-Sheng, GUO Guang-Can

Chin. Phys. Lett. 2008, 25 (7): 2366-2369 .

Abstract

PDF(pc) (160KB) ( 673 )

A class of unlockable bound entangled states and their applications are presented. They can be considered as quasi generalized Smolin states [Phys. Rev. A 63(2001)032306], which are the states of N+N qubits. No pure entanglement can be distilled from this class of states by local quantum operations and classical communications. However, if certain parties group together, they become distillable. Although they are bound entangled states, they could be used to achieve some non-trivial tasks, such as quantum secret sharing shown in the study.

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Controlled Manipulation with a Bose--Einstein Condensates N-Soliton Train under the Influence of Harmonic and Tilted Periodic Potentials

ZONG Feng-De, ZHANG Jie-Fang

Chin. Phys. Lett. 2008, 25 (7): 2370-2374 .

Abstract

PDF(pc) (952KB) ( 691 )

A model of the perturbed complex Toda chain (PCTC) to describe the dynamics of a Bose--Einstein condensate (BEC) N-soliton train trapped in an applied combined external potential consisting of both a weak harmonic and tilted periodic component is first developed. Using the developed theory, the BEC N-soliton train dynamics is shown to be well approximated by 4N coupled nonlinear differential equations, which describe the fundamental interactions in the system arising from the interplay of amplitude, velocity, centre-of-mass position, and phase. The simplified analytic theory allows for an efficient and convenient method for characterizing the BEC N-soliton train behaviour. It further gives the critical values of the strength of the potential for which one or more localized states can be extracted from a soliton train and demonstrates that the BEC N-soliton train can move selectively from one lattice site to another by simply manipulating the strength of the potential.

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High Field Seeking State Atom Laser and Properties of Flux

XIA Lin, XIONG Wei, YANG Fan, YI Lin, ZHOU Xiao-Ji, CHEN Xu-Zong

Chin. Phys. Lett. 2008, 25 (7): 2374-2377 .

Abstract

PDF(pc) (927KB) ( 769 )

We present an experimental study on the continuous atom laser. The experiments show that a high field seeking state atom laser with stable flux can be formed by increasing the strength of outcoupling before large density fluctuations appear. It is easy to obtain a long length or high speed output with this kind of atom laser.

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Double Degenerate Stars

LUO Xin-Lian, BAI Hua, ZHAO Lei

Chin. Phys. Lett. 2008, 25 (7): 2378-2381 .

Abstract

PDF(pc) (269KB) ( 800 )

Regardless of the formation mechanism, an exotic object, the double degenerate star (DDS), is introduced and investigated, which is composed of baryonic matter and some unknown fermion dark matter. Different from the simple white dwarfs (WDs), there is additional gravitational force provided by the unknown fermion component inside DDSs, which may strongly affect the structure and the stability of such kind of objects. Many possible and strange observational phenomena connecting with them are concisely discussed. Similar to the normal WD, this object can also experience thermonuclear explosion as type Ia supernova explosion when DDS's mass exceeds the maximum mass that can be supported by electron degeneracy pressure. However, since the total mass of baryonic matter can be much lower than that of WD at Chandrasekhar mass limit, the peak luminosity should be much dimmer than what we expect before, which may throw a slight shadow on the standard candle of SN Ia in the research of cosmology.

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An Inflationary Solution of Scalar Field in Finsler Universe

LIN Kai, YANG Shu-Zheng

Chin. Phys. Lett. 2008, 25 (7): 2382-2384 .

Abstract

PDF(pc) (133KB) ( 776 )

Using the energy-dependent rainbow metric, we investigate the rainbow universe metric as a Finsler metric, and obtain an inflationary solution of the universe. The theoretical results are in agreement with the astronomical bservations.

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Canonical Entropy and Phase Transition of Rotating Black Hole

ZHAO Ren, WU Yue-Qin, ZHANG Li-Chun

Chin. Phys. Lett. 2008, 25 (7): 2385-2388 .

Abstract

PDF(pc) (105KB) ( 1189 )

Recently, the Hawking radiation of a black hole has been studied using the tunnel effect method. The radiation spectrum of a black hole is derived. By discussing the correction to spectrum of the rotating black hole, we obtain the canonical entropy. The derived canonical entropy is equal to the sum of Bekenstein--Hawking entropy and correction term. The correction term near the critical point is different from the one near others. This difference plays an important role in studying the phase transition of the black hole. The black hole thermal capacity diverges at the critical point. However, the canonical entropy is not a complex number at this point. Thus we think that the phase transition created by this critical point is the second order phase transition. The discussed black hole is a five-dimensional Kerr-AdS black hole. We provide a basis for discussing thermodynamic properties of a higher-dimensional rotating black hole.

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Strange Nonchaotic Attractors in a Time-Delay System

SUN Jin-Tu, ZHANG Yan, WANG Ying-Hai

Chin. Phys. Lett. 2008, 25 (7): 2389-2391 .

Abstract

PDF(pc) (148KB) ( 860 )

A nonchaotic attractor is observed in an infinite-dimensional system which is related to optical bistability and described by a nonlinear time-delay differential equation. The observed nonchaotic attractor is characterized by the strange trajectory of attractor but with negative value for the largest Lyapunov exponent, as well as the Fourier power spectra.

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Synchronization in Coupled Oscillators with Two Coexisting Attractors

ZHU Han-Han, YANG Jun-Zhong

Chin. Phys. Lett. 2008, 25 (7): 2392-2395 .

Abstract

PDF(pc) (182KB) ( 987 )

Dynamics in coupled Duffing oscillators with two coexisting symmetrical attractors is investigated. For a pair of Duffing oscillators coupled linearly, the transition to the synchronization generally consists of two steps: Firstly, the two oscillators have to jump onto a same attractor, then they reach synchronization similarly to coupled monostable oscillators. The transition scenarios to the synchronization observed are strongly dependent on initial conditions

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A Hyperchaotic Attractor Coined from Chaotic Lü System

BAO Bo-Cheng, , LIU Zhong

Chin. Phys. Lett. 2008, 25 (7): 2396-2399 .

Abstract

PDF(pc) (1506KB) ( 1041 )

We report a new hyperchaotic attractor coined from the chaotic Lü system by using a state feedback controller. Theoretical analyses and simulation experiments are conducted to investigate the dynamical behaviour of the proposed hyperchaotic system

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On Some Classes of New Solutions of Continuous β-FPU Chain

XU Quan, TIAN Qiang

Chin. Phys. Lett. 2008, 25 (7): 2400-2402 .

Abstract

PDF(pc) (1943KB) ( 590 )

A continuous β-Fermi--Pasta--Ulam (FPU) chain is investigated by using the knowledge of elliptic equation and Jacobian elliptic functions. We obtain the new solutions, two-kink soliton solution, breather solution and breather lattice solution, of the continuous β-FPU chain, besides the kink-soliton solution and chaos solution.

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Inverse Scattering Transform in Squared Spectral Parameter for DNLS Equation under Vanishing Boundary Conditions

HE Jin-Chun, CHEN Zong-Yun, YAN Tian, HUANG Nian-Ning

Chin. Phys. Lett. 2008, 25 (7): 2403-2406 .

Abstract

PDF(pc) (107KB) ( 761 )

After a transformation, the inverse scattering transform for the derivative nonlinear Schrödinger (DNLS) equation is developed in terms of squared spectral parameter. Following this approach, we obtain the orthogonality and completeness relations of free Jost solutions, which is impossibly constructed with usual spectral parameter in the previous works. With the help these relations, the Zakharov--Shabat equations as well as Marchenko equations of IST are derived in the standard way.

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Modification of AFM Tips for Facilitating Picking-up of Nanoparticles

WANG Peng, YANG Hai-Jun, WANG Hua-Bin, LI Hai, WANG Xin-Yan, WANG Ying, LÜ, Jun-Hong, LI Bin, ZHANG Yi, HU Jun,

Chin. Phys. Lett. 2008, 25 (7): 2407-2409 .

Abstract

PDF(pc) (1086KB) ( 995 )

The radius of atomic force microscope (AFM) tip is a key factor that influences nonspecific interactions between AFM tip and nanoparticles. Generally, a tip with larger radius contributes to a higher efficiency of picking up nanoparticles. We provide two methods for modifying the AFM tip: one is to wear a tip apex on a solid substrate and the other is to coat a tip with poly (dimethylsiloxane) (PDMS). Both the approaches can enhance the adhesion force between the tip and nanoparticles by increasing tip radius. The experimental results show that a modified tip, compared to an unmodified one, achieves six-fold efficiency improvement in the capture of targeted colloidal gold nanoparticles.

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High-Pressure Phase Transition in Cyclo-octane

GAO Ling-Ling, JIANG Sheng, LIU Dan, HAO Jian, JIN Yun-Xia, WANG Feng, WANG Qiu-Shi, LIU Jing, CUI Qi-Liang, ZOU Guang-Tian

Chin. Phys. Lett. 2008, 25 (7): 2410-2412 .

Abstract

PDF(pc) (999KB) ( 1415 )

Structural behaviour of cyclo-octane under high pressure is studied by using a synchrotron x-ray source in a diamond anvil cell (DAC) up to 40.2GPa at room temperature. The cyclo-octane firstly solidifies to the triclinic phase at 0.87GPa. With the increasing pressure, the phase of cyclo-octane changes to the tetragonal phase at about 6.0GPa and then transforms to amorphous phase above 18.2GPa, which is kept till to 40.2GPa. All the phase transitions of cyclo-octane are irreversible.

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Conserved Quantities and Conformal Mechanico-Electrical Systems

FU Jing-Li, WANG Xian-Jun, XIE Feng-Ping

Chin. Phys. Lett. 2008, 25 (7): 2413-2416 .

Abstract

PDF(pc) (154KB) ( 869 )

The conformal mechanico-electrical systems are presented by infinitesimal point transformations of time and generalized coordinates. The necessary and sufficient conditions that the conformal mechanico-electrical systems possess Lie symmetry are given. The Noether conserved quantities of the conformal mechanico-electrical systems are obtained from Lie symmetries.

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Analysis on B→VV with the Flavour SU(3) Symmetry

LIU Shao-Min, JIN Hong-Ying, LI Xue-Qian

Chin. Phys. Lett. 2008, 25 (7): 2417-2420 .

Abstract

PDF(pc) (115KB) ( 556 )

It is noted that the rescattering and annihilation effects are significant in the penguin-dominant Bi→VV decays. In this work, we suggest to use a unique
operator at the quark level to describe all the rescattering and the penguin-induced annihilation effects in B→φK*, and the coefficient of the operator depends on the polarizations of the produced mesons. By the flavour SU(3) symmetry, we apply the same scenario to all the penguin-dominant B→VV modes.

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A Simply Modified Single Pole Scenario For B→K* Form Factors

LIU Shao-Min, JIN Hong-Ying

Chin. Phys. Lett. 2008, 25 (7): 2421-2424 .

Abstract

PDF(pc) (144KB) ( 613 )

We revisit the form factors of B→ K* by using the heavy quark limit and large energy limit, assuming that the form factors have single pole forms near the zero recoil. The deviation from the single pole model is taken into account by adding a term proportional to (v・v' -1)². On the other hand, we require the form factors to obey the large recoil symmetry relationships when v・v' becomes very large. A self-consistent set of B→K* form factors is found. This set of form factors is checked to be consistent with the experimental data about B→K* ll modes.

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Parity Violating Electron Scattering in the Relativistic Eikonal Approximation

DONG Tie-Kuang, REN Zhong-Zhou,

Chin. Phys. Lett. 2008, 25 (7): 2425-2428 .

Abstract

PDF(pc) (187KB) ( 621 )

The parity violating electron scattering is investigated in the relativistic Eikonal approximation. The parity violating asymmetry parameters for many isotopes are calculated. In calculations the proton and neutron densities are obtained from the relativistic mean-field theory. We take Ni isotopes as examples to analyse the behaviour of the parity violating asymmetry parameters. The results show that the parity violating asymmetry parameter is sensitive to the difference between the proton and neutron densities. The amplitude of the parity violating asymmetry parameter increases with the distance between the minima of proton and neutron form factors. Our results are useful for future parity violating electron scattering experiments. By comparing our results with experimental data one can test the validity of the relativistic mean-field theory in calculating the neutron densities of nuclei.

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Challenge on the Astrophysical R-Process Calculation with Nuclear Mass Models

SUN Bao-Hua, MENG Jie, ,

Chin. Phys. Lett. 2008, 25 (7): 2429-2431 .

Abstract

PDF(pc) (283KB) ( 984 )

Our understanding of the rapid neutron capture nucleosynthesis process in universe depends on the reliability of nuclear mass predictions. Initiated by the newly developed mass table in the relativistic mean field theory (RMF), we investigate the influence of mass models on the r-process calculations, assuming the same astrophysical conditions. The different model predictions on the so far unreachable nuclei lead to significant deviations in the calculated r-process abundances.

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U(5)--O(6) Phase Transition in the SD-Pair Shell Model

WANG Fu-Rong, LIU Lin, LUO Yan-An, PAN Feng, DRAAYER J. P.

Chin. Phys. Lett. 2008, 25 (7): 2432-2435 .

Abstract

PDF(pc) (228KB) ( 524 )

U(5)-O(6) transitional behaviour in the SD-pair shell model is studied. The results show that the U(5)-O(6) transitional patterns of the interacting boson model can be reproduced in the SD-pair shell model approximately.

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Entrance-Channel Dependence of Isospin Effects on Double n/p Ratio in HIC

ZHANG Fang, ZUO Wei

Chin. Phys. Lett. 2008, 25 (7): 2436-2439 .

Abstract

PDF(pc) (162KB) ( 651 )

Within the hadronic transport model IBUU04, we investigate the effect of density-dependent symmetry energy on double neutron/proton (n/p) ratio of free nucleons in heavy ion collisions by taking four isotopic Sn+Sn reaction systems. Especially the entrance-channel asymmetry and impact-parameter dependence of the effect of symmetry energy are discussed. It is found that in both central and semi-central collisions the sensitivity of the double n/p ratio to the density-dependent symmetry energy is more pronounced in neutron-richer systems. Our results also indicate clearly that the effect of symmetry energy is stronger in central collisions than that in semi-central collisions.

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Experimental Characterization of Sub-picosecond Electron Bunch Length with Coherent Diffraction Radiation

XIANG Dao, YANG Xing-Fan, HUANG Wen-Hui, TANG Chuan-Xiang, LIN Yu-Zheng, LI Wei-Hua, PAN Qing, LI Ming

Chin. Phys. Lett. 2008, 25 (7): 2440-2443 .

Abstract

PDF(pc) (773KB) ( 753 )

Diffraction radiation is one of the most promising candidates for electron beam diagnostics for the International Linear Collider, x-ray free electron lasers and energy recovery linac due to its non-intercepting characteristics. We report the non-intercepting measurement of sub-ps electron bunch length with coherent diffraction radiation. The bunch length is measured with a Martin--Puplett interferometer and the detailed longitudinal bunch shape is reconstructed with the Kramers--Kronig relation. The rms bunch length is found to be about 0.73ps, which confirms a successful commissioning of the bunch compressor and the interferometer.

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Construction of Different Kinds of Atomic and Molecular Orbitals Using Complete Orthonormal Sets of Ψ^α-ETO in Single Exponent Approximation

Guseinov I. Israfil, Ertürk Murat

Chin. Phys. Lett. 2008, 25 (7): 2444-2447 .

Abstract

PDF(pc) (154KB) ( 738 )

Using complete orthonormal sets of Ψ^α-exponential type orbitals in single exponent approximation the new approach has been suggested for construction of different kinds of functions which can be useful in the theory of linear combination of atomic orbitals. These functions can be chosen properly according to the nature of the problems under consideration. This is rather important because the choice of the basis set may be play a crucial role in applications to atomic and molecular problems. As an example of application, different atomic orbitals for the ground states of the neutral and the first ten cationic members of the isoelectronic series of He atom are constructed by the solution of Hartree--Fock--Roothaan equations using Ψ¹, Ψ⁰and Ψ^-1 basis sets. The calculated results are close to the numerical Hartree-Fock values. The total energy, expansion coefficients, orbital exponents and virial ratio for each atom are presented.

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Theoretical Study of Interesting Fine-Structure Splittings for 2³P_{0, 1, 2} States along Helium Isoelectronic Sequence

QING Bo, CHEN Shao-Hao, GAO Xiang, LI Jia-Ming,

Chin. Phys. Lett. 2008, 25 (7): 2448-2451 .

Abstract

PDF(pc) (121KB) ( 756 )

Using the multi-configuration Dirac--Fock method including the Breit interactions and QED corrections, we calculate the fine-structure energy levels of the 2³P_{0, 1, 2} states along the helium isoelectronic sequence with atomic number up to Z=36, where LS-coupling is appropriate. Our calculation results agree with the experimental results within about 1%. We elucidate the mechanism of the interesting fine-structure splittings for the 2³P_{0, 1, 2} states along the helium isoelectronic sequence, i.e. the competitions between the spin--orbit interactions and the Breit interactions which represent the relativistic retardation effect of electromagnetic interactions.

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Radiative Transition Line Shape in Warm and Dense Argon Plasma: a Two-Centre Model Study

MENG Cong-Sen, ZHAO Zeng-Xiu, YUAN Jian-Min

Chin. Phys. Lett. 2008, 25 (7): 2452-2456 .

Abstract

PDF(pc) (167KB) ( 687 )

A two-centre model is employed to study the electronic structure of argon plasma at a density of 10²²cm^-3 and a temperature of 5eV. The model takes into account the influence of the nearest neighbour on the electronic structure of the radiator and gives a proper description of the transient molecular behaviour in dense plasmas where the mean interatomic distance can be the order of the orbital spatial extent. The orbital energies of quasi-molecular Ar₂ against the interatomic distance are calculated in the framework of density functional theory. It is shown that the orbital energies are not monotonic functions of the distance because of two competitive effects: the repulsive potential between electrons and the attractive potential between electrons and nuclei. The characteristics of this two-centre system can be categorized by three regimes depending on the ratio between the electron wavelength and the interatomic distance: atomic regime, screened atomic regime, and quasi-molecular regime. This classification agrees qualitatively with the conclusion of full quantum-mechanical approach [Yonger S M et al 1988 Phys. Rev. Lett. 61 962].

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Two-Photon Absorption and Excited State Dynamics of Two Organic Molecules Containing Donor/Acceptor Moieties

YAN Yong-Li, LI Bo, LIU Kang-Jun, DONG Zhi-Wei, MA Guo-Hong, WANG Xiao-Mei, QIAN Shi-Xiong

Chin. Phys. Lett. 2008, 25 (7): 2456-2459 .

Abstract

PDF(pc) (189KB) ( 1061 )

The wave motion on the charged surface of a viscous Newtonian liquid is solved as an initial-value problem. Both the leaky dielectric and perfect dielectric cases are considered. The amplitude of wave is assumed to be small. The electric field induced by surface charge is shown to have a generally destabilizing effect on surface wave. The neutral stability curve is drawn in the (G, N_e) plane (G: the gravitational bond number; N_e: the electrical Bond number). The Ohnesorge number, Taylor--Melcher number and permittivity ratio have little influence on the neutral stability curve. It is testified that the classical normal mode method cannot predict wave behaviour at small times.

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Transfer Ionization of Helium in Collisions with C^q+and O^q+ (q =1-3)

WANG Bao-Hong, FU Hong-Bin, DING Bao-Wei, YU De-Yang, SUN Guang-Zhi, LIU Zhao-Yuan

Chin. Phys. Lett. 2008, 25 (7): 2460-2463 .

Abstract

PDF(pc) (203KB) ( 612 )

Cross-section ratios σ_TI/σ_SC of transfer ionization (TI) to single capture (SC) of C^q+- and O^q+-He (q=1-3) collisions in the energy range of 15--440keV/u (0.8--4.2v_Bohr) are experimentally determined. It is shown that σ_TI/σ_SC strongly depends on the projectile velocity, and there is a maximum for E(keV/u)/q^1/2≈150. Combining the Bohr--Lindhard model and the statistical model, a theoretical estimate is presented, in reasonable agreement with the experimental data when E(keV/u)/q^1/2 >35.

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A Formula of Propagating Beams Driven by Few-Cycle Gaussian Pulse in Dispersive Media

LU Da-Quan, HU Wei, QIAN Lie-Jia, FAN Dian-Yuan

Chin. Phys. Lett. 2008, 25 (7): 2464-2466 .

Abstract

PDF(pc) (174KB) ( 625 )

A formula is developed to describe the propagation of beams driven by few-cycle Gaussian pulse in a media with group velocity dispersion (GVD). With the method, the spatiotemporal evolution of the pulsed beam can be straightforwardly quantified as long as the monochromatic beam solutions in free space, which have been widely investigated in previous works, are known. The method makes it possible to analytically deal with the few-cycle pulsed beams with transverse profiles other than the Gaussian one, which is, to our knowledge, the one mainly investigated previously, in GVD media.

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Microwave Experimental Observation of Transmitted Enhanced Goos--Hänchen Displacement in Symmetry-Double-Prism Configuration

DUAN Tao, GE Guo-Ku, LI Chun-Fang, JIN Peng-Cheng

Chin. Phys. Lett. 2008, 25 (7): 2467-2469 .

Abstract

PDF(pc) (384KB) ( 659 )

It is theoretically proven that the transmitted Goos--Hänchen (GH) displacement in the symmetry-double prism could be resonantly enhanced when the incident angle is less than but near the critical angle, and is modulated by the slab thickness between two prisms and the incident angle. This enhancement effect is directly observed in microwave experiments in which the incident angle is properly chosen. The measured data are in good agreement with the result of the numerical simulation.

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Temperature Influence on Divergence Angles of Quartz Crystal Wollaston Prism

ZHAO Shuang, WU Fu-Quan, ZHANG Dong-Sheng, ZHAO Xin, WANG Jin-Xi, XUE Mei, ZHONG Wei-Gang

Chin. Phys. Lett. 2008, 25 (7): 2470-2472 .

Abstract

PDF(pc) (183KB) ( 902 )

We propose a structural angle and main refractive indices as two key factors to understand the temperature influence on the divergence angles of the Wollaston prism. The temperature influence on the divergence angles of quartz crystal Wollaston prism is studied theoretically. The results show that divergence angles decrease with increasing temperature, while the divergence angle of e-light decrease more quickly than that of o-light. The testing system is established to verify the above results, and the experimental results are in agreement well with the theoretical analysis.

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Property of Image-Object Using TE/TM-polarized Wave in the Near-Field Optics with CCGM-FFT

MA Ye-Wan, ZHANG Yu, WU Zhao-Wang ZHANG Jie, JIAN Guo-Shu

Chin. Phys. Lett. 2008, 25 (7): 2473-2476 .

Abstract

PDF(pc) (1515KB) ( 930 )

Discretization of the Lippmann--Schwinger integral equation with complex conjugate gradient method and fast Fourier transform (CCGM-FFT) is solved, which can reduce the memory storage and the CPU time compared with the traditional method, MOM. Thus objects with large size and multiple scattering objects could be simulated with CCGM-FFT. The total intensity and the distribution of each field component of the dielectric and metallic objects under the excitation of the TE/TM-polarized wave are calculated with photon scanning tunnelling microscopy (PSTM) at the constant height. The simulating results are analysed and explained reasonably. The results show that the polarization plays an important role for imaging of PSTM.

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Optical Image Encryption with Simplified Fractional Hartley Transform

LI Xin-Xin, ZHAO Dao-Mu

Chin. Phys. Lett. 2008, 25 (7): 2477-2480 .

Abstract

PDF(pc) (2913KB) ( 1084 )

In summary, we have proposed a new method for image encryption on the basis of SFRHT. Other than the ever-known encryption methods, we have found another useful image encryption technique. This method has the virtues of both FRFT and HT. As a special form for FRHT, SFRHT can add fractional orders in encryption and consequently strengthens the information security to some extent. In addition, being a real transform like HT, it is more convenient and efficient in practical applications since coherent light can be used in this method and the amount of required storage is saved additionally. Some simulation results are also carried out to prove its reliability of this method.

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Novel Ghost Imaging Method for a Pure Phase Object

ZHANG Ying-Tao, HE Chen-Juan, LI Hong-Guo, WANG Kai-Ge

Chin. Phys. Lett. 2008, 25 (7): 2481-2484 .

Abstract

PDF(pc) (130KB) ( 693 )

We propose a novel ghost imaging scheme which is especially served to a pure phase object. A spatially incoherent beam is mixed with a coherent beam of the same frequency field by a beamsplitter. Then we perform the ghost imaging scheme using the mixed beam. Our theoretical result shows that this approach is capable of reconstructing a pure phase object in joint-intensity measurement. The visibility of the images is also analysed for two pure phase objects, an optical wedge and a phase grating.

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Experimental Study on Practical Quantum Key Distribution Scheme with Time-Multiplexed Technique

HUANG Yu-Xian, HU Hua-Peng, LIANG Rui-Sheng*, LU Yi-Qun, WANG Jin-Dong

Chin. Phys. Lett. 2008, 25 (7): 2485-2487 .

Abstract

PDF(pc) (235KB) ( 683 )

We present a scheme that is capable of detecting photon numbers during the quantum key distribution (QKD) based on an improved differential phase shift (DPS) system without Trojan horse attack. A time-multiplexed detector (TMD) is set in for the photon-number resolution. Two fibre loops are used for detecting photon numbers as well as distributing keys. The long-term stabilization is guaranteed by two Faraday mirrors (FM) at Bob's site to automatically compensate for polarization defect. Our experimental study (90km QKD is completed) indicates that such a system is stable and secure which nearly reaches the performance of a single photon scheme.

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Teleportation of Entangled States through Divorce of Entangled Pair Mediated by a Weak Coherent Field in a High-Q Cavity

W. B. Cardoso, N. G. de Almeida

Chin. Phys. Lett. 2008, 25 (7): 2488-2491 .

Abstract

PDF(pc) (158KB) ( 714 )

We propose a scheme to partially teleport an unknown entangled atomic state. A high-Q cavity, supporting one mode of a weak coherent state, is needed to accomplish this process. By partial teleportation we mean that teleportation will occur by changing one of the partners of the entangled state to be teleported. The entangled state to be teleported is composed by one pair of particles, we called this surprising characteristic of maintaining the entanglement, even when one of the particle of the entangled pair being teleported is changed, of divorce of entangled states.

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Entanglement and Its Dynamics with Atomic Spontaneous Decay

H. A. Hessian, A. -B. A. Mohamed

Chin. Phys. Lett. 2008, 25 (7): 2492-2495 .

Abstract

PDF(pc) (146KB) ( 821 )

The atomic decay for a two-level atom interacting with a single mode of electromagnetic field is considered. For a chosen initial state, the exact solution of the master equation is found. Therefore, effect of the atomic damping on entanglement (purity loss), degree of entanglement by the negativity, mutual information and atomic coherence through the master equation are studied.

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Comparison of Laser Performances of 5at.% Yb:Gd_2xY_2(1-x)SiO₅ Crystals between Different Cutting Directions

YU Hai-Bo, LIANG Xiao-Yan, HE Jin-Ping, LENG Yu-Xin, LI Ru-Xin, XU Zhi-Zhan, ZHENG Li-He, ZHAO Guang-Jun, SU Liang-Bi, XU Jun

Chin. Phys. Lett. 2008, 25 (7): 2496-2499 .

Abstract

PDF(pc) (265KB) ( 850 )

We investigate the laser actions of 5at.% Yb:Gd_2xY_2(1-x)SiO₅ (Yb:GYSO; x=0.1) crystals with different cutting directions, parallel and vertical to the growth axis. Our results show that the cutting direction of the sample plays an astonished role in the laser operation. The sample cut vertically to the growth axis possesses the favourable lasing characteristics. Its output power reaches 3.13W at 1060nm with a slope efficiency of 44.68% when the absorbed pump power is 8.9,W. In contrast, the sample cut parallel reaches only 1.65W at 1044nm with a slope efficiency of 33.76% with absorbed pump power of 7.99W. The absorption and emission spectra of the two samples are examined and the merit factor M is calculated. Our analysis is in agreement well with the experimental results. The wavelength tuning range of the superior sample covers from 1013.68nm to 1084.82nm.

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Transverse Writing of Multimode Interference Waveguides inside Silica Glass by Femtosecond Laser Pulses

LIU Da-Yong, LI Yan, DOU Yan-Ping, GUO Heng-Chang, YANG Hong, GONG Qi-Huang

Chin. Phys. Lett. 2008, 25 (7): 2500-2503 .

Abstract

PDF(pc) (1597KB) ( 615 )

Multi-mode interference waveguides are fabricated inside silica glass by transverse writing geometry with femtosecond laser pulses. The influences of several writing and reading factors on the output mode are systematically studied. The experimental results of straight waveguides are in good agreement with the simulations by the beam propagation method. By integrating a straight waveguide with a bent waveguide, a 1×2 multi-mode splitter is formed and 2×3 lobes are observed in the output mode.

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Pulse Temporal Cleaner Based on Nonlinear Ellipse Rotation by Using BK7 Glass Plate

ZHANG Chun-Mei, WANG Jian-Liang, LI Chuang, CHEN Xiao-Wei, LENGYu-Xin, LIN Li-Huang, LI Ru-Xin, XU Zhi-Zhan

Chin. Phys. Lett. 2008, 25 (7): 2504-2507 .

Abstract

PDF(pc) (134KB) ( 842 )

We report a new pulse cleaning technique to enhance the contrast ratio of intense ultra-short laser pulses. A pulse temporal cleaner based on nonlinear ellipse rotation by using BK7 glass plate is developed, and a contrast ratio improvement of two orders of magnitude for the milli-joule level femtosecond input pulses is demonstrated, the total transmission efficiency of the pulse cleaner is 16.7%.

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High-Order Harmonic Generation from a Model of Ar⁺Ionized Clusters

LI Na-Na, ZHAI Zhen, LIU Xue-Shen

Chin. Phys. Lett. 2008, 25 (7): 2508-2510 .

Abstract

PDF(pc) (134KB) ( 811 )

We theoretically study high-order harmonic generation (HHG) due to the interaction of a model of Ar⁺ ionized clusters with intense laser pulses. The plateau of HHG can be extended, which results from the application of a multi-well potential. The classical theory is used to explain the phenomenon.

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Mechanism of Current Oscillations in Gallium ArsenidePhotoconductive Semiconductor Switches

TIAN Li-Qiang, SHI Wei

Chin. Phys. Lett. 2008, 25 (7): 2511-2513 .

Abstract

PDF(pc) (176KB) ( 865 )

Semi-insulating photoconductive semiconductor switch with an electrode gap of 4mm, triggered by a laser pulse with energy of 0.5mJ, and applied bias of 2.5kV, the periodicity current oscillation with a cycle of 12ns is obtained. It is indicated that the current oscillation is one mode of transferred electron effect, namely quenched domain mode. This mode of trans-electron oscillator is obtained when the instantaneous bias electric field drops below the sustaining field (the minimum electric field required to support the domain) before the domain reaches the anode, which leads to the domain disappears somewhere in the bulk of the switch and away from the ohmic contacts. We mainly analyse the time-dependent characteristic of the mode, the theoretical analysis results are in excellent agreement with the experiment.

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High-Conversion-Efficiency and Broadband Tunable Femtosecond Noncollinear Optical Parametric Amplifier

WEI Peng-Fei, LI Chuang, ZHANG Chun-Mei, WANG Jian-Liang, LENG Yu-Xin, LI Ru-Xin

Chin. Phys. Lett. 2008, 25 (7): 2514-2517 .

Abstract

PDF(pc) (635KB) ( 835 )

We build a compact high-conversion-efficiency and broadband tunable noncollinear optical parametric amplifier (OPA) in the infra-red (IR) pumped by a femtosecond Ti:sapphire CPA laser. The OPA consists of an internal seed of white-light continuum generator (WLG) and two noncollinear optical parametric amplifiers. The tunable wavelength range is from 1.2μm to 2.4μm for both signal and idle pulses. The total OPA efficiency in the last OPA stage reaches about 40% in a wider tunable spectral range (from 1.3μm to 1.7μm for signal pulse, from 1.5μm to 2.0μm for idle pulse respectively).

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Tunable Infrared Luminescence and Optical Amplification in PbS Doped Glasses

HUANG Wei, CHI Ying-Zhi, WANG Xi, ZHOU Shi-Feng, WANG Li, WUE, ZENG He-Ping, QIU Jian-Rong

Chin. Phys. Lett. 2008, 25 (7): 2518-2520 .

Abstract

PDF(pc) (230KB) ( 638 )

PbS-doped glasses are prepared. Absorption and luminescence spectra show that both the absorption and infrared emission can be tuned widely by thermal treatment conditions. Optical amplification at 1300nm is observed, and amplified spontaneous emission (ASE) spectrum is also measured to confirm the optical gain from PbS quantum dots.

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A Compact All-Solid-State 630-ps 9.43-kHz High Power Nd:YAG/Nd:YVO₄ Hybrid Laser System

XU Shi-Xiang, WEI Xiao-Yu, DU Ke-Ming, LI Jing-Zhen

Chin. Phys. Lett. 2008, 25 (7): 2521-2523 .

Abstract

PDF(pc) (144KB) ( 1077 )

We present a simple and compact design for an all-solid-state laser amplifier system which can output 9.43-kHz 630-ps, 3.5-W pulse trains under 20W absorbed pumping power. The excellent matching between the repetition of its seed source and the fluorescence lifetime of the amplifying medium makes it quiet efficient for the four-pass amplifier to be pumped in cw mode without need of any synchronization device between the oscillator and the amplifier. The entire setup just covers an area of 55×25cm². The output average power fluctuation is less than ±pm1.5% within 10min and 3% within 6h.

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Fabrication of a Mono-Domain Alignment Ferroelectric Liquid Crystal Device Using a Polar Self-Assembled Monolayer

ZOU Zhong-Fei, YAO Li-Shuang, TANG Xian-Zhu, JI Xin-Jian, XUAN Li

Chin. Phys. Lett. 2008, 25 (7): 2524-2526 .

Abstract

PDF(pc) (1919KB) ( 770 )

A mono-domain ferroelectric liquid crystal device (FLCD) is fabricated using a novel method. The cell used in this method is an asymmetric cell, typically the combination of a polar self-assembled monolayer (SAM) for one substrate and a rubbed polyimide for the other substrate. A defect-free alignment of ferroelectric liquid crystal is fabricated without applying a dc voltage to remove degeneracy in the layer structure. The contact angles of self-assembled monolayer and PI-2942 are measured and the polarity of SAM is higher than the PI alignment. It is found that the polarity of self-assembled monolayer is a key factor in the formation of mono-domain alignment of FLC.

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Fluorescence Emission Centres and the Corresponding Infrared Fluorescence Saturation in a Bismuth-Doped Silica Fibre

QIU Yan-Qing, SHEN Yong-Hang

Chin. Phys. Lett. 2008, 25 (7): 2527-2530 .

Abstract

PDF(pc) (181KB) ( 590 )

We investigate the fluorescence characteristics of bismuth doped silica fibres with and without Al co-dopant which are fabricated by means of modified chemical vapour deposition (MCVD) technique, and find that the fluorescences in the red region (centred around 750nm) and in the infrared region (centred around 1100nm) may originate from different emission sites in the fibre. Strong upconversion phenomena are observed in both Al-codoped and non Al codoped bismuth fibres when the fibres are excited by an acoustic-optic Q-switched Nd:YVO₄ laser. Both the aspects indicate that the upper energy level absorption reported in the work of the bismuth doped silica fibre lasers may result from the fluorescence emission sites that are not responsible for the infrared emission. It is thus expected that optimizing the compositions and the fabrication conditions of the fibre and then transferring more fluorescence emission centres are helpful for the infrared emission.

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Design of Photonic Bandgap Fibre with Novel Air-Hole Structure

LI Jing, ZHANG Wei-Gang, DU Jiang-Bing, WANG Zhi, LIU Yan-Ge, DONG Xiao-Yi

Chin. Phys. Lett. 2008, 25 (7): 2531-2534 .

Abstract

PDF(pc) (990KB) ( 608 )

We introduce PBGFs with the cladding made of our newly designed quasi-hexagonal air holes and demonstrate how it actually operates. This cladding structure is introduced for the first time to the best of our knowledge, and is realized by making use of the hydrofluoric acid's corrosive properties. The fibre corrosion can be accurately controlled, thus opening us the gate for the design and fabrication of new PBGFs with more complex and more efficient cladding structures. Numerical results and actual simulations indicate that PBGFs built with this cladding structure have improved bandgap properties and guiding bands as wide as 500nm have been theoretically reached. Using the same method, we have also been able to design two other types of PBGFs with improved cladding structure.

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An Intelligent Segmented Burst Assembly Mechanism in Optical Burst Switching Networks

XIE Yi-Yuan, ZHANG Jian-Guo

Chin. Phys. Lett. 2008, 25 (7): 2535-2538 .

Abstract

PDF(pc) (197KB) ( 611 )

We focus on the burst assembly mechanism and propose a new intelligent method in which the burst is assembled from several internet protocol (IP) packets in which the number of IP packets is changed according to the traffic load and the burst is segmented into several parts, called the ISOBS mechanism. The average burst assembly time of the ISOBS mechanism decreases as compared with the fixed-assembly-time and fixed-assembly-time-and-length mechanisms. The loss ratio decreases 50% as compared with the general optical burst switching (OBS) mechanism. The last segment can carry high quality of service (QOS) information. We can achieve that the loss ratio of the last segment is almost zero when the traffic load is less than 0.05. When the traffic load is 0.9, the loss ratio of the last segment is 0.0041. The ISOBS can support to transmit different QOS data.

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Frequency Dependence of Longitudinal Correlation Length inthe Yellow Sea

LI Feng-Hua, ZHANG Ren-He

Chin. Phys. Lett. 2008, 25 (7): 2539-2541 .

Abstract

PDF(pc) (135KB) ( 681 )

Spatial correlation coefficient is one of the most important parameters for the description of sound propagation in shallow water. Frequency dependence of the longitudinal correlation length is still an open topic. We observe in a shallow water experiment that the longitudinal correlation length in units of wavelength increases with the increase of frequency. This phenomenon has not been seen in the published papers. The theoretical analysis and numerical simulations indicate that the non-linear frequency relationship of the bottom attenuation is the main cause of this phenomenon.

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Air-Driven Segregation in Binary Granular Mixtures with Same Size but Different Densities

LU Chang-Hong, SHI Qing-Fan, YANG Lei, SUN Gang

Chin. Phys. Lett. 2008, 25 (7): 2542-2545 . DOI: 0

Abstract

PDF(pc) (2824KB) ( 537 )

We investigate the segregation effect of binary granular mixtures with the same size but different densities under vibration at different air pressures. Our experiments show that the segregation state is seriously dependent on the air pressure and there is a new type of partially segregated state at high air pressure, which has the characteristic that the lighter grains tend to stay at the bottom and form a pure layer, while heavier grains and remained lighter ones tend to rise and to form a mixed layer on the top of the system. We redefine the order parameter to study the variation of the segregation effect with the air pressure and vibration parameter in detail. Finally, the mechanism of the air-driven segregation is illustrated by the faster acceleration due to the airflow through the granular bed for lighter particles.

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Two-Dimensional Wave Motion on the Charged Surface of a Viscous Liquid

LI Fang, YIN Xie-Yuan, YIN Xie-Zhen

Chin. Phys. Lett. 2008, 25 (7): 2546-2549 .

Abstract

PDF(pc) (165KB) ( 678 )

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Experimental Investigations on Leading-Edge Vortex Structures for Flow over Non-Slender Delta Wings

WANG Jin-Jun, ZHANG Wang

Chin. Phys. Lett. 2008, 25 (7): 2550-2553 .

Abstract

PDF(pc) (2031KB) ( 1810 )

The dye injection and hydrogen bubble visualization techniques are used to investigate the dual-vortex structure including its development, breakdown and the spatial location of vortex core over nonslender delta wings. It is concluded that the dual-vortex structure can be affected significantly by sweep angle and Reynolds number, and generated only at small angle of attack. The angle between the projection of outer vortex core on delta wing surface and the root chord line has nothing to do with the Reynolds Number and angle of attack, but has simple linear relation with the sweep angle of the model tested.

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Numerical Simulation of Solitary Kinetic Alfvén Waves

DING Jian, LI Yi, WANG Shui

Chin. Phys. Lett. 2008, 25 (7): 2554-2557 .

Abstract

PDF(pc) (651KB) ( 553 )

Using the two-fluid model in the case of α>>gg 1 (α=βbe/2Q, β is the ratio of thermal pressure to magnetic pressure, and Q=m_e/m_i), we numerically investigate the interactions between two solitary kinetic Alfvén waves (SKAWs) and between an SKAW and a density discontinuity. The results show that the two SKAWs would remain in their original shapes and propagate at their initiating speeds, which indicates that SKAWs behave just like standard solitons. The simulation also shows that SKAWs will reflect and refract when crossing a discontinuity and propagating into a higher density region. The transmission wave is an SKAW with increasing density, and the reverberation is a disturbance with lower amplitude.

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Density Fluctuation Measurements Using FIR Interferometer on HL-2A Tokamak

ZHOU Yan, LI Lian-Cai, LI Yong-Gao, JIAO Yi-Ming, DENG Zhong-Chao, YI Jiang, LIU Yi, ZHAO Kai-Jun, JI Xiao-Quan, PENG Bei-Bin, YANG Qing-wei, DUAN Xu-Ru, DING Xuan-Tong

Chin. Phys. Lett. 2008, 25 (7): 2558-2561 .

Abstract

PDF(pc) (186KB) ( 845 )

Density fluctuations were first measured in the core region of HL-2A tokamak plasma using a newly developed multi-channel FIR interferometer system. In divertor ohmic discharges, we measured the radial density fluctuation levels of 5%, which increase to 10--20% during the appearance of MHD activity. Most of the power density in the density fluctuation spectrum is directly associated with m=2 tearing modes. The fluctuation levels reduce to 1/3 and plasma confinement is improved during off-axis electron-cyclotron-resonance heating (ECRH).

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Reflection of Electromagnetic Waves by a Nonuniform Plasma Layer Covering a Metal Surface

GAO Hong-Mei, FA Peng-Ting

Chin. Phys. Lett. 2008, 25 (7): 2562-2565 .

Abstract

PDF(pc) (343KB) ( 1622 )

Reflection coefficients of electromagnetic waves in a nonuniform plasma layer with electrons, positive ions and negative ions, covering a metal surface are
investigated by using the finite-difference-time-domain method. It is shown that the reflection coefficients are influenced greatly by the density gradient on the layer edge, layer thickness and electron proportion, i.e., the effect of the negative ions. It is also found that low reflection or high attenuation can be reached by properly choosing high electron proportion, thick plasma layer, and smooth density gradient in the low frequency regime, but sharp density gradient in the high frequency regime.

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Simulation and Experimental Research of a Novel Vircator

LI Zhi-Qiang, ZHONG Hui-Huang, FAN Yu-Wei, SHU Ting, YANG Jian-Hua, YUAN Cheng-Wei, XU Liu-Rong, ZHAO Yan-Song

Chin. Phys. Lett. 2008, 25 (7): 2566-2568 .

Abstract

PDF(pc) (458KB) ( 1233 )

A new configuration of an axially-extracted vircator with three resonant cavities is put forward and optimized by simulation with the PIC code. The output power of over 1GW is obtained at around 4.1GHz in the experiment, in agreement well with the PIC simulation results. The beam to wave power conversion efficiency is more than 6.6%.

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Numerical Study on Characteristics of Argon Radio-Frequency Glow Discharge with Varying gas Pressure

YU Qian, DENG Yong-Feng, LIU Yue, HAN Xian-Wei

Chin. Phys. Lett. 2008, 25 (7): 2569-2572 .

Abstract

PDF(pc) (227KB) ( 817 )

A one-dimensional fluid simulation on argon rf glow discharge with varying linearly gas pressure from 1Torr to 100Torr is performed. The model based on mass conservation equations for electron and ion under diffusion and mobility approximation, and the electron energy conservation equation is solved numerically by finite volume method. The numerical results show that a uniform plasma with high density can be obtained from rf glow discharge with varying gas pressure, and the density of plasma becomes higher as the gas pressure varies from 1Torr to 100Torr. It is also shown that in the range of the gas pressure from 1Torr to 100Torr with the slower rate of varying gas pressure, higher density of plasma can be obtained.

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Phase Transition and High Piezoactivity of Sr Doped Lead-Free (Na_0.53K_0.422Li_0.048)(Nb_0.89Sb_0.06Ta_0.05)O₃ Ceramics

ZHENG Li-Mei, WANG Jin-Feng, MING Bao-Quan, QI Peng, DU Juan

Chin. Phys. Lett. 2008, 25 (7): 2573-2576 .

Abstract

PDF(pc) (3411KB) ( 967 )

Lead-free piezoelectric ceramics ((Na_0.53K_0.422Li_0.048)(Nb_0.89Sb_0.06Ta_0.05)O₃ (NKLNST) + x mol SrCO₃ are prepared by conventional solid state sintering method. The specimens with pure perovskite structure show tetragonal phase at x≤0.01, and become pseudo-cubic phase at x≥0.02. A lattice parameter discontinuity is found in the specimens with 0.004≤x≤0.0075, along with a great improvement in piezoactivity. The 0.004mol SrCO₃ added NKLNST ceramics possesses outstanding performances of k_p=0.53, k_t =0.26, and d₃₃=309pC/N. Moreover, the Sr²⁺ modification inhibits the grain growth, decreases the Curie temperature, and induces a diffuse phase transition.

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Nonlinear Deformation Processes and Damage Modes of Super Carbon Nanotubes with Armchair-Armchair Topology

CHEN Yu-Li, LIU Bin, YIN Ya-Jun, HUANG Yong-Gang, HWUANG Keh-Chih

Chin. Phys. Lett. 2008, 25 (7): 2577-2580 .

Abstract

PDF(pc) (1342KB) ( 926 )

The tensile deformations and fractures of super carbon nanotubes (SCNTs) with armchair-armchair topology are investigated by using the atomic-scale finite element method. SCNTs generated from carbon nanotubes (CNTs) with different characteristic aspect ratios are found to have different nonlinear behaviours under uniaxial tensions. Specifically, an SCNT with higher aspect ratio has three distinct stages: rotation, stretch and rupture, while an SCNT with lower aspect ratio has only two stages. This information may compensate for previous work and enrich our knowledge about Y-branched CNTs and SCNTs

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Strain Rate Sensitivities of Face-Centred-Cubic Metals Using Molecular Dynamics Simulation

QIN Kun, YANG Li-Ming, HU Shi-Sheng

Chin. Phys. Lett. 2008, 25 (7): 2581-2584 .

Abstract

PDF(pc) (1151KB) ( 686 )

We use dislocation theory and molecular dynamics (MD) simulations to investigate the effect of atom properties on the macroscopic strain rate sensitivity of fcc metals. A method to analyse such effect is proposed. The stress dependence of dislocation velocity is identified as the key of such study and is obtained via 2-D MD simulations on the motion of an individual dislocation in an fcc metal. Combining the simulation results with Orowan's relationship, it is concluded that strain rate sensitivities of fcc metals are mainly dependent on their atomic mass rather than the interatomic potential. The order of strain rate sensitivities of five fcc metals obtained by analysing is consistent with the experimental results available.

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Effect of Annealing Temperature on Structural and Optical Properties of N-Doped ZnO Films

ZHONG Sheng, ZHANG Wei-Ying, WU Xiao-Peng, LIN Bi-Xia, FU Zhu-Xi

Chin. Phys. Lett. 2008, 25 (7): 2585-2587 .

Abstract

PDF(pc) (160KB) ( 767 )

Nitrogen-doped ZnO (ZnO:N) films are prepared by thermal oxidation of sputtered Zn₃N₂ layers on Al₂O₃ substrates. The correlation between the structural and optical properties of ZnO:N films and annealing temperatures is investigated. X-ray diffraction result demonstrates that the as-sputtered Zn₃N₂ films are transformed into ZnO:N films after annealing above 600°C. X-ray photoelectron spectroscopy reveals that nitrogen has two chemical states in the ZnO:N films: the N_O acceptor and the double donor (N₂)_O. Due to the No acceptor, the hole concentration in the film annealed at 700°C is predicted to be highest, which is also confirmed by Hall effect measurement. In addition, the temperature dependent photoluminescence spectra allow to calculate the nitrogen acceptor binding energy.

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Kinetic Study on Channelling of Protons in Metallic Carbon Nanotubes

ZHAO Dan, SONG Yuan-Hong, WANG You-Nian

Chin. Phys. Lett. 2008, 25 (7): 2588-2591 .

Abstract

PDF(pc) (203KB) ( 756 )

Based on the kinetic model and the dielectric response theory, a theoretical model is put forward to describe the transport of protons along nanotube axes. With the introduction of electron band structure for different nanotubes like zigzag and armchair nanotubes of metallic properties, the collective excitation of electrons on the cylinders induced by the incident ions is studied, showing several distinct peaks in the curves of the energy loss function. Furthermore, the stopping power and the self-energy are calculated as functions of ion velocities, especially taking into account the influence of damping coefficients. It is conceivable from the results that, in the kinetic formulation, plasmon excitation plays a major role in the stopping. And as the damping increases, the peaks of the stopping power shift to the lower velocities, with the broadening of the plasmon resonance.

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First-Principles Calculations of Elastic Properties of LaNi_4.75Sn_0.25 Alloys under Pressure

XIONG Bao-Ku, GONG Ke, ZHOU Jing-Jing, YU Ben-Hai, CHEN Dong, SHI De-Heng

Chin. Phys. Lett. 2008, 25 (7): 2592-2595 .

Abstract

PDF(pc) (230KB) ( 798 )

The equilibrium lattice constants, bulk modulus, shear modulus, elastic constants and Debye temperature of LaNi_4.75Sn_0.25 under pressure are calculated using the full-potential linearized augmented plane wave (FP-LAPW) method as well as the quasi-harmonic Debye model. The results at zero pressure are in excellent agreement with the experimental data. The Sn atom is found to occupy the equivalent 3g site (0.5a, 0.75b, 0.5c) in the quadruple cell. The Debye temperature of LaNi_4.75Sn_0.25 is lower than that of LaNi₅. The dependences of bulk modulus on finite temperature and on finite pressure are also investigated. The results show that the bulk modulus B increases monotonously as pressure increases.

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Increasing Superplasticity and Strong Dynamic Behaviour of Zr--Cu--Ni--Al Bulk Metallic Glass

WANG Dan, SUN Min-Hua, FENG Li-Feng, ZHANG Qiang, XIN Li-Juan, LIUJia, BU Wen-Bin

Chin. Phys. Lett. 2008, 25 (7): 2596-2598 .

Abstract

PDF(pc) (126KB) ( 851 )

The plasticity and the dynamic fragility of bulk metallic glass of a Zr₆₂Cu₁₈Ni₁₀Al₁₀ alloy are studied by three-point beam bending methods. We find that the alloy behaves super plastic not only at room temperature, but also at high temperatures. More importantly, it is found that the superplasticity increases with increasing temperature. In addition, the dynamic fragility parameter m for the supercooled liquid of this alloy is measured to be 34.87 and the supercooled liquid of Zr₆₂Cu₁₈Ni₁₀ Al₁₀ alloy behaves as a strong liquid.

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Finite-Size Scaling Analysis of a Three-Dimensional Blume--Capel Model in the Presence of External Magnetic Field

H. Demirel, A.Ozkan, B. Kutlu

Chin. Phys. Lett. 2008, 25 (7): 2599-2602 .

Abstract

PDF(pc) (250KB) ( 789 )

The Blume--Capel model in the presence of external magnetic field H has been simulated using a cellular automaton algorithm improved from the Creutz cellular automaton in three-dimension lattice. The field critical exponent δ is estimated using the power law relations and the finite size scaling functions for the magnetization and the susceptibility in the range -0.1≤h=H/J≤0. The estimated value of the field critical exponent δ is in good agreement with the universal value (δ =5) in three dimensions. The simulations are carried out on a simple cubic lattice under periodic boundary conditions.

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First-Principles Calculations for Thermodynamic Properties of Perovskite-Type Superconductor MgCNi₃

ZHANG Wei, LI Zhe, CHEN Xiang-Rong, CAI Ling-Cang, JING Fu-Qian,

Chin. Phys. Lett. 2008, 25 (7): 2603-2606 .

Abstract

PDF(pc) (155KB) ( 1043 )

The ground state properties and equation of state of the non-oxide perovskite-type superconductor MgCNi₃ are investigated by first-principles calculations based on the plane-wave basis set with the local density approximation (LDA) as well as the generalized gradient approximation (GGA) for exchange and correlation, which agree well with both theoretical calculations and experiments. Some thermodynamic properties including the heat capacity, the thermal expansion coefficient and the Grüneisen parameter for perovskite structure MgCNi₃ are obtained. The dependences of these thermodynamic properties on pressure and temperature are given for the first time.

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Mn Nanowhiskers of a Novel Hexagonal Phase Grown from Hydrogen Activated Laves Phase Alloys

WU Er-Dong, GUO Xiu-Mei

Chin. Phys. Lett. 2008, 25 (7): 2607-2609 .

Abstract

PDF(pc) (2621KB) ( 646 )

With the aid of hydrogenation/dehydrogenation, nanorod whiskers of transition metal Mn can grow spontaneously from Zr_1-xTi_xMnCr Laves phase alloys at room temperature. The finding introduces a distinguishingly different element into metal whisker family, and provides a potential technique for fabrication of one-dimensional metal nanostructures. Moreover, it is found that the segregated Mn in whiskers forms a novel hexagonal structure, which partially fulfills the long predicted allotropic form and adds more complexity to the structures of Mn.

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Phase Transition and Optical Properties of Solid Oxygen under High Pressure: A Density Functional Theory Study

LIU Yan-Hui, TIAN Fu-Bo, MA Yan-Ming, HE Zhi, CUI Tian, LIU Bing-Bing, ZOU Guang-Tian

Chin. Phys. Lett. 2008, 25 (7): 2610-2613 .

Abstract

PDF(pc) (332KB) ( 729 )

Crystal structures and optical properties of the δ--O₂ phase and the ε--O₈ phase have been investigated by using the initio pseudopotential plane-wave method. It is found that the phase transition is of the first order with a discontinuous volumetric change from the antiferromagnetic δ--O₂ phase to the nonmagnetic ε--O₈ phase, consistent with the experimental findings. The energy band calculations show that the direct band gap changes into an indirect band gap after the phase transition. The apparent change in the optical properties can be used for identifying the phase transition from δ--O₂ to ε--O₈.

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Structural and Optical Properties of Nonpolar m-Plane GaN and GaN-Based LEDs on γ-LiAlO_₂

XIE Zi-Li, ZHANG Rong, HAN Ping, ZHOU Sheng-Ming, LIU Bin, XIU Xiang-Qian, CHEN Peng, SHI Yi, ZHENG You-Dou

Chin. Phys. Lett. 2008, 25 (7): 2614-2617 .

Abstract

PDF(pc) (490KB) ( 986 )

We report the structural and optical properties of nonpolar m-plane GaN and GaN-based LEDs grown by MOCVD on a γ-LiAlO₂ (100) substrate. The TMGa, TMIn and NH₃are used as sources of Ga, In and N, respectively. The structural and surface properties of the epilayers are characterized by x-ray diffraction, polarized Raman scattering and atomic force microscopy (AFM). The films have a very smooth surface with rms roughness as low as 2nm for an area of 10×10μm² by AFM scan area. The XRD spectra show that the materials grown on γ-LiAlO₂(100) have <1-100> m-plane orientation. The EL spectra of the m-plane InGaN/GaN multiple quantum wells LEDs are shown. This demonstrates that our nonpolar LED structure grown onthe γ-LiAlO₂ substrate is indeed free of internal electric field. The current voltage characteristics of these LEDs show the rectifying behaviour with a turn on oltage of 1--3V.

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Effect of Carrier Differences on Spin Polarized Injection into Organic and Inorganic Semiconductors

REN Jun-Feng, XIU Ming-Xia

Chin. Phys. Lett. 2008, 25 (7): 2618-2621 .

Abstract

PDF(pc) (126KB) ( 772 )

Spin polarized injection into organic and inorganic semiconductors are studied theoretically from the spin diffusion theory and Ohm's law, and the emphases are placed on the effect of the carrier differences on the current spin polarization. The mobility and the spin-flip time of carriers in organic and inorganic semiconductors are different. From the calculation, it is found that current spin polarization at a ferromagnetic/organic interface is higher than that at a ferromagnetic/inorganic interface because of different carriers in them. Effects of the conductivity matching, the spin dependent interfacial resistances, and the bulk spin polarization of the ferromagnetic layer on the spin polarized injection are also discussed.

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Defect-Related Photoresponse and Polarization-Sensitive Photodetection of Single ZnO Nanowires

LIAO Zhi-Min, XU Jun, ZHANG Jing-Min, YU Da-Peng,

Chin. Phys. Lett. 2008, 25 (7): 2622-2624 .

Abstract

PDF(pc) (762KB) ( 823 )

Defect-related photoconductivity of single ZnO nanowires is investigated. The photoconductivity shows power-law dependence with incident green laser intensity due to the defect mechanisms including both recombination centres and traps. The device based on single ZnO nanowire shows a sensitive photoresponse to green light with significant on/off ratios. In addition, the photocurrent is highly sensitive to the polarization of the incident illumination. Therefore, the nanowire may act as apolarized photodetector.

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Magnetoresistance Probe of Ultrathin Mn₅Ge₃Films with Anderson Weak Localization

CHEN Li-Jun, WANG De-Yong, ZHAN Qing-Feng, HE Wei, LI Qing-An

Chin. Phys. Lett. 2008, 25 (7): 2625-2627 .

Abstract

PDF(pc) (399KB) ( 763 )

We present the magnetoresistance measurements of ultrathin Mn₅Ge₃}$ films with different thicknesses at low Temperatures. Owing to the lattice mismatch between Mn₅Ge₃ and Ge (111), the thickness of Mn₅Ge₃films has a significant effect on the magnetoresistance. When the thickness of Mn is more than 72 monolayers (MLs), the magnetoresistance of the Mn₅Ge₃ films appears a peak at about 6kOe, which shows that the magnetoresistance results from the Anderson weak localization effect and the variable range hopping in the presence of a magnetic field. The magnetic and semiconducting properties indicate that the Mn₅Ge₃ film is a potential material for spin injection.

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Quantum-Confined Stark Effects in a Single GaN Quantum Dot

LIU Yong-Hui, WANG Xue-Feng, LI Shu-Shen

Chin. Phys. Lett. 2008, 25 (7): 2628-2630 .

Abstract

PDF(pc) (122KB) ( 788 )

Using analytical expressions for the polarization field in GaN quantum dot, and an approximation by separating the potential into a radial and an axial, we investigate theoretically the quantum-confined Stark effects. The electron and hole energy levels and optical transition energies are calculated in the presence of an electric field in different directions. The results show that the electron and hole energy levels and the optical transition energies can cause redshifts for the lateral electric field and blueshifts for the vertical field. The rotational direction of electric field can also change the energy shift

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Shape Dependence of Low-Temperature Magnetic Relaxation of Mn₁₂Ac

LIU Hai-Qing, SU Shao-Kui, JING Xiu-nian, LIU Ying, LI Yan-rong, HE Lun-Hua, GE Pei-Wen, YAN Qi-Wei, WANG Yun-Ping

Chin. Phys. Lett. 2008, 25 (7): 2631-2633 .

Abstract

PDF(pc) (143KB) ( 891 )

We report the discovery that the low-temperature magnetic relaxation in Mn₁₂Ac single crystals strongly depends on the shape of the samples. The relaxation time exhibits a minimum at the phase transition point between ferromagnetic and antiferromagnetic phases. The shape dependence is attributed to the dipolar interaction between molecular magnets.

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Phase Diagram of Antiferromagnetically Exchange-Coupled Bilayer

GUO Guang-Hua, ZHANG Guang-Fu, SUN Li-Yuan, Peter A. J. de Groot

Chin. Phys. Lett. 2008, 25 (7): 2634-2637 .

Abstract

PDF(pc) (127KB) ( 656 )

Magnetic hysteresis properties of antiferromagnetically exchange-coupled bilayer structures, in which the two magnetic layers have different magnetic parameters and thicknesses, are studied within the framework of the Stoner--Wohlfarth model. Analytical expressions for the switching fields corresponding to the linear magnetic states are obtained. By adjusting the magnetic parameters or thicknesses of layers, nine different types of easy-axis hysteresis loops may exist. The phase diagram of easy-axis hysteresis loops is mapped in the k₁and k₂ plane, where k₁ and k₂ are the ratios of magnetic anisotropy to the interlayer exchange coupling of the two magnetic layers, respectively.

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Vacuum Annealing Induced Room-Temperature Ferromagnetism in Co_0.1Ti_0.9O_2-δ Films Prepared by Sol-Gel Method

LIU Li-Feng, KANG Jin-Feng, WANG Yi, ZHANG Xing, HAN Ru-Qi

Chin. Phys. Lett. 2008, 25 (7): 2638-2641 .

Abstract

PDF(pc) (3444KB) ( 760 )

The Co-doped TiO₂ films (Co_0.1Ti_0.9O_2-∆) are prepared on silicon substrates by sol-gel method and post annealing. The Co_0.1Ti_0.9O_2-∆ film annealed in air is non-ferromagnetic at room temperature. After further annealed in a vacuum, the room-temperature ferromagnetism (RTFM) is observed. Experimental evidences show that the RTFM in the Co_0.1Ti_0.9O_2-∆ film may come from the Co-doped TiO₂ matrix and is related to the oxygen vacancies created by vacuum annealing.

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Fabrication and Characterization of SmCo₅/Fe₆₅Co₃₅ and SmCo₅/Fe Composite Spring Exchange Magnets

F. Shahzad, S. A. Siddiqi, J. Zhou

Chin. Phys. Lett. 2008, 25 (7): 2642-2644 .

Abstract

PDF(pc) (220KB) ( 928 )

SmCo₅/Fe₆₅Co₃₅ and SmCo₅/Fe spring exchange magnets are fabricated by dc magnetron sputtering on MgO substrates and 100-nm-thick Si₃N₄ membranes, respectively. The base pressure of sputtering chamber is kept below 10^-7 Torr, and Ar pressure is 3 to 8mTorr. The samples are characterized by an x-ray diffractometer, a superconducting quantum interference magnetometer, and high resolution magnetic soft x-ray microscopy. We obtain the complete exchange coupling and single phase behaviour of composite magnets. The (BH)_max value achieved is 28.8MGOe.

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Electronic Energy Levels in an Asymmetric Quantum-Dots-in-a-Well Structure for Infrared Photodetectors

WANG Zhi-Cheng, XU Bo, CHEN Yong-Hai, SHI Li-Wei, LIANG Zhi-Mei, WANGZhan-Guo

Chin. Phys. Lett. 2008, 25 (7): 2645-2648 .

Abstract

PDF(pc) (154KB) ( 592 )

Theoretical calculation of electronic energy levels of an asymmetric InAs/InGaAs/GaAs quantum-dots-in-a-well (DWELL) structure for infrared photodetectors is performed in the framework of effective-mass envelope-function theory. Our calculated results show that the electronic energy levels in quantum dots (QDs) increase when the asymmetry increases and the ground state energy increases faster than the excited state energies. Furthermore, the results also show that the electronic energy levels in QDs decrease as the size of QDs and the width of quantum well (QW) in the asymmetric DWELL structure increase. Additionally, the effects of asymmetry, the size of QDs and the width of QW on the response peak of asymmetry DWELL photodetectors are also discussed.

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Effect of GaAs/GaSb Combination Strain-Reducing Layer on Self-Assembled InAs Quantum Dots

JIANG Zhong-Wei, WANG Wen-Xin, GAO Han-Chao, LI Hui, YANG Cheng-Liang, HE Tao, WU Dian-Zhong, CHEN Hong, ZHOU Jun-Ming

Chin. Phys. Lett. 2008, 25 (7): 2649-2652 .

Abstract

PDF(pc) (392KB) ( 789 )

Self-assembled quantum dots capping with a GaAs/Gasb combined strain-reduced layer (CSRL) are grown by MBE. Their structural and optical properties are investigated by AFM and photoluminescence (PL). PL measurements have shown that stronger emission about 1.3μm can be
obtained by Sb irradiation and capping QDs with 3ML GaAs/2ML GaSb CSRL at room temperature. The full width at half maximum (FWHM) of the PL spectrum is about 20.2meV (19.9meV) at room temperature (20K), indicating that the QDs have high uniform, The result of FWHM is much better than the recently reported result, which is due to the fact that lower QD growth rate and growth interruption after the QDs deposition are adopted in our experiments.

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Fluorescence Enhancement Ratio Dropdown at Low Fluences during Femtosecond Double Pulse Laser Ablation

Sima SINGHA, Robert J. GORDON, HU Zhan

Chin. Phys. Lett. 2008, 25 (7): 2653-2656 .

Abstract

PDF(pc) (123KB) ( 1338 )

In the study of double pulse ablation of materials (silicon and copper), a dropdown of double pulse to single pulse fluorescence signal enhancement at low fluences is observed. The dropdown is analysed with a simple theoretical one-dimensional heat diffusion model and verified by fluorescence time constants change as a function of fluence. The dropdown is explained as a result of liquid-solid mixture layer at the liquid and solid boundary. The effect of the layer becomes important at low fluences.

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Enhancement of Field Emission Properties in La-Doped ZnO Films Prepared by Magnetron Sputtering

LI Jun, WANG Ru-Zhi, LAN Wei, ZHANG Xing-Wang, DUAN Zhi-Qiang, WANG Bo, YAN Hui

Chin. Phys. Lett. 2008, 25 (7): 2657-2660 .

Abstract

PDF(pc) (2160KB) ( 941 )

Field emissions (FE) from La-doped zinc oxide (ZnO) films are both experimentally and theoretically investigated. Owing to the La-doped effect, the FE characteristic of ZnO films is remarkably enhanced compared with an undoped sample, and a startling low turn-on electric field of about 0.4V/μm (about 2.5V/μm for the undoped ZnO films) is obtained at an emission current density of 1μA/cm² and the stable current density reaches 1mA/cm² at an applied field of about 2.1V/μm. A self-consistent theoretical analysis shows that the novel FE enhancement of the La-doped sample may be originated from its smaller work function. Due to the effect of doping with La, the Fermi energy level lifts, electrons which tunnelling from surface barrier are consumedly enhancing, and then leads to a huge change of field emission current. Interestingly, it suggests a new effective method to improve the FE properties of film materials.

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Measurement of Ionization Threshold of Ultracold Cesium Rydberg Atoms in Static Electric Field

FENG Zhi-Gang, ZHANG Lin-Jie, ZHAO Jian-Ming, LI Chang-Yong, LI An-Ling, JIA Suo-Tang

Chin. Phys. Lett. 2008, 25 (7): 2661-2663 .

Abstract

PDF(pc) (234KB) ( 842 )

We investigate the field ionization spectra of ultracold cesium Rydberg atoms in dc electric field. The ionization thresholds of different electric fields are measured and shift of the ionization threshold relative to field-free ionization threshold is accurately described by (6.06±0.14)F^1/2, which is in good agreement with the classical saddle-point model for field ionization. We obtain the field-free ionization threshold of cesium (6P_3/2) as 19674.89±2.99cm^-1 by fitting experimental data.

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Enhancement in Thermoelectrical Power Factor of N-Type Si₈₀Ge₂₀ Alloys

XU Ya-Dong, XU Gui-Ying, LIU Yan-Hong, GE Chang-Chun

Chin. Phys. Lett. 2008, 25 (7): 2664-2666 .

Abstract

PDF(pc) (2751KB) ( 831 )

Influences of the carrier concentration and mobility of heavily doped n-type Si₈₀Ge₂₀ alloys on the thermoelectrical power factor are investigated. The experimental results indicate that thermoelectrical power factors of 32--36μWcm^-1K^-2could be consistently achieved with carrier concentrations of 2.1--2.9×10²⁰cm^-3 and carrier mobilities of 36--40cm²V^-1s^-1. However, many samples with suitable carrier concentrations do not always have high mobilities and high power factors. Some possible explanations for this behaviour are discussed.

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HPHT Synthesis of Micron Grade Boron-Doped Diamond Single Crystal in Fe-Ni-C-B Systems

ZHANG He-Min, ZANG Chuan-Yi, LI Xiao-Lei, MA Hong-An, LI Shang-Sheng, ZHOU Sheng-Guo, GUO Wei, JIA Xiao-Peng,

Chin. Phys. Lett. 2008, 25 (7): 2667-2669 .

Abstract

PDF(pc) (1918KB) ( 1304 )

Micron grade boron-doped diamond crystals with octahedral morphology are successfully synthesized in a Fe--Ni--C--B system under high pressure and high temperature (HPHT). The effects of the additive boron on synthesis conditions, nucleation and growth, crystal morphology of diamond are studied. The synthesized micron grade diamond crystals were characterized by optical microscope (OM), scanning electron microscope (SEM), x-ray diffraction (XRD) and Raman spectroscopy. The research results show that the V-shaped section of synthetic diamond moves downwards to the utmost extent due to 0.3a wt% (a is a constant.) boron added in the synthesis system. The crystal colour is black, and the average crystal size is about 25μm. The crystal faces of synthetic diamond are mainly 111 face. The synthesis of this kind of diamond is few reported, and it will have important and widely applications.

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Surface Erosion of GaN Bombarded by Highly Charged ²⁰⁸Pb^q+-Ions

ZHANG Li-Qing, ZHANG Chong-Hong, YANG Yi-Tao, YAO Cun-Feng, LI Bing-Sheng, JIN Yun-Fan, SUN You-Mei, SONG Shu-Jian

Chin. Phys. Lett. 2008, 25 (7): 2670-2673 .

Abstract

PDF(pc) (1283KB) ( 1009 )

Surface change of gallium nitride specimens after bombardment by highly charged Pb^q+-ions (q=25, 35) at room temperature is studied by means of atomic force microscopy. The experimental results reveal that the surface of GaN specimens is significantly etched and erased. An unambiguous step-up is observed. The erosion depth not only strongly depends on the charge state of ions, but also is related to the incident angle of Pb^q+-ions and the ion dose. The erosion depth of the specimens in 60°incidence (tilted incidence) is significantly deeper than that of the normal incidence. The erosion behaviour of specimens has little dependence on the kinetic energy of ion (E_k=360, 700keV). On the other hand, surface roughness of the irradiated area is obviously decreased due to erosion compared with the un-irradiated area. A flat terrace is formed.

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Observation of Hydration--Drying Effect on Clotrimazole--Carbopol System

M. Todica

Chin. Phys. Lett. 2008, 25 (7): 2674-2676 .

Abstract

PDF(pc) (114KB) ( 1214 )

The possibility to use the polyacrylic acid (carbopol) as polymeric matrix for the clotrimazole is analysed. The hydration--drying effect on the polymeric matrix is observed by Raman spectroscopy. Similar observations are obtained on the clotrimazole included in the polymeric matrix. No modifications of the properties of the clotrimazole and of the polymeric matrix are observed under the repeated action of water.

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Measurement and Analysis of Composition and Depth Profile of H in Amorphous Si_1-xC_x:H Films

HUA Wei, YAO Shu-De, WANG Kun, DING Zhi-Bo

Chin. Phys. Lett. 2008, 25 (7): 2677-2679 .

Abstract

PDF(pc) (133KB) ( 678 )

Composition in amorphous Si_1-xC_x:H heteroepitaxial thin films on Si (100) by plasma enhanced chemical vapour deposition (PECVD) is analysed. The unknown x (0.45--0.57) and the depth profile of hydrogen in the thin films are characterized by Rutherford backscattering spectrum (RBS), resonance-nuclear reaction analysis (R-NRA) and elastic recoil detection (ERD), respectively. In addition, the depth profile of hydrogen in the unannealed thin films is compared to that of the annealed thin films with rapid thermal annealing (RTA) or laser spike annealing (LSA) in nitrogen atmosphere. The results indicate that the stoichiometric amorphous SiC can be produced by PECVD when the ratio of CH₄/SiH₄ is approximately equal to 25. The content of hydrogen decreases suddenly from 35% to 1% after 1150°C annealing. RTA can reduce hydrogen in SiC films effectively than LSA.

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Lattice Dynamical Simulation of Guest-Host Interaction in N₂ Clathrate Hydrate

LIU Zheng-Bo, DONG Shun-Le, WANG Lin

Chin. Phys. Lett. 2008, 25 (7): 2680-2682 .

Abstract

PDF(pc) (167KB) ( 604 )

We perform the lattice dynamical simulation studies of hydrate host lattice interacting with Xe, Ar, and N₂ atoms/molecules. The calculated results show that the well-defined peaks (2.0meV and 3.8meV) and another peak (6.2meV) are assigned to the vibrations of N₂ molecules in large and small cages, respectively. It is confirmed that the double N₂ molecule occupancies of large cage lead to filling of the mode gap between the small cage and the large cage.

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High-Speed InGaAs/InP Double Heterostructure Bipolar Transistor with High Breakdown Voltage

JIN Zhi, SU Yong-Bo, CHENG Wei, LIU Xin-Yu, XU An-Huai, QI Ming

Chin. Phys. Lett. 2008, 25 (7): 2683-2685 .

Abstract

PDF(pc) (128KB) ( 1005 )

e design and fabricate an InGaAs/InP double heterostructure bipolar transistor (DHBT). The spike of the conduction band discontinuity between InGaAs base and InP collector is successfully eliminated by insertion of an InGaAs layer and two InGaAsP layers. The current gain cutoff frequency and maximum oscillation frequency are as high as 155 and 144GHz. The breakdown voltage in common-emitter configuration is more than 7V. The high cutoff frequency and high breakdown voltage make high-speed and
high-power circuits possible

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High-Breakdown-Voltage Submicron InGaAs/InP Double Heterojunction Bipolar Transistor with f_t=170GHz and f_max=253GHz

JIN Zhi, SU Yong-Bo, CHENG Wei, LIU Xin-Yu, XU An-Hai, QI Ming

Chin. Phys. Lett. 2008, 25 (7): 2686-2689 .

Abstract

PDF(pc) (631KB) ( 1197 )

The layer structure of InGaAs/InP double heterojunction bipolar transistor (DHBT) is designed to enhance the frequency performance and breakdown voltage. The composition-graded base structure is used to decrease the base transit time. The InGaAs setback layer and two highly doped InGaAsP layers are used to eliminate the conduction band spike of the collector. The submicron-emitter InGaAs/InP DHBT is fabricated successfully. The base contact resistance is greatly decreased by optimization of contact metals. The breakdown voltage is more than 6V. The current gain cutoff frequency is as high as 170GHz and the maximum oscillation frequency reached 253GHz. The DHBT with such high performances can be used to make W-band power amplifier.

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Large Storage Window in a-SiN_x/nc-Si/a-SiN_xSandwiched Structure for Nanocrystalline Silicon Floating Gate Memory Application

WANG Xiang, HUANG Jian, DING Hong-Lin, ZHANG Xian-Gao, YU Lin-Wei, HUANG Xin-Fan, LI Wei, CHEN Kun-Ji

Chin. Phys. Lett. 2008, 25 (7): 2690-2693 .

Abstract

PDF(pc) (1137KB) ( 2849 )

An a-SiN_x/nanocrystalline silicon [(nc-Si)/a-SiN_x] sandwiched structure is fabricated in a plasma enhanced chemical vapour deposition (PECVD) system at low temperature (250°C). The nc-Si layer is fabricated from a hydrogen-diluted silane mixture gas by using a layer-by-layer deposition technique. Atom force microscopy measurement shows that the density of nc-Si is about 2×10¹¹cm^-2. By the pretreatment of plasma nitridation, low density of interface states and high-quality interface between the Si substrate and a-SiN_xinsulator layer are obtained. The density of interface state at the midgap is calculated to be 1×10¹⁰cm^-2eV^-1 from the quasistatic and high frequency C-V data. The charging and discharging property of nc-Si quantum dots is studied by capacitance-voltage (C-V) measurement at room temperature. An
ultra-large hysteresis is observed in the C-V characteristics, which is attributed to storage of the electrons and holes into the nc-Si dots. The long-term charge-loss process is studied and ascribed to low density of interface states at SiN_x/Si substrate.

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Preparation and Characterization of BPO Film as Electrode for Using of FeRAM

WEN Xin-Yi, YU Jun, WANG Yun-Bo, ZHOU Wen-Li, GAO Jun-Xiong, CHU Xiao-Hui

Chin. Phys. Lett. 2008, 25 (7): 2694-2697 .

Abstract

PDF(pc) (795KB) ( 816 )

Conductive perovskite BaPbO3 (BPO) films as a potential electrode material of PZT capacitors used in ferroelectric random access memory are prepared by rf magnetron sputtering. An x-ray diffractometer and standard four probe method are employed to investigate the dependence of growth conditions on crystal structure and conductivity of BPO films. It is found that BPO films with perovskite phase can be obtained at substrate temperatures above 425°C, and the sample with the lowest resistivity is obtained at 450°C under pure argon atmosphere. Using this BPO film as electrode, ferroelectric properties of BPO/PZT/BPO and Pt/PZT/BPO sandwiched structures are evaluated. Their remanent polarization and coercive field are 36.6μC/cm² (81.3kV/cm) and 36.9μC/cm²(89.1kV/cm), respectively. The coercive field of the former structure is lower than that of the latter, but remanent polarizations are almost the same. In addition, the results imply that BPO electrode is helpful to improve the fatigue resistance of PZT. The reasons are discussed.

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A Single Photon Imaging System Based on Wedge and Strip Anodes

MIAO Zhen-Hua, ZHAO Bao-Sheng, ZHANG Xing-Hua, LIU Yong-An

Chin. Phys. Lett. 2008, 25 (7): 2698-2701 .

Abstract

PDF(pc) (479KB) ( 825 )

A new prototype of single photon imaging system based on wedge and strip anodes is developed. The prototype can directly measure the intensity and position information for an ultra-weak radiant source which takes on the character of single photons. The image of the ultra-weak radiant source can be reconstructed with a wedge and strip anodes detector and an electronic readout subsystem by photon counting and photon position sensitive detecting in a period of time. With proper evaluation, the prototype reveals a spatial resolution superior to 150μm, a 66-kHz maximal counting rate and a dark-count below 0.67count/cm²s.

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Modelling the SOS Response by Semi-Stochastic Simulation

NI Ming, WANG Si-Yuan, OUYANG Qi

Chin. Phys. Lett. 2008, 25 (7): 2702-2705 .

Abstract

PDF(pc) (270KB) ( 579 )

The SOS (save our soul) response induced by DNA damage in bacteria E coli has raised a great interests in biophysics and has been extensively studied. Previously we have developed a stochastic simulation model to explain the oscillatory-like modulation of SOS gene expression observed in experiment. Here we present an improved semi-stochastic model which has higher simulation efficiency, taking into account the updated knowledge about SOS response. The improved model suggests that frequency of the modulation is controlled by the negative feedback in the system. DNA polymerase V, the key enzyme for error-prone translesion synthesis during SOS response, plays a major role in closing up the negative feedback. It is also indicated that the correlation between the modulation and cellular growth observed in experiment is due to DNA damage induced slowing down of transcription and translation.

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Suppression of Spiral Waves by Voltage Clamp Techniques in a Conductance-Based Cardiac Tissue Model

YU Lian-Chun, MA Jun, ZHANG Guo-Yong, CHEN Yong,

Chin. Phys. Lett. 2008, 25 (7): 2706-2709 .

Abstract

PDF(pc) (1251KB) ( 774 )

A new control method is proposed to control the spatio-temporal dynamics in excitable media, which is described by the Morris–Lecar cells model. It is confirmed that successful suppression of spiral waves can be obtained by spatially clamping the membrane voltage of the excitable cells. The low voltage clamping induces breakup of spiral waves and the fragments are soon absorbed by low voltage obstacles, whereas the high voltage clamping generates travel waves that annihilate spiral waves through collision with them. However, each method has its shortcomings. Furthermore, a two-step method that combines both low and high voltage clamp techniques is then presented as a possible way of out this predicament.

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Realization and Comparison of Several Regression Algorithms for Electron Energy Spectrum Reconstruction

LI Gui, LIN Hui, WU Ai-Dong, SONG Gang, WU Yi-Can

Chin. Phys. Lett. 2008, 25 (7): 2710-2713 .

Abstract

PDF(pc) (196KB) ( 624 )

To determine the electron energy spectra for medical accelerator effectively, we investigate a nonlinear programming model with several nonlinear regression algorithms, including Levenberg--Marquardt, Quasi--Newton, Gradient, Conjugate Gradient, Newton, Principal-Axis and NMinimize algorithms. The local relaxation-bound method is also developed to increase the calculation accuracy. The testing results demonstrate that the above methods could reconstruct the electron energy spectra effectively. Especially, further with the local relaxation-bound method the Levenberg--Marquardt, Newton and NMinimize algorithms could precisely obtain both the electron energy spectra and the photon contamination. Further study shows that ignoring about 4% photon contamination would increase error greatly, and it also inaccurately makes the electron energy spectra `drift' to the low energy.

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A Novel Filter Scheme of Data Processing for SQUID-Based Magnetocardiogram

LIU Dang-Ting, TIAN Ye, REN Yu-Feng, YU Hong-Wei, ZHANG Li-Hua, YANGQian-Sheng, CHEN Geng-Hua

Chin. Phys. Lett. 2008, 25 (7): 2714-2717 .

Abstract

PDF(pc) (144KB) ( 736 )

We present a new filter scheme for magnetocardiogram (MCG) signal processing based on the quasi-periodic characteristic of the signals. The key points of this scheme are to determine the exact numbers of data points in each cardiac cycle by using electrocardiogram (ECG) data acquired simultaneously with the MCG signal and to normalize the MCG data sequence in each cycle into an identical length. Compared with conventional filters, the scheme has the advantage of more powerful noise suppression with less signal distortion. The desire for having high quality output signals from raw MCG data acquired in a simple shielded room or even in unshielded environment may be realized with the scheme.

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Step-by-Step Random Walk Network with Power-Law Clique-Degree Distribution

YANG Han-Xin, WANG Bing-Hong, LIU Jian-Guo, HAN Xiao-Pu, ZHOU Tao,

Chin. Phys. Lett. 2008, 25 (7): 2718-2720 .

Abstract

PDF(pc) (160KB) ( 695 )

We propose a simple mechanism for generating scale-free networks with degree exponent γ= 3, where the new node is connected to the existing nodes by step-by-step random walk. It is found that the clique-degree distribution based on our model obeys a power-law form, which is in agreement with the recently empirical evidences. In addition, our model displays the small-world effect and the hierarchical structure.

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Storm-Time Strong Field-Aligned Ion Upflow in Region of the SED Plume

YUAN Zhi-Gang, DENG Xiao-Hua, WANG Jing-Fang

Chin. Phys. Lett. 2008, 25 (7): 2721-2724 .

Abstract

PDF(pc) (293KB) ( 710 )

We report the observations from the GPS TEC and DMSP F-13 satellites showing that very strong upward field-aligned (FA) ion velocity and flux in the outer region of the storm-enhanced density (SED) occurred in the event of the geomagnetic storm on 29--31 May 2003. By a method of coordinate transformation, upward FA ion velocities in excess of 250m/s are obtained from the observations of the DMSP F-13 satellite. Further, an FA ion flux is estimated to be about 4.5i×10¹³ions/m²s in the dusk sector. The estimated FA ion velocity and flux provide a powerful direct proof to support the scenario that there is a strong coupling of particles between the ionosphere and plasmasphere in the region of the SED plume. In the process, FA ion flux transports from the ionosphere to the plasmasphere in the region of the SED plume. Therefore, the plume of SED in the ionosphere provides an important source to the enhanced density of O⁺ in the storm-time plasmasphere.

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Nonlinear Evolution of Lower-Hybrid Drift Instability in Harris Current Sheet

GUO Fan, LU Quan-Ming, GUO Jun, WANG Shui

Chin. Phys. Lett. 2008, 25 (7): 2725-2728 .

Abstract

PDF(pc) (2332KB) ( 626 )

We perform 2.5-dimensional particle-in-cell simulations to investigate the nonlinear evolution of the lower hybrid drift instability (LHDI) in Harris current sheet. Due to the drift motion of electrons in the electric field of the excited low hybrid drift (LHD) waves, the electrons accumulate at the outer layer, and therefore there is net positive charge at the inner edge of the current sheet. This redistribution of charge can create an electrostatic field along the z direction, which then modifies the motions of the electrons along the y direction by E×B drift. This effect strongly changes the structure of the current sheet.

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Screened Thermonuclear Reaction Rates on Magnetar Surfaces

LIU Hong-Lin, LUO Zhi-Quan, LIU Jing-Jing, LAI Xiang-Jun

Chin. Phys. Lett. 2008, 25 (7): 2729-2731 .

Abstract

PDF(pc) (1010KB) ( 494 )

Improving Salpeter's method, we discuss the effect of superstrong magnetic fields (such as those of magnetars) on thermonuclear reaction rates. These most interesting reactions, including the hydrogen burning by the CNO cycle and the helium burning by the triple alpha reaction, are investigated as examples on the magnetar surfaces. The obtained result shows that the superstrong magnetic fields can increase the thermonuclear reaction rates by many orders of magnitude. The enhancement may have significant influence for further study research of the magnetars, especially for the x-ray luminosity observation and the evolution of magnetars.

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Statefinder Diagnostic for Born--Infeld Type Dark Energy Model

HUANG Zeng-Guang, LU Hui-Qing

Chin. Phys. Lett. 2008, 25 (7): 2732-2734 .

Abstract

PDF(pc) (183KB) ( 719 )

Using a new method called the statefinder diagnostics which can make one dark energy model differ from the others, we investigate the dynamics of Born--Infeld (B-I) type dark energy model. The evolution trajectory of B-I type dark energy with Mexican hat potential model with respect to e-folding time N is shown in the r(s) diagram. When the parameter of noncanonical kinetic energy term η→0 or kinetic energy φ²→0, the B-I type dark energy (K-essence) model reduces to the quintessence model or the ΛCDM model corresponding to the statefinder pair {r, s}={1,0} respectively. As a result, the evolution trajectory of our model in the r(s) diagram in Mexican hat potential is quite different from those of other dark energy models. The current values of parameters Ω_φ and ω_φ in this model meet the latest observations WMAP5 well.

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