#### Current Issue

Volume 22 Issue 7
Online Date:
Original Articles
 Select Group Foliation Method and Functional Separation of Variables to Nonlinear Diffusion Equations QU Chang-Zheng, ZHANG Shun-Li Chin. Phys. Lett. 2005, 22 (7): 1563-1566 .   Abstract   PDF(pc) (206KB) ( 850 ) Generalized functional separation of variables to nonlinear diffusion equations is studied in terms of the extended group foliation method. A complete classification for the nonlinear diffusion equation with source term which admits functional separable solutions is presented.
 Select From Bäcklund Transformation to a Linear System of Sine-Gordon Theory in Superspace M. Siddiq, M. Hassan Chin. Phys. Lett. 2005, 22 (7): 1567-1569 .   Abstract   PDF(pc) (163KB) ( 636 ) A systematic approach is presented to find a linear system associated with the sine-Gordon equation from a given set of super Riccati systems. The Riccati system is shown to be related to the super Bäcklund transformation and the linear eigenvalue problem.
 Select Asymptotic Behaviour of Solitons with a Double Spectral Parameter for the Bogomolny Equation in (2+1)-Dimensional Anti de Sitter Space JI Xue-Feng, ZHOU Zi-Xiang Chin. Phys. Lett. 2005, 22 (7): 1570-1572 .   Abstract   PDF(pc) (295KB) ( 488 ) The asymptotic behaviour of the solitons with a double spectral parameter for the Bogomolny equation in (2+1)-dimensional anti de Sitter space is obtained. The asymptotic solution has two ridges close to each other which locates beside the geodesic of the Poincaré half-plane.
 Select Kepler Problem in Hamiltonian Formulation Discussed from Topological Viewpoint XU Gong-Ou, XU Ming-Jie, YANG Ya-Tian Chin. Phys. Lett. 2005, 22 (7): 1573-1575 .   Abstract   PDF(pc) (201KB) ( 456 ) The Kepler problem in Hamiltonian formulation is discussed from a topological viewpoint. Topological properties for a set of cases designated with conserved quantities l,e and E(l,e) (0≤e<1) are expressed with action-angle variables. The involved canonical transformations are all carried out with classical Poisson brackets. Thus it is possible to extend such a formulation to corresponding quantum-mechanical study under quasi-classical conditions.
 Select Simulation of Ionic Populations in Hot Dense Plasmas via a New Method beyond the Average Atom Model WANG Min-Sheng, LIU Ling-Tao, LI Jia-Ming, Chin. Phys. Lett. 2005, 22 (7): 1576-1579 .   Abstract   PDF(pc) (262KB) ( 397 ) In theoretical simulations and analysis of diagnostic measurements for hot dense plasmas in the inertial confinement fusion researches, it is usually necessary to consider thousands of transition arrays between a huge number of ionic energy states. Average atom models are adopted for practical purposes. In order to calculate ionic populations of hot dense plasmas more accurately either in local thermodynamic equilibrium or in non-local thermodynamic equilibrium conditions, a simple method beyond the AA model is proposed.
 Select Determination of Field Configuration and Eigenvalues of Planar Optical Waveguides with Arbitrary Index Profiles ZHU Hai-Dong, DING Yuan, CAO Zhuang-Qi, SHEN Qi-Shun Chin. Phys. Lett. 2005, 22 (7): 1580-1583 .   Abstract   PDF(pc) (250KB) ( 623 ) We extend the analytic transfer matrix (ATM) method to solve the field configuration of planar optical waveguides with arbitrary index profiles including several turning points. The results are compared with the predictions obtained from the finite element method and the Wentzel--Kramer--Brillouin approximation technique. It is shown that the ATM method not only can produce accurate eigenvalues, but also reach correct and meaningful field configuration for any type of optical planar waveguides.
 Select A Lower Bound on the Entanglement in the Jaynes--Cummings Model CAI Jin-Fang, ZOU Jian Chin. Phys. Lett. 2005, 22 (7): 1584-1587 .   Abstract   PDF(pc) (399KB) ( 526 ) The entanglement between an atom and field is investigated by using the Jaynes--Cummings model. The initial atomic state is supposed in a mixed state and the field is in a squeezed state. The lower bound on the entanglement quantified by concurrence is calculated. It is found that the entanglement with the atom being initially in a mixed state can be larger than that with the atom being initially in a pure state. The entanglement is not a monotone function of the squeezing parameter r of the field and it achieves the maximum for certain r and then decreases with further increase of r.
 Select Multiparty Quantum Secret Sharing of Key Using Practical Faint Laser Pulses ZHANG Zhan-Jun, MAN Zhong-Xiao Chin. Phys. Lett. 2005, 22 (7): 1588-1591 .   Abstract   PDF(pc) (191KB) ( 974 ) Based on a bidirectional quantum key distribution protocol [Phys. Rev. A 70(2004)012311], we propose a (m-1,m-1)-threshold scheme of m (m≥3)-party quantum secret sharing of key by using practical faint laser pulses. In our scheme, if all the m-1 sharers collaborate, they can obtain the joint secret key from the message sender. Our scheme is more feasible according to the present-day technology.
 Select Explicit Protocol for Deterministic Entanglement Concentration GU Yong-Jian, GAO Peng, GUO Guang-Can Chin. Phys. Lett. 2005, 22 (7): 1592-1595 .   Abstract   PDF(pc) (196KB) ( 711 ) We present an explicit protocol for extraction of an EPR pair from two partially entangled pairs in a deterministic fashion via local operations and classical communication. This protocol is constituted by a local measurement described by a positive operator-valued measure (POVM), one-way classical communication, and a corresponding local unitary operation or a choice between the two pairs. We explicitly construct the required POVM by the analysis of the doubly stochastic matrix connecting the initial and the final states. Our scheme might be useful in future quantum communication.
 Select Strong Outcoupling from Spin-2 87Rb Bose--Einstein Condensates YANG Fan, XIA Lin, ZHOU Xiao-Ji, MA Xiu-Quan, CHEN Xu-Zong Chin. Phys. Lett. 2005, 22 (7): 1596-1599 .   Abstract   PDF(pc) (366KB) ( 466 ) A pulsed atom laser is experimentally demonstrated by means of outcoupling coherent atoms from 87Rb Bose--Einstein condensates in magnetic trap via radio-frequency pulses. To study the strong outcoupling dynamics of the atom laser, the original |F=2,mF=2> condensate and the coupled |F=2,mF=1> component, both of which overlap in space usually, are separated spatially by collective oscillations. The number of atoms in three of the five Zeeman states are measured and compared with the theoretical results.
 Select Cosmic Microwave Background Radiation Constraints on a Modified Chaplygin Gas Model LIU Dao-Jun, LI Xin-Zhou Chin. Phys. Lett. 2005, 22 (7): 1600-1603 .   Abstract   PDF(pc) (292KB) ( 543 ) A modified Chaplygin gas model of unifying dark energy and dark matter with the exotic equation of state p=Bρ-A/ρα, which can also explain the recent expansion of the universe, is investigated by means of constraining the location of the peak of the cosmic microwave background radiation spectrum. We find that the result of CMBR measurements does not exclude the nonzero value of parameter B, but allows it in the range -0.35≤B≤0.025.
 Select Rotational Deformation of Neutron Stars WEN De-Hua, CHEN Wei, LIU Liang-Gang Chin. Phys. Lett. 2005, 22 (7): 1604-1607 .   Abstract   PDF(pc) (233KB) ( 359 ) The rotational deformations of two kinds of neutron stars are calculated by using Hartle's slow-rotation formulism. The results show that only the faster rotating neutron star gives an obvious deformation. For the slow rotating neutron star with a period larger than hundreds of millisecond, the rotating deformation is very weak.
 Select Entropy of Nonstatic Black Hole with the Internal Global Monopole and the Generalized Uncertainty Relation HAN Yi-Wen, LIU Shou-Yu Chin. Phys. Lett. 2005, 22 (7): 1608-1610 .   Abstract   PDF(pc) (191KB) ( 672 ) The new equation of state density is obtained by the utilization of the generalized uncertainty relation. With the help of coordinates and the Wentzel--Kramers--Brillouin approximation, direct calculation of the scalar field entropy of the non-state black hole with an internal global monopole is performed. The entropy obtained from the calculation is proportional to the horizon area. The calculation can be free from convergence if without any cutoff, which is different from the brick-wall method. However, the pertinent result is limited.
 Select Hawking Radiation from the Horowitz--Strominger Black Hole FANG Heng-Zhong, HU Ya-Peng, ZHAO Zheng Chin. Phys. Lett. 2005, 22 (7): 1611-1613 .   Abstract   PDF(pc) (197KB) ( 512 ) When a black hole radiates particles, it losses energy and shrinks, the horizon contracts from its original radius to a new smaller radius. This leads to the separation between the initial and final radii, which sets the barrier for the particles to tunnel. We develop the work of Parikh [Phys. Rev. Lett. 85(2000)5042; Gen. Rel. Grav. 36,(2004)2419] to a Horowitz--Strominger black hole, i.e. applying the Wentzel--Kramers--Brillouin approximation and semi-classical method to calculate the rate of the Hawking radiation. The result agrees with Γ ～ e-2ImI=eΔSBH. It is also proven that the energy spectrum deviates from exact thermality.
 Select Time-Domain Smoothing Processing for Equivalence-Principle Test Using Free-Fall Method ZHOU Ze-Bing, WANG Shi-Fang, LUO Jun Chin. Phys. Lett. 2005, 22 (7): 1614-1617 .   Abstract   PDF(pc) (245KB) ( 592 ) We investigate the effect of the time-domain smoothing processing for the equivalence-principle test using the free falling method, compared to the low-pass-filter method. Theoretical calculation shows that the time-domain smoothing processing can suppress the high-frequency noises and does not cause pseudo-acceleration. The physical reason is that the time-domain smooth-processing method is an unweighted filtering and is unrelated to the polynomial fitting. The uncertain acceleration difference due to high-frequency mechanical vibrations in the equivalence-principle test for extended rotating bodies can be suppressed from 2μGal to 0.05μGal after the time-domain smoothing processing.
 Select Dynamical Equations for Quantum Information and Application in Information Channel BI Qiao, XING Xiu-San, H. E. Ruda Chin. Phys. Lett. 2005, 22 (7): 1618-1621 .   Abstract   PDF(pc) (219KB) ( 521 ) We establish several dynamical equations for quantum information density. It is demonstrated that quantum information density shares the same formalism of the Liouville equation, subdynamics kinetic equation and Fokker--Planck equation as the density operator and also possesses the superposition property. These allow one to use quantum information density directly to model quantum information. The kinetic equations for quantum information density reveal that the dynamical process of quantum information may be related to dissipative, Markovian, or diffusional information flows, together causing irreversibility. Finally, we discuss superposition of quantum information density, which allows us to construct a quantum information channel in the coherent state representation using harmonic oscillator based encoded quantum information, and obtain a formula for quantum dynamical mutual information.
 Select Isobaric Identification Using Gas-Filled Time-of-Flight Measurements in an Accelerator Mass Spectrometry GUAN Yong-Jing, RUAN Xiang-Dong, HE Ming, WANG Hui-Juan, LI Guo-Qiang, WU Shao-Yong, DONG Ke-Jun, LIN Min, JIANG Shan Chin. Phys. Lett. 2005, 22 (7): 1622-1624 .   Abstract   PDF(pc) (226KB) ( 414 ) A gas-filled time-of-flight (GF-TOF) detector has been built and developed to improve the ability of isobaric identification in accelerator mass spectrometry (AMS) measurements, and a time resolution (without gas filled) of better than 350ps is achieved. The GF-TOF detector is tested by means of measuring a standard AgCl (36Cl/Cl =7.6×10-9g/g) sample with the 36Cl ion energy of 64, 49 and 33MeV, respectively. 36Cl and 36S particles were successfully separated in the TOF spectra output from the GF-TOF detector. The comparison between the gas-filled time-of-flight method and the ΔE-E method is described. Some results relative to the GF-TOF method are given as well.
 Select Super-Resolution Imaging on Microfluidic Super-Resolution Near-Field Structure WANG Pei, TANG Lin, ZHANG Dou-Guo, LU Yong-Hua, JIAO Xiao-Jin, XIE Jian-Ping, MING Hai Chin. Phys. Lett. 2005, 22 (7): 1625-1627 .   Abstract   PDF(pc) (333KB) ( 464 ) We present a new concept of the microfluidic super-resolution near-field structure (MSRENS) based on a microfluidic structure and a super-resolution near-field structure. The near-field distance control, "nano-probe" and scanning can be realized simultaneously using the MSRENS, which is similar to a near-field scanning optical microscope. The design and simulation results are presented. Numerical simulation has demonstrated that the MSRENS with spatial resolution beyond the diffraction limit could be applicable in chemistry, biologics, and many other fields.
 Select Measurements of g-Factor of Rotational Levels in 83Y YUAN Da-Qing, ZHENG Yong-Nan, ZHOU Dong-Mei, ZUO Yi, DU En-Peng, DUAN Xiao, WANG Chao-Hui, LUO Qi, WU Xiao-Guang, LI Guang-Sheng, WEN Shu-Xian, XU Guo-Ji, GAO Zao-Chun, CHEN Yong-Shou, ZHU Sheng-Yun Chin. Phys. Lett. 2005, 22 (7): 1628-1630 .   Abstract   PDF(pc) (227KB) ( 790 ) The g-factors of the positive parity rotational levels up to spin I=41/2+ in 83Y have been measured by a transient-magnetic-field ion implantation perturbed angular distribution method. The experimentally measured g-factors show the g9/2 proton alignment followed by the g9/2 neutron alignment. The measured g-factors are in good agreement with the results calculated by an empirical formula based on the cranking shell model.
 Select Thermalization of Quark Matter Produced at the Highest Energy of a Relativistic Heavy-Ion Collider XU Xiao-Ming Chin. Phys. Lett. 2005, 22 (7): 1631-1633 .   Abstract   PDF(pc) (210KB) ( 502 ) Thermalization of quark matter is studied via a transport equation, which includes triple-quark elastic scattering amplitudes calculated in perturbative QCD. The triple-quark scatterings are demonstrated to be important for an anisotropic initial quark distribution produced in central Au-Au collisions at √SNN=200GeV. By examining momentum isotropy to which the transport equation leads, we can determine a thermalization time of 2.2fm/c for quark matter itself to thermalize by the two-quark and the triple-quark elastic scatterings. Meanwhile, an initial thermal quark distribution function is obtained.
 Select Electronic Transport Properties through Gold--Dithiol-Molecule--Gold Junctions in Equilibrium NING Zhan-Yu, CHEN Jing-Zhe, HOU Shi-Min, ZHANG Jia-Xing, LIANG Zhen-Yu, ZHANG Jin, HAN Ru-Shan Chin. Phys. Lett. 2005, 22 (7): 1634-1637 .   Abstract   PDF(pc) (472KB) ( 454 ) We consider the electronic transport through gold--dithiol-molecule--gold junctions. We used an atomically-contacted extended molecule model for the description of such systems. The calculations are based on the matrix Green function method combined with the hybrid tight-binding density functional theory. In order to determine the position of Fermi level, we referenced the experimental results from ultraviolet photoelectron spectroscopy. Our calculation of molecular conductance near the Fermi level qualitatively reproduces the experimental values measured previously [Science 301(2003)1221; J. Am. Chem. Soc. 125(2003)16164; Nano Lett. 4(2004)267]. In addition, we discuss the relationship between different molecular electronic structures and transport properties.
 Select Lifetime Measurements for Electric-Dipole Δn =0 Transitions in the Beryllium-Like Sulfur DU Shu-Bin, YANG Zhi-Hu, CHANG Hong-Wei, SU Hong Chin. Phys. Lett. 2005, 22 (7): 1638-1640 .   Abstract   PDF(pc) (206KB) ( 353 ) We have measured lifetimes of Δn = 0 allowed transitions in beryllium-like sulfur using beam foil spectroscopic techniques. The measured values, derived from analysis of arbitrarily normalized decay curves, are presented and compared with theoretical calculations and previous measurements. Accurate probabilities have been determined by the well-known relationship.
 Select A Single Laser Cooled Trapped 40Ca+ Ion in a Miniature Paul Trap SHU Hua-Lin, GUAN Hua, HUANG Xue-Ren, LI Jiao-Mei, GAO Ke-Lin Chin. Phys. Lett. 2005, 22 (7): 1641-1644 .   Abstract   PDF(pc) (227KB) ( 908 ) We have observed the phenomenon of phase transition of a few trapped ions in a miniature Paul trap. Judging from the quantum jump signals, a single laser-cooled trapped Ca+ ion has been realized. The ion temperature is estimated to be 22mK. The result shows that the amplitude of ion micromotion is strongly dependent on the rf voltage.
 Select A Movable-Cavity Cold Atom Space Clock BIAN Feng-Gang, WEI Rong, JIANG Hai-Feng, WANG Yu-Zhu Chin. Phys. Lett. 2005, 22 (7): 1645-1648 .   Abstract   PDF(pc) (312KB) ( 387 ) We present an experimental scheme of a cold atom space clock with a movable cavity. By using a single microwave cavity, we find that the clock has a significant advantage, i.e. the longitudinal cavity phase shift is eliminated. A theoretical analysis has been carried out in terms of the relation between the atomic transition probability and the velocity of the moving cavity by taking into account the velocity distribution of cold atoms. The requirements for the microwave power and its stability for atomic π/2 excitation at different moving velocities of the cavity lead to the determination of the proper working parameters of the rubidium clock in frequency accuracy 10-17. Finally, the mechanical stability for the scheme is analysed and the ways of solving the possible mechanical instability of the device are proposed.
 Select Electron Momentum Distributions of the Highest Occupied Molecular Orbital of CF3Br: Delocalization of Halogen Lone-Pair Orbitals WU Xing-Ju, CHEN Xiang-Jun, CHEN Li-Qing, LI Zhong-Jun, YANG Xue-Feng, SHAN Xu, ZHENG Yan-You, XU Ke-Zun Chin. Phys. Lett. 2005, 22 (7): 1649-1651 .   Abstract   PDF(pc) (295KB) ( 450 ) The highest occupied molecular orbital (HOMO) of trifluorobromomethane (CF3Br) is studied by binary (e, 2e) electron momentum spectroscopy. The experimental momentum profile of the HOMO is compared with the Hartree-Fock (HF) and density functional theory (DFT-B3LYP) calculations. The calculated results largely depend on the size of basis sets rather than theoretical methods. Both the HF and DFT calculations using the 6-311++G** basis set give a good explanation to the experiment. Delocalization of halogen lone-pair orbitals in the series molecules CF3X (X= F, Cl, Br) has been investigated.
 Select Femtosecond Laser Pumped Conical Emission and Seeded Ring Amplification in BBO Crystals ZHANG Jia-Sen, LI Feng-Ming, WANG Shu-Feng, GONG Qi-Huang Chin. Phys. Lett. 2005, 22 (7): 1652-1655 .   Abstract   PDF(pc) (252KB) ( 509 ) The characteristics of femtosecond laser pumped conical emission in quadratic media of β-barium borate (BBO) crystals are analysed. A minimized dispersion phase-matching angle, by which a wide-range spectrum can be obtained, is used for broadband amplification. When a seed of a chirped supercontinuum pulse is input, it is found that the seed in wavelength 500nm--750nm is amplified and time resolved.
 Select Beam Shaping by Using the Liquid Crystal Panel of a Commercial Display Device SUI Zhan, ZHAO Run-Chang, ZHU He-Yuan, ZHANG Xiao-Min, ZHENG Wan-Guo, QIAN Lie-Jia Chin. Phys. Lett. 2005, 22 (7): 1656-1659 .   Abstract   PDF(pc) (363KB) ( 871 ) The liquid crystal (LC) panel of a commercially-available LCD projector is successfully used for beam shaping, and a Gaussian beam is converted to a square super-Gaussian beam using the configuration of amplitude modulation. The additional phase modulations imposed by the LC modulator on the shaped beams are measured precisely using an interferometric technique. The experimental results have demonstrated that such a commercially-available programmable spatial light modulator is applicable to beam shaping with negligible additional phase modulation.
 Select Experimental Study of Effect of Medium Boundary on Light Distribution in Tissue Phantoms XU Tang, ZHANG Chun-Ping, TIAN Jian-Guo, SONG Feng, WANG Xin-Yu, ZHAO Cheng-Mei Chin. Phys. Lett. 2005, 22 (7): 1660-1663 .   Abstract   PDF(pc) (274KB) ( 408 ) An experimental method for investigating the effect of medium boundary on distributions of light in the biological tissue phantom intralipid is presented. Measurements of distributions of light in intralipid-10% suspensions at 633nm are described, in which a narrow collimated beam is incident on the surface of the phantoms and into the different depths inside of the phantoms. The experimental results show that the effect of the boundary of the medium on the curves geometry of light distributions is trivial, but the effect on intensity of scattering light is obvious, the maximal relative change of the energy fluence reaches 53.8 % and the position of the peak of the energy fluence curve has a shift of 1.1mm in the reverse direction of incident light for the phantom with albedo a = 0.998, and the effect of the boundary is decreased with the increase of the absorption coefficients of tissue phantoms. The experimental results were analysed by the diffusion theory. These studies will be helpful for further understandings of the relation between the boundary of biological tissue and the distribution of light in tissue.
 Select Three-Photon Resonant Six-Wave Mixing with Phase-Conjugation Geometry in Na Atomic Vapour ZUO Zhan-Chun, SUN Jiang, MI Xin, YU Zu-He, JIANG Qian, WU Ling-An, FU Pan-Ming Chin. Phys. Lett. 2005, 22 (7): 1664-1667 .   Abstract   PDF(pc) (248KB) ( 354 ) We report a three-photon resonant six-wave mixing (SWM) with phase- conjugation geometry. It has advantages that phase matching condition is not critical and the generation of SWM signal is efficient. This technique provides a new spectroscopic tool for studying the highly excited atomic or molecular states with high resolution. The feasibility of this technique is demonstrated in sodium vapour.
 Select Experimental Observation of Autler--Townes Splitting in Sub-Doppler Selective Reflection Spectroscopy ZHAO Yan-Ting, ZHAO Jian-Ming, HUANG Tao, XIAO Lian-Tuan, JIA Suo-Tang Chin. Phys. Lett. 2005, 22 (7): 1668-1671 .   Abstract   PDF(pc) (237KB) ( 495 ) We present an experimental study of Autler--Townes splitting of non-linear selective reflection spectroscopy in a Λ-type driven three-level system. The sub-Doppler reflection spectroscopy is observed and the Autler--Townes splitting is measured as functions of the different coupling laser intensity and detuning. The coherent drive splits the excited state into two dressed states and an Autler-Townes splitting emerges in the probe reflection. The experimental results are in good agreement with theoretical fit.
 Select Abnormal Phenomenon of ac Stark splitting in Magneto-Optical Traps ZHOU Shu-Yu, XU Zhen, ZHOU Shan-Yu, WANG Yu-Zhu Chin. Phys. Lett. 2005, 22 (7): 1672-1675 .   Abstract   PDF(pc) (217KB) ( 443 ) We experimentally study the ac Stark splitting in D2 line of cold 87Rb atoms. The frequency span between the Autler--Townes doublets is obviously larger than that derived from theoretical calculation. Two physical effects, which increase the effective Rabi frequency, contribute to the splitting broadening. First, atoms tend to distribute in strong field places of a inhomogeneous red-detuned light field. Second, atoms reabsorb scattered light when they are huge in number and high in density.
 Select Theoretical Analysis of Quantum Noise in Ghost Imaging CHENG Jing, HAN Shen-Sheng Chin. Phys. Lett. 2005, 22 (7): 1676-1679 .   Abstract   PDF(pc) (212KB) ( 423 ) Ghost imaging is a method to image nonlocally an object by transmitting pairs of entangled photons through the object and a reference optical system respectively. We present a theoretical analysis of the quantum noise in this imaging technique. The dependence of the noise on the properties of the apertures in the imaging system are discussed and demonstrated with a numerical example. For a given source, the resolution and the signal-to-noise ratio cannot be improved simultaneously.
 Select Nonlinear Response of One-Dimensional Magneto-Optical Photonic Crystals WANG Wei-Zhong Chin. Phys. Lett. 2005, 22 (7): 1680-1683 .   Abstract   PDF(pc) (247KB) ( 505 ) We numerically investigate the magneto-optical Cotton--Mouton effect in an alternating multilayer structure with a nonlinear dielectric constant. The multistability and polarization of the transmission of electromagnetic field near the edges of the stop gap are studied in detail. The resonant transmission is accompanied by solitons of intensity of the field. This investigation provides a way to select the transmission property with different polarizations since both the amplitude and the phase of the output field can be adjusted by the input power and by the magneto-optical coefficient depending on the external magnetic field.
 Select Laser Diode Integrated with a Dual-Waveguide Spot-Size Converter by Low-Energy Ion Implantation Quantum Well Intermixing HOU Lian-Ping, ZHU Hong-Liang, ZHOU Fan, WANG Lu-Feng, BIAN Jing, WANG Wei Chin. Phys. Lett. 2005, 22 (7): 1684-1686 .   Abstract   PDF(pc) (221KB) ( 565 ) A ridge laser diode monolithically integrated with a buried-ridge-structure dual-waveguide spot-size converter operating at 1.58μm is successfully fabricated by means of low-energy ion implantation quantum well intermixing and asymmetric twin waveguide technology. The passive waveguide is optically combined with a laterally tapered active core to control the mode size. The devices emit in a single transverse and quasi single longitudinal mode with a side mode suppression ratio of 40.0dB although no grating is fabricated in the LD region. The threshold current is 50mA. The beam divergence angles in the horizontal and vertical directions are as small as 7.3°× 18.0°, respectively, resulting in 3.0dB coupling loss with a cleaved single-mode optical fibre.
 Select Large and Fast Resonant Third-Order Optical Nonlinearities of Silicon 2,3-Naphthalocyanine Bi (trihexylsilyloxide) FU Gang, Kazuo Kasatani, Hiroaki Okamoto, Shunsuke Takenaka Chin. Phys. Lett. 2005, 22 (7): 1687-1690 .   Abstract   PDF(pc) (231KB) ( 495 ) Third-order optical nonlinearities of silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) (SiNc) were measured by femtosecond degenerate four-wave mixing technique under resonant conditions. The time dependence of the signals indicates that the electronic response dominates the mechanism. The electronic molecular hyperpolarizability γe of SiNc was determined to be as high as 2×10-28 esu, which is the largest value reported so far to our knowledge. The electronic third-order susceptibility for a pure SiNc film has been measured to be 4×10-7esu. The large nonlinear susceptibility was discussed in terms of J-type molecular arrangement.
 Select High-Average-Power Nanosecond Quasi-Phase-Matched Single-Pass Optical Parametric Generator in Periodically Poled Lithium Niobate ZHANG Bai-Gang, , YAO Jian-Quan, , LU Yang, XU De-Gang, JI Feng, ZHANG Tie-Li, ZHAO Xin, WANG Peng, , XU Ke-Xin Chin. Phys. Lett. 2005, 22 (7): 1691-1693 .   Abstract   PDF(pc) (231KB) ( 461 ) A pulsed nanosecond optical parametric generator (OPG) in periodically poled lithium niobate (PPLN) crystal is presented. The pump laser is an acousto-optically Q-switched Nd:YVO4 laser with the maximum average power of 6.58W. When the repetition rate is 50kHz and the pulse width of the pump source is 80ns, the maximum average total output power of the single-pass PPLN OPG is about 1.9W, which includes 1.322W of 1.536μm signal radiation. The length of the PPLN crystal is only 38.7mm (at room temperature) with a grating period of 28.93μm (at room temperature). The 1.502--1.536μm signal radiation and 3.652--3.465μm idler radiation are obtained by adjusting the PPLN crystal temperature from 155°C to 250°C.
 Select A 18-W Signal Average Power Nanosecond LiB3O5 Optical Parametric Oscillator around 860nm and the Beam Quality LI Hui-Qing, GENG Ai-Cong, BO Yong, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan Chin. Phys. Lett. 2005, 22 (7): 1694-1697 .   Abstract   PDF(pc) (341KB) ( 600 ) We report a compact high average power optical parametric oscillator (OPO) pumped by an all-solid-state nanosecond 532-nm laser. Based on the merit of non-critically phase-matched crystals without walk-off effect, a 60-mm-long LiB3O5 (LBO) crystal is used as the OPO nonlinear crystal to enhance the conversion efficiency and to increase the output power. The maximum average power of signal output is up to 18W at 860nm for pump power of 65W. This is the highest signal average power generated by a nanosecond OPO in single bulk LBO, to the best of our knowledge. The dynamic characteristics of beam quality are investigated. Our experimental results demonstrate that good OPO conversion efficiency and high output power can be obtained even with relatively poor pump beam quality.
 Select Investigation and Modification of Coupling of Photonic Crystal Defects LIN Xu-Sheng, CHEN Xiong-Wen, LAN Sheng Chin. Phys. Lett. 2005, 22 (7): 1698-1701 .   Abstract   PDF(pc) (365KB) ( 405 ) We investigate the coupling of photonic crystal (PC) defects by using coupled-mode theory. The PC molecules formed by the coupling of two identical PC atoms are the focus of our study. It is revealed that the flatness of the transmission spectra of the PC molecules is determined uniquely by the phase shift of the travelling wave between the two coupled PC atoms. By properly adjusting the distance between the two constitutional PC atoms, we are able to modify the transmission spectrum of the resulting PC molecule. Theoretical analyses based on the coupled-mode theory are in good agreement with the simulation results obtained by the transfer matrix method and the finite-difference time-domain technique.
 Select Direct Numerical Simulation of Supersonic Turbulent Boundary Layer Flow GAO Hui, FU De-Xun, MA Yan-Wen, LI Xin-Liang Chin. Phys. Lett. 2005, 22 (7): 1700-1712 .   Abstract   PDF(pc) (378KB) ( 508 ) Direct numerical simulations of a spatially evolving supersonic flat-plate turbulent boundary layer flow with free Mach number M∞=2.25 and Reynolds number Re=365000/in are performed. The transition process from laminar to turbulent flow is obtained by solving the three-dimensional compressible Navier--Stokes equations, using high-order accurate difference schemes. The obtained statistical results agree well with the experimental and theoretical data. From the numerical results it can be seen that the transition process under the considered conditions is the process which skips the Tollmien--Schlichting instability and the second instability through the instability of high gradient shear layer and becomes of laminar flow breakdown. This means that the transition process is a bypass-type transition process. The spanwise asymmetry of the disturbance locally upstream imposed is important to induce the bypass-type transition. Furthermore, with increasing the time disturbance frequency the transition will delay. When the time disturbance frequency is large enough, the transition will disappear.
 Select Long-Period Fibre Grating Thin Film Sensors Based on Cladding Mode Coupling XU Yan-Ping, GU Zheng-Tian, CHEN Jia-Bi Chin. Phys. Lett. 2005, 22 (7): 1702-1705 .   Abstract   PDF(pc) (344KB) ( 369 ) Based on a method of rigorous vector-field analysis, a numerical model of triple-clad long-period fibre grating is established. The vector components of the electric field for the HE11 cladding mode are plotted to study the field distribution of the cladding mode. The local intensity curves of the first six l = 1 cladding modes are also given. It is found that the low-order HE modes have a larger proportion of intensity localized in the core than the low-order EH modes, just like the double-clad LPFG. Further, the coupling constant between the core mode and the cladding mode is analysed. The results show that the coupling constant of the low-order HE increases monotonously when the mode number becomes larger, and it varies monotonously with the film thickness except for a certain specific region.
 Select Complete Band Gaps for Lamb Waves in Cubic Thin Plates with Periodically Placed Inclusions CHEN Jiu-Jiu, QIN Bo, CHENG Jian-Chun Chin. Phys. Lett. 2005, 22 (7): 1706-1708 .   Abstract   PDF(pc) (498KB) ( 737 ) We present a theoretical study for propagation of Lamb waves in cubic thin plates consisting of solid inclusions placed periodically in the host material. The dispersion curves of Lamb waves propagating parallel to the surfaces of the plates are calculated based on the plane wave expansion method for triangular lattices. We realize the existence of full band gaps in the systems composed of W cylinders embedded in a Si matrix with filling ratio f=0.176 for different thickness ratios of h/a, where h is the plate thickness and a is the lattice spacing.
 Select Interactions of a Projectile Charge with Two-Dimensional Dusty Plasmas JIANG Ke, HOU Lu-Jing, WANG You-Nian Chin. Phys. Lett. 2005, 22 (7): 1713-1716 .   Abstract   PDF(pc) (343KB) ( 736 ) The interactions of a moving charge (namely, one additional dust particle) with a two-dimensional dusty plasma in gas discharge experiment are studied by means of the linearized hydrodynamic theory for the dusty plasma. Expressions are derived for the induced potential and the stopping power of the moving charge, when the charge flights parallel to and over the dust layer. The numerical results are obtained for different discharge pressures and different distances from the moving charge to the dust layer. The results show that the moving charge excites a V-shaped disturbance of induced potential or the so-called Mach cone in the dust layer, while the charge itself loses its energy.
 Select Thomson Scattering Process in Laser-Produced Plasmas YU Quan-Zhi, ZHANG Jie, LI Yu-Tong, ZHENG Jun, YAN Fei, LU Xin, WANG Zhe-Bin, ZHENG Jian, YU Chang-Xuan, JIANG Xiao-Hua, LI Wen-Hong, LIU Shen-Ye, ZHENG Zhi-Jian Chin. Phys. Lett. 2005, 22 (7): 1717-1720 .   Abstract   PDF(pc) (375KB) ( 483 ) We present the evolutions of the electron temperature and plasma expansion velocity with Thomson scattering experiment. The observed time-resolved ion-acoustic image is reproduced by a numerical code which couples the Thomson scattering theory with the output parameters of the one-dimensional hydrocode MEDUSA.
 Select Ohmic Radio-Frequency Synergy Current Drive and Transformer Recharging Experiments in the HT-7 Tokamak CHEN Zhong-Yong, WAN Bao-Nian, SHI Yue-Jiang, HU Li-Qun, XU Han-Dong Chin. Phys. Lett. 2005, 22 (7): 1721-1724 .   Abstract   PDF(pc) (233KB) ( 554 ) Lower hybrid current drive (LHCD) experiments for investigating the interaction between lower hybrid (LH) wave and residual dc electric field were performed in extensive plasma parameter ranges in the HT-7 superconducting tokamak. The experimental results are well fitted to the Karney--Fisch theory on the efficiency of LH waves energy converted to poloidal magnetic field energy. The fraction of absorbed LH power is about 0.75 for the HT-7 machine, and the upshift of the LH-wave parallel refraction index during LHCD experiments have been derived by the optimizing fitting parameters. The LH wave is also used for the transformer recharging when the plasma current is maintained unchanged. The highest efficiency about 7% has been achieved in HT-7 machine.
 Select Effects of Confined Laser Ablation on Laser Plasma Propulsion ZHENG Zhi-Yuan, ZHANG Jie, LU Xin, HAO Zuo-Qiang, Xu Miao-Hua, WANG Zhao-Hua, WEI Zhi-Yi Chin. Phys. Lett. 2005, 22 (7): 1725-1728 .   Abstract   PDF(pc) (323KB) ( 538 ) We investigate the effects of confined laser ablation on laser plasma propulsion. Compared with planar ablation, the cavity ablation provides an effective way to obtain a large target momentum and a high coupling coefficient. When laser pulses are focused into a cavity with 1mm diameter and 2mm depth, a high coupling coefficient is obtained. By using a glass layer to cover the cavity, the coupling coefficient is enhanced by 10 times. Meanwhile, it is found that with the increase of the target surface size, the target momentum presents a linear increase.
 Select Interface Properties of InAs/AlSb Superlattices Characterized by Grazing Incidence X-Ray Reflectivity LI Zhi-Hua, GUO Li-Wei, WU Shu-Dong, WANG Wen-Xin, HUANG Qi, ZHOU Jun-Ming Chin. Phys. Lett. 2005, 22 (7): 1729-1731 .   Abstract   PDF(pc) (224KB) ( 527 ) Two kinds of superlattice interfaces of InAs/AlSb superlattices are realized in an optimized interface growth process, where one is AlAs-like and the other is InSb-like grown on a relaxed AlSb buffer layer. The superlattice properties such as interface roughness and layer thickness are studied by grazing incidence x-ray reflectivity. The reflectivity curves are simulated by standard software till the simulation curves match well with the experimental curves. The simulation indicates that AlAs-like interfaces are much rougher than InSb-like interfaces. Grazing incidence x-ray reflectivity is also discussed as a powerful tool to assessing the structure properties of superlattices.
 Select Electron Holography of Barrier Structures in Co/ZrAlOx/Co Magnetic Tunnel Junctions ZHANG Zhe, ZHU Tao, SHEN Feng, SHENG Wen-Ting, WANG Wei-Gang, XIAO John Q, ZHANG Ze, Chin. Phys. Lett. 2005, 22 (7): 1732-1735 .   Abstract   PDF(pc) (563KB) ( 372 ) We investigate the potential profiles and elemental distribution of barriers in Co/ZrAlOx/Co magnetic tunnel junctions (MTJs) using electron holography (EH) and scanning transmission electron microscopy. The MTJ barriers are introduced by oxidizing a bilayer consisting with a uniform 0.45-nm Al layer and a wedge-shaped Zr layer (0-2nm). From the scanning transmission electron microscopy, AlOx and ZrOx layers are mixed together, indicating that compact AlOx layer cannot be formed in such a bilayer structure of barriers. The EH results reveal that there are no sharp interfaces between the barrier and magnetic electrodes, which may be responsible for a smaller tunnelling magnetoresistance compared with the MTJs of Co/AlOx/Co.
 Select Glass-Forming Ability of an Iron-Based Alloy Enhanced by Co Addition and Evaluated by a New Criterion CHEN Qing-Jun, SHEN Jun, FAN Hong-Bo, SUN Jian-Fei, HUANG Yong-Jiang, MCCARTNEY D. G. Chin. Phys. Lett. 2005, 22 (7): 1736-1738 .   Abstract   PDF(pc) (222KB) ( 823 ) A new Fe-based alloy that can be cast into a fully amorphous rod with a diameter of at least 16mm by the conventional copper-mould casting technique is obtained by partially replacing Fe with Co in a previously reported Fe-based bulk metallic glass. The preliminary thermodynamic analysis indicates that the Co-containing alloy has a significantly lower Gibbs free energy difference between the undercooled melt and the corresponding crystalline solid, compared to the Co-free alloy, reflecting the dramatic role of the Co addition in stabilizing the supercooled melt and facilitating glass formation in iron-based alloys. Here, a new criterion, derived from the classical nucleation and growth theory, is introduced to evaluate the glass-forming ability of Fe-based bulk metallic glasses.
 Select Growth of Zinc Oxide Thornballs by a Novel Method DENG Guo-Chu, DING Ai-Li, ZHENG Xin-Sen, CHENG Wen-Xiu, QIU Ping-Sun Chin. Phys. Lett. 2005, 22 (7): 1739-1741 .   Abstract   PDF(pc) (399KB) ( 550 ) Thornballs of zinc oxide (ZnO) is firstly synthesized by a simple solid vapour deposition process under lead oxide (PbO) atmosphere. The micro-thornballs were constituted by numerous needles, which extend outwards in all directions symmetrically. The balls have the dimensions of 120μm in diameter, while the average diameter of the needles was about 100--200nm. The needles on the balls grow along the <0001> orientation and have gradient cross-sectional radii. Control experiments proved that PbO plays an important role in the growth. The excitation-emission measurement exhibits that the synthesized ZnO thornballs possess intensive photoluminescence property, which provides the evidence that PbO does not deteriorate the optical properties of ZnO thornballs.
 Select Sound Velocity and Release Behaviour of Shock-Compressed LY12 Al YU Yu-Ying, TAN Hua, DAI Cheng-Da, HU Jian-Bo, CHEN Da-Nian Chin. Phys. Lett. 2005, 22 (7): 1742-1745 .   Abstract   PDF(pc) (236KB) ( 810 ) A velocity interferometer system for any reflector (VISAR) is used to measure the sound velocity of LY12 Al shock-compressed to peak pressures of 20, 32, 55 and 71GPa. Unloading wave velocities from these pressures are obtained from the observed particle velocity profiles at the LY12 Al/LiF window interface; and the longitudinal, bulk and shear sound velocities at the initial Hugoniot state are well determined. The histories of stress, strain, density or volume, and particle velocity along the release paths are calculated by the impedance-matching method based on the unloading sound velocity data. It is revealed that the release behaviour of shocked LY12 Al departures obviously from the elastic perfectly-plastic response.
 Select Fabrication and Characterization of Nanocrystalline VO$_{2}$ Thin Films WANG Hong-Chen, YI Xin-Jian, LAI Jian-Jun, LI Yi, Chin. Phys. Lett. 2005, 22 (7): 1746-1748 .   Abstract   PDF(pc) (403KB) ( 1358 ) Nanocrystalline VO2 films with phase transition temperature 34°C have been fabricated on Si3N4-film-coated silicon and quartz substrates by argon-annealing films of metastable VO2(B). The original VO2(B) films are obtained by ion beam sputtering in an argon-oxygen atmosphere at 200°C. The nanocrystalline VO2 films exhibit strong changes in electrical and optical properties when a phase transition is completed. The phase transition temperature in the as-fabricated samples is about 34°C, which is smaller in comparison with 68°C in the single-crystalline VO2 material. A lower phase transition temperature is favorable for device applications such as smart window coating and low power consumption optical switching.
 Select Simulation of Anisotropic Resistivity for Mixed-Phase Manganite La2/3Ca1/3MnO3 Thin Films ZHOU Qing-Li, GUAN Dong-Yi, JIN Kui-Juan, ZHAO Kun, CHEN Zheng-Hao, LU Hui-Bin, ZHOU Yue-Liang, HAN Peng, YANG Guo-Zhen Chin. Phys. Lett. 2005, 22 (7): 1749-1752 .   Abstract   PDF(pc) (259KB) ( 484 ) We utilize the random network model based on phase separation scenario to simulate the conductive behaviour and anisotropic characteristics of resistivity for La2/3Ca1/3MnO3 (LCMO) thin films. The simulated results agree well with our experimental data, showing a metal-to-insulator transition from a high-T paramagnetic (PM) insulating phase to a low-T ferromagnetic (FM) metallic phase in both the untilted film deposited on a (001) SrTiO3 (STO) substrate and the tilted film grown on a vicinal cut STO substrate. It is found that the resistivity of the tilted sample is higher than that of the untilted one, displaying prominent anisotropic characteristics. The studies reveal that the tilting not only decreases the conduction of the FM domains, but also increases the activation energy of the PM regions, inducing the enhancement of resistivity. All those results suggest that the intrinsic inhomogeneity in the phase separation system plays a significant role in the electrical conductivity and the resistive anisotropy is related to the structure of the crystal lattice.
 Select Compositional Dependence of Electronic Specific Heat in AlCuCo Decagonal Quasicrystals: Evidence for the Hume--Rothery Mechanism of Phase Formation FAN Zhen-Jun, JING Xiu-Nian, ZHANG Dian-Lin Chin. Phys. Lett. 2005, 22 (7): 1753-1756 .   Abstract   PDF(pc) (237KB) ( 669 ) There is no consensus whether the electron density of states of decagonal quasicrystals has a pseudogap at the Fermi energy similar to that of the icosahedron phase. We answer this question by measuring the electronic specific heat coefficient of AlCuCo decagonal single-quasicrystals over a wide range of composition. While the average valence electron number per atom, e/a, for all the resultant samples changes only within 1.5%, from ～1.92 to less than 1.95. The specific heat coefficient decreases by 15% with the increasing e/a. The large change and the negative slope give strong evidence for Hume--Rothery mechanism of the decagonal phase.
 Select Investigation of Laser-Induced Damage on Multi-Layer Dielectric Gratings KONG Wei-Jin, SHEN Zi-Cai, SHEN Jian, SHAO Jian-Da, FAN Zheng-Xiu Chin. Phys. Lett. 2005, 22 (7): 1757-1760 .   Abstract   PDF(pc) (829KB) ( 672 ) We investigate mechanisms of laser induced damage thresholds (LIDTs) of multi-layer dielectric gratings (MDGs). It is found that the laser damage thresholds of MDGs and unstructured dielectric multi-layer coatings (the substrate of MDG) are 3.15J/cm2 and 9.32/cm2, respectively, at 1064nm (12ns) with the Littrow angle 51.2° and the TEM00 mode. The laser-induced damage mechanism of multi-layer dielectric is presented with the analysis of the following factors: The dominant factor is the pollution on the corrugated surface, which is induced by the complex manufacture process of multi-layer dielectric gratings; another is the electric field distribution along the corrugated surface. The third reason is due to the reduction in stoichiometry of oxide films, resulting from the manufacture process of etching.
 Select Investigation of Composition in Nano-Scaled Self-Assembled SiGe Islands DENG Ning, ZHANG Lei, CHEN Pei-Yi Chin. Phys. Lett. 2005, 22 (7): 1761-1763 .   Abstract   PDF(pc) (301KB) ( 514 ) A modified model is proposed to explain the influence of Si concentration on shape transition of self-assembled SiGe islands on Si substrates. The experimental results show that the critical sizes for shape transition from pyramids to domes (44, 50 and 60nm) increase with the increasing Si concentration (0.032, 0.09 and 0.17) from sample A to C. Based on the proposed model, the quantitative relation between the Si concentration and the critical size is established. Then the composition exactly in nano-scaled self-assembled SiGe islands is calculated from the measured critical size. The result shows that the Si concentration deduced from Raman spectrum is much larger than the actual values. It is demonstrated that the quantitative relation we obtained can be used to investigate the composition in nano-scaled SiGe islands.
 Select First-Principles Calculations of Elastic Constants of Superconducting MgB2 GUO Hua-Zhong, CHEN Xiang-Rong, ZHU Jun, CAI Ling-Cang, GAO Jie Chin. Phys. Lett. 2005, 22 (7): 1764-1767 .   Abstract   PDF(pc) (229KB) ( 526 ) The five independent elastic constants of superconducting MgB2 are obtained using the first-principles plane wave method with the new relativistic analytic pseudopotential of the Hartwigsen--Goedecker--Hutter (HGH) scheme in the frame of local density approximation. The dependences of bulk modulus on temperature and pressure are also obtained. It is suggested that the HGH-type pseudopotentials are successful in investigating the ground-state mechanical properties of any solids.
 Select Binding Energies of Negatively Charged Donors in a Gaussian Potential Quantum Dot XIE Wen-Fang Chin. Phys. Lett. 2005, 22 (7): 1768-1771 .   Abstract   PDF(pc) (203KB) ( 603 ) We investigate a negatively charged donor centre (D-) trapped by a quantum dot, which is subjected to a Gaussian potential confinement. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian within the effective-mass approximation. The dependence of the ground state of the negatively charged donor on the dot size and the potential depth is studied. The same calculations performed with the parabolic approximation of the Gaussian potential lead to the results that are qualitatively and quantitatively different.
 Select Fabrication and Magnetic Properties of Co-Doped TiO2 Powders Studied by Nuclear Magnetic Resonance GE Shi-Hui, WANG Xin-Wei, KOU Xiao-Ming, ZHOU Xue-Yun, XI Li, ZUO Ya-Lu, YANG Xiao-Lin, ZHAO Yu-Xuan Chin. Phys. Lett. 2005, 22 (7): 1772-1775 .   Abstract   PDF(pc) (247KB) ( 560 ) Co0.04Ti0.96O2 powders are fabricated by sol-gel method. The structure and magnetic properties are investigated under different annealing conditions systematically with emphasis on the influence of oxygen pressure. Pure anatase structure was acquired for all the samples annealed at 450°C for one hour. The samples annealed in air exhibit evident room-temperature ferromagnetism (RTFM) with a small magnetic moment of 0.029μB per Co atom and coercivity Hc of 26Oe, while the samples annealed in vacuum have strong RTFM with a larger magnetic moment of 1.18μB per Co atom and Hc of 430Oe. The zero-field spin echo nuclear magnetic resonance spectrum of 59Co is obtained to prove the existence of Co clusters in the latter samples, implying that the Co clusters are responsible for the strong RTFM in the samples annealed in vacuum. No Co cluster could be observed using both XPS and NMR techniques in the samples annealed in air, implying that the RTFM found in these samples is intrinsic.
 Select Magnetic and Crystalline Microstructures of Fe--Pt--B Nanocomposite Ribbons FANG Yi-Kun, CHANG Cheng-Wu, CHANG Wen-Cheng, XIA Ai-Lin, CHEN Qiang, GE Hong-Liang, HAN Bao-Shan Chin. Phys. Lett. 2005, 22 (7): 1776-1779 .   Abstract   PDF(pc) (525KB) ( 492 ) We investigate magnetic and crystalline microstructures of melt-spun (Fe0.675Pt0.325)100-xBx (x=12, 14, 16, 18, 20) nanocomposite ribbons after optimal thermal treatment using a magnetic force microscope. The magnetic microstructures are characterized by darker spots adjacent to brighter ones in a sub-micro scale and in random distribution. It is found that the strength of the exchange coupling interaction between the crystals in the 10-100nm scale, implied by the maximum value (δM)max of the Henkel plot, could be roughly described by the ratio of the average width of the magnetic spots w to the average crystal size for the ribbons. Moreover, we find that the intrinsic coercivity jHc of the ribbons is sensitive to their crystal sizes, and the smaller D, the higher jHc. Finally, by using roughness analysis, the curve of the root mean square values (δФ)rms of the phase shift of the magnetic force images versus the boron content x is obtained, which is qualitatively consistent with that of the magnetization σ12kOe of the ribbons versus x.
 Select Electron Spin Resonance Studies of Mn2+ in Freshwater Snail Shells: Pomacea Canaliculata Lamarck and Fossilized Snail Shell N. Udomkan, S. Meejoo, P. Limsuwan, P. Winotai, Y. Chaimanee Chin. Phys. Lett. 2005, 22 (7): 1780-1783 .   Abstract   PDF(pc) (219KB) ( 795 ) We study paramagnetic Mn2+ ions present in the nowadays shells of univalve freshwater snails of Pomacea canaliculata lamarck (PCL) and the fossilized freshwater snail (FFS), Viviparus. All these shells are abundant in Thailand. The PCL shells were ground into fine powder. A set of seven samples were then separately annealed for 2h in air atmosphere at different annealing temperatures while the FFS powder was characterized as-received. The PCL shells mainly consist of aragonite and a fraction of calcite. The heat treatments of the PCL powder samples at temperature higher than 450°C resulted in an irreversible phase transformation from aragonite to calcite. However, it is found that the FFS shell is mainly made of calcite, with a minor fraction of aragonite. The crystal structure of the high-temperature-annealed PCL samples are quite similar to that of FFS, which indicates that the metamorphosis (aragonite → calcite) in the FFS shell had occurred but was not yet completed, although it had remained under the pressure and temperature of the Earth’s crusts over millions of years. Our detailed ESR spectral analyses of PCL and FFS show that Mn2+ ions enter the Ca2+ sites during a biomineralization process. Simulated ESR parameters of PCL-500 of Mn2+ at a uniaxial site of calcite are reported. It is surprising to find that the ratio of Mn2+ concentration present in FFS to those in PCL shells evaluated from ESR spectra is as much as 10:1.
 Select Resonant Transmission of Narrow Metallic Slit with Imperfect Inner Face LIU Cheng, YAN Chang-Chun, LIU Ying, CHEN Hao Chin. Phys. Lett. 2005, 22 (7): 1784-1786 .   Abstract   PDF(pc) (404KB) ( 408 ) We numerically analyse the spectral properties of resonant transmission of light through a sub-wavelength metal slit with imperfect inner face. It is found that slight defects on the inner face of the slit can remarkably increase the spectrum shift of its resonant transmission, and this spectra-shift enhancement can be attributed to the induced evanescent waves by the defects. This finding reveals the relationship between the spectrum shift of resonant transmission and the evanescent waves and is potentially useful to explain some extraordinary phenomena in practical experiments, in which the metallic slit is always not ideally smooth.
 Select Effect of Microstructure of TiO2 Thin Films on Optical Band Gap Energy TIAN Guang-Lei, HE Hong-Bo, SHAO Jian-Da Chin. Phys. Lett. 2005, 22 (7): 1787-1789 .   Abstract   PDF(pc) (239KB) ( 1489 ) TiO2 coatings are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for four hours, the spectra and XRD patterns of TiO2 thin film are obtained. XRD patterns reveal that only anatase phase can be observed in TiO2 coatings regardless of the different annealing temperatures, and with the increasing annealing temperature, the grain size gradually increases. The relationship between the energy gap and microstructure of anatase is determined and discussed. The quantum confinement effect is observed that with the increasing grain size of TiO2 thin film, the band gap energy shifts from 3.4eV to 3.21eV. Moreover, other possible influence of the TiO2 thin-film microstructure, such as surface roughness and thin film absorption, on band gap energy is also expected.
 Select Elastic and Piezoelectric Properties of Ce:BaTiO3 Single Crystals DING Shuo, ZHU Yong, LIU Yu-Long, SIU G. G., LEE C. M., JIANG Yi-Jian Chin. Phys. Lett. 2005, 22 (7): 1790-1792 .   Abstract   PDF(pc) (212KB) ( 603 ) Laser Brillouin scattering is applied to measure the sound velocity and the sound anisotropic velocity in high-quality single-domain tetragonal Ce:BaTiO3 single crystals at room temperature. The elastic and piezoelectric constants are thus determined. Based on the sound propagation equations and these results, the directional dependence of the compressional and shear modulus of Ce:BaTiO3 in the (010) and (001) planes are investigated. Some properties of sound propagation and electromechanical coupling in the crystal are discussed.
 Select Highly Efficient Electrophosphorescence from a Grafted Biscyclometalated Iridium Complex with Triarylamine Unit in Polymer Light-Emitting Devices ZHU Mei-Xiang, WU Zhong-Lian, JIANG Chang-Yun, LIU Jian, LI Jian-Ren, XING Kong-Qiang, YANG Yu-Ping, GAN Quan, CAO Yong, ZHU Wei-Guo Chin. Phys. Lett. 2005, 22 (7): 1793-1796 .   Abstract   PDF(pc) (265KB) ( 459 ) The electroluminescence performance from a novel grafted cyclometalated iridium complex (BuPhNPPy)$_{2}$Ir(acac) with triarylmine unit, where BuPhNPPy is N,N-di(4-tert-butylphenyl)-4-(2-pyridyl) phenylamine and Hacac is acetylacetone, is demonstrated in the double-layered polymer light-emitting devices (PLEDs). The PLEDs emit intense green phosphorescence at 533nm with a shoulder peak of 566nm employing 4wt.% (BuPhNPPy)2Ir(acac) doped a blend of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) as the emitting layer. A maximum luminance of 14610cd/m2 at voltage of 24V and a maximum external quantum efficiency Eext of 10.4% photons per electron (ph/el) at current density of 32mA/cm2 are achieved. When the current density is raised to 100mA/cm2, Eext of the device still remained to 8.3% ph/el. This indicates that the triplet--triplet annihilation is restrained more effectively at high current density. The improvement of electrophosphorescence performances of the iridium complex may be contributed to an ortho-substituent effect of grafted triarylmine unit.
 Select White Organic Light-Emitting Devices Based on 2-(2-Hydroxyphenyl) Benzothiazole and Its Chelate Metal Complex WU Xiao-Ming, HUA Yu-Lin, WANG Zhao-Qi, ZHENG Jia-Jin, FENG Xiu-Lan, SUN Yuan-Yuan Chin. Phys. Lett. 2005, 22 (7): 1797-1799 .   Abstract   PDF(pc) (275KB) ( 842 ) We present three kinds of organic light-emitting devices (OLED) fabricated to achieve the emission of bright and pure white light. Device A, with a double-layered structure using 2-(2-hydroxyphenyl) benzothiazole (HBT) and poly (N-vinylcarbazole) (PVK) as the emitting layer (EML) and the hole transport layer (HTL) respectively, could realize the blue-green light emission. Bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTZ)2), synthesized with zinc acetate dihydrate and HBT to form a complex, is used as main EMLs in a similar structure to fabricate devices B and C. Bright and pure white light emissions can be obtained from device C which was fabricated with a green-white emitting host Zn(BTZ)2 and red dopant 5,6,11,12-tetraphenylnaphthacene (rubrene). The maximum quantum efficiency of device C could reach 0.63%, and the corresponding brightness and CIE coordinates were 4000cd/m2 and (x= 0.341, y= 0.334) at the driving voltage of 20V.
 Select Growth of Large High-Quality Type-II a Diamond Crystals WANG Xian-Cheng, MA Hong-An, ZANG Chuan-Yi, TIAN Yu, LI Shang-Sheng, JIA Xiao-Peng, Chin. Phys. Lett. 2005, 22 (7): 1800-1802 .   Abstract   PDF(pc) (470KB) ( 708 ) Large high-quality type-II a diamond crystals in size of about 4.0mm have been grown under the condition of 5.5GPa and 1200--1300°C by using the temperature gradient method in a domestic cubic anvil high-pressure apparatus. The Fe55Co16Ni25 alloy (KOV) is used as the solvent metal, and Ti with the content 1.5wt.% of the solvent metal is selected as the nitrogen getter to reduce the impurity of nitrogen in the diamond crystal. To avoid the impurities and cave in the crystal, the growth rate of the initial stage of the growing process is controlled within 0.45mg/h and the ring carbon source of the size Ф8mm-Ф6mm×3mm is used to grow large diamond crystals.
 Select Phase Transition Phenomena in Ultra-Thin Ge2Sb2Te5 Film ZHANG Ting, LIU Bo, SONG Zhi-Tang, LIU Wei-Li, FENG Song-Lin, CHEN Bomy Chin. Phys. Lett. 2005, 22 (7): 1803-1805 .   Abstract   PDF(pc) (206KB) ( 580 ) We observe reversible phase transition phenomena in proto-type chalcogenide random access memory (C-RAM) devices adopting ultra-thin (12nm) Ge2Sb2Te5 thin film. In this kind of proto-type device, the ultra-thin amorphous Ge2Sb2Te5 thin film undergoes a crystallization process when a voltage is applied. The polycrystalline Ge2Sb2Te5 remain unchanged when the voltage is below 0.6V. A higher power is needed if the transition from polycrystalline to amorphous is expected. The re-amorphization process can be realized by applying a voltage higher than 0.7V. The threshold voltage Vth and threshold electric field Eth of the transition from the polycrystalline state to the amorphous state in this proto-type device are ～0.7V and ～5×105V/cm, respectively. The programming voltage is significantly reduced compared to the values of C-RAM devices adopting a 200-nm-thick Ge2Sb2Te5 inset.
 Select Fabrication and Investigation of an Upconversion Quantum-Well Infrared Photodetector Integrated with a Light-Emitting Diode ZHEN Hong-Lou, LI Ning, XIONG Da-Yuan, ZHOU Xu-Chang, LU Wei, LIU Hui-Chun Chin. Phys. Lett. 2005, 22 (7): 1806-1808 .   Abstract   PDF(pc) (204KB) ( 640 ) We report the fabrication of an upconversion infrared detector, i.e. a quantum well infrared photodetector integrated with a light-emitting diode (named as QWIP-LED). The infrared photo-response spectrum in the upconversion process is in good agreement with the normal photocurrent spectrum of the QWIP, which demonstrates that the long wavelength infrared band at 8μm has been transferred to the near infrared band at 0.8μm by the upconversion process.
 Select Folding Behaviour for Proteins BBL and E3BD with Go-like Models ZUO Guang-Hong, ZHANG Jian, WANG Jun, WANG Wei Chin. Phys. Lett. 2005, 22 (7): 1809-1812 .   Abstract   PDF(pc) (342KB) ( 687 ) Folding behaviour of protein BBL and its homologue domain E3BD are studied by using an off-lattice Go-like model. It is found that the folding behaviours of these two proteins are different. Protein BBL folds in a downhill manner, which is consistent with experiments. In contrast, protein E3BD folds cooperatively and has a bimodal distribution of the Q values (the similarity to the native state). By analysing the native structures of the two proteins, it is found that the difference in folding behaviours can be attributed to the different structural features described by the number of nonlocal contacts per residue.
 Select Effects of Screw Instability on Extracting Energy from a Rotating Black Hole LEI Wei-Hua, LAN Xiao-Xia, WANG Ding-Xiong Chin. Phys. Lett. 2005, 22 (7): 1813-1816 .   Abstract   PDF(pc) (382KB) ( 511 ) Magnetic extraction of energy from a rotating black hole (BH) is discussed in the coexistence of the Blandford--Znajek (BZ) process and the magnetic coupling (MC) process by considering the effects of the screw instability of the magnetic field. It is shown that the screw instability affects the configuration of the magnetosphere and the evolution characteristics of the BH, augmenting the energy extracted in the BZ and MC processes. In addition, the observed energy and duration of several gamma-ray bursts can be fitted well by virtue of our model.
 Select Numeric Spectrum of Relic Gravitational Waves in Accelerating Universe ZHANG Yang, ZHAO Wen, YUAN Ye-Fei, XIA Tian-Yang Chin. Phys. Lett. 2005, 22 (7): 1817-1820 .   Abstract   PDF(pc) (260KB) ( 861 ) The accelerating expansion of the Universe in the present stage is a process that will change the spectrum of relic gravitational waves. Here we present a numerical calculation for the power spectrum of relic gravitational waves in the accelerating Universe. The results show that although the overall features of the power spectrum are similar to those in the non-accelerating models, the amplitude is smaller in order of 10-1. We also find that the spectrum is very sensitive to the index β of the inflationary expansion with the scale factor a(τ) ∝ |τ|1+β. With increase of β, the resulting spectrum tends to be flatter with more power on high frequencies, and the sensitivity of the second science run of the LIGO detectors puts a restriction on the parameter β < -1.8. The influence of reheating followed by the inflation has been examined.
 Select Transmission Properties of THz Radiation Pulses through Very Deep Zero-Order Metallic Gratings XING Qi-Rong, LI Shu-Xin, ZHANG Wei-Li, LANG Li-Ying, MAO Fang-Lin, XU Shi-Xiang, CHAI Lu, WANG Qing-Yue, Chin. Phys. Lett. 2005, 22 (7): 1824-1824 .   Abstract   PDF(pc) (297KB) ( 716 ) Very deep zero-order metallic grating structures are processed to study the transmission properties of THz radiation pulses. The experiments have been performed with two samples. The delay of the THz pulses and the corresponding resonantly enhanced transmission spectra through the samples are observed. To explain the extraordinary transmission we have treated the samples as Fabry--Perot resonators through resonant excitation of the coupled surface plasmon polaritons filled in the cavities between the metal slats. The experimental results are in reasonable agreement with the numerical simulation. Our results show that THz-time-domain spectroscopy may be an effective technique for studying the optical properties of various THz microstructured devices.
 Select Raman Spectrum Analysis on the Solid--Liquid Boundary Layer of BGO Crystal Growth ZHANG Xia, YIN Shao-Tang, WAN Song-Ming, YOU Jing-Lin, CHEN Hui, ZHAO Si-Jie, ZHANG Qing-Li Chin. Phys. Lett. 2005, 22 (7): 1898-1900 .   Abstract   PDF(pc) (448KB) ( 418 ) We study the Raman spectra of Bi4Ge3O12 crystal at different temperatures, as well as its melt. The structure characters of the single crystal, melt and growth solid--liquid boundary layer of BGO are investigated by their high-temperature Raman spectra for the first time. The rule of structure change of BGO crystal with increasing temperature is analysed. The results show that there exists [GeO4] polyhedral structure and Bi ion independently in BGO melt. The bridge bonds Bi--O--Bi and Bi--O--Ge appear in the crystal and at the boundary layer, but disappear in the melt. The structure of the growth solid--liquid boundary layer is similar to that of BGO crystal. In the melt, the long-range order structure of the crystal disappears. The thickness of the growth solid--liquid boundary layer of BGO crystal is about 50μm.
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