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Volume 22 Issue 1
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Original Articles
 Select Searching for Infinitely Many Symmetries and Exact Solutions via Repeated Similarity Reductions LOU Sen-Yue, LAIN Zeng-Ju Chin. Phys. Lett. 2005, 22 (1): 1-4 .   Abstract   PDF(pc) (210KB) ( 898 ) A simple symmetry reduction procedure is repeatedly used to obtain infinitely many symmetries and then the exact solutions of the Burgers equation. Some sets of exact solutions such as the rational solutions, rational-kink solutions and error function solutions are explicitly given. As a byproduct the recursion operators can be re-obtained at the same time.
 Select Generalized Fokker--Planck Equation with Time-Dependent Transport Coefficients and a Quadratic Potential: Its Application in Econophysics WANG Peng, WANG Shun-Jin, ZHANG Hua Chin. Phys. Lett. 2005, 22 (1): 5-8 .   Abstract   PDF(pc) (311KB) ( 1233 ) In order to control non-equilibrium processes and to describe the fat-tail phenomenon in econophysics, we generalize the traditional the Fokker--Planck equation (FPE) by including a quadratic correlation potential, and by making the time-dependent drift--diffusion coefficients. We investigate the su(1,1)⊕u(1) algebraic structure and obtain the exact solutions to the generalized time-dependent FPE by using the algebraic dynamical method. Based on the exact solution, an important issue in modern econophysics, i.e.~the fat-tail distribution in stock markets, is analysed.
 Select Quantum Spectra and Classical Orbits in Two-Dimensional Equilateral Triangular Billiards LIN Sheng-Lu, GAO Feng, HONG Zheng-Pin, DU Meng-Li Chin. Phys. Lett. 2005, 22 (1): 9-11 .   Abstract   PDF(pc) (365KB) ( 530 ) We study the correspondence between quantum spectra and classical orbits in the equilateral triangular billiards. The eigenstates of such systems are not separable functions of two variables even though the problem is exactly solvable. We calculate the Fourier transform of a quantum spectral function and find that the positions of the peaks match well with the lengths of the classical orbits. This is another example showing that the quantum spectral function provides a bridge between quantum and classical mechanics.
 Select Manipulation of Quantum Nonlocality of the Single-Photon Entangled State via Beam Splitter ZHOU Qing-Ping, , FANG Mao-Fa, LIU Xiao-Juan Chin. Phys. Lett. 2005, 22 (1): 12-14 .   Abstract   PDF(pc) (499KB) ( 683 ) Quantum nonlocality of the single-photon entangled state emerging from a beam splitter with arbitrary controlling parameters is investigated by means of the parity measurement. The condition of the maximal violation of the Bell-CHSH inequality is obtained for the single-photon entangled state. Under the condition of the small coherent intensity J (J=0.1) and the phase difference γαβ of the two coherent displacements being opposite to the internal phase shift Ф of the beam splitter (γαβ =-Ф), we find that the quantum nonlocality depends only on the reflection coefficient $R$ of the beam splitter, while Ф plays an important role for selecting γαβ . The strongest quantum nonlocality can be observed for a 50:50 beam splitter. If R deviates from the intermediate value 0.5, the quantum nonlocality decreases gradually, even vanishes. Our results provide a method to observe and manipulate the quantum nonlocality of the single-photon entangled state by adjusting the parameters of the coherent displacements and the beam splitter.
 Select Entanglement Purification with Higher Error Threshold for Imperfection of Local Operations and Bell State Measurements SONG Xin-Guo, FENG Xun-Li Chin. Phys. Lett. 2005, 22 (1): 15-17 .   Abstract   PDF(pc) (299KB) ( 514 ) We analyse further the entanglement purification protocol proposed by Feng et al. [Phys. Lett. A 271(2000)44] in the case of imperfect local operations and measurements. It is found that this protocol allows of higher error threshold. Compared with the standard entanglement purification proposed by Bennett et al. [Phys. Rev. Lett. 76(1996)722], it turns out that this protocol is remarkably robust against the influences of imperfect local operations and measurements.
 Select Deterministic Secure Direct Communication by Using Swapping Quantum Entanglement and Local Unitary Operations MAN Zhong-Xiao, ZHANG Zhan-Jun, LI Yong Chin. Phys. Lett. 2005, 22 (1): 18-21 .   Abstract   PDF(pc) (323KB) ( 5170 ) A deterministic direct quantum communication protocol is proposed by using swapping quantum entanglement and local unitary operations. The present protocol is secure for the proof of the security of the present scheme, the same as that in the two-step protocol [Phys. Rev. A 68(2003)042317]. Additionally, the advantages and disadvantages of the present protocol is also discussed.
 Select Quantum Dialogue Revisited MAN Zhong-Xiao, ZHANG Zhan-Jun, LI Yong Chin. Phys. Lett. 2005, 22 (1): 22-24 .   Abstract   PDF(pc) (188KB) ( 709 ) An entanglement-based quantum dialogue protocol [Phys. Lett. A 328(2004)6] is proven to be insecure: that is, in the protocol an eavesdropper can steal the secret messages without being detected provided that he/she adopts the intercept-and-resend attack strategy. We modify the protocol, i.e. in the control mode, by introducing and randomly choosing two sets of measuring basis: the intercept-and-resend attack can be accordingly detected. Hence, within the present version two users can securely and simultaneously exchange their secret messages.
 Select Behaviour of Rotating Bose--Einstein Condensates Under Shrinking ZHAI Hui, ZHOU Qi Chin. Phys. Lett. 2005, 22 (1): 25-28 .   Abstract   PDF(pc) (365KB) ( 585 ) When the repulsive interaction strength between atoms decreases, the size of a rotating Bose--Einstein condensate will consequently shrink. We find that the rotational frequency will increase during the shrinking of condensate, which is a quantum mechanical analogy to ballet dancing. Compared to a non-rotating condensate, the size of a rotating BEC will eventually be saturated at a finite value when the interaction strength is gradually reduced. We also calculate the vortex dynamics induced by the atomic current, and discuss the difference of vortex dynamics in this case and that observed in a recent experiment carried out by the JILA group [Phys. Rev. Lett. 90(2003)170405].
 Select Bianchi Type-III String Cosmological Model with Bulk Viscosity in General Relativity WANG Xing-Xiang Chin. Phys. Lett. 2005, 22 (1): 29-32 .   Abstract   PDF(pc) (199KB) ( 984 ) The Bianchi type-III cosmological model for a cloud string with bulk viscosity are studied. To obtain a determinate solution, it is assumed that the coefficient of bulk viscosity is a power function of the scalar of expansion zeta = kθm and the shear scalar is proportional to scalar of expansion σ ∝ θ, which leads to the relation between metric potentials B = Cn. The physical features of the model are also discussed. It is found that the power index m has significant influence on the string model. There is a big bang'' start in the model when m≤1 but there is no the big-bang start when m > 1. In the special case m = 0, the model reduces to the string model of constant coefficient of bulk viscosity that was the result previously given in the literature.
 Select Probing the Microscopic Origin of Gravity via Precision Polarization and Spin Experiments NI Wei-Tou Chin. Phys. Lett. 2005, 22 (1): 33-35 .   Abstract   PDF(pc) (221KB) ( 463 ) As in other parts of physics, we advocate the interaction approach: experiments ,<-> (...are influenced and their importance is determined by...and vice versa) phenomenology <-> low-energy effective (field) theory <-> microscopic theory to probe the microscopic origin of gravity. Using the x-g phenomenological framework, we discuss the tests of equivalence principles. The only experimentally unconstrained degree of freedom is the axion freedom. It has effects on the long-range astrophysical/cosmological propagation of electromagnetic waves and can be tested/measured using the future generation of polarization measurement of cosmic background radiation. The verification or refutal of this axionic effect will be a crucial step for constructing an effective theory and probing the microscopic origin of gravity. The interaction of spin with gravity is another important clue for probing the microscopic origin of gravity. The interplay of experiments, phenomenology and effective theory are expounded. An ideal way to reveal the microscopic origin of gravity is to measure the gyrogravitational ratio of particles. Three potential experimental methods are considered.
 Select Theoretical Studies of One-Dimensional Asymmetrical Finite Crystal in Terahertz Laser HE Shan, QIN Jia-Yin, ZENG Jian-Fen Chin. Phys. Lett. 2005, 22 (1): 36-39 .   Abstract   PDF(pc) (420KB) ( 778 ) Based on the analytical solution to quantum confinement states in one-dimensional crystals with asymmetric potentials, it is shown that the confined states within the energy bands of asymmetric quantum well (AQW) have potentials to be sources of THz radiation. The calculation demonstrates that it is the band mixture effect of AQW that makes the energy separation variable to favour THz emission. Compared with single the quantum well with symmetric potentials, the electronic structure of AQW makes it a desirable source of THz emission.
 Select Experimental Study of Optical Nonlinearities in a Broadband Semiconductor Saturable Absorber Mirror XING Qi-Rong, MAO Fang-Lin, LANG Li-Ying, WANG Zhuan, WANG Kai, LI Shu-Xin, CHAI Lu, ZHANG Zhi-Gang, WANG Qing-Yue Chin. Phys. Lett. 2005, 22 (1): 40-42 .   Abstract   PDF(pc) (311KB) ( 475 ) The negative nonlinear index of a semiconductor saturable absorber mirror (SESAM) was investigated by using the reflection Z-scan technique. This is an experimental demonstration, for the first time to our knowledge, that the SESAM possesses comparable negative nonlinear index n2= -2.35×10-10,esu, which may have important implications in design and alignment of Kerr-lens mode-locking based on the self-focusing effect.
 Select Ferroelectric Domain Imaging Mechanism in High-Vacuum Scanning Force Microscopy ZENG Hua-Rong, YU Han-Feng, CHU Rui-Qing, LI Guo-Rong, YIN Qing-Rui Chin. Phys. Lett. 2005, 22 (1): 43-45 .   Abstract   PDF(pc) (369KB) ( 581 ) High-vacuum scanning force microscopy of the domain structures in PMN-PT single crystals is investigated. It has been shown that under high vacuum conditions, the polarization charges are not effectively compensated for by intrinsic screening charges from the ferroelectrics. This result suggests that the electrostatic tip--sample interaction plays a great contribution to the domain imaging mechanism in PMN-PT ferroelectric single crystals under high vacuum conditions.
 Select Density Dependence of the Mass and Decay Constant of Pion in Nuclear Matter in the Dyson--Schwinger Equation Approach of QCD LIU Yu-Xin, , CHAO Jing-Yi, CHANG Lei, YUAN Wei Chin. Phys. Lett. 2005, 22 (1): 46-49 .   Abstract   PDF(pc) (269KB) ( 520 ) With the Dyson--Schwinger equation formalism at finite chemical potential, we study the density dependence of the mass and decay constant of pion in nuclear matter. The calculated results indicate that both the mass and the decay constant remain almost constant at small chemical potential. As the chemical potential gets quite large, the decay constant increases and the mass decreases with the increasing of the chemical potential, and both of them vanish suddenly as a critical value is reached.
 Select Theoretical Calculation of Rotational Bands of 179Pt in the Particle--Triaxial--Rotor Model CHEN Guo-Jie, SONG Hui-Chao, LIU Yu-Xin, Chin. Phys. Lett. 2005, 22 (1): 50-53 .   Abstract   PDF(pc) (267KB) ( 574 ) Theoretical calculations have been performed for nucleus 179Pt in the particle--triaxial--rotor model with variable moment of inertia. The obtained energy spectrum agrees with the experimental data quite well. The calculated results indicate that the bands 1/2- and 7/2+ are triaxial deformation bands and originate mainly from the v[521]1/2- and v[633]7/2+ configurations respectively.
 Select Isoscaling of the Fission Fragments with Langevin Equation WANG Kun, MA Yu-Gang, WEI Yi-Bin, CAI Xiang-Zhou, CHEN Jin-Gen, FANG De-Qing, GUO Wei, MA Guo-Liang, SHEN Wen-Qing, TIAN Wen-Dong, ZHONG Chen, ZHOU Xing-Fei Chin. Phys. Lett. 2005, 22 (1): 53-56 .   Abstract   PDF(pc) (396KB) ( 676 ) The Langevin equation is used to simulate the fission process of 112Sn + 112Sn and 116Sn + 116Sn. The mass distribution of the fission fragments are given by assuming the process of symmetric fission or asymmetric fission with the Gaussian probability sampling. The isoscaling behaviour has been observed from the analysis of fission fragments of both the reactions, and the isoscaling parameter α seems to be sensitive to the width of fission probability and the beam energy.
 Select Highly Sensitive Tunable Diode Laser Absorption Spectroscopy of CO2 Around 1.57μm SHAO Jie, GAO Xiao-Ming, ZHANG Wei-Jun, YUAN Yi-Qian, YANG Yong, PEI Shi-Xin Chin. Phys. Lett. 2005, 22 (1): 57-60 .   Abstract   PDF(pc) (313KB) ( 517 ) he absolute absorption spectrum intensities of carbon dioxide samples has been recorded with a tunable diode laser spectrometer in the spectral range 6350--6364cm-1, which is suitable for the in-situ sensing of carbon dioxide in the lower stratosphere studied using a commercial telecommunication-type diode laser. It was found that the typical uncertainty of experimental line intensities is about 1% compared with the values listed in the HITRAN database, which are calculated by direct numerical diagonalization. The intensity of the weakest line we detected in this experiment is 1.116×10-26cm-1/(molecule.cm-2) at the pressure of 0.5 Torr, and the corresponding absorption is 3.2×10-6 with SNR of 4.53.
 Select Parallel Momentum Distribution of 28Si Fragments from 29P WEI Yi-Bin, MA Yu-Gang, CAI Xiang-Zhou, ZHONG Chen, CHEN Jin-Gen, ZHANG Hu-Yong, FANG De-Qing, WANG Kun, MA Guo-Liang, GUO Wei, TIAN Wen-Dong, SHEN Wen-Qing, ZHAN Wen-Long, XIAO Guo-Qing, XU Hu-Shan, SUN Zhi-Yu, Li Jia-Xing, GUO Zhong-Yan, WANG Meng, CHEN Zhi-Qiang, HU Zheng-Guo, CHEN Li-Xin, LI Chen, MAO Rui-Shi, BAI Jie Chin. Phys. Lett. 2005, 22 (1): 61-64 .   Abstract   PDF(pc) (443KB) ( 570 ) Distribution of the parallel momentum of 28Si fragments from the breakup of 30.7MeV/nucleon 29P has been measured on C targets. The distribution has the FWHM with the value of 110.5±23.5MeV/c, which is quantitatively consistent with the Galuber model calculation assuming by a valence proton in 29P. The density distribution is also predicted by the Skyrme--Hartree--Fock calculation. The results show that the proton-skin structure may exist in 29P.
 Select Isospin Momentum-Dependent Interaction and Its Role on the Isospin Fractionation Ratio in Intermediate Energy Heavy Ion Collisions LIU Jian-Ye, , GUO Wen-Jun, XING Yong-Zhong, LEE Xi-Guo, Chin. Phys. Lett. 2005, 22 (1): 65-68 .   Abstract   PDF(pc) (361KB) ( 716 ) We investigate the role of isospin momentum-dependent interaction on the isospin fractionation ratio and its dynamical mechanism in the intermediate energy heavy ion collisions, by inserting an isospin degree of freedom into the momentum-dependent interaction to obtain an isospin momentum-dependent interaction given in a form practically usable in the isospin-dependent quantum molecular dynamics model. It is found that the isospin momentum-dependent interaction brings an important isospin effect into the isospin fractionation ratio. In particular, the isospin momentum-dependent interaction reduces obviously the reduction of isospin fractionation ratio. Thus the isospin dependence of momentum-dependent interaction is thus important for studying accurately the equation of state of isospin asymmetry nuclear matter.
 Select Inter-relationship of Various Results in Analysis of (14.0MeV/U) Pb+Pb Reaction Using Mica and CN-85 Track Detectors F. N. Khattak, E. U. Khan, Tabassum Nasir, J. J. Baluch, F. U. Khan Chin. Phys. Lett. 2005, 22 (1): 69-71 .   Abstract   PDF(pc) (376KB) ( 529 ) Two detector materials mica and cellulose-nitrate(CN)-85 have been used to study (14.0MeV/u) Pb + Pb reaction. Events of different multiplicities were registered in mica and CN-85 detectors using the 2π-geometry technique of solid state nuclear track detection. After removing the target material from the detectors the damaged trails in the detectors were revealed as tracks by proper chemical etching. The irradiated area of each sample was scanned and events of different multiplicities were traced. The binary events were bifurcated into elastic and inelastic events. The elastic binary events and three prong events, observed in the reaction, have been used to search out coefficients Cμv in the presence of both the detectors, for the reaction under study. Using these coefficients 3- and 4-prong events have been analysed. From the detailed analysis of the results of (14.0MeV/u) Pb+Pb reaction, obtained from mica and CN-85 track detectors we observed a great resemblance of results obtained from the two detectors. Combining the results of both the detectors, we report some important outcomes.
 Select Molecular Dynamics Simulation of Ion Implantation into HfO2 and HfOx/Si Multi-Layer Structure SHI Hao, YU Min, HUANG Ru, WANG Yang-Yuan, SUZUKI Kunihiro, OKA Hideki Chin. Phys. Lett. 2005, 22 (1): 76-79 .   Abstract   PDF(pc) (707KB) ( 635 ) We simulate the B, As and P implantations into HfO2 from 3keV to 40keV by a simulator LEACS developed based on molecular dynamics method and by the traditional Monte Carlo simulator TSUPREM4 respectively. The LEACS results accurately fit with the SIMS (secondary ion mass spectroscopy) data, while the TSUPREM4 results deviate from the SIMS data obviously except B implantation. Based on the verification of the simulator, influence of the oxide thickness on the retained range profiles in the Si layer has been quantitatively investigated in the case of HfO2/Si and SiO2/Si structures. The range profiles in the Si layer through HfO2 shift to the surface obviously for about 0.68 times of the oxide layer thickness on the average in comparison to those through SiO2. It can be predicted that this effect will have a significant impact on MOSFET (metallic oxide semiconductor field effect transistor) device performance in the integrated circuit process of the next decade if HfO2 is used to replace SiO2 as the gate dielectric.
 Select Optical Transition Probability of Nd3+ Ions Doped in Ferroelectric PLZT for Active Electro-Optical Applications LI Bao-Zeng, ZHENG Zhi-Qiang, YANG Ji-Wen, LI Ke-Wen, Jiang Hua, CHEN Xue-Sheng, WANG An-Ting, XIE Jian-Ping, MING Hai Chin. Phys. Lett. 2005, 22 (1): 80-82 .   Abstract   PDF(pc) (329KB) ( 573 ) The optical transition probability of Nd3+ (0.5mol%) doped lanthanum-modified lead zirconate titanate (PLZT) is investigated. The absolute intensities of its forced electric dipole transitions between 400nm and 1000nm were measured, from which we obtain three phenomenological parameters, Ω2= 0.787×10-20cm2, Ω4= 1.182×10-20cm2, and Ω6=1.042×10-20cm-20, according to the Judd--Ofelt theory. The radiation lifetime (346.9μs) of the 4F3/2 metastable state, the stimulated emission cross-section σij= (2.49×10-21cm2, 6.51×10-21cm2, 2.17×10-21cm2), and the fluorescence branch ratios are calculated. We also measured the fluorescence lifetime (155.84μs) and calculated the quantum efficiency (46.1%). The analysis reveals that Nd103+-doped PLZT, based on its large electro-optical effect, has potential applications in active optical devices.
 Select Trapping of Neutral Atoms with a Radio-Frequency Field ZHANG Hai-Chao, ZHANG Peng-Fei, XU Xin-Ping, HAN Jiu-Rong, WANG Yu-Zhu Chin. Phys. Lett. 2005, 22 (1): 83-86 .   Abstract   PDF(pc) (402KB) ( 584 ) Based on the dressed-atom approach, we discuss a two-dimensional (2D) radio-frequency trap for neutral atoms, in which the trap potential derives from the magnetic-dipole transitions among the hyperfine Zeeman sublevels. By adjusting the detuning of the radiation from resonance, the trapping states will be changed predominantly from the bare states of mF gF > 0 to other states of mF gF < 0, where mF and gF are the quantum numbers of Zeeman sublevels and the Landé factor, respectively. This character contrasts finely with that of a static magnetic trap that can only trap or guide the states of mF gF > 0. In comparison to the optical field, the radio-frequency trap eliminates the spontaneous emission heating of the atoms. Unlike other oscillating traps reported in the literature, the configuration of the radio frequency trap is suitable for realization of a miniature magnetic guide.
 Select Calculation of Electron-Impact 2s22p4 3P→ 2p33s3S0 Transition in Atomic Oxygen WANG Yang, LI Yan-Hua, ZHOU Ya-Jun Chin. Phys. Lett. 2005, 22 (1): 87-90 .   Abstract   PDF(pc) (609KB) ( 400 ) The inelastic scattering of electron from oxygen for the 2s22p4 3P→ 2p33s3S0 transition is studied using the momentum-space coupled channel optical method at 15, 17.5, 20, 22.5, 25, 27.5, 30, 50, and 100eV. Direct ionization cross sections, i.e. differential and integral cross sections, are reported. Important continuum states are included in the coupled channel calculation via a complex equivalent-local optical potential. The present results are compared with the available experimental data and other theoretical calculation results.
 Select Monte Carlo Simulation on Energy Deposition of Low-Energy Electrons in Liquid Water TAN Zhen-Yu, XIA Yue-Yuan, ZHAO Ming-Wen, LIU Xiang-Dong, HUANG Bo-Da, LI Feng, JI Yan-Ju Chin. Phys. Lett. 2005, 22 (1): 91-94 .   Abstract   PDF(pc) (379KB) ( 653 ) A Monte Carlo approach to simulate the transport and energy deposition of low energy electrons (E10 ≤ 10keV) in liquid water is presented. The elastic scattering of electrons is described by Mott cross section, which is derived from the relativistic wave equation of Dirac. The inelastic scattering model of electrons is based on the dielectric response theory with exchange effect included. A new method of sampling various inelastic scattering events is proposed in the simulation. Using the approach stated, the spatial distribution of inelastic scattering events and energy deposition of electrons in liquid water are computed and the results are compared with other theoretical studies.
 Select Silicon-on-Insulator Based Electro-optic Variable Optical Attenuator with a Series Structure HE Yue-Jiao, LI Fang, LIU Yu-Liang Chin. Phys. Lett. 2005, 22 (1): 95-98 .   Abstract   PDF(pc) (359KB) ( 959 ) An electro-optic variable optical attenuator in silicon-on-insulator is designed and fabricated. A series structure is used to improve the device efficiency. Compared to the attenuator in the single p-i-n diode structure in the same modulating length, the attenuation range of the device in the series structure improves 2--3 times in the same injecting current density, while the insertion loss is not affected. The maximum dynamic attenuation of the device is greater than 30dB. The response frequency is obtained to be about 2MHz.
 Select Investigation of Kinematics of the Portevin--Le Chatelier Deformation Bands with Dynamic Digital Speckle Pattern Interferometry JIANG Hui-Feng, ZHANG Qing-Chuan, JIANG Zhen-Yu, CHEN Zhong-Jia, WU Xiao-Ping Chin. Phys. Lett. 2005, 22 (1): 99-102 .   Abstract   PDF(pc) (647KB) ( 742 ) The Portevin--Le Chatelier (PLC) effect with typical temporal instabilities in the recorded stress is closely associated with local inhomogeneities of deformation. By employing the dynamic digital speckle pattern interferometry technology, the characterizations for the PLC deformation bands of type A (continuous propagation along the specimen), type B (''hopping'' propagation along the specimen) and type C (random nucleation in the sample) were distinctly clarified. The corresponding positions of deformation bands were traced throughout the whole tensile process. By systemic experiments, the range of the applied strain rates for each type of bands existing was investigated respectively. The evolution of the band velocity (for types A and B) was also statistically investigated and qualitatively interpreted.
 Select Holographic Reversed-Mode Polymer-Stabilized Liquid Crystal Grating MA Ji, SONG Jing, LIU Yong-Gang, RUAN Sheng-Ping, XUAN Li Chin. Phys. Lett. 2005, 22 (1): 103-106 .   Abstract   PDF(pc) (395KB) ( 709 ) We demonstrate the "reversed-mode" polymer-stabilized liquid crystal device. The incidence light goes through the film without the applied voltage and is diffracted with it. Because of relatively high liquid crystal percentage of 94%, the operating voltage of the device is less than 20V. We explain this phenomenon using the molecular orientation model and the refractive index profile. The device can be used as display, optical switch, optical modulator and especially optical cross-connect deflector.
 Select Holographic Grating Formation in Photochromic Diarylethene-Doped Polymeric Thin Films LUO Shou-Jun, LIU Guo-Dong, HE Qing-Sheng, JIN Guo-Fan Chin. Phys. Lett. 2005, 22 (1): 107-109 .   Abstract   PDF(pc) (439KB) ( 385 ) We introduce a model to describe real-time grating formation in holographic photochromic diarylethene-doped polymeric thin films. This model, which combines photochromic chemical reaction with the coupled-wave theory, indicates that the grating recording time depends on the molecular absorption coefficient of molecules and the quantum yield of the photochromic reaction at a certain holographic recording intensity. The model is validated by comparing its predictions with the experimental results in which photochromic molecule 1,2-bis(2-methyl-5-(4-formylphenyl)-3-thienyl) perfluorocyclopentene doped PMMA films were used.
 Select An Advanced Dynamic Model for Semiconductor Optical Amplifiers and Laser Diodes CHEN Gen-Xiang, LI Wei, HUANG Wei-Ping, JIAN Shui-Sheng Chin. Phys. Lett. 2005, 22 (1): 110-113 .   Abstract   PDF(pc) (716KB) ( 399 ) We propose a unified time-domain dynamic model for both semiconductor optical amplifiers and laser diodes by employing a set of multi-longitudinal-mode coupled wave rate equations. A novel split-step method has been developed for the numerical solution of the equation set. To demonstrate the capabilities of the model, some calculation results for conventional and distribute feedback-type gain-clamped semiconductor optical amplifiers are presented.
 Select Ridge Waveguide Laser Integrated with Spot-Size Converter in a Single Step Epitaxial for High Coupling Efficiency to Single-Mode Fibres HOU Lian-Ping, WANG Wei, ZHU Hong-Liang Chin. Phys. Lett. 2005, 22 (1): 114-116 .   Abstract   PDF(pc) (331KB) ( 939 ) A 1.55-μm laser diode integrated with a spot-size converter was fabricated in a single step epitaxial by using the conventional photolithography and chemical wet etching process. The device was constructed by a conventional ridge waveguide active layer and a larger passive ridge-waveguide layer. The threshold current was 40mA together with high slope efficiency of 0.24W/A. The beam divergence angles in the horizontal and vertical directions were as small as 12.0°× 15.0°, respectively, resulting in about 3.2-dB coupling losses with a cleaved optical fibre.
 Select Controllable Passively Q-Switched Laser YANG Cheng-Wei, HUO Yu-Jing, HE Shu-Fang, YIN Xiao-Dong, ZHANG Bao-Shun Chin. Phys. Lett. 2005, 22 (1): 117-119 .   Abstract   PDF(pc) (378KB) ( 974 ) We present a novel kind of pulsed laser named controllable passively Q-switched laser (CPQL). A CPQL of Nd:YVO4 with Cr:YAG as saturable absorber was demonstrated and studied as an example of the kind of pulsed lasers. In CPQL, as the actively controlling signal, a diode laser beam was focused onto the saturable absorber in the resonant cavity of the passively Q-switched laser (PQL) and was absorbed by the absorber to realize the active control of the CPQL. The characters of the CPQL output laser pulses, such as generation time, repetition rate, pulse width, peak power and energy per pulse, can be controlled by the operator. The CPQLs possess the advantages of both passively Q-switched laser and actively Q-switched laser. Because of their compactness, low cost and controllability, the CPQLs will find wide applications in many fields.
 Select Design of a Compact Diode-Pumped Intracavity-Doubled Nd:GdVO4 Laser with 820-mW Red Light ZHANG Ling, LI De-Hua, WEI Zhi-Yi, FENG Bao-Hua, FU Pan-Ming, ZHANG Zhi-Guo Chin. Phys. Lett. 2005, 22 (1): 120-121 .   Abstract   PDF(pc) (305KB) ( 782 ) We report a design of diode-pumped high power Nd:GdVO4/LBO red laser with a compact linear cavity, which can output 820-mW red light at 670nm with an optical conversion efficiency of 9.6%. The maximum output power of the fundamental light at 1.34μm was 4W with a slope efficiency of 45%.
 Select A Room-Temperature Multiwavelength Erbium-Doped Fibre Laser by Exploiting Polarization Hole Burning ZHANG Hao, XIONG Ling-Yun, DOU Qing-Ying, LI Yao, YU Ling, LIU Yan-Ge, LIU Li-Hui, YUAN Shu-Zhong, KAI Gui-Yun, DONG Xiao-Yi Chin. Phys. Lett. 2005, 22 (1): 122-124 .   Abstract   PDF(pc) (521KB) ( 535 ) Multiwavelength operation of a linear cavity erbium-doped fibre laser (EDFL) is proposed and demonstrated. A 3-dB fibre loop mirror and a high birefringence (HiBi) fibre loop mirror are utilized as the cavity reflectors. By utilizing the wavelength-dependent polarization rotation induced by the HiBi fibre loop mirror and by using a fibre polarizer to control the intracavity polarization state, the polarization states of different wavelengths are diversified. Therefore, the polarization hole burning (PHB) effect has been greatly enhanced and the homogeneous broadening of erbium-doped fibre is suppressed to a large extent. By simply tuning a polarization controller, we experimentally obtained simultaneous lasing of four and five wavelengths with wavelength spacing of ～1.8nm and less than 2\,nm at room temperature, respectively. The repeated scans show that all of these lasers have good stability.
 Select High Beam Quality Green Generation with Output 140W Based on a Thermally-Near-Unstable Flat--Flat Resonator GENG Ai-Cong, BO Yong, BI Yong, SUN Zhi-Pei, YANG Xiao-Dong, PENG Qin-Jun, LI Hui-Qing, ZHOU Yi, LI Rui-Ning, CUI Da-Fu, XU Zu-Yan Chin. Phys. Lett. 2005, 22 (1): 125-127 .   Abstract   PDF(pc) (389KB) ( 738 ) By using a diode-side-pumped Q-switched Nd:YAG rod laser based on a thermally-near-unstable flat--flat resonator, an intracavity-frequency-doubled green beam generation is investigated. Output power 140W is obtained at a repetition rate of 10kHz and a pulse width of 110ns. The green beam quality factors M2x and M2y, which are measured by a laser beam analyser, are 10.65 and 10.85, respectively, at output power of 124W.
 Select Incoherently Coupled Grey Photovoltaic Spatial Soliton Families WANG Hong-Cheng, SHE Wei-Long Chin. Phys. Lett. 2005, 22 (1): 128-131 .   Abstract   PDF(pc) (303KB) ( 379 ) A theory is developed for incoherently coupled grey photovoltaic soliton families in unbiased photovoltaic crystals. Both the properties and the forming conditions of these soliton families are discussed in detail. The theory can also be used to investigate the dark photovoltaic soliton families. Some relevant examples are presented, in which the photovoltaic-photorefractive crystal is of lithium niobate type.
 Select Luminescent Properties and Mechanism of Gd1-x-yAlO3Eux,REy LUO Lan, LIU Qing-Feng, LIU Qian Chin. Phys. Lett. 2005, 22 (1): 131-134 .   Abstract   PDF(pc) (332KB) ( 874 ) GAP:Eu,Re(Gd1-x-yAlO3Eux,REy, RE=Pr or Ce) powders were prepared by a nitrate--citrate process. It is found that luminescent intensity decreases when GAP:Eu is co-doped with Pr or Ce. The phenomena of spectra prove that there is a resonant energy transfer between Eu and Pr, by the absorption and emission of lower-energy phonon, and also Ce sensitizer decreases the activator energy level from host→Eu. The two factors are considered to be the main reasons for decrease of the luminescent intensity for the co-doped GAP:Eu,Re.
 Select Fabrication, Testing and Integration Technologies of Polymer Microlens for Pt/Si Schottky-Barrier Infrared Charge Coupled Device Applications KE Cai-Jun, YI Xin-Jian, LAI Jian-Jun, CHEN Si-Hai Chin. Phys. Lett. 2005, 22 (1): 135-138 .   Abstract   PDF(pc) (413KB) ( 521 ) A novel polymer refractive microlens array has been formed on the surface of 256(V)×290(H) PtSi Schottky-barrier infrared charge coupled device (IRCCD) image sensors to improve the photoresponsivity of the IRCCD. The fabrication process flows of polymer microlens array are described. An effective aperture ratio in excess of 92% of microlens array has been achieved. An experimental facility to evaluate the optical performance of microlens array is introduced. The measurement results show that the microlens array indicates better than 4% non-uniformity of focal length and high optical performance. The application of the microlens array to improve the photosensitivity of infrared CCD is discussed.
 Select Silicon-on-Insulator-Based Waveguide Switch with Fast Response CHEN Yuan-Yuan, LI Yun-Tao, XIA Jin-Song, LIU Jing-Wei, CHEN Shao-Wu, YU Jin-Zhong Chin. Phys. Lett. 2005, 22 (1): 139-141 .   Abstract   PDF(pc) (286KB) ( 581 ) Based on thermo-optical effect of silicon, a 2×2 switch is fabricated in silicon-on-insulator by chemical etching. The switch presents an extinction ratio of 26dB and a power consumption of 169mW. The response time is ～ 10.5μs.
 Select Novel Folding Large-Scale Optical Switch Matrix with Total Internal Reflection Mirrors on Silicon-on-Insulator by Anisotropy Chemical Etching LIU Jing-Wei, YU Jin-Zhong, CHEN Shao-Wu Chin. Phys. Lett. 2005, 22 (1): 142-145 .   Abstract   PDF(pc) (357KB) ( 636 ) A compact optical switch matrix was designed, in which light circuits were folded by total internal reflective (TIR) mirrors. Two key elements, 2×2 switch and TIR mirror, have been fabricated on silicon on-insulator wafer by anisotropy chemical etching. The 2×2 switch showed very low power consumption of 140mW and a very high speed of 8±1μs. An improved design for the TIR mirror was developed, and the fabricated mirror with smooth and vertical reflective facet showed low excess loss of 0.7±0.3dB at 1.55μm.
 Select A Novel Method to Measure Acoustic Power of Focusing Transducer with Spherical Surface Based on Self-Reciprocity Theorem DUAN Shi-Mei, SHOU Wen-De, HE Pei-Zhong, QIAN De-Chu, XIA Rong-Min Chin. Phys. Lett. 2005, 22 (1): 146-149 .   Abstract   PDF(pc) (501KB) ( 741 ) A novel method to measure acoustic power of focusing transducer based on the self-reciprocity theorem of convergent spherical acoustic wave is proposed. The performance of this reciprocity method is compared with that of the radiation force balance (RFB) method and the admittance circle method. The average deviations of the reciprocity method from RFB in measurements of the acoustic power and the radiation conductance for a focusing transducer of 1.525MHz are 7.5% and 3.6% respectively, and for another focusing transducer of 5.27MHz, they are 1.7% and 1.1%. The measured radiation conductance deviation by the reciprocity method from the admittance circle method for the focusing transducer of 1.525MHz is 7.9%. It presents encouraging results even in measuring low acoustic power level. The overall uncertainty of acoustic power measurement using the method is evaluated below 10%, and it has many advantages such as high signal-to-noise ratio, good stability and less interference of bubbles and environment.
 Select Laboratory Studies of Low Vortices in a Low Froude Number Flow Pasting over an Isolated Obstacle PING Fan, GAO Shou-Ting Chin. Phys. Lett. 2005, 22 (1): 150-153 .   Abstract   PDF(pc) (319KB) ( 599 ) The present paper mainly focuses on the generation and development of lee vortices for the low Froude number density stratified flow passing over an isolated obstacle. A series of laboratory experiments were carried out by towing-tank equipments to simulate the airflow passing over a large terrain. Based on the similarity principle, the Froude number of the stratified flow, the stratified condition, and the rotation parameter are chosen in the specified scope. Our studies show that the lee vortices can appear in the non-rotational and rotational cases. For the non-rotational fluid, the lee vortices generate only under the condition of strong stratification and the small Froude number (0.1 < Fr <0.3). However, the lee vortices can be formed under the condition of relatively strong stratification and the proper Froude number (0.1< F r <0.5) for the rotational fluid. The results of the divided experiments including non-rotational and rotational cases show that the formation mechanism of lee vortices is different for non-rotational flow and rotational flow. The lee vortices are created by the tilting term of perturbation velocity for the non-rotational flow, but for the rotational flow, the β-effect associated with the horizontal convergence and divergence of the horizontal perturbation velocity is more important.
 Select Flow Structures Around Micro-bubbles During Subcooled Nucleate Boiling WANG Hao, PENG Xiao-Feng, David M. Christopher, WANG Bu-Xuan Chin. Phys. Lett. 2005, 22 (1): 154-157 .   Abstract   PDF(pc) (424KB) ( 600 ) The flow structures were investigated around micro bubbles on extremely thin wires during subcooled nucleate boiling. Jet flows emanating from the bubbles were observed visually with the fluid field measurement using high-speed photography and a PIV system. The jet flows induced a strong pumping effect around a bubble. The multi-jet structure was further observed experimentally, indicating the evolution of flow structure around micro bubbles. Numerical simulations explore that the jet flows were induced by a strong Marangoni effect due to high temperature gradients near the wire. The bubble interface with multi-jet structure has abnormal temperature distribution such that the coolest parts were observed at two sides of a bubble extending into the subcooled bulk liquid rather than at the top. Evaporation and condensation on the bubble interface play important roles not only in controlling the intensity of the jet flow, but also in bringing out the multi-jet structure.
 Select Fractal Character for Tortuous Streamtubes in Porous Media YU Bo-Ming Chin. Phys. Lett. 2005, 22 (1): 158-160 .   Abstract   PDF(pc) (331KB) ( 1099 ) An analytical model for fractal dimension of tortuous streamtubes in porous media is derived. The proposed fractal dimension for tortuous streamtubes in porous media is expressed as a function of porosity and scale, and there is no empirical constant in the proposed expression. The model predictions for the fractal dimension of tortuous streamtubes in porous media are in good agreement with those by the box-counting method and with the observations of other researchers.
 Select A Novel Reactive Gas Source and Its Application to Carbon Nanotube Film Deposition JIANG Nan, CHEN Han-Yuan, QIAN Sheng-Fa Chin. Phys. Lett. 2005, 22 (1): 161-163 .   Abstract   PDF(pc) (326KB) ( 391 ) Generally, gaseous discharge at pressure higher than 10kPa will collapse to filamentary form or streamer, which will produce a non-uniform treatment on the sample surface. Thus, atmospheric pressure glow discharge (APGD) is developed. However the realization of the APGD is not obvious, it needs special conditions. We propose a new concept to solve the non-uniformity problem. By using a grid electrode and putting the sample downstream of the discharge plasma, the streamers, instead of striking on sample surface, will strike on the grid, and the neutral active species produced in the discharge diffuse out to reach the sample surface uniformly. Finally, a carbon nanotube (CNT) film was produced to test this new concept.
 Select A Compact Magnetically Insulated Line Oscillator with New-Type Beam Dump FAN Yu-Wei, SHU Ting, LIU Yong-Gui, ZHONG Hui-Huang, LI Zhi-Qiang, WANG Yong, ZHAO Yan-Song, LUO Ling Chin. Phys. Lett. 2005, 22 (1): 164-167 .   Abstract   PDF(pc) (423KB) ( 1448 ) We present a compact improved model of the magnetically insulated line oscillator with new-type beam dump and other novel features. In the experiments, high-power microwave of the TM01 mode is generated from the device with a frequency range of 1.73--1.78GHz and a peak power level of above 2GW, when the diode voltage is taken in the range 520--540kV, and the diode current is in the range 58--62kA. This confirms the simulation results.
 Select New Microwave Diagnostic Theory for Measurement of Electron Density in Atmospheric Plasmas ZHANG Shu, HU Xi-Wei Chin. Phys. Lett. 2005, 22 (1): 168-170 .   Abstract   PDF(pc) (399KB) ( 520 ) We present the phase shift of an electromagnetic wave passing through an atmospheric plasma layer. In this kind of plasma, the phase shift depends not only on the line average electron density and layer width, but also on the electron-neutral collision frequency. Since the collision frequency is close to or even larger than the incident microwave frequency, a one-dimensional code for the numerical solution of the wave equation with full time and space variables is established to give the phase shift. When the width and the pressure (hence the electron-neutral collision frequency) are known, the measurement of phase shift will uniquely determine the line average electrons density in an atmospheric plasma.
 Select Radial Evolution of the Atmospheric Pressure Glow Discharge in Helium Controlled by Dielectric Barrier ZHANG Yuan-Tao, WANG De-Zhen, WANG Yan-Hui, LIU Cheng-Sen Chin. Phys. Lett. 2005, 22 (1): 171-174 .   Abstract   PDF(pc) (507KB) ( 435 ) The radial evolution of atmospheric pressure glow discharge in helium is presented by numerical simulation. The calculations reveal the mechanism of two current peaks per half cycle. The first breakdown occurs firstly in the central region of the electrode, and then spreads to the edge, while the second breakdown ignites at the periphery firstly, and then propagates toward the discharge central region. The simulations indicate that radial electric fields and radial sheath play an important role in the evolution of the second peak. These results agree fundamentally with the experimental observations.
 Select Optical Properties of CuCl+-Implantation and Observation of Sub-micrometre Particles in α-Al2O3 Crystals WANG Chun-Fen, LEI Jia-Rong, WANG De-Zhi, HUANG Ning-Kang Chin. Phys. Lett. 2005, 22 (1): 175-177 .   Abstract   PDF(pc) (426KB) ( 440 ) Crystal samples of α-Al2O3 were implanted in different crystalline orientations with CuCl+ at intensities from 6×1016 ions/cm2 to 5×1017 ions/cm2 and energies from 350 to 380keV at different temperatures. A strong absorption of UV section can be seen in optical absorption spectra for all of the specimens. Gaussian fitting for the absorption curves with luminescence measurements confirmed that there were point defects such as F, F+, F2+, and F2 centres in the CuCl+-implanted α-Al2O3 samples. It is found that the absorption intensity is decreased by annealing treatment, thus the number of the colour centres was decreased due to annealing. It is also found that the variety of colour centre number was dependent greatly on implantation conditions, substrate orientation and annealing temperature. Sub-micrometre particles after annealing have been observed by using the SEM technique.
 Select Polaronic Tunnelling in Organic Triblock Copolymers LIU De-Sheng, , ZHANG Da-Cheng, XIE Shi-Jie, MEI Liang-Mo, Chin. Phys. Lett. 2005, 22 (1): 178-181 .   Abstract   PDF(pc) (363KB) ( 467 ) Polaron tunnelling is studied in xPA/nPPP/xPA (PA for polyacetylene and PPP poly (p-phenylene)) triblock copolymer, which has a well--barrier--well structure. An extended tight-binding Hamiltonian including external electric field is adopted. Without electric field, the injected electrons would not extend over the whole copolymer chain but instead be confined in the segments of PA. This is different from the behaviour of the traditional semiconductors. It is found that the polaron can transfer to the potential barrier-PPP segment when the applied electric field reaches a certain value. The critical polaron tunnelling electric fields depend upon the lengths of PPP segments.
 Select N-Doped LaAlO3/Si(100) Films with High-k, Low-Leakage Current and Good Thermal Stability XIANG Wen-Feng, LU Hui-Bin, CHEN Zheng-Hao, HE Meng, LU Xu-Bing, LIU Li-Feng, GUO Hai-Zhong, ZHOU Yue-Liang Chin. Phys. Lett. 2005, 22 (1): 182-184 .   Abstract   PDF(pc) (413KB) ( 491 ) High quality amorphous N-doped LaAlO3 (LaAlON) films have been deposited on Si (100) in nitrogen gas by laser molecular beam epitaxy. The chemical nature and physical distribution of N in LaAlON films has been performed by x-ray photoemission spectroscopy. Compared with LaAlO3, a significant improvement in the interfacial quality and leakage current density was obtained by nitrogen additive. At gate voltage +1V, the leakage current density of the LaAlON film with an equivalent oxide thickness as thin as 2nm is obtained to be 2.9× 10-6A/cm2, which decreases almost two orders of magnitude from that of LaAlO3 film with the same thickness. Moreover, high-resolution transmission electron microscope analysis show that the LaAlON sample is still amorphous with a very sharp interface between the LaAlON layer and the Si substrate after annealed at 900°C for 60s.
 Select Influence of Interface Charge on Electrical Properties of ZnO/Si Heterojunction LEI Huan, LIU Ci-Hui, LIN Bi-Xia, FU Zhu-Xi, Chin. Phys. Lett. 2005, 22 (1): 185-187 .   Abstract   PDF(pc) (331KB) ( 550 ) The capacitance--voltage and current--voltage properties of the samples before and after annealing are investigated at 300K and 195K. It is found that the interface charge plays an important role for the heterojunction properties. After annealing, the samples exhibit typical junction properties. The heterojunction shows a built-in potential 0.62eV consistent with the theoretical result 0.67eV. However, the sample exhibits more complex behaviour before annealing. The experimental results can be explained by heterojunction theory when introducing interface charge, which suggests that the annealing can reduce interface charge and can improve the junction properties of the samples.
 Select Ultrafast Relaxation of Coherent Control Photocurrent in AlGaAs/GaAs Multi Quantum Wells LIN Wei-Zhu, SHOU Qian, LIU Lu-Ning, WU Yu, WEN Jin-Hui, LAI Tian-Shu Chin. Phys. Lett. 2005, 22 (1): 188-190 .   Abstract   PDF(pc) (293KB) ( 421 ) We theoretically and experimentally study the ultrafast dynamics of coherent control photocurrent in AsGaAs/GaAs multi quantum wells at room temperature. A ballistic photocurrent relaxation time of ～200fs is deduced based on the theory of density matrix and is evidenced with the three-colour femtosecond pump--probe measurements.
 Select Optical Conductivity of Anisotropic Quantum Dots in Magnetic Fields GUO Kang-Xian, CHEN Chuan-Yu Chin. Phys. Lett. 2005, 22 (1): 191-194 .   Abstract   PDF(pc) (332KB) ( 537 ) Optical conductivity of anisotropic double-parabolic quantum dots is investigated with the memory-function approach, and the analytic expression for the optical conductivity is derived. With characteristic parameters pertaining to GaAs, the numerical results are presented. It is shown that: (1) the larger the optical phonon frequency ωLO, the stronger the peak intensity of the optical conductivity, and the more asymmetric the shape of the optical conductivity; (2) the magnetic field enhances the optical conductivity for levels l=0 and l=1, with or without electron--LO--phonon interactions; (3) the larger the quantum dot thickness lz, the smaller the optical conductivity σ(ω).
 Select Translational Invariance in Phase Diagram of S=1/2, 3/2 Spin Glass Systems SHANG Yu-Min, YAO Kai-Lun Chin. Phys. Lett. 2005, 22 (1): 195-198 .   Abstract   PDF(pc) (520KB) ( 428 ) By using the replica method and the functional integral technique, the quantum XY spin glass model with ferromagnetic coupling is investigated numerically. From the numerical results of the thermodynamic and magnetic quantities we found that these quantities do not vary with the mean exchange interaction when the mean exchange interaction is lower than 1. This feature demonstrates that there are the mean interaction translational symmetries in the spin-glass and paramagnetic phases.
 Select A Spin Glass Model with Vibrations of Crystal Lattices SHANG Yu-Min, CHENG Li-Min, YAO Kai-Lun Chin. Phys. Lett. 2005, 22 (1): 199-202 .   Abstract   PDF(pc) (367KB) ( 406 ) With the help of the replica method and imaginary-time functional-integrate technique, the spin glass model with the vibrations of crystal lattices is investigated. In the limit of the replica symmetry and the imaginary-time static approximation, the magnetic and thermodynamic quantities have been obtained. By the numerical calculations, we found that the magnetization of the system has the typical spin-glass behaviour. A peak is found in the susceptibility--temperature curve and is shifted to lower temperature with increasing applied field. Due to the lattice contribution, the specific heat increases strongly at high temperature. Due to the magnetic contribution, the anomaly in the specific heat--temperature curve forms a λ-type peak, which agrees with the observation of Rojo et al. [Phys. Rev. B 66 (2002) 094406].
 Select Structural and Magnetic Properties of Ultrathin Fe Films on Pt(001) Surface ZHANG Li-Juan, HE Ke, JIA Jin-Feng, XUE Qi-Kun Chin. Phys. Lett. 2005, 22 (1): 203-206 .   Abstract   PDF(pc) (476KB) ( 443 ) Magnetic anisotropy evolution of ultrathin Fe films grown on Pt(001) single-crystal surface is investigated by UHV in situ surface magneto-optical Kerr effect (SMOKE) measurement. After annealing at ～600K, the magnetic anisotropy of Fe film switches from in-plane to perpendicular at low coverage, leading to a spin reorientation transition (SRT). Meanwhile, in the range of 3--4 monolayer (ML) thickness, the coercivity of the Fe polar hysteresis loop decreases dramatically. Further scanning tunnelling microscopy (STM) and low energy electron diffraction (LEED) investigation correlates the magnetic properties with the film structures. We attribute this SRT to the formation of Fe--Pt ordered alloy.
 Select Unusual Transport Properties near the Insulator--Metal Transition in Colossal Magnetoresistive Manganites YUAN Song-Liu, ZHONG Qiang-Hua, DOYANANDA Debnath, CHEN Wei, ZHAO Li-Feng, MIAO JU-Hong, CAO Heng, LIU Sheng, XIA Zheng-Cai Chin. Phys. Lett. 2005, 22 (1): 207-210 .   Abstract   PDF(pc) (367KB) ( 603 ) It is argued that a combination of the Griffiths theory and the double-exchange mechanism predicts the random distribution of ferromagnetic metallic clusters above the Curie temperature TC in colossal magnetoresistive manganites. Along this line, we propose a model for the temperature dependence of resistivity that yields a quantitative agreement with experimental data obtained in a typical manganite La2/3Ca1/3MnO3. Our result indicates that the formation and growth of ferromagnetic metallic clusters are responsible for the observation of unusual transport properties near the insulator--metal transition.
 Select Switching Behaviour of Magnetic Particles with Dipolar Interaction XU Chen, HUI Pak-Ming, CHOW Chow-Wang, LI Zhen-Ya Chin. Phys. Lett. 2005, 22 (1): 211-214 .   Abstract   PDF(pc) (428KB) ( 379 ) We study the switching in the magnetic moments of interacting magnetic particles. The dynamics of the magnetic moments is governed by a coupled set of Landau--Lifshitz--Gilbert equations. The magnetic particles are assumed to be spherical in shape, single domain, and have uniaxial anisotropy. Effects of dipolar interaction between the particles, anisotropy energy, an applied switching field with finite spatial extent and a small bias field are considered. When the separation between the particles is small, the dipolar field is significant and it affects the reversal of the magnetic moments. The final configuration attained depends sensitively on the decaying length of the switching field, the inter-particle separation, and the initial configuration. A bias field tends to suppress the effects of a spatially decaying switching field and dipolar interaction between neighbouring particles.
 Select Origin of the 420nm Absorption Band and Effect of Doping Fluorine in PbWO4 Crystals TAO Kun, ZHANG Qi-Ren, LIU Ting-Yu, ZHANG Fei-Wu Chin. Phys. Lett. 2005, 22 (1): 215-218 .   Abstract   PDF(pc) (488KB) ( 506 ) The electronic structures for three types of PbWO4 (PWO) crystals, the perfect PWO, the PWO containing lead vacancy (PWO-Vpb) and fluorine doped PWO crystal (F-:PWO), are systematically studied within the framework of density functional theory. The computational results show that the Pb 6s state situates below the valence band so that Pb2 ions are unable to trap holes forming Pb3+ or Pb4+ to compensate for Vpb2-. The hole-trappers in PWO-Vpb are O2- ions. Two of the longer-bond O2- ions share a hole forming O23-, and four of the longer-bond oxygen ions trap two holes forming an associated color centre [O23--Vpb-O23-], which may be the origin of the 420nm absorption band. It is also concluded that the doping of F- would reduce the band gap and F- ions substituting for O2- can effectively restrict the formation of [O23--Vpb-O23-] and weaken the 420nm absorption band and hence enhance the scintillation property of PWO.
 Select Effects of External Electric Field on Ferroelectric Superlattice with Two Alternating Layers JIANG Wei, LO Veng-Cheong Chin. Phys. Lett. 2005, 22 (1): 219-222 .   Abstract   PDF(pc) (242KB) ( 462 ) The effects of the external electric field on the ferroelectric superlattice with two alternating layers have been studied using the transverse Ising model based on the effective-field theory with the differential technique. The hysteresis loops and susceptibility of the system have been given. The stronger the external electric field, the smaller the susceptibility, reflecting that the polarization is weaker.
 Select Effective Medium Model for Refractive Indices of Thin Films with Oblique Columnar Structure WANG Jian-Guo, SHAO Jian-Da, FAN Zheng-Xiu Chin. Phys. Lett. 2005, 22 (1): 221-223 .   Abstract   PDF(pc) (323KB) ( 718 ) The refractive indices of thin films, containing dielectric and voids in an oblique columnar structure, are modelled in the quasi-static limit. The dielectric function is shown to be strongly dependent on the angle of incidence and on the columnar orientation for p-polarized light. This model is applied to model ZnS thin films with oblique columnar structures and the computed results have been given.
 Select Modelling Analysis of Influence of Substrate Surface Defect on Optical Characteristics of Single-Layer Coating SHEN Zi-Cai, KONG Wei-Jin, SHAO Jian-Da, FAN Zheng-Xiu Chin. Phys. Lett. 2005, 22 (1): 224-226 .   Abstract   PDF(pc) (357KB) ( 394 ) A simple and practical model is used to analyse the influence of substrate surface defect on the optical characteristics of a single-layer coating. A single-layer coating is prepared and its optical properties are fitted. Some explanations for the origin of the transition layer are presented. It is concluded that there is a transition layer forming between the substrate and coating, which is attributed to substrate surface defects, and its refractive index change is nearly of linearity.
 Select Influence of LiB3O5 Structure on Microstructure and Optical Properties of ZrO2 Thin Films repared by Electron Beam Evaporation TAN Tian-Ya, ZHANG Da-Wei, ZHAN Mei-Qiong, SHAO Jian-Da, FAN Zheng-Xiu Chin. Phys. Lett. 2005, 22 (1): 227-229 .   Abstract   PDF(pc) (426KB) ( 807 ) ZrO2 thin films were deposited by using an electron beam evaporation technique on three kinds of lithium triborate (LiB3O5 or LBO) substrates with the surfaces at specified crystalline rientations. The influences of the LBO structure on the structural and optical properties of ZrO2 thin films are studied by spectrophotometer and x-ray diffraction. The results indicate that the substrate structure has obvious effects on the structural and optical properties of the film: namely, the ZrO2 thin film deposited on the X-LBO, Y-LBO and Z-LBO orients to m(-212), m(021) and o(130) directions. It is also found that the ZrO2 thin film with m(021) has the highest refractive index and the least lattice misfit.
 Select Modified Photoluminescence by Silicon-Based One-Dimensional Photonic Crystal Microcavities CHEN San, QIAN Bo, WEI Jun-Wei, CHEN Kun-Ji, XU Jun, LI Wei, HUANG Xin-Fan Chin. Phys. Lett. 2005, 22 (1): 230-232 .   Abstract   PDF(pc) (300KB) ( 509 ) Photoluminescence (PL) from one-dimensional photonic band structures is investigated. The doped photonic crystal with microcavities are fabricated by using alternating hydrogenated amorphous silicon nitride (a-SiNx:H/a-SiNy:H) layers in a plasma enhanced chemical vapour deposition (PECVD) chamber. It is observed that microcavities strongly modify the PL spectra from active hydrogenated amorphous silicon nitride (a-SiNz:H) thin film. By comparison, the wide emission band width 208nm is strongly narrowed to 11\,nm, and the resonant enhancement of the peak PL intensity is about two orders of magnitude with respect to the emission of the λ/2-thick layer of a-SiNz:H. A linewidth of Δλ=11nm and a quality factor of Q=69 are achieved in our one-dimensional a-SiNz photonic crystal microcavities. Measurements of transmittance spectra of the as-grown samples show that the transmittance resonant peak of a cavity mode at 710nm is introduced into the band gap of one-dimensional photonic crystal distributed Bragg reflector (DBR), which further verifies the microcavity effects.
 Select Top-Emitting Organic Light-Emitting Devices Based on Silicon Substrate with High Luminance and Low Turn-on Voltage WU Zhi-Jun, CHEN Shu-Fen, YANG Hui-Shan, ZHAO Yi, LI Chuan-Nan, HOU Jing-Ying, LIU Shi-Yong Chin. Phys. Lett. 2005, 22 (1): 233-235 .   Abstract   PDF(pc) (389KB) ( 820 ) We have fabricated a top-emitting organic light-emitting device on silicon substrate with high yellow luminance based on 5,6,11,12-tetraphenylnaphthacene sub-monolayer. It consists of a thin layer of highly conductive silver as the semitransparent cathode and surfaced-modified Ag as the anode. The device turns on at 3V with the luminance of 8.4cd/m2. The maximum current efficiency is 1.3cd/A at 6V and the luminance reaches 14790cd/m2 at 14V. The performance of the device is excellent in top-emitting organic light-emitting devices according to our knowledge.
 Select In-Situ Measurement of Electrical Character of PbTe at High Pressure and High Temperature REN Guo-Zhong, JIA Xiao-Peng, ZHU Pin-Wen, ZANG Chuan-Yi, MA Hong-An, WANG Xian-Cheng Chin. Phys. Lett. 2005, 22 (1): 236-238 .   Abstract   PDF(pc) (370KB) ( 603 ) There is a widespread interest in lead telluride (PbTe) as a good thermoelectric material. We report the temperature dependence of thermopower S(T) and resistance R(T) for PbTe at the different pressures of from 1.8GPa to 5GPa obtained by using the cubic anvil high pressure apparatus. With increasing pressure, R(T) and S(T) decrease. The effect of pressure on R(T) is larger than that on S(T). The power factor that is determined by thermopower and resistivity increases with increasing pressure. This method is an efficient tool for synthesizing good thermoelectric materials at high pressure and high temperature.
 Select Absorption Spectra and Ionic Conductivity of RbxCs1-xAg4I5 Superionic Conductors Thin Films CAO Yang, SUN Jia-Lin, ZHANG Guo-Sheng, GUO Ji-Hua, WANG Zheng-Ping Chin. Phys. Lett. 2005, 22 (1): 239-242 .   Abstract   PDF(pc) (621KB) ( 526 ) A series of RbxCs1-xAg4I5 (x=0--1) thin films were grown by vacuum evaporation on NaCl crystal substrates at 350K. The absorption spectra of these films were measured at 80K in the wavelength range from 240nm to 400nm. It is shown that superionic conductor thin films of quaternary compound Rb0.5Cs0.5Ag4I5 and ternary compound RbAg4I5 can be obtained at x=0.5--0.6 and x=0.7--1, respectively. At x=0.65, the combined compound film of the mixture of 30mol\% RbAg4I5 and 70mol% Rb0.5Cs0.5Ag4I5 is presented. Then, based on the spectral positions of the A1 and A2 peaks, we determined that the Rb0.5Cs0.5Ag4I5 exciton coupling energy Rex is 0.21eV, the forbidden zone width Eg is 3.82eV and the exciton radius aex is 0.70nm. Furthermore, the ionic conductivities of superionic conductor thin films of RbAg4I5 and Rb0.5Cs0.5Ag4I5 and their mixture film are investigated, respectively, in the temperature range 303K--393K.
 Select Superconductivity in LiTi2O4 Prepared by Hybrid Microwave Method YANG Li-Hong, DONG Cheng, SONG Hui-Hua, GUO Juan, FU Guang-Cai Chin. Phys. Lett. 2005, 22 (1): 243-245 .   Abstract   PDF(pc) (360KB) ( 890 ) The well-known superconducting oxide LiTi2O4 has a structural phase transition from spinel to ramsdellite around 900°C. We have successfully obtained the superconducting spinel phase and the non-superconducting ramsdellite phase of LiTi2O4 using a hybrid microwave method. The samples are characterized by x-ray powder diffraction, scanning electron microscopy, and measurements of resistivity and magnetic susceptibility. The results show that the low-temperature spinel phase is a superconductor with Tc=13K, while the high-temperature ramsdellite phase is a semiconductor. By comparison between the crystal structures of the spinel and the ramsdellite phases, it is suggested that the geometrical frustration plays an important role in the superconductivity of the spinel LiTi2O4.
 Select A Self-Consistent Theory for the Inter- and Intramolecular Correlation Functions of a Hard-Sphere-Yukawa-Chain Fluids YU Yang-Xin, WU Jian-Zhong, YOU Feng-Qi, GAO Guang-Hua Chin. Phys. Lett. 2005, 22 (1): 246-249 .   Abstract   PDF(pc) (494KB) ( 416 ) An extended test-particle method is used to predict the inter- and intramolecular correlation functions of freely jointed hard-sphere-Yukawa-chain fluids by calculating the segmental density distributions around a fixed segment. The underlying density functional theory for chain fluids is based on a modified fundamental measure theory for the hard-sphere repulsive and a mean-field approximation for attraction between different segments. The calculated intra- and inter-molecular distribution functions agree well with the results from Monte Carlo simulations, better than those from alternative approaches.
 Select InGaAs Photodetectors Cut-off at 1.9μm Grown by Gas-Source Molecular Beam Epitaxy ZHANG Yong-Gang, HAO Guo-Qiang, GU Yi, ZHU Cheng, LI Ai-Zhen, LIU Tian-Dong Chin. Phys. Lett. 2005, 22 (1): 250-253 .   Abstract   PDF(pc) (475KB) ( 497 ) Using a linear graded InxGa1-xAs as the buffer layer, positive-intrinsic-negative wavelength-extended In0.6Ga0.4 As photodetectors with 50% cut-off wavelength of 1.9μm at room temperature were grown by using gas-source molecular beam epitaxy, and their performance over a wide temperature range has been extensively investigated. The detectors show typical dark current at bias voltage 50mV and the resistance--area product R0A of 7nA/765\Ωcm2 and 31pA/404kΩcm2 at 290K and 210K, respectively. The thermal activation energy of the dark current in the temperature range 250--350K is 0.488eV.
 Select Swarm Dynamics of a Group of Mobile Autonomous Agents LIU Bo, CHU Tian-Guang, WANG Long, WANG Zhan-Feng Chin. Phys. Lett. 2005, 22 (1): 254-257 .   Abstract   PDF(pc) (408KB) ( 604 ) We propose a simple swarm model to study collective behaviour of a group of mobile autonomous agents interacting through a long range attraction and short range repulsion function. It is shown that the individuals (agents) will aggregate and eventually form a cohesive cluster of finite size around the swarm centre in a finite time, and the size depends only on the parameters of the swarm model. Furthermore, it is also shown that all the individuals will converge to equilibrium positions of the swarm model, and thus the configuration of the swarm converges to a constant constellation. Numerical simulations are also worked out to illustrate the analytical results.
 Select Protein Folding in Nano-Sized Cylinders XU Wei-Xin, WANG Jun, WANG Wei Chin. Phys. Lett. 2005, 22 (1): 258-261 .   Abstract   PDF(pc) (302KB) ( 500 ) The folding of a model protein confined in a nano-sized cylinder is studied by the off-lattice G$\overline {\rm o}$-like model. The entropy and anisotropy effects of confinement on thermodynamics and dynamics for folding are investigated. Our results show that due to reduction of the search on conformations, the folding rate can be sped up and the thermodynamic stability is enhanced at the cost of the decrease of folding cooperativity. In addition, it is found that these are shape-dependent. Folding is optimized in a cylinder with an appropriate shape when the volume is fixed. This is probably related to the shape of the protein molecule. Furthermore, our results also suggest that there is an orientational transition for the protein molecule following the variation of the radius of cylinder.
 Select Phase Control of Few-Cycle Coherent Terahertz Radiation Pulses XING Qi-Rong, LANG Li-Ying, LI Shu-Xin, MAO Fang-Lin, CHAI Lu, WANG Qing-Yue Chin. Phys. Lett. 2005, 22 (1): 262-265 .   Abstract   PDF(pc) (426KB) ( 599 ) We report a method to control the carrier-envelope phase shift in nearly single-cycle coherent terahertz (THz) radiation pulses, in which we used Kerr effect and two-photon absorption in the generated crystals due to the pump beam peak intensity. Dependence of relative carrier-envelope phase shift of THz pulses on the pump beam intensity in the ZnTe crystal was measured experimentally. Under our experimental condition, we measured that maximum relative phase shift is 0.29 radians.
 Select Errata: A Method for Distinguishing Attosecond Single Pulse from Attosecond Pulse Train HUO Yi-Ping, ZENG Zhi-Nan, LI Ru-Xin, XU Zhi-Zhan Chin. Phys. Lett. 2005, 22 (1): 266-266 .   Abstract   PDF(pc) (146KB) ( 576 ) In our recent Letter,[1] we made some mistakes in our calculation. The interference between the two pulses should be considered and the spectrum will contain fringes. However, the two-colour field assisted XUV photoionization remains valid and the conclusion in the Letter remains correct.
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