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Volume 24 Issue 10
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Original Articles
A Discrete Lax-Integrable Coupled System Related to Coupled KdV and Coupled mKdV Equations
LIU Ping, JIA Man, LOU Sen-Yue,
Chin. Phys. Lett. 2007, 24 (10): 2717-2719 .  
Abstract   PDF(pc) (187KB) ( 592 )
A modified Korteweg--de Vries (mKdV) lattice is found to be also a discrete Korteweg--de Vries (KdV) equation. A discrete coupled system is derived from the single lattice equation and its Lax pair is proposed. The coupled system is shown to be related to the coupled KdV and coupled mKdV systems which are widely used in physics.
Modification of the Clarkson--Kruskal Direct Method for a Coupled System
QIAN Su-Ping, TIAN Li-Xin
Chin. Phys. Lett. 2007, 24 (10): 2720-2723 .  
Abstract   PDF(pc) (224KB) ( 352 )
A new idea is put forward to modify the Clarkson--Kruskal (CK) direct method. Using the usual CK direct method to a coupled KdV system, two types of usual similarity reductions can be obtained. However, the application of the modified CK direct method leads to three types of new similarity reductions different from the usual ones.
A New Quantum Secure Direct Communication Protocol Using Decoherence-Free Subspace
GE Hua, LIU Wen-Yu
Chin. Phys. Lett. 2007, 24 (10): 2727-2729 .  
Abstract   PDF(pc) (176KB) ( 432 )
A new quantum secure direct communication (QSDC) protocol is proposed by
using decoherence free subspace (DFS) to avoid insecurity of the present
QSDC protocols in a quantum noise channel. This protocol makes it easily for Bob and Alice to find eavesdropping in channel because the collective dephasing noise disappears in DFS. The probability of successful attack by Eve in this protocol is smaller than in BB84 protocol. Thus this protocol realizes secure QSDC and is feasible with present-day technology.
Efficient Scheme for Implementing a Fredkin Gate via Resonant Interaction with Two-Mode Cavity Quantum Electrodynamics
SHAO Xiao-Qiang, WEN Jing-Ji, JIN Xing-Ri, ZHU Ai-Dong, ZHANG Shou, YEON Kyu-Hwang
Chin. Phys. Lett. 2007, 24 (10): 2730-2732 .  
Abstract   PDF(pc) (206KB) ( 805 )
A scheme for implementing a Fredkin gate with an atom sent through a microwave cavity is proposed. The scheme is based on the resonant atom-cavity interaction so that the gating time is sharply short, which is important in view of decoherence.
A Scheme for Implementing the Deutsch--Jozsa algorithm via Josephson Charge Qubits Coupled through Microwaves
GAO Guo-Jun, ZHENG Xiao-Hu, CAO Zhuo-Liang
Chin. Phys. Lett. 2007, 24 (10): 2733-2736 .  
Abstract   PDF(pc) (310KB) ( 512 )
Based on the Josephson charge qubits coupled through microwaves, a
scheme for implementation of the Deutsch--Jozsa algorithm is proposed
under the present scalable and feasible microfabrication technique. It would
be a valuable step toward complex quantum computation.
Pairwise Entanglement and Quantum Phase Transitions in Spin Systems
GU Shi-Jian, TIAN Guang-Shan, LIN Hai-Qing
Chin. Phys. Lett. 2007, 24 (10): 2737-2740 .  
Abstract   PDF(pc) (256KB) ( 595 )
We examine several well-known quantum spin models and categorize
the behaviour of pairwise entanglement at quantum phase transitions. A
unified picture on the connection between the entanglement and quantum
phase transition in spin systems is presented.
Quantum Theory of Electronic Double-Slit Diffraction
WU Xiang-Yao, ZHANG Bai-Jun, LI Hai-Bo, LU Jing-Bin, LIU Xiao-Jing, WANG Li, ZHANG Chun-Li, LIU Bing, FAN Xi-Hui, GUO Yi-Qing
Chin. Phys. Lett. 2007, 24 (10): 2741-2744 .  
Abstract   PDF(pc) (286KB) ( 549 )
Phenomena of electron, neutron, atomic and molecular diffraction have been studied in many experiments, and these experiments have been explained by some theoretical works. We study electronic double-slit diffraction with a quantum mechanical approach and obtain the following results: (1) When the ratio of d+a/a=n (n=1, 2, 3,...), orders n, 2n, 3n,... are missing in diffraction pattern. (2) When the ratio of d+a/a≠n (n=1, 2, 3,...), there is not missing order in diffraction pattern. (3) The slit thickness c has a large affect on the electronic diffraction pattern, which is a new quantum effect. We believe that all the predictions in our work can be tested by the electronic double slit diffraction experiment.
Ground Band and Excited Band of Spin-1 BEC in Cigar Shaped Laser Trap
PANG Wei, LI Zhi-Bing, BAO Cheng-Guang
Chin. Phys. Lett. 2007, 24 (10): 2745-2748 .  
Abstract   PDF(pc) (256KB) ( 543 )

The wavefunctions that conserve the total spin are constructed for the fully condensed states and the states with one particle excited. A set of equations are deduced for the spatial longitudinal wavefunctions and the chemical potentials. These equations are solved numerically for 23Na and 87Rb condensates. The deformed trap shows significant effects on the spectrum. This implies that the spin effect of the spinor BEC are more easily detected in an optical trap of larger aspect ratio.

Quasinormal Modes of Electromagnetic Perturbation around a Stringy Black Hole
ZHANG Yu, GUI Yuan-Xing, YU Fei, WANG Fu-Jun
Chin. Phys. Lett. 2007, 24 (10): 2749-2751 .  
Abstract   PDF(pc) (214KB) ( 470 )
We investigate the electromagnetic perturbation around a stringy black hole. A second-order differential equation is obtained for the perturbation. The variation of the effective potential with r is presented. The complex frequencies of the quasinormal modes of electromagnetic perturbation around a stringy black hole are computed by the third Wentzel--Kramers--Brillouin (WKB) approximation. The results show that the parameters resulted from the
compactification of higher dimensions can influence the quasinormal complex
frequencies, and the Maxwell field around a stringy black hole damps more
slowly than that around a Schwarzschild black hole.
Wave Grouping of a Drifting Spiral Wave in the Presence of an External Field
YANG Hu-Jiang, YANG Jun-Zhong, HU Gang
Chin. Phys. Lett. 2007, 24 (10): 2752-2755 .  
Abstract   PDF(pc) (956KB) ( 606 )
The phenomenon of wave grouping, in which the dense waves and the sparse waves can form groups in front of the spiral tip when the spiral wave is meandering, has been reported in a chemical reaction system recently. We present a method to realize the phenomenon of wave grouping by applying an external field to the system. The numerical simulations are carried out on the basis of the FitzHugh--Nagumo equations.
Experimental Confirmation of a Modified Lorenz System
LIU Ling, LIU Chong-Xin, ZHANG Yan-Bin
Chin. Phys. Lett. 2007, 24 (10): 2756-2758 .  
Abstract   PDF(pc) (459KB) ( 677 )
We experimentally demonstrate the butterfly-shaped chaotic attractor we
have proposed before [Int. J. Nonlin. Sci. Numerical Simulation 7 (2006) 187]. Some basic dynamical properties and chaotic behaviour of this new butterfly attractor are studied and they are in agreement with the results of our theoretical analysis. Moreover, the proposed system is experimental demonstrated.
Average Synchronization and Temporal Order in a Noisy Neuronal Network with Coupling Delay
WANG Qing-Yun, DUAN Zhi-Sheng, LU Qi-Shao
Chin. Phys. Lett. 2007, 24 (10): 2759-2761 .  
Abstract   PDF(pc) (222KB) ( 547 )
Average synchronization and temporal order characterized by the rate of firing are studied in a spatially extended network system with the coupling time delay, which is locally modelled by a two-dimensional Rulkov map neuron. It is shown that there exists an optimal noise level, where average synchronization and temporal order are maximum irrespective of the coupling time delay. Furthermore, it is found that temporal order is weakened when the coupling time delay appears. However, the coupling time delay has a twofold effect on average synchronization, one associated with its increase, the other with its decrease. This clearly manifests that random perturbations and time delay play a complementary role in synchronization and temporal order.
Two-Player and Two-Strategy Symmetric Evolutionary Game with Fluctuations
LIU Wei-Bing, WANG Xian-Jia
Chin. Phys. Lett. 2007, 24 (10): 2762-2765 .  
Abstract   PDF(pc) (378KB) ( 533 )

Research on evolutionary games in a noisy environment is still a non-solved problem. By using Markov process, we build a dynamic model for two-player and two-strategy symmetric game in noisy environment. Some illustrative examples are presented and the results are determined by simulation experiments.

Duplication: a Mechanism Producing Disassortative Mixing Networks in Biology
ZHAO Dan, LIU Zeng-Rong, WANG Jia-Zeng
Chin. Phys. Lett. 2007, 24 (10): 2766-2768 .  
Abstract   PDF(pc) (207KB) ( 700 )
Assortative/disassortative mixing is an important topological property of a network. A network is called assortative mixing if the nodes in the network tend to connect to their connectivity peers, or disassortative mixing if nodes with low degrees are more likely to connect with high-degree nodes. We have known that biological networks such as protein--protein interaction networks (PPI), gene regulatory networks, and metabolic networks tend to be disassortative. On the other hand, in biological evolution, duplication and divergence are two fundamental processes. In order to make the relationship between the property of disassortative mixing and the two basic biological
principles clear and to study the cause of the disassortative mixing property in biological networks, we present a random duplication model and an anti-preference duplication model. Our results show that disassortative mixing networks can be obtained by both kinds of models from uncorrelated initial networks. Moreover, with the growth of the network size, the disassortative mixing property becomes more obvious.
Transition Temperature of Two-Degenerate-Flavour QCD in the Chiral Limit
WU Liang-Kai, LUO Xiang-Qian
Chin. Phys. Lett. 2007, 24 (10): 2769-2772 .  
Abstract   PDF(pc) (253KB) ( 418 )
We present the results for the transition temperature of quantum chromodynamics (QCD) with two degenerate flavours (Nf=2) of Wilson quarks. On lattice 83×4 with 4 representing the temporal extent, by using the Ferrenberg--Swendsen reweighting method, we determine the critical β=6/g2 where the transition occurs, g is the coupling constant. On lattice 82×20×4, by using the axial vector Ward--Takahashi identity, we calculate the current quark mass amq, a is the lattice spacing. Assuming the O(4) scaling, the critical β in the chiral limit is determined. We calculate the ρ meson mass amρ at zero temperature on lattice 83×20. By using the experimental ρ meson mass to set the scale, we obtain 194(1)MeV for the transition temperature in the chiral limit.
Lie Symmetries and Conserved Quantities for Super-Long Elastic Slender Rod
ZHAO Wei-Jia, WENG Yu-Quan, FU Jing-Li,
Chin. Phys. Lett. 2007, 24 (10): 2773-2776 .  
Abstract   PDF(pc) (354KB) ( 327 )
DNA is a nucleic acid molecule with double-helical structures that are special symmetrical structures attracting great attention of numerous researchers. The super-long elastic slender rod, an important structural model of DNA and other long-train molecules, is a useful tool in analysing the symmetrical properties and the stabilities of DNA. We study the Lie symmetries of a super-long elastic slender rod by using the methods of infinitesimal transformation. Based on Kirchhoff's analogue, generalized Hamilton canonical equations are
analysed. The infinitesimal transformations with respect to the radian
coordinate, the generalized coordinate, and the quasi-momentum of the model are introduced. The Lie symmetries and conserved quantities of the model are presented.
Analysis of Bd→ψ KS CP Asymmetry in a Flavour Changing Z' Model
WANG Shuai-Wei, SONG Tai-Ping, LU Gong-Ru, ZHONG Zhi-Guo
Chin. Phys. Lett. 2007, 24 (10): 2777-2780 .  
Abstract   PDF(pc) (285KB) ( 511 )
According to the recent experimental data, the time-dependent CP asymmetry SψKS for Bd→KS decay might still be inconsistent with the standard model (SM) expectations. We try to understand the anomaly with a Z' model associated with flavour changing neutral currents (FCNCs) at the tree level. We find that (i) if neglecting the contributions from the right-handed flavour changing coupling BRsb and setting ξLLLR=ξ and ξLL=ξ, ξLR=0, we may obtain 0.01< ξ <0.014, 0.0175< ξ <0.0205, 0.021< ξ <0.0255 and 0.004< ξ <0.008, 0.018< ξ <0.028, 0.042< ξ <0.048 for the Bd→ψ KS decay, respectively; (ii) if considering the contributions coming from BRsb and setting
ξLLRLLRRR=ξ and ξLLRL=ξ, ξLRRR=0, we can obtain 0.005<
ξ<0.075, 0.0085< ξ<0.0105, 0.011<ξ<0.013 and 0.0125<ξ<0.0177, 0.0224< ξ<0.025. These results are consistent with the constraints and the assumptions in some literature.
Electromagnetic Form Factor of Charged Scalar Meson
LI Heng-Mei, CHEN Ning, WANG Zhi-Gang, WAN Shao-Long
Chin. Phys. Lett. 2007, 24 (10): 2781-2784 .  
Abstract   PDF(pc) (235KB) ( 468 )
Wavefunctions and the electromagnetic form factor of charged scalar mesons are studied with the vector--vector-type flat-bottom potential model under the framework of the spinor--spinor Bethe--Salpeter equation. The obtained results are in agreement with other theories.
Single-Proton Pickup Reaction of the Halo Nucleus 6He on a 9Be Target at 25MeV/nucleon
PANG Dan-Yang, YE Yan-Lin, JIANG Dong-Xing, ZHENG Tao, LI Zhi-Huan, LI Xiang-Qing, GE Yu-Cheng, HUA Hui, WU Cui-E, LOU Jian-Ling, LUFei, FAN Feng-Ying, A. Ozawa, Y. Yamaguchi, R. Kanungo, D. Fang, I.Tanihata
Chin. Phys. Lett. 2007, 24 (10): 2785-2788 .  
Abstract   PDF(pc) (323KB) ( 717 )
The inclusive differential cross sections of the 7Li nucleus in a reaction induced by 6He on a 9Be target are measured at an incident energy of 5MeV/nucleon. Finite-range distorted-wave Born approximation calculations suggest that these 7Li particles are formed in a direct single-proton pickup reaction 9Be(6He,7Li)8Li. The experimental data can be well reproduced by taking into account of the contributions of both the ground states and the first excited states of 7Li and 8Li.
Intermittency of Target Fragments in 16O--AgBr Collisions at 4.5A GeV/c
LI Jun-Sheng, LIU Fu-Hu, ZHANG Dong-Hai
Chin. Phys. Lett. 2007, 24 (10): 2789-2791 .  
Abstract   PDF(pc) (232KB) ( 487 )
We report the angular distributions of grey and black particles produced in 16O--AgBr interactions at 4.5A GeV/c in nuclear emulsion. Intermittency and fractal behaviour are studied for emission spectra of target associated grey and black particles. Intermittent behaviour is observed for both grey and black particles. In both the cases, anomalous dimensions are seen to increase linearly with the order of moments, thereby indicating the association of multifractility with production mechanism of both grey and black particles.
Neutron Generation and Kinetic Energy of Expanding Laser Plasmas
HUANG Yong-Sheng, WANG Nai-Yan, DUAN Xiao-Jiao, LAN Xiao-Fei, TAN Zhi-Xin, TANG Xiu-Zhang, HE Ye-Xi
Chin. Phys. Lett. 2007, 24 (10): 2792-2795 .  
Abstract   PDF(pc) (274KB) ( 673 )
We investigate the kinetic energy of expanding plasma of a solid target heated by a ultra-short and ultra-intense laser pulse and the efficiency of energy coupling between the ultra-intense laser pulse and the solid target, in order to increase the utilization ratio of laser energy and to raise the neutron generation farther. Some new ideas about improving the energy utilization by head-on collisions between the expanding plasmas are proposed. The significance is the raise of generation of shorter duration neutron, of the order of picoseconds, which allows for an increase of energy resolution in time-of-flight experiments and also for the investigation of the dynamics of nuclear processes with high temporal resolution.
The Average Lifetime of Giant Composite Systems Formed in Strongly Damped Collisions
TIAN Jun-Long, WU Xi-Zhen, OU Li, LI Zhu-Xia,
Chin. Phys. Lett. 2007, 24 (10): 2796-2799 .  
Abstract   PDF(pc) (468KB) ( 272 )
The dynamic, adiabatic and diabatic entrance potentials in strongly damped reactions of 238U+238U, 232Th+250Cf are calculated and compared. The feature of the dynamical potential implies that it is possible for the composite systems to stick together for a period of time. By means of the improved quantum molecular dynamics model the time evolution of the density and
charge distributions of giant composite systems and their fragments for reactions 238U+238U, 232Th+250Cf are investigated, from which the lifetimes of giant composite systems at different energies are obtained. The longest average lifetime of 238U+238U is found when the incident energy is about
Ec.m=1080MeV, which is about 1200fm/c.
Fragmentation Cross Sections of 158AGeV Pb Projectiles
G. Sher, M. I. Shahzad, M. Hussain
Chin. Phys. Lett. 2007, 24 (10): 2800-2803 .  
Abstract   PDF(pc) (227KB) ( 538 )
We investigate the fragmentation cross sections of 158AGeV207Pb projectile interacting with different targets using CR39 nuclear track detectors. The exposure is made at SPS beam facility of CERN. The detectors are chemically etched to obtain data in the form of etched cone length. The nuclear and electromagnetic contributions to the measured total charge-changing cross sections are investigated. The estimated results are compared with those found in the literature for similar research work.
Vapour-to-Liquid Nucleation in Associating Lennard-Jones Fluids with Multiple Association Sites
FU Dong, LIAO Tao
Chin. Phys. Lett. 2007, 24 (10): 2804-2807 .  
Abstract   PDF(pc) (274KB) ( 610 )
The excess Helmholtz free energy functional for associating Lennard-Jones (LJ) fluid is formulated in terms of a weighted density approximation for short-ranged interactions and a Weeks--Chandler--Andersen approximation for long-range attraction. Within the framework of density functional theory, phase equilibria, vapour--liquid surface tension and vapour--liquid nucleation properties including the density profile, work of formation, excess number of
particles and critical supersaturation are investigated for associating LJ fluids with different numbers of association sites (M =1, 2, 3, 4) per particle. The influences of association energy and association sites on phase equilibria, surface tension and vapour-liquid nucleation properties are discussed.
Relativistic Multichannel Treatment of Ionic Rydberg States of Lanthanum
ZHANG Xin-Feng, JIA Feng-Dong, ZHONG Zhi-Ping, XUE Ping, XU Xiang-Yuan, YAN Jun
Chin. Phys. Lett. 2007, 24 (10): 2808-2811 .  
Abstract   PDF(pc) (281KB) ( 609 )
Ionic Rydberg energy levels of lanthanum are calculated from first principles by relativistic multichannel theory within the framework of multichannel quantum defect theory. The present calculated results are in better agreement with the experimental measurements than the previous calculations [J. Phys. B 34(2001)369] due to the consideration of dynamical polarizations. Moreover, in the experimental spectra achieved by a five-laser resonance excitation via the intermediate state 5d6d3 F2, a series of weak ionic Rydberg states and some of perturbing states are found and assigned in this work.
Effective Atomic Numbers for Fe--Mn Alloy Using Transmission Experiment
Iskender AKKURT
Chin. Phys. Lett. 2007, 24 (10): 2812-2814 .  
Abstract   PDF(pc) (430KB) ( 652 )
The effective atomic numbers (Zeff) and effective electron density (Ne) for Fe--Mn alloy with different Mn contents are calculated using the mass attenuation coefficients μ/ρ obtained via XCOM in the photon energy range of 1keV--1GeV. The results are compared with the values measured at the photon energy of 662, 1170 and 1332keV.
Theoretical Investigation of Femtosecond-Resolved Photoelectron Spectrum of Na2 Molecules
MIAO Xiang-Yang, WANG Lei, YAO Li, SONG He-Shan
Chin. Phys. Lett. 2007, 24 (10): 2815-2818 .  
Abstract   PDF(pc) (218KB) ( 538 )
Effect of laser fields on Na2 interaction potentials is studied by calculating the time-resolved photoelectron spectrum (TRPES) with the time-dependent wave-packet method. It is shown that the photoelectron spectrum at different delay times reflects the population in different electronic states. We inspect the periodicity of vibrational motion in neutral states, and map the vibrational
wave-packet propagation in corresponding internuclear coordinate.
Additivity Rule for Electron--Molecule Total Cross Section Calculations at 50--5000eV: A Geometrical Approach
SHI De-Heng, SUN Jin-Feng, MA Heng, ZHU Zun-Lue, YANG Xiang-Dong
Chin. Phys. Lett. 2007, 24 (10): 2819-2822 .  
Abstract   PDF(pc) (239KB) ( 537 )
To quantify the changes of the geometric shielding effect in a molecule as the incident electron energy varies, we present an empirical fraction, which represents the total cross section (TCS) contributions of shielded atoms in a molecule at different energies. Using this empirical fraction, a new formulation of the additivity rule is proposed. Using this new additivity rule, the TCSs for electron scattering by CO2, C2H2, C6H12 (cyclo-hexane) and C8H16 (cyclo-octane) are calculated in the range 50--5000eV. Here the atomic cross sections are derived from the experimental TCS results of simple molecules (H2, O2, CO). The quantitative TCSs are compared with those obtained by experiments and other theories, and good agreement is attained over a wide energy range.
Quantitative Evaluation Methods of In-Line X-Ray Phase Contrast Techniques
LI Chen, LI Zheng, LI Cheng-Quan, YU Ai-Min
Chin. Phys. Lett. 2007, 24 (10): 2823-2826 .  
Abstract   PDF(pc) (542KB) ( 502 )
By revealing the relationship between edge visibility and imaging parameters in in-line phase contrast imaging (PCI), we propose a method to quantitatively measure the contribution of absorption and phase shift from acquired images. We also prove that edge visibility will grow with the increasing source-object distance and object-detector distance. The result is validated by relative phase factor and by experiments conducted on a microfocus x-ray source. This method provides a new approach to evaluate in-line PCI images and is helpful for deciding imaging parameters.
SNOM Observations of Surface Plasmon Polaritons on Metal Heterostructures
Chin. Phys. Lett. 2007, 24 (10): 2827-2829 .  
Abstract   PDF(pc) (475KB) ( 725 )
We observe surface plasmon polariton (SPP) refraction on a metal heterostructured sample with a scattered-type scanning near-field optical microscope (SNOM). The sample consists of Al and Au in-plane whose boundary is smooth enough with proper etching time. SPPs excited on the Al film travel to the boundary and a portion of SPPs propagates into the Au film. In addition, interference fringes appear in the SNOM image bent at the boundary. The result is analysed with effective index method and the refracted angle is explained by Snell's law.
Fabrication of Nanoimprint Stamp Using Interference Lithography
CHEN Xian-Zhong, LI Hai-Ying
Chin. Phys. Lett. 2007, 24 (10): 2830-2832 .  
Abstract   PDF(pc) (967KB) ( 596 )
Interference lithography is used to fabricate a nanoimprint stamp, which is a key step for nanoimprint lithography. A layer of chromium in thickness of about 20nm is deposited on the newly cleaned fused silica substrate by thermal evaporation, and a layer of positive resist in thickness of 150nm is spun on the chromium layer. Some patterns, including lines, holes and pillars, are observed on the photoresist film by exposing the resist to interference patterns and they are then transferred to the chromium layer by wet etching. Fused silica stamps are fabricated by reactive ion etching with CHF3/O2 as
etchants using the chromium layer as etch mask. An atomic force microscope is used to analyse the pattern transfer in each step. The results show that regular hole patterns of fused silica, with average full width 143nm at half maximum (FWHM), average hole depth of 76nm and spacing of 450nm, have been fabricated. The exposure method is fast, inexpensive and applicable for fabrication of nanoimprint stamps with large areas.
Manipulation of Particles with Counter-Propagating Evanescent Waves
Xiang YU, Takamasa TORISAWA, Norihiro UMEDA
Chin. Phys. Lett. 2007, 24 (10): 2833-2835 .  
Abstract   PDF(pc) (494KB) ( 619 )
Two counter-propagating evanescent beams are used to align and manipulate polystyrene particles on a prism surface. Since the radiation pressure transferred laterally from the evanescent wave is negated on both sides, particles can be stably aligned. By projecting a circular and a linear beam spot onto the interface, both multiple and single arrays of particles are achieved. Arrays of particles trapped on the interface can be easily moved adjusting the intensity of incident beams on either side. We also simulate electromagnetic distribution of scattering light that is converted from the evanescent wave using the FDTD method. The results show that scattering light converts from an evanescent wave propagating through a particle array and has a distance longer than that propagating from a normal evanescent wave.
Far-Field Distributions of Double-Heterostructure Diode Lasers: an Improved Non-Equiphase Model
ZHAO Zhi-Guo, DUAN Kai-Liang, LU Bai-Da
Chin. Phys. Lett. 2007, 24 (10): 2836-2838 .  
Abstract   PDF(pc) (252KB) ( 521 )
A non-equiphase Gaussian model is proposed to simulate the far-field distributions of double-heterostructure diode lasers, which is physically reasonable because the phase along the junction of diode lasers could not be equal. A comparison of the numerically calculated intensity profiles in using the equal phase and non-equiphase models with the experimentally measured intensity profiles given by Nemoto shows that in the x direction perpendicular to the junction plane, the non-equiphase Gaussian model is as good as the equal phase Gaussian model. Specifically, in the y direction parallel to the junction plane and the 45°direction with respect to the x axis in the xoy plane, the numerical results by using the non-equiphase model are in good agreement with the experimental data, as the propagation distance is larger than a certain value.
An Innovative Gas Sensor with On-Chip Reference Using Monolithic Twin Laser
ZHANG Yong-Gang, TIAN Zhao-Bing, ZHANG Xiao-Jun, GU Yi, LI Ai-Zhen, ZHU Xiang-Rong, ZHENG Yan-Lan, LIU Sheng
Chin. Phys. Lett. 2007, 24 (10): 2839-2841 .  
Abstract   PDF(pc) (263KB) ( 602 )
An innovative gas sensor with on-chip reference using a monolithic twin laser is proposed. In this sensor a monolithic twin laser generates two closer laser beams with slight different wavelengths alternatively, one photodiode is used to catch both absorption and reference signals by time division multiplexing. The detection of nitrous oxide adopting this scheme using a 2.1μm antimonide laser and an InGaAs photodiode has been demonstrated experimentally with detection limit below 1ppm. Using this on chip reference scheme the fluctuations from the optical path and devices can be compensated effectively; the sensor system is simplified distinctly.
Realization of an All-Fibre Self-Organization Intra-Cavity Coherent Erbium-Doped Fibre Laser
JIA Xiu-Jie, LIU Yan-Ge, LIU Feng-Nian, FU Sheng-Gui, LIU Bo, YUAN Shu-Zhong, KAI Gui-Yun, DONG Xiao-Yi
Chin. Phys. Lett. 2007, 24 (10): 2842-2845 .  
Abstract   PDF(pc) (252KB) ( 580 )
An intra-cavity coherent coupling Michelson Er-doped fibre (EDF) laser (MCEDFL) is proposed and demonstrated. Characteristics of the MCEDFL are
investigated. It is found that the MCEDFL with a polarizer can be coherent combined effectively. By the experiment based on fibre Bragg gratings (FBGs) with different reflectivity, we find that the reflectivity of the FBG play a vital role in improving the performance of the MCEDFL. This outcome adequately shows many favourable features, such as high efficiency, easy operation, and simple all-fibre configuration.
A Compact 532-nm Source by Frequency Doubling of a Diode Stack End-Pumped Nd:YAG Slab Laser
ZHANG Heng-Li, LIU Xiao-Meng, LI Dai-Jun, SHI Peng, Alex Schell, Claus Rüdige Haas, Du Ke-Ming
Chin. Phys. Lett. 2007, 24 (10): 2846-2848 .  
Abstract   PDF(pc) (528KB) ( 563 )
A near-diffraction-limited green source is generated at 1kHz repetition rate by frequency doubling of a diode stack end-pumped electro-optically Q-switched Nd:YAG slab laser. We obtain 9.7mJ green light with pulse width of 12.2ns at a repetition rates of 1kHz. The pump to green optical conversion efficiency is 12.9%. The energy pulse stability at 532nm is about 0.8%
All-Optical Switching Based on Azo Polymer Material
DENG Yan, LUO Yan-Hua, WANG Pei, LU Yong-Hua, MING Hai, ZhANG Qi-Jing
Chin. Phys. Lett. 2007, 24 (10): 2849-2851 .  
Abstract   PDF(pc) (214KB) ( 551 )
Conventional all-optical switches based on azo polymer films and the all-optical switches based on the attenuated total reflection (ATR) geometry are investigated. A conventional switch system, including a pump beam of 532nm and a probe beam of 650nm, is based on the photoinduced birefringence effect of azo polymer. An ATR switch in a prism-multilayer configuration is achieved by changing the reflectance of the probe beam with an external pump beam. The ATR method provides the substantial improvement of the speed and the efficiency of the modulation over the conventional method. Although the azo polymer response still remains relatively slow, an enhanced nonlinear refractive index of the azo polymer film can effectively increase the
Period-Doubling in 10GHz Gain-Switched DFB Laser Diode
WU Jian, QIU Ji-Fang, LIN Jin-Tong
Chin. Phys. Lett. 2007, 24 (10): 2852-2854 .  
Abstract   PDF(pc) (265KB) ( 630 )
The distinct period doubling behaviour in a 10GHz gain-switched (GS) DFB laser is experimentally investigated in frequency domain and in time domain. The period doubling occurs as the frequency of the rf driving signal is close to or higher than the -3dB cutoff frequency of the DFB laser diode, and the amplitude of the rf driving signal required to achieve period doubling increases linearly with the increasing bias current of the laser diode.
Partially Coherent cosh-Gaussian Beams in Atmospheric Turbulence with the Same Directionality as a Laser
Lü Su-Ye, JI Xiao-Ling, Lü Bai-Da
Chin. Phys. Lett. 2007, 24 (10): 2855-2858 .  
Abstract   PDF(pc) (226KB) ( 493 )
Directionality of a class of partially coherent cosh-Gaussian beams propagating in atmospheric turbulence is studied. It is shown that two partially coherent cosh-Gaussian beams may generate the same angular spread, and there exist equivalent partially coherent cosh-Gaussian beams which may have the same directionality as a fully coherent Gaussian laser beam in free space and also in atmospheric turbulence. The theoretical results are interpreted physically and illustrated numerically.
A Scanning Multi-Axis Differential Optical Absorption Spectroscopy System for Measurement of Tropospheric NO2 in Beijing
LI Ang, XIE Pin-Hua, LIU Cheng, LIU Jian-Guo, LIU Wen-Qing
Chin. Phys. Lett. 2007, 24 (10): 2859-2862 .  
Abstract   PDF(pc) (332KB) ( 610 )

A scanning multi-axis differential optical absorption spectroscopy (DOAS) system is developed for monitoring tropospheric NO2 abundance. Measurements at different viewing angles near the horizon can be performed sequentially with one telescope collecting scattered sunlight reflected by a moving mirror. Tropospheric NO2 diurnal variations can be derived from slant column densities (SCDs) of different elevation angles. The result from a field campaign in Beijing in summer of 2005 reveals potential possibility for the monitoring of tropospheric NO2 by multi-axis DOAS technique.

Transmission Properties of W3 Y-Branch Filters in Two-Dimensional Photonic Crystal Slabs
REN Cheng, REN Kun, LIU Rong-Juan, TAO Hai-Hua, FENG Shuai, XIONGZhi-Gang, LIU Ya-Zhao, TIAN Jie, LI Zhi-Yuan, CHENG Bing-Ying, ZHANG Dao-Zhong
Chin. Phys. Lett. 2007, 24 (10): 2863-2866 .  
Abstract   PDF(pc) (895KB) ( 527 )
A highly efficient W3 Y-branch filter in a two-dimensional photonic crystal slab with triangular lattice of air holes is designed and fabricated, and its transmission properties are measured. By accurately adjusting the size of the resonant cavities, the minimum wavelength spacing of 7nm between two channels is realized. The corresponding resonant wavelengths of the two cavities agree well with the calculated ones. This implies that this kind of filter may be promising in integrated wavelength division multiplexing system.
Formation for Bass-Relief Microprofiles Based on an Analytic Formulation
SHI Li-Fang, DONG Xiao-Chun, DENG Qi-Ling, LUO Xian-Gang, DU Chun-Lei
Chin. Phys. Lett. 2007, 24 (10): 2867-2869 .  
Abstract   PDF(pc) (351KB) ( 413 )
A method of fast design and fabrication for bass-relief micro-profiles is developed by using an analytic formulation to determine the exposure distribution. Based on an equivalent exposure threshold model, the formulation is simplified for the case of bass-relief profile corresponding to the smaller exposure dose. The mask function for a microlens array is designed without iteration involved by the analytic formulation. The experiment is performed to validate the method, and the fabrication result is obtained with the profile error less than 30nm (rms).
Propagation Properties of Gaussian-Shaped and Double-Side Unsymmetrical Metallic Nano-Corrugations
LUO Xian-Gang
Chin. Phys. Lett. 2007, 24 (10): 2870-2872 .  
Abstract   PDF(pc) (246KB) ( 484 )
A Gaussian-shaped and double-side unsymmetrical groove structure is presented. Rigorous calculation of the optical properties of the structure is performed on the basis of a multiple multipole program. We analyse the effect of the grating period, the groove width and the film thickness on transmission and reflectance. Simulation results demonstrate that surface-plasmon-polariton resonance positions depend strongly on the structure period and can be changed slightly by the variation of incomplete perforation thickness, while the resonance peak values can be controlled by tuning the groove width. Our results not only give an insight into the physical mechanisms of the
double-side unsymmetrical gratings, but also open a way to design novel
nano-photonic devices.
Influence of Vacuum Organic Contaminations on Laser-Induced Damage of 1064nm Anti-Reflective Coatings
CUI Yun, LIU Shi-Jie, HE Hong-Bo, ZHAO Yuan-An, SHAO Jian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2007, 24 (10): 2873-2875 .  
Abstract   PDF(pc) (723KB) ( 530 )
We investigate the influence of vacuum organic contaminations on laser-induced damage threshold (LIDT) of optical coatings. Anti-reflective (AR) coatings at 1064\,nm made by Ta2O5/SiO2 are deposited by the ion beam
sputtering method. The LIDTs of AR coatings are measured in vacuum and
in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5J/cm2 in air to 15.7J/cm2 in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.
Fabrication of Pure Silica Core Multimode Ultraviolet Optical Fibre Probes by Tube Etching
HUO Xin, PAN Shi, WU Shi-Fa
Chin. Phys. Lett. 2007, 24 (10): 2876-2878 .  
Abstract   PDF(pc) (562KB) ( 761 )
As a light wave-guide component for transmitting ultraviolet (UV) laser pulses, pure silica core UV fibre probes have attracted a great deal of attention in the near-field optical data storage and bio-medical studies. We fabricate UV fibre probes with tips in dimension of about 2--5μm and taper angle 16°by the tube etching method, using 40% HF acid as etching solution and xylene as overlayer. Probes produced have curvy configuration with smooth surface. The yield of fine probes is rather high and etching operation greatly simplified. With higher damage threshold, pure silica core multimode UV fibre probes can be coupled into more laser power. In addition, using UV light reduces the cutoff wavelength of the fibre probes, which is in favour of increasing the
transmission efficiency of the probe. Furthermore, the larger tip dimension helps to enhance the light throughput either. The advances of fabrication technique of UV optical fibre probe may further support the studies of UV light data storage, pulsed laser biosurgery and UV photolithography.
Birefringence of Irregular-Microstructure Fibre
LI Yan, LIU Jian-Guo, KAI Gui-Yun, LIU Yan-Ge, XUE Li-Fang, WANG Zhi, YUAN Shu-Zhong, DONG Xiao-Yi
Chin. Phys. Lett. 2007, 24 (10): 2879-2882 .  
Abstract   PDF(pc) (283KB) ( 510 )
Birefringence of a microstructure fibre with irregular structures is investigated using the finite element method. The birefringence of each sample is statistically analysed, and the relation between the birefringence and the irregular structure of the microstructure fibre is derived. The results indicate that the irregular structure of the symmetrical microstructure fibre result in the birefringence which is more strongly affected by disorder of air holes than the
nonuniformity. Moreover, lower birefringence can be obtained with smaller air holes and larger pitch in the fibre structure.
Controlled Teleportation of Multi-Qudit Quantum Information
JI Hua, ZHAN Xiao-Gui, ZENG Hao-Sheng
Chin. Phys. Lett. 2007, 24 (10): 2880-2726 .  
Abstract   PDF(pc) (221KB) ( 696 )
We present a controlled teleportation scheme for teleporting an arbitrary superposition state of an M-qudit quantum system. The scheme employs only one entangled state as quantum channel, which consists of the qudits from Alice, Bob and every agent. The quantum operations used in the teleportation process are a series of qudit Bell measurements, single-qudit projective measurements, qudit H-gates, qudit-Pauli gates and qudit phase gates. It is shown that the original state can be restored by the receiver only on the condition that all the agents collaborate. If any agent does not cooperate, the original state can not be fully recovered.
Guided Waves in a Multi-Layered Cylindrical Elastic Solid Medium
ZHANG Bi-Xing, CUI Han-Yin, XIAO Bo-Xun, ZHANG Cheng-Guang
Chin. Phys. Lett. 2007, 24 (10): 2883-2886 .  
Abstract   PDF(pc) (273KB) ( 582 )
We investigate the guided waves in a multi-layered cylindrical elastic solid medium. The dispersion function of guided waves is usually complex and the dispersion curves of all modes are not conveniently obtained. Here we present an effective method to obtain the dispersion curves of all modes. First, the dispersion function of the guided waves is transformed into a real function. The dispersion curves are then calculated for all the modes of the guided waves by the bisection method. The modes with the orders n=0, 1, and 2 are analysed in two- and three-layer media. The existence condition of Stoneley wave is discussed. The modes of the guided waves are also investigated in a two-layer medium, in which the velocity of shear wave in the outer layer is less than that in the inner layer.
Solitary Wave Interactions in Granular Media
WEN Zhen-Ying, WANG Shun-Jin, ZHANG Xiu-Ming, LI Lei
Chin. Phys. Lett. 2007, 24 (10): 2887-2890 .  
Abstract   PDF(pc) (271KB) ( 548 )
We numerically study the interactions of solitary waves in granular media, by considering a chain of beads, which repel upon contact via the Hertz-type potential, V ∝ δn, with 5/2≤n≤3 and δ≥0, δ being the bead--bead overlap. There are two collision types of solitary waves, overtaking collision and head-on collision, in the chain of beads. Our quantitative results show that after collision the large solitary wave gains energy and the small one loses energy for overtaking type while the large one loses energy, and the small one gains energy for head-on type. The scattering effects decrease with n for overtaking collision whereas increase with n for head-on collision.
Influence of Length of Opposing bi-Au Cone-Tips and Different Environment on Field Enhancement in Feed Gap
LI Xu-Feng, WU Shi-Fa
Chin. Phys. Lett. 2007, 24 (10): 2891-2894 .  
Abstract   PDF(pc) (263KB) ( 542 )
Electric field enhancement distributions encountered in feed gap of opposing bi-Au cone-tips is studied using a frequency-domain three-dimensional finite element method to solve Maxwell's equations of electric field distributions. Both the influences of cone-tip length and surrounding medium on electric field enhancement are investigated. The maximal enhancement value is discussed in terms of a simple physical model based on a standing wave on the tip surface associated with the antenna effect and surface plasmon. Simulated results demonstrate the enhancement is sensitive to the tip length.
By selecting a suitably matched scale according to the incident wavelength, a large enhancement value can be observed within a small focused spot between the opposing tips permitting a high spatial resolution. The relative position of the opposing tips is also found for the optimum enhancement. All of the results suggest that our configuration is suitable for the site-specific Raman spectroscopic analysis at nanoscale.
Boundary Layer Flow over a Continuously Moving Thin Needle in a Parallel Free Stream
Anuar Ishak, Roslinda Nazar, Ioan Pop
Chin. Phys. Lett. 2007, 24 (10): 2895-2897 .  
Abstract   PDF(pc) (206KB) ( 921 )
We investigate the boundary-layer flow on a moving isothermal thin needle parallel to a moving stream. The governing equations are solved numerically by a finite-difference method. Dual solutions are found to exist when the needle and the free stream move in the opposite directions.
Lattice Boltzmann Simulation for the Optimized Surface Pattern in a Micro-Channel
WANG Jin-Feng, LIU Yang, XU You-Sheng, WU Feng-Min
Chin. Phys. Lett. 2007, 24 (10): 2898-2901 .  
Abstract   PDF(pc) (352KB) ( 353 )
Based on the Bhatangar--Gross--Krook (BGK) models, numerical simulation
using the lattice Boltzmann model is performed to investigate the optimized surface pattern in a micro-channel. In order to simulate the practical situation correctly, a slip/no-slip boundary condition is applied with making several assumptions. To assess the validity and efficiency of the model, one benchmark problem with considering the surface patterns is studied. Numerical results show the value of rms velocity Vrms increases with the increasing ratio β and larger Reynolds number Re, higher fluctuation of the rms oscillating velocity. Furthermore, the results show that a good mixing
effect can be obtained when Re is large enough and the ratio β is about 1.618, which is the appropriate choice, i.e. the well known golden section phenomenon.
Discrete Dipole Approximation Aided Design Method for Nanostructure Arrays
ZHU Shao-Li, LUO Xian-Gang, DU Chun-Lei
Chin. Phys. Lett. 2007, 24 (10): 2902-2905 .  
Abstract   PDF(pc) (323KB) ( 563 )
A discrete dipole approximation (DDA) aided design method is proposed to determine the parameters of nanostructure arrays. The relationship between the thickness, period and extinction efficiency of nanostructure arrays for the given shape can be calculated using the DDA. Based on the calculated curves, the main parameters of the nanostructure arrays such as thickness and period can be determined. Using this aided method, a rhombic sliver nanostructure array is designed with the determinant parameters of thickness (40nm) and period (440nm). We further fabricate the rhombic sliver nanostructure arrays and testify the character of the extinction spectra. The obtained extinction spectra is within the visible range and the full width at
half maximum is 99nm, as is expected.
Near-Field Birefringence Response of Liquid Crystal Molecules in Thickness Direction of Liquid Crystal Thin Film Orientated by Shear Force
Jing QIN, Norihiro UMEDA
Chin. Phys. Lett. 2007, 24 (10): 2906-2909 .  
Abstract   PDF(pc) (778KB) ( 611 )
Information of molecular orientation in nematic liquid crystal (LC) is attractive and important for applications in the field of display devices. We demonstrate a novel method using a birefringence scanning near-field optical microscope (Bi-SNOM) with a probe which is inserted into the LC thin film to detect the molecular orientation from its birefringence responses in the thickness direction of the LC thin film. The probe is laterally vibrated when going forward into the LC thin film, and the retardation and azimuth angle are recorded as the probe going down. Firstly, the thickness of the LC thin film is measured by the shear force detection. Since the shear force acts as a stimulation to reorientate the LC molecules above the substrate surface, we can detect the molecular orientation caused by a polyimide alignment
substrate and the effect to molecular orientation caused by vibration of fibre probe. As a result, the orientation profiling of the LC film in depth direction is obtained in both the cases that the direction of probe vibrating is vertical/parallel to the rubbing direction of the alignment film.
Furthermore, the thickness of completely orientated layers just above the substrate surface can also be obtained by either vibrating probe or no-vibrating probe. Ultimately, the LC thin film can be modelled in thickness direction from all the results using this method.
A New Cellular Automata Model Considering Finite Deceleration and Braking Distance
YAMG Meng-Long, LIU Yi-Guang, YOU Zhi-Sheng
Chin. Phys. Lett. 2007, 24 (10): 2910-2913 .  
Abstract   PDF(pc) (303KB) ( 579 )
We present a new cellular automata model for one-lane traffic flow. In this model, we consider the driver prejudgment according to the state of the leading car. We also consider that the vehicle deceleration capability is finite and the braking distance of the high-speed running cars cannot be ignored, which is not considered in most models. Furthermore, comfortable driving is considered, too. Using computer simulations we obtain some basic qualitative results and the fundamental diagram of the proposed model. In comparison with the known models, we find that the fundamental diagram of the proposed model is more realistic than that of the known models.
Non-Contact to Contact Transition: Direct Measurements of Interaction Forces between a Solid Probe and a Planar Air--Water Interface
WU Di, WANG Yi-Zhen, ZHANG Jin-Xiu
Chin. Phys. Lett. 2007, 24 (10): 2914-2917 .  
Abstract   PDF(pc) (318KB) ( 585 )
The interaction force between a solid probe and a planar air--water interface is measured by using an atomic force microscope. It is demonstrated that during the approach of the probe to the air--water interface, the force curves decline all the time due to the van der Waals attraction and induces a stable profile of water surface raised. When the tip approaches very close to the water surface, force curves jump suddenly, reflecting the complex behaviour of the unstable water surface. With a theoretical analysis we conclude that before the tip touches water surface, two water profiles appear, one stable and the other unstable. Then, with further approaching, the tip touches water
surface and the non-contact to contact transition occurs.
Low-Dimensional Forest-Like and Desert-Like Fractal Patterns Formed in a DDAN Molecular System
CAI Jin-Ming, BAO Li-Hong, GUO Wei, CAI Li, HUAN Qing, LIAN Ji-Chun, GUO Hai-Ming, WANG Ke-Zhi, SHI Dong-Xia, PANG Shi-Jin, GAO Hong-Jun
Chin. Phys. Lett. 2007, 24 (10): 2918-2921 .  
Abstract   PDF(pc) (972KB) ( 512 )
Two kinds of forest-like and desert-like patterns are formed by thermal
evaporation of 4-dicyanovinyl-N, N-dimethylamino-1-naphthalene (DDAN)
onto SiO2 substrates. Based on thermal kinetics of the molecules on the substrate the transformation between the forest and desert patterns is due to two factors. The first one is the diffusion length, which is related to the deposition rate, the diffusion potential energy barrier and the substrate temperature. The second one is the strong interaction between the two polarity chemical groups of the molecules, which is beneficial to the formation of branches. Totally different patterns are also found on mica substrates, and are attributed to the anisotropic diffusion and the stronger interaction between DDAN molecules and the mica surface.
Numerical Investigation of Surface Plasmons Associated Subwavelength Optical Single-Pass Effect
MIN Chang-Jun, WANG Pei, JIAO Xiao-Jin, MING Hai
Chin. Phys. Lett. 2007, 24 (10): 2922-2925 .  
Abstract   PDF(pc) (437KB) ( 672 )
Surface plasmons (SPs) associated optical single-pass effect has been investigated in novel subwavelength metallic structures, including single slit and grating structures. With influence of SPs, these metallic structures can enhance transmission in incident direction and suppress it in the opposite direction, exhibiting a single-pass effect. The finite difference time domain method is employed to study the influences of structure parameters on far-field transmission, near-field electric field distribution and extinction ratio of the single-pass transmission effect. A maximal extinction ratio of 47.83dB
is achieved in the grating structure.
Quantum Phase Transition and Ferromagnetic Spin Correlation in Parallel Double Quantum Dots
DING Guo-Hui, YE Fei
Chin. Phys. Lett. 2007, 24 (10): 2926-2929 .  
Abstract   PDF(pc) (242KB) ( 406 )
We investigate electronic transport through a parallel double quantum dot (DQD) system with strong on-site Coulomb interaction, as well as the interdot tunnelling. By applying numerical renormalization group method, the ground state of the system and the transmission probability at zero temperature are obtained. For a system of quantum dots with degenerate energy levels and
small interdot tunnel coupling, the spin correlations between the DQDs is ferromagnetic, and the ground state of the system is a spin-1 triplet state. The linear conductance will reach the unitary limit (2e2/h) due to the Kondo effect at low temperature. As the interdot tunnel coupling increases, there is a quantum phase transition from ferromagnetic to anti-ferromagnetic spin correlation in DQDs and the linear conductance is strongly suppressed.
Electron Transport in Ga-Rich InxGa1-xN Alloys
A. Yildiz, S. B. Lisesivdin, S. Acar, M. Kasap, M. Bosi
Chin. Phys. Lett. 2007, 24 (10): 2930-2933 .  
Abstract   PDF(pc) (234KB) ( 463 )
Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN (0.06≤x≤e 0.135) alloys grown by metal-organic vapour phase epitaxy (MOVPE) technique are carried out as a function of temperature (15--350K). Within the experimental error, the electron concentration in InxGa1-xN
alloys is independent of temperature while the resistivity decreases as
the temperature increases. Therefore, InxGa1-xN (0.06≤x≤0.135) alloys are considered in the metallic phase near the Mott transition. It has been shown that the temperature-dependent metallic conductivity can be well explained by the Mott model that takes into account electron--electron interactions and weak localization effects.
Electric Field Enhancement of Nano Gap of Silver Prisms
KENZO Yamaguchi, TOMOHIRO Inoue, MASAMITSU Fujii, MASANOBU Haraguchi, TOSHIHIRO Okamoto, MASUO Fukui, SHU Seki, SEIICHI Tagawa
Chin. Phys. Lett. 2007, 24 (10): 2934-2937 .  
Abstract   PDF(pc) (937KB) ( 835 )

Using numerical calculation, we examine the effects of gap distance of a pair of nano gap silver prisms with rounded corners on the local light intensity enhancement. Two peaks due to localized surface plasmon (LSP) excitation are observed in a wavelength range from 900nm to 300nm. The results demonstrate that peaks at a longer and a shorter wavelength corresponded to dipole-like and quadrupole-like LSP resonances, respectively. It is found that a gap distance up to 20nm provides larger light intensity enhancement than that of a single silver nano prism with rounded corners. Furthermore, nano gap silver prisms are fabricated by direct focused ion beam processing, and we measure the scattering light spectrum of a pair of nano prisms by a
confocal optical system. However, the two LSP peaks are not observed in
visible range because the sizes of the nano gap and prisms are too large.

Barrier Enhancement Effect of Postannealing in Oxygen Ambient on Ni/AlGaN Schottky Contacts
SANG Li-Wen, QIN Zhi-Xin, CEN Long-Bin, CHEN Zhi-Zhong, YANG Zhi-Jian, SHEN Bo, ZHANG Guo-Yi
Chin. Phys. Lett. 2007, 24 (10): 2938-2941 .  
Abstract   PDF(pc) (276KB) ( 628 )
Al0.2Ga0.8N/GaN samples are grown by metalorganic chemical vapour deposition (MOCVD) method on (0001) sapphire substrates. A 10nm-thick Ni layer is deposited on AlGaN as the transparent Schottky contact. The effect of postannealing in oxygen ambient on the electrical properties of Ni/AlGaN is studied by current--voltage--temperature (I--V--T) measurement. The annealing at a relatively low temperature of 300°C for 90s results in a
decrease of the ideality factor from 2.03 to 1.30 and an increase of the
Schottky barrier height from 0.77eV to 0.954eV. The I--V--T analysis confirms the improvement originated from the formation of NiO, a layer with higher resistance, which could passivate the surface states of AlGaN and suppress the tunnelling current. Furthermore, the annealing also leads to an increase of the transmittance of the contacts from 57.5% to 78.2%, which would be favourable for AlGaN-based photodetectors.
Electrical Characterization of Metal--Insulator--Metal Capacitors with Atomic-Layer-Deposited HfO2 Dielectrics for Radio Frequency Integrated Circuit Application
HUANG Yu-Jian, HUANG Yue, DING Shi-Jin, ZHANG Wei, LIU Ran
Chin. Phys. Lett. 2007, 24 (10): 2942-2944 .  
Abstract   PDF(pc) (251KB) ( 3165 )
Metal--insulator--metal (MIM) capacitors with atomic-layer-deposited HfO2 dielectric and TaN electrodes are investigated for rf integrated circuit applications. For 12nm HfO2, the fabricated capacitor exhibits a high capacitance density of 15.5fF/μm2 at 100kHz, a small leakage current density of 6.4×10-9A/cm2 at 1.8\,V and 125°C, a breakdown electric field of 2.6MV/cm as well as voltage coefficients of capacitance (VCCs) of 2110ppm/V2 and -824ppm/V at 100kHz. Further, it is deduced that the conduction mechanism in the high field range is dominated by the Poole--Frenkel emission, and the conduction mechanism in the low field range is possibly related to trap-assisted tunnelling. Finally, comparison of various HfO2 MIM capacitors is present, suggesting that the present MIM capacitor is a promising candidate for future rf integrated circuit application.
Intense Green Upconversion Luminescence in Er3+:Yb3+ Codoped Fluorophosphate Glass Ceramic Containing SrTe5O11 Nanocrystals
ZHANG Li-Yan, XU Shi-Qing, HU Li-Li
Chin. Phys. Lett. 2007, 24 (10): 2945-2946 .  
Abstract   PDF(pc) (204KB) ( 623 )
Er3+:Yb3+ codoped tellurite-fluorophosphate (TFP) glass ceramic exhibits much stronger upconversion luminescence. The intensity of the 540nm green light and 651nm red light of the TFP glass ceramic is 120 times and 44 times stronger than that of the fluorophospahte (FP) glass, respectively. XRD analysis shows that the nanocrystal in TFP glass ceramic is SrTe5O11. TFP glass ceramic also displays much higher upconversion fluorescence lifetime and crystallization stability. The narrow and strong peak at 540nm is very
ideal for practical upconversion luminescence realization. This work is a new trial for exploring non-PbF2 involved nanocrystal upconversion glass ceramics.
Light Irradiation through Small Particles and Its Applications for Surface Nanostructuring in Near Field
Chin. Phys. Lett. 2007, 24 (10): 2947-2950 .  
Abstract   PDF(pc) (1012KB) ( 454 )
We investigate the light scattering through small particles and its applications in nanostructuring, such as nanobumping, nanopatterning and dry laser cleaning. The theoretical calculation based on Mie theory provides an exact solution for sphere cavity resonance and plasmon resonance, which are two mechanisms for dielectric and metallic particles assisted surface nanostructuring in near field. The experimental results indicate that nanobumps on glass surface and subwavelength holes array on silicon surface can be formed without cracks with the self-assembly of 1μm silica particle mask under laser irradiation. It is also found that the scattering wave by 40nm gold particles can propagate 200 times away in terms of particle radius as recorded by photoresist under the UV light irradiation. Meanwhile, dry laser cleaning of 40nm gold particle on silicon wafer is demonstrated
at plasmonic resonance frequency. The total cleaning efficiency is estimated to be 80%.
Epitaxial Properties of Co-Doped ZnO Thin Films Grown by Plasma Assisted Molecular Beam Epitaxy
CAO Qiang, DENG Jiang-Xia, LIU Guo-Lei, CHEN Yan-Xue, YAN Shi-Shen, MEILiang-Mo
Chin. Phys. Lett. 2007, 24 (10): 2951-2954 .  
Abstract   PDF(pc) (572KB) ( 862 )
High quality Co-doped ZnO thin films are grown on single crystalline Al2O3(0001) and ZnO(0001) substrates by oxygen plasma assisted molecular beam epitaxy at a relatively lower substrate temperature of 450°C. The epitaxial conditions are examined with in-situ reflection high energy electron diffraction (RHEED) and ex-situ high resolution x-ray diffraction (HRXRD). The epitaxial thin films are single crystal at film thickness smaller than 500nm and nominal concentration of Co dopant up to 20%. It is indicated that the Co cation is incorporated into the ZnO matrix as Co2+ substituting Zn2+ ions. Atomic force microscopy shows smooth surfaces with rms roughness of 1.9nm. Room-temperature magnetization measurements reveal that the Co-doped ZnO thin films are ferromagnetic with Curie temperatures TC above room temperature.
Defect-Bound Carrier Mediated Room-Temperature Ferromagnetism in Co-Doped ZnO Powders
WEN Qi-Ye, ZHANG Huai-Wu, SONG Yuan-Qiang, YANG Qing-Hui, John Q.Xiao
Chin. Phys. Lett. 2007, 24 (10): 2955-2958 .  
Abstract   PDF(pc) (529KB) ( 666 )
We prepare pure single-phase Co:ZnO powders introducing controllable
interstitial Zni by Zn vapour annealing. The as-ground powder shows that no room-temperature ferromagnetism (RT-FM) exists, while the Zn vapour treated samples exhibit unambiguous RT-FM with a maximum magnetic moment of 0.2μB/Co. The FM of Co:ZnO strongly depends on the Zn diffusion process, suggesting that not only carriers but also Zni defects play an important role in mediating FM in diluted magnetic semiconductors. A new core-shell model is proposed to interpret the mixture behaviour of FM and paramagnetism observed in the Zn vapour annealed Co:ZnO powders.
Dielectric Performance of Porous Methyl Silsesquioxane/Triacetyl-β-Cyclodextrin Thin Films
HU Yi-Fan, FU Dan-Rong, ZHANG Ying, ZHANG Fan, TANG Ting
Chin. Phys. Lett. 2007, 24 (10): 2959-2962 .  
Abstract   PDF(pc) (366KB) ( 597 )
Porous methyl silsesquioxane thin films with low dielectric constant are successfully synthesized by means of the sol-gel spin-coating method. The precursor solutions are prepared by properly mixing the polymer as a matrix with different contents of triacetyl-β-cyclodextrin (TABCD) as a porogen. The chemical structure, dielectric constants, optical constants and void fraction are investigated by the ellipsometric porosimetry, Fourier transform infrared (FTIR)
spectroscopy, and other methods. Influences of TABCD and methyl trimethoxysilane (MTMS) on the dielectric properties are discussed. For those samples with higher porogen loading, orientation and electronic polarizations are lower in low and high frequency regions, respectively, because of a considerably smaller number of polar molecules. The FTIR results suggest that high R value (molar ratio of H2O to MTMS) is more advantageous for formation of cage structures and the cage/network structural ratio increases with the
increasing R value.
Influences of Annealing on Residual Stress and Structure of HfO2 Films
SHEN Yan-Ming, SHAO Shu-Ying, DENG Zhen-Xia, HE Hong-Bo, SHAOJian-Da, FAN Zheng-Xiu
Chin. Phys. Lett. 2007, 24 (10): 2963-2966 .  
Abstract   PDF(pc) (244KB) ( 472 )
HfO2 films are deposited on BK7 glass substrates by electron beam evaporation. The influences of annealing between 100°C and 400°C on residual stresses and structures of HfO2 films are studied. It is found that little differences of spectra, residual stresses and structures are obtained after annealing at lower temperatures. After annealing at higher temperatures, the spectra shift to short wavelength, the residual stress increases with the increasing annealing temperature. At the same time, the crystallite size increases and interplanar distance decreases. The variations of optical spectra and residual stress correspond to the evolutions of structures induced by annealing.
Influence of Annealing Temperature on Structure, Optical Loss andLaser-Induced Damage Threshold of TiO2 Thin Films
Chin. Phys. Lett. 2007, 24 (10): 2967-2969 .  
Abstract   PDF(pc) (269KB) ( 384 )
TiO2 thin films are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for 4h, the spectra and XRD patterns of the TiO2 thin film are obtained. Weak absorption of coatings is measured by the surface thermal lensing technique, and laser-induced damage threshold (LIDT) is determined. It is found that with the increasing annealing temperature, the transmittance of TiO2 films decreases.
Especially when coatings are annealed at high temperature over 1173K, the optical loss is very serious. Weak absorption detection indicates that the absorption of coatings decreases firstly and then increases, and the absorption and defects play major roles in the LIDT of TiO2 thin films.
Ultra-Fast Decay Process of Electrons in LiNbO3 Crystal Induced by Femtosecond Pulse
CHEN Li, JIANG Hong-Bing, ZHANG Xi-Peng, TANG Shan-Chun, YANG Hong, GONG Qi-Huang
Chin. Phys. Lett. 2007, 24 (10): 2970-2972 .  
Abstract   PDF(pc) (412KB) ( 388 )
Temporal evolution of absorption induced by single femtosecond pulse (130fs, 800nm) with high intensity in LiNbO3 is obtained using the probe shadow imaging technique in order to investigate light-induced electron relaxation processes. By saturating the polaron density with a high intensity laser pulse, ultra-fast decay process on picosecond time scale is observed. The decay time constant is about 141ps and it is attributed to the direct interband electron--hole recombination process.
Electrochemical Deposition and Properties of ZnTe Nanowire Array
YANG You-Wen, LI Liang, YE Min, WU Yu-Cheng, XIE Ting, LIGuang-Hai
Chin. Phys. Lett. 2007, 24 (10): 2973-2976 .  
Abstract   PDF(pc) (526KB) ( 900 )
Pulsed electrodeposited technique is applied to fabricate ZnTe nanowire arrays with different diameters into the anodic alumina membrane in citric acid solution. The x-ray powder diffraction, scanning electron microscopy and transmission electron microscopy indicate that the high ordered, uniform and single-crystalline nanowires have been fabricated. The optical absorption spectra of the nanowire array show that the optical absorption band edge of the ZnTe nanowire array exhibit a blue shift compared with that of bulk ZnTe, and the nonlinear current-voltage characteristic is observed.
Preparation and Luminescence Characteristics of Ca3Y2(BO3)4:Eu3+ Phosphor
LI Pan-Lai, YANG Zhi-Ping, WANG Zhi-Jun, Guo Qing-Lin
Chin. Phys. Lett. 2007, 24 (10): 2977-2979 .  
Abstract   PDF(pc) (221KB) ( 1074 )
Ca3Y2(BO3)4:Eu3+ phosphor is synthesized by high temperature solid-state reaction method, and the luminescence characteristics are investigated. The emission spectrum exhibits two strong red emissions at 613 and 621nm corresponding to the electric dipole 5D0--7F2 transition of Eu3+ under 365nm excitation, the reason is that Eu3+ substituting for Y3+ occupies the non-centrosymmetric position in the crystal structure of Ca3Y2(BO3)4. The excitation spectrum for 613nm indicates that the phosphor can be effectively excited by ultraviolet (UV) (254nm, 365nm and 400nm) and blue (470nm) light. The effect of Eu3+ concentration on the emission intensity of Ca3Y2(BO3)4:Eu3+ phosphor is measured, the result shows that the emission intensities increase with increasing Eu3+ concentration, then decrease. The CIE colour
coordinates of Ca3Y2(BO3)4:Eu3+ phosphor is (0.639, 0.357) at 15mol% Eu3+.
Low Threshold Distributed Feedback Quantum Cascade Lasers with Widely Spaced Emission Wavelengths
LI Yao-Yao, XU Gang-Yi, LI Ai-Zhen, WEI Lin, LI Hua, MEI Bin
Chin. Phys. Lett. 2007, 24 (10): 2980-2983 .  
Abstract   PDF(pc) (444KB) ( 498 )
We report lasing properties of distributed feedback quantum cascade lasers (DFB QCLs) including a double-phonon-resonance active region, at wavelength of about 8.4μm. A broad gain spectrum is generated due to the coupling between the lower laser level in the active region and the levels in the injector, and is demonstrated by the lasing spectrum of the corresponding Fabry--Perot QCLs whose width is 0.5μm at 1.5 times of the threshold current. As a result, the DFB QCLs employing different grating periods exhibit a wavelength span of 0.18μm at room temperature and total wavelength coverage of 0.28μm at various heat sink temperatures. A high side mode
suppression ratio of about 30dB and a low threshold current density of 1.78kA/cm2 are achieved as the lasers operate at room temperature in pulsed mode.
Gain Measurement and Anomalous Decrease of Peak Gain at Long Wavelength for InAs/GaAs Quantum-Dot Lasers
XIAO Jin-Long, HUANG Yong-Zhen, DU Yun, ZHAO Huan, NI Hai-Qiao, NIU Zhi-Chuan
Chin. Phys. Lett. 2007, 24 (10): 2984-2986 .  
Abstract   PDF(pc) (328KB) ( 461 )
Mode gain spectrum is measured by the Fourier series expansion method for InAs/GaAs quantum-dot (QD) lasers with seven stacks of QDs at different injection currents. Gain spectra with distinctive peaks are observed at the short and long wavelengths of about 1210nm and 1300nm. For a QD laser with the cavity length of 1060μm, the peak gain of the long wavelength first increases slowly or even decreases with the injection current as the peak gain of the short wavelength increases quickly, and finally increases quickly before approaching the saturated values as the injection current further
Local Surface-Plasmons in Nonspherical Metal Nanoparticles
CHEN Chun-Chong, LU Yong-Hua, WANG Pei, MING Hai
Chin. Phys. Lett. 2007, 24 (10): 2987-2990 .  
Abstract   PDF(pc) (441KB) ( 737 )
When a small metallic nanoparticle is irradiated by incident light, the oscillating electric field can cause the conduction electrons to oscillate coherently, which excites the local surface plasmons (LSPs). As is well known, excited LSPs can gather the energy of incident light to the surface of metallic nanoparticle. Recently, some nonspherical particles, e.g. tetrahedron, are suggested to obtain stronger localized electric field. We employ the discrete dipole approximation method to calculate the optical response of the tetrahedron nanoparticle, including the extinction and distribution of the electric field around the particle. The influences of some parameters, including the nanoparticle size, incident direction and polarization, are investigated to analyse the response modes and to obtain stronger localized electric field.
Surface Structure of Large Synthetic Diamonds by High Temperature and High Pressure
ZANG Chuan-Yi, HUANG Guo-Feng, MA Hong-An, JIA Xiao-Peng,
Chin. Phys. Lett. 2007, 24 (10): 2991-2993 .  
Abstract   PDF(pc) (907KB) ( 899 )
With NiMnCo and FeCoNi alloys as solvent metals, large single-crystal diamonds of about 3mm across are grown by temperature gradient method
(TGM) under high temperature and high pressure (HPHT). Although both {100} and {111} surfaces are developed by a layer growth mechanism, some different characteristic patterns are seen clearly on the different surfaces, no matter whether NiMnCo or FeCoNi alloys are taken as the solvent metals. For {100} surface, it seems to have been melted or etched greatly, no dendritic patterns to be found, and only a large number of growth hillocks are dispersed net-likely; while for {111} surface, it often seems to be more smooth-faced, no etched or melted traces are present even when a lot of depressed trigonal growth layers. This distinct difference between {111} and {100} surfaces is considered to be related to the difference of surface-atom distribution of different surfaces, and {111} surfaces should be more
difficult to be etched and more steady than {100} surfaces.
Preparation and Dielectric Properties of Nanostructured ZnO Whiskers
SHI Xiao-Ling, YUAN Jie, ZHOU Wei, RONG Ji-Li, CAO Mao-Sheng
Chin. Phys. Lett. 2007, 24 (10): 2994-2997 .  
Abstract   PDF(pc) (612KB) ( 574 )
By a novel controlled combustion synthesis method, a large number of nanostructured ZnO whiskers with different morphologies, such as tetra-needles, long-leg tetra-needles and multi-needles, are prepared without any additive in open air at high temperature. The morphologies and crystalline structures of the as-prepared ZnO nanostructured whiskers are investigated by SEM and XRD. The possible growth mechanism on the nanostructured ZnO whiskers is proposed. The experimental results indicate that the dielectric constants and losses of the nanostructured ZnO whiskers are very low, demonstrating that the nanostructured ZnO whiskers are low-loss materials for microwave absorption in X-band. However, obvious microwave absorption in nanostructured ZnO whiskers is observed. The quasi-microantenna model may be attributed to the microwave absorption of the ZnO whiskers.
A Physics-Based Compact Direct-Current and Alternating-Current Model for AlGaN/GaN High Electron Mobility Transistors
LI Miao, WANG Yan
Chin. Phys. Lett. 2007, 24 (10): 2998-3001 .  
Abstract   PDF(pc) (286KB) ( 422 )
A set of analytical models for the dc and small signal characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) are presented. A modified transferred-electron mobility model is adapted and a phenomenological low-field mobility model is developed. We calculate the channel charge considering the neutralization of donors and the contribution of free electrons in the AlGaN layer. The gate-to-source and gate-to-drain capacitances are obtained analytically, and the cut-off frequency is predicted. The models are implemented into the HSPICE simulator for the dc, ac and transient simulations and verified by experimental data for the first time. A high efficiency class-E GaN HEMT power amplifier is designed and simulated by the HSPICE to verify the applicability of our models.
Scaling Behaviour and Memory in Heart Rate of Healthy Human
CAI Shi-Min, PENG Hu, YANG Hui-Jie, ZHOU Tao, ZHOU Pei-Ling, WANG Bing-Hong,
Chin. Phys. Lett. 2007, 24 (10): 3002-3005 .  
Abstract   PDF(pc) (329KB) ( 646 )
We investigate a set of complex heart rate time series from healthy human in different behaviour states with the detrended fluctuation analysis and diffusion entropy (DE) method. It is proposed that the scaling properties are influenced by behaviour states. The memory detected by DE exhibits an approximately same pattern after a detrending procedure. Both of them demonstrate the long-range strong correlations in heart rate. These findings may be helpful to understand the underlying dynamical evolution process in the heart rate control system, as well as to model the cardiac dynamic process.
Near-Field Characterization of Optical Micro/Nanofibres
MA Zhe, WANG Shan-Shan, YANG Qing, TONG Li-Min
Chin. Phys. Lett. 2007, 24 (10): 3006-3008 .  
Abstract   PDF(pc) (663KB) ( 698 )
Near-field scanning optical microscopy is used to investigate the waveguiding properties of optical micro/nanofibres (MNFs) by means of detecting optical power carried by evanescent waves. Taper drawn silica and tellurite MNFs, supported on low-index substrates, are used to guide a 532-nm-wavelength light beam for the test. Modification of the single-mode condition of the MNF in the presence of a substrate is observed. Spatial modulation of the longitudinal field intensity (with a 195-nm period) near the output end of a 760-nm-diameter silica MNF is well resolved. Energy exchange through evanescent coupling between two parallel MNFs is also investigated.
Leptonic Origin of TeV Gamma-Ray Emission from Crab Nebula
ZHANG Li, WEI Bing-Tao, FANG Jun
Chin. Phys. Lett. 2007, 24 (10): 3009-3012 .  
Abstract   PDF(pc) (258KB) ( 541 )
We study the nonthermal emission of the Crab nebula in the bands from radio to TeV γ-ray on a simplified time-dependent injection model. In this model, relativistic electrons in the Crab nebula consists of two components and their injected spectrum is a broken power law with different indices and a break energy. The relativistic electrons emit nonthermal photons through synchrotron and inverse Compton scattering off soft photon fields inside the
nebula. The resulting spectrum calculated with the model is well consistent with the observed data ranging from radio to very high energy γ-rays for the Crab nebula, where the emission from radio to medium γ-rays is from electron's synchrotron emission, whereas the emission above ~100MeV primarily comes from the inverse Compton scattering of the relativistic electrons on synchrotron photons.
Higher Dimensional Strange Quark Matter Coupled to the String Cloud with Electromagnetic Field Admitting One Parameter Group of Conformal Motion
Chin. Phys. Lett. 2007, 24 (10): 3013-3015 .  
Abstract   PDF(pc) (209KB) ( 743 )
We solve Einstein's field equations in higher-dimensional spherically symmetric spacetime with strange quark matter attached to the string cloud, assuming one parameter group of conformal motions. The solutions match with the higher-dimensional Reissner--Nordstrom metric on the boundary at r = r0. The features of the solutions are also discussed in the framework of higher-dimensional spacetime.
83 articles