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Volume 26 Issue 11
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GENERAL
Nonsensitive Nonlinear Homotopy Approach
GAO Yuan, TANG Xiao-Yan, LOU Sen-Yue,
Chin. Phys. Lett. 2009, 26 (11): 110201 .   DOI: 10.1088/0256-307X/26/11/110201
Abstract   PDF(pc) (442KB) ( 676 )
Generally, natural scientific problems are so complicated that one has to establish some effective perturbation or nonperturbation theories with respect to some associated ideal models. We construct a new theory that combines perturbation and nonperturbation. An artificial nonlinear homotopy parameter plays the role of a perturbation parameter, while other artificial nonlinear parameters, which are independent of the original problems, introduced in the nonlinear homotopy models are nonperturbatively determined by means of the principle of minimal sensitivity. The method is demonstrated through several quantum anharmonic oscillators and a non-hermitian parity-time symmetric Hamiltonian system. In fact, the framework of the theory is rather general and can be applied to a broad range of natural phenomena. Possible applications to condensed matter physics, matter wave
systems, and nonlinear optics are briefly discussed.
A New Type of Conserved Quantity of Mei Symmetry for Holonomic Mechanical System
FANG Jian-Hui, ZHANG Ming-Jiang, LU Kai
Chin. Phys. Lett. 2009, 26 (11): 110202 .   DOI: 10.1088/0256-307X/26/11/110202
Abstract   PDF(pc) (264KB) ( 640 )
A new type of conserved quantity which is directly induced by the Mei symmetry of the holonomic system is studied. Firstly, the definition and criterion of the Mei symmetry for a holonomic mechanical system is given. Secondly, the condition of existence of the new conserved quantity as well as its form is obtained. Lastly, an example is given to illustrate the application of the results.
A Simple Scheme for Two-Qubit Grover Search in Hot Trapped Ions
ZHENG Xiao-Juan, FANG Mao-Fa, XU Hui,
Chin. Phys. Lett. 2009, 26 (11): 110301 .   DOI: 10.1088/0256-307X/26/11/110301
Abstract   PDF(pc) (318KB) ( 599 )
An alternative simple scheme is proposed to implement the two-qubit Grover search algorithm in trapped ions by applying a single standing-wave laser pulse during the two-qubit operation. The scheme is insensitive to the heating of vibrational motion, which is important in view of decoherence. Moreover a third auxiliary internal electronic state is eliminated, and the qubit definitions are the same for both ions, which makes the experiment easier and simpler.
Relation between Characteristic Function of Density Operator and Tomogram
FAN Hong-Yi, JIANG Nian-Quan
Chin. Phys. Lett. 2009, 26 (11): 110302 .   DOI: 10.1088/0256-307X/26/11/110302
Abstract   PDF(pc) (293KB) ( 838 )
In terms of the intermediate coordinate-momentum representation (Chin.Phys.Lett. 18(2001)850) and using the technique of integration within an ordered product of operators, we put the tomography theory into operator version. We reveal the new relation between the tomogram and the characteristic function of the density operator. The new expansion of the density operator in terms of the intermediate coordinate-momentum representation is also obtained.
Stochastic Alternating Dynamics for Synchronous EAD-Like Beating Rhythms in Cultured Cardiac Myocytes
ZHANG Ning, ZHANG Hui-Min, LIU Zhi-Qiang, DING Xue-Li, YANG Ming-Hao, GUHua-Guang, REN Wei
Chin. Phys. Lett. 2009, 26 (11): 110501 .   DOI: 10.1088/0256-307X/26/11/110501
Abstract   PDF(pc) (479KB) ( 725 )
Dissolved cardiac myocytes can couple together and generate synchronous beatings in culture. We observed a synchronized early after-depolarization(EAD)-like rhythm in cultured cardiac myocytes and reproduced the experimental observation in a network mathematical model whose dynamics are close to a Hopf bifurcation. The mechanism for this EAD-like rhythm is attributed to noised-induced stochastic alternatings between the focus and the limit cycle. These results provide novel understandings for pathological heart rhythms like the early immature beatings.
Regular Small-World Network
ZOU Zhi-Yun, MAO Bao-Hua, HAO Hai-Ming, GAO Jian-Zhi, YANG Jie-Jiao
Chin. Phys. Lett. 2009, 26 (11): 110502 .   DOI: 10.1088/0256-307X/26/11/110502
Abstract   PDF(pc) (1050KB) ( 698 )
According to the deficiencies in Watts and Strogatz's small-world network model, we present a new regular model to establish the small-world network. Besides the property of the small-world, this model has other properties such as accuracy in controlling the average shortest path length L, and the average clustering coefficient C, also regular network topology as well as enhanced network robustness. This method improves the construction of the small-world network essentially, so that the regular small-world network closely resembles the actual network. We also present studies on the relationships among the quantities of a variety of edges, L and C in regular small-world network in detail. This research lays the foundation for the establishment of the regular small-world network and acts as a good guidanc
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Jet-Photon Production at RHIC and LHC
FU Yong-Ping, LI Yun-De
Chin. Phys. Lett. 2009, 26 (11): 111201 .   DOI: 10.1088/0256-307X/26/11/111201
Abstract   PDF(pc) (511KB) ( 556 )
We calculate the production of prompt and thermal photons which includes the contribution of gluons in relativistic heavy ion collisions with the equilibrium and non-equilibrium quark-gluon plasma. We develop a new thermal jet-photon conversion mechanism which plays a vital role in the low transverse momentum region. The effect of the non-equilibrium quark-gluon plasma enhances the contribution of the thermal photons. The shadowing and iso-spin of the nucleus which can properly estimate the prompt photon production are also considered in our calculation.
NUCLEAR PHYSICS
Three-Body Faddeev Approach to Two-Proton Emissions from 18Ne Excited State
YU Ning, LIU Fu-Qing, ZHANG Huan-Qiao,
Chin. Phys. Lett. 2009, 26 (11): 112101 .   DOI: 10.1088/0256-307X/26/11/112101
Abstract   PDF(pc) (362KB) ( 531 )
The proton drip line nucleus 18Ne is considered as a system of two protons and a 16O core. The excitation-energy spectrum of 18Ne and the relative-momentum distribution of the two protons emitted from the 6.15MeV level of 18Ne are calculated using the Faddeev approach.
Deformation Effect on the Center-of-Mass Correction Energy in Nuclei Ranging from Oxygen to Calcium
ZHAO Peng-Wei, SUN Bao-Yuan, MENG Jie,
Chin. Phys. Lett. 2009, 26 (11): 112102 .   DOI: 10.1088/0256-307X/26/11/112102
Abstract   PDF(pc) (363KB) ( 788 )
The microscopic c.m. correction energies for nuclei ranging from oxygen to calcium are systematically calculated by both spherical and axially deformed relativistic mean-field (RMF) models with the effective interaction PK1. The microscopic c.m. correction energies strongly depend on the isospin as well as deformation and deviate from the phenomenological ones. The deformation effect is discussed in detail by comparing the deformed with the spherical RMF calculation. It is found that the direct and exchange terms of the c.m. correction energies are strongly correlated with the density distribution of nuclei and are suppressed in the deformed case.
Isospin Effects on Anisotropic Flows in Intermediate Energy Heavy Ion Collisions
YAN Ting-Zhi, HU Si-Ke, GUO Wen-Xue, WANG Sheng-Long, XU Jin-Ping
Chin. Phys. Lett. 2009, 26 (11): 112501 .   DOI: 10.1088/0256-307X/26/11/112501
Abstract   PDF(pc) (495KB) ( 489 )
Anisotropic flows per nucleon (v1/A, v2/A, v3/A and v4/A) of light fragments up to the mass number 4 as a function of transverse momentum per nucleon are studied for 55MeV/nucleon 58Fe+58Fe and 58Ni+58Ni at large impact parameters by the isospin-dependent quantum molecular dynamics model. The effects of symmetry energy and nucleon-nucleon cross sections, which are both isospin-dependent on anisotropic flows, are studied in detail. In comparison of the two systems with or without symmetry potential term, the results show that the strength of flows is sensitive to symmetry potential and nucleon-nucleon cross sections, which mainly cause a repulsion effect in this energy region.
A Discussion on Whether 15-20C Are All Skin Nuclei via Isospin-dependent Boltzmann-Langevin Equation
CHEN Yu, ZHANG Feng-Shou, , SU Jun,
Chin. Phys. Lett. 2009, 26 (11): 112502 .   DOI: 10.1088/0256-307X/26/11/112502
Abstract   PDF(pc) (484KB) ( 632 )
A new attempt of calculation for the total reaction cross sections (σR) has been carried out within the isospin-dependent Boltzmann-Langevin equation in the intermediate energy heavy-ion collision of isotopes of C. The σR of both stable and exotic nuclei are reproduced rather well. The incident energy and isospin dependencies of σR have been investigated. It is found that the isospin effect is comparatively remarkable at intermediate energy. It is also found that 15-18C are neutron skin nuclei but for 19C and 20C we cannot draw a conclusion whether they have halo structures.
Measurement of Electron-Drift Velocity in Ar+CH4 Mixtures Using Double-Grid Method
ZHANG Jia-Guo, ZHANG Guo-Hui, CHEN Jin-Xiang
Chin. Phys. Lett. 2009, 26 (11): 112901 .   DOI: 10.1088/0256-307X/26/11/112901
Abstract   PDF(pc) (566KB) ( 664 )
Based on analyzing the induced signals from the double-grids of an ionization chamber, the electron-drift time between the two grids is determined and the electron-drift velocity is derived. A waveform digitizer is employed to record pulses from the two grids of the ionization chamber. The electron-drift velocity is measured as a function of the reduced electric field E/p for eight different ratios of Ar+CH4 mixtures. By analyzing the experimental data of this study, self-consistency of experimental data is achieved, and formulae for calculating electron-drift velocity in any ratio of Ar+CH4 mixtures are obtained.
ATOMIC AND MOLECULAR PHYSICS
Synthesizing Metastable Rocksalt-Type MgTe Based on High-Pressure Solid-State Phase Transition: A First-Principles Study
CAI Ying-Xiang, XU Rui
Chin. Phys. Lett. 2009, 26 (11): 113101 .   DOI: 10.1088/0256-307X/26/11/113101
Abstract   PDF(pc) (423KB) ( 888 )
The controllability of pressure-induced structural transformation in the hexagonal wurtzite-type MgTe is studied by a first-principles pseudopotential method within the generalized gradient approximation (GGA). Based on the transitional mechanisms of the wurtzite → NiAs and the wurtzite → rocksalt, a special method of loading biaxial pressure on the (010) and (001) planes of an orthorhombic cell is designed. At equal biaxial pressure of 2.75GPa, an abrupt volume collapse is found and the WZ phase transforms into an orthorhombic phase with a tiny distortion. While the pressure decreases to zero, three lattice parameters a, b and c become equal and a metastable rocksalt-type MgTe is obtained.
Generation of Continuum Extreme-Ultraviolet Radiation by Carrier-Envelope-Phase-Stabilized 5-fs Laser Pulses
TENG Hao, YUN Chen-Xia, ZHU Jiang-Feng, HAN Hai-Nian, ZHONG Xin, ZHANG Wei, HOU Xun, WEI Zhi-Yi
Chin. Phys. Lett. 2009, 26 (11): 113201 .   DOI: 10.1088/0256-307X/26/11/113201
Abstract   PDF(pc) (885KB) ( 532 )
Coherent extreme-ultraviolet (XUV) radiation is studied by interaction of carrier-envelope (CE) phase stabilized high energy 5-fs infrared (800\,nm) laser pulses with neon gas at a repetition rate of 1kHz. A broadband continuum XUV spectrum in the cut-off region is demonstrated when the CE phase is shifted to about zero, rather than modulated spectral harmonics when setting of CE phase is nonzero. The results show the generation of isolated attosecond XUV pulses.
Population Swap of a Pair of Quantum Dots Coupling to a Plasmonic Nanocavity
LI Jian-Bo, CHENG Mu-Tian, YANG Zhong-Jian, HAO Zhong-Hua
Chin. Phys. Lett. 2009, 26 (11): 113202 .   DOI: 10.1088/0256-307X/26/11/113202
Abstract   PDF(pc) (504KB) ( 557 )
We theoretically design a single-mode plasmonic ring nanocavity. Based on the plasmonic cavity, the exciton dynamics between two identical quantum dots (QD-p, QD-q) coupled to the nanocavity are investigated. It is shown that the coupling factors gi (i=p,q) between QD-i and surface plasmons are both equal to 12.53meV in our model and exciton population swap between the two QDs can be realized. The periods and amplitudes of population oscillations can be modified by the coupling factors. Our results may have potential applications in quantum information and quantum computation on a chip.
Generation of a Super Strong Attosecond Pulse from an Atomic Superposition State Irradiated by a Shape-Optimized Short Pulse
GUO Fu-Ming, YANG Yu-Jun, JIN Ming-Xing, DING Da-Jun, ZHU Qi-Ren
Chin. Phys. Lett. 2009, 26 (11): 113203 .   DOI: 10.1088/0256-307X/26/11/113203
Abstract   PDF(pc) (1010KB) ( 600 )
Using a linearly polarized, phase-stabilized 3-fs driving pulse of 800nm central wavelength shape-optimized on its ascending edge by its an amplitude-reduced pulse irradiating on a superposition state of the helium atom, we demonstrate theoretically the generation of a super strong isolated 176-attosecond pulse in the spectral region of 93-124eV. The unusually high intensity of this attosecond pulse is marked by the Rabi-like oscillations emerging in the time-dependent populations of the ground state and the continuum during the occurrence of the electron recombination, which is for the first time observed in this work.
High-Temperature Raman Investigation on Phase Transition of LBO Crystal
ZHANG Xia, WAN Song-Ming, YIN Shao-Tang, YOU Jing-Lin
Chin. Phys. Lett. 2009, 26 (11): 113301 .   DOI: 10.1088/0256-307X/26/11/113301
Abstract   PDF(pc) (484KB) ( 610 )
The high-temperature Raman spectroscopy technique is applied to investigate the phase transition of LiB3O5 crystal. The result shows that the crystal is stable in the range of 293-893K. When the temperature increases up to above 1107K, the phase transition occurs. In the liquid phase, Li2B4O7 crystal precipitates out. Up to 1173K, the Li2B4O7 crystal disappears in the melt.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Composite Scattering from the Electrically Very Large Ship-Sea Model Using the Hybrid High-Frequency Method
LUO Wei, ZHANG Min, ZHOU Ping, YIN Hong-Cheng
Chin. Phys. Lett. 2009, 26 (11): 114101 .   DOI: 10.1088/0256-307X/26/11/114101
Abstract   PDF(pc) (513KB) ( 645 )
A hybrid high-frequency method is proposed to analyze the bistatic electromagnetic scattering of the ship target on a very large two-dimensional randomly rough sea surface. The scattering of the ship-sea model is evaluated with the method of equivalent currents (MEC). The iterative physical optics method (IPO) is utilized to study the electromagnetic coupling effect caused by the hull and rough surface. The shadowing correction based on the Z-Buffer technology is introduced to eliminate the effects of the irrelevant scattering resources. The validity of the hybrid method is confirmed by the SAR simulation results and the scattering property of the ship-sea model is discussed.
Planar Metamaterial Microwave Absorber for all Wave Polarizations
ZHU Bo, WANG Zheng-Bin, YU Zhen-Zhong, ZHANG Qi, ZHAO Jun-Ming, FENG Yi-Jun, JIANG Tian,
Chin. Phys. Lett. 2009, 26 (11): 114102 .   DOI: 10.1088/0256-307X/26/11/114102
Abstract   PDF(pc) (707KB) ( 1424 )
We present a design for a polarization insensitive metamaterial absorber at 9.5GHz by utilizing properly arranged resonant unit cells with orthogonal polarization sensitivity. Full-wave electromagnetic simulation demonstrates nearly perfect microwave absorption, which has been verified by experimental measurement with a maximum absorption of about 92% for incident wave with different polarizations. Furthermore, we find such a metamaterial thin absorber could work for a wide incident angle ranging from 0°to 50° with absorption no less than 80% for both the transverse electric mode and transverse magnetic mode.
Linear Analysis of Folded Double-Ridged Waveguide
HE Jun, WEI Yan-Yu, GONG Yu-Bin, WANG Wen-Xiang
Chin. Phys. Lett. 2009, 26 (11): 114103 .   DOI: 10.1088/0256-307X/26/11/114103
Abstract   PDF(pc) (550KB) ( 1320 )
A novel slow-wave structure (SWS), the folded double-ridged waveguide structure, is presented and its linear gain properties are investigated. The perturbed dispersion equation is derived and the small signal growth rate is calculated for dimensions of the ridge-loaded region and the parameters of the electron beam. The novel structure has potential applications in the production of high power and broad band radiation. For a cold beam, the linear theory predicts a gain of 1.1-1.27dB/period and a 3-dB small-signal gain bandwidth of 30% in W-band. A comparison between the folded double-ridged waveguide SWS and folded waveguide SWS (FWSWS) shows that with the same physical parameters, the novel SWS has an advantage over the FWSWS on the bandwidth and electron efficiency.
Pulse Operation of Chemical Oxygen-Iodine Laser by Pulsed Gas Discharge with the Assistance of Spark Pre-ionization
LI Guo-Fu, YU Hai-Jun, DUO Li-Ping, JIN Yu-Qi, WANG Jian, SANG Feng-Ting, FANG Ben-Jie, WANG De-Zhen
Chin. Phys. Lett. 2009, 26 (11): 114201 .   DOI: 10.1088/0256-307X/26/11/114201
Abstract   PDF(pc) (550KB) ( 782 )
The continuous wavelength chemical oxygen-iodine laser can be turned into pulse operation mode in order to obtain high energy and high pulse power. We propose an approach to produce iodine atoms instantaneously by pulsed gas discharge with the assistance of spark pre-ionization to achieve the pulsed goal. The influence of spark pre-ionization on discharge homogeneity is discussed. Voltage-current characteristics are shown and discussed in existence of the pre-ionization capacitor and peaking capacitor. The spark pre-ionization and peaking capacitor are very helpful in obtaining a stable and homogeneous discharge. The lasing is achieved at the total pressure of 2.2-2.9kPa and single pulse energy is up to 180mJ, the corresponding specific output energy is 1.0J/L.
Design of a High-Nonlinearity Single-Mode Holey Fiber with Flattened Dispersion around 800nm
WANG Wei, HOU Lan-Tian, LIU Zhao-Lun, ZHOU Gui-Yao,
Chin. Phys. Lett. 2009, 26 (11): 114202 .   DOI: 10.1088/0256-307X/26/11/114202
Abstract   PDF(pc) (442KB) ( 566 )
We numerically demonstrate a high-nonlinearity single-mode holey fiber with flattened dispersion around the Ti-Za laser band at 800nm. The dispersion profile of the fiber has the shape of a quadratic curve, which reaches its maximum 5.96ps・km-1・nm-1 at 800nm and its minimum -0.897ps・km-1・nm-1 at both 750 and 850nm. The nonlinear coefficient is 170W-1km-1 at 800nm and no higher order modes exit. A six-layer air-hole cladding ensures a loss less than 0.067db/m in the 750 to 850nm range. Two more air-hole rings will reduce the loss to below 0.1db/km.
Influence of Post-Annealing Temperature on Properties of Ta-Doped ZnO Transparent Conductive Films
CAO Feng, WANG Yi-Ding, YIN Jing-Zhi, CONG Meng-Long, HAN Liang-Yu
Chin. Phys. Lett. 2009, 26 (11): 114203 .   DOI: 10.1088/0256-307X/26/11/114203
Abstract   PDF(pc) (671KB) ( 885 )
Ta-doped ZnO transparent conductive films are deposited on glass substrates by rf sputtering at 300°C. The influence of the post-annealing temperature on the structural, morphologic, electrical, and optical properties of the films is investigated by x-ray diffraction, Hall measurement, and optical transmission spectroscopy. The lowest resistivity of 3.5×10-4Ω・cm is obtained from the film annealed at 400°C in N2. The average optical transmittance of the films is over 90%. The optical bandgap is found to decrease with the increase of the annealing temperature.
Polarization-Independent Directional Beaming of Light by a Subwavelength Metal Slit
ZHANG Xiang, LI Cheng-Fang
Chin. Phys. Lett. 2009, 26 (11): 114204 .   DOI: 10.1088/0256-307X/26/11/114204
Abstract   PDF(pc) (480KB) ( 558 )
We present the directional beaming effect of light at the terahertz frequency by using a subwavelength slit in the metal film. The metal is dressed with anisotropic dielectric so that both the transverse electric (TE) and transverse magnetic (TM) polarized waves can be well guided on the metal surface and reach the phase matching. By using a periodical array of dielectric ridges and grooves around the slit, the guided waves can be scattered out of the slit and interfere with the transmitted light directly through the slit. The results performed by finite-difference at time-domain computations indicate that the directional beaming of light can be obtained simultaneously for both the TE and TM polarized waves after optimizing the geometric parameters. The structure may find great applications in polarization-independent optical devices such as couplers, connectors, beam collimator, and etc.
Design of Double Cladding Nearly Zero Dispersion Flattened Nonlinear Photonic Crystal Fiber
WANG Wei, HOU Lan-Tian, LU Ming, ZHOU Gui-Yao,
Chin. Phys. Lett. 2009, 26 (11): 114205 .   DOI: 10.1088/0256-307X/26/11/114205
Abstract   PDF(pc) (534KB) ( 835 )
We present a design of double cladding nearly zero dispersion flattened nonlinear photonic crystal fiber (PCF) with the core consisting of seven missing holes. The dispersion of the designed PCF fluctuates from -0.28 to 0.29ps・km-1・nm-1 in the range of 1.35-1.795μm and the dispersion slope is -0.0038ps・km-1・nm-2 at 1.55μm. Due to its small air-hole to air-hole pitch in the inner cladding, the effective mode area is 6.48μm2 and the effective nonlinearity γ is as high as 13.78W-1km-1 at 1.55μm. Two layers of air-hole rings in the outer cladding ensures the loss of the fundamental mode to be 2.9dB/km at 1.55μm and two more air-hole rings can further reduce the fundamental mode's loss to the level of 4.2×10-3,dB/km.
High-Efficiency High-Power Nd:YAG Laser under 885nm Laser Diode Pumping
LI Fang-Qin, ZHANG Xiao-Fu, ZONG Nan, YANG Jing, PENG Qin-Jun, CUI Da-Fu, XU Zu-Yan,
Chin. Phys. Lett. 2009, 26 (11): 114206 .   DOI: 10.1088/0256-307X/26/11/114206
Abstract   PDF(pc) (387KB) ( 1321 )
A high-efficiency high-power Nd:YAG laser under 885nm laser diode (LD) pumping is demonstrated. The laser crystal is carefully designed, and the overlapping between the pump modes and the laser modes is optimized. The maximum output power at 1064nm is 87W under the absorbed pump power 127.7W, corresponding to a slope efficiency of 72.4% and an optical-optical efficiency of 68.1%. The optical-optical efficiency is 58.4% for the pump power emitted directly from the LD. To our best knowledge, this is the maximal optical-optical conversion efficiency obtained for the LD end-pumped Nd:YAG lasers so far.
Analysis of a Novel Ka-band Folded Waveguide Amplifier for Traveling-Wave Tubes
LIAO Ming-Liang, WEI Yan-Yu, HE Jun, GONG Yu-Bin, WANG Wen-Xiang, Gun-Sik Park
Chin. Phys. Lett. 2009, 26 (11): 114207 .   DOI: 10.1088/0256-307X/26/11/114207
Abstract   PDF(pc) (923KB) ( 550 )
A novel Ka-band folded waveguide (FW) amplifier for traveling wave tubes (TWT) is investigated. The dispersion curve and interaction impedance are obtained and compared to the normal FW circuit by numerical simulation. The interaction impedance is higher than a normal circuit through the whole band. We also study the beam-wave interaction in this novel circuit, and the nonlinear large-signal performance is analyzed by a 3-D particle-in-cell code MAGIC3D. A much higher continuous-wave (CW) output power with a considerably shorter circuit compared to a normal circuit is predicted by our simulation. Moreover, the novel FW even has a broader 3-dB bandwidth. It therefore will be useful in designing a miniature but high-power and broadband millimeter-wave TWT.
Intensity Correlation Function of Light Scattering from a Weakly One-Dimensional Random Rough Surface
WU Zhen-Sen, ZHANG Geng
Chin. Phys. Lett. 2009, 26 (11): 114208 .   DOI: 10.1088/0256-307X/26/11/114208
Abstract   PDF(pc) (470KB) ( 625 )
Based on the Kirchhoff approximation and Gaussian moment theorem, we present a general expression of the intensity correlation scattered from a weakly one-dimensional rough surface, which is applicable to the cases by either two different wavelengths or two different angles of incidence. By using a Gaussian surface model, we give the numerical results for the
intensity correlation function with two different wavelengths specially. The results show that with the increasing surface roughness and the decreasing surface correlation length, the correlation function decreases in specular direction and increases in other directions, which indicates that the study of the correlation of the intensities is helpful when investigating the statistical parameters of rough objects. Also the results show that the increase of rms roughness can result in the narrower correlation bandwidth.
A Sensitive Scheme to Observe Weak Photo-Refraction Effects in Some Nonlinear Optical Crystals Pumped by Ultrashort Optical Pulses
XU Shi-Xiang, GAO Yan-Xia, CAI Hua, LI Jing-Zhen
Chin. Phys. Lett. 2009, 26 (11): 114209 .   DOI: 10.1088/0256-307X/26/11/114209
Abstract   PDF(pc) (615KB) ( 397 )
We present a sensitive scheme, for the first time to our knowledge, to observe photo-refraction (PR) effects in some nonlinear optical crystals, e.g. β-BBO, LBO and BIBO, pumped by an intense ultrashort laser pulse chain. These quite weak effects are "amplified' by sensitive cw intracavity loss modulation. Our results show that they are repeatable and are dependent on pumping power and wavelength, and their response time ranges from tens of seconds to several minutes. The recorded dynamical transitions between the self-focusing to the self-defocusing (or vice versa) induced by the PR effect may be critically important for us to give more insight into the stability of some cascade nonlinear frequency conversions, e.g. multi-stage optical parametric amplifiers.

See Also: XU Shi-Xiang, Withdrawal of Chinese Physics Letters 26 (2009) 114209

Measurement of Refractive Index for High Reflectance Materials with Terahertz Time Domain Reflection Spectroscopy
SUN Wen-Feng, WANG Xin-Ke, ZHANG Yan
Chin. Phys. Lett. 2009, 26 (11): 114210 .   DOI: 10.1088/0256-307X/26/11/114210
Abstract   PDF(pc) (374KB) ( 2590 )
A method to measure the refractive index for high reflectance materials in the terahertz range with terahertz time domain reflection spectroscopy is proposed. In this method, the THz waveforms reflected by a silicon wafer and high reflectance sample are measured respectively. The refractive index of the silicon wafer, measured with the THz time domain transmission spectroscopy, is used as a reference in the THz time domain reflective spectroscopy. Therefore, the complex refractive index of the sample can be obtained by resorting to the known reflective index of the silicon and the Fresnel law. To improve the accuracy of the phase shift, the Kramers-Kronig transform is adopted. This method is also verified by the index of the silicon in THz reflection spectroscopy. The bulk metal plates have been taken as the sample, and the experimentally obtained metallic refractive indexes are compared with the simple Drude model.
Enhanced Spin Depolarization and Storage Time in a Rb Vapor
QI Yue-Rong, GAO Hong, ZHANG Shou-Gang
Chin. Phys. Lett. 2009, 26 (11): 114211 .   DOI: 10.1088/0256-307X/26/11/114211
Abstract   PDF(pc) (342KB) ( 658 )
The experiment of measuring the spin depolarized time and light storage time in a Rb vapor under different conditions is performed. Typically, these measurements are accomplished in three different containers: atoms in a bare glass cell, atoms in a buffer gas cell, and atoms in a tetracontane (C40H82) coating cell. The increasing depolarization and storage times are observed in both the buffer gas cell and the tetracontane coating cell. In the latter case, a storage time greater than 400μs is obtained.
Coupling of Acoustical Plane p-Wave to a Cased Borehole
QIU Chang-Chun, ZHANG Bi-Xing, ZHANG Yu-Jun, CUI Zhi-Wen
Chin. Phys. Lett. 2009, 26 (11): 114301 .   DOI: 10.1088/0256-307X/26/11/114301
Abstract   PDF(pc) (1952KB) ( 503 )
Theoretical and numerical study on the coupling acoustic field of the plane p-wave to a cased borehole is carried out. The medium outside the cased borehole is modeled as the porous medium. The scattering field characteristics in the cased borehole are investigated when a plane fast p-wave is incident in tilt to the cased borehole from the porous medium. The scattering fields inside and outside the cased borehole are analyzed and deduced by Biot's theory under the boundary conditions on each interface, and they are numerically studied. It is found that the scattering field has strong resonant characteristics and there exists a series of resonant frequencies and peaks. The effects of the frequency, radii of each interface, incident angle, porosity, and other parameters on the resonant acoustic field have been investigated in detail in the fast and slow formations respectively.
The resonant characteristics of the scattering field are also analyzed from the physical sense.
Theoretical Development of Nonlinear Spring Models for the Second Harmonics on an Interface between Two Solids
AN Zhi-Wu, WANG Xiao-Min, LI Ming-Xuan, DENG Ming-Xi, MAO Jie
Chin. Phys. Lett. 2009, 26 (11): 114302 .   DOI: 10.1088/0256-307X/26/11/114302
Abstract   PDF(pc) (350KB) ( 598 )
Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representations termed as `nonlinear spring models' relating the stresses and displacements on both sides of the interface are rigorously developed by asymptotic expansions of the wave fields for an elastic layer in the limit of small thickness to wavelength ratio. The applicability for the so-called nonlinear spring models is numerically analyzed by comparison with exact solutions for the second harmonic wave reflections. The present nonlinear spring models lay a theoretical foundation to evaluate the interfacial properties by nonlinear acoustic waves.
Water Surface Wave in a Trough with Periodical Topographical Bottom under Vertical Vibration
HU Yi, MIAO Guo-Qing, WEI Rong-Jue
Chin. Phys. Lett. 2009, 26 (11): 114303 .   DOI: 10.1088/0256-307X/26/11/114303
Abstract   PDF(pc) (413KB) ( 618 )
We investigate the water surface waves in a vertically vibrated long rectangular trough with several identical Plexiglas rectangles lined periodically on the bottom. The band structure is computed theoretically by the method of transfer matrix. Some interesting phenomena, such as the localized wave, especially the solitary-like wave inside the band gap, are observed in the experiments.
Influence of Rayleigh-Taylor Instability on Liquid Propellant Reorientation in a Low-Gravity Environment
LI Zhang-Guo, LIU Qiu-Sheng, LIU Rong, HU Wei, DENG Xin-Yu
Chin. Phys. Lett. 2009, 26 (11): 114701 .   DOI: 10.1088/0256-307X/26/11/114701
Abstract   PDF(pc) (754KB) ( 618 )
A computational simulation is conducted to investigate the influence of Rayleigh-Taylor instability on liquid propellant reorientation flow dynamics for the tank of CZ-3A launch vehicle series fuel tanks in a low-gravity environment. The volume-of-fluid (VOF) method is used to simulate the free surface flow of gas-liquid. The process of the liquid propellant reorientation started from initially flat and curved interfaces are numerically studied. These two different initial conditions of the gas-liquid interface result in two modes of liquid flow. It is found that the Rayleigh-Taylor instability can be reduced evidently at the initial gas-liquid interface with a high curve during the process of liquid reorientation in a low-gravity environment.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Effect of Air Gap on Uniformity of Large-Scale Surface-Wave Plasma
LAN Chao-Hui, HU Xi-Wei, JIANG Zhong-He, LIU Ming-Hai
Chin. Phys. Lett. 2009, 26 (11): 115201 .   DOI: 10.1088/0256-307X/26/11/115201
Abstract   PDF(pc) (1017KB) ( 636 )
The effect of air gap on the uniformity of large-scale surface-wave plasma (SWP) in a rectangular chamber device is studied by using three-dimensional numerical analyses based on the finite difference time-domain (FDTD) approximation to Maxwell's equations and plasma fluid model. The spatial distributions of surface wave excited by slot-antenna array and the plasma parameters such as electron density and temperature are presented. For different air gap thicknesses, the results show that the existence of air gap would severely weaken the excitations of the surface wave and thereby the SWP. Thus the air gap should be eliminated completely in the design of the SWP source, which is opposite to the former research results.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
A Model for Fractal Dimension of Rough Surfaces
LI Jian-Hua, YU Bo-Ming, ZOU Ming-Qing
Chin. Phys. Lett. 2009, 26 (11): 116101 .   DOI: 10.1088/0256-307X/26/11/116101
Abstract   PDF(pc) (523KB) ( 606 )
We report a model for the fractal dimension Ds of rough surfaces based on the fractal distribution of roughness elements on surfaces and the fractal character of surface profiles. The proposed model for the fractal dimension Ds is expressed as a function of the fractal dimensions D for conic roughness diameter/height and Dp for surface profile, maximum roughness base diameter λmax, the ratio β of conic roughness height to its base radius as well as the ratio λminmax of the minimum to the maximal base diameter.
Structural and Electrical Properties of Single Crystalline a-Doped ZnO Thin Films Grown by Molecular Beam Epitaxy
LU Zhong-Lin, , ZOU Wen-Qin, XU Ming-Xiang, ZHANG Feng-Ming, DU You-Wei
Chin. Phys. Lett. 2009, 26 (11): 116102 .   DOI: 10.1088/0256-307X/26/11/116102
Abstract   PDF(pc) (595KB) ( 1441 )
High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a-plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2at.% and the lowest resistivity can reach 1.92×10-4Ω・cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.
Synthesis and Properties of Magnetic Composites of Carbon Nanotubes/Fe Nanoparticle
XU Mei-Hua, QI Xiao-Si, ZHONG Wei, YE Xiao-Juan, DENG Yu, AUChaktong, JIN Chang-Qing, YANG Zai-Xing, DU You-Wei
Chin. Phys. Lett. 2009, 26 (11): 116103 .   DOI: 10.1088/0256-307X/26/11/116103
Abstract   PDF(pc) (567KB) ( 1033 )
Magnetic composites of carbon nanotubes (CNTs) are synthesized by the in situ catalytic decomposition of benzene at temperatures as low as 400°C over Fe nanoparticles (mean grain size = 26nm) produced by sol-gel fabrication and hydrogen reduction. The yield of CNT composite is up to about 3025% in a run of 6h. FE-SEM and HRTEM investigations reveal that one-dimensional carbon species are produced in a large quantity. A relatively high value of magnetization is observed for the composite due to the encapsulation of ferromagnetic Fe3C and/or α-Fe. The method is suitable for the mass-production of CNT composites that contain magnetic nanoparticles.
Electro-oxidation of Formic Acid on Carbon Supported Edge-Truncated Cubic Platinum Nanoparticles Catalysts
LI She-Qiang, FU Xing-Qiu, HU Bing, DENG Jia-Jun, CHEN Lei
Chin. Phys. Lett. 2009, 26 (11): 116104 .   DOI: 10.1088/0256-307X/26/11/116104
Abstract   PDF(pc) (495KB) ( 706 )
The oxidation of formic acid on edge-truncated cubic platinum nanoparticles/C catalysts is investigated. X-ray photoelectron spectroscopy analysis indicates that the surface of edge-truncated cubic platinum nanoparticles is composed of two types of coordination sites. The oxidation behavior of formic acid on edge-truncated cubic platinum nanoparticles/C is investigated using cyclic voltammetry. The apparent activation energies are found to be 54.2, 55.0, 61.8, 69.5, 71.9, 69.26, 65.28kJ/mol at 0.15, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7V, respectively. A specific surface area activity of 1.76mA・cm-2 at 0.4V indicates that the edge-truncated cubic Platinum nanoparticles are a promising anode catalyst for direct formic acid fuel cells.
Efficient and Robust Design for Absorbing Boundary Conditions in Atomistic Computations
FANG Ming, TANG Shao-Qiang
Chin. Phys. Lett. 2009, 26 (11): 116201 .   DOI: 10.1088/0256-307X/26/11/116201
Abstract   PDF(pc) (360KB) ( 555 )
We propose an efficient and robust way to design absorbing boundary conditions in atomistic computations. An optimal discrete boundary condition is obtained by minimizing a functional of a reflection coefficient integral over a range of wave numbers. The minimization is performed with respect to a set of wave numbers, at which transparent absorption is reached. Compared with the optimization with respect to the boundary condition coefficients suggested by E and Huang [Phys.Rev.Lett. 87(2001)133501], we reduce considerably the number of independent variables and the computing cost. We further demonstrate with numerical examples that both the optimization and the wave absorption are more robust in the proposed design.
Fabrication and Characterization of Multi-layer Heat Mirror with Photocatalytic Properties
Tran Le, Tuan Tran, Huu Chi Nguyen, Dac Ngoc Son Luu, Minh Nam Hoang, Dinh Quan Nguyen
Chin. Phys. Lett. 2009, 26 (11): 116801 .   DOI: 10.1088/0256-307X/26/11/116801
Abstract   PDF(pc) (587KB) ( 746 )
A novel TiO2(5)/TiO2(buffer)/Ti(4)/Ag(3)/Ti(2)/TiO2(1) multi-layer film coating with corning glass is designed and fabricated by a dc magnetron sputtering method as a renovation of the well-known TiO2/Ti/Ag/Ti/TiO2 system in order to obtain a heat mirror system with photocatalytic properties due to sufficient thickness of the TiO2 layer. The outer TiO2 layer is fabricated in two steps, possibly claimed as two layers TiO2(5) and TiO2(buffer), among which the 70-nm-thick layer TiO2(buffer) deposited in poor oxygen effectively minimizes the oxidation toward its neighbor Ti(4) layer. The optimal total thickness of the TiO2(5) and TiO2(buffer) di-layer is found to be 300nm to yield a highly photo-catalytic property of the film without affecting the optical properties considerably. This multi-layer film can transmit light of above 75-85% in the visible spectrum (380≤λ ≤760nm) and reflect radiation of above 90% in the infrared spectrum (λ≥760nm). Such multi-layer coatings are strongly recommended not only as promising transparent heat mirrors but also as photo-catalytic films for architectural window coatings.
Growth of High Quality Strained-Si on Ultra-Thin SiGe-on-Insulator Substrate
LIU Xu-Yan, LIU Wei-Li, MA Xiao-Bo, CHEN Chao, SONG Zhi-Tang, LIN Cheng-Lu
Chin. Phys. Lett. 2009, 26 (11): 116802 .   DOI: 10.1088/0256-307X/26/11/116802
Abstract   PDF(pc) (566KB) ( 589 )
Ultra-thin and near-fully relaxed SiGe substrate is fabricated using a modified Ge condensation technique, and then a 25-nm-thick biaxially tensile strained-Si with a low rms roughness is epitaxially deposited on a SiGe-on-Insulator (SGOI) substrate by ultra high vacuum chemical vapor deposition (UHVCVD). High-Resolution cross-sectional transmission electron microscope (HR-XTEM) observations reveal that the strained-Si/SiGe layer is dislocation-free and the atoms at the interface are well aligned. Furthermore, secondary ion mass spectrometry (SIMS) results show a sharp interface between layers and a uniform distribution of Ge in the SiGe layer. One percent in-plane tensile strain in the strained-Si layer is confirmed by ultraviolet (UV) Raman spectra,
and the stress maintained even after a 30-s rapid thermal annealing (RTA) process at 1000°C. According to those results, devices based on strained-Si are expected to have a better performance than the conventional ones.
Analogies between a Meniscus and a Cantilever
LIU Jian-Lin
Chin. Phys. Lett. 2009, 26 (11): 116803 .   DOI: 10.1088/0256-307X/26/11/116803
Abstract   PDF(pc) (353KB) ( 613 )
Systematic and quantitative analyses of exact analogies between a meniscus and an elastica are performed. It is shown that the two governing equations take the same style after coordinate translation and scale transformation. The morphologies of the liquid bridge and the cantilever are calculated in terms of elliptic integrations, which can be reduced to the same shape after converting the boundary conditions. The present analyses can make us grasp the nature of this physical phenomenon deeply and show some inspiration for designing the analogy experiments. Moreover, the calculated results are helpful to engineering applications, such as design and fabrication of MEMS, and micro-manipulations in micro/nano- technology.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Effects of Grain Boundary Barrier in ZnO/Si Heterostructure
LIU Bing-Ce, LIU Ci-Hui, FU Zhu-Xi, Yi Bo
Chin. Phys. Lett. 2009, 26 (11): 117101 .   DOI: 10.1088/0256-307X/26/11/117101
Abstract   PDF(pc) (883KB) ( 895 )
The influence of ZnO microstructure on electrical barriers is investigated using capacitance-voltage (C-V), current-voltage (I-V) and deep level transient spectroscopy (DLTS) measurements. A deep level center located at EC-0.24eV obtained by DLTS in the ZnO films is an intrinsic defect related to Zni. The surface states in the ZnO grains that have acceptor behavior of capturing electrons from Zni defects result in the formation of grain barriers. In addition, we find that the current transport is dominated by grain barriers after annealing at 600°C at O2 ambient. With the increment of the annealing temperature, the current transport mechanism of ZnO/Si heterostructure is mainly dominated by thermo-emission.
Electronic Structure and Elastic Properties of Ti3AlC from First-Principles Calculations
DU Yu-Lei
Chin. Phys. Lett. 2009, 26 (11): 117102 .   DOI: 10.1088/0256-307X/26/11/117102
Abstract   PDF(pc) (490KB) ( 952 )
We perform a first-principles study on the electronic structure and elastic properties of Ti3AlC with an antiperovskite structure. The absence of band gap at the Fermi level and the finite value of the density of states at the Fermi energy reveal the metallic behavior of this compound. The elastic constants of Ti3AlC are derived yielding c11=356GPa, c12=55GPa, c44=157GPa. The bulk modulus B, shear modulus G and Young's modulus E are determined to be 156, 151 and 342GPa, respectively. These properties are compared with those of Ti3AlC2 and Ti2AlC with a layered structure in the Ti-Al-C system and Fe3AlC with the same antiperovskite structure.
Metal-Insulator Transition in CuIr2(S1-xTex)4
YUE Song, DU Juan, ZHANG Yuan, ZHANG Yu-Heng
Chin. Phys. Lett. 2009, 26 (11): 117103 .   DOI: 10.1088/0256-307X/26/11/117103
Abstract   PDF(pc) (426KB) ( 587 )
The resistivity and magnetization for the CuIr2(S1-xTex)4 (0≤x≤0.10) system are investigated. Compared with the Se doping, the substitution of Te for S leads to stronger suppression on the metal-insulator transition. Vacancies and imperfections in the sample lattice are found to modify the magnetization, which can be qualitatively understood to consist of the Pauli paramagnetism, Landau diamagnetism, Larmor diamagnetism and Curie magnetism contributions.
Various Recipes of SiNx Passivated AlGaN/GaN High Electron Mobility Transistors in Correlation with Current Slump
YANG Ling, HAO Yue, MA Xiao-Hua, QUAN Si, HU Gui-Zhou, JIANG Shou-Gao, YANG Li-Yuan
Chin. Phys. Lett. 2009, 26 (11): 117104 .   DOI: 10.1088/0256-307X/26/11/117104
Abstract   PDF(pc) (429KB) ( 1047 )
The current slump of different recipes of SiNx passivated AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. The dc and pulsed current-voltage curves of AlGaN/GaN HEMTs using different recipes are analyzed. It is found that passivation leakage has a strong relationship with NH3 flow in the plasma-enhanced chemical vapor phase deposition process,
which has impacted on the current collapse of SiNx passivated devices. We analyze the pulsed IDS-VDS characteristics of different recipes of SiNx passivation devices for different combinations of gate and drain quiescent biases (VGS0, VDS0) of (0, 0), (-6, 0), (-6, 15) and (0, 15)V. The possible mechanisms are the traps in SiNx passivation capturing the electrons and the surface states at the SiNx/AlGaN interface, which can affect the channel of two-dimensional electron gas and cause the current collapse.
Spin Relaxation of Electrons in Single InAs Quantum Dots
MA Shan-Shan, DOU Xiu-Ming, CHANG Xiu-Ying, SUN Bao-Quan, XIONG Yong-Hua, NIU Zhi-Chuan, NI Hai-Qiao
Chin. Phys. Lett. 2009, 26 (11): 117201 .   DOI: 10.1088/0256-307X/26/11/117201
Abstract   PDF(pc) (411KB) ( 482 )
By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots (QDs) with the configuration of positively charged excitons X+ (one electron, two holes). The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.
Properties of Graphene Based Parametric Pump
LUO Song-Lin, WEI Ya-Dong
Chin. Phys. Lett. 2009, 26 (11): 117202 .   DOI: 10.1088/0256-307X/26/11/117202
Abstract   PDF(pc) (520KB) ( 562 )
The adiabatic parametric electron pump of the infinite zigzag graphene ribbons and the infinite armchair graphene ribbons is investigated by the tight binding method. The pumping signals are added by two gates around the ribbons. It is shown that the dc current can be pumped out by cyclically varying the two gate voltages and the pumped current strongly depends on the driving frequency, the pumping amplitude and the phase difference of the gate voltages. The pumped current is mediated by the graphene energy levels and its peaks occur around the energies where transmission coefficients and density of states are large. The pump current may give one peak or two opposite peaks corresponding to each transmission peak or transmission pair peaks. The height and width of the current peaks increase with the amplitude of the pumping driving voltages. The pumped current is antisymmetric about the phase difference Φ=π and for small pumping amplitude the pumped current is a sinusoidal function of the phase difference. Some graphene ribbons, although with different widths, have very similar contours of the transmission coefficients and give the same pumped current figures.
Derivative of Electron Density in Non-Equilibrium Green's Function Technique and Its Application to Boost Performance of Convergence
YUAN Ze, CHEN Zhi-Dong, ZHANG Jin-Yu, HE Yu, ZHANG Ming, YU Zhi-Ping
Chin. Phys. Lett. 2009, 26 (11): 117203 .   DOI: 10.1088/0256-307X/26/11/117203
Abstract   PDF(pc) (814KB) ( 498 )
The non-equilibrium Green's function (NEGF) technique provides a solid foundation for the development of quantum mechanical simulators. However, the convergence is always of great concern. We present a general analytical formalism to acquire the accurate derivative of electron density with respect to electrical potential in the framework of NEGF. This formalism not only provides physical insight on non-local quantum phenomena in device
simulation, but also can be used to set up a new scheme in solving the Poisson equation to boost the performance of convergence when the NEGF and Poisson equations are solved self-consistently. This method is illustrated by a simple one-dimensional example of an N++N+N++ resistor. The total simulation time and iteration number are largely reduced.
Synthesis and Multiferroic Properties of BiFeO3 Nanotubes
WANG Jing, LI Mei-Ya, LIU Xiao-Lian, PEI Ling, LIU Jun, YU Ben-Fang, ZHAO Xing-Zhong,
Chin. Phys. Lett. 2009, 26 (11): 117301 .   DOI: 10.1088/0256-307X/26/11/117301
Abstract   PDF(pc) (1016KB) ( 778 )
Highly ordered BiFeO3(BFO) nanotubes with about 200nm in diameter and 60μm in length are fabricated by a sol-gel AAO template method. A perovskite-type structure of BFO is confirmed in the nanotubes by transmission electron microscopy and selected area electron diffraction analysis. The coexistence of ferroelectric and ferromagnetic ordering of these BFO nanotubes at room temperature is demonstrated, giving a remnant polarization of 26μC/cm2, a low coercive electric field of 60kV/cm, and a magnetization of 0.18emu/g. In addition, it is found that the leakage behavior of these nanotubes is dominated by the ohmic contact mechanism.
Influence of Oxygen Pressure on Structural and Sensing Properties of β-Ga2O3 Nanomaterial by Thermal Evaporation
MA Hai-Lin, FAN Duo-Wang,
Chin. Phys. Lett. 2009, 26 (11): 117302 .   DOI: 10.1088/0256-307X/26/11/117302
Abstract   PDF(pc) (496KB) ( 611 )
We prepare the gallium oxide (β-Ga2O3) nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and research their oxygen sensing under UV illumination with different oxygen pressures. X-ray diffraction reveals that the synthesized product is monoclinic gallium oxide, it is further confirmed by electron diffraction of transmission electron microscope, and its morphology through the observation using scanning electron microscope reveals that β-Ga2O3 nanobelts with a breadth less than 100nm and length of several micrometers are synthesized under low oxygen pressure, while the nano/microbelts are synthesized under high oxygen pressure. Room-temperature oxygen sensing is tested under at 254nm illumination and it is found that the current decreases quickly first and then slowly with oxygen pressure from low to high.
Operation Mechanism of Double-Walled Carbon Nanotubes Transistors Investigated By ab initio Calculations
LAN Hai-Ping, ZHANG Shuang
Chin. Phys. Lett. 2009, 26 (11): 117303 .   DOI: 10.1088/0256-307X/26/11/117303
Abstract   PDF(pc) (529KB) ( 542 )
Recently, a new switching characteristic of double-walled carbon nanotubes (DWNTs) transistors is found in during experiments. We carry out a series of ab intio calculations on DWNTs' electronic properities, together with verification on the electronic response under the electric field. Our results reveal that the peculiar energy states relation in DWNTs and related contact modes should account for the distinct switching behavior of DWNT transistors. We believe these results have important implications in the fabrication and understanding of electronic devices with DWNTs.
Microstructure and Magnetic Domains of Iron Films on Liquid Surfaces
XIE Jian-Ping, XIA A-Gen, ZHANG Chu-Hang, YANG Bo, FANG Zheng-Nong, YE Gao-Xiang
Chin. Phys. Lett. 2009, 26 (11): 117501 .   DOI: 10.1088/0256-307X/26/11/117501
Abstract   PDF(pc) (862KB) ( 794 )
Iron (Fe) films with a thickness ranging from 1.0nm to 80.0nm are deposited on silicone oil surfaces by a vapor phase deposition method. The films with a thickness of d<2.0nm do not exhibit planar morphology but ramified aggregates instead. Magnetic force microscopy studies for the Fe films (10.0nm≤d ≤80.0nm) show that the domain wall structure is widespread and irregularly shaped and the oscillation phase shift &#8710; θ, which records as the magnetic force image, changes from 0.29° to 0.81°. Correspondingly, the magnetic force gradient varies from 1.4×10-3 to 4.0×10-3 N/m, respectively. In our measurement, the characteristic domain walls, such as Bloch walls, Néel walls and cross-tie walls, are not observed in the film system clearly.
Grain Size Effect on Electrical Conductivity and Giant Magnetoresistance of Bulk Magnetic Polycrystals
LUO Wei, ZHU Lin-Li, ZHENG Xiao-Jing
Chin. Phys. Lett. 2009, 26 (11): 117502 .   DOI: 10.1088/0256-307X/26/11/117502
Abstract   PDF(pc) (384KB) ( 3847 )
By solving the Boltzmann transport equation and considering the spin-dependent grain boundary scattering, the distribution of electrons in grains and the electrical transport properties in the applied magnetic field are studied. With regard to the dominant influence of grain boundary scattering which is taken as a boundary condition for the electrical transport, the grain size-dependent electrical conductivity is investigated. In addition, the reorientation of the relative magnetization between grains brings the change of the electron spin when the magnetonanocrystalline material is subjected to the magnetic field, resulting in the remarkable giant magnetoresistance effect.
Room-Temperature Anisotropic Ferromagnetism in Fe-Doped In2O3 Heteroepitaxial Films
XING Peng-Fei, CHEN Yan-Xue, TANG Min-Jian, YAN Shi-Shen, LIU Guo-Lei, MEI Liang-Mo, JIAO Jun,
Chin. Phys. Lett. 2009, 26 (11): 117503 .   DOI: 10.1088/0256-307X/26/11/117503
Abstract   PDF(pc) (681KB) ( 775 )
Fe-doped In2O3 films are grown epitaxially on YSZ (100) substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the (100) direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2.5kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.
Effect of Temperature on Structural and Magnetic Properties of Laser Ablated Iron Oxide Deposited on Si(100)
Shahid M. Ramay, Saadat A. Siddiqi, M. Sabieh Anwar, S. C. Shin
Chin. Phys. Lett. 2009, 26 (11): 117504 .   DOI: 10.1088/0256-307X/26/11/117504
Abstract   PDF(pc) (576KB) ( 757 )
We fabricate Fe3O4 thin films on Si(100) substrates at different temperatures using pulsed laser deposition, and study the effect of annealing and deposition temperature on the structural and magnetic properties of Fe3O4 thin films. Subsequently, the films are characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and vibrating sample magnetometery (VSM). The XRD results of these films confirm the presence of the Fe3O4 phase and show room-temperature ferromagnetism, as observed with VSM. We demonstrate the optimized deposition and annealing conditions for an enhanced magnetization of 854emu/cm3 that is very high when compared to the bulk sample.
Improvement in Dielectric Tunability of Ba0.6Sr0.4TiO4-Mg2TiO4 Composite Ceramics via Heterogeneous Nucleation Processing
WANG Zhuo, LI Yong-Xiang
Chin. Phys. Lett. 2009, 26 (11): 117701 .   DOI: 10.1088/0256-307X/26/11/117701
Abstract   PDF(pc) (661KB) ( 699 )
Dielectric tunable composite ceramics Ba0.6Sr0.4TiO3-Mg2TiO4 (BST-MT) are prepared with a heterogeneous nucleation sol-gel approach. The Mg2TiO4 powders are synthesized by the conventional solid-state reaction method. The micro-sized MT powders with dispersant Ciba-4010 are introduced into Ba-Sr-Ti sol to obtain uniform and homogeneous mixture compounds with nano-sized BST particles synthesized via heterogeneous nucleation (HN) in the sol-gel process. Thus, the microstructural and dielectric properties can be tailored. The dielectric constants of BST-MT composite ceramics can be adjusted in a large range from 294 to 1790, and the dielectric tunability can be adjusted from 29.4% to 37.0% with different MT contents from 60wt% to 20wt%. Compared to the samples prepared by the conventional solid-state (SS) process, the BST-MT composite ceramics by the heterogeneous nucleation sol-gel process exhibit a more uniform microstructure, and improve dielectric properties.
AlGaN-Based Deep-Ultraviolet Light Emitting Diodes Fabricated on AlN/sapphire Template
SANG Li-Wen, QIN Zhi-Xin, FANG Hao, ZHANG Yan-Zhao, LI Tao, XU Zheng-Yu, YANG Zhi-Jian, SHEN Bo, ZHANG Guo-Yi, LI Shu-Ping, YANG Wei-Huang, CHEN Hang-Yang, LIU Da-Yi, KANG Jun-Yong
Chin. Phys. Lett. 2009, 26 (11): 117801 .   DOI: 10.1088/0256-307X/26/11/117801
Abstract   PDF(pc) (530KB) ( 1099 )
We report on the growth and fabrication of deep ultraviolet (DUV) light emitting diodes (LEDs) on an AlN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.
Energy Transfer from Ce3+ to Eu2+ in LiSrBO3 and Its Potential Application in UV-LED-Based White LEDs
WANG Zhi-Jun, LI Pan-Lai, YANG Zhi-Ping, GUO Qing-Lin, FU Guang-Sheng
Chin. Phys. Lett. 2009, 26 (11): 117802 .   DOI: 10.1088/0256-307X/26/11/117802
Abstract   PDF(pc) (506KB) ( 617 )
Ce3+/Eu2+ codoped LiSrBO3 phosphor is synthesized, and its luminescent characteristics are investigated. LiSrBO3:Ce3+,Eu2+ phosphor exhibits varied hues from blue to white and eventually to yellow by resonance-type energy transfer from Ce3+ ion to Eu2+ ion and tuning the relative proportion of Ce3+/Eu2+ properly. Energy transfer mechanism in LiSrBO3:Ce3+, Eu2+ phosphor is dominated by the dipole-dipole interaction, and the critical distance of the energy transfer is estimated to be about 2nm by both spectral overlap and concentration quenching methods. Under UV radiation, white light is generated by coupling 436 and 565nm emission bands attributed to Ce3+ and Eu2+ radiations, respectively.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Simulation of SET Operation in Phase-Change Random Access Memories with Heater Addition and Ring-Type Contactor for Low-Power Consumption by Finite Element Modeling
GONG Yue-Feng, SONG Zhi-Tang, LING Yun, LIU Yan, FENG Song-Lin
Chin. Phys. Lett. 2009, 26 (11): 118101 .   DOI: 10.1088/0256-307X/26/11/118101
Abstract   PDF(pc) (510KB) ( 638 )
A three-dimensional finite element model for phase change random access memory (PCRAM) is established for comprehensive electrical and thermal analysis during SET operation. The SET behaviours of the heater addition structure (HS) and the ring-type contact in bottom electrode (RIB) structure are compared with each other. There are two ways to reduce the RESET current, applying a high resistivity interfacial layer and building a new device structure. The simulation results indicate that the variation of SET current with different power reduction ways is little. This study takes the RESET and SET operation current into consideration, showing that the RIB structure PCRAM cell is suitable for future devices with high heat efficiency and high-density, due to its high heat efficiency in RESET operation.
Structural Feature and Solute Trapping of Rapidly Grown Ni3Sn Intermetallic Compound
QIN Hai-Yan, WANG Wei-Li, WEI Bing-Bo
Chin. Phys. Lett. 2009, 26 (11): 118102 .   DOI: 10.1088/0256-307X/26/11/118102
Abstract   PDF(pc) (735KB) ( 511 )
The rapid dendritic growth of primary Ni3Sn phase in undercooled Ni-30.9%Sn-5%Ge alloy is investigated by using the glass fluxing technique. The dendritic growth velocity of Ni3Sn compound is measured as a function of undercooling, and a velocity of 2.47m/s is achieved at the maximum undercooling of 251K (0.17TL). The addition of the Ge element reduces its growth velocity as compared with the binary Ni75Sn25 alloy. During rapid solidification, the Ni3Sn compound behaves like a normal solid solution and it displays a morphological transition of "coarse dendrite-equiaxed grain-vermicular structure'' with the increase of undercooling. Significant solute trapping of Ge atoms occurs in the whole undercooling range.
Bilayer Photoresist Insulator for High Performance Organic Thin-Film Transistors on Plastic Films
WANG He, LI Chun-Hong, PAN Feng, WANG Hai-Bo, YAN Dong-Hang
Chin. Phys. Lett. 2009, 26 (11): 118501 .   DOI: 10.1088/0256-307X/26/11/118501
Abstract   PDF(pc) (797KB) ( 591 )
A novel bilayer photoresist insulator is applied in flexible vanadyl-phthalocyanine (VOPc) organic thin-film transistors (OTFTs). The micron-size patterns of this photoresisit insulator can be directly defined only by photolithography without the etching process. Furthermore, these OTFTs exhibit high field-effect mobility (about 0.8cm2/Vs) and current on/off ratio (about 106). In particular, they show rather low hysteresis (<1V). The results demonstrate that this bilayer photoresist insulator can be applied in large-area electronics and in the facilitation of patterning insulators.
Environmental Impacts on Spiking Properties in Hodgkin-Huxley Neuron with Direct Current Stimulus
YUAN Chang-Qing, ZHAO Tong-Jun, ZHAN Yong, ZHANG Su-Hua, LIU Hui, ZHANG Yu-Hong
Chin. Phys. Lett. 2009, 26 (11): 118701 .   DOI: 10.1088/0256-307X/26/11/118701
Abstract   PDF(pc) (432KB) ( 500 )
Based on the well accepted Hodgkin-Huxley neuron model, the neuronal intrinsic excitability is studied when the neuron is subject to varying environmental temperatures, the typical impact for its regulating ways. With computer simulation, it is found that altering environmental temperature can improve or inhibit the neuronal intrinsic excitability so as to influence the neuronal spiking properties. The impacts from environmental factors can be understood that the neuronal spiking threshold is essentially influenced by the fluctuations in the environment. With the environmental temperature varying, burst spiking is realized for the neuronal membrane voltage because of the environment-dependent spiking threshold. This burst induced by changes in spiking threshold is different from that excited by input currents or other stimulus.
Worldwide Marine Transportation Network: Efficiency and Container Throughput
DENG Wei-Bing, GUO Long, LI Wei, CAI Xu
Chin. Phys. Lett. 2009, 26 (11): 118901 .   DOI: 10.1088/0256-307X/26/11/118901
Abstract   PDF(pc) (377KB) ( 860 )
Through empirical analysis of the global structure of the Worldwide Marine Transportation Network (WMTN), we find that the WMTN, a small-world network, exhibits an exponential-like degree distribution. We hereby investigate the efficiency of the WMTN by employing a simple definition. Compared with many other transportation networks, the WMTN possesses relatively low efficiency. Furthermore, by exploring the relationship between the topological structure and the container throughput, we find that strong correlations exist among the container throughout the degree and the clustering coefficient. Also, considering the navigational process that a ship travels in a real shipping line, we obtain that the weight of a seaport is proportional to the total probability contributed by all the passing shipping lines.
A Realistic Cellular Automaton Model for Synchronized Traffic Flow
ZHAO Bo-Han, HU Mao-Bin, JIANG Rui, WU Qing-Song
Chin. Phys. Lett. 2009, 26 (11): 118902 .   DOI: 10.1088/0256-307X/26/11/118902
Abstract   PDF(pc) (973KB) ( 668 )
A cellular automaton model is proposed to consider the anticipation effect in drivers' behavior. It is shown that the anticipation effect can be one of the origins of synchronized traffic flow. With anticipation effect, the congested traffic flow simulated by the model exhibits the features of synchronized flow. The spatiotemporal patterns induced by an on-ramp are also consistent with the three-phase traffic theory. Since the origin of synchronized flow is still controversial, our work can shed some light on the mechanism of synchronized flow.
Diffusion-Based Recommendation in Collaborative Tagging Systems
SHANG Ming-Sheng, ZHANG Zi-Ke
Chin. Phys. Lett. 2009, 26 (11): 118903 .   DOI: 10.1088/0256-307X/26/11/118903
Abstract   PDF(pc) (364KB) ( 1020 )
Recently, collaborative tagging systems have attracted more and more attention and have been widely applied in web systems. Tags provide highly abstracted information about personal preferences and item content, and therefore have the potential to help in improving better personalized recommendations. We propose a diffusion-based recommendation algorithm considering the personal vocabulary and evaluate it in a real-world dataset: Del.icio.us. Experimental results demonstrate that the usage of tag information can significantly improve the accuracy of personalized recommendations.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
Evolution of Ring Current Protons Induced by Electromagnetic Ion Cyclotron Waves
XIAO Fu-Liang, TIAN Tian, CHEN Liang-Xu, SU Zhen-Peng, ZHENG Hui-Nan
Chin. Phys. Lett. 2009, 26 (11): 119401 .   DOI: 10.1088/0256-307X/26/11/119401
Abstract   PDF(pc) (478KB) ( 359 )
We investigate the evolution of the phase space density (PSD) of ring current protons induced by electromagnetic ion cyclotron (EMIC) waves at the location L=3.5, calculate the diffusion coefficients in pitch angle and momentum, and solve the standard two-dimensional Fokker-Planck diffusion equation. The pitch angle diffusion coefficient is found to be larger than the momentum diffusion coefficient by a factor of about 103 or above at lower pitch angles. We show that EMIC waves can produce efficient pitch angle scattering of energetic (~100keV) protons, yielding a rapid decrement in PSD, typically by a factor of ~10 within a few hours, consistent with observational data. This result further supports previous findings that wave-particle interaction is responsible for the rapid ring current decay.
ULF Waves Associated with Solar Wind Deceleration in the Earth's Foreshock
FU Hui-Shan, CAO Jin-Bin, YANG Biao, Lucek E, Rème H, Dandouras I
Chin. Phys. Lett. 2009, 26 (11): 119402 .   DOI: 10.1088/0256-307X/26/11/119402
Abstract   PDF(pc) (875KB) ( 602 )
Characteristics of ULF waves associated with the solar wind deceleration in the Earth's foreshock on 6-7 April 2003 is studied using the wave telescope technique. In the satellite frame, the ULF waves are the left-handed polarized and quasi anti-parallel propagating mode, with a power peak at about 18.63mHz. The wave vector in the GSE coordinates is estimated to be k = (-4.29, 2.28, 1.21)×10-4km-1. In the solar wind frame, the frequency of waves becomes -9.39mHz after the Doppler shift correction. The propagation direction of the waves is thus reversed and correspondingly the polarization of the waves becomes right-handed. The above-mentioned characteristics of the ULF waves in the solar wind frame indicate that the ULF waves associated with the solar wind deceleration are the Alfven-whistler waves, which have been frequently reported in both the observations and computer simulations.
The Communicating Pipe Model for Icy Plumes on Enceladus
MA Qian-Li, CHEN Chu-Xin
Chin. Phys. Lett. 2009, 26 (11): 119601 .   DOI: 10.1088/0256-307X/26/11/119601
Abstract   PDF(pc) (405KB) ( 535 )
We analyze the communicating pipe model on Enceladus, and predict that Saturn's strong tidal force in Enceladus plays a significant role in the plumes. In this model, the scale of the volcanoes can be evaluated based on the history of the craters and plumes. The correspondence of the data and observation make the model valid for the eruption. So it is imaginable that the tidal force is pulling the liquid out through the communicating pipe while reshaping the surface on Enceladus.
71 articles