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Volume 27 Issue 12
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Special Lie–Mei Symmetry and Conserved Quantities of Appell Equations Expressed by Appell Fun
XIE Yin-Li, JIA Li-Qun
Chin. Phys. Lett. 2010, 27 (12): 120201 .   DOI: 10.1088/0256-307X/27/12/120201
Abstract   PDF(pc) (369KB) ( 643 )
Special Lie–Mei symmetry and conserved quantities for Appell equations expressed by Appell functions in a holonomic mechanical system are investigated. On the basis of the Appell equation in a holonomic system, the definition and the criterion of special Lie–Mei symmetry of Appell equations expressed by Appell functions are given. The expressions of the determining equation of special Lie–Mei symmetry of Appell equations expressed by Appell functions, Hojman conserved quantity and Mei conserved quantity deduced from special Lie–Mei symmetry in a holonomic mechanical system are gained. An example is given to illustrate the application of the results.
Effects of Degree on Cooperation in Evolutionary Prisoner's Dilemma Games on Structured Populations
DAI Qiong-Lin, CHENG Hong-Yan, LI Hai-Hong, YANG Jun-Zhong
Chin. Phys. Lett. 2010, 27 (12): 120202 .   DOI: 10.1088/0256-307X/27/12/120202
Abstract   PDF(pc) (545KB) ( 445 )
We focus on the effects of individuals' degrees on spontaneous cooperation. By investigating evolutionary PDGs on random networks with two distinct degrees, we find some resonance-type behaviors of the cooperator frequency with the variation of degree. We also find that increasing hub's degree actually disfavors the cooperation though the heterogeneity in degree can enhance cooperation in the population.
Maximal Violation of Bell Inequality for Any Given Two-Qubit Pure State
Chin. Phys. Lett. 2010, 27 (12): 120301 .   DOI: 10.1088/0256-307X/27/12/120301
Abstract   PDF(pc) (424KB) ( 524 )
In the case of bipartite two-qubit systems, we derive an analytical expression of bound Bell operator for any given pure state. Our result not only manifests some properties of Bell inequality, for example, which may be violated by any pure entangled state and only be maximally violated for a maximally entangled state, but also gives the explicit values of maximal violation for any pure state. Finally we point out that any mixed states which can produce maximal violation of Bell inequality must have a maximal concurrence value.
Bidirectional Mapping between a Biphoton Polarization State and a Single-Photon Two-Qubit State
LIN Qing
Chin. Phys. Lett. 2010, 27 (12): 120302 .   DOI: 10.1088/0256-307X/27/12/120302
Abstract   PDF(pc) (361KB) ( 350 )
How to manipulate (operate or measure) single photons efficiently and simply is the basic problem in optical quantum information processing. We first present an efficient scheme to transform a biphoton polarization state to a corresponding single-photon state encoded by its polarization and spatial modes. This single-photon state carries both the information of the controlled and target photons. It will make the realization of bipartite positive-operator-valued measurements efficiently and simply. Moreover, the inverse transformation from the single-photon state back to the corresponding biphoton polarization state is also proposed. Using both the transformations, the realization of the arbitrary two-qubit unitary operation is simple with an M-Z interferometer. All the schemes are feasible with the current experimental technology.
The Time Division Multi-Channel Communication Model and the Correlative Protocol Based on Quantum Time Division Multi-Channel Communication
LIU Xiao-Hui, **, PEI Chang-Xing, NIE Min
Chin. Phys. Lett. 2010, 27 (12): 120303 .   DOI: 10.1088/0256-307X/27/12/120303
Abstract   PDF(pc) (498KB) ( 412 )
Based on the classical time division multi-channel communication theory, we present a scheme of quantum time-division multi-channel communication (QTDMC). Moreover, the model of quantum time division switch (QTDS) and correlative protocol of QTDMC are proposed. The quantum bit error rate (QBER) is analyzed and the QBER simulation test is performed. The scheme shows that the QTDS can carry out multi-user communication through quantum channel, the QBER can also reach the reliability requirement of communication, and the protocol of QTDMC has high practicability and transplantable. The scheme of QTDS may play an important role in the establishment of quantum communication in a large scale in the future.
Quantum Correlations Reduce Classical Correlations with Ancillary Systems
LUO Shun-Long, LI Nan
Chin. Phys. Lett. 2010, 27 (12): 120304 .   DOI: 10.1088/0256-307X/27/12/120304
Abstract   PDF(pc) (359KB) ( 449 )
We illustrate the dichotomy of classical/quantum correlations by virtue of monogamy. More precisely, we show that correlations in a bipartite state are classical if and only if each party of the state can be perfectly correlated with other ancillary systems. In particular, this means that if there are quantum correlations between two parties, then the classical (as well as quantum) correlating capabilities of the two parties with other systems have to be strictly reduced.
Analytical Solution for the SU(2) Hedgehog Skyrmion and Static Properties of Nucleons
JIA Duo-Jie, WANG Xiao-Wei, LIU Feng
Chin. Phys. Lett. 2010, 27 (12): 121201 .   DOI: 10.1088/0256-307X/27/12/121201
Abstract   PDF(pc) (585KB) ( 686 )
An analytical solution for symmetric Skyrmion is proposed for the SU(2) Skyrme model, which takes the form of the hybrid form of a kink-like solution, given by the instanton method. The static properties of nucleons is then computed within the framework of collective quantization of the Skyrme model, in a good agreement with that given by the exact numeric solution. The comparisons with the previous results as well as the experimental values are also presented.
The Renormalized Equation of State and Quark Star
LI Hua, LUO Xin-Lian, JIANG Yu, ZONG Hong-Shi, **
Chin. Phys. Lett. 2010, 27 (12): 121202 .   DOI: 10.1088/0256-307X/27/12/121202
Abstract   PDF(pc) (583KB) ( 518 )
By means of the EOS of QCD at zero temperature and finite quark chemical potential we proposed [Phys. Rev. D 78 (2008) 054001] in the framework of rainbow-ladder approximation of Dyson–Schwinger approach, we investigate the structure of quark star and its property. It is found that the mass-radius relation in our model is very different from that of usual quark star models, but similar to neutron star models. The obtained mass of quark star is about 1.75Mʘ ∼ 2.2Mʘ. The obtained radius of quark star is 2226 km, which is obviously larger than the results in other models. The reason for this discrepancy is analyzed.
Bs→ φπ0Decay in the Extra Down-Type Quark Model
WANG Shuai-Wei, HUANG Jin-Shu, LÜ, Lin-Xia
Chin. Phys. Lett. 2010, 27 (12): 121301 .   DOI: 10.1088/0256-307X/27/12/121301
Abstract   PDF(pc) (496KB) ( 329 )
Using the QCD factorization approach, we investigate the electro-weak penguin dominated process Bs→φπ0 in the extra down-type quark (EDQS) model. We calculate the effects of new physics (NP) on the branching fraction and direct CP asymmetry of the decay mode. It is found that the branching fraction can be increased by 15% points or dropped by 13% points than the standard model (SM) value, and its direct CP asymmetry can be increased by 35% points or dropped by 37% points than the SM one. The effects of NP on the direct CP asymmetry are more obvious than on the branching fraction. If this decay mode could be measured in the upcoming LHCb experiment, these results we obtain will be useful for further studies of the EDQS model.
Exotic Magnetic Rotation in 22F
PENG Jing**, YAO Jiang-Ming, ZHANG Shuang-Quan, MENG Jie,
Chin. Phys. Lett. 2010, 27 (12): 122101 .   DOI: 10.1088/0256-307X/27/12/122101
Abstract   PDF(pc) (635KB) ( 424 )
The rotation structure in exotic neutron-rich nucleus 22F is investigated based on the configuration πd5/2νd15/2 with the newly developed tilted axis cranking relativistic mean field theory in a fully microscopic and self-consistent way. The possible existence of magnetic rotation is suggested for 22F via investigating the spectra, the relation between the rotational frequency and the angular momentum, the electromagnetic transition probabilities B(M1) and B(E2) together with the shears mechanism characteristic of magnetic rotation. The effect of the nuclear current is also discussed by comparing the calculation results with and without currents.
Density-Functional-Theory Studies of C20 in Femtosecond Laser Pulses
WANG Zhi-Ping, BIAN Bao-An, WANG Li-Guang
Chin. Phys. Lett. 2010, 27 (12): 123101 .   DOI: 10.1088/0256-307X/27/12/123101
Abstract   PDF(pc) (492KB) ( 427 )
We study the electron response of C20 excited by strong femtosecond laser pulses by applying the time−dependent local-density approximation, an approach which has proven to provide a robust tool for investigations of fullerene. The optical response as well as the full electronic dipolar response and ionization processes of C20 subject to the laser field are explored. A strong correlation between induced electronic dipole oscillations and electron emission is observed.
Ab initio Study of He Stability in hcp-Ti
DAI Yun-Ya, YANG Li**, PENG Shu-Ming, LONG Xing-Gui, GAO Fei, ZU Xiao-Tao
Chin. Phys. Lett. 2010, 27 (12): 123102 .   DOI: 10.1088/0256-307X/27/12/123102
Abstract   PDF(pc) (609KB) ( 464 )
The stability of He in hcp-Ti is studied using the ab initio method based on the density functional theory. The results indicate that a single He atom prefers to occupy the tetrahedral site rather than the octahedral site. The interaction of He defects with Ti atoms is employed to explain the relative stabilities of He point defects in hcp-Ti. The relative stability of He defects in hcp-Ti is useful for He clustering and bubble nucleation in metal tritides, which provides the basis for development of improved atomistic models.
Theoretical Study of Isotopic Effect of Oxygen Atom on the Stereodynamics for the O(3P)+ D2 → OD+D Reaction
LIU Shi-Li, SHI Ying
Chin. Phys. Lett. 2010, 27 (12): 123103 .   DOI: 10.1088/0256-307X/27/12/123103
Abstract   PDF(pc) (630KB) ( 456 )
Quasi-classical trajectory theory is used to study the isotope effect of oxygen atoms on the vector correlations in the O(3P)+D2 reaction at a collision energy of 25kcal/mol using accurate potential energy surface of the 3A' triplet state. The distributions of p(θr) and the distribution of dihedral angel p(φr) as well as p(θr, φr) are calculated. Moreover, four polarization-dependent generalized differential cross sections (PDDCSs) of product are presented in the center-of-mass frame. The results indicate that the polarization of the product presents different characters for the isotope effect of oxygen atoms. Isotopic substitute can cause obviously different effects on the four PDDCSs.
Electron Correlation in Nonsequential Double Ionization of Helium by Two-Color Pulses
ZHOU Yue-Ming, LIAO Qing, HUANG Cheng, TONG Ai-Hong, LU Pei-Xiang
Chin. Phys. Lett. 2010, 27 (12): 123201 .   DOI: 10.1088/0256-307X/27/12/123201
Abstract   PDF(pc) (514KB) ( 449 )
We investigate the momentum and energy correlations between the two electrons from nonsequential double ionization (NSDI) of helium by strong two-color pulses with the classical three-dimensional ensemble model. The correlated momentum distribution in the direction parallel to the laser field exhibits an arc-like structure and the sum-energy spectrum shows a sharp peak for the NSDI of helium in the two-color fields. Back analysis reveals that the narrow time interval during which recollisions occur, the low returning energy and the short time delay between recollision and double ionization lead to the novel momentum and energy correlations.
Analysis of Nanometer Structure for Chromium Atoms in Gauss Standing Laser Wave
ZHANG Wen-Tao, ZHU Bao-Hua, XIONG Xian-Ming
Chin. Phys. Lett. 2010, 27 (12): 123202 .   DOI: 10.1088/0256-307X/27/12/123202
Abstract   PDF(pc) (2719KB) ( 326 )
The equation of motion of two-level chromium atoms in Gauss standing laser wave is discussed and the distribution of chromium atoms is given under different transverse velocity conditions. The results show that the focusing position of atoms will be affected by the transverse velocity of atoms. Based on the four-order Runge–Kutta method, the locus of chromium atoms in Gauss standing laser wave is simulated. The three-dimensional characteristics of nanometer structures are stimulated under perfect and emanative conditions.
Strings of Ion Crystals in a Linear Trap for Quantum Information Processing
ZHOU Fei, XIE Yi, XU You-Yang, HUANG Xue-Ren, FENG Mang**
Chin. Phys. Lett. 2010, 27 (12): 123203 .   DOI: 10.1088/0256-307X/27/12/123203
Abstract   PDF(pc) (557KB) ( 435 )
Strings of laser cooled 40Ca+ crystals have been successfully confined in our home-built linear ion trap, and ready for quantum information processing. We find the cloud-crystal phase transition of the trapped ions to be strongly sensitive to the frequencies of the Doppler cooling lasers and to the trapping voltage. The quantum jump of a single ion has been observed by controlling the quadrupole transition of the ion by a weak laser with ultra-narrow bandwidth.
Electron Capture Process in Collisions of Proton with Excited State of Helium
WANG Xue-Rong, LIU Ling, WANG Jian-Guo
Chin. Phys. Lett. 2010, 27 (12): 123401 .   DOI: 10.1088/0256-307X/27/12/123401
Abstract   PDF(pc) (628KB) ( 438 )
Total and state–selective cross sections for single electron capture (SEC) from the n=2 excited state of helium colliding by protons are calculated in the energy range of 1.0–100.0 keV/u by using the two–center atomic orbital close–coupling method. The interaction of the active electron with helium ion is represented by a model potential. Total SEC cross sections show a monotonic decreasing trend with increasing collision energy, and display a different behavior compared with the case from the ground state of helium. It is also found that the dominant reaction channel is captured to the H(2p) state up to 40 keV/u, and then the capture to the H(1s) or H(2s) state becomes more pronounced. Moreover, the alignment dependence on the initial states is obtained for the electron capture from He(2p0) and He (2p1).
Quantum Phase Transition of the Bosonic Atoms near the Feshbach Resonance in an Optical Lattice
LI Ben, CHEN Jing-Biao
Chin. Phys. Lett. 2010, 27 (12): 123701 .   DOI: 10.1088/0256-307X/27/12/123701
Abstract   PDF(pc) (1029KB) ( 426 )
The quantum phase transition from the Mott insulator to the superfluid phases of the bosonic atoms trapped in an optical lattice, in which the on-site interaction can be tuned by a Feshbach resonance, is investigated by a variational approach within mean-field theory. We derive an extended Bose–Hubbard model to describe this ultracold atomic system. By theoretical calculation and analysis, the phase diagram is shown clearly, and we find an exciting and novel phenomenon that is the appearance of the Mott insulator-sea (MI-sea). Meanwhile, the experimental feasibility of observing the MI-sea is discussed by analyzing the published data related to the Fashbach resonance at present. Finally, the potential application of the MI-sea for quantum information processing and quantum computation is also discussed in detail.
Coherent Beam Combining of Two Fiber Amplifiers Seeded by Multi-Wavelength Fiber Laser
WANG Xiao-Lin, ZHOU Pu, MA Yan-Xing, MA Hao-Tong, XU Xiao-Jun, LIU Ze-Jin, ZHAO Yi-Jun
Chin. Phys. Lett. 2010, 27 (12): 124201 .   DOI: 10.1088/0256-307X/27/12/124201
Abstract   PDF(pc) (503KB) ( 732 )
Multi-wavelength seed laser can mitigate stimulated Brillouin scattering (SBS) and improve the output power of the narrow-linewidth fiber amplifier. In this present study, coherent combining of two fiber amplifiers seeded by a multi-wavelength laser is proposed and demonstrated using stochastic parallel gradient descent (SPGD) algorithm. The long-exposure visibility of the far field interference pattern is increased from 0.15 to 0.97 when the system evolves from open-loop to closed-loop. The feasibility of coherent combining of fiber amplifiers seeded by multi-wavelength seed laser is validated.
Nonlinear Optical Properties and Ultrafast Dynamics of Undoped and Doped Bulk SiC
DING Jin-Liang, WANG Yao-Chuan, ZHOU Hui, CHEN Qiang, QIAN Shi-Xiong**, FENG Zhe-Chuan, LU Wei-Jie
Chin. Phys. Lett. 2010, 27 (12): 124202 .   DOI: 10.1088/0256-307X/27/12/124202
Abstract   PDF(pc) (673KB) ( 776 )
Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect (OKE) techniques at the wavelength of 800 nm. The Z-scan measurement shows that the third-order nonlinear optical susceptibilities of the doped samples are improved in comparison to the intrinsic sample. The OKE results additionally reveal that the instantaneous nonlinear optical response of the samples can be ascribed to the distortion of the electron cloud. The ultrafast transient spectroscopic measurements with the one-color and two-color pump-probe techniques demonstrate that the ultrafast recovery process in subpicosecond domain is induced by two-photon absorption process, while the slow relaxation component reflects the carrier dynamics of the excited electrons.
Highly Efficient Continuous-Wave Mid-Infrared Intracavity Singly Resonant Optical Parametric Oscillator Based on MgO:PPLN
YAN Bo-Xia**, BI Yong, ZHOU Mi, WANG Dong-Dong, QI Yan, FANG Tao, WANG Bin, WANG Yan-Wei, ZHENG Guang, CHENG Hua
Chin. Phys. Lett. 2010, 27 (12): 124203 .   DOI: 10.1088/0256-307X/27/12/124203
Abstract   PDF(pc) (602KB) ( 650 )
We present a compact all-solid-state cw mid-infrared intracavity singly resonant optical parametric oscillator (OPO) that is based on a self-fabricated 1-mm-thick 40-mm-long doped MgO periodically poled lithium niobate (MgO:PPLN). At a diode pump power of 15.6 W, the compact intracavity Nd:YVO4/MgO:PPLN OPO produced 1.9 W output power at 3.19 μm, corresponding to conversion efficiency of 12.2% from the laser diode pump to OPO idler output.
Off-Resonant Third-Order Optical Nonlinearity of Au Nanoparticle Array by Femtosecond Z-scan Measurement
WANG Kai, LONG Hua, FU Ming, YANG Guang**, LU Pei-Xiang, **
Chin. Phys. Lett. 2010, 27 (12): 124204 .   DOI: 10.1088/0256-307X/27/12/124204
Abstract   PDF(pc) (781KB) ( 504 )
A periodic triangular-shaped Au nanoparticle array is fabricated on a quartz substrate using nanosphere lithography and pulsed laser deposition, and the linear and nonlinear optical properties of metal particles are studied. The morphology of the polystyrene nanosphere mask (D=820 nm) and the Au nanoparticle array are investigated by scanning electron microscopy. The surface plasmon resonance absorption peak is observed at 606 nm, which is in good agreement with the calculated result using the discrete dipole approximation method. By performing the Z−scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearities of Au nanoparticle array are determined. The results show that the Au particles exhibit negative nonlinear absorption and positive nonlinear refractive index with the effective third-order optical nonlinear susceptibility χeff(3) can be up to (8.8±1.0)×10−10 esu under non-resonant femtosecond laser excitation.
Stimulated Brillouin Scattering Damage of Large-Aperture Fused Silica Grating
HAN Wei, HUANG Wan-Qing, LI Ke-Yu, WANG Fang, FENG Bin, JIA Huai-Ting, LI Fu-Quan, XIANG Yong, JING Feng, ZHENG Wan-Guo
Chin. Phys. Lett. 2010, 27 (12): 124205 .   DOI: 10.1088/0256-307X/27/12/124205
Abstract   PDF(pc) (473KB) ( 462 )
Laser induced damage experiment is carried out on a large aperture laser facility. Severe damage is observed on a large-aperture fused silica grating which presents dense craters on the front surface and six cracks alternatively located at the front and the rear surface. The bizarre fact about the damage on the grating is that, unlike other optics, the damage craters are almost on the front surface. According to observation, damage phenomenon is due to the stimulated Brillouin scattering (SBS) effect occurring in the grating, which includes the transverse SBS, the back SBS and the zigzag SBS.
Experiment of C-Band Wavelength Conversion in a Silicon Waveguide Pumped by Dispersed Femtosecond Laser Pulse
GAO Shi-Ming, **, TIEN En-Kuang, SONG Qi, HUANG Yue-Wang, Salih Kagan KALYONCU
Chin. Phys. Lett. 2010, 27 (12): 124206 .   DOI: 10.1088/0256-307X/27/12/124206
Abstract   PDF(pc) (525KB) ( 462 )
We experimentally demonstrate the C-band wavelength conversion using four-wave mixing in a 17-mm-long silicon-on-insulator waveguide pumped by a dispersed mode-locked femtosecond laser pulse. The idler can be observed with an incident average pump power lower than 4 dBm, and about 35 nm of conversion bandwidth from 1530 nm to 1565 nm is measured by using a 1550-nm pump wavelength. The pulse-pumped efficiency is demonstrated to be higher, by more than 22 dB, than the cw-pumped efficiency. The conversion efficiency variations with respect to the pump and signal powers are also investigated.
Velocity Measurement Based on Laser Doppler Effect
ZHANG Yan-Yan**, HUO Yu-Jing, HE Shu-Fang, GONG Ke
Chin. Phys. Lett. 2010, 27 (12): 124207 .   DOI: 10.1088/0256-307X/27/12/124207
Abstract   PDF(pc) (560KB) ( 961 )
A novel method for velocity measurement is presented. In this scheme, a parallel-linear-polarization dual-frequency laser is incident on the target and senses the target velocity with both the frequencies, which can increase the maximum measurable velocity significantly. The theoretical analysis and verification experiment of the novel method are presented, which show that high-velocity measurement can be achieved with high precision using this method.
Correlated Photon Pair Generation in Silicon Wire Waveguides at 1.5 μm
CHENG Jie-Rong, ZHANG Wei, ZHOU Qiang, FENG Xue, HUANG Yi-Dong, PENG Jiang-De
Chin. Phys. Lett. 2010, 27 (12): 124208 .   DOI: 10.1088/0256-307X/27/12/124208
Abstract   PDF(pc) (587KB) ( 466 )
Correlated photon pairs at 1.5 μm are generated in a silicon wire waveguide (SWW) with a length of only 1.6 mm. Experimental results show that the single−side count rates on both sides increase quadratically with pump light, indicating that photons are generated from the spontaneous four-wave mixing (SFWM) processes. The quantum correlation property of the generated photons is demonstrated by the ratio between coincident and accidental coincident count rates. The highest ratio measured at room temperature is to be about 19, showing that generated photon pairs have strong quantum correlation property and low noise. What is more, the wavelength correlation property of the coincident count is also measured to demonstrate the correlated photon pair generation. The experimental results demonstrate that SWWs have great potential in on-chip integrated low-noise correlated photon pair sources at 1.5 μm.
High-Quality Continuous-Wave Imaging with a 2.53THz Optical Pumped Terahertz Laser and a Pyroelectric Detector
BING Pi-Bin, **, YAO Jian-Quan, XU De-Gang, XU Xiao-Yan, LI Zhong-Yang,
Chin. Phys. Lett. 2010, 27 (12): 124209 .   DOI: 10.1088/0256-307X/27/12/124209
Abstract   PDF(pc) (561KB) ( 517 )
A cw terahertz (THz) transmission imaging system is demonstrated and a high-quality THz image can be obtained using a pyroelectric detector. The factors that affect the imaging quality, such as the THz wavelength, spot size on the sample surface, step length of the motor, and frequency of the chopper, are theoretically and experimentally investigated. The experimental results show that the maximum resolution of the THz image can reach 0.4 mm with the THz wavelength of 118.8 μm, the spot size of 1.8 mm and the step length of 0.25 mm.
Pseudo-Rhombus-Shaped Subwavelength Crossed Gratings of GaAs for Broadband Antireflection
CHEN Xi**, FAN Zhong-Chao, ZHANG Jing, SONG Guo-Feng, CHEN Liang-Hui
Chin. Phys. Lett. 2010, 27 (12): 124210 .   DOI: 10.1088/0256-307X/27/12/124210
Abstract   PDF(pc) (1008KB) ( 458 )
Holographic lithography coupled with the nonlinear response of photoresist to the exposure is adopted to fabricate porous photoresist (PR) mask. Conventional dot PR mask is also generated, and both patterns are transferred into a underlying GaAs substrate by the optimal dry etching process to obtain tapered subwavelength crossed gratings (SWCGs) to mimic the moth-eye structure. In comparison of the experiment and simulation, the closely-packed pseudo-rhombus-shaped GaAs SWCGs resulting from the porous mask outperforms the conical counterpart which comes from the dot mask, and achieves a reported lowest mean spectral reflectance of 1.1%.
Observation of Modulation Transfer Spectroscopy in the Deep Modulation Regime
ZHOU Zi-Chao, WEI Rong**, SHI Chun-Yan, WANG Yu-Zhu**
Chin. Phys. Lett. 2010, 27 (12): 124211 .   DOI: 10.1088/0256-307X/27/12/124211
Abstract   PDF(pc) (482KB) ( 494 )
We observe the modulation transfer spectroscopy on the D2 line of 87Rb in a rubidium cell with acoustic-optic modulator in the deep modulation regime. In this regime, the sidebands of the pump beam are involved in the four-wave mixing processes, which increase the signal gradients and the peak-to-peak amplitudes of both the absorption and dispersion components.
A Simple and Accurate Method for Calculating the Gaussian Beam Expansion Coefficients
Chin. Phys. Lett. 2010, 27 (12): 124301 .   DOI: 10.1088/0256-307X/27/12/124301
Abstract   PDF(pc) (563KB) ( 648 )
The calculation of the diffraction field radiated from the ultrasonic transducer can be simplified by using the Gaussian beam expansion technique. The key problem of this technique is how to determine the coefficients of Gaussian functions. We present a simple and accurate optimization method to calculate the Gaussian beam expansion coefficients. Half of the coefficients are obtained by solving linear equations. The other half are derived from the Fourier series expansion. Wave field simulation results demonstrate the validity of the new method.
Directivity of Spherical Polyhedron Sound Source Used in Near-Field HRTF Measurements
YU Guang-Zheng**, XIE Bo-Sun, RAO Dan
Chin. Phys. Lett. 2010, 27 (12): 124302 .   DOI: 10.1088/0256-307X/27/12/124302
Abstract   PDF(pc) (673KB) ( 505 )
The omnidirectional character is one of important requirements for the sound source used in near-field head-related transfer function (HRTF) measurements. Based on the analysis on the radiation sound pressure and directivity character of various spherical polyhedron sound sources, a spherical dodecahedral sound source with radius of 0.035 m is proposed and manufactured. Theoretical and measured results indicate that the sound source is approximately omnidirectional below the frequency of 8 kHz. In addition, the sound source has reasonable magnitude response from 350 Hz to 20 kHz and linear phase characteristics. Therefore, it is suitable for the near-field HRTF measurements.
Effects of Slip on Unsteady Mixed Convective Flow and Heat Transfer Past a Stretching Surface
S. Mukhopadhyay
Chin. Phys. Lett. 2010, 27 (12): 124401 .   DOI: 10.1088/0256-307X/27/12/124401
Abstract   PDF(pc) (508KB) ( 760 )
Unsteady mixed convective boundary layer flow and heat transfer over a stretching vertical surface in the presence of slip are investigated. It is noted that fluid velocity decreases due to the increasing velocity slip parameter resulting in an increase in the temperature field. The rate of heat transfer decreases with the velocity slip parameter while it increases with unsteadiness parameter. The same feature is also noticed for thermal slip parameter.
Cluster Model for Wave-Like Motions of a 2D Vertically Vibrated Granular System
CAI Hui, MIAO Guo-Qing
Chin. Phys. Lett. 2010, 27 (12): 124501 .   DOI: 10.1088/0256-307X/27/12/124501
Abstract   PDF(pc) (470KB) ( 476 )
The fact that trapezoid clusters exist in 2D vertically vibrated granular systems leads us to construct a cluster model, in which wave-like motions are explained as the result of cluster-plate and cluster-cluster collisions. By analyzing the collision of one cluster with the plate in detail, we deduce a basic equation from velocity relationship, which could be separated into two correlative equations: one relates wave-like motion with exciting acceleration, and we call it the excitation condition; the other relates wavelength with exciting frequency, viz., the dispersion relation. The theoretical results are in agreement with the experimental ones, which supports the idea of the cluster model. Moreover, from the cluster model, we also predict a possibility of abnormal dispersion relation of a 2D granular system.
Static Structure of Two-Dimensional Granular Chain
WEN Ping-Ping, LI Liang-Sheng, ZHENG Ning, SHI Qing-Fan
Chin. Phys. Lett. 2010, 27 (12): 124502 .   DOI: 10.1088/0256-307X/27/12/124502
Abstract   PDF(pc) (1094KB) ( 485 )
Static packing structures of two-dimensional granular chains are investigated experimentally. It is shown that the packing density approximates the saturation with the exponential law as the length of chain increases. The packing structures are globally disordered, while the local square crystallization is found by using the radial distribution function. This characteristic phase of chain packing is similar to a liquid crystal state, and has properties between a conventional liquid and solid crystal.
Can We Obtain a Fractional Lorenz System from a Physical Problem?
YANG Fan, ZHU Ke-Qin
Chin. Phys. Lett. 2010, 27 (12): 124701 .   DOI: 10.1088/0256-307X/27/12/124701
Abstract   PDF(pc) (1095KB) ( 448 )
A new fractional-order Lorenz system is obtained from the convection of fractional Maxwell fluids in a circular loop. This is the first fractional-order dynamical system derived from an actual physical problem, and rich dynamical properties are observed. In the case of short fluid relaxation time, with the decreasing effective dimension Σ, we find a critical value of the effective dimension Σcr1, at which the solution of the system undergoes a transition from the chaotic motion to the periodic motion and another critical value Σcr2cr2cr1)at which the regular dynamics of the system returns to the chaotic one. In the case of long relaxation time, the phenomenon of overstability is observed and the decrease of Σ is found to delay the onset of it.
Slip Magnetohydrodynamic Viscous Flow over a Permeable Shrinking Sheet
FANG Tie-Gang, ZHANG Ji, YAO Shan-Shan
Chin. Phys. Lett. 2010, 27 (12): 124702 .   DOI: 10.1088/0256-307X/27/12/124702
Abstract   PDF(pc) (634KB) ( 924 )
The magnetohydrodynamic (MHD) flow under slip conditions over a shrinking sheet is solved analytically. The solution is given in a closed form equation and is an exact solution of the full governing Navier–Stokes equations. Interesting solution behavior is observed with multiple solution branches for certain parameter domain. The effects of the mass transfer, slip, and magnetic parameters are discussed.
Quantum Effects on Rayleigh–Taylor Instability of Incompressible Plasma in a Vertical Magnetic Field
G. A. Hoshoudy
Chin. Phys. Lett. 2010, 27 (12): 125201 .   DOI: 10.1088/0256-307X/27/12/125201
Abstract   PDF(pc) (516KB) ( 481 )
Quantum effects on Rayleigh–Taylor instability of a stratified incompressible plasmas layer under the influence of vertical magnetic field are investigated. The solutions of the linearized equations of motion together with the boundary conditions lead to deriving the relation between square normalized growth rate and square normalized wave number in two algebraic equations and are numerically analyzed. In the case of the real solution of these two equations, they can be combined to generate a single equation. The results show that the presence of vertical magnetic field beside the quantum effect will bring about more stability on the growth rate of unstable configuration.
Radiation Temperature Measurement of an Imploded X-Ray Source with a Filtered-Multi-Channel Pinhole Camera
WANG Shou-Jun, DONG Quan-Li**, ZHANG Yi, LI Yu-Tong, ZHANG Lei, Shinsuke Fujioka, Norimasa Yamamoto, Hiroaki Nishimura, ZHANG Jie, **
Chin. Phys. Lett. 2010, 27 (12): 125202 .   DOI: 10.1088/0256-307X/27/12/125202
Abstract   PDF(pc) (741KB) ( 931 )
The Plankian radiation temperature of an intense x-ray source driven by imploding spherical CH plastic shell is measured with a filtered-multi-channel pinhole camera. With all the twelve laser beams of the GEKKO-XII laser facility applied, the average radiation temperature is measured to be around 465 eV while the temperature at the core is as high as 818 eV. This value is confirmed by other instruments applied.
Jet-Like Long Spike in Nonlinear Evolution of Ablative Rayleigh–Taylor Instability
YE Wen-Hua, **, WANG Li-Feng, , HE Xian-Tu,
Chin. Phys. Lett. 2010, 27 (12): 125203 .   DOI: 10.1088/0256-307X/27/12/125203
Abstract   PDF(pc) (837KB) ( 461 )
We report the formation of jet-like long spike in the nonlinear evolution of the ablative Rayleigh–Taylor instability (ARTI) experiments by numerical simulations. A preheating model κ(T)=κSH[1+f(T)], where κSH is the Spitzer–Härm (SH) electron conductivity and f(T) interprets the preheating tongue effect in the cold plasma ahead of the ablative front [Phys. Rev. E 65 (2002) 57401], is introduced in simulations. The simulation results of the nonlinear evolution of the ARTI are in general agreement with the experiment results. It is found that two factors, i.e., the suppressing of ablative Kelvin–Helmholtz instability (AKHI) and the heat flow cone in the spike tips, contribute to the formation of jet-like long spike in the nonlinear evolution of the ARTI.
Preparation of a Pd-Cu-Si Bulk Metallic Glass with a Diameter up to 11mm
DING Hong-Yu, LI Yang, YAO Ke-Fu
Chin. Phys. Lett. 2010, 27 (12): 126101 .   DOI: 10.1088/0256-307X/27/12/126101
Abstract   PDF(pc) (870KB) ( 573 )
Pd77.5Cu6Si16.5(at.%) bulk metallic glass with a diameter up to 11 mm was successfully fabricated by water quenching method together with melt purification. By using x-ray diffraction and transmission electron microscopy techniques, the structure of the as-prepared sample is confirmed to be glassy. The resulted sample with 11 mm diameter indicates that the melt purification by fluxing method can effectively enhance the glass forming ability of Pd-Cu-Si alloy, and increase its critical size of glassy sample.
Deflections of Nanowires with Consideration of Surface Effects
LI He, YANG Zhou, ZHANG Yi-Min, WEN Bang-Chun
Chin. Phys. Lett. 2010, 27 (12): 126201 .   DOI: 10.1088/0256-307X/27/12/126201
Abstract   PDF(pc) (478KB) ( 431 )
The elementary beam model is modified to include the surface effects and used to analyze the deflections of nanowires under different boundary conditions. The results show that compared to deflections of nanowires without consideration of surface effects, the surface effects can enlarge or reduce deflections of nanowires, and nanowire buckling occurs under certain conditions. This study might be helpful for design of nanowire-based nanoelectromechanical systems.
Characterization and Magnetic Properties of Nickel Ferrite Nanoparticles Prepared by Ball Milling Technique
G. Nabiyouni**, M. Jafari Fesharaki, M. Mozafari, J. Amighian
Chin. Phys. Lett. 2010, 27 (12): 126401 .   DOI: 10.1088/0256-307X/27/12/126401
Abstract   PDF(pc) (676KB) ( 6588 )
Nickel ferrite nanoparicles with various grain sizes are synthesized using annealing treatment followed by ball milling of its bulk component materials. Commercially available nickel and iron oxide powders are first mixed, and then annealed at 1100°C in an oxygen environment furnace and for 3 h. The samples are then milled for different times in an SPEX mill. X-ray diffraction pattern indicates that in this stage the sample is single phase. The average grain size is estimated by scanning electron microscopy (SEM) and x-ray diffraction techniques. Magnetic behavior of the sample at room temperature is studied using a superconducting quantum interference device (SQUID). The Curie temperature of the powders is measured by an LCR–meter unit. The x-ray diffraction patterns clearly indicate that increasing the milling time leads to a decrease in the grain size and consequently leads to a decrease in the saturation magnetization as well as the Curie temperatures. This result is attributed to the spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core.
Strain-Engineered Low-Density InAs Bilayer Quantum Dots for Single Photon Emission
LI Zhan-Guo, LIU Guo-Jun**, LI Lin, FENG Ming, LI Mei, LU Peng, ZOU Yong-Gang, LI Lian-He, GAO Xin
Chin. Phys. Lett. 2010, 27 (12): 126801 .   DOI: 10.1088/0256-307X/27/12/126801
Abstract   PDF(pc) (680KB) ( 458 )
We investigate the growth of strain-engineered low-density InAs bilayer quantum dots (BQDs) on GaAs by molecular beam epitaxy. Owing to increasing dot size and In composition of the upper QDs, low-density BQDs in a GaAs matrix with an emission wavelength up to 1.4 μm at room temperature are achieved. Such a wavelength is larger than that of conventional QDs in a GaAs matrix (generally of about 1.3 μm). The optical properties of the BQDs are sensitive to annealing temperature used after spacer layer growth. Significant decrease of integrated PL intensity is observed as the annealing temperature increases. At 10 K, single photon emission from the BQDs with wavelength around 1.3 μm is observed.
Effect of High Temperature Annealing on Conduction-Type ZnO Films Prepared by Direct-Current Magnetron Sputtering
SUN Li-Jie, HE Dong-Kai, XU Xiao-Qiu, ZHONG Ze, WU Xiao-Peng, LIN Bi-Xia, FU Zhu-Xi
Chin. Phys. Lett. 2010, 27 (12): 126802 .   DOI: 10.1088/0256-307X/27/12/126802
Abstract   PDF(pc) (642KB) ( 687 )
We experimentally find that the ZnO thin films deposited by dc-magnetron sputtering have different conduction types after annealing at high temperature in different ambient. Hall measurements show that ZnO films annealed at 1100°C in N2 and in O2 ambient become n−type and p-type, respectively. This is due to the generation of different intrinsic defects by annealing in different ambient. X-ray photoelectron spectroscopy and photoluminescence measurements indicate that zinc interstitial becomes a main defects after annealing at 1100°C in N2 ambient, and these defects play an important role for n−type conductivity of ZnO. While the ZnO films annealed at 1100°C in O2 ambient, the oxygen antisite contributes ZnO films to p-type.
Effects of H on Electronic Structure and Ideal Tensile Strength of W: A First-Principles Calculation
LIU Yue-Lin, ZHOU Hong-Bo, JIN Shuo, ZHANG Ying, LU Guang-Hong
Chin. Phys. Lett. 2010, 27 (12): 127101 .   DOI: 10.1088/0256-307X/27/12/127101
Abstract   PDF(pc) (504KB) ( 416 )
We investigate the structure, energetics, and the ideal tensile strength of tungsten (W) with hydrogen (H) using a first-principles method. Both density of states (DOS) and the electron localization function (ELF) reveal the underlying physical mechanism that the tetrahedral interstitial H is the most energetically favorable. The first-principles computational tensile test (FPCTT) shows that the ideal tensile strength is 29.1 GPa at the strain of 14% along the [001] direction for the intrinsic W, while it decreases to 27.1 GPa at the strain of 12% when one impurity H atom is embedded into the bulk W. These results provide a useful reference to understand W as a plasma facing material in the nuclear fusion Tokamak.
First-Principles Investigations of the Phase Transition and Optical Properties of Solid Oxygen
LIU Yan-Hui, DUAN De-Fang, WANG Lian-Cheng, ZHU Chun-Ye, CUI Tian**
Chin. Phys. Lett. 2010, 27 (12): 127102 .   DOI: 10.1088/0256-307X/27/12/127102
Abstract   PDF(pc) (723KB) ( 510 )
Using density-functional-theory calculations, a monoclinic metallic post-ζ phase (space group C2/c) is predicted at 215 GPa. The calculated phonon dispersion curves suggest that this structure is stable at least up to 310 GPa. Oxygen remains a molecular crystal and there is no dissociation in the related pressure range. Moreover, it is found that the phase transition from ζ to post−ζ phase is attributed to phonon softening. The significant change in the optical properties can be used to identify the phase transition.
Annealing Effect on Photovoltages of Quartz Single Crystals
TIAN Lu, ZHAO Song-Qing, ZHAO Kun, **
Chin. Phys. Lett. 2010, 27 (12): 127301 .   DOI: 10.1088/0256-307X/27/12/127301
Abstract   PDF(pc) (587KB) ( 529 )
We investigate the photovoltaic effects of quartz single crystals annealed at high temperatures in ambient atmosphere. The open-circuit photovoltages and surface morphologies strongly depend on the heating treatments. When the annealing temperature increases from room temperature to 900°C, the rms roughness of quartz single crystal wafers increases from 0.207 to 1.011 nm. In addition, the photovoltages decrease from 1.994 μV at room temperature to 1.551 μV after treated at 500°C, and then increase up to 9.8 μV after annealed at 900°C. The inner mechanism of the present photovoltaic response and surface morphologies is discussed.
Influence of O2 Flux on Compositions and Properties of ITO Films Deposited at Room Temperature by Direct-Current Pulse Magnetron Sputtering
WANG Hua-Lin, DING Wan-Yu, LIU Chao-Qian, CHAI Wei-Ping
Chin. Phys. Lett. 2010, 27 (12): 127302 .   DOI: 10.1088/0256-307X/27/12/127302
Abstract   PDF(pc) (557KB) ( 755 )
Indium tin oxide (ITO) films were deposited on glass substrates at room temperature by dc pulse magnetron sputtering. Varying O2 flux, ITO films with different properties are obtained. Both x−ray diffractometer and x-ray photoelectron spectrometer are used to study the change of crystalline structures and bonding structures of ITO films, respectively. Electrical properties are measured by four-point probe measurements. The results indicate that the chemical structures and compositions of ITO films strongly depend on the O2 flux. With increasing O2 flux, ITO films display better crystallization, which could decrease the resistivity of films. On the contrary, ITO films contain less O vacancies with increasing O2 flux, which could worsen the conductive properties of films. Without any heat treatment onto the samples, the resistivity of the ITO film could reach 6.0×104 Ω⋅cm, with the optimal deposition parameter of 0.2 sccm O2 flux.
GaN-Based Thin Film Vertical Structure Light Emitting Diodes Fabricated by a Modified Laser Lift-off Process and Transferred to Cu
SUN Yong-Jian, YU Tong-Jun, JIA Chuan-Yu, CHEN Zhi-Zhong, TIAN Peng-Fei, KANG Xiang-Ning, LIAN Gui-Jun, HUANG Sen, ZHANG Guo-Yi
Chin. Phys. Lett. 2010, 27 (12): 127303 .   DOI: 10.1088/0256-307X/27/12/127303
Abstract   PDF(pc) (811KB) ( 975 )
GaN-based thin film vertical structure light-emitting diodes (VS-LEDs) were fabricated by a modified YAG laser lift-off (LLO) process and transferred to Cu substrates. With a comparison of the electrical and optical properties of conventional LEDs on sapphire substrates and of lateral structure thin film LEDs by a KrF LLO process, the vertical structure of LLO LEDs shows obvious superiority. LLO VSLEDs made by modified YAG LLO process show less increase of leakage current than the devices made by conventional KrF LLO process. Furthermore, owing to the well current spreading and less current path, the ideality factors and series resistance of vertical structure LEDs reduce greatly and the efficiency increases more obviously than the lateral structure LEDs, which is also reflected on the relative LI curves. The output power of vertical structure LEDs is over 3 times greater than that of the lateral structure LLO LEDs within 300 mA.
Effect of Indium Ambient on Electrical Properties of Mg-Doped AlxGa1-xN
XU Zheng-Yu, QIN Zhi-Xin**, SANG Li-Wen, ZHANG Yan-Zhao, SHEN Bo, ZHANG Guo-Yi, ZHAO Lan, ZHANG Xiang-Feng, CHENG Cai-Jing, SUN Wei-Guo
Chin. Phys. Lett. 2010, 27 (12): 127304 .   DOI: 10.1088/0256-307X/27/12/127304
Abstract   PDF(pc) (527KB) ( 473 )
Mg-doped AlxGa1−xN epilayers were grown on AlN/sapphire templates by metal organic chemical vapor deposition (MOCVD) using an indium-assisted growth method. At room temperature, the resistivity of Mg-doped Al0.43Ga0.57N epilayer grown under indium (In) ambient is of the order of 104 Ω⋅cm, while the resistivity of Mg−doped Al0.43Ga0.57N grown without In assistance is of the order of 106 Ω⋅cm. The ultraviolet light−emitting diodes (UV-LEDs) using the In-assisted Mg-doped Al0.43Ga0.57N as the p−type layers were fabricated to verify the function of indium ambient. It is found that there are a lower turn-on voltage and a lower diode series resistance in the UV-LEDs fabricated with p-type Al0.43Ga0.57N layers grown under In-ambient.
Optical and Structural Properties of Cr-Doped GaN Grown by HVPE Method
YAN Huai-Yue, XIU Xiang-Qian, HUA Xue-Mei, LIU Zhan-Hui, ZHOU An, ZHANG Rong, XIE Zi-Li, HAN Ping, SHI Yi, ZHENG You-Dou
Chin. Phys. Lett. 2010, 27 (12): 127801 .   DOI: 10.1088/0256-307X/27/12/127801
Abstract   PDF(pc) (613KB) ( 523 )
Single crystalline Cr-doped GaN films are successfully grown by hydride vapor phase epitaxy. The structure analysis indicates that the film is uniform without detectable Cr precipitates or clusters and the Cr atoms are substituted for Ga sites. The impurity modes in the range 510–530 cm−1 are observed by the Raman spectra. The modes are assigned to the host lattice defects caused by substitutional Cr. The donor-acceptor emission is found to locate at Ec0.20 eV by analyzing the photoluminescence spectrum obtained at different temperatures, and the emission is attributed to the structural defects caused by CrGa−VN complex. The superconductor quantum interference device results show that the Cr-doped GaN film without detectable Cr precipitates or clusters exhibits paramagnetic properties.
Highly Efficient Simplified Organic Light-Emitting Diodes Utilizing F4-TCNQ as an Anode Buffer Layer
DONG Mu-Sen, , WU Xiao-Ming, , HUA Yu-Lin, **, QI Qing-Jin, , YIN Shou-Gen,
Chin. Phys. Lett. 2010, 27 (12): 127802 .   DOI: 10.1088/0256-307X/27/12/127802
Abstract   PDF(pc) (647KB) ( 1584 )
We demonstrate that the electroluminescent performances of organic light-emitting diodes (OLEDs) are significantly improved by evaporating a thin F4-TCNQ film as an anode buffer layer on the ITO anode. The optimum Alq3−based OLEDs with F4-TCNQ buffer layer exhibit a lower turn-on voltage of 2.6 V, a higher brightness of 39820 cd/m2 at 13 V, and a higher current efficiency of 5.96 cd/A at 6 V, which are obviously superior to those of the conventional device (turn−on voltage of 4.1 V, brightness of 18230 cd/m2 at 13 V, and maximum current efficiency of 2.74 cd/A at 10 V). Furthermore, the buffered devices with F4−TCNQ as the buffer layer could not only increase the efficiency but also simplify the fabrication process compared with the p-doped devices in which F4-TCNQ is doped into β-NPB as p-HTL (3.11 cd/A at 7 V). The reason why the current efficiency of the p-doped devices is lower than that of the buffered devices is analyzed based on the concept of doping, the measurement of absorption and photoluminescence spectra of the organic materials, and the current density-voltage characteristics of the corresponding hole-only devices.
Quantum-Confined Stark Effect in Ensemble of Colloidal Semiconductor Quantum Dots
WANG Zhi-Bing, ZHANG Hui-Chao, ZHANG Jia-Yu**, Huaipeng Su, Y. Andrew Wang
Chin. Phys. Lett. 2010, 27 (12): 127803 .   DOI: 10.1088/0256-307X/27/12/127803
Abstract   PDF(pc) (589KB) ( 523 )
The presence of a strong, changing, randomly-oriented, local electric field, which is induced by the photo-ionization that occurs universally in colloidal semiconductor quantum dots (QDs), makes it difficult to observe the quantum-confined Stark effect in ensemble of colloidal QDs. We propose a way to inhibit such a random electric field, and a clear quantum-confined Stark shift is observed directly in close-packed colloidal QDs. Besides the applications in optical switches and modulators, our experimental results indicate how the oscillator strengths of the optical transitions are changed under external electric fields.
Preparation, Morphology Transformation and Magnetic Behavior of Co3O4 Nano-Leaves
MENG Ling-Rong, CHEN Wei-Meng, CHEN Chin-Ping, ZHOU He-Ping, PENG Qing**
Chin. Phys. Lett. 2010, 27 (12): 128101 .   DOI: 10.1088/0256-307X/27/12/128101
Abstract   PDF(pc) (1373KB) ( 497 )
A series of cubic phase Co3O4 nano−leaves were prepared via a combined approach of solution reaction and calcination. According to x-ray diffraction and electron microscopy, we find that the Co3O4 grain size increases with calcination temperature. This can induce many gaps in the products. MT and MH magnetization measurements reveal the typical antiferromagnetic behavior of nano−leaves. The effective moments of the samples prepared at 300, 400 and 500°C are 5.6, 5.8 and 5.7 μB per formula unit (FU), respectively, larger than the bulk value of 4.14 μB/FU.
Fabrication and Characteristics of AlInN/AlN/GaN MOS-HEMTs with Ultra-Thin Atomic Layer Deposited Al2O3 Gate Dielectric
MAO Wei, ZHANG Jin-Cheng, XUE Jun-Shuai, HAO Yao, MA Xiao-Hua, WANG Chong, LIU Hong-Xia, XU Sheng-Rui, YANG Lin-An, BI Zhi-Wei, LIANG Xiao-Zhen, ZHANG Jin-Feng, KUANG Xian-Wei
Chin. Phys. Lett. 2010, 27 (12): 128501 .   DOI: 10.1088/0256-307X/27/12/128501
Abstract   PDF(pc) (1294KB) ( 926 )
Al0.85In0.15N/AlN/GaN metal−oxide-semiconductor high electron mobility transistors (MOS-HEMTs) employing a 3-nm ultra-thin atomic-layer deposited (ALD) Al2O3 gate dielectric layer are reported. Devices with 0.6 μm gate lengths exhibit an improved maximum drain current density of 1227 mA/mm at a gate bias of 3 V, a peak transconductance of 328 mS/mm, a cutoff frequency fT of 16 GHz, a maximum frequency of oscillation fmax of 45 GHz, as well as significant gate leakage suppression in both reverse and forward directions, compared with the conventional Al0.85In0.15N/AlN/GaN HEMT. Negligible CV hysteresis, together with a smaller pinch−off voltage shift, is observed, demonstrating few bulk traps in the dielectric and high quality of the Al2O3/AlInN interface. It is most notable that not only the transconductance profile of the MOS-HEMT is almost the same as that of the conventional HEMT with a negative shift, but also the peak transconductance of the MOS-HEMT is increased slightly. It is an exciting improvement in the transconductance performance.
Effect of Annealing on Microstructure and Electrical Characteristics of Doped Poly (3-Hexylthiophene) Films
MA Liang
Chin. Phys. Lett. 2010, 27 (12): 128502 .   DOI: 10.1088/0256-307X/27/12/128502
Abstract   PDF(pc) (841KB) ( 567 )
The effect of annealing on the microstructure and electrical characteristics of poly (3-hexylthiophene) (P3HT) films doped with very small amounts of the electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4−TCNQ) is studied. X-ray diffraction and UV-vis spectrum studies show that unlike the pure P3HT film, the thermal treatment on the doped films under an Ar atmosphere can effectively enhance the crystalline order of P3HT films, as well as successfully facilitate the orientation of the polymer chains. This improvement is attributed to the electrostatic force between P3HT and F4−TCNQ molecules. This force induces the polymer chains to crystallize and orient during the annealing process. As a result, annealing significantly improves performance, especially for the Ion/Ioff ratio of the TFTs based on the doped P3HT films.
10.7μm InGaAs/InAlAs Quantum Cascade Detector
KONG Ning**, LIU Jun-Qi, LI Lu, LIU Feng-Qi, WANG Li-Jun, WANG Zhan-Guo, LU Wei
Chin. Phys. Lett. 2010, 27 (12): 128503 .   DOI: 10.1088/0256-307X/27/12/128503
Abstract   PDF(pc) (669KB) ( 484 )
A 10.7 μm quantum cascade detector based on lattice matched InGaAs/InAlAs/InP is demonstrated and characterized in terms of responsivity, resistivity and detectivity. The device operates in the 8–14 μm atmospheric window up to 140 K and shows a peak reponsivity of 14.4 mA/W at 78 K. With a resistance−area product value of 159 Ωcm2, the Johnson noise limited detectivity DJ is 2.8×109 Jones (cm⋅Hz1/2W−1) at 78 K.
ZnO-Based Transparent Thin-Film Transistors with MgO Gate Dielectric Grown by in-situ MOCVD
ZHAO Wang, DONG Xin, ZHAO Long, SHI Zhi-Feng, WANG Jin, WANG Hui, XIA Xiao-Chuan, CHANG Yu-Chun, ZHANG Bao-Lin, DU Guo-Tong
Chin. Phys. Lett. 2010, 27 (12): 128504 .   DOI: 10.1088/0256-307X/27/12/128504
Abstract   PDF(pc) (610KB) ( 881 )
ZnO transparent thin-film transistors with MgO gate dielectric were fabricated by in-situ metal organic chemical vapor deposition (MOCVD) technology. We used an uninterrupted growth method to simplify the fabrication steps and to avoid the unexpectable contaminating during epitaxy process. MgO layer is helpful to reduce the gate leakage current, as well as to achieve high transparency in visible light band, due to the wide band gap (7.7 eV) and high dielectric constant (9.8). The XRD measurement indicates that the ZnO layer has high crystal quality. The field effect mobility and the on/off current ratio of the device is 2.69 cm2V−1s−1 and 1×104, respectively.
A Unifying Modularity in Networks
HAO Jun-Jun, CAI Shui-Ming, HE Qin-Bin, LIU Zeng-Rong, **
Chin. Phys. Lett. 2010, 27 (12): 128901 .   DOI: 10.1088/0256-307X/27/12/128901
Abstract   PDF(pc) (498KB) ( 519 )
We propose a new modularity criterion in complex networks, called the unifying modularity q which is independent of the number of partitions. It is shown that, for a given network, the relationship between the upper limit of Q and the number of the partitions, k, is sup(Qk)=(k−1)/k. Since the range of Q for each partition number is inconsistent, we try to extend the concept Q to unifying modularity q, which is independent of the number of partitions. Subsequently, we indicate that it is more accurately to determine the number of partitions by using unifying modularity q than Q.
Nuclear Magnetic Resonance Measurements of Original Water Saturation and Mobile Water Saturation in Low Permeability Sandstone Gas
GAO Shu-Sheng, **, YE Li-You, XIONG Wei, GUO He-Kun, HU Zhi-Ming
Chin. Phys. Lett. 2010, 27 (12): 128902 .   DOI: 10.1088/0256-307X/27/12/128902
Abstract   PDF(pc) (448KB) ( 494 )
We use nuclear magnetic resonance (NMR) and centrifugation to measure the original water saturation and mobile water saturation of cores from the Xujiahe low permeability sandstone gas reservoir, and compare the NMR results with the corresponding field data. It is shown that the NMR water saturation after 300 psi centrifugation effectively represents the original water saturation measured by weighing fresh cores. There is a good correlation between mobile water saturation and the water production performance of the corresponding gas wells. The critical mobile water saturation whether reservoir produces water of the Xujiahe low permeability sandstone gas is 6%. The higher the mobile water saturation, the greater the water production rate of gas well. This indicates that well's water production performance can be forecasted by mobile water saturation of cores.
Chorus-Driven Outer Radiation Belt Electron Dynamics at Different L-Shells
ZHANG Sai, XIAO Fu-Liang**
Chin. Phys. Lett. 2010, 27 (12): 129401 .   DOI: 10.1088/0256-307X/27/12/129401
Abstract   PDF(pc) (514KB) ( 354 )
Energetic outer radiation belt electron phase space density (PSD) evolution due to interaction with whistler-mode chorus at different L−shells is investigated by solving the diffusion equation including cross diffusion terms. It is found that the difference of diffusion rates for different L−shells occurs primarily at pitch angles 0°–50° and around 90°. In particular, diffusion rates for L=6.5 are found to be 5–10 times larger than that for L=3.5 at these pitch angles. In the presence of cross terms, PSD for MeV electrons after 24 h decreases by about 25, 12, 10 and 8 times at L=3.5, 4.5, 5.5 and 6.5 near the loss cone, and increases by about 55, 45, 30 and 20 times at larger pitch angles, respectively. After 24 h, the ratios between MeV electron PSDs from simulations without and with cross diffusion at L=3.5, 4.5, 5.5 and 6.5 are about 350, 600, 800 and 800 near the loss cone, and become 5, 5.5, 6.5 and 8 at pitch angle 90°, respectively. These results demonstrate that neglect of cross diffusion generally results in the overestimate of PSD, and the cross diffusion plays a more significant role in the resonant interaction between chorus waves and outer radiation belt electrons at larger L.
61 articles