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Volume 30 Issue 10
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GENERAL
Modified (1+1)-Dimensional Displacement Shallow Water Wave System
LIU Ping, YANG Jian-Jun, REN Bo
Chin. Phys. Lett. 2013, 30 (10): 100201 .   DOI: 10.1088/0256-307X/30/10/100201
Abstract   PDF(pc) (526KB) ( 569 )
Recently, a (1+1)-dimensional displacement shallow water wave system (1DDSWWS) was constructed by applying variational principle of the analytic mechanics under the Lagrange coordinates. However, fluid viscidity is not considered in the 1DDSWWS, which is the same as the famous Korteweg-de Vries (KdV) equation. We modify the 1DDSWWS and add the term related to fluid viscosity to the model by means of dimension analysis. For the perfect fluids, the coefficient of kinematic viscosity is zero, then the modified 1DDSWWS (M1DDSWWS) will degenerate to 1DDSWWS. The KdV-Burgers equation and the Abel equation can be derived from the M1DDSWWS. The calculation on symmetry shows that the system is invariant under the Galilean transformations and the spacetime translations. Two types of exact solutions and some evolution graphs of the M1DDSWWS are proposed.
A Method to Construct the Nonlocal Symmetries of Nonlinear Evolution Equations
XIN Xiang-Peng, CHEN Yong
Chin. Phys. Lett. 2013, 30 (10): 100202 .   DOI: 10.1088/0256-307X/30/10/100202
Abstract   PDF(pc) (432KB) ( 637 )
A method is proposed to seek the nonlocal symmetries of nonlinear evolution equations. The validity and advantages of the proposed method are illustrated by the applications to the Boussinesq equation, the coupled Korteweg-de Vries system, the Kadomtsev–Petviashvili equation, the Ablowitz–Kaup–Newell–Segur equation and the potential Korteweg-de Vries equation. The facts show that this method can obtain not only the nonlocal symmetries but also the general Lie point symmetries of the given equations.
Distance Ranging Based on Quantum Entanglement
XIAO Jun-Jun, FANG Chen, HAN Xiao-Chun, ZHAO Jian-Kang, ZENG Gui-Hua
Chin. Phys. Lett. 2013, 30 (10): 100301 .   DOI: 10.1088/0256-307X/30/10/100301
Abstract   PDF(pc) (847KB) ( 418 )
In the quantum metrology, applications of quantum techniques based on entanglement bring in some better performances than conventional approaches. We experimentally investigate an application of entanglement in accurate ranging based on the second-order coherence in the time domain. By a fitting algorithm in the data processing, the optimization results show a precision of ±200 μm at a distance of 1043.3 m. In addition, the influence of jamming noise on the ranging scheme is studied. With some different fitting parameters, the result shows that the proposed scheme has a powerful anti-jamming capability for white noise.
Kochen-Specker Sets with a Mixture of 16 Rank-1 and 14 Rank-2 Projectors for a Three-Qubit System
S. P. Toh
Chin. Phys. Lett. 2013, 30 (10): 100302 .   DOI: 10.1088/0256-307X/30/10/100302
Abstract   PDF(pc) (419KB) ( 274 )
Kochen-Specker (KS) theorem denies the possibility for the noncontextual hidden variable theories to reproduce the predictions of quantum mechanics. A set of projection operators (projectors) and bases used to show the impossibility of noncontextual definite values assignment is named as the KS set. Since one KS set with a mixture of 16 rank-1 projectors and 14 rank-2 projectors was proposed in 1995 [Kernaghan M and Peres A Phys. Lett. A 198 (1995) 1] for a three-qubit system, there have been plenty of the same type KS sets and we propose a systematic way to produce them. We also propose a probabilistic state-dependent proof of the KS theorem that mainly focuses on the values assignment for all the rank-2 projectors.
State-Independent Proof of Kochen–Specker Theorem with Thirty Rank-Two Projectors
S. P. Toh
Chin. Phys. Lett. 2013, 30 (10): 100303 .   DOI: 10.1088/0256-307X/30/10/100303
Abstract   PDF(pc) (378KB) ( 222 )
The Kochen–Specker theorem states that noncontextual hidden variable theories are incompatible with quantum mechanics. We provide a state-independent proof of the Kochen–Specker theorem using the smallest number of projectors, i.e., thirty rank-2 projectors, associated with the Mermin pentagram for a three-qubit system.
Measurement of Berry Phase Associated with Higher Dimensional Orbital Angular Momentum of Light by Interference Method
XU Yuan, HUANG Yuan-Yuan, HU Ling, ZHANG Pei, WEI Dong, LI Hong-Rong, GAO Hong, LI Fu-Li
Chin. Phys. Lett. 2013, 30 (10): 100304 .   DOI: 10.1088/0256-307X/30/10/100304
Abstract   PDF(pc) (1903KB) ( 325 )
Berry phase of higher-dimensional orbital angular momentum of light is studied. When an Nth order orbital state, described by a vector in (N+1)-dimensional space, evolves through a closed path in space of orbital states, there will exist a higher order orbital Berry phase. We calculate this phase by using the matrix transformation theory. A direct measurement of the higher-order orbital Berry phase is also carried out by the interference method. The experimental results are in good agreement with the theoretical description, which shows that the Berry phase is proportional to the orbital angular momentum of light.
Collision of Two General Geodesic Particles around a Kerr–Newman Black Hole
LIU Chang-Qing
Chin. Phys. Lett. 2013, 30 (10): 100401 .   DOI: 10.1088/0256-307X/30/10/100401
Abstract   PDF(pc) (461KB) ( 398 )
Collision of two general geodesic particles around the Kerr–Newman black hole is studied and the center-of-mass (c.m.) energy of the non-marginally and marginally bound critical particles in the direct collision and the last stable orbit collision scenarios is obtained. The constraint conditions that arbitrarily high c.m. energy can be obtained for the near-horizon collision of two general geodesic particles in the extremal Kerr–Newman black hole is found, and it is noted that the charge decreases the value of the latitude in which arbitrarily high c.m. energy can occur.
Pulsar Timing Residuals Induced by Gravitational Waves from Single Non-evolving Supermassive Black Hole Binaries with Elliptical Orbits
TONG Ming-Lei, YAN Bao-Rong, ZHAO Cheng-Shi, YIN Dong-Shan, ZHAO Shu-Hong, YANG Ting-Gao, GAO Yu-Ping
Chin. Phys. Lett. 2013, 30 (10): 100402 .   DOI: 10.1088/0256-307X/30/10/100402
Abstract   PDF(pc) (540KB) ( 297 )
The pulsar timing residuals induced by gravitational waves from non-evolving single binary sources with general elliptical orbits are analyzed. For different orbital eccentricities, the timing residuals present different properties. The standard deviations of the timing residuals induced by a fixed gravitational wave source are calculated for different values of the eccentricity. We also analyze the timing residuals of PSR J0437-4715 induced by one of the best known single gravitational wave sources, the supermassive black hole binary in the blazar OJ287.
Thermodynamics of Phantom Energy Accreting onto a Black Hole in Einstein–Power–Maxwell Gravity
G. Abbas, R. M. Ramzan
Chin. Phys. Lett. 2013, 30 (10): 100403 .   DOI: 10.1088/0256-307X/30/10/100403
Abstract   PDF(pc) (412KB) ( 320 )
We investigate the phantom energy accretion onto a 3D black hole formulated in the Einstein–Power–Maxwell theory, and present the conditions for critical accretion of phantom energy onto the black hole. Further, we discuss the thermodynamics of phantom energy accreting onto the black hole and find that the first law of thermodynamics is easily satisfied while the second law and the generalized second law of thermodynamics remain invalid and conditionally valid, respectively. The results for the Banados–Teitelboim–Zanelli black hole can be recovered by taking Maxwellian contribution equal to zero.
A Nanosize Quantum-Dot Photoelectric Refrigerator
LI Cong, ZHANG Yan-Chao, HE Ji-Zhou
Chin. Phys. Lett. 2013, 30 (10): 100501 .   DOI: 10.1088/0256-307X/30/10/100501
Abstract   PDF(pc) (613KB) ( 347 )
We investigate the thermodynamic performance of a nanosized photoelectric refrigerator consisting of two single energy levels embedded between two reservoirs at different temperatures. Based on the quantum master equation, expressions for the cooling power and coefficient of performance (COP) of the refrigerator are derived. The characteristic curves between the cooling power and COP are plotted. Moreover, the optimal performance parameters are analyzed by the numerical calculation and graphic method. The influence of the nonradiative processes on the performance characteristics and optimal performance parameters are discussed in detail.
Enhanced Second-Order Resonance Actuation and Frequency Response Modulation of Microcantilever by Dual Coplanar Counter Electrodes
FENG Zhao-Bin, LIU Duo
Chin. Phys. Lett. 2013, 30 (10): 100701 .   DOI: 10.1088/0256-307X/30/10/100701
Abstract   PDF(pc) (747KB) ( 270 )
We achieve enhanced actuation of the 2nd-order resonance of a microcantilever in a capacitive microcantilever structure featured by a dual coplanar counter electrodes configuration. A torque about the static point of the 2nd eigenmode is generated in this configuration and therefore enables effective actuation of the 2nd-order resonance. It is further confirmed that the torque has the effect of suppressing the 1st-order resonance. As a result, the frequency response curve of the microcantilever beam can be modulated. Our results suggest that electric actuation of any higher-order resonances of the microcantilever can be realized through a rational design of counter electrodes.
A Photoacoustic Imaging System with Optimized Real-Time Parallel Reconstruction
FENG Ting, YUAN Jie, YU Yao, ZHOU Yu, XU Guan
Chin. Phys. Lett. 2013, 30 (10): 100702 .   DOI: 10.1088/0256-307X/30/10/100702
Abstract   PDF(pc) (798KB) ( 327 )
Biomedical photoacoustic tomography (PAT) provides anatomical, functional, metabolic, molecular, and genetic contrasts of vasculature, hemodynamics, oxygen metabolism, biomarkers, and gene expression. These attributes bring PAT to a wide variety of applications in clinical medicine and preclinical research. We report the development of a real-time PAT imaging system, which integrates signal scanning, image reconstruction and displaying photoacoustic images in real time. An optimized back projection algorithm for PAT imaging is proposed and tested on a latest graphics process unit based card. The whole system is built and tested in an experiment for monitoring moving blood events to validate the real-time performance of this system to image moving events.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Semileptonic Production of Scalar and Tensor p-Wave Charmed Mesons
JIANG Yue, WANG Guo-Li, WANG Tian-Hong, JU Wan-Li
Chin. Phys. Lett. 2013, 30 (10): 101101 .   DOI: 10.1088/0256-307X/30/10/101101
Abstract   PDF(pc) (502KB) ( 268 )
With the same constituents of quark and antiquark, the p-wave state has a higher mass than the corresponding s-wave state, but the relativistic corrections are much larger in the processes of which p-wave mesons are involved. Considering this, the relativistic Bethe–Salpeter method is applied to estimate the branching fractions of semileptonic decays B(s)D*(sJ) (J=0,2). Our predictions are Br[B0sD*+s0(2317)l?ν]=0.50%, Br[B0sD*+s2(2573)l?ν]=0.40%, Br[B?D*00(2400)l?ν]=0.79%, Br[B?D*02(2460)l?ν]=0.28%, Br[B0D*+0(2400)l?ν]=0.58% and Br[B0D*+2(2460)l?ν]=0.27%.
NUCLEAR PHYSICS
An Alternative Description of the Prolate-Oblate Shape Phase Transition in the Interacting Boson Model
ZHANG Zhuo, ZHANG Yu, AN Yang, LI Sheng-Xin, XU Jia
Chin. Phys. Lett. 2013, 30 (10): 102101 .   DOI: 10.1088/0256-307X/30/10/102101
Abstract   PDF(pc) (618KB) ( 375 )
The prolate-oblate shape phase transition in the interacting boson model is investigated for finite N as well as in the large-N classical limit by adopting the Hamiltonian with a linear dependence on the control parameter. The results indicate that the critical dynamics in the new scheme is of the γ-soft type similar to the O(6) dynamics. It is also shown that the structural evolution in the Hf-Hg mass region can be well reproduced in the present scheme.
S-Factor of the 3H(α,γ)7Li Reaction at Astrophysical Energies
H. Sadeghi
Chin. Phys. Lett. 2013, 30 (10): 102501 .   DOI: 10.1088/0256-307X/30/10/102501
Abstract   PDF(pc) (541KB) ( 297 )
The astrophysical S-factor for α-3H radiative capture is calculated at astrophysical energies. We construct conserved two- and three-body electromagnetic currents, using minimal substitution in the explicit momentum dependence of the two- and three-nucleon interactions. The realistic Argonne v18 two-nucleon and Urbana IX or Tucson–Melbourne three-nucleon interactions are considered for calculation. By extrapolation of results for the astrophysical S-factor at zero energy, the energy in the order of 1 keV and less is found to be S(0)=0.107(0.112) keV?b, with(without) three-body interactions in satisfactory agreement with other theoretical results and experimental data.
The Analysis of the Fusion Reaction of Two Colliding Nuclei Using the FCC Lattice Model
M. Golshanian, O. N. Ghodsi, R. Gharaei, V. Zanganeh
Chin. Phys. Lett. 2013, 30 (10): 102502 .   DOI: 10.1088/0256-307X/30/10/102502
Abstract   PDF(pc) (696KB) ( 390 )
The complete fusion channel of two approaching nuclei, including the interaction potential and fusion cross section, is systematically analyzed using the face-center-cubic (FCC) approach. For this purpose, we assume that the initial distribution of the nucleons in target and projectile nuclei is formed based on the FCC lattice model. Moreover, the density-dependent nucleon-nucleon interaction (CDM3Y6) is employed to parameterize the nuclear interactions between the participant nuclei. The obtained results for 45 fusion reactions reveal that the FCC+CDM3Y6 model is able to reproduce the corresponding experimental data of the barrier heights and positions within ±10%, on average. The analytical calculations of the fusion cross section are performed by employing the coupled-channel approach which includes couplings to the low-lying2+ and 3? states in target and projectile nuclei. It is shown that the theoretical values of the fusion excitation functions based on the selected microscopic framework are consistent with the experimental data.
ATOMIC AND MOLECULAR PHYSICS
Role of the Permanent Dipole Moment in Coulomb Explosion
ZHANG Cai-Ping, MIAO Xiang-Yang
Chin. Phys. Lett. 2013, 30 (10): 103101 .   DOI: 10.1088/0256-307X/30/10/103101
Abstract   PDF(pc) (658KB) ( 350 )
By numerically solving the non-Born–Oppenheimer time-dependent Schr?dinger equation in a few-cycle chirped laser field (5-fs, 800-nm), the effect of the permanent dipole moment on the Coulomb explosion is studied by the kinetic-energy-release spectra with the "virtual detector" method. The results indicate that with the effect of the permanent dipole moment, different multiphoton processes for heteronuclear and homonuclear diatomic molecular ions may take place when the wave packets transit from the ground state (1g) to the first excited state (2u), and then move along the excited potential curve, and finally charge-resonant enhanced ionization occurs at critical internuclear distance. As a result, despite the similar ionization probabilities for these two systems at higher vibrational level with larger chirp parameter β, the structure of the Coulomb explosion spectrum for the former is prominently different from that for the latter.
Self-Healing of Stone–Wales Defects in Boron Nitride Monolayer by Irradiation: Ab Initio Molecular Dynamics Simulations
XUE Shu-Wen, CHEN Jian, ZHANG Jun
Chin. Phys. Lett. 2013, 30 (10): 103102 .   DOI: 10.1088/0256-307X/30/10/103102
Abstract   PDF(pc) (1026KB) ( 369 )
We show an effective method of healing the Stone–Wales (SW) defects through low energy electron irradiation using ab initio molecular dynamics simulation. The SW defects can be healed by irradiation through bond rotation. Although the healing energy shows an anisotropic behavior, it is lower than the displacement threshold energy. The healing of the SW defect through electron irradiation can be effectively used in other sp2-bonded materials.
Alignment-Dependent Ionization of CO2 in the Intense Laser Fields: Single-Active-Electron Approach
HU Shi-Lin, ZHAO Zeng-Xiu, SHI Ting-Yun
Chin. Phys. Lett. 2013, 30 (10): 103103 .   DOI: 10.1088/0256-307X/30/10/103103
Abstract   PDF(pc) (581KB) ( 328 )
We perform Hartree–Fock calculations to obtain occupied orbitals for triatomic molecule CO2, based on one-center method and B-splines to deal with cusps and speed up convergence. Both the orbital energies and charge distribution are in good accordance with the reference data. The valence orbital is propagated with single-active-electron approximation, and the alignment-dependent ionization yield peaks about 40°. However, there are discrepancies between our results and the experimental data, and many-electron effects may need to be exploited further to describe them.
Experimental Measurement of the Absolute Frequencies and Hyperfine Coupling Constants of 133Cs Using a Femtosecond Optical Frequency Comb
JIN Li, ZHANG Yi-Chi, XIANG Shao-Shan, WANG Li-Rong, MA Jie, ZHAO Yan-Ting, XIAO Lian-Tuan, JIA Suo-Tang
Chin. Phys. Lett. 2013, 30 (10): 103201 .   DOI: 10.1088/0256-307X/30/10/103201
Abstract   PDF(pc) (628KB) ( 365 )
High resolution two-photon spectrum of the transitions 6S1/26P3/28S1/2, 9S1/2 and 6S1/26P1/27D3/2 in neutral 133Cs are presented in a room-temperature vapor cell using a femtosecond optical frequency comb. Spectra are obtained by scanning the repetition frequency of the femtosecond optical frequency comb over the two-photon hyperfine structure. The centroid frequency of the 6S1/28S1/2, 9S1/2, 7D3/2 transitions are 729009798.80(17) MHz, 806761363.96(11) MHz, and 780894762.595(23) MHz, respectively. The hyperfine coupling constants of the corresponding states are also obtained. The results are consistent with the previous measurements.
Reduction of the Differential Light Shift by the Spatial Periodicity in an Optical Lattice
YUE Xu-Guang, XU Xia, CHEN Xu-Zong, ZHOU Xiao-Ji
Chin. Phys. Lett. 2013, 30 (10): 103701 .   DOI: 10.1088/0256-307X/30/10/103701
Abstract   PDF(pc) (530KB) ( 279 )
We study the spatial periodicity effects on the differential light shift of noninteracting atoms in an optical lattice. Through the Rabi-spectrum approach, when the wavelength of the optical lattice is not magic, a reduction to the differential light shift is expected. The reduction results from the Bloch bands induced by the quantized motion in the periodic potential. Taking the microwave transition of rubidium atoms as an example, this reduction at some wavelengths can reach one order of magnitude, compared to the data without considering the spatial profile of the optical lattice. When the atomic temperature is considered, the differential light shift increases or decreases with temperature, depending on the wavelength of the lattice. Our results should be beneficial for microwave optical lattice clock and precision measurements.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Darboux Transformation and Solutions of the Two-Component Hirota–Maxwell–Bloch System
YANG Jie-Ming, LI Chuan-Zhong, LI Tian-Tian, CHENG Zhao-Neng
Chin. Phys. Lett. 2013, 30 (10): 104201 .   DOI: 10.1088/0256-307X/30/10/104201
Abstract   PDF(pc) (1952KB) ( 339 )
We derive the n-fold Darboux transformation of the two-component Hirota and Maxwell–Bloch (TH-MB) equations and its determinant representation. Using Darboux determinant representation, we provide soliton solutions, positon solutions of the TH-MB equations.
Continuous-Wave Dual-Wavelength Nd:YAG Ceramic Laser at 1112 and 1116 nm
ZHANG Hua-Nian, CHEN Xiao-Han, WANG Qing-Pu, LI Ping
Chin. Phys. Lett. 2013, 30 (10): 104202 .   DOI: 10.1088/0256-307X/30/10/104202
Abstract   PDF(pc) (494KB) ( 403 )
An efficient dual-wavelength laser-diode-pumped Nd:YAG ceramic laser operating at 1112 and 1116 nm is demonstrated. We obtain a maximum total output power of 3.43 W including a 1.77 W 1112 nm component and a 1.66 W 1116 nm component under a pump power of 16.1 W, corresponding to a slope efficiency of 23.7% and a total optical-to-optical efficiency of 21.3%.
A Wide Spaced Femtosecond Ti:Sapphire Frequency Comb at 15 GHz by a Fabry–Pérot Filter Cavity
HOU Lei, HAN Hai-Nian, ZHANG Jin-Wei, LI De-Hua, WEI Zhi-Yi
Chin. Phys. Lett. 2013, 30 (10): 104203 .   DOI: 10.1088/0256-307X/30/10/104203
Abstract   PDF(pc) (671KB) ( 231 )
We realize a wide spaced frequency comb by using an external low-fineness Fabry–Pérot (F-P) cavity to filter few-cycle laser pulses from a Kerr-lens mode-locked Ti:sapphire laser at the fundamental repetition rate of 350 MHz. Mode spacing as wide as 15 GHz with spectrum covered from 690 nm to 710 nm is demonstrated, corresponding to a filter multiple of about 43. The scanning transmission peaks after the F-P cavity with cavity lengths are also simulated numerically, and the results are in agreement with the experiment.
High-Q Photonic Crystal Cavity in a Single-Mode Silicon Ridge Waveguide
YU Ping, QIU Chen, HU Ting, QIU Hui-Ye, GE Fang-Fang, JIANG Xiao-Qing, YANG Jian-Yi
Chin. Phys. Lett. 2013, 30 (10): 104204 .   DOI: 10.1088/0256-307X/30/10/104204
Abstract   PDF(pc) (628KB) ( 361 )
We demonstrate experimentally a high-Q one-dimensional photonic crystal cavity in a widely-used 450×220 nm single mode silicon ridge waveguide. Transmission spectrum measurement is performed by using the vertical fiber-grating coupling characterization method. The Q factor up to 2.6×104 is found by fitting the line shape of the transmission spectrum, and the normalized transmission of nearly 20% is achieved. Three-dimensional finite difference time domain calculations show that the modal volume of the fundamental mode is 1.1(λ/n)3. With the standard silicon waveguide width, the demonstrated 1D PhC cavity may be used as a building block for integrated photonic circuits and on-chip sensing applications.
A High Power InGaN-Based Blue-Violet Laser Diode Array with a Broad-Area Stripe
CHEN Ping, ZHAO De-Gang, FENG Mei-Xin, JIANG De-Sheng, LIU Zong-Shun, ZHANG Li-Qun, LI De-Yao, LIU Jian-Ping, WANG Hui, ZHU Jian-Jun, ZHANG Shu-Ming, ZHANG Bao-Shun, YANG Hui
Chin. Phys. Lett. 2013, 30 (10): 104205 .   DOI: 10.1088/0256-307X/30/10/104205
Abstract   PDF(pc) (629KB) ( 1169 )
An array of high power InGaN/GaN multi-quantum-well laser diodes with a broad waveguide is fabricated. The laser diode structure is grown on a GaN substrate by metal-organic chemical vapor deposition. The laser diode array consists of five emitter stripes which share common electrodes on one laser chip. The electrical and optical characteristics of the laser diode array are investigated under the pulse current injection with 10 kHz frequency and 100 ns pulse width. The laser diode array emits at the wavelength of 409 nm, which is located in the blue-violet region, and the threshold current is 2.9 A. The maximum output light peak power is measured to be 7.5 W at the wavelength of 411.8 nm under the current of 25 A.
Topological Charge Conversion with Spiral-Slit Screens
LI Zhen-Hua, ZHANG Mei-Na, LI Xing, LIU Chun-Xiang, CHENG Chuan-Fu
Chin. Phys. Lett. 2013, 30 (10): 104206 .   DOI: 10.1088/0256-307X/30/10/104206
Abstract   PDF(pc) (2314KB) ( 531 )
We propose a method of converting the topological charge (TC) of an incident vortex light wave with spiral-slit screens. The phase in the incident vortex beam is redistributed via the optical path adjustment realized by changing the in-plane radial distance of the spiral slit. We numerically calculate the light field with Fresnel diffraction theory, and find the expected TC conversion on the observation plane. Our calculations also show that screens of pinholes distributed in a spiral curve can be used for the implementation instead of spiral slits. The method can also be used to distinguish the TCs of the incident vortices by reading the diffracted intensity patterns.
Suppression of the Thermal Effects in the Femtosecond Laser Processing of Fiber Bragg Gratings
CUI Wei, SI Jin-Hai, CHEN Tao, YAN Fei, CHEN Feng, HOU Xun
Chin. Phys. Lett. 2013, 30 (10): 104207 .   DOI: 10.1088/0256-307X/30/10/104207
Abstract   PDF(pc) (690KB) ( 345 )
The thermal effects on the processing of type-I IR fiber Bragg gratings (FBGs) using a femtosecond laser with a phase mask are investigated. Thermal effects are significantly suppressed by using interval exposure mode and reducing the tension on the fiber. FBGs with improved photo-induced refractive index modulation are fabricated in the standard telecom fiber. The index modulation reaches 1.6×10?3. The reflectivity and bandwidth are measured to be ?0.36 dB and 1.27 nm, respectively.
Photodarkening-Induced Absorption and Fluorescence Changes in Yb Fibers
CHEN Gui, XIE Lu, WANG Yi-Bo, ZHAO Nan, LI Hai-Qing, JIANG Zuo-Wen, PENG Jing-Gang, YANG Lü-Yun, DAI Neng-Li, LI Jin-Yan
Chin. Phys. Lett. 2013, 30 (10): 104208 .   DOI: 10.1088/0256-307X/30/10/104208
Abstract   PDF(pc) (603KB) ( 342 )
We study the photodarkening effect in a double clad ytterbium-doped silica fiber fabricated by modified chemical vapor deposition and solution doping. A common measurement technology for photodarkening is used to study the photodarkening-induced absorption spectra. We present a fast and simple method to observe the PD effect by measurement of the fluorescence spectra. The method proposed here can be used to observe the influence for a short time, and thus reduces the requirements of system stability and heat management. It is obtained that under the condition of 45.5% Yb ion inversion level, photodarkening-induced excessive loss at an equilibrium state is above 4.5 dB/m and florescence intensity degradation is above 10% after 500 min pumping at 1041 nm for the home-made normal Yb/Al co-doped silica fiber.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Faraday Effect on Negative Refraction in Uniaxial Anisotropic Plasma Metamaterials
GUO Bin
Chin. Phys. Lett. 2013, 30 (10): 105201 .   DOI: 10.1088/0256-307X/30/10/105201
Abstract   PDF(pc) (760KB) ( 457 )
Negative refraction is the name for an electromagnetic phenomenon in which light rays are refracted at an interface in the reverse sense to that normally expected. A uniaxial anisotropic plasma metamaterial that exhibits negative refraction is demonstrated and the necessary conditions are derived for negative refraction. The Faraday effect on the negative refraction in the proposed plasma metamaterials is discussed. Parameter dependences such as plasma filling factor, dielectric constant of background materials, and external magnetic field are calculated and discussed.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Ground States of Silicon-Multisubstituted Fullerene: First-Principles Calculations and Monte Carlo Simulations
FAN Bing-Bing, SHI Chun-Yan, ZHANG Rui, JIA Yu
Chin. Phys. Lett. 2013, 30 (10): 106101 .   DOI: 10.1088/0256-307X/30/10/106101
Abstract   PDF(pc) (935KB) ( 467 )
We present a systematical study on the possible stable structures of C60?xSix (x=1–12) fullerenes using first-principles calculations combined with Monte-Carlo simulations. The initial fullerenes randomly substituting with silicon atoms are firstly generated and then their total energies are calculated quickly. The ground-state structures are found by the annealing process where Si atoms exchange their positions with C atoms. The stable structures are finally obtained through first-principles calculations with high precision. For the cases with a small amount of Si atoms (x4), results similar to those report previously are achieved. Some new stable Si-doped fullerenes with more Si atoms are also predicated. The results show that Si atoms in the C60?xSix (x4) fullerenes have a trend of segregation with C atoms. The minimum-energy structure changes from a chemical unstable state to a chemical stable state when x8.
Correlation between the Local Atomic Structure of Melts and Glass Forming Ability in Zr-Cu-Ni-Al Alloys
WU Chen, HUANG Yong-Jiang, SHEN Jun
Chin. Phys. Lett. 2013, 30 (10): 106102 .   DOI: 10.1088/0256-307X/30/10/106102
Abstract   PDF(pc) (560KB) ( 341 )
The correlation between the atomic structure of melts and glass forming ability (GFA) in Zr53Cu18.7Ni12Al16.3 and Zr50.7Cu28Ni9Al12.3 (abbreviated as Zr53 and Zr507, respectively) alloys are studied by first principle simulations. The topological structure can be described by the Al-centered Kasper polyhedra and other distorted clusters with extrinsic disclinations. Due to the lower Al content in the Zr507 melts, its number of icosahedra is larger than that of the Zr53 melts. Also, the icosahedra in the Zr507 melts possess smaller distortion than those of the Zr53 melts, making the icosahedra more stable in the Zr507 melts. These two structural differences contribute to the slow dynamics and further enhance the GFA in the Zr507 alloy.
Biaxiality of Liquid Crystal Formed by Bent-Core Molecules with a Transverse Dipole Moment Deviating from their Angular Bisector
YE Xiao-Fang, MERLITZ Holger, WU Chen-Xu
Chin. Phys. Lett. 2013, 30 (10): 106103 .   DOI: 10.1088/0256-307X/30/10/106103
Abstract   PDF(pc) (682KB) ( 340 )
Monte Carlo simulations are performed to study the phase diagram of liquid crystals formed by bent-core molecules with a strong transverse dipole moment deviating from their angular bisector. The results show that the strong dipolar interaction, after suppressing uniaxial phases, encourages biaxiality, which leads to a Landau point or even to a Landau line in the phase diagram, inducing a more stable biaxial nematic phase. It is also found that a deviation of dipole moment from the angular bisector also suppresses uniaxiality in the small bend-angle regime.
Surface Oxidation Properties in a Topological Insulator Bi2Te3 Film
GUO Jian-Hua, QIU Feng, ZHANG Yun, DENG Hui-Yong, HU Gu-Jin, LI Xiao-Nan, YU Guo-Lin, DAI Ning
Chin. Phys. Lett. 2013, 30 (10): 106801 .   DOI: 10.1088/0256-307X/30/10/106801
Abstract   PDF(pc) (589KB) ( 1272 )
Bi2Te3 films are grown on (111)-oriented GaAs substrates by using the hot wall epitaxy method and the surface oxidation properties in the films are investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, and x-ray diffraction. The results show that the films are c-axis oriented. Two pairs of new peaks in the XPS spectra involved with the binding energies from Bi 4f and Te 3d electrons correspond to Bi–O–Te bonds. Besides the A1g1, Eg2 andA1g2 vibration modes from Bi2Te3 films, two new peaks at 93.5 cm?1 and 123 cm?1 are observed in Raman spectra, which are assigned to α-Bi2O3 and TeO2, respectively. Our results are helpful for analyzing the degradation mechanism of topological surface states in Bi2Te3.
Topography Multiplicity of Titanyl Phthalocyanine on Ultrathin Insulating Films Observed by STM
YUAN Bing-Kai, CHEN Peng-Cheng, ZHANG Jun, DENG Ke, CHENG Zhi-Hai, WANG Chen
Chin. Phys. Lett. 2013, 30 (10): 106802 .   DOI: 10.1088/0256-307X/30/10/106802
Abstract   PDF(pc) (949KB) ( 323 )
Individual titanyl phthalocyanine (TiOPc) molecules on ultrathin sodium chloride striped films grown on Cu(110) exhibit two different topographies with 8-lobes and 6-lobes when imaged by scanning tunneling microscopy (STM). Direct images of the molecular orbitals of the molecules with 8-lobes are obtained, indicating that the electronic structure of the TiOPc molecule are decoupled from the metallic substrate. For the TiOPc molecule with 6-lobes, the STM images at negative and positive bias polarities show the same structures as 2-fold symmetry except for the 90° rotation with respect to each other. This phenomenon may be attributed to the splitting of the two former degenerate lowest unoccupied molecular orbitals due to the negative charging of the molecule. The identification of the molecular orbital splitting on the ultrathin insulating layer could deepen the understanding of the intrinsic properties of semi-conducting molecules.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Thick-Film Negative-Temperature-Coefficient Thermistors with a Linear Resistance-Temperature Relation
LING Zhi-Yuan, HE Lin
Chin. Phys. Lett. 2013, 30 (10): 107201 .   DOI: 10.1088/0256-307X/30/10/107201
Abstract   PDF(pc) (1098KB) ( 440 )
The effect of the resistance R of Mn1.85Co0.3Ni0.85O4 (MCN) thick-film negative-temperature-coefficient (NTC) thermistors on temperature T is studied carefully. Interestingly, the RT relation is found to be decided simultaneously by the characteristic of the MCN oxide and the electrode structure of the NTC thermistor. For plane end electrodes, the RT relation is nonlinear. However, for plane fork electrodes, the RT relation can be linear. To clarify the intrinsic mechanism of the linear RT relation, the electric field distribution in the MCN thick film is simulated. The obtained results suggest that the non-uniform electric field distribution between the electrodes is responsible for the RT relation linearization.
Nonlinear Optical Properties in a Quantum Dot of Some Polar Semiconductors
A. Azhagu Parvathi, A. John Peter, Chang Kyoo Yoo
Chin. Phys. Lett. 2013, 30 (10): 107301 .   DOI: 10.1088/0256-307X/30/10/107301
Abstract   PDF(pc) (673KB) ( 491 )
Exciton binding energy, interband emission energy, oscillator strength, and some nonlinear optical properties in quantum dots made up of polar semiconductors are computed with the geometrical confinement. The effects of the interaction of charge carriers with the longitudinal optical phonons on the exciton binding energy are included. The anisotropy of the effective masses of holes is incorporated throughout the calculations. Nonlinear optical exciton absorption of II–VI systems based on some polar semiconductors in the presence of LO phonons is discussed. The optical rectification coefficient associated with the intersubband transitions in a quantum dot of polar semiconductors is investigated. Changes of refractive index with the photon energy in a polar quantum dot are found. Our results show that the polar bound excitons in II–VI based polar semiconductors depend on the geometrical confinement, and the nonlinear optical properties strongly depend on the polar materials.
Bipolar Resistive Switching Characteristics of TiN/HfOx/ITO Devices for Resistive Random Access Memory Applications
TAN Ting-Ting, CHEN Xi, GUO Ting-Ting, LIU Zheng-Tang
Chin. Phys. Lett. 2013, 30 (10): 107302 .   DOI: 10.1088/0256-307X/30/10/107302
Abstract   PDF(pc) (656KB) ( 527 )
Resistive switching characteristics of hafnium oxide are studied for possible nonvolatile memory device applications. The HfOx films with different oxygen contents are deposited by rf magnetron sputtering under different O2 flow rates. The films are amorphous, and the stoichiometric of the film is improved by increasing the O2 flow rate. Current-voltage characteristics of the TiN/HfOx/ITO device are investigated with 1 mA compliance. The bipolar resistive switching behavior is observed for the TiN/HfOx/ITO structure, and the resistive switching mechanism of the TiN/HfOx/ITO structure is explained by trap-controlled space charge limit current conduction.
Effects of Contact Geometry on the Transport Properties of a Silicon Atom
LIU Fu-Ti, CHENG Yan, YANG Fu-Bin, CHEN Xiang-Rong
Chin. Phys. Lett. 2013, 30 (10): 107303 .   DOI: 10.1088/0256-307X/30/10/107303
Abstract   PDF(pc) (689KB) ( 290 )
Contact geometry and electronic transport properties of a silicon atom sandwiched between Au electrodes in three different anchoring configurations are investigated by using the density functional theory combined with the non?equilibrium Green function method. We simulate the nanoscale junction breaking process and calculate the corresponding cohesion energy, obtain the equilibrium conductance and the projected density of states of junctions in an optimal postion. We also calculate the conductance and the current of junctions at the equilibrium position under small bias voltage. It is found that all junctions have large conductance and show a linear IV relationship, but the current and conductance of a hollow-hollow configuration is always the biggest under the voltage range of -1.2 V1.2V. The calculated results proved that the coupling morphology of a silicon atom connected with electrodes has an important effect on the electronic transport properties of the nanoscale junction.
Low Bias Negative Differential Resistance Behavior in Carbon/Boron Nitride Nanotube Heterostructures
WU Qiu-Hua, ZHAO Peng, LIU De-Sheng
Chin. Phys. Lett. 2013, 30 (10): 107304 .   DOI: 10.1088/0256-307X/30/10/107304
Abstract   PDF(pc) (2437KB) ( 509 )
Based on the non-equilibrium Green's method and density functional theory, we investigate the electronic transport properties of ternary heterostructures based on carbon nanotubes and boron nitride nanotubes, with different atomic compositions, coupled to gold electrodes. Negative differential resistance (NDR) behavior can be observed due to suppression of the conduction channel at a certain bias. More importantly, the position of NDR can be tuned into the bias range as low as tens of meV by increasing the length of boron nitride nanotube. The peak-to-valley ratio, which is a typical character of NDR behavior, is also sensitive to the atomic compositions.
Dirac Points in Two-Dimensional Inverse Opals
G. D. Mahan
Chin. Phys. Lett. 2013, 30 (10): 107305 .   DOI: 10.1088/0256-307X/30/10/107305
Abstract   PDF(pc) (752KB) ( 317 )
The electron energy states and energy bands are calculated for a two-dimensional inverse opal structure. Assume that the opal structure is closed-packed circles, the inverse opal has the honeycomb lattice. The honeycomb lattice in two dimensions has a Diract point. Its properties can be manipulated by altering the structure of the inverse opal: the radius of the circle, and the small gap between circles.
Hydrogen Storage Capacity Study of a Li+Graphene Composite System with Different Charge States
SUI Peng-Fei, ZHAO Yin-Chang, DAI Zhen-Hong, WANG Wei-Tian
Chin. Phys. Lett. 2013, 30 (10): 107306 .   DOI: 10.1088/0256-307X/30/10/107306
Abstract   PDF(pc) (1396KB) ( 363 )
Based on first-principles plane-wave calculations, we firstly reconfirm that the Li+graphene complex can be taken as a hydrogen storage medium with capacity of 12.8wt%. Then metal adsorption properties of this Li+graphene system with different charge states are investigated. Finally, the hydrogen storage ability of the charging system is calculated. Our calculations show that adding positive charge on a Li+graphene composite results in a conspicuous reduction of Li 2s and Li 2p orbital occupation with respect to the C 2p state. As a result, a stronger bonding between Li and graphene is formed, and a special double-layer hydrogen adsorption structure has been found. Compared to the neutral system, utilizing the positive charged Li+graphene to store hydrogen molecules can solve the issue of clustering of metal atoms after releasing hydrogen, and can improve hydrogen storage capacity up to a gravimetric density of 20.4wt%, correspondingly one adsorbed Li atom can effectively absorb up to seven H2 molecules.
The Observation of Small Polaron Tunnelling in the ab-Plane of K0.85Fe1.66Se2.0
MA Yong-Chang, YAN Qian, ZHAO Jie, LU Cui-Min
Chin. Phys. Lett. 2013, 30 (10): 107401 .   DOI: 10.1088/0256-307X/30/10/107401
Abstract   PDF(pc) (833KB) ( 309 )
The temperature-dependent conductivity spectrum from 3×102 Hz to 1×108 Hz in the ab-plane of a K0.85Fe1.66Se2.0 single crystal is probed. The dc measurements indicate that the charge transport can be described well by the variable range hopping model. From the ac conductivity spectrum, clear evidence for small polaron tunnelling with an activation energy of about 155 meV in ab-plane is revealed. With decreasing temperature, the real part of the dielectric spectrum shifts towards lower frequencies and also shows a wider distribution of the relaxation time. Below 140 K, the peak position of the dielectric loss spectra begins to deviate from thermal excitation behavior, reflecting the freezing of the phonon which assists the tunnelling.
X-Ray Magnetic Linear Dichroism of Co35Fe65 Alloy Films Annealed with and without Oxygen Gas
WANG De-Lai, CUI Ming-Qi, YANG Dong-Liang, XI Shi-Bo, LIU Li-Juan
Chin. Phys. Lett. 2013, 30 (10): 107501 .   DOI: 10.1088/0256-307X/30/10/107501
Abstract   PDF(pc) (620KB) ( 387 )
X-ray magnetic linear dichroism (XMLD) experiments were carried out at beam line 3W1B of the Beijing Synchrotron Radiation Facility. The results demonstrate the experimental XMLD spectra of Co35Fe65 alloy film annealed with and without oxygen gas, in agreement with the ligand field multiplet calculation. It can be concluded that cobalt atoms are more difficult to oxidize than iron atoms. The oxygen atoms inserting into the sample surface interval lead to the lattice distortion and the fine tuning of the occupation number of absorption atom d-orbits.
Dynamic Control of Tunneling Conductance in Ferroelectric Tunnel Junctions
ZOU Ya-Yi, CHEW Khian-Hooi, ZHOU Yan
Chin. Phys. Lett. 2013, 30 (10): 107701 .   DOI: 10.1088/0256-307X/30/10/107701
Abstract   PDF(pc) (703KB) ( 316 )
We investigate the dynamic characteristics of electric polarization P(t) in a ferroelectric junction under ac applied voltage and stress, and calculate the frequency response and the cut-off frequency f0, which provides a reference for the upper limit of the working frequency. Our study might be significant for sensor and memory applications of nanodevices based on ferroelectric junctions.
Effective Electromagnetic Parameters and Absorbing Properties for Honeycomb Sandwich Structures with a Consideration of the Disturbing Term
HU Ji-Wei, HE Si-Yuan, RAO Zhen-Min, ZHU Guo-Qiang, YIN Hong-Cheng
Chin. Phys. Lett. 2013, 30 (10): 107702 .   DOI: 10.1088/0256-307X/30/10/107702
Abstract   PDF(pc) (504KB) ( 866 )
The interaction between particles cannot be ignored when a high frequency electromagnetic wave is incident on a mixed media. Strong fluctuation theory with correlation function is a suitable method to describe the problem. Materials with honeycomb sandwich structures with an absorber included are investigated. The effective electromagnetic parameters and reflection coefficient of these materials are deduced and numerical results are given. Compared with the method with a disturbing term not considered, this method shows better absorbing properties.
Bulk Heterojunction Photovoltaic Devices Based on a Poly(2-Methoxy, 5-Octoxy)-1, 4-Phenylenevinylene-Single Walled Carbon Nanotube-ZnSe Quantum Dots Active Layer
QU Jun-Rong, ZHENG Jian-Bang, WU Guang-Rong, CAO Chong-De
Chin. Phys. Lett. 2013, 30 (10): 107801 .   DOI: 10.1088/0256-307X/30/10/107801
Abstract   PDF(pc) (1827KB) ( 295 )
A solution-processed bulk heterojunction photovoltaic cell is fabricated based on poly[(2-methoxy, 5-octoxy)-1, 4-phenylenevinylene](MOPPV)-single walled carbon nanotube(SWNT)-ZnSe quantum dots. The surface morphology shows the formation of an interpenetrating network between well-dispersed SWNTs and ZnSe in the MOPPV matrix. A blue-shifted absorption band indicates the strong electron interaction between SWNTs, ZnSe and MOPPV. A marked increase in the short-circuit current and power conversion efficiency (PCE) of ITO/PEDOT:PSS/MOPPV-SWNT-ZnSe/LiF/Al devices was achieved and compared with that without SWNTs. Results indicate that the enhanced performance is contributed by a high photocurrent due to efficient exciton dissociation and increased mobility for carrier transport in the SWNT pathway.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Structure and Absorbability of a Nanometer Nonmetallic Polymer Thin Film Coating on Quartz Used in Piezoelectric Sensors
GU Yu, LI Qiang, TIAN Fang-Fang, XU Bao-Jun
Chin. Phys. Lett. 2013, 30 (10): 108101 .   DOI: 10.1088/0256-307X/30/10/108101
Abstract   PDF(pc) (574KB) ( 244 )
We present a new type of gas piezoelectric sensor taking quartz piezoelectric crystal as the basal material and nanometer nonmetallic polymer thin film coating as the surface. The coating, plated by vacuum electron beam dispersion (EBD) coating technology, is carried out by employing a nanometer nonmetallic polymer thin film that has properties of selecting and identifying characteristic materials. An experimental survey shows that EBD coating technology can produce a uniform thickness of the thin film coating, and the physical and chemical analyses show that the coating has a high performance of absorption using the method of infrared spectroscopy. Meanwhile, the absorption and sensitivity performance of the thin film coating will change if other organic materials are added to the coated thin film. Through the measurement of the thin film coating, the feature of sensitivity to the change of humidity is acquired. Based on the above description, a new type of gas piezoelectric sensor is designed and manufactured reasonably, which provides a valid method to rapidly monitor and distinguish complex gases.
Fabrication and Characterization of Single-Crystalline AgSbTe Nanowire Arrays
YANG You-Wen, LI Tian-Ying, ZHU Wen-Bin, MA Dong-Ming, CHEN Dong
Chin. Phys. Lett. 2013, 30 (10): 108102 .   DOI: 10.1088/0256-307X/30/10/108102
Abstract   PDF(pc) (2666KB) ( 337 )
Ternary semiconducting AgSbTe2 nanowire arrays were synthesized for the first time by using the direct-current electrodeposition technique. X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and transmission electron microscopy analyses indicate that the nanowire arrays are high filling, ordered, single crystalline and the nanowires have a highly preferential orientation grown along the [100] direction. Annealing studies show that compared with other temperatures, annealing at 100°C can significantly increase the crystallinity of AgSbTe2 nanowires. The optical absorbance spectra of the AgSbTe2 nanowire arrays show that the optical band gap has a strong blue shift with decreasing the diameter of the nanowire.
Effect of Hydrogen and Nitrogen Carrier Gas Ratio on the Structural and Optical Properties of AlInGaN Alloy
FENG Xiang-Xu, LIU Nai-Xin, ZHANG Lian, ZHANG Ning, ZENG Jian-Ping, WEI Xue-Cheng, LIU Zhe, WEI Tong-Bo, WANG Jun-Xi, LI Jin-Min
Chin. Phys. Lett. 2013, 30 (10): 108103 .   DOI: 10.1088/0256-307X/30/10/108103
Abstract   PDF(pc) (2655KB) ( 733 )
Undoped AlInGaN epilayers on GaN templates with different hydrogen (H2) and nitrogen (N2) carrier gas ratios (1:8, 2:8, and 3:8 as samples 1, 2 and 3, respectively) were grown. When the flow ratio of H2 and N2 rises from 1:8 to 3:8, an indium composition decrease from 3% to 1.2% is observed while the aluminum content stays constant at any flow ratio. Due to the quantum-dot-like effect, photoluminescence intensity is enhanced in the sample with the low carrier gas flow ratio of H2/N2. However, the potential well caused by indium uneven distribution is nonuniform, which is more severe in the sample with carrier gas flow ratio 1:8. The process of carrier transfer from shallow to deep potential wells would be more difficult to accomplish, resulting in the reduction of the photoluminescence intensity. This is found to be consistent with the carriers' lifetime with the help of time-resolved photoluminescence.
The Geometry-Induced Superhydrophobic Property of Carpet-like Zinc Films
LIANG Li-Xing, DENG Yuan, WANG Yao
Chin. Phys. Lett. 2013, 30 (10): 108104 .   DOI: 10.1088/0256-307X/30/10/108104
Abstract   PDF(pc) (1060KB) ( 226 )
Carpet-like zinc films with unique nanowires are fabricated by using a simple physical evaporation method. The definite morphologies of the films endow the superhydrophobic material with a contact angle of about 157.9°, and by additional modification of CF3(CF2)7CH2CH2Si(OCH3)3 the water adhesive force could be tuned from 58.3 μN to 14.6 μN. In order to analyze the controllable adhesion of superhydrophobic Zn films, we study the microstructure and chemical compositions of the films by x-ray diffraction SEM, TEM, HRTEM and EDAX. Furthermore, a model based on the balance of micro-surface energy is proposed to illustrate the relationship of the geometry and wettability properties of the films. The model provides new insights into how to design-oriented microchannels and micro-protuberance on material surfaces, which is of benefit for controlling their ability of caught-collection in air bubbles and water-pinning collection.
The Effect of Using 1-Dodecanethiol as a Processing Additive on the Performances of Polymer Solar Cells
YANG Shao-Peng, WANG Tie-Ning, SHI Jiang-Bo, ZHANG Ye, LI Xiao-Wei, FU Guang-Sheng
Chin. Phys. Lett. 2013, 30 (10): 108401 .   DOI: 10.1088/0256-307X/30/10/108401
Abstract   PDF(pc) (634KB) ( 236 )
We introduce 1-Dodecanethiol (DT) to poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester based polymer solar cells as a processing additive. When the amount of DT is 1vol%, the device performance is best. A final power conversion efficiency of 3.1% is achieved, which is an improvement of more than 40% compared to the reference solar cell without DT. To investigate the causes of improvement of the PCE, UV-vis spectroscopy, external quantum efficiency (EQE) is measured and an AFM is used. The enhanced photovoltaic performances are discussed in terms of optical properties and the film morphology.
Temperature Characteristics of Monolithically Integrated Wavelength-Selectable Light Sources
HAN Liang-Shun, ZHU Hong-Liang, ZHANG Can, MA Li, LIANG Song, WANG Wei
Chin. Phys. Lett. 2013, 30 (10): 108501 .   DOI: 10.1088/0256-307X/30/10/108501
Abstract   PDF(pc) (744KB) ( 269 )
The temperature characteristics of monolithically integrated wavelength-selectable light sources are experimentally investigated. The wavelength-selectable light sources consist of four distributed feedback (DFB) lasers, a multimode interferometer coupler, and a semiconductor optical amplifier. The oscillating wavelength of the DFB laser could be modulated by adjusting the device operating temperature. A wavelength range covering over 8.0 nm is obtained with stable single-mode operation by selecting the appropriate laser and chip temperature. The thermal crosstalk caused by the lateral heat spreading between lasers operating simultaneously is evaluated by oscillating-wavelength shift. The thermal crosstalk approximately decreases exponentially as the increasing distance between lasers.
Electrical Characteristics of High Mobility Si/Si0.5Ge0.5/SOI Quantum-Well p-MOSFETs with a Gate Length of 100 nm and an Equivalent Oxide Thickness of 1.1 nm
MU Zhi-Qiang, YU Wen-Jie, ZHANG Bo, XUE Zhong-Ying, CHEN Ming
Chin. Phys. Lett. 2013, 30 (10): 108502 .   DOI: 10.1088/0256-307X/30/10/108502
Abstract   PDF(pc) (588KB) ( 255 )
Short-channel high-mobility Si/Si0.5Ge0.5/silicon-on-insulator (SOI) quantum-well p-type metal-oxide-semiconductor field effect transistors (p-MOSFETs) were fabricated and electrically characterized. The transistors show good transfer and output characteristics with Ion/Ioff ratio up to 105 and sub-threshold slope down to 100 mV/dec. HfO2/TiN gate stack is employed and the equivalent oxide thickness of 1.1 nm is achieved. The effective hole mobility of the transistors reaches 200 cm2/V?s, which is 2.12 times the Si universal hole mobility.
Thermal and Structural Study of Mono- and Multi-Layered Thin Films Composed of CuAlS2 Chalcogenide
Taher Ghrib, Rawdha Brini, Amel Lafi Al-otaibi, Muneera Abdullah Al-messiere
Chin. Phys. Lett. 2013, 30 (10): 108503 .   DOI: 10.1088/0256-307X/30/10/108503
Abstract   PDF(pc) (1608KB) ( 285 )
Thin films constituted of CuAlS2 nanoparticles deposited with various deposition velocities in single and multilayers onto silicon Si(111) substrates by thermal evaporation have been studied by lifting their structural and thermal properties. Thermal properties of Si(111) and Si(111)/CuAlS2 structures are determined by using the photothermal deflection technique by comparing experimental and theoretical signals. We succeed in extracting the thermal conductivity, the thermal diffusivity, and the electron free mean path of these deposited chalcogenide layers. For the multilayers, the obtained values of the thermal conductivity are in good agreement with the theoretical data.
Osmolyte Effects on the Unfolding Pathway of β-Lactoglobulin
MENG Wei, PAN Hai, QIN Meng, CAO Yi, WANG Wei
Chin. Phys. Lett. 2013, 30 (10): 108701 .   DOI: 10.1088/0256-307X/30/10/108701
Abstract   PDF(pc) (729KB) ( 227 )
There are large amounts of osmolytes inside cells, which impact many physiological processes by complicated mechanisms. The osmolyte effects on the stability and folding of proteins have been studied in detail using simple two-state folding proteins. However, many important functional proteins fold in complex pathways involving various intermediates. Little is known about the osmolyte effects on the folding and unfolding of these proteins. It is noted that β-lactoglobulin (BLG) is an example of such proteins, whose unfolding involves an obvious intermediate state. Using equilibrium chemical denaturation and stopped-flow kinetics, we investigate the unfolding of BLG in the presence of different osmolytes, e.g., glycerol, ethylene glycol (EG) and poly(ethylene glycol)400 (PEG400). It is found that all these osmolytes can stabilize the unfolding intermediate by modulating the relative unfolding kinetics of the native and the intermediate states. The stabilization effects are similar for EG and PEG400 but distinct for glycerol. Since the unfolding intermediates of many proteins are directly related to protein misfolding diseases, evaluation of the osmolyte effects for the unfolding of these proteins in vitro should be beneficial for the understanding of the occurrence of the related diseases in vivo.
Analysis of Electron Recombination in Dye Sensitized Solar Cells Based on the Forward Bias Dependence of Dark Current and Electroluminescence Characterization
XIAO Wen-Bo, LIU Wei-Qing, HE Xing-Dao
Chin. Phys. Lett. 2013, 30 (10): 108801 .   DOI: 10.1088/0256-307X/30/10/108801
Abstract   PDF(pc) (447KB) ( 701 )
The current-voltage and electroluminescence characteristics of dye-sensitized solar cells (DSSCs) are investigated under forward dc bias in a dark environment at room temperature. The results show that the presence of dyes can play an important role in improving device performance, and also produce defects at the TiO2/dye/electrolyte interfaces, which dominate the electron-hole recombination process and become a limiting factor in obtaining high-efficiency DSSCs. The goodness of fit between measured and calculated data supports these conclusions.
Structural Robustness of Weighted Complex Networks Based on Natural Connectivity
ZHANG Xiao-Ke, WU Jun, TAN Yue-Jin, DENG Hong-Zhong, LI Yong
Chin. Phys. Lett. 2013, 30 (10): 108901 .   DOI: 10.1088/0256-307X/30/10/108901
Abstract   PDF(pc) (428KB) ( 861 )
Natural connectivity has been recently proposed to efficiently characterize the structural robustness of complex networks. The natural connectivity, interpreted as the Helmholtz free energy of a network, can be derived from the graph spectrum. We extend the concept of natural connectivity to weighted complex networks, in which the weight represents the number of multiple edges. We prove that the weighted natural connectivity changes monotonically when the weights are increased or decreased. We investigate the influence of weight on the network robustness within scenarios of weight changing and show that the weighted natural connectivity allows a precise quantitative analysis of the structural robustness for weighted complex networks.
Cooperation of a Dissatisfied Adaptive Prisoner's Dilemma in Spatial Structures
ZHANG Wen, LI Yao-Sheng, DU Peng, XU Chen
Chin. Phys. Lett. 2013, 30 (10): 108902 .   DOI: 10.1088/0256-307X/30/10/108902
Abstract   PDF(pc) (457KB) ( 258 )
We study the cooperative behavior of a dissatisfied adaptive prisoner's dilemma via a pair updating rule. We compare two kinds of relationship among the competing agents, one is the well-mixed population and the other is the two-dimensional square lattice. It is found that the cooperation emerges in both the cases and the frequency of cooperation is enhanced in the square lattice. Though it is impossible for the cooperators to have a higher average payoff than that of the defectors in the well-mixed case, the cooperators in the spatial square lattice could have higher average payoffs in certain regions of the game parameters. We theoretically analyze the well-mixed case exactly and the square lattice by pair approximation. The theoretic results are in agreement with the simulation data.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS
The Relation between the Magnetic Field and Spin Period of a Millisecond Pulsar
PAN Yuan-Yue, WANG Na, ZHANG Cheng-Min
Chin. Phys. Lett. 2013, 30 (10): 109701 .   DOI: 10.1088/0256-307X/30/10/109701
Abstract   PDF(pc) (631KB) ( 215 )
Based on the function of the accretion induced magnetic decay, the analytical relationship between the magnetic field B and spin period P of a millisecond pulsar (MSP) is investigated, from which the minimum spin period of about one millisecond can be obtained. With this minimum spin period, the range of the neutron star (NS) radius is constrained in comparison with the measured spin period of MSP. Furthermore, we also study the relation between the spin period and the accretion mass ΔM of the NS, and find that the minimum spin period is achieved with the accretion mass of about 0.2M?, while the bottom magnetic field of about 108 G is obtained.
60 articles