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Volume 30 Issue 2
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GENERAL
Numerical Computation of the Tau Approximation for the Delayed Burgers Equation
F. Khaksar Haghani, S. Karimi Vanani, J. Sedighi Hafshejani
Chin. Phys. Lett. 2013, 30 (2): 020201 .   DOI: 10.1088/0256-307X/30/2/020201
Abstract   PDF(pc) (396KB) ( 809 )
We investigate an efficient extension of the operational Tau method for solving the delayed Burgers equation(DBE) arising in physical problems. This extension gives a useful numerical algorithm for the DBE including linear and nonlinear terms. The orthogonality of the Laguerre polynomials as the basis function is the main characteristic behind the method to decrease the volume of computations and runtime of the method. Numerical results are also presented for some experiments to demonstrate the usefulness and accuracy of the proposed algorithm.
Effective Jump Length of Coupled Continuous Time Random Walk
LIU Jian, BAO Jing-Dong
Chin. Phys. Lett. 2013, 30 (2): 020202 .   DOI: 10.1088/0256-307X/30/2/020202
Abstract   PDF(pc) (417KB) ( 588 )
The concept effective jump length is proposed. Due to the joint probability density function of jump length and waiting time, it is complicated to distinguish the diffusion types. However, we calculate the probability density function of effective jump length for the coupled continuous time random walk model we proposed previously. The mean square displacements deduced are coincident with the known results. More importantly, we find that the anomalous diffusion induced by the coupled model is equivalent to the competition between long jump length and long waiting time.
Bäcklund Transformations and Interaction Solutions of the Burgers Equation
JIN Yan, JIA Man, LOU Sen-Yue
Chin. Phys. Lett. 2013, 30 (2): 020203 .   DOI: 10.1088/0256-307X/30/2/020203
Abstract   PDF(pc) (483KB) ( 790 )
The Burgers equation is one of the most important prototypic models in nonlinear physics. Various exact solutions of the Burgers equation have been found by many methods. However, it is very difficult to find interactive solutions among different types of nonlinear excitations. We develop a generalized tanh function expansion approach, which can be considered as the B?cklund transformation, to find interactive solutions between the soliton and other types of Burgers waves.
Finding Discontinuous Solutions to the Differential-Difference Equations by the Homotopy Analysis Method
ZOU Li, ZOU Dong-Yang, WANG Zhen, ZONG Zhi
Chin. Phys. Lett. 2013, 30 (2): 020204 .   DOI: 10.1088/0256-307X/30/2/020204
Abstract   PDF(pc) (444KB) ( 512 )
An analytic method, namely the homotopy analysis method, is applied to nonlinear problems with discontinuity governed by the differential-difference equation. Purely analytic solutions are given for nonlinear problems with discontinuity with a global convergence. This method provides a new analytical approach to solve nonlinear problems with discontinuity. Comparisons are made between the results of the proposed method and the exact solutions. The results reveal that the proposed method is very effective and convenient.
Remotely Sharing a Single-Qubit Operation with a Five-Qubit Genuine State
YE Biao-Liang, LIU Yi-Min, LIU Xian-Song, ZHANG Zhan-Jun
Chin. Phys. Lett. 2013, 30 (2): 020301 .   DOI: 10.1088/0256-307X/30/2/020301
Abstract   PDF(pc) (416KB) ( 432 )
A three-party scheme for remotely sharing a single-qubit operation with Brown state and local operation and classical communication is proposed. Some discussions are made to show its important features, including determinacy, symmetry, security, expansibility and nowaday's experimental feasibility.
Quantum Correlations in a Family of Bipartite Qubit-Qutrit Separable States
YE Biao-Liang, LIU Yi-Min, LIU Xian-Song, ZHANG Zhan-Jun
Chin. Phys. Lett. 2013, 30 (2): 020302 .   DOI: 10.1088/0256-307X/30/2/020302
Abstract   PDF(pc) (468KB) ( 704 )
Quantum correlations in a family of bipartite separable qubit-qutrit quantum-classical correlated states are investigated by using two popular measures, i.e., the original quantum discord (OQD) method by Ollivier and Zurek [Phys. Rev. Lett. 88 (2001) 017901] and the measurement-induced disturbance (MID) method by Luo [Phys. Rev. A 77 (2008) 022301]. It is found that both of them are functions of a parameter partially characterizing the concerned states, however, quantum correlations evaluated via the convenient MID method are somewhat overestimated.
A New Proof for the Harmonic-Potential Theorem
CHEN Jin-Wang, YANG Tao, PAN Xiao-Yin
Chin. Phys. Lett. 2013, 30 (2): 020303 .   DOI: 10.1088/0256-307X/30/2/020303
Abstract   PDF(pc) (441KB) ( 344 )
We investigate the time evolution of the wave function for a many-particle system in an external harmonic potential and a spatially homogeneous time-dependent driving field. The time-dependent wave function is found to be a phase factor times the shifted initial state wave function. This then provides a new proof of the harmonic-potential theorem.
Quantum Random Walk in Periodic Potential on a Line
LI Min, ZHANG Yong-Sheng, GUO Gunag-Can
Chin. Phys. Lett. 2013, 30 (2): 020304 .   DOI: 10.1088/0256-307X/30/2/020304
Abstract   PDF(pc) (543KB) ( 382 )
We investigate the discrete-time quantum random walks on a line in periodic potential. The probability distribution with periodic potential is more complex compared to the normal quantum walks, and the standard deviation σ has interesting behaviors for different period q and parameter θ. We study the behavior of standard deviation with variation in walk steps, period, and θ. The standard deviation increases approximately linearly with θ and decreases with 1/q for θ∈(0,π/4), and increases approximately linearly with 1/q for θ∈[π/4,π/2). For θ∈(π/4, 3π/4), the transmission is larger than the reflection, with sensibility the diffussion will be accelerated. However, when q=2, the standard deviations are nearly the same, and when q>2, the standard deviation will decrease.
Approximate Eigensolutions of the Deformed Woods–Saxon Potential via AIM
Sameer M. Ikhdair, Babatunde J. Falaye, Majid Hamzavi
Chin. Phys. Lett. 2013, 30 (2): 020305 .   DOI: 10.1088/0256-307X/30/2/020305
Abstract   PDF(pc) (527KB) ( 627 )
Using the Pekeris approximation, the Schr?dinger equation is solved for the nuclear deformed Woods–Saxon potential within the framework of the asymptotic iteration method. The energy levels are worked out and the corresponding normalized eigenfunctions are obtained in terms of hypergeometric function.
Operator Product Formulas in the Algebraic Approach of the Refined Topological Vertex
CAI Li-Qiang, WANG Li-Fang, WU Ke, YANG Jie
Chin. Phys. Lett. 2013, 30 (2): 020306 .   DOI: 10.1088/0256-307X/30/2/020306
Abstract   PDF(pc) (481KB) ( 304 )
The refined topological vertex of Iqbal–Koz?az–Vafa has been investigated from the viewpoint of the quantum algebra of type W1+∞ by Awata, Feigin, and Shiraishi. They introduced the trivalent intertwining operator ? which is normal ordered along with some prefactors. We manage to establish formulas from the infinite operator product of the vertex operators and the generalized ones to restore this prefactor, and obtain an explicit formula for the vertex realization of the topological vertex as well as the refined topological vertex.
Revisiting Conserved Currents in the F(R) Theory of Gravity via Noether Symmetry
Nayem Sk., Abhik Kumar Sanyal
Chin. Phys. Lett. 2013, 30 (2): 020401 .   DOI: 10.1088/0256-307X/30/2/020401
Abstract   PDF(pc) (451KB) ( 310 )
Noether symmetry of the F(R) theory of gravity in a vacuum and in the presence of pressureless dust yields F(R)∝R3/2 along with the conserved current d/dt(aR) in the Robertson–Walker metric and nothing else. However, some authors recently claimed to have obtained four conserved currents setting F(R)∝R3/2 a-priori, taking time translation along with a gauge term. We show that the first one of these does not satisfy the field equations and the second one is the Hamiltonian which is constrained to vanish in gravity and thus a part and parcel of the field equations. We also show that the other two conserved currents, which do not contain time translation, are the same in disguise and identical to the one mentioned above. Thus the claim is wrong.
Effect of Temperature on a Two-Phase Clock-Driven Discrete-Time Chaotic Circuit
ZHOU Ji-Chao, SONG Han-Jung
Chin. Phys. Lett. 2013, 30 (2): 020501 .   DOI: 10.1088/0256-307X/30/2/020501
Abstract   PDF(pc) (803KB) ( 1286 )
The effects of temperature on a two-phase clock-driven discrete-time chaotic circuit are presented. The circuit for temperature analysis consists of two switches for sample and hold, a source follower, and a nonlinear function for nonlinearity in the feedback. The chaotic dynamics of this circuit, such as time series, state transitions, frequency spectra bifurcation diagrams and Lyapunov exponents are analyzed as functions of the temperature. It is confirmed that the dynamics of the chaotic circuit have a temperature dependence. Further, we find that the circuit can generate discrete chaotic signals only within specific temperature regions.
Synthesis and Improved Acetone Sensing Properties of Porous α-Fe2O3 Nanowires
LIU Li, CHI Xiao, WANG Guo-Guang, LIU Chang-Bai, SHAN Hao, ZHANG Xiao-Bo, WANG Lian-Yuan, GUAN Hong-Yu
Chin. Phys. Lett. 2013, 30 (2): 020701 .   DOI: 10.1088/0256-307X/30/2/020701
Abstract   PDF(pc) (1004KB) ( 462 )
Porous α-Fe2O3 nanowires are synthesized by a simple wet chemical method with a precursor of peroxyacetyl nitrate (PAN), and α-Fe2O3 nanoparticles are also synthesized in the same way except for the addition of PAN. Gas sensors are fabricated by coating the samples on ceramic tubes with Au signal electrodes and Ni-Cr heaters. A sensing investigation reveals that the porous α-Fe2O3 nanowires have a higher sensitivity compared to α-Fe2O3 nanoparticles at 260°C. The corresponding sensor response (Ra/Rg) is 18.2 at the maximum to 100 ppm acetone, and the response and recovery times are about 8 and 12 s, respectively. The porous and one-dimensional nanostructures of the porous α-Fe2O3 nanowires benefit for the gas-absorption and electrical-signal-transfer, and thus improve the sensor sensitivity consequentially.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
Calculation of a Three-Jet Cross Section via the e+e→Hadronic Rindler Horizon→ qqg Process
Ali Reza Sepehri, Somayyeh Shoorvazi
Chin. Phys. Lett. 2013, 30 (2): 021301 .   DOI: 10.1088/0256-307X/30/2/021301
Abstract   PDF(pc) (526KB) ( 301 )
The cross section for three-jet events via the e+e?→hadronic Rindler horizon→ qqg process is compared to experimental data from the OPAL collaboration. It is found that the model is consistent with the QCD experiments.
NUCLEAR PHYSICS
Alpha-Decay Study of Unfavored Transitions in Bismuth Isotopes
NI Dong-Dong, REN Zhong-Zhou
Chin. Phys. Lett. 2013, 30 (2): 022101 .   DOI: 10.1088/0256-307X/30/2/022101
Abstract   PDF(pc) (427KB) ( 329 )
The unfavored α transitions of bismuth isotopes, including the newly observed α-decay fine structure in 209Bi [Beeman et al., Phys. Rev. Lett. 108 (2012) 062501] are investigated by the generalized density-dependent cluster model (GDDCM). Instead of the Wentzel–Kramers–Brillouin barrier penetration probability, the exact solution of the Schr?dinger equation under outgoing Coulomb wave boundary conditions is presented. The calculated α-decay half-lives are found to be in good agreement with the experimental data for both odd-A and odd-odd nuclei. This indicates that the GDDCM has good applicability for unfavored α transitions in addition to favored ones. Some predictions on α-decay half-lives are also made for reference in future experiments.
Dependence of Charged Particle Pseudorapidity Distributions on Centrality in Pb–Pb Collisions at √sNN=2.76 TeV
SUN Jian-Xin, TIAN Cai-Xing, WANG Er-Qin, LIU Fu-Hu
Chin. Phys. Lett. 2013, 30 (2): 022501 .   DOI: 10.1088/0256-307X/30/2/022501
Abstract   PDF(pc) (728KB) ( 332 )
The dependence of charged particle pseudorapidity distributions on centrality in Pb–Pb collisions at √sNN=2.76 TeV is studied by using a multi-source thermal model (previously the two-cylinder model or the multi-source ideal gas model). The rapidity shifts of the interacting system are almost independent of the centrality class. The contribution of leading nucleons increases with the increasing centrality class (percent). The calculated results are compared and found to be in agreement with the experimental data of the ATLAS, ALICE, and CMS collaborations.
Porous Structure Analysis of the Packed Beds in a High-Temperature Reactor Pebble Bed Modules Heat Transfer Test Facility
REN Cheng, YANG Xing-Tuan, SUN Yan-Fei
Chin. Phys. Lett. 2013, 30 (2): 022801 .   DOI: 10.1088/0256-307X/30/2/022801
Abstract   PDF(pc) (1090KB) ( 670 )
We analyse the porous structure of the packed beds in the heat transfer test facility built for high temperature gas cooled reactors from several aspects, such as oscillatory porosity, average porosity, thickness effect, coordination number and contact angle. An understanding and comparison of the porous structure of the facility bed and the real reactor core are developed to make recommendations for the design and analysis of the heat transfer test facility. The results show that there is very little difference between the porous characteristics of the two packed beds of spheres.
ATOMIC AND MOLECULAR PHYSICS
Analysis of Laser-Diode and Lamp Optical Pumping for a Rubidium Beam
GUO Jian, WANG Yan-Hui
Chin. Phys. Lett. 2013, 30 (2): 023201 .   DOI: 10.1088/0256-307X/30/2/023201
Abstract   PDF(pc) (576KB) ( 380 )
The time evolution of populations of the ground state hyperfine Zeeman levels of 87Rb atoms is analyzed using the Runge–Kutta method for the case that a rubidium beam is optically pumped, under different conditions of polarization, with a weak monochromatic laser and an 87Rb lamp. On the base of the results above, the least estimated laser and 87Rb lamp power for the best population inversion is obtained, aiding further investigations.
Elliptical High-Order Harmonic Generation from H2+ in Linearly Polarized Laser Fields
ZHANG Bin, ZHAO Zeng-Xiu
Chin. Phys. Lett. 2013, 30 (2): 023202 .   DOI: 10.1088/0256-307X/30/2/023202
Abstract   PDF(pc) (494KB) ( 437 )
We investigate the elliptical high-order harmonic generation (HHG) from the ground state of H2+ subjected to linearly polarized laser fields, by numerically solving the three-dimensional (3D) time-dependent Schr?dinger equation (TDSE) and using the strong-field approximation (SFA) models. Highly elliptical HHG is yielded at intermedial alignment angles from the TDSE, while the standard SFA model fails to predict this. By including the coulomb potential and the stark shift corrections, we yield qualitative agreement results with the TDSE. The comparisons show that in the description of elliptical HHG, both the coulomb potential and the stark-shift are necessary.
Suppression of Recollision-Excitation Ionization in Nonsequential Double Ionization of Molecules by Mid-Infrared Laser Pulses
ZHANG Dong-Ling, TANG Qing-Bin, GAO Yang
Chin. Phys. Lett. 2013, 30 (2): 023203 .   DOI: 10.1088/0256-307X/30/2/023203
Abstract   PDF(pc) (611KB) ( 330 )
The electron dynamics in strong field non-sequential double ionization of nitrogen molecules is investigated with the three-dimensional (3D) classical ensemble model. The numerical results show that the longitudinal momentum spectrum of the doubly charged ions evolves from a wide single-hump structure at the near-infrared (NIR) regime into a double-hump structure when the wavelength enters the mid-infrared (MIR) regime. Back analysis reveals that in the MIR regime, the recollision excitation with subsequent ionization (RESI) is strongly suppressed with increasing wavelength, which results in the double-hump structure of the ions momentum spectra. This double-hump structure becomes more pronounced as the wavelength further increases because the contribution of the RESI further decreases.
Coherent Control of Molecular Orientation by a Terahertz Few-Cycle Laser Pulse
QIN Chao-Chao, LIU Yu-Zhu, ZHANG Xian-Zhou, LIU Yu-Fang
Chin. Phys. Lett. 2013, 30 (2): 023301 .   DOI: 10.1088/0256-307X/30/2/023301
Abstract   PDF(pc) (962KB) ( 333 )
The coherent control of molecular orientation by a terahertz few-cycle laser pulse is theoretically studied. It is demonstrated that the field-free molecular orientation results from the interference contributions between the odd and even rotational wave packet, and therefore the constructive and destructive interferences lead to the observation of the positive and negative orientations, corresponding to the positive and negative degrees. Furthermore, the enhancement or suppression of the molecular orientation can be coherently manipulated by precisely controlling the carrier-envelope phase of the terahertz few-cycle pulse.
Coherent Control of Molecular Alignment and Orientation by a Femtosecond Two-Color Laser Pulse
QIN Chao-Chao, ZHAO Xing-Dong, ZHANG Xian-Zhou, LIU Yu-Fang
Chin. Phys. Lett. 2013, 30 (2): 023302 .   DOI: 10.1088/0256-307X/30/2/023302
Abstract   PDF(pc) (946KB) ( 367 )
The coherent control of molecular alignment and orientation by a femtosecond two-color laser pulse is studied theoretically. The effect of the carrier-envelope phase of the femtosecond two-color laser pulse on molecular alignment and orientation is discussed, and it is shown that the enhancement or suppression of the molecular orientation can be coherently manipulated by precisely controlling the carrier-envelope phase of the femtosecond two-color laser pulse. In addition, the time-dependent angular distributions of the molecular axis are presented.
S-Wave Scattering Properties for Na–K Cold Collisions
ZHANG Ji-Cai, ZHU Zun-Lue, SUN Jin-Feng, LIU Yu-Fang
Chin. Phys. Lett. 2013, 30 (2): 023401 .   DOI: 10.1088/0256-307X/30/2/023401
Abstract   PDF(pc) (568KB) ( 350 )
Scattering properties of ultracold atoms are sensitive to the interatomic potential. Based on the accurate triplet least-bound state energy, we calculate the triplet s-wave scattering length for 23Na–40K. The scattering length is ?814.1?31.3+29 a0 with a0 being the Bohr radius. By using the mass scaling method, those scattering lengths are also obtained for 23Na–41K and 23Na–39K. The degenerate internal state approximation is used to estimate the scattering data of atoms colliding in different spin states.
Theory of X-Ray Anisotropy and Polarization Following the Dielectronic Recombination of Initially Hydrogen-Like Ions
SHI Ying-Long, DONG Chen-Zhong, FRITZSCHE Stephan, ZHANG Deng-Hong, XIE Lu-You
Chin. Phys. Lett. 2013, 30 (2): 023402 .   DOI: 10.1088/0256-307X/30/2/023402
Abstract   PDF(pc) (699KB) ( 369 )
The angular distribution and polarization of the x-ray photoemission of highly charged helium-like ions is studied following the KLL dielectronic recombination of initially hydrogen-like ions. Calculation is carried out within the framework of the density matrix theory combined with the multiconfiguration Dirac–Fock approach. Attention is paid to magnetic sublevel alignment in the resonant intermediate state and to its nonuniform radiative decay processes. It is shown that the Breit interaction between the incident and target electrons plays a significant role for the alignment of the resonant state and thus causes a substantial change in the x-ray emission characteristic, when compared to the incorporation of only the (non-relativistic) Coulomb interaction. The most prominent difference in alignment parameter is found in the 2s2p1/2 J=1 resonant state for a wide range of atomic numbers from 9 to 92. For this resonant state of helium-like ions, the Breit interaction becomes significant for ions with nuclear charge Z~30 already.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
First Application of Single-Shot Cross-Correlator for Characterizing Nd:glass Petawatt Pulses
WANG Yong-Zhi, OUYANG Xiao-Ping, MA Jin-Gui, YUAN Peng, XU Guang, QIAN Lie-Jia
Chin. Phys. Lett. 2013, 30 (2): 024201 .   DOI: 10.1088/0256-307X/30/2/024201
Abstract   PDF(pc) (536KB) ( 379 )
We report the first application of a single-shot cross-correlator for pulse duration and pulse contrast diagnostics in Nd:glass petawatt laser. The information of pulse duration, measured in the single-shot, guides the fine adjustment of the pulse compressor in real time. By integrating several shots of measurements at different time delays together, the petawatt pulse profile is obtained within an overall temporal window of ~100 ps, indicating a contrast of ~104. The measurements suggest that the additional contrast improvement is necessary for the Nd:glass petawatt laser system, which should be different from conventional Ti:sapphire lasers and is also discussed.
Stable Single Polarization, Single Frequency, and Linear Cavity Er-Doped Fiber Laser Using a Saturable Absorber
LI Qi, YAN Feng-Ping, PENG Wan-Jing, FENG Su-Chun, FENG Ting, TAN Si-Yu, LIU Peng
Chin. Phys. Lett. 2013, 30 (2): 024202 .   DOI: 10.1088/0256-307X/30/2/024202
Abstract   PDF(pc) (812KB) ( 587 )
A simple approach for stable single polarization, single frequency, and linear cavity erbium doped fiber laser is proposed and demonstrated. A Fabry–Pérot filter, polarizer and saturable absorber are used together to ensure stable single frequency, single polarization operation. The optical signal-to-noise ratio of the laser is approximately 57 dB, and the Lorentz linewidth is 13.9 kHz. The polarization state of the laser with good stability is confirmed and the degree of polarization is >99%.
Fluorescence and Four-Wave Mixing in Electromagnetically Induced Transparency Windows
WANG Zhi-Guo, LI Cheng, ZHANG Zhao-Yang , CHE Jun-Ling, QIN Meng-Zhe, HE Jia-Nan, ZHANG Yan-Peng
Chin. Phys. Lett. 2013, 30 (2): 024203 .   DOI: 10.1088/0256-307X/30/2/024203
Abstract   PDF(pc) (700KB) ( 332 )
We simultaneously compare the probe transmission, Four-Wave Mixing (FWM) and fluorescence signals with dressing effects in a four-level atomic system. The variation rules of three types of signals are exhibited by changing the frequency detuning and power of incident laser beams. The interplay between two ladder subsystems is investigated in the Y-type atomic system. In particular, the fluorescence signal with ultra-narrow linewidth is obtained due to being sheared twice by the electromagnetically induced transparency window. Such fluorescence with very high coherence and monochromaticity can be used for the quantum correlation and narrow linewidth laser.
Collisions between Solitons Modulated by Gain/Loss and Phase in the Complex Ginzburg–Landau Equation
LIU Bin, HE Xing-Dao, LI Shu-Jing
Chin. Phys. Lett. 2013, 30 (2): 024204 .   DOI: 10.1088/0256-307X/30/2/024204
Abstract   PDF(pc) (825KB) ( 370 )
We present a systematic analysis for influence of phase φ on collisions of dissipative solitons, using the cubic-quintic complex Ginzburg–Landau equation in the absence of viscosity. Four generic outcomes are revealed upon the variation of gain/loss: merger of the two solitons into a single one; quasi-elastic interactions; creation of an extra soliton; and dissipation of the two solitons for in-phase. The velocities of the merger-soliton and the extra soliton can be effectively controlled by relative phase. The above features have potential applications in optical switching and logic gates based on interaction of optical solitons.
Double-Brillouin-Frequency Spaced Multiwavelength Generation in a Ring Brillouin-Erbium Fiber Laser
LI Jun, CHEN Tao, SUN Jun-Qiang, SHEN Xiang
Chin. Phys. Lett. 2013, 30 (2): 024205 .   DOI: 10.1088/0256-307X/30/2/024205
Abstract   PDF(pc) (620KB) ( 685 )
We demonstrate the double-Brillouin-frequency spaced multiwavelength generation at room temperature by using a simple ring Brillouin-erbium fiber laser. The Brillouin pump is pre-amplified before entering the single-mode fiber, the odd Stokes and even Stokes are amplified in two opposite directions. All amplification provided by a home-made bi-directional operation erbium-doped fiber may achieve high intensity of Brillouin Stokes that leads to the homogenous gain saturation. Twelve even Stokes and thirteen odd Stokes with a wavelength spacing of 0.172 nm (20 GHz) are simultaneously obtained for 6 dBm Brillouin pump power and 120 mW pump power at 980 nm. The influence of different Brillouin and erbium-doped-fiber pump powers on multiwavelength and tuning range are investigated in detail.
Evolution of Residual Stress and Structure in YSZ/SiO2 Multilayers with Different Modulation Ratios
XIAO Qi-Ling, HU Guo-Hang, HE Hong-Bo, SHAO Jian-Da
Chin. Phys. Lett. 2013, 30 (2): 024206 .   DOI: 10.1088/0256-307X/30/2/024206
Abstract   PDF(pc) (473KB) ( 308 )
The multilayer (ML) YSZ/SiO2 films with different modulation ratios ranging from 1:3, 4:9, 1:1 to 3:1 (the thickness ratio of the YSZ to SiO2) are deposited on BK7 glass substrates by electron beam evaporation under the same processing conditions. The effect of modulation ratio on the residual stresses and structure are investigated by an optical interferometer and Grazing incidence x-ray diffraction. The results show that the total residual stress in MLs is compressive and decreases to tensile when the modulation ratio is changed from 1:3 to 3:1. The YSZ films are of cubic phase structure and the SiO2 films are amorphous in all the MLs. The change of residual stress in these MLs can be attributed to the variation of an individual layer?s stress with thickness, which indicates that adjusting the thickness ratio of two materials is an effective measure for depositing near-zero stress MLs.
Intracavity Optical Deposition of Graphene Saturable Absorber for Low-Threshold Passive Mode-Locking of a Fiber Laser
LUO Zhi-Chao, CAO Wen-Jun, LUO Ai-Ping, XU Wen-Cheng
Chin. Phys. Lett. 2013, 30 (2): 024207 .   DOI: 10.1088/0256-307X/30/2/024207
Abstract   PDF(pc) (656KB) ( 631 )
A compact, intracavity optical deposition of graphene saturable absorber (SA) for low-threshold passively mode-locked fiber laser is proposed and demonstrated. The optical deposition is implemented in the laser cavity by using a slot collimator. Utilizing the fabricated graphene SA, the fiber laser achieves self-starting, passively mode-locked operation at a low threshold of 32 mW pump power, delivering a 13.1-MHz 2.36-ps pulse train.
Graphene Oxide-Based Q-Switched Erbium-Doped Fiber Laser
Y. K. Yap, N. M. Huang, S. W. Harun, H. Ahmad
Chin. Phys. Lett. 2013, 30 (2): 024208 .   DOI: 10.1088/0256-307X/30/2/024208
Abstract   PDF(pc) (481KB) ( 820 )
We demonstrate a pulsed ring erbium-doped fiber laser based on graphene oxide (GO), employing a simplified Hummer's method to synthesize the GO via chemical oxidation of graphite flakes at room temperature. By dipping a fiber ferrule end face onto the GO suspension, GO is successfully coated onto the end face, making it a simple saturable absorption device. A stable Q-switched pulsed fiber laser is achieved with a low pump threshold of 9.5 mW at 980 nm. The pulse repetition rate ranges from 16.0 to 57.0 kHz. The pulse width and the pulse energy are studied and discussed.
High Intensity Single-Mode Peak Observed in the Lasing Spectrum of InAs/GaAs Quantum Dot Laser
YUE Li, GONG Qian, YAN Jin-Yi, CAO Chun-Fang, LIU Qing-Bo, WANG Yang, CHENG Ruo-Hai, WANG Hai-Long, LI Shi-Guo
Chin. Phys. Lett. 2013, 30 (2): 024209 .   DOI: 10.1088/0256-307X/30/2/024209
Abstract   PDF(pc) (642KB) ( 324 )
We report on abnormal lasing spectra of InAs/GaAs quantum dot lasers, where a single-mode peak exists with optical intensity several times larger than that of other modes. The maximum side mode suppression ratio of the single-mode peak is measured to be 10.11 dB at 29°C with injection current of 413 mA. It is found that the emergence of this abnormal lasing spectrum happens in a certain range of operation temperature and current. The sharp increase in optical intensity of the single-mode peak is closely related to the disappearance of optical lasing modes located at the higher energy side of the enhanced mode.
Room Temperature Diode-Pumped Tunable Single-Frequency Tm:YAG Ceramic Laser
YAO Bao-Quan, YU Xiao, JU You-Lun, LIU Wen-Bin, JIANG Ben-Xue, PAN Yu-Bo
Chin. Phys. Lett. 2013, 30 (2): 024210 .   DOI: 10.1088/0256-307X/30/2/024210
Abstract   PDF(pc) (656KB) ( 508 )
A single-longitudinal-mode (SLM) Tm:YAG ceramic laser under room temperature conditions using double Fabry–Pérot etalons is investigated. The maximum single-frequency output power is 318 mW with a slope efficiency of 12.6%. The wavelength tuning range from 2005 nm to 2029 nm is achieved by tuning the obliquity of a 0.1-mm-thick etalon. The single frequency laser has a beam quality of M2=1.3 at the maximum single-frequency output power. The result is reported for the first time to the best of our knowledge. This SLM Tm:YAG ceramic laser can replace the Tm:YAG single crystal laser to be used as the seed laser for LIDAR laser systems.
Band Structure of Bose-Einstein Condensates in a Cavity-Mediated Triple-Well System
WANG Bin, CHEN Yan
Chin. Phys. Lett. 2013, 30 (2): 024211 .   DOI: 10.1088/0256-307X/30/2/024211
Abstract   PDF(pc) (1474KB) ( 285 )
We investigate the band structure and the dynamics of Bose-Einstein condensates in a triple-well trap, which are located in a high-finesse optical cavity. For the noninteracting atoms, the band structure of the eigenenergies are obtained using the numerical methods under the mean-field approximation. It is demonstrated that the energy band structure is strongly dependent on the value of reduced cavity detuning. Under some conditions, the atomic band structure develops loop structures and swallowtail structure, which mean the atom-cavity system exhibits bistability. We attribute the appearance of new states to the nonlinearity of the cavity-field-induced tilt. For the interacting atoms, the structure of the eigenenergy band appears more complicated for the interaction between atoms.
High Energy Terahertz Parametric Oscillator Based on Surface-Emitted Configuration
XU De-Gang, ZHANG Hao, JIANG Hao, WANG Yu-Ye, LIU Chang-Ming, YU Hong, LI Zhong-Yang, SHI Wei, YAO Jian-Quan
Chin. Phys. Lett. 2013, 30 (2): 024212 .   DOI: 10.1088/0256-307X/30/2/024212
Abstract   PDF(pc) (664KB) ( 398 )
We experimentally demonstrate a high power nanosecond pulsed terahertz (THz)-wave parametric oscillator (TPO) by using a wide pump beam. A surface emitted cavity configuration is employed to reduce the THz absorption in MgO:LiNbO3 crystal. The THz wave can be tuned from 1 THz to 3 THz. A maximum THz output energy of 438 nJ/pulse is achieved at 1.56 Hz using a 4.5-mm-diameter pump beam with a pulse energy of 226 mJ pump energy with the repetition of 10 Hz, corresponding to the energy conversion efficiency of 1.94×10?6.
Effect of Phase Noise on the Stationary Entanglement of an Optomechanical System with Kerr Medium
ZHANG Dan, ZHENG Qiang
Chin. Phys. Lett. 2013, 30 (2): 024213 .   DOI: 10.1088/0256-307X/30/2/024213
Abstract   PDF(pc) (487KB) ( 482 )
We theoretically investigate the effect of phase noise on the stationary entanglement of an optomechanical system, which has the additional Kerr medium in the cavity. There are two kinds of interactions in the system, photon-mirror interaction and photon-photon interaction. We find that the optomechanical entanglement can be suppressed by the phase noise of the pumping laser and Kerr interaction of photons. We also find that Kerr interaction can make the phase-noise-induced double peak of the stationary entanglement change to a single peak.
Matched Field Source Localization via Environmental Focalization
LI Qian-Qian, LI Zheng-Lin, ZHANG Ren-He
Chin. Phys. Lett. 2013, 30 (2): 024301 .   DOI: 10.1088/0256-307X/30/2/024301
Abstract   PDF(pc) (472KB) ( 355 )
In a realistic application of matched field processing for source localization, the ability to localize an acoustic source is strongly affected by the uncertainty of the environment. However, accurate environment measurement is a difficult task in large regions of the ocean. We employ a Bayesian approach, referred to here as focalization, to overcome the mismatch by including the environment in the parameter search space. Focalization maximizes the posterior probability density over the unknown source and environmental parameters. The broadband signals recorded by a vertical line array in a Yellow Sea experiment are presented to demonstrate the feasibility of focalization.
Lesions in Porcine Liver Tissues Created by Continuous High Intensity Ultrasound Exposures in Vitro
ZHANG Zhe, CHEN Tao, ZHANG Dong
Chin. Phys. Lett. 2013, 30 (2): 024302 .   DOI: 10.1088/0256-307X/30/2/024302
Abstract   PDF(pc) (936KB) ( 364 )
Lesions in porcine liver tissues created by continuous high intensity focused ultrasound (HIFU) exposures in vitro are theoretically and experimentally investigated, with the transmitter moving along a linear path at a fixed speed. Numerical simulations of the lesion formation are performed based on the Khokhlov–Zabolotskaya–Kuznetov equation and the bio-heat equation. In order to verify the theoretical predictions, experiments are performed in the one-dimensional scanning mode to measure the cross-sectional area of lesions created in the in vitro porcine liver exposed to 1.01-MHz HIFU pulses with the acoustic power of 70 W. The results indicate that, compared to the traditional discrete treatment protocol, the application of a continuous scanning model can create more uniform lesions in tissues and significantly reduces the total treatment time from 47 s to 30 s.
Effects of Magnetic Field on Entropy Generation in Flow and Heat Transfer due to a Radially Stretching Surface
Adnan Saeed Butt, Asif Ali
Chin. Phys. Lett. 2013, 30 (2): 024701 .   DOI: 10.1088/0256-307X/30/2/024701
Abstract   PDF(pc) (526KB) ( 861 )
We investigate the effects of magnetic field on the entropy generation during fluid flow and heat transfer due to the radially stretching surface. The partial differential equations governing the flow and heat transfer phenomenon are transformed into nonlinear ordinary differential equations by using suitable similarity transformations. These equations are then solved by the homotopy analysis method and the shooting technique. The effects of the magnetic field parameter M and the Prandtl number Pr on velocity and the temperature profiles are presented. Moreover, influence of the magnetic field parameter M and the group parameter Br/Ω on the local entropy generation number Ns as well as the Bejan number Be are inspected. It is observed that the magnetic field is a strong source of entropy production in the considered problem.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Double-Relativistic-Electron-Layer Proton Acceleration with High-Contrast Circular-Polarization Laser Pulses
HUANG Yong-Sheng, WANG Nai-Yan, TANG Xiu-Zhang, SHI Yi-Jin, ZHANG Shan
Chin. Phys. Lett. 2013, 30 (2): 025201 .   DOI: 10.1088/0256-307X/30/2/025201
Abstract   PDF(pc) (2025KB) ( 355 )
A new laser-proton acceleration scheme consisting of two relativistic electron layers, a suprathermal electron layer and a thermal electron cloud is proposed for a0?80σ0, where a0 is the normalized laser field and σ0 is the normalized plasma surface density. This is essentially different from target normal sheath acceleration and radiation pressure acceleration. The persistent opaqueness of the first relativistic electron layer for the incident circular-polarization laser pulse and electron recirculation are key points in forming the new acceleration scheme. A proton beam with a uniform energy distribution in the energy range 1–2 GeV and a monoenergetic proton beam with hundreds of MeV have been predicted for a0=39.5.
Estimating the Radial Profile of Edge Plasma Electrical Fluctuations in the IR-T1 Tokamak
K. Mikaili Agah, M. Ghoranneviss, M. K. Salem, A. Salar Elahi, S. Mohammadi, R. Arvin
Chin. Phys. Lett. 2013, 30 (2): 025202 .   DOI: 10.1088/0256-307X/30/2/025202
Abstract   PDF(pc) (785KB) ( 436 )
The radial dependence of edge plasma turbulence is investigated in the IR-T1 tokamak. The radial profile of the fluctuation level and spectra are measured using an array of Langmuir probes (rake probe) in the r/a=0.75–1.2 region. In all radial positions the edge plasma is turbulently unstable, with a broad band fluctuation spectrum in the frequency range f= 10–1000 kHz. The relative fluctuation level, as monitored by the ion saturation current J+, is always highest near the wall and decreases monotonically toward the plasma center, while the shape of the fluctuation power spectra is almost unchanged. The result of this experiment shows that in contrast to the more inner regions, the plasma near the wall does not simply have a small density fluctuation about a mean, but rather a shredded structure in which one can imagine that discrete shreds of plasma interact with one another rather than with the average background.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
AlGaN/GaN MISHEMTs with Sodium-Beta-Alumina as the Gate Dielectrics
TIAN Ben-Lang, CHEN Chao, ZHANG Ji-Hua, ZHANG Wan-Li, LIU Xing-Zhao
Chin. Phys. Lett. 2013, 30 (2): 026101 .   DOI: 10.1088/0256-307X/30/2/026101
Abstract   PDF(pc) (1039KB) ( 358 )
AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) with sodium beta-alumina (SBA) thin films as the gate dielectrics are studied. AlGaN/GaN metal-semiconductor high-electron-mobility transistors (MESHEMTs) and MISHEMTs with Al2O3 thin-film gate dielectrics are also fabricated for comparative study. The MISHEMTs with SBA gate dielectrics show nearly four orders of magnitude lower gate leakage current and an approximately 60% increase in maximum transconductance, indicating that SBA can serve as an effective dielectric for AlGaN/GaN MISHEMTs. However, SBA gate dielectrics result in threshold voltage modulation of AlGaN/GaN MISHEMTs. Compared with those of AlGaN/GaN MESHEMTs, the threshold voltages of AlGaN/GaN MISHEMTs with Al2O3 gate dielectrics shift negatively from ?5.5 V to ?7.5 V. In contrast with the normally used gate dielectrics, the threshold voltages of MISHEMTs with SBA gate dielectrics shift positively from ?5.5 V to ?3.5 V. Based on an x-ray photoelectron spectrum study and energy band spectrum calculation, the primary mechanism of the threshold voltage modulation is attributed to the decrease in the surface valence-band maximum and the increase in the barrier height by SBA gate dielectrics.
A Single Cluster Covering for Dodecagonal Quasiperiodic Ship Tiling
LIAO Long-Guang, ZHANG Wen-Bin, YU Tong-Xu, CAO Ze-Xian
Chin. Phys. Lett. 2013, 30 (2): 026102 .   DOI: 10.1088/0256-307X/30/2/026102
Abstract   PDF(pc) (416KB) ( 318 )
The single cluster covering approach provides a plausible mechanism for the formation and stability of octagonal and decagonal quasiperiodic structures. For dodecagonal quasiperiodic patterns, such a single cluster covering scheme is still unavailable. We demonstrate that ship tiling, one of the dodecagonal quasiperiodic structures, can be completely covered by a single cluster. A deflation procedure is devised by assigning proper orientations to different tiles, and nine types of vertex configurations, if the mirror patterns are considered to be identical, have been identified, which fulfill the closure condition under deflation and all result in a T-cluster centered at the vertex.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Topological Invariants of Metals and the Related Physical Effects
ZHOU Jian-Hui, JIANG Hua, NIU Qian, SHI Jun-Ren
Chin. Phys. Lett. 2013, 30 (2): 027101 .   DOI: 10.1088/0256-307X/30/2/027101
Abstract   PDF(pc) (548KB) ( 524 )
The total reciprocal space magnetic flux threading through a closed Fermi surface is a topological invariant for a three-dimensional metal. For a Weyl metal, the invariant is nonzero for each of its Fermi surfaces. We show that such an invariant can be related to the magneto-valley-transport effect, in which an external magnetic field can induce a valley current. We further show that a strain field can drive an electric current, and that the effect is dictated by a second-class Chern invariant. These connections open the pathway to observe the hidden topological invariants in metallic systems.
Plasmon-Enhanced Upconversion Fluorescence in Er3+:Ag Phosphate Glass: the Effect of Heat Treatment
Raja J. Amjad, M. R. Sahar, S. K. Ghoshal, M. R. Dousti, S. Riaz, A. R. Samavati, M. N. A Jamaludin, S. Naseem
Chin. Phys. Lett. 2013, 30 (2): 027301 .   DOI: 10.1088/0256-307X/30/2/027301
Abstract   PDF(pc) (606KB) ( 548 )
The melt quenching method is used to prepare erbium-doped silver nanoparticle (NP) embedded phosphate glass. The effect of annealing on the glass on the formation of silver NPs produced by the reduction of silver (Ag+Ago) is studied. The glass samples are characterized by x-ray diffraction, UV-vis-NIR absorption, photoluminescence spectroscopy and transmission electron microscopy (TEM) imaging. The absorption spectra reveal not only the peaks due to Er3+ ions, but also the surface plasmon resonance band of silver NPs located around ~442 nm. The TEM imaging shows the homogeneous distribution of silver NPs of almost spherical shape with an average diameter of ~5 nm. Upconversion luminescence spectra show two major emissions at 550 and 638 nm, originating from the 4S3/2 and 4F9/2 energy levels of the Er3+ ions, respectively. The enhancement in the luminescence intensity of both the green and red bands is found to be due to the effective local field of the silver NPs as well as the energy transfer from the nanoclusters, comprised of centers with silver ions bound to silver atoms in dimers or trimers to Er3+ ions, whereas quenching occurred due to the energy transfer from erbium ions to silver NPs (Er3+Ago).
Research with KNbO3 Bulk and Surface Properties Based on Density Functional Theory
SUN Hong-Guo, ZHOU Zhong-Xiang, YUAN Cheng-Xun, YANG Xiao-Niu
Chin. Phys. Lett. 2013, 30 (2): 027302 .   DOI: 10.1088/0256-307X/30/2/027302
Abstract   PDF(pc) (537KB) ( 512 )
The geometrical structure optimization, band structure, density of states, and charge density contour of potassium niobate (KNbO3) in the bulk [100] direction and (100) surface are calculated and analyzed using density functional theory. The elastic constants, which can describe the bonding characteristics and structural stability, are also computed, and the dielectric function, which can be used to calculate all the other optical properties of the material, is evaluated. Local density approximation functional analysis using CASTEP software is also employed. Several similarities and differences are observed in the properties of the KNbO3 bulk and surface. Almost all of the calculated results for the bulk sample are twice those of the surface sample. The results are consistent with the experiment.
P-type ZnO:N Films Prepared by Thermal Oxidation of Zn3N2
ZHANG Bin, LI Min, WANG Jian-Zhong, SHI Li-Qun
Chin. Phys. Lett. 2013, 30 (2): 027303 .   DOI: 10.1088/0256-307X/30/2/027303
Abstract   PDF(pc) (1171KB) ( 572 )
We prepare p-type ZnO:N films by annealing Zn3N2 films in oxygen over a range of temperatures. The prepared films are characterized by various techniques, such as Rutherford backscattering spectroscopy, x-ray diffraction, x-ray photoemission spectroscopy, the Hall effect and photoluminescence spectra. The results show that the Zn3N2 films start to transform to ZnO at 300°C and the N content decreases with an increase in annealing temperature. N has two local chemical states: zinc oxynitride (ZnO1?xNx) and substitutional NO in O-rich local environments (α -NO). The conduction type changes from n-type to p-type upon oxidation at 400–600°C, indicating that N is an effective acceptor in the ZnO film. The photoluminescence spectra show the UV emission and defect-related emissions of ZnO:N films. The mechanism and efficiency of p-type doping are briefly discussed.
The Predicted fcc Superconducting Phase for Compressed Se and Te
ZHOU Da-Wei, PU Chun-Ying, Szczęániak Dominik, ZHANG Guo-Fang, LU Cheng, LI Gen-Quan, SONG Jin-Fan
Chin. Phys. Lett. 2013, 30 (2): 027401 .   DOI: 10.1088/0256-307X/30/2/027401
Abstract   PDF(pc) (774KB) ( 327 )
In the framework of the ab initio random structure search method, we show that elemental Se and Te undergo pressure-induced structural transition from the bcc to fcc phase, in agreement with the theoretical results previously reported. By means of the pseudopotential plane-wave method based on density functional perturbation theory, the fcc structure for both elements is found to be another phonon-mediated superconducting phase of these materials. With a reasonable value for the Coulomb pseudopotential μ?=0.12, the maximum superconducting transition temperature Tc in the fcc phase of Se and Te is estimated to be about 5.7 K and 4.6 K, respectively. Furthermore, we show that in the entire fcc phase for Se and Te, the superconducting transition temperature decreases together with the increase in pressure, leading to the final suppression of the superconductivity. It is suggested that such behavior is mainly caused by the rapid increase in the mean-square phonon frequency 2? with pressure. Finally, a very strong electron-phonon coupling value, for both Se and Te in the fcc phase, is found along the GK high symmetry lines.
Superconductivity Tuned by the Iron Vacancy Order in KxFe2−ySe2
BAO Wei, LI Guan-Nan, HUANG Qing-Zhen, CHEN Gen-Fu, HE Jun-Bao, WANG Du-Ming, M. A. Green, QIU Yi-Ming, LUO Jian-Lin, WU Mei-Mei
Chin. Phys. Lett. 2013, 30 (2): 027402 .   DOI: 10.1088/0256-307X/30/2/027402
Abstract   PDF(pc) (909KB) ( 572 )
Combining in-depth neutron diffraction and systematic bulk studies, we discover that the √5×√5 Fe vacancy order, with its associated block antiferromagnetic order, is the ground state with varying occupancy ratios of the iron 16#em/em# and vacancy 4d sites across the phase-diagram of KxFe2?ySe2. The orthorhombic order, with one of the four Fe sites vacant, appears only at intermediate temperatures as a competing phase. The material experiences an insulator to metal crossover when the √5×√5 order is highly developed. Superconductivity occurs in such a metallic phase.
The Hysteretic Behavior of Angular Dependence of Exchange Bias in NiFe/granular-FeMn-MgO Bilayers
HU Hai-Ning, QIU Xue-Peng, SHI Zhong
Chin. Phys. Lett. 2013, 30 (2): 027501 .   DOI: 10.1088/0256-307X/30/2/027501
Abstract   PDF(pc) (774KB) ( 291 )
We investigate the hysteretic behavior of the angular dependence of exchange bias for a series of polycrystalline NiFe/(FeMn)1?x(MgO)x bilayers with varying x. For x=0.025, the antiferromagnetic layer is of the largest degree of the fcc (111) preferred texture. At the same x, both the exchange field and blocking temperature acquire maximal values. In particular, the hysteretic behavior of the angular dependence between clockwise and counter-clockwise rotations shows minimal angular shift. These results can be explained in terms of the thermal activation model.
The Thickness Dependence of Optical Constants of Ultrathin Iron Films
GAO Shang, LIAN Jie, SUN Xiao-Fen, WANG Xiao, LI Ping, LI Qing-Hao
Chin. Phys. Lett. 2013, 30 (2): 027801 .   DOI: 10.1088/0256-307X/30/2/027801
Abstract   PDF(pc) (521KB) ( 640 )
Ultrathin iron films with different thicknesses from 7.1 to 51.7 nm are deposited by magnetron sputtering and covered by tantalum layers protecting them from being oxidized. These ultrathin iron films are studied by spectroscopic ellipsometry and transmittance measurement. An extra tantalum film is deposited under the same sputtering conditions and its optical constants and film thickness are obtained by a combination of ellipsometry and transmission measurement. After introducing these obtained optical constants and film thickness into the tantalum-iron film, the optical constants and film thicknesses of ultrathin iron films with different thicknesses are obtained. The results show that combining ellipsometry and transmission measurement improves the uniqueness of the obtained film thickness. The optical constants of ultrathin iron films depend strongly on film thicknesses. There is a broad absorption peak at about 370 nm and it shifts to 410 nm with film thickness decreasing.
A Theoretical Analysis of Ultraslow Optical Solitons via Exciton Spin Coherence in GaAs/AlGaAs Multiple Quantum Wells
YAN Wei, WANG Tao, LI Xiao-Ming
Chin. Phys. Lett. 2013, 30 (2): 027802 .   DOI: 10.1088/0256-307X/30/2/027802
Abstract   PDF(pc) (902KB) ( 335 )
We show the formation of ultraslow bright and dark optical solitons in a Λ-type three-level system with a GaAs/AlGaAs multiple quantum well (MQW) structure based on the exciton spin coherence. The propagation of the pulse across the quantum wells is studied analytically and numerically with Maxwell–Schr?dinger equations. The research of ultraslow optical solitons of MQWs in the present work may provide important applications in optical devices and optical communication systems.
The Luminescence of a CuI Film Scintillator Controlled by a Distributed Bragg Reflector
TONG Fei, ZHU Zhi-Chao, LIU Bo, YI Ya-Sha, GU Mu, CHEN Hong
Chin. Phys. Lett. 2013, 30 (2): 027803 .   DOI: 10.1088/0256-307X/30/2/027803
Abstract   PDF(pc) (516KB) ( 343 )
We investigate the emission properties of CuI film scintillators and the effect of distributed Bragg reflectors. The free-exciton emission and the donor-acceptor pair emission from the CuI thin film with the peak wavelengths of 410 nm and 420 nm are observed. However, for the two emission bands, the distributed Bragg reflector reflection results in different enhancements, which is interpreted by the varying transmittance with wavelength. Angle-dependence of emission profile is decided by the transmittance and DBR reflection, which may be useful in scintillation detection applications.
Vacancy-Induced Ferromagnetism in SnO2 Nanocrystals: A Positron Annihilation Study
CHEN Zhi-Yuan, CHEN Zhi-Quan, PAN Rui-Kun, WANG Shao-Jie
Chin. Phys. Lett. 2013, 30 (2): 027804 .   DOI: 10.1088/0256-307X/30/2/027804
Abstract   PDF(pc) (621KB) ( 579 )
SnO2 nanopowders were pressed into pellets and annealed in air from 100 to 1400°C. Both XRD and Raman spectroscopy confirm that all annealed samples were single phase with a tetragonal rutile structure. Annealing induces an increase in the SnO2 grain size from 30 to 83 nm. Positron annihilation measurements reveal vacancy defects in the grain boundary region, and the interfacial defects remain stable after annealing below 400°C, then they are gradually recovered with increasing annealing temperature up to 1200°C. Room temperature ferromagnetism was observed for SnO2 nanocrystals annealed below 1200°C, and the magnetization decreases continuously with increasing annealing temperature. However, the ferromagnetism disappears at 1200°C annealing. This shows good coincidence with the recovery of interfacial defects in the nanocrystals, suggesting that the ferromagnetism is probably induced by vacancy defects in the interface region.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
The Influence of Graded AlGaN Buffer Thickness for Crack-Free GaN on Si(111) Substrates by using MOCVD
XU Pei-Qiang, JIANG Yang, MA Zi-Guang, DENG Zhen, LU Tai-Ping, DU Chun-Hua, FANG Yu-Tao, ZUO Peng, CHEN Hong
Chin. Phys. Lett. 2013, 30 (2): 028101 .   DOI: 10.1088/0256-307X/30/2/028101
Abstract   PDF(pc) (789KB) ( 1258 )
GaN films with different thicknesses of Al composition graded AlGaN buffer are grown on substrates of Si(111) by metal-organic chemical vapor deposition (MOCVD). The thicknesses of graded AlGaN buffer are fixed at 200 nm, 300 nm, and 450 nm, respectively. Optical microscopy, atomic force microscopy, x-ray diffraction, and Raman spectroscopy are employed to characterize these samples. We find that the thickness of the graded AlGaN buffer layer plays a key role on the following growth of GaN films. The optimized thickness of the graded AlGaN buffer layer is 300 nm. Under such conditions, the GaN epitaxial film is crack-free, and its dislocation density is the lowest.
Graphene Domains Synthesized on Electroplated Copper by Chemical Vapor Deposition
WANG Wen-Rong, LIANG Chen, LI Tie, YANG Heng, LU Na, WANG Yue-Lin
Chin. Phys. Lett. 2013, 30 (2): 028102 .   DOI: 10.1088/0256-307X/30/2/028102
Abstract   PDF(pc) (2277KB) ( 1123 )
Electroplated Cu, which can be compatible with integrated circuit technology and large-scale silicon wafers, is explored as a substrate to synthesize graphene domains by ambient-pressure chemical vapor deposition. Hexagonal single crystal domains of graphene are synthesized on electroplated Cu under dilute methane gas flow. Scanning electron microscopy images of graphene domains grown on electroplated Cu indicate that the domain size is time-dependent, and the domains can cross Cu grain boundaries and are distributed more uniformly on electroplated Cu surface than those grown on Cu foil.
The Stress Distribution in Polydisperse Granular Packings in Two Dimensions
SUN Qi-Cheng, ZHANG Guo-Hua, JIN Feng
Chin. Phys. Lett. 2013, 30 (2): 028301 .   DOI: 10.1088/0256-307X/30/2/028301
Abstract   PDF(pc) (598KB) ( 345 )
We study the effect of size polydispersity on the stress distributions and structural properties of static frictionless packings under isotropic compressions. More than 50 isostatic packings with constant mean stress of 1 kPa are generated for each size polydispersity s with a uniform distribution of diameter between (d0 ? s/2) and (d0 + s/2). In order to vary the degree of positional order, the size polydispersity s ranges from 0 to 0.5. Several typical structural characterizations, (i.e., the height of the first pair correlation peak, the global and the local order parameters), the probability distribution of the normalized mean stress and the stress-stress correlation are calculated. The result shows that (i) the stress distribution scales as a power law in the limit of small stresses, and the distribution displays a Gaussian tail in the limit of large stresses; (ii) s has no evident influence on the structural and mechanical properties when s> 0.2.
Sparse Transform Matrices and Their Application in the Calculation of Electromagnetic Scattering Problems
CAO Xin-Yuan, CHEN Ming-Sheng, WU Xian-Liang
Chin. Phys. Lett. 2013, 30 (2): 028401 .   DOI: 10.1088/0256-307X/30/2/028401
Abstract   PDF(pc) (524KB) ( 358 )
When compressed sensing is introduced into the moment method, a 3D electromagnetic scattering problem over a wide angle can be solved rapidly, and the selection of sparse basis has a direct influence on the performance of this algorithm, especially the number of measurements. We set up five sparse transform matrices by discretization of five types of classical orthogonal polynomials, i.e., Legendre, Chebyshev, the second kind of Chebyshev, Laguerre, and Hermite polynomials. Performances of the algorithm using these matrices are compared via numerical experiments, and the results show that some of them obviously work excellently and can accelerate wide angle scattering analysis greatly.
Stable Organic Field Effect Transistors with Low-Cost MoO3/Al Source-Drain Electrodes
ZHANG Hui, MI Bao-Xiu, LI Xin, GAO Zhi-Qiang, ZHAO Lu, HUANG Wei
Chin. Phys. Lett. 2013, 30 (2): 028501 .   DOI: 10.1088/0256-307X/30/2/028501
Abstract   PDF(pc) (512KB) ( 532 )
Stable organic field effect transistors (OFETs) based on copper phthalocyanine (CuPc) are reported using MoO3/Al as source-drain top contacts. By annealing the fabricated device at 130°C in air, the mobility and the stability of the OFETs can be significantly improved in comparison with the untreated device. The heat-treated devices without encapsulation show a device storage stability of nearly 400 h while the untreated one only 183 h. This improvement is suggested to be mainly attributed to the reduction of the contact barrier between CuPc and the electrode, as well as the better alignment of CuPc molecules via post annealing.
An Analytical Model of SiGe Heterojunction Bipolar Transistors on SOI Substrate for Large Current Situations
XU Xiao-Bo, ZHANG Bin, YANG Yin-Tang, LI Yue-Jin
Chin. Phys. Lett. 2013, 30 (2): 028502 .   DOI: 10.1088/0256-307X/30/2/028502
Abstract   PDF(pc) (498KB) ( 277 )
The large current effect of silicon germanium heterojunction bipolar transistors fabricated on thin silicon-on-insulator is included in the model. As the current is two-dimensional, the injection for large current is vertical plus horizontal and is quite different from that of the bulk device. Critical parameters modeling the large current, such as the collector injection width, the hole density and the corresponding potential in the injection region, are discussed, and the influence to the transit time is also analyzed.
An Ultrathin AlGaN Barrier Layer MIS-HEMT Structure for Enhancement-Mode Operation
QUAN Si, MA Xiao-Hua, ZHENG Xue-Feng, HAO Yue
Chin. Phys. Lett. 2013, 30 (2): 028503 .   DOI: 10.1088/0256-307X/30/2/028503
Abstract   PDF(pc) (662KB) ( 637 )
A GaN-based enhancement-mode (E-Mode) metal-insulator-semiconductor (MIS) high electron mobility transistor (HEMT) with a 2 nm/5 nm/1.5nm-thin GaN/AlGaN/AlN barrier is presented. We find that the formation of a two-dimensional electron gas (2DES) in the GaN/AlGaN/AlN/GaN heterostructure can be controlled by the presence of the plasma-enhanced chemical-vapor deposition (PECVD) Si3N4 on the barrier layer, and the degree of decrease in sheet resistance Rsh is dependent on the Si3N4 thickness. We choose 13 nm Si3N4 as the gate insulator to decrease gate current and to improve the threshold voltage of devices. With selective etching of the passivation Si3N4 under gate and over fluorine plasma treatment, the MIS-HEMT exhibits a high threshold voltage of 1.8 V. The maximum drain current Id,max and the maximum transconductance are 810 mA/mm and 190 mS/mm, respectively. The devices show a wide operation range of 4.5 V.
The Effects of a Low-Temperature GaN Interlayer on the Performance of InGaN/GaN Solar Cells
LI Liang, ZHAO De-Gang, JIANG De-Sheng, LIU Zong-Shun, CHEN Ping, WU Liang-Liang, LE Ling-Cong, WANG Hui, YANG Hui
Chin. Phys. Lett. 2013, 30 (2): 028801 .   DOI: 10.1088/0256-307X/30/2/028801
Abstract   PDF(pc) (557KB) ( 561 )
An InGaN/GaN p-i-n solar cell inserted with a 5-nm low-temperature (LT) GaN interlayer between the p-GaN cap layer and the InGaN i-layer is grown on a c-plane sapphire substrate by metal organic chemical vapor deposition. The effects of the LT GaN interlayer on the performance of the InGaN/GaN solar cells are investigated. It is found that the LT-GaN interlayer prevents the extension of threading dislocations from the InGaN layer to the p-GaN layer and improves the crystal quality of both the p-GaN cap layer and the InGaN i-layer, ultimately leading to an increasing external quantum efficiency and photocurrent density of the InGaN/GaN solar cells.
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