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Volume 30 Issue 1
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A Method of Choosing the Optimal Number of Singular Values in the Inverse Laplace Transform for the Two-Dimensional NMR Distribution Function
JIANG Zhi-Min, WANG Wei-Min
Chin. Phys. Lett. 2013, 30 (1): 010201 .   DOI: 10.1088/0256-307X/30/1/010201
Abstract   PDF(pc) (1007KB) ( 906 )
Two-dimensional (2D) nuclear magnetic resonance (NMR) distributions as functions of diffusion coefficient and relaxation time are powerful tools in the study of porous media. We propose a practical method to perform proper truncation of singular value decomposition (TSVD) in Laplace inversion for obtaining 2D-NMR distributions from measured NMR data. By analyzing basic algorithms for Laplace inversion, it is well known that proper TSVD does not affect the inversion result for an ill-posed problem with zero-order Tikhonov regularization, but can greatly increase the inversion speed. In this new method, the optimal number of singular values for data compression is applied to each dimension separately. The method also makes full use of the redundancy nature of the data with a finite signal-to-noise ratio and well balances the tradeoff between the speed and the bias. The method does not require the stochastic information of the estimated parameters when obtaining the optimal number of singular values.
Double Barrier Resonant Tunneling in Spin-Orbit Coupled Bose–Einstein Condensates
LI Zhi, WANG Jian-Zhong, FU Li-Bin
Chin. Phys. Lett. 2013, 30 (1): 010301 .   DOI: 10.1088/0256-307X/30/1/010301
Abstract   PDF(pc) (546KB) ( 488 )
We study the double barrier tunneling properties of Dirac particles in spin-orbit coupled Bose–Einstein Condensates. The analytic expression of the transmission coefficient of Dirac particles penetrating into a double barrier is obtained. An interesting resonance tunneling phenomenon is discovered in the Klein block region which has been ignored before.
An Alternative Approach to Construct the Initial Hamiltonian of the Adiabatic Quantum Computation
DUAN Qian-Heng, ZHANG Shuo, WU Wei, CHEN Ping-Xing
Chin. Phys. Lett. 2013, 30 (1): 010302 .   DOI: 10.1088/0256-307X/30/1/010302
Abstract   PDF(pc) (462KB) ( 437 )
The adiabatic quantum computation (AQC) has been proven to be equivalent to the standard circuit model. Conventionally, AQC evolves from the initial Hamiltonian which has a uniform equal superposition of the computational basis to the final Hamiltonian whose ground state encodes the solution to a computation problem. We propose an alternative approach to construct the initial Hamiltonian of the AQC which has an unequal superposition of the possible solutions to the problem and show that an educated guess can improve the performance of AQC.
One-Way Quantum Computation with Cluster State and Probabilistic Gate
DIAO Da-Sheng
Chin. Phys. Lett. 2013, 30 (1): 010303 .   DOI: 10.1088/0256-307X/30/1/010303
Abstract   PDF(pc) (452KB) ( 503 )
We present a scheme for efficiently constructing a two-dimensional cluster state, which serves as the central physical resource for one-way quantum computation. In this scheme, we successfully make the required computational overhead scale efficiently with the qubit number by using a probabilistic entangling quantum gate.
Computation of Quantum Bound States on a Singly Punctured Two-Torus
CHAN Kar-Tim, Hishamuddin Zainuddin, Saeid Molladavoudi
Chin. Phys. Lett. 2013, 30 (1): 010304 .   DOI: 10.1088/0256-307X/30/1/010304
Abstract   PDF(pc) (771KB) ( 431 )
We study a quantum mechanical system on a singly punctured two-torus with bound states described by the Maass waveforms which are eigenfunctions of the hyperbolic Laplace–Beltrami operator. Since the discrete eigenvalues of the Maass cusp form are not known analytically, they are solved numerically using an adapted algorithm of Hejhal and Then to compute Maass cusp forms on the punctured two-torus. We report on the computational results of the lower lying eigenvalues for the punctured two-torus and find that they are doubly-degenerate. We also visualize the eigenstates of selected eigenvalues using GridMathematica.
Four-State Modulation Continuous Variable Quantum Key Distribution over a 30-km Fiber and Analysis of Excess Noise
WANG Xu-Yang, BAI Zeng-Liang, WANG Shao-Feng, LI Yong-Min, PENG Kun-Chi
Chin. Phys. Lett. 2013, 30 (1): 010305 .   DOI: 10.1088/0256-307X/30/1/010305
Abstract   PDF(pc) (519KB) ( 700 )
We report a fiber-based four-state discrete modulation continuous variable quantum key distribution system based on homodyne detection. A secret key rate of 1 kbit/s is achieved at a transmission distance of 30.2 km. Two factors that result in the excess noises of the quantum key distribution system are analyzed. The first is the relative phase dithering between the signal and local fields, and the second is the local field leakage into the signal field due to the scattering process that depolarizes the local field. It is found that the latter has a significant impact on the excess noise, which is the main limiting factor to the long-distance secure quantum transmission. Some protocols are also given to decrease the excess noise effectively.
Fractals in Quantum Information Process
BI Feng, LI Chuan-Feng
Chin. Phys. Lett. 2013, 30 (1): 010306 .   DOI: 10.1088/0256-307X/30/1/010306
Abstract   PDF(pc) (584KB) ( 503 )
In the recent work of Kiss et al. [Phys. Rev. Lett. 107 (2011) 100501], the evolvement of two-qubit quantum states in a measurement-based purification process is studied. As they pointed out, the purification results manifest sensitivity to the applied initial states. The convergence regions to different stable circles are depicted on a complex plane. Because of the result patterns' likeness to typical fractals, we make further study on the interesting patterns' connection to fractals. Finally, through a numerical method we conclude that the boundaries of different islands of the patterns are fractals, which possess a non-integral fractal dimension. Also, we show that the fractal dimension would vary with the change of the portion of the noise added to the initial states.
Efficiency at Maximum Power of a Quantum Dot Heat Engine in an External Magnetic Field
ZHANG Yan-Chao, HE Ji-Zhou
Chin. Phys. Lett. 2013, 30 (1): 010501 .   DOI: 10.1088/0256-307X/30/1/010501
Abstract   PDF(pc) (616KB) ( 519 )
We investigate the efficiency at maximum power of a nanothermoelectric heat engine consisting of one spin-degenerate quantum dot embedded between two reservoirs at different temperatures and chemical potentials in an external magnetic field. Based on the stochastic master equation the maximum power and the corresponding efficiency at maximum power are calculated in different external magnetic fields. The result shows that both the maximum power and the corresponding efficiency at maximum power decrease with an increase of the external magnetic field. In the weak magnetic field the corresponding efficiency at maximum power is slightly larger than the Curzon–Ahlborn (CA) efficiency, while in the large magnetic field it is obviously lower than CA efficiency.
Nonergodic Brownian Motion in a Collinear Particle-Coupled Harmonic Chain Model
LU Hong, BAO Jing-Dong
Chin. Phys. Lett. 2013, 30 (1): 010502 .   DOI: 10.1088/0256-307X/30/1/010502
Abstract   PDF(pc) (446KB) ( 540 )
We investigate the nonergodic Brownian dynamics in a collinear particle-coupled harmonic chain model, in which the chain is free at one end and fixed at the other end. The behaviors of the particle are mainly studied: the velocity thermalizes faster than the coordinate, and the asymptotic result depends on its initial coordinate preparation which is indeed a kind of the nonergodic behavior.
Single-Hopf Bursting in Periodic Perturbed Belousov–Zhabotinsky Reaction with Two Time Scales
LI Xiang-Hong, BI Qin-Sheng
Chin. Phys. Lett. 2013, 30 (1): 010503 .   DOI: 10.1088/0256-307X/30/1/010503
Abstract   PDF(pc) (1294KB) ( 405 )
By introducing weak periodic perturbation to the Oregonator, we investigate a mathematical model with two time scales. The novel dynamical phenomena called the single-Hopf bursting with unusually quiescent state are observed. The related bifurcation mechanism is presented by means of the transition portrait and slow-fast analysis, which has rarely been reported in the previous works associated with the Oregonator model. Furthermore, the influence of forcing amplitude on bursting behaviors is studied. Further investigation finds that excitation amplitude may play an important role in a two-timescale system with the slow procedure dominated by periodic perturbation.
Accuracy Evaluation of NIM5 Cesium Fountain Clock
LIU Nian-Feng, FANG Fang, CHEN Wei-Liang, LIN Ping-Wei, WANG Ping, LIU Kun, SUO Rui, LI Tian-Chu
Chin. Phys. Lett. 2013, 30 (1): 010601 .   DOI: 10.1088/0256-307X/30/1/010601
Abstract   PDF(pc) (563KB) ( 571 )
The NIM5 fountain clock is the second fountain clock built at NIM (National Institute of Metrology, China), and has been operating stably and sub-continually since 2008. The fountain operates with a simple one-stage optical molasses to collect cold atoms, which reduces the collisional frequency shift dramatically. The fractional frequency uncertainty is estimated to be 2×10?15. The typical frequency instability of 2.5×10?14 is obtained at 10 s. Comparisons with other fountain frequency standards worldwide demonstrate agreement within the stated uncertainties.
Research of Infrared Imaging at Atmospheric Pressure Using a Substrate-Free Focal Plane Array
WU Jian-Xiong, CHENG Teng, ZHANG Qing-Chuan, ZHANG Yong, MAO Liang, GAO Jie, CHEN Da-Peng, WU Xiao-Ping
Chin. Phys. Lett. 2013, 30 (1): 010701 .   DOI: 10.1088/0256-307X/30/1/010701
Abstract   PDF(pc) (895KB) ( 383 )
An equivalent circuit model to the substrate-free focal plane array (FPA) is established. Using this fast and effective model, the performance of infrared (IR) imaging at atmospheric pressure is investigated and it is found that the substrate-free FPA has the ability of IR imaging at atmospheric pressure, whereas it has a slightly degraded noise equivalent temperature difference (NETD) as compared with IR imaging under a high vacuum. This feature is also identified experimentally by a substrate-free FPA with pixel size of 50×50 μm 2. The NETDs are measured to be 160 mK at 10?2 Pa pressure and 1.08 K at atmospheric pressure.
Photoproduction of Large Transverse Momentum Dimuonium (μ+μ) in Relativistic Heavy Ion Collisions
YU Gong-Ming, LI Yun-De
Chin. Phys. Lett. 2013, 30 (1): 011201 .   DOI: 10.1088/0256-307X/30/1/011201
Abstract   PDF(pc) (861KB) ( 261 )
The photoproduction processes of large transverse momentum (pT) dimuonium (μ+μ?) in AA collisions is calculated. We argue that the modification of electromagnetic radiation processes at large transverse momentum (pT>2 GeV). Through perturbative quantum chromodynamics (pQCD) calculation, we determine the electromagnetic production cross section of large transverse momentum dimuonium (μ+μ?) in quark-gluon plasma (QGP) at RHIC and LHC. The numerical results indicate that the contribution of photoproduction processes of dimuonium is evident in relativistic heavy ion collisions at RHIC energies and LHC energies.
Cluster Structure in Be Isotopes within Point-Coupling Covariant Density Functional
TANG Zhong-Hua, LI Jia-Xing, JI Juan-Xia, ZHOU Tao
Chin. Phys. Lett. 2013, 30 (1): 012101 .   DOI: 10.1088/0256-307X/30/1/012101
Abstract   PDF(pc) (1051KB) ( 322 )
The potential energy surfaces and density distributions of ground states in even-mass Be isotopes are studied by using the point-coupling covariant density functional theory with the PC-F1 effective interaction. The clustering structure is exhibited automatically in most of the Be isotopes. The results indicate that 6Be has an α+2p clustering structure, while 8,10,14Be have the 2α clustering structure. The αα distances and the corresponding quadrupole deformation parameters have a similar evolution trend against the neutron number.
Variational-Integral Perturbation Corrections for Hydrogen Atoms in Magnetic Fields
ZHAO Yun-Hui, PAN Yi-Qing, LI Wen-Juan, DENG Xia, HAI Wen-Hua
Chin. Phys. Lett. 2013, 30 (1): 013101 .   DOI: 10.1088/0256-307X/30/1/013101
Abstract   PDF(pc) (545KB) ( 408 )
A variational-integral perturbation method (VIPM) has been established by combining the variational perturbation with the integral perturbation. We present the results obtained by the application of VIPM to the ground and excited states associated with the Zeeman effect on a hydrogen atom. We construct correction wave functions and calculate energy corrections for the ground state and some high excited states. These values are compared with results of Smith and Jason et al.; our results are more accurate than those from Smith and Jason, especially in the 4f excited state where we find a very interesting result that when magnetic fields increase, the energy level trap appears.
Visible Light Emission in Highly Charged Kr17+ Ions Colliding with an Al Surface
YANG Zhi-Hu, XU Qiu-Mei, GUO Yi-Pan, WU Ye-Hong, SONG Zhang-Yong
Chin. Phys. Lett. 2013, 30 (1): 013201 .   DOI: 10.1088/0256-307X/30/1/013201
Abstract   PDF(pc) (454KB) ( 358 )
We report light emission during the bombardment of Kr ions on an Al surface in the wavelength range 300–700 nm. The three spectral lines of the sputtered Al atoms belong to transitions of Al I – at 309.26, Al I –4s 2S1/2 at 394.72 and Al I 3p 2Po3/2–4s 2S1/2 at 396.50 nm. During the neutralization process, the seven spectral lines of Kr I and Kr II from the incident ion of Kr17+ attribute to transitions of Kr I 5p 2[3/2]2–7d 2[1/2]o1 at 616.33, Kr II 5s 2D5/2–5p 2Do3/2 at 410.86, Kr II 5p 4Po5/2–6s 4P5/2 at 430.58, Kr II 4d 2D3/2–4f 2[3]o5/2 at 434.42, Kr II 4d 4D1/2–5p 2So1/2 at 485.80, Kr II 4p 4S3/2–6s 4Po3/2 at 618.57 and Kr II 5p 4Po3/2–4d 2D5/2 at 656.41 nm. Light emissions of sputtered species depend on energy of the incident ions deposited on the target surface atoms. Light emissions of the neutralized projectiles are formed due to many electrons of the conduction band of the solid surface captured in excited states of the incident ion.
Trapping, Transporting, and Splitting Cold Molecules Employing a Spatial Liquid Crystal Modulator
GONG Tian-Lin, HUANG Yun-Xia, MU Ren-Wang, JI Xian-Ming, YANG Xiao-Hua
Chin. Phys. Lett. 2013, 30 (1): 013701 .   DOI: 10.1088/0256-307X/30/1/013701
Abstract   PDF(pc) (1937KB) ( 588 )
Optically transporting and splitting cold molecules are proposed by spatially pure phase modulating a Gaussian laser beam with a spatial liquid crystal modulator (SLM). Taking the experimentally available cold KRb molecules (350 nK) as an example, the computations show that the trapping depth is about 460 μK and the trap can be split and transported up to 1 cm when a commercially available SLM is employed.
Demonstration of Cold 40Ca+ Ions Confined in a Microscopic Surface-Electrode Ion Trap
CHEN Liang, WAN Wei, XIE Yi, WU Hao-Yu, ZHOU Fei, FENG Mang
Chin. Phys. Lett. 2013, 30 (1): 013702 .   DOI: 10.1088/0256-307X/30/1/013702
Abstract   PDF(pc) (605KB) ( 460 )
40Ca+ ions are successfully confined, under the cooling of a red-detuned laser, in a home-built microscopic surface-electrode (MSE) trap. With all electrodes deposited on a low-rf-loss substrate, our 500-μm-scale MSE trap is designed involving three potential wells and manufactured by the standard technique of the printed circuit board. Both linear and two-dimensional crystals of 40Ca+ are observed in the trap after preliminary micromotion compensation is carried out. The development of the MSE trap aims at large-scale trapped-ion quantum information processing.
Cooling and Crystallization of Trapped 113Cd+ Ions for Atomic Clock
WANG Shi-Guang, ZHANG Jian-Wei, MIAO Kai, WANG Zheng-Bo, WANG Li-Jun
Chin. Phys. Lett. 2013, 30 (1): 013703 .   DOI: 10.1088/0256-307X/30/1/013703
Abstract   PDF(pc) (788KB) ( 383 )
We report recent experimental progress toward a trapped 113Cd+ ion microwave frequency standard. With laser cooling, a large number of trapped cadmium ions are cooled to crystallization and the temperature of the ion crystal is measured to be 16 ± 3 mK. The second order Doppler frequency shift, a main limiting factor of the atomic clock's performance, is estimated to be less than 1 × 10?16.
Birefringence Optical Feedback with a Folded Cavity in HeNe Laser
WU Yun, TAN Yi-Dong
Chin. Phys. Lett. 2013, 30 (1): 014201 .   DOI: 10.1088/0256-307X/30/1/014201
Abstract   PDF(pc) (917KB) ( 276 )
The birefringence optical feedback with a folded cavity in HeNe laser is investigated. A theory model based on the equivalent cavity of the Fabry–Perot interferometer is presented. The phase difference between the two intensities in birefringence feedback is twice the retardation of the wave plate. The phase difference is invariable when the length of the feedback cavity changes. With the adoption of a cube corner prism (CCP) to form a folded cavity, the fringe frequency is doubled, and the resolution of the displacement sensor based on birefringence optical feedback with a folded cavity is improved. A resistance chain of 5-fold subdivision and 4-fold logic subdivision is used as further subdivision. The resolution of λ/80 is obtained eventually; for 632.8 nm HeNe laser it is 7.91 nm. The displacement sensor based on birefringence optical feedback with a folded cavity is simple and of high resolution, large measurement range, low cost, and is of great application potential in industry.
Research on High-Intensity Picosecond Pump Laser in Short Pulse Optical Parametric Amplification
PAN Xue, PENG Yu-Jie, WANG Jiang-Feng, LU Xing-Hua, OUYANG Xiao-Ping, CHEN Jia-Lin, JIANG You-En, FAN Wei, LI Xue-Chun
Chin. Phys. Lett. 2013, 30 (1): 014202 .   DOI: 10.1088/0256-307X/30/1/014202
Abstract   PDF(pc) (1166KB) ( 509 )
A 527 nm pump laser generating 1.7 mJ energy with peak power of more than 0.12 GW is demonstrated. The theoretical simulation result shows that it has 106 gain in the picosecond-pump optical parametric chirped pulse amplification when the pump laser peak power is 0.1 GW and the intensity is more than 5 GW/cm2, and that it can limit the parametric fluorescence in the picosecond time scale of pump duration. The pump laser system adopts a master-oscillator power amplifier, which integrates a more than 30 pJ fiber-based oscillator with a 150 μJ regenerative amplifier and a relay-imaged four-pass diode-pump Nd glass amplifier to generate a 1 Hz top hat spatial beam and about 14 ps temporal Guassian pulse with <2% pulse-to-pulse energy stability. The output energy of the power amplifier is limited to 4 mJ for B-integral concern, and the frequency doubling efficiency can reach 65% with input intensity 10 GW/cm2.
Effect of Laser Pulse Width on the Laser Lift-off Process of GaN Films
CHEN Ming, ZHANG Jiang-Yong, LV Xue-Qin, YING Lei-Ying, ZHANG Bao-Ping
Chin. Phys. Lett. 2013, 30 (1): 014203 .   DOI: 10.1088/0256-307X/30/1/014203
Abstract   PDF(pc) (961KB) ( 968 )
Laser lift-off (LLO), by which GaN is separated from sapphire, is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices. Its physical insight, however, is still not fully understood. We study systematically the effect of laser pulse width on the LLO process and the property of GaN. To estimate accurately the temperature distribution and the decomposed thickness of GaN, fluctuation in the pulse laser energy is taken into account. It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width. In addition, less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area, lower transient temperature and lower N2 vapor pressure encountered during LLO. Some experimental results reported in literature are explained well. Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures.
Spectral Characteristic Based on Fabry–Pérot Laser Diode with Two-Stage Optical Feedback
WU Jian-Wei, Bikash NAKARMI
Chin. Phys. Lett. 2013, 30 (1): 014204 .   DOI: 10.1088/0256-307X/30/1/014204
Abstract   PDF(pc) (1667KB) ( 378 )
An optical device, consisting of a multi-mode Fabry–Pérot laser diode (MMFP-LD) with two-stage optical feedback, is proposed and experimentally demonstrated. The results show that the single-mode output with side-mode suppression ratio (SMSR) of ~21.7 dB is attained by using the first-stage feedback. By using the second-stage feedback, the SMSR of single-mode operation could be increased to ~28.5 dB while injection feedback power of ?29 dBm is introduced into the laser diode. In the case of up to ?29 dBm feedback power, the outcome SMSR is rapidly decayed to a very low level so that an obvious multi-mode operation in the output spectrum could be achieved at the feedback power level of ?15.5 dBm. Thus, a transition between single- and multi-mode operations could be flexibly controlled by adjusting the injected power in the second-stage feedback system. Additionally, in the case of injection locking, the outcome SMSR and output power at the locked wavelength are as high as ~50 dB and ~5.8 dBm, respectively.
Principal State Analysis for a Compact in-Line Fiber Polarization Controller
LI Zheng-Yong, WU Chong-Qing, WANG Zhi-Hao, QIN Tao, WANG Yi-Xu
Chin. Phys. Lett. 2013, 30 (1): 014205 .   DOI: 10.1088/0256-307X/30/1/014205
Abstract   PDF(pc) (562KB) ( 359 )
A compact in-line fiber-based polarization controller (FPC) made of a rotatable fiber squeezer is investigated in detail with the Mueller matrix model established based on the generalized principal state of polarization (PSP). The PSP caused by the fiber squeezing is in the equator plane, which turns around S3 axis on the Poincaré sphere when rotating the squeezer. Subsequently, a programmable polarization control method is proposed to realize the polarization conversion between arbitrary polarization states, in which only two parameters of phase shift and rotation angle need to be controlled. This type of FPC, which has a highly compact structure, lower insertion loss, and can be directly embedded into any fiber devices without any extra delay, will be an ideal PC for high-speed optical communication and all-optical signal processing.
Magnetic Field Induced Spectroscopy of 88Sr Atoms Probed with a 10 Hz Linewidth Laser
LIN Yi-Ge, WANG Qiang, LI Ye, LIN Bai-Ke, WANG Shao-Kai, MENG Fei, ZHAO Yang, CAO Jian-Ping, ZANG Er-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2013, 30 (1): 014206 .   DOI: 10.1088/0256-307X/30/1/014206
Abstract   PDF(pc) (538KB) ( 402 )
We present our experiment on magnetic field induced spectroscopy of the 1S03P0 transition of 88Sr atoms with a 10 Hz linewidth laser. The 88Sr atoms are cooled by two stage laser cooling. After the second stage narrow line laser cooling, the temperature of the atoms is reduced to ~3 μK. The atoms are then loaded into an 813 nm one-dimensional optical lattice. A homemade 698 nm laser with 10 Hz linewidth and maximum intensity of more than 100 W/cm2 is used to probe the 88Sr atoms in the lattice. By means of a magnetic field of ~1 mT and a probe laser with 50 ms pulse and ~6 W/cm2 intensity, the Doppler free 88Sr 1S03P0 transition spectrum with a linewidth of 208 Hz is obtained.
High Efficiency Grating Coupler for Coupling between Single-Mode Fiber and SOI Waveguides
ZHANG Can, SUN Jing-Hua, XIAO Xi, SUN Wei-Min, ZHANG Xiao-Jun, CHU Tao, YU Jin-Zhong , YU Yu-De
Chin. Phys. Lett. 2013, 30 (1): 014207 .   DOI: 10.1088/0256-307X/30/1/014207
Abstract   PDF(pc) (641KB) ( 727 )
A high efficiency grating coupler between single?mode fiber and silicon-on-insulator waveguide is designed by a formula method. Over 78.5% coupling efficiency (>-1.05 dB) with 3 dB bandwidth about 50 nm for one grating coupler is obtained experimentally and this result is the highest one as far as we know. This grating coupler is CMOS compatible which needs only one etch-step and is designed for a standard SOI chip without any Bragg reflector or bottom reflector.
Two-Crystal Design and Numerical Simulations for High-Average-Power Second-Harmonic Generation
ZHONG Hai-Zhe, YUAN Peng, ZHU He-Yuan, QIAN Lie-Jia
Chin. Phys. Lett. 2013, 30 (1): 014208 .   DOI: 10.1088/0256-307X/30/1/014208
Abstract   PDF(pc) (587KB) ( 387 )
Temperature-insensitive phase-matching of second-harmonic generation (SHG) can be realized using two nonlinear crystals with opposite signs of the temperature derivation of phase mismatch. The design procedure for optimizing crystal lengths is presented, and full numerical simulations for the SHG process, based on realistic crystals, are performed at a typical high-power-laser wavelength of ~1 μm. It is suggested that the proposed two-crystal design can support high efficiency (60–70%) of SHG in the high-average power regime of a kilowatt.
Stop Band Gap in Periodic Layers of Confined Atomic Vapor/Dielectric Medium
LI Yuan-Yuan, LI Li, LU Yi-Xin, ZHANG Yan-Peng, XU Ke-Wei
Chin. Phys. Lett. 2013, 30 (1): 014209 .   DOI: 10.1088/0256-307X/30/1/014209
Abstract   PDF(pc) (531KB) ( 321 )
A stop band gap is predicted in periodic layers of a confined atomic vapor/dielectric medium. Reflection and transmission profile of the layers over the band gap can be dramatically modified by the confined atoms and the number of layer periods. These gap and line features can be ascribed to the enhanced contribution of slow atoms induced by atom-wall collision, transient behavior of atom-light interaction and Fabry–Pérot effects in a thermal confined atomic system.
Effect of Interstitial Media on Segregation in Vertically Vibrated Granular Mixtures
YUAN Xiao-Xian, LI Liang-Sheng, WEN Ping-Ping, SHI Qing-Fan, ZHENG Ning
Chin. Phys. Lett. 2013, 30 (1): 014501 .   DOI: 10.1088/0256-307X/30/1/014501
Abstract   PDF(pc) (677KB) ( 384 )
Vertically vibrated segregation behaviors of binary granular mixtures with different interstitial media are experimentally investigated. To study the role of interstitial media on the segregation, two types of interstitial fluids are adopted and the resulting phase diagrams are compared. The water-immersed granular mixture exhibits two kinds of complete segregation behaviors: Brazil nut effect and sandwich patterns, at least the latter is absent in the same air-immersed mixture. Additionally, the segregation extent is improved remarkably for the water-immersed mixture. The experimental observation further confirms that the effect of interstitial media on the relative motion of grains is one of the predominant mechanisms for granular segregation.
Dynamic Characteristics of Gas Transport in Nanoporous Media
SONG Hong-Qing, YU Ming-Xu, ZHU Wei-Yao, ZHANG Yu, JIANG Shan-Xue
Chin. Phys. Lett. 2013, 30 (1): 014701 .   DOI: 10.1088/0256-307X/30/1/014701
Abstract   PDF(pc) (440KB) ( 470 )
Special flow mechanism and percolation characteristics for gas transport are presented in nanoporous media, which cannot be explained by the traditional motion equation of Darcy's law. On the basis of theoretical analysis, we establish a low velocity nonlinear transfer equation of gas in nanoporous media and a mathematical model of gas volume flow in multi-scale porous media. By utilizing nonlinear numerical calculation methodology, a detailed quantitative analysis of the diffusion and convective rate of gas flow is presented, providing a theoretical foundation for the development of nanoporous media.
Super-X Divertor Simulation for HCSB-DEMO Conception Design
ZHENG Guo-Yao, PAN Yu-Dong, FENG Kai-Ming, HE Hong-Da, CUI Xue-Wu
Chin. Phys. Lett. 2013, 30 (1): 015201 .   DOI: 10.1088/0256-307X/30/1/015201
Abstract   PDF(pc) (641KB) ( 293 )
HCSB-DEMO concept design is carried out at SWIP. In order to handle power from a core plasma region, a super-X divertor is preliminarily designed and investigated for HCSB-DEMO. It increases the target surface area by expanding the magnetic flux surface with another X-point generated near the targets and increases the parallel connection length by moving the outer divertor target to larger R and Z. The heat load at the targets is investigated by B2.5-Eirene. With heating power flowing into SOL/divertor regions being P=600 MW, when the density at the separatrix is ne=3.5×1019 m?3, the peak heat load at the inner and outer divertor is 9.2 MW/m2 and 3.7 MW/m2, respectively, which is much less than those of the standard divertor without impurity seeding, and also below the design targets (10 MW/m2). Thus the super-X divertor may work well for HCSB-DEMO to solve the high heat load problem at the divertor target without impurity seeding from this preliminary concept design and simulation.
Influence of Discharge Voltage on Charged Particles in a Multi-Dipole Device in the Presence of an Ion Collecting Surface
M. K. Mishra, A. Phukan, M. Chakraborty
Chin. Phys. Lett. 2013, 30 (1): 015202 .   DOI: 10.1088/0256-307X/30/1/015202
Abstract   PDF(pc) (506KB) ( 362 )
The influence of discharge voltage on ion collecting surfaces in the form of a metal plate and a mesh grid is investigated in a multi-dipole device. In the experiment, a solid metal plate and a mesh grid are placed alternately at one end of the multi-dipole device. It is seen that except for high negative bias, the ion space charge layer in front of the grid gets depleted with the increase in discharge voltage whereas it gets thickened in front of the plate. It is also observed that the electron loss at the cusp (anode current) changes accordingly in both the cases. The increase in discharge voltage can enhance the Bohm speed of ions towards the ion collecting surfaces. Further, the negative potential applied to the ion collecting surfaces lowers the bulk plasma potential, which in turn affects the anode current.
Formation of Co-implanted Silicon Ultra-Shallow Junctions for Low Thermal Budget Applications
Rehana Mustafa, S. Ahmed, E. U. Khan
Chin. Phys. Lett. 2013, 30 (1): 016101 .   DOI: 10.1088/0256-307X/30/1/016101
Abstract   PDF(pc) (500KB) ( 678 )
We present a systematic study to create ultra-shallow junctions in n-type silicon substrates and investigate both pre- and post-annealing processes to create a processing strategy for potential applications in nano-devices. Starting wafers were co-implanted with indium and C atoms at energies of 70 keV and 10 keV, respectively. A carefully chosen implantation schedule provides an abrupt ultra-shallow junction between 17 and 43 nm with suppressed sheet resistance and appropriate retained sheet carrier concentration at low thermal budget. A defect doping matrix, primarily the behavior and movement of co-implant generated interstitials at different annealing temperatures, may be engineered to form sufficiently activated ultra-shallow devices.
Temperature Effects of Electrorheological Fluids Based on One-Dimensional Calcium and Titanium Precipitate
YAN Ren-Jie, WU Jing-Hua, LI Cong, XU Gao-Jie, ZHOU Lu-Wei
Chin. Phys. Lett. 2013, 30 (1): 016202 .   DOI: 10.1088/0256-307X/30/1/016202
Abstract   PDF(pc) (806KB) ( 381 )
Electrorheological (ER) fluids based on nanorods of calcium and titanium precipitate (CTP) possess good ER performance. We investigate the shear stress and leaking current of CTP suspension from ?15 to 230°C, and it is found that the ER effect increases at up to 150°C. Dielectric spectra of the CTP suspension at different temperatures indicate that the change of interface polarization can perfectly interpret the increment of ER effect and leaking current. The Fourier transform infrared (FTIR) spectroscopy test shows that some compositions of the CTP particles decompose at temperature of 180°C, which leads to a consequential decrease of ER effect. Through thermogravimetric and differential thermal analyses (TG-DTA), we find that TiOC2O4(H2O)2 plays a key role in the dielectric property and ER effect of CTP suspension.
Dynamic Mechanical Behavior and Failure Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Whiskers
RONG Ji-Li, WANG Dan, WANG Xi, LI Jian, XU Tian-Fu, LU Ming-Ming, CAO Mao-Sheng
Chin. Phys. Lett. 2013, 30 (1): 016203 .   DOI: 10.1088/0256-307X/30/1/016203
Abstract   PDF(pc) (1719KB) ( 426 )
Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers (T-ZnOw) in two loading directions are investigated by a split Hopkinson pressure bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope. Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data. The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties. Finally, the strengthening and toughening mechanisms of T-ZnOw are analyzed. It is shown that T-ZnOw can improve mechanical properties of the composites, and can make the composites have some new features. The present results provide a reliable basis for advanced composite design and manufacture, and have broad applications in the field of aerospace.
Electric-Field Switching of Bright and Dark Excitons in Semiconductor Crossed Nanowires
LI Xiao-Jing, K. S. Chan
Chin. Phys. Lett. 2013, 30 (1): 016801 .   DOI: 10.1088/0256-307X/30/1/016801
Abstract   PDF(pc) (675KB) ( 338 )
We investigate theoretically the exciton states in semiconductor crossed nanowires (CNWs) and it is found that the energy spectrum and electro-PL spectrum of the exciton in the CNWs can be tuned by the size of the nanowires using electric fields. An interesting bright-to-dark exciton transition can be found and it significantly affects the photoluminescence spectrum by the electric fields, which can be used to design new types of optoelectronic devices.
Electronic Structure, Lattice Dynamics and Thermoelectric Properties of PbTe from First-Principles Calculation
LU Peng-Xian, QU Ling-Bo
Chin. Phys. Lett. 2013, 30 (1): 017101 .   DOI: 10.1088/0256-307X/30/1/017101
Abstract   PDF(pc) (693KB) ( 839 )
The electronic structure and the lattice dynamics of lead telluride (PbTe) are investigated by using the density functional theory. The thermoelectric properties are then calculated using the semi-classical Boltzmann theory. Moreover, the relationships among the thermoelectric properties, the electronic structure and the lattice dynamics are also studied. Some strategies aiming at optimizing the thermoelectric properties are proposed. The related theoretical calculations therefore give a valuable insight on how to further enhance the thermoelectric properties of PbTe.
Ultrafast and Broadband Terahertz Switching Based on Photo-Induced Phase Transition in Vanadium Dioxide Films
CHEN Zhi, WEN Qi-Ye, DONG Kai, SUN Dan-Dan, QIU Dong-Hong, ZHANG Huai-Wu
Chin. Phys. Lett. 2013, 30 (1): 017102 .   DOI: 10.1088/0256-307X/30/1/017102
Abstract   PDF(pc) (638KB) ( 1412 )
Single-phase VO2 thin films are sputtering deposited on BK7 substrates, and sharp insulator-to-metal phase transition is obtained with a resistivity change of four orders of magnitude. Terahertz (THz) pump-probe measurements reveal that by illuminating the films with a low pumping power of 143 μJ/cm2, VO2 films exhibit an ultrafast optical switching to THz transmission within 8 ps. Furthermore, the THz switching ratio reaches over 80% in a wide frequency range from 0.3 to 2.5 THz. All these outstanding features indicate a strong potential of VO2 films for broadband terahertz wave switching and modulation applications.
First-Principles Calculation of Lithium Adsorption and Diffusion on Silicene
HUANG Juan, CHEN Hong-Jin, WU Mu-Sheng, LIU Gang, OUYANG Chu-Ying, XU Bo
Chin. Phys. Lett. 2013, 30 (1): 017103 .   DOI: 10.1088/0256-307X/30/1/017103
Abstract   PDF(pc) (683KB) ( 827 )
The adsorption and diffusion of lithium on silicene are studied by using the first-principles method. It is found that the adsorption energy of Li adsorbing on silicene is significantly larger than that of Li adsorbing on graphene. With the increasing concentration of adsorbed Li atoms, the adsorption energy also increases. The diffusion barrier of Li on silicene is relatively low, which is insensitive to the concentration of adsorbed atoms.
Spin-Dependent Electron Transport in an Armchair Graphene Nanoribbon Subject to Charge and Spin Biases
ZHANG Xiao-Wei, ZHAO Hua, SANG Tian, LIU Xiao-Chun, CAI Tuo
Chin. Phys. Lett. 2013, 30 (1): 017201 .   DOI: 10.1088/0256-307X/30/1/017201
Abstract   PDF(pc) (457KB) ( 622 )
We study the spin-dependent electron transport in an armchair graphene nanoribbon sample driven by both the charge and the spin biases within the tight-binding framework. By numerical calculations we give the spin-dependent currents for a fixed spin bias as a function of the charge bias. It is found that we can let only one type of spin current pass through the graphene nanoribbon for a wide range of charge bias, which is due to the difference of the bias voltage windows for different spin electrons when the charge and the spin biases coexist. Moreover, the pure spin current can be controlled via the charge bias. Our results are suggestive for developing new kinds of spin filters.
Efficiency Enhancement of MEH-PPV:PCBM Solar Cells by Addition of Ditertutyl Peroxide as an Additive
LI Yan-Fang, YANG Li-Ying, QIN Wen-Jing, YIN Shou-Gen, ZHANG Feng-Ling
Chin. Phys. Lett. 2013, 30 (1): 017202 .   DOI: 10.1088/0256-307X/30/1/017202
Abstract   PDF(pc) (655KB) ( 571 )
Improved power conversion efficiency (PCE) and stability of organic bulk heterojunction (BHJ) solar cells based on poly (2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends are obtained by using ditert butyl peroxide (DTBP) as an additive. The effect of the DTBP contents on the performance of photovoltaic cells is investigated. The results reveal that efficiency enhancement of MEH-PPV:PCBM solar cells can be realized by carefully tuning the contents of DTBP. Compared to the control device, the optimized device with 0.5wt% DTBP additive exhibits enhanced performance with Jsc of (3.51±0.21) mA/cm2, FF of (44.45±0.71)%, and PCE of (1.31±0.08)%, increased by 9.3%, 8.0% and 22.4%, respectively. The stability of the device is found to be improved by adding 0.5wt% of DTBP.
On the Voltage and Frequency Distribution of Dielectric Properties and ac Electrical Conductivity in Al/SiO2/p-Si (MOS) Capacitors
Ahmet Kaya, Şemsettin Altındal, Yasemin Şafak Asar, Zekayi Sönmez
Chin. Phys. Lett. 2013, 30 (1): 017301 .   DOI: 10.1088/0256-307X/30/1/017301
Abstract   PDF(pc) (571KB) ( 538 )
An Al/SiO2/p-Si (MOS) capacitor with a thick (826 ?) interfacial oxide layer (SiO2) which is formed by using the thermal oxidation method is fabricated to investigate both frequency and applied bias voltage dependences of real and imaginary parts of dielectric constant (ϵ' and ϵ") and electric modulus (M' and M"), loss tangent (tanδ) and ac electrical conductivity (σac) in a wide frequency range from 1 kHz to 1 MHz at room temperature. The dielectric properties of the MOS capacitor are obtained using the forward and reverse bias capacitance-voltage (CV) and conductance-voltage (G/ωV) measurements in the applied bias voltage range 1.4–5.6 V. The values of ϵ', ϵ", tanδ, M', M" and σac are found to be strong functions of frequency and applied bias voltage in the depletion region due to excess capacitance Cex and conductance Gex especially at low frequencies. The experimental results show that the interfacial polarization can occur at low frequencies more easily, consequently contributing to the dispersion in ϵ', ϵ", tanδ, M', M" and σac values of the MOS capacitor. The other reason for dispersion in the dielectric properties may be attributed to a particular density distribution of interface states (Nss) localized at the Si/SiO2 interface, as well as space charge carriers and inhomogeneity of interfacial oxide layer. The increase in conductivity with increasing frequency can be attributed to the hopping type conduction mechanism. It can be concluded that the ϵ', ϵ", tanδ, M', M" and σac values of the Al/SiO2/p-Si (MOS) capacitor are strongly dependent on both the frequency and applied bias voltage especially in the depletion region.
High Deep-Ultraviolet Quantum Efficiency GaN P–I–N Photodetectors with Thin P-GaN Contact Layer
LIAN Hai-Feng, WANG Guo-Sheng, LU Hai, REN Fang-Fang, CHEN Dun-Jun, ZHANG Rong, ZHENG You-Dou
Chin. Phys. Lett. 2013, 30 (1): 017302 .   DOI: 10.1088/0256-307X/30/1/017302
Abstract   PDF(pc) (629KB) ( 404 )
GaN ultraviolet (UV) p-i-n photodetectors (PDs) with a 40 nm thin p-GaN contact layer are fabricated on sapphire substrates, which exhibit enhanced quantum efficiency especially in a deep-UV wavelength range. The PDs show good rectification behavior and low dark current in pA level for reverse bias up to ?10 V. Under zero bias, the maximum quantum efficiency of the PD at 360 nm is close to 59.4% with a UV/visible rejection ratio more than 4 orders of magnitude. Even at a short wavelength of 280 nm, the quantum efficiency of the PD is still around 47.5%, which is considerably higher than that of a control device with a thicker p-GaN contact layer. The room temperature thermal noise limited detectivity of the PD is calculated to be ~4.96×1014 cm?Hz1/2W?1.
Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group
LIU Wen, XIA Cai-Juan, LIU De-Sheng
Chin. Phys. Lett. 2013, 30 (1): 017303 .   DOI: 10.1088/0256-307X/30/1/017303
Abstract   PDF(pc) (625KB) ( 439 )
The electronic transport properties of a kind of phenylacetylene compound (4-mercaptophenyl)-phenylacetylene (MPPA) are studied by the first-principles method. A dithiocarboxylate conjugated linker (–CS2) is used to anchor the molecule to one gold electrode. Rectification behavior is observed, which is mainly brought about by the asymmetrical coupling of electrodes to the molecule. There is a drastic increase in current as the electrode-electrode distance is reduced, and the rectification ratio increases by 40% as the electrode-electrode distance is diminished from 16 ? to 15.7 ?. For comparison, we also perform simulations with the –CS2 linker replaced by thiol linkage. It shows an obvious reduction in current. We find that the stronger interface coupling induced by the –CS2 linker broadens transmission resonances near the Fermi energy, which leads to the current enhancement of the molecular junction with –CS2 linker.
Intra-Valley Spin-Triplet p+ip Superconducting Pairing in Lightly Doped Graphene
ZHOU Jian-Hui, QIN Tao, SHI Jun-Ren
Chin. Phys. Lett. 2013, 30 (1): 017401 .   DOI: 10.1088/0256-307X/30/1/017401
Abstract   PDF(pc) (590KB) ( 440 )
We analyze various possible superconducting pairing states and their relative stabilities in lightly doped graphene. It is shown that, when inter-sublattice electron-electron attractive interaction dominates and the Fermi level is close to the Dirac points, the system will favor intra-valley spin-triplet p+ip pairing state. Based on the novel pairing state, we further propose a scheme for doing topological quantum computation in graphene by engineering local strain fields and external magnetic fields.
Experimental Investigation of the Electronic Structure of Ca0.83La0.17Fe2As2
HUANG Yao-Bo, RICHARD Pierre, WANG Ji-Hui, WANG Xiao-Ping, SHI Xun, XU Nan, WU Zheng, LI Ang, YIN Jia-Xin, QIAN Tian, LV Bing, CHU Ching-Wu, PAN Shu-Heng, SHI Ming, DING Hong
Chin. Phys. Lett. 2013, 30 (1): 017402 .   DOI: 10.1088/0256-307X/30/1/017402
Abstract   PDF(pc) (1053KB) ( 378 )
We performed a combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy study of the electronic structure of electron-doped Ca0.83La0.17Fe2As2. A surface reconstruction associated with the dimerization of As atoms is observed directly in the real space, as well as the consequent band folding in the momentum space. Besides this band folding effect, the Fermi surface topology of this material is similar to that reported previously for BaFe1.85Co0.15As2, with Γ-centered hole pockets quasi-nested to M-centered electron pockets by the antiferromagnetic wave vector. Although no superconducting gap is observed by ARPES possibly due to low superconducting volume fraction, a gap-like density of states depression of 7.7±2.9 meV is determined by scanning tunneling microscopy.
Magnetoelastic Anisotropy of FeSiB Glass-Coated Amorphous Microwires
LIU Kai-Huang, LU Zhi-Chao, LIU Tian-Cheng, LI De-Ren
Chin. Phys. Lett. 2013, 30 (1): 017501 .   DOI: 10.1088/0256-307X/30/1/017501
Abstract   PDF(pc) (641KB) ( 433 )
The magnetoelastic anisotropy of Fe77.5Si7.5B15 glass-coated amorphous microwires is investigated by the law of approach to saturation magnetization in comparison with the ferromagnetic resonance technique. The anisotropy field of the inner core determined by the former method is 7.6×104 A/m, which is larger than the value 2.5×104 A/m measured by the ferromagnetic resonance method. This difference is ascribed to the skin effect and the uneven distribution of the internal stresses. However, the anisotropy field of the outer shell has a negative value indicating that it has an easy basal plane.
Detecting Larmor Precession of a Single Spin with a Spin-Polarized Tunneling Current
GUO Xiao-Dong, DONG Li, GUO Yang, SHAN Xin-Yan, ZHAO Ji-Min, LU Xing-Hua
Chin. Phys. Lett. 2013, 30 (1): 017601 .   DOI: 10.1088/0256-307X/30/1/017601
Abstract   PDF(pc) (573KB) ( 338 )
Detection and manipulation of a single spin is essential for spin-based quantum information and computation. We propose an experimental method to detect the Larmor precession of a single spin with a spin-polarized tunneling current. The calculation demonstrates that the modulation of the tunneling current is significantly increased as compared with the non-spin-polarized current. The signal-to-noise ratio in the current power spectrum will be dramatically improved by this method. The longitudinal relaxation time can be measured by temporal control of spin orientation with pulses of magnetic field or radio frequency electromagnetic wave, while the transverse relaxation time can be derived by analyzing the resonant peak profile with a spectrum analyzer. Such ability in characterizing spin relaxation is of particular interest in providing insights into the coherence/decoherence of a single spin.
Dosimetric Characteristics of a LKB:Cu,Mg Solid Thermoluminescence Detector
Yasser Saleh Mustafa Alajerami, Suhairul Hashim, Ahmad Termizi Ramli, Muneer Aziz Saleh, Ahmad Bazlie Bin Abdul Kadir, Mohd. Iqbal Saripan
Chin. Phys. Lett. 2013, 30 (1): 017801 .   DOI: 10.1088/0256-307X/30/1/017801
Abstract   PDF(pc) (579KB) ( 330 )
We present the main thermoluminescence characteristics of a newly borate glass dosimeter modified with lithium and potassium carbonate (LKB) and co-doped with CuO and MgO. An enhancement of about three times has been shown with the increment of 0.1mol% MgO as a co-dopant impurity. The effects of dose linearity, storage capacity, effective atomic number and energy dose response are studied. The proposed dosimeter shows a simple glow curve, good linearity up to 103 Gy, close effective atomic number and photon energy independence. The current results suggest using the proposed dosimeter in different dosimetric applications.
Phase Shift of Polarized Light after Transmission through a Biaxial Anisotropic Thin Film
HOU Yong-Qiang, LI Xu, HE Kai, QI Hong-Ji, YI Kui, SHAO Jian-Da
Chin. Phys. Lett. 2013, 30 (1): 017802 .   DOI: 10.1088/0256-307X/30/1/017802
Abstract   PDF(pc) (583KB) ( 490 )
Based on the theoretical analysis of biaxial birefringent thin films with characteristic matrix method, we investigate the phase shift on transmission of a tilted columnar biaxial film at normal and oblique incidence over 300–1200 nm for s- and p-polarized waves. Compared with the simplified calculation method, the interference effects of the birefringent thin film are considered to yield more accurate results. The quarter wavelength phase shift calculated with the characteristic matrix method is consistent with that monitored with in situ measurement by two-angle ellipsometry, which validates our complied program for the calculation of the phase shift of the biaxial anisotropic thin film. Furthermore, the characteristic matrix method can be easily used to obtain continuous adjustable phase retardation at oblique incidence, whereas the simplified calculation method is valid for the case of normal incidence. A greater generality and superiority of the characteristic matrix method is presented.
Current Density-Sensitive Welding of a Semiconductor Nanowire to a Metal Electrode
TAN Yu, WANG Yan-Guo
Chin. Phys. Lett. 2013, 30 (1): 017901 .   DOI: 10.1088/0256-307X/30/1/017901
Abstract   PDF(pc) (577KB) ( 293 )
In situ welding of a single ZnSe nanowire (NW) to an Au electrode has been successfully achieved by means of current-induced Joule heating. The parameter governing the welding of semiconductor NW to the metal electrode is highly dominated by the current density at the Au-ZnSe NW (M-S) contact because current density at the M-S contact can change the temperature profile along the NW. The self-heating behaviors of the Au-ZnSe NW-Au (M-S-M) nanostructure can be changed from the electrical failure of the ZnSe NW to the melting of the Au electrode localized at the M-S contact when the current density at the M-S junction was adjusted to be larger than in the NW. Consequently, the self-welding is the current density-sensitive and controllable since the current density at the M-S contact can be controlled by adjusting the contact area between the NW and metal electrode. This controlled self-welding may have potential applications in the construction of a complex nanostructure and improvement of the thermal stability of the M-S contact as well as the enhanced performance of the nanodevices based on the M-S-M nanostructure.
Elimination of the Schottky Barrier at an Au-ZnSe Nanowire Nanocontact via in Situ Joule Heating
TAN Yu, WANG Yan-Guo
Chin. Phys. Lett. 2013, 30 (1): 017902 .   DOI: 10.1088/0256-307X/30/1/017902
Abstract   PDF(pc) (757KB) ( 484 )
In order to improve electron transport, in situ Joule heating of an Au-ZnSe nanowire-Au (M-S-M) nanostructure is conducted inside transmission electron microscopy (TEM) until the Au metal is molten at the reversely biased Au-ZnSe nanowire (M-S) nanocontact. The observed microstructural evolution is responsible for the electron transport property changes, i.e. a nonlinear to linear transformation in the current-voltage (IV) relationship was measured in situ before and after the Joule annealing. The linear characteristic in the IV relationship confirms elimination of the Schottky barrier at the M-S nanocontact and formation of ohmic contacts. Consequently, electron transport at the M-S nanocontact can be significantly improved by the removal of the Schottky barrier via in situ Joule heating.
Fabrication of Thin Graphene Layers on a Stacked 6H-SiC Surface in a Graphite Enclosure
DENG Peng-Fei, LEI Tian-Min, LU Jin-Jun, LIU Fu-Yan, ZHANG Yu-Ming, GUO Hui, ZHANG Yi-Men, WANG Yue-Hu, TANG Xiao-Yan
Chin. Phys. Lett. 2013, 30 (1): 018101 .   DOI: 10.1088/0256-307X/30/1/018101
Abstract   PDF(pc) (1105KB) ( 402 )
Thin and homogeneous epitaxial graphene (EG) layers on a 6H-SiC (0001) substrate are fabricated and they cover the whole substrate (10×10 mm2). The sample surface is capped by another 6H-SiC (0001) wafer in a graphite enclosure to form a relatively high Si partial pressure between them, which significantly reduces the extremely high growth rate of EG. The structure and morphology of the EG layers are investigated by Raman spectroscopy, atomic force microscopy and field-emission scanning electronic microscopy. The results are compared with an uncapped sample surface, and reveal the obvious existence of ridges on the surface of the EG, and show that capping is indeed beneficial to obtain homogeneous graphene.
Phase Structure and Electrical Conduction of CaTi1−xScxO3−δ Ceramics
ZHANG Qi-Long, LIU Yang, YANG Hui
Chin. Phys. Lett. 2013, 30 (1): 018102 .   DOI: 10.1088/0256-307X/30/1/018102
Abstract   PDF(pc) (597KB) ( 295 )
The electrical conduction of CaTi1?xScxO3 ceramics is investigated by ac impedance spectra. A complete solid solution is formed, in which Sc (x≤0.17) substitutes for a Ti-site with the creation of oxygen vacancies. The samples of x≤0.1 contain two main resistances, the bulk resistance R1 and the grain boundary resistance R2. However, only R1 and a low-frequency 'spike' representing charge build-up at the blocking metal electrodes are obtained for x≥0.15. CaTiO3 ceramics doped with Sc exhibits a relativly high electrical conductivity. With increasing x, both σ1 and σ2 of CaTi1?xScxO3 increase first, reach a maximum value at x=0.05, and then decrease to x≥0.1.
Characterization of Modified Tapioca Starch in Atmospheric Argon Plasma under Diverse Humidity by FTIR Spectroscopy
P. Deeyai, M. Suphantharika, R. Wongsagonsup, S. Dangtip
Chin. Phys. Lett. 2013, 30 (1): 018103 .   DOI: 10.1088/0256-307X/30/1/018103
Abstract   PDF(pc) (552KB) ( 1964 )
Tapioca is economical crop grown in Thailand and continues to be one of the major sources of starch. Nowadays, tapioca starch has been widely used in industrial applications, however the native form of starch has limited the applications. Thus scientists try to modify the properties of starch for increasing the stability of the granules, pastes to low pH, heat, and shear during the food process. We modify the tapioca starch by plasma treatment under an argon atmosphere. The degree of modification is determined by following water content in the starch granules. The tablet samples of native starch are also prepared and compared with the plasma treated starch. Before plasma treatment, the starch tablets are stored under three different relative humilities (RH) including 11%, 68%, and 78%RH, respectively. The samples are characterized using FTIR spectroscopy associated with the degree of cross-linking. The results show that the water molecules are engulfed into the starch structure in two ways, a tight bond and a weak absorption of water molecules which is represented at two wave number of 1630 cm?1 and 3272 cm?1, respectively. The degree of cross-linking can be identified from the relative intensity of these two peaks with the C–O–H peak at 993 cm?1. The results show that the degree of cross-linking increase in the plasma treated starch. The degree of cross-linking of the treated starch with high relative humidity is less than that of the treated starch with low relative humidity.
A SQUID Bootstrap Circuit with a Large Parameter Tolerance
ZHANG Guo-Feng, ZHANG Yi, Hans-Joachim Krause, KONG Xiang-Yan, Andreas Offenhäusser, XIE Xiao-Ming
Chin. Phys. Lett. 2013, 30 (1): 018501 .   DOI: 10.1088/0256-307X/30/1/018501
Abstract   PDF(pc) (609KB) ( 356 )
The voltage biased (SQUID) bootstrap circuit (SBC) was recently introduced as an effective means to reduce the preamplifier noise contribution. We analyze the tolerances of the SBC noise suppression performance to spreads in SQUID and SBC circuit parameters. It is found that the tolerance to spread mainly caused by the integrated circuit fabrication process could be extended by a one-time adjustable current feedback. A helium-cooled niobium SQUID with a loop inductance of 350 pH is employed to experimentally verify the analysis. From this work, design criteria for fully integrated SBC devices with a high yield can be derived.
Enhanced Response to Subthreshold Signals by Phase Noise in a Hodgkin–Huxley Neuron
KANG Xiao-Sha, LIANG Xiao-Ming, LÜ Hua-Ping
Chin. Phys. Lett. 2013, 30 (1): 018701 .   DOI: 10.1088/0256-307X/30/1/018701
Abstract   PDF(pc) (527KB) ( 428 )
Noise has been revealed as an important cue for understanding the extraordinary ability of sensory neurons to detect or amplify external weak signals. We demonstrate that phase noise originating from the time-varying signal phase can enable an excitable neuron to excite spikes upon a periodic signal even though the signal amplitude is subthreshold. In addition, we find that there exists an optimal value on the phase noise at which the neuron's response to the subthreshold periodic signal can be significantly improved, resulting in a resonance-like behavior. Since phase noise makes the external signal aperiodic, our findings show that sensory neurons might evolve with a better performance on detecting aperiodic signals than periodic signals.
A Micro-Community Structure Merging Model Using a Community Sample Matrix
LI Lin, PENG Hao, LU Song-Nian, TIAN Ying
Chin. Phys. Lett. 2013, 30 (1): 018901 .   DOI: 10.1088/0256-307X/30/1/018901
Abstract   PDF(pc) (466KB) ( 428 )
Detecting an overlapping and hierarchical community structure can give a significant insight into structural and functional properties in complex networks. We propose a micro-community structure merging model to detect overlapping and hierarchical communities. The algorithm maps communities to random variables using the community sample matrix to evaluate similarity between communities. After finding density-based micro-community structures, the algorithm merges these reasonable micro-communities iteratively to form communities. Simulation results in three real networks show that the proposed algorithm is more accurate than some existing mechanisms. In this way, we can obtain a detailed understanding of the overlapping and hierarchical communities.
Large Bi-Polar Signature in a Perpendicular Electric Field of Two-Dimensional Electrostatic Solitary Waves Associated with Magnetic Reconnection: Statistics and Discussion
LI Shi-You, ZHANG Shi-Feng, DENG Xiao-Hua, CAI Hong
Chin. Phys. Lett. 2013, 30 (1): 019401 .   DOI: 10.1088/0256-307X/30/1/019401
Abstract   PDF(pc) (624KB) ( 304 )
More than 300 electrostatic solitary waves (ESWs) with a large perpendicular component which is a bi-polar waveform structure are observed in the boundary layer within the magnetic reconnection diffusion region in the near-Earth magnetotail. Such ESWs are called two-dimensional ESWs. A Singe-reconnection-based-statistical study of two-dimensional ESWs shows that: (1) ESWs can be continuously observed in the plasma sheet boundary layer (PSBL) associated with the magnetic reconnection diffusion region, and their amplitude ranges are mainly from several tens to hundreds of μV/m; (2) both one-dimension-like ESWs (very small magnitude on E) and two-dimension-like ESWs (large magnitude on E, which are even comparable to that in the E||) are observed within a small time interval; (3) within the observation time spans, more than 61% of ESWs are regarded as two-dimensional ESWs for the I2D>20%. We discuss the bi-polar structure in E. The observation of ESWs with a large bi-polar structure in the perpendicular electric field gives evidence that the unique waveform differs from previous understanding from observations and simulations which suggests that it should be a uni-polar waveform structure in the E of ESWs.
Spatial Distribution and Anisotropy of Energetic Particles Accelerated by Shock Waves: Focused Transport Model
ZUO Ping-Bing, FENG Xue-Shang
Chin. Phys. Lett. 2013, 30 (1): 019601 .   DOI: 10.1088/0256-307X/30/1/019601
Abstract   PDF(pc) (462KB) ( 277 )
The focused transport equation (FTE) contains the necessary physics of shock acceleration but avoids the limitation of small pitch-angle anisotropy inherent in the cosmic ray transport equation. We present a focused transport model based on FTE to investigate the spatial distribution and anisotropy of energetic particles accelerated by shock waves from pickup ions. It is found that in the upstream of the shock, the accelerated particles are highly anisotropic, but in the downstream it is approximately isotropic. An intensity spike is formed across the shock. These simulation results are qualitatively consistent with the observations of the termination shock particles by two Voyager spacecraft in the vicinity of the termination shock.
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