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Multi-Scale Time Asymmetry for Detecting the Breakage of Slug Flow Structure
HAO Qing-Yang, JIN Ning-De, HAN Yun-Feng, GAO Zhong-Ke, ZHAI Lu-Sheng
Chin. Phys. Lett. 2014, 31 (12):
120501
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DOI: 10.1088/0256-307X/31/12/120501
We first employ multi-scale time asymmetry (MSA) to analyze typical chaotic signals from Schuster maps and indicate that the MSA method can characterize the distinct time asymmetry of chaotic time series. Then we propose a modified MSA method, i.e., multi-scale weighted time asymmetry, and a novel time asymmetry index to investigate fractal Brownian motion signals and demonstrate its effects on discriminating between fractal signals with different Hurst exponents. Considering that the dynamic behavior of slug flow exhibits chaotic features, we apply the MSA method to analyze experimental signals from a gas-liquid two-phase flow and find that slug flow presents a unique time asymmetric structure. In addition, we further explore the mechanism leading to the formation of time asymmetry in terms of adaptive optimal kernel time-frequency representation. The results suggest that the MSA method can be a useful tool for detecting the complex flow structure underlying a gas-liquid two-phase flow.
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Periodic States in Chaotic R?ssler Oscillators with On-Off Coupling
CHU Shuang-Tian, LIANG Xiao-Ming, LÜ Hua-Ping
Chin. Phys. Lett. 2014, 31 (12):
120503
.
DOI: 10.1088/0256-307X/31/12/120503
It has been revealed that two coupled chaotic R?ssler oscillators can transit to a period-5 splay state in an extremely weak coupling region [Zhan et al., Phys. Rev. Lett. 86 (2001) 1510]. Here we show that with further increase of coupling, two other coupling regions exist that may induce the period-4 splay state and period-5 synchronous state. Using an on-off coupling strategy, we find that the coupling regions for inducing period-5 states can be significantly extended and the extending effect is regulated by the match of two time scales: one is of the on-off coupling and the other is of the individual R?ssler oscillator. We then compare the sensitivity of the periodic states with the initial conditions of the oscillators. We also analyze the mechanism behind these two new types of periodic states.
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Laser 728 nm Spectroscopy of Electrodeless Discharge Rb Lamp
LIU Zhong-Zheng, XUE Xiao-Bo, NIU Fu-Zeng, ZHANG Li-Guo, LING Li, CHEN Jing-Biao
Chin. Phys. Lett. 2014, 31 (12):
120601
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DOI: 10.1088/0256-307X/31/12/120601
We mainly report the 728.0 nm transition between 7S1/2 and 5P1/2 laser spectroscopy of an electrodeless discharge Rb vapor lamp, which is the clock transition of a potential four-level active optical clock, once laser cooled and trapped Rb atoms are pumped by 359.2 nm laser. To realize this proposition, we study the linewidth and absorption characteristics of the 728.0 nm laser absorption spectrum of a rubidium electrodeless discharge vapor lamp with varying lamp temperature and rf driving power respectively, measured by an external cavity diode laser in a Littrow configuration. The measured 728.0 nm spectrum of a glass cell filled with Rb and Ar buffer gases in the electrodeless discharge Rb lamp based Faraday filter stabilized laser can be a heterodyne comparison reference for the weak power output of a possible cold Rb four-level active optical clock at 728.0 nm clock transition with laser cooled and trapped atoms. To the best of our knowledge, there has not been any research reported on Rb 728.0 nm laser spectroscopy in detail.
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Ion Transportation Study for Thick Gas Electron Multipliers
WANG Bin-Long, LIU Qian, LIU Hong-Bang, ZHOU Xiao-Kang, CHEN Shi, GE Dong-Sheng, HUANG Wen-Qian, XIE Yi-Gang, ZHENG Yang-Heng, DONG Yang, ZHANG Qiang, JIAO Xin-Da, WANG Jing, LI Min, CHANG Jie
Chin. Phys. Lett. 2014, 31 (12):
122901
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DOI: 10.1088/0256-307X/31/12/122901
Ion back flow(IBF) is defined as the ions that are generated during multiplication in a thick-gas-electron-multiplier (THGEM) detector flow along the electric field. In order to suppress the IBF effect, we study ion transportation for THGEMs with various high voltages and geometrical parameters. By measuring the currents of all the electrodes of the THGEMs, the effective gain and ion back flow ratio are calculated. The measurement and simulation results reveal that with a staggered triple THGEM configuration, ion back flow can be suppressed to 1% with a proper working high voltage. The gain of the staggered configuration is less than that of the aligned configuration by 5% under the same high voltage condition. The design and the results are presented.
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Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock
WANG Qiang, LIN Yi-Ge, LI Ye, LIN Bai-Ke, MENG Fei, ZANG Er-Jun, LI Tian-Chu, FANG Zhan-Jun
Chin. Phys. Lett. 2014, 31 (12):
123201
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DOI: 10.1088/0256-307X/31/12/123201
We report our observation of the spin polarized 1S0→ 3P0 clock transition spectrum in an optical lattice clock based on fermionic 87Sr. The atoms are trapped and pre-cooled to about 2 μK with two stages of laser cooling at 461 nm and 689 nm, respectively. Then the atoms are loaded into an optical lattice formed by the interference of counter-propagating laser beams at 813 nm. An external cavity diode laser at 698 nm, which is stabilized to a high finesse cavity with a linewidth of about 5 Hz and a drift rate of less than 0.2 Hz/s, is used to excite the atoms to the 3P0 state. The π-polarized clock transition spectrum of resolvable mF states is obtained by applying a small bias magnetic field along the polarization axis of the probe beam. A spin polarized clock transition spectrum as narrow as 10 Hz with an 80 ms probe pulse is obtained.
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Passive Q-Switching Laser Performance of Yb:YVO4 Crystal
LI Xiao-Hong, CHEN Xiao-Wen, HAN Wen-Juan, KONG Wei-Jin, LIU Jun-Hai
Chin. Phys. Lett. 2014, 31 (12):
124202
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DOI: 10.1088/0256-307X/31/12/124202
We report on the passive Q-switching laser performance of Yb:YVO4 crystal. Utilizing a Cr4+:YAG crystal plate as the saturable absorber, which is of an initial transmission as high as 99.3%, we demonstrate a stable passively Q-switched laser operation at 1017.2 nm, producing an average output power of 0.87 W at a pulse repetition rate of 71.4 kHz, with a slope efficiency of 30%. The resulting pulse energy, duration, and peak power are 12.2 μJ, 87 ns, and 0.14 kW, respectively.
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Diffraction Properties for 1000 Line/mm Free-Standing Quantum-Dot-Array Diffraction Grating Fabricated by Focused Ion Beam
ZHANG Ji-Cheng, LIU Yu-Wei, HUANG Cheng-Long, ZHANG Qiang-Qiang, YI Yong, ZENG Yong, ZHU Xiao-Li, FAN Quan-Ping, QIAN Feng, WEI Lai, WANG Hong-Bin, WU Wei-Dong, CAO Lei-Feng
Chin. Phys. Lett. 2014, 31 (12):
124204
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DOI: 10.1088/0256-307X/31/12/124204
The traditional fabrication technique of quantum-dot-array diffraction grating (QDADG) is a hybrid lithography method that includes electron-beam lithography and x-ray lithography. In this work, 1000 line/mm free-standing QDADG has successfully been fabricated by focused ion beams (FIBs) for the first time. The diffraction patterns of the grating are measured in the 250–450 nm wavelength range from the xenon lamp source. In consequence, the QDADG in this experiment can be used to disperse light without high-order diffraction. The present inspiriting result demonstrates the prospect of FIB fabrication for high energy QDADG in the soft x-ray region.
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In-Band Pumped High Power Ho:YAG Ceramic Laser by a Tm:YLF Laser
YUAN Jin-He, YAO Bao-Quan, DUAN Xiao-Ming, SHEN Ying-Jie, CUI Zheng, YU Kuai-Kuai, LI Jiang, PAN Yu-Bai
Chin. Phys. Lett. 2014, 31 (12):
124205
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DOI: 10.1088/0256-307X/31/12/124205
We demonstrate a high power Ho:YAG ceramic laser resonantly pumped by a Tm:YLF laser at 1908 nm. The lasing characteristics of a 1.0 at.% Ho3+-doped YAG ceramic are investigated and compared with different output couplers. By using an output coupler of 50% transmission and 100 mm radius of curvature, a 26.8 W continuous wave is obtained at 2091 nm, corresponding to a slope efficiency of 57.9% and an optical to optical efficiency of 55.8% with respect to the absorbed pump power.
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A Multiple Resonant Mode Film Bulk Acoustic Resonator Based on Silicon-on-Insulator Structures
CHEN Xiao, YANG Yi, CAI Hua-Lin, ZHOU Chang-Jian, Mohammad Ali MOHAMMAD, REN Tian-Ling
Chin. Phys. Lett. 2014, 31 (12):
124302
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DOI: 10.1088/0256-307X/31/12/124302
We report a multiple resonant mode film bulk acoustic resonator (FBAR) with different AlN film thicknesses of 605 nm, 640 nm and 680 nm. With the tilted c?axis orientation of the AlN piezoelectric film providing polarization vertical to the c-axis, acoustic wave resonant peaks have been observed for both the thickness shear modes (TSM 0th, TSM 1st, TSM 2nd) and the thickness extension modes (TEM 0th, TEM 1st). The corresponding parallel resonant frequencies are around 1.60 GHz, 2.41 GHz, 3.45 GHz, 2.75 GHz and 4.10 GHz, respectively. The latter two TEM modes also have good quality factors, and high equivalent electromechanical coupling coefficients K2eff of 647, 3.13% and 113, 6.23%, respectively. By etching the 1.8 μm silicon sacrificial layer, the air gap FBAR devices have been fabricated in an easier and cleaner way resulting in a low insertion loss of -2.2 dB. The overall device structure of the top electrode/AlN film/bottom electrode on SiO2/silicon-on-insulator (SOI) substrate potentially enables CMOS compatibility. These multiple resonant mode FBAR devices will promote the integration of multi-band filters on a single chip. Improvements of the fabrication process, the influence of different AlN film thicknesses and theoretical analyses of the coexistence of multiple resonant modes are presented.
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Electrical Resistivity of Silane Multiply Shock-Compressed to 106 GPa
ZHONG Xiao-Feng, LIU Fu-Sheng, CAI Ling-Cang, XI Feng, ZHANG Ming-Jian, LIU Qi-Jun, WANG Ya-Ping, HAO Bin-Bin
Chin. Phys. Lett. 2014, 31 (12):
126201
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DOI: 10.1088/0256-307X/31/12/126201
The liquid silane sample, prepared by liquifying pure silane gas at 88.5 K, is multiply shock-compressed to 106 GPa by means of a two-stage light-gas gun and a coolant target system. Electrical resistivity is measured for fluid silane during the period of multi-shock compression in the pressure range from 63.5 GPa to 106 GPa. It is shown that the electrical resistivity reduces to the order of 10?3–10?4 ohm?m after the second shock arrived, which is two orders higher than those of typical melt metals. Though the metallization transition could not be confirmed under the loading condition of our shock experiments, its resistivity drops sharply along with the pressure rise. The phenomenon might be caused by silane decomposed during the pressure loading, due to the fact that, above 100 GPa, we find that its resistivity is close to hydrogen under the same pressure.
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Observation of a Flat Band in Silicene
FENG Ya, FENG Bao-Jie, XIE Zhuo-Jin, LI Wen-Bin, LIU Xu, LIU De-Fa, ZHAO Lin, CHEN Lan, ZHOU Xing-Jiang, WU Ke-Hui
Chin. Phys. Lett. 2014, 31 (12):
127303
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DOI: 10.1088/0256-307X/31/12/127303
The electronic structure of silicene on Ag(111) is studied by scanning tunneling microscopy and angle resolved photoemission spectroscopy. A flat band at 0.9 eV below the Fermi level is revealed. We find that the flat band is strongly suppressed near atomic defects, domain boundaries and step edges compared to that on the flat terraces. The discovery of the flat band and its sensitivity to local perturbations provides a new way to manipulate the electronic structure and properties of silicene.
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High-Pressure Single-Crystal Neutron Scattering Study of Magnetic and Fe Vacancy Orders in (Tl,Rb)2Fe4Se5 Superconductor
YE Feng, BAO Wei, CHI Song-Xue, Antonio M. dos Santos, Jamie J. Molaison, FANG Ming-Hu, WANG Hang-Dong, MAO Qian-Hui, WANG Jin-Chen, LIU Juan-Juan, SHENG Jie-Ming
Chin. Phys. Lett. 2014, 31 (12):
127401
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DOI: 10.1088/0256-307X/31/12/127401
The magnetic and iron vacancy orders in superconducting (Tl,Rb)2Fe4Se5 single-crystals are investigated by using a high-pressure neutron diffraction technique. Similar to the temperature effect, the block antiferromagnetic order gradually decreases upon increasing pressure while the Fe vacancy superstructural order remains intact before its precipitous disappearance at the critical pressure Pc=8.3 GPa. Combined with previously determined Pc for superconductivity, our phase diagram under pressure reveals the concurrence of the block AFM order, the √5×√5 iron vacancy order and superconductivity for the 245 superconductor. A synthesis of current experimental data in a coherent physical picture is attempted.
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Electron Trap Energy Distribution in HfO2 by the Discharge-Based Pulse I–V Technique
ZHENG Xue-Feng, FAN Shuang, KANG Di, ZHANG Jian-Kun, CAO Yan-Rong, MA Xiao-Hua, HAO Yue
Chin. Phys. Lett. 2014, 31 (12):
127701
.
DOI: 10.1088/0256-307X/31/12/127701
The electron traps in HfO2 are a major concern of the reliability of metal-oxide-semiconductor field effect transistors (MOSFETs) beyond the 30 nm technology generation. In this work, the principle of the discharge-based pulse I–V technique is demonstrated in detail. By using this technique, the thorough energy distribution of electron traps across the 4 nm HfO2 layer is identified, which overcomes the shortcomings of the current techniques. It is observed that there are two peaks in HfO2. The large peak is at around 1.0 eV below the HfO2 conduction band bottom. The small peak is at about 1.43 eV below the HfO2 conduction band bottom. The results provide valuable information for theoretical modeling establishment, fast material assessment and process optimization for MOSFETs with high-k gate dielectrics.
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Unique Charge Storage Characteristics of FEP/THV/FEP Sandwich Electret Membrane Polarized by Thermally Charging Technology
CHEN Gang-Jin, LEI Ming-Feng, XIAO Hui-Ming, WU Ling
Chin. Phys. Lett. 2014, 31 (12):
127702
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DOI: 10.1088/0256-307X/31/12/127702
Utilizing the synergy of three processes (space charge injection, dipole orientation and interfacial polarization) which determine the electret properties, a sandwich electret membrane FEP/THV/FEP (FEP: fluorinated ethylene propylene, THV: tetrafluoroethylene-hexafluoropropylene-vinylidene) is prepared by the laminating method and the thermal charging technology. The surface potential measurement indicates that the sandwich electret membrane exhibits excellent charge storage stability. When washing the sample surface with alcohol, its surface potential first undergoes decay to zero, and then quickly restores to a high value. The surface potential value is associated with the charging electric field and temperature. The best charging condition is 18.75 MV?m?1 and 130°C. A charge storage profile is proposed, and the experimental results are in good agreement with this profile.
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Ultrafast Imaging of Electronic Relaxation in Ortho-xylene: New Features from Fragmentation-Ion Spectroscopy
LIU Yu-Zhu, KNOPP Gregor, XIAO Shao-Rong, GERBER Thomas
Chin. Phys. Lett. 2014, 31 (12):
127802
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DOI: 10.1088/0256-307X/31/12/127802
As a continuous work of tracking electronic relaxation of the S 2 state in o-xylene by photoelectron imaging [Y. Liu et al., Phys. Chem. Chem. Phys. 15 (2013) 18101], we report another contribution from the view of fragment-ion spectroscopy. Three components with time constants of τ1?60 fs, τ2=55(±20) fs and τ3=6.99(±0.25) ps are observed for the only fragment-ion C 6H 4CH 3+. The velocity map image of the fragment-ion against the delay time are also measured. Transient information about the kinetic energy of the fragment-ion and angular distribution are analyzed and discussed. New features for competing ultrafast internal conversion and intersystem crossing are obtained.
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Growth of High-Quality GaAs on Ge by Controlling the Thickness and Growth Temperature of Buffer Layer
ZHOU Xu-Liang, PAN Jiao-Qing, YU Hong-Yan, LI Shi-Yan, WANG Bao-Jun, BIAN Jing, WANG Wei
Chin. Phys. Lett. 2014, 31 (12):
128101
.
DOI: 10.1088/0256-307X/31/12/128101
High-quality GaAs thin films grown on miscut Ge substrates are crucial for GaAs-based devices on silicon. We investigate the effect of different thicknesses and temperatures of GaAs buffer layers on the crystal quality and surface morphology of GaAs on Ge by metal-organic chemical vapor deposition. Through high resolution x-ray diffraction measurements, it is demonstrated that the full width at half maximum for the GaAs epilayer (Ge substrate) peak could achieve 19.3 (11.0) arcsec. The value of etch pit density could be 4×104 cm?2. At the same time, GaAs surfaces with no pyramid-shaped pits are obtained when the buffer layer growth temperature is lower than 360°C, due to effective inhibition of initial nucleation at terraces of the Ge surface. In addition, it is shown that large island formation at the initial stage of epitaxial growth is a significant factor for the final rough surface and that this initial stage should be carefully controlled when a device quality GaAs surface is desired.
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Growth of Atomically Flat Ultra-Thin Ag Films on Si(111) by Introducing a √3×√3-Ga Buffer Layer
HE Jie-Hui, JIANG Li-Qun, QIU Jing-Lan, CHEN Lan, WU Ke-Hui
Chin. Phys. Lett. 2014, 31 (12):
128102
.
DOI: 10.1088/0256-307X/31/12/128102
It is known that, when Ag is deposited on Si(111)-7×7 substrates in a conventional growth procedure at room temperature, no atomically flat Ag film could be obtained. We use scanning tunneling microscopy and low-energy electron diffraction to investigate the growth of ultra-thin Ag films on the Si(111) substrates at room temperature. Our study reveals that, upon introducing a Si(111)-√3×√3-Ga buffer layer, atomically flat Ag films can easily grow on Si(111) with a critical thickness of two monolayers. Moreover, Ag film growth follows a layer-by-layer mode with further deposition. This novel growth behavior of Ag can be explained in terms of a free electron model (i.e., particle in a box) and kinetic Monte Carlo simulations.
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Effects of Annealing on Schottky Characteristics in AlGaN/GaN HEMT with Transparent Gate Electrode
WANG Chong, ZHANG Kun, HE Yun-Long, ZHENG Xue-Feng, MA Xiao-Hua, ZHANG Jin-Cheng, HAO Yue
Chin. Phys. Lett. 2014, 31 (12):
128501
.
DOI: 10.1088/0256-307X/31/12/128501
AlGaN/GaN high-electron-mobility transistors (HEMTs) with AZO and Ni/AZO transparent gate electrodes are fabricated, respectively. In addition, the Ni/Au-gated HEMTs are also produced for comparison. An excellent transparency is achieved by the AZO-gated electrodes. The effects of annealing on Schottky characteristics are investigated. Furthermore, the effects of annealing on the Schottky barrier height, and the ideality factor values of all the contacts are also evaluated. The lower gate reverse leakage current and good Schottky rectifying characteristics of all the contacts are obtained as well. Moreover, the C–V characteristics of the Ni/AZO gate electrode before and after annealing are measured by the C–V dual sweep. It is obviously observed that the interface traps and defects are significantly reduced.
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41 articles
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