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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2014, 31 (12)   Published: 24 November 2014
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GENERAL

Eigen Spectra of the Dirac Equation for Deformed Woods–Saxon Potential via the Similarity Transformation

ALSADI Khalid S
Chin. Phys. Lett. 2014, 31 (12): 120301 doi: 10.1088/0256-307X/31/12/120301
Full Text: [PDF 477 KB] (17)
Show Abstract
The Dirac equation for the deformed Woods–Saxon potential is converted to a form that is nearly similar to the Schrödinger equation by using the similarity transformation. The resulting equation is a simple one and is ready to be used directly by the asymptotic iteration method to find the solution of the problem under consideration.

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 doi: 10.1088/0256-307X/31/12/120501
Full Text: [PDF 845 KB] (11)
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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.

Harmonic Noise-Induced Resonant Passing in an Inverse Harmonic Potential

HAN Jie, BAO Jing-Dong
Chin. Phys. Lett. 2014, 31 (12): 120502 doi: 10.1088/0256-307X/31/12/120502
Full Text: [PDF 477 KB] (5)
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The problem of a Brownian particle driven by harmonic noise passing over the saddle point in an inverse harmonic potential is studied. The passing probability over the saddle point is obtained analytically. The stationary passing probability is found to arrive at its maximal value when the frequency parameter of the harmonic noise is close to the frequency of the inverse harmonic potential, which results in a resonance phenomenon. With an increase in the frequency parameter of noise, the Brownian particle will recross the barrier, thereby increasing the escape rate and resulting in a decrease in the passing probability.

Periodic States in Chaotic Rössler 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
Full Text: [PDF 874 KB] (7)
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It has been revealed that two coupled chaotic Rössler 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 Rössler 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.

Darboux Transformation with a Double Spectral Parameter for the Myrzakulov-I Equation

CHEN Hai, ZHOU Zi-Xiang
Chin. Phys. Lett. 2014, 31 (12): 120504 doi: 10.1088/0256-307X/31/12/120504
Full Text: [PDF 1113 KB] (3)
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The Darboux transformation with a double spectral parameter for the Myrzakulov-I equation is obtained by taking a suitable limit of the parameters. The globalness of the derived solutions is proved.

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 doi: 10.1088/0256-307X/31/12/120601
Full Text: [PDF 703 KB] (2)
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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.

Cs 728 nm Laser Spectroscopy and Faraday Atomic Filter

LIU Zhong-Zheng, TAO Zhi-Ming, JIANG Zhao-Jie, CHEN Jing-Biao
Chin. Phys. Lett. 2014, 31 (12): 120602 doi: 10.1088/0256-307X/31/12/120602
Full Text: [PDF 613 KB] (2)
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We mainly present the 728 nm laser spectroscopy and Faraday atomic filter of Cs atoms with 650 MHz linewidth and 2.6% transmission based on an electrodeless discharge vapor lamp, compared with Rb 728 nm laser spectroscopy. Accidentally, this remarkably strong Cs 728 nm transition from the 6F7/2 state to the 5D5/2 state is only about 2.5 GHz away from the Rb 728 nm transition of the future potential four-level active optical clock, once laser cooled and trapped from the 7S1/2 state to the 5P1/2 state, as we proposed previously. A Faraday atomic filter stabilized 728 nm laser using a Cs electrodeless discharge vapor lamp with a power of 10 mW will provide a frequency reference to evaluate the performance of the potential Rb four-level active optical clock at 728 nm with power less than 1 nW by 2.5 GHz heterodyne measurements.
NUCLEAR PHYSICS

Fabrication of Nano-Columnar Tungsten Films and Their Deuterium and Helium Ion Irradiation Effects

CAI Ya-Nan, HAN Wen-Jia, CHEN Zhe, YU Jian-Gang, FENG Hong-Li, ZHU Kai-Gui
Chin. Phys. Lett. 2014, 31 (12): 122801 doi: 10.1088/0256-307X/31/12/122801
Full Text: [PDF 1127 KB] (2)
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We fabricate nano-columnar tungsten (W) films on polycrystalline silicon substrates by magnetron sputtering using a grazing angle deposition technique. The deposition process is performed at a base pressure of 5×10−4 Pa. The intersection angle between the direction of the incident beam and the normal direction of the substrate is set as 85°. Separate as well as synergetic irradiations of 30/50 keV deuterium ions and 60 keV helium ions are carried out for the nano-columnar W. Samples of normal structure W are also irradiated under the same conditions as a comparison. Scanning electron microscopy and x-ray diffraction are used to characterize the structure of the as-prepared as well as the irradiated samples. The experimental results show that blisters are difficult to form on the surface of nano-columnar W under the irradiation conditions in this work, which could be due to the particular structure.

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 doi: 10.1088/0256-307X/31/12/122901
Full Text: [PDF 578 KB] (3)
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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.

High-Precision Calibration of Electron Beam Energy from the Hefei Light Source Using Spin Resonant Depolarization

LAN Jie-Qin, XU Hong-Liang
Chin. Phys. Lett. 2014, 31 (12): 122902 doi: 10.1088/0256-307X/31/12/122902
Full Text: [PDF 657 KB] (7)
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The electron beam energy at the Hefei Light Source (HLS) in the National Synchrotron Radiation Laboratory is highly precisely calibrated by using the method of spin resonant depolarization for the first time. The spin tune and the beam energy are determined by sweeping the frequency of a radial rf stripline oscillating magnetic field to artificially excite a spin resonance and depolarize the beam. The resonance signal is recognized by observing the sudden change of the Touschek loss counting rate of the beam. The possible systematic errors of the experiment are presented and the accuracy of the calibrated energy is shown to be about 10−4. A series of measurements show that the energy stability of the machine is of the order of 9×10−3.
ATOMIC AND MOLECULAR PHYSICS

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 doi: 10.1088/0256-307X/31/12/123201
Full Text: [PDF 510 KB] (2)
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We report our observation of the spin polarized 1S03P0 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.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)

Theoretical Investigation on THz Generation from Optical Rectification with Tilted-Pulse-Front Excitation

DU Hai-Wei, YANG Nan
Chin. Phys. Lett. 2014, 31 (12): 124201 doi: 10.1088/0256-307X/31/12/124201
Full Text: [PDF 452 KB] (5)
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The generation of THz pulses from stoichiometric LiNbO3 (sLN) crystal with tilted-pulse-front excitation is studied. In this scheme, THz absorption by sLN is obtained by numerical interpolation based on the measured data. It shows that THz generation can be enhanced by decreasing the temperature of sLN. The refractive indices of the laser from visible to mid-infrared regime are calculated from the Sellmeier dispersion equation. Then the THz generation law pumped by visible and mid-infrared laser pulses is calculated. It is found that the THz amplitude and energy increase in the near-infrared regime and then tread to a constant value when the wavelength of the laser pulses increases.

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 doi: 10.1088/0256-307X/31/12/124202
Full Text: [PDF 553 KB] (3)
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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.

Q-Switching Pulse Generation with Thulium-Doped Fiber Saturable Absorber

Zian Cheak Tiu, Arman Zarei, Sin Jin Tan, Harith Ahmad, Sulaiman Wadi Harun
Chin. Phys. Lett. 2014, 31 (12): 124203 doi: 10.1088/0256-307X/31/12/124203
Full Text: [PDF 510 KB] (3)
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A simple Q-switched erbium-doped fiber laser (EDFL) is proposed and demonstrated by using a 2-m-long thulium-doped fiber (TDF) as a passive saturable absorber (SA). The EDFL generates a Q-switching pulse operating at 1557.6 nm at a threshold pump power as low as 20.0 mW. The Q-switching operation is maintained before disappearance when the pump power is above 33.7 mW. This is due to the fact that the TDF SA could not fully recover in time after a pulse and less gain population is excited before the next pulsing. With the SA, the laser produces a stable pulse train with repetition rate ranging from 3.9 to 12.7 kHz and the pulse width reduces from 20.6 to 7.4 μs while varying the 1480 nm pump power from 20 mW to 33.7 mW. The maximum pulse energy of 22.8 nJ is obtained at a pump power of 20.0 mW. The laser is perspective for technology processes and medicine.

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 doi: 10.1088/0256-307X/31/12/124204
Full Text: [PDF 993 KB] (1)
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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.

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 doi: 10.1088/0256-307X/31/12/124205
Full Text: [PDF 557 KB] (1)
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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.

Low-Frequency Hydroacoustic Experiments on the Shelf Using the Data of Geoacoustic Sediment Model

SAMCHENKO A. N., KOSHELEVA A. V., SHVYREV A. N., PIVOVAROV A. A.
Chin. Phys. Lett. 2014, 31 (12): 124301 doi: 10.1088/0256-307X/31/12/124301
Full Text: [PDF 646 KB] (1)
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We present the results of hydroacoustic experiments carried out in 2010 in the Peter the Great Bay, the Sea of Japan, using low-frequency emitters (26 and 33 Hz). These studies are conducted in the waters where the information on geological conditions in the upper sediment layer have been obtained before and the geoacoustic sediment model has been built. An example of the influence of large inhomogeneities in bottom sediments on the acoustic signal propagation along the route is given.

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 doi: 10.1088/0256-307X/31/12/124302
Full Text: [PDF 681 KB] (2)
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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.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Laser Heated Emissive Probes Design and Development under National Fusion Program and Potential Measurement

MEHTA Payal, SARMA Arun, GHOSH Joydeep
Chin. Phys. Lett. 2014, 31 (12): 125201 doi: 10.1088/0256-307X/31/12/125201
Full Text: [PDF 1041 KB] (1)
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This work addresses the challenges in the design, construction and use of laser heated emissive probes (LHEPs). The choice of a suitable material for the probe plays an important role. We describe the basic theory of a laser heated emissive probe, along with an analysis of the materials suitable for the probe. Furthermore, we present a comparison of the plasma potential measurements carried out with a conventional filament emissive probe and an LHEP.

Observation of Runaway Electrons with Soft X-Ray Camera on HT-7 Tokamak

CHEN Ye-Bin, CHEN Kai-Yun, XU Li-Qing, ZHOU Rui-Jie, HU Li-Qun
Chin. Phys. Lett. 2014, 31 (12): 125202 doi: 10.1088/0256-307X/31/12/125202
Full Text: [PDF 919 KB] (0)
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Runaway electrons produced during minor disruptions, which are confirmed by the hard x-ray system and the runaway energy spectrum system, are observed by a soft x-ray camera on the HT-7 Tokamak. In this observation, the soft x-ray system can also provide the size information and the position information of the runaway electron current directly from the signal information on the chord. This observation implies that the soft x-ray system can provide the control system with the physical information of the runaway electron current on future devices to avoid electrons hitting the first wall.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES

Enhanced Total Ionizing Dose Hardness of Deep Sub-Micron Partially Depleted Silicon-on-Insulator n-Type Metal-Oxide-Semiconductor Field Effect Transistors by Applying Larger Back-Gate Voltage Stress

ZHENG Qi-Wen, CUI Jiang-Wei, YU Xue-Feng, GUO Qi, ZHOU Hang, REN Di-Yuan
Chin. Phys. Lett. 2014, 31 (12): 126101 doi: 10.1088/0256-307X/31/12/126101
Full Text: [PDF 535 KB] (1)
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The larger back-gate voltage stress is applied on 130 nm partially depleted silicon-on-insulator n-type metal-oxide-semiconductor field-effect transistors isolated by shallow trench isolation. The experimental results show that the back-gate sub-threshold hump of the device is eliminated by stress. This observed behavior is caused by the high electric field in the oxide near the bottom corner of the silicon island. The total ionizing dose hardness of devices with pre back-gate stress is enhanced by the interface states induced by stress.

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 doi: 10.1088/0256-307X/31/12/126201
Full Text: [PDF 626 KB] (2)
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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.

The Impact of Shallow-Trench-Isolation Mechanical Stress on the Hysteresis Effect of Partially Depleted Silicon-on-Insulator n-Type Metal-Oxide-Semiconductor Field Effects

LUO Jie-Xin, CHEN Jing, CHAI Zhan, L Kai, HE Wei-Wei, YANG Yan, WANG Xi
Chin. Phys. Lett. 2014, 31 (12): 126601 doi: 10.1088/0256-307X/31/12/126601
Full Text: [PDF 868 KB] (1)
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The impact of shallow trench isolation (STI) mechanical stress on the hysteresis effect in the output characteristics is measured in partially depleted (PD) silicon-on-insulator (SOI) metal-oxide-semiconductor field effect transistors (MOSFETs). We develop ID hysteresis, which is defined as the difference between ID versus VD forward sweep and reverse sweep. The fabricated devices show positive and negative peaks in ID hysteresis. The experimental results show that ID hysteresis declined as the STI mechanical stress increases. We also elaborate on the impact of STI mechanical stress on the ID hysteresis of PD SOI n-type MOSFETs.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

An Alternating-Current Voltage Modulated Thermal Probe Technique for Local Seebeck Coefficient Characterization

XU Kun-Qi, ZENG Hua-Rong, YU Hui-Zhu, ZHAO Kun-Yu, LI Guo-Rong, SONG Jun-Qiang, SHI Xun, CHEN Li-Dong
Chin. Phys. Lett. 2014, 31 (12): 127201 doi: 10.1088/0256-307X/31/12/127201
Full Text: [PDF 556 KB] (1)
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An ac voltage-modulated thermal probe technique based on the atomic force microscope is developed to measure local Seebeck coefficients (S) of thermoelectric bulk and films. The characterization principle is based on the strictly quadratic relationship between the excited local dc Seebeck voltage and the applied ac voltage at high frequency. Excellent agreement is found between local S values and their corresponding macro-S values of thermoelectric bulk and thin films. This thermoelectric probe technique provides a very convenient, promising tool for local thermoelectric parameters with sub-micrometer scale resolution.

Nonlinear Intersubband Transitions in Square and Graded Quantum Wells Modulated by Intense Laser Field

Emine Ozturk, Ismail Sokmen
Chin. Phys. Lett. 2014, 31 (12): 127301 doi: 10.1088/0256-307X/31/12/127301
Full Text: [PDF 488 KB] (1)
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The intersubband optical absorption coefficients and the refractive index change depending on the intense laser field (ILF); both are calculated in a square quantum well (SQW) and a graded quantum well (GQW). Our results show that the position and the magnitude of the linear, nonlinear and total absorption coefficients and refractive index changes depend on the laser field parameter and the quantum well (QW) shape. By increasing the ILF value, we can obtain a red shift or a blue shift in the intersubband optical transitions as dependent on the shape of the QW. For the SQW, the intersubband absorption spectrum shows a blue shift up to the critical laser field value. This spectrum shows a red shift for ILF values larger than this certain value. For the GQW, the intersubband absorption spectrum shows a red shift by increasing the ILF. Thus the absorption coefficients and the refractive index changes, which can be suitable for great performance optical modulators and multiple infrared optical device applications, can be easily obtained by tuning the ILF value and the QW shape.

Electronic Transport of the Adsorbed Trigonal Graphene Flake: A First Principles Calculation

TAN Xun-Qiong
Chin. Phys. Lett. 2014, 31 (12): 127302 doi: 10.1088/0256-307X/31/12/127302
Full Text: [PDF 574 KB] (2)
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Based on the non-equilibrium Green's function method combined with the density functional theory, we investigate the transport properties of a zigzag trigonal graphene flake (zTGF) adsorbed by a single atom (F or H) or a single group (OH or CH3) at the central site and connected to two symmetric Au electrodes by Au–S bonds. The results show that the OH adsorption can enhance the conductance, followed by the negative differential resistance effects, while the conductance for the zTGF adsorbed by H and CH3 is lowered obviously, and rectifying characteristics can be observed for the H-adsorbed system. The adsorbing action alters the molecular level position and the spatial distribution of the molecular orbital, leading to different transport properties.

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 doi: 10.1088/0256-307X/31/12/127303
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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.

Current Fluctuations in a Semiconductor Quantum Dot with Large Energy Spacing

JEONG Heejun
Chin. Phys. Lett. 2014, 31 (12): 127304 doi: 10.1088/0256-307X/31/12/127304
Full Text: [PDF 454 KB] (2)
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We report on the measurements of the current noise properties of electron tunneling through a split-gate GaAs quantum dot with large energy level spacing and a small number of electrons. Shot noise is full Poissonian or suppressed in the Coulomb-blockaded regime, while it is enhanced to show as super-Poissonian when an excited energy level is involved by finite source-drain bias. The results can be explained by multiple Poissonian processes through multilevel sequential tunneling.

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 doi: 10.1088/0256-307X/31/12/127401
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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.

Effect of Crystalline Quality on Magnetic Properties of Mn-Doped ZnO Nanowires

CHANG Yong-Qin, SUN Qing-Ling, LONG Yi, WANG Ming-Wen
Chin. Phys. Lett. 2014, 31 (12): 127501 doi: 10.1088/0256-307X/31/12/127501
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Mn-doped ZnO nanowires are synthesized by a vapor phase deposition method in air and in a vacuum, respectively. X-ray diffraction results show that all the diffraction peaks correspond to the hexagonal wurtzite structure. X-ray absorption fine structure spectra suggest that a single Mn2+-containing phase exists and Mn2+ions occupy Zn2+ ions in the ZnO lattice. Photoluminescence spectra show that many defects exist in the doped nanowires as the samples grown in air, and the crystalline quality decreases with the increase of Mn. These samples exhibit obvious room-temperature ferromagnetic characteristics, and the magnetization increases with the increase of Mn. The sample with higher crystal quality grown in a vacuum exhibits the paramagnetic behavior at room temperature. As the as-grown samples are annealed, the crystalline quality improves, while the magnetization of the samples grown under the air condition translates from room-temperature ferromagnetism to the paramagnetism behavior. The above results indicate that the magnetic property of the Mn-doped ZnO nanowires can be controlled by the crystalline quality.

Electron Trap Energy Distribution in HfO2 by the Discharge-Based Pulse IV 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
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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 IV 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.

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 doi: 10.1088/0256-307X/31/12/127702
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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.

Detecting Cells with the Scatter Plot Pattern of an Orthogonal Scattering Mueller Matrix

WANG Qing-Hua, LI Zhen-Hua, LAI Jian-Cheng, HE An-Zhi
Chin. Phys. Lett. 2014, 31 (12): 127801 doi: 10.1088/0256-307X/31/12/127801
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We investigate the characteristics of the elements of an orthogonal scattering Mueller matrix for spherical cells. Two parameter scatter plots with x- and y-coordinates determined by s11+s12 and s11−s12 values are drawn. The unexpected patterns of these two parameter scatter plots are more sensitive to the relative refractive index of cells. When a series of scatter plots in a database for cells' light scattering are prepared in advance, an image correlation technique can be used to judge the patterns of scatter plots, which shows a promising approach to reveal the tiny change of cells in a flow cytometry.

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 doi: 10.1088/0256-307X/31/12/127802
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As a continuous work of tracking electronic relaxation of the S2 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 C6H4CH3+. 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.

Current Density-Dependent Thermal Stability of ZnSe Nanowire in M-S-M Nanostructure

TAN Yu, WANG Yan-Guo
Chin. Phys. Lett. 2014, 31 (12): 127901 doi: 10.1088/0256-307X/31/12/127901
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To enhance the thermal stability of metal-semiconductor nanowire(NW)-metal (M-S-M) nanostructure under high electrical and thermal stress conditions, current-induced failure of ZnSe NWs in the M-S-M nanostructure is studied by in situ transmission electron microscopy. When the single NW is replaced by a bundle of NWs, the large current density flowing through the single NW protruding out of the bundle of NWs is responsible for the electrical breakdown of NWs. In this case, the failure mechanism of the NW changes from the bias polarity-dependent mode to the current density-dependent mode. Consequently, a decrease of current density at the reversely biased metal-semiconductor (M-S) nanocontacts can significantly improve the thermal stability of ZnSe NWs in the M-S-M nanostructure and can enhance the performance of the semiconductor NW-based nanoelectronics.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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
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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.

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
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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.

Synthesis and Optical Properties of InP Semiconductor Nanocombs

YU Yan-Long, ZHAO Yi-Song, GAO Fa-Ming
Chin. Phys. Lett. 2014, 31 (12): 128103 doi: 10.1088/0256-307X/31/12/128103
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InP semiconductor nanocombs are successfully synthesized by the chemical vapor deposition method. The detailed morphology and crystalline structures of the products are characterized by x-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy. The optical properties of InP nanocombs, including Raman and photoluminescence spectra, are studied. The possible growth mechanism of InP nanocombs is briefly discussed.

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
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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 CV characteristics of the Ni/AZO gate electrode before and after annealing are measured by the CV dual sweep. It is obviously observed that the interface traps and defects are significantly reduced.

A Quasi-3D Threshold Voltage Model for Dual-Metal Quadruple-Gate MOSFETs

Visweswara Rao Samoju, Satyabrata Jit, Pramod Kumar Tiwari
Chin. Phys. Lett. 2014, 31 (12): 128502 doi: 10.1088/0256-307X/31/12/128502
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A threshold voltage model for dual-metal quadruple-gate (DMQG) metal-oxide-semiconductor field effect transistors (MOSFETs) is presented by using the virtual-cathode potential formulated from the quasi-3D scaling equation adopting the equivalent number of gates concept. The threshold voltage of the DMQG MOSFET is formulated analytically for different length ratios of control and screen gates at different channel lengths. Moreover, the drain induced barrier lowering of the DMQG MOSFET is also analyzed and compared with the same quadruple-gate MOSFET. The analytical model results are compared with the 3D ATLAS simulation data to validate the derived model.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

Energy Extraction from a Black Hole and Its Influence on X-Ray Spectra

HUANG Chang-Yin, GONG Xiao-Long, WANG Ding-Xiong
Chin. Phys. Lett. 2014, 31 (12): 129701 doi: 10.1088/0256-307X/31/12/129701
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Taking into account the energy and angular momentum transferred from a rotating black hole (BH) to the inner accretion disk by the magnetic connection (MC) process, we simulate the x-ray spectra from the disk-corona system with two different magnetic configurations using the Monte Carlo method. The results show that the MC process reduces the ratio of the power dissipated in the corona to the total and softens the spectrum. The influence of the MC process is stronger with a higher BH spin, a larger accretion rate, and a larger and more centralized magnetic flux threading the disk. The comparison of the model spectra with the observational data suggests that large-scale magnetic fields accumulating in the inner disk could be a candidate explanation for the hard-to-soft state evolutions in BH binaries.
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