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Rogue Waves in the Three-Dimensional Kadomtsev–Petviashvili Equation
Chao Qian, Ji-Guang Rao, Yao-Bin Liu, Jing-Song He
Chin. Phys. Lett. 2016, 33 (11):
110201
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DOI: 10.1088/0256-307X/33/11/110201
Breathers and rogue waves as exact solutions of the three-dimensional Kadomtsev–Petviashvili equation are obtained via the bilinear transformation method. The breathers in three dimensions possess different dynamics in different planes, such as growing and decaying periodic line waves in the $(x,y)$, $(x,z)$ and $(y,t)$ planes. Rogue waves are localized in time, and are obtained theoretically as a long wave limit of breathers with indefinitely larger periods. It is shown that the rogue waves possess growing and decaying line profiles in the $(x,y)$ or $(x,z)$ plane, which arise from a constant background and then retreat back to the same background again.
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Molybdenum Disulphide Tape Saturable Absorber for Mode-Locked Double-Clad Ytterbium-Doped All-Fiber Laser Generation
M. F. M. Rusdi, A. A. Latiff, E. Hanafi, M. B. H. Mahyuddin, H. Shamsudin, K. Dimyati, S. W. Harun
Chin. Phys. Lett. 2016, 33 (11):
114201
.
DOI: 10.1088/0256-307X/33/11/114201
We demonstrate the generation of passive mode-locked double-clad ytterbium-doped fiber laser operating in a 1-micron region. We prepare the saturable absorber from commercial crystal of molybdenum disulphide (MoS$_{2}$). Without chemical procedure, the MoS$_{2}$ is mechanically exfoliated by using a clear scotch tape. A few layers of MoS$_{2}$ flakes are obtained on the tape. Then, a piece of $1\times1$ mm tape containing MoS$_{2}$ thin flakes is inserted between two fiber ferrules and is integrated in the ring cavity. Stable mode-locking operation is attained at 1090 nm with a repetition rate of 13.2 MHz. Our mode-locked laser has a maximum output power of 20 mW with 1.48 nJ pulse energy. These results validate that the MoS$_{2}$ has a broad operating wavelength which covers the 1-micron region, and it is also able to work in a high-power cavity.
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Coherent Transfer of Optical Frequency over 112km with Instability at the 10$^{-20}$ Level
Xue Deng, Jie Liu, Dong-Dong Jiao, Jing Gao, Qi Zang, Guan-Jun Xu, Rui-Fang Dong, Tao Liu, Shou-Gang Zhang
Chin. Phys. Lett. 2016, 33 (11):
114202
.
DOI: 10.1088/0256-307X/33/11/114202
We demonstrate optical-carrier transfer over a 112-km single-span urban fiber link. By actively compensating the phase noise induced along the fiber link, a noise suppression of 55 dB at 1 Hz is obtained. A fractional frequency instability of $2.5\times10^{-16}$ at 1 s is achieved, and reaching $7.5\times10^{-20}$ at 10000 s. The system is stable and able to run for a long time. This work will contribute to optical frequency distribution and remote comparison among atomic clocks.
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Silicon Wafer: a Direct Output Coupler in Tm:YLF Laser
Xi-Kui Ren, Chen-Lin Du, Chun-Bo Li, Li Yu, Jun-Qing Zhao, Shuang-Chen Ruan
Chin. Phys. Lett. 2016, 33 (11):
114203
.
DOI: 10.1088/0256-307X/33/11/114203
We present a high power diode-pumped continuous-wave Tm:YLF (Tm$^{3+}$-doped lithium yttrium fluoride) laser with a piece of silicon wafer as the output coupler (Si-OC laser) directly. Under the pump power of 40 W at 793 nm, a maximum output power of 12.1 W is obtained with a beam quality of $M^{2}\le 1.55$ at 1887 nm, corresponding to an optical-to-optical efficiency of 30.25% and a slope efficiency of 33.21%. To the best of our knowledge, this is the first report on directly utilizing silicon as an output coupler (Si-OC) in the solid Tm:YLF laser system. Due to the intriguing characteristics of silicon, such as negligible absorption in the wavelength region around 2 μm, high damage threshold, low cost and long-pass filter properties, double-side polished monocrystalline silicon wafer is considered as an outstanding candidate output coupler in the high-power laser system 2 μm spectral region, which may dramatically reduce the total manufacturing costs of the 2 μm laser system.
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Improving Plasma Confinement by Controlling Hard X-Ray
N. Hasanvand, M. R. Riazifar, R. Alipour, S. Meshkani, M. Ghoranneviss
Chin. Phys. Lett. 2016, 33 (11):
115202
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DOI: 10.1088/0256-307X/33/11/115202
Since runaway electrons and magnetohydrodynamics activity can contribute to serious damage and energy losses in tokamaks, the effect of an external electric field on runaway electrons and hard x-ray spectra is investigated. Parameters such as the plasma current, the hard x-ray photons count and the mean energy of runaway electrons are measured. Positive and negative voltages of 300 V are applied at 10 ms after the plasma initiation (while the plasma is forming), at 15 ms (while the plasma is stable) and at 20 ms (while the plasma is fading away) to attain the most effective time of applying the external electric field. The number of hard x-ray photons has the most changes in the range of 0–200 keV when the external electric fields are applied. Also in the duration of 20–30 ms of plasma the greatest number of hard x-ray spectra is detected. When the external electric fields are applied, the mean energy of runaway electrons reduces significantly, especially at 15 ms (while the plasma is stable).
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Graphene/Rh(111) Structure Studied Using In-Situ Scanning Tunneling Microscopy
Guo-Cai Dong, D. V. Baarle, J. Frenken, Qi-Wen Tang
Chin. Phys. Lett. 2016, 33 (11):
116101
.
DOI: 10.1088/0256-307X/33/11/116101
Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh(111). That is, when graphene is formed on Rh(111), the substrate remains flat and does not develop a supporting nail structure.
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An Experimental Study of Thermophysical Properties for Quinary High-Entropy NiFeCoCrCu/Al Alloys
Wei-Li Wang, Li-Jun Meng, Liu-Hui Li, Liang Hu, Kai Zhou, Zhang-Huan Kong, Bing-Bo Wei
Chin. Phys. Lett. 2016, 33 (11):
116102
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DOI: 10.1088/0256-307X/33/11/116102
Two quinary high-entropy alloys (HEAs) with equiatomic concentrations formed by doping either Cu or Al elements into the quaternary NiFeCoCr alloy are produced by arc melting and spray casting techniques. Their entropy of fusion, thermal expansion coefficient and thermal diffusivity are experimentally investigated with differential scanning calorimetry, dilatometry and laser flash methods. The NiFeCoCrCu HEAs contain a face-centered cubic high-entropy phase plus a minor interdendritic (Cu) phase and display a lower entropy of fusion and the Vickers hardness. The NiFeCoCrAl HEAs consist of two body-centered cubic high-entropy phases with coarse dendritic structures and show higher entropy of fusion and the Vickers hardness. Both the thermal expansion coefficient and the thermal diffusivity of the former Cu-doped alloy are significantly larger than those of the latter Al-doped alloy. Although the temperature dependence of thermal diffusivity is similar for both HEAs, it is peculiar that the thermal expansion curve of the NiFeCoCrAl alloy exhibits an inflexion at temperatures of 860–912 K.
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Imaging Ultrafast Plasmon Dynamics within a Complex Dolmen Nanostructure Using Photoemission Electron Microscopy
Jiang Qin, Peng Lang, Bo-Yu Ji, N. K. Alemayehu, Han-Yan Tao, Xun Gao, Zuo-Qiang Hao, Jing-Quan Lin
Chin. Phys. Lett. 2016, 33 (11):
116801
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DOI: 10.1088/0256-307X/33/11/116801
We report direct nanoscale imaging of ultrafast plasmon in a gold dolmen nanostructure excited with the 7 fs laser pulses by combining the interferometric time-resolved technology with the three-photon photoemission electron microscopy (PEEM). The interferometric time-resolved traces show that the plasmon mode beating pattern appears at the ends of the dimer slabs in the dolmen nanostructure as a result of coherent superposition of multiple localized surface plasmon modes induced by broad bandwidth of the ultrafast laser pulses. The PEEM measurement further discloses that in-phase of the oscillation field of two neighbor defects are surprisingly observed, which is attributed to the plasmon coupling between them. Furthermore, the control of the temporal delay between the pump and probe laser pluses could be utilized for manipulation of the near-field distribution. These findings deepen our understanding of ultrafast plasmon dynamics in a complex nanosystem.
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The Transport Mechanisms of Reverse Leakage Current in Ultraviolet Light-Emitting Diodes
Feng Dai, Xue-Feng Zheng, Pei-Xian Li, Xiao-Hui Hou, Ying-Zhe Wang, Yan-Rong Cao, Xiao-Hua Ma, Yue Hao
Chin. Phys. Lett. 2016, 33 (11):
117301
.
DOI: 10.1088/0256-307X/33/11/117301
The transport mechanisms of the reverse leakage current in the UV light-emitting diodes (380 nm) are investigated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms, the space-limited-charge conduction, the variable-range hopping and the Poole–Frenkel emission, are proposed to explain the transport process of the reverse leakage current above 295 K, respectively. With the in-depth investigation, the former two transport mechanisms are excluded. It is found that the experimental data agree well with the Poole–Frenkel emission model. Furthermore, the activation energies of the traps that cause the reverse leakage current are extracted, which are 0.05 eV, 0.09 eV, and 0.11 eV, respectively. This indicates that at least three types of trap states are located below the bottom of the conduction band in the depletion region of the UV LEDs.
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Effect of Back Diffusion of Mg Dopants on Optoelectronic Properties of InGaN-Based Green Light-Emitting Diodes
Ning Zhang, Xue-Cheng Wei, Kun-Yi Lu, Liang-Sen Feng, Jie Yang, Bin Xue, Zhe Liu, Jin-Min Li, Jun-Xi Wang
Chin. Phys. Lett. 2016, 33 (11):
117302
.
DOI: 10.1088/0256-307X/33/11/117302
The effect of back-diffusion of Mg dopants on optoelectronic characteristics of InGaN-based green light-emitting diodes (LEDs) is investigated. The LEDs with less Mg back-diffusion show blue shifts of longer wavelengths and larger wavelengths with the increasing current, which results from the Mg-dopant-related polarization screening. The LEDs show enhanced efficiency with the decreasing Mg back-diffusion in the lower current region. Light outputs follow the power law $L\propto I^{m}$, with smaller parameter $m$ in the LEDs with less Mg back-diffusion, indicating a lower density of trap states. The trap-assisted tunneling current is also suppressed by reducing Mg-defect-related nonradiative centers in the active region. Furthermore, the forward current–voltage characteristics are improved.
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Comparison of GaN/AlGaN/AlN/GaN HEMTs Grown on Sapphire with Fe-Modulation-Doped and Unintentionally Doped GaN Buffer: Material Growth and Device Fabrication
Jia-Min Gong, Quan Wang, Jun-Da Yan, Feng-Qi Liu, Chun Feng, Xiao-Liang Wang, Zhan-Guo Wang
Chin. Phys. Lett. 2016, 33 (11):
117303
.
DOI: 10.1088/0256-307X/33/11/117303
AlGaN/GaN high electron mobility transistors (HEMTs) grown on Fe-modulation-doped (MD) and unintentionally doped (UID) GaN buffer layers are investigated and compared. Highly resistive GaN buffers (10$^{9}$ $\Omega$$\cdot$cm) are induced by individual mechanisms for the electron traps' formation: the Fe MD buffer (sample A) and the UID buffer with high density of edge-type dislocations ($7.24\times10^{9}$ cm$^{-2}$, sample B). The 300 K Hall test indicates that the mobility of sample A with Fe doping (2503 cm$^{2}$V$^{-1}$s$^{-1}$) is much higher than sample B (1926 cm$^{2}$V$^{-1}$s$^{-1})$ due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed $I$–$V$ measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage ($-$2.63 V) compared with device B ($-$3.71 V). Lower gate leakage current $|I_{\rm GS}|$ of device A ($3.32\times10^{-7}$ A) is present compared with that of device B ($8.29\times10^{-7}$ A). When the off-state quiescent points $Q_{2}$ ($V_{\rm GQ2}=-8$ V, $V_{\rm DQ2}=0$ V) are on, $V_{\rm th}$ hardly shifts for device A while device B shows +0.21 V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed $I$–$V$ and transconductance $G_{\rm m}$–$V_{\rm GS}$ measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.
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Boron-Doped Diamond-Film-Based Two-Dimensional Electrode of Electrophoresis Tank
Jun-Song Liu, Hang Li, Bo-Wen Sun, Zhan-Hui Ding, Qi-Liang Wang, Shao-Heng Cheng, Hong-Dong Li
Chin. Phys. Lett. 2016, 33 (11):
118101
.
DOI: 10.1088/0256-307X/33/11/118101
Chemically robust conductive p-type boron-doped diamond (BDD) films are an important electrode material and have been widely applied in electrochemistry. In this study, BDD films are taken as a two-dimensional (2D) electrode in a electrophoresis tank system instead of the conventional one-dimensional platinum wire electrode. The theoretical simulations by finite element numerical analysis reveal that the 2D BDD electrodes have relatively high intensity and uniformity of electric field in the tank. Experimentally, the 2D BDD electrodes with smaller size show excellent properties for the separation of DNA fragments. The advantages of the 2D BDD electrodes with chemical inertness, sustainability, high intensity and uniformity electronic field, as well as reduced small size of electrophoresis tank would open a possibility for realizing new generation, high-performance biological devices.
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Effects of Fe-Oxide and Mg Layer Insertion on Tunneling Magnetoresistance Properties of CoFeB/MgO/CoFeB Magnetic Tunnel Junctions
Yong-Le Lou, Yu-Ming Zhang, Hui Guo, Da-Qing Xu, Yi-Men Zhang
Chin. Phys. Lett. 2016, 33 (11):
118501
.
DOI: 10.1088/0256-307X/33/11/118501
To study the influence of CoFeB/MgO interface on tunneling magnetoresistance (TMR), different structures of magnetic tunnel junctions (MTJs) are successfully prepared by the magnetron sputtering technique and characterized by atomic force microscopy, a physical property measurement system, x-ray photoelectron spectroscopy, and transmission electron microscopy. The experimental results show that TMR of the CoFeB/Mg/MgO/CoFeB structure is evidently improved in comparison with the CoFeB/MgO/CoFeB structure because the inserted Mg layer prevents Fe-oxide formation at the CoFeB/MgO interface, which occurs in CoFeB/MgO/CoFeB MTJs. The inherent properties of the CoFeB/MgO/CoFeB, CoFeB/Fe-oxide/MgO/CoFeB and CoFeB/Mg/MgO/CoFeB MTJs are simulated by using the theories of density functions and non-equilibrium Green functions. The simulated results demonstrate that TMR of CoFeB/Fe-oxide/MgO/CoFeB MTJs is severely decreased and is only half the value of the CoFeB/Mg/MgO/CoFeB MTJs. Based on the experimental results and theoretical analysis, it is believed that in CoFeB/MgO/CoFeB MTJs, the interface oxidation of the CoFeB layer is the main reason to cause a remarkable reduction of TMR, and the inserted Mg layer may play an important role in protecting Fe atoms from oxidation, and then increasing TMR.
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33 articles
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