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Realization of Closed-Loop Operation of Optical Lattice Clock Based on $^{171}$Yb
Hui Liu, Xi Zhang, Kun-Liang Jiang, Jin-Qi Wang, Qiang Zhu, Zhuan-Xian Xiong, Ling-Xiang He, Bao-Long Lyu
Chin. Phys. Lett. 2017, 34 (2):
020601
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DOI: 10.1088/0256-307X/34/2/020601
We report the realization of closed-loop operation of an optical lattice clock based on $^{171}$Yb atoms. We interrogate the $^{1}\!S_{0}\rightarrow^{3}\!\!P_{0}$ clock transition using single Rabi pulses of 578 nm laser light. The two $\pi$-transitions from $m_{F}=\pm1/2$ ground states are alternatively interrogated, and the clock laser frequency is locked to the center of the two resonances. The in-loop error signal stability of the clock reaches $3\times10^{-17}$ for an average time of 3500 s. We also perform interleaved operations of the clock with two independent servo loops, and the fractional frequency difference averages down to $2\times10^{-16}$ in 7200 s.
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Passively Q-Switched Ho:SSO Laser by Use of a Cr$^{2+}$:ZnSe Saturable Absorber
Xiao-Tao Yang, Long Liu, Wen-Qiang Xie
Chin. Phys. Lett. 2017, 34 (2):
024201
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DOI: 10.1088/0256-307X/34/2/024201
A cw operation and a passively Q-switched (PQS) Ho:SSO laser (Cr$^{2+}$:ZnSe as a saturable absorber) end-pumped by a Tm:YAP laser operating at near room temperature are reported. It is the first time to report a PQS Ho:SSO laser. For the cw mode, a maximum cw output power of 3.0 W is obtained, corresponding to a slope efficiency of 31.4%. For the PQS mode, a Cr$^{2+}$:ZnSe is used as the saturable absorber, with transmission of 88.4% at 2112 nm. A maximum pulse energy of 1.29 mJ is obtained, corresponding to the pulse repetition frequency of 2.42 kHz. In this study, we change the distance between Cr$^{2+}$:ZnSe and the output mirror to research the pulse characteristic of the PQS Ho:SSO laser. The minimum pulse width of 73.5 ns is obtained, corresponding to the pulse energy of 0.9 mJ and the pulse repetition frequency of 2.65 kHz.
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Refractive Plasmonic Sensor Based on Fano Resonances in an Optical System
Wei-Jie Mai, Yi-Lin Wang, Yun-Yun Zhang, Lu-Na Cui, Li Yu
Chin. Phys. Lett. 2017, 34 (2):
024204
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DOI: 10.1088/0256-307X/34/2/024204
A symmetric plasmonic structure consisting of metal–insulator–metal waveguide, groove and slot cavities is studied, which supports double Fano resonances deriving from two different mechanisms. One of the Fano resonances originates from the interference between the resonances of groove and slot cavities, and the other comes from the interference between slot cavities. The spectral line shapes and the peaks of the double Fano resonances can be modulated by changing the length of the slot cavities and the height of the groove. Furthermore, the wavelength of the resonance peak has a linear relationship with the length of the slot cavities. The proposed plasmonic nanosensor possesses a sensitivity of 800 nm/RIU and a figure of merit of 3150, which may have important applications in switches, sensors, and nonlinear devices.
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A CMOS Compatible MEMS Pirani Vacuum Gauge with Monocrystal Silicon Heaters and Heat Sinks
Le-Min Zhang, Bin-Bin Jiao, Shi-Chang Yun, Yan-Mei Kong, Chih-Wei Ku, Da-Peng Chen
Chin. Phys. Lett. 2017, 34 (2):
025101
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DOI: 10.1088/0256-307X/34/2/025101
We present a micro-Pirani vacuum gauge using the low-resistivity monocrystal silicon as the heaters and heat sinks fabricated by the post complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) process. The metal interconnection of the device is fabricated by a 0.5 μm standard CMOS process on 8-inch silicon wafer. Then, a SiO$_{2}$–Si low-temperature fusion bonding is developed to bond the CMOS wafer and the MEMS wafer, with the electrical connection realized by the tungsten through silicon via process. Wafer-level AlGe eutectic bonding is adopted to package the Pirani gauge in a non-hermetic cavity to protect the gauge from being damaged or contaminated in the dicing and assembling process, and to make it suitable for actual applications. To increase the accuracy of the test and restrain negative influence of temperature drift, the Wheatstone bridge structure is introduced. The test results show that before capping, the gauge has an average sensitivity of $1.04\times10^{4}$ K$\cdot$W$^{-1}$Torr$^{-1}$ in dynamic range of 0.01–20 Torr. After capping, the sensitivity of the gauge does not decrease but increases to $1.12\times10^{4}$ K$\cdot$W$^{-1}$Torr$^{-1}$.
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Weak Anti-Localization and Quantum Oscillations in Topological Crystalline Insulator PbTe
Ke-Jie Wang, Wei Wang, Min-Hao Zhang, Xiao-Qian Zhang, Pei Yang, Bo Liu, Ming Gao, Da-Wei Huang, Jun-Ran Zhang, Yu-Jie Liu, Xue-Feng Wang, Feng-Qiu Wang, Liang He, Yong-Bing Xu, Rong Zhang
Chin. Phys. Lett. 2017, 34 (2):
026201
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DOI: 10.1088/0256-307X/34/2/026201
Topological crystalline insulators (TCIs) have attracted worldwide interest since their theoretical predication and have created exciting opportunities for studying topological quantum physics and for exploring spintronic applications. In this work, we successfully synthesize PbTe nanowires via the chemical vapor deposition method and demonstrate the existence of topological surface states by their 2D weak anti-localization effect and Shubnikov–de Haas oscillations. More importantly, the surface state contributes $\sim$61% of the total conduction, suggesting dominant surface transport in PbTe nanowires at low temperatures. Our work provides an experimental groundwork for researching TCIs and is a step forward for the applications of PbTe nanowires in spintronic devices.
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Up-Hill Diffusion of Phase-Separated FeCu Melt by Molecular Dynamics Simulation
Wen-Chao Cui, Chuan-Xiao Peng, Yun Cheng, Kai-Kai Song, Xue-Lian Li, Zhen-Ting Zhang, Sheng-Zhong Yuan, Li Wang
Chin. Phys. Lett. 2017, 34 (2):
026401
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DOI: 10.1088/0256-307X/34/2/026401
Molecular dynamics simulation is performed to characterize the concentration fluctuation of FeCu melts during the liquid–liquid phase separation process, which undergoes the following stages: the formation of interconnected structure and its coarsening, migration and coagulation of droplets driven by the decreasing of potential energy. The up-hill diffusion happens at the early relaxation period in which Cu atoms in Fe-rich region are forced to move toward Cu-rich region by spinodal decomposition with 90% Cu content in Cu-rich region and 95% Fe content in Fe-rich region at temperature of 1500 K. The higher diffusion rate of homogeneous atom can be observed at lower temperature, which is attributed to the larger potential energy difference between Cu-rich region and Fe-rich region. It also exhibits energy heterogeneity in the separated liquid. The domain size decreases sharply during the aggregation and coarsening of droplets, after that it keeps unchanged until the coagulation of droplets begins. The studies characterize concentration and energy heterogeneity of phase-separated liquid on the atomic scale.
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Intrinsic Features of an Ideal Glass
Deyan Sun, Cheng Shang, Zhipan Liu, Xingao Gong
Chin. Phys. Lett. 2017, 34 (2):
026402
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DOI: 10.1088/0256-307X/34/2/026402
In order to understand the long-standing problem of the nature of glass states, we perform intensive simulations on the thermodynamic properties and potential energy surface of an ideal glass. It is found that the atoms of an ideal glass manifest cooperative diffusion, and show clearly different behavior from the liquid state. By determining the potential energy surface, we demonstrate that the glass state has a flat potential landscape, which is the critical intrinsic feature of ideal glasses. When this potential region is accessible through any thermal or kinetic process, the glass state can be formed and a glass transition will occur, regardless of any special structural character. With this picture, the glass transition can be interpreted by the emergence of configurational entropies, as a consequence of flat potential landscapes.
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Influence of the Diamond Layer on the Electrical Characteristics of AlGaN/GaN High-Electron-Mobility Transistors
Xue-Feng Zheng, Ao-Chen Wang, Xiao-Hui Hou, Ying-Zhe Wang, Hao-Yu Wen, Chong Wang, Yang Lu, Wei Mao, Xiao-Hua Ma, Yue Hao
Chin. Phys. Lett. 2017, 34 (2):
027301
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DOI: 10.1088/0256-307X/34/2/027301
The thermal management is an important issue for AlGaN/GaN high-electron-mobility transistors (HEMTs). In this work, the influence of the diamond layer on the electrical characteristics of AlGaN/GaN HEMTs is investigated by simulation. The results show that the lattice temperature can be effectively decreased by utilizing the diamond layer. With increasing the drain bias, the diamond layer plays a more significant role for lattice temperature reduction. It is also observed that the diamond layer can induce a negative shift of threshold voltage and an increase of transconductance. Furthermore, the influence of the diamond layer thickness on the frequency characteristics is investigated as well. By utilizing the 10-μm-thickness diamond layer in this work, the cutoff frequency $f_{\rm T}$ and maximum oscillation frequency $f_{\max}$ can be increased by 29% and 47%, respectively. These results demonstrate that the diamond layer is an effective technique for lattice temperature reduction and the study can provide valuable information for HEMTs in high-power and high-frequency applications.
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Micromagnetic Studies of Finite Temperature $M$–$H$ Loops for FePt-C Media
Long-Ze Wang, Jing-Yue Miao, Zhen Zhao, Chuan Liu, Dan Wei
Chin. Phys. Lett. 2017, 34 (2):
027501
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DOI: 10.1088/0256-307X/34/2/027501
We have recently developed a new micromagnetic method at finite temperature, where the Hybrid Monte Carlo method is employed to realize the Boltzmann distribution with respect to the magnetic free energy. Hence, the hysteresis loops and domain structures at arbitrary temperature below the Curie point $T_{\rm c}$ can be simulated. The Hamilton equations are used to find the magnetization distributions instead of the Landau–Lifshitz (LL) equations. In our previous work, we applied this method on a simple uniaxial anisotropy nano-particle and compared it with the micromagnetic method using LL equations. In this work, we use this new method to simulate an L10 FePt-C granular thin film at finite temperatures. The polycrystalline Voronoi microstructure is included in the model, and the effects of the misorientation of FePt grains are also simulated.
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Improved Polarization Retention of BiFeO$_{3}$ Thin Films Using GdScO$_{3}$ (110) Substrates
Shuai-Qi Xu, Yan Zhang, Hui-Zhen Guo, Wen-Ping Geng, Zi-Long Bai, An-Quan Jiang
Chin. Phys. Lett. 2017, 34 (2):
027701
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DOI: 10.1088/0256-307X/34/2/027701
Epitaxial ferroelectric thin films on single-crystal substrates generally show a preferred domain orientation in one direction over the other in demonstration of a poor polarization retention. This behavior will affect their application in nonvolatile ferroelectric random access memories where bipolar polarization states are used to store the logic 0 and 1 data. Here the retention characteristics of BiFeO$_{3}$ thin films with SrRuO$_{3}$ bottom electrodes on both GdScO$_{3}$ (110) and SrTiO$_{3}$ (100) substrates are studied and compared, and the results of piezoresponse force microscopy provide a long time retention property of the films on two substrates. It is found that bismuth ferrite thin films grown on GdScO$_{3}$ substrates show no preferred domain variants in comparison with the preferred downward polarization orientation toward bottom electrodes on SrTiO$_{3}$ substrates. The retention test from a positive-up domain to a negative-down domain using a signal generator and an oscilloscope coincidentally shows bistable polarization states on the GdScO$_{3}$ substrate over a measuring time of 500 s, unlike the preferred domain orientation on SrTiO$_{3}$, where more than 65% of upward domains disappear after 1 s. In addition, different sizes of domains have been written and read by using the scanning tip of piezoresponse force microscopy, where the polarization can stabilize over one month. This study paves one route to improve the polarization retention property through the optimization of the lattice-mismatched stresses between films and substrates.
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TiO$_{2}$-Loaded WO$_{3}$ Composite Films for Enhancement of Photocurrent Density
Wen-Gui Wang, Li Zhu, Yu-Yan Weng, Wen Dong
Chin. Phys. Lett. 2017, 34 (2):
028201
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DOI: 10.1088/0256-307X/34/2/028201
Titanium dioxide (TiO$_{2}$) loaded tungsten trioxide (WO$_{3}$) composite films are prepared by an E-beam vapor system. Associated with the existence of a heterojunction at the interface of TiO$_{2}$ and WO$_{3}$, the prepared TiO$_{2}$-WO$_{3}$ composite film shows enhanced photocurrent density, four times than the pure WO$_{3}$ film illuminated under xenon lamp, and higher incident-photon-to-current conversion efficiency. By varying the initial TiO$_{2}$ film thickness, such composite structures could be optimized to obtain the highest photocurrent density. We believe that thin TiO$_{2}$ films improve the light response and increase the surface roughness of WO$_{3}$ films. Furthermore, the existence of the heterojunction results in the efficient charge carriers' separation, transfer process, and a lower recombination of electron-hole pairs, which is beneficial for the enhancement of photocurrent density.
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Initiation Mechanism of Kinesin's Neck Linker Docking Process
Yi-Zhao Geng, Hui Zhang, Gang Lyu, Qing Ji
Chin. Phys. Lett. 2017, 34 (2):
028701
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DOI: 10.1088/0256-307X/34/2/028701
The neck linker (NL) docking to the motor domain is the key force generation process of a kinesin motor. In the initiation step of NL docking the first three residues (LYS325, THR326 and ILE327 in 2KIN) of the NL must form an 'extra turn', thus the other parts of the NL could dock to the motor domain. How the extra turn is formed remains elusive. We investigate the extra turn formation mechanism using structure-based mechanical analysis via molecular dynamics simulation. We find that the motor head rotation induced by ATP binding first drives ILE327 to move towards a hydrophobic pocket on the motor domain. The driving force, together with the hydrophobic interaction of ILE327 with the hydrophobic pocket, then causes a clockwise rotation of THR326, breaks the locking of LYS325, and finally drives the extra turn formation. This extra turn formation mechanism provides a clear pathway from ATP binding to NL docking of kinesin.
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Application of AlGaInP with Sb Incorporation in Lattice-Matched 5-Junction Tandem Solar Cells
Yang Zhang, Qing Wang, Xiao-Bin Zhang, Na Peng, Zhen-Qi Liu, Bing-Zhen Chen, Shan-Shan Huang, Zhi-Yong Wang
Chin. Phys. Lett. 2017, 34 (2):
028802
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DOI: 10.1088/0256-307X/34/2/028802
It is well known that conventional GaInP/GaInAs/Ge three-junction (3J) solar cells are difficult to continue to ascend when the efficiencies reach 32% and 42% under AM0 and AM1.5D concentrated, respectively. In AlGaInP/AlGaInAs/GaInAs/GaInNAs/Ge five-junction (5J) solar cells, the performance of the AlGaInP, AlGaInAs and GaInNAs sub cell is the key factor for conversion efficiency of the 5J solar cell. We investigate the AlGaInP/AlGaInAs/Ge 3J solar cell. By incorporating surfactant trimthylantimony into the AlGaInP material, the crystal quality of AlGaInP is improved and the spectrum absorption range of AlGaInAs is extended. The current density of each sub cell exceeds 11.3 mA/cm$^{2}$ as is desired. Then we apply this 3J structure to grow the lattice-matched 5J solar cell and obtain the short circuit current of 134.96 mA, open circuit voltage of 4399.6 mV, fill factor of 81.7% and conversion efficiency of 29.87%.
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33 articles
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