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Chin. Phys. Lett.  
  Chin. Phys. Lett.--2017, 34 (02)   Published: 25 January 2017
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A New Fractional Model for the Falling Body Problem

A. Ebaid, B. Masaedeh, E. El-Zahar
Chin. Phys. Lett. 2017, 34 (02): 020201 doi: 10.1088/0256-307X/34/2/020201
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Recently, a conformable fractional derivative has been proposed to calculate the derivative of non-integer order of time functions. It has been shown that this new fractional derivative definition obeys many advantages over the preceding definitions. For mathematical models in applied sciences and to preserve the dimensionality of the physical quantities, an auxiliary parameter ($\sigma$) which has the dimension of seconds should be implemented in the fractional derivative definition. We obtain analytic solutions for the resulting conformable fractional differential equations describing the vertical velocity and the height of the falling body. It is shown that the dimensions of velocity and height are always correct without any restrictions on the auxiliary parameter $\sigma$ which contradicts with the results in the literature when applying the Caputo definition to the same problem. This may open the door for many future works either to describe the role of such an auxiliary parameter or to derive a more suitable definition for the fractional derivative.

An Improved Experiment to Determine the 'Past of a Particle' in the Nested Mach–Zehnder Interferometer

A. Ben-Israel, L. Knips, J. Dziewior, J. Meinecke, A. Danan, H. Weinfurter, L. Vaidman
Chin. Phys. Lett. 2017, 34 (02): 020301 doi: 10.1088/0256-307X/34/2/020301
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We argue that the modification proposed by Li et al. [Chin. Phys. Lett. 32 (2015) 050303] to the experiment of Danan et al. [Phys. Rev. Lett. 111 (2013) 240402] does not test the past of the photon as characterized by local weak traces. Instead of answering the questions: (i) were the photons in $A$? (ii) were the photons in $B$? and (iii) were the photons in $C$? the proposed experiment measures a degenerate operator answering the questions: (i) were the photons in $A$? and (ii) were the photons in $B$ and $C$ together? A negative answer to the last question does not tell us if photons were present in $B$ or $C$. On the other hand, a simple variation of the proposal by Li et al. does provide conceptually better evidence for the past of the pre- and post-selected photon, but this evidence will be in agreement with the results of Danan et al.

Proof of Security of a Semi-Device-Independent Quantum Key Distribution Protocol

Peng Xu, Wan-Su Bao, Hong-Wei Li, Yang Wang, Hai-Ze Bao
Chin. Phys. Lett. 2017, 34 (02): 020302 doi: 10.1088/0256-307X/34/2/020302
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Semi-device-independent quantum key distribution (SDI-QKD) has been proposed by applying the quantum dimension correlation, and the security relies on the violation of quantum dimension witness inequalities. We prove the security of the SDI-QKD protocol under the depolarization channel by considering the quantum dimension witness inequalities and minimum entropy and the specific process of the QKD protocol, combining with a four-quantum-state preparation and three measurement bases. We also provide the relationship between the dimension witness value, the error rate and the security key rate by the numerical simulation.

Spin-1/2 Fermion Gas in One-Dimensional Harmonic Trap with Attractive Delta Function Interaction

Ya-Hui Wang, Zhong-Qi Ma
Chin. Phys. Lett. 2017, 34 (02): 020501 doi: 10.1088/0256-307X/34/2/020501
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In terms of the Thomas–Fermi method, we solve the ground state energy of the $N$-body 1D harmonically trapped spin-1/2 fermion gas with the attractive $\delta$-function interaction in the limit $N \to \infty$.

Note on Divergence of the Chapman–Enskog Expansion for Solving Boltzmann Equation Hot!

Nan-Xian Chen, Bo-Hua Sun
Chin. Phys. Lett. 2017, 34 (02): 020502 doi: 10.1088/0256-307X/34/2/020502
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Within about a year (1916–1917) Chapman and Enskog independently proposed an important expansion for solving the Boltzmann equation. However, the expansion is divergent or indeterminant in the case of relaxation time $\tau \geq 1$. Since then, this divergence problem has puzzled researchers for a century. Using a modified Möbius series inversion formula, we propose a modified Chapman–Enskog expansion with a variable upper limit of the summation. The new expansion can give not only a convergent summation but also the best-so-far explanation on some unbelievable scenarios occurring in previous practice.

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 (02): 020601 doi: 10.1088/0256-307X/34/2/020601
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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.

Thick Target Neutron Production on Aluminum and Copper by 40MeV Deuterons

Chang-Lin Lan, Jia Wang, Tao Ye, Wei-Li Sun, Meng Peng
Chin. Phys. Lett. 2017, 34 (02): 022401 doi: 10.1088/0256-307X/34/2/022401
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The thick target neutron yields (TTNYs) of deuteron-induced reaction on Al and Cu isotopes are analyzed by combining the improved nuclear models and particle transport effects. The modified Glauber model is employed mainly to produce the peak of double differential cross section for the breakup process, and the exciton model and the Hauser–Feshbach theory are used for the statistical processes. The thin-layer accumulation method is used to calculate the TTNYs considering the neutron attenuation effects in the target. The calculated results are compared with the existing experimental data, and the analysis method can predict the TTNY data well at the deuteron energy of 40 MeV.

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 (02): 024201 doi: 10.1088/0256-307X/34/2/024201
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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.

Static and Dynamic Analysis of Lasing Action from Single and Coupled Photonic Crystal Nanocavity Lasers

Peng-Chao Zhao, Fan Qi, Ai-Yi Qi, Yu-Fei Wang, Wan-Hua Zheng
Chin. Phys. Lett. 2017, 34 (02): 024202 doi: 10.1088/0256-307X/34/2/024202
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The single and coupled photonic crystal nanocavity lasers are fabricated in the InGaAsP material system and their static and dynamic features are compared. The coupled-cavity lasers show a larger lasing efficiency and generate an output power higher than the single-cavity lasers, results that are consistent with the theoretical results obtained by rate equations. In dynamic regime, the single-cavity lasers produce pulses as short as 113 ps, while the coupled-cavity lasers show a significantly longer lasing duration. These results indicate that the photonic crystal laser is a promising candidate for the light source in high-speed photonic integrated circuit.

Supercontinuum Generation in Lithium Niobate Ridge Waveguides Fabricated by Proton Exchange and Ion Beam Enhanced Etching

Bing-Xi Xiang, Lei Wang, Yu-Jie Ma, Li Yu, Huang-Pu Han, Shuang-Chen Ruan
Chin. Phys. Lett. 2017, 34 (02): 024203 doi: 10.1088/0256-307X/34/2/024203
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We report on the fabrication of the 10-mm-long lithium niobate ridge waveguide and its supercontinuum generation at near-visible wavelengths (around 800 nm). The waveguides are fabricated by a combination of MeV copper ion implantation followed by wet etching in a proton exchanged lithium niobate planar waveguide. Using a mode-locked Ti:sapphire laser with a central wavelength of 800 nm, the generated broadest supercontinuum through the ridge waveguides spans 302 nm (at $-$30 dB points), from 693 to 995 nm. Temporal coherence properties of the supercontinuum are experimentally studied by a Michelson interferometer and the coherence length of the broadest supercontinuum is measured to be 5.2 μm. Our results offer potential for a compact and integrated supercontinuum source for applications including bio-imaging, spectroscopy and optical communication.

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 (02): 024204 doi: 10.1088/0256-307X/34/2/024204
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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.

Spectral-Phase-Modulated Cross-Polarized Wave for Chirped Pulse Amplifier with High Contrast Ratio

Shuang Qin, Zhao-Hua Wang, Shuai-Shuai Yang, Zhong-Wei Shen, Quan-Li Dong, Zhi-Yi Wei
Chin. Phys. Lett. 2017, 34 (02): 024205 doi: 10.1088/0256-307X/34/2/024205
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We demonstrate a high-quality cross-polarized-wave filter based on spectral phase modulation. Driven by well-compressed spectral-phase fully-compensated fundamental laser pulses, the filter stretches the pulse bandwidth from 35 nm to 70 nm with a conversion efficiency of 20%. After implementing the filter into a femtosecond TW Ti:sapphire laser system, we generate 40 mJ output pulse energy with pulse duration of 18.9 fs. The temporal contrast of the compressed pulse is enhanced to 10$^{9}$.

Horizontal–Longitudinal Spatial Correlation of Acoustic Field with Deep Receiver in the Direct Zone in Deep Water

Kun-De Yang, Hui Li, Rui Duan
Chin. Phys. Lett. 2017, 34 (02): 024301 doi: 10.1088/0256-307X/34/2/024301
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The horizontal–longitudinal correlation of acoustic field for the receiver near the bottom is analyzed by using numerical modeling. An approximate analytical solution of horizontal–longitudinal correlation coefficient is derived based on the ray method. Combining the characteristic of Lloyd's mirror interference pattern, the variability of acoustic field and its effect on horizontal–longitudinal spatial correlation are discussed. The theoretical prediction agrees well with the numerical results. Experimental results confirm the validity of analytical solution. Finally, the applicability of the analytical solution is summarized. The conclusion is beneficial for the design of bottom-moored array and the estimation of integral time for moving source localization.

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 (02): 025101 doi: 10.1088/0256-307X/34/2/025101
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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$^{-1}$.

Nonlinear Energy Cascading in Turbulence during the Internal Reconnection Event at the Sino-United Spherical Tokamak

Song Chai, Yu-Hong Xu, Zhe Gao, Wen-Hao Wang, Yang-Qing Liu, Yi Tan
Chin. Phys. Lett. 2017, 34 (02): 025201 doi: 10.1088/0256-307X/34/2/025201
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The characteristics of the energy transfer and nonlinear coupling among edge electromagnetic turbulence in thermal quench sub-period of the internal reconnection event (IRE) are studied at the sino-united spherical tokamak device using multiple Langmuir and magnetic probe arrays. The wavelet bispectral analysis and the modified Kim method are applied to investigate linear growth/damping and nonlinear energy transfer rates, along with multi-field turbulence interactions. The results show a multi-field nonlinear energy transfer from electrostatic to magnetic turbulence that results in two-mode coupling in magnetic turbulence, which may play a crucial role to trigger the IRE.

Growth of Single-Crystalline Silicon Nanocone Arrays by Plasma Sputtering Reaction Deposition

Zhi-Cheng Wu, Lei-Lei Guan, Hui Li, Jia-Da Wu, Jian Sun, Ning Xu,
Chin. Phys. Lett. 2017, 34 (02): 025202 doi: 10.1088/0256-307X/34/2/025202
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Vertically aligned single-crystalline silicon nanocone (Si-NC) arrays are grown on nickel-coated silicon (100) substrates by a novel method i.e., abnormal glow-discharge plasma sputtering reaction deposition. The experimental results show that the inlet CH$_{4}$/(N$_{2}$+H$_{2}$) ratio has great effects on the morphology of the grown Si-NC arrays. The characterization of the morphology, crystalline structure and composition of the grown Si-NCs indicates that the Si-NCs are grown epitaxially in the vapor–liquid–solid mode. The analyses of optical emission spectra further reveal that the inlet methane can promote the growth of Si-NCs by raising the plasma temperature and enhancing the ion-sputtering. The understanding of the growth mechanism of the Si-NC arrays will be helpful for fabrication of required Si-NC arrays.

Radiation Damage Analysis of Individual Subcells for GaInP/GaAs/Ge Solar Cells Using Photoluminescence Measurements

Yong Zheng, Tian-Cheng Yi, Jun-Ling Wang, Peng-Fei Xiao, Rong Wang
Chin. Phys. Lett. 2017, 34 (02): 026101 doi: 10.1088/0256-307X/34/2/026101
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The radiation damage of three individual subcells for GaInP/GaAs/Ge triple-junction solar cells irradiated with electrons and protons is investigated using photoluminescence (PL) measurements. The PL spectra of each subcell are obtained using different excitation lasers. The PL intensity has a fast degradation after irradiation, and decreases as the displacement damage dose increases. Furthermore, the normalized PL intensity varying with the displacement damage dose is analyzed in detail, and then the lifetime damage coefficients of the recombination centers for GaInP top-cell, GaAs mid-cell and Ge bottom-cell of the triple-junction solar cells are determined from the PL radiative efficiency.

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 (02): 026201 doi: 10.1088/0256-307X/34/2/026201
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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.

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 (02): 026401 doi: 10.1088/0256-307X/34/2/026401
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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.

Intrinsic Features of an Ideal Glass Hot!

Deyan Sun, Cheng Shang, Zhipan Liu, Xingao Gong
Chin. Phys. Lett. 2017, 34 (02): 026402 doi: 10.1088/0256-307X/34/2/026402
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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.


D-Type Anti-Ferromagnetic Ground State in Ca$_{2}$Mn$_{2}$O$_{5}$

Pan Liu, Wei-Hua Wang, Wei-Chao Wang, Ya-Hui Cheng, Feng Lu, Hui Liu
Chin. Phys. Lett. 2017, 34 (02): 027101 doi: 10.1088/0256-307X/34/2/027101
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We study the electronic and magnetic properties of an oxygen-deficient perovskite Ca$_{2}$Mn$_{2}$O$_{5}$ based on the first principle calculations. The calculations show that the ground state of Ca$_{2}$Mn$_{2}$O$_{5}$ is a D-type anti-ferromagnetic structure with the anti-ferromagnetic spin coupling along the $c$-direction. The corresponding electronic structure of the D-type state is investigated, and the results display that Ca$_{2}$Mn$_{2}$O$_{5}$ is an insulator with an indirect energy gap of $\sim$2.08 eV. By the partial density-of-state analysis, the valence band maximum is mainly contributed to by the O-2$p$ orbitals and the conduction band minimum is contributed to by the O-2$p$ and Mn-3$d$ orbitals. Due to the Coulomb repulsion interaction between electrons, the density of state of Mn-3$d$ is pulled to $-$6–$-$4.5 eV.

Molybdenum Carbide: A Stable Topological Semimetal with Line Nodes and Triply Degenerate Points Hot!

Jian-Peng Sun, Dong Zhang, Kai Chang
Chin. Phys. Lett. 2017, 34 (02): 027102 doi: 10.1088/0256-307X/34/2/027102
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We propose that the hexagonal crystal form of MoC is a stable and new type of topological semimetal. It hosts an exotic Fermi surface consisting of two concentric nodal rings in the presence of spin-orbit coupling, and possesses four pairs of triply degenerate points (TDPs) in the vicinity of the Fermi energy. The coexistence of the nodal ring Fermi surface and TDPs in MoC leads to extraordinary properties such as distinguishable drumhead surface states and manipulatable new fermions, which make MoC a fertile platform for in-depth understanding of topological phenomena and a potential candidate material for topological electronic devices.

Electron Transport Properties of Two-Dimensional Si$_{1}$P$_{1}$ Molecular Junctions

Rui-Fang Gao, Wen-Yong Su, Feng-Wang, Wan-Xiang Feng
Chin. Phys. Lett. 2017, 34 (02): 027201 doi: 10.1088/0256-307X/34/2/027201
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We focus on two new 2D materials, i.e., monolayer and bilayer silicon phosphides (Si$_{1}$P$_{1})$. Based on the elastic-scattering Green's function, the electronic-transport properties of two-dimensional monolayer and bilayer Au-Si$_{1}$P$_{1}$-Au molecular junctions are studied. It is found that their bandgaps are narrow (0.16 eV for a monolayer molecular junction and 0.26 eV for a bilayer molecular junction). Moreover, the calculated current-voltage characteristics indicate that the monolayer molecular junction provides constant output current (20 nA) over a wide voltage range, and the bilayer molecular junction provides higher current (42 nA).

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 (02): 027301 doi: 10.1088/0256-307X/34/2/027301
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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.

Ballistic Transport through a Strained Region on Monolayer Phosphorene

Yi Ren, Fang Cheng
Chin. Phys. Lett. 2017, 34 (02): 027302 doi: 10.1088/0256-307X/34/2/027302
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We investigate quantum transport of carriers through a strained region on monolayer phosphorene theoretically. The electron tunneling is forbidden when the incident angle exceeds a critical value. The critical angles for electrons tunneling through a strain region for different strengths and directions of the strains are different. Owing to the anisotropic effective masses, the conductance shows a strong anisotropic behavior. By tuning the Fermi energy and strain, the channels can be transited from opaque to transparent, which provides us with an efficient way to control the transport of monolayer phosphorene-based microstructures.

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 (02): 027501 doi: 10.1088/0256-307X/34/2/027501
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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.

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 (02): 027701 doi: 10.1088/0256-307X/34/2/027701
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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.

Low-Temperature Solid State Synthesis and Characterization of Superconducting Vanadium Nitride

Liang-Biao Wang, Zheng-Song Lou, Ke-Yan Bao, Wei-Qiao Liu, Quan-Fa Zhou
Chin. Phys. Lett. 2017, 34 (02): 028101 doi: 10.1088/0256-307X/34/2/028101
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Superconducting vanadium nitride (VN) is successfully synthesized by a solid-state reaction of vanadium pentoxide, sodium amide and sulfur in an autoclave at a relatively low temperature (240–400$^{\circ}\!$C). The obtained samples are characterized by x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy. The result of the magnetization of the obtained VN product as a function of temperature indicates that the onset superconducting transition temperature is about 8.4 K. Furthermore, the possible reaction mechanism is also discussed.

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 (02): 028201 doi: 10.1088/0256-307X/34/2/028201
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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.

Initiation Mechanism of Kinesin's Neck Linker Docking Process

Yi-Zhao Geng, Hui Zhang, Gang Lyu, Qing Ji
Chin. Phys. Lett. 2017, 34 (02): 028701 doi: 10.1088/0256-307X/34/2/028701
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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.

The 18.3% Silicon Solar Cells with Nano-Structured Surface and Rear Emitter

Jun-Na Zhang, Lei Wang, Zhun Dai, Xun Tang, You-Bo Liu, De-Ren Yang
Chin. Phys. Lett. 2017, 34 (02): 028801 doi: 10.1088/0256-307X/34/2/028801
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A nano-structured surface is formed on the pyramid structure of n-type silicon solar cells by size-controlled silver nano-particle assisted etching. Such a nano-structure creates a front average weighted reflectance of less than 2.5% in the 300–1200 nm range due to the broadband reflection suppression. The sodium hydroxide is used to obtain the low-area surface by post-etching the nano-structure, thus the severe carrier recombination associated with the nano-structured surface could be reduced. After emitter forming, screen printing and firing by means of the industrial fabrication protocol, an 18.3%-efficient nano-structured silicon solar cell with rear emitter is fabricated. The process of fabricating the solar cells matches well with industrial manufacture and shows promising prospects.

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 (02): 028802 doi: 10.1088/0256-307X/34/2/028802
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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%.

Evolutionary Games in Two-Layer Networks with the Introduction of Dominant Strategy

Chang-Quan Chen, Qiong-Lin Dai, Wen-Chen Han, Jun-Zhong Yang
Chin. Phys. Lett. 2017, 34 (02): 028901 doi: 10.1088/0256-307X/34/2/028901
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We study evolutionary games in two-layer networks by introducing the correlation between two layers through the C-dominance or the D-dominance. We assume that individuals play prisoner's dilemma game (PDG) in one layer and snowdrift game (SDG) in the other. We explore the dependences of the fraction of the strategy cooperation in different layers on the game parameter and initial conditions. The results on two-layer square lattices show that, when cooperation is the dominant strategy, initial conditions strongly influence cooperation in the PDG layer while have no impact in the SDG layer. Moreover, in contrast to the result for PDG in single-layer square lattices, the parameter regime where cooperation could be maintained expands significantly in the PDG layer. We also investigate the effects of mutation and network topology. We find that different mutation rates do not change the cooperation behaviors. Moreover, similar behaviors on cooperation could be found in two-layer random networks.
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