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Volume 33 Issue 08
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Matching Boundary Conditions for a Heterogeneous Atomic Chain
Xing-Ru Chen, Shu-Yu Liu, Shao-Qiang Tang
Chin. Phys. Lett. 2016, 33 (08): 080201 .   DOI: 10.1088/0256-307X/33/8/080201
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We propose accurate boundary treatments for a heterogeneous atomic chain, in terms of matching boundary conditions (MBCs). The main challenge lies in reproducing the physical reflection across the boundary to a correct amount. With reflection coefficients we demonstrate that the accuracy is improved when more atoms are used under the boundary condition. The inclusion of an atom in the embedded sublattice B may considerably enhance the performance. Numerical testing illustrates the effectiveness of the proposed MBCs.
Nonlocality Distillation and Trivial Communication Complexity for High-Dimensional Systems
Yan Li, Xiang-Jun Ye, Jing-Ling Chen
Chin. Phys. Lett. 2016, 33 (08): 080301 .   DOI: 10.1088/0256-307X/33/8/080301
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A nonlocality distillation protocol for arbitrary high-dimensional systems is proposed. We study the nonlocality distillation in the 2-input $d$-output bi-partite case. Firstly, we give the one-parameter nonlocal boxes and their correlated distilling protocol. Then, we generalize the one-parameter nonlocality distillation protocol to the two-parameter case. Furthermore, we introduce a contracting protocol testifying that the 2-input $d$-output nonlocal boxes make communication complexity trivial.
Time-Modulated Hamiltonian for Interpreting Delayed-Choice Experiments via Mach–Zehnder Interferometers
Zhi-Yuan Li
Chin. Phys. Lett. 2016, 33 (08): 080302 .   DOI: 10.1088/0256-307X/33/8/080302
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Many delayed-choice experiments based on Mach–Zehnder interferometers (MZI) have been considered and made to address the fundamental problem of wave-particle duality. Conventional wisdom long holds that by inserting or removing the second beam splitter (BS2) in a controllable way, microscopic particles (photons, electrons, etc.) transporting within the MZI can lie in the quantum superposition of the wave and particle state as $\psi =a_{\rm w} \psi _{\rm wave} +a_{\rm p} \psi _{\rm particle}$. Here we present an alternative interpretation to these delayed-choice experiments. We notice that as the BS2 is purely classical, the inserting and removing operation of the BS2 imposes a time-modulated Hamiltonian $H_{\bmod} (t)=a(t)H_{\rm in} +b(t)H_{\rm out}$, instead of a quantum superposition of $H_{\rm in}$ and $H_{\rm out}$ as $H=a_{\rm w} H_{\rm in} +a_{\rm p} H_{\rm out}$, to act upon the incident wave function. Solution of this quantum scattering problem, rather than the long held quantum eigen-problem yields a synchronically time-modulated output wave function as $\psi _{\bmod} (t)=a(t)\psi _{\rm wave} +b(t)\psi _{\rm particle}$, instead of the stationary quantum superposition state $\psi =a_{\rm w} \psi _{\rm wave} +a_{\rm p} \psi _{\rm particle}$. As a result, the probability of particle output from the MZI behaves as if they are in the superposition of the wave and particle state when many events over time accumulation are counted and averaged. We expect that these elementary but insightful analyses will shed a new light on exploring basic physics beyond the long-held wisdom of wave-particle duality and the principle of complementarity.
A Realistic Model for Observing Spin-Balanced Fulde–Ferrell Superfluid in Honeycomb Lattices
Bei-Bing Huang
Chin. Phys. Lett. 2016, 33 (08): 080303 .   DOI: 10.1088/0256-307X/33/8/080303
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The combination of spin–orbit coupling (SOC) and in-plane Zeeman field breaks time-reversal and inversion symmetries of Fermi gases and becomes a popular way to produce single plane wave Fulde–Ferrell (FF) superfluid. However, atom loss and heating related to SOC have impeded the successful observation of FF state until now. In this work, we propose the realization of spin-balanced FF superfluid in a honeycomb lattice without SOC and the Zeeman field. A key ingredient of our scheme is generating complex hopping terms in original honeycomb lattices by periodical driving. In our model the ground state is always the FF state, thus the experimental observation has no need of fine tuning. The other advantages of our scheme are its simplicity and feasibility, and thus may open a new route for observing FF superfluids.
Abbott–Deser–Tekin Charge of Dilaton Black Holes with Squashed Horizons
Jun-Jin Peng, Wen-Chang Xiang, Shao-Hong Cai
Chin. Phys. Lett. 2016, 33 (08): 080401 .   DOI: 10.1088/0256-307X/33/8/080401
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We consider the conserved charge of static black holes with squashed horizons in the Einstein–Maxwell–dilaton theory via both the Abbott–Deser–Tekin (ADT) method and its off-shell generalization. We first make use of the original ADT method to compute the mass of the dilaton squashed black holes in terms of three different reference spacetimes, which are the asymptotic geometry, the flat background and the spacetime of the Kaluza–Klein monopole with boundary matched to the original metric, respectively. Each mass satisfies the first law of black hole thermodynamics, although the mass computed on the basis of the boundary matching the Kaluza–Klein monopole is different from that of the other two reference spacetimes. Then the mass of the black holes is evaluated through the off-shell generalized ADT method.
The Three-Arm Michelson–Fabry–Pérot Detector for Gravitational Waves
Chao-Guang Huang, Yong-Gui Li, Ning Zhu
Chin. Phys. Lett. 2016, 33 (08): 080402 .   DOI: 10.1088/0256-307X/33/8/080402
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A three-arm Michelson–Fabry–Pérot detector for gravitational waves is designed. It consists of three Michelson–Fabry–Pérot interferometers, one for each pair of arms. The new detector can be used to confirm whether the gravitational waves are in general relativity polarization states and to set the strong constraints on non-GR gravitational wave polarization states. By the new detectors, the angular resolution of sources can be improved significantly. With the new detector, it is easier to search for and confirm a gravitational wave signal in the observation data.
A Maxwell Demon Model Connecting Information and Thermodynamics
Pei-Yan Peng, Chang-Kui Duan
Chin. Phys. Lett. 2016, 33 (08): 080501 .   DOI: 10.1088/0256-307X/33/8/080501
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In the past decades several theoretical Maxwell's demon models have been proposed to exhibit effects such as refrigerating, doing work at the cost of information, and some experiments have been carried out to realize these effects. We propose a model with a two-level demon, information represented by a sequence of bits, and two heat reservoirs. The reservoir that the demon is interacting with depends on the bit. When the temperature difference between the two heat reservoirs is large enough, the information can be erased. On the other hand, when the information is pure enough, heat transfer from one reservoir to the other can happen, resulting in the effect of refrigeration. Genuine examples of such a system are discussed.
Analysis of the Diffractive Deep Inelastic Scattering Data with Running Coupling and Gluon Number Fluctuations
Wen-Chang Xiang, Zhi-Hai Hu, Wan-Song Liu, Jun-Jin Peng, Shao-Hong Cai
Chin. Phys. Lett. 2016, 33 (08): 082501 .   DOI: 10.1088/0256-307X/33/8/082501
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We study the effects of running coupling and gluon number fluctuations in the latest diffractive deep inelastic scattering data. It is found that the description of the data is improved once the running coupling and gluon number fluctuations are included with $\chi^{2}/{\rm d.o.f.}=0.867$, $\chi^{2}/{\rm d.o.f.}=0.923$ and $\chi^{2}/{\rm d.o.f.}=0.878$ for three different groups of experimental data. The values of diffusive coefficient subtracted from the fit are smaller than the ones obtained by considering only the gluon number fluctuations in our previous studies. The smaller values of the diffusive coefficient are in agreement with the theoretical predictions, where the gluon number fluctuations are suppressed by the running coupling which leads to smaller values of the diffusive coefficient.
Theoretical Study of Carrier Mobility in Two-Dimensional Tetragonal Carbon Allotrope from Porous Graphene
Song Gao, Hui Xiang, Bo Xu, Yi-Dong Xia, Jiang Yin, Zhi-Guo Liu
Chin. Phys. Lett. 2016, 33 (08): 083101 .   DOI: 10.1088/0256-307X/33/8/083101
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The carrier mobility of two-dimensional tetragonal carbon allotrope (T-CA) from porous graphene is investigated by first-principles calculations. T-CA can be constructed from divacancy and Stone–Thrower–Wales defects from graphene. T-CA is a direct semiconductor with a band gap of 0.4 eV at ${\it \Gamma}$ point. T-CA possesses a high carrier mobility of the order of 10$^{4}$ cm$^{2}$V$^{-1}$s$^{-1}$. As our study demonstrates, T-CA has potential applications for next-generation electronic materials.
Continuous Dynamic Rotation Measurements Using a Compact Cold Atom Gyroscope
Zhan-Wei Yao, Si-Bin Lu, Run-Bing Li, Kai Wang, Lei Cao, Jin Wang, Ming-Sheng Zhan
Chin. Phys. Lett. 2016, 33 (08): 083701 .   DOI: 10.1088/0256-307X/33/8/083701
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We present an experimental demonstration of the rotation measurement using a compact cold atom gyroscope. Atom interference fringes are observed in the stationary frame and the rotating frame, respectively. The phase shift and contrast of the interference fringe are experimentally investigated. The results show that the contrast of the interference fringe is well held when the platform is rotated, and the phase shift of the interference fringe is linearly proportional to the rotation rate of the platform. The long-term stability, which is evaluated by the overlapped Allan deviation, is $8.5\times10^{-6}$ rad/s over the integrating time of 1000 s.
Convention of Optical Vortices in Two-Helix Long-Period Fiber Gratings
Xiao-Qiang Zhang, Rui-Shan Chen, Yong Zhou, Hai Ming, An-Ting Wang
Chin. Phys. Lett. 2016, 33 (08): 084201 .   DOI: 10.1088/0256-307X/33/8/084201
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An effective method to fabricate two-helix long-period fiber gratings (TH-LFGs) is presented. Based on the coupling mode theory, the conversion of optical vortices (OVs) in TH-LFGs are analyzed in detail. The conversions of OVs with different topological charges: $0\to \pm2$ and $1\to3$ are simulated as three examples and the conversion efficiency higher than 98% can be realized.
Extreme Light Concentration and High Absorption of the Double Cylindrical Microcavities
Hang Heng, Rong Wang
Chin. Phys. Lett. 2016, 33 (08): 084202 .   DOI: 10.1088/0256-307X/33/8/084202
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We numerically study the enhancement factor of energy density and absorption efficiency inside the double cylindrical microcavities based on a triple-band metamaterial absorber. The compact single unit cell consists of concentric gold rings with a gold disk in the center and a metallic ground plane separated by a dielectric layer. We demonstrate that the multilayer structure with subwavelength electromagnetic confinement allows 10$^{4}$–10$^{5}$-fold enhancement of the electromagnetic energy density inside the double cavities and contains the most energy of the incoming light. Particularly, the enhancement factor of energy density $G$ shows strong ability of localizing light and some regularity as the change of the thickness of the dielectric slab and dielectric constant. At the normal incidence of electromagnetic radiation, the obtained reflection spectra show that the resonance frequencies of the double microcavities operate in the range of 10–30 μm. We also calculate the absorption efficiency $C$, which can reach 95%, 97% and 95% at corresponding frequency by optimizing the structure's geometry parameters. Moreover, the proposed structure will be insensitive to the polarization of the incident wave due to the symmetry of the double cylindrical microcavities. The proposed optical metamaterial is a promising candidate as absorbing elements in scientific and technical applications due to its extreme confinement, multiband absorption and polarization insensitivity.
Phase Relation of Harmonics in Nonlinear Focused Ultrasound
Zhe-Fan Peng, Wei-Jun Lin, Shi-Lei Liu, Chang Su, Hai-Lan Zhang, Xiu-Ming Wang
Chin. Phys. Lett. 2016, 33 (08): 084301 .   DOI: 10.1088/0256-307X/33/8/084301
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The phase relation of harmonics in high-intensity focused ultrasound is investigated numerically and experimentally. The nonlinear Westervelt equation is solved to model nonlinear focused sound field by using the finite difference time domain method. Experimental waveforms are measured by a robust needle hydrophone. Then the relative phase quantity is introduced and obtained by using the zero-phase filter. The results show that the $n$th harmonic relative phase quantity is approximately $(n-1)\pi/3$ at geometric center and increases along the axial direction. Moreover, the relative phase quantity decreases with the increase of source amplitude. This phase relation gives an explanation of some nonlinear phenomena such as the discrepancy of positive and negative pressure.
The Relationship of Cavitation to the Negative Acoustic Pressure Amplitude in Ultrasonic Therapy
Ting-Bo Fan, Juan Tu, Lin-Jiao Luo, Xia-Sheng Guo, Pin-Tong Huang, Dong Zhang
Chin. Phys. Lett. 2016, 33 (08): 084302 .   DOI: 10.1088/0256-307X/33/8/084302
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The relationship between the cavitation and acoustic peak negative pressure in the high-intensity focused ultrasound (HIFU) field is analyzed in water and tissue phantom. The peak negative pressure at the focus is determined by a hybrid approach combining the measurement with the simulation. The spheroidal beam equation is utilized to describe the nonlinear acoustic propagation. The waveform at the focus is measured by a fiber optic probe hydrophone in water. The relationship between the source pressure amplitude and the excitation voltage is determined by fitting the measured ratio of the second harmonic to the fundamental component at the focus, based on the model simulation. Then the focal negative pressure is calculated for arbitrary voltage excitation in water and tissue phantom. A portable B-mode ultrasound scanner is applied to monitor HIFU-induced cavitation in real time, and a passive cavitation detection (PCD) system is used to acquire the bubble scattering signals in the HIFU focal volume for the cavitation quantification. The results show that: (1) unstable cavitation starts to appear in degassed water when the peak negative pressure of HIFU signals reaches 13.5 MPa; and (2) the cavitation activity can be detected in tissue phantom by B-mode images and in the PCD system with HIFU peak negative pressures of 9.0 MPa and 7.8 MPa, respectively, which suggests that real-time B-mode images could be used to monitor the cavitation activity in two dimensions, while PCD systems are more sensitive to detect scattering and emission signals from cavitation bubbles.
Monitoring the Heavy Element of Cr in Agricultural Soils Using a Mobile Laser-Induced Breakdown Spectroscopy System with Support Vector Machine
Yan-Hong Gu, Nan-Jing Zhao, Ming-Jun Ma, De-Shuo Meng, Yang Yu, Yao Jia, Li Fang, Jian-Guo Liu, Wen-Qing Liu
Chin. Phys. Lett. 2016, 33 (08): 085201 .   DOI: 10.1088/0256-307X/33/8/085201
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Due to its complicated matrix effects, rapid quantitative analysis of chromium in agricultural soils is difficult without the concentration gradient samples by laser-induced breakdown spectroscopy. To improve the analysis speed and accuracy, two calibration models are built with the support vector machine method: one considering the whole spectra and the other based on the segmental spectra input. Considering the results of the multiple linear regression analysis, three segmental spectra are chosen as the input variables of the support vector regression (SVR) model. Compared with the results of the SVR model with the whole spectra input, the relative standard error of prediction is reduced from 3.18% to 2.61% and the running time is saved due to the decrease in the number of input variables, showing the robustness in rapid soil analysis without the concentration gradient samples.
A Particle-in-Cell Simulation Study on Harmonic Waves Excited by Electron Beams in Unmagnetized Plasmas
Jun Guo
Chin. Phys. Lett. 2016, 33 (08): 085202 .   DOI: 10.1088/0256-307X/33/8/085202
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The excitation of harmonic waves by an electron beam is studied with electrostatic simulations. The results suggest that the harmonic waves are excited during the linear stage of the simulation and are developed in the nonlinear stage. First, the Langmuir waves (LWs) are excited by the beam electrons. Then the coupling of the forward propagating LWs and beam modes will excite the second harmonic waves. The third harmonic waves will be produced if the lower velocity side of the beam still has a positive velocity gradient. The beam velocity decreases at the same time, which provides the energy for wave excitation. We find that it is difficult to excite the harmonic waves with the increase of the thermal velocity of the beam electrons. The beam electrons will be heated after waves are excited, and then the part of the forward propagating LWs will turn into electron acoustic waves under the condition with a large enough intensity of beam electrons. Moreover, the action of ions hardly affects the formation of harmonic waves.
Spectral Broadening of Ion Bernstein Wave Due to Parametric Decay Instabilities
Chun-Yun Gan, Nong Xiang, Zhi Yu
Chin. Phys. Lett. 2016, 33 (08): 085203 .   DOI: 10.1088/0256-307X/33/8/085203
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The parametric decay instabilities (PDIs) of ion Bernstein wave with different input power levels are investigated via particle-in-cell simulation. It is found that the number of decay channels increases with the input power. Resonant mode–mode couplings dominate for a low input power. With increasing the input power, the nonresonant PDIs appear to dissipate the energy of the injected wave and give rise to edge ion heating. The generated child waves couple with each other as well as the injected wave and/or act as a pump wave to excite new decay channels. As a result, the frequency spectrum is broadened with the increase of the input power.
Magnetosonic Shocks in Ultra-Relativistic Dissipative Degenerate Plasmas
S. Hussain, N. Akhtar, N. Mustafa
Chin. Phys. Lett. 2016, 33 (08): 085204 .   DOI: 10.1088/0256-307X/33/8/085204
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Magnetosonic shock structures in dissipative magnetized degenerate electron ion plasma are studied. The two fluid quantum magnetohydrodynamic equations for non-degenerate ions and ultra-relativistic degenerate electron fluids with the Maxwell equations are presented. Using the reductive perturbation technique the Korteweg de Vries Burgers (KdVB) equation is derived and its solution is presented with the $\tanh$ method. Astrophysical plasma parameters are used to study the effects of variation of plasma density, magnetic field intensity and kinematic viscosity on the propagation characteristics of nonlinear shock structures in such plasma systems.
Evolution of a Cold Non-neutral Electron–Positron Plasma Slab
You-Mei Wang, M. Y. Yu, L. Stenflo, A. R. Karimov
Chin. Phys. Lett. 2016, 33 (08): 085205 .   DOI: 10.1088/0256-307X/33/8/085205
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Evolution of a non-neutral cold electron–positron plasma slab is investigated. Initially the slab consists of a quasineutral plasma core bounded on both sides by layers containing only positrons (or electrons). Results from a nonperturbative, or mathematically exact, analysis of the governing fluid conservation equations and the Poisson equation show that despite their equal mass and charge magnitude, the electron and positron fronts can expand separately as well as a single fluid, and that nonlinear surface oscillations can be excited on the expansion fronts.
Radiation Resistance of Fluorine-Implanted PNP Using Gated-Controlled Lateral PNP Transistor Structure
Xin Wang, Wu Lu, Wu-Ying Ma, Qi Guo, Zhi-Kuan Wang, Cheng-Fa He, Mo-Han Liu, Xiao-Long Li, Jin-Cheng Jia
Chin. Phys. Lett. 2016, 33 (08): 086101 .   DOI: 10.1088/0256-307X/33/8/086101
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The radiation damage responses of fluorinated and non-fluorinated lateral PNP transistors are studied with specially designed gated-controlled lateral PNP transistors that allow for the extraction of the oxide trapped charge ($N_{\rm ot}$) and interface trap ($N_{\rm it}$) densities. All the samples are exposed in the Co-60$\gamma $ ray with the dose rate of 0.5 Gy(Si)/s. After the irradiation, the buildup of $N_{\rm ot}$ and $N_{\rm it}$ of the samples with total dose is investigated by the gate sweep test technique. The results show that the radiation resistance of fluorinated lateral PNP transistors is significantly enhanced compared with the non-fluorinated ones.
Pressure-Induced Metallization and Electrical Phase Diagram for Polycrystalline CaB$_{6}$ under High Pressure and Low Temperature
Jie Yang, Yang Jiao, Yong-Hao Han, Jing Li
Chin. Phys. Lett. 2016, 33 (08): 086201 .   DOI: 10.1088/0256-307X/33/8/086201
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The electrical properties of polycrystalline CaB$_{6}$ are revealed by in-situ resistance measurements under high pressure and low temperature. Due to the existence of grain boundaries, polycrystalline CaB$_{6}$ behaves with semiconducting transport properties, which is different from the semimetallic CaB$_{6}$ single crystals. The temperature-dependent resistance measurement results show that before the structural phase transition at 12.3 GPa the high pressure first induces the metallization at 6.5 GPa for CaB$_{6}$. Moreover, the phase diagram for CaB$_{6}$ is drawn based on the investigated electric conducting properties and at least three different conducting phases are found even at moderate high pressure and low temperature, indicating that the electric nature of CaB$_{6}$ is very sensitive to the environment.
Analysis of the Intrinsic Uncertainties in the Laser-Driven Iron Hugoniot Experiment Based on the Measurement of Velocities
Huan Zhang, Xiao-Xi Duan, Chen Zhang, Hao Liu, Hui-Ge Zhang, Quan-Xi Xue, Qing Ye, Zhe-Bin Wang, Gang Jiang
Chin. Phys. Lett. 2016, 33 (08): 086202 .   DOI: 10.1088/0256-307X/33/8/086202
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One of the most challenging tasks in the laser-driven Hugoniot experiment is how to increase the reproducibility and precision of the experimental data to meet the stringent requirement in validating equation of state models. In such cases, the contribution of intrinsic uncertainty becomes important and cannot be ignored. A detailed analysis of the intrinsic uncertainty of the aluminum–iron impedance-match experiment based on the measurement of velocities is presented. The influence of mirror-reflection approximation on the shocked pressure of Fe and intrinsic uncertainties from the equation of state uncertainty of standard material are quantified. Furthermore, the comparison of intrinsic uncertainties of four different experimental approaches is presented. It is shown that, compared with other approaches including the most widely used approach which relies on the measurements of the shock velocities of Al and Fe, the approach which relies on the measurement of the particle velocity of Al and the shock velocity of Fe has the smallest intrinsic uncertainty, which would promote such work to significantly improve the diagnostics precision in such an approach.
Porosity Evaluation and the Power Spectral Densities Analyses of Carbon–Nickel Composite Films Annealed at Different Temperatures
V. Dalouji, S. M. Elahi, A. Ghaderi, S. Solaymani
Chin. Phys. Lett. 2016, 33 (08): 086601 .   DOI: 10.1088/0256-307X/33/8/086601
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The densification and the fractal dimensions of carbon–nickel films annealed at different temperatures 300, 500, 800, and 1000$^{\circ}\!$C with emphasis on porosity evaluation are investigated. For this purpose, the refractive index of films is determined from transmittance spectra. Three different regimes are identified, $T < 500^{\circ}\!$C, 500$^{\circ}\!$C$\, < T < 800^{\circ}\!$C and $T>800^{\circ}\!$C. The Rutherford backscattering spectra show that with increasing the annealing temperature, the concentration of nickel atoms into films decreases. It is shown that the effect of annealing temperatures for increasing films densification at $T < 500^{\circ}\!$C and $T>800^{\circ}\!$C is greater than the effect of nickel concentrations. It is observed that the effect of decreasing nickel atoms into films at 500$^{\circ}\!$C$\, < T < 800^{\circ}\!$C strongly causes improving porosity and decreasing densification. The fractal dimensions of carbon–nickel films annealed from 300 to 500$^{\circ}\!$C are increased, while from 500 to 1000$^{\circ}\!$C these characteristics are decreased. It can be seen that at 800$^{\circ}\!$C, films have maximum values of porosity and roughness.
Comparative Study of Monolayer and Bilayer Epitaxial Graphene Field-Effect Transistors on SiC Substrates
Ze-Zhao He, Ke-Wu Yang, Cui Yu, Qing-Bin Liu, Jing-Jing Wang, Xu-Bo Song, Ting-Ting Han, Zhi-Hong Feng, Shu-Jun Cai
Chin. Phys. Lett. 2016, 33 (08): 086801 .   DOI: 10.1088/0256-307X/33/8/086801
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Monolayer and bilayer graphenes have generated tremendous excitement as the potentially useful electronic materials due to their unique features. We report on monolayer and bilayer epitaxial graphene field-effect transistors (GFETs) fabricated on SiC substrates. Compared with monolayer GFETs, the bilayer GFETs exhibit a significant improvement in dc characteristics, including increasing current density $I_{\rm DS}$, improved transconductance $g_{\rm m}$, reduced sheet resistance $R_{\rm on}$, and current saturation. The improved electrical properties and tunable bandgap in the bilayer graphene lead to the excellent dc performance of the bilayer GFETs. Furthermore, the improved dc characteristics enhance a better rf performance for bilayer graphene devices, demonstrating that the quasi-free-standing bilayer graphene on SiC substrates has a great application potential for the future graphene-based electronics.
Contribution of Surface Defects to the Interface Conductivity of SrTiO$_{3}$/LaAlO$_{3}$
Li Guan, Feng-Xue Tan, Guo-Qi Jia, Guang-Ming Shen, Bao-Ting Liu, Xu Li
Chin. Phys. Lett. 2016, 33 (08): 087301 .   DOI: 10.1088/0256-307X/33/8/087301
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Based on the first-principles method, the structural stability and the contribution of point defects such as O, Sr or Ti vacancies on two-dimensional electron gas of n- and p-type LaAlO$_{3}$/SrTiO$_{3}$ interfaces are investigated. The results show that O vacancies at p-type interfaces have much lower formation energies, and Sr or Ti vacancies at n-type interfaces are more stable than the ones at p-type interfaces under O-rich conditions. The calculated densities of states indicate that O vacancies act as donors and give a significant compensation to hole carriers, resulting in insulating behavior at p-type interfaces. In contrast, Sr or Ti vacancies tend to trap electrons and behave as acceptors. Sr vacancies are the most stable defects at high oxygen partial pressures, and the Sr vacancies rather than Ti vacancies are responsible for the insulator-metal transition of n-type interface. The calculated results can be helpful to understand the tuned electronic properties of LaAlO$_{3}$/SrTiO$_{3}$ heterointerfaces.
Low-Frequency Noise in Gate Tunable Topological Insulator Nanowire Field Emission Transistor near the Dirac Point
Hao Zhang, Zhi-Jun Song, Jun-Ya Feng, Zhong-Qing Ji, Li Lu
Chin. Phys. Lett. 2016, 33 (08): 087302 .   DOI: 10.1088/0256-307X/33/8/087302
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Low-frequency flicker noise is usually associated with material defects or imperfection of fabrication procedure. Up to now, there is only very limited knowledge about flicker noise of the topological insulator, whose topologically protected conducting surface is theoretically immune to back scattering. To suppress the bulk conductivity we synthesize antimony doped Bi$_2$Se$_3$ nanowires and conduct transport measurements at cryogenic temperatures. The low-frequency current noise measurement shows that the noise amplitude at the high-drain current regime can be described by Hooge's empirical relationship, while the noise level is significantly lower than that predicted by Hooge's model near the Dirac point. Furthermore, different frequency responses of noise power spectrum density for specific drain currents at the low drain current regime indicate the complex origin of noise sources of topological insulator.
Energy Levels of Coupled Plasmonic Cavities
Chuan-Pu Liu, Xin-Li Zhu, Jia-Sen Zhang, Jun Xu, Yamin Leprince-Wang, Da-Peng Yu
Chin. Phys. Lett. 2016, 33 (08): 087303 .   DOI: 10.1088/0256-307X/33/8/087303
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We demonstrate the hybridization of the plasmonic modes in directly coupled whispering gallery cavities fabricated on silver films and present the mode patterns and energy levels using cathodoluminescence spectroscopy. Although the energy of the most antisymmetrically coupled modes is higher than that of the corresponding symmetrically coupled ones, the contrary cases happen for small quantum number modes. We attribute the phenomenon to the different surface plasmon polariton paths between the symmetrically and antisymmetrically coupled modes. These results provide an understanding of the resonant properties in coupled plasmonic cavities, which have potential applications in nanophotonic devices.
Theoretical Investigation of Influence of Mechanical Stress on Magnetic Properties of Ferromagnetic/Antiferromagnetic Bilayers Deposited on Flexible Substrates
Yu-Hao Bai, Xia Wang, Lin-Ping Mu, Xiao-Hong Xu
Chin. Phys. Lett. 2016, 33 (08): 087501 .   DOI: 10.1088/0256-307X/33/8/087501
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Effect of mechanical stress on magnetic properties of an exchange-biased ferromagnetic/antiferromagnetic bilayer deposited on a flexible substrate is investigated. The hysteresis loops with different magnitudes and orientations of the stress can be classified into three types. The corresponding physical conditions for each type of the loop are deduced based on the principle of minimal energy. The equation of the critical stress is derived, which can judge whether the loops show hysteresis or not. Numerical calculations suggest that except for the magnitude of the mechanical stress, the relative orientation of the stress is also an important factor to tune the exchange bias effect.
Phase Transformation and Enhancing Electron Field Emission Properties in Microcrystalline Diamond Films Induced by Cu Ion Implantation and Rapid Annealing
Yan-Yan Shen, Yi-Xin Zhang, Ting Qi, Yu Qiao, Yu-Xin Jia, Hong-Jun Hei, Zhi-Yong He, Sheng-Wang Yu
Chin. Phys. Lett. 2016, 33 (08): 088101 .   DOI: 10.1088/0256-307X/33/8/088101
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Cu ion implantation and subsequent rapid annealing at 500$^{\circ}\!$C in N$_{2}$ result in low surface resistivity of 1.611 ohm/sq with high mobility of 290 cm$^{2}$V$^{-1}$S$^{-1}$ for microcrystalline diamond (MCD) films. Its electrical field emission behavior can be turned on at $E_{0}=2.6$ V/μm, attaining a current density of 19.5 $\mu$A/cm$^{2}$ at an applied field of 3.5 V/μm. Field emission scanning electron microscopy combined with Raman and x-ray photoelectron microscopy reveal that the formation of Cu nanoparticles in MCD films can catalytically convert the less conducting disorder/a-C phases into graphitic phases and can provoke the formation of nanographite in the films, forming conduction channels for electron transportation.
Fabrication of GaN-Based Heterostructures with an InAlGaN/AlGaN Composite Barrier
Ru-Dai Quan, Jin-Cheng Zhang, Jun-Shuai Xue, Yi Zhao, Jing Ning, Zhi-Yu Lin, Ya-Chao Zhang, Ze-Yang Ren, Yue Hao
Chin. Phys. Lett. 2016, 33 (08): 088102 .   DOI: 10.1088/0256-307X/33/8/088102
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GaN-based heterostructures with an InAlGaN/AlGaN composite barrier on sapphire (0001) substrates are grown by a low-pressure metal organic chemical vapor deposition system. Compositions of the InAlGaN layer are determined by x-ray photoelectron spectroscopy, structure and crystal quality of the heterostructures are identified by high resolution x-ray diffraction, surface morphology of the samples are examined by an atomic force microscope, and Hall effect and capacitance–voltage measurements are performed at room temperature to evaluate the electrical properties of heterostructures. The Al/In ratio of the InAlGaN layer is 4.43, which indicates that the InAlGaN quaternary layer is nearly lattice-matched to the GaN channel. Capacitance–voltage results show that there is no parasitic channel formed between the InAlGaN layer and the AlGaN layer. Compared with the InAlGaN/GaN heterostructure, the electrical properties of the InAlGaN/AlGaN/GaN heterostructure are improved obviously. Influences of the thickness of the AlGaN layer on the electrical properties of the heterostructures are studied. With the optimal thickness of the AlGaN layer to be 5 nm, the 2DEG mobility, sheet density and the sheet resistance of the sample is 1889.61 cm$^{2}$/V$\cdot$s, $1.44\times10^{13}$ cm$^{-2}$ and as low as 201.1 $\Omega$/sq, respectively.
Nearly Perfect Absorbers Operating Associated with Fano Resonance in the Infrared Range
Wan-Xia Huang, Guo-Ren Zhao, Juan-Juan Guo, Mao-Sheng Wang, Jian-Ping Shi
Chin. Phys. Lett. 2016, 33 (08): 088103 .   DOI: 10.1088/0256-307X/33/8/088103
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We fabricate a three-layer metamaterial of metal patterns/dielectric/metal films. The optical properties associated with Fano resonance of the metamaterials are investigated experimentally and theoretically. The results indicate that the introduction of Fano resonance due to symmetry breaking leads to a much wider absorption range. Furthermore, the amplitude and phase of reflection can be modulated effectively by adjusting various free parameters using the proposed structure.
Design of a Broadband E-Plane Power Combiner Based on Quarter-Arc Bent Rectangular Waveguides for Sub-THz and THz Wave
Xiao-Pin Tang, Zi-Qiang Yang, Zong-Jun Shi, Feng Lan
Chin. Phys. Lett. 2016, 33 (08): 088401 .   DOI: 10.1088/0256-307X/33/8/088401
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A method of designing an E-plane power combiner composed of two quarter-arc bent rectangular waveguides is proposed for sub-THz and THz waves. The quarter-arc bent-waveguide power combiner has a simple geometry which is easy to design and fabricate. By HFSS codes, the physical mechanism and performance of the power combiner are analyzed, and the relationship between the output characteristics and the structure/operating parameters is given. Simulation results show that our power combiner is suitable for the combining of two equal-power and reversed-phase signals, the bandwidth of the combiner is wide and can be adjusted by the radius of the quarter-arc, and the isolation performance of the combiner can be improved by adding thin film resistive septa at the junction of two quarter-arc bent waveguides. Meanwhile, an approximate method based on the analytic geometrical analysis is given to design this power combiner for different frequency bands.
High Efficiency and Stable Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitter
Xiao-Peng Lv, Hui Wang, Ling-Qiang Meng, Xiao-Fang Wei, Yong-Zhen Chen, Xiang-Bin Kong, Jian-Jun Liu, Jian-Xin Tang, Peng-Fei Wang, Ying Wang
Chin. Phys. Lett. 2016, 33 (08): 088501 .   DOI: 10.1088/0256-307X/33/8/088501
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High efficiency, stable organic light-emitting diodes (OLEDs) based on 2-pheyl-4'-carbazole-9-H-Thioxanthen-9-one-10,10-dioxide (TXO-PhCz) with different doping concentration are constructed. The stability of the encapsulated devices are investigated in detail. The devices with the 10 wt% doped TXO-PhCz emitter layer (EML) show the best performance with a current efficiency of 52.1 cd/A, a power efficiency of 32.7 lm/W, and an external quantum efficiency (EQE) of 17.7%. The devices based on the 10 wt%-doped TXO-PhCz EML show the best operational stability with a half-life time (LT50) of 80 h, which is 8 h longer than that of the reference devices based on fac-tris(2-phenylpyridinato)iridium(III) (Ir(ppy)$_{3}$). These indicate excellent stability of TXO-PhCz for redox and oxidation processes under electrical excitation and TXO-PhCz can be potentially used as the emitters for OLEDs with high efficiency and excellent stability. The high-performance device based on TXO-PhCz with high stability can be further improved by the optimization of the encapsulation technology and the development of a new host for TXO-PhCz.
Superconducting Nanowire Single Photon Detector with Optical Cavity
Jie Liu, Li-Qun Zhang, Zhen-Nan Jiang, Kamal Ahmad, Jian-She Liu, Wei Chen
Chin. Phys. Lett. 2016, 33 (08): 088502 .   DOI: 10.1088/0256-307X/33/8/088502
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Increasing the detection efficiency (DE) is a hot issue in the development of the superconducting nanowire single photon detector (SNSPD). In this work, a cavity-integrated structure coupled to the SNSPD is used to enhance the light absorption of nanowire. Ultra-thin Nb films are successfully prepared by magnetron sputtering, which are used to fabricate Nb/Al SNSPD with the curve of 100 nm and the square area of $4\times4$ μm$^2$ by sputtering and the lift-off method. To characterize the optical and electrical performance of the cavity-integrated SNSPD, a reliable cryogenic research system is built up based on a He$^{3}$ system. To satisfy the need of light coupling, a packaging structure with collimator is conducted. Both DE and the dark count rates increase with $I_{\rm b}$. It is also found that the DE of SNSPD with cavities can be up to 0.17% at the temperature of 0.7 K under the infrared light of 1550 nm, which is obviously higher than that of the SNSPD directly fabricated upon silicon without any cavity structure.
Efficiency of Blue Organic Light-emitting Diodes Enhanced by Employing an Exciton Feedback Layer
Qian-Qian Yu, Xu Zhang, Jing-Xuan Bi, Guan-Ting Liu, Qi-Wen Zhang, Xiao-Ming Wu, Yu-Lin Hua, Shou-Gen Yin
Chin. Phys. Lett. 2016, 33 (08): 088503 .   DOI: 10.1088/0256-307X/33/8/088503
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We report that a novel exciton feedback effect is observed by introducing the bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (BAlq) inserted between the emitting layer (EML) and the electron transporting layer in blue organic light emitting diodes. As an exciton feedback layer (EFL), the BAlq does not act as a traditional hole blocking effect. The design of this kind of device structure can greatly reduce excitons' quenching due to accumulated space charge at the exciton formation interface. Meanwhile, the non-radiative energy transfer from EFL to the EML can also be utilized to enhance the excitons' formation, which is confirmed by the test of photolumimescent transient lifetime decay and electroluminescence enhancement of these devices. Accordingly, the optimal device presents the improved performances with the maximum current efficiency of 4.2 cd/A and the luminance of 24600 cd/m$^{2}$, which are about 1.45 times and 1.75 times higher than those of device A (control device) without the EFL, respectively. Simultaneously, the device shows an excellent color stability with a tiny offset of the CIE coordinates ($\Delta x=\pm0.003$, $\Delta y=\pm0.004$) and a relatively lower efficiency roll-off of 26.2% under the driving voltage varying from 3 V to 10 V.
Pairing Mismatched ssDNA to dsDNA Studied with Reflectometric Interference Spectroscopy Sensor
Qing-Qing Wu, Kai-Ge Wang, Dan Sun, Shuang Wang, Chen Zhang, Wei Zhao
Chin. Phys. Lett. 2016, 33 (08): 088701 .   DOI: 10.1088/0256-307X/33/8/088701
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The interaction between two single-stranded DNA (ssDNA) molecules as pairing to a double-stranded DNA (dsDNA) molecule is studied by the reflectometric interference spectroscopy (RIFS) technology. A nano-porous anode alumina membrane coated an Au layer is employed as the sensor substrate. The results indicate that when there are mismatched nucleotide bases, the effective optical thicknesses (${\rm OT}_{\rm eff})$ have obvious difference, and the changes of ${\rm OT}_{\rm eff}$ are connected with the sensor layer thickness and the effective refractive index. It is also demonstrated that the RIFS technique can be used to precisely detect the ssDNA molecules with individual base mismatched as pairing to dsDNA.
A Possible Cause of Magnetic Anomalies on the Southern Martian Hemisphere
Chu-Xin Chen
Chin. Phys. Lett. 2016, 33 (08): 089601 .   DOI: 10.1088/0256-307X/33/8/089601
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From the topology of a synthetic aurora map, we propose a mechanism for the magnetic anomalies on the southern martian hemisphere, i.e., impacts by asteroids when the dynamo is active. The quasi concentric circles of aurora suggest that there are two-to-three convectional cells for each impact. The whole synthetic aurora is induced by three major impacts of asteroids. The east–west lineation features of crust magnetizations are due to the east–west trending locations of three impacts. The alternatively changed sign of crust magnetization originates from the alternatively changed flow direction on the tops of adjacent convectional cells.
37 articles