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Chin. Phys. B  
  Chin. Phys. B--2016, Vol.25, No.8
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GENERAL

Testing the validity of the Ehrenfest theorem beyond simple static systems: Caldirola-Kanai oscillator driven by a time-dependent force

Salim Medjber, Hacene Bekkar, Salah Menouar, Jeong Ryeol Choi
Chin. Phys. B 2016, 25 (8): 080301;  doi: 10.1088/1674-1056/25/8/080301
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The relationship between quantum mechanics and classical mechanics is investigated by taking a Gaussian-type wave packet as a solution of the Schrödinger equation for the Caldirola-Kanai oscillator driven by a sinusoidal force. For this time-dependent system, quantum properties are studied by using the invariant theory of Lewis and Riesenfeld. In particular, we analyze time behaviors of quantum expectation values of position and momentum variables and compare them to those of the counterpart classical ones. Based on this, we check whether the Ehrenfest theorem which was originally developed in static quantum systems can be extended to such time-varying systems without problems.

Non-relativistic scattering amplitude for a new multi-parameter exponential-type potential

Yazarloo B H, Mehraban H, Hassanabadi H
Chin. Phys. B 2016, 25 (8): 080302;  doi: 10.1088/1674-1056/25/8/080302
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In this paper, we study the scattering properties of s-wave Schrödinger equation for the multi-parameter potential, which can be reduced into four special cases for different values of potential parameters, i.e., Hulthén, Manning-Rosen, and Eckart potentials. We also obtain and investigate the scattering amplitudes of these special cases. Some numerical results are also obtained and reported.

New useful special function in quantum optics theory

Feng Chen, Hong-Yi Fan
Chin. Phys. B 2016, 25 (8): 080303;  doi: 10.1088/1674-1056/25/8/080303
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By virtue of the operator Hermite polynomial method[Fan H Y and Zhan D H 2014Chin. Phys. B 23 060301] we find a new special function which is useful in quantum optics theory, whose expansion involving both power-series and Hermite polynomials, i.e.,
(n!m!(-1)l/l!(n-l)!(m-l)!)Hn-l(x)ym-l≡ϑn, m(x, y).
By virtue of the operator Hermite polynomial method and the technique of integration within ordered product of operators (IWOP) we derive its generating function. The circumstance in which this new special function appears and is applicable is considered.

Quantum speed limits of a qubit system interacting with a nonequilibrium environment

Zhi He, Chun-Mei Yao, Li Li, Qiong Wang
Chin. Phys. B 2016, 25 (8): 080304;  doi: 10.1088/1674-1056/25/8/080304
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The speed of evolution of a qubit undergoing a nonequilibrium environment with spectral density of general ohmic form is investigated. First we reveal non-Markovianity of the model, and find that the non-Markovianity quantified by information backflow of Breuer et al. [Phys. Rev. Lett. 103 210401 (2009)] displays a nonmonotonic behavior for different values of the ohmicity parameter s in fixed other parameters and the maximal non-Markovianity can be achieved at a specified value s. We also find that the non-Markovianity displays a nonmonotonic behavior with the change of a phase control parameter. Then we further discuss the relationship between quantum speed limit (QSL) time and non-Markovianity of the open-qubit system for any initial states including pure and mixed states. By investigation, we find that the QSL time of a qubit with any initial states can be expressed by a simple factorization law: the QSL time of a qubit with any qubit-initial states are equal to the product of the coherence of the initial state and the QSL time of maximally coherent states, where the QSL time of the maximally coherent states are jointly determined by the non-Markovianity, decoherence factor and a given driving time. Moreover, we also find that the speed of quantum evolution can be obviously accelerated in the wide range of the ohmicity parameter, i.e., from sub-Ohmic to Ohmic and super-Ohmic cases, which is different from the thermal equilibrium environment case.

Scheme for preparation of multi-partite entanglement of atomic ensembles

Peng Xue, Zhi-Hao Bian
Chin. Phys. B 2016, 25 (8): 080305;  doi: 10.1088/1674-1056/25/8/080305
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We show a scheme of preparing multipartite W type of maximally entangled states among many atomic ensembles with the generation time increasing with the party number only polynomially. The scheme is based on laser manipulation of atomic ensembles and single-photon detection, and fits well the status of the current experimental technology. We also show one of the applications of this kind of W state, demonstrating Bell theorem without inequalities.

Quantum dual signature scheme based on coherent states with entanglement swapping

Jia-Li Liu, Rong-Hua Shi, Jin-Jing Shi, Ge-Li Lv, Ying Guo
Chin. Phys. B 2016, 25 (8): 080306;  doi: 10.1088/1674-1056/25/8/080306
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A novel quantum dual signature scheme, which combines two signed messages expected to be sent to two diverse receivers Bob and Charlie, is designed by applying entanglement swapping with coherent states. The signatory Alice signs two different messages with unitary operations (corresponding to the secret keys) and applies entanglement swapping to generate a quantum dual signature. The dual signature is firstly sent to the verifier Bob who extracts and verifies the signature of one message and transmits the rest of the dual signature to the verifier Charlie who verifies the signature of the other message. The transmission of the dual signature is realized with quantum teleportation of coherent states. The analysis shows that the security of secret keys and the security criteria of the signature protocol can be greatly guaranteed. An extensional multi-party quantum dual signature scheme which considers the case with more than three participants is also proposed in this paper and this scheme can remain secure. The proposed schemes are completely suited for the quantum communication network including multiple participants and can be applied to the e-commerce system which requires a secure payment among the customer, business and bank.

Transferring information through a mixed-five-spin chain channel

Hamid Arian Zad, Hossein Movahhedian
Chin. Phys. B 2016, 25 (8): 080307;  doi: 10.1088/1674-1056/25/8/080307
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We initially introduce one-dimensional mixed-five-spin chain with Ising-XY model which includes mixture of spins-1/2 and spins-1. Here, it is considered that nearest spins (1, 1/2) have Ising-type interaction and nearest spins (1/2, 1/2) have both XY-type and Dzyaloshinskii-Moriya (DM) interactions together. Nearest spins (1, 1) have XX Heisenberg interaction. This system is in the vicinity of an external homogeneous magnetic field B in thermal equilibrium state. We promote the quantum information transmitting protocol verified for a normal spin chain with simple model (refer to Rossini D, Giovannetti V and Fazio R 2007 Int. J. Quantum Infor. 5 439) (widely in reference: Giovannetti V and Fazio R 2005 Phys. Rev. A 71 032314) by means of considering the suggested mixed-five-spin chain as a quantum communication channel for transmitting both qubits and qutrits ideally. Hence, we investigate some useful quantities such as quantum capacity and quantum information transmission rate for the system. Finally, we conclude that, when the DM interaction between spins (1/2, 1/2) increases the system is a more ideal channel for transmitting information.

Cryptanalysis and improvement of quantum broadcast communication and authentication protocol with a quantum one-time pad

Zhi-Hao Liu, Han-Wu Chen
Chin. Phys. B 2016, 25 (8): 080308;  doi: 10.1088/1674-1056/25/8/080308
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The security of quantum broadcast communication (QBC) and authentication protocol based on Greenberger-Horne-Zeilinger (GHZ) state and quantum one-time pad is analyzed. It is shown that there are some security issues in this protocol. Firstly, an external eavesdropper can take the intercept-measure-resend attack strategy to eavesdrop on 0.369 bit of every bit of the identity string of each receiver without being detected. Meanwhile, 0.524 bit of every bit of the secret message can be eavesdropped on without being detected. Secondly, an inner receiver can take the intercept-measure-resend attack strategy to eavesdrop on half of the identity string of the other's definitely without being checked. In addition, an alternative attack called the CNOT-operation attack is discussed. As for the multi-party QBC protocol, the attack efficiency increases with the increase of the number of users. Finally, the QBC protocol is improved to a secure one.

Quantum hacking of two-way continuous-variable quantum key distribution using Trojan-horse attack

Hong-Xin Ma, Wan-Su Bao, Hong-Wei Li, Chun Chou
Chin. Phys. B 2016, 25 (8): 080309;  doi: 10.1088/1674-1056/25/8/080309
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We present a Trojan-horse attack on the practical two-way continuous-variable quantum key distribution system. Our attack mainly focuses on the imperfection of the practical system that the modulator has a redundancy of modulation pulse-width, which leaves a loophole for the eavesdropper inserting a Trojan-horse pulse. Utilizing the unique characteristics of two-way continuous-variable quantum key distribution that Alice only takes modulation operation on the received mode without any measurement, this attack allows the eavesdropper to render all of the final keys shared between the legitimate parties insecure without being detected. After analyzing the feasibility of the attack, the corresponding countermeasures are put forward.

Decoherence suppression for three-qubit W-like state using weak measurement and iteration method

Guang Yang, Bao-Wang Lian, Min Nie
Chin. Phys. B 2016, 25 (8): 080310;  doi: 10.1088/1674-1056/25/8/080310
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Multi-qubit entanglement states are the key resources for various multipartite quantum communication tasks. For a class of generalized three-qubit quantum entanglement, W-like state, we demonstrate that the weak measurement and the reversal measurement are capable of suppressing the amplitude damping decoherence by reducing the initial damping factor into a smaller equivalent damping factor. Furthermore, we propose an iteration method in the weak measurement and the reversal measurement to enhance the success probability of the total measurements. Finally, we discuss how the number of the iterations influences the overall effect of decoherence suppression, and find that the “half iteration” method is a better option that has more practical value.

Demonstration of a cold atom beam splitter on atom chip

Xiaojun Jiang, Xiaolin Li, Haichao Zhang, Yuzhu Wang
Chin. Phys. B 2016, 25 (8): 080311;  doi: 10.1088/1674-1056/25/8/080311
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We report an experimental demonstration of a new scheme to split cold atoms on an atom chip. The atom chip consists of a U-wire and a Z-wire. The cold atom cloud is initially loaded and prepared in the Z-trap, which is split into two separate parts by switching on the current of the U-wire. The two separate atom clouds have a distance more than one millimeter apart from each other and show almost symmetrical profiles, corresponding to about a 50/50 splitting ratio.

Influence of the colored noise on determining the period of a torsion pendulum

Jie Luo, Wen-Ze Zhan, Wei-Huang Wu, Cheng-Gang Shao, Dian-Hong Wang
Chin. Phys. B 2016, 25 (8): 080401;  doi: 10.1088/1674-1056/25/8/080401
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Based on statistical properties, two typical models are considered to calculate the uncertainties for some random noise sequences on the period extraction of a torsion pendulum, which is important and instructive in the measurement of gravitational constant G with the time-of-swing method. An expression of the uncertainty for the period measurement is obtained, which is dependent on the ratio Δt/(1/λ) where Δt is the interval of the sample time and 1/λ is the length of the correlation time. The result of processing experimental data shows that as the interval of the sample time Δt gradually shortens, the uncertainty of the period becomes smaller, and further when the ratio Δt/(1/λ) is less than 1, the uncertainty remains substantially unchanged.

Robust pre-specified time synchronization of chaotic systems by employing time-varying switching surfaces in the sliding mode control scheme

Alireza Khanzadeh, Mahdi Pourgholi
Chin. Phys. B 2016, 25 (8): 080501;  doi: 10.1088/1674-1056/25/8/080501
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In the conventional chaos synchronization methods, the time at which two chaotic systems are synchronized, is usually unknown and depends on initial conditions. In this work based on Lyapunov stability theory a sliding mode controller with time-varying switching surfaces is proposed to achieve chaos synchronization at a pre-specified time for the first time. The proposed controller is able to synchronize chaotic systems precisely at any time when we want. Moreover, by choosing the time-varying switching surfaces in a way that the reaching phase is eliminated, the synchronization becomes robust to uncertainties and exogenous disturbances. Simulation results are presented to show the effectiveness of the proposed method of stabilizing and synchronizing chaotic systems with complete robustness to uncertainty and disturbances exactly at a pre-specified time.

Study of a ternary blend system for bulk heterojunction thin film solar cells

Zubair Ahmad, Farid Touati, Shakoor R A, Al-Thani N J
Chin. Phys. B 2016, 25 (8): 080701;  doi: 10.1088/1674-1056/25/8/080701
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In this research, we report a bulk heterojunction (BHJ) solar cell consisting of a ternary blend system. Poly(3-hexylthiophene) P3HT is used as a donor and [6, 6]-phenyl C61-butyric acid methylester (PCBM) plays the role of acceptor whereas vanadyl 2, 9, 16, 23-tetraphenoxy-29H, 31H-phthalocyanine (VOPcPhO) is selected as an ambipolar transport material. The materials are selected and assembled in such a fashion that the generated charge carriers could efficiently be transported rightwards within the blend. The organic BHJ solar cells consist of ITO/PEDOT:PSS/ternary BHJ blend/Al structure. The power conversion efficiencies of the ITO/PEDOT:PSS/P3HT:PCBM/Al and ITO/PEDOT:PSS/P3HT:PCBM:VOPcPhO/Al solar cells are found to be 2.3% and 3.4%, respectively.

Experimental research on spectrum and imaging of continuous-wave terahertz radiation based on interferometry

Tie-Lin Lu, Hui Yuan, Ling-Qin Kong, Yue-Jin Zhao, Liang-Liang Zhang, Cun-Lin Zhang
Chin. Phys. B 2016, 25 (8): 080702;  doi: 10.1088/1674-1056/25/8/080702
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A system for measuring terahertz spectrum is proposed based on optical interferometer theory, and is experimentally demonstrated by using a backward-wave oscillator as the terahertz source. A high-resolution, high-precision interferometer is constructed by using a pyroelectric detector and a chopper. The results show that the spectral resolution is better than 1 GHz and the relative error of frequency is less than 3%. The terahertz energy density distribution is calculated by an inverse Fourier transform and tested to verify the feasibility of the interferometric approach. Two kinds of carbon-fiber composites are imaged. The results confirm that the interferometer is useful for transmission imaging of materials with different thickness values.
ATOMIC AND MOLECULAR PHYSICS

Band structure, Fermi surface, elastic, thermodynamic, and optical properties of AlZr3, AlCu3, and AlCu2Zr: First-principles study

Parvin R, Parvin F, Ali M S, Islam A K M A
Chin. Phys. B 2016, 25 (8): 083101;  doi: 10.1088/1674-1056/25/8/083101
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The electronic properties (Fermi surface, band structure, and density of states (DOS)) of Al-based alloys AlM3 (M=Zr and Cu) and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation (GGA). The structural parameters and elastic constants are evaluated and compared with other available data. Also, the pressure dependences of mechanical properties of the compounds are studied. The temperature dependence of adiabatic bulk modulus, Debye temperature, specific heat, thermal expansion coefficient, entropy, and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T=0 K-100 K. The parameters of optical properties (dielectric functions, refractive index, extinction coefficient, absorption spectrum, conductivity, energy-loss spectrum, and reflectivity) of the compounds are calculated and discussed for the first time. The reflectivities of the materials are quite high in the IR-visible-UV region up to ~15 eV, showing that they promise to be good coating materials to avoid solar heating. Some of the properties are also compared with those of the Al-based Ni3Al compound.

Diode laser using narrow bandwidth interference filter at 852 nm and its application in Faraday anomalous dispersion optical filter

Zhaojie Jiang, Qi Zhou, Zhiming Tao, Xiaogang Zhang, Shengnan Zhang, Chuanwen Zhu, Pingwei Lin, Jingbiao Chen
Chin. Phys. B 2016, 25 (8): 083201;  doi: 10.1088/1674-1056/25/8/083201
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We demonstrate an 852-nm external cavity diode laser (ECDL) system whose wavelength is mainly determined by an interference filter instead of other wavelength selective elements. The Lorentzian linewidth measured by the heterodyne beating between two identical lasers is 28.3 kHz. Moreover, we test the application of the ECDL in the Faraday atomic filter. Besides saturated absorption spectrum, the transmission spectrum of the Faraday atomic filter at 852 nm is measured by using the ECDL. This interference filter ECDL method can also be extended to other wavelengths and widen the application range of diode laser.

FDTD simulation study of size/gap and substrate-dependent SERS activity study of Au@SiO2 nanoparticles

Jing-Liang Yang, Ruo-Ping Li, Jun-He Han, Ming-Ju Huang
Chin. Phys. B 2016, 25 (8): 083301;  doi: 10.1088/1674-1056/25/8/083301
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We use Au@SiO2 nanoparticles (NPs) to systematically and comprehensively study the relationship between nanostructure and activity for surface-enhanced Raman scattering. Calculation simulation using the finite different time domain method verifies the experiment results and further reveals that the particle size and the distance between the NPs play vital roles in the surface-enhanced Raman scattering (SERS). Furthermore, in order to better simulate the real experiment, a Au@SiO2 nanosphere dimer is placed on the silicon substrate and Au substrate, separately. The simulation results show that the large EM field coupling is due to the “hot spots” transferred from the NP-NP gaps to NP-surface of metal gaps, meanwhile, more “hot spots” occur. We also find that the signal intensity strongly depends on the position of the probe molecule. This work provides a better understanding of EM field enhancement.

Understanding charge transfer of Li+ and Na+ ions scattered from metal surfaces with high work function

Lin Chen, Wen-Bin Wu, Pin-Yang Liu, Yun-Qing Xiao, Guo-Peng Li, Yi-Ran Liu, Hao-Yu Jiang, Yan-Ling Guo, Xi-Meng Chen
Chin. Phys. B 2016, 25 (8): 083401;  doi: 10.1088/1674-1056/25/8/083401
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For Li+ and Na+ ions scattered from high work function metal surfaces, efficient neutralization is observed, and it cannot be explained by the conventional free electron model. In order to explain these experimental data, we investigate the velocity-dependent neutral fraction with the modified Brako-Newns (BN) model. The calculated results are in agreement with the experimental data. We find that the parallel velocity effect plays an important role in neutralizing the Li+ and Na+ ions for large angle scattering. The nonmonotonic velocity behavior of neutral fraction is strongly related to the distance-dependent coupling strength between the atomic level and metal states.

Effects of collision energy and rotational quantum number on stereodynamics of the reactions: H(2S)+NH(v=0, j=0, 2, 5, 10)→N(4S)+H2

Wei Wang, Yong-Jiang Yu, Gang Zhao, Chuan-Lu Yang
Chin. Phys. B 2016, 25 (8): 083402;  doi: 10.1088/1674-1056/25/8/083402
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The stereodynamical properties of H(2S)+NH(v=0, j=0, 2, 5, 10)→N(4S)+H2 reactions are studied in this paper by using the quasi-classical trajectory (QCT) method with different collision energies on the double many-body expansion (DMBE) potential energy surface (PES) (Poveda L A and Varandas A J C 2005Phys. Chem. Chem. Phys. 7 2867). In a range of collision energy from 2 to 20 kcal/mol, the vibrational rotational quantum numbers of the NH molecules are specifically investigated on v=0 and j=0, 2, 5, 10 respectively. The distributions of P(θr), P(φr), P(θr, φr), (2π/σ)(dσ00/dωt) differential cross-section (DCSs) and integral cross-sections(ICSs) are calculated. The ICSs, computed for collision energies from 2 kcal/mol to 20 kcal/mol, for the ground state are in good agreement with the cited data. The results show that the reagent rotational quantum number and initial collision energy both have a significant effect on the distributions of the k-j', the k-k'-j', and the k-k' correlations. In addition, the DCS is found to be susceptible to collision energy, but it is not significantly affected by the rotational excitation of reagent.
REVIEW

Effects of 5f-elements on electronic structures and spectroscopic properties of gold superatom model

Yang Gao, Zhigang Wang
Chin. Phys. B 2016, 25 (8): 083102;  doi: 10.1088/1674-1056/25/8/083102
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5f-elements encaged in a gold superatomic cluster are capable of giving rise to unique optical properties due to their hyperactive valence electrons and great radial components of 5f/6d orbitals. Herein, we review our first-principles studies on electronic structures and spectroscopic properties of a series of actinide-embedded gold superatomic clusters with different dimensions. The three-dimensional (3D) and two-dimensional (2D) superatom clusters possess the 18-electron configuration of 1S21P61D10 and 10-electron configuration of 1S21P41D4, respectively. Importantly, their electronic absorption spectra can also be effectively explained by the superatom orbitals. Specifically, the charge transfer (CT) transitions involved in surface-enhance Raman spectroscopy (SERS) spectra for 3D and 2D structures are both from the filled 1D orbitals, providing the enhancement factors of the order of ~104 at 488 nm and ~105 at 456 nm, respectively. This work implies that the superatomic orbital transitions involved in 5f-elements can not only lead to a remarkable spectroscopic performance, but also a new direction for optical design in the future.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Utra-thin anisotropic transmitting metasurface for polarization beam splitter application

Wen-Long Guo, Guang-Ming Wang, Shan-Shan Ding, Hai-Peng Li, Tong Cai
Chin. Phys. B 2016, 25 (8): 084101;  doi: 10.1088/1674-1056/25/8/084101
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We report a polarization beam splitter based on phase gradient metasurface for microwave frequency region. The metasurface is constructed by anisotropic cells with independent phase response for differently-polarized waves. Through putting different gradient phases for orthogonally-polarized waves on a focusing metasurface, the anisotropic sample has the ability to enhance gain and split orthogonally-polarized waves. The simulation results indicate that the incident spherical waves are converted into plane waves and split into an x-polarized wave with a refraction angle of -24° and a y-polarized wave with a refraction angle of 37.6° in the y direction. For verification, a metasurface sample with a size of 102.5 mm×102.5 mm is fabricated and measured. The consistence between numerical and experimental results validates the improved gain of 10.5-dB against the feed source and the splitting effect. Moreover, the thickness of the proposed metasurface is 3 mm which is ultra-thin against the wavelength at 15 GHz. The proposed prescription opens a new route to the applications of anisotropic metasurface in microwave band.

Interaction of Airy-Gaussian beams in saturable media

Meiling Zhou, Yulian Peng, Chidao Chen, Bo Chen, Xi Peng, Dongmei Deng
Chin. Phys. B 2016, 25 (8): 084102;  doi: 10.1088/1674-1056/25/8/084102
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Based on the nonlinear Schrödinger equation, the interactions of the two Airy-Gaussian components in the incidence are analyzed in saturable media, under the circumstances of the same amplitude and different amplitudes, respectively. It is found that the interaction can be both attractive and repulsive depending on the relative phase. The smaller the interval between two Airy-Gaussian components in the incidence is, the stronger the intensity of the interaction. However, with the equal amplitude, the symmetry is shown and the change of quasi-breathers is opposite in the in-phase case and out-of-phase case. As the distribution factor is increased, the phenomena of the quasi-breather and the self-accelerating of the two Airy-Gaussian components are weakened. When the amplitude is not equal, the image does not have symmetry. The obvious phenomenon of the interaction always arises on the side of larger input power in the incidence. The maximum intensity image is also simulated. Many of the characteristics which are contained within other images can also be concluded in this figure.

Enhanced chiral response from the Fabry-Perot cavity coupled meta-surfaces

Ze-Jian Yang, De-Jiao Hu, Fu-Hua Gao, Yi-Dong Hou
Chin. Phys. B 2016, 25 (8): 084201;  doi: 10.1088/1674-1056/25/8/084201
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The circular dichroism (CD) signal of a two-dimensional (2D) chiral meta-surface is usually weak, where the difference between the transmitted (or reflected) right and left circular polarization is barely small. We present a general method to enhance the reflective CD spectrum, by adding a layer of reflective film behind the meta-surface. The light passes through the chiral meta-surface and propagates towards the reflector, where it is reflected back and further interacts with the chiral meta-surface. The light is reflected back and forth between these two layers, forming a Fabry-Perot type resonance, which interacts with the localized surface plasmonic resonance (LSPR) mode and greatly enhances the CD signal of the light wave leaving the meta-surface. We numerically calculate the CD enhancing effect of an L-shaped chiral meta-surface on a gold film in the visible range. Compared with the single layer meta-surface, the L-shaped chiral meta-surface has a CD maximum that is dramatically increased to 1. The analysis of reflection efficiency reveals that our design can be used to realize a reflective circular polarizer. Corresponding mode analysis shows that the huge CD originates from the hybrid mode comprised of FP mode and LSPR. Our results provide a general approach to enhancing the CD signal of a chiral meta-surface and can be used in areas like biosensing, circular polarizer, integrated photonics, etc.

Ultra-broadband and high-efficiency polarization conversion metasurface with multiple plasmon resonance modes

Guo-Xiang Dong, Hong-Yu Shi, Song Xia, Wei Li, An-Xue Zhang, Zhuo Xu, Xiao-Yong Wei
Chin. Phys. B 2016, 25 (8): 084202;  doi: 10.1088/1674-1056/25/8/084202
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In this paper, we present a novel metasurface design that achieves a high-efficiency ultra-broadband cross polarization conversion. The metasurface is composed of an array of unit resonators, each of which combines an H-shaped structure and two rectangular metallic patches. Different plasmon resonance modes are excited in unit resonators and allow the polarization states to be manipulated. The bandwidth of the cross polarization converter is 82% of the central frequency, covering the range from 15.7 GHz to 37.5 GHz. The conversion efficiency of the innovative new design is higher than 90%. At 14.43 GHz and 40.95 GHz, the linearly polarized incident wave is converted into a circularly polarized wave.

Locating the position of objects in non-line-of-sight based on time delay estimation

Xue-Feng Wang, Yuan-Qing Wang, Jin-Shan Su, Xing-Yu Yang
Chin. Phys. B 2016, 25 (8): 084203;  doi: 10.1088/1674-1056/25/8/084203
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Non-line-of-sight imaging detection is to detect hidden objects by indirect light and intermediary surface (diffuser). It has very important significance in indirect access to an object or dangerous object detection, such as medical treatment and rescue. An approach to locating the positions of hidden objects is proposed based on time delay estimation. The time delays between the received signals and the source signal can be obtained by correlation analysis, and then the positions of hidden objects will be located. Compared with earlier systems and methods, the proposed approach has some modifications and provides significant improvements, such as quick data acquisition, simple system structure and low cost, and can locate the positions of hidden objects as well: this technology lays a good foundation for developing a practical system that can be used in real applications.

Quantum polarization fluctuations of partially coherent dark hollow beams in non-Kolmogorov turbulence atmosphere

Xiang Yan, Peng-Fei Zhang, Jing-Hui Zhang, Chun-Hong Qiao, Cheng-Yu Fan
Chin. Phys. B 2016, 25 (8): 084204;  doi: 10.1088/1674-1056/25/8/084204
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Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained. It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.

Time gap for temporal cloak based on spectral hole burning in atomic medium

Abdul Jabar M S, Bakht Amin Bacha, Iftikhar Ahmad
Chin. Phys. B 2016, 25 (8): 084205;  doi: 10.1088/1674-1056/25/8/084205
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We demonstrate the possibility of creating a time gap in the slow light based on spectral hole burning in a four-level Doppler broadened sodium atomic system. A time gap is also observed between the slow and the fast light in the hole burning region and near the burnt hole region, respectively. A cloaking time gap is attained in microseconds and no distortion is observed in the transmitted pulse. The width of the time gap is observed to vary with the inverse Doppler effect in this system. Our results may provide a way to create multiple time gaps for a temporal cloak.

High power-efficiency terahertz quantum cascade laser

Yuan-Yuan Li, Jun-Qi Liu, Feng-Qi Liu, Jin-Chuan Zhang, Shen-Qiang Zhai, Ning Zhuo, Li-Jun Wang, Shu-Man Liu, Zhan-Guo Wang
Chin. Phys. B 2016, 25 (8): 084206;  doi: 10.1088/1674-1056/25/8/084206
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We demonstrate continuous-wave (CW) high power-efficiency terahertz quantum cascade laser based on semi-insulating surface-plasmon waveguide with epitaxial-side down (Epi-down) mounting process. The performance of the device is analyzed in detail. The laser emits at a frequency of ~3.27 THz and has a maximum CW operating temperature of ~70 K. The peak output powers are 177 mW in pulsed mode and 149 mW in CW mode at 10 K for 130-μm-wide Epi-down mounted lasers. The record wall-plug efficiencies in direct measurement are 2.26% and 2.05% in pulsed and CW mode, respectively.

980-nm all-fiber mode-locked Yb-doped phosphate fiber oscillator based on semiconductor saturable absorber mirror and its amplifier

Ping-Xue Li, Yi-Fei Yao, Jun-Jie Chi, Hao-Wei Hu, Guang-Ju Zhang, Bo-Xing Liang, Meng-Meng Zhang, Chun-Mei Ma, Ning Su
Chin. Phys. B 2016, 25 (8): 084207;  doi: 10.1088/1674-1056/25/8/084207
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A 980-nm semiconductor saturable absorber mirror (SESAM) mode-locked Yb-doped phosphate fiber laser is demonstrated by using an all-fiber linear cavity configuration. Two different kinds of cavity lengths are introduced into the oscillator to obtain a robust and stable mode-locked seed source. When the cavity length is chosen to be 6 m, the oscillator generates an average output power of 3.5 mW and a pulse width of 76.27 ps with a repetition rate of 17.08 MHz. As the cavity length is optimized to short, 4.4-mW maximum output power and 61.15-ps pulse width are produced at a repetition rate of 20.96 MHz. The output spectrum is centered at 980 nm with a narrow spectral bandwidth of 0.13 nm. In the experiment, no undesired amplified spontaneous emission (ASE) nor harmful oscillation around 1030 nm is observed. Moreover, through a two-stage all-fiber-integrated amplifier, an output power of 740 mW is generated with a pulse width of 200 ps.

Comparison of the compensation effects of fiber nonlinear impairments with mid-span optical phase conjugation between PDM CO-OFDM system and PDM QPSK system

Fei Xu, Meng-Qi Guo, Lei Wang, Yao-Jun Qiao, Hui-Ping Tian
Chin. Phys. B 2016, 25 (8): 084208;  doi: 10.1088/1674-1056/25/8/084208
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The compensation effects of fiber nonlinearity in 112 Gb/s polarization division multiplexing (PDM) coherent optical systems by mid-span optical phase conjugation (OPC) based on four wave mixing (FWM) effect are studied. Comparisons of the compensation results between PDM coherent optical-orthogonal frequency division multiplexing (CO-OFDM) system and the single carrier (SC) PDM quadrature phase shift keying (QPSK) system are provided as well. The results demonstrate that nonlinear compensation effect with mid-span OPC in PDM CO-OFDM system is much more obvious than that in SC PDM QPSK system.

Spectral modulation of third-harmonic generation by molecular alignment and preformed plasma

Min Li, An-Yuan Li, Bo-Qu He, Shuai Yuan, He-Ping Zeng
Chin. Phys. B 2016, 25 (8): 084209;  doi: 10.1088/1674-1056/25/8/084209
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We demonstrate spectral modulation of third-harmonic generation from molecular alignment effects. The third harmonic spectrum is broadened or narrowed under different influences of cross-phase modulations originating from various molecular alignment revivals. Furthermore, the spectrum and spatial distribution of the generated third harmonic pulse change dramatically in the presence of a preformed plasma. Under the influence of a preformed plasma, a narrower third harmonic spectrum is observed, and the conical third-harmonic pulse increases while the axial part decreases. The investigation provides an effective method to modulate the spectral characteristic and spatial distribution of third-harmonic generation from intense femtosecond filament.

Controllable soliton propagation based on phase-front curvature in asymmetrical nonlocal media

Huafeng Zhang, Hua Lü, Jianghua Luo, Lihui Sun
Chin. Phys. B 2016, 25 (8): 084210;  doi: 10.1088/1674-1056/25/8/084210
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The influence of phase-front curvature on the dynamical behavior of the fundamental mode soliton during its transmission in asymmetrical nonlocal media is studied in detail and the phase-front curvature can be imposed on the fundamental mode soliton by reshaping or phase imprinting technologies. By changing the phase-front curvature or its imposed position, controllable soliton propagation in asymmetrical nonlocal media can be achieved.

High contrast all-optical diode based on direction-dependent optical bistability within asymmetric ring cavity

Xiu-Wen Xia, Xin-Qin Zhang, Jing-Ping Xu, Ya-Ping Yang
Chin. Phys. B 2016, 25 (8): 084211;  doi: 10.1088/1674-1056/25/8/084211
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We propose a simple all-optical diode which is comprised of an asymmetric ring cavity containing a two-level atomic ensemble. Attributed to spatial symmetry breaking of the ring cavity, direction-dependent optical bistability is obtained in a classical bistable system. Therefore, a giant optical non-reciprocity is generated, which guarantees an all-optical diode with a high contrast up to 22 dB. Furthermore, its application as an all-optical logic AND gate is also discussed.

Apodized grating coupler using fully-etched nanostructures

Hua Wu, Chong Li, Zhi-Yong Li, Xia Guo
Chin. Phys. B 2016, 25 (8): 084212;  doi: 10.1088/1674-1056/25/8/084212
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A two-dimensional apodized grating coupler for interfacing between single-mode fiber and photonic circuit is demonstrated in order to bridge the mode gap between the grating coupler and optical fiber. The grating grooves of the grating couplers are realized by columns of fully etched nanostructures, which are utilized to digitally tailor the effective refractive index of each groove in order to obtain the Gaussian-like output diffractive mode and then enhance the coupling efficiency. Compared with that of the uniform grating coupler, the coupling efficiency of the apodized grating coupler is increased by 4.3% and 5.7%, respectively, for the nanoholes and nanorectangles as refractive index tunes layer.

Effect of radiation-induced color centers absorption in optical fibers on fiber optic gyroscope for space application

Jing Jin, Ya Li, Zu-Chen Zhang, Chun-Xiao Wu, Ning-Fang Song
Chin. Phys. B 2016, 25 (8): 084213;  doi: 10.1088/1674-1056/25/8/084213
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The effects of color centers' absorption on fibers and interferometric fiber optical gyroscopes (IFOGs) are studied in the paper. The irradiation induced attenuation (RIA) spectra of three types of polarization-maintaining fibers (PMFs), i.e., P-doped, Ge-doped, and pure silica, irradiated at 100 Gy and 1000 Gy are measured in a wavelength range from 1100 nm to 1600 nm and decomposed according to the Gaussian model. The relationship of the color centers absorption intensity with radiation dose is investigated based on a power model. Furthermore, the effects of all color centers' absorption on RIA and mean wavelength shifts (MWS) at 1300 nm and 1550 nm are discussed respectively. Finally, the random walk coefficient (RWC) degradation induced from RIA and the scale factor error induced by MWS of the IFOG are simulated and tested at a wavelength of 1300 nm. This research will contribute to the applications of the fibers in radiation environments.

A new brain stimulation method: Noninvasive transcranial magneto-acoustical stimulation

Yi Yuan, Yu-Dong Chen, Xiao-Li Li
Chin. Phys. B 2016, 25 (8): 084301;  doi: 10.1088/1674-1056/25/8/084301
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We investigate transcranial magneto-acoustical stimulation (TMAS) for noninvasive brain neuromodulation in vivo. TMAS as a novel technique uses an ultrasound wave to induce an electric current in the brain tissue in the static magnetic field. It has the advantage of high spatial resolution and penetration depth. The mechanism of TMAS onto a neuron is analyzed by combining the TMAS principle and Hodgkin-Huxley neuron model. The anesthetized rats are stimulated by TMAS, resulting in the local field potentials which are recorded and analyzed. The simulation results show that TMAS can induce neuronal action potential. The experimental results indicate that TMAS can not only increase the amplitude of local field potentials but also enhance the effect of focused ultrasound stimulation on the neuromodulation. In summary, TMAS can accomplish brain neuromodulation, suggesting a potentially powerful noninvasive stimulation method to interfere with brain rhythms for diagnostic and therapeutic purposes.

The anisotropy of free path in a vibro-fluidized granular gas

Yifeng Mei, Yanpei Chen, Wei Wang, Meiying Hou
Chin. Phys. B 2016, 25 (8): 084501;  doi: 10.1088/1674-1056/25/8/084501
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The free path of a vibro-fluidized two-dimensional (2D) inelastic granular gas confined in a rectangular box is investigated by 2D event-driven molecular simulation. By tracking particles in the simulation, we analyze the local free path. The probability distribution of the free path shows a high tail deviating from the exponential prediction. The anisotropy of the free path is found when we separate the free path to x and y components. The probability distribution of y component is exponential, while x component has a high tail. The probability distribution of angle between the relative velocity and the unit vector joined two particle centers deviates from the distribution of two random vectors, indicating the existence of the dynamic heterogeneities in our system. We explain these results by resorting to the kinetic theory with two-peak velocity distribution. The kinetic theory agrees well with the simulation result.

Improved algorithm for solving nonlinear parabolized stability equations

Lei Zhao, Cun-bo Zhang, Jian-xin Liu, Ji-sheng Luo
Chin. Phys. B 2016, 25 (8): 084701;  doi: 10.1088/1674-1056/25/8/084701
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Due to its high computational efficiency and ability to consider nonparallel and nonlinear effects, nonlinear parabolized stability equations (NPSE) approach has been widely used to study the stability and transition mechanisms. However, it often diverges in hypersonic boundary layers when the amplitude of disturbance reaches a certain level. In this study, an improved algorithm for solving NPSE is developed. In this algorithm, the mean flow distortion is included into the linear operator instead of into the nonlinear forcing terms in NPSE. An under-relaxation factor for computing the nonlinear terms is introduced during the iteration process to guarantee the robustness of the algorithm. Two case studies, the nonlinear development of stationary crossflow vortices and the fundamental resonance of the second mode disturbance in hypersonic boundary layers, are presented to validate the proposed algorithm for NPSE. Results from direct numerical simulation (DNS) are regarded as the baseline for comparison. Good agreement can be found between the proposed algorithm and DNS, which indicates the great potential of the proposed method on studying the crossflow and streamwise instability in hypersonic boundary layers.

Achieving acoustic cloak by using compressible background flow

Ruo-Yang Zhang, Qing Zhao, Mo-Lin Ge
Chin. Phys. B 2016, 25 (8): 084702;  doi: 10.1088/1674-1056/25/8/084702
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We propose a scheme of acoustic spherical cloaking by means of background irrotational flow in compressible fluid. The background flow forms a virtual curved spacetime and directs the sound waves to bypass the cloaked objects. To satisfy the laws of real fluid, we show that spatially distributed mass source and momentum source are necessary to supply. The propagation of sound waves in this system is studied via both geometric acoustics approximation and full wave approach. The analytic solution of sound fields is obtained for plane wave incidence. The results reveal the effect of phase retardation (or lead) in comparison with the ordinary transformation-acoustic cloak. In addition, the ability of cloaking is also evaluated for unideal background flows by analyzing the scattering cross section.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

Theoretical analysis of the EAST 4-strap ion cyclotron range of frequency antenna with variational theory

Jia-Hui Zhang, Xin-Jun Zhang, Yan-Ping Zhao, Cheng-Ming Qin, Zhao Chen, Lei Yang, Jian-Hua Wang
Chin. Phys. B 2016, 25 (8): 085201;  doi: 10.1088/1674-1056/25/8/085201
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A variational principle code which can calculate self-consistently currents on the conductors is used to assess the coupling characteristic of the EAST 4-strap ion cyclotron range of frequency (ICRF) antenna. Taking into account two layers of antenna conductors without lateral frame but with slab geometry, the antenna impedances as a function of frequency and the structure of RF field excited inside the plasma in various phasing cases are discussed in this paper.

A new ignition hohlraum design for indirect-drive inertial confinement fusion

Xin Li, Chang-Shu Wu, Zhen-Sheng Dai, Wu-Di Zheng, Jian-Fa Gu, Pei-Jun Gu, Shi-Yang Zou, Jie Liu, Shao-Ping Zhu
Chin. Phys. B 2016, 25 (8): 085202;  doi: 10.1088/1674-1056/25/8/085202
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In this paper, a six-cylinder-port hohlraum is proposed to provide high symmetry flux on capsule. It is designed to ignite a capsule with 1.2-mm radius in indirect-drive inertial confinement fusion (ICF). Flux symmetry and laser energy are calculated by using three-dimensional view factor method and laser energy balance in hohlraum. Plasma conditions are analyzed based on the two-dimensional radiation-hydrodynamic simulations. There is no Ylm (l≤4) asymmetry in the six-cylinder-port hohlraum when the influences of laser entrance holes (LEHs) and laser spots cancel each other out with suitable target parameters. A radiation drive with 300 eV and good flux symmetry can be achieved by using a laser energy of 2.3 MJ and peak power of 500 TW. According to the simulations, the electron temperature and the electron density on the wall of laser cone are high and low, respectively, which are similar to those of outer cones in the hohlraums on National Ignition Facility (NIF). And the laser intensity is also as low as those of NIF outer cones. So the backscattering due to laser plasma interaction (LPI) is considered to be negligible. The six-cyliner-port hohlraum could be superior to the traditional cylindrical hohlraum and the octahedral hohlraum in both higher symmetry and lower backscattering without supplementary technology at an acceptable laser energy level. It is undoubted that the hohlraum will add to the diversity of ICF approaches.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Magnetostatic interaction in electrodeposited Ni/Au multilayer nanowire arrays

Li-Zhong He, Li-Rong Qin, Jian-Wei Zhao, Ying-Ying Yin, Yu Yang, Guo-Qing Li
Chin. Phys. B 2016, 25 (8): 086101;  doi: 10.1088/1674-1056/25/8/086101
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Ordered Ni/Au multilayer nanowire arrays are successfully fabricated inside the nanochannels of anodic aluminum oxide template by pulse electrodeposition method. The thickness of the alternating layers is controlled to examine the magnetostatic interaction in Ni/Au multilayer nanowires. The magnetic easy axis parallel to the nanowires indicates that here the magnetostatic coupling along the wire axis dominates over the interactions perpendicular to the nanowires. However, the magnetostatic interaction between adjacent nanowires with larger magnetic layers is enhanced, leading to the existence of an optimum coercivity value.

First-principles calculation of the structural, electronic, elastic, and optical properties of sulfur-doping ε-GaSe crystal

Chang-Bao Huang, Hai-Xin Wu, You-Bao Ni, Zhen-You Wang, Ming Qi, Chun-Li Zhang
Chin. Phys. B 2016, 25 (8): 086201;  doi: 10.1088/1674-1056/25/8/086201
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The structural, electronic, mechanical properties, and frequency-dependent refractive indexes of GaSe1-xSx (x=0, 0.25, and 1) are studied by using the first-principles pseudopotential method within density functional theory. The calculated results demonstrate the relationships between intralayer structure and elastic modulus in GaSe1-xSx (x=0, 0.25, and 1). Doping of ε-GaSe with S strengthens the Ga-X bonds and increases its elastic moduli of C11 and C66. Born effective charge analysis provides an explanation for the modification of cleavage properties about the doping of ε-GaSe with S. The calculated results of band gaps suggest that the distance between intralayer atom and substitution of SSe, rather than interlayer force, is a key factor influencing the electronic exciton energy of the layer semiconductor. The calculated refractive indexes indicate that the doping of ε-GaSe with S reduces its refractive index and increases its birefringence.

Influence of shockwave profile on ejecta from shocked Pb surface: Atomistic calculations

Guo-Wu Ren, Shi-Wen Zhang, Ren-Kai Hong, Tie-Gang Tang, Yong-Tao Chen
Chin. Phys. B 2016, 25 (8): 086202;  doi: 10.1088/1674-1056/25/8/086202
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We conduct molecular dynamics simulations of the ejection process from a grooved Pb surface subjected to supported and unsupported shock waves with various shock-breakout pressures (PSB) inducing a solid-liquid phase transition upon shock or release. It is found that the total ejecta mass changing with PSB under a supported shock reveals a similar trend with that under an unsupported shock and the former is always less than the latter at the same PSB. The origin of such a discrepancy could be unraveled that for an unsupported shock, a larger velocity difference between the jet tip and its bottom at an early stage of jet formation results in more serious damage, and therefore a greater amount of ejected particles are produced. The cumulative areal density distributions also display the discrepancy. In addition, we discuss the difference of these simulated results compared to the experimental findings.

Investigation of mechanical properties of twin gold crystal nanowires under uniaxial load by molecular dynamics method

Guo-Wei Zhang, Zai-Lin Yang, Gang Luo
Chin. Phys. B 2016, 25 (8): 086203;  doi: 10.1088/1674-1056/25/8/086203
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Twin gold crystal nanowires, whose loading direction is parallel to the twin boundary orientation, are simulated. We calculate the nanowires under tensile or compressive loads, different length nanowires, and different twin boundary nanowires respectively. The Young modulus of nanowires under compressive load is about twice that under tensile load. The compressive properties of twin gold nanowires are superior to their tensile properties. For different length nanowires, there is a critical value of length with respect to the mechanical properties. When the length of nanowire is greater than the critical value, its mechanical properties are sensitive to length. The twin boundary spacing hardly affects the mechanical properties.

Edge effects on the characteristics of uranium diffusion on graphene and graphene nanoribbons

Cheng Cheng, Han Han, Cui-Lan Ren, Chang-Ying Wang, Kuan Shao, Ping Huai
Chin. Phys. B 2016, 25 (8): 086301;  doi: 10.1088/1674-1056/25/8/086301
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The first principles density-functional theoretical calculations of U adatom adsorption and diffusion on a planar graphene and quasi-one-dimensional graphene nanoribbons (GNRs) are performed. An energetic preference is found for U adatom diffusing to the hollow sites of both graphene and GNRs surface. A number of U distinctive diffusion paths either perpendicular or parallel to the ribbon growth direction are examined. The edge effects are evidenced by the calculated energy barriers of U adatom diffusion on armchair and zigzag nanoribbons surfaces. The calculation results indicate that the diffusion of U adatom from the inner site toward the edge site is a feasible process, particularly in zigzag GNR. It is viable to control the initial morphology of nuclear carbon material to retard the diffusion and concentration of nuclides.

Structural, elastic, electronic, and thermodynamic properties of MgAgSb investigated by density functional theory

Jun-Fei Wang, Xiao-Nan Fu, Xiao-Dong Zhang, Jun-Tao Wang, Xiao-Dong Li, Zhen-Yi Jiang
Chin. Phys. B 2016, 25 (8): 086302;  doi: 10.1088/1674-1056/25/8/086302
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The structural, elastic, electronic, and thermodynamic properties of thermoelectric material MgAgSb in γ, β, α phases are studied with first-principles calculations based on density functional theory. The optimized lattice constants accord well with the experimental data. According to the calculated total energy of the three phases, the phase transition order is determined from α to γ phase with cooling, which is in agreement with the experimental result. The physical properties such as elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factor are also discussed and analyzed, which indicates that the three structures are mechanically stable and each has a ductile feature. The Debye temperature is deduced from the elastic properties. The total density of states (TDOS) and partial density of states (PDOS) of the three phases are investigated. The TDOS results show that the γ phase is most stable with a pseudogap near the Fermi level, and the PDOS analysis indicates that the conduction band of the three phases is composed mostly of Mg-3s, Ag-4d, and Sb-5p. In addition, the changes of the free energy, entropy, specific heat, thermal expansion of γ-MgAgSb with temperature are obtained successfully. The obtained results above are important parameters for further experimental and theoretical tuning of doped MgAgSb as a thermoelectric material at high temperature.

Near-zero thermal expansion of In2(1-x)(HfMg)xMo3O12 with tailored phase transition

Yong-Guang Cheng, Yan-Chao Mao, Xain-Sheng Liu, Bao-He Yuan, Ming-Ju Chao, Er-Jun Liang
Chin. Phys. B 2016, 25 (8): 086501;  doi: 10.1088/1674-1056/25/8/086501
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Solid solutions of In2(1-x)(HfMg)xMo3O12 are synthesized by solid state reaction with the aim to reduce the phase transition temperature of In2Mo3O12 and improve its thermal expansion property. The effects of (HfMg)6+ incorporation on the phase transition and thermal expansion are investigated. It is shown that the monoclinic-to-orthorhombic phase transition temperature obviously decreases and the coefficient of thermal expansion (CTE) of the orthorhombic becomes less negative and approaches to zero with increasing the content of (HfMg)6+. A near zero thermal expansion covering the case at room temperature (RT) is achieved for the solid solutions with x≥0.85, implying potential applications of this material in many fields.

Influence of surface scattering on the thermal properties of spatially confined GaN nanofilm

Yang Hou, Lin-Li Zhu
Chin. Phys. B 2016, 25 (8): 086502;  doi: 10.1088/1674-1056/25/8/086502
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Gallium nitride (GaN), the notable representative of third generation semiconductors, has been widely applied to optoelectronic and microelectronic devices due to its excellent physical and chemical properties. In this paper, we investigate the surface scattering effect on the thermal properties of GaN nanofilms. The contribution of surface scattering to phonon transport is involved in solving a Boltzmann transport equation (BTE). The confined phonon properties of GaN nanofilms are calculated based on the elastic model. The theoretical results show that the surface scattering effect can modify the cross-plane phonon thermal conductivity of GaN nanostructures completely, resulting in the significant change of size effect on the conductivity in GaN nanofilm. Compared with the quantum confinement effect, the surface scattering leads to the order-of-magnitude reduction of the cross-plane thermal conductivity in GaN nanofilm. This work could be helpful for controlling the thermal properties of GaN nanostructures in nanoelectronic devices through surface engineering.

Collective diffusion in carbon nanotubes: Crossover between one dimension and three dimensions

Pei-Rong Chen, Zhi-Cheng Xu, Yu Gu, Wei-Rong Zhong
Chin. Phys. B 2016, 25 (8): 086601;  doi: 10.1088/1674-1056/25/8/086601
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Using non-equilibrium molecular dynamics and Monte Carlo methods, we study the collective diffusion of helium in carbon nanotubes. The results show that the collective diffusion coefficient (CDC) increases with the dimension of the channel. The collective diffusion coefficient has a linear relationship with the temperature and the concentration. There exist a ballistic transport in short carbon nanotubes and a diffusive transport in long carbon nanotubes. Fick's law has an invalid region in the nanoscale channel.

Stable structure and optical properties of fused silica with NBOHC-E' defect

Peng-Fei Lu, Li-Yuan Wu, Yang Yang, Wei-Zheng Wang, Chun-Fang Zhang, Chuang-Hua Yang, Rui Su, Jun Chen
Chin. Phys. B 2016, 25 (8): 086801;  doi: 10.1088/1674-1056/25/8/086801
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First-principles method is used to simulate the stable structure and optical properties of a 96-atom fused silica. The preferable structure of NBOHC-E' (non-bridging oxygen hole center (NBOHC) and E' center) pair defect is predicted to be located at 2.4 Å for the Si-O bond length. The quasi-particle G0W0 calculations are performed and an accurate band gap is obtained in order to calculate the optical absorption properties. With the stretching of the Si1-O1 bond, an obvious redshift can be observed in the absorption spectrum. In the case of NBOHC-E' pair, the p-orbital DOS of Si1 atom will shift to the conduction band. Two obvious absorption peaks can be observed in the absorption spectrum. The calculation reproduced the peak positions of the well-known optical absorption bands.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Numerical and experimental study of the mesa configuration in high-voltage 4H-SiC PiN rectifiers

Xiao-Chuan Deng, Xi-Xi Chen, Cheng-Zhan Li, Hua-Jun Shen, Jin-Ping Zhang
Chin. Phys. B 2016, 25 (8): 087201;  doi: 10.1088/1674-1056/25/8/087201
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The effect of the mesa configuration on the reverse breakdown characteristic of a SiC PiN rectifier for high-voltage applications is analyzed in this study. Three geometrical parameters, i.e., mesa height, mesa angle and mesa bottom corner, are investigated by numerical simulation. The simulation results show that a deep mesa height, a small mesa angle and a smooth mesa bottom (without sub-trench) could contribute to a high breakdown voltage due to a smooth and uniform surface electric field distribution. Moreover, an optimized mesa structure without sub-trench (mesa height of 2.2 μm and mesa angle of 20°) is experimentally demonstrated. A maximum reverse blocking voltage of 4 kV and a forward voltage drop of 3.7 V at 100 A/cm2 are obtained from the fabricated diode with a 30-μm thick N- epi-layer, corresponding to 85% of the ideal parallel-plane value. The blocking characteristic as a function of the JTE dose is also discussed for the PiN rectifiers with and without interface charge.

Advantages of using gold hollow nanoshells in cancer photothermal therapy

Sattar Abbasi, Mojtaba Servatkhah, Mohammad Mehdi Keshtkar
Chin. Phys. B 2016, 25 (8): 087301;  doi: 10.1088/1674-1056/25/8/087301
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Lots of studies have been conducted on the optical properties of gold nanoparticles in the first region of near infrared (650 nm-950 nm), however new findings show that the second region of near-infrared (1000 nm-1350 nm) penetrates to the deeper tissues of the human body. Therefore, using the above-mentioned region in photo-thermal therapy (PTT) of cancer will be more appropriate. In this paper, absorption efficiency is calculated for gold spherical and rod-shaped nanoshells by the finite element method (FEM). The results show that the surface plasmon frequency of these nanostructures is highly dependent on the dimension and thickness of shell and it can be adjusted to the second region of near-infrared. Thus, due to their optical tunability and their high absorption efficiency the hollow nanoshells are the most appropriate options for eradicating cancer tissues.

Spin-controlled directional launching of surface plasmons at the subwavelength scale

Tao Huang, Jia-jian Wang, Zi-wei Li, Wei Liu, Feng Lin, Zhe-yu Fang, Xing Zhu
Chin. Phys. B 2016, 25 (8): 087302;  doi: 10.1088/1674-1056/25/8/087302
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In this paper, we demonstrate a spin-controlled directional launching of surface plasmons at the subwavelength scale. Based on the principle of optical spin's effect for the geometric phase of light, the nanostructures were designed. The inclination of the structures decides the spin-related geometric phase and their relative positions decide the distance-related phase. Hence, the propagation direction of the generated surface plasmon polaritons (SPPs) can be controlled by the spin of photons. Numerical simulations by the finite difference time domain (FDTD) method have verified our theoretical prediction. Our structure is fabricated on the Au film by using a focused ion beam etching technique. The total size of the surface plasmon polariton (SPP) launcher is 320 nm by 180 nm. The observation of the SPP launching by using scanning near-field optical microscopy is in agreement with our theory and simulations. This result may provide a new way of spin-controlled directional launching of SPP.

Impurity effect on surface states of Bi (111) ultrathin films Hot!

Kai Zhu(朱凯), Dai Tian(田岱), Lin Wu(伍琳), Jianli Xu(许建丽), Xiaofeng Jin(金晓峰)
Chin. Phys. B 2016, 25 (8): 087303;  doi: 10.1088/1674-1056/25/8/087303
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The surface impurity effect on the surface-state conductivity and weak antilocalization (WAL) effect has been investigated in epitaxial Bi (111) films by magnetotransport measurements at low temperatures. The surface-state conductivity is significantly reduced by the surface impurities of Cu, Fe, and Co. The magnetotransport data demonstrate that the observed WAL is robust against deposition of nonmagnetic impurities, but it is quenched by the deposition of magnetic impurities which break the time reversal symmetry. Our results help to shed light on the effect of surface impurities on the electron and spin transport properties of a 2D surface electron systems.

Groove-type channel enhancement-mode AlGaN/GaN MIS HEMT with combined polar and nonpolar AlGaN/GaN heterostructures

Xiao-Ling Duan, Jin-Cheng Zhang, Ming Xiao, Yi Zhao, Jing Ning, Yue Hao
Chin. Phys. B 2016, 25 (8): 087304;  doi: 10.1088/1674-1056/25/8/087304
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A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor (GTCE-HEMT) with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 mS/mm, and subthreshold slope of 85 mV/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage (VB) is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode (D-mode) polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits.

Study on influences of TiN capping layer on time-dependent dielectric breakdown characteristic of ultra-thin EOT high-k metal gate NMOSFET with kMC TDDB simulations

Hao Xu, Hong Yang, Wei-Chun Luo, Ye-Feng Xu, Yan-Rong Wang, Bo Tang, Wen-Wu Wang, Lu-Wei Qi, Jun-Feng Li, Jiang Yan, Hui-Long Zhu, Chao Zhao, Da-Peng Chen, Tian-Chun Ye
Chin. Phys. B 2016, 25 (8): 087305;  doi: 10.1088/1674-1056/25/8/087305
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The thickness effect of the TiN capping layer on the time dependent dielectric breakdown (TDDB) characteristic of ultra-thin EOT high-k metal gate NMOSFET is investigated in this paper. Based on experimental results, it is found that the device with a thicker TiN layer has a more promising reliability characteristic than that with a thinner TiN layer. From the charge pumping measurement and secondary ion mass spectroscopy (SIMS) analysis, it is indicated that the sample with the thicker TiN layer introduces more Cl passivation at the IL/Si interface and exhibits a lower interface trap density. In addition, the influences of interface and bulk trap density ratio Nit/Not are studied by TDDB simulations through combining percolation theory and the kinetic Monte Carlo (kMC) method. The lifetime reduction and Weibull slope lowering are explained by interface trap effects for TiN capping layers with different thicknesses.

Temperature- and voltage-dependent trap generation model in high-k metal gate MOS device with percolation simulation

Hao Xu, Hong Yang, Yan-Rong Wang, Wen-Wu Wang, Wei-Chun Luo, Lu-Wei Qi, Jun-Feng Li, Chao Zhao, Da-Peng Chen, Tian-Chun Ye
Chin. Phys. B 2016, 25 (8): 087306;  doi: 10.1088/1674-1056/25/8/087306
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High-k metal gate stacks are being used to suppress the gate leakage due to tunneling for sub-45 nm technology nodes. The reliability of thin dielectric films becomes a limitation to device manufacturing, especially to the breakdown characteristic. In this work, a breakdown simulator based on a percolation model and the kinetic Monte Carlo method is set up, and the intrinsic relation between time to breakdown and trap generation rate R is studied by TDDB simulation. It is found that all degradation factors, such as trap generation rate time exponent m, Weibull slope β and percolation factor s, each could be expressed as a function of trap density time exponent α. Based on the percolation relation and power law lifetime projection, a temperature related trap generation model is proposed. The validity of this model is confirmed by comparing with experiment results. For other device and material conditions, the percolation relation provides a new way to study the relationship between trap generation and lifetime projection.

Self-aligned-gate AlGaN/GaN heterostructure field-effect transistor with titanium nitride gate

Jia-Qi Zhang, Lei Wang, Liu-An Li, Qing-Peng Wang, Ying Jiang, Hui-Chao Zhu, Jin-Ping Ao
Chin. Phys. B 2016, 25 (8): 087308;  doi: 10.1088/1674-1056/25/8/087308
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Self-aligned-gate heterostructure field-effect transistor (HFET) is fabricated using a wet-etching method. Titanium nitride (TiN) is one kind of thermal stable material which can be used as the gate electrode. A Ti/Au cap layer is fixed on the gate and acts as an etching mask. Then the T-shaped gate is automatically formed through over-etching the TiN layer in 30% H2O2 solution at 95℃. After treating the ohmic region with an inductively coupled plasma (ICP) method, an Al layer is sputtered as an ohmic electrode. The ohmic contact resistance is approximately 0.3 Ω·mm after annealing at a low-temperature of 575℃ in N2 ambient for 1 min. The TiN gate leakage current is only 10-8 A after the low-temperature ohmic process. The access region length of the self-aligned-gate (SAG) HFET was reduced from 2 μm to 0.3 μm compared with that of the gate-first HFET. The output current density and transconductance of the device which has the same gate length and width are also increased.

Vortex quasi-crystals in mesoscopic superconducting samples Hot!

Jing-Kun Wang(王璟琨), Wei Zhang(张威), Sá de Melo C A R
Chin. Phys. B 2016, 25 (8): 087401;  doi: 10.1088/1674-1056/25/8/087401
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There seems to be a one to one correspondence between the phases of atomic and molecular matter (AMOM) and vortex matter (VM) in superfluids and superconductors. Crystals, liquids, and glasses have been experimentally observed in both AMOM and VM. Here, we propose a vortex quasi-crystal state which can be stabilized due to boundary and surface energy effects for samples of special shapes and sizes. For finite sized pentagonal samples, it is proposed that a phase transition between a vortex crystal and a vortex quasi-crystal occurs as a function of magnetic field and temperature as the sample size is reduced.

Entanglement in a two-spin system with long-range interactions

Soltani M R, Mahdavifar S, Mahmoudi M
Chin. Phys. B 2016, 25 (8): 087501;  doi: 10.1088/1674-1056/25/8/087501
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The quantum entanglement between two spins in the Ising model with an added Dzyaloshinsky-Moriya (DM) interaction and in the presence of the transverse magnetic field is studied. The exchange interaction is considered as a function of the distance between spins. The negativity as a function of magnetic field, exchange and DM interaction is calculated. The effect of the distance between spins is studied based on the negativity. In addition, the effect of the thermal fluctuation on the negativity is also investigated.

Magnetocaloric and magnetic properties of La2NiMnO6 double perovskite

Masrour R, Jabar A
Chin. Phys. B 2016, 25 (8): 087502;  doi: 10.1088/1674-1056/25/8/087502
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The magnetic effect and the magnetocaloric effect in La2NiMnO6(LNMO) double perovskite are studied using the Monte Carlo simulations. The magnetizations, specific heat values, and magnetic entropies are obtained for different exchange interactions and external magnetic fields. The adiabatic temperature is obtained. The transition temperature is deduced. The relative cooling power is established with a fixed value of exchange interaction. According to the master curve behaviors for the temperature dependence of ΔSmmax predicted for different maximum fields, in this work it is confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of a second order. The near room-temperature interaction and the superexchange interaction between Ni and Mn are shown to be due to the ferromagnetism of LNMO.

Magnetoelectric memory effect in the Y-type hexaferrite BaSrZnMgFe12O22

Fen Wang, Shi-Peng Shen, Young Sun
Chin. Phys. B 2016, 25 (8): 087503;  doi: 10.1088/1674-1056/25/8/087503
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We report on the magnetic and magnetoelectric properties of the Y-type hexaferrite BaSrZnMgFe12O22, which undergoes transitions from a collinear ferrimagnetic phase to a proper screw phase at 310 K and to a longitudinal conical phase at 45 K. Magnetic and electric measurements revealed that the magnetic structure with spiral spin order can be modified by applying a magnetic field, resulting in magnetically controllable electric polarization.It was observed that BaSrZnMgFe12O22 exhibits an anomalous magnetoelectric memory effect: the ferroelectric state can be partially recovered from the paraelectric phase with collinear spin structure by reducing magnetic field at 20 K. We ascribe this memory effect to the pinning of multiferroic domain walls, where spin chirality and structure are preserved even in the nonpolar collinear spin state.

Electron trapping properties at HfO2/SiO2 interface, studied by Kelvin probe force microscopy and theoretical analysis

Man-Hong Zhang
Chin. Phys. B 2016, 25 (8): 087701;  doi: 10.1088/1674-1056/25/8/087701
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Electron trapping properties at the HfO2/SiO2 interface have been measured through Kelvin Probe force microscopy, between room temperature and 90℃. The electron diffusion in HfO2 shows a multiple-step process. After injection, electrons diffuse quickly toward the HfO2/SiO2 interface and then diffuse laterally near the interface in two sub-steps: The first is a fast diffusion through shallow trap centers and the second is a slow diffusion through deep trap centers. Evolution of contact potential difference profile in the fast lateral diffusion sub-step was simulated by solving a diffusion equation with a term describing the charge loss. In this way, the diffusion coefficient and the average life time at different temperatures were extracted. A value of 0.57 eV was calculated for the activation energy of the shallow trap centers in HfO2.

Enhanced energy storage behaviors in free-standing antiferroelectric Pb(Zr0.95Ti0.05)O3 thin membranes

Zheng-Hu Zuo, Qing-Feng Zhan, Bin Chen, Hua-Li Yang, Yi-Wei Liu, Lu-Ping Liu, Ya-Li Xie, Run-Wei Li
Chin. Phys. B 2016, 25 (8): 087702;  doi: 10.1088/1674-1056/25/8/087702
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Free-standing antiferroelectric Pb(Zr0.95Ti0.05)O3 (PZT(95/5)) thin film is fabricated on 200-nm-thick Pt foil by using pulsed laser deposition. X-ray diffraction patterns indicate that free-standing PZT(95/5) film possesses an a-axis preferred orientation. The critical electric field for the 300-nm-thick free-standing PZT(95/5) film transiting from antiferroelectric to ferroelectric phases is increased to 770 kV/cm, but its saturation polarization remains almost unchanged as compared with that of the substrate-clamped PZT(95/5) film. The energy storage density and energy efficiency of the substrate-clamped PZT(95/5) film are 6.49 J/cm3 and 54.5%, respectively. In contrast, after removing the substrate, the energy storage density and energy efficiency of the free-standing PZT(95/5) film are enhanced up to 17.45 J/cm3 and 67.9%, respectively.

Exciton-phonon interaction in Al0.4Ga0.6N/Al0.53Ga0.47N multiple quantum wells

Ya-Li Liu, Peng Jin, Gui-Peng Liu, Wei-Ying Wang, Zhi-Qiang Qi, Chang-Qing Chen, Zhan-Guo Wang
Chin. Phys. B 2016, 25 (8): 087801;  doi: 10.1088/1674-1056/25/8/087801
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The exciton-phonon interaction in Al0.4Ga0.6N/Al0.53Ga0.47N multiple quantum wells (MQWs) is studied by deep-ultraviolet time-integrated and time-resolved photoluminescence (PL). Up to four longitudinal-optical (LO) phonon replicas of exciton recombination are observed, indicating the strong coupling of excitons with LO phonons in the MQWs. Moreover, the exciton-phonon coupling strength in the MQWs is quantified by the Huang-Rhys factor, and it keeps almost constant in a temperature range from 10 K to 120 K. This result can be explained in terms of effects of fluctuations in the well thickness in the MQWs and the temperature on the exciton-phonon interaction.

Microtrap on a concave grating reflector for atom trapping

Hui Zhang, Tao Li, Ya-Ling Yin, Xing-Jia Li, Yong Xia, Jian-Ping Yin
Chin. Phys. B 2016, 25 (8): 087802;  doi: 10.1088/1674-1056/25/8/087802
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We propose a novel scheme of optical confinement for atoms by using a concave grating reflector. The two-dimension grating structure with a concave surface shape exhibits strong focusing ability under radially polarized illumination. Especially, the light intensity at the focal point is about 100 times higher than that of the incident light. Such a focusing optical field reflected from the curved grating structure can provide a deep potential to trap cold atoms. We discuss the feasibility of the structure serving as an optical dipole trap. Our results are as follows. (i) Van der Waals attraction potential to the surface of the structure has a low effect on trapped atoms. (ii) The maximum trapping potential is ~1.14 mK in the optical trap, which is high enough to trap cold 87Rb atoms from a standard magneto-optical trap with a temperature of 120 μK, and the maximum photon scattering rate is lower than 1/s. (iii) Such a microtrap array can also manipulate and control cold molecules, or microscopic particles.
SPECIAL TOPIC—Soft matter and biological physics (Review)
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Ultra-wideband reflective polarization converter based on anisotropic metasurface

Jia-Liang Wu, Bao-Qin Lin, Xin-Yu Da
Chin. Phys. B 2016, 25 (8): 088101;  doi: 10.1088/1674-1056/25/8/088101
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In this paper, we propose an ultra-wideband reflective linear cross-polarization converter based on anisotropic metasurface. Its unit cell is composed of a square-shaped resonator with intersectant diagonal and metallic ground sheet separated by dielectric substrate. Simulated results show that the converter can generate resonances at four frequencies under normal incident electromagnetic (EM) wave, leading to the bandwidth expansion of cross-polarization reflection. For verification, the designed polarization converter is fabricated and measured. The measured and simulated results agree well with each other, showing that the fabricated converter can convert x- or y-polarized incident wave into its cross polarized wave in a frequency range from 7.57 GHz to 20.46 GHz with a relative bandwidth of 91.2%, and the polarization conversion efficiency is greater than 90%. The proposed polarization converter has a simple geometry but an ultra wideband compared with the published designs, and hence possesses potential applications in novel polarization-control devices.

Preparation of patterned boron nanowire films with different widths of unit-cell and their field emission properties

Yong-Xin Zhang, Fei Liu, Cheng-Min Shen, Jun Li, Shao-Zhi Deng, Ning-Sheng Xu, Hong-Jun Gao
Chin. Phys. B 2016, 25 (8): 088102;  doi: 10.1088/1674-1056/25/8/088102
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Large-area patterned films of boron nanowires (BNWs) are fabricated at various densities by chemical vapor deposition (CVD). Different widths of unit-cell of Mo masks are used as templates. The widths of unit-cell of Mo masks are 100 μm, 150 μm, and 200 μm, respectively. The distance between unit cells is 50 μm. The BNWs have an average diameter of about 20 nm and lengths of 10 μm-20 μm. High-resolution transmission electron microscopy analysis shows that each nanowire has a β-tetragonal structure with good crystallization. Field emission measurements of the BNW films show that their turn-on electric fields decrease with width of unit-cell increasing.

Enhanced biocompatibility of ZnS:Mn quantum dots encapsulated with Aloe vera extract for therapeutic applications

Anilkumar M, Bindu K R, Sneha Saj A, Anila E I
Chin. Phys. B 2016, 25 (8): 088103;  doi: 10.1088/1674-1056/25/8/088103
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Toxicity of nanoparticles remains to be a major issue in their application to the biomedical field. Aloe vera (AV) is one of the most widely exploited medicinal plants that have a multitude of amazing properties in the field of medicine. Methanol extract of Aloe vera can be used as a novel stabilising agent for quantum dots to reduce toxicity. We report the synthesis, structural characterization, antibacterial activity and cytotoxicity studies of ZnS:Mn quantum dots synthesized by the colloidal precipitation method, using methanol extract of Aloe vera (AVME) as the capping agent. The ZnS:Mn quantum dots capped with AVME exhibit superior performances in biocompatibility and antibacterial activity compared with ZnS:Mn quantum dots without encapsulation.

Effects of Mg on diamond growth and properties in Fe-C system under high pressure and high temperature condition

Guo-Feng Huang, You-Jin Zheng, Zhan-Chang Li, Qiang Gao, Zhuo Ma, Si-Ming Shi, Bao-Gang Jiang, He Zhao
Chin. Phys. B 2016, 25 (8): 088104;  doi: 10.1088/1674-1056/25/8/088104
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Diamond crystal crystallized in Fe-Mg-C system with Archimedes buoyancy as a driving force is established under high pressure and high temperature conditions. The experimental results indicate that the addition of the Mg element results in the nitrogen concentration increasing from 87 ppm to 271 ppm in the diamond structure. The occurrence of the 100 plane reveals that the surface character is remarkably changed due to the addition of Mg. Micro-Raman spectra indicate that the half width of full maximum is in a range of 3.01 cm-1-3.26 cm-1, implying an extremely good quality of diamond specimens in crystallization.

Correlation of polishing-induced shallow subsurface damages with laser-induced gray haze damages in fused silica optics

Xiang He, Heng Zhao, Gang Wang, Peifan Zhou, Ping Ma
Chin. Phys. B 2016, 25 (8): 088105;  doi: 10.1088/1674-1056/25/8/088105
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Laser-induced damage in fused silica optics greatly restricts the performances of laser facilities. Gray haze damage, which is always initiated on ceria polished optics, is one of the most important damage morphologies in fused silica optics. In this paper, the laser-induced gray haze damages of four fused silica samples polished with CeO2, Al2O3, ZrO2, and colloidal silica slurries are investigated. Four samples all present gray haze damages with much different damage densities. Then, the polishing-induced contaminant and subsurface damages in four samples are analyzed. The results reveal that the gray haze damages could be initiated on the samples without Ce contaminant and are inclined to show a tight correlation with the shallow subsurface damages.

Novel Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites: High-efficiency and magnetic recyclable catalysts for organic dye degradation

Chao Li, Jun-Jie Sun, Duo Chen, Guang-Bing Han, Shu-Yun Yu, Shi-Shou Kang, Liang-Mo Mei
Chin. Phys. B 2016, 25 (8): 088201;  doi: 10.1088/1674-1056/25/8/088201
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A facile step-by-step approach is developed for synthesizing the high-efficiency and magnetic recyclable Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites. This method involves coating Fe2O3 nanorods with a uniform silica layer, reduction in 10% H2/Ar atmosphere to transform the Fe2O3 into magnetic Fe3O4, and finally depositing Ag@Ni core-shell nanoparticles on the L-lysine modified surface of Fe3O4@SiO2 nanorods. The fabricated nanocomposites are further characterized by x-ray diffraction, transmission electron microscopy, scanning electron microscope, Fourier transform infrared spectroscopy, and inductively coupled plasma mass spectroscopy. The Fe3O4@SiO2@Ag@Ni trepang-like nanocomposites exhibit remarkably higher catalytic efficiency than monometallic Fe3O4@SiO2@Ag nanocomposites toward the degradation of Rhodamine B (RhB) at room temperature, and maintain superior catalytic activity even after six cycles. In addition, these samples could be easily separated from the catalytic system by an external magnet and reused, which shows great potential applications in treating waste water.

Metallic spherical anechoic chamber for antenna pattern measurement

Ali Farahbakhsh, Mohammad Khalaj-Amirhosseini
Chin. Phys. B 2016, 25 (8): 088401;  doi: 10.1088/1674-1056/25/8/088401
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Anechoic chambers are used for indoor antenna measurements. The common method of constructing an anechoic chamber is to cover all inside walls by the electromagnetic absorbers. In this paper, a fully metallic spherical chamber structure is presented in which the propagation of the electromagnetic waves inside the chamber is controlled and they are guided to an absorber. In the proposed method, an appropriate quiet zone is obtained, and unlike ordinary anechoic chambers, the absorber usage amount is reduced greatly. The performance of the chamber is evaluated by simulation. The results show that the proposed method could provide a useful technique for the indoor antenna measurements.

Compensation of body shake errors in terahertz beam scanning single frequency holography for standoff personnel screening

Wei Liu, Chao Li, Zhao-Yang Sun, Yu Zhao, Shi-You Wu, Guang-You Fang
Chin. Phys. B 2016, 25 (8): 088402;  doi: 10.1088/1674-1056/25/8/088402
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In the terahertz (THz) band, the inherent shake of the human body may strongly impair the image quality of a beam scanning single frequency holography system for personnel screening. To realize accurate shake compensation in imaging processing, it is quite necessary to develop a high-precision measure system. However, in many cases, different parts of a human body may shake to different extents, resulting in greatly increasing the difficulty in conducting a reasonable measurement of body shake errors for image reconstruction. In this paper, a body shake error compensation algorithm based on the raw data is proposed. To analyze the effect of the body shake on the raw data, a model of echoed signal is rebuilt with considering both the beam scanning mode and the body shake. According to the rebuilt signal model, we derive the body shake error estimated method to compensate for the phase error. Simulation on the reconstruction of point targets with shake errors and proof-of-principle experiments on the human body in the 0.2-THz band are both performed to confirm the effectiveness of the body shake compensation algorithm proposed.

Fabrication of Al/AlOx/Al junctions using pre-exposure technique at 30-keV e-beam voltage

Dong Lan, Guangming Xue, Qiang Liu, Xinsheng Tan, Haifeng Yu, Yang Yu
Chin. Phys. B 2016, 25 (8): 088501;  doi: 10.1088/1674-1056/25/8/088501
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We fabricate high-quality Al/AlOx/Al junctions using improved bridge and bridge-free techniques at 30-keV e-beam voltage, in which the length of undercut and the size of junction can be well controlled by the pre-exposure technique. The dose window is 5 times as large as that used in the usual Dolan bridge technique, making this technique much more robust. Similar results, comparable with those achieved using a 100-keV e-beam writer, are obtained, which indicate that the 30-keV e-beam writer could be an economic choice for the superconducting qubit fabrication.

Modeling of trap-assisted tunneling on performance of charge trapping memory with consideration of trap position and energy level

Zhi-Yuan Lun, Yun Li, Kai Zhao, Gang Du, Xiao-Yan Liu, Yi Wang
Chin. Phys. B 2016, 25 (8): 088502;  doi: 10.1088/1674-1056/25/8/088502
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In this work, the trap-assisted tunneling (TAT) mechanism is modeled as a two-step physical process for charge trapping memory (CTM). The influence of the TAT mechanism on CTM performance is investigated in consideration of various trap positions and energy levels. For the simulated CTM structure, simulation results indicate that the positions of oxide traps related to the maximum TAT current contribution shift towards the substrate interface and charge storage layer interface during time evolutions in programming and retention operations, respectively. Lower programming voltage and retention operations under higher temperature are found to be more sensitive to tunneling oxide degradation.

Improvement in the electrical performance and bias-stress stability of dual-active-layered silicon zinc oxide/zinc oxide thin-film transistor

Yu-Rong Liu, Gao-Wei Zhao, Pai-To Lai, Ruo-He Yao
Chin. Phys. B 2016, 25 (8): 088503;  doi: 10.1088/1674-1056/25/8/088503
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Si-doped zinc oxide (SZO) thin films are deposited by using a co-sputtering method, and used as the channel active layers of ZnO-based TFTs with single and dual active layer structures. The effects of silicon content on the optical transmittance of the SZO thin film and electrical properties of the SZO TFT are investigated. Moreover, the electrical performances and bias-stress stabilities of the single- and dual-active-layer TFTs are investigated and compared to reveal the effects of the Si doping and dual-active-layer structure. The average transmittances of all the SZO films are about 90% in the visible light region of 400 nm-800 nm, and the optical band gap of the SZO film gradually increases with increasing Si content. The Si-doping can effectively suppress the grain growth of ZnO, revealed by atomic force microscope analysis. Compared with that of the undoped ZnO TFT, the off-state current of the SZO TFT is reduced by more than two orders of magnitude and it is 1.5×10-12 A, and thus the on/off current ratio is increased by more than two orders of magnitude. In summary, the SZO/ZnO TFT with dual-active-layer structure exhibits a high on/off current ratio of 4.0×106 and superior stability under gate-bias and drain-bias stress.

Analysis of the damage threshold of the GaAs pseudomorphic high electron mobility transistor induced by the electromagnetic pulse

Xiao-Wen Xi, Chang-Chun Chai, Yang Liu, Yin-Tang Yang, Qing-Yang Fan, Chun-Lei Shi
Chin. Phys. B 2016, 25 (8): 088504;  doi: 10.1088/1674-1056/25/8/088504
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An electromagnetic pulse (EMP)-induced damage model based on the internal damage mechanism of the GaAs pseudomorphic high electron mobility transistor (PHEMT) is established in this paper. With this model, the relationships among the damage power, damage energy, pulse width and signal amplitude are investigated. Simulation results show that the pulse width index from the damage power formula obtained here is higher than that from the empirical formula due to the hotspot transferring in the damage process of the device. It is observed that the damage energy is not a constant, which decreases with the signal amplitude increasing, and then changes little when the signal amplitude reaches up to a certain level.

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

Ping Qin, Wei-Dong Song, Wen-Xiao Hu, Yuan-Wen Zhang, Chong-Zhen Zhang, Ru-Peng Wang, Liang-Liang Zhao, Chao Xia, Song-Yang Yuan, Yi-an Yin, Shu-Ti Li, Shi-Chen Su
Chin. Phys. B 2016, 25 (8): 088505;  doi: 10.1088/1674-1056/25/8/088505
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We investigate the performances of the near-ultraviolet (about 350 nm-360 nm) light-emitting diodes (LEDs) each with specifically designed irregular sawtooth electron blocking layer (EBL) by using the APSYS simulation program. The internal quantum efficiencies (IQEs), light output powers, carrier concentrations in the quantum wells, energy-band diagrams, and electrostatic fields are analyzed carefully. The results indicate that the LEDs with composition-graded p-AlxGa1-xN irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs. The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface, which results in less electron leakage and better hole injection efficiency, thus reducing efficiency droop and enhancing the radiative recombination rate.

Effect of a force-free end on the mechanical property of a biopolymer–A path integral approach

Zicong Zhou, Béla Joós
Chin. Phys. B 2016, 25 (8): 088701;  doi: 10.1088/1674-1056/25/8/088701
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We study the effect of a force-free end on the mechanical property of a stretched biopolymer. The system can be divided into two parts. The first part consists of the segment counted from the fixed point (i.e., the origin) to the forced point in the biopolymer, with arclength Lf. The second part consists of the segment counted from the forced point to the force-free end with arclength ΔL. We apply the path integral technique to find the relationship between these two parts. At finite temperature and without any constraint at the end, we show exactly that if we focus on the quantities related to the first part, then we can ignore the second part completely. Monte Carlo simulation confirms this conclusion. In contrast, the effect for the quantities related to the second part is dependent on what we want to observe. A force-free end has little effect on the relative extension, but it affects seriously the value of the end-to-end distance if ΔL is comparable to Lf.

Sodium chloride methanol solution spin-coating process for bulk-heterojunction polymer solar cells

Tong-Fang Liu, Yu-Feng Hu, Zhen-Bo Deng, Xiong Li, Li-Jie Zhu, Yue Wang, Long-Feng Lv, Tie-Ning Wang, Zhi-Dong Lou, Yan-Bing Hou, Feng Teng
Chin. Phys. B 2016, 25 (8): 088801;  doi: 10.1088/1674-1056/25/8/088801
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The sodium chloride methanol solution process is conducted on the conventional poly(3-hexylthiophene) (P3HT)/[6, 6]-phenyl-C61-butyric acid methyl ester (PC61BM) polymer bulk heterojunction solar cells. The device exhibits a power conversion efficiency of up to 3.36%, 18% higher than that of the device without the solution process. The measurements of the active layer by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and ultraviolet photoelectron spectroscopy (UPS) indicate a slight phase separation in the vertical direction and a sodium chloride distributed island-like interface between the active layer and the cathode. The capacitance-voltage (C-V) and impedance spectroscopy measurements prove that the sodium chloride methanol process can reduce the electron injection barrier and improve the interfacial contact of polymer solar cells. Therefore, this one-step solution process not only optimizes the phase separation in the active layers but also forms a cathode buffer layer, which can enhance the generation, transport, and collection of photogenerated charge carriers in the device simultaneously. This work indicates that the inexpensive and non-toxic sodium chloride methanol solution process is an efficient one-step method for the low cost manufacturing of polymer solar cells.

Influence of bus stop with left-turn lines between two adjacent signalized intersections

Ming-Bao Pang, Lan-Hang Ye, Ya-Nan Pei
Chin. Phys. B 2016, 25 (8): 088901;  doi: 10.1088/1674-1056/25/8/088901
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Based on the symmetric two-lane Nagel-Schreckenberg (STNS) model, a three-lane cellular automaton model between two intersections containing a bus stop with left-turning buses is established in which model the occurrences of vehicle accidents are taken into account. The characteristics of traffic flows with different ratios of left-turn lines are discussed via the simulation experiments. The results indicate that the left-turn lines have more negative effects on capacity, accident rate as well as delay if the stop is located close to the intersections, where the negative effect in a near-side stop is more severe than that in a far-side one. The range of appropriate position for a bus stop without the bottleneck effect becomes more and more narrow with the increase of the ratio of left-turn bus lines. When the inflow is small, a short signal cycle and a reasonable offset are beneficial. When the inflow reaches or exceeds the capacity, a longer signal cycle is helpful. But if the stop position is inappropriate, the increase of cycle fails in reducing the negative effect of left-turning buses and the effectiveness of offset is weakened.

Optimized routing strategy for complex network with multiple priorities

Shi-Bao Li, Zong-Xing Sun, Jian-Hang Liu, Hai-Hua Chen
Chin. Phys. B 2016, 25 (8): 088902;  doi: 10.1088/1674-1056/25/8/088902
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Different loads in the network require distinct QoS standard, while present routing strategies for complex networks ignored this fact. To solve this problem, we designed a routing strategy RS-MP with multiple priorities by which packets are classified into privileged-packets and common-packets. In RS-MP, privileged-packets route by the Shortest Path Algorithm, and do not need to queue up. Common-packets' routes are determined by a new factor BJmax of the network. The BJmax stands for the largest betweenness centrality. By minimizing BJmax, the throughout capacity of the network can be maximized. The simulation results show that RS-MP can guarantee privileged-packets with the shortest path length and smallest delay, and maximized throughout capacity for common packets in the no-congestion state.
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