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Electron localization of linear symmetric molecular ion H32+
Zheng-Mao Jia(贾正茂), Zhi-Nan Zeng(曾志男), Ru-Xin Li(李儒新)
Chin. Phys. B, 2017, 26 (1): 013203
Energy sharing induced by the nonlinear interaction
Yuan Liu(刘渊), Zhifang Feng(冯志芳), Weidong Li(李卫东)
Chin. Phys. B, 2017, 26 (1): 013401
Implementation of LDA+Gutzwiller with Newton's method
Jian Zhang(张健), Ming-Feng Tian(田明锋), Guang-Xi Jin(金光希), Yuan-Feng Xu(徐远锋), Xi Dai(戴希)
Chin. Phys. B, 2017, 26 (1): 017103
Chin. Phys. B  
  Chin. Phys. B--2017, Vol.26, No.1
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TOPICAL REVIEW — Amorphous physics and materials

Granular packing as model glass formers

Yujie Wang(王宇杰)
Chin. Phys. B, 2017, 26 (1): 014503 doi: 10.1088/1674-1056/26/1/014503
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Static granular packings are model hard-sphere glass formers. The nature of glass transition has remained a hotly debated issue. We review recent experimental progresses in using granular materials to study glass transitions. We focus on the growth of glass order with five-fold symmetry in granular packings and relate the findings to both geometric frustration and random first-order phase transition theories.

Five-fold local symmetry in metallic liquids and glasses

M Z Li(李茂枝), H L Peng(彭海龙), Y C Hu(胡远超), F X Li(李福祥), H P Zhang(张华平), W H Wang(汪卫华)
Chin. Phys. B, 2017, 26 (1): 016104 doi: 10.1088/1674-1056/26/1/016104
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The structure of metallic glasses has been a long-standing mystery. Owing to the disordered nature of atomic structures in metallic glasses, it is a great challenge to find a simple structural description, such as periodicity for crystals, for establishing the structure-property relationship in amorphous materials. In this paper, we briefly review the recent developments of the five-fold local symmetry in metallic liquids and glasses and the understanding of the structure-property relationship based on this parameter. Experimental evidence demonstrates that five-fold local symmetry is found to be general in metallic liquids and glasses. Comprehensive molecular dynamics simulations show that the temperature evolution of five-fold local symmetry reflects the structural evolution in glass transition in cooling process, and the structure-property relationship such as relaxation dynamics, dynamic crossover phenomena, glass transition, and mechanical deformation in metallic liquids and glasses can be well understood base on the simple and general structure parameter of five-fold local symmetry.

Interstitialcy theory of condensed matter states and its application to non-crystalline metallic materials

V A Khonik
Chin. Phys. B, 2017, 26 (1): 016401 doi: 10.1088/1674-1056/26/1/016401
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A comprehensive review of a novel promising framework for the understanding of non-crystalline metallic materials, i.e., interstitialcy theory of condensed matter states (ITCM), is presented. The background of the ITCM and its basic results for equilibrium/supercooled liquids and glasses are given. It is emphasized that the ITCM provides a new consistent, clear, and testable approach, which uncovers the generic relationship between the properties of the maternal crystal, equilibrium/supercooled liquid and glass obtained by melt quenching.

Secondary relaxation and dynamic heterogeneity in metallic glasses: A brief review

J C Qiao(乔吉超), Q Wang, D Crespo, Y Yang(杨勇), J M Pelletier
Chin. Phys. B, 2017, 26 (1): 016402 doi: 10.1088/1674-1056/26/1/016402
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Understanding mechanical relaxation, such as primary (α) and secondary (β) relaxation, is key to unravel the intertwined relation between the atomic dynamics and non-equilibrium thermodynamics in metallic glasses. At a fundamental level, relaxation, plastic deformation, glass transition, and crystallization of metallic glasses are intimately linked to each other, which can be related to atomic packing, inter-atomic diffusion, and cooperative atom movement. Conceptually, β relaxation is usually associated with structural heterogeneities intrinsic to metallic glasses. However, the details of such structural heterogeneities, being masked by the meta-stable disordered long-range structure, are yet to be understood. In this paper, we briefly review the recent experimental and simulation results that were attempted to elucidate structural heterogeneities in metallic glasses within the framework of β relaxation. In particular, we will discuss the correlation among β relaxation, structural heterogeneity, and mechanical properties of metallic glasses.

Multiscale structures and phase transitions in metallic glasses: A scattering perspective

Si Lan(兰司), Zhenduo Wu(吴桢舵), Xun-Li Wang(王循理)
Chin. Phys. B, 2017, 26 (1): 017104 doi: 10.1088/1674-1056/26/1/017104
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Amorphous materials are ubiquitous and widely used in human society, yet their structures are far from being fully understood. Metallic glasses, a new class of amorphous materials, have attracted a great deal of interests due to their exceptional properties. In recent years, our understanding of metallic glasses increases dramatically, thanks to the development of advanced instrumentation, such as in situ x-ray and neutron scattering. In this article, we provide a brief review of recent progress in study of the structure of metallic glasses. In particular, we will emphasize, from the scattering perspective, the multiscale structures of metallic glasses, i.e., short-to-medium range atomic packing, and phase transitions in the supercooled liquid region, e.g., crystallization and liquid-to-liquid phase transition. We will also discuss, based on the understanding of their structures and phase stability, the mechanical and magnetic properties of metallic glasses.

Amorphous phase formation rules in high-entropy alloys

Qiu-Wei Xing(邢秋玮), Yong Zhang(张勇)
Chin. Phys. B, 2017, 26 (1): 018104 doi: 10.1088/1674-1056/26/1/018104
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There have been many interesting studies on high-entropy alloys (HEAs), also known as multi-component (MC) alloys (MCAs), in recent years. MC metallic-glasses (MGs) have shown the potential to express the advantages of MCAs and MGs in tandem. Amorphous phase formation rules are a crucial issue in the HEA and MCA field. For equal or near-equal atomic ratio alloys, mixed-entropy among the elements has a significant effect on the phase formation. This paper focuses on HEA amorphous phase formation rules. In the first two sections, the recent progress in amorphous phase formation in HEAs and MCAs is reviewed, including the effective factors and correlative parameters related to amorphous phase formation. In the third section, novel MCMGs including high-entropy (HE) bulk-metallic-glass (HE-BMG) and MCMG films developed in recent decades are summarized, and the giant-magnetic-impedance (GMI) effect of MC amorphous fibers is discussed.

Universal properties of relaxation and diffusion in condensed matter

K L Ngai(倪嘉陵)
Chin. Phys. B, 2017, 26 (1): 018105 doi: 10.1088/1674-1056/26/1/018105
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By and large the research communities today are not fully aware of the remarkable universality in the dynamic properties of many-body relaxation/diffusion processes manifested in experiments and simulations on condensed matter with diverse chemical compositions and physical structures. I shall demonstrate the universality first from the dynamic processes in glass-forming systems. This is reinforced by strikingly similar properties of different processes in contrasting interacting systems all having nothing to do with glass transition. The examples given here include glass-forming systems of diverse chemical compositions and physical structures, conductivity relaxation of ionic conductors (liquid, glassy, and crystalline), translation and orientation ordered phase of rigid molecule, and polymer chain dynamics. Universality is also found in the change of dynamics when dimension is reduced to nanometer size in widely different systems. The remarkable universality indicates that many-body relaxation/diffusion is governed by fundamental physics to be unveiled. One candidate is classical chaos on which the coupling model is based, Universal properties predicted by this model are in accord with diverse experiments and simulations.

SPECIAL TOPIC — Amorphous physics and materials

Effect of icosahedral clusters on β-relaxations in metallic glasses

X Q Gao(高选乔), Y T Sun(孙奕韬), Z Wang(王峥), M Z Li(李茂枝), H Y Bai(白海洋)
Chin. Phys. B, 2017, 26 (1): 016101 doi: 10.1088/1674-1056/26/1/016101
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The most pronounced β-relaxation was found in the Y-based binary metallic glasses (MGs). The correlation between β-relaxation and local atomic structure was studied. The dynamic mechanical measurements were performed for three chosen binary systems:Zr-, Ti-, and Y-based MGs. The experimental results show that, in each system,the larger negative enthalpy of mixing (ΔHm) between the component elements makes β-relaxation become more pronounced. The less negative value of ΔHm facilitates the formation of icosahedral clusters, which have a pinning effect on the excitation of β-relaxations and correspondingly make the β-relaxation become less pronounced. These chemical effects on β-relaxations can only be compared in the same MG system, and it is not suitable for the comparison between different systems due to the different features of the major metallic elements.

LaGa-based bulk metallic glasses

Lin-Zhi Zhao(赵林志), Rong-Jie Xue(薛荣洁), Wei-Hua Wang(汪卫华), Hai-Yang Bai(白海洋)
Chin. Phys. B, 2017, 26 (1): 018106 doi: 10.1088/1674-1056/26/1/018106
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We report the formation of LaGa-based bulk metallic glasses. Ternary La-Ga-Cu glassy rods of 2-3 mm in diameter can be easily formed in a wide composition range by the conventional copper mold casting method. With minor addition of extra elements such as Co, Ni, Fe, Nb, Y, and Zr, the critical diameter of the full glassy rods of the La-Ga-Cu matrix can be markedly enhanced to at least 5 mm. The characteristics and properties of these new LaGa-based bulk metallic glasses with excellent glass formation ability and low glass transition temperature are model systems for fundamental issues investigation and could have some potential applications in micromachining field.


Electron localization of linear symmetric molecular ion H32+ Hot!

Zheng-Mao Jia(贾正茂), Zhi-Nan Zeng(曾志男), Ru-Xin Li(李儒新)
Chin. Phys. B, 2017, 26 (1): 013203 doi: 10.1088/1674-1056/26/1/013203
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Electron localization in the dissociation of the symmetric linear molecular ion H32+ is investigated. The numerical simulation shows that the electron localization distribution is dependent on the central frequency and peak electric field amplitude of the external ultrashort ultraviolet laser pulse. When the electrons of the ground state are excited onto the 2pσ2Σu+ by a one-photon process, most electrons of the dissociation states are localized at the protons on both sides symmetrically. Almost no electron is stabilized at the middle proton due to the odd symmetry of the wave function. With the increase of the frequency of the external ultraviolet laser pulse, the electron localization ratio of the middle proton increases, for more electrons of the ground state are excited onto the higher 3pσ2Σu+ state. 50.9% electrons of all the dissociation events can be captured by the middle Coulomb potential well through optimizing the central frequency and peak electric field amplitude of the ultraviolet laser pulse. Besides, a direct current (DC) electric field can be utilized to control the electron motions of the dissociation states after the excitation of an ultraviolet laser pulse, and 68.8% electrons of the dissociation states can be controlled into the middle proton.

Energy sharing induced by the nonlinear interaction Hot!

Yuan Liu(刘渊), Zhifang Feng(冯志芳), Weidong Li(李卫东)
Chin. Phys. B, 2017, 26 (1): 013401 doi: 10.1088/1674-1056/26/1/013401
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Strong energy sharing is shown by numerically investigating coupled multi-component Bose-Einstein condensates (BECs) with a harmonic trap to simulate the Fermi-Pasta-Ulam model (FPU). For two-component BECs, the energy exchanging between each part, from regular, quantum beating to complete energy sharing, is explored by simulating their Husimi distributions, the time evolution of energies and the statistical entropy. Meanwhile, in the three-component case, a more complex energy sharing behavior is reported and a strong energy sharing is found.


Search algorithm on strongly regular graphsbased on scattering quantum walks

Xi-Ling Xue(薛希玲), Zhi-Hao Liu(刘志昊), Han-Wu Chen(陈汉武)
Chin. Phys. B, 2017, 26 (1): 010301 doi: 10.1088/1674-1056/26/1/010301
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Janmark, Meyer, and Wong showed that continuous-time quantum walk search on known families of strongly regular graphs (SRGs) with parameters (N,k,λ,μ) achieves full quantum speedup. The problem is reconsidered in terms of scattering quantum walk, a type of discrete-time quantum walks. Here, the search space is confined to a low-dimensional subspace corresponding to the collapsed graph of SRGs. To quantify the algorithm's performance, we leverage the fundamental pairing theorem, a general theory developed by Cottrell for quantum search of structural anomalies in star graphs. The search algorithm on the SRGs with k scales as N satisfies the theorem, and results can be immediately obtained, while search on the SRGs with k scales as √N does not satisfy the theorem, and matrix perturbation theory is used to provide an analysis. Both these cases can be solved in O(√N) time steps with a success probability close to 1. The analytical conclusions are verified by simulation results on two SRGs. These examples show that the formalism on star graphs can be applied more generally.

Measurement-device-independent quantum cryptographic conferencing with an untrusted source

Rui-Ke Chen(陈瑞柯), Wan-Su Bao(鲍皖苏), Yang Wang(汪洋), Hai-Ze Bao(包海泽), Chun Zhou(周淳), Mu-Sheng Jiang(江木生), Hong-Wei Li(李宏伟)
Chin. Phys. B, 2017, 26 (1): 010302 doi: 10.1088/1674-1056/26/1/010302
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Measurement-device-independent quantum cryptographic conferencing (MDI-QCC) protocol puts MDI quantum key distribution (MDI-QKD) forwards to multi-party applications, and suggests a significant framework for practical multi-party quantum communication. In order to mitigate the experimental complexity of MDI-QCC and remove the key assumption (the sources are trusted) in MDI-QCC, we extend the framework of MDI-QKD with an untrusted source to MDI-QCC and give the rigorous security analysis of MDI-QCC with an untrusted source. What is more, in the security analysis we clearly provide a rigorous analytical method for parameters' estimation, which with simple modifications can be applied to not only MDI-QKD with an untrusted source but also arbitrary multi-party communication protocol with an untrusted source. The simulation results show that at reasonable distances the asymptotic key rates for the two cases (with trusted and untrusted sources) almost overlap, which indicates the feasibility of our protocol.

Speeding up transmissions of unknown quantum information along Ising-type quantum channels

W J Guo(郭伟杰), L F Wei(韦联福)
Chin. Phys. B, 2017, 26 (1): 010303 doi: 10.1088/1674-1056/26/1/010303
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Quantum teleportation with entanglement channels and a series of two-qubit SWAP gates between the nearest-neighbor qubits are usually utilized to achieve the transfers of unknown quantum state from the sender to the distant receiver. In this paper, by simplifying the usual SWAP gates we propose an approach to speed up the transmissions of unknown quantum information, specifically including the single-qubit unknown state and two-qubit unknown entangled ones, by a series of entangling and disentangling operations between the remote qubits with distant interactions. The generic proposal is demonstrated specifically with experimentally-existing Ising-type quantum channels without transverse interaction; liquid NMR-molecules driven by global radio frequency electromagnetic pulses and capacitively-coupled Josephson circuits driven by local microwave pulses. The proposal should be particularly useful to set up the connections between the distant qubits in a chip of quantum computing.

A self-cited pixel summation based image encryption algorithm

Guo-Dong Ye(叶国栋), Xiao-Ling Huang(黄小玲), Leo Yu Zhang(张愉), Zheng-Xia Wang(王政霞)
Chin. Phys. B, 2017, 26 (1): 010501 doi: 10.1088/1674-1056/26/1/010501
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In this paper, a novel image encryption algorithm is presented based on self-cited pixel summation. With the classical mechanism of permutation plus diffusion, a pixel summation of the plain image is employed to make a gravity influence on the pixel positions in the permutation stage. Then, for each pixel in every step of the diffusion stage, the pixel summation calculated from the permuted image is updated. The values from a chaotic sequence generated by an intertwining logistic map are selected by this summation. Consequently, the keystreams generated in both stages are dependent on both the plain image and the permuted image. Because of the sensitivity of the chaotic map to its initial conditions and the plain-image-dependent keystreams, any tiny change in the secret key or the plain image would lead to a significantly different cipher image. As a result, the proposed encryption algorithm is immune to the known plaintext attack (KPA) and the chosen plaintext attack (CPA). Moreover, experimental simulations and security analyses show that the proposed permutation-diffusion encryption scheme can achieve a satisfactory level of security.

Uphill anomalous transport in a deterministic system with speed-dependent friction coefficient

Wei Guo(郭伟), Lu-Chun Du(杜鲁春), Zhen-Zhen Liu(刘真真), Hai Yang(杨海), Dong-Cheng Mei(梅冬成)
Chin. Phys. B, 2017, 26 (1): 010502 doi: 10.1088/1674-1056/26/1/010502
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We investigate the transport of a deterministic Brownian particle theoretically, which moves in simple one-dimensional, symmetric periodic potentials under the influence of both a time periodic and a static biasing force. The physical system employed contains a friction coefficient that is speed-dependent. Within the tailored parameter regime, the absolute negative mobility, in which a particle can travel in the direction opposite to a constant applied force, is observed. This behavior is robust and can be maximized at two regimes upon variation of the characteristic factor of friction coefficient. Further analysis reveals that this uphill motion is subdiffusion in terms of localization (diffusion coefficient with the form D(t)~t-1 at long times). We also have observed the non-trivially anomalous subdiffusion which is significantly deviated from the localization; whereas most of the downhill motion evolves chaotically, with the normal diffusion.

Optimal quantum parameter estimation of two-qutrit Heisenberg XY chain under decoherence

Hong-ying Yang(杨洪应), Qiang Zheng(郑强), Qi-jun Zhi(支启军)
Chin. Phys. B, 2017, 26 (1): 010601 doi: 10.1088/1674-1056/26/1/010601
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Adopting the Milburn decoherence model, we investigate the performance of quantum Fisher information of the two-qutrit isotropic Heisenberg XY chain under decoherence. We find that the quantum Fisher information with respect to the decoherence rate and the magnetic field decreases exponentially in the long-time limit, which significantly reduces the precision of optimal quantum estimation. We also show that with the increase of the decoherence rate or the magnetic field, the QFIs go down considerably. Furthermore, we find that the precision of optimal quantum estimation can be enhanced by the entanglement in the input state.

Ultralow detection limit of giant magnetoresistance biosensor using Fe3O4-graphene composite nanoparticle label

Jie Xu(徐洁), Ji-qing Jiao(焦吉庆), Qiang Li(李强), Shan-dong Li(李山东)
Chin. Phys. B, 2017, 26 (1): 010701 doi: 10.1088/1674-1056/26/1/010701
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A special Fe3O4 nanoparticles-graphene (Fe3O4-GN) composite as a magnetic label was employed for biodetection using giant magnetoresistance (GMR) sensors with a Wheatstone bridge. The Fe3O4-GN composite exhibits a strong ferromagnetic behavior with the saturation magnetization MS of approximately 48 emu/g, coercivity HC of 200 Oe, and remanence Mr of 8.3 emu/g, leading to a large magnetic fringing field. However, the Fe3O4 nanoparticles do not aggregate together, which can be attributed to the pinning and separating effects of graphene sheet to the magnetic particles. The Fe3O4-GN composite is especially suitable for biodetection as a promising magnetic label since it combines two advantages of large fringing field and no aggregation. As a result, the concentration x dependence of voltage difference |ΔV| between detecting and reference sensors undergoes the relationship of |ΔV|=240.5lgx+515.2 with an ultralow detection limit of 10 ng/mL (very close to the calculated limit of 7 ng/mL) and a wide detection range of 4 orders.

Morphological and electrical properties of SrTiO3/TiO2/SrTiO3 sandwich structures prepared by plasma sputtering

Saqib Jabbar, Riaz Ahmad, Paul K Chu
Chin. Phys. B, 2017, 26 (1): 010702 doi: 10.1088/1674-1056/26/1/010702
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SrTiO3 (STO) and TiO2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage (α). Insertion of a TiO2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. TiN was deposited as the top and bottom metal electrodes to form a metal-insulator metal (MIM) structure, which exhibited a very large linear capacitance density of 21 fF/um2 that decreased by increasing the thickness of the TiO2 film. The leakage current decreased with an increase in the thickness of TiO2, and for a 27-nm-thick film, the measured leakage current was 2.0×10-10 A. X-ray diffraction and Raman spectroscopy revealed that TiN, STO, and TiO2 films are crystalline and TiO2 has a dominant anatese phase structure.


Atomic structure and transition properties of H-like Al in hot and dense plasmas

Xiang-Fu Li(李向富), Gang Jiang(蒋刚), Hong-Bin Wang(王宏斌), Qian Sun(孙乾)
Chin. Phys. B, 2017, 26 (1): 013101 doi: 10.1088/1674-1056/26/1/013101
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The atomic structure and transition properties of H-like Al embedded in hot and dense plasmas are investigated using modified GRASP2K code. The plasma screening effect on the nucleus is described using the self-consistent field ion sphere model. The effective nuclear potential decreases much more quickly with increasing average free electron density, but increases slightly with increasing electron temperature. The variations of the transition energies, transition probabilities, and oscillator strengths with the free electron density and electron temperature are the same as that of the effective nuclear potential. The results reported in this work agree well with other available theoretical results and are useful for plasma diagnostics.

Electron localization of H2+ in a dc electric field

Z M Jia(贾正茂), Z N Zeng(曾志男), W T Tang(唐文涛), R X Li(李儒新)
Chin. Phys. B, 2017, 26 (1): 013201 doi: 10.1088/1674-1056/26/1/013201
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A dc electric field is utilized to steer the electron motion after the molecular ion H2+ is excited by an ultrashort ultraviolet laser pulse. The numerical simulation shows that the electron localization distribution and the dissociation control ratio are dependent on the polarization direction and amplitude of the dc electric field. Most electrons of the dissociation state move opposite to the dc electric field and stabilize at the dressed-up potential well, for the dressed-down well is occupied by the electrons of the 1sσg state.

Two-center interference in high-harmonic generation of H2+ in a combination of a mid-infrared laser field and a terahertz field

Jun Zhang(张军), Xue-Fei Pan(潘雪飞), Tong-Tong Xu(徐彤彤), Hong-Dan Zhang(张宏丹), Hui Du(杜慧), Jing Guo(郭静), Xue-Shen Liu(刘学深)
Chin. Phys. B, 2017, 26 (1): 013202 doi: 10.1088/1674-1056/26/1/013202
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We theoretically investigate the two-center interference in high-order harmonics generated from the H2+ in a combination of a mid-infrared laser and a terahertz field by numerically solving the time-dependent Schrödinger equation (TDSE). The interference minima in high-order harmonic generation (HHG) are effectively suppressed when a THz field is added. The contribution to HHG from the two separate nuclei is used to demonstrate the locating order of the harmonic minima. Furthermore, we also investigate the emission time of harmonics. The results show that the intensity of the short path around 60th order after adding a THz field is stronger than that in the mid-infrared laser field, which further illustrates the suppression of the interference minima in HHG.

Electric-field-modified Feshbach resonances in ultracold atom-molecule collision

Dong Cheng(程冬), Ya Li(李亚), Eryin Feng(凤尔银), Wuying Huang(黄武英)
Chin. Phys. B, 2017, 26 (1): 013402 doi: 10.1088/1674-1056/26/1/013402
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We present a detailed analysis of near zero-energy Feshbach resonances in ultracold collisions of atom and molecule, taking the He-PH system as an example, subject to superimposed electric and magnetic static fields. We find that the electric field can induce Feshbach resonance which cannot occur when only a magnetic field is applied, through couplings of the adjacent rotational states of different parities. We show that the electric field can shift the position of the magnetic Feshbach resonance, and change the amplitude of resonance significantly. Finally, we demonstrate that, for narrow magnetic Feshbach resonance as in most cases of ultracold atom-molecule collision, the electric field may be used to modulate the resonance, because the width of resonance in electric field scale is relatively larger than that in magnetic field scale.


Second-order temporal interference of two independent light beams at an asymmetrical beam splitter

Jianbin Liu(刘建彬), Jingjing Wang(王婧婧), Zhuo Xu(徐卓)
Chin. Phys. B, 2017, 26 (1): 014201 doi: 10.1088/1674-1056/26/1/014201
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The second-order temporal interference of classical and nonclassical light at an asymmetrical beam splitter is discussed based on two-photon interference in Feynman's path integral theory. The visibility of the second-order interference pattern is determined by the properties of the superposed light beams, the ratio between the intensities of these two light beams, and the reflectivity of the asymmetrical beam splitter. Some requirements about the asymmetrical beam splitter have to be satisfied in order to ensure that the visibility of the second-order interference pattern of nonclassical light beams exceeds the classical limit. The visibility of the second-order interference pattern of photons emitted by two independent single-photon sources is independent of the ratio between the intensities. These conclusions are important for the researches and applications in quantum optics and quantum information when an asymmetrical beam splitter is employed.

Electromagnetically induced grating in a thermal N-type four-level atomic system

Ya-Bin Dong(董雅宾), Jun-Yan Li(李俊燕), Zhi-Ying Zhou(周志英)
Chin. Phys. B, 2017, 26 (1): 014202 doi: 10.1088/1674-1056/26/1/014202
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The electromagnetically induced grating effect in thermal and cold atoms has been studied theoretically. Studies have shown that, by adjusting the parameters, the first-order diffraction efficiency of the probe beam in the cold atomic system and the thermal atomic system is 34% and 31%, respectively, which is very close to the ideal diffraction efficiency of the sinusoidal grating. However, it is more difficult to prepare the cold atomic system than to prepare the thermal atomic system in the practical application, so the study of the electromagnetically induced grating effect in the thermal atomic system may be helpful for practical applications.

Single fundamental mode photonic crystal VCSEL with high power and low threshold current optimized by modal loss analysis

Yi-Yang Xie(解意洋), Qiang Kan(阚强), Chen Xu(徐晨), Kun Xu(许坤), Hong-Da Chen(陈弘达)
Chin. Phys. B, 2017, 26 (1): 014203 doi: 10.1088/1674-1056/26/1/014203
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The characteristics of the photonic crystal vertical cavity surface emitting lasers (PhC-VCSELs) were investigated by using the full vector finite-difference time-domain (FDTD) method through the transverse mode loss analysis. PhC-VCSELs with different photonic crystal structures were analyzed theoretically and experimentally. Through combining the dual mode confinement of oxide aperture and seven-point-defect photonic crystal structure, the PhC-VCSELs with low threshold current of 0.9 mA and maximum output power of 3.1 mW operating in single fundamental mode were demonstrated. Mode loss analysis method was proven as a reliable and useful way to analyze and optimize the PhC-VCSELs.

A single-longitudinal-mode continuous-wave Ho3+: YVO4 laser at 2.05 μm pumped by a Tm-fibre laser

Jing Wu(吴婧), Youlun Ju(鞠有伦), Zhenguo Zhang(张振国), Liwei Xu(徐丽伟), Tongyu Dai(戴通宇), Baoquan Yao(姚宝权), Yuezhu Wang(王月珠)
Chin. Phys. B, 2017, 26 (1): 014204 doi: 10.1088/1674-1056/26/1/014204
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We present a single-longitudinal-mode continuous-wave Ho3+:YVO4 laser at 2.05 μm pumped by a Tm-doped fibre laser. Use of a cavity etalon enables spectral selectivity for single-mode operation. The highest power achieved in the single longitudinal mode at 2052.5 nm is 282 mW at a slope efficiency of 6.9%, corresponding to an optical conversion efficiency of 3.0%. These features demonstrate that this single-longitudinal-mode Ho:YVO4 laser is suitable for use as a seed laser in some Lidar systems (e.g., coherent Lidar or differential absorption Lidar). To the best of our knowledge, this is the first report on such a single-longitudinal-mode Ho:YVO4 laser at 2.05 μm.

Observation of wavelength-switchable solitons in an all-polarization-maintaining erbium-doped fiber cavity based on graphene saturable absorber reflector

Kuo Meng(孟阔), Lian-Qing Zhu(祝连庆), Fei Luo(骆飞)
Chin. Phys. B, 2017, 26 (1): 014205 doi: 10.1088/1674-1056/26/1/014205
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We present the generation of wavelength-switchable single-polarization solitons in an all-polarization-maintaining erbium-doped fiber laser mode-locked by a graphene saturable absorber. Ultrashort pulses centered at the wavelength of 1531.6 nm with the duration of 816 fs and centered at the wavelength of 1557.8 nm with the duration of 402 fs are separately obtained from the same fiber laser cavity. The cavity loss adjusted by the gold reflector plays a crucial role in wavelength switching.

Kerr-lens mode-locked polycrystalline Cr: ZnS femtosecond laser pumped by a monolithic Er: YAG laser

Chengfeng Hu(胡呈峰), Jiangfeng Zhu(朱江峰), Zhaohua Wang(王兆华), Xintong Sun(孙芯彤), Long Wei(魏龙), Weijun Ling(令维军), Zhong Dong(董忠), Qing Wang(王庆), Chunqing Gao(高春清), Zhiyi Wei(魏志义)
Chin. Phys. B, 2017, 26 (1): 014206 doi: 10.1088/1674-1056/26/1/014206
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We demonstrated a Kerr-lens mode-locked polycrystalline Cr:ZnS laser pumped by a narrow-linewidth linear-polarised monolithic Er:YAG nonplanar ring oscillator operated at 1645 nm. With a 5-mm-thick sapphire plate for intracavity dispersion compensation, a compact and stable Kerr-lens mode-locking operation was realised. The oscillator delivered 125-fs pulses at 2347 nm with an average power of 80 mW. Owing to the special polycrystalline structure of the Cr:ZnS crystal, the second to fourth harmonic generation was observed by random quasi-phase-matching.

Wavelength tunable ultra-short pulses based on a flat broadbandspectrum generated in a nonlinear ytterbium-dopedfiber amplifier

Run-Qin Xu(徐润亲), Zi-Kai Dong(董自凯), Jin-Rong Tian(田金荣), Ke-Xuan Li(李克轩), Yan-Rong Song(宋晏蓉)
Chin. Phys. B, 2017, 26 (1): 014207 doi: 10.1088/1674-1056/26/1/014207
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We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050-1225 nm with a maximum average output power of 7.8 W at 14 W pump power. Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum (center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges. Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm, the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around 1200 nm, and its output power and pulse width are 40 mW and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.

Spatiotemporal propagation dynamics of intense optical pulses in loosely confined gas-filled hollow-core fibers

Rui-rui Zhao(赵睿睿), Ding Wang(王丁), Zhi-yuan Huang(黄志远), Yu-xin Leng(冷雨欣), Ru-xin Li(李儒新)
Chin. Phys. B, 2017, 26 (1): 014208 doi: 10.1088/1674-1056/26/1/014208
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We numerically study the propagation dynamics of intense optical pulses in gas-filled hollow-core fibers (HCFs). The spatiotemporal dynamics of the pulses show a transition from tightly confined to loosely confined characteristics as the fiber core is increased, which manifests as a deterioration in the spatiotemporal uniformity of the beam. It is found that using the gas pressure gradient does not enhance the beam quality in large-core HCFs, while inducing a positive chirp in the pulse to lower the peak power can improve the beam quality. This indicates that the self-focusing effect in the HCFs is the main driving force for the propagation dynamics. It also suggests that pulses at longer wavelengths are more suitable for HCFs with large cores because of the lower critical power of self-focusing, which is justified by the numerical simulations. These results will benefit the generation of energetic few-cycle pulses in large-core HCFs.

Simultaneous detection of the acoustic-field aberration and Doppler shift in forward acoustic scattering

Chuan-Lin He(何传林), Kun-De Yang(杨坤德), Yuan-Liang Ma(马远良), Bo Lei(雷波)
Chin. Phys. B, 2017, 26 (1): 014301 doi: 10.1088/1674-1056/26/1/014301
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The aberration in the received acoustic field and the Doppler shift in the forward scattered field are simultaneously induced when a submerged target crosses the source-receiver line. Formulations for the two variations are developed upon an ideal forward scattering configuration. Both the field aberration and the Doppler shift are expressed as functions of the same argument–the target motion time. An experimental validation was carried out in a tank, in which the continuous wave was transmitted. The field aberration and the Doppler shift were extracted from the collected data by the simple Hilbert transform and a hybrid technique, respectively. The measured aberration and Doppler shift agree with the theoretical results. Simultaneous detection outputs are beneficial to enhance the reliability on target detection by providing both the aberrations in the received acoustic field and the Doppler shift in the forward scattered field.

Membrane-based acoustic metamaterial with near-zero refractive index

Yi-Feng Li(李义丰), Jun Lan(蓝君), Hui-Yang Yu(余辉洋), Xiao-Zhou Liu(刘晓宙), Jia-Shu Zhang(张嘉澍)
Chin. Phys. B, 2017, 26 (1): 014302 doi: 10.1088/1674-1056/26/1/014302
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We investigate a one-dimensional acoustic metamaterial with a refractive index of near zero (RINZ) using an array of very thin elastic membranes located along a narrow waveguide pipe. The characteristics of the effective density, refractive index, and phase velocity of the metamaterial indicate that, at the resonant frequency fm, the metamaterial has zero mass density and a phase transmission that is nearly uniform. We present a mechanism for dramatic acoustic energy squeezing and anomalous acoustic transmission by connecting the metamaterial to a normal waveguide with a larger cross-section. It is shown that at a specific frequency f1, transmission enhancement and energy squeezing are achieved despite the strong geometrical mismatch between the metamaterial and the normal waveguide. Moreover, to confirm the energy transfer properties, the acoustic pressure distribution, acoustic wave reflection coefficient, and energy transmission coefficient are also calculated. These results prove that the RINZ metamaterial provides a new design method for acoustic energy squeezing, super coupling, wave front transformation, and acoustic wave filtering.

Methods of reduction for Lagrange systems on time scaleswith nabla derivatives

Shi-Xin Jin(金世欣), Yi Zhang(张毅)
Chin. Phys. B, 2017, 26 (1): 014501 doi: 10.1088/1674-1056/26/1/014501
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The Routh and Whittaker methods of reduction for Lagrange system on time scales with nabla derivatives are studied. The equations of motion for Lagrange system on time scales are established, and their cyclic integrals and generalized energy integrals are given. The Routh functions and Whittaker functions of Lagrange system are constructed, and the order of differential equations of motion for the system are reduced by using the cyclic integrals or the generalized energy integrals with nabla derivatives. The results show that the reduced Routh equations and Whittaker equations hold the form of Lagrnage equations with nabla derivatives. Finally, two examples are given to illustrate the application of the results.

Nonlinear control of spacecraft formation flying with disturbance rejection and collision avoidance

Qing Ni(倪庆), Yi-Yong Huang(黄奕勇), Xiao-Qian Chen(陈小前)
Chin. Phys. B, 2017, 26 (1): 014502 doi: 10.1088/1674-1056/26/1/014502
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A nonlinear controller for disturbances rejection and collision avoidance is proposed for spacecraft formation flying. The formation flying is described by a nonlinear model with the J2 perturbation and atmospheric drag. Based on the theory of the state-dependent Riccati equation (SDRE), a finite time nonlinear control law is developed for the nonlinear dynamics involved in formation flying. Then, a compensative internal mode (IM) control law is added to eliminate disturbances. These two control laws compose a finite time nonlinear tracking controller with disturbances rejection. Moreover, taking safety requirements into account, the repulsive control law is incorporated in the composite controller to perform collision avoidance manoeuvres. A numerical simulation is presented to demonstrate the effectiveness of the proposed method. Compared to the conventional control method, the proposed method provides better performance in the presence of the obstacles and external disturbances.

Dynamics of a self-propelled particle under different driving modes in a channel flow

Zhenyu Ouyang(欧阳振宇), Jianzhong Lin(林建忠), Xiaoke Ku(库晓珂)
Chin. Phys. B, 2017, 26 (1): 014701 doi: 10.1088/1674-1056/26/1/014701
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In this paper, a model that combines the lattice Boltzmann method with the singularity distribution method is proposed to simulate a self-propelled particle swimming (exhibiting translation and rotation) in a channel flow. The results show that the velocity distribution for a self-propelled particle swimming deviates from a Maxwellian distribution and exhibits high-velocity tails. The influence of an eccentric potential doublet on the translation velocity of the particle is significant. The velocity decay process can be described using a double exponential model form. No large differences in the velocity distribution were observed for different translation Reynolds numbers, rotation Reynolds numbers, or regular intervals.

Particle transport behavior in air channel flow with multi-group Lagrangian tracking

Hao Lu(卢浩), Wen-Jun Zhao(赵文君), Hui-Qiang Zhang(张会强), Bing Wang(王兵), Xi-Lin Wang(王希麟)
Chin. Phys. B, 2017, 26 (1): 014702 doi: 10.1088/1674-1056/26/1/014702
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The particle motions of dispersion and transport in air channel flow are investigated using a large eddy simulation (LES) and Lagrangian trajectory method. The mean and fluctuating velocities of the fluids and particles are obtained, and the results are in good agreement with the data in the literature. Particle clustering is observed in the near-wall and low-speed regions. To reveal the evolution process and mechanism of particle dispersion and transport in the turbulent boundary layer, a multi-group Lagrangian tracking is applied when the two-phase flow has become fully developed:the fluid fields are classified into four sub-regions based on the flow characteristics, and particles in the turbulent region are divided accordingly into four groups when the gas-particle flow is fully developed. The spatiotemporal transport of the four groups of particles is then tracked and analyzed. The detailed relationship between particle dispersion and turbulent motion is investigated and discussed.

Three-dimensional turbulent flow over cube-obstacles

Hao Lu(卢浩), Wen-Jun Zhao(赵文君), Hui-Qiang Zhang(张会强), Bing Wang(王兵), Xi-Lin Wang(王希麟)
Chin. Phys. B, 2017, 26 (1): 014703 doi: 10.1088/1674-1056/26/1/014703
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In order to investigate the influence of surface roughness on turbulent flow and examine the wall-similarity hypothesis of Townsend, three-dimensional numerical study of turbulent channel flow over smooth and cube-rough walls with different roughness height has been carried out by using large eddy simulation (LES) coupled with immersed boundary method (IBM). The effects of surface roughness array on mean and fluctuating velocity profiles, Reynolds shear stress, and typical coherent structures such as quasi-streamwise vortices (QSV) in turbulent channel flow are obtained. The significant influences on turbulent fluctuations and structures are observed in roughness sub-layer (five times of roughness height). However, no dramatic modification of the log-law of the mean flow velocity and turbulence fluctuations can be found by surface cube roughness in the outer layer. Therefore, the results support the wall-similarity hypothesis. Moreover, the von Karman constant decreases with the increase of roughness height in the present simulation results. Besides, the larger size of QSV and more intense ejections are induced by the roughness elements, which is crucial for heat and mass transfer enhancement.

Three-dimensional MHD flow over a shrinking sheet: Analytical solution and stability analysis

Sumaira Afzal, Saleem Asghar, Adeel Ahmad
Chin. Phys. B, 2017, 26 (1): 014704 doi: 10.1088/1674-1056/26/1/014704
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The magnetohydrodynamic (MHD) steady and unsteady axisymmetric flows of a viscous fluid over a two-dimensional shrinking sheet are addressed. The mathematical analysis is carried out in the presence of a large magnetic field. The steady state problem results in a singular perturbation problem having an infinite domain singularity. The secular term appearing in the solution is removed and a two-term uniformly valid solution is derived using the Lindstedt-Poincaré technique. This asymptotic solution is validated by comparing it with the numerical solution. The solution for the unsteady problem is also presented analytically in the asymptotic limit of large magnetic field. The results of velocity profile and skin friction are shown graphically to explore the physical features of the flow field. The stability analysis of the unsteady flow is made to validate the asymptotic solution.

Fluid simulation of the pulsed bias effect on inductively coupled nitrogen discharges for low-voltage plasma immersion ion implantation

Xiao-Yan Sun(孙晓艳), Yu-Ru Zhang(张钰如), Xue-Chun Li(李雪春), You-Nian Wang(王友年)
Chin. Phys. B, 2017, 26 (1): 015201 doi: 10.1088/1674-1056/26/1/015201
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Planar radio frequency inductively coupled plasmas (ICP) are employed for low-voltage ion implantation processes, with capacitive pulse biasing of the substrate for modulation of the ion energy. In this work, a two-dimensional (2D) self-consistent fluid model has been employed to investigate the influence of the pulsed bias power on the nitrogen plasmas for various bias voltages and pulse frequencies. The results indicate that the plasma density as well as the inductive power density increase significantly when the bias voltage varies from 0 V to -4000 V, due to the heating of the capacitive field caused by the bias power. The N+ fraction increases rapidly to a maximum at the beginning of the power-on time, and then it decreases and reaches the steady state at the end of the glow period. Moreover, it increases with the bias voltage during the power-on time, whereas the N2+ fraction exhibits a reverse behavior. When the pulse frequency increases to 25 kHz and 40 kHz, the plasma steady state cannot be obtained, and a rapid decrease of the ion density at the substrate surface at the beginning of the glow period is observed.

Dust acoustic waves in collisional uniform dense magnetoplasma

Jian-Rong Yang(杨建荣), Ting Xu(徐婷), Jie-Jian Mao(毛杰键), Ping Liu(刘萍), Xi-Zhong Liu(刘希忠)
Chin. Phys. B, 2017, 26 (1): 015202 doi: 10.1088/1674-1056/26/1/015202
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In order to study the characteristics of dust acoustic waves in a uniform dense dusty magnetoplasma system, a nonlinear dynamical equation is deduced using the quantum hydrodynamic model to account for dust-neutral collisions. The linear dispersion relation indicates that the scale lengths of the system are revised by the quantum parameter, and that the wave motion decays gradually leading the system to a stable state eventually. The variations of the dispersion frequency with the dust concentration, collision frequency, and magnetic field strength are discussed. For the coherent nonlinear dust acoustic waves, new analytic solutions are obtained, and it is found that big shock waves and wide explosive waves may be easily produced in the background of high dusty density, strong magnetic field, and weak collision. The relevance of the obtained results is referred to dense dusty astrophysical circumstances.

Nonlinear parametric interactions in ion-implanted semiconductor plasmas having strain-dependent dielectric constants

N Yadav, S Ghosh, P S Malviya
Chin. Phys. B, 2017, 26 (1): 015203 doi: 10.1088/1674-1056/26/1/015203
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We report nonlinear parametric interactions using a hydrodynamic model of ion-implanted semiconductor plasmas having strain-dependent dielectric constants (SDDC). High-dielectric-constant materials are technologically important because of their nonlinear properties. We find that the third-order susceptibility varies in the range 10-14-10-12 m2·V-2 for ion-implanted semiconductor plasmas, which is in good agreement with previous results. It is found that the presence of SDDC in ion-implanted semiconductor plasma modifies the characteristic properties of the material.

Femtosecond laser induced nanostructuring of zirconium in liquid confined environment

Nisar Ali, Shazia Bashir, Umm-i-Kalsoom, M. Shahid Rafique, Narjis Begum, Wolfgang Husinsky, Ali Ajami, Chandra S. R. Natahala
Chin. Phys. B, 2017, 26 (1): 015204 doi: 10.1088/1674-1056/26/1/015204
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The surface, structural, and mechanical properties of zirconium after irradiation with Ti:sapphire laser (800 nm, 30 fs, 1 kHz) have been investigated. The zirconium targets were exposed for a varying number of laser pulses ranging from 500 to 2000 at a fixed fluence of 3.6 J/cm2 corresponding to an intensity of 1.2×1014 W/cm2 in ambient environments of de-ionized water and propanol. A scanning electron microscope (SEM) was employed to investigate the surface morphology of the irradiated zirconium. The SEM analysis shows the formation of various kinds of features including nanoscale laser induced periodic surface structures (LIPSS), sponge like surface structure, flakes, conical structures, droplets, pores, and cavities. The energy dispersive x-ray spectroscopy (EDS) analysis exhibits the variation in chemical composition along with an enhanced diffusion of oxygen under both ambient conditions. The crystal structure and phase analyses of the exposed targets were explored by x-ray diffraction (XRD) and Raman spectroscopy techniques, respectively. The XRD analysis confirms the presence of various phases of zirconium hydride and zirconia after ablation in both de-ionized water and propanol. However, excessive hydrides are formed in the case of propanol. The Raman analysis supports the EDS and XRD results. It also reveals the presence of oxides (zirconia) after irradiation in both de-ionized water and propanol environments. The chemical reactivity of zirconium was significantly improved in the presence of liquids which were accountable for the growth of novel phases and modification in the chemical composition of the irradiated Zr. A nanohardness tester was employed to measure the nanohardness of the laser treated targets. The initial increase and then decrease in nanohardness was observed with an increase in the number of laser pulses in the de-ionized water environment. In the case of propanol, a continuous decrease in hardness was observed.

Thermal and induced flow characteristics of radio frequency surface dielectric barrier discharge plasma actuation at atmospheric pressure

Wei-long Wang(王蔚龙), Jun Li(李军), Hui-min Song(宋慧敏), Di Jin(金迪), Min Jia(贾敏), Yun Wu(吴云)
Chin. Phys. B, 2017, 26 (1): 015205 doi: 10.1088/1674-1056/26/1/015205
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Thermal and induced flow velocity characteristics of radio frequency (RF) surface dielectric barrier discharge (SDBD) plasma actuation are experimentally investigated in this paper. The spatial and temporal distributions of the dielectric surface temperature are measured with the infrared thermography at atmospheric pressure. In the spanwise direction, the highest dielectric surface temperature is acquired at the center of the high voltage electrode, while it reduces gradually along the chordwise direction. The maximum temperature of the dielectric surface raises rapidly once discharge begins. After several seconds (typically 100 s), the temperature reaches equilibrium among the actuator's surface, plasma, and surrounding air. The maximum dielectric surface temperature is higher than that powered by an AC power supply in dozens of kHz. Influences of the duty cycle and the input frequency on the thermal characteristics are analyzed. When the duty cycle increases, the maximum dielectric surface temperature increases linearly. However, the maximum dielectric surface temperature increases nonlinearly when the input frequency varies from 0.47 MHz to 1.61 MHz. The induced flow velocity of the RF SDBD actuator is 0.25 m/s.

End-on x-ray backlighting experiments for axial diagnostics of wire-array Z-pinch plasma on PPG-1

Shen Zhao(赵屾), Xinlei Zhu(朱鑫磊), Huantong Shi(石桓通), Xiaobing Zou(邹晓兵), Xinxin Wang(王新新)
Chin. Phys. B, 2017, 26 (1): 015206 doi: 10.1088/1674-1056/26/1/015206
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An X-pinch axial backlighting system has been designed to quantitatively measure the density distribution of wire-array Z-pinch plasmas. End-on backlighting experiments were carried out on a 200 kA, 100 ns pulsed-power generator (PPG-1) at the Tsinghua University. Compared with side-on backlighting, end-on measurements provide an axial view of the evolution of Z-pinch plasmas. Early stages of 2-, 4-, and 8-wire Z-pinch plasmas were observed via point-projection backlighting radiography with a relatively high success rate. The density distribution of Z-pinch plasma on the r-θ plane was obtained directly from the images with the help of step wedges, and the inward radial velocity was calculated. The ablation rates obtained by X-pinch backlighting experiments are compared in detail with those calculated by the rocket model and the results show consistency.


Abnormal breakdown of Stokes-Einstein relation in liquid aluminium

Chen-Hui Li (李晨辉), Xiu-Jun Han(韩秀君), Ying-Wei Luan(栾英伟), Jian-Guo Li(李建国)
Chin. Phys. B, 2017, 26 (1): 016102 doi: 10.1088/1674-1056/26/1/016102
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We present the results of systematic molecular dynamics simulations of pure aluminium melt with a well-accepted embedded atom potential. The structure and dynamics were calculated over a wide temperature range, and the calculated results (including the pair correlation function, self-diffusion coefficient, and viscosity) agree well with the available experimental observations. The calculated data were used to examine the Stokes-Einstein relation (SER). The results indicate that the SER begins to break down at a temperature Tx (~1090 K) which is well above the equilibrium melting point (912.5 K). This high-temperature breakdown is confirmed by the evolution of dynamics heterogeneity, which is characterised by the non-Gaussian parameter α2(t). The maximum value of α2(t), α2,max, increases at an accelerating rate as the temperature falls below Tx. The development of α2,max was found to be related to the liquid structure change evidenced by local five-fold symmetry. Accordingly, we suggest that this high-temperature breakdown of SER has a structural origin. The results of this study are expected to make researchers reconsider the applicability of SER and promote greater understanding of the relationship between dynamics and structure.

Studies on the nucleation of MBE grown III-nitride nanowires on Si

Yanxiong E(鄂炎雄), Zhibiao Hao(郝智彪), Jiadong Yu(余佳东), Chao Wu(吴超), Lai Wang(汪莱), Bing Xiong(熊兵), Jian Wang(王健), Yanjun Han(韩彦军), Changzheng Sun(孙长征), Yi Luo(罗毅)
Chin. Phys. B, 2017, 26 (1): 016103 doi: 10.1088/1674-1056/26/1/016103
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GaN and AlN nanowires (NWs) have attracted great interests for the fabrication of novel nano-sized devices. In this paper, the nucleation processes of GaN and AlN NWs grown on Si substrates by molecular beam epitaxy (MBE) are investigated. It is found that GaN NWs nucleated on in-situ formed Si3N4 fully release the stress upon the interface between GaN NW and amorphous Si3N4 layer, while AlN NWs nucleated by aluminization process gradually release the stress during growth. Depending on the strain status as well as the migration ability of III group adatoms, the different growth kinetics of GaN and AlN NWs result in different NW morphologies, i.e., GaN NWs with uniform radii and AlN NWs with tapered bases.

Zero and controllable thermal expansion in HfMgMo3-xWxO12

Tao Li(李涛), Xian-Sheng Liu(刘献省), Yong-Guang Cheng(程永光), Xiang-Hong Ge(葛向红), Meng-Di Zhang(张孟迪), Hong Lian(连虹), Ying Zhang(张莹), Er-Jun Liang(梁二军), Yu-Xiao Li(李玉晓)
Chin. Phys. B, 2017, 26 (1): 016501 doi: 10.1088/1674-1056/26/1/016501
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HfMgMo3-xWxO12 with x=0.5, 1.0, 1.5, 2.0, and 2.5 are developed with a simple solid state method. With increasing the content of W, solid solutions of HfMgMo3-xWxO12 crystallize in an orthorhombic structure for x≤2.0 and a monoclinic structure for x>2.0. A near-zero thermal expansion (ZTE) is realized for HfMgMo2.5W0.5O12 and negative coefficients of thermal expansion (NCTE) are achieved for other compositions with different values. The ZTE and variation of NCTE are attributed to the difference in electronegativity between W and Mo and incorporation of a different amount of W, which cause variable distortion of the octahedra and softening of the MoO4 tetrahedra, and hence an enhanced NCTE in the a- and c-axis and reduced CTE in the b-axis as revealed by Raman spectroscopy and x-ray diffraction.

Crystallization of amorphous silicon beyond the crystallized polycrystalline silicon region induced by metal nickel

Dongli Zhang(张冬利), Mingxiang Wang(王明湘), Man Wong(王文), Hoi-Sing Kwok(郭海成)
Chin. Phys. B, 2017, 26 (1): 016601 doi: 10.1088/1674-1056/26/1/016601
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Crystallization of amorphous silicon (a-Si) which starts from the middle of the a-Si region separating two adjacent metal-induced crystallization (MIC) polycrystalline silicon (poly-Si) regions is observed. The crystallization is found to be related to the distance between the neighboring nickel-introducing MIC windows. Trace nickel that diffuses from the MIC window into the a-Si matrix during the MIC heat-treatment is experimentally discovered, which is responsible for the crystallization of the a-Si beyond the MIC front. A minimum diffusion coefficient of 1.84×10-9 cm2/s at 550℃ is estimated for the trace nickel diffusion in a-Si.

Tuning the thermal conductivity of strontium titanate through annealing treatments

Liang Zhang(张喨), Ning Li(李宁), Hui-Qiong Wang(王惠琼), Yufeng Zhang(张宇锋), Fei Ren(任飞), Xia-Xia Liao(廖霞霞), Ya-Ping Li(李亚平), Xiao-Dan Wang(王小丹), Zheng Huang(黄政), Yang Dai(戴扬), Hao Yan(鄢浩), Jin-Cheng Zheng(郑金成)
Chin. Phys. B, 2017, 26 (1): 016602 doi: 10.1088/1674-1056/26/1/016602
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Strontium titanate (SrTiO3) is a promising n-type material for thermoelectric applications. However, its relatively high thermal conductivity limits its performance in efficiently converting heat into electrical power through thermoelectric effect. This work shows that the thermal conductivity of SrTiO3 can be effectively reduced by annealing treatments, through an integrated study of laser flash measurement, scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray absorption fine structure, and first-principles calculations. A phonon scattering model is proposed to explain the reduction of thermal conductivity after annealing. This work suggests a promising means to characterize and optimize the material for thermoelectric applications.

Measurement and analysis of the surface roughness of Ag film used in plasmonic lithography

Gao-Feng Liang(梁高峰), Jiao Jiao(焦蛟), Xian-Gang Luo(罗先刚), Qing Zhao(赵青)
Chin. Phys. B, 2017, 26 (1): 016801 doi: 10.1088/1674-1056/26/1/016801
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The silver (Ag)/photoresist (PR)/Ag structure, widely used in plasmonic photolithography, is fabricated on silicon substrate. The surface roughness of the top Ag film is measured and analyzed systematically. In particular, combined with template stripping technology, the lower side of the top Ag film is imaged by an atomic force microscope. The topographies show that the lower side surface is rougher than the initial surface of the subjacent PR film, which is mainly attributable to the deformation caused by particle collisions during the deposition of the Ag film. Additionally, further measurements show that the Ag film deposited on the PR exhibits a flatter upper side morphology than that directly deposited on the silicon substrate. This is explained by the different growth modes of Ag films on different substrates. This work will be beneficial to morphology analysis and performance evaluation for the films in optical and plasmonic devices.

Ultrafast optical probe of coherent acoustic phonons in Co2MnAl Heusler film

Wei Yan(闫炜), Hai-Long Wang(王海龙), Jian-Hua Zhao(赵建华), Xin-Hui Zhang(张新惠)
Chin. Phys. B, 2017, 26 (1): 016802 doi: 10.1088/1674-1056/26/1/016802
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In this work, pronounced oscillations in the time-resolved reflectivity of Heusler alloy Co2MnAl films which are epitaxially grown on GaAs substrates are observed and investigated as a function of film thickness, probe wavelength, external magnetic field and temperature. Our results suggest that the oscillation response at 24.5 GHz results from the coherent phonon generation in Co2MnAl film and can be explained by a propagating strain pulse model. From the probe wavelength dependent oscillation frequency, a sound velocity of (3.85±0.1)×103 m/s at 800 nm for the epitaxial Co2MnAl film is determined at room temperature. The detected coherent acoustic phonon generation in Co2MnAl reported in this work provides a valuable reference for exploring the high-speed magnetization manipulation via magnetoelastic coupling for future spintronic devices based on Heusler alloy films.


Electronic structure and magnetic properties of rare-earthperovskite gallates from first principles

A Dahani, H Alamri, B Merabet, A Zaoui, S Kacimi, A Boukortt, M Bejar
Chin. Phys. B, 2017, 26 (1): 017101 doi: 10.1088/1674-1056/26/1/017101
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The density functional calculation is performed for centrosymmetric (La-Pm) GaO3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA+U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U=0.478 Ry on the magnetic phase stability and the densities of states. LSDA+U calculation shows that the ferromagnetic (FM) state of RGaO3 is energetically more favorable than the anti-ferromagnetic (AFM) one, except for LaGaO3 where the NM state is the lowest in energy. The energy band gaps of RGaO3 are found to be in the range of 3.8-4.0 eV, indicating the semiconductor character with a large gap.

Control of topological phase transitions in Dirac semimetal films by exchange fields

Fei Yang(杨菲), Hai-Long Wang(王海龙), Hui Pan(潘晖)
Chin. Phys. B, 2017, 26 (1): 017102 doi: 10.1088/1674-1056/26/1/017102
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The exchange field effects on topological Dirac semimetal (DSM) films are discussed in this article. A topological phase transition can be controlled by tuning the exchange field together with the quantum confinement effects. What is more interesting is that the system can transit into the quantum anomalous Hall (QAH) state from the topologically trivial state (Z2=0) or from the topologically nontrivial state (Z2=1), depending on the thickness of the DSM films. This provides a useful mechanism to realize the QAH state from the DSM.

Implementation of LDA+Gutzwiller with Newton's method Hot!

Jian Zhang(张健), Ming-Feng Tian(田明锋), Guang-Xi Jin(金光希), Yuan-Feng Xu(徐远锋), Xi Dai(戴希)
Chin. Phys. B, 2017, 26 (1): 017103 doi: 10.1088/1674-1056/26/1/017103
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In order to calculate the electronic structure of correlated materials, we propose implementation of the LDA+Gutzwiller method with Newton's method. The self-consistence process, efficiency and convergence of calculation are improved dramatically by using Newton's method with golden section search and other improvement approaches. We compare the calculated results by applying the previous linear mix method and Newton's method. We have applied our code to study the electronic structure of several typical strong correlated materials, including SrVO3, LaCoO3, and La2O3Fe2Se2. Our results fit quite well with the previous studies.

Direct spin-phonon coupling of spin-flip relaxation in quantum dots

Ji-Wen Yin(尹辑文), Wei-Ping Li(李伟萍), Hong-Juan Li(李红娟), Yi-Fu Yu(于毅夫)
Chin. Phys. B, 2017, 26 (1): 017201 doi: 10.1088/1674-1056/26/1/017201
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Within the frame of the Pavlov-Firsov spin-phonon coupling model, we study the spin-flip assisted by the acoustical phonon scattering between the first-excited state and the ground state in quantum dots. We analyze the behaviors of the spin relaxation rates as a function of an external magnetic field and lateral radius of quantum dot. The different trends of the relaxation rates depending on the magnetic field and lateral radius are obtained, which may serve as a channel to distinguish the relaxation processes and thus control the spin state effectively.

Improved thermoelectric performance in p-type Bi0.48Sb1.52Te3 bulk material by adding MnSb2Se4

Binglei Cao(曹丙垒), Jikang Jian(简基康), Binghui Ge(葛炳辉), Shanming Li(李善明), Hao Wang(王浩), Jiao Liu(刘骄), Huaizhou Zhao(赵怀周)
Chin. Phys. B, 2017, 26 (1): 017202 doi: 10.1088/1674-1056/26/1/017202
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Bismuth telluride (Bi2Te3) based alloys, such as p-type Bi0.5Sb1.5Te3, have been leading candidates for near room temperature thermoelectric applications. In this study, Bi0.48Sb1.52Te3 bulk materials with MnSb2Se4 were prepared using high-energy ball milling and spark plasma sintering (SPS) process. The addition of MnSb2Se4 to Bi0.48Sb1.52Te3 increased the hole concentration while slightly decreasing the Seebeck coefficient, thus optimising the electrical transport properties of the bulk material. In addition, the second phases of MnSb2Se4 and Bi0.48Sb1.52Te3 were observed in the Bi0.48Sb1.52Te3 matrix. The nanoparticles in the semi-coherent second phase of MnSb2Se4 behaved as scattering centres for phonons, yielding a reduction in the lattice thermal conductivity. Substantial enhancement of the figure of merit, ZT, has been achieved for Bi0.48Sb1.52Te3 by adding an Mn0.8Cu0.2Sb2Se4 (2 mol%) sample, for a wide range of temperatures, with a peak value of 1.43 at 375 K, corresponding to ~40% improvement over its Bi0.48Sb1.52Te3 counterpart. Such enhancement of the thermoelectric (TE) performance of p-type Bi2Te3 based materials is believed to be advantageous for practical applications.

Spin-valley Hall conductivity of doped ferromagnetic silicene under strain

Bahram Shirzadi, Mohsen Yarmohammadi
Chin. Phys. B, 2017, 26 (1): 017203 doi: 10.1088/1674-1056/26/1/017203
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The spin-valley Hall conductivity (SHC-VHC) of two-dimensional material ferromagnetic graphene's silicon analog, silicene, is investigated in the presence of strain within the Kubo formalism in the context of the Kane-Mele Hamiltonian. The Dirac cone approximation has been used to investigate the dynamics of carriers under the strain along the armchair (AC) direction. In particular, we study the effect of external static electric field on these conductivities under the strain. In the presence of the strain, the carriers have a larger effective mass and the transport decreases. Our findings show that SHC changes with respect to the direction of the applied electric field symmetrically while VHC increases independently. Furthermore, the reflection symmetry of the structure has been broken with the electric field and a phase transition occurs to topological insulator for strained ferromagnetic silicene. A critical strain is found in the presence of the electric field around 45%. SHC (VHC) decreases (increases) for strains smaller than this value symmetrically while it increases (decreases) for strains larger than one.

Dynamic control of the terahertz rainbow trapping effect based on a silicon-filled graded grating

Shu-Lin Wang(王书林), Lan Ding(丁岚), Wen Xu(徐文)
Chin. Phys. B, 2017, 26 (1): 017301 doi: 10.1088/1674-1056/26/1/017301
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We theoretically propose a scheme to realize the dynamic control of the properties of the terahertz (THz) rainbow trapping effect (RTE) based on a silicon-filled graded grating (SFGG) in a relatively broad band via optical pumping. Through the theoretical analysis and finite-element method simulations, it is conceptually demonstrated that the band of the RTE can be dynamically tuned in a range of ~0.06 THz. Furthermore, the SFGG can also be optically switched between a device for the RTE and a waveguide for releasing the trapped waves. The results obtained here may imply applications for the tunable THz plasmonic devices, such as on-chip optical buffers, broad band slow-light systems, and integrated optical filters.

Diffraction properties of binary graphene sheet arrays

Yang Fan(樊洋), Cong Chen(陈聪), Ding-Guo Li(李定国)
Chin. Phys. B, 2017, 26 (1): 017302 doi: 10.1088/1674-1056/26/1/017302
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We theoretically and numerically investigate the diffraction properties of surface plasmon polariton (SPP) in binary graphene sheet arrays. The single SPP band splits into two minibands by alternatively arranging the graphene waveguides with two different chemical potentials. Numerical simulations show that SPP beams in the array split into two different paths due to the different diffraction relation.

First-principles study of structural, electronic, and optical properties of cubic InAsxNyP1-x-y triangular quaternary alloys

I Hattabi, A Abdiche, F Soyalp, R Moussa, R Riane, K Hadji, S Bin-Omran, R Khenata
Chin. Phys. B, 2017, 26 (1): 017303 doi: 10.1088/1674-1056/26/1/017303
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In this paper, we investigated the structural, electronic and optical properties of InAs, InN and InP binary compounds and their related ternary and quaternary alloys by using the full potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The total energies, the lattice parameters, and the bulk modulus and its first pressure derivative were calculated using different exchange correlation approximations. The local density approach (LDA) and Tran-Blaha modified Becke-Johnson (TB-mBJ) approximations were used to calculate the band structure. Nonlinear variations of the lattice parameters, the bulk modulus and the band gap with compositions x and y are found. Furthermore, the optical properties and the dielectric function, refractive index and loss energy were computed. Our results are in good agreement with the validated experimental and theoretical data found in the literature.

Low power fluorine plasma effects on electrical reliability of AlGaN/GaN high electron mobility transistor

Ling Yang(杨凌), Xiao-Wei Zhou(周小伟), Xiao-Hua Ma(马晓华), Ling Lv(吕玲), Yan-Rong Cao(曹艳荣), Jin-Cheng Zhang(张进成), Yue Hao(郝跃)
Chin. Phys. B, 2017, 26 (1): 017304 doi: 10.1088/1674-1056/26/1/017304
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The new electrical degradation phenomenon of the AlGaN/GaN high electron mobility transistor (HEMT) treated by low power fluorine plasma is discovered. The saturated current, on-resistance, threshold voltage, gate leakage and breakdown voltage show that each experiences a significant change in a short time stress, and then keeps unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. These results suggest that the low power fluorine implant ion stays in an unstable state. It causes the electrical properties of AlGaN/GaN HEMT to present early degradation. A new migration and degradation mechanism of the low power fluorine implant ion under the off-stress electrical stress is proposed. The low power fluorine ions would drift at the beginning of the off-state stress, and then accumulate between gate and drain nearby the gate side. Due to the strong electronegativity of fluorine, the accumulation of the front fluorine ions would prevent the subsequent fluorine ions from drifting, thereby alleviating further the degradation of AlGaN/GaN HEMT electrical properties.

Quantum critical behavior in an antiferromagnetic heavy-fermion Kondo lattice system (Ce1-xLax)2Ir3Ge5

Rajwali Khan, Qianhui Mao(毛乾辉), Hangdong Wang(王杭栋), Jinhu Yang(杨金虎), Jianhua Du(杜建华), Binjie Xu(许彬杰), Yuxing Zhou(周宇星), Yannan Zhang(张燕楠), Bing Chen(陈斌), Minghu Fang(方明虎)
Chin. Phys. B, 2017, 26 (1): 017401 doi: 10.1088/1674-1056/26/1/017401
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The measurements on temperature dependences of magnetic susceptibility χ(T), specific heat C(T), and electrical resistivity ρ(T) were carried out for the antiferromagnetic (AFM) (Ce1-xLax)2Ir3Ge5 (0≤x≤0.66) system. It was found that the Neel temperature TN decreases with increasing La content x, and reaches 0 K near a critical content xcr=0.6. A new phase diagram was constructed based on these measurements. A non-Fermi liquid behavior in ρ(T) and a logT relationship in C(T) were found in the samples near xcr, indicating them to be near an AFM quantum critical point (QCP) with strong spin fluctuation. Our finding indicates that (Ce1-xLax)2Ir3Ge5 may be a new platform to search for unconventional superconductivity.

Effect of Sb-doping on martensitic transformation and magnetocaloric effect in Mn-rich Mn50Ni40Sn10-xSbx (x=1, 2, 3, and 4) alloys

Ishfaq Ahmad Shah, Najam ul Hassan, Jun Liu(刘俊), Yuanyuan Gong(龚元元), Guizhou Xu(徐桂舟), Feng Xu(徐锋)
Chin. Phys. B, 2017, 26 (1): 017501 doi: 10.1088/1674-1056/26/1/017501
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We investigate the influence of Sb-doping on the martensitic transformation and magnetocaloric effect in Mn50Ni40Sn10-xSbx (x=1, 2, 3, and 4) alloys. All the prepared samples exhibit a B2-type structure with the space group Fm3m at room temperature. The substitution of Sb increases the valence electron concentration and decreases the unit cell volume. As a result, the magnetostructural transformation shifts rapidly towards higher temperatures as x increases. The changes in magnetic entropy under different magnetic field variations are explored around this transformation. The isothermal magnetization curves exhibit typical metamagnetic behavior, indicating that the magnetostructural transformation can be induced by a magnetic field. The tunable martensitic transformation and magnetic entropy changes suggest that Mn50Ni40Sn10-xSbx alloys are attractive candidates for applications in solid-state refrigeration.

Faster vortex core switching with lower current density using three-nanocontact spin-polarized currents in a confined structure

Hua-Nan Li(李化南), Zhong Hua(华中), Dong-Fei Li(李东飞)
Chin. Phys. B, 2017, 26 (1): 017502 doi: 10.1088/1674-1056/26/1/017502
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We perform micromagnetic simulations on the switching of magnetic vortex core by using spin-polarized currents through a three-nanocontact geometry. Our simulation results show that the current combination with an appropriate current flow direction destroys the symmetry of the total effective energy of the system so that the vortex core can be easier to excite, resulting in less critical current density and a faster switching process. Besides its fundamental significance, our findings provide an additional route to incorporating magnetic vortex phenomena into data storage devices.

Diverse features of magnetization curves of uniaxial crystals: A simulation study

Hala A. Sobh, Samy H. Aly
Chin. Phys. B, 2017, 26 (1): 017503 doi: 10.1088/1674-1056/26/1/017503
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We present a simulation of the magnetization curves, energy, probability, and torque landscapes of uniaxial systems with up to five anisotropy constants. The total energy used in the simulation is the sum of the anisotropy and Zeeman energies. The exchange interaction is not considered in the present work in which we treat single-domain-particle systems within a classical mechanics-based model. Diverse features of the calculated magnetization curves are highlighted for the studied systems. These diverse features are strongly dependent on the sign and magnitude of the simulation parameters. The model is versatile enough to handle both hypothetical and real material systems, e.g. HoFe11Ti and Y2Co17.

A novel P-channel SOI LDMOS structure with non-depletion potential-clamped layer

Wei Li(李威), Zhi Zheng(郑直), Zhigang Wang(汪志刚), Ping Li(李平), Xiaojun Fu(付晓君), Zhengrong He(何峥嵘), Fan Liu(刘凡), Feng Yang(杨丰), Fan Xiang(向凡), Luncai Liu(刘伦才)
Chin. Phys. B, 2017, 26 (1): 017701 doi: 10.1088/1674-1056/26/1/017701
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A novel structure is proposed for doubling the vertical breakdown voltage of silicon-on-insulator (SOI) devices. In this new structure, the conventional buried oxide (BOX) in an SOI device is split into two sections:the source-section BOX and the drain-section BOX. A highly-doped Si layer, referred to as a non-depletion potential-clamped layer (NPCL), is positioned under and close to the two BOX sections. In the split BOXes and the Si region above the BOXes, the blocking voltage (BV) is divided into two parts by the NPCL. The voltage in the NPCL is clamped to be nearly half of the drain voltage. When the drain voltage approaches a breakdown value, the voltage sustained by the source-section BOX and the Si region under the source are nearly the same as the voltage sustained by the drain-section BOX and the Si region under the drain. The vertical BV is therefore almost doubled. The effectiveness of this new structure was verified for a P-channel SOI lateral double-diffused metal-oxide semiconductor (LDMOS) and can be applied to other high-voltage SOI devices. The simulation results show that the BV in an NPCL P-channel SOI LDMOS is improved by 55% and the specific on-resistance (Ron,sp) is reduced by 69% in comparison to the conventional structure.

Semi-analytical method of calculating the electrostatic interaction of colloidal solutions

Hongqing Tian(田洪庆), Zengju Lian(连增菊)
Chin. Phys. B, 2017, 26 (1): 017801 doi: 10.1088/1674-1056/26/1/017801
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We present a semi-analytical method of calculating the electrostatic interaction of colloid solutions for confined and unconfined systems. We expand the electrostatic potential of the system in terms of some basis functions such as spherical harmonic function and cylinder function. The expansion coefficients can be obtained by solving the equations of the boundary conditions, combining an analytical translation transform of the coordinates and a numerical multipoint collection method. The precise electrostatic potential and the interaction energy are then obtained automatically. The method is available not only for the uniformly charged colloids but also for nonuniformly charged ones. We have successfully applied it to unconfined diluted colloid system and some confined systems such as the long cylinder wall confinement, the air-water interfacial confinement and porous membrane confinement. The consistence checks of our calculations with some known analytical cases have been made for all our applications. In theory, the method is applicable to any dilute colloid solutions with an arbitrary distribution of the surface charge on the colloidal particle under a regular solid confinement, such as spherical cavity confinement and lamellar confinement.

Temperature-dependent photoluminescence on organic-inorganicmetal halide perovskite CH3NH3PbI3-xClx prepared onZnO/FTO substrates using a two-step method

Shiwei Zhuang(庄仕伟), Deqian Xu(徐德前), Jiaxin Xu(徐佳新), Bin Wu(伍斌), Yuantao Zhang(张源涛), Xin Dong(董鑫), Guoxing Li(李国兴), Baolin Zhang(张宝林), Guotong Du(杜国同)
Chin. Phys. B, 2017, 26 (1): 017802 doi: 10.1088/1674-1056/26/1/017802
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Temperature-dependent photoluminescence characteristics of organic-inorganic halide perovskite CH3NH3PbI3-xClx films prepared using a two-step method on ZnO/FTO substrates were investigated. Surface morphology and absorption characteristics of the films were also studied. Scanning electron microscopy revealed large crystals and substrate coverage. The orthorhombic-to-tetragonal phase transition temperature was ~140 K. The films' exciton binding energy was 77.6±10.9 meV and the energy of optical phonons was 38.8±2.5 meV. These results suggest that perovskite CH3NH3PbI3-xClx films have excellent optoelectronic characteristics which further suggests their potential usage in perovskitebased optoelectronic devices.

High-efficiency InGaN/AlInGaN multiple quantum wells with lattice-matched AlInGaN superlattices barrier

Feng Xu(徐峰), Peng Chen(陈鹏), Fu-Long Jiang(蒋府龙), Ya-Yun Liu(刘亚云), Zi-Li Xie(谢自立), Xiang-Qian Xiu(修向前), Xue-Mei Hua(华雪梅), Yi Shi(施毅), Rong Zhang(张荣), You-Liao Zheng(郑有炓)
Chin. Phys. B, 2017, 26 (1): 017803 doi: 10.1088/1674-1056/26/1/017803
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A new approach to fabricating high-quality AlInGaN film as a lattice-matched barrier layer in multiple quantum wells (MQWs) is presented. The high-quality AlInGaN film is realized by growing the AlGaN/InGaN short period superlattices through metalorganic chemical vapor deposition, and then being used as a barrier in the MQWs. The crystalline quality of the MQWs with the lattice-matched AlInGaN barrier and that of the conventional InGaN/GaN MQWs are characterized by x-ray diffraction and scanning electron microscopy. The photoluminescence (PL) properties of the InGaN/AlInGaN MQWs are investigated by varying the excitation power density and temperature through comparing with those of the InGaN/GaN MQWs. The integral PL intensity of InGaN/AlInGaN MQWs is over 3 times higher than that of InGaN/GaN MQWs at room temperature under the highest excitation power. Temperature-dependent PL further demonstrates that the internal quantum efficiency of InGaN/AlInGaN MQWs (76.1%) is much higher than that of InGaN/GaN MQWs (21%). The improved luminescence performance of InGaN/AlInGaN MQWs can be attributed to the distinct reduction of the barrier-well lattice mismatch and the strain-induced non-radiative recombination centers.

Roles of voltage in semi-insulating GaAs photoconductive semiconductor switch

Hai-Juan Cui(崔海娟), Hong-Chun Yang(杨宏春), Jun Xu(徐军), Yu-Ming Yang(杨宇明), Zi-Xian Yang(杨子贤)
Chin. Phys. B, 2017, 26 (1): 017804 doi: 10.1088/1674-1056/26/1/017804
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An experimental study of leakage current is presented in a semi-insulating (SI) GaAs photoconductive semiconductor switch (PCSS) with voltages up to 5.8 kV (average field is 19.3 kV/cm). The leakage current increases nonlinearly with the bias voltage increasing from 1.2×10-9 A to 3.6×10-5 A. Furthermore, the dark resistance, which is characterized as a function of electric field, does not monotonically decrease with the field but displays several distinct regimes. By eliminating the field-dependent drift velocity, the free-electron density n is extracted from the current, and then the critical field for each region of n(E) characteristic of PCSS is obtained. It must be the electric field that provides the free electron with sufficient energy to activate the carrier in the trapped state via multiple physical mechanisms, such as impurity ionization, field-dependent EL2 capture, and impact ionization of donor centers EL10 and EL2. The critical fields calculated from the activation energy of these physical processes accord well with the experimental results. Moreover, agreement between the fitting curve and experimental data of J(E), further confirms that the dark-state characteristics are related to these field-dependent processes. The effects of voltage on SI-GaAs PCSS may give us an insight into its physical mechanism.

Analysis of localization effect in blue-violet light emitting InGaN/GaN multiple quantum wells with different well widths

Xiang Li(李翔), De-Gang Zhao(赵德刚), De-Sheng Jiang(江德生), Jing Yang(杨静), Ping Chen(陈平), Zong-Shun Liu(刘宗顺), Jian-Jun Zhu(朱建军), Wei Liu(刘炜), Xiao-Guang He(何晓光), Xiao-Jing Li(李晓静), Feng Liang(梁锋), Jian-Ping Liu(刘建平), Li-Qun Zhang(张立群), Hui Yang(杨辉), Yuan-Tao Zhang(张源涛), Guo-Tong Du(杜国同), Heng Long(龙衡), Mo Li(李沫)
Chin. Phys. B, 2017, 26 (1): 017805 doi: 10.1088/1674-1056/26/1/017805
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Four blue-violet light emitting InGaN/GaN multiple quantum well (MQW) structures with different well widths are grown by metal-organic chemical vapor deposition. The carrier localization effect in these samples is investigated mainly by temperature-dependent photoluminescence measurements. It is found that the localization effect is enhanced as the well width increases from 1.8 nm to 3.6 nm in our experiments. The temperature induced PL peak blueshift and linewidth variation increase with increasing well width, implying that a greater amplitude of potential fluctuation as well as more localization states exist in wider wells. In addition, it is noted that the broadening of the PL spectra always occurs mainly on the low-energy side of the PL spectra due to the temperature-induced band-gap shrinkage, while in the case of the widest well, a large extension of the spectral curve also occurs in the high energy sides due to the existence of more shallow localized centers.

Tunable band gap and optical properties of surface functionalized Sc2C monolayer

Shun Wang(王顺), Yu-Lei Du(杜宇雷), Wen-He Liao(廖文和)
Chin. Phys. B, 2017, 26 (1): 017806 doi: 10.1088/1674-1056/26/1/017806
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Using the density functional theory, we have investigated the electronic and optical properties of two-dimensional Sc2C monolayer with OH, F, or O chemical groups. The electronic structures reveal that the functionalized Sc2C monolayers are semiconductors with a band gap of 0.44-1.55 eV. The band gap dependent optical parameters, like dielectric function, absorption coefficients, reflectivity, loss function, and refraction index were also calculated for photon energy up to 20 eV. At the low-energy region, each optical parameter shifts to red, and the peak increases obviously with the increase of the energy gap. Consequently, Sc2C monolayer with a tunable band gap by changing the type of surface chemical groups is a promising 2D material for optoelectronic devices.

Effects of thickness & shape on localized surface plasmon resonance of sexfoil nanoparticles

Yan Chen(陈艳), Xianchao Liu(刘贤超), Weidong Chen(陈卫东), Zhengwei Xie(谢征微), Yuerong Huang(黄跃容), Ling Li(李玲)
Chin. Phys. B, 2017, 26 (1): 017807 doi: 10.1088/1674-1056/26/1/017807
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Localized surface plasmon (LSPR) resonance and sensing properties of a novel nanostructure (sexfoil nanoparticle) are studied using the finite-difference time-domain method. For the sandwich sexfoil nanoparticle, the calculated extinction spectrum shows that with the thickness of the dielectric layer increasing, long-wavelength peaks blueshift, while short-wavelength peaks redshift. Strong near-field coupling of the upper and lower metal layers leads to electric and magnetic field resonances; as the thickness increases, the electric field resonance gradually increases, while the magnetic field resonance decreases. The obtained refractive index sensitivity and figure of merit are 332 nm/RIU and 3.91 RIU-1, respectively. In order to obtain better sensing ability, we further research the LSPR character of monolayer Ag sexfoil nanoparticle. After a series of trials to optimize the thickness and shape, the refractive index sensitivity approximates 668 nm/RIU, and the greatest figure of merit value comes to 14.8 RIU-1.

Rare earth Ce-modified (Ti,Ce)/a-C: H carbon-based filmon WC cemented carbide substrate

Shengguo Zhou(周升国), Zhengbing Liu(刘正兵), Shuncai Wang(王顺才)
Chin. Phys. B, 2017, 26 (1): 018101 doi: 10.1088/1674-1056/26/1/018101
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WC cemented carbide suffers severe wear in water environments. A novel carbon-based film could be a feasible way to overcome this drawback. In this study, a rare earth Ce-modified (Ti,Ce)/a-C:H carbon-based film is successfully prepared on WC cemented carbide using a DC reactive magnetron sputtering process. The microstructure, mechanical properties, and tribological behavior of the as-prepared carbon-based film are systematically investigated. The results show that the doping Ti forms TiC nanocrystallites that are uniformly dispersed in the amorphous carbon matrix, whereas the doping Ce forms CeO2 that exists with the amorphous phase in the co-doped (Ti,Ce)/a-C:H carbon-based film. The mechanical properties of this (Ti,Ce)/a-C:H film exhibit remarkable improvements, which could suggest higher hardness and elastic modulus as well as better adhesive strength compared to solitary Ti-doped Ti/a-C:H film. In particular, the as-prepared (Ti,Ce)/a-C:H film presents a relatively low friction coefficient and wear rate in both ambient air and deionized water, indicating that (Ti,Ce)/a-C:H film could feasibly improve the tribological performance of WC cemented carbide in a water environment.

High thermal stability of diamond-cBN-B4C-Si composites

Hong-Sheng Jia(贾洪声), Pin-Wen Zhu(朱品文), Hao Ye(叶灏), Bin Zuo(左斌), Yuan-Long E(鄂元龙), Shi-Chong Xu(徐仕翀), Ji Li(李季), Hai-Bo Li(李海波), Xiao-Peng Jia(贾晓鹏), Hong-An Ma(马红安)
Chin. Phys. B, 2017, 26 (1): 018102 doi: 10.1088/1674-1056/26/1/018102
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Improving the thermal stability of diamond and other superhard materials has great significance in various applications. Here, we report the synthesis and characterization of bulk diamond-cBN-B4C-Si composites sintered at high pressure and high temperature (HPHT, 5.2 GPa, 1620-1680 K for 3-5 min). The results show that the diamond, cBN, B4C, BxSiC, SiO2 and amorphous carbon or a little surplus Si are present in the sintered samples. The onset oxidation temperature of 1673 K in the as-synthesized sample is much higher than that of diamond, cBN, and B4C. The high thermal stability is ascribed to the covalent bonds of B-C, C-N, and the solid-solution of BxSiC formed during the sintering process. The results obtained in this work may be useful in preparing superhard materials with high thermal stability.

Magnetoelectric effect in multiferroic NdMn2O5

Syed Hamad Bukhari, Javed Ahmad
Chin. Phys. B, 2017, 26 (1): 018103 doi: 10.1088/1674-1056/26/1/018103
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We have measured the dielectric constant for NdMn2O5 in an external magnetic field to map out the magnetoelectric phase diagram. The phase diagram corresponds well with the previously reported data of neutron diffraction and magnetic susceptibility. Our main finding is the observation of a dielectric anomaly in the low temperature phase with a strong magnetoelectric effect, which is attributed to the independent Nd3+ ordering. Moreover, the absence of the dielectric anomaly in the paramagnetic phase is discussed, keeping in view the exchange interaction and its dependence on the rare-earth R3+ ionic radius.

Highly sensitive polymer photodetectors with a wide spectral response range

Mile Gao(高米勒), Wenbin Wang(王文斌), Lingliang Li(李凌亮), Jianli Miao(苗建利), Fujun Zhang(张福俊)
Chin. Phys. B, 2017, 26 (1): 018201 doi: 10.1088/1674-1056/26/1/018201
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A series of highly sensitive polymer photodetectors (PPDs) was fabricated with P3HT100-x:PBDT-TS1x:PC71BM1 as the active layers, where x represents the PBDT-TS1 doping weight ratio in donors. The response range of PPDs can cover from the UV to near-infrared regions by adjusting the PBDT-TS1 doping weight ratio. The best external quantum efficiency (EQE) values of ternary PPDs with P3HT:PBDT-TS1:PC71BM (50:50:1 wt/wt/wt) as the active layers reach 830%, 720%, and 330% under 390-, 625-, and 760-nm light illumination and -10 V bias, respectively. The large EQE values indicate that the photodetectors utilise photomultiplication (PM). The working mechanism of PM-type PPDs can be attributed to interfacial trap-assisted hole tunnelling injection from the external circuit under light illumination. The calculated optical field and photogenerated electron volume density in the active layers can well explain the EQE spectral shape as a function of the PBDT-TS1 doping weight ratio in donors.

Alleviating hysteresis and improving device stability of perovskite solar cells via alternate voltage sweeps

Chao Xia(夏超), Wei-Dong Song(宋伟东), Chong-Zhen Zhang(张崇臻), Song-Yang Yuan(袁松洋), Wen-Xiao Hu(胡文晓), Ping Qin(秦萍), Ru-Peng Wang(王汝鹏), Liang-Liang Zhao(赵亮亮), Xing-Fu Wang(王幸福), Miao He(何苗), Shu-Ti Li(李述体)
Chin. Phys. B, 2017, 26 (1): 018401 doi: 10.1088/1674-1056/26/1/018401
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The anomalous hysteresis in a perovskite solar cell induced by an asymmetric field is confirmed by a capacitance-voltage measurement. By applying several cycles of alternating reverse and forward scans, this hysteresis phenomenon is obviously alleviated, resulting in a hysteresis-less state in the perovskite solar cell. Meanwhile, the open-circuit voltage and power conversion efficiency of the perovskite solar cell are enhanced by 55.74% and 61.30%, respectively, while the current density and fill factor keep almost invariable. The operation of alleviating hysteresis is essential for further research and is likely to bring in performance gains.

Impact of neutron-induced displacement damage on the single event latchup sensitivity of bulk CMOS SRAM

Xiao-Yu Pan(潘霄宇), Hong-Xia Guo(郭红霞), Yin-Hong Luo(罗尹虹), Feng-Qi Zhang(张凤祁), Li-Li Ding(丁李利), Jia-Nan Wei(魏佳男), Wen Zhao(赵雯)
Chin. Phys. B, 2017, 26 (1): 018501 doi: 10.1088/1674-1056/26/1/018501
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Since the displacement damage induced by the neutron irradiation prior has negligible impact on the performance of the bulk CMOS SRAM, we use the neutron irradiation to degrade the minority carrier lifetime in the regions responsible for latchup. With the experimental results, we discuss the impact of the neutron-induced displacement damage on the SEL sensitivity and qualitative analyze the effectiveness of this suppression approach with TCAD simulation.

Random telegraph noise on the threshold voltage of multi-level flash memory

Yiming Liao(廖轶明), Xiaoli Ji(纪小丽), Yue Xu(徐跃), Chengxu Zhang(张城绪), Qiang Guo(郭强), Feng Yan(闫锋)
Chin. Phys. B, 2017, 26 (1): 018502 doi: 10.1088/1674-1056/26/1/018502
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We investigate the impact of random telegraph noise (RTN) on the threshold voltage of multi-level NOR flash memory. It is found that the threshold voltage variation (ΔVth) and the distribution due to RTN increase with the programmed level (Vth) of flash cells. The gate voltage dependence of RTN amplitude and the variability of RTN time constants suggest that the large RTN amplitude and distribution at the high program level is attributed to the charge trapping in the tunneling oxide layer induced by the high programming voltages. A three-dimensional TCAD simulation based on a percolation path model further reveals the contribution of those trapped charges to the threshold voltage variation and distribution in flash memory.

Photoemission cross section: A critical parameter in the impurity photovoltaic effect

Jiren Yuan(袁吉仁), Haibin Huang(黄海宾), Xinhua Deng(邓新华), Zhihao Yue(岳之浩), Yuping He(何玉平), Naigen Zhou(周耐根), Lang Zhou(周浪)
Chin. Phys. B, 2017, 26 (1): 018503 doi: 10.1088/1674-1056/26/1/018503
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A numerical study has been conducted to explore the role of photoemission cross sections in the impurity photovoltaic (IPV) effect for silicon solar cells doped with indium. The photovoltaic parameters (short-circuit current density, open-circuit voltage, and conversion efficiency) of the IPV solar cell were calculated as functions of variable electron and hole photoemission cross sections. The presented results show that the electron and hole photoemission cross sections play critical roles in the IPV effect. When the electron photoemission cross section is <10-20 cm2, the conversion efficiency η of the IPV cell always has a negative gain (Δη<0) if the IPV impurity is introduced. A large hole photoemission cross section can adversely impact IPV solar cell performance. The combination of a small hole photoemission cross section and a large electron photoemission cross section can achieve higher conversion efficiency for the IPV solar cell since a large electron photoemission cross section can enhance the necessary electron transition from the impurity level to the conduction band and a small hole photoemission cross section can reduce the needless sub-bandgap absorption. It is concluded that those impurities with small (large) hole photoemission cross section and large (small) electron photoemission cross section, whose energy levels are near the valence (or conduction) band edge, may be suitable for use in IPV solar cells. These results may help in judging whether or not an impurity is appropriate for use in IPV solar cells according to its electron and hole photoemission cross sections.

Heteromaterial-gate line tunnel field-effect transistor based on Si/Ge heterojunction

Shuqin Zhang(张书琴), Renrong Liang(梁仁荣), Jing Wang(王敬), Zhen Tan(谭桢), Jun Xu(许军)
Chin. Phys. B, 2017, 26 (1): 018504 doi: 10.1088/1674-1056/26/1/018504
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A Si/Ge heterojunction line tunnel field-effect transistor (LTFET) with a symmetric heteromaterial gate is proposed. Compared to single-material-gate LTFETs, the heteromaterial gate LTFET shows an off-state leakage current that is three orders of magnitude lower, and steeper subthreshold characteristics, without degradation in the on-state current. We reveal that these improvements are due to the induced local potential barrier, which arises from the energy-band profile modulation effect. Based on this novel structure, the impacts of the physical parameters of the gap region between the pocket and the drain, including the work-function mismatch between the pocket gate and the gap gate, the type of dopant, and the doping concentration, on the device performance are investigated. Simulation and theoretical calculation results indicate that the gap gate material and n-type doping level in the gap region should be optimized simultaneously to make this region fully depleted for further suppression of the off-state leakage current.

Very long wavelength infrared focal plane arrays with 50% cutoff wavelength based on type-II InAs/GaSb superlattice

Xi Han(韩玺), Wei Xiang(向伟), Hong-Yue Hao(郝宏玥), Dong-Wei Jiang(蒋洞微), Yao-Yao Sun(孙姚耀), Guo-Wei Wang(王国伟), Ying-Qiang Xu(徐应强), Zhi-Chuan Niu(牛智川)
Chin. Phys. B, 2017, 26 (1): 018505 doi: 10.1088/1674-1056/26/1/018505
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A very long wavelength infrared(VLWIR) focal plane array based on InAs/GaSb type-II super-lattices is demonstrated on a GaSb substrate. A hetero-structure photodiode was grown with a 50% cut-off wavelength of 15.2 μm, at 77 K. A 320×256 VLWIR focal plane array with this design was fabricated and characterized. The peak quantum efficiency without an antireflective coating was 25.74% at the reverse bias voltage of -20 mV, yielding a peak specific detectivity of 5.89×1010 cm·Hz1/2·W-1. The operability and the uniformity of response were 89% and 83.17%. The noise-equivalent temperature difference at 65 K exhibited a minimum at 21.4 mK, corresponding to an average value of 56.3 mK.

Nonlinear profile order for three-dimensional hybrid radial acquisition applied to self-gated free-breathing cardiac cine MRI

Yanchun Zhu(朱艳春), Pascal Spincemaille, Jing Liu(刘静), Shuo Li(李硕), Thanh D Nguyen, Martin R Prince, Yaoqin Xie(谢耀钦), Yi Wang(王乙)
Chin. Phys. B, 2017, 26 (1): 018701 doi: 10.1088/1674-1056/26/1/018701
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This paper presents a nonlinear profile order scheme for three-dimensional (3D) hybrid radial acquisition applied to self-gated, free-breathing cardiac cine magnetic resonance imaging (MRI). In self-gated, free-breathing cardiac cine MRI, respiratory and cardiac motions are unpredictable during acquisition, especially for retrospective reconstruction. Therefore, the non-uniformity of the k-space distribution is an issue of great concern during retrospective self-gated reconstruction. A nonlinear profile order with varying azimuthal increments was provided and compared with the existing golden ratio-based profile order. Optimal parameter values for the nonlinear formula were chosen based on simulations. The two profile orders were compared in terms of the k-space distribution and phantom and human image results. An approximately uniform distribution was obtained based on the nonlinear profile order for persons with various heart rates and breathing patterns. The nonlinear profile order provides more stable profile distributions and fewer streaking artifacts in phantom images. In a comparison of human cardiac cine images, the nonlinear profile order provided results comparable to those provided by the golden ratio-based profile order, and the images were suitable for diagnosis. In conclusion, the nonlinear profile order scheme was demonstrated to be insensitive to various motion patterns and more useful for retrospective reconstruction.

Community detection in signed networks based on discrete-time model

Jianrui Chen(陈建芮), Li Zhang(张莉), Weiwei Liu(刘维维), Zaizai Yan(闫在在)
Chin. Phys. B, 2017, 26 (1): 018901 doi: 10.1088/1674-1056/26/1/018901
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Community detection in signed networks has been studied widely in recent years. In this paper, a discrete difference equation is proposed to imitate the consistently changing phases of the nodes. During the interaction, each node will update its phase based on the difference equation. Each node has many different nodes connected with it, and these neighbors have different influences on it. The similarity between two nodes is applied to describe the influences between them. Nodes with high positive similarities will get together and nodes with negative similarities will be far away from each other. Communities are detected ultimately when the phases of the nodes are stable. Experiments on real world and synthetic signed networks show the efficiency of detection performance. Moreover, the presented method gains better detection performance than two existing good algorithms.

Entropy-based link prediction in weighted networks

Zhongqi Xu(许忠奇), Cunlai Pu(濮存来), Rajput Ramiz Sharafat, Lunbo Li(李伦波), Jian Yang(杨健)
Chin. Phys. B, 2017, 26 (1): 018902 doi: 10.1088/1674-1056/26/1/018902
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Information entropy has been proved to be an effective tool to quantify the structural importance of complex networks. In a previous work[Xu et al. Physica A, 456 294 (2016)], we measure the contribution of a path in link prediction with information entropy. In this paper, we further quantify the contribution of a path with both path entropy and path weight, and propose a weighted prediction index based on the contributions of paths, namely weighted path entropy (WPE), to improve the prediction accuracy in weighted networks. Empirical experiments on six weighted real-world networks show that WPE achieves higher prediction accuracy than three other typical weighted indices.

Asymptotic bounded consensus tracking of double-integratormulti-agent systems with bounded-jerk target based onsampled-data without velocity measurements

Shuang-Shuang Wu(吴爽爽), Zhi-Hai Wu(吴治海), Li Peng(彭力), Lin-Bo Xie(谢林柏)
Chin. Phys. B, 2017, 26 (1): 018903 doi: 10.1088/1674-1056/26/1/018903
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This paper investigates asymptotic bounded consensus tracking (ABCT) of double-integrator multi-agent systems (MASs) with an asymptotically-unbounded-acceleration and bounded-jerk target (AUABJT) available to partial agents based on sampled-data without velocity measurements. A sampled-data consensus tracking protocol (CTP) without velocity measurements is proposed to guarantee that double-integrator MASs track an AUABJT available to only partial agents. The eigenvalue analysis method together with the augmented matrix method is used to obtain the necessary and sufficient conditions for ABCT. A numerical example is provided to illustrate the effectiveness of theoretical results.

Theoretical and experimental study on broadband terahertz atmospheric transmission characteristics

Shi-Bei Guo(郭拾贝), Kai Zhong(钟凯), Mao-Rong Wang(王茂榕), Chu Liu(刘楚), Yong Xiao(肖勇), Wen-Peng Wang(王文鹏), De-Gang Xu(徐德刚), Jian-Quan Yao(姚建铨)
Chin. Phys. B, 2017, 26 (1): 019501 doi: 10.1088/1674-1056/26/1/019501
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Broadband terahertz (THz) atmospheric transmission characteristics from 0 to 8 THz are theoretically simulated based on a standard Van Vleck-Weisskopf line shape, considering 1696 water absorption lines and 298 oxygen absorption lines. The influences of humidity, temperature, and pressure on the THz atmospheric absorption are analyzed and experimentally verified with a Fourier transform infrared spectrometer (FTIR) system, showing good consistency. The investigation and evaluation on high-frequency atmospheric windows are good supplements to existing data in the low-frequency range and lay the foundation for aircraft-based high-altitude applications of THz communication and radar.
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