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Chin. Phys. B  
  Chin. Phys. B--2019, Vol.28, No.8
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SPECIAL TOPIC—Recent advances in thermoelectric materials and devices

Spin transport in antiferromagnetic insulators

Zhiyong Qiu, Dazhi Hou
Chin. Phys. B 2019, 28 (8): 088504;  doi: 10.1088/1674-1056/28/8/088504
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Electrical spin, which is the key element of spintronics, has been regarded as a powerful substitute for the electrical charge in the next generation of information technology, in which spin plays the role of the carrier of information and/or energy in a similar way to the electrical charge in electronics. Spin-transport phenomena in different materials are central topics of spintronics. Unlike electrical charge, spin transport does not depend on electron motion, particularly spin can be transported in insulators without accompanying Joule heating. Therefore, insulators are considered to be ideal materials for spin conductors, in which magnetic insulators are the most compelling systems. Recently, we experimentally studied and theoretically discussed spin transport in various antiferromagnetic systems and identified spin susceptibility and the Néel vector as the most important factors for spin transport in antiferromagnetic systems. Herein, we summarize our experimental results, physical nature, and puzzles unknown. Further challenges and potential applications are also discussed.

The evolution of cooperation in public good game with deposit

Xian-Jia Wang, Wen-Man Chen
Chin. Phys. B 2019, 28 (8): 080201;  doi: 10.1088/1674-1056/28/8/080201
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The emergence of cooperation still remains a fundamental conundrum in the social and behavior sciences. We introduce a new mechanism, deposit mechanism, into theoretical model to explore how this mechanism promotes cooperation in a well-mixed population. Firstly, we extend the common binary-strategy combination of cooperation and defection in public good game by adding a third strategy, namely, deposit cooperation. The players with deposit cooperation strategy pay a deposit in advance to obtain the benefits of public good at a lower contributions compared with the players with cooperation strategy, when the provision of public good is successful. Then, we explore the evolution of cooperation in the public good game with deposit by means of the replicator dynamics. Theoretical computations and stimulations show that the deposit mechanism can promote cooperation in a well-mixed population, and the numbers of equilibrium point are determined by variables of public good game. On the one hand, when the coexistence of cooperators and defectors is the stable equilibrium point in the evolutionary system, increasing the threshold of public good and adopting the weak altruism way for share benefits can enhance the level of cooperation in the population. On the other hand, if the coexistence of deposit cooperators and defectors is the stable equilibrium point, it is effective to promote the deposit cooperation by lowering the values of discount and deposit, and raising the threshold of public good.

The upper bound function of nonadiabatic dynamics in parametric driving quantum systems

Lin Zhang, Junpeng Liu
Chin. Phys. B 2019, 28 (8): 080301;  doi: 10.1088/1674-1056/28/8/080301
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The adiabatic control is a powerful technique for many practical applications in quantum state engineering, light-driven chemical reactions and geometrical quantum computations. This paper reveals a speed limit of nonadiabatic transition in a general time-dependent parametric quantum system that leads to an upper bound function which lays down an optimal criteria for the adiabatic controls. The upper bound function of transition rate between instantaneous eigenstates of a time-dependent system is determined by the power fluctuations of the system relative to the minimum gap between the instantaneous levels. In a parametric Hilbert space, the driving power corresponds to the quantum work done by the parametric force multiplying the parametric velocity along the parametric driving path. The general two-state time-dependent models are investigated as examples to calculate the bound functions in some general driving schemes with one and two driving parameters. The calculations show that the upper bound function provides a tighter real-time estimation of nonadiabatic transition and is closely dependent on the driving frequencies and the energy gap of the system. The deviations of the real phase from Berry phase on different closed paths are induced by the nonadiabatic transitions and can be efficiently controlled by the upper bound functions. When the upper bound is adiabatically controlled, the Berry phases of the electronic spin exhibit nonlinear step-like behaviors and it is closely related to topological structures of the complicated parametric paths on Bloch sphere.

On a biseparability criterion of bipartite qudit state

B Benzimoun, M Daoud
Chin. Phys. B 2019, 28 (8): 080302;  doi: 10.1088/1674-1056/28/8/080302
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In this paper, we propose a new approach to tackle the separability problem for bipartite qudit mixed-states. This is based on the Majorana representation which allows to represent a N-spinors (qudit) as a symmetric state of N spin-1/2. We also discuss how we can exploit such representation and the notion of the biseparability of multipartite qubit states in the sense to establish new criteria of the separability problem based on the PPT and concurrence.

Dissipative generation for steady-state entanglement of two transmons in circuit QED

Shuang He, Dan Liu, Ming-Hao Li
Chin. Phys. B 2019, 28 (8): 080303;  doi: 10.1088/1674-1056/28/8/080303
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We present a dissipative scheme to generate an entangled steady-state between two superconducting transmon qutrits separately embedded in two coupled transmission line resonators in a circuit quantum electrodynamics (QED) setup. In our scheme, the resonant qutrit-resonator interaction and photon hopping between resonators jointly induce asymmetric energy gaps in the dressed state subspaces. The coherent driving fields induce the specific dressed state transition and the dissipative processes lead to the gradual accumulation in the population of target state, combination of both drives the system into a steady-state entanglement. Numerical simulation shows that the maximally entangled state can be produced with high fidelity and strong robustness against the cavity decay and qutrit decay, and no requirements for accurate time control. The scheme is achievable with the current experimental technologies.

Temperature effects on atmospheric continuous-variable quantum key distribution

Shu-Jing Zhang, Hong-Xin Ma, Xiang Wang, Chun Zhou, Wan-Su Bao, Hai-Long Zhang
Chin. Phys. B 2019, 28 (8): 080304;  doi: 10.1088/1674-1056/28/8/080304
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Compared with the fiber channel, the atmospheric channel offers the possibility of a broader geographical coverage and more flexible transmission for continuous-variable quantum key distribution (CVQKD). However, the fluctuation of atmospheric conditions will lead to the loss of performance in atmospheric quantum communication. In this paper, we study how temperature affects atmospheric CVQKD. We mainly consider the temperature effects on the transmittance and interruption probability. From the numerical simulation analysis, it can be shown that the performance of atmospheric CVQKD is improved as temperature increases, with the other factors fixed. Moreover, the results in this work can be used to evaluate the feasibility of the experimental implementation of the atmospheric CVQKD protocols.

Tunable coupling between Xmon qubit and coplanar waveguide resonator

He-Kang Li, Ke-Min Li, Hang Dong, Qiu-Jiang Guo, Wu-Xin Liu, Zhan Wang, Hao-Hua Wang, Dong-Ning Zheng
Chin. Phys. B 2019, 28 (8): 080305;  doi: 10.1088/1674-1056/28/8/080305
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Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing. Here, we design and characterize a tunable coupling element based on Josephson junction, which can be adapted to an all-to-all connected circuit architecture where multiple Xmon qubits couple to a common coplanar waveguide resonator. The coupling strength is experimentally verified to be adjustable from 0 MHz to about 40 MHz, and the qubit lifetime can still be up to 12 μs in the presence of the coupling element.


Efficient solver for time-dependent Schrödinger equation with interaction between atoms and strong laser field

Sheng-Peng Zhou, Ai-Hua Liu, Fang Liu, Chun-Cheng Wang, Da-Jun Ding
Chin. Phys. B 2019, 28 (8): 083101;  doi: 10.1088/1674-1056/28/8/083101
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We present a parallel numerical method of simulating the interaction of atoms with a strong laser field by solving the time-depending Schrödinger equation (TDSE) in spherical coordinates. This method is realized by combining constructing block diagonal matrices through using the real space product formula (RSPF) with splitting out diagonal sub-matrices for short iterative Lanczos (SIL) propagator. The numerical implementation of the solver guarantees efficient parallel computing for the simulation of real physical problems such as high harmonic generation (HHG) in these interaction systems.

Ellipticity-dependent ionization yield for noble atoms

Hristina Delibašić, Violeta Petrović
Chin. Phys. B 2019, 28 (8): 083201;  doi: 10.1088/1674-1056/28/8/083201
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The photoionization in the frame of the Ammosov-Delone-Krainov theory has been theoretically examined for noble gases, argon, krypton, and xenon, in an elliptically polarized laser field. We consider the intermediate range of the Keldysh parameter, γ~1, and analyze the influence of shifted ionization potential and temporal profile to eliminate disagreement between theoretical and experimental findings. By including these effects in the ionization rates, we solve rate equations in order to determine an expression for the ionization yield. The use of modified ionization potential shows that the ionization yields will actually decrease below the values predicted by original (uncorrected) formulas. This paper will discuss the causes of this discrepancy.

Controlling Rydberg excitation process with shaped intense ultrashort laser pulses

Xiao-Yun Zhao, Chun-Cheng Wang, Shi-Lin Hu, Wei-Dong Li, Jing Chen, Xiao-Lei Hao
Chin. Phys. B 2019, 28 (8): 083202;  doi: 10.1088/1674-1056/28/8/083202
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We perform a theoretical investigation on the control over the atomic excitation of Rydberg states with shaped intense ultrashort laser pulses. By numerically solving the time-dependent Schrödinger equation (TDSE), we systematically study the dependence of the population of the Rydberg states on the π phase step position in the frequency spectra of the laser pulse for different intensities, central wavelengths and pulse durations. Our results show that the Rydberg excitation process can be effectively modulated using shaped intense laser pulses with the laser intensity as high as 1×1014 W/cm2. Our work also have benefit to the future investigation to find out the dominant mechanism behind the excitation of Rydberg states in strong laser fields.

Synthesis and surface plasmon resonance of Au-ZnO Janus nanostructures

Jun Zhou, Jian-Shuo Zhang, Guo-Yu Xian, Qi Qi, Shang-Zhi Gu, Cheng-Min Shen, Zhao-Hua Cheng, Sheng-Tai He, Hai-Tao Yang
Chin. Phys. B 2019, 28 (8): 083301;  doi: 10.1088/1674-1056/28/8/083301
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Metal-semiconductor Janus nanostructures with asymmetry and directionality have recently aroused significant interest, both in fundamental light-matter interactions mechanism and in technological applications. Here we report the synthesis of different Au-ZnO Janus nanostructures via a facile one-pot colloid method. The growth mechanism is revealed by a series of designed synthesis experiments. The light absorption properties are determined by both the decrease of dipole oscillations of the free electrons and the plasmon-induced hot-electron transfer. Moreover, the finite-difference time-domain (FDTD) simulation method is used to elucidate the electric field distributions of these Janus nanostructures.

Surface plasmon polaritons generated magneto-optical Kerr reversal in nanograting

Le-Yi Chen, Zhen-Xing Zong, Jin-Long Gao, Shao-Long Tang, You-Wei Du
Chin. Phys. B 2019, 28 (8): 083302;  doi: 10.1088/1674-1056/28/8/083302
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Controlling the phase of light in magnetoplasmonic structures is receiving increasing attention because of its already shown capability in ultrasensitive and label-free molecular-level detection. Magneto-optical Kerr reversal has been achieved and well explained in nanodisks by using the phase of localized plasmons. In this paper, we report that the Kerr reversal can also be produced by surface plasmon polaritons independently. We experimentally confirm this in Co and Ag/Co/Ag metal nanogratings, and can give a qualitative explanation that it is the charge accumulation at the interface between the grating surface and air that acts as the electromagnetic restoring force to contribute necessary additional phase for Kerr reversal. Our finding can enrich the means of designing and fabricating magneto-optical-based biochemical sensors.

Energetics and diffusion of point defects in Au/Ag metals:A molecular dynamics study

Zhi-Yong Liu, Bin He, Xin Qu, Li-Bo Niu, Ru-Song Li, Fei Wang
Chin. Phys. B 2019, 28 (8): 083401;  doi: 10.1088/1674-1056/28/8/083401
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To reveal the potential aging mechanism for self-irradiation in Pu-Ga alloy, we choose Au-Ag alloy as its substitutional material in terms of its mass density and lattice structure. As a first step for understanding the microscopic behavior of point defects in Au-Ag alloy, we perform a molecular dynamics (MD) simulation on energetics and diffusion of point defects in Au and Ag metal. Our results indicate that the octahedral self-interstitial atom (SIA) is more stable than the tetrahedral SIA. The stability sequence of point defects for He atom in Au/Ag is:substitutional site > octahedral interstitial site > tetrahedral interstitial site. The He-V cluster (HenVm, V denotes vacancy) is the most stable at n=m. For the mono-vacancy diffusion, the MD calculation shows that the first nearest neighbour (1NN) site is the most favorable site on the basis of the nudged elastic band (NEB) calculation, which is in agreement with previous experimental data. There are two peaks for the second nearest neighbour (2NN) and the third nearest neighbour (3NN) diffusion curve in octahedral interstitial site for He atom, indicating that the 2NN and 3NN diffusion for octahedral SIA would undergo an intermediate defect structure similar to the 1NN site. The 3NN diffusion for the tetrahedral SIA and He atom would undergo an intermediate site in analogy to its initial structure. For diffusion of point defects, the vacancy, SIA, He atom and He-V cluster may have an analogous effect on the diffusion velocity in Ag.

Quasi-classical trajectory study of H+LiH (v=0, 1, 2, j=0)→Li+H2 reaction on a new global potential energy surface

Yu-Liang Wang, De-Zhi Su, Cun-Hai Liu, Hui Li
Chin. Phys. B 2019, 28 (8): 083402;  doi: 10.1088/1674-1056/28/8/083402
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Quasi-classical trajectory (QCT) calculations are reported for the H+LiH (v=0-2, j=0)→Li+H2 reaction on a new ground electronic state global potential energy surface (PES) of the LiH2 system. Reaction probability and integral cross sections (ICSs) are calculated for collision energies in the range of 0 eV-0.5 eV. Reasonable agreement is found in the comparison between present results and previous available theoretical results. We carried out statistical analyses with all the trajectories and found two main distinct reaction mechanisms in the collision process, in which the stripping mechanism (i.e., without roaming process) is dominated over the collision energy range. The polarization dependent differential cross sections (PDDCSs) indicate that forward scattering dominates the reaction due to the dominated mechanism. Furthermore, the reactant vibration leads to a reduction of the reactivity because of the barrierless and attractive features of PES and mass combination of the system.

Interference effect of photoionization of hydrogen atoms by ultra-short and ultra-fast high-frequency chirped pulses

Ningyue Wang, Aihua Liu
Chin. Phys. B 2019, 28 (8): 083403;  doi: 10.1088/1674-1056/28/8/083403
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The photoionization of a hydrogen atom from its ground state with ultra-fast chirped pulses is investigated by numerically solving the time-dependent Schrödinger equation within length, velocity, and Kramers-Henneberger gauges. Converged results for all gauges for chirp-free pulses agree with the prediction of dynamic interference for ground state hydrogen atoms predicted recently by Jiang and Burgdörfer[Opt. Express 26, 19921 (2018)]. In addition, we investigated photoelectron spectra of hydrogen atoms by chirped laser pulses, and showed that dynamic interference effect will be weaken for pulses with increasing linear chirp. Our numerical results can be understood and discussed in terms of an interplay of photoelectron wavepackets from first and second halves of laser enevelop, including the ac Stark energy level shift of the photoelectron final state and atomic stabilization effect at ultra-high intensities.

Optical design of common-aperture multispectral and polarization optical imaging system with wide field of view

Xin Liu, Jun Chang, Shuai Feng, Yu Mu, Xia Wang, Zhao-Peng Xu
Chin. Phys. B 2019, 28 (8): 084201;  doi: 10.1088/1674-1056/28/8/084201
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Multispectral and polarization cameras that can simultaneously acquire the spatial, spectral, and polarization characteristics of an object have considerable potential applications in target detection, biomedical imaging, and remote sensing. In this work, we develop a common-aperture optical system that can capture multispectral and polarization information. An off-axis three-mirror optical system is mounted on the front end of the proposed system and used as a common-aperture telescope in the visible light (400 nm-750 nm) and long-wave infrared (LWIR, 8 μm-12 μm) waveband. The system can maintain a wide field of view (4.5°) and it can demonstrate an enhanced identification ability. The off-axis three-mirror system gets rid of central obscuration while further yielding stable system resolution and energy. Light that has passed through the front-end common-aperture reflection system is divided into the visible light and LWIR waveband by a beamsplitter. The two wavebands then converge on two detectors through two groups of lenses. Our simulation results indicate that the proposed system can obtain clear images in each waveband to meet the diverse imaging requirements.

Optimized dithering technique in frequency domain for high-quality three-dimensional depth data acquisition

Ning Cai, Zhe-Bo Chen, Xiang-Qun Cao, Bin Lin
Chin. Phys. B 2019, 28 (8): 084202;  doi: 10.1088/1674-1056/28/8/084202
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On the basis of the objective functions, dithering optimization techniques can be divided into the intensity-based optimization technique and the phase-based optimization technique. However, both types of techniques are spatial-domain optimization techniques, while their measurement performances are essentially determined by the harmonic components in the frequency domain. In this paper, a novel genetic optimization technique in the frequency domain is proposed for high-quality fringe generation. In addition, to handle the time-consuming difficulty of genetic algorithm (GA), we first optimize a binary patch, then join the optimal binary patches together according to periodicity and symmetry so as to generate a full-size pattern. It is verified that the proposed technique can significantly enhance the measured performance and ensure the robustness to various amounts of defocusing.

Phase retrieval algorithm for optical information security

Shi-Qing Wang, Xiang-Feng Meng, Yu-Rong Wang, Yong-Kai Yin, Xiu-Lun Yang
Chin. Phys. B 2019, 28 (8): 084203;  doi: 10.1088/1674-1056/28/8/084203
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As a typical technology for optical encryption, phase retrieval algorithms have been widely used in optical information encryption and authentication systems. This paper presents three applications of two-dimensional (2D) phase retrieval for optical encryption and authentication:first, a hierarchical image encryption system, by which multiple images can be hidden into cascaded multiple phase masks; second, a multilevel image authentication system, which combines (t, n) threshold secret sharing (both t and n are positive integers, and tn) and phase retrieval, and provides both high-level and low-level authentication; and finally, a hierarchical multilevel authentication system that combines the secret sharing scheme based on basic vector operations and the phase retrieval, by which more certification images can be encoded into multiple cascaded phase masks of different hierarchical levels. These three phase retrieval algorithms can effectively illustrate phase-retrieval-based optical information security. The principles and features of each phase-retrieval-based optical security method are analyzed and discussed. It is hoped that this review will illustrate the current development of phase retrieval algorithms for optical information security and will also shed light on the future development of phase retrieval algorithms for optical information security.

Mask-based denoising scheme for ghost imaging

Yang Zhou, Shu-Xu Guo, Fei Zhong, Tian Zhang
Chin. Phys. B 2019, 28 (8): 084204;  doi: 10.1088/1674-1056/28/8/084204
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Ghost imaging (GI) is thought of as a promising imaging method in many areas. However, the main drawback of GI is the huge measurement data and low signal-to-noise ratio. In this paper, we propose a novel mask-based denoising scheme to improve the reconstruction quality of GI. We first design a mask through the maximum between-class variance (OTSU) method and construct the measurement matrix with speckle patterns. Then, the correlated noise in GI can be effectively suppressed by employing the mask. From the simulation and experimental results, we can conclude that our method has the ability to improve the imaging quality compared with traditional GI method.

Single-shot phase-shifting digital holography with a photon-sieve-filtering telescope

You Li, Yao-Cun Li, Jun-Yong Zhang, Yan-Li Zhang, Xue-Mei Li
Chin. Phys. B 2019, 28 (8): 084205;  doi: 10.1088/1674-1056/28/8/084205
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A method of single-shot phase-shifting digital holography with a photon-sieve-filtering telescope is proposed. Three copy images with different phases are first generated by use of a monofocal photon-sieve filter in Kepler telescope, and then interfere with the reference plane wave by a beam combiner. The hologram is captured by a charge-coupled device (CCD) in one single exposure. The complex-valued amplitude of the test object can be reconstructed by three-step phase-shifting interferometry through three frames of extracted sub-interferograms from the single-exposure hologram. The principle and simulation experiments are carried out and verified the validity of our proposed method. This method can be applied for snapshot imaging and three-dimensional object construction.

Evolution of quantum states via Weyl expansion in dissipative channel

Li-Yun Hu, Zhi-Ming Rao, Qing-Qiang Kuang
Chin. Phys. B 2019, 28 (8): 084206;  doi: 10.1088/1674-1056/28/8/084206
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Based on the Weyl expansion representation of Wigner operator and its invariant property under similar transformation, we derived the relationship between input state and output state after a unitary transformation including Wigner function and density operator. It is shown that they can be related by a transformation matrix corresponding to the unitary evolution. In addition, for any density operator going through a dissipative channel, the evolution formula of the Wigner function is also derived. As applications, we considered further the two-mode squeezed vacuum as inputs, and obtained the resulted Wigner function and density operator within normal ordering form. Our method is clear and concise, and can be easily extended to deal with other problems involved in quantum metrology, steering, and quantum information with continuous variable.

Zinc-oxide nanoparticle-based saturable absorber deposited by simple evaporation technique for Q-switched fiber laser

Syarifah Aloyah Syed Husin, Farah Diana Muhammad, Che Azurahanim Che Abdullah, Siti Huzaimah Ribut, Mohd Zamani Zulkifli, Mohd Adzir Mahdi
Chin. Phys. B 2019, 28 (8): 084207;  doi: 10.1088/1674-1056/28/8/084207
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A Q-switched erbium-doped fiber laser (EDFL) incorporating zinc-oxide (ZnO) nanoparticles-based saturable absorber (SA) is proposed and demonstrated. To form the SA, the ZnO nanoparticles, which are originally in the powder form, are first dissolved in ethanol and subsequently deposited onto the surface of fiber ferrule by using the adhesion effect with the evaporation technique. By integrating the ZnO nanoparticle-based SA into a laser cavity of an EDFL, a self-started and stable Q-switching is achieved at a low threshold power of 20.24 mW. As the pump power is increased, the pulse repetition rate is tunable from 10.34 kHz to 25.59 kHz while pulse duration decreases from 21.39 μs to 3.65 μs. Additionally, this Q-switched laser has a maximum energy per pulse of 19.34 nJ and an average output power of 0.46 mW. These results indicate the feasibility and functionality of the ZnO nanoparticles-based SA for Q-switched generation, which offers the flexibility and easy integration of the SA into a ring laser cavity.

Pulse generation of erbium-doped fiber laser based on liquid-exfoliated FePS3

Qing Yin, Jin Wang, Xin-Yao Shi, Tao Wang, Jie Yang, Xin-Xin Zhao, Zhen-Jiang Shen, Jian Wu, Kai Zhang, Pu Zhou, Zong-Fu Jiang
Chin. Phys. B 2019, 28 (8): 084208;  doi: 10.1088/1674-1056/28/8/084208
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As a preferable material in the field of photo-detection and catalysis, the characteristics of FePS3 in broad wavelength range have been proven by many experimental studies. However, FePS3 has not been used as a saturable absorber (SA) in fiber lasers yet. We propose and demonstrate the generation of a single wavelength and dual-wavelength based on an Er-doped fiber laser (EDFL) at 1.5 μm by using an innovative FePS3 saturable absorber for the first time. The result shows that a stable passively Q-switched pulse can be generated, which demonstrates that the new two-dimensional (2D) material FePS3 served as SA provides a valid method to realize passively Q-switched laser. In addition, we achieve the output of the dual-wavelength pulse by properly rotating the polarization controller. To the best of our knowledge, the dual-wavelength pulse EDFL could be applied in biomedicine, spectroscopy, and sensing research.

The 2-μm to 6-μm mid-infrared supercontinuum generation in cascaded ZBLAN and As2Se3 step-index fibers

Jinmei Yao, Bin Zhang, Ke Yin, Jing Hou
Chin. Phys. B 2019, 28 (8): 084209;  doi: 10.1088/1674-1056/28/8/084209
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Fiber-based mid-infrared (MIR) supercontinuum (SC) sources benefit from their spectral brightness and spatial coherence that are needed for many applications, such as spectroscopy and metrology. In this paper, an SC spanning from 2 μm to 6 μm is demonstrated in cascaded ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) and As2Se3 step-index fibers. The pump source is a ZBLAN fiber-based MIR SC laser with abundant high-peak-power soliton pulses between 3000 nm and 4200 nm. By concatenating the ZBLAN fiber and the As2Se3 fiber, efficient cascading red-shifts are obtained in the normal dispersion region of the As2Se3 fiber. The spectral behavior of cascaded SC generation shows that the long-wavelength proportion of MIR SC generated in the ZBLAN fiber plays a critical role for further spectral extension in the As2Se3 fiber.

Multi-wavelength continuous-wave Nd:YVO4 self-Raman laser under in-band pumping

Li Fan, Xiao-Dong Zhao, Yun-Chuan Zhang, Xiao-Dong Gu, Hao-Peng Wan, Hui-Bo Fan, Jun Zhu
Chin. Phys. B 2019, 28 (8): 084210;  doi: 10.1088/1674-1056/28/8/084210
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Multi-wavelength continuous-wave self-Raman laser with an a-cut composite YVO4/Nd:YVO4/YVO4 crystal pumped by an 879-nm wavelength-locked laser diode is demonstrated for the first time. Multi-wavelength Raman lasers at 1168.4, 1176, 1178.7, and 1201.6 nm are achieved by the first Stokes shift of the multi-wavelength fundamental lasers at 1064, 1066.7, 1073.6, 1084, and 1085.6 nm with two Raman shifts of 890 and 816 cm-1. A maximum Raman output power of 2.56 W is achieved through the use of a 20-mm-long composite crystal, with a corresponding optical conversion efficiency of 9.8%. The polarization directions of different fundamental and Raman lasers are investigated and found to be orthogonal π and σ polarizations. These orthogonally polarized multi-wavelength lasers with small wavelength separation pave the way to the development of a potential laser source for application in spectral analysis, laser radar and THz generation.

Non-crossover sub-Doppler DAVLL in selective reflection scheme

Lin-Jie Zhang, Hao Zhang, Yan-Ting Zhao, Lian-Tuan Xiao, Suo-Tang Jia
Chin. Phys. B 2019, 28 (8): 084211;  doi: 10.1088/1674-1056/28/8/084211
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We demonstrate a non-crossover sub-Doppler dichroic atomic vapor laser locking (DAVLL) in selective reflection scheme, which allows us to obtain a modulation-free laser locking with wide tuneable range. The dependence of peak-to-peak amplitude, tuneable range and the slope near the zero-crossing point of error signal on the frequency shift induced by the magnetic fields are studied. The adjustable error signal by the varying external magnetic field can offer the laser locking from the order of tens MHz to hundreds MHz. The ultimate dither of locked laser frequency is less than 0.5 MHz. The square root of Allan variance of the error signals reaches a minimum of 3×10-10 for an averaging time of 130 s.

Vertical profile of aerosol extinction based on the measurement of O4 of multi-elevation angles with MAX-DOAS

Fusheng Mou, Jing Luo, Suwen Li, Wei Shan, Lisha Hu
Chin. Phys. B 2019, 28 (8): 084212;  doi: 10.1088/1674-1056/28/8/084212
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A method for aerosol extinction profile retrieval using ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) is studied, which is based on a look-up table algorithm. The algorithm uses parametric method to represent aerosol extinction profiles and simulate different atmospheric aerosol states through atmospheric radiation transfer model. Based on the method, aerosol extinction profile was obtained during six cloud-free days. The O4 differential air mass factor (dAMF) measured by MAX-DOAS is compared with the corresponding model results under different atmospheric conditions (R2=0.78). The aerosol optical thickness, aerosol weight factor in boundary layer, and the height of the boundary layer are obtained after the process of minimization and look-up table method. The retrieved aerosol extinction in boundary layer is compared with PM2.5 data measured by ground point instrument. The diurnal variation trends of the two methods are in good agreement. The correlation coefficients of the two methods are 0.71 when the aerosol optical thickness is smaller than 0.5. The results show that the look-up table method can obtain the aerosol state of the troposphere and provide validation for other instrument data.

Non-Stokes drag coefficient in single-particle electrophoresis:New insights on a classical problem Hot!

Mai-Jia Liao, Ming-Tzo Wei, Shi-Xin Xu, H Daniel Ou-Yang, Ping Sheng
Chin. Phys. B 2019, 28 (8): 084701;  doi: 10.1088/1674-1056/28/8/084701
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We measured the intrinsic electrophoretic drag coefficient of a single charged particle by optically trapping the particle and applying an AC electric field, and found it to be markedly different from that of the Stokes drag. The drag coefficient, along with the measured electrical force, yield a mobility-zeta potential relation that agrees with the literature. By using the measured mobility as input, numerical calculations based on the Poisson-Nernst-Planck equations, coupled to the Navier-Stokes equation, reveal an intriguing microscopic electroosmotic flow near the particle surface, with a well-defined transition between an inner flow field and an outer flow field in the vicinity of electric double layer's outer boundary. This distinctive interface delineates the surface that gives the correct drag coefficient and the effective electric charge. The consistency between experiments and theoretical predictions provides new insights into the classic electrophoresis problem, and can shed light on new applications of electrophoresis to investigate biological nanoparticles.

Opto propeller effect on Micro-Rotors with different handedness

Yiwen Tang, Zhibing Li
Chin. Phys. B 2019, 28 (8): 084702;  doi: 10.1088/1674-1056/28/8/084702
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Manipulating biomacromolecules and micro-devices with light is highly appealing. Opto driving torque can propel micro-rotors to translational motion in viscous liquid, and then separate microsystems according to their handedness. We study the torque of dielectric loss generated by circular polarized lasers. The unwanted axial force which causes the handedness independent translational motion is cancelled by the counter propagating reflection beams. The propelling efficiency and the friction torque of water are obtained by solving the Navier-Stokes equation. In the interesting range of parameters, the numerical friction torque is found to be linear to the angular velocity with a slope depending on the radius of rotor as r3. The time-dependent distribution of angular velocity is obtained as a solution of the Fokker-Planck equation, with which the thermal fluctuation is accounted. The results shed light on the micro-torque measurement and suggest a controllable micro-carrier.

Novel transit-time oscillator (TTO) combining advantages of radial-line and axial TTO

Wei-Li Xu, Jun-Tao He, Jun-Pu Ling, Li-Li Song, Bing-Fang Deng, Ouzhixiong Dai, Xing-Jun Ge
Chin. Phys. B 2019, 28 (8): 085201;  doi: 10.1088/1674-1056/28/8/085201
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A novel transit-time oscillator (TTO) is proposed in this paper. An axial cathode which has been widely used in high power microwave (HPM) source and an extractor with radial feature are adopted. In this way, the inherent advantages of axial and radial TTO, both of which can be utilized as high-quality intense relativistic electron beam (IREB), can be generated and the power capacity is also increased. The working mode is π/2 mode of TM01 based on small-signal theory, and under the same energy storage, the maximum electric field in extractor decreases 16.3%. Besides, by utilizing the natural bending of the solenoid, this TTO saves over 60% of the length required by the uniform magnetic field, and consequently reduces the energy consumed by solenoid. The PIC simulation shows that by using 1.0-T decreasing magnetic field generated by the shorter solenoid, 3.37-GW microwave at 12.43 GHz is generated with 620-kV and 13.27-kA input, and the overall conversion efficiency is 41%.

Damage characteristics of laser plasma shock wave on rear surface of fused silica glass

Xiong Shen, Guo-Ying Feng, Sheng Jing, Jing-Hua Han, Ya-Guo Li, Kai Liu
Chin. Phys. B 2019, 28 (8): 085202;  doi: 10.1088/1674-1056/28/8/085202
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The damage to the rear surface of fused silica under the action of high power laser is more severe than that incurred by the front surface, which hinders the improvement in the energy of the high power laser device. For optical components, the ionization breakdown by laser is a main factor causing damage, particularly with laser plasma shock waves, which can cause large-scale fracture damage in fused silica. In this study, the damage morphology is experimentally investigated, and the characteristics of the damage point are obtained. In the theoretical study, the coupling and transmission of the shock wave in glass are investigated based on the finite element method. Thus, both the magnitude and the orientation of stress are obtained. The damage mechanism of the glass can be explained based on the fracture characteristics of glass under different stresses and also on the variation of the damage zone's Raman spectrum. In addition, the influence of the glass thickness on the damage morphology is investigated. The results obtained in this study can be used as a reference in understanding the characteristics and mechanism of damage characteristics induced by laser plasma shock waves.

Nucleation and growth of helium bubble at (110) twist grain boundaries in tungsten studied by molecular dynamics

Fang-Biao Li, Guang Ran, Ning Gao, Shang-Quan Zhao, Ning Li
Chin. Phys. B 2019, 28 (8): 085203;  doi: 10.1088/1674-1056/28/8/085203
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Migration of He atoms and growth of He bubbles in high angle twist grain boundaries (HAGBs) in tungsten (W) are investigated by atomic simulation method. The energy and free volume (FV) of grain boundary (GB) are affected by the density and structure of dislocation patterns in GB. The migration energy of the He atom between the neighboring trapping sites depends on free volume along the migration path at grain boundary. The region of grain boundary around the He bubble forms an ordered crystal structure when He bubble grows at certain grain boundaries. The He atoms aggregate on the grain boundary plane to form a plate-shape configuration. Furthermore, high grain boundary energy (GBE) results in a large volume of He bubble. Thus, the nucleation and growth of He bubbles in twist grain boundaries depend on the energy of grain boundary, the dislocation patterns and the free volume related migration path on the grain boundary plane.


Crystal structure and magnetic properties of disordered alloy ErGa3- xMnx

Cong Wang, Yong-Quan Guo, Shuo-Wang Yang
Chin. Phys. B 2019, 28 (8): 086101;  doi: 10.1088/1674-1056/28/8/086101
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ErGa3-xMnx disordered alloy is successfully prepared by the vacuum arc melting technology, and the crystal structure and magnetic properties are investigated by using the x-ray diffraction and magnetic measurements. The Rietveld structural analysis indicates that the ErGa3-xMnx crystallizes into a cubic structure with space group of Pm3m in Mn doping range of x=0-0.1. However, the disordered alloy with structural formula of Er0.8Ga2I(Ga, Mn)0.4 as the second phase is separated from cubic phase for the samples with x=0.2 and 0.3, which is induced by substituting the (Ga, Mn)-(Ga, Mn) pair at 2e crystal position for the rare earth Er at 1a site. The lattice parameters tend to increase with Mn content increasing due to the size effect at Ga (1.30 Å) site by substituting Mn (1.40 Å) for Ga. The paramagnetic characteristic is observed by doping Mn into ErGa3 at room temperature. With Mn content increasing from x=0 to 0.1, the magnetic susceptibility χ tends to increase. This phenomenon can be due to the increase of effective potential induced by doping Mn into ErGa3. However, the magnetic susceptibility χ continues to decrease with the increase of Mn content in a range of x>0.2, which is due to the phase separation from the cubic Er(Ga, Mn)3 to the hexagonal Er0.8Ga2(Ga, Mn)0.4.

Impeding anion exchange to improve composition stability of CsPbX3 (X=Cl, Br) nanocrystals through facilely fabricated Cs4PbX6 shell

Zhaohui Shen, Pengjie Song, Bo Qiao, Jingyue Cao, Qiongyu Bai, Dandan Song, Zheng Xu, Suling Zhao, Gaoqian Zhang, Yuanjun Wu
Chin. Phys. B 2019, 28 (8): 086102;  doi: 10.1088/1674-1056/28/8/086102
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Inorganic lead halide perovskite nanocrystals (NCs) with superior photoelectric properties are expected to have excellent performance in many fields. However, the anion exchange changes their features and is unfavorable for their applications in many fields. Hence, impeding anion exchange is important for improving the composition stability of inorganic lead halide perovskite NCs. Herein, CsPbX3 (X=Cl, Br) NCs are coated with Cs4PbX6 shell to impede anion exchange and reduce anion mobility. The Cs4PbX6 shell is facily fabricated on CsPbX3 NCs through high temperature injection method. Anion exchange experiments demonstrate that the Cs4PbX6 shell completely encapsulates CsPbX3 NCs and greatly improves the composition stability of CsPbX3 NCs. Moreover, our work also sheds light on the potential design approaches of various heterostructures to expand the application of CsPbM3 (M=Cl, Br, I) NCs.

Electronic structure of single-crystalline graphene grown on Cu/Ni (111) alloy film

Xue-Fu Zhang, Zhong-Hao Liu, Wan-Ling Liu, Xiang-Le Lu, Zhuo-Jun Li, Qing-Kai Yu, Da-Wei Shen, Xiao-Ming Xie
Chin. Phys. B 2019, 28 (8): 086103;  doi: 10.1088/1674-1056/28/8/086103
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Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices. For epitaxially grown graphene, the process conditions and the microstructures are strongly dependent on various substrate materials with different lattice constants and interface energies. Utilizing angle-resolved photoemission spectroscopy, here we report an investigation of the electronic structure of single-crystalline graphene grown on Cu/Ni (111) alloy film by chemical vapor deposition. With a relatively low growth temperature, graphene on Cu/Ni (111) exhibits a Dirac cone-like dispersion comparable to that of graphene grown on Cu (111). The linear dispersions forming Dirac cone are as wide as 2 eV, with the Fermi velocity of approximately 1.1×106 m/s. Dirac cone opens a gap of approximately 152 meV at the binding energy of approximately 304 meV. Our findings would promote the study of engineering of graphene on different substrate materials.

Electronic and optical properties of GaN-MoS2 heterostructure from first-principles calculations

Dahua Ren, Xingyi Tan, Teng Zhang, Yuan Zhang
Chin. Phys. B 2019, 28 (8): 086104;  doi: 10.1088/1674-1056/28/8/086104
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Heterostructures (HSs) have attracted significant attention because of their interlayer van der Waals interactions. The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory. The results indicate that the direct band gap (1.95 eV) of the GaN-MoS2 HS is lower than the individual band gaps of both the GaN layer (3.48 eV) and the MoS2 layer (2.03 eV) based on HSE06 hybrid functional calculations. Specifically, the GaN-MoS2 HS is a typical type-Ⅱ band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency. Under tensile or compressive strain, the direct band gap of the GaN-MoS2 HS undergoes redshifts. Additionally, the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5% or -5%. Therefore, the results reported above can be used to expand the application of GaN-MoS2 HSs to photovoltaic cells and photocatalysts.

Structural, mechanical, and electronic properties of 25 kinds of Ⅲ-V binary monolayers:A computational study with first-principles calculation

Xue-Fei Liu, Zi-Jiang Luo, Xun Zhou, Jie-Min Wei, Yi Wang, Xiang Guo, Bing Lv, Zhao Ding
Chin. Phys. B 2019, 28 (8): 086105;  doi: 10.1088/1674-1056/28/8/086105
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Using first-principle calculations, we investigate the mechanical, structural, and electronic properties and formation energy of 25 kinds of Ⅲ-V binary monolayers in detail. A relative radius of the binary compound according to the atomic number in the periodic table is defined, and based on the definition, the 25 kinds of Ⅲ-V binary compounds are exactly located at a symmetric position in a symmetric matrix. The mechanical properties and band gaps are found to be very dependent on relative radius, while the effective mass of holes and electrons are found to be less dependent. A linear function between Young's modulus and formation energy is fitted with a linear relation in this paper. The change regularity of physical properties of B-V (V=P, As, Sb, Bi) and -N (=Al, Ga, In, Tl) are found to be very different from those of other Ⅲ-V binary compounds.

Effects of surface charges on phonon properties and thermal conductivity in GaN nanofilms

Shu-Sen Yang, Yang Hou, Lin-Li Zhu
Chin. Phys. B 2019, 28 (8): 086501;  doi: 10.1088/1674-1056/28/8/086501
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Surface charges can modify the elastic modulus of nanostructure, leading to the change of the phonon and thermal properties in semiconductor nanostructure. In this work, the influence of surface charges on the phonon properties and phonon thermal conductivity of GaN nanofilm are quantitatively investigated. In the framework of continuum mechanics, the modified elastic modulus can be derived for the nanofilm with surface charges. The elastic model is presented to analyze the phonon properties such as the phonon dispersion relation, phonon group velocity, density of states of phonons in nanofilm with the surface charges. The phonon thermal conductivity of nanofilm can be obtained by considering surface charges. The simulation results demonstrate that surface charges can significantly change the phonon properties and thermal conductivity in a GaN nanofilm. Positive surface charges reduce the phonon energy and phonon group velocity but increase the density of states of phonons. The surface charges can change the size and temperature dependence of phonon thermal conductivity of GaN nanofilm. Based on these theoretical results, one can adjust the phonon properties and temperature/size dependent thermal conductivity in GaN nanofilm by changing the surface charges.

Measurement scheme to detect α relaxation time of glass-forming liquid

Xing-Yu Zhao, Li-Na Wang, Hong-Mei Yin, Heng-Wei Zhou, Yi-Neng Huang
Chin. Phys. B 2019, 28 (8): 086601;  doi: 10.1088/1674-1056/28/8/086601
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A measurement scheme for detecting the α relaxation time (τ) of glass-forming liquid is proposed, which is based on the measured ionic conductivity of the liquid doped with probing ions by low- and middle-frequency dielectric spectroscopy and according to the Nernst-Einstein, Stokes-Einstein, and Maxwell equations. The obtained τ values of glycerol and propylene carbonate by the scheme are consistent with those obtained by traditional dielectric spectroscopy, which confirms its reliability and accuracy. Moreover, the τ of 1,2-propanediol in a larger temperature range is compared with existing data.

Organic field-effect transistor floating-gate memory using polysilicon as charge trapping layer

Wen-Ting Zhang, Fen-Xia Wang, Yu-Miao Li, Xiao-Xing Guo, Jian-Hong Yang
Chin. Phys. B 2019, 28 (8): 086801;  doi: 10.1088/1674-1056/28/8/086801
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In this study, we present an organic field-effect transistor floating-gate memory using polysilicon (poly-Si) as a charge trapping layer. The memory device is fabricated on a N+-Si/SiO2 substrate. Poly-Si, polymethylmethacrylate, and pentacene are used as a floating-gate layer, tunneling layer, and active layer, respectively. The device shows bidirectional storage characteristics under the action of programming/erasing (P/E) operation due to the supplied electrons and holes in the channel and the bidirectional charge trapping characteristic of the poly-Si floating-gate. The carrier mobility and switching current ratio (Ion/Ioff ratio) of the device with a tunneling layer thickness of 85 nm are 0.01 cm2·V-1·s-1 and 102, respectively. A large memory window of 9.28 V can be obtained under a P/E voltage of ±60 V.

Electronic structure from equivalent differential equations of Hartree-Fock equations

Hai Lin
Chin. Phys. B 2019, 28 (8): 087101;  doi: 10.1088/1674-1056/28/8/087101
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A strict universal method of calculating the electronic structure of condensed matter from the Hartree-Fock equation is proposed. It is based on a partial differential equation (PDE) strictly equivalent to the Hartree-Fock equation, which is an integral-differential equation of fermion single-body wavefunctions. Although the maximum order of the differential operator in the Hartree-Fock equation is 2, the mathematical property of its integral kernel function can warrant the equation to be strictly equivalent to a 4th-order nonlinear partial differential equation of fermion single-body wavefunctions. This allows the electronic structure calculation to eliminate empirical and random choices of the starting trial wavefunction (which is inevitable for achieving rapid convergence with respect to iterative times, in the iterative method of studying integral-differential equations), and strictly relates the electronic structure to the space boundary conditions of the single-body wavefunction.

SymTopo:An automatic tool for calculating topological properties of nonmagnetic crystalline materials Hot!

Yuqing He, Yi Jiang, Tiantian Zhang, He Huang, Chen Fang, Zhong Jin
Chin. Phys. B 2019, 28 (8): 087102;  doi: 10.1088/1674-1056/28/8/087102
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Topological materials have novel properties both in their bulk and boundaries, thereby attracting a wide interest in the theoretical and experimental communities. The recent development of the topological quantum chemistry and symmetry-based indicator theory in this field has significantly simplified the procedure for determining the topological properties of nonmagnetic crystalline materials. Accordingly, a large number of new topological materials have been found by scanning large crystal databases. This study provides details on the algorithm used in the Catalogue of Topological Electronic Materials. Moreover, based on the algorithm, we develop an automatic package named SymTopo, which calculates the symmetry representations of any given nonmagnetic crystalline material and predicts its topological properties. This package may facilitate the discovery of more topological materials in the future.

Effect of strain on exciton dynamics in monolayer WS2

Lu Zhang, Da-Wei He, Jia-Qi He, Yang Fu, Yong-Sheng Wang
Chin. Phys. B 2019, 28 (8): 087201;  doi: 10.1088/1674-1056/28/8/087201
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The exciton dynamics in a WS2 monolayer with strain are studied by transient absorption measurements. We measure the differential transmission signal from monolayer WS2 as a function of the probe wavelength at different levels of strain applied to the sample. The differential transmission spectrum has a positive maximum value at about 614 nm and shows no significant strain dependence. By time-resolving the differential transmission signal, we find that the strain has a minimal effect on the exciton formation process. However, the exciton lifetime is significantly reduced by strain. These results provide useful information for applications of WS2 in flexible electronic and optoelectronic devices where strain is inevitable.

Energy band alignment at Cu2O/ZnO heterojunctions characterized by in situ x-ray photoelectron spectroscopy

Yan Zhao, Hong-Bu Yin, Ya-Jun Fu, Xue-Min Wang, Wei-Dong Wu
Chin. Phys. B 2019, 28 (8): 087301;  doi: 10.1088/1674-1056/28/8/087301
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With the increasing interest in Cu2O-based devices for photovoltaic applications, the energy band alignment at the Cu2O/ZnO heterojunction has received more and more attention. In this work, a high-quality Cu2O/ZnO heterojunction is fabricated on a c-Al2O3 substrate by laser-molecular beam epitaxy, and the energy band alignment is determined by x-ray photoelectron spectroscopy. The valence band of ZnO is found to be 1.97 eV below that of Cu2O. A type-Ⅱ band alignment exists at the Cu2O/ZnO heterojunction with a resulting conduction band offset of 0.77 eV, which is especially favorable for enhancing the efficiency of Cu2O/ZnO solar cells.

Effects of active layer thickness on performance and stability of dual-active-layer amorphous InGaZnO thin-film transistors

Wenxing Huo, Zengxia Mei, Yicheng Lu, Zuyin Han, Rui Zhu, Tao Wang, Yanxin Sui, Huili Liang, Xiaolong Du
Chin. Phys. B 2019, 28 (8): 087302;  doi: 10.1088/1674-1056/28/8/087302
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Dual-active-layer (DAL) amorphous InGaZnO (IGZO) thin-film transistors (TFTs) are fabricated at low temperature without post-annealing. A bottom low-resistance (low-R) IGZO layer and a top high-resistance (high-R) IGZO layer constitute the DAL homojunction with smooth and high-quality interface by in situ modulation of oxygen composition. The performance of the DAL TFT is significantly improved when compared to that of a single-active-layer TFT. A detailed investigation was carried out regarding the effects of the thickness of both layers on the electrical properties and gate bias stress stabilities. It is found that the low-R layer improves the mobility, ON/OFF ratio, threshold voltage and hysteresis voltage by passivating the defects and providing a smooth interface. The high-R IGZO layer has a great impact on the hysteresis, which changes from clockwise to counterclockwise. The best TFT shows a mobility of 5.41 cm2/V…, a sub-threshold swing of 95.0 mV/dec, an ON/OFF ratio of 6.70×107, a threshold voltage of 0.24 V, and a hysteresis voltage of 0.13 V. The value of threshold voltage shifts under positive gate bias stress decreases when increasing the thickness of both layers.

Effects of oxygen vacancy concentration and temperature on memristive behavior of SrRuO3/Nb:SrTiO3 junctions

Zhi-Cheng Wang, Zhang-Zhang Cui, Hui Xu, Xiao-Fang Zhai, Ya-Lin Lu
Chin. Phys. B 2019, 28 (8): 087303;  doi: 10.1088/1674-1056/28/8/087303
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Metal/semiconductor memristive heterostructures have potential applications in nonvolatile memory and computing devices. To enhance the performance of the memristive devices, it requires a comprehensive engineering to the metal/semiconductor interfaces. Here in this paper, we discuss the effects of oxygen vacancies and temperature on the memristive behaviors of perovskite-oxide Schottky junctions, each consisting of SrRuO3 thin films epitaxially grown on Nb:SrTiO3 substrates. The oxygen partial pressure and laser fluence are controlled during the film growth to tune the oxygen defects in SrRuO3 films, and the Schottky barrier height can be controlled by both the temperature and oxygen vacancies. The resistive switching measurements demonstrate that the largest resistance switching ratio can be obtained by controlling oxygen vacancy concentration at lower temperature. It suggests that reducing Schottky barrier height can enhance the resistive switching performance of the SrRuO3/Nb:SrTiO3 heterostructures. This work can conduce to the development of high-performance metal-oxide/semiconductor memristive devices.

Quaternary antiferromagnetic Ba2BiFeS5 with isolated FeS4 tetrahedra

Shaohua Wang, Xiao Zhang, Hechang Lei
Chin. Phys. B 2019, 28 (8): 087401;  doi: 10.1088/1674-1056/28/8/087401
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We report the detailed physical properties of quaternary compound Ba2BiFeS5 with the key structural ingredient of isolated FeS4 tetrahedra. Magnetization and heat capacity measurements clearly indicate that Ba2BiFeS5 has a paramagnetic to antiferromagnetic transition at about 30 K. The calculated magnetic entropy above ordering temperature is much smaller than theoretical value for high-spin Fe3+ ion with S=5/2, implying the possible short-range antiferromagnetic fluctuation in Ba2BiFeS5.

Model of output characteristics of giant magnetoresistance (GMR) multilayer sensor

Jiao-Feng Zhang, Zheng-Hong Qian, Hua-Chen Zhu, Ru Bai, Jian-Guo Zhu
Chin. Phys. B 2019, 28 (8): 087501;  doi: 10.1088/1674-1056/28/8/087501
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In this paper, the giant magnetoresistance (GMR) multilayer sensor is fabricated with a Wheatstone bridge, and it exhibits excellent performance with a sensitivity of 2.8349 mV/(V/Oe) (1 Oe=79.5775 A·m-1) and a saturation field of 26 Oe along the sensitive axis. The GMR sensor is also characterized in a high magnetic field. The sensitivity decreases from 2.8349 mV/(V/Oe) at an angle of 0° to 0.0175 mV/(V/Oe) at an angle of 90°. Then, the sensor is placed in a series of rotating magnetic fields. We propose a model to express the output characteristics of the GMR multilayer sensor. The transfer curves of the sensor can be shown as two exactly symmetrical circles with an increasing radius when the magnetic field increases. The experimental results are consistent with the simulation results of the model. The advantage of this model is that it is simpler and more intuitive.

Thermal stability, crystallization, and magnetic properties of FeNiBCuNb alloys

Zhe Chen, Qian-Ke Zhu, Shu-Ling Zhang, Ke-Wei Zhang, Yong Jiang
Chin. Phys. B 2019, 28 (8): 087502;  doi: 10.1088/1674-1056/28/8/087502
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Amorphous (Fe40Ni40B19Cu1)100-xNbx (x=1, 3, 5, 7) ribbons are prepared by using the melt-spinning method. We find that the glass forming ability (GFA) of the as-melt spun ribbons is significantly improved by adding Nb element. In addition, the thermal stability evaluated in steps of ΔT=Tx2-Tx1 effectively increases from 16 K to 75 K with Nb content increasing. The as-melt spun (Fe40Ni40B19Cu1)97Nb3 ribbon exhibits a lowest coercivity of 2 A/m and relatively large saturation magnetization of 103.7 A·m2/kg and thus it can be further treated by being annealed at 809 K. The crystallization behavior is confirmed to be determined by two individual crystallization processes corresponding to the precipitation of (Fe,Ni)23B6 phase and γ-(Fe,Ni) phase. With increasing annealing time, the single (Fe,Ni)23B6 phase can be transformed into a mixture of (Fe,Ni)23B6 and γ-(Fe,Ni) phase, and the grain size of γ-(Fe, Ni) phase increases from 5 nm to 80 nm while the grain size of (Fe,Ni)23B6 remains almost unchanged. Finally, we find that the grain growth in each of (Fe,Ni)23B6 and γ-(Fe, Ni) deteriorates the overall magnetic properties.

Spectral properties of Pr:CNGG crystals grown by micro-pulling-down method

Yan-Yan Xue, Na Li, Dong-Hua Hu, Qing-Song Song, Xiao-Dong Xu, Dong-Hai Wang, Qing-Guo Wang, Dong-Zhen Li, Zhan-Shan Wang, Jun Xu
Chin. Phys. B 2019, 28 (8): 087801;  doi: 10.1088/1674-1056/28/8/087801
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Pr3+-doped calcium niobium gallium garnet (Pr:CNGG) single crystals with different Pr3+concentrations are successfully grown by the micro-pulling-down (μ-PD) method. The crystal structure, room-temperature absorption spectra, and fluorescence spectra of Pr:CNGG crystals are measured and discussed. The fluorescence results indicate their large dependence on the doping concentration. The fluorescence lifetime of the 1D2 energy level is also determined. The results indicate that Pr:CNGG crystal could be a potential solid-state laser gain medium.

Monolithic semi-polar (1101) InGaN/GaN near white light-emitting diodes on micro-striped Si (100) substrate

Qi Wang, Guo-Dong Yuan, Wen-Qiang Liu, Shuai Zhao, Lu Zhang, Zhi-Qiang Liu, Jun-Xi Wang, Jin-Min Li
Chin. Phys. B 2019, 28 (8): 087802;  doi: 10.1088/1674-1056/28/8/087802
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The epitaxial growth of novel GaN-based light-emitting diode (LED) on Si (100) substrate has proved challenging. Here in this work, we investigate a monolithic phosphor-free semi-polar InGaN/GaN near white light-emitting diode, which is formed on a micro-striped Si (100) substrate by metal organic chemical vapor deposition. By controlling the size of micro-stripe, InGaN/GaN multiple quantum wells (MQWs) with different well widths are grown on semi-polar (1101) planes. Besides, indium-rich quantum dots are observed in InGaN wells by transmission electron microscopy, which is caused by indium phase separation. Due to the different widths of MQWs and indium phase separation, the indium content changes from the center to the side of the micro-stripe. Various indium content provides the wideband emission. This unique property allows the semipolar InGaN/GaN MQWs to emit wideband light, leading to the near white light emission.

Non-perturbative multiphoton excitation studies in an excitonic coupled quantum well system using high-intensity THz laser fields

Monica Gambhir, Vinod Prasad
Chin. Phys. B 2019, 28 (8): 087803;  doi: 10.1088/1674-1056/28/8/087803
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Multiphoton excitations and nonlinear optical properties of exciton states in GaAs/AlxGa1-xAs coupled quantum well structure have been theoretically investigated under the influence of a time-varying high-intensity terahertz (THz) laser field. Non-perturbative Floquet theory is employed to solve the time-dependent equation of motion for the laser-driven excitonic quantum well system. The response to the field parameters, such as intensity and frequency of the laser electric field on the state populations, can be used in various optical semiconductor device applications, such as photodetectors, sensors, all-optical switches, and terahertz emitters.

Analysis of elliptical thermal cloak based on entropy generation and entransy dissipation approach

Meng Wang, Shiyao Huang, Run Hu, Xiaobing Luo
Chin. Phys. B 2019, 28 (8): 087804;  doi: 10.1088/1674-1056/28/8/087804
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In this work, we designed the elliptical thermal cloak based on the transformation thermotics. The local entropy generation rate distribution and entransy dissipation rate distribution were obtained, and the total entropy generation and entransy dissipation of different types of elliptical cloaks were evaluated. We used entropy generation approach and entransy dissipation approach to evaluate the performance of the thermal cloak, and heat dissipation analysis was carried out for models with different parameters. Finally, the optimized elliptical thermal cloak with minimum entropy generation and minimum entransy dissipation is found, and some suggestions on optimizing the structure of elliptical thermal cloak were given.

Thin-film growth behavior of non-planar vanadium oxide phthalocyanine

Tian-Jiao Liu, Hua-Yan Xia, Biao Liu, Tim S Jones, Mei Fang, Jun-Liang Yang
Chin. Phys. B 2019, 28 (8): 088101;  doi: 10.1088/1674-1056/28/8/088101
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The thin film properties of organic semiconductors are very important to the device performance. Herein, non-planar vanadyl phthalocyanine (VOPc) thin films grown on rigid substrates of indium tin oxide, silicon dioxide, and flexible substrate of kapton by organic molecular beam deposition under vacuum conditions are systematically studied via atomic force microscopy and x-ray diffraction. The results clearly reveal that the morphology and grain size are strongly dependent on the substrate temperature during the process of film deposition. Meanwhile, the VOPc films with the structure of phase I or phase Ⅱ can be modulated via in situ annealing and post-annealing temperature. Furthermore, the crystalline structure and molecular orientation of vapor-deposited VOPc can be controlled using molecular template layer 3, 4, 9, 10-perylene-tetracarboxylic dianhydride (PTCDA), the VOPc film of which exhibits the phase I structure. The deep understanding of growth mechanism of non-planar VOPc film provides valuable information for controlling structure-property relationship and accelerates the application in electronic and optoelectronic devices.

Structural model of substitutional sulfur in diamond

Hongyu Yu, Nan Gao, Hongdong Li, Xuri Huang, Defang Duan, Kuo Bao, Mingfeng Zhu, Bingbing Liu, Tian Cui
Chin. Phys. B 2019, 28 (8): 088102;  doi: 10.1088/1674-1056/28/8/088102
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Based on ab initio calculations, it is found that the donor center of substitutional sulfur (S) in diamond with C2v symmetry is more stable than that with C3v symmetry, which is different from previous reports in literature. The energy difference of C2v and C3v structures is qualitatively affected by the supercell size, and the 216-atom supercell could be proposed as the minimum to obtain stable configuration of substitutional S in diamond. Using supercells of up to 512 atoms, the donor level of substitutional S with C2v symmetry is deep.

Study on the nitridation of β-Ga2O3 films

Fei Cheng, Yue-Wen Li, Hong Zhao, Xiang-Qian Xiu, Zhi-Tai Jia, Duo Liu, Xue-Mei Hua, Zi-Li Xie, Tao Tao, Peng Chen, Bin Liu, Rong Zhang, You-Dou Zheng
Chin. Phys. B 2019, 28 (8): 088103;  doi: 10.1088/1674-1056/28/8/088103
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Single-crystal GaN layers have been obtained by nitriding β-Ga2O3 films in NH3 atmosphere. The effect of the temperature and time on the nitridation and conversion of Ga2O3 films have been investigated. The nitridation process results in lots of holes in the surface of films. The higher nitridation temperature and longer time can promote the nitridation and improve the crystal quality of GaN films. The converted GaN porous films show the single-crystal structures and low-stress, which can be used as templates for the epitaxial growth of high-quality GaN.

Structural response of aluminum core-shell particles in detonation environment

Qing-Jie Jiao, Qiu-Shi Wang, Jian-Xin Nie, Hong-Bo Pei
Chin. Phys. B 2019, 28 (8): 088201;  doi: 10.1088/1674-1056/28/8/088201
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Natural aluminum particles have the core-shell structure. The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences. The dynamic behavior of the structural response of aluminum core-shell particles before combustion is of great importance for the aluminum powder burning mechanism and its applications. In this paper, an aluminum particle combustion experiment in a detonation environment is conducted and analyzed; the breakage factors of aluminum particles shell in detonation environment are analyzed. The experiment results show that the aluminum particle burns in a gaseous state and condenses into a sub-micron particle cluster. The calculation and simulation demonstrate that the rupture of aluminum particle shell in the detonation environment is mainly caused by the impact of the detonation wave. The detonation wave impacts the aluminum particles, resulting in shell cracking, and due to the shrinkage-expansion of the aluminum core and stripping of the detonation product, the cracked shell is fractured and peeled with the aluminum reacting with the detonation product.

Improving robustness of GGNMOS with P-base layer for electrostatic discharge protection in 0.5-μm BCD process

Fei Hou, Ruibo Chen, Feibo Du, Jizhi Liu, Zhiwei Liu, Juin J Liou
Chin. Phys. B 2019, 28 (8): 088501;  doi: 10.1088/1674-1056/28/8/088501
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Gate-grounded N-channel MOSFET (GGNMOS) has been extensively used for on-chip electrostatic discharge (ESD) protection. However, the ESD performance of the conventional GGNMOS is significantly degraded by the current crowding effect. In this paper, an enhanced GGNMOS with P-base layer (PB-NMOS) are proposed to improve the ESD robustness in BCD process without the increase in layout area or additional layer. TCAD simulations are carried out to explain the underlying mechanisms of that utilizing the P-base layer can effectively restrain the current crowing effect in proposed devices. All devices are fabricated in a 0.5-μm BCD process and measured using the transmission line pulsing (TLP) tester. Compared with the conventional GGNMOS, the proposed PB-NMOS devices offer a higher failure current than its conventional counterpart, which can be increased by 15.38%. Furthermore, the PB-NMOS_type3 possesses a considerably lower trigger voltage than the conventional GGNMOS to protect core circuit effectively.

Negative gate bias stress effects on conduction and low frequency noise characteristics in p-type poly-Si thin-film transistors

Chao-Yang Han, Yuan Liu, Yu-Rong Liu, Ya-Yi Chen, Li Wang, Rong-Sheng Chen
Chin. Phys. B 2019, 28 (8): 088502;  doi: 10.1088/1674-1056/28/8/088502
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The instability of p-channel low-temperature polycrystalline silicon thin film transistors (poly-Si TFTs) is investigated under negative gate bias stress (NBS) in this work. Firstly, a series of negative bias stress experiments is performed, the significant degradation behaviors in current-voltage characteristics are observed. As the stress voltage decreases from -25 V to -37 V, the threshold voltage and the sub-threshold swing each show a continuous shift, which is induced by gate oxide trapped charges or interface state. Furthermore, low frequency noise (LFN) values in poly-Si TFTs are measured before and after negative bias stress. The flat-band voltage spectral density is extracted, and the trap concentration located near the Si/SiO2 interface is also calculated. Finally, the degradation mechanism is discussed based on the current-voltage and LFN results in poly-Si TFTs under NBS, finding out that Si-OH bonds may be broken and form Si* and negative charge OH- under negative bias stress, which is demonstrated by the proposed negative charge generation model.

Rectifying characteristics and solar-blind photoresponse in β-Ga2O3/ZnO heterojunctions

Xiao-Fei Ma, Yuan-Qi Huang, Yu-Song Zhi, Xia Wang, Pei-Gang Li, Zhen-Ping Wu, Wei-Hua Tang
Chin. Phys. B 2019, 28 (8): 088503;  doi: 10.1088/1674-1056/28/8/088503
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Heterojunctions composed of β-Ga2O3 and ZnO films are fabricated on sapphire substrates by using the laser molecular beam epitaxy method. The heterojunction possesses excellent rectifying characteristics with an asymmetry ratio over 105. Prominent solar-blind photoresponse effect is also observed in the formed heterojunction. The photodetector exhibits a self-powered behavior with a fast response speed (rise time and decay time are 0.035 s and 0.032 s respectively) at zero bias. The obtained high performance can be related to the built-in field driven photogenerated electron-hole separation.

Effects of bismuth on structural and dielectric properties of cobalt-cadmium spinel ferrites fabricated via micro-emulsion route

Furhaj Ahmed Sheikh, Muhammad Khalid, Muhammad Shahzad Shifa, H M Noor ul Huda Khan Asghar, Sameen Aslam, Ayesha Perveen, Jalil ur Rehman, Muhammad Azhar Khan, Zaheer Abbas Gilani
Chin. Phys. B 2019, 28 (8): 088701;  doi: 10.1088/1674-1056/28/8/088701
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Spinel ferrites have a significant role in high-tech applications. In the present work nano-crystalline ferrites having general formula Co0.5Cd0.5BixFe2-xO4 with (x=0.0, 0.05, 0.1, 0.15, 0.2, and 0.25) are synthesized via micro-emulsion route. Powder x-ray diffraction (XRD) studies discover the FCC spinel structure. Crystalline size is calculated in a range of 11 nm-15 nm. Lattice parameter calculations are reduced due to its substitution which leads to the exchange of large ionic radius of Fe3+ for small ionic radius of Bi3+. The x-ray density is analyzed to increase with doping. Fourier transform infrared spectroscopy (FTIR) is performed to analyze absorption band spectra. The two absorption bands are observed in a range of 400 cm-1-600 cm-1, and they are the characteristic feature of spinel structure. Thermo-gravimetric analysis (TGA) reveals the total weight loss of nearly 1.98%. Dielectric analysis is carried out by impedance analyzer in a frequency span from 1 MHz to 3 GHz by using the Maxwell Wagner model. Dielectric studies reveal the decrease of dielectric parameters. The alternating current (AC) conductivity exhibits a plane behavior in a low frequency range and it increases with the applied frequency increasing. This is attributed to the grain effects in a high frequency range or may be due to the reduction of porosity. Real and imaginary part of impedance show the decreasing trend which corresponds to the grain boundary action. The imaginary modulus shows the occurrence of peak that helps to understand the interfacial polarization. Cole-Cole graph shows a single semicircle which confirms that the conduction mechanism is due to the grain boundaries at low frequency. Dielectric studies reveal the applicability of these ferrites in high frequency equipment, microwave applications, high storage media, and semiconductor devices.

New design of ferroelectric solar cell combined with luminescent solar concentrator

Slimane Latreche, Mohamed Fathi, Abderrahmane Kadri
Chin. Phys. B 2019, 28 (8): 088801;  doi: 10.1088/1674-1056/28/8/088801
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A new transparent photovoltaic panel composed of a luminescent solar concentrator and Al/BaTiO3/ZnO/Pt ferroelectric solar cells is presented, in which a portion of the incoming solar illumination is converted by the fluorophores to ultraviolet (UV) light which is then absorbed by ZnO. Firstly, the solar cells are simulated using Atlas-Silvaco. Then, the panel is modelled based on the obtained solar cell characteristics. This panel would be of great importance for building integrated photovoltaics domain because of its high transparency.

Exploring alkylthiol additives in PBDB-T:ITIC blended active layers for solar cell applications

Xiang Li, Zhiqun He, Mengjie Sun, Huimin Zhang, Zebang Guo, Yajun Xu, Han Li, Chunjun Liang, Xiping Jing
Chin. Phys. B 2019, 28 (8): 088802;  doi: 10.1088/1674-1056/28/8/088802
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Bulk heterojunction, non-fullerene PBDB-T:ITIC blend polymer solar cells have been fabricated. The active layers consisting of PBDB-T as a donor and ITIC as an acceptor are optimized using a series of alkylthiol additives (1,3-propanedithiol, 1,4-butanedithiol, and 1,8-octanedithiol). It is found that the donor and acceptor are phase separated with different crystalline domains. The additives effectively re-organize the morphology and extend the molecule ordering in lamellar structure with increased correlation length in ITIC domain, benefiting the generation and dissociation of exciton and reducing charge recombination. A substantial improvement in power conversion efficiency of the devices from 8.13% to 9.44% is observed. This study shows that the application of alkylthiol additives is a simple and effective approach to improve the device performance in solar cells based on polymer/non-fullerene blend system.

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