bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-doped iron-based superconductors with intergrowth structures
Authors: Wang Zhi-Cheng  , Cao Guang-Han  ,   State Key Laboratory of Silicon Materials, Department of Physics, Zhejiang University, Hangzhou 310027, China;,   Collaborative Innovation Centre of Advanced Microstructures, Nanjing 210093, China
Published: December 2020

The key structural unit of iron-based superconductors (FeSCs) is the Fe2X2 (X refers to a pnictogen or a chalcogen element) layer which stacks alternately along the crystallographic c axis with other spacer layers. This structural feature makes it possible to find FeSCs via rational material design. In this paper, we first review the crystal structure of FeSCs along with the relevant progress. Then we summarize several rules for designing the intergrowth structures. The rules include the following points. 1) Lattice match between the intergrowth layers should be good enough. Quantitatively, the lattice mismatch, defined as =2(aA-aB)/(aA + aB), where aA and aB are respectively the lattice parameters of the two constituent compounds, should be no larger than~2%. 2) The charge transfer between the intergrowth layers is mostly essential, which acts as the glue that combines the constituent layers together. Such a charge transfer also induces the extra charge carriers in the superconducting key layer to give rise to superconductivity without extrinsic doping (so-called self doping). 3) For the structure with similar yet crystallographically distinct sites, one needs to avoid forming solid solutions. 4) Each intergrowth layer is preferably thermodynamically stable. 5) The designed structure can be preliminary evaluated with the hard and soft acids and bases conception and ab initio calculations. Following these empirical rules, we introduce and analyze five examples, namely, (Li0.8Fe0.2OH)FeSe, Ba2Ti2Fe4As4O, 42214-type Ln4Fe2As2Te1-xO4 (Ln=Pr, Sm, Gd), 1144-type AkAeFe4As4 (Ak=K, Rb, Cs; Ae=Ca, Sr, Eu), and 12442-type AkCa2Fe4As4F2 and AkLn2Fe4As4O2 (Ak=K, Rb, Cs; Ln=Nd-Ho). For the last 12442-type compounds, we also discuss the unusual relation between superconducting transition temperature and crystallographic parameters. We conclude that the structural-design approach may serve as an effective route, not only for discovering new FeSCs but also for exploring other relevant functional materials with similar crystal structures.
Infrared spectroscopy study of ironbased superconductor Li0.8Fe0.2 ODFeSe
Authors: Lin Tong  , Hu Die  , Shi Li-Yu  , Zhang Si-Jie  , Liu Yan-Qi  , Lv Jia-Lin  , Dong Tao  , Zhao Jun  , Wang Nan-Lin  ,   International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China;,   State Key Laboratory of Surface Physics, Department of Physics, Fudan University, Shanghai 200433, China
Published: December 2020

We perform an in-plane optical spectroscopy measurement on iron-based superconductor Li0.8Fe0.2ODFeSe single crystal. At room temperature, the low frequency optical conductivity shows an incoherent characteristic; the Drude component is absent. With temperature decreasing, the Drude component develops and narrows rapidly. A well-defined plasma edge is observed in reflectance spectrum at temperature below 100 K, indicating a dramatically reduced scattering rate. The spectral weight contributed from free carriers is even smaller than that of FeSe single crystal. A number of phonon modes are visible in the measured spectra. We also observe clear spectral change below 160 cm-1 at 10 K, associated with the formation of superconducting energy gap in the superconducting state. The energy scale of the superconducting gap is comparable to the value measured by angle-resolved photoemission spectroscopy technique. Like FeSe and other iron pnictides, a clear temperature-induced spectral weight transfer at high energy is observed for Li0.8Fe0.2ODFeSe, indicating the presence of strong correlation effect.
Electrical transport properties and related mechanism of single SnO2 nanowire device
Authors: Chen Ya-Qi  , Xu Hua-Kai  , Tang Dong-Sheng  , Yu Fang  , Lei Le  , Ouyang Gang  ,   1. School of Electronic Information and Electrical Engineering, Xiangnan University, Chenzhou 423000, China;,   2. Key Laboratory of Low Dimensional Quantum Structures and Quantum Control, School of Physics and Electronics, Hunan Normal University, Changsha 410006, China
Published: December 2020

Defect engineering in a semiconductor nanowire-based device has aroused intensive attention due to its fascinating properties and the potential applications in nanoelectronics. Here in this work, in order to investigate the effect of oxygen defects on the electrical transport properties in a SnO2-nanowire-based device under normal environment, we synthesize an individual SnO2 nanowire, by a thermal chemical vapor deposition method and further construct a two-terminal Au/SnO2 nanowire/Au device by using optical lithography. The electrical transport properties of a single SnO2 nanowire device are measured under the condition of air and vacuum after hydrogen reduction. It is found that the transport performances in air are unusually different from those in vacuum. Strikingly, the reduction of electric current through the device and the increment of contact barrier of the Au/SnO2 interface in air can be observed with the I-V scan times increasing. While in vacuum, the current increases and a change from Schottky contact to ohmic contact at the interface between Au and SnO2 can be obtained by performing more scans. Our results demonstrate that the oxygen vacancy concentrations caused by the oxygen atom adsorption and desorption on the surface of nanowires play the key role in the transport properties. Furthermore, we calculate the relevant electronic properties, including energy band structure, density of states, as well as I-V characters and transmission spectrum at the interface of Au/SnO2 within the framework of density functional theory. We find that the bandgap of SnO2 nanowires decreases with oxygen vacancy concentration increasing. Also, the existence of oxygen defects enlarges the electron transmission at the interface of Au/SnO2 and enhances electrical transport. Therefore, our results provide a new strategy for designing the integrated nano-functional SnO2-based devices.
Horizontal refraction effects of seamounts on sound propagation in deep water
Authors: Li Sheng-Hao  , Li Zheng-Lin  , Li Wen  , Qin Ji-Xing  ,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The seamounts usually have important effects on sound propagation in deep water. A sound propagation experiment was conducted in the South China Sea in 2016. One of the experimental goals is to investigate the three-dimensional(3D) effects of seamounts on sound propagation. Phenomena about horizontal refraction of acoustic waves are observed in different propagation tracks which go through the seamount along different directions when the source depth is 200 m. Ray methods (BELLHOP N×2D and 3D models) which can calculate sound field efficiently and show clear physical images, are used to analyze and explain the causes of the phenomena. The experimental and numerical results show that the convergent zone structures are destroyed by the direct blockage of seamount due to the multiple reflection of acoustic waves, which leads to the increase of transmission loss (TL), and horizontal-refraction zone with obvious boundaries appears behind the seamount. Some experiment phenomena cannot be explained by BELLHOP N×2D model in which the horizontal refraction effects are not taken into consideration. The experimental sound field structure behind the seamount is obviously different from N×2D model numerical result, i.e.the width of shadow zone based on the experimental data is wider than that calculated by N×2D model, and the width of strong horizontal-refraction zone from the experiment is narrower than the N×2D model result. Moreover, the TLs calculated by N×2D model is about 10 dB less than the experimental result in horizontal refraction zone. After analyzing the difference between experimental data and N×2D model numerical results by BELLHOP 3D model which contains the azimuth-coupling capability, it can be concluded that sound waves reach the receiver through horizontal refraction after the interaction with seamount when the source is located behind the seamount. The eigenrays obtained from 3D model are less than N×2D model numerical result because some of sound beams cannot reach the receiver as a result of the horizontal refraction effects, which leads to the experimental TLs larger than the numerical results calculated by N×2D model. Therefore, 3D effect of seamount has an obvious influence on sound field within a certain angle range behind the seamount, and the investigation of 3D effects of seamounts is meaningful for the sound propagation and target detection in deep water.
Concentration and thermal quenching of SrGdLiTeO6: Eu3+ red-emitting phosphor for white light-emitting diode
Authors: Zhao Wang  , Ping Zhao-Yan  , Zheng Qing-Hua  , Zhou Wei-Wei  ,   Anhui Key Laboratory of Low Temperature Co-fired Materials, School of Electronic Engineering, Huainan Normal University, Huainan 232038, China
Published: December 2020

A series of SrGd1-xLiTeO6:xEu3+ (x=0.1-1) red-emitting phosphors, prepared by high-temperature solid-state reaction at 1100℃, is thoroughly investigated by means of X-ray diffraction, diffuse reflectance spectra, photoluminescence spectra, and electroluminescence spectra. These double-perovskite-type phosphors crystallize into monoclinic systems with space group P21/n(14), accommodate Eu3+ in a highly distorted C1 site symmetry without inversion center, and facilitate the enhancing of the 5D0 → 7F2 hypersensitive transition. The excitation spectra, emission spectra and decay curves indicate that the optimum doping concentration of Eu3+ is x=0.6. The SrGd0.4LiTeO6:0.6Eu3+ presents the strongest excitation peak at 395 nm, which is adequate for near-UV light-emitting diode (LED) pumping; meanwhile, it exhibits an intense red emission with chromaticity coordinates of (0.6671, 0.3284), an asymmetry ratio of 7.56, a color purity of 98.6%, and a luminous efficacy of radiation of 249 lm/W. The fluorescence lifetime is 721 μs, from which the internal quantum efficiency is determined to be 89.7% via the Judd-Ofelt analysis. The formula proposed by van Uiter (van Uitert L G 1967 J. Electrochem. Soc. 114 1048), is used to elucidate the energy transfer mechanism. However, the plot of log(I/x)-log(x) produces a confusing index s=4.26, which makes it difficult to distinguish the dipole-dipole interaction from the exchange interaction. After analyzing the reason of error, we present a new plot of log(I0'/I-1)-log(x), in which I0'=I0/x0 and I'=I/x, with x0 corresponding to the low doping content without nonradiative energy transfer. This plot gives rise to s=5.25, a more reasonable value for the dipole-dipole interaction. The integrated emission intensity at 423 K is as high as 85.2% of that at ambient temperature. The thermal activation energy is determined to be 0.2941 eV according to the model based on a temperature-dependent pathway through a charge transfer state. The prototypical LED based on it can emit a bright red light beam. In conclusion, the phosphor exhibits favorable luminous efficiency, color purity and thermal stability of luminescence, which promises solid-state lighting and display applications.
Optical transmission characteristics of multi-band triangular-lattice photonic crystal coupling cavity waveguide based on annular microcavity
Authors: Liu Xing  , Guo Hong-Mei  , Fu Rao  , Fan Hao-Ran  , Feng Shuai  , Chen Xiao  , Li Chuan-Bo  , Wang Yi-Quan  ,   School of Science, Minzu University of China, Beijing 100081, China
Published: December 2020

The light localization characteristics of the near-infrared triangular-lattice photonic crystal annular microcavity are studied theoretically in this paper. The photonic crystal has a lattice constant of a=540 and it is composed of silicon rods each with a radius of r=135 immersed in air background. The two kinds of annular microcavities are obtained by removing 12 silicon rods which are located respectively at a distance of 2a and at a distance of √3a to the central rod. Five resonant wavelengths and the corresponding eigen mode profiles of the microcavity are studied. A coupled resonant optical waveguide is formed by integrating the microcavities with a periodic length of 7a in space. The group velocity of light beam propagation within multiple guiding bands are analyzed by the tight-binding approximation method. The maximum and minimum velocity of 0.0028c and 0.00082c are obtained, where c is the light velocity in vacuum. The light transmittance values and spatial steady distributions of the electric field's amplitude through the structure at several wavelengths within the guiding bands are studied by the finite-difference time-domain method. The results are consistent with that calculated by the plane wave expand method. Interleaving circular microcavities perpendicular to the direction of optical transmission at a lateral distance of 2√3a, the coupling region between the adjacent microcavities is changed, the difference in group velocity between guiding bands apparently decreases and the transmittance values of two frequency bands are enhanced.
Keeping the size of silicon rods unchanged, two kinds of microcavities are constructed by removing the six rods with the distances of 2a and √3a from the center of the central silicon rod, respectively. The resonant wavelengths supported by the above two microcavities are studied. Two coupled-resonant optical waveguides with a periodic length of 7a are proposed. Connecting these two coupled cavity optical waveguides with the W1-typed input/output waveguides, the selecting and sharing function of guiding band are finally achieved for wavelengths within different frequency bands. Keeping the group velocity slowing down, a maximum value of one guiding band reaches 0.00047c.
Tunable microwave frequency comb generation based on double-loop mixing-frequency optoelectronic oscillator
Authors: Ma Yan-Na  , Huang Tian-Tian  , Wang Wen-Rui  , Song Kai-Chen  ,   1. College of Biomedical Engineering and Instrument Science, Zhejiang University, Hangzhou 310027, China;,   2. College of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China
Published: December 2020

With the development of wireless communication technology and micro-cell technology, optical-borne microwave technology, specially optical-borne multi-carrier technology has become one of the most important trends for generating high-quality sources. Therefore, the efficient generation of high-quality microwave signals has always been a requirement in wireless communication systems. Due to its low-noise and high-frequency output characteristics, photoelectric oscillator is widely used to generate high-quality microwave frequency sources in communication systems. Combining the advantages of photoelectric oscillator's low-noise output and direct-modulated laser's gain-switching state characteristics, a tunable optical-borne microwave frequency comb scheme based on dual-loop mixing-frequency photoelectric oscillator is proposed in this paper. And a direct-modulated laser operating in a gain-switching state is used to generate the original optical-borne microwave frequency comb signals. The dual-loop adjacent resonant frequencies are separated by two different high-frequency microwave bandpass filters. The beat frequency of adjacent frequencies mentioned above is injected back into laser to form photoelectric resonance, and thus enhancing the generated original optical-borne microwave frequency comb signals. To suppress the side modes caused by long resonant cavity, a polarized dual-loop structure is used in the system, and thus improving the noise characteristics of output signals. After experimental analysis, the dual-loop filtered resonant microwave signals and low-phase-noise microwave comb signals with a frequency interval of 797.4 MHz are all obtained. The microwave output side-mode suppression ratio after polarized dual-loop adjustment is improved to 47 dB. And microwave comb signal's first-order carrier phase noise is lower than-101.7 dBc/Hz at 10 kHz,-115.2 dBc/Hz at 50 kHz. In addition, higher-order carriers all come from the light multiplication of first-order carrier, they share the same low noise characteristics with first-order microwave comb signal. The output power of first-to-fourth, fifth-to-thirteenth order carriers are balanced to 10 dB by photoelectric resonance injection. And their side-mode suppression ratios are all better than 40 dB. Furthermore, theoretically, the comb interval can be adjusted to any frequencies by changing the center frequencies of two high-frequency bandpass microwave filters. Therefore, optical-borne multi-carrier microwave signals are generated efficiently and cost-effectively by this tunable optical-borne microwave frequency comb scheme, and the generated low-noise multi-carrier frequency sources meet the demand of an optical-borne microwave wireless communication system.
Optical properties of niobium nitride nanowires
Authors: Wu Yang  , Chen Qi  , Xu Rui-Ying  , Ge Rui  , Zhang Biao  , Tao Xu  , Tu Xue-Cou  , Jia Xiao-Qing  , Zhang La-Bao  , Kang Lin  , Wu Pei-Heng  ,   School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China
Published: December 2020

Niobium nitride (NbN) nanowires are commonly used as photosensitive materials for superconducting nanowire single-photon detectors (SNSPDs). Their optical properties are the key factors influencing the performance of SNSPD. According to the experimental data and simulation results, in this paper we systematically study the optical properties of various niobium nitride nanowire detector device structures, and characterize the reflection spectra and transmission spectra of the following four device structures:1) Backside optical devices with SiO2 as the antireflection layer, 2) backside optical devices with SiN as the antireflection layer, 3) front-facing optical devices with Au+SiN as a mirror, and 4) front-facing optical devices with distributed Bragg reflector (DBR) as a mirror. The NbN films with different thickness are grown on the basis of the four device structures, and the absorption efficiencies of the NbN films with different thickness are observed. The relationships between the optimal NbN thickness and the optical absorption rate for different device structures are found as follows:The maximum absorption rate of NbN on the SiO2 antireflection layer is 91.7% at 1606 nm, while the absorption rates of the remaining structures at the optimal thickness of NbN can reach 99% or more. The absorption rate of the SiN device, the Au+SiN device and the DBR device are 99.3%, 99.8% and 99.9%, respectively. The measured results and simulation structure of DBR device are analyzed. These results are of significance for guiding the design and development of high efficiency SNSPD.
Angle-resolved photoemission studies on iron based high temperature superconductors
Authors: Zhao Lin  , Liu Guo-Dong  , Zhou Xing-Jiang  ,   National Lab for Superconductivity, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100871 China
Published: December 2020

Copper oxide superconductors and iron-based superconductors are two important families of high temperature superconductors. Their high-temperature superconductivity mechanism is a long-standing issue and still in hot debate in the field of condensed matter physics. The extensive and in-depth exploration of iron-based superconductors and their comparative study with copper oxide high-temperature superconductors are of great significance for the development of new quantum theory, the solution of high-temperature superconducting mechanism, the exploration of new superconductors and practical applications of superconductors. The macroscopic properties of materials are determined by their microscopic electronic structure. Revealing the microscopic electronic structure of high temperature superconductors is fundamental for understanding high temperature superconductivity. Angle-resolved photoelectron spectroscopy, due to its unique simultaneous energy, momentum and even spin resolving ability, has become the most direct and powerful experimental tool for detecting the microscopic electronic structure of materials, and has played an important role in the study of iron-based high-temperature superconductors. The revealing and discovery of the Fermi surface topology, superconducting energy gap and its symmetry, three-dimensionality, orbital selectivity, and electronic coupling mode in different iron-based superconductor systems provide an important basis for identifying and proposing new theory of iron-based superconductivity to solve high temperature superconductivity mechanism.
Single photon detection and circular polarized emission manipulated with individual quantum dot
Authors: Li Tian-Xin  , Weng Qian-Chun  , Lu Jian  , Xia Hui  , An Zheng-Hua  , Chen Zhang-Hai  , Chen Ping-Ping  , Lu Wei  ,   National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China;,   Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241, China;,   State Key Laboratory of Surface Physics and Institute of Advanced Materials, Fudan University, Shanghai 200433, China;,   Key Laboratory of Micro and Nano Photonic Structures(Ministry of Education) Fudan University, Shanghai 200433, China
Published: December 2020

Studies on quantum dots (QDs) provide great opportunities in single photon detection as well as single circular polarized photon emission, which are the key technology for future quantum information processing. For single photon detection, the quantum-dot-resonant-tunneling-diode (QD-RTD) is evaluated as one of the most promising scheme but still suffering from the ultralow working temperature (～5 K) and lack the capability to discriminate photon numbers. Here we demonstrate a photon-number-resolving detector based on quantum dot coupled resonant tunneling diodes (QD-cRTD). Individual QDs coupled closely with adjacent quantum well (QW) of resonant tunneling diode operate as photon-gated switches which turn on (off) the RTD tunneling current when they trap photon-generated holes (recombine with injected electrons). With proper decision regions defined, 1-photon and 2-photon states are resolved in 4.2 K with excellent propabilities of accuracy of 90% and 98% respectively. Further, by identifying step-like photon responses, the photon-number-resolving capability is sustained to 77 K, making the detector a promising candidate for advanced quantum information applications where photon-number-states should be accurately distinguished. On the other hand, we firstly performed the magneto-optical studies on single InGaAs/GaAs self-assembled QDs. We observed the exciton Zeeman splitting and diamagnetic shift of a single QD under magnetic field, and the exciton g factor and diamagnetic coefficient was extracted by fitting the magnetic field dependent PL energies. By comparing with theories, we discussed on the effect of QD size, shape and composition on these two parameters. Based on these work, we investigated the single QD exciton-cavity mode coupling effect under external magnetic field. By first time we observed the interaction of Zeeman splitted exciton spin states with the cavity mode and realized the selective enhancement of the SE rate of the exciton state with specific spin configuration by means of magnetic manipulation of Purcell effect. In this sense, single QD emission with higher circular polarization degree under non-polarized excitation was realized. Our results have high potential to open up a way to novel quantum light sources and quantum information processing applications based on cavity quantum electrodynamics effects.
Investigation of the two-color polarization spectroscopy between the excited states based on cesium atoms
Authors: Zhang Jin-Fang , Ren Ya-Na , Wang Jun-Min , Yang Bao-Dong ,   College of Physics and Electronic Engineering, Shanxi University, Taiyuan 030006, China,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Two-color polarization spectroscopy (TCPS) of cesium 6S1/2-6P3/2-8S1/2 (852.3 nm + 794.6 nm) ladder-type system in a room-temperature vapor cell are investigated. The frequency of 852.3 nm laser used as a pump beam is locked on one of the hyperfine transitions between the ground state 6S1/2 and excited state 6P3/2 by the saturated absorption spectroscopy technique, which can populate some atoms on the 6P3/2 excited state and induce anisotropy in the atomic medium. The frequency of 794.6 nm laser serving as a probe beam is scanned across the whole 6P3/2→8S1/2 transition to ascertain this anisotropy, and thus the TCPS is obtained. In experiment, we measure and analyse the influence of frequency detuning of 852.3 nm pump laser on TCPS, and especially reveal that some of hyperfine energy levels of intermediate excited state 6P3/2, which has no direct interaction with the 852.3 nm pump laser, are also populated by a small fraction of atoms with a specific speed in the direction of pump laser beam due to Doppler effect, so they also have contribution to the TCPS when the 794.6 nm probe laser is scanned to the resonance transition line between the 6P3/2 and 8S1/2 states after the Doppler frequency shift has been considered. In addition, we prove that the atomic coherence like electromagnetically induced transparency effect obviously results in a narrower line width of TCPS in the case of counter-propagating experimental configuration than that in the case of pump beam co-propagating with the probe beam in the Cs vapor cell. Finally, we apply the TCPS with dispersive shaped feature to frequency stabilization with no modulation, and the frequency fluctuations of 794.6 nm laser are ～0.5 MHz and ～9.2 MHz for the frequency-locking and free running in ～225 s, respectively. The above research work is expected to play a role in precisely measuring the atomic energy level structure and its related hyperfine structure constant (magnetic dipole and electric quadrupole coupling constants), and also in stabilizing the laser frequency to the excited state transition especially for the optical fiber communication, two-color laser cooling/trapping neutral atoms, optical filter, etc.
Molecular dynamics simulation of void nucleation, growth and closure of nano-Cu/Al films under cyclic loading
Authors: Liu Qiang , Guo Qiao-Neng , Qian Xiang-Fei , Wang Hai-Ning , Guo Rui-Lin , Xiao Zhi-Jie , Pei Hai-Jiao ,   School of Physical Engineering, Zhengzhou University, Zhengzhou 450001, China,   International College, Zhengzhou university, Zhengzhou 450001, China
Published: December 2020

In this paper, molecular dynamics method is used to simulate the evolution mechanism of void nucleation, growth and closure of diffusion-welded copper/aluminum bilayer film under cyclic loading condition with a strain-to-width ratio of R = –1. It is found that under cyclic loading condition, the voids mainly nucleate inside the aluminum side of the copper/aluminum bilayer film, and two kinds of evolution modes of voids I and II are found. The void I nucleates at the position of the gap defect produced by the Kirkendall effect when the copper-aluminum diffuses to form the bilayer film. Under this nucleation mode, after the gap defects have become void, the void moves into the area where copper atoms are relatively dense inside the OTHER structure on the aluminum side. When gaps accumulate to form voids, the voids grow at a fixed position. The void II on the aluminum side nucleates at the position of the gap defect formed by overcoming the stair-rod dislocation and then remains motionless in the process of nucleation, growth and closure. Comparing with the void I, the stress corresponding to the nucleation of void II is large, the growth speed of the void II is fast and the size of the void II is slightly large in the process of strain loading. The void II closure speed is also faster in the strain unloading stage. The two kinds of voids have two common characteristics in the process of nucleation, growth and closure. 1) Both kinds of voids nucleate at the position of the gap defect inside OTHER structure on the aluminum side. 2) In the process of voids growth and closure, both kinds of voids have the same shape changes. In the void growth stage, both kinds of voids first grow along the strain loading direction, then expand in the direction perpendicular to the strain loading direction, and finally, the shapes of two kinds of voids tend to become spherical. In the stage of void closure, the two kinds of voids are first compressed into ellipsoidal shape along the strain loading direction, and then disappear from both ends of the void to the center of the void in the direction perpendicular to the strain loading direction. In the subsequent cyclic loading process, none of new voids appears again at the position where the voids disappearred, but the nucleation of voids at other position of gap defect forms inside the other structure located on the aluminum side.
Molecular dynamics simulations for tensile behaviors of mono-layer MoS2 with twin boundary
Authors: Shao Yu-Fei , Meng Fan-Shun , Li Jiu-Hui , Zhao Xing ,   Institute of Applied Physics and Technology, Liaoning Technical University, Huludao 125105, China,   College of Sciences, Liaoning University of Technology, Jinzhou 121001, China,   College of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
Published: December 2020

Grain boundary (GB) plays a key role in determining the electrical and mechanical properties of mono-layer transition metal dichalcogenide (TMDC), however it is still a challenge to uncover the GB-mediated TMDC material experimentally. In this paper, the effect of twin boundary on the tensile behaviors of mono-layer MoS2 is investigated by using the molecular dynamics simulation combined with the Stillinger-Weber potential. Mono-layer MoS2 model under the varied size and temperature condition is adopted. Stress calculation is performed by using Virial theorem. The results are obtained as follows. 1) Twin boundary promotes the brittle fracture of an undefected mono-layer MoS2 sheet by inducing the nucleation of the crack near boundaries, thus the fracture strength and strain are weakened. 2) Increasing the ambient temperature from 1 K to 600 K, the crack nucleation process near the twin boundary is intensely accelerated, and the fracture strength and strain are further declined. 3) Twin lamellar spacing also plays an important role in the tensile process of mono-layer MoS2, and the specimen with dense twin boundary, especially with void, shows higher fracture strain. 4) Stress analysis at an atomic level outlines the stress concentration caused by voids and the shielding effect of twin boundary. Because of the interactions between voids and twin boundary, the fracture strength and strain of a voided mono-layer MoS2 sheet can be greatly improved.
Generation and application of novel Chua multi-scroll chaotic attractors
Authors: Jia Mei-Mei , Jiang Hao-Gang , Li Wen-Jing ,   Department of Automation, College of Electric Power, Inner Mongolia University of Technology, Hohhot 010080, China
Published: December 2020

Chaos has great potential applications in engineering fields, such as secure communication and digital encryption. Since the double-scroll Chua’s circuit was developed first by Chua, it has quickly become a paradigm to study the double-scroll chaotic attractors. Compared with the conventional double-scroll chaotic attractors, the multi-scroll chaotic attractors have complex structures and rich nonlinear dynamical behaviors. The multi-scroll chaotic attractors have been applied to various chaos-based information technologies, such as secure communication and chaotic cryptanalysis. Hence, the generation of the multi-scroll chaotic attractors has become a hot topic in research field of chaos at present. In this paper, a novel Chua multi-scroll chaotic system is constructed by using a logarithmic function series. The nonlinear dynamical behaviors of the novel Chua multi-scroll chaotic system are analyzed, including symmetry, invariance, equilibrium points, the largest Lyapunov exponent, etc. The existence of chaos is confirmed by theoretical analyses and numerical simulations. The results show that the rich Chua multi-scroll chaotic attractors can be generated by combining the logarithmic function series with the novel Chua double-scroll chaotic system. The generation mechanism of the Chua multi-scroll chaotic attractors is that the saddle-focus equilibrium points of index 2 are used to generate the scrolls, and the saddle-focus equilibrium points of index 1 are used to connect these scrolls. Then, three recursive back-stepping controllers are designed to control the chaotic behavior in the novel Chua multi-scroll chaotic system. The recursive back-stepping controllers can control the novel Chua multi-scroll chaotic system to a fixed point or a given sinusoidal function. Finally, a new method of detecting a weak signal embedded in the Gaussian noise is proposed on the basis of the novel Chua multi-scroll chaotic system and the recursive back-stepping controllers. The immunity of the novel Chua multi-scroll chaotic system to the Gaussian noise with the zero mean is analyzed by using the stochastic differential equation theory. The results show that the proposed new method of detecting the weak signal can detect the frequencies of the multi-frequency weak periodic signal embedded in the Gaussian noise. In addition, the novel Chua multi-scroll chaotic system has strong immunity to any Gaussian noise with the zero mean. The proposed method provides a new thought for detecting the weak signal.
Fresnel incoherent digital holography with large field-of-view
Authors: Tang Ming-Yu , Wu Meng-Ting , Zang Rui-Huan , Rong Teng-Da , Du Yan-Li , Ma Feng-Ying , Duan Zhi-Yong , Gong Qiao-Xia ,   School of Physics Engineering, Zhengzhou University, Zhengzhou 450001, China
Published: December 2020

Incoherent digital holography (IDH) is a recently proposed technique to record three-dimensional (3D) information about the object under incoherent illumination, which breaks the limitation that the holographic recording must be illuminated by coherent light sources and thus makes it usable in white-light and fluorescence illuminating circumstance. In particular, the fresnel incoherent correlation holography (FINCH) is an exemplary method which improves the imaging resolution power and efficiency of incoherent digital holography, and it can obtain 3D distribution of objects swiftly without scanning and moving. However, compared with the conventional optical holography, the FINCH system has a very small field-of-view due to the limitation of the pixel number and size of spatial light modulator (SLM). Therefore, expanding the recording field-of-view of FINCH system is very significant for the application of IDH. In the FINCH, the SLM is used as a diffractive beam splitter so that each spherical beam, originating from each object point, is split into two spherical beams with two different curve radii. Then the interference fringes between the two beams are recorded by CCD. In this paper, the field-of-view angle recorded by the SLM is proposed and analyzed based on the physical and numerical principles of the FINCH system. The field-of-view of imaging system is improved by increasing the effective diameter of SLM through moving the center of the dual-lens optical axis mounted on the SLM to the edge in different directions respectively. An optical setup of reflection mode is constructed to verify the theoretical analysis of this study, and the sub-holograms in different field-of-views are obtained by CCD through changing the masks displayed on the SLM sequentially. Then, the complex holograms in different field-of-views are obtained by using the three-step phase-shifting method, and the reconstructed images are acquired respectively through the angular spectrum method (ASM) by using a computer. Finally, the large field-of-view image is obtained by stitching the reconstructed images in each field-of-view by utilizing the matlab program. The experimental results show that the efficient recording field-of-view of SLM can be increased by 2.77 times with our proposed method. Accordingly, the recording field-of-view of the system is improved significantly. The recording field-of-view of the FINCH system will increase further if the center of the dual-lens optical axis continues to move toward the edge. Therefore, this study provides an important support for the further application of high resolution microscopic imaging with large field-of-view.
Effect of annealing temperature on structure and stress properties of Ta2O5/SiO2 multilayer reflective coatings
Authors: Liu Bao-Jian , Duan Wei-Bo , Li Da-Qi , Yu De-Ming , Chen Gang , Wang Tian-Hong , Liu Ding-Quan ,   Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
Published: December 2020

In the optical system of spaceborne laser altimeter, dielectric mirror is an indispensable optical film element. Its surface shape quality directly affects the resolution and accuracy of distance measurement of the detection system. It is pressing and necessary to carry out research on the surface shape control technology of dielectric mirror to eliminate or reduce the effect of film stress on surface shape. The Ta2O5/SiO2 multilayer reflective coatings are deposited on quartz substrates by using the ion beam assisted electron beam evaporation (IBE), and then annealed in air in a temperature range from 200 to 600 ℃. The effect of annealing temperature on the structure, optical and stress properties of Ta2O5/SiO2 multilayer reflective coatings are systemically investigated by using x-ray diffraction, atomic force microscope, spectrophotometer and laser interferometer. The results show that all the Ta2O5/SiO2 multilayer reflective coatings, after being annealed, are amorphous in structure. The annealing temperature has a great influence on the surface roughness of reflective coating. With the increase of annealing temperature, the surface roughness of reflective coating first decreases and then gradually increases, but is still smaller than that of as-deposited sample. After being annealed, the reflectance spectrum of reflective coating shifts slightly toward the long-wave direction, and the reflectivity increases a little. When being annealed at 500－600 ℃, the compressive stress of reflective coating could be transformed into tensile stress, and the surface is changed from convex to concave shape. It can be concluded that annealing at an appropriate temperature can effectively release residual stress of Ta2O5/SiO2 multilayer reflective coating and eliminate the deformation of substrate caused by film stress, and thus improving the surface shape quality of dielectric mirror., After being annealed, the reflective coating still possesses the stable structure and spectral properties, so that dielectric mirror can meet the application requirements of spaceborne laser altimeter. In this paper, the experimental results are of great significance for applying the annealing technology to the surface shape control technology of dielectric mirrors.
Measurement of ultrashort laser pulses with rapid-scanning frequency-resolved optical gating device
Authors: Wen Jin-Hui , Hu Ting , Wu Qin-Fei ,   School of Physics, Sun Yat-Sen University, Guangzhou 510275, China
Published: December 2020

Frequency-resolved optical gating (FROG) is now one of the main methods of characterizing the ultrashort laser pulses. There are mainly three SHG-FROG methods, i.e. the standard FROG, the single-shot FROG and GRENOUILLE, each of which has its own features and application areas. Although the standard SHG-FROG has balanced advantages in sensitivity, accuracy and applicability for various test pulses, its speed is much slower than the others’: it often takes a few seconds or even minutes to record the FROG trace, which is dependent on the size of FROG image. Nowadays continuous development of the technique of digital imaging brings to high resolution CCD/CMOS image cameras with tens of millions pixels and fast refreshing rate. Unfortunately the standard FROG cannot make use of these image cameras for the real-time measurement of ultrashort pulses. To solve this problem, in this paper a rapid-scanning FROG device based on the standard SHG-FROG is demonstrated, where sinusoidal waves from a signal generator synchronously drive a voice coil actuator and a galvo-scanner, so that the spectra of the autocorrelation at different delays are successively reflected onto an area camera. As long as the camera is triggered to shoot continuously, the entire FROG trace can be recorded quickly within 1 s. Furthermore, several guidelines for good performance with this device are provided, including the settings of the amplitude and frequency of the driving sinusoidal waves, the selections of the focuses of the collimating lens F1 and the focusing lens F2, and the method of delay calibration. This device is suitable for the real-time measurement of ultrashort pulses with large chirps or complex structures where large-size FROG images need to be captured. In order to show the capability of this device, femtosecond pulses delivered directly from a home-made Kerr-lens mode-locked Ti: sapphire laser as well as the chirp pulses dispersed by a 200 mm-thick BK7 slab are measured. Two scan ranges are selected in order to achieve enough effective data points in the FROG traces of these two test pulses. Using standard procedure of pulse retrieval of FROG, the two pulses are reconstructed with pulse widths 58 fs and 492 fs, respectively. From the retrieved spectral phases of these test pulses, the GDD value of the BK7 slab can be deduced to be 8740 fs2, which is in good agreement with the theoretical value of 8815 fs2. Thus the experimental results confirm the accuracy and applicability of this FROG device.
Direct synthesis of [Ca24Al28O64]4+(4e–) electride and its thermionic emission performance
Authors: Li Fan , Zhang Xin , Zhang Jiu-Xing ,   College of Materials Science and Engineering, Beijing University of Technology, Beijing 100124, China,   School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China
Published: December 2020

[Ca24Al28O64]4+(4e–) eletride, as the first room-temperature stable inorganic electride, has attracted intensive attention because of its fascinating chemical, electrical, optical, and magnetic properties. However, it usually needs synthesizing through a complicated multistep process involving high temperature (e.g., 1350 °C), severe reduction (e.g., 700–1300 ℃ for up to 240 h in Ca or Ti metal vapor atmosphere) and post-purification. Owing to the H2O sensitivity of mayenite, the post-purification is quite troublesome once impurities are introduced. High-density, loosely bound encaged electrons with a low work function make it promise to possess practical applications. Therefore the facile method of massively producing the high-quality C12A7:e– with high Ne is extremely desired. In this work, C12A7:e– bulks are for the first time synthesized by simple spark plasma sintering process directly from a mixture of C12A7, CA and Ca powders under milder conditions (e.g., sintered at 1070 ℃ for 10 min in a vacuum). The obtained electride, which exhibits a relative density of 99%, an electron concentration of ~2.3×1021 cm–3 and an obvious absorption peak at 2.5 eV, is obtained via SPS process at 1100 ℃ for 10 min. Electronic structure is also investigated by electron paramagnetic resonance. The occurrence of Dysonian characteristic, a typical feature of good electronic conductors, strongly suggests that the electrons are trapped in mayenite cavities. Furthermore, the obtained C12A7:e– exhibits good sinterabilty on a crystal scale of 5–40 μm. Thermionic emission test results show that the thermionic emission begins to occur at 700 K and a large current density of 1.75 A/cm2 is obtained in the electron thermal emission from a flat surface of the polycrystalline C12A7:e– with an effective work function of 2.09 eV for a temperature of 1373 K with an applied electric field of ~35000 V/cm in a vacuum. Owing to no external reductant is needed, this developed route exhibits notable superiority over the conventional reduction method for phase-pure C12A7:e–. Therefore, these results not only suggest a novel precursor for fabricating mayenite electride but also make it possible to produce efficiently the electride in large volume.
Bouncing-with-spray mode and residence time of droplet impact on heated surfaces
Authors: Rong Song , Shen Shi-Quan , Wang Tian-You , Che Zhi-Zhao ,   State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
Published: December 2020

The impact of droplets on surfaces is a ubiquitous phenomenon, and reducing the droplet residence time is the aim of many studies because of the potential applications in self-cleaning, anti-icing, corrosion resistance, etc. This study identifies a mode of droplet bouncing (bouncing-with-spray) that can reduce the residence time significantly. And compared with the way of using complex microstructures on the substrate employed in previous studies, simply heating the substrate to reduce the residence time is novel and simple. The dimensionless residence time decreases down to about 40% compared with that from the traditional retraction-bouncing mode. The reduction in the residence time is due to the burst of vapor bubbles in the liquid film, which results in holes forming in the liquid film and consequently the liquid film recoiling from the holes. The reduction in the recoiling distance leads to the reduction in the recoiling time. Then a simplified theoretical model with considering the energy balance and the critical condition of the bubble burst is proposed. According to this theoretical model, a scaling law is proposed for the transition boundary between the retraction-bouncing mode and the bouncing-with-spray mode in the film boiling regime, and it accords well with our experimental data. This model can also explain the transition boundary between these two modes in the transition boiling regime.