bluuebunny/crossref_metadata_2025 huggingface dataset:
High-power narrow-linewidth single-frequency pulsed fiber amplifier based on self-phase modulation suppression via sawtooth-shaped pulses
Authors: Sheng Quan , Wang Meng , Shi Chao-Du , Tian Hao , Zhang Jun-Xiang , Liu Jun-Jie , Shi Wei , Yao Jian-Quan ,   School of Precision Instrument and Optoelectronics Engineering, Tianjin University, Tianjin 300072, China,   Key Laboratory of Optoelectronic Information Science and Technology (Ministry of Education), Tianjin University, Tianjin 300072, China,   Tianjin Jinhang Institute of Technical Physics, Tianjin 300308, China
Published: August 2021

Fiber laser system in master oscillator power amplifier (MOPA) scheme is a promising technique for high-power narrow-linewidth laser output. With modulation-generated pulsed seed laser, the fiber MOPA benefits the flexible temporal behavior. However, the spectral linewidth broadening induced by self-phase modulation (SPM) is the main obstacle to achieving high-power single-frequency laser output with narrow spectral linewidth, especially for pulsed fiber MOPA in which the kilowatts level peak power results in strong nonlinearity. The SPM induced linewidth broadening is related to the derivative of light intensity with respect to time (dI/dt). Theoretically, if the dI/dt of the laser pulse is a constant, the SPM process will not generate any new frequency components. Hence, the linewidth broadening can be suppressed. In this work, we demonstrate a high-power single-frequency Yb fiber amplifier at 1064 nm, in which a sawtooth laser pulse is employed to suppress the SPM induced linewidth broadening, for obtaining the output with near-transform-limited narrow linewidth. The sawtooth-shaped seed pulse train is generated through using an electro-optic intensity modulator to modulate the continuous-wave (CW) output of a single-frequency fiber laser. After being pre-amplified, the seed laser with a pulse repetition rate of 20 kHz is coupled into the main amplifier, in which a piece of 0.9-m-long Yb-doped silica fiber with core and clad diameters of 35 μm and 250 μm, respectively, is used as a gain medium. The seed laser is enhanced to an average power value of 3.13 W under a launched 976-nm pump power value of 11.3 W before the onset of stimulate Brillouin scattering. The pulse energy 157 μJ and the pulse width 6.5 ns give a peak power of 24 kW. The spectral linewidth measured using a scanning Fabry-Perot interferometer at the maximum power is only 83 MHz, which is quite close to the 76-MHz transform-limited linewidth of the 6.5-ns sawtooth-shaped pulse. For comparison, we also conduct an experiment with a common Gaussian-shaped seed laser, in which the spectral linewidth is broadened significantly with a peak power value of only 1.5 kW. The results here reveal that the using of the sawtooth-shaped pulse is a promising technique to suppress the SPM induced spectral linewidth broadening in high-peak-power fiber amplifiers and acquire near-transform-limited narrow-linewidth laser output.
Effect of ion-beam surface treatment on photocathode emission
Authors: Wang Guo-Jian , Liu Yan-Wen , Li Fen , Tian Hong , Zhu Hong , Li Yun , Zhao Heng-Bang , Wang Xiao-Xia , Zhang Zhi-Qiang ,   Chinese Academy of Sciences Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: August 2021

To meet the needs of high-frequency, miniaturized vacuum microwave devices, a new photocathode for microwave vacuum electronic device has been studied. Untreated oxygen-free copper, commonly used for photocathode substrate, exhibits relatively high photoemission characteristics. In this paper, we describe a specialized ion-beam bombardment procedure for textured copper surfaces, thereby improving the photoemission properties relative to untreated copper. The emission characteristics of antimony cesium photocathode on oxygen-free copper substrate before and after surface treatment are studied The photoemission and texture of post-treated oxygen-free copper surface are examined by scanning electron microscope. The results show that the treated surface has a particle-free, robust, uniformly highly-textured all-metal structure. This processing technology does not require to modify the copper machining and brazing, nor normal fabrication procedures of other photocathodes. In the experiment, the maximum photoemission current density of photocathode for the untreated substrate is 60.5 and that for the treated substrate is 146.0 mA/cm2, and their corresponding quantum efficiencies are calculated to be 2.67 × 10–3 and 1.71 × 10–2, respectively. So, the quantum efficiency is enhanced by 6.41 times. The analysis indicates that the improvement of the quantum efficiency of the treated photocathode is mainly due to the enhancement of the light absorption rate. The results show that the photoemission is enhanced significantly after the substrate has been treated, and there is still much room for improvement.
Vibro-acoustic performance of acoustic metamaterial plate with periodic lateral local resonator
Authors: Guo Zhi-Wei , Guo Han-Bei , Wang Ting ,   School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China,   The Second Ship-Designing Institute of Wuhan, Wuhan 430064, China,   School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Published: August 2021

Based on the Bloch theory and the flexural wave propagation theorem, the model for calculating the vibration response, sound radiation power and radiation efficiency of an acoustic metamaterial plate is established. The modal analysis of a bare pate and the plate attached to periodical lateral local resonators are developed to investigate the vibration regulation. In addition, the patterns of the sound radiation power and radiation efficiency of the plate attached to periodical lateral local resonators versus frequency are studied. The results show that 1) in a specific frequency range, the mean square velocity and the sound radiation power are far lower than those of the bare plate, which is due to the resonance of the lateral local resonator; 2) unlike the vibration response and sound radiation power, the radiation efficiency of the plate attached to periodical lateral local resonator is higher than that of the bare plate. The investigation of the plate attached to lateral local resonator in this paper lays a solid foundation for the practical engineering in the field of vibration suppression and noise reduction.
Reversal behavior of optical absorption rate of bimetallic core-shell nanoparticles based on finite-difference time-domain method
Authors: Hong Wen-Peng , Lan Jing-Rui , Li Hao-Ran , Li Bo-Yu , Niu Xiao-Juan , Li Yan ,   School of Energy and Power Engineering, Northeast Electric Power University, Jilin 132012, China
Published: August 2021

The bimetallic nanoparticle can effectively integrate the physical and chemical properties of two metals and simultaneously exhibits the unique natures of each metal. It also serves as a good candidate for improving light scattering, photothermal conversion, plasmon resonance decay, and photon excitation. Investigating the optical properties of an individual nanoparticle can avoid the interaction between nanoparticles during experimental research, which allows us to more effectively analyze the interaction between the incident light and nanoparticles. In this work, the finite-difference time-domain method is used to study the spectral absorption characteristics of the plasmon bimetallic core-shell nanoparticles by calculating the spectroscopic properties, and also the distributions of the magnetic field, electric field, and absorption power during energy transmission and decaying. The results show that the resonance wavelength is red-shifted if the core diameter is increased. In addition, the absorption rate of Ag@Pt bimetallic nanoparticles is higher than that of pure Ag@Ag nanoparticles when the core diameter is bigger than 100 nm. This is because the strong shielding effect between the shell metal material and the core metal material leads the incident light to interact only with the outer atoms, resulting in resonance. Meanwhile, the plasmon of the Ag core decays faster than that of the Pt shell and more energies are transferred to the Pt shell. As a result, the surface of the Pt shell shows more concentrated magnetic and electric fields associated with an enlarged absorbing power. Moreover, the energy in the Ag core tends to transfer to the nearby Pt shell, which is characterized by the energy absorption in the Pt shell close to the Ag core, and is more concentrated. This paper provides theoretical guidance for designing plasmon bimetallic core-shell nanoparticles, thereby satisfying the demands for special spectral responses.
Influence of photoelectric conversion noise on closed-loop performance of adaptive SMF coupling device
Authors: Huang Guan , Geng Chao , Li Feng , Li Xin-Yang , Lv Guo-Yun , Fan Yang-Yu ,   School of Electronics and Information, Northwestern Polytechnical University, Xi’an 710129, China,   The key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu 610209, China,   Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
Published: August 2021

The single-mode fiber (SMF) adaptive coupling device can efficiently and stably couple the space laser into SMF, which plays an important role in the fiber-based free space optical communication (FSOC) technology. Therefore, a novel corrector named adaptive fiber coupler (AFC) is developed and successfully used in the adaptive SMF coupling applications. However, in the FSOC system under long-range turbulent atmosphere, the closed loop performance of AFC will be seriously disturbed by the photoelectric conversion noise. This problem is studied in depth in this paper. The operational principle of the photoelectric conversion noise is analyzed, and the corresponding evaluation index isgiven. Furthermore, The numerical simulation experiments are conducted to study the specific influence of the photoelectric conversion noise. The results show that the averaged closed-loop coupling efficiency, control accuracy, and control bandwidth of AFC are seriously affected. According to the results, the empirical formula is given. This formula can be used to calculate the optical and electrical parameters that the AFC device should meet under the condition of strong noise interference. The theoretical and simulation results in this paper can provide a theoretical basis for designing the AFC device under long-range turbulent atmosphere.
Seabed seismic wave simulation by finite difference time domain scheme in marine environment with complex seafloor topography
Authors: Wang Ying , Wang Xue-Feng , Zhou Shi-Hong , Zhao Chen , Zhao Jun-Peng , Yang Yong ,   Research Center, Beijing Institute of Aerospace Control Devices, Beijing 100094, China,   Beijing Engineering Research Center of Optical Fiber Sensing System, Beijing 100094, China,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
Published: August 2021

The studying of the excitation and propagation characteristics of seabed seismic waves in a complex marine environment is of great significance in investigating seafloor physical and mechanical properties and exploring resources. At present, the research of time-domain seabed seismic waves is mostly restricted in a marine environment with horizontal stratification, but the actual geological conditions of seafloor are relatively complex, and the numerical solutions obtained under ideal assumption are quite different from those in an actual complex environment. To master the propagation characteristics of seabed seismic wave in the environment that is closer to the actual one, a complex and long range model including layers of water, soft mud and bedrocks is designed in the paper, where non-horizontal seafloor topography with a dipping and uplifting structure is considered. The staggered-grid finite difference method with 2nd-order accuracy in time and 10th-order accuracy in space is used to simulate the seabed seismic waves under such a complex marine environment. Meanwhile, multi axial perfectly matched layer is used as an artificial boundary condition to ensure the numerical long-term stability in a liquid-solid medium. Considering the dipping structure, the acoustic signals excited by sources at different positions of the model are compared to determine the favorable style of source excitation for Scholte interface wave receiving. Through the time-domain waveform of the calculated acoustic field, the propagation characteristics of the seabed seismic wave in the complex marine environment are analyzed. The results show that the staggered-grid finite difference method with high-order spatial accuracy can improve the dispersion problem in numerical calculation. The multi-axial perfectly matched layer used to replace the traditional perfectly matched layer can solve the instability problem in the numerical simulation of acoustic field in liquid-solid media for a long range. Through the comparison among the acoustic signal amplitudes excited by sources at different positions, a better performance can be achieved when the source-receiver is placed along the updip direction. In such a case, the acoustic signal is stronger, which is more advantageous to receive and analyze the Scholte interface wave. In the complex seabed model with a dipping and uplifting structure, the uplift of seafloor bedrock changes the propagation direction of Scholte wave, which makes it possible to receive Scholte wave at shallower depth.
Research status and progress of metal contacts of SiC power devices
Authors: Huang Ling-Qin , Zhu Jing , Ma Yue , Liang Ting , Lei Cheng , Li Yong-Wei , Gu Xiao-Gang ,   School of Electrical Engineering and Automation, Jiangsu Normal University, Xuzhou 221000, China,   Science and Technology on Electronic Test & Measurement Laboratory, North University of China, Taiyuan 030051, China
Published: August 2021

Silicon carbide (SiC) is a promising candidate for applications in high temperature, high voltage, high power, and low-power dissipation devices due to its unique properties like wide band gap, high critical electric field, and high thermal conductivity. However, one of the main bottlenecks hindering the SiC power devices from developing and being put into practical application is the fabrication of good metal/SiC contact. In this review, the research status of Ohmic contact and Schottky contact of SiC device are compared and analyzed. The complicated interface properties and uncontrollable barrier height at metal/SiC interface are revealed. In addition, the research status of metal/SiC contact barrier and interface state properties are analyzed, and the important significance of effective control of interface barrier is highlighted. Furthermore, the research progress of metal/SiC contact interface regulation technology is specially analyzed. The future development directions in the nature of metal/SiC interface states and interface control technology are finally prospected.
Gate capacitance model of AlGaN/GaN high electron mobility transistor
Authors: Liu Nai-Zhang , Yao Ruo-He , Geng Kui-Wei ,   School of Microelectronics, South China University of Technology, Guangzhou 510640, China,   Sino-Singapore International Joint Research Institute, Guangzhou 510700, China
Published: August 2021

The research on capacitance model of AlGaN/GaN high electron mobility transistor (HEMT) is of great significance in modern communication technology and circuit simulation. At present, many modeling methods of AlGaN/GaN HEMT capacitance models have been proposed. The gate capacitance is composed of intrinsic capacitance and fringe capacitance. However, most researches focus on the intrinsic capacitance but ignore the fringe capacitance, which leads to a large error in the final results. A total gate capacitance model including fringe capacitance needs to be established.

In this paper, the conformal mapping method and transition functions are used to establish the inner fringe capacitance model, and the intrinsic capacitance model is derived based on the Ward-Dutton charge distribution principle. The intrinsic capacitance model and the outer fringe capacitance model are combined to obtain the source/drain total gate capacitance model. Based on this model, the relationship between the bias condition and the fringe capacitance is analyzed. We compare the difference between the effects of external bias on gate capacitance with and without the fringe capacitance considered, and the error rate of the gate capacitance in the on state is calculated without considering the fringe capacitance.

The results show that the fringe capacitance is mainly affected by the gate bias. When the fringe capacitance is taken into account in the intrinsic capacitance model, the total capacitance model is larger than that without considering the fringe capacitance. For the gate capacitance, if the influence of fringing capacitance is not considered, the gate capacitance error rate of the device in the OFF state can reach 80%; for fringing capacitance, the error rate is over 65% when the device is working in the saturation region.
Measurement and profile inversion of atmospheric N2O absorption spectrum based on laser heterodyne detection
Authors: Xue Zheng-Yue , Li Jun , Liu Xiao-Hai , Wang Jing-Jing , Gao Xiao-Ming , Tan Tu ,   School of Environmental Science and Optoelectronic Technology, University of Science and Technology of China, Hefei 230031, China,   Anhui Institute of Optics and Fine Mechanics, Hefei Institute of Material Science, Chinese Academy of Sciences, Hefei 230031, China
Published: August 2021

aser heterodyne spectroscopy detection has rapidly developed in recent years due to its high spectral resolution, small size, and light weight. It can be used to measure the atmospheric greenhouse gas vertical profile and calibrate the carbon satellite ground. This paper reports a laser heterodyne system for measuring atmospheric N2O, with a 3.939-µm interband cascade laser used as a local oscillator light source. A homemade high-precision solar tracker collects sunlight as a laser heterodyne signal source. The tracking accuracy reaches 7 arcsec, and the spectral resolution of the laser heterodyne system arrives at 0.004 cm–1. The atmospheric N2O absorption spectrum in Hefei area (31.902°N, 117.167°E) is measured, and two strong absorption peaks respectively at 288.336 and 2539.344 cm–1 are obtained. In addition, the wavelength calibration of the absorption signal, and the entire atmospheric transmittance spectrum of N2O molecules are obtained, and the signal-to-noise ratio is 93. The high-resolution spectrum data are normalized and frequency is corrected, and the N2O atmospheric concentration profile is obtained by using the reference forward model and the optimal estimation algorithm. The standard deviation of volume fraction is in a range of 0.000031—0.0026 ppm, and the corresponding relative error range is 0.009%—0.83%. The research results show that the laser heterodyne system built in this work can be used to measure the absorption spectrum of N2O in the atmosphere and realize the inversion of the N2O profile, which provides a guarantee for long-term observation of atmospheric N2O concentration.
Effect of monovacancy on stability and hydrogen storage property of Sc/Ti/V-decorated graphene
Authors: Ma Li-Juan , Han Ting , Gao Sheng-Qi , Jia Jian-Feng , Wu Hai-Shun ,   Key Laboratory of Magnetic Molecules & Magnetic Information Materials Ministry of Education, School of Chemical and Material Science, Shanxi Normal University, Linfen 041004, China
Published: August 2021

With the depletion of fossil fuels and the environmental problems, the development and utilization of new energy resources is imminent. Hydrogen energy is one of the main new energy sources in the 21st century. Finding stable and efficient hydrogen storage materials is the key to achieving the hydrogen economy. Transition metal (TM)-decorated graphenes have been widely studied as hydrogen storage materials theoretically, but they suffer metal agglomeration and H2 dissociation. Our calculations show that the reconstruction energy of Sc, Ti, V decorated pristine graphenes in the process of adsorption and desorption of hydrogen molecules are only 0.00, 0.12 and 0.08 eV, respectively. The adsorption energy values of the first H2 dissociation adsorption on the Sc, Ti, V decorated pristine graphenes are –1.34, –1.34, and –1.16 eV, respectively. So, some hydrogen molecules are difficult to desorb at room temperature and medium pressure. In this paper, the stability and hydrogen storage properties of Sc, Ti, V decorated monovacancy graphene are also investigated based on density functional theory. The results show that the binding energy values between Sc, Ti, V and themonovacancy graphene are –6.93, –8.82, –9.30 eV, respectively, which indicate monovacancy can effectively avoid metal aggregation. The Sc, Ti and V atoms decorated on the monovacancy graphene would transfer more electrons to the carbon material with charge of +1.24|e|–+1.37|e|. They can adsorb 7, 3 and 4 hydrogen molecules through electrostatic interaction. When a monovacancy is introduced, all of the hydrogen molecules are adsorbed in molecular form. The average adsorption energy values of H2 are –0.13, –0.20 and –0.18 eV, respectively, which are in the best energy range for the adsorption/desorption process at room temperature and medium pressure. The most important thing is that their deformations in the adsorption/desorption process are very small, which is conducive to the rapid hydrogen adsorption/desorption. The calculated results show that the monovacancy introduction can effectively solve the two major problems, i.e. metal agglomeration and hydrogen molecular dissociation during hydrogen storage on Sc, Ti, V decorated pristine graphenes. The research in this paper will be helpful to further understand the hydrogen storage mechanism of 3d TM-decorated carbon nanomaterials.
Resistive switching behavior and mechanism of multilayer MoS2 memtransistor under control of back gate bias and light illumination
Authors: Deng Wen , Wang Li-Sheng , Liu Jia-Ning , Yu Xue-Ling , Chen Feng-Xiang ,   Department of Physics Science and Technology, School of Science, Wuhan University of Technology, Wuhan 430070, China
Published: August 2021

Memtransistor is a new multi-terminal device which combines the properties of memristor and field effect transistor and simultaneously realizes information storage and processing. In this paper, the multilayer MoS2 is prepared by micromechanical exploration method, then the back gate MoS2 memtransistor with field effect transistor structure is fabricated, and the resistive switching characteristics and mechanism of the device under electric field, light field and their synergistic regulation are systematically studied. The experimental results show that the multilayer MoS2 memtransistor has excellent bipolar resistance behavior and good cycle durability. Under the control of gate voltage, the switching ratio of the device can be tuned in a range of 100－105, up to 1.56 × 105, which indicates that the device has a strong gating effect. Under the control of light illumination, the resistance characteristics of the device are strongly dependent on the incident wavelength. When photoelectric synergistic regulation is performed, the device displays excellent four-terminal control capability, and the switching ratio is enhanced up to 4.8 × 104. The mechanism of resistive switching characteristics can be attributed to the changes of charge capture state and Schottky barrier height at the interface between MoS2 and metal electrodes, and the continuous photoconductance effect caused by photogenerated carriers in MoS2 channel.
Density functional theory study on influence of tensile deformation and electric field on electrical properties of Si atom adsorbed on black phosphorene
Authors: Wei Lin , Liu Gui-Li , Wang Jia-Xin , Mu Guang-Yao , Zhang Guo-Ying ,   College of Architecture and Civil Engineering, Shenyang University of Technology, Shenyang 110870, China,   College of Physics, Shenyang Normal University, Shenyang 110034, China
Published: August 2021

In this paper, a model of Si atom adsorbed on black phosphorene with a coverage of 2.778% is constructed and the electronic properties of the model are calculated based on density functional theory. Moreover, the electronic properties are regulated by stress and electric field. Under the coverage of the current research, the results show that the adsorption of Si atoms results in the destruction of the black phosphorene’s geometric symmetry, which intensifies the charge transfer in the system and completes the orbital re-hybrid. The band gap of black phosphorene thus disappears and the transition from semiconductor to quasi metal is completed. The stable adsorption is at the H site in the middle of the P atomic ring. Both tensile field and electric field reduce the stability of the system. Owing to the tensile deformation, the band gap is opened by the structure of Si atom adsorbed on black phosphorene. And since the band gap is proportional to the deformation variable, it can be regulated and controlled. Under the combined action of electric field and tensile, the introduction of the electric field leads the band gap of Si adsorbed on black phosphorene system to be narrowed and the transition from the direct band gap to an indirect one to be completed. The band gap still goes up in proportion to the increase of deformation. The band gap of Si atom adsorbed on black phosphorene system is more adjustable than that of the Si atom that is not adsorbed on black phosphorene system, and the stable adjustment of the band gap is more likely to be realized.
Effects of photoelectric properties of monolayer MoS2 under tensile strain
Authors: Liu Kai-Long , Peng Dong-Sheng ,   School of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518000, China
Published: August 2021

Monolayer molybdenum disulfide is an ideal material for making various micro/nano components and flexible electronic devices. However, the strain of material caused by the environment is a key problem that cannot be avoided in practical applications, and the electronic structure of material will also change with the strain. In this paper, the effect of tensile strain on the photoelectric properties of monolayer MoS2 is studied based on first principles and tensile tests after wet transfer. The results are obtained as follows. 1) Intrinsic monolayer MoS2 is a direct bandgap semiconductor with a band gap of 1.68 eV, the highest peak of the absorption coefficient curve is nearly 10.92 eV, and a maximum absorption coefficient is 1.66 × 105 cm–1. 2) A small tensile strain (1%) will result in the transition from direct to indirect gap for monolayer MoS2. With the increase of strain, the feature of the indirect gap can be preserved but the gap decreases linearly. The gap will decrease to 0 eV when the tensile strain is 10%, and the absorption coefficient curve is red-shifted as a whole with strain. 3) The in-plane mode peak and the out-of-plane mode A1g peak in Raman spectra are re-dshifted with stretching by tensile test of wet-transferred monolayer MoS2, and the difference in peak frequency between the two peaks is maintained at about 18.6 cm–1. The strong emission peak of an exciton of monolayer MoS2 is observed at 1.83 eV of the photoluminescenc spectrum. With the increase of tensile strain, the relative strength of the peak decreases and is linearly re-dshifted, which means that the band gap decreases linearly. It is consistent with the theoretical calculation result.
Tuning metal-insulator transition in δ-doped La:SrTiO3 superlattice by varying doping dimensionality and concentration
Authors: Li Yun , Lu Wen-Jian ,   School of Physics and Electronic Engineering, Hanshan Normal University, Chaozhou 521041, China,   Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China
Published: August 2021

Electronic properties in δ-doped La:SrTiO3 superlattices varying with the doping dimensionality and concentration are systematically studied through using first-principles calculation. The superlattices consist of periodically repeated La-doped single SrTiO3 layers in SrTiO3 film, and the doping dimensionality can be tuned by varying the space of the neighboring doped layers. At 25% doping concentration, the spacing between SrTiO3 layers increases from 1 unit-cell layer to 5 unit-cell layers, i.e. the doping dimensionality changes three dimensions to two dimensions, the superlattice charater changes from metallic character into insulating character, and the charge sequence, spin sequence and orbital sequence are present in a localized state. This metal-insulator transition is ascribed to the stronger correlation effect in the two-dimensional electron system. With the two-dimensional doping concentration increasing to 50%, the correlation effect becomes weak and the system becomes metallic.
Improving efficiency and stability of organic-inorganic hybrid perovskite solar cells by absorption layer ion doping
Authors: Yan Jia-Hao , Chen Si-Xuan , Yang Jian-Bin , Dong Jing-Jing ,   School of Science, China University of Geosciences (Beijing), Beijing 100083, China,   School of Science, Tianjin University of Technology, Tianjin 300384, China
Published: August 2021

ABX3 crystalline perovskite material has many advantages: good photoelectric absorption property, high charge carrier mobility, good film formation, long charge carrier lifetime, and easy bandgap adjustment for absorption layer of perovskite solar cells. As a result, the power conversion efficiency (PCE) of the organic-inorganic halide perovskite solar cells (PSCs) has taken a tremendous step forward, from 3.9% in 2009 to a recently reported value over 25.5%. Thus, it shows great potential to compete with traditional silicon solar cells. However, PSCs preparing conditions are harsh and susceptible to environmental influences, thus leading to instability. Therefore, it is essential to prepare high-performance and stable PSCs in an air environment. This study aims to use the ion doping method to improve the performance and stability of PSCs and analyze the mechanism. This work focuses on enhancing PSCs efficiency and stability by performing FA+ and Cl– doping experiments on MAPbI3 films in air. The results show that a single Cl–-doping increases the carrier diffusion length, reducing the recombination of electrons and holes, and inducing the perovskite intermediate hydrate (CH3NH3)4PbI6·2H2O to form, promoting the crystallization of the thin film, and improving the device performance. On the other hand, a single FA+-doping will reduce the bandgap of perovskite and increase the short-circuit current density (JSC) of the device, and FA+ is susceptible to the influence of water vapor to induce a yellow δ-FAPbI3 perovskite film to form, which leads the device performance to degrade. However, the prepared co-doping Cl–, FA+ significantly improves overall PSCs device performance, yielding the highest PCE of 17.29%, and showing excellent stability by maintaining over 80% of the original PCE without any encapsulation after 1000-hour storage in ambient air.
Multi-beam multi-mode vortex beams generation based on metasurface in terahertz band
Authors: Li Guo-Qiang , Shi Hong-Yu , Liu Kang , Li Bo-Lin , Yi Jian-Jia , Zhang An-Xue , Xu Zhuo ,   MOE Key Laboratory for Multifunctional Materials and Structures, Xi’an Jiaotong University, Xi’an 710049, China,   School of Information and Communications Engineering, Faculty of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China,   College of Electronic Science and Technology, National University of Defense Technology, Changsha 410073, China,   Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education, Xi’an Jiaotong University, Xi’an 710049, China
Published: August 2021

The generating of vortex beams in the terahertz (THz) band attracts significant attention due to their applications in high-speed communication and high-resolution imaging. In this article, a novel reflective metasurface working in the THz band is designed to generate four vortex beams with different topological charges in different directions. The unit cell is designed based on the geometric phase, and it consists of two metallic (gold) layers and one dielectric layer in between. The top layer of the unit cell includes an elliptic patch and a circular ring, and the bottom layer of the unit cell is a metallic ground. The reflection efficiency of the unit cell is very high due to the presence of metallic ground. To break through the limitations of traditional methods, the metasurface is a good choice to generate beams that carry orbital angular momentum (OAM). Using the concept of geometric phase, the reflection phase of reflective circular polarization (CP) electromagnetic waves can be controlled in an ingenious way. Owing to the property of the geometric phase, inverse phase shift can be achieved for left-handed circular polarization and right-handed circular polarization waves. By utilizing this trait of geometric phase, one can decompose a linear polarization wave into two orthogonal circular polarization waves and control their properties respectively. By rotating the top layer of the unit cell, 360-degree phase shift and the phase distribution satisfying the requirement for generating the multi-beam multi-mode vortex beam can be achieved. In order to control the direction and the topological charge of each beam, based on the geometric phase, the theory of reflectarray and the phase composition principle, the phase distribution of the reflective metasurface is calculated to provide the phase compensation to make the vortex beams point to certain directions. It is worthwhile to point out that the method presented in this paper provides a way to generate complex multi-mode vortex beams in the THz band. The simulations and measurements show that the metasurface can generate four vortex beams with topological charges l = ± 1 and ± 2 in different directions in the THz band. These results also indicate that our design has great potential applications in wireless communication and high-resolution imaging.
Research progress of measurement-based quantum computation
Authors: Zhang Shi-Hao , Zhang Xiang-Dong , Li Lü-Zhou ,   Institute of Quantum Computing and Computer Theory, School of Computer Science and Engineering, Sun Yat-Sen University, Guangzhou 510006, China,   Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurements of Ministry of Education, School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: August 2021

Compared with the quantum gate circuit model, the measurement-based quantum computing model provides an alternative way to realize universal quantum computation, and relevant contents have been greatly enriched after nearly two decades of research and exploration. In this article, we review the research history and status of the measurement-based quantum computing model. First, we briefly introduce the basic theories of this model, including the concept and working principles of quantum graph states as resource states, the model’s computational universality and classical simulation methods, and relevant applications in the field of quantum information processing such as designing quantum algorithms and fault-tolerant error correction schemes. Then, from the perspective of quantum physical properties, which include the specific roles of quantum entanglement, contextuality, quantum correlations, symmetry-protected topological order, and quantum phases of matter as computing resources, the close relationship between measurement-based quantum computing model and quantum many-body system is presented. For example, a type of measurement-based computing model for exploiting quantum correlations can show a quantum advantage over the classical local hidden variable models, or certain symmetry-protected topological order states enable the universal quantum computation to be conducted by using only the measurements of single-qubit Pauli operators. Next, a variety of different technical routes and experimental progress of realizing the measurement-based quantum computing model are summarized, such as photonic systems, ion traps, superconducting circuits, etc. These achievements in various physical areas lay the foundation for future scalable and fault-tolerant quantum computers. Finally, we discuss and prospect the future research directions in this field thereby inspiring readers to further study and explore the relevant subjects.
Liquid crystal tunable vertical cavity surface emission laser with inner cavity sub-wavelength grating
Authors: Wang Zhi-Peng , Guan Bao-Lu , Zhang Feng , Yang Jia-Wei ,   Laboratory of Opto-electronics Technology, Faculty of Information Technology, Beijing University of Technology, Beijing 100124, China
Published: August 2021

With the rapid development of information technology, a wavelength-tunable vertical cavity surface emitting laser (VCSEL) is urgently needed as an optical signal source in dense wavelength division multiplexing (DWDM). Liquid crystal tunable VCSEL realized by utilizing the birefringence characteristics of liquid crystal has the advantages of stable polarization, high reliability, continuous wavelength tuning. In this paper, a liquid crystal tunable VCSEL structure based on intracavity sub wavelength grating is designed, and the influence of liquid crystal layer and sub wavelength grating on the wavelength tuning characteristics of VCSEL are analyzed and studied in depth. The results show that the thickness of the liquid crystal layer in the tunable VCSEL structure not only affects the wavelength tuning range, but also determines the mode hopping in the tuning process. In addition, an effective refractive index antireflection layer is formed by designing the subwavelength grating structure, and the refractive index difference between the liquid crystal layer and the semiconductor layer is optimized to further improve the wavelength tuning range and tuning efficiency. When the center wavelength is 980 nm, the tuning range is increased by 42%, reaching 41 nm, and the wavelength tuning efficiency is increased by 41%. It provides a new method of designing the VCSEL laser with high beam quality and continuous wavelength tuning.
A method of evaluating importance of nodes in complex network based on Tsallis entropy
Authors: Yang Song-Qing , Jiang Yuan , Tong Tian-Chi , Yan Yu-Wei , Gan Ge-Sheng ,   Institute of Information Engineering, Nanchang Hangkong University, Nanchang 330063, China,   Institute of Automation, Nanjing University of Science and Technology, Nanjing 210094, China
Published: August 2021

Evaluating the importance of nodes in complex networks is an important topic in the research of network characteristics. Its relevant research has a wide range of applications, such as network supervision and rumor control. At present, many methods have been proposed to evaluate the importance of nodes in complex networks, but most of them have the deficiency of one-sided evaluation or too high time complexity. In order to break through the limitations of existing methods, in this paper a novel method of evaluating the importance of complex network nodes is proposed based on Tsallis entropy. This method takes into account both the local and global topological information of the node. It considers the structural hole characteristics and K-shell centrality of the node and fully takes into account the influence of the node itself and its neighboring nodes. To illustrate the effectiveness and applicability of this method, eight real networks are selected from different fields and five existing methods of evaluating node importance are used as comparison methods. On this basis, the monotonicity index, SIR (susceptible-infectious-recovered) model, and Kendall correlation coefficient are used to illustrate the superiority of this method and the relationship among different methods. Experimental results show that this method can effectively and accurately evaluate the importance of nodes in complex networks, distinguish the importance of different nodes significantly, and can show good accuracy of evaluating the node importance under different proportions of nodes. In addition, the time complexity of this method is \begin{document}$ O({n^2}) $\end{document}, which is suitable for large-scale complex networks.
In-plane manipulation of single particle based on phase-modulating acoustic tweezer
Authors: Zhu Ji-Lin , Gao Dong-Bao , Zeng Xin-Wu ,   College of Meteorology and Oceanography, National University of Defense Technology, Changsha 410073, China
Published: August 2021

The acoustic radiation force allows acoustic tweezers to suspend and move tiny particles. The horizontal movement is one of the common forms in which acoustic tweezers manipulate particles. In this paper, the direct relationship between acoustic radiation force and sound pressure is derived theoretically. The results show that there is a corresponding relationship between the maximum point of sound pressure (focus point) and the minimum point of acoustic radiation force potential energy. A model for focused acoustic field in acoustic tweezers is established based on the principle of phase modulating. In the numerical simulation, taking the double-sided 16-element acoustic tweezers device for example, the method of controlling the horizontal movement of particles and its stability are analyzed. Owing to the influence of gravity, the balance in the vertical direction must be considered in the horizontal movement of particles. Horizontal movement shows different stabilities at different positions in acoustic filed. The closer to the center of the array the particle is, the more stably it moves. The step length (accuracy) also has an important influence on the moving stability. In general, the shorter the step size is, the higher the stability is. In this model, when moving step length is reduced by one-half, the stability is improved by nearly 40%. The research results have theoretical significance for designing acoustic tweezers, planning particle movement paths, and promoting the application of acoustic tweezers technology.
Theoretical prediction of solution in ScxY1–x Fe2 and order-disorder transitions in V2x Fe2(1–x)Zr
Authors: Jiang Yong-Lin , He Chang-Chun , Yang Xiao-Bao ,   Department of Physics, South China University of Technology, Guangzhou 510640, China
Published: August 2021

Alloying is an important way to increase the diversity of material structure and properties. In this paper, we start from Ising model considering nearest neighbor interaction, in which a ferromagnetic system corresponds to a low temperature phase separation and high temperature solid solution of binary alloy, while antiferromagnetic system corresponds to a low temperature ordered solid solution and a high temperature disorder. The high-throughput first-principles calculation based on the structure recognition is realized by the program SAGAR (structures of alloy generation and recognition) developed by our research group. By considering the contribution of structural degeneracy to the partition function, theoretical prediction of alloy materials can be carried out at finite temperature. Taking hydrogen storage alloy (ScxY1–x Fe2 and V2x Fe2(1–x)Zr) for example, the formation energy of ground state (at zero temperature) can be obtained by the first-principles calculations. It is found that the formation energy of ScxY1–x Fe2 is greater than zero, thereby inducing the phase separation at low temperature. The free energy will decrease with the temperature and concentration increasing, where the critical temperature of solid solution of alloy is determined according to the zero point of free energy. The formation energies of V2x Fe2(1–x)Zr are all lower than zero, and the ordered phase occurs at low temperature. The order-disorder transition temperature of V0.5Fe1.5Zr and V1.5Fe0.5Zr are both about 100 K, while the transition temperature of VFeZr is nearly 50 K. The calculation process will effectively improve the high throughput screening efficiency of alloy, and also provide relevant theoretical reference for experimental research.
Coherent mode coupling in shallow water overlaying sloping elastic ocean bottom
Authors: Zhang Shi-Zhao , Piao Sheng-Chun ,   Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China,   Key Laboratory of Marine Information Acquisition and Security, Ministry of Industry and Information Technology, Harbin Engineering University, Harbin 150001, China,   College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China
Published: August 2021

In this paper, a sound field model of elastically coupled normal mode suitable for complex eigenvalues is established. The normalization and coupling coefficient expression of elastic normal mode are given when the leaky mode is included. The coupling coefficients satisfy the conservation of sound energy flow. This model is used to analyze the coherent coupling characteristics of the normal mode of the sound field under the condition of the inclined elastic seabed. It is found that when the leaky mode is considered, the normal mode coupling will not only cause the amplitude of the normal mode to change, but also bring additional phase shift. The simulation calculation shows that under the condition of inclined elastic seabed, the acoustic propagation loss obtained by considering the effect of the additional phase shift of the leaky mode coupling is closer to the calculation result obtained by using the finite element commercial software, and that the mode coupling greatly enhances the amplitude of interface wave. In addition, this paper also analyzes the influence of changes in marine environmental parameters on sound transmission loss.
Review of partially coherent diffraction imaging
Authors: Xu Wen-Hui , Ning Shou-Cong , Zhang Fu-Cai ,   Harbin Institute of Technology, Harbin 150001, China,   Department of Electrical and Electronic Engineering, Southern University of Science and Technology, Shenzhen 518055, China,   Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore
Published: August 2021

Coherent diffraction imaging (CDI), a type of lensless imaging method, relies on the use of light source with high-degree coherence to compute highly resolved complex-valued objects. The coherence of light source consists of temporal coherence and spatial coherence. In practice, it is difficult to obtain a fully coherent source. Spatial decoherence can be generated in the following three scenarios: no synchronization mechanism for the whole radiation source, a finite (non-zero) point spread function of the detector, and the sample variation within exposure time. Partial temporal coherence means that the beam is not quasi-monochromatic, behaving as the energy spread of the illumination. The consequence of reduced degree of temporal and/or spatial coherence in CDI is the decrease of visibility in the measured diffraction intensity. A fundamental assumption of CDI is the full temporal and spatial coherence, and even a relatively small deviation from full coherence can prevent the phase retrieval algorithm from converging accurately. It is necessary to break the barrier of limited coherence by improving the experimental setups directly or optimizing the phase retrieval algorithms to mitigate decoherence. Based on the Wolf’s model of coherence-mode of light and the framework of CDI using partially coherent light proposed by Nugent et al., various methods have been proposed to solve the problems induced by low coherence. Those methods generally experience a similar development process, that is, from the requirement for measuring the spatial (coherent length or complex coherent factor) or temporal (spectrum distribution) coherence properties to without the need for such priori knowledge. Here in this work, the principles of partial coherent CDI, and the major progress of CDI with partial spatial- and temporal-coherent light are reviewed.