bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on single crystal MgB2 nanosheets grown by hybrid physical-chemical vapor deposition
Authors: Zhang Yan  , Wang Yue  , Ma Ping  , Feng Qing-Rong  ,   State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, Applied Superconductivity Research Center, Department of Physics, Peking University, Beijing 100871, China
Published: December 2020

This report is focused on the MgB2 nanosheets which have a hexagonal single crystal structure with variable thickness and different radial dimensions. The nanosheets are fabricated by hybird physical-chemical vapor deposition for the first time, as far as we know, and meanwhile they can be site-specific transferred so as to make physical properties measurement. Results of electrical and magnetic measurements indicate that the nanosheets is superconductive with a Tconset=38 K, Tc (0)=33 K. The images of scanning electrical microscope show that the nanosheets have a nanoscale thickness and have not only a large scale in wildth from several microns to hundreds of microns but also a flat cleaning surface. The selected area electrical diffraction data is consistent with the early report of MgB2 diffraction. According to those results, the single crystal nanosheets with high quality can be surely indentified as MgB2. It suggests a new technique for MgB2 single crystal fabrication, and a zero electrical behavior is observed in nanoscale single crystal MgB2. This could be a new opportunity to make a right material for the afterward research such as flux vortices, nanoscale mechanical properties.
Magnetic and transport properties of bilayered perovskite manganites (La0.8Eu0.2)4/3Sr5/3Mn2O7
Authors: Wan Su-Lei  , He Li-Min  , Xiang Jun-You  , Wang Zhi-Guo  , Xing Ru  , Zhang Xue-Feng  , Lu Yi  , Zhao Jian-Jun  ,   School of Physical Science and Technology, Baotou Normal University, Inner Mongolia University of Science and Technology, Baotou 014030, China;,   Key Laboratory of Integrated Exploitation of Bayan Obo Muti-Metal Resources, Inner Mongolia University of Science and Technology, Baotou 014010, China
Published: December 2020

Samples of (La0.8Eu0.2)4/3Sr5/3Mn2O7 were prepared by solid state reaction method. X-ray diffraction patterns indicated that the sample shows no any asymmetry and no any trace of secondary phase. The magnetization curve as a function of temperature (M-T), the magnetization versus magnetic field (M-H) at different temperatures, and the electron spin resonance spectrum have been detected. The magnetization measurement reveals that with lowing temperature, all of the samples undergo a complex magnetic transition. They transform from the two-dimensional short-range ferromagnetic order at TC2D ≈ 282 K, and enter the three-dimensional long-range ferromagnetic state at TC3D ≈ 259 K. Then they step into the antiferromagnetic state at TN ≈ 208 K and enter electric charge temperature order at TCO ≈ 35 K. The antimagnetic phase is found in the sample (La0.8Eu0.2)4/3Sr5/3Mn2O7below TN. When TC3D=370 K, the paramagnetic phase and antimagnetic phase co-exist. When TC3D is above 370 K, only paramagnetic phase exists in the sample. Besides, through electrical resistivity versus temperature curve ρ-T, the sample shows the maximum magnetization electrical resistivity when metal-insulator transition temperature is reached TP ≈ 80 K, TP being far from TC3D. And the transition shows the phenomenon of intrinsic magnetization electrical resistance, MR ≈ 61%. The resistance begins to increase below TCO. Because of the lowing temperature, the itinerant electron eg becomes increasingly spontaneously localized. One can see from the fitted ρ-T curves that (La0.8Eu0.2)4/3Sr5/3Mn2O7 in high temperature range is in accordance with the small polaron mode range hopping conduction.
Fe/Cr doping effects on the magnetism in charge-ordered manganite La0.4Ca0.6MnO3
Authors: Hu Ni  , Liu Yong  , Tang Wu-Feng  , Pei Ling  , Fang Peng-Fei  , Xiong Rui  , Shi Jing  ,   Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, School of Physics and Technology, Wuhan University, Wuhan 430072, China;,   School of Science, Hubei University of Technology, Wuhan 430068, China
Published: December 2020

We have investigated the Fe/Cr doping effects on the magnetic property of a charge-ordered antiferromagnetic manganite La0.4Ca0.6MnO3. Magnetic measurements reveal interesting doping effects. While all the Fe-doped samples still have antiferromagnetic ground state, strong ferromagnetic tendency can be seen in the Cr-doped samples. Meanwhile, Cr-doped samples show clear metallic transport behavior, indicating an inherent double exchange mechanism responsible for the ferromagnetic metallic state. We thus propose that the magnetic exchange interaction between Mn and dopants, and the d-orbital electronic structure of Cr/Fe are essential for the distinct doping effect of Fe and Cr.
Subwavelength focusing of cylindrical vector beams by plano-concave lens based on one dimensional metallic photonic crystal
Authors: Zhong Yi  , Xu Ji  , Lu Yun-Qing  , Wang Min-Juan  , Wang Jin  ,   School of Opto-Electronic Engineering, Nanjing University of Posts and Telecommunications, Nanjing 210023, China
Published: December 2020

Cylindrical vector beams (CVB) can exhibit a unique optical field distribution and focusing characteristic, due to the cylindrical symmetry in polarization. They are widely used in optical micro-manipulation, super-resolution imaging etc. and can be extended to subwavelength scale applications rapidly. Usually, the focusing CVB in subwavelength dimensions is realized by using plasmonic lens. However, this method is restricted by the state of polarization of electromagnetic waves. Nevertheless, when the negative refraction effect of photonic crystals is utilized, subwavelength focusing or imaging can be achieved in orthogonal states of polarization simultaneously. In this paper, the one-dimensional metallic photonic crystal (1D-MPC) with stronger manipulation ability is discussed. The calculated band structure and equi-frequency surfaces show negative refraction for both orthogonal states of polarization in a specific wavelength band. A cylindrical 1D-MPC plano-concave lens is designed to simultaneously focus radially and azimuthally polarized beams to subwavelength dimensions in visible spectrum. This phenomenon is simulated using the finite element method. Furthermore, variation of the polarization components in CVB can directly modulate the spacial intensity and the polarization distribution in the focal field. In fact, subwavelength focusing of CVB with arbitrary polarization components can be achieved by using the 1D-MPC plano-concave lens. The scheme proposed in this paper can be taken as reference for other wavelength bands as well. This study is also valuable for optical micro-manipulation of small particle, super-resolution imaging, and other related areas.
Study on the effect of delayed recovery of extracellular potassium ion concentration on spiral wave
Authors: Qiao Cheng-Gong  , Li Wei-Heng  , Tang Guo-Ning  ,   College of Physical Science and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Frequency-dependent changes in the extracellular potassium ion concentration have been added to the Luo-Rudy phase I heart model. Effects of the delayed restoration of extracellular potassium ion concentration on spiral waves are studied. Numerical simulation results show that due to the state of spiral wave, the delayed restoration of extracellular potassium ion concentration can lead to periodic oscillations of concentration, and the period and amplitude of the oscillation increase with the delayed recovery time, resulting in the emergence of various phenomena, such as the breathing spiral wave, the coexistence of multiple spiral waves, the meandering of spiral waves in the manner of Lévy flight, and the disappearance of spiral wave through different ways. These results are compatible with the experimental results.
Correction of migration through resolution cell in bistatic inverse synthetic aperture radar in the presence of time-varying bistatic angle
Authors: Guo Bao-Feng  , Shang Chao-Xuan  , Wang Jun-Ling  , Gao Mei-Guo  , Fu Xiong-Jun  ,   Department of Electronic and Optical Engineering, Ordnance Engineering College, Shijiazhuang 050003, China;,   School of Information and Electronics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

When the size of target or the rotation angle is big, migration through resolution cell may occur in the bistatic inverse synthetic aperture radar (ISAR), which will affect the imaging quality. Aiming at the problem of migration through resolution cell of bistatic ISAR in the presence of time-varying bistatic angle, a correction algorithm is proposed in this paper. Firstly, the echo model of bistatic ISAR is built, and the mechanism of migration through resolution cell is analyzed. Migration through range cell may be corrected through the generalized Keystone transformation, and the effect of non-uniform rotation is eliminated at the same time. Then the rotating center is estimated according to the maximum criterion of image contrast, and the range bin is scaled absolutely. A phase compensation term is constructed and the correction of migration through Doppler cell is finished. Finally, the simulations are carried out and the results show that the method proposed in this paper can solve the problem of migration through resolution cell and improve the image quality.
Study on intrinsic carrier concentration of direct bandgap Ge1-xSnx
Authors: Bai Min  , Xuan Rong-Xi  , Song Jian-Jun  , Zhang He-Ming  , Hu Hui-Yong  , Shu Bin  ,   Key Lab of Wide Band-Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi'an 710071, China
Published: December 2020

Indirect bandgap Ge can be turned to a direct bandgap semiconductor by the alloy-modified technique, which can be applied to advanced photonic devices and electronic devices. Based on 8 bands Kronig-Penny Hamilton, this paper focuses on the physical parameters of direct bandgap Ge1-xSnx, such as conduction band effective density of states, valence band effective density of states and the intrinsic carrier concentration, and aims to provide valuable references for understanding the direct bandgap modified Ge materials and device physics as well as their applications. Results show that: conduction band effective density of states in direct bandgap Ge1-xSnx alloy decreases obviously with increasing Sn fraction, while its valence band effective density of states almost does not change with increasing Sn fraction. Compared with bulk Ge, the conduction band effective density of states and valence band effective density of states in direct bandgap Ge1-xSnx alloy are lower by two and one orders of magnitude respectively; the intrinsic carrier concentration in direct bandgap Ge1-xSnx alloy increases with increasing Sn fraction, and its value is an order of magnitude higher than that of bulk Ge.
Research on the light emitting diode array launching performance for indoor visible light communication
Authors: Liu Hao-Jie  , Lan Tian  , Ni Guo-Qiang  ,   Key Laboratory of Photoelectronic Imaging Technology and System, Ministry of Education, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

A kind of illumination calculation of array antenna composed of light emitting diode (LED) source based on Lambert radiation model is proposed. This paper puts emphasis on the optimal design for the transmitting antenna of indoor visible light communication. And it also analyzes the influence of the forms of the spatial distribution of the light source, the distance between light sources, and the angle between the center beam of light source and optical axis of the system, as well as the layer spacing of space distribution on illumination uniformity. A circular array antenna is superior to a rectangular array antenna containing the same number of light sources in illumination uniformity and stability of signal transmission, which may increase by 10%. As the distance between light sources and the angle between the center beams of light sources and optical axis keep increasing, the illumination uniformity of array antenna composed of LED source increases first and then starts to drop. As a result, there exist the optimal values in the distance and the angle respectively. Illumination uniformity increases with the decrease of the distance of space distribution. The optimal value of design parameter of transmitting antenna array in a common room has been given, therefore, it optimizes launch performance, saves as much as 13% the number of light source and reduces the cost. These studies for the design of the transmitting antenna system provide a theoretical basis and practical values.
A new sampling method based on radiation energy density for location of radiative source particles
Authors: Li Shu  , Deng Li  , Tian Dong-Feng  , Li Gang  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100094, China;,   China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

When using the implicit Monte Carlo method to simulate the thermal radiative photon transfer in materials, the radiative source particles emitted by the material should be treated carefully. In traditional sampling method for the location of radiative source particles can be regarded as uniform in a single cell, and this is reasonable for most of thermal radiative transfer problems. But it may result in unacceptable error in the problem which has a large absorption cross-section and remarkable temperature difference in a single cell. The reason for this error is discussed in this paper. A new method based on radiation energy density distribution is proposed and the sampling formula is derived. Numerical test indicates that the new method will give results much better than the old method and in agreement with the analytical results.
Homotopic mapping solving method of transfers model with a class of generalized femtosecond pulse laser for nano metal
Authors: Xie Feng  , Lin Wan-Tao  , Mo Jia-Qi  ,   College of Science, Donghua University, Shanghai 201620, China;,   State Key Laboratory of Numerical Modeling for Atmospheric and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China;,   Department of Mathematics, Anhui Normal University, Wuhu 241003, China
Published: December 2020

A class of transfer model for femtosecond pulse laser nano metal film is investigated. Firstly, the exact solution of a typical model is obtained. And then, the arbitrary order approximate analytic solution of corresponding model is obtained by using the functional homotopic mapping method. Finally, the meaning of solution is discussed.
Expanded four-dimensional variatiaonal data assimilation method to optimize model physical parameters
Authors: Wang Yun-Feng  , Gu Cheng-Ming  , Zhang Xiao-Hui  , Wang Yu-Shun  , Han Yue-Qi  ,   Institute of Meteorology and Oceanography, People's Libration Army University of Science and Technology, Nanjing 211101, China;,   School of Mathematical Sciences, Nanjing Normal University, Nanjing 210046, China
Published: December 2020

A critical error in numerical simulation stems from the physical parameters in the model. To better assess the accuracy of the numerical stimulation, a mthod of impoving physical parameters is urgently desired. By modifying the four-dimensional variatiaonal data assimilation 4DVAR technique, in this paper a new method is proposed based on the use of observational data to optimize initial field and subsequent physical model. Ekman boundary layer model and Lorenz model are taken for example to conduct numerical experiment. The results show that through the variations in observational data, physical parameters and initial field are improved, thus effectively enhancing the accuracy of the model. This method improves the numerical model and physical parameters.
Analytical solutions to pulsed eddy current field excited by a differently oriented probe coil outside a conducting ferromagnetic pipe
Authors: Chen Xing-Le  , Lei Yin-Zhao  ,   School of Automation Science and Electrical Engineering, Beihang University, Beijing 100191, China
Published: December 2020

Using the second-order vector potential and Lorentz reciprocity theorem, the non-axisymmetric eddy current field induced by a probe coil outside a conducting ferromagnetic pipe is obtained analytically, where the probe coil is differently oriented: its axis being along the pipe radial direction, parallel to the pipe axis, along the pipe circumferential direction. Then, the time-domain expressions of induced voltage and eddy current density in the pipe are obtained through the Laplace inverse transformation, by calculating the residues of poles. Furthermore, the diffusion process of pulsed eddy current in the pipe, and the detection sensitivity of the time-domain induced voltage signal to the wall thickness are studied. Finally, the analytical solutions are verified through the experimental results of a steel pipe. It is found that when the probe coil is positioned such that its axis is perpendicular to the pipe axis, the strongest and the most sensitive induction voltage signal for detecting the wall thickness of a ferromagnetic pipe is obtained.
Modeling and analysis of piezoelectric vibration energy harvesting system using permanent magnetics
Authors: Tang Wei  , Wang Xiao-Pu  , Cao Jing-Jun  ,   School of Automation, Northwestern Polytechnical University, Xi'an 710129, China
Published: December 2020

Modeling and analyzing of the piezoelectric vibration energy harvester using permanent magnets are systematically investigated to facilitate the evaluation and optimization of such a harvester. We set up a distributed-parameter model for describing nonlinear dynamic behaviors of these harvesters，and present harmonic analytical solution by using harmonic balance method. An analysis is performed using the simulation model to determine the effects of the distance between two magnets, amplitude of acceleration, electrical load resistance on the level of the output power. The optimum resistive loads under different vibration frequencies and accelerations are also compared. The results show that the bistable configuration is applicable to a small excitation case, and the closer to the transition region the small excitation position, the more the power can be harvested. Conversely, the monostable hardening configuration is suited for the large excitation case, the corresponding optimal magnet distance is not close to the transition region. Furthermore, the large amplitude oscillation between two potential wells and small amplitude oscillation within one potential well also bring forth coexisting phenomena of high-energy response and low-energy response; the closer to the transition region the oscillation position, the more obivious the coexisting phenomenon is. It is also demonstrated that exciting frequency is a decisive factor of optimum load resistance.
A new approach to designing circular grating focusing reflector
Authors: Ma Chang-Lian  , Huang Yong-Qing  , Duan Xiao-Feng  , Ren Xiao-Min  , Wang Qi  , Wang Jun  , Zhang Xia  , Cai Shi-Wei  ,   State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

A new approach to designing planar, high numerical aperture, low loss, focusing reflectors using circular subwavelength high contrast gratings is presented. Through analyzing particular physical scene, a mathematical transformation from existing “focus line” convergent beam, which can be achieved by bar grating reflector, to the convergent beam with a “focus point”, is obtained. By changing the shape of the bar grating reflector with the mathematical transformation obtained, a circular grating reflector, which can achieve “focus point” convergent beam, is obtained. The focusing properties and reflection characteristic of the circular grating reflector are numerically studied with the finite element method. After the radially polarized light reflected from circular grating reflector with a diameter of 29.788 μm, the beam will focus at 10 μm away from the reflector, resulting in a numerical aperture of 0.8302 and a reflectivity of 0.9163. In the focal plane, the numerical simulation results present a field distribution with a full width half maximum value of 1.5548μm, which is extremely close to diffraction limit.
Structural and electronic properties of the BnY (n=1-11) clusters
Authors: Ruan Wen  , Yu Xiao-Guang  , Xie An-Dong  , Wu Dong-Lan  , Luo Wen-Lang  ,   College of Mathematics and Physics, Jinggangshan University, Ji'an 343009, China
Published: December 2020

The geometric structures, electronic properties, average binding energies, second-order energy differences and energy gaps of BnY (n=1-11) clusters are systematically studied using the density functional theory (DFT) TPSSh method with 6-311+G(d) basis set for B atoms and Lanl2dz relativistic effective core potential basis set for Y atom. It is found that with the size increasing, the lowest energy structures of BnY (n=1-11) clusters gradually evolve from planar shape to cubic structure. With the atoms of B increasing, the average binding energies of the ground state of BnY (n=1-11) clusters increase. The second-order energy differences and the energy gaps of the ground states of BnY (n=1-11) clusters show that B3Y, B5Y and B7Y clusters possess relatively high stabilities. The polarization and the first static hyperpolarizability studied show that the plane structures of B5Y, B4Y, B3Y and B6Y clusters have larger nonlinear optical properties.
Modified equivalent current approximation and graphical electromagnetic computing method of analyzing radar cross section of missile target scatterer covered with thermal protection layer
Authors: Zhu Yan-Ju  , Jiang Yue-Song  , Hua Hou-Qiang  , Zhang Chong-Hui  , Xin Can-Wei  ,   School of Electronic Information Engineering, Beihang University, Beijing 100191, China
Published: December 2020

In this paper, we combine the modified equivalent current approximate method and graphical electromagnetic computing method to solve the electromagnetic scattering problems in the missile target covered with the thermal protective layer. The modified equivalent current approximate method is used to calculate the lossy dielectric and combining graphical electromagnetic method, and using a computer display technology, blanking and occlusion, a three-dimensional surface is projected on a computer screen, and the pixels are calculated. The calculation in three-dimensional space is converted into the calculation in two-dimensional space, thereby greatly reducing the computation time and complexity. The results show that when the incident frequency is low, the thickness of the thermal protection layer does not affect the radar cross section value. When the frequency is increased with the thickness of the thermal protection layer, the radar cross section value continuously decreases, which indicates that the thermal barrier coating is a lossy medium: the bigger the imaginary part of the dielectric, the stronger the ability to consume the energy is and the more obvious the change of missile radar cross section is. When the thermal protective layer has pores, the higher the porosity, the greater the value of the radar cross section is; when the porosity is zero, the value of the radar cross section is minimal; when the porosity is the same, the thinner the thermal protection layer, the bigger the radar cross section is. When the projectile phenomenon occurs, it does not affect the radar cross section.
Design of a novel wideband directivity patch antenna
Authors: Guo Rong  , Cao Xiang-Yu  , Yuan Zi-Dong  , Xu Xue-Fei  ,   Information and Navigation College, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

A wideband strong-directivity patch antenna is designed based on the metamaterial concept on the ground plane and the Yagi antenna concept of reflector and director. Due to the fact that the effective medium parameters of substrate of antenna are affected by the left-hand characteristics, the wave propagation direction of antenna is changed, which induces the strongest radiation in horizontal direction rather than the vertical direction of the conventional patch antenna. The reflector and director induce a directivity of the radiation. The simulation results show that the relative bandwidth of the designed antenna is 65.3% (6.9-13.6 GHz), the return loss is less than -10 dB, and the average gain is over 4.4 dBi in the operating range. Experimental results are in good agreement with the simulation results.
Measuring topology charge of vortex beam using digital holography
Authors: Wang Lin  , Yuan Cao-Jin  , Nie Shou-Ping  , Li Chong-Guang  , Zhang Hui-Li  , Zhao Ying-Chun  , Zhang Xiu-Ying  , Feng Shao-Tong  ,   Key Laboratory for Opto-Electronic Technology of Jiangsu Province, Nanjing Normal University, Nanjing 210023, China;,   Laser Research Institute, Kunming University of Science and Technology, Kunming 650051, China
Published: December 2020

In this paper we propose a method to detect the topology charge of vortex beam using digital holography. Hologram of vortex beam interference with reference beam is recorded, and the phase of vortex beam is reconstructed. The topology charge can be accurately determined by judging the periodicity of reconstructed phase distribution around the phase singularity. The phases of vortex beams generated by numerical simulation and those obtained by experiment of vortex beams with integral and fractional topology charges are compared with each other. The feasibility of the method of detecting the topology charge of vortex beam using digital holography is proved by comparing the results.
Acquiring narrow linewidth microwave signals based on an optical injection semiconductor laser under subharmonic microwave modulation
Authors: Mao Song  , Wu Zheng-Mao  , Fan Li  , Yang Hai-Bo  , Zhao Mao-Rong  , Xia Guang-Qiong  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China;,   State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
Published: December 2020

The performances of microwave signals generated by an optically injected semiconductor laser operated at the period-one (P1) oscillation under 1/2 subharmonic microwave modulation, are investigated experimentally. The experimental results show that under suitable injection condition, the microwave signal output from an optically injected semiconductor operated at P1 oscillation can reach a frequency of 26.5 GHz limited to the experimental conditions and may have a single sideband optical spectrum structure, but the linewidth of the microwave signal is relatively wide (on the order of MHz). After adopting 1/2 subharmonic locking technique, the linewidth of the obtained microwave signal can be reduced from tens of MHz to tens of kHz. Furthermore, we analyze the influences of the power and frequency of the subharmonic microwave on the phase noise of the generated microwave signals, and further map the subharmonic microwave locking region in the parameter space of the power and frequency of the subharmonic microwave.
Single-atom transfer in a strongly coupled cavity quantum electrodynamics: experiment and Monte Carlo simulation
Authors: Li Wen-Fang  , Du Jin-Jin  , Wen Rui-Juan  , Yang Peng-Fei  , Li Gang  , Zhang Tian-Cai  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

The process of single-atom transfer in strongly coupled cavity quantum electrodynamics (QED) with free falling atoms is investigated by experiment and Monte Carlo simulation. We conduct the simulation of the whole physical process and give the corresponding experimental results. In experiment, a high finesse optical cavity is used for real-time detection of the single-atom transits from which the interaction information between single atoms and cavity can be extracted, including the transmission spectra of the cavity strongly coupled to single atoms, the interaction duration of the single atoms in the mode, the probability distribution of atom arrival time and the atomic kinetic energy distribution when arriving at the mode. All these can be completely derived from the transmission spectra of the different initial status. An intracavity far-off resonance trap (FORT) has been established and the single-atom trapping time inside the cavity is about 5 ms which is about 30 times longer than that without FORT. This study gives the detailed analysis of the whole procedure of free-falling atom transfer in cavity QED system and is helpful for optimizing the experimental parameters and design.
Tamm state of semi-infinite photonic crystal based on surface defect cavity with porous silicon and its refractive index sensing mechanism
Authors: Chen Ying  , Fan Hui-Qing  , Lu Bo  ,   Hebei Province Key Laboratory of Test/Measurement Technology and Instrument, School of Electrical Engineering, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

A refractive index sensing structure based on the Tamm state of photonic crystal with surface defect is proposed by combing the Tamm state of semi-infinite photonic crystal with the optical sensing mechanism of porous silicon, in which the efficient bearing mechanism of the porous silicon is introduced into the surface defect cavity. The existence of Tamm state is demonstrated at the edge between the defect cavity and the periodical photonic crystal structure, and the total reflection in the defect cavity is formed by adjusting the incident angle. The resonant defect peak is obtained in the reflection spectrum by adding an absorbing medium into the defect cavity in order to reduce the reflectivity of the resonant wavelength. The full width at half maximum and the quality factor (Q value) can be optimized by adjusting the parameters of photonic crystal. Based on those results, according to the relationship between Goos-Hänchen phase shift and the resonant wavelength, the model for the relationship between the resonant wavelength and the effective refractive index variation of porous silicon adsorbing layer caused by the change of the refractive index of the sample is established, and its refractive index sensing characteristics are analyzed. The numerical simulation results show that the Q value can attain to 1429 and the sensitivity is about 546.67 nm·RIU-1, which can demonstrate the effectiveness of the structure design and provide some theoretical references for designing the refractive index sensors with high Q values and sensitivities.
Shock response and evolution mechanism of brittle material containing micro-voids
Authors: Yu Yin  , He Hong-Liang  , Wang Wen-Qiang  , Lu Tie-Cheng  ,   Key Laboratory for Radiation Physics and Technology of Ministry of Education, Department of Physics, Sichuan University, Chengdu 610064, China;,   National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

Micro-voids significantly affect shock responses of brittle materials. Knowledge about the meso-scale evolution mechanism and macro-scale shock behavior will help to utilize micro-void in applications and avoid its disadvantages. A lattice-spring model, which can represent both elastic property and fracture evolution accurately, is built in this work. Simulations reveal that severe stress relaxation, which is contributed from collapse deformation induced by voids and slippage deformation induced by shear cracks extending from voids, modulates the propagation of shock wave. In a porous brittle material, the shock wave broadens into an elastic wave and a deformation wave. On a macro-scale, the deformation wave behaves as a plastic wave in ductile metal; on a meso-scale, it corresponds to the processes of collapse and slippage deformations. It is found that porosity of the sample determines the Hugoniot elastic limit of material; whereas the porosity and shock stress affect the propagation speed of the deformation wave and stress amplitude in a final state of shock. Brittle materials containing micro-voids have potential applications in complex shock loading experiments, precaution of shock induced function failure, and crashworthiness of buildings. Shock behaviors reported in this work will benefit the design and optimization of shock responses and dynamic mechanical properties of brittle materials used in specific applications.
Optical properties and laser damage performance of SiO2 irradiated by high-power pulsed electron beam
Authors: Zhong Mian  , Yang Liang  , Ren Wei  , Xiang Xia  , Liu Xiang  , Lian You-Yun  , Xu Shi-Zhen  , Guo De-Cheng  , Zheng Wan-Guo  , Yuan Xiao-Dong  ,   School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China;,   Center for Fusion Science of Southwestern Institute of Physics, Chengdu 610041, China;,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

A 60 kW electron beam is used to study the microstructure and optical property evolutions as well as laser induced damage threshold of fused silica after irradiation at room temperature. Optical microscopic results indicate that cracks appear at the surface of SiO2 after electron beam irradiation, owing to the thermal effect, and that the crack density and size increase with increasing radiation dose. The morphology of the surface cracks is analyzed by using atomic force microscope and the width of crack is about 1 μm. In addition, there are a large number of debris particles with sizes of 0.1-1 μm on the surface. From the optical absorption spectrum of each of all samples, a weak absorption peak at 394 nm is observed and the absorbance increases at the beginning then decreases with increasing electron-radiation dose. Before and after irradiation, three absorption bands at 460 nm, 496 nm and 520 nm are clearly observed and their intensities first increase and then decrease, which is consistent with the results of absorption spectra. The effect of electron dose on the laser induced damage threshold (LIDT) at 355 nm is investigated and the results indicate that the LIDT decreases with increasing dose. At the lower electron doses, the color centers are responsible for the decrease of LIDT. However, at the higher electron doses, the decrease of LIDT is due to the light modulation and absorption induced by microscale cracks and debris particles at the surface of irradiated fused silica.
Effect of titanium ion energy on surface structure during the amorphous titanium dioxide film deposition
Authors: Chen Xian  , Wang Yan-Wu  , Wang Xiao-Yan  , An Shu-Dong  , Wang Xiao-Bo  , Zhao Yu-Qing  ,   Key Laboratory for Physical Electronics and Devices of Ministry of Education, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

In this paper, we investigate the influences of the surface structure formation mechanism and the film properties on the incident titanium ion energy in the amorphous TiO2 thin film deposition process. The results show that the surface roughness of the film is reduced by increasing the energy of the incident titanium ions, and then the optical scattering loss of the film surface will decrease. It is also found that when the incident ion energy is increased, the film growth pattern changes from the “island-like” growth to the “layer-like” growth, and the surface diffusion coefficient of ions near the incident point is also significantly increased, which is conducive to the formation of more smooth film surface.
First-principles study of Ag2ZnSnS4 as a photocatalyst
Authors: Huang Dan  , Ju Zhi-Ping  , Li Chang-Sheng  , Yao Chun-Mei  , Guo Jin  ,   College of Physics and Electronic Sciences, Hunan University of Arts and Science, Changde 415000, China;,   Key Laboratory of Novel Energy Materials and Related Technology of Guangxi Colleges and Universities, College of Physics Science and Technology, Guangxi University, Nanning 530004, China
Published: December 2020

By using the first-principles calculation based on density functional theory, we propose some approaches to improving the efficiency for the photocatalyst Ag2ZnSnS4 from a theoretical aspect. Comparing its band edge positions with those of other similar compounds, we find that Cu, Ge codoping can adjust both the band gaps and band edge positions of Ag2ZnSnS4 at the same time, which can optimize its band structure for water splitting. In addition, Ag2ZnSnS4 has a type-Ⅱ band offset with another photocatalyst CuGaSe2. Preparation of its homojunction can also improve their efficiencies of photocatalysis hydrolyzation.
Spectroscopic properties of ～2 μm emissions of Tm3+-doped germanate-tellurite glasses
Authors: Gao Song  , Wang Xin  , Fan Xiao-Kang  , Li Ke-Feng  , Liao Mei-Song  , Hu Li-Li  ,   Research and Development Center of High Power Laser Components, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Tm2O3-doped 40GeO2-35TeO2-15PbO-5Al2O3-2.5CaO-2.5SrO glasses with different Tm3+ ion concentrations are fabricated by conventional melt-quenching method. From the measurements of thermal properties it follows that the glass transition temperature is 446 ℃ and crystallization peak does not exist. The maxmium phonon energy of the host is ~ 750 cm-1. The Judd-Ofelt strength parameter Ωt (t = 2, 4, 6), the radiative transition probalities, the branching ratios and the radiative lifetime are calculated according to Judd-Ofelt theory. The emission spectra of Tm3+ doped glasses with different Tm2O3 concentrations are measured under the excitation by an 808 nm diode laser. The result shows that the emission intensity at ~ 1.8 μm reaches a maximal value when the Tm2O3-doping concentration is 1 mol% and then it decreases with the further increase of Tm2O3-doping concentration. The emission cross section of 3F4 → 3H6 is calculated based on the McCumber theory. The peak emission cross-section is 6.5 × 10-21 cm2. The non-radiative transition rate of 3F4 caused by OH is calculated quantitatively by rate equation. The results indicate that the germanate-tellurite glass is a new candidate for mid-infrared laser application.
Nanocrystalline aluminum studied by positron annihilation lifetime spectroscopy
Authors: Li Yu  , Luo Jiang-Shan  , Wang Zhu  , Yang Meng-Sheng  , Xing Pi-Feng  , Yi Yong  , Lei Hai-Le  ,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China;,   Institute of Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China;,   College of Physics Science and Technology, Wuhan University, Wuhan 430070, China
Published: December 2020

Aluminum nanoparticles with an average diameter of about 48 nm are compressed in a cemented-carbide mold under different pressures to produce nanocrystalline aluminum by the hot-pressing technology in a high vacuum condition. The X-ray diffraction and the positron annihilation lifetime spectroscopy (PALS) are used to characterize the microscopic structures of nanocrystalline aluminum. The PALS experimental results indicate that there are three types of defects in nanocrystalline aluminum, i.e., vacancy-like defects, vacancy clusters, and microvoids, which are corresponding to three lifetime components of positrons. The pressure for compaction has a great influence on the positron annihilating behavior. The vacancy clusters transform into the vacancy-like defects with increasing the pressure when it is below 0.39 GPa. The three types of defects tend to be rapidly eliminated in a pressure range from 0.39 GPa to 0.72 GPa. When pressure is above 0.72 GPa, the defects are further eliminated in nanocrystalline aluminum. The density and microhardness of nanocrystalline aluminum increase significantly with increasing the pressure for compaction.
Nano-scale lithography and in-situ electrical measurements based on the micro-chips in a transmission electron microscope
Authors: Zhang Chao  , Fang Liang  , Sui Bing-Cai  , Xu Qiang  , Wang Hui  ,   State Key Laboratory of High Performance Computing, National University of Defense Technology, Changsha 410073, China;,   School of Computer, National University of Defense Technology, Changsha 410073, China;,   Delft University of Technology, Kavli Institute of Nanoscience, 2628 CJ, Delft, The Netherlands;,   Key Laboratory of Aerospace Materials and Performance of the Ministry of Education, School of Materials Science and Engineering, Beihang University, Beijing 100191, China
Published: December 2020

In this paper, the in-situ membrane chips with the electrodes are fabricated with the micro-chip technique. Using a home-made in-situ holder, the fine lithography on the InAs nanowires is demonstrated by the focused electron beam at low temperature in a transmission electron microscope. It is found that the conductance of the nanowires decreases linearly with the cross section area decreasing from bigger than 10000 nm2 down to 800 nm2 by lithography. With this lithography at low temperature, a 10 nm nano-dot is fabricated on an InAs nanowire, and its electrical properties are measured at 77 and 300 K. The coulomb blockade effect is observed at 77 K due to the electron tunneling, while this phenomenon disappears at 300 K due to the stronger thermal fluctuation.
Efficiency improvement in organic solar cells by doping cholesteric liquid crystal
Authors: Li Meng  , Niu He-Ying  , Yao Lu-Yan  , Wang Dong-Liang  , Zhou Zhong-Po  , Ma Heng  ,   College of Physics and Electronic Engineering, Henan Normal University, Xinxiang 453007, China;,   Henan Key Laboratory of Photovoltaic Materials, Xinxiang 453007, China
Published: December 2020

A series of poly(3-hexylthiophene) (P3HT)/indene-C60 bisadduct (ICBA) bulk heterojunction polymer solar cells is fabricated with different cholesteric liquid crystalline (LC)-cholesteryl chloride doping concentrations. The open circuit voltage (Voc) is increased from 0.78 V to 0.65 V, meanwhile the short circuit current density (Jsc) is reduced from 4.23 mA·cm-2 to 4.10 mA·cm-2 when the LC doping concentration is 5%, and fill factor is almost unchanged. The optimized power conversion efficiency of polymer solar cells (PSCs) with LC doping is about 1.51%. The crystallinity of the active layer and the light absorption characteristics are analyzed by X-ray diffraction, photoluminescence, UV-visible absorption spectroscopy and atomic force microscope, respectively.
Realization and experiment of vertical multijunction integrated photovoltaic Si X-ray detector
Authors: Zhang Zhi-Guo  ,   Institute of Functional Material, Quanzhou Normal University, Quanzhou 362000, China;,   School of Physics and Information Engineering, Quanzhou Normal University, Quanzhou 362000, China
Published: December 2020

The structure of the vertical multijunction detector is introduced, and the result and technologcial conditions of preparing junction by thermomigration method are presented. In addition, the insulation line method of processing electrode wire is specially introduced; the problem of photoetching electrode after thermomigration is solved; the effects of technologcial conditions on device performance are analyzed. Besides, the difficulty in connecting all P regions is solved, and the aim of zero shade for sensitive regions is achieved. Specially, in order to realize integrating multicell device, a method of widening the size of electrode wire is described. Several important parameters are described, and the math model for the relationship of the X-ray intensity with both photovoltage and photocurrent is set up. At the same time, we introduce the measurement relation between the output voltage of the device and X-ray intensity, which shows that the measurement data and theoretical results are consistent. Finally, we analyze the measurement data, and demonstrate that the device has good enough sensibility and resolution.
Three-dimensional simulation study of bias effect on single event effects of SiGe heterojunction bipolar transistor
Authors: Zhang Jin-Xin  , He Chao-Hui  , Guo Hong-Xia  , Tang Du  , Xiong Cen  , Li Pei  , Wang Xin  ,   Xi' an Jiaotong University, Xi'an 710049, China;,   Key Laboratory of Functional Materials and Devices for Special Environments of Chinese Academy of Sciences, Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Urumqi 830011, China;,   Northwest Institution of Nuclear Technology, Xi'an 710024, China
Published: December 2020

In this paper we establish a three-dimensional (3D) numerical simulation model of domestic SiGe heterojunction bipolar transistor (SiGe HBT) by using technology computer aided design tools, to study the bias effect on single event effect (SEE) of SiGe HBT. The response relationship between SEE and the bias of SiGe HBT is identified based on the analyses of transient current peak and charge collection of each terminal. The results show that the worst biases for SEE are different for different terminals. Even for the same terminal, the worst biases for charge collection and transient current peak are different. This phenomenon is caused mainly by the influence of applied electric field and the change of carrier transport mode.
Magnetocardiac signal analysis based on multiple time windows beamformer method
Authors: Wang Wei-Yuan  , Jiang Shi-Qin  , Zhou Da-Fang  , Zhu Jia-Chen  , Yan Yu-Rui  , Quan Wei-Wei  ,   School of Electronics and Information Engineering, Tongji University, Shanghai 201804, China;,   Department of Cardiology, Rui Jin Hospital and College of Medicine, Shanghai Jiao Tong University, Shanghai 200025, China
Published: December 2020

A beamformer method based on multiple time windows is proposed to estimate the equivalent current sources of different strength and duration from multi-channel magnetocardiography data. This technique of visualizing cardiac electric activities will be a great help to the diagnosis of relevant heart diseases. Feasibility of this beamformer method has been proved by simulation experiments of two known sources. Source estimation results and two-dimensional excitation propagation diagrams of a complete left bundle branch block and a complete right bundle branch block patients during QRS complex are taken to be compared. The revealed characteristics of their electrophysiological phenomena are analyzed.