bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectrum detection based on compressive sensing inside multimode fibers
Authors: Meng Fan , Zhang Yun-Zuo , Feng Wei-Wei , Wu Peng-Fei , Zou Ge-Yin ,   School of Information Science and Technology, Shijiazhuang Tiedao University, Shijiazhuang 050043, China,   Training Department, Shijiazhuang Post and Telecommunication Technical College, Shijiazhuang 050021, China
Published: December 2020

With the rapid development of integrated photonics, expensive and bulky commercial spectrometers force people to make more efforts to investigate high-performance, integrated and low-cost spectrometers. Spectrometers benefiting from the complementary metal-oxide semiconductor (CMOS) technology have greatly enriched the applications of spectrum detection while devices based on optical fibers still have potential development room. Owing to the strong dependence of multimode interference on wavelength generated in a multimode fiber, probe signals of arbitrary spectra could be detected by a detector array integrated on the top and reconstructed by using a compressive sensing (CS) algorithm. The CS algorithm has been widely used in signal processing, which saves more computing storage and time but maintains the same precision. With the interference pattern system, our spectrometer based on a fiber taper achieves a spectral resolution of 20 pm (one order of magnitude better than commercial spectrometers) and a detection bandwidth of more than 200 nm on a device length of 1 mm. After optimizing the energy function, the spectral reconstruction results show excellent detection capability and metamerism effect superior to RGB cameras or human eyes, providing a significant role for portable multi-functional on-chip systems in future.
Ions beam induced luminescence study of variation of defects in zinc oxide during ion implant and after annealing
Authors: Luo Chang-Wei , Qiu Meng-Lin , Wang Guang-Fu , Wang Ting-Shun , Zhao Guo-Qiang , Hua Qing-Song ,   Key Laboratory of Beam Technology of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China,   Beijing Radiation Center, Beijing 100875, China
Published: December 2020

The optical and electrical properties of ZnO related on the type and the concentration of defects in ZnO crystal. Ion implantation and annealing can change the type and the concentration of defects in ZnO. To understand the variation of defects in ZnO during ion implantation and after different temperature annealing, in situ luminescence measurements of ZnO crystal samples were carried out by ion beam induced luminescence (IBIL) during ion implantation of 2 MeV H+ and then after annealing at 473 K and 800 K in vacuum on the GIC4117 tandem accelerator in Beijing Normal University.

IBIL spectra of ZnO showtwo emission peaks: UV emission, which is called near band emission (NBE), and visible emission, which is called deep band emission (DBE).The high-intensity of DBE and weak NBE of IBIL spectra of ZnOmay be due to the NBE is intrinsic to ZnO samples and therefore is just visibly observed from samples that are virtually defect-free. With the ion implantation, the destruction of the crystal structure and the arising of a mass of defects, inducing the weak intensity NBE and intense DBE.In addition, the overall IBIL spectra of ZnOreveal decrease intensity with the ion fluence,which indicates that the concentration of luminescence centersdecreases duringion implantation.With the H+ fluence, the concentration of the point defects increases. The point defects migrate and subsequently agglomerate into larger defect clusters. These defect clusters serve as traps for catching electrons and holes, which result in the quenching of luminescence centres. Annealing can help todecompose the defect clusters and repair the defects of crystal. However, amounts of defects and clusters still remain in the irradiated sample annealed at 473 K in vacuum, which acted as nonradiative center and suppress the luminescence induced weak intensity of IBIL. Annealing the sample at 800 K in vacuum may facilitate the decomposition of defect clusters during ion irradiation to point defects and the point defect return to the lattice position that can reduce the nonequilibrium defects inside the crystal and improve the crystallinity of the crystal, which increase the intensity of its IBIL.
Study of multiscale entropy model to evaluate the cognitive behavior of healthy elderly people based on resting state functional magnetic resonance imaging
Authors: Zhang Fu-Yi , Ge Man-Ling , Guo Zhi-Tong , Xie Chong , Yang Ze-Kun , Song Zi-Bo ,   State Key Laboratory of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300130, China,   Hebei Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability, Hebei University of Technology, Tianjin 300130, China
Published: December 2020

At present, resting state functional magnetic resonance imaging (rfMRI) has provided an efficient, rapid and advanced technology for brain function detection. Entropy can capture the dynamic characteristics of neural signals and might be used as a quantitative evaluation parameter. However, there are some problems remain solved yet, such as the entropy model computing with a fixed scale, and whether the entropy model could evaluate the cognitive performance.These problems will affect the accuracy of detection. Therefore, the multi-scale entropy model combined with a machine learning method is proposed here to investigate the relationship between complexity derived from BOLD signal and cognitive score of healthy elderly people, so as to some new imaging biomarkers could be illuminate by rfMRI. A total of 98 healthy old volunteers were selected and divided into two groups according to the pre-scan scores for the cognitive questions test (regarded as cognitive performance here): excellent group and poor group. Firstly, the multi-scale entropy model was constructed, the entropy of scanning data was calculated in two groups, and the parameters of the model were optimized by statistics and comparison with the help machine learning method. Secondly, the eigenvectors were constructed by the entropy values of the indicative brain areas with high statistical significance under the optimized parameters of multi-scale model. Finally, the sample data were divided into either training set or testing set, in which 78 people were randomly included in the training set and the rest of 20 people were included in the testing set. The two groups of data were classified and tested by the extreme learning machine. It was found that there was a significant difference between the frontal and temporal regions in the assessment of cognitive scores of the elderly by the multi-scale entropy model based on rfMRI, and the sorting rate for the cognitive scores could reach up to 80%. Conclusion: the optimized multi-scale entropy model can effectively distinguish the cognitive scores of healthy elderly people at the frontal lobe, temporal lobe and other marker brain regions. This study has highlighted the optimization advantage of the multi-scale entropy model with the help of machine learning, and might provide a new detection parameter and a potential method for rfMRI to replace the subjective and tedious traditional cognitive scale form tests.
Parametric analysis of mode coupling and liner energy deposition properties of helicon and Trivelpiece-Gould waves in helicon plasma
Authors: Li Wen-Qiu , Zhao Bin , Wang Gang , Xiang Dong ,   Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China,   Princeton Plasma Physics Laboratory, Princeton University, New Jersey 08543, USA,   School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China,   Beijing Institute of Aerospace Micro-electromechanical Technology, Beijing 100094, China
Published: December 2020

Based on the finite temperature plasma dielectric tensor model which contains the particle thermal effect, by numerically solving the eigenmode dispersion relation of electromagnetic waves propagating in radially uniform and magnetized warm plasma column which is surrounded by conducting boundary, the mode coupling characteristic and liner damping mechanism induced wave power deposition properties of helicon and Trivelpiece-Gould (TG) waves are parametrically analyzed. The detailed investigations show as follows. Under typical helicon plasma parameter conditions, i.e. wave frequency ω/(2π) = 13.56 MHz, ion temperature is much smaller than electron temperature, for the helicon wave, there exist a cut-off magnetic field B0,H,cutoff and a cut-off plasma density n0,H,cutoff, for which under the conditions of B0 > B0,H,cutoff or n0 < n0,H,cutoff, the helicon wave becomes an evanescent wave. When the magnetic field intensity changes from 48.4 to 484 G, i.e., ω/ωce ranges from 0.01 to 0.1, for the power deposition intensity, Landau damping of TG wave dominates for the m = 0 mode, meanwhile, for the m = 1 mode, which wave, i.e. helicon wave or TG wave, plays a major role in power deposition mainly depends on the magnitude of the magnetic field. On the other hand, for a given magnetic field B0 = 100 G, when ωpe/ωce changes from 3 to 100, for both the m = 0 mode and the m = 1 mode, the power deposition induced by Landau damping of TG wave plays a major role, further, one may notice that the power deposition of TG wave decreases while the power deposition of the helicon wave increases as plasma density increases. Finally, for both the m = 0 mode and the m = 1 mode, the power deposition due to the Landau damping plays a dominant role. All these conclusions provide us with some useful clues to better understanding the high ionization mechanism of helicon wave discharges.
Two-parameter fitting of temperature profile and its characteristics in turbulent convection
Authors: Fang Ming-Wei , He Jian-Chao , Bao Yun ,   School of Aeronautics and Astronautics, Sun Yat-Sen University, Guangzhou 510275, china
Published: December 2020

The two-dimensional thermal convection with three-Pr series Ra number is calculated by using the highly efficient parallel DNS method. The two-parameter temperature boundary layer theory, with the pulsation influence taken into account, is used to fit the temperature boundary layer profile for the field averaged over all calculations. The distributions of the fitted parameters a and c are obtained. Parameter a determines the basic characteristics of the temperature profile, and parameter c plays a role in correcting the outer area of the temperature profile. Therefore, the simulation results of the temperature boundary layer profile is well matched with the theoretical solution in the 5 boundary layers. The variation characteristic of parameter c is the opposite to that of parameter a, and the c value decreases as the a value increases. The fitting parameters for the different Pr numbers have different distribution characteristics as the Ra number changes, but they have all suddenly decreasing interruptions, and as the Pr number becomes large, the characteristic Ra number for the interruption increases. The variation characteristic of parameter c is the opposite to that of parameter a. With the same Ra number, the larger the Pr number, the smaller the fitting parameter of the temperature profile is, indicating that the influence of pulsation in the temperature boundary layer is smaller. The heat transfer characteristic Nu/Ra0.3, the large-scale circulation path circumference for the characteristics of plume movement, and the temperature boundary layer fitting parameter all have the interruptions with the change of Ra number, and their corresponding characteristic Ra numbers are identical. The results show that the three have good correlation and are directly related to the change of flow pattern.
Effect of biquadratic exchange and anisotropy on the critical temperature of antiferromagnet
Authors: Wen Lin , Hu Ai-Yuan ,   College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China
Published: December 2020

The existence of biquadratic exchange had been well established by Anderson, Huang and Allen. Early investigations indicated that the biquadratic exchange term in spin Hamiltonian was found to have significant effects on the magnetic properties of compounds containing iron-group ions or rare-earth metal ions. Recently, studying the anisotropic magnetic excitation of iron-based superconducting materials indicated that the experimental phenomenon cannot be explained well only by a simple collinear Heisenberg antiferromagnetic model. However, if the nearest neighbor biquadratic spin coupling is introduced, the experiment can be well explained. Similar results had also been obtained in the investigation of the superconducting material FeSe. As a result, exploring the effect of biquadratic exchange interactions on the magnetic properties of magnetic systems is significance. In this paper, we use the double-time Green's function method to study the properties of the spin-1 Heisenberg antiferromagnets with biquadratic exchange interactions and anisotropy on a three-dimensional lattice. We derive the equation of motion of the Green's function by a standard procedure. In the course of this, the higher order Green functions have to be decoupled. For the higher order Green functions of different lattice points, a Tyablikov or random phase approximation decoupling are used to decuple. For the higher order Green functions of the same lattice points, we adopt the Anderson-Callen decoupling to decouple. Based on the above procedures, the analytic expressions of the magnetization and critical temperature are obtained. The effects of biquadratic exchange interactions and anisotropy on the critical temperature are discussed in detailed. Our results show that the critical temperature increases with the increase of the anisotropy for a given biquadratic interaction. Regardless of the value of the anisotropy, the critical temperature always decreases with the increase of the biquadratic interaction. As the value of anisotropic parameter \begin{document}$\eta = 0$\end{document}, there is an obvious linear relationship between the critical temperature and the biquadratic interaction. However, when the anisotropy of the system becomes weaker, there is no such linear relationship between them. By comparing similar ferromagnetic models, it is found that the results of this paper are significantly different from those of the ferromagnetic model. When the biquadratic interaction is equal to 0, our results agree with other theoretical results.
An improved low magnetic Reynolds magnetohydrodynamic method based on computing induced magnetic vector potential by integrating induced current
Authors: Ding Ming-Song , Jiang Tao , Liu Qing-Zong , Dong Wei-Zhong , Gao Tie-Suo , Fu Yang-Aoxiao ,   Computational Aerodynamics Institute, China Aerodynamics Research and Development Center, Mianyang 621000, China
Published: December 2020

Aming at the applicability of low magnetic Reynolds number method, in this paper we analyze the differences in the application of low magnetic Reynolds number condition and the limitation of full MHD method when it is applied to hypersonic flow. According to the low magnetic Reynolds number magneto-hydrodynamic control numerical simulation method, computing magnetic vector potential through integrating induced current, and considering the reduction of computation domain caused by truncation factors, we propose a low magnetic Reynolds number MHD computation method which is adjusted by the induced magnetic field, and the validation of this method is also presented. Through the numerical simulation of RAM-C blunt cone in flight test condition, we analyze the discrepancy caused by “neglecting induced magnetic field”, and also discuss the principle of the application of low magnetic Reynolds number assumption of hypersonic flow. The obtained results are as follows. (1) The adjusted computation method developed in this paper breaks through the limit of low magnetic Reynolds number, and expands the application range of low magnetic Reynolds number method to hypersonic flow, the numerical simulation result is reliable; Compared with direct integration of Biot-Savart law, the computation efficiency is considerably improved. (2) In the hypersonic flow, the influence of induced magnetic field is presented, thus weakening and distorting the applied magnetic field macroscopically, as a result weakening the effect of magnetic control to some extent. Under the condition of this paper, the low magnetic Reynolds number condition “Rem < 0.1” is probably too conservative, and it is better to adopt Rem < 1.0, and the characteristic conductivity and characteristic length should be chosen according to the actual plasma distribution.
Multiband plasmon-induced transparency based on silver nanorods and nanodisk hybrid model
Authors: Hu Bao-Jing , Huang Ming , Li Peng , Yang Cheng-Fu ,   School of Information Science and Engineering, Yunnan University, Kunming 650091, China,   College of Science, Yunnan Agricultural University, Kunming 650201, China
Published: December 2020

In this paper, the dual-band and four-band plamon-induced transparency(PIT) hybrid model based on silver nanorod and silver nanodisk hybrid model are proposed. The electromagnetic characteristics of the two PIT hybrid models are also estimated respectively. The results show that in the double-band PIT model, the silver nanodisk (bright mode) and the silver nanorod (dark mode) can form the bright-dark-dark mode coupling. Because of the destructive interference produced by nanodisk and nanorod and the emergence of new SPs resonance modes between nanorod and nanorod, the double-band PIT model can produce two transparent windows. When the length of the nanorods and the distance between the nanorods and nanodisk are changed, the resonant frequencies and transmission amplitudes of two transparent windows will be changed accordingly.

In the four-band PIT model, the silver nanodisk and the silver nanorods will form the dark-dark-bright-dark-dark mode coupling. The resonant peaks of four transparent windows almost coincide with those of the two asymmetric double-band PIT models. Therefore, the four-band PIT model can be regarded as the superposition of two asymmetric double-band PIT models. The resonant frequencies and transmission amplitudes of four transparent windows also vary with the the length of nanorods and the distance between nanorods and nanodisk.

Finally, the sensing performance of the four-band PIT model is investigated. It is found that the model can produce four transparent windows from beginning to end when the refractive index of the background material is changed. As the refractive index is changed from 1.0 to 1.4, the resonant frequencies in four transparent windows are approximately linearly related to the refractive index. At the same time, the maximum sensitivity of the four transparent windows can reach 326.2625 (THz/RIU) and the maximum figure of merit can arrive at 26.4 (1/RIU), which is higher than those of similar similar sensors in other literatures. This work provides the theoretical support for these models’ potential applications in many areas such as optical storage, absorption, filtering and the design of sensors in infrared band.
Attitude awareness of on-orbit space object based on analysis of time-series spectral signals
Authors: Tan Fan-Jiao , Su Jin-Yu , Hou Qing-Yu , Wang Jia-Xuan , Wang Yi-Hui ,   Research Center for Space Optical Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

In order to estimate the attitude parameters of space objects under the condition of space-based long-distance observation, a hierarchical solving method based on the time-series spectral signal is proposed to estimate the parameters of surface reflection characteristics and the attitude of the space objects. The first step is to let the space object in three-axis stabilization state be equivalent to a two-facet model. Then multi-level fusion model of bidirectional reflectance distribution function (BRDF) is introduced to describe the spectral reflection characteristics of complex material surfaces. Based on the time-series spectral signal and its model, the product of area and spectral BRDF of the two-facet can be reconstructed. The second step is to set up the two-facet characteristic difference model to select the optimum wavelength based on the maximum of the difference thereby minimizing the influence of coupling characteristics on of the two-facet on attitude estimate. The third step is to construct the time-series spectral signal model under the change of object attitude. The objective function is defined as the error between the model data and the measured data, then the attitude parameter can be estimated using Levenberg-Marquardt algorithm. The simulation result shows that the method is more suitable for the object with cube body, and the error between inversion value and real value will increase as the phase angle and the detector noise increase. When signal-to-noise ratio is greater than or equal to 10, the inversion error is within 2%.
A method of adaptively adjusting dissipation for the simulation of separated flow
Authors: Li Hao , Liu Wei , Wang Sheng-Ye ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Separate flow is a typical complex turbulent phenomenon. The full development of small-scaled structures is of great importance for accurate numerical simulation. However, these small-scaled structures can be easily damped by the inherent dissipation of numerical method. Therefore, based on the 5th-order dissipative compact scheme (DCS), we propose an adaptive dissipative compact scheme (ADCS), which can adjust the numerical dissipation with self-adaptive capability by incorporating a flow related adjusting parameter. Combining with the delay detached eddy simulation (DDES), the ADCS can reduce the influence of numerical dissipation in LES region to enhance the ability to discern small-scaled structures, and restore the normal dissipation level in the RANS region to keep numerical stability. In the process of numerical simulation, firstly, the approximate dispersion relation (ADR) is obtained, it shows that the ADCS method can effectively reduce the influence of dissipation in the high wave number region, without contaminating the dispersive performance, which is conducive to enhancing the resolution of turbulent structures. Secondly, the advection of vortical structure is simulated. Compared with DCS, the ADCS can reach the theoretical accuracy in an efficient way and acquire more advanced resolution of vortical structure even on a relatively coarse mesh scale, which proves that the ADCS reduces the negative influence of dissipation on vortical structure. The third case is the decay of isotropic turbulence. The energy spectral curves stay close to the reference before cut-off number, showing that more small-scaled structures can be distinguished by the ADCS method, and most of the vortical dominated regions are solved at a near-minimum level. The forth case is the plate channel turbulent flow. Both of DCS method and ADCS method give acceptable results. The ADCS method is performed with optimal dissipation in the near-wall region and reduces the dissipative level in the vortex dominated region, and it is also exhibited that the ADCS method can maintain the stability for flow with high gradient and avoid divergence. Finally, the sub-critical Re = 3900circular cylinder is simulated, and the fully separate flow is developed in the wake. The turbulent fluctuation near the wall is sensitive to the effect of numerical dissipation. The contour of flow field shows that the ADCS method obtains more small-scale structures. As for the pressure coefficient and mean velocity, the ADCS method shows an acceptable accuracy. Considering the Reynolds stress profile, which can be easily affected by the dissipation, the ADCS exhibits more accurate results than the traditional DCS method. Generally, the ADCS method can reduce the influence of dissipation and is beneficial to acquiring more accurate results in separate flow.
Inter-mode stimulated Brillouin scattering and simultaneous temperature and strain sensing in M-shaped few-mode fiber
Authors: Li Xue-Jian , Cao Min , Tang Min , Mi Yue-An , Tao Hong , Gu Hao , Ren Wen-Hua , Jian Wei , Ren Guo-Bin ,   Key Laboratory of All Optical Network and Advanced Telecommunication Network, Ministry of Education, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

Stimulated Brillouin scattering (SBS) in a few-mode fiber (FMF) is of significance for the distributed temperature and strain sensing. An FMF with M-shaped refractive index distribution (M-FMF) is proposed in order to improve the performance of simultaneous temperature and strain sensing based on SBS. Propagation of four optical modes is supported by the M-FMF, so that the Brillouin gain spectrum (BGS) can be obtained by both intra-mode and inter-mode SBS. The BGSs produced by the interactions of LP01-LP01 mode pair, LP01-LP11 mode pair, and LP11-LP11 mode pair are analyzed, respectively. Meanwhile, the temperature and strain sensing performance based on the BGS of LP01-LP11 mode pair are studied in detail. Considering a common step-index FMF, only one obvious scattering peak is usually present in the BGS obtained from the interaction between different optical mode pairs, therefore, it is inconvenient to achieve multi-parameter sensing measurement. In this paper, the BGS of LP01-LP11 mode pair has two scattering peaks, which are contributed by the acousto-optic coupling between the acoustic modes L1n (n = 1, 2) and the optical modes LP01 and LP11. The two Brillouin scattering peaks have large gain values of 0.1004 m–1·W–1 and 0.0463 m–1·W–1, respectively. More importantly, the gain difference between two Brillouin scattering peaks is small, and the frequency interval is 75 MHz, which can be applied to simultaneous temperature and strain sensing. The influences of the refractive index and the fiber core radius on the BGS of LP01-LP11 mode pair are studied. By selecting the optimal structure parameters, we discuss the effect of temperature and strain on the BGS of LP01-LP11 mode pair. The errors for simultaneous temperature and strain measurement are reduced to 0.23 ℃ and 5.67 με. Compared with other reported results, our obtained temperature and strain sensitivity are high and sensing errors are low in the considered M-FMF. In other words, based on the BGS of LP01-LP11 mode pair, the performance of temperature and strain sensing are improved in the M-FMF. This work is of great significance for studying intra-mode and inter-mode SBS in an FMF. Moreover, the results also provide a guideline for further improving the performance of simultaneous temperature and strain sensing.
Theoretical study on the modulation characteristics of THz wave by two-dimensional black phosphorus
Authors: Song Ke-Chao , Huo Shuai-Nan , Tu Dong-Ming , Hou Xin-Fu , Wu Xiao-Jing , Wang Ming-Wei ,   College of Electronic Information and Optical Engineering, Nankai University, Tianjing 300350, China,   Nankai University Affiliated Hospital, Laboratory of Biomedicine and Nanophotonics, Tianjin 300121, China
Published: December 2020

Using the Delude model. we theoretically calculate the dispersion of conductivity with frequency in the orthogonal direction of the two-dimensional black phosphorus (2D BP) x and y direction in the THz band. We find that the conductivity in the x direction is more sensitive to the electron doping concentration. The difference between 2D BP conductivities in both directions leads to the difference in dielectric constant which in turn can modulate light in different polarization directions. Using 2D BP to polarize the THz wave, the 2D BP-SiO2 periodic sandwich structure is designed. The three-dimensional electromagnetic field simulation software CST Microwave Studio can be used to calculate the regulation characteristics of this structure to THz wave. It is found that this structure has different polarization directions, and the incident THz wave has different absorption. By changing the thickness of the underlying SiO2 layer in the structure it is found that the absorption rate of this structure also changes accordingly. When the polarization direction of the THz pulse is parallel to the x axis, the absorption rate first increases and then decreases. When d5 = 9.5 μm, the absorption rate reaches 93% near 3.86 THz; when the polarization direction of the THz pulse is parallel to the y axis, the absorption rate gradually increases. The absorption peak has a significant red shift.
Nonequilibrium statistical theoretical analysis method of TDDB of gate oxide
Authors: Zhao Wen-Jing , Ding Meng-Guang , Yang Xiao-Li , Hu Hai-Yun ,   School of Physics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

As one of the important factors affecting the reliability of Complementary metal oxide semiconductor integrated circuits, the time-dependent dielectric breakdown of gate oxide has always been the focus of domestic and foreign scientists. The previous researches have shown that when the electrons pass through the silicon dioxide lattice and collide with it, part of their kinetic energy will be dissipated, then among of which can create some sort of defects that behave as electron traps. However, when the electron traps density reaches a critical value in the gate oxide, the destructive thermal effects open a low-resistance ohmic path between the electrodes, thus, triggering the breakdown conducting mechanism. In this paper, in order to employing a statistical theoretical analysis method, the behavior related with time-dependent dielectric breakdown of gate oxide was investigated in detail. The following useful results are obtained, (i) According to the microscopic mechanism of the time-dependent dielectric breakdown of gate oxide under electrical stresses associated with the randomness and irreversibility of the electron traps generation in gate oxide, a theoretical analysis method has been proposed, which is based on the equation of the electron traps generation rate combined with the Langevin equation in random theory and the Fokker-Planck equation in the non-equilibrium statistical theory. (ii) In light of the dynamic equilibrium model, the generation rate equations of electron traps under constant current stress and constant voltage stress as well as the probability density distribution functions of electron traps density were determined. By integrating these distribution function, the cumulative failure rate was further obtained. (iii) Taking the specific metal oxide semiconductor capacitors as examples, the relationship between the most probable lifetime of the gate oxide and the constant current stress, constant voltage stress, as well as its thickness have been revealed. And the concept of "breakdown limit" was defined by analogy with the concept of "fatigue limit" in the phenomenon of solid fracture. (iv) The dependence of the cumulative failure rate on the current stress, voltage stress, and time has been presented. A characteristic value of the time was introduced to indicate the time when the cumulative failure rate reaches 0.63. At this time, most devices have breakdown failure. Besides, the test parameters are not affected by previous failures, and they are close to that of the cumulative failure rate of 1. The results show that the probability density distribution function of electron traps density satisfies lognormal distribution, and the obtained distribution of failures fits well with the experimental statistical data.
Studies of circular dichroism of planar composite metal nanostructure arrays
Authors: Tudahong Aba , Qu Yu , Bai Jun-Ran , Zhang Zhong-Yue ,   School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710119, China
Published: December 2020

Circular dichroism effects have been widely used in circular polarizers, optical modulators and optoelectronic devices. Periodically arranged artificial metal chiral nanostructures has a strong electromagnetic coupling effect with light, which can greatly increase the interaction between the light and matter. Three-dimensional helix and helix-like chiral nanostructures show a larger circular dichroism effect due to the strong interactions between electric and magnetic resonance. The double-layer structures also can produce large circular dichroism, which signals also results from electric dipoles with different orientations between the two layers. Although the three dimensional plasmonic structures have shown large circular dichroism signals, however, three dimensional devices hold disadvantages in wide practical applications because of their complicated fabricating process, especially at micro- and nanoscales. Recent years, circular dichroism signals of planar nanostructures have been studied owing to their easy fabrication and wide potential applications. The resonance mode of planar metal nanostructures is sensitive to the shape, geometry, materials and surrounding environment of nanostructures, which provides a feasible technical approach for adjusting the circular dichroism signal of planar metal nanostructures. In this article, larger circular dichroism signals are realized through planar composite golden nanostructures, which composed of infinite long nanowire and G-shaped nanostructure. The absorption spectra, surface charge distributions at resonance wavelength of planar composite golden nanostructure are calculated by finite element method. For comparison, a circular dichroism signal with only G-shaped nanostructures is also studied. The numerical results show that under the illumination of right-handed polarized and left-handed polarized light, the planar composite golden nanostructure and G-shaped nanostructure exhibit electric dipole, quadrupolar, octupolar resonance modes, respectively. When the G-shaped nanostructure is connected to an infinitely long nanowire, all resonance peaks have a red shift and infinitely long nanowire increases the local surface resonance intensity under different circularly polarized light excitation. Therefore, it significantly enhances the circular dichroism signal of the planar composite golden nanostructure. At the same time, the influence of geometric parameters such as the different length of each nanorod of the G-shaped nanostructure and the thickness of the infinitely length nanowire on the circular dichroism modes are also studied. The findings may provide some guideline and methods for improving the circular dichroism signal of planar chiral nanostructure.
Generation of 8 Gb/s physical random numbers based on spontaneous chaotic oscillation of GaAs/Al0.45Ga0.55As superlattices
Authors: Liu Yan-Fei , Chen Cheng , Yang Dong-Dong , Li Xiu-Jian ,   Department of Basic Courses, Rocket Forces Engineering University, Xi’an 710025, China,   College of Liberal Arts and Sciences, National University of Defense Technology, Changsha 410073, China
Published: December 2020

Secret key is required in secure communications, and random numbers are generally used as keys to encrypt the original information. So it is crucial for cryptography and secure communication to generate the physical random number, which is completely safer than pseudo random number. However, Existing physical random number generator systems are difficult to satisfy the requirements of high-speed communication due to their complexity, large size, and limited equipment bandwidth. The GaAs/Al0.45Ga0.55 superlattices is based on a structure formed by the alternating growth of two semiconductor materials, and has a good low-dimensional structure for studying the nonlinear behavior of electrons. Recent studies have shown that the GaAs/Al0.45Ga0.55 superlattices under the DC voltage could appear chaos current oscillation states in some certain voltage ranges.

An all-solid-state real-time high-speed physical true random number generator based on superlattices is presented. The superlattices, excited by appropriate DC bias voltage, could generate a high-frequency chaotic oscillation signal as a source of physical entropy. A multi-bit analog-to-digital converter with 2 GHz sampling frequency is used for quantization to generate 12-bit binary random bits. Then, the field programmable gate array extracts the lowest 4 bits as valid bits and inverts bits to improve its randomness, and finally a true random number with a real-time rate of 8 Gbit/s is obtained. To obtained a superlattices signal with a higher degree of chaos, the Lyapunov exponent was used to assist in selecting a more suitable DC bias. The random number generated by the superlattices, owning excellent statistical characteristics, could pass the test of the random number industry standard (NIST SP 800-22), which is expected to be miniaturized and integrated on high-speed communication equipment.
Size Regulation and Photoluminescence Properties of β-Ga2O3 Nanomaterials
Authors: Ma Teng-Yu , Li Wan-Jun , He Xian-Wang , Hu Hui , Huang Li-Juan , Zhang Hong , Xiong Yuan-Qiang , Li Hong-Lin , Ye Li-Juan , Kong Chun-Yang ,   Chongqing Key Laboratory of Photo-Electric Functional Materials, College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China
Published: December 2020

Gallium oxide (Ga2O3) nanomaterials have great potential in the fields of ultraviolet transparent electrodes, high-temperature gas sensors, solar blind ultraviolet detectors and power devices, while achieving Ga2O3 nanomaterials with high crystalline quality and controllable size and morphology still remains challenge. Herein, size-controllable Gallium oxide hydroxide (GaOOH) nanorods, nanorod bundles, and spindles were prepared by hydrothermal method. After high temperature calcination, GaOOH nanomaterials were successfully transformed into higher-quality single-crystal β-Ga2O3 nanomaterials which well retained the morphological characteristics of the pristine GaOOH.With the help of X-ray diffraction (XRD), Raman scattering spectroscopy (Raman) and field emission scanning electron microscope (FE-SEM), we systematically studied the influence of the pH value and the concentration of anionic surfactants in the precursor solution on the crystal structure and surface morphology of GaOOH and β-Ga2O3 nanomaterials, and explored the different growth mechanism of GaOOH nanomaterials under different conditions. Simultaneously, room temperature photoluminescence (PL) tests revealed that β-Ga2O3 nanomaterials with different morphologies exhibit typical broad blue-green emission and sharp red emission, which are closely related to the existence of intrinsic defects in nanomaterials.The above research results provide valuable information for the controllable preparation of high-quality β-Ga2O3 nanomaterials.
Recent advances in flexible fiber-shaped supercapacitors
Authors: Zhang Xin , Chen Xing , Bai Tian , You Xing-Yan , Zhao Xin , Liu Xiang-Yang , Ye Mei-Dan ,   Research Institute for Soft Matter and Biomimetics, College of Physical Science and Technology, Xiamen University, Xiamen 361005, China,   Faculty of Science, National University of Singapore, Singapore 119077, Singapore,   Jiujiang Research Institute of Xiamen University, Jiujiang 332000, China
Published: December 2020

With the continuous development of today's flexible electronic products, fiber-shaped supercapacitors (fiber-shaped supercapacitors, FSCs) have attracted continuous attention. That’s due to their advantages such as light weight, controllable volume, good bending and tensile properties, and weavable. Fiber-shaped supercapacitors, with their unique one-dimensional fiber structure, can be combined with various other electrical or power generation devices into multifunctional integrated fiber-shaped electronic devices, which have huge application prospects in the field of wearable electronic textiles. This article describes the latest developments in fiber-shaped supercapacitor devices. Firstly, different fiber substrates are introduced and their advantages and disadvantages are analyzed as well. It also summarizes the electrode materials such as carbon materials, metal oxides and sulfides, conductive polymers, and hybrid nanocomposites of fiber-shaped supercapacitors. By analyzing the differences and characteristics of different electrode materials, it is shown that different electrode materials are suitable for different uses in fiber-shaped supercapacitors. Then we also summarize the application of fiber-shaped supercapacitors in cooperation with other devices to form integrated devices, including integration with general power devices, sensors, other photoelectric conversion devices and other power generation devices into hybrid devices and applied to practice. Finally, by summarizing the recent development results of fiber-shaped supercapacitors and the current challenges in the field, some current bottlenecks and problems of fiber-shaped supercapacitors are proposed, and some suggestions and ideas for the future development direction are put forward.
Memristive and magnetoresistance effects of SnSe2
Authors: He Bin , He Xiong , Liu Guo-Qiang , Zhu Can , Wang Jia-Fu , Sun Zhi-Gang ,   State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China,   School of Science, Wuhan University of Technology, Wuhan 430070, China
Published: December 2020

Memristor and magnetoresistance (MR) are widely used in the field of information storage. In recent years, SnSe2, as an information storage material with both memristor and MR effects, has received a lot of attention of the researchers. It is of great significance to further explore its electrical transport mechanism. In this paper, the high-purity bulk SnSe2 samples are prepared by melting method together with spark plasma sintering. The V-I curves are measured under different temperatures and magnetic fields. The memristive and MR effect of SnSe2 are systematically investigated. After the memristive characteristics are excluded from interfacial junction effect, phase transition and conductive wire channels, the memristive effect at different temperatures is attributed to the space charge limiting current effect under defect control. Under low electric field conditions, the internal carrier concentration of material is much higher than the injected carrier concentration and the V-I curve obeys ohmic conduction. When the voltage increases to the switching voltage Von, the internal defects of the material are filled with the injected carriers as the transport time of the injected carrier is less than the dielectric relaxation time, and the V-I curves deviate from ohmic conductivity. When the voltage reaches the transition voltage VTFL, the injected carrier increases exponentially, and the V-I curve presents negative differential phenomenon. Finally, the space charge inside the material will limit the further injection of external carriers, and the V-I curve follows the Child law. As the temperature decreases to 10 K, the memristive phenomenon weakens because a large number of defects for accepting the injected carriers are reduced due to the decrease of impurity ionization at low temperatures. At the same time, the sample exhibits a large negative MR at 10 K and 100 K. When impurity scattering predominates, the electrons will be subjected to multiple scattering by the impurities, resulting in localization of carriers. The negative MR effect is related to the inhibition of the carrier localization by the magnetic field. In our work, a large negative MR of about –37% at 0.6 T and 10 K are obtained, which is likely to originate from the disordered distribution of Se vacancy in the material. With the increase of temperature, the scattering mechanism gradually evolves from the impurity scattering into the lattice scattering, and the negative MR effect gradually develops into the positive MR effect.
Control of self-organization: From equilibrium to non-equilibrium
Authors: Shi Yan , Zhang Tian-Hui ,   Center for Soft Condensed Matter Physics and Interdisciplinary Research, School of Physical Science and Technology, Soochow University, Suzhou 215006, China
Published: December 2020

Self-organization represents a ubiquitous transition from disorder to order. It plays a critical role in forming crystalline materials and functional structures in biology. Functional structures are generally hybrid on a multiple scale in which nano-structures are often organized in a specific way such that they can perform functions. There are two typical functional structures: static equilibrium structures and dynamic non-equilibrium structures. In this review, recent advances in understanding and mimicking functional structures are summarized. Although great advances have been achieved, it is still a big challenge to realize dynamic non-equilibrium structures. In this case, we suggest that the controlling of self-organization in active systems may be a route toward interactive and adaptive structures.
Effect of Gd doping on the structure, dielectric and multiferroic properties of 0.7BiFe0.95Ga0.05O3-0.3BaTiO3 ceramics
Authors: Yang Ru-Xia , Lu Yu-Ming , Zeng Li-Zhu , Zhang Lu-Jia , Li Guan-Nan ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China,   Faculty of Materials and Energy, Southwest University, Chongqing 400715, China
Published: December 2020

The 0.7Bi1–xGdxFe0.95Ga0.05O3-0.3BaTiO3 (BGxFG-BT, x = 0, 0.05, 0.1, 0.15, 0.2) ceramics were successfully synthesized via the conventional solid-state reaction method. The effects of Gd doping on crystal structure, microstructure, dielectric, ferroelectric and magnetic properties were systematically investigated. X-ray diffraction analysis indicates that Gd doping induce a structural transition from rhombohedral (R3c) to pseudo-cubic (P4mm) in BGxFG-BT ceramics. Scanning electron microscopy results show a decrease of grain size with doping Gd in BFG-BT. The average grain sizes of the ceramics range from 3.2 μm to 6.2 μm. The dielectric constant and loss tangent are drastically increased and reduced respectively with introducing Gd into the ceramics. Temperature dependent dielectric constant presents a broad peak in the vicinity of Néel temperature (TN) for all the samples, signifying strong magnetoelectric coupling. An increment in TN is also observed as a result of Gd-doping in the temperature regions of 230 to 340 ℃. The leakage current density is reduced by about two orders of magnitude under the electric field of 20 kV/cm. This can be ascribed to the reduction of the oxygen vacancy concentration, which is confirmed by the X-ray photoelectron spectroscopy result. The ferroelectricity and ferromagnetism are also improved after the addition of Gd seen from the polarization hysteresis (P-E ) loops and the magnetization hysteresis (M-H) loops. The greatly enhanced magnetism with Mr = 0.0186 emu/g and Ms = 1.084 emu/g is obtained in the ceramic with x = 0.2, almost three point six times larger than that of the undoped ceramic.