bluuebunny/crossref_metadata_2025 huggingface dataset:
Lamb wave imaging method based on difference signal in reverse path
Authors: Jiao Jing-Pin , Li Hai-Ping , He Cun-Fu , Wu Bin , Xue Yan ,   College of Mechanical Engineering and Applied Electronics Technology, Beijing University of Technology, Beijing 100124, China,   PetroChina Natural Gas Pipeline Science Research Institute Corporation Limited, Langfang 065000, China
Published: December 2020

The traditional Lamb wave structure health monitoring imaging method based on reference signal is affected by environmental factors such as temperature change. To solve this problem, considering the difference in the scattered fields generated by the interaction between ultrasonic waves and defects in the reverse path, a Lamb wave imaging method is proposed in this paper based on the difference signal of sparse array in inverse path. Numerical simulations are carried out to determine the generation conditions of difference signal in inversion path, and the influences of the angles and distances between the defect and the two sensors on the amplitude of difference signal in inversion path. It is found that the difference signal in reverse path is much more obvious when the defect appears as asymmetric distribution towards the excitation sensor and receiving sensors; the amplitude of difference signal in inverse path is affected by distance difference of the Lamb wave propagating in reverse path and the scattering coefficient of the defect. On this basis, the effectiveness of the Lamb wave imaging method based on the difference signal in inverse path is studied numerically and experimentally. The results show that the Lamb wave imaging method based on the difference signal in inversion path can perfectly eliminate the interference between direct wave and the boundary reflection wave, and the imaging method can detect the defect at different positions in the plate. Moreover, the imaging resolution is higher and the defect location is accurate. The research work provides a new feasible scheme for the extensive health monitoring of plate structure.
Tuning of cyclotron resonant frequency and magnetic field of medical cyclotron
Authors: Wu Yong-Cun , Yang Xing-Lin , Shi Jin-Shui , Zhao Liang-Chao , He Xiao-Zhong ,   Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The high-frequency resonant cavity is affected by factors such as beam load, gravity and heat loss caused by cavity deformation during the actual operation of the medical cyclotron. The resonant frequency will shift to a certain extent, resulting in the high-frequency operation frequency varying with the resonant frequency of the resonator cavity. In order to meet the requirements for isochronous acceleration, the magnetic field strength should also be changed correspondingly when the high-frequency operation frequency changes, that is, the magnitude of the magnet current needs changing accordingly, so that the particle cyclotron frequency matches the high-frequency resonant frequency to overcome the sliding phase. Firstly, the static magnetic field model is established by finite element simulation software to simulate the average magnetic field of cyclotron under different magnet currents. Then the relationship between the magnetic field and the resonant frequency is theoretically analyzed. Finally, the relationship between the magnet current and the resonant frequency is obtained when the magnet current varies in a small interval. According to the optimal magnet current corresponding to different resonance frequencies, the automatic frequency tracking of magnet current is completed. In the case of ensuring the maximum carbon film beam, the optimal magnet current corresponding to different resonance frequencies is obtained, which makes the theory validated. According to the relationship, the magnet current is automatically adjusted, which overcomes the slip phase and ensures the stable output of the Faraday beam. The method enables the magnet current to be quickly and accurately find and track the cavity frequency, overcomes the slip phase caused by the frequency offset, and completes the stable output of the beam.
Inverse spin Hall effect in Nb doped SrTiO3
Authors: He Dong-Mei , Peng Bin , Zhang Wan-Li , Zhang Wen-Xu ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China
Published: December 2020

The inverse spin Hall effect (ISHE), namely spin flows converted into charge currents due to spin orbital interaction, is investigated extensively in heavy metals, such as Pt, W, Au, etc. Recently, the effect was also found in Cu doped with Au. Their difference is that the spin Hall effect is from the intrinsic effect which is related to the topological character of the electronic bands, while the ISHE is mainly from the extrinsic spin dependent scattering by the impurities. The impurity scattering can give opportunities to tune the effect, for example by impurity concentration, which is impossible by the intrinsic mechanism. In this work, we extend the material to the doped oxides. NiFe films are deposited on undoped and doped SrTiO3 substrates by magnetron sputtering, respectively. The spins are injected from the magnetic thin films by spin pumping through using a shorted microstrip transmission line fixture at different frequencies and room temperature. The spin rectification voltage and the inverse spin Hall voltage in the doped sample are separated by the inverting spin injection direction method, which is realized by flipping the samples. The results show that in the undoped SrTiO3 substrate, the voltage curves before and after flipping the sample are basically the same, which is due to the voltage generated by the spin rectification effect of the NiFe film. For Nb-doped SrTiO3 substrates with Nb concentration x = 0.028, 0.05, 0.1, 0.15 and 0.2, the inverse spin Hall voltage decreases with doping concentration increasing and is not detectable in sample with doping concentration of 0.15, nor with doping concentration of 0.2. The decrease of the ISHE effect may be due to the spin coherent length decreasing with the increase of the impurity concentration. The correlation between spin-charge conversion and transportation needs knowing in detail. Nevertheless, the results show that by doping strong spin-orbit coupling impurities into SrTiO3, thus by changing the doping concentration, the inverse spin Hall effect in SrTiO3 can be controlled. This tunable spin-charge conversion provides more possibilities for developing the spintronic devices and it will have great potential applications in the future.
Application of variable-time-period harmonic balance method to periodic unsteady vortex shedding
Authors: Chai Zhen-Xia , Liu Wei , Yang Xiao-Liang , Zhou Yun-Long ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The harmonic balance method (HBM) is an efficient frequency-domain approach to computing periodically unsteady flows. The basic principle of this method is to decompose the flow variables into a Fourier series, and transform the unsteady flow into several steady problems coupled by a spectral time-derivative operator, from which the whole time history of a complete unsteady periodic flow can be reconstructed. In the present work, we investigate the ability of the HBM to be used for modeling the periodic unsteady vortex shedding behind a bluff body at low Reynolds numbers via solving the unsteady incompressible Navier-Stokes equations. For the periodic problem where the time period T of the unsteadiness is unknown, a variable-time-period method based on residual gradients is used to compute the exact time period iteratively starting from an initial guess T0. By simulating the two-dimensional laminar flows over a circular cylinder and a square cylinder, the accuracy and efficiency of the HBM are investigated and the effects of different parameters on the final results are analyzed. Comparisons with the results of fixed-time-period HBM using a constant time period are also implemented. Three practical methods of optimization are used to iterate the time period, and the values of accuracy and efficiency of different methods are compared with each other. The results show that the HBM can accurately capture the complex nonlinear flow field physics with only three harmonics. The Strouhal frequency and mean drag coefficient each as a function of the Reynolds number agree well with existing experimental and computational data. For both test cases, the computational efficiency of HBM is higher than that from the traditional time-domain method. For the square cylinder test case, the HBM offers speedup rate up to nearly 18 times. The real time period of vortex shedding can be predicted by the gradient based variable-time-period method, and the final result is insensitive to search step λ. The calculation result is sensitive to the initial T0, and when such a variable is greater than a certain value, the result will converge to an approximate integer multiple of the real one. Therefore, it deserves further exploration on how to specify this initial condition. The shedding time periods computed by different optimization methods are converged to the same value. The computational efficiency from the FR conjugate gradient method and that from Newton method are both equivalent to that from the steepest descent method with the maximum search step λ = 100. Avoiding prescribing parameters such as the search step λ, the Newton method possesses higher application value in engineering calculation than the other two schemes.
Research progress of metal-insulator phase transition in VO2 induced by electric field
Authors: Sun Xiao-Ning , Qu Zhao-Ming , Wang Qing-Guo , Yuan Yang , Liu Shang-He ,   National Key Laboratory on Electromagnetic Environment Effects, Army Engineering University, Shijiazhuang 050003, China
Published: December 2020

Vanadium dioxide (VO2) is a typical representative of strongly correlated electronic systems, which undergoes a reversible transition from the insulator phase to metal phase, induced by a certain threshold for each of temperature, electric field, illumination and pressure. The crystal structure of VO2 will undergo a reversible transition from monoclinic structure to tetragonal rutile structure when the phase transition happens, which is considered as the microscopic mechanism of VO2 metal-insulator transition (MIT). The conductivity of VO2 can be increased by 2—5 orders of magnitude when the MIT is induced by electric field, which makes VO2 possess good application prospects in the fields of restructurable slot antenna, terahertz radiation, intelligent electromagnetic protection materials, etc. Therefore, the reversible metal-insulator phase transition in VO2, induced by electric field, has long been a research hotspot, which however, has been seldom reported. Firstly, in this paper, the changes of the crystal structure and energy band structure of VO2 during MIT are introduced briefly. The methods of regulating the phase transition are given, including temperature control, bandwidth and band-filling control. Then, the important discovery and research progress of VO2 MIT induced by electric field based on the research method, response time, critical threshold field and phase transition mechanism are summarized and reviewed comprehensively. The method of studying the VO2 phase transition relates to its structure, including planar structure, three-terminal gated ?eld effect switch and sandwiched layer structure. The sandwich layer structure is more suitable for investigating the MIT characteristics of VO2 in experimental stage because of its structural advantage of preparation and test. The response time of VO2 MIT can be completed in nanoseconds, of which the substantial parameter has been revealed by many reports, also including the excellent reversibility of VO2 MIT. The MIT critical threshold field of the VO2 film can be tuned by element doping, coexistence of multivalent vanadium oxides and multiple physical field synergism effectively. The MIT mechanism of VO2 induced by electric field has been proposed so far, which includes joule heating mechanism and pure electric field mechanism, and the latter is considered to be more likely to give a reasonable explanation. Finally, in the paper the current problems of the VO2 MIT research and the near-future development direction of the VO2 MIT materials are also pointed out.
Temporal imaging based on first-order field correlation
Authors: Zhang Rui-Xue , Li Hong-Guo , Li Zong-Guo ,   School of Science, Tianjin University of Technology, Tianjin 300384, China
Published: December 2020

Different from second-order temporal ghost imaging usually realized by means of second-order correlation measurement, in this paper, we investigate theoretically temporal imaging with temporally thermal light via first-order field correlation based on a Mach-Zehnder interferometer. The paraxial wave equation describing the diffraction of light and the differential equation characterizing the dispersion of light pulse are given. Based on the similarity between these equations, the duality between the paraxial diffraction of the light in the spatial domain and the dispersion of the temporal narrow-band pulse in the dispersive medium (i.e. the space-time duality) is obtained, and the impulse response functions in the time domain for several optical systems are also presented. Then in terms of the space-time duality, we design the scheme for temporal imaging via first-order thermal field correlation based on a Mach-Zehnder interferometer and obtain the intensity expression for first-order temporal imaging according to the temporal impulse response functions, and discuss the influences of the source pulse width and coherence time on the image visibility and resolution. The result shows that the temporal signal can be reconstructed through temporal first-order temporal imaging. Furthermore, when the source’s coherence time is fixed, the image visibility decreases as the pulse width increases. However, the image resolution increases. When the source’s pulse width is fixed, the image visibility increases as the coherence time increases. And yet the image resolution decreases. Specially, when the source’s pulse width is 100 ps and the coherence time is 0.5 ps, the image quality (taking both the visibility and resolution into account) of a temporally rectangular object is satisfactory. In the simulation, the distance and width of the temporal rectangular object are 20 ps and 8 ps, respectively. It is shown that there is a dilemma between the visibility and resolution of first-order temporal imaging which is similar to the result of second-order ghost imaging. Our result discussed herein could be valuable in the reconstruction and detection of temporal signal via first-order temporal ghost imaging with temporally thermal light.
Entropy measurement of ordered patterns in neuronal network with repulsive coupling
Authors: Huang Zhi-Jing , Li Qian-Yun , Bai Jing , Tang Guo-Ning ,   College of Physical Science and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Traveling waves, standing waves, and spiral waves occur spontaneously in the brain neural network in some brain states. The occurrence of these ordered spatiotemporal patterns is often related to some neurological diseases. However, the mechanisms behind the generation of the ordered pattern are not fully understood. How to quantitatively describe the nature of these spatiotemporal patterns still needs further exploring. In order to solve these problems, the Hindmarsh-Rose neuron model is used to study the dynamic behavior of the two-dimensional (2D) neuronal network with double-coupling layer, which is composed of nearest-neighbor excitatory coupling and long-range repulsive coupling layers and evolves from an initial state with a random phase distribution. An improved cluster entropy is proposed to describe the spatiotemporal pattern of the neuronal network. The numerical simulation results show that the repulsive coupling can either promote the formation of ordered patterns or suppress the formation of ordered patterns. When the repulsive coupling strength and excitatory coupling strength are appropriately selected, the chaotic network can spontaneously generate single spiral wave, multiple spiral wave, traveling wave, the coexistence of spiral wave and others wave state, the coexistence of target wave and others wave state, the coexistence of traveling wave and standing wave, etc. The probability with which spiral wave and traveling wave occur reach 0.4555 and 0.1667 respectively. The probability with which target wave and other states co-occur, and the probability with which the traveling wave and the standing wave co-occur, are 0.0389 and 0.1056, respectively. These ordered wave patterns and chaotic states can be distinguished by using the proposed cluster entropy. When the repulsive coupling strength is large enough, the neuronal network is generally in chaotic state. It is found by calculating cluster entropy that a large cluster can appear in the neuronal network when the excitatory coupling strength and repulsive coupling strength are both weak. These results can conduce to understanding the self-organization phenomena occurring in the experiments and also to treating various neurological diseases.
Surface effects on Couette gas flows in nanochannels
Authors: Zhang Ye , Zhang Ran , Chang Qing , Li Hua ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

A three-dimensional non-equilibrium molecular dynamics method is adopted to investigate the influence of wall force field on the nanoscale gas flow in the transition regime. For the gas flow under nanoscale condition, the dominant effect of the wall force field on the flow field is more obvious, and the flow physical quantity is more sensitive to the change of the wall condition and system temperature. The motion of the wall atoms is governed by the Einstein theory, with using an elastic coefficient k to model the surface stiffness. The results indicate that the surface stiffness has little effect on the physical quantity distribution of the bulk flow region, but a certain influence on that of the near wall region. Increasing the value of the stiffness changes the velocity peak of the gas in the near-wall region and the tangential momentum adaptation coefficient (TMAC) towards lower values, thus demoting the momentum adaptability of the gas molecules to the surface. The wall roughness is simulated by a typical pyramidal model. It is found that the influence of wall roughness on the flow is very obvious, whether it is in the bulk flow region or in the near wall region. For the former case, the increase of roughness leads gas velocity and shear stress to increase, with density and normal stress remaining constant. The linear distribution of physical quantities is also affected to some extent. While for the latter case, as the roughness increases, the velocity of the fluid increases rapidly and approaches to the wall velocity. The peak of density increases, and the adsorption of gas molecules at the surface is obvious. The TMAC approaches to 1, suggesting that the gas and the surface achieve a complete momentum adaptation. Besides, the influence of system temperature on the gas flow in the nanochannel is also studied. The system temperature is controlled by the Nose-Hoover thermostat, making the flow field maintained at the target temperature through the damping coefficient. The results show that the effect of temperature is global in the whole flow region. The increase of temperature causes the flow velocity of the whole flow field to decrease, while the normal stress and shear stress to increase. A higher temperature leads to more frequent collisions between gas molecules, thus increasing the effective viscosity of the gas. At the same time, the degree of gas molecule adsorption in the near-wall region is reduced, contributing to a smaller TMAC value, and consequently a weaker gas-surface interaction.
Electro-static discharge failure analysis and design optimization of gate-driver on array circuit in InGaZnO thin film transistor backplane
Authors: Ma Qun-Gang , Zhou Liu-Fei , Yu Yue , Ma Guo-Yong , Zhang Sheng-Dong ,   School of Electronic and Computer Engineering, Peking University, Shenzhen 518055, China,   School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China,   Nanjing CEC Panda FPD Technology Co., Ltd., Nanjing 210033, China
Published: December 2020

There is a risk of InGaZnO thin film transistor (IGZO TFT) failure, especially electro-static discharge (ESD) damage of gate driver on array (GOA) circuits, due to the combination of Cu interconnect, InGaZnO (IGZO) active layer and SiNx/SiO2 insulating layer used to realize large-scale ultra-high resolution display. It is found that the IGZO TFT damage position caused by ESD occurs between the source/drain metal layer and the gate insulator. The Cu metal of gate electrode diffuses into the gate insulator of SiNx/SiO2. The closer to the ESD damage area the IGZO TFT is, the more serious the negative bias of its threshold voltage (Vth) is until the device is fully turned on. The IGZO TFT with a large channel width-to-length ratio(W/L) in GOA circuit results in a serious negative bias of threshold voltage. In this paper, the ESD failure problem of GOA circuit in the IGZO TFT backplane is systematically analyzed by combining the ESD device level analysis with the system level analysis, which combines IGZO TFT device technology, difference in metal density between GOA region and active area on backplane, non-uniform thickness distribution of gate metal layer and gate insulator and so on. In the analysis of ESD device level, we propose that the diffusion of Cu metal from gate electrode into SiNx/SiO2 leads to the decrease of effective gate insulator layer, and that the built-in space charge effect leads to the decrease of the anti-ESD damage ability of IGZO TFT. In the analysis of ESD system level, we propose that the density of metal layers in GOA region is 4.5 times higher than that in active area of display panel, which makes the flatness of metal layer in GOA region worse. The non-uniformity of thickness of Cu metal film, SiNx film and SiO2 film around glass substrate lead to the position dependence of the anti-ESD damage ability of IGZO TFT in the GOA region. If there is a transition zone of film thickness change in IGZO TFT with large area, the ESD failure will occur easily. Accordingly, we propose to split large area IGZO TFT into several sub-TFT structures, which can effectively improve the ESD failure.
Tomographic reconstruction of stack plume based on sparse optimization
Authors: Zhong Ming-Yu , Xi Liang , Si Fu-Qi , Zhou Hai-Jin , Wang Yu ,   Anhui Institute of Optics and Fine Mechanics,Chinese Academy of Sciences, Hefei 230031, China,   University of Science and Technology of China, Hefei 230031, China,   College of Electrical and Information enginenering, Anhui University of Science and Technology, Huainan 232001, China
Published: December 2020

In this paper, we present a novel method of computing tomography , i.e. the low third deviation total variation (LTD-TV) method to reconstruct the two-dimensional distribution of SO2 of stack plume. The path-integral data of the plume are collected by only two imaging differential absorption spectrometers (IDOASs). However, due to the insufficient number of IDOASs, conventional reconstruction methods result in severe streaking artifacts. The traditional low third derivative method is widely used to reconstruct the gas distribution. It suggests a spatial distribution of gas concentrations, which has a low third spatial derivative in every direction and at every point. The derivatives are usually set to be zero. The method improves the reconstructed images by providing extra information which contains the gas concentration in line with the distribution of the second order polynomial, but it also gives rise to the extra artifacts. To address this issue, we further improve the traditional low third deviation (LTD) method by suggesting that the third derivative of gas concentration is sparse. We therefore adopt the compressed sensing (CS) based total variation (TV) optimization framework. In the LTD-TV method, a logarithmic barrier function with TV is used as an objective function. The objective function is then optimized by numerical optimization method, in which the gradient projection is used to determine its descent direction and a Barzilai-Borwein scheme to determine its step-size. The final results are obtained by iterative optimization. Numerical simulations are performed to simulate the reconstruction of gas distribution which is in line with Gaussian distribution. Compared with the conventional LTD method, the LTD-TV method enhances the proximity by 20%—80%, and greatly corrects the artifacts near the edges of images. The result of field campaign suggests that concordance correlation factor between the collected data and reconstructed image is 0.9023. It also shows that it has good noise immunity. In summary, it is the first time that we have introduced the CS theory into the field of gas plume reconstruction. Compared with the existing methods, the LTD-TV method can greatly reduce the artifacts and increase the credibility of the reconstruction.
Organic ammonium salt surface treatment stabilizing all-inorganic CsPbI2Br perovskite
Authors: Liu Xiao-Min , Li Yi-Hui , Wang Xing-Tao , Zhao Yi-Xin ,   School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
Published: December 2020

All-inorganic perovskite cesium lead halides with superior stability, suitable bandgap and high absorption efficient have become a promising candidate for photovoltaic application. In all-inorganic cesium lead halide perovskites, CsPbX3 (X = Br, I) exhibits excellent photoelectric properties, which are similar to those of organic-inorganic hybrid perovskites. The CsPbI3 faces a challenge of unideal tolerant factor for perovskite phase while CsPbI3–xBrx has better tolerant factor. Among them, CsPbI2Br is one of most popular candidates because of its good thermal stability. Nevertheless, CsPbI2Br shows instability due to the phase transition caused by moisture and lower efficiency because of defects. For all inorganic perovskite devices, the alkyl chain length of surface treatment agent should be taken into account when using organic cationic passivation method. In this paper, CsPbI2Br perovskite is treated with different organic ammonium salts to enhance its phase stability. The experimental results show that α-phase CsPbI2Br is more stable with the increase of the alkyl chain length. Butylamine iodine (BAI) among three kinds of surface treating agents is proved to have the best defect passivation and phase stabilization effect. With the increase of alkyl chain length, the hydrophobicity of the organic molecular layer increases, which plays a crucial role in protecting optically active CsPbI2Br. Meanwhile, it is found that the stability of perovskite is enhanced with the concentration of the BAI solution increasing. This should be related to the organic cation termination formed on the surface of CsPbI2Br film. Solar cell devices based on the CsPbI2Br thin films treated with different concentrations of BAI are assembled and then the effect of organic ion surface treatment on the photoelectric performance of batteries is further explored. The experimental results show that when the concentration of BAI is relatively high (4 mg/mL and 8 mg/mL), the device’s photovoltaic performance decreases especially the photocurrent obviously decreases, while the post-treatment process using 2 mg/mL BAI will enhance not only the phase stability but also the photovoltaic parameters after defect passivation. Considering both humidity resistance and device efficiency, this work demonstrates that the CsPbI2Br thin film with suitable BAI treatment can improve the wet stability of perovskite, and enhance the photovoltaic performance.
Exact solution to a kind of multi-level Rosen-Zener models
Authors: Yao Shao-Wu , Cao Hong , Cen Li-Xiang ,   Center of Theoretical Physics, College of Physical Science and Technology, Sichuan University, Chengdu 610065, China,   School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074, China
Published: December 2020

Exact solution to the driven quantum system with an explicitly time-dependent Hamiltonian is not only an issue of fundamental importance to quantum mechanics itself, but also a ubiquitous problem in the design for quantum control. In particular, the nonadiabatic transition induced by the time-dependent external field is often involved in order to target the quantum state for the atomic and molecular systems. In this paper we investigate the exact dynamics and the associated nonadiabatic transition in a typical driven model, the Rosen-Zener model and its multi-level extension, by virtue of the algebraic dynamical method. Previously, this kind of driven models, especially of the two-level case, were solved by converting the corresponding Schrödinger equation to a hypergeometric equation. The property of the dynamical transition of the system was then achieved by the asymptotic behavior of the yielded hypergeometric function. A critical drawback related to such methods is that they are very hard to be developed so as to treat the multi-level extension of the driven model. Differing from the above mentioned method, we demonstrate that the particular kind of the Rosen-Zener model introduced here could be solved analytically via a canonical transformation or a gauge transformation approach. In comparison, we show that the present method at least has two aspects of advantages. Firstly, the method enables one to describe the evolution of the wavefunction of the system analytically over any time interval of the pulse duration. Moreover, we show that the method could be exploited to deal with the multi-level extensions of the model. The explicit expression of the dynamical basis states, including the three-level system and the four-level system, is presented and the transition probabilities induced by the nonadiabatic evolution among different levels are then characterized for the model during the time evolution. In addition, our study reveals further that the dual model of the driven system can be constructed. Since the dynamical invariant of a solvable system can always be obtained within the framework of the algebraic dynamical method, the general connection between the dual model and the original one, including the solvability and their dynamical invariants, are established and characterized distinctly.
Microstructural and electrochemical properties of sulfur ion implanted nanocrystalline diamond films
Authors: Jiang Mei-Yan , Zhu Zheng-Jie , Chen Cheng-Ke , Li Xiao , Hu Xiao-Jun ,   College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, China
Published: December 2020

Nanocrystalline diamond (NCD) films have a composite structure composed of diamond grains and amorphous carbon grain boundaries. Compared with microcrystalline diamond (MCD) films, the NCD film grain boundaries are rich in a large number of π bonds, thus providing conductive channels. Its conductivity is 3−7 orders of magnitude higher than that of MCD, and the surface of NCD film is uniform and dense, and the roughness is lower, so the NCD film is a promising electrode material. In our previous study, microwave plasma chemical vapor deposition was successfully used to prepare n-type sulfur-doped diamond films with good electrical properties. However, the electrochemical properties of sulfur-doped nanocrystalline diamond films have not been studied till now. In the present work, the nanocrystalline diamond films are prepared by the hot-wire chemical vapor deposition. The films are subjected to ion implantation and vacuum annealing. The effects of annealing temperature on the microstructure and electrochemical properties of the films are investigated. The results show that the sulfur ion implantation is beneficial to the improvement of the electrochemical reversibility of the film. When annealed at 800 °C and below, the amorphous carbon phase at the grain boundary in the film gradually changes into the trans-acetylene phase, resulting in a gradual deterioration of electrochemical performance. When the annealing temperature rises to 900 °C, Raman spectrum and TEM results show that the film has more diamond phase content and better lattice quality, and the trans-polyacetylene in the grain boundary is cracked; XPS results indicate that the CO bond at this time, C=O bond, and π—π* content increase significantly; Hall test shows that the film mobility and carrier concentration are significantly higher than those of unannealed film. The redox peak in the electrolyte is highly symmetrical, the peak potential difference is reduced to 0.20 V, the electrochemical active area is increased to 0.64 mC/cm2, and the electrochemical reversibility is much better thanthose of samples annealed at 600 °C, 700 °C, and 800 °C, respectively.
Demonstration of wide-bandgap GaN-based heterojunction vertical Hall sensors for high-temperature magnetic field detection
Authors: Cao Ya-Qing , Huang Huo-Lin , Sun Zhong-Hao , Li Fei-Yu , Bai Hong-Liang , Zhang Hui , Sun Nan , Yung C. Liang ,   School of Optoelectronic Engineering and Instrumentation Science, Dalian University of Technology, Dalian 116024, China,   School of Physics, Dalian University of Technology, Dalian 116024, China,   Department of Electrical and Computer Engineering, National University of Singapore, Singapore 119260, Singapore
Published: December 2020

Magnetic fields are generally sensed by a device that makes use of the Hall effect. Hall-effect sensors are widely used for proximity switching, positioning, speed detecting for the purpose of control and condition monitoring. Currently, the Hall sensor products are mainly based on the narrow-bandgap Si or GaAs semiconductor, and they are suitable for room temperature or low temperature environment, while the novel wide-bandgap GaN-based Hall sensors are more suitable for the application in various high-temperature environments. However, the spatial structure of the GaN-based sensor is mainly horizontal and hence it is only able to detect the magnetic field perpendicular to it. To detect the parallel field on the sensor surface, the vertical structure device is required despite encountering many difficulties in technology, for example reducing the vertical electric field in the two-dimensional electron gas (2-DEG) channel. The vertical Hall sensor has not been reported so far, so it is technically impossible to realize three-dimensional magnetic field detection on single chip. To address the mentioned issues, in this paper we propose a design of the vertical Hall sensor based on the wide-bandgap AlGaN/GaN heterojunction material, which adopts a shallow etching of 2-DEG channel barrier to form a locally trenched structure. The material parameters and physical models of the proposed device are first calibrated against real device test data, and then the key structural parameters such as device electrode spacing ratio, mesa width and sensing electrode length are optimized by using technology computer aided design, and the device characteristics are analyzed. Finally, the simulation results confirm that the proposed Hall sensor has a higher sensitivity of magnetic field detection and lower temperature drift coefficient (\begin{document}$\sim $\end{document}600 ppm/K), and the device can work stably in a high-temperature (greater than 500 K) environment. Therefore, the vertical and horizontal devices can be fabricated simultaneously on the same wafer in the future, thus achieving a three-dimensional magnetic field detection in various high-temperature environments.
Dynamical study of ultrafast exciton migration in coujugated polymers driven by nonuniform field
Authors: Wang Wen-Jing , Li Chong , Zhang Mao-Mao , Gao Kun ,   Institute of Physics and Electronic Engineering, Qilu Normal University, Jinan 250013, China,   School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
Published: December 2020

Due to the exciton migration dynamics playing an important role in the photovoltaic process of organic solar cells, which are usually composed of polymer donor and fullerene (or non-fullerene) acceptor, in this paper we propose a new strategy to achieve the ultrafast exciton migration in polymers. Here, the effects of some nonuniform fields on the exciton migration dynamics in polymers are emphasized, such as the nonuniform electric field and the nonuniform polymer packing configuration field. Both of the two kinds of nonuniform fields can be intrinsically existent or modulated in an actual photovoltaic system. In this work, the nonuniform electric field and the nonuniform configuration field are assumed to be separately created by a confined charge and a linear polymer packing, therefore, their model Hamiltonian is established. In dynamical simulations of the exciton migration dynamics in polymers, an extended version of one-dimensional Su-Schrieffer-Heeger tight-binding model combined with a nonadiabatic evolution method is employed. It is found that the nonuniform electric field and the nonuniform configuration field both can drive exciton to an ultrafast migration process. Compared with the exciton migration speed dominated by the traditional Förster or Dexter mechanism, the exciton migration speed dominated by the nonuniform electric field and that by the nonuniform configuration field can be increased by one and two orders of magnitude, respectively. In addition, the driving mechanisms of the two kinds of nonuniform fields for the exciton migration dynamics are separately clarified, where the corresponding driving forces are also quantitatively calculated. Finally, in view of the factors affecting the distributions of the two kinds of nonuniform fields (such as the distance d between confined charge and polymer, and the linear packing slope k between polymers), we discuss their effects on the exciton migration dynamics. It is found that the exciton migration in polymer can be apparently accelerated by shortening the distance d between confined charge and polymer, and there exists a critical value of d, beyond which the exciton will be dissociated into free charges in its migration process. For the linear packing slope k between polymers, we find that there exists an optimal value, at which the exciton has the highest migration speed in polymers.
Lorentz-violating theory and tunneling radiation characteristics of Dirac particles in curved spacetime of Vaidya black hole
Authors: Pu Jin , Yang Shu-Zheng , Lin Kai ,   College of Physics and Space Science, China West Normal University, Nanchong 637002, China,   School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China,   Hubei Subsurface Multi-scale Imaging Key Laboratory, Institute of Geophysics and Geomatics,China University of Geosciences, Wuhan 430074, China,   Escola de Engenharia de Lorena, Universidade de Sao Paulo, 12602-810, Lorena, Sao Paulo, Brazil
Published: December 2020

In this paper, the modified Hawking radiation for Dirac particles via tunneling from the apparent horizon of Vaidya black hole is studied by using the Lorentz-violating Dirac field theory. We first extend the gamma matric from flat spacetime to the curved spacetime in the Lorentz-violating Dirac field theory, and generalize the general derivative to the covariant derivative. Then, by considering the commutative relation of the gamma matric, the Dirac equation in the Lorentz-violating Dirac field theory is obtained, which contains three correction terms related to the Lorentz-symmetry violation. In the semiclassical approximation, the modified Hamilton-Jacobi equation is obtained by using the commutative relation of gamma matric and treating the aether-like vector in the Lorentz-violating theory as a constant. We find that the modified Hamilton-Jacobi equation contains only two correction terms based on the Lorentz-symmetry violation, i.e. the corrected term containing the parameter a affects the mass term of the Dirac field, and the aether-like term containing the parameter c modifies the coefficient term of the action S of the separating variable. According to the modified Hamilton-Jacobi equation, we study the effect of Lorentz-symmetry violation on the characteristics of Hawking radiation for Dirac particles via tunneling from the apparent horizon ra = 2M(v) of Vaidya black hole (the apparent horizon of Vaidya black hole coincides with the timelike limit surface, so the apparent horizon can be regarded as the boundary of Vaidya black hole). Since the Hawking tunneling radiation of black holes is the radial property at the horizon of black holes, we finally find that only the aether-like term containing the parameter c can modify the characteristics of Dirac particles’ tunneling radiation from the black hole. In addition, the corrected Hawking temperature of the black hole caused by considering the effect on the Lorentz-violating Dirac field theory has a small correction related to the aether-like term, which is consistent with the results obtained by studying the characteristics of Hawking tunneling radiation for scalar particles in the Lorentz-violating scalar field theory. The results suggest that the Lorentz-symmetry violation theory may provide a new method to further study the information loss paradox of black holes.
Spontaneous magnetic field and odd-frequency pairing state in multiband superconductors
Authors: Zhang Yan-Yan , Chen Jia-Lin , Zha Guo-Qiao , Zhou Shi-Ping ,   Shanghai Key Laboratory of High Temperature Superconductors, Department of Physics, Shanghai University, Shanghai 200444, China
Published: December 2020

We investigate the interband coupling induced odd-frequency pairing state by solving the microscopic Ginzburg-Landau model for the two band superconductor magnesium diboride (MgB2). It is found that the interband coupling can induce a new domain structure and a heliacal spontaneous magnetic vortex-antivortex pair around the cyclical domain wall, which breaks down spin-rotational symmetry and supports a time-reversal violating bound state, allowing the coexistence of spin-singlet and spin-triplet state close to the spontaneous vortex core. The odd-frequency spin-triplet even parity pairing state occurs since a successive operation in the orbital parity (P) and the time-reversal (T) obeys PT = + 1(–1) for spin-singlet (spin-triplet) pairing amplitude. A general phase diagram is presented.
Radiative and Auger transitions of K-shell excited resonance states in boron-like sulfur ion
Authors: Sun Yan , Hu Feng , Sang Cui-Cui , Mei Mao-Fei , Liu Dong-Dong , Gou Bing-Cong ,   School of Mathematic and Physical Science, Xuzhou University of Technology, Xuzhou 221018, China,   College of Science, Lanzhou University of Technology, Lanzhou 730050, China,   School of Physics, Beijing institute of Technology, Beijing 100081, China
Published: December 2020

Non-relativistic energy values and wave functions of the K-shell excited resonance states 1s2s22p2, 1s2s2p3, 1s2p4 2, 4L (L = S, P, D) in boron-like sulfur ion are calculated in the frame of multi-configuration saddle-point variation method. The electron correlation effects are considered by the expansion of configuration wave function. The wave functions are constructed and optimized by the orbital-spin angular momentum partial waves selected based on the rule of configuration interaction. To saturate the wave functional space and to improve the non-relativistic energy, the restricted variational method is used to calculate the restricted variational energy. Then, the mass polarization effect and relativistic correction are calculated by the perturbation theory. The quantum electrodynamics (QED) effect and higher-order relativistic correction are considered by the screened hydrogenic formula. Furthermore, the energy shift originating from the interaction between closed channel and open channel is also calculated. Finally, the accurate relativistic energy levels for these resonance states are obtained by adding the non-relativistic energy and all corrections.

Using the optimized wave functions, the line strengths, oscillator strengths, radiative transition rates and transition wavelengths of electric-dipole transitions for the K-shell excited resonance states in boron-like sulfur ion are systematically calculated. In this work, the oscillator strengths and transition rates are given in the length, velocity, and acceleration gauges. The good agreement among the three gauges reflects that the calculated wave functions are reasonably accurate. The calculated radiative transition rates and transition wavelengths are compared with other theoretical data. Good agreement is obtained except the transition: 1s2s(3S)2p3 2Po→1s22s2p2 2D. The deviation between our theoretical result and the MCDF theoretical value is about 46%, which needs further verifying. The Auger rates, Auger branching ratios, and Auger electron energy values of the important decay channels of the K-shell excited states are calculated by the saddle-point complex-rotation method. The calculated Auger rates and Auger electron energy values are also in good agreement with the corresponding reference data. For some K-shell states, the related energy levels and Auger branching ratios are reported for the first time. The present calculations results will provide valuable theoretical data for the calibration of spectral lines and Auger electron spectra in the relevant experiments.