bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple weak-line laser operation from Nd:YAG 4F3/2-4I13/2 translation in ceramic and crystal
Authors: Lin You-You  , Li Jiang-Tao  , Zhu Hai-Yong  , Liao Xiao-Qing  , Duan Yan-Min  , Zhang Jian  , Tang Ding-Yuan  ,   College of Physics and Electronic Information Engineering, Wenzhou University, Wenzhou 325035, China;,   Key Laboratory for Advanced Laser Materials and Devices of Jiangsu Province, Jiangsu Normal University, Xuzhou 221116, China
Published: December 2020

Laser diode end-pumped Nd:YAG based multiple weak-lines laser from 4F3/2-4I13/2 translation is reported. Fluorescence spectra for both Nd:YAG crystal and ceramic are present. Simple two-mirror cavity with reasonable optical coating is used for multiple weak-line laser operation around 1.3 and 1.4 μm. The variations of laser output and spectra with the pump power are compared experimentally between 1.0 at.% Nd3+ doped Nd:YAG ceramic with 3 mm×3 mm×7.5 mm in size and 0.8 at.% Nd3+-doped Nd:YAG crystal with 3 mm×3 mm×8 mm in size. First, 1338 and 1356 nm dual-wavelength laser outputs are achieved using output coupler with transmittance values of 9.6%, 6.2%, 2.4% and 1.8% at 1338, 1356, 1414 and 1444 nm, respectively. Under low pump power around the threshold, the 1356 nm single wavelength laser is obtained. With increasing the pump power, the laser with a wavelength of 1338 nm appears first in the ceramic. At an incident pump power of 11.8 W, a 1338 and 1356 nm dual-wavelength laser with an output power of 3.7 W and an intensity ratio of 1 : 5 for crystal, and a 1338 and 1356 nm dual-wavelength laser with an output power of 3.5 W and an intensity ratio of 1:3 for ceramic are obtained. Replacing the output couplers with transmittance values of 15.4%, 6.5%, 1.1% and 0.8% at wavelengths of 1338, 1356, 1414 and 1444 nm, respectively, 1356 and 1414 nm dual-wavelength laser outputs are achieved. Under the low pump power, even triple-wavelength (1356, 1414 and 1444 nm) laser is obtained. With increasing the pump power, the intensities of 1414 and 1444 nm wavelengths turned down and the 1444 nm wavelength disappears first in ceramic. At an incident pump power of 11.8 W, a 1356 and 1414 nm dual-wavelength output power of 3.56 W with intensity ratio of 44 : 1 for crystal and a 1356 and 1414 nm dual-wavelength laser output power of 3.25 W with intensity ratio of 12 : 1 for ceramic are obtained. The results show that slight difference between fluorescence spectra results from the difference in laser spectrum between transparent ceramic and single crystal materials for multi-wavelength output. Thresholds of two different output couplers are both about 2 W. When the incident pump power increases to 13.5 W, a 1338 and 1356 nm dual-wavelength laser output power of 4.05 W and a 1356 and 1414 nm dual-wavelength laser output power of 3.65 W are achieved in Nd:YAG transparent ceramic. The corresponding slope efficiency values are 33.9% and 31.9%, respectively.
Quantum dot lasers on silicon substrate for silicon photonic integration and their prospect
Authors: Wang Ting  , Zhang Jian-Jun  , Huiyun Liu  ,   Institute of Physics, Chinese Academy Sciences, Beijing 100190, China;,   Department of Electrical and Electronic Engineering, University College London, Torrington Place, London, UK
Published: December 2020

In this article, the recent progress of III-V quantum dot lasers on silicon substrates for silicon photonic integration is reviewed. By introducing various epitaxial techniques, room-temperature 1.3-m InAs/GaAs quantum dot laser on Si, Ge and SiGe substrates have been achieved respectively. Quantum dot lasers on Ge substrate has an ultra-low threshold current density of 55.2 A/cm2 at room temperature, which can operate over 60 ℃ in continuous-wave mode. Futhermore, by using the SiGe virtual substrate, at 30 ℃ and an output power of 16.6 mW, a laser lifetime of 4600 h has been reached, which indicates a bright future for the large-scale photonic integration.
Effect of plasma on boron-based two-phase flow diffusion combustion
Authors: Zhang Peng  , Hong Yan-Ji  , Ding Xiao-Yu  , Shen Shuang-Yan  , Feng Xi-Ping  ,   State Key Laboratory of Laser Propulsion & Application, Equipment Academy, Beijing 101416, China;,   Science and Technology on Combustion, Internal Flow and Thermal-Structure Laboratory, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

A parallel intake diffusion combustion physical model is designed to study the influence of plasma on the secondary combustion of boron-based gas in the after-burning chamber, with excluding mixing effects of the intake air. The flame images of the diffusion combustion of the boron-based gas in the after-burning chamber are obtained by a high-speed photographic apparatus. The diffusion combustion characteristics of the physical model and the secondary ignition distance of boron particles are analyzed. The King ignition model, finite-rate/eddy-dissipation model, particle-trajectory model, RNG k-ε model, and plasma model are adopted to simulate the influence of plasma on the diffusion combustion of boron-based two-phase flow in a certain condition. The results show that the secondary ignition distance of boron particles, which is based on the boron-based flame image, is consistent well with the numerical simulation result, which verifies the accuracy of the boron-based two-phase flow diffusion combustion numerical model and the calculation method. When the boron-based gas passes through the plasma area, the temperature of the boron particles increases while the diameter decreases significantly on their trajectory. The distribution area of the B2O3 mass fraction increases significantly, and more than 70% boron particles reach a 100% combustion efficiency before they arrive at the area of the two-thirds after-burning chamber. More heat is released by fully burning the boron particles under the influence of plasma, which results in a half increase of the central area. It can be indicated that plasma can obviously enhance the combustion process of the boron-based gas, which improves the combustion efficiency of boron particles and releases more energy.
Theoretical study on the stream formation in the nitrogen switch
Authors: Zhou Qian-Hong  , Dong Zhi-Wei  , Jian Gui-Zhou  , Zhou Hai-Jing  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   Science and Technology on High Power Microwave Laboratory, Mianyang 621900, China;,   Beijing Microelectronics Technology Institute, Beijing 100076, China
Published: December 2020

The stream formation in a 1-atm nitrogen gas switch is investigated by the two-dimensional and three-velocity (2D3V) particles through the cell-Monte Carlo collision (PIC-MCC) simulation and theoretical analysis. For simplicity, two parallel plane electrodes of 0.6 mm width are separated by a distance of 1.6 mm. It is found that the analytical solution of the electron density equation can be used to study the evolution of the plasma before the stream breaks down, for the ionization frequency, mean electron energy and electron drift velocity are all constant. After the breakdown of the stream, random collisions destroy the symmetry of the plasma region and cause plasma to branch. As plasma density increases, the electric field inside the plasma region decreases due to the shielding effect. However, charge densities at both ends of the plasma region increase and the density at the anode end is larger than that at the cathode end, for the plasma exponentially grows as electrons move from the cathode toward the anode. This causes the electric field at the end of plasma near the anode to be larger than that near the cathode. It is found that the electrons can achieve their stable mean energy in several picoseconds due to the high transfer frequency (1011-1012 Hz) of the electron energy in the nitrogen plasma. After the breakdown of the stream, the mean electron energy decreases due to the decrease of the electron energies inside the plasma. By increasing the electrode voltage, it is found that the mean electron energy increases, the electron drift velocity increases linearly, and the variation rate of ionization frequency with electric field is in a range between E4 and E5. Therefore, the time taking for breaking down the stream decreases with the increase of the electrode voltage.
Wettability of surfaces with different surface microstructures textured by laser
Authors: Xiong Qi-Yu  , Dong Lei  , Jiao Yun-Long  , Liu Xiao-Jun  , Liu Kun  ,   Institute of Tribology, Hefei University of Technology, Hefei 230009, China;,   School of Mechanical and Power Engineering, North University of China, Taiyuan 030051, China
Published: December 2020

In order to study the effects of working conditions and solid surface topography on the wettability of material, a series of No. 45 steel specimens with the same surface arithmetic average height Sa and different surface microstructures is designed and manufactured by laser surface texturing. All the surfaces are measured by a non-contact three-dimensional (3D) optical profiler Talysulf CCI Lite and characterized by the ISO25178. A series of wetting experiments is carried out with the No. 32 turbine oil on an optical contact angle and surface tension meter SL200 KS. The effects of temperature, droplet volume and surface structure on the wettability are analyzed. Meanwhile, quantitative research of the relationship between the random characteristics of topography and wettability of the solid surface is conducted with parameters obtained from the ISO25178. Based on the fact that the contact angle is an acute angle, the results show that the contact angle of the droplet on the solid surface decreases rapidly to a stable value in the wetting process. The stable value decreases with the increase of the temperature, while it first increases and then decreases with the increase of the droplet volume. The surface wettability can be affected by the laser micro-texturing. Surfaces with similar values of Sa show different wettabilities for different micro-textures with different shapes and directions. Textured surfaces with grooves along the spreading direction of the droplet perform the best wettability in our research. Results also predicate that the wettability of surface is greatly influenced by the amplitude parameters (Sku, Ssk), spatial parameters (Str, Sal), hybrid parameters (Sdq, Sdr), and feature parameters (Sda, Sdv), which are all obtained from the ISO25178. The wettability of hydrophilic surface becomes better with increasing Sku, Sal, and Sdr and reducing Ssk, Str, and Sdq.
Extinction properties of gold nanorod complexes
Authors: Huang Yun-Huan  , Li Pu  ,   Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan 030024, China;,   College of Physics and Optoelectronics, Taiyuan University of Technology, Taiyuan 030024, China
Published: December 2020

Plasmonics with subwavelength characteristics can break the diffraction limit of light and be used to produce the sub-wavelength optoelectronic device, thus it has aroused great interest for decades. Local surface plasmon resonance of metal nanoparticles has become one of the research hotspots due to the fact it can produce extinction and near-field enhancement effect. How to achieve controllable plasmon line shape and generate strong electromagnetic field enhancement is of great significance for improving the sensing performance, nonlinear effect and surface enhanced Raman factor of metallic nanostructures. The optical properties of plasmonic oligomer clusters composed of normal and L-shaped nanrod dimers are investigated by using the finite-difference time-domain method in this paper. There are two energy modes for an L-shaped nanorod due to its shaped anisotropy, where plasmons oscillate along the arms of the L-shaped nanorod or oscillate over the whole length of the L-shaped nanorod. Therefore, two bonding resonances appear in the spectrum of an L-shaped nanorod dimer, while only one bonding resonance exists for normal nanorod dimer. When a normal nanorod dimer and an L-shaped nanorod dimer are aligned together to form a quadrumer, the three bonding resonances can be excited simultaneously and radiative damping can be suppressed effectively around the dip spectral positions. It is shown that the optical responses of quadrumer can be strongly tuned by manipulating the geometry parameters. For example, the coupling between the two dimers can be modified by adjusting the separation, and the three resonances shift toward higher energies with the increasing of the separation. In addition, the optical responses of individual nanorod depend on the corresponding arm length. As a result, the three resonances of the quadrumer can also be well tuned by adjusting the arm length. Comparing the variation of resonance peak positions between L-shaped nanorod dimer and normal nanorod dimer, we can more intuitively understand spectral lineshape variation of quadrumer. These results can be used for guiding the design of nano-photonic devices for plasmonic oligomer clusters and also for developing the application of surface-enhanced Raman scattering and biological sensing.
Analytical model of secondary electron yield from metal surface with regular structures
Authors: Zhang Na  , Cao Meng  , Cui Wan-Zhao  , Hu Tian-Cun  , Wang Rui  , Li Yun  ,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, School of Electronic and Information Engineering, Xi'an Jiaotong University, Xi'an 710049, China;,   Science and Technology on Space Microwave Laboratory, China Academy of Space Technology (Xi'an), Xi'an 710100, China
Published: December 2020

An analytical model of secondary electron (SE) emission (SEE) from metal surface with regular structure is presented. In this model, the quantitative relationship between the SE emission yield (SEY) and surface topography is examined. Using the idea of multi-generation for SE emission, the first-generation of SEs is considered as being dominant in total SEs. The shielding effect of the surface structures on the SE is found to be the main factor influencing final SEY. On the basis of the cosine distribution of secondary electrons emission direction, the quantitative relationship between the SEY and surface topography parameters is revealed. Then taking the rectangular and triangular grooves for example, the analytical formulas of first-generation SEY are derived for both normal and oblique incidence. The analytical results are then verified with the Monte Carlo simulation results and experimental data. The results show that a rectangular groove with a bigger depth-to-width ratio can suppress the SEE more efficiently. For a triangular groove, owing to having both enhancing and suppressing effects on SEE, a small groove angle is required for effective SEE suppression. The present analytical model gives an insight into the relationship between the SEY and the surface topography parameters and is helpful for the structure design to modify SEY.
Research on the development mechanism: from two-sided multipactor to one-sided multipactor
Authors: Zhang Xue  , Wang Yong  , Xu Qiang  ,   Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Multipactor discharge always causes disastrous damage to a vacuum window in high power microwave system, which actually becomes a limiting factor for the output power of vacuum device. To explore the multipactor phenomenon of complicated pill-box window, the mulitpactor in normal field between the metal boundary and the window disk is studied. Through Monte Carlo (MC) simulations, the susceptive curve is fitted and analyzed. The secondary electrons' avalanche behavior under the normal RF field is discussed. It is noticed that the one-sided multipactor is excited within a very limited Vrf-fD region when two-sided multipactor is excited initially. The development condition from two-sided multipactor to the one-sided multipactor is proposed. Through analyzing and MC simulation, the condition is achieved. When the normal RF electric field can satisfy the phase focus conditions of one-sided multipactor, the two-sided multipactor will develop into one-sided multpactor and then reach a saturation value. Meanwhile, the initial effect of electrostatic field on one-sided multipactor is also discussed. On condition that two-sided multipactor can be excited, the number of secondary electrons can increase up to a saturation value when Edc0 is lower than the minimal saturate value of Edc. When Edc0 is lager than the minimal saturate value of Edc and in the Edc/Erf threshold of one-sided resonant multipactor, the number of secondary electrons can also increase to a saturate value. However, When Edc0 is lager than the minimal saturate value of Edc but beyond the Edc/Erf threshold of one-sided resonant multipactor, secondary electrons will be suppressed.
Effect of prior stress-relief on the gliding of indentation dislocations on silicon wafers
Authors: Zhao Ze-Gang  , Tian Da-Xi  , Zhao Jian  , Liang Xing-Bo  , Ma Xiang-Yang  , Yang De-Ren  ,   State Key Laboratory of Silicon Materials, School of Materials and Engineering, Zhejiang University, Hangzhou 310027, China;,   QL Electronic Co. Ltd, Ningbo 315800, China
Published: December 2020

The mechanical strengths of silicon wafers are crucial for the manufacturing yield of integrated circuits (ICs), which have received intensive attention over the years. With reducing the feature size of ICs, the mechanical strengths of silicon wafers become more significant. Actually, the gliding of indentation dislocations on single-crystalline silicon wafers at a given temperature reflects the mechanical strengths of silicon wafers. Since the gliding of indentation dislocations is driven by the residual stress around the indentation, the investigation on the correlation between the residual stress and dislocation gliding is of significance. In this paper, we first use micro-Raman microscopy to characterize the relief of stress around the indentation due to the annealling at 300 or 500 ℃. Then the effect of such a relief-stress on the gliding of indentation dislocations at 700-900 ℃ is investigated. In the case without the prior stress-relief, the indentation dislocations glide to the maximum distance after 2 h annealling at 700-900 ℃. With the prior stress-relief due to the annealling at 300 or 500 ℃, the indentation dislocations can still glide to the maximum distance after 2 h annealling at 900 ℃, however the gliding velocity significantly decreases and the gliding distance is remarkably reduced after 2 h annealling at 700 or 800 ℃. Such a reduction of gliding distance is most significant in the case of 700 ℃ annealling following the stress-relief with the 500 ℃/2 h annealling. Despite the prior stress-relief, as long as the annealing time at 700 or 800 ℃ is sufficiently extended, the indentation dislocations can glide to the maximum distance. In view of the above results, it is believed that the maximum gliding distance of indentation dislocations at a given temperature is independent of the values of residual stress around the indentation provided that the residual stresses are larger than the critical stress for driving the dislocation movement. Nevertheless, the annealing time for achieving the maximum gliding distance at a given temperature should be remarkably extended as the residual stresses around the indentation are relieved.
Thermo-fluid coupling of unsteady flow in Czochralski crystal growth
Authors: Huang Wei-Chao  , Liu Ding  , Jiao Shang-Bin  , Zhang Ni  ,   National & Local Joint Engineering Research Center of Crystal Growth Equipment and System Integration, Xi'an University of Technology, Xi'an 710048, China;,   Shaanxi Key Laboratory of Complex System Control and Intelligent Information Processing, Xi'an 710048, China
Published: December 2020

In a crystal growth system, the crystal quality is greatly affected by the coupling properties between unsteady melt flow and thermal transfer. In this paper, an improved lattice Bolzmann method is proposed. This incompressible axisymmetric model based method transforms the fluid equations of cylindrical coordinate into those of the two-dimensional Cartesian coordinate and constructs the evolutionary relationship of the external force terms, such as rotational inertia force and the thermal buoyancy. In the unsteady melt, the temperature distribution and the rotational angular velocity are determined based on the D2Q4 model and the velocity of axisymmetric swirling fluid is calculated based on the D2Q9 model. The mirror bounce format is adopted as the boundary conditions of the free surface and the axis symmetry. For the remaining boundary conditions, the non-equilibrium extrapolation format is used. In the simulation, 12 sets of flow function results are obtained by choosing different sets of Grashof number and Reynolds number. By comparing with the finite crystal growth results, the effectiveness of the proposed method can be shown. Furthermore, by studying the convection shape and the temperature distribution of the melt under coupling between high Grashof number and high Reynolds number, it can be concluded that the thermal coupling properties and flow in the unsteady melt relate to Grashof number and Reynolds number. By adjusting the high Reynolds number generated by the crystal and crucible rotation, the strength of the forced convection in the melt can be changed. Therefore, the natural convection in the melt can be suppressed effectively and the temperature distribution results can be improved significantly. In addition, it is worth mentioning that the findings in this paper can be straightforwardly extended to the silicon single crystal growth experiment by turning the dimensionless crystal rotation Reynolds number and crucible rotation Reynolds number into the actual rotation speed.
Research progress of high mobility germanium based metal oxide semiconductor devices
Authors: An Xia  , Huang Ru  , Li Zhi-Qiang  , Yun Quan-Xin  , Lin Meng  , Guo Yue  , Liu Peng-Qiang  , Li Ming  , Zhang Xing  ,   Key Laboratory of Microelectronic Devices and Circuits, Institute of Microelectronics, Peking University, Beijing 100871, China
Published: December 2020

Germanium based metal oxide semiconductor (MOS) device has been a research hotspot and considered as a potential candidate for future complementary MOS (CMOS) technology due to its high and symmetric carrier mobility. However, the poor quality of gate dielectric/channel interface significantly restricts the performances of germanium based MOS devices. Besides, the solid-solubility and activation concentration of dopants in Ge are both quite low, and the dopants diffuse fast in Ge, which makes it difficult to achieve ultra-shallow junction with high dopant concentration, especially for Ge NMOS devices.To solve these problems, different techniques are proposed and overviewed. The proposed nitrogen-plasma-passivation method can effectively suppress the regrowth of germanium sub-oxide and reduce the interface state density. Thus the performance of the fabricated Ge NMOS device is significantly improved. To enhance the n-type dopant activation in Ge, the multiple implantation technique and the multiple annealing technique are proposed. High electrical activation over 1 1020 cm-3 is achieved, and the corresponding contact resistivity is reduced to 3.8 10-7 cm2. Besides, the implantation after germanide (IAG) technique is first proposed to modulate the Schottky barrier height (SBH). The record-low electron SBH of 0.10 eV is obtained by IAG technique, and the optimized process window is given. In addition, the poor thermal stability of NiGe restricts the further improvement in performance of Ge MOS device. P and Sb co-implantation technique and novel ammonium fluoride pretreatment method are proposed to improve the thermal stability of NiGe. The electrical characteristic of NiGe/Ge diode is also improved simultaneously. The results provide the guidelines for further enhancing the performances of germanium-based MOS devices.
Influence of PTCBI as cathode modification on the performances of Rubrene/C70 based organic solar cells
Authors: Tu Cheng-Wei  , Tian Jin-Peng  , Wu Ming-Xiao  , Liu Peng-Yi  ,   Siyuan Laboratory, Department of Physics, Jinan University, Guangzhou 510632, China
Published: December 2020

Organic solar cells (OSCs) with the structure of ITO/MoO3(6 nm)/Rubrene(30 nm)/C70(30 nm)/PTCBI(x nm)/Al(150 nm) are fabricated. Role of perylenebisimide with extended pi system (PTCBI) modified cathode layer in Rubrene/C70 based organic solar cells is investigated. Experimental results show that the insertion of PTCBI between C70 and Al electrode can significantly improve the performance of the devices. PTCBI contributes to an Ohmic contact between the C70 layer and Al cathode, which enhances the built-in potential in OSCs. Furthermore, PTCBI avoids the contact between the excitons and the Al electrode, and reduces the damage of high energy Al ions to C70 in the cathode preparation process. The effect of PTCBI thickness on the performances of OSC is also studied. The results indicate that the optimized PTCBI thickness is 6 nm. Compared with the performances of OSC without PTCBI, the open circuit voltage (VOC), fill factor (FF), short current density (JSC), and power conservation efficiency (P) of the optimum device are ameliorated by 70.4%, 55.5%, 125.1%, 292.2%, respectively. The cause of S-shape J-V curve in organic solar cells with thick modified cathode layer is analyzed. The modified cathode layer can be divided into two regions: the PTCBI layer and the Al permeated PTCBI layer. The electron mobility of PTCBI layer is lower than the hole mobility of Rubrene layer, which results in the charge accumulation on the unaffected PTCBI layer. When the thickness value of PTCBI layer is small, the whole modified cathode layer is permeated by Al ions, and this layer has better electron mobility than the unaffected one. When the thickness of PTCBI layer is 6 nm or more, the series resistance of OSC will increase and the S-shape J-V curve appears.
Application status and future of multi-scale numerical models for lithium ion battery
Authors: Cheng Yun  , Li Jie  , Jia Ming  , Tang Yi-Wei  , Du Shuang-Long  , Ai Li-Hua  , Yin Bao-Hua  , Ai Liang  ,   School of Metallurgy and Environment, Central South University, Changsha 410083, China;,   Hunan Aihua Group Co., Ltd, Yiyang 413002, China
Published: December 2020

Lithium ion battery is nowadays one of the most popular energy storage devices due to its high energy, power density and cycle life characteristics. It has been known that the overall performance of battery depends on not only electrolyte and electrode materials, but also operation condition and choice of physical parameters. Designers need to understand the thermodynamic and kinetic characteristics of battery, which is costly and time-consuming by experimental methods. However, lithium ion battery is a complicated electrochemical system with multi physicochemical processes including the mass, charge, and energy conservations as well as the electrochemical kinetics. It not only has a typical multiple level arrangement: across the electrode level, cell level, and extending to the battery module level, which is different from the basic active material particle level arrangement, but also confronts the challenges to meeting the requirements for sorting and consistency method for battery. These facts increase the difficulties in designing the battery and evaluating the overall performance. Owing to the rapid development of multi-scale numerical simulation technology, the multi-scale mathematical models for lithium ion battery are developed to help battery designer comprehensively and systematically gain the interaction mechanisms between different physicochemical fields in the battery working process and analyze the regulations of these interaction mechanisms, which is significant in providing theoretical supports for designing and optimizing the battery systems. At present, multi-type lithium ion battery models coupled with many physicochemical processes have been developed on different scales to study different issues, such as thermal behavior, inner polarization, micro structure, inner stress and capacitance fading, etc. In this paper, we review the research statuses and development trends of multi-scale mathematical models for lithium ion battery. The primary theoretical models for lithium ion battery are systemized and their features, application ranges and limitations are also summarized. Furthermore, the future research area and the difficulty in industry application are discussed. All of these are helpful for the theoretic research and engineering application of the multi-scale numerical models for lithium ion battery.
Vibration energy harvesting from a piezoelectric bistable system with two symmetric stops
Authors: Lan Chun-Bo  , Qin Wei-Yang  ,   Department of Engineering Mechanics, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Random vibration energy is widely existing in the environment. To efficiently harvest it, many researchers have designed lots of harvesters up till now. A lot of research works have found that when a harvester with bistable piezoelectric energy is excited by stochastic forces, if the intensity of them is low, the system's motion will be trapped in a single potential well. This will result in a low output voltage. In order to overcome the difficult of it and improve the harvesting efficiency, we develop an impact facility with two stops and incorporate it to a bi-stable energy harvester. This design can improve the harvesting efficiency greatly. First the electromechanical coupling equations are derived based on the Euler-Bernoulli beam theory and Kirchhoff's law. Then, we analyze the symmetric stops' effect on the potential function and the elastic restoring force of the system. Results show that both the potential energy and the magnitude of restoring force will be enhanced when collision takes place. Furthermore, we investigate the impact's effect on the system's dynamic responses and efficiency at harmonic excitation. Results reveal that a well designed impact can transform an intrawell motion into an interwell, and then increase the output voltage. And the chaotic motion can be changed into the large amplitude periodic one. Then, the harvester's dynamic responses under random excitations at a low intensity are obtained by using Euler-Maruyama method. Results indicate that the collision gaps can greatly influence the efficiency of the energy harvester. Collisions between the beam and the stops can force the system to oscillate between two potential wells more frequently. According to the relationship between the gap and the standard deviation of output voltage, we know that there exists an optimal collision gap for a definite intensity of stochastic excitation. The bistable energy harvester with this optimal gap will oscillate between the two wells frequently, and output a large voltage. Moreover, the collision stiffness can influence the system's performance as well. With the increase of collision stiffness, the system will exhibit a more frequently jumping between the two potential wells, but the stiffness has a limitation, exceeding which it cannot increase the frequency of jumping and improve the output power any more. So by properly designing the collision gap and stiffness, the system can most frequently jump between the two wells with a large amplitude of displacement, hence can attain the highest harvesting efficiency.
Chaotic circuit of ion migration memristor and its application in the voice secure communication
Authors: Min Guo-Qi  , Wang Li-Dan  , Duan Shu-Kai  ,   School of Electronic and information engineering, Southwest University, Chongqing 400715, China
Published: December 2020

A memristor is a nonlinear element of nanoscale size with memory function and when it works as the nonlinear part in a chaotic system, the physical size of the system will be greatly reduced, rich nonlinear curve will be produced, and at the same time, the complexity of the chaotic systems and the randomness of signals will be enhanced. So in this paper, a new chaotic system is designed based on an ion migration memristor. The complex dynamic characteristics of the memristive system are investigated by means of theoretical derivation, numerical simulation, Lyapunov exponent spectrum, power spectrum, and Poincaré map. In addition, the change of system dynamic behaviors with the different parameters are analyzed. Then, a SPICE-based analog circuit is presented. The SPICE simulation results are in conformity with the numerical analysis, and thus verify that the chaotic systems can produce chaos. The linear feedback control structure is simple, economic and easy to realize in engineering practice, so the linear feedback control method has a high application value. At present, most studies focus on memristors' applications in memory and analog neural networks, but little research work is for voice security transmission. Therefore, by using the method of linear feedback control of chaotic synchronization, this paper proves the effectiveness of this method by numerical simulation experiments. As a result, it can achieve secure communication of voice signals. Finally, we conclude that the linear synchronous control method based on memristive chaotic system when applied to the secure communications can achieve the purpose of covering a specific speech. In addition, this method is able to restore the specific speech signal without distortion, which is very meaningful for the promotion of applications of memristor.
Theoretical study on the photodissociation reaction of α-cyclohexanedione in ground state
Authors: Yang Xue  , Yan Bing  , Lian Ke-Yan  , Ding Da-Jun  ,   College of Science, Jilin Institute of Chemical Technology, Jilin 132022, China;,   Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
Published: December 2020

The α-cyclohexanedione (α-CHD) molecule is an important structural unit in the six-membered ring systems with a large number ofbiologically meaningfulmoleculeswhich have been found. It has important applications in synthetic science also. It is found that some fragments can be obtained through vacuum ultraviolet absorption spectrum and induction photolysis experiments for α-CHD molecules. In order to understand the dissociation reaction mechanism of α-CHD and reveal the resource of those fragments, the potential energy surface of the dissociation reaction for α-CHD molecules in ground state is studied by B3LYP and CCSD(T) methods. The reaction paths of the products are obtained, such as P1(c-C5H8O+ CO), P2(2 C2H4+ 2 CO), P3 (CH2CHCH2CH2CHO+ CO), P4(2 C2H2O+ C2H4), P5(CH3CHCO+ CH2CHCHO). And the structure parameters of the reactant, products, intermediates and transition states in the reaction processes are also obtained. Their reaction mechanisms can be summarized as the isomerization and dissociation processes, and these processes mainly involve the hydrogen atom transfer, ring-opening and C–C bond cleavages. A reactionchannel in which α-CHD dissociates into cyclopentanone and CO needs lower energy, so it is more advantage our to make dissociation study than other studies. In addition, we think that α-dissociationreaction cannotoccur directly in ground state from our calculations. Based on the UV photolysis experiment of α-CHD with a wavelength of 253.7 nm (112.7 kcal/mol) and the theoretical calculation of potential energy surface in ground state, we obtain that Path 1 (α-CHD→ c-C5H8O+ CO) is the most possible channel, Path 3 (α-CHD→ CH2CHCH2CH2CHO+ CO) is the next, and Path 5(α-CHD→ CH3CHCO+ CH2CHCHO) is the third, while Path 2 (α-CHD→ 2 C2H4+ 2 CO) and Path 4 (α-CHD→ 2 CH2CO+ C2H4) are difficult to be achieved. So c-C5H8O and CO are the major fragment products, CH2CHCH2CH2CHO is the subsidiary one, maybe a minor distribution of CH3CHCO and CH2CHCHO, but the fragments C2H4 and CH2CO are difficult to obtain. This agrees well with the analysis using mass spectrometry in experiment. Results can clarify the microcosmic reaction mechanism of the photodissociation reaction for α-CHD molecule in ground state. It may provide an important reference for realizing its spectrum in-depth. The obtained results are informative for future studies on α-CHD relative.
Research of data retention for charge trapping memory by first-principles
Authors: Jiang Xian-Wei  , Lu Shi-Bin  , Dai Guang-Zhen  , Wang Jia-Yu  , Jin Bo  , Chen Jun-Ning  ,   Anhui Provincial Key Lab of Integrated Circuit Design, School of Electronics and Information Engineering, Anhui University, Hefei 230601, China;,   School of Electronics and Information Engineering, Hefei Normal University, Hefei 230601, China
Published: December 2020

In this paper, the influence of charge trapping memory storage feature is studied by doping the substitutional impurity Al and introducing oxygen vacancy within HfO2. HfO2 is widely used in trapping layer of charge trapping memory, for it belongs to high dielectric constant materials with the abilities to shrink the device size and improve the device performance. Materials studio and Vienna Ab-initio Simulation Package are used to investigate the influence of doping Al on the formation of the oxygen vacancy in HfO2 as a trapping layer. At the same time, the interaction energy of two defects at different distances is calculated. Results show that doping the substitutional impurity Al reduces the formation energy of oxygen vacancies in HfO2, and the reduced formation energy of the three-fold-coordinated O vacancy is larger than that of the four-fold-coordinated O vacancy. After having studied three different defect distances between the substitutional impurity Al and the three-fold-coordinated O vacancy, the results indicate that the system acquires the largest charge trapping energy, the most of quantum states, the smallest population number, and the longest Al–O bond length when the distance between the defects is 2.107 Å. Studying the bond length changes of the three systems after writing a hole, we obtain a result that the change of Al–O bond length is the smallest when the distance between defects is 2.107 Å. In conclusion, the data retention in the trapping layer of monoclinic HfO2 can be improved by doping the substitutional impurity Al. This work will provide a theoretical guidance for the performance improvement in the data retention of charge trapping memory.
Numerical simulation of heat transfer and natural convection of the indirect-driven cryogenic target
Authors: Huang Xin  , Peng Shu-Ming  , Zhou Xiao-Song  , Yu Ming-Ming  , Yin Jian  , Wen Cheng-Wei  ,   Institute of Nuclear Physics and Chemistry, CAEP, P. O. Box 919-988, Mianyang 621900, China
Published: December 2020

ICF design requires smooth and uniform deuterium-tritium (D-T) ice layers in a spherical shell. Thermal environment around the capsule is the key to reach the low-mode ice layer roughness requirement and obtain a high quality ice layer. In this paper, we present the results of three-dimensional simulation for an indirect-driven cryogenic target, focusing on the issues of heat transfer and natural convection flow inside the hohlraum. A thermal and hydrodynamic calculation is first proposed to investigate the convection heat transfer effect on the D-T ice layer. Comparing the two cases with gravity considered or neglected, we find that the temperature variation at the ice layer inner surface caused by the natural convection flow and the hohlraum's structure are of the same order of magnitude. Then the parameters study on Rayleigh number, which is a dimensionless number associated with free convection, is carried out. Thermal simulations on different Rayleigh number are provided. Temperature variation at the D-T ice layer inner surface is to increase as soon as the Rayleigh number reaches 60. Comparisons among different gases under different operating pressure conditions are made. In order to avoid the convection heat transfer effect in a wide range of pressure, it is necessary to take pure helium or mixture gas with a small amount of hydrogen as the tamping gas. The influence of hohlraum's orientation on the natural convection is also studied. It is found that the convective heat transfer effect in a horizontally orientated hohlraum is stronger than that in a vertical one. Based on these, we discuss the possibility to eliminate the convection flow by partitioning the hohlraum into several regions. The calculated results for several cases of different gas-region models indicate that the convection flow can be eliminated with an appropriate division in a vertically orientated hohlaum but cannot in a horizontally orientated one. The conclusions in this paper have certain guiding significance for further design and experiments of cryogenic target.
First-principles study on the hydrogenation of the O2 on TiN4 embedded graphene
Authors: Lu Zhan-Sheng  , Li Yan  , Cheng Ying-Jie  , Li Shuo  , Zhang Xi-Lin  , Xu Guo-Liang  , Yang Zong-Xian  ,   College of Physics and Electronic Engineering Henan, Key Laboratory of Photovoltaic Materials, Xinxiang 453007, China
Published: December 2020

As a kind of clean and high efficient energy conversion devices, the proton exchange membrane fuel cell (PEMFC) is a promising technology for clean and sustainable power generation. Metal-coordinated nitrogen-doped graphene is attractive since its use as a cathode material for the PEMFC. The mechanism of O2 activation and hydrogenation on TiN4 embedded graphene has been investigated in terms of the dispersion-corrected density functional theory (DFT-D) method. It is found that: 1) O2 prefers to stay on top of the Ti atom with the side-on configuration, forming the O-Ti-O three-member ring with an adsorption energy of 4.96 eV. 2) According to the Mulliken atomic charges analysis, the absorbed O2 molecule are negatively charged by 0.60 e in the side-on configuration. 3) Upon the chemisorption of the O2 on TiN4-graphene, there are two possible pathways during the activation of the O2 molecule: dissociation and hydrogenation. In the dissociation pathway, the adsorbed O2 molecule is first dissociated into two O atoms, with a fairly big reaction barrier of 0.95 eV and an endothermic reaction energy of 0.20 eV. Subsequently, the two O atoms are hydrogenated into O+OH with a reaction barrier of 0.40 eV and an exothermic reaction energy of 2.46 eV. In the hydrogenation pathway, the reaction barrier of the hydrogenation of the adsorbed O2 is 0.52 eV. The OOH formed subsequently is dissociated into O+OH with a small reaction barrier of 0.04 eV and an exothermic reaction of 2.14 eV. The hydrogenation pathways of the adsorbed O2 is more preferable, and the corresponding rate-limiting step of this pathway is the hydrogenation of the O2 with a reaction barrier of 0.52 eV and an exothermic reaction energy of 0.64 eV.#br#In summary, the preferable path of the hydrogenation reactions of O2 on TiN4-Graphene is O2(ads)+H(ads) → OOH(ads)→O+OH(ads). Current results may be benefitial to the design of new electrocatalyst materials based on graphene.
Thermal rectification of heterojunction nanotubes
Authors: Wen Jia-Le  , Xu Zhi-Cheng  , Gu Yu  , Zheng Dong-Qin  , Zhong Wei-Rong  ,   Department of Physics and Siyuan Laboratory, College of Science and Engineering, Jinan University, Guangzhou 510632, China
Published: December 2020

Using non-equilibrium molecular dynamics method, we have studied the thermal rectification of heterojunction nanotubes (HCNTs). All of these HCNTs, composed of two 4 nm long carbon nanotubes (CNTs), only have a pentagon-heptagon defects pair. Here the positive direction is defined as the direction where the heat flux flows from the large diameter CNTs to the small diameter CNTs. We have found that the thermal rectification depends on the diameter, the chirality and the temperature.#br#Diameter effect: We fix the diameter on one side and changed it on another side, i.e., the left side of the HCNTs is (3, 3) while the right side of the HCNTs is (n, n), in which n changes from 4 to 9. It is found that the thermal rectification efficiency of HCNTs increases with n (also with the diameter difference). If considering the temperature field of (3, 3)-(4, 4) HCNTs, one can find that there exists a region near the HCNT where the temperature changes sharply. This region when the flux is positive is similar to that when the flux is negative. However, if taking into consideration the (3, 3)-(9, 9) HCNTs, we find that the distribution of temperature field shows different behaviors when the directions of the heat flux are different, and the length of this region becomes longer than (3, 3)-(4, 4). It can be explained that the thermal rectification is caused by different temperature distributions in HCNTs.#br#Chirality effect: We keep the chirality unchanged on one side of HCNTs and change the chirality of the other side, namely, the chirality of the left side of HCNTs are (3, 3) and the right side are (9, 9), (11, 7), (13, 4) and (15, 1), all of their diameters are close to 4.1 Å. We can find that the intersection angle between two CNTs decreases when the right side of HCNTs changes from (9, 9) to (15, 1), and the thermal rectification efficiency will be enhanced. It can be explained that the phonon is scattered and absorbed more effectively at the hetero-junction as the intersection angle decreases.#br#Temperature effect: We have constructed a HCNT (3, 3)-(9, 9) and changed its average temperature from 200 to 400 K. Our results show that the thermal rectification efficiency will be weakened with the rise in average temperature because of increasing heat flux in the negative direction.#br#This research may be helpful to the research in nanoscale thermal diodes, thermal logical gates and controlling heat flux.
Effect of low As pressure annealing on the morphology and reconstruction of GaAs (001)
Authors: Zhou Xun  , Luo Zi-Jiang  , Wang Ji-Hong  , Guo Xiang  , Ding Zhao  ,   School of Physics and Electronics Science, Guizhou Normal University, Guiyang 550001, China;,   School of Education Administration, Guizhou University of Finance and Economics, Guiyang 550004, China;,   College of Science, Guizhou University, Guiyang 550025, China
Published: December 2020

In the low As beam equivalent pressure condition, the in-situ annealing treatment is carried out for the previously atomically flat GaAs(001) βup 2(2×4) reconstruction surface. Utilizing scanning tunneling microscopy, the surface is found to change its morphology simultaneously with the surface reconstruction during the increase of low As beam equivalent pressure annealing time. The surface morphology undergos from ordered flat to disordered flat and then gradually returns to the ordered flat state again. The surface reconstruction turns from βup 2(2×4) to (2×6) and then changes to “zig-zag” (2×6) state. And there is a correlation between the evolution of the surface morphology and surface reconstruction.