bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic simulation of SiyHx structure configuration in a-Si:H thin films
Authors: Zhai Shi-Ming , Liao Huang-Sheng , Zhou Nai-Gen , Huang Hai-Bin , Zhou Lang ,   School of Materials Science and Engineering, Institute of Photovoltaics, Nanchang University, Nanchang 330031, China
Published: December 2020

The hydrogenated amorphous silicon (a-Si:H) film is the core structure of hetero junction with intrinsic thin layer solar cell. Its quality determinates the photoelectric conversion efficiency of this solar cell directly. The configuration of SiyHx is an important structure characteristic of a-Si:H films, and it can influence on the quality of a-Si:H thin films and their application properties. However, it is difficult to study them in depth and detail by the existing analytical and testing methods. In this paper, the structure configuration of SiyHx in a-Si:H /c-Si thin films and the effect of substrate temperature on its content have been simulated and analyzed by molecular dynamics method. A modified Tersoff potential developed by Murty was used to calculate the inter-atomic forces. The results showed that the SiyHx structure in a-Si:H thin films can be summarized into six configurations. Three traditional configurations, including SiH, SiH2 and SiH3, can be referred to as SiHx configurations.The other three nove configurations, including HSi2(s), HSi2(l) and HSi3, can be referred to as HSiy configurations. The main differences between the configurations of HSi2(l) and HSi2(s) are the longer Si—H bonds and bigger bond angle in HSi2(l) configuration than those in HSi2(s) configuration. All of the Si-H bonds in SiHx configurations are strong chemical bonds, while the Si—H bonds in HSiyconfigurations are weak physical bonds. The further calculations of the Si-H bond energies in six configurations have been carried out by the first principle method. According the bond energies results, we can deduce that the order of the stability of six configurations from high to low is SiH > SiH2 > SiH3 > HSi2(s) > HSi2(l) > HSi3. Comparing the Si—H bond energies of the six configurations with the solar energy, it is found that the Si-H bond energy in HSiy configuration is in the range of visible and infrared light in solar light. Si—H physical bonds are easy to fracture in HSiy configuration caused by solar light. This may be the main mechanism of producing Steabler-Wronski (S-W) effect in amorphous silicon thin film cells. In addition, the rise of substrate temperature in the deposition process of a-Si:H films will lead to a significant decrease in the configuration content of all kinds of SiyHx configurations.
Mode control of electrically injected semiconductor laser with parity-time symmetry
Authors: Wang Xue-You , Wang Yu-Fei , Zheng Wan-Hua ,   The CAS Key Laboratory of Solid State Optoelectronics Information Technology, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China,   College of Materials Science and Opto-Electronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China,   College of Future Technology, University of Chinese Academy of Sciences, Beijing 101408, China,   The State Key Laboratory on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
Published: December 2020

The non-Hermitian description is of great significance for open systems, and the Hamiltonian which satisfies parity-time symmetry can make the energy have real eigenvalue within a certain range. The properties of parity-time symmetry have bright application prospects in optical systems. For semiconductor lasers, the parity-time symmetry can be constructed by adjusting the level of electrical injection to help achieve better mode control. Electric injection is easier to realize than optical pump when the device size is small and the structure is complex. Therefore, we hope to analyze the characteristics of the laser that satisfies the parity-time symmetry condition under the condition of electric injection. In this paper, we simulate the effects of different set loss values on parity-time symmetry. It is found that with the increase of set loss value, the imaginary part of the refractive index of the gain cavity corresponding to the parity-time symmetry breaking point so-called exceptional point will decrease, and the imaginary part of the characteristic frequency corresponding to the exceptional point will also decrease. We also simulate the effect of structural size ratio of gain region and loss region on parity-time symmetry. On condition that the total cavity length and the imaginary part of the refractive index of the loss region remain unchanged, as the gain cavity becomes longer and the loss cavity becomes shorter, the imaginary part of the refractive index of the gain cavity corresponding to the exceptional point will increase, and the imaginary part of the characteristic frequency corresponding to the exceptional point will also increase. And we qualitatively explain the above phenomenon through the coupled mode equations. Through experiments, metal organic chemical vapor deposition (MOCVD) and standard lithography techniques are used to fabricate asymmetric ridge lasers. Under thermoelectric cooler (TEC) refrigeration and by controlling the injection level of the gain area, the doubled mode spacing and halved mode number of ridge waveguide are found for the first time due to the parity-time symmetry breaking under the condition of electric injection. We believe that the study of parity-time symmetry in ridge laser under the condition of electric injection will be of great help in implementing the mode control.
Electronic structure and photocatalytic properties of H, F modified two-dimensional GeTe
Authors: Fang Wen-Yu , Zhang Peng-Cheng , Zhao Jun , Kang Wen-Bin ,   School of Public Health and Management, Hubei University of Medicine, Shiyan 442000, Chin,   Hubei Biomedical Detection Sharing Platform in Water Source Area of South to North Water Diversion Project, Shiyan 442000, China
Published: December 2020

Using the first principle calculation based on the density functional theory, we have systematically investigated the structure stability, electronic structure and photocatalytic properties of two-dimensional single-layered GeTe crystal structure modified by H and F. The results show that the lattice constant, bond angle and bond length of GeTe increase after being modified. The stability analysis shows that all the materials have excellent dynamical, mechanical, and thermal stabilities. The electronic structure analysis shows that the two-dimensional GeTe is an indirect bandgap semiconductor with an energy gap of 1.797 eV, and its energy band is mainly composed of Ge-4p and Te-5p, while it is converted into a direct bandgap semiconductor by H or F modification and H-F co-modification (F and Ge on one side, H and Te on the other), and their corresponding energy gaps are reduced to 1.847 eV (fH-GeTe), 0.113 eV (fF-GeTe) and 1.613 eV (hF-GeTe-hH). However, hH-GeTe-hF is still an indirect band gap semiconductor, and its energy gap is reduced to 0.706 eV. The results of the density of states show that part of the Ge-4p and Te-5p electrons are transferred to a deeper level due to the adsorption of H or F atoms, resulting in a strong orbital hybridization between them and the adsorbed atoms. The effective mass shows that the effective mass of H or F modified and H-F co-modified GeTe (F and Ge on one side, H and Te on the other) decrease, and their carrier mobilities increase. The carrier recombination rates of all modified GeTe materials are lower than that of the intrinsic GeTe, so the semiconductor will be more durable. The electron density difference shows that due to the electronegativities of atoms being different from each other, when H or F is used to modify GeTe, some electrons transfer to H and F atoms, resulting in the weakening of covalent bond between Ge and Te atoms and the enhancement of ion bond. The results of band-edge potential analysis show that GeTe can produce hydrogen and oxygen by photolysis of water. However, the valence band edge potential of the modified GeTe decreases significantly, and its oxidation ability increases considerably, the photocatalytic water can produce O2, H2, O3, OH·, etc. Optical properties show that the modified GeTe can enhance the absorption of visible and ultraviolet spectrum, which indicates that they have great application prospects in the field of photocatalysis.
Ion implantation isolation based micro-light-emitting diode device array properties
Authors: Gao Cheng-Hao , Xu Feng , Zhang Li , Zhao De-Sheng , Wei Xing , Che Ling-Juan , Zhuang Yong-Zhang , Zhang Bao-Shun , Zhang Jing ,   Institute of Optoelectronic Engineering, Changchun University of Science and Technology, Changchun 085202, China,   Department of Physics, Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123, China,   Institute of Opto-Electronic, Nanjing University & Yangzhou, Yangzhou 225009, China
Published: December 2020

Compared with conventional light-emitting diode (LED), micro-LED has excellent photo-electric properties such as high current density, light output power density, light response frequency. It has widespread application prospects in the field of light display, optical tweezers, and visible light communication. However, dry etching inevitably leads the sidewall to be damaged, which results in the degradation of device properties. In this letter, a micro-LED array device based on F ions implantation isolation technology is presented to avoid damaging the sidewall. We systemically investigate the influence of fluorine ion implantation energy and light-emitting apertures on the photoelectric properties of the micro-LED array device by testing the current-voltage characteristic and light output power. The investigation results show that comparing with F ion 50 keV single implantation device, the reverse leakage of 50/100 keV double implantation device decreases by 8.4 times and the optical output density increases by 1.3 times. When the light-emitting apertures are different (6, 8, 10 μm respectively), the reverse leakage current remains constant, and the forward operating voltage decreasesfrom 3.3 V to 3.1 V and to 2.9 V with the increase of the aperture. Besides, the available area ratio, i.e. the ratio of actual light-emitting area to device area of single micro-LED with different light-emitting apertures are 85%, 87%, and 92%, respectively. The electrical isolation of the micro-LED array is realized by ion implantation isolation technology, and the micro-LED has some advantages over the conventional mesa etching micro-LED device, such as low reverse leakage current density, high optical output power density, and high effective light-emitting area ratio.
A novel Y2Hf2O7 ceramic cathode applied to high power magnetron tube
Authors: Qi Shi-Kai , Wang Xiao-Xia , Wang Xing-Qi , Hu Ming-Wei , Liu Li , Zeng Wei ,   School of Electronic Engineering, Jiujiang University, Jiujiang 332005, China,   Key Laboratory of High Power Microwave Sources and Technologies, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physics and Optoelectronic Engineering, Xidian University, Xi’an 710071, China
Published: December 2020

Nowadays, the output power and lifetime of a single magnetron are far from the requirements of industrial applications. So the new materials and methods are urgently needed to enhance the output power and prolong the lifetime of the magnetron. As the heart of a magnetron, cathode, whose quality directly affects the output power and lifetime of the magnetron, plays an important role. In order to enhance the output power and prolong the lifetime of the high power magnetron, a method of doping rare earth oxide Y2O3 into transition metal oxide HfO2 is used to prepare Y2Hf2O7 ceramic cathode. The thermionic emission and lifetime characteristics of the Y2Hf2O7 cathode are measured. The results show that the cathode can provide 0.15, 0.2, 0.5, 1.1, 1.8, 2.5, 3.5 A/cm2 current density for the space charge limitation at 1300, 1350, 1400, 1450, 1500, 1550, 1600 ℃br under 300 V anode voltage, respectively. Absolute zero work function of the cathode is only 1.26 eV obtained by the Richardson line method. The effective work function of the cathode is 3.10, 3.15, 3.21, 3.26 eV obtained by the Richardson-Dushman formula at 1450, 1500, 1550, 1600 ℃br respectively. The lifetime of the cathode is more than 4000 h under an initial load of 0.5 A/cm2 at 1400 ℃br, the lifetime which is much longer than the 2000 h average life span for the 2450 MHz continuous wave magnetron cathode used in production. Finally, the molecular structure, surface microstructure, element composition and content of the Y2Hf2O7 ceramic cathode are analyzed by the X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, Auger electron spectroscopy with argon ion etching respectively. The analysis results show that the single Y2Hf2O7 phase forms under the high sintering temperature. When the Y3+ valence Y2O3 is doped into the Hf4+ valence HfO2, the substitutional solid solution will form. An oxygen vacancy is generated in the lattice, thus maintaining the electrical neutrality of the Y2Hf2O7 lattice. During the cathode activating, aging, and thermally testing, the oxygen vacancy is generated fast. The more the obtained oxygen vacancies, the higher the conductivity of the cathode surface will be. Besides, due to the improvement of the electro-conductivity thus enhancing the thermionic emission capability of the cathode, the work function of the cathode can be reduced.
The spring oscillator model degenerated into the coupled-mode theory by using secular perturbation theory
Authors: Zhu Cun-Yuan , Li Chao-Gang , Fang Quan , Wang Mao-Sheng , Peng Xue-Cheng , Huang Wan-Xia ,   School of Physics and Electronic Information, Anhui Normal University, Wuhu 241002, China,   State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
Published: December 2020

In the past few decades, although coupled-mode theory (CMT) has been extensively studied in quantum system, atomic system, plasmon system, circuit system, and so on, the theoretical origin is still plaguing many researchers. In the book of waves and fields in optoelectronics, the second-order differential equations of the simplest LC simple harmonic vibration circuit was turned into the first-order differential equation using the method of variable substitution by Haus. However, there is not loss in the simplest LC simple harmonic vibration circuit, loss term is introduced by qualitative analysis. Although this method of dealing with problems has no problems from a physical point of view, it is not rigorous enough from a mathematical point of view. In this paper, based on the secular perturbation theory, the well-known spring oscillator model is degenerated into two-mode CMT. Starting from the second-order differential equations of the spring oscillator model, the secular perturbation theory is used to obtain first order differential equations of two-mode CMT. The results show the relationships between each term’s coefficients in two-mode CMT and the physical quantities in Classical Mechanics are established by using the secular perturbation theory. Through solving two-mode coupled-mode equations, the energy transfer efficiency has been obtained. To verify the correctness of two-mode CMT, we design a coupled tuning fork mechanical vibration system, which consists of two experimental instruments to provide driving force and receive signals, two tuning forks and springs. The amplitude spectra are measured by an experimental instrument of forced vibration and resonance (HZDH4615), which provides a periodic driving signal for the tuning fork. To clarify the mechanism of the spectra, the numerical fitting has been performed by mathematica software based on the energy transfer efficiency. Theoretically, the obtained fitting parameters can also evaluate some important attributes of the system. The theoretical results are in close correspondence with the experiment. That is to say, two-mode CMT is suitable for classical vibration system.This study provides a more rigorous derivation for each term’s origin in two-mode CMT, and has guiding significance in the theoretical research of linear coupled vibration system.
Synchronization transition from bursting to spiking and bifurcation mechanism of the pre-Bötzinger complex
Authors: Yang Yong-Xia , Li Yu-Ye , Gu Hua-Guang ,   College of Mathematics and Computer Science, Chifeng University, Chifeng 024000, China,   Institute of Applied Mathematics, Chifeng University, Chifeng 024000, China,   School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China
Published: December 2020

The pre-Bötzinger complex is a neuronal network with excitatory coupling, which participates in modulation of respiratory rhythms via the generation of complex firing rhythm patterns and synchronization transitions of rhythm patterns. In the present paper, a mathematical model of single neuron that exhibits complex transition processes from bursting to spiking is selected as a unit, the network model of the pre-Bötzinger complex composed of two neurons with excitatory coupling is constructed, multiple synchronous rhythm patterns and complex transition processes of the synchronous rhythm patterns related to the biological experimental observations are simulated, and the corresponding bifurcation mechanism is acquired with the fast-slow variable dissection method. When the initial values of two neurons of the pre-Bötzinger complex are the same, with increasing the excitatory coupling strength, the theoretical model of the pre-Bötzinger complex shows complete synchronization transition processes from "fold/homoclinic" bursting, to "subHopf/subHopf" bursting, and at last to period-1 spiking. When the initial values are different, with the increases of the excitatory coupling intensity, the rhythm transition processes begin from phase synchronization behaviors including "fold/homoclinic" bursting, "fold/fold limit cycle" bursting, mixed bursting composed of "subHopf/subHopf" bursting and "fold/fold limit cycle" bursting, and "subHopf/ subHopf" bursting in sequence, and to anti-phase synchronous behavior of the period-1 spiking. The complete (in-phase) synchronous period-1 spiking for the same initial values exhibits bifurcation mechanism different from the anti-phase synchronous period-1 spiking for different initial values. The anti-phase synchronous period-1 spiking presents a novel and abnormal example of the synchronization at large excitatory coupling strength, which is different from the traditional viewpoint that large excitatory coupling often induces in-phase synchronous behavior. The results present the synchronization transition process and complex bifurcation mechanism from bursting to period-1 spiking of the pre-Bötzinger complex, and the abnormal synchronization example enriches the contents of nonlinear dynamics.
Numerical analysis on flow and heat transfer of supercritical CO2 in horizontal tube
Authors: Yan Chen-Shuai , Xu Jin-Liang ,   Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy, North China Electric Power University, Beijing 102206, China
Published: December 2020

In the present study, the three-dimensional steady-state numerical simulation has been performed by using ANSYS Fluent15.0 with SST k-ω low Reynolds turbulence model to study flow and heat transfer characteristics for supercritical CO2 in the horizontal straight tube with inner diameter di = 22.14 mm and heating length Lh = 2440 mm under heating condition. The reliability and accuracy of the numerical model was verified by the experimental data of flow and heat transfer of supercritical CO2 in horizontal tube. Firstly, flow and heat transfer characteristics of supercritical CO2 was studied in horizontal tube. Based on the assumption that the supercritical CO2 will undergoes “phase transition” between liquid-like and vapor-like at pseudocritical temperature Tpc, the differences between top generatrix and bottom generatrix of horizontal tube at flow and heat transfer behaviors were revealed. The results show flow and heat transfer characteristics of supercritical CO2 in horizontal tube are similar to those under subcritical pressure. Then, the influences of heat flux qw and mass flux G on flow and heat transfer of supercritical CO2 were analyzed. The higher heat flux qw is or the smaller mass flux G is, the higher inner wall temperature Tw,i at top generatrix is. The reasons for difference in the distribution of inner wall temperature Tw,i at top generatrix under different heat flux qw and mass flux G were explained by capturing detailed information about thermophysical properties distribution including specific heat at constant pressure cp and thermal conductivity λ, axial velocity distribution and turbulent kinetic energy distribution in the fluid domain. It is observed that vapor-like film thickness δ, vapor-like film property characterized by specific heat at constant pressure cp and thermal conductivity λ, axial velocity u and turbulent kinetic energy k are the main factors affecting the difference in inner wall temperature distribution at top generatrix. The present work can provide a theoretical guidance for design and safe operation of heat exchanger for supercritical CO2 Brayton cycle.
A method of controlling adaptive optical system combined with image restoration technology
Authors: Yong Jia-Wei , Tian Yu , Xu Ke-Feng , Rao Chang-Hui ,   Key Laboratory on Adaptive Optics, Chinese Academy of Sciences, Chengdu 610209, China,   Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China,   Institute of Software, Chinese Academy of Sciences, Beijing 100190, China,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In the field of astronomical high resolution imaging, adaptive optical correction and image restoration are necessary, and these two techniques can be used either separately or jointly to improve the quality of observed images. However, for a long time, adaptive optics and image restoration technology have been developing independently because they belong to different research fields, and even though they are combined together, it is just a simple splicing of the two technologies, with no crossover between the two. Such a control method results in adaptive optical correction producing only the best possible intermediate result—optical imaging, but is out of control for the final result—restored image. Therefore, it is of great significance to study a control method that combines the two methods in order to obtain the high-quality restored image. In this paper, the traditional hybrid method (adaptive optics + image post-deconvolution) is analyzed and its defects are expounded. The idea of combining adaptive optics and image restoration for system analysis is proposed for the first time, and the concept of correction degree of deformable mirror (the scaling ratio of control voltage of deformable mirror to that of traditional control voltage) is proposed. By changing the degree of correction, the correction residual of the deformation mirror and the detection error of the wavefront sensor can be adjusted. It is proved that there exists an optimal value of the quality of the reconstructed image in the direction of reducing correction degree, and a new control method is obtained by using the optimal correction degree to correct the control voltage of the deformation mirror. For the application in point target imaging, the simulations are carried out with 37-element and 61-element deformable mirrors under several typical wavefront aberrations, and the results show that this method can obtain a better restoration image than traditional methods. This method has more potential applications in adaptive optical systems with large fitting residuals. The idea that adaptive optics and image restoration are considered as a whole, has not been reported in the literature before, so the work of this paper provides a new way of thinking for the research in related fields.
Influence of microcavity effect on the performance of top emission tandem blue organic light emitting devices
Authors: Zhang Juan , Jiao Zhi-Qiang , Yan Hua-Jie , Chen Fu-Dong , Huang Qing-Yu , Kang Liang-Liang , Liu Xiao-Yun , Wang Lu , Yuan Guang-Cai ,   Beijing Oriental Science and Technology Group Co. Ltd., Beijing 102600, China
Published: December 2020

Comparing with traditional single organic light-emitting device (OLED), the luminance efficiency and lifetime of tandem OLED are significantly improved. Therefore, it is of crucial importance to in depth study the influence of microcavity effect on the performance of top emitting tandem OLED. In this paper, taking the blue organic light emitting device for example, the change rule of optical and electrical properties of top-emitting tandem blue-light device are studied by combining optical simulation with practical experiments. The specific experiment is as follows. The top emitting tandem blue organic light devices are fabricated, in which the two light-emitting layers are located at the first anti node and second anti node, the second anti node and third anti node, and the third anti node and fourth anti node in the optical structure of the device respectively. It is found that the performance of the device is better when the two emitting layers of the top-emitting tandem blue light device are located at the second anti node and third anti node in the optical structure of the device respectively. That is to say, when the current density of the device is 15 mA/cm2, the current efficiency of the device reaches 10.68 cd/A, color coordinate (CIEx, y) of the device is (0.14, 0.05), and the time of the brightness decreases from 100% to 95% in 1091.55 hours, which is likely to be due to the fact that when the cavity length of the device is long, it can not only improve the recombination rate of hole and electron in the first light-emitting unit, weaken the surface plasmon polarition effect, reduce the influence of the fluctuation of the film thickness on the cavity length of the device, but also play a role of wrapping partials to a certain extent, improve the efficiency and prolong the device lifetime. The research results provide an important theoretical and data basis for designing the top-emitting tandem blue light device with high efficiency and long lifetime. In the future, we will continue to systematically and detailedly study the top emitting tandem organic light-emitting devices, which will provide strong support for preparing the laminated devices with high efficiency long-lifetime, and lower cost.
Analytical algorithem of stretcher dispersion in chirp pulse amplification laser system
Authors: Wang Nan , Ruan Shuang-Chen ,   College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China,   Shenzhen Key Laboratory of Laser Engineering, Shenzhen University, Shenzhen 518060, China,   Key Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   Shenzhen Technology University, Shenzhen 518118, China
Published: December 2020

Dispersion control is one of many key techniques in ultrashort laser pulse generation and its applications. By controlling the optical path of wavelength in the laser pulse to generate relative time delay, the pulse width of laser can be changed. The stretcher is the optical scheme to broaden the pulse width in chirp pulse amplification. By using ray trace, the pulse stretch time can be evaluated. However, due to the complicated formula of optical path in stretcher, it is difficult to obtain an analytical expression of high-order dispersion by using direct derivative. In this case, the present numerical methods are commonly used and error would be introduced into the optical system design and optimization inevitably. In this paper we introduce an analytical algorithm of stretcher dispersion. By summarizing the characteristic of stretcher formula, four fundamental functions are introduced to help to calculate the analytical derivative. By substituting the separate terms of the expressions step by step, analytical calculation of stretcher dispersion can be realized. In this paper, the ray trace of Martinez stretcher is first introduced to achieve similar phase expressions to them of existing Offner stretcher, then accurate high order dispersion results are attained by using analytical method, finally the calculation results by using the analytical method and numerical method are compared with each other. The algorithm introduced into this paper for calculating the dispersion is practical and hopeful in designing the chirp pulse amplification laser systems.
Highly efficient all-phosphorescent white organic light-emitting diodes with low efficiency roll-off and stable-color by managing triplet excitons in emissive layer
Authors: Xiao Xin-Ming , Zhu Long-Shan , Guan Yu , Hua Jie , Wang Hong-Mei , Dong He , Wang Jin ,   Jilin Engineering Vocational College, Siping 136001, China,   Key Laboratory of Functional Materials Physics and Chemistry of Ministry of Education, College of Information & Technology, Jilin Normal University, Siping 136000, China
Published: December 2020

White organic light-emitting diodes (WOLEDs) have drawn considerable attention for next-generation lighting and display applications owing to their remarkable advantages. Phosphorescent OLED technology is crucial to realize high-efficiency white OLEDs because phosphorescent emitters enable to achieve almost 100% internal quantum efficiency (IQE) by harvesting all the excitons of 75% of triplets and 25% of singlets. However, an efficiency roll-off at high-brightness and a shift in color under various operation biases remains challenges. With the goal towards commercial applications, it requires WOLEDs should simultaneously realize high efficiency at high-brightness region over 1000 cd/m2 and good color stability over a wide electroluminescent range. In this paper, we first investigated the energy transfer process between the blue-emitting Bis (3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium (III) (Firpic) and the orange emitting Iridium (III) bis(4-(4-tert-butylphenyl)thieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01-TB), in addition to the behavior of the carrier trapping in the phosphorescent OLEDs with double emissive layers. Then we successfully fabricated phosphorescent WOLED with multiple emissive layers. The resulting phosphorescent WOLED achieves the maximum forward-viewing current efficiency (CE) of 34.6 cd/A and external quantum efficiency (EQE) of 13.5%, and the CE and the EQE remain 33.9 cd/A and 13.3% at 1000 cd/m2, respectively, indicating that the WOLED exhibits low efficiency roll-off. Furthermore, the WOLED shows very stable white emission with small Commission Internationale de L’Eclairage (CIE) coordinate varying range of (0.016, 0.011) from 1000 to 10000 cd/m2. The results provide a promising avenue to simultaneously achieve high efficiency, lower the efficiency roll-off at high brightness and color-stability for phosphorescent WOLEDs by carefully designing the device architecture to redistribute the charge carriers and excitons in the recombination zone.
Theoretical study on thermodynamic properties of NO gas
Authors: Jian Jun , Lei Jiao , Fan Qun-Chao , Fan Zhi-Xiang , Ma Jie , Fu Jia , Li Hui-Dong , Xu Yong-Gen ,   Key Laboratory of High Performance Scientific Computation, School of Science, Xihua University, Chengdu 610039, China,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, College of Physics and Electronics Engineering, Shanxi University, Taiyuan 030006, China
Published: December 2020

Nitric oxide (NO) is one of atmospheric molecules of interest and has attracted considerable attention due to its important role in the chemical process taking place in a flow field of hypersonic vehicle, in which the thermodynamic properties are required in the calculation of the aerothermodynamic flow field. Moreover, the total internal partition function is the key to calculating the thermodynamic properties of high-temperature gases. For diatomic molecules, according to the product approximation, the total internal partition function is split into three parts: electronic, vibration and rotation partition function. In this paper, by using the quantum statistical ensemble theory based on some classical thermodynamic and statistical formulae, the thermodynamic properties of NO are analyzed and discussed.

Firstly, in order to obtain an accurate energy of molecule, the variational algebraic method (VAM) is employed to calculate the full vibrational energy, the resultis in good agreement with the experimental result and thus yielding the realistic predictions of the unobserved higher vibrational energy that converges to the dissociation limit. Secondly, an attempt is to use the full VAM vibrational energy, the Rydberg-Klein-Rees (RKR) vibrational energy, the simple Harmonic oscillator (SHO) model and the quantum-mechanical vibrational energy obtained by the multiconfiguration self-consistent-field (MCSCF) to calculate the vibrational partition function. Then, with the rotational contributions from the Müller-McDowell formula, the internal partition function can be determined by combining the product of electronic, vibration and rotation partition functions. Thirdly, according to the thermodynamic and statistical formulae, it is easy to calculate the internal energy, entropy and heat capacity for the NO molecule in a range of 1000－5000 K. Comparison of different calculated heat capacities with the experimental ones reveals the heat capacity, of which vibrational contributions determined by the full VAM vibrational energy accord better with the experimental ones, with the maximum relative error being no more than 2.4%, whereas it can be seen that those thermodynamic results evaluated from the SHO model attest to a failure for the summation of infinite vibrational energy. The thermodynamic results of NO may have proper applications in areas that can be of great importance in theoretical and (or) experimental aspects.
Pressure-induced rapid solidification of polyphenylene sulfide melt
Authors: Wang Zhi-Fei , Wang Lu , Wang Ju , Liu Xiu-Ru ,   School of Physical Science and Technology, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China
Published: December 2020

In this work, pressure-induced rapid solidification of polyphenylene sulfide (PPS) melt is studied on a pressure-jump apparatus. Five PPS samples under a pressure of 0.1 GPa are heated to 563 K, 573 K, 583 K, 603 K and 613 K, respectively. These samples are rapidly compressed to 2.4 GPa in about 20 ms. The solidified samples are quenched to room temperature and then depressured to ambient pressure. The X-ray diffraction (XRD) analyses of the recovered samples indicate that three PPS samples, prepared at 563 K, 573 K and 583 K, contain crystal phases but their crystallinity is lower than that of the original PPS powder. The remaining two PPS samples, prepared at 603 K and 613 K, are in amorphous state but do not sharp crystal diffraction peaks in the XRD patterns. Differential scanning calorimetry curves of the five PPS samples each display an endothermic step of glass transition at about 325 K and an exothermic peak of recrystallization around 360 K. The glass transition temperature decreases roughly with the increase of preparation temperature. The thermal enthalpy of recrystallization process increases with the increase of preparation temperature, indicating that the content of amorphous phase increases. We speculate that the recovered samples are in a “frozen state” of their parent liquid. At 563 K, 573 K and 583 K, the crystalline phases partially melt. More crystal phases melt with the increase of preparation temperature. The molten part is rapidly solidified into amorphous phase. At a temperature higher than 603 K, the crystalline phase fully melts, and after being rapidly compressed, amorphous PPS sample is obtained. For the amorphous PPS sample prepared at 613 K, we investigate whether the interior of this amorphous PPS sample is also in amorphous state. Micro XRD analysis indicates that the central part of the PPS sample is also in amorphous state, which suggests that this PPS sample is of a fully amorphous bulk. For the amorphous PPS sample prepared at 613 K, we investigate its recrystallization product. After being annealed at 425 K for 2 h, the amorphous phase, which is solidified from the melt of crystal phase, is recrystallized into the orthorhombic crystal phase. The results in this work indicate that the rapid compression can inhibit the PPS melt from being crystalized, so, it is a way to prepare amorphous PPS bulk. Since the solidification of polymer melt is realized by increasing pressure instead of quenching and is not limited by polymer thermal conductivity, it is a promising way to prepare amorphous polymer bulks with large size.
Simulation of nonlinear Cahn-Hilliard equation based on local refinement pure meshless method
Authors: Ren Jin-Lian , Jiang Rong-Rong , Lu Wei-Gang , Jiang Tao ,   School of Mathematical Sciences, Yangzhou University, Yangzhou 225002, China,   School of Hydraulic Science and Engineering, Yangzhou University, Yangzhou 225002, China
Published: December 2020

The phase separation phenomenon between different matters plays an important role in many science fields. And the high order nonlinear Cahn-Hilliard (C-H) equation is often used to describe the phase separation phenomenon between different matters. However, it is difficult to solve the high-order nonlinear C-H equations by the theorical methods and the grid-based methods. Therefore, in this work the meshless methods are addressed, and a local refinement finite pointset method (LR-FPM) is proposed to numerically investigate the high-order nonlinear C-H equations with different boundary conditions. Its constructive process is as follows. 1) The fourth derivative is decomposed into two second derivatives, and then the spatial derivative is discretized by FPM based on the Taylor series expansion and weighted least square method. 2) The local refinement and quintic spline kernel function are employed to improve the numerical accuracy. 3) The Neumann boundary condition with high-order derivatives is accurately imposed when solving the local linear equation sets. The 1D/2D C-H equations with different boundary conditions are first solved to show the ability of the LR-FPM, and the analytical solutions are available for comparison. Meanwhile, we also investigate the numerical error and convergence order of LR-FPM with uniform/non-uniform particle distribution and local refinement. Finally, 1D/2D C-H equation without analytical solution is predicted by using LR-FPM, and compared with the FDM result. The numerical results show that the implement of the boundary value condition is accurate, the LR-FPM indeed has a higher numerical accuracy and convergence order, is more flexible and applicable than the grid-based FDM, and can accurately predict the time evolution of nonlinear diffusive phase separation phenomenon between different materials time.
Research on few-mode PAM regenerator based on nonlinear optical fiber loop mirror
Authors: Wang Yu-Hao , Wu Bao-Jian , Guo Biao , Wen Feng , Qiu Kun ,   Key Laboratory of Optical Fiber Sensing and Communication, Ministry of Education, School of Information & Communication Engineering, University of Electonic Science and Technology of China, Chengdu 611731, China
Published: December 2020

In recent years, the demand for network bandwidth has increased significantly, and the capacity of wave division multiplexing (WDM) systems has reached the nonlinear Shannon limit. In order to adapt to the development of future networks, space division multiplexing (SDM) technology attracts more and more attention. In this paper, we put forward a novel structure of pulse amplitude modulation(PAM) regenerator based on few-mode nonlinear optical fiber loop mirror (FM-NOLM) for the first time, and theoretically analyze the working principle for few-mode reshaping. It can regenerate degraded PAM signals and improve transmission performance in SDM system. The detailed design steps of the regenerator are given, in which the sulfide highly nonlinear fiber and multimode coupler are used to build up the FM-NOLM and their mode characteristics are simulated by COMSOL software. The parameters of the regenerator are determined by taking the few-mode optical fiber supporting LP01, LP11, and LP21 modes as an example, and then the power transfer function (PTF) curve of each mode for PAM signals is calculated. We simulate and analyze the noise reduction ratio (NRR) performance of the few-mode regenerator for PAM-4 signals, and compare with the case of single mode fiber. Our simulation shows that: (1) for each spatial mode of PAM signal, all regenerative levels have the same consistent power transfer performance; (2) for the input signal-to-noise ratio (SNR) greater than 20 dB, the NRR for each mode can exceed 3 dB, and increase with the input SNR at the slope of about 1.2; (3) the NRR difference between the three modes is less than 1.1 dB for the same input SNR. In order to illustrate the reshaping function of the regenerator, we also present the power distribution histograms for PAM-4 signals before and after regeneration when the input SNR is 25 dB. This scheme proposed here has some advantages over the existing regenerators in the applicability for the long-haul SDM system with high spectral efficiency and regeneration of any level number of PAM signals in theory due to its uniform multi-level regeneration function, but also is capable of being extended to the wavelength domain for higher transmission capacity.
Efficient angle and polarization parameter estimaiton for electromagnetic vector sensors multiple-input multiple-output radar by using sparse array
Authors: Xie Qian-Peng , Pan Xiao-Yi , Chen Ji-Yuan , Xiao Shun-Ping ,   State Key Laboratory of Complex Electromagnetic Environment Effects on Electronics and Information System, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In this paper, a new sparse transmitting and receiving array is designed to improve the joint angle and polarization parameter estimation performance for bistatic electromagnetic vector sensors Multiple-Input Multiple-Output radar. Firstly, large array aperture can be obtained with the aid of the sparse transmitting and receiving array. Then, an effective third-order tensor model is constructed in order to make full use of the multidimensional space-time characteristics of output data after matching filtering. And, the Parallel Factor trilinear alternating least square algorithm is proposed to deal with the constructed third-order tensor model, which can yield closed-form automatically paired two dimensional Direction of Departure and two dimensional Direction of Departure estimation without additional angle pair matching process. Furthermore, two sets of high accuracy rotation invariance relationships corresponding to transmit elevation angle and receive elevation angle can be achieved by using the estimated transmit steering vector matrix and receive steering vector matrix. After the accuracy transmit elevation angle and receive angle are obtained, the corresponding transmitting and receiving azimuth angle, polarization angle and polarization phase difference can be accurately estimated by using the vector-cross-product algorithm. Compared with existing algorithms, the proposed algorithm can avoid high dimensional eigenvalue decomposition and additional parameter matching process. Moreover, the high estimation performance of the proposed can be further guaranteed by using the designed sparse array. Finally, simulation results demonstrate the effectiveness and superiority of the proposed method in terms of estimation accuracy and angle resolution.
The physics-based model of AlGaN/GaN high electron mobility transistor outer fringing capacitances
Authors: Liu Nai-Zhang , Zhang Xue-Bing , Yao Ruo-He ,   School of Electronics and Information Technology, South China University of Technology, Guangzhou 510640, China
Published: December 2020

 With the development of the application of AlGaN/GaN high electron mobility transistors in the radio frequency field, a capacitance model that can accurately describe the C-V characteristics of the device has become an important research topic. The gate capacitance of GaN HEMT can be divided into two parts: intrinsic capacitance and fringing capacitance related to two-dimensional electronic gas (2DEG) electrode. The fringing capacitance plays an important part in the switching device. The outer fringing capacitance Cofs/d dominates the fringing capacitance and is affected by the bias applied, especially the drain outer fringing capacitance Cofd.

 In order to establish the Cofd model which is related to the bias condition, the physics-based model of Cofd is established based on the conformal mapping, including the drain channel length variable. Since the drain channel length is related to the bias applied, the channel length modulation effect can be used to study how bias apllied effect the channel, and the relationship between Cofd and the bias condition is obtained. In addition, the threshold voltage variable is introduced when the channel length modulation effect is considered, and the threshold voltage drift caused by changes in the internal parameters and temperature of the device is studied using the threshold voltage variable in the model, and the relationship between Cofd and threshold voltage and temperature under different bias was obtained.

 It is found from the results of the study that as drain bias increases from zero, the channel length modulation effect keeps Cofd unchanged at lower drain bias. When the drain bias continues to increase, Cofd begins to decay again, and its decay rate slows down with the increase of gate bias. The decrease of donor impurity concentration and Al component in AlGaN barrier layer may increase the threshold voltage, which will strengthen the channel length modulation effect on Cofd, resulting in linear attenuation of Cofd. With the increasing of drain bias, the influence of threshold voltage shift on Cofd is enhanced, and the change of device operating temperature will enhance the threshold voltage shift and cause the deviation of Cofd. Moreover, with the continuous increase of drain bias, Cofd becomes more sensitive to the temperature variation.