bluuebunny/crossref_metadata_2025 huggingface dataset:
Ag@SiO2 coupled structure’s design and regulation and control of response to thin film solar cells
Authors: Gong Bu-Qing , Chen Xiao-Yu , Wang Wei-Peng , Wang Zhi-Ye , Zhou Hua , Shen Xiang-Qian ,   School of Physical Science and Technology, Xinjiang University, Urumqi 830046, China,   School of Physics, Shandong University, Jinan 250100, China
Published: December 2020

The coupled nano-structure Ag@SiO2 has both plasmon excitation like metallic nanoparticles and diffraction scattering like a dielectric nanosphere, which effectively controls the propagation path and the energy distribution of incident light and shows great potential applications in light trapping for thin film solar cells. In this work, we construct a three-dimensional electromagnetic model based on the finite-difference time-domain (FDTD) and rigorous coupled-wave analysis (RCWA) method to investigate the regulation mechanism of Ag@SiO2 coupling structure to the spectral response of amorphous silicon cells. By being optimally designed, a high-efficiency cell device is achieved. The results show that the transmitted light into the active layer reaches a maximum value when Ag and SiO2 have their feature sizes of 18 and 150 nm, respectively. The absorption spectrum of the corresponding cell device also arrives at its maximum value. The photoelectric conversion efficiency is enhanced from 7.19% to 7.80%, with an increment of 8.48% compared with the flat solar cell with an equivalent thickness of absorbing layer.
High sensitivity fiber displacement sensor based compound ring laser cavity with linear variation of beat frequency signal
Authors: Tian Jing , Hou Mei-Jiang , Jiang Yang , Zhang Hong-Xu , Bai Guang-Fu , Feng Hao ,   College of Physics, Guizhou University, Guiyang 550025, China
Published: December 2020

A novel fiber sensor based compound ring laser cavity with linear variation of frequency is proposed and demonstrated experimentally. The compound ring laser cavity is comprised of a ring cavity and a straight cavity. This system can generate the beat frequency spectrum by employing an erbium doped fiber amplifier, a fiber Bragg grating is used as a sensor head and the straight cavity reflector, a π phase shifted fiber Bragg grating serves as a microwave photonic passband filter. The principle of the proposed sensor is theoretically analyzed, showing that as the displacement increases the beat frequency decreases, and there exists a linear relationship between displacement change and beat frequency shift. In experiment, it is shown that the sensor has a high sensitivity of about 86.19 kHz/mm and can achieve a good linear response (R2 = 0.9973), and that the minimum monitored displacement is about 10 μm. The measurement results demonstrate that the sensor is accurate, sensitive, and the proposed sensor system has a compact and simple structure, which makes it convenient for more applications in future.
Biosonar emission characteristics and beam control of odontocetes
Authors: Song Zhong-Chang , Zhang Yu , Wei Chong , Yang Wu-Yi , Xu Xiao-Hui ,   Key Laboratory of Underwater Acoustic Communication and Marine Information Technology of the Ministry of Education, College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China,   Centre for Marine Science and Technology, Curtin University, GPO Box U1987, Perth WA 6845, Australia
Published: December 2020

Odontocetes have evolved for millions of years to own a unique echolocation system. The exceptional performance of odontocetes echolocation system can provide reference to artificial sonar systems, acoustic metamaterials and sound control designs. Research on odontocetes biosonar requires interdisciplinary effort, including acoustics, biology, biomimetics, anatomy, physiology and signal analysis. In this paper, we review odontoctes’ biosonar emission process from aspects of anatomy, biosonar signal and beam formation. To begin, computed tomography scanning and untrasound measurements are combined to reconstruct the sound speed and density distributions. To follow, efforts are thrown to probe into the biosonar signal and its corresponding acoustic behavior. Numerical simulations are used to investigate the odontocetes’ biosonar beam formation. The secret of exceptional performance of odontocetes’ echolocation system lies in their unique anatomy. Odontocete integrates acoustic structures with different acoustic impedances, namely solid bony structures, air space and soft tissues as a whole emission system to efficiently modulate sound propagation and sound beam formation. These acoustic structures are well organized in the forehead, forming a natural acoustic metamaterial to perform a good control of sounds. These results can enlighten artificial sonar designs.
Monte Carlo simulation on the adsorption of polymer chains on polymer brushes
Authors: Wang Chao , Zhou Yan-Li , Wu Fan , Chen Ying-Cai ,   Department of Physics, Taizhou University, Taizhou 318000, China
Published: December 2020

 The adsorption of polymer on surface is a hot topic in physical, chemical and biological communities, which is influenced by many factors, such as the topological structure and the flexibility of the polymer, the attractive interaction between the polymer and the surface, the detailed structure of the surface, etc. The adsorption of polymers on solid surfaces is extensively studied, while the adsorption behaviors of polymers on soft surfaces are still unclear.

 In this work, the static and dynamical characters of the adsorption of a free polymer chain on polymer brushes are studied by using Monte Carlo simulation. The brush is formed by grafted polymers with length Nb and distance d. Results indicate that, with increasing the adsorption energy (ε) between the free polymer and the brush, the free polymer shows a phase transition from a desorbed state to an adsorbed state. Based on the dependence of the number of the adsorption segment of the free polymer (mad) on the adsorption energy ε, we defined the critical adsorption point (εC) where the phase transition occurs. εC is nearly independent of the length of the free polymer, but it increases with decreasing the length of the grafted polymer or increasing the distance between the grafted polymers. When ε < εC, the free polymer is desorbed and its size is the same as that in free space. When ε ≈ εC, the free polymer is sucked into the brush and meanwhile the size is compressed. While when ε \begin{document}$\gg $\end{document} εC, the free polymer is strongly adsorbed on the surface of the brush and forms a quasi two-dimensional conformation, and meanwhile the whole adsorption process contains two stages: the adsorption process of the free polymer and the diffusion process of the brush. Moreover, with the increase of ε, the diffusion of the free polymer shows an obvious transition from the normal model to the sub-diffusion model near εC. The transition of the diffusion model maybe useful for separation of polymers with different attractive polymer-brush interactions. For example, one may construct a brush surface and use it as a polymer separation device. Under weak driving force parallel to the surface, polymers with polymer-brush interaction ε < εC can move quickly, while polymers with ε > εC will move slowly or be trapped on the brush.
Theoretical and computational methods of protein liquid-liquid phase separation
Authors: Zhang Peng-Cheng , Fang Wen-Yu , Bao Lei , Kang Wen-Bin ,   School of Public Health and Management, Hubei University of Medicine, Shiyan 442000, China,   Hubei Biomedical Detection Sharing Platform in Water Source Area of South to North Water Diversion Project, Shiyan 442000, China
Published: December 2020

Liquid-liquid phase separation (LLPS) of proteins is an emerging field in the research of biophysics. Many intrinsically disordered proteins (IDPs) are known to have the ability to assemble via LLPS and to organize into protein-rich and dilute phases both in vivo and in vitro. Such a kind of phase separation of proteins plays an important role in a wide range of cellular processes, such as the formation of membraneless organelles (MLOs), signaling transduction, intracellular organization, chromatin organization, etc. In recent years, there appeared a great number of theoretical analysis, computational simulation and experimental research focusing on the physical principles of LLPS. In this article, the theoretical and computational simulation methods for the LLPS are briefly reviewed. To elucidate the physical principle of LLPS and to understand the phase behaviors of the proteins, biophysicists have introduced the concepts and theories from statistical mechanics and polymer sciences. Flory-Huggins theory and its extensions, such as mean-field model, random phase approximation (RPA) and field theory simulations, can conduce to understanding the phase diagram of the LLPS. To reveal the hidden principles in the sequence-dependent phase behaviors of different biomolecular condensates, different simulation methods including lattice models, off-lattice coarse-grained models, and all-atom simulations are introduced to perform computer simulations. By reducing the conformational space of the proteins, lattice models can capture the key points in LLPS and simplify the computations. In the off-lattice models, a polypeptide can be coarse-grained as connected particles representing repeated short peptide fragments. All-atom simulations can describe the structure of proteins at a higher resolution but consume higher computation-power. Multi-scale simulation may provide the key to understanding LLPS at both high computational efficiency and high accuracy. With these methods, we can elucidate the sequence-dependent phase behaviors of proteins at different resolutions. To sum up, it is necessary to choose the appropriate method to model LLPS processes according to the interactions within the molecules and the specific phase behaviors of the system. The simulations of LLPS can facilitate the comprehensive understanding of the key features which regulate the membraneless compartmentalization in cell biology and shed light on the design of artificial cells and the control of neurodegeneration.
Drift wave in strong collisional dusty magnetoplasma
Authors: Yang Jian-Rong , Mao Jie-Jian , Wu Qi-Cheng , Liu Ping , Huang Li ,   School of Physics and Electronics, Shangrao Normal University, Shangrao 334001, China,   Engineering Technology Research Center of Intelligent Electric Vehicle Components of Jiangxi Province, Shangrao 334001, China,   College of Electron and Information Engineering, University of Electronic Science and Technology of China Zhongshan Institute, Zhongshan 528402, China
Published: December 2020

The study about the wave mechanism of magnetized dusty plasmas has important value to related experiment, industrial processing and exploring celestial space. The linear and nonlinear fluctuation characteristics of the nonuniform magnetized dust plasma system are researched in this paper. For the homogeneous external magnetic field and the nonuniform environment with density and temperature gradients, a two-dimensional nonlinear dynamic magnetoplasma equation is derived considering the strong impact between dust and neutral particles. The linear dispersion relation is obtained by the linearized method. There are both the damping wave causing by strong collision and the harmonic wave by particle drift. Employing the typical numerical parameters for analysis, the results display that the quantum parameter modifies the system lengths; the real wave frequency is proportion to the drift frequency; the imaginary wave frequency has complex relationship with the collision frequency between dust and neutrals, and the collision of particles causes the dissipation effects to the system. Besides, the analytical solutions of drift shock wave and explosive wave are solved by function change method. The variation about the electrostatic potential with the main physical parameters is discussed in detail. It is shown that the strength of the electrostatic shock wave and the width of the explosive wave increase with increasing the dust density and magnetic field intensity, decrease with increasing the collision frequency, change with the drift velocity. When the space-time phase is small, the electrostatic potential changes quickly; once big enough, the potential tends to be stable value and reaches stable state eventually. Finally, the stability of the system is discussed. It is found that the dusty charge, quantum parameter, drift velocity all appear in the disturbed solution. All these results in the paper show that the strong collision effect, quantum effect, particle drift and magnetic field all play important role to the generation, evolution and stability of drift waves.
Evolutionary dynamics of single-multiple columns in atmospheric helium dielectric barrier discharge
Authors: Wan Hai-Rong , Hao Yan-Peng , Fang Qiang , Su Heng-Wei , Yang Lin , Li Li-Cheng ,   School of Electric Power, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Dielectric barrier discharge is widely used as a low-temperature plasma source in industry. Columnar discharge is an important form of dielectric barrier discharge. However, its discharge theory has not been clear yet. In this paper, the dielectric barrier discharges in helium at atmospheric pressure are carried out between parallel dielectric barrier electrodes to study the evolutionary dynamics of single-multiple columns. By reducing the applied voltages to a value lower than the initial discharge voltage, the pattern of the columnar discharge evolves from a single column into multiple columns. Discharge images from the bottom are taken to observe the evolution of discharge and measure the diameter of discharge column and spacing between columns. The applied voltage, the Lissajous figure, the discharge current, and the discharge transferred charge are measured in order to calculate the Coulomb force and the magnetic field force exerted on the column by the other columns. It is found that in columnar discharge, there is a dynamic evolution process that the single columnar discharge evolves into the two-layered columnar discharge when the applied voltage slightly decreases instantaneously. On the one hand, the column diameter is different in different layer: the column diameter increases from the center to the outer layer. On the other hand, as the applied voltage decreases, the diameter of the center column grows and the spacing between the center column and its adjacent column decreases. The calculations show that the Coulomb force is far greater than the magnetic field force when the evolution is stable, which indicates that, as mentioned in the established knowledge, there is a confinement potential to balance the Coulomb force, thereby keeping the distribution of discharge columns stable. Furthermore, the results also show that the Coulomb force on the discharge columns at different voltage and position is different. The strength of Coulomb force on column is different at different layer: it decreases from the outermost layer to the center column, which is zero on the center column. Based on the balance between the Coulomb force and the confinement potential in columnar discharge, it is suggested that the strength of the latter may also follow the same law. In addition, as the applied voltage decreases, the charges accumulated on the surface of the dielectric and the number of discharge columns both increase, which results in the increase of the maximum of the Coulomb force. The confinement potential may increase as well and follow the same law.
Preparation and characteristics of ultra-wide Ga2O3 nanoribbons up to millimeter-long level without catalyst
Authors: Qi Qi , Chen Hai-Feng , Hong Zi-fan , Liu Ying-Ying , Guo Li-Xin , Li Li-Jun , Lu Qin , Jia Yi-Fan ,   Key Laboratory of Advanced Semiconductor Devices and Materials, School of Electronic Engineering, Xi’an University of Posts & Telecommunications, Xi’an 710121, China
Published: December 2020

Gallium oxide (Ga2O3) single crystal nanoribbons have the potential applications in electronic devices due to their unique properties. However, the current small surface area makes the fabrication of device based on this nano-material very complex and challenging, and the introduction of catalyst also makes the growth process of Ga2O3 nanomaterial complicated and hard to control. Therefore, it is very important to study the growth method and physical mechanism of Ga2O3 nanoribbon with the larger surface area without catalyst.

In this paper, the carbothermal reduction method is used to grow the Ga2O3 nanomaterial. In this paper, the gallium oxide powder mixes with the carbon nanotubes at a mass ratio of 1:1.5 without the catalyst, and then they are put into a high temperature diffusion furnace for the growth of Ga2O3 nanomaterials with different structures on silicon-based substrates by controlling the reaction temperature. In this paper, it is found that the reaction temperature directly affects the diameter and ratio of gallium oxide nanostructures. The reason is that the bonding energy of gallium oxide crystal is different in different crystal directions which leads to the different growth speed. The interface energy along the growth direction is the smallest and the growth speed is the fastest, while the growth speed along the vertical direction is slow. Finally, the crystal gradually grows into nanoriband, nanometer sheet and other structures.

 In addition, the ultra-wide β-Ga2O3 single crystal nanobelt up to the millimeter level was prepared in this paper. This nanobelt’s lateral dimension is observed to reach 44.3 μm under the scanning electron microscope (SEM), and the transmission electron microscope (TEM) is used to confirm that the nanoribbons have a single crystal structure. Further, Raman spectroscopy (Raman) shows that the β-Ga2O3 nanoribbons grown by this method have the smaller strain and the lower defect density. Additionally, the room temperature photoluminescence spectrum (PL) test shows that the gallium oxide nanoribbon emits a stable and high-brightness blue light at 425 nm at the excitation wavelength of 295 nm. This growth method can provide a useful way for the preparation of device-level gallium oxide nanoribbons in the future.
Density functional theory studies on the excited-state properties of Bilirubin molecule
Authors: Li Yuan-Yuan , Hu Zhu-Bin , Sun Hai-Tao , Sun Zhen-Rong ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
Published: December 2020

Bilirubin is the main pigment in human bile, which is closely related to human health. Bilirubin combining with fluorescent protein represents a new type of fluorescent chromophore and has important applications in the field of biological imaging and biosensor. Due to the lack of efficient and accurate electronic structure methods, the electronic structure and excited-state properties of bilirubin molecule are not characterized quantitatively and accurately. Firstly, the vertical absorption energy, oscillator strength and vertical emission energy of the lowest singlet excited state of bilirubin molecule are calculated by combining the implicit solvent model and the linear response time-dependent density functional theory (TDDFT) method. Compared to the experimental data and high-level RI-ADC(2) calculation, the prediction performance of a series of density functional methods is systematically investigated. The results show that the optimally-tuned range separated density functional method has the best overall performance and the minimum absolute and relative errors. This is obviously due to the fact that the suitable proportion of exact exchange included in density functionals can produce neither delocalized nor localized electronic structures. Based on the produced wavefunction by the optimally-tuned method, the excited-state characteristics of the S1 state of bilirubin molecule indicate a hybrid local and charge transfer excitation, based on the quantitative characterization using hole-electron analysis and interfragment charge transfer method. This work can provide a theoretical basis for the study of excited-state dynamics and spectral properties of bilirubin molecules and the optimally tuned range-separated DFT method also provide a reliable and efficient theoretical tool to study the excited-state properties of other biomolecular systems in the future.
Effects of suface hydroxylated strontium titanate nanofibers on dielectric and energy storage properties of polyvinylidene fluoride composites
Authors: Wang Jiao , Liu Shao-Hui , Zhou Meng , Hao Hao-Shan , Zhai Ji-Wei ,   School of Science, Henan Institute of Engineering, Zhengzhou 451191, China,   School of Materials Science and Engineering, Tongji University, Shanghai 201804, China
Published: December 2020

With the rapid development of the electronics industry, the dielectric materials with high energy storage density, fast charge and discharge speed, easy-to-process and easy-to-mold, and stable performance are urgently needed to meet the requirements for lightweight and miniaturization of electronic component equipment. Dielectric ceramics has a high dielectric constant, but low breakdown field strength. Polyvinylidene fluoride (PVDF) has the advantages of good flexibility, high breakdown field strength, and light weight, but its dielectric constant is low. Achieving the ability to tailor the interface between dielectric ceramics filler and PVDF polymer matrix is a key issue for realizing the desirable dielectric properties and high energy density in the nanocomposites. As a result, much effort has been made to prepare the polymer composites through the surface modification of the nanoparticles with high dielectric constant fillers dispersed in a matrix, with the hope of preparing composites containing the high dielectric constant of the ceramic fillers and the high breakdown strength of polymers. In this work, in order to obtain the high dielectric-constant and high-energy-storage-density dielectric ceramics, the electrospinning method is used to prepare the SrTiO3 one-dimensional nanofibers as the inorganic fillers and the casting method is adopted to prepare PVDF as the polymer matrix. To improve the interface between inorganic nanofiber fillers and PVDF matrix, the SrTiO3 nanofibers are modified by surface hydroxylation. The effects of suface hydroxylated SrTiO3 nanofibers on the dielectric properties and energy storage properties of PVDF composites are studied. The correlation between interface modification and energy storage performance of composites is investigated to reveal the mechanism of enhanced energy storage performance of SrTiO3 nanofibers/PVDF composites. The results show that the dispersion of surface-hydroxylating SrTiO3 nanofibers in PVDF polymer can be improved. The composites exhibit improved dielectric properties and enhanced breakdown strength. When the filling quantity of the surface-hydroxylating SrTiO3 nanofiber fillers is 2.5 vol%, the energy storage density of the composite reaches 7.96 J/cm3. Suface-hydroxylating SrTiO3 nanofibers exhibit excellent dispersion in the PVDF polymer matrix and strong interfacial adhesion with the matrix, leading the composites to possess excellent dielectric constant and energy storage performance. The surface hydroxylation of ceramic fillers can improve the energy storage performance of the composites.
Electrical characteristics of cells with electrical impedance spectroscopy
Authors: Yao Jia-Feng , Wan Jian-Fen , Yang Lu , Liu Kai , Chen Bai , Wu Hong-Tao ,   College of Electrical and Mechanical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

Bioelectrical impedance spectroscopy is a noninvasive, label-free and quantitative detection technology, which has great advantages in the physiological and pathological analysis of biological cells and tissues. In this paper, the relationship between the electrical properties of a single cell and its structure is studied by numerical simulation. Moreover, experiments are conducted to verify the simulation results. For simulation, three single cell models are used to express its structure. Among of the three models, No Shell Model (NS) is proposed in this paper to study the influence of cell membrane on bioelectrical impedance spectroscopy. In addition, the effects of cell type, cell membrane and cell nucleus on its electrical properties are studied by simulation based on Single Shell Model (SS) and Two Shell Model (TS). The simulation results show that: 1) the electrical characteristics of cells can reflect its structure, therefore, the cell type can be accurately distinguished by its electrical characteristics; 2) the high frequency part of the Cole-Cole Plot is caused by ionic polarization of cytoplasm or extracellular fluid, and the low frequency part of the Cole-Cole Plot is caused by interface polarization between cell membrane and the extracellular fluid; 3) the influence of cell nucleus size on impedance measurement is mainly in the low frequency range, which is caused by the polarization of the interface between cell nucleus and intracellular fluid, and when the nucleocytoplasmic ratio is less than 0.25, the effect of nuclear size on impedance analysis could be ignored. Finally, an experiment was conducted on 20% yeasts suspension with different activity to verify the simulation results. It is known that the cell membranes of dead yeasts are destroyed, however, living yeasts have completed cell structures. The structure difference between living and dead yeast is distinguished by electrical impedance spectroscopy through numerical simulation. The experimental results are consistent with the simulation results, which verifies the fact that the high frequency part of the Cole-Cole Plot is caused by ionic polarization of cytoplasm or extracellular fluid, and the low frequency part of the Cole-Cole Plot is caused by interface polarization between cell membrane and the extracellular fluid.
Density fluctuations and sub-Poisson distribution in the ultracold Fermi gas of 6Li
Authors: Wang Juan , Zhang Xiao-Tian , Wu Ze-Mao , Deng Shu-Jin , Wu Hai-Bin ,   State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200241, China
Published: December 2020

In this paper, we study the spatial noise fluctuations of the density distribution of non-interacting 6Li ultracold Fermi gases. For ideal ultracold Fermi gases, the Fermi-Dirac statistics governs its quantum distribution. The suppression of density fluctuations at low temperature, due to Pauli exclusion principle, is observed in a large cloud of fermions. To clearly reveal the density noise fluctuations of the ideal Fermi gases, other noises, such as the background noise, imaging laser noise, CCD photon counting noise, are greatly suppressed. The noise fluctuation shows a sub-Poissonian statistics in excess of 10,000 atoms per spin state. The dependence of the spatial atom noise fluctuation on the quantum degeneracy is also investigated by changing the temperature of the degenerated Fermi gases. The Fermi gases with lower temperature exhibit larger suppression of the noise fluctuations. The results may have great applications in measuring the temperature of strongly correlated many-body physics and observing the phase transition of incompressible quantum phases.
Research progress of Rydberg many-body interaction
Authors: Zhang Zheng-Yuan , Zhang Tian-Yi , Liu Zong-Kai , Ding Dong-Sheng , Shi Bao-Sen ,   CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The interaction of many-body quantum system is a critical problem to be solved in the field of quantum information science. Rydberg atoms have large dipole moment, enabling them to interact with others in a long range, thereby offering us a powerful tool for studying many-body quantum physics. Meanwhile, atoms in the ground state are stable, which makes it easy to manipulate them. Therefore, Rydberg-atom many-body system is an ideal platform for studying the interaction of many-body quantum system. Studies of Rydberg-atom many-body system may contribute to understanding the properties of many-body system and putting the interaction of many-body quantum system into practical applications. In this review, we introduce some studies of properties of interaction of Rydberg-atom many-body system, including the Rydberg excitation blockade, the variation of Rabi frequencies of the many-body system and special spatial distribution of Rydberg atoms in a many-body system. Firstly, the Rydberg excitation blockade, the most important property in the Rydberg-atom many-body system, indicates that atoms’ excitation will be suppressed in a certain range around one Rydberg excitation because the interaction between the Rydberg excitation and atoms leads the energy level to shift so that atoms cannot be excited by the same pulse. Secondly, there is a collective Rabi frequency in the system, which is proportional to the square of the number of atoms in the suppressed area. And additionally, because of the Rydberg blockade effect, Rydberg excitations in the ensemble cannot be at casual positions but a regular distribution is formed. Besides the studies of properties, several researches on the applications of interaction of Rydberg-atom many-body system are introduced, including single-photon source, quantum storage, single-atom imaging, quantum simulation, etc. These applications contribute to the development of quantum community and quantum computing, which may bring us a quantum-technology time. Finally, we discuss the future development of Rydberg-atom many-body system and its further applications. Further development includes the development of many-body system with a larger number of atoms, the development of many-body system of atoms with more than one electron, and some other specific subjects based on many-system, such as Rydberg dimer and topological phase. Also some promising applications such as in studying optimization problem by quantum annealing, may become true.
Theoretical and computational study on defects of solar cell materials
Authors: Yin Yuan , Li Ling , Yin Wan-Jian ,   Institute for Energy and Materials Innovation, Soochow University, Suzhou 215006, China,   Institute of Physics & Optoelectronics Technology, Baoji University of Arts and Sciences, Baoji 721013, China
Published: December 2020

Defect control of semiconductors is critical to the photoelectric conversion efficiency of solar cells, because the defect and doping directly determine the carrier distribution, concentration, charge transfer and non-radiative recombination of photogenerated carriers. The defect types, structures and properties are complicated in the real semiconductors, which makes experimental characterization difficult, especially for the point defects. In this review, we firstly introduce the approaches of defect calculation based on the first-principles calculations, and take a series of typical solar cell materials for example, including CdTe, Cu(In/Ga)Se2, Cu2ZnSnS(Se)4 and CH3NH3PbI3. The elucidating of computations is also conducible to understanding and controlling the defect properties of solar cell materials in practical ways. The comparative study of these solar cell materials indicates that their efficiency bottlenecks are closely related to their defect properties. Unlike the traditional four-coordination semiconductor, the unique “defect tolerance” characteristic shown in the six-coordination perovskite materials enables the battery to have a high photoelectric conversion efficiency even when it is prepared not under harsh experimental conditions. Based on the first principles, the defect calculation plays an increasingly important role in understanding the material properties of solar cells and the bottleneck of device efficiency. At present, the calculation of defects based on the first principle mainly focuses on the formation energy and transition energy levels of defects. However, there is still a lack of researches on the dynamic behavior of carriers, especially on the non-radiative recombination of carriers, which directly affects the photoelectric conversion efficiency. Recently, with the improvement of computing power and the development of algorithms, it is possible to quantitatively calculate the electron-ion interaction, then quantitatively calculate the carriers captured by defect state. These methods have been used to study the defects of solar cells, especially perovskite solar cells. In this direction, how to combine these theoretical calculation results with experimental results to provide a more in-depth understanding of experimental results and further guide experiments in improving the efficiency of solar cells is worthy of further in-depth research.
Resonant Multi-phonon Raman scattering of black phosphorus
Authors: Meng Da , Cong Xin , Leng Yu-Chen , Lin Miao-Ling , Wang Jia-Hong , Yu Bin-Lu , Liu Xue-Lu , Yu Xue-Feng , Tan Ping-Heng ,   State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China,   Center of Materials Science and Optoelectronics Engineering & CAS Center of Excellence in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100049, China,   Shenzhen Engineering Center for the Fabrication of Two-Dimensional Atomic Crystals, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China,   Beijing Academy of Quantum Information Science, Beijing 100193, China
Published: December 2020

Black phosphorus (BP) has been attracting intense interest due to its unique anisotropic properties. The investigations on phonon dispersion and electronic band structure could expand the understanding of the properties of BP and promote its application on next generation nano-electronic devices. As the fingerprint of materials, Raman spectroscopy can provide the information of their phonon dispersion and electronic band structure. According to the Raman selection rule, Raman process involving multiple (two or more) phonons can be used to probe the phonon density of states within the whole Brillouin zone. However, the intensity of high-order Raman modes is much lower than that of the first-order Raman mode. To break through the limit of low intensity, here, we measured the resonant Raman spectroscopy of BP excited by several wavelength lasers and observed rich information about high-order Raman modes in the spectral range of 680–930 cm–1. To further investigate high-order Raman modes and avoid the birefringence effects from optical anisotropy on Raman intensity, we employ a special polarization configuration to obtain resonant Raman spectra and Raman intensity as a function of excitation wavelength. All the observed high-order Raman modes are certainly assigned, according to the phonon dispersion and symmetry analysis of related phonons. This indicates the great contribution of phonons within the Brillouin zone to the second- and third-order Raman scattering. This work proposes a general and systematical method to investigate high-order Raman modes, and paves ways for the researches of phonon dispersion and resonance Raman spectroscopy in other anisotropic materials.
Numerical solution of three-dimensional time-dependent Schrödinger equation based on graphic processing unit acceleration
Authors: Tang Fu-Ming , Liu Kai , Yang Yi , Tu Qian , Wang Feng , Wang Zhe , Liao Qing ,   Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, China
Published: December 2020

In the field of quantum mechanics, the theoretical study of the interaction between intense laser field and atoms and molecules depends very much on the numerical solution of the time-dependent Schrödinger equation. However, solving the three-dimensional time-dependent Schrödinger equation is not a simple task, and the analytical solution cannot be obtained, so it can only be solved numerically with the help of computer. In order to shorten the computing time and obtain the results quickly, it is necessary to use parallel methods to speed up computing. In this paper, under the background of strong field ionization, the three-dimensional time-dependent Schrödinger equation of hydrogen atom is solved in parallel, and the suprathreshold ionization of hydrogen atom under the action of linearly polarized infrared laser electric field is taken for example. Based on the spherical polar coordinate system, the time-dependent Schrödinger equation is discretized by the splitting operator-Fourier transform method, and the photoelectron continuous state wave function under the length gauge can be obtained. In Graphics processing unit (GPU) accelerated applications, the sequential portion of the workload runs on central processing unit (CPU) (which is optimized for single-threaded performance), while the compute-intensive part of the application runs in parallel on thousands of GPU cores. The GPU can make full use of the advantage of fine-grained parallelism based on multi-thread structure to realize parallel acceleration of the whole algorithm. Two accelerated computing modes of CPU parallel and GPU parallel are adopted, and their parallel acceleration performance is discussed. Compared with the results from the existing physical laws, the calculation error is also within an acceptable range, and the result is also consistent with the result from the existing physical laws of suprathreshold ionization, which also verifies the correctness of the program. In order to obtain a relatively accurate acceleration ratio, many different experiments are carried out. Computational experiments show that under the condition of ensuring accuracy, the GPU parallel computing speeds by up to about 60 times maximally based on the computational performance of CPU. It can be seen that the accelerated numerical solution of three-dimensional time-dependent Schrödinger equation based on GPU can significantly shorten the computational time. This work has important guiding significance for rapidly solving the three-dimensional time-dependent Schrödinger equation by using GPU.
Wavelet analysis of density fluctuation in supersonic turbulent boundary layer
Authors: Zhang Bo , He Lin , Yi Shi-He ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China
Published: December 2020

In order to obtain the time-varying information and dynamic characteristics of density fluctuation in compressible turbulence, the wavelet method is used to analyze the flow density field of zero-pressure-gradient flat plate turbulent boundary layer at Ma = 3.0, which is measured based on Nano-tracer plane laser scattering technique. Utilizing Taylor’s frozen hypothesis, the spatial signal of density field converts into the temporal signal. The one-dimensional orthogonal wavelet multi-resolution analysis is used to reveal multi-scale turbulent structures, and the results suggest that large-scale structures play a leading role in the density fluctuation of turbulent boundary layer while the small-scale structures make the probability density function (PDF) of density fluctuation manifested as an “M” distribution. The density fluctuation scalar PDF deviates from Gaussian distribution. The Hilbert transformation is used to analyze amplitude modulation effects between large- and small-scale structure, and the results suggest that positive (negative) large scale density excursion in the outer layer induces local enhancement (suppression) of the small scale density fluctuation in the inner layer near the wall. The time-varying spectral density estimation method based on the wavelet transform is used to analyze the density fluctuation at different heights of turbulent boundary layer after proving its viability in time and frequency domain. The results suggest a wide range of frequencies throughout the turbulent boundary layer, mainly distributed within 1 MHz. The density fluctuation in the dominant frequency band is intermittent, most of which transits from high frequency to low frequency while the spectral density first increases and then decreases. Near the wall, the time-frequency distributions of density fluctuation in the logarithmic layer are similar. In the middle part of the turbulent boundary layer, the frequency distribution and spectral density of the density fluctuation each reach a peak. Near the mainstream region, the spectral density decreases obviously, which is mainly distributed near the structure formed by the interaction between the boundary layer and mainstream. The wall constraint, viscous dissipation, and uniform mainstream make the fluctuation nearby the region relatively weak. As a result, the spectrum amplitude of density fluctuation first increases and then decreases from the wall to the mainstream.
Composite polarization conversion metasurface and its application in integrated regulation radiation and scattering of antenna
Authors: Guo Ze-Xu , Cao Xiang-Yu , Gao Jun , Li Si-Jia , Yang Huan-Huan , Hao Biao ,   Information and Navigation College, Air Force Engineering University, Xi’an 710077, China
Published: December 2020

The transmission polarization conversion metasurface has been widely concerned, because it has the advantage of being easy to be conformal with the antenna. Based on the reasonable arrangement of transmission polarization conversion units, various and complex electromagnetic functions can be realized. As the electromagnetic open window on the flight platform, the antenna is the bottleneck that restricts the decrease of radar cross section (RCS) of the whole flight platform. It is difficult to simultaneously realize the normal and efficient radiation of the antenna and the decrease of the RCS of the antenna. When the designed transmission metasurface is used in the antenna design, the radiation and scattering of the antenna can be regulated comprehensively. In this paper, a composite polarization conversion metasurface is proposed and verified. The unit cell of composite polarization conversion metasurface consists of two mirror symmetrical anisotropic metal patches in the upper layer, a dielectric layer and a polarization gate in the lower layer. When the polarization direction of the incident electromagnetic wave is perpendicular to the extension direction of the polarization gate and arrives at the composite polarization conversion surface, the conversion surface can realize the conversion from transmission linear polarization to right-hand circular polarization in a frequency range from 9.3 GHz to 10.9 GHz. When the polarization direction of the incident electromagnetic wave is parallel to the extension direction of the polarization gate, co-polarized total reflection can be realized. The chessboard arrangement metasurface is composed of composite polarization conversion unit and its mirror unit. A novel linearly polarized chessboard arrangement metasurface antenna is composed of the linearly polarized source microstrip antenna with a bandwidth of 9.4–10.7 GHz and the chessboard arrangement metasurface. By using the counter rotating cancellation characteristic of circular polarization, the chessboard arrangement metasurface antenna maintains linearly polarized radiation. Comparing with the source microstrip antenna, the linear polarization purity of chessboard arrangement metasurface antenna is improved from 9.5 GHz to 10.5 GHz. At the same time, the forward gain of the chessboard arrangement antenna increases and the radar cross section decreases. The maximum reduction is 39.2 dB. To further verify the practicability of the design and analysis, the chessboard arrangement metasurface antenna sample is fabricated and measured in microwave anechoic chamber with an Agilent 5230C network analyzer. The experimental results are in good agreement with the simulation results. This study has important reference value in the design of high gain, low RCS antenna and integrated regulation radiation and scattering of antenna.
Generation and research progress of femtosecond optical frequency combs in extreme ultraviolet
Authors: Zheng Li , Liu Han , Wang Hui-Bo , Wang Ge-Yang , Jiang Jian-Wang , Han Hai-Nian , Zhu Jiang-Feng , Wei Zhi-Yi ,   School of Physics and Optoelectronic Engineering, Xidian University, Xi’an 710071, China,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Femtosecond optical frequency combs have revolutionized the precision measurement of optical frequency and ultrafast science. Furthermore, the frequency combs expended to extreme ultraviolet (XUV) wavelength could provide an effective tool in attosecond pulse generation, nonlinear optics in ultraviolet, spectroscopy of electronic transitions and experiment of quantum electrodynamics. XUV femtosecond optical frequency combs need to be indirectly obtained by means of high-harmonic generation (HHG) drived by femtosecond pulses with high-repetition rate and extremely high peak power. In this review, firstly, the generation principle and the driving laser source requirements of femtosecond pulses generation in XUV spectral range are introduced. Basing on the requirements of driving laser sources, the several femtosecond laser amplification techniques are described, such as chirped pulse amplification (CPA), optical parametric chirped pulse amplification (OPCPA), double cladding pumped fiber amplifier and femtosecond enhancement cavity (fsEC). Meanwhile, the relative merits and applicability of which for XUV femtosecond optical frequency combs generation are compared. Secondly, in the HHG process, the XUV is generated collinearly or non-collinearly with the optical driving field. For the collinear generation process, one of the fundamental challenges is the design of a high-efficiency XUV output coupler. Here, three methods for out-coupling the XUV are expounded. Also, the theory of non-collinear XUV generation is mentioned. Finally, some typical research progress of XUV femtosecond optical frequency combs generation based on fsEC, OPCPA and femtosecond oscillators are reviewed respectively, as well as the current problems that need to be optimized are summarized.