bluuebunny/crossref_metadata_2025 huggingface dataset:
Point defects: key issues for II-oxides wide-bandgap semiconductors development
Authors: Xie Xiu-Hua , Li Bing-Hui , Zhang Zhen-Zhong , Liu Lei , Liu Ke-Wei , Shan Chong-Xin , Shen De-Zhen ,   State Key Laboratory of Luinescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China,   Zhengzhou University, School of Physics and Engineering, Zhengzhou 450001, China
Published: December 2020

II-oxides wide-bandgap semiconductor, including the beryllium oxide (BeO), magnesium oxide (MgO), zinc oxide (ZnO), have large exciton binding energy (ZnO 60 meV, MgO 80 meV), high optical gain (ZnO 300 cm–1) and wide tunable band gap (3.37 eV ZnO, MgO 7.8 eV, BeO 10.6 eV), which are the advantages of achieving low-threshold laser devices in the ultraviolet wavelength. It is also one of the important candidates to replace the traditional gas arc lamp (such as mercury lamp, deuterium lamp, excimer lamp, xenon lamp etc.) as the source of deep ultraviolet and even vacuum ultraviolet. Although, during the past decades, the ZnO-based pn homojunction devices have made great progress in the near-UV electroluminescence, but as the band gap broadens, the acceptor (or donor) ionization energy becomes higher (On the order of hundreds meV), which causing the room temperature equivalent thermal energy (26 meV) cannot make the impurities ionizing effectively. In addition, the self-compensation effect in the doping process further weakens the carrier yield. These above drawbacks have become the bottleneck that hinders II-oxides wide-bandgap semiconductor from achieving ultraviolet laser devices and expanding to shorter wavelengths, and are also a common problem faced by other wide-bandgap semiconductor materials. The regulation of the electrical and luminescent properties of materials often depends on the control of critical defect states. The rich point defects and their combination types make the II-oxides wide-bandgap semiconductors an important platform for studying defect physics. For the identification and characterization of specific point defects, it is expected to discover and further construct shallower defect states, which will provide a basis for the regulation of electrical performance. In this paper, recent research results of II-oxides wide-bandgap semiconductors will be described from three aspects: high-quality epitaxial growth, impurity and point defects, p-type doping and ultraviolet electroluminescence. Through the overview of related research works, II-oxides wide-bandgap semiconductors are clarified as deep ultraviolet light sources materials. Meanwhile, indicates that the key to the regulation of electrical performance in the future lies in the regulation of point defects.
Semiconductor yellow light-emitting diodes
Authors: Jiang Feng-Yi , Liu Jun-Lin , Zhang Jian-Li , Xu Long-Quan , Ding Jie , Wang Guang-Xu , Quan Zhi-Jue , Wu Xiao-Ming , Zhao Peng ,  Liu Bi-Yu ,  Li Dan , Wang Xiao-Lan , Zheng Chang-Da , Pan Shuan , Fang Fang , Mo Chun-Lan ,   National Institute of LED on Si Substrate, Nanchang University, Nanchang 330096, China
Published: December 2020

The development of semiconductor light-emitting diode (LED) in the visible emission range is very unbalance, as the power efficiency of yellow LED is far below other colors. Based on the GaN/Si technology, the authors and his team made a systematic research from the aspect of material growth, chip fabrication, device physics and equipment design, resolved the problems of epi-film cracking, high dislocation density, large strain in quantum well (QW), phase separation in QW, low QW growth temperature, low hole concentration, light absorption by substrate and light blocking by electrode, successfully made a breakthrough in fabricating efficient yellow LED. The yellow LED chip achieves a power efficiency of 26.7% at 20 A/cm2 with 565 nm wavelength and efficacy of 164 lm/W, and the power efficiency goes up to 42.8% at 1 A/cm2 with 577 nm wavelength and efficacy of 248 lm/W. New LED light source with multi-colors and without phosphor was developed based on the efficient yellow LEDs, opened up a new direction of pure LED healthy lighting.
Topological surface plasmon polaritons
Authors: Geng Yi-Fei , Wang Zhu-Ning , Ma Yao-Guang , Gao Fei ,   State Key Laboratory of Modern Optical Instruments, Zhejiang University, Hangzhou 310027, China,   College of Information Science & Electronic Engineering, Zhejiang University, Hangzhou 310027, China
Published: December 2020

The miniaturization of electromagnetic devices is a long-term theme for the development of modern technologies to achieve higher flexibilities, better performances, and higher density integration. Surface plasmon polaritons (SPPs) provide a powerful solution for reducing the size of integrated electromagnetic device due to its deep subwavelength confinement. However, materials or structures that support SPPs inevitably have impurities or structural defects, which leads to the loss of the propagating mode. In order to avoid scattering from impurities or defects, topological structures are introduced to address issues of discontinuities and have been proved to be an effective solution. In this paper, we first review the recent efforts devoted to SPPs based optical devices and those of artificial surface plasmon in terahertz/microwave band, and then summarize several important topological systems of SPPs. Finally, we present our perspectives on the future developments of this field.
Higher-order topological insulators and superconductors
Authors: Yan Zhong-Bo ,   School of Physics, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

Very recently, higher-order topological insulators and superconductors have attracted wide attention and aroused the great interest of researchers. Owing to their unconventional bulk-boundary correspondence, higher-order topological insulators and superconductors possess novel boundary modes whose dimensions are always lower than the first-order (or say conventional) topological insulators and superconductors, provided that their bulk dimensions are the same. The essence of higher-order topological phase is the formation of Dirac-mass domain walls on the gapped one-dimensional lower boundary. Roughly speaking, the origins of the formation can be classified as " intrinsic” and " extrinsic” type. For the former case, the formation of domain walls is forced by symmetry, suggesting that the resulting higher-order topological phases can be taken as topological crystalline phases. For this case, the domain walls are quite robust if the corresponding symmetry is preserved. For the latter case, the domain walls are formed simply because the one-dimensional lower boundary modes are gapped in a nontrivial way, however, the nontrivial way is not forced by symmetry. For this case, the domain walls are also stable against perturbations as long as the separations between them are large enough. The domain walls can have various patterns, which indicates that the higher-order topological phases are very rich.

In this paper, we first reveal the connection between the higher-order topological phase and the first-order topological phase. Concretely, we show how to realize a higher-order topological phase by breaking some symmetries of a first-order topological phase, as well as stacking lower-dimensional first-order topological systems in an appropriate way. After these, we review the recent progress of theoretical and experimental study of higher-order topological insulators and superconductors. For the higher-order topological insulators, we find that the electronic materials are still laking though a lot of experimental realizations have been achieved. For higher-order topological superconductors, we find that their experimental realization and investigation are still in the very primary stage though quite a lot of relevant theoretical studies have been carried out. In order to comprehensively understand this newly-emerging field there are still many things to be done.
Hypervelocity impact damage properties of solar arrays by using two-stage light gas gun
Authors: Zheng Jian-Dong , Niu Jin-Chao , Zhong Hong-Xian , Gong Zi-Zheng , Cao Yan ,   Institute of Telecommunication Satellite, China Academy of Space Technology, Beijing 100094, China,   Beijing Institute of Spacecraft Environment Engineering, National Key Laboratory of Science and Technology on Reliability and Environment Engineering, Beijing 100094, China,   School of Civil Engineering and Communication, North China University of Water Resources and Electric Power, Zhengzhou 450045, China
Published: December 2020

Using two-stage light gas gun, we study the hypervelocity impact characteristics of spacecraft key component, solar cell arrays. The damage morphologies in the ground simulation tests match well with those on-situ orbital impacts. The main characteristics of mechanical damage, including the central pit, cover glass shatter zone, and conchiodal spallation, are measured by using a microscope under 20 times magnification. To study the mechanical damage properties in solar arrays, we carry out 15 shots totally, under different impact locations, impact velocities, and particle diameters. Under the condition of impact angel of zero degree, the damage equation of perforation diameter of solar arrays and the damage equation of the diameter of shatter zone in cover glass are developed, respectively. The results show that the perforation diameter and the diameter of cover glass shatter zone are mainly related to the diameter of particle with 2/3 power, while related to the velocity of impact with 1/6 power. Compared with the damage equation in the literature, the damage equations in this article are very suitable for describing hypervelocity impact damage properties of solar arrays used in our country's spacecraft. The results are of significance for our country's aerospace engineering.
Transport performance of coupled Brownian particles in rough ratchet
Authors: Liu Chen-Hao , Liu Tian-Yu , Huang Ren-Zhong , Gao Tian-Fu , Shu Yao-Gen ,   College of Physical Science and Technology, Shenyang Normal University, Shenyang 110034, China,   Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Molecular motor is a kind of protein macromolecule, which moves along the microfilament or microtubule in cell directionally and participates in all kinds of intracellular life activities fully. In order to study the directional motion of molecular motor, a series of ratchet models have been proposed. However, the potentials used in most of the ratchet models are smooth sawtooth potential or harmonic potential. Recently, the experimental studies show that intracellular impurities, spatial inhomogeneity or the folding process of protein can yield deviation from a smooth ratchet profile. This kind of deviation will roughen the known smooth potential. In fact, the roughness of potential is not only closely related to the properties of protein, but also has an important implication in transition rate. Therefore, the rough ratchet will be used to simulate the interaction between molecular motor and trajectory in this work. In addition, experimental researches show that there is a class of molecular motor that can move directionally without dragging load in organism. According to the theory presented by Wang and Oster (Wang H, Oster G 2002 Europhys. Lett. 57 134), the directional transport capability of this kind of motor can be investigated by means of Stokes efficiency. The higher the Stokes efficiency of the motor, the stronger the ability of the motor to use external input energy for directional motion.

Here in this work, the overdamped Brownian transport of the two harmonically interacting particles is investigated, and the performance of transport is analyzed by studying the mean velocity and Stokes efficiency of the dimer induced by the introduction of roughness into the potential profile. The influences of the amplitude of perturbation, the wavenumber, the coupling strength and the free length of coupled Brownian particles on the directional transport performance are discussed in detail. According to the structure of ratchet, it is found that the roughness can either restrain or enhance the ratchet performance. It is shown that the appropriate amplitude and wavenumber of rough ratchet can promote the directional transport and enhance the Stokes efficiency of coupled Brownian particles. Moreover, one can distinguish between the optimal value of the coupling strength and free length that leads to a local maximum current. In addition, the directional transport of rough ratchet can be reversed by modulating the suitable coupling strength and free length. The conclusions obtained in this paper can provide theoretical guidance for understanding the motion behavior of molecular motor in experiment, and can also provide experimental inspiration for developing the nanometer machines and realizing the particle separation technology.
Tunable terahertz wave broadband absorber based on metamaterial
Authors: Chen Jun , Yang Mao-Sheng , Li Ya-Di , Cheng Deng-Ke , Guo Geng-Liang , Jiang Lin , Zhang Hai-Ting , Song Xiao-Xian , Ye Yun-Xia , Ren Yun-Peng , Ren Xu-Dong , Zhang Ya-Ting , Yao Jian-Quan ,   School of Mechanical and Engineering, Jiangsu University, Zhenjiang 212013, China,   Institute of Micro-nano Optoelectronics and Terahertz Technology, Jiangsu University, Zhenjiang 212013, China,   College of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
Published: December 2020

With the increasing scarcity of spectrum resources, terahertz wave technologies have attracted more and more attention in recent decades, and have made tremendous progress. Terahertz wave referring to electromagnetic waves with a frequency in a range of 0.1－10 THz has a wide range of applications in wireless communication, nondestructive imaging and remote sensing. Due to the advantages of high absorption, ultra-thin thickness, frequency selectivity and design flexibility, metamaterial absorbers have attracted more attention in terahertz band. In this paper, two terahertz metamaterial absorbers with different performances are designed which are named “T” terahertz multi-band absorber and “T” terahertz tunable broadband absorber, respectively. The absorbers are both comprised of three layers: metal substrate, matched dielectric layer and surface metamaterial layer. The main structures of these two absorbers are composed of four T-shape Au plates on the top of polyimide dielectric layer and an Au sheet acting as a bottom layer. The only difference between these two absorbers is that the terahertz broadband tunable absorber possesses a square photosensitive silicon in the metamaterial layer. The simulations results show that the terahertz multi-band absorber has six absorption peaks at 2.918, 3.7925, 4.986, 6.966, 7.2685, and 7.4665 THz, with the absorptivity peaks of 95.631%, 99.508%, 96.34%, 94.835%, 96.485%, 94.732%, respectively, and the average absorption rate is 96.26%. Terahertz tunable broadband absorber has the characteristics of broadband absorption. When the conductivity of silicon is 1600 S/m, the absorber reaches its absorption peak at 0.786 THz with the absorptivity of 99.998%, and the frequency bandwidth with the absorption rate exceeding 90% reaches 240 GHz. The more interesting thing is that by changing the conductivity of silicon, the terahertz tunable broadband absorber shows the ability to dynamically control the existence of absorption band and adjust the frequency position of absorption peak. For terahertz tunable broadband absorber, the frequency of absorption peak can be regulated in a bandwidth of about 30 GHz. The terahertz wave absorbers designed in this paper possess rather simple structures, therefore the proposed absorbers are easy to fabricate. Because of these excellent properties, the absorbers may have potential applications in optical switch, optical detection, optical imaging, band-stop devices, and other fields.
Theoretical progress of polarized interfaces in semiconductors
Authors: Zhang Dong , Lou Wen-Kai , Chang Kai ,   SKLSM, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China,   Center for Excellent in Topological Quantum Computation, University of Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

The manipulation of electronic structures of conventional semiconductors remains the key issue of modern semiconductor physics and devices. Compare to limited modulation of semiconductors by conventional gate technique, we theoretically demonstrate that, polarized interfaces can generate a strong built-in electric field (about 10 MV/cm) in both polar and non-polar semiconductors, and the polarized interfaces can tune the band gaps in a wide range (approximately 0—2 eV), and significantly enhances the Rashba spin-orbit coupling strength as well. In this paper, we introduce polarized interfaces in polar semiconductor InN and non-polar semiconductor Ge, and generate topological insulator phases by polarized interfaces. The polarized interface is compatible with conventional semiconductor fabrication techniques and shows interesting physics and potential optoelectronic applications.
First-principles study on structural stability of graphene oxide and catalytic activity of nitric acid
Authors: Lin Qi-Min , Zhang Xia , Lu Qi-Chao , Luo Yan-Bin , Cui Jian-Gong , Yan Xin , Ren Xiao-Min , Huang Xue ,   State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China,   State Key Laboratory of Dynamic Testing Technology, North University of China, Taiyuan 030051, China,   Beijing Computing Center, Beijing 100094, China
Published: December 2020

The stability and electronic structure properties of graphene fumigated by nitric acid are systematically studied by the first-principles method based on ultrasoft pseudopotentials. The model of graphene oxide fumigated by nitric acid is built based on the 2 × 2 supercell model with orthogonal graphene unit cells, which contains 15 carbon and 2 oxygen atoms. The results show that the fumigated graphene containing a carbon atom bonded to an oxygen atom is a stable structure with lower energy, which is consistent with the experimental result. In addition, the mechanical stability analysis shows \begin{document}${ {C_{66}} > 0,\;{C_{11}} > 0,\;{C_{11}}{C_{22}} > C_{12}^2} $\end{document}, which satisfies the mechanical stability condition. By analyzing the reactant and product, it can be concluded that the nitric acid acts as catalyst. Moreover, the process of graphene oxidation catalyzed by nitric acid is endothermic and the reaction needs heating. By analyzing the electronic properties of the structure, the graphene oxide is determined to be an intrinsic semiconductor with a direct band gap of 1.12 eV and work function of 5.28 eV. These results provide theoretical basis for preparing the graphene oxide and its applications in the field of optoelectronic devices.
Ultrafast charge and spin dynamics on topological insulators
Authors: Xiang Tian , Cheng Liang , Qi Jing-Bo ,   State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 611731, China,   Guangdong Institute of Electronic Information Engineering, University of Electronic Science and Technology, Dongguan 523808, China
Published: December 2020

Topological insulators (TIs), with unique bulk insulating and two-dimensional surface conducting states, show great promise of future optospintronics and spintronics applications, where a complete knowledge of the charge and spin dynamics is quite essential. Thus, the non-equilibrium properties inside TIs have attracted enormous attention. Here in this paper, we review the latest achievements in this field. The focus will be mainly on the experimental study, covering the ultrafast dynamical properties of charge, phonon, and spin. We hope that this review can stimulate further studies, especially theoretical research concerning the properties of topological insulators out of thermodynamic equilibrium.
Link prediction model based on dynamic network representation
Authors: Han Zhong-Ming , Li Sheng-Nan , Zheng Chen-Ye , Duan Da-Gao , Yang Wei-Jie ,   College of Computer and Information Engineering, Beijing Technology and Business University, Beijing 100048, China,   Beijing Key Laboratory of Food Safety Big Data Technology, Beijing Technology and Business University, Beijing 100048, China
Published: December 2020

Link prediction is an important issue in network analysis tasks, which aims at detecting missing, spurious or evolving links in a network, based on the topology information of the network and/or the attributes of the nodes. It has been applied to many real-world applications, such as information integration, social network analysis, recommendation systems, and bioinformatics. Existing link prediction methods focus on static networks and ignore the transmission of dynamic information in the network. However, many graphs in practical applications are dynamic and evolve constantly over time. How to capture time information in a dynamic network and improve the accuracy of link prediction remains a conspicuous challenge. To tackle these challenges, we propose a dynamic network representation based link prediction model, named DNRLP. DNRLP can be mainly divided into two modules: a representation learning module on dynamic network and a link prediction module, where the representation learning module is composed of a node information dynamic update unit and a node neighborhood update unit. Node information dynamic update unit leverages the benefits of the long short-term memory (LSTM) in capturing time information and uses a Time Interval based Filter Unit (TIFU) to introduce time interval information between two links, while for the node neighborhood update unit we present a random walk algorithm based on connection strength to simulate the diffusion of dynamic information. Through the above two parts, the model can obtain the node representation at the new moment, then link prediction is performed by the link prediction module by measuring the similarity between the node representations. The experiment uses MRR and Recall@k indicators to evaluate performance of model on four public dynamic network datasets. The experiments demonstrate the effectiveness and the credibility of the proposed model in link prediction tasks as compared with the comparison models, the MNR index of the DNRLP is increased by 30.8%. The model proposed in this paper not only learns the dynamic information in the network, but also considers its influence on neighbors and the impact of time interval on information update. Therefore, the model has learned more abundant dynamic information and has obvious advantages for link prediction tasks.
Molecular dynamics simulation of effect of cooling rate on the microstructures and deformation behaviors in metallic glasses
Authors: Zhou Bian , Yang Liang ,   College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

Since the discovery of the first metallic glass (MG) in 1960, vast efforts have been devoted to the understanding of the structural mechanisms of unique properties, in particular, mechanical properties in MGs, which is helpful for the applications of such novel alloys. As is well known, the cooling rate during the quenching as well as the sample size, significantly affects the mechanical properties in MGs. In order to study the effect of cooling rate on microstructure and deformation behavior in MG by excluding the size effect, Zr48Cu45Al7 ternary composition with good glass-forming ability is selected as a research prototype in this work. The classical molecular dynamics simulation is utilized to construct four structural MG models with the same size under different cooling rates, and the uniaxial compressive deformation for each model is also simulated. It is found that an MG model prepared at a lower cooling rate has a higher yield strength and is more likely to form shear bands that lead the strain to be localized, resulting in a lower plasticity. The Voronoi tessellation, together with atomic packing efficiency and free volume algorithms that have been designed by ourselves, is used to analyze the four as-constructed models and high-temperature liquid model. It is found that the as-constructed model, which is prepared by quenching metallic melt at a higher cooling rate, can preserve more structural characteristics of the high-temperature liquid. In other words, the higher cooling rate leads to more clusters with relatively low five-fold symmetry, loose atomic packing and large fraction of free volumes in MG. By calculating the distribution of the free volumes, a new computational approach to detecting liquid-like regions in MG models is adopted. It is found that there are more liquid-like regions in the as-constructed model which is prepared by quenching metallic melt at a relatively high cooling rate. This should be the structural origin of the effect of cooling rate on the deformation behavior, in particular, the yield strength and the plasticity. This work provides an understanding of how the cooling rate during quenching affects the microstructure and deformation behavior, and will shed light on the development of new MGs with relatively large plasticity.
The entropy production rate of double quantum-dot system with Coulomb coupling
Authors: Lin Zhi-Yuan , Shen Wei , Su Shan-He , Chen Jin-Can ,   College of Physical science and technology, Xiamen University, Fujian 361005, China
Published: December 2020

In thermodynamics of irreversible processes, the entropy production rate (EPR) is usually generated by the rate of the entropy change of the system due to its internal transitions and the entropy flows due to the interactions between the system and the environment. For the bipartite system, in addition to the factors mentioned above, the energy and information exchanges between the two subsystems will generate an additional entropy production in the EPR of a subsystem. To reveal the essence and role of the information flow, we build an open dissipative quantum system coupled to multiple electronic reservoirs with the same temperature and different chemical potentials. Based on the thermal and electron transport properties of a double quantum-dot system with Coulomb coupling, the EPR of each quantum dot and the information flow between subsystems are studied. Starting from the quantum master equation under the Born, Markov, and rotating-wave (or secular) approximations, we derive the EPRs of the total system and subsystems at the steady state. For purposes of relating the thermodynamic properties to the fundamental fluxes and affinities, a graph representation of the dynamics of the four-state model is introduced. Selecting a directed graph and a complete set of basic cycles by using Schnakenberg’s network theory, we show how the EPRs of the total system and the subsystems relate to global and local cycle fluxes. It is found that the energy and information exchanges between the quantum dots depend on the global cycle flux. The EPRs induced by the electron flows due to the chemical potential difference as well as the energy and information exchanges between the subsystems are the key elements of thermodynamic irreversibilities. The EPRs caused by the information exchange guarantee the continuous electron transports. The EPRs and the coarse-grained EPRs of the subsystems varying with the Coulomb coupling strength are obtained numerically. The results demonstrate that the information flows in the process of internal exchange become important to fully understand the operation mechanism of the bipartite system. Without violating the second law of thermodynamics, the information can be regarded as a driving force to move electrons from low to high chemical potential.
The electron emission characteristics of GaAs photocathode with vacuum-channel structure
Authors: Hao Guang-Hui , Han Pan-Yang , Li Xing-Hui , Li Ze-Peng , Gao Yu-Juan ,   National Key Laboratory of Science and Technology on Vacuum Electronics, Beijing Vacuum Electronics Research Institute, Beijing 100015, China
Published: December 2020

The photocathode was an ideal electronic source with fast response, centralized distribution of electronic capabilities, and many other advantages. But for its low emission current density and short lifetime at ion bombardment environment, it will not be used in power devices and large scientific devices. Although the emission current of the photocathode can be increased with the aid of electric filed, it was not reach the milliamperelevel. In the field emission cathode, the strong electric field can effectively reduce the surface barrier of the emitter, so that the cathode produces electron emission. Based on the photoelectric conversion mechanism of photocathode and the electron emission theory of field emission cathode, a vacuum channel structure photocathode module is designed. The cathode modules with GaAs substrate were fabricated by the peritoneal and etching process. The parameters of vacuum channel were 3 μm × 700 μm, and its array structure was 1 × 100. The deep of the vacuum channels were 400 nm. It can be seen from the test result, the emission current of the photocathode was 26.12 mA with the laser beam power 5 W, and its emission current density was 5.33 A/cm2. During cathode operation, the laser beam and emission will cause the temperature of the photocathode material to rise, and this could icreasing the conductivity of the GaAs, the efficiency of electron supplement from negative electrode to electron emission area of the GaAs will also be improving. Its emission current could reach 89.69 mA at 400 ℃. Because there is no active atom on the photocathode surface, its lifetime was longer than the traditional photocathode that astivated by Cs/O. The life test of the photocathode modules was carried out, its emission current was 4.5 mA ± 0.3 mA within the 144 h, and its performance was not attenuate significantly. The vacuum channel was the main area of the photocatode electron emission, and the shape of electron beam can be easily obtained by adjusting the structure of the vacuum channel parameters. This advantage can improve the applicability of high current density photocathode in vacuum electronic devices and equipment.
Exciton-polaron interaction in blue fluorescent organic light-emitting diodes
Authors: Guan Sheng-Jie , Zhou Lin-Jian , Shen Cheng-Mei , Zhang Yong ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

OLEDs are popular as display technology nowadays, which have been widely used in commercial application. However, there are still some problems that blue light devices are not as efficient or stable as red and green light devices. Although the use of phosphorescent dyes can significantly improve the internal quantum efficiency, the high production cost and unstable performance limit the industrialization of phosphorescent OLEDs. In the development of OLEDs, the researchers found that OLEDs suffered from a decline in their efficiency at high brightness levels, a behavior known as “efficiency roll-off”. The efficiency roll-off is more pronounced in phosphorescent devices due to the longer lifetime of triplet exciton than singlet exciton, so that it has been widely investigated in recent years. Little is known, still, about fluorescent devices. Accordingly, unraveling the exciton loss mechanism in blue fluorescent OLEDs is particularly important, as it is a limiting factor for the improvement of efficiency. In this work, the efficiency roll-off in blue fluorescent OLEDs is investigated by observing the quenching of DPAVBI excitons. Firstly, the effects of electron current and hole current on photoluminescence(PL) behavior of unipolar devices are studied by steady-state and transient-state measurements, and we analyze PL spectrum and calculate the exciton quenching rate constant according to the transient PL decay curves to clarify the exciton quenching dynamics. The results show that the holes are much more efficient in quenching the excitons when the host is a hole transport material. This is different from the general understanding that exciton-polaron quenching effect with higher carrier mobility is weaker. Because the existence of bound charges produces additional charge density, and it is inferred that the exciton is mainly quenched by trapped charge rather than moving charge. We also exclude the effect of exciton–exciton annihilation and electric-field-induced dissociation on the efficiency degradation of the OLEDs. It is confirmed experimentally that exciton-polaron interaction is the dominant mechanism of the efficiency roll-off in fluorescent OLEDs. We then fabricate organic light-emitting diode devices with different doping concentrations to figure out the effect of doping concentration on exciton-polaron interaction, and obtain a blue fluorescence device with good comprehensive performance. We also summarize some feasible methods to optimize the efficiency of the OLEDs. In this paper, our findings about exciton-polaron interaction might provide a viable source for efficiency improvement by regulating charge trapping in light emitting layer.
Angular distribution of L characteristic X-ray emission from Au target impacted by photons
Authors: Liu Yu , Xu Zhong-Feng , Wang Xing , Hu Peng-Fei , Zhang Xiao-An ,   Ion Beam and Optical Physical Laboratory of Xianyang Normal University and Institute of Modern Physics, Chinese Academy of Sciences, Xianyang 712000, China,   School of Science, Xi’an Jiaotong University, Xi’an 710049, China
Published: December 2020

The vacancy can be produced through impact ionization of target atom by energetic particles. It is of significant importance to study the vacancy state by the measurement of angular distribution of typical X-rays. At present, accurate ionization cross-section data of the atomic inner shell are urgently required in many areas. However, the precise measurement of ionization cross-section of the atomic inner shell is largely dependent on the fact that whether the characteristic radiation (e.g., X-ray) is isotropic.

In this experiment, the characteristic Lι, Lα, Lβ and Lγ1 X-rays for Au target are measured by a silicon drift detector in an emission angle range from 130° to 170° in steps of 10°. A mini-X ray source is utilized to produce bremsstrahlung with the center energy of 13.1 keV.

Considering detection efficiency of the detector and the absorption of the target, relative intensity ratios, I(Lα)/I(Lγ1) and I(Lι)/I(Lγ1), are obtained at different detection angles based on the experimental energy spectrum results. Moreover, the angular dependence of X-ray intensity ratio is investigated and it is found that the X-rays Lι and Lα exhibit anisotropic emission.

According to the X-ray intensity ratio I(Lι)/I(Lγ1) and the P2(cosθ), and using the least square method, the anisotropic parameter β of characteristic X-ray Lι is derived to be 0.25. Due to the relation β = ακA20, the value of the alignment degree A20 for L3 sub-shell is determined to be 0.577 ± 0.08. Alignment degree A20 for L3 sub-shell is dependent on its intrinsic physical properties, while the anisotropy parameter β of typical X-rays can be affected by Coster-Kronig transition process.

The behavior of the alignment for inner-shell vacancy states calls for more research results both in theory and in experiment. Therefore, it is quite relevant and meaningful to perform more experiments to further study the angular distribution of vacancy states by electrons, photons and ions impacting a target.
Super-resolution imaging system based on integrated microsphere objective lens
Authors: Song Yang , Yang Xi-Bin , Yan Bing , Wang Chi , Sun Jian-Mei , Xiong Da-Xi ,   School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China,   Research Center of Light for Health, Suzhou Institute of Biomedical Engineering and Technology, Chinese Academy of Sciences, Suzhou 215163, China
Published: December 2020

White-light super-resolution imaging, proposed in 2011, has been achieved by combining the transparent microspheres of the micron scale with an ordinary optical microscope. At present, in most of the researches employed is the way of spreading microspheres directly onto the surface of sample, which causes the randomness and discontinuity of microspheres. It is impossible to achieve the complete imaging of specific regions, which greatly limits the application scope of this technology. Such an issue can be solved by using microprobes or micro-cantilevers to precisely transfer the location of microsphere, but for doing so, a sophisticated controlling system is required, which is costly and not user-friendly. In this paper, a robust, controllable, easy-to-use integrated design which can efficiently consolidate microsphere and objective together is demonstrated for super-resolution imaging. The PDMS and customized metal sleeve are used to encapsulate the microsphere semi-submerged on the ordinary objective lens to achieve an integrated design. In this system, the distances among the microsphere, objective lens and the sample are controlled accurately by building a side-view imaging and position feedback system. With the help of a universal microscopic imaging system, the super-resolution imaging of specific controlled areas is realized. Based on theoretical analysis, the semi-submerged structure of the 100-μm-diameter BaTiO3 microsphere has a strong focusing effect, which can form the so-called ‘photonic nanojet’ on a micro-scale in length and on a sub-diffraction scale in waist to possess the ability to break through the diffraction limit within the range of focal length. At the same time, experiments are carried out for investigating imaging performances at various working distances in the air. According to the experimental results, the system can clearly distinguish between the CPU lattice features of 200 nm and the Blu-ray disc fringe of 100 nm, which means that the resolution of the ordinary microscopic objective lens (40×, NA 0.6) is significantly enhanced by 4.78×. In addition, with the increase of working distance, the magnification factor increases gradually, but the image contrast becomes worse, and the super-resolution effect fades. The integrated design which can match with ordinary optical microscope to achieve super resolution imaging has universality of installation and operation, and greatly conduces to super-resolution imaging of sub-diffraction limit samples.
Corrosion and tribological properties of TiAlCN/TiAlN/TiAlcomposite system deposited by magneticfliter cathode vacuum arctechnique
Authors: Chen Shu-Nian , Liao Bin , Chen Lin , Zhang Zhi-Qiang , Shen Yong-Qing , Wang Hao-Qi , Pang Pan , Wu Xian-Ying , Hua Qing-Song , He Guang-Yu ,   Key Laboratory of Beam Technology of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China,   Beijing Radiation Center, Beijing 100875, China,   Science and Technology on Plasma Dynamics Laboratory, Air Force Engineering University, Xi’an 710038, China
Published: December 2020

The experiment is based on novel magnetic filtered cathodic vacuum arc (FCVA) technology, the effects of the structure and C contents of TiAlCN/TiAlN/TiAl composite coating on anticorrosion and wear resistance were studied. The macro/micro properties of the coatings were systematically characterized by SEM, XRD, XPS, electrochemical tests and friction equipment. The results show that, with the increase of C content,the form of C element in the coatings transforms from the TiAlCN solid solution to the coexistence of crystallized TiAlCN/amorphous carbon. The TiAlCN/TiAlN/TiAl coating with TiAlCNcrystallized/amorphous carbon nanocomposite structure demonstrated excellent performanceby combining the advantages of each layer, which the hardness reaches an ultrahigh leveland the amorphous carbonwith excellent self-lubricating effect exists in the coating structure. In 3.5% NaCl electrochemical corrosion test, Ecorr increased by 5.6 times to 0.271 V, Icorr decreased by 1/52 to 8.092 ×10–9 A·cm–2. During the dry sliding, friction coefficient decreased by 1/3 to 0.43, and wear rate decreased by 1/1.4 to 1.13×10–5 mm3·N–1·m–1.
In situ luminescence measurement from lithium fluoride under various ions
Authors: Qiu Meng-lin , Zhao Guo-qiang , Wang Ting-shun , Luo Chang-wei , Wang Guang-fu , Zhang Feng-shou , Lv Sha-sha , Liao Bin ,   Key Laboratory of beam technology of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China,   Beijing Radiation Center, Beijing 100875, China
Published: December 2020

To contrast the generation and their evolution behaviors of irradiation damage in lithium fluoride under various ion, in situ luminescence measurements from lithium fluoride are carried out under 100 keV H+, He+ and O+ on the ion beam induced luminescence(IBIL) experimental setup on BNU400 ion implanter. Combined with Stopping and Range of Ions in Matter (SRIM) calculation of 100 keV H+, He+ and O+ stopping power in lithium fluoride, the emission intensity under He+ is the strongest,due to the higher excitation density of electron-hole pairs than them under H+ and the rising non-radiative recombination ratio under heavy ion O+. With the mass number increase of the incident ion, the nuclear stopping power would be increased, resulting in the faster rate of both formation and annihilation of point defects、the lower fluence for F-type centers reaching the highest intensity and the weaker luminescence intensity at the state of equilibrium. The irradiation resistance of \begin{document}$ \rm F_3^{-}/F_2^+ $\end{document} centers at 880 nm are better than the F2 centers at 670 nm, shown not only in the slower formation and annihilation rates of \begin{document}$ \rm F_3^{-}/F_2^+ $\end{document} centers but also the higher luminescence intensity of \begin{document}$ \rm F_3^{-}/F_2^+ $\end{document} centers under heavy ion O+.
Tribocorrosion performance of Nitrogen-doped diamond like carbon coating by high power impulse magnetron sputtering technique
Authors: Shen Yong-Qing , Zhang Zhi-Qiang , Liao Bin , Wu Xian-Ying , Zhang Xu , Hua Qing-Song , Bao Man-Yu ,   Key Laboratory of Beam Technology and Materials Modification of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China,   Beijing Radiation Center, Beijing 100875, China,   Beijing Jinlunkuntian Special Machine Co., Ltd., Beijing 100083, China
Published: December 2020

Nitrogen-doped diamond like carbon film is promising in biological applications, studying the synergistic tribocorrosion performance is indispensable. In this paper, Nitrogen-doped diamond like carbon films were deposited on AISI 304L austenitic stainless steels and Si substrate by using the high power impulse magnetron sputtering technique using Ar and N2 as precursors at room temperature. The effect of target pulse duration on the structure, mechanical properties, corrosion resistance and tribocorrosion properties in Hank's equilibrium salt solution and the corresponding mechanism were studied. The results of scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and nano-hardness test showed that the nitrogen-doped diamond like carbon coatings prepared at a target pulse duration of 60 μs showed the sp3 bonding content of 33.9% with the hardness of 12.4 GPaand the root mean square roughness of 0.63 nm. With the increase in pulse duration to 90 μs, the sp2 bonding increased, meanwhile the surface roughness increased. The results of potentiodynamic polarization indicated that the Nitrogen-doped diamond like carbon coating prepared at 60μs had best corrosion resistance with the corrosion current density of 7.65 × 10–8 A·cm–2. The effect of the target pulse duration on tribocorrosionbehaviour of the Nitrogen-doped diamond like carboncoating was investigated in Hank’s solution by a reciprocating tribometer equipped with a three-electrode electrochemical cell.The coatings at 60 μs exhibited excellent tribocorrosion properties with high open circuit potential of 39 mV, low COF of 0.05 without pitting corrosion due to high corrosionresistance, low contact angel and dense microstructure.The results indicated that corrosion can be accelerated by friction, but it also affect the mechanical properties of the Nitrogen-doped diamond like carbon coatings. The increase in pulse duration to 90 μs, leading to the reduction of sp3 bonds which can form a cross-linking structure. The degraded cross-linking structure decreased the corrosion resistance of the coating via the increased porosity in the coating, which weakened the interfacial strength of the coating, and ultimately led to failure of the coatingunder the action of wear.
Statistical analysis of the relationship between type II radio enhancement and solar energetic particle event
Authors: Zhou Kun-Lun , Ding Liu-Guan , Qian Tian-Qi , Zhu Cong , Wang Zhi-Wei , Feng Li ,   Institute of Space Weather, Nanjing University of Information Science and Technology, Nanjing 210044, China,   Binjiang College, Nanjing University of Information Science and Technology, Nanjing 210044, China,   Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China,   China Polar Research Center, Shanghai 200000, China
Published: December 2020

In this paper, we investigated 82 type-II radio burst events detected by some ground stations Learmonth, YNAO, and BIRS and spacecraft Wind/WAVES, STEREO/WAVES from January 2007 to December 2015. And we identified 39 events associated with radio enhancement and 43 events without enhancement. We found that: 1) The CME velocity, mass, kinetic energy and flare class with respect to type II radio enhancement events were generally higher than that of no enhancement events, and these properties in the solar energetic particle (SEP) events were significantly higher than that no SEP event, regardless of whether radio enhancement or not. 2) As shown in the characteristic time analysis, the initial release time of SEPs is generally earlier than the start time of radio enhancement, so we can the radio enhancement is only as a signature of the shock enhancement rather than the direct generator of SEP events. 3) Whether radio enhancement or not, the onset height of type IIs associated with SEP event is slightly lower than that of event without SEP. For the absence height, the SEP events are significantly higher than the no-SEP events, and that the absence height of enhancement events are also distinctly higher than that non-enhancement events, which reveals that the enhanced CME shock characterized by enhanced radio burst can keep propagating to more higher or further space. 4) When one fast and wide CME fully sweeps over another slow and narrow preceding CME, CME interaction can more easily generate radio enhancement, but no distinctive difference between SEP events and non-SEP events. So the results of this paper reveal that radio enhancement can be regarded as a manifestation of CME shock becoming strong during interacting with other CME, and the enhanced shock can accelerate the particle to generate large SEP events more easily. However, the type II radio enhancement is not the direct producer or causer that generate large SEP event.