bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic properties of Eu 4f76p1/2ns autoionization process
Authors: Li Qiong  , Shen Li  , Yan Jun-Gang  , Dai Chang-Jian  , Yang Yu-Na  ,   Key Laboratory of Display Materials and Photoelectric Devices, Ministry of Education, Tianjin 300384, China;,   School of Science, Tianjin University of Technology, Tianjin 300384, China
Published: December 2020

To explore the dynamic properties of Eu 4f76p1/2ns autoionization process, the autoionization branching ratios of ions and the angular distributions of ejected electrons from the Eu 4f76p1/2ns (n=7, 9) autoionizing states are systematically investigated with the combination of the three-step isolated-core excitation (ICE) and the velocity-map imaging techniques The Eu 4f76sns Rydberg states are populated via a two-step laser excitation, from which the Eu 4f76p1/2ns autoionizing states are excited by the wavelength of the third laser around the Eu 6s+6p1/2+ ionic resonance in order to obtain autoionization spectra and the velocity-map images of ejected electrons from the Eu 4f76p1/2ns autoionizing states. Once the velocity-map images have been measured, both the energy distribution and angular distribution of ejected electrons can be acquired. Moreover, the spectra of the branching ratios and the anisotropic parameters within the autoionization resonances are also measured to observe their energy dependence and the relation with the autoionization spectra. Comparisons of the observed spectra of 4f76p1/2ns autoionizing states with n = 7, 8, and 9 manifest that the ICE technique is more suitable for the higher-n members of autoionization series. It is found that the Eu atoms in the 4f76p1/2ns (n = 8, 9) autoionizing states mainly decay into 4f75d+(9D) ionic state, leading to the population inversion between 4f75d+(9D) and 4f76s+ (7S) or 4f76s+ (9S) ionic states, which is significant for developing the autoionization laser. The angular distributions of the ejected electrons from the Eu 4f76p1/2ns autoionizing states show simple patterns at the energy points corresponding to the peaks of autoionization spectra, and have complicated patterns in the energy regions off the peaks of autoionization spectra, especially in the regions corresponding to the sharp increase or decrease in the autoionization spectra. The above phenomena can be explained with the strength of configuration interaction among different autoionization series converging to different ionic states, which is fluctuated within the energy region of autoionization spectra. In addition, within the autoionization resonance both the spectra of branching ratios and anisotropic parameters vary irregularly, and no obvious correlation with the spectra of 4f76p1/2ns autoionizing states can be found.
Ptychographical algorithm of the parallel scheme
Authors: Xiao Jun  , Li Deng-Yu  , Wang Ya-Li  , Shi Yi-Shi  ,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Phychography is an important technique in the quantitative phase imaging research domain, which employs the illuminating probes to scan the specimen in an overlapped requirement, and the reconstruction is conducted by using the ptychographic iterative engine. But the contradiction between the imaging efficiency and quality has become a bottleneck for its wide applications. In this paper, we start with the fundamental principle of the iterative algorithms for ptychographical imaging, and propose two parallel schemes based on CPU and GPU, besides the influences of the specimen size, the number of blocks and illuminating beams on the speedup of the two schemes are investigated via simulation experiment. The result shows that the complex amplitude of the specimen can be correctly reconstructed, meanwhile, the speed is significantly improved, which reduces the time consumed by one order of magnitude. This improvement solves the above contradiction, so that we can expect to achieve quasi-real-time imaging. The experimental data also indicate that 1) in optimal partition, parallel speedup is related to the size of the specimen, bigger size is corresponding to more obvious acceleration; 2) the same specimen under different partitions will speed up to different extents, which is closely related to the experimental hardware, however the number of illuminating beams has no significant effect on the speedup.
High magnetic field influence on the molecular orientation and the morphology of iron phthalocyanine thin films
Authors: Huang Chao  , Liu Ling-Yun  , Fang Jun  , Zhang Wen-Hua  , Wang Kai  , Gao Pin  , Xu Fa-Qiang  ,   National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China;,   High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China
Published: December 2020

Molecular orientation and stacking mode are commonly considered to have vital influence on the optoelectronic performances of organic semiconductor devices via changing the dynamics of charge carriers transferring among the molecules. Highly ordered and homogeneous stacking would allow a fast band transfer mechanism in the phase domain. Therefore the controls of the molecular orientation and the stacking behavior are of great significance for optimizing the device natures. In this work, the modification and control of iron phthalocyanine (FePc) molecular orientation on Si(111) are accomplished with the aid of high steady magnetic field at room temperature. The FePc films are grown in situ by organic molecular beam deposition on the Si(111) substrates under a high magnetic field strength of 8.5 T. The Si(111) substrates are preserved at room temperature and are kept perpendicular to the magnetic field. The influences of magnetic field on the molecular orientations and the morphologies of FePc thin films are investigated by X-ray diffraction, angle dependent near edge X-ray absorption fine structure (NEXAFS), Raman spectroscopy and atomic force microscopy (AFM). In the presence of the external magnetic field, the deposited FePc films each show a higher crystallinity and slightly closer packing in (002) plane than those without magnetic field. The AFM images verifies more ordered and uniform morphologies of the FePc films grown in the magnetic field. NEXAFS and Raman results both reveale a standing-up configuration of FePc molecules on the Si(111) substrate surface. The average tilting angle of the molecules changes from 63.6 to 67.1 when 8.5 T magnetic field is employed. The results demonstrate that the external high magnetic field distinctly enhances the orientation order of FePc molecules on Si(111) surface due to the magnetic-magnetic interactions between the magnetic field and the molecular magnetic moment. This work also demonstrates that external magnetic field is an efficient means to regulate the orientation and stacking behavior of magnetic molecules, which may open a new way to optimize the performances of the organic semiconductor devices.
Effect of Rh content on the mechanical properties of Ir-Rh alloy based on the first principle
Authors: Pan Xin-Dong  , Wei Yan  , Cai Hong-Zhong  , Qi Xiao-Hong  , Zheng Xu  , Hu Chang-Yi  , Zhang Xu-Xiang  ,   State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals, Kunming Institute of Precious Metals, Kunming 650106, China
Published: December 2020

Platinum metal Ir-Rh alloy presents a promising candidate as future ultra-high-temperature gas turbine material due to its excellent high-temperature properties. In this paper, the mechanical properties of Ir-xRh (x=0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100) alloys with different rhodium content are investigated. Self-consistent, periodic, density functional theory calculations, Perdew-Burke-Ernzerhof functional, virtual crystal approximation are employed to calculate the elastic constants C11, C12, C44, Cauchy pressure (C12-C44), Young modulus E, shear modulus G, bulk modulus B and the ratio G/B, anisotropic factor A, and strain energy of dislocation per unit length. These parameters are adopted to characterize and assess the effect of Rh content on the mechanical property of Ir-Rh alloy. The results indicate that it is reasonable to use the virtual crystal approximation to calculate the mechanical properties of Ir-Rh alloys. The Young modulus E, shear modulus G and bulk modulus B increase rapidly with the increase of rhodium content, and the maximum value is reached at rhodium content 10%. Then it fast dereases down to a minimum value at 40% after the slowly rises and then slowly drops down. It is found to be in remarkable agreement with the strain energy of dislocation per unit length. This indirectly explains its changing trend. The Cauchy pressure (C12-C44), G/B value and the Poisson's ratio reflect the change of the brittleness of the alloy. Therefore, we can come to a conclusion: the addition of Rh can cause the brittleness of the Ir-Rh alloys. The value of the brittleness first increases and then decreases with the increase of Rh content, and its maximum value is reached at 50%. The charge densities and the densities of states of pure Ir, Ir-10Rh, Ir-50Rh and pure Rh are calculated and compared. At the same time, we also establish a 2 2 1 solid solution supercell structure of Ir-Rh alloy and calculate its differential charge density. The results show that in the Ir-Rh alloys exists a pseudo covalent bond, which leads to the abnormal mechanical properties. The pseudo covalent bond is not a metal bond nor a covalent bond but a kind of transition bond or a mixed type. Finally, the experimental results show that the calculation method is reasonable and it can play an important role in understanding the microscopic mechanism of the abnormal mechanical properties of Ir-Rh alloys.
Study on tunneling magnetoresistance effects in parabolic well magnetic tunneling junction with double barriers
Authors: Huang Zheng  , Long Chao-Yun  , Zhou Xun  , Xu Ming  ,   Electrical Engineering College, Guizhou Institute of Technology, Guiyang 550003, China;,   Key Laboratory for Photoelectric Technology and Application, Guizhou University, Guiyang 550025, China;,   School of Physics and Electronic Science, Guizhou Normal University, Guiyang 550001, China;,   College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066, China
Published: December 2020

In this paper, we construct a ferromagnet/semiconductor/ferromagnet parabolic well magnetic tunneling junction with double barriers as research object by inserting another semiconductor as a barrier between ferromagnetic and semiconductor potential wells. On the basis of the quantum coherent transport theory and transfer matrix method, we investigate the spin polarized electron transport and the tunnel magnetic resistance (TMR) in parabolic well magnetic tunneling junction with double barriers. We derive the analytical expressions of transmission probability, tunnel magnetic resistance and spin polarization from the new magnetic tunneling junction mode. The significant quantum size, Rashba spin orbit interaction, the angle effect and the thickness of the double barriers layer are discussed simultaneously. The results indicate that the tunnel magnetic resistance shows periodic variation as the width of the parabolic-well at different angles. The TMR is monotonically decreasing when the angle varying from 0 to up, which reflects the structure of the spin valve effect. Meanwhile, results also show that the spin polarization and the tunnel magnetic resistance oscillate with the same period for different barriers thickness. The phase difference appears after inserting the barriers. With increasing the barriers width, phase difference becomes large. The amplitude and peak to alley ratio of the spin polarization and the tunnel magnetic resistance are increase with the barrier width increases. Furthermore, the spin polarization make quasiperiodic oscillation that the oscillation amplitudes become large, the period and peak to alley ratio are decrease as the Rashba spin-orbit coupling strength increases. It appears the spin flip phenomenon as increasing the thickness of the barriers. The TMR shows the typical properties of resonant tunneling with the increasing of the spin orbit coupling strength. In order to better reveal the role of the symmetry double tunnel barriers in the parabolic well structure, we calculate TMR against the thickness of the double barriers. It is found that the existence of the double tunnel barriers increase the TMR and the spin polarization significantly, which shows that the large TMR value can be obtained with the suitable layer thickness of the double barriers layer and the Rashba spin-orbital coupling coefficients. These characteristics are helpful to promote the development and application of new magnetic tunnel junctions.
Band-gap structures of two-dimensional magnonic crystals with complex lattices
Authors: Liu Yan-Ling  , Liu Wen-Jing  , Bao Jia-Mei  , Cao Yong-Jun  ,   College of Physics and Electronic Information, Inner Mongolia Normal University, Huhhot 010022, China
Published: December 2020

Magnonic crystals with spin waves as information carriers are the magnetic counterparts of photonic and phononic crystals. The studies of spin waves or magnons in magnonic crystals have attracted increasing attention, especially for the characteristics of band gaps. However, most of the previous work has paid attention to the magnonic crystals with simple lattices. In this paper, the model of magnonic crystals with complex lattices which is composed of two different scatterers of ferromagnetic materials periodically embedded in another kind of ferromagnetic matrix material is proposed for the first time. Then, the plane-wave expansion method is developed by using the idea of super cells, in which the Fourior coefficient of exchange constant in the space of reciprocal lattice vector is analytically derived, and this method can be used to numerically investigate the eigen-properties of spin waves in magnonic crystals with complex lattices. Of course, it can be applied to the fields of other artificial crystals with complex lattices after the corresponding process, such as photonic crystals and phononic crystals. Band structures of two-dimensional magnonic crystal with complex lattices consisting of two different sizes of Fe cylinders alternately arranged in Euo matrix, are numerically calculated by using the above plane-wave expansion method. The behaviors of band gaps of spin waves changing with the total filling fraction of volume f and also with the mismatch of the filling fraction of volume of two Fe cylinders in EuO matrix are numerically studied. The results of magnonic crystals with complex lattices are compared with those of magnonic crystal with simple latticeic. Some conclusions are summarized as follows. In the same filling fraction of volume f, the width of band gap B4, 5 in the magnonic crystal with complex lattice is always larger than that with the simple lattice, but the width of band gap B8, 9 in the complex lattice is less than that in the simple lattice. When f = (fA + fB)/2 = 0.5, the width of band gap B4, 5 increases as the mismatch between fA and fB increases, but the behavior of the gap B8, 9 is opposite. Moreover, some new spin-wave gaps can be generated by changing the mismatch between fA and fB. This is because the gaps in our studied systems result from the mechanism of Bragg scattering of spin wave in periodic ferromagnetic materials. When the mismatch between fA and fB increases, the multiple scattering effects become stronger. All of these results show that the width or the frequency of band gap can be optimized or tuned by using the complex lattice. Such an approach through fabricating complex lattices may open a new scope for engineering and designing the band gaps of magnonic crystals.
Adsorption, film growth, and electronic structures of 2,7-dioctyl[1]benzothieno-[3,2-b][1]benzothiophene (C8-BTBT) on Cu (100)
Authors: Zhang Yu-He  , Niu Dong-Mei  , Lü Lu  , Xie Hai-Peng  , Zhu Meng-Long  , Zhang Hong  , Liu Peng  , Cao Ning-Tong  , Gao Yong-Li  ,   Institute of Super-Microstructure and Ultrafast Process in Advanced Materials, Central South University, Changsha 410083, China;,   Department of Physics and Astronomy, University of Rochester, Rochester 14627, USA
Published: December 2020

Using ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), and grazing X-ray diffraction measurement(GIXRD), we systematically investigate the correlations of interface energy level structure, film growth and the molecular orientation of 2, 7-dioctyl[1]benzothieno-[3, 2-b][1]benzothiophene (C8-BTBT) on Cu(100). We find that the adsorption of the first layer of C8-BTBT molecules on Cu(100) is a stable physical one, and there is no chemical shift of the S 2p peaks of XPS and the ratio of the output of C to that of S is the same as the stoichiometric value of the molecular C8-BTBT. The heights of the steps of the upper layers of C8-BTBT in the AFM images are ～ 30 , close to the length of the molecular long c-axis, indicating the standing-up configuration of the upper molecules. AFM image shows that the upper molecules tend to grow into islands while the bottom molecules tend to grow into layer, suggesting an Stranski-Krastanov growth mode of multilayer C8-BTBT on Cu(100). The GIXRD shows an out-of-plane period of 30.21 , which consistently proves the standing-up configuration of the outer molecule layer. There is an electric dipole of 0.41 eV at the very interface pointing from the substrate copper to C8-BTBT, which will reduce the barrier for electron transport and increase the barrier for hole transport from Cu to C8-BTBT. The vacuum level (Evac) starts to bend downward after 16 deposition, and with the increase of the thickness of the film, a total downward shift of 0.42 eV is observed. The downward shift is ascribed to the changing of molecular orientation from lying down before 16 to standing up after 16 , which establishes an outward-pointing layer of C-H bonds and accordingly forms a dipole layer depressing the surface barrier. The shape and leading edge of the hightest occupied molecular orbit (HOMO) also change with the increase of film thickness. These changes are due to the anisotropy of electron ionization from molecular orbit. The total downward shift of the HOMO is about 0.63 eV. The downward bending of 0.42 eV for Evac and 0.63 eV for HOMO with increasing film thickness lead to a slightly decreasing ionization potential (IP) about 0.1 eV before 32 and then an increasing IP about 0.31 eV, which finally results in a total increase of 0.21 eV for IP. The bending electronic structures facilitate electron transport from interface to surface and hole transport from surface to interface. Our Investigation provides valuable information for relevant device design.
Modeling and simulation of the insulated gate bipolar transistor turn-off voltage slope under inductive load
Authors: Tan Ji  , Zhu Yang-Jun  , Lu Shuo-Jin  , Tian Xiao-Li  , Teng Yuan  , Yang Fei  , Zhang Guang-Yin  , Shen Qian-Xing  ,   Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029, China;,   Jiangsu R&D Center for Internet of Things, Wuxi 214135, China
Published: December 2020

The insulated gate bipolar transistor (IGBT) has developed rapidly as a key power device for medium power application since it was first introduced. It is well known for its relatively low conduction loss and easy gate control. The IGBT is commonly seen in the inductive load application circuit. Due to the large inductive load, the current of the IGBT will stay high until the voltage rises to the bus voltage during the IGBT turn-off. After that, the current starts to decrease and IGBT goes into the tail-current procedure withstanding high voltage. When evaluating the turn-off loss of IGBT, the fall time and the tail current are commonly taken into consideration because these two features are known as good representations of power loss during tail-current procedure. However, the power loss occurring during the voltage rise, which is usually neglected, can also be a significant contributor to the total turn-off loss. The dv/dt determines the voltage rise time and the power loss during this procedure. Thus, predicting the dv/dt is essential for evaluating the power loss during the IGBT turn-off. In this paper, the turn-off transient is divided into four stages and the physical mechanism which determines the dv/dt during the turn-off transient is carefully investigated. An analytical model to characterize the dv/dt during IGBT inductive turn-off is derived based on the calculated miller capacitance values. The functions of the miller capacitance and the dv/dt against time are presented to predict the collector voltage waveform during the IGBT turn-off. To make the model more accurate, the current dependence is considered when calculating the miller capacitance as well as the voltage dependency. The derived model shows that the dv/dt increases nonlinearly with the time going by and can be influenced by several factors, including the drive circuit conditions, the collector current and the carrier concentration profile in the ON-state. Further investigation indicates that the ON-state carrier concentration is greatly influenced by the IGBT cell structure. Thus, the model presented in this paper is effective in both the estimation of IGBT turn-off loss and the guidance of device structure design. The prediction of the derived model shows good agreement with the two-dimensional numerical simulation by Sentaurus TCAD (with the relative error not exceeding 10%) for the IGBT turn-off over a broad range of the collector current values. The device structure simulated in this paper is based on the 650 V/60 A trench-FS-IGBT. The thickness values of the total structure and the buffer layer are 80 m and 20 m, respectively.
Moving source parameter estimation in an uncertain environment
Authors: Li Qian-Qian  , Yang Fan-Lin  , Zhang Kai  , Zheng Bing-Xiang  ,   College of Geomrtics, Shandong University of Science and Technology, Qingdao 266590, China;,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China;,   Offshore Oil Engineering (Qingdao) Co., Ltd, Qingdao 266520, China
Published: December 2020

Environmental uncertainty is one of the limiting factors in the matched-field localization. Within a Bayesian framework, environmental focalization has been widely used to solve the augmented localization problem, in which the environmental parameters, source ranges and depths are considered to be the unknown variables. However, the position of the moving source varies with time, which limits the observation interval and the number of acoustic signals. Therefore, it has to estimate lots of unknown parameters with the limited observation information. When the source moves fast or the environment has great uncertainty, the environmental focalization gets worse. Taking the parameter estimation of Kalman filter in the non-stationary process as a reference, the acoustic signals from a series of observations are treated in a simultaneous inversion. This provides the most informative solution, since data from multiple source locations are brought to bear simultaneously on the environmental unknowns, which in turn constrain the source locations better. In this article, the time-unvarying parameters are introduced to describe the source position. The source positions are inverted indirectly by the time-unvarying parameters, which reduces the estimated parameter dimension effectively. At the same time, the current estimated results are treated as the priori information of the next inversion, which establishes the new prior distribution and cost function. It could compensate for some individual abnormal data effectively and realize continuous localization of the moving source. The noise signals radiated from a surface ship target are processed and analyzed. The Bayesian tracking algorithm greatly increases the observation interval and the number of acoustic signals, and enhances the localization accuracy in an uncertain water environment. Tracking results of the ship noise indicate that simultaneous inversion of multiple acoustic observations with constant velocity track model and the Thikhonov regularization provides a better solution than sequential independent inversions. It is indicated that the Bayesian tracking method learns the uncertain environment as more observations become available. It is discovered that the maximum a posteriori solution and the two-dimensional solution have similar results according to the global positioning system value. The reason is that the source locations are treated implicitly by the source speed, which is similar to the marginal probability distribution by reducing the multidimensional posterior probability density to the representative two-dimensional probability distributions.
Comparative study on the spatial evolution of liquid jet under linear and nonlinear stability theories
Authors: Lü Ming  , Ning Zhi  , Yan Kai  ,   School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

In the injecting process of liquid jet, the disturbance wave on jet interface will grow continually, leading to the spatial development and atomization of liquid jet. Studying the spatial evolution of liquid jet will help to deepen the understanding of the mechanism of jet breakup and atomization. In this paper, based on the linear and nonlinear stability theories, the first-order and second-order dispersion equations describing the stability of liquid jet with cavitation bubbles in a coaxial swirling compressible airstream are built, respectively, and the dispersion equation and its solving method are verified by the data in the literature. On this basis, the developments of first-order and second-order disturbance are analyzed, and the spatial evolutions of liquid jet are compared under linear and nonlinear stability theories. The results show that the wavelength and amplitude of the second-order disturbance are much smaller than those of the first-order disturbance. The disturbance development on jet surface is mainly dominated by the development of the first-order disturbance along the axial direction. With the increasing of axial distance, the second-order disturbance gradually begins to play a role in the developing of disturbance. The role of second-order disturbance is mainly reflected in three aspects, i. e., obviously increasing the disturbance amplitude at wave crest, reducing the disturbance amplitude at wave trough (sometimes ups and downs occur), and changing the waveform to a certain degree. The dominant disturbance mode on jet surface will not change under two kinds of theories. By using the nonlinear stability theory, satellite droplets which are found on jet surface in experiments can be reflected, and the shape of main droplet changes obviously from the ellipsoid to sphere. Also, the change of dimensionless radius of liquid jet is greater by nonlinear stability theory than by linear stability theory, which indicates that the oscillation extent of jet surface increases due to considering the second-order disturbance. Therefore, compared with the linear stability theory, the nonlinear stability theory has the advantage that it considers the effects of high-order disturbance on the spatial evolution of liquid jet in addition to the first-order disturbance on jet surface. The nonlinear stability theory can predict the spatial development of liquid jet in more detail than the linear stability theory.
A new method to determine the dislocation density in wurtzite n-GaN
Authors: He Ju-Sheng  , Zhang Meng  , Pan Hua-Qing  , Qi Wei-Jing  , Li Ping  ,   School of Science and Technology, Nanchang University, Nanchang 330029, China;,   School of Material Science and Engineering, Nanchang University, Nanchang 330031, China;,   Department of Mechanical Engineering, Shangrao Vocational and Technical College, Shangrao 334100, China;,   Modern Education Technology Center of Nanchang University, Nanchang 330031, China
Published: December 2020

We develop a new method to determine the edge and screw dislocation density in wurtzite n-GaN film. The method is to fit the van der Pauw variable temperature Hall-effect measurements with a analytic expression of low-field electron mobility in n-GaN. Our calculations take the comprehensive effect between the dislocation line and the shallow-donor defects as the main cause to depress the carrier mobility. Because of the crystal distortion near the dislocation line, the energy is so high that shallow-donor defects in the GaN crystal can be captured near the dislocation line. In other words, the shallow-donor defects distribute in lines along the dislocation line, but the shallow-donor defects along the screw and edge dislocation line have different energy levels. The shallow-donor defects take energy from lattice and the carrier, which is in relaxation process, then deliver the energy through ionizing. So, it is found that the following assumptions need to be made in order to obtain the model function for the mobility over a wide temperature range: i) there are 6 shallow-donor defect lines around one dislocation line; ii) two donor energy levels belonging to the screw and edge dislocation respectively must be taken into account; iii) the exchange energy between the carrier and the shallow-donor defect is ħωLO, the energy value of polar optical phonon. Under these assumptions, experiments indicate that our calculation function can fit the experimental curve best. The values of dislocation density from our model and others determined by x-ray diffraction or by chemical etching method are in good agreement, and the values of donor energy levels from our model and Rode iterative method to solve the Boltzmann equation are also in good accordance with each other. This method is applicable for the wurtzite n-GaN films grown by various preparation technologies under any condition, which is for the sample with the peak-mobility temperature about or under 200 K, not for the sample with the peak-mobility temperature about or above 300 K, which room-temperature mobility usually is about or less than 100 cm2/(V·s).
Electron-electron scattering in three-dimensional amorphous IGZO films
Authors: Zhang Hui  , Yang Yang  , Li Zhi-Qing  ,   Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Faculty of Science, Tianjin University, Tianjin 300350, China
Published: December 2020

Electron dephasing process is important and interesting in disordered conductors. In general three-dimensional (3D) disordered metals, the electron-electron (e-e) scattering is negligibly weak compared with the electron-phonon (e-ph) scattering. Thus, the theoretical prediction concerning the e-e scattering rate 1/τee as a function of temperature T in 3D disordered conductor has not been fully tested so far, though it was proposed four decades ago. In the frame of free-electron-like model, the e-ph relaxation rate 1/τep is proportional to carrier concentration n, while the small-and large-energy-transfer e-e scattering rate obey the laws 1/τeeS ∝ n-4/3 and 1/τeeL ∝ n-2/3, respectively. In other words, e-e scattering may dominate the dephasing processes in 3D disordered metals with sufficient low carrier concentrations. In the present work, we systematically investigate the electronic transport properties of amorphous indium gallium zinc oxide (a-IGZO) prepared by the radio frequency sputtering method. The carrier concentrations of the highly degenerate IGZO films are all ～ 5×1019 cm-3, which are 3-4 orders of magnitude lower than those of typical metals. Our thick films (～ 800 nm) are 3D systems with respect to weak-localization (WL) effect and e-e scattering. X-ray diffraction patterns of the films indicate that our films are all amorphous. For each film, the resistivity increases with the increase of the temperature in the high temperature region (T ≥ 200 K) and the carrier concentration is almost invariable in the whole measured temperature range. This indicates that the films possess metal-like transport properties. By comparing the low-field magnetoconductivity versus magnetic field data σ (B) with that from the 3D WL theory, we extract the electron dephasing rate 1/τφ at different temperatures in the low temperature region. It is found that 1/τφ varies linearly with T3/2 for each film. The T3/2 behavior of 1/τφ can be quantitatively described by the 3D small-energy-transfer e-e scattering theory. The e-ph scattering rate 1/τep and large-energy-transfer e-e scattering rate 1/τeeL are negligibly weak in this low-carrier-concentration conductor. Thus, we can observe the T3/2 behavior of 1/τφ.
Design and performance analysis of THz microcavity-enhanced graphene photodetector
Authors: Liang Zhen-Jiang  , Liu Hai-Xia  , Niu Yan-Xiong  , Liu Kai-Ming  , Yin Yi-Heng  ,   School of Instrument Science and Optoelectronic Engineering, Beihang University, Beijing 100191, China
Published: December 2020

Detection of the terahertz (THz) electromagnetic spectrum(wavelengths range 0.03-3 mm) is a promising technique for a large variety of strategic applications, such as biomedical diagnostics and process, quality control, homeland security, and environmental monitoring, etc. Graphene has been recognized internationally to have dominant advantages in photodetectors operating due to its high carrier mobility, gapless spectrum, and frequency-independent absorption coefficient. Graphene photodetector operating in the THz region has been extensively studied with great interests.
A graphene microcavity photodetector with THz electromagnetic spectrum is demonstrated in this paper, and its responsivity and detectivity under THz electromagnetic spectrum are evaluated. In the designed device, we adopt a distributed bragger reflection (DBR) consisting of two semiconductor materials SiO2 and TiO2 to form an alternating cavity with high-finesse planar, sandwich the absorbing graphene layer between the cavitys top and bottom layers, and design the DBRs reflectivity by the optical transmission matrix method. The monolayer graphenes optical absorption mechanism of the THz radiation spectrum is studied by the conductivity matrix and Maxwells equations with the electromagnetic boundary conditions. Graphenes transfer matrix and absorption coefficient equation are further derived. It is found that at THz region, graphenes conductivity plays an important role in its absorptionand its absorption is 9-22 times enhanced compared with that at the visible region. An optical absorption model of microcavity-enhanced graphene photodetector at THz region is established. The photodetectors absorption rate and responsitivity are analyzed specifically. Theoretical analysis shows that absorption rate is symmetrical to the microcavitys center position and changes periodically, and the shift of the microcavity length influences the period numbers. The maximum rate of the photodetectors absorption reaches 0.965 at 0.12 THz, which increases 93% compared with its maximum absorption rate 0.5 with no cavity. The optimal structure parameters for the designed photodetector are as follows, the top and bottom mirrors reflectivity are 0.928 and 0.998 respectively, the microcavity length is 2.5 mm, the graphene is 0.035 mm away from the top mirror. Under the optimal structure, the photodetectors responsivity reaches 236.7 A/W, and its full width at half maximum reaches 0.035 THz. The designed graphene microcavity photodetector can exhibit high responsivity and detectivity in THz radiation spectrum.
Distance regularized level set evolution in magnetic resonance image segmention based on bi-dimensional ensemble empirical mode decomposition
Authors: Fan Hong  , Wei Wen-Jin  , Zhu Yan-Chun  ,   School of Computer Science, Shaanxi Normal University, Xi’an 710062, China;,   Institute of Biomedical and Health Engineering, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, China
Published: December 2020

Original image is directly processed by the existing image segmentation algorithms, which is easily affected by noise. A bi-dimensional ensemble empirical mode decomposition (BEEMD) method is introduced to improve the accuracy of MR image segmentation by distance regularized level set (DRLSE) method. The BEEMD method is the extension of one-dimensional noise assisted data analysis from ensemble empirical mode decomposition (EEMD). The key points of BEEMD are as follows. four-neighborhood optimization is used to find extermum; three-spline interpolation is used to obtain the envelope; amplitude standard of added white noise is restricted; a certain time of integration is used to avoid modality aliasing problem. The main steps of the proposed method are as follows. Firstly, the MR image is decomposed into a number of two-dimensional intrinsic mode functions (BIMF) by BEEMD method; different weighting coefficients are endued to BIMF for image reconstruction to enhance the segmentation target. Secondly, part of BIMF components are added into edge indicator function of DRLSE to recover the blurring boundary caused by Gauss smooth operation. Then DRLSE is used to segment the reconstructed MR image. High accuracy and robustness of proposed algorithm are obtained in both simulations and clinical MR images. However, compared with DRLSE, the proposed method is complex and time consuming because using BEEMD for preprocessing the segmentation image.
Effects of Dzyaloshinskii-Moriya interacton and decoherence on entanglement dynamics in Heisenberg spin chain system with different initial states
Authors: Cong Mei-Yan  , Yang Jing  , Huang Yan-Xia  ,   College of Physics and Electronic Science, Hubei Normal University, Huangshi 435000, China;,   Key Laboratory of Quantum Information, University of Science and Technology of China, Chinese Academy of Science, Hefei 230026, China
Published: December 2020

With considering the intrinsic decoherence, the dynamic behaviors of quantum entanglement in a three-qubit XXZ Heisenberg system with Dzyaloshinskii-Moriya (DM) interaction and anisotropy for different initial states are investigated. The research result shows that the anisotropy parameter does not affect the system entanglement, however, the intrinsic decoherence has obvious inhibitory effect on entanglement. When the initial state of system is an entangled state, we can obtain the stable value of entanglement by adjusting DM interaction parameters appropriately. As the system initial state is a separation state, entanglement oscillates, and the amplitude of oscillation decays with time periodically, and there will appear the death phenomenon after each oscillation, and with time going on, its concurrence will be zero. When the initial state is entangled, by choosing the proper DM parameter, the three pairs of entanglements oscillate with time and eventually approach to a steady value. The increase of accelerates the decay of concurrence. When the initial state is separated, entanglement oscillates, and the amplitude of oscillation decays with time periodically, and there will appear the death phenomenon after each oscillation, with time going on, its concurrence will be zero. Therefore, the proper initial state and DM interaction parameters can control the concurrence effectively under the intrinsic decoherence, thereby obtaining the preferable entanglement resource.
Synchronization of fractional-order chaotic systems based on adaptive fuzzy control
Authors: Chen Ye  , Li Sheng-Gang  , Liu Heng  ,   Department of Mathematics and Information Sciences, Shaanxi Normal University, Xi'an 710119, China;,   Department of Mathematics and Computational Sciences, Huainan Normal University, Huainan 232038, China
Published: December 2020

In this paper the synchronization problem for fractional-order chaotic system with unknown external disturbance is investigated by adaptive fuzzy control. Based on the fractional Lyapunov stability theorem, an adaptive fuzzy controller, which is accompanied with fractional adaptation law, is established. Fuzzy logic system is used to approximate an unknown nonlinear function. The fuzzy approximation error can be canceled by the proposed fractional adaptation law. Just like the stability analysis in an integer-order chaotic system, the quadratic Lyapunov function is used to analyze the stability of the fractional-order closed-loop system. The control method can realize good synchronization performances between two fractional-order chaotic systems, and the synchronization error tends to zero asymptotically. Besides, the proposed controller can also guarantee the boundedness of all signals in the closed-loop system. Finally, the numerical simulation results illustrate the effectiveness of the proposed control method for fractional-order chaotic system in the presence of the external disturbances.
Writing and displaying by the laser on a long lag phosphor material
Authors: Mei Yi-Feng  , Tang Yuan-He  , Mei Xiao-Ning  , Liu Han-Chen  , Liu Qian  , Yu Yang  , Li Nin-Yuan  , Gao Heng  ,   School of science, Xi'an University of Technology, Xi'an 710048, China;,   School of higher vocational and technical education, Xi'an University of Technology, Xi'an 710082, China;,   School of water resources and hydroelectric engineering, Xi'an University of Technology, Xi'an 710048, China;,   School of Science, Xi'an Polytechnic University, Xi'an 710048, China
Published: December 2020

We make a machine that can perform as an invisible hand able to write and draw smoothly accompanied with the incidental music. And this machine can be used in the commercial advertising display, artmobile poster writing, the accessory equipment of the multimedium classrooms, stage effect, new art pattern especially in dark. We present a new display application of the long lag phosphor (LLP) material in this paper. A prototype is fabricated which can be written, drawn and displayed by controlling a laser beam on the screen which is made from the LLP material.
For selecting the match laser beam wavelength for different LLP material screens, the energy band structure of the LLP material Mn(H2PO4)2 of 3-4 eV band gap is calculated by VASP (Vienna abinitio simulation package) software and its Raman shift peaks of Mn(H2PO4)2 are tested at 625 nm, 769 nm, 1049 nm and in far infrared wavelength range. The intensity of powdery LLP SrAl2O4: Eu2+, Dy3+, which is tested by the instrument of UWLA(ultra-weak luminescence analyzer), can decay from 43479 to 9570 electronic counts in 5 min, and then descend slowly. The intensity decay of coated film LLP Mn(H2PO4)2, which is tested by the instrument of HANDYSCOPE HS3, can decay quickly at the beginning and then slowly after 400s. These intensity decay results can explain that LLP materials of SrAl2O4:Eu2+, Dy3+ and Mn (H2PO4)2 are suitable for displaying the image by our prototype.
A prototype is successfully made by our group for writing English and Chinese words and drawing picture. Arduino Board is used to control two step motors, and X mirror and Y mirror are rotated to reflect the laser beam. An excitation dot is formed on the surface of LLP display screen. By drawing vectorgragh with Coreldraw and convert it into .nc file, the computer runs G-code in CNC (computer numerical control) automatically. Arduino controlled mirror rotation drives the laser beam. The trace of the laser dot is left on the screen and becomes article or graphs in afterglow. The whole device can be energy saving, eyes comfortable, low cost and easy to pick up.
Magnetless circulator based on phase gradient metasurface
Authors: Qiu Tian-Shuo  , Wang Jia-Fu  , Li Yong-Feng  , Wang Jun  , Yan Ming-Bao  , Qu Shao-Bo  ,   College of Science, Air Force Engineering University, Xi'an 710051, China
Published: December 2020

Circulators are widely used microwave components that rely on magnetic materials. They have been a subject of extensively theoretical and experimental development for over 50 years. Nowadays, commercial circulators require ferrite and external bias magnetic field to realize circulation performance. However, ferrite circulators suffer major drawbacks: they are too heavy, incompatible with integrated circuit technologies, expensive, sensitive to temperature, etc. So, it is very hard to further improve the characteristic of traditional ferrite circulator. And it is important to overcome the major drawbacks of the traditional ferrite circulator. In this paper, the anomalous refraction feature of the phase gradient metasurface is utilized to realize nonreciprocal characteristics. Magnetless circulator based on phase gradient metasurface is proposed and then analyzed. The circulator consists of phase gradient metasurfaces and a three-port waveguide. Three metasurfaces are arranged into 60-degree angle with respect to each other. The metasurface shows high efficiency in anomalous refraction. With the help of phase gradient metamaterial, the signal can only be refracted to the next port in rotation along one direction. That makes the circulation performance. To design and optimize the circulator for better circulation performance, the numerical simulations are performed using the full-wave electromagnetic simulator CST Microwave Studio 2013. To verify the design of the circulator based on phase gradient metasurface, the circulator is fabricated using waveguide and metasurfaces. The scattering parameters of the magnetless circulator based on phase gradient metasurface are measured using a vector network analyzer (Agilent N5230 A). The measured S-parameters show that the circulator exhibits good circulation performances at a frequency of 20.8 GHz. At 20.8 GHz, the insertion loss is 0.8 dB. And the return loss and isolation degree can reach -10 dB. In this paper, a new method is used to design the circulators. This work makes it possible to reduce the weight of the device. Moreover, it is also insensitive to temperature. Therefore, we can make a conclusion that the magnetless circulator based on phase gradient metasurface has potential value in application. However, there is still lots of work to do to improve the performance of the circulator. In future work, we will use wideband metasurfaces to broaden the bandwidth, improve the isolation degree, reduce the insertion loss, and reduce the return loss. And free space can be lead into the circulator to reduce the bulk of the circulator and improve the circulation performance.
Recent theoretical development in confined liquid-crystal polymers
Authors: Liang Qin  , Jeff Z. Y. Chen  ,   Faculty of Mathematics and Computational Science, Xiangtan University, Xiangtan 411105, China;,   Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
Published: December 2020

Liquid-crystal polymers in confined system is a fundamental issue in soft matter. Theoretical method plays animportant role in studying these systems. The intention of this work is to give a thorough reviewof the theoretical methodologies used in tackling confined liquid crystals. At first, some basic concept of liquid crystal, such as a vital order parameter for orientation, phases of liquid crystal, the uniaxial and biaxial of liquid crystal, are presented. After that, a brief review of the development of liquid-crystal theories, which include the Onsager model, the Maier-Saupe model, the McMillanmodel, the Landau-de Gennes expansion, the Frank elastic model and the self-consistent field model for liquid-crystal polymers, are given. All these theories havetheir own advantages and disadvantages. For example, the phenomenological Frank elastic model is the most widely used model due to its simplicity. In contrast, parameters in the self-consistent field model are physically meaningful, however, it is rather complicated. During recent decades, with these theories and suitable boundary treatment, plenty confined liquid crystal systems are investigated. In this review, we focus on three kinds of confined systems: 1) the surface wetting behavior in slits; 2) the two-dimensional liquid crystals confined by a boundary line and 3) defects in the orientational field of rigid rods on spherical surface. Results arrived from different At the end of this review, we give a list of frontier issues and an outlook for thecoming ten years.