bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum control of nuclear magnetic resonance spin systems
Authors: Li Jun  , Cui Jiang-Yu  , Yang Xiao-Dong  , Luo Zhi-Huang  , Pan Jian  , Yu Qi  , Li Zhao-Kai  , Peng Xin-Hua  , Du Jiang-Feng  ,   Hefei National Laboratory for Physical Sciences at Microscale, Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China;,   Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

With the development of quantum information science, the active manipulation of quantum systems is becoming an important research frontier. To build realistic quantum information processors, one of the challenges is to implement arbitrary desired operations with high precision on quantum systems. A large number of quantum control methods and relevant numerical techniques have been put forward in recent years, such as quantum optimal control and quantum feedback control. Nuclear magnetic resonance (NMR) spin systems offer an excellent testbed to develop benchmark tools and techniques for controlling quantum systems. In this review paper, we briefly introduce some of the basic control ideas developed for NMR systems in recent years. We first explain, for the liquid spin systems, the physics of various couplings and the causes of relaxation effects. These mechanisms govern the system dynamics, and thus are crucial for constructing rigorous and efficient control models. We also identify three types of available control means: 1) raido-frequency fields as coherent controls; 2) phase cycling, gradient fields and relaxation effects as non-unitary controls; 3) radiation damping effect as feedback control mechanism. Then, we elucidate some important control tasks, which may arise from the conventional NMR spectroscopy (e.g., pulse design and polarization transfer) or from quantum information science (e.g., algorithmic cooling and pseudo-pure state preparation). In the last part, we review some of the most important control methods that are applicable to NMR control tasks. For systems with a relatively small number of spins, it is possible to use analytic optimal control theory to realize the target unitary operations. However, for larger systems, numerical methods are necessary. The gradient ascent pulse engineering algorithm and pulse compiler techniques are the most successful techniques for implementing complicated quantum networks currently. There are some interesting topics of utilizing radiation damping and relaxation effects to achieve more powerful controls. Finally, we give an outline of the possible future work.
Phosphorescent hybrid organic-inorganic light emitting devices with solution-processed small molecule emissive layers
Authors: Fan Chang-Jun  , Wang Rui-Xue  , Liu Zhen  , Lei Yong  , Li Guo-Qing  , Xiong Zu-Hong  , Yang Xiao-Hui  ,   School of Physical Science and Technology, Southwest University, Chongqing 400715, China
Published: December 2020

We report efficient phosphorescent hybrid organic-inorganic light emitting devices using poly(ethylenimine) as electron-injection layer and interfacial modifier for metal oxides and solution-processed small molecule emissive layers. As a first step, the hole transport layers with various HOMO levels and the hole mobility values including TAPC, TCTA and mCP are evaluated. The results indicate that devices using a TAPC layer show the best luminance and power efficiencies. Subsequently, the optimum phosphor concentration is determined to be ca. 5%. Enlarged efficiency roll-off with increasing current density is observed in devices using the phosphor concentration above the optimum value. We also investigate the morphologies of films having different phosphor concentrations on the top of bare or PEIE-covered glass substrates, which is closely related to device performance. All the films have the RMS values of ca. 1 nm, indicating high-quality solution processed small molecule films. The blue, yellow and red devices show the maximum external quantum efficiencies of 17.3%, 10.7% and 7.3%, respectively. These efficiencies are 17.0%, 10.6% and 5.8% at 1000 cd·m-2, only showing a small roll-off, which can be attributed to alleviated triplet-triplet and triplet-polaron interactions in a broad carrier recombination zone due to using the mixed hole-transport and electron-transport materials as the co-hosts. In addition, these devices exhibit the respective Commission International Eclairage (CIE) coordinates of (0.16, 0.36), (0.50, 0.49) and (0.66, 0.32), which almost traverse the whole visible light region. Furthermore, the hybrid two-colored white devices show a luminance efficiency of 31 cd·A-1, power efficiency of 14.8 lm·W-1 at 1000 cd·m-2 and the operating current-insensitive CIE coordinates of (0.32, 0.42). The efficiencies represent the significant improvement over the previously reported values, which can be attributed to high-quality small molecule films on PEIE, and in particular to the unique properties of small molecule host materials such as balanced carrier transport and high triplet energy. Further efforts including selection of high-mobility electron transport host material and phosphors with high luminescence quantum yield are made to increase the efficiency and reliability of hybrid organic-inorganic light emitting device.
High mobility thin-film transistor with solution-processed hafnium-oxide dielectric and zinc-indium-tin-oxide semiconductor
Authors: Zhu Le-Yong  , Gao Ya-Na  , Zhang Jian-Hua  , Li Xi-Feng  ,   School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China;,   Key Laboratory of Advanced Display and System Applications of Ministry of Education, Shanghai University, Shanghai 200072, China
Published: December 2020

In this paper, bottom-gate-top-contact structured thin-film transistors (TFTs) are fabricated by solution-processing of hafnium oxide (HfO2) dielectrics and zinc-indium-tin-oxide (ZITO) semiconductors. Solution-processed HfO2 films are annealed at different temperatures, and the 500℃ annealed HfO2 dielectrics can exhibit optimizing film properties such as smooth surfaces (the RMS value of HfO2 films is less than 1 nm), low leakage current density (1.25×10-7 A/cm2 at 1 MV/cm), high transmittance (above 80% at the wavelength ranging from 400 to 800 nm) and high relative dielectric constant (about 12). The smooth surface of HfO2 dielectrics is attributed to the decreased charge trapping states at the interface between the HfO2 dielectrics and ZITO semiconductors, and thus improves the device electrical performance and stability. Hence, TFT devices of HfO2 dielectrics annealed at 500℃ show a high saturated field effect mobility of more than 100 cm2·V-1·s-1 a low threshold voltage of -0.5 V, an on-to-off current ratio of 5×106 and a small subthreshold swing of 105 mV/dec. An almost negligible threshold voltage shift is observed under a positive bias stress for 1000 s, indicating the excellent stability of HfO2 TFT devices.
Time-optimized quantum QFT gate in an Ising coupling system
Authors: Ling Hong-Sheng  , Tian Jia-Xin  , Zhou Shu-Na  , Wei Da-Xiu  ,   Physics Department and Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, Shanghai 200062, China.
Published: December 2020

Quantum Fourier transform (QFT) is a quantum analogue of the classical discrete Fourier transform. It is a fundamental quantum gate in quantum algorithms which has an exponential advantage over the classical computation and has been excessively studied. Normally, an n-qubit quantum Fourier transform could be resolved into the tensor product of n single-qubit operations, and each operation could be implemented by a Hadamard gate and a controlled phase gate. Then the complexity of an n-qubit QFT is of order O(n2). To reduce the complexity of quantum operations, optimal control (OC) method has recently been used successfully to find the minimum time for implementing a quantum operation. Up to now, two types of quantum optimal control methods have been presented, i.e. analytical and numerical methods. The analytical approach is to change the problem of efficient synthesis of unitary transformations into the geometrical one of finding the shortest paths. Numerical optimal control procedures are based on the gradient methods (GRAPE, Gradient Ascent Pulse Engineering) and Krotov methods. Notable application mainly focus on nuclear magnetic resonance fields, including imaging, liquid-state NMR, solid-state NMR, and NMR quantum computation. One obvious advantage of optimal control NMR quantum computation is that the OC unitary evolution transformation pulse sequences are normally shorter than the conventional corresponding ones. Here we use the optimal control method to find the minimum duration for implementing QFT quantum gate. A linear spin chain with nearest-neighbor Ising interaction is used to find the optimization. And the optimized pulse sequence is experimentally demonstrated on an NMR quantum information processor. By using optimal control method with numerical calculation, a three-qubit QFT in an indirect-linear-coupling chain system is optimized. The duration of the OC QFT is obviously shorter than that of conventional approaches. The OC pulse sequence has been experimentally implemented on a liquid-state NMR spectrometer. To verify the optimally controlled pulse sequence for the three-qubit QFT, different initial states are assumed. The accuracy of the OC pulse sequence could be demonstrated by the consistency of theoretical simulation spectra with the experimental results. The good consistency between the simulation and the experimental spectra demonstrates that the OC QFT is of high fidelity.
The directional transport phenomenon in fractional logarithm coupled system under a non-periodic external force
Authors: Yang Jian-Qiang  , Ma Hong  , Zhong Su-Chuan  ,   Department of Mathematics, Sichuan University, Chengdu 610064, China;,   Department of Aeronautics and Astronautics, Sichuan University, Chengdu 610065, China
Published: December 2020

Using the fractional calculus theory, we investigate the directional transport phenomenon in a fractional logarithm coupled system under the action of a non-periodic external force. When a Brownian particle moves in the media with memory such as viscoelastic media, the system should be modeled as a nonlinear fractional logarithm coupled one. Using the method of fractional difference, we can solve the model numerically and discuss the influences of the various system parameters on the average transport velocity of the particles. Numerical results show that: 1) The directional transport phenomenon in this fractional logarithmic coupled model appears only when the external force exists, and the value of the average transport velocity of the particles increases with increasing external force. 2) When the fractional order of the system is small enough, the damping memory has a significant impact on the average transport velocity of the particles. Furthermore, the average transport velocity of the particles has an upper bound (although it is very small), no matter how the external force, coupled force and the intensity of noise change, the average transport velocity of the particles is no more than the upper bound. When there is no external force and the damping force is big enough, the directional transport phenomenon disappears. 3) When the fractional order of the system and the external force are big enough, although the directional transport phenomenon appears, the coupled force and the intensity of noise have no impact on the system. 4) Only when the external force is small enough, could the coupled force and noise intensity influence the average transport velocity of the particles. In this situation, the directional transport phenomenon appears when the fractional order of the system is big enough, and the average transport velocity of the particles changes along with the change of the coupled force and the noise intensity.
Indoor wireless propagation under line of sight and no line of sight comprehensive channel modeling
Authors: null  ,   Department of Communications, Nanjing University of Information Science and Technology, Nanjing 210044, China;
Published: December 2020

This paper mainly deals with the indoor wireless propagation channel under line of sight (LOS) and non-line of sight (NLOS) propagation conditions, introducing the reference model and studing the design and simulation of modeling and the relevant statistical properties. This paper will present a comprehensive and improved indoor reference channel model based on a geometric scattering model. The reference channel model assumes that infinite number of scatterers will be uniformly distributed on the two-dimensional (2D) horizontal plane of a three-dimensional space. This paper also derives analytical expressions for the probability density function (PDF) of the angle-of-arrival (AOA), the Doppler power spectral density (PSD), and the temporal autocorrelation function (ACF) of an electromagnetic arrival signal; it also analyzes the influences of the important parameters of the functions. It presents a highly efficient sum-of-cisoids (SOC) channel simulation model from the unrealistic reference model, also proposes two efficient parameter computation methods for the design of sum-of-cisoids indoor channel simulation model and compares the computing performances of both. It is shown by simulation results that the statistical properties of the sum-of-cisoids channel simulation model match perfectly the reference channel model. It turns out that the indoor reference model can be approximated by an SOC channel simulation model. Meanwhile the channel simulation model can be well applied to evaluate the performance of indoor wireless communication systems. It also extends the research for indoor wireless channel modeling while reduces the realization expenditure.
Frabrication and properties of self-powered ultraviolet detectors based on one-demensional ZnO nanomaterials
Authors: Qi Jun-Jie  , Xu Min-Xuan  , Hu Xiao-Feng  , Zhang Yue  ,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

ZnO micro/nanowires were synthesized by chemical vapor deposition method. The morphology and structure of the products have been characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL) and micro-Raman scattering spectrometer, etc. Results show that the surface of the highly uniform ZnO wire is smooth and the as-synthesized ZnO wires show high crystal quality. Three types of UV detector are constructed using a single ZnO nanowire with different contact characteristics, and their corresponding performances are investigated systematically by using Keithley 4200-SCS and other equipments. All of the three different devices exhibit good rectifying characters and significant responsivity to ultraviolet light. The devices show self-driven features at zero bias. Compared with the devices made from Schottky contact and ZnO/PEDOT:PSS film, the present single ZnO nanowire/p-Si film devices with heterojunctions have the best self-powered function, which can be attributed to the stronger built-in electric field as well as the smaller dark current due to the insulating layer on the p-Si film. At zero bias, the fabricated ZnO nanowire/p-Si film device can deliver a dark current of 1.210-3 nA and a high photosensitivity of about 4.5103 under UV illumination. The response of the devices made from ZnO nanowire/p-Si film to UV illumination in air is pretty fast with the rise time of about 0.7 s and the fall time of about 1 s, which could be attributed to the fact that the photo-generated electron-hole pairs in the depletion layer is quickly separated by the built-in electric field, leading to a rapid response speed and a larger photocurrent. Comparison among the three kinds of devices indicates that the devices made from ZnO nanowire/p-Si film are the best candidate for UV detectors.
Exploring the stereodynamics of C(3P)+NO(X2)CO(X1+)+N(4S) reaction on 4A potential energy surface
Authors: Wei Qiang  ,   Department of Applied Physics, Chongqing University of Technology, Chongqing 400054, China
Published: December 2020

Studies on the dynamical stereochemistry of the titled reaction are carried out by the quasi-classical trajectory (QCT) method based on a new accurate 4A potential energy surface constructed by Abrahamsson and coworkers (Abrahamsson E Andersson S, Nyman G, Markovic N 2008 Phys. Chem. Chem. Phys. 10 4400) at a collision energy of 0.06 eV. The distribution p(r) of the angle between k-j' and the angle distribution P(r in terms of k-k'-j' correlation have been calculated. Results indicate that the rotational angular momentum vector j' of CO is preferentially aligned perpendicular to k and also oriented with respect to the k-k' plane. Three polarization-dependent differential cross sections (2/)(d00/dt), (2/)(d20/dt), and (2/)(d22+/dt) have also been calculated. The preference of backward scattering is found from the results of (2/)(d00/dt). The behavior of (2/)(d20/dt) shows that the variation trend is opposite to that of (2/)(d00/dt), which indicates that j' is preferentially polarized along the direction perpendicular to k. The value of (2/)(d22/dt) is negative for all scattering angles, indicating the marked preference of product alignment along the y-axis. Furthermore, the influences of initial rotational and vibrational excitation on the reaction are shown and discussed. It is found that the initial vibrational excitation and rotational excitation have a larger influence on the alignment distribution of j' but a weaker effect on the orientation distribution of j' in the titled reaction. The influence of the initial vibrational excitation on the three polarization-dependent differential cross sections of product CO is stronger than that of the initial rotational excitation effect.
Theoretical studies of electrostatic Stark deceleration for subsonic NH3 molecular beams
Authors: Liu Jian-Ping  , Hou Shun-Yong  , Wei Bin  , Yin Jian-Ping  ,   State Key Laboratory of Precision spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

In this paper, we investigate theoretically the Stark deceleration and cooling of subsonic NH3 molecular beams based on our second-generation electrostatic Stark decelerator with 180 stages. Firstly, we calculate the Stark shifts of NH3 molecules in the |J=1, K=1 ightangle states and show the stable area of longitudinal phase space for different synchronous phase angles. Secondly, we study the slowing performance of NH3 molecular beams in the traditional mode, and discuss the relationships between various parameters (such as the kinetic energy loss per stage, final velocity and the slowing efficiency) and the synchronous phase angle 0, as well as the dependence of final velocity on the applied voltages. It is found that a subsonic NH3 molecular beam can be decelerated from 280 to 6.7 m/s at 0=26.08 when the high voltages applied on the electrodes are 13 kV, corresponding to a removal of 99.9% kinetic energy. The translational temperature of the molecular packets in the moving frame is significantly reduced from 1.34 K to 80 mK. Finally, we study the slowing performance of NH3 molecules and the dependence of final velocity on the synchronous phase angle in an alternate operation mode. In this mode, a synchronous phase angle 0=0 is chosen to bunch the molecules by using the first 15 stages. The remaining 165 stages are then used to slow a subsonic molecular beam at a certain synchronous phase angle. Our result shows that a molecular beam with a mean velocity of 280 m/s can be decelerated to 20.7 m/s at 0=65.4 when the voltages applied are 6.5 kV, indicating a 99.4% kinetic energy removal, and the translational temperature of the molecular packets can be reduced from 1.34 K to 1.6 mK. By comparing the results obtained from the two operational modes, the temperature of the slowed molecular packet in the alternate mode is 50 times lower than that in the traditional mode. It is shown that our second-generation 180-stage Stark decelerator can effectively produce slow and cold molecules with relatively small electric dipole moment like NH3. These monochromatic NH3 molecular beams offer a promising starting point for high resolution spectroscopy, precision measurement, cold collisions and cold chemistry. This theoretical work provides a reliable basis in our further experimental research.
Analysis on dispersion characteristics of rectangular metal grating based on spoof surface plasmons
Authors: Liu Yong-Qiang  , Kong Ling-Bao  , Du Chao-Hai  , Liu Pu-Kun  ,   School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China
Published: December 2020

The unique optical and physical properties of surface plasmon polaritons (SPP) has brought about a series of novel phenomena such as SPP-enhanced transmission, local resonance, etc., and SPP has become a research hotspot around the world. In this paper, the dispersion characteristics and modes of rectangular metal grating based on spoof surface plasmons (SSP) are studied theoretically and numerically. The electromagnetic fields of SSP which are below and above the grating surface are presented using eigenmode expansion method and under periodic boundary conditions, besides the fact that the SSP dispersion relations are obtained by matching the boundary conditions of electromagnetic fields both for rectangular metal grating with roofed metal plate and that without roofed metal plate. Results for these two different cases are given according to numerical calculation and it is found that the roofed metal plate can introduce an additional fast wave mode which is beyond the light line in the dispersion diagram. And the results of analytical SSP dispersion are verified by electromagnetic simulations based on the finite difference method and finite integration method. The dependence of the dispersion characteristics and mode distributions on various parameters of metal grating is studied theoretically. It is shown that the dispersion relations obtained by eigenmode expansion method agree well with the results of electromagnetic simulations. The phase velocity of SSP on the grating surface can be decreased by increasing metal grating depth or decreasing grating period. The bandwidth of electron beam-SSP interaction can be extended by increasing grating period ratio. The influence of the distance between the roofed metal plate and the grating surface on the SSP dispersion is studied and is found that the role of roofed metal plate is insensitive to the slow wave SSP mode. The SSP dispersion and modes for the 3-D metal grating which are extended from the above 2-D SSP dispersion are also given. The SSP symmetric modes and anti-symmetric modes manifest themself alternately in the dispersion diagram on the 3-D grating surface. Compared with the 2-D SSP bound mode without roofed metal plate, it is found that in the 3-D grating structure the slow wave SSP modes and fast wave SSP modes coexist. The 3-D SSP mode with various grating lateral width is studied, and the competition and degeneracy of modes are analyzed particularly. The SSP mode intervals can be enlarged by decreasing the lateral width of the grating, which is optimum for avoiding mode competitions. Studies on dispersion and modes of the 2-D and 3-D metal grating structures based on SSP will lay the foundations for further studies of electron beam-SSP interaction, and development of the novel terahertz vacuum electronic source with high-efficiency and wide-bandwidth.
Design of triple bandpass frequency selective surface in terahertz wave band for radio astronomy
Authors: Liu Hai-Wen  , Zhan Xin  , Ren Bao-Ping  ,   Department of Information Engineering, East China Jiaotong University, RF Communications and Sensor Networks, Jiangxi Province Key Laboratory, Nanchang 330013, China;,   Unit 73681 of PLA, Nanjing 210042, China
Published: December 2020

A single screen terahertz frequency selective surface (FS) using the improved split ring resonators (SRRs) is designed in this paper. The resonance unit of an improved SRR consists of an open seam metal patch, while the physical size of the open seam metal patch will directly affect the stepped impedance characteristics. In the paper, LC equivalent circuit model for the improved SRR unit structure is established to extract the equivalent circuit model parameters. Then the relationship between the fundamental frequency of the FSS formula and the harmonics is obtained from the basic theory of the transmission line. Compared to the traditional uniform SRR, the control of multi-band in the improved SRR is more flexible. It is an outstanding characteristic for multi-band FSS design. Based on this characteristic, the triple-band terahertz FSS centered at 0.46, 0.86 and 1.03 THz respectively is designed successively, which can be used in radio astronomy application. By using HFSS 13.0 electromagnetic software simulation, many important indicators such as the key parameters that affect the transmission characteristics of the FSS, periodic intervals, miniaturization degree and the sensitivity of the incidence angle have been studied and analyzed. Both the theoretical analysis and simulated results demonstrate the validity of the method. The triple-band FSS using the improved SRR has a lot of reformative performances. It is shown that the reflection coefficients of triple-band FSS using the improved SRR are -37.6 dB, -13 dB, and -19.6 dB, respectively. On the other hand, it owns the stable frequency response characteristics in the 0°–60° range, which is beneficial to a large incidence angle. In addition, a high degree of miniaturization and the low loss characteristics are the another two significant advantages of this FSS. This triple-band FSS with improved SRR has potential applications in the terahertz frequency radio astronomy polarizer, beam splitter, mirror and resonator mirror, etc.
Adaptive weighted constrained least squares algorithm based microphone array robustness beamforming algorithm
Authors: Guo Ye-Cai  , Zhang Ning  , Wu Li-Fu  , Sun Xin-Yu  ,   Jiangsu Key Laboratory of Meteorological Observation and Information Processing, Nanjing University of Information Science & Technology, Nanjing 210044, China;,   Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology (CICAEET), Nanjing 210044, China
Published: December 2020

In order to solve the problem of robustness of beamforming algorithm with microphone array channel mismatch, an adaptive dynamic-weighted constrained least square algorithm-based microphone array robustness frequency invariant beamforming algorithm is proposed. In the proposed algorithm, by analyzing the microphone array model, with or without channel mismatch, the disadvantages of the constrained least square frequency invariant beamforming algorithm with channel mismatch are studied. After the probability density functions of the microphones are defined as the robustness factors and added to the constraint least square frequency invariant beamforming algorithm, the robustness is improved to a certain extent, but it is still poor. In order to further improve the robustness of the algorithm, dynamic-weighted coefficients for controlling frequency invariance in the cost function are used to regulate the sidelobe spectrum energy. The fluctuation error is defined as the ratio of the maximum to minimum value of array response formed by the same angle of arrival at different frequencies, within the frequency range of frequency invariant, to compare the proposed algorithm with the constrained least square robustness frequency invariant and minmax robustness broadband beamforming algorithm. Experimental results of the algorithms show that the fluctuation errors of the proposed algorithm are the smallest and its robustness is the best; it can effectively overcome the poor robustness of the beamforming algorithm caused by microphone array channel mismatch, and can be applied to any arbitrary array structure.
Relations among different energy dissipations of Euler disk
Authors: Zhu Pan-Cheng  , Bian Qing-Yong  , Li Jin-Bin  ,   College of Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;,   College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

The energy dissipation of a disc spinning on a horizontal plane is studied, as the angle α of the coin made with the horizontal plane decreases, while the angular velocity Ω of the point of contact increases. Effect of the ratio x between the thickness and diameter of an Euler disc and the α on the energy dissipation is studied. We find, by using numerical simulation, that when x is small enough, the lose of the kinetic energy and the gravitational potential energy of the mass center is dominant in energy dissipations; when x>0.4142, the rotational kinetic energy dissipation of the disc around the axis that is parallel to the disc surface, is the leading factor. The requirements in which thickness can be neglected are also obtained, and they can give some hints to the relevant theories and experiments. Our results show that when α≥10° and b/a[26] data very well. We also discuss the main energy dissipation distributed among different forms: variation of rolling friction and viscous shear of the air with x and α, also show their transition in the process of the motion. Furthermore, we find that the pure rolling friction is the unique dissipation as x=0.1733 and α>18°, which improves the results obtained before. We speculate that the dominant dissipation is the gliding friction in the final stage of the motion, because when the disc is motionless, one face of the disc lies absolutely in contact with the horizontal surface just before the disc halts. One can assume that they are in contact completely but the disc does not halt, thus axis 1 and axis Z are almost in the same direction. In this case, the energy dissipation of the Euler disc is due to the gliding friction. To some extent, this accounts for the disc final halt.
Electro-osmotic slip flow of Eyring fluid in a slit microchannel
Authors: Jiang Yu-Ting  , Qi Hai-Tao  ,   School of Mathematics and Statistics, Shandong University, Weihai, Weihai 264209, China
Published: December 2020

The electro-osmotic flow of a non-Newtonian fluid in a slit micro-channel under the Navier's slip boundary condition is investigated. The Eyring constitutive relationship model is adopted to describe the non-Newtonian characteristics of the flow driven by the applied electric field force and pressure. In consideration of the micro-scale effects, electric field, non-Newtonian behavior and slip boundary condition, a mechanical model is built and the effects of these factors on the flow are studied. Analytical expressions are derived for the electric potential and velocity profile by solving the linearized Poisson-Boltzmann equation and the modified Cauchy equation. Approximate expressions of the velocity distribution are also given and discussed. Furthermore, by comparing the effects of electric force with that of pressure on the velocity distribution, some meaningful conclusions are drawn from the obtained graphics.
A temperature and emissivity separation algorithm based on maximum entropy estimation of alpha spectrum's scaling and translation
Authors: Liu Jun-Chi  , Li Hong-Wen  , Wang Jian-Li  , Liu Xin-Yue  , Ma Xin-Xue  ,   Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China;,   University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

In the thermal infrared (TIR) waveband, solving the target emissivity spectrum and temperature leads to an ill-posed problem in which the number of unknown parameters is larger than that of available measurements. Generally, the approaches developed for solving this kind of problems are called, by a joint name, the TES (temperature and emissivity separation) algorithm. As is shown in the name, the TES algorithm is dedicated to separating the target temperature and emissivity in the calculating procedure. In this paper, a novel method called the new MaxEnt (maximum entropy) TES algorithm is proposed, which is considered as a promotion of the MaxEnt TES algorithm proposed by Barducci. The maximum entropy estimation is utilized as the basic framework in the two preceding algorithms, so that the two algorithms both could make temperature and emissivity separation, independent of experiential information derived by some special data bases. As a result, the two algorithms could be applied to solve the temperature and emissivity spectrum of the targets which are absolutely unknown to us. However, what makes the two algorithms different is that the alpha spectrum derived by the ADE (alpha derived emissivity) method is considered as priori information to be added in the new MaxEnt TES algorithm. Based on the Wien approximation, the ADE method is dedicated to the calculation of the alpha spectrum which has a similar distribution to the true emissivity spectrum. Based on the preceding promotion, the new MaxEnt TES algorithm keeps a simpler mathematical formalism. Without any doubt, the new MaxEnt TES algorithm provides a faster computation for large volumes of data (i.e. hyperspectral images of the Earth). Some numerical simulations have been performed; the data and results show that, the maximum RMSE of emissivity estimation is 0.017, the maximum absolute error of temperature estimation is 0.62 K. Added with Gaussian white noise in which the signal to noise ratio is measured to be 11, the relative RMSE of emissivity estimation is 2.67%, the relative error of temperature estimation is 1.26%. Conclusion shows that the new MaxEnt TES algorithm may achieve high accuracy and fast calculating speed, and also get nice robustness against noise.
Study on magnetic moment of cation-vacancy
Authors: Pan Feng-Chun  , Lin Xue-Ling  , Chen Huan-Ming  ,   School of Physics and Electric Information Engineering, Ningxia University, Yinchuan 750021, China
Published: December 2020

We use the group theory and molecular orbital theory to systematically study the origin of magnetic moment of cation-vacancy in un-doped magnetic semiconductors, and illustrate the mechanism of exchange-coupling between magnetic moments by Heisenberg model. It is found that the magnetic moment is related to the number of unpaired electrons, and the distribution of defects energy level is correlated closely with the symmetry of vacancy crystal field. The exchange-coupling coefficients J0 is estimated by the energy difference between antiferromagnetic and ferromagnetic states. And J0 can be used to predict the magnetic coupling. Positive J0 means the ferromagnetic coupling between magnetic moments, otherwise the coupling is antiferromagnetic. Moreover, we indicate that reduction of degeneracy of defect energy-level bears a direct relationship to the electron number occupied in the defect energy-level orbital, and therefore results in the structure distortion (John-Teller effect) of a cation-vacancy.
Phase change properties of ZnSb-doped Ge2Sb2Te5 films
Authors: Tian Man-Man  , Wang Guo-Xiang  , Shen Xiang  , Chen Yi-Min  , Xu Tie-Feng  , Dai Shi-Xun  , Nie Qiu-Hua  ,   Research Institute of Advanced Technologies, Ningbo University, Ningbo 315211, China;,   College of Information Science and Engineering, Ningbo University, Ningbo 315211, China
Published: December 2020

ZnSb-doped Ge2Sb2Te5 films have been deposited by magnetron co-sputtering using separated ZnSb and Ge2Sb2Te5 alloy targets. The concentrations of ZnSb dopant in the ZnSb-added Ge2Sb2Te5 films, measured by using energy dispersive spectroscopy (EDS), are identified to be 5.4, 9.9, 18.7 and 24.3 at. %, respectively. X-ray diffraction (XRD), in situ sheet resistance measurements, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), are used to analyze the relationships among the composition, structures and properties of the films. The sheet resistance as a function of the temperature (R-T) is in situ measured using the four-probe method in a home-made vacuum chamber. It is found that the crystallization temperature of ZnSb-doped Ge2Sb2Te5 films are much higher than that of conventional Ge2Sb2Te5 (～168℃). The higher crystallization temperature is helpful to improve the amorphous thermal stability. Data retention can be obtained by the extrapolated fitting curve based on the Arrhenius equation. It is shown that the values of 10-yr data retention for ZnSb-doped Ge2Sb2Te5 films are higher than that of conventional Ge2Sb2Te5 film (～ 88.9℃). XRD patterns of the as-deposited films when annealed at 200℃, 250℃, 300℃, and 350℃ show that ZnSb-doping can suppress the phase transition from fcc phase to hex phase. XPS spectra are further used to investigate the binding state of (ZnSb)18.7(Ge2Sb2Te5)81.3, suggesting that the Zn–Sb and Zn–Te bonds may exist in an amorphous state. In addition, we have measured the dark-field TEM images, selected area electron diffraction patterns, and high-resolution transmission electron microscopy images of the (ZnSb)18.7(Ge2Sb2Te5)81.3 films. Apparently, the films show a uniform distribution of crystalline phase with the dark areas surrounded by bright ones (Zn–Te or Zn–Sb domain). A static tester using pulsed laser irradiation is employed to investigate the phase transition behavior in nanoseconds. Results show that the ZnSb-doped Ge2Sb2Te5 films exhibit a faster crystallization speed. Among these samples, the (ZnSb)24.3(Ge2Sb2Te5)75.7 film exhibits a higher crystallization temperature of 250℃ and the 10 years data retention is 130.1℃. The duration of time for crystallization of (ZnSb)24.3(Ge2Sb2Te5)75.7 is revealed to be as short as ～64 ns at a given proper laser power 70 mW. A reversible repetitive optical switching behavior can be observed in (ZnSb)24.3(Ge2Sb2Te5)75.7, confirming that the ZnSb doping is responsible for a fast switching and the compound is stable with cycling. These excellent properties indicate that the (ZnSb)24.3(Ge2Sb2Te5)75.7 film is a potential candidate as the high-performance phase change material.
Simulation of localized surface plasmon resonance of hexagonal Ag nanoarrays and amorphous oxidized silicon nitride
Authors: Zhang Wen-Ping  , Ma Zhong-Yuan  , Xu Jun  , Xu Ling  , Li Wei  , Chen Kun-Ji  , Huang Xin-Fan  , Feng Duan  ,   School of Electric Science and Engineer, Nanjing University China, Nanjing 210093, China;,   Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China;,   Jiangsu Provincial Key Laboratory of Photonic Electronic Materials Science and Technology, Nanjing University, Nanjing 210093, China
Published: December 2020

Simulation on the properties of localized surface plasmon resonance (LSPR) of different sized hexagonal Ag nanoarrays embedded in the amorphous oxidized silicon nitride(a-SiNx:O) matrix has been carried out by using COMSOL Multiphysics and FDTD Solution simulation software. Through the calculation of the scattering and absorption cross section of Ag array with different radius, we find that the position of extinction peaks red-shift from 460 to 630 nm when the radius of nanoparticles of hexagonal Ag arrays increases from 25 to 100 nm with the distance between particles 100 nm. The enhanced scattering cross section of the localized surface plasmon (LSP) and blue-shift of the extinction peak can be obtained by tunning the distance between Ag nanoparticles from 100 to 50 nm with the radius of Ag nanoparticles fixed at 50 and 75 nm, respectively. However the mismatch between the extinction peak of hexagonal Ag nanoarrays and the blue light emission of 460 nm from a-SiNx:O films still exists. The novel overlap between the scattering cross section of LSP from hexagonal Ag arrays with a radius of 25 nm and the blue light emission of a-SiNx:O films at 460 nm further confirms that the hexagnoal Ag arrays with a radius of 25 nm is the optimal option to enhance the blue light emission from a-SiNx:O films. Therefore, strong coupling between LSP and blue light emission at 460 nm from a-SiNx:O films with a thickness of 70 nm can be realized when the radius of Ag nanoparticle is 25 nm. We also investigate the enhancement of near field radiative intensity of LSP from hexagnoal Ag arrays with a radius of 25 nm. When the excitation wavelength is 460 nm, the maximum enhancement of near field intensity of LSP from hexagnoal Ag arrays with a radius of 25 nm reaches 1.46104 V/m. The calculated polarization intensity and charge distribution of hexagonal Ag nanoparticle with a radius of 25 nm embedded in a-SiNx:O films reveal that the enhancement of electromagnetic field-intensity is through the dipolar plasmon coupling with the excitons in a-SiNx:O films in bright field mode under the excitation of 460 nm. Further calculation of perpendicular radiative intensity for LSP from the hexagonal Ag array with a radius of 25 nm embedded in a-SiNx:O films indicates that the maximum radiative intensity can be realized in a-SiNx:O matrix with an optimum thickness of 30 nm for a-SiNx:O films. Our theoretical calculations and analysis can provide valuable reference for the design of Si-base blue LED with light emission around 460 nm.
Study on the effect of stress state and crystal orientation on micro-crack tip propagation behavior in phase field crystal method
Authors: Guo Liu-Yang  , Chen Zheng  , Long Jian  , Yang Tao  ,   State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

A nanometer scale mechanism for micro crack propagation under uniaxial tension in single crystals is investigated using phase field crystal (PFC) simulation. The uniaxial tensile loading is strain controlled. And three initial typical stresses of pre-existing center crack in (111) crystal plane of face centered cubic structure are chosen to study the effects of initial stress state on micro-crack propagation. Moreover, the influences of different crystal orientations, when the crystal suffers from uniaxial tension, are also investigated. Due to the influence of time scale and length scale in the PFC method, the motion of dislocations, vacancies, shear band and twinning structure should be observed and described during the propagation process of micro cracks. In addition, the free energy curves of different processes are drawn and discussed in order to explain the different behaviors of the crystal in the propagation of cracks. Simulation results show that the propagation behavior of micro cracks can be closely associated with the initial stress state. It is found that the propagation behavior mainly occurs in the 11>(111) slip system. Besides, the crystal orientation has a significant effect on the mechanism of activation and evolution. In the pre-stretching system, slip dislocation is induced near the micro-crack tip, and then its slide in [011] direction will cause the cleavage of a certain crystal plane, and promote the micro cracks to extend. However, to a certain level, the propagating direction of the micro-crack tip will turn to another slip direction [101]. As a result, zigzag edge appears. By contrast, in the pre-shear system, the tip of the micro crack propagates in a cleavage mode, and results in the appearance of slip dislocation [101] near the micro-crack tip. Afterwards, the motion of slip dislocation promotes the production of vacancies. And owing to the aggregation and combination of vacancies, secondary cracks form and propagate in the process that follows. At the same time, in a pre-deviatoric system, the micro crack propagates forward with direct cleavage of [101] slip direction near the micro-crack tip until the single crystal sample fractures. Furthermore, no slip dislocation appears during the whole process. The mechanism of micro-crack tip propagating behavior varies with crystal orientation. When the crystal orientation angle is lower, the micro-crack tip prefers to produce slip dislocation around it, and the following dislocation slide will induce vacancies, then a secondary crack also forms because of the aggregation and combination of vacancies. On the other hand, when the aggregation degree is higher, the micro-crack tip is inclined to directly propagate in a cleavage mode, and its propagating direction is nearly perpendicular to the stretching direction.
ZnO:Al textured films for improved performance in organic photovoltaics
Authors: Zhang Ke  , Hu Zi-Yang  , Huang Li-Ke  , Xu Jie  , Zhang Jing  , Zhu Yue-Jin  ,   Department of Microelectronic Science and Engineering, Ningbo Collabrative Innovation Center of Nonlinear Harzard System of Ocean and Atmosphere, Ningbo University, Ningbo 315211, China
Published: December 2020

A major issue in organic photovoltaics (OPVs) is the poor mobility and recombination of the photogenerated charge carriers. The active layer has to be kept thin to facilitate charge transport and minimize recombination losses. However, optical losses due to inefficient light absorption in the thin active layers can be considerable in OPVs. Therefore, light trapping schemes are critically important for efficient OPVs. In this paper, high efficient OPVs are demonstrated by introducing randomly nanostructured front electrodes, which are fabricated using commercially available ZnO:Al (AZO) films by means of a wet etching method. The etched AZO front electrode induces strong diffusion and scattering of the incident light, leading to the efficient light trapping within the device and enhancement of light absorption in the active layer. Such a nanostructured electrode can achieve an improved device performance by maintaining simultaneously high open-circuit voltage and fill factor values, while providing excellent short-circuit current enhancement through efficient light trapping. The best device obtained based on the textured electrode shows a 11.29% improvement in short current density and a 8.17% improvement in power conversion efficiency, as compared with the device with a flat electrode. The improvement in PCE is directly correlated with the enhancement of light absorption in the active layer due to the light scattering and trapping effect induced by the randomly nanotextured electrodes, which is confirmed by a haze factor measurement and an external quantum efficiency characterization. The well-established contact interfaces between the etched electrodes and active layers are made, and thus reduce the impact on the open-circuit voltage and fill factor values in OPVs. We thus conclude that the method of light manipulation developed in this paper will provide a promising and practical approach to fabricate high-performance and low-cost OPVs.