bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of defects on the melting and premelting of carbon nanotubes
Authors: Zhang Kai-Wang  , Zhong Jian-Xin  ,   湘潭大学材料与光电物理学院，湘潭  411105
Published: December 2020

We report results of molecular dynamics simulations of melting and premelting of single-walled carbon nanotubes (SWNTs) with different types of point defects, namely, the Stone-Wales defect, vacancy defect, and impurity defect. Using the Lindemann parameter, we found that the melting temperature of perfect SWNTs is around 4800K. We further show that premelting occurs in the regions close to the defects with premelting temperatures of 2600K for the Stone-Wales defect and3200K for the cavity defect. The SWNTs with Si impurity defects are thermally stable up to 3800K.
Field emission properties of titanium carbide-modified carbon nanotubes
Authors: Qin Yu-Xiang  , Hu Ming  ,   天津大学电子信息工程学院，天津  300072
Published: December 2020

Titanium carbide with low work function was formed on the surface of CNTs after deposition of a thin layer of titanium film and subseguest vacuum annealing at high temperature. The CNTs modified by titanium carbide was characterized by XPS, and the field emission characteristics of the CNTs film before and after modification were investigated. The characterization results indicated that carbon atoms reacted with the coated titanium atoms to form titanium carbide during annealing. The field emission measurements showed that, compared to that of unmodified sample, the turn on electric field of the modified CNTs film decreased from 1.21V/μm to 1.04V/μm and the emission current density at applied electric field of 2.34 V/μm increased from 2.3mA/cm2 to 13.5mA/cm2 Also, the emission stability of the titanium carbide-modified CNTs was improved. The mechanism of the CNTs film modified by titanium carbide has been discussed.
First-principles study on electronic structure and optical properties of Al and Mg doped GaN
Authors: Guo Jian-Yun  , Zheng Guang  , He Kai-Hua  , Chen Jing-Zhong  ,   (1)中国地质大学材料科学与化学工程学院，武汉  430074; (2)中国地质大学数学与物理学院，武汉  430074；中国地质大学材料模拟与计算物理研究所，武汉  430074
Published: December 2020

The electronic structure and optical properties of pure and Al_and Mg-doped cubic-blende GaN have been studied based on the density functional theory and the generalized gradient approximation method. The relationship between the distribution of the electronic states and their structures has been analyzed.The dielectric function and the complex refractive index function on the doping GaN system have been obtained. The calculation results indicate that the hole concentration of Mg-doped GaN is increased and the Mg-doping markedly enhanced the conductivity of the material.But the carrier concentration of Al-doped GaN is not changed and optical bandgap is broadened.The mechanism of luminescence has been explained in terms of an analysis of the dielectric function and the complex refractive index function. It offers theoretical data for the design and application of GaN optoelectronic materials. By comparison, our results are in good agreement with that published in the literatures.
The effective viscosity of silicon melt in magnetic field
Authors: Zhang Wen  , Liu Cai-Chi  , Wang Hai-Yun  , Xu Yue-Sheng  , Shi Yi-Qing  ,   河北工业大学信息功能材料研究所,天津  300130
Published: December 2020

A magnetic field generated by a magic ring was applied to the space containing the silicon melt, and the effective viscosities of silicon melt were measured by the method of rotary vibration. The magic ring was constructed by permanent magnets made of NdFeB permanent-magnet material. The results showed that, at certain temperature, the effective viscosity increased with the increase of magnetic field intensity, and they are parabolically related. The magnet field had stronger effect when the silicon melt temperature increased, which was indicated by a more warped up parabola. In the range of 1490 to 1610℃, the viscosity had an extraordinary fluctuation which indicated a structure change in the silicon-melt. The value of silicon melt viscosity increased by 2—3 orders of magnitude when the magnetic field reached 0.068T. The results indicated that applying a magnetic field to the silicon melt space is an effective way to suppress thermal convection during the growth of large diameter single crystal silicon.
A pure rotational Raman-lidar based on three-stage Fabry-Perot etalons for monitoring atmospheric temperature
Authors: Wang Shao-Lin  , Su Jia  , Zhao Pei-Tao  , Cao Kai-Fa  , Hu Shun-Xing  , Wei He-Li  , Tan Kun  , Hu Huan-Ling  ,   (1)中国科学院安徽光学精密机械研究所大气光学实验室,合肥  230031; (2)中国科学院安徽光学精密机械研究所大气光学实验室,合肥  230031；中国科学院研究生院,北京  100049
Published: December 2020

A new pure rotational Raman-lidar system for monitoring atmospheric temperature is presented. Instead of using the double grating monochromator, the system employs two high resolution spectral resolving channels,each of which is composed of a three-stage Fabry-Perot etalon combined with a filter with band width of 7nm. The transmitting light source is an injection-seeded Nd:YAG laser. This configuration can achieve a high rejection rate (10-10) to Mie-Rayleigh elastic scattering (at 532nm wavelength)，and has an extremely narrow receiving bandwidth (less than 10pm) for pure rotation Raman scattering of N2 with quantum numbers of ±6 and ±12 respectively. Therefore, the system effectively rejects the interference of background radiation and pure rotational Raman scattering of O2, and the measurement of daytime tropospheric temperature from a single Raman spectral line intensity ratio using the lidar system is made possible because of the narrow receiving bandwidth. The temperature measurement precision of this Raman-lidar is improved at the same time. At last, two_channels signals were simulated by using balloon-based sounding temperature profile. The simulation demonstrated the feasibility of this lidar for atmospheric temperature profile measurement.
Electron correlation effects on transition probabilities from 4d8—4d75p of Xe10+
Authors: Gao Cheng  , Shen Yun-Feng  , Zeng Jiao-Long  ,   国防科技大学理学院，长沙  410073
Published: December 2020

The atomic data such as energy levels and transition probabilities of Xe10+ have been obtained basing on multi-configuration Dirac-Fock (MCDF) method. The electron correlation effects on transition probabilities of 4d8—4d75p have been investigated by adding the electron correlation of 4dn—5pn(n=1, 2, 3) step by step, which shows the effects are so obvious that one should include at least up to the correlation of 4d2—45p2 to get a convergent result. The calculated wavelengths are in good accordance with the experimental ones. The agreement between the length and velocity forms of transition probabilities is excellent, which shows the atomic wavefunction is accurate and the present result is reliable.
Effect of the carrier phase of ultra-short laser pulses on high-order harmonic generation spectra
Authors: Chen Ji-Gen  , Chen Gao  , Zeng Si-Liang  , Yang Yu-Jun  , Zhu Qi-Ren  ,   (1)北京应用物理与计算数学研究所，北京  100088; (2)长春理工大学理学院，长春  130022; (3)吉林大学原子与分子物理研究所，长春  130012; (4)台州学院物理系，椒江  318000
Published: December 2020

We numerically calculated the high-order harmonic generation (HHG) power spectra from a one-dimensional model atom irradiated by linearly polarized ultra-short laser pulses whose duration is two optical cycles. It was found that, the cut-off positions of the HHG spectra change when the carrier phases of the ultra-short laser pulses are altered, and the distinct double plateau structure appears in some special carrier phases. The above issues are reasonably explaned by the three-step model. Finally, the wavelet time-frequency analysis verifies that the three-step model can accurately exactly predict the cut-off frequencies of the ultra-short pulse HHG spectra.
Study on the chemical states of the surface of SiC epilayer
Authors: Ma Ge-Lin  , Zhang Yu-Ming  , Zhang Yi-Men  , Ma Zhong-Fa  ,   宽禁带半导体材料与器件教育部重点实验室，西安电子科技大学微电子学院，西安  710071
Published: December 2020

In this paper, the composition structures of SiC epilayer surface are characterized by high resolution X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectrum. The results of XPS wide scan spectroscopy, infrared glancing reflection absorption spectrum and infrared specular reflection spectroscopy show that the amorphous phase SiCxOy:H is made up of Si-O-Si and Si-CH2-Si polymers. The chemical state structures are composed of Si(CH2)4, SiO(CH2)3, SiO2(CH3)2, SiO3(CH3), Si-Si, dissociative H2O, combined OH，Si-OH, O and O2. The order of the atom core electron binding energy values is determined by chemical state structures and element electronegativity. Compared with the XPS narrow scan spectrum fitting results, the corresponding relation between chemical states and its binding energies is established, and all chemical state binding energies are obtained using the calibration of C 1s binding energy of Si(CH2)4. The result shows that the C 1s and O 1s binding energy values of SiCxO4-x(x=1,2,3) are different from each other, similar as their Si 2p binding energies, of which the C 1s of SiO2(CH3)2 and SiO3(CH3) are respectively close to those of CHm and C—O. The reasonable explanation is presented in terms of chemical state structures, electronegativity and neighbouring site effects.
Generalized synchronization by coupling of restoring force and determination of parameters in vibration systems
Authors: Qin Wei-Yang  , Wang Hong-Jin  , Gao Hang-Shan  ,   西北工业大学工程力学系，西安  710072
Published: December 2020

For a class of vibration systems excited by external harmonic force，generally the restoring force cannot be given an accurate analytical expression. For such system, a derived system of generalized synchronization (GS) is set up. The GS between the two systems is proved. Since there is no time element in the equations of the derived system，the derived system can reach GS with the original system automatically，even if the frequency and amplitude of external force are varied. By using GS，a novel method to determine parameters in a vibration system，e.g.，the damping coefficient and the amplitude and frequency of external exciting force，is presented and proved. From the simulation of Duffing system，it can be seen that the presented method is effective and can give a result of high accuracy.
Investigation of hollow-core photonic band-gap fiber at visible wavelengths
Authors: Yuan Jin-Hui  , Hou Lan-Tian  , Zhou Gui-Yao  , Wei Dong-Bin  , Wang Hai-Yun  , Dong Shi-Rui  , Wang Qing-Yue  , Liu Bo-Wen  , Hu Ming-Lie  ,   (1)天津大学精密仪器与光电工程学院超快激光研究室,天津  300072; (2)燕山大学红外光纤与传感研究所，秦皇岛  066004; (3)燕山大学红外光纤与传感研究所，秦皇岛  066004；燕山大学亚稳材料制备技术与科学国家重点实验室，秦皇岛  066004
Published: December 2020

Based on full-vector plane-wave method (FVPWM), the hollow-core photonic band-gap fiber (HC-PBGF) fabricated using the improved twice stack-and-draw technique has been simulated. Under given values of propagation constant β, some valid photonic band-gaps (PBGs) with different sizes will emerge within the wave band of 500—1000 nm. For different values of the effective refractive index, the air-guided modes can exist in different forms in part of PBGs. Comparing the experimental data with the simulation result, we have discovered that the measured positions of PBGs are shifted to shorter wavelengths distinctly. The primary reasons are considered to be the structure asymmetry along longitudinal direction and the existence of interstitial holes at nodes in the cladding region.
The impact of high-k dielectrics on the performance of Schottky barrier source/drain (SBSD) ultra-thin body (UTB) SOI MOSFET
Authors: Luan Su-Zhen  , Liu Hong-Xia  , Jia Ren-Xu  , Cai Nai-Qiong  , Wang Jin  ,   西安电子科技大学微电子学院，宽禁带半导体材料与器件教育部重点实验室，西安  710071
Published: December 2020

The impact of high-k dielectrics on the performance of Schottky barrier source/drain (SBSD) ultra-thin body (UTB) SOI is investigated in this paper. With the dielectric constants increasing, the on-state currents of SBSD UTB SOI MOSFET decrease, which suggests that the fringing induced barrier lowering (FIBL) is not the major mechanism for the variation of Schottky barrier height. This phenomenon can be understood in terms of the fringing induced barrier shielding (FIBS). It is also shown that the influence of high-k dielectrics on the performance is quite different in the cases that source/drain and gate electrode have an offset or overlap. For the device with an overlap， the structure with a low-k interfacial layer between high-k gate dielectric and substrate is quite effective in suppressing the degradation of drive current due to FIBS. However, for the device with an offset, the combination of high-k dielectric spacer with stack gate can significantly improve the on-state current. This fact can be explained in terms of the refraction of lines of electric force from gate electrode at interfaces of two materials with different dielectric constants. These lines of electric force with refraction can concentrate at the source region, thus lowering the barrier heights and improving the drive currents. Besides, it is shown that on-state current has a local maximum in the case that source/drain and gate electrode has an offset. The structure parameters can be optimized to improve the drive current.
Superconducting proprties of noncentrosymmetric Mg10±δIr19B16?δ
Authors: Li Zheng  , Luo Jian-Lin  ,   中国科学院物理研究所,北京  100190
Published: December 2020

Two non-centrosymmetric superconductors Mg9.3Ir19B16.7 and Mg11Ir19B15 are synthesized. The normal state electronic coefficient of specific heat γn, the Debye temperature ΘD and the superconducting upper critical field Hc2 are found to be sample-dependent, while the electron-phonon interaction constant λ=0.58 and the normalized specific heat jump ΔC/γnTC=1.66 are sample-independent. The higher superconducting transition temperature (TC=5.7K) in Mg9.3Ir19B16.7 is found to be due to the higher density of states and higher Debye temperature ΘD compared with that of Mg11Ir19B15. We also obtained other characteristic parameters of both superconductors, including the Ginzburg-London coherence ξGL, penetration λGL, lower critical field HC1 and thermodynamic critical field HC.
Synthesis and properties of nanocrystal up-converting materials for thin film solar cells
Authors: Jin Xin  , Zhang Xiao-Dan  , Lei Zhi-Fang  , Xiong Shao-Zhen  , Song Feng  , Zhao Ying  ,   (1)河北工业大学信息工程学院，天津  300130; (2)南开大学光电子薄膜器件与技术研究所，光电信息技术科学教育部重点实验室，光电子薄膜器件与技术天津市重点实验室，天津  300071; (3)南开大学物理学院光子学中心，天津  300071
Published: December 2020

Nanocrystals of up-conversion phosphor，rare earth-doped sodium yttrium fluoride were prepared by hydro-thermal method for the application in thin film solar cells. Effect of Yb3+ and/or Er3+ doped materials on the crystal structure and optical properties were studied. Up-conversion materials with Yb3+/Er3+ co-doped absorb the infrared near 980 nm and 1530nm and emit red (653nm)and green (520nm，540nm)light，which is well adapted for use in thin film solar cells. Nanoparticels with efficient near-infrared to visible up-conversion fluorescence with appropriate doping concentrations of 18% Yb3+ and 2% Er3+ were prepared.
Field evaporation of the end of a carbon nanotube
Authors: Bai Xin  , Wang Ming-Sheng  , Liu Yang  , Zhang Geng-Min  , Zhang Zhao-Xiang  , Zhao Xing-Yu  , Guo Deng-Zhu  , Xue Zeng-Quan  ,   北京大学信息科学技术学院电子学系，纳米器件物理与化学教育部重点实验室，北京  100871
Published: December 2020

A single multi-walled carbon nanotube (MWCNT)was assembled onto a W tip and transferred to an ultrahigh vacuum field-emission/field-ion microscope (UHV-FEM/FIM)for the study of field evaporation and field emission. The results showed that the field evaporation lowered the work function of the MWCNT and thus enhanced its field emission. The evaporation field of the MWCNT was estimated to be lower than 1.3×108V·cm-1 and the evaporation rate under this field was measured to be 9.4nm·min-1. The physical origin of the fact that the evaporation field of the MWCNT was much lower than the theoretical value for carbon is also qualitatively explained. Firstly，the clean end of the MWCNT，which resulted from field desorption，contained a large number of dangling bonds and the C atoms on it had small coordination number，thus the heat of sublimation of these C atoms was low. Secondly，H atoms that possibly existed in the MWCNT could collide with the C atoms under strong electric field and make the latter evaporate easier. These results indicated an effective approach to obtaining better field emission performance of a carbon nanotube by cutting it short using field evaporation.
Small-signal theoretical analysis and design of Kα band dielectric loaded gyro-TWT
Authors: Yan Ran  , Lou Yong  , Li Jia-Ying  , Pu You-Lei  , Wang Jian-Xun  , Lei Chao-Jun  , Liu Ying-Hui  ,   电子科技大学物理电子学院，成都  610054
Published: December 2020

Using the small-signal theory of the gyro-TWT, a pinch-point analysis based on the theory of Briggs and Bers in combination with the cold field analysis of the dielectric-loaded waveguide is employed to analysis the threshold current of the operation modes and critical oscillation lengths of the spurious mode under different load condition. The analysis concludes that the improvement in the dielectric loss, through altering the load condition can enhance the threshold current and critical oscillation length. The cold field analysis of the dielectric-loaded waveguide and a smooth waveguide dispersion relation is used to analyse the small signal gain of the dielectric-loaded gyro-TWT. The analysis gives the gain-frequency response of a dielectric-loaded gyro-TWT with the normalized background magnetic flux density B0/Bg, the thickness of the dielectric and beam current as parameters. Through the analysis of the self-oscillation and the small signal gain, the optimum operating parameters of a Kα-band dielectric-loaded gyro-TWT can be got to support the nonlinear analysis.
Phase separation in a three-dimensional granular gas system
Authors: Liu Rui  , Li Yin-Chang  , Hou Mei-Ying  ,   中国科学院物理研究所北京凝聚态物理国家实验室，北京  100190
Published: December 2020

Granular systems, without any energy injection, tend to be clustered or condensed due to inelasticity of the particle collisions. Even in a driven granular gas, this notable phenomenon would be present locally and lead to a spatial inhomogeneity, just like the forming of liquid droplets in gases. The present work, by extending an existing two-dimensional theory, offers a three-dimensional model for such a phase-separation phenomenon in a driven granular gas under zero gravity. According to the model, exact conditions for phase separation are obtained through numerical calculations. Event-driven molecular dynamics simulations confirm the theoretical results, and show new morphologies of phase separation in three-dimensional granular gases.
Current collapse mechanism of field-plated AlGaN/GaN HEMTs
Authors: Wei Wei  , Lin Ruo-Bing  , Feng Qian  , Hao Yue  ,   西安电子科技大学微电子学院，宽禁带半导体材料与器件教育部重点实验室，西安  710071
Published: December 2020

Current collapse restrain ability of passivated AlGaN/GaN HEMTs and AlGaN/GaN HEMTs with varying field-plate(FP) length is investigated under different drain bias. The results show that, the passivated HEMTs suffer no current collapse at relatively low but not at higher drain bias, while the HEMTs with optimal field-plate suffer no current collapse for all drain bias used in our tests. Under high drain bias, the FP length plays a crucial role in the current collapse removal. After a thoroughly analysis, it can be concluded that FP structure not only restrains the trapping of virtual gate, but also discharge the virtual gate. Finally, a discharging model of dielectric under FP is presented to explain the effect of FP length on current collapse removal.
Encoding and decoding of quantum convolutional codes
Authors: Xing Li-Juan  , Li Zhuo  , Bai Bao-Ming  , Wang Xin-Mei  ,   西安电子科技大学综合业务网国家重点实验室,西安  710071
Published: December 2020

The research on quantum convolutional codes is aimed at protecting a flow of information over long distance communications. The polynomial representation of a quantum state is defined. Based on the Calderbank-Shor-Steane(CSS)-type construction of quantum codes, a new method for encoding and decoding of CSS-type quantum convolutional codes is presented and corresponding networks are described. The basis state of the code is transformed into the product of an information polynomial by the generator polynomial. Then networks can be realized by operations of polynomial multiplication. Finally, inspired by classical convolutional decoding idea, a quantum Viterbi algorithm with linear complexity is put forward.
Chaotic synchronization of network of Chen’s chaotic attractors using nonlinear coupling function
Authors: Yu Hong-Jie  , Zheng Ning  ,   上海交通大学工程力学系，上海  200240
Published: December 2020

This article offers a method to realize the synchronization of non-symmetrically nonlinear-coupled chaotic systems, studies the chaotic synchronization of Chen's chaotic attractors, and analyzes the influence of chaotic synchronization by numerical simulation under different coupling strengths and different initial conditions. We also extend the synchronization method of non-symmetrically nonlinear-coupled systems to the study of large network linked by numerous Chen's attractor system units by all-to-all-coupling and star coupling. We deduced the equation of errors which ensures the stability of synchronous state, studied the influence of different coupling strengths on synchronization stability and determined the range of coupling strengths which ensures the synchronization. By numerical simulation we proved that if we choose nonlinear functions as coupling functions, it effectively realizes the synchronization of all-to-all-coupling network and large network linked from star sub-networks. We can foresee that the non-symmetrically nonlinear-coupled synchronization method could be widely used in network synchronization.
Design and implementation of chaotic generators based on IEEE-754 standard and field programmable gate array technology
Authors: Zhou Wu-Jie  , Yu Si-Min  ,   广东工业大学自动化学院，广州  510006
Published: December 2020

A new approach for the design and hardware implementation of field programmable gate array (FPGA) general chaotic and hyperchaotic signal generators based on IEEE-754 standard is proposed. Firstly, using Euler algorithm and appropriate discrete processing, the continuous chaotic systems can be converted to discrete chaotic systems, which is appropriate for realization by digital signal processor. Secondly, according to IEEE-754 standard and module-based design idea, five basic floating-point operational modules, namely the multiplication operation module, addition operation module, symbolic function operation module, positive and negative absolute operation module, and initial and iteration value selection module, are constructed by using Verilog-HDL. Based on this method, different types of chaotic and hyperchaotic signals via FPGA are generated. Finally, using configurable voice device, chaotic signals are output through the stereo left and right channels and attractors can be observed by the oscillograph. The characteristic of this method is its universality. Furthermore, the floating-point algorithm and working principle are analyzed. The algorithm flow chart, technical development process, hardware design and realization result are given.
Characteristics of multistage quartz optical filter based on the optical rotatory dispersion effect
Authors: Zhang Shan  , Wu Fu-Quan  , Wu Wen-Di  ,   曲阜师范大学激光研究所，曲阜  273165
Published: December 2020

Based on optical rotatory dispersion effect, the principle of the multistage quartz crystal filter was theoretically analyzed by using Muller matrix and Stokes parameter. The wavelength of the main peak and full width at half maximum (FWHM) of peaks of the multistage optical filter were deduced. The characteristics of the single and multistage quartz crystal optical filters were systematically investigated by the spectrometer, and the experimental results verified the theoretical analysis. The results proved that, compared with the single quartz crystal optical filter, the FWHM can be effectively compressed by multistage quartz crystal optical filter, and the compression ability increases with the increase of the stage number.
Studies on nanosecond laser induced damage to fused fibers
Authors: Zhao Xing-Hai  , Gao Yang  , Xu Mei-Jian  , Duan Wen-Tao  , Yu Hai-Wu  ,   (1)中国工程物理研究院电子工程研究所，绵阳  621900; (2)中国工程物理研究院激光聚变研究中心，绵阳  621900
Published: December 2020

The properties of high_peak pulsed laser induced damage to fibers have been investigated by damage experiments. It was found that all of damaged parts are located on fiber endings, and the damage topography fall into three classes: the pit damage, fusion damage and sputtering damage. The experimental setup of laser induced damage to fibers, fiber damage judgment criterions and data processing methods were developed and validated. The zero probability damage threshold was calculated by linear fitting to be 3.85GW/cm2. The processes of laser induced damage to fibers were summarized and the fiber end face damage mechanism was studied. The experimental results indicated that the main factor that makes the fiber end faces susceptible to laser induce damage is the existence of surface imperfections. The nanosecond laser induce damage to fiber end faces are detected experimentally; the central areas of input end faces are damaged probably because the input laser beam is Gaussian. So the use of uniform beam for injecting the fiber is favorable to the laser-induced damage resistance.
Study of space voltage distribution between large-area parallel-plate electrodes for very high frequency plasma enhanced chemical vapor deposition
Authors: Ge Hong  , Zhang Xiao-Dan  , Yue Qiang  , Zhao Jing  , Zhao Ying  ,   (1)南开大学光电子薄膜器件与技术研究所，光电子薄膜器件与技术天津市重点实验室，光电信息技术科学教育部重点实验室，天津  300071; (2)天津新华职工大学，天津  300040
Published: December 2020

The two-dimensional quasi-planar circuit model is used to study the space voltage distribution between large-area parallel-plate electrodes of very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) reactor. The results show that the voltage standing wave effects become the important factor affecting non-uniform voltage distribution when the electrode dimensions and excitation frequency are increased. For a large-area parallel-plate electrode with 1.2m by 0.8 m lateral dimension, driven respectively at frequencies of 40.68 and 60MHz， the space voltage non-uniformity about ±2.5% and ±5.5% are obtained by optimization of the number and position of the power feeding points. These results provide important theoretical guidance for large-area parallel-plate electrodes used for VHF-PECVD.
Coalescence of helium clusters in titanium crystals: Molecular dynamics simulation
Authors: Xie Zhao  , Hou Qing  , Wang Jun  , Sun Tie-Ying  , Long Xing-Gui  , Luo Shun-Zhong  ,   (1)四川大学原子核科学技术研究所，辐射物理及技术教育部重点实验室，成都  610064; (2)中国工程物理研究院核物理与化学研究所，绵阳  621900
Published: December 2020

In this paper, the helium behavior in titanium crystals has been simulated by molecular dynamics method. The coalescence of helium clusters has been investigated in great detail in a range from 300 to 800K. It was found that increasing temperature contributes to the coalescence of helium clusters. However, the helium cluster resulting from coalescence assumes its three-dimensional configuration in this temperature range for the time scale of simulation. The simulation results also indicate that, at room temperature, the attractive force between helium clusters plays a key role in helium cluster coalescence.
Ag doped p-type ZnO films and its optical and electrical properties
Authors: Wang Jing-Wei  , Bian Ji-Ming  , Sun Jing-Chang  , Liang Hong-Wei  , Zhao Jian-Ze  , Du Guo-Tong  ,   大连理工大学物理与光电工程学院，三束材料改性国家重点实验室，大连  116024
Published: December 2020

Ag doped ZnO films (ZnO：Ag) were deposited on quartz glass substrates by ultrasonic spray pyrolysis technology. Zn(CH3COO)2 and Ag(NO3)3 aqueous solution were used as the sources of Zn and Ag， respectively. The effect of substrate temperature on structural， electrical and optical properties of ZnO：Ag films were studied using X-ray diffraction， Hall effect measurement， photoluminescence spectra， and transmittance spectra measurement. All the measurements were performed at room temperature. It is found that the electrical and optical properties of the obtained ZnO：Ag thin films change dramatically due to Ag doping. The Ag doped p-type ZnO films with hole carrier concentration of 5.295×1015cm-3 and Hall mobility of 6.61cm2·V-1s-1 at room temperature have been successfully obtained at optimal conditions. In photoluminescence measurements， a strong ultraviolet emission centered at 379nm and a relatively weak green emission band were observed， and in transmittance measurements， a high transmittance of～70% in the visible region and a sharp absorption edge at 375nm were observed for all samples.
Positive magnetoresistance in In0.53Ga0.47As/In0.52Al0.48As quantum well
Authors: Shang Li-Yan  , Lin Tie  , Zhou Wen-Zheng  , Li Dong-Lin  , Gao Hong-Ling  , Zeng Yi-Ping  , Guo Shao-Ling  , Yu Guo-Lin  , Chu Jun-Hao  ,   (1)中国科学院半导体研究所，北京  100083; (2)中国科学院上海技术物理研究所红外物理国家重点实验室，上海  200083; (3)中国科学院上海技术物理研究所红外物理国家重点实验室，上海  200083；广西大学物理科学与工程技术学院，南宁  530004
Published: December 2020

Magnetotransport measurements have been carried out on In0.53Ga0.47As/In0.52Al0.48As quantum wells in a temperature range between 1.5 and 77K. We have observed a large positive magnetoresistance in the low magnetic field range， but saturating in high magnetic fields. The magnetoresistance results from two occupied subbands in the two-dimensional electron gas. With the intersubband scattering considered， we obtained the subband mobility by analyzing the positive magnetoresistance. It is found that the second subband mobility is larger than that of the first due to the existence of the intersubband scattering.
Low energy oscillatory phenomena in photoreflectance and photo-modulation reflectance spectra of GaMnAs films grown by low temperature molecular-beam epitaxy
Authors: Luo Xiang-Dong  , Ji Chang-Jian  , Wang Yu-Qi  , Wang Jian-Nong  ,   (1)香港科技大学物理系，香港; (2)香港科技大学物理系，香港；中国科学院固体物理研究所，合肥  230031；南通大学专用集成电路设计重点实验室，南通  226007; (3)中国科学院固体物理研究所，合肥  230031
Published: December 2020

GaMnAs grown by low temperature molecular beam epitaxy have been investigated by Fourier transform infrared and photo-modulation reflectance (PR) measurements. Besides the band gap of Ga(Mn)As，Franz-Keldysh oscillations and spin-orbit coupling energy， low energy oscillations， lower than the GaAs band gap， were well observed in the PR spectra of GaMnAs. And these oscillations were also observed clearly in reflectance spectra of GaMnAs. By fitting the oscillations of the reflectance spectra， it was attributed to the variable refractive indexes induced by the high hole density in GaMnAs， which was caused by Mn doping in GaAs. At the same time， the PR spectra of high-resistance GaMnAs at low temperature were also studied.
Effect of exciton rotational relaxation on luminescence decay of low-doped porphyrin side-chain polymers
Authors: Chen Zhi-Feng  , Wang Hui  , Zhang Wei  , Shen Han  , Yu Han-Cheng  , Huang Jin-Wang  , Lai Tian-Shu  , Ji Liang-Nian  ,   (1)中山大学光电材料与技术国家重点实验室，广州  510275; (2)中山大学光电材料与技术国家重点实验室，广州  510275；中山大学化学与化学工程学院，广州  510275; (3)中山大学化学与化学工程学院，广州  510275
Published: December 2020

Effect of rotational motion of porphyrin molecules on the luminescence dynamic of low-doped porphyrin side-chain polymers has been studied by using the theory of exciton rotational diffusion. It is shown that the rotational motion of porphyrin molecules is an important way that induces the nonradiative relaxation of excitons. The more easily porphyrins rotate， the more rapidly energy decays， therefore， the faster the luminescence decay process. In the case of low doping concentration of porphyrins and long interchain distance， the rotational motion of porphyrin molecules is the main reason of fast luminescence decay and low luminescence efficiency. The transient luminescence relaxation processes of two kinds of polymers were fitted with the theoretical expression， the theoretical analysis are in good agreement with the experimental results.
Routh method of reduction of Birkhoffian systems
Authors: Zhang Yi  ,   苏州科技学院土木工程学院，苏州  215011
Published: December 2020

Reduction of Birkhoffian systems is studied. First, the differential equations of motion for the Birkhoffian systems are established and their cyclic integrals are given. Second, the Routh functions of Birkhoffian systems are constructed, and the order of the systems is reduced by using the cyclic integrals and the Birkhoffian form made to hold. Finally, an example is given to illustrate the application of the results.
The effect of impurity on the thermal entanglement in three-qutrit spin-1 Heisenberg XXX chain
Authors: Qin Meng  , Tian Dong-Ping  , Tao Ying-Juan  ,   (1)解放军理工大学理学院，南京  211101；西安交通大学理学院，西安  710049; (2)西安交通大学理学院，西安  710049; (3)西安邮电学院，西安  710061
Published: December 2020

We investigate the impurity entanglement of 3-qutrit XXX-type Heisenberg chains in the presence of a uniform magnetic field along z axis by means of negativity. The entanglement is calculated as a function of the coupling constants J, impurity parameter J1, magnetic fields B and temperature T. Through calculating the negativity between sites 1 and (2,3) N1-23 and sites 3 and (1,2) N12-3, we show that the critical temperature Tc above which the entanglement vanishes increases with the increase of J1. The existence of magnetic fields B can obviously reduce the entanglement, and it is found that the limiting temperature Tc depends on the impurity parameter J1 but not on the magnetic field.
Instability of spiral wave in small-world networks
Authors: Gan Zheng-Ning  , Ma Jun  , Zhang Guo-Yong  , Chen Yong  ,   (1)兰州大学理论物理研究所,兰州  730000; (2)兰州大学理论物理研究所,兰州  730000；兰州大学磁学与磁性材料教育部重点实验室，兰州  730000; (3)兰州大学理论物理研究所,兰州  730000；兰州理工大学物理系，兰州  730050; (4)兰州理工大学物理系，兰州  730050
Published: December 2020

Using a FitzHugh-Nagumo system as an example, we studied the stabilities of spiral waves in two-dimensional small-world network. It was found that there exists a critical rewiring probability p such that the spiral instability appears for p>pc due to the small-world connectivity. It was also confirmed that this spiral instability is different from the Eckhaus instability and the Doppler instability.
Variational investigation of Hermite-Gaussian beam propagation in nonlocal Kerr media
Authors: Bai Dong-Feng  , Guo Qi  , Hu Wei  ,   华南师范大学光子信息技术广东省高校重点实验室，广州  510006
Published: December 2020

The reduced Lagrange density of nonlocal nonlinear Schrdinger equation(NNLSE) is obtained by expanding the real symmetric response function in Taylor’s series in strongly nonlocal Kerr media. The problem of higher-order beam propagation can be analyzed by a variational approach, the equations are obtained for the evolution during propagation of the parameters of the trial solution and exact analytical Hermite-Gaussian(HG) solutions are found. HG solitons are formed when the input power is equal to the critical power. We demonstrated that the analytical HG solutions are in good agreement with the numerical simulations in the case of strong nonlocality.
Modal characteristics and leakage loss of hollow-core photonic-bandgap fibers based on a square lattice
Authors: Zhang Hu  , Wang Qiu-Guo  , Yang Bo-Jun  , Yu Li  ,   北京邮电大学理学院，光通信与光波技术教育部重点实验室，北京  100876
Published: December 2020

In this paper the modal characteristics and leakage loss of hollow-core photonic bandgap fibers based on a square lattice with rounded square air holes was investigated by using a full-vector finite element method. It was found that hollow-core photonic bandgap fibers with air core arranged in square lattice can operate in the broad bandgap single mode. The leakage loss was analyzed comprehensively. Simulations show that the core diameter and the hole-to-hole spacing have a small influence on leakage loss, but for a given wavelength the desired lowest leakage loss could be obtained by tuning the value of hole-to-hole spacing, while the rounded diameter has a larger influence on leakage loss than the former factors and it has an optimal value dc/d=0.4. The number of cladding rings plays a key role in the leakage loss and the leakage loss is reduced by nearly 2 orders of magnitude per 2 additional cladding rings.
Ab initio investigation of anisotropic optical properties of MgB2
Authors: Shang Xue-Fu  , Tao Xiang-Ming  , Chen Wen-Bin  , Chen Hui-Xian  , Wang Miao  , Tan Ming-Qiu  ,   浙江大学物理系，杭州  310027
Published: December 2020

The density functional theory and full-potential linearized augmented plane wave (FLAPW) method are used to study the anisotropic optical properties of superconductor MgB2. The optical conductivity spectra，the reflectivity spectra and electron energy loss spectra have been calculated. The calculated optical conductivity spectra along xx-axis display quite different features in comparison with that along the zz-axis，while the reflectivity spectra coincide well with the corresponding electron energy loss spectra，especially with respect to the characteristic peaks. In the optical conductivity spectra，the first intra-band absorption peak along xx-axis appears at 20000cm-1 while along zz-axis it appears at a high frequency of about 40000cm-1. In order to simulate the temperature effect in these spectra，the Lorentz expansion (δ=0.10eV) is added to the optical matrix elements in the calculation for 0K. In comparison with existing experimental data，a minor discrepancy of 1000cm-1 (～0.124eV) has been found in the calculated optical spectra.
The effect of 60Co γ-ray irradiation on the 1/f noise of Schottky barrier diodes
Authors: Yang Li-Xia  , Du Lei  , Bao Jun-Lin  , Zhuang Yi-Qi  , Chen Xiao-Dong  , Li Qun-Wei  , Zhang Ying  , Zhao Zhi-Gang  , He Liang  ,   (1)西安电子科技大学技术物理学院，西安  710071; (2)西安电子科技大学微电子学院，西安  710071
Published: December 2020

Based on the analysis of the mechanism of irradiation damage and total dose effect on Schottky barrier diodes (SBD), using the model of the carrier mobility fluctuation and carrier number fluctuation of 1/f noise, the effect of irradiation damage on 1/f noise of SBD was studied in this paper. The research shows that, the irradiation induced interface states change the distributing of interface state density, and, moreover, modulate the Schottky barrier height and increase the velocity of recombination in the surface, leading to the degradation of device performance as well as the significant increasing of 1/f noise level. So, 1/f noise is closely related to SBD's degradation, namely, the larger the magnitude of 1/f noise and the deviation from standard value, the worse the reliability of device, and it's also an indicator of bad radiation-proof performance, which causes its high failure rate in radiation environment. Thus the 1/f noise acts as a researching tool on the mechanism of irradiation damage of SBD, also provides the theoretical basis for nondestructive irradiation hardness assessment.
Analysis of non-degenerate four-wave-mixing crosstalk in DWDM system
Authors: Du Jian-Xin  ,   南京邮电大学光电工程学院光通信研究所，南京  210046
Published: December 2020

Four-wave mixing (FWM) tone degrades system performance in dense wavelength-division-multiplexed (DWDM) optical transmission. A method of evaluating the efficiency of non-degenerate FWM tone for return-to-zero modulation scheme is developed without ignoring group-velocity walk-off of random bit sequence between channels. A theoretical model evaluating the standard deviation of FWM tone is then given. Some calculation examples show that, when the duty cycle and channel separation become small, the initial relative time delay of random bit sequences in different channels and fiber dispersion are more important to the FWM noise. Choosing optimal values of them is important to make the system to have low dispersion and small FWM crosstalk.
Discrete element simulation of the segregation in Brazil nut problem
Authors: Zhao Yong-Zhi  , Jiang Mao-Qiang  , Zheng Jin-Yang  ,   浙江大学化学工程与生物工程学系化工机械研究所,杭州  310027
Published: December 2020

The segregation of the binary granular mixture in Brazil nut problem was simulated by using discrete element model. The influences of the frequency and the amplitude of the vibration on the segregation are discussed. The simulation results show that the segregation between big and small particles can be predicted accurately. When the frequency or the amplitude of the vibration is low, the final segregation efficiency is low, but the segregation is quite stable. When the frequency or the amplitude of the vibration is high, the final segregation efficiency is still low, but the segregation is unstable. An optimum operating point with a moderate frequency and a moderate amplitude of the vibration exists in the process of segregation in Brazil nut problem.
Discrete element simulation of the microscopic mechanical structure in sandpile
Authors: Zhao Yong-Zhi  , Jiang Mao-Qiang  , Xu Ping  , Zheng Jin-Yang  ,   (1)浙江大学化工机械研究所,杭州  310027; (2)浙江大学应用力学研究所,杭州  310027
Published: December 2020

The formation of three-dimensional sandpile was simulated by using discrete element model. The influence of sliding friction and rolling friction of particles on the formation of sandpile was discussed. The simulation results show that the angle of repose of sandpile is determined by both sliding friction and rolling friction. The trec-shaped microscopic mechanical structure in the sandpile was revealed by the simulation. The stress distribution at the bottom of sandpile was also obtained by the simulation. The simulation results show that when the angle of repose of sandpile is large, normal stress profiles with a clear stress dip near the center of the pile is generally formed, and when the angle of repose of sandpile is small, the maximal normal stress generally appears near the center of the pile. Which type of the stress distribution at the bottom of sandpile will emerge is rather accidental,depending on the real process of pileing.
The structure and potential energy function of BeH2(X1Σ+g) and H2S(X1A1) molecules
Authors: Linghu Rong-Feng  , Li Jin  , Lü Bing  , Xu Mei  , Yang Xiang-Dong  ,   (1)贵州师范大学理学院,贵阳  550001; (2)四川大学原子与分子物理研究所,成都  610065; (3)四川大学原子与分子物理研究所,成都  610065;贵州师范大学理学院,贵阳  550001; (4)四川大学原子与分子物理研究所,成都  610065;海南大学材料与化工学院,海口  570228
Published: December 2020

Quadratic configuration interaction method including single and double substitutions has been used to optimize the possible structures of BeH2 and H2S molecules with the 6-311++g(3df,3pd) basis set. The results show that the ground state of BeH2 molecule is of D∞h symmetry and is in the X1Σ+g state, the ground state of H2S molecule is of C2v symmetry and in the X1A1 state. The equilibrium geometry, dissociation energy, harmonic frequencies and force constants have been calculated. The potential energy functions of BeH2 and H2S have been derived by using the many-body expansion theory. The potential energy functions describe correctly the configurations and the dissociation energies of the two ground-state molecules.
Electromigration in Sn3.0Ag0.5Cu flip chip solder joint
Authors: Lu Yu-Dong  , He Xiao-Qi  , En Yun-Fei  , Wang Xin  , Zhuang Zhi-Qiang  ,   (1)华南理工大学材料学院，特种功能材料教育部重点实验室，广州  510640; (2)华南理工大学材料学院，特种功能材料教育部重点实验室，广州  510640；信息产业部电子第五研究所，电子元器件可靠性物理及其应用技术国家级重点实验室,广州  510610; (3)信息产业部电子第五研究所，电子元器件可靠性物理及其应用技术国家级重点实验室,广州  510610
Published: December 2020

Electromigration in Sn30Ag05Cu flip chip solder joints was investigated under a current density of the order of 104 A/cm2. The transfer of atoms or vacancies and the formation of Joule heating induced by electromigration were studies in terms of microstructural evolution. The formation of pancake-type void at the interface between solder and intermetallic compound was dominated by current concentration and the directional transfer of vacancies induced by electromigration. Series of voids were also found at the interface between Ni（P） finishes and solder joint. The area of voids at substrate side are less than that at chip side. The flux of Cu atoms in the pad has the same direction as the electron flux. The transfer of Cu atoms from pad to solder joint led to the formation of large areas of intermetallic compound in solder joint, and the amount of intermetallic compound increased along the direction of electron flux.
Stability and approximate solution of a relative-rotation nonlinear dynamical system with coupled terms
Authors: Shi Pei-Ming  , Jiang Jin-Shui  , Liu Bin  ,   燕山大学测试计量技术及仪器河北省重点实验室，秦皇岛  066004
Published: December 2020

The dynamic behaviors of a relative-rotation nonlinear dynamic system with cubic coupled terms are studied. First, the dynamic equation of coupled system with nonlinear elastic force and generalized friction and harmonic excitation is deduced. The approximate solution of coupled unautonomous equation under harmonic excitation is obtained by the method of multiple scales. The effect of coupled terms on system resonance is analyzed in respect of principal resonance and internal resonance. The singularity stability of bifurcation function of principal resonance is studied by singularity theory, and the transfer concourse and topological structure of bifurcation function are obtained.
A novel stablility theorem for fractional systems and its applying in synchronizing fractional chaotic system based on back-stepping approach
Authors: Hu Jian-Bing  , Han Yan  , Zhao Ling-Dong  ,   中北大学电子测试技术国家重点实验室,仪器科学与动态测试教育部重点实验室,太原  030051
Published: December 2020

A stablility theorem is proposed for fractional systems whose order is not greater than 1. Based on this theorem, back-stepping approach for designing controller is extended to fractional order chaotic system. And the fractional order Newton-Leipnik chaotic system is synchronized based on the extended backstepping approach. Numerical simulation certifies effectiveness of the method.
The fast- and slow-scale stabilities and chaotic motion of H-bridge sine inverter
Authors: Wang Xue-Mei  , Qiu Dong-Yuan  , Zhang Bo  ,   (1)华南理工大学电力学院,广州  510640; (2)华南理工大学电力学院,广州  510640；湖南工业大学电气与信息工程学院,株洲  412008
Published: December 2020

Sine inverter is a time varying nonlinear system, for which two scales, namely the fast and slow-scale, can be used to analyses its stability. Based on this, fast- and slow-scale discrete model of H-bridge sine inverter under proportional control are derived respectively. For the fast-scale stability, folded diagram and spectrum analysis are introduced. For the slow-scale stability, slow-scale fixed points and a theorem of slow-scale instability of a discrete-time periodically varying system are proposed. It is shown that slow-scale instability is an effective criterion for chaos motions of discrete-time periodically varying system. Research shows that proposed methods can be used to analyse the fast- and slow-scale instability and chaotic behavior of H-bridge sine inverter.
Theoretical study of the molecular super-excited states: assignment and theoretical relative intensities of the photofragment yield spectra for F- from F2 ion-pair production
Authors: Zhang Wei-Hua  , Hao Yu-Song  , He Chun-Long  , Li Jia-Ming  , Mo Yu-Xiang  ,   (1)清华大学物理系,原子分子纳米科学教育部重点实验室,北京  100084; (2)上海交通大学物理系,上海市激光制造与材料改性重点实验室,上海  200030；清华大学物理系,原子分子纳米科学教育部重点实验室,北京  100084
Published: December 2020

In the framework of quantum defect theory, the photofragment yield spectra for F- from F2 ion-pair production have been studied. The multiple-scattering self-consistent field method and the theoretical time-dependent wave-packet dynamics method are employed. Based on our calculated results, the vibrational resolved assignment and the calculated relative intensity are provided.