bluuebunny/crossref_metadata_2025 huggingface dataset:
Layer by layer growth of CdTe nanocrystal thin films and its photoluminescence
Authors: Dai Ming  , Liao Yuan-Bao  , Liu Dong  , Gan Xin-Hui  , Xu Ling  , Ma Zhong-Yuan  , Xu Jun  , Chen Kun-Ji  ,   南京大学物理系,固体微结构物理国家重点实验室,南京  210093
Published: December 2020

We synthesized size-controlled，uniformly distributed, and thioglycolic-stabilized CdTe nanocrystals by wet chemistry method. The multilayer nanocrystals were assembled on Si substrate by bifunctional linker molecule and the resonance energy transfer between different sized CdTe nanocrystals embedded in gelatin film was investigated. The results showed that the multilayer nanocrystals were in a good order because the distance between the layers was nearly the same. The distance between different sized nanocrystals was relatively short in the directly dried sample. We can observe the resonance energy transfer by the red shift in its photoluminescence.
Spatio-temporal distributions of evaporation duct for the West Pacific Ocean
Authors: Yang Kun-De  , Ma Yuan-Liang  , Shi Yang  ,   西北工业大学航海学院,西安  710072
Published: December 2020

The evaporation duct is a natural microwave trapping phenomenon over water surfaces, which has a strong impact on near-surface electromagnetic propagation. For radar and communication system designs and operations,it is of great significance to obtain the long-term mean features of evaporation duct in a large-scale sea. In order to overcome the shortcomings of single-point measurement at local sea, a method for calculating the statistical features of the evaporation duct in a large scale-sea based on the NCEP （National Centers for Environmental Prediction） reanalysis data was presented. This method was confirmed by using the weather buoy data at the Pacific Ocean and the measurement data on the Weizhou Island in the South Sea of China. With NCEP reanalysis data of 18 years, the spatio-temporal features of evaporation duct in the West Pacific Ocean were studied. The distribution features of the evaporation duct height for different seas and months were obtained. The evaporation duct database was established with spatial resolution of about 1875°×19°, which is 28 times higher than the existing 10°×10°database.
Growth of graphene structure on 6H-SiC(0001): Molecular dynamics study
Authors: Tang Chao  , Ji Lu  , Meng Li-Jun  , Sun Li-Zhong  , Zhang Kai-Wang  , Zhong Jian-Xin  ,   (1)量子工程与微纳能源技术湖南省普通高等学校重点实验室,湘潭  411105; (2)量子工程与微纳能源技术湖南省普通高等学校重点实验室,湘潭  411105；湘潭大学物理系,湘潭  411105
Published: December 2020

The growth process of graphene structure on 6H-ＳiC（0001） surface has been studied using the classical molecular dynamics （MD） simulation and the simulated annealing technique. We show that carbon atoms of the 6H-ＳiC（0001） subsurface after sublimation of Si atoms can be self-organized to form local monolayer graphene structures. This process is similar to the formation of graphene on the 6H-ＳiC（0001） surface, depending strongly on annealing temperature and coverage of carbon atoms on the SiC（0001）surface. The local graphene structures can be formed on 6H-ＳiC（0001）as the annealing temperature is around 1400 K. This transformation temperature is in good agreement with experimental observations （1080 ℃）, but is lower than that of growing graphene on SiC（0001） surface （T≈1450　K）. In addition, not only single layer but also bilayer graphene structure can be formed, associated with the increase of the coverage of carbon atoms on SiC（0001）surface.
Chaotic time series prediction based on information entropy optimized parameters of phase space reconstruction
Authors: Zhang Chun-Tao  , Ma Qian-Li  , Peng Hong  ,   (1)South China University of Technology, Guangzhou 51006, China; (2)South China University of Technology, Guangzhou 51006, China;Chongqing Three Gorges University, Chongqing Wanzhou 40400, China
Published: December 2020

This paper proposes a method of information entropy optimized parameters (IEOP) of pahse space recon struction. First, it establishes an information entropy optimum model in phase space for embedding dimension and delay time by using conditional entropy. It then solves these two parameters with genetic algorithm (GA) simultaneously. IEOP constructs an optimum phase space, which maintains independence of reconstruction coordinate and retains the dynamic characteristics of the original system. In the numerical simulations, results of the Lorenz system and Mackey-Glass system show that it not only determines two parameters at the same time, but also can obtains more information in the optimized phase space, there by improving the performance of chaotic time series prediction.
First-principles study of electronic and optical properties of Ni-doped silicon nanowires
Authors: Liang Wei-Hua  , Ding Xue-Cheng  , Chu Li-Zhi  , Deng Ze-Chao  , Guo Jian-Xin  , Wu Zhuan-Hua  , Wang Ying-Long  ,   College of Physics Science and Technology,Hebei University,Baoding 071002,China
Published: December 2020

Structural stability,electronic and optical properties of Ni-doped silicon nanowires are investigated by first-principles calculations based on the density functional theory. The results show that Ni can preferentially occupy substitutional sites near the surface of silicon nanowire. The doping of Ni atom in silicon nanowire introduces the impurity levels. The impurity level is mainly contributed by Ni 3d orbital. The decrease of the band gap results from the coupling of Ni 3d and Si 3p states. A strong absorption peak occurs in the low energy region of Ni-doped silicon nanowire,accompanied by the widening of the absorption band.
Design and simulation of a simple two-dimensional left-handed metamaterials
Authors: Guo Yun-Sheng  , Zhang Xue-Feng  ,   Department of Applied Physics, Inner Mongolia University of Science and Technology, Baotou 014010, China
Published: December 2020

Negative permittivity can be realized from the periodic unit cells of the metallic bar structure, and the effects of the length and the width of the metallic bar on negative permittivity is discussed. Through arraying two unit cells along the direction of the wave vector k , the negative permeability can be achieved from a strong resonance response of the two metallic bars to external magnetic field, so a one-dimensional left-handed metamaterials is obtained. The left-handed properties can also be obtained if magnetic boundary conditions of the two unit cells are interchanged with those of wave ports, but electrical boundary conditions are unchanged, i.e., the wave vector k rotates by 90°. So a two-dimensional left-handed metamaterials is achieved.
Effect of Al and N codoping on the optical properties of Zn1-xMgxO
Authors: Yang Ze-Jin  , Li De-Hua  , Liu Qiang  , Cheng Xin-Lu  ,   (1)College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610066, China; (2)Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China; (3)Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China;School of Optical and Electronical Information, Chongqing University of Technology, Chongqing 400054, China
Published: December 2020

Effects of Al and N codoping on the optical properties of Zn1-xMgxO in ultraviolet and visual spectral regions have been systematically investigated using density functional theory based on the first-principles method. It is found that the optical properties of Zn1-xMgxO are caused by the codoped Al and N to vary mainly in a low energy region, whereas they remain almost unchanged in a high energy region. The detailed calculations, including the imaginary part of the dielectric constant, absorption spectrum and extinction coefficient, indicate that due to the codoped Al and N, the optical absorption of Zn1-xMgxO shifts toward lower energy and the absorption of the ultraviolet and the visible absorption increase. Study on the real part of the dielectric constant and reflection spectrum of Zn1-xMgxO shows that the codoped Al and N are responsible for the increased reflection peak intensity, and also for the static dielectric constant increasing from 2.64 to 3.23. In addition, the calculations from the current electron energy loss function indicate that the codoped Al and N lead to the enhanced amplitude and the blue shift of the plasma resonant frequency of Zn1-xMgxO.
Effects of V substitution for Mn on charge ordering and spin-glass state in La0.45Ca0.55MnO3 sample
Authors: Wang Gui-Ying  , Guo Huan-Yin  , Mao Qiang  , Yang Gang  , Peng Zhen-Sheng  ,   (1)Department of Electronic and Electrical Engineering, Suzhou University, Suzhou 234000, China; (2)Department of Electronic and Electrical Engineering, Suzhou University, Suzhou 234000, China;Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China
Published: December 2020

The polycrystalline samples of La0.45Ca0.55Mn1-xVxO3(x=0.00, 0.10) have been prepared by the solid-phase reaction. Efects of V5+ substitution for Mn3+/Mn4+ on charge ordering and spin-glass state are studied by X-ray diffraction spectrum, temperature dependence of magnetization, and electron spin resonance spectra. The results indicate that charge ordering of the original system is almost destroyed, and spin-glass state at about 40 K is melted by 10% of V substitution for Mn. The charge ordering phase is destroyed mainly because of V5+ ions substitution for Mn3+/Mn4+, which increases the ratio of Mn3+ to Mn4+ and so causes ferromagnetic double-exchange to be superior to antiferromagnetic super-exchange. In addition, the spin-glass state is melted because V substitution for Mn destroys the formation condition of spin-glass state that a small quantity of ferromagnetic components exist under the antiferromagnetic backgrornd.
Synthesis of MgxZn1-xO under high pressure and high temperature
Authors: Qin Jie-Ming  , Wang Hao  , Zeng Fan-Ming  , Li Jian-Li  , Wan Yu-Chun  , Liu Jing-He  ,   (1)School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, China; (2)School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, China;College of Physics, Inner Mongolia University for the Nationalities, Tongliao 028000, China
Published: December 2020

The synthetic process of MgxZn1-xO (0.30xxZn1-xO (x=0.4, 0.5, 0.6) are fabricated reproducibly by sintering mixture of ZnO and MgO powders under pressures of 4—5.6 GPa and temperatures of 1000—2000 ℃, and the problem of phase separation is solved. The MgxZn1-xO sample is characterized through several measurements of X-ray diffraction, scanning electron microscope, etc. The synthetic mechanism of cubic MgxZn1-xO is clarified and the phase diagram between temperature and components of MgxZn1-xO is obtained based on the experimental results.
Frictional properties of fluorinated diamond-like carbon films prepared by radio frequency reactive magnetron sputtering
Authors: Wang Pei-Jun  , Jiang Mei-Fu  , Du Ji-Long  , Dai Yong-Feng  ,   Department of Physics, Suzhou University, Suzhou 215006, China
Published: December 2020

The fluorinated diamond-like carbon (F-DLC) films are prepared by radio frequency reactive magnetron sputtering with different flow ratios of CHF3 and Ar as a source gas and pure graphite as a target. Surface morphology, hardness, bonding configuration and tribological properties are investigated by atomic force microscope, nanoindenter, Raman spectra, Fourier transform infrared (FTIR) spectra and a ball-on-disk test rig, respectively. The results show that the F-DLC films are distributed compactly and homogeneously and exhibit good friction-reducing behaviors. The minimum of friction coefficient reaches about 0.42 at r=1 ∶6 while the hardness of films is highest. Raman spectra and FTIR spectra reveal that with the increase of r, the fluorine content gradually increases. However, the intensity ratio ID/IG of Raman bands of disordered graphite (D-band) and graphite (G-band) of F-DLC films decreases, which is indicative of the decrease of the fraction of aromatic ring. The results also show that the F content is another significant factor which affects the friction coefficient. The weakening of —CF2 asymmetric stretch vibration intensity and the formation of CFH in C C chains may result in a lower friction coefficient of F-DLC films.
A finite-time stable theorem about fractional systems and finite-time synchronizing fractional super chaotic Lorenz systems
Authors: Zhao Ling-Dong  , Hu Jian-Bing  , Bao Zhi-Hua  , Zhang Guo-An  , Xu Chen  , Zhang Shi-Bing  ,   School of Electronics & Information, Nantong University, Nantong 226019, China
Published: December 2020

Finite-time stable theorem about fractional system and finite-time synchronizing fractional chaotic system are studied in this paper. A finite-time stable theorem is proposed and proved according to the properties of fractional equation. Using this theorem, fractional super chaotic Lorenz systems is synchronized in finite-time. Numerical simulation certifies the effectiveness of the theorem proposed in this paper.
Generation of Raman light source with an anti-reflection-coated edge-emitting laser diode in an external cavity
Authors: Zhang Yan-Feng  , Li Gang  , Zhang Yu-Chi  , Zhang Peng-Fei  , Wang Jun-Min  , Zhang Tian-Cai  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices,Institute of Opto-Electronics, Shanxi University, Taiyuan 030006, China
Published: December 2020

Phase locked two laser beams with a tunable and controllable frequency difference in a range of several GHz play a major role in the stimulated Raman transition, coherent population trapping, quantum states preparation and other quantum manipulation researches. We demonstrate such leaser beams with a tunable frequency difference in a range of 6.09.3GHz. In particular, the frequency differences of 6.835GHz and 9.192GHz corresponding to the ground state's hyperfine splitting in Rb87 and Cs133 respectively are realized experimentally. The power of the modulated beam is measured to be 6.87mW. With an antireflection-coated edge-emitting diode placed in an external cavity, we can suppress the carrier completely when the modulation frequency is lower than 4.0GHz by adjusting the external cavity length, the temperature, the current of the diode, and the power of the modulation. When the modulation is higher than 4.0GHz we cannot fully suppress the carrier, but we can also obtain the laser beams each with a high modulation depth due to modulation enhancement by external cavity resonance.
Influence of optical simple pulse coding on the Brillouin optical time domain analyzer based on bi-directional Raman amplification
Authors: Zhang Chao  , Rao Yun-Jiang  , Jia Xin-Hong  , Deng Kun  , Chang Liang  , Ran Zeng-Ling  ,   Key Laboratory of Optical Fiber Sensing & Communications, Ministry of Education, School of Communication & Information Engineering, University of Electronic Science & Technology of China, Chengdu 611731, China
Published: December 2020

We report the influence of optical simple pulse coding on the Brillouin optical time domain analyzer (BOTDA) based on bi-directional Raman amplification. This method is proposed to reduce the frequency uncertainty in long-distance BOTDA under higher spatial resolution. The experimental characterization of 49.6 km temperature sensing with a measurement accuracy of ~1 ℃ under ~2.5 m spatial resolution over the whole length of sensing fiber is demonstrated. The signal-to-noise ratio (SNR) and the optical signal power distribution characteristics of the system are studied experimentally in this paper.
Chaotic characteristics of gas bubble motion in acoustic field
Authors: Shen Zhuang-Zhi  , Lin Shu-Yu  ,   Institute of Appiled Acoustics, Key Laboratory of Ultrasonics of Shaanxi Province, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

Considering liquid compressibility, the dynamical behaviors of gas bubble in acoustic field are investigated by regarding water as a work medium. The effects of acoustic frequency, acoustic pressure, initial radius of gas bubble, liquid surface tension, and viscosity coefficient on bubble motion state are numerically simulated. The relationship between cavitation treatment effect and gas bubble motion state is analysed.The results show that when the gas bubble motion is in a chaotic state, it is the most important factor for enhancing acoustic cavitation degradation of organic pollutants ability.
Measurements of rotational and vibrational temperatures based on flame emission spectroscopy
Authors: Peng Zhi-Min  , Ding Yan-Jun  , Zhai Xiao-Dong  ,   State Key Laboratory of Power Systems, Dept of Thermal Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

This study addresses emission spectra of Air-ethanol and Air-kerosene flames by using optical multichannel analysis system (OMA). Experimental results show that there are several bands of molecular spectrum in a range from 275 to 600nm. Among them, the OH A2+X2r(300330 nm), the CH A2X2(410440 nm), and C2 A3gX3u (500 520 nm) emissions have the strongest intensity. In turn, the fine structures of OH (A2+X2r) and CH (A2X2) emission are studied by using a high resolution grating in experiment, and the distributions of spectra intensity are calculated at different rotational and vibrational temperatures based on the molecular spectroscopy. Moreover, by comparing the simulated spectra with the experimental spectra of OH (A2+X2r) and CH (A2X2) emissions, the rotational and the vibrational temperatures of Air-ethanol flame are determined in this paper.
First-principles study of the electronic structure and electric conductivity in W-type hexagonal ferrite BaFe18O27
Authors: Ri Chung-Ho  , Li Lin  , Zhu Lin  ,   Department of Physics, Northeastern University, Shenyang 110819, China;,   Department of Physics, University of Science, Pyongyang, D.P.R.Korea
Published: December 2020

The electronic ground state and the electric conductivity of W-type hexagonal ferrite BaFe18O27 are investigated in the generalized gradient approximation (GGA) as well as the GGA plus Hubbard U(GGA+U) scheme. The ionic relaxation calculation of the experimental crystal structure shows that oxygen ions at 6h site in the BaO layer move away from the surface position in the unit cell, resulting in a structural distortion. The magnetic moment of the cell is calculated to be 28 B/f.u., in agreement with previous experimental results. By taking account of electronic band structure and crystal ionic configuration it is found that the material is a weak half-metal and the effective mass of conduction electrons along the c axis is much heavier than that perpendicular to this axis. Fe ions on octahedral 6 g sites and O ions around them of the spinel block form a conductive layer. Therefore the electric conductivity perpendicular to the c axis is much greater than that parallel to the c axis.
High-efficiency blue fluorescence organic light-emitting diodes with DPVBi inserted in the doping emmision layer
Authors: Wang Jin  , Zhao Yi  , Xie Wen-Fa  , Duan Yu  , Chen Ping  , Liu Shi-Yong  ,   State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China;,   College of Information Technology, Jinlin Normal University, Siping 136000, China
Published: December 2020

We have fabricated high-efficiency blue fluorescence organic light-emitting diodes(OLEDs) with DPVBi inserted in the doping emmision layer(EML). The OLEDs with a configuration of ITO/2T-NATA/NPB/DPVBi:DSA-ph(inserted with DPVBi thin layer)/Alq3/LiF/Al are fabricated, using 2T-NATA as hole injection layer, NPB as hole transport layer, DPVBi:DSA-ph as emission layer and Alq3 as electron transport layer, respectively. The DPVBi thin layer inserted in EML leads to an increase in device efficiency as a results of an improvement of the balanced carrier injection, which results in an efficient radiative recombination in the emission zone. In addition, DPVBi ability of hole blocking can also be another reason for the improvement on the luminous gain. Hence, high radiative recombination is expected to take place in DPVBi:DSA-ph emission layer. This high efficient recombination results in high brightness and enhanced efficiency in our OLEDs. By optimizing the location and the number of layers of DPVBi thin layer, a maximum current efficiency of 6.77 cd/A is achieved at a current density 6.84 mA/cm2, which is nearly 67.6% more than that of non-inserted device. At a luminance of 1000 cd/m2, the current efficiency of the optimizing device is 6.49 cd/A at 6.7 V with a CIE (0.179, 0.317).
A review of the turbulent mixing by wind wave breaking
Authors: Zhang Shu-Wen  , Cao Rui-Xue  , Zhu Feng-Qin  ,   Guangdong Key Lab. of Climate, Resource and Environment in Continental Shelf Sea and Deep Sea, College of Oceanology and Meterorology, Guangdong Ocean University, Zhanjiang 524088, China
Published: December 2020

It is formidable task to provide a comprehensive investigation of wave breaking and its turbulence process. In this review paper, the observations of turbulence by wave breaking and its parameterizations since 1990 are presented. Among them, the following are the most important. (1)Wave breaking induced turbulent mixing process cannot be described by the wall-layer theory, that is, the rate of dissipation of turbulent kinetic energy is not proportional to the inverse of water depth. In fact, a significant turbulent mixing enhancement in near-surface layer for a depth of several meters is achived by wave breaking. The dissipation rate of turbulence kinet energy is one to three orders larger than the value predicted by the wall-layer scaling. (2)In the crest region above the mean waterline, the dissipation rate increases as disz-2.3, while in the region below the trough, the dissipation rate decreases as disexp(-z) or disz-2. (3)The turbulent mixing length is a critical physical quantity to study the wave breaking. Up to now, however, there has been a large difference between the values given by the previous studies. Extensive work on the mixing depth and turbulent mixing length by wave breaking is also needed in the future.
Quantum Fisher information and chaos in the system of Bose-Einstein condensate
Authors: Song Li-Jun  , Yan Dong  , Liu Yie  ,   School of Science, Changchun University, Changchun 130022, China;,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

Quantum Fisher information,derived from the classical Fisher information, is closely related to the quantum entanglement in quantum information. The entanglement and the quantum information which are both associated with the classical phase space are investigated in a two-component Bose-Einstein condensate impacted by the impulses. The results reveal that the states regardless of disorder of the phase space after the first impulse are entangled. However, the quantum information is very sensitive to the state centred in the classical phase space, concretely, the value of the quantum information centred in the chaotic region is greater than in the regular region. By employing the good quantum-classical correspondence, we conclude that the quantum information can serve as a signature of the quantum chaos.
Three-dimensional tunable colloidal photonic crystal self-assembled on the end face of an optical fiber
Authors: Guo Wen-Hua  , Wang Ming  , Xia Wei  , Dai Li-Hua  , Cui En-Ying  , Ni Hai-Bin  ,   Key Laboratory on Opto-Electronic Technology of Jiangsu Province, School of Physics and Technology, Nanjing Normal University, Nanjing 210046, China;,   School of Physics and Electronic Engineering, Changshu Institute of Technology, Changshu 215500, China
Published: December 2020

High-quality three-dimensional nanostructure colloidal crystal-fiber structure is obtained by the modified vertical deposition method. The morphology of the colloidal crystal is examined by the scanning electron microscope, which illustrates that the (111) plane is parallel to the substrate of the fiber end face. The optical characterization of the colloidal crystal is also analyzed with an all-fiber network system. Reflection spectra show the existence of photonic band gap, which is located at 845 nm. As the liquid refractive index filled in the voids of the sample increases, the tunable wavelength of reflected light which is predicted by Bragg's equation with considering the effect of photonic band gap shows a good agreement with experimental results. Also, as the refractive index is changed because of different concentrations of solution, the colloidal photonic crystal-fiber system can also be distinguished by recording the shift of the maximum of Bragg reflection spectra.
Raman spectroscopy study on the C/H interaction between benzene and chloroform
Authors: Liu Tian-Yuan  , Sun Cheng-Lin  , Li Zuo-Wei  , Zhou Mi  ,   State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012, China
Published: December 2020

Raman spectra of benzene and chloroform with different relative concentrations are measured. The frequencies of CH stretching vibration in chloroform shift to lower wave number with the increase of benzene concentration, which can be explained by C/H interaction. This interaction is saturated when the chloroform volume fraction is less than 40%: the frequencies of CH stretching vibration remain the same. Taking the chloroform volume fraction of 70% chloroform and benzene mixed solution as the research object, the Raman spectra of binary solution and pure liquid are measured at different pressures and temperatures. According to the relationship between pressure and temperature of the frequencies of CH stretching vibration in chloroform, the regular pattern of C/H interaction is obtained.
A radiation degradation model of metal-oxide-semiconductor field effect transistor
Authors: Sun Peng  , Du Lei  , Chen Wen-Hao  , He Liang  , Zhang Xiao-Fang  ,   School of Technical Physics, Xidian University, Xi'an 710071, China
Published: December 2020

Based on the production kinetics of oxide-trapped charge and interface-trapped charge and the microscopic mechanism of radiation damage, a model of post-irradiation threshold voltage drift due to oxide trap and interface trap as a function of radiation dose is proposed. This model predicts that the post-irradiation threshold voltage drift due to oxide trap and interface trap would be linear in dose at low dose levels. At high dose levels, the post-irradiation threshold voltage drift due to oxide trap tend to be saturated, its peak value has no correlation with radiation dose, and the post-irradiation threshold voltage drift due to interface trap has an exponential relationship with radiation dose. In addition, the model indicates that the oxide-trapped charge and the interface-trapped charge start a saturation phenomenon at different radiation doses, and the saturation phenomenon of oxide-trapped charge appears earlier than interface-trapped charge. Finally, the experimental results accord well with the model. This model provides a more accurate prediction for radiation damage in metal-oxide-semiconductor field effect transistor.
The preparation and performance analysis of GaN-based high-voltage DC light emitting diode
Authors: Cao Dong-Xing  , Guo Zhi-You  , Liang Fu-Bo  , Yang Xiao-Dong  , Huang Hong-Yong  ,   Laboratory of Nanophotonic Functional Materials and Devices, Institute of Optoelectronic Material and Technology, South China Normal University, Guangzhou 510631, China;,   Yinyu Semiconductor Photonics Ltd., Jiangmen 529728, China
Published: December 2020

The design and the preparation of GaN-based high-voltage DC light emitting diode are realized. It is found that the device, whose chip structure is truncated pyramid using the epitaxial wafer whose subsrate is a patterned sapphire substrate, has a higher luminous efficiency than other chip structures. The luminous efficiency increases up to 116.06 lm/W when the device is packaged into white LED at a color temperature of 4500 K which is driven by 20 mA, and the corresponding voltage is 50 V. The I-V curve shows that the threshold voltage is 36 V, corresponding to a drive current of 1.5 mA. The optical power increases approximately linearly with the increase of driving current when the driving current increases from 15 mA to 50 mA, and the luminous efficiency in this range decreases more slowly with the increase of driving current, indicating that the GaN-based high-voltage DC LED is favourably driven by large current density, and severe efficiency droop will not appear as the drive current density increases, which offers a new idea for studying and solving the efficiency droop problem from the chip level.
A differentiable thresholding function and an adaptive threshold selection technique for pulsar signal denoising
Authors: Gao Guo-Rong  , Liu Yan-Ping  , Pan Qiong  ,   College of Science, Northwest A & F University, Yangling 712100, China
Published: December 2020

Because of the extremely low signal-to-noise ratio of pulsar signals, it is difficult to suppress noise while preserving details by the traditional denoise methods. Therefore, a wavelet domain pulsar signal denoising method based on a differentiable thresholding function and an adaptive threshold selection technique is presented. The signal-to-noise ratio(SNR), the root mean square error(RMSE), the relative error of the peak value (REPV) and the error of the peak position (EPP) are used to evaluate the performance of the proposed denoising method. Experimental results show that the proposed method can remove the pulsar signal noise and keep the useful information effectively. At the same time, it can achieve a higher PSNR, a lower RMSE, a lower REPV and a lower EPP than the soft thresholding and hard thresholding methods.
A theoretical study on electron impact ionization helium (e, 2e) reactions at 64.6 eV
Authors: Chen Zhan-Bin  , Liu Li-Juan  , Dong Chen-Zhong  ,   Key Laboratory of Atomic and Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China
Published: December 2020

The triple differential cross sections for electron impact ionization helium (e, 2e) reactions are calculated by use of the BBK and modified BBK model at different gun angles of incident electron energy 64.6 eV. The structures of the cross sections and the physical natures of these structures are discussed in detail. It is found that for the non-coplanar geometry, cross sections are determined by a variety of effects together and these effects are converted to each other under different conditions. Moreover, strong dynamical screening effect is observed in the final state of the perpendicular plane symmetric geometry.
The analysis of droplet surface temperature field during dropwise condensation process
Authors: Lan Zhong  , Zhu Xia  , Peng Ben-Li  , Lin Meng  , Ma Xue-Hu  ,   Institute of Chemical Engineering, Dalian University of Technology, Dalian 116024, China
Published: December 2020

The invistigations on dropwise condensation process and the mechanism of heat transfer enhancement are usually based on the droplet distribution and the movement principle of droplets on condensing surface. In the meanwhile, a single droplet is treated as a stable individual and the movement property inside the droplet is rarely considered. With infrared thermography, the surface temperature distribution of condensate droplet during steam dropwise condensation process is observed. The result shows that the temperature of droplet surface first decreases and then increases and up to a value higher than the initial one as the droplet migrates from one position to another. The droplet will roll and the surface film would be tracked when the droplet moves on the hydrophobic surface. With the convection inside the droplet, condensate near the wall moves to the surface side. The analysis of surface temperature evolution of droplet indicates that the continuous condensation on droplet surface may occur when the surface subcooling exceeds a critical value. The direct condensation on large droplet surface can be promoted by the dynamic process such as droplet coalescence or falling off, which provides a new approach to the condensation heat transfer enhancement.
Design and optimization of a novel broadband and polarization-insensitive dual-core photonic crystal fiber coupler over the whole optical communication band
Authors: Wang Li-Wen  , Lou Shu-Qin  , Chen Wei-Guo  , Lu Wen-Liang  , Wang Xin  ,   Key Lab of All Optical Network & Advanced Telecommunication Network of EMC, Beijing Jiaotong University, Institute of Lightwave Technology, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

In this paper, a novel broadband polarization-insensitive dual-core photonic crystal fiber with elliptical central hole is proposed and the influence of its structural parameters on coupling characteristic is investigated in detail by the full-vector finite element method. Through optimizing the fiber structural parameters, broadband and polarization-insensitive characteristics are achieved over the whole optical communication band from 1.225 m to 1.675 m. The variation of coupling ratio is stabilized at 50% 1%, and the coupling ratio difference between x polarization and y polarization is less than 0.5% overall the wavelength range. Due to its relatively independent of cores and elliptical central hole and suitable structural parameters, this fiber meets the application requirements, that is, easy to fabricate, easy to splice and low splice loss. This research is freed from the current coupler limit: narrow bandwidth, wavelength dependence, polarization-sensitive, difficulty of fabricating, thereby provides the theoretical basis for the study of the large capacity high speed all-optical networks and multi-wavelength tunable fiber laser.
Analysis of convection heat transfer mechanism in nanofluids
Authors: Xiao Bo-Qi  , Fan Jin-Tu  , Jiang Guo-Ping  , Chen Ling-Xia  ,   Department of Physics and Electromechanical Engineering, Sanming University, Sanming 365004, China;,   Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong 99907, China;,   Earthquake Engineering Research Test Center, Guangzhou University, Guangzhou 510405, China
Published: December 2020

Energy shortage and environment pollution are the major and large problems presently encountered by human all over the world. It is an effective way to save energy and reduce emission of polluted gas by using the nanofluids technology. There has been not a widely recognized theory which can explain flow and heat transfer of nanofluids until now. So the mechanism of flow and heat transfer of nanofluids is not clear. Considering the Brownian motion of nanoparticles in nanofluids, a mechanism model for heat transfer by heat convection is proposed based on the fractal distribution of nanoparticle. No additional/new empirical constant is introduced. The proposed fractal model for heat flux of nanofluids is found to be a function of temperature, average nanoparticle size, concentration, fractal dimension of nanoparticles, fractal dimension of active cavities on boiling surfaces and basic fluid property in pool boiling. The model predictions are compared with the existing experimental data, and fair agreement between the model predictions and experimental data is found for the cases of different nanoparticle concentrations and different average nanoparticle diameters. The analytical model can reveal the physical principles for convection heat transfer in nanofluids.
Thermal conductivity measurements on PANI/SBA-15 and PPy/SBA-15
Authors: Huang Cong-Liang  , Feng Yan-Hui  , Zhang Xin-Xin  , Li Wei  , Yang Mu  , Li Jing  , Wang Ge  ,   School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China;,   School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Published: December 2020

Conductive polymers polyaniline (PANI) and polypyrrole (PPy) loaded mesoporous silica (SBA-15) composites are prepared and characterized. The one-dimensional reference bar method and the relevant devices to measure the thermal conductivity are introduced and established. The equivalent pore diameter is proposed to characterize the mesostructures of conductive polymers polyaniline (PANI) and polypyrrole (PPy) in PANI/SBA-15 and PPy/SBA-15 composites. The effects of the equivalent and the measurement pore diameters on thermal conductivities of PANI/SBA-15 and PPy/SBA-15 composites are analyzed. The result shows that thermal conductivities of PANI/SBA-15 and PPy/SBA-15 are higher than that of the substrate SBA-15; the thermal conductivity of PANI/SBA-15 is higher than that of PPy/SBA-15; loading of PANI and PPy in pores of PANI/SBA-15 and PPy/SBA-15 composites is more effective than loading outside of pores for improving the thermal conductivities of PANI/SBA-15 and PPy/SBA-15 composites.
Fabrication of erbium-doped chalcogenide glass and study on mid-IR amplifying characteristics of its microstructured fiber
Authors: Zhou Ya-Xun  , Yu Xing-Yan  , Xu Xing-Chen  , Dai Shi-Xun  ,   College of Information Science and Engineering, Ningbo University, Ningbo 315211, China
Published: December 2020

In order to demonstrate the characteristics of chalcogenide glass Er3+-doped microstructured optical fiber (MOF) amplifying the mid-infrared band signal, Er3+-doped Ga5Ge20Sb10S65 chalcogenide glass is prepared with high temperature melt-quenching method. The absorption spectrum and 2.7 m band fluorescence spectrum of glass sample are measured, and the spectroscopic parameters such as radiative transition probability, radiative lifetime and 2.7 m band stimulated emission cross-section of Er3+ ion are calculated and analyzed according to the Judd-Ofelt and Futchbauer-Ladenburg theories. The 2.7 m band mid-infrared signal amplifying model of Ga5Ge20Sb10S65 chalcogenide glass Er3+-doped MOF under the excitation of 980 nm is presented, and the amplifying characteristics of 2.7 m-band mid-infrared signals for chalcogenide glass Er3+-doped MOF are investigated theoretically. The results show that the chalcogenide glass Er3+-doped MOF exhibits a higher signal gain and very broad gain spectrum: its maximal gain of small signal exceeds 40 dB and amplifying bandwidth of higher than 30 dB gain reaches about 120 nm (26962816 nm) for a 100 cm long chalcogenide glass erbium-doped MOF with a pump power of 200 mW. The theoretical studies indicate that the Ga5Ge20Sb10S65 chalcogenide glass Er3+-doped MOF is an excellent gain medium which can be applied to broadband amplifiers in the mid-infrared wavelength region.
Photonic-crystal-waveguide based Mach-Zehnder interferometer for terahertz switch and modulator
Authors: Wang Chang-Hui  , Zhao Guo-Hua  , Chang Sheng-Jiang  ,   Institute of Modern Optics, Nankai University, Tianjin 300071, China;,   Element 90, No. 73146 Troop, PLA, Quanzhou 362321, China
Published: December 2020

We propose a novel tunable photonic crystal (PC) waveguide Mach-Zehnder interferometer (MZI) based on nematic liquid crystals (LCs) 5CB and investigate its interference properties numerically by using the finite-difference time-domain method. We can change the refractive index of LC by rotating the directors of the LC molecules. The line defect modes of the PC waveguide with different liquid crystal refractive indices are analyzed by using the plane wave expansion method. Owing to the slow group velocity region of the line defect mode, when the index of 5CB changes from 1.53 to 1.63, the variation of the effective index of the line defect mode arrives at 0.168. This property helps to significantly control the phase of light propagation in a PC waveguide MZI. The novel interferometer can be used as either an optically controlled on-off switch or an amplitude modulator in optical circuits.
Design and analysis of two-stage transmitted-reflected concentration PV/thermal system with spectral beam splitter
Authors: Wang Gang  , Hu Peng  , Chen Ze-Shao  , Cheng Xiao-Fang  ,   Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei 230027, China
Published: December 2020

For the traditional photovoltaic (PV) system which is under a full spectral concentrating condition, only a part of solar energy can be used by solar cells for PV power generation, the other part is not effective for the PV power generation and can result in temperature of solar cells increasing. High temperature can reduce the PV transformation efficiency of solar cells. In this study, a concentration PV/thermal system with beam splitter is proposed, which is composed of a linear Fresnel lens, a concave lens, a beam splitter, solar cells and a thermal receiver. The selective transmission coating on the splitter is designed to improve the incident condition of the sunlight on the surface of solar cells and reflect the noneffective part of sunlight to the thermal receiver for recycling. Theoretical analysis of the PV/thermal system is made and the results show that compared with the traditional concentration PV system, the two-stage transmitted- reflected concentration spectral beam splitting PV/thermal system has a high efficiency.
Study on the variation of static dielectric constant with temperature and the corresponding orientational correlation in polar liquids by using Weiss's molecular field theory
Authors: Zhang Li-Li  , Huang Xin-Ru  , Zhou Heng-Wei  , Huang Yi-Neng  ,   Xinjiang Laboratory of Phase Transitions and Microstructures in Condensed Matters, College of Physical Science and Technology, Yili Normal University, Yining 835000, China;,   National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093, China;,   Department of Physics, Shihezi University, Shihezi 832003, China
Published: December 2020

There is no widely accepted microscopic theoretical model of the static dielectric constant of liquids so far. This is mainly because the orientational correlation between molecules in liquids, belonging to the strong correlation systems, is still not clear. In this paper, the variations of the static dielectric constants of 4 kinds of polar liquids, i.e., water, methanol, ethanol and 1-propanol, specifically the Curie-Weiss constant, Curie temperature and Weiss molecular field factor with temperature are studied according to the Weiss's molecular field theory (WMFT), and it is concluded that 1) ferroelectric correlations (FCs) and anti-ferroelectric correlations (AFCs) between molecules coexist in the liquids, and FC is stronger than AFC, as well as FC becomes weak and/or AFC stronger with temperature decreasing; 2) WMFT of homogeneous structure cannot quantitatively describe the abnormally large values of εs of the liquids at low enough T. It can be expected that the coexistence of FC and weak AFC must lead to the spatial distribution of the correlation orders, and consequently, we propose an WMFT of coarse grain approximation of the spatial distribution correlation orders, and use the WMFT to explain why the static dielectric constant varies rapidly with temperature. The above results can benefit the understanding of the liquid physics, including the glass transition mechanism.
Development of fiber-optic surface plasmon resonance sensor based on tapered structure probe
Authors: Feng Li-Hang  , Zeng Jie  , Liang Da-Kai  , Zhang Wei-Gong  ,   State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;,   School of Instrument Science and Engineering, Southeast University, Nanjing 210096, China
Published: December 2020

A fiber-optic surface plasmon resonance sensor (SPR) based on tapered structure probe is studied. The incentive mode of tapered probe calculated by finite-difference time-domain method serves as design references, and the tapered structure of sensor probe fabricated by polishing and grinding at the end of a fiber is similar to Kretschmann prism SPR model, which can realize the modulation of SPR wave. The results show that in the refractive index detection range from 1.3330 to 1.4215, tapered structure FO-SPR sensor has a sensitivity of 1-6 times higher than common FO-SPR sensor and it still keeps a limiting resolution level of 10-5 RIU. The designed tapered structure SPR sensor, which has the advantages of tapered incentive mode, design flexibility, user practical applicability, simple preparation process, a relatively small sample need, and high stability, will fulfill different environment and measuring conditions of biochemical testing and environment monitoring.
Photoluminescences and structrue performances of Si-rich silicon nitride thin films containing Si quantum dots
Authors: Liao Wu-Gang  , Zeng Xiang-Bin  , Wen Guo-Zhi  , Cao Chen-Chen  , Ma Kun-Peng  , Zheng Ya-Juan  ,   School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China
Published: December 2020

Silicon-rich silicon nitride (SiNx) thin films are deposited at 220 ℃ on n-type monocrystalline silicon substrates by plasma enhanced chemical vapor deposition using NH3 and SiH4 as the reaction gases. The samples are annealed at temperature in a range of 500-1100 ℃ in N2 atmosphere. We analyze the crystalline states of silicon quantum dots (Si-QDs) and calculate the crystalline ratios of samples under different annealing conditions according to the Raman spectra. The crystalline ratio is less than 18% when the annealing temperature is lower than 950 ℃, when the temperature reaches 1100 ℃, the crystalline ratio is increased to 53%, which indicates that most of the Si-QDs have been converted into crystallines. Fourier transform infrared spectra are measured at room temperature to investigate the evolutions of the bonding structures within the SiN_x matrix. We find that the wavelengths of Si-N and Si-H bond shift toward higher wavelength, which manifests the formation of near stoichiometric silicon nitride. Photoluminescence generated from all samples is investigated in detail. We find five luminescence peaks, whose origins are analyzed. We conclude that the obvious green luminescence (centred at 500-550 nm) oringinates from Si-QDs and the others come from different defects in the films. The effects of sizes and distribution of Si-QDs on the shift of the luminescence peak are discussed. We acquire that the sizes of Si-QDs are in a rang from 1.6 nm to 3 nm, which have an obvious confinement effect. These results are useful for fabricating contronllable Si-QDs and achievement of luminescent devices based on Si-QDs.
Design, fabrication, and experimental demonstration of a diffractive optical element with long depth of field for nanoscale three-dimensional multi-molecule tracking
Authors: Yu Bin  , Li Heng  , Chen Dan-Ni  , Niu Han-Ben  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering,Shenzhen University, Shenzhen 518060, China;,   State Key Laboratory of Precision Measurement Technology and Instruments, Tsinghua University, Beijing 100084, China
Published: December 2020

The development of real-time single-molecule detection and tracking technology in time and space for multiple bio-molecules in intact cells has important significance for the study on molecular behaviors in life processes. However, limited depth of field is the main drawback of conventional microscopy that prevents observation and tracking of multiple molecules in intact cells. Based on the principle of wavefront coding, the design and fabrication of a novel diffractive optical element (DOE) which combines a distorted diffraction grating with a double-helix point spread function (PSF) phase plate so that it can simultaneously perform multi-plane imaging with double-helix PSF and realize an extended depth of field is presented. Experiments have been carried out on a self-built microscopic system based on the novel DOE, showing that a depth of field can be up to 12 μm. Experimental results are in good agreement with the theoretical predictions, thus proving the feasibility of this method.