bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanolithography based on two-surface-plasmon-polariton-absorption
Authors: Liu Fang  , Li Yun-Xiang  , Huang Yi-Dong  ,   Tsinghua National Laboratory for Information Science and Technology, Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
Published: December 2020

Lithography is one of most important technologies for fabricating micro- and nano-structures. Limited by the light diffraction limit, it becomes more and more difficult to reduce the feature size of lithography. Surface plasmon polariton (SPP) is due to the interaction between electromagnetic wave and oscillation of free-electron on metal surface. For the shorter wavelength, higher field intensity and abnormal dispersion relation, the SPP would play an important role in breaking through the diffraction limit and realizing nanolithography. In this paper, we theoretically and experimentally study the optical nonlinear effect of SPP (two-SPP-absorption) in the photoresist and its application of nanolithography with large field. First, the concept and features of two-SPP-absorption are introduced. Like two-photo-absorption, the two-SPP-absorption based lithography is able to realize nanopatterns beyond the diffraction limit: 1) the absorption rate quadratically depends on the light intensity, which can further squeeze the exposure spot; 2) the pronounced power threshold provides a possibility for precisely controlling the linewidth by manipulating the illumination power. Nevertheless, unlike the two-photo-absorption lithography which focuses light onto a single spot and scans point by point, the two-SPP-absorption method could obtain the subwavelength field pattern by simply illuminating the plasmonic mask. The subwavelength field pattern due to the short wavelength of SPP would further result in the overcoming-diffraction-limit resist pattern. Besides, the highly concentrated SPP field leads to the strong electromagnetic field enhancement at the metal-dielectric interface, which could reduce the input power density of exposure source or enlarge the exposure area. Then the two-SPP absorption is realized under the illuminations of femtosecond lasers with vacuum wavelengths of 800 nm and 400 nm. Meanwhile, the interference periodic patternis realized and it is observed that the linewidth could be adjusted by controlling the exposure dose. The minimum linewidth of resist pattern is only one tenth of the vacuum wavelength. By utilizing the features of two-SPP-absorption, namely shorter wavelength, enhanced field and threshold effect, the lithography field could be of millimeter size, which is about four to five orders of magnitude larger than the characteristic size of nanostructure. Therefore, this two-SPP-absorption scheme could be used for large-area plasmonic lithography beyond the diffraction limit with the help of various plasmonic structures and modes.
Inversion and reconstruction of the macroscopic photometric characterization model for on-orbit space object
Authors: Hou Qing-Yu  , Gong Jin-Nan  , Fan Zhi-Peng  , Wang Yi-Hui  ,   Research Center for Space Optical Engineering, Harbin Institute of Technology, Harbin 150001, China
Published: December 2020

In the field of space object optical situational awareness by space-based optics, the current research focuses on the detecting of long distance point target, the predicting and confirming of target trajectory. It is very important to analyze the on-orbit operation status and basic physical attribution of the space object by remote imaging without any structure or texture information. The analysis method can be used effectively to support the space object status discrimination and the related decision for on-orbit maintenance. In recent years, the number of three-axis stabilization space objects in orbit has increased dramatically. In order to retrieve the optical characteristic parameters of the three-axis stabilization space object surface in a long on-orbit distance, a new method is proposed to reconstruct the macroscopic photometric characterization based on analyzing visible photometric sequence signal. Firstly, based on the principle that solar panel can receive the maximum solar radiation energy, a directing model of solar panel is proposed. Considering the structural characteristics of space object, surface material characteristics, directing characteristics of the solar panels, illumination-observation geometry and the optical system characteristics, the photometric modeling method of the space object oriented to space-based observation is improved. Secondly, the photometric model is equivalent to a two-facet model, then multi-level fusion model of bidirectional reflectance distribution function (BRDF) is used to characterize optical reflection characteristics of complex material surfaces of the space object, and the product of area and reflection corresponding to multi-level BRDF is taken as the parameter of the reconstruction model. Finally, the minimum error between the measured result and reconstruction model of photometric signal is used as the optimization goal, and the linear optimization method is established to realize the inversion of the model parameters. As the space object and the observing satellite are in the same orbit or near orbit condition, the simulating experiment of photometric sequence signal and reconstructing experiment of macroscopic characterization model of optical characteristics are carried out. The simulation result shows that the proposed photometric model can describe the dynamic characteristics of on-orbit space object more comprehensively. And using the on-orbit reconstruction method of the macroscopic photometric model, the photometric signal reconstruction accuracy achieves more than 97% in the near orbit condition. So it is demonstrated that the on-orbit reconstruction method is correct. The method can provide a solution of optical situational awareness for space object on space-based platform, and provides technical support for inversing the attitude and shape of space object.
Growth and carrier transport properties of highly oriented films of the semiconducting polymers via solution dip-casting
Authors: Pan Guo-Xing  , Li Tian  , Tang Guo-Qiang  , Zhang Fa-Pei  ,   High Magnetic Field Laboratory, Chinese Academy of Science, Hefei 230031, China;,   University of Science and Technology of China, Hefei 230026, China
Published: December 2020

Effective control of molecular orientation and packing as well as the film texture of organic semiconductor plays a crucial role in achieving high performance of the electronic device such as high carrier mobility. Development of facile and scalable solution processing method for film deposition is one of the important routes to such a goal.
In this paper, we report on the successful preparation of the large area, macroscopically aligned film of the semiconducting polymer P(NDI2OD-T2) and PTHBDTP via an improved solution dip-coating process in which a tilted substrate is immersed in the dilute solution. Polarized optical microscopy images reveal the parallel stripe structures of both kinds of the deposited films. The chain backbones of both P(NDI2OD-T2) and PTHBDTP are highly aligned along the descending direction of solution level in the dip-coating process as indicated from polarized UV-vis spectra and X-ray diffraction measurements. Furthermore, the atomic force microscopy images of the oriented films of both kinds of polymers clearly exhibit the highly preferentially oriented nanofibril-like domains, parallel to the alignment direction of chain backbone. We elucidate the dip-coating growth process in our experiment in terms of the surface tension-and solvent evaporation-guided self-assembly of chain backbones at the substrate-solution interface near the solution surface. The influence of film texture on carrier transport property is examined by fabricating field effect transistor (FET) based on the aligned film of semiconducting polymer. The FET device of the aligned P(NDI2OD-T2) exhibits a remarkable enhancement of electron mobility by a factor of four compared with the unaligned devices, as well as a large mobility anisotropy of 19. Such a transport behavior is proposed to be attributed to the characteristic charge conducting pathways induced by chain backbone alignment in the polymeric film. In this case, fast intra-chain transport contributes to the majority of device current when the channel current is parallel to the alignment direction of the film, while charge transport will be limited severely by the inter-chain hopping within the fibrous domain and across the disordered domain boundary when the current is perpendicular to alignment direction. The facile method developed here presents a promising approach to fabricating the low-cost, high-performance organic electronic devices.
Particle simulation and analysis of threshold for multicarrier multipactor
Authors: Wang Xin-Bo  , Zhang Xiao-Ning  , Li Yun  , Cui Wan-Zhao  , Zhang Hong-Tai  , Li Yong-Dong  , Wang Hong-Guang  , Zhai Yong-Gui  , Liu Chun-Liang  ,   Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China;,   National Key Laboratory of Science and Technology on Space Microwave, Xi'an Institute of Space Radio Technology, Xi'an 710100, China
Published: December 2020

The multicarrier multipactor is a phenomenon that can be observed in vacuum environment due to the effect of secondary electron emission. Accurate analysis of the threshold of multicarrier multipactor is crucial for the long-term reliability of high-power spaceborne microwave system, and therefore it has been attracting more and more interests in fields of high-power microwave community, plasma physics and aerospace engineering. Recently, a new mechanism of multicarrier multipactor, termed long-term multipactor, induced by sustained accumulation of residual electrons between successive envelope periods of multicarrier signals has received much attention. Comparing with the single-event multipactor induced by the electron accumulation inside a single envelop period, researchers tend to believe that the threshold of the long-term discharge should be lower. However, recent experimental results show an opposite conclusion. In this work, in order to investigate the contradiction between the experimental and theoretical studies on the thresholds of multicarrier multipactors, particle simulations are used to simulate the evolution process of the multicarrier multipactor under the same conditions and judgement criterion. The behavioral characteristics and occurrence condition for multicarrier multipactors, especially the single-event ones, are analyzed based on a power scanning analysis, and the conflicting results are effectively explained. Our simulations show that if the evolution process of a multipactor can be divided into three phases, i.e., establishment phase, critical phase and saturation phase, the experimental reflection coefficient can be corresponding to the reflection coefficient simulated in the critical phase. The simulation results indicate that the type of the multipactor discharge would depend on the configuration of multicarrier signals. For multicarrier signals with relatively narrow bandwidths, single-event multicarrier multipactors could occur in the first place at a lower threshold power. Therefore, the threshold of a long-term discharge is not necessarily lower than that of a single-event one. This conclusion is important for estimating and suppressing the multicarrier multipactors in the design of high-power spaceborne microwave components.
Noninvasive temperature monitoring for high intensity focused ultrasound therapy based on electrical impedance tomography
Authors: Guo Ge-Pu  , Su Hui-Dan  , Ding He-Ping  , Ma Qing-Yu  ,   School of Physics and Technology, Nanjing Normal University, Nanjing 210023, China
Published: December 2020

As a new treatment modality with little thermal damage and few cell metastases to surrounding normal tissues, high intensity focused ultrasound (HIFU) therapy is considered to be one of the most promising technologies for tumor therapy in the 21st century. However, noninvasive temperature monitoring for the focal region exhibits great significance of precise thermal dosage control in HIFU treatment. By combining electrical impedance measurement and HIFU, an electrical impedance tomography (EIT) based temperature monitoring method using surface voltages is proposed to reconstruct the distribution of electrical conductivity inside the focal plane on the basis of the temperature dependent electrical impedance of tissues. In theoretical study, a comprehensive system of EIT measurement during HIFU therapy is established. With the consideration of acoustic absorption in viscous tissues, three-dimensional Helmholtz equation for HIFU is simplified into two-dimensional axisymmetric cylindrical coordinates, and the characteristics of temperature rising in the focal region are derived using Pennes bio-heat transfer equation. Then, by introducing the temperature-conductivity relation into tissues, the processing methods for electrical field and surface voltage in the focal region are constructed with constant current injection from two symmetrical electrodes. In simulation study, by applying the experimental parameters of the focused transducer, the distributions of acoustic pressure and temperature are simulated at a fixed acoustic power, and then the corresponding distributions of conductivity in the focal plane are achieved at different treatment times for centric and eccentric focusing. Furthermore, with the simulations of current density and electrical potential generated by the rotating current injection from 16 pairs of symmetrical electrodes, 32×32 voltages are detected by the 32 surface electrodes placed around the focal plane of the model. In conductivity image reconstruction, the modified Newton-Raphson (MNR) algorithm is employed to conduct iterative calculation. It shows that with the increase of HIFU treatment time, the electrical conductivity in the focal region increases accordingly and reaches a maximum value in the center due to the highest acoustic pressure and the most energy accumulation. It is proved that not only the position of the focal center, but also the conductivity distribution inside the focal region can be restored accurately by the proposed EIT based reconstruction algorithm. The favorable results demonstrate the feasibility of temperature monitoring during HIFU therapy, and also provide a new method of evaluating the noninvasive efficacy and controlling the dose based on electrical impedance measurements.
Pressure-induced metallization transition in Mg2Ge
Authors: Wang Jun-Long  , Zhang Lin-Ji  , Liu Qi-Jun  , Chen Yuan-Zheng  , Shen Ru  , He Zhu  , Tang Bin  , Liu Xiu-Ru  ,   School of Physical Science and Technology, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu 610031, China;,   School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, China
Published: December 2020

Mg2Ge with anti-fluorite structure at ambient pressure is characterized as a narrow band semiconductor and increasing pressure results in a decrease of the gap. In this work, the band structure of anti-fluorite Mg2Ge under high pressure is studied by first principles calculations, which suggests that Mg2Ge becomes metallic at 7.5 GPa as a result of band gap closure. The enthalpy difference between anti-fluorite phase and anti-cotunnite phase under high pressure is calculated by the first-principles plane-wave method within the pseudopotential and generalized gradient approximation. The results show that Mg2Ge undergoes a phase transition from the anti-fluorite structure to anti-cotunnite structure at 11.0 GPa. Then we investigate experimentally the pressure-induced metallization of Mg2Ge by electric resistance measurement in strip anvil cell and Raman spectroscopy by diamond anvil cell. The pressure distribution is homogeneous along the central line of the strip anvil and the pressure is changed ccontinuously by using a hydraulically driven two-anvil press. Raman scattering experiment is performed at pressure up to 21.1 GPa on a back scattered Raman spectrometer. The wavelength of excitation laser is 532 nm. No pressure-transmitting is used and pressure is determined by the shift of the ruby luminescence line. It is found that neither a discontinuous change of electrical resistance at 8.7 GPa nor Raman vibration modes of Mg2Ge appear above 9.8 GPa. The disappearance of the Raman vibration mode is ascribed to the metallization since the the free carrier concentration rises after metallization has prevented the laser light from penetrating into the sample. We compare these results with those of resistivity measurements in diamond anvil cell. Li et al.[2015 Appl. Phys. Lett. 107 142103] reported that Mg2Ge becomes metallic phase at 7.4 GPa and is transformed into metallic anti-cotunnite phase at around 9.5 GPa. We speculate that the discontinuous change in electric resistance at 8.7 GPa is ascribed to the gap closure of anti-fluorite phase and Mg2Ge may transform into the anti-cotunnite phase above 9.8 GPa.
Progress of nanostructured metallic glasses
Authors: Feng Tao  , Horst Hahn  , Herbert Gleiter  ,   Herbert Gleiter Institute of Nanoscience, School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;,   Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe 76021, Germany
Published: December 2020

Today's technologies are primarily based on crystalline materials (metals, semiconductors, etc.), for their properties can be controlled by changing their chemical and/or defect microstructures. This is not possible in today's glasses. The new features of nanostructured glasses consisting of nanometer-sized glassy regions connected by interfaces are that their properties may be controlled by changing their chemical and/or defect microstructures, and that their interfaces each have a new kind of non-crystalline structure. In this paper we mainly discuss the research progress of nanostructured metallic glasses, including their preparation methods, structure characteristics and new properties. By utilizing these new features, an era of new technologies based on non-crystalline materials (a “glass age”) can be opened up.
Applications of colloids in glass researches
Authors: Chen Ke  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

As a soft matter material, the unique properties of colloidal glasses make it a particularly useful platform to study fundamental physics of amorphous solids. In the article, we briefly review the connections between colloidal glasses and molecular amorphous materials by surveying applications of colloids in different aspects of glass researches. And we also give future directions of colloidal glasses researches in the end.
High-order detached-eddy simulation method based on a Reynolds-stress background model
Authors: Wang Sheng-Ye  , Wang Guang-Xue  , Dong Yi-Dao  , Deng Xiao-Gang  ,   College of Aerospace Science and Engineering, National University of Defense Technology, Changsha 410073, China;,   School of Physics, Sun Yat-sen University, Guangzhou 510275, China
Published: December 2020

Referring to the construction of shear stress transport-improved delayed detached-eddy simulation (SST-IDDES) method, a variant of IDDES method based on the Speziale-Sarkar-Gatski/Launder-Reece-Rodi (SSG/LRR)-ω Reynolds-stress model (RSM) as Reynolds-averaged Navier-Stokes (RANS) background model, is proposed. Through combining high-order weighted compact nonlinear scheme (WCNS), the SSG/LRR-IDDES method is applied to three aeronautic cases and compared with traditional methods:SST-unsteady Reynolds-averaged Navier-Stokes (URANS), SSG/LRR-URANS, and SST-IDDES. To verify the SSG/LRR-IDDES method in simulating airfoil stalled flow, NACA0012 airfoil is adopted separately at attack angles of 17°, 45° and 60°. At the attack angle of 17°, SST-URANS, SSG/LRR-URANS, and SST-IDDES methods each predict a higher lift coefficient than the experimental data, while the SSG/LRR-IDDES method obtains a better lift coefficient result and a higher fidelity vortical flow structure. It indicates that the RSM can improve the prediction of RANS-mode for pressure-induced separations on airfoil surfaces in detached-eddy simulation. At the attack angles of 45° and 60°, the SSG/LRR-IDDES method captures the massively separated flow with three-dimensional vortical structures and obtains a good result, which is the same as that from the traditional SST-IDDES method. To indicate the improvement of the SSG/LRR-IDDES method in simulating airfoil trailing edge separation, NACA4412 airfoil is adopted. At the attack angle of 12° (maximum lift), the trailing edge separation is mainly induced by pressure gradient. The SSG/LRR-IDDES method can predict the separation process reasonably and obtains a good lift coefficient and location of separation compared with experimental results. However, none of other methods can predict trailing edge separation. It confirms that when RSM is adopted as RANS background model in detached-eddy simulation, the ability to predict pressure-induced separation on airfoil surface is improved. For further verifying the SSG/LRR-IDDES method for simulating three-dimensional separated flow, blunt-edge deltawing at the attack angle of 24.6° is adopted. At this attack angle, the primary vortex will break, which is difficult to predict by using the SST-URANS method. For the SSG/LRR-URANS method, it predicts the vortex breakdown successfully, but the breakdown process does not show any significant unsteady characteristic. The SST-IDDES and the SSG/LRR-IDDES methods both predict a significant unsteady vortex breakdown. But in terms of the accuracy of surface pressure and the fidelity of unsteady flow, the result obtained by the SSG/LRR-IDDES method is better than by the SST-IDDES method.
Characteristics of radio-frequency emission from nanosecond laser-induced breakdown plasma of air
Authors: Dai Yu-Jia  , Song Xiao-Wei  , Gao Xun  , Wang Xing-Sheng  , Lin Jing-Quan  ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

The radio-frequency (RF) emissions in a range from 30 MHz to 800 MHz from the plasma, which is produced by the nanosecond laser (532 nm, 8 ns) induced breakdown of atmospheric air, are presented. A spectrum analyzer which can scan over a spectral range of 9 kHz-26.5 GHz is used to record the RF-range radiation intensities of the emission from the plasma. RF electromagnetic radiations from the laser induced breakdown of atmospheric air are obtained for different input laser energies. A half-wave plate and a Glan prism are used to vary the input laser energy. Experimental results show that the intensities of RF radiation in a range of 30-200 MHz increase with the increase of laser energy, but the intensities of RF radiation in a 360-600 MHz frequency range decrease. To study the effect of input laser polarization on the RF radiation, we adopt the input lasers with vertical and horizontal polarization respectively. When the polarizations of the input laser and the antenna are the same, the RF radiation intensity is relatively high, and the frequency lines are relatively abundant. The changing relationship between the total power of RF radiation and the energy of the input laser is calculated and analyzed. It is observed that the total power of RF radiation first increases and then decreases with the increase of input laser energy. The influences of the plasma electron density on the plasma frequency and the plasma attenuation coefficient are investigated to explain the relationship between the total power of the RF radiation and the laser energy. The RF radiation is caused by the following processes. The generated electrons and ions are accelerated away from the core by their thermal pressures. This leads to charge separation and forming the electric dipole moments. These oscillating electric dipoles radiate electromagnetic waves in the RF range. Furthermore, the interactions of electrons with atomic and molecular clusters within the plasma play a major role in RF radiation, and the low frequency electromagnetic radiation takes place from the plasma that is far from fully ionized state. Further study of the characteristics of RF electromagnetic radiation is of great significance for understanding the physical mechanism of the interaction between laser and matter.
Electronegativity of capacitively coupled Ar+O2 plasma excited at very high frequency
Authors: Yang Yu  , Tang Cheng-Shuang  , Zhao Yi-Fan  , Yu Yi-Qing  , Xin Yu  ,   College of Physics, Optoelectronics and Energy, Soochow University, Suzhou 215006, China
Published: December 2020

By using pulsed laser induced detachment technique assisted with a Langmuir probe, the electronegative characteristics of the capacitively coupled Ar plasma doped with 5% O2 are studied in this paper. We first focus on the electrical signal of the probe after laser pulse has induced negative ion detachment, and then analyze characteristics of the probe signal with the probe bias below or above the plasma space potential. When the bias is set to be lower than the plasma potential, the probe signal usually shows a downward surge signal. As the bias is higher than the plasma potential, the main characteristics of the signal takes on an upward wide wave packet. The evolution behavior of the probe signal with bias from the downward surge valley to the upward wide wave packet might be due to the potential difference between the plasma space potential and the probe bias voltage. Furthermore, it shows that the position of the upward peak appears later than that of the downward surge valley, which may be related to the changing of the rate of the electron diffusion flux and the electric field drift flux. According to the dependence of probe collection signal on bias, the electronegativity describing the Ar+O2 plasma electronegative property is defined as saturation ratio of electron current after pulsed laser radiation to that of collection probe at a potential above plasma spatial potential. Plasma electronegativity is diagnosed with discharge pressure, radio-frequency (RF) input power and axial position. The experimental results show that the electronegativity of plasma decreases with input RF power increasing. As the gas pressure is kept at 12.0 Pa, the plasma electronegativity decreases from 5.05 to 0.98 with RF input power increasing from 50 to 300 W. It also shows an increasing trend of electronegativity with plasma discharge pressure increasing. Due to asymmetrical distribution of electrodes, the plasma electronegativity also takes on asymmetric one with respect to the axial position. In our experiments, the electronegativity near the power electrode shows about 1-4 times higher than that near the ground electrode, the lowest point of the plasma electronegativity seems to be located in the center of the plasma discharge. This may be related to the dynamics of the secondary electrons emitted from electrode and the competition processes between negative ion production in collisional dissociation of oxygen molecules and the losses of high energy electron and negative ion in collisional detachment of negative ion with oxygen molecule.
Study of Bloom resolving G-quadruplex process by using high resolution magnetic tweezer with illumination of total internal reflection
Authors: Zhao Zhen-Ye  , Xu Chun-Hua  , Li Jing-Hua  , Huang Xing-Yuan  , Ma Jian-Bing  , Lu Ying  ,   Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China;,   Material and Energy School, Guangdong University of Technology, Guangzhou 510006, China
Published: December 2020

G-quadruplex (G4) is a DNA structure which commonly exists in human genome, and it is considered as an important structure in DNA metabolism such as replication, transcription and homologous recombination. The G-quadruplex helicases have been widely investigated these years. Of them, the Bloom (BLM) helicase is most thoroughly studied. However, there are some basic problems that are still unclear. Most of previous studies of G4 are performed by single molecule fluorescence resonance energy transfer technique. The G4 is in a free state in these experiments, which is different from the physiological environment in cells. The traditional magnetic tweezers have a limitation of spatial resolution in a low force circumstance. Thus here we use high resolution magnetic tweezer under the illumination of total internal reflection fluorescence to study the process of BLM resolving G4. Our modification of magnetic tweezer is to separate the measurements of force and distance of magnetic tweezer in order to improve the spatial resolution, which allows us to observe the unfolding process of G4. With a 2-3 pN force we find that the process of BLM unfolding G4 in low ATP concentration is stepwise, and the G4 is mainly in the state between G-quadruplex and G-triplex. We also find that the BLM could interact with G4 for a long time. Our apparatus is also able to obtain the long time observation results compared with the single molecule fluorescence technique. So we perform experiments with a nearly saturated ATP concentration. We find that the BLM has two ways to maintain G4 dissolution in this condition. The BLM could unfold the G4 repetitively in a long period and it could also keep the G4 in unfolding state for a long time after it has opened the G4. Finally, we also perform single molecule fluorescence resonance energy transfer experiment in the same condition, and we find that the 2-3 pN force in magnetic tweezers has a rare influence on the process of BLM interacting with G4. The results of single molecule fluorescence resonance energy transfer experiments are corresponding to the results of magnetic tweezer in the same conditions. All of our experimental results show that ATP dependent BLM has a high affinity with G4 and BLM has a different way to resolve G4 in high ATP concentration. These results could provide new ideas of the mechanism of BLM resolving G4. Our modified magnetic tweezer shows its capacity in G4 single molecule study, and it could be a useful tool in the future single molecule studies.
Phase transition properties for the spatial public goods game with self-questioning mechanism
Authors: Yang Bo  , Fan Min  , Liu Wen-Qi  , Chen Xiao-Song  ,   Data Science Research Center, Kunming University of Science and Technology, Kunming 650500, China;,   Faculty of Science, Kunming University of Science and Technology, Kunming 650500, China;,   Institute of Theoretical Physics, Key Laboratory of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China;,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China}
Published: December 2020

The spatial public goods game is one of the most popular models for studying the emergence and maintenance of cooperation among selfish individuals. A public goods game with costly punishment and self-questioning updating mechanism is studied in this paper. The theoretical analysis and Monte Carlo simulation are involved to analyze this model. This game model can be transformed into Ising model with an external field by theoretical analysis. When the costly punishment exists, the effective Hamiltonian includes the nearest-, the next-nearest-and the third-nearest-neighbor interactions and non-zero external field. The interactions are only determined by costly punishment. The sign of the interaction is always greater than zero, so it has the properties of ferromagnetic Ising. The external field is determined by the factor r of the public goods game, the fine F on each defector within the group, and the relevant punishment cost C. The Monte Carlo simulation results are consistent with the theoretical analysis results. In addition, the phase transitions and critical behaviors of the public goods game are also studied using the finite size scaling theory. The results show that the discontinuous phase transition has the same finite size effects as the two-dimensional Ising model, but the continuous phase transitions is inconsistent with Ising model.
Molecular dynamics simulation of fluid flow and heat transfer in an asymmetric nanochannel
Authors: Wang Sheng  , Xu Jin-Liang  , Zhang Long-Yan  ,   Beijing Key Laboratory of Multiphase Flow and Heat Transfer for Low Grade Energy, North China Electric Power University, Beijing 102206, China
Published: December 2020

Fluid flow and heat transfer in a nanochannel may depart from the traditional behavior due to the scale effect, and the velocity slip and temperature jump at the fluid-solid interface must be taken into account. A lot of papers about fluid flows in nanochannels with the same wettability at two surfaces have been published. It is necessary to investigate fluid flow and heat transfer in nanochannels with the asymmetric wettability by the molecular dynamics method. The fluid velocity and temperature distributions, interfacial velocity slip and temperature jump in a rough nanochannel are evaluated. The effects of asymmetric wettability on the velocity slip, temperature jump and internal fluid heat transfer are analyzed. The results indicate that the velocity of the fluid flow under an external force in a nanochannel in a bulk region is of a parabolic distribution, but the parabolic distribution is not centrosymmetric because of the centrosymmetric density profile. The difference in density distribution can affect the fluid flow. Viscous dissipation due to shear flow will increase the fluid temperature. The range that is affected by the interaction between solid and liquid is small. So the wettability of the cold wall hardly affects the velocity of the fluid near the hot wall, and the slip velocity is almost constant. At this time, the negative slip will take place at the fluid-solid interface near the hot wall. But the velocity of the fluid near the cold wall comes up with the increasing hydrophobicity of the cold wall, and the slip velocity increases. The temperature jump on both sides of interface increases with the increasing hydrophobicity of the cold wall, but the degree of temperature jump at a liquid-cold solid interface is higher than that at a liquid-hot solid interface. Then the fluid temperature near the cold wall gradually exceeds the fluid temperature near the hot wall. The internal heat flow of the fluid will be reversed. The inverted temperature profile of the fluid will appear. The inverted temperature profile becomes more obvious when the degree of asymmetric wettability increases.
Effect of lithium-free flux B2O3 on the ion conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte
Authors: Shi Mao-Lei  , Liu Lei  , Tian Fang-Hui  , Wang Peng-Fei  , Li Jia-Jun  , Ma Lei  ,   College of Electronic and Information Engineering, Hebei University, Baoding 071002, China
Published: December 2020

Using solid electrolyte instead of liquid electrolyte is regarded as an important measure to solve the safety problems of lithium ion batteries, and has attracted wide attention of researchers. Among many solid electrolytes, Li1.3Al0.3Ti1.7(PO4)3 (LATP) is considered to be one of the most commercially available solid electrolytes for its high ionic conductivity. However, as a replacement substitute of for liquid electrolyte, the LATP solid electrolyte has an ionic transport property of LATP solid electrolyte that still needs to be improved. In this paper, LATP solid electrolyte used for lithium ion batteries is successfully prepared by solid reaction process, and the influences of different sintering temperatures and addition of flux B2O3 and or LiBO2 on the ionic conductivity of LATP solid electrolyte are discussed. The structures, element content, morphologies, and ionic conductivities of the sintered samples are investigated at room temperature by X-ray diffraction, energy dispersive spectrometer, electrochemical impedance spectrum and scanning electron microscopy. It is found that pure phase LATP ceramic solid electrolyte can be obtained at the sintering temperatures between 800 and 1000℃. And the ionic conductivities of the samples first increase first and then decrease with the increasing sintering temperatures increasing. The sample with a highest ionic conductivity of 4.1610-4 S/cm can be obtained at the a sintering temperature of 900℃. Further research shows that the ionic conductivities of the sintered samples can also be effectively improved by using B2O3 instead of LiBO2 as flux. Moreover, the ionic conductivities of the samples first increase first and then decrease with the increasing amount of the flux increasing. And the highest ionic conductivity of 1.6110-3 S/cm is obtained with the sampleby adding B2O3 with a mass fraction of 2% into the sample. The results indicate that the elevating of sintering temperature and the adding of flux B2O3 and or LiBO2 can both decreasing reducing the grain boundary impedances of the LATP samples, so as to thereby improve improving their ionic conductivities. However, when the sintering temperature is higher than 900℃ or the amount of flux B2O3 and or LiBO2 exceeds the mass percentage of 2%, the ionic conductivities of the LATP samples will drop. In addition, the ionic conductivities of the samples used using B2O3 as flux are higher than that those of the samples used LiBO2 as flux. These results also indicate that the increases of ionic conductivities of LATP samples with flux is are closely related to their densities density and compactness, and is irrespective of no matter whether or not the flux contains lithium ion.
Theory and verification of a microwave transmission method of measuring sheet resistance of metallic thin film
Authors: Wang Lu  , Ye Ming  , Zhao Xiao-Long  , He Yong-Ning  ,   School of Microelectronics, Xi'an Jiaotong University, Xi'an 710049, China
Published: December 2020

Metallic thin films deposited on non-conductive substrates are widely used in areas like microwave absorbers, photovoltaic, packaging, electromagnetic shielding, and integrated circuits. From scientific and engineering point of view, measuring sheet resistance of metallic thin films is important. In this study, we develop a theory of evaluating sheet resistance by using transmission coefficient of a rectangular waveguide (RG) and verify it with sputtered silver films of various thickness values. According to the field distribution of RG working under the fundamental mode and corresponding electromagnetic boundary conditions, we first analytically derive the transmission coefficient of an RG with the metallic thin film exactly occupying its cross section. Comparing existing theory, we take the effect of the non-conductive substrate supporting the metallic thin film into consideration. According to this derivation, we establish a method to calculate the sheet resistance of metallic thin films from the amplitude of RG transmission coefficient. To verify our derivation, we also conduct full-wave simulations of a standard WR-75 RG used for characterizing the metallic thin film at 13.65 GHz. Both the analytical derivations and full-wave simulations show that the amplitude of the transmission coefficient depends on the logarithm of the sheet resistance in a linear manner. It is also demonstrated that the substrate effect may not be ignored. To facilitate measurement, we propose a sandwiched structure by placing the metallic thin film between two waveguide flanges. This modification removes the stringent requirements for sample preparation. Simulations of this sandwiched structure indicate that it is possible to realize non-contact measurement if the air gap between metallic thin film and waveguide flange is below 0.1 mm. Through full-wave simulations, we also show the feasibility of metallic thin film evaluation by using such transmission lines as dielectric filled RG, circular waveguide, and coaxial line. Finally, we prepare various silver films with sheet resistances ranging from 20 m/square to 1 /square (measured by the four-point probe technique) on the top of high resistance silicon and glass substrates, respectively. We measure the amplitudes of transmission coefficient of these metal films in RG by using vector network analyzer. The obtained experimental results are well consistent with the derivation and simulation results, thereby verifying the proposed method. It is recommended that the proposed method is suitable for conductive films with sheet resistances ranging from 0.05 /square to 0.5 /square. The results of this study are of potential value for characterizing the conductive thin films in micro/nano fabrication and relevant areas.
Autler-Townes splitting of ultracold cesium Rydberg atoms
Authors: Xue Yong-Mei  , Hao Li-Ping  , Jiao Yue-Chun  , Han Xiao-Xuan  , Bai Su-Ying  ,   Zhao Jian-Ming  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China;,   Extreme Optical Collaborative Innovation Center of Shanxi University, Taiyuan 030006, China
Published: December 2020

Autler-Townes (A-T) splitting, known as an AC Stark effect, shows a change of an absorption/emission spectral line of a probe beam when an oscillating field is tuned in resonance with the atomic or molecular transition. The A-T splitting is observed in different three-level atoms and widely investigated in a vapor cell and in a magneto-optical trap (MOT). The A-T splitting plays an important role in the atom-based microwave electric-field measurements where a cascade three-level system involving Rydberg state is adopted.
In this work, an A-T splitting is observed in an ultracold cesium Rydberg gas, which is cooled down to about 100 pK and center density is about 1010 cm-3 in a conventional MOT by using the laser cooling technology. We present the A-T spectrum in a ladder three-level atomic system involving a 34D5/2 Rydberg state. The cesium ground state (6S1/2), excited state (6P3/2) and Rydberg state (34D5/2) constitute a Rydberg three-level system. A coupling laser, locked to the Rydberg transition by using a Rydberg electromagnetically induced transparency signal that is obtained from a cesium room-temperature vapor cell, couples 6P3/2 (F'=5) 34D5/2 Rydberg transition. A weak probe laser, stabilized to a ground-state transition by using a polarization spectroscopy, is swept, covering the transition 6S1/2 (F=4) 6P3/2 (F'=5) with a double-passed acousto-optic modulator. The probe and coupling lasers are counter-propagated through the MOT center. The power of probe light is 200 pW, corresponding Rabi frequency p=21.05 MHz. During the experiment, 50 s after turning off the trapping laser, both the coupling and probe beams are switched on and last 100 s. The A-T spectrum as a function of the probe detuning is detected with a single-photon counter module detector. We use Gaussian multiple peak fitting to obtain the positions of the A-T peaks and the A-T splitting. The measured A-T splitting is proportional to the Rabi frequency of the coupling light. We numerically solve the density matrix equations to obtain the A-T spectrum, and the calculations reproduce A-T spectra well. The measured A-T splitting shows good agreement with the theoretical calculation for Rabi frequency of the coupling light c29 MHz. The A-T splitting is less than the calculation for the case of c29 MHz, the deviation is mainly attributed to the increased dephasing rate induced by the strong interaction between Rydberg atoms, whose number increases with the coupling laser Rabi frequency. In this work, the adopted method for the cascade three-level system involving Rydberg state is also suitable for -and V-type cases.
Research progress of direct synthesis of graphene on dielectric layer
Authors: Yang Hui-Hui  , Gao Feng  , Dai Ming-Jin  , Hu Ping-An  ,   School of Materials and Science Engineering, Harbin Institute of Technology, Harbin 150080, China;,   Key Lab of Microsystem and Microstructure(Ministry of Education), Harbin Institute of Technology, Harbin 150080, China
Published: December 2020

As one of the most appealing materials, graphene possesses remarkable electric, thermal, photoelectric and mechanic characteristics, which make it extremely valuable both for fundamental researches and practical applications. Nowadays the synthesis of graphene is commonly achieved by growing on metal substrate via chemical vapor deposition. For the integration in micro-electric device, the as-grown graphene needs to be transferred onto target dielectric layer. However, wrinkles, cracks, damages, and chemical residues from the metal substrate and the auxiliary polymer are inevitably introduced to graphene during such a transfer process, which are greatly detrimental to the performances of the graphene devices. Therefore, the direct synthesis of graphene on dielectric layer is of great importance. Many researches about this subject have been carried out in the last few years. While only few papers have systematically reviewed the direct growth of graphene on dielectric layer. For the in-depth understanding and further research of it, a detailed overview is required. In this paper, we summarize the recent research progress of the direct syntheses of graphene on dielectric layers, and expatiate upon different growth methods, including metal assisted growth, plasma enhanced growth, thermodynamics versus kinetics tailored growth, et al. Then differences in property between graphenes grown on various dielectric and insulating layers which serve as growth substrates in the direct growing process are discussed, such as SiO2/Si, Al2O3, SrTiO3, h-BN, SiC, Si3N4 and glass. Some kinds of mechanisms for graphene to be directly grown on dielectric layers have been proposed in different reports. Here in this paper, we review the possible growth mechanisms and divide them into van der Waals epitaxial growth and catalytic growth by SiC nanoparticles or oxygen atoms. Detailed data including Raman signals, sheet resistances, transmittances, carrier motilities are listed for the direct comparison of the quality among the graphenes grown on dielectric layers. The research focus and major problems existing in this field are presented in the last part of this paper. We also prospect the possible developing trend in the direct syntheses of high quality graphenes on dielectric layers in the future.