bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of interaction between single-layer graphene on copper substrate and groove
Authors: Zhang Zhong-Qiang  , Jia Yu-Xia  , Guo Xin-Feng  , Ge Dao-Han  , Cheng Guang-Gui  , Ding Jian-Ning  ,   Micro/Nano Science and Technology Center, Jiangsu University, Zhenjiang 212013, China;,   Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164, China;,   State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
Published: December 2020

The two-dimensional material graphene is usually required to be transferred on the target substrate for some special applications, thus it is important to understand the adsorption properties in the graphene transferring and stripping processes. In this paper, the adsorption properties of a single-layered graphene on the grooved copper substrate are investigated using molecular dynamics simulations. The influence of geometric characteristic size of the groove on the adsorption force of the graphene deriving from the substrate is explored. For the fixed boundary conditions of the graphene, the adsorption force increases up to maximum and then decreases with reducing the distance between the graphene and substrate in the adsorbing process. The maximum adsorption force increases with groove depth increasing, with the groove width kept constant. Nevertheless, as the groove depth increases continuously, the adsorption force decreases greatly until the graphene cannot be adsorbed into the groove. In the graphene stripping process, the critical force that can strip the graphene completely from the substrate increases first and then decreases with the increase of the groove depth, which is also dependent on the steady adsorbing configuration of the system before stripping. With the groove depth kept constant, the magnitude of the adsorption force between the graphene and substrate is determined by the steady adsorbing configuration of the graphene in the groove region. The adsorption force versus the distance between the graphene and the grooved substrate can be divided into two groups according to whether the graphene can be adsorbed into the groove. In both adsorbing and stripping processes, the adsorption force for the graphene adsorbed into the groove is obviously larger than that for the graphene covered on the groove. Moreover, the influence of the boundary condition of the graphene on the adsorption properties in the groove region on the substrate is considered preliminarily. It indicates that the tensile plane stress within the graphene sheet induced by the fixed boundaries can hinder the graphene from being adsorbed into the groove. The findings may be helpful for the graphene-based fabrication of nano-apparatus and functionalized surface modification.
Theoretical study on the isotope shift factors for the 3s2 1S0 → 3s3p 3,1P1o transitions in Al+ ion
Authors: Zhang Ting-Xian  , Li Ji-Guang  , Liu Jian-Peng  ,   Institute of Applied Physics and Computational Mathematics, Beijing 100088, China;,   College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070, China;,   College of Liberal Arts and Science, National University of Defense Technology, Changsha 410073, China
Published: December 2020

The accurate calculation of the isotope shift factors is helpful in extracting the mean-square charge radius of the nucleus,which is an important nuclear parameter to investigate the nuclear properties and improve nuclear structure theories.However,for atomic systems with many electrons the uncertainties of the calculated isotope shift factors are difficult to evaluate accurately,since high sensitivity of the isotope shift factor to the electron correlation and limitation of the computational resource.Based on the calculations of the isotope shift factors of the 3s2 1S0→ 3s3p 3,1P1o transitions in Al+by using the multi-configuration Dirac-Hartree-Fock method,the convergences of these physical quantities with the expansion of the configuration space are investigated in detail.In our calculation,the electron correlations are divided into the first-order correlation and the higher-order correlations according to the perturbation theory,and captured by using the active space approach.The effect of the first-order correlation are considered by including configuration state functions (CSFs) that are generated by the single and double substitutions from the occupied orbitals in the single reference configuration set.After the first-order correlation effect are taken into account adequately,the reference configuration sets are augumented by adding the dominant CSFs from the first-order correlation configuration space,in order to consider the higher-order correlation effect.We find that the convergence of the mass shift factors (including the normal shift factor and the specific mass shift factor) is linearly correlated with the convergence of the level energies in our computational model.For the transitions,the linear correlation of the convergence between the mass shift factors and the transition energies is not so good as that for the levels involved in the transitions due to the limited computational resource,but it can be improved with the expansion by including more higher-order correlation related 2s and 2p core electrons.Furthermore,we made use of the linear correlation to estimate the uncertainties of our isotope shift factors, and obtain the reasonable value of error.The authors hope that the linear correlation between the convergence of the mass shift factors and the level or transition energies can be proved and explained in more atomic systems,and the linear correlation can be used to evaluate accurately the uncertainties of the mass shift factors for the atoms and ions with many electrons in the near future.
Nonlinear ultrasonic evaluation of damage to bonding interface under cyclic temperature fatigue
Authors: Yuan Bo  , Shui Guo-Shuang  , Wang Yue-Sheng  ,   Department of Mechanics, Beijing Jiaotong University, Beijing 100044, China
Published: December 2020

Adhesively bonded structures possess various industrial applications, such as safety-critical structures in the aerospace and automotive industries. With the increasing using of adhesive joints, corresponding methods of evaluating and testing the structural integrity and quality of bonded joints have been widely investigated and developed for the structural health monitoring. Studies show that the damage and degradation of material are closely related to the nonlinearity of ultrasonic waves propagating within the material. In this paper, for the evaluating of the damage to bonding interface under cyclic temperature fatigue, acoustic nonlinear parameters (ANPs) of specimens made of aluminum alloy 6061 and modified acrylate adhesive are measured experimentally by using the nonlinear ultrasonic technique; and thus the variations of the ANPs with the fatigue time under high and low cyclic temperature are obtained for the bonded specimens. The study shows that the ANP, which serves as an indicator of material properties, remains nearly unchanged in the initial stage of high temperature cyclic fatigue test, and the ANP obviously increases with temperature cyclic time increasing. For low temperature cyclic fatigue test, the ANP increases rapidly with the increase of temperature cyclic time in the initial stage, and its value growth slows down in the later stage. Further discussion shows that the increase of third order elastic constant is the main reason for the change of ANP for high temperature cyclic fatigue, and that the change of the tensile stiffness of the bonding interface is the main source for the change of the ANP for low temperature cyclic fatigue. It is shown that the ANP based on the theoretical model increases consistently with the experimentally measured values. The present research is expected to provide a promising way of characterizing and monitoring the damage to bonding interface under cyclic temperature fatigue.
Anisotropic polarization beam splitter based on metal slit array
Authors: Ma Jing  , Liu Dong-Dong  , Wang Ji-Cheng  , Feng Yan  ,   Department of Opto-electronical Information Science and Engineering, School of Science, Jiangnan University, Wuxi 214122, China;,   School of Mathematics and Physics Science, Xuzhou University of Technology, Xuzhou 221018, China;,   State Key Laboratory of Millimeter Waves, Southeast University, Nanjing 210096, China
Published: December 2020

Polarizing beam splitter (PBS) can separate the propagating directions of two incident orthogonally polarized light beams. However, conventional PBS and multi-layered metamaterial structures are complicated and neither of them can meet the requirements for broadband characteristics due to their resonant characters. In this paper, an anisotropic beam splitter based on metal slit array of the metal-dielectric structure is proposed in order to simplify the structure and improve the beam splitting efficiency. Because of the transverse momentum generated by the inhomogeneous interface, the transverse magnetic (TM) wave is negatively reflected from the surface of the gold film after it has entered into the slit with the waveguide mode of the plasma. When the free electrons on the metal surface oscillate, the transverse electric (TE) wave parallel to the grating direction can cause electrons to oscillate along the grating direction, so that the TE light cannot enter into the slit, resulting in specular reflection. The finite element method is used to study the effects of TM and TE polarized light such as negative reflection (NR) and specular reflection (SR). The results show that when the incident angle of the polarized light is set to be in a range from 20 to 70, the incident TM light has a strong NR of about 0.9, but the TE light is weakly reflected and decreases sharply with the increase of the wavelength. The ideal NR points of the beam splitter and the perfect symmetrical response of the reflection surface are calculated, and the ideal NR point satisfies P=/(2sin 0). When the incident light angle changes, the variations of the wavelength of the negative and zero order reflection peak are different from those of TM and TE wave, which is more conducive to the tuning of the interaction between light and grating structure. The NR and SR spectral reflectance of different polarized light beams are calculated by rigorous coupled-wave analysis, and the extinction ratios in the two cases are both 106. In addition, those designs of plasmonic splitters will pave the way for the practical applications of plasmonic devices in data storages and optical holography.
Enhanced performance of inverted polymer solar cell based on Al2O3/MoO3 as composite anode buffer layer
Authors: Li Qi  , Zhang Yong  ,   Laboratory of Nanophotonic Functional Materials and Devices, Institute of Optoelectronic Materials and Technology, South China Normal University, Guangzhou 510631, China;,   Guangdong Engineering Technology Research Center of Low Carbon and Advanced Energy Materials, Guangzhou 510631, China
Published: December 2020

Inverted polymer solar cell with P3HT:PC61BM as an active layer is fabricated based on Al2O3/MoO3 composite anode buffer layer. Effects of Al2O3/MoO3 composite anode buffer layers with the Al2O3 precursor solutions of different concentrations on the device performance are investigated. It can be found that the Al2O3/MoO3 composite anode buffer layer can effectively enhance the photovoltaic performance and device stability of inverted polymer solar cell. The open-circuit voltage (Voc), short-circuit current (Jsc), filling factor (FF), and photoelectric conversion efficiency (PCE) are 0.64 V, 8.62 mA/cm2, 63.86%, and 3.85% respectively for the control device with MoO3 single buffer layer. In addition, with the increase of the concentration of Al2O3 precursor solution, the photovoltaic performance of the inverted polymer solar cell with Al2O3/MoO3 composite anode buffer layer is gradually improved. For the Al2O3 precursor solution of 0.15%, the photovoltaic performance of the device reaches an optimal value, and the corresponding Voc, Jsc, FF, and PCE are 0.65 V, 11.04 mA/cm2, 64.46%, and 4.64%, respectively. The Jsc and PCE significantly increase by 28% and 20%, respectively, compared with those of the control device with MoO3 single buffer layer. Moreover, after 80 days of measuring the device lifetime, the PCE of the device with the composite anode buffer layer remains at 76% of the original value while the PCE with the single buffer layer is reduced below 50%. The improvement of the device performance should be attributed to the PC61BM receptor near the anode dissolved and washed by isopropyl alcohol solvent from the Al2O3 precursor solution. At the same time, a large number of pits on the surface of the active layer are filled with Al2O3 to make it more smoothly contact the composite anode buffer layer. Therefore, the contact resistance between the active layer and the anode decreases, which enhances hole collection performance of the anode. Simultaneously, the Al2O3 layer can passivate the active layer of the device, thus improving the photovoltaic performance and device stability of inverted polymer solar cell.
First-principles study of electronic structures and optical properties of Mn and Cu doped potassium hexatitanate (K2Ti6O13)
Authors: Qi Yu-Min  , Chen Heng-Li  , Jin Peng  , Lu Hong-Yan  , Cui Chun-Xiang  ,   School of Material Science and Engineering, Hebei University of Technology, Tianjin 300130, China;,   School of Physics and Electronic Information, Huaibei Normal University, Huaibei 235000, China
Published: December 2020

Potassium hexatitanate (K2Ti6O13) is a kind of wide band-gap semiconductor material with potential applications in photocatalysis. Unfortunately, it only responds to the short wavelengths of ultraviolet light, which seriously limits the utilization efficiency of solar energy. To extend its response to visible light, a promising strategy is to partly substitute some other transition metals for the Ti element. In this work, the electronic structures and optical properties of Mn-and Cu-doped K2Ti6O13 are systematically investigated by the first-principles calculations with the aid of the CASTEP module in the Materials Studio software package. The PW91 exchange-correlation functional is used with a plane wave basis set up to a 340 eV cutoff. The computational results show that the Mn-and Cu-doped K2Ti6O13 have impurity bands mainly stemming from the mix of Mn or Cu 3d states with Ti 3d states and O 2p states. Compared with the band gap of pristine K2Ti6O13 (2.834 eV), the band gap of Mn-doped one becomes narrow (2.724 eV), and its impurity energy level in the middle of the band gap can be used as a bridge for electronic transitions to facilitate the absorption of visible light. Although the band gap of Cu-doped K2Ti6O13 slightly increases (2.873 eV), it could be greatly narrowed (1.886 eV) when taking into consideration the impurity energy levels closely connected to the valence band. In addition, the impurity energy levels may form a shallow acceptor and suppress the carrier recombination in the Cu-doped K2Ti6O13. As usual, the calculated imaginary part of dielectric function as a function of photon energy shows that the ε2(ω) value is nearly zero for pure K2Ti6O13 when the photon energy is less than 3.5 eV, whereas there are finite values and also some peaks for the Mn-and Cu-doped ones. These peaks may originate from the impurity energy levels, whose occurrence makes the electron excitation occur readily by low photon energy. Thus, the absorption edges in the doped ones can red-shift to the visible-light region with enhancing absorption intensity. Finally, the simulated absorption spectra of the pristine and doped K2Ti6O13 are consistent with their electronic structures, which further confirms the above analysis. All the results show that the Cu-doped K2Ti6O13 exhibits higher visible-light photocatalytic efficiency than the Mn-doped one. The current work demonstrates that the absorption of visible light can be realized by the Mn or Cu doped potassium hexatitanate, with the effect of the latter being better than that of the former. The obtained conclusions are of great significance for understanding and further developing the potential applications of K2Ti6O13 in the field of photocatalysis.
Entropy spectrum and area spectrum of Kerr black hole in gravity's rianbow
Authors: Liu Cheng-Zhou  , Deng Yue-Jun  , Luo Ye-Cheng  ,   Department of Physics, Shaoxing University, Shaoxing 312000, China
Published: December 2020

Black hole spectroscopy is an important content in the quantum properties of black holes. In this paper, we use the adiabatic invariants of black holes to investigate the entropy spectrum and area spectrum of the Kerr black hole in gravity's rainbow. Firstly, by considering the particles passing through the event horizon, the adiabatic invariance action for the modified Kerr black hole is calculated. Here, the Euclidean coordinate and the period of the Euclidean time of a loop about the event horizon are used. Combined the obtained adiabatic invariants with the Bohr-Sommerfen quantization condition, the equally spaced entropy spectra that are the same as the original Beckenstein spectra are derived. The entropy spectrum of the gravity's rainbow is independent of the test particle energy. Next, using the first law of the black hole thermodynamics and the black hole entropy spectrum, the area spectrum of the modified Kerr black hole is studied. Due to the quantum gravity effect of the gravity's rainbow, the obtained area spectrum is different from the original Beckenstein spectrum. The present area spectrum is non-equidistant and dependent on the horizon area of the black hole. With the decrease of black hole area, the area space gradually turns smaller. When the black hole reaches the minimum area on a Planck scale, the area quantum is zero. Thus the black hole area no longer decrease and a remnant of the black hole radiation appears. In the case of a large black hole, the correction of the area spectrum to the equally spaced spectra can be ignored, and the area spectrum of the Kerr black hole in gravity's rainbow can return to the original Beckenstein spectrum. It is also shown that like the entropy spectrum, the area spectrum of the gravity's rainbow does not depend on the energy of the test particles either. In addition, the entropy of the modified Kerr black hole in gravity's rainbow is discussed by using the first law of the black hole thermodynamics. The black hole entropy with quantum correction items as the area reciprocal to the Beckenstein-Hawking entropy is derived and the relation between the quantum correction items and the area is discussed. In addition, the consistency between the entropy correction and the area correction for the modified black hole is analyzed. The current research supports that in different spacetimes including quantum corrected spacetimes, the black hole entropy spectrum has the universality, but the black hole area spectrum is dependent on the area due to the spacetime quantum properties.
Effect of inner diameter of hollow cylindrical permanent magnet on levitation force of single domain GdBCO bulk superconductor
Authors: Ma Jun  , Chen Zhang-Long  , Xian Tao  , Wei Xue-Gang  , Yang Wan-Min  , Chen Sen-Lin  , Li Jia-Wei  ,   College of Physics and Electronic Information Engineering, Qinghai Normal University, Xining 810008, China;,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710062, China
Published: December 2020

The influence of inner diameter of hollow cylindrical permanent magnet on the levitation force of single domain GdBCO bulk superconductor is investigated by measuring the levitation force between the hollow cylindrical permanent magnet and the single domain GdBCO bulk superconductor. The results show that the levitation force is closely related to the inner diameter of the hollow cylindrical permanent magnet when the inner diameter (d) increases from 0 mm to 26 mm (minimum measuring gap distance Z=2 mm), and all the superconducting magnetic levitation force curve shows magnetic hysteresis phenomenon. With the increase of the inner diameter of the hollow cylindrical permanent magnet, the levitation force at a minimum distance decreases gradually from 14.8 N at d=0 mm to -0.1 N at d=26 mm. The levitation force at the minimum gap distance is negative when d ≥ 20 mm. When 0 mm ≤ dd ≥ 5 mm. The larger magnetic field strength of the superconductor can be obtained, and the levitation force can be effectively improved by the scientific and reasonable designing of the permanent magnet structure. The results have certain guiding significance for designing and optimizing the magnetic suspension bearing system, ring track and superconductor.
Molecular dynamics study on permeability of water in graphene-carbon nanotube hybrid structure
Authors: Zhang Zhong-Qiang  , Li Chong  , Liu Han-Lun  , Ge Dao-Han  , Cheng Guang-Gui  , Ding Jian-Ning  ,   Micro/Nano Science & Technology Center, Jiangsu University, Zhenjiang 212013, China;,   Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Changzhou 213164, China;,   State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China
Published: December 2020

In this paper, the classical molecular dynamics method is used to investigate the permeability of pressure-driven water fluid in the hybrid structure of graphene-carbon nanotube (CNT). The results indicate that the permeability of water molecules for the hybrid structure of graphene-CNT is obviously higher than that for the assembled structure of graphene-CNT. The combination between the graphene sheet and CNT in the hybrid structure is found to be a key point to improve the permeability of water molecules. Subsequently, the potential of mean force (PMF) is calculated in order to explain the influences of the combined structure on the permeabilities for the water fluid passing through both the hybrid and assembled graphene-CNT structures. The result shows that the PMF for the water molecules penetrating through the assembled structure is larger than that for the hybrid structure appreciably. It implies that the structure of the combined chemical bonds in the hybrid structure can efficiently improve the permeability of water molecules. As for the water penetrating through the hybrid structured graphene-CNT, the permeability of water increases with water pressure rising, and decreases with the electric field intensity increasing. The water molecules cannot pass through the proposed hybrid structure below a pressure threshold of 100 MPa. The permeability of water in the hybrid structure decreases with the increasing charge quantity on CNT below a threshold of 0.8e. The PMF for water penetrating through the hybrid structure decreases with charge quantity decreasing. The results suggest that the water permeability can be controlled by regulating the water pressure and the electric field intensity. Furthermore, the influences of the temperature and the axis spacing of two CNTs in the hybrid structure on the water permeability are considered. The permeability of water in the hybrid structure increases with the increasing temperature above a threshold of 200 K. The PMF for water penetrating through the hybrid structure increases with the decreasing temperature. Interestingly, the water permeability decreases with the increasing axis spacing. As the axial spacing increases, the water permeability decreases gradually and even approaches to two times of the permeability in the case of the hybrid structure with a single CNT channel. The findings can provide a theoretical basis for designing nanopumps or osmotic membranes based on the graphene-CNT hybrid structures.
Effects of Ca2+ doping on dielectric, ferromagnetic properties and magnetic phase transition of SmFeO3 ceramics
Authors: Li De-Ming  , Fang Song-Ke  , Tong Jin-Shan  , Su Jian  , Zhang Na  , Song Gui-Lin  ,   Henan Key Laboratory of Photovoltail Materials, College of Physics and Materials Science, Henan Normal University, Xinxiang 453007, China
Published: December 2020

In this paper we deal with the preparation of Sm1-xCaxFeO3(x=0-0.3) ceramics by the solid stat reaction and study the influences of Ca2+ doping on the dielectric,ferromagnetic properties and magnetic phase transition of SmFeO3.The crystalline structures of the Sm1-xCaxFeO3(x=0-0.3) samples are characterized by X-ray diffraction.The dielectric property is measured by a precisive impedance analyzer (HP4294A) in a frequency range from 40 to 110 MHz.The microstructures of Sm1-xCaxFeO3 are imaged with scanning electron microscope under an operating voltage of 20 kV.The coexistence of Fe3+/2+ ions in Sm1-xCaxFeO3 samples is investigated with X-ray photoelectron spectroscopy (XPS).The magnetic properties of Sm1-xCaxFeO3 are measured with the physical property measurement system.The result shows that all the peaks for Sm1-xCaxFeO3 samples can be indexed according to the crystal structure of pure SmFeO3 and their fine crystal structures are obtained by XRD.The lattice parameter a value of SmFeO3 gradually increases,while the values of b and c decrease,and the unit cell volume (V) shrinks slightly with the increase of x.The scan electron microscope images indicate that Ca2+ doping significantly increases the grain size of SmFeO3 ceramic.The average grain sizes of Sm1-xCaxFeO3 samples range from 0.5 to 2μm with Ca2+ doping.The εr values of Sm1-xCaxFeO3(x=0.1,0.2,0.3) measured at 1 kHz are about 5,3 and 2.6 times greater than that of SmFeO3,respectively,and dielectric loss increases by an order of magnitude.The increase of εr is mainly caused by the interaction between the dipole and the space charge orientation polarization.Both the conductance current and the space charge limiting current are the main factors to increase the dielectric loss.The magnetic measurements show that the M-H curves of Sm1-xCaxFeO3(x=0-0.3) samples exhibit saturated magnetic hysteresis loops with the increase of Ca2+,and the Mr values of Sm1-xCaxFeO3(x=0.1,0.2,0.3) are 20,31,and 68 times that of SmFeO3,respectively,indicating the weakly ferromagnetic behavior.The XPS spectrum indicates that the Fe2+ and Fe3+ co-exist in each of Sm1-xCaxFeO3 samples.The ratio of Fe2+/Fe3+ increases with doping Ca2+ increasing,and the magnetic preparation of SmFeO3 is enhanced.It can be attributed to the structural distortion and the formation of Fe2+–O2-–Fe3+ super-exchange.The spin recombination temperature (TSR) and the Neel temperature (TN) are obtained,respectively,to be 438 K and 687 K by measuring the M-T curves.It is noted that both TSR and TN of SmFeO3 samples move toward low temperature with the increase of x,and the spin recombination disappears when x=0.3.This is mainly due to the stability of the magnetic structure of SmFeO3 sample and the interactions of Fe3+–O2-–Fe3+ and Sm3+–O2-–Fe3+ super-exchange.
Measurement of bulk viscosity of nitrogen based on spontaneous Rayleigh-Brillouin scattering
Authors: Wu Tao  , Shang Jing-Cheng  , He Xing-Dao  , Yang Chuan-Yin  ,   Jiangxi Engineering Laboratory for Optoelectronic Testing Technology, National Engineering Laboratory for Non Destructive Testing and Optoelectronic Sensing Technology and Application, Nanchang Hangkong University, Nanchang 330063, China
Published: December 2020

Bulk viscosity is an important parameter to understand gas viscosity in micro perspective. The traditional ultrasound absorbtion method with acoustic frequencies in a megahertz range cannot be directly applied to high frequencies field, where acoustic waves are in the gigahertz domain. However, gas bulk viscosity at high frequency can be measured by spontaneous Rayleigh-Brillouin scattering (SRBS) and coherent Rayleigh-Brillouin scattering (CRBS). Recent researches show that the bulk viscosity of nitrogen measured by CRBS at a wavelength of 532 nm is obviously different from the values from SRBS in the near-ultraviolet region. In order to obtain accurate bulk viscosity of nitrogen at the wavelength of 532 nm, the SRBS spectra of nitrogen excited by a 532 nm laser are measured in a pressure range from 1 bar to 9 bar at the constant room temperature. The measured SRBS spectrum at the pressure of 7 bar is compared with the theoretical spectrum to obtain optimal scattering angle by using the principle of minimum value of χ2. The theoretical spectrum is calculated by convolving the Tenti S6 model with the instrument transmission function of measurement system. Given that the effect of pressure on the bulk viscosity is negligible, the bulk viscosity value (1.46±0.14)×10-5 kg·m-1-1 of nitrogen at a temperature of 299 K is acquired by averaging the values of bulk viscosity under different pressures (4-9 bar), each value is obtained by comparing the measured spectra at different pressures with the theoretical spectra by using the optimal scattering angle and the principle of minimum value of χ2. The values of bulk viscosity of nitrogen over the pressure of 1-3 bar are not considered because of its big deviation compared with the values under higher pressures (4-9 bar). The results show that the average value of bulk viscosity obtained in our experiment is close to that from the theoretical calculation and SRBS experiments reported in the literature but different obviously from the bulk viscosity obtained by CRBS. In order to testify the bulk viscosity of nitrogen measured in our experiment, it is used to retrieve temperature of nitrogen under pressure ranging from 1 bar to 9 bar. The results show that the absolute error between the retrieved temperature and the reference temperature under different pressures are all below 2.50 K and the difference between the average temperature and the reference temperature is less than 0.15 K. This demonstrates that the measured bulk viscosity of nitrogen in our experiment is accurate and reliable for the gas parameters retrieved by SRBS.
Effect of transition metal element X (X=Mn, Fe, Co, and Ni) doping on performance of ZnO resistive memory
Authors: Guo Jia-Jun  , Dong Jing-Yu  , Kang Xin  , Chen Wei  , Zhao Xu  ,   Key Laboratory of Advanced Films of Hebei Province, College of Physics Science and Information Engineering, Hebei Normal University, Shijiazhuang 050024, China
Published: December 2020

Resistance random access memory (RRAM) based on resistive switching in metal oxides has attracted considerable attention as a promising candidate for next-generation nonvolatile memory due to its high operating speed, superior scalability, and low power consumption. However, some operating parameters of RRAM cannot meet the practical requirement, which impedes its commercialization. A lot of experimental results show that doping is an effective method of improving the performance of RRAM, while the study on the physical mechanism of doping is rare. It is generally believed that the formation and rupture of conducting filaments, caused by the migration of oxygen vacancies under electric field play a major role in resistive switching of metal oxide materials. In this work, the first principle calculation based on density functional theory is performed to study the effects of transition metal element X (X=Mn, Fe, Co, and Ni) doping on the migration barriers and formation energy of oxygen vacancy in ZnO. The calculation results show that the migration barriers of both the monovalent and divalent oxygen vacancy are reduced significantly by Ni doping. This result indicates that the movement of oxygen vacancies in Ni doped ZnO is easier than in undoped ZnO RRAM device, thus Ni doping is beneficial to the formation and rupture of oxygen vacancy conducting filaments. Furthermore, the calculation results show that the formation energy of the oxygen vacancy in ZnO system can be reduced by X doping, especially by Ni doping. The formation energy of the oxygen vacancy decreases from 0.854 for undoped ZnO to 0.307 eV for Ni doped ZnO. Based on the above calculated results, Ni doped and undoped ZnO RRAM device are prepared by using pulsed laser deposition method under an oxygen pressure of 2 Pa. The Ni doped ZnO RRAM device shows the optimized forming process, low operating voltage (0.24 V and 0.34 V for Set and Reset voltage), and long retention time (>104 s). Set and Reset voltage in Ni doped ZnO device decrease by 80% and 38% respectively compared with those in undoped ZnO device. It is known that the density of oxygen vacancies in the device is dependent on the oxygen pressure during preparation. The Ni doped ZnO RRAM device under a higher oxygen pressure (5 Pa) is also prepared. The Ni doped ZnO RRAM device prepared under 5 Pa oxygen pressure shows a little higher Set and Reset voltage than the device prepared under 2 Pa oxygen pressure, while the operating voltages are still lower than those of undoped ZnO RRAM. Thus, the doping effect in the ZnO system is affected by the density of oxygen vacancies in the device. Our work provides a guidance for optimizing the performance of the metal oxide based RRAM device through element doping.
Influence of annealing temperature on properties of Cu2O thin films deposited by electron beam evaporation
Authors: Li Hai-Tao  , Jiang Ya-Xiao  , Tu Li-Min  , Li Shao-Hua  , Pan Ling  , Li Wen-Biao  , Yang Shi-E  , Chen Yong-Sheng  ,   Key Laboratory of Material Physics of the Ministry of Education, College of Physics Engineering, Zhengzhou University, Zhengzhou 450052, China
Published: December 2020

Inorganic-organic metal halide perovskite solar cells (PSCs) have drawn tremendous attention as a promising next-generation solar-cell technology because of their high efficiencies and low production cost. Since the first report in 2009, the recorded power conversion efficiency (PCE) of PSCs has rapidly risen to 22.1% by using 2, 2', 7, 7'-tetrakis (N,Ndi-p-methoxyphenyl-amine) 9,9-spirobifluorene (spiro-MeoTAD) as hole transport material (HTM), with the efforts devoted to the device architecture optimization, material compositional engineer and interface engineering. Nevertheless, the synthesis and cost of the organic HTM (OHTM) become a major challenging issue and therefore alternative materials are required. In the past few years, the applications of inorganic HTMs (IHTMs) in PSCs have shown large improvement in PCE and stability. For example, PSCs with CuOx as IHTM reached a PCE of 19.0% with better stability. Even more exciting, the theoretical PCE of PSC based on Cu2O HTM reaches 24.4%. So, Cu2O is a promising IHTM for future optimized PSC and the large area uniform preparation is very important. In this paper, Cu2O films have been successfully prepared using electron beam evaporation followed by air annealing. The influences of annealing temperature and time on the composition, structure, and photoelectric characteristics of film are investigated in detail. It is found that the as-deposited film is a mixture of Cu2O and Cu. With the increase of annealing temperature, material composition is transformed from mixture to pure Cu2O phase, and then to CuO, due to the oxidation in air. In an annealing temperature between 100℃ to 150℃, pure Cu2O film can be obtained with an average transmission rate over 70%, optical band-gap of 2.5 eV, HOMO level of -5.32 eV, and a carrier mobility of 30 cm2·V-1·s-1. When the film is treated with a UV lamp, the structure and composition of the film can be changed more easily because of the enhancement of oxidation. Finally, reverted planar PSCs with the structure of Ag/PCBM/CH3NH3PbI3/HTMs/ITO are constructed and compared carefully based on HTMs of Cu2O, with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS), and Cu2O/PEDOT:PSS layers, respectively. An optimum thickness of 40 nm of Cu2O HTM is achieved with high carrier extraction rate. However, the performances of all of the PSCs are inferior to those of PEDOT:PSS-based devices, due to the formation of pinholesin absorber layer resulting from the strong hydrophobicity of Cu2O film. However, the efficiency of PSC based on Cu2O/PEDOT:PSS double-HTM is deteriorated because of the chemical interaction between PEDOT:PSS and Cu2O. These findings provide some important guidelines for the design of HTMs.
First-principles calculation of effects of deformation and electric field action on electrical properties of Graphene
Authors: Liu Gui-Li  , Yang Zhong-Hua  ,   Department of Mechanics, Shenyang University of Technology, Shenyang 110870, China;,   Department of Building Environment and Energy Engineering, Shenyang University of Technology, Shenyang 110870, China
Published: December 2020

Based on the first-principles method of density functional theory, a systematic research is conducted on the electron mechanism of the effect of deformation, electric field action and combined action on the electrical properties of graphene. The research results show that the energy gap and density of states of graphene are both 0 at the Fermi level, indicating semi-metallic character, which implies that the calculation model and the parameter setting are reasonable in this paper. After some deformation actions, such as shear, stretch, torsion and bending deformation on the graphene, it is found that shear and torsion exert an obvious effect on opening the energy gap of graphene, but the effects of tensile and bending deformation on the energy gap of graphene are negligible. Therefore, shear deformation and torsion deformation are a preferred alternative to controlling the energy gap of graphene. By adding the electric field to the graphene in different directions, it is found that the , and direction electric fields which are parallel to the plane of graphene exert a strong effect on opening the energy gap of graphene, but the effect of direction electric field which is perpendicular to the plane of graphene is weak. Especially, the direction electric field has the strongest effect on opening the energy gap of the graphene because the positive value of the population of graphene C–C atoms in the direction is relatively large and bond energy is high while the negative value is small and the antibond energy is low. In order to investigate the influence of electric field strength on energy gap of graphene, the electric field strength is increased linearly from 0.1 eV/Å/e to 0.5 eV/Å/e. It can be observed that the energy gap of graphene increases in turn, and shows a linear growth. Under the action of 0.1 eV/Å/e electric field strength, shear deformation, stretch deformation, torsion deformation and bending deformation take place on the grapheme. It is found that under the combined action of deformation and electric field, the electric field improves the effect of deformation on the energy gap, but the effect is not so good asunder the superposition of two fields.
Material equation of state by coupling static and dynamic loading
Authors: Shu Hua  , Tu Yu-Chun  , Wang Jun-Yue  , Jia Guo  , Ye Jun-Jian  , Deng Wen  , Shu Hai-Yun  , Yang Yan-Ping  , Du Xue-Yan  , Xie Zhi-Yong  , He Zhi-Yu  , Fang Zhi-Heng  , Hua Neng  , Huang Xiu-Guang  , Pei Wen-Bing  , Fu Si-Zu  ,   Shanghai Institute of Laser Plasmas, Shanghai 201800, China;,   Center for High Pressure Science and Technology Advance Research, Beijing 100094, China;,   Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Published: December 2020

Materials can be experimentally characterized up to terapascal pressures by sending a laser-induced shock wave through a sample that is pre-compressed inside a diamond-anvil cell. Pre-compression expands the ability to control the initial condition, allowing access to thermodynamic states from the principal Hugoniot and enter into the 10 TPa to 100 TPa (0.1-1 Gbar) pressure range that is relevant to planetary science. We demonstrate here a laser-driven shock wave in a water sample that is pre-compressed in a diamond anvil cell. The compression factors of the dynamic and static techniques are multiplied. This approach allows access to a family of Hugoniot curves which span the P-T phase diagram of fluid water to high density. According to the loading characteristics of the SG-Ⅱ high-power laser, the traditional diamond anvil cell is improved and optimized, and a new diamond anvil cell target adapting to high power laser loading is developed. In order to adapt to laser shock, the diamond window should be thin (100 μm) enough so that the shock can propagate to the sample before the side rarefaction erodes too much the shock planarity. With a thickness of 100 mm over an aperture of 600 μm diameter, a pre-compressed water sample at 0.5 GPa can be obtained. The water is pre-compressed to 0.5 GPa by using the diamond anvil cell. Hugoniot curve is partially followed starting from pre-compression at a pressure of 0.5 GPa. Pressure, density, and temperature data for pre-compressed water are obtained in a pressure range from 150 GPa to 350 GPa by using the laser-driven shock compression technique. Our P-ρ-T data totally agree with the results from the model based on quantum molecular dynamics calculations. These facts indicate that this water model can be used as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range and should improve our understanding of these types of planets.
Spiral wave breakup manner in the excitable system with early afterdepolarizations
Authors: Wei Bin  , Tang Guo-Ning  , Deng Min-Yi  ,   College of Physical Science and Technology, Guangxi Normal University, Guilin 541004, China
Published: December 2020

Early afterdepolarization (EAD) is an important cause of lethal ventricular arrhythmias in heart failure because afterdepolarizations can promote the transition from ventricular tachycardia to fibrillation, which is related to the transition from spiral wave to spatiotemporal chaos. However, it remains unclear about how the EAD results in the breakup of spiral wave. In this paper, we explore the manner of spiral wave breakup induced by EADs under evenly distributed cells. The two-dimensional tissue is simulated with the Greenberg-Hasting cellular automaton model. The normal cells and aging cells are introduced into the model, in which the EAD only occurs in aging cells and can excite the resting cells. The numerical results show that the EAD can produce backward waves as well as forward waves. The EAD has no influence on the behavior of spiral wave in a few cases. The ratio of the number of unaffected spiral waves to the number of all tests is about 26.4%. The EAD can have various effects on spiral wave in other cases. The small influences on spiral wave are that the EAD leads to the meander, drift, and the deformation of spiral wave. The serious influences on spiral wave are that the EAD results in the disappearance and breakup of spiral wave. We find that spiral wave can disappear through the conduction block and transition from spiral wave to target wave. We observe the eight kinds of spiral wave breakups in connection with the excitation of EADs, such as symmetry breaking-induced breakup, nonsymmetry breaking-induced breakup, asymmetric excitation-induced breakup, conduction block-induced breakup, double wave-induced breakup, etc. Spiral wave generally breaks up into multiple spiral waves and spatiotemporal chaos. The ratio of the number of spiral wave breakup to the number of all tests is about 13.8%. However, the ratio of spiral wave breakup can reach about 32.4% under appropriately chosen parameters. The results are basically consistent with the survey results of arrhythmia-induced death rate. Furthermore, we also find that the excitation of EAD can prevent the spiral wave from disappearing and promote the breakup of spiral wave. The physical mechanisms underlying those phenomena are also briefly analyzed.
Coercivity enhancement of waste Nd-Fe-B magnets by Pr70Cu30 grain boundary diffusion process
Authors: Xiao Jun-Ru  , Liu Zhong-Wu  , Lou Hua-Shan  , Zhan Hui-Xiong  ,   School of Material Science and Engineering, South China University of Technology, Guangzhou 510640, China;,   School of Mechanical and Electrical Engineering, Liuzhou Vocational and Technical College, Liuzhou 545000, China;,   Guangdong Yutong New Material Technology Co. Ltd, Chaozhou 515738, China
Published: December 2020

Considerable quantities of Nd-Fe-B magnet wastes are produced every year worldwide. Some Nd-Fe-B magnet wastes in the bulk form, produced during manufacturing, have low coercivity and cannot meet the requirements for applications. Finding an effective way to reuse those wastes by improving the coercivity, without powdering or reproducing process, becomes very important for saving energy and raw materials in manufacture. In this work, the grain boundary diffusion process is carried out on waste Nd-Fe-B sintered magnets by using Pr70Cu30 as a diffusion medium. The effects of diffusion temperature, diffusion time, and annealing time on the magnetic properties of the magnets are investigated. It is found that the coercivity increases when the diffusion temperature increases from 500 to 800℃, the diffusion time increases from 1 to 3 h, or the annealing time increases from 1 to 3 h. By comparing the diffused sample with the simply heat treated sample, we find that the coercivity enhancement by grain boundary diffusion process indeed results from the infiltration of Pr and Cu elements. The coercivity of the magnet increases by 51.9%, from 7.88 kOe (1 Oe=79.5775 A/m) to 11.97 kOe, after 4-hour diffusion at 800℃ followed by 3-hour annealing, with a negligible reduction of remanence Br, achieving a 99.8% recovery of coercivity compared with the commercial N35 magnet. It is noted that 500℃ annealing for 3 h after 800℃ diffusion only slightly increases the coercivity by 4.6%, from 11.44 kOe to 11.97 kOe, which indicates that the annealing process after Pr-Cu grain boundary diffusion may be not indispensable. Based on the microstructure analysis, the diffusion of Pr and Cu is confirmed. However, the distributions of Pr and Cu are inhomogeneous within a range of tens of microns near the surface even though the diffusion has spread throughout the magnet. The structure of main phase grains separated by the continuous grain boundary phase is formed after the grain boundary diffusion process while the core-shell structure is not observed, which suggests that the modification of the grain boundary structure is the main reason for the coercivity improvement. Cu element plays an important role in forming continuous grain boundary phase. In addition, the electrochemical corrosion test shows that higher corrosion current is obtained in the diffused magnet than in the original magnet, though the corrosion potential is improved. The reduced corrosion resistance may be related to the increased RE-rich phase content and the formation of continuous grain boundary phase. The present work is of great importance for increasing the production yield of Nd-Fe-B magnets.