bluuebunny/crossref_metadata_2025 huggingface dataset:
Near field enhancement of TiO2 nanoparticle array on different substrates for femtosecond laser processing
Authors: Jiao Yue  , Tao Hai-Yan  , Ji Bo-Yu  , Song Xiao-Wei  , Lin Jing-Quan  ,   School of Science, Changchun University of Science and Technology, Changchun 130022, China
Published: December 2020

Optical near field enhancement on substrate can be achieved by localizing femtosecond laser energy with nanoparticles. The enhanced field is located in the region between nanoparticles and the substrate. The localized femtosecond optical field is of great significance for fabricating the micro/nano structure with characteristic size beyond the diffraction limit. Up to now, femtosecond processing nanohole assisted by particle array is only possible for metal particle (Au) and low-refractive-index dielectric polystyrene particle. However, previous research results show that it cannot be realized for metal particle arrays (Au) to form periodic nanohole arrays, and it is limited for polystyrene particle to choose the corresponding substrate. In this paper, a novel method is proposed, in which high refractive index TiO2 arrayed particles are placed on the substrate to achieve laser induced near field enhancement. This makes feasible the nanoscale processing beyond the diffraction limit. In this paper, near field distributions of TiO2 particle array on Si, Pt and SiO2 substrates are simulated by the finite-difference time-domain (FDTD) method. The results show that TiO2 particles concentrate the laser energy to a region with a diameter of 100 nm around the particle and the near field enhancement is 140 times higher than the incident laser intensity, which is beneficial to fabricating the nanostructure of super diffraction limit, such as sub-hundred nanometer nanohole ablation by femtosecond laser. For Si substrate, the near field enhancement is only about 30% lower for TiO2 particle array than that for single TiO2 particle. In order to explore the influence mechanism of the substrate material parameters on the near field enhancement of TiO2 nanoparticle array, we further simulate the enhancement factor for the substrates of different refractive indices. It is found that the near field is enhanced with the increase of substrate refractive index, and this is attributed to an increased interaction of the particle with the near field of substrate and the scattering effect in which the TiO2 particle supports forward near field intensity pattern. Moreover, the image charge model is introduced to analyze the effect of substrate optical parameters on local field enhancement. Results in this paper can be applied to most metals as well as dielectric substrate surfaces, and they open a new way for femtosecond laser near field nano-processing with characteristic size beyond the diffraction limit.
Advances in the far-field sub-diffraction limit focusing and super-resolution imaging by planar metalenses
Authors: Qin Fei  , Hong Ming-Hui  , Cao Yao-Yu  , Li Xiang-Ping  ,   Institute of Photonics Technology, Jinan University, Guangzhou 510632, China;,   Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583, Singapore
Published: December 2020

Due to the fundamental laws of wave optics, the spatial resolution of traditional optical microscopy is limited by the Rayleigh criterion. Enormous efforts have been made in the past decades to break through the diffraction limit barrier and in depth understand the dynamic processes and static properties. A growing array of super-resolution techniques by distinct approaches have been invented, which can be assigned to two categories: near-field and far-field super-resolution techniques. The near-field techniques, including near-field scanning optical microscopy, superlens, hyperlens, etc., could break through the diffraction limit and realize super-resolution imaging by collecting and modulating the evanescent wave. However, near-field technique suffers a limitation of very short working distances because of the confined propagation distance of evanescent wave, and certainly produces a mechanical damage to the specimen. The super-resolution fluorescence microscopy methods, such as STED, STORM, PALM, etc., could successfully surpass the diffractive limit in far field by selectively activating or deactivating fluorophores rooted in the nonlinear response to excitation light. But those techniques heavily rely on the properties of the fluorophores, and the labelling process makes them only suitable for narrow class samples. Developing a novel approach which could break through the diffraction limit in far field without any near-field operation or labelling processes is of significance for not only scientific research but also industrial production. Recently, the planar metalenses emerge as a promising approach, owing to the theoretical innovation, flexible design, and merits of high efficiency, integratable and so forth. In this review, the most recent progress of planar metalenses is briefly summarized in the aspects of sub-diffractive limit focusing and super-resolution imaging. In addition, the challenge to transforming this academic concept into practical applications, and the future development in the field of planar metalenses are also discussed briefly.
Recent progress on super-resolution imaging and correlative super-resolution microscopy
Authors: Lin Dan-Ying  , Qu Jun-Le  ,   Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
Published: December 2020

The diffraction of the finite aperture in the optical imaging system restricts further improvement of the resolution of optical microscopy, which is called the diffraction limit. Since raised by Ernst Abbe in 1873, the problem of diffraction limit has been one of the foci of academic research. In recent years, with the rapid development of related fields such as the development of optoelectronic devices including high energy lasers and high sensitivity detectors and the development of new fluorescent probes, the problem of diffraction limit in optical microscopy ushered in a new opportunity, and super-resolution microscopy (SRM) has made remarkable achievements in the past decade. The basic principles of diffraction limited resolution in both space and frequency domains are reviewed, and on this basis, the mechanisms for the various SRM technologies to circumvent the diffraction limit and improve the resolution are explained in detail. The development trends and research directions of various SRM techniques are also introduced. As a new and important development trend of SRM, correlative super-resolution microscopy and its recent progress are reviewed, including correlative studies on SRM and time-lapse live cell fluorescence microscopy, fluorescence lifetime imaging microscopy, spectrometry and spectroscopy, electron microscopy, atomic force microscopy, etc. The role and significance of various correlative super-resolution microscopy are discussed. The future development of super-resolution microscopy and correlative super-resolution microscopy is also prospected.
Geometrical optimization of Cu-Au-Pd clusters based on the construction of inner cores
Authors: Wu Xia  , Wei Zheng  ,   School of Chemistry and Chemical Engineering, Anqing Normal University, Anqing 246011, China;,   Anhui Key Laboratory of Functional Coordination Compounds, Anqing Normal University, Anqing 246011, China
Published: December 2020

The trimetallic cluster has become a hot topic in the field of basic scientific research due to its special catalytic, magnetic and chemical activities. It is very important to determine the stable structures of clusters. In order to optimize the stable structure of large size Cu-Au-Pd cluster, a modification algorithm of adaptive immune optimization algorithm based on the construction of inner cores, called AIOA-IC algorithm, is proposed. The only difference between AIOA and AIOA-IC lies in their starting structures. Instead of generating the starting structure randomly in AIOA, an inner core in the AIOA-IC method is used for generating the starting structure. Several motifs, such as decahedron, icosahedron, face centered cubic, six-fold pancake structure, and Leary tetrahedron, are randomly selected as the inner cores. The size of the inner core is determined according to the cluster size. The Gupta potential based on the second moment approximation of tight binding potential is used to describe the interatomic interaction between Cu-Au-Pd clusters, and the corresponding potential parameters, such as the cohesive energy, lattice constants, and elastic constants are obtained by fitting the experimental values. To test the efficiency of the proposed algorithm, the stable structure of Ag-Pd-Pt cluster with 60 atoms is optimized. The results show that the new structure has lower energy than the cluster reported in the literature. It can be seen that the AIOA-IC algorithm has a stronger ability to search for the potential energy surface of the Gupta potential. Furthermore, the proposed algorithm is used to optimize the stable structures of 38-atom and 55-atom Cu-Au-Pd clusters. The structures of the investigated Cu6AunPd32-n, CunAu6Pd32-n and CunAu32-nPd6 (n=1-31) clusters can be categorized into three types:five-fold, six-fold, and truncated octahedron. Moreover, it is found that the compositions of Cu, Au and Pd atoms in the trimetallic clusters affect the structural type of the cluster. However, the Cu13AunPd42-n, CunAu13Pd42-n, and CunAu42-nPd13 (n=1-41) clusters each have a structure of complete Mackay icosahedron. Furthermore, the order parameter results show that Cu, Au and Pd atoms each have a significant segregation phenomenon. For the 147-atom Cu12Au93Pd42 cluster, the structure is also of an icosahedron. The central atom is Au, and the inner shell and sub-outer shell are occupied by 12 Cu and 42 Pd atoms, respectively. The outer shell is filled with 92 Au atoms. The results show that the Cu, Pd and Au atoms tend to be distributed in the inner shell, sub-outer shell, and outer shell, respectively. This can be further explained by the results of the atomic radius and the surface energy.
Method and experiment of path rainfall intensity inversion using a microwave link based on nonspherical rain-induced model
Authors: Song Kun  , Gao Tai-Chang  , Liu Xi-Chuan  , Yin Min  , Xue Yang  ,   College of Meteorology and Oceanography, National University of Defense Technology, Nanjing 211101, China
Published: December 2020

It is important to measure rainfall accurately with high spatial and temporal resolution in meteorology, hydrology, agriculture industry, environment conservation, flood warning and weather forecasting. The use of attenuated information about microwave propagation in rainfall areas to acquire surface precipitation intensity has been shown to be a practical approach to measuring rainfall in recent years. However, the inversion of a single-frequency link is based on the assumption of rainfall attenuation under a certain frequency condition. Further, obtaining parameters that comply with all rainfall events for the rainfall attenuation model is a challenge, often leading to an overestimation of the rainfall intensity. Therefore, based on extended boundary condition method and Gamma raindrop size distribution, an inversion method of the path rainfall intensity by using a microwave link rain-induced attenuation is proposed in order to improve the accuracy of rainfall measurement by microwave rain-induced attenuation. In this paper, we use the characteristics of an atmospheric attenuation model to eliminate the influence of non-rainfall-caused attenuation on the process of rainfall inversion. On the basis of scattering theory and by utilizing the Gamma raindrop size drop, we use the extended boundary condition method to calculate the characteristics of microwave attenuation for Pruppacher-Beard raindrop shape model. The correction model of rainfall effective attenuation and rainfall inversion model of line-of-sight microwave links are proposed, based on the microwave rain attenuation characteristics and raindrop size distribution statistics. In this paper, we propose 15-20 GHz inversion model of path-average rainfall intensity based on nonspherical rain-induced model by using Levenberg-Marquardt optimization algorithm. Meanwhile, we analyze the variations of parameters of rain-induced model under the condition of different temperatures. Besides, we design a line-of-sight microwave experimental system for measuring the rainfall, and the path average rain rate is inversed by rainfall inversion model, which is compared with an OTT disdrometer. The results show that the correlation coefficient of rain rate inversed by microwave link and that of disdrometer are both higher than 0.6 mostly, and the maximum value is 0.96; the error of accumulated rain amount is less than 2.47 mm, the minimum value is 0.28 mm; the relative error of accumulated rain amount is less than 1.84%, the minimum value is 0.44%. The experimental results validate the feasibility and accuracy of rainfall inversion method proposed in this paper. In addition, the experimental result reflects that rainfall intensity retrieved method based on nonspherical raindrop model has advantages over the method based on spherical raindrop model.
Acoustic focusing by thermoacoustic phased array
Authors: Liu Chen  , Sun Hong-Xiang  , Yuan Shou-Qi  , Xia Jian-Ping  , Qian Jiao  ,   Research Center of Fluid Machinery Engineering and Technology, Faculty of Science, Jiangsu University, Zhenjiang 212013, China;,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Broadband acoustic focusing effect based on a thermoacoustic phased array is studied. In this work, according to the relationship between the sound velocity and the temperature, a new type of a thermoacoustic phase control unit is designed by using air with different temperatures surrounded by rigid insulated boundaries and thermal insulation films. The acoustic wave velocity could be adjusted by changing the temperature of air in the unit, and the transmitted and reflected acoustic phase delays can cover the whole 2 interval. On the basis of this thermoacoustic phased array, we design four different types of acoustic focusing lenses. By using eight or two kinds of such units, we realize the transmitted and reflected acoustic focusing effect, respectively. The results show that the thermoacoustic phased array lens has a good focusing performance in a frequency range of 4.0-15.0 kHz. In addition, the center intensity of the focal spot is much greater in the focusing lens with eight phase units, and the design method is simpler and more robust in the focusing lens with two phase units. Compared with other types of focusing lenses, the proposed focusing lens based on the thermoacoustic phased array has the advantages of broad bandwidth, high focusing performance and simple designed method. The results provide a theoretical basis and experimental reference for designing the broadband thermoacoustic phased array devices and new types of acoustic focusing lenses.
Electronic structure and optical absorption properties of -AgVO3 with vacancy defects
Authors: Ren Chao  , Li Xiu-Yan  , Luo Quan-Wei  , Liu Rui-Ping  , Yang Zhi  , Xu Li-Chun  ,   College of Physics and Optoelectronics, Taiyuan University of Technology, Jinzhong 030600, China
Published: December 2020

Semiconductor photocatalysts have received much attention due to their applications of wastewater treatment and air purification. The monoclinic -AgVO3, which has narrow band gap (2.11 eV) and can respond to visible light, has been considered as one of the promising semiconductor photocatalysts. The vacancy defects always exist in -AgVO3 prepared under the conventional synthesis conditions and have important influences on the structure and properties of -AgVO3. Systematic theoretical study of the vacancy defects in -AgVO3 is still lacking. In this paper, using density functional theory plus U (DFT+U) approach, the Ag vacancy, O vacancy and Ag-O bivacancy in -AgVO3 are studied. The formation energy, band structure, differential charge density and optical absorption spectrum of -AgVO3 with vacancy defects are carefully investigated. When the U values are chosen as 6 eV and 2.7 eV for the Ag-4d and V-3d electrons respectively, the reasonable lattice parameters and band gap value can be obtained for -AgVO3. By comparing the formation energies of different Ag and O vacancies, we find that the dominating vacancy defects in -AgVO3 are Ag3 and O1 vacancies, and the formation of Ag vacancy is much easier than that of O vacancy. The analyses of the total and partial density of states indicate that the conduction band arises mainly from V-3d orbit, and the valence band is mainly composed of Ag-4d and O-2p states for -AgVO3. With Ag3 vacancy, O1 vacancy or Ag3-O1 bivacancy, the band gaps of -AgVO3 all decrease in different degrees. The Ag3 vacancy behaves as p-type donor, allowing the Fermi level to shift down to the valence band maximum. However, O1 vacancy and Ag3-O1 bivacancy both act as n-type donors, and the Fermi level shifts to the conduction band minimum. The change of the Fermi level for the vacancy defect systems also means that the charge transfer occurs among the atoms around the vacancy, which is analyzed by calculating the differential charge density. The Ag3 vacancy and O1 vacancy have little effects on the light absorption of -AgVO3 in the range of visible light, while O1 vacancy and Ag3-O1 bivacancy in -AgVO3 cause the obvious absorption of light in the near infrared region.
Shape transformations of opening-up vesicles with one hole
Authors: Liang Yue-Feng  , Zhang Shao-Guang  ,   College of Physics and Information Technology, Shaanxi Normal University, Xi'an 710119, China
Published: December 2020

So far two kinds of solutions to the problem of opening-up vesicles with one hole have been found. One is cup-like shape found by Umeda and Suezaki (2005 Phys. Rev. E 71 011913), the other is dumbbell shape with one hole, found by our group. As seen in the context of the bilayer coupling (BC) model, the former corresponds to relatively small reduced area difference a, and the latter corresponds to relatively large value of a. The relationship between these two kinds of shapes is not clear. Viewing from the angle of the cup-like shape, whether one can obtain the dumbbell shape by increasing a is not known. In this paper, we try to clarify this problem by solving the shape equations for free vesicles and adhesive vesicles based on the BC model. Firstly, we solve the set of Euler-Lagrange shape equations that satisfy certain boundary conditions for free vesicles. A branch of solution with an inward hole is found with the reduced area difference a slightly greater than 1. It is verified that the solution named cuplike vesicles, which was found by Umeda and Suezaki, belongs to another solution branch (a 1) with an outward hole near a=1. According to this result, we make a detailed study of these two solution branches for free vesicles and vesicles with adhesion energy. We find that there is a gap near a=1 between the two solution branches. For a in this gap, there is no opening-up solution. For adhesive vesicles, the gap will move towards the right side slowly with increasing adhesive radius. In order to check whether the two solution branches can evolve into closed shapes, we also make a calculation for closed vesicles. For free closed vesicles, we find that there is only the sphere solution when a is exactly equal to 1 for p=0 (in order to comply with the opening-up vesicle, no volume constraint is imposed on it), while for adhesive vesicles there exist closed solutions in a region of a without volume constraint. Both studies for free vesicles and adhesive vesicles show that these two kinds of opening-up vesicles belong to different solution branches. They cannot evolve from one to the other with continuous parameter changing. And strictly speaking, they cannot evolve into the closed vesicles. With increasing a, the opening-up branch on the right side of the gap can evolve into an opening-up dumbbell shape with one hole via the self-intersection intermediate shapes. Another interesting result is that for adhesive opening-up vesicles, in the a parametric space, the solutions are folded for a solution branch, which means that there exist several shapes corresponding to the same a value in the folding domain. This phenomenon has never occurred in previous study of the closed vesicles under the BC model. The influences of a on the shape and energy of the free vesicles and adhesive vesicles are also studied.
Effective-mass approach to controlling double-well dynamics of atomic Bose-Einstein condensates
Authors: Liu Xiao-Wei  , Zhang Ke-Ye  ,   Department of Physics and Material Science, East China Normal University, Shanghai 200062, China
Published: December 2020

The realization of Bose-Einstein condensation in dilute atomic gases opens an exciting way to quantum mechanics and begins a new area of quantum simulation. As a macroscopic quantum object and a many-body bosonic system, the Bose-Einstein condensates can show numerous exotic quantum effects and have naturally attracted great attention. One of the simplest quantum many-body systems to be realized experimentally and studied theoretically is ultra-cold atoms in a double-well potential. This system can exhibit a great variety of quantum interference phenomena such as tunneling oscillation, self-trapping and the entanglement of macroscopic superpositions. Specifically, the double-well potentials built by optical or magnetic fields are easy to change and the many-body interaction between ultra-cold atoms can be changed by the method of Feshbach resonance, enabling the precise quantum control of the double-well dynamics of the condensates. In the present work, we study the dynamics of a condensate in a trapping potential consisting of an unalterable double-well trap and an additional moving optical lattice. If the lattice space is much smaller than the size of the double-well trap, the system can be simplified into a double-well trapped condensate with a tunable effective mass. Using the mean-field factorization assumption, together with a two-mode approximation, we obtain the analytic expressions for the dependence of the tunneling rate and the self-collision strength on the effective mass. The tunneling rate decays and the collision strength grows up with the increase of the effective mass. As a consequence of their different changes, we conclude that the adjustment of the effective mass of the ultra-cold atoms, rather than the changing of the trap barrier or adjusting of the atomic scattering length, is an alternative approach to controlling the double-well dynamics of the condensate. Via numerical simulations of the mean-field dynamical equations with some realistic parameters, we show that a transition between the quantum coherent tunneling and the self-trapping behaviors is experimentally realizable with the mass-control approach. Specifically, we show that the approach is still valid for the case of negative mass. Moreover, we find that the negative-mass case can be used even to stimulate the double-well dynamics of the condensate with a negative atomic scattering length.
Theoretical investigation of laser cooling for BD+cation by ab inito calculation
Authors: Li Ya-Chao  , Meng Teng-Fei  , Li Chuan-Liang  , Qiu Xuan-Bing  , He Xiao-Hu  , Yang Wen  , Guo Miao-Jun  , Lai Yun-Zhong  , Wei Ji-Lin  , Zhao Yan-Ting  ,   School of Applied Science, Taiyuan University of Science and Technology, Taiyuan 030024, China;,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
Published: December 2020

Based on consistent basis set aug-cc-pV5Z, five low-lying potential energy curves and transition dipole moments X2∑+, A2Π, B2∑+, a4Π and b4∑+ of BD+ are calculated by using internally contracted multi-reference configuration interaction approach. According to the calculation results, ro-vibrational levels of theses electronic states are derived through solving the radial Schrödinger equation ro-vibrational equation, and then the molecular parameters, Franck-Condon factors (FCFs) and radiation life are obtained by fitting and calculations. The FCFs (f00=0.923) and radiation life for v"=0 (τ=235 ns) of A2Π-X2∑+ are suitable for achieving rapid laser cooling. Therefore, an optical-cycle for Doppler laser cooling scheme is proposed:the system includes the A2Π1/2(v'=0)-X2∑+(v"=0, 1), where the case of v'=0 contains 2 rotational levels, the cases of v"=0 and v"=1 contain 6 and 4 rotational levels, respectively. According to the proposal, we simulate the dynamic process of the molecular population in laser cooling. The BD+ can be decelerated from initial velocity of 100 m/s to 4.6 m/s (13 mK) after scattering 1150 photons during 5.4 ms.
Numerical study of Rayleigh-Taylor instability by using smoothed particle hydrodynamics
Authors: Yang Xiu-Feng  , Liu Mou-Bin  ,   Department of Mechanical Engineering, Iowa State University, Ames, IA 50011, USA;,   BIC-ESAT, College of Engineering, Peking University, Beijing 100187, China
Published: December 2020

In this paper, we present a smoothed particle hydrodynamics (SPH) method for modeling multiphase flows. The multiphase SPH method includes a corrective discretization scheme for density approximation around the fluid interface to treat large density ratio, a small repulsive force between particles from different phases to prevent particles from unphysically penetrating fluid interface, and a newly-developed hyperbolic-shaped kernel function to remove possible stress instability. This multiphase SPH method is then used to study the single-and multi-mode Rayleigh-Taylor instability problems. A comparison between our results with the results from existing literature shows that our results are obviously better than most available results from other SPH simulations. The present results are close to those by Grenier et al. while the present multiphase SPH method is simpler and easier to implement than that in the work by Grenier et al. (Grenier, et al. 2009 J. Comput. Phys. 228 8380). For the single-mode Rayleigh-Taylor instability, the evolutions of the interface pattern and vortex structures, and the penetration depth each as a function of time are investigated. For the multi-mode Rayleigh-Taylor instability, the merging of small structures into a large structure during the evolution of the interface is studied. The horizontal average density and the penetration each as a function of height are also studied.
Effects of relaxation time on local structural and magnetic properties of Fe80.8B10P8Cu1.2 amorphous alloy
Authors: Cao Cheng-Cheng  , Fan Jue-Wen  , Zhu Li  , Meng Yang  , Wang Yin-Gang  ,   College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
Published: December 2020

Over past decades, Fe-based amorphous and nanocrystalline alloys have aroused a popular research interest because of their ability to achieve high saturation magnetic flux density and low coercivity, but the mechanisms for modifying annealing-induced magnetic properties on an atomic scale in amorphous matrix due to structural relaxation has not been enough understood. In this work, we study the effects of pre-annealing time on local structural and magnetic properties of Fe80.8B10P8Cu1.2 amorphous alloy to explore the mechanisms for structural relaxation, particularly the evolution of chemical short range order. The alloy ribbons, both melt spun and annealed, are characterized by differential scanning calorimetry, X-ray diffractometry, Mössbauer spectroscopy and magnetometry. The magnetic hyperfine field distribution of Mössbauer spectrum is decomposed into four components adopting Gaussian distributions which represent FeB-, Fe3P-, Fe3B- and α-Fe-like atomic arrangements, respectively. The fluctuation of magnetic hyperfine field distribution indicates that accompanied with the aggregation of Fe atoms, the amorphous structures in some atomic regions tend to transform from Fe3B- to FeB-like chemical short-range order with the pre-annealing time increasing, but the amorphous matrix begins to crystallize when the pre-annealing time reaches 25 min. Before crystallization, the spin-exchange interaction between magnetic atoms is strengthened due to the increase of the number of Fe clusters and the structure compaction. Thus, saturation magnetic flux density increases gradually, then shows a drastic rise when there appear α-Fe grains in the amorphous matrix. Coercivity first declines to a minimum after 5 min pre-annealing and then increases drastically. This is attributed to the fact that excess free volume and residual stresses in the melt spun sample are released out during previous pre-annealing, which can weaken magnetic anisotropy significantly, while the subsequent pre-annealing destroys the homogeneity of amorphous matrix, resulting in the increase of magnetic anisotropy. In addition, the separation of Cu atoms from the first near-neighbor shell of Fe atoms and the obvious decrease in the Fe-P coordination number suggest the formation of CuP clusters, which can provide heterogeneous nucleation sites for α-Fe and contribute to the grain refinement. Therefore, through controlling the pre-annealing time, we successfully tune the content values of CuP and Fe clusters in the amorphous matrix to promote the precipitation of α-Fe and refine grains during crystallization. For Fe80.8B10P8Cu1.2 nanocrystalline alloy, an enhancement of soft magnetic properties is achieved by a pre-annealing at 660 K for 5-10 min followed by a subsequent annealing at 750 K for 5 min.
First-principles calculation of influence of alloying elements on NbC heterogeneous nucleation in steel
Authors: Xiong Hui-Hui  , Liu Zhao  , Zhang Heng-Hua  , Zhou Yang  , Yu Yuan  ,   School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China;,   School of Metallurgy and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China
Published: December 2020

The NbC precipitated in steel is in favor of the heterogeneous nucleation of ferrite, which is affected by the alloying elements at the ferrite/NbC interface. However, it is difficult to clearly understand the effect of alloying elements on the ferrite/NbC interface behavior experimentally. Therefore, the first-principles calculation is employed to address this problem in this paper. First of all, the segregation behaviors of alloying element X (=Cr, Mn, Mo, W, Zr, V, Ti, Cu and Ni) on the ferrite(100)/NbC(100) interface are systematically explored. And then, we investigate the influences of these alloying elements on the property of the ferrite/NbC interface. The work of adhesion (Wad), interfacial energy (γint) and electronic structure of ferrite/NbC interface alloyed by these elements are also analyzed. The results show that the (Cr, V, Ti)-doped interfaces have negative segregation energies, which indicates that Cr, V and Ti are easily segregated at the ferrite/NbC interface. Conversely, the Mn, W, Mo, Zr, Cu and Ni are difficult to segregate at the interface. When Mn, Zr, Cu and Ni replace the Fe atoms in the ferrite/NbC interface, the adhesive strength of the interface will decrease, thus weakening the heterogeneous nucleation of ferrite on NbC surface. However, the introduction of Cr, W, Mo, V and Ti will improve the stability of the ferrite/NbC interface due to the larger Wad and lower γint. Therefore, the Cr, W, Mo, V and Ti on the ferrite side of the interface can effectively promote ferrite heterogeneous nucleation on NbC surface to form fine ferrite grain. The analysis of difference charge density indicates that after the introduction of Zr and Cu in ferrite/NbC interface, the interactions among interfacial Zr, Cu and C atoms was weaken. However, when Cr and W are introduced into the clean interface, the strong Cr-C and W-C non-polar covalent bonds are formed, which enhances the adhesion strength of the ferrite/NbC interface. In addition, the minimum Cr-C bonding length at the Cr-doped interface suggests that the interface has the highest interface strength. The Mulliken population analysis shows that for the (Cr, W, Mo, V, Ti)-doped interfaces, the transfer charges of Cr, W, Mo, V and Ti are 1.12, 0.84, 0.54, 0.33 and 0.28, respectively. Nevertheless, for the clean interface, the transfer charge of Fe is only 0.05. Therefore, the interactions among interfacial Cr, W, Mo, V, Ti and C atoms are stronger than that between interfacial Fe and C atoms, which is in good accordance with the above analysis.
Wetting kinetics of water droplets on the metallic glass
Authors: Sun Chuan-Qin  , Huang Hai-Shen  , Bi Qing-Ling  , Lü Yong-Jun  ,   School of Physics, Beijing Institute of Technology, Beijing 100081, China;,   School of Physics and Electronics, Zunyi Normal College, Zunyi 563006, China
Published: December 2020

Water absorption and wetting at metal surface have received considerable attention due to the important role in many relevant areas including catalysis and corrosion. The glassy surface has unique physical and chemical properties, displaying promising applications in surface science and technology. However, the water wetting of metallic glass surface is less studied than that of crystal metal surface. In this paper, the wetting kinetics of water droplets at the surface of Cu50Zr50 glass is studied by using molecular dynamics simulations. The water droplets show a complete wetting behavior at the glassy surface as in the cases of the CuZr (110) and (110) crystal surfaces. However, the spreading rate of water droplets on the glassy surface is remarkably fast. Despite different spreading rates, the time dependence of the spreading radius for crystal and glass surfaces consistently follows a power law, Rn t with the same exponent n = 7, which conforms with the universal law of the water spreading at non-reactive solid surfaces. An advancing adsorption monolayer of water is formed at the glassy surface, whereas the front of spreading water droplets displays a foot-like morphology at each of the (110) and (110) surfaces. The spreading of water droplets can be described as the process that water molecules diffuse from the droplet surface to the front of the adsorption layer. To reveal the microscopic mechanism of the fast spreading at the glassy surface, the interactions between surface and water are analyzed. We find that the water molecules in the adsorption layer at the glassy surface display a disordered arrangement in contrast to those of the ordered and double-layer structure. The structure of adsorption layer is closely related to the orientations of water molecules in it. The water molecules in the adsorption layer at the glassy surface are mostly parallel to the surface, and those at the crystal surface tend to point to the interiors of droplets. The molecular orientation is proved to determine the relatively weak hydrogen-bond interactions between the adsorption layer and the droplet interior at the Cu50Zr50 glassy surface, thus facilitating the diffusion of water molecules from the droplet surface to the front of the adsorption layer and improving the spreading. On the contrary, the strong interactions associated with the crystal surfaces hinder the droplet from spreading by slowing down the molecular diffusion. The present work provides an insight into the microscopic mechanism of water spreading at metallic glassy surfaces and conduces to in depth understanding the physical and chemical processes associated with metallic-glass/water interfaces.
Combinatorial fabrication and high-throughput characterization of metallic glasses
Authors: Liu Yan-Hui  ,   Key Laboratory of Extreme Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Metallic glasses, which exhibit outstanding mechanical, physical, and chemical properties and rich phenomena, are important technologically and fundamentally. The progress in the field of metallic glasses has largely relied on the development of new glass forming alloys. However, due to the multi-component nature of metallic glass, discovery of new alloy is slow. The fabrication combined with high-throughput characterization under the umbrella of materials genome initiative has been demonstrated to be helpful for accelerating the material discovery. In addition, the big data generated during high-throughput characterization can conduce to understanding the science behind the behaviors of various materials. In the paper, we summarize the techniques that can be used for the combinatorial fabrication of metallic glasses, and relevant approaches to realize the high-throughput characterization.
Five-fold local symmetries in metallic liquids and glasses
Authors: Li Mao-Zhi  ,   Department of Physics, Renmin University of China, Beijing 100872, China
Published: December 2020

In this article, we review the experimental, theoretical and simulation studies on five-fold local symmetries in metallic liquids and glasses. In the early study on simple liquid structure, it has been realized that five-fold local symmetry plays a key role in irregular structures, supercooling and crystallization of simple liquids. In particular, icosahedral short-range order, representative of five-fold local symmetry, has attracted much attention. In addition, researches proposed a dense random packing model for simple liquid structure in 1959, and found a wide variety of polyhedra and absolute predominance of pentagonal faces in simple liquids, and also pointed out that pentagonal arrangements can only occur in very complex structures such as some of the alloy structures. Based on the Frank's hypothesis of icosahedral short-range order as blocking unit in a simple liquid, a lot of theoretical and experimental efforts have been made to confirm its existence in simple liquids, metallic liquids and glasses. So far, several theoretical methods have been developed for characterizing local atomic structures in simple liquids, such as bond-orientational order parameter, Honeycutt-Andersen index, and Voronoi tessellation. Although the local atomic symmetries in atomic structures in metallic liquids and glasses can be characterized by these methods and the geometries of the atomic structures in liquids and glasses have received much more attention, an atomic cluster model has been developed for establishing the structure-property relationship in metallic liquid and glass. Due to the diversity of the atomic clusters in both type and population of different metallic liquids and glasses, the atomic cluster model could not present a simple description of structure-property relationship. Based on the fundamental characteristics of metallic liquids and glasses, five-fold local symmetry, the structure-property relationship in metallic liquids and glasses, such as dynamic crossover, glass transition, liquid-liquid phase transition, and deformation can be well described in simple, quantitative and unified ways, and therefore a clear physical picture can be provided. All these studies indicate that five-fold local symmetry as a structural parameter is simple, general and effective.
Ductilization of bulk metallic glassy material and its mechanism
Authors: Wu Yuan  , Song Wen-Li  , Zhou Jie  , Cao Di  , Wang Hui  , Liu Xiong-Jun  , Lü Zhao-Ping  ,   State Key Laboratory for Advanced Metals and Materials, University of Science and Technology, Beijing 100083, China
Published: December 2020

Bulk metallic glass has aroused intensive interest due to its unique atomic structure and properties, while its structural application is restricted by the shortcomings of its mechanical properties-room temperature brittleness and strain softening. To make up for these shortcomings, various approaches have been proposed, including tailoring intrinsic parameters such as elastic modulus and structural heterogeneity, and changing stress state or defect concentration. Bulk metallic glass composites with ex-situ added or in-situ formed crystallites have been fabricated, series of bulk metallic glasses and their composites with good mechanical properties have been designed, especially TRIP (Transformation-induced plasticity)-reinforced bulk metallic glass composites with large tensile ductility and work-hardening. In this paper, we review the ductilization of bulk metallic glass and its composites, as well as the related mechanism. Particularly, fabrication, properties, structure control and the ductilization mechanism of TRIP-reinforced bulk metallic glass composite are introduced in detail. A perspective of the challenges of ductilization of bulk metallic glassy materials is also mentioned briefly.
Heterogeneity: the soul of metallic glasses
Authors: Guan Peng-Fei  , Wang Bing  , Wu Yi-Cheng  , Zhang Shan  , Shang Bao-Shuang  , Hu Yuan-Chao  , Su Rui  , Liu Qi  ,   Beijing Computational Science Research Center, Beijing 100193, China;,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

Owing to the superior mechanical and physical properties, metallic glasses (MGs) have attracted tremendous attention as promising candidates for structural and functional applications. Unfortunately, the ability to form uncontrollable glasses, the poor stability and the unpredicted catastrophic failure stemming from the disordered structure, as the Achilles' heel of MGs, severely restrict their large-scale applications. A number of phenomenological models, such as free volume model, shear transformation zone (STZ) model, flow unit model, etc., have been proposed, intending to relate microstructures to properties of MGs. However, few sophisticated structure-property relationships are established due to a poor understanding of the microstructure of MGs. Recently, heterogeneity is commonly believed to be intrinsic to MGs, and it can be used to establish the structure-property relationship of MGs. In this paper, we review the recent progress of MGs from the angle of heterogeneity, including the static heterogeneities and dynamic heterogeneities. The perspectives of the scientific problems and the challenges of metallic glass researches are also discussed briefly.
β-relaxation in glass forming systems
Authors: Wen Ping  ,   Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

As soon as crystallization is suspended at constant pressure, cooling liquids turn inevitably into rigid amorphous solids, i.e. glasses. The process is a universal phenomenon in nature, termed as glass transition involving many fundamental problems in many-body interaction system and material science. Among the decades research on the glass transition, the universality of β-relaxation, its mechanism and its effects on the understanding of liquids and glasses have been studied argumentatively. In this paper we review the research progress of β-relaxation and also try to point out the tendency of β-relaxation study in future.
Development of ultrahigh strength bulk metallic glasses
Authors: Wei Xin-Quan  , Bi Jia-Zi  , Li Ran  ,   School of Materials Science and Engineering, Beihang University, Beijing 100191, China
Published: December 2020

It is always desirable to develop bulk metal materials with extremely mechanical properties. Ultrahigh strength bulk metallic glass (BMG) is a kind of advanced metallic material with extremely high strength (above 4 GPa), high thermal stability (the glass transition temperature: normally above 800 K), and high hardness (normally above 12 GPa). A typical system of the ultrahigh strength BMG is Co-Ta-B alloy with a fracture strength of above 6 GPa, which is the highest value in the fracture strengths for all kinds of bulk metallic materials (including crystalline and amorphous ones) that we have known so far. In this paper, the compositions, thermal properties, elastic constants, and mechanical properties for all of the reported ultrahigh strength BMGs are summarized. The research progress of these BMGs is also introduced. The correlations among the characteristic temperature, elastic constants, hardness and mechanical properties are built, and the natures of chemical bonding for the ultrahigh strength and high hardness of these BMGs are revealed. The results relating to the structure and physical properties of this kind of ultrahigh strength BMG are significant for potential applications in advanced manufacture, super-durable components and machining.
Liquid-liquid phase transition and anomalous properties
Authors: Li Ren-Zhong  , Wu Zhen-Wei  , Xu Li-Mei  ,   International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China;,   Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
Published: December 2020

In most of liquids, densities increase as temperature decreases. However, the densities of water and water-like liquids, such as silicon and germanium, are anomalous, which increase as temperature increases. Such substances also show other anomalous behaviors, such as diffusivity anomalies (diffusivities increase as density increases), and thermodynamic anomalies (the fluctuations increase as temperature decreases). The chemical properties of these materials are very different from each other, but they all share similar physical properties. Further studies indicate that most of them have two distinct liquid states, i.e., a low-density liquid and a high-density liquid, and a first order liquid-liquid phase transition (LLPT) between these two liquids. We mainly discuss the anomalous properties of materials each of which has a predicted LLPT and their relations with anomalous behaviors (thermodynamic, dynamic and structural) as those of water and water-like liquids, such as hydrogen and gallium. In particular, we discuss the supercritical phenomenon of the liquid-liquid phase transition of hydrogen, as well as the liquid-liquid phase transition of gallium and its relation with the thermodynamic, dynamic, and structural anomalies. It is found that the liquid hydrogen and gallium both have the LLPT and share similar anomalous behaviors as water and water-like liquids, such as density anomaly, dynamics anomaly, thermodynamic anomaly Since the chemical properties of these materials are very different from those of others having the LLPT, the anomalous behaviors may be common features for substances predicted to have the LLPT.